Three New Polyoxygenated Steroids from Two Species of the South China Sea Gorgonian Muricella flexuosa and Menella verrucosa Brundin

Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds.     

空气/水界面水分子的取向和运动

对四种不同的实验构型下空气／水界面自由O-H键在3700cm~(-1)的和频振动光谱的分析表明,水分子在空气／水界面的取向运动只可能是在平衡位置附近有限角度之内的受限转动。界面水分子的自由O-H键取向距界面法线约33°,而取向分布或运动的宽度不超过15°。这一图像显著地不同于Wei等人(Phys. Rev. Lett.86,4799(2001))只通过单一的SFG实验构型所得出结论,即：空气／水界面的水分子在超快的振动弛豫时间内在很大的角度范围内运动。     

Spectral line suppression and sideband narrowing via quantum interference

We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states.     

模糊对向传播网络数据融合目标识别方法

重点研究了模糊对向传播网络 (FCPN)模型。针对数据融合和目标识别的特点 ,提出了基于模糊对向传播网络的融合目标识别方法和改进的模糊对向传播网络 (MFCPN)融合结构。利用仿真数据对网络的训练算法和融合结构进行了实验研究。结果表明 ,模糊对向传播网络较误差后向传播网络 (BPN)能够有效地实现融合识别 ;改进的模糊对向传播网络融合结构是可行的。同时还对FCPN和MFCPN应用于前视红外 (FLIR)和可见光摄像机目标跟踪系统进行了应用研究。     

Combined effect of PMD and PDL on four-wave-mixing-induced crosstalk in WDM system

We derive an explicit autocorrelation function (ACF) formula of state of polarization for a fiber transmission system with polarization mode dispersion (PMD) and polarization dependent loss (PDL), which is found to agree well with Monte Carlo simulation. Then we use the new ACF to investigate the combined effect of PMD and PDL on the polarization multiplexed scheme. We find the performance of the polarization multiplexed scheme can be deteriorated more severely than the case without PDL.     

微光像增强器图像传递信噪比的测试研究

图像传递信噪比是微光像增强器的重要特性参数．能够全面定量地表征像增强器在探测弱辐射图像时的综合性能，对于确定像增强器的图像探测灵敏闽具有重要意义。针对其测试原理．采用高灵敏度低噪声CCD器件作为像管输出图像的探测接收器．并引入数字图像处理技术。利用设计的测试系统实现了典型目标图像传递信噪比的自动测试．多次实验结果表明．陔测试系统具有测试过程自动快速及测试数据准确稳定的优点．相同测试条件下的不确定度优于±3%。     

Effects of B′-site transition metal on the properties of double perovskites Sr2FeMO6 (M=Mo, W): B′ 4d-5d system

The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr₂FeMO₆ (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr₂FeMoO₆ is a ferromagnet and Sr₂FeWO₆ is an antiferromagnet with T_N∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr₂FeWO₆ compound. However, the Sr₂FeMoO₆ compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions.     

Defect operators, defect functions and defect indices for analytic submodules

This paper mainly concerns defect operators and defect functions of Hardy submodules, Bergman submodules over the unit ball, and Hardy submodules over the polydisk. The defect operator (function) carries key information about operator theory (function theory) and structure of analytic submodules. The problem when a submodule has finite defect is attacked for both Hardy submodules and Bergman submodules. Our interest will be in submodules generated by polynomials. The reason for choosing such submodules is to understand the interaction of operator theory, function theory and algebraic geometry.     

一个线性约束优化问题的广义梯度投影法

本文对线性约束优化问题提出了一个新的广义梯度投影法，该算法采用了非精确线性搜索，并在每次迭代运算中结合了广义投影矩阵和变尺度方法的思想确定其搜索方向．在通常的假设条件下，证明了该算法的整体收敛性和超线性收敛速度．     

The structure of invertible substitutions on a three-letter alphabet

We study the structure of invertible substitutions on three-letter alphabet. We show that there exists a finite set of invertible substitutions such that any invertible substitution can be written as I_wσ₁σ₂σ_k, where I_w is the inner automorphism associated with w, and for 1jk. As a consequence, M is the matrix of an invertible substitution if and only if it is a finite product of non-negative elementary matrices.