RATCHETS DRIVEN BY HARMONIC AND WHITE-NOISE

The synthesis of overdamped Brownian motion in a periodic potential wh ich lacks reflection symmetry (ratchet device) with unbiased nonequili brium forces epsilon(t) yields an ordered, directed particle current. In this work, epsilon(t) is made up of a noisy oscillator dynamics (ha rmonic noise). Such noise is able to account for inertial dynamic feat ures; as a consequence we observe multiple current reversals upon vary ing the noise correlation time of the colored noise epsilon(t). The pr ecise form of the particle current is determined by use of matrix-cont inued-fraction methods. As a function of noise color the current depic ts a characteristic bell-shaped behavior. The precise numerical result s concur with both, limiting analytical exact results and with an appr oximation scheme (unified colored noise approximation).