Statistical and Biological Physics
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The spontaneous formation of vortices is a hallmark of collective cellular activity. We have studied the onset and persistence of coherent angular motion as a function of the number of cells confined in circular micropatterns. We find that the persistence of coherent angular motion increases with the number of cells but exhibits a pronounced discontinuity accompanied by a geometric rearrangement of cells to a configuration containing a central cell. Computer simulations based on a generalized Potts model reproduce the emergence of vortex states and show in agreement with experiment that their stability depends on the interplay of the spatial arrangement and internal polarization of neighboring cells. Hence, the distinct migrational states in finite size ensembles reveal significant insight into the local interaction rules guiding collective migration. more

Bosons are quantum particles that like to be together. When a dilute gas of bosons is cooled to a temperature close to absolute zero, a macroscopic fraction of the bosons will occupy the energetic ground state of the system; the bosons form a Bose-Einstein condensate. Only recently has it been proposed that bosons may also group into multiple condensates when they are driven by a time-periodic force and dissipate into the environment. In our manuscript, we show that the condensation of bosons in such a nonequilibrium system corresponds to the selection of strategies in evolutionary game theory. We applied mathematical concepts of this theory to explain why and under which conditions bosons form multiple condensates. We found that the condensation dynamics follows a simple physical guiding principle: the vanishing of relative entropy production guides the selection of condensates. more