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Though stochastic resonance was usually shown to occur in bistable systems whereas ratchet effect necessarily occurs in periodic potential systems, it was conjectured [Nature 369, 181 (1994), ibid 369,271 (1994)] that these two non-equilibrium phenomena have some commonalities. Since for proper comparison both the phenomena need to occur in the same system, in the present work, we show first that stochastic resonance too occurs in periodic potential system, and then, in addition show that the ratchet effect also occurs in the same parameter space of the system where stochastic resonance occurs. In order to obtain ratchet effect we consider periodic non-uniformity of the friction coefficient of the medium to provide the necessary asymmetry in the symmetrically driven sinusoidal potential system. However, the temperature at which stochastic resonance occurs is different from the temperature at which ratchet current peaks. [ABSTRACT FROM AUTHOR]

Superconducting Nb thin films were grown on different arrays of triangle-shape metallic islands. The vortex lattice dynamics could be strongly modified by these asymmetric vortex traps. These asymmetric pinning potentials lead to a rectification effect on the vortex motion: Injecting an ac supercurrent on the sample yields a net dc vortex flow. This vortex ratchet effect is adiabatic and reversible: The effect is frequency independent and the polarity of the dc voltage output could be tuned by the applied magnetic fields and the input ac currents. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]