  We study the effect of turbulence on a sedimenting layer of particles by
means of direct numerical simulations. A Lagrangian model in which particles
are considered as tracers with an additional downward settling velocity is
integrated together with an isotropic homogeneous turbulent flow. We study the
spatial distribution of particles when they are collected on a plane at
non-asymptotic times. We relate the resulting coarse-grained particle density
to the history of the stretching rate along the particle trajectory and the
projection of the density onto the accumulation plane, and analyse the
deviation from homogeneity in terms of the Reynolds number and the settling
velocity. We identify two regimes that arise during the early and during the
well-mixed stage of advection. In the former regime, more inhomogeneity in the
particle distribution is introduced for decreasing settling velocity or
increasing Reynolds number, while the tendencies are opposite in the latter
regime. A resonant-like crossover is found between these two regimes, where
inhomogeneity is maximal.
