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.     

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.     

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.     

中国城市化的第四波

建国以来,我国城市化经历了不同的发展阶段。尤其是1978年开始的改革开放对城市化进程、动因、模式都产生了深远影响。本文通过对我国城市化历程的回顾,将我国建国以来城市化划分为四个主要阶段(波),并对各阶段城市化的特征进行总结。在此基础上,提出我国城市化正进入快速发展的第四波,并对第四波城市化所面临的问题和挑战进行了分析。     

Fatigue crack growth in hybrid boron/glass/aluminium fibre metal laminates

The crack growth behaviour of hybrid boron/glass/aluminium fibre metal laminates (FMLs) under constant‐amplitude fatigue loading was investigated. The hybrid FMLs consist of Al 2024‐T3 alloy as the metal layers and a mixture of boron fibres and glass fibres as the fibre layers. Two types of boron/glass/aluminium laminates were fabricated and tested. In the first type, the glass fibre/prepreg and the boron fibre/prepreg were used separately in the fibre layers, and in the second type, the boron fibres and the glass fibres were uniformly mingled together to form a hybrid boron fibre/glass fibre prepreg. An analytical model was also proposed to predict the fatigue crack growth behaviour of hybrid boron/glass/aluminium FMLs. The effective stress intensity factor at a crack tip was formulated as a function of the remote stress intensity factor, crack opening stress intensity factor, and the bridging stress intensity factor. The bridging stress acting on the delamination boundary along the crack length was also calculated based on the crack opening relations. Then, the empirical Paris‐type fatigue crack growth law was used for predicting the crack growth rates. A good correlation between the predicted and experimental crack growth rates has been obtained.