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Accurate Rayleigh and Raman scattering cross sections, tensor components, depolarization ratios, and reversal coefficients for all rovibrational transitions within the X 1 Σ g + ground electronic state of H2 have been calculated. Raman spectra have been generated using these data. A method for calculating Raman scattering cross sections is formulated that is valid below the ionization threshold and in the region containing resonances, which explicitly accounts for all bound and dissociative vibrational levels of the bound intermediate electronic states and approximately accounts for the ionization continuum. A representative set of cross sections is presented for incident photon energies below 15 eV and compared with existing results in the literature where possible. Convergence of our results with an increasing number of bound intermediate electronic states is demonstrated. The accuracy of the Placzek–Teller approximation is discussed. The effect of accounting for the intermediate ionization continuum is investigated. Local thermal equilibrium cross sections are calculated for Rayleigh and Raman scattering. This work represents the most accurate and complete treatment of Raman scattering for molecular hydrogen to date. A total of 9582 Rayleigh and Raman scattering cross sections have been generated and are openly available on Zenodo under an open-source Creative Commons Attribution license at https://zenodo.org/doi/10.5281/zenodo.13441471. [ABSTRACT FROM AUTHOR]

Point defects are thermodynamically stabilized in all crystalline materials, with increased densities negatively impacting the properties and performance of transition metal dichalcogenides (TMDs). While recent point defect reduction methods have led to considerable improvements in the optoelectronic properties of TMDs, there is a clear need for theoretical work to establish the lower limit of defect densities, as represented by thermal equilibrium. To that end, an ab initio and thermodynamic analysis of the equilibrium densities of intrinsic point defects in MoSe2 and WSe2 is presented. The intrinsic defect formation energies at the limits of the selenium and metal-rich regimes are determined by density functional theory (DFT) and then augmented with elemental chemical potential functions to determine temperature- and pressure-dependent formation energies. Equilibrium defect densities are determined for MSe, SeM, vM, and vSe, where M and v, respectively, represent the metal and the vacancy, as a function of synthesis temperature and pressure. The effects of vibrational free energy contributions and treatment of the DFT exchange–correlation potential are found to be non-negligible. Calculated equilibrium densities are several orders of magnitude below reported defect densities in TMDs made by chemical vapor deposition, chemical vapor transport, and flux methods, thereby establishing that current synthesis methods are either kinetically limited or impurity dominated. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations are widely employed to measure the physical properties of glass-forming liquids in thermal equilibrium. Combined with local Monte Carlo moves, the Metropolis algorithm can also be used to simulate the relaxation dynamics, thus offering an efficient alternative to molecular dynamics. Monte Carlo simulations are, however, more versatile because carefully designed Monte Carlo algorithms can more efficiently sample the rugged free energy landscape characteristic of glassy systems. After a brief overview of Monte Carlo studies of glass-formers, we define and implement a series of Monte Carlo algorithms in a three-dimensional model of polydisperse hard spheres. We show that the standard local Metropolis algorithm is the slowest and that implementing collective moves or breaking detailed balance enhances the efficiency of the Monte Carlo sampling. We use time correlation functions to provide a microscopic interpretation of these observations. Seventy years after its invention, the Monte Carlo method remains the most efficient and versatile tool to compute low-temperature properties in supercooled liquids. [ABSTRACT FROM AUTHOR]

In past decades, enormous effort has been expended to develop algorithms and even to construct special-purpose computers in order to efficiently evaluate total energies and forces for long-range-interacting particle systems, with the particle-mesh Ewald and the fast multipole methods as well as the "Anton" series of supercomputers serving as examples for biomolecular simulations. Cutoffs in the range of the interaction have also been used for large systems. All these methods require extrapolations. Within Markov-chain Monte Carlo, in thermal equilibrium, the Boltzmann distribution can, however, be sampled natively without evaluating the total energy. Using as an example the Lennard-Jones interaction, we review past attempts in this direction and then discuss in detail the class of cell-veto algorithms that allow for the fast, native sampling of the Boltzmann distribution without any approximation, extrapolation, or cutoff even for the slowly decaying Coulomb interaction. The computing effort per move remains constant with increasing system size, as we show explicitly. We provide worked-out illustrations and pseudocode representations of the discussed algorithms. Python scripts are made available in an associated open-source software repository. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the formation and dissociation of boron–hydrogen (BH) pairs in crystalline silicon under thermal equilibrium conditions. Our samples span doping concentrations of nearly two orders of magnitude and are passivated with a layer stack consisting of thin aluminum oxide and hydrogen-rich silicon nitride (Al 2 O 3 /SiN x :H). This layer stack acts as a hydrogen source during a following rapid thermal annealing. We characterize the samples using low-temperature Fourier-transform infrared spectroscopy and four-point-probe resistivity measurements. Our findings show that the proportion of hydrogen atoms initially bound to boron (BH pairs) rises with increasing boron concentration. Upon isothermal dark annealing at (163 ± 2) °C, hydrogen present in molecular form, H 2 , dissociates at a rate directly proportional to the concentration of boron atoms, ∝ [ B − ], leading to the formation of BH pairs. With prolonged annealing, an unknown hydrogen complex is formed at a rate that is inversely proportional to the square of the boron concentration, ∝ 1/[B − ] 2 , resulting in the disappearance of BH pairs. Based on experimental observations, we derive a kinetic model in which we describe the formation of the unknown complex through neutral hydrogen H 0 binding to a sink. Additionally, we investigate the temperature dependence of the reaction rates and find that the H 2 dissociation process has an activation energy of (1.11 ± 0.05) eV, which is in close agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

Recent studies including our own report (I) have revealed that heavily phosphorus (P) doped Czochralski-silicon (HP-Cz-Si) exhibits peculiar defect behaviors during crystal growth. HP-Cz-Si crystals with a low resistivity of around 0.6 mΩ cm (P concentration of 1.3 × 1020 P cm−3) have interstitial-type stacking faults (SFs) and dislocations, which degrade device characteristics. The purpose of this paper is to clarify what causes the defect behavior in HP-Cz-Si through theoretical calculations. The thermal equilibrium concentrations of substitutional P (Ps), interstitial P (Pi), and (Ps)n-vacancy (V) clusters (n = 1−4) were determined by using density functional theory (DFT) calculations. The concentrations of Pi ([Pi]) and (Ps)nV ([(Ps)nV]) balanced with the given Ps concentration ([Ps]) were obtained as a function of the total P concentration ([P]) and the temperature. On the basis of the calculated results those can quantitatively explain our experimental results in the report (I), we propose a defect model that accurately represents HP-Cz-Si crystal growth. The main feature of the model is that the incorporated Pi atoms at the solid/liquid interface around [Pi] = 1017 Pi cm−3 cause the formation of SFs and dislocations during the HP-Cz-Si crystal growth with around [P] = 1020 P cm−3. Furthermore, DFT calculations were performed for Pi segregation on the SF and for the photoelectron spectra of P 1s measured by hard x-ray photoelectron spectroscopy to explain the other experimental results in the report (I). [ABSTRACT FROM AUTHOR]

We report the two-photon absorption laser-induced fluorescence rotational spectrum of the CO B 1Σ+ ← X 1Σ+ Hopfield–Birge system (v′ = 0, v″ = 0) Q-branch in an ∼4850 K, atmospheric pressure plasma torch plume at thermal equilibrium in both the quenching-dominated (low laser intensity) and photoionization-dominated (high laser intensity) regimes. We provide a detailed analysis of the photophysics in these two regimes using a rate equation approach and propose modeling considerations for them as well. In the experimental spectra, distinct rotational transitions up to J″ = 83 are observed, allowing analysis over a very large range of rotational states. Evidence of predissociation is observed for J′ ≥ 64 and is likely due to the interaction with the D′1Σ+ electronic state, which has been proposed in the literature but never observed in the v′ = 0 state. The line positions of higher rotational states show disagreement with line positions calculated from molecular constants in the available literature, suggesting the need for modifications to the constants, which are reported here. A shift in the B 1Σ+ ← X 1Σ+ absorption spectrum toward higher two-photon energy as a result of the second-order Stark shift was observed in the photoionization-dominated spectrum, and the second-order Stark shift cross section was estimated to be 7 ± 3 × 10−18 cm2. The mean photoionization cross section of the excited upper state was inferred by comparing the line broadening of the two spectra and was estimated to be 11 ± 7 × 10−18 cm2. In addition, weak J′-dependent variations of the photoionization cross section were observed and are reported here. [ABSTRACT FROM AUTHOR]

Several types of dynamics at stationarity can be described in terms of a Markov jump process among a finite number N of representative sites. Before dealing with the dynamical aspects, one basic problem consists in expressing the a priori steady-state occupation probabilities of the sites. In particular, one wishes to go beyond the mere black-box computational tools and find expressions in which the jump rate constants appear explicitly, therefore allowing for a potential design/control of the network. For strongly connected networks admitting a unique stationary state with all sites populated, here we express the occupation probabilities in terms of a formula that involves powers of the transition rate matrix up to order N − 1. We also provide an expression of the derivatives with respect to the jump rate constants, possibly useful in sensitivity analysis frameworks. Although we refer to dynamics in (bio)chemical networks at thermal equilibrium or under nonequilibrium steady-state conditions, the results are valid for any Markov jump process under the same assumptions. [ABSTRACT FROM AUTHOR]

The effects of carbon in heavily phosphorus-doped Czochralski (HP-Cz) silicon (Si) substrates, with the concentrations across an order of magnitude from 1016 to 1017 cm−3, on the out-diffusion of phosphorus impurities within n/n+ epitaxial Si (Epi-Si) wafers have been investigated. It is found that the increase in the carbon concentration ([C]) from 1.0 × 1016 to 1.0 × 1017 cm−3 leads to the enhanced phosphorus out-diffusion within the n/n+ Epi-Si wafer when subjected to anneal at 1100 °C in an N2 or an O2 ambient or to anneal at 1150 °C in an N2 ambient, but hardly affects the phosphorus out-diffusion within the n/n+ Epi-Si wafer when subjected to anneal at 1150 °C in an O2 ambient. Based on the density functional theory calculations, it is derived that the increase in the [C] from 1.0 × 1016 to 1.0 × 1017 cm−3 in the HP-Cz Si substrate results in a significantly increased thermal equilibrium concentration of self-interstitial silicon (SiI) atoms at 1100 or 1150 °C, which, in turn, leads to the increased concentration of the SiI atoms that out-diffuse from the substrate to the epitaxial layer because the SiI atoms diffuse extremely fast in Si. Such a carbon-induced increase in the concentration of SiI atoms is believed to be responsible for the aforementioned enhanced phosphorus out-diffusion, which is predominantly dictated by the interstitialcy mechanism. In the case of anneal in the O2 ambient at sufficiently high temperatures such as 1150 °C, a large number of excessive SiI atoms injected into the Epi-Si wafer substantially mask the carbon enhancement effect on the phosphorus out-diffusion. Of technological significance, it is deduced that the [C] should be not higher than 1.0 × 1016 cm−3 in the HP-Cz Si wafers as the substrates of n/n+ Epi-Si wafers used for power devices. [ABSTRACT FROM AUTHOR]

The photovoltaic signal is an important characteristic of photodetectors, including but not limited to those that are based on p–n or p–i–n photodiodes. In an open-circuit configuration, pulsed excitation of the detector with ultrafast (femto or nanosecond) pulses leads to a photovoltaic signal that decays slowly (micro-second time scale). If the physics in the detector is dominated by the recombination of the photo-excited charge carriers, one expects the signal to decay without changing its sign. However, some experiments using short-pulse excitation have found that photovoltaic signals can undergo a sign change as a function of time following excitation, with positive signals immediately following the excitation, turning to negative signals several microseconds later. Here, we study various physical effects (density, temperature, electrostriction, pressure, photostriction, and bandgap renormalization) and determine their effect on photovoltaic signals. If, following ultrafast excitation, the carrier density and temperature are increased, and during relaxation the system reaches a state sufficiently close to the quasi-thermal equilibrium in which the carrier density is still elevated, but smaller than the intrinsic thermal equilibrium density at the elevated temperature, then the signal can become negative. [ABSTRACT FROM AUTHOR]

A topology optimization-based design method for liquid cooling garments (LCGs) is proposed, aiming to enhance the heat flow performance of LCG systems by optimizing the internal microchannel structures. The primary objective is to improve flow and heat transfer characteristics in high-temperature environments, ensuring efficient heat dissipation. To achieve this, a novel liquid cooling film replaces traditional fixed hose structures and integrates with a water-cooled heat exchanger, forming a modular system that facilitates rapid assembly. A variable-density topology optimization model is applied to refine the microchannel configurations, examining the effects of fluid domain volume fractions and multi-objective weighting factors. The findings indicate that as the volume fractions increase, the microchannel designs become finer, leading to improved heat dissipation efficiency and reduced pressure drop. Numerical simulations and experimental validations reveal that the topology-optimized (TO) model outperforms traditional designs (TRA and TRB) in terms of heat flow performance, as observed in studies on flow fields, pressure distributions, temperature profiles, and Nusselt numbers. Specifically, the TO model reduces the average temperature by 30.96% compared to TRA and the maximum temperature by 19.46% compared to TRB at a flow rate of 240 ml/min. At a voltage of 8 V and a flow rate of 700 ml/min, the TO-designed LCGs achieve a steady-state temperature of 24 °C, exhibiting superior performance under high-flow scenarios. The TO design also demonstrates faster thermal equilibrium and a reduced temperature gradient, contributing to enhanced wearer comfort. This research confirms the efficacy of topology optimization, offering a theoretical basis and practical framework for developing high-performance LCG systems. [ABSTRACT FROM AUTHOR]

As a therapeutic approach for cancer, hyperthermia involves selectively increasing the temperature of affected tissues while preserving adjacent healthy tissues. This study explores the efficacy of pristine and coated silver, copper, and gold nanostructures such as nanorods, nanospheres, and nanoellipsoids for hyperthermia. This study performed finite element analysis to assess the relative performance of pristine nanostructures and those covered with different coating thicknesses. The metallic nanostructures were enclosed within the spherical zone of malignant tissue of 500 nm size, and the ambient temperature of these nanostructures was increased to 42–46 °C. Thermal equilibrium was reached after 0.1 μs of heating in the treatment region. Compared to other geometries, the nanorods quickly attained the required temperature in the treatment region. The nanorods with 1 nm coating thickness showed a fast heating response compared to 2 and 3 nm coatings. Silver, gold, and copper nanorods reached a temperature of 44.2, 43.6, and 43.5 °C, respectively, after 0.1 μs of heating. Gold-coated silver nanorods were discovered to be most efficient at achieving the highest temperature of 44.2 °C. [ABSTRACT FROM AUTHOR]

This work proposes an extended version of the quantum-kinetic chemistry models, aiming to accurately reproduce experimental measurements and high-fidelity calculations in both thermal equilibrium and non-equilibrium. The extension involves the development of new formulations, incorporating a set of tunable parameters obtained from a non-linear least squares fit on the dataset. The newly derived analytical expressions are implemented in a direct simulation Monte Carlo (DSMC) solver. These formulations are applied to the 19 most representative chemical reactions of an air mixture involving dissociation and exchange reactions. The DSMC reaction rates demonstrate excellent agreement with the newly derived analytical expressions, providing verification of the successful implementation in the DSMC solver. The study demonstrates excellent reproduction of the baseline dataset for both thermal equilibrium and non-equilibrium. Furthermore, the new formulations are applied to simulate the surface heat flux during the second space transport system (STS-II) mission at an altitude of 92.35 km. [ABSTRACT FROM AUTHOR]

Most engineering tools dealing with detonation waves in condensed explosives are based on the reactive Euler equations, which involve a thermodynamic closure based on temperature and pressure equilibrium conditions. Indeed, the reactant and the detonation products are assumed to evolve in mechanical and thermal equilibrium. Although the assumption of thermal equilibrium is physically questionable, the reactive Euler equations are used for convenience. This choice is supported by several reasons. When considering thermal equilibrium, the assessment of thermal exchanges between the reactant and the detonation products is simplified, as no exchange coefficient needs to be determined. Furthermore, the reactive Euler equations are in conservative form and the shock relations are well-defined. This model appears to be the simplest option for addressing detonations in condensed explosives. However, this simplicity has limitations and conceals a subtle difficulty that can lead to pathological detonations. The present contribution investigates this difficulty and presents a global exothermic condition to preserve exothermic detonations in the frame of temperature–pressure equilibrium flow models. This condition depends on the equations of state only. It is independent of the kinetics used to model the decomposition of the explosive. By meticulously selecting the thermodynamic parameters of the equations of state for the reactant and detonation products, pathological detonations are prevented, thereby maintaining a globally exothermic reaction consistent with the Zeldovich–von Neumann–Döring theory. [ABSTRACT FROM AUTHOR]

A numerical bifurcation analysis is presented for an industrial application where direct resistance heating through a DC is applied to a flat metallic plate, which is cooled by a turbulent boundary layer and radiation. The process is modeled with a conjugate heat transfer between the plate and the cooling air steam. The convective part of the heat transfer mechanism is formulated in the framework of an integral approach, considering a turbulent core based on power law velocity and temperature profiles and a thin laminar sublayer thermally coupled with axial conduction along the plate. The analysis reveals that the problem admits two solutions: one stable and one unstable, separated by a limit point. The existence of multiple solutions is a consequence of the nonlinear electric resistivity–temperature relationship, allowing thermal equilibrium between heat generation and heat dissipation in multiple points. The application of realistic boundary conditions at the wall–fluid interface shows that the thermal to the hydrodynamic boundary layer thicknesses ratio along the plate is no longer close to the value of 1.25, as it is the case with a constant wall temperature. Instead, significant deviations occur due to the thermal coupling between the wall and the cooling fluid. The multiplicity structure and, consequently, the limit points depend on the plate Reynolds number and on the conduction–convection parameter. The locus of the limit points defines an instability threshold beyond which any excess applied current will trigger a thermal runaway phenomenon. This is also an equivalent of the maximum current carrying capacity of the plate. [ABSTRACT FROM AUTHOR]

Droplet manipulation is a multidisciplinary field with broad applications across various industries. It holds significant potential in areas such as microfluidics, oil–water separation, water harvesting, and heat transfer. However, there is still a lack of comprehensive knowledge regarding droplet migration on restricted surfaces. In this study, we conducted a numerical simulation using the front-tracking method to investigate the heat transfer associated with droplet migration on a cold plate with a wettability gradient. We examined the effects of relative temperature differences, surface wettability, low initial impact velocities (W e ≤ 10), and wettability constraints (the width of the wettability stripe capable of driving droplet movement) on various droplet-related heat transfer characteristics and the resulting temperature field distribution. Our key findings indicate that as the temperature difference between the droplet and the surface increases, the heat flux experienced by the droplet after deposition also increases. Additionally, the decline in the heat flux curve during the descending phase becomes more significant. The surface contact angle plays a crucial role in the heat transfer dynamics during droplet migration. Droplets reach thermal equilibrium more quickly on hydrophilic surfaces with smaller contact angles. Higher initial impact velocities initially cause droplets to rebound on the surface, leading to more pronounced fluctuations in transient heat flux during the impact phase. However, as droplets transition from the rebound phase to the migration phase, the impact velocity's influence diminishes. Additionally, the restricted wettability ( W * ) affects the droplet-surface heat transfer through variations in the wetting area. We observed a fourfold difference in the relative wetting area between W * = 0. 4 and W * = 2. 5 in the final stage. [ABSTRACT FROM AUTHOR]

The article discusses the use of Arduino in introductory thermal energy experiments, specifically focusing on thermal equilibrium. By utilizing Arduino Uno boards and DS18B20 temperature sensors, students can explore heat transfer between two objects at different temperatures. The experiment is suitable for high school or college students in nonmajor science courses and can be adapted for elementary or middle school students. The article emphasizes the advantages of using sensors in STEM education, making experiments engaging and accessible to all students, regardless of their prior knowledge or skills. [Extracted from the article]

Modeling environments that are not in local thermal equilibrium, such as protoplanetary disks or planetary atmospheres, with molecular spectroscopic data from space telescopes requires knowledge of the rate coefficients of rovibrationally inelastic molecular collisions. Here, we present such rate coefficients in a temperature range from 10 to 500 K for collisions of CO2 with He atoms in which CO2 is (de)excited in the bend mode. They are obtained from numerically exact coupled-channel (CC) calculations as well as from calculations with the less demanding coupled-states approximation (CSA) and the vibrational close-coupling rotational infinite-order sudden (VCC-IOS) method. All of the calculations are based on a newly calculated accurate ab initio four-dimensional CO2–He potential surface including the CO2 bend (ν2) mode. We find that the rovibrationally inelastic collision cross sections and rate coefficients from the CSA and VCC-IOS calculations agree to within 50% with the CC results at the rotational state-to-state level, except for the smaller ones and in the low energy resonance region, and to within 20% for the overall vibrational quenching rates except for temperatures below 50 K where resonances provide a substantial contribution. Our CC quenching rates agree with the most recent experimental data within the error bars. We also compared our results with data from Clary et al. calculated in the 1980s with the CSA [A. J. Banks and D. C. Clary, J. Chem. Phys. 86, 802 (1987)] and VCC-IOS [D. C. Clary, J. Chem. Phys. 78, 4915 (1983)] methods and a simple atom-atom model potential based on ab initio Hartree–Fock calculations and found that their cross sections agree fairly well with ours for collision energies above 500 cm−1, but that the inclusion of long range attractive dispersion interactions is crucial to obtain reliable cross sections at lower energies and rate coefficients at lower temperatures. [ABSTRACT FROM AUTHOR]

In the present work, we demonstrate the ability of a technique based on Monte Carlo resolution of the Boltzmann transport equation associated to the Green–Kubo autocorrelation of the phonon heat flux to predict, at thermal equilibrium, the thermal conductivity tensor of nanoporous structures. This methodology, which is derived from a former work [D. Lacroix, M. Isaiev, G. Pernot, Phys. Rev. B 104, 165 202 (2021)] developed in the case of bulk systems, is used to predict thermal transport properties of Si porous matrices and Si phononic membranes at room temperature. A broad range of porosities and different pore network organizations are considered. Our results are compared to available experimental data and former modeling techniques. In addition, analytical models based on the phonon mean free path are detailed and compared to numerical simulations. [ABSTRACT FROM AUTHOR]

The self-consistent phonon (SCP) method allows one to include anharmonic effects when treating a many-body quantum system at thermal equilibrium. The system is then described by an effective temperature-dependent harmonic Hamiltonian, which can be used to estimate its various dynamic and static properties. In this paper, we combine SCP with ab initio (AI) potential energy evaluation in which case the numerical bottleneck of AI-SCP is the evaluation of Gaussian averages of the AI potential energy and its derivatives. These averages are computed efficiently by the quasi-Monte Carlo method utilizing low-discrepancy sequences leading to a fast convergence with respect to the number, S, of the AI energy evaluations. Moreover, a further substantial (an-order-of-magnitude) improvement in efficiency is achieved once a numerically cheap approximation of the AI potential is available. This is based on using a perturbation theory-like (the two-grid) approach in which it is the average of the difference between the AI and the approximate potential that is computed. The corresponding codes and scripts are provided. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations of gas-phase chemical reactions are typically carried out on a small number of molecules near thermal equilibrium by means of various thermostatting algorithms. Correct equipartitioning of kinetic energy among translations, rotations, and vibrations of the simulated reactants is critical for many processes occurring in the gas phase. As thermalizing collisions are infrequent in gas-phase simulations, the thermostat has to efficiently reach equipartitioning in the system during equilibration and maintain it throughout the actual simulation. Furthermore, in non-equilibrium simulations where heat is released locally, the action of the thermostat should not lead to unphysical changes in the overall dynamics of the system. Here, we explore issues related to both obtaining and maintaining thermal equilibrium in MD simulations of an exemplary ion–molecule dimerization reaction. We first compare the efficiency of global (Nosé–Hoover and Canonical Sampling through Velocity Rescaling) and local (Langevin) thermostats for equilibrating a system of flexible compounds and find that of these three only the Langevin thermostat achieves equipartition in a reasonable simulation time. We then study the effect of the unphysical removal of latent heat released during simulations involving multiple dimerization events. As the Langevin thermostat does not produce the correct dynamics in the free molecular regime, we only consider the commonly used Nosé–Hoover thermostat, which is shown to effectively cool down the reactants, leading to an overestimation of the dimerization rate. Our findings underscore the importance of thermostatting for the proper thermal initialization of gas-phase systems and the consequences of global thermostatting in non-equilibrium simulations. [ABSTRACT FROM AUTHOR]

A one-dimensional Vlasov–Poisson system is considered to elucidate how the information entropies of the probability distribution functions of the electron position and velocity variables evolve in the Landau damping process. Considering the initial condition given by the Maxwellian velocity distribution with the spatial density perturbation in the form of the cosine function of the position, we derive linear and quasilinear analytical solutions that accurately describe both early and late time behaviors of the distribution function and the electric field. The validity of these solutions is confirmed by comparison with numerical simulations based on contour dynamics. Using the quasilinear analytical solution, the time evolutions of the velocity distribution function and its kurtosis indicating deviation from the Gaussian distribution are evaluated with the accuracy of the squared perturbation amplitude. We also determine the time evolutions of the information entropies of the electron position and velocity variables and their mutual information. We further consider Coulomb collisions that relax the state in the late-time limit in the collisionless process to the thermal equilibrium state. In this collisional relaxation process, the mutual information of the position and velocity variables decreases to zero, while the total information entropy of the phase-space distribution function increases by the decrease in the mutual information and demonstrates the validity of Boltzmann's H-theorem. [ABSTRACT FROM AUTHOR]

Quantifying the degree of universality in compressible turbulence is challenging due to the existence of different modes and their complex interactions. For a restricted family of flows, Donzis and John [Phys. Rev. Fluids 5, 084609 (2020)] showed that universal behavior is indeed observed in compressible turbulence if the ratio of dilatational to solenoidal root mean square (rms) velocities (δ = u ′ d / u ′ s ) is incorporated as a scaling parameter along with the traditional turbulent Mach number ( M t = u ′ / 〈 c 〉 , where u ′ is the rms velocity and 〈 c 〉 is the mean speed of sound). In this paper, we argue for the generality of those results by analyzing a wide range of compressible turbulent flows spanning a variety of flow configurations and setups to assess the degree of universal behavior. These include, among others, reacting flows, flows with solenoidal, thermal, and dilatational forcing, and flows with mean shear and bulk viscosity. We also performed new direct numerical simulations, which include turbulence in situations where vibrational modes of constitutive molecules are not in thermal equilibrium. Collectively, we offer the largest comparison across studies in the literature to date. We find that despite the wide range of forcing conditions and physical processes, universality holds across all these turbulent flows to a very satisfactory degree when both δ and Mt are considered as intrinsic compressibility parameters. The statistics investigated here—single-point statistics up to order four—are chosen such that they represent different ranges across the spectrum of dynamically relevant turbulence scales. We discuss the applicability of the purposed universal behavior for other key statistics in these turbulent flows, including two-point statistics and inhomogeneity effects, and the perspective it opens for modeling them. [ABSTRACT FROM AUTHOR]

This work presents a new formulation of the quantum-kinetic (QK) chemistry models, in which the vibrational excitation is modeled with an anharmonic oscillator model. The new formulations are applied to some of the most representative dissociation reactions occurring during an Earth re-entry. The newly derived analytical expressions are implemented in a direct simulation Monte Carlo (DSMC) solver. The DSMC reaction rates demonstrate excellent agreement with the newly derived analytical expressions, verifying the successful implementation in the DSMC solver. The new models suggest that dissociation reactions are more likely to occur than with the original QK models. Furthermore, the new formulations are compared against experimental measurements, high-fidelity calculations, and well-established chemistry models for both thermal equilibrium and non-equilibrium conditions, presenting reasonable agreement with the baseline database. Additionally, the limitations of the new formulations are assessed for thermal non-equilibrium conditions where an excessive utilization of the relative translational energy and insufficient utilization of the pre-collision vibrational energy to promote dissociation reactions is found. [ABSTRACT FROM AUTHOR]

This article investigates the onset of convection in a bidispersive porous medium, considering the impact of viscous dissipation and throughflow using both linear and nonlinear theories. The flow is modeled using the Oberbeck–Boussinesq approximation and Darcy's law, with local thermal equilibrium between the fluid and solid phases. The temperature field depends solely on the vertical coordinate in the basic solution. The study employs a two-pronged approach to analyze the system's stability, utilizing the normal mode technique for linear analysis and the energy method for nonlinear analysis. The article confirms the validity of the principle of exchange of stabilities. The numerical solution of the eigenvalue problem for both linear and nonlinear theories is obtained using the bvp4c routine. The research explores the influence of various physical parameters on the system's stability. Viscous dissipation's effect on convection onset is noticeable only with significant throughflow. In the absence of viscous dissipation, the throughflow direction does not affect the system's stability. The effective permeability ratio stabilizes the system with upward throughflow and exhibits opposite behavior with downward throughflow. The sub-critical region remains unchanged for the Gebhart number range but increases with higher moment transfer coefficient and effective permeability ratio. Additionally, an analytical expression is derived for the small Peclet number regime of the Rayleigh number using asymptotic analysis. [ABSTRACT FROM AUTHOR]

We contrast Dirac's theory of transition probabilities and the theory of nonadiabatic transition probabilities, applied to a perturbed system that is coupled to a bath. In Dirac's analysis, the presence of an excited state |k0⟩ in the time-dependent wave function constitutes a transition. In the nonadiabatic theory, a transition occurs when the wave function develops a term that is not adiabatically connected to the initial state. Landau and Lifshitz separated Dirac's excited-state coefficients into a term that follows the adiabatic theorem of Born and Fock and a nonadiabatic term that represents excitation across an energy gap. If the system remains coherent, the two approaches are equivalent. However, differences between the two approaches arise when coupling to a bath causes dephasing, a situation that was not treated by Dirac. For two-level model systems in static electric fields, we add relaxation terms to the Liouville equation for the time derivative of the density matrix. We contrast the results obtained from the two theories. In the analysis based on Dirac's transition probabilities, the steady state of the system is not an equilibrium state; also, the steady-state population ρkk,s increases with increasing strength of the perturbation and its value depends on the dephasing time T2. In the nonadiabatic theory, the system evolves to the thermal equilibrium with the bath. The difference is not simply due to the choice of basis because the difference remains when the results are transformed to a common basis. [ABSTRACT FROM AUTHOR]

Trajectory-based methods that propagate classical nuclei on multiple quantum electronic states are often used to simulate nonadiabatic processes in the condensed phase. A long-standing problem of these methods is their lack of detailed balance, meaning that they do not conserve the equilibrium distribution. In this article, we investigate ideas for restoring detailed balance in mixed quantum–classical systems by tailoring the previously proposed spin-mapping approach to thermal equilibrium. We find that adapting the spin magnitude can recover the correct long-time populations but is insufficient to conserve the full equilibrium distribution. The latter can however be achieved by a more flexible mapping of the spin onto an ellipsoid, which is constructed to fulfill detailed balance for arbitrary potentials. This ellipsoid approach solves the problem of negative populations that has plagued previous mapping approaches and can therefore be applied also to strongly asymmetric and anharmonic systems. Because it conserves the thermal distribution, the method can also exploit efficient sampling schemes used in standard molecular dynamics, which drastically reduces the number of trajectories needed for convergence. The dynamics does however still have mean-field character, as is observed most clearly by evaluating reaction rates in the golden-rule limit. This implies that although the ellipsoid mapping provides a rigorous framework, further work is required to find an accurate classical-trajectory approximation that captures more properties of the true quantum dynamics. [ABSTRACT FROM AUTHOR]

A hallmark of meso-scale interfacial fluids is the multi-faceted, scale-dependent interfacial energy, which often manifests different characteristics across the molecular and continuum scale. The multi-scale nature imposes a challenge to construct reliable coarse-grained (CG) models, where the CG potential function needs to faithfully encode the many-body interactions arising from the unresolved atomistic interactions and account for the heterogeneous density distributions across the interface. We construct the CG models of both single- and two-component polymeric fluid systems based on the recently developed deep coarse-grained potential [Zhang et al., J. Chem. Phys. 149, 034101 (2018)] scheme, where each polymer molecule is modeled as a CG particle. By only using the training samples of the instantaneous force under the thermal equilibrium state, the constructed CG models can accurately reproduce both the probability density function of the void formation in bulk and the spectrum of the capillary wave across the fluid interface. More importantly, the CG models accurately predict the volume-to-area scaling transition for the apolar solvation energy, illustrating the effectiveness to probe the meso-scale collective behaviors encoded with molecular-level fidelity. [ABSTRACT FROM AUTHOR]

The Soret effect is the tendency of fluid mixtures to exhibit concentration gradients in the presence of a temperature gradient. Using molecular-dynamics simulation of two-component Lennard-Jones liquids, it is demonstrated that spatially sinusoidal heat pulses generate both temperature and pressure gradients. Over short timescales, the dominant effect is the generation of compressional waves, which dissipate over time as the system approaches mechanical equilibrium. The approach to mechanical equilibrium is also characterized by a decrease in particle density in the high-temperature region and an increase in particle density in the low-temperature region. It is demonstrated that concentration gradients develop rapidly during the propagation of compressional waves through the liquid. Over longer timescales, heat conduction occurs to return the system to thermal equilibrium, with the particle current acting to restore a more uniform particle density. It is shown that the Soret effect arises due to the fact that the two components of the fluid exhibit different responses to pressure gradients. First, the so-called isotope effect occurs because light atoms tend to respond more rapidly to evolving conditions. In this case, there appears to be a connection to previous observations of "fast sound" in binary fluids. Second, it is shown that the partial pressures of the two components in equilibrium, and more directly, the relative magnitudes of their derivatives with respect to temperature and density, determine which species accumulate in the high- and low-temperature regions. In the conditions simulated here, the dependence of the partial pressure on density gradients is larger than the dependence on temperature gradients. This is directly connected to the accumulation of the species with the largest partial pressure in the high-temperature region and the accumulation of the species with the smallest partial pressure in the low-temperature region. The results suggest that further development of theoretical descriptions of the Soret effect might begin with hydrodynamical equations in two-component liquids. Finally, it is suggested that the recently proposed concept of "thermophobicity" may be related to the sensitivity of partial pressures in a multicomponent fluid to changes in temperature and density. [ABSTRACT FROM AUTHOR]

The surface erosion of polyethylene is interrogated using pulsed x rays at the Z Machine (Sandia National Laboratories) and with proton beams at the Gamble II generator (Naval Research Laboratory) to validate a coupled model for volumetric thermal ablation, photoionization, finite-rate decomposition, and molecular recombination of radicals. The intense radiation pulses (up to ∼ 10 14 W / m 2 over tens of nanoseconds) are used to generate one-dimensional vapor flows with low ionization fractions and a simplified geometry compared to typical laser ablation, allowing for evaluation of the model under local thermal equilibrium conditions. Areal momentum carried by the ensuing uniaxial hydrodynamic shock is used to indicate the extent of ablation. The threshold fluence for ablation is found to be in close correspondence with the bulk melt transition, and reasonable agreement with the model is obtained for peak temperatures in polyethylene up to 5500 K and heating rates up to 10 11 K / s where thermal decomposition reactions are also active. [ABSTRACT FROM AUTHOR]

In this study, we revisit the oxidation reactions of a single-crystal silicon wafer and compare the reported crystal structures of the formed oxides with the original diamond structure of single-crystal silicon. It is commonly assumed that interstitial silicon atoms are always emitted during oxidation at the reactive interface between silicon and the formed oxide due to volume differences. However, it is important to acknowledge that this phenomenon may not always be observed. Thermal equilibrium studies have revealed that a certain percentage of silicon atoms in the diamond structure remains even after surface oxidation [Kamiyama and Sueoka, J. Appl. Phys. 134, 115301 (2023)]. These retained silicon atoms undergo a transformation into a different crystal structure, presenting as β-cristobalite (space group: P41212) rather than the anticipated non-ideal cristobalite (space group: Fd-3m). Our ab initio calculations indicated that the latter remains stable next to a quartz-based structure, exhibiting optimal compatibility with the Si (001) surface. This quartz-based structure is formed through the emission of a Si atom during the oxidation of single-crystal silicon, finally forming a quartz/Si (001) interface. Therefore, we propose a coexisting model involving an alternative β-cristobalite and a quartz crystal structure originating from the surface oxidation of single-crystal silicon. This model offers an explanation for why thermally oxidized films derived from single-crystal silicon exhibit an amorphous nature. In addition, studies have revealed that the oxide precipitates observed in Si crystals are cristobalite and coesite. Hence, the qualitative differences in SiO2/Si interfaces between surface and internal oxidations in metal-gettering effectivity shown in experimental literature require clarification. We also discuss the conditions that prevent the emission of Si atoms. [ABSTRACT FROM AUTHOR]

In this study, we revisit the oxidation reactions of a single-crystal silicon wafer and compare the reported crystal structures of the formed oxides with the original diamond structure of single-crystal silicon. It is commonly assumed that interstitial silicon atoms are always emitted during oxidation at the reactive interface between silicon and the formed oxide due to volume differences. However, it is important to acknowledge that this phenomenon may not always be observed. Thermal equilibrium studies have revealed that a certain percentage of silicon atoms in the diamond structure remains even after surface oxidation [Kamiyama and Sueoka, J. Appl. Phys. 134, 115301 (2023)]. These retained silicon atoms undergo a transformation into a different crystal structure, presenting as β-cristobalite (space group: P41212) rather than the anticipated non-ideal cristobalite (space group: Fd-3m). Our ab initio calculations indicated that the latter remains stable next to a quartz-based structure, exhibiting optimal compatibility with the Si (001) surface. This quartz-based structure is formed through the emission of a Si atom during the oxidation of single-crystal silicon, finally forming a quartz/Si (001) interface. Therefore, we propose a coexisting model involving an alternative β-cristobalite and a quartz crystal structure originating from the surface oxidation of single-crystal silicon. This model offers an explanation for why thermally oxidized films derived from single-crystal silicon exhibit an amorphous nature. In addition, studies have revealed that the oxide precipitates observed in Si crystals are cristobalite and coesite. Hence, the qualitative differences in SiO2/Si interfaces between surface and internal oxidations in metal-gettering effectivity shown in experimental literature require clarification. We also discuss the conditions that prevent the emission of Si atoms. [ABSTRACT FROM AUTHOR]

Efficient heat dissipation and thermal protection present urgent challenges in high-power integrated circuits (ICs). Although applying a coating of highly thermally conductive materials on the surface of ICs is anticipated to mitigate heat concentration issues, ensuring thermal protection for adjacent devices continues to pose a challenge. Inspired by the microstructure of unidirectional nutrient transport in plant roots, this study utilizes magnetic liquid metal droplets to develop a high thermal conductivity network capable of adaptively manipulating the heat transfer path. This approach aims to tackle the challenges of heat concentration, disordered thermal dissipation, and thermal protection for high-power ICs, thereby enhancing thermal management efficiency. By controlling the distribution of the magnetic field, this study orchestrates the structure of the thermal conduction network to ensure rapid and orderly heat dissipation of ICs while simultaneously validating the network's thermal protection performance. The temperature in the IC thermal concentration zone reaches thermal equilibrium at 399.1 K when the ambient temperature is at 295 K. As the ambient temperature rises to 333 K, the temperature in the IC heat concentration zone stabilizes at approximately 400 K. Simultaneously, the temperature at a specific point in the thermal path of the network registers at 341 K, with the temperatures of the devices flanking this point at 314 K. The magnetron thermal conduction network, inspired by the root structure of bionic plants, not only boosts the thermal management efficiency of ICs but also shows promising application prospects in aerospace, electronics, and other related industries. [ABSTRACT FROM AUTHOR]

In strongly scattering elastic media without attenuation and dispersion, the wavefield is dominated by shear waves, and in three dimensions, the ratio of the S to P energy is given by E S / E P = 2 (v P / v S) 3 . This study investigates how this ratio is influenced by attenuation. Both the case of the ringdown mode, where the energy evolves from initial values, and the case of energy equilibrium, where the attenuation is balanced by energy injection sources, are treated. It is shown that in ringdown mode, the energy ratio E S / E P satisfies a Ricatti equation in time: hence, the energy ratio is not an exponential function of time. It is also shown that the long-time energy ratio differs from the value in non-attenuating media when the attenuation coefficients for P and S waves are different. In the case of energy equilibrium, the energy ratio only is equal to the value in non-attenuating media when (1) the time scale of P- and S-wave equilibration is much smaller than the attenuation time or (2) the energy injection rate for each wave type is balanced by the dissipation for that wave type. The latter situation happens when the wavefield is excited by thermal fluctuations in thermal equilibrium. [ABSTRACT FROM AUTHOR]

Granular matter like sand is composed of a large number of interacting grains and is, thus, expected to be amenable to a statistical physics treatment. Yet, the frictional properties of grains make the statistical physics of granular matter significantly different from the equilibrium statistical physics of atomic or molecular systems. We use three simple models to illustrate some of the key concepts of the statistical physics introduced by Edwards and co-workers more than 30 years ago to describe shaken granular piles: non-interacting frictional grains attached to a wall by a spring, a chain of frictional grains connected by springs, and a simplified mean-field model of a granular packing. We observe that a chain of frictional grains connected by springs exhibits a critical point at an infinite effective temperature (i.e., infinitely strong shaking) at odds with the zero-temperature critical point generically found in one-dimensional systems at thermal equilibrium in the presence of local interactions. Since the late 20th century, granular materials have been recognized as forming a distinct state of matter, neither solid nor liquid, but amenable to a statistical description. It turns out that dissipation, through inter-grain friction, governs the large-scale properties of these systems, so that the usual Boltzmann–Gibbs statistics is replaced by the Edwards statistics. These statistics are full of surprises. For instance, model granular systems can exhibit a critical point at infinite-temperature. To know more, you can delve into this paper, which can be used in advanced statistical physics courses, or as a graduate-level introduction to soft matter. [ABSTRACT FROM AUTHOR]

We investigate the statistical properties of fluctuations in active systems that are governed by nonsymmetric responses. Both an underdamped Langevin system with an odd resistance tensor and an overdamped Langevin system with an odd elastic tensor are studied. For a system in thermal equilibrium, the time-correlation functions should satisfy time-reversal symmetry and the antisymmetric parts of the correlation functions should vanish. For the odd Langevin systems, however, we find that the antisymmetric parts of the time-correlation functions can exist and that they are proportional to either the odd resistance coefficient or the odd elastic constant. This means that the time-reversal invariance of the correlation functions is broken due to the presence of odd responses in active systems. Using the short-time asymptotic expressions of the time-correlation functions, one can estimate an odd elastic constant of an active material such as an enzyme or a motor protein. [ABSTRACT FROM AUTHOR]

We describe a numerical algorithm for approximating the equilibrium-reduced density matrix and the effective (mean force) Hamiltonian for a set of system spins coupled strongly to a set of bath spins when the total system (system + bath) is held in canonical thermal equilibrium by weak coupling with a "super-bath". Our approach is a generalization of now standard typicality algorithms for computing the quantum expectation value of observables of bare quantum systems via trace estimators and Krylov subspace methods. In particular, our algorithm makes use of the fact that the reduced system density, when the bath is measured in a given random state, tends to concentrate about the corresponding thermodynamic averaged reduced system density. Theoretical error analysis and numerical experiments are given to validate the accuracy of our algorithm. Further numerical experiments demonstrate the potential of our approach for applications including the study of quantum phase transitions and entanglement entropy for long range interaction systems. [ABSTRACT FROM AUTHOR]

Astrophysical modeling of processes in environments that are not in local thermal equilibrium requires the knowledge of state-to-state rate coefficients of rovibrational transitions in molecular collisions. These rate coefficients can be obtained from coupled-channel (CC) quantum scattering calculations, which are very demanding, however. Here, we present various approximate but more efficient methods based on the coupled-states approximation (CSA), which neglects the off-diagonal Coriolis coupling in the scattering Hamiltonian in body-fixed coordinates. In particular, we investigated a method called NNCC (nearest-neighbor Coriolis coupling) [Yang et al., J. Chem. Phys. 148, 084101 (2018)] that includes Coriolis coupling to first order. The NNCC method is more demanding than the common CSA method but still much more efficient than full CC calculations, and it is substantially more accurate than CSA. All of this is illustrated by showing state-to-state cross sections and rate coefficients of rovibrational transitions induced in CO2 by collisions with He atoms. It is also shown that a further reduction of CPU time, practically without loss of accuracy, can be obtained by combining the NNCC method with the multi-channel distorted-wave Born approximation that we applied in full CC calculations in a previous paper. [ABSTRACT FROM AUTHOR]

In 4H-SiC semiconductors, carbon vacancies act as traps, which limit the carrier lifetime. During high-temperature treatment of 4H-SiC, the concentration of carbon vacancies can be increased or decreased by several atomistic processes, including the diffusion of carbon vacancies and carbon self-interstitials, and the thermal generation–recombination of defects. In this work, an analytic process model has been developed and calibrated against a collection of measured data. The model describes the concentration of carbon vacancies after thermal processing for a wider range of process conditions than previous works. For inert annealings, bulk recombination, bulk generation, and diffusion of carbon vacancies and carbon interstitials play a critical role. For oxidation processes, carbon interstitials are injected at the oxidizing surface. The injection rate of carbon interstitials at the oxidizing surface and their diffusivity from the surface into the bulk govern the reduction of carbon vacancies via bulk recombination. Basic properties of carbon vacancies and carbon self-interstitials in 4H-SiC, such as the thermal equilibrium concentrations, diffusivities, and bulk recombination rates, are reflected by model parameters and have been determined by model calibration for the temperature range of 1150–1950 °C. High-quality epitaxial films and low-quality substrates are described consistently, when assuming that carbon interstitials can be trapped by defects present only in the substrate. [ABSTRACT FROM AUTHOR]

Many symmetric top molecules are among the most important polyatomic molecules. The orientation of a polyatomic molecule is a challenging task, which is at the heart of its quantum control and crucial for many subsequent applications in various fields. Most recent studies focus on the temporary orientation achieved via the quantum revivals. In this study, we reveal the underlying mechanism behind the observed permanent orientation and discuss strategies for a higher degree of permanent orientation. By a careful analysis of symmetry and unitary, it is possible to estimate an upper bound of ⟨ ⟨ cos θ ⟩ ⟩ < (2 − 2 ) / 4 ≈ 0.1464 for a molecule in its thermal equilibrium states using a linear field. We show that this bound can be reached for an oblate symmetric-top molecule in the high temperature limit. To demonstrate different possible schemes, we take CHCl3 as an example. Simply with designed microwave fields, one can permanently orient CHCl3 with a degree of ⟨cos θ⟩ ≈ 0.045. We show that this value can be significantly increased by adding one or more pump pulses. [ABSTRACT FROM AUTHOR]

We consider a molecular junction immersed in a solvent where the electron transfer is dominated by Marcus-type steps. However, the successive nature of the charge transfer through the junction does not imply that the solvent reaches thermal equilibrium throughout the transport. In our previous work [Kirchberg et al., J. Phys. Chem. Lett. 11, 1729 (2020)], we have determined the nonequilibrium distribution of the solvent where its dynamics, expressed by a friction, is considered in two limiting regimes of fast and slow solvent relaxation. In dependence of the nonequilibrium solvent dynamics, we investigate now the electrical, thermal, and thermoelectric properties of the molecular junction. We show that by suitable tuning of the friction, we can reduce the heat dissipation into the solvent and enhance the heat transfer between the electrodes. Interestingly, we find that the Seebeck coefficient grows significantly by adapting the solvent friction in both regimes. [ABSTRACT FROM AUTHOR]

We studied electrical properties of n-Si/n-Ga2O3 heterojunctions fabricated by surface-activated bonding. The energy barrier heights (qϕb) at the Si/Ga2O3 interface for different reverse voltages (Vrev) were derived from temperature-dependent current density–voltage (J–V–T) characteristics. With shifting Vrev to the negative direction, qϕb gradually decreased and reached a constant value due to negatively charged interface states. The conduction band offset at the heterointerface was estimated to be 0.18 eV from the Vrev dependence of qϕb. The qϕb calculated from a capacitance of the heterojunction at thermal equilibrium was larger than those derived from the J–V–T characteristics, attributing to spatially inhomogeneous qϕb caused by the non-uniform distribution of the charged interface states. The density of shallow interface states was also extracted from the reverse J–V–T characteristics, which was estimated to be about 6 × 1012 cm−2 eV−1. [ABSTRACT FROM AUTHOR]

We report on the spin and occupation noise of a single, positively charged (InGa)As quantum dot emitting photons in the telecommunication C-band. The spin noise spectroscopy measurements are carried out at a temperature of 4.2 K in dependence on intensity and detuning in the regime beyond thermal equilibrium. The spin noise spectra yield in combination with an elaborate theoretical model the hole-spin relaxation time of the positively charged quantum dot and the Auger recombination and the electron-spin relaxation time of the trion state. The extracted Auger recombination time of this quantum dot emitting at 1.55 μ m is comparable to the typical Auger recombination times on the order of a few μ s measured in traditionally grown InAs/GaAs quantum dots emitting at around 900 nm. [ABSTRACT FROM AUTHOR]

Dust plasma readily forms during hypervelocity impact, which serves as a source of plasma macroscopic charge separation and strong electromagnetic fields. In this study, we examine the dynamic evolution of surface charging of aluminum dust grains with micrometer or submicrometer sizes in a hypervelocity impact plasma environment based on the theory of orbital motion limited. As dust grains traverse the expanding plasma, plasma density and temperature decrease with increasing distance from the impact point. This leads to longer relaxation times for charging equilibrium (ranging from picoseconds to microseconds) and reduced equilibrium charges. The model incorporates thermionic and secondary electron emission effects on dust grain charging processes while also examining the impacts of five heating and cooling mechanisms on the thermal equilibrium temperatures of dust grains. Near the impact point, thermal equilibrium temperatures exceed aluminum's boiling point, which results in phase transition ablation processes. As dust grain temperatures increase, thermionic emission currents may dominate charging dynamics and influence final equilibrium charge numbers. High-temperature dust grains tend to acquire positive charges. Moreover, we observe that the radius of dust grains considerably affects charging processes, and smaller grain radii correspond to low equilibrium charges and longer relaxation times. [ABSTRACT FROM AUTHOR]

Numerical computations have become a pillar of all modern quantitative sciences. Any computation involves modeling—even if often this step is not made explicit—and any model has to neglect details while still being physically accurate. Equilibrium statistical mechanics guides both the development of models and numerical methods for dynamics obeying detailed balance. For systems driven away from thermal equilibrium, such a universal theoretical framework is missing. For a restricted class of driven systems governed by Markov dynamics and local detailed balance, stochastic thermodynamics has evolved to fill this gap and to provide fundamental constraints and guiding principles. The next step is to advance stochastic thermodynamics from simple model systems to complex systems with tens of thousands or even millions of degrees of freedom. Biomolecules operating in the presence of chemical gradients and mechanical forces are a prime example for this challenge. In this Perspective, we give an introduction to isothermal stochastic thermodynamics geared toward the systematic multiscale modeling of the conformational dynamics of biomolecular and synthetic machines, and we outline some of the open challenges. [ABSTRACT FROM AUTHOR]

Accumulated charge measurement (ACM) is an experimental technique for studying the charge-injection and extraction processes in a condenser comprising the following: metal electrode 1, insulator (INS), organic semiconductor (OS), and metal electrode 2 (M2). In this method, the change in the accumulated charge (Qacc) is estimated by integrating the displacement current when the applied voltage changes from Voff to Voff + Va. Voff is the constant offset voltage and Va is the alternating voltage that is changed step-by-step; Qacc is expressed as a function Va. From the observed dataset of Qacc and Va, ΔQ and VOS are derived, where ΔQ is the degree of charge injection and VOS is the voltage drop within the OS layer caused by Va. The injection barrier at the OS/M2 interface can be evaluated from the plot of ΔQ as a function of VOS. In this study, two theoretical models for analyzing ACM data are developed using the Poisson–Boltzmann equation. On the one hand, the thermal equilibrium (TE) model reflects the TE process, in which charge evacuation simultaneously occurs at the INS/OS and OS/M2 boundaries. On the other hand, the non-thermal equilibrium (NTE) model assumes a two-step charge evacuation process at the interfaces: charge evacuation at the OS/M2 boundary occurs in the first step, followed by charge evacuation at the INS/OS boundary in the second step. The ACM data for condensers constituting pentacene and H2Pc are well reproduced by the TE and NTE models, respectively. The different behaviors of the two condensers can be attributed to the difference in their diffusion constants. [ABSTRACT FROM AUTHOR]