BROWNIAN RATCHETS - TRANSPORT CONTROLLED BY THERMAL NOISE

We analyze directed transport of overdamped Brownian particles in a 1D spatially periodic potential that art subjected to both zero-mean the rmal equilibrium Nyquist noise and zero-mean exponentially correlated dichotomous fluctuations. We show that particles can reverse the direc tion of average motion upon a variation of noise parameters if two fun damental symmetries, namely, the reflection symmetry of the spatial pe riodic structure, and the statistical symmetry of dichotomous fluctuat ions, are broken. There is a critical thermal noise intensity D-c, or equivalently a critical temperature T-c, at which the mean velocity of particles is zero. Below T-c and above T-c particles move in opposite directions. At fixed temperature, there is a region of noise paramete rs in which particles of different linear size are transported in oppo site directions.