Entropy Decay Research Articles

On Uniform Decay of the Entropy for Reaction–Diffusion Systems

This work provides entropy decay estimates for classes of nonlinear reaction–diffusion systems modeling reversible chemical reactions under the detailed-balance condition. We obtain explicit bounds for the exponential decay of the relative logarithmic entropy, being based essentially on the application of the Log-Sobolev estimate and a convexification argument only, making it quite robust to model variations. An important feature of our analysis is the interaction of the two different dissipative mechanisms: pure diffusion, forcing the system asymptotically to the homogeneous state, and pure reaction, forcing the solution to the (possibly inhomogeneous) chemical equilibrium. Only the interaction of both mechanisms provides the convergence to the homogeneous equilibrium. Moreover, we introduce two generalizations of the main result: (i) vanishing diffusion constants in some chemical components and (ii) usage of different entropy functionals. We provide a few examples to highlight the usability of our approach and shortly discuss possible further applications and open questions.

Fractional entropy decay and the third law of thermodynamics.

We report in this paper a theoretical study on the quantum thermodynamic properties of a fractional damping system. Through the analysis, few nontrivial characteristics are revealed, which include (1) a fractional power-law decay entropy function, which provides an evidence for the validity of the third law of thermodynamics in the quantum dissipative region and (2) the varying of the entropy from a nonlinear divergent function to a semilinear decay function with a fractional exponent as the temperature approaches absolute zero.

The Kac Model Coupled to a Thermostat

In this paper we study a model of randomly colliding particles interacting with a thermal bath. Collisions between particles are modeled via the Kac master equation while the thermostat is seen as an infinite gas at thermal equilibrium at inverse temperature $\beta$. The system admits the canonical distribution at inverse temperature $\beta$ as the unique equilibrium state. We prove that any initial distribution approaches the equilibrium distribution exponentially fast both by computing the gap of the generator of the evolution, in a proper function space, as well as by proving exponential decay in relative entropy. We also show that the evolution propagates chaos and that the one-particle marginal, in the large-system limit, satisfies an effective Boltzmann-type equation.

A conservative spectral method for the Boltzmann equation with anisotropic scattering and the grazing collisions limit

We present the formulation of a conservative spectral method for the Boltzmann collision operator with anisotropic scattering cross-sections. The method is an extension of the conservative spectral method of Gamba and Tharkabhushanam [17,18], which uses the weak form of the collision operator to represent the collisional term as a weighted convolution in Fourier space. The method is tested by computing the collision operator with a suitably cut-off angular cross section and comparing the results with the solution of the Landau equation. We analytically study the convergence rate of the Fourier transformed Boltzmann collision operator in the grazing collisions limit to the Fourier transformed Landau collision operator under the assumption of some regularity and decay conditions of the solution to the Boltzmann equation. Our results show that the angular singularity which corresponds to the Rutherford scattering cross section is the critical singularity for which a grazing collision limit exists for the Boltzmann operator. Additionally, we numerically study the differences between homogeneous solutions of the Boltzmann equation with the Rutherford scattering cross section and an artificial cross section, which give convergence to solutions of the Landau equation at different asymptotic rates. We numerically show the rate of the approximation as well as the consequences for the rate of entropy decay for homogeneous solutions of the Boltzmann equation and Landau equation.

Enthalpy relaxation and annealing effect in polystyrene

The effects of thermal history on the enthalpy relaxation in polystyrene are studied by differential scanning calorimetry. The temperature dependence of the specific heat in the liquid and the glassy states, that of relaxation time, and the exponent of the Kohlrausch-Williams-Watts function are determined by measurements of the thermal response against sinusoidal temperature variation. A phenomenological model equation previously proposed to interpret the memory effect in the frozen state is applied to the enthalpy relaxation and the evolution of entropy under a given thermal history is calculated. The annealing below the glass transition temperature produces two effects on enthalpy relaxation: the decay of excess entropy with annealing time in the early stage of annealing and the increase in relaxation time due to physical aging in the later stage. The crossover of these effects is reflected in the variation of temperature of the maximum specific heat observed in the heating process after annealing and cooling.

RICCI CURVATURE OF MARKOV CHAINS ON POLISH SPACES REVISITED

Recently, Y. Ollivier defined the Ricci curvature of Markov chains on Polish spaces. In this paper, we will discuss further about the spectral gap, entropy decay, and logarithmic Sobolev inequality for the -range gradient operator. As an application, given resistance forms (i.e. symmetric Dirichlet forms with finite effective resistance) on frac- tal sets, we can construct Markov chains with positive Ricci curvature, which yields the Gaussian-then-exponential concentration of invariant probability measures for Lipschitz test functions.

Entropy decay for interacting systems via the Bochner-Bakry-Émery approach

We obtain estimates on the exponential rate of decay of the relative entropy from equilibrium for Markov processes with a non-local infinitesimal generator. We adapt some of the ideas coming from the Bakry-Emery approach to this setting. In particular, we obtain volume-independent lower bounds for the Glauber dynamics of interacting point particles and for various classes of hardcore models.

Thermodynamics of microstructure evolution: Grain growth

It is gradually getting clear that the macroscopic description of microstructure evolution requires additional thermodynamic parameters, entropy of microstructure and temperature of microstructure. It was claimed that there is “one more law of thermodynamics”: entropy of microstructure must decay in isolated thermodynamically stable systems. Such behavior is opposite to that of thermodynamic entropy. This paper aims to illustrate the concept of microstructure entropy by one example, the grain growth in polycrystals. The grain growth is treated within the framework of a theory which is a modification of Hillert theory. The modification is made in order to reach simultaneously two goals: to get a coincidence of theoretical predictions with experimentally observed results and to obtain the equations that admit analytical solutions. Due to these features, the modified theory is of independent interest. In the modified Hillert theory one observes the decay of total microstructure entropy when the system approaches the self-similar regime. The microstructure entropy per one grain grows indicating a chaotization of grain sizes. It is shown also that there exits an equation of state of grain boundary microstructure that links entropy of microstructure, energy of microstructure, average grain size and a characteristic of the inhomogeneity of the large grain distribution.

Shock dynamics in layered periodic media

Solutions of constant-coefficient nonlinear hyperbolic PDEs generically develop shocks, even if the initial data is smooth. Solutions of hyperbolic PDEs with variable coefficients can behave very differently. We investigate formation and stability of shock waves in a one-dimensional periodic layered medium by computational study of time-reversibility and entropy evolution. We find that periodic layered media tend to inhibit shock formation. For small initial conditions and large impedance variation, no shock formation is detected even after times much greater than the time of shock formation in a homogeneous medium. Furthermore, weak shocks are observed to be dynamically unstable in the sense that they do not lead to significant long-term entropy decay. We propose a characteristic condition for admissibility of shocks in heterogeneous media that generalizes the classical Lax entropy condition and accurately predicts the formation or absence of shocks in these media.

Dissipative Cyclotron Motion of a Charged Quantum-Oscillator and Third Law

In this work, low temperature thermodynamic behavior in the context of cyclotron motion of a charged-oscillator with different coupling schemes is analyzed. We find that finite dissipation substitutes the zero-coupling result of exponential decay of entropy by a power law behavior at low temperature. The power of the power law explicitly depends on the nature of the power spectrum of the heat bath. It is seen that velocity–velocity coupling is the most advantageous coupling scheme to ensure the third law of thermodynamics. The cases of confinement (ω 0≠0) and without confinement (ω 0=0) are discussed separately. It is also revealed that different thermodynamic functions are independent of magnetic field at very low temperature for ω 0≠0, but they depend on cyclotron frequency (ω c =eB/mc) for ω 0=0.

Convex entropy decay via the Bochner–Bakry–Emery approach

Nous développons une méthode, insiprée par une identité de Bochner, pour obtenir des estimées sur la decroissance exponentielle de l’entropie relative de processus de Markov avec sauts. Lorsque nous pouvons appliquer cette méthode, l’entropie relative est une fonction convexe du temps. On montre que la méthode s’applique de facon efficace à une large classe de processus de naissance et mort. On considère aussi d’autres exemples, comme les processus de zero-range et de Bernoulli–Laplace dans des cas non-homogènes. Pour ces derniers modèles les résultats connus, obtenus par la méthode de martingale, étaient limités au cas homogène.

Convergent discretizations for the Nernst–Planck–Poisson system

We propose and compare two classes of convergent finite element based approximations of the nonstationary Nernst–Planck–Poisson equations, whose constructions are motivated from energy versus entropy decay properties for the limiting system. Solutions of both schemes converge to weak solutions of the limiting problem for discretization parameters tending to zero. Our main focus is to study qualitative properties for the different approaches at finite discretization scales, like conservation of mass, non-negativity, discrete maximum principle, decay of discrete energies, and entropies to study long-time asymptotics.

The Third Law of Quantum Thermodynamics in the Presence of Anomalous Couplings

The quantum thermodynamic functions of a harmonic oscillator coupled to a heat bath through velocity-dependent coupling are obtained analytically. It is shown that both the free energy and the entropy decay fast with the temperature in relation to that of the usual coupling from. This implies that the velocity-dependent coupling helps to ensure the third law of thermodynamics.

Improved entropy decay estimates for the heat equation

Improved entropy decay estimates for the heat equation are obtained by selecting well-parametrized Gaussians. Either by mass centering or by fixing the second moments or the covariance matrix of the solution, relative entropy toward these Gaussians is shown to decay with better constants than classical estimates.

Boundary effects on entropy and two-site entanglement of the spin-1 valence-bond solid

We investigate the von Neumann entropy of a block of subsystem for the valence-bond solid (VBS) state with general open boundary conditions. We show that the effect of the boundary on the von Neumann entropy decays exponentially fast in the distance between the subsystem considered and the boundary sites. Further, we show that as the size of the subsystem increases, its von Neumann entropy exponentially approaches the summation of the von Neumann entropies of the two ends, the exponent being related to the size. In contrast to critical systems, where boundary effects to the von Neumann entropy decay slowly, the boundary effects in a VBS, a non-critical system, decay very quickly. We also study the entanglement between two spins. Curiously, while the boundary operators decrease the von Neumann entropy of L spins, they increase the entanglement between two spins.

ENTROPY STABLE APPROXIMATIONS OF NAVIER–STOKES EQUATIONS WITH NO ARTIFICIAL NUMERICAL VISCOSITY

We construct a new family of entropy stable difference schemes which retain the precise entropy decay of the Navier–Stokes equations, [Formula: see text] To this end we employ the entropy conservative differences of [24] to discretize Euler convective fluxes, and centered differences to discretize the dissipative fluxes of viscosity and heat conduction. The resulting difference schemes contain no artificial numerical viscosity in the sense that their entropy dissipation is dictated solely by viscous and heat fluxes. Numerical experiments provide a remarkable evidence for the different roles of viscosity and heat conduction in forming sharp monotone profiles in the immediate neighborhoods of shocks and contacts.

Entropy decay of discretized fokker-planck equations I—Temporal semidiscretization

In this paper, we study the large time behavior of a fully implicit semidiscretization (in time) of parabolic Fokker-Planck type equations. Using logarithmic Sobolev inequalities exponential decay of the relative entropy (w.r.t. the steady state) is proved which yields convergence of the discrete scheme towards the unique steady state. The exponential decay rate recovers as At J 0 the decay rate of the original Fokker-Planck type equations.

Exponential decay of entropy in the random transposition and Bernoulli-Laplace models

We give bounds on the exponential decay rate of entropy in the random transposition model and the Bernoulli--Laplace model which are independent of the number of sites and the number of particles. This is then used to give a bound on the time to stationarity in the total variation norm.

Asymptotic behavior for doubly degenerate parabolic equations

We use mass transportation inequalities to study the asymptotic behavior for a class of doubly degenerate parabolic equations of the form (1) ∂ρ ∂t = div ρ∇c ∗ ∇ F′(ρ)+V in (0,∞)×Ω, andρ(t=0)=ρ 0 in {0}×Ω, where Ω is R n , or a bounded domain of R n in which case ρ∇c ∗[∇(F′(ρ)+V)]·ν=0 on (0,∞)×∂Ω. We investigate the case where the potential V is uniformly c-convex , and the degenerate case where V=0. In both cases, we establish an exponential decay in relative entropy and in the c-Wasserstein distance of solutions – or self-similar solutions – of (1) to equilibrium, and we give the explicit rates of convergence. In particular, we generalize to all p>1, the HWI inequalities obtained by Otto and Villani (J. Funct. Anal. 173 (2) (2000) 361–400) when p=2. This class of PDEs includes the Fokker–Planck, the porous medium, fast diffusion and the parabolic p-Laplacian equations. To cite this article: M. Agueh, C. R. Acad. Sci. Paris, Ser. I 337 (2003).

Exclusion Processes with Degenerate Rates: Convergence to Equilibrium and Tagged Particle

Stochastic lattice gases with degenerate rates, namely conservative particle systems where the exchange rates vanish for some configurations, have been introduced as simplified models for glassy dynamics. We introduce two particular models and consider them in a finite volume of size $\ell$ in contact with particle reservoirs at the boundary. We prove that, as for non--degenerate rates, the inverse of the spectral gap and the logarithmic Sobolev constant grow as $\ell^2$. It is also shown how one can obtain, via a scaling limit from the logarithmic Sobolev inequality, the exponential decay of a macroscopic entropy associated to a degenerate parabolic differential equation (porous media equation). We analyze finally the tagged particle displacement for the stationary process in infinite volume. In dimension larger than two we prove that, in the diffusive scaling limit, it converges to a Brownian motion with non--degenerate diffusion coefficient.