Onsager coefficients of a finite-time Carnot cycle.

We study a finite-time Carnot cycle of a weakly interacting gas which we can regard as a nearly ideal gas in the limit of T(h)-T(c) --> 0 where T(h) and T(c) are the temperatures of the hot and cold heat reservoirs, respectively. In this limit, we can assume that the cycle is working in the linear-response regime and can calculate the Onsager coefficients of this cycle analytically using the elementary molecular kinetic theory. We reveal that these Onsager coefficients satisfy the so-called tight-coupling condition and this fact explains why the efficiency at the maximal power eta(max) of this cycle can attain the Curzon-Ahlborn efficiency from the viewpoint of the linear-response theory.