Inhomogeneous friction leading to current in periodic system

We study the diffusion process of a Brownian particle moving in a one-dimen sional ratchet with space-dependent friction that is subjected to an extern al source. The equation of motion for a particle involves a multiplicative fluctuation, a nonlinear friction and an external driving force or a Gaussi an white noise. The average position of the particle is simulated numerical ly in terms of the Langevin Monte Carlo method and discussed by means of th e adiabatic approximation and the effective potential. The influence of coo rdinate-dependent friction on the average position and the direction of cur rent of the particle is investigated. The results show that a net drift can be produced in the presence of both a coordinate-dependent friction and an external fluctuation, even when the ratchet potential and the temporal for ce are completely symmetrical. (C) 1999 Elsevier Science B.V. All rights re served.