激光散斑相关性和位移的关系研究

用统计理论研究激光散斑的相关性与位移的关系,并对此关系进行了实验研究,理论和实验结果对于数字散斑相关测量具有一定的指导意义。     

激光散斑时间漂移效应研究

报道了激光散斑时间漂移效应.引入了散斑模型,接收面上散斑场复振幅的强度和位相的统计性质证明了模型的合理性.基于此模型和相关算法,模拟了所有可能导致激光散斑时间漂移效应的物理因素的影响.模拟结果显示两个因素起主要作用.通过巧妙地改变VCSEL和CCD的工作状态,也证明了两个因素其主要作用,即激光器对表面的加热引起的表面膨胀和CCD的热效应带来的噪声增加.相比之下,其他因素仅仅会带来散斑图像的微小变化.     

全息干涉计量中干涉计量场的统计特性

本文运用统计学方法推导了全息干涉计量中散斑计量场的统计特性.证明了:干涉计量场的复振幅为复圆高斯随机变量;干扰计量场强度的概率密度服从负指数分布;散斑干涉计量场的系综平均值代表变形信息.     

固体折射率的激光散斑测量实验

根据透明固体的光学折射特性,对激光散斑法测量固体折射率遇到的关键问题进行分析讨论,搭建了近场散斑、远场散斑和像面散斑三种光学测量系统并进行了测量,即首先记录了固体折射前后的两幅散斑图,然后获得折射前后的微小面内偏移量,再根据理论公式计算出固体折射率。利用现有方法和改进方法,对厚度为3mm的固体玻璃折射率分别进行了传统全息和数字全息的实验对比研究。     

一类弱散射界面背向散射超声散斑一阶统计特性

对超声入射至分布有细小凹坑的界平面,这一类弱散射界面背向散射所形成的超声散斑的一阶统计特性进行了研究.在假设条件下,理论分析的结果表明,空间超声散斑的振幅服从Rice分布,而它们的相位概率密度函数是一个包含Gauss分布函数和Gauss概率积分函数的复合函数.当细孔密度非常大时,超声散斑的振幅就趋于Rayleigh分布.应用作者建立的由计算机控制扫描的实验系统,对这一类弱散射界面反射超声散斑的振幅分布进行了测量.实验结果表明,理论分析的结果是正确的,由此,所作的假设条件也是成立的.关键词：弱散射超声散斑统计特性     

像面散斑平均尺寸对激光散斑成像的影响

以激光散斑衬比分析为基础的激光散斑成像技术,是一种无需扫描的全场光学成像方法,在监测生理及病理状态下组织血流动态变化中的应用日益广泛.在实际应用中,像面散斑平均尺寸等多种因素影响散斑衬比值,使得该技术在反映血流变化的准确性方面受到影响.采用一种成像散斑计算机模拟方法研究了像面散斑平均尺寸对成像散斑统计特性的影响,分析了成像参数与像面散斑尺寸的定量关系,并通过物理模型实验对模拟结果进行了验证.研究结果确认了合理的像面散斑平均尺寸计算公式,证实了散斑衬比值随像面散斑平均尺寸增大而减小的现象,并为确定合理的成像参数提供了依据.     

象平面散斑场相位差的统计性质

运用弱散射体产生的部分显现散斑场相位差自由标准偏差的近似表达式,计算和分析了由单会聚透镜成象产生的象平面部分显现高斯散斑场相位差的自由统计性质.     

激光散斑的漂移现象以及数值模拟方法

当一束激光照射到粗糙表面上时会产生散斑.即使接收端保持静止,收集到的散斑图案依然会发生变化,看起来像是在“漂移”一样.我们的研究发现,此时散斑漂移的主要原因来自粗糙表面吸热膨胀导致反射光的相位变化,从而使得干涉图样发生变化.我们采集大量实验数据并且使用相关系数及其变化率对散斑的动态变化进行描述和分析.另外,我们还通过数值计算模拟了散斑漂移现象.     

透过散射介质的散斑统计特性研究

复杂散射介质的衍射通常会形成散斑图像,该特性使得其在激光技术、电子和光电子等领域具有重要的应用价值.搭建了透过散射介质衍射形成的散斑测量系统,研究了CCD曝光时间、衍射距离和散射面直径对散斑统计特性的影响.实验结果表明：改变光学系统参量,透过散射片的散斑特性也会随之改变;选择合适的曝光时间能够获取对比度和光强分布适中的散斑图像,其空间衍射特性可用散斑平均尺寸表征,但对于散斑特性的微小变化,则可利用相关系数和数字图像相关结果进行辅助分析.     

地震预测与统计物理

将现代统计物理学的理论和方法应用于地震和地震预测问题的研究，近年来取得了长足的进展，成为物理学和地震学之间一个最为活跃的交叉领域，这一领域所取得的成果，例如，将地震作为一种临界现象的模型，不仅丰富和深化了对地震的认识，而且改变了地震预测研究中的一些传统观念。文章介绍了这方面的研究进展，讨论了与这一领域相关的一些重要的物理概念和悬而未决的科学问题。     

主动光学成象系统衬比传递特性及有效作用距离的分析

从传输介质对照明和成象光束衰减作用(吸收和散射)的分析入手,通过细致的定量分析,得出了主动系统(包括同轴和非同轴两架)成象材比传模型.这些模型都是将系统参数和衬比联系起来的明确的等式,而且还给出了精度较好的简化模型.这些模型可以为定量分析介质对成象的影响和有关系统设计提供有效而方便的理论工具.     

等厚条纹对比度与暗背景光学元件

本文讨论了影响等厚条纹对比度的原因,指出了暗背景光学元件的优点。     

双参数变形玻色湮没算符高次幂的本征态及其量子统计性质

本文构造了双参数变形玻色湮没算符高次幂a^'k(k≥3)的k个正交归一木征态的数学结构,发现它们能构成一个完备的Hilbert空间,并且讨论了它们的量子统计性质.     

High pressure ‘cell’ model of compressed methane

Abstract

The Thomas-Fermi method is used to treat self-consistently a model of compressed methane. Two assumptions underlying the treatment are (i) the use of spherical averaging of the proton potential about the C atom in the methane molecule and (ii) the compressed spherical ‘cell’ model. Within this framework, the equilibrium bond length of CH₄ is calculated as a function of cell volume. The free space bond length given by this model is too large, and so results are presented for R_e/R_e(∞) versus cell volume. The volume is finally converted to an estimated pressure using an empirical equation of state. The relevance of the work to ices in planetary material is pointed out.     

Non-Lorentzian spectral functions for Coulomb quantum kinetics

Numerical solutions of the Kadanoff-Baym equations with self-energies in second Born approximation are presented for electrons in a bulk semiconductor. The results are used to analyze in detail the two-time spectral function .In particular, (I) the damping of the spectral function is investigated over a broad density range both, for low and high temperatures; (II), is compared to analytical expressions - an exponential and a recently proposed inverse hyperbolic cosine decay law; (III), the two analytical spectral functions are studied with respect to conservation of total energy, where for the inverse hyperbolic cosine an improved behavior is demonstrated. Received 7 August 1998     

Collective excitations of a degenerate Fermi vapour in a magnetic trap

We evaluate the small-amplitude excitations of a spin-polarized vapour of Fermi atoms confined inside a harmonic trap. The dispersion law is obtained for the vapour in the collisional regime inside a spherical trap of frequency , with n the number of radial nodes and the orbital angular momentum. The low-energy excitations are also treated in the case of an axially symmetric harmonic confinement. The collisionless regime is discussed with main reference to a Landau-Boltzmann equation for the Wigner distribution function: this equation is solved within a variational approach allowing an account of non-linearities. A comparative discussion of the eigenmodes of oscillation for confined Fermi and Bose vapours is presented in an Appendix. Received 23 February 1999 and Received in final form 21 April 1999     

Collective excitations of a periodic Bose condensate in the Wannier representation

We study the dispersion relation of the excitations of a dilute Bose-Einstein condensate confined in a periodic optical potential and its Bloch oscillations in an accelerated frame. The problem is reduced to one-dimensionality through a renormalization of the s-wave scattering length and the solution of the Bogolubov-de Gennes equations is formulated in terms of the appropriate Wannier functions. Some exact properties of a periodic one-dimensional condensate are easily demonstrated: (i) the lowest band at positive energy refers to phase modulations of the condensate and has a linear dispersion relation near the Brillouin zone centre; (ii) the higher bands arise from the superposition of localized excitations with definite phase relationships; and (iii) the wavenumber-dependent current under a constant force in the semiclassical transport regime vanishes at the zone boundaries. Early results by Slater [Phys. Rev. 87, 807 (1952)] on a soluble problem in electron energy bands are used to specify the conditions under which the Wannier functions may be approximated by on-site tight-binding orbitals of harmonic-oscillator form. In this approximation the connections between the low-lying excitations in a lattice and those in a harmonic well are easily visualized. Analytic results are obtained in the tight-binding scheme and are illustrated with simple numerical calculations for the dispersion relation and semiclassical transport in the lowest energy band, at values of the system parameters which are relevant to experiment. Received 3 December 1999 and Received in final form 22 March 2000     

缔合流体在高温高压下的自扩散系数研究

在统计力学理论基础上,本文提出了一个考虑氢键对自扩散系数影响的方程．这个方程为非氢键贡献部分与氢键贡献部分之积,其中自扩散系数的非氢键部分由Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ链模型求得,而一个分子中的平均氢键数随温度和密度的变化关系使用统计缔合流体理论得到。链节之间的相互作用能量参数由粘度的关联式获得,其它四个参数则由扩散系数的实验数据获得。对７个典型的缔合流体在相当宽的温度压力范围内计算的平均相对百分误差为５．９８％。     

Weakly nonextensive thermostatistics and the Ising model with long-range interactions

We introduce a new nonextensive entropic measure that grows like , where N is the size of the system under consideration. This kind of nonextensivity arises in a natural way in some N-body systems endowed with long-range interactions described by interparticle potentials. The power law (weakly nonextensive) behavior exhibited by is intermediate between (1) the linear (extensive) regime characterizing the standard Boltzmann-Gibbs entropy and (2) the exponential law (strongly nonextensive) behavior associated with the Tsallis generalized q-entropies. The functional is parametrized by the real number in such a way that the standard logarithmic entropy is recovered when . We study the mathematical properties of the new entropy, showing that the basic requirements for a well behaved entropy functional are verified, i.e., possesses the usual properties of positivity, equiprobability, concavity and irreversibility and verifies Khinchin axioms except the one related to additivity since is nonextensive. For , the entropy becomes superadditive in the thermodynamic limit. The present formalism is illustrated by a numerical study of the thermodynamic scaling laws of a ferromagnetic Ising model with long-range interactions. Received 24 May 2000