负声速梯度浅海中的平均声强

本文首先把能够到达接收器的那些简正波按能量相加,然后对发射深度与接收深度进行平均,导出了负声速梯度浅海中平均声强的表式。用这表式讨论了平均声强的空间结构的问题。     

浅海平均声场的数值预报方法

本文介绍了浅海平滑平均声场的理论,并将适合于远距离的平滑平均声强表式同适合于近距离的虚源声强表式结合起来,给出一种比较完整的计算平均声场的方法。编制了相应的计算机程序,使平均声场的计算变得容易而迅速。文中给出了一些应用的例子,计算结果与实验很好地符合。     

由小斜率近似计算空气声经粗糙海面透射至深海中的声场

采用一级小斜率近似方法处理空气声经粗糙海面透射至深海中的声场问题,导出了透射场及其相干分量的表达式。假定海面高度一维变化且频谱满足PM谱,采用小斜率近似方法计算了相应的透射场。对于空气中的线源,小斜率近似与积分方程方法结果一致。当水下测量点距离较远且深度较浅时,平均声强随海面均方根高度增加而增加至一极限值,相干声强则随海面均方根高度增加而一致减小。对于空气中的点源,小斜率近似计算表明,水下平均声强还依赖于测量点相对于声源的方位,而相干声强则与测量点的方位无关。      

Pekeris波导中简正波的复声强及其应用

在Pekeris波导模型下,关注了简正波的矢量场,讨论了简正波水平复声强和垂直复声强的表述,并分析了其特征.单阶简正波在水平方向是行波,相应的水平复声强仅为有功的;在垂直方向为驻波,相应的垂直复声强仅为无功的.而多阶简正波相互干涉,因此总声场的复声强既有有功分量,也有无功分量,其中只有有功分量参与声能的输运,但无功分量是反映声场信息的重要组成部分.通过对垂直(交互)复声强无功分量和水平交互复声强有功分量的数值分析,对于甚低频率的点源声场,发现当声源深度变化时,上述声场分量的正负号呈有规变化,当接收传感器置 关键词： 目标深度分类 复声强 矢量场 Pekeris波导     

反转点附近声场的渐近理论

水下声道中一般有三类反转点,在它们附近形成不同类型的反转点会聚区。收、发深度不等的第Ⅲ类反转点会聚区的强度比前两类稍低,但其空间分布范围广泛,在低频远程声场中占有重要地位。本文着重讨论第Ⅲ类反转点附近的声场,给出了计算反转点附近以及焦散线声强的简明表式,提出了形成焦散线会聚的物理条件。理论分析表明,低频情况下第Ⅲ类反转点会聚区的声强与距离的平方成反比、与频率的1/3次方成正比。     

基于单矢量有源平均声强器的码分多址水声通信

基于单矢量传感器对码分多址水声通信进行了研究. 利用单个矢量传感器自身指向性进行方位估计最为常用的方法是平均声强器和复声强器, 但这些方法对于同频带的多用户来说, 理论极限仅能测量两个用户. 提出了有源平均声强器, 利用扩频通信中伪随机码优良的自相关和互相关特性, 可同时测得多个用户的方位, 利用估计的用户方位构建矢量组合, 调整矢量传感器的指向性, 实现各用户定向通信, 抑制多址干扰, 增加处理增益, 降低误码率. 对频带相同的扩频多用户通信进行了仿真及试验研究, 验证了有源平均声强器的有效性和实用性.     

基于单矢量有源平均声强器的码分多址水声通信

基于单矢量传感器对码分多址水声通信进行了研究. 利用单个矢量传感器自身指向性进行方位估计最为常用的方法是平均声强器和复声强器, 但这些方法对于同频带的多用户来说, 理论极限仅能测量两个用户. 提出了有源平均声强器, 利用扩频通信中伪随机码优良的自相关和互相关特性, 可同时测得多个用户的方位, 利用估计的用户方位构建矢量组合, 调整矢量传感器的指向性, 实现各用户定向通信, 抑制多址干扰, 增加处理增益, 降低误码率. 对频带相同的扩频多用户通信进行了仿真及试验研究, 验证了有源平均声强器的有效性和实用性.     

单矢量水听器估计目标方位的方法与实验

为评估基于单矢量水听器的方位估计能力,在黄海海域对矢量水听器进行实验。矢量水听器吊放于接收船尾部,采用平均声强器和复声强器方位估计方法,并提出以概率密度值最大的方位角作为目标方位估计值的具体处理准则,对恒定方向、匀速行驶的目标船方位进行估计,并求出两种方法的方位估计误差。结果表明,水听器布放深度10 m时,对正横距离为0.42 km的航速10 kn的目标船,平均声强器方法的水平方位角估计误差18°,极角估计误差为5°,可以在离目标船最远1.17 km处估计其方位;复声强法的水平方位角估计误差为13°,极角估计误差为8°,可以在离目标船最远2.35 km处估计其方位。在有接收船的噪声干扰情况下,复声强器比平均声强器方法估计的方位更准确,可以对更远处的噪声源进行方位估计。     

Pekeris波导中简正波声强流及其互谱信号处理

探讨了Pekeris波导中声压场和质点振速场的联合描述,尤其关注垂直声强流的分析.研究表明,由于各阶简正波的干涉作用,水平和垂直声强流均既有有功分量,亦有无功分量.低频声场的垂直声强流的无功分量虽不参与声能的输运,当单个声矢量传感器做适当放置后却可用以判断声源的特定深度.这对于矢量信号处理是有意义的.给出了声压和质点振速联合互谱处理进行目标判别的算法.     

大深度接收时深海直达波区的复声强及声线到达角估计

基于射线模型给出了质点水平振速、垂直振速及复声强的表达式.结合深海直达波区的声线到达结构,分析了大深度接收时深海直达波区复声强的特点,理论分析与仿真结果表明,利用声场中不同组声线的复声强可以估计声线到达接收点的掠射角.根据在2014年进行的一次深海实验中布放在3146 m深处的矢量水听器获取的实验信号,利用直达波和海面反射波的复声强估计了直达声线与海面反射声线到达接收矢量水听器处的掠射角,结果表明,估计的声线到达角与理论计算结果基本一致.     

铥原子收敛于4f13(2F7/2o)6s(7/2,1/2)4o和4f13(2F7/2o)6s(7/2,1/2)3o偶宇称里德伯系列能级的电子关联效应

本文在多通道量子亏损理论框架下,利用相对论多通道理论,计算了铥原子收敛于4f¹³（²F_7/2^o）6s（7/2,1/2）₄^o和4f¹³（²F_7/2^o）6s（7/2,1/2）₃^o的三个偶宇称里德伯系列.通过将计算结果与美国国家标准与技术研究院数据进行比较,展示了两种类型的电子关联效应：1）里德伯系列之间的相互作用,导致里德伯系列的能级出现整体偏移;2）一个孤立的干扰态镶嵌在一个里德伯系列中,破坏了该里德伯系列能级的规则性.     

Universal enveloping algebra and differential calculi on inhomogeneous orthogonal q-groups

We review the construction of the multiparametric quantum group ISO_q,r(N) as a projection from SO_q,r (N + 2) and show that it is a bicovariant bimodule over SO_q,r(N). The universal enveloping algebra U_q,r(iso(N)), characterized as the Hopf algebra of regular functionals on ISO_q,r(N), is found as a Hopf subalgebra of U_q,r(so(N + 2)) and is shown to be a bicovariant bimodule over U_q,r(so(N)).

An R-matrix formulation of U_q,r(iso(N)) is given and we prove the pairing U_q,r(iso(N)) — ISO_q,r(N)). We analyze the subspaces of U_q,r(iso(N)) that define bicovariant differential calculi on ISO_q,r(N).     

Natural embedding of group in NMR spin algebras

NMR aspects of finite group natural-embeddings in higher n-fold spin algebras over Hilbert space are considered in the context of icosahedral cage clusters associated with specific ¹¹B borohydride, -deuteride anions for which n = 12. The focus of the discussion is on the abstract and physical models derived from permutation modules in the form of λ ├ n partitions over , where . Hence, the related Kostka expansion coefficients from the pure abstract spin space of mapping and other -combinatorial aspects, including the nature of inner tensor products arising in the high-n limit, are especially pertinent. Further insight into spin cluster NMR problems is provided by studies of -induced algebras derived from the [λ_SA] self-associated irreps. Motivation for the work comes from its potential physical applications for higher-n bi-cluster NMR problems, e.g., in spin dynamics. The representational properties derived are essential in understanding the structure of Liouville space for both SU(2) and higher spin SU(m) clusters. The Hilbert space aspects presented here impact strongly on the somewhat neglected question of the nature of subduction, i.e., involving a finite group naturally embedded in a higher group, within an implicit dual Racah symmetry chain. The essential mappings presented here include both the λ module-onto-{[λ′]} set and the aspects, where the Kostka integers of the former arise naturally in the realization of λ module mappings over .     

核磁共振碳谱研究:烷烃化学位移和(CSS)与分子路径指数矢量(VPM)

系统研究了核磁共振碳谱和化学位移规律及其定量构谱关系(QSSR).本文研究了一组十元素分子路径指数矢量VPM,并发现它与烷烃化学位移和CCS有良好线性相关性.采用多元线性回归进行准确估计与预测,结果优良.     

Reduced s-d model with antiferromagnetically coupled impurity spins

An antiferromagnetic equivalent-neighbour Heisenberg interaction H_i between impurity spins is added to the reduced s-d Hamiltonian H_r previously introduced by simplifying the Kondo s-d exchange Hamiltonian H_K. Asymptotic mean-field theory is developed for H_r + H_i, in the presence and absence of external magnetic field, and applied to (La_1−xCe_x)Al₂ alloys. Specific heat c_i(T) and zero-field susceptibility χ_i(0,T) curves for (La_1−xCe_x)Al₂ are depicted. The coupling constants of H_r + H_i and conduction bandwidth are adjusted so that T_c temperatures for x = 0.2, 0.1 are equal to the experimental values. c_i(T) exhibits a jump at T_c and is decreasing for T < T_c. χ_i(0,T) has a first order pole at T_c which corresponds to the maximum of experimental susceptibility and χ_i(0,0) > 0. These results improve those obtained earlier on the grounds of H_r theory.     

Characteristic Shear Rate for Nonlinear Viscoelastic Behavior in a Polydisperse Polymer Solution

The characteristic shear rate for nonlinear viscoelastic behavior in a polydisperse polymer system was investigated by the study of the stress overshoot behavior of polybutadiene solutions. The frequency at the crossing point of the dynamic moduli () was determined by oscillation frequency sweeps. For the stress overshoot observed in the shear flow at a fixed rate, the dependency of the stress drop, , defined as the difference between the stress at the peak and the stress at the steady state, on the shear rate can be well described by a fitting function: , and a critical shear rate () can be obtained using this fitting function. The correlation between and for the solutions can be expressed as and the proportionality factor is dependent on the degree of chain interpenetration. When the shear rate was normalized by , the dependency of the stress drop on this normalized shear rate for the solutions with different concentrations can be superposed well. This observation indicates that can be viewed as a characteristic shear rate for nonlinear viscoelastic behavior in a polydisperse polymer solution.     

Interrelations of discrete Painlevé equations through limiting procedures

We study the discrete Painlevé equations associated to the affine Weyl group which can be obtained by the implementation of a special limits of -associated equations. This study is motivated by the existence of two -associated discrete both having a double ternary dependence in their coefficients and which have not been related before. We show here that two equations correspond to two different limits of a -associated discrete Painlevé equation. Applying the same limiting procedures to other -associated equations we obtained several -related equations most of which have not been previously derived.