Inhomogeneous Systems and their Rectification Properties

We explore the possibility of obtaining unidirectional current in a symmetric (periodic) potential system without the application of any obvious (apparent) externally applied bias. There are many physical models proposed to accomplish this nonequilibrium effect. In the present work we consider inhomogeneous systems so that the friction coefficient and/or temperature could vary in space. We find out a model with minimal conditions that the inhomogeneous system assisted by fluctuating forces must satisfy, in order to obtain unidirectional current. In the process we discuss about thermal and frictional ratchets that are of current interest. We argue that different models of frictional ratchets work under the same basic principle of alteration of relative stability of otherwise locally stable states in the presence of temperature inhomogeneity. We also discuss in detail the nature of currents in rocked frictional ratchets. In particular we analyse a novel phenomenon of multiple current reversals and the efficiency of the energy transduction in these systems.