思想实验的作用和意义

文中阐明思想实验是具体实验的延伸又作为理论的必要补充 ,并通过实例说明思想实验的作用和意义 .     

关于"气垫导轨实验中光电计时系统误差研究"实验的探索

在全面解析"气垫导轨实验中光电计时系统误差研究"实验案例的基础上,对从学生兴趣入手,以学生发现作为实验研究的起点,依托学生在实验中自己发现的问题而将其设置成为一种设计性实验的实验方式进行了探讨.     

静电场描绘实验中导电介质的制备

模拟法描绘静电场是大学物理实验必修实验项目之一。在实验开设过程中,随着实验仪器的使用,产生稳恒电流场的导电介质不断磨损,介质层均匀性的破坏对实验结果的影响极大。通过配比10wt%的导电炭黑环氧树脂基导电涂料作为静电场描绘仪的导电介质,在满足介质硬度要求和制备成本低廉的前提下,实验结果表明:采用导电涂料作为同轴圆柱面间的导电介质,其电压分布的测量结果和无限长同轴线缆横断面上理论电势分布较为吻合,相对误差在3%以内。     

激光双反射镜实验

在导师的指导下，参加了导航研究中有关卡塞格伦天线应用的实验工作。根据高教部改进和更新实验的要求，拟将天线中激光的双反射镜实验引入物理教学作为物理实验课的内容改革之一。这个实验可以取代以几何光学为基础的透镜实验。按其要求可以作为综合物理实验或中级物理实验。为此，将我们参加激光双反射镜的实验，根据实验的教学要求写成此文，以供物理实验改革的参考和应用。     

实验考试的两种新尝试

1 问题的提出 物理是一门实验科学。在物理教学中,物理实验的重要性是不言而喻的,而作为物理教学的一个重要组成部分,实验考试的必要性也是众所周知的,现在已有相当多的学校把实验作为单列课程。但大多采取的是抽签考核,这样,每考一次的准备工作和考试过程工作量增     

微脉冲电子枪的初步实验研究

给出了微脉冲电子枪的模拟计算及其初步实验结果. 该电子枪采用铜铝镁合金作为冷阴极材料, 在以磁控管作为微波功率源的出束实验中得到了100mA/cm²的电流密度.实验结果与次级电子倍增解析计算和SEEG程序的模拟计算结果基本符合, 初步验证了微脉冲电子枪的基本原理, 为今后实验中得到更大的电流密度打下了基础.     

单摆实验剖析

单摆是一个传统的实验,许多学生在中学已经做过,但我们还是把它作为一个可以在简单中见深度、有丰富实验思想和训练内容,可以面对各种不同层次学生的必做实验。下面从实验的各个方面提出一些问题来进行剖析。     

思想实验的作用和意义

文中阐明思想实验是具体实验的延伸又作为理论的必要补充，并通过实例说明思想实验的作用和意义。     

光敏电阻响应时间的研究实验

用半定量方法研究了光敏电阻的响应时间与照射光的照度和波长的关系,并给出了光敏电阻的上升时间和下降时间的测量方法.该实验可作为本科生的探索性实验,有助于培养学生的综合和研究能力.     

探索性实验

我校编写的《物理实验教程》中,把物理实验分为三大类,即探索性实验、验证性实验及应用性实验。后两类实验(尤其是应用性实验)在传统的物理实验课程中已有大量的现成课题,且对每个具体的实验常有多方面深入研究的报道。但极少见到有关探索性实验的介绍(《物理实验》1982年第4期载有《逆行式实验》一文),而探索性实验是一类很有科学意义的实验类型,它有助于学生科学实验能力的培养,因此它应在物理实验课程中占有一席之地。通过实验去寻找有关物理量之间的函数关系式(或称经验公式),从而揭示其内在的物理规律。以此作为目的的一类实验称之谓探索性实验。它是物理规律研究的起始,科学实验的原貌。由于教学时数及实验室各种     

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.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

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.     

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.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

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.