The ZIH colloquium is a public event and takes place on each 4th Thursday of the month at 15:00 o'clock in the room Willers-Bau A 317.
For additional or extraordinary events time and room are explicitly mentioned.
16. February 2017: Thomas Ihle (Ernst-Moritz-Arndt University Greifswald,
Institute for Physics) "Kinetic theory of active matter: coarse-graining and invasion waves"
Models of self-driven agents similar to the Vicsek model are studied by means of kinetic theory. In these models, particles try to align their travel directions with the average direction of their neighbors plus some noise. At low noise, a globally ordered state of collective motion forms. These models have a discrete time step, consist of a simple streaming and collision step and are easily implemented on a computer.
A kinetic theory is derived from an exact equation for the N-particle probability density using Boltzmann’s approximation of Molecular Chaos. A coarse-graining procedure, called Chapman-Enskog expansion is performed to derive hydrodynamic equations from the kinetic theory.
The kinetic theory is also solved numerically by a Lattice-Boltzmann-like algorithm. Steep soliton-like waves are observed that lead to an abrupt jump of the global order parameter if the noise level is changed. The shape of the waves is shown to quantitatively agree within 3% with agent-based simulations at large particle speeds. At small densities and realistic particle speeds, the mean-field assumption of Molecular
Chaos is invalid near the onset of collective motion, and correlation and memory effects become relevant.
I will show how to self-consistently include correlation effects at the level of ring-kinetic theory. Instead of just one kinetic equation, an additional equation for the time evolution of the two-particle correlations will be derived. This equation is solved numerically for a homogeneous system and shown to be in excellent agreement with agent-based simulations in certain parameter ranges.
Thomas Ihle studierte Physik an der Universität Leipzig, wechselte 1991 als Diplomand an das Forschungszentrum Jülich und promovierte 1996 an der RWTH Aachen. Nach Postdoc-Aufenthalten in Paris, Grenoble, Minneapolis und Stuttgart wurde Prof. Ihle 2004 an die North Dakota State University berufen, wo er 2010 Tenure erhielt. 2015 erfolgte die Ernennung zum Professor an der Ernst-Moritz-Arndt Universität Greifswald. Hauptarbeitsgebiete sind kinetische Theorie und Computersimulation selbstgetriebener Teilchen, Entwicklung teilchenbasierter Algorithmen für komplexe Flüssigkeiten sowie Musterbildung beim Kristallwachstum.