On the energetics of a nonlinear system rectifying thermal fluctuations

We discuss an approach to the energetics of nonlinear systems based on the local, detailed-balanced scheme and consider a simple model consisting of a linear and a nonlinear resistor (diode) in contact with two heat baths kept at different temperatures. We calculate the power, the absorbed heat and the efficiency of a system as a heat engine. We show that this efficiency is always smaller than the Carnot value, thus indicating the intrinsically irreversible mode of operation.