An inviscid model for the base pressure of transonic turbine cascade

An inviscid base pressure model for transonic turbine blade has been presented. It has been shown that for a given back pressure the base pressure at the trailing edge, and the profile loss of a turbine blade are fixed according to the model and the base pressure can be calculated with the help of an inviscid numerical scheme. A parameteric study on the model shows that a blade profile with positive curvature downstream of the throat is advantageous for generating less loss, whilst the worst situation is when the exit flow reaches the sonic condition.     

跨音涡轮叶栅底压的无粘模型

本文提出一个无粘的底部压力模型。证明了在给定反压的情况下,超音出口的涡轮叶栅的叶片尾缘的底压以及叶型损失可由该模型确定。与无粘的流场计算相结合,可用该模型计算二维叶栅的底压。对模型的参数研究表明:具有正曲率的喉道下游叶背型面将有利于减少损失;而出口为音速时流动则最为不利。     

具有Washer型输入线圈的超导量子干涉放大器的制备与表征

超导量子干涉仪(SQUID)放大器具有低输入阻抗、低噪声、低功耗等优点, 目前被广泛用于微弱信号的检测领域. 与其他工艺相比, Nb/Al-AlO_x/Nb结构的约瑟夫森结具有相对较高的转变温度(T_c)、高的磁通电压调制系数以及良好的热循环能力、较宽的临界电流范围, 因此是制备SQUID放大器的很好选择. 设计并制作了欠阻尼、过阻尼约瑟夫森结以及具有Washer型输入线圈的单SQUID放大器, 通过在He³制冷机3 K温区下对器件电流-电压特性进行测量, 得到良好的结I-V特性曲线、SQUID调制特性, 初步实现利用SQUID进行放大作用, 并计算了SQUID的电流分辨率. 此项工作对于超导转变边沿传感器读出电路的实现具有重要的意义.     

g-C3N4/SnS2异质结构:一类有潜力的光解水催化剂

采用第一性原理方法研究了层间耦合作用对g-C₃N₄/SnS₂异质结构的电子结构和吸光性质的影响.发现g-C₃N₄/SnS₂是一类典型的范德瓦异质结构,能有效吸收可见光,其价带顶和导带底与水的氧化还原势匹配,且由于电荷转移而导致的界面处极化场有利于光生载流子的分离.这些理论研究结果表明g-C₃N₄/SnS₂异质结构是一类非常有潜力的光解水催化材料.     

FeS2多晶薄膜电子结构的实验研究

用磁控溅射方法制各纯Fe薄膜，并硫化合成FeS₂. 采用同步辐射X射线近边吸收谱与X射线光电子能谱研究了薄膜的电子结构. 结果表明，合成的FeS₂薄膜，在费米能级附近，有较强的Fe 3d态密度存在，同时，在价带谱中2—10eV处有强度较大的S 3p态密度存在；Fe的3d轨道在八面体配位场作用下分别为t_2g和e_g轨道，实验中由Fe的吸收谱计算得到两分裂能级之差为2.1eV;实验测得FeS₂价带结构中导带宽度约为2.4eV，导带上方仍存在第二能隙，其宽度约为2.8eV. 关键词： 磁控溅射 二硫化铁 X射线吸收近边结构 电子结构     

锯齿型石墨烯纳米窄带中量子霍尔体系的电场调控

应用含自洽格点在位库仑作用的Kane-Mele模型,研究锯齿型石墨烯纳米窄带平面内横向电场对边界带能带结构和量子自旋霍尔(QSH)体系的影响.研究结果显示,当电场强度较弱时,外加电场的方向可以调控自旋向下的两个边界带一起朝不同方向移动,导致波矢q=0.5处自旋向下的两个纯边界态的能量简并劈裂方向可由电场调控;当电场强度进一步增强到超过0.69 V/nm,自旋向下的两个边界带出现较大带隙,能带反转,而自旋向上的电子结构无能隙,系统呈现半金属性,同时QSH体系不再是B类.特别当电场强度为1.17 V/nm时,在自旋向下能带的能隙中,q=0.5处存在自旋向上的纯边界态,意味着在8格点边界处可以产生自旋向上的纯边界电流.当电场强度持续增加时,QSH系统从B类到C类经历3个阶段的变化.当电场强度超过1.42 V/nm后,自旋向上的两个边界带也出现能带反转,分别成为导带和价带,系统成为C类的普通量子霍尔体系.     

Finding Postal Carrier Walk Paths in Mixed Graphs

The postman problem requires finding a lowest cost tour in a connected graph that traverses each edge at least once. In this paper we first give a brief survey of the literature on postman problems including, the original Chinese postman problem on undirected graphs, the windy Chinese postman problem on graphs where the cost of an arc depends on the direction the arc is transversed, the directed postman problem on graphs with directed edges, and the mixed postman problem on graphs in which there are some directed and some undirected arcs.We show how the mixed postman problem can be solved as an integer program, using the formulation of Gendreau, Laporte and Zhao, by a new row addition branch and bound algorithm, which is a modification of the column subtraction algorithm for set partitioning problems of Harche and Thompson. Computational experience shows that a slack variable heuristic is very effective in finding good solutions that are frequently optimal for these problems.     

Gauss point mass lumping schemes for Maxwell's equations

Finite element and finite difference methods for approximating the Maxwell system propagate numerical waves with slightly incorrect velocities, and this results in phase error in the computed solution. Indeed this error limits the type of problem that can be solved, because phase error accumulates during the computation and eventually destroys the solution. Here we propose a family of mass-lumped finite element schemes using edge elements. We emphasize in particular linear elements that are equivalent to the standard Yee FDTD scheme, and cubic elements that have superior phase accuracy. We prove theorems that allow us to perform a dispersion analysis of the two common families of edge elements on rectilinear grids. A result of this analysis is to provide some justification for the choice of the particular family we use. We also provide a limited selection of numerical results that show the efficiency of our scheme. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 63–88, 1998     

基于多分辨率小波变换的复合材料晶粒边缘的检测

材料晶粒的边缘检测是材料三维重构的一个基础性问题,本文简要介绍了利用小波变换探测图像边缘的原理和材料SEM图像的特点,根据Mallat小波理论中图像边缘对应于小波变换模的局部极大值点的理论,采用二次B样条小波对复合材料SEM图像进行了多分辨率小波变换,从低分辨率到高分辨率逐步搜索边缘,并根据不同分辨率噪声的小波系数变化较大的特点,抑制了噪声.成功的检测出FeAl-ZrO2复合材料第二相晶粒的边缘.文章的最后给出了实验结果并且对实验结果进行了讨论.