Changes in the structural phase state and elastic and inelastic properties of superplastic eutectic Sn-38% wt Pb alloy during the aging process

We investigate how the dynamic Young’s modulus E and decrement δ change due to the compression and natural aging of eutectic Sn-38% wt Pb alloy, which exhibits superplastic properties at room temperature. We also study how the structural phase state of the alloy changes due to compression and natural aging. The revealed peculiarities of elastic and inelastic behavior are associated with the initial phase non-equilibrium state of the alloy and the internal stresses in the samples.     

辐射场非平衡性对CH薄膜烧蚀特性的影响

 为研究辐射场非平衡性对ICF内爆靶丸辐射烧蚀效果的影响,在普朗克谱的高频区（Au的M带）叠加高斯谱人为地构造辐射源的能谱,利用1维多群辐射输运流体力学程序RDMG模拟CH薄膜的烧蚀过程,考察烧蚀压、预热、压缩比、冲击波速度等物理量受辐射场非平衡性的影响。模拟结果表明,Au的M带辐射有明显的增强预热、减小冲击波压缩比的作用,从而间接地影响了烧蚀冲击波的速度。     

稀薄气体流动非线性耦合本构关系研究进展

临近空间高超声速飞行器流场蕴含着复杂的非线性流动机理与丰富的热化学非平衡流动现象, 基于Newton摩擦定律和Fourier热传导定律的Navier-Stokes(N-S)方程不足以描述高超声速飞行器从连续流到稀薄流的多尺度非平衡现象。非线性耦合本构关系(nonlinear coupled constitutive relations, NCCR)作为一种全新的本构方程体系, 在严格满足热力学熵条件的基础上, 巧妙地构建了应力与热流的非线性表达形式。然而, NCCR方程的强非线性耦合特性是求解过程的一大难题。为了克服这一技术瓶颈, 提出了混合迭代算法, 为实现NCCR方程的高效稳定求解提供了坚实的理论基础。在该理论研究的基础上, 考虑到原始NCCR方程对热通量演化方程的简化处理, 降低了方程的计算精度, 提出了改进的NCCR+方程。该方程在强激波压缩区域和膨胀区域表现出比传统NCCR方程更高的计算精度与更强的非平衡流动模拟能力。同时, 为了解决临近空间高超声速空气动力学的多尺度与多物理效应耦合难题, 提出了NCCR与转动非平衡的耦合计算模型, 拓展了NCCR方程在双原子气体中的模拟能力。为了揭示稀薄气体效应与真实气体效应的耦合作用机理, 进一步建立了NCCR与热化学反应的耦合计算方法。大量研究结果表明, 考虑多物理效应的NCCR方程在低Kn下能够恢复到与N-S方程一致的解。随着Kn的增加, 流场的非平衡程度逐渐增强, 其结果与N-S方程差异显著, 而与DSMC方法计算结果和实验数据具有更好的一致性。      

<Emphasis Type="Italic">β</Emphasis>-distribution for Reynolds stress and turbulent heat flux in relaxation turbulent boundary layer of compression ramp

A challenge in the study of turbulent boundary layers (TBLs) is to understand the non-equilibrium relaxation process after sep-aration and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model.     

Rotational energy conversion and thermal evolution of neutron stars

Pulsars are rapidly spinning, strongly magnetized neutron stars. Their electromagnetic dipole radiation is usually assumed to be at the expense of the rotational energy. In this work, we consider a new channel through which rotational energy could be radiated away directly via neutrinos. With this new energy conversion channel, we can improve the chemical heating mechanism that originates in the deviation from β equilibrium due to spin-down compression. The improved chemical and thermal evolution equations with different magnetic field strengths are solved numerically. The results show that the new energy conversion channel could raise the surface temperature of neutron stars, especially for weak field stars at later stages of their evolution. Moreover, our results indicate that the new energy conversion channel induced by the non-equilibrium reaction processes should be taken into account in the study of thermal evolution.     

从头算方法研究面心立方铝在高温高压下的热力学状态方程

用从头算方法优化计算了面心立方铝的电子结构和总能,得到了它在零温下的状态方程和弹性性质.将得到的总能与晶格体积拟合到Debye模型,获得了非平衡态下的Gibbs自由能与温度、压力之间的关系,在此基础上计算了相应的热状态方程,利用Burakovsky-Preston-Silbar （BPS） 熔化模型计算了铝的熔化曲线.所有的电子结构和总能计算都是基于局域密度近似（LDA）和广义梯度近似（GGA）的平均得到的.计算得到的铝在高温、高压下的状态方程与一些热力学性质和熔化曲线同冲击波和静高压实验数据在225 G 关键词： 铝 热力学状态方程 从头算 熔化曲线     

Raman probe studies of Nd: YAlG laser generated non-equilibrium excitations in GaAs

A survey is presented of the non-equilibrium excitations in GaAs that can be probed by Raman scattering. Intense Q-switched Nd:YAlG laser pulses are used both for generating the non-equilibrium excitations at low temperature, and for in-situ Raman scattering probe measurements. Particular emphasis is placed on the search for non-equilibrium, zone-edge slow TA phonons. We discovered that the difference frequency combination spectrum involving slow TA phonons is surprisingly coincident with the acceptor excitation line spectrum for the Zn impurity. The discrimination between the non-equilibrium phonon population and a non-equilibrium hole population on minority acceptors in n-GaAs is discussed.     

Discussions on the non-equilibrium effects in the quantitative phase field model of binary alloys

All the quantitative phase field models try to get rid of the artificial factors of solutal drag,interface diffusion and interface stretch in the diffuse interface.These artificial non-equilibrium effects due to the introducing of diffuse interface are analysed based on the thermodynamic status across the diffuse interface in the quantitative phase field model of binary alloys.Results indicate that the non-equilibrium effects are related to the negative driving force in the local region of solid side across the diffuse interface.The negative driving force results from the fact that the phase field model is derived from equilibrium condition but used to simulate the non-equilibrium solidification process.The interface thickness dependence of the non-equilibrium effects and its restriction on the large scale simulation are also discussed.     

Non-equilibrium 2PI potential and its possible application to evaluation of bulk viscosity

Within non-equilibrium Green’s function technique on the real-time contour and the two-particle irreducible Φ-functional method, a non-equilibrium potential is introduced. It naturally generalizes the conventional thermodynamic potential with which it coincides in thermal equilibrium. Variations of the non-equilibrium potential over respective parameters result in the same quantities as those of the thermodynamic potential but in arbitrary non-equilibrium. In particular, for slightly non-equilibrium inhomogeneous configurations a variation of the non-equilibrium potential over volume is associated with the trace of the non-equilibrium stress tensor. The latter is related to the bulk viscosity. This provides a novel way for evaluation of the bulk viscosity.     

Particle-particle correlation and fluctuations in non-equilibrium Fermi/Bose gases

A theory of fluctuations and correlations in non-equilibrium Fermi and Bose gases is developed. A specific quantum correlation is predicted in non-equilibrium collisional quasi-classical gases, created by collisions between particles. The expressions for correlation sources entering the equation for an equal-time two-particle correlation function are obtained and analyzed. The expressions are valid for arbitrary particle-particle interaction potentials. The possibility of display of the quantum correlation in the macroscopic characteristics of fluctuation phenomena in non-equilibrium gases (e.g., current fluctuations in semiconductors) is discussed. A comparison with correlations in a Lorentz gas is made.     

The “harmonic liquid” away from equilibrium: I. Stationary correlation functions

Some aspects of the linear chain of harmonic oscillators (“harmonic liquid”) are studied. In particular we compute the stationary correlation functions of coordinates and momenta of the oscillators for a particular non-equilibrium steady state. We find that the coordinates and momenta autocorrelation functions are analogous to their equilibrium counterparts whereas the coordinates-momenta correlation functions exhibit long-range behaviour due to time reversal symmetry breaking. The non-equilibrium entropy of the chain is also computed. It contains a non-equilibrium part that depends on the temperature of the external sources and on the stationary temperature. A comparison with a non-equilibrium entropy obtained from information theory is made.     

Benford’s law in non-equilibrium processes: Droplet collisions case

Benford’s law is investigated for the simulation results generated from non-equilibrium molecular dynamics. A statistic to measure how closely a set of the numbers follows Benford’s law is defined. The simulation data are from the collisions of two nano droplets with different impact velocities. When a non-equilibrium system returns to its equilibrium state, some physical quantities relevant to the non-equilibrium settings follow Benford’s law more closely. The initial settings for the non-equilibrium state can be interpreted as a data fabrication of its corresponding equilibrium state. A connection with the Shannon entropy for the first digit distribution is also discussed.     

Statistical physics of shear flow: a non-equilibrium problem

Complex fluids are easily and reproducibly driven into non-equilibrium steady states by the action of shear flow. The statistics of the microstructure of non-equilibrium fluids is important to the material properties of every complex fluid that flows, e.g. axle grease on a rotating bearing; blood circulating in capillaries; molten plastic flowing into a mould; the non-equilibrium onion phase of amphiphiles used for drug delivery; the list is endless. Such states are as diverse and interesting as equilibrium states, but are not governed by the same statistics as equilibrium materials. I review some recently discovered principles governing the probabilities of various types of molecular re-arrangements taking place within a sheared fluid. As well as providing new foundations for the study of non-equilibrium matter, the principles are applied to some simple models of particles interacting under flow, showing that the theory exhibits physically convincing behaviour.     

Non-equilibrium phenomena and molecular reaction dynamics: mode space,energy space and conformer space

The ability to characterise and control matter far away from equilibrium is a frontier challenge facing modern science. In this article, we sketch out a heuristic structure for thinking about the different ways in which non-equilibrium phenomena can impact molecular reaction dynamics. Our analytical schema includes three different regimes, organised according to increasing dynamical resolution: at the lowest resolution, we have conformer phase space, at an intermediate resolution, we have energy space; and at the highest resolution, we have mode space. Within each regime, we discuss practical definitions of non-equilibrium phenomena, mostly in terms of the corresponding relaxation timescales. Using this analytical framework, we discuss some recent non-equilibrium reaction dynamics studies spanning isolated small-molecule ensembles, gas-phase ensembles and solution-phase ensembles. This includes new results that provide insight into how non-equilibrium phenomena impact the solution-phase alkene–hydroboration reaction. We emphasise that interesting non-equilibrium dynamical phenomena often occur when the relaxation timescales characterising each regime are similar. In closing, we reflect on outstanding challenges and future research directions to guide our understanding of how non-equilibrium phenomena impact reaction dynamics.     

Some topological properties of the kinetic modeling of a non-equilibrium system

The topological properties of the kinetic modeling of a non-equilibrium system, which are due to the inhomogeneity of the structure of its energy spectrum, are considered. In particular, it was shown that the layered structure of the energy spectrum of a non-equilibrium system can be interpreted from a topological point of view as the incoherence of the energy spectra of its quasi-equilibrium subsystems. The possibility of using the Riemann and the scalar curvature of the hypersurface of the total entropy production as local and global characteristics of the non-equilibrium state of the system is shown.     

The dependence of electronic transport on compressive deformation of C60 molecule

The dependence of electronic transport on compressive deformation of C₆₀ molecule is studied theoretically in this work. Brenner's “second generation” empirical potential is used to describe the many-body short-range interatomic interactions for C₆₀ in the molecular dynamics simulations. Our results demonstrate that C₆₀ can be compressed up to a strain ε=0.31 before collapsing. Electronic transport under an applied bias is calculated by using a self-consistent field approach coupled with non-equilibrium Green's function (NEGF) formalism. The transmission probability, conductance gap, and conductance spectrum are found to be sensitive to the compression. The peak value of conductance decreases with the increase of strain until the C₆₀ is compressed up to a strain ε=0.31.     

Relativistic heavy-ion collisions: An approach based on non-equilibrium thermodynamics

A new theory of particle production in high energy collisions is proposed which is based on non-equilibrium thermodynamics. The non-equilibrium model is a major extension of the equilibrium thermodynamic model of relativistic heavy-ion collisions developed earlier. While the equilibrium thermodynamic theory is appropriate for the formation of light nuclei and for pions, the non-equilibrium theory applies to the creation of particles heavier than the pion, which include such particles as the strange mesons, strange baryons and the anti-nucleons. Using an approach based on the degree of the reaction of kinetic theory, the time evolution of the composition of hadronic systems in incomplete equilibrium is investigated. Densities of produced particles are related to space-time quantities and to the production cross sections of the underlying dynamic processes. An application of the non-equilibrium approach to the production of strange matter is given. The importance of secondary processes, following pion production, in the formation of strange matter is shown. In fact, the secondary production process for kaons is as important as the direct production process arising from initial nucleon-nucleon (NN) collision of a first collision picture. Thus, kaons can be produced in a late stage of the collision of two nuclei and they do not necessarily reflect the early stages of the collision as first thought. Using the experimental number of kaons, the time of reaction is also estimated. No evidence for a long-lived state of the nuclear system is found. Expressions for particle production ratios are developed. The results of an equilibrium theory and a non-equilibrium theory are found to be similar for such ratios. The chemical equilibrium constant is shown to be present in the non-equilibrium theory; the Boltzmann factor in the production threshold energy appears in the equilibrium theory. The K^?/K⁺ ratio is estimated. Surprisingly, reasonable agreement with experiment is found in the K^?/K⁺ ratio using the equilibrium theory, even though the production processes for K⁺'s and K^?'s treated individually, are not ones for which the equilibrium theory applies. It is shown that a fundamental difference between the equilibrium and non-equilibrium theory is lost when particle ratios for non-equilibrium particles are taken. Expressions for the production of complex composite structures made of strange particles are developed. The non-equilibrium model with some modifications may be useful for high energy NN and pion-nucleon collisions.     

基于格子Boltzmann方法的超声速非平衡流模拟

基于D1Q4可压缩格子Boltzmann模型,按照流通矢量分裂方法的思路,采用坐标旋转技术构造求解三维带化学反应Navier-Stokes方程对流通量求解器.结合有限体积法求解三维化学非平衡流Navier-Stokes方程,采用时间算子分裂算法解决化学反应刚性问题,数值模拟超声速化学非平衡流的三个经典算例.数值结果表明:在高马赫数下,采用D1Q4可压缩格子Boltzmann模型构造的三维对流通量求解器数值模拟中没有出现非物理解,同时在超声速化学非平衡流场中正确分辨激波、燃烧波等物理现象,精度和分辨率均较高,验证了本文构造的三维对流通量求解器的可靠性,拓宽了D1Q4可压缩格子Boltzmann模型的应用范围,为计算超声速化学非平衡流提供一种新方法.