X-ray scattering from a randomly rough surface

Abstract

On the basis of the method of reduced Rayleigh equations we present a simple and reciprocal theory of the coherent and incoherent scattering of x-rays from one- and two-dimensional randomly rough surfaces, that appears to be free from the limitations of earlier theories of such scattering based on the Born and distorted-wave Born approximations. In our approach, the reduced Rayleigh equation for the scattering amplitude(s) is solved perturbatively, with the small parameter of the theory η(ω) = 1 - ε(ω), where ε(ω) is the dielectric function of the scattering medium. The magnitude of η(ω) for x-rays is in the range from 10^?6 to 10^?3, depending on the wavelength of the x-rays. The contributions to the mean differential reflection coefficient from the coherent and incoherent components of the scattered x-rays are calculated through terms of second order in η(ω). The resulting expressions are valid to all orders in the surface profile function. The results for the incoherent scattering display a Yoneda peak when the scattering angle equals the critical angle for total internal reflection from the vacuum-scattering medium interface for a fixed angle of incidence, and when the angle of incidence equals the critical angle for total internal reflection for a fixed scattering angle. The approach used here may also be useful in theoretical studies of the scattering of electromagnetic waves from randomly rough dielectric-dielectric interfaces, when the difference between the dielectric constants on the two sides of the interface is small.     

骨折长骨中超声导波传播特性的仿真研究

采用超声导波评价长骨骨折已成为近两年来的一个研究热点.本文采用混合边界元方法(HBEM)对超声导波在骨裂长骨中的传播情况以及各导波模式的反射系数和透射系数进行了数值分析.研究结果表明,入射导波模式经由裂纹处模式转换后依然保持为主要接收模式不变.对某一裂纹,各模式透射系数常在相近的频率点上达到局部峰值.对于不同深宽比(d/w)裂纹,某些模式透射系数曲线局部峰值所对应的频率存在着相互错开的现象,这些结果可用于选择最优入射导波模式和频率,以便更好地定量评价骨质以及骨裂状况.     

Hydrothermal Synthesis and Crystal Structure of a Novel Polyoxometalate K(C_4N_2H_(12))_4(C_4N_2H_(11))_(2-)[Mo_8~ⅤMo_4~ⅥCdP_8O_(54)(OH)_8]F·6H_2O

The title compound 1 has been synthesized by the reaction of H_2MoO_4, CdCl_2, H_3PO_4, KF, piperazine hexahydrate and water in aqueous solution under mild hydrothermal conditions. Single-crystal X-ray analysis reveals that the title compound crystallizes in the triclinic system, space group P(-1) with a = 14.049(3), b = 15.972(3), c = 20.043(4) (A), α = 85.82(3), β = 81.28(3),γ = 67.15(3)°, V= 4095.9(14) (A)~3, M_r = 3204.62, Z=2,D_c = 2.598 g/cm~3,μ = 2.360 mm~(-1), F(000) = 3124, the final R = 0.0314, wR = 0.0826 and S = 0.989 for 18592 observed reflections with I > 2σ(I). The crystal packing is stabilized by N-H…O and O-H…O intra- and intermolecular hydrogen bonds to form an infinite 3D network.     

A Simple and Rapid Label-free Fluorimetric “Turn Off-on” Sensor for Cadmium Detection Using Glutathione-capped CdS Quantum Dots

A convenient label-free fluorescence(FL) nanoprobe for rapid detection of cadmium(Cd) was established using glutathione-capped CdS quantum dots(QDs) and 1,10-phenanthroline(phen). The prepared CdS QDs exhibited a strong FL emission at 536 nm, which could be quenched by phen due to the photoinduced hole transfer(PHT) mechanism. The existence of Cd effectively recovered the FL intensity of CdS QDs, which was due to the easy detachment of phen from the surface of QDs to form[Cd(phen)₂(H₂O)₂]²⁺ in solution. Cd concentrations were linearly correlated with the FL intensity in the range of 0.0625-1.25 μmol/L under the optimized conditions and the detection limit was 0.01 μmol/L. Finally, the Cd concentration was accurately quantified in real water sample using the proposed sensor.     

基频估计算法研究平均骨小梁间距

超声背散射信号能提供松质骨微结构信息从而能有效的诊断骨质疏松,而平均骨小梁间距(MTBS)是表征松质骨微结构的重要参数之一.本文提出了一种基频估计的MTBS估计算法,对仿真信号和离体牛胫骨松质骨中的超声背散射信号分别进行分析处理,并和现有的两种算法(简易反向滤波跟踪(SIFT)算法和AR倒谱法)进行比较.实验结果表明基频估计算法对噪卢和随机散射回波有更好的鲁棒性,在信噪比较低和随机散射回波幅度较大时估计值更加精确,且有很好的方差性能.充分说明了本文算法是一种有效的MTBS估计算法.     

纳米尺度CeO2在多相催化反应中的形貌效应

CeO2的催化性能不仅与粒子大小有关,而且与其形貌密切相关. 本文分析了CeO2的纳米结构和氧化还原特性,综述了CeO2在催化反应中的形貌效应,着重介绍了CeO2的结构和形貌对CO氧化、水气变换和乙醇水蒸气重整制氢以及二元醇脱水反应活性的影响.     

Interference of a pair of symmetric Collett-Wolf beams

We present a study of the interference of light produced by a pair of mutually correlated Gaussian Schell-model sources. The spatial distributions of the fields produced by these sources are symmetric with respect to a plane through their common center and differ by a phase factor exp(i phi). When phi = 0, the resulting radiation is a beam with an intensity distribution that displays a narrow bright line at its center. When the sources can be regarded as Collett-Wolf sources, the resulting bright line diverges much more slowly than the beam itself. When phi = pi the radiated beam has an intensity distribution with a narrow dark line at its center. The theoretical results are supported by experimental results obtained by use of a modified Michelson interferometer and suggest that the interference of a pair of correlated Collett-Wolf beams can be used to produce a pseudo-nondiffracting beam.