运动电荷的电/磁场高斯定理的直接验证

尽管麦氏方程组的张量协变形式已然揭示了高斯定理的相对论协变性,但在大学物理的教学中仍然缺乏对运动电荷的高斯定理的切身体会与直接验证.本文首先运用电磁场张量变换的方法推导出运动电荷的电场与磁场强度,再运用积分及矢量运算的若干技巧,直接而简单地验证了高斯定理对于运动电荷的电场与磁场仍然满足,从而直接验证了电场与磁场的高斯定...     

在洛伦兹变换下磁单极的电磁规律

从磁库仑定律出发，用洛伦兹变换导出磁单极的电磁场及其散度，旋度公式和磁单极在电磁场中的受力公式；给出它们的相对论协变形式；最后对讨论推广的麦克斯韦方程组。     

电磁场的复矢量表示

在麦克斯韦方程组及洛伦兹力密度公式基础上引入电磁场复矢量,讨论了电磁场普遍规律的新公式,包括对复矢量电磁场的建立,电荷守恒定律,能量守恒定律,电磁场矢势与标势,电磁场动量、能量、张量、相对论协变性等的研究,并和电动力学相比较,得出一些结论.     

建立麦克斯韦方程组的其他途径

麦克斯韦方程组是电磁场遵从的基本规律,是经典电磁现象的理论基础.十九世纪六十年代,麦克斯韦根据库仑、安培和法拉第等人分别在特定条件下获得的实验定律,经过分析推广到普遍情形,发现存在着不协调的因素,在此基础上作了两个重要的假设:变化的磁场产生涡旋电场,变化的电场产生涡旋磁场,从而建立了电磁场的统一理论,其基础就是电磁场普遍遵从的麦克斯韦方程组. 在麦克斯韦以后,许多物理学家研究从别的方面建立麦克斯韦方程组的可能性,取得一些成果.本文拟介绍三种建立麦克斯韦方程组的其他途径:(1)根据能量原理和近距作用原理建立麦克斯韦…     

从麦克斯韦方程组到电磁波方程

<正>麦克斯韦方程组的威名可谓如雷贯耳,是经典电磁学的最高成就。先来看看麦克斯韦方程组的样子:方程组写成以上形式,需要一个前提:空间中的媒质是各向同性的(即,媒质中的每一点的物理性质不随方向改变)。方程组的一式描述了电荷产生电场的高斯定律,二式描述了变化的磁场产生电场的法拉第电磁感应定律,三式描述了磁单极子不存在的高斯磁定律,四式描述了电流和变化的电场产生磁场的麦克斯韦-安培环路定律。有物理意义上的场必定存在物理意义上的源,因此,我们可以发现,麦克斯韦方程组等式的左边是场,     

大学生对麦克斯韦方程组的理解研究

本研究通过收集麦克斯韦方程组概念测试题的课堂讨论录音及书面回答,获得物理专业大学生对麦克斯韦方程组的错误理解,总结出学生常见的错误概念为不清楚方程式来源、对电场和磁场的相互关系理解有误、将电场和磁场进行不恰当类比、不能正确理解平行板间电磁场的来源、对感生电场和位移电流理解不到位等,对此提出有针对性的教学建议,为电磁学教学提供参考.     

伽利略协变和洛伦兹协变电磁场论趣谈

针对狭义相对论课程中的相对性原理和光速不变原理之间逻辑关系的争论,本文假设空间中存在以太,把麦克斯韦方程组写成了伽利略协变的形式。此时的光波波速变换满足伽利略速度变换,人可以和光同步运动。伽利略协变理论满足相对性原理而不满足光速不变原理。论文然后假设空间中充满均匀洛伦兹协变以太,把介质中的麦克斯韦方程组写成洛伦兹协变形式。重新定义的波相实现了洛伦兹速度变换。只要真空中的光速无限接近极限速度,实验无法排除这种协变介质理论。伽利略协变电磁理论和洛伦兹协变介质电磁理论之间不是一种简单的推广关系。     

再论洛仑兹关系的协变性及其速度的含义

洛仑兹关系式 F=qE+qv×B通常也称为洛仑兹力公式,它与麦克斯韦方程组一起,给出了电动力学的基本规律.在宏观电磁现象中,洛仑兹力公式和麦克斯韦方程组是普遍成立的,并适用于一切惯性参考系,具有相对论协变性. 公式F=qE + qv×B中的速度v,与E=0时,公式F=qv×B中的速度v,含义完全相同,是指电荷相对于观察者的速度,也就是电荷相对于与观察者固接的参考系的速度.但最近有的作者又一次强调[1],它也是电荷相对于磁场的速度,应当把“总是误认为公式中的v是带电粒子相对于导体或磁场的速度,实际上应当是指相对于观察者的速度[2]”改为“总是误…     

麦克斯韦如何构建力学模型来解释电磁感应和发现位移电流

电磁学的核心就是麦克斯韦方程组,今天它被认为是物理学中最美的方程组之一.本文主要介绍了麦克斯韦当初如何通过构建力学模型来解释电磁感应定律和发现了位移电流,从而完整地发展出了麦克斯韦方程组.     

运动介质洛伦兹协变电磁理论

虽然麦克斯韦方程组可以写成协变形式,但由于本构关系协变性质不明显,所以大多数教科书中的介质电磁理论不是明显洛伦兹协变的。本文列举了物理学家给出的不同的介质麦克斯韦方程组,并重点讨论了最广泛使用的形式:闵可夫斯基公式和朱公式的异同。利用空间平均的方法分析了运动介质微观极化与磁化的相关规律。然后将本构关系写成了洛伦兹协变形式,借此得到了介质协变电磁学理论。采用的宏观处理办法可以弥补微观非相对论方法的缺陷。最后将介质中不明显协变的波动方程推广为洛伦兹协变的波动方程,验证运动介质中速度的相对论叠加公式,并推广了多普勒频移公式。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.