It was recalled that there existed a general mobility-diffusion relationship, for drifting particles, which held true regardless of equilibrium and reflected a differential-geometric property of phase space. It was associated with the fact that a force field was devoid of entropy. Near to equilibrium, it became the usual Nernst-Townsend relationship while, at high fields, it described an energy balance. It greatly facilitated the calculation of non-equilibrium diffusion tensors.

Anatomy of the Drift-Diffusion Relationship E.Bringuier: Philosophical Magazine B, 1998, 77[4], 959-64