自旋1/2非对易朗道问题的Wigner函数(英文)

Wigner函数在对量子体系状态的描述方面具有重要的意义。 讨论了自旋1/2非对易朗道问题的Wigner函数。首先回顾了对易空间中Wigner函数所服从的星本征方程, 然后给出了非对易相空间中自旋1/2朗道问题的Hamiltonian, 最后利用星本征方程（Moyal 方程）计算了非对易相空间中自旋1/2朗道问题具有矩阵表示形式的Wigner函数及其能级。With great significance in describing the state of quantum system, the Wigner function of the spin half non commutative Landau problem is studied in this paper. On the basis of the review of the Wigner function in the commutative space, which is subject to the *eigenvalue equation, Hamiltonian of the spin half Landau problem in the non commutative phase space is given. Then, energy levels and Wigner functions in the form of a matrix of the spin half Landau problem in the non commutative phase space are obtained by means of the _*-eigenvalue equation (or Moyal equation).     

Zur Frage der Landau-Dämpfung im anisotropen Plasma

Starting from a wellknown form of the dispersion equation in quasistatic approximation some expressions for the Landau damping in anisotropic electron plasmas are derived. For special distribution functions they are of the form given by Jackson for a plasma without magnetic field. The essential part of the general stability criterion is derived. Using the Dawson model for Landau damping we obtain exactly the above expressions.     

The Landau Equation in a Periodic Box

 The Landau equation, which was proposed by Landau in 1936, is a fundamental equation to describe collisions among charged particles interacting with their Coulombic force. In this article, global in time classical solutions near Maxwellians are constructed for the Landau equation in a periodic box. Our result also covers a class of generalized Landau equations, which describes grazing collisions in a dilute gas. Received: 4 February 2002 / Accepted: 10 July 2002 Published online: 29 October 2002     

Electron oscillations in a plasma: Effect of collisions on Landau damping

Summary Electron oscillations in a plasma are analysed starting from the integral form of Boltzmann-Vlasov equation. The effects of collisions on Landau damping are shown. The conditions for Landau damping existence are derived.

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Riassunto Onde elettrostatiche in un plasma sono studiate ricorrendo alla forma integrale dell'equazione di Boltzmann-Vlasov. In particolare, sono stati evidenziati gli effetti prodotti sul Landau damping dalle collisioni. Si è ricavato che in certe condizioni le collisioni possono impedire il Landau damping e si sono ottenuti i valori di soglia.

     

Lorentz-covariant dissipative lagrangian systems

The concept of dissipative hamiltonian system is converted to Lorentz-covariant form, with evolution generated jointly by two scalar functionals, the lagrangian action and the global entropy. A bracket formulation yields the local covariant laws of energy-momentum conservation and of entropy production. The formalism is illustrated by a derivation of the covariant Landau kinetic equation.     

New solution of the Landau kinetic equation for the energy loss of fast particles in crystals

A solution of the Landau kinetic equation for the energy loss of fast particles in crystals has been constructed in the form of a series, each term of which corresponds to the Gaussian distribution. The calculated results are compared with the experimental ones.     

Phase transitions in shape memory alloys: A non-isothermal Ginzburg–Landau model

We propose a model to describe non-isothermal transitions from the austenite to the martensite phase occurring in shape memory materials. The phenomenon is set in the context of the Ginzburg–Landau theory of phase transitions, postulating a free energy depending on the temperature, the stress and the order parameter. In the one-dimensional case, when only two martensitic variants are involved and stress and deformation have a fixed direction, our choice of free energy allows us to deduce a phase diagram describing the main features of a typical SMA. The Ginzburg–Landau equation ruling the evolution of the order parameter is coupled with the equations of thermoelasticity by assuming a constitutive equation relating stress, strain and order parameter. The consistency of the model with the second law of Thermodynamics in the form of the Clausius–Duhem inequality is proved. Finally a possible generalization to a three-dimensional model is proposed, by introducing a tensor-valued order parameter.     

Nonlinear Rayleigh–Taylor instability of the cylindrical fluid flow with mass and heat transfer

The nonlinear Rayleigh–Taylor stability of the cylindrical interface between the vapour and liquid phases of a fluid is studied. The phases enclosed between two cylindrical surfaces coaxial with mass and heat transfer is derived from nonlinear Ginzburg–Landau equation. The F-expansion method is used to get exact solutions for a nonlinear Ginzburg–Landau equation. The region of solutions is displayed graphically.     

Brownian motion in a quantizing magnetic field

A model previously discussed by the author to study Brownian motion of charged carriers in a quantizing magnetic field is extended to include a Landau level-dependent friction parameter. A phase-space Fokker-Planck equation is used to derive a generalized diffusion equation describing spatial diffusion of the carriers, coupled with random jumps between adjacent Landau levels. This partial differential-difference equation is solved analytically. The longitudinal “global” diffusion coefficient is calculated and shown to be enhanced over the value in the extreme quantum limit.     

Convergence from Boltzmann to Landau Processes with Soft Potential and Particle Approximations

Our aim in this paper is to show how a probabilistic interpretation of the Boltzmann and Landau equations gives a microscopic understanding of these equations. We firstly associate stochastic jump processes with the Boltzmann equations we consider. Then we renormalize these equations following asymptotics which make prevail the grazing collisions, and prove the convergence of the associated Boltzmann jump processes to a diffusion process related to the Landau equation. The convergence is pathwise and also implies a convergence at the level of the partial differential equations. The best feature of this approach is the microscopic understanding of the transition between the Boltzmann and the Landau equations, by an accumulation of very small jumps. We deduce from this interpretation an approximation result for a solution of the Landau equation via colliding stochastic particle systems. This result leads to a Monte-Carlo algorithm for the simulation of solutions by a conservative particle method which enables to observe the transition from Boltzmann to Landau equations. Numerical results are given.     

Ion-acoustic soliton-like waves undergoing Landau damping

Effects of Landau damping on ion-acoustic soliton-like waves are investigated experimentally and numerically. Landau damping is enhanced by increasing the ion temperature in the experiments. A ramp which is composed of resonant ions is observed in front of a soliton-like wave. The ramp is also seen in numerical simulations of an extended Korteweg–de Vries equation with a term of Landau damping. Experimental results of the height of the ramp are found to agree with numerical ones.     

Micromagnetic simulation of thermally activated switching in fine particles

Effects of thermal activation are included in micromagnetic simulations by adding a random thermal field to the effective magnetic field. As a result, the Landau–Lifshitz equation is converted into a stochastic differential equation of Langevin type with multiplicative noise. The Stratonovich interpretation of the stochastic Landau–Lifshitz equation leads to the correct thermal equilibrium properties. The proper generalization of Taylor expansions to stochastic calculus gives suitable time integration schemes. For a single rigid magnetic moment the thermal equilibrium properties are investigated. It is found, that the Heun scheme is a good compromise between numerical stability and computational complexity. Small cubic and spherical ferromagnetic particles are studied.     

Ginzburg–Landau theory of multi-band superconductivity and applications to Fe pnictides

We investigate multi-component superconductors, in relation to iron pnictides, by using the Ginzburg–Landau theory. We show that a three-band superconductor exhibits several significant properties that are not found in single-band or two-band superconductors. The frustrating pairing interaction among Fermi surfaces may lead to a time-reversal symmetry broken pairing state. In fact, we have a solution with time-reversal symmetry breaking, that is, a chiral solution when there is such a frustration. The Ginzburg–Landau equation for three-component superconductors leads to a double sine-Gordon equation. A kink solution exists to this equation that results in the existence of fractional-quantum flux vortices on the domain wall.     

量子等离子体中波的色散关系以及朗道阻尼

利用动理学理论研究量子等离子体中波的色散关系和电子朗道阻尼.从电子的量子流体动力学方程和动理学描述下的光子运动方程出发,研究量子效应对光子朗道阻尼的修正.研究发现量子效应只对纵波模式,即电子等离子体波的色散关系有修正,对横向电磁波的色散关系没有影响.量子效应减小了朗道阻尼,起着朗道增长的作用. 关键词： 量子等离子体 朗道阻尼 电子等离子体波 色散关系     

Transport equation for a gas of bosons

A kinetic equation for the Wigner density function of a Bose gas of quasiparticles (magnons) is derived in the region of linear response. The method uses a simple factorization procedure to transform the Hierarchy equations into a system which can be solved iteratively. The first nontrivial approximation is examined in the limit of slow time and space variation. It gives the linearized Boltzmann equation in the form assumed in the Landau theory. The correction of lowest order in (coupling constant × density) is shown to be a correction to the Born approximation of the scattering cross section.Work supported by the Fonds zur Förderung der wissenschaftlichen Forschung.     

Vlasov equation for photons and quasi-particles in a plasma

We show that, in quite general conditions, a Vlasov equation can be derived for photons in a medium. The same is true for other quasi-particles, such as plasmons, phonons or driftons, associated with other wave modes in a plasma. The range of validity of this equation is discussed. We also discuss the Landau resonance, and its relation with photon acceleration. Exact and approximate expressions for photon and quasi-particle Landau damping are stated. Photon and quasi-particle acceleration and trapping is also discussed. Specific applications to laser-plasma interaction, and to magnetic fusion turbulence, are considered as illustrations of the general approach.     

Landau damping in a bounded magnetized plasma column

The damping decrement of Landau damping and the effect of thermal velocity on the frequency spectrum of a propagating wave in a bounded plasma column are investigated.The magnetized plasma column partially filling a cylindrical metallic tube is considered to be collisionless and non-degenerate.The Landau damping is due to the thermal motion of charge carriers and appears whenever the phase velocity of the plasma waves exceeds the thermal velocity of carriers.The analysis is based on a self-consistent kinetic theory and the solutions of the wave equation in a cylindrical plasma waveguide are presented using Vlasov and Maxwell equations.The hybrid mode dispersion equation for the cylindrical plasma waveguide is obtained through the application of appropriate boundary conditions to the plasma-vacuum interface.The dependence of Landau damping on plasma parameters and the effects of the metallic tube boundary on the dispersion characteristics of plasma and waveguide modes are investigated in detail through numerical calculations.     

Second-phase nucleation on an edge dislocation

A model for nucleation of second phase at or around a dislocation in a crystalline solid is considered. The model employs the Ginzburg–Landau theory of phase transitions comprising the sextic term in the order parameter (η⁶) in the Landau free energy. The ground state solution of the linearised time-independent Ginzburg–Landau equation is derived, through which the spatial variation of the order parameter is delineated. Moreover, a generic phase diagram indicating tricritical behaviour near and away from the dislocation is depicted. The relation between classical nucleation theory and the Ginzburg–Landau approach is discussed, for which the critical formation energy of the nucleus is related to the maximum of the Landau potential energy. A numerical example illustrating the application of the model to the case of nucleation of hydrides in zirconium alloys is provided.     

Quantum plasma description and Landau damping

The Schrödinger equation is shown to replace the Vlasov equation to simulate a classical collisionless plasma, provided we take a sophisticated initial condition. The Landau damping is then recovered within a high degree of accuracy.