  We studied the transport process of overdamped Brownian particles, in a chain
of asymmetric cavities, interacting through a hard-core potential. When a force
is applied in opposite directions a difference in the drift velocity of the
particles inside the cavity can be observed. Previous works on similar systems
deal with the low concentration regime, in which the interaction is irrelevant.
In this case it was found that large particles show a stronger asymmetry in the
drift velocity when a small force is applied, allowing for the separation of
different size particles (Reguera et al., Phys. Rev. Lett 108, 020604, 2012).
We found that when the interaction between particles is considered, the
behavior of the system is substantially different. For example, as
concentration is increased, the small particles are the ones that show a
stronger asymmetry. For the case where all the particles in the system are of
the same size we took advantage of the particle-vacancy analogy to predict that
the left and right currents are almost equal in a region around the
concentration 0.5 despite the asymmetry of the cavity.
