Research Institute of Mathematics and Computing Science

University of Groningen

FACULTY OF M ATHEMATICS AND NATURAL S CIENCES

Research Institute of Mathematics and Computing Science

ANNUAL REPORT 2008

IWI Annual Report

Introduction Some statistics In 2008 the institute comprised 31 tenured scientific staff members and seven support staff members. 62 PhD candidates were enrolled, including 2 Ubbo Emmius scholarships for students from abroad, 18 PhD positions funded by the Netherlands Organisation for Scientific Research (NWO) and 12 PhD positions funded by the European Union, industry or other external funding. Nine postdocs worked at the institute of whom four funded by NWO. 17 doctoral dissertations were successfully defended. A total of 115 journal papers, 6 contributions to books, 65 refereed contributions to conference proceedings and 25 other professional publications were published. Members of the institute served as editors-in-chief, associated editors or members of the editorial boards of 32 international journals and book series. The institute was visited by 86 foreign scientists. Organisation In January the research groups: Applied Analysis and Systems and Control were joined under the name: Systems, Control and Applied Analysis. That same month the name of the research group: Dynamical Systems and Analysis was changed into: Dynamical Systems and Mathematical Physics. Personalia In June, Ernst Wit was appointed as Chair of Statistics and Probability. Before his appointment he was a professor of statistics and director of the Medical Statistics Unit at Lancaster University. He obtained his Ph.D. in Philosophy from the Pennsylvania State University and his Ph.D. in Statistics from the University of Chicago. His first academic appointment was as a lecturer at the University of Glasgow. He has interest in algebraic statistics, statistical bioinformatics, medical statistics and normative reasoning under uncertainty.

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In August, Edwin van den Heuvel was appointed honorary professor in statistics for life sciences. He is currently also the departmental head of the Statistical Department of Schering-Plough at Oss, The Netherlands. Before these appointments he was a consultant at the Institute for Business and Industrial Statistics of the University of Amsterdam. He obtained his Ph.D. in mathematical statistics at the University of Amsterdam. He has interest in variance component models, non-linear mixed models and measurement reliability. Prof.dr. H.W. Broer Scientific Director September 2009

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Contents Introduction

1

Governing body and support staff

4

Address information

5

List of scientific programmes and tenured scientific staff

6

Research schools

8

1. Algebra

11

2. Computational Mechanics and Numerical Mathematics

17

3. Dynamical Systems & Mathematical Physics

27

4. Geometry

47

5. Probability and Statistics

53

6. Systems, Control and Applied Analysis

61

7. Distributed Systems and Software Engineering

77

8. Fundamental Computing Science

89

9. Intelligent Systems

93

10. Scientific Visualization and Computer Graphics

111

Colloquium Computing Science 2008 – List of Speakers

127

Colloquium Mathematics 2008 – List of Speakers

131

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Governing body and support staff 2008 Scientific director Prof.dr.sc.techn. N. Petkov Advisory council Prof.dr. W.C. Nieuwpoort – chairman (emeritus, professor of theoretical chemistry, RUG) Prof.dr. J.B.T.M. Roerdink (professor of computing science, RUG) Prof.dr. H.W. Broer (professor of mathematics, RUG) Prof.dr. H.A. van der Vorst (professor of mathematics, University of Utrecht) Management team Prof.dr.sc.techn. N. Petkov (director) J. de Jong-Schlukebir (controller) A. Navest (controller)

fte 0.6 0.5 0.5

Administrative staff

4

Secretaries E.D. Elshof D.J. Hansen I. Schelhaas

1.0 0.8 0.8

Secretary of Research Institute H. Steenhuis

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Address: Post: P.O. Box 407 9700 AK Groningen Visitors: Nijenborgh 9 9747 AG Groningen The Netherlands Tel : Fax : email : www :

050-3633973 050-3633800 [email protected], [email protected] http://www.cs.rug.nl, http://www.math.rug.nl

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List of scientific programmes and tenured scientific staff Mathematics page Programme 1

: Prof.dr. J. Top

Algebra

11

Programme 2

: Numerical Mathematics

Computational Mechanics and

17

Dr. K.W.A. Lust Prof.dr. A.E.P. Veldman Dr.ir. R.W.C.P. Verstappen Dr.ir. F.W. Wubs

6

Programme 3

:

Dynamical Systems & Mathematical Physics Prof.dr. H.W. Broer Dr. C. Külske Prof.dr.ir. H.S.V. de Snoo Prof.dr. A.C.D. van Enter Prof.dr. H. Waalkens Prof.dr. E. Verbitskiy

27

Programme 4

:

Geometry Prof.dr. G. Vegter

47

Programme 5

:

Probability and Statistics Prof.dr. E. Wit Prof.dr. E.R. van den Heuvel

53

Programme 6

:

Systems, Control and Applied Analysis Prof.dr. A.J. van der Schaft Dr. K. Camlibel Prof.dr. H.L. Trentelman

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Computing Science

Programme 7

:

Distributed Systems and Software Engineering Dr. P. Avgeriou Prof.dr. M. Aiello

77

Programme 8

:

Fundamental Computing Science Prof.dr. W.H. Hesselink Prof.dr. G.R. Renardel de Lavalette

89

Programme 9

:

Intelligent Systems Dr. M. Biehl Prof.dr.sc.techn. N. Petkov Dr. M.H.F. Wilkinson Dr. J.H. van Hateren

93

Programme 10

:

Scientific Visualization and Computer Graphics Dr. H. Bekker Prof.dr. J.B.T.M. Roerdink Prof.dr. A. Telea Dr. T. Isenberg

111

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Research schools Researchers of the IWI participate in the following research schools: 1. Mathematical Research Institute (MRI) Coordinating institution: Director: Participating IWI programme(s):

University of Utrecht Prof.dr. D. Siersma 1, 2, 3, 5

2. Dutch Institute of Systems and Control (DISC) Coordinating institution: Director: Participating IWI programme(s):

Delft University of Technology Prof.dr.ir. P.M.J. van den Hof 4

3. The J.M. Burgers Centre for Fluid Dynamics Coordinating institution: Director: Participating IWI programme(s):

Delft University of Technology Prof.dr.ir. G. Ooms 6

4. Dutch Graduate School in Logic (LOGICA) Coordinating institution: Director: Participating IWI programme(s):

University of Utrecht Prof.dr. A. Visser 8

5. Institute for Programming Research and Algorithmics (IPA) Coordinating institution: Director: Participating IWI programme(s):

University of Eindhoven Prof.dr. M.T. de Berg 8

6. Advanced School of Computing and Imaging (ASCI) Coordinating institution: Director: Participating IWI programme(s):

Delft University of Technology Prof.dr.ir. A.W.M. Smeulders 9, 10

7. School of Behavioral and Cognitive Neurosciences (BCN) Coordinating institution: Director: Participating IWI programme(s):

8

University of Groningen Prof.dr. G.J. ter Horst 9, 10

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1.

Algebra

Group leader: Prof.dr. J. Top

Tenured staff (IWI members) Prof.dr. J. Top

source RuG

fte 1.0

Emeritus Prof.dr. M. van der Put

source RuG

fte 0.0

Basque University of Bilbao

1.0

NWO

1.0

RuG

1.0

RuG

1.0

RuG

1.0

Postdocs J. González Sánchez

PhD students L. Taelman (supervisors: van der Put, Top) C. Poirier (supervisors: Top) S. Meagher (supervisor: Top) Nguyen An Khuong (supervisors: van der Put, Top) Guests Masa-Hiko Saito, Kobe, Japan M. Barakat, Aachen, Germany A. Garbanati, Milano, Italy A. Garnier, Toulouse, France

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1.1

Research Program

1. Number theory and Algebraic geometry. Arithmetic properties of elliptic curves over a number field or a function field, like the rank of the Mordell-Weil group, the conductor, associated Galois representations, are the subject of study. Also work is done on applications to Diophantine equations, coding theory and arithmetic algebraic geometry; in particular a study of the number of rational points on curves over finite fields. The history and the algebraic geometry of various series of models of surfaces is studied. 2. Ordinary differential equations. This concerns algebraic, analytic (e.g., multisummability) and algorithmic aspects of linear differential and linear difference equations; differential Galois theory and its applications, in particular to symbolic (algorithmic) solvability of equations; (Lie) symmetries of non-linear differential equations; isomonodromy and the six Painlevé equations. 3. Rigid analytic geometry. In particular: Abhyankar’s conjecture, Mumford curves and applications to arithmetic algebraic geometry. 4. Drinfeld modules and t-motives. This concerns a theory in positive characteristic which has similarities with the theory of elliptic curves, respectively motives. The motivic Galois groups that occur here are related to the differential Galois groups.

1.2

Overview of scientific results

ad (1) S. Meagher Worked in 2008 on a project (concerning curves of genus 3) suggested by J.-P. Serre in two privately circulating letters to Jaap Top. This led to a precise, algebraic formulation of a criterion for a principally polarized abelian threefold over a given field, to be a jacobian. The results became part of Meagher’s PhD thesis, which he successfully defended in September. Meagher presented lectures at the national intercity seminar and in Sydney university, Australia. With Jaap Top he started rewriting a second part of his thesis, dealing with twists of curves over finite fields, which will become a joint paper. J. Top With M. van der Put and I. Polo Blanco, Top continued research on ruled surfaces of degree 4. A joint paper, including historical aspects of the topic as well as a modern algebraic geometric perspective, is expected to be finished in the spring of 2009. Top and Polo Blanco also submitted a joint paper concerning parametrizations of cubic surfaces, a subject with applications in Computer Aided Geometric 12

IWI Annual Report

Design. Another paper with Polo Blanco, on cubic surfaces over the real numbers, appeared in the Canadian Math. Bull. The paper with master’s student Frank de Zeeuw, on a new method for proving results on MordellWeil ranks of certain elliptic surfaces, will appear in the Rocky Mountain Journal of Mathematics. Top published a joint paper with N. Yui on variants of the congruent number problem, in a MSRI book edited by J.P. Buhler and P. Stevenhagen. Top gave invited lectures in Göttingen in June, in Oldenburg in november and in Banff in December. With T. Dokchitser (Durham, UK) Top has applied methods of T. Shioda in order to compute MordellWeil ranks of certain elliptic surfaces. A joint publication on this is in preparation, and extensions of these results are the topic of Bas Heijne’s PhD project funded by NWO during the period 2008-2011. The first examples and results in this project were already obtained by B. Heijne in 2008, and a text on it is in preparation. Top also initiated a collaboration with T. Kodama and T. Washio on maximal hyperelliptic curves over finite fields. A joint paper was submitted to the journal Finite Fields and Their Applications, and it will appear in 2009. Heijne and Top proved results on binary cyclic selfdual codes. A joint paper was submitted. Top served on one of the panels of the National Science Foundation (January 2008).

ad (2) Khuong An Nguyen Jointly with M. van der Put and J. Top, Khuong finished the complete classification of the algebraic subgroups of GL2 (C). A joint paper of the results appeared in Indagationes Mathematicae. Khuong completed the explicit realizations of all these algebraic subgroups as Galois groups of linear differential equations of order 2. He successfully defended his Ph.D. thesis in October.

M. van der Put Van der Put published two joint papers on linear differential equations, one with B.L.J. Braaksma and one with M. Reversat. The Ph.D. student C. Poirier finished her PhD thesis with Van der Put on the subject Geometric Langlands Correspondence. The joint work with Masa-Hiko Saito on moduli spaces, Riemann Hilbert correspondence and Painlevé equations continued throughout 2008. Van der Put presented invited lectures in Oberwolfach, Toulouse, and at national intercity seminars. Van der Put became one of the promotors of Diego Napp Avelli, after understanding the precise algebraic structure of Diego’s study of implementability of behaviours (systems theory). He also took over, in consultance with Heide Gluessing and Ruth Curtain, the supervision of PhD student T. Tsang. Both Tsang and Napp Avelli successfully defended their thesis in 2008. 13

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1.3

Research subjects

B. Heijne: elliptic surfaces. Nguyen An Khuong: algebraic aspects of differential equations. S. Meagher: curves over finite fields. C. Poirier: Geometric Langlands. M. van der Put: rigid analytic geometry, Drinfeld modules, differential equations, difference equations, computer algebra. J. Top: arithmetical algebraic geometry, in particular: elliptic curves and surfaces, curves over finite fields, Galois representations, number theory, Drinfeld modules. T. Tsang: convolutional codes.

1.4

Publications Dissertations – D. Napp Avelli, An algebraic approach to multidimensional behaviors, promotores: M. van der Put en H. Trentelman, Faculty of Mathematics and Natural Sciences, University of Groningen, 18 januari 2008, 126 pages. – C. Poirier, On geometric Langlands theory and stacks, promotores: M. van der Put en M. Reversat, Faculty of Mathematics and Natural Sciences, University of Groningen, 16 mei 2008, 196 pages. – F.L. Tsang, Skew rings, convolutional codes and discrete systems, promotor: M. van der Put, copromotor: H. Gluesing-Luerssen, Faculty of Mathematics and Natural Sciences, University of Groningen, 23 juni 2008, 159 pages. – S. Meagher, Twists of genus three curves and their Jacobians, promotor: J. Top, Faculty of Mathematics and Natural Sciences, University of Groningen, 26 september 2008, 67 pages. – N.A. Khuong, A modern perspective on Fano’s approach to linear differential equations, promotores: M. van der Put en J. Top, Faculty of Mathematics and Natural Sciences, University of Groningen, 17 oktober 2008, 101 pages. Contributions to books – J. Top and N. Yui, Congruent number problems and their variants, in Algorithmic Number Theory (J.P. Buhler and P. Stevenhagen, eds.), MSRI publications 44, Cambridge University Press, 2008, 613-640.

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Articles in scientific journals – B.L.J. Braaksma and M. van der Put, Singular Linear Differential Equations in Two Variables, Funkc. Ialaj Ekvac.-Ser. Internacia, 51 (3), 2008, 459–462. – K.A. Nguyen, M. van der Put and J. Top, Algebraic subgroups of GL2 (C), Indag. Mathem., N.S., 19, 2008, 287–297. – I. Polo-Blanco and J. Top, Explicit real cubic surfaces, Canad. Math. Bull., 51 (1), 2008, 125–133. – M. van der Put and M. Reversat, A local-global problem for linear differential equations, Pacific J. Math., 238 (1), 2008, 171–199. Other publications – L. Danes en J. Top, De fascinerende wereld van de priemgetalle, aflevering van het tv-programma Adams Appel (programmamaker: Koen de Koning), TV-Noord, 2007. Ziehttp://www.rug.nl/Corporate/nieuws/adamsAppel/archief2007/afl14 – J. Top en J. Top, Totaal geflipt, Scholierenmaandblad Pythagoras, 47 (5), 2008, 22-23. – J. Top, zeven bijdragen in de Wetenschappelijke scheurkalender 2009, Uitgave Natuur Wetenschap Techniek, Diemen: Veen magazines, 2008. – J. Top, Van de Vakgroep, Perio∗diek, jaargang 2008, no. 2, p. 6.

1.5

External funding and collaboration

External funding NWO. This concerns the Ph.D. position of Bas Heijne (4 years, all funded by NWO). Moreover, Top assisted M. Afzal Soomro (lecturer at Quaid-E-Awam university in Nawabshah, Pakistan)) in successfully applying for a grant from the Faculty Development Programme of his university. The grant will be used to fund his stay in Groningen in the next four years, where he intends to work on a PhD project supervised by Top. External collaboration See 1.2. Also, Top and A. Stein (Oldenburg) consider possibilities of joint Oldenburg-Groningen projects. In particular, this will involve a joint supervision of PhD student Vivija Ceprkalo (2009– 2012). 15

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1.6

Further information

J. Top was responsible for the satellites committee of the fifth European Congress of Mathematics (Amsterdam, 2008). In 2008, J. Top was a member of several PhD thesis evaluation committees outside Groningen. This concerned students of Van der Geer (Amsterdam), Beukers (Utrecht), Reversat (Toulouse) and Edixhoven (Leiden). J. Top is involved in the European Community project GTEM (Galois Theories and Explicit Methods), in the North German Algebraic Geometry Seminars (NoGAGS, a collaboration between Göttingen, Hannover, Berlin, Hamburg, Bremen and Groningen), and in the NWO-cluster DIAMANT.

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2.

Computational Mechanics and Numerical Mathematics

Group leader: Prof.dr. A.E.P. Veldman

Tenured staff (IWI members) Dr.ir. K.W.A. Lust (till 15-07-2008) Prof.dr. A.E.P. Veldman Dr.ir. R.W.C.P. Verstappen Dr.ir. F.W. Wubs

source RuG RuG RuG RuG

fte 1.0 1.0 1.0 1.0

Postdocs Dr.ir. R. Luppes

STW, CSA

0.5

ECN

1.0

NWO-SWON

1.0

UE bursaal

1.0

RuG

1.0

NWO-ALW

1.0

STW

1.0

PhD students Ir. H.A. Bijleveld (since 1-4-2008) (supervisor: Veldman) Ir. J.A. Helder (supervisor: Verstappen) H. Kırbas¸ MSc (since 16-06-2008) (supervisors: Verstappen, Wubs) Ir. G. Rozema (till 30-11-2008) (supervisor: Veldman) J. Thies, MSc (supervisor: Wubs) Ir. R. Wemmenhove (till 31-05-2008) (supervisor: Veldman)

Foreign guests Prof.dr. I. Ania, UNAM, Mexico City, Mexico Dr. T. Finnigan, Chevron Energy Technology, San Ramon, Ca., USA Prof. D.F. Garcia Nocetti, UNAM, Mexico City, Mexico Dr. A. Gorobets, Universitat Politècnica de Catalunya, Barcelona, Spain (3 months) Dr. B. Iwanowski, FORCE Technology, Oslo, Norway Dr. R. Seah, Chevron-Texaco, San Ramon, Ca., USA Dr. F.X. Trias Miquel, Universitat Politècnica de Catalunya, Barcelona, Spain (12 months)

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2.1

Research Program

With the continuing progress in numerical mathematics and computer technology, the impact of computer simulation on society is rapidly increasing. Our group specializes in the numerical simulation of fluid dynamics and transport phenomena (Computational Fluid Dynamics CFD). On the one hand research is focussed on basic advancement of numerical algorithms; on the other hand - through extensive cooperation with external research groups - these methods are made available to advance knowledge in other (applied) areas of science and technology. In-house developed software plays an essential role in the knowledge transfer. An animated impression of the group’s research can be found at the website www.math.rug.nl/∼veldman/cfd-gallery.html. Turbulent flow: Industrial simulation methods use turbulence models to keep computational effort within reasonable limits, but a price is paid in terms of accuracy. Thus research into higher-resolution methods, such as large-eddy simulation (LES) and direct numerical simulation (DNS) methods, is essential. The mathematical rationale behind our methods in this area focusses on preserving symmetry and conservation properties of the continuous flow equations. Free-surface flow: As a spin-off of our research on sloshing in spacecraft (with NLR), our main freesurface flow research concerns application in maritime and coastal engineering. Numerical simulation methods are developed to predict hydrodynamic wave loading on offshore platforms and coastal structures. Partners in this research are the Maritime Research Institute MARIN, TU Delft, Deltares and several offshore companies and shipyards. Basic tool is the in-house developed simulation method ComFLOW. Sparse-matrix solvers: The repeated solution of large systems of equations in most simulation methods makes the quest for improved matrix solvers another major research area. In-house a multilevel method (MRILU) has been developed. A major application area is the modelling of flow patterns in global ocean circulation (with UU-IMAU). Bifurcation analysis: Research focuses on numerical methods to investigate stability and bifurcation behaviour of large-scale problems from our other research applications. Of particular interest are the stability of the global ocean circulation and of coherent structures in turbulent flow. Cooperation is with the Institute for Marine and Atmospheric Research IMAU in Utrecht and the Dynamical Systems group in Groningen. Bio-medical fluid mechanics: Our bio-medical applications fit in the area of fluid-structure interaction. In cooperation with UMCG we study arterial blood flow in elastic vessels and its influence on 18

IWI Annual Report

atherosclerosis. Also the design of voice prostheses has our attention. Wind energy: A new application area concerns the aerodynamic design of turbine blades. The research builds on the boundary-layer interaction approach developed (more than) a decade ago. It is carried out in cooperation with the Energy Center Netherlands in Petten.

2.2


The central theme of the turbulent flow project is to model and simulate turbulence in such a way that the symmetry and conservation properties of the Navier-Stokes equations are preserved. The extention of symmetry-preserving discretization method to unstructured grids has been continued in cooperation with prof. Soria and dr. Trias (UPC, Barcelona). The symmetry-preserving regularization models have been studied both analytically (within the framework devised by Leray) and numerically (channel flow, differentially heated cavity). A procedure for determining the regularization parameter has been worked out in one spatial dimension. A large (20003 ) simulation of homogeneous, isotropic turbulence has been prepared. The STW-funded free-surface project (ComFLOW-2) on hydrodynamic wave loading was finished at the end of the year; the follow-up project (ComFLOW-3) has been granted already (see below). A highlight in 2008 was the PhD defense of Wemmenhove, whose research focussed on two-phase flow modelling during wave impact. Much emphasis was paid to the validation of the flow model, making use of extensive experiments carried out by MARIN (sloshing in LNG tanks; wave run-up against platforms, interactive buoy motion). The TU Delft contribution to the project focusses on zonal-modelling; in cooperation with Deltares, absorbing boundary conditions were developed. In November 2008 the official two-phase ComFLOW code has been released to the project participants. As a spin-off, in cooperation with the University of Manitoba (Canada) embryo development under microgravity was studied. In the research on sparse-matrix solvers a combination of MRILU is made with Trilinos to parallelize the ocean flow model. Speed-up tests were performed showing that a factor 20 out of 30 processors can be obtained on the national supercomputer Huygens. This code was used to generate and analyse the solution on a fine grid covering the Atlantic ocean. Figure 1 shows a plot of the surface flow. The results were the first with an implicit model on this fine scale. Wubs visited prof. Y. Notay from the Université Libre de Bruxelles, to study the application of aggregation multigrid to CFD problems. A combination of this multigrid type and MRILU as a smoother is considered for the ocean flow model. Moreover he visited prof. M. Bollhoeffer (Technical University Braunschweig) to develop an iterative solver for (Navier-)Stokes problems on a C-grid. Interest in 19

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this work was also shown by prof. I.S. Duff (Rutherford Appleton Laboratory, Harwell). Research is in progress on the feasibility of incorporating our ordering in his codes (e.g. MA57).

Figure 1: Visualization of the Gulf Stream: heat source of the Meridional Overturning Circulation (Jonas Thies).

In the numerical bifurcation analysis project, dr. Lust has left the department for a position at the University of Leuven (Belgium). Yet, his work on solutions of systems with continuous symmetry finds continuation with the arrival of a fresh PhD student (Kırbas¸). The emphasis is shifted towards the computation of coherent structures (unstable periodic solutions) in flow models in the turbulent regime. In this way a firm link with our turbulent flow research is established. The bio-medical fluid mechanics project studies cardio-vascular flow in elastic blood vessels and its relation with artherosclerosis (in cooperation with UMCG): an example of two-way fluid-structure interaction. An overall 0D model for the global blood circulation is being combined with a detailed 3D model of the flow in the arteria carotis. A highlight in this project is the numerical coupling approach, which is stable for all values of the physiological parameters. The new wind energy project has started in the spring of 2008 with a PhD student (Bijleveld) funded by ECN. It concerns the aerodynamic optimization of turbine blades. The simulation approach builds on viscous-inviscid bounday-layer interaction. The numerical coupling between boundary layer and inviscid outer flow is similar to that used in the bio-medical project mentioned above. 20

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2.3

Research subjects

H.A. Bijleveld: aerodynamic design of wind turbines. J.A. Helder: symmetry-preserving large-eddy simulation. H. Kırbas¸: exact coherent structures in shear flow. A.J.A. Kort: local grid refinement for the simulation of turbulent flow. R. Luppes: two-phase flow modelling for maritime and biological applications. K.W.A. Lust: numerical bifurcation analysis of large-scale systems, applications to fluid problems, lattice Boltzmann models and multiscale simulation techniques. G. Rozema: fluid-structure interaction in viscous flows, with cardio-vascular applications. J. Thies: spin-up in ocean climate models. A.E.P. Veldman: development of simulation methods for various flow problems – free-surface flow, boundary-layer flow, turbulence, biomedical fluid dynamics, industrial applications. R.W.C.P. Verstappen: development of simulation methods for turbulent flow (direct and large-eddy simulation DNS/LES). R. Wemmenhove: hydrodynamic wave loading on floating and moored offshore structures. F.W. Wubs: development of a multi-level ILU preconditioner for sparse systems; application to eigenvalue and continuation problems in the simulation of ocean circulation.

2.4

Publications Dissertations – R. Wemmenhove, Numerical simulation of two-phase flow in offshore environments, Promotor: A.E.P. Veldman; co-promotor: R. Luppes, Faculty of Mathematics and Natural Sciences, University of Groningen, May 16, 2008, 132 pages. Articles in scientific journals – E. Bernsen, H.A. Dijkstra and F.W. Wubs, A method to reduce the spin-up time of ocean models, Ocean Modelling, 20(4), 2008, 380–392. – J. Helder and R. Verstappen, On restraining convective subgrid-scale production in Burgers’ equation, Int. J. Num. Meth. Fluids, 56, 2008, 1289–1295. – C. Nouri, R. Luppes, A.E.P. Veldman, J.A. Tuszynski and R. Gordon, Rayleigh instability of the inverted one-cell amphibian embryo, Physical Biology, 5(1), 2008, article number 015006. – A.E.P. Veldman and K.-W. Lam, Symmetry-preserving upwind discretization of convection on non-uniform grids, Appl. Num. Math., 58, 2008, 1881–1891. 21

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– R. Verstappen, On restraining the production of small scales of motion in a turbulent channel flow, Comput. Fluids, 7(7), 2008, 887–897. Articles in conference proceedings – T. Bunnik, A.E.P. Veldman and P.R. Wellens, Prediction of extreme wave loads in focused wave groups, In: Proc. 18th Int. Symp. Offshore and Polar Eng. ISOPE2008, Vancouver, 6-11 July 2008, paper 2008-TPC-175, 7 pages. – G. Rozema, N.M. Maurits and A.E.P. Veldman, Linking an artery to the circulation: introducing a quasi-simultaneous coupling approach for partitioned systems in hemodynamics, In: Proc. 4th Europ. Cong. Medic. Biol. Eng. MBEC08, Antwerpen, 23-27 November 2008, CD-ROM, 4 pages. – F.X. Trias, R.W.C.P. Verstappen, M. Soria, A. Gorobets and A. Oliva, Regularization modelling of a turbulent differentailly heated cavity at Ra =1011 , In: G.G.M. Stoffels, T.H. van der Meer and A.A. van Steenhoven (eds.) Proc. 5th Europ. Thermal-Sciences Conf., Eurotherm 2008 CD-Rom, ISBN 976-90-386-1274-4, Eindhoven, The Netherlands (2008). – F.X. Trias, R. Verstappen, M. Soria and A. Oliva, Symmetry-preserving regularization modelling of a turbulent differentially heated cavity, In: Proc. Conf. LES in Science and Technology, Poznan, 21-22 April 2008. – R. Wemmenhove, R. Luppes and A.E.P. Veldman, Application of a VOF method to model compressible two-phase flow in sloshing tanks, In: Proc. 27th Conf. Offshore Mech. Arctic Eng. OMAE2008, Estoril, 16-19 June 2008, paper OMAE2008-57254, 10 pages. Other publications – Arthur Veldman, Rekenen aan monstergolven. ITW-nieuws, 14(1), 2008, 26–29.

2.5


External funding Most of our PhD projects are being funded externally from national and international resources: currently STW, NWO, ECN and CSA (Canadian Space Agency) (see also above). We summarize the new developments: – The Energy Center Netherlands ECN (Petten) started funding a PhD project on the aerodynamics of windturbine blades (320 kEuro, including consultancy). 22

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– The Dutch Technology Foundation STW has awarded a follow-up project on the impact of extreme waves on offshore platforms and coastal structures (projectleader Veldman). The project is embedded in the ComFLOW-3 joint industry project, coordinated by MARIN. It is the continuation of the successful ComFLOW-2 project (see below). The budget of the awarded project is over 1.5 MEuro. Our group participates with 2 PhD students and one 4-yr post-doc (RUG budget about 0.8 MEuro). – A contract (35 k$ for consultancy) has been signed with Hyundai Heavy Industries (Korea) for a one-year visit of one of their research scientists, to extend the ComFLOW simulation method with fluid-structure interaction (hydroelasticity). – The Distributed European Infrastructure for Supercomputing Applications (DEISA) Consortium (an EU FP6 Research Infrastructure Project) has awarded our proposal entitled Numerical simulation of turbulent flow past a circular cylinder at Re=20,000-200,000 within the DEISA Extreme Computing Initiative (DECI). The resource allocation for this project is equivalent to 700,000 CPU-core-hours. – The two-year (June 2007-June 2009) postdoctoral stay of Dr. F.X. Trias Miquel is funded by a Beatriu de Pinos grant from the Generalitat de Catalunya (Agència de Gestió d’Ajuts Universitaris i de Recerca AGAUR). – Wubs obtained 1.3 kE from Le Fonds de la Recherche Scientifique - FNRS for his visit to Brussels. Furthermore he received 0.8 kE from the Technical University Braunschweig for his visits and 1.1kE from the London Mathematical Society for his stay at the Rutherford Appleton Laboratory and presentations at English universities. Furthermore, he received a grant of 100.000 CPU hours on the dutch national computer facility Huygens.

Societal relevance As indicated above, most of our PhD and MSc research is carried out in physical or technological applications. The most important application areas are offshore and coastal safety, ocean modelling, health care and sustainable energy (for details see above). Close cooperation exists with several university research laboratories, with all Dutch Technological Research Centers (GTI’s), and with several industries: multi-nationals as well as small and medium enterprises (SME’s).

(Inter)national collaboration Various bilateral contacts exist with research groups inside and outside the Netherlands, leading to e.g. joint PhD projects, traineeships for our Masters’ students and/or to joint publications. – On an international scale, a major project is the cooperation with MARIN, TU Delft and around twenty offshore companies and ship yards throughout Europe, the America’s and Asia, 23

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which studies hydrodynamic wave loading (ComFLOW-2&3 Joint Industry Projects). In 2006 Deltares joined the project, extending its application area with coastal protection. Other free-surface flow projects are cooperations with NLR, ESTEC and NASA (on liquid sloshing in spacecraft), the University of Manitoba in Winnipeg (on embryo development in microgravity) and SCK-CEN in Mol (on spalation devices). A further, bio-medical, spin-off is the cooperation with UMCG on cardio-vascular fluid dynamics. – The research on ocean circulation models is carried out in close cooperation with the Institute for Marine and Atmospheric Research (IMAU) in Utrecht. Its parallelization aspects are studied in cooperation with Sandia National Laboratories (Albuquerque, USA). Further, the cooperation with Prof. Y. Notay from Numerical Analysis Group, Service de Métrologie Nucléaire, Université Libre de Bruxelles was continued. New collaboration was started with Prof. M. Bollhoeffer from the Technical University of Braunschweig and with Prof. I. Duff from the Rutherford Appleton Laboratory. – With the Energy Center Netherlands ECN (Petten) a project on the aerodynamical design of wind turbines was started. – Our turbulence research comprises cooperation with the Universitat Politècnica de Catalunya in Barcelona and the Universität der Bundeswehr München.

(Inter)national PhD committees Finally, the participation of group members in 4 defense committees outside IWI can be reported: Veldman UT, 2×RUG; Verstappen UPC Barcelona.

2.6

Further information

Veldman is a member of the Directory Staff of the National Aerospace Laboratory NLR (Amsterdam) as a scientific consultant. Moreover, he is a member of the Advisory Board of the Maritime Research Institute MARIN (Wageningen). Also, he has been elected chairman of the Dutch Contactgroup on Computational Fluid Dynamics. A one-day meeting (in Eindhoven) has been organized in cooperation with the Working Community on Scientific Computing. Further, he is on the editorial board of Computers and Fluids, Journal of Engineering Mathematics and Journal of Algorithms and Computational Technology. Veldman (co-)presented lectures at the 27th Conf. Offshore Mech. Arctic Eng. OMAE2008 (Estoril, P), 18th Symp. Offshore Polar Eng. ISOPE2008 (Vancouver, Ca), Europ. Comm. Comp. Meth. Appl. Sci. ECCOMAS2008 (Venezia, I), 4th Europ. Cong. Medic. Biol. Eng. MBEC08 (Antwerpen, B) and the IMPACT Colloquium (Enschede). Additionally, he was invited to provide a contribution to the 24

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Dutch NWO-NCF stand at the Int. Conf. High-Performance Computing SC08 (Austin, Tx, USA). Verstappen stayed three weeks at the Universitat Politècnica de Catalunya (Barcelona) as visiting professor; he gave four lectures at the Centre Tecnològic de Transferència de Calor (CTTC). Also, he was member of the PhD-committee of A. Gorobets (UPC,Barcelona). Further, he (co-)presented lectures at the 5th Europ. Thermal-Sciences Conf. Eurotherm 2008 (Eindhoven) and LES in Science and Technolgy (Poznan, PO). Wubs spent one month at the Universitë Libre (Brussels), three months at the Technical University of Braunschweig (TUB) and two months at the Rutherford Appleton Laboratory (Harwell/Oxford) as visiting scientist. He co-organized and chaired the Minisymposium ”Numerical dynamical systems analysis of nonlinear climate models” at ECCOMAS2008 (Venezia, I). Moreover, he was co-presenter of a talk in this minisymposium. Furthermore, presentations were given at the TUB, Brunel university and the University of Reading. Luppes’ research was partly funded by STW and by a contract from the Canadian Space Agency. He held a keynote lecture at ECCOMAS2008 (Venezia, I), and gave presentations at 27th Conf. Offshore Mechanics and Arctic Engineering OMAE2008 (Estoril, P) and the Microgravity Platform Meeting (Delft).

Figure 2: Our computeranimation of vortex shedding behind a circular cylinder was shown in the TV series “Numb3rs” (episode “Blowback”, original broadcast by CBS on 17 October 2008).

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3.

Dynamical Systems & Mathematical Physics

Group leader: Prof.dr. H.W. Broer

Tenured staff (IWI member) Prof.dr. H.W. Broer Prof.dr. A.C.D. van Enter Dr. C. Külske Prof.dr.ir. H.S.V. de Snoo Prof.dr. E. Verbitskiy Prof.dr. H. Waalkens

source RuG RuG RuG RuG NWO / Philips RuG

fte 1.0 1.0 1.0 1.0 0.1 1.0

Postdocs Dr. K. Efstathiou

RuG

1.0

RUG

1.0

RUG

1.0

Telekom

0.0

NWO

1.0

NWO

1.0

NWO

1.0

RuG

1.0

RuG

1.0

NWO

1.0

RuG

1.0

NWO

1.0

PhD students Sarma M. Chandramoulli (till November) (supervisor: Martens) V. Ermolaev (supervisor: Külske) S. Fleurke (supervisor: Külske) G. Iacobelli (supervisors: Külske and Van Enter) P. Hazard (till September) (supervisor: Martens) S. Holtman (supervisors: Broer and Vegter) O. Lukina (till October) (supervisor: Broer) A. Opuku (supervisor: Külske) M. Potoˇcný, (supervisor: Broer) W. Ruszel (supervisor: Van Enter) A. Sterk (supervisor: Broer)

27

IWI Annual Report Guests T. Kaper, Boston University, USA M. Levi, Pennsylvania State University, USA R.H. Cushman, University of Calgary, Canada D. Sadovski, Université du Littoral, Dunkerque, France S.J. van Strien, University of Warwick, UK F. den Hollander, Leiden Universiteit, The Netherlands F. Redig, Leiden University, The Netherlands H. Hanßmann, Universiteit Utrecht, The Netherlands M. Krupa, Radboud Universiteit Nijmegen, The Netherlands M. Toda, Nara Women University, Japan R. Hales, Bristol University, UK R. Schubert, Bristol University, UK A. Goussev, Bristol University, UK V. Derkach, Donetsk National University, Ukraine J. Behrndt, TU Berlin, Germany H. Woracek, TU Wien, Austria S. Hassi, University of Vaasa, Finland F. Szafraniec, Jagillonian University Krakow, Poland A. Sandovici, Collegiul National Petru Rares, Pietra Neamt, Romania M. Wojtylak, Jagillonian University Krakow, Poland H. Winkler, TU Berlin, Germany Long Term Guests V. Gaiko, Belarus State University, Minsk, Belarus M. Formentin, University of Padova, Italy R. Fernàndez, University of Rouen, France

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3.1

Research program

The research programme Dynamical Systems & Mathematical Physics covers a broad area with a solid basis in Analysis, Geometry and Measure Theory. Groningen subdisciplines are the qualitative and quantitative theory of ordinary differential equations and other dynamical systems, the geometry of torus bundles in the phase space of integrable Hamiltonian systems, statistical mechanics and operator theory, in particular studied by stochastic approaches. Apart from pure mathematics also many applications are studied.

3.1.1

Dynamical Systems

The discipline of Dynamical Systems is concerned with mathematical models for deterministic time evolutions. A simple example is derived from the oscillator, which generally only displays periodic dynamics. If subject to periodic driving or to coupling with another oscillator, it can illustrate many parts of the Dynamical Systems research program. One possible state of the system is resonance, where the combined system assumes one globally periodic state, the frequency of which is an integer combination of the individual periodic motions. Another possible state is multi- or quasi-periodicity, where the individual periodic motions combine in a rationally independent way. When coupling three oscillators, a third possible combined state exists, where a continuous range of frequencies is present: this is the state of chaos. The occurrence of resonance, quasi-periodicity and chaos as well as the transitions or bifurcations in between, is the central theme of research in the current Dynamical Systems program – not only for a few coupled oscillators but for a wide class of systems. The questions posed vary from fundamental to applied, where the focus can be on different classes of systems. Examples of this are the world of general ‘dissipative’ systems with a finite-dimensional state space, the classes of Hamiltonian or reversible systems or systems with a very low-dimensional state space. Also concrete examples are being studied, where sometimes numerical or symbolic algorithms have to be developed. The mathematics of these different levels strongly interact. For instance, in order to know what to look for in a special case, one has to know what can be expected and what is logically possible. There is cooperation with groups in other sciences on the analysis of specific systems. This concerns the Department of Engineering, University of Bristol (Champneys, Krauskopf, Osinga), the Depart` Jorba) ment of Applied Mathematics and Analysis of the University of Barcelona (C. Simó and A. as well as the University of Utrecht (O. Diekmann, H.A. Dijkstra, J.J. Duistermaat, T. Opsteegh, F. Verhulst), Boston University (R.L. Devaney, T. Kaper) and Twente University / Radboud University Nijmegen (M. Krupa). Various PhD students and postdocs at all these institutions are involved as 29

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well. The theoretical work is also internationally oriented and involves intensive cooperation with a.o. the universities of Dijon (R. Roussarie), Houston (M. Golubitsky), IMPA Rio de Janeiro (J. Palis, W. de Melo, M. Peixoto and M. Viana), the universities of Stony Brook and Toronto (M. Lyubich, M. Martens), the KTH Stockholm (M. Benedicks), the Université de Marseille (J.C. Poggiale and S. Troubetskoy), the Russian Academy of Sciences (M.B. Sevryuk), resulting in joint publications at a regular basis.

3.1.2

Mathematical Physics

Mathematical Physics is the study of problems originating in physics by state of the art methods from mathematics. The research of our group covers a broad spectrum of applications ranging from celestial mechanics, atomic and molecular physics, nanostructures and microlasers to phase transitions. The mathematical methods involves techniques from statistical mechanics, stochastics and dynamical systems theory, where the time evolution can be classical, quantum mechanical or stochastic.

Statistical Mechanics and Stochastics. The contribution of statistical mechanics to this part of the programme is substantial. Both equilibrium and non-equilibrium questions are considered. In comparison with dynamical systems, the emphasis is on systems with infinitely many, rather than finitely many, degrees of freedom. Links between the two can be fruitfully studied in the thermodynamic limit, where one can consider the asymptotics of systems with a large (but finite) number of degrees of freedom. Such questions lead often to the use of stochastic methods. The general aim of the stochastics part of the program is to understand interacting stochastic systems on a mathematical level. Even when the interaction is local, such systems typically exhibit a complex global behavior, with a spatial long-range dependence resulting in phase transitions. In this picture phase transitions are characterized by discontinuous behavior of the possible states of the system as a function of external parameters. For specifically tuned values of the parameters there can be more than one global state (=Gibbs measure). The equilibrium properties of such systems, as described by the Gibbs measures can be highly non-trivial, and in one direction of research we are focussing on these. Moreover we are also interested in the time-evolution of such measures. It was discovered a few years ago that time-evolved measures may lose (and recover) their Gibbsian nature as a function of time. We are trying to approach this phenomenon in case studies. In a related line of research we are investigating continuous interfaces. Related stochastic methods also are of use in applied problems like telecommunications, as an external PhD project with agentschap Telekom shows. We are also working on models for temperature-dependence of n−vector models, on the theory of disordered systems and on models for metastability and in general on examples of phase transitions of physical and conceptual interest. We are also starting to develop the theory in relationship with the theory of networks. 30

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The work is done in various collaborations, including in the last years J.-R. Chazottes (Paris), P. Collet (Paris), R. Fernández (Rouen, this year Groningen-Leiden-Eindhoven), F. Redig (Leiden), A. Le Ny (Orsay), W.Th.F. den Hollander (Leiden), E. Orlandi (Rome), R. van der Hofstad (Eindhoven), M. Biskup (UCLA), H.G. Dehling (Bochum), S. Shlosman (Marseille), V. Zagrebnov (Marseille), M. Formentin (Padova), S. Romano (Pavia), K. Netocný (Prague).

Dynamics. Reaction type dynamics is typically associated with the phase space transport across certain types of saddle equilibrium points. A general theory has been developed which describes how this transport is controlled by various high-dimensional invariant manifolds. The manifolds can be explicitly constructed from normal forms. This opens the way to understand many key problems in reaction dynamics like the realization of Wigner’s transition state theory for multidimensional systems. The research has a wide range of applications ranging from chemical reactions to ballistic electron transport problems and even capture and escape problems in celestial mechanics. A quantum version of the theory is being developed. Based on a quantum normal form an efficient algorithm has been developed to compute quantum reaction rates. The quantum results can be related to classical phase space structures using methods from semiclassical analysis like the Weyl calculus. This research is of central interest for recent spectroscopic results in molecular collision experiments. The research is carried out in collaboration with R. Schubert and S. Wiggins (Bristol University) and S. Keshavamurthy (Indian Institute of Technology, Kanpur). New fabrication techniques allow one to build lasers and optical resonators on a microscopic scales. Such microcavities utilize the principle of total internal reflection and have great potential for miniaturing spectroscopic devices and diagnostic tools. Of crucial importance for many applications is to optimize the quality factors of these devices in combination with the directionality of the optical output. This can be achieved by, e.g., a suitable choice of the morphology of the cavity boundary. Significant insight into the output directionality for a given cavity shape can be obtained on the level of the ray dynamics from studying the corresponding billiard map. Combining this with techniques from semiclassical quantum mechanics (short wavelength asymptotic) leads to the design of cavities with laser modes which are both long lived and directional. Further ideas like perturbing circular disk cavities by a point scatterer are also exploited. This research involves the collaboration with C. Dettmann, M. Sieber and G. Morozov (Bristol). In the theory of Hamiltonian dynamics the geometry of the phase space plays an important role, in particular the bundle structure of invariant tori in integrable systems. The nontriviality of such bundles is studied by methods from differential geometry and algebraic topology, where this has led to the development of monodromy and Chern classes. These results have a counterpart in semi-classical quantum theoretical approximations where quantum monodromy helps to explain certain spectral defects. Molecular and atomic systems are also studied from this point of view. This research is carried out in cooperation with various groups like the Université du Littoral, Dunkerque (B. Zhilinski´ı, D. Sadovski´ı), University of Calgary (R.H. Cushman), Utrecht University (J.J. Duistermaat, H. Hanß31

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mann), the University of Padova (F. Fassò), Sydney University (H.R. Dullin) and Bremen University (P.H. Richter). The rigorous mathematical study of coupled cell networks is a field of research in statu nascendi. Coupled cell networks are used to model the behavior of biological systems such as neural networks, social networks and genetic regulatory networks. The dynamics of such networks can exhibit interesting dynamical behavior including synchronisation, pattern formation, chaotic behavior, unstable attractors, and heteroclinic dynamics.

3.1.3

Analysis – Operator Theory

The central theme is the extension theory of symmetric and sectorial operators in Hilbert spaces and in Pontryagin spaces. This extension theory is closely connected to mathematical physics, in particular to explicitly solvable models and singular perturbations. Also there is a connection to system theory, cf. the realization of Herglotz-Nevanlinna functions in terms of transfer functions of conservative systems. Furthermore, there is an intimate relationship with analysis, in particular with moment problems, interpolation problems, differential operators and canonical systems. The general framework is an abstract boundary value space for which an analogue of Green’s identity holds and which gives rise to a so-called Weyl function (which may be unbounded and multivalued). The Weyl function itself gives rise to functional models, like reproducing kernel Hilbert or reproducing kernel Pontryagin spaces, but also like abstract conservative systems. The research in this section is concerned with the development of the general theory and the applications to the above mentioned fields. This is done in collaboration with the following group of mathematicians: Yu.M. Arlinski˘ı (Lugansk), J. Behrndt (Berlin), V.A. Derkach (Donetsk), A. Fleige (Dortmund), S. Hassi (Vaasa), M. Kaltenbäck (Wien), J.Ph. Labrousse (Nice), M.M. Malamud (Donetsk), M. Möller (Johannesburg), A. Sandovici (Piatra Neamt) Z. Sebestyén (Budapest), F.H. Szafraniec (Krakow), M. Wojtylak (Amsterdam / Krakow), R. Wietsma (Vaasa), H. Winkler (Berlin) and H. Woracek (Wien).

3.2


Handbook and textbook in Dynamical Systems Broer, together with F. Takens (Groningen) and B. Hasselblatt (Tufts, Boston) is editing a volume in the Handbook of Dynamical Systems series, issued by Elsevier (North-Holland), expected to appear in 2009. Together with Takens, Sevryuk (Moscow) and Vanderbauwhede (Ghent) we have three chapters in this volume. Broer and Takens almost finished their preparations on a textbook Dynamical Systems and Chaos, which is to appear in 2009. 32

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KAM theory In KAM theory several projects are running in cooperation with Broer. One paper on quasi-periodic stability of normally resonant tori, with M.C. Ciocci (London), H. Hanßmann (Utrecht) and A. Vanderbauwhede (Ghent), in 2009 will appear in Physica D. A paper concerning the destruction of resonant Lagrangean tori, with H. Hanßmann and J. You (Nanjing), has been submitted. A chapter by Broer and Sevryuk in the Handbook volume, mentioned before, is in preparation and is expected to appear in 2009. A monograph on quasi-periodic bifurcation theory, co-authored by Hanßmann and F.O.O. Wagener (UvA) is in preparation. Bifurcation theory and applications In cooperation with M. Golubitsky (Houston) and G. Vegter (RUG) the geometry of resonance tongues was investigated in a general (universal) Hopf-Ne˘ımark-Sacker setting. Following earlier publications in 2007 a joint paper on feed-forward coupled cell systems by Broer and Vegter in 2008 was published in Nonlinearity. Another paper of Broer, Vegter and the PhD student S.J. Holtman on the recognition problem in mildly degenerate Hopf-Ne˘ımark-Sacker bifurcations also was published in Nonlinearity and two more papers are submitted, c.q., in preparation. Also the former PhD student R. Vitolo (Exeter) is participating in this research. Two paper regarding the Hopf-Ne˘ımark-Sacker bifurcation for 3D maps have been written by Broer, in cooperation with C. Simó (Barcelona) and R. Vitolo. One appeared in Physica D and the other in the Bull. Belgian Math. Society Simon Stevin. Two papers of Broer, K. Efstathiou and E. Subramanian on unstable attractors and heteroclinic cycles in coupled cell systems appeared in Nonlinearity. Mathematical Physics About the Gibbsian-non-Gibbsian program, around which the PhD projects of Ermolaev, Opoku and Ruszel are centered there were a number of developments. In this program one studies which measures can and cannot be written as a Gibbs measure for an effective Hamiltonian. This is often done in physics, although it turns out to be not always mathematically justified. Various examples of physical interest occur, e.g. in Renormalization Group theory, in the theory of disordered systems and in the study of non-equilibrium problems. For nearest-neighbour n-vector models with diffusive evolutions, various results were obtained, showing both preservation of Gibbsianness for short times, and loss of Gibbsianness after long times. Two papers by van Enter and Ruszel in Stoch. Proc. and Appl.1 and in J. Math.Phys, and two papers by Külske and Opoku (in El. J. Prob. and in J. Math. Phys.) appeared. A joint paper by van Enter, Külske, Opoku and Ruszel was submitted 2 A paper by Ruszel and T. LaCour Jansen (theoretical physics) appeared in J. Chem. Phys. Ruszel has started a collaboration with F. Redig (Leiden) and S. Roelly (Potsdam) on short-time Gibbsianness under general diffusion processes, and has also started a collaboration with C. Spitoni and P.-Y. Louis (Potsdam) on Probabilistic Cellular Automata. Also a review by van Enter, Redig and Verbitskiy appeared in Statistica 1 2

Electronically available at http://dx.doi.org/10.1016/j.spa.2008.09.005 . Electronically available at arXiv.

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Neerlandica, describing the activities at Eurandom during the last ten years on (non-) Gibbsian topics. Van Enter, in collaboration with Fernàndez (Rouen), den Hollander and Redig (Leiden) is studying the space-time picture of the transition in simple examples. Külske and LeNy provided a complete analysis of the transition between Gibbsian and non-Gibbsian behavior as a function of time in the ferromagnetic Ising mean-field model, for non-interacting stochastic dynamics. Based on this work, the PhD research of Ermolaev aims at a similarly complete description including the low-temperature regime of dynamics and initial measure in the corresponding mean-field model, based on different (path-large-deviation) methods. Van Enter and Külske studied disordered random surface models, and showed that not only their location, but also their tilt fluctuates so much in two dimensions that not even the gradient metastate exists. A paper appeared in the Annals of Applied Probability. Külske and Orlandi studied the influence of an additional pinning force at a given height on such models. They showed that an arbitrarily weak random term is enough to beat an arbitrarily strong pinning force in 2 dimensions and will cause delocalization. The corresponding paper has appeared in Stochastic processes and Applications. Van Enter and Verbitskiy are working on the erasure entropy in the two-dimensional Ising model; a paper is in preparation. Ruszel made good progress. Two papers with van Enter were accepted one of which appeared, the other of which is already available electronically, and a further paper with van Enter,Külske and Opoku was submitted. Moreover a paper with T. LaCour Jansen (Theoretical Physics) appeared. She developed collaborations with F. Redig (Leiden) and S. Roelly (Potsdam), and with C. Spitoni (Eindhoven / Leiden) and P.-Y. Louis (Potsdam). E.Verbitskiy in collaboration with K. Schmidt (Vienna) completed the project establishing a connection between Abelian Sandpile Models of mathematical physics and algebraic dynamical systems. (Preprint will be available electronically in coming days.) Verbitskiy in collaboration with B. Schoenmakers, B. Skoric, P. Tuyls (all Eindhoven), worked on applications of probabilistic techniques to cryptography. In particular, estimates of extractable randomness have been derived for non-uniform sources. Two preprints have been submitted for publication. Results have been presented at the 3rd Benelux Workshop on Information and System Security (Eindhoven, September 2008). Verbitskiy moreover has started collaborating with R. Fernàndez on thermodynamics of hidden Markov chains. In particular, first results on cluster expansions for hidden Markov sources have been obtained. Külske, in a publication J.-R. Chazottes (Paris), P. Collet (Paris) and Redig, developed a coupling method to derive concentration inequalitites for certain strongly dependent random fields. In collaboration with the same co-authors, E. Verbitskiy established similar concentration inequalities for non-uniformly dynamical systems. A first paper is about to be submitted. A second paper employing the coupling approach is being prepared. In an further collaboration Külske, Dehling and the external PhD student Fleurke found a closed form solution for the classical parking model on a random tree. A paper appeared in J. Stat. Phys. The study 34

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of a related probabilistic interacting model for frequency assignment, was finished; a paper by Kuelske and Fleurke describing the two-line distribution for the parking problem, providing a solution in closed form, was submitted.3 In a collaboration with Formentin Külske works on extremality properties of Gibbs measures on trees. Külske studied the pureness of the Gibbs measure for Potts models on random trees. Sharper bounds than known in the literature were obtained. A paper on these results has been submitted. Concerning the Dynamics part regarding (isotropic) torus bundles in integrable Hamiltonian systems, Efstathiou with D. Sadovski´ı and B. Zhilinski´ı studied the hydrogen atom in combined electric and magnetic fields as a classical dynamical system in order to uncover qualitative features of the phase space that are important for the semiclassical quantization. A joint paper has been published in Proc. Roy. Soc. London Ser. A. More papers are in preparation. Waalkens studied scattering problems where the analogue of monodromy leads to a nontrivial foliation by invariant cylinders. A paper together with H.R. Dullin has been published in Phys. Rev. Lett. Broer and Lukina in cooperation with F. Takens (emeritus professor) have studied the classification of symplectic torus bundles, using integer affine structures and monodromy and Chern and Lagrangian classes. A joint paper has appeared in Regular & Chaotic Dynamics. In coupled cell networks, Broer with Efstathiou and Subramanian showed the robust existence of unstable attractors and heteroclinic connections in networks with a Mirollo-Strogatz type interaction. Two papers now have appeared in Nonlinearity. Efstathiou, in collaboration with D. Sadovski´ı and O. Lukina, studied the qualitative properties of an integrable approximation to the hydrogen atom in electric and magnetic fields. One paper has been published in Phys. Rev. Lett. in 2008 and a second paper will appear in J. Phys. A in 2009. A review of the subject has been commissioned by Rev. Mod. Phys. and is currently under preparation. In the study of fractional monodromy Efstathiou, H.W. Broer and O.V. Lukina have shown that integrable 2-DOF systems with reverse hyperbolic corank-1 singularities have fractional monodromy. A paper is under preparation and we work on generalizing this result to higher dimensional systems. Efstathiou worked on bidromy in collaboration with H. Jauslin, P. Mardesic, M. Peletier and D. Sugny. Two papers are in preparation. The first clarifies the concept of bidromy through the study of the parallel transport of homology cycles in integrable Hamiltonian systems in which the bifurcation diagram has a characteristic swallowtail structure and the second studies bidromy from the complex analytic point of view and its relation to Picard-Lefschetz monodromy. The relation of Hamiltonian monodromy and Picard-Lefschetz monodromy of Ak type singularities is under investigation by Efstathiou in collaboration with D. Sadovski´ı, R. Cushman and F. Beukers. In this direction we expect to uncover ”exotic” types of monodromy that are known to exist in Hamiltonian systems but for which there are currently no specific examples. Concerning the research on reaction-type dynamics Waalkens recently focused on the quantum me3

Electonically available at the arXiv.

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chanical aspects of reaction dynamics. In collaboration with R. Schubert and S. Wiggins (Bristol) he developed an efficient algorithm based on a quantum normal form to compute cumulative reaction probabilities and Siegert resonances associated with saddle equilibrium points. Using methods from semiclassical analysis the quantum-classical correspondence of reaction dynamics like the localization of scattering states on classical phase space structures has been studied in detail. After a Physical Review Letter in 2006 this has resulted in an extensive invited paper in Nonlinearity, that has been featured on the IOP web page http//www.iop.org/ej/authors_edition. Another paper on this subject has been accepted for publication in Few-Body Systems. A post-doc (Arseni Goussev) also started working with Waalkens on this project in order to develop a semiclassical theory of stateto-state reactivities. Concerning classical reaction rates Waalkens started a collaboration with G.S. Ezra (Cornell University) and S. Wiggins (Bristol University). This has resulted in a paper submitted to J. Chem. Phys. With R. Hales (Bristol University) Waalkens studied the classical and quantum transport through entropy barriers modelled by hardwall hyperboloidal constrictions. A joint paper on this subject has been accepted for publication in Ann. Phys. (NY). A joint paper with S. Wiggins on geometric models of reaction dynamics is about to be completed. In the research on microlasers and optical microcavities a work on a system consisting of a circular microdisk and a point scatterer has been completed by Waalkens in collaboration with C. Dettmann, M. Sieber and G. Morozov (Bristol). This work has been published in Europhysics Letters. The system is appealing due to its analytic tractability which enables a detailed study of resonance states under variation of the strength and position of the point scatterer. This way highly directional longlived laser methods could be found. This work resulted into two conference proceedings (ICTON 2008 and MMW POB) and collaborations with experimental groups at the Universities of Erlangen and Paris. Extension theory The theory of abstract boundary values and Weyl functions is being carried forward (with Derkach, Hassi, Malamud). The theory of singular perturbations of selfadjoint operators is being further investigated. The decomposition of operators and forms is being studied with S. Hassi, Z. Sebestyén and F.H. Szafraniec; and in another sense with J.Ph. Labrousse, Sandovici and Winkler. Extension theory and system-theoretic interpretations are being carried forward (with Arlinski˘ı, Hassi). Normal extensions of symmetric operators are being studied (with Hassi, Szafraniec). Sectorial relations and their factorizations are being studied with Hassi, Sandivici and Winkler. The representation of not necessarily semibounded sesquilinear forms in a Hilbert space remains a research topic (with Fleige, Hassi, Winkler). The perturbation of eigenvalues in a gap of a selfadjoint operator is being studied by Hassi, Sandovici, de Snoo, Winkler. An extension to an indefinite setting is done with Wojtylak. Work concerning boundary relations in Hilbert and in Pontryagin spaces has been initiated with Derkach, Hassi and Behrndt. Generalized Nevanlinna functions in the setting of almost Pontryagin spaces are being studied with Woracek. Multi-variable interpretations of boundary relations are being studied with Alpay, Behrndt, Hassi. The 36

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spectral theory of canonical differential equations is a new topic, being developed by Behrndt, Hassi and Wietsma. Moment problems are being studied with Derkach and Hassi. PhD research The research of Subramanian, Lukina, Chandramoulli and Hazard was concluded succesfully in 2008 and also already led to several publications. A few more are in preparation. Holtman has one paper in cooperation with his supervisors Broer and Vegter, and a few more are in preparation. Sterk is making good progress in cooperation with his supervisors Broer, Dijkstra (IMAU) and Simó (Barcelona). Also Vitolo (Exeter) is participating and several papers are in preparation. The research of Potoˇcný stopped as his appointment was terminated. This research project will soon be continued. Ruszel made good progress: two papers with her supervisor Van Enter appeared and one with T. Latour Jansen from theoretical physics (condensed matter group). A paper with Van Enter, Kuelske and Opoku was submitted. See above. Opoku made good progress. Two papers in collaboration with his supervisor Külske appeared, a third one in collaboration with Külske, Van Enter and Ruszel was submitted. Ermolaev made good progress. He obtained a number of results on the description of mean-field models with low-temperaturedynamics, a preprint is in preparation. Iacobelli made good progress on getting familiar with the field of networks. Fleurke, as an external Ph D student, published one paper with H.G.Dehling and Külske and submitted another one with C. Külske.

3.3

Research subjects

H.W. Broer: Perturbation and KAM-theory, bifurcation theory, non-integrable and resonance phenomena, applications of singularity theory, exploration of complicated systems. S.M. Chandramoulli: Renormalization in low-dimensional dynamics: border cases. A.C.D. van Enter: Lattice statistical mechanics and thermodynamic formalism, Gibbs-non-Gibbs transitions, bootstrap percolation, nonlinear vector models, disordered systems and spin-glasses, metastates and chaotic size-dependence, non-crystalline long-range order. K. Efstathiou: Applications of Hamiltonian mechanics in physical systems, integrable Hamiltonian systems, normal-forms, monodromy, coupled cell networks. V. Ermolaev: Path variational principle of mean-field measures. S. Fleurke: Blocking models and frequency assignment. P. Hazard: Renormalization of critical circle maps. S.J. Holtman: Computation of a universal four dimensional bifurcation set and associated recognition problems for maps and ODE’s. G. Iacobelli: statistical mechanical models on random graphs. ¨ Ch. Kulske: Interacting stochastics systems, short-range vs. mean-field models, Gibbs measures vs. non-Gibbsian measures, interfaces, disordered systems, concentration inequalities, networks. O. Lukina: Geometry of torus bundles in Hamiltonian systems. A. Opoku: Relation between short-range and long-range models. 37

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M. Potoˇcný: Dynamics and bifurcation of discontinuous systems. W.M. Ruszel: Vector models, Gibbs measures versus non-Gibbsian measures. H.S.V. de Snoo: Extension and realization theory with their applications to analytical problems. A.E. Sterk: Climate models. E. Verbitskiy: Lattice statistical mechanics, thermodynamic formalism, Gibbs-non-Gibbs transitions, dynamical systems and time-series prediction. H. Waalkens: Theoretical and application oriented aspects of Hamiltonian systems including integrable systems, monodromy, reaction type dynamics, invariant manifolds, normal forms, and semiclassical quantum mechanics (short wavelength asymptotics) with applications to micro lasers and quantum reaction dynamics.

3.4

Publications Dissertations - E.N. Subramanian, Attractor switching in neuron networks and Spatiotemporal filters for motion processing, Promotores: H.W. Broer and N. Petkov (RuG, Computing Science), Faculty of Mathematics and Natural Sciences, University of Groningen, 29 February 2008, 107 pages. - O. Lukina, Geometry of torus bundles in Hamiltonian systems, Promotor: H.W. Broer, Faculty of Mathematics and Natural Sciences, University of Groningen, 26 September 2008, 106 pages. - S. Chandramouli, Renormalization and non-rigidity, Promotores: H.W. Broer and M. Martens (Stony Brook University), Faculty of Mathematics and Natural Sciences, University of Groningen, 8 December 2008, 107 pages. - P. Hazard, Hénon-like maps and renormalization, Promotores: H.W. Broer and M. Martens (Stony Brook University), Faculty of Mathematics and Natural Sciences, University of Groningen, 8 December 2008, 122 pages. Articles in scientific journals - J. Behrndt, S. Hassi, and H.S.V. de Snoo, Functional models for Nevanlinna families, Opuscula Mathematica, 28, 2008, 233-245. - H.W. Broer, K. Efstathiou and E. Subramanian, Robustness of unstable attractors in arbitrarily sized pulse-coupled systems with delay, Nonlinearity, 21(1), 2008, 13-49. - H.W. Broer, K. Efstathiou and E. Subramanian, Heteroclinic cycles between unstable attractors, Nonlinearity, (21), 2008, 1385-1410.

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- H.W. Broer, S.J. Holtman and G. Vegter, Recognition of the bifurcation type of resonance in mildly degenerate Hopf-Neimark-Sacker families, Nonlinearity, 21, 2008, 2463-2482. - H.W. Broer, C. Simó and R. Vitolo, The Hopf-Saddle-Node bifurcation for fixed points of 3Ddiffeomorphisms, analysis of a resonance ‘bubble’, Physica D, 237, 2008, 1773-1799. - H.W. Broer, C. Simó and R. Vitolo, The Hopf-Saddle-Node bifurcation for fixed points of 3Ddiffeomorphisms, the Arnol’d resonance web, Bull. Belgian Math. Soc. Simon Stevin, 15, 2008, 769-787. - H.W. Broer and G. Vegter, Generic Hopf-Ne˘ımark-Sacker bifurcations in feed forward systems, Nonlinearity, 21, 2008, 1547-1578. - H.W. Broer and R. Vitolo, Dynamical systems modeling of low-frequency variability in loworder atmospheric models, Discrete and Continous Dynamical Systems - Series B, 10(2/3), 2008, 401-419. - H. Dehling, S. Fleurke and C. Külske, Parking on a random tree, J. Stat. Phys., 133 (1), 2008, 151-157. - C.P. Dettmann, G.V. Morozov, M. Sieber and H. Waalkens, Directional Emission from an Optical Microdisk Resonator with a Point Scatterer, Europhys. Lett., 82, 2008, 34002. - H.R. Dullin and H. Waalkens, Nonuniqueness of the Phase Shift in Central Scattering due to Monodromy, Phys. Rev. Lett., 101, 2008, 070405. - K. Efstathiou, O.V. Lukina and D.A. Sadovski´ı, Most typical 1:2 resonant perturbation of the hydrogen atom by weak electric and magnetic fields, Phys. Rev. Lett., 101,2008, 253003. - A.C.D. van Enter and C. Külske, Non-existence of random gradient Gibbs measures in continuous interface models in d=2, Ann. Appl. Prob., 18(1), 2008, 109-119. - A.C.D. van Enter and W.M. Ruszel, Loss and recovery of Gibbsianness for XY models in small external fields, J.Math.Phys., 49(12), 2008, 125208. - A.C.D. van Enter, F. Redig and E. Verbitskiy, Gibbsian and non-Gibbsian states at Eurandom , Stat. Neerlandica, 62(3), 2008, 331-344. - S. Hassi, A. Sandovici, H.S.V. de Snoo, and H. Winkler, One-dimensional perturbations, asymptotic expansions, and spectral gaps, Oper. Theory Adv. Appl., 188, 2008, 149-173. - C. Külske and A. Opoku, The posterior metric and the goodness of Gibbsianness for transforms of Gibbs measures, El. J. Prob., 13, 2008, 1307-1344. - C. Külske and A. Opoku, Continuous-spin mean-field models: limiting kernels and Gibbs properties of local transforms, J. Math. Phys., 49(12), 2008, 125215. 39

IWI Annual Report

- C. Külske and E. Orlandi, Continuous interfaces with disorder: Even strong pinning is too weak in 2 dimensions, Stoch. Proc. Appl., 118(11), 2008, 1973-1981. - T. LaCour Jansen and W.M. Ruszel, Narrowing in the time-averaging approximation for simulating two-dimensional nonlinear infrared spectra, J. Chem. Phys., 128, 2008, 214501. - O.V. Lukina, F. Takens and H.W. Broer, Global properties of integrable Hamiltonian systems, Regular and Chaotic Dynamics, 13(6), 2008, 588-630. - H. Waalkens, R. Schubert and S. Wiggins, Wigner’s Dynamical Transition State Theory in Phase Space: Classical and Quantum, Nonlinearity, 21, 2008, R1-R118. (Invited paper; featured on the IOP webpage under http://www.iop.org/ej/authors_edition ) Articles in conference proceedings - G. von Basum, E. Verbitskiy, P. de Bokx, I. Sadaane, C. van Put, H.R. Haak, Novel approach to stochastic modeling and prediction of continuous glucose data, 8th annual Diabetes Technology Meeting, (abstract), 2008. - C.P. Dettmann, G. V. Morozov, M. Sieber and H. Waalkens, TM and TE Directional Modes of an Optical Microdisk Resonator with a Point Scatterer, Proc. 10th Int. Conf. on Transparent Optical Networks (ICTON2008), 4, 2008, 65-68. - C.P. Dettmann, G. V. Morozov, M. Sieber and H. Waalkens, Optical Microdisk Resonator with a Small but Finite Size Scatterer. Proc. 3rd Int. Conf. on Mathematical Modeling of Wave Phenomena (MMWP08) (2008), 287-289. Other publications - H.W. Broer and H. Hanßmann, Perturbation theory (dynamical systems), Scholarpedia, 3(9), 2008, 2399.

3.5


External funding PhD grants (supervisor Broer): Drs. Sijbo J. Holtman has an NWO grant (open competition, cosupervisor G. Vegter) and was appointed September 1, 2005. Drs. Alef E. Sterk has an NWO-grant in the research-area Earth- and Life Sciences, with collaboration 40

IWI Annual Report

of H.A. Dijkstra (IMAU-UU) and C. Simó (UBarcelona), appointed September 1, 2005. Martin Potoˇcný works on a third NWO grant (open competition Applied Mathematics) with collaboration of H. Nijmeijer (TU/e) and was appointed March 1, 2007. His contract was terminated December 19, 2008. PhD grant (supervisor M. Martens): Peter Hazard has an NWO grant (open competition) and was appointed September 1, 2004. PhD grant (supervisor C. Külske): Drs G. Iacobelli has an NWO grant (co-supervisors A.C.D. van Enter and R.W. v.d. Hofstad-TU/e) and was appointed on January 1, 2008. Broer obtained an NWO bezoekersbeurs for half a year for V. Gaiko (Belarus University, Minsk). Van Enter, together with Den Hollander (Leiden) acquired an NWO bezoekersbeurs for R. Fernàndez. K. Efstathiou obtained a bezoekersbeurs from the NWO-cluster NDNS+ for D.A. Sadovsk´ı (Université du Littoral, Dunkerque). The nation-wide NWO-cluster Nonlinear Dynamics in Natural Sciences to enhance the infrastructure in the mathematics research, was initiated April 2005, with proposers H.W. Broer, A. Doelman (CWI), S.M. Verduyn Lunel (UL) and A. van der Vaart (VU). The fundings are provided by the Ministeries of OCW and EZ. Groningen has become the center of the cluster, with H.W. Broer as managing director. Nodes are the CWI, UL and VU (Amsterdam) and cluster members are spread all over the Netherlands. Groningen acquired 1.7 MEuro for research infrastructure, in particular one full professor and a tenure track assistant professor in the group Applied Analysis and another tenure track assistant professor in the group Dynamical Systems & Mathematical Physics. The full professor is A.J. van der Schaft, appointed 1 September 2006, and the two tenure trackers are K. Camlibel (Applied Analysis) and H. Waalkens (Dynamical Systems), both appointed 1 September 2007.4 Moreover funding is available for 0.2 fte full professor Mathematics of Life Sciences, with the help of which E. Verbitskiy (Philips), is appointed professor Mathematics of Life Sciences in the group Dynamical Systems & Mathematical Physics per 1 October 2007; moreover E.R. van den Heuvel (Organon) is appointed professor Statistics of Life Sciences in the group Probability and Statistics per 1 January 2008. PhD grant (supervisor H. Waalkens): Drs. Robert Hales has been appointed in October 2006 to work on quantum resonances and micro lasers. This research is carried out at the University of Bristol and is funded by EPSRC (British Research Council). Post-doctoral research grants (supervisor H. Waalkens): Funding for two post-doc positions (three years each) has been claimed from EPSRC (British Research Council). The first concerns asymptotic and numerical approaches to the theory of optical microresonators and microlasers (in collaboration 4

Waalkens got tenure immediately.

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IWI Annual Report

with M. Sieber and C. Dettmann at Bristol University) and Dr. Gregory Morozov has started working on this project in February 2006. The project for the second position is entitled Quantum Transition State Theory and Dr. Arseni Goussev has been appointed to work on this project in August 2007. Both post-docs are located at Bristol University. H.S.V. de Snoo became Mercator visiting professor at the TU Berlin for half a year. External collaboration K. Efstathiou visited the Université de Bourgogne (Dijon) in the periods 27-31 January 2008 and 15-17 October 2008 for collaboration. During the first visit he gave a talk in the seminar of the Department of Physics on Standard and fractional monodromy in physical systems. Efstathiou also visited the Université du Littoral (Dunkerque) in the period 6-15 February 2008 for collaboration. A.C.D. van Enter acted as a jury member for the thesis of Adnene Besbes, Contributions a l’ e´ tude de quelques systèmes quasi-crystallographiques., supervisor A. Boutet de Monvel, Université de Paris 7. E. Verbitskiy continued collaboration with the University Medical Center Groningen. An STW application for funding of 2 PhD students in the field of patient monitoring in Intensive Care Units has been submitted in December 2008. Research proposal aims at the development of mathematical apparatus for accurate methabolic regulation in critically-ill patients. The application is co-supported by 3 commercial enterprizes. A.C.D. van Enter and E. Verbitskiy served on the Working group for Mathematics (KNAW). E. Verbitskiy has been a member of the working group which prepared Masterplan Toekomst Wiskunde. This documents was commissioned by the Netherlands Ministry of Education, Culture and Science, and outlines proposals for the development of Dutch Mathematics in coming years. H. Waalkens visited the University of Bristol in March and December 2008 for research collaborations. As a member of the network Mathematical Challenges in Molecular Dynamics he visited the Maxwell Institute of Mathematical Sciences (Edinburgh) in November. H.S.V. de Snoo was a jury member for the thesis defence of Maria Nafalska, TU Berlin (24 November). De Snoo visited: - University of Vaasa (Hassi; twice) - Julianadorp (Fleige, Winkler) 42

IWI Annual Report

- TU Berlin (Behrndt, Winkler; thrice, partly in the Mercator programme) - Eötvös Loránd University Budapest (Hassi, Szafraniec, Sebestyen)

3.6

Further information

H.W. Broer participated in the following conferences: - Conference in honour of Robert L. Devaney’s sixtieth birthday, Barcelona, April 2008, invited talk On Parametrized KAM-Theory. - Dynamics Days 2008, Delft University, August 2008, organizer minisymposium on Hamiltonian Dynamics. - Lorentz Center workshop KAM-Theory and its Applications, organizer together with H. Hanßmann (Utrecht) and M.B. Sevryuk (Moscow). H.W. Broer became a member of the Royal Academy of Arts and Sciences (KNAW), afdeling Natuurkunde, sectie Wiskunde. He became coordinating editor of Indagationes Mathematicæ (jointly with M. Keane of Wesleyan University), which forms the Proceedings of the KNAW. Broer moreover is Division Editor of the Journal of Mathematical Analysis and Applications (JMAA), for the area of Ordinary Differential Equations and Dynamical Systems and Associate Editor of Discrete and Continuous Dynamical Systems – Series S. Broer is acting chairman of the KWG (the Royal Netherlands Mathematical Society). In this role he was active in the 5th European Congress of Mathematics (5ECM), July 2008, in particular with the Brouwer Memorial Lecture, where he awarded the Brouwer Medal to Philip Griffiths (Princeton University). Also he is a member of the Mathematics Board of the Lorentz Center (Leiden).

A.C.D. van Enter gave invited lectures at the - meeting Gradient models and elasticity, at Warwick University, UK, - at the XII Brazilian school of probability in Ouro Preto, Brazil, - and gave an invited minicourse at the Institut Henri Poincaré, Paris, France. Moreover he gave seminars at the mathematics department of the University of Bielefeld (Germany) and at the Industrial Engineering Department of the Technion Haifa (Israel). He participated in the 43

IWI Annual Report

5ECM conference in Amsterdam. Van Enter is in the Editorial Board of Markov Processes and Related Fields and of het Nederlands Tijdschrift voor Natuurkunde. He is a member of the Akademie Werkgroep Wiskunde of the Royal Netherlands Academy of Arts and Sciences (KNAW). He organises the Mark Kac seminar, together with R.W. v.d. Hofstad, which is supported by FOM. He is a participant of the NSF-supported US-Brazil-Netherlands PIRE collaboration: Percolative and disordered systems. Lectures W.M. Ruszel - What it takes to be Gibbsian for planar rotors Dynamical Systems seminar, RUG 28th January 2008 - What it takes to be Gibbsian for planar rotors Kansrekening en statistiek seminar, TU Delft 28th May 2008 - Loss of temperature for XY models Forschungsseminar, Universität Potsdam 4th July 2008

C. Külske gave invited lectures at - YEP (Young European Probabilists) V meeting, March 2008 at EURANDOM, Eindhoven. - La Pietra week in Probability , June 2008, Firenze, Italy

H.S.V. de Snoo gave lectures in - College of William and Mary, Williamsburg IWOTA - University of Helsinki Operator Theory and Numerical Analysis - TU Berlin Operator Theory in Krein spaces and inverse problems

E. Verbitskiy gave invited talks at - Miniymposium Back to GIK, May 2008, - Conference on Codes and Skew Rings, June 2008, - Mark Kac Seminar, December 2008. 44

IWI Annual Report

H. Waalkens gave invited talks at - University of Edinburgh (UK), Wigner’s Transition State Theory - Workshop Critical Stability, Erice (Italy), Classical and Quantum Reaction Dynamics - University of Utrecht, on Classical and Quantum Reaction Dynamics - Dynamics Days 2008, contributed talk on Classical and Quantum Reaction Dynamics

K. Efstathiou gave talks in the following conferences - 5th European Congress of Mathematics, Amsterdam, Unstable attractors and heteroclinic cycles in pulse coupled networks with delay. - Dynamics Days Europe 2008, Delft, The hydrogen atom in near orthogonal electric and magnetic fields. - KAM Theory and its applications, Lorentz Center, Leiden, Integer and fractional monodromy of integrable Hamiltonian systems.

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4.

Geometry

Group leader: Prof.dr. G. Vegter

Tenured staff (IWI members) Prof.dr. G. Vegter

source RuG

fte 1.0

Postdocs S. Plantinga

EU and RuG

0.8

NWO

1.0

EU

1.0

NWO

1.0

PhD students A. Chattopadhyay (supervisor: Vegter) S. Ghosh (supervisor: Vegter) S. Holtman (member of Dynamical Systems) (supervisors: Broer, Vegter)

Guests Prof.dr. B. Aronov, Polytechnic University, New York, USA

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4.1

Research Program

Our research topics fall within several subfields of Geometry, like Differential Geometry and Singularity Theory on the more theoretical side, and Computational Geometry on the more applied side. In collaboration with other local and international groups in Mathematics and Computer Science, this research is also focused on applications in Geometric Modeling, Dynamical Systems, and Astrophysics. A key role is played by concepts and results from Differential Geometry and Topology, like curvature in geometric approximation problems, and Morse Theory in topologically correct shape approximation, or in determining visibility features of evolving objects, from Singularity Theory, e.g., for the description of the Medial Axis and other skeletal structures, for the evolution of visible contours, and for the analysis of bifurcations in dynamical systems, from Dynamical Systems and Mathematical Physics, e.g., for analyzing bifurcations in physical systems, and for computing invariant manifolds, and from Algebraic Topology, e.g., for the computation of Betti numbers for the classification of objects and patterns in spatial data and for detecting structures in astrophysical data of galaxy distributions. The goal is to obtain constructive and certified methods for the study of geometric and topological structures arising in a wide range of scientific problems. G EOMETRIC A PPROXIMATION . Geometric shapes often arise as submanifolds of Euclidean spaces. Objects of this type occur, e.g., as solution sets of geometric constraint problems, like boundaries of configuration spaces in robotics, or as iso-energy hypersurfaces in six-dimensional phase space in physical applications. Such submanifolds may have boundaries and may exhibit singularities (like sharp features). Processing the topology or geometry of such submanifolds (e.g., when computing topological invariants like connectivity, or geometric characteristics like volume or Minkowski functionals) often requires constructing approximations from a restricted class of objects, like polyhedral or piecewise quadratic hypersurfaces. These approximations have to be close to the submanifold in a metric sense, and have to share the relevant topological or geometric properties. In many cases, the construction of such approximations entails the extraction of an optimal sample from a distribution on the manifold based on geometric features like curvature. To deal with the curse of dimensionality we are willing to sacrifice true optimality of the approximation in return for acceptable computing time. The challenge is to determine the complexity of an optimal approximation in spaces of high dimension, especially in dependence on the dimension, subsequently, to use this knowledge for developing criteria for acceptable error measures for near-optimal approximations, and, finally, to design efficient methods for the construction of such near-optimal objects. 48

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4.2


G. Vegter In the context of the European project5 Algorithms for Complex Shapes (ACS) we have shifted our focus from piecewise linear approximation to certified shape approximation by piecewise smooth objects, with good approximation of first and second order differential invariants like normals and curvatures. Furthermore, complexity issues are crucial in our approach. In several cases we have succeeded in expressing the quality, i.e., the complexity, of our approximations in terms of intrinsic geometric invariants of the shape to be approximated, like Euclidean or affine curvature. These results have direct implications for the design of efficient approximation algorithms. Certified approximation of geometric shapes is also a central theme in the PhD projects of Chattopadhyay and Ghosh, and a new PhD project that will start in 2009. With Broer (Dynamical Systems) and Golubitsky we worked on complicated dynamics in simple coupled cell networks, where the time evolution of each cell is governed by the same simple dynamic law, with inputs from adjacent cells in the network. In particular, we refuted an earlier conjecture that simple dynamic laws generate only simple dynamics, by showing that complicated Hopf-Ne˘ımarkSacker bifurcations may occur in such networks. This work fits within the PhD project of Holtman on the geometry of resonance tongues. The Cosmic Web, the foamlike pattern permeating the universe, represents a striking example of a complex geometric pattern in nature and defines the cosmic environment in which galaxies emerge. In both the observed galaxy distribution as well as in computer simulations of cosmic structure formation we see matter accumulate in walls, filaments and dense compact clusters, surrounding vast near empty voids. Continuing ongoing co-operation with Rien van de Weygaert and co-workers of the Kapteyn Astronomical Institute in this area, we are applying methods from computational topology to detect these global geometric structures by analysing data from N -body simulations and galaxy redshift survey data (2dFGRS, SDSS, 2MASS). A new PhD project on this topic will start in 2009. S. Plantinga In collaboration with the computational geometry groups of the Freie Universität Berlin, Germany (Buchin, Rote and Sturm) and Graz Technical University, Austria (Aurenhammer, Aichholzer and Kornberger) we succeeded in developing a new method for the approximation of sampled shapes in higher dimensions preserving the topology of the input shape. S. Ghosh We extended our earlier work on approximation of planar curves by conic splines to the approximation of space curve by helix splines. In particular, we determined the complexity of an optimal approximating helix spline in terms of intrinsic differential invariants like curvature and torsion. This work is still in progress. 5

http://acs.cs.rug.nl

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IWI Annual Report

A. Chattopadhyay In the PhD project on Certified Shape Reconstruction ongoing work is concerned with topologically correct reconstruction of shapes from sufficiently dense point samples. We completed a method for certified isosurface extraction for interpolants defined in terms of Radial Basis Functions. In cooperation with Chee Yap (New York University) we are currently extending the work on certified computation to Morse-Smale complexes. S. Holtman In this joint PhD project with the Dynamical Systems group we extended earlier work on resonance tongues, associated with the bifurcation of periodic orbits from fixed points in discrete systems depending on parameters, or with the birth of q-th order harmonics in families of periodic systems. In co-operation with Vitolo (University of Exeter) we extended our earlier work on the exploration and visualization of the complicated geometry of resonance regions in higher dimensional parameter spaces by incorporating the full bifurcation set. We are currently extending this work to continuous systems.

4.3

Research subjects

A. Chattopadhyay: Certified surface reconstruction, Radial Basis Functions, certified computation of Morse-Smale complexes. S. Ghosh: Differential geometry in geometric approximation. S. Holtman: Geometry of resonance tongues, bifurcations sets in higher dimensional spaces. S. Plantinga: Geometric approximation of curves and surfaces, certified meshing. G. Vegter: Certified geometric approximation, computational topology, computational differential geometry, singularity theory and its applications, dynamical systems.

4.4

Publications Articles in scientific journals – J.-D. Boissonnat, D. Cohen-Steiner and G. Vegter, Isotopic Implicit Surface Meshing, Discrete and Computational Geometry, 39, 2008, 138–157. – H.W. Broer, S.J. Holtman and G. Vegter, Recognition of the bifurcation type of resonance in mildly degenerate Hopf-Neimark-Sacker families, Nonlinearity, 21, 2008, 2463–2482. – H.W. Broer and G. Vegter, Generic Hopf-Neimark-Sacker bifurcations in feed-forward systems, Nonlinearity, 21, 2008, 1547–1578.

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Articles in conference proceedings – O. Aichholzer, F. Aurenhammer, T. Hackl, B. Kornberger, S. Plantinga, G. Rote, A. Sturm and G. Vegter, Seed Polytopes for Incremental Approximation, Abstracts of the 24th European Workshop on Computational Geometry, Nancy, France, 2008, 13–16. – S. Ghosh and G. Vegter, Minimizing the Symmetric Difference Distance in Conic Spline Approximation, Abstracts of the 24th European Workshop on Computational Geometry, Nancy, France, 2008, 21–24.

4.5


External funding. The PhD position of A. Chattopadhyay is funded by NWO. The PhD position of S. Ghosh is funded by the European Commission in the Information Society Technologies (IST) program, funded under the 6th Framework Program of the European Commission, project Algorithms for Complex Shapes (ACS). The postdoc position of S. Plantinga is partially funded from the same EC-grant. The PhD position of S. Holtman (PI: H. Broer, Dynamical Systems) is funded by NWO. Another grant for a PhD position has awarded by NWO. This position is going to be filled in 2009. The Geometry group forms an e´ quipe associée with the project team Geometrica of INRIA Sophia Antipolis – Méditerranée. This joint project is funded by INRIA, and covers exchange visits, travel, and organization of workshops.

External collaboration. Vegter is co-ordinator of the European project Algorithms for Complex Shapes (ACS), a European consortium of leading groups in Computational Geometry (Freie Universität Berlin, ETH Zürich, Max Planck Institut für Informatik Saarbrücken, INRIA Sophia Antipolis, University of Athens, Tel Aviv University and the company GeometryFactory). He has also been a member of the a member of the reading committee and external examiner for the following PhD theses: 51

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E.J. Moet, Computation and complexity of visibility in geometric environments, Utrecht University, April 9, 2008. O.V. Lukina, Geometry of torus bundles in integrable Hamiltonian systems, University of Groningen, October, 2008. Vegter attended workshops and conferences in Nancy, France (European Workshop on Computational Geometry, March 2008), Brussels, Belgium (ACS final review, May 2008), and Amsterdam (Fifth European Congress of Mathematics, July 2008), and visited the Courant Institute of Mathematical Sciences, New York University (two weeks in October). He was co-organizer of the Computational Geometry Algorithms Library user event (Nancy, March 2008). Plantinga visited the Free University of Berlin (one week in May 2008), and attended a workshop in Nancy, France (European Workshop on Computational Geometry, March 2008). Ghosh attended a workshop in Nancy, France (European Workshop on Computational Geometry, March 2008).

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5.

Probability and Statistics

Group leader: Prof.dr. E. Wit Tenured staff (IWI member)

source

fte

Prof.dr. E.R. van den Heuvel Dr. C. Külske

RuG RuG

0.2 1.0

RUG

1.0

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PhD students V. Ermolaev (supervisor: Külske) S. Fleurke (supervisor: Külske) G. Iacobelli (supervisors: Külske and Van Enter) A. Opuku (supervisor: Külske)

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5.1

Research program

After being absent for a number of years, the research programme Statistics and Probability has returned to the Institute as a result of the appointments of Prof. Dr. E. Wit as Chair and Prof. Dr. E.R. van den Heuvel in 2008. Dr. C. Külske also joined this new research programme, coming across from Dynamical Systems & Analysis. The Statistics and Probability research programme intends to focus on the methodological aspects of the field. The aim is to link to the applied statistics colleagues around the university, while maintaining its applied mathematical roots. Currently the strengths of the research programme lie in statistical design, high-dimensional statistical inference with applications in the life sciences, pharmaceutical statistics and interacting stochastic systems.

5.1.1

Statistical Genomics and Pharmaceutical Statistics

Statistical genomics. Statistical methodology has always responded to latest developments in (measurement) advances in the substantial sciences. At the end of the 90s, new genomic technologies made it possible to obtain snapshots of the activity of 10,000s of genes simultaneously. This has lead to a new impulse in areas such as experimental design, sparse inference and functional statistics. The structure of such experiments has opened up a renewed interest in so-called row-column designs. Theoretical work combined with computer simulations have shown how graph theoretical considerations inform ideas about optimal statistical design of such experiments. Work in recent years has focussed on extending the ideas for multifactorial models and dependent data. The dimensionality of the problem in genomics has been archetypical for the types of inference required in modern high-throughput experiments in many areas of science and industry. The dimensionality of the feature space is often orders of magnitude larger than the number of observations. L1 -penalized methods has opened up a way for doing sparse inference. In this past year, we have been involved in extending these ideas to generalized linear models using differential geometry. Parallel to the high-dimensionality, exploratory route, the group is involved in explanatory modelling of genomics data via network modelling. From detailed kinetic differential equation models for the interaction of genomic particles to the graphical modelling of genetical network structures, this research programme is rather comprehensive and involves many international collaborations. During this year we had several collaborative projects, involving Dr. A. Recchia (University of Lancaster, GB), Dr. V. Purutçuoglu (Middle Eastern Technical University, Ankara, Turkey) and Dr. L. Augugliaro (University of Palermo, Italy). 54

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Statistics for measurement reliability. A measurement system quantifies or identifies one or more characteristics of an object. There are many types of measurement systems for measuring biological, medical, chemical and physical phenomena, including sensory measurements. Our research focusses on three distinct research questions. The first programme entails statistical modeling used to quantify the measurement value itself with respect to the standard. This part has already a prominent and long history in bioassays for example. The second programme involves statistical modeling used to validate the measurement system or quantify its performance. Estimation and construction of confidence intervals for the performance parameters is an important area. The third research interest is about reducing the effect of measurement reliability on decision making. Collaborative work has been done with Dr. A. Di Bucchianico (Mathematics and Computer Science, Eindhoven University of Technology). The collaboration was on the research for the construction of confidence intervals for linear combinations of variance components in the presence of missing data. This research was funded by NWO under Casimir project 018.002.029.

5.1.2

Interacting stochastic systems

Systems consisting of a large number of components which interact with each other in a stochastic way arise in physics, biology, social sciences, and finance. What makes them interesting is that they might show collective behavior and long range order. Our particular interest are disordered systems that pose a challenge to the mathematical physicist and probabilist. The general of aim of this program is to understand interacting stochastic systems on a mathematical level. Even when the interaction is local, such systems typically exhibit a complex global behavior, with a spatial long-range dependence resulting in phase transitions. Here phase transitions are characterized by discontinuous behaviour of the possible states of the system as a function of external parameters. For specifically tuned values of the parameters there can be more than one global state, i.e. a Gibbs measure. The equilibrium properties of such systems, as described by the Gibbs measures can be highly non-trivial, and in one direction of research we are focussing on these. Moreover we are also interested in the time-evolution of such measures. It is was discovered a few years ago that time-evolved measures may lose (and recover) their Gibbsian nature as a function of time. We are trying to approach this phenomenon in case studies. In a related line of research we are investigating continuous interfaces. We are also working on models for temperature-dependence of n−vector models, on the theory of disordered systems and on models for metastability and in general on examples of phase transitions of physical and conceptual interest. We are developing the theory in relationship with the theory of networks. Related stochastic methods also have use in applied problems like telecommunications, as an external PhD project with agentschap Telekom shows. 55

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The work is done in various collaborations, including in the last years J.-R. Chazottes (Paris), P. Collet (Paris), R. Fernández (Rouen, this year Groningen-Leiden-Eindhoven), F. Redig (Leiden), A. Le Ny (Orsay), W.Th.F. den Hollander (Leiden), E. Orlandi (Rome), R. van der Hofstad (Eindhoven), M. Biskup (UCLA), H.G. Dehling (Bochum), S. Shlosman (Marseille), V. Zagrebnov (Marseille), S. Romano (Pavia), K. Netocný (Prague).

5.2


Statistical genomics. Wit, together with A. Recchia and V. Vinciotti, extended previous statistically embedded differential equation models for analyzing gene expression data from a small herpes virus system. This systems approach has been also a them in work by Wit with V. Purutcuoglu. They used stochastic differential equations via diffusions to model a larger MAPK/ERK pathway system. Papers have appeared in IET Systems Biology and Bayesian Analysis. Wit has collaborated with L. Augugliaro on extending the LARS algorithm to generalized linear model using differential geometry. The results have been written up and submitted for publication. Wit also assisted a group of applied geneticists at the University of Liverpool, led by Steve Patterson. They were interested in detecting the molecular mechanisms by which parasitic nematodes reproduce and have adapted to life within a host. Wit designed the microarray experiment and used a mixed model to analyze the data from the experiment. A paper was published in the International Journal for Parasitology.

Methods for measurement reliability. Van den Heuvel generalized the Satterthwaite approximation method for the construction of confidence intervals for linear combinations of variance components in order to be applicable for any estimation method and for analysis of variance models with missing data. He also compared two linear regression analyses of long-term stability data with multiple storage conditions for the purpose of estimating the shelf life of drug products.

Mathematical Physics. About the Gibbsian-non-Gibbsian program, around which the PhD projects of Ermolaev, Opoku and Iacobelli are centered there were a number of developments. In this program one studies which measures can and cannot be written as a Gibbs measure for an effective Hamiltonian. This is often done in physics, although it turns out to be not always mathematically justified. Various examples of physical interest occur, e.g. in Renormalization Group theory, in the theory of disordered systems and in the study of non-equilibrium problems. A paper by Opuku and Külske regarding limiting kernels and Gibbs properties of local transforms of continuous Spin Mean-Field models appeared in the Journal of Math. Physics. They also worked on a whether transforms of Gibbs measures are still Gibbsian and published the results in the Electronic Journal of Probability. 56

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Külske toether with Dehling and Ph.D. Fleurke worked on the occupation probability of a parking process on a random tree. They derived the large-time limit and published the results in J. Stat. Phys. Külske together with Orlandi showed that an arbitrary weak random field term is is enough to beat an arbitrarily strong delta-pinning in 2 dimensions and will cause delocalization. This was published in Stochastic Processes and their Applications. Finally Van Enter and Külske proved the non-existence of random gradient Gibbs measures in continuous interface models in d = 2. A paper with this result appeared in Annals of Applied Probability.

PhD research. Opoku has made good progress in his PhD research with supervisor Külske. Two articles have been accepted for publication and another preprint is in preparation. Previously Külske and LeNy provided a complete analysis of the transition between Gibbsian and non-Gibbsian behavior as a function of time in the ferromagnetic Ising mean-field model, for non-interacting stochastic dynamics. The PhD research of Ermolaev aims at a similarly complete description including the lowtemperature regime of dynamics and initial measure in the corresponding mean-field model, based on different (path-large-deviation) methods. Ermolaev has made good progress in his second year with Külske. Fleurke as an external has made good progress: One article has been completed, another has been submitted. Iacobelli, also working with Külske has started his first year by reading up on the relevant literature.

5.3

Research subjects

V. Ermolaev: Path variational principle of mean-field measures. S. Fleurke: Blocking models and frequency assignment. E.R. van den Heuvel: statistics of bioassays, validating measurement systems, reducing the effect of measurement reliability on decision making. bf G. Iacobelli: Interacting stochastic models on small-world networks. ¨ Ch. Kulske: Interacting stochastics systems, short-range vs. mean-field models, Gibbs measures vs. non-Gibbsian measures, interfaces, disordered systems, concentration inequalities, networks. A. Opoku: Relation between short-range and long-range models. E.C. Wit: Statistical design, high-dimensional inference, statistical bioinformatics, statistical network modelling.

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5.4

Publications Articles in scientific journals – H.G. Dehling, S.R. Fleurke, C. Külske, Parking on a random tree, J. Statistical Physics, 133 (1), 2008, 151-157. – H. Evans, LV Mello, YX Fang, E. Wit, et al., Microarray analysis of gender- and parasitespecific gene transcription in Strongyloides ratti, Int. J. Parasitology, 38 (11), 2008, 1329-1341. – Purutçuoglu, E. Wit, Bayesian inference for the MAPK/ERK pathway by considering the dependency of the kinetic parameters, Bayesian Analysis, 3 (4), 2008, 851-868. – A. Recchia, E. Wit, V. Vinciotti, et al., Computational inference of replication and transcription activator regulator activity in herpesvirus from gene expression data, IET Systems Biology, 2 (6), 2008, 385-396. Articles in conference proceedings – Y.X. Fang, E. Wit, Test the overall significance of p-values by using joint tail probability of ordered p-values as test statistic, Advanced Data Mining and Applications, Proc. 4th Int. Conf., ADMA 2008, 2008, 435-43.

5.5


External funding PhD grant (supervisor C. Külske): An NWO grant (open competition, co-supervisors A.C.D. van Enter and R. van der Hofstad (TU/e)) was acquired for PhD research in the area of interacting stochastic models on small-world networks. G. Iacobelli was appointed on this grant on January 1, 2008. External collaboration E.C. Wit acted as the external examiner to the M.Sc. degree in Statistics and Statistical Bioinformatics at the School of Mathematics, University of Leeds. E.C. Wit was external examiner for the MSc thesis of Alberto Caimo, Applications and extensions of sure independence screening, supervisor A. Montanari, University of Bologna. 58

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5.6

Further information

E.C. Wit gave invited lectures at the following occasions: – “Reverse engineering pathway dynamics from microarray data”, invited talk, IBS-EMR Conference, Istanbul, Turkey, 13 May 2009. – “Muddling or modelling your way through normalization?”, CAMDA, Vienna, Austria, 5 December 2008. – “Nesting and other replication issues in two-channel microarray designs”, invited talk, International Biometric Conference, 17 July 2008. – “High-dimensional inference in bioinformatics and genomics,” Newton Institute, Future Directions in High-dimensional Data Analysis: New Methodologies, New Data Types and New Applications, Cambridge, 24 June 2008. – “From genomes to systems and ‘some’ statistics in-between”, invited talk, From Genomes to Systems Conference, Manchester, UK, 19 March, 2008. – “Modelling transcription activation using microarray data”, invited talk, 6th workshop: Statistical Methods for Post-genomic Data”, Rennes, France, 31 January 2008.

C. Külske gave talks at: – “On transforms of measures on graphs and the posterior metric”, Statistical Mechanics on Random Structures, Eurandom, Eindhoven, The Netherlands, March 10-14, 2008. – “What disorder can do to continuous interfaces”, invited talk, 3rd La Pietra Week in Probability, June 23-27, 2008.

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6. Systems, Control and Applied Analysis Group leader: Prof.dr. A.J. van der Schaft Tenured staff (IWI members) Dr. M.K. Camlibel Prof.dr. H.L. Trentelman Prof.dr. A.J. van der Schaft Prof.dr. H. Gluesing-Luerssen Emeritus Prof.dr.ir. A. Dijksma

PhD students S. Fiaz (supervisor: H.L. Trentelman) F. Kerber (supervisor: A.J. van der Schaft) Ha Bin Minh (supervisor: H.L. Trentelman) R. Polyuga (supervisor: A.J. van der Schaft) H.-G. Schneider (till September 1) (supervisor: H. Gluesing-Luerssen) Q.T. Le (since September 1) (supervisor: M.K. Camlibel) F.L. Tsang (till June 1) (supervisor: H. Gluesing-Luerssen, M. van der Put) A. Venkatraman (supervisor: A.J. van der Schaft) H. Vinjamoor (supervisor: A.J. van der Schaft) M. Younas (supervisor: H.L. Trentelman)

source RuG RuG RuG University of Kentucky, USA

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IWI Annual Report Guests J.-S. Pang, University of Illinois at Urbana-Champaign, USA M. Barakat, Aachen University of Technology, Germany J.C. Willems, University of Leuven, Belgium U. Oberst, Innsbruck, Austria E. Zerz, Aachen University of Technology, Germany S. Shankar, Chennai Mathematical Institute, India I. Masubuchi, University of Hiroshima, Japan B.M. Maschke, Univ. Claude Bernard Lyon-1, France A. Fernandez Villaverde, University of Vigo, Spain M. Opmeer, University of Bath, UK M. Dür, University of Dortmund, Germany A. Palmigiano, Palermo University, Italy J. Rosenthal, University of Zürich, Switzerland W. Schmale, University of Oldenburg, Germany D. Napp Avelli, University of Aveiro, Portugal A. Macchelli, University of Bologna, Italy D. Alpay, Ben-Gurion University, Israel B. Curgus, Western Washington University, Bellingham, WA, USA V. Andrieu, LAAS-CNRS, France F. Castanos, LSS-Supelec, Gif-sur-Yvette, France A.C. Antoulas, Rice University, Houston, USA J.P. Fortney (Fulbright Fellow), Arizona State University, Phoenix Az, USA

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6.1

Research Program

The research program Systems, Control and Applied Analysis (SCAA) is devoted to the analysis and control of complex dynamical systems. The mathematical research in this program is motivated by various application areas, including physical engineering systems, coding theory and networked control systems, and system biology. Common themes in the research are the modelling of complex systems as interconnection of open subsystems, the analysis of the behavior of systems and their structural properties, and the design of controlled systems. The five main lines of research are: 1. Modeling and control of multi-physics systems as port-Hamiltonian systems (Arjan van der Schaft, Rostyslav Polyuga, Aneesh Venkatraman, Jon Pierre Fortney) 2. Behavioral systems and control theory (Harry Trentelman, Shaik Fiaz, Ha Binh Minh, Harsh Vinjamoor, Mohammed Younas) 3. Analysis and design of hybrid dynamical systems (Kanat Camlibel, Arjan van der Schaft, Florian Kerber, Thuan Quang Le, Harsh Vinjamoor) 4. Algebraic methods in systems and control theory and coding theory (Heide Gluesing-Luerssen, Gert Schneider, Fai-Lung Tsang) 5. Schur analysis and operator theory in spaces with indefinite metric Port-Hamiltonian systems are generalized Hamiltonian systems where the geometric structure is derived from the interconnection structure of the complex system. The aim of this work is to provide a systematic mathematical theory for the mathematical modelling, analysis and simulation of multiphysics, mixed lumped- and distributed parameter, systems by making explicit the underlying physical structure, including energy balances and other conservation laws. Furthermore, the port-Hamiltonian framework is employed for controller design, by attaching controller port-Hamiltonian systems and shaping the Hamiltonian and other conserved quantities to a desired Lyapunov function for the controlled system, leading to physically inspired and robust control strategies. The traditional way of modeling dynamical systems that interact with their environment is by an input-output map. However, physical systems in general do not exhibit the information flow direction that is pre-supposed by the input-output structure. In the behavioral approach, all external system variables are therefore a priori treated on an equal footing, while the mathematical model specifies a subset of the set in which the external variables take their values as being possible. This subset is called the behavior of the system. Many modeling and control questions are fruitfully studied in this novel setting. Although most of the research aims at linear differential systems it also provides inspiration for nonlinear and hybrid dynamical systems. 63

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Hybrid systems are a mixture of interacting continuous and discrete dynamics, and arise naturally in embedded systems and physical systems modeling. Important research issues concern the systematic modelling of complex hybrid systems, the analysis of hybrid systems and their solution trajectories, the development of compositional reasoning techniques, the analysis of structural properties of controllability and stabilizability, and the design of controllers. From a mathematical point of view hybrid systems necessitate the merging of concepts and tools from continuous dynamics with those from discrete dynamics, thus linking to formal verification tools from computer science. The mathematical analysis of hybrid systems is heavily intertwined with optimization theory and non-smooth analysis. Coding theory is concerned with reliability of data transmission. When data are sent over a noisy channel, they undergo in general some outside errors and are therefore corrupted when they reach the receiver. Coding theory aims at preprocessing (encoding) the data such that the receiver will be able to recover the correct data from the erroneous ones (decoding). The most widely known tool for this task are block codes. However, since decades engineers also make use of convolutional codes. These codes can, in a certain sense, be regarded as discrete-time dynamical systems over a finite field. Since the mid 1990’s this insight has led to quite some developments in the mathematical theory of convolutional codes. The research in convolutional coding theory aims at the construction of good codes and at the analysis of these codes. Besides state-space representations also image and kernel representations of convolutional codes are helpful in this regard. Due to their nature as systems over finite fields this area requires mainly algebraic methods. Schur analysis and operator theory in indefinite metric spaces deals with the extension of classical Schur analysis, in particular interpolation problems and the properties of the generalized Schur transformation. The state spaces are reproducing kernel Pontryagin spaces. The research group organizes together with the Control Engineering group at the Institute for Industrial Engineering and Management, University of Groningen (Jacquelien Scherpen, Bayu Jayawardhana, Ming Cao) the joint Systems & Control Seminar, as well as a ”Journal Club”.

6.2

Overview of scientific results and outlook

D. Alpay (Beer Sheva, Israel), A. Dijksma and H. Langer (Vienna) introduced a Schur transformation and a corresponding sequence of Schur parameters for a Nevanlinna function and a generalized Nevanlinna function and applied them to approximate the Nevanlina function or the generalized Nevanlinna function by rational ones. The research in Schur Analysis will be continued with a study of boundary interpolation for generalized Nevanlinna functions in connection with so-called rigidity (or uniqueness) problems. A. Dijksma, A. Luger (Lund) and Y. Shondin (Niznhy Novgorod) obtained explicit state space models for a special class of Nevanlinna functions which appear in the theory of, for example, the Bessel differential operator. The state spaces are reproducing kernel Pontryagin spaces 64

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whose reproducing kernel is a matrix function constructed from the data in the representation of the Nevanlinna function. In a sequel these models will be used to approximate a singular Bessel differential operator by regular ones. This approximation involves the theory of approximating an operator by operators acting in different Pontryagin spaces. K. Camlibel continued conducting research in the area of non-smooth and hybrid dynamical systems. The scientific results that were achieved in the last year can be summarized as follows: – Full algebraic characterizations of the two fundamental system-theoretic properties of controllability and stabilizability have been established for a subclass of piecewise affine systems, namely conewise linear systems. – For bimodal (possibly discontinuous) piecewise linear systems, the problem of existence and uniqueness of solutions has been investigated within a differential inclusion setting. These efforts yield necessary and sufficient conditions under which the so-called Filippov solutions exist and are unique. – Convergence of the backward Euler numerical scheme for linear complementarity systems that arise in the context of power electronics was addressed. It was shown that the backward Euler numerical scheme produces approximations that converge to the actual solutions of linear complementarity systems under investigation. Harry Trentelman and PhD students worked along the following lines: – Within the project on the behavioral approach to nD systems, on January 18, 2008, D. Napp Avelli obtained his doctoral degree with his dissertation entitled ”An Algebraic Approach to Multidimensional Behaviors”. Research within this project continues, and is currently aimed at the problem of developing a theory of H-infinity filtering for nD behaviors. – Within the project on control as interconnection, we have started a study on the issue of robust control in a behavioral context. In particular, we have studied the following problem: given a nominal plant behavior together with a ball of a certain radius around this nominal plant, find necessary and sufficient conditions for the existence of a single controller behavior such that the interconnection of plant behavior and controller behavior is stable and regular. For the socalled full interconnection case, i.e., the case that the to be stabilized variables coincide with the interconnection variables, we have solved the problem of finding the optimal stability radius, i.e. the maximal radius of the ball around the nominal plant for which a single stabilizing controller exists. Our results use recent ideas of rational representations of system behaviors, and have a nice interpretation in terms of the existence of sign-definite storage functions. Research in the area continues in several directions. In particular we study problems of optimal robust stabilization under uncertainty structures represented by integral quadratic constraints. 65

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– In the context of model reduction, we have continued to work on model reduction of dissipative systems using balanced truncation methods. We have formulated the problem in a general behavioral setting, and have succeeded in characterizing the characteristic values associated with positive real balancing and bounded real balancing in terms of the ”generalized” singular values of particular linear maps from past two future behavior. These maps are defined in terms of the concepts of required supply and available storage of the to be reduced behavior. For the special case of strictly bounded real systems, we have established new error bounds under balanced truncation. Finally, the doctoral dissertation of Ha Binh Minh (”Model Reduction in a Behavioiral Framework”) was completed in December 2008. Research within this project continues, and is currently aimed at establishing new error bounds for positive real balanced truncation. Within the research of Arjan van der Schaft and PhD students the following main results have been obtained: – In collaboration with B. Maschke (Lyon) a new approach to lumping of distributed conservation laws has been proposed, making explicit use of the theory of k-complexes, and directly leading to finite-dimensional port-Hamiltonian system models. This is currently applied to many cases of physical interest, and is expected to lead to new views on network modeling of physical systems, as well as to new methodologies for control of networked dynamical systems. – The work together with R. Polyuga and J.M.A. Scherpen on structure-preserving model reduction of port-Hamiltonian systems has been continued, leading to new results on structurepreserving moment matching for linear port-Hamiltonian systems and on the Kalman decomposition of nonlinear port-Hamiltonian systems. – With F. Kerber notions of ’assume-guarantee’ compositional reasoning techniques from concurrent processes have been extended to linear continuous-time dynamical systems. Next step in this research is to extend these results to switching linear systems, as an important class of hybrid systems. – Together with H. Vinjamoor the theory of control by interconnection and the notion of canonical controllers has been extended to systems in state-space description. A complete characterization has been given of the achievable closed-loop behavior up to bisimulation. Crucial notion in this endeavor is the concept of the ’canonical controller’. Currently it is being investigated under which conditions this canonical controller can be reduced to a regular feedback controller. – The work with A. Venkatraman, as well as with R.Ortega and F. Castanos (LSS-Supelec, France), on control by interconnection and observer design of nonlinear port-Hamiltonian systems has been continued. This has led to strong results on the relation with the InterconnectionDamping-Assignment Passivity-Based control methodology, as well as on passivity-based observer design. 66

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Heide Gluesing-Luerssen and PhD students worked along the following lines: – The concept of cyclicity for convolutional codes has been introduced in the seventies of the last century, but only recently an algebraic theory of cyclic convolutional codes (CCC’s, for short) could be established. It provides both a huge class of powerful codes and a nice generalization of the algebraic theory of cyclic block codes. This research project is concerned with a continuation of the algebraic theory and with an investigation of the class of CCC’s with respect to its coding theoretic properties. We have worked on the construction of CCC’s with prescribed algebraic parameters (Forney indices). This investigation aims at a clarification of the richness of the class of CCC’s within the class of all convolutional codes. – The project ”Weight distribution for convolutional codes” a convolutional encoder interpreted as an input-state-output system over a finite field. The main tool for computing the weight distribution is the weight adjacency matrix associated with the system. Factoring out a natural group action it turns into an invariant of the code. This matrix is in the center of the project. It fully determines the classical weight distribution, but actually contains even more information about the error-correcting quality of the code. Recently we could establish a MacWilliams type identity in terms of this invariant for convolutional codes and their duals. Furthermore, we could generalize the identity to the complete weight adjacency matrix, in which also the values of the nonzero coordinates are being accounted for. – The project ”Equivalence of convolutional codes” aims at clarifying as to when one may declare two codes as identical with respect to their error-correcting properties. Up to now such a classification of convolutional codes does not exist. It is immediately clear that weight- and degree-preserving isomorphisms are too weak in order to yield a coding-theoretically sound notion of equivalence for convolutional codes since many important parameters of the code are not invariant under such isometries. This project concentrates on those degree-preserving isometries that also leave those parameters invariant. For isometries a type of MacWilliams Equivalence Theorem could be established, that is, the isometries are all given by permutations and suitable rescaling of the codeword coordinates. For strong isometries examples show that such a characterization is not true. Further considerations of the weight adjacency matrix however leads to some deeper insight for this case as well.

6.3

Research subjects

M.K. Camlibel: Hybrid and piecewise-linear systems. A. Dijksma: Operator theory in spaces with an indefinite metric. Schur analysis. Spectral problems. Approximation theory of singular differential operators by regular ones. S. Fiaz (PhD student, with H.L. Trentelman): Control by interconnection, stability analysis and synthesis, rational representations. Robust stabilization in a behavioral context. 67

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J.P. Fortney (Fulbright fellow, with A.J. van der Schaft): Geometric modeling of RLC-circuits H. Gluesing-Luerssen: Algebraic methods in systems and control theory and coding theory. Convolutional coding theory. Cyclicity and weigth distribution. Equivalence of convolutional codes. B.M. Ha (PhD student, with H.L. Trentelman): Model reduction in a behavioral context. Approximation of dissipative systems by dissipative systems of lower complexity. Balancing in a behavioral framework. F. Kerber (PhD student, with A.J. van der Schaft): Compositional analysis and control of linear systems and hybrid systems. Bisimulation of linear and hybrid systems. Assume-guarantee reasoning. Q.T. Le (PhD student with M.K. Camlibel): System-theoretic properties of piecewise affine dynamical systems by employing geometric control techniques. D. Napp Avelli (PhD student, with H.L. Trentelman): Modeling and control of systems decribed by linear partial differential equations with constant coefficients. Behavioral interconnections of nDsystems, implementability of nD system behaviors. H-infinity filtering for behavioral nD systems, spectral factorization, sums of squares. R. Polyuga (PhD student, with A.J. van der Schaft): Model reduction of linear port-Hamiltonian systems. Structure preserving model reduction by balancing and Krylov methods. A.J. van der Schaft: Geometric network modeling, analysis and control of physical systems. Thermodynamic systems and chemical reaction networks. Nonlinear control. Compositional modelling, analysis and control of hybrid systems. H.-G. Schneider (PhD student, with H. Gluesing-Luerssen): Convolutional codes, Weigth adjacency matrices and MacWilliams identities for convolutional codes. H.L. Trentelman: Modeling and control of nD system behaviors, Control by interconnection, optimal robust stabilization of system behaviors, Structure preserving model reduction in a behavioral context. F.L. Tsang (PhD student, with H. Gluesing-Luerssen and M. van der Put): Convolutional codes and discrete systems. A. Venkatraman (PhD student, with A.J. van der Schaft): Control of port-Hamiltonian systems. Passivity-based control and control by interconnection. Design of observers for nonlinear port-Hamiltonian systems. H. Vinjamoor (PhD student, with A.J. van der Schaft: Control by interconnection up to bisimulation. Reduction of the canonical controller and regular feedback achievability. M. Younas (PhD student, with H.L. Trentelman): Controllability and observability of descriptor systems, connections with system behaviors. Reduction by balancing of descriptor systems.

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6.4

Publications Dissertations – D. Napp Avelli, An algebraic approach to multidimensional behaviors, promotores: M. van der Put en H. Trentelman, Faculty of Mathematics and Natural Sciences, University of Groningen, 18 januari 2008, 126 pages. – F.L. Tsang, Skew rings, convolutional codes and discrete systems, promotor: M. van der Put, copromotor: H. Gluesing-Luerssen, Faculty of Mathematics and Natural Sciences, University of Groningen, 23 juni 2008, 159 pages. – H.-G. Schneider, On the weight adjacency matrix of convolutional codes, Promotor: R.F. Curtain, Co-promotor: H. Gluesing-Luerssen, Faculty of Mathematics and Natural Sciences, University of Groningen, the Netherlands, 26 september 2008, 88 pages. Articles in scientific journals – M.K. Camlibel, W.P.M.H. Heemels, and J.M. Schumacher, A full characterization of stabilizability of bimodal piecewise linear systems with scalar inputs, Automatica, 44(5), 2008, 12611267. – M.K. Camlibel, W.P.M.H. Heemels, and J.M. Schumacher, Algebraic necessary and sufficient conditions for the controllability of conewise linear systems, IEEE Trans. on Automatic Control, 53(3), 2008, 762-774. – H. Gluesing-Luerssen, G. Schneider, On the MacWilliams identity for convolutional codes, IEEE Trans. Inf. Theory, 54, 2008, 1536–1550. – H. Gluesing-Luerssen, F.-L. Tsang, A matrix ring description for cyclic convolutional codes, Advances in Mathematics of Communications, 2, 2008, 55-81. – A.A. Julius, J.W. Polderman, A.J. van der Schaft, Parametrization of the regular equivalences of the canonical controller, IEEE Transactions on Automatic Control, 53, 2008, 1032–1036. – D. Napp Avelli and H.L. Trentelman, Algorithms for multidimensional spectral factorization and sum of squares, Linear Algebra and its Applications, 429, 2008, 1114-1134. – D. Napp Avelli, S. Shankar and H.L. Trentelman, Regular implementation in the space of compactly supported functions, Systems and Control Letters, 57, 2008, 851 - 855. – R. Ortega, A.J. van der Schaft, F. Castaños, A. Astolfi, Control by interconnection and standard passivity-based control of port-Hamiltonian systems, IEEE Transactions on Automatic Control, 53, 2008, 2527–2542. 69

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– N. Sakamoto, A.J. van der Schaft, Analytical approximation methods for the stabilizing solution of the Hamilton-Jacobi equation, IEEE Transactions on Automatic Control, 53, 2008, 2335– 2350. – A.J. van der Schaft, Balancing of lossless and passive systems, IEEE Transactions on Automatic Control, 53, 2008, 2153–2157. Articles in conference proceedings – D. Alpay, A. Dijksma, and H. Langer, Augmented Schur parameters for generalized Nevanlinna functions and approximation, Theory: Adv., Appl., 188, Birkhäuser Verlag, Basel, 2008, 1–30. – M.K. Camlibel, Controllability and stabilizability of bimodal systems with discontinuous vector fields, 18th Int. Symposium on Mathematical Theory of Networks and Systems, 2008, Blacksburg, USA. – M.K. Camlibel, Well-posed bimodal piecewise linear systems do not exhibit Zeno behavior, 17th IFAC World Congress on Automatic Control, 2008, Seoul, South Korea. – J. Carrasco, A. Baos, A.J. van der Schaft, A passivity approach to reset control of nonlinear systems, in Proc. 34th Annual Conf. of the IEEE Industrial Electronics Society (IECON’08), Orlando, FL, USA, November 10-13, 2008, 61–66. – A. Dijksma, A. Luger, and Y. Shondin, Approximation of Nκ∞ -functions I: models and regularization, Operator Theory: Adv., Appl., 188, Birkhäuser Verlag, Basel, 2008, 87–112. – R. Frasca, M.K. Camlibel, I.C. Goknar, L. Iannelli, and F. Vasca, State discontinuity analysis of linear switched systems via energy function optimization, 2008 IEEE Int. Symposium on Circuits and Systems, 2008, Seattle, USA. – H. Gluesing-Luerssen, G. Schneider, Duality for Convolutional Codes, in Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, Blacksburg (Va./USA), 2008. – H. Gluesing-Luerssen, Equivalence Notions for Convolutional Codes, in Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems Blacksburg (Va./USA), 2008. – W.P.M.H. Heemels and M.K. Camlibel, Null controllability of discrete-time linear systems with input and state constraints, 47th IEEE Conference on Decision and Control, 2008, Cancun, Mexico. – W.P.M.H. Heemels, M.K. Camlibel, B. Brogliato, and J.M. Schumacher, Observer-based control of linear complementarity systems, Hybrid Systems: Computation and Control, LNCS 4981 (M. Egerstedt and B. Mishra editors) 2008, Springer, Berlin, 259-272. 70

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– D. Jeltsema, A.J. van der Schaft, Symplectic Hamiltonian formulation of transmission line systems with boundary energy flow, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA/ – H.B. Minh, H.L. Trentelman and P.Rapisarda, Model reduction of dissipative systems by balanced truncation, Proc. 17h IFAC World Congress , (IFAC WC 2008), 2008. – R. Pasumarthy, V. R. Ambati, A.J. van der Schaft, Port-Hamiltonian formulation of shallow water equiations with coriolis forces and topography, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA, 124 –136. – R. Polyuga, A.J. van der Schaft, Structure preserving model reduction of port-Hamiltonian systems, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA. – I. Sarras, A. Venkatraman, R. Ortega, A.J. van der Schaft, Partial linearization of mechanical systems with application to observer design, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA. – A.J. van der Schaft, B.M. Maschke, Conservation laws and open systems on higher-dimensional networks, in Proc. 47th IEEE Conf. on Decision and Control, Cancun, Mexico, December 9-11, 2008, 799–804. – J.M.A. Scherpen, A.J. van der Schaft, A structure preserving minimal representation of a nonlinear port-Hamiltonian system, in Proc. 47th IEEE Conf. on Decision and Control, Cancun, Mexico, December 9-11, 2008, 4885–4890. – K. Takaba, H.L. Trentelman and J.C. Willems, On polynomial and rational quadratic differential forms, Proc. 17h IFAC World Congress , (IFAC WC 2008), 2008. – A. Venkatraman, R. Ortega, I. Sarras, A.J. van der Schaft, Control of underactuated mechanical systems: Observer design and position feedback stabilization, in Proc. 47th IEEE Conf. on Decision and Control, Cancun, Mexico, December 9-11, 2008, 4969–4974. – A. Venkatraman, A.J. van der Schaft, Full-order observer design for a class of port-Hamiltonian systems, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA. – T. Voss, J.M. Scherpen, A.J. van der Schaft, Modeling for control of an inflatable space reflector, the linear 1-D case, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA. Other publications A. Dijksma, After dinner speech on the inventor of the equality sign, Operator Theory: Adv., Appl., 188, Birkhäuser Verlag, Basel, 2008, 1–3. 71

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6.5

Seminars

The following seminars and (semi-)plenary talks were delivered elsewhere: – M.K. Camlibel, Controllability and stabilizability of bimodal systems with discontinuous vector fields 18th Int. Symposium on Mathematical Theory of Networks and Systems 2008, Blacksburg, USA. – M.K. Camlibel, Well-posed bimodal piecewise linear systems do not exhibit Zeno behavior 17th IFAC World Congress on Automatic Control 2008, Seoul, South Korea. – A. Dijksma, The Schur transformation for Nevanlinna functions at ∞, Schur Analysis seminar, Beer Sheva, Israel, January 28. – A. Dijksma, Augmented Schur parameters for generalized Nevanlinna functions and approximation, one day workshop on January 31, Rehovot, Israel, in honor of Prof. H.Dym. – A. Dijksma, Quadratic (weakly) hyperbolic matrix polynomials: Direct spectral problems, Workshop Operator Theory in Krein spaces, TU Berlin, December 18-21. – H. Gluesing-Luerssen, 18th Int. Symposium on Mathematical Theory of Networks and Systems, Blacksburg (Va./USA); invited talks in two special sessions, July 2008. – H. Gluesing-Luerssen, Workshop Mathematical Systems Theory, Elgersburg (Germany), February 2008. – H.L. Trentelman, Control in a Behavioral Framework, Semi-plenary talk at the 18th Symposium on Mathematical Theory of Networks and Systems, MTNS 2008, Virginia Tech, Blacksburg, Virginia, USA. – H.L. Trentelman, Positive and Bounded Real Balanced Model Reduction, Seminar at the Department of Electrical Engineering, Hiroshima University, Japan, October 2008. – H.L. Trentelman, Reduction by Balanced Truncation of Dissipative Behaviors, with error bounds, Plenary talk at the SdeBoker Workshop on Linear Systems 2008, SdeBoker, Israel, September 2008. – A.J. van der Schaft, On balancing of passive and port-Hamiltonian systems, Department Seminar LSS-Supelec, Gif-sur-Yvette, January 13, 2008. – A.J. van der Schaft, Stabilizing switching control of power converters, Meeting EU Network of Excellence HYCON, Workpackage 4a, Delft University of Technology, January 30. 72

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– A.J. van der Schaft, The port-Hamiltonian approach to physical system modeling and control, Part I ”Network modeling and Analysis”, Part II, Control of port-Hamiltonian systems, Minicourse Benelux Meeting, Heeze, March 18–20. – A.J. van der Schaft, Synthesis of Engineering Systems: a Theoretical Perspective, Plenary Talk Kick-off Meeting Centre for Synthetic Biology, University of Groningen May 23. – A.J. van der Schaft, Port-Hamiltonian formulation of shallow water equiations with coriolis forces and topography, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA. – A.J. van der Schaft, Static impedance shaping and stabilization by non-collocated control, Proc. 18th Int. Symposium on Mathematical Theory of Networks and Systems, July 28 - August 1, 2008, Blacksburg, VA, USA. – A.J. van der Schaft, Conservation laws and open systems on higher-dimensional networks, Department Seminar Delft University of Technology, October 15. – A.J. van der Schaft, The port-Hamiltonian approach to physical system modeling and control, Graduate Course, Université de Namur, Belgium, November 18. – A.J. van der Schaft, Conservation laws and open systems on higher-dimensional networks, 47th IEEE Conf. on Decision and Control, Cancun, Mexico, December 9-11.

6.6

External funding

6.7

NWO funding

– The project ’Stability Analysis and Robust Stabilization for System Behaviors’ (Applicant H.L.Trentelman) was funded in the ’Vrije Competitie Exacte Wetenschappen’, NWO, Spring 2008. – The project ’Structure Preserving Model Reduction for Port Hamiltonian Systems’ (Applicants A.J. van der Schaft, with J.M.A. Scherpen) was funded in the ’Vrije Competitie Exacte Wetenschappen’, NWO, Spring 2008.

6.8

Internalization

– In June 2008 the PhD student Ha Binh Minh spent two weeks at the University of Southampton to collaborate with Professor P. Rapisarda. – In February 2008 the PhD student A. Venkatraman spent one month at the Laboratoire des Signaux et Syst’emes, Gif-sur-Yvette, france, working with prof. R. Ortega. 73

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– The Fulbright Fellow J.P. Fortney (visiting the University of Groningen from September 1, 2007 till June 1, 2008) defended his PhD thesis entitled ”Dirac structures in pseudogradient systems with an emphasis on electrical networks” at the Arizona State University in June 2008.

6.9

Editorial activities

M.K. Camlibel: – Subject Editor for the International Journal of Robust and Nonlinear Control – Associate Editor for the 17th IFAC World Congress on Automatic Control, Seoul, Korea, 2008 M.K. Camlibel serves as a member of the IFAC Technical Committee on Linear Systems, the IFAC Technical Committee on Control Design, and the IFAC Technical Committee member on Discrete Event and Hybrid Systems. A.Dijksma is member of the Editorial Board of the journals Integral Equations and Operator Theory and Complex Analysis and Operator Theory. H. Gluesing-Luerssen: – Associate Editor of SIAM Journal on Control and Optimization – Associate Editor of Advances in Mathematics of Communications. – Member of the Steering Committee of the Mathematical Theory of Networks and Systems Symposium (Biennial International Conference) since August 2008. – Co-organizer of a special session on Coding Theory for the sectional AMS meeting at Bloomington/In., April 2008. H.L. Trentelman: Associate editor for Systems and Control Letters A.J. van der Schaft: – Editor-at-Large for European Journal of Control – Associate Editor for ESAIM COCV – Associate Editor for Systems & Control Letters – Associate Editor for Journal of Geometric Mechanics – Member of the Steering Committee of the Mathematical Theory of Networks and Systems Symposium (Biennial International Conference) 74

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6.10

Further signs of recognition and news items

– The paper ’An approximation method for the stabilizing solution of the Hamilton-Jacobi equation for integrable systems, a Hamiltonian perturbation approach”, Transactions of the Society of Instrument and Control Engineers (SICE), vol. 43, pp. 572–580, 2007, by N. Sakamoto and A.J. van der Schaft, received the SICE Takeda Best Paper Prize 2008. – In February 2008 H.L. Trentelman was among the 10 nominees for the annual Teaching Award of the University of Groningen. – A.J. van der Schaft organized the DISC Summer school ”Cells and Systems”, Woudschoten, June 17-20. – From October 26 to November 11 H.L. Trentelman visited the Department of Applied Mathematics and Physics, Kyoto University, Japan. – A. Dijksma visited Prof. D. Alpay at the Ben Gurion University of the Negev, Beer Sheva, Israel, January 27–February 3 and Prof. T. Azizov at the Voronezh State University in Voronezh, Russia, April 2–April 19 and participated in the workshop on Operator Theory in Krein spaces, TU Berlin, December 18–21.

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7.

Distributed Systems and Software Engineering

Group leader: Prof.dr.ir. M. Aiello Tenured staff (IWI members) Prof.dr.ir. M. Aiello Dr.ir. P. Avgeriou

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Tenured staff (other) Dr. R. Smedinga

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Honorary professors Prof.dr.ir. J. Bosch Prof.dr. S. Dustdar

Intuit TU Wien

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Hanzehogeschool Groningen Fontys Hogeschool Techniek en Logistiek EU FP7

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Postdocs A. Jansen (till 01-10-2008) (supervisor: Avgeriou) Dr. P. Liang (supervisor: Avgeriou) PhD students T.B. Collo Arias (supervisor: Avgeriou) E. El-Khoury (supervisor: Aiello) N. Harrison (supervisor: Avgeriou) E. Kaldeli (supervisor: Aiello) A.W. Kamal (supervisor: Avgeriou) P. Kamphuis (since 01-09-2008) (supervisor: Aiello) U. van Heesch (since 01-10-2008) (supervisor: Avgeriou) M.C. Doˇganay (since 15-12-2008) (supervisor: Aiello)

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IWI Annual Report Guests S. Tai, Karlsruhe, Germany L. Alvisi, The University of Texas at Austin, United States L. Penserini, Utrecht University, The Netherlands E. Erdem, Sabanici University, Turkey I. Bloch, ENST Paris, France F. Arbab, CWI, The Netherlands O. Zimmermann, IBM Zurich, Switzerland J. Jeuring, Open University and Utrecht University, the Netherlands S. Giesecke, University of Oldenburg, Germany A. Tang, Swinburne University of Technology, Australia J. Andersson, Vaxjo University, Sweden M. Wermelinger, The Open University, UK U. Zdun, Technical University of Vienna, Austria

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7.1

Research Program

The Distributed Systems and Software Engineering research program is concerned with theoretical and practical aspects of engineering software and systems. The program is divided into two distinct research groups: – The Service-Oriented Systems (SOS) Group devoted to Distributed Systems and ServiceOriented Computing. The group is lead by M. Aiello. – The Software Engineering and Architecture (SEARCH) group devoted to Software Engineering and particularly, Software Architecture, Patterns, Evolution and Architectural Knowledge. The group is lead by P. Avgeriou. The two research groups are working on the following research topics. Service-Oriented Systems group Service-Oriented Computing (SOC) is an emerging computing paradigm for building distributed information systems in which the concepts of distribution, openness, asynchronous messaging and loose coupling take a leading role. In this context, applications are built out of individual services that expose functionalities by publishing their interfaces into appropriate repositories, abstracting entirely from the underlying implementation. Published interfaces may be searched by other services or users and subsequently be invoked. The interest in Service-Oriented Computing is a consequence of the shift from a vision of a web based on the presentation of information to a vision of the web as computational infrastructure, where systems and services can interact in order to fulfill users’ requests. Web Services (WS), the best-known example, are the realization of service-oriented systems based on open standards and infrastructures, extending the XML syntax. Service-Oriented Systems are built following the SOC paradigm to create highly dynamic systems able to reuse existing implementations and to modify their run-time behavior based on the execution environment. In this context, the group’s research focuses on representation of runtime variability, quality, and architectures to accommodate for runtime dynamism. In particular, the group is active in a number of areas, detailed next. Dynamic Web Service composition using automated planning techniques. In a dynamic environment of web services, the ability to effectually select and integrate existing services in order to realize more complex functionalities opens up new prospects for the development of service oriented applications. Viewing the Web Service composition problem as a planning task, and presuming a given description of a business domain, the aim is to derive a sequence of actions-WS operations, that achieve some desired goals specified by the user. Most approaches to this problem so far are bound to some quite restricting predefined templates of anticipated user behaviours. In order to move towards a more flexible, on-demand composition, we propose 79

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a framework, that can support extended flexibility in terms of request variety. Our main focus is on presenting an appropriate constraint-based domain and goal representation formalism, as well as addressing efficiently a number of important associated problems such as incomplete knowledge and contingency handling. Towards a Generic Service-Oriented Architecture for the Energy Market. Electrical power grids are becoming bidirectional. That is, consumers of energy can also produce energy, e.g. with µCHP = (µ Combined Heat Power), windmills and solar cells. A future trend is that end users in the energy domain will have a peer-to-peer relationship with other end users to exchange electrical energy bottom up. Devices at homes will communicate with devices of other end users (Energy Hub). In this context, we study the current energy infrastructure and was needs to change in order to realize the vision of peer-to-peer energy distribution and negotiation. Middleware for Pervasive systems. Embedded systems are specialised computers used in larger systems or machines to control equipments such as automobiles, home appliances, communication, control and office machines. Such pervasivity is particularly evident in immersive realities, i.e., scenarios in which invisible embedded systems need to continuosly interact with human users, in order to provide continuous sensed information and to react to service requests from the users themselves. In this context, we investigate middleware platforms for interworking of smart embedded services in immersive and person-centric environments, through the use of composability and semantic techniques for dynamic service reconfiguration. The key features of such middleware are to leverage on P2P technologies to make such a platform scalable and able to resist to devices churn and failures, while preserving the privacy of its human users as well as the security of the whole environment. The application domain is that of domotics.

Software Engineering and Architecture group Software architecture is one of the key disciplines that can help to deal with the hard but also interesting challenges that we are facing in our century: increasing integration of Systems and Software Engineering; focus on the end user and the offered added value; increasing demand on software dependability; dealing with rapid, accelerating change; continuous distribution, mobility, interoperability and globalization; emergence of ultra-large systems (systems of systems); demand for reusability and legacy integration; proliferation of data- and computation-intensive applications; the trend of autonomous or self-managing software; the combinations of biology and computing. The group aims to contribute in architecting industrial software systems that meet quality standards by carrying out joint research projects with universities, research institutes, and industrial partners, thus combining academic know-how with industrial practice. The research topics of the group include pattern-based architecture design and evaluation, architectural patterns and 80

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pattern languages, architecture-centric evolution, and architectural knowledge. These topics are further elaborated in the following paragraphs. Architectural knowledge and architectural knowledge sharing. There is a growing awareness of the importance of Architectural Knowledge (AK) in the software architecture community. Within the context of the Griffin project, we investigate this notion of AK and do this in the context of an envisioned architectural knowledge grid. This knowledge grid is an omnipresent knowledge infrastructure for capturing, publishing, sharing, and managing architectural knowledge. So far, we have investigated what AK entails, how this can be captured in architectural documentation, the relationship between architectural analysis and AK, and architectural decisions, which are an important form of AK. Currently, we are investigating the AK sharing and reusing across organizations, especially in geographically distributed context using various AK domain models. The objective of this research is to (1) predict the AK sharing quality more accurately, (2) facilitate the AK sharing activity before real sharing cost was spent, and (3) take the user involvement into account for the AK sharing in different sharing context, and (4) carry out and evaluate AK sharing AK in industrial organizations. Requirements knowledge management. Knowledge management has played an increasingly prominent role in software engineering in both academic and industrial perspectives. Meanwhile, the software architecture community has recently witnessed a paradigm shift towards managing architectural knowledge, and consolidated research results have been achieved. However, within the software development lifecycle, requirements engineering and architecting are two closely related activities, and so are their associated knowledge. We target specific problems from requirements engineering and present general ideas as well as concrete research results from the architecture knowledge community. This work can hopefully stimulate further research in knowledge-based requirements engineering, which may in turn feed its results back into software architecture. Architecture-centric evolution. In the context of the Darwin project, in which the group is involved, the topics of research is to develop methods and tools for optimizing system evolvability, i.e. the ability of a system to evolve easily in the face of changing requirements. In this project, our research is performed in an empirically manner exploring forward and reverse engineering processes to construct and maintain architecture views. In particular, we have developed a method to collect dynamic information and build execution architecture views of an MRI system, a real large and complex software-intensive system. The architecture views constructed or recovered using our method, provide architectural information about the actual MRI system behavior. This information is useful for architects and designers to understand the actual MRI system behavior, conduct dependency analysis activities, and identify the impact and propagation of changes, which is important to efficiently response to changing requirements. Pattern based architecture design and evaluation. Software architecture must balance the quality attributes of the system to be built. However, major architectural decisions have consequences that affect the quality attributes. Software architecture patterns are a powerful tool 81

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in architecture design and evaluation, but their impact and use has not been systematically researched. We continue to analyze the impact of architecture patterns on quality attributes. We have investigated the interaction of architecture patterns and quality attribute tactics used to improve software reliability. We have designed and validated a method for reviewing architectures based on architecture patterns. We are creating a general model of the interaction of patterns, quality attributes, and quality attribute tactics. This includes a notation to annotate architecture diagrams with information about how tactics are to be implemented. This will help architects produce strong architectures, review them effectively, and understand the architecture of existing systems. Architectural patterns and pattern languages. Modeling architectural patterns effectively in a system design is a challenging task. This is because of the inherent pattern variability and because pattern participants do not match the architectural abstractions present in modeling language. My research work during the past one year has been focused on solving the aforementioned problems. I wrote three papers on the subjects related to modeling architectural patterns in system design. The first paper was focused on modeling ’architectural primitives’ in system design using the Primus tool which produced quite satisfactory results for the successful modeling and verification of primitives in system design. The second paper was aimed at modeling variants of architectural patterns in system design while the 3rd paper targeted modeling architectural patterns’ behavior using UML’s interaction model. The results generated from these three papers and the feedback received from the audience of the conferences and workshops provided a good basis for the further extension of my ongoing research work i.e. modeling pattern variability, views synchronization etc. Using patterns to support and document architectural decisions. Documenting architectural decisions when applying patterns in software architecture preserves an important part of the thinking and rationale that went into the decisions, while asking a reasonable effort of the architect. Architectural patterns and pattern languages capture reusable architectural knowledge in the form of well proven solutions to recurring design problems. However, discovering patterns that fit to a concrete design problem is difficult, as multiple sources for patterns exist and the format of documentation varies. We have started to create a meta model to capture the most relevant architectural knowledge entities from patterns and pattern languages and to link these entities to concrete project specific architectural decisions. The model serves two purposes. On one hand it captures reusable architectural knowledge from patterns and pattern relationships, on the other hand it documents and assists project specific architectural decisions related to the selection of patterns based on architecture relevant requirements.

7.2

Research subjects

M. Aiello: Service-Oriented Computing, Ubiquitous computing and Domotics, Spatial Representation and Reasoning. 82

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P. Avgeriou: Software Architecture Design and Modeling, Patterns and Pattern Languages, Architectural Knowledge, Architecture-Centric Evolution. J. Bosch: Compositional Software Product Families, Software Architecture Design Decisions. T.B. Callo Arias: Reverse engineering, Execution Architecture. S. Dustdar: Service-Oriented Architectures And Computing, Mobile and Ubiquitous Computing, And Context-Aware Computing. E. El-Khoury: Web service composition and monitoring, transactional web services. N. Harrison: Pattern-Based Architecting and Review Processes, Quality Attributes and Tactics. A. Jansen: Architectural Design Decisions. E. Kaldeli: Web Service Composition, Automated Planning, Constraint Satisfaction. A.W. Kamal: Architectural Patterns, Patterns Modeling, UML. P. Liang: Architectural Knowledge Sharing, Requirements Knowledge Management. R. Smedinga: Oo-Approach, Architecture Design Decision Representation. U. van Heesch: Architectural Knowledge, Architectural Decision Model (ADM), Pattern Language, Architectural Pattern, Pattern Repository.

7.3

Publications

Dissertations – A. Jansen, Architectural design decisions, promotor: J. Bosch, co-promotor: D.K. Hammer and P. Avgeriou, Faculty of Mathematics and Natural Sciences, University of Groningen, 19 September 2008, 230 pages, ISBN 978-90-367-3494-3. – E. Kesseler, Safety is no accident : contributions to achieving certifiable safe software, promotor: J. Bosch, co-promotor: M. D. Guenov, Faculty of Mathematics and Natural Sciences, University of Groningen, 19 September 2008, 196 pages, ISBN 978-90-3673488-2. – S. Deelstra and M. Sinnema, Managing the complexity of variability in software product families, promotor: J. Bosch, co-promotor: J.A.G. Nijhuis, Faculty of Mathematics and Natural Sciences, University of Groningen, 9 May 2008, 278 pages, ISBN 978-90-3673266-1.

Book chapters – C. Prehofer, J. van Gurp and J. Bosch, Compositionality in Software Product Lines, in Emerging Methods, Technologies and Process Management in Software Engineering, Wiley, 2008, 21–42. 83

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Articles in scientific journals – M. Aiello and S. Dustdar, Are our Homes Ready for Services? A Domotic Infrastructure based on the Web Service Stack, Pervasive and Mobile Computing, Elsevier, 4(4), 2008, 506–525. – A. Jansen, J. Bosch and P. Avgeriou, Documenting after the fact: Recovering architectural design decisions, J. Systems and Software, Elsevier, 81(4), 2008, 536–557. – M. Koning, M. Sinnema, C. Sun and P. Avgeriou, VxBPEL: Supporting variability for Web services in BPEL, (in press) Information and Software Technology, Elsevier, 2008. – U. Zdun and P. Avgeriou, A Catalog of Architectural Primitives for Modeling Architectural Patterns, Information and Software Technology, Elsevier, 50(9-10), 2008, 1003– 1034. Articles in conference and workshop proceedings – M. Aiello, N. van Benthem and E. el Khoury, Visualizing Compositions of Services from Large Repositories, In Joint 10th IEEE Conf. on E-Commerce Technology and the 5th IEEE Conf. Enterprise Computing, E-Commerce and E-Services, (CEC’08), 2008, 359362. – P. Avgeriou, P. Lago and P. Kruchten, 3rd Int. Workshop on Sharing and Reusing Architectural Knowledge (SHARK 2008), In Companion to the Proc. 30th Int. Conf. Software Engineering, (ICSE’08), Leipzig, Germany, May 10-18, 2008, IEEE Computer Society, Washington, DC, 2 pages. – T.B. Callo Arias, P. Avgeriou and P. America, Analyzing the Actual Execution of a Large Software-Intensive System for Determining Dependencies, In 15th Working Conf. Reverse Engineering, (WCRE’08), 2008, 49–58. – T.B. Callo Arias and P. America, Top-down generation of execution architecture views of large embedded systems, In ESI Symposium Applied Academic and Industrial Research on Embedded Systems, 2008. – N. Harrison and P. Avgeriou, Analysis of Architecture Pattern Usage in Legacy System Architecture Documentation, Working IEEE/IFIP Conf. Software Architecture, (WICSA’08), February 2008, Vancouver, Canada, 10 pages. – N. Harrison and P. Avgeriou, Incorporating Fault Tolerance Tactics in Software Architecture Patterns, Int. Workshop on Software Engineering for Resilient Systems, (SERENE’08), November 2008, Newcastle upon Tyne, England, 10 pages. – A. Jansen, T. de Vries, P. Avgeriou and M. van Veelen, Sharing the Architectural Knowledge of Quantitative Analysis, 4th Int. Conf. Quality of Software Architectures, (QoSA’08), October 14-17, Germany, 2008, Springer LNCS 5281, 220–234. 84

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– M. Jaring, R. Krikhaar and J. Bosch, Modeling Variability and Testability Interaction in Software Product Line Engineering, In IEEE Int. Conf. Composition-Based Software Systems, (ICCBSS’08), 2008, 120–129. – A.W. Kamal and P. Avgeriou, Modeling Architectural Patterns’ Behavior Using Architectural Primitives, 2nd European Conference on Software Architecture, (ECSA’08), September 29-October 1, 2008, Pathos, Cyprus, Springer LNCS 5292, 16 pages. – A.W. Kamal, P. Avgeriou and U. Zdun, Modeling Variants of Architectural Patterns, European Pattern Languages of Programming, (EuroPLOP’08), July 9-13, 2008, Irsee, Germany, 23 pages. – A. W. Kamal, N. Kirtley and P. Avgeriou, Developing a Modeling Tool Using Eclipse, Int. Workshop on Advanced Software Development Tools and Techniques, (WASDeTT’08), July 8, 2008, Paphos, Cyprus, 11 pages. – P. Lago, P. Avgeriou, R. Capilla and P. Kruchten, Wishes and Boundaries for a Software Architecture Knowledge Community, Working IEEE/IFIP Conf. Software Architecture, (WICSA’08), February, Vancouver, Canada, 2008, 271–274. – P. Liang, A. Jansen and P. Avgeriou, Selecting a High-Quality Central Model for Sharing Architectural Knowledge, In IEEE Int. Conf. Quality Software, (QSIC’08), August 12-13, 2008, 357–365. – R. Peng, K. He and P. Liang, Automatic System Modeling Approach based on Semantic Association, In IEEE Int. Workshop on Semantic Computing and Systems, (WSCS’08), July 14-15, 2008, 82–88. – C. Sun and M. Aiello, Towards Variable Service Compositions using VxBPEL, In Int. Conf. Software Reuse, (ICSR’08), 2008, 257–261. – U. Zdun, P. Avgeriou, C. Hentrich, and S. Dustdar, Architecting as Decision Making with Patterns and Primitives, 3rd Workshop on SHAring and Reusing architec-tural Knowledge, (SHARK’08), ACM, 2008, 11-18. Technical report of the RuG – R. Smedinga and T. Isenberg, Proc. 5th Student Colloquium 2007-2008, Computing Science, University of Groningen. Bibliotheek der R.U., 2008.

7.4

External funding and collaborations

External funding In 2008, two new large projects were acquired: SM4All and SAS-Leg. SM4All, Smart Homes for All, is a 7th framework STREP project on middleware for embedded systems (Aiello). It 85

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was kicked-off on September 1st, 2008. SAS-LeG is an NWO Jacquard project on Software as a Service Architectures for Local eGovernemnts (Aiello, Avgeriou). It was kicked-off on July 1st, 2008. Projects funded in the previous years and running in 2008 are NWO Jacquard— GRIFFIN project (Avgeriou, Jansen); NWO SenterNovem Bsik—DARWIN (Avgeriou, Callo), NWO Hefboomsubsidie (Avgeriou, Peng). External Collaborations Avgeriou works together with the Astron Foundation, Philips Research, Getronics PinkRoccade, CIBIT, LogicaCMG and the VU University Amsterdam in the context of the GRIFFIN research project. Furthermore he works together with Philips Medical Systems and the Embedded Systems Institute in Eindhoven, in the context of the Darwin research project. Finally he works together with Cordys, EGEM, and Project Wonen, Welzijn Zorg (WWZ) in the context of the SAS-LEG project. He had short-term collaborations with Neopost BV and Siemens/TomTom in the context of the research project of Harrison. He has signed Socrates-Erasmus agreements between the RUG and Tampere Technical University (Finland), Technical University of Crete (Greece), Universidad Rey Juan Carlos (Spain), University of Limerick (Ireland), Vaxjo University (Sweden). He is the co-supervisor of Klaas-Jan Stol, a PhD student at Lero - the Irish Software Engineering Research Centre, University of Limerick (joint supervision with M. Ali Babar). Finally he was worked together and written joint publications with Uwe Zdun, Technical University of Vienna (Austria), and Antony Tang, Swinburne University of Technology (Australia).

7.5

Further activities

In 2008, M. Aiello was the Information Director of the Transactions on Computational Logic of the Association of Computing Machinery (ACM). He was member of the editorial board of the Journal on Service Oriented Computing and Applications, Springer. He was invited speaker at the Trends in Logic VI: Logic and the foundations of physics: space, time and quanta at the Studia Logica International Conference held in Brussels in December 2008. He was Keynote speaker at the Parasoft Userday workshop (Industrial event organized by Parasoft for the Dutch testing community) held in Den Haag in September 2008. P. Avgeriou was member of the editorial board of Transactions on Pattern Languages of Programming, Springer. He was member of the World-wide Institute of Software Architects (http://www.wwisa.org/). He was member of Hillside Europe (http://hillside-europe.net/). He was member of ERCIM Working Group on Rapid Integration of Software Engineering techniques (http://rise.uni.lu). He co-organized the following events: Thematic Track on Pragmatic and systematic approaches in applying patterns, European Pattern Languages of Programming (EuroPLoP’08), July 9-13, 2008, Irsee Monastery, Bavaria, Germany. Third Workshop on SHAring and Reusing architectural Knowledge (SHARK’08), 30th Int. Conf. on Software Engineering (ICSE 2008), Leipzig, Germany, May 10-18, 2008, Groningen Workshop on Software 86

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Variability and Product Lines, 9th May 2008, Groningen, the Netherlands, Workshop on Empirical Assessment in Software Architecture (EASA’08), collocated with the Working IEEE/IFIP Conference on Software Architecture (WICSA’08), 18 February, 2008, Vancouver, Canada. He gave invited talks on ASML (about Architectural traceability), on the Workshop on Empirical Assessment in Software Architecture, 18 February 2008, Vancouver, Canada (about Evaluating Tools for Architectural Knowledge) and Philips Healthcare (about Architecture Knowledge). J. Bosch was member of the editorial board of the Science of Computer Programming, Elsevier. He was the chair of the 32nd Annual IEEE International Computer Software and Applications Conference (COMPSAC’08), July 28 - August 1, 2008, Turku, Finland. He was invited as keynote speaker at following conferences: the Ericsson Software Research Conference held in Stockholm, Sweden in November 2008; the Eight Conference on Software Engineering Research and Practice in Sweden held in Karlskrona, Sweden in November 2008; the Brazilian Conference on Adoption of Reuse in Companies held in Recife, Brazil in June 2008. He was also invited to give presentations on following subjects: the software product line initiative kickoff at Rolls-Royce Controller Unit in February 2008; software product lines at Océ in May 2008; software product lines at University of Reno in May 2008; software architecture at University of California at Irvine, ISR, in June 2008. N. Harrison was member of the editorial board of the Transactions on Pattern Languages of Programming, Springer. He was in the board of directors, of Hillside USA (http://hillside.net). He was also member of Hillside Europe (http://hillside-europe.net). He was the co- program chair of the 7th Latin American Conference on Pattern Languages of Program Design, (SugarLoafPLoP’08), August 24-27, 2008, Fortaleza, Brazil. He was awarded the Faculty Excellence Award, College of Technology and Computing, Utah Valley University, April 2008.

7.6

Awards

M. Aiello, N. van Benthem, and E. el Khoury were awarded the First place for the Architecture, second place for performance at IEEE 2008 Web Service Challenge held in Washington DC in July 2008. T.B. Callo Arias, P. Avgeriou, and P. America were awarded the Best Paper Award in the 15th Working Conference on Reverse Engineering (WCRE’08), October 15th-18th, 2008, Antwerp, Belgium.

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8.

Fundamental Computing Science

Group leader: Prof.dr. G.R. Renardel de Lavalette

Tenured staff (IWI members) Prof.dr. W.H. Hesselink Prof.dr. G.R. Renardel de Lavalette

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8.1

Research Program

The objective of this programme is to contribute to the understanding of the logical and mathematical foundations of computing science and to realize a two-way transfer between this fundamental research and more applied subdisciplines of computing science. Our research focuses on formal methods, which are based on concepts and theories from discrete mathematics and logic. They are applied to enhance the reliability of computer systems and computer software, and also to further the understanding of the possibilities of computing in general. The following themes are studied: equational reasoning, modal and dynamic logic, multi-agent systems, programming methodology. Equational reasoning is a well-known kind of mathematical reasoning that is practised e.g. in algebra and in many correctness proofs. Its standard formalization is equational logic, a simple but very general reasoning system that is often used in computing science, e.g. in algebraic specification and rewrite systems (Mathematica is a well-known example). Proof theory for this logic, addressing structural properties of equational proofs, hardly exists, and the group tries to fill in the gap. Modal logic studies reasoning involving modalities like it is necessary that . . . , I know that . . . , you believe that . . . , etc. They are applied frequently in Artificial Intelligence research. We concentrate on dynamic logics, addressing reasoning about change, and on hybrid logic, an interesting recent extension of modal logic. We focus on fundamental properties like completeness: is a given proof system strong enough to prove all true statements? Multi-agent systems (MAS, also known as Agent Computing or just Agency) is a subdiscipline of both Computing Science and Artificial Intelligence. Agents are intelligent, possibly mobile processes to which intentions can be attributed: beliefs, desires and commitments. A multiagent system consists of agents that cooperate to perform a task. As an example, think of a travel agency trying to compose a holiday trip that best fits the client’s wishes: this requires collaboration between the agents that perform subtasks such as hotel booking and airplane reservation. MAS is inspired by process theory and concurrency on the one hand, and logic and formal specification on the other hand. Process theory and concurrency provide the notion of concurrent and communicating processes; logic (especially modal logic) and formal specification provide high-level languages for description of and reasoning about agents and their intentions. We try to apply the logical approach in concurrent algorithm design for MAS. For programming methodology, the group aims to contribute to the design, specification, and verification of sequential, parallel and distributed algorithms, programs, and systems. We prove properties of such algorithms or systems by assertional means, i.e., by reasoning about individual states and computation steps, rather than considering entire execution sequences. Even so, seemingly modest algorithms may require a host of case distinctions that a human prover finds difficult to control. In such situations, we use mechanical theorem provers for the administration of proof obligations. 90

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8.2

Research subjects

Hesselink: design and verification of concurrent and geometric algorithms. Renardel: proof theory of equational logic and related logics; modal and dynamic logic.

8.3

Publications Edited books

– J. Aisbett, G. Gibbon, A.J. Rodrigues, J. Kizza Migga, R. Nath, G.R. Renardel (eds.): Strengthening the Role of ICT in Development, Special Topics in Computing and ICT Research, IV, Fountain Publishers, Kampala, Uganda, ISBN 978-9970-02-871-2, 2008, xviii + 420 p. Articles in scientific journals – W.H. Hesselink, Universal extensions to simulate specifications, Information and Computation, 206, 2008, 108–128. – W.H. Hesselink, A challenge for atomicity verification, Science of Computer Programming, 71, 2008, 57–72. – W.H. Hesselink, J.B.T.M. Roerdink, Euclidean skeletons of digital image and volume data in linear time by integer medial axis transform, IEEE Transactions on Pattern Analysis and Machine Intelligence, 30, 2008, 2204–2217. – G.R. Renardel de Lavalette, B. Kooi, R. Verbrugge, Strong completeness and limited canonicity for PDL, J. Logic, Language and Information, 17, 2008, 69–87. – G.R. Renardel de Lavalette, Interpolation in computing science, the semantics of modularization, Synthese, 164, 2008, 437–450. – M.H.F. Wilkinson, H. Gao, W.H. Hesselink, J.-E. Jonker, A. Meijster, Concurrent computation of attribute filters on shared memory parallel machines, IEEE Transactions on Pattern Analysis and Machine Intelligence, 30, 2008, 1800–1813.

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Articles in conference proceedings – W. H. Hesselink, Simulation refinement for concurrency verification, Electronic Notes in Theoretical Computer Science, 214, 2008, 3–23, Proc. 13th BAC-FACS Refinement Workshop (REFINE 2008).

8.4

External funding, collaboration and internationalization

Hesselink collaborated with A.A. Aravind (University of Northern British Columbia) on the progress properties of a mutual exclusion algorithm. Hesselink collaborated with M.H.F. Wilkinson, H. Gao, J.-E. Jonker and A. Meijster on concurrent computation of attribute filters on shared memory parallel machines. Hesselink collaborated with J.B.T.M. Roerdink on Euclidean skeletons of image and volume data in linear time by integer medial axis transform. Renardel collaborated with B.P. Kooi (Philosophy, Groningen) and L.C. Verbrugge (Artificial Intelligence, Groningen) on dynamic logic. Renardel collaborated with S.M. Zwart (Delft/Eindhoven) on verisimilitude and belief revision. Renardel collaborated with D.H.J. de Jongh (Amsterdam) on exact models for intuitionistic propositional logic.

8.5

Further information

Hesselink is an editor of the international scientific journal Science of Computer Programming. He is a member of the Board of the Dutch Research School IPA (Institute for Programming Research and Algorithmics). He gave an invited lecture at the Refinement Workshop of the International Conference FM 2008: Formal Methods (Turku, Finland), and two invited lectures at the University of Electronic Science and Technology of China in Chengdu. Renardel is member of the Board of the Dutch Research School in Logic, the Board of the Dutch Society for Theoretical Computer Science, the VIDI selection committee for the division Physical Sciences of the Netherlands Organisation for Scientific Research (NWO-EW), and the Academic Advisory Board of the NUFFIC-funded project Strengthening ICT Training and Research Capacity in the Four Public Universities in Uganda (2007-2011). He chaired the Peer Review Committee of the School for Information en Knowledge Systems (SIKS), and the Computer Science Committee of the 4th annual International Conference on Computing and ICT Research.

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9.

Intelligent Systems

Group leader: Prof.dr.sc.techn. N. Petkov

Tenured staff (IWI members) Dr. M. Biehl (tenure track) Prof.dr.sc.techn. N. Petkov Dr. J.H. van Hateren Dr. M.H.F. Wilkinson

PhD students G. Azzopardi (since October 1) (supervisor: Petkov) K. Bunte (supervisor: Biehl) I.E. Giotis (since September 1) (supervisor: Petkov) F.N. Kiwanuka (supervisor: Wilkinson) G. Papari (supervisor: Petkov) P. Schneider (supervisor: Biehl) A. Witoelaar (supervisor: Biehl) E. Mwebaze (co-supervision: Biehl) A. Offringa (co-supervision: Biehl)


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IWI Annual Report Guests Prof. Dr. W. Arlt, University of Birmingham, UK Prof. Dr. G. de Haan, Techn. University of Eindhoven and Philips, The Netherlands Prof. Dr. B. Hammer, Technical University of Clausthal, Germany Dr. G. Ouzounis, Democritus University of Thrace, Alexandroupoli, Greece Dr. J. Quinn, Makerere University, Kampala, Uganda Prof. Dr. F. Rossi, INRIA Rocqencourt, France Dr. F.-M. Schleif, University of Leipzig, Germany Prof. Dr. A. Smeulders, University of Amsterdam, The Netherlands Prof. Dr. D. G. Stork, Ricoh Innovations and Stanford University, USA Dr. F.-M. Schleif, University of Leipzig, Germany Prof. Dr. M. Viergever, University of Utrecht, The Netherlands Prof. Dr. L. van Vliet, Techn. University of Delft, The Netherlands

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9.1

Research Program

The research program Intelligent Systems includes interrelated topics from image processing, computer vision, pattern recognition, machine learning and neural networks. Biologically motivated computer vision Models of information processing in the visual cortex are developed and used in computer algorithms. This research is relevant for the areas of image processing, computer vision, pattern recognition, visual perception, and computational neuroscience. Our goal is to understand how people see and to deploy principles of natural vision in computer algorithms for artificial vision. Using facts from neuroscience and visual perception, we build models of visual information processing in the brain and use them in computer simulations to obtain insights and derive practical computer vision algorithms. One example is a model of a grating cell that we developed [Petkov, Kruizinga: 1997 Biological Cybernetics 76 83-96] and used in a texture operator [Kruizinga, Petkov: 1999 IEEE Transactions on Image Processing 8 1395-1407], [Grigorescu, Petkov, Kruizinga: 2002 IEEE Trans. on Image Processing 11 1160-1167]. By means of computer simulations we demonstrated that grating cells may play an important role in the disambiguation of edge information in early vision (texture vs. contours). Another example is our model of non-classical receptive filed inhibition, also called surround suppression, in orientation selective neurons [Petkov, Westenberg: 2003 Biological Cybernetics 88 236-246]. We demonstrated that the biological role of this inhibitory mechanism is quick pre-attentive detection of object contours and region boundaries in natural images that are rich in texture. We proposed various contour detection algorithms that deploy this mechanism and showed that they are more effective in detecting object contours and region boundaries than traditional computer vision algorithms for edge detection [Grigorescu, Petkov, Westenberg: 2003 IEEE Trans. on Image Processing 12 729-739], [Grigorescu, Petkov, Westenberg: 2004 Image and Vision Computing 22 609–622], [Papari, Campisi, Petkov, Neri: 2007 EURASIP Journal on Advances in Signal Processing, Article ID 71828]. We also studied the orientation and speed tuning properties of spatiotemporal 3D Gabor and motion energy filters with surround suppression as models of time-dependent receptive fields of simple and complex cells in primary visual cortex (V1) [Petkov, Subramanian: 2007 Biological Cybernetics, 97 423-439]. We demonstrated how these filters are related to motion detection, noise reduction, texture suppression and contour enhancement. Another result of our research that is inspired by psychological research on the human visual system is a method for the evaluation of the robustness of shape recognition algorithms to incompleteness of contours [Ghosh, Petkov: 2005 IEEE Trans. on Pattern Analysis and Machine Intelligence 27 1793-1804]. 95

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After Hans van Hateren joined the group in 2007, this direction of the research programme was extended with computational modelling of image processing by retinal neurons, see results. Image processing and computer vision In shape analysis we study geometrical approaches in which a feature point is characterized by the spatial arrangement of other feature points around it. The collection of local geometrical descriptors for the different feature points of an object is used as a shape characteristics of that object [Grigorescu and Petkov: 2003 IEEE Trans. on Image Processing 12 1274-1286]. We also study the robustness of shape recognition algorithms to incomplete contour representations [Ghosh and Petkov, 2005 IEEE Trans. on Pattern Analysis and Machine Intelligence 27 17931804]. A new direction in our work is the development of image processing operators that add artistic effects to photographic images [Papari, Petkov, Campisi: 2007 IEEE Trans. on Image Processing, 16 2449-2662]. On the applications side, we collaborate with researchers from the University of Leon, Spain, in the area of automatic classification of boar spermatozoa [Sanchez, Petkov, Alegre: 2006 Cellular and Molecular Biology, 52 2006, 38-43], [Petkov, Alegre, Biehl, Sanchez: 2008 Comp. in Biol. and Medicine 38, 461-468]. In 2007 we started a new collaboration with the department of dermatology of the academic hospital of the University of Groningen on the application of content based image retrieval and expert systems to dermatological problems. Connected filters are a comparatively new field of research within mathematical morphology. They are edge preserving operators which have found use in noise removal, texture analysis, image compression and description, and feature extraction. Research on connected operators in our group entails algorithm development (including parallelization), development of new classes of filters, applications to 2-D and 3-D medical images, and the development of new connectivity measures for these filters for increased robustness. Recently, content-based image retrieval (CBIR) has been added to the list of application areas. One line of this research links to visual cortex modelling: developing morphological analogues of texture operators based on models of certain visual cortical cells. It is hoped these morphological counterparts will be an order of magnitude faster, whilst retaining the useful properties of the cortical cell models. Finally, fast visualization based on connected attribute filters is being explored. Recently, work has begun expanding this line into hyperconnected filters and attribute-space-connected filters, which increase the flexibility of perceptual groupings available, and allow dealing with overlap explicitly. Segmentation is a core problem in image analysis, and methods based on both simple thresholding methods and more advanced methods such as watersheds and deformable models are being explored. Application areas are many, but the focus lies on biomedical imaging, both macroscopic (MRI, CT) and microscopic. New application domains in astronomy are also be96

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ing explored. Machine learning and neural networks The term machine learning has been coined for an area of computer science which deals with the analysis of example data for, e.g., supervised classification or regression problems. Furthermore, unsupervised learning addresses problems like clustering, dimension reduction, or correlation analysis. In our working group, learning algorithms are developed and employed for data driven parameter adaptation in, for instance, neural networks or other adaptive systems. In our research, we are currently mainly interested in prototype based learning schemes. In the context of supervised learning they provide typical representatives of the classes which can be used to parameterize distance based classification schemes. A prominent example for such techiques is the very flexible and successful Learning Vector Quantization (LVQ). Similarly, in unsupervised Vector Quantization (VQ), the prototypes are used to represent large amounts of data by means of clustering or dimension reduction. A key question in all distance or similarity based learning is the choice of a suitable distance measure or metrics. The technique of Relevance Learning plays a most important role in this context. A quite general distance measure is parameterized and adapted in the training phase, together with the prototypes. Hence, the classifier and a discriminative similarity measure are identified in the same data driven process. We have extended the basic idea of relevance learning to algorithms which account for correlations of features. The main aim of these matrixbased relevance algorithms is two-fold: to achieve better classification performance and to obtain deeper insight into the structure of the data. Furthermore, rank controlled and regularized versions of matrix relevance learning have been developed which provide discriminative lowdimensional projections of the data. This technique constitutes a powerful tool for avoiding overfitting and oversimplification effects. At the same time, it can be used for the discriminative visualization of classification problems in high-dimensional data. In our theoretical investigations we aim at a better understanding of algorithms, learning processes and their performance. In the framework of model situations, we study the dynamics of on-line learning and systematically compare different algorithms. Similar investigations, which borrow basic concepts from statistical physics, concern the typical properties of large learning systems in the context of batch- or offline training. The ulitimate goal of these studies is to design and optimize practical training algorithms. Consequently, we aim at testing the developed methods in real world applications. Recently, we have addressed several classification problems in bioinformatics and the analysis of medical data. An important example concerns tumor classification based on metabolomics data. Another project deals with the analysis of tiling microarray data and the potential detection of novel genes. 97

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As an additional area of research, projects in the modelling and simulation of nano-structured crystal surfaces are being pursued.

9.2


Biologically motivated computer vision In the article ”Adaptive Pseudo-Dilation for Gestalt Edge Grouping for Contour Detection” [Papari, Petkov: 2008 IEEE Trans. Image Proc. 17 1950-1962], we introduce a new morphological operator which uses context dependent structuring elements in order to identify long curvilinear structures in an edge map. The dilation is limited to the Voronoi cell of each edge pixel and the results are in a good agreement with the gestalt law of good continuation. The grouping algorithm is then embedded in a multithresholding which makes the algorithm less sensitive to the values of the input parameters. Both qualitative and quantitative comparison with existing approaches prove the superiority of the proposed contour detector in terms of larger amount of suppressed texture and more effective detection of low-contrast contours. In the article ”Fast Multiresolution Contour Completion” [Papari,Petkov: Proc. SPIE 2008, vol. 6812, art. no. 68121B], we extend the above mentioned scheme in two directions: (i) by considering curved structuring elements instead of elliptic ones, and (ii) by working in a multiresolution framework. Specifically, each edge point is replaced by a curved elongated patch, whose orientation and curvature match the local edge orientation and curvature. The proposed contour completion algorithm is integrated in a multiresolution framework for contour detection. Experimental results show the superiority of the proposed method to other wellestablished approaches. Image processing and computer vision

A quite unexpected result was the development of an algorithm for grey-scale dilations and erosions with arbitrary flat structuring elements. These operators form the cornerstone of much of (non-connected) mathematical morphology, and a great deal of work has been doneto speed them up. Therefore, it came as a surprise that any improvementcouldstill be made,especially given the apparent simplicity of our approach. The new method is far faster than the best existing algorithm, especially for images with large numbers of bits per pixel (such as found in astronomy and medical imaging), and can handle floating-point data well (only 30% slower than integer). A first version was presented at ICIP-2006, but further speed-up (by a factor of 4-8) has been achieved since then. These new results have been published in IEEE Trans. Image Proc., and is now in the top 1% most cited papers. The method also works in 3-D, and is very useful in implementing the second-generation connectivities developed previously. 98

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Work on CBIR is continuing, with extensions to incorporate color and spatial information into pattern spectra. A comparison of spatial pattern spectra has been made and has been accepted in the International Symposium on Mathematical Morphology 2009. Earlier work usingExtensions of this work to content-based image retrieval were presented and the ImageClef 2007 workshop, and an imrpovement of the work in 2007 has been published in the proceedings of ImageClef 200, which appeared in 2008. A problematic property of so-called partitioning-based second-order connectivity was proven, and a possible solution proposed. In a partitioning-based connectivity, object linked by narrow “bridges” are split apart, and the pixels in the bridges are treated as singletons. This destroys all spatial information contained in the bridge regions. If the bridges themselves are of interest, as in the case of dendrites in neural images, this is unacceptable. As a solution, a new class of filter called attribute-space connected filters was proposed, in which the image is first embedded in a higher dimensional space (the attribute space), in which the connected filtering takes place. The resulting filtered volume is then projected back into image space. This work has been was published in a special issue of Image Vis. Comp.. In particular, a demonstration is given of the ability of attribute-space connectivity to deal with overlap, which is impossible to do with any normal connectivity. We have also extended an alternative approach to deal with the oversegmentation problem of contraction-based connectivity to grey scale images. It has been shown that though grey-scale filters are not easily implemented, pseudo pattern spectra can be devised, and improve diatom identification. These results were submitted to Pattern Recognition. Serra also proposed the notion of hypoconnectivities, which could also deal with the fragmentation problem discussed above. We can now show that the axiomatixs of hyperconnectivity can be improved, leading to hyperconnected operators similar to connectivity openings. A very new result is that standard, structural morphology is a special case of hyperconnectivity. This is important because connectivity is also a special case of hyperconnectivity. This means that hyperconnectivity bridges the gap between structural and connected morphology. This means that there should be a continuum of filters which are increasingly shape preserving as we approach the connectivity end of the spectrum. We show that reconstruction using reconstruction criteria, and path openings both can be seen as part of this continuum. The first results of this theoretical work have been accepted for publication in the International Symposium on Mathematical Morphology 2009. Reconstruction by reconstruction criteria is a an interesting technique, in that it is possible to tune it continuously from fully edge preserving connected filters at the one extreme, and structural morphology at the other. It can be used to great effect to improve cartoon/texture separation in images. An example is shown in Fig. 3. Despite this it has not found much use, because of its O(N 2 ) complexity, with N the number of pixels. We have developed a new approach to the problem, based on viscous hyperconnectivity, which produces very similar results in linear time (a factor 500 faster on 3 megapixel images). This was presented at the 99

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International Conference on Image Processing 2008 in the special session on connected filters organized by Wilkinson and Salembier (UPC, Barcelona, Spain). The work on attribute-space connectivity has lead to speculations about a possible link between attribute-space connectivity and hyperconnectivity, which could also deal better with overlap. We can now prove that hyperconnectivity is a special case of attribute-space connectivity, but that there exist attribute-space connectivities which are not hyperconnectivities. This result is purely theoretical, but shows that attribute-space connections bring something new. This this result has been accepted for publication in the International Symposium on Mathematical Morphology 2009. In image segmentation the following results were obtained. A variant of the charged particle model including springs to define shape priors was developed for segmentation of the spine in X-ray images for scoliosis analysis, in collaboration with the Department for Biomedical Engineering. It has been submitted to IEEE Trans. Image Proc.. It is shown that we can correctly segment 96% of scoliotic human spinal columns in X-ray images. The Max-Tree algorithm, which is the basis of much of our filtering work has been parallelized on shared memory parallel computers, showing a speed-up of between 8 and 14 on 16 processors. The method was also tested on more common parallel hardware, such as a dual-socket, dual-core AMD Opteron machine,on which speed-ups of more than four were achieved,despite the fact that the machine has four processor cores. The explanation for this lies in reduced cash thrashing and lower memory latency when the load is distributed. This parallelization is particularly difficult, because, unlike most image processing operators, connected filters are neither local nor separable. The results have been published in IEEE Trans. Pattern Anal. Mach. Intell.. Ouzounis and Wilkinson developed one of the first practical hyperconnected attribute filters based on so called k-flat zones, were k is a tunable parameter denoting the allowed range of grey-level variation within a flat zone. These allow filters to become more robust to noise and other unimportant low contrast image features. A fast algorithm based on the Max-tree was developed which allows interactive setting of k and visualization of filtering results, based on earlier work on interactive visualization and attribute filtering in 3D. In 2D, the method shows much promise in separation of galaxies from stars, which is important for automatic source extraction in astronomy. An example is shown in Fig. 4. The results have been submitted to IEEE Trans. Pattern Anal. Mach. Intell.. Machine learning and neural networks Our theoretical investigations of learning dynamics and off-line learning have lead to a number of publications: In the article Learning Dynamics of Neural Gas and Vector Quantization [Witoelar, Biehl, Ghosh, and Hammer, Neurocomputing 71: 1210-1219 (2008)] we study and compare systematically several heuristic algorithms for unsupervised on-line Vector Quantization. In off-line training, discontinuous effects can be observed which dominate the learning process 100

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(a) original f

(b) marker g = G16 ∗ f

(c) cartoon

(d) texture

(e) cartoon with criteria

(f) texture with criteria

Figure 3: Levelings: Part (c) shows cartoon obtained by leveling of image (a) using marker obtained by Gaussian smoothing with σ = 16 (b); (d) shows the texture signal obtained by subtracting (c) from (a); (e) and (f) same as (c) and (d) respectively, but using viscous reconstruction. 101

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and may cause inevitable practical problems. In the conference contribution Phase transitions in Vector Quantization [Witoelar, Ghosh, Biehl, Proc. ESANN 2008, 221-226] we exemplify the importance of this effect in terms of unsupervised batch training from clustered data. An example application of relevance learning and LVQ has been discussed in the paper Generalized Matrix LVQ for the analysis of spectral data [Schneider, Schleif, Villmann, Biehl, Proc. ESANN 2008, 451-456] which has been presented at the European Symposium on Artificial Neural Networks in Brugge/Belgium. The journal publication Automatic classification of the acrosome status of boar spermatozoa using digital image processing and LVQ [Petkov, Alegre, Biehl, Sanchez, Comp. in Biol. and Medicine 38, 2008, 461-468] presents an application of machine learning in the context of medical image analysis. First results concerning our novel methods of rank-controlled matrix relevance learning and regularized versions thereof have been published as Technical Reports. The paper Regularization in matrix relevance learning [Schneider, Bunte, Hammer, Villmann, Biehl, Machine Learning Reports MLR-02-2008, Vol. 2, 2008, 19-36] presents a novel method to avoid over-simplification, over-fitting, and numerical instabilities in relevance matrix learning. The identification of discriminative low-dimensional data representations is addressed in Discriminative visualization by limited rank matrix learning [Bunte, Schneider, Hammer, Schleif, Villmann, Biehl, Machine Learning Reports MLR-03-2008, Vol. 2, 2008, 37-51]. The modelling of complex crystal growth processes is addressed in the journal publication ”Simulation of self-assembled nano-patterns in strained 2D alloys on the fcc(111) surface” [Weber, Biehl, Kinzel, Kotrla, J.Phys.: Cond. Matter 20: Art.No. 265004 (2008)]. There we demonstrate how microscopic interactions between single atoms can result in highly complex collective phenomena such as the formation of spatial structures on the nm-scale. Four recent publications have been accepted for publication in the Proc. of ESANN 2009: Equilibrium properties of offline LVQ [Witoelar, Biehl, Hammer], Hyperparameter learning in Robust Soft lVQ [Schneider, Biehl, Hammer], Nonlinear discriminative data visualization [Bunte, Biehl, Hammer], and Adaptive metrics for content based image retrieval in dermatology [Bunte, Biehl, Petkov, Jonkman]. Furthermore, the paper Distance learning in discriminative vector quantization [Schneider, Biehl, Hammer] hase been accepted for publication in Neural Computation. It addresses the efficient incorporation of matrix relevance learning in various LVQ based training schemes.

9.3

Research subjects

G. Azzopardi: shape. M. Biehl: machine learning, neural networks, LVQ, scientific computing. K. Bunte: adaptive distance measures in LVQ. I. E. Giotis: CBIR and expert systems in dermatology. F.N. Kiwanuka: Medical volume analysis using (hyper)connected filters. 102

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R. Nakibuule: classification of video sequences: detection of traffic jams. E. Mwebaze: machine learning and causality detection in medical data. A. Offringa: pattern recognition in radio-astronomical data. G. Papari: contour detection, non-photorealistic rendering. N. Petkov: contour detection, non-photorealistic rendering, shape, health care. P. Schneider: feature selection and matrix relevance learning. F. Tushabe: multimedia applications of mathematical morphology. J.H. van Hateren: modelling of retinal neurons. M.H.F. Wilkinson: morphological image analysis, biomedical modelling. A. Witoelar: dynamics of Neural Gas and LVQ algorithms.

9.4

Publications Dissertations

– E.R. Urbach, Advanced morphological pattern spectra and multi-scale filtering, Promotor: N. Petkov, copromotor: M.H.F. Wilkinson, University of Groningen, 2008, ISBN 978-90367-3610-7, 128 pages. – E.N. Subramanian. Attractor switching in neuron networks and spatiotemporal filters for motion processing. Promotores: H.W. Broer and N. Petkov, University of Groningen, 2008, ISBN 978-90-367-3315-1, 140 pages. Articles in scientific journals – H. Broer, K. Efstathiou and E. Subramanian, Robust existence of unstabe attractors in arbitrarily sized pulse-coupled networks with delay, Nonlinearity, 21, 2008, 13-49. – J.H. van Hateren, Fast recursive filters for simulating nonlinear dynamic systems, Neural Computation, 20, 2008, 1821-1846. – G. Papari and N. Petkov, Adaptive Pseudo-Dilation for Gestalt Edge Grouping for Contour Detection, IEEE Trans. Image Proc., 17, 2008, 1950-1962. – N. Petkov, E. Alegre, M. Biehl, L. Sanchez, Automatic classification of the acrosome status of boar spermatozoa using digital image processing and LVQ, Computers in Biology and Medicine, 38, 2008, 461-468. – E.R. Urbach and M.H.F. Wilkinson, Efficient 2-D gray-scale morphological transformations with arbitrary flat structuring elements, IEEE Trans. Image Proc., 17, 2008, 1-8. – S. Weber, M. Biehl, W. Kinzel, M. Kotrla, Simulation of self-assembled nano-patterns in strained 2D alloys on the fcc(111) surface, J. Phys.: Condensed Matter, 20, 2008, Art.No. 265004. 103

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– M.H.F. Wilkinson, H. Gao, W.H. Hesselink, J.E. Jonker and A. Meijster, Concurrent computation of attribute filters on shared memory parallel machines, IEEE Trans. Pattern Anal. Mach. Intell., 30, 2008, 1800-1813. – A. Witoelar, M. Biehl, A. Ghosh, B. Hammer, Learning Dynamics of Neural Gas and Vector Quantization, Neurocomputing, 71, 2008, 1210-1219. Articles in conference proceedings – G. Papari, N. Petkov, Fast Multiresolution Contour Completion, in Proc. SPIE 2008, 6812, (68121B), San Jose, CA, USA, Jan. 28-31, 2008, (SPIE, Bellingham, Washington; IS&T, Springfield, Virginia, 2008), 68121B-1 - 68121B-8. – P. Schneider, F.-M. Schleif, T. Villmann, M. Biehl, Generalized Matrix Learning Vector Quantizer for the Analysis of Spectral Data, Proc. Europ. Symposium on Artificial Neural Networks ESANN, Brugge/Belgium April 2008, M. Verleysen (ed.), d-side publishing, 2008, 451-456. – M. Strickert, P. Schneider, J. Keilwagen, T. Villmann, M. Biehl, B. Hammer, Discriminatory data mapping by matrix-based supervised learning metrics, Proc. Third Int. Workshop on Artificial Neural Networks in Pattern Recognition ANNPR, Paris/France, July 2-4, 2008, L. Provost, S. Marinai, F. Schwenker (eds.). Springer Lecture Notes in Computer Science 5064, 2008, 78-89. – M. Strickert, K. Witzel, J. Keilwagen, H.P. Mock, P. Schneider, M. Bieh, T. Villmann, Adaptive Matrix Metrics for attribute dependence analysis in differential high throughput data, Proc. Fifth Int. Workshop on Computational Systems Biology WCSB 2008, Leipzig/Germany, June 11-13, 2008, M. Ahdesmäki et al. (eds.), Tampere Int. Center for Signal Processing, TICSP Series 41, 2008, 181-184. – M.H.F. Wilkinson, Filtering by reconstruction: Reconstruction criteria revisited, Int. Conf. Image Proc. (ICIP) 2008, San Diego, USA, 2180-2183. – A. Witoelar, A. Ghosh, M. Biehl, Phase transitions in Vector Quantizations, Proc. Europ. Symposium on Artificial Neural Networks ESANN, Brugge/Belgium April 2008, M. Verleysen (ed.), d-side publishing, 2008, 221-226. Other publications – C. Angulo, M. Biehl, F. Rossi, Progress in machine learning and computational intelligence (editorial of a special issue), Neurocomputing, 71, 2008, 1117-1119. – K. Bunte, P. Schneider, B. Hammer, F.-M. Schleif, T. Villmann, M. Biehl, Discriminative visualization by limited rank matrix learning, Technical Report, Machine Learning Reports MLR-03-2008, University Leipzig, 2, 2008, 37-51. 104

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– G.K. Ouzounis and M.H.F. Wilkinson, Hyperconnected attribute filters based on k-flat zones, Poster in Scientific ICT Research Event Netherlands (SIREN) 2008, 29 September 2008, Amsterdam, The Netherlands. – P. Schneider, M. Biehl, B. Hammer, Matrix adaptation in discriminative vector quantization, Technical Report, Series Ifl-08-08, TU Clausthal, 2008. – P. Schneider, K. Bunte, B. Hammer, T. Villmann, M. Biehl, Regularization in matrix relevance learning, Technical Report, Machine Learning Reports MLR-02-2008, University Leipzig, 2, 2008, 19-36.

9.5


External funding The position of Papari is financed by a grant to Petkov in the open competition 2003 of NWO Exact Sciences. The position of Kerstin Bunte is financed by a grant to Biehl and Petkov in the open competition 2006/07 of NWO. The positions of Tushabe and Kiwanuka are funded through a grant by NUFFIC. External collaboration Biehl collaborates with B. Hammer from the Technical Univ. Clausthal-Zellerfeld, Germany, in the context of the theory and application of Learning Vector Quantization. Further theoretical aspects of machine learning dynamics are investigated in collaboration with P. Riegler from the Fachhochschule Wolfenb”uttel. Practical applications of LVQ are explored together with Th. Villmann in Leipzig/Germany and with M. Strickert in Gatersleben/Germany. In the context of bioinformatics applications he collaborates with R. Breitling at the Biocentrum Haren. The application of LVQ to tumor classification in medicine is studied in a project with W. Arlt from the University Hospital Birmingham/UK. In the area of computational science Biehl collaborates with the groups of W. Kinzel in Würzburg and M. Kotrla from the Academy of Sciences in Prague. He has signed Erasmus-Socrates agreements with Profs. Riegler, Hammer, and Villmann. Petkov visited the Institute for Physiology (Vasilev) of the Bulgarian Academy of Sciences, Sofia. He visited and gave talks at INSA Lyon (Jolion, Wolf), the Univ. of Edinburg (Fisher, Vijayakumar), the Univ. of Newcastle (Hurlbert), and Frankfurth Institue of Advanced Studies (Triesch). He was external examiner for the PhD thesis and defense of Graham McNeill at the Univ. of Edinburg. He participated in the Summer School on Cognitive Science in Sofia. He collaborates with Jonkman from the Department of Dermatology on the application of content based image retrieval and expert systems to dermatologic problems. Together with Biehl he collaborates with Wolffenbuttel from the LifeLines project of the University Medical Center Groningen on the large scale analysis of patient data for the relation of genotype and phenotype. 105

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He has signed Socrates-Erasmus agreements between the RuG and the TU Vienna, Univ. of Salerno, Univ. of Leon and Univ. of Rome III. Wilkinson collaborates with the Radiology and Dermatology departments of the Academic Hospital in Groningen in an NWO-project. A further collaboration with the Department of Biomedical Engineering, University of Groningen, concerning image analysis of scoliosis is also underway. Within this project a collaboration with B. Brendel and S. Winter of the Ruhr-Universität Bochum has also been initialized. This year a collaboration with the Kapteyn Institute has been initialized, to explore the sue of connected filters,and especially vector-attribute filters in automatic source extraction in image data bases. He has started a collaboration with L. Najman (ESIEE, Paris) on mathematical morphology, and in particular topological watersheds, and with Jean Serra (same institute) on connectivity theory. He visited and lectured at Makerere University in Kampala Uganda in April 2008, and is external supervisor for PhD students there.

9.6

Further information

Biehl is associated editor of Pattern Recognition and was invited to be guest editor of a special issue of Neurocomputing. He furthermore became associated editor of Neural Processing Letters. He was member of the scientific board of the IDEAL 2007 conference in Birmingham (UK). He organized a Dagstuhl seminar on Similarity based clustering and its applications in biology and medicine, together with M. Verleysen, B. Hammer, and T. Villmann. The seminar brought together ca. 40 invited speakers for one week in March 2007. Furthermore, he co-organized a workshop at the Max-Planck-Institute for the Physics of Complex Systems in Dresden, Germany. It took place from October 1-20 2007 with about 30 participants and it was fully funded by the Max-Planck society. Petkov is member of the editorial boards of J. of Neural, Parallel and Scientific Computations (Dynamic Publ.), Int. J. for Computational Vision and Biomechanics (Serials Publ.) and Int. J. of Hybrid Intelligent Systems (IOS Press). He was conferred upon the title of visiting professor to the School of Computing, Engineering and Information Sciences of Northumbria University, Newcastle, till July 2008. He is member of the Programme Advisory Council Scientific Computing of Forschungszentrum Jülich GmbH till 2009. He is member of the grant committee ”Middelgroot” of NWO. He is member of the steering committee of the CAIP (Int. Conf. on Analysis of Images and Patterns) series of conferences and is co-chair (with X. Jiang) of CAIP 2009 to be held in Münster. He was member of the program committees of the following international conferences: Australasian Joint Conference on Artificial Intelligence (AI-08), Auckland, New Zealand, December 1-5, 2008; the 13th Iberoamerican Congress on Pattern Recognition, CIARP’2008, Havana, Cuba, December 9-12, 2008; the 12th International Workshop on Combinatorial Image Analysis (IWCIA08), Buffalo, NY, USA, April 7-9, 2008. 106

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In 2008 he reviewed papers for the following journals: Elcvia,, IEEE Trans. on Image Processing, IEEE Trans. PAMI, Neurocomputing, J. Pattern Analysis and Applications. His publications in the last 10 years (1999-2008) included in the Web of Science (WoS) of Thomson Scientific collect 350 citations. According to the Essential Scientific Indicators of Thomson Scientific, the threshold for inclusion in the top-1% group of most cited computer scientists in this period was about 130 citations. Wilkinson organized and chaired a special session on connected filters at the International Conference on Image Processing 2008 in San Diego, together with Philippe Salembier of the Universita Polytècnica de Catalunya, Barcelona Spain. This has lead to an invitation to write a feature article for IEEE Signal Processing Magazine, also together with Philippe Salembier. He was member of the program committee of the 2008 IEEE Pacific-Rim Symposium on Image and Video Technology (PSIVT’08), and reviewer for ICIP 2008. Is chair of the International Symposium on Mathematical Morphology 2009 in Groningen, together with Jos Roerdink. He is treasurer of the Dutch Society for Pattern Recognition and Image Processing (NVPHBV). He was also invited to lecture at the ESIEE in Paris. Finally, he is member of the Cluster Computer Vision Noord Nederland, a consortium of companies and academia seeking to stimulate the field of computer vision in the Northern Netherlands. A number of our research articles in the last eleven years (1997-2006) belong to the group of highly cited publications in Computer Science, Electrical Engineering or Physics according to the number of citations they collect in the Web of Science of Thompson Scientific: top-1%: - Grigorescu, Petkov, Kruizinga: 2002 IEEE Trans. Im. Proc. 11 1160-1167 - Grigorescu, Petkov, Westenberg: 2003 IEEE Trans. Im. Proc. 12 729-739 - Grigorescu, Petkov, Westenberg: 2004 Image and Vis. Comp. 22 609-622 - Jalba, Wilkinson, Roerdink: 2006 IEEE Trans. Im. Proc. 15 331-341 - Urbach, Wilkinson: 2008 IEEE Trans. Im. Proc. 17 1-8 – top-10%: - Meijster, Wilkinson: 2002 IEEE Trans. PAMI 24 484-494 - Grigorescu, Petkov: 2003 IEEE Trans. Im. Proc. 12 1274-1286 - Petkov, Westenberg: 2003 Biological Cybernetics 88 236-246 - Jalba, Wilkinson, Roerdink: 2004 IEEE Trans. PAMI 26 1320-1335 - Jalba, Wilkinson, Roerdink, Bayer, Juggins: 2005 Machine Vision and Applications, 16 217228 - Ghosh, Petkov: 2005 IEEE Trans. PAMI 27 1793-1804 107

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- Sanchez, Petkov, Alegre: 2005 LNCS 3773 154-160 - Biehl, Ghosh, Hammer: 2006 Neurocomputing 69 660-670 - Sanchez, Petkov, Alegre: 2006 Cellular and Molecular Biology 52 38-43 - Ouzounis, Wilkinson: 2007 IEEE Trans. PAMI 29:990-1004 - Papari, Campisi, Petkov, Neri: 2007 EURASIP J. Adv. Sign. Pro. Art nr: 71828 - Urbach, Roerdink, Wilkinson: 2007 IEEE Trans. PAMI 29: 272-285 - Wilkinson: 2007 Image and Vision Computing, 25 426-435 - Wilkinson, Gao, Hesselink, Jonker, Meijster: 2008 IEEE Trans. PAMI 30 1800-1813 – top-20%: - Biehl, Ghosh, Hammer: 2007 J. Machine Learning Research 8 323-360 - Ghosh, Biehl, Hammer: 2006 Neural Networks 19 817-829 - Much, Biehl: 2003 Europhysics Letters 63 14-20 - Sanchez, Petkov, Alegre: 2005 LNCS 3691 88-95 - Ghosh, Petkov: 2006 Int J Patt Rec Art Intell 20 913-924 - Jalba, Roerdink, Wilkinson: 2004 Pattern Recognition 37 901-915 We made available some of our image processing algorithms as web-enabled applications at http://matlabserver.cs.rug.nl where external researchers can use them with their own image material. This internet site gets around 100 unique visitors per day from around 80 different countries per month (since 2003). Some of our image processing operators that add artistic effects to photographic images are available at http://www.cs.rug.nl/˜imaging/artisticsmoothing,http:// www.cs.rug.nl/˜imaging/glassart/java/Main.html,http://www.cs.rug. nl/˜imaging/PSIVT2009/java/Main.html.

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(a)

(b)

(c)

(d)

Figure 4: Separating galaxies from stars: (a) spiral galaxy M81, original image, courtesy Giovanni Benintende; (b) stars suppressed by an opening with a disk of radius 8; (c) area attribute filter with 2000 ≤ area ≤ 240000; (d) filtered result using k-flat version of area attribute filter used in (c). The latter shows the best preservation of edge detail, and the best suppression of stellar signal.

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10.

Scientific Visualization and Computer Graphics

Group leader: Prof. dr. J.B.T.M. Roerdink

Tenured staff (IWI members) Dr. H. Bekker Dr. T. Isenberg Prof.dr. J.B.T.M. Roerdink Prof.dr. A.C. Telea Postdocs Dr. A. Jalba (until 24-4-2008) (supervisor: Roerdink) Dr. M.A. Westenberg (until 1-6-2008) (supervisor: Roerdink) Dr. F. Li (until 15-11-2008) (supervisor: Roerdink) PhD students R. van den Berg (until 1-12-2008) (supervisor: Roerdink) H. Byelas (supervisor: Telea) A. Crippa (supervisor: Roerdink) M.H. Everts (supervisors: Bekker, Roerdink) B.J. Ferdosi (supervisor: Roerdink) M. Gerl (since 1-6-2008) (supervisor: Isenberg) W.J. van der Laan (supervisor: Roerdink) L. Yu (since 15-9-2008) (supervisor: Isenberg)


fte 0.2 1.0 1.0 1.0

NWO

1.0

NBIC & RuG

1.0

NWO

1.0

RuG

0.8

RuG

1.0

RuG

1.0

NWO

1.0

NWO

1.0

RuG

1.0

NWO

1.0

RuG

1.0

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Guests Prof.dr. G. Dzemyda, Institute of Mathematics and Informatics, Lithuania Prof. S. Carpendale, University of Calgary, Canada Prof. J. Sijbers, University of Antwerp, Belgium Prof. B. Preim, University of Magdeburg, Germany

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10.1

Research Program

The research group Scientific Visualization and Computer Graphics carries out research in the area of scientific visualization, information and software visualization, computer graphics and innovative interfaces using large, touch-sensitive displays. With respect to applications, the research concentrates on fundamental and applied problems from the life sciences, in particular functional brain imaging and bioinformatics, and astronomy. Scientific visualization Visualization of large data sets requires advanced techniques in image processing and segmentation, hierarchical data management, and data reduction. This covers a wide range, from classical medical imaging to simulation of natural phenomena. Data volumes generated by scientific simulations can easily grow into the range of gigabytes. In a functional neuroimaging experiment (PET, fMRI), a large number of data volumes is obtained, thus increasing data size even further. Both the increasing size and complexity of these data ask for new techniques for interactive visualization. The possibility of interaction during evaluation will significantly reduce the time required to interpret and present results. To arrive at interactive visualization and analysis for large data sets, many techniques are available, such as auxiliary data structures; special (multiresolution) data transforms, e.g., wavelets or multiscale morphological methods; extraction of features from the volume data and visualizing the features only. In such interactive data visualization, the speed of the data processing stage should be comparable to that of the visualization step. We address this demand by developing efficient algorithms and/or by mapping the involved computations to programmable Graphics Processing Units (GPUs), which are capable of outperforming CPUs for compute-intensive applications. Another important aspect is the determination and visualization of uncertainty in three- and higher dimensional data. Software visualization A new research direction within the group focuses on Software Visualization and Program Understanding. Software visualization has recently rapidly grown to become one of the important research fields within Information Visualization (InfoVis). The goal of software visualization is to provide methods, techniques, and tools that assist the entire range of activities in the software engineering discipline. These include software design, architecting, and development; software understanding; corrective, preventive, and perfective maintenance; and software documentation and reverse engineering. Software maintenance has become in the last years by far the most expensive and time-consuming activity within software engineering, accounting for over 80% of the total resources in the field. Of these, over 50% are dedicated to program understanding. Software visualization targets the maintenance and understanding challenges by offering new, scalable and intuitive visual representations and interactive navigation and analysis methods for all aspects of a software product, including source code, program structure and behavior, documentation, and evolution. Effective use of software visualization in practice requires a tight 113

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integration of software visualization techniques and tools within the classical software analysis, forward, and reverse engineering pipelines. Finally, assessing the actual impact in practice of newly developed methods requires designing and conducting detailed user studies involving software engineers working on concrete large-scale problems in the field. Perception-based visualization A rapidly growing area within the visualization research field is perception-based visualization. Here one takes advantage of knowledge about the human visual system to improve current visualization techniques. The underlying idea is that a better understanding of biological vision will lead to artificial visual stimuli that are better adapted to our visual system. On the other hand, by studying visual stimuli in artificial environments, visualization technology can contribute to human vision research. An important issue is which ‘visual cues’ of a scene (such as shape, size and distance of objects) can be used to encode independent information dimensions. Non-photorealistic and illustrative rendering Non-photorealistic rendering (NPR) is a sub-area of computer graphics that is inspired by a long tradition of artistic and illustrative depiction. We apply NPR techniques to illustration and visualization problems in medical, technical, and other domains. We also work on combining NPR methods with other rendering techniques to create hybrid rendering styles for illustration and visualization. In addition, we work on identifying the differences between the hand-drawn and computer-generated images and to understand what this means for a viewer. One of the goals of this work is to improve NPR techniques to better be able to mimic hand-drawn techniques. Another goal is to be better able to target NPR rendering to achieve certain goals, which do not necessarily have to be the same as those of hand-drawn images or illustrations. Innovative interfaces In order to use the developed visualization techniques successfully, it is vital to provide effective and intuitive interfaces. In our research in this area we concentrate on interfaces to use nonphotorealistic and illustrative rendering techniques that are used, for example, for visualization applications. We employ novel touch-sensitive, large displays that enable users to make use of a larger screen area, interact with applications using direct-touch or pens, and work in groups to profit from collaborations. Applications In functional neuroimaging techniques such as fMRI, the goal is to detect significant changes in brain activity. Since these changes are small and distributed over the whole brain and the images are noisy, the detection process is complex, requiring image processing to obtain high quality images, mathematical and statistical analysis for quantitative characterization of significant effects, and volume visualization for interpretation of the results. A second goal is to study connectivity between brain regions, making use of structural (e.g., Diffusion Tensor Imaging) and functional imaging data. 114

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In bioinformatics, the group is involved in a research program aiming to reconstruct the cellular processes, metabolic potential (metabolome) and gene regulatory networks of selected organisms (gram-positive bacteria and Archaea), by in-silico analysis of all proteins encoded by their chromosome. Research focuses on tools for interactive visualization of gene regulatory networks, metabolic pathways, and integration of gene expression data with volume visualization, based on knowledge from the scientific literature, information encoded in distributed databases, and experimental data. Also, evaluation of the effectiveness of visualization methods is part of this research. The group participates in a research effort on problems from astronomy. Astronomical data sets are growing to enormous sizes. Modern surveys provide not only image data but also catalogues of millions of objects, each object with hundreds of associated parameters. To explore these data sets effectively, new and scalable tools must be developed that can cope with the sheer data volume which has entered the tens of terabytes regime. In this research the focus is on feature extraction and interactive visualization techniques for high-dimensional data.

10.2


Scientific visualization In the field of general-purpose computing using graphics hardware, we are studying image processing and volume visualization algorithms using NVidia’s CUDA compute paradigm. We are also investigating the use of adaptive wavelets and possibilities for efficiently mapping level set methods on GPUs. We also investigated an approach for rendering the surface of a particlebased fluid, which has real-time performance with a configurable trade-off between speed and quality . Perception-based visualization The effectiveness of an information visualization is strongly affected by the amount of visual clutter. Today, the notion of clutter is poorly understood. Although there seems to be quite a strong agreement between subjective judgements of clutter, it is not at all obvious how to measure clutter in an objective way. A model was developed that makes predictions about clutter by estimating the amount of visual ’crowding’ in an image. The predictions of this model strongly correlate with subjective judgements of clutter and also with visual search data. Software visualization and program understanding Within this new research line, work has continued in the direction of creating new techniques for visualizing combinations of software architecture diagrams and software quality metrics. Several techniques have been developed in this direction. These techniques, integrated in a UML visualization environment, enable users such as software architects and designers to analyze large software systems by combining structural information, software metrics extracted directly from source code, and design-level metrics using novel techniques such as shading and 115

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texturing; see Figure 5 for an example. A separate related research direction, visual reverse engineering, has produced several new methods for interactive static analysis and understanding of large C and C++ software systems, including the scalable presentation of various software metrics and identification of design patterns. The developed methods have been extensively tested on both open-source and industrial software systems. Within this theme, work has continued also in the direction of understanding the evolution of large software systems. Previous work in this field has been extended in the direction of extracting and understanding the evolution of software metrics, with the aid of new visualization techniques. Applications of the proposed techniques have been completed in the field of assessing the maintainability and build performance of large software systems together with industrial partners.

Figure 5: Visualization of software architecture and quality metrics. The architecture, modeled as an UML diagram, is decomposed into seven so-called areas of interest, which capture several functional aspects. The areas are overlaid with several software metrics defined on the system components. Using a technique based on blended texturing, scattered point interpolation and shading, the extents of the areas and variation of metric values over each area, are visualized. Taken from: H. Byelas, A. Telea, Texture-Based Visualization of Metrics on Software Architectures, Proc. ACM SoftVis ’08.

Skeletonisation and shape analysis We have successfully applied a second skeletonisation method developed earlier to several ap116

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plications in computer graphics and medical imaging. Our results include robust patch-type and part-type (semantic) segmentation of complex, noisy 3D voxel shapes, as well as a new robust method for classification of cortical surfaces extracted from MRI and CT scans that eliminates the need of performing noise-sensitive curvature estimations. We also developed a general algorithm for computing Euclidean skeletons of 2D and 3D data sets in linear time using the integer medial axis (IMA) transform; see Figure 6 for an example. Non-photorealistic and illustrative rendering In collaboration with Purdue University, USA, and the University of Victoria, Canada, we continued our work on the evaluation of non-photorealistic and illustrative rendering techniques. In the first project with Purdue University we compared texture stippling in hand-drawn and computer-generated illustrations, using image processing analysis techniques and stipple distribution statistics. The analysis of their correlation, contrast, and energy demonstrated that there were clear differences between hand-drawn and computer-generated images. In the second project with the University of Victoria we analyzed hand-drawn pencil strokes and used statistical measures derived from this input to synthesize new strokes that mimic the characteristics of hand-drawn ones. We continued our work on interaction with non-photorealistic rendering. Based on a previously created framework for responsive interaction on large, touch-sensitive displays, several approaches for interacting with non-photorealistic and illustrative rendering techniques were developed and evaluated, in collaboration with the University of Calgary. The new techniques allow users to employ hand postures as the main means for specifying options in the interface and we used this technique successfully to control a stroke-based rendering application on large, touch-sensitive displays. Innovative interfaces We continued the work on applying the hand-posture based interaction techniques to the exploration and visualization of vector field and flow datasets. The newly created interface allows users such as physicists, biologists, or meteorologists to interactively explore unknown flow datasets in order to get an understanding about their properties, and then to annotate and illustrate them for later use or for discussions with colleagues. The interaction techniques allow users to create and sketch their own glyphs to represent aspects of the data, and then to apply the newly created glyphs to the data for exploration and visualization. The entire interaction is hand-posture based and the interface can be learned within a few minutes. The interaction technique is currently being evaluated and results of this evaluation are expected soon. In collaboration with the University of Calgary, Canada, we created mobile spatial tools to support fluid interaction which is increasingly important for effective work on interactive displays such as tabletops. We addressed this issue by affecting the properties of objects in the interface spatially rather than temporally. The created tools allow us to control multiple objects simultaneously using high-level, task-driven actions without the need for setting low-level properties 117

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of objects. We demonstrated a number of specific tools and their application in fluid interaction scenarios. Finally, based on previous work on finger tracking with consumer hardware (Nintendo Wii Remote), we created a finger tracking system that uses the Wii Remote and gloves fitted with retro-reflective markers; see Figure 7. The hardware setup consists of the Wii Remote, an array of infrared LEDs, and a bluetooth dongle, in addition to a laptop and projector presentation setup. The project aimed at enabling free-handed multi-touch interaction, where problems arise such as having to identify the fingers of each hand and to recognize pinching for interaction. The final system allows dual-“touch” interaction with videos, images, and slide decks, and is designed to be used for presentations. Visualization in functional neuroimaging Work continued in the area diffusion tensor imaging (DTI), which is an MRI-based technique enabling the visualization of nerve fibers and connectivity of brain regions. Jointly with researchers from the University Medical Center Groningen, we applied this technique to investigate possible sources of the ‘tinnitus’ phenomenon, which is defined as the perception of sounds in the absence of an external sound source. Using a probabilistic DTI approach, we studied characteristics of white matter fiber tracts defining the (classical) auditory pathway, as well as connections between the auditory system and the amygdala, which is involved in some forms of tinnitus and which is important in the emotional content of sounds. More work is needed to assess the significance of the results found so far. Gene network visualization We developed an application for visualizing gene expression data from time series experiments in both a gene regulatory network and metabolic pathway context. Regulatory networks consist of regulator proteins that control the expression of their respective target genes, and metabolic pathways are networks of chemical reactions catalyzed by gene products. This application can (i) visualize the data from time series experiments in a context of a regulatory network and KEGG metabolic pathways; (ii) identify and visualize active regulatory subnetworks from the gene expression data; (iii) perform a statistical test to identify and subsequently visualize pathways that are affected by differentially expressed genes. We demonstrated the benefits of our approach and software by a case study. Astronomical visualization We explored clustering of data sets obtained from large simulations of astronomical data to get a hierarchical visualization which enables one to explore large datasets interactively. For establishing relations between the spatial arrangement of galaxies and the distribution of various attributes in parameter space, accurate density estimation methods are required. We compared three such methods. Preliminary results show that a modification of a method originally due to Breiman performs best. 118

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10.3

Research subjects

H. Bekker: Shape similarity measure evaluation, visualization of DTI data, visualization of molecular dynamics data. R. van den Berg: perception-based visualization. H. Byelas: software visualization. A. Crippa: visualization of functional neuroimaging data. M.H. Everts: particle-based data segmentation and visualization; graphics hardware computing. B.J. Ferdosi: visualization of astronomical data. M. Gerl: non-photorealistic and illustrative rendering. T. Isenberg: non-photorealistic and illustrative rendering; computer graphics interaction and innovative interfaces. A. Jalba: volumetric shape modelling, segmentation and visualization; graphics hardware computing. W. van der Laan: Multiscale visualization based on adaptive morphological wavelets; graphics hardware computing. F. Li: visualization of astronomical data. J.B.T.M. Roerdink: scientific visualization; morphological and wavelet-based multidimensional data processing; neuroimaging; bioinformatics. A.C. Telea: software visualization and program understanding; information visualization; multiscale skeletons. M.A. Westenberg: scientific visualization, bioinformatics. L. Yu: computer graphics interaction and innovative interfaces.

10.4

Publications

Dissertations – M. ten Caat, Multichannel EEG Visualization, Institute of Mathematics and Computing Science, University of Groningen, Febr. 1, 2008, 112 pages.

Edited books – Proceedings of the 6th Symposium on Software Visualization (SOFTVIS), A. Telea, C. Hundhausen, R. Koschke (eds.), ACM, 2008. – Proceedings of the 10th Eurographics/IEEE Data Visualization Symposium (EuroVis), A. Vilanova, A. Telea, G. Scheuermann, T. Moller (eds.), Wiley-Blackwell, 2008. 119

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Contributions to books – D. Reniers, A. Telea, Tolerance-based Feature Transforms, in Advances in Computer Graphics and Computer Vision, (Intl. Confs. VISAPP and GRAPP, Setubal, Portugal, Feb. 25-28, 2006, Revised Selected Papers), 4, Springer LNCS, 2008, 107-114.

Articles in scientific journals – R. van den Berg, F.W. Cornelissen and J.B.T.M. Roerdink, Perceptual Dependencies in Information Visualization Assessed by Complex Visual Search, ACM Transactions on Applied Perception, 4(4), 2008, 1-21. – H. Byelas, A. Telea, Visual Software Analytics for Assessing the Maintainability of ObjectOriented Software Systems, Intl. J. of Information, Interaction and Intelligence, 8 (1), 2008, 24-40. – M. ten Caat, M.M. Lorist, E. Bezdan, J.B.T.M. Roerdink and N.M. Maurits, High-Density EEG Coherence Analysis Using Functional Units Applied to Mental Fatigue. J. Neuroscience Methods, 171(2), 2008, 271-278. – M. ten Caat, N.M. Maurits and J.B.T.M. Roerdink, Data-Driven Visualization and Group Analysis of Multichannel EEG Coherence with Functional Units, IEEE Trans. Visualization and Computer Graphics, 14(4), 2008, 756-771. – W.H. Hesselink and J.B.T.M. Roerdink, Euclidean skeletons of digital image and volume data in linear time by the integer medial axis transform, IEEE Trans. Pattern Analysis and Machine Intell., 30(12), 2008, 2204-2217. – T. Isenberg, M. Everts, J. Grubert, and S. Carpendale, Interactive Exploratory Visualization of 2D Vector Fields, Computer Graphics Forum, 27(3), 2008, 983–990. – R. Maciejewski, T. Isenberg, W.M. Andrews, D.S. Ebert, M. Costa Sousa, and W. Chen, Measuring Stipple Aesthetics in Hand-Drawn and Computer-Generated Images, Computer Graphics & Applications, 28(2), 2008, 62–74. – D. Reniers, A. Telea, Part-type segmentation of articulated voxel shapes using the junction rule, Computer Graphics Forum, 27 (7), 2008, 1845-1852. – D. Reniers, A. Telea, Patch-type segmentation of voxel shapes using simplified surface skeletons, Computer Graphics Forum, 27 (7), 2008, 1837-1844. – D. Reniers, A. Telea, Hierarchical part-type segmentation using voxel-based curve skeletons, The Visual Computer, 24 (6), 2008, 383-395. – D. Reniers, J.J. van Wijk, A. Telea, Computing multiscale curve and surface skeletons of genus 0 shapes using a global importance measure, IEEE Transactions of Visualization and Computer Graphics, 14 (2), 2008, 353-368. 120

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– A. Telea, D. Auber, Code flows: Visualizing structural evolution in source code, Computer Graphics Forum, 27 (3), 2008, 89-98. – A. Telea, H. Byelas, L. Voinea, Architecting an open system for querying large C and C++ code bases, South African Computer Journal, 41, 2008, 43-56. – M.A. Westenberg, S.A.F.T. van Hijum and O.P. Kuipers and J.B.T.M. Roerdink, Visualizing Genome Expression and Regulatory Network Dynamics in Genomic and Metabolic Context, Computer Graphics Forum, 27(3), 2008, 887-894. – A.M. Wink, H. Hoogduin and J.B.T.M. Roerdink, Data-driven haemodynamic response function extraction using Fourier-wavelet regularised deconvolution, BMC Medical Imaging, 8 (7), 2008. Articles in conference proceedings – H. Byelas, A. Telea, The Metric Lens: Visualizing Metrics and Structure on Software Diagrams, Proc. 15th Working Conference on Reverse Engineering (WCRE), 15-18 October 2008, Antwerp, Belgium, IEEE, 340-342. – F. Li and R. Klette, A Variant of Adaptive Mean Shift-Based Clustering, In Proc. ICONIP 2008 - 15th Int. Conf. Neural Information Processing of the Asia-Pacific Neural Network Assembly, November 25-28, 2008, Auckland, New Zealand. – Z. Meraj, B. Wyvill, T. Isenberg, A. Gooch, and R. Guy, Mimicking Hand-Drawn Pencil Lines, In: P. Brown, D.W. Cunningham, V. Interrante, and J. McCormack, editors, Proc. Int. Symposium on Computational Aesthetics in Graphics, Visualization, and Imaging (CAe 2008, June 18–20, 2008, Lisbon, Portugal), Aire-la-Ville, Switzerland, Eurographics Association, 2008, 73–80. – D. Reniers and A. Telea, Segmented Simplified Surface Skeletons, Proc. Intl. Conf. on Discrete Geometry for Computer Imagery (DGCI), Springer LNCS, 2008, 262-274. – D. Reniers, A. Jalba, A. Telea, Robust Classification and Analysis of Anatomical Surfaces Using 3D Skeletons, Proc. Visual Computing for Biomedicine (VCBM), Eurographics, 2008, 32-39. – M. Sensalire, P. Ogao, A. Telea, Classifying Desirable Features of Software Visualization Tools for Corrective Maintenance, Proc. ACM SoftVis, A. Telea, C. Hundhausen, R. Koschke (eds.), Herrsching, Germany, 2008, 87-90. – A. Telea, L. Voinea, An interactive reverse-engineering environment for large-scale C++ code, In Proc. ACM SoftVis, A. Telea, C. Hundhausen, R. Koschke (eds.), Herrsching, Germany, 2008, 67-76. – L. Vlaming, J. Smit, and T. Isenberg, Presenting using Two-Handed Interaction in Open Space, In Sriram Subramaniam and Shahram Izadi, editors, Proc. 3rd Annual IEEE Workshop on Horizontal Interactive Human-Computer Systems (Tabletop 2008, October 1–3, Amsterdam, The Netherlands), Los Alamitos, IEEE Computer Society, 2008, 31–34. 121

IWI Annual Report

– L. Voinea, A. Telea, A Tool for Optimizing the Build Performance of Large Software Code Bases, Proc. 12th European Conf. Software Maintenance and Reeningeering (CSMR), Athens, Greece, 1-4 April 2008, IEEE, 355-357. – L. Voinea, A. Telea, SolidFX: An Interactive Reverse Engineering Environment for C++, Proc. 12th European Conf. Software Maintenance and Reeningeering (CSMR), Athens, Greece, 1-4 April 2008, IEEE, 358-360. Other publications – R. van den Berg, J.B.T.M. Roerdink, and F.W. Cornelissen, Crowding explained by population coding, Perception, 37, ECVP Abstract Supplement, p. 170. – H. Byelas, A. Telea, Texture-Based Visualization of Metrics on Software Architectures, Proc. ACM SoftVis, A. Telea, C. Hundhausen, R. Koschke (eds.), Herrsching, Germany, 2008 (poster), 205-206. – H. Byelas, A. Telea, Evaluating Visual Realism in Drawing Areas of Interest on UML Diagrams, Proc. of the 14th Annual Conf. Advanced School for Computing and Imaging (ASCI), June 11-13, Heijen, The Netherlands, 2008, 265-272. – M.H.Everts, H. Bekker and J.B.T.M. Roerdink, Graph Algorithms for Fast Preview of Global Brain White Matter Structure, In: SIREN: Scientific ICT Research Event Netherlands, 29 September 2008, VU Amsterdam, 2008. Poster. – J. Grubert, S. Carpendale, and T. Isenberg, Interactive Stroke-Based NPR using Hand Postures on Large Displays, In: K. Mania and E. Reinhard, editors, Short Papers at Eurographics 2008 (EG 2008, April 14–18, 2008, Crete, Greece), 279–282, Aire-la-Ville, Switzerland, 2008. Eurographics Association. Short paper and poster. – U. Hinrichs, H. Schmidt, T. Isenberg, M.S. Hancock, and S. Carpendale, BubbleType: Enabling Text Entry within a Walk-Up Tabletop Installation, Technical Report 2008-89306, Department of Computer Science, University of Calgary, Canada, February 2008. – T. Isenberg, J. Grubert, M. Everts, and S. Carpendale, Hands-On Analysis and Illustration: Interactive Exploratory Visualization of Vector Fields, In: Proc. Fourteenth Annual Conf. Advanced School for Computing and Imaging (ASCI CONFERENCE 2008, June 11–13, 2008, Het Heijderbos, Heijen, The Netherlands), 2008, 222–229. – T. Isenberg, S. Nix, M. Schwarz, A. Miede, S.D. Scott, and S. Carpendale, Mobile Spatial Tools for Fluid Interaction, In Sriram Subramaniam and Shahram Izadi, editors, Posters of the 3rd IEEE Tabletop Workshop (Tabletop 2008, October 1–3, 2008, Amsterdam, The Netherlands), Los Alamitos, 2008. IEEE Computer Society. Extended abstract and poster. – Z. Meraj, B. Wyvill, T. Isenberg, A. Gooch, and R. Guy. Mimicking Hand-Drawn Pencil Lines, In: K. Anjyo and P. Barla, editors, Poster and Animation Proc. Sixth Int. Symposium on Non-Photorealistic Animation and Rendering (NPAR 2008, June 9–11, 2008, Annecy, France), 2008, page 9. 122

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– D. Reniers, A. Telea, Patch-type Segmentation of voxel Shapes using Simplified Surface Skeletons, Proc. Shape Modeling International (SMI), IEEE, 2008, 273-274 (poster). – Proc. 6th Symposium on Software Visualization (SOFTVIS), A. Telea, C. Hundhausen, R. Koschke (eds.), ACM, 2008. – Proc. 10th Eurographics/IEEE Data Visualization Symposium (EuroVis), A. Vilanova, A. Telea, G. Scheuermann, T. Moller (eds.), Wiley-Blackwell, 2008. – A. Telea, L. Voinea, Visual Analytics for Understanding the Evolution of Large Software Projects, Proc. 7th Belgium-Netherlands Software Evolution Workshop (BENEVOL), Eindhoven, Netherlands, 11-12 December 2008, 23-27. – V. Valeanu, A. Telea, M. Marin, P. de Hillerin, A. Vizitiu, Automatic Warning for Abnormal Vital Parameters Evolution in Tele- and Home-Care Applications, Proc. Intl. Conf. on Space Applications, 22-25 April 2008, Toulouse, France.

10.5


External funding A grant of 20 kEuro from the European Commission was obtained in 2008. This is part of FP7 Coordination Action VISMASTER on Visual Analytics by a European consortium of visualization groups. Period: 2008-2010. Currently the following other externally funded projects are carried out in the group: – Scalable analysis and visualization of high-dimensional, astronomical data sets (ASTROVIS) (2006-2010); jointly with Kapteyn Astronomical Institute, University of Groningen. Funding: Netherlands Organization for Scientific Research (NWO): two PhD students, one postdoc. – Interactive morphological and wavelet-based volume processing and visualization (IMOVIS) (2005-2009). Funding: Netherlands Organization for Scientific Research (NWO): two PhD students, one postdoc. External collaboration Roerdink collaborates with the Visualization and Interactive Systems Institute, University of Stuttgart, headed by professor Thomas Ertl, who is an external advisor on the NWO-VIEW project IMOVIS. He participates in the Groningen Neuroimaging Center of the local research school BCN (Behavioural, Cognitive and Neurosciences), and collaborates on visualization problems related to neuroimaging with the Dep. of Clinical Neurophysiology of the University Medical Center Groningen and the Lab. for Experimental Ophthalmology of the University of Groningen. In the area of Bioinformatics, he collaborates with the Dep. of Molecular Genetics (prof. dr. O.P. Kuipers). He has a joint project with the Kapteyn Astronomical Institute of the University of Groningen on scalable visualization of astronomical data (prof. Th. van der Hulst, prof. E. Valentijn). 123

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Isenberg collaborates with the Innovations in Visualization group University of Calgary, headed by Prof. Dr. Sheelagh Carpendale, on interactions on large displays. In addition, he participates in a collaboration with the PURPL lab at Purdue University, USA, headed by Prof. Dr. David Ebert, on non-photorealistic rendering and illustration. He also collaborates with Professors Dr. Brian Wyvill and Dr. Amy Gooch at the University of Victoria, Canada, on synthesis evaluation and of pencil drawing. Finally, he started a collaboration with artists and illustrators at the Academie Minerva, Groningen. Telea collaborates with the Visualization group headed by prof. J. J. van Wijk at the Eindhoven University of Technology, the Netherlands, where he is the main advisor of a PhD student in multiscale skeletonisation. He also collaborates with the MaBioVis group at the INRIA/CNRS LaBRI institute in Bordeaux, France (prof. G. Melancon, prof. M. Delest) on information visualization, where he was co-advisor of a recently completed PhD thesis. Other collaborations include the Numerical Analysis Group, University of Bonn, Germany (prof. M. Rumpf) on multiscale visualization methods and the National Institute of Sports Research in Bucharest, Romania (prof. P. de Hillerin) on information visualization.

10.6

Further information

Roerdink has a joint appointment with the Faculty of Medicine. He is on the editorial board of the Journal of Mathematical Imaging and Vision, member of the Eurographics Association and Senior Member of the IEEE. He was reviewer for a large number of international journals, and member of the program committees of EuroVis08, IEEE Vis08, IWCIA08, and VG08. He was member of the PhD reading committees of H. Pretorius (TU Eindhoven). He co-organised (with J. Van Wijk, E. Valentijn, F. Arbab, C. De Laat) an international I-science workshop on data mining, distributed computing and visualization for astronomy, from October 13-17, 2008, at the Lorentz Center in Leiden. Isenberg was reviewer for numerous international journals and conferences, and member of the program committees of CAe 2008, NPAR 2008, TABLETOP 2008, and EGVE 2008. In addition, we as a member of the organizing committee of CAe 2008. He is a member of ACM, ACM SIGGRAPH, IEEE, and the Eurographics Association. He gave invited talks at Purdue University, USA, Philips Research, Eindhoven, and TNO, Groningen. Telea acted as co-chair in the organization of the IEEE EuroVis Visualization Symposium (May 2008) and the ACM SoftVis Symposium on Software Visualization (September 2008). He was member of the PhD reading committees of R. Bourqui and F. Chevalier (University of Bordeaux, France). He gave several invited talks at the 6th Data and Information Visualization symposium (DataViz) in Bremen, Germany, and the Intl. FASTAR-Espresso Workshop on Finite Automata in Johannesburg, South Africa. The GENeVis program developed by Westenberg was elected second-best bioinformatics application during the Application Showcase contest of the BioRange Meeting 2008, held in Lunteren, The Netherlands. 124

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Input volume

IMA-1

IMA-2

Figure 6: Example of skeletonisation by the Integer Medial Axis (IMA) transform. Volume renderings of binary horse data (128×280×232 voxels) and its skeletons (side, front and top views). First column: input data. Second and third column: IMA skeletons with different ways of pruning. In the skeleton renderings, the input volume is rendered partially transparent. Taken from: W. H. Hesselink and J. B. T. M. Roerdink. Euclidean skeletons of digital image and volume data in linear time by the integer medial axis transform. IEEE Trans. Pattern Analysis and Machine Intell., 30(12):2204-2217, December 2008.

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Figure 7: Setup for the finger tracking with consumer hardware: A Nintendo Wii Remote next to the laptop track thumb and index finger from both hands, allowing a person to interact in the open space in front of him or her in the context of a presentation environment.

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Colloquium Computing Science 2008 – List of Speakers – December 1 Dr. M. Wermelinger, The Open University, UK Eclipse’s Architecture - Design Principles and Socio-Technical Congruence – November 6 J. Anderson, Vaxjo University, Sweden A Modeling Framework for Self-adaptive Software Systems – October 30 Dr. U. Zdun, TU Vienna Compliance in service-oriented architectures: A model-driven and view-based approach – October 23 D.G. Stork, Ricoh Innovations and Stanford University When Computers look at Art, Computer Vision and Image Analysis in Humanistic Studies of Visual Arts – October 20 B. Hammer, TU Clausthal Clustering and Visualization of Large Dissimilarity Datasets – October 13 Prof.dr. S. Tai, Univ. Karlsruhe Cloud Computing: On-demand compute utilities - and opportunities - in the hands of many – October 6 Dr. S. Carpendale Univ. of Calgary Observation for design – October 6 A. Tang, Swinburne University of Technology, Australia Towards Independent Software Architecture Review – September 8 O. Zimmermann , IBM Zurich Reusable Architectural Decision Models for Enterprise Application Develpment – July 16 Prof. L. Alvisi, Univ. of Texas ”The Long March of hte Byzantine Generals” – June 30 L. Penserini, Univ. Utrecht Dealing with Adaptivity Qualities within different Agent-Oriented Development Frameworks

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– June 23 G. Dzemyda, Inst. of Mathematics and Informatics, Vilnius/Lithania Visualization of Multidimensional Data by Using Neural Networks: Methods and Applications – June 20 E. Erdem Inferring phylogenetic trees using answer set programming – June 16 Prof. W. Niessen, Erasmus MC, Delft University of Technology Image Analysis for developing Quantitative Imaging Biomarkers – June 9 Prof.dr.-Ing. T. Ach, RWTH Aachen Analysing Superimposed Oriented Patterns – May 29 O. Amft, ETH Zurich Activity-awareness for smart personal assistants – May 29 Dr. S. Subrananian, ERCIM Fellow Enhancement of BPEL engines for Self-Healing Composite Web Services – May 19 Prof.dr. J. Sijbers, Univ. of Antwerp Diffusion tensor imaging: current and future research at Vision Lab Antwerp – May 6 I. Bloch, Telecom Paris Tech (ENST) Fuzzy morphology and its applications to spatial reasoning – April 14 A.W.M. Smeulders, Intelligent Systems Lab Amsterdam The notion of an object in computer vision – April 7 Dr. F.M. Schleif, Univ. Leipzig/Germany Algorithms for spectral data analysis and applications – March 31 J. Jeuring, Univ. Utrecht and OU Strategies for exercises – March 17 AIO Colloquium: G. Ouzounis Hyper-connectivity, operators and applications 128

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– March 10 G. de Haan, Video Processing Group, Philips Research, Eindhoven Moving images on modern displays: How to choose your next flat screen TV – March 3 T. Villmann, Univ. Leipzig Fuzzy classification and class-imaging using fuzzy-labelled self-organizing maps – February 26 AIO Colloquium: E. Subramanian Attractor switching i neuronal networks and Spatiotemporal filters for motion processing – February 25 F. Rossi, INRIA Rocquencourt/France An introduction to functional data analysis – February 22 M. Angelova, Northumbria University, Newcastle/UK Combined clustering models for the analysis of gene expression of prokaryotic organisms – February 18 M. Viergever, Univ. Utrecht Image Registration and Fusion for Medical Research, Diagnosis and Intervention – February 15 Prof.dr. K.D. Schewe, Information Science Research Centre New Zealand Exploiting ASMs as Foundation of Software Engineering – February 11 L.J. van Vliet, Pattern Recognition Group, Dept. Applied Physics, TU Delft Robust Super-Resolution: Algorithms and Performance Measures – February 4 T. Isenberg, IWI Illustrative Computer Graphics, Visualization, and Interaction – February 1 Prof.dr.-Ing. B. Preim, Univ. Magdeburg Visual Computing for medical education, diagnosis and treatment planning – February 1 Prof.dr.ir. J.J. van Wijk, TU Eindhoven Visualization of Seifert Surfaces – January 28 F. Arbab, CWI, Amsterdam and Univ. Leiden Third-Party Coordination of Distributed Services – January 21 N. Grgurina, University Center for Learning Teaching Computer Science in Higher Education 129

IWI Annual Report

– January 14 I. Aizenberg, Texas AM University, Computer and Information Sciences Multi-Valued and Universal Binary Neurons

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Colloquium Mathematics 2008 – List of Speakers – October 14 AIO Colloquium: A.K. Nguyen A Modern Perspective on Fano’s Approach to Linear Differential Equations – October 8 J. Behrndt, TU Berlijn Elliptic differential operators and Dirichlet-to-Neumann maps – September 25 AIO Colloquium: O.V. Lukina Geometry of torus bundles in integrable Hamiltonian systems – September 22 AIO Colloquium: S. Meagher Curves with many points and a problem of Serre – September 17 AIO Colloquium: G. Schneider On the weight adjacency matrix of convolutional codes – June 10 AIO Colloquium: F.L. Tsang Convolution and codes – May 27 Prof. M. Gehrke Automata, discrete dynamics, and duality theory – May 20 Dr. O. Kirillov, TU Darmstadst How to play a disc brake: a dissipation-induced sque al – May 15 AIO Colloquium: C. Poirier What is a stack – May 14 AIO Colloquium: R. Wemmenhove Numerical Simulation of Two-Phase Flow in Offshore Environments – March 18 Branko Curgus, Western Washington University Eigenvalue problems with boundary conditions depending polynomially on the eigenparameter

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– March 14 F.H. Szafraniec, University Jagiellonski, Krakow How much indeterminacy may fit in a moment problem? – February 26 AIO Colloquium: E. Subramanian Attractor switching in neural networks and Spatiotemporal filters for motion processing – January 29 R. Gill, University of Leiden The case of Lucia de Berk: Science versus Justice – February 19 V. Gaiko, Belarusian State University of Informatics and Radioelectronics Minsk, Belarus Global Analyis of Planar Dynamical Systems – January 22 B. Aronov, Polytechnic University Brooklyn, New York Unions of geometric objects – January 17 AIO Colloquium: D. Napp Avelli An Algebraic Approach to Multidimensional Systems

132

Research Institute of Mathematics and Computing Science

Research Institute of Mathematics and Computing Science

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