(Al_xGa_(1-x)As)_m/(GaAs)_m(001)超晶格的能带结构与合金组分x间的关系

采用紧束缚的重整化方法研究了(Al_xGa_(1-x)As)_m/(GaAs)_m(001)超晶格的电子能带结构与合金组分x及层厚间的变化关系。给出了临界组分x_o与层厚m间的变化关系图。并以二次函数形式给出了直接能隙和间接能隙与合金组分x间的变化关系。最后,也用Kronig—Penney模型对超晶格的电子能带结构进行了计算,并与紧束缚的计算结果进行了比较。     

卫浴设施市场的动向及对策

卫生洁具市场随着我国的经济飞速发展,显得非常活跃。要崭露头角,必须从调研市场和攀比国外产品着手,制订出自己的相应的对策。     

电磁带隙结构在抑制电源层上噪声的应用

本文在阐述电磁带隙结构的基础上,从理论上分析其原理,结合印制电路板电源层存在的瓶颈,即目标阻抗随着设计频率的不断上升而变得越来越难控制。电磁带隙结构最早应用在天线结构中,而本文引用到PCB板电源完整性的设计中来达到抑制高频谐振的目的,并且通过Slwave建模仿真验证了其正确性。     

中国水泥工业消纳社会废弃物与发达国家的差距

预分解水泥窑消纳各种含有可燃质的废物,既可充分利用其残留的热值,还能彻底干净地处置其燃烧后的残渣,消除二次污染隐患;加之水泥窑适应范围广,可以消纳各种状态的废料,处置能力很大。此法比新建垃圾填埋场或焚烧厂等办法经济得多,收效更快。水泥工业还可以将各种工业废渣用作混合材掺于水泥熟料中一并粉磨成水泥;有的工业废料还可以用作水泥原料以替代天然的石灰石、粘土或铁矿石等。在水泥工业消纳社会废弃物方面,我国与德日美等发达国家,在理念和技术上还有差距：我国看似消纳混合材不少,实为部分超掺滥掺所致;我国原料和石膏的替代率尚有较大提升空间;我国替代燃料的应用十分滞后,须急起直追。     

磁悬浮列车的多路串行异步通信系统

磁悬浮列车的多路串行异步通信系统,在DSP并行总线上扩展UART芯片,采用RS-485总线串行通信,并以硬件实现异步数据传输.系统软件设计包括ADMC401及STl6C554的初始化程序和通信协议等,其初始化负责设置操作每个通道所需参数.而悬浮间隙传感器和控制器间则采用半双工方式工作.     

FA502型细纱机前区牵伸工艺的优选

为进一步提高FA502型细纱机牵伸改造机台纺纱质量水平,在气压加压,V形牵伸改造基础上采用增大胶辊前冲量和上销前冲量及下销下沉等工艺技术措施,并在牵伸前区选取罗拉隔距、钳口隔距及前胶辊与上胶圈间的间隙等参数进行多方案工艺试验,摸索出对CJ 18 tex和CJ 14.5 tex均有较好适应性的细纱机牵伸工艺:金属上销,钳口隔距2.0mm,罗拉隔距17.5 mm×27 mm,前胶辊与上胶圈间的间隙0.5 mm,使条干CV值达到2007年乌斯特公报7%～9%良好水平。     

Stiffness improvement of swirl gripper based on gap height and force estimation

The swirl gripper is an electrically activated noncontact handling device that uses swirling airflow to generate a lifting force. This force can be used to pick up a workpiece placed underneath the swirl gripper without any contact. It is applicable, for example, on a semiconductor wafer production line, where contact must be avoided during the handling and moving of a workpiece to minimize damage. When a workpiece levitates underneath a swirl gripper, the gap height between them is critical for safe handling. Therefore, in this study, we develop a theoretical model of the swirl gripper, based on which a method to estimate the levitation gap height by detecting pressure at two points is proposed. Experiments indicate that the estimated gap height can track changes in actual gap height accurately in real time, when the gap height is relatively small and the inertia of airflow in the gap is negligible. In addition, the force between the gripper and workpiece can also be estimated using the detected pressure. As a result, a desired relationship between the force and gap height can be achieved by adjusting the rotating speed of the fan according to the real-time estimated force and gap height using a microcontroller. The control system was experimentally verified using a desired linear relationship. Because the stiffness of the force decreases with increasing gap height for a constant gripper fan rotating speed, the linear relationship between the force and gap height, which means a constant stiffness, is expected to enhance handling stability of workpieces.     

On robustness in the gap metric and coprime factor uncertainty for LTV systems

In this paper, we study the problem of robust stabilization for discrete linear time-varying (LTV) systems subject to time-varying normalized coprime factor uncertainty. Operator theoretic results which generalize similar results known to hold for linear time-invariant (infinite-dimensional) systems are developed. In particular, we compute an upper bound for the maximal achievable stability margin under TV normalized coprime factor uncertainty in terms of the norm of an operator with a time-varying Hankel structure. We point to a necessary and sufficient condition which guarantees compactness of the TV Hankel operator, and in which case singular values and vectors can be used to compute the time-varying stability margin and TV controller.     

Flow distribution and mass removal in floating treatment wetlands arranged in series and spanning the channel width

Floating treatment wetlands (FTWs) use plants’ roots for water quality improvement. The plants are supported by a buoyant structure deployed at the water surface. The roots form a porous zone beneath the structure and remove pollutants carried in suspension through filtering, absorption and uptake. This paper used CFD simulation to model FTWs arranged in series and spanning the channel width and to study the effects of root length and spacing between FTWs on flow distribution and mass removal. The root zone was modelled as a porous media, and removal was computed using first-order decay, for which a range of removal constants was tested. Longer roots increased the reactive volume of the root zone, which increased the fraction of pollutant inflow entering the FTWs. Increasing the distance between FTWs allowed greater mixing between water that went through and beneath the upstream FTW. This increased the concentration entering each FTW, which enhanced mass removal per FTW. However, a larger distance between FTWs reduced the number of FTWs in the channel, reducing the reactive volume. In the tradeoff between mixing and reactive volume, the reactive volume was more important, such that total removal in the channel increased with longer roots and more units of FTW (shorter gap distance). However, removing the gap entirely was detrimental, as FTWs in series removed more mass than a continuous FTW of same volume. This study points to two design recommendations for FTWs in series. First, if resources for building FTWs are not limiting, but the channel length is, it is preferable to prioritize higher reactive volume (shorter gap distance) to achieve maximum removal per channel length. Second, if resources for FTWs are limiting, but channel length is not, it is better to place the FTWs with a longer gap distance, preferably along enough to allow mixing over the full depth between FTWs, as this will achieve maximum removal per FTW.