Randomly rattled ratchets

Summary Ratchets are anisotropic periodic potentials. Particles subject to ratchet forces and simultaneously to thermal and nonthermal fluctuations can rectify the nonequilibrium noise, thereby extracting energy from incoherent and otherwise symmetric random forces. In this paper I describe some simple models which illustrate this phenomenon, highlighting two particular mechanisms leading to fluctuation-induced current. Paper presented at the International Workshop ?Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena?, Elba, 5–10 June 1994. Address after July 1, 1994: Center for Nonlinear Studies, MS-B258, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.