Berlin 2018 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 59: Microswimmers II (joint session DY/CPP/BP)

DY 59.6: Vortrag

Donnerstag, 15. März 2018, 11:30–11:45, BH-N 243

Crowd localisation and cohesion of micro-swimmers with perception-dependent motility — •Francois Lavergne, Hugo Wendehenne, and Clemens Bechinger — Department of Physics, University of Konstanz, 78464 Konstanz, Germany

The origin of crowd formation and cohesion in natural contexts remains an important question of collective dynamics, especially in the absence of taxis, communication, confinement, or attractive forces between the individuals. In this work, we show that the mere variation of the motility depending on the perception of other individuals is enough to induce such behaviour. We introduce a long-range indicator of crowd perception that only assumes the ability of an individual to count others within its vision cone. When this quantity exceeds a certain threshold for a given individual, its velocity is increased. This simple rule is applied in an experiment involving photo-responsive colloidal micro-swimmers, whose velocities can be individually varied by live-tuning the intensity of laser spots directed onto them. We observe that initially very dilute ensembles of these micro-swimmers localise into isolated groups, with virtually empty surroundings in unbound space, in sharp contrast with the long-time diffusive behaviour expected in the case of a constant motility. These groups remain cohesive, despite the activity of individuals within them and the absence of alignment, due to a kinetic stabilisation mechanism stemming from the modulation of the motility upon the non-reciprocal perception.