Directed current of Brownian ratchet randomly circulating between two thermal sources

We consider a Brownian ratchet system which circulates fast and randomly be tween two thermal sources with different temperatures. The steady current o f the system is evaluated by the Langevin simulations. An analytical expres sion of the current for fast exchange of the noises is obtained. The featur e of temperature-dependent current is discussed. The results show that the current for randomly exchanging two white noises is larger than that of per iodically changing temperature under the same parameters. (C) 1999 Elsevier Science B.V. All rights reserved.