XDS: a flexible beamline for X‐ray diffraction and spectroscopy at the Brazilian synchrotron

The majority of the beamlines at the Brazilian Synchrotron Light Source Laboratory (LNLS) use radiation produced in the storage‐ring bending magnets and are therefore currently limited in the flux that can be used in the harder part of the X‐ray spectrum (above ～10 keV). A 4 T superconducting multipolar wiggler (SCW) was recently installed at LNLS in order to improve the photon flux above 10 keV and fulfill the demands set by the materials science community. A new multi‐purpose beamline was then installed at the LNLS using the SCW as a photon source. The XDS is a flexible beamline operating in the energy range between 5 and 30 keV, designed to perform experiments using absorption, diffraction and scattering techniques. Most of the work performed at the XDS beamline concentrates on X‐ray absorption spectroscopy at energies above 18 keV and high‐resolution diffraction experiments. More recently, new setups and photon‐hungry experiments such as total X‐ray scattering, X‐ray diffraction under high pressures, resonant X‐ray emission spectroscopy, among others, have started to become routine at XDS. Here, the XDS beamline characteristics, performance and a few new experimental possibilities are described.     

Study of a magnetic alloy-loaded cavity for compact synchrotrons

Magnetic alloy(MA)-loaded cavities have been widely used in compact proton and heavy-ion synchrotrons,and the MA core is the key issue in their development.Chinese-produced MA has never yet been adopted as core material for an MA-loaded cavity.To use Chinese-produced MA as the core material,it is necessary to study its properties,and compare with MA material produced elsewhere.In this paper,the properties of several MA cores made of Chinese-produced material are measured.Based on the measured results,a schematic design is produced for a cavity which could obtain 1 kV gap voltage with less than 1.5 kW power dissipation in the frequency range of0.5-7 MHz.The difference between resonant frequencies obtained from simulation and analytical results is less than10%.     

Improving microwave dielectric properties of La2.98/3Sr0.01(Mg0.5Sn0.5)O3 ceramics with CuO additive

The microwave dielectric properties of CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were investigated with a view to their application in microwave devices. CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics exhibited no significant variation of phase with sintering temperature. By adding 0.75 wt.% CuO, a dielectric constant of 20.07, a quality factor (Q × f) of 63,000 GHz, and a temperature coefficient of resonant frequency τ_f (−77.0 ppm/°C) were obtained when La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were sintered at 1500 °C for 4 h.     

含有序孔洞的多孔氧化铝薄膜的弹性模量测量

高纯铝箔在特定的溶液下经过电化学阳极氧化腐蚀，可在其表面生成一层多孔的非晶氧化铝层，孔大致呈六方密排，孔径分布均匀。此类薄膜具有规则的纳米级孔径，大的比表面积，可用在微纳滤方面和纳米材料组装方面。然而，对于此类薄膜力学性能的研究较少，在一定程度上限制其功能的开发和应用。为了获得此类多孔膜的弹性常数，本文用鼓膜法结合散斑干涉实验方法、单轴拉伸结合双光束干涉法和多普勒测振仪三种方法测量氧化铝多孔膜的弹性模量，得到的宏观弹性模量基本相同，并对三种方法的优缺点进行了比较，分析了多孔氧化铝膜与块状氧化铝材料或致密氧化铝膜力学性能的差并。     

旋转悬臂Rayleigh轴的Galerkin近似解1)

主要研究旋转悬臂Rayleigh轴的涡动频率和临界转速。基于Rayleigh 梁模型建立旋转悬臂Rayleigh轴的运动方程,通过Galerkin法将运动方程离散化,Galerkin 过程分别选择不旋转Euler--Bernoulli 轴的振型函数和旋转Rayleigh 轴的振型函数为试探函数,对不同方法得到的数值结果进行收敛性验证和对比分析,并且将其与涡动频率和临界转速的经典解 进行比较。结果表明,采用不旋转振型函数简单快捷,能够极大地方便计算过程,因此,将其用于近似求解旋转悬臂轴的动力学特性具有明显的优越性。     

基于FPGA的高精度硅微谐振加速度计数据采集与参数补偿系统设计与实现

硅微谐振加速度计因具有小体积优势和高精度潜力,成为硅微惯性传感器研制的热点之一。频率信号的高精度采集和系统参数补偿是提高硅微谐振加速度计性能的重要手段之一。在分析硅微谐振加速度计工作机理的基础上,从双路差动频率信号的精确采集和系统误差参数补偿角度出发,分析了数据采集的原理,提出了一种高精度硅微谐振加速度计用数据采集与参数补偿方法。给出了设计思路和电路实现方法,讨论了误差来源与改进方法。所设计的数据采集系统针对中心频率18 k Hz.,标度因数400 Hz/g,量程±20g的加速度计,数据更新周期200 ms下频率分辨率为0.0005 Hz,等效加速度分辨率达到1.25μg。测试表明,补偿后的硅微谐振加速度计,在全温(-40~+70℃)内,K0温度系数从262μg/℃降低到29.9μg/℃,K1变化量从4.18%降低到2.04‰,全量程非线性从7.16‰降低到0.128‰,系统参数满足设计指标。     

基于谱元法的空间刚架动力学特性分析

以空间刚架结构为研究对象,应用谱元法研究其动力学特性,依次推导出杆、轴和铁木辛柯梁的动力学刚度阵,进而得到空间刚架的动力学刚度阵和频域响应的理论方程,拓展了谱元法应用范围。编程计算获得空间刚架的固有频率和点的谐响应曲线,与有限元分析相比较,进一步得到载荷下的瞬态响应。研究表明,谱元法在刚架结构的动力学特性分析中,比有限元方法高效高精度,更适宜解决中高频振动问题。     

有多阶固有频率要求的组合结构设计

在各子结构的振动固有特性（固有频率、振型）已知下，通过设计子结构间的连接元件，使得组合结构的多阶固有频率得到满足。在组合结构动力重分析中，以各子结构的剩余附着模态作为其保留模态的补充，进行模态缩减，保证了计算的精度，提高了计算速度。对具有刚体模态的子结构采取了移频处理技术。文中给出的两个设计计算实例，表明了本文方法的有效性。     

Initiation of Combustion in a Supersonic Hydrogen-Air Mixture Flow by CO<Subscript>2</Subscript>-Laser Radiation

Features of the ignition kinetics of an H₂/air mixture in the supersonic flow behind an inclined shock front are analyzed when asymmetric vibrations of a small amount (<1%) of O₃ molecules specially introduced into the initial mixture are excited by 9.7 μm wavelength radiation. It is shown that this radiation leads to intensification of the chain reactions and makes it possible to organize combustion at small distances from the front (of the order of 1 m) of even relatively weak shocks at small values of the laser radiation energies absorbed by the gas. This method of initiating combustion in a supersonic flow is 10–100 times more efficient than the thermal method.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 157–167.Original Russian Text Copyright © 2005 by Lukhovitskii, Starik, and Titova.     

三维电磁场辛有限元列式及电磁共振腔的计算

针对三维共振腔的电磁场分析,利用Maxwell方程的对偶方程体系形式,从其相应的对偶变量变分原理出发,导出了三维电磁场辛有限单元的详细列式。为了有限元列式的保辛,变分原理被积函数可导向对于对偶变量为对称的形式。变分原理的边界积分项对于相邻单元相互抵消。由于采用了对偶变量的插值函数,使得电磁场单元构造可以在层面上进行,从而避免了所谓的连续性问题。无物理意义的零本征解可采用奇异值分解加以排除。文末分别对矩形及圆柱形的共振腔做了数值计算并与解析解和棱边元计算结果进行对比,算例表明了列式及算法的有效性。