PARALLEL HIERARCHICAL MATRIX PRECONDITIONERS FOR THE CURL-CURL OPERATOR

This paper deals with the preconditioning of the curl-curl operator. We use H（curl）- conforming finite elements for the discretization of our corresponding magnetostatic model problem. Jumps in the material parameters influence the condition of the problem. We will demonstrate by theoretical estimates and numerical experiments that hierarchical matrices are well suited to construct efficient parallel preconditioners for the fast and robust iterative solution of such problems.     

What if there are superluminal signals?

Recent experiments with microwaves indicate the existence of signals travelling faster than the vacuum velocity of light. At first glance these signals lead to paradoxical situations which seem to be in conflict with special relativity. We show that the arguments which lead to this contradiction presuppose that superluminal signals are not generally available and that the space-time geometry must be established by means of light rays. Hence we argue that superluminal signals will not necessarily invalidate special relativity. Received 1 July 1999     

On the radiation of the electromagnetic impulse pendulum

Summary In this paper we clarify the sources of radiation in a number of experiments, concerning the electromagnetic impulse pendulum, carried out by various authors. The calculated radiated energy was found to be negligible, in all cases, compared to the energy stored in their systems, in contradiction to their claim. We elucidate the way by which Newton's third law is applicable and how the reaction force of the moving pendulum is transferred to the stationary frame. In the MIT experiment of Graneauet al., average values for quantities like the time constant, resistance etc. are given ignoring their standard deviations. Calculating and taking into account their errors, due to their dependence on the temperature, we found agreement between the theoretical and experimental values of the pendulum momentum.     

大学物理教学中不应忽视电磁学与狭义相对论的内在联系

文章指出大学物理教学中关于电磁学和狭义相对论的缺憾,并提出了可行的教学方案.由此可以使学生深化对电磁场的认识,同时深刻理解狭义相对论时空观的内在意义.     

The Maxwell-Lodge effect: Significance of electromagnetic potentials in the classical theory

The Aharonov-Bohm effect has been the starting point of the reconsideration of the reality of the vector potential within quantum physics. We argue that the Maxwell-Lodge effect is its classical equivalent: what is the origin of the electromotive force induced in a coil surrounding a (finite) solenoid fed by an alternative current? We demonstrate theoretically, experimentally and numerically that the effect can be understood using the vector potential while it cannot using only the fields.     

《电磁学》课堂教学的设计

结合数年的教学经验和教学资源,总结出帮助学生克服以上困难的四个方面:充分建立电磁场图景、利用演示实验和视频动画、加强对物理参数的理解以及电磁原理的应用。     

A finite-element analysis of critical-state models for type-II superconductivity in 3D

^** Email: c.m.elliott{at}sussex.ac.uk^*** Corresponding author. Email: y.kashima{at}sussex.ac.uk We consider the numerical analysis of evolution variationalinequalities which are derived from Maxwell's equations coupledwith a nonlinear constitutive relation between the electricfield and the current density and governing the magnetic fieldaround a type-II bulk superconductor located in 3D space. Thenonlinear Ohm's law is formulated using the subdifferentialof a convex energy so the theory is applied to the Bean critical-statemodel, a power law model and an extended Bean critical-statemodel. The magnetic field in the nonconducting region is expressedas a gradient of a magnetic scalar potential in order to handlethe curl-free constraint. The variational inequalities are discretizedin time implicitly and in space by Nédélec's curl-conformingfinite element of lowest order. The nonsmooth energies are smoothedwith a regularization parameter so that the fully discrete problemis a system of nonlinear algebraic equations at each time step.We prove various convergence results. Some numerical simulationsunder a uniform external magnetic field are presented.     

居室常用传输线的工频电磁干扰

本文讨论家用电器常用传输线（同轴线和双导线）,在工频条件下的电磁场量值,特性和分布。为增进对此类场的了解,开拓工频估产污染的研究和预防可能对人体生理机能的影响,提供了参考。     

A possible mechanism of current in medium under electromagnetic wave

In this paper a possible mechanism of current in medium is presented. Comparison between this current and the magnetization current was made. Expression for this current was derived. This work is helpful to understanding the interaction between medium and electromagnetic wave.     

微波谐振器系统的调谐实验研究

圆台谐振腔和微波产生及传输装置可以形成一套和外界独立的微波谐振器系统.由于壁面上电磁压强差的作用,圆台谐振腔可能产生净电磁力,这需要从实验上给予证明.为此首先应对独立的微波谐振器系统进行调谐实验研究,使系统时刻处于谐振状态,这是实验证明净电磁力存在的重要保证.为此,本文对圆台谐振腔进行低信号调谐实验,同时配合调谐元件,准确地调试2.45 GHz频率下的谐振状态,分析温度对谐振状态的影响.实验结果表明该微波谐振器谐振频率2.44895 GHz、品质因数117495.0823,而且当腔体壁温升高时谐振频率减小、品质因数出现周期性振荡.