Thermodynamic conditions ensure the stability of third-order extended heat conduction

Fuente: arXiv
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Autores principales: Ván, Peter, Somogyfoki, Réka
Formato: Preprint
Publicado: 2026
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author Ván, Peter
Somogyfoki, Réka
author_facet Ván, Peter
Somogyfoki, Réka
contents In a recent work, Somogyfoki et al. (J. Non-Equilib. Thermodyn. 50, 59-76, 2025) analysed the linear stability of homogeneous equilibrium in third-order non-Fourier heat conduction within the framework of non-equilibrium thermodynamics with internal variables. They identified a stability condition, their equation (49), which could not be derived from the standard thermodynamic inequalities for the 2X2 conductivity blocks, and concluded that the Second Law does not guarantee stability in the most general case. Here we show that this conclusion was due to an overly conservative proof strategy: the standard thermodynamic conditions (concave entropy and non-negative entropy production, as expressed by the $2\times2$ block positive-definiteness inequalities (19)-(20) of the original paper) do suffice for linear stability. The key observation is that all coefficients of the dispersion polynomial remain positive for all physical wave numbers because their structure prevents positive real roots. This result confirms that thermodynamics, understood as a stability theory, ensures fundamental dynamic stability in all thermodynamically consistent third-order extended heat conduction theories. A comparison with the rate-equation approach of Giorgi, Morro and Zullo (Meccanica 59, 1757-1776, 2024) is also presented.
format Preprint
id arxiv_https___arxiv_org_abs_2604_13110
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Thermodynamic conditions ensure the stability of third-order extended heat conduction
Ván, Peter
Somogyfoki, Réka
Statistical Mechanics
Other Condensed Matter
In a recent work, Somogyfoki et al. (J. Non-Equilib. Thermodyn. 50, 59-76, 2025) analysed the linear stability of homogeneous equilibrium in third-order non-Fourier heat conduction within the framework of non-equilibrium thermodynamics with internal variables. They identified a stability condition, their equation (49), which could not be derived from the standard thermodynamic inequalities for the 2X2 conductivity blocks, and concluded that the Second Law does not guarantee stability in the most general case. Here we show that this conclusion was due to an overly conservative proof strategy: the standard thermodynamic conditions (concave entropy and non-negative entropy production, as expressed by the $2\times2$ block positive-definiteness inequalities (19)-(20) of the original paper) do suffice for linear stability. The key observation is that all coefficients of the dispersion polynomial remain positive for all physical wave numbers because their structure prevents positive real roots. This result confirms that thermodynamics, understood as a stability theory, ensures fundamental dynamic stability in all thermodynamically consistent third-order extended heat conduction theories. A comparison with the rate-equation approach of Giorgi, Morro and Zullo (Meccanica 59, 1757-1776, 2024) is also presented.
title Thermodynamic conditions ensure the stability of third-order extended heat conduction
topic Statistical Mechanics
Other Condensed Matter
url https://arxiv.org/abs/2604.13110