Low-Temperature Sintering of Aluminum Oxide

A fine-sized (∼0.1 μm), agglomerate-free Al₂O₃ dispersion was used to prepare homogeneous green bodies with ∼69% relative density and ∼10-nm median pore radius. Samples could be sintered at 1150°C to a relative density >99.5% and an average grain size of 0.25 μm.     

Optimal sensitivity bound estimation and controller design

An explicit computational form is given for the estimation of the smallest upper bound on the sensitivity function over an operating band for a given stability margin in a single right half-plane (RHP) zero scalar system. A stable minimum-phase weighting function is constructed to meet such an infimum and the given stability margin with the H^∞ criterion. A numerical example is presented to demonstrate the optimal sensitivity estimation, weighting function construction and controller design.     

Covariance control with observed-state feedback gains for continuous nonlinear systems using T-S fuzzy models

The design problem of state variance constrained control for stochastic systems has received rather extensive attention in recent years. This paper solves the state variance constrained controller design problem by using the covariance control theory, with observed-state feedback gains for continuous Takagi-Sugeno (TS) fuzzy models. By incorporating the technique of state estimation into the practical covariance control theory, a variance constrained control methodology is developed for the continuous TS fuzzy models. Finally, a numerical example is shown to demonstrate the efficiency and applicability of the proposed approach.     

Unified approach to H∞-optimization,Hankel approximation and balanced realization problems

A unified approach is proposed here to solve three problems simultaneously, namely H ∞ -optimization, Hankel approximation and minimal balanced realization for scalar systems. It is shown that all these problems can be reduced to the same standard form wherein merely the singular-value decomposition (SVD) of an easily constructed square matrix is required to establish the final solutions. The formulation is solely in terms of the coefficients of a transfer function and the resulting algorithm can be performed in a very computationally efficient way.     

新时期珠三角"城市区域"重构的空间分析——以跨行政边界的基础设施建设为例

20世纪后半期以来,区域特别是城市区域重新成为研究关注的焦点,而区域管治作为应对一体化困境的新手段在世界范围内盛行.本文以珠三角的跨行政边界基础设施建设案例为实证,通过对相关行为主体的深度访谈和对典型事件的分析,展现处于特殊制度背景下的珠三角区域管治新图景.研究表明,在政府所主导的珠三角"城市区域"重构中,对空间性的跨境基础设施的规划建设正成为实施管治最为重要的手段.正是通过空间,中央、省、市各级政府的权力才得以流通,管治目标才得以达成;同时,对空间管理权的争夺也重置了各层级政府的管理边界,并有可能进一步促进城市、区域和国家的政治经济转型.     

A Provably Secure Multi-server Based Authentication Scheme

With the rapid growth of electronic commerce and demand on variants of Internet based applications, the system providing resources and business services often consists of many servers around the world. So far, a variety of authentication schemes have been published to achieve remote user authentication on multi-server communication environment. Recently, Pippal et al. proposed a multi-server based authentication protocol to pursue the system security and computation efficiency. Nevertheless, based on our analysis, the proposed scheme is insecure against user impersonation attack, server counterfeit attack, and man-in-the-middle attack. In this study, we first demonstrate how these malicious attacks can be invoked by an adversary. Then, a security enhanced authentication protocol is developed to eliminate all identified weaknesses. Meanwhile, the proposed protocol can achieve the same order of computation complexity as Pippal et al.’s protocol does.     

广州市生产服务业发展初期空间格局形成机理研究

1990年代,广州的生产服务业进入起飞发展阶段.不仅表现在数量上的快速增加,在空间分布上也表现出从分散到集中的特征.现以信息咨询服务业为例,分析了广州生产服务业在起飞阶段的最初10年的空间格局及形成机理.认为,来自城市、政府、企业三方主体的相互作用,对生产服务业在这一阶段的空间分布起到至关重要的作用.传统城市格局的空间重构、土地使用制度改革和地方政府调控以及生产服务业自身空间行为差异是其空间集聚发展的内在动因.其中,通过对生产服务业企业的调研.对企业自身的空间行为差异做了较为深入的分析.