We present a numerical study of classical particles obeying a Langevin equation moving on a solid bcc(110) surface. The particles are subject to a two dimensional periodic and symmetric potential of rectangular symmetry and to an external dc field along one of the diagonals of the structure. One observes a bias current with a component orthogonal to the dc field. The drift velocity (magnitude and direction) and diffusion of the particle depend on the surface potential and external field parameters, the temperature, and the friction coefficient. We numerically explore these dependences. Because the potential perceived by a particle as well as its friction coefficient depend on the nature of the particle, so might the angle between the particle velocity and the dc field. This scenario may thus provide a useful particle sorting technique.
We present here a study of multiplicative-noise Stochastic Partial
Differential Equations (SPDE) and their sensitivity to the
stochastic interpretation (Ito or Stratonovich). We analyze both static effects such as noise-induced phase transitions and dynamical ones such as the domain growth of the spatial structures in their way towards the steady state. We discuss in which circumstances a particular choice of stochastic interpretation induces qualitative changes.
In the present work we review recent results concerning stochastic phenomena in semiconductor lasers with optical feedback which operate in the low-frequency fluctuation (LFF) regime. Under these conditions the output intensity of the laser shows an irregular pulsated behavior in the form of sudden intensity dropouts. In the first two sections we show numerically the existence of stochastic and coherence resonance in the dropout appearance. These resonances are caused by the help of external colored noise introduced through the pumping current of the laser. In the third section we describe a recently reported new type of stochastic resonance, where a nonlinear system shows a resonance at a frequency not present neither at its internal time scales nor at any external perturbation. This phenomenon, known as ghost resonance, is reported both numerically and experimentally.