Inelastic particles in compartments.

A simple experiment produces interesting results: put sand in a box which
is divided in two compartments by a short sect. Then shake the box,
obtaining a gas of grains of sand: the grains can eventually jump over the
sect, leaving a compartment and entering the other. You will observe that
under a certain treshold in the strenght of the shaking (frequency or
amplitude) the most of the grains will stay all together in the same
compartment. We will describe a very simplified microscopic model
consisting of two inelastic particle in a double well potential with
noise, reproducing this scenario. Reducing the intensity of the noise the
most stable configuration change from the one with both the wells occupied
by a particle to the one with both the particles in the same well. This
can be described in terms of a renormalized Arrhenius law with two
typical escape times.