Cartesian积与邻点可区别着色之间的关系

图G的一个正常k-边着色是指k种颜色1,2,…,k对图G各边的一个分配,使得任意2条相邻边染以不同的颜色.对于图G的一个正常边染色f和G中任何一个顶点x,S_f（x）或S（x）表示与顶点x关联的边在f下的颜色所构成的集合.若对于图G中任意2个相邻顶点u和v,有S（u）≠S（v）,则称f为图G的邻点可区别正常边染色.对图G进行邻点可区别正常边染色所需的最少颜色数,称为G的邻点可区别正常边色数,记为χ'_a（G）.图G的一个正常k-全染色是指k种颜色对图G的顶点和边的一个分配,使得任意2个相邻的或相关联元素染以不同的颜色.对于图G的一个正常全染色g和G中任何一个顶点 x,使用C_g（x）或C（x）来表示顶点x的颜色（在g下）以及与顶点x关联的边在g下的颜色所构成的集合.若对于G中任意2个相邻顶点u和v,有C（u）≠C（v）,则称g为图G的邻点可区别全染色.图G的邻点可区别全染色所需的最少颜色数称为图G的邻点可区别正常全色数,记为χ″_a（G）.主要讨论了Cartesian积和2种邻点可区别染色之间的关系.     

AlGaN双势垒结构对高In组分InGaN/GaN MQWs太阳能电池材料晶体质量和发光性能的影响

本文利用金属有机化合物化学气相沉积(MOCVD)技术在(001)面图形化蓝宝石衬底(PSS)上生长了一种含有AlGaN-InGaN/GaN MQWs (multiple quantum wells)-AlGaN双势垒结构的高In组分太阳能电池外延材料。高分辨率X射线衍射(HRXRD)和光致发光(PL)谱分析表明,与含有AlGaN电子阻挡层的低In组分的量子阱结构太阳能电池外延材料相比,该结构材料具有较小的半峰全宽(FWHM),计算表明:此结构材料的位错密度降低了一个数量级,达到10⁷ cm^-2;同时,有源区中的应变弛豫降低了51%;此外,此结构材料的发光强度增强了35%。研究结果表明含有AlGaN双势垒结构的外延材料可以减小有源区的位错密度,降低非辐射复合中心的数目,增大有源区有效光生载流子的数目,为制备高质量太阳能电池提供实验依据。     

Dislocation structure and dynamics govern pop-in modes of nanoindentation on single-crystal metals

ABSTRACT

There are two types of pop-in mode that have been widely observed in nanoindentation experiments: the single pop-in, and the successive pop-in modes. Here we employ the molecular dynamics (MD) modelling to simulate nanoindentation for three face-centred cubic (FCC) metals, including Al, Cu and Ni, and two body-centred cubic (BCC) metals, such as Fe and Ta. We aim to examine the deformation mechanisms underlying these pop-in modes. Our simulation results indicate that the dislocation structures formed in single crystals during nanoindentation are mainly composed of half prismatic dislocation loops. These half prismatic dislocation loops in FCC metals are primarily constituted of extended dislocations. Lomer–Cottrell locks that result from the interactions between these extended dislocations can resist the slipping of half dislocation loops. These locks can build up the elastic energy that is needed to activate the nucleation of new half dislocation loops. A repetition of this sequence results in successive pop-in events in Al and other FCC metals. Conversely, the half prismatic dislocation loops that form in BCC metals after first pop-in are prone to slip into the bulk, which sustains plastic indentation process after first pop-in and prevents subsequent pop-ins. We thus conclude that pop-in modes are correlated with lattice structures during nanoindentation, regardless of their crystal orientations.     

Tailoring edge and interface states in topological metastructures exhibiting the acoustic valley Hall effect

In this study, we investigate the acoustic topological insulator or topological metastructure, where an acoustic wave can exist only in an edge or interface state instead of propagating in bulk. Breaking the structural symmetry enables the opening of the Dirac cone in the band structure and the generation of a new band gap, wherein a topological edge or interface state emerges.Further, we systematically analyze two types of topological states that stem from the acoustic valley Hall effect mechanism;one type is confined to the boundary, whereas the other type can be observed at the interface between two topologically different structures. Results denote that the selection of different boundaries along with appropriately designed interfaces provides the acoustic waves in the band gap range with abilities of one-way propagation, dual-channel propagation, immunity from backscattering at sharp corners, and/or transition between propagation at interfaces and boundaries. Furthermore, we show that the acoustic wave propagation paths can be tailored in diverse and arbitrary ways by combing the two aforementioned types of topological states.     

基于滑移界面耦合技术的旋转电机磁场仿真方法

提出了一种基于滑移界面耦合技术的旋转电机磁场仿真方法。首先,对旋转电机问题建立等效弱形式,用Lagrange乘子法施加Coulomb规范条件和滑移界面处的磁矢势连续性条件;然后,采用混合单元方法离散整个求解域中的未知量,采用棱边单元法离散滑移界面处的Lagrange矢量乘子,并采用多点约束法耦合滑移界面处的Lagrange标量乘子自由度,该方法无须在旋转电机模型的非匹配网格中构建生成树,即可自动保证磁矢势解的唯一性;最后,采用旋转线圈案例和简化的永磁同步电机案例验证了本文方法的有效性。     

Cutting of aramide fiber-reinforced plastics by Co2 laser

Comparative characteristics of aramide fiber reinforced plastics (AFRP) made by laser cutting or machining are presented. It is found that the strength of the specimens cut out by laser is 4–25% higher, while the moisture absorption is at least 2 times lower as compared to those cut out by machining. The deviation of the cutting edge size for AFRP 2 mm thick does not exceed 0.4 mm. Calculated and experimental data are given. The possibilities and conditions of cutting the AFRP up to 6 mm thick are determined.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 3, pp. 375–384, May–June, 1999.     

自由边界条件轴对称薄圆柱壳体的混合有限元数值解

基于文「８」发展的混合结构问题稳定方法的框架,针对自由边界条件轴对称薄圆柱壳体问题,给出了其新型混合有限元计算模型。应用线性元,已证明该模型是强制的,其对称正定代数方程组的条件数Ｏ（ｈ＾－２）。     

可渗透壁对翼型声涡相互作用下流场及声场的影响

由仿生学原理构建的可渗透翼型对湍流气动噪声抑制作用已展现良好的应用前景。对NACA 0012可渗透翼型和实体翼型进行了数值计算,得到了声涡相互作用下气动噪声声场和流场,分析了可渗透壁对翼型流场和声场的影响。研究表明,相对实体翼型,可渗透壁通过减小声源强度降低了主纯音噪声声压级幅值和远场总声压级,消除了高阶离散纯音,但对噪声的指向性没有较大改变。进一步的流场分析表明,可渗透壁对翼型气动性能影响不大的情况下能够降低边界层扰动和翼型后缘大尺度涡旋强度,并推迟分离泡转捩和再附位置。     

Anisotropic mesh adaptation: towards user‐independent,mesh‐independent and solver‐independent CFD. Part I: general principles

The present paper is the lead article in a three‐part series on anisotropic mesh adaptation and its applications to structured and unstructured meshes. A flexible approach is proposed and tested on two‐dimensional, inviscid and viscous, finite volume and finite element flow solvers, over a wide range of speeds. The directional properties of an interpolation‐based error estimate, extracted from the Hessian of the solution, are used to control the size and orientation of mesh edges. The approach is encapsulated into an edge‐based anisotropic mesh optimization methodology (MOM), which uses a judicious sequence of four local operations: refinement, coarsening, edge swapping and point movement, to equi‐distribute the error estimate along all edges, without any recourse to remeshing. The mesh adaptation convergence of the MOM loop is carefully studied for a wide variety of test cases. The mesh optimization generic coupling of MOM with finite volume and finite element flow solvers is shown to yield the same final mesh no matter what the starting point is. It is also shown that on such optimized meshes, the need for computational fluid dynamics (CFD) stabilization artifices, such as upwinding or artificial viscosity, are drastically reduced, if not altogether eliminated, in most well‐posed formulations. These two conclusions can be considered significant steps towards mesh‐independent and solver‐independent CFD. The structure of the three‐part series is thus, 1, general principles; 2, methodology and applications to structured and unstructured grids; 3, applications to three‐dimensional flows. Copyright © 2000 John Wiley & Sons, Ltd.