物理学──新技术的先导

物理学是研究物质运动的最普遍的形态(力学的、热学的、电磁学的等等)以及它们之间相互转化的一门基础科学.物理学基础研究的目的在于认识物质运动的客观规律和揭示不同层次的物质的内部结构.但历史事实证明,作为基础科学的物理学其研究结果往往能够变成改造世界的强有力的工具     

大气的激光监测

在人口稠密的工业区,大气污染已成为严重的问题,研究污染物以及它们和大气组分的反应已成为迫切的需要了.为了预示与日俱增的污染源对环境的影响和采取及时而有效的措施,需要建立大气的数学模型.这些模型的发展、完善和与之相关的连续监测,要求具有广泛的监测功能. 地球上的生命不仅直接或间接地受近地面的大气组分的影响,而且还受到平流层及平流层以上的大气组分的影响.要用合理的成本来恰当地监测这广阔的区域,为此激光监测是唯一可能提供这种功能的技术. 一、大气遥感技术的特点 激光器的发现促进了人们对物质的非线性特性的研究,以及关…     

时空的对称性

 时空的对称性是大自然的奇妙特性之一,这种特性几乎是无处不在。例如,从宏观的角度看,人和动物的形体结构是左右对称的,植物的结构也是左右对称的,飘落的雪花的结构也是对称的。从微观的角度看,所有晶体都是对称排列的,水分子的排列也是具有严格的对称性。对称性无论在人们的日常生活中,还是在科学研究和应用技术领域,都具有非常重要的作用和地位;它潜移默化地影响着人类的观念和思维,这点可以从人类建筑的对称结构和人的对称审美观来说明;尤其在物理科学的研究中,例如基本粒子的研究、半导体物理的研究等等,时空对称性都是处于核心地位的重要概念。     

纯相对的运动观必须批判──试评相对性原理

一、从牛顿的纯绝对运动观到 爱因斯坦的纯相对运动观 在经典力学中,牛顿把物体的运动机械地割裂为“绝对的和相对的,真正的和表现的,数学的和通常的”.在他看来,相对运动“不过是整体的和绝对的运动的一部分”,“是真正运动之差”.他认为自己的“水桶实验”找到了“直接与相对运动相反的水的真正绝对的旋转运动”。当物理学的发展深入到电磁现象的新领域时,光的传播定律就与体现这种形而上学的纯绝对运动观的经典相对性原理发生了严重的抵触. 爱因斯坦抓住电磁观象对于惯性运动也具有相对性的事实,把经典相对性原理推广为狭义相对性原理.他…     

在QCD中核子的静态性质

基于参数化的完全穿衣服的夸克传播子,　利用量子色动力学（QCD）研究了核子的磁矩和电荷半径平方的平均值与夸克动量的依赖关系。预言的核子磁矩和电荷半径的数值与文献中广泛应用的经验值和其他许多具有QCD特征的理论模型所预言的值一致。结果说明了核子的磁矩和电荷半径不是人们通常所理解的一个不变的常数,　而是依赖于核子中夸克动量的一个跑动量,　对于不同动量它们的值是不同的。计算结果也清楚地表明了所采用的参数化的夸克传播子的适用性和可靠性。     

物理学和天文学

历史上，物理学和天文学的发展是密切联系的。它们在整个现代科学的发展和技术的发达上起到了先锋的作用。物理学的基本规律和天文学提供的广亵的实验室构成了理想的科学发展的基础。20世纪的一系列科学上的重要突破正是这种优良结合的产物。今天，天文学和物理学又共同面对着更新的前测问题，并一道酝酿着新的科学上的重大进展。它们所取得的每一个进展也必然伴随着技术的创新和提高，也不断更新着人类的认识和文明。     

时间,计时标准和原子时钟

一、时间和它的标准问题在这星球土发展、生存和繁衍的人类,他们起始有时间观念恐怕不比有空间的观念来得迟。这种时间观念存在的表现有时是非常自然的。人是生存在三维空间里的,但是人类思维的发展是动的,辩证地开展的,是四维空间的。人类对于时间的感觉,是从因时而异的物质变化而觉察得的。最简单的物质的变化是一种物体的运动。不要以为颐和园门前的铜狮是     

赝标Goldstone玻色子的手征拉氏量的 Gasser-Leutwyler系数

基于我们提出的参数化的完全穿衣服的夸克传播子,我们预言了未知的赝标Goldstone玻色子的手征拉氏量的Gasser-Leutwyler系数Li。预言的G-L系的数值与在文献中广泛应用的经验值和其他许多具有QCD特征的理论模型所预言的值一致。说明参数化的夸克传播子的适用性和可靠性。     

焦耳在能量转化与守恒定律建立过程中的实验创新

能量转化与守恒定律的确立与19世纪初期工业革命的蓬勃发展有着直接的关系,不同行业的进展为定律的确立提供了坚实的事实基础.但是,固有的思想惯性又成为新思想建立的阻碍,给新定律的建立者制造了很多的麻烦.迈耶和亥姆霍兹的探索,奠定了能量转化与守恒定律的理论基础,焦耳的热功当量实验以丰富的实验内容、精确的实验数据,为定律的最终确立提供了坚实的实验基础.     

夸克喷注与胶子喷注角分布特性的研究

用蒙特卡洛模拟Jetset 7.4产生质心能量为91.2GeV的正负电子对撞事件. 在引入喷注的圆锥角后, 对不同味的夸克喷注和由不同味夸克发射的胶子产生的喷注的角分布特性进行了仔细研究. 结果发现, 在相同的能量下, 胶子喷注的角分布范围比夸克喷注的角分布范围要明显宽一些. 在带电粒子数、横动量相同的条件下, 胶子喷注的平均圆锥角比夸克喷注的平均圆锥角大很多. 喷注的平均圆锥角随带电多重数以及喷注的横动量的分布都呈线性正关联. 由不同味的夸克发射的胶子产生的喷注的圆锥角分布特性相同；而不同味的夸克喷注的圆锥角分布存在明显的差异.     

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.     

Investigation on characteristics of self-organization in Mach-Zehnder erbium-doped fiber laser cavity

The characteristics of coherent coupling in Mach-Zehnder erbium-doped fiber laser cavity are experimentally studied. By virtue of a seemly controlling of length difference between two interferometric arms, the obtained comb-like spectrum of interferometer resonator with a period of 0.06 nm commendably agrees with the theory of self-organization coherence. The coherent output exits from the output mirror of a fiber Bragg grating with 4.5% reflectivity. A high coherent combining efficiency of 94% is obtained. Investigation on characteristics of the leak power opens out self-organization mechanism in Mach-Zehnder composite cavity.     

Experimental study on SC RF cavities by using China large grain niobium for ILC

Large grain niobium has the potential of simplifying the production sequence and consequently reducing the cost of the superconducting RF cavities for ILC.To investigate the feasibility of fabrication and the possibility to achieve high gradient by large grain cavities,two 1.3 GHz cavities were made of China large grain niobium and a series of vertical tests were carried out following several different surfaces treatment procedures.Two cavities have both reached the high gradient of more than 43 MV/m repeatedly and the maximum accelerating field of 47.9 MV/m has been achieved by China large grain niobium.This paper introduces the features of the fabrication and surface treatments on the large grain cavities and presents the preliminary results of the research.     

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.     

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.     

The width of the rotational contour of vibrational and vibronic bands of complex molecules in the gas phase as a temperature indicator

From the independence of the contour of spectral density of the rotational (orientation) correlation function of a rigid molecular top of arbitrary symmetry on temperature in the frequency scale based on the reduced time of rotational orientation relaxation and from the near independence of the rotational contour of vibrational and vibronic absorption bands of dipole transitions in the same coordinates in a model of “regular diffusion” of the transition oscillator with a classically rotating rigid molecular top, it is suggested that it is possible to use the halfwidth of the contour for estimation of temperatures. Data are presented on the halfwidth of 48 contours of bands of A, B, and C types at this frequency for 12 compounds for a temperature range of from units to 500 degrees of absolute temperature measured experimentally and (for low temperatures) calculated by the quantum theory. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 312–317, May–June, 1997.     

Rotation of the light polarization plane by an ensemble of oriented linear associates: Model representations

In an “oriented gas” model expressions are obtained for the angle of nongyrotropic rotation of the polarization plane (NRPP) of transmitted light by an ensemble of oriented associates consisting of nongyrotropic molecules. The cluster character of the nongyrotropic rotation of the polarization plane and the dependence of its angle on the incident light polarization vector azimuth are noted, which distinguish linear and circular polarization effects. Measurement of linear dichroism by the angle of nongyrotropic rotation of the polarization plane with the use of commercial spectropolarimeters is theoretically justified. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072 Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 95–101, January–February, 1998.     

A modified voice conversion algorithm using compressed sensing

A voice conversion algorithm,which makes use of the information between continuous frames of speech by compressed sensing,is proposed in this paper.According to the sparsity property of the concatenated vector of several continuous Linear Spectrum Pairs（LSP）in the discrete cosine transformation domain,this paper utilizes compressed sensing to extract the compressed vector from the concatenated LSPs and uses it as the feature vector to train the conversion function.The results of evaluations demonstrate that the performance of this approach can averagely improve 3.21%with the conventional algorithm based on weighted frequency warping when choosing the appropriate numbers of speech frame.The experimental results also illustrate that the performance of voice conversion system can be improved by taking full advantage of the inter-frame information,because those information can make the converted speech remain the more stable acoustic properties which is inherent in inter-frames.     

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.     

Optimizing the imaging of the monkey auditory cortex: sparse vs. continuous fMRI

The noninvasive imaging of the monkey auditory system with functional magnetic resonance imaging (fMRI) can bridge the gap between electrophysiological studies in monkeys and imaging studies in humans. Some of the recent imaging of monkey auditory cortical and subcortical structures relies on a technique of “sparse imaging,” which was developed in human studies to sidestep the negative influence of scanner noise by adding periods of silence in between volume acquisition. Among the various aspects that have gone into the ongoing optimization of fMRI of the monkey auditory cortex, replacing the more common continuous-imaging paradigm with sparse imaging seemed to us to make the most obvious difference in the amount of activity that we could reliably obtain from awake or anesthetized animals. Here, we directly compare the sparse- and continuous-imaging paradigms in anesthetized animals. We document a strikingly greater auditory response with sparse imaging, both quantitatively and qualitatively, which includes a more expansive and robust tonotopic organization. There were instances where continuous imaging could better reveal organizational properties that sparse imaging missed, such as aspects of the hierarchical organization of auditory cortex. We consider the choice of imaging paradigm as a key component in optimizing the fMRI of the monkey auditory cortex.