2H-PbI_2晶体的电子结构和力学性质

采用基于密度泛函平面波赝势方法(PWP)方法,计算了六角晶系2H-PbI2晶体的电子结构、力学性质和硬度.采用局域密度近似(LDA)方法计算的晶格常数、带隙、弹性常数与实验值和理论值符合较好.计算表明,2H-PbI2是一种直接带隙的半导体,带隙大约为2.38eV.运用复杂晶体硬度计算公式计算了六角晶系2H-PbI2晶体的硬度,硬度值大约为2.54GPa.还发现2H-PbI2晶体的各向异性非常明显.     

低频液体表面波衍射条纹正负级次的不应性

基于声光衍射原理,利用光学方法对低频液体表面波的光衍射特性进行了研究,给出了非对应级数的解析表达式并进行了数值模拟,解释了非对应分布的机理.实验观察到清晰、稳定的衍射图样,且条纹间距具有明显的不对称性;随入射角度增大,正负级衍射条纹具有明显的不对应分布,即正条纹级数多于负条纹级数.研究表明:衍射条纹级数的不对应程度与入射角有关,随入射角的增大,正负级数不对应程度加剧;负级衍射条纹级数存在最大值,超过该最大值的负级衍射条纹缺失;理论分析和实验结果吻合较好.     

全漏光导波技术确定液晶材料的挠曲电系数

利用全漏光导波技术,测量负性向列相液晶材料MS-N01300-000的展曲和弯曲挠曲电系数之和.根据液晶弹性和多层光学理论得到同一电压下不同挠曲电系数的反射率随内角(入射到液晶层角度)的理论变化曲线.实验中,将液晶材料灌注到混合排列向列相液晶盒中,在液晶盒上分别加交流电和直流电,采用全漏光导波技术得到反映液晶指向矢分布的液晶波导反射率随内角变化曲线.实验发现,由于液晶挠曲电作用,同一电压值下反射率随内角变化曲线发生微小移动.对比理论与实验曲线,由曲线移动距离得到MS-N01300-000液晶材料展曲和弯曲挠曲电系数之和为2.5×10-11 C/m.     

First-principles study of the structural,elastic, and optical properties for Sr0.5Ca0.5TiO3

A detailed theoretical study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3 is carried out by first- principles calculations. The band structure exhibits a direct bandgap of 2.08 eV at the F point in the Brillouin zone. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are derived based on the calculated elastic constants. The bulk modulus B = 153 GPa and shear modulus G = 81GPa are in good agreement with available experimental data. Poisson＇s ratio v = 0.275 suggests that Sr0.sCa0.sTiO3 should be classified as being a ductile material. Using the electronic band structure and density of states, we analyze the interband contribution to the optical properties. The real and imaginary parts of the dielectric function, as well as the optical properties such as the optical absorption coefficient, refractive index, extinction coefficient, and energy-loss spectrum are calculated. The static dielectric constant ε1 （0） and the refractive index n（0） are also investigated.     

列车分布式吸能系统的波传播特性和参数分析

建立了考虑车厢中弹性波传播影响的列车分布式吸能系统的简化理论模型。基于一维应力波理论，对碰撞过程中各吸能器的响应进行了理论分析，得到相关的控制方程并求解。观察到各吸能器界面上典型的阶段性、平台样的速度响应，并分析了其机理，进而对如何合理设置和排布吸能器进行了分析。结果表明:对于相邻的吸能器，碰撞前端吸能器的压垮强度应高于后端，否则后端吸能器无法同时发挥作用；各吸能器的平台应力的大小和排布是决定吸能系统作用效果的控制参量，能够决定各吸能器的吸能时长和吸能总量。具体分析了相邻吸能器的平台应力分布对系统吸能性能的影响，得到了在所研究的情况下使总吸能量最大的优化设计参数。该研究可为列车分布式吸能系统的优化设计提供理论指导。     

圆截面激光晶体热变形的弹性力学分析

采用热弹性理论建立了关于激光晶体热变形的微分方程和边界条件;对方程进行简化并利用级数法和伽辽金法进行求解,得到了圆截面激光晶体热变形的解析表达式。分析结果表明:晶体内的热变形是坐标r、z的非线性函数;变形与弹性模量E无关,而与晶体的尺寸、泊松比、热传导系数有关。     

封面图片说明

封面图为高分辨率热像仪所拍摄的某结构的红外热像图,从中可以清晰地看到物体经过时因热弹性效应导致的结构表面温度场的变化,进而判断出结构局部的高应力区域。疲劳热像法作为一种无损、实时、全场、非接触的测试手段,不仅可在较     

Theoretical investigation on the electronic structure,elastic properties, and intrinsic hardness of Si2N20

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli （bulk modulus, Young’s mod-ulus, and shear modulus） are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.     

CHINESE PHYSICS B AUTHOR INDEX TO VOLUME 21

<正>Abbas Ibrahim A(Ibrahim A Abbas) and Othman Mohamed I A(Mohamed I A Othman),Generalized thermoelsticity of the thermal shock problem in an isotropic hollow cylinder and temperature dependent elastic moduli,2012 21(1) 014601 Abbas Ibrahim A(Ibrahim A Abbas),Kumar Rajneesh(Rajneesh Kumar) and Chawla Vijay(Vijay Chawla), Response of thermal source in a transversely isotropic thermoelastic half-space with mass diffusion by using a finite element method,2012 21(8) 084601     

光纤布喇格光栅沉降传感器

根据光纤布喇格光栅的光学传感原理,提出了一种基于悬臂梁及金属弹性膜片的光纤布喇格光栅沉降传感器结构,对其传感特性进行了实验研究.实验通过产生水的液位差来模拟地基沉降,分析结果显示,光纤布喇格光栅中心反射波长漂移对液位差呈现良好的线性关系,线性度高于0.999,灵敏度可达一2.11 pm/mm.通过改变悬臂梁厚度和有效长...