Cell adhesion and culture medium dependent changes in the high frequency mechanical vibration induced proliferation, osteogenesis, and intracellular organization of human adipose stem cells

High frequency (HF) mechanical vibration appears beneficial for in vitro osteogenesis of mesenchymal stem cells (MSCs). However, the current mechanobiological understanding of the method remains insufficient. We designed high-throughput stimulators to apply horizontal or vertical high magnitude HF (HMHF; 2.5 Gpeak, 100 Hz) vibration on human adipose stem cells (hASCs). We analyzed proliferation, alkaline phosphatase (ALP) activity, mineralization, and effects on the actin cytoskeleton and nuclei using immunocytochemical stainings. Proliferation was studied on a standard tissue culture plastic (sTCP) surface and on an adhesion supporting tissue culture plastic (asTCP) surface in basal (BM) and osteogenic (OM) culture medium conditions. We discovered that the improved cell adhesion was a prerequisite for vibration induced changes in the proliferation of hASCs. Similarly, the adhesion supporting surface enabled us to observe vibration initiated ALP activity and mineralization changes in OM condition. The horizontal vibration increased ALP activity, while vertical stimulation reduced ALP activity. However, mineralization was not enhanced by the HMHF vibration. We performed image-based analysis of actin and nuclei to obtain novel data of the intracellular-level responses to HF vibration in BM and OM conditions. Our quantitative results suggest that actin organizations were culture medium and stimulation direction dependent. Both stimulation directions decreased OM induced changes in nuclear size and elongation. Consequently, our findings of the nuclear deformations provide supportive evidence for the involvement of the nuclei in the mechanocoupling of HF vibration. Taken together, the results of this study enhanced the knowledge of the intracellular mechanisms of HF vibration induced osteogenesis of MSCs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Computational Biophysics and Imaging Group, BioMediTech, Tampere University Hospital
Contributors: Halonen, H. T., Ihalainen, T. O., Hyväri, L., Miettinen, S., Hyttinen, J. A.
Publication date: 1 Jan 2020
Peer-reviewed: Yes

Publication information

Journal: Journal of the Mechanical Behavior of Biomedical Materials
Volume: 101
Article number: 103419
ISSN (Print): 1751-6161
Original language: English
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering, Mechanics of Materials
Keywords: Adipose stem cells, Bone tissue engineering, HMHF vibration, Horizontal stimulation, Mechanobiology, Vertical stimulation
Electronic versions: 
Source: Scopus
Source ID: 85072013214

Research output: Contribution to journalArticleScientificpeer-review

First principles prediction of the solar cell efficiency of chalcopyrite materials  AgMX2(M=In, Al; X=S, Se, Te)

Using the spectroscopic limited maximum efficiency, and Shockley and Queisser predictor models, we compute the solar efficiency of the chalcopyrites AgMX 2 (M = In, Al; X = S, Se, Te). The results presented are based on the estimation of the electronic and optical properties obtained from first principles density functional theory as well as the many-body perturbation theory calculations. The results from this report were consistent with the experimental data.The optical bandgap was accurately estimated from the absorption spectra, obtained by solving the Bethe and Salpeter equation. Fitting the Tauc's plot on the absorption spectra, we also predicted that the materials studied have a direct allowed optical transition. The theoretical estimations of the solar cell performance showed that the efficiencies from the Shockley and Queisser model are higher than those from the spectroscopic limited maximum efficiency model. This improvement is attributed to the absorption, the recombination processes and the optical transition accounted in the calculation of the efficiency.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, University of South Africa, University of Witwatersrand
Contributors: Dongho-Nguimdo, G. M., Igumbor, E., Zambou, S., Joubert, D. P.
Publication date: 1 Dec 2019
Peer-reviewed: Yes

Publication information

Journal: Computational Condensed Matter
Volume: 21
Article number: e00391
ISSN (Print): 2352-2143
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Materials Science (miscellaneous), Condensed Matter Physics, Materials Chemistry
Keywords: Chalcopyrites, First principles, Solar cell efficiency
Source: Scopus
Source ID: 85065198754

Research output: Contribution to journalArticleScientificpeer-review

Microscale fracture of chromia scales

Native protective oxide scales offer resistance against corrosion for high temperature materials, which often work in extreme conditions of varying mechanical and thermal loads. The integrity of such layers is of critical importance, since their damage can lead to significant reduction in material life. Mechanical data such as fracture strain and elastic modulus are required to include oxides in material life estimation models for high temperature materials, but there is lack of such data. Their thickness is in the μm range, which makes mechanical testing for property determination difficult. Here we present a micro-mechanical testing method, based on bending of micro-cantilevers produced by focused ion beam milling, capable of circumventing the limitations of conventional approaches. We apply this method to chromia thermally grown on pure chromium, and measure fracture strains at room and high temperatures (600 °C). The measured fracture strains were found to be higher at room temperature, due to a larger fraction of transgranular fracture. Surprisingly, a large fraction of transgranular fracture was seen even in the presence of stress concentrations at grain boundaries. Removal of the stress concentrations accentuated the propensity for transgranular cracking at room temperature. Realistic values of room temperature elastic modulus were obtained as well. The observed mixed trans- and intergranular cracking points towards the need for dedicated investigations of both oxide grain boundary strength and cleavage resistance of single crystals in order to fully understand the failure mechanisms in thermally grown oxide scales.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Chalmers University of Technology, Swiss Federal Laboratories for Materials Science and Technology
Contributors: Iyer, A. H., Mohanty, G., Stiller, K., Michler, J., Colliander, M. H.
Publication date: 1 Dec 2019
Peer-reviewed: Yes

Publication information

Journal: Materialia
Volume: 8
Article number: 100465
ISSN (Print): 2589-1529
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: Chromia, Electron microscopy, Fracture mechanisms, Micromechanics, Oxide
Source: Scopus
Source ID: 85072022463

Research output: Contribution to journalArticleScientificpeer-review

Miniature CoCr laser welds under cyclic shear: Fatigue evolution and crack growth

Miniature laser welds with the root depth in the range of 50–300 μm represent air-tight joints between the components in medical devices, such as those in implants, growth rods, stents and various prostheses. The current work focuses on the development of a fatigue test specimen and procedure to determine fatigue lives of shear-loaded laser welds. A cobalt-chromium (CoCr) alloy is used as a benchmark case. S–N graphs, damage process, and fracture surfaces are studied by applying x-ray analysis, atomic force microscopy, and scanning electron microscopy both before and after the crack onset. A non-linear material model is fitted for the CoCr alloy to run finite element simulations of the damage and deformation. As a result, two tensile-loaded specimen designs are established and the performance is compared to that of a traditional torque-loaded specimen. The new generation specimens show less variation in the determined fatigue lives due to well-defined crack onset point and, therefore, precise weld seam load during the experiments. The fatigue damage concentrates to the welded material and the entire weld experiences fatigue prior to the final, fracture-governed failure phase. For the studied weld seams of hardened CoCr, a regression fatigue limit of 10.8–11.8 MPa, where the stress refers to the arithmetic average shear stress computed along the region dominated by shear loading, is determined.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Orton Orthopaedic Hospital, Surface and Corrosion Science
Contributors: Kanerva, M., Besharat, Z., Pärnänen, T., Jokinen, J., Honkanen, M., Sarlin, E., Göthelid, M., Schlenzka, D.
Number of pages: 11
Pages: 93-103
Publication date: 1 Nov 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of the Mechanical Behavior of Biomedical Materials
Volume: 99
ISSN (Print): 1751-6161
Original language: English
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering, Mechanics of Materials
Keywords: CoCr, Crack growth, Fatigue, Implant, Laser weld
Electronic versions: 

Bibliographical note

EXT="Pärnänen, T."

Source: Scopus
Source ID: 85069732362

Research output: Contribution to journalArticleScientificpeer-review

Recycling lithium mine tailings in the production of low temperature (700–900 °C) ceramics: Effect of ladle slag and sodium compounds on the processing and final properties

This paper deals with the valorization of quartz and felspar rich lithium mine tailings (QFS) in the development of construction materials. Ladle slag was used as green strength increasing agent. Sodium hydroxide and carbonate were used as fluxing agents to allow sintering at 700–900 °C. Of these, sodium hydroxide was found to be the more efficient. The sintered ceramics were characterized by X-ray diffraction, scanning electron microscopy, compressive test, water absorption, apparent density and dilatometry; the results were found to comply with ASTM C62-99 specifications for building brick, and interesting for a sustainable use of resources.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Research group: Ceramic materials, Tampere University of Technology, Univ of Oulu
Contributors: Lemougna, P. N., Yliniemi, J., Ismailov, A., Levänen, E., Tanskanen, P., Kinnunen, P., Roning, J., Illikainen, M.
Number of pages: 13
Pages: 332-344
Publication date: 10 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Construction and building materials
Volume: 221
ISSN (Print): 0950-0618
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Building and Construction, Materials Science(all)
Keywords: Building applications, Ceramic, Fluxing agent, Ladle slag, Lithium mine tailings, Sodium compounds
Source: Scopus
Source ID: 85067302331

Research output: Contribution to journalArticleScientificpeer-review

Tribocorrosion behaviour of two low-alloy steel grades in simulated waste solution

The tribocorrosion behaviour of two low-alloy steels not previously investigated, was examined in a Pin-on-Disc test device, both in the presence and absence of mechanical wear and/or corrosion in simulated waste solution. Volume losses through wear, corrosion and synergy processes were calculated and changes in the material surfaces investigated. The tribocorrosion behaviour and the volume losses caused by the synergy processes were found to be dependent on the steel grade, instead of applied potential. For both steel grades, material losses were caused by two main degradation mechanisms: wear and wear-induced corrosion. Total material losses and the percentage of wear-corrosion synergy were higher for the ferritic grade than for the martensitic grade. These results are presented and discussed in this paper.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, VTT Technical Research Centre of Finland, Microscopy Center
Contributors: Mäntyranta, A., Heino, V., Isotahdon, E., Salminen, T., Huttunen-Saarivirta, E.
Number of pages: 13
Pages: 250-262
Publication date: 1 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Tribology International
Volume: 138
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Contact: sliding, Synergism: tribochemistry, Wear: corrosive

Bibliographical note

EXT="Heino, Vuokko"
EXT="Isotahdon, Elisa"

Source: Scopus
Source ID: 85066497579

Research output: Contribution to journalArticleScientificpeer-review

Analytical computation of the demagnetizing energy of thin-film domain walls

Due to its nonlocal nature, calculating the demagnetizing field remains the biggest challenge in understanding domain structures in ferromagnetic materials. Analytical descriptions of demagnetizing effects typically approximate domain walls as uniformly magnetized ellipsoids, neglecting both the smooth rotation of magnetization from one domain to the other and the interaction between the two domains. Here, instead of the demagnetizing field, we compute analytically the demagnetizing energy of a straight domain wall described by the classical tanh magnetization profile in a thin film with perpendicular magnetic anisotropy. We then use our expression for the demagnetizing energy to derive an improved version of the 1D model of field-driven domain wall motion, resulting in accurate expressions for important properties of the domain wall such as the domain wall width and the Walker breakdown field. We verify the accuracy of our analytical results by micromagnetic simulations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics
Contributors: Skaugen, A., Murray, P., Laurson, L.
Publication date: 25 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 100
Issue number: 9
Article number: 094440
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85072773246

Research output: Contribution to journalArticleScientificpeer-review

Special Issue: Temperature Dependence of Material Behaviour at High Strain-Rate

General information

Publication status: Published
MoE publication type: C2 Edited books
Organisations: Materials Science and Environmental Engineering, Politecnico di Torino, Universiteit Gent, Université de Strasbourg
Contributors: Scapin, M. (ed.), Verleysen, P. (ed.), Hokka, M. (ed.), Bahlouli, N. (ed.)
Publication date: 15 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Dynamic Behavior of Materials
Volume: 5
Issue number: 3
ISSN (Print): 2199-7446
Original language: English
ASJC Scopus subject areas: Materials Science (miscellaneous), Mechanics of Materials
Source: Scopus
Source ID: 85070087495

Research output: Contribution to journalSpecial issueScientificpeer-review

Multiresonant High-Q Plasmonic Metasurfaces

Resonant metasurfaces are devices composed of nanostructured subwavelength scatterers that generate narrow optical resonances, enabling applications in filtering, nonlinear optics, and molecular fingerprinting. It is highly desirable for these applications to incorporate such devices with multiple high-quality-factor resonances; however, it can be challenging to obtain more than a pair of narrow resonances in a single plasmonic surface. Here, we demonstrate a multiresonant metasurface that operates by extending the functionality of surface lattice resonances, which are the collective responses of arrays of metallic nanoparticles. This device features a series of resonances with high-quality factors (Q ∼ 40), an order of magnitude larger than what is typically achievable with plasmonic nanoparticles, as well as a narrow free spectral range. This design methodology can be used to better tailor the transmission spectrum of resonant metasurfaces and represents an important step toward the miniaturization of optical devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Nonlinear Optics, Iridian Spectral Technologies, University of Rochester Institute of Optics
Contributors: Reshef, O., Saad-Bin-Alam, M., Huttunen, M. J., Carlow, G., Sullivan, B. T., Ménard, J. M., Dolgaleva, K., Boyd, R. W.
Number of pages: 6
Pages: 6429-6434
Publication date: 11 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Nano Letters
Volume: 19
Issue number: 9
ISSN (Print): 1530-6984
Original language: English
ASJC Scopus subject areas: Bioengineering, Chemistry(all), Materials Science(all), Condensed Matter Physics, Mechanical Engineering
Keywords: gold nanoparticles, nanophotonics, Plasmonics, resonant metasurface, surface lattice resonance
Source: Scopus
Source ID: 85072133592

Research output: Contribution to journalArticleScientificpeer-review

Carbon nanotube doped pericardial matrix derived electroconductive biohybrid hydrogel for cardiac tissue engineering

Cardiovascular diseases represent a major socio-economic burden. In recent years, considerable effort has been invested in optimizing cell delivery strategies to advance cell transplantation therapies to restore heart function for example after an infarct. A particular issue is that the implantation of cells using a non-electroconductive matrix potentially causes arrhythmia. Here, we demonstrate that our hydrazide-functionalized nanotubes-pericardial matrix-derived electroconductive biohybrid hydrogel provides a suitable environment for maturation of human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. hiPSC-derived cardiomyocytes exhibited an improved contraction amplitude (>500%) on conductive hydrogels compared to cells cultured on Matrigel®. This was accompanied by increased cellular alignment, enhanced connexin 43 expression, and improved sarcomere organization suggesting maturation of the hiPSC-derived cardiomyocytes. Sarcomeric length of these cells increased from 1.3 to 1.7 μm. Moreover, 3D cell-laden engineered tissues exhibited enhanced calcium handling as well as positive response to external electrical and pharmaceutical stimulation. Collectively, our data indicate that our biohybrid hydrogels consisting of solubilized nanostructured pericardial matrix and electroconductive positively charged hydrazide-conjugated carbon nanotubes provide a promising material for stem cell-based cardiac tissue engineering.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Friedrich-Alexander-Universität Erlangen-Nürnberg, Muscle Research Center Erlangen (MURCE), University of Tehran, Bioengineering and Nanomedicine Lab, Angstrom Laboratory
Contributors: Roshanbinfar, K., Mohammadi, Z., Sheikh-Mahdi Mesgar, A., Dehghan, M. M., Oommen, O. P., Hilborn, J., Engel, F. B.
Number of pages: 12
Pages: 3906-3917
Publication date: 1 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Biomaterials Science
Volume: 7
Issue number: 9
ISSN (Print): 2047-4830
Original language: English
ASJC Scopus subject areas: Biomedical Engineering, Materials Science(all)
Source: Scopus
Source ID: 85071394455

Research output: Contribution to journalArticleScientificpeer-review

Parametric study on temperature distribution of square hollow section joints

The resistance of a steel joint is one of the most crucial elements of a structure under fire conditions. The aim of the study was to investigate the temperature distribution within the square hollow section (SHS) joints with different geometric parameters under fire conditions. The commercial finite element (FE) software, Abaqus/Standard CAE, was used to simulate the behaviour of the SHS joints. Extensive numerical research was conducted on different joint types (T-, Y-, and K-joints) to examine the influence of the joint configuration on the temperature distribution within the joint. To provide reliable observations, a model was validated against the experimental results. The FE simulation results were compared to the predictions of Eurocode equations. The FE simulation results showed that the simulated temperatures are different from the temperatures determined using the Eurocode method. The β parameter was found to have hardly any influence on the temperature distribution within the joint area, whereas different joint configurations strongly influence the distribution.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Research group: Metal and Light-wight structures
Contributors: Bączkiewicz, J., Pajunen, S., Malaska, M., Heinisuo, M.
Number of pages: 9
Pages: 490-498
Publication date: 1 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Constructional Steel Research
Volume: 160
ISSN (Print): 0143-974X
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Building and Construction, Mechanics of Materials, Metals and Alloys
Keywords: Component method, Hollow section, Parametric study, Steel joint, Temperature distribution
Source: Scopus
Source ID: 85067525966

Research output: Contribution to journalArticleScientificpeer-review

Porous polybutylene succinate films enabling adhesion of human embryonic stem cell-derived retinal pigment epithelial cells (hESC-RPE)

In the last decade, several studies have shown that polybutylene succinate (PBSu)has a high potential as a biomaterial enabling cell adhesion and growth. In this study, porous PBSu films have been prepared by the breath figure method (BF)and by particulate leaching (PL), and characterized in terms of thickness, surface properties, diffusion capacity and in vitro stability. Because porous films are of high interest for tissue engineering of retinal pigment epithelium (RPE), the initial viability and adhesion of human embryonic stem cell-derived RPE onto the PBSu films was then evaluated. To the best of our knowledge, this is the first study on the adhesion behavior of hESC-RPE onto porous and biodegradable polymer surfaces. The results clearly demonstrated that the two manufacturing methods produced materials with very distinct properties. Films produced by BF expressively demonstrated the highest roughness and surface area, and the lowest water contact angle. These features likely contributed to increase the biocompatibility of the surface, particularly when coated with laminin and collagen IV, as observed by the improved cell viability, cell morphology, adhesion and production of extracellular matrix proteins. Altogether, our results showed not only that PBSu holds high potential in retinal tissue engineering, but also that the physical properties and biocompatibility of the material are highly dependent on the adopted casting method.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Tampere University, Tampere University Hospital
Contributors: Calejo, M. T., Haapala, A., Skottman, H., Kellomäki, M.
Number of pages: 10
Pages: 78-87
Publication date: 1 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: European Polymer Journal
Volume: 118
ISSN (Print): 0014-3057
Original language: English
ASJC Scopus subject areas: Physics and Astronomy(all), Polymers and Plastics, Organic Chemistry, Materials Chemistry
Keywords: Biodegradable films, Breath figures, Cell adhesion, Polybutylene succinate, Retinal pigment epithelium
Source: Scopus
Source ID: 85066269398

Research output: Contribution to journalArticleScientificpeer-review

Bioactive glass ions for in vitro osteogenesis and microvascularization in gellan gum-collagen hydrogels

Lack of bone grafts appeals for bone augmentation solutions. We aimed at osteogenic differentiation of human adipose stem cells (hASCs) and microvascularization in coculture with human umbilical vein endothelial cells (HUVECs) embedded in three-dimensional (3D) gellan gum (GG) and collagen type I (COL) hydrogel mixture. We compared endothelial growth medium-2 (EGM-2) and bioactive glass extract-based endothelial and osteogenic medium (BaG EM-OM) for vascularized bone-like graft development in vitro. Cell viability, cell number, and osteogenic and endothelial gene expression were analyzed. Mineralized hydroxyapatite residues, immunocytochemical staining of endothelial marker CD31 production and late osteogenic marker osteocalcin were imaged. With both media, good cell viability was observed within 3D hydrogel. EGM-2 condition induced significantly higher cell number compared to BaG EM-OM condition at both 7 and 14 days. Interestingly, both media supported osteogenic as well as endothelial marker gene expression. Moreover, formation of reticulated cellular structures was observed in both EGM-2 and BaG EM-OM conditions. However, hydroxyapatite mineralization and strong osteocalcin staining were detected only in BaG EM-OM condition. Importantly, strong production of CD31 and elongated tube-like structures were apparent in EGM-2 culture alone. In conclusion, we demonstrated efficient hASC osteogenic differentiation and microvessel-like network formation in coculture with HUVECs.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Research group: Biomaterials and Tissue Engineering Group, Tampere University Hospital, Abo Akad Univ, Abo Akademi University, Dept Phys
Contributors: Vuornos, K., Huhtala, H., Kääriäinen, M., Kuismanen, K., Hupa, L., Kellomäki, M., Miettinen, S.
Publication date: 31 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Biomedical Materials Research - Part B Applied Biomaterials
ISSN (Print): 1552-4973
Original language: English
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering
Keywords: adipose stem cell, bioactive glass, collagen type I hydrogel, gellan gum hydrogel, human umbilical vein endothelial cell, osteogenic differentiation, vascularization
Source: Scopus
Source ID: 85071483860

Research output: Contribution to journalArticleScientificpeer-review

Detection of gaseous species during KCl-induced high-temperature corrosion by the means of CPFAAS and CI-APi-TOF

Two different analytical approaches—collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) and chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (CI-APi-TOF)—were applied to detect and identify the online gaseous KOH and HCl formed in the addressed high-temperature reactions. Samples of pure KCl, KCl+Cr, KCl+Fe, and KCl+316 L were studied at 550°C under dry and humid conditions with varying oxygen concentrations. The goal was to shed more light on the gas-phase chemistry during KCl-induced corrosion under conditions relevant to biomass combustion. CI-APi-TOF proved to be a valuable tool for high-temperature corrosion studies: HCl was identified to have formed during the reactions under humid conditions. On the contrary, despite the known sensitivity of CPFAAS, the formation of KOH could not be verified in any of the performed measurements.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Research area: Aerosol Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Physics, Research group: Applied Optics, Åbo Akademi University
Contributors: Lehmusto, J., Olin, M., Viljanen, J., Kalliokoski, J., Mylläri, F., Toivonen, J., Dal Maso, M., Hupa, L.
Number of pages: 10
Publication date: 30 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Materials and Corrosion
ISSN (Print): 0947-5117
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Mechanics of Materials, Mechanical Engineering, Surfaces, Coatings and Films, Metals and Alloys, Materials Chemistry
Keywords: CI-APi-TOF, CPFAAS, gaseous KCl, HCl formation, high-temperature corrosion
Source: Scopus
Source ID: 85071360769

Research output: Contribution to journalArticleScientificpeer-review

Influence of ions to modulate hydrazone and oxime reaction kinetics to obtain dynamically cross-linked hyaluronic acid hydrogels

Dynamic covalent chemistry forming hydrazone and oxime linkages is attractive due to its simplicity, selectivity and compatibility under aqueous conditions. However, the low reaction rate at physiological pH hampers its use in biomedical applications. Herein, we present different monovalent and bivalent aqueous salt solutions as bio-friendly, non-toxic catalysts which can drive the hydrazone and oxime reactions with excellent efficacy at physiological pH. Direct comparison of hydrazone and oxime reactions using a small molecule model, without any salt catalysis, indicated that oxime formation is 6-times faster than hydrazone formation. Addition of different salts (NaCl, NaBr, KCl, LiCl, LiClO4, Na2SO4, MgCl2 and CaCl2) accelerated the pseudo-first-order reaction kinetics by ∼1.2-4.9-fold for acylhydrazone formation and by ∼1.5-6.9-fold for oxime formation, in a concentration-dependent manner. We further explored the potential of such catalysts to develop acylhydrazone and oxime cross-linked hyaluronic acid (HA) hydrogels with different physicochemical properties without changing the degree of chemical modification. Analogous to the small molecule model system, the addition of monovalent and divalent salts as catalysts significantly reduced the gelling time. The gelling time for the acylhydrazone cross-linked HA-hydrogel (1.6 wt%) could be reduced from 300 min to 1.2 min by adding 100 mM CaCl2, while that for the oxime cross-linked HA-hydrogel (1.2 wt%) could be reduced from 68 min to 1.1 min by adding 50 mM CaCl2. This difference in the gelling time also resulted in hydrogels with differential swelling properties as measured after 24 h. Our results are the first to demonstrate the use of salts, for catalyzing hydrogel formation under physiologically relevant conditions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Research group: Biomaterials and Tissue Engineering Group, University of Montreal, Uppsala University
Contributors: Wang, S., Nawale, G. N., Oommen, O. P., Hilborn, J., Varghese, O. P.
Number of pages: 6
Pages: 4322-4327
Publication date: 21 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Polymer Chemistry
Volume: 10
Issue number: 31
ISSN (Print): 1759-9954
Original language: English
ASJC Scopus subject areas: Bioengineering, Biochemistry, Polymers and Plastics, Organic Chemistry
Electronic versions: 
Source: Scopus
Source ID: 85070404630

Research output: Contribution to journalArticleScientificpeer-review

Characterizing the micro-impact fatigue behavior of APS and HVOF-sprayed ceramic coatings

The fatigue life of thermally sprayed Al2O3- and Cr2O3-based coatings has been studied under low-energy (0.7–5 mJ) impact conditions. A threshold impact energy and amount of repetitions the coatings can endure with said energy before catastrophic failure was obtained. The catastrophic failure was determined to occur when the fracture mode of the coating switched from brittle cone cracking to quasi-plastic radial cracking. The results are examined relative to the microstructural features along with other properties of the coatings - hardness and cavitation resistance. The experiment provided a new approach for a straightforward comparison of the micro-scale impact fatigue life of thermally sprayed coatings unachievable with previous methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Université Bourgogne Franche-Comté - ICB - UTBM - LERMPS
Contributors: Kiilakoski, J., Langlade, C., Koivuluoto, H., Vuoristo, P.
Pages: 245-254
Publication date: 15 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Surface and Coatings Technology
Volume: 371
ISSN (Print): 0257-8972
Original language: English
ASJC Scopus subject areas: Chemistry(all), Condensed Matter Physics, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Ceramic coating, Characterization, Fracture, Impact test, Surface fatigue, Thermal spray
Electronic versions: 
Source: Scopus
Source ID: 85055977332

Research output: Contribution to journalArticleScientificpeer-review

Elevated and cryogenic temperature micropillar compression of magnesium–niobium multilayer films

The mechanical properties of multilayer films consisting of alternating layers of magnesium and niobium are investigated through micropillar compression experiments across a broad range of temperatures. The data collected from the variable temperature micropillar compression tests and strain rate jump tests are used to gain insight into the operative deformation mechanisms within the material. At higher temperatures, diffusion-based deformation mechanisms are shown to determine the plastic behavior of the multilayers. Diffusion occurs more readily along the magnesium–niobium interface than within the bulk, acting as pathway for magnesium diffusion. When individual layer thicknesses are sufficiently small, diffusion can remain the dominant deformation mechanism down to room temperature. Multilayer strengthening models historically rely solely on dislocation-based arguments; therefore, consideration of diffusion-based deformation in nanolaminates with low melting temperature components offers improved understanding of multilayer behavior.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Swiss Federal Laboratories for Materials Science and Technology, HCI e 486.1, University of California, Santa Barbara, University of Nevada, Reno, University of Minnesota Twin Cities
Contributors: Thomas, K., Mohanty, G., Wehrs, J., Taylor, A. A., Pathak, S., Casari, D., Schwiedrzik, J., Mara, N., Spolenak, R., Michler, J.
Number of pages: 18
Pages: 10884-10901
Publication date: 15 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Science
Volume: 54
Issue number: 15
ISSN (Print): 0022-2461
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Mechanical Engineering
Source: Scopus
Source ID: 85065435834

Research output: Contribution to journalArticleScientificpeer-review

Fluorine losses in Er3+oxyfluoride phosphate glasses and glass-ceramics

Er 3+ doped phosphate glasses with the composition 75NaPO 3- 25CaF 2 (mol%)were prepared at different melting temperatures to demonstrate the importance to quantify the fluorine content when preparing oxyfluoride glasses. Indeed, increasing the melting temperature from 900 to 1000 °C leads to a small reduction in the fluorine content from 9.4 at % to 8.8 at % as quantified using EPMA. Whereas this loss of fluorine can be suspected from small changes in the thermal properties of the glass, it increases significantly the glass crystallization tendency in this glass system. This means that a heat treatment of the as-prepared glass should be performed when evaporation of fluorine during the glass melting is suspected. Sample preparation for the characterization of the spectroscopic properties of the glasses is discussed here as well; bulk glasses should be used when measuring the spectroscopic properties of oxyfluoride glasses, which are known to be hygroscopic. It is shown, in this work, that a heat treatment of the glass within the investigated glass system leads to transparent glass-ceramics with volume precipitation of Er 3+ doped CaF 2 crystals with strong upconversion.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Materials Characterization, Materials Science and Environmental Engineering, Physics, Tampere University of Applied Sciences, Fondazione LINKS – Leading Innovation & Knowledge for Society
Contributors: Szczodra, A., Mardoukhi, A., Hokka, M., Boetti, N. G., Petit, L.
Number of pages: 7
Pages: 797-803
Publication date: 15 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Alloys and Compounds
Volume: 797
ISSN (Print): 0925-8388
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Keywords: Crystal, Erbium, Fluorine, Glass, Glass-ceramic, Luminescence
Source: Scopus
Source ID: 85065824926

Research output: Contribution to journalArticleScientificpeer-review

Chlorine induced high-temperature corrosion mechanisms in HVOF and HVAF sprayed Cr3C2-based hardmetal coatings

A novel method that combines thermal analysis and traditional furnace corrosion tests was used to study the corrosion behaviour of thermally sprayed Cr3C2-based hardmetal coatings at 450 °C and 550 °C under a KCl deposit. This method enabled the identification of the onset temperature of chlorine-induced oxidation to be within 450–500 °C. Two corrosion mechanisms were suggested for these temperatures. At 450 °C, the corrosion rate was slow and mainly controlled by the formation of K2CrO4. Exposure at 550 °C caused the formation of fine interconnected secondary-carbide precipitates in the metal matrix. Their fast corrosion was identified as the major cause of degradation.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Research group: Surface Engineering, Valmet Automation Oy
Contributors: Fantozzi, D., Matikainen, V., Uusitalo, M., Koivuluoto, H., Vuoristo, P.
Publication date: 14 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Corrosion Science
Article number: 108166
ISSN (Print): 0010-938X
Original language: English
ASJC Scopus subject areas: Chemistry(all), Chemical Engineering(all), Materials Science(all)
Keywords: A. Metal matrix composites, A. Superalloys, B. SEM, B. TGA, B. XRD, C. Chlorination, C. High temperature corrosion, C. Thermodynamic diagrams

Bibliographical note

EXT="Uusitalo, Mikko"

Source: Scopus
Source ID: 85072275416

Research output: Contribution to journalArticleScientificpeer-review

Magnetic non-contact friction from domain wall dynamics actuated by oscillatory mechanical motion

Magnetic friction is a form of non-contact friction arising from the dissipation of energy in a magnet due to spin reorientation in a magnetic field. In this paper, we study magnetic friction in the context of micromagnetics, using our recent implementation of smooth spring-driven motion (Rissanen and Laurson 2018 Phys. Rev. E 97 053301) to simulate ring-down measurements in two setups where domain wall dynamics is induced by mechanical motion. These include a single thin film with a domain wall in an external field and a setup mimicking a magnetic cantilever tip and substrate, in which the two magnets interact through dipolar interactions. We investigate how various micromagnetic parameters influence the domain wall dynamics actuated by the oscillatory spring-driven mechanical motion and the resulting damping coefficient. Our simulations show that the magnitude of magnetic friction can be comparable to other forms of non-contact friction. For oscillation frequencies lower than those inducing excitations of the internal structure of the domain walls, the damping coefficient is found to be independent of frequency. Hence, our results obtained in the frequency range from 8-112 MHz are expected to be relevant also for typical experimental setups operating in the 100 kHz range.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Aalto University, COMP Centre of Excellence
Contributors: Rissanen, I., Laurson, L.
Publication date: 13 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physics D: Applied Physics
Volume: 52
Issue number: 44
Article number: 445002
ISSN (Print): 0022-3727
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Acoustics and Ultrasonics, Surfaces, Coatings and Films
Keywords: magnetic friction, micromagnetics, thin films
Source: Scopus
Source ID: 85072336407

Research output: Contribution to journalArticleScientificpeer-review

Characterisation and in vitro and in vivo evaluation of supercritical-CO2-foamed β-TCP/PLCL composites for bone applications

Most synthetic bone grafts are either hard and brittle ceramics or paste-like materials that differ in applicability from the gold standard autologous bone graft, which restricts their widespread use. Therefore, the aim of the study was to develop an elastic, highly porous and biodegradable β-tricalciumphosphate/poly(L-lactide-co-ε-caprolactone) (β-TCP/PLCL) composite for bone applications using supercritical CO2 foaming. Ability to support osteogenic differentiation was tested in human adipose stem cell (hASC) culture for 21 d. Biocompatibility was evaluated for 24 weeks in a rabbit femur-defect model. Foamed composites had a high ceramic content (50 wt%) and porosity (65-67 %). After 50 % compression, in an aqueous environment at 37 °C, tested samples returned to 95 % of their original height. Hydrolytic degradation of β-TCP/PLCL composite, during the 24-week follow-up, was very similar to that of porous PLCL scaffold both in vitro and in vivo. Osteogenic differentiation of hASCs was demonstrated by alkaline phosphatase activity analysis, alizarin red staining, soluble collagen analysis, immunocytochemical staining and qRT-PCR. In vitro, hASCs formed a pronounced mineralised collagen matrix. A rabbit femur defect model confirmed biocompatibility of the composite. According to histological Masson-Goldner's trichrome staining and micro-computed tomography, β-TCP/PLCL composite did not elicit infection, formation of fibrous capsule or cysts. Finally, native bone tissue at 4 weeks was already able to grow on and in the β-TCP/PLCL composite. The elastic and highly porous β-TCP/PLCL composite is a promising bone substitute because it is osteoconductive and easy-to-use and mould intraoperatively.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech
Contributors: Pitkänen, S., Paakinaho, K., Pihlman, H., Ahola, N., Hannula, M., Asikainen, S., Manninen, M., Morelius, M., Keränen, P., Hyttinen, J., Kellomäki, M., Laitinen-Vapaavuori, O., Miettinen, S.
Number of pages: 16
Pages: 35-50
Publication date: 5 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: European cells & materials
Volume: 38
ISSN (Print): 1473-2262
Original language: English
ASJC Scopus subject areas: Bioengineering, Biochemistry, Biomaterials, Biomedical Engineering, Cell Biology
Electronic versions: 
Source: Scopus
Source ID: 85071152630

Research output: Contribution to journalArticleScientificpeer-review

Te incorporation and activation as n-type dopant in self-catalyzed GaAs nanowires

Dopant atoms can be incorporated into nanowires either via the vapor-liquid-solid mechanism through the catalyst droplet or by the vapor-solid growth on the sidewalls. Si is a typical n-type dopant for GaAs, but in nanowires it often suffers from a strongly amphoteric nature in the vapor-liquid-solid process. This issue can be avoided by using Te, which is a promising but less common alternative for n-type doping of GaAs nanowires. Here, we present a detailed investigation of Te-doped self-catalyzed GaAs nanowires. We use several complementary experimental techniques, such as atom probe tomography, off-axis electron holography, micro-Raman spectroscopy, and single-nanowire transport characterization, to assess the Te concentration, the free-electron concentration, and the built-in potential in Te-doped GaAs nanowires. By combing the experimental results with a theoretical model, we show that Te atoms are mainly incorporated by the vapor-liquid-solid process through the Ga droplet, which leads to both axial and radial dopant gradients due to Te diffusion inside the nanowires and competition between axial elongation and radial growth of nanowires. Furthermore, by comparing the free-electron concentration from Raman spectroscopy and the Te-atom concentrations from atom probe tomography, we show that the activation of Te donor atoms is 100% at a doping level of 4×1018cm-3, which is a significant result in terms of future device applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Electrical Engineering, Universidade Federal de São Carlos, Risø Campus, Lund University, Eindhoven University of Technology, R. Giuseppe Máximo Scolfaro, Radboud University Nijmegen, ITMO University
Contributors: Hakkarainen, T., Rizzo Piton, M., Fiordaliso, E. M., Leshchenko, E. D., Koelling, S., Bettini, J., Vinicius Avanço Galeti, H., Koivusalo, E., Gobato, Y. G., De Giovanni Rodrigues, A., Lupo, D., Koenraad, P. M., Leite, E. R., Dubrovskii, V. G., Guina, M.
Publication date: 5 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review Materials
Volume: 3
Issue number: 8
Article number: 086001
ISSN (Print): 1098-0121
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physics and Astronomy (miscellaneous)
Source: Scopus
Source ID: 85070548104

Research output: Contribution to journalArticleScientificpeer-review

Modelling thermodynamics in a high erature superconducting dipole magnet: An inverse problem based approach

The use of practical high temperature superconductors (HTS), REBCO tapes especially, in magnet applications has become possible thanks to the increasing interest of manufacturers. One difficulty has been the nonlinear material properties that are challenging to measure and model. To advance in such, demo systems are needed and they must be thoroughly analyzed. Recently, one of the first HTS dipole magnets was built to study the usability of REBCO Roebel cables in particle accelerator magnets. The prototype magnet Feather-M2 was designed, constructed and tested within EUCARD2 collaboration project at CERN in 2017. In the measurements, the magnet behaved in an unexpected way: the magnet was able to be operated at operation currents above the maximum current that was predicted based on short-sample measurements. Additionally, unexpectedly gradual dependency between magnet's resistive voltage and operation current was observed. In this work, a thermodynamical model is formulated in order to study the behavior of Feather-M2. The model was parametrized and the parameters were solved via inverse problem by finding the best match to experimental results. Thereby insight was gained on the prospects of the utilized thermodynamical model and also on the behavior and operation conditions of the magnet via the inverse problem solutions. To summarize, this paper presents a new methodology for analyzing magnets in operation and applies it to a state-of-the-art magnet.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Research area: Power engineering, Research group: Modelling and superconductivity, European Organization for Nuclear Research
Contributors: Ruuskanen, J., Stenvall, A., Lahtinen, V., Nugteren, J. V., Kirby, G., Murtomäki, J.
Publication date: 2 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Superconductor Science and Technology
Volume: 32
Issue number: 9
Article number: 094007
ISSN (Print): 0953-2048
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Condensed Matter Physics, Metals and Alloys, Electrical and Electronic Engineering, Materials Chemistry
Keywords: HTS magnets, modelling, optimization, thermal stability
Source: Scopus
Source ID: 85072121234

Research output: Contribution to journalArticleScientificpeer-review

3-D mechanical modeling of 20 T HTS clover leaf end coils - Good practices and lessons learned

Very high electromagnetic forces are generated in the superconducting coils of high field accelerator magnets. The cables, which are used to wind the coils, can withstand limited pressure levels and strains generated during the powering without degradation. To protect the cables from mechanical damage, reliable prediction of strain and stress inside the coil is paramount for designing suitable support structure of the magnet. This is naturally done before a magnet is built and tested, which emphasizes the need for reliable modeling. Conventionally, the mechanics in superconducting coils are modeled assuming homogenized material properties inside a homogenized coil volume. Using this so-called coil block approach, predicting the actual cable strain or stress inside the homogenized volume is unreliable. In order to predict reliably the stress in the cable, more detailed representation of the modeling domain is needed. This paper presents a workflow to perform a detailed mechanical analysis using finite-element analysis following the envisioned and more detailed approach. As an example, a high field 20 T+ magnet with clover leaf ends is studied, and results are discussed. The results reveal considerable difference between the behavior of modeled homogenized coil blocks and coils where turns are individually considered.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, European Organization for Nuclear Research
Contributors: Murtomäki, J. S., Van Nugteren, J., Stenvall, A., Kirby, G., Rossi, L.
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 5
Article number: 8642381
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator magnets: dipoles, computer aided engineering, correctors, finite element methods, HTS magnets, magnet structure, magnet supports, modeling, quadrupoles, simulation, stress, superconducting magnet mechanical factors
Source: Scopus
Source ID: 85065098308

Research output: Contribution to journalArticleScientificpeer-review

AlGaAs/AlGaInP VECSELs with Direct Emission at 740-770 nm

An optically-pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) with 3.25-W output power emitting around 750 nm is demonstrated. The gain structure incorporates AlGaAs quantum wells (QWs) and barriers, and AlGaInP claddings. The emission wavelength could be tuned from 740 to 770 nm. The development addresses the need for high brightness lasers at a wavelength range that has proven difficult to reach. The demonstrated structure exhibits polarization-related peculiarities, which cause polarization switching under increased pump power due to mode competition. The presence of birefringence inside the active region is attributed to known long-range ordering within the AlGaInP claddings which causes distorted beam profiles. This influence on laser features has not been reported in VECSELs so far.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics
Contributors: Nechay, K., Kahle, H., Penttinen, J., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Number of pages: 4
Pages: 1245-1248
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 31
Issue number: 15
ISSN (Print): 1041-1135
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: AlGaAs, AlGaInP, quantum well lasers, semiconductor disk lasers, semiconductor growth, semiconductor laser, vertical-external-cavity surface-emitting lasers (VECSELs)

Bibliographical note

INT=phys,"Rajala, Patrik"

Source: Scopus
Source ID: 85069529749

Research output: Contribution to journalArticleScientificpeer-review

Exploration of Two Layer Nb3Sn Designs of the Future Circular Collider Main Quadrupoles

The goal of this study is to propose an alternative FCC quadrupole design where the risk from both their fabrication and their operation in the machine is reduced compared to previous analysis. Therefore, the number of coil layers has been reduced from four to two and the load-line margin has been increased from 14% to 20% compared to previous investigations ('Design of a Nb3Sn 400 T/m quadrupole for the future circular collider,' IEEE Trans. Appl. Supercond., vol. 28, no. 3, p. 4004905, Apr. 2018). Indeed, the idea is to only challenge the ∼5000 FCC main dipoles and stay at a relatively low complexity for the ∼700 FCC main quadrupoles so they have a limiting impact on the machine operation and reliability. An exploration of the strand diameter (0.7-0.9 mm), the cable size (40-60 strands), as well as the protection delay (30-40 ms) is performed on two-dimensional (2-D) magnetic designs of the FCC main quadrupole. A discussion on cable windability allows for the selection of one design generating 367 T/m. The design is mechanically constrained with a conventional collar structure leading to collaring peak stress of 115 MPa. A single coupling-loss-induced quench unit ensures a safe magnet operation with a 300 K hotspot temperature.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, IRFM, European Organization for Nuclear Research
Contributors: Lorin, C., Fleiter, J., Salmi, T., Schoerling, D.
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 5
Article number: 4001005
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: collar structure,CLIQ protection system, MQ, Nb Sn coil
Source: Scopus
Source ID: 85061237007

Research output: Contribution to journalArticleScientificpeer-review

Highly efficient charge separation in model Z-scheme TiO2/TiSi2/Si photoanode by micropatterned titanium silicide interlayer

Atomic layer deposited (ALD) TiO2 is an attractive material for improving the photoactivity and chemical stability of semiconductor electrodes in artificial photosynthesis. Using photoelectrochemical (PEC) measurements, we show that an interfacial, topographically microstructured TiSi2 layer inside the TiO2/Si heterojunction improves the charge carrier separation and shifts the water dissociation onset potential to more negative values. These observations are correlated with the X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) measurements, which reveal an increased band bending due to the TiSi2 interlayer. Combined with the UV–Vis absorption results, the photoelectron spectroscopy measurements allow the reconstruction of the complete energy band diagram for the TiO2/TiSi2/Si heterojunction and the calculation of the valence and conduction band offsets. The energy band alignment and improvements in PEC results reveal that the charge transfer across the heterojunction follows a Z-scheme model, where the metal-like TiSi2 islands act as recombination centers at the interface.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Surface Science, Physics
Contributors: Hannula, M., Ali-Löytty, H., Lahtonen, K., Saari, J., Tukiainen, A., Valden, M.
Number of pages: 9
Pages: 237-245
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Acta Materialia
Volume: 174
ISSN (Print): 1359-6454
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Polymers and Plastics, Metals and Alloys
Keywords: Electrochemical characterization, Electronic band structure, Titanium dioxide, Transition metal silicides, X-ray photoelectron spectroscopy (XPS)
Source: Scopus
Source ID: 85066305210

Research output: Contribution to journalArticleScientificpeer-review

Erosion wear performance of WC-10Co4Cr and Cr3C2-25NiCr coatings sprayed with high-velocity thermal spray processes

Thermally sprayed hardmetal coatings are widely used to protect components and surfaces against wear in various applications. Hard and wear resistant coatings increase the component lifetime and can generate significant savings promoting ecological manufacturing. This study focuses on the performance of tungsten carbide (WC-10Co4Cr)and chromium carbide (Cr 3 C 2 -25NiCr)based hardmetal coatings sprayed with gaseous and liquid fuelled high-velocity oxygen-fuel (HVOF)spray processes and a modern high-velocity air-fuel (HVAF)spray process. The coating characterisation revealed reduced carbide dissolution with decreasing process temperature and denser feedstock powder particles. Smaller carbide size in the Cr 3 C 2 -25NiCr material significantly reduced the carbide rebounding leading to higher carbide content in the sprayed coating and improved erosion wear resistance. Most significant improvements were observed in cavitation erosion for HVAF sprayed WC-10Co4Cr coatings (0.4 μm/h)compared to the HVOF sprayed coatings (1.5–3.7 μm/h). The cavitation erosion resistance of the HVAF sprayed coatings was almost at the level of the WC-10Co sintered bulk (0.2 μm/h).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Tampere University, VZÚ Plzeň - Research and Testing Institute
Contributors: Matikainen, V., Rubio Peregrina, S., Ojala, N., Koivuluoto, H., Schubert, J., Houdková, Vuoristo, P.
Number of pages: 17
Pages: 196-212
Publication date: 25 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: Surface and Coatings Technology
Volume: 370
ISSN (Print): 0257-8972
Original language: English
ASJC Scopus subject areas: Chemistry(all), Condensed Matter Physics, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Cavitation erosion, Coating, Hardmetal, Slurry erosion, Thermal spray

Bibliographical note

INT=msee,"Rubio Peregrina, S."

Source: Scopus
Source ID: 85065223119

Research output: Contribution to journalArticleScientificpeer-review

Temporal ghost imaging using wavelength conversion and two-color detection

Ghost imaging constructs an image by correlating two signals: one that interacts with an object but possesses no spatial information, and the other that contains spatial information but does not interact with the object. Ghost imaging can be extended into the time domain by using laser intensity fluctuations to reconstruct an unknown time-varying pattern, but this requires the measurement of laser fluctuations on ultrafast timescales, a significant limitation at wavelengths where ultrafast detectors are not available.We overcome this by using wavelength conversion to shift the probe laser into a spectral region where ultrafast detectors are available, and we apply this technique to image a temporal object at 2 μm. Our results demonstrate that temporal correlation information can be transferred to an arbitrary spectral region, opening possibilities for ultrafast ghost imaging at new wavelengths.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Electronic Science and Technology of China, UMR 6174, Ita-Suomen yliopisto
Contributors: Wu, H., Ryczkowski, P., Friberg, A. T., Dudley, J. M., Genty, G.
Number of pages: 5
Pages: 902-906
Publication date: 20 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 6
Issue number: 7
ISSN (Print): 2334-2536
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Wu, Han"

Source: Scopus
Source ID: 85071154886

Research output: Contribution to journalArticleScientificpeer-review

3D Scaffolds of Polycaprolactone/Copper-Doped Bioactive Glass: Architecture Engineering with Additive Manufacturing and Cellular Assessments in a Coculture of Bone Marrow Stem Cells and Endothelial Cells

The local delivery of Cu2+ from copper-doped bioactive glass (Cu-BaG) was combined with 3D printing of polycaprolactone (PCL) scaffolds for its potent angiogenic effect in bone tissue engineering. PCL and Cu-BaG were, respectively, dissolved and dispersed in acetone to formulate a moderately homogeneous ink. The PCL/Cu-BaG scaffolds were fabricated via direct ink writing into a cold ethanol bath. The architecture of the printed scaffolds, including strut diameter, strut spacing, and porosity, were investigated and characterized. The PCL/Cu-BaG scaffolds showed a Cu-BaG content-dependent mechanical property, as the compressive Young's modulus ranged from 7 to 13 MPa at an apparent porosity of 60%. The ion dissolution behavior in simulated body fluid was evaluated, and the hydroxyapatite-like precipitation on the strut surface was confirmed. Furthermore, the cytocompatibility of the PCL/Cu-BaG scaffolds was assessed in human bone marrow stem cell (hBMSC) culture, and a dose-dependent cytotoxicity of Cu2+ was observed. Here, the PCL/BaG scaffold induced the higher expression of late osteogenic genes OSTEOCALCIN and DLX5 in comparison to the PCL scaffold. The doping of Cu2+ in BaG elicited higher expression of the early osteogenic marker gene RUNX2a but decreased the expression of late osteogenic marker genes OSTEOCALCIN and DLX5 in comparison to the PCL/BaG scaffold, demonstrating the suppressing effect of Cu2+ on osteogenic differentiation of hBMSCs. In a coculture of hBMSCs and human umbilical vein endothelial cells, both the PCL/BaG and PCL/Cu-BaG scaffolds stimulated the formation of a denser tubule network, compared to the PCL scaffold. Meanwhile, only slightly higher gene expression of vWF was observed with the PCL/Cu-BaG scaffold than with the PCL/BaG scaffold, indicating the potent angiogenic effect of the released Cu2+.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Research group: Computational Biophysics and Imaging Group, Johan Gadolin Process Chemistry Centre, Abo Akademi University, University of Wollongong, Tampere University Hospital, Tampere University
Contributors: Wang, X., Molino, B. Z., Pitkänen, S., Ojansivu, M., Xu, C., Hannula, M., Hyttinen, J., Miettinen, S., Hupa, L., Wallace, G.
Pages: 4496-4510
Publication date: 18 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: ACS Biomaterials Science and Engineering
Volume: 5
Issue number: 9
ISSN (Print): 2373-9878
Original language: English
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering
Keywords: 3D printing, angiogenesis, coculture of mesenchymal stem cells and endothelial cells, copper-doped bioactive glass, gradient porosity, polycaprolactone, tissue engineering scaffold
Electronic versions: 
Source: Scopus
Source ID: 85070677224

Research output: Contribution to journalArticleScientificpeer-review

Observation of Coexistence of Yu-Shiba-Rusinov States and Spin-Flip Excitations

We investigate the spectral evolution in different metal phthalocyanine molecules on NbSe2 surface using scanning tunnelling microscopy (STM) as a function of the coupling with the substrate. For manganese phthalocyanine (MnPc), we demonstrate a smooth spectral crossover from Yu-Shiba-Rusinov (YSR) bound states to spin-flip excitations. This has not been observed previously and it is in contrast to simple theoretical expectations. We corroborate the experimental findings using numerical renormalization group calculations. Our results provide fundamental new insight on the behavior of atomic scale magnetic/SC hybrid systems, which is important, for example, for engineered topological superconductors and spin logic devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Aalto University, Jozef Stefan Institute, University of Ljubljana
Contributors: Kezilebieke, S., Žitko, R., Dvorak, M., Ojanen, T., Liljeroth, P.
Number of pages: 6
Pages: 4614-4619
Publication date: 10 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: Nano Letters
Volume: 19
Issue number: 7
ISSN (Print): 1530-6984
Original language: English
ASJC Scopus subject areas: Bioengineering, Chemistry(all), Materials Science(all), Condensed Matter Physics, Mechanical Engineering
Keywords: Magnetic impurity, scanning tunneling microscopy (STM), spin-flip excitation, superconductor, Yu-Shiba-Rusinov state
Electronic versions: 
Source: Scopus
Source ID: 85069329661

Research output: Contribution to journalArticleScientificpeer-review

0.6V threshold voltage thin film transistors with solution processable indium oxide (In2O3) Channel and Anodized High-κ Al2O3 Dielectric

Low-voltage operation and low processing temperature of metal oxide transistors remain a challenge. Commonly metal oxide transistors are fabricated at very high processing temperatures (above 500°C) and their operating voltage is quite high (30-50 V). Here, thin-film transistors (TFT) are reported based upon solution processable indium oxide (In2O3) and room temperature processed anodized high- κ aluminum oxide (Al2O3) for gate dielectrics. The In2O3 TFTs operate well below the drain bias (Vds) of 3.0 V, with on/off ratio 105, subthreshold swing (SS) 160 mV/dec, hysteresis 0.19 V, and low threshold voltage (Vth)~0.6 V. The electron mobility (μ) is as high as 3.53 cm2/V.s in the saturation regime and normalized transconductance (gm) is 75μS/mm. In addition, the detailed capacitance-voltage (C-V) analysis to determine interface trap states density was also investigated. The interface trap density (Dit) in the oxide/semiconductor interface was quite low, i.e., 0.99 × 1011 - 2.98 × 1011 eV-1· cm2, signifying acceptable compatibility of In2O3 with anodic Al2O3.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Columbia University in the City of New York, VTT Technical Research Centre of Finland, Department of Electrical and Computer Engineering, Ohio State University
Contributors: Bhalerao, S. R., Lupo, D., Zangiabadi, A., Kymissis, I., Leppäniemi, J., Alastalo, A., Berger, P. R.
Number of pages: 4
Pages: 1112-1115
Publication date: 1 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Electron Device Letters
Volume: 40
Issue number: 7
ISSN (Print): 0741-3106
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: anodization, indium oxide (InO), interface state density, low voltage, Metal oxide semiconductors, solution processing, TFT
Source: Scopus
Source ID: 85068181785

Research output: Contribution to journalArticleScientificpeer-review

FCC-hh: The Hadron Collider: Future Circular Collider Conceptual Design Report Volume 3

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Electrical Engineering, CNRS Centre National de la Recherche Scientifique, Istituto Nazionale di Fisica Nucleare Sezione di Bari (INFN BA), Universita degli Studi di Bari, Shahid Beheshti University, Bochvar Institute of Inorganic Materials (VNIINM), University of Oxford, Royal Holloway University (RHUL), University of Applied Sciences Technikum Wien (UAS TW), TOBB University of Economics and Technology, University of Belgrade, Harvard University, Universidad de Granada, Universitat Politecnica de Valencia, Spain, Paul Scherrer Institut, European Organization for Nuclear Research, Laboratorio Accelatori e Superconduttività Applicata, University Tor Vergata, Kahramanmaras Sutcu Imam University (KSU), Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Università degli Studi di Catania, University of Manchester, French Atomic Energy Commission (CEA) Saclay, Fermi National Accelerator Laboratory, Istituto Nazionale di Fisica Nucleare, Sezione di Milano, University of Cambridge, University of Birmingham, Eskişehir Technical University (ESTU), Istanbul University, University of California Santa Cruz (UCSC), Linde Kryotechnik AG (Linde), Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, CNR-INO, Università degli Studi di Milano, Massachusetts Institute of Technology, MAN Energy Solutions Schweiz AG (MAN ES), University of Münster, Laboratori Nazionali di Frascati (INFN LNF), Sezione di Padova (INFN PD), Universita degli Studi di Padova, Italy, Università di Insubria (UNINSUBRIA)
Contributors: the FCC Collaboration, Abada, A., Abbrescia, M., AbdusSalam, S. S., Abdyukhanov, I., Abelleira Fernandez, J., Abramov, A., Aburaia, M., Acar, A. O., Adzic, P. R., Agrawal, P., Aguilar-Saavedra, J. A., Aguilera-Verdugo, J. J., Aiba, M., Aichinger, I., Aielli, G., Akay, A., Akhundov, A., Aksakal, H., Albacete, J. L., Albergo, S., Alekou, A., Aleksa, M., Aleksan, R., Alemany Fernandez, R. M., Alexahin, Y., Alía, R. G., Alioli, S., Alipour Tehrani, N., Allanach, B. C., Allport, P. P., Altınlı, M., Altmannshofer, W., Ambrosio, G., Amorim, D., Amstutz, O., Anderlini, L., Andreazza, A., Andreini, M., Andriatis, A., Andris, C., Andronic, A., Angelucci, M., Antinori, F., Antipov, S. A., Antonelli, M., Antonello, M., Lehtinen, T., Penttinen, J. P., Salmi, T., Stenvall, A.
Number of pages: 353
Pages: 755-1107
Publication date: 1 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: European Physical Journal: Special Topics
Volume: 228
Issue number: 4
ISSN (Print): 1951-6355
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physics and Astronomy(all), Physical and Theoretical Chemistry
Source: Scopus
Source ID: 85068232451

Research output: Contribution to journalArticleScientificpeer-review

Characterization of cracks formed in large flat-on-flat fretting contact

Fretting fatigue may lead to severe damage in machines. Adhesive material transfer spots in millimeter scale have previously been observed on fretted surfaces, which have been related to cracking. In this study, fretting-induced cracks formed in a large annular flat-on-flat contact are characterized. Optical and scanning electron microscopy of the fretting scar cross-section samples of self-mated quenched and tempered steel specimens revealed severe cracking and deformed microstructure. Two major cracks typically formed around an adhesion spot, which propagated at an oblique angle, regardless of the test parameters used. Millimeter-scale cracks were observed already within a few thousand loading cycles.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Tribology and Machine Elements, Materials Science and Environmental Engineering, Research group: Materials Characterization, Wärtsilä, University of Oulu, Tampere University
Contributors: Juoksukangas, J., Nurmi, V., Hintikka, J., Vippola, M., Lehtovaara, A., Mäntylä, A., Vaara, J., Frondelius, T.
Number of pages: 10
Pages: 361-370
Publication date: Jul 2019
Peer-reviewed: Yes

Publication information

Journal: International Journal of Fatigue
Volume: 124
ISSN (Print): 0142-1123
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Mechanical Engineering, Surfaces, Coatings and Films, Surfaces and Interfaces
Keywords: Crack formation, Cracks, Damage, Fretting fatigue, Microscopy
Electronic versions: 

Bibliographical note

INT=msee,"Nurmi, Verner"
EXT="Hintikka, Jouko"

Source: Scopus
Source ID: 85062887941

Research output: Contribution to journalArticleScientificpeer-review

An architectural understanding of natural sway frequencies in trees

The relationship between form and function in trees is the subject of a longstanding debate in forest ecology and provides the basis for theories concerning forest ecosystem structure and metabolism. Trees interact with the wind in a dynamic manner and exhibit natural sway frequencies and damping processes that are important in understanding wind damage. Tree-wind dynamics are related to tree architecture, but this relationship is not well understood. We present a comprehensive view of natural sway frequencies in trees by compiling a dataset of field measurement spanning conifers and broadleaves, tropical and temperate forests. The field data show that a cantilever beam approximation adequately predicts the fundamental frequency of conifers, but not that of broadleaf trees. We also use structurally detailed tree dynamics simulations to test fundamental assumptions underpinning models of natural frequencies in trees. We model the dynamic properties of greater than 1000 trees using a finite-element approach based on accurate three-dimensional model trees derived from terrestrial laser scanning data. We show that (1) residual variation, the variation not explained by the cantilever beam approximation, in fundamental frequencies of broadleaf trees is driven by their architecture; (2) slender trees behave like a simple pendulum, with a single natural frequency dominating their motion, which makes them vulnerable to wind damage and (3) the presence of leaves decreases both the fundamental frequency and the damping ratio. These findings demonstrate the value of new three-dimensional measurements for understanding wind impacts on trees and suggest new directions for improving our understanding of tree dynamics from conifer plantations to natural forests.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, University of Oxford, SCION, University of Connecticut, Delft University of Technology, Wageningen University and Research Centre, University of Massachusetts Amherst, National Parks Board, University of Melbourne, Oregon State University, Universiteit Gent, National Physical Laboratory, University College London, NERC National Centre for Earth Observation (NCEO), 16 Center for International Forestry Research (CIFOR), Swedish University of Agricultural Sciences, INRA
Contributors: Jackson, T., Shenkin, A., Moore, J., Bunce, A., van Emmerik, T., Kane, B., Burcham, D., James, K., Selker, J., Calders, K., Origo, N., Disney, M., Burt, A., Wilkes, P., Raumonen, P., Gonzalez de Tanago Menaca, J., Lau, A., Herold, M., Goodman, R. C., Fourcaud, T., Malhi, Y.
Number of pages: 1
Publication date: 28 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of the Royal Society. Interface
Volume: 16
Issue number: 155
ISSN (Print): 1742-5689
Original language: English
ASJC Scopus subject areas: Biotechnology, Biophysics, Bioengineering, Biomaterials, Biochemistry, Biomedical Engineering
Keywords: finite-element analysis, fundamental frequency, natural frequencies, terrestrial laser scanning, tree architecture, wind damage
Source: Scopus
Source ID: 85067464325

Research output: Contribution to journalArticleScientificpeer-review

Photocontrol of Supramolecular Azo-Containing Block Copolymer Thin Films during Dip-Coating: Toward Nanoscale Patterned Coatings

Dip-coating allows nanostructured block copolymer (BCP) thin film fabrication in a fast and facile one-step process. It can also be coupled with external controls, such as illumination. Herein, we expose several design principles that enable photocontrol of the nanostructured surface pattern and thickness of supramolecular BCP thin films. This is done using a polystyrene-poly(4-vinylpyridine) (PS-P4VP) BCP and two hydroxy-functionalized small-molecule (SM) azo derivatives that have different photochemical characteristics and that hydrogen bond to the P4VP block. We show how the film preparation concept provides tunability through the chemical structure of the photoactive SM, the relative amount of SM in the dip-coating solution, and the choice of solvent. It was found that the film thickness and SM uptake in the films are increased by illumination when THF is used but are unchanged when toluene is used as solvent, which is attributed to an optical heating effect observable with volatile solvents. The photocontrol of surface patterns is a result of photoinduced changes in the effective volume fraction of the P4VP+SM phase, which is increased by a greater volume of cis isomers, by higher SM uptake (using THF), and by more trans-cis-trans cycling for systems with shorter cis lifetime. The extent of photoinduced change can also be increased by higher molecular mobility due to more flexible SMs, lower BCP molecular weight, and nonmicellar or softer micellar solutions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Research group: Chemistry & Advanced Materials, Département de Chimie, Succ. Centre-Ville
Contributors: Vapaavuori, J., Grosrenaud, J., Siiskonen, A., Priimägi, A., Pellerin, C., Bazuin, C. G.
Number of pages: 12
Pages: 3526-3537
Publication date: 28 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: ACS Applied Nano Materials
Volume: 2
Issue number: 6
ISSN (Print): 2574-0970
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: azo-containing, block copolymer thin films, dip-coating, nanoscale patterns, photocontrol, supramolecular

Bibliographical note

EXT="Vapaavuori, Jaana"

Source: Scopus
Source ID: 85068593381

Research output: Contribution to journalArticleScientificpeer-review

Crystalline Wax Esters Regulate the Evaporation Resistance of Tear Film Lipid Layers Associated with Dry Eye Syndrome

Dry eye syndrome (DES), one of the most common ophthalmological diseases, is typically caused by excessive evaporation of tear fluid from the ocular surface. Excessive evaporation is linked to impaired function of the tear film lipid layer (TFLL) that covers the aqueous tear film. The principles of the evaporation resistance of the TFLL have remained unknown, however. We combined atomistic simulations with Brewster angle microscopy and surface potential experiments to explore the organization and evaporation resistance of films composed of wax esters, one of the main components of the TFLL. The results provide evidence that the evaporation resistance of the TFLL is based on crystalline-state layers of wax esters and that the evaporation rate is determined by defects in the TFLL and its coverage on the ocular surface. On the basis of the results, uncovering the nonequilibrium spreading and crystallization of TFLL films has potential to reveal new means of treating DES.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Helsinki Eye Lab, University of Helsinki, J. Heyrovský Institute of Physical Chemistry, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Computational Physics Laboratory, MEMPHYS-Centre for Biomembrane Physics
Contributors: Paananen, R. O., Javanainen, M., Holopainen, J. M., Vattulainen, I.
Number of pages: 6
Pages: 3893-3898
Publication date: 25 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry Letters
Volume: 10
Issue number: 14
ISSN (Print): 1948-7185
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physical and Theoretical Chemistry
Electronic versions: 

Bibliographical note

EXT="Paananen, Riku O."

Source: Scopus
Source ID: 85069849171

Research output: Contribution to journalArticleScientificpeer-review

Water-Responsive and Mechanically Adaptive Natural Rubber Composites by in Situ Modification of Mineral Filler Structures

A new biomimetic stimuli-responsive adaptive elastomeric material, whose mechanical properties are altered by a water treatment is reported in this paper. This material is a calcium sulphate (CaSO4) filled composite with an epoxidized natural rubber (ENR) matrix. By exploiting various phase transformation processes that arise when CaSO4 is hydrated, several different crystal structures of CaSO4·xH2O can be developed in the cross-linked ENR matrix. Significant improvements in the mechanical and thermal properties are then observed in the water-treated composites. When compared with the untreated sample, there is approximately 100% increase in the dynamic modulus. The thermal stability of the composites is also improved by increasing the maximum degradation rate temperature by about 20 °C. This change in behavior results from an in situ development of hydrated crystal structures of the nanosized CaSO4 particles in the ENR matrix, which has been verified using Raman spectroscopy, transmission electron microscopy, atomic force microscopy, and X-ray scattering. This work provides a promising and relatively simple pathway for the development of next generation of mechanically adaptive elastomeric materials by an eco-friendly route, which may eventually also be developed into an innovative biodegradable and biocompatible smart polymeric material.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Leibniz-Institut für Polymerforschung Dresden E.V., University of Massachusetts Lowell, Vodafone Department of Mobile Communications Systems, Queen Mary University of London
Contributors: Banerjee, S. S., Hait, S., Natarajan, T. S., Wießner, S., Stöckelhuber, K. W., Jehnichen, D., Janke, A., Fischer, D., Heinrich, G., Busfield, J. J., Das, A.
Number of pages: 8
Pages: 5168-5175
Publication date: 20 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry B
Volume: 123
Issue number: 24
ISSN (Print): 1520-6106
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Surfaces, Coatings and Films, Materials Chemistry
Source: Scopus
Source ID: 85067653290

Research output: Contribution to journalArticleScientificpeer-review

Epitaxial phases of high Bi content GaSbBi alloys

GaSbBi alloys have recently emerged as attractive materials for mid-infrared optoelectronics owing to strong band gap reduction enabled by Bi incorporation into the GaSb matrix. The fundamental understanding of the epitaxial process required to demonstrate high quality crystals is in an early-developmental phase. From this perspective, we report on the key role played by the Sb/Ga flux ratio in controlling the structural quality and incorporation of high Bi content GaSbBi (up to 14.5%-Bi), revealing three distinct epitaxial phases. The first phase (below stoichiometric Sb/Ga) exhibits Ga-Bi compound droplets, low crystal quality, and reduced Bi content. At the second phase (above stoichiometric Sb/Ga), the crystal exhibits smooth surfaces and excellent crystallinity with efficient Bi incorporation. The last phase corresponds to exceeding a Sb/Ga threshold that leads to reduced Bi incorporation, Bi droplets and degraded crystallinity. This threshold value that defines the optimal growth window is controlled by the temperature as well as the Bi/Ga ratio. Increasing temperature increases the threshold, albeit simultaneously reducing Bi incorporation. Conversely, increasing the Bi/Ga flux ratio increases Bi incorporation, while narrowing down and ultimately closing the window. This study provides a general framework enabling development of high quality GaSbBi heterostructures for emerging mid-infrared optoelectronics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC
Contributors: Hilska, J., Koivusalo, E., Puustinen, J., Suomalainen, S., Guina, M.
Number of pages: 5
Pages: 67-71
Publication date: 15 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Crystal Growth
Volume: 516
ISSN (Print): 0022-0248
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Inorganic Chemistry, Materials Chemistry
Keywords: A3. Molecular beam epitaxy, B1. Antimonides, B1. Bismuth compounds, B2. Semiconducting III-V materials, B2. Semiconducting ternary compounds
Source: Scopus
Source ID: 85063780657

Research output: Contribution to journalArticleScientificpeer-review

Photovoltaic properties of low-bandgap (0.7–0.9 eV) lattice-matched GaInNAsSb solar junctions grown by molecular beam epitaxy on GaAs

We demonstrate single junction GaInNAsSb solar cells with high nitrogen content, i.e. in the range of 5–8%, and bandgap energies close to 0.7 eV grown by molecular beam epitaxy. A good crystalline quality is demonstrated for the entire range of N concentrations. An average external quantum efficiency of 0.45 is demonstrated for GaInNAsSb solar cell with 6.2% N exhibiting a bandgap of 0.78 eV (no antireflection coatings has been applied). The internal quantum efficiency for the cell is 0.65 at E g + 0.2 eV. The solar cells exhibited bandgap-voltage offsets between 0.55 V (for N = 5.3%) and 0.66 V (for N = 7.9%). When used in a six-junction solar cell architecture under AM1.5D illumination, the estimated short-circuit current density corresponding to the 0.78 eV cell is 8.2 mA/cm 2 . Furthermore, using the parameters obtained for the GaInNAsSb junction with 6.2% N, we have estimated that such six-junction solar cell architecture could realistically attain an efficiency of over 50% at 1000 suns concentration.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, Research group: Nanophotonics, Microscopy Center
Contributors: Isoaho, R., Aho, A., Tukiainen, A., Aho, T., Raappana, M., Salminen, T., Reuna, J., Guina, M.
Number of pages: 6
Pages: 198-203
Publication date: 15 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Solar Energy Materials and Solar Cells
Volume: 195
ISSN (Print): 0927-0248
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films
Keywords: Dilute nitrides, GaInNAsSb, Molecular beam epitaxy, Multijunction solar cells
Source: Scopus
Source ID: 85062810786

Research output: Contribution to journalArticleScientificpeer-review

Role of fracture toughness in impact-abrasion wear

Two new low alloyed steels were developed with different fracture toughness values but at similar level of hardness with same composition and microstructural phase. The steels were subjected to impact-abrasion wear test. This work examines specifically the additional role of toughness during impact-abrasion wear, using a newly developed high toughness steel. Microstructural characterisation of the damaged samples revealed that better toughness helps resist both impact and abrasion damage.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, University of Cambridge, Tata Steel Ltd.
Contributors: Chintha, A. R., Valtonen, K., Kuokkala, V. T., Kundu, S., Peet, M. J., Bhadeshia, H. K.
Number of pages: 8
Pages: 430-437
Publication date: 15 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Wear
Volume: 428-429
ISSN (Print): 0043-1648
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Abrasion, Fracture toughness, Impact-abrasion, Steel, Wear testing
Electronic versions: 
Source: Scopus
Source ID: 85064619336

Research output: Contribution to journalArticleScientificpeer-review

Tailoring Second-Harmonic Emission from (111)-GaAs Nanoantennas

Second-harmonic generation (SHG) in resonant dielectric Mie-scattering nanoparticles has been hailed as a powerful platform for nonlinear light sources. While bulk-SHG is suppressed in elemental semiconductors, for example, silicon and germanium due to their centrosymmetry, the group of zincblende III-V compound semiconductors, especially (100)-grown AlGaAs and GaAs, have recently been presented as promising alternatives. However, major obstacles to push the technology toward practical applications are the limited control over directionality of the SH emission and especially zero forward/backward radiation, resulting from the peculiar nature of the second-order nonlinear susceptibility of this otherwise highly promising group of semiconductors. Furthermore, the generated SH signal for (100)-GaAs nanoparticles depends strongly on the polarization of the pump. In this work, we provide both theoretically and experimentally a solution to these problems by presenting the first SHG nanoantennas made from (111)-GaAs embedded in a low index material. These nanoantennas show superior forward directionality compared to their (100)-counterparts. Most importantly, based on the special symmetry of the crystalline structure, it is possible to manipulate the SHG radiation pattern of the nanoantennas by changing the pump polarization without affecting the linear properties and the total nonlinear conversion efficiency, hence paving the way for efficient and flexible nonlinear beam-shaping devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Nonlinear Optics, Physics, Australian National University, Friedrich-Schiller-University Jena, School of Engineering and Information Technology, University of New South Wales (UNSW) Australia, Russian Academy of Sciences
Contributors: Sautter, J. D., Xu, L., Miroshnichenko, A. E., Lysevych, M., Volkovskaya, I., Smirnova, D. A., Camacho-Morales, R., Zangeneh Kamali, K., Karouta, F., Vora, K., Tan, H. H., Kauranen, M., Staude, I., Jagadish, C., Neshev, D. N., Rahmani, M.
Number of pages: 7
Pages: 3905-3911
Publication date: 12 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Nano Letters
Volume: 19
Issue number: 6
ISSN (Print): 1530-6984
Original language: English
ASJC Scopus subject areas: Bioengineering, Chemistry(all), Materials Science(all), Condensed Matter Physics, Mechanical Engineering
Keywords: Dielectric nanoantennas, directional emission, III-V semiconductors, Mie resonance, multipolar interference, second harmonic generation
Source: Scopus
Source ID: 85067057047

Research output: Contribution to journalArticleScientificpeer-review

The Role of Temperature and Lipid Charge on Intake/Uptake of Cationic Gold Nanoparticles into Lipid Bilayers

Understanding the molecular mechanisms governing nanoparticle–membrane interactions is of prime importance for drug delivery and biomedical applications. Neutron reflectometry (NR) experiments are combined with atomistic and coarse-grained molecular dynamics (MD) simulations to study the interaction between cationic gold nanoparticles (AuNPs) and model lipid membranes composed of a mixture of zwitterionic di-stearoyl-phosphatidylcholine (DSPC) and anionic di-stearoyl-phosphatidylglycerol (DSPG). MD simulations show that the interaction between AuNPs and a pure DSPC lipid bilayer is modulated by a free energy barrier. This can be overcome by increasing temperature, which promotes an irreversible AuNP incorporation into the lipid bilayer. NR experiments confirm the encapsulation of the AuNPs within the lipid bilayer at temperatures around 55 °C. In contrast, the AuNP adsorption is weak and impaired by heating for a DSPC–DSPG (3:1) lipid bilayer. These results demonstrate that both the lipid charge and the temperature play pivotal roles in AuNP–membrane interactions. Furthermore, NR experiments indicate that the (negative) DSPG lipids are associated with lipid extraction upon AuNP adsorption, which is confirmed by coarse-grained MD simulations as a lipid-crawling effect driving further AuNP aggregation. Overall, the obtained detailed molecular view of the interaction mechanisms sheds light on AuNP incorporation and membrane destabilization.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Biological Physics and Soft Matter, Research area: Computational Physics, Physics, Computational Physics Laboratory, University of Helsinki, Politecnico di Milano, Institut Laue-Langevin, Max Planck Institute of Colloids and Interfaces, MEMPHYS−Center for Biomembrane Physics, Norwegian Univ. of Sci. and Technol., G2Elab/Institut Néel
Contributors: Lolicato, F., Joly, L., Martinez-Seara, H., Fragneto, G., Scoppola, E., Baldelli Bombelli, F., Vattulainen, I., Akola, J., Maccarini, M.
Publication date: 7 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Small
Volume: 15
Issue number: 23
Article number: 1805046
ISSN (Print): 1613-6810
Original language: English
ASJC Scopus subject areas: Biotechnology, Biomaterials, Chemistry(all), Materials Science(all)
Keywords: gold nanoparticles, lipid membranes, molecular dynamics simulations, nanotoxicity, neutron reflectometry
Electronic versions: 

Bibliographical note

EXT="Martinez-Seara, Hector"

Source: Scopus
Source ID: 85064688737

Research output: Contribution to journalArticleScientificpeer-review

Analytical Expressions for Spring Constants of Capillary Bridges and Snap-in Forces of Hydrophobic Surfaces

When a force probe with a small liquid drop adhered to its tip makes contact with a substrate of interest, the normal force right after contact is called the snap-in force. This snap-in force is related to the advancing contact angle or the contact radius at the substrate. Measuring snap-in forces has been proposed as an alternative to measure the advancing contact angles of surfaces. The snap-in occurs when the distance between the probe surface and the substrate is hS, which is amenable to geometry, assuming the drop was a spherical cap before snap-in. Equilibrium is reached at a distance hE < hS. At equilibrium, the normal force F = 0, and the capillary bridge is a spherical segment, amenable again to geometry. For a small normal displacement Δh = h - hE, the normal force can be approximated with F ≈ -k1Δh or F ≈ -k1Δh - k2Δh2, where k1 = -∂F/∂h and k2 = -1/2·∂2F/∂h2 are the effective linear and quadratic spring constants of the bridge, respectively. Analytical expressions for k1,2 are found using Kenmotsu's parameterization. Fixed contact angle and fixed contact radius conditions give different forms of k1,2. The expressions for k1 found here are simpler, yet equivalent to the earlier derivation by Kusumaatmaja and Lipowsky (2010). Approximate snap-in forces are obtained by setting Δh = hS - hE. These approximate analytical snap-in forces agree with the experimental data from Liimatainen et al. (2017) and a numerical method based on solving the shape of the interface. In particular, the approximations are most accurate for super liquid-repellent surfaces. For such surfaces, readers may find this new analytical method more convenient than solving the shape of the interface numerically.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech
Contributors: Sariola, V.
Number of pages: 7
Pages: 7129-7135
Publication date: 4 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Langmuir
Volume: 35
Issue number: 22
ISSN (Print): 0743-7463
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Surfaces and Interfaces, Spectroscopy, Electrochemistry
Electronic versions: 
Source: Scopus
Source ID: 85066806357

Research output: Contribution to journalArticleScientificpeer-review

Correlation of Surface Morphology and Interfacial Adhesive Behavior between Cellulose Surfaces: Quantitative Measurements in Peak-Force Mode with the Colloidal Probe Technique

A better understanding of cellulose-cellulose interactions is needed in applications such as paper making and all-cellulose composites. To date, cellulose-cellulose studies have been chemistry-oriented. In these studies, the sample surfaces have been modified with different chemicals and then tested under an atomic force microscope (AFM) using a colloidal probe (CP). Studies of cellulose-cellulose interaction based on sample morphology and mechanical properties have been rare as a result of the complex surface structure and the soft texture of the cellulose. The current surface interaction models, such as the Johnson-Kendall-Roberts (JKR) model in which the studied bodies are assumed to have smooth surfaces, can no longer fully reveal the interfacial behavior between two cellulose surfaces. Therefore, we propose a new type of contact model for rough-rough interaction by dividing the surface contacts into primary and secondary levels. The main idea of the new model is to take into account local individual contact details between rough surfaces. The model considers the effect of the surface topography by including the asperities and valleys on a cellulose sphere used as the colloidal probe in imaging the topography of a cellulose membrane (CM). In addition, the correlation between the surface morphology and adhesion is studied. To verify the importance of including the effect of the surface roughness in contact analysis and validate our hypothesis on the correlation between the surface morphology and adhesion, an extensive set of experiments was performed. In the experiments, a combination of the AFM peak-force mode (PFM) and the CP technique was employed to acquire a massive amount of information on cellulose-cellulose interactions by measuring the adhesion among six CSs of different sizes and a CM.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Micro and Nanosystems Research Group, BioMediTech, Harbin Institute of Technology, Tokyo University of Science
Contributors: Lai, Y., Zhang, H., Sugano, Y., Xie, H., Kallio, P.
Number of pages: 10
Pages: 7312-7321
Publication date: 4 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Langmuir
Volume: 35
Issue number: 22
ISSN (Print): 0743-7463
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Surfaces and Interfaces, Spectroscopy, Electrochemistry
Electronic versions: 
Source: Scopus
Source ID: 85066731882

Research output: Contribution to journalArticleScientificpeer-review

Bioactive glass ions induce efficient osteogenic differentiation of human adipose stem cells encapsulated in gellan gum and collagen type I hydrogels

Background: Due to unmet need for bone augmentation, our aim was to promote osteogenic differentiation of human adipose stem cells (hASCs) encapsulated in gellan gum (GG) or collagen type I (COL) hydrogels with bioactive glass (experimental glass 2-06 of composition [wt-%]: Na 2 O 12.1, K 2 O 14.0, CaO 19.8, P 2 O5 2.5, B 2 O 3 1.6, SiO 2 50.0) extract based osteogenic medium (BaG OM) for bone construct development. GG hydrogels were crosslinked with spermidine (GG-SPD) or BaG extract (GG-BaG). Methods: Mechanical properties of cell-free GG-SPD, GG-BaG, and COL hydrogels were tested in osteogenic medium (OM) or BaG OM at 0, 14, and 21 d. Hydrogel embedded hASCs were cultured in OM or BaG OM for 3, 14, and 21 d, and analyzed for viability, cell number, osteogenic gene expression, osteocalcin production, and mineralization. Hydroxyapatite-stained GG-SPD samples were imaged with Optical Projection Tomography (OPT) and Selective Plane Illumination Microscopy (SPIM) in OM and BaG OM at 21 d. Furthermore, Raman spectroscopy was used to study the calcium phosphate (CaP) content of hASC-secreted ECM in GG-SPD, GG-BaG, and COL at 21 d in BaG OM. Results: The results showed viable rounded cells in GG whereas hASCs were elongated in COL. Importantly, BaG OM induced significantly higher cell number and higher osteogenic gene expression in COL. In both hydrogels, BaG OM induced strong mineralization confirmed as CaP by Raman spectroscopy and significantly improved mechanical properties. GG-BaG hydrogels rescued hASC mineralization in OM. OPT and SPIM showed homogeneous 3D cell distribution with strong mineralization in BaG OM. Also, strong osteocalcin production was visible in COL. Conclusions: Overall, we showed efficacious osteogenesis of hASCs in 3D hydrogels with BaG OM with potential for bone-like grafts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Biomaterials and Tissue Engineering Group, BioMediTech, Research group: Computational Biophysics and Imaging Group, Tampere University Hospital, Research, University of Jyvaskyla, Abo Akad Univ, Abo Akademi University, Dept Phys, Tampere University of Applied Sciences
Contributors: Vuornos, K., Ojansivu, M., Koivisto, J. T., Häkkänen, H., Belay, B., Montonen, T., Huhtala, H., Kääriäinen, M., Hupa, L., Kellomäki, M., Hyttinen, J., Ihalainen, J. A., Miettinen, S.
Number of pages: 14
Pages: 905-918
Publication date: 1 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Materials Science and Engineering C
Volume: 99
ISSN (Print): 0928-4931
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Mechanics of Materials, Mechanical Engineering
Keywords: Adipose stem cell, Bioactive glass, Collagen type I hydrogel, Gellan gum hydrogel, Osteogenic differentiation
URLs: 

Bibliographical note

DUPL=47148426

Source: Scopus
Source ID: 85061661719

Research output: Contribution to journalArticleScientificpeer-review

Energy density-method: An approach for a quick estimation of quench temperatures in high-field accelerator magnets

Accelerator magnets for future particle accelerators are designed to work with as high energy densities as possible to achieve high fields and compact magnet designs. A key factor limiting the energy density is given by the protection in case of quench: If a quench occurs, the stored energy must be first absorbed by the windings, and the magnet temperature shall not exceed a given limit. In this paper, we present a back-of-the-envelope method for estimating the magnet&#x0027;s maximum temperature after a quench based on its stored energy. The method combines the existing concepts of MIITs, time margin, and protection delay to allow for easy and direct calculation of the hot-spot temperature. We apply the proposed method to several Nb3Sn dipole and quadrupole magnets developed for HL-LHC (High Luminosity LHC) and the FCC-hh (Future Circular Collider for hadron-hadron collisions) and compare the results to a more detailed simulation. The proposed Energy density-method is a useful tool for fast feedback in the early magnet design phase to ensure that the magnet is not impossible to protect.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research area: Power engineering, Research group: Modelling and superconductivity, European Organization for Nuclear Research
Contributors: Salmi, T., Schoerling, D.
Publication date: Jun 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 4
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Conductivity, Copper, Energy storage, Heating systems, Magnetic circuits, Superconducting magnets, Temperature
Source: Scopus
Source ID: 85056300732

Research output: Contribution to journalArticleScientificpeer-review

Simulation of Delamination Growth at CFRP-Tungsten Aerospace Laminates Using VCCT and CZM Modelling Techniques

Delamination analysis in advanced composites is required for the laminate design phase and also during the operation of composite aerospace structures to estimate the criticality of flaws and damage. The virtual crack closure technique (VCCT) and cohesive zone modelling (CZM) have been applied to delamination simulation as numerical tools of crack modelling. VCCT and CZM have their unique advantages and disadvantages per application. This study focuses on the application of VCCT to a brittle delamination in a hybrid tungsten–carbon-fibre reinforced composite (CFRP-W) and pursues to identify the challenges due to very high internal residual stresses and strain energy as well as unstable crack propagation. The CFRP-W composites have application areas in high-performance, light-weight radiation protection enclosures of satellite electronics and ultra-high frequency (e.g. 5G) systems. In our work, we present the effects of free-edge stress concentrations and interfacial separation prior to nodal release on a combined VCCT-CZM model and compare the results to pure VCCT and CZM models of the interfacial crack. Parameter notes are given based on the results to apply the combined method for delamination analyses with interfaces heavily loaded by internal residual strains.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Plastics and Elastomer Technology
Contributors: Jokinen, J., Kanerva, M.
Number of pages: 13
Pages: 709-721
Publication date: Jun 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Applied Composite Materials
Volume: 26
Issue number: 3
ISSN (Print): 0929-189X
Original language: English
ASJC Scopus subject areas: Ceramics and Composites
Keywords: CZM, Delamination, Finite element simulation, Satellite enclosure, VCCT
Source: Scopus
Source ID: 85056829668

Research output: Contribution to journalArticleScientificpeer-review

Lasing in Ni Nanodisk Arrays

We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Aalto University, University of Eastern Finland, Campus de la UAB
Contributors: Pourjamal, S., Hakala, T. K., Nečada, M., Freire-Fernández, F., Kataja, M., Rekola, H., Martikainen, J. P., Törmä, P., Van Dijken, S.
Number of pages: 7
Pages: 5686-5692
Publication date: 28 May 2019
Peer-reviewed: Yes

Publication information

Journal: ACS Nano
Volume: 13
Issue number: 5
ISSN (Print): 1936-0851
Original language: English
ASJC Scopus subject areas: Materials Science(all), Engineering(all), Physics and Astronomy(all)
Keywords: loss-compensated magnetoplasmonics, nanolasing, Ni nanodisk array, plasmonics, surface lattice resonance
Electronic versions: 
Source: Scopus
Source ID: 85064967811

Research output: Contribution to journalArticleScientificpeer-review

Fabrication of soft devices with buried fluid channels by using sacrificial 3D printed molds

Casting silicone elastomers into 3D printed molds has seen a surge of applications in soft robots, soft manipulators, microfluidics, wearable technologies and stretchable sensors. In such devices, buried fluid channels are used to transport fluids, as fluidic actuators and as sensors with liquid metal. However, it is difficult to demold structures with buried channels or overhangs. As a solution, using sacrificial molds made of dissolvable materials has been proposed. In this paper, we evaluate different commercially available 3D printing materials as dissolvable mold materials. We tested dissolving prints made of high-impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polyvinyl butyral (PVB) and polyvinyl alcohol (PVA) in limonene, acetone, isopropanol/ethanol and water, respectively. We further studied the effect of magnetic stirring and ultrasonic bath on the dissolution times. Finally, we fabricated buried channels using different mold materials and silicone elastomers. The results show that at least ABS, PVB and PVA can be used as mold materials. In particular, PVA is a promising material as it is soluble in water. The studied method simplifies the fabrication of soft devices, allowing the fabrication of overhangs and buried channels in a single casting step.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech
Contributors: Koivikko, A., Sariola, V.
Number of pages: 5
Pages: 509-513
Publication date: 24 May 2019

Host publication information

Title of host publication: 2019 2nd IEEE International Conference on Soft Robotics (RoboSoft)
Publisher: IEEE
ISBN (Electronic): 9781538692608
ASJC Scopus subject areas: Materials Science (miscellaneous), Artificial Intelligence, Mechanical Engineering, Control and Optimization
Source: Scopus
Source ID: 85067126836

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Multistep Bloch-line-mediated Walker breakdown in ferromagnetic strips

A well-known feature of magnetic field driven dynamics of domain walls in ferromagnets is the existence of a threshold driving force at which the internal magnetization of the domain wall starts to precess - a phenomenon known as the Walker breakdown - resulting in an abrupt drop of the domain-wall propagation velocity. Here, we report on micromagnetic simulations of magnetic field driven domain-wall dynamics in thin ferromagnetic strips with perpendicular magnetic anisotropy which demonstrate that in wide enough strips Walker breakdown is a multistep process: It consists of several distinct velocity drops separated by short linear parts of the velocity vs field curve. These features originate from the repeated nucleation, propagation, and annihilation of an increasing number of Bloch lines within the domain wall as the driving field magnitude is increased. This mechanism arises due to magnetostatic effects breaking the symmetry between the two ends of the domain wall.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Aalto University, COMP Centre of Excellence, Computational Physics Laboratory
Contributors: Hütner, J., Herranen, T., Laurson, L.
Publication date: 24 May 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 99
Issue number: 17
Article number: 174427
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85066395811

Research output: Contribution to journalArticleScientificpeer-review

Reaction between Peroxy and Alkoxy Radicals Can Form Stable Adducts

Peroxy (RO 2 ) and alkoxy (RO) radicals are prototypical intermediates in any hydrocarbon oxidation. In this work, we use computational methods to (1) study the mechanism and kinetics of the RO 2 + OH reaction for previously unexplored "R" structures (R = CH(O)CH 2 and R = CH 3 C(O)) and (2) investigate a hitherto unaccounted channel of molecular growth, R′O 2 + RO. On the singlet surface, these reactions rapidly form ROOOH and R′OOOR adducts, respectively. The former decomposes to RO + HO 2 and R(O)OH + O 2 products, while the main decomposition channel for the latter is back to the reactant radicals. Decomposition rates of R′OOOR adducts varied between 103 and 0.015 s -1 at 298 K and 1 atm. The most long-lived R′OOOR adducts likely account for some fraction of the elemental compositions detected in the atmosphere that are commonly assigned to stable covalently bound dimers.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Helsinki
Contributors: Iyer, S., Rissanen, M. P., Kurtén, T.
Number of pages: 7
Pages: 2051-2057
Publication date: 2 May 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry Letters
Volume: 10
Issue number: 9
ISSN (Print): 1948-7185
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physical and Theoretical Chemistry
Electronic versions: 
Source: Scopus
Source ID: 85064871304

Research output: Contribution to journalArticleScientificpeer-review

Artificial intelligence yesterday, today and tomorrow

Artificial Intelligence (AI) is one of the current emerging technologies. In the history of computing AI has been in the similar role earlier - almost every decade since the 1950s, when the programming language Lisp was invented and used to implement self-modifying applications. The second time that AI was described as one of the frontier technologies was in the 1970s, when Expert Systems (ES) were developed. A decade later AI was again at the forefront when the Japanese government initiated its research and development effort to develop an AI-based computer architecture called the Fifth Generation Computer System (FGCS). Currently in the 2010s, AI is again on the frontier in the form of (self-)learning systems manifesting in robot applications, smart hubs, intelligent data analytics, etc. What is the reason for the cyclic reincarnation of AI? This paper gives a brief description of the history of AI and also answers the question above. The current AI “cycle” has the capability to change the world in many ways. In the context of the CE conference, it is important to understand the changes it will cause in education, the skills expected in different professions, and in society at large.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences, Tallinn University of Technology, University of Lapland, Computer Science Institute
Contributors: Jaakkola, H., Henno, J., Mäkelä, J., Thalheim, B.
Number of pages: 8
Pages: 860-867
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 42nd International Convention on Information and Communication Technology, Electronics and Microelectronics, MIPRO 2019 - Proceedings
Publisher: IEEE
Editors: Skala, K., Car, Z., Pale, P., Huljenic, D., Janjic, M., Koricic, M., Sruk, V., Ribaric, S., Grbac, T. G., Butkovic, Z., Cicin-Sain, M., Skvorc, D., Mauher, M., Babic, S., Gros, S., Vrdoljak, B., Tijan, E.
ISBN (Electronic): 9789532330984
ASJC Scopus subject areas: Computer Networks and Communications, Hardware and Architecture, Information Systems, Energy Engineering and Power Technology, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Artificial Intelligence, Computer, Computer-supported decision-making, Deep learning, Education, Emerging technology, Expert Systems, Fifth Generation Computer, Frontier technology, Learning, Lisp, Prolog
Source: Scopus
Source ID: 85070299568

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Double-side pumped membrane external-cavity surface-emitting laser (MECSEL) with increased efficiency emitting > 3 W in the 780 nm region

We demonstrate a double-side pumped MECSEL emitting more than 3 W of output power in the 780 nm wavelength region. The laser exhibits an efficiency as high as 34.4 %.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics
Contributors: Kahle, H., Phung, H., Penttinen, J., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Rajala, Patrik"

Source: Scopus
Source ID: 85069191246

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Energy-dependent diffusion in a soft periodic Lorentz gas

The periodic Lorentz gas is a paradigmatic model to examine how macroscopic transport emerges from microscopic chaos. It consists of a triangular lattice of circular hard scatterers with a moving point particle. Recently this system became relevant as a model for electronic transport in low-dimensional nanosystems such as molecular graphene. However, to more realistically mimic such dynamics, the hard Lorentz gas scatterers should be replaced by soft potentials. Here we study diffusion in a soft Lorentz gas with Fermi potentials under variation of the total energy of the moving particle. Our goal is to understand the diffusion coefficient as a function of the energy. In our numerical simulations we identify three different dynamical regimes: (i) the onset of diffusion at small energies; (ii) a transition where for the first time a particle reaches the top of the potential, characterized by the diffusion coefficient abruptly dropping to zero; and (iii) diffusion at high energies, where the diffusion coefficient increases according to a power law in the energy. All these different regimes are understood analytically in terms of simple random walk approximations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research area: Computational Physics, Research group: Quantum Control and Dynamics, Physics, School of Mathematical Sciences, Technische Universität Berlin, Universitat zu Koln, Computational Physics Laboratory
Contributors: Gil-Gallegos, S., Klages, R., Solanpää, J., Räsänen, E.
Number of pages: 18
Pages: 143-160
Publication date: 1 May 2019
Peer-reviewed: Yes

Publication information

Journal: European Physical Journal: Special Topics
Volume: 228
Issue number: 1
ISSN (Print): 1951-6355
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physics and Astronomy(all), Physical and Theoretical Chemistry
Source: Scopus
Source ID: 85066258822

Research output: Contribution to journalArticleScientificpeer-review

Frequency Comb Generation in a Continuous-Wave Pumped Second-Order Nonlinear Waveguide Resonator

Optical frequency comb generation has been experimentally studied using an integrated system based on a lithium niobate waveguide resonator featuring a strong quadratic nonlinearity. Our theoretical model shows good agreement with the experimental results.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Paderborn University, University of Helsinki, VTT Technical Research Centre of Finland
Contributors: Abdallah, Z., Stefszky, M., Ulvila, V., Silberhorn, C., Vainio, M.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85069196416

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

GaInAsSb/AlGa(In)AsSb type I quantum wells emitting in 3 μm range for application in superluminescent diodes

In this paper, we present results of Fourier-transformed photoluminescence measurements of quaternary GaInAsSb quantum wells with quinary AlGaInAsSb barriers grown on GaSb substrate, designed for spectral range of mid-infrared. Here, we show an emission shift towards longer wavelength as a result of incorporation of indium into the quantum wells reaching up to 3 μm at room temperature (RT). Additionally, we have observed an additional low-energy photoluminescence signal with maximum wavelength of 3.5 μm at RT, which we have attributed as states localised on the layer interfaces. The activation energy of carriers trapped in those states is estimated to be 35 meV.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: ORC, Physics, Wrocław University of Technology
Contributors: Kurka, M., Dyksik, M., Suomalainen, S., Koivusalo, E., Guina, M., Motyka, M.
Number of pages: 5
Pages: 274-278
Publication date: 1 May 2019
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 91
ISSN (Print): 0925-3467
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Fourier-transformed spectroscopy, MBE, Optical gas sensing, Photoluminescence, Superluminescent diodes
Source: Scopus
Source ID: 85063381328

Research output: Contribution to journalArticleScientificpeer-review

High-Q resonance train in a plasmonic metasurface

We experimentally demonstrate a plasmonic surface that supports a series of high-quality-factor (Q ≈ 100) surface lattice resonances. These resonances are enabled by tuning the thickness of the top-cladding layer to confine higher order diffraction-orders.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, University of Ottawa, Canada, Iridian Spectral Technologies, University of Rochester Institute of Optics
Contributors: Saad-Bin-Alam, M., Reshef, O., Huttunen, M. J., Carlow, G., Sullivan, B., Menard, J. M., Dolgaleva, K., Boyd, R. W.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85069156893

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Intelligent data service for farmers

The agricultural sector in Finland has been lagging behind in digital development. Development has long been based on increasing production by investing in larger machines. Over the past decade, change has begun to take place in the direction of digitalization. One of the challenges is that different manufacturers are trying to get farmers' data on their own closed cloud services. In the worst case, farmers may lose an overall view of their farms and opportunities for deeper data analysis because their data is located in different services. The goals and previously studied challenges of the 'MIKÄ DATA' project are described in this research. This project will build an intelligent data service for farmers, which is based on the Oskari platform. In the 'Peltodata' service, farmers can see their own field data and many other data sources layer by layer. The project is focused on the study of machine learning techniques to develop harvest yield prediction and find out the correlation between many data sources. The 'Peltodata' service will be ready at the end of 2019.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences
Contributors: Linna, P., Narra, N., Grönman, J.
Number of pages: 4
Pages: 1072-1075
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 42nd International Convention on Information and Communication Technology, Electronics and Microelectronics, MIPRO 2019 - Proceedings
Publisher: IEEE
Editors: Skala, K., Car, Z., Pale, P., Huljenic, D., Janjic, M., Koricic, M., Sruk, V., Ribaric, S., Grbac, T. G., Butkovic, Z., Cicin-Sain, M., Skvorc, D., Mauher, M., Babic, S., Gros, S., Vrdoljak, B., Tijan, E.
ISBN (Electronic): 9789532330984
ASJC Scopus subject areas: Computer Networks and Communications, Hardware and Architecture, Information Systems, Energy Engineering and Power Technology, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Agriculture, Artificial intelligence, Platform
Source: Scopus
Source ID: 85070273282

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Optical Frequency Comb Photoacoustic Spectroscopy

We combine for the first time a mid-infrared optical frequency comb Fourier transform spectrometer with cantilever-enhanced photoacoustic detection and measure high-resolution broadband spectra of the fundamental band of methane in a few milliliter sample volume.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Energy Technology and Thermal Process Chemistry, University of Helsinki
Contributors: Sadiek, I., Mikkonen, T., Vainio, M., Toivonen, J., Foltynowicz, A.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85069190764

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Screen printed temporary tattoos for skin-mounted electronics

This paper focus on fabrication and analyzation of screen-printed temporary transfer electrical tattoos. Stretchable conductors and insulators are printed on temporary transfer tattoo paper. The printed lines are electrically and electromechanically characterized. Four different test structures were used to evaluate the sheet resistance and the quality of the printing process. The acquired sheet resistance of the tattoos was 42 mΩ/□ with a standard deviation of 6 mΩ/□. The maximum tensile strain before breaking was 19.4 %. Finally, on-skin performance was evaluated by attaching a printed tattoo on a knee and backhand of a test person. The skin-mounted tattoo showed good electrical performance and conformability.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Electrical Engineering, Research group: Wireless Communications and Positioning
Contributors: Tuominen, S., Mäntysalo, M.
Number of pages: 6
Pages: 1252-1257
Publication date: 1 May 2019

Host publication information

Title of host publication: IEEE 69th Electronic Components and Technology Conference, ECTC 2019
Publisher: IEEE
ISBN (Electronic): 9781728114989
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: Printed electronics, Stretchable electronics, Temporary electrical tattoo

Bibliographical note

INT=elen,"Tuominen, Samuli"

Source: Scopus
Source ID: 85072291977

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Surface reactivity and silanization ability of borosilicate and Mg-Sr-based bioactive glasses

Borosilicate bioactive glasses are attracting an increasing interest due to their good hot forming ability, low crystallization tendency and high bioactivity. Surface functionalization of bioactive glasses is a versatile tool for modulation of their properties and consequently of their biological response and it is still an unexplored topic in the case of borosilicate glasses. The possibility to graft 3-aminopropyltriethoxysilane (APTES) to various borosilicate bioactive glasses have been investigated in the present research work. Glasses were produced by melting and completely characterized (SEM-EDS, density, FTIR-ATR, Raman, NMR, zeta potential and reactivity in SBF and TRIS/HCl). Then, APTES was grafted to the surface of the glasses and its presence was verified by means of XPS, contact angle and zeta potential measurements. This study has shown the possibility to silanize borosilicate bioactive glasses for the first time, however, this silanization protocol does not induce the formation of a continuous coating on the glass surface.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Politecnico di Torino
Contributors: Ferraris, S., Nommeots-Nomm, A., Spriano, S., Vernè, E., Massera, J.
Number of pages: 13
Pages: 43-55
Publication date: 1 May 2019
Peer-reviewed: Yes
Early online date: 26 Dec 2018

Publication information

Journal: Applied Surface Science
Volume: 475
ISSN (Print): 0169-4332
Original language: English
ASJC Scopus subject areas: Surfaces, Coatings and Films
Keywords: APTES, Borosilicate bioactive glasses, Silanization
Source: Scopus
Source ID: 85059228057

Research output: Contribution to journalArticleScientificpeer-review

Teaching for virtual work

Universities are still mainly preparing students for the world, where 'do something useful', i.e. 'do something with your hands' was the main principle and work was done during strictly regulated time. But world has changed and traditional areas of human activity (what also are the main target in University courses) are rapidly diminishing. More important have become virtual products - computer programs, mobile apps, social networks, new types of digital currencies, IOT (voice in your bathroom suggesting to buy the next model of Alexa), video games, interactive TV, virtual reality etc. Most of these new areas are not present in current curricula and there are problems with involving them in curricula - (working) students know (some aspects of) these areas better than many of university teachers, since corresponding knowledge is not yet present in textbooks - it is present only on Internet. The Internet strongly influences both what we teach and how we teach.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences, Tallinn University of Technology, University of Lapland
Contributors: Henno, J., Jaakkola, H., Mäkelä, J.
Number of pages: 9
Pages: 818-826
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 42nd International Convention on Information and Communication Technology, Electronics and Microelectronics, MIPRO 2019 - Proceedings
Publisher: IEEE
Editors: Skala, K., Car, Z., Pale, P., Huljenic, D., Janjic, M., Koricic, M., Sruk, V., Ribaric, S., Grbac, T. G., Butkovic, Z., Cicin-Sain, M., Skvorc, D., Mauher, M., Babic, S., Gros, S., Vrdoljak, B., Tijan, E.
ISBN (Electronic): 9789532330984
ASJC Scopus subject areas: Computer Networks and Communications, Hardware and Architecture, Information Systems, Energy Engineering and Power Technology, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 85070323079

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Moiré superlattices and 2D electronic properties of graphite/MoS2 heterostructures

Heterostructures of graphite/MoS2 display a wide range of lattice registry due to rotational alignment and/or lattice mismatch. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS) we investigated electronic properties of these heterostructures and observed changes in the bandgap as a function of the twist angle between the layers. Green's function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap changes. Indirect coupling between the pz orbitals of the substrate Carbon atoms and the dz2 orbitals of the MoS2 layers (mediated by the pz orbitals of the bottom S layers) is found to be responsible for changes in the valence-band edge. Simple stacking of van der Waals materials with diverse properties have the potential to enable the fabrication of novel materials and device structures with tailored electronic properties.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Temple University, Russian Academy of Sciences, Northeastern University, National Tsing-Hua University, Institute of Physics Academia Sinica Taiwan, National University of Singapore
Contributors: Trainer, D. J., Putilov, A. V., Wang, B., Lane, C., Saari, T., Chang, T. R., Jeng, H. T., Lin, H., Xi, X., Nieminen, J., Bansil, A., Iavarone, M.
Pages: 325-330
Publication date: May 2019
Peer-reviewed: Yes
Early online date: 2017

Publication information

Journal: Journal of Physics and Chemistry of Solids
Volume: 128
ISSN (Print): 0022-3697
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all), Condensed Matter Physics
Source: Scopus
Source ID: 85036647170

Research output: Contribution to journalArticleScientificpeer-review

Spin filtering in silicene by edges and chemically or electrically induced interfaces

Silicene is a graphene-like material with relatively strong spin-orbit coupling exhibiting gapless topologically protected edge states. In addition, it has a buckled structure, and hence, it stands as a feasible candidate for spintronic applications, where spin-polarized channels could be controlled with external electric fields realized with voltage gates attached to a Silicene sheet. Breaking the periodicity in 2D-materials with spin-orbit coupling produces one-dimensional edge and interface nanostructures that may give rise to an intrinsic locking of spin-polarization to electron momentum. We consider field induced and chemical ways to create interfaces to give way to spin polarized states for both zigzag and armchair alignments. While the spin polarization of a field induced interface channel can be feasibly tuned, a chemical interface is less flexibly tunable. However, controlling Fermi-level, e.g. with a gate voltage, might serve as a spin valve along the interface.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Northeastern University
Contributors: Saari, T., Nieminen, J.
Pages: 316-324
Publication date: May 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Journal of Physics and Chemistry of Solids
Volume: 128
ISSN (Print): 0022-3697
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all), Condensed Matter Physics
Keywords: Electronic structure, Green's function techniques, Interfaces, Silicene, Spin-orbit coupling
Source: Scopus
Source ID: 85040567725

Research output: Contribution to journalArticleScientificpeer-review

Comparison of various high-stress wear conditions and wear performance of martensitic steels

The demanding environments typically encountered by the wear resistant steels create challenges for the materials selection, because the hardness grades of the steels alone do not reveal the true nature of their wear behavior. In this study, five commercial wear resistant steels were tested using three application oriented test methods with five different test variables for abrasion, impact-abrasion, and slurry erosion. All the used test methods produced high-stress conditions that crushed the used mineral abrasive, plastically deformed the sample surfaces, and led to the formation of adiabatic shear bands. When the results produced by the chosen methods were compared, the normalization of the wear losses by the wear area and test time revealed well the differences between the methods. The test methods ranked the steels similarly, but there were clear differences in the wear rates and wear mechanisms between the tests. In addition, the abrasive methods produced surface adiabatic shear bands, while subsurface shear bands were initiated by the more impacting methods. In the studied conditions, the work hardening ability of the steel had a clear influence on its wear resistance, which largely explains the marked differences in the wear rates of the studied commercial 500HB grade steels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Materials Characterization, Materials Science and Environmental Engineering, Robit Ltd, Univ of Oulu
Contributors: Valtonen, K., Ojala, N., Haiko, O., Kuokkala, V.
Number of pages: 11
Pages: 3-13
Publication date: 30 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Wear
Volume: 426-427
Issue number: Part A
ISSN (Print): 0043-1648
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Materials Chemistry, Surfaces, Coatings and Films, Surfaces and Interfaces
Keywords: Abrasion, Impact wear, Steel, Wear testing, ABRASIVE WEAR, BEHAVIOR, FIELD, RESISTANT STEELS, COMPRESSION, MICROSTRUCTURE
Source: Scopus
Source ID: 85058455176

Research output: Contribution to journalArticleScientificpeer-review

Complex Behavior of Phosphatidylcholine-Phosphatidic Acid Bilayers and Monolayers: Effect of Acyl Chain Unsaturation

Phosphatidic acids (PAs) have many biological functions in biomembranes, e.g., they are involved in the proliferation, differentiation, and transformation of cells. Despite decades of research, the molecular understanding of how PAs affect the properties of biomembranes remains elusive. In this study, we explored the properties of lipid bilayers and monolayers composed of PAs and phosphatidylcholines (PCs) with various acyl chains. For this purpose, the Langmuir monolayer technique and atomistic molecular dynamics (MD) simulations were used to study the miscibility of PA and PC lipids and the molecular organization of mixed bilayers. The monolayer experiments demonstrated that the miscibility of membrane components strongly depends on the structure of the hydrocarbon chains and thus on the overall lipid shape. Interactions between PA and PC molecules vary from repulsive, for systems containing lipids with saturated and unsaturated acyl tails (strongly positive values of the excess free energy of mixing), to attractive, for systems in which all lipid tails are saturated (negative values of the excess free energy of mixing). The MD simulations provided atomistic insight into polar interactions (formation of hydrogen bonds and charge pairs) in PC-PA systems. H-bonding between PA monoanions and PCs in mixed bilayers is infrequent, and the lipid molecules interact mainly via electrostatic interactions. However, the number of charge pairs significantly decreases with the number of unsaturated lipid chains in the PA-PC system. The PA dianions weakly interact with the zwitterionic lipids, but their headgroups are more hydrated as compared to the monoanionic form. The acyl chains in all PC-PA bilayers are more ordered compared to single-component PC systems. In addition, depending on the combination of lipids, we observed a deeper location of the PA phosphate groups compared to the PC phosphate groups, which can alter the presentation of PAs for the peripheral membrane proteins, affecting their accessibility for binding. ©

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Biological Physics and Soft Matter, Research area: Computational Physics, University of Helsinki, Uniwersytet Jagiellonski w Krakowie
Contributors: Kulig, W., Korolainen, H., Zatorska, M., Kwolek, U., Wydro, P., Kepczynski, M., Róg, T.
Number of pages: 13
Pages: 5944-5956
Publication date: 30 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Langmuir
Volume: 35
Issue number: 17
ISSN (Print): 0743-7463
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Surfaces and Interfaces, Spectroscopy, Electrochemistry
Source: Scopus
Source ID: 85065022226

Research output: Contribution to journalArticleScientificpeer-review

Engineering of Chern insulators and circuits of topological edge states

Impurities embedded in electronic systems induce bound states which under certain circumstances can hybridize and lead to impurity bands. Doping of insulators with impurities has been identified as a promising route toward engineering electronic topological states of matter. In this paper we show how to realize tuneable Chern insulators starting from a three-dimensional topological insulator whose surface is gapped and intentionally doped with magnetic impurities. The main advantage of the protocol is that it is robust and in particular not very sensitive to the impurity configuration. We explicitly demonstrate this for a square lattice of impurities as well as a random lattice. In both cases we show that it is possible to change the Chern number of the system by one through manipulating its topological state. We also discuss how this can be used to engineer circuits of edge channels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University College Dublin, Ireland, Christina Thorpe, Utrecht University, Aalto University, COMP Centre of Excellence
Contributors: Minarelli, E. L., Poÿhönen, K., Van Dalum, G. A., Ojanen, T., Fritz, L.
Publication date: 10 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 99
Issue number: 16
Article number: 165413
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85065257719

Research output: Contribution to journalArticleScientificpeer-review

Analysis of GaAsBi growth regimes in high resolution with respect to As/Ga ratio using stationary MBE growth

The control of Bi incorporation and material properties in III-V-Bi alloys has proved challenging due to their high sensitivity to the epitaxial growth parameters. Here, we present a methodology for determining the variation in the Ga, As, and Bi fluxes and the temperature across a stationary substrate in molecular beam epitaxy. By correlating the flux distributions with material properties, we identify distinct regimes for epitaxy of GaAsBi. In particular, we devise a detailed image of the interplay between Bi incorporation and structural properties of a bulk GaAs 0.96 Bi 0.04 layer grown on GaAs(1 0 0) with respect to the As/Ga ratio. The influence of As/Ga is analyzed with high resolution over the important stoichiometric range (i.e. As/Ga = 0.6–1.6). Growth outside the near-stoichiometric As/Ga regime leads to decreased Bi incorporation, decreased structural quality and the formation of Ga, Ga/Bi or Bi droplets. On the other hand, growth at As/Ga = 1.00–1.17 leads to maximized material quality. For this regime, the surface roughness is further optimized by fine-tuning the As/Ga ratio to suppress surface mounding to a value of 0.5 nm. The results reveal the extreme sensitivity of GaAsBi growth to small variations in the As/Ga ratio, and demonstrate the applicability of stationary growth in studying these effects.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC
Contributors: Puustinen, J., Hilska, J., Guina, M.
Number of pages: 9
Pages: 33-41
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Crystal Growth
Volume: 511
ISSN (Print): 0022-0248
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Inorganic Chemistry, Materials Chemistry
Keywords: A3. Molecular beam epitaxy, B1. Bismuth compounds, B2. Semiconducting III-V materials, B2. Semiconducting ternary compounds
Source: Scopus
Source ID: 85060893423

Research output: Contribution to journalArticleScientificpeer-review

Hydrolysis and drug release from poly(ethylene glycol)-modified lactone polymers with open porosity

The ability to release active agents from a porous scaffold structure in situ enables the simultaneous structural support for the cells proliferating and differentiating towards tissue as well as the stimulation of tissue regeneration. Due to the great potentiality of such approach, drug-releasing scaffolds were fabricated from hydrolytically degradable polymers. Three copolymers of poly(ethylene glycol), ɛ-caprolactone, L- and D,L-lactide were synthesized and blended with bone-growth inducing active agents, dexamethasone (DM) and 2-phospho-L-ascorbic acid trisodium salt (AS). Porous scaffolds were prepared by means of super-critical carbon dioxide foaming. In the final scaffold structures, the particle size, location and the water solubility of the drug affected the release kinetics. As the large and water soluble AS particles were more exposed to the buffer solution compared to small DM particles, the AS release was burst-like whereas DM showed a long-term release. The material structure had a significant effect on the release kinetics as the porous scaffolds released active agents faster compared to the solid cylinders. Furthermore, this study showed the strong effect of polymer degradation and wettability on the release, which were more determinative than the pore architecture.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Aalto University, Orton Orthopaedic Hospital
Contributors: Asikainen, S., Paakinaho, K., Kyhkynen, A. K., Hannula, M., Malin, M., Ahola, N., Kellomäki, M., Seppälä, J.
Number of pages: 11
Pages: 165-175
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: European Polymer Journal
Volume: 113
ISSN (Print): 0014-3057
Original language: English
ASJC Scopus subject areas: Physics and Astronomy(all), Organic Chemistry, Polymers and Plastics, Materials Chemistry
Keywords: 2-Phospho-L-ascorbic acid trisodium salt, Bulk degradation, Dexamethasone, Drug release, Hydrolytic degradation, Supercritical carbon dioxide foaming
Source: Scopus
Source ID: 85060767586

Research output: Contribution to journalArticleScientificpeer-review

Vibration-based delamination detection in curved composite plates

Delamination is one of common damages in fibre-reinforced composite laminates. It is known to cause changes in the vibration characteristics of the laminates, which allows for the use of vibration-based indicators for assessing structural health conditions and identifying potential risk of catastrophic failures. This paper presents a vibration-based approach to assess delamination in fibre reinforced composite curved plates through frequency shifts as indicative parameters. Two algorithms based on computational intelligence, namely artificial neural network (ANN) and surrogate assisted genetic algorithm (SAGA), were employed as inverse algorithms for predicting the location, size and interface of the delamination. The validation of the two algorithms is realized numerically through finite element (FE) studies conducted using a structured selection of parameters of genetic algorithms, number of frequency shifts and database size. Experimental modal testing was conducted using scanning laser vibrometer on five carbon fibre reinforced polymer (CFRP) curved plates. Among these, one was intact and the other four were manufactured with artificially induced laminations. It was confirmed that the two inverse algorithms were able to reasonably predict delamination parameters in curved composite plates. Among the two, SAGA's performance was observed to be better. A sensitivity analysis was further conducted by adding artificial noise to the numerical data to simulate measurement errors for investigating the influence of noise on the accuracy of the two algorithms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Materials Characterization, Materials Science and Environmental Engineering, Guangzhou University, University of New South Wales (UNSW) Australia
Contributors: Zhang, Z., Pan, J., Luo, W., Ramakrishnan, K. R., Singh, H. K.
Number of pages: 14
Pages: 261-274
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Composites Part A: Applied Science and Manufacturing
Volume: 119
ISSN (Print): 1359-835X
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Mechanics of Materials
Keywords: Artificial neural network, Curved plate, Delamination detection, Genetic algorithm, Natural frequency, Structural health monitoring, Surrogate model
Source: Scopus
Source ID: 85061304366

Research output: Contribution to journalArticleScientificpeer-review

Ternary borosilicates as potential cladding glasses for semiconductor core optical fibers

Our study advances the development of new ternary silicate glasses for use as a designed cladding for semiconductor core optical fibers using molten core draw process. In order to fabricate high-quality hybrid fibers (homogeneous core shape, low amount of bubbles, low internal stress, no cracking), oxide glasses are the best choice as cladding materials. These glasses should be engineered with tailored thermal properties (coefficient of thermal expansion (CTE) and drawing temperature) so they match those of the semiconductor. Glasses in the system (50SiO2-(20 − x)Na2O-(25 + x)B2O3-5MO) with x = 0 and 10 and MO = ZnO, TiO2, GeO2, Ga2O3, and Al2O3 and in the system 50SiO2-10Na2O-(40 − y)B2O3-yTiO2 with y = 0, 1.25, 2.5, and 5 were investigated. Their thermal properties were measured and discussed with regard to the glass structure analyzed using FTIR spectroscopy. Due to their rigid network, which leads to beneficial thermal properties including low CTE (~5 ppm K−1), the Ge-containing glass with x = 10 is a promising cladding candidate when preparing a Ge core fiber and the Ga or Zn- containing glasses when preparing an InAs core.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Photonics Glasses, Politecnico di Torino
Contributors: Dmitrieva, I., Lopez-Iscoa, P., Milanese, D., Petit, L.
Number of pages: 6
Pages: 151-156
Publication date: Apr 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: International Journal of Applied Glass Science
Volume: 10
Issue number: 2
ISSN (Print): 2041-1286
Original language: English
ASJC Scopus subject areas: Materials Science(all)

Bibliographical note

INT=fot,"Dmitrieva, Iuliia"

Source: Scopus
Source ID: 85054029936

Research output: Contribution to journalArticleScientificpeer-review

Antibacterial activity of silver and titania nanoparticles on glass surfaces

A liquid flame spray (LFS) nanoparticle deposition process was used to generate glass surfaces with silver (Ag) and titania (TiO2) nanoparticles for antibacterial activity against two common pathogenic bacteria causing community-associated and hospital-acquired infections, gram positive Staphylococcus aureus (S aureus) and gram negative Escherichia coli (E coli). All nanoparticle coatings increased antibacterial activity compared to a reference glass surface. The Ag nanoparticle coatings showed the highest antibacterial activity with E coli. On the contrary, TiO2 nanoparticle coatings were found to have a higher antibacterial activity against S aureus than E coli. No significant differences in antibacterial activity were observed between the two used nanoparticle deposition amounts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Aerosol Synthesis, Research area: Aerosol Physics, Physics, Abo Akad Univ, Abo Akademi University, Dept Phys, University of Turku, Turku University Hospital, University of Eastern Finland
Contributors: Kummala, R., Brobbey, K. J., Haapanen, J., Mäkelä, J. M., Gunell, M., Eerola, E., Huovinen, P., Toivakka, M., Saarinen, J. J.
Publication date: 20 Mar 2019
Peer-reviewed: Yes

Publication information

Journal: ADVANCES IN NATURAL SCIENCES: NANOSCIENCE AND NANOTECHNOLOGY
Volume: 10
Issue number: 1
Article number: 015012
ISSN (Print): 2043-6254
Original language: English
ASJC Scopus subject areas: Materials Science(all), Industrial and Manufacturing Engineering, Electrical and Electronic Engineering
Keywords: antibacterial, E coli, glass, nanoparticle, S aureus
Source: Scopus
Source ID: 85067126373

Research output: Contribution to journalArticleScientificpeer-review

Advancements in Solution Processable Devices using Metal Oxides For Printed Internet-of-Things Objects

Internet-of-things (IoT) objects are expected to exceed 75 billion objects by 2020, and a large part of the expansion is expected to be at a finer granularity than existing silicon-based IoT objects (i.e. tablets and cell phones) can deliver [1]. Currently, placing a room light or a thermostat on the internet for remote control is considered progressive. However, if printed electronics can achieve performance increases, then IoT objects could be affixed to almost anything, such as coffee creamer cartons, cereal boxes, or that missing sock. Each of these IoT objects could be driving a sensor, perhaps position, temperature or pressure, essentially a multitude of applications. In order for IoT objects to emulate a simple postage stamp, with self-powering from energy scavenging and local energy storage, all housed in a non-toxic flexible form factor, advances in solution processable devices need to occur.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Electrical Engineering, Ohio State University, Wayne State University
Contributors: Berger, P. R., Li, M., Mattei, R. M., Niang, M. A., Talisa, N., Tripepi, M., Harris, B., Bhalerao, S. R., Chowdhury, E. A., Winter, C. H., Lupo, D.
Number of pages: 3
Pages: 160-162
Publication date: 1 Mar 2019

Host publication information

Title of host publication: 2019 Electron Devices Technology and Manufacturing Conference, EDTM 2019
Publisher: IEEE
ISBN (Electronic): 9781538665084
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Instrumentation, Hardware and Architecture
Keywords: ALD, CMOS and SOI, energy scavenging, IoT, low-power electronics, Manufacturing, NDR, tunnel diodes
Source: Scopus
Source ID: 85067814337

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Emission measurements with gravimetric impactors and electrical devices: An aerosol instrument comparison

Particulate matter in the atmosphere is known to affect Earth’s climate and to be harmful to human health. Accurately measuring particles from emission sources is important, as the results are used to inform policies and climate models. This study compares the results of two ELPI + devices, two PM10 cascade impactors and an eFilter, in combustion emission measurements. The comparison of the instruments in a realistic setting shows what types of challenges arise from measuring an emission aerosol with unknown particle morphologies and densities, different particle concentrations and high temperature. Our results show that the PM10 cascade impactors have very good intercorrelation when the collected mass is greater than 150 µg, but below that, the uncertainty of the results increases with decreasing mass. The raw signals of two ELPI + devices were nearly identical in most samples, as well as the particle number concentrations and size distributions calculated from raw signals; however, transforming the current distributions into mass distributions showed variation in the mass concentration of particles larger than 1 µm. The real-time time signal measured by eFilter was similar to the total current measured by ELPI+. The eFilter and PM10 cascade impactors showed similar particle mass concentrations, whereas ELPI + showed clearly higher ones in most cases. We concluded that the difference is at least partially due to volatile components being measured by ELPI+, but not by the mass collection measurements.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics, Estonian Environmental Research Centre, Dekati Ltd, Tallinn University of Technology, Finnish Meteorological Institute
Contributors: Salo, L., Mylläri, F., Maasikmets, M., Niemelä, V., Konist, A., Vainumäe, K., Kupri, H. L., Titova, R., Simonen, P., Aurela, M., Bloss, M., Keskinen, J., Timonen, H., Rönkkö, T.
Number of pages: 14
Pages: 526-539
Publication date: 1 Mar 2019
Peer-reviewed: Yes

Publication information

Journal: Aerosol Science and Technology
Volume: 53
Issue number: 5
ISSN (Print): 0278-6826
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Source: Scopus
Source ID: 85062494308

Research output: Contribution to journalArticleScientificpeer-review

Stable and unstable friction in fretting contacts

Designing contacts susceptible to fretting is a challenging task due to uncertainties related to friction. For example, coefficient of friction has shown to vary as a function of load cycles and so-called non-Coulomb friction can exist during individual load cycles. Concepts of stable and unstable friction are presented in this manuscript. Based on experiments, no fretting is to be expected if the utilization of friction is kept below unstable friction threshold. If contact is subjected to tangential load above this threshold, reciprocating slippage, fretting, is to be expected even if the contact was initially in stick. Experimental evidence for existence of such threshold is presented in form of friction data, slip data and fretting scars.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Tribology and Machine Elements, Materials Science, Wärtsilä, Univ of Oulu
Contributors: Hintikka, J., Mäntylä, A., Vaara, J., Frondelius, T., Lehtovaara, A.
Number of pages: 10
Pages: 73-82
Publication date: 1 Mar 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Tribology International
Volume: 131
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Fretting, Friction, Stick-slip, Wear
Electronic versions: 
Source: Scopus
Source ID: 85055737240

Research output: Contribution to journalArticleScientificpeer-review

The formation and characterization of fretting-induced degradation layers using quenched and tempered steel

Fretting movement is dangerous for machines, because it can cause cracking and surface degradation. The aim of this work was to characterize fretting-induced material degradation in large flat-on-flat contacts without edge effects in a sliding direction using quenched and tempered steel 34CrNiMo6. The focus was on the adhesive contact spots, which were formed under a wide variety of operating conditions. Characterization methods were optical microscopy, Vickers hardness tests and scanning electron microscopy. Three different degradation areas were observed: a general deformation layer, a tribologically transformed structure and a third body layer. All the degradation phases have high hardness and low ductility compared to the base material. The formation and behavior of the degradation layers in different operating conditions were discussed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Tribology and Machine Elements, Research group: Materials Characterization, Wärtsilä
Contributors: Nurmi, V., Hintikka, J., Juoksukangas, J., Honkanen, M., Vippola, M., Lehtovaara, A., Mäntylä, A., Vaara, J., Frondelius, T.
Number of pages: 10
Pages: 258-267
Publication date: 1 Mar 2019
Peer-reviewed: Yes
Early online date: 14 Sep 2018

Publication information

Journal: Tribology International
Volume: 131
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Adhesion, Fretting, Friction, Microscopy
Electronic versions: 

Bibliographical note

INT=mol,"Nurmi, Verner"
EXT="Hintikka, Jouko"

Source: Scopus
Source ID: 85056207084

Research output: Contribution to journalArticleScientificpeer-review

Transverse deformation of a lamellar TiAl alloy at high temperature by in situ microcompression

The distribution of strain in hard mode oriented lamellar stacks of the two-phase γ-TiAl/α2-Ti3Al alloy Ti-45Al-2Nb-2Mn (at.%)-0.8 vol% TiB2 was measured at several temperatures up to 633 °C by in situ micropillar compression, complemented by electron backscatter diffraction orientation mapping and digital image correlation strain mapping of a thermally stable surface Pt speckle pattern. Post-mortem transmission electron microscopy further identified the finest scale deformation structures. It was found that slip and twinning transverse to the lamellae operates within discreet bands that zigzag across the lamellar structure. The shear strain within each band is approximately constant across the pillar width. This is inconsistent with current energetic models for transverse twin formation in γ-TiAl, which assume independent, non-interacting twins. This is explained using a mathematical formulation for the stress required to operate this transverse mechanical twinning as a function of strain. This study has elucidated how the multi-scale combination of several transverse twinning systems on different {111} planes in γ-TiAl lamellae can relieve the elastic stresses generated at a lamellar interface by the primary (highest Schmid factor) twinning system. It is thought that the facilitation of this mechanism will promote the ductilisation of lamellar γ-TiAl alloys. This is crucial for an increased damage tolerance and ease of component manufacture, leading to a more widespread use of γ-TiAl alloys.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, University of Cambridge, Swiss Federal Laboratories for Materials Science and Technology
Contributors: Edwards, T. E. J., Di Gioacchino, F., Goodfellow, A. J., Mohanty, G., Wehrs, J., Michler, J., Clegg, W. J.
Number of pages: 15
Pages: 85-99
Publication date: 1 Mar 2019
Peer-reviewed: Yes
Early online date: 27 Nov 2018

Publication information

Journal: Acta Materialia
Volume: 166
ISSN (Print): 1359-6454
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Polymers and Plastics, Metals and Alloys
Keywords: Deformation twinning, Digital image correlation, Electron backscattering diffraction (EBSD), Scanning transmission electron microscopy, Titanium aluminide polysynthetically twinned crystal (PST)
Source: Scopus
Source ID: 85058779138

Research output: Contribution to journalArticleScientificpeer-review

Mining tailings as raw materials for reaction-sintered aluminosilicate ceramics: Effect of mineralogical composition on microstructure and properties

This paper presents studies on the utilization of aluminosilicate-based mining tailings as raw materials for mullite-based ceramics. Based on the 3:2 stoichiometric composition, mullite was synthesised by reactive sintering with a series of powder mixtures with alumina additions. X-ray diffractometry and scanning electron microscopy analyses revealed that, at the specific mineralogical composition, mullite structure formed surrounded by an amorphous glass phase in reaction-sintered powder mixtures. Results demonstrated that the chemical and mineralogical composition of mining tailings do have an effect on mullite formation possibilities and, only with the particular mineralogical composition, the mullite formation is possible regardless of the correct Al:Si ratio in tailings. Physical and mechanical properties of the formed ceramics were defined, showing comparable values to 3:2 mullite reference. Mullite structure formation enables a better thermal resistance up to above 1450 °C of the formed tailings-based ceramics compared to other aluminosilicates, reflecting their utilization potential for refractory ceramic applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, VTT Technical Research Centre of Finland, Geologian tutkimuskeskus
Contributors: Karhu, M., Lagerbom, J., Solismaa, S., Honkanen, M., Ismailov, A., Räisänen, M. L., Huttunen-Saarivirta, E., Levänen, E., Kivikytö-Reponen, P.
Pages: 4840-4848
Publication date: Mar 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Ceramics International
Volume: 45
Issue number: 4
ISSN (Print): 0272-8842
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Mining tailings, Mullite, Reaction sintering, Refractory ceramics, Utilization

Bibliographical note

EXT="Lagerbom, Juha"

Source: Scopus
Source ID: 85057276435

Research output: Contribution to journalArticleScientificpeer-review

DLC-treated aramid-fibre composites: Tailoring nanoscale-coating for macroscale performance

This work aims to quantify the effect of a diamond-like carbon coating (DLC) treatment of aramid fibres and to reveal the conversion of a fibre-level performance leap on the macroscale mechanical behaviour. The DLC-based coating is applied directly to the reinforcement and laminates are infused with an epoxy matrix. After characterisation of the coated surfaces, the performance of the composite is analysed via interlaminar shear testing, fatigue testing and damage tolerance testing, microbond tests, and 3D finite element simulation using a cohesive zone model of the interface. The results show that the coating treatment improves the fatigue life and the S-N curve slope for the laminates, while the residual strength after impact damage and environmental conditioning (water immersion at 60 °C) remains high. The scaling factor to convert the performance on macroscale was determined to be 0.17–0.39 for the DLC-based fibre treatment.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Faculty of Natural Sciences, Photonics, Aalto University, DIARC-Technology Oy
Contributors: Kanerva, M., Korkiakoski, S., Lahtonen, K., Jokinen, J., Sarlin, E., Palola, S., Iyer, A., Laurikainen, P., Liu, X. W., Raappana, M., Tervakangas, S., Valden, M.
Number of pages: 8
Pages: 62-69
Publication date: 8 Feb 2019
Peer-reviewed: Yes
Early online date: 30 Nov 2018

Publication information

Journal: Composites Science and Technology
Volume: 171
ISSN (Print): 0266-3538
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Engineering(all)
Keywords: Aramid fibre, Damage tolerance, Finite element analysis (FEA), Interfacial strength, Photoelectron spectroscopy (XPS)
Electronic versions: 
Source: Scopus
Source ID: 85058435801

Research output: Contribution to journalArticleScientificpeer-review

Initial axial stiffness of welded RHS T joints

Recently, CIDECT (International Committee for the Development and Study of Tubular Structures) has proposed the component method as a unified approach for the design of many types of connections, including welded tubular joints. Although CIDECT provides clear and simple equations for the resistance of welded tubular joints, the design of initial stiffness remains complicated and includes a number of uncertainties. This paper analyzes the theoretical approach for the initial axial stiffness of rectangular hollow section T joints. The validation against experimental data has shown that the component method considerably overestimates the stiffness of T joints. The paper develops new equations for the stiffness of the components “chord face in bending” and “chord side walls in compression”. The equations are based on simplified mechanical models, employing finite element analyses to calculate the parameters for which analytical solutions are found extremely complicated. In addition, the article numerically investigates the effect of chord axial stresses on the axial stiffness of joints and proposes a corresponding chord stress function.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Research group: Metal and Light-wight structures, St. Petersburg State Polytechnical University, Technische Universitat Munchen
Contributors: Garifullin, M., Bronzova, M., Pajunen, S., Mela, K., Heinisuo, M.
Number of pages: 14
Pages: 459-472
Publication date: 1 Feb 2019
Peer-reviewed: Yes
Early online date: 11 Nov 2018

Publication information

Journal: Journal of Constructional Steel Research
Volume: 153
ISSN (Print): 0143-974X
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Building and Construction, Mechanics of Materials, Metals and Alloys
Keywords: Axial stiffness, Component method, Initial stiffness, Rectangular hollow section, Tubular joint
Source: Scopus
Source ID: 85056210825

Research output: Contribution to journalArticleScientificpeer-review

Conductive cellulose based foam formed 3D shapes—from innovation to designed prototype

In this article, we introduce for the first time, a method to manufacture cellulose based electrically conductive non-woven three-dimensional (3D) structures using the foam forming technology. The manufacturing is carried out using a minimum amount of processing steps, materials, and hazardous chemicals. The optimized solution applies a single surfactant type and a single predefined portion for the two main processing steps: (1) the dispersing of nanocellulose (NC) and carbon nanotubes (CNT) and (2) the foam forming process. The final material system has a concentration of the used surfactant that is not only sufficient to form a stable and homogeneous nanoparticle dispersion, but it also results in stable foam in foam forming. In this way, the advantages of the foam forming process can be maximized for this application. The cellulose based composite material has a highly even distribution of CNTs over the NC network, resulting a conductivity level of 7.7 S/m, which increased to the value 8.0 S/m after surfactant removal by acetone washing. Also, the applicability and a design product case 'Salmiakki' were studied where the advantages of the material system were validated for a heating element application.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Automation Technology and Mechanical Engineering, Research group: Plastics and Elastomer Technology, Research and Innovation Services, BioMediTech, Research group: Nanoscale Phenomena and Measurements (NPM), Research group: Sensor Technology and Biomeasurements (STB), Materials Science and Environmental Engineering, Aalto University, VTT Technical Research Centre of Finland
Contributors: Siljander, S., Keinänen, P., Ivanova, A., Lehmonen, J., Tuukkanen, S., Kanerva, M., Björkqvist, T.
Number of pages: 12
Publication date: 31 Jan 2019
Peer-reviewed: Yes

Publication information

Journal: Materials
Volume: 12
Issue number: 3
Article number: 430
ISSN (Print): 1996-1944
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: Carbon nanotube, Conductivity, Foam forming, Nanocellulose, Salmiakki
Source: Scopus
Source ID: 85060971565

Research output: Contribution to journalArticleScientificpeer-review

Ultrahigh-pressure form of Si O2 glass with dense pyrite-type crystalline homology

High-pressure synthesis of denser glass has been a longstanding interest in condensed-matter physics and materials science because of its potentially broad industrial application. Nevertheless, understanding its nature under extreme pressures has yet to be clarified due to experimental and theoretical challenges. Here we reveal the formation of OSi4 tetraclusters associated with that of SiO7 polyhedra in SiO2 glass under ultrahigh pressures to 200 gigapascal confirmed both experimentally and theoretically. Persistent homology analyses with molecular dynamics simulations found increased packing fraction of atoms whose topological diagram at ultrahigh pressures is similar to a pyrite-type crystalline phase, although the formation of tetraclusters is prohibited in the crystalline phase. This critical difference would be caused by the potential structural tolerance in the glass for distortion of oxygen clusters. Furthermore, an expanded electronic band gap demonstrates that chemical bonds survive at ultrahigh pressure. This opens up the synthesis of topologically disordered dense oxide glasses.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Research group: Materials and Molecular Modeling, HCI e 486.1, Tohoku University, National Institute for Materials Science (NIMS), Japan Synchrotron Radiation Research Institute, Japan Advanced Institute of Science and Technology, Japan Science and Technology Agency, Tokyo University of Science, Norwegian Univ. of Sci. and Technol., University of Tokyo, Waseda University, National Institute of Advanced Industrial Science and Technology, Research and Services Division of Materials Data and Integrated System (MaDIS) NIMS, Kyoto Women's University, RIKEN Center for Integrative Medical Sciences, Aalto University, COMP Centre of Excellence, Department of Applied Physics, Aalto University, Division of Electrical Engineering and Computer Science, Kanazawa University
Contributors: Murakami, M., Kohara, S., Kitamura, N., Akola, J., Inoue, H., Hirata, A., Hiraoka, Y., Onodera, Y., Obayashi, I., Kalikka, J., Hirao, N., Musso, T., Foster, A. S., Idemoto, Y., Sakata, O., Ohishi, Y.
Publication date: 29 Jan 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 99
Issue number: 4
Article number: 045153
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics

Bibliographical note

EXT="Foster, A. S."

Source: Scopus
Source ID: 85060951368

Research output: Contribution to journalArticleScientificpeer-review

Deformation of lamellar γ-TiAl below the general yield stress

The occurrence of plasticity below the macroscopic yield stress during tensile monotonic loading of nearly lamellar Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB2 at both 25 °C and 700 °C, and in two conditions of lamellar thickness, was measured by digital image correlation strain mapping of a remodelled Au surface speckle pattern. Such initial plasticity, not necessarily related to the presence of common stress concentrators such as hard particles or cracks, could occur at applied stresses as low as 64% of the general yield stress. For a same applied strain it was more prominent at room temperature, and located as slip and twinning parallel to, and near to or at (respect.) lamellar interfaces of all types in soft mode-oriented colonies. These stretched the full colony width and the shear strain was most intense in the centre of the colonies. Further, the most highly operative microbands of plasticity at specimen fracture were not those most active prior to yielding. The strain mapping results from polycrystalline tensile loading were further compared to those from microcompression testing of soft-mode stacks of lamellae milled from single colonies performed at the same temperatures. Combined with post-mortem transmission electron microscopy of the pillars, the initial plasticity by longitudinal dislocation glide was found to locate within 30–50 nm of the lamellar interfaces, and not at the interfaces themselves. The highly localised plasticity that precedes high cycle fatigue failure is therefore inherently related to the lamellar structure, which predetermines the locations of plastic strain accumulation, even in a single loading cycle.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, University of Cambridge, Swiss Federal Laboratories for Materials Science and Technology
Contributors: Edwards, T. E. J., Di Gioacchino, F., Goodfellow, A. J., Mohanty, G., Wehrs, J., Michler, J., Clegg, W. J.
Number of pages: 18
Pages: 122-139
Publication date: 15 Jan 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Acta Materialia
Volume: 163
ISSN (Print): 1359-6454
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Polymers and Plastics, Metals and Alloys
Keywords: Deformation twinning, Digital image correlation, Electron backscattering diffraction (EBSD), Pre-yield plasticity, Titanium aluminide
Source: Scopus
Source ID: 85055112164

Research output: Contribution to journalArticleScientificpeer-review

Solvent Welding and Imprinting Cellulose Nanofiber Films Using Ionic Liquids

Cellulose nanofiber films (CNFF) were treated via a welding process using ionic liquids (ILs). Acid-base-conjugated ILs derived from 1,5-diazabicyclo[4.3.0]non-5-ene [DBN] and 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) were utilized. The removal efficiency of ILs from welded CNFF was assessed using liquid-state nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The mechanical and physical properties of CNFF indicated surface plasticization of CNFF, which improved transparency. Upon treatment, the average CNFF toughness increased by 27%, and the films reached a Young's modulus of ∼5.8 GPa. These first attempts for IL "welding" show promise to tune the surfaces of biobased films, expanding the scope of properties for the production of new biobased materials in a green chemistry context. The results of this work are highly relevant to the fabrication of CNFFs using ionic liquids and related solvents.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Paper Converting and Packaging, Universidad Del Bío-Bío, Aalto University
Contributors: Reyes, G., Borghei, M., King, A. W. T., Lahti, J., Rojas, O. J.
Pages: 502-514
Publication date: 14 Jan 2019
Peer-reviewed: Yes
Early online date: 12 Dec 2018

Publication information

Journal: Biomacromolecules
Volume: 20
Issue number: 1
ISSN (Print): 1525-7797
Original language: English
ASJC Scopus subject areas: Bioengineering, Biomaterials, Polymers and Plastics, Materials Chemistry
Source: Scopus
Source ID: 85059629357

Research output: Contribution to journalArticleScientificpeer-review

A Fast Quench Protection System for High-Temperature Superconducting Magnets

For reaching very high magnetic fields in fully superconducting magnets, beyond 16 T for particle accelerators dipoles and beyond 23 T for solenoids, the use of High-Temperature Superconductors (HTS) is unavoidable. Due to the high Minimum Quench Energy in HTS these coils are much more difficult to protect against quenches using conventional methods such as quench heaters or Coupling Loss Induced Quench (CLIQ). Although it is possible to use a dump resistor on a short HTS magnet, extracting the energy externally, this does not provide a solution for longer magnets or magnets operated in a string, because the extraction voltage becomes unacceptably high. Here a method named E3SPreSSO is proposed that allows for fast energy extraction in HTS magnets. The E3SPreSSO comprises of units with a near-zero self-inductance superconducting circuit, connected in series with the main magnet. When the protection is triggered, these devices are turned resistive, using quench heaters, over-current or CLIQ, causing them to absorb the energy of the system. The units can be located outside the main magnet and do not generate magnetic field. Therefore it is possible to use relatively cost-efficient and robust Nb-Ti or possibly MgB_2 (at higher temperatures). This paper introduces the concept and provides an analytical method weighing the different options for designing the E3SPreSSO units themselves.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research, CERN
Contributors: van Nugteren, J., Murtomäki, J., Ruuskanen, J., Kirby, G., Hagen, P., DeRijk, G., Ten Kate, H., Bottura, L., Rossi, L.
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 15 Jun 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 1
Article number: 4700108
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Coils, Heating systems, High-temperature superconductors, High-Temperature-Superconductors (HTS), Magnetic circuits, Quench Protection, Resistance, Resistors, Superconducting magnets, Superconducting Magnets, Switch

Bibliographical note

EXT="Murtomäki, Jaakko"

Source: Scopus
Source ID: 85048658780

Research output: Contribution to journalArticleScientificpeer-review

An Artificial Nocturnal Flower via Humidity-Gated Photoactuation in Liquid Crystal Networks

Beyond their colorful appearances and versatile geometries, flowers can self-shape-morph by adapting to environmental changes. Such responses are often regulated by a delicate interplay between different stimuli such as temperature, light, and humidity, giving rise to the beauty and complexity of the plant kingdom. Nature inspires scientists to realize artificial systems that mimic their natural counterparts in function, flexibility, and adaptation. Yet, many of the artificial systems demonstrated to date fail to mimic the adaptive functions, due to the lack of multi-responsivity and sophisticated control over deformation directionality. Herein, a new class of liquid-crystal-network (LCN) photoactuators whose response is controlled by delicate interplay between light and humidity is presented. Using a novel deformation mechanism in LCNs, humidity-gated photoactuation, an artificial nocturnal flower is devised that is closed under daylight conditions when the humidity level is low and/or the light level is high, while it opens in the dark when the humidity level is high. The humidity-gated photoactuators can be fueled with lower light intensities than conventional photothermal LCN actuators. This, combined with facile control over the speed, geometry, and directionality of movements, renders the “nocturnal actuator” promising for smart and adaptive bioinspired microrobotics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Eindhoven University of Technology
Contributors: Wani, O. M., Verpaalen, R., Zeng, H., Priimagi, A., Schenning, A. P.
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Advanced Materials
Volume: 31
Issue number: 2
Article number: 1805985
ISSN (Print): 0935-9648
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Mechanical Engineering
Keywords: actuator, azobenzene, bioinspired, humidity, light, liquid crystal, multi-responsive
Source: Scopus
Source ID: 85056318113

Research output: Contribution to journalArticleScientificpeer-review

Characterization of Powder-Precursor HVOF-Sprayed Al2O3-YSZ/ZrO2 Coatings

Thermal spraying using liquid feedstock can produce coatings with very fine microstructures either by utilizing submicron particles in the form of a suspension or through in situ synthesis leading, for example, to improved tribological properties. The focus of this work was to obtain a bimodal microstructure by using simultaneous hybrid powder-precursor HVOF spraying, where nanoscale features from liquid feedstock could be combined with the robustness and efficiency of spraying with powder feedstock. The nanostructure was achieved from YSZ and ZrO2 solution-precursors, and a conventional Al2O3 spray powder was responsible for the structural features in the micron scale. The microstructures of the coatings revealed some clusters of unmelted nanosized YSZ/ZrO2 embedded in a lamellar matrix of Al2O3. The phase compositions consisted of γ- and α-Al2O3 and cubic, tetragonal and monoclinic ZrO2. Additionally, some alloying of the constituents was found. The mechanical strength of the coatings was not optimal due to the excessive amount of the nanostructured YSZ/ZrO2 addition. An amount of 10 vol.% or 7 wt.% 8YSZ was estimated to result in a more desired mixing of constituents that would lead to an optimized coating architecture.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, ELCOGEN OY, Univ of Oulu
Contributors: Kiilakoski, J., Puranen, J., Heinonen, E., Koivuluoto, H., Vuoristo, P.
Pages: 98-107
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Journal of Thermal Spray Technology
Volume: 28
Issue number: 1-2
ISSN (Print): 1059-9630
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Surfaces, Coatings and Films, Materials Chemistry
Keywords: AlO-ZrO, ceramic matrix composite, coating, HVOF, hybrid, solution-precursor spraying
Source: Scopus
Source ID: 85058214735

Research output: Contribution to journalArticleScientificpeer-review

Charge carrier dynamics in tantalum oxide overlayered and tantalum doped hematite photoanodes

We employ atomic layer deposition to prepare 50 nm thick hematite photoanodes followed by passivating them with a 0.5 nm thick Ta 2 O 5 -overlayer and compare them with samples uniformly doped with the same amount of tantalum. We observe a three-fold improvement in photocurrent with the same onset voltage using Ta-overlayer hematite photoanodes, while electrochemical impedance spectroscopy under visible light irradiation shows a decreased amount of surface states under water splitting conditions. The Ta-doped samples have an even higher increase in photocurrent along with a 0.15 V cathodic shift in the onset voltage and decreased resistivity. However, the surface state capacitance for the Ta-doped sample is twice that of the reference photoanode, which implies a larger amount of surface hole accumulation. We further utilize transient absorption spectroscopy in the sub-millisecond to second timescale under operating conditions to show that electron trapping in both Ta 2 O 5 -passivated and Ta-doped samples is markedly reduced. Ultrafast transient absorption spectroscopy in the sub-picosecond to nanosecond timescale shows faster charge carrier dynamics and reduced recombination in the Ta-doped hematite photoanode resulting in the increased photoelectrochemical performance when compared with the Ta 2 O 5 -overlayer sample. Our results show that passivation does not affect the poor charge carrier dynamics intrinsic to hematite based photoanodes. The Ta-doping strategy results in more efficient electron extraction, solving the electron trapping issue and leading to increased performance over the surface passivation strategy.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Chemistry & Advanced Materials, Materials Science and Environmental Engineering, Physics, Research group: Surface Science
Contributors: Ruoko, T., Hiltunen, A., Iivonen, T., Ulkuniemi, R., Lahtonen, K., Ali-Löytty, H., Mizohata, K., Valden, M., Leskelä, M., Tkachenko, N. V.
Number of pages: 10
Pages: 3206-3215
Publication date: Jan 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Chemistry A
Volume: 7
Issue number: 7
ISSN (Print): 2050-7488
Original language: English
ASJC Scopus subject areas: Chemistry(all), Renewable Energy, Sustainability and the Environment, Materials Science(all)
Electronic versions: 

Bibliographical note

INT=phys,"Ulkuniemi, Riina"

Source: Scopus
Source ID: 85061474749

Research output: Contribution to journalArticleScientificpeer-review

Phosphate glasses with blue persistent luminescence prepared using the direct doping method

Phosphate glasses with the composition (90NaPO3-(10-x)Na2O-xNaF) (mol%) with x = 0 and 10 were prepared with blue persistent luminescence (PeL) using direct particles doping method. Commercial CaAl2O4:Eu2+,Nd3+ microparticles (MPs) with blue PeL were added in the glass melt at a lower temperature than the melting temperature. The PeL properties of the glasses were related to the diffusion of Al from the MPs to the glass occurring during the glass preparation, which was found to depend on the temperature at which the MPs are added in the melt and also on the time before casting the melt after adding the MPs. The glass with x = 0 can be prepared with homogeneous PeL if the MPs are added at 575 °C. This Tdoping temperature can be reduced to 550 °C by replacing Na2O by NaF in the glass.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Turun Yliopisto/Turun Biomateriaalikeskus
Contributors: Ojha, N., Tuomisto, M., Lastusaari, M., Petit, L.
Pages: 151-156
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Optical Materials
Volume: 87
ISSN (Print): 0925-3467
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: CaAlO:Eu,Nd microparticles, Corrosion, Fluorophosphate glass, Persistent luminescence
Source: Scopus
Source ID: 85044951460

Research output: Contribution to journalArticleScientificpeer-review

1.3μm U-bend traveling wave SOA devices for high efficiency coupling to silicon photonics

We present a U-bend design for traveling wave III-V gain devices, such as semiconductor optical amplifiers and laser diodes. The design greatly simplifies the butt-coupling between the III-V chip and silicon-on-insulator photonic circuit by bringing the I/O ports on one facet. This removes the need for precise dimension control otherwise required for 2-side coupling, therefore increasing the yield of mounted devices towards 100%. The design, fabrication and characterization of the U-bend device based on Euler bend geometry is presented. The losses for a bend with a minimum bending radius of 83 μm are 1.1 dB. In addition, we present an analysis comparing the yield and coupling losses of the traditionally cleaved devices with the results that the Euler bend approach enable, with the final conclusion that the yield is improved by several times while the losses are decreased by several dB.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, VTT Technical Research Centre of Finland
Contributors: Viheriälä, J., Tuorila, H., Zia, N., Cherchi, M., Aalto, T., Guina, M.
Publication date: 2019

Host publication information

Title of host publication: Silicon Photonics XIV
Publisher: SPIE, IEEE
Editors: Reed, G. T., Knights, A. P.
Article number: 109230E
ISBN (Electronic): 9781510624887

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10923
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Coupling losses, Hybrid integration, III-V, Semiconductor optical amplifiers, Silicon-on-insulator

Bibliographical note

jufoid=71479

Source: Scopus
Source ID: 85065404814

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

1.55-μm wavelength wafer-fused OP-VECSELs in flip-chip configuration

Optically-pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55-μm wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors, which were incorporated in a linear and a V-cavity configurations. A maximum output power of 3.65 W was achieved for a heatsink temperature of 11°C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. The demonstration represents more than 10-fold increase of the output power compared to state-of-the-art flip-chip VECSELs previously demonstrated at the 1.55-μm wavelength range, and opens a new perspective for developing practical VECSEL-based laser system for applications such as LIDAR, spectroscopy, communications and distributed sensing.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, CRPP, LakeDiamond SA
Contributors: Mereuta, A., Nechay, K., Caliman, A., Suruceanu, G., Gallo, P., Guina, M., Kapon, E.
Publication date: 2019

Host publication information

Title of host publication: Vertical External Cavity Surface Emitting Lasers (VECSELs) IX
Publisher: SPIE, IEEE
Editor: Keller, U.
Article number: 1090103
ISBN (Electronic): 9781510624443

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10901
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Optically-pumped VECSELs, Semiconductor lasers, Wafer-Fusion

Bibliographical note

jufoid=71479

Source: Scopus
Source ID: 85066636665

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

405-nm pumped Ce 3+ -doped silica fiber for broadband fluorescence from cyan to red

A pure Ce-doped silica fiber is fabricated using modified chemical vapor deposition (MCVD) technique. Fluorescence characteristics of a Ce-doped silica fiber are experimentally investigated with continuous wave pumping from 440 nm to 405 nm. Best pump absorption and broad fluorescence spectrum is observed for ∼ 405 nm laser. Next, the detailed analysis of spectral response as a function of pump power and fiber length is performed. It is observed that a-10dB spectral width of ∼ 280 mn can be easily achieved with different combinations of the fiber length and pump power. Lastly, we present, for the first time to the best of our knowledge, a broadband fluorescence spectrum with-10dB spectral width of 301 nm, spanning from ∼ 517.36 nm to ∼ 818 nm, from such fibers with non-UV pump lasers.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Aston University, Fiber Optics Research Center of the Russian Academy of Sciences, Russian Academy of Sciences
Contributors: Yadav, A., Chichkov, N. B., Gumenyuk, R., Zherebtsov, E., Melkumov, M. A., Yashkov, M. V., Dianov, E. M., Rafailov, E. U.
Publication date: 2019

Host publication information

Title of host publication: Optical Components and Materials XVI
Publisher: SPIE, IEEE
Editors: Digonnet, M. J. F., Jiang, S.
Article number: 1091406
ISBN (Electronic): 9781510624702

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10914
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Broadband spectrum, Ce-doped fiber, Ce-ion, Rare earth doped

Bibliographical note

jufoid=71479

Source: Scopus
Source ID: 85066046508

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Analysis of hygrothermal parameters in Finnish and Lithuanian multi-family buildings before and after energy retrofits

This study focuses on analyzing temperature- and moisture-related parameters based on data from 45 Finnish and 20 Lithuanian multi-family buildings. The data consist of two rounds of 2-month data-logging (1-h interval) of indoor temperature and relative humidity at two locations: one representing average occupied zone and the other one nearby the coldest spot of the building envelope. Between the two rounds of data-logging, 37 buildings from Finland and 15 buildings from Lithuania underwent retrofits, aiming to improve their energy efficiency. Measurement data were coupled with outdoor data from national weather stations, based on which a temperature factor (fc) and excess indoor moisture content (Δv) were calculated. Based on the results, fc was significantly higher in Lithuanian case buildings after the retrofits, whereas no significant differences were observed in Finnish buildings. In addition, Δv was significantly lower in Finnish case buildings after retrofits, whereas an opposite trend was seen in the Lithuanian buildings.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Research group: Concrete and Bridge Structures, Kaunas University of Technology, National Public Health Institute
Contributors: Leivo, V., Kiviste, M., Aaltonen, A., Prasauskas, T., Martuzevicius, D., Haverinen-Shaughnessy, U.
Number of pages: 17
Publication date: 2019
Peer-reviewed: Yes
Early online date: 1 Apr 2018

Publication information

Journal: Journal of Building Physics
Volume: 42
Issue number: 4
ISSN (Print): 1744-2591
Original language: English
ASJC Scopus subject areas: Building and Construction, Materials Science(all)
Keywords: indoor moisture excess, relative humidity, surface temperature, Temperature, temperature factor
Electronic versions: 
Source: Scopus
Source ID: 85045857327

Research output: Contribution to journalArticleScientificpeer-review

Analyzing Competition and Cooperation Dynamics of the Aerial mmWave Access Market

Cellular operators have always relied on static deployments for providing wireless access. However, even the emerging fifth-generation (5G) networks may face difficulty in supporting the increased traffic demand with a rigid, fixed infrastructure without substantial over-provisioning. This is particularly true for spontaneous large-scale events that require service providers to augment the capacity of their networks quickly. Today, the use of aerial devices equipped with high-rate radio access capabilities has the potential to offer the much needed 'on-demand' capacity boost. Conversely, it also threatens to rattle the long-standing business strategies of wireless operators, especially as the 'gold rush' for cheaper millimeter wave (mmWave) spectrum lowers the market entry barriers. However, the intricate structure of this new market presently remains a mystery. This paper sheds light on competition and cooperation behavior of dissimilar aerial mmWave access suppliers, concurrently employing licensed and license-exempt frequency bands, by modeling a vertically differentiated market where customers have varying preferences in price and quality. To understand viable service provider strategies, we begin by constructing the Nash equilibrium for the initial market competition by employing the Bertrand and Cournot games. We then conduct a unique assessment of short-term market dynamics, where licensed-band service providers may cooperate to improve their competitive positions against the unlicensed-band counterparts intruding on the market. Our analysis studies the effects of various market interactions, price-driven demand evolution, and dynamic profit balance in this novel type of ecosystem.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Universita degli Studi di Reggio Calabria, YLVerkot Oy, Intel Corporation
Contributors: Galinina, O., Militano, L., Andreev, S., Pyattaev, A., Johnsson, K., Orsino, A., Araniti, G., Iera, A., Dohler, M., Koucheryavy, Y.
Number of pages: 20
Pages: 87192-87211
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: 5G systems, aerial access points, Bertrand and Cournot models, competition and cooperation behavior, dynamic games, mmWave technology, UAV, vertically differentiated market

Bibliographical note

EXT="Pyattaev, Alexander"

Source: Scopus
Source ID: 85069789803

Research output: Contribution to journalArticleScientificpeer-review

An automated algorithm for reliable equation of state fitting of magnetic systems

In computational physics and materials science ground-state properties are often extracted from an equation of state fit to energy-volume data. Magnetic systems often have multiple magnetic phases present in the energy-volume data, which poses a challenge for the fitting approach because the results are sensitive to the selection of included fitting points. This is because practically all popular equation of state fitting functions, such as Murnaghan and Birch-Murnaghan, assume just one phase and therefore cannot correctly fit magnetic energy-volume data that contains multiple phases. When fitting magnetic energy-volume data it is therefore important to select the range of fitting points in such a way that only points from the one relevant phase are included. We present a simple algorithm that makes the point selection automatically. Selecting fitting points automatically removes human bias and should also be useful for large-scale projects where selecting all fitting points by hand is not feasible.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Uppsala University, Department of Physics and Astronomy, University of Turku, Royal Institute of Technology
Contributors: Levämäki, H., Tian, L., Vitos, L., Ropo, M.
Number of pages: 8
Pages: 121-128
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Computational Materials Science
Volume: 156
ISSN (Print): 0927-0256
Original language: English
ASJC Scopus subject areas: Computer Science(all), Chemistry(all), Materials Science(all), Mechanics of Materials, Physics and Astronomy(all), Computational Mathematics
Keywords: EOS, Equation of state fitting
Source: Scopus
Source ID: 85053772857

Research output: Contribution to journalArticleScientificpeer-review

Antibacterial polymer fibres by rosin compounding and melt-spinning

The antibacterial features of natural pine/spruce rosin are well established, yet the functionality in various thermoplastics has not been surveyed. This work focuses on the processing of industrial grade purified rosin mixed with polyethylene (PE), polypropylene (PP), polylactic acid (PLA), polyamide (PA)and corn starch based biopolymer (CS). Homopolymer masterbatches were extrusion-compounded and melt-spun to form fibres for a wide range of products, such as filters, reinforcements, clothing and medical textiles. Due to the versatile chemical structure of rosin, it was observed compatible with all the selected polymers. In general, the rosin-blended systems were shear-thinning in a molten condition. The doped fibres spun of PE and PP indicated adequate melt-spinning capability and proper mechanical properties in terms of ultimate strength and Young's modulus. The antibacterial response was found dependent on the selected polymer. Especially PE with a 10 wt% rosin content showed significant antibacterial effects against Escherichia coli DH5α and Staphylococcus aureus ATCC 12598 when analysed in the Ringer's solution for 24 h.

General information

Publication status: Accepted/In press
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Research group: Plastics and Elastomer Technology, Department of Microbiology, Bundesanstalt für Materialforschung und -prüfung (BAM), Premix Oy, Aalto University, COMP Centre of Excellence, University of Helsinki
Contributors: Kanerva, M., Puolakka, A., Takala, T. M., Elert, A. M., Mylläri, V., Jönkkäri, I., Sarlin, E., Seitsonen, J., Ruokolainen, J., Saris, P., Vuorinen, J.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Materials Today Communications
Article number: 100527
ISSN (Print): 2352-4928
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Materials Chemistry
Keywords: Antibacterial, Fibre, Melt spinning, Thermoplastics
Electronic versions: 

Bibliographical note

EXT="Mylläri, V."

Source: Scopus
Source ID: 85066275027

Research output: Contribution to journalArticleScientificpeer-review

Behaviour of leaded tin bronze in simulated seawater in the absence and presence of tribological contact with alumina counterbody: Corrosion, wear and tribocorrosion

Corrosion, wear and tribocorrosion behaviours of leaded tin bronze were examined in simulated seawater using alumina counterbody for tribological contact. Active dissolution of alloy and corrosion product development on surfaces were the dominant corrosion mechanisms. Tribological contact with counterbody removed majority of the products, thus contributing to active dissolution of freshly exposed surface. This wear-induced corrosion mechanism contributed to 45% and 60% of total material losses at the two highest potentials, 50 mV and 250 mV vs. Ag/AgCl. Pure wear of alloy occurred in the form of abrasive wear. At anodic potentials under tribological contact, corrosion raised the friction coefficient as compared to pure wear and increased wear of the alloy. These results are presented and discussed in this paper.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, VTT Technical Research Centre of Finland
Contributors: Huttunen-Saarivirta, E., Isotahdon, E., Metsäjoki, J., Salminen, T., Ronkainen, H., Carpén, L.
Number of pages: 15
Pages: 257-271
Publication date: 2019
Peer-reviewed: Yes
Early online date: 22 Aug 2018

Publication information

Journal: Tribology International
Volume: 129
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Contact: sliding, Surface: chemical analysis, Synergism: tribochemistry, Wear: corrosive

Bibliographical note

EXT="Metsäjoki, J."
EXT="Isotahdon, E."

Source: Scopus
Source ID: 85052665246

Research output: Contribution to journalArticleScientificpeer-review

Benchmarking of several disparity estimation algorithms for light field processing

A number of high-quality depth imaged-based rendering (DIBR) pipelines have been developed to reconstruct a 3D scene from several images taken from known camera viewpoints. Due to the specific limitations of each technique, their output is prone to artifacts. Therefore, the quality cannot be ensured. To improve the quality of the most critical and challenging image areas, an exhaustive comparison is required. In this paper, we consider three questions of benchmarking the quality performance of eight DIBR techniques on light fields: First, how does the density of original input views affect the quality of the rendered novel views? Second, how does disparity range between adjacent input views impact the quality? Third, how does each technique behave for different object properties? We compared and evaluated the results visually as well as quantitatively (PSNR, SSIM, AD, and VDP2). The results show some techniques outperform others in different disparity ranges. The results also indicate using more views not necessarily results in visually higher quality for all critical image areas. Finally, we have shown a comparison for different scene's complexity such as non-Lambertian objects.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences, Moving Picture Technologies
Contributors: Zakeri, F. S., Bätz, M., Jaschke, T., Keinert, J., Chuchvara, A.
Publication date: 2019

Host publication information

Title of host publication: Fourteenth International Conference on Quality Control by Artificial Vision
Publisher: SPIE, IEEE
Editors: Bazeille, S., Verrier, N., Cudel, C.
Article number: 111721C
ISBN (Electronic): 9781510630536

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 11172
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Depth image-based rendering, Disparity estimation, Quality evaluation

Bibliographical note

jufoid=71479

Source: Scopus
Source ID: 85070208910

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Charge transfer dynamics in CsPbBr3 perovskite quantum dots-anthraquinone/fullerene (C60) hybrids

An advantage of colloidal quantum dots, particularly perovskite quantum dots (PQDs), as photoactive components is that they easily form complexes with functional organic molecules, which results in hybrids with enriched photophysical properties. Herein, we demonstrate the formation of stable ground state complexes of CsPbBr3 PQD with two widely used molecular electron acceptors, fullerene (C60) and anthraquinone, (AQ) which contain carboxylic anchor groups. Dynamics of the photo-induced electron transfer in the hybrids were compared. The use of carboxylic groups for binding results in stable complex formation and their photophysical properties depend on the ratio of components but not the absolute concentrations (up to micromolar concentrations). Time-resolved transient absorption (TA) spectroscopy shows that in both cases, a charge separated (CS) state is formed. Data analysis was aimed to evaluate the CS time constant in ideal one-to-one complexes and was found to be in the range of 30-190 ps. The CS state of PQD-AQ complexes recombines directly to the ground state in roughly one microsecond. Recombination of the CS state of PQD-C60 is more complex and points to strong inhomogeneity of these complexes. Majority of the CS states relax by first forming the C60 triplet state.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering
Contributors: Mandal, S., George, L., Tkachenko, N. V.
Number of pages: 8
Pages: 862-869
Publication date: 2019
Peer-reviewed: Yes
Early online date: 10 Dec 2018

Publication information

Journal: Nanoscale
Volume: 11
Issue number: 3
ISSN (Print): 2040-3364
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Source: Scopus
Source ID: 85060171357

Research output: Contribution to journalArticleScientificpeer-review

Crystallography and Mechanical Properties of Intercritically Annealed Quenched and Partitioned High-Aluminium Steel

The quenching and partitioning response of intercritically annealed steel with aluminum contents in the 2–3 wt.% range and a carbon content of 0.2 wt.% was studied. Two types of morphologies for retained austenite were observed in electron backscatter diffraction studies: blocky, untransformed austenite grains and partially transformed austenite located primarily at prior austenite and packet boundaries. The amount of retained austenite was found to correlate with the initial quench temperature, as well as with the uniform elongation of the specimens in subsequent tensile testing. The transformation characteristics of austenite were rationalized on the basis of prior austenite grain size and inhomogeneous carbon distribution. The martensite transformed during the initial quench was found to favor Σ3 twin-type lath combinations, supplemented by neighboring variants providing self-accommodation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Metals Technology, Materials Science, Colorado School of Mines, Golden, CO 80401 USA, Outotec Oyj
Contributors: Nyyssönen, T., Peura, P., De Moor, E., Kuokkala, V., Williamson, D. L.
Number of pages: 31
Publication date: 2019
Peer-reviewed: Yes
Early online date: 11 Dec 2018

Publication information

Journal: Materials Characterization
ISSN (Print): 1044-5803
Original language: English
ASJC Scopus subject areas: Metals and Alloys
Keywords: steels, crystallography, mechanical properties, microstructure, martensite

Bibliographical note

EXT="Nyyssönen, Tuomo"

Research output: Contribution to journalArticleScientificpeer-review

Design, processing, and characterization of an optical core-bioactive clad phosphate fiber for biomedical applications

The aim of this study was to fabricate a bioactive optical fiber able to monitor “in situ” its reaction with the body through changes in its optical properties. Core and cladding preforms were prepared with the composition (97.25*(0.50P2O5-0.40SrO-0.10Na2O)-2.5ZnO-0.25Er2O3) and (98.25*(0.50P2O5-0.40SrO-0.10Na2O)-1.75ZnO) (in mol%), respectively, and successfully drawn into a multimode core/clad optical fiber. Optical and near-Infrared images assessed the proper light guiding properties of the fiber. The fibers favor the precipitation of a Ca-P reactive layer at its surface concomitant with a reduction in the fiber diameter, when immersed in SBF, often assigned as a sign of bioactivity. It is clearly shown here that the bio-response of the fiber upon immersion in SBF can be tracked from the decrease in the intensity of the Er3+ ions emission at 1.5 µm. This confirms that the newly developed optical fiber, which combines good optical properties with a suitable bioactive behavior, is a promising platform for the development of novel biomedical devices for biophotonic and photomedical applications. Finally, the successful splicing of the newly developed fiber with commercial optical fibers was an evidence of the possibility to integrate the newly developed phosphate fiber within existing components used in the field of biomedicine.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, BioMediTech, Politecnico di Torino, Fondazione LINKS – Leading Innovation & Knowledge for Society, UMR CNRS 6226 Sciences Chimiques de Rennes, University of Parma, Photonics Laboratory
Contributors: Lopez-Iscoa, P., Ojha, N., Pugliese, D., Mishra, A., Gumenyuk, R., Boetti, N. G., Janner, D., Troles, J., Bureau, B., Boussard-Plédel, C., Massera, J., Milanese, D., Petit, L.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: JOURNAL OF THE AMERICAN CERAMIC SOCIETY
ISSN (Print): 0002-7820
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Materials Chemistry
Keywords: bioactivity, Er luminescence property, optical fiber, phosphate glass
Source: Scopus
Source ID: 85066458189

Research output: Contribution to journalArticleScientificpeer-review

Fabrication and Characterization of a Wireless Bioresorbable Pressure Sensor

Embedding sensors into orthopedic devices can enable these implants to monitor the progress of the healing process or detect cues of complications. The simple structure of inductor–capacitor (LC) resonance sensors combined with their wireless readout offers a desirable basis for such sensors. A set of eight bioresorbable inductively coupled pressure sensors is fabricated. The conductors are formed by e-beam evaporation of magnesium (7 µm) directly onto the substrates, after which two substrates are adhered to a holed spacer to form an LC sensor. All the sensors show a fairly linear pressure response in the physiological pressure range from 0 to 200 mm Hg with an average pressure sensitivity of −6.0 ± 0.5 kHz mm Hg−1. After the pressure response tests, the effects of known error sources are determined. Finally, the sensor performance in vitro in buffer solution at +37 °C is evaluated. The sensors function tolerably for the first 8 h in immersion, after which they are disabled by mechanical changes in the sensor structure. To conclude, a bioresorbable battery-free wireless pressure sensor architecture with an adequate sensitivity for biomedical applications is described. However, further studies are required to improve the stability of the sensors under physiological conditions.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Research group: Biomaterials and Tissue Engineering Group
Contributors: Palmroth, A., Salpavaara, T., Lekkala, J., Kellomäki, M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Advanced Materials Technologies
Article number: 1900428
ISSN (Print): 2365-709X
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Industrial and Manufacturing Engineering
Keywords: bioresorbable electronics, capacitive sensors, inductive coupling, pressure sensors, transient electronics
Source: Scopus
Source ID: 85070686346

Research output: Contribution to journalArticleScientificpeer-review

Feature Engineering for Mid-Price Prediction with Deep Learning

Mid-price movement prediction based on the limit order book data is a challenging task due to the complexity and dynamics of the limit order book. So far, there have been very limited attempts for extracting relevant features based on the limit order book data. In this paper, we address this problem by designing a new set of handcrafted features and performing an extensive experimental evaluation on both liquid and illiquid stocks. More specifically, we present an extensive set of econometric features that capture the statistical properties of the underlying securities for the task of mid-price prediction. The experimental evaluation consists of a head-to-head comparison with other handcrafted features from the literature and with features extracted from a long short-term memory autoencoder by means of a fully automated process. Moreover, we develop a new experimental protocol for online learning that treats the task above as a multi-objective optimization problem and predicts: 1) the direction of the next price movement and; 2) the number of order book events that occur until the change takes place. In order to predict the mid-price movement, features are fed into nine different deep learning models based on multi-layer perceptrons, convolutional neural networks, and long short-term memory neural networks. The performance of the proposed method is then evaluated on liquid and illiquid stocks (i.e., TotalView-ITCH US and Nordic stocks). For some stocks, results suggest that the correct choice of a feature set and a model can lead to the successful prediction of how long it takes to have a stock price movement.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Multimedia Research Group - MRG, Computing Sciences, Danmarks Nationalbank, Aarhus Universitet
Contributors: Ntakaris, A., Mirone, G., Kanniainen, J., Gabbouj, M., Iosifidis, A.
Number of pages: 23
Pages: 82390-82412
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: Deep learning, econometrics, high-frequency trading, limit order book, mid-price, U.S. data

Bibliographical note

EXT="Iosifidis, Alexandros"

Source: Scopus
Source ID: 85068671731

Research output: Contribution to journalArticleScientificpeer-review

Flip-chip Wafer-fused OP-VECSELs emitting 3.65 W at the 1.55-&#x03BC;m waveband

Optically-pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55-&#x03BC;m wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors fixed on a diamond heat-sink substrate in a flip-chip geometry, incorporated in a V-cavity configuration. A maximum output power of 3.65 W was achieved for a heat sink temperature of 11&#x00B0;C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. This demonstration represents more than 5-fold increase of the output power compared to state-of-the-art flip-chip VECSELs previously reported at the 1.55 &#x03BC;m wavelength range. It opens new perspectives for developing practical VECSEL-based laser systems operating at a wavelength range widely used in many applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, CRPP, LakeDiamond SA
Contributors: Mereuta, A., Nechay, K., Caliman, A., Suruceanu, G., Rudra, A., Gallo, P., Guina, M., Kapon, E.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Journal of Selected Topics in Quantum Electronics
Volume: 25
Issue number: 6
ISSN (Print): 0792-1233
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Atomic and Molecular Physics, and Optics, Materials Chemistry, Electrical and Electronic Engineering
Keywords: diode pumped, Flip-chip devices, Heating systems, Lasers, Mirrors, Optical pumping, Power generation, Semiconductor lasers, Temperature measurement, Vertical cavity surface emitting lasers, Vertical emitting lasers
Source: Scopus
Source ID: 85067801249

Research output: Contribution to journalArticleScientificpeer-review

Gas-foamed poly(lactide-co-glycolide) and poly(lactide-co-glycolide) with bioactive glass fibres demonstrate insufficient bone repair in lapine osteochondral defects

Deep osteochondral defects may leave voids in the subchondral bone, increasing the risk of joint structure collapse. To ensure a stable foundation for the cartilage repair, bone grafts can be used for filling these defects. Poly(lactide-co-glycolide) (PLGA) is a biodegradable material that improves bone healing and supports bone matrix deposition. We compared the reparative capacity of two investigative macroporous PLGA-based biomaterials with two commercially available bone graft substitutes in the bony part of an intra-articular bone defect created in the lapine femur. New Zealand white rabbits (n = 40) were randomized into five groups. The defects, 4 mm in diameter and 8 mm deep, were filled with neat PLGA; a composite material combining PLGA and bioactive glass fibres (PLGA–BGf); commercial beta-tricalcium phosphate (β-TCP) granules; or commercial bioactive glass (BG) granules. The fifth group was left untreated for spontaneous repair. After three months, the repair tissue was evaluated with X-ray microtomography and histology. Relative values comparing the operated knee with its contralateral control were calculated. The relative bone volume fraction (∆BV/TV) was largest in the β-TCP group (p ≤ 0.012), which also showed the most abundant osteoid. BG resulted in improved bone formation, whereas defects in the PLGA–BGf group were filled with fibrous tissue. Repair with PLGA did not differ from spontaneous repair. The PLGA, PLGA–BGf, and spontaneous groups showed thicker and sparser trabeculae than the commercial controls. We conclude that bone repair with β-TCP and BG granules was satisfactory, whereas the investigational PLGA-based materials were only as good as or worse than spontaneous repair.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, University of Helsinki Faculty of Medicine, Helsinki University Central Hospital, Department of Medical Physics, Tampere University Hospital, Abo Akad Univ, Abo Akademi University, Dept Phys
Contributors: Salonius, E., Muhonen, V., Lehto, K., Järvinen, E., Pyhältö, T., Hannula, M., Aula, A. S., Uppstu, P., Haaparanta, A. M., Rosling, A., Kellomäki, M., Kiviranta, I.
Number of pages: 10
Pages: 406-415
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Tissue Engineering and Regenerative Medicine
Volume: 13
Issue number: 3
ISSN (Print): 1932-6254
Original language: English
ASJC Scopus subject areas: Medicine (miscellaneous), Biomaterials, Biomedical Engineering
Keywords: animal model, biomaterial, bone repair, intra-articular, poly(lactide-co-glycolide)
Source: Scopus
Source ID: 85061916720

Research output: Contribution to journalArticleScientificpeer-review

High-speed production of antibacterial fabrics using liquid flame spray

Healthcare associated infections (HAIs) are known as one of the major problems of the modern healthcare system, which result in additional cost and mortality. It has also been shown that pathogenic bacteria are mostly transferred via surfaces in healthcare settings. Therefore, antibacterial surfaces, which include fabrics and textiles, can be used in a healthcare environment to reduce the transfer of pathogenic bacteria, hence reducing HAIs. Silver nanoparticles have been shown to have broad spectrum antibacterial properties, and therefore they have been incorporated into fabrics to provide antibacterial functionality. Liquid flame spray (LFS) nanoparticle synthesis allows nanoparticles to be produced and deposited on surfaces at speeds up to and beyond 300 m/min. Herein, LFS is used to deposit silver nanoparticles onto two fabrics that are commonly used in the hospital environment with the aim of producing antibacterial fabrics. A thin plasma coating on top of the fabrics after silver deposition is used to improve nanoparticle adhesion. Fabrics coated with silver nanoparticles demonstrated antibacterial properties against Escherichia coli. Nanoparticle imaging and surface chemical characterization are performed using scanning electron microscopy and X-ray photoelectron spectroscopy. The highlights of this research are as follows: • high-speed synthesis and deposition of silver nanoparticles on fabrics; • plasma coating onto fabrics with silver nanoparticles; • antibacterial fabrics for potential use in healthcare environments.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Aerosol Synthesis, Physics, Abo Akad Univ, Abo Akademi University, Dept Phys, RISE Research Institutes of Sweden AB, Turun yliopisto, University of Eastern Finland
Contributors: Brobbey, K. J., Haapanen, J., Tuominen, M., Mäkelä, J., Gunell, M., Eerola, E., Saarinen, J. J., Toivakka, M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Textile Research Journal
ISSN (Print): 0040-5175
Original language: English
ASJC Scopus subject areas: Chemical Engineering (miscellaneous), Polymers and Plastics
Keywords: antibacterial, fabrics, liquid flame spray, nanoparticles, plasma deposition, silver
Source: Scopus
Source ID: 85071117647

Research output: Contribution to journalArticleScientificpeer-review

Human Neural Tissues from Neural Stem Cells Using Conductive Biogel and Printed Polymer Microelectrode Arrays for 3D Electrical Stimulation

Electricity is important in the physiology and development of human tissues such as embryonic and fetal development, and tissue regeneration for wound healing. Accordingly, electrical stimulation (ES) is increasingly being applied to influence cell behavior and function for a biomimetic approach to in vitro cell culture and tissue engineering. Here, the application of conductive polymer (CP) poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) pillars is described, direct-write printed in an array format, for 3D ES of maturing neural tissues that are derived from human neural stem cells (NSCs). NSCs are initially encapsulated within a conductive polysaccharide-based biogel interfaced with the CP pillar microelectrode arrays (MEAs), followed by differentiation in situ to neurons and supporting neuroglia during stimulation. Electrochemical properties of the pillar electrodes and the biogel support their electrical performance. Remarkably, stimulated constructs are characterized by widespread tracts of high-density mature neurons and enhanced maturation of functional neural networks. Formation of tissues using the 3D MEAs substantiates the platform for advanced clinically relevant neural tissue induction, with the system likely amendable to diverse cell types to create other neural and non-neural tissues. The platform may be useful for both research and translation, including modeling tissue development, function and dysfunction, electroceuticals, drug screening, and regenerative medicine.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Computational Biophysics and Imaging Group, BioMediTech, University of Wollongong, The University of Auckland, Department of Chemistry and Bioengineering, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Melbourne
Contributors: Tomaskovic-Crook, E., Zhang, P., Ahtiainen, A., Kaisvuo, H., Lee, C. Y., Beirne, S., Aqrawe, Z., Svirskis, D., Hyttinen, J., Wallace, G. G., Travas-Sejdic, J., Crook, J. M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: ADVANCED HEALTHCARE MATERIALS
Article number: 1900425
ISSN (Print): 2192-2640
Original language: English
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering, Pharmaceutical Science
Keywords: 3D electrical stimulation, conductive biogels, human neural tissue, printed conducting polymer electrodes, stem cells
Source: Scopus
Source ID: 85067695878

Research output: Contribution to journalArticleScientificpeer-review

Impact wear and mechanical behavior of steels at subzero temperatures

In this study, the deformation behavior of three steels was studied at Arctic temperatures by controlled single and multiple oblique angle impacts. The results were compared with the mechanical properties of the steels determined at the corresponding temperatures. At subzero temperatures, the hardness and strength of the studied steels increased and their ability to deform plastically steadily decreased. In the martensitic steels, adiabatic shear bands were observed to form during the impacts at subzero temperatures, indicating that the deformation ability of the steels was critically impaired. At −60 °C, the adiabatic shear bands commonly acted as initiation sites for subsurface cracks. Moreover, the surface characterization of the test samples revealed formation of cracks and wear particles, which was connected to the opening of grain boundaries and martensite laths at low temperatures. Finite Element Modeling was also used to obtain more information about the impact event.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, University of Nottingham
Contributors: Valtonen, K., Ratia, V., Ramakrishnan, K. R., Apostol, M., Terva, J., Kuokkala, V.
Number of pages: 18
Pages: 476-493
Publication date: 2019
Peer-reviewed: Yes
Early online date: 17 Aug 2018

Publication information

Journal: Tribology International
Volume: 129
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Impact, Low temperature, Steel, Wear
Electronic versions: 
Source: Scopus
Source ID: 85053014382

Research output: Contribution to journalArticleScientificpeer-review

Integrated Use of Licensed-and Unlicensed-Band mmWave Radio Technology in 5G and beyond

The 3GPP standardization rapidly moves forward with studies of a wide-bandwidth waveform as well as an adaptation of the emerging 5G new radio (NR)-based access to the unlicensed spectrum (NR-U). One of the basic architectures for NR-U involves carrier aggregation of an anchor-licensed-NR carrier and a secondary carrier in unlicensed spectrum, which altogether allows for seamless traffic offloading in scenarios where multi-gigabit data rates are required. While today's research on NR-U addresses mostly physical-and protocol-layer aspects, a system-level performance of the NR-U offloading mechanisms has not been investigated thoroughly. In this paper, we develop a mathematical queuing-Theoretic framework that is mindful of the specifics of millimeter-wave (mmWave) session dynamics and may serve as a flexible tool for the analysis of various strategies for the integrated use of licensed and unlicensed mmWave bands in terms of the session drop probability and system utilization. To illustrate this, we select three distinct strategies (based on sequential service, probabilistic offloading, or proportional splitting), and complement our mathematical models with a detailed performance evaluation in a representative massive augmented/virtual reality scenario. Based on this quantitative analysis of the selected schemes, we conclude that proportional splitting of traffic between the two mmWave bands leads to a better performance. We believe that the contributed mathematical analysis can become an important building block in further system development and service optimization across many usage scenarios.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, King’s College London, Peoples’ Friendship University of Russia, Department of Applied Mathematics and Probability Theory
Contributors: Lu, X., Sopin, E., Petrov, V., Galinina, O., Moltchanov, D., Ageev, K., Andreev, S., Koucheryavy, Y., Samouylov, K., Dohler, M.
Number of pages: 16
Pages: 24376-24391
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: 5G and beyond, 5G-U, integration of licensed and unlicensed bands, massive AR/VR, mathematical analysis, mmWave-based access, NR-U, radio resource allocation
Source: Scopus
Source ID: 85062961977

Research output: Contribution to journalArticleScientificpeer-review

In-vitro dissolution characteristics and human adipose stem cell response to novel borophosphate glasses

The main drawbacks of traditional silicate bioactive glasses are their narrow hot forming domain and noncongruent dissolution. In this article, we report on new borophosphate glasses [xMnOm + (100 − x) (47.5P2O5 + 2.5B2O3 + 10Na2O + 20CaO + 20SrO)], MnOm being CuO, Ag2O, and CeO2, having high thermal processability, hence suitable for fiber drawing and sintering into scaffolds. Furthermore, the glasses dissolve congruently in simulated body fluid (SBF) and TRIS buffer solution, eventually leading to the precipitation of a reactive layer. Human adipose stem cells (hASC) were cultured in media enriched with glass extract at different dilutions, to investigate the optimal ion concentration for cell survival. Cells grew in all the extracts, except in the undiluted Cu-doped glass extract. At dilution 1:10, the lactate dehydrogenase (LDH) activity and cell proliferation were comparable to the control, while at 1:100, the cells proliferated faster than the control. Thus, the reference (undoped), Ag and Ce-doped glasses were found to be suitable for cell viability and proliferation. Cytotoxicity assessments using the LDH assay indeed revealed the high cytotoxicity of the Cu extract. This raises questions about the use of Cu in bioactive glasses and its optimal concentration as a dopant.

General information

Publication status: Accepted/In press
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Health Sciences, Karolinska Institutet, Adult Stem Cell Group, Tampere University, Tampere University Hospital
Contributors: Mishra, A., Ojansivu, M., Autio, R., Vanhatupa, S., Miettinen, S., Massera, J.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Biomedical Materials Research - Part A
ISSN (Print): 1549-3296
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Biomaterials, Biomedical Engineering, Metals and Alloys
Keywords: bioactive glass, borophosphate glass, cell proliferation, cytotoxicity, in-vitro dissolution

Bibliographical note

EXT="Ojansivu, Miina"

Source: Scopus
Source ID: 85066908676

Research output: Contribution to journalArticleScientificpeer-review

Low-dimensional formamidinium lead perovskite architectures via controllable solvent intercalation

We report the formation of a new class of solvent-intercalated two-dimensional (SI-2D) formamidinium lead halide perovskites. They can be mixed with three-dimensional (3D) stoichiometric perovskites by controlling the ratio of the precursor solutions. The composite leads to greatly improved photoluminescence quantum yield (PLQY) over the 3D compound. The enhanced PLQY is attributed to a type-I band alignment between the 3D and SI-2D, as revealed by first-principles calculations, which results in confined excitons with enhanced radiative recombination. The films exhibited excellent thermal and air stability retaining PLQY > 20% over 2 months in ambient conditions. Assemblies of halide perovskites with mixed dimensionality offer a pathway to enhance optoelectronic performance and device lifetimes.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), Yonsei University
Contributors: Shin, M., Kim, J., Jung, Y. K., Ruoko, T., Priimagi, A., Walsh, A., Shin, B.
Number of pages: 7
Pages: 3945-3951
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Chemistry C
Volume: 7
Issue number: 13
ISSN (Print): 2050-7534
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Chemistry
Source: Scopus
Source ID: 85064717293

Research output: Contribution to journalArticleScientificpeer-review

MECSELs with direct emission in the 760 nm to 810 nm spectral range: A single- and double-side pumping comparison and high-power continuous-wave operation

We compared single-side pumping (SSP) and double-side pumping (DSP) of a semiconductor membrane external-cavity surface-emitting laser (MECSEL). The MECSEL's active region was based on a 4×3 AlGaAs quantum well (QW) structure. This structure was embedded between two silicon carbide (SiC) wafer pieces that were used as transparent intra-cavity (IC) heat spreaders creating a symmetrical cooling environment. The MECSEL structure targeted emission at 780nm and was operated at 20°C heat sink temperature. Via DSP the differential efficiency was improved from 31.9% to 34.4 %. The laser threshold was reduced from 0.79 W to 0.69 W of absorbed pump power while the maximum output power was increased from 3.13 W to 3.22 W. The DSP configuration enabled these improvements by a reduced thermal resistance of the gain element by 9 %. The MECSEL operated at a fundamental Gaussian TEM00 mode profile and the beam quality was measured to be M2 <1.09. We further demonstrate a maximum tuning range from 767 nm to 811 nm. A similar active region with about half the thickness (2×3 AlGaAs QWs) was investigated using the DSP configuration and first results are presented here. 500-μm-thick sapphire IC heat spreaders were used instead of SiC. The output power exceeded 0.5W and the emission was spectrally located around 770 nm.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics
Contributors: Kahle, H., Penttinen, J. P., Phung, H. M., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Publication date: 2019

Host publication information

Title of host publication: Vertical External Cavity Surface Emitting Lasers (VECSELs) IX
Publisher: SPIE, IEEE
Editor: Keller, U.
Article number: 109010D
ISBN (Electronic): 9781510624443

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10901
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: AlGaAs, DBR-free, MECSEL, Near infra-red, Thermal management, Thermal resistance, VECSEL

Bibliographical note

INT=phys,"Rajala, Patrik"
jufoid=71479

Source: Scopus
Source ID: 85066635597

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Microstructure-property relationships of novel ultra-high strength press hardening steels

The industrial significance of microalloyed martensitic steels manufactured via cold rolling, reaustenitization, and quenching has been typically recognized as low. However, it is currently believed that microalloying can improve the in-service properties of ultra-high-strength press hardening steels. In this work, five 34MnB5-based steels were designed to address the role of Ti and V when combined with Cr or Mo. Microstructure-property relationships were analyzed after die quenching and additional bake hardening (BH) heat treatment using advanced methods of microscopy, glow discharge optical emission spectroscopy, quasi-static tensile tests, and three-point bending tests. Results indicate that both Ti and V can provide grain size refinement through the formation of stabile nanosized precipitates. The BH treatment improved postuniform elongation values, indicating a trend of improved ductility. However, the expected improvements in bendability were clearly confirmed only for two V-microalloyed steels with the alloying concepts of 0.3Cr-0.15V-0.03Al-0.02Ti-0.0020B and 0.3Mo-0.15V-0.0060N (without Al-Ti-B additions) (wt pct). Thus, it was discovered that microalloying with V, when combined with either Cr or Mo, provides a promising combination of mechanical properties as far as the austenitization parameters are appropriately controlled.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Metals Technology, Research group: Materials Characterization, SSAB Europe Oy
Contributors: Järvinen, H., Honkanen, M., Oja, O., Järvenpää, M., Peura, P.
Number of pages: 21
Pages: 816-836
Publication date: 2019
Peer-reviewed: Yes
Early online date: 29 Nov 2018

Publication information

Journal: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume: 50
Issue number: 2
ISSN (Print): 1073-5623
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Metals and Alloys
Keywords: Press hardening, Bake hardening, Martensite, EBSD, TEM, Mechanical behavior

Research output: Contribution to journalArticleScientificpeer-review

Multiphoton Excitation of CsPbBr3 Perovskite Quantum Dots (PQDs): How Many Electrons Can One PQD Donate to Multiple Molecular Acceptors?

Metastable multiexcitonic states (MESs) of semiconductor quantum dots can be involved in multielectron transfer reactions, which opens new perspectives in nanomaterials-based optoelectronic applications. Herein, we demonstrate the generation of a MES in CsPbBr3 perovskite quantum dots (PQDs) and its dissociation dynamics through multiple electron transfers to molecular electron acceptors, anthraquinones (AQs), bound to the PQD surface by a carboxylic anchor. As many as 14 excitons are produced at an excitation density of roughly 220 μJ cm-2 without detectable PQD degradation. Addition of AQ results in the formation of PQD-AQ hybrids with excess of AQs (PQD:AQ ≈ 1:20), which opens the possibility of multielectron transfer acts from MES to AQs. We found that the electron transfer saturates after roughly five transfer acts and that the first electron transfer (ET) time constant is as short as 1 ps. However, each ET increases the Coulomb potential barrier for the next ET, which decreases the rate of ET, resulting in a saturation after five ETs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Bio- and Circular Economy, Materials Science and Environmental Engineering
Contributors: Mandal, S., Tkachenko, N. V.
Number of pages: 7
Pages: 2775-2781
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry Letters
ISSN (Print): 1948-7185
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physical and Theoretical Chemistry
Electronic versions: 
Source: Scopus
Source ID: 85066897133

Research output: Contribution to journalArticleScientificpeer-review

Observation of local electroluminescent cooling and identifying the remaining challenges

The cooling of a light emitting diode (LED) by photons carrying out more energy than was used to electrically bias the device, has been predicted decades ago. 1, 2 While this effect, known as electroluminescent cooling (ELC), may allow e.g. fabricating thermophotonic heat pumps (THP) providing higher efficiencies than the existing solid state coolers, 3 ELC at powers sufficient for practical applications is still not demonstrated. To study high-power ELC we use double diode structures (DDSs), which consist of a double heterojunction (DHJ) LED and a photodiode (PD) grown within a single technological process and, thus, enclosed in a cavity with a homogeneous refractive index. 4, 5 The presence of the PD in the structure allows to more directly probe the efficiency of the LED, without the need for light extraction from the system, reducing undesirable losses. Our analysis of experimentally measured I - V curves for both the LED and the PD suggests that the local efficiency of the high-performance LEDs we have fabricated is approximately 110%, exceeding unity over a wide range of injection current densities of up to about 100A/cm 2 . At present the efficiency of the full DDS, however, still falls short of unity, not allowing direct evidence of the extraction of thermal energy from the LED. Here we review our previous studies of DDS for high-power EL cooling and discuss in more detail the remaining bottlenecks for demonstrating high-power ELC in the DDS context: the LED surface states, resistive and photodetection losses. In particular we report our first surface passivation measurements. Further optimization therefore mainly involves reducing the influence of the surface states, e.g. using more efficient surface passivation techniques and optimizing the PD. This combined with the optimization of the DDS layer thicknesses and contact metallization schemes is expected to finally allow purely experimental observation of high-power ELC.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Aalto University
Contributors: Radevici, I., Sadi, T., Tripurari, T., Tiira, J., Ranta, S., Tukiainen, A., Guina, M., Oksanen, J.
Publication date: 2019

Host publication information

Title of host publication: Photonic Heat Engines : Science and Applications
Publisher: SPIE, IEEE
Editors: Seletskiy, D. V., Epstein, R. I., Sheik-Bahae, M.
Article number: 109360A
ISBN (Electronic): 9781510625143

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10936
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Double diode structures, Electroluminescent cooling, III-V semiconductors, Quantum efficiency, Surface states

Bibliographical note

jufoid=71479

Source: Scopus
Source ID: 85065604697

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

On the limit of superhydrophobicity: Defining the minimum amount of TiO2 nanoparticle coating

Fabrication of superhydrophobic surfaces in large scale has been in high interest for several years, also titanium oxide nanostructures having been applied for the purpose. Optimizing the amount and structure of the TiO2 material in the coating will play a key role when considering upscaling. Here, we take a look at fabricating the superhydrophobic surface in a one-step roll-to-roll pilot scale process by depositing TiO2 nanoparticles from a Liquid Flame Spray onto a moving paperboard substrate. In order to find the minimum amount of nanomaterial still sufficient for creating superhydrophobicity, we varied nanoparticle production rate, flame distance from the substrate and line speed. Since the deposited amount of material sideways from the flame path was seen to decrease gradually, spatial analysis enabled us to consistently determine the minimum amount of TiO2 nanoparticles on the substrate needed to achieve superhydrophobicity. Amount as low as 20-30 mg m-2 of TiO2 nanoparticles was observed to be sufficient. The scanning electron microscopy revealed that at this amount, the surface was covered with nanoparticles only partially, but still sufficiently to create a hierarchical structure to affect wetting significantly. Based on XPS analysis, it became apparent that TiO2 gathers hydrocarbons on the surface to develop the surface chemistry towards hydrophobic, but below the critical amount of TiO2 nanoparticles, the chemistry could not enable superhydrophobicity anymore. While varying the deposited amount of TiO2, besides the local spatial variance of the coating amount, also the overall yield was studied. Within the text matrix, a yield up to 44% was achieved. In conclusion, superhydrophobicity was achieved at all tested line speeds (50 to 300 m min-1), even if the amount of TiO2 varied significantly (20 to 230 mg m-2).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Aerosol Synthesis, Research area: Aerosol Physics, Materials Science, Packaging Technology Research Team, Physics at Interfaces, Max Planck Institute for Polymer Research, Bioscience and Materials/Surface, RISE Research Institutes of Sweden AB, Finnish Environment Institute, Abo Akad Univ, Abo Akademi University, Dept Phys, AGH University of Science and Technology, University of Eastern Finland
Contributors: Haapanen, J., Aromaa, M., Teisala, H., Juuti, P., Tuominen, M., Sillanpää, M., Stepien, M., Saarinen, J. J., Toivakka, M., Kuusipalo, J., Mäkelä, J. M.
Publication date: 2019
Peer-reviewed: Yes
Early online date: 5 Dec 2018

Publication information

Journal: Materials Research Express
Volume: 6
Issue number: 3
Article number: 035004
ISSN (Print): 2053-1591
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Surfaces, Coatings and Films, Polymers and Plastics, Metals and Alloys
Keywords: liquid flame spray, nanocoatings, nanoparticles, superhydrophobic, TiO, titanium dioxide, wetting
Source: Scopus
Source ID: 85059238010

Research output: Contribution to journalArticleScientificpeer-review

Packet level performance assessment of mmWave backhauling technology for 3GPP NR Systems

Recently standardized millimeter-wave (mmWave) band 3GPP New Radio systems are expected to bring extraordinary rates to the air interface efficiently providing commercial-grade enhanced mobile broadband services in hotspot areas. One of the challenges of such systems is efficient offloading of the data from access points (AP) to the network infrastructure. This task is of special importance for APs installed in remote areas with no transport network available. In this paper, we assess the packet level performance of mmWave technology for cost-efficient backhauling of remote 3GPP NR APs connectivity 'islands'. Using a queuing system with arrival processes of the same priority competing for transmission resources, we assess the aggregated and per-AP packet loss probability as a function environmental conditions, mmWave system specifics, and generated traffic volume. We show that the autocorrelation in aggregated traffic provides a significant impact on service characteristics of mmWave backhaul and needs to be compensated by increasing either emitted power or the number of antenna array elements. The effect of autocorrelation in the per-AP traffic and background traffic from other APs also negatively affects the per-AP packet loss probability. However, the effect is of different magnitude and heavily depends on the load fraction of per-AP traffic in the aggregated traffic stream. The developed model can be used to parameterize mmWave backhaul links as a function of the propagation environment, system design, and traffic conditions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Research group: Wireless Communications and Positioning, National Research University Higher School of Economics, St. Petersburg State Polytechnical University
Contributors: Ometov, A., Moltchanov, D., Komarov, M., Volvenko, S. V., Koucheryavy, Y.
Number of pages: 12
Pages: 9860-9871
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: 5G mobile communication, mathematical model, millimeter wave communication, Next generation networking, queueing analysis, wireless communication

Bibliographical note

EXT="Ometov, Aleksandr"
EXT="Komarov, Mikhail"

Source: Scopus
Source ID: 85061089480

Research output: Contribution to journalArticleScientificpeer-review

Printed flexible microelectrode for application of nanosecond pulsed electric fields on cells

Medical treatment is increasingly benefiting from biomedical microsystems, especially the trending telemedical application. A promising modality for tumor therapy showed the application of nanosecond pulsed electric fields (nsPEF) on cells to achieve nanoporation, cell death, and other cell reactions. A key technology for this method is the generation of pulsed fields in the nanosecond range with high-field strengths in the range of several kilovolts per centimeter. For further biomedical applications, state-of-the-art setups need to decrease in size and improve their capability of integration into microsystems. Due to demanding electronic requirements, i.e., using high voltages and fast pulses, miniaturization and low-cost fabrication of the electrode is first considered. This paper proposes a proof-of-concept for a miniaturized printed flexible electrode that can apply nsPEF on adherent fibroblast cells. The interdigital gold electrode was printed on polyimide with line-width of about 10 μm using an electrohydrodynamic inkjet printer. Furthermore, an electrical circuit was developed to generate both electrical pulses in the nano-second range and voltages up to 180 V. The electrode was integrated into an experimental setup for in-vitro application to human fibroblasts. Field strengths up to 100 kV/cm with 45 ns pulse duration were applied, depending on the degree of cell confluence. The cells show contraction, detachment from the electrode, and lethal reactions after the nsPEF treatment. Furthermore, this printed miniaturized electrode was found to be suitable for subsequent microsystem integration and further cell experiments to optimize pulse parameters for control of cell reaction and behavior.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Vodafone Department of Mobile Communications Systems
Contributors: Schubert, M., Rasche, J., Laurila, M., Vuorinen, T., Mäntysalo, M., Bock, K.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Materials
Volume: 12
Issue number: 7
Article number: 2713
ISSN (Print): 1996-1944
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: E-jet printing, Electropermeabilization, Flexible electronics, Printed electronics, Pulsed electric field treatment
Electronic versions: 
Source: Scopus
Source ID: 85071832987

Research output: Contribution to journalArticleScientificpeer-review

Reliability evaluation of wearable radio frequency identification tags: Design and fabrication of a two-part textile antenna

Passive radio frequency identification-based technology is a convincing approach to the achievement of versatile energy- and cost-efficient wireless platforms for future wearable applications. By using two-part antenna structures, the antenna-electronics interconnections can remain non-stressed, which can significantly improve the reliability of the textile-embedded wireless components. In this article, we describe fabrication of two-part stretchable and non-stretchable passive ultra-high frequency radio frequency identification textile tags using electro-textile and embroidered antennas, and test their reliability when immersed as well as under cyclic strain. The results are compared to tags with traditional one-part dipole antennas fabricated from electro-textiles and by embroidery. Based on the results achieved, the initial read ranges of the two-part antenna tags, around 5 m, were only slightly shorter than those of the one-part antenna tags. In addition, the tag with two-part antennas can maintain high performance in a moist environment and during continuous stretching, unlike the one-part antenna tag where the antenna-integrated circuit attachment is under stress.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Wireless Identification and Sensing Systems Research Group
Contributors: Chen, X., Ukkonen, L., Virkki, J.
Publication date: 2019
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Textile Research Journal
Volume: 89
Issue number: 4
ISSN (Print): 0040-5175
Original language: English
ASJC Scopus subject areas: Chemical Engineering (miscellaneous), Polymers and Plastics
Keywords: E-textile antenna, embroidery antenna, radio frequency identification
Source: Scopus
Source ID: 85045121603

Research output: Contribution to journalArticleScientificpeer-review

Remote diagnostics application software for remote handling equipment

The ITER Remote Handling Control System (RHCS) controllers provide measurement and diagnostics data about the remote handling equipment and tools they control. This paper presents the Remote Diagnostics Application (RDA) software for the analysis and archiving of the RHCS diagnostics data. The RDA provides a basic set of diagnostics tools, including trends, spectra, histograms, scatter plots, cross-correlation plots, as well as archiving and retrieval of history data. The ITER RH operators can extend diagnostics capabilities for specific RH equipment needs by incorporating custom diagnostics functions. To facilitate customization, RDA implements an architecture with three nested levels: the RDA Framework, its Diagnostics Workbenches and their Diagnostics Primitives. The RDA Framework has a user interface that can load one or several special diagnostics cases implemented as custom Diagnostics Workbenches with custom or default Diagnostics Primitives, such as rules, analysis functions and filters. As a result, the RDA features a diagnostics framework to execute complex and dedicated diagnostics and prognostics for the RH experts to monitor performance data, to run diagnostics tests and rules on equipment systems and to analyse historical data. The RDA helps the RH operators reduce downtime of the Remote Handling systems by exposing failure conditions and maintenance needs.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Automation Technology and Mechanical Engineering, VTT Technical Research Centre of Finland, Fusion For Energy (F4E)
Contributors: Alanen, J., Ruiz Morales, E., Muhammad, A., Saarinen, H., Minkkinen, J.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Fusion Engineering and Design
ISSN (Print): 0920-3796
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Nuclear Energy and Engineering, Materials Science(all), Mechanical Engineering
Keywords: Control system, Diagnostics, Prognostics, Remote handling, Software

Bibliographical note

EXT="Saarinen, Hannu"

Source: Scopus
Source ID: 85060619368

Research output: Contribution to journalArticleScientificpeer-review

Robocasting of SiO2-based bioactive glass scaffolds with porosity gradient for bone regeneration and potential load-bearing applications

Additive manufacturing of bioactive glasses has recently attracted high interest in the field of regenerative medicine as a versatile class of fabrication methods to process bone substitute materials. In this study, melt-derived glass particles from the SiO2-P2O5-CaO-MgO-Na2O-K2Osystem were used to fabricate bioactive scaffolds with graded porosity by robocasting. A printable ink made of glass powder and Pluronic F-127 (binder) was extruded into a grid-like three-dimensional structure with bimodal porosity, i.e., the inner part of the scaffold had macropores with smaller size compared to the periphery. The crystallization behavior of the glass powder was studied by hot-stage microscopy, differential thermal analysis, and X-ray diffraction; the scaffolds were sintered at a temperature below the onset of crystallization so that amorphous structures could be obtained. Scaffold architecture was investigated by scanning electron microscopy and microtomographic analysis that allowed quantifying the microstructural parameters. In vitro tests in Kokubo's simulated body fluid (SBF) confirmed the apatite-forming ability (i.e., bioactivity) of the scaffolds. The compressive strength was found to slightly decrease during immersion in SBF up to 4 weeks but still remained comparable to that of human cancellous bone. The pH and concentration of released ions in SBF were also measured at each time point. Taken together, these results (favorable porosity, mechanical strength, and in vitro bioactivity) show great promise for the potential application of these robocast scaffolds in bone defect repair.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Politecnico di Torino, Interuniversity Center for the Promotion of the 3Rs Principles in Teaching and Research, Innovation Center Iceland (ICI), Department of Mining and Materials Engineering, McGill University
Contributors: Barberi, J., Baino, F., Fiume, E., Orlygsson, G., Nommeots-Nomm, A., Massera, J., Verné, E.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Materials
Volume: 12
Issue number: 7
Article number: 2691
ISSN (Print): 1996-1944
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: 3D printing, Additive manufacturing, Bioactive glass, Bioactivity, Bone, Porosity, Scaffold, Tissue engineering
Electronic versions: 

Bibliographical note

EXT="Nommeots-Nomm, Amy"

Source: Scopus
Source ID: 85071877398

Research output: Contribution to journalArticleScientificpeer-review

Role of Steel Plate Thickness on the Residual Stress Formation and Cracking Behavior During Flame Cutting

Thick wear-resistant steel plates are utilized in challenging applications, which require a high hardness and toughness. However, utilization of the thick plates is problematic as they often have nonuniform mechanical properties along the thickness direction due to the manufacturing-induced segregations. In addition, the processing of thick plates commonly involves flame cutting, which causes several challenges. Flame cutting forms a heat-affected zone and generates high residual stresses during the cutting process. In the worst case, flame cutting causes cracking of the cut edge. The aim of this study is to investigate the role of plate thickness on the residual stress formation and cracking behavior when utilizing flame cutting. Residual stress profiles are measured by X-ray diffraction, plates and cut edges and are mechanically tested and characterized by electron microscopy. The results show that thicker plates generate more unfavorable residual stress state during flame cutting. Thick plates also contain segregations, which have decreased mechanical properties. The combination of high residual tensile stresses and segregations increase the risk of cracking during flame cutting. To prevent the cracking, the residual stresses should be lowered by lower cutting speeds and preheating. In addition, manufacturing practices should be aimed at lowering segregation formation in thick plates.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering
Contributors: Jokiaho, T., Santa-aho, S., Peura, P., Vippola, M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
ISSN (Print): 1073-5623
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Metals and Alloys
Source: Scopus
Source ID: 85068025007

Research output: Contribution to journalArticleScientificpeer-review

Running-in effects on friction of journal bearings under slow sliding speeds

Hydrodynamic thrust and journal bearings are facing challenges in modern heavy-duty machinery where full film lubrication cannot always be achieved or sustained. This is due to reasons such as start–stop operation, increased power density and the use of thinner lubricants. Although this leads to increased overall efficiency, bearings are operating more often under mixed lubrication conditions. This is why the running-in behavior of the bearing material is important. In this study, running-in behavior of traditional leaded tin bronze and its environmentally sustainable alternative, bimetal bismuth, was studied. Experimental friction tests were performed with journal bearings under full film and mixed lubrication conditions in order to find the Stribeck curves. The results are analyzed using frictional energy, and friction coefficient values based on continuous friction monitoring. Remarkable reduction of friction was observed with both bearing materials due to running-in.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Tribology and Machine Elements, Materials Science and Environmental Engineering, Metso Minerals, Inc., Kugler Bimetal SA
Contributors: Linjamaa, A., Lehtovaara, A., Kallio, M., Léger, A.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology
ISSN (Print): 1350-6501
Original language: English
ASJC Scopus subject areas: Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Bearings, continuous monitoring, friction, hydrodynamic lubrication, journal bearing, running-in
Source: Scopus
Source ID: 85069872376

Research output: Contribution to journalArticleScientificpeer-review

Temperature scanning stress relaxation behavior of water responsive and mechanically adaptive elastomer nanocomposites

The decrease of stress at constant strain, that is, the stress relaxation process as a function of temperature, is a central mechanical characteristics of elastomer nanocomposites for their potential applications. However, in the conventional stress relaxation test, the relaxation behavior is usually determined as a function of time at constant temperature. The present work reports the temperature scanning stress relaxation (TSSR) characteristics of a new kind of mechanically adaptive elastomer nanocomposite by monitoring the nonisothermal relaxation behavior as a function of temperature. This kind of adaptive elastomer nanocomposite was prepared by introducing calcium sulfate (CaSO4), as the water-responsive phase into the hydrophilic elastomer matrix. The influence of water-induced structural changes on TSSR behavior was investigated. Water treatment had a strong effect on the shape of the relaxation spectrum of the nanocomposite. It was revealed that the in situ development of hydrated nano-rod crystal structures of CaSO4 in the elastomer matrix was responsible for the changes in the mechanical relaxation behavior of the composites. Atomic force microscopy was used to verify this nano-rod crystal morphology in the elastomer matrix. The mechanism of water-induced mechanical reinforcement of the composite was explored from dynamic mechanical analysis of the material and correlated with its stress relaxation behavior.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Leibniz-Institut für Polymerforschung Dresden E.V., University of Massachusetts Lowell, Vodafone Department of Mobile Communications Systems
Contributors: Banerjee, S. S., Natarajan, T. S., Subramani B., E., Wießner, S., Janke, A., Heinrich, G., Das, A.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Applied Polymer Science
Article number: 48344
ISSN (Print): 0021-8995
Original language: English
ASJC Scopus subject areas: Chemistry(all), Surfaces, Coatings and Films, Polymers and Plastics, Materials Chemistry
Keywords: adaptive elastomer nanocomposite, calcium sulphate, mechanical reinforcement, morphology, temperature scanning stress relaxation
Source: Scopus
Source ID: 85070677934

Research output: Contribution to journalArticleScientificpeer-review

Textile-integrated three-dimensional printed and embroidered structures for wearable wireless platforms

In this paper, we present fabrication and performance evaluation of three-dimensional (3D) printed and embroidered textile-integrated passive ultra high frequency radio frequency identification (RFID) platforms. The antennas were manufactured by 3D printing a stretchable silver conductor directly on an elastic band. The electric and mechanical joint between the 3D printed antennas and microchips was formed by gluing with conductive epoxy glue, by printing the antenna directly on top of the microchip structure, and by embroidering with conductive yarn. Initially, all types of fabricated RFID tags achieved read ranges of 8–9 meters. Next, the components were tested for wetting as well as for harsh cyclic strain and bending. The immersing and cyclic bending slightly affected the performance of the tags. However, they did not stop the tags from working in an acceptable way, nor did they have any permanent effect. The epoxy-glued or 3D printed antenna–microchip interconnections were not able to endure harsh stretching. On the other hand, the tags with the embroidered antenna–microchip interconnections showed excellent wireless performance, both during and after a 100 strong stretching cycles. Thus, the novel approach of combining 3D printing and embroidery seems to be a promising way to fabricate textile-integrated wireless platforms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Wireless Identification and Sensing Systems Research Group
Contributors: He, H., Chen, X., Ukkonen, L., Virkki, J.
Publication date: 2019
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Textile Research Journal
Volume: 89
Issue number: 4
ISSN (Print): 0040-5175
Original language: English
ASJC Scopus subject areas: Chemical Engineering (miscellaneous), Polymers and Plastics
Keywords: antennas, embroidery, interconnections, passive ultra high frequency radio frequency identification, stretchable electronics, textile-integrated electronics, three-dimensional printing, wearable platforms
Source: Scopus
Source ID: 85045101109

Research output: Contribution to journalArticleScientificpeer-review

Unique Degradation of Flash Memory as an Identifier of ICT Device

The counterfeit and stolen information and communication technologies (ICT) devices are an essential and growing problem. Reliable technology for the identification of ICT devices is required to enable blocking of these devices in the network worldwide. Motivated by this challenge, we elaborate on the idea of using the unique degradation image of flash memory chip (DFMC) as the identifier of the device. This idea is based on the assumption that the distribution of degraded segments in the memory chip is unique enough to provide reliable identification of the device. In this paper, we provide a proof of concept through a hardware experiment. For this experiment, we developed a custom test bed and special software enabling the forced degradation of NOR-flash memory chips. We, then, consider the uniqueness of such identifiers using combination theory and consider practical issues of DFMC implementation, including the initial identification procedure, light dynamic identifiers, and identification using a cross-correlation function and options of dynamic identification. We conclude that using DFMC addresses relevant challenges of ICT devices identification.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, St. Petersburg State University of Telecommunication, Applied Mathematics Communications Technology Institute, Peoples’ Friendship University of Russia
Contributors: Vladimirov, S. S., Pirmagomedov, R., Kirichek, R., Koucheryavy, A.
Number of pages: 9
Pages: 107626-107634
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: communication system security, counterfeiting, flash memory cells, Internet of things, network security, physical identification, system identification
Source: Scopus
Source ID: 85071079644

Research output: Contribution to journalArticleScientificpeer-review

Validation of Printed, Skin-Mounted Multilead Electrode for ECG Measurements

An electrocardiography (ECG) monitoring can be used to detect heart-related abnormalities by recording cardiac activity over a period of time. The conventional 12-lead ECG measurement system is the standard practice for the evaluation of the heart's electrical activity. However, a recent trend is to develop patch-type measurement devices for unobtrusive ECG monitoring by reducing device size and number of electrodes on the skin. This development aims to minimize the discomfort for the user from the wearable recording devices. A printed, bandage-type hybrid system for continuous ECG monitoring to allow as much comfort as possible while maintaining the signal quality required for medical evaluation is proposed. Movement artifacts in recorded ECG signals are a challenge in long-term monitoring while the patients are engaged in their everyday activities. The movement artifacts from the printed skin-conformable electrode are compared to commercial exercise stress-test ECG electrodes during different physical activities and stationary periods. The results show that the signal quality obtained with the multilead patch ECG electrode, manufactured with printing technologies, is comparable to electrodes currently used in healthcare.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, BioMediTech, Univ of Oulu, Tampere University, Tampere Uni. of Applied Sci.
Contributors: Vuorinen, T., Noponen, K., Vehkaoja, A., Onnia, T., Laakso, E., Leppänen, S., Mansikkamäki, K., Seppänen, T., Mäntysalo, M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Advanced Materials Technologies
Article number: 1900246
ISSN (Print): 2365-709X
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Industrial and Manufacturing Engineering
Keywords: electrocardiography, epidermal electronics, screen printing, stretchable electronics
Source: Scopus
Source ID: 85067471725

Research output: Contribution to journalArticleScientificpeer-review

Vocal Effort Based Speaking Style Conversion Using Vocoder Features and Parallel Learning

Speaking style conversion (SSC) is the technology of converting natural speech signals from one style to another. In this study, we aim to provide a general SSC system for converting styles with varying vocal effort and focus on normal-to-Lombard conversion as a case study of this problem. We propose a parametric approach that uses a vocoder to extract speech features. These features are mapped using parallel machine learning models from utterances spoken in normal style to the corresponding features of Lombard speech. Finally, the mapped features are converted to a Lombard speech waveform with the vocoder. A total of three vocoders (GlottDNN, STRAIGHT, and Pulse model in log domain (PML)) and three machine learning mapping methods (standard GMM, Bayesian GMM, and feed-forward DNN) were compared in the proposed normal-to-Lombard style conversion system. The conversion was evaluated using two subjective listening tests measuring perceived Lombardness and quality of the converted speech signals, and by using an instrumental measure called Speech Intelligibility in Bits (SIIB) for speech intelligibility evaluation under various noise levels. The results of the subjective tests show that the system is able to convert normal speech into Lombard speech and that there is a trade-off between quality and Lombardness of the mapped utterances. The GlottDNN and PML stand out as the best vocoders in terms of quality and Lombardness, respectively, whereas the DNN is the best mapping method in terms of Lombardness. PML with the standard GMM seems to give a good compromise between the two attributes. The SIIB experiments indicate that intelligibility of converted speech compared to that of normal speech improved in noisy conditions most effectively when DNN mapping was used with STRAIGHT and PML.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Aalto University
Contributors: Seshadri, S., Juvela, L., Räsänen, O., Alku, P.
Number of pages: 17
Pages: 17230-17246
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: Bayesian GMM, DNN, GlottDNN, Lombard speech, pulse model in log domain, speaking style conversion, vocal effort
Source: Scopus
Source ID: 85061789099

Research output: Contribution to journalArticleScientificpeer-review

Oxidation-Induced Changes in the ALD-Al2O3/InAs(100) Interface and Control of the Changes for Device Processing

InAs crystals are emerging materials for various devices like radio frequency transistors and infrared sensors. Control of oxidation-induced changes is essential for decreasing amounts of the harmful InAs surface (or interface) defects because it is hard to avoid the energetically favored oxidation of InAs surface parts in device processing. We have characterized atomic-layer-deposition (ALD) grown Al2O3/InAs interfaces, preoxidized differently, with synchrotron hard X-ray photoelectron spectroscopy (HAXPES), low-energy electron diffraction, scanning tunneling microscopy, and time-of-flight elastic recoil detection analysis. The chemical environment and core-level shifts are clarified for well-embedded InAs interfaces (12 nm Al2O3) to avoid, in particular, effects of a significant potential change at the vacuum-solid interface. High-resolution As 3d spectra reveal that the Al2O3/InAs interface, which was sputter-cleaned before ALD, includes +1.0 eV shift, whereas As 3d of the preoxidized (3 × 1)-O interface exhibits a shift of -0.51 eV. The measurements also indicate that an As2O3 type structure is not crucial in controlling defect densities. Regarding In 4d measurements, the sputtered InAs interface includes only a +0.29 eV shift, while the In 4d shift around -0.3 eV is found to be inherent for the crystalline oxidized interfaces. Thus, the negative shifts, which have been usually associated with dangling bonds, are not necessarily an indication of such point defects as previously expected. In contrast, the negative shifts can arise from bonding with O atoms. Therefore, specific care should be directed in determining the bulk-component positions in photoelectron studies. Finally, we present an approach to transfer the InAs oxidation results to a device process of high electron mobility transistors (HEMT) using an As-rich III-V surface and In deposition. The approach is found to decrease a gate leakage current of HEMT without losing the gate controllability.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Department of Physics and Astronomy, University of Turku, University of Turku, Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin, University of Jyvaskyla
Contributors: Tuominen, M., Mäkelä, J., Yasir, M., Dahl, J., Granroth, S., Lehtiö, J. P., Félix, R., Laukkanen, P., Kuzmin, M., Laitinen, M., Punkkinen, M. P., Hedman, H. P., Punkkinen, R., Polojärvi, V., Lyytikäinen, J., Tukiainen, A., Guina, M., Kokko, K.
Number of pages: 9
Pages: 44932-44940
Publication date: 26 Dec 2018
Peer-reviewed: Yes

Publication information

Journal: ACS Applied Materials and Interfaces
Volume: 10
Issue number: 51
ISSN (Print): 1944-8244
Ratings: 
  • Scopus rating (2018): CiteScore 8.69 SJR 2.596 SNIP 1.539
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: atomic layer deposition, III-V semiconductor, InAs, oxidation, photoelectron, synchrotron

Bibliographical note

EXT="Mäkelä, Jaakko"
EXT="Kuzmin, Mikhail"
EXT="Laukkanen, Pekka"

Source: Scopus
Source ID: 85059448335

Research output: Contribution to journalArticleScientificpeer-review

Reversible photodoping of TiO2 nanoparticles

Observations on strong photochromic effect of crystalline TiO2 quantum dots (mean size ≈ 4 nm) are presented. The synthesized quantum dots consist of irregularly shaped anatase TiO2 nanoparticles (NPs) and are dispersed in butanol (8 % by mass). Obtained NPs exhibit a dramatic photo-response to UV light, enabling effective transmittance modula-tion of in a broad wavelength range extending from visible to near-infrared region, and even the thermal black body radiation regime beyond 10 μm. The exceptional photo-response is attributed to hole-scavenging by butanol, TiO2 self-reduction, injection of electrons to the conduction band, and consequent localized surface plasmon resonances in NPs. Observed optical effect is reversible and the initial high transmittance state can be restored simply by exposing the NPs to air. Applied NP synthesis route is economic and can be easily scaled for applications such as smart window technol-ogies.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Surface Science, Univ Tartu, University of Tartu, University of Tartu Institute of Physics, Inst Phys, University of Tartu
Contributors: Joost, U., Sutka, A., Oja, M., Smits, K., Doebelin, N., Loot, A., Järvekülg, M., Hirsimäki, M., Valden, M., Nommiste, E.
Pages: 8968-8974
Publication date: 26 Dec 2018
Peer-reviewed: Yes
Early online date: 10 Dec 2018

Publication information

Journal: Chemistry of Materials
Volume: 30
Issue number: 24
ISSN (Print): 0897-4756
Ratings: 
  • Scopus rating (2018): CiteScore 9.92 SJR 4.224 SNIP 1.769
Original language: English
ASJC Scopus subject areas: Inorganic Chemistry, Materials Chemistry, Surfaces and Interfaces, Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Keywords: tio2, nano, nanoparticle, photochromic, anatase, light, photonics, functional
URLs: 

Bibliographical note

INT=fot,"Joost, Urmas"

Research output: Contribution to journalArticleScientificpeer-review

Less Is More: Enhancement of Second-Harmonic Generation from Metasurfaces by Reduced Nanoparticle Density

We investigate optical second-harmonic generation (SHG) from metasurfaces where noncentrosymmetric V-shaped gold nanoparticles are ordered into regular array configurations. In contrast to expectations, a substantial enhancement of the SHG signal is observed when the number density of the particles in the array is reduced. More specifically, by halving the number density, we obtain over 5-fold enhancement in SHG intensity. This striking result is attributed to favorable interparticle interactions mediated by the lattice, where surface-lattice resonances lead to spectral narrowing of the plasmon resonances. Importantly, however, the results cannot be explained by the improved quality of the plasmon resonance alone. Instead, the lattice interactions also lead to further enhancement of the local fields at the particles. The experimental observations agree very well with results obtained from numerical simulations including lattice interactions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Institute of Physics, Nicolaus Copernicus University, University of Eastern Finland, CRPP
Contributors: Czaplicki, R., Kiviniemi, A., Huttunen, M. J., Zang, X., Stolt, T., Vartiainen, I., Butet, J., Kuittinen, M., Martin, O. J., Kauranen, M.
Number of pages: 6
Pages: 7709-7714
Publication date: 12 Dec 2018
Peer-reviewed: Yes

Publication information

Journal: Nano Letters
Volume: 18
Issue number: 12
ISSN (Print): 1530-6984
Ratings: 
  • Scopus rating (2018): CiteScore 12.71 SJR 6.211 SNIP 2.396
Original language: English
ASJC Scopus subject areas: Bioengineering, Chemistry(all), Materials Science(all), Condensed Matter Physics, Mechanical Engineering
Keywords: interparticle interactions, Metal nanoparticles, nonlinear optics, plasmonic resonances, second-harmonic generation, surface-lattice resonances
Additional files: 
URLs: 
Source: Scopus
Source ID: 85058303843

Research output: Contribution to journalArticleScientificpeer-review

Experimental moment resistance of rectangular hollow section T joints

Resistance is the main property of tubular joints. The determination of the joint resistance from the experimental load-deformation curve always represents a challenging task. Currently there are two main methods to find the experimental resistance, which are called plastic and ultimate resistance. However, there is no single opinion on which one should be commonly used. Based on the experimental results, this paper directly compares the two existed approaches. The study is restricted to welded square hollow section T joints under in-plane bending moment. The paper considers only the joints with β < 0.85, i.e. when the behaviour of the joint is governed by chord face failure. The results show that plastic resistance leads to more conservative results than ultimate resistance, providing thus safer results. However, attention should be also paid to the difference between the labour intensity of the presented methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering
Contributors: Garifullin, M.
Publication date: 5 Dec 2018
Peer-reviewed: Yes

Publication information

Journal: MATEC Web of Conferences
Volume: 245
Article number: 08003
ISSN (Print): 2274-7214
Ratings: 
  • Scopus rating (2018): CiteScore 0.42 SJR 0.169 SNIP 0.548
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all), Engineering(all)
Electronic versions: 
Source: Scopus
Source ID: 85058463414

Research output: Contribution to journalConference articleScientificpeer-review

Considerations in analysing elemental carbon from marine engine exhaust using residual, distillate and biofuels

Elemental carbon (EC) concentrations in the exhaust of a medium-speed marine engine was evaluated using thermal-optical analysis (TOA). Particulate matter (PM) samples were collected at 75% and 25% engine loads using residual and distillate fuels with sulphur contents of 2.5%, 0.5% and 0.1%, and a biofuel (30% of bio-component). The EC analysis of PM samples from a marine engine proved to be challenging. For example, transformations of structure of the sampled particles in the inert and the oxygen mode were observed for marine engine exhaust samples. The relationship between constituents present in the samples from the marine engine using different fuels, and phenomena observed in the thermograms are discussed. Temperature protocol selection and sample pre-treatment (extractions and drying) affected the reported EC mass. Modifications in the methodology were suggested to increase the accuracy of the analysis. Repeatability and reproducibility of the EC analysis was studied in the round-robin of three laboratories.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics, VTT Technical Research Centre of Finland, Finnish Meteorological Institute, University of Eastern Finland, Public Health Service (GGD) Amsterdam
Contributors: Aakko-Saksa, P., Koponen, P., Aurela, M., Vesala, H., Piimäkorpi, P., Murtonen, T., Sippula, O., Koponen, H., Karjalainen, P., Kuittinen, N., Panteliadis, P., Rönkkö, T., Timonen, H.
Number of pages: 14
Pages: 191-204
Publication date: Dec 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Aerosol Science
Volume: 126
ISSN (Print): 0021-8502
Ratings: 
  • Scopus rating (2018): CiteScore 2.33 SJR 0.696 SNIP 1.039
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Keywords: Elemental carbon EC, Fuel, Marine engine, Round-robin, Thermal-optical analysis TOA, Thermogram
Source: Scopus
Source ID: 85054296019

Research output: Contribution to journalArticleScientificpeer-review

Effects of Microstructure on the Dynamic Strain Aging in Ferritic-Pearlitic Steels

Effects of microstructure on the high strain rate high temperature mechanical response and dynamic strain aging of C45 and 27MnCr5 ferritic-pearlitic steels were studied using four different microstructural variants of the standard alloys. The high strain rate high temperature behavior of the steels was studied using a compression Split Hopkinson Pressure Bar device with high temperature testing capabilities. The steels were studied at strain rates up to 4500 s−1 and at temperatures from RT to 680 °C. Strong dynamic strain aging was observed for both steels in the studied temperature range. The results also show that the microstructure has a strong effect on the dynamic strain aging sensitivity of the steel. This is especially true at low plastic strains, where the effect of the microstructure is strongest. The effect of microstructure decreases as plastic strain increases. A coarse-grained microstructure showed the strongest dynamic strain aging sensitivity for both steels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Swerea KIMAB AB, Schmolz+Bichenbach Group CREAS
Contributors: Hokka, M., Rämö, J., Mardoukhi, A., Vuoristo, T., Roth, A., Kuokkala, V. T.
Pages: 452-463
Publication date: Dec 2018
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Journal of Dynamic Behavior of Materials
Volume: 4
Issue number: 4
ISSN (Print): 2199-7446
Ratings: 
  • Scopus rating (2018): CiteScore 2.16 SJR 0.653 SNIP 1.573
Original language: English
ASJC Scopus subject areas: Materials Science (miscellaneous), Mechanics of Materials
Keywords: Dynamic strain aging, Effects of microstructure, High strain rate, High temperature, Steels
Source: Scopus
Source ID: 85051680227

Research output: Contribution to journalArticleScientificpeer-review

ICED - Inductively Coupled Energy Dissipater for Future High Field Accelerator Magnets

Future high field accelerator magnets, like the ones foreseen in the design study of the FCC project and for the EuCARD2 "Future Magnets" program, operate with magnetic fields in the range of 16<formula><tex>$\times$</tex></formula>20T. For such magnets the energy density is higher than in the accelerator magnets at present in operation, posing a challenge for the quench protection. Traditionally quench protection has relied on generating large normal zones in the coil by firing quench protection heaters. The increase of the coil internal resistance results in a fast current decay. This paper introduces the Inductively Coupled Energy Dissipater (ICED) system, based on low resistance loops which are inductively coupled with the coil. These loops greatly accelerate the current decay by rapidly extracting the energy from the coil, thereby lowering its peak temperature. Because of the potential reduction in stabilizer volume within the conductor, ICED may enable higher engineering current densities in the coil than with the protection relying entirely on dissipating the magnet's energy in the windings. The efficiency of ICED as a passive quench protection system is studied in this paper. We present the effect of such protection structure on the field quality during standard powering of the magnets and on the cryogenic system. We study electromagnetic forces in the loops and mechanically stable geometric locations within the magnet structure. For the proof of the concept, this system has been employed in Feather-M2 dipole demonstrator. We compare our modeling approach to results gained from a cryogenic test.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research
Contributors: Murtomäki, J. S., van Nugteren, J., Kirby, G., DeRijk, G., Rossi, L., Stenvall, A.
Publication date: Dec 2018
Peer-reviewed: Yes
Early online date: 28 May 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 8
Article number:  4009015
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator magnets, Electromagnetic Induction, Heating systems, High-temperature superconductors, High-Temperature-Superconductors, Magnetomechanical effects, Resistance, Superconducting magnets, Superconducting Magnets, Windings
Source: Scopus
Source ID: 85047834232

Research output: Contribution to journalArticleScientificpeer-review

Cell response to round and star-shaped polylactide fibers

The surface topography of tissue engineering biomaterials is known to affect cell behavior. Polymer fibers can be processed into a variety of diameters and shapes, which both affect the orientation and organization of cells. The fibers can be used to manufacture tissue engineering scaffolds. The aim of this work was to study cell response to microfibers with round and star-shaped cross-sections. In addition, the retention of fiber properties during hydrolytic degradation was evaluated.

Melt spinning method was used to process poly-L/D-lactide 96/4 (PLDLA 96/4) fibers. Knitted scaffolds were manufactured from the fibers for the cell culture experiment. A hydrolytic degradation experiment was conducted for the fibers to evaluate retention of mechanical properties and changes in crystallinity and thermal properties. Human urothelial cells (hUCs) and human foreskin fibroblasts (hFFs) were used in the cell culture experiment. Cell response was assessed using live/dead analysis and crystal violet staining.

Both fibers had suitable mechanical properties to be processed into knitted scaffolds. The hydrolytic degradation experiment demonstrated good retention of properties for the fibers. The number of cells attached to the fibers increased throughout the experiment. The hFFs oriented to the fiber direction on both fibers. The cell culture experiment demonstrated good biocompatibility and no observable difference in cell response was seen between the fiber types.

General information

Publication status: Published
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, University of Tampere, Faculty of Medicine and Life Sciences, Lääkärinkatu 1, 33520 Tampere, Finland, Adult Stem Cell Research Group
Contributors: Kroon, M., Talvitie, E., Miettinen, S., Kellomäki, M.
Publication date: 23 Nov 2018
Peer-reviewed: Unknown
Event: Paper presented at BioMediTech Research Day 2018, Tampere, Finland.
ASJC Scopus subject areas: Biomaterials
Keywords: Polylactide, Tissue Engineering, Cell Culture, Scaffolds, Biotextiles

Research output: Other conference contributionPaper, poster or abstractScientific

Cascaded crystalline raman lasers for extended wavelength coverage: Continuous-wave, third-stokes operation

The development of high-power laser sources with narrow emission, tunable within the water transmission window around 1.7 μm, is of interest for applications as diverse as medical imaging and atmospheric sensing. Where suitable laser gain media are not available, operation in this spectral region is often achieved via nonlinear frequency conversion, and optical parametric oscillators (OPOs) are a common solution. A practical alternative to OPOs, to avoid birefringent-or quasi-phase-matching requirements, is the use of stimulated Raman scattering within a suitable material to convert a pump source to longer wavelengths via one or more Stokes shifts; however, as this is a χ3 nonlinear process, such frequency conversion is usually the preserve of high-energy pulsed lasers. Semiconductor disk lasers (SDLs), on the other hand, have very high-finesse external resonators, suitable for efficient intracavity nonlinear conversion even in continuous-wave (CW) operation. Here we report, to the best of our knowledge, the first continuous-wave third-Stokes crystalline Raman laser and the longest emission wavelength from an SDL-pumped Raman laser, achieving high power, CW output, and broad wavelength tuning around 1.73 μm. The KGd WO4 2 (KGW) Raman laser, which was intracavity-pumped by a 1.18 μm InGaAs-based SDL, demonstrated cascaded CW Stokes oscillation at 1.32 μm, 1.50 μm, and 1.73 μm with watt-level output achievable at each wavelength. The 1.73 μm Stokes emission was diffraction limited (M2 < 1.01) and narrow linewidth (<46 pm FWHM; measurement limited). By rotation of a birefringent filter placed within the fundamental resonator, we attained three tunable emission wavelength bands, one centred at each Stokes component, and achieved up to 65 nm tuning for the third-Stokes Raman laser from 1696 nm to 1761 nm. We have thus demonstrated a platform laser technology that takes well-developed InGaAs-based SDLs and provides spectral coverage and high performance in the near-infrared water transmission windows using commercially available components.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Strathclyde
Contributors: Casula, R., Penttinen, J., Guina, M., Kemp, A. J., Hastie, J. E.
Number of pages: 8
Pages: 1406-1413
Publication date: 20 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 5
Issue number: 11
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2018): CiteScore 10.26 SJR 4.914 SNIP 3.088
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85059018872

Research output: Contribution to journalArticleScientificpeer-review

Optical properties of GaAs1-xBix/GaAs quantum well structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates

In this work, the electronic bandstructure of GaAs1-xBix/GaAs single quantum well (QW) samples grown by molecular beam epitaxy is investigated by photomodulated reflectance (PR) measurements as a function of Bi content (0.0065 ≤ x ≤ 0.0215) and substrate orientation. The Bi composition is determined via simulation of high-resolution x-ray diffraction measurement and is found to be maximized in the 2.15%Bi and 2.1%Bi samples grown on (100) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi QW layer but extends out of the GaAsBi QW towards the GaAs barrier and forms a GaAsBi epilayer. PR spectra are fitted with the third derivative function form (TDFF) to identify the optical transition energies. We analyze the TDFF results by considering strain-induced modification on the conduction band (CB) and splitting of the valence band (VB) due to its interaction with the localized Bi level and VB interaction. The PR measurements confirm the existence of a GaAsBi epilayer via observed optical transitions that belong to GaAsBi layers with various Bi compositions. It is found that both Bi composition and substrate orientation have strong effects on the PR signal. Comparison between TDFF and calculated optical transition energies provides a bandgap reduction of 92 meV/%Bi and 36 meV/%Bi and an interaction strength of the isolated Bi atoms with host GaAs valence band (C BiM ) of 1.7 eV and 0.9 eV for (100) and (311)B GaAs substrates, respectively.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Adana Science and Technology University, Istanbul University, University of Cukurova, University of Nottingham, Universidade Federal de São Carlos, Leibniz Institute for Crystal Growth
Contributors: Gunes, M., Ukelge, M. O., Donmez, O., Erol, A., Gumus, C., Alghamdi, H., Galeti, H. V., Henini, M., Schmidbauer, M., Hilska, J., Puustinen, J., Guina, M.
Publication date: 13 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 12
Article number: 124015
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.002
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: high-index substrate, oriented GaAsBi, photomodulated reflectance, strained quantum well, type I band line-up
Source: Scopus
Source ID: 85057810892

Research output: Contribution to journalArticleScientificpeer-review

Tunable Reflection Type Plasmon Induced Transparency with Graphene

Plasmon induced transparency (PIT) has always been investigated in transmission mode, which makes the design dependent upon the type of substrate. In this work, we propose a first tunable reflection type PIT (RPIT) device based on simple design of two parallel gold strips on graphene. We have numerically investigated the design by using Finite Difference Time-Domain (FDTD) method. This response is tunable by changing the Fermi level (Ef) of graphene. High tunability of 215 nm shift was observed by changing the Ef of graphene from 0 to 0.8 eV. The spectral contrast ratio of our device is 99.2%.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Department of Electrical and Electronics Engineering, Bilkent University, Nanotechnology Research Center
Contributors: Habib, M., Ozbay, E., Caglayan, H.
Number of pages: 3
Pages: 170-172
Publication date: 13 Nov 2018

Host publication information

Title of host publication: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018
Publisher: IEEE
ISBN (Electronic): 9781538647028
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Acoustics and Ultrasonics, Atomic and Molecular Physics, and Optics, Radiation

Bibliographical note

EXT="Habib, M."

Source: Scopus
Source ID: 85058538366

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Enhanced multiaxial fatigue criterion that considers stress gradient effects

Modification of a fatigue criterion valid for homogeneous multiaxial stress states to account for the beneficial effect of stress gradients is traditionally performed by modifying the stress terms in the fatigue criterion and thereby introducing new parameters that need to be calibrated. Here the stress terms are left unchanged and, instead, the parameters in the fatigue criterion are modified. This modification is performed, in principle, along the lines of Siebel and Stieler and it introduces Neuber's parameter as the only new parameter; however, as soon as the ultimate strength of the material is known, also Neuber's parameter is known. Therefore, the methodology introduced implies that no new calibration process is needed. Here a specific fatigue criterion valid for homogeneous multiaxial stress states is enhanced by this procedure and predictions of this simple approach are compared with a broad range of experimental data and good accuracy is achieved. Moreover, the approach adopted can be applied to other fatigue criteria than the one considered here.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Lund University
Contributors: Ottosen, N. S., Ristinmaa, M., Kouhia, R.
Number of pages: 12
Pages: 128-139
Publication date: 1 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: International Journal of Fatigue
Volume: 116
ISSN (Print): 0142-1123
Ratings: 
  • Scopus rating (2018): CiteScore 4.21 SJR 2.059 SNIP 2.412
Original language: English
ASJC Scopus subject areas: Modelling and Simulation, Materials Science(all), Mechanics of Materials, Mechanical Engineering, Industrial and Manufacturing Engineering
Keywords: Fatigue, Gradient effects, Multiaxial fatigue
Source: Scopus
Source ID: 85048733879

Research output: Contribution to journalArticleScientificpeer-review

Tribocorrosion behaviour of aluminium bronze in 3.5 wt.% NaCl solution

Tribocorrosion behaviour of aluminium bronze CuAl10Fe5Ni5 in 3.5 wt.% NaCl solution was investigated in a pin-on-disc facility containing an electrochemical cell. Oxidising capacity and contact pressure to alumina counterbody were varied. Pure corrosion occurred as selective dissolution of α phase included in the eutectoid structure. Contact to counterbody introduced plastic deformation, extrusion of the material and abrasive wear. Wear-corrosion interactions varied between the two contact pressures, with lower material losses appearing at the higher pressure. The significant acceleration of material degradation by the interactions was not clearly reflected to kinetics or thermodynamics of corrosion. These results are presented and discussed here.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, VTT Technical Research Centre of Finland
Contributors: Huttunen-Saarivirta, E., Isotahdon, E., Metsäjoki, J., Salminen, T., Carpén, L., Ronkainen, H.
Number of pages: 17
Pages: 207-223
Publication date: 1 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Corrosion Science
Volume: 144
ISSN (Print): 0010-938X
Ratings: 
  • Scopus rating (2018): CiteScore 6.76 SJR 2.131 SNIP 2.595
Original language: English
ASJC Scopus subject areas: Chemistry(all), Chemical Engineering(all), Materials Science(all)
Keywords: Corrosion, Plastic deformation, Selective dissolution, Tribocorrosion, Wear

Bibliographical note

EXT="Huttunen-Saarivirta, E."
EXT="Isotahdon, E."
EXT="Metsäjoki, J."

Source: Scopus
Source ID: 85053038794

Research output: Contribution to journalArticleScientificpeer-review

Sensitivity Analysis of Inverse Thermal Modeling to Determine Power Losses in Electrical Machines

Inverse analysis is a known mathematical approach, which has been used to solve physical problems of a particular nature. Nevertheless, it has seldom been applied directly for loss reconstruction of electrical machines. This paper aims to verify the accuracy of an inverse methodology used in mapping power loss distribution in an induction motor. Conjugate gradient method is used to iteratively find the unique inverse solution when simulated temperature measurement data are available. Realistic measurement situations are considered and the measurement errors corresponding to thermographic measurements and temperature sensor measurements are used to generate simulated numerical measurement data. An accurate 2-D finite-element thermal model of a 37 kW cage induction motor serves as the forward solution. The inverse model's objective is to map the power loss density in the motor accurately from noisy temperature measurements made on the motor housing's outer surface. Furthermore, the sensitivity of the adopted inverse methodology to variations in the number of available measurements is also considered. Filtering the applied noise to acceptable ranges is shown to improve the inverse mapping results.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Aalto University
Contributors: Nair, D. G., Rasilo, P., Arkkio, A.
Publication date: Nov 2018
Peer-reviewed: Yes
Early online date: 23 Jul 2018

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 54
Issue number: 11
Article number: 8109405
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2018): CiteScore 1.71 SJR 0.539 SNIP 0.996
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: Heat transfer, Heating systems, induction motor, Induction motors, inverse problems, Loss measurement, Noise measurement, Stator windings, Temperature measurement
Electronic versions: 
Source: Scopus
Source ID: 85050587914

Research output: Contribution to journalArticleScientificpeer-review

An efficient highly flexible strain sensor: Enhanced electrical conductivity, piezoresistivity and flexibility of a strongly piezoresistive composite based on conductive carbon black and an ionic liquid

Flexible strain sensors based on conductive carbon black (CB) filled styrene-butadiene rubber were developed. The use of ionic liquid (IL) allows improvement of the filler dispersion, rubber-filler interaction and flexibility of the sample that finally enhances the piezoresistive performance and the sensibility. At filler loading close to the percolation threshold, the electrical conductivity increases by two orders of magnitude when the IL/CB ratio is increased from 0 to 1.5. In contrast to the use of normal plasticisers, the loss in piezoresistivity at low strains is overcome. The sensitivity at 2.5% strain using an IL/CB ratio of 1.5 is about 600% higher compared with the sample without IL. Also, the response consistency becomes better with higher IL/CB ratios. Moreover, the use of IL allows the composites to be deformed more easily while still providing high responsivity to small strains. This enables the construction of better flexible strain sensors with long-term stability.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Mahidol University, Leibniz-Institut für Polymerforschung Dresden E.V., Vodafone Department of Mobile Communications Systems, Mahidol University
Contributors: Narongthong, J., Das, A., Le, H. H., Wießner, S., Sirisinha, C.
Number of pages: 9
Pages: 330-338
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Composites Part A: Applied Science and Manufacturing
Volume: 113
ISSN (Print): 1359-835X
Ratings: 
  • Scopus rating (2018): CiteScore 6.9 SJR 1.907 SNIP 2.592
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Mechanics of Materials
Keywords: A. Polymer-matrix composites (PMCs), B. Electrical properties, B. Mechanical properties, Piezoresistivity
Source: Scopus
Source ID: 85051249560

Research output: Contribution to journalArticleScientificpeer-review

Demonstration of optical nonlinearity in InGaAsP/InP passive waveguides

We report on the study of the third-order nonlinear optical interactions in InxGa1-xAsyP1-y/InP strip-loaded waveguides. The material composition and waveguide structures were optimized for enhanced nonlinear optical interactions. We performed self-phase modulation, four-wave mixing and nonlinear absorption measurements at the pump wavelength 1568 nm in our waveguides. The nonlinear phase shift of up to 2.5π has been observed in self-phase modulation experiments. The measured value of the two-photon absorption coefficient α2 was 19 cm/GW. The four-wave mixing conversion range, representing the wavelength difference between maximally separated signal and idler spectral components, was observed to be 45 nm. Our results indicate that InGaAsP has a high potential as a material platform for nonlinear photonic devices, provided that the operation wavelength range outside the two-photon absorption window is selected.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Ottawa, Canada, Middle East Technical Univ.
Contributors: Saeidi, S., Rasekh, P., Awan, K. M., Tüğen, A., Huttunen, M. J., Dolgaleva, K.
Number of pages: 7
Pages: 524-530
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 84
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2018): CiteScore 2.6 SJR 0.59 SNIP 1.009
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Integrated optics, Nonlinear optics, Optical devices
Source: Scopus
Source ID: 85050358317

Research output: Contribution to journalArticleScientificpeer-review

Novel osteoconductive β-tricalcium phosphate/poly(L-lactide-co-e-caprolactone) scaffold for bone regeneration: a study in a rabbit calvarial defect

The advantages of synthetic bone graft substitutes over autogenous bone grafts include abundant graft volume, lack of complications related to the graft harvesting, and shorter operation and recovery times for the patient. We studied a new synthetic supercritical CO2 –processed porous composite scaffold of β-tricalcium phosphate and poly(L-lactide-co-caprolactone) copolymer as a bone graft substitute in a rabbit calvarial defect. Bilateral 12 mm diameter critical size calvarial defects were successfully created in 18 rabbits. The right defect was filled with a scaffold moistened with bone marrow aspirate, and the other was an empty control. The material was assessed for applicability during surgery. The follow-up times were 4, 12, and 24 weeks. Radiographic and micro-CT studies and histopathological analysis were used to evaluate new bone formation, tissue ingrowth, and biocompatibility. The scaffold was easy to shape and handle during the surgery, and the bone-scaffold contact was tight when visually evaluated after the implantation. The material showed good biocompatibility and its porosity enabled rapid invasion of vasculature and full thickness mesenchymal tissue ingrowth already at four weeks. By 24 weeks, full thickness bone ingrowth within the scaffold and along the dura was generally seen. In contrast, the empty defect had only a thin layer of new bone at 24 weeks. The radiodensity of the material was similar to the density of the intact bone. In conclusion, the new porous scaffold material, composed of microgranular β-TCP bound into the polymer matrix, proved to be a promising osteoconductive bone graft substitute with excellent handling properties. [Figure not available: see fulltext.].

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Faculty of Biomedical Sciences and Engineering, Research group: Computational Biophysics and Imaging Group, Faculty of Veterinary Medicine, University of Helsinki, Orton Orthopaedic Hospital, Muonio Health Center
Contributors: Pihlman, H., Keränen, P., Paakinaho, K., Linden, J., Hannula, M., Manninen, I. K., Hyttinen, J., Manninen, M., Laitinen-Vapaavuori, O.
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Science: Materials in Medicine
Volume: 29
Issue number: 10
Article number: 156
ISSN (Print): 0957-4530
Ratings: 
  • Scopus rating (2018): CiteScore 2.51 SJR 0.612 SNIP 0.824
Original language: English
ASJC Scopus subject areas: Biophysics, Bioengineering, Biomaterials, Biomedical Engineering
Source: Scopus
Source ID: 85054473480

Research output: Contribution to journalArticleScientificpeer-review

Solvothermal synthesis derived Co-Ga codoped ZnO diluted magnetic degenerated semiconductor nanocrystals

Here we are reporting solvothermal synthesis derived diluted magnetic and plasmonic Co-Ga co-doped ZnO nanocrystals with high magnetization values (from 1.02 to 4.88 emu/g) at room temperature. Co-Ga co-doped ZnO nanocrystals show up to 2 fold increase in saturation magnetization compared to Co doped ZnO nanocrystals at the same Co concentration, with the observed room temperature magnetization higher than previously reported values for multifunctional magnetic and plasmonic nanocrystals, and the effect of Ga suggesting some role of the correspondingly introduced itinerant charge. While at the lowest Ga content the nanoparticles appear homogeneously doped, we note that already a moderate Ga content of several percent triggers a fraction of Co to segregate in metallic form in the bulk of the nanoparticles. However, the amount of segregated Co is not sufficient to account for the total effect, whereas a dominating contribution to the observed magnetism has to be related to itinerant charge mediated exchange interactions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Institute of Physics, University of Tartu, Riga Technical University, University of Turku, Helmholtz Centre Berlin for Materials and Energy, University of Latvia, RMS Foundation, Institute of Solid State Physics University of Latvia
Contributors: Šutka, A., Käämbre, T., Joost, U., Kooser, K., Kook, M., Duarte, R. F., Kisand, V., Maiorov, M., Döbelin, N., Smits, K.
Number of pages: 9
Pages: 164-172
Publication date: 30 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Alloys and Compounds
Volume: 763
ISSN (Print): 0925-8388
Ratings: 
  • Scopus rating (2018): CiteScore 4.12 SJR 1.065 SNIP 1.386
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Keywords: Degenerated semiconductors, Diluted magnetic semiconductors, Doping, Plasmonic nanocrystals, Solvothermal synthesis, ZnO

Bibliographical note

int=fot,"Joost, Urmas"

Source: Scopus
Source ID: 85048730804

Research output: Contribution to journalArticleScientificpeer-review

Processing and Characterization of Bioactive Borosilicate Glasses and Scaffolds with Persistent Luminescence

In this proceeding, we report our latest results on the development of borosilicate glasses with persistent luminescence (PeL). Those PeL glasses were processed by adding PeL microparticles (MPs) in the glass using the direct doping method. First, we explain the challenges to balance the survival and dispersion of MPs when preparing borosilicate glasses using this method. Then, we show that scaffold can be obtained using the sintering process from these glasses but also by adding PeL microparticles (MPs) in the glass powder prior to sintering. Finally, we discuss the impact of the scaffold fabrication process on the PeL properties of the MPs.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Photonics, Research group: Photonics Glasses, Turku University of Applied Science
Contributors: Del Cerro, P. R., Saarinen, M., Massera, J., Norrbo, I., Lastusaari, M., Petit, L.
Number of pages: 5
Publication date: 26 Sep 2018

Host publication information

Title of host publication: 2018 20th International Conference on Transparent Optical Networks, ICTON 2018
Volume: 2018-July
Publisher: IEEE COMPUTER SOCIETY PRESS
Article number: 8473916
ISBN (Electronic): 9781538666043

Publication series

Name: Conference proceedings : International Conference on Transparent Optical Networks
ISSN (Print): 2161-2056
ASJC Scopus subject areas: Computer Networks and Communications, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: borosilicate glasses, direct particles doping method, Dy microparticles, persistent luminescence, sintering, SrAlO:Eu

Bibliographical note

INT=fot,"Del Cerro, P. Roldan"

Source: Scopus
Source ID: 85055532457

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Further enhancement of mechanical properties of conducting rubber composites based on multiwalled carbon nanotubes and Nitrile Rubber by solvent treatment

Post-treatment removal of dispersion agents from carbon nanotube/rubber composites can greatly enhance the mechanical properties by increasing the filler-matrix interaction. In this study, multiwall carbon nanotubes (MWNT) were dispersed in water by sonication and nonionic surfactant, octyl-phenol-ethoxylate was used as a dispersion agent. The dispersed MWNTs were incorporated in thermo-reactive acrylonitrile butadiene rubber (NBR) latex and nanocomposite films were prepared by solution casting. As a post-treatment, the surfactant was removed with acetone and films were dried in air. Dispersion quality of the colloid before casting was determined, and mechanical, electrical and thermal properties of the composites before and after the acetone post-treatment were studied. It was found that removal of dispersion agent increased the storage modulus of films between 160-300% in all samples. Relative enhancement was greater in samples with better dispersion quality, whereas thermal conductivity changed more in samples with smaller dispersion quality values. Electrical properties were not notably affected.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Plastics and Elastomer Technology, Leibniz-Institut für Polymerforschung Dresden E.V.
Contributors: Keinänen, P., Das, A., Vuorinen, J.
Number of pages: 12
Publication date: 23 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Materials
Volume: 11
Issue number: 10
Article number: 1806
ISSN (Print): 1996-1944
Ratings: 
  • Scopus rating (2018): CiteScore 3.26 SJR 0.686 SNIP 1.2
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: CNT, Dispersion, Nanocomposite, NBR, Post-treatment
Electronic versions: 
Source: Scopus
Source ID: 85053892020

Research output: Contribution to journalArticleScientificpeer-review

Mechanical, thermal, and burning properties of viscose fabric composites: Influence of epoxy resin modification

The influence of epoxy resin modification by 3-aminopropyltriethoxysilane (APTES) on various properties of warp knitted viscose fabric is reported in this study. Dynamic mechanical, impact resistance, flexural, thermal properties, and burning behavior of the epoxy/viscose fabric composites are studied with respect to varying content of silane coupling agent. The results obtained for APTES-modified epoxy resin based composites reinforced with unmodified viscose fabric composites are compared to unmodified epoxy resin based composites reinforced with APTES-modified viscose fabric. The dynamic mechanical behavior of the APTES-modified resin based composites indicates improved interfacial adhesion. The composites prepared from modified epoxy resin exhibited a twofold increase in impact resistance. The improved adhesion between the fiber and modified resin was also visible from the scanning electron microscope analysis of the impact fracture surface. There was less influence of resin modification on the flexural properties of the composites. The 5% APTES modification induced early degradation of composites compared to all other composites. The burning rate of all the composites under study is rated to be satisfactory for use in automotive interior applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Centria University of Applied Sciences, University of Borås, Yanbu Industrial College, Jozef Stefan Institute, Swedish Centre for Resource Recovery
Contributors: Rajan, R., Rainosalo, E., Ramamoorthy, S. K., Thomas, S. P., Zavašnik, J., Vuorinen, J., Skrifvars, M.
Publication date: 20 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Applied Polymer Science
Volume: 135
Issue number: 36
Article number: 46673
ISSN (Print): 0021-8995
Ratings: 
  • Scopus rating (2018): CiteScore 2.25 SJR 0.554 SNIP 0.814
Original language: English
ASJC Scopus subject areas: Chemistry(all), Surfaces, Coatings and Films, Polymers and Plastics, Materials Chemistry
Keywords: cellulose and other wood products, functionalization of polymers, mechanical properties, thermal properties, thermosets

Bibliographical note

EXT="Skrifvars, Mikael"

Source: Scopus
Source ID: 85049105961

Research output: Contribution to journalArticleScientificpeer-review

A COMPARATIVE IN VITRO STUDY OF CELL GROWTH ON TEXTILE SCAFFOLDS FOR TISSUE ENGINEERING APPLICATIONS

General information

Publication status: Published
MoE publication type: Not Eligible
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Tampere University of Technology, BioMediTech, University of Tampere, BioMediTech, Adult Stem Cell Research Group
Contributors: Kroon, M., Talvitie, E., Miettinen, S., Kellomäki, M.
Publication date: 12 Sep 2018
Peer-reviewed: Unknown
Event: Paper presented at ESB2018 - 29th Annual Meeting of European Society for Biomaterials, Maastricht, Netherlands.
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering

Research output: Other conference contributionPaper, poster or abstractScientific

Performance evaluation of the HR-ELPI + inversion

Data inversion methods used in aerosol measurement instruments have significant influence on the resolution and quality of the result. A freshly launched new electrical low pressure impactor (ELPI) instrument version, high resolution ELPI+ (HR-ELPI+, Dekati Ltd.), uses an iterative inversion calculation method to improve particle size resolution, concentration, and data analysis quality. In this article, the performance of the HR-ELPI + is critically analyzed by simulations and experiments in laboratory and field conditions, and the results are compared with a conventional inversion data analysis method (cut-point diameter concept) and with common reference instruments (e.g., SMPS and EEPS). The results showed that the HR-ELPI + inversion has limited performance at the lower and upper limits of the instrument’s size range, and can suffer if the raw currents have signal dependent noise more than 50% or electric noise more than 1%. However, the HR-ELPI + clearly provide remarkably better resolution and quality with low oscillation risk compared to the conventional cut-point diameter concept of the ELPI. The HR-ELPI + also showed generally very similar size distributions and number concentrations compared to the reference instruments.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics
Contributors: Saari, S., Arffman, A., Harra, J., Rönkkö, T., Keskinen, J.
Number of pages: 11
Pages: 1037-1047
Publication date: 2 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Aerosol Science and Technology
Volume: 52
Issue number: 9
ISSN (Print): 0278-6826
Ratings: 
  • Scopus rating (2018): CiteScore 2.35 SJR 0.786 SNIP 0.976
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Keywords: Pramod Kulkarni
Source: Scopus
Source ID: 85052142628

Research output: Contribution to journalArticleScientificpeer-review

Post operation inactivation of acidophilic bioleaching microorganisms using natural chloride-rich mine water

The H2020 BIOMOre project (www.biomore.info, Grant Agreement #642456) tests the feasibility of in situ bioleaching of copper in deep subsurface deposits in the Rudna mine, Poland. Copper is leached using biologically produced ferric iron solution, which is recycled back to the in situ reactor after re-oxidation by iron-oxidizing microorganisms. From a post operational point of view, it is important that the biological processes applied during the operation can be controlled and terminated. Our goal was to determine the possibility to use natural saline mine water for the inactivation of the introduced iron-oxidizing microorganisms remaining in the in situ reactor after completion of the leaching process of the ore block. Aerobic and anaerobic microcosms containing acid-leached (pH 2) sandstone or black shale from the Kupferschiefer in the Rudna mine were further leached with the effluent from a ferric iron generating bioreactor at 30 °C for 10 days to simulate the in situ leaching process. After the removal of the iron solution, residing iron-oxidizing microorganisms were inactivated by filling the microcosms with chloride-rich water (65 g L−1 Cl) originating from the mine. The chloride-rich water irreversibly inactivated the iron-oxidizing microorganisms and showed that the naturally occurring saline water of the mine can be used for long-term post process inactivation of bioleaching microorganisms

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, VTT Technical Research Centre of Finland
Contributors: Bomberg, M., Miettinen, H., Wahlström, M., Kaartinen, T., Ahoranta, S., Lakaniemi, A., Kinnunen, P.
Number of pages: 10
Pages: 236-245
Publication date: 1 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Hydrometallurgy
Volume: 180
ISSN (Print): 0304-386X
Ratings: 
  • Scopus rating (2018): CiteScore 4 SJR 1.014 SNIP 1.817
Original language: English
ASJC Scopus subject areas: Industrial and Manufacturing Engineering, Metals and Alloys, Materials Chemistry
Keywords: BIOMOre, in situ bioleaching, Inactivation, Iron-oxidizing bacteria, Quantitative PCR
Source: Scopus
Source ID: 85051388591

Research output: Contribution to journalArticleScientificpeer-review

Recent progress in biohydrometallurgy and microbial characterisation

Since the discovery of microbiological metal dissolution, numerous biohydrometallurgical approaches have been developed to use microbially assisted aqueous extractive metallurgy for the recovery of metals from ores, concentrates, and recycled or residual materials. Biohydrometallurgy has helped to alleviate the challenges related to continually declining ore grades by transforming uneconomic ore resources to reserves. Engineering techniques used for biohydrometallurgy span from above ground reactor, vat, pond, heap and dump leaching to underground in situ leaching. Traditionally biohydrometallurgy has been applied to the bioleaching of base metals and uranium from sulfides and the biooxidation of sulfidic refractory gold ores and concentrates before cyanidation. More recently the interest in using bioleaching for oxide ore and waste processing, as well as extracting other commodities such as rare earth elements has been growing. Bioprospecting, adaptation, engineering and storing of microorganisms has increased the availability of suitable biocatalysts for biohydrometallurgical applications. Moreover, the advancement of microbial characterisation methods has increased the understanding of microbial communities and their capabilities in the processes. This paper reviews recent progress in biohydrometallurgy and microbial characterisation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, CSIRO Land and Water, School of Biomedical Sciences, University of Western Australia, CSIRO Mineral Resources, Murdoch University
Contributors: Kaksonen, A. H., Boxall, N. J., Gumulya, Y., Khaleque, H. N., Morris, C., Bohu, T., Cheng, K. Y., Usher, K. M., Lakaniemi, A.
Number of pages: 19
Pages: 7-25
Publication date: 1 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Hydrometallurgy
Volume: 180
ISSN (Print): 0304-386X
Ratings: 
  • Scopus rating (2018): CiteScore 4 SJR 1.014 SNIP 1.817
Original language: English
ASJC Scopus subject areas: Industrial and Manufacturing Engineering, Metals and Alloys, Materials Chemistry
Keywords: Biohydrometallurgy, Bioleaching, Biooxidation, Characterisation, Microbiology

Bibliographical note

EXT="Kaksonen, Anna H."

Source: Scopus
Source ID: 85049805480

Research output: Contribution to journalArticleScientificpeer-review

Dilute nitride triple junction solar cells for space applications: Progress towards highest AM0 efficiency

We report a detailed performance assessment of triple junction dilute nitride solar cells fabricated by a combined molecular beam epitaxy-metal organic chemical vapor deposition process and designed for space applications. The experimental sample exhibits an efficiency level of 30.8% under AM0 illumination. Analyses of the isotype single junction dilute nitride bottom cells reveal a band gap voltage offset of 0.49 V at one sun illumination and a value as low as 0.47 V for full spectrum excitation without filter layers. The analyses point out the limitation of the design in terms of current balancing. With optimized design, an efficiency of 32.1% is possible, revealing the maturity reached by dilute nitride technology in the quest for improving the efficiency of lattice-matched multijunction solar cells.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, CESI S.p.A.
Contributors: Aho, A., Isoaho, R., Tukiainen, A., Gori, G., Campesato, R., Guina, M.
Number of pages: 5
Pages: 740-744
Publication date: Sep 2018
Peer-reviewed: Yes
Early online date: Apr 2018

Publication information

Journal: Progress in Photovoltaics: Research and Applications
Volume: 26
Issue number: 19
ISSN (Print): 1062-7995
Ratings: 
  • Scopus rating (2018): CiteScore 6.68 SJR 1.942 SNIP 2.413
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Condensed Matter Physics, Electrical and Electronic Engineering
Source: Scopus
Source ID: 85045098254

Research output: Contribution to journalArticleScientificpeer-review

Fluorescence bandwidth of 280nm from broadband Ce3+-doped silica fiber pumped with blue laser diode

Fluorescence properties of a Ce3+-doped silica fiber at different pump wavelengths between 405nm to 450 nm are investigated. With 405 nm pump wavelength and a fiber length of ∼130-140 cm broadband fluorescence of ∼280nm is achieved.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Research group: Nanophotonics, Aston University, Fiber Optics Research Center of the Russian Academy of Sciences, Russian Academy of Sciences
Contributors: Yadav, A., Chichkov, N. B., Gumenyuk, R., Zherebtsov, E., Melkumov, M. A., Yashkov, M. V., Dianov, E. M., Rafailov, E. U.
Number of pages: 1
Pages: 133-133
Publication date: 13 Aug 2018

Host publication information

Title of host publication: 2018 International Conference Laser Optics (ICLO)
Publisher: IEEE
Article number: 8435861
ISBN (Electronic): 9781538636121
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Broadband source, Ce-doped fiber, Ce ions, Fluorescence
Source: Scopus
Source ID: 85052525711

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Extending the Faraday cup aerosol electrometer based calibration method up to 5 µm

A Faraday cup aerosol electrometer based electrical aerosol instrument calibration setup from nanometers up to micrometers has been designed, constructed, and characterized. The set-up utilizes singly charged seed particles, which are grown to the desired size by condensation of diethylhexyl sebacate. The calibration particle size is further selected with a Differential Mobility Analyzer (DMA). For micrometer sizes, a large DMA was designed, constructed, and characterized. The DMA electrical mobility resolution was found to be 7.95 for 20 L/min sheath and 2 L/min sample flows. The calibration is based on comparing the instrument’s response against the concentration measured with a reference Faraday cup aerosol electrometer. The set-up produces relatively high concentrations in the micrometer size range (more than 2500 1/cm3 at 5.3 µm). A low bias flow mixing and splitting between the reference and the instrument was constructed from a modified, large-sized mixer and a four-port flow splitter. It was characterized at different flow rates and as a function of the particle size. Using two of the four outlet ports at equal 1.5 L/min flow rates, the particle concentration bias of the flow splitting was found to be less than ±1% in the size range of 3.6 nm–5.3 µm. The developed calibration set-up was used to define the detection efficiency of a condensation particle counter from 3.6 nm to 5.3 µm with an expanded measurement uncertainty (k = 2) of less than 4% over the entire size range and less than 2% for most of the measurement points.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics
Contributors: Järvinen, A., Keskinen, J., Yli-Ojanperä, J.
Number of pages: 13
Pages: 828-840
Publication date: 3 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Aerosol Science and Technology
Volume: 52
Issue number: 8
ISSN (Print): 0278-6826
Ratings: 
  • Scopus rating (2018): CiteScore 2.35 SJR 0.786 SNIP 0.976
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Keywords: Pramod Kulkarni
Source: Scopus
Source ID: 85051115278

Research output: Contribution to journalArticleScientificpeer-review

Enhanced resonant nonlinear absorption and optical limiting in Er3+ ions doped multicomponent tellurite glasses

Nonlinear optical properties of multicomponent tellurite glasses doped with Er3+ ions were investigated by open aperture Z-scan measurements. Compositional and linear optical properties of the glasses were examined by the energy dispersive X-ray spectrum and UV–vis–NIR absorption spectrum analysis respectively. The mechanism behind the optical nonlinearity and optical limiting efficiency was successfully explained by evaluating the physical properties such as density, refractive index and polarizability of the glasses. The nonlinear properties critically depend on the polarizability, which is found to increase with the addition of Er3+ ions by the creation of non-bridging oxygen ions. By the systematic addition of Er3+ ions, we have dictated the physical properties and thus tuned the optical limiting efficiency of the glasses. This makes the Er3+-doped multicomponent tellurite glasses flexible tunable optical limiters for potential device applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Mahatma Gandhi University
Contributors: Sajna, M. S., Perumbilavil, S., Prakashan, V. P., Sanu, M. S., Joseph, C., Biju, P. R., Unnikrishnan, N. V.
Number of pages: 9
Pages: 227-235
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Materials Research Bulletin
Volume: 104
ISSN (Print): 0025-5408
Ratings: 
  • Scopus rating (2018): CiteScore 3.12 SJR 0.744 SNIP 0.907
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Mechanics of Materials, Mechanical Engineering
Keywords: Multiphoton absorption, Optical limiting, Optical nonlinearity, Tellurite glasses, Z-scan technique
Source: Scopus
Source ID: 85046365437

Research output: Contribution to journalArticleScientificpeer-review

High surface quality welding of aluminum using adjustable ring-mode fiber laser

A method to improve penetration and stabilize the welding phenomenon at a high welding speed has been described through experimental and numerical investigations. Using a high power laser beam consisting of a center and a ring part, influences of shielding gas direction and flow rate, laser power density, and welding mode defined by variable intensity distribution have been clarified. The weld bead was evaluated in terms of width, height, shape and roughness. Dual-mode laser irradiation of center and ring power made it possible to stabilize the welding process. The center power helps to achieve sufficient deep penetration, while ring power ensures good temperature distribution. Good surface quality and deep penetration welding could be achieved with dual-mode welding, using low flow rate of shielding gas supplied from the backside direction.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mechanical Engineering and Industrial Systems, Okayama University, Corelase Oy
Contributors: Maina, M. R., Okamoto, Y., Okada, A., Närhi, M., Kangastupa, J., Vihinen, J.
Number of pages: 9
Pages: 180-188
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Processing Technology
Volume: 258
ISSN (Print): 0924-0136
Ratings: 
  • Scopus rating (2018): CiteScore 5.08 SJR 1.719 SNIP 2.773
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Computer Science Applications, Metals and Alloys, Industrial and Manufacturing Engineering
Keywords: Adjustable ring-mode fiber laser, Aluminum, Laser welding, Shielding gas, Surface quality
Source: Scopus
Source ID: 85044959061

Research output: Contribution to journalArticleScientificpeer-review

Near-threshold high spin amplification in a 1300 nm GaInNAs spin laser

Using continuous-wave optical pumping of a spin-VCSEL at room temperature, we find high spin amplification of the pump close to threshold within the communications wavelength window, here at 1300 nm. This facilitates a strong switch from left to right circularly polarised light emission, which has potential applications in polarisation encoding for data communications. We use a simple spin flip model to fit the experimental results and discuss the VCSEL parameters that affect this amplification.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Research group: Semiconductor Technology and Applications, University of Essex, University of Bristol
Contributors: Cemlyn, B., Adams, M., Harbord, E., Li, N., Henning, I. D., Oulton, R., Korpijärvi, V. M., Guina, M.
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 9
Article number: 094005
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.002
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: spin amplification, spin laser, spin VCSEL
Source: Scopus
Source ID: 85053167963

Research output: Contribution to journalArticleScientificpeer-review

Geometry Analysis in Screen-Printed Stretchable Interconnects

Deformability of interconnects and conductors as the skeleton of soft electronic devices plays an important role in the stretchability of the whole system. To make the interconnects stretchable, either employing deformable materials or tailoring the design are the primary approaches. It is also possible to combine the two strategies. In advanced stretchable electronic circuits, there is a frequently need for the interconnects to transform from a narrow to a wide geometry. Therefore, this paper assesses three different geometries that accommodate a narrow-to-wide transition along the interconnects. First, the geometry is modeled using Finite Element (FE) analysis. Second, in order to verify the accuracy of the FE model, screen-printed interconnects are fabricated accordingly by using silver flake ink on a deformable substrate. The geometrical modification shows a considerable improvement in the stretchability of the whole system. Additionally, the effect of encapsulation with thermoplastic polyurethane (TPU) on the performance of stretchable interconnects is investigated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Materials Science
Contributors: Mosallaei, M., Jokinen, J., Honkanen, M., Iso-Ketola, P., Vippola, M., Vanhala, J., Kanerva, M., Mantysalo, M.
Pages: 1344-1352
Publication date: Aug 2018
Peer-reviewed: Yes
Early online date: 8 Jul 2018

Publication information

Journal: IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume: 8
Issue number: 8
ISSN (Print): 2156-3950
Ratings: 
  • Scopus rating (2018): CiteScore 2.26 SJR 0.552 SNIP 1.236
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Industrial and Manufacturing Engineering, Electrical and Electronic Engineering
Keywords: Conductivity, finite element analysis, Geometry, Integrated circuit interconnections, Plastics, printed electronics, screen-printing, Strain, Stress, stretchable interconnects., Substrates
Source: Scopus
Source ID: 85049772255

Research output: Contribution to journalArticleScientificpeer-review

Design aspects of all atomic layer deposited TiO2–Fe2O3 scaffold-absorber photoanodes for water splitting

Iron and titanium oxides have attracted substantial attention in photoelectrochemical water splitting applications. However, both materials suffer from intrinsic limitations that constrain the final device performance. In order to overcome the limitations of the two materials alone, their combination has been proposed as a solution to the problems. Here we report on the fabrication of an atomic layer deposited (ALD) Fe2O3 coating on porous ALD-TiO2. Our results show that successful implementation requires complete mixing of the TiO2 and Fe2O3 layers via annealing resulting in the formation of a photoactive iron titanium oxide on the surface. Moreover, we found that incomplete mixing leads to crystallization of Fe2O3 to hematite that is detrimental to the photoelectrochemical performance. IPCE and transient photocurrent measurements performed using UV and visible light excitation confirmed that the iron titanium oxide extends the photocurrent generation to the visible range. These measurements were complemented by transient absorption spectroscopy (TAS), which revealed a new band absent in pristine hematite or anatase TiO2 that we assign to charge transfer within the structure. Taken together, these results provide design guidelines to be considered when aiming to combine TiO2 and Fe2O3 for photoelectrochemical applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, Research group: Surface Science, Photonics, Materials Science, Research group: Plastics and Elastomer Technology
Contributors: Hiltunen, A., Ruoko, T., Iivonen, T., Lahtonen, K., Ali-Löytty, H., Sarlin, E., Valden, M., Leskelä, M., Tkachenko, N.
Pages: 2124-2130
Publication date: 31 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Sustainable Energy & Fuels
Volume: 2
Issue number: 9
ISSN (Print): 2398-4902
Ratings: 
  • Scopus rating (2018): CiteScore 4.94 SNIP 0.841
Original language: English
ASJC Scopus subject areas: Electrochemistry, Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films
Keywords: Water splitting, Atomic layer deposition (ALD), Titanium dioxide, Hematite, Cellulose, Template

Research output: Contribution to journalArticleScientificpeer-review

Processing of printed silver patterns on an ETFE substrate

Printed electronics makes it possible to fabricate devices on thin and flexible substrates at a low cost and with simple processing. However, substrate characteristics can make patterning challenging. Here, we report our approach for processing printed silver patterns on an extremely hydrophobic ethylene-Tetrafluoroethylene (ETFE) foil substrate. The effects of selected surface modification methods on substrate characteristics and final print quality were studied, and the thermal characteristics of ETFE were determined. Conductive silver patterns were fabricated using both screen printing and inkjet printing techniques. Additionally, intense pulse light method was compared to thermal annealing as an alternative annealing method. The surface modification of ETFE was observed to affect ink wetting and print quality. It was concluded that the impact of the chosen annealing method on the final characteristics of the printed structures was significant.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Electronics and Communications Engineering, Trelic Ltd.
Contributors: Mikkonen, R., Lahokallio, S., Frisk, L., Mäntysalo, M.
Number of pages: 7
Pages: 1-7
Publication date: 31 Jul 2018

Host publication information

Title of host publication: Proceedings - 2018 IMAPS Nordic Conference on Microelectronics Packaging, NORDPAC 2018
Publisher: IEEE
Article number: 8423860
ISBN (Print): 9789526815053
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: DSC, ETFE, IPL, Printed electronics, TMA
Electronic versions: 

Bibliographical note

EXT="Lahokallio, Sanna"
EXT="Frisk, Laura"

Source: Scopus
Source ID: 85051476038

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Wound healing of human embryonic stem cell-derived retinal pigment epithelial cells is affected by maturation stage

Background: Wound healing of retinal pigment epithelium (RPE) is a complex process that may take place in common age-related macular degeneration eye disease. The purpose of this study was to evaluate whether wounding and wound healing has an effect on Ca2+ dynamics in human embryonic stem cell (hESC)-RPEs cultured different periods of time. Methods: The 9-day-cultured or 28-day-cultured hESC-RPEs from two different cell lines were wounded and the dynamics of spontaneous and mechanically induced intracellular Ca2+ activity was measured with live-cell Ca2+ imaging either immediately or 7days after wounding. The healing time and speed were analyzed with time-lapse bright field microscopy. The Ca2+ activity and healing speed were analysed with image analysis. In addition the extracellular matrix deposition was assessed with confocal microscopy. Results: The Ca2+ dynamics in hESC-RPE monolayers differed depending on the culture time: 9-day-cultured cells had higher number of cells with spontaneous Ca2+ activity close to freshly wounded edge compared to control areas, whereas in 28-day-cultured cells there was no difference in wounded and control areas. The 28-day-cultured, wounded and 7-day-healed hESC-RPEs produced wide-spreading intercellular Ca2+ waves upon mechanical stimulation, while in controls propagation was restricted. Most importantly, both wave spreading and spontaneous Ca2+ activity of cells within the healed area, as well as the cell morphology of 28-day-cultured, wounded and thereafter 7-day-healed areas resembled the 9-day-cultured hESC-RPEs. Conclusions: This acquired knowledge about Ca2+ dynamics of wounded hESC-RPE monolayers is important for understanding the dynamics of RPE wound healing, and could offer a reliable functionality test for RPE cells. The data presented in here suggests that assessment of Ca2+ dynamics analysed with image analysis could be used as a reliable non-invasive functionality test for RPE cells.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Computational Biophysics and Imaging Group, University of Eastern Finland, University Central Hospital Kuopio
Contributors: Abu Khamidakh, A. E., Rodriguez-Martinez, A., Kaarniranta, K., Kallioniemi, A., Skottman, H., Hyttinen, J., Juuti-Uusitalo, K.
Publication date: 31 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: BioMedical Engineering Online
Volume: 17
Issue number: 1
Article number: 102
ISSN (Print): 1475-925X
Ratings: 
  • Scopus rating (2018): CiteScore 2.44 SJR 0.595 SNIP 1.047
Original language: English
ASJC Scopus subject areas: Radiological and Ultrasound Technology, Biomaterials, Biomedical Engineering, Radiology Nuclear Medicine and imaging
Keywords: Ca waves, Cell maturation, HESC-RPE, Image analysis, Mechanical stimulation, Mechanically induced intercellular Ca waves, RPE, Spontaneous [Ca] increases, Wound healing
Electronic versions: 
Source: Scopus
Source ID: 85050745629

Research output: Contribution to journalArticleScientificpeer-review

Exciton localization and structural disorder of GaAs1-xBix/GaAs quantum wells grown by molecular beam epitaxy on (311)B GaAs substrates

In this work, we have investigated the structural and optical properties of GaAs(1-x)Bix/GaAs single quantum wells (QWs) grown by molecular beam epitaxy on GaAs (311)B substrates using x-ray diffraction, atomic force microscopy, Fourier-transform Raman (FT-Raman) and photoluminescence spectroscopy techniques. The FT-Raman results revealed a decrease of the relative intensity ratio of transverse and longitudinal optical modes with the increase of Bi concentration, which indicates a reduction of the structural disorder with increasing Bi incorporation. In addition, the PL results show an enhancement of the optical efficiency of the structures as the Bi concentration is increased due to important effects of exciton localization related to Bi defects, nonradiative centers and alloy disorder. These results provide evidence that Bi is incorporated effectively into the QW region. Finally, the temperature dependence of the PL spectra has evidenced two distinct types of defects related to the Bi incorporation, namely Bi clusters and pairs, and alloy disorder and potential fluctuation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Universidade Federal de São Carlos, University of Nottingham, Adana Science and Technology University, University of São Paulo
Contributors: Prando, G. A., Orsi Gordo, V., Puustinen, J., Hilska, J., Alghamdi, H. M., Som, G., Gunes, M., Akyol, M., Souto, S., Rodrigues, A. D., Galeti, H. V., Henini, M., Gobato, Y. G., Guina, M.
Publication date: 17 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 8
Article number: 084002
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.002
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: dilute bismide, exciton localization, photoluminescence, structural disorder
Source: Scopus
Source ID: 85051332383

Research output: Contribution to journalArticleScientificpeer-review

Fluid flow simulations meet high-speed video: Computer vision comparison of droplet dynamics

Hypothesis: While multiphase flows, particularly droplet dynamics, are ordinary in nature as well as in industrial processes, their mathematical and computational modelling continue to pose challenging research tasks - patent approaches for tackling them are yet to be found. The lack of analytical flow field solutions for non-trivial droplet dynamics hinders validation of computer simulations and, hence, their application in research problems. High-speed videos and computer vision algorithms can provide a viable approach to validate simulations directly against experiments. Experiments: Droplets of water (or glycerol-water mixtures) impacting on both hydrophobic and superhydrophobic surfaces were imaged with a high-speed camera. The corresponding configurations were simulated using a lattice-Boltzmann multiphase scheme. Video frames from experiments and simulations were compared, by means of computer vision, over entire droplet impact events. Findings: The proposed experimental validation procedure provides a detailed, dynamic one-on-one comparison of a droplet impact. The procedure relies on high-speed video recording of the experiments, computer vision, and on a software package for the analyzation routines. The procedure is able to quantitatively validate computer simulations against experiments and it is widely applicable to multiphase flow systems in general.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Natural Resources Institute Finland (Luke), BioFluidix GmbH, Faculty of Information Technology, Jyväskylän yliopisto
Contributors: Kulju, S., Riegger, L., Koltay, P., Mattila, K., Hyväluoma, J.
Number of pages: 9
Pages: 48-56
Publication date: 15 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Colloid and Interface Science
Volume: 522
ISSN (Print): 0021-9797
Ratings: 
  • Scopus rating (2018): CiteScore 5.93 SJR 1.29 SNIP 1.322
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Surfaces, Coatings and Films, Colloid and Surface Chemistry
Keywords: Computer vision, Droplet, Experimental, High-speed video, Hydrophobic, Lattice Boltzmann, Simulation

Bibliographical note

EXT="Kulju, S."

Source: Scopus
Source ID: 85044153494

Research output: Contribution to journalArticleScientificpeer-review

Mechanical stress analysis during a quench in CLIQ protected 16 T dipole magnets designed for the future circular collider

Protecting the magnets in case of a quench is a challenge for the 16 T superconducting dipole magnets presently designed for the 100 TeV: Future Circular Collider (FCC). These magnets are driven to the foreseen technological limits in terms of critical current, mechanical strength and quench protection. The magnets are protected with CLIQ (Coupling-Loss Induced Quench) system, which is a recently developed quench protection method based on discharging a capacitor bank across part of the winding. The oscillation of the magnet currents and the dissipation of the high stored energy into the windings cause electrodynamic forces and thermal stresses, which may need to be considered in the magnet mechanical design. This paper focuses on mechanical stress analysis during a quench of the 16 T cos-θ and block type dipole magnets. A finite element model allowed studying the stress due to the non-uniform temperature and current distribution in the superconducting coils. Two different CLIQ configurations were considered for the cos-θ design and one for the block type magnet. The analyses of the mechanical behavior of two magnets during a quench without or with hot spot turn were separately carried out. The simulation results show that the stress related to a quench should be considered when designing a high field magnet.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research group: Modelling and superconductivity, Lanzhou University, European Organization for Nuclear Research, Laboratorio Accelatori e Superconduttività Applicata, French Atomic Energy Commission (CEA) Saclay, Università degli Studi di Milano
Contributors: Zhao, J., Prioli, M., Stenvall, A., Salmi, T., Gao, Y., Caiffi, B., Lorin, C., Marinozzi, V., Farinon, S., Sorbi, M.
Number of pages: 8
Pages: 27-34
Publication date: 15 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Physica C: Superconductivity and its Applications
Volume: 550
ISSN (Print): 0921-4534
Ratings: 
  • Scopus rating (2018): CiteScore 1.46 SJR 0.463 SNIP 0.905
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Energy Engineering and Power Technology, Electrical and Electronic Engineering
Keywords: Accelerator magnet, CLIQ protection system, Finite element analysis, Lorentz forces, Quench, Thermal stress
Source: Scopus
Source ID: 85045717268

Research output: Contribution to journalArticleScientificpeer-review

Directions in QPPR development to complement the predictive models used in risk assessment of nanomaterials

There is an increasing need for predictive risk assessment of nanomaterials (NMs) using methods that are rapid, accurate and resource efficient. To fulfill this need, the development and use of Quantitative Property Property Relationships (QPPRs) for estimating the hazard of NMs and NM-related parameters in exposure modelling seems eminent. In this study, we analyze a selection of models used for hazard and/or exposure assessment of NMs. This analysis was done by identifying all the NM-related properties used in these models related to three categories of data: (i) Intrinsic properties specific to the NM, matrix or experimental conditions, (ii) Extrinsic NM properties related to interaction between the intrinsic properties and (iii) Measured hazard or exposure data. This analysis is combined with the current state of QPPR development to recommend further development of QPPRs for predictive risk assessment of NMs. In particular, the use of descriptors related to the interaction between a NM and its surroundings, e.g. the attachment efficiency is proposed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics, National Institute for Public Health and the Environment, Radboud University Nijmegen, Leiden University
Contributors: Quik, J. T., Bakker, M., van de Meent, D., Poikkimäki, M., Dal Maso, M., Peijnenburg, W.
Number of pages: 9
Pages: 58-66
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: NanoImpact
Volume: 11
ISSN (Print): 2452-0748
Ratings: 
  • Scopus rating (2018): CiteScore 5.52 SJR 1.322 SNIP 0.936
Original language: English
ASJC Scopus subject areas: Materials Science (miscellaneous), Safety, Risk, Reliability and Quality, Safety Research, Public Health, Environmental and Occupational Health
Keywords: In silico, Modelling, Nanomaterial, QNAR, QPPR, Risk assessment
URLs: 
Source: Scopus
Source ID: 85042321286

Research output: Contribution to journalArticleScientificpeer-review

Evaluation of screen printed silver trace performance and long-term reliability against environmental stress on a low surface energy substrate

Otherwise attractive substrate materials for printed electronics may have such surface characteristics that make patterning challenging. This article focuses on the printability and performance characterization of conductive patterns on a low surface energy substrate. Surface characteristics of a hydrophobic polyphenylene ether (PPE) substrate and the effects of surface modification using chemical and physical pre-treatments were studied. In addition, silver ink performance and its reliability on this substrate were evaluated. The surface was characterized by surface energy measurements and surface profile analysis. Screen-printed test patterns were characterized to evaluate print quality and electrical and mechanical performance. A further inspection of substrate-ink interactions was conducted using environmental reliability tests. It was observed that ink adhesion could be significantly promoted by choosing a suitable surface pre-treatment method. Low sheet resistances were obtained, and thus, suitable inks for further characterization were found. In addition, it was observed that environmental stress has a significant impact on ink-substrate interactions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Nano Communication Centre
Contributors: Mikkonen, R., Mäntysalo, M.
Number of pages: 12
Pages: 54-65
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Microelectronics Reliability
Volume: 86
ISSN (Print): 0026-2714
Ratings: 
  • Scopus rating (2018): CiteScore 1.7 SJR 0.376 SNIP 0.983
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Safety, Risk, Reliability and Quality, Surfaces, Coatings and Films, Electrical and Electronic Engineering
Keywords: Adhesion, Environmental stress, PPE, Printed electronics, Reliability, Surface modification
URLs: 
Source: Scopus
Source ID: 85047240351

Research output: Contribution to journalArticleScientificpeer-review

Persistent luminescent borosilicate glasses using direct particles doping method

Persistent luminescence (PeL) was obtained, from the first time to the best of our knowledge, from borosilicate bulk glasses. The glasses were prepared using direct doping method. Commercial PeL SrAl2O4:Eu2+,Dy3+ microparticles (MPs) were added in the borosilicate glass after melting. The persistent luminescence can be augmented when casting the glass 3 min after adding the MPs at 950 °C. Although the borosilicate glasses exhibit persistent luminescence, the glass melt has a corrosive behavior on the MPs leading to the diffusion of Al and Sr into the glasses.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Turku University of Applied Science
Contributors: Roldán Del Cerro, P., Salminen, T., Lastusaari, M., Petit, L.
Number of pages: 4
Pages: 38-41
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Scripta Materialia
Volume: 151
ISSN (Print): 1359-6462
Ratings: 
  • Scopus rating (2018): CiteScore 5.03 SJR 2.185 SNIP 1.95
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Mechanics of Materials, Mechanical Engineering, Metals and Alloys
Keywords: Borosilicate glasses, Corrosion, Direct particle doping method, Persistent luminescence, SrAlO:Eu,Dy microparticles
Source: Scopus
Source ID: 85056171139

Research output: Contribution to journalArticleScientificpeer-review

Luminescence of Er3+ doped oxyfluoride phosphate glasses and glass-ceramics

Glasses with the composition (75 NaPO3-(25-x) CaO-xCaF2) (in mol %) were prepared with 0.15 mol% of Er2O3. The effect of the glass composition and of heat treatment on the spectroscopic properties of the newly developed glasses is reported. With the progressive replacement of CaO by CaF2, the Er3+:4I13/2 lifetime and the intensity of the upconversion emission increase whereas the intensity of the emission at 1.5 μm decreases due to the decrease in the phonon energy in the as-prepared glasses. The glasses were heat treated at 20 °C above their respective glass transition temperature for 17 h to form nuclei and then at their crystallization temperature from 15min to 1 h to grow the nuclei into crystals. The heat treatment leads to the precipitation of crystalline phases, the composition of which depends upon the glass composition. As the Er3+:4I13/2 lifetime increases and the intensity of the upconversion increases for the glass with x = 0 after heat treatment, the Er3+ ions are expected to be incorporated into the phosphate-based crystals. However, as the shape of the emission band at 1.5 μm remains unchanged and the intensity of the upconversion decreases significantly after heat treatment of the glasses with x > 10, the crystals found in the glass-ceramics with x > 10 are thought to free of Er3+ ions. Although Er3+ ions entered in the CaF2 crystals precipitating in aluminosilicate glass, the Er3+ ions are believed to remain in the amorphous phosphate part of the glass-ceramic containing CaF2 crystals.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Faculty of Engineering Sciences, Research group: Biomaterials and Tissue Engineering Group, Materials Science, Photonics, Istituto Superiore Mario Boella
Contributors: Nommeots-Nomm, A., Boetti, N. G., Salminen, T., Massera, J., Hokka, M., Petit, L.
Number of pages: 7
Pages: 224-230
Publication date: 30 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Alloys and Compounds
Volume: 751
ISSN (Print): 0925-8388
Ratings: 
  • Scopus rating (2018): CiteScore 4.12 SJR 1.065 SNIP 1.386
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Keywords: CaF crystals in glass, Er luminescence, Oxyfluoride phosphate glasses and glass-ceramics
Source: Scopus
Source ID: 85045405038

Research output: Contribution to journalArticleScientificpeer-review

Manufacturing of calibration samples for barkhausen noise method: case studies on temperature controlled laser and hydrogen-oxygen flame

Non-destructive magnetic Barkhausen noise (BN) measurements are most widely used for studying the grinding burns from hardened and ground samples. The formation of the grinding burns occurs due to excess of heat generation and produces thus changes in the residual stresses and microstructure. The BN method can be used for quality control purposes because it is sensitive to changes both in stresses and microstructure. The important part of the BN inspection procedure is the verification that the sensor and the equipment are working properly. One option is to use calibration pieces to evaluate the operation of the sensor before the actual measurements. The best way is to use similar components and same measurement procedure as to be studied. The components should have artificially produced burn marks to mimic the damaged areas of grinding burns. To validate the BN measurement results properly, the BN sensor needs to be verified with both thermally damaged and thermally undamaged sample surfaces.

In this work, two different procedures to manufacture artificial burn marks were studied. A temperature controlled, robotic assisted, laser system was used to perform temperature controlled tempering marks to carburised gear wheel teeth surfaces. Also, hydrogen-oxygen flame with robotic control was used to produce artificial burn marks on the surfaces of carburised gear wheel teeth surfaces.

The aim was to analyse the suitability of thermal damages created by these two methods by comparing the BN readings of them to each other. The new, temperature controlled, laser system was found to produce uniform quality thermal damages. While the hydrogen-oxygen process was found to be more unpredictable and it needs to be controlled extremely carefully i.e. with robotic manipulation of the hydrogen-oxygen flame. The speed of the hydrogen-oxygen flame affected the RMS values greater than the other tested parameters.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Materials Science, Research group: Materials Characterization, Stresstech Oy
Contributors: Santa-aho, S., Deveci, M., Savolainen, S., Vippola, M.
Number of pages: 8
Publication date: 11 Jun 2018

Host publication information

Title of host publication: Proceedings of the 12th ECNDT : June 11-15, Gothenburg, Sweden, 2018
ISBN (Print): 978-91-639-6217-2
ASJC Scopus subject areas: Materials Science(all)
Keywords: Barkhausen noise, calibration sample, laser processing, hydrogen-oxygen flame
Electronic versions: 

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Fabrication and reliability evaluation of passive UHF RFID T-shirts

In this paper, we present textile antennas fabricated for T-shirt RFID applications by cutting from commercially available electro-textile, by sewing with conductive thread, and by 3D printing with stretchable silver ink on a 100 % cotton fabric. The ready tags with attached ICs are coated with a protective stretchable encapsulant. The wireless performance of the T-shirt tags is evaluated initially as well as after seven washing cycles, followed by nine washing-drying cycles in a household washing and drying machines. The initial read ranges of all kinds of tags, when measured on-body, are around 3.5 meters. Based on the reliability testing results, the coating effectively protects the components from cyclic washing and drying.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Wireless Identification and Sensing Systems Research Group, Department of Electronic Engineering, City University of Hong Kong
Contributors: Chen, X., He, H., Ukkonen, L., Virkki, J., Lu, Y., Lam, H.
Number of pages: 4
Pages: 1-4
Publication date: 8 Jun 2018

Host publication information

Title of host publication: 2018 IEEE International Workshop on Antenna Technology, iWAT2018 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781538618516
ASJC Scopus subject areas: Instrumentation, Computer Networks and Communications, Electronic, Optical and Magnetic Materials
Keywords: 3D Printing, electro-textiles, embroidery, passive UHF RFID, T-shirts, textiles, washing, wearable electronics

Bibliographical note

jufoid=79362

Source: Scopus
Source ID: 85050037887

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Alkali-silica reaction in Southern-Finland's bridges

In Central Europe and Scandinavia, alkali-aggregate reaction (AAR) typically occurs in massive concrete structures such as bridges and dams. Despite of having similar bedrock with Sweden, Finland has been considered as an AAR free country. The scope of this study was to find out the existence of alkali-silica reaction (ASR) in Finnish bridges. It was also studied how the age of the bridge as well as the aggregate type has affected the occurrence of ASR. The research material consists of 97 condition assessment reports from concrete bridges constructed between 1912 and 1999. The condition assessments were carried out during 2001–2014. All studied bridges are situated in southern or south-western Finland. Alkali-silica reaction was detected by petrographic analysis in 27 bridges, which is 27.8% of all studied bridges. Of the bridges built in the 1970s (38 bridges in the sample) 42.1% was affected by ASR. In the 1960s bridges (33 bridges in the sample) 17.6% was affected. The bridges showing ASR were 31–44 and 43–52 years old, respectively. Thus, there is a potential risk for having ASR damage in concrete bridges also in the Finnish construction and climate. The study shows, however, that the reaction has taken a considerable amount of time to be detected.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering
Contributors: Lahdensivu, J., Köliö, A., Husaini, D.
Number of pages: 7
Pages: 469-475
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Case Studies in Construction Materials
Volume: 8
ISSN (Print): 2214-5095
Ratings: 
  • Scopus rating (2018): CiteScore 2.79 SJR 0.584 SNIP 1.709
Original language: English
ASJC Scopus subject areas: Materials Science (miscellaneous)
Keywords: Alkali-silica reaction, Concrete bridges, Initiation period, Portland cement
Electronic versions: 

Bibliographical note

INT=rak,"Husaini, David"

Source: Scopus
Source ID: 85045094273

Research output: Contribution to journalArticleScientificpeer-review

Progress on HL-LHC Nb3Sn Magnets

The high-luminosity Large Hadron Collider (HL-LHC) project aims at allowing to increase the collisions in the LHC by a factor of ten in the decade 2025-2035. One essential element is the superconducting magnet around the interaction region points, where the large aperture magnets will be installed to allow to further reduce the beam size in the interaction point. The core of this upgrade is the Nb3Sn triplet, made up of 150-mm aperture quadrupoles in the range of 7-8 m. The project is being shared between the European Organization for Nuclear Research and the US Accelerator Upgrade Program, based on the same design, and on the two strand technologies. The project is ending the short model phase, and entering the prototype construction. We will report on the main results of the short model program, including the quench performance and field quality. A second important element is the 11 T dipole that replaces a standard dipole making space for additional collimators. The magnet is also ending the model development and entering the prototype phase. A critical point in the design of this magnet is the large current density, allowing increase of the field from 8 to 11 T with the same coil cross section as in the LHC dipoles. This is also the first two-in-one Nb3Sn magnet developed so far. We will report the main results on the test and the critical aspects.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research area: Power engineering, Research group: Modelling and superconductivity, European Organization for Nuclear Research, Brookhaven National Laboratory, Fermi National Accelerator Laboratory, Lawrence Berkeley National Laboratory
Contributors: Todesco, E., Annarella, M., Ambrosio, G., Apollinari, G., Ballarino, A., Bajas, H., Bajko, M., Bordini, B., Bossert, R., Bottura, L., Cavanna, E., Cheng, D., Chlachidze, G., De Rijk, G., Dimarco, J., Ferracin, P., Fleiter, J., Guinchard, M., Hafalia, A., Holik, E., Izquierdo Bermudez, S., Lackner, F., Marchevsky, M., Loeffler, C., Nobrega, A., Perez, J. C., Prestemon, S., Ravaioli, E., Rossi, L., Sabbi, G., Salmi, T., Savary, F., Schmalzle, J., Stoynev, S., Strauss, T., Tartaglia, M., Vallone, G., Velev, G., Wanderer, P., Wang, X., Willering, G., Yu, M.
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 4
Article number: 4008809
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: niobium-tin, superconducting coils, Superconducting magnets, type II superconductors
Source: Scopus
Source ID: 85046361406

Research output: Contribution to journalArticleScientificpeer-review

Quench simulation results for a 12-T twin-aperture dipole magnet

A 12-T twin-aperture subscale dipole magnet is being developed for SPPC pre-study at the Institute of High Energy Physics (IHEP). The magnet is comprised of 6 double-pancake coils which include 2 Nb3Sn coils and 4 NbTi coils. As the stored energy of the magnet is 0.452 MJ and the operation margin is only about 20% at 4.2 K, a quick and effective quench protection system is necessary during the test of this high field magnet. For the design of the quench protection system, attention was not only paid to the hotspot temperature and terminal voltage, but also the temperature gradient during the quench process due to the poor mechanical characteristics of the Nb3Sn cables. With the adiabatic analysis, numerical simulation and the finite element simulation, an optimized protection method is adopted, which contains a dump resistor and quench heaters. In this paper, the results of adiabatic analysis and quench simulation, such as current decay, hot-spot temperature and terminal voltage are presented in details.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research area: Power engineering, Research group: Modelling and superconductivity, Institute of High Energy Physics Chinese Academy of Science, Chinese Academy of Sciences, University of Science and Technology of China
Contributors: Cheng, D., Salmi, T., Xu, Q., Peng, Q., Wang, C., Wang, Y., Kong, E., Zhang, K.
Number of pages: 7
Pages: 13-19
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Cryogenics
Volume: 92
ISSN (Print): 0011-2275
Ratings: 
  • Scopus rating (2018): CiteScore 1.57 SJR 0.523 SNIP 1.204
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physics and Astronomy(all)
Keywords: Adiabatic analysis, Heater design, Quench protection, Quench simulation
Source: Scopus
Source ID: 85044967086

Research output: Contribution to journalArticleScientificpeer-review

The effect of carbon and nickel additions on the precursor synthesis of Cr3C2-Ni nanopowder

Decreasing crystal size to nanoscale is a proven method to enhance material properties. In this study, nanosize Cr3C2 and Cr3C2-Ni were synthetized and the reaction sequence was studied. Aqueous precursors using only water-soluble raw materials with varying carbon contents and a nickel addition were spray-dried. Glycine was used as a carbon source and chromium acetate hydroxide as a chromium source in the precursor solutions. Nickel nitrate hexahydrate was introduced as a nickel source to yield a metallic binder into the carbide nanopowder.Resulting powders were heat-treating to identify an applicable precursor composition producing the targeted Cr3C2 phase with crystal size of tens of nanometers. Thermal synthesis tests of the precursor powders to yield Cr3C2 took place at a temperature between 900 and 1300 °C under an Argon atmosphere. The synthesis of nanosize Cr3C2-Ni powder was successful at 1000 °C in 30 min, in a case of the best precursor. In order to produce the carbide phase with no residual oxide traces, relative carbon load has to be 48 wt%, while the stoichiometric amount of carbon in Cr3C2 is 13 wt%. When also introducing the nickel source into the precursor, an even higher carbon load was required. The carbon surplus needed to enable the Cr3C2 synthesis attributes to the non-homogeneity of the precursor composition.The chemical synthesis starting from water-soluble raw materials is a promising way of preparing nanosize Cr3C2-Ni with the targeted phase configuration.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, VTT Technical Research Centre of Finland
Contributors: Kaunisto, K., Kotilainen, M., Karhu, M., Lagerbom, J., Vuorinen, T., Honkanen, M., Vippola, M., Turunen, E.
Pages: 9338-9346
Publication date: 1 Jun 2018
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Ceramics International
Volume: 44
Issue number: 8
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.888 SNIP 1.279
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: A. Nanosize CrC synthesis, A. Powders: chemical preparation, B. Grain size, D. Carbides, E. Wear parts

Bibliographical note

EXT="Vuorinen, Tommi"
EXT="Lagerbom, Juha"
EXT="Kaunisto, Kimmo"

Source: Scopus
Source ID: 85042300396

Research output: Contribution to journalArticleScientificpeer-review

Computational design of a novel medium-carbon, low-alloy steel microalloyed with niobium

The design of a new steel with specific properties is always challenging owing to the complex interactions of many variables. In this work, this challenge is dealt with by combining metallurgical principles with computational thermodynamics and kinetics to design a novel steel composition suitable for thermomechanical processing and induction heat treatment to achieve a hardness level in excess of 600 HV with the potential for good fracture toughness. CALPHAD-based packages for the thermodynamics and kinetics of phase transformations and diffusion, namely Thermo-Calc® and JMatPro®, have been combined with an interdendritic segregation tool (IDS) to optimize the contents of chromium, molybdenum and niobium in a proposed medium-carbon low-manganese steel composition. Important factors taken into account in the modeling and optimization were hardenability and as-quenched hardness, grain refinement and alloying cost. For further investigations and verification, the designed composition, i.e., in wt.% 0.40C, 0.20Si, 0.25Mn, 0.90Cr, 0.50Mo, was cast with two nominal levels of Nb: 0 and 0.012 wt.%. The results showed that an addition of Nb decreases the austenite grain size during casting and after slab reheating prior to hot rolling. Validation experiments showed that the predicted properties, i.e., hardness, hardenability and level of segregation, for the designed composition were realistic. It is also demonstrated that the applied procedure could be useful in reducing the number of experiments required for developing compositions for other new steels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Metals Technology, Univ of Oulu, Materials Science Research Group, EFD Induction a.s
Contributors: Javaheri, V., Nyyssönen, T., Grande, B., Porter, D.
Number of pages: 15
Pages: 2978-2992
Publication date: Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Engineering and Performance
Volume: 27
Issue number: 6
ISSN (Print): 1059-9495
Ratings: 
  • Scopus rating (2018): CiteScore 1.67 SJR 0.541 SNIP 0.868
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Mechanical Engineering
Keywords: CALPHAD, computational design, homogenization, IDS, JMatPro, microsegregation, prior austenite grain size, Thermo-Calc, wear resistance steel
Source: Scopus
Source ID: 85045890232

Research output: Contribution to journalArticleScientificpeer-review

Influence of the phosphate glass melt on the corrosion of functional particles occurring during the preparation of glass-ceramics

We report our findings on the impact of the glass composition on the corrosion of microparticles occurring during the preparation of glass-ceramics using the direct doping method. Microparticles (MPs) with the composition Sr4Al14O25:Eu2+,Dy3+ with blue-green persistent luminescence were chosen as the changes in their spectroscopic properties can be related to the MPs’ corrosion. The MPs were added in phosphate-based glasses with different compositions. When using the same doping parameters, the glass system with the composition 90NaPO3-10Na2O (mol%) was found to be the least corrosive on the MPs whereas the glass system with the composition 90NaPO3-10NaF (mol%) is the most corrosive on the MPs probably due to their different viscosity at 575 °C, the temperature at which the MPs are added in the glass melts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Nanophotonics, Turun Yliopisto/Turun Biomateriaalikeskus, Laboratory of Photonics
Contributors: Ojha, N., Laihinen, T., Salminen, T., Lastusaari, M., Petit, L.
Pages: 11807-11811
Publication date: Jun 2018
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Ceramics International
Volume: 44
Issue number: 10
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.888 SNIP 1.279
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Corrosion, Direct doping method, Glass melt, Phosphate glass-ceramics, SrAlO:Eu, Dy microparticles
Source: Scopus
Source ID: 85044921933

Research output: Contribution to journalArticleScientificpeer-review

Investigation of REBCO Roebel Cable Irreversible Critical Current Degradation Under Transverse Pressure

The Roebel cable utilized in High Field accelerator magnets is subject to high transversal electromagnetic forces. The conductor response to exerted pressure depends from the geometry and materials of the cable. A transverse loading test was performed for an impregnated cable in cryogenic conditions. The test revealed Roebel cable being able to withstand elevated average pressure level common to dipole magnets, when the pressure load is exerted by a stiff press tool. However, the mechanism for irreversible current degradation during the transverse loading during powering remains so far unknown. This paper focuses on finding likely failure mechanisms when a magnet is powered. The cable is wound with a glass-fiber sleeve and impregnated with epoxy. Epoxy has much lower stiffness than the coated conductor. When the cable is subjected to transverse loading, abrupt changes in cable thickness and material properties may lead to irreversible degradation of the conductor. As the tape crosses the epoxy-filled central gap region of the cable, the discontinuous change of the support stiffness generates bending strains and shear stress in the conductor. The cable is mechanically modeled. By modeling, the measured axial strain limit of the conductor is connected to transverse pressure limit of the cable.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Civil Engineering, European Organization for Nuclear Research
Contributors: Murtomäki, J. S., Kouhia, R., Stenvall, A., Bottura, L., Kirby, G., van Nugteren, J., DeRijk, G., Rossi, L.
Publication date: Jun 2018
Peer-reviewed: Yes
Early online date: 20 Apr 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 4
Article number: 4802506
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator dipoles, Conductors, Critical current density (superconductivity), Degradation, Finite Element Methods, Geometry, HTS Cables, HTS Magnets, Load modeling, Strain, Superconducting cables
Source: Scopus
Source ID: 85045735242

Research output: Contribution to journalArticleScientificpeer-review

The effects of laser patterning 10CeTZP-Al2O3 nanocomposite disc surfaces: Osseous differentiation and cellular arrangement in vitro

Customized square grid arrangements of different groove depths (1.0, 1.5 and 3.0 μm) and separations (10 and 30 μm) were successfully laser patterned, using a nanosecond pulsed fibre laser, on the surface of 10 mol% ceria-stabilized zirconia and alumina (10CeTZP-Al2O3) nanocomposite discs (diameter: 10 mm; thickness: 1.5 mm). The patterned surfaces and the in vitro biological response of osteoblasts (SAOS-2) towards them were thoroughly analysed. In terms of composition, the laser treatment was found to cause superficial monoclinic-tetragonal zirconia phase transformation and alumina evaporation. In vitro, the most effective grid configuration for osseous differentiation was found to be 1.5 μm groove depth and 10 μm groove separation, and confocal microscopy revealed that the cells show a tendency to be sorted as groove depth increases. It is thought that custom-made patterns could be produced to guide cell attachment in vivo, which could favour implant integration and reduce healing time.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Mechanical Engineering and Industrial Systems, Nanoker Research, Universidad de Oviedo
Contributors: Goyos-Ball, L., Prado, C., Díaz, R., Fernández, E., Ismailov, A., Kumpulainen, T., Levänen, E., Torrecillas, R., Fernández, A.
Pages: 9472-9478
Publication date: Jun 2018
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Ceramics International
Volume: 44
Issue number: 8
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.888 SNIP 1.279
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Alumina, Cellular arrangement, Ceramic nanocomposite, Laser patterning, Osseous differentiation, Zirconia
Source: Scopus
Source ID: 85042621677

Research output: Contribution to journal