具有初应力的1-3型压电复合材料的横向共振分析

1-3型压电复合材料在极化处理过程中会出现极化残余应力,基于线性压电理论,采用解析方法研究了极化残余应力对1-3型压电复合材料的横向共振模态的影响．首先建立含有初始应力的平面波波动方程,基于Bloch波函数理论构建了位移和电势函数,从而最终得到方程的解．数值结果表明初始残余应力的出现降低了复合材料的横向振动频率,而材料的压电性则使得横向振动频率提高．初始剪应力对对横向振动的频率影响较小,可以忽略．第一阶及第二阶振动频率将随着初始应力的大小呈线性变化．得出的结论对超声换能器的制作和研究将提供有意义的指导作用．     

横向划痕对光场调制的近场模拟

熔石英亚表面划痕对入射激光的近场调制是导致光学元件低阈值损伤的主要因素之一. 用三维时域有限差分方法研究了连续横向划痕的近场分布, 对比了尖锐截面与光滑截面场调制的差异, 着重探讨了光场调制与划痕宽深比R的关系. 研究表明: 酸蚀后的光滑截面有助于减弱近场调制, 这类划痕的R>10.0时调制较弱且相互接近, R<5.0时调制显著增强. 当R取1---3时, 亚表面的调制达最大值, 最大电场幅值为入射波幅值的4.3倍. 当R取1.0---3.5时, 缺陷附近有80%以上取样点的最大电场幅值超过入射波幅值的2倍. 随着深度的增大, 强场区具有明显的"趋肤效应": 位于划痕正下方的强场区首先往左右两侧移动, 然后移向抛物口界面以及水平界面, 同时衍生出的多条增强线诱导整个亚表面层的光场增强.     

横向外延过生长磷化铟材料的生长速率模型

分别考虑气相扩散和掩膜表面扩散过程，建立了金属有机化学气相沉积条件下横向外延过生长的速率模型. 在砷化镓衬底上外延磷化铟条件下，模拟得到了生长速率随掩膜/窗口宽度(m/w)变化的关系. 通过讨论掩膜/窗口宽度的影响，说明了掩膜宽度、窗口宽度以及有效掩膜宽度是决定生长速率的关键因素. 以上结论与实验结果一致. 关键词： 横向外延 生长模型 扩散 生长速率     

三向受压混凝土的动态特性研究

为探究混凝土在三向受压状态下的动态特性,利用自行研制的大型多功能三轴材料试验机,进行不同应变速率(10-5/s、10-4/s、10-3/s、10-2/s)下混凝土不同定侧压比(1∶1、2∶1、3∶1、4∶1)的动态真三轴抗压试验,研究了混凝土在动态抗压下的强度和变形特性.结果表明:混凝土在三向受压状态下表现出明显的应变...     

斜拉桥中斜拉索的面内外耦合内共振分析

研究了桥面侧振引起的斜拉索非线性振动问题。基于Hamilton原理建立了拉索的非线性振动控制方程,并利用多尺度法得到了斜拉索振动方程的二阶近似解。通过具体算例分析了斜拉索面内一阶模态与面外一阶模态相互耦合发生内共振的可能性,讨论了拉索倾斜角对拉索振动的影响,比较了在零初始条件和非零初始条件下拉索振动响应的区别。研究发现:拉索内共振发生在一定的激励频率和激励幅值区域内;改变倾斜角度,会影响拉索发生内共振时激励频率区域的大小;初始条件的不同,拉索的振动形式会相差很大。     

Summary of ISO/TC 201 International Standard ISO 18516:2019 Surface chemical analysis—Determination of lateral resolution and sharpness in beam-based methods with a range from nanometres to micrometres and its implementation for imaging laboratory X-ray photoelectron spectrometers (XPS)

ISO 18516:2019 Surface chemical analysis—Determination of lateral resolution and sharpness in beam-based methods with a range from nanometres to micrometres revises ISO 18516:2006 Surface chemical analysis—Auger electron spectroscopy and X-ray photoelectron spectroscopy—Determination of lateral resolution. It implements three different methods delivering parameters useful to express the lateral resolution: (1) the straight edge method, (2) the narrow line method and (3) the grating method. The theoretical background of these methods is introduced in ISO/TR 19319:2013 Surface chemical analysis—Fundamental approaches to determination of lateral resolution and sharpness in beam-based methods. The revised International Standard ISO 18516 delivers standardized procedures for the determination of the (1) effective lateral resolution by imaging of square-wave gratings, the (2) lateral resolution expressed as the parameter D_12–88 characterizing the steepness of the sigmoidal edge spread function (ESF) determined by imaging a straight edge and (3) the lateral resolution expressed as the full width of half maximum of the line spread function (LSF), w_LSF, determined by imaging a narrow line. The last method also delivers information on the shape of the LSF, which characterizes an individual imaging instrument. Finally, the implementation of all three standardized methods in the field of imaging laboratory X-ray photoelectron spectroscopy (XPS) is shortly presented. This part of the letter is based on the use of a new test sample developed at ETH Zurich, Switzerland. This test sample displays a micrometre scaled pattern motivated by the resolving power of recent imaging XPS instruments.     

高温超导磁悬浮系统中横向运动对悬浮力和导向力影响的研究

高温超导磁悬浮列车在运行过程中，导轨磁场的不连续或者机电耦合会引起车身的横向偏移．针对这一实际问题，本文研究了横向运动对竖直悬浮力和水平导向力的影响．实验中系统同时测试横向运动过程中不断变化悬浮力和导向力．研究发现运动过程中的悬浮力衰减与最大横向偏移量和往返运动次数有关；但导向力在第一次往返运动之后的往返运动中迟滞曲线基本不变．该工作可能为高温超导磁悬浮列车系统提供一定科学依据．     

Convergent-Divergent Nozzle under Highly Overexpanded Conditions

Quantitative results for the thrust and flow-rate performance of axisymmetric nozzles in highly overexpanded regimes are presented. Estimates for the lateral component of the reactive force and its range of possible existence are obtained for axisymmetric nozzles differing in the divergent region geometry. Empirical formulas for the gas flow rate in the subcritical outflow regime and the pressure range on which this regime can take place are proposed.     

相位测量轮廓术中三维坐标校准新方法

提出了一种新的用于相位测量轮廓术中的三维坐标校准方法。该方法用一个含有三个虚拟校准平面的标准块代替传统相位测量轮廓术校准方法中使用的标准平面，每个虚拟校准平面由多个高度相同但空间离散分布的子区域组成，相应的连续相位恢复是通过一个迭代过程实现的，同时各个子区域还被用于横向坐标的校准。由于各个虚拟校准平面间高度是垂直变化的，传统的相位展开不能得到正确的相对位置关系，基于等效波长概念，提出了一种准确的虚拟校准平面连续相位间相对位置恢复的办法。此校准方法的特点是：在校准过程中不需要标准平面的多次精确平移；仅需要一次测量就可以完成高度和横向坐标的同时校准。文中给出的实验结果说明了该校准方法的有效性和可行性。     

Dynamic and thermodynamic consequences of adsorbate lateral interactions in surface reaction kinetics

The effects of lateral interactions on the two-dimensional distribution of adspecies on solid surfaces and their consequences for reaction kinetics are demonstrated for the bimolecular reactive systemA+BAB. The discussion concentrates on systems where one reactant,A, is stationary while the other,B, is freely diffusing and instantaneously relaxing. A modified Bethe-Peierls-type lattice gas approximation is formulated in order to account for the rapidly-equilibrating distribution ofB atoms. The approximation takes into account all nearest and next nearest neighbor interactions between the adspecies and the nonuniformity of the lattice available toB implied by the presence of immobileA's on the surface. This model is combined with a Monte Carlo simulation of the reactive events in order to calculate reaction rates, e.g., in temperature-programmed processes. The rates are compared with full Monte Carlo simulations (for all kinetic processes), showing good agreement between the two schemes, except at very high coverages, where very long range correlations in the system which are ignored in the lattice gas approximation must be taken into account.This paper is dedicated to Howard Reiss in celebration of his 66th birthday.