Approximate Controllability for Navier–Stokes Equations in 3D Rectangles Under Lions Boundary Conditions

The 3D Navier–Stokes system, under Lions boundary conditions, is proven to be approximately controllable provided a suitable saturating set does exist. An explicit saturating set for 3D rectangles is given.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mathematics, Johann Radon Institute for Computational and Applied Mathematics
Contributors: Phan, D., Rodrigues, S. S.
Number of pages: 26
Pages: 351-376
Publication date: Jul 2019
Peer-reviewed: Yes
Early online date: 10 Jul 2018

Publication information

Journal: Journal of Dynamical and Control Systems
Volume: 25
Issue number: 3
ISSN (Print): 1079-2724
Ratings: 
  • Scopus rating (2019): CiteScore 2.2 SJR 0.487 SNIP 1.178
Original language: English
ASJC Scopus subject areas: Control and Systems Engineering, Algebra and Number Theory, Numerical Analysis, Control and Optimization
Keywords: Approximate controllability, Navier–Stokes equations, Saturating set
Source: Scopus
Source ID: 85049619310

Research output: Contribution to journalArticleScientificpeer-review

Integral kernels for k-hypermonogenic functions

We consider the modified Cauchy–Riemann operator (Formula presented.) in the universal Clifford algebra (Formula presented.) with the basis (Formula presented.). The null-solutions of this operator are called k-hypermonogenic functions. We calculate the k-hyperbolic harmonic fundamental solutions, i.e. solutions to (Formula presented.), and use these solutions to find k-hypermonogenic kernels for a Cauchy-type integral formula in the upper half-space.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mathematics, University of Helsinki
Contributors: Vuojamo, V., Eriksson, S.
Number of pages: 12
Pages: 1-12
Publication date: 2017
Peer-reviewed: Yes
Early online date: 21 Feb 2017

Publication information

Journal: Complex Variables and Elliptic Equations
Volume: 62
Issue number: 9
ISSN (Print): 1747-6933
Ratings: 
  • Scopus rating (2017): CiteScore 0.73 SJR 0.616 SNIP 1.018
Original language: English
ASJC Scopus subject areas: Analysis, Numerical Analysis, Computational Mathematics, Applied Mathematics
Keywords: Cauchy integral formula, Clifford algebra, hyperbolic Laplace–Beltrami, k-hyperbolic harmonic, k-hypermonogenic

Bibliographical note

EXT="Eriksson, Sirkka-Liisa"

Source: Scopus
Source ID: 85013192611

Research output: Contribution to journalArticleScientificpeer-review

Simulation of photon-photon resonance enhanced direct modulation bandwidth of DFB lasers

Simulations and experimental results of high-frequency photon-photon resonance are used to examine the possibilities to extend the direct modulation bandwidth in dual-mode distributed feedback lasers beyond the conventional limit set by the carrier-photon resonance.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, Brighterwave Inc, Politecnico di Torino
Contributors: Dumitrescu, M., Uusitalo, T., Virtanen, H., Laakso, A., Bardella, P., Montrosset, I.
Number of pages: 2
Pages: 147-148
Publication date: 17 Aug 2016

Host publication information

Title of host publication: 16th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2016
Publisher: IEEE
ISBN (Electronic): 978-1-4673-8603-6
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Modelling and Simulation, Numerical Analysis

Bibliographical note

EXT="Laakso, A."

Source: Scopus
Source ID: 84987641496

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

Simulation studies of DFB laser longitudinal structures for narrow linewidth emission

Simulation studies targeting high-power narrow-linewidth emission from DFB lasers are presented. The linewidth and output power calculations take into account the mirror losses, including the grating and the facets, as well as spontaneous emission noise, effective refractive index, power and carrier density variations inside the cavity. The longitudinal power and carrier density distributions have been evaluated and their effects on longitudinal spatial hole burning and possible side mode lasing are discussed.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications
Contributors: Virtanen, H., Uusitalo, T., Dumitrescu, M.
Number of pages: 2
Pages: 153-154
Publication date: 17 Aug 2016

Host publication information

Title of host publication: 16th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2016
Publisher: IEEE
ISBN (Electronic): 9781467386036
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Modelling and Simulation, Numerical Analysis
Source: Scopus
Source ID: 84987641768

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

Transverse structure optimization of laterally-coupled ridge waveguide DFB lasers

A new figure of merit for single transverse mode operation and an accurate procedure for calculating the coupling coefficient in distributed feedback lasers with laterally-coupled ridge waveguide surface grating structures are introduced. Based on the difference in optical confinement between the pumped and un-pumped regions in the transverse plane, the single transverse mode figure of merit is effective and easy to calculate, while the improved coupling coefficient calculation procedure gives experimentally confirmed better results than the standard calculation approaches.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications
Contributors: Uusitalo, T., Virtanen, H., Dumitrescu, M.
Number of pages: 2
Pages: 79-80
Publication date: 17 Aug 2016

Host publication information

Title of host publication: 16th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2016
Publisher: IEEE
Article number: 7547038
ISBN (Electronic): 9781467386036
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Modelling and Simulation, Numerical Analysis
Source: Scopus
Source ID: 84987653468

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

Geometric solution strategy of Laplace problems with free boundary

This paper introduces a geometric solution strategy for Laplace problems. Our main interest and emphasis is on efficient solution of the inverse problem with a boundary with Cauchy condition and with a free boundary. This type of problem is known to be sensitive to small errors. We start from the standard Laplace problem and establish the geometric solution strategy on the idea of deforming equipotential layers continuously along the field lines from one layer to another. This results in exploiting ordinary differential equations to solve any boundary value problem that belongs to the class of Laplace's problem. Interpretation in terms of a geometric flow will provide us with stability considerations. The approach is demonstrated with several examples.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research area: Electromagnetics, Department of Electrical Engineering
Contributors: Poutala, A., Tarhasaari, T., Kettunen, L.
Number of pages: 24
Pages: 723-746
Publication date: 9 Mar 2016
Peer-reviewed: Yes

Publication information

Journal: International Journal for Numerical Methods in Engineering
Volume: 105
Issue number: 10
ISSN (Print): 0029-5981
Ratings: 
  • Scopus rating (2016): CiteScore 2.64 SJR 1.751 SNIP 1.608
Original language: English
ASJC Scopus subject areas: Engineering(all), Applied Mathematics, Numerical Analysis
Keywords: Bernoulli problem, Cauchy condition, Differential equations, Elliptic partial differential equations, Equipotential layers, Field lines, Inverse problem, Laplace problem, Mean curvature, Shape design
Source: Scopus
Source ID: 84956739407

Research output: Contribution to journalArticleScientificpeer-review

Target tracking via combination of particle filter and optimisation techniques

Particle filters (PFs) have been used for the nonlinear estimation for a number of years. However, they suffer from the impoverishment phenomenon. It is brought by resampling which intends to prevent particle degradation, and therefore becomes the inherent weakness of this technique. To solve the problem of sample impoverishment and to improve the performance of the standard particle filter we propose a modification to this method by adding a sampling mechanism inspired by optimisation techniques, namely, the pattern search, particle swarm optimisation, differential evolution and Nelder-Mead algorithms. In the proposed methods, the true state of the target can be better expressed by the optimised particle set and the number of meaningful particles can be grown significantly. The efficiency of the proposed particle filters is supported by a truck-trailer problem. Simulations show that the hybridised particle filter with Nelder-Mead search is better than other optimisation approaches in terms of particle diversity.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Signal Processing, University of Toledo, Bowling Green State University
Contributors: Hosseini, S. S. S., Jamali, M. M., Astola, J., Gorsevski, P. V.
Number of pages: 18
Pages: 212-229
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: International Journal of Mathematical Modelling and Numerical Optimization
Volume: 7
Issue number: 2
ISSN (Print): 2040-3607
Ratings: 
  • Scopus rating (2016): CiteScore 2.6 SJR 0.351 SNIP 0.935
Original language: English
ASJC Scopus subject areas: Numerical Analysis, Modelling and Simulation, Applied Mathematics
Keywords: Differential evolution, Nelder-Mead, Particle filter, Particle swarm optimisation, Pattern search, PSO, Target tracking
Source: Scopus
Source ID: 84990239582

Research output: Contribution to journalArticleScientificpeer-review

A comparative analysis of multidimensional features of objects resembling sets of graphs

In the present paper, we introduce a notion of a style representing abstract, complex objects having characteristics that can be represented as structured objects. Furthermore, we provide some mathematical properties of such styles. As a main result, we present a novel approach to perform a meaningful comparative analysis of such styles by defining and using graph-theoretic measures. We compare two styles by comparing the underlying feature sets representing sets of graph structurally. To determine the structural similarity between the underlying graphs, we use graph similarity measures that are computationally efficient. More precisely, in order to compare styles, we map each feature set to a so-called median graph and compare the resulting median graphs. As an application, we perform an experimental study to compare special styles representing sets of undirected graphs and present numerical results thereof.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: TU Vienna, Department of Biostatistics, Visiting Graduate Student in Department of Urban Design and Planning, University of Washington, Seattle, USA 1.1.2012-15.6.2012 (12.9.2011 alkaen), University of Veterinary Medicine Vienna
Contributors: Dehmer, M., Emmert-Streib, F., Gesell, T.
Number of pages: 15
Pages: 221-235
Publication date: 15 Feb 2008
Peer-reviewed: Yes

Publication information

Journal: Applied Mathematics and Computation
Volume: 196
Issue number: 1
ISSN (Print): 0096-3003
Ratings: 
  • Scopus rating (2008): SJR 0.778 SNIP 0.983
Original language: English
ASJC Scopus subject areas: Applied Mathematics, Computational Mathematics, Numerical Analysis
Keywords: Classification, Object comparison, Similarity, Structural similarity, Structured objects
Source: Scopus
Source ID: 38049038817

Research output: Contribution to journalArticleScientificpeer-review

Structural similarity of directed universal hierarchical graphs: A low computational complexity approach

In the present paper we mainly introduce an efficient approach to measure the structural similarity of so called directed universal hierarchical graphs. We want to underline that directed universal hierarchical graphs can be obtained from generalized trees which are already introduced. In order to classify these graphs, we state our novel graph similarity method. As a main result we notice that our novel algorithm has low computational complexity.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: University of Veterinary Medicine Vienna, Stowers Institute for Medical Research
Contributors: Dehmer, M., Emmert-Streib, F.
Number of pages: 14
Pages: 7-20
Publication date: 1 Dec 2007
Peer-reviewed: Yes

Publication information

Journal: Applied Mathematics and Computation
Volume: 194
Issue number: 1
ISSN (Print): 0096-3003
Ratings: 
  • Scopus rating (2007): SJR 0.869 SNIP 1.113
Original language: English
ASJC Scopus subject areas: Applied Mathematics, Computational Mathematics, Numerical Analysis
Keywords: Complexity analysis, Graph classes, Graph classification, Graph similarity, Hierarchical models, Structured objects
Source: Scopus
Source ID: 35648968162

Research output: Contribution to journalArticleScientificpeer-review

Information theoretic measures of UHG graphs with low computational complexity

We introduce a novel graph class we call universal hierarchical graphs (UHG) whose topology can be found numerously in problems representing, e.g., temporal, spacial or general process structures of systems. For this graph class we show, that we can naturally assign two probability distributions, for nodes and for edges, which lead us directly to the definition of the entropy and joint entropy and, hence, mutual information establishing an information theory for this graph class. Furthermore, we provide some results under which conditions these constraint probability distributions maximize the corresponding entropy. Also, we demonstrate that these entropic measures can be computed efficiently which is a prerequisite for every large scale practical application and show some numerical examples.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Stowers Institute for Medical Research, University of Veterinary Medicine Vienna
Contributors: Emmert-Streib, F., Dehmer, M.
Number of pages: 12
Pages: 1783-1794
Publication date: 15 Jul 2007
Peer-reviewed: Yes

Publication information

Journal: Applied Mathematics and Computation
Volume: 190
Issue number: 2
ISSN (Print): 0096-3003
Ratings: 
  • Scopus rating (2007): SJR 0.869 SNIP 1.113
Original language: English
ASJC Scopus subject areas: Applied Mathematics, Computational Mathematics, Numerical Analysis
Keywords: Entropy, Graph classes, Graph measures, Hierarchical graphs, Information theory
Source: Scopus
Source ID: 34250623666

Research output: Contribution to journalArticleScientificpeer-review

Comparing large graphs efficiently by margins of feature vectors

Measuring the structural similarity of graphs is a challenging and outstanding problem. Most of the classical approaches of the so-called exact graph matching methods are based on graph or subgraph isomorphic relations of the underlying graphs. In contrast to these methods in this paper we introduce a novel approach to measure the structural similarity of directed and undirected graphs that is mainly based on margins of feature vectors representing graphs. We introduce novel graph similarity and dissimilarity measures, provide some properties and analyze their algorithmic complexity. We find that the computational complexity of our measures is polynomial in the graph size and, hence, significantly better than classical methods from, e.g. exact graph matching which are NP-complete. Numerically, we provide some examples of our measure and compare the results with the well-known graph edit distance.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: University of Veterinary Medicine Vienna, Stowers Institute for Medical Research
Contributors: Dehmer, M., Emmert-Streib, F.
Number of pages: 12
Pages: 1699-1710
Publication date: 15 May 2007
Peer-reviewed: Yes

Publication information

Journal: Applied Mathematics and Computation
Volume: 188
Issue number: 2
ISSN (Print): 0096-3003
Ratings: 
  • Scopus rating (2007): SJR 0.869 SNIP 1.113
Original language: English
ASJC Scopus subject areas: Applied Mathematics, Computational Mathematics, Numerical Analysis
Keywords: Degree vectors, Directed and undirected graphs, Graph similarity, Similarity measures
Source: Scopus
Source ID: 34248165422

Research output: Contribution to journalArticleScientificpeer-review

Topological mappings between graphs, trees and generalized trees

We present novel topological mappings between graphs, trees and generalized trees that means between structured objects with different properties. The two major contributions of this paper are, first, to clarify the relation between graphs, trees and generalized trees, a graph class recently introduced. Second, these transformations provide a unique opportunity to transform structured objects into a representation that might be beneficial for a processing, e.g., by machine learning techniques for graph classification.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Stowers Institute for Medical Research, Universität Rostock, Albert
Contributors: Emmert-Streib, F., Dehmer, M.
Number of pages: 8
Pages: 1326-1333
Publication date: 15 Mar 2007
Peer-reviewed: Yes

Publication information

Journal: Applied Mathematics and Computation
Volume: 186
Issue number: 2
ISSN (Print): 0096-3003
Ratings: 
  • Scopus rating (2007): SJR 0.869 SNIP 1.113
Original language: English
ASJC Scopus subject areas: Applied Mathematics, Computational Mathematics, Numerical Analysis
Keywords: Applied graph theory, Graph transformation, Hierarchical graphs
Source: Scopus
Source ID: 33947616843

Research output: Contribution to journalArticleScientificpeer-review

A similarity measure for graphs with low computational complexity

We present and analyze an algorithm to measure the structural similarity of generalized trees, a new graph class which includes rooted trees. For this, we represent structural properties of graphs as strings and define the similarity of two graphs as optimal alignments of the corresponding property stings. We prove that the obtained graph similarity measures are so called Backward similarity measures. From this we find that the time complexity of our algorithm is polynomial and, hence, significantly better than the time complexity of classical graph similarity methods based on isomorphic relations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Technical University Darmstadt, Stowers Institute for Medical Research
Contributors: Dehmer, M., Emmert-Streib, F., Kilian, J.
Number of pages: 13
Pages: 447-459
Publication date: 1 Nov 2006
Peer-reviewed: Yes

Publication information

Journal: Applied Mathematics and Computation
Volume: 182
Issue number: 1
ISSN (Print): 0096-3003
Ratings: 
  • Scopus rating (2006): SJR 0.809 SNIP 1.217
Original language: English
ASJC Scopus subject areas: Applied Mathematics, Computational Mathematics, Numerical Analysis
Keywords: Computational complexity, Dynamic programming, Graph similarity, Graph theory
Source: Scopus
Source ID: 33750819438

Research output: Contribution to journalArticleScientificpeer-review