开壳层微扰理论的性能研究

采用一系列开壳层分子来检验我们最近提出的开壳层微扰理论(J Chem Theory Comput,2009,5:931―936,简称OSPT)的有效性.我们首先采用双重态分子NH2来讨论OSPT的收敛性.微扰能量计算至400阶.基函数为6-13G.选择这个基函数是为了易于进行完全组态相互作用计算(简称FCI),以及和FCI结果比较.几何结构有3种:(1)N-H键长为平衡键长,(2)N-H键长为平衡键长的1.5倍,(3)N-H键长为平衡键长的2.0倍.在这3种情况下,键角∠HNH均为103.2°.在第一种情况,NH2完全为单参考态分子.随着N-H键长逐渐偏离平衡键长,NH2波函数开始显示出多参考态性质.从微扰量能的角度来看,在第一种情况,微扰能量很快就单调收敛至完全组态相互作用(简称FCI)的计算结果.第二种情况,微扰能量稍微有一点振荡,但也很快收敛至FCI的结果.第三种情况对单参考态微扰理论是一种考验,微扰能量振荡比较明显,收敛较慢.在这3种情况下,我们提出的OSPT微扰方法均比文献中报道的ZAPT(the Z-averaged perturbation theory)方法和RMP方法(restricted ...     

气相中Co+催化N2O与C2H6循环反应催化剂活性的理论研究

采用密度泛函理论UB3LYP方法对Co⁺在三重态及五重态势能面上催化N₂O与C₂H₆进行循环反应的两态反应机理进行了研究. 运用Harvery方法优化了两自旋态势能面5个最低能量交叉点（MECP）,计算了MECP处自旋-轨道耦合作用. 采用Landau-Zener公式计算了自旋翻转处的系间窜越几率,各MECP处均可发生有效系间窜越. 通过应用Kozuch提出的能量跨度模型,Co⁺催化N₂O与C₂H₆在298K下反应生成CH₃CHO时有最大的TOF值3.35×10^-21 s^-1.     

数字离子阱质谱仪低质量截止值的改进方法

本研究在实验室自制的线形数字离子阱质量分析器上,通过改变数码电源的频率扫描方式,在CID过程中,通过扫描数字束缚方波电源的频率和数字激发方波的频率实现母体解离。例如对于利血平母体离子,当将离子数字束缚方波频率从500 kHz扫描到560 kHz,可以测量到低质荷比的碎片离子,成功实现了串级质谱分析的低质量碎片离子的分析。通过与利血平三重四极质谱串级质谱分析实验结果的比较,发现可以在数字离子阱质谱仪上获得与三重四极质谱相同的串级质谱测量结果。结果表明,本方法可以用于低质量离子的测量,克服了传统离子阱质谱进行串级质谱分析的一个主要难点,显著提高数字离子阱质谱的性能。     

Theory Study of the Adsorption of Hydrocyanic Acid onto Small Silver Clusters

Density functional theory calculations have been performed to study the interaction of small silver clusters, Ag2 ~Ag9, with HCN. The adsorption of HCN on-top site of the silver cluster, among various possible sites, is energetically preferred. The adsorption energies of HCN on the silver clusters reach a local maximum at n = 4, which is only about 0.450 eV, indicating that the adsorbed HCN molecule is weakly perturbed. The adsorbed C–N and C–H stretching frequencies are blue- and red-shifted compared with the values of free HCN, respectively.     

一种模拟动边界绕流的锐利界面浸入边界法

When the structural wall moves over a fixed grid, the structure coverage will change, resulting in many dead and emerging elements. To avoid the influence of malformation and reconstruction of body-fitted grids on the calculation efficiency and accuracy of the fluid-structure interaction problems with coupled boundary movement on the fixed grid, an improved numerical method for describing the interaction between an immersed rigid body and fluid based on a sharp-interface is proposed. In this method, both the fluid and solid are regarded as pure fluid domains in the whole computational domain, and the solid boundary is divided into several Lagrangian grid points. The flow parameter or velocity is reconstructed by interpolation at the interface element, which is then directly used as the boundary condition of the flow field, thus reflecting the influence of the wall boundary conditions. The method constructs the calculation structure of “virtual point, force point and vertical foot point”, and the velocity of the virtual point is obtained by bilinear interpolation. Then, the velocity of the force point is calculated by forcing the solid boundary to meet the no-slip condition, and the equations of the coupling system based on the immersion boundary method are finally solved to realize the numerical simulation of the flow with a complex moving boundary. The numerical program for this immersed boundary method is established using C++, then the accuracy and reliability of the proposed method are validated by comparison with the literature and experimental results of the basic numerical example of flow around a cylinder. Furthermore, the effects of the structural shape and the angle of attack on the trailing vortex structure, the vortex shedding frequency, and the lift/ coefficient characteristics of the flow around the elliptical cylinder have been analyzed. The anti-symmetric S-type, “P+S” Ⅰ-type and “P+S” Ⅱ-type trailing vortex shedding modes, as well as the variation laws of the vortex structure size, vortex shedding frequency and lift-drag coefficients ratio with axis ratio and angle of attack, are captured. The critical angle of attack (25°) corresponding to the maximum lift-drag ratio is determined as 25°.     

铷原子饱和吸收光谱与偏振光谱对780nm半导体激光器稳频的比较

将激光频率锁定于合适的参考频率,可以有效地抑制激光器的频率起伏。本文采用铷原子D2线超精细跃迁线的饱和吸收光谱和偏振光谱分别获得鉴频曲线,通过电子伺服系统将频率校正信号负反馈到780 nm光栅外腔反馈半导体激光器外腔的压电陶瓷上的方法对激光器进行稳频。介绍了两种方法的基本原理和实验方案。与激光器自由运转300s时激光器典型的频率起伏约6.6 MHz相比,采用饱和吸收光谱和偏振光谱进行稳频,运转300 s时激光器典型的残余频率起伏分别约为1.5 MHz和0.6 MHz。分析表明,饱和吸收光谱稳频采用了相敏检波技术,需要对激光器进行频率调制,带来了额外的频率噪声,而偏振光谱稳频则是一种完全无频率调制的稳频方案。     

测量行波管电子注的法拉第筒的热分析

利用ANSYS软件对测量行波管电子注截面的法拉第筒探头进行了热分析研究.分析了在单脉冲情况下,测量各种直径的不同脉冲功率密度的电子注、不同脉冲宽度对法拉第筒温度的影响,研究了测量不同功率密度的电子注可以使用的脉冲宽度.结果表明,仅法拉第筒上的注斑区域温度迅速上升,温度梯度较大,其它部分温度基本不变,为保证法拉第筒能够持...     

kHz激光器在武汉卫星观测站的测距实验

高重复频率激光器是kHz卫星激光测距系统的重要组成部分,提高激光发射频率可以有效地获得更多的观测数据,这是当今卫星激光测距领域的发展方向.针对武汉卫星观测站进行的kHz激光测距实验,介绍了kHz激光器的工作过程和原理,分析了影响高重复频率回波探测的因素.实验结果表明:对实验过程中所观测到的中低轨卫星,观测数据量提高了1...     

微波射频场在微波管中产生爆炸电子发射特性初步分析

 对微波射频场在微波管内引起的场致发射和爆炸电子发射及等离子体的产生进行了分析,推导了等离子体产生强度与微波振幅、材料的电阻率、热传导系数、质量密度和比热容之间的关系,得到了晶须温度分布的表达式,通过数值解析的方式总结出在远大于微波周期的时间尺度上晶须温度提高随时间线性上升。在模型所述材料特性下,温度的上升率达到了3.22×10¹⁰ ℃/s,在100 ns量级就可以使晶须发生气化形成等离子体。     

应用于地形匹配导航的激光高度计设计

为解决基于雷达高度表探测的地形匹配导航系统探测精度不高、易受电子干扰影响而失效、且在跨海飞行时无法导航的难题,设计了一种激光高度计来代替雷达高度表进行地形探测。采用二极管泵浦固体激光器技术设计激光发射装置,输出近红外/蓝绿双波长激光,既可以测量陆地地形高度,又可以穿透海水探测海底地形;并根据激光高度计拟达到的性能指标选择合适的光电探测器,优化设计了光学系统、扫描系统和信号处理系统。所设计的激光高度计具有体积小、重量轻、高重频、探测灵敏度高、抗电磁干扰能力强等特点。