Playgrounds: Radical Failure in the Amazon

Covering more than 8.1 million square kilometres (3.127 million square miles), the Amazon is a vast territory that has captured people's imaginations and ambitions. These range from Henry Ford's attempt in 1928 to build a rubber company town near Santarém, Brazil, to more contemporary projects that have aimed to boost and connect the continent's economy. Gary Leggett explores the failure of such totalising projects across time and asks why they might have proved inherently flawed. Copyright © 2011 John Wiley & Sons, Ltd.     

如何有效实施课堂教学中的自由与控制

交际法作为目前外语教学中比较流行的方法,在应用中仍存在着许多问题,其中对自由和控制的理解仍然存在的偏差显得尤为突出.因此我们在教学中应该对学生的自由予以科学的控制并建立相应的评价机制.     

论考试与人事管理的关系

论文从人事管理的社会功能,考试在现代人事管理中的作用以及与人事管理的关系,人事管理促进考试结果"社会价值"的实现等四个方面阐述考试与人事管理之间相互依赖、互相促进的辩证关系.     

电网规划与城市总体规划有效结合的探讨

电网规划是城市总体规划的重要组成部分,随着社会经济的发展,用电负荷不断攀升,电网结构因此也越来越密集,电网项目建设与城市总体规划矛盾日益显现,如何化解因土地资源紧张而制约电网快速发展的矛盾,结合铜陵电网规划的工作实际,探讨了电网规划与城市规划有效结合的工作途径,为电网的发展寻觅到了一条行之有效的科学方法。     

冲击载荷作用下Mg-Li合金的力学性能及显微组织

采用分离式霍普金森压杆(SHPB)对真空熔炼制备的Mg-Li合金进行了静、动态试验研究,试件的加载应变率范围为1.7×10-3～1026s-1,得到了材料在不同应变率下的应力-应变曲线。并根据实验结果确立了Mg-Li合金在一维应力高应变率冲击状态下的本构关系。同时还分析了不同应变率冲击后Mg-Li合金的金相组织。结果表明,该Mg-Li合金在室温下的动态冲击性能对应变率不敏感。Mg-Li合金在一维应力高应变率冲击状态下的本构关系为σ=1.5ε,(σ0.12GPa),σ=0.12+2.7ε1.2(σ≥0.12GPa)。随着应变率的增加,晶粒尺寸先变小,再趋于不规则形状,而且晶界处分布的短条状化合物也逐渐集中。     

Inverse extraction of cohesive zone laws by field projection method using numerical auxiliary fields

The cohesive zone law relates the cohesive tractions with the cohesive separations within the fracture process zone of a material and is used to quantify the strength and toughness of the material. Determining the material's cohesive zone law, however, is a nontrivial inverse problem of finding unknown tractions and separations from measurement data. Previously, a field projection method was established to extract the cohesive zone laws from far‐field data using interaction J‐integrals between the physical field of interest and auxiliary analytical probing fields. Here, we extend the universality of the field projection method and its ease of numerical implementation by using numerical auxiliary fields. These numerical fields are generated by systematically imposing uniform surface tractions element‐by‐element along the crack faces in finite element models. Then, interaction J‐ and M‐integrals between these auxiliary probing fields and the measurement field are used to reconstruct the traction and separation relationship along the crack faces. The effectiveness of this method in extracting the cohesive zone law from measured displacements in the far‐field region is demonstrated through numerical experiments. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical investigation into multi-delamination failure of composite T-piece specimens under mixed mode loading using a modified cohesive model

This paper investigated the failure mechanism of fibre composite T-piece specimens under mixed mode loading conditions by simulation of multi-delamination using a modified cohesive model with a coupled damage scale and added thermal effects. A mixed mode load includes pulling and bending. Multi-delamination was simulated in the way modelling the dominated multi-delamination in the deltoid region of T-piece. Failure predictions in the mixed mode loading case, individual bending and pulling case together with part of tested solutions were presented in this paper. It was exposed that the interaction between pulling and bending in the mixed mode loading case plays an important role in the failure mechanism of T-piece. The effect of thermal initial crack in the deltoid of T-piece on prediction of the capacity to resist mixed mode loading was also investigated. A significant effect of thermal initial crack on delamination was found in the mixed mode loading case. This investigation supplied important information for the design of T-piece related composite components under mixed mode loading conditions.     

Modification of fatigue strain‐life equation for sheet metals considering anisotropy due to crystallographic texture

The fatigue behaviour of cold rolled and annealed sheet metals are influenced by the anisotropy of mechanical properties due to crystallographic texture. However, the existing fatigue strain‐life models are primarily meant for isotropic material behaviour. In the present work, the Coffin‐Manson equation for strain‐life is modified to include the effect of anisotropy using phenomenological plasticity models. It is observed that the variation of strain hardening exponent is critical to model the strain‐life behaviour. Variation of strain hardening exponent with orientation is modelled using existing anisotropic yield criteria. The prediction of fatigue life using the proposed model correlates well with the experimental results of Al6061‐T6 along different orientations. The proposed model can be used to predict the fatigue properties along any orientation from the fatigue data along one orientation and monotonic mechanical properties along longitudinal, transverse and diagonal directions.     

基于灰色关联投影分析的矿井通风方案优化研究

矿井通风系统方案优化实际上是一个灰色多目标决策问题。通过构造灰色关联系数矩阵,确定加权向量、灰色关联投影角余弦、相关模数和计算投影值等步骤建立了综合考虑5种因素的矿井通风方案优化决策灰色关联投影模型。利用灰色关联投影决策模型确定了某矿井下通风系统最佳方案,该通风方案实施后,井下作业环境得到了很大的改善,测定数据表明各项指标都达到矿山安全规程要求。利用灰色关联投影法确定矿井通风方案十分有效。     

混合值不完备信息系统中一种拓展粗糙集模型

针对混合值不完备信息系统,提出了基于邻域联系度的拓展粗糙集模型。首先定义了一种邻域联系度容差关系,然后通过所确定出的最大相容类得到了上、下近似集,并证明了所得到的近似集是基于联系度容差关系得到的近似集的一种推广和改进,最后进行了实例分析。