arXiv subjects

Songhao Yin

Publications and source records attributed to Songhao Yin.

3 recordsLinked to original sources

arXiv2026

Continuum mean-field theory of spatiotemporal pattern formation in a three-state active Potts model

We investigate the spatiotemporal dynamics of a three-state active Potts model with a cyclic transition bias. Starting from microscopic Glauber-type dynamics, we derive macroscopic continuum field equations through a spatial mean-field approximation. Linear stability and weakly nonlinear analyses reveal that increasing the coupling strength induces a Hopf bifurcation, near which the critical amplitude dynamics is described by the complex Ginzburg--Landau equation. In the spatially homogeneous limit, the system exhibits limit-cycle oscillations and ordered states, with an intermediate regime of bistability bounded by a $\mathbb{Z}_3$-symmetric heteroclinic bifurcation. In two dimensions, the system sustains stable rotating spiral waves. Using perturbation theory based on one-dimensional traveling fronts, we semianalytically predict the curvature-dependent propagation velocity of circular fronts, as well as the rotational angular velocity and pitch of spiral waves. Finally, we compare the continuum model with discrete Monte Carlo simulations to clarify the role of thermal fluctuations and evaluate the validity of the mean-field approximation.

nlin.PS↗

arXiv2025

Nonequilibrium thermodynamics of populations of weakly-coupled low-temperature-differential Stirling engines with synchronous and asynchronous transitions

This study developed the theory of nonequilibrium thermodynamics for populations of low-temperature-differential (LTD) Stirling engines weakly-coupled in a general class of networks to clarify the effects of synchronous and asynchronous transitions on the power and thermal efficiency. We first show that synchronous (asynchronous) transitions increase (decrease) the power and thermal efficiency of weakly-coupled LTD Stirling engines based on quasilinear response relations between formally defined thermodynamic fluxes and forces. After that, we construct a conceptual model satisfying the quasilinear response relations to give a physical interpretation of the changes in power and thermal efficiency due to synchronous and asynchronous transitions, and justify the use of this conceptual model. We then show that the conceptual model, rather than the quasilinear response relations, preserves the thermodynamic irreversibility of the original model and thus gives more accurate results than those using the quasilinear response relations. Finally, we compare the dynamics between the original and the conceptual models for two-engine systems and show that the conceptual models roughly preserve the dynamical characteristics leading up to the synchronous transitions, while some detailed dynamical structures are lost.

cond-mat.stat-mech↗

arXiv2023

Synchronization approach to achieving maximum power and thermal efficiency for weakly-coupled low-temperature-differential Stirling engines

Low-temperature-differential (LTD) Stirling engines are heat engines that can operate autonomously with a slight temperature difference between low-temperature heat reservoirs and are thus expected to contribute to a sustainable society. A minimal dynamical-system model with only two variables has been proposed to explain the principle of autonomous rotational motion caused by temperature differences, and the maximum efficiency of the engine was formulated [Y. Izumida, Europhys. Lett. 121, 50004 (2018); Phys. Rev. E 102, 012142 (2020)]. This paper aims to clarify the coupling effects on the dynamics, power, and thermal efficiency of a pair of weakly coupled LTD Stirling engines and formulate the maximum thermal efficiency of the coupled system in the quasilinear response regime. We show that the dependence relation between the effective frequency difference and the coupling strength is characterized by a hysteresis, which comes from different kinds of bifurcations in the process of increasing and decreasing the value of the coupling strength. Then, by generalizing thermodynamic fluxes and forces and their quasilinear relations for engines under weak coupling, we show that the coupling improves the power exerted against the load torques and the thermal efficiency. We further show that their maximum values are achieved when the engines are synchronized. Since the thermal efficiency depends on the frequency difference, the dependence of thermal efficiency on the coupling strength is also characterized by a hysteresis. Finally, the load torque that achieves the maximum thermal efficiency of the coupled system is formulated.

nlin.AO↗