Bang-Bang Control Class D Amplifiers: Total Harmonic Distortion and Supply Noise

The total harmonic distortion (THD) and the power supply noise, qualified by the power supply rejection ratio (PSRR) and by the power supply induced intermodulation distortion (PS-IMD), are recognized to be potential drawbacks of class D amplifiers. In this paper, analytical expressions for the THD, PSRR, and PS-IMD of the bang-bang control class D amplifier (bang-bang amp) are derived; the bang-bang amp is arguably the most power-efficient class D amp for low-voltage power-critical applications including hearing aids. Based on the derived expressions, the effects of important parameters on the THD, PSRR, and PS-IMD are investigated, providing good insight to the design of the bang-bang amp to meet given design specifications. The analytical analyses are verified by comparing them against HSPICE simulations and hardware measurements. The bang-bang amp is also compared against the prevalent pulsewidth modulation class D amp, and in most cases, the former is shown to possess superior parameters, including lower power dissipation and hardware advantages for low-voltage power-critical applications.     

基坑围护中SMW工法的应用

结合工程实例,简要介绍了基坑围护结构SMW工法在施工过程中的各施工要点及该施工工艺的特点。     

Decentralized adaptive controller design of large-scale uncertain robotic systems

In this paper, we develop a decentralized neural network control design for robotic systems. Using this design, it is not necessary to derive the robotic dynamical system (robotic model) for the control of each of the robotic components, as in traditional robot control. The advantage of the proposed neural network controller is that, under a mild assumption, unknown nonlinear dynamics such as inertia matrix and Coriolis/centripetal matrix and friction, as well as interconnections with arbitrary nonlinear bounds can be accommodated with on-line learning.     

第7次普通高等学校图学教育现状的调查与研究

2008年初对全国高等院校图学教育的现状进行了问卷调查.这是继1997、1998、2000、2002、2004、2006年6次调查之后的第7次大规模调查.此次调查的内容是在总结了前6次调查的基础上,根据形势的发展,由中国工程图学学会图学教育专业委员会开会讨论确定的.在对本次调查结果汇总和分析的基础上,介绍了我国普通高等学校图学教育的现状与发展趋势,供广大图学工作者参考.     

Synthesis and formation mechanism of hematite hollow microspheres by a one-pot templateless surfactant-free hydrothermal process

Hollow microspheres of hematite (α-Fe₂O₃) were prepared by a simple hydrothermal treatment of ferrous ammonium sulphate hexahydrate ((NH₄)₂Fe(SO₄)₂·6H₂O) aqueous solution without any surfactants and additives at 180–200 °C. The products were characterized by XRD, FE-SEM and TEM. The results show that α-Fe₂O₃ hollow microspheres are about 1 μm in diameters and are composed of α-Fe₂O₃ nanoparticles with a diameter range from 50 nm to 150 nm. The effects of reaction parameters such as reaction time, temperature and [(NH₄)₂Fe(SO₄)₂·6H₂O] on the morphology of the final product were investigated. A potential formation mechanism of α-Fe₂O₃ hollow microspheres was also proposed, where the intermediate, urchin-like goethite, served as a sacrificial template for the formation of hollow structure. The reaction parameters-depended morphologies of the final products consisted well with the proposed formation mechanism.     

从软硬件发展看影视后期制作核心任务的变迁

随着计算机技术的发展，数字技术被广泛地应用到影视制作当中，增强并完善了影视后期制作的功能，尤其满足了大规模制作的需求。数字技术已经开始对影视制作的流程本身进行改造，如媒体资产管理系统。本文重点分析了不同时期影视后期制作的自身特征，并根据目前影视制作的需求趋势讨论了影视后期制作系统的发展趋势。     

Wafer defect pattern recognition by multi-class support vector machines by using a novel defect cluster index

Wafer yield is an important index of efficiency in integrated circuit (IC) production. The number and cluster intensity of wafer defects are two key determinants of wafer yield. As wafer sizes increase, the defect cluster phenomenon becomes more apparent. Cluster indices currently used to describe this phenomenon have major limitations. Causes of process variation can sometimes be identified by analyzing wafer defect patterns. However, human recognition of defect patterns can be time-consuming and inaccurate. This study presents a novel recognition system using multi-class support vector machines with a new defect cluster index to efficiently and accurately recognize wafer defect patterns. A simulated case demonstrates the effectiveness of the proposed model.     

Al—Si—Cr—Mo合金蠕铁热物性的研究

采用正交设计法，对Ａｌ－Ｓｉ－Ｃｒ－Ｍｏ合金蠕铁的热物理性能进行了测试，并分别结合方差分析，对Ａｌ、Ｓｉ、Ｃｒ、Ｍｏ各项性能影响的显著性进行了判断．结果表明，Ａｌ－Ｓｉ－Ｃｒ－Ｍｏ蠕铁具有很好的抗氧化性、抗生长性和抗热疲劳性能，是一种较好的玻璃模具材料．     

汽轮机汽缸热应力的试验研究

汽缸的热应力，对汽轮机的运行安全很重要。本文对此进行了试验研究。在试验中，对一台多机汽轮机的汽缸进行了模拟加热，测量了热应力的变化情况。找出某些部位热应力的理论计算值与实测值比较一致，而另一些部位有较大差距。这一结果可作为建立热应力监视数学模型时参考。此外还测量了不同温升速度下法兰的热应力，并用理论方法修正到适于不同法兰厚度的情况。     

大型锅炉燃烧室三维辐射传热模型及其应用

在网络分析法基础上，建立了一种新的炉内辐射传热三维数值计算方法，并应用于大坝电厂３００ＭＷ机组仿真和哈尔滨锅炉厂６００ＭＷ机组炉内过程全模拟计算。应用结果不但实时性好，同时各排燃烧器运行工况对过热汽温的影响，以及屏式过热器辐射吸热特性都得到充分反映，具有很好的动态响应。