Cooperative rectification in confined Brownian ratchets
  We analyze the rectified motion of a Brownian particle in a confined environment. We show the emergence of strong cooperativity between the inherent rectification of the ratchet mechanism and the entropic bias of the fluctuations caused by spatial confinement. Net particle transport may develop even in situations where separately the ratchet and the geometric restrictions do not give rise to particle motion. The combined rectification effects can lead to bidirectional transport depending on particle size, resulting in a new route for segregation. The reported mechanism can be used to control transport in mesostructures and nanodevices in which particles move in a reduced space. 
Paolo Malgaretti, Ignacio Pagonabarraga and J. Miguel Rubi
cond-mat.mes-hall cond-mat.stat-mech