Nonequilibrium phase transition in the sedimentation of reproducing particles

Phys Rev Lett. 2008 Sep 5;101(10):100602. doi: 10.1103/PhysRevLett.101.100602. Epub 2008 Sep 5.


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 nonequilibrium 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.