编写SPnenu安卓软件分析单摆视频计算重力加速度

为了增强"单摆测量重力加速度"实验的效果,编写了运动视频分析安卓应用程序-SPnenu,分析单摆视频,计算重力加速度。首先,介绍了安卓软件的组成模块;然后,使用该应用程序分析单摆运动视频中周期、摆长和视频当地重力加速度;最后,与计算机平台下的视频分析软件Tracker进行对比实验,并对误差进行了讨论分析。实验表明,将基于安卓智能手机的运动视频分析软件引入物理实验教学,有助于打破实验的时间和空间限制,减小了"周期测量"带来的误差,能实现对单摆小球运动轨迹的精确追踪记录和数据分析。     

大摆角单摆“周期”变化的解析解及其实验应用

大摆角单摆实验由于忽略空气阻尼带来周期测量的系统误差.基于弱阻尼大摆角单摆的运动方程,推导了累计"周期"随摆次变化的解析公式,分析了"周期"随摆次减小的基本规律.结合实验数据分析,验证了将其用于大摆角单摆实验进行系统误差修正,从而通过累计测量减小随机误差的可行性.     

由“嫦娥一号”引起的思考

由扣人心弦的"嫦娥一号"几次变轨,使笔者追寻一个问题:即决定椭圆运动周期的最简单公式是什么?进而对卫星的圆运动问题,椭圆运动问题的普遍公式作了一个小结.这对于学过普通物理的大学生都会有帮助.     

如何实现宏观量子单摆

利用等效质心方法描写单摆运动,经典力学通过牛顿方程得到摆球在空间做周期振动,而量子力学却给出完全不同的结论:摆球做无"周期"的随机运动.本文分析了量子力学等效质心模型成立的条件,在此基础上计算了经典单摆过渡至量子单摆的实验条件,表明在目前的实验水平上观察宏观摆球(微米量级)的空间量子跃迁行为是简便易行的.     

利用智能手机磁传感器测重力加速度

利用智能手机中的磁传感器和Sensor Kinetics软件研究磁性复摆的运动情况,通过绘制复摆振动时"磁场强度-时间"图像计算振动周期,从而计算出当地的重力加速度。     

周期运动观测实验仪

当周期运动超出视觉停留范围时,直接观测周期运动(如转动、振动)就较为困难.利用计算机进行图像采集处理,既不直观,价格又不菲.为此,设计了周期运动观测实验仪.该仪器利用锁相成像观测法观测周期运动的物体,设置光源闪烁频率与周期运动频率一致,当光源开启时间足够短时,即可获得锁相状态下物体的准静态图像.     

用能量法简捷推导可动悬点单摆的谐运动周期

"可动悬点的单摆"是指如下体系:如图1,质量为M的小圆环套在光滑的固定水平杆上,通过一长度为L的轻杆将质量为m的小球与圆环连接,圆环、小球均视为质点.证明此体系在小角度下的运动是谐运动,并求出谐运动的周期.     

光束运动特性对焦斑束匀滑效果的影响

提出了光束运动的概念和物理模型,针对光谱色散匀滑技术方案,以正弦位相调制脉冲和线性啁啾脉冲为例,理论分析了啁啾宽带光束的横向"运动"特性及其对焦斑匀滑效果的影响,详细讨论了运动速度大小、运动周期以及运动方式等对焦斑束匀滑特性的影响,得到在相同带宽下线性啁啾脉冲的匀滑效果要优于正弦位相调制脉冲匀滑效果的结论.     

“绳连三球”系统运动的轨迹方程和周期的研究

对于光滑水平面上由"绳连三球"构成的系统,利用参数方程分别对其运动轨迹和周期进行了研究,发现子球运动轨迹与绳子的长度和质量比有关,系统运动的周期与绳子的长度、质量比及初速度有关,利用软件模拟出子球运动轨迹、速度相图和速度时间图象.     

振动颗粒物质中倍周期运动对尺寸分离的影响

实验研究了竖直振动颗粒床中,倍周期运动对尺寸分离的影响.实验中,当振动加速度足够大时,系统中出现稳定的对称对流,进一步增大振动加速度到某个临界值时,还会出现倍周期运动.观察表明,背景颗粒的对流运动对分离过程起主导作用,对流速度决定着分离过程的快慢,而在2倍周期和4倍周期分岔之后,分离时间有所减慢.对引起对流运动的起因进行了分析,以此为基础分析了倍周期运动产生影响的物理机理,并对分离时间进行了定量计算,结果与实验值符合很好. 关键词： 颗粒物质 “巴西果”效应 倍周期分岔 对流     

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.     

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.     

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.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.