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BP: Fachverband Biologische Physik

BP 11: Posters: Statistical Physics in Biological Systems (joint with DY)

BP 11.5: Poster

Montag, 11. März 2013, 17:30–19:30, Poster B2

Collective behavior and structure formation of hydrodynamically interacting active particles — •Marc Hennes, Katrin Wolff, and Holger Stark — Institut für Theoretische Physik TU Berlin

Lattice Boltzmann simulations of active run-and-tumble particles (RTPs) subject to an external trapping force have shown the emergence of a self-assembled pump in the presence of hydrodynamic interactions[1]. Here, we extend these results to active Brownian particles (ABPs), simulated by means of Brownian Dynamics simulation including hydrodynamic interactions. ABPs, in contrast to RTPs, do not tumble but reorient smoothly due to thermal noise, external torques, and vorticity fields in the fluid. Here, we clarify that the pump is a dynamic cluster of ABPs which only forms above a threshold value for the swimming speed. We assign an effective dipole moment to the pump and show that in this non-equilibrium situation the orientations of the particles are Boltzmann-distributed around the pump direction. We also consider bottom-heavy particles in an external gravitational field. Without hydrodynamic interactions and at sufficiently large swimming speeds, these particles accumulate at the top of the simulation box. However, when they interact hydrodynamically, we find this steady state to be unstable and observe the emergence of spatially separated, dynamical toroidal structures, reminiscent of classical bioconvection.

[1] M.E.Cates et al., Phys.Rev.Lett. 104, 258101 (2010)