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30 octobre 2017: 1 événement

  • Séminaires Invités

    Lundi 30 octobre 2017 14:00-15:30 - Thomas IHLE - Greifswald University, Germany

    Kinetic Theory of Active Particles : Correlation and Memory Effects

    Résumé : We consider Vicsek-type models for self-propelled agents. In these models, active agents 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. Starting from the exact evolution equation for the
    N-particle probability distribution, using the Molecular Chaos assumption an Enskog-like kinetic equation is derived, which is solved numerically. 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 with agent-based simulations at large speeds. Often, Molecular Chaos is invalid near the onset of collective motion, and correlation effects become relevant. It is shown how to self-consistently include correlations at the level of ring-kinetic theory. For a particular Vicsek-style model with bounded confidence interactions, we observe the so-called Kovacs-effect. This effect becomes huge under certain conditions and describes strong memory effects. This provides an indirect proof that the usual Toner-Tu theory for polar active matter should not be applicable here. A nonlinear theory for the Kovacs effect is developed, which agrees quantitatively with our data.

    contact : Chaouqi Misbah

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères

    En savoir plus : Séminaires Invités