伦琴对电磁理论的重要贡献

提到伦琴,人们往往想到的是他对X射线的发现,而对他在电磁理论方面的重要贡献则较少提及.文章详细叙述了伦琴为论证“位移电流”存在而做的实验,此实验曾被誉为是19世纪最重要的物理实验之一,在当时广受赞誉,但今天却被人们渐渐遗忘了.希望该文能够使人们对伦琴为构建19世纪物理学宏伟大厦而取得成就的重要性有更深入的认识.     

诺贝尔物理学奖百年回顾

 ２０世纪,物理学成就辉煌．诺贝尔物理学奖,从一个侧面纪录了当代最优秀物理学家奋斗的足迹．值此世纪交替之际,我们编写这篇文章,对诺贝尔物理学奖作百年回顾,以飨读者．１９０１年伦琴（ＷｉｌｈｅｌｍＣｏｎｒａｄＲｏｎｔｇｅｎ１８４５～１９２３）因发现伦琴射线（即通常所说的Ｘ射线）以及对伦琴射线性质的研究,获得了第一届（１９０１年度）诺贝尔物理学奖．１８９５年１１月８日,当伦琴用克鲁克斯管做实验时,发现工作台上的氰亚铂酸钠纸屏能发出荧光．他分别用纸和书本遮住纸屏,纸屏仍然发光．使伦琴更为惊讶的是,当他把手放在纸屏前时,纸屏上留下了手骨的阴影．     

邮票上得诺贝尔奖的物理学家和工作──X射线的发现

 １９０１年是２０世纪开始的一年,诺贝尔奖也于这一年开始颁发。第一届诺贝尔物理奖授给了德国物理学家伦琴,因为他于１８９５年发现了Ｘ射线。在上期的图７中我们已看到向伦琴授奖的盛况。图１为瑞典１９６１年发行的纪念１９０１年诺贝尔奖的邮票,最右为伦琴;图２为德国１９５１年纪念第一次诺贝尔物理奖５０周年的邮票,除伦琴肖像外,右上角有他在实验中所用的Ｘ射线管。在他之后,还有多项与Ｘ射线有关的研究工作获得诺贝尔奖。伦琴发现Ｘ射线伦琴（图３,东德１９６５,诞生１２０周年;图４,西班牙１９６７,欧洲放射学大会;图５,古巴１９９３,伟大科学家）在发现Ｘ射线时是德国维尔茨堡大学的物理学教授。     

邮票上的物理学史B37——X射线的发现

前两节介绍了上一次世纪之交时经典物理学理论和已知实验事实的矛盾.这些实验事实才刚刚触及高速和微观领域.19世纪末，在实验上还有三大发现，即X射线、电子和放射性，这些发现进一步打开了微观世界的大门.这三项发现都直接或间接与阴极射线的研究有关.阴极射线是当时的热门研究题目，早在19世纪30年代，法拉第就发现了稀薄气体放电中的辉光现象.随着真空技术不断进步和真空度不断提高，物理学家又发现了阴极射线.它产生于高真空放电管的阴极，撞击对面的管壁，使之发荧光.用现在的话来说，所谓阴极射线，就是电场从阴极拉出来的电子流.电子的发现当然直接与阴极射线有关，X射线是伦琴在研究阴极射线时发现的，而放射性则是贝克勒尔研究X射线时发现的.     

约飞（Joffe，Abram Fetorovich，1880-1960）俄国物理学家（Physicist，Russia）

约飞1902年在彼得堡工业大学毕业后去德国留学，师从伦琴。1905年回国。十月革命后，他建议并参与筹建在前苏联各地的16所物理研究机构，包括他担任所长多年的列宁格勒前苏联科学院物理技术研究所，对前苏联物理学的发展功勋卓著。他培养了不少人才，卡皮察和朗道都是他的学生。他本人毕生致力于固体物理学的研究，特别是半导体的研究。他在20世纪30年代初就指出，半导体是电子技术的新材料。     

伦琴（Roentgen，Wilhelm Konrad，1845-1923）德国物理学家（Physicist，Germany）

伦琴因为发现X射线，1901年获得第一届诺贝尔物理学奖。这一发现宣布了现代物理学时代的到来，使医学发生了革命。伦琴是斯特拉斯堡大学、吉森大学、维尔茨堡大学和慕尼黑大学的物理学教授。1895年，伦琴进行阴极射线管中电流的实验时，观察到附近的一块氰亚铂酸钡在管中通电时发光。据此建立理论：当阴极射线（电子）撞击管的玻璃壁时，形成了某种未知的辐射，穿过室内，照射某些化学样品而引起荧光。     

莫尔斯（Morse，Samuel Finley Breese，1791-1872）美国发明家（Inventor，America）

莫尔斯1810年毕业于耶鲁大学。在19世纪30年代，由于在一次航海中受到同船乘客杰克逊的影响，莫尔斯开始热衷于电的实验。他决定制造一台电报机，但又觉得力不胜任，因为他对电的知识一无所知。他偶然地遇到了亨利。亨利毫不吝惜地帮助了他，回答了他的所有问题。此后莫尔斯开始为制造电报机谋求援助，在这里，莫尔斯作为一个持之以恒、决心果断的人显示了他的真正才干。他发明．了迄今仍被称为“莫尔斯电码”的点、划电报符号。     

玻尔兹曼科学创造的深远影响与思想渊源

1906年9月5日，一颗物理学界的巨星意外地陨落了，他就是奥地利首屈一指的物理学家——L．玻尔兹曼（Ludwig Boltzmann，1844-1906）．玻尔兹曼是另两位伟大的理论物理学家——19世纪的麦克斯韦和20世纪的爱因斯坦之间的中间环节，是连接19世纪和20世纪物理学的桥梁．在玻尔兹曼悲惨谢世一百周年之际，回顾玻尔兹曼科学创造的深远影响，挖掘玻尔兹曼科学创造的思想渊源，对实施创新教育，培养创新思维能力，造就创新人才是大有裨益的。     

关于伦琴传的一点补充

《物理》１９８１年第１０卷第５２页上,有戴念祖同志写的《伦琴》一文．这篇文章可以补充两张照片（图１,图２）．在１８９５年圣诞前几天,伦琴在实验室工作时,用的一块硬纸板上面镀了一层叫氰亚铂酸钡的晶体材料,接通电源后,这块硬纸板就发出绿色的荧光,此实验反复做,结果都是一样．他情不自禁地问自己,“是克鲁克斯管中有某种未知的射线到纸板上引起的吗？”想到这里,他立即接通了电源,随手拿起一本书,挡在管与?...     

伦琴对热学和电磁学的贡献

 1895年,德国物理学家伦琴发现了X射线,这是具有划时代意义的伟大发现.从此,伦琴的名字和X射线紧紧连在一起,人们称X射线为伦琴射线.发现X射线是伦琴为人类做出的最大贡献,这一成就极大地影响了人类生活的各个方面,使伦琴的名字为世人所共知.除此之外,伦琴在物理学其他方面的工作也毫不逊色,只是由于发现X射线这一巨大成就的衬托,相对而言它们却鲜为人知.本文就伦琴在热学和电磁学方面的成就做一探讨.     

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.