46 research outputs found
Active nematics are intrinsically phase-separated
Two-dimensional nonequilibrium nematic steady states, as found in agitated
granular-rod monolayers or films of orientable amoeboid cells, were predicted
[Europhys. Lett. {\bf 62} (2003) 196] to have giant number fluctuations, with
standard deviation proportional to the mean. We show numerically that the
steady state of such systems is {\em macroscopically phase-separated}, yet
dominated by fluctuations, as in the Das-Barma model [PRL {\bf 85} (2000)
1602]. We suggest experimental tests of our findings in granular and
living-cell systems.Comment: 4 pages, 6 .eps figures, accepted for publication in PRL 3 Aug 0
Ordering dynamics of self-propelled particles in an inhomogeneous medium
Ordering dynamics of self-propelled particles in an inhomogeneous medium in
two-dimensions is studied. We write coarse-grained hydrodynamic equations of
motion for coarse-grained density and velocity fields in the presence of an
external random disorder field, which is quenched in time. The strength of
inhomogeneity is tuned from zero disorder (clean system) to large disorder. In
the clean system, the velocity field grows algebraically as . The density field does not show clean power-law growth; however, it
follows approximately. In the inhomogeneous system,
we find a disorder dependent growth. For both the density and the velocity,
growth slow down with increasing strength of disorder. The velocity shows a
disorder dependent power-law growth for intermediate times. At late times, there is a crossover to
logarithmic growth , where
is a disorder independent exponent. Two-point correlation functions
for the velocity shows dynamical scaling, but the density does not