On the theory of thermodynamic fluctuations in nonlinear systems

A method is developed for finding the correlation functions of thermodynamic fluctuations in nonlinear systems. It is shown that of the nonlinear parameters that characterize the system only those that determine irreversible processes in the system affect the correlation properties. With regard to dissipative processes , only the dissipation coefficients of the linearized system occur in the correlation functions. In particular, the correlation functions of the fluctuations of the current and voltage of a $C$, $R$ circuit are determined by the nonlinear capacitance and do not depend on the nonlinearity of the resistance.