Crack-healing behaviour of MoSi2 dispersed Yb2Si2O7 environmental barrier coatings

MoSi₂ doped Yb₂Si₂O₇ composites were designed to extend the lifetime of Yb₂Si₂O₇ environmental barrier coatings (EBCs) via self-healing cracks during high-temperature applications. Yb₂Si₂O₇–Yb₂SiO₅–MoSi₂ composites with different mass fractions were prepared by applying spark plasma sintering. X-ray diffraction results confirmed that the composites consisted of Yb₂Si₂O₇, Yb₂SiO₅, and MoSi₂. The thermal expansion coefficients (CTEs) of the composites increased with an increase in the MoSi₂ content. The average CTE of the 15 wt% MoSi₂ doped Yb₂Si₂O₇ composite was 5.24 × 10^?6 K^?1, indicating that it still meets the CTE requirement of EBC materials. After being pre-cracked by using the Vickers indentation technique, the samples were annealed for 0.5 h at 1100 or 1300 °C to evaluate the crack-healing ability. Microstructural studies showed that cracks in 15 wt% MoSi₂ doped Yb₂Si₂O₇ composites were fully healed during annealing at 1300 °C. Two mechanisms may be responsible for crack healing. First, the cracks were filled with SiO₂ glass formed by MoSi₂ oxidation. Second, the formed SiO₂ continued to react with Yb₂SiO₅ to form Yb₂Si₂O₇, which can cause cracks to heal owing to volumetric expansion. The Yb₂Si₂O₇ formation with smaller volume expansion is more beneficial.     

钢管混凝土结构在高层建筑中的技术经济优势

钢管混凝土结构在高层建筑中具有明显的技术经济优势.高层建筑中钢管混凝土柱内的混凝土由于受到钢管的约束,三个方向同时受压,混凝土承载能力明显提高.由于钢管内混凝土的存在,可有效地防止钢管的局部届曲变形.这两种材料的结合克服了各自的缺点、充分发挥他们的长处.通过与钢筋混凝土结构比较,表明高层建筑钢管混凝土结构用钢量比钢筋混凝土结构略有节约,而混凝土用量仅为钢筋混凝土结构的一半左右.另外,由于钢管混凝土柱不需要支设模板,可节约大量模板材料和支模、拆模的人工费用.分析表明建筑高度越高,钢管混凝土结构的经济效益越明显.     

Reduction of residual vibration in a rotating flexible beam

Summary. The reduction of residual vibrations of the position control of a rotating flexible beam is investigated. The control scheme is achieved by combining Input Shaping Technique (IST) with a piezoceramic actuator ( PZT ) attached to the surface of the beam. IST reduces residual vibration in the beam by convolving the desired torque with a sequence of impulses. A majority of the current IST is inherently open-loop where impulse application at an inaccurate instance can lead to system performance degradation. Thus, in order to improve the control performance of a flexible manipulator, the residual vibration generated due to those or the uncertainty model was further suppressed by the PZT. The optimal control voltage was determined by the Linear Quadratic Regulator (LQR) technique. The dynamic simulation shows that the proposed method has not only nice robustness properties for suppressing the vibration due to an inaccurate model or the instance of impulse application, but also the voltage applied on the PZT decreases 50% or more than only using PZT, in other words, the extra energy consumption is reduced significantly by the proposed method.     

Verifying functions in online stock trading systems

Temporal colored Petri nets, an extension of temporal Petri nets, are introduced in this paper. It can distinguish the personality of individuals (tokens), describe clearly the causal and temporal relationships betwee nevents in concurrent systems, and represent elegantly certain fundamental properties of concurrent systems, such as eventuality and fairness. The use of this method is illustrated with an example of modeling and formal verification of an online stock trading system. The functional correctness of the modeled system is formally verified based on the temporal colored Petri net model and temporal assertions. Also, some main properties of the system are analyzed. It has been demonstrated sufficiently that temporal colored Petri nets can verify efficiently some time-related properties of concurrent systems, and provide both the power of dynamic representation graphically and the function of logical inference formally. Finally. future work is described.     

单级倒立摆的PID控制研究

对单级倒立摆系统的平衡控制问题进行了研究，分别采用PD，PI和PID三种方案实现了单级倒立摆系统的平衡控制。首先，建立系统的数学模型，然后通过仿真实验设计并整定各方案的控制器参数，将所设计的控制器分别在实际的物理设备上进行实时控制实验，都成功地实现了倒立摆的平衡控制。实际控制结果验证了各方案的正确性和有效性。     

FTP在工程设计管理系统中的应用

工程设计过程中批量数据及图形处理、文档编辑等工作已逐渐趋于多专业人员的多人协作来完成.针对特定的应用背景,通过对大量数据文件传输的分析,引入FTP技术,并和PowerBuilder技术相结合来实现工程设计管理系统中数据文件的上传和下载.     

ZnO花状微结构合成研究

在无表面活性剂的条件下,通过水热法在3种不同的基底上制备了由纳米棒组成的花状氧化锌微结构,其纳米棒沿c轴方向生长.通过X线衍射仪(XRD)、扫描电子显微镜(SEM)对花状氧化锌微结构进行了表征.XRD测试结果表明ZnO为纤锌矿结构,扫描电镜照片表明ZnO微结构具有花状形貌.简单讨论了反应物浓度对花状ZnO纳米棒形成的影响及生长机理.     

基于蚁群算法的神经网络配电网故障选线方法

为了克服基于神经网络的故障选线方法收敛速度慢、易于陷入局部极小点的缺点,提出了蚁群算法和神经网络相结合的故障选线方法。利用ATP-EMTP做单相接地仿真试验,得到各线路的零序电流信号,通过小波变换和傅里叶变换提取其中的故障特征作为神经网络的输入。利用蚁群算法对神经网络进行训练,完成训练的神经网络模型即可实现故障选线。仿真结果表明,该方法训练速度快、误判率低。     

第三代网络技术：网格计算技术

为了实现分散的资源共享、充分利用网上的闲置资源,网格计算应时而生。本文介绍了网格技术产生背景、概念、功能、关键技术,并讨论了网格技术发展亟需解决的问题和未来的发展趋势。     

我国手机企业的销售渠道策略分析

本文首先回顾了手机企业渠道策略发展的历程,着重从国际品牌和国产品牌两种模式来分析了现在我国手机企业的销售渠道策略,并在此基础之上对我国手机企业销售渠道策略的现状进行了总结。