Kinetic condition and the Gibbs function

We study the Cauchy problem for a 3 x 3-system of conservation laws describing the phase transition: u(t) - v(x) = 0, v(t) - sigma(u)(x) = 0, (e + 1/2v(2))t - (sigma v)(x) = 0. A phase boundary is said to be admissible if it satisfies the Abeyaratne-Knowles kinetic condition. We give a physical account of the kinetic condition by means of the Gibbs function. We also obtain a useful description of the entropy function using the Gibbs function.