广州体育馆屋盖结构设计

介绍广州体育馆大跨度钢屋盖的结构设计 ,包括荷载取值 ,静、动力计算分析与屈曲分析 ,节点设计等 ,并介绍了预应力拉索作为柔性支撑体系在屋盖中的应用     

高面板坝周边缝止水的整体解决方案研究

在指出现有阿里亚坝止水模式局限性的基础上，提出了高面板坝周边缝止水的整体解决方案，并对该方案的目标、安装工艺、采用的技术措施以及独立止水设计作了详细探讨。     

武隆鸡尾山滑坡形成机理数值模拟研究

2009年发生的重庆武隆鸡尾山滑坡,因滑源区斜坡岩层整体缓倾山内,缺乏有效的临空面和滑移空间,因此,在滑坡孕育过程中存在前缘岩溶带压缩变形、底部剪切滑移、后缘拉裂以及最终前缘关键块体(岩溶带)侧向剪断滑出等一系列的复杂动力学行为。这一过程存在显著的连续变形向非连续变形的过渡与转化,单纯用连续介质的有限元和离散介质的离散元来分析模拟都很难取得较好的效果。为探究鸡尾山滑坡的孕育过程和失稳机理,运用将连续–非连续单元有机耦合的大型数值模拟软件CDEM,模拟鸡尾山滑坡的失稳过程和形成机制。研究表明:滑体前方岩溶发育带具有"可压缩性",为滑体运动提供了一定的变形空间;滑源区下方的采矿活动产生应力重分布,滑带抗剪强度降低,滑体沿其底部软弱带发生剪切蠕滑,并逐渐形成滑体后缘拉裂缝;滑动块体在向前滑移过程中不断挤压向前缘"易压缩带",坡体应力自组织调整,并逐渐在前部三角区形成垂直的第二破裂面,前缘抗力体(关键块体)形成,最后剪断岩溶带个别与稳定山体咬合岩块,整体失稳破坏。数值模拟结果较好地揭示了武隆鸡尾山滑坡前缘视倾向展布岩溶带"软基效应"所提供"准临空面",重现了鸡尾山滑坡"蠕滑—拉裂—压缩(压碎)—剪切滑出"的致灾机理。     

浅谈住宅小区电子周界防护系统设计

电子周界防护系统是住宅小区安全技术防范的重要手段之一。本文从系统功能和结合工程实例,介绍电子周界防护系统的组成及设计要点。     

Layer thickness and draft angle selection for stereolithography injection mould tooling

The introduction of rapid prototyping has allowed engineers and designers to generate physical models of required parts very early on in the design and development phase. Further to this, the use of stereolithography (SL) cavities as a rapid tooling method has allowed plastic prototype parts to be produced in their most common production manner -- by injection moulding. The process is best suited to small production runs where the high costs of conventionally machined tooling is prohibitive. One of the major drawbacks of the SL injectionmoulding process is the susceptibility of the tools to premature failure. SL tools may break under the force exerted by part ejection when the friction between a moulding and a core is greater than the tensile strength of the core, resulting in tensile failure. Very few justified recommendations exist about the choice of mould design variables that can lower the part ejection force experienced and reduce the risk of SL tool failure. This research investigates the ejection forces resulting from SL injection moulding tools which are identical in all respects except for their build layer thickness and incorporated draft angles in an attempt to identify appropriate evidence for recommendations with respect to these design variables and SL injection moulding. The results show that adjustment of draft angle results in a change of part ejection force as a reasonably linear relationship. An adjustment of the build layer thickness results in a change in part ejection force as a more non-linear relationship. The adjustment of build layer thickness had a greater effect on ejection force than the adjustment of draft angle. The results also show that the surface roughness of all tools remains unchanged after moulding a number of parts in polypropylene. A mathematical model was used in an attempt to predict ejection forces according to the moulding material used. This model reflected the experimental results in terms of relative values but not in absolute values, which may be due to inappropriate specific values used in their calculation. Finite element analysis (FEA) was used in an attempt to identify the factors involved in the ejection process. Results indicate that the effect of draft angle on ejection force is due to elastic deformation of the surface roughness. A fact borne out by the lack of damage to the surface after ejection.     

Effect of Drying on Microstructure of Plant Tissue

Abstract

Drying causes many chemical and physical changes in plant tissue. Physical changes are mostly due to stresses developed in the tissue and are pronounced by macro- and microalterations of size, shape and internal structure. The extent and direction of these changes depend on the mode of drying. Convective drying of apple tissue results in numerous breaks of cell walls and formation of many microcavities. In consequence, the dominating cross-sectional area of cells moves toward values smaller than those observed in raw apple. Cavities formed during convective drying can be pictured in 2D plane as pentagons joined together or ellipses with large ratio between axes. Puff-drying forms porous structure with cavities twice as large as in raw apple. The process homogenizes the structure, and spread of cell sizes is even smaller than that observed in raw apple. Broken cell walls are clearly visible in microphotographs of sliced samples. Many large cavities with cross-sectional area exceeding 40,000 µm² are characteristic of puff-dried apple while such areas are hardly found in raw apple. The structure of freeze-dried apple is similar to that formed during puff-drying. Large irregular cavities and broken cell walls are clearly seen in microphotographs. However, larger cavities are present in freeze-dried apple than in puff-dried one. Cross-sectional area of cavities in freeze-dried apple can be simulated by pentagons joined together or elongated ellipses.     

Minkowski和的一些性质

给出了混合面积A（t）和混合周长L（t）的表达式，并证明了√A（t）和A（t）／L（t）的凹凸性．这一性质建立了混合面积和混合周长与等周不等式之间的联系．     

平面图形周长和面积测量仪原理的理论推导

研究了一种简单机械结构的周长和面积测量仪原理,并对其做了理论推导。其测量采用变换器原理,从而使得测量方法变得简捷,简单的数据记录方法精确、实用、有效。该理论推导为其实际运用打下理论基础。     

特大型椭圆封头的分瓣计算

对12m近似椭圆封头实施合理的分瓣，创造了足球瓣顶圆的新方法，并进行了瓣片尺寸计算。     

一种漏缆入侵探测系统的接收机设计与实现

基于漏泄电缆的周界入侵探测系统因具有良好的安全隐蔽、随形安装、全方位警戒和全天候工作等特点,吸引了安防领域研究者和市场的注意力。文中提出了一种新型零中频正交解调接收机设计方法,该方法将高频信号搬移到基带进行处理,避免常规设计中采用超高速AD器件的高昂成本,同时改善了漏缆入侵探测系统的性能。ADS仿真表明:80120 MHz工作频段内接收机具有2.8 dB的噪声系数及69 dB的链路增益。测试结果表明,同一工作频段内接收机具有3.2 dB的噪声系数及67 dB的链路增益,实测和仿真结果吻合良好。系统试验表明采用该接收机的周界入侵探测系统,其定位精度优于10 m、误报率和漏报率优于5%。