Design of distributed compliant micromechanisms with an implicit free boundary representation

In this paper, a parameterization approach is presented for structural shape and topology optimization of compliant mechanisms using a moving boundary representation. A level set model is developed to implicitly describe the structural boundary by embedding into a scalar function of higher dimension as zero level set. The compactly supported radial basis function of favorable smoothness and accuracy is used to interpolate the level set function. Thus, the temporal and spatial initial value problem is now converted into a time-separable parameterization problem. Accordingly, the more difficult shape and topology optimization of the Hamilton–Jacobi equation is then transferred into a relatively easy size optimization with the expansion coefficients as design variables. The design boundary is therefore advanced by applying the optimality criteria method to iteratively evaluate the size optimization so as to update the level set function in accordance with expansion coefficients of the interpolation. The optimization problem of the compliant mechanism is established by including both the mechanical efficiency as the objective function and the prescribed material usage as the constraint. The design sensitivity analysis is performed by utilizing the shape derivative. It is noted that the present method is not only capable of simultaneously addressing shape fidelity and topology changes with a smooth structural boundary but also able to avoid some of the unfavorable numerical issues such as the Courant–Friedrich–Levy condition, the velocity extension algorithm, and the reinitialization procedure in the conventional level set method. In particular, the present method can generate new holes inside the material domain, which makes the final design less insensitive to the initial guess. The compliant inverter is applied to demonstrate the availability of the present method in the framework of the implicit free boundary representation.     

Gas-phase ion chemistry in organometallic systems

This review essentially deals with positive ion/molecule reactions occurring in gas-phase organometallic systems, and encompasses a period of time of approximately 7 years, going from 1997 to early 2004. Following the example of the excellent review by Eller & Schwarz (1991; Chem Rev 91:1121-1177), in the first part, results of reaction of naked ions are presented by grouping them according to the neutral substrate, while in the second part, ligated ions are grouped according to the different ligands. Whenever possible, comparison among similar studies is attempted, and general trends of reactivities are evidenced.     

甘肃景电灌区次生盐化土壤的性质及其发生机理

本文对甘肃景电灌区次生盐化土壤的理化性质进行了研究 .该区次生盐渍化土壤主要为硫酸盐氯化物和氯化物硫酸盐型 ,水溶性钠离子在阳离子中占绝对优势 .土壤通体碳酸钙含量很高 ,并有少量的石膏 .钠离子饱和度很高 ,具有钠质特性或钠质化现象 ,盐化与钠质化同时进行 .在此基础上对次生盐渍化的机理和改良进行了讨论     

跨国公司子公司角色的研究

跨国公司与传统公司管理方式上的不同,即我们所说的跨国公司组织管理者控制其复杂组织模式的程序和协调机制的差异:允许他们独立的地区子公司自主地应对所在地区的机遇与危机。本文基于A-PJ(Autonomy&Proce-dural Justice)模型,将子公司分为合作者(Collaborator)、附庸(Vassal)、斗士(Militant)和伙伴(Partner)四种类型,分析他们在一体化和当地化的需求下,在整个跨国公司网络中扮演的角色。     

重(特)大泄漏事故统计分析及事故模式研究

对新中国成立以来我国化工系统发生的重（特）大、典型泄漏事故进行了统计分析，总结出应优先进行控制和管理的危险性物质，分析了造成这些重（特）大典型泄漏事故的基本原因。结合对已经发生的重（特）大典型泄漏事故的剖析，总结出泄漏扩散事故的7大影响因素，建立了泄漏事故模式，并对各种事故模式的泄漏机理和发生条件进行了研究分析。     

Nanocrystalline diamond growth on different substrates

Nanocomposite films consisting of diamond nanoparticles of 3-5 nm diameter embedded in an amorphous carbon matrix have been deposited by means of microwave plasma chemical vapour deposition (MWCVD) from CH₄/N₂ gas mixtures. Si wafers, Si coated with TiN, polycrystalline diamond (PCD) and cubic boron nitride films, and Ti-6Al-4V alloy have been used as substrates. Some of the substrates have been pretreated ultrasonically with diamond powder in order to enhance the nucleation density n_nuc. It turned out that n_nuc depends critically on the chemical nature of the substrate, its smoothness and the pretreatment applied. No differences to the nucleation behaviour of CVD PCD films were observed. On the other hand, the growth process seems to be not affected by the substrate material. The crystallinity (studied by X-ray diffraction) and the bonding environment (investigated by Raman spectroscopy) show no significant differences for the various substrates. The mechanical and tribological properties, finally, reflect again the influence of the substrate material: on TiN, a lower hardness was measured as compared to Si, PCD and c-BN, whereas the adhesion of c-BN/nanocrystalline diamond (NCD) system was determined by that of the c-BN film on the underlying Si substrate.     

DDoS攻击防御机制综述

DDoS攻击是目前威胁网络安全的主要因素之一。本文分类介绍了现有的DDoS攻击防御机制,阐明了各种机制之间的关系,给出了每种防御机制的应用实例,全面分析了各种防御机制的优缺点。对正确认识DDoS攻击及其防御有很大的参考价值。     

柴油机球墨铸铁曲轴的早期断裂机制研究

采用化学成分分析、金相检测、宏观与微观断口形貌分析等方法，对柴油机QT600-3球墨铸铁曲轴的早期断裂机制进行了分析研究．结果表明，轴颈圆角处的表面氧化皮及显微裂纹是引起疲劳开裂的主要原因，淬火组织缺陷诱发裂纹源的形成，对曲轴早期断裂也有一定的影响，断裂机制为解理与准解理断裂，具有典型的脆性断裂特征。