磁控溅射气体团簇源中团簇形成的DSMC研究

利用直接模拟蒙特卡洛方法(DSMC) ,模拟了磁控溅射气体团簇源中Cu+ (Cu-)的含量比例不同的条件下,Cu团簇的尺寸分布。模拟结果表明：随着含量比例的增加,团簇的尺寸分布变窄了,不带电的团簇的比例增加,不带电的铜团簇分布的最大值减小,相应的带正电荷和带负电荷团簇的比例减小;相同的含量比例下,带正电的团簇的尺寸分布与带负电荷的团簇的尺寸分布基本相同;初始Cu- 比Cu+ 的含量比例大时,输出的主要是带负电荷的团簇,带正电荷和不带电的团簇占很小的比例;Cu-含量比例的增加,负Cu团簇的尺寸分布减小。     

磁控溅射气体团簇源中团簇形成的DSMC研究

利用直接模拟蒙特卡洛方法(DSMC) ,模拟了磁控溅射气体团簇源中Cu+ (Cu-)的含量比例不同的条件下,Cu团簇的尺寸分布。模拟结果表明：随着含量比例的增加,团簇的尺寸分布变窄了,不带电的团簇的比例增加,不带电的铜团簇分布的最大值减小,相应的带正电荷和带负电荷团簇的比例减小;相同的含量比例下,带正电的团簇的尺寸分布与带负电荷的团簇的尺寸分布基本相同;初始Cu- 比Cu+ 的含量比例大时,输出的主要是带负电荷的团簇,带正电荷和不带电的团簇占很小的比例;Cu-含量比例的增加,负Cu团簇的尺寸分布减小。     

惠斯通电桥实验的分析

惠斯通电桥的灵敏度是影响电阻测量精度的一个主要因素。本论文探究了惠斯通电桥的灵敏度与电源的电动势、桥臂的电阻、桥臂的比例之间的关系。理论分析显示了，电路的总电流保持恒定的情况下，桥臂的比例越大，惠斯通电桥的灵敏度越低，电阻测量的精度越低。另外，桥臂的比例保持不变且电路总电流不大的情况下，电路的总电流越大，惠斯通电桥的灵敏度越高，电阻测量的精度越高。实验测量得到的数据肯定了理论分析得到的结论。     

GW170817:爱因斯坦对了吗?

来自双中子星并合的引力波事件GW170817和伴随的电磁波段的观测,是天文学研究上的一个重要突破。它不仅带给人类史无前例的关于中子星、伽马暴、千新星的知识,也提供了一个检验强场引力的极端天体实验室。爱因斯坦的广义相对论在不同的方面得到了全新的检验,包括引力的速度、引力子的质量、时空的对称性、引力波的辐射和偏振等。这些检验在更高的精度与更广的视角上肯定了广义相对论的预言。     

带有任意自旋粒子衰变产物的角分布

本文研究了具有任意自旋的粒子衰变为一个自旋为零,另一个自旋为1/2的粒子的角分布。给出了球谐函数展开式系数的表式。发现偶次球谐函数项的系数是和引起衰变的相互作用哈密顿量具体形式无关的。但是在球谐函数展开式的奇次项的系数却和一个参变数α有关,而α的值却反映了宇称守恒的相互作用和宇称不守恒的相互作用之间干涉作用的大小。我们给出了这些系数的极大值,发现凡是偶次项系数的极大值是随着衰变粒子自旋的增加而增加的,而奇次项系数的极大值却随着衰变粒子自旋的增加而减小。本文还给出了衰变着的粒子的密度矩阵作为展开式的系数的函数的表式。当这些展开式系数已经知道以后,用这些函数就能决定衰变前的粒子的极化状态,决定宇称守恒相互作用和宇称不守恒相互作用之间的干涉的程度。     

世界范围发光研究的现状

当今的发光研究涉及到一些新奇的和有结构的材料,涉及到尖端的实验技术和高深的理论方法。材料在成分和结构上是多种多样的,并且包括:纯的半导体,例如杂质浓度低于10~9杂质/cm~3的锗;同位素掺杂的有机晶体,例如在质子化的蒽基质中的氘化的蒽;大原胞的化学配比材料,其激活剂是有序排列的,不象在通常的发光体中那样位于无规的格位上;结构性很强的材料,包括用分子束外延制备的异质结、在组分上有单调梯度变化的材料     

光量子信息传输技术

指出光量子信息传输与常规光通信不同的特点。量子信息的传输的载体选用单光子。单光子是由复振幅概率波迭加的波函数来表示的。其本征函数是一组完全正交的偏振态。量子编码即是由表征光子量子态的复数概率波振幅的变化来实现的，传输光纤的双折射和光子的偏振性质是要考虑的一个关键问题。指出用于量子信息编码的三组互为共轭的量子态之间的转化及相位调制对量子态演化的作用，由此比较了各种量子信息传输的方法。     

论散射过程相分析中的不定性问题

从散射过程的相分析中存在不同的相移的选取所必须满足的条件出发,在本工作中,讨论了任意自旋粒子的弹性散射过程的相分析中的不定性问题。给出了全部不同的相的集合之间的变换矩阵,其中所含的实参数由二阶代数方程组决定,因此相分析中的不定性问题化为解这些代数方程的实根的问题。指出此实根的组数之半即为相分析中不同选取的组数。这样,相分析中的运动学不定性问题已完全解决。当道自旋为1/2时,只存在两组不同的相移,当道自旋为1时,也只有两组不同的相移,因此证明了,已知的南氏不定性是这样的自旋值下的全部不定性。在道自旋为3/2时,给出了四给不同的相移。因此除已找出的相移间的变换外,还存在两种新的变换。物理上说,相分析中的不定性相应于自旋的某种运动,它保持自旋张量在动量方向的分量不变,且表征此种运动的参量取一定数值。从讨论中得出,道自旋为整数的情况和为半整数的情况,相移的变换矩阵中所含的实参数所满足的代数方程组具有十分不同的性质,因此实根的组数也不同。这表示,道自旋为整数和为半整数的情况的相移的不同选取的组数也完全不同。一般的推测是,道自旋为整数的情况时的相移不同选取要比为半整数时的少很多。 关键词：     

习题教学后的反思点剖析

习题教学的根本,在于知识点的应用和思维与能力点的突破．常规教学中重视习题的求解过程,即物理过程的展示、物理量之间的等量、常量及关系量的寻找．教学后的反思重在知识点的综合与衔接．其实习题教学的反思应该重在思维和能力的突破,形成解决物理的方法和能力．下面从例题的反思中展现思维与能力的反思点．     

费因曼对凝聚态物理的贡献

费因曼是一位著名的物理学家,他对理论物理的很多方面作出过重要贡献.费因曼的思想是十分机敏且具有独创性的.他喜欢用不同于其他人的角度去注视物理学中的每一个问题,不论是重要的或不重要的,他经常喜欢说的一句话是:“看看问题的其他方面.”正是这种独特的思维方式加上他的极端努力,使费因曼成为一个与众不同的人.任何一个从事创造性工作的人,为了摆脱常规的思想,去掉一些看来是可接受的但却是错误的方式,而需要找出解决问题的更好的途径时,总是以各种方式冲击着原有的传统.但费因曼的这种“看看问题其他方面”的做法,往往与别人不同.其结…     

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.     

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.     

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.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.