微波波谱法研究分子间相互作用

微波波谱是一种微波频段的波谱学方法,近年来在研究分子系统结构及分子间弱相互作用上发展迅速,是一种高分辨率和高灵敏度的分析工具. 本文介绍了它的原理及应用,尤其是对脉冲喷射傅里叶变换微波谱仪研究范德华力配合物、氢键配合物、弱氢键配合物、卤键配合物等弱相互作用体系的微波转动谱也作了简要的综述.      

超弦

基本粒子物理(或称高能物理)的一个重要问题就是寻求各种相互作用力的统一理论.现在人们已经认识到自然界中存在着四种相互作用力:引力、电磁力、弱相互作用力和强相互作用力,而超弦理论就是关于这四种力的最新的,也是迄今为止最有希望的统一理论. 物理学家已经成功地将.电磁相互作用和弱相互作用统一起来了.包括强相互作用在内的“大统一理论”能成功地预言弱电统一理论中决定这两种力相对强度的参数,不过现在还缺少有关大统一理论的直接实验验证. 在某种程度上由于没有一个与量子力学原理自洽的引力理论,因此包括引力在内的统一理论的尝试…     

走向统一的自然力 弱力和电磁力的统一(Ⅲ)

<正>3.弱电统一理论及其实验验证前面提到,在揭示弱力物理本质的过程中,费米在他的"?衰变理论"中首先指出,弱力和电磁力一样,是矢量相互作用。经过许多科学家近30年的实验和理论研究,终于证明了弱力确实是矢量相互作用。费米的这一想法,后来被费曼和盖尔曼进一步推广为守恒矢量流理论,并最终导致温伯格、格拉肖和萨拉姆建立了弱力与电磁力的统一理论。这一讲,我们介绍这两个理论及其实验验证。(1)守恒矢量流理论及其实验验证     

弱力和电磁力的统一(Ⅰ)

 弱力,又称弱相互作用(简称弱作用),因其强度, 在微观世界起作用的三种基本相互作用中,比强相互作用和电磁相互作用都要弱,故而得名。     

基于原子干涉仪的微观粒子弱等效原理检验

等效原理是广义相对论的两个基本假设之一,也是爱因斯坦对弱等效原理的推广.目前,大量实验证明弱等效原理在一定的实验精度内是成立的.将引力与标准模型统一起来的新理论都要求弱等效原理破缺,因此更高精度的弱等效原理检验具有重要的科学意义.本文介绍了原子干涉仪的原理,回顾了利用原子干涉仪开展微观粒子弱等效原理检验实验研究的历史和现状,介绍了双组分原子干涉仪检验弱等效原理实验涉及的振动噪声抑制、拉曼光移频与相位噪声抑制、四波双衍射拉曼跃迁原子干涉、信号探测与数据处理等关键问题及研究进展,分析了高精度微观粒子弱等效原理检验研究的发展趋势,介绍了长基线原子干涉仪、空间原子干涉仪、超冷原子源以及纠缠原子源制备等方面的研究动态,展望了微观粒子弱等效原理检验研究的发展前景.     

τ轻子物理

 粒子物理学中所研究的粒子,如果按照它们自身所具有的相互作用力来划分,可以分为强子和轻子两大类,各种相互作用的性质是十分不同的,具有了某一种相互作用力的粒子就会按照这种相互作用力的性质发生衰变、反应过程,强子具有强相互作用力,电磁相互作用力和弱相互作用力。但是,轻子就只具有电磁相互作用力(如果它带有电荷的话)和弱相互作用力。所以,强子和轻子的各种行为是十分不同的。     

用近距离引力实验检验粒子的洛伦兹对称性

正自然界存在着四种基本相互作用力:引力、强相互作用力、弱相互作用力和电磁相互作用力。目前,人们对自然界的描述基于两个成功的理论,即广义相对论和描述电磁、强、弱相互作用的统一理论。前者是一种经典理论,描述了一切宏观引力现象;后者是一种量子理论,描述了其他三种相互作用力。尽管这两种理论并未完全融合,但是人们相     

广义相对论中的等效原理与时空观

等效原理是广义相对论建立的基本思想实验原理, 它指出引力场和加速度的效应等价. 在等效原理中 有弱等效原理和强等效原理两个层次, 弱等效原理和强等效原理之间存在一定的联系. 以等效原理为基础将有助于 理解爱因斯坦的时空观     

走向统一的自然力弱力和电磁力的统一（Ⅱ）

 β 衰变的研究对揭示弱力的物理本质起了主要的,甚至可以说是决定性的作用。这一讲主要介绍通过β衰变实验和理论研究揭示弱力物理本质的过程：从费米提出β 衰变理论到普适（V-A）费米相互作用的确立。     

磁致伸缩材料弱磁场响应特性的实验研究

针对磁致伸缩材料在弱磁场传感器领域的应用需要,采用迈克耳逊干涉原理实验测量了零应力条件下Tb-Dy-Fe材料和Fe-Ga合金的磁场响应灵敏度,以及不同应力下Fe-Ga合金的磁场响应特性和温度响应特性.实验结果表明：在零应力,外加磁场16 mT条件下,Fe-Ga合金的磁场响应灵敏度远高于Tb-Dy-Fe材料,更合适作为弱磁场传感器敏感材料;同时,在1.2 MPa预应力和26 mT偏置磁场下,Fe-Ga合金材料具有较好的磁场响应灵敏度和较大的饱和磁致伸缩系数,因而处在最佳工作状态.所得到的材料的磁场和温度响应曲线可作为弱磁场传感器参量设计的参考依据.     

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.