  We apply a hybrid Molecular Dynamics and mesoscopic simulation technique to
study the steady-state sedimentation of hard sphere particles for Peclet
numbers (Pe) ranging from 0.08 to 12. Hydrodynamic back-flow causes a reduction
of the average sedimentation velocity relative to the Stokes velocity. We find
that this effect is independent of Pe number. Velocity fluctuations show the
expected effects of thermal fluctuations at short correlation times. At longer
times, non-equilibrium hydrodynamic fluctuations are visible, and their
character appears to be independent of the thermal fluctuations. The
hydrodynamic fluctuations dominate the diffusive behavior even for modest Pe
number, while conversely the short-time fluctuations are dominated by thermal
effects for a surprisingly large Pe numbers. Inspired by recent experiments, we
also study finite sedimentation in a horizontal planar slit. In our simulations
distinct lateral patterns emerge, in agreement with observations in the
experiments.
