抽指加权宽带扇形叉指声表面波滤波器的等效电路分析

扇形换能器可以看成若干个沿孔径方向划分的均匀孔径换能器电端并联而成，根据梅森(Mason)等效电路模型以及由其延伸的混合场等效电路模型，推导出整个扇形换能器的导纳矩阵和频率响应，其中采用复阻抗模型考虑了叉指电极与自由表面的阻抗不连续的因素。本方法能够模拟指间反射、三次行程、指条寄生阻抗以及外围电路等对器件性能的影响；理论模拟与实验结果吻合。     

Effective stability for generalized Hamiltonian systems

An effective stability result for generalized Hamiltonian systems is obtained by applying the simultaneous approximation technique due to Lochak. Among these systems, dimensions of action variables and angle variables might be distinct.     

基于DS/AHP的供应商选择方法

供应商选择方法有很多种，在众多的方法中层次分析法以能够将定性指标定量化而被广泛应用于供应商选择决策中。考虑到供应商选择问题中包含有很多的不确定性而证据理论在处理不确定问题又有着独特的优点，因此本文采用了一种由层次分析法和证据理论结合而产生的DS／AHP决策方法，并将其应用于供应商选择决策问题中，该方法综合了层次分析法和证据理论的优点，可以更科学的进行供应商选择决策，最后通过一个例子说明这种方法在供应商选择中的应用。     

技术创新与增长期权定价

本采用了净现值(NPV)和实物期权定价方法对一个实际的MMDS的发射放大器项目进行了定价，并对两种方法定价的结果进行了分析和对比。由于实物期权方法定价的结果包含项目中的增长期权和放弃期权的价值，因而实物期权方法定价的结果比NPV方法定价的结果更合理和更高。     

磁电垒结构中自旋极化输运性质的研究

研究了电子隧穿几类磁电垒结构的自旋极化输运性质，导出统一的传输概率公式，揭示了非 均匀磁场的分布与自旋过滤的关系，同时表明采用有效朗德因子较大的半导体材料可以显著 增强磁电垒结构的自旋过滤效果. 关键词： 磁电垒 自旋过滤 自旋电子学 自旋极化     

E-酉正则半群

本文定义了PO-六元组的概念,给出了E-酉正则半群的一种结构.     

A Large Conformational Change of a Bridged b-Cyclodextrin Dimer in Aqueous Solution

As artificial enzymes, the binding constants of cyclodextrins (CDs) and their substrates are expected to be high1. For this purpose, many kinds of bridged cyclodextrin dimers2 whose two cyclodextrins are linked by various spacers have been constructed. It was of interest to make the dimers, whose binding constants would exceed 108dm3/mol3. Up to date, the bridged cyclodextrin dimers have been extensively studied as enzyme models and as molecular receptors4-6. Recently, we synthesized a brid…     

一种有机电致发光共聚物的制备和性能

采用Suzuki方法合成了9，9-二辛基芴与萘并硒二唑的两种无规共聚物并研究了其紫外光谱、光致发光和电致发光性能。两种聚合物的电致发光波长为650～666nm，均为发饱和红光的LED材料，其电致发光外量子效率最高达到了1．05％。随着共聚物中萘并硒二唑含量的增加，共聚物的光致发光和电致发光的发射波长均有少量红移。证明了根据共轭高聚物链内能量转移原理，在聚芴链中引入不同含量的窄带隙杂环单元可实现对聚芴发光颜色的调节。     

A parallel cell‐based DSMC method on unstructured adaptive meshes

A parallel DSMC method based on a cell‐based data structure is developed for the efficient simulation of rarefied gas flows on PC‐clusters. Parallel computation is made by decomposing the computational domain into several subdomains. Dynamic load balancing between processors is achieved based on the number of simulation particles and the number of cells allocated in each subdomain. Adjustment of cell size is also made through mesh adaptation for the improvement of solution accuracy and the efficient usage of meshes. Applications were made for a two‐dimensional supersonic leading‐edge flow, the axi‐symmetric Rothe's nozzle, and the open hollow cylinder flare flow for validation. It was found that the present method is an efficient tool for the simulation of rarefied gas flows on PC‐based parallel machines. Copyright © 2004 John Wiley & Sons, Ltd.     

Least‐squares meshfree method for incompressible Navier–Stokes problems

A least‐squares meshfree method based on the first‐order velocity–pressure–vorticity formulation for two‐dimensional incompressible Navier–Stokes problem is presented. The convective term is linearized by successive substitution or Newton's method. The discretization of all governing equations is implemented by the least‐squares method. Equal‐order moving least‐squares approximation is employed with Gauss quadrature in the background cells. The boundary conditions are enforced by the penalty method. The matrix‐free element‐by‐element Jacobi preconditioned conjugate method is applied to solve the discretized linear systems. Cavity flow for steady Navier–Stokes problem and the flow over a square obstacle for time‐dependent Navier–Stokes problem are investigated for the presented least‐squares meshfree method. The effects of inaccurate integration on the accuracy of the solution are investigated. Copyright © 2004 John Wiley & Sons, Ltd.