Seminar by Thomas Heimburg

Linear nonequilibrium thermodynamics of reversible periodic processes and chemical oscillations

Thomas Heimburg, The Niels Bohr Institute

This talk presents some thoughts about the thermodynamic nature of adiabatic processes, and discusses the possibility that such considerations present a way to understand chemical and biological oscillations, but also nerve pulses. I present a theory which shows that adiabatic propagation phenomena and oscillations can be understood by using nonequilibrium thermodynamics. In the simplest approximation, nonequilibrium thermodynamics is described by Onsager’s phenomenological equations that successfully describe irreversible thermodynamic processes. They assume a symmetric coupling matrix between thermodynamic fluxes and forces. It is easily shown that the antisymmetric part of a coupling matrix does not contribute to dissipation.

Here, we focus on the antisymmetric contributions which describe isentropic oscillations with well-defined equations of motion. The formalism contains variables that are equivalent to momenta and coefficients that are analogous to inertial mass. We apply this formalism to simple problems with known answers such as an oscillating piston containing an ideal gas, and oscillations in an LC-circuit. One can extend this formalism to other pairs of variables, including chemical systems with oscillations. In isentropic thermodynamic systems, all extensive and intensive variables including temperature can display oscillations reminiscent of adiabatic waves.  We discuss the possibility of electromechanical oscillations in membranes and the nervous impulse.