# Amic Frouvelle : Macroscopic limits of a system of self-propelled particles with phase transition

The Vicsek model, describing alignment and self-organisation in large systems of self-propelled particles, such as fish schools or flocks of birds, has attracted a lot of attention with respect to its simplicity and its ability to reproduce complex phenomena. We consider here a time-continuous version of this model, in the spirit of the one proposed by P. Degond and S. Motsch, but where the rate of alignment is proportional to the mean speed of the neighboring particles. In the hydrodynamic limit, this model undergoes a phase transition phenomenon between a disordered and an ordered phase, when the local density crosses a threshold value. We present the two different macroscopic limits we can obtain under and over this threshold, namely a nonlinear diffusion equation for the density, and a first-order non-conservative hydrodynamic system of evolution equations for the local density and orientation. (joint work with Pierre Degond and Jian-Guo Liu).

**Category**: Applied Math and Analysis**Duration**: 01:34:26**Date**: January 16, 2012 at 4:25 PM**Views**: 110-
**Tags:**seminar, Applied Math And Analysis Seminar

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