Hydrodynamic Limit for an Anharmonic Chain under Boundary Tension

TL;DR

This paper establishes the hydrodynamic limit for an anharmonic chain with boundary tension, showing convergence to hyperbolic conservation laws and deriving thermodynamic principles through stochastic analysis.

Contribution

It extends the theory of hydrodynamic limits to include boundary conditions and stochastic noise, connecting microscopic dynamics to macroscopic thermodynamics.

Findings

Convergence to weak solutions of isothermal Euler equations with boundary conditions.

Inclusion of shock regimes in the hydrodynamic limit.

Derivation of thermodynamic principles from microscopic models.

Abstract

We study the hydrodynamic limit for the isothermal dynamics of an anharmonic chain under hyperbolic space-time scaling under varying tension. The temperature is kept constant by a contact with a heat bath, realised via a stochastic momentum-preserving noise added to the dynamics. The noise is designed to be large at the microscopic level, but vanishing in the macroscopic scale. Boundary conditions are also considered: one end of the chain is kept fixed, while a time-varying tension is applied to the other end. We show that the volume stretch and momentum converge (in an appropriate sense) to a weak solution of a system of hyperbolic conservation laws (isothermal Euler equations in Lagrangian coordinates) with boundary conditions. This result includes the shock regime of the system. This is proven by adapting the theory of compensated compactness to a stochastic setting, as developed by J. Fritz in \cite{Fritz1} for thesame model without boundary conditions. Finally, changing the external tension allows us to define thermodynamic isothermal transformations between equilibrium states. We use this to deduce the first and the second principle of Thermodynamics for our model.