Reference-wave solutions for high-frequency fields propagating in random media

Ray theory plays an important role in determining the propagation properties of high-frequency fields and their statistical measures in complicated random environments. According to the ray approach, the field at the observer can be synthesized from a variety of field species arriving along multiple ray trajectories resulting from refraction and scattering from boundaries and from scattering centers embedded in the random medium. For computations of the statistical measures, it is desirable therefore to possess a solution for the high-frequency field propagating along an isolated ray trajectory. For this reason, a new reference-wave method was developed to provide an analytic solution of the parabolic-wave equation.     

蒙特卡洛法、离散传递法中的假散射与射线效应

本文构造了激光平行入射二维半透明介质的物理模型,研究了蒙特卡洛法、离散传递法中的假散射。通过分析 边界净热流研究了蒙特卡洛法、离散传递法中的射线效应。计算分析表明:蒙特卡洛法、离散传递法不存在假散射。蒙特 卡洛法不存在射线效应,离散传递法存在射线效应。在离散传递法中,随着射线数的增加,射线效应逐渐减少。     

Optical ray paths in a quasi-periodic waveguide or a multipass cavity with smoothly varying properties

Ray paths in a quasi-periodic optical system (waveguide of cavity) with smoothly varying properties have been constructed along the ray path. The ray-transfer matrix is constructed for a large number of ray paths; it has been shown that the conventional stability condition (the modulus of the ray-transfer matrix trace for a ray path is smaller than two) does not ensure the boundedness of the beam path after a large number of paths.     

Frequency-dependent shot noise in long disordered superconductor-normal-metal-superconductor contacts

The shot noise in long diffusive superconductor-normal-metal-superconductor contacts is calculated using the semiclassical approach. At low frequencies and for purely elastic scattering, the voltage dependence of the noise is of the form S(I) = (4Delta+2eV)/3R. The electron-electron scattering suppresses the noise at small voltages resulting in vanishing noise yet infinite dS(I)/dV at V = 0. The distribution function of electrons consists of a series of steps, and the frequency dependence of noise exhibits peculiarities at omega = neV, omega = neV-2Delta, and omega = 2Delta-neV for integer n.     

Detection of Supersymmetric Dark Matter

A re-analysis of a heavy charged particle production event observed at the cloudy chamber of the Yunnan Cosmic Ray Station (YCRS) in 1972 indicates that the mysterious heavy particle may be identified as a supersymmetric (SUSY) particle produced by a bombard of a neutral SUSY cosmic ray particle on proton. Based on the assumption, following the literatures that the neutral SUSYparticle which constitutes the main fiaction of the cold dark matter is scalar neutrino (sneutrino) or neutralino (photino), we evaluate the flux of such SUSY particles which gain sufficient energies via elastic scattering with charged cosmic particles on the way to an Earth detector and the capture rates in both the sneutrino and photino cases respectively. The errors appearing in the study are briefly discussed and this work may provide a basis of designing cosmic ray detectors to search for SUSY particles from the heaven.     

软 X射线共振非弹性光散射及其应用

软 X射线共振非弹性光散射是近年来随着高亮度第三代同步辐射出现而发展起来的光散射光谱技术 ,可以用于对多原子构成的分子、凝聚态物质进行位置选择的价电子态结构的研究。与 X射线光电子能谱 ( XPS)或紫外光电子能谱 ( UPS)相比 ,这一光谱方法由于测量样品激发后产生的散射 X射线 ,因而不仅可以获得表面的原子分子信息 ,而且可以用于研究样品体内或掩埋薄层的原子分子。同时这一方法的共振特性使得其可以进行灵敏的元素选择测量。本文将介绍这一光散射光谱技术及其在原子分子物理、表面物理及凝聚态物理中的应用     

Finite element modeling of reverberation and transmission loss in shallow water waveguides with rough boundaries

A finite element model for the reverberation and propagation in a shallow water waveguide with a sandy bottom was calculated for five different environments at a center frequency of 250 Hz. The various environments included a rough water/sediment interface, a rough air/water interface, roughness at both interfaces and downward and upward refracting sound speed profiles with roughness at both interfaces. When compared to other models of reverberation such as ray theory, coupled modes, and parabolic equations, finite elements predicted higher levels of reverberation. At early times, this is due to the "fathometer" return, energy that is normally incident on the boundaries at zero range. At later times, the increased reverberation was due to high angle scattering paths between the two interfaces. Differences in reverberation levels among the environments indicated that scattered energy from the air/water interface is transmitted into the bottom at steep angles. This led to a large decrease in reverberation for a rough air/water interface relative to a rough water/sediment interface. Sound speed profile effects on reverberation were minimal at this frequency range. Calculations of the scintillation index of the different environments indicated that most of the reverberation was relatively Rayleigh-like with heavier tailed distributions at longer ranges.     

Quantitative speciation of manganese oxide mixtures by RIXS/RRS spectroscopy

Resonant inelastic X‐ray scattering, also named X‐ray resonant Raman scattering, was recently used to discriminate local chemical environments. By means of this novel technique, the speciation of samples could be attained in a variety of samples and experimental conditions. Until now, this discrimination methodology had been applied only to pure compounds, being the speciation possible by two different mathematical treatments. Nevertheless, the effectiveness/sensitivity of this technique has not been tested yet in samples containing mixtures of oxides of the same element. In this work, the first results of quantitative speciation of mixtures of manganese compounds, using resonant inelastic X‐ray scattering/X‐ray resonant Raman scattering spectroscopy, are presented. The results show that it is possible to discriminate and quantify oxide mixtures of the same element in slightly different proportions, allowing a quantitative speciation of compound mixtures in a variety of experimental conditions, presenting also several advantages over conventional spectroscopic techniques. Copyright © 2017 John Wiley & Sons, Ltd.     

Particle acceleration at astrophysical shocks: A theory of cosmic ray origin

The theory of first order Fermi acceleration at collisionless astrophysical shock fronts is reviewed. Observations suggest that shock waves in different astrophysical environments accelerate cosmic rays efficiently. In the first order process, high energy particles diffuse through Alfvén waves that scatter them and couple them to the background plasma. These particles gain energy, on the average, every time they cross the schock front and bounce off approaching scattering centers. Calculations demonstrate that the distribution function transmitted by a plane shock is roughly a power law in momentum with slope similar to that inferred in galactic cosmic ray sources. The generation of the scattering Alfvén waves by the streaming cosmic rays is described and it is argued that the wave amplitude is probably non-linear within sufficiently strong astrophysical shocks. Hydromagnetic scattering can operate on the thermal particles as well, possibly establishing the shock structure. This suggests a model of strong collisionless shocks in which high energy particles are inevitably produced very efficiently. Observable consequences of this model, together with its limitations and some alternatives, are described. Cosmic ray origin and astrophysical shocks can no longer be considered separately.     

球谐函数法求解辐射传输方程的假散射和射线效应

假散射和射线效应是辐射传输方程近似解法中出现的特有误差.从辐射传输方程的近似求解过程出发,在定性分析的基础上构造物理模型,通过数值模拟研究球谐函数法(P₁和P₃近似法)的假散射和射线效应.构造激光平行入射和倾斜入射二维半透明介质的物理模型,通过内部温度场的分布特征研究假散射.构造顶部侧面保持高温而其余侧面保持低温的二维半透明介质方案,通过对比底面边界净热流密度分析射线效应.计算结果表明球谐函数法中同时存在假散射和射线效应,P₃近似比P₁近似减小了射线效应.同时,球谐函数法的射线效应随光学厚度的增加而减小.     

Differential sum rule for the relaxation rate in the cuprates

Motivated by recent experiments by Basov et al., we study the differential sum rule for the effective scattering rate 1/tau(omega). We show that, in a dirty BCS superconductor, the area under 1/tau(omega) does not change between the normal and the superconducting states. For magnetically mediated pairing, a similar result holds between Tor=T(c), while, in the pseudogap phase, 1/tau(omega) is just suppressed compared to 1/tau(omega) in the normal state. We argue that this violation of the differential sum rule in the pseudogap phase is due to the absence of the feedback effects from the pairing.     

Geometric optics analysis of non-circular,graded-index fibres

The cross-sections of practical optical fibres do not have perfect circular symmetry. The appropriate mathematical representation of the refractive index profile is discussed and it is shown that the basic power law profile in circular fibres should be replaced by a grading functionF which is a homogeneous function of thex andy coordinates. Multimode optical fibres of this type are analysed using geometric optics. General properties of ray paths are described. The fundamental quantities of interest in fibre optics (power acceptance, ray transit time, impulse response) are shown to depend on the degree of homogeneity ofF but not on its specific form. Thus, fibres need not have circular symmetry in order to retain the desirable properties of the circular power law fibres. Ray paths and classifications are analysed in detail for elliptical, parabolic-index fibres. Splicing losses are examined and are shown to be not drastically dependent on deviations from circular symmetry.     

X‐ray‐Raman‐scattering‐based EXAFS beyond the dipole limit

X‐ray Raman scattering (XRS) provides a bulk‐sensitive method of measuring the extended X‐ray absorption fine structure (EXAFS) of soft X‐ray absorption edges. Accurate measurements and data analysis procedures for the determination of XRS‐EXAFS of polycrystalline diamond are described. The contributions of various angular‐momentum components beyond the dipole limit to the atomic background and the EXAFS oscillations are incorporated using self‐consistent real‐space multiple‐scattering calculations. The properly extracted XRS‐EXAFS oscillations are in good agreement with calculations and earlier soft X‐ray EXAFS results. It is shown, however, that under certain conditions multiple‐scattering contributions to XRS‐EXAFS deviate from those in standard EXAFS, leading to noticeable changes in the real‐space signal at higher momentum transfers owing to non‐dipole contributions. These results pave the way for the accurate application of XRS‐EXAFS to previously inaccessible light‐element systems.     

Temperature dependence of electron mobility in GaAs/GaAlAs modulation doped quantum wells

We report the temperature dependence of the drift mobility in GaAsGa_1−x Al_x As modulation doped quantum wells. A theoretical model is formulated which includes scattering by (i) residual impurities located in the well, in the barrier, and at the “inverted” interface, (ii) Si donors and (iii) accoustic phonons. Contributions from the diffused profile of doped Si impurities and the background impurities piled up at the interface, are separated through S.I.M.S. experiments and temperature dependence of the scattering rate. The density of interface scattering centers increases with alloy composition x.     

A large‐solid‐angle X‐ray Raman scattering spectrometer at ID20 of the European Synchrotron Radiation Facility

An end‐station for X‐ray Raman scattering spectroscopy at beamline ID20 of the European Synchrotron Radiation Facility is described. This end‐station is dedicated to the study of shallow core electronic excitations using non‐resonant inelastic X‐ray scattering. The spectrometer has 72 spherically bent analyzer crystals arranged in six modular groups of 12 analyzer crystals each for a combined maximum flexibility and large solid angle of detection. Each of the six analyzer modules houses one pixelated area detector allowing for X‐ray Raman scattering based imaging and efficient separation of the desired signal from the sample and spurious scattering from the often used complicated sample environments. This new end‐station provides an unprecedented instrument for X‐ray Raman scattering, which is a spectroscopic tool of great interest for the study of low‐energy X‐ray absorption spectra in materials under in situ conditions, such as in operando batteries and fuel cells, in situ catalytic reactions, and extreme pressure and temperature conditions.     

Reference-wave solutions for the high-frequency fields in inhomogeneous-background random media

Ray theory plays an important role in determining the propagation properties of high-frequency fields and their statistical measures in complicated random environments. For computations of the statistical measures it is therefore desirable to have a solution for the high-frequency field propagating along an isolated ray trajectory. A new reference wave is applied to obtain an analytic solution of the parabolic wave equation that describes propagation along the ray trajectory of the deterministic-background medium. The methodology is based on defining a paired-field measure as a product of an unknown field propagating in a disturbed medium and the complex-conjugate component propagating in a medium without random fluctuations. When a solution of the equation for the paired-field measure is obtained, the solution of the deterministic component can be extracted from the paired solution to determine the solution of the unknown field in an explicit form.     

The cosmic ray actinide charge spectrum derived from a 10 m array of solid state nuclear track detectors in Earth orbit

The DIAS-ESTEC Ultra Heavy Cosmic Ray Experiment (UHCRE) on the Long Duration Exposure Facility, collected approximately 3000 cosmic ray nuclei with Z>65 in the energy region E>1.5 GeVnucleon⁻¹ during a six year exposure in Earth orbit. The entire accessible collecting area of the solid state nuclear track detector (SSNTD) array has been scanned for actinides, yielding a sample of 30 from an exposure of ≈150 m² sryr. The UHCRE experimental setup is described and the observed charge spectrum presented. The current best value for the cosmic ray actinide relative abundance, (Z>88)/(74Z87), is reported.     

Physical interpretation of the spectrum of black hole quasinormal modes

When a classical black hole is perturbed, its relaxation is governed by a set of quasinormal modes with complex frequencies omega=omega R +i omega I. We show that this behavior is the same as that of damped harmonic oscillators whose real frequencies are (omega R2+omega I 2)1/2, rather than simply omega R. Since, for highly excited modes, omega I>omega R, this observation changes drastically the physical understanding of the black hole spectrum and forces a reexamination of various results in the literature. In particular, adapting a derivation by Hod, we find that the area of the horizon of a Schwarzschild black hole is quantized in units Delta A=8pi l Pl2, in contrast with the original result Delta A=4log(3)l Pl2.     

Pressure and scattering regime influence on the EDS profile resolution at a composite interface in environmental SEM

Gas impact on the EDS profile resolution at the interface of composite interface resin/Al was investigated with two gaseous environments: helium and water vapor. Two main components of the global profile at the interface were investigated: the contrast of the profile and the spatial resolution. A complementary approach was developed by comparing gas nature impact versus the pressure and versus the scattering regime. The results show that the unscattered electron beam mainly governs EDS profile spatial resolution as long as the scattering regime is single or oligo scattering. Then for plural scattering, spatial resolution is dramatically degraded. In addition, the contrast is degraded since a gas is introduced, whatever the gas, the pressure and so the scattering regime. This approach would enable to better understand the respective contributions of the unscattered beam and the skirt and the influence of the gases nature on them.     

The search for electron rings inside atoms led to the Debye‐Scherrer method

When physicists perform and evaluate experiments they sometimes have to learn that their results differ significantly from their initial expectations. An example of this are the findings of physicists Peter Debye from the Netherlands (1884–1966) (Fig. 2) and Paul Scherrer from Switzerland (1890–1969) (Fig. 3). Their 1915 report, Interferences on Randomly Distributed Particles in X‐Ray Light, Part I (Interferenzen an regellos orientierten Teilchen im Röntgenlicht I) described the development of a new approach to solve the atomic structure of crystals: X‐ray powder diffractometry [1].