Mesoscopic nonequilibrium thermodynamics; irreversible processes and fluctuations

A theory of mesoscopic nonequilibrium thermodynamics is proposed, incorporating into thermodynamics of irreversible processes the treatment of fluctuations of macroscopic variables, as well as of fluctuations of their distribution functions. The theory developed leads in a simple way to the multivariate Fokker–Planck equations obeyed by these fluctuations. The formalism developed also permits to derive Fokker–Planck–Langevin equations for the distribution function of the macroscopic variables. A brief discussion is given of the properties of the random force terms in these equations.