Microscopic Crowd Control published in Nature Commun.

Disorder-mediated crowd control in an active matter system

Disorder-mediated crowd control in an active matter system
Erçağ Pinçe, Sabareesh K. P. Velu, Agnese Callegari, Parviz Elahi, Sylvain Gigan, Giovanni Volpe & Giorgio Volpe
Nature Communications 7, 10907 (2016)
DOI: 10.1038/ncomms10907

Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-from- equilibrium interactions. The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. Here, we demonstrate that the presence of spatial disorder can alter the long-term dynamics in a colloidal active matter system, making it switch between gathering and dispersal of individuals. At equilibrium, colloidal particles always gather at the bottom of any attractive potential; however, under non-equilibrium driving forces in a bacterial bath, the colloids disperse if disorder is added to the potential. The depth of the local roughness in the environment regulates the transition between gathering and dispersal of individuals in the active matter system, thus inspiring novel routes for controlling emerging behaviours far from equilibrium.

 

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The Small-mass Limit for Langevin Dynamics published in J. Stat. Phys.

The small-mass limit for Langevin dynamics with unbounded coefficients and positive friction

The small-mass limit for Langevin dynamics with unbounded coefficients and positive friction
David P. Herzog, Scott Hottovy & Giovanni Volpe
Journal of Statistical Physics 163(3), 659—673 (2016)
DOI: 10.1007/s10955-016-1498-8
arXiv: 1510.04187

A class of Langevin stochastic differential equations is shown to converge in the small-mass limit under very weak assumptions on the coefficients defining the equation. The convergence result is applied to three physically realizable examples where the coefficients defining the Langevin equation for these examples grow unboundedly either at a boundary, such as a wall, and/or at the point at infinity. This unboundedness violates the assumptions of previous limit theorems in the literature. The main result of this paper proves convergence for such examples.