非傍轴矢量余弦-高斯光束两种光强表示的比较研究

从矢量瑞利-索末菲衍射积分公式出发,以非傍轴矢量余弦－高斯(CoG)光束为例,对非傍轴矢量光束的两种光强表示式,即传统光强公式和时间平均坡印廷矢量的z分量进行了比较研究.对非傍轴矢量CoG光束轴上和横向光强分布详细的数值计算和比较结果表明,两种光强表示式之间的相对误差η与w0/λ、z/λ和偏心参量b有关,其中w0,λ和z分别为束腰宽度,波长和传输距离.当偏心参量b较小,且束腰宽度与波长相比不很小时,例如,b≤0.8,w0/λ≥0.8,z/λ=10时,二者间的最大相对误差ηmax＜2%,传统光强公式可以使用.     

The influence of time delay on forward masking when spatially separated sound image reproduced with headphone

With the virtual reproduction of headphone, the influence of delay time between masker and masked signal on forward masking when sound images are virtually spatial separated in azimuth is studied. The result shows that the thresholds tend to decrease dramatically with the increase in delay time. Furthermore, in case of spatial separation, there are differences of masking thresholds with the maximum about 15 dB. However, when the masker level is 70 dB, the difference of the thresholds increases a little as the delay time increases from 20 ms to 40 ms, which can be explained by the time integration effect and basilar membrane response.     

吸气式高超声速飞行器气动力气动热的数值模拟方法及应用

对吸气式高超声速飞行器而言,物面热流和摩阻的准确预测对飞行器设计及安全十分关键.介绍采用CFD准确预测气动力和气动热的方法,包括流动的控制方程、湍流模型及湍流的先进壁面函数边界条件,介绍流动的数值求解方法.对典型超声速层流和湍流流动的摩擦阻力和热流进行详细的验证与确认,考察CFD工具在使用先进壁面函数边界条件后,湍流计算的法向网格无关性能力.对设计的一种吸气式高超声速飞行器的气动力和气动热进行数值模拟,为飞行器的气动设计及热防护提供了可靠的数据.     

空间频率对透射式全息图衍射率的影响

为研究干涉条纹空间频率与透射式全息图衍射率的关系,在相同条件下,拍摄以平面波、发散的和会聚的球面波分别作参考光、物光的透射式全息图,通过实验测量其衍射效率,同时计算了干涉条纹的空间频率。然后以会聚的球面波为物光,平面波为参考光,分别改变入射角和球面波会聚点到记录面的距离制作另外4块透射式全息图,并计算了它们的空间频率,测量了其衍射效率。结果表明：在相同条件下制作透射式全息图时,衍射效率只由空间频率决定,与使用何种参考光和物光无关,空间频率仅随参考光和物光的夹角变化而变化。     

压差式矢量水听器方位估计中的干扰抵消

矢量水听器由于能获取声场中标量（声压）和矢量（振速）信息，因此单个的矢量水听器就可实现目标方位估计。单个矢量水听器是利用信号的声压和质点振速之间相关性进行信号方位估计，但是当存在干扰，并且干扰和信号之间相关时，如果对运用能量流进行方位估计的方法不加改进，则会出现很大的误差，甚至出现错误的估计。本文提出一种存在已知噪声干扰情况下的干扰抵消方法，并针对该方法进行了仿真试验，最后运用湖试数据进行了验证。结果表明，该方法能有效地减弱相千千柑对信号的影响，实现对信号的方位估计。     

Li2、LiH的激发态和Li2H的基态结构与势能函数

使用“对称性匹配簇-组态相互作用”方法,对Li2分子三重态的第一激发态、LiH分子的基态、单重态的第一和第二激发态的几何构型与谐振频率进行了优化计算.利用“群操作求和”方法分别对这4个态进行单点能扫描计算,并拟合出了相应各态的Murrell-Sorbie势能函数.使用多种方法对Li2H分子的基态结构进行优化,并用优选出的密度泛函(B3P86)方法对该分子进行了进一步的频率计算.结果发现Li2H分子的基态稳态结构为C2v构型,在此基础上用多体项展式理论导出了它的解析势能函数,其等值势能图准确再现了Li2H分子的结构特征和离解能.首次报导了该分子对称伸缩振动等值势能图中存在的两个对称鞍点,对应于反应LiH Li→Li2H,活化能大约为18.7×4.184 KJ/mol.     

Analytic solutions for degenerate Raman-coupled model

The Raman-coupled interaction between an atom and a single mode of a cavity field is studied. For the cases in which a light field is initially in a coherent state and in a thermal state separately, we have derived the analytic expressions for the time evolutions of atomic population difference W, modulus B of the Bloch vector, and entropy E. We find that the time evolutions of these quantities are periodic with a period of π. The maxima of W and B appear at the scaled interaction time points τ- = kπ（k = 0, 1, 2,...）. At these time points, E = 0, which shows that the atom and the field are not entangled. Between these time points, E ≠ 0, which means that the atom and the field are entangled. When the field is initially in a coherent state, near the maxima, the envelope of W is a Gaussian function with a variance of 1/（4n^-）（n^- is the mean number of photons）. Under the envelope, W oscillates at a frequency of n^-/π. When the field is initially in a thermal state, near the maxima, W is a Lorentz function with a width of 1/n^-.     

Perturbation to Mei symmetry and Mei adiabatic invariants for mechanical systems in phase space

For a perturbed mechanical system in phase space, considering d/dt in the structure equation and process of proof including infinitesimal parameter ε obviously, this paper studies the perturbation to Mei symmetry and adiabatic invariants. Firstly, the exact invariant induced directly from the Mei symmetry of the system without perturbation is given. Secondly, based on the concept of high-order adiabatic invariant, the determining equations of the perturbation to Mei symmetry are established, the condition of existence of the Mei adiabatic invariant led by the perturbation to Mei symmetry is obtained, and its form is presented. Lastly, an example is given to illustrate the application of the results.     

用耦合簇理论及相关一致基研究NH2自由基的解析势能函数

运用CCSD(T)理论和Dunning等的系列相关一致基对NH2分子的基态结构进行了优化, 并使用优选出的cc-pV5Z基组对其进行了频率计算. 得到的结果是: 平衡核间距RNH= 0.10247 nm, 键角∠HNH = 102.947°, 离解能De = 4.2845 eV, 振动频率ν1(a1) = 1546.0342 cm-1, ν2(a1) = 3379.5543 cm-1和ν3(b2) = 3474.4784 cm-1. 对NH及H2分子, 使用优选出的cc-pV6Z基组对其基态的几何构型与谐振频率进行了计算并进行了单点能扫描, 且将扫描结果拟合成了解析的Murrell-Sorbie函数. 采用多体项展式理论导出了NH2分子的解析势能函数, 其等值势能图准确再现了NH2分子的离解能和结构特征. 报导了NH2分子对称伸缩振动等值势能图中存在的两个对称鞍点, 对应于反应NH+H→NH2, 势垒高度约为0.1378×4.184 kJ/mol.     

用耦合簇理论及相关一致基研究NH2自由基的解析势能函数

运用CCSD(T)理论和Dunning等的系列相关一致基对NH2自由基的基态结构进行了优化,并使用优选出的cc-pV5Z基组对其进行了频率计算.得到的结果是:平衡核间距RNH=0.10247 nm,键角∠HNH=102.947°,离解能De=4.2845 eV,振动频率ν1(a1)=1546.0342 cm-1,ν2(a1)=3379.5543 cm-1和ν3(b2)=3474.4784 cm-1.对NH自由基及H2分子,使用优选出的cc-pV6Z基组对其基态的几何构型与谐振频率进行了计算并进行了单点能扫描,且将扫描结果拟合成了解析的Murrell-Sorbic函数.采用多体项展式理论导出了NH2自由基的解析势能函数,其等值势能图准确再现了它的离解能和结构特征.报导了NH2自由基对称伸缩振动等值势能图中存在的两个对称鞍点,对应于反应NH+H→NH2,势垒高度约为0.1378×4.184 kJ/mool.