Nonequilibrium phase transition in the sedimentation of reproducing particles

TL;DR

This paper investigates the non-equilibrium phase transition in sedimenting suspensions of reproducing active particles, combining numerical and analytical methods to understand steady states, fluctuations, and sedimentation kinetics.

Contribution

It introduces a combined numerical and analytical study of phase transitions in active, reproducing particle suspensions under gravity, highlighting the role of fluctuations.

Findings

Identifies a phase transition between sedimentation and uniform regimes.

Analyzes the impact of density fluctuations on the transition.

Describes the early-time sedimentation kinetics.

Abstract

We study numerically and analytically the dynamics of a sedimenting suspension of active, reproducing particles, such as growing bacteria in a gravitational field. In steady state we find a non-equilibrium phase transition between a `sedimentation' regime, analogous to the sedimentation equilibrium of passive colloids, and a `uniform' regime, in which the particle density is constant in all but the top and bottom of the sample. We discuss the importance of fluctuations in particle density in locating the phase transition point, and report the kinetics of sedimentation at early times.