Anomalous velocity distributions in active Brownian suspensions

Abstract

Large-scale simulations and analytical theory have been combined to obtain the nonequilibrium velocity distribution, f(v), of randomly accelerated particles in suspension. The simulations are based on an event-driven algorithm, generalized to include friction. They reveal strongly anomalous but largely universal distributions, which are independent of volume fraction and collision processes, which suggests a one-particle model should capture all the essential features. We have formulated this one-particle model and solved it analytically in the limit of strong damping, where we find that f(v) decays as 1/v for multiple decades, eventually crossing over to a Gaussian decay for the largest velocities. Many particle simulations and numerical solution of the one-particle model agree for all values of the damping.

Collective rotations of active particles interacting with obstacles

“…Their packing fraction is denoted by φ o = M πR 2 o /L 2 . Equations ( 1) and (2) were simulated with an event driven algorithm, described in [28], in a peridoc box and with packing fraction φ p . The active acceleration, a dr e, is implemented by kicks at regular time intervals τ dr = 0.1α, which change the particle's velocity by an amount a dr τ dr along its momentary orientation.…”

A classical long-time tail in a driven granular fluid

“…This could possibly help to settle the question about the nature of the long-time tails in the sheared granular fluid. Another step away from idealizations would be to relax the assumption of an infinite driving frequency and go to a more realistic finite frequency [38]. I hope that the explicit expressions for the amplitudes will aid experimenters to judge whether the long-time tails are observable in their set-ups.…”

Anomalous velocity fluctuation in one-dimensional defect turbulence

“…However, velocity fluctuations in nonequilibrium systems, where energy and/or momentum exchange, exhibit abundant anomalous behaviors being subject to non-Gaussian statistics with large deviations. Many-body interactions among collective inelastic gases, where momentum decreases after collision, display Levy type velocity distributions [2], In general, topological defects in phase-ordering systems have velocity distributions with fat tails [3]. Lagrangian particles in porous media show intermittent motions with long-time rests, for which the velocity distribution is also characterized by large deviations [4].…”