Dynamics of Patterns Day

The third Dynamics of Patterns Day (DoP-Day) for an audience of physicists, mathematicians, theoretical biologists and other interested disciplines in The Netherlands and beyond will be held on Oct. 19, 2006 in the Trippenhuis (KNAW-building) in walking distance from Amsterdam Centraal Station, i.e., at the same location as previous meetings. For directions see http://www.knaw.nl/contact/contact.html.

Please note the other DoP-event in the academic year 2006/07: a DoP-Symposium on April 26 and 27, 2007 at Twente University.

Updated information on DoP-events can be found at : http://www.cwi.nl/events/regular/DoP-Days/index.html

Programme

13:00 - 13:30 Tea and coffee

13:30 - 13:50 U. Ebert, CWI and TUE, Streamer experiments versus Laplacian growth

13:50 - 14:40 B. Davidovitch, UL/CWI, UMass, Amherst, Discrete versus continuous models of Laplacian growth

14:40 - 15:10 Tea and coffee

15:10 - 16:00 A. Morozov, Instituut Lorentz, UL, How is turbulence in wall-bounden flows sustained? or Exact coherent structures in Newtonian and non-Newtonian fluids

16:10 - 17:00 K. ten Tusscher, Theor. Biol./Bioinformatics, UU, Ventricular fibrillation in the human heart: spiral wave dynamics

17:00 - 18:00 Tea and coffee

About speakers and talks:

Ute Ebert is themeleader at CWI Amsterdam and professor of physics at TUE. She will briefly review recent experiments on electrical breakdown (streamer) patterns in air and nitrogen performed at TUE and discuss applications, limitations and challenges for Laplacian growth models.

Benny Davidovitch got his Ph.D. at the Weizmann Institute, Israel, and was postdoc at Harvard. Until January, he visits UL and CWI, then he will move to an assistent professorship at U. Mass., Amherst. He will talk about discrete versus continuous models of Laplacian growth. Well-known examples are diffusion limited aggregation (DLA) versus viscous fingering.

Alexander Morozov got a Ph.D. in polymer physics at UG and then thoroughly studied pattern formation in non-Newtonian fluids at UL. In January, he will move on to a new position at Univ. Edinburgh.

Abstract of the talk:

Flows of fluids are known to become turbulent at large enough Reynolds numbers. Until now, it was virtually impossible to predict the Reynolds number of the laminar -- turbulent transition or to describe flow dynamics even in the vicinity of the transition. Recently, however, it has been discovered that in simple shear flows (like pressure-driven flows in a pipe or between two plates) there exist so-called coherent structures which organize the turbulent dynamics close to the laminar-turbulent transition. I will review the modern developments in the field and present a new theory by F.Waleffe which proposes a pictorial view of how turbulent state is constructed from coherent structures and allows one to estimate the transitional Reynolds number. In the second part of the talk, I will present recent results on how small amounts of polymers affect turbulence -- question relevant for the drag-reduction problem. I will derive a low-dimensional model for this process and discuss how coherent structures change in the presence of polymers.

Kirsten ten Tusscher is a postdoc working in the field of whole heart modelling. In particular she developed a model for human ventricular tissue that can be used to study cardiac arrhythmias. These are related to break-ups of spiral patterns.

Abstract of the talk:

Sudden cardiac death (SCD) is a major health problem in the industrialised world, leading to over 300,000 mortalities in the US alone anually. SCD is most frequently caused by a cardiac arrhythmia called ventricular fibrillation (VF). During VF, the synchronous, coordinated contraction of the heart is replaced by asynchronous, chaotic contractions that render the heart ineffective to pump around blood and oxygenate the body.

Modeling studies of the cardiac electrical excitation process that triggers and coordinates cardiac contraction play an important role in gaining more insights in VF. Using both experiments and modeling studies it was found that rotors (spiral waves) may arise in cardiac tissue, just as in other excitable media. These spiral waves take over control of cardiac excitation and contraction from the sinus node. Using analytical and modeling studies it was furthermore found that through an instability, spiral waves may become unstable, leading to spiral wave fragmentation and multiplication. It is this turbulent multi-spiral wave excitation pattern that underlies VF.

Most modeling studies thus far have used phenonomenological models to obtain qualitative insights in VF mechanisms and patterns. Some other studies have used animal heart models to study VF. In our modeling studies we combine a detailed electrophysiological model of human cardiac cells together with an anatomically realistic model of the human heart to gain more quantitative insights in human VF. We study both the conditions under which instabilities arise and the number of spiral waves driving human VF.