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Thomas Heimburg

University of Copenhagen

Title: Non-equilibrium thermodynamics of adiabatic oscillatory processes

Abstract: Linear non-equilibrium thermodynamics has been used successfully to describe dissipative phenomena where different thermodynamic forces and fluxes can couple via the Onsager's phenomenological equations. The underlying idea is that the entropy can be considered as a harmonic potential depending on the extensive variables. During such processes, the entropy increases, and temperature typically is not constant. A completely different class of phenomena considers processes where entropy is conserved. Such phenomena are described by the methods of analytical mechanics, i.e., Hamilton's equation of motion. Examples are sound propagation, or oscillations of a pendulum. Similar processes are oscillations in electrical circuits. We show here that these phenomena lead can also be described by the methods of linear non-equilibrium thermodynamics. A property of such reversible oscillations is that due to entropy conservation the temperature oscillates as well. Surprisingly, temperature oscillations have also been found in chemical oscillations such as the Belousov-Zhabotinsky reaction, or the growth cycles in yeast -processes that are typically considered dissipative phenomena. We investigate the possibility that chemical oscillations are in fact entropy-conserving processes reminiscent of mechanical oscillations. We also discuss the fact that the temperature of nerves shows similar reversible changes in temperature during a nerve pulse.

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