小功率通用变频器的设计与实现

交流异步电动机的变频调速应用十分广泛。根据交-直-交变频理论,设计了一种基于MOSFET的低成本、高效率的通用变频器。详细介绍了逆变电路结构、驱动电路的具体设计、脉冲信号产生方法等。经实验和实际使用证实,该变频器具有控制电路结构简单,调频操作方便,可应用于通用异步电动机,具有运行安全、稳定、可靠等特点。     

复杂的建筑物下有软弱下卧层时的基础设计

工程建设直接涉及人民的生命财产安全、环境保护和其他公众利益，成功的建筑结构设计，应当是安全、合理、经济和可行的。而地基基础则是建筑结构设计的重要组成部分之一。由国家建设部颁布的《工程建设标准强制性条文》明确规定：地基设计在满足地基承载力要求的同时，应满足地基变形要求。因此，我们在建筑物的地基设计中，不仅要使地基有足够的强度安全储备，而且要限制基础的不均匀沉降量，来保证建筑物的安全和正常使用。     

干涉／强度调制型自校准F—P腔光纤传感器的应变测量

文中介绍了强度/干涉调制型自校准F-P腔光纤传感器系统及其工作原理,系统采用中心波长为1 310 nm的LED作为光源,粗波分复用器将传感头反射回的光分为宽谱和窄谱2路,其比值可以消除光源以及光纤损耗引起的光功率波动对测量的影响.此系统结合了强度调制型和干涉型光纤传感器的优点,既可对静态应变进行测量,又可对动态应变进行实时监测.测量结果表明:系统对于静态应变测量的线性范围为200 με,最小分辨率可达0.5 με;在动态应变测量中,可以准确获得悬臂梁的振动频率.     

Plasma-Assisted Chemical Vapor Deposition of Titanium Oxide Films by Dielectric Barrier Discharge in TiCl_4/O_2/N_2 Gas Mixtures

Low-pressure dielectric barrier discharge（DBD） TiCl4/O2and N2 plasmas have been used to deposit titanium oxide films at different power supply driving frequencies. A homemade large area low pressure DBD reactor was applied, characterized by the simplicity of the experimental set-up and a low consumption of feed gas and electric power, as well as being easy to operate. Atomic force microscopy, scanning electron microscopy, energy dispersive spectroscopy,and contact angle measurements have been used to characterize the deposited films. Experimental results show all deposited films are uniform and hydrophilic with a contact angle of about 15 o.Compared to titanium oxide films deposited in TiCl4/O2gas mixtures, those in TiCl4/O2/N2gas mixtures are much more stable. The contact angle of titanium oxide films in TiCl4/O2/N2gas mixtures with the addition of 50% N2 and 20% TiCl4 is still smaller than 20 o, while that of undoped titanium oxide films is larger than 64 owhen they are measured after one week. The low-pressure TiCl4/O2plasmas consist of pulsed glow-like discharges with peak widths of several microseconds, which leads to the uniform deposition of titanium oxide films. Increasing a film thickness over several hundreds of nm leads to the film’s fragmentation due to the over-high film stress. Optical emission spectra（OES） of TiCl4/O2DBD plasmas at various power supply driving frequencies are presented.     

Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions

Polycrystalline tungsten(W)and molybdenum(Mo)materials both non-annealed and annealed at temperatures of 800-1750~C have been irradiated with low-energy(220 eV),high-flux(~10~(21)ions/m~2.s)He~+at an irradiation temperature of 600℃and at a dose of1.0×10~(25)ions/m~2.This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials.A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He+dose of 1.0×10~(25)ions/m~2.Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W.Compared to W,Mo suffered much less surface damage after being irradiated at various He~+doses.     

He~+辐照对非晶碳氢薄膜表面硬度的影响

在室温下,利用等离子体增强的化学气相沉积法(PECVD)在硅衬底上制备了非晶碳氢薄膜。采用100keV,剂量分别为1.0×1015、5.0×1015、5.0×1016和1.0×1017ions/cm2的He离子(He+)对非晶碳氢薄膜进行辐照实验。通过基于原子力显微镜(AFM)的纳米压痕和纳米划痕技术,对He+辐照前后碳氢薄膜的表面硬度进行分析。结果表明,经He+辐照后碳氢薄膜的表面硬度明显增加,并且随着He+辐照剂量增加,碳氢薄膜的表面硬度呈逐渐增加的趋势。傅里叶变换红外光谱(FT-IR)和拉曼光谱分析表明,He+辐照会导致碳氢薄膜中sp2C键含量明显增加,而sp3C键及H原子的含量明显降低,这可能是引起碳氢薄膜硬度变化的主要原因。     

抗风结构多级设防理论在柱式两面广告牌设计中的应用

一、问题的提出某施工单位拟承建一柱式两面广告牌，牌面顶部距地面18.00m，广告牌面6×18m2，独立圆柱作为承重结构。建设单位要求该广告牌能抗12级台风，并与施工单位签订了合同。为此，施工单位来我单位咨询，并委托我们进行结构设计。建设地点的基本风压ω0=0.35kN/m2,只相当于当地10 m高空旷地段的风速V0=23.66m/s即约9级大风。而12级台风的平均风速V0=32.7m/s。显然按现行荷载规范，不可能抵抗12级台风。12级台风若发生在建设地点，为人力不可抗拒的外力。那么，要求抗拒12级台风是没有必要。然而，风荷载是一种很强随机的荷载，在…