涡电流电磁感应演示仪的设计

以一个新的角度--涡电流效应演示电磁感应现象.演示仪器引入气垫导轨,由悬挂的钕铁硼永磁铁与铝板小车在接近无外界阻力的状态下相互作用来演示动生电动势现象;由高频交流电磁铁加热铝板小车或点亮接有线圈的小灯泡演示感生电动势现象.     

改进的静电滚筒实验——静电电动机模型

物理教学中为演示静电的力效应,通常设计静电滚筒或富兰克林电动机实验．这些实验巧妙地演示带电粒子流冲击滚筒而产生的力矩作用,它将人眼观察不到的微观电荷定向运动与宏观物体的转动有机结合起来,加强了学生对电荷作用力的现象观察与深入思考．     

热学演示实验二则

热学演示实验二则朱连生（国家教委教学仪器研究所北京１０００３９）一、金属环的热胀冷缩实验中学现配备的金属球热胀冷缩演示器只能演示金属球的热胀冷缩现象，为了增加实验内容，可用铝板（厚３一４ｍｍ）再自制一个带柄的金属环．环的内径要略小于球的直径（差１一２...     

富兰克林电动机实验的探索和研究

自制了富兰克林电动机实验装置.通过大量实验探索,详细介绍了富兰克林电动机在各种情况下的工作原理及运转状态.     

大学物理课堂演示实验应定位在科学性实验

目前大学物理课堂教学中演示实验通常用于演示物理现象,没有充分发挥出演示实验的作用.本文指 出,演示实验应定位在科学性实验.为此,课堂演示实验的设计要体现出物理的严密性、科学性,在验证理论知识的 同时,让学生也学会科学的分析方法与实验方法.学生应作为大学物理演示实验的主体,参与到演示实验的操作、 数据采集、分析中;教师在课堂教学中主要是提出问题、启发思路和引导争论,充当实验操作员与引导学生的角色.     

演示电荷守恒的实验

演示电荷守恒的实验（译者按；富兰克林在静电学方面已设计了很多巧妙的实验，但是许多是受到气候因素的制约。在这里介绍的这个测量电荷守恒的实验，是最为可靠的一个实验。）一、引吉电荷不能创生也不能消灭，但是可以转移。例如：把毛皮与聚四氯乙烯摩擦后，电荷（电子...     

针孔点背光技术实验

在“星光Ⅱ”装置上进行针孔点背光技术的演示实验.利用激光辐照φ50μm的小孔产生的堵孔效应使X光的脉宽缩短，起到类似于短脉冲点背光源的作用.另外利用成像方法，实验演示了由面背光方式获得点背光技术，称之为点针孔背光技术.实验结果表明：结合堵孔效应和点背光方式，能获得与点背光同样的结果，这样可以避开点背光对激光器较为苛刻的要求.     

发挥物理演示实验的创新教育功能

 在当前大力倡导创新教育的形势下,不少物理教师提出并努力实践着将演示实验改为学生分组实验,将演示实验改为边讲边做实验,这无疑能增加学生的动手机会,提高学生的实践能力,符合创新教育改革的需要。但从另一个侧面却反映了许多物理教师不能正确认识和对待演示实验,将演示实验教学与创新教育相对立,认为演示实验的主体是教师,演示实验只能起到激发兴趣、看看现象、调节课堂气氛等作用,只有学生亲自动手实验,才能培养创新能力。     

充分利用力学演示实验培养学员创新思维能力

在工程力学教学中要充分发挥演示实验的作用,培养学员的创新思维,教员应该对演示实验教学进行合理的创新设计,开发出力学演示实验独有的构思和方法,利用形式多样的演示实验来培养学员的创新思维能力.     

激光辐照受拉铝板破坏行为的时空多尺度数值模拟

推导耦合过渡区内参变量信息交换的元/网格动量传递多尺度算法,建立离散元与有限元耦合时空多尺度计算模型,并应用于激光辐照下受拉铝板破坏行为的数值模拟中.通过对比有限元计算模型、空间多尺度计算模型与时空多尺度计算模型在激光辐照下受拉铝板破坏算例的模拟结果,验证离散元与有限元耦合时空多尺度计算模型的准确性和数值计算高效率优势.使用该多尺度计算模型从宏观和细观尺度对铝板破坏行为进行数值模拟,模拟结果与实验结果基本一致.     

The noteworthy involvement of Jacques de Romas in the experiments on the electric nature of lightning

We cannot evoke the discovery of lightning without telling briefly that of electricity. Started in the seventeenth century with the design of the first electrostatic machines, the characterisation of the “electric fluid” is given a boost in the first half of the eighteenth century with an alternation of competition and collaboration between European and American scientists. The demonstration of the analogy between lightning and electricity reaches its maturity with the personal involvement of Benjamin Franklin in 1746 and the epistolary publication of his innovating ideas through his friend Peter Collinson.A first wave of experiments on lightning is triggered by the translation into French of the ideas of Franklin (Dalibard, Delor, Buffon and Jacques de Romas). The famous kite experiment is invented by Franklin and Romas independently. Romas produces very long sparks in front of enthusiastic crowds (first success in 1753). Franklin and Romas will argue about the priority of invention which prefigures the modern conception of the lightning rod. The “Universal History” retained only the name of Franklin, what is justified as regards to his great talent but rather inequitable for the memory of Romas which led with obstinacy research works on the nature and effects of lightning.     

Surface plasmon coupled fluorescence in deep-ultraviolet excitation by Kretschmann configuration

We report the experimental demonstration of fluorescence of CdSe quantum dots with surface plasmon excitation in deep-ultraviolet （deep-UV） region. Surface plasmon resonance in deep-UV is excited by aluminum thin film in the Kretschmann-Raether geometry. Considering the oxidation thickness of aluminum, the experimental results of incident angle dependence of reflectance show good agreement with Fresnel theory. Surface plasmon resonance with 19 nm-thick aluminum and 5 nm-thick almnina was excited at the incident angle of 48 degrees for 266 nm excitation. Fluorescence of CdSe quantum dots coated on this aluminum film was observed by the surface plasmon excitation.     

Computational interpretation of megagauss-magnetic-field-induced metallic surface plasma initiation and evolution

Numerical simulations of experiments in which plasma is formed on an aluminum surface by megagauss magnetic fields provide the first computational demonstration of a magnetic-field threshold that must be reached for aluminum plasma to begin to form. The computed times of plasma initiation agree reasonably well with the observations across the full range of rod diameters, leading to the conclusion that plasma formation is a thermal process. Computationally, plasma forms first in low-density material that is resistive enough to expand across the magnetic field and yet conductive enough that Ohmic heating exceeds expansion cooling.     

用波尔共振仪研究混沌现象

用半导体激光器作为光源,用鼠标作为位移传感器,将波尔共振仪摆轮的振动转化为鼠标的运动轨迹,并通过Ghost Mouse-Setup软件记录鼠标轨迹,最后通过Labview软件对记录的轨迹进行信号处理,通过观察分析吸引子来研究波尔共振仪中的混沌现象。实验结果表明:波尔共振仪中摆轮做阻尼振动时,其振动振幅出现随时间逐渐减小,最终停止摆动的确定性规律,但每一次摆轮的运动过程都是随机的,各不相同。只要时间足够长,摆轮最终都会收缩成一点,形成稳定的焦点,即混沌吸引子。这就是波尔共振仪中摆轮做阻尼振动出现的混沌现象。     

Some mechanisms of excitation of a railway wheel

Railway wheel vibrations are caused by a number of mechanisms. Two of these are considered: (a) gravitational load reaction acting on different points of the wheel rim, as the wheel rolls on, and (b) random fluctuating forces generated at the contact patch by roughness on the mating surfaces of the wheel and rail. The wheel is idealized as a thin ring, and the analysis is limited to a single wheel rolling on a rail. It is shown that the first mechanism results in a stationary pattern of vibration, which would not radiate any sound. The acceleration caused by roughness-excited forces is much higher at higher frequencies, but is of the same order as that caused by load reaction at lower frequencies. The computed acceleration level (and hence the radiated SPL) caused by roughness is comparable with the observed values, and is seen to increase by about 10 dB for a doubling of the wagon speed. The driving point impedance of the periodic rail-sleeper system at the contact patch, which is used in the analysis, is derived in a companion paper.     

Time-domain prediction of impact noise from wheel flats based on measured profiles

Railway impact noise is caused by discrete rail or wheel irregularities, such as wheel flats, rail joints, switches and crossings. In order to investigate impact noise generation, a time-domain wheel/rail interaction model is needed to take account of nonlinearities in the contact zone. A nonlinear Hertzian contact spring is commonly used for wheel/rail interaction modelling but this is not sufficient to take account of actual surface defects which may include large geometry variations. A time-domain wheel/rail interaction model with a more detailed numerical non-Hertzian contact is developed here and used with surface roughness profiles from field measurements of a test wheel with a flat. The impact vibration response and noise due to the wheel flat are predicted using the numerical model and found to be in good agreement with the measurements. Moreover, compared with the Hertzian theory, a large improvement is found at high frequencies when using the detailed contact model.     

A HYBRID MODEL FOR THE NOISE GENERATION DUE TO RAILWAY WHEEL FLATS

A numerical model is developed to predict the wheel/rail dynamic interaction occurring due to excitation by wheel flats. A relative displacement excitation is introduced between the wheel and rail that differs from the geometric form of the wheel flat due to the finite curvature of the wheel. To allow for the non-linearity of the contact spring and the possibility of loss of contact between the wheel and the rail, a time-domain model is used to calculate the interaction force. This includes simplified dynamic models of the wheel and the track. In order to predict the consequent noise radiation, the wheel/rail interaction force is transformed into the frequency domain and then converted back to an equivalent roughness spectrum. This spectrum is used as the input to a linear, frequency-domain model of wheel/rail interaction to predict the noise. The noise level due to wheel flat excitation is found to increase with the train speed V at a rate of about 20 log₀V whereas rolling noise due to roughness excitation generally increases at about 30 log₀V. For all speeds up to at least 200 km/h the noise from typical flats exceeds that due to normal levels of roughness. When the wheel load is doubled the predicted impact noise increases by about 3 dB.     

Basic Aspect of Relativistic Rotation: Franklin Rotation of a Sphere

We give a relativistic treatment to the dynamics of spherical bodies rotating at very high speed. It is found that most of the mass of a homogeneous spherical quark with Franklin rotation is due to the relativistic increase of the mass.     

Low noise spinning wheel technique for THz material parameter extraction

Double-modulated terahertz differential time-domain spectroscopy (double-modulated THz-DTDS), is a technique that is based on dithering the sample under test. In this paper, we report a measurement technique based on mounting the sample on a spinning wheel, in order to overcome fundamental limitations imposed by linear dithering. We demonstrate a proof-of-principle showing that noise decreases as a function of the spinning wheel modulation frequency. This technique does not suffer the mechanical noise limitation of traditional linear dithering and thus opens up future scope for further noise reduction via hardware advances in the modulation frequency of the wheel. The spinning wheel technique enables a rapid succession of measurements between the reference and sample signals with a single mechanical delay scan. As a result, an improvement in measurement time by at least a factor of two, as compared to the conventional THz-TDS measurement technique is observed. The spinning wheel technique is experimentally verified by measuring the dielectric properties of a thick polymer material.