Speedups in nonequilibrium thermal relaxation: Mpemba and related effects

The Mpemba and Kovacs effects are two notable memory phenomena observed in nonequilibrium relaxation processes. In a recent study [Phys. Rev. E 109, 044149 (2024)2470-004510.1103/PhysRevE.109.044149], these effects were analyzed within the framework of the time-delayed Newton's law of cooling under the assumption of instantaneous temperature quenches. Here, the analysis is extended to incorporate finite-rate quenches, characterized by a nonzero quench duration σ. The results indicate that a genuine Mpemba effect is absent under finite-rate quenches if both samples experience the same thermal environment during the quenching process. However, if σ remains sufficiently small, the deviations in the thermal environment stay within an acceptable range, allowing the Mpemba effect to persist with a slightly enhanced magnitude. In contrast, the Kovacs effect is significantly amplified, with the transient hump in the temperature evolution becoming more pronounced as both the waiting time and σ increase. These findings underscore the importance of incorporating finite-time effects in nonequilibrium thermal relaxation models and offer a more realistic perspective for experimental studies.

We uncover a finite-time dynamical phase transition in the thermal relaxation of a mean-field magnetic model. The phase transition manifests itself as a cusp singularity in the probability distribution of the magnetization that forms at a critical time. The transition is due to a sudden switch in the dynamics, characterized by a dynamical order parameter. We derive a dynamical Landau theory for the transition that applies to a range of systems with scalar, parity-invariant order parameters. Close to criticalilty, our theory reveals an exact mapping between the dynamical and equilibrium phase transitions of the magnetic model, and implies critical exponents of mean-field type. We argue that interactions between nearby saddle points, neglected at the mean-field level, may lead to critical, spatiotemporal fluctuations of the order parameter, and thus give rise to novel, dynamical critical phenomena.

This paper reports some preliminary progress in developing a gaskinetic Computational Fluid Dynamic scheme, based on the Bhatnagar-Gross-Krook(BGK) model, to simulate a planar nitrogen shock wave with thermochemical nonequilibrium effects. The scheme is applicable for gas flows with thermal nonequilibrium effects, i.e., translational, rotational and vibrational energy relaxations, and with dissociation and recombination chemical reactions. We determine the post-shock boundary conditions with a consideration of detailed equilibrium satisfying general Rankine-Hugoniot relations. Different from those past studies which are based on the Boltzmann-like equation and split the collision term into elastic and chemical collision terms, here we consider the chemical reactions by treating them as source terms. This treatment renders us a much simpler scheme than gaskinetic schemes relying on detailed collisions. The merits of this scheme include a relatively faster computation speed than particle simulation methods and gaskinetic schemes based on the full Boltzmann equation. The gaskinetic BGK simulation results are validated with those obtained with the direct simulation Monte Carlo (DSMC) method.

Transient two-dimensional infrared (2DIR) spectroscopy is applied to the photodissociation of Mn2(CO)10 to 2 Mn(CO)5 in cyclohexane solution. By varying both the time delay between the 400 nm phototrigger and the 2DIR probe as well as the waiting time in the 2DIR pulse sequence, we directly determine the orientational relaxation of the vibrationally hot photoproduct. The orientational relaxation slows as the photoproduct cools, providing a measure of the transient temperature decay time of 70 +/- 16 ps. We compare the experimental results with molecular dynamics simulations and find near quantitative agreement for equilibrium orientational diffusion time constants but only qualitative agreement for nonequilibrium thermal relaxation. The simulation also shows that the experiment probes an unusual regime of thermal excitation, where the solute is heated while the solvent remains essentially at room temperature.

Thermal conductivity enhancement of defective graphene nanoribbons

Ultrafast thermalisation dynamics in an Au film excited by a polarization-shaped femtosecond laser double-pulse

Data-driven stochastic particle scheme for collisional plasma simulations

Effect of water/carbon interaction strength on interfacial thermal resistance and the surrounding molecular nanolayer of CNT and graphene flake

Superconducting resonators have to date been used for photon detection in a non-equilibrium manner. In this paper, we demonstrate that such devices can also be used in a thermal quasi-equilibrium manner to detect x-ray photons. We have used a resonator to measure the temperature rise induced by an x-ray photon absorbed in normal metal and superconducting absorbers on continuous and perforated silicon nitride membranes. We observed two distinct pulses with vastly different decay times. We attribute the shorter pulses to non-equilibrium quasiparticle relaxation and the longer pulses to a thermal relaxation process. In addition, we have measured the temperature dependence of the x-ray induced temperature rise and decay times. Finally, we have measured the resonator sensitivity and energy resolution.

Study of the thermal relaxation effects in polymers by a conjugated use of thermally stimulated depolarization and polarization current methods

This study attempts to combine the principles of nonequilibrium thermodynamics and photoacoustic Fourier transform infrared (PAFT-IR) spectroscopic detection as utilized in the analysis of nonequilibrium processes in matter. Such processes as diffusion and glass transition temperatures in polymers are analyzed. It is shown that the nonequilibrium mass balance equation, which governs diffusion processes, and the nonequilibrium internal energy balance responsible for the photoacoustic detection can be correlated. As a result, the relationship between the concentration of diffusant molecules in time and the photoacoustic intensity as a function of concentration can be established. Analysis of a nonequilibrium nature of the thermal processes near glass transmission temperatures shows that thermal nonequilibrium relaxations can be described in terms of rate constants for which the weight fractions with various energies can be correlated to the temperature fluctuations in a photoacoustic experiment. In this case, the internal energy balance equation can be represented by a regular heat expression.

The direct simulation Monte Carlo (DSMC) method is used to model transient thermal and chemical relaxation behind reflected shock waves in oxygen–argon and air mixtures under conditions reproducing earlier shock-tube experiments. Two vibration–translation and three popular DSMC chemical reaction models are tested. Where possible, model parameters are adjusted to match equilibrium and nonequilibrium relaxation times and reaction rates. A number of factors that impact relaxation and reaction model validation are examined, including gas–surface interactions, time-varying freestream properties, location of the observation point, electronic excitation, and nonequilibrium populations of vibrational states probed in the experiments. Comparison of numerical and experimental results has demonstrated that the reflected shock configuration is a platform very convenient for validation and analysis of high-temperature chemical reaction models. Computations have shown that the Bias reaction model is superior to the total collision energy and quantum kinetic models, providing reasonable agreement with measured absorbance time histories and vibrational temperatures in oxygen–argon mixtures and pure . There are some modeling-versus-experiment differences observed for air that may warrant additional studies focused on Zeldovich reaction rates and oxygen–nitrogen vibrational excitation and nonequilibrium dissociation rate.

Using reactive force field (ReaxFF) and molecular dynamics simulation, we investigate the combustion process of hydrogen-oxygen systems in initial thermal nonequilibrium states with different translational and rovibrational temperatures for oxygen. The system studied in this work contains 300 oxygen molecules and 700 hydrogen molecules with a density of 7 times the air density. For this system, the characteristic relaxation times of oxygen and hydrogen vibrational energies are 0.173 and 0.249 ns, respectively. 0.6% of hydrogen undergoes a chemical reaction with oxygen during the thermal nonequilibrium relaxation stage. For the distribution of translational energy and vibrational energy of oxygen in the thermal nonequilibrium state, the maximum mean error of the statistical distribution in the simulation and the Boltzmann distribution at temperature calculated from the average kinetic energy of molecules is about 2.25 × 10-5. At the same time, it was observed in the simulation that many-body interactions play a certain role in the combustion process. Furthermore, we compare the ignition time and temperature rise behavior of different combustion mechanisms and molecular dynamics simulations starting from the thermal equilibrium state. These results will provide meaningful references for the construction of thermal nonequilibrium combustion chemical reaction mechanisms.

Relaxation and Dynamics in Magnetic Systems.- Experiments on Spin Glass Dynamics.- Attempt at a Comprehensive Description of the Slow Spin Glass Dynamics.- Spin-Glass Dynamics in the Two-Dimensional Ising System Rb2Cu1?xCoxF4.- Cluster Model for Non-Equilibrium Relaxation in Spin Glasses.- Some Aspects of the Dynamics of Random Anisotropy Systems.- Static and Dynamic Properties of Fine Magnetic Particles.- Kinetic Aspects of Magnetic Relaxation in Amorphous Ferromagnetic Alloys.- Dynamic Crossover in Dipolar Ferromagnets.- Magnetic Excitations in the Disordered System Mg1?xCoxCl2.- Dynamic Properties of Critical and Paramagnetic Spin Fluctuations in Simple Magnets: Confrontation of Experimental and Theoretical Findings.- Relaxation and Dynamics in Superconductors.- Thermally Activated Flux Motion in High-Tc-Superconductors.- Flux Motion in Bi2Sr2Ca1Cu2O8+x Single Crystals.- Relaxation of the Vortex Lattice in Type II Superconductors.- Investigation of the Relaxation Behaviour in High Tc Superconductors.- Relaxation Experiments in Short Coherence Length Superconductors.- Quasi-Equilibrium Dynamics and Non-Debye Relaxation in High Tc Granular Superconductors.- Relaxation and Dynamics in Granular Superconductors and Superconducting Arrays.- Numerical Simulation of the Magnetic Relaxation in Superconducting Systems.- Noise Measurements in dc-SQUIDs Based on Nb-Nbox-PbAuIn Josephson Junctions.- The Resistive Transition of Inhomogeneous Superconductors: Effects of Mild Granularity, Dimensionality, Gaussian Fluctuations and Critical Behaviour.- Relaxation and Dynamics in Molecular and Biological Systems.- Comparison of Spin Glass Relaxation and Energy Transport at Dynamic Percolation.- Stretched-Exponential Relaxation of Electric Birefringence in Critical Systems and Colloidal Solutions.- The Glass Transition of Hard Spherical Colloids.- Structural Relaxation and Dynamics of Water in Disordered MX-RH2O Systems.- Glassy Dynamics and Relaxation in Proteins.- Models for Relaxation in Glasses and Protein Channels.- Information Classification Acquired by Organization of Neuronic Connections.- Long-Term Behavior of Neural Networks.- Information Storage and Relaxation in Biological Systems.- Relaxation and Dynamics in Other Complex Systems.- Dynamical Properties of Hierarchical Polymeric Cluster Solutions.- Critical Scaling in Glassy Glasses.- Flow in Granular Materials: Self-Organized Non-Critical Behavior.- Non-Exponential Thermal Relaxation and Low-Energy Excitations in CDW Compounds.- Non-Debye-Like Dielectric Relaxation in Ionically and Electronically Conducting Glasses.- Anelastic Relaxation due to Interacting Point Defects.- Complexity and Chaos in Thermal Convection.- About the Fractal Relationship Between Kohlrausch-Williams-Watts Decay, Cole-Cole and Davidson-Cole Relaxations.- Polarization Decay in Glass-Forming and Ferroelectric Perovskites.- General Theoretical Aspects of Relaxation in Complex Systems.- Localization as a Mechanism for the Transition to Anomalous Relaxation.- Complexity of Hierarchical Relaxation.- Probability Density of Random Walks on Random Fractals: Stretched Gaussians and Multifractal Features.- The Symmetric and Fully Distributed Solution to a Generalized Dining Philosophers Problem: An Analogue of the Coupling Theory of Relaxations in Complex Correlated Systems.- Onsager-Machlup Functions for Ising Networks.- Simple Models for Complex Relaxation.- to the Lattice Boltzmann Equation for Fluid Dynamics.- Author Index.

Nonthermal fragmentation of C 60