不同结构金刚石涂层刀具的制备及性能参数优化

利用化学气相沉积(Chemical Vapor Deposition)法,选取最佳工艺参数,在硬质合金刀具上制备微米、纳米及微/纳米金刚石复合涂层,采用SEM、Raman光谱、XRD测试分析涂层的表面形貌和化学纯度.结果显示,微米金刚石涂层结晶质量好,晶面取向以(111)(220)为主且金刚石纯度很高,纳米金刚石涂层表面光滑无明显择优取向,微/纳米复合涂层聚具有两种涂层的优点.采用压痕法、划痕法、微粒冲浆喷蚀(MSE)法对涂层的膜/基结合力及耐磨性进行测定.结果显示微米金刚石涂层的膜/基结合力最好,纳米金刚石涂层的最差.微/纳米金刚石复合涂层的耐磨性最好,纳米金刚石涂层的耐磨性最差.     

含有Al组分阶变AlGaN过渡层的Si基AlGaN/GaN HEMT

采用一个AlN缓冲层和两个Al组分阶变的AlGaN过渡层作为中间层,在76.2mm Si衬底上外延生长出1.7μm厚无裂纹AlGaN/GaN异质结材料,利用原子力显微镜、X射线衍射、Hall效应测量和CV测量等手段对材料的结构特性和电学性能进行了表征。材料表面平整光滑,晶体质量和电学性能良好,2DEG面密度为1.12×1013cm-2,迁移率为1 208cm2/(V.s)。由该材料研制的栅长为1μm的AlGaN/GaN HEMT器件,电流增益截止频率fT达到10.4GHz,这些结果表明组分阶变AlGaN过渡层技术可用于实现高性能Si基GaN HEMT。     

关于长方矩阵的加权群逆的存在性

本文讨论长方矩阵的加权群逆．分别利用减逆和泛分解,给出了长方矩阵的加权群逆存在的几个充要条件以及加权群逆的计算公式．     

制冷系统模拟仿真技术的应用与发展

文中对仿真技术在制冷系统领域的发展现状进行了综述,并对其未来发展趋势进行了展望。     

基于轻量级金字塔密集残差网络的红外图像超分辨增强

现有的红外制导武器严重依赖操作手对目标的捕获,其捕获的精度与目标的纹理细节正相关.为了提升弱小区域的显示质量,满足现有导引头小型化、模块化、低成本的设计要求,本文设计了一种基于轻量级金字塔密集残差网络的图像增强模型,该模型在密集残差网络基础上通过密集连接层和残差网络来学习不同尺度图像之间的非线性映射,充分利用多尺度特征...     

Application of the quadrilateral area coordinate method： a new element for laminated composite plate bending problems

Recently, some new quadrilateral finite elements were successfully developed by the Quadrilateral Area Coordinate (QAC) method. Compared with those traditional models using isoparametric coordinates, these new models are less sensitive to mesh distortion. In this paper, a new displacement-based, 4-node 20-DOF (5-DOF per node) quadrilateral bending element based on the first-order shear deformation theory for analysis of arbitrary laminated composite plates is presented. Its bending part is based on the element AC-MQ4, a recent-developed high-performance Mindlin-Reissner plate element formulated by QAC method and the generalized conforming condition method; and its in-plane displacement fields are interpolated by bilinear shape functions in isoparametric coordinates. Furthermore, the hybrid post-processing procedure, which was firstly proposed by the authors, is employed again to improve the stress solutions, especially for the transverse shear stresses. The resulting element, denoted as AC-MQ4-LC, exhibits excellent performance in all linear static and dynamic numerical examples. It demonstrates again that the QAC method, the generalized conforming condition method, and the hybrid post-processing procedure are efficient tools for developing simple, effective and reliable finite element models. The project is supported by the National Natural Science Foundation of China (10502028), the Special Foundation for the Authors of the Nationwide (China) Excellent Doctoral Dissertation (200242), and the Science Research Foundation of China Agricultural University (2004016).     

Acoustic carpet invisibility cloak with two open windows using multilayered homogeneous isotropic material

We present a method for designing an open acoustic cloak that can conceal a perturbation on flat ground and simultaneously meet the requirement of communication and matter interchange between the inside and the outside of the cloak. This cloak can be constructed with a multilayered structure and each layer is an isotropic and homogeneous medium. The design scheme consists of two steps: firstly, we apply a conformal coordinate transformation to obtain a quasi-perfect cloak with heterogeneous isotropic material; then, according to the profile of the material distribution, we degenerate this cloak into a multilayered-homogeneous isotropic cloak, which has two open windows with negligible disturbance on its invisibility performance. This may greatly facilitate the fabrication and enhance the applicability of such a carpet-type cloak.     

Non-uniform distribution of gas–solid flow through six parallel cyclones in a CFB system: An experimental study

In large-scale circulating fluidized bed (CFB) boilers, it is common to use multiple cyclones in parallel for the capture of solids, assuming that gas–solid flow to be the same in the cyclones. This article presents a study investigating gas–solid flow through six parallel cyclones in a CFB cold test rig. The six cyclones were located asymmetrically on the left and right walls of the riser. Solid volume fraction and particle velocity profiles at the riser outlets and in the horizontal ducts were measured using a fiber optical probe. Cyclone pressure drop and solid circulating rate were measured for each individual cyclone. Measurements showed good agreement as to the non-uniform distribution of the gas–solid flow, which occurred mainly across the three cyclones on one side: the middle cyclones on both sides had higher particle velocities. Conversely, the solid volume fractions, solid fluxes and solid circulating rates of the middle cyclones were lower than those of the other four cyclones. The apparent reason for the flow non-uniformity among the cyclones is the significant flow non-uniformity at the riser outlets. Under typical operating conditions, the solid volume fractions at the riser outlets had a deviation of up to 26% whereas the solid circulating rates at the stand pipes, 7%. These results are consistent with most other studies in the literature.     

基于峰值变换的信号稀疏表示及重建

压缩感知(CS)近年来的出现引起了学术界的极大关注,其要求信号本身是稀疏的或者在某种正交基下可以稀疏的表示。该文针对信号本身及小波变换下均不稀疏的情况(如线调频信号),结合峰值变换(PT),提出了PTCS的信号压缩感知算法,对于PT变换产生的峰值变换点序列采用可逆数字水印中的数值扩展方法,将峰值变换点序列嵌入测量信号中,避免了由于引入PT变换而额外增加测量点。通过PT变换,可以将不稀疏的小波系数变为稀疏系数,从而大大提升信号重构效果。仿真结果表明,该文提出的PTCS算法恢复信号与已有的基于正交匹配追踪算法的CS算法相比较,恢复信号质量有着较大的提高。     

基于CMMB的外辐射源雷达信号模糊函数分析与处理

根据中国移动多媒体广播(CMMB)信号结构,该文分析了该信号作为雷达辐射源的模糊函数特性,研究了副峰产生的机理,并与欧洲数字视频地面广播(DVB-T)信号特性做了比对;针对因循环前缀引起的模糊函数副峰和同步信号引起的多普勒模糊带对目标探测产生的不利影响,提出了副峰抑制的方法。仿真和实测结果验证了文中副峰产生机理分析的正确性,同时所采用的方法能有效抑制模糊副峰,为目标探测奠定了基础。