A day on Cell Motion

LJLL, December 17, 2012

Seminar room 15-16 309

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Program

10:30 - 11:15	Pierre Degond
11:15 - 12:00	Enkeleida Lushi
12:00 - 14:00	Lunch
14:00 - 14:45	Fernando Peruani
14:45 - 15:30	Vincent Calvez
15:30 - 16:00	Coffe Break
16:00 - 16:45	Francis Filbet

Vincent Calvez (ENS Lyon) : Modèles cinétiques pour les populations de bactéries.

Abstract : Je présenterai un modèle cinétique bien adapté à la description du chimiotactisme au sein d'une population de bactéries E. coli. Je décrirai la limite d'échelle de diffusion (quand elle est valide) et je mentionnerai des résultats quantitatifs de comparaison avec des expériences. Ceci est un travail en collaboration avec Jonathan Saragosti, Nikolaos Bournaveas, Benoît Perthame, Axel Buguin et Pascal Silberzan.

Pierre Degond (IMT, Toulouse 3) : Modèles de type Navier-Stokes avec contrainte géométrique pour la dynamique en essaims.

Abstract: Swarm dynamics becomes increasingly important in biology and social sciences. Swarms consist of a large number of self-propelled interacting particles (such as e.g. bird flocks, fish schools, swimming bacteria or crowds). Swarm dynamics also provides a model for certain social phenomena such as consensus formation, mimetic behavior, bubble formation so on. In this talk, we focus on macroscopic models that can be derived from self-propelled particles interacting through alignment. These models are of the form of non-standard compressible Navier-Stokes like models which involve a geometrical constraint on the velocity. We will review how they can be derived and what we know (and do not know) about these models.

Francis Filbet (UCBL, Lyon 1) : Une méthode numérique pour un modèle cinétique de chemotaxis - prise en compte de la géometrie.
Enkeleida Lushi (Imperial College London) : Collective chemotactic motion of micro-swimmers in the presence of self-generated fluid flows.

Abstract : In suspensions of micro-swimmers locomotion generates fluid motion, and it is known that such flows can lead to collective behavior from unbiased swimming. We examine the complementary problem of how collective chemotactic motion is affected by these self-generated flows. A kinetic theory coupling run-and-tumble chemotaxis to the flows of collective swimming shows separate branches of chemotactic and hydrodynamic instabilities for isotropic suspensions, the first driving aggregation, the second producing increased orientational order in suspensions of pushers and maximal disorder in suspensions of pullers. Nonlinear simulations show that hydrodynamic interactions can limit and modify the chemotactically driven aggregation dynamics.

Fernando Peruani (Univ. Nice-Sophia Antipolis) : Collective motion and nonequilibrium cluster formation in gliding bacteria.

Abstract : I will show that in experiments with gliding bacteria there is a transition to collective motion in which cell self-organized into larger moving clusters. Collective motion by non-equilibrium cluster formation is detected for a critical cell packing fraction around 17%. This transition is characterized by a scale-free power-law cluster-size distribution, with an exponent 0.88±0.07, and the appearance of (apparent) giant number fluctuations. We show that these findings can be understood through a general theory for non-equilibrium clustering in self-propelled particle systems. This suggests that bacterial collective motion, vortex formation, and aggregation, traditionally believed to require chemotaxis, can arise without invoking any biochemical signaling. The collective self-organization in our experiments is the result of the interplay of the self-propulsion and the rod shape of the cells.