二维费密液体理论(Ⅲ)——输运性质和声传播特性

本文研究了二维费密液体的输运性质和声传播特性,得到了扩散系数、粘滞系数和热导率的微观表达式以及零声和第一声的有关结果。通过对碰撞积分的讨论,认为须用一系列弛豫时间参数来描述二维液体,这与在三维情形可用一个唯象参数来描述不同。 关键词：     

Transport properties of H–N2 mixtures

Transport coefficients (shear viscosity, volume viscosity, thermal conductivity, and mass and thermal diffusion coefficients) of H–N₂ mixtures in the dilute-gas limit have been calculated from the intermolecular potential in the temperature range 300–2000K using the classical trajectory method. The intermediate results pertaining to H–N₂ binary interactions are reported, mainly in terms of cross-section ratios. Cross-sections evaluated with the Mason–Monchick approximation yield very good results for this system, the largest deviations, about 2.5%, being observed for the thermal diffusion coefficient. The accuracy here of this approximation can primarily be attributed to a light H atom and a weakly non-spherical potential resulting in a high rotational collision number. Furthermore, we investigate to which H–N₂ cross-sections and their ratios the values of the mixture transport coefficients are most sensitive. Our results indicate that, for some cross-section ratios, reliance on universal correlations at high temperatures, often used in flame codes, can induce sizeable errors in the thermal conductivity coefficient and especially in the thermal diffusion coefficients. We also observed that the volume viscosity is particularly sensitive to the value of the cross-section for internal energy relaxation in H–N₂ collisions.     

Oscillations quantiques des coefficients de pouvoir thermoelectrique et de conductivite thermique: theorie et mesures dans Cd3As2

Quantum oscillations have been observed in the thermoelectric power and thermal conductivity coefficients of a semiconductor Cd₃As₂ single crystal. Theoretical expressions for these coefficients, taking into account the Landau level broadening, are derived in this paper. The good agreement found between the thermoelectric power measurements and the corresponding theoretical expressions for the temperature and magnetic field dependence of the quantum oscillation amplitudes and the absolute values of the amplitudes has allowed us to calculate effective mass values which are in agreement with Shubnikov-de Haas measurements.     

Microscopic transport theory of heavy-ion collisions

Analytical expressions for the diffusion coefficients for the transfer of neutrons and protons in a heavy-ion collision are derived. The mass diffusion coefficient implied by these two coefficients is compared with previous theoretical calculations and the values extracted from experiment for a variety of systems. Drift coefficients are related to the diffusion coefficients and the driving potential by the usual Einstein relations. On approximating the driving potential by a second-order form, the Fokker-Planck equation is solved analytically by the moment expansion method. A comparison of the predictions of this theory with a variety of recent experimental data gives generally good agreement. Thus we conclude that the experimental data currently available can be interpreted in purely statistical terms. Some deviations between theory and experiment indicate a possible influence of shell effects and/or direct transfer processes in the early stages of the reaction.     

A collisional approach to the calculation of time correlation functions. Transport coefficients of gases

A method of successive approximations is proposed for the evaluation of the time-correlation functions such as those that give the thermal transport coefficients of gases. The method is based on a calculation of the changes in correlations of appropriate functions of the molecular velocity which are a result of collisions in the gas. The decaying rates of the correlations are expressed as integrals of the differential collision cross section. When the first approximation is introduced in the expressions for thermal transport coefficients, results are obtained for the coefficient of binary diffusion and the viscosity and thermal conductivity of single-component systems which are identical with those of the first Chapman-Enskog solutions of the Boltzmann and Enskog equations. For the coefficients of viscosity and thermal conductivity in multicomponent systems, it is shown that the first approximation leads to expressions of the form of the Sutherland and Wassiljewa relations, respectively.     

Transport coefficients of quark-gluon plasma

Transport coefficients of quark-gluon plasma are discussed in the framework of relativistic kinetic theory with the relaxation time approximation of Boltzmann transport equation. The expressions for the coefficients of shear and volume viscosities and heat conductivity are derived assuming quark-gluon plasma to be a non-reactive mixture of quarks, anti-quarks and gluons. A lowest order in deviations from local thermal equilibrium and in plasma phase, lowest order in coupling constant are assumed. Entropy production due to irreversible processes is discussed.     

Thermal diffusion effects in hydrogen-air and methane-air flames

The influence of thermal diffusion on the structure of hydrogen-air and methane-air flames is investigated numerically using complex chemistry and detailed transport models. All the transport coefficients in the mixture, including thermal diffusion coefficients, are evaluated using new algorithms which provide, at moderate computational costs, accurate approximations derived rigorously from the kinetic theory of gases. Our numerical results show that thermal diffusion is important for an accurate prediction of flame structure.     

Kinetic theory of transport coefficients of a relativistic binary mixture

Within the framework of relativistic kinetic theory expressions are derived for the diffusion and thermal diffusion coefficient of a binary mixture.     

低温下粗糙表面接触间隙气体热导的研究

对低温非真空环境下粗糙接触界面间隙中介质气体的传热进行了理论分析．依据克努森数的大小,建立了不同传热区域的间隙气体热导理论模型．并对影响接触界面间隙热导的克努森数、普朗特数、热导率、适应系数、压力等参数进行了分析,为实际情况下接触界面的传热提供了理论基础．而且通过实验证明了在界面接触压力较小的情况下,即使对于硬度较小导热性能好的接触固体,间隙气体的导热量仍大于通过实际接触点的导热量．     

Green–Kubo relations for dynamic interfacial excess properties

In this paper we analyze the fluctuations of the in-plane interfacial excess fluxes in multiphase systems, in the context of the extended irreversible thermodynamics formalism. We derive expressions for the time correlation functions of the surface extra stress tensor, the surface mass flux vector, and the surface energy flux vector, and use these expressions to derive Green–Kubo relations for the surface shear viscosity, the surface dilatational viscosity, the surface diffusion coefficient, and the surface thermal conductivity. These Green-Kubo relations can be used to compute these excess transport coefficients using for example molecular dynamics simulations.     

A simultaneous electronic transition of the oxygen-naphthalene complex

Thorne's extension of the Enskog theory to thermal conductivity and viscosity of binary hard sphere fluid mixtures is examined. It is shown that for molecules of the same size and different mass the expression for the thermal conductivity of such a mixture obtained by Longuet-Higgins, Pople and Valleau is identical to the collisional term in Thorne's equation arising from the locally maxwellian velocity distribution. Thorne's equations are evaluated by using the Percus-Yevick approximation for the contact radial distribution functions obtained by Lebowitz. The variations of the transport coefficients are examined as functions of pressure, composition and ratios of diameters and masses of the two species. Some comparison is made with experimental results.     

两相复合材料有效热导率的理论推导

复合材料有效热导率的解析表达式一直是传热问题中人们想要解决的问题.本文选用合适的单元体,采用热阻模型和积分平均方法,分别对分散相为球体和圆柱体的两相复合材料的有效热导率进行了推导.对于多孔复合材料,当孔隙率较大或温度较高时辐射换热的影响不能忽略,本文分析了气孔为球体或圆柱体时辐射换热对其有效热导率的影响.将计算所得有效热导率与相关实验数据进行了比较,结果表明两者吻合较好,证明了公式的准确性.     

On the validity of magnetohydrodynamics for ionic mixtures

The collective mode spectrum of the magnetized ionic mixture consisting ofs components is studied by starting from the microscopic balance equations and the fluctuation formulas for the microscopic densities. Apart from a heat mode ands-1 diffusion modes with frequencies of second order in the wavenumber, four modes with complex finite frequencies for vanishing wavenumber are found. If the mixture consist of particles with equal ratios of charge and mass, these four modes become similar to the gyroplasmon modes of the magnetized one-component plasma of which the frequencies are real in lowest order in the wavenumber. Green-Kubo relations are derived for the transport coefficients which appear in the frequencies of the heat mode and the diffusion modes. The long-time behavior of the integrands of the Green-Kubo expressions is evaluated with the help of mode-coupling theory. The static transport coefficients are found to be finite unless the mixture consists of species with equal ratios of charge and mass. It is concluded that the presence of species with different charge-mass ratios is essential for the validity of magnetohydrodynamics for an ionic mixture.     

Correlation effects in the diffusion and electrical conductivity of an interacting lattice gas

A simple and effective self-consistent scheme is proposed for the determination of the average potentials which allows thermodynamic functions and other characteristics of lattice systems in equilibrium to be calculated with high accuracy and short computing time. This scheme has been used for analysis of the expressions for the coefficients of diffusion and electrical conductivity obtained on the basis of the modern statistical theory of nonequilibrium processes. Results of the simulations are correlated with the data of Monte Carlo simulations obtained using parallel vector algorithms on a Cray TZE computer of the Max Plank Society (Germany).     

气体在平行平板间微槽内的二维层流换热

在已求得贴壁层内气体粘度和导热系数变化的基础上,求解了微槽内气体完全发展的二维层流换热．得到两表面等热流、且ｑ１＝ｑ２＝ｑ以及一表面等热流、另一表面绝热条件下的温度分布和对流换热系数．     

Diffusion and thermal diffusion in binary mixtures of sulphur hexafluoride with noble gases

Diffusion coefficients and thermal diffusion factors are reported for binary mixtures of sulphur hexafluoride with noble gases. The results are compared with theoretical values calculated by means of the Chapman-Enskog theory, spherical potentials for the like interactions and multi-parameter anisotropic potentials for the unlike interactions.     

A theoretical relation between viscosity and thermal conductivity of gases based on macroscopic balance equations

Classical theoretical methods for estimation of viscosity and thermal conductivity of gases are based on the kinetic theory and on the corresponding-state methods. By means of these methods, approximate relations between viscosity and thermal conductivity can be formulated. In this paper, a theoretical relation between viscosity and thermal conductivity based on the macroscopic balance equations is derived using the van der Waals equation of state for calculating density. The new developed relation, which is an analogy to the Eucken formula, is tested on computing viscosity of eight arbitrarily chosen non-polar gases in wide temperature and pressure ranges. Comparison with experimental data shows an agreement better than 5% which is within the margin of experimental errors. This agreement with the measured values for all the studied gases is either better than or equal to that of the three most often used theoretical methods.     

Thermal cellular automata fluids

The concepts of local temperature and local thermal equilibrium are introduced in the context of lattice gas cellular automata (LGGAs) whose dynamics conserves energy. Green-Kubo expressions for thermal transport coefficients, in particular for the heat conductivity, are derived in a form, equivalent to those for continuous fluids. All thermal transport coefficients are evaluated in Boltzmann approximation as thermal averages of matrix elements of the inverse Boltzmann collision operator, fully analogous to the results for continuous systems, and fully model-independent. The collision operator is expressed in terms of transition probabilities between in- and out-states. Staggered diffusivities arising from spuriously conserved quantities in LGCAs are also calculated. Examples of models with either cubic or hexagonal symmetries are discussed, where particles may or may not have internal energies.     

Yb:CaF2-SrF2激光晶体光谱性能以及热学性能的研究

采用坩埚下降法生长了Yb: CaF₂-SrF₂晶体,测试了该晶体的吸收和荧光光谱 以及在不同温度下晶体的热扩散系数和热膨胀系数,并且计算了晶体的热膨胀系数以及在常温下的热导率. 采用对比的方法,对晶体的吸收光谱,荧光光谱,热学性能进行了分析.从吸收和荧光光谱结果表明: 在掺杂相对较高浓度的SrF₂的混晶中, Yb³⁺吸收截面和发射截面比较大. Yb: CaF₂-SrF₂ (19%)晶体在1040 nm附近的发射截面比较大,光谱也比较宽. 这说明在掺杂相同浓度Yb时,混晶中CaF₂, SrF₂的比例不同,晶体的光谱性质不同, 主要原因是在混晶中晶体的无序度不同,晶体对称性降低,形成低对称光学中心. 从热扩散系数计算的热导率结果看出晶体具有比较好的热导率.     

场反向箍缩位形的电阻性互换不稳定性及其对能量约束性能的影响

本文解析研究了电阻性互换不稳定性的湍性行为和它所引起的电子热传导及其所带来的场反向箍缩能量约束性能下降的情形。对于两种不同的模宇称计算了磁场饱和涨落水平,并由此求得了磁颤动扩散系数及碰撞区、非碰撞区的热传导系数。得到了能量约束时间的定标律。 关键词：