Fluctuations and Onsager relations in fluids outside equilibrium

We review some aspects of fluctuations and Onsager relations in fluid systems away from equilibrium. In particular, we show that the mobility tensor for a particle moving through an arbitrary homogeneous stationary flow, satisfies generalized Onsager symmetry relations in which the time reversal transformation should also be applied to the external forces which keep system in the stationary state (Author)