Mie理论递推公式计算散射相位函数

在激光雷达探测中,关于多次散射雷达回波的研究,散射相位函数是个非常重要的物理量。本文利用Mie理论的递推公式,对单一粒径介质的散射相位函数进行了计算,计算结果与散射理论中前、后向散射峰值大小随粒子半径的增大而增大相一致。同时,对非单一粒径介质的散射相位函数进行了计算,可用于大气、雾和云等气溶胶多次散射的研究。     

α粒子散射实验的理论模拟

本文在α粒子一次散射理论的基础上,进一步考虑了第二个原子对散射概率的贡献,建立了散射角与各散射参数间的关系.通过改变α粒子的入射能量以及两原子的位置参量,较好地模拟了各种情况下的散射概率随散射角的分布情况.     

X-ray magnetic scattering

The magnetic scattering of synchrotron X-rays has been developed to the point where it is now a standard technique for the study of magnetism and magnetic materials, often complementing neutron investigations of magnetic structures. In this article, after a brief historical introduction, examples of experiments on lanthanide and actinide antiferromagnets are presented. X-ray diffraction and Compton scattering studies of ferromagnets are then considered. Finally future prospects and possibilities are discussed.     

Fundamental cosmic strings

Cosmic strings are linear concentrations of energy that may be formed at phase transitions in the very early universe. At one time they were thought to provide a possible origin for the density inhomogeneities from which galaxies eventually develop, though this idea has been ruled out, primarily by observations of the cosmic microwave background (CMB). Fundamental strings are the supposed building blocks of all matter in superstring theory or its modern version, M-theory. These two concepts were originally very far apart, but recent developments have brought them closer. The ‘brane-world’ scenario in particular suggests the existence of macroscopic fundamental strings that could well play a role very similar to that of cosmic strings.

In this paper, we outline these new developments, and also analyse recent observational evidence, and prospects for the future.     

基于自发瑞利-布里渊散射测量空气的温度

瑞利-布里渊散射的散射截面比拉曼散射大,因而其在大气散射中实现对大气对流层温度廓线的准确测量方面具有一定的优势,同时利用瑞利-布里渊散射实现高压环境下温度的准确测量对于航天飞机主引擎状态的监测和超燃发动机燃烧室参数测量方面具有重要意义。基于自发瑞利-布里渊散射分别采用反卷积方法和卷积方法来实现空气在不同压力条件下的温度反演,研究引起温度反演误差的原因,并对利用两种方法获得的温度测量结果进行了比较。在利用基于维纳滤波器的反卷积方法对测量光谱直接处理实现温度反演之前,首先利用反卷积方法对由自发瑞利-布里渊散射模型与仪器函数卷积得到的卷积光谱进行处理获得反卷积光谱,将反卷积光谱与未经卷积的理论计算光谱进行比较实现温度反演, 并基于温度反演误差小于1.0 K,光谱拟合误差相对较小,光谱处理时间短的参数优化原则对反卷积方法中的关键参数奇异值叠加数进行了优化处理,得到优化后的奇异值叠加数为150。随后实验测量了由532 nm波长的连续激光激发的纯净空气在温度为294.0 K,压强为1～7 bar条件下的自发瑞利-布里渊散射光谱,并结合理论计算光谱和最小χ2值原理对光谱信号散射角进行优化,优化值为90.7°,同时利用反卷积和卷积方法分别对实验测量光谱进行处理实现空气在不同压强下的温度反演。实验结果表明反卷积方法在一定程度上可以提高信号光谱分辨率,而且利用反卷积和卷积方法均可以实现空气在不同压力（1～7 bar）条件下温度的准确测量,温度测量的最大误差均小于2.0 K;利用反卷积方法的温度反演结果随着气体压强的增大随之得到改善,实现温度反演测量所需要的光谱处理时间减少;在空气压强较低（≤2 bar）时,由卷积方法获得的温度反演结果要优于反卷积方法,压强较高（>2 bar）时,两种方法的温度反演结果相近, 其绝对误差均小于1.0 K。通过分析得到引起两种方法温度反演误差的原因主要包括环境温度的波动（±0.2 K）,散射角存在一定的不确定度以及气体的各已知参数的微量偏差对温度测量结果的影响以及反卷积对光谱噪声的非线性放大引起的光谱扰动对温度测量结果的影响。在实验中可以通过提高测量光谱的信噪比、提高散射角的优化精度及改善反卷积方法来获得更加准确的参数测量结果。     

Role of IUC-DAEF in promoting neutron beam research in India

Inter University Consortium for Department of Atomic Energy Facilities (IUC-DAEF) is an autonomous institute of the University Grants Commission and provides an interface between the university fraternity and the institutions of Department of Atomic Energy. Mumbai Centre of IUC-DAEF promotes and supports the use of neutron facilities at Dhruva reactor by the university scientists. To augment the existing neutron scattering facilities, IUC-DAEF has developed a neutron beam line at Dhruva reactor. The present paper gives a brief survey of the activities and achievements of Mumbai Centre of IUC-DAEF.     

Pockels效应对布里渊散射张量的修正

从电磁场方程和压电本构方程出发。借助于准静态近似的物理图像，导出了压电晶体中准静电场的表达式。给出了Ｐｏｃｋｅｌｓ效应对布里渊散射张量修正的一般形式．对１９种非中心对称点群晶体的高对称方向纯模作了具体计算，并对结果作了讨论．     

Light scattering theories and computer codes

In aerosol science today light scattering simulations are regarded as an indispensable tool to develop new particle characterization techniques or in solving inverse light scattering problems. Light scattering theories and related computational methods have evolved rapidly during the past decade such that scattering computations for wavelength sized nonspherical scatterers can be easily performed. This significant progress has resulted from rapid advances in computational algorithms developed in this field and from improved computer hardware.In this paper a review of the recent progress of light scattering theories and available computational programs is presented. We will focus on exact theories and will not cover approximate methods such as geometrical optics. Short outlines of the various theories are given alongside with informations on their capabilities and restrictions.     

火灾烟雾颗粒532 nm光散射矩阵实验研究

基于自主研制的结合偏振调制和锁相检测技术的光散射实验装置,测量了两种典型火灾烟雾颗粒(棉绳阴燃烟雾和正庚烷池火烟雾)及超声雾化水滴颗粒的532 nm光散射矩阵元素随散射角的分布. 通过水滴颗粒测量结果与数值计算结果的比较验证了实验装置的可靠性. 对比分析了棉绳阴燃烟雾和正庚烷池火烟雾光散射矩阵元素随散射角的分布特征,讨论了该特征在颗粒区分上的应用. 研究了烟雾颗粒微观形貌特征对光散射矩阵的影响,发现可以利用Lorenz-Mie理论描述棉绳阴燃烟雾的光散射,表明其形貌为球形,并利用模拟退火拟合的方法得到了棉 关键词： 光散射 散射矩阵 烟雾     

稀土配合物的喇曼散射和超喇曼散射效应

以可见光为激发光,观测了稀土配合物的喇曼散射和超瑞利、超喇曼散射光谱,简单论述了超瑞利和超喇曼散射的理论,对实验测出的谱线进行了认证与分析     

Rayleigh and hyper-Rayleigh scatterings in solution

A concept of concentration gradient induced by incident radiation which describes the dependence of the Rayleigh (I_ω) and hyper-Rayleigh (I_2ω) intensities on the power as well as background concentration is proposed. In our previous paper, we have demonstrated the effect of concentration gradient on the first-, second- and third-order polarizabilities and discussed that concentration gradient in the system can be created in a different way. Here we demonstrate the most important origin of the concentration gradient in a system, i.e., the concentration gradient generation by the incident radiation. The formulae developed here can be applied to describe the optical behaviour of solution and gas-phase systems.     

Scaling of differential cross-section in high energy proton-helium scattering

Possible occurrence of scaling of differential cross-section for high energy hadronnucleus elastic scattering is demonstrated takingp-⁴He scattering as an example and using three well-known scaling variables proposed earlier for hadron-hadron scattering. The available data on differential cross-section ratio betweenE _lab=45 and 393 GeV are found to scale in all the three variables reasonably well and the positions of the dip and the secondary maximum are found to follow the predicted patterns of behaviour as a function of energy. Extrapolating the fits to the available slope-parameter data onto higher energies and using the scaling curves, the positions of the dip and the secondary maximum and the differential cross-section ratio as a function of |t| are predicted for higher energies.     

神光Ⅲ原型装置的全孔径背向散射诊断技术

为了更好地研究神光Ⅲ原型实验中激光与等离子体相互作用产生的散射光,研制了新的全孔径背向散射诊断系统。该系统根据布里渊散射与拉曼散射的性质区别,使用二向色镜对散射光进行分光提纯,采用真空滤波器、挡光板、高反滤波片以及改变倍频晶体角度等进行消杂光处理,进而减少杂散光对测量结果的影响。同时,该系统采用特制的全口径大光斑激光器模拟打靶散射光对光路透过率进行标定。实验结果表明:新的全孔径背向散射诊断系统工作状态稳定,明显减少了杂散光的影响,所测数据更加真实可靠。     

Boson peak, flickering noise, backscattering processes and radiative transfer in random media

The method of matrix Green’s functions in the classical theory of electromagnetic waves is stated. This method allows to obtain a closed equation system in the presence of the random media for the calculation both coherent, and incoherent (fluctuating) components of radiation. The density and heterogeneity of scattering media can be arbitrary. The coherent channel is calculated independently. The fluctuating radiation distribution in the medium is developed initially by an interference pattern generated by the coherent channel. The limitations of the processes speed are absent. The theory embraces such phenomena as the boson peak, flickering noise, memory effect, backscattering processes and also conventional radiative transfer equation and Fresnel’s formulae.     

动态光散射实验中散射光偏振状态的研究

颗粒散射光的偏振状态对提高动态光散射实验系统空间相干性和测量结果正确性有着重要影响,因此研究散射光的偏振状态具有重要现实意义的。本文利用米散射理论分析了入射光与散射光偏振状态之间的关系,在此基础上揭示了在动态光散射中使用垂直偏振光作为入射光的理论依据,并在实验中验证了上述理论的正确性。     

Existence of the transverse relaxation time in optically excited bulk semiconductors

Two basic types of depolarization mechanisms, carrier-carrier (CC) and carrier-phonon (CP) scattering, are investigated in optically excited bulk semiconductors (3D), in which the existence of the transverse relaxation time is proven based on the vector property of the interband transition matrix elements. The dephasing rates for both CC and CP scattering are determined to be equal to one half of the total scattering-rate-integrals weighted by the factors (1-\cos\chi), where \chi are the scattering angles. Analytical expressions of the polarization dephasing due to CC scattering are established by using an uncertainty broadening approach, and analytical ones due to both the polar optical-phonon and non-polar deformation potential scattering (including inter-valley scattering) are also presented by using the sharp spectral functions in the dephasing rate calculations. These formulas, which reveal the trivial role of the Coulomb screening effect in the depolarization processes, are used to explain the experimental results at hand and provide a clear physical picture that is difficult to extract from numerical treatments.     

Chou-Yang model and predictions for high-energy pion-deuteron scattering

Using fits to the available data on the pion and deuteron electromagnetic form factors and the Chou-Yang model, the computed values of differential cross-sections for high-energy pion-deuteron elastic scattering agree reasonably well with the available experimental data. Whereas only a shoulder is expected to appear up to energies of several hundreds of GeV, a dip and a secondary maximum are predicted to be conspicuous only forP _lab≫400 GeV/C. The position of the dip starts at a much lower value, |t _d| ≅ 0.5–0.6 GeV², as compared to the corresponding position in thepp scattering. The positions of the first dip are plotted against total cross-section which can be verified by future high-energy experiments. Limitations of the model predictions for ultrahigh energies are pointed out.     

布里渊增强非简并四波混频

在CS₂介质中观测到由声波引起的布里渊增强非简并四波混频(NFWM)和由分子取向栅产生的瑞利型NFWM.研究发现,分子取向栅与声波之间并不是相互独立的,声波的存在会破坏瑞利型NFWM和布里渊增强NFWM极化之间的相位关系. 关键词： 四波混频 布里渊散射 瑞利散射     

Neutron reflectivity study of adsorbed diblock copolymers

Summary In this paper, we summarize our cumulative work on neutron reflectivity studies of polystyrene-poly(vinyl-2-pyridine) (PS-PVP) and polystyrene-polyethylene oxide (PS-PEO) adsorbed at a quartz-solvent interface. Deuterated toluene was chosen as the solvent since it is a good solvent for PS and a poor one for either of the other two blocks. In this case, the polystyrene dangles into the solvent while the other block acts as an anchor. The neutron reflectivity studies reveal that the form of the polymer density profile normal to the substrate may be varied from an extended ?brush? to a condensed ?mushroom? conformation by manipulating the ratio of the molecular weights of the two blocks. In addition, we present new data on the PS-PEO system in a poor solvent, deuterated cyclohexane, under conditions of shear flow in Poiseuille geometry. We find that when the PS-PEO diblock is absorbed from cyclohexane and is allowed to relax, the PS chain takes on a ?mushroom? conformation. However, when the shear is applied, the layer shear thickens due to the PS chains extending to nearly twice their original lengths. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Small-angle light scattering studies of dense AOT-water-decane microemulsions

Summary We have performed extensive studies of a three-component microemulsion system composed of AOT-water-decane (AOT=sodium-bis-ethylhexyl-sulfosuccinate is an ionic surfactant) using small-angle light scattering (SALS). The small-angle scattering intensities are measured in the angular interval 0.001–0.1 radians, corresponding to a Bragg wave number range of 0.14 μm⁻¹<Q<<1.4 μm⁻¹. The measurements were made by changing temperature and volume fraction ϕ of the dispersed phase (water + AOT) in the range 0.05<ϕ<0.75. All samples have a fixed water-to-AOT molar ratio,w=[water]/[AOT]=40.8, in order to keep the same average droplet size in the stable one-phase region. With the SALS technique, we have been able to observe all the phase boundaries of a very complex phase diagram with a percolation line and many structural organizations within it. We observe at the percolation transition threshold, a scaling behavior of the intensity data. This behavior is a consequence of a clustering among microemulsion droplets near the percolation threshold. In addition, we describe in detail a structural transition from a droplet microemulsion to a bicontinuous one as suggested by a recent small-angle neutron scattering experiment. The loci of this transition are located several degrees above the percolation temperatures and are coincident with the maxima previously observed in shear viscosity. From the data analysis, we show that both the percolation phenomenon and this novel structural transition are derived from a large-scale aggregation between microemulsion droplets.