关于热的输运过程的动力学理论

本文由温度不同之平衡系统引入温度差的概念,以其边界接触作用为微扰,对热的输运过程进行了动力学的讨论。得到了热导系数的准确表示式。对于体积大的均匀系统,所得的公式简化为Kubo的公式。     

量子统计中的线性输运系数理论

本文利用van Hove的趋向平衡理论讨论了Kubo的输运系数表达式,得到了没有任何无规相位假设的结果,并将其与玻耳兹曼方程作了比较。由本文的讨论,我们期望在强作用系统的高频现象中能观测到相位关联效应。高频线性输运系数的宏观测量不会破坏这种相位关联。 关键词：     

等离子体在均匀强磁场中的横向输运系数

本文利用Kubo型线性输运系数公式和Landau表象计算了等离子体在强磁场中的扩散系数、热导率和粘滞系数。和以往解Boltzmann方程的方法相比,本文所用方法有如下优点:在处理强磁场、多体长程相互作用体系时没有原则上的困难;物理图象简单、清晰;在准确到相互作用的二次项时,不用解输运方程就能得到上述的横向输运系数的解析表达式。本文结果和用Chapman-Enskog法解线性Boltzlmann方程时得到的数值结果基本相符而略有不同,在对离子电荷数Z的依赖关系上则有较明显的不同。     

用子动力学理论研究介观体系的输运——电导响应函数的计算

从子动力学理论出发,计算了介观体系的输运公式,得到了包含高阶修正的Kubo公式,这对于任意外场的作用下的介观体系具有重要的意义。     

用子动力学理论研究介观体系的输运

从子动力学理论出发,计算了介观体系的输运公式,得到了包含高阶修正的Kubo公式,这对于任意外场的作用下的介观体系具有重要的意义     

用软X射线成像观察HL-2A装置中的杂质注入过程

激光吹气是主动性研究等离子体内部杂质输运的最佳方法之一。杂质的注入用杂质粒子流表示 Г=-DVn＋Lvn 式中，D为输运系数，V为对流速度。激光吹气实验可在放电中选择不同时段注入可控量的杂质。由于杂质注入量很小且附加脉冲信号持续时间很短，等离子体电流和温度都没有明显扰动。杂质约束时间可根据中心道信号衰减时间来计算。     

在弛豫时间近似下QGP中夸克输运系数的一种计算

从动力论方程出发,考虑QGP中平均场效应,采用弛豫时问近似,给出了关于QGP输运系数的一种分析方法,推导出QGP中夸克输运系数解析式,讨论了QGP粘滞效应与导热效应.     

超越阿贝尔优势近似和色等离子体的输运系数计算

给出了一种超越阿贝尔优势近似求解夸克胶子等离子体输运方程的方法，并用它计算了夸克、反夸克等离子体的输运系数，讨论了输运系数的非阿贝尔修正．     

电激励Ne-Xe-HCl混合物的电子能量分布函数和输运系数

用解波尔兹曼输运方程的方法计算了电激励Ne-Xe-HCl混合物的电子能量分布函数和有关的输运系数,并对计算结果作了讨论。     

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用密度调制的方法研究了等离子体中粒子输运问题。采用了注入脉冲式补充送气和超声分子束两种不同的密度调制方法。在HL-2A装置常规欧姆放电的情况下,运用有限差分法和Nagashima矩阵技术,求解了粒子平衡方程。计算出了粒子的输运系数(对流速度v和扩散系数D)。研究了粒子输运系数与等离子体线平均密度之间的关系。实验结果表明,在欧姆放电的情况下,等离子体芯部的粒子对流速度方向始终是向内的,并且密度低时,粒子输运系数(粒子扩散系数D和对流速度v)较大;密度高时,粒子输运系数较小。     

Dynamic critical behavior of semi-infinite systems: the study of the model C

The dynamic critical behavior of semi-infinite model C near the special and ordinary transitions is investigated using field theoretic renormalization-group approach. It is shown that the dynamic surface quantities have different critical behavior aginst their bulk analogues and their scaling laws can be expressed entirely in terms of static (bulk and surface) exponents and dynamic exponents. It is found that at the critical point the surface transport coefficient reaches a finite value via a cusplike singularity and the surface-bulk transport coefficient diverges, but the bulk transport coefficient remains finite as that of the infinite model C.     

关于强磁场下输运过程的附注

这篇短文是对论文[1]的补充,同时也是对论文[2]中一些论点的答复,我们强调的一点是在久保公式中首先令ν→∞,然后令△t→∞,就会得到正确的输运系数,依据趋近平衡的理论来表达输运系数能使之充分确定,而在力学形式体系中它是不确定的,并且指出在输运理论中引进宏观流算符是不必要的。 关键词：     

Observation of dirac holes and electrons in a topological insulator

We show that in the new topological-insulator compound Bi(1.5)Sb(0.5)Te(1.7)Se(1.3) one can achieve a surfaced-dominated transport where the surface channel contributes up to 70% of the total conductance. Furthermore, it was found that in this material the transport properties sharply reflect the time dependence of the surface chemical potential, presenting a sign change in the Hall coefficient with time. We demonstrate that such an evolution makes us observe both Dirac holes and electrons on the surface, which allows us to reconstruct the surface band dispersion across the Dirac point.     

On Island Formation in a Locally Perturbed Tokamak Equilibrium

To control the plasma transport at the edge of a tokamak the outer flux surfaces can be artificially destroyed by applying a resonant helical magnetic field, as it is demonstrated at Pulsator [1],[2], [3], Tore Supra [4],[5] and proposed for TEXTOR-94 [6] in the concept of “ergodic divertors”. As a measure of the efficiency of the perturbation field e.g. the level of the field line diffusion coefficient DFL the width Δ_i of the magnetic islands and the related Chirikov parameter are of importance [7],[8],[9],[10]. For the planned Dynamic Ergodic Divertor (DED) at TEXTOR-94 where the perturbation coils are located at the high field side the standard expression for Δ_i using the Fourier components of the magnetic field perturbation [7] leads to results significantly different from field line tracing calculations [11]. The standard expression is commonly used in terms of the perturbation magnetic field δB [5],[7],[8],[9],[12],[13]. But when replacing the Fourier components of the perturbation vector potential by those of the magnetic field finite aspect ratio effects have been neglected so far. For present tokamaks with ? = r/R ? 0.3 this can lead to an error in the field line diffusion of one to two orders of magnitude. In this paper it is shown that taking into account the finite aspect ratio at this point leads to correct results compared to the highly precise field line tracing calculations by the Gourdon code. The island width then is recognized to depend significantly on the poloidal position of the perturbation field. This is in contrast to the standard expression. Also the role of the choice of the magnetic coordinate system is considered.     

Observation of velocity-independent electron transport in the reversed field pinch

Confinement of runaway electrons has been observed for the first time in a reversed field pinch during improved-confinement plasmas in the Madison Symmetric Torus. Energy-resolved hard-x-ray flux measurements have been used to determine the velocity dependence of the electron diffusion coefficient, utilizing computational solutions of the Fokker-Planck transport equation. With improved-confinement, the fast electron diffusivity drops by 2 orders of magnitude and is independent of velocity. This suggests a change in the transport mechanism away from stochastic magnetic field diffusion.     

对称双势垒量子阱中自旋极化输运的时间特性

电子的隧穿时间是描述量子器件动态工作范围的重要指标. 本文考虑k³ Dresselhaus 自旋轨道耦合效应对系统哈密顿量的修正, 结合转移矩阵方法和龙格-库塔法来解含时薛定谔方程, 进而讨论了电子在非磁半导体对称双势垒结构中的透射系数及隧穿寿命等问题. 研究结果发现:由于k³ Dresselhaus 自旋轨道耦合效应使自旋简并消除, 并在时间域内得到了表达, 导致自旋向上和自旋向下电子的透射峰发生了自旋劈裂; 不同自旋取向的电子构建时间和隧穿寿命不同, 这是导致自旋极化的原因之一; 电子的自旋极化在时间上趋于稳定. 关键词： 自旋极化输运 透射系数 隧穿寿命 自旋极化率     

Dynamics of the universe with disformal coupling between the dark sectors

We use a dynamical analysis to study the evolution of the universe at late time for the model in which the interaction between dark energy and dark matter is inspired by a disformal transformation. We extend the analysis in the existing literature by assuming that the disformal coefficient depends both on the scalar field and its kinetic terms. We find that the dependence of the disformal coefficient on the kinetic term of scalar field leads to two classes of the scaling fixed points that can describe the acceleration of the universe at late time. The first class exists only for the case where the disformal coefficient depends on the kinetic terms. The fixed points in this class are saddle points unless the slope of the conformal coefficient is sufficiently large. The second class can be viewed as the generalization of the fixed points studied in the literature. According to the stability analysis of these fixed points, we find that the stable fixed point can take two different physically relevant values for the same value of the parameters of the model. These different values of the fixed points can be reached for different initial conditions for the equation of state parameter of dark energy. We also discuss the situations in which this feature disappears.     

Generalized reference fields and source interpolation for the difference formulation of radiation transport

In the difference formulation for the transport of thermally emitted photons the photon intensity is defined relative to a reference field, the black body at the local material temperature. This choice of reference field combines the separate emission and absorption terms that nearly cancel, thereby removing the dominant cause of noise in the Monte Carlo solution of thick systems, but introduces time and space derivative source terms that cannot be determined until the end of the time step. The space derivative source term can also lead to noise induced crashes under certain conditions where the real physical photon intensity differs strongly from a black body at the local material temperature.In this paper, we consider a difference formulation relative to the material temperature at the beginning of the time step, or in cases where an alternative temperature better describes the radiation field, that temperature. The result is a method where iterative solution of the material energy equation is efficient and noise induced crashes are avoided. We couple our generalized reference field scheme with an ad hoc interpolation of the space derivative source, resulting in an algorithm that produces the correct flux between zones as the physical system approaches the thick limit.     

Light Absorption by Impurity Structures with Quantum Points in an External Magnetic Field

The light absorption by the quantum point - impurity center complex in an external quantizing magnetic field is studied in the effective mass approximation for the model of zero-radius potential. An expression for the absorption coefficient of light having longitudinal polarization by an impurity is derived when the influence of the magnetic field on the ground state of the impurity at the quantum point can be neglected. It is demonstrated that the edge of the absorption band of the impurity is shifted toward shorter wavelengths with increasing magnetic field strength. In this case, the absorption coefficient increases several times, which is interpreted as the effect of magnetic freezing-in of the ground state of the quantum point.     

Benchmark calculations for Monte Carlo simulations of electrontransport

Benchmark calculations have been performed for electron transport coefficients with an aim to produce a body of data required to verify the codes used in plasma modeling. The present code for the time resolved Monte Carlo simulation (MCS) was shown to represent properly DC transport coefficients in a purely electric field, in crossed electric and magnetic fields, and in the presence of nonconservative collisions, ionization, and attachment. In addition, we have suggested tests of the time dependent solutions. Relaxation of the initial transport coefficient may serve as an accurate test of the code as well as the input data for some fluid codes. In this paper, we show only one example, but several different sets of conditions and cross sections should be used as well. Finally, we propose application of the quasi-steady state results in RF fields. As an example we suggest calculation of the components of diffusion tensor showing anomalous longitudinal diffusion and calculations made with nonconservative collisions (ionization in this case). We also check the application of approximate formulas to determine drift velocity on the basis of total collision frequency and to determine a diffusion coefficient by using the Einstein relation. Other tests required to verify the transport data calculations are discussed as well