Review of Mechanically Related Failures of Ceramic Capacitors and Capacitor Materials

This paper reviews the brittle fracture behavior of dielectric ceramics such as barium titanate, and describes some of the relationships between defects such as cracks and electrical degradation and failure of multilayer capacitors. Stresses arising from the ferroelectric phase transformation in these dielectric materials are shown to play a part as a driving force for crack growth. In addition, possible contributions to failure from stresses arising from thermal excursions in the capacitor are discussed. Low-voltage failures arising from a short between the electrodes in multilayer capacitors are shown to be related to the growth of cracks in the dielectric. A technique for predicting the onset of these types of failures based upon fracture mechanics techniques is described. Possible effects of the electric field itself in promoting or retarding the growth of cracks are discussed.     

Atmospheric Dependence on Dielectric Loss of 1/6Ba5Nb4O15· 5/6BaNb2O6 Ceramics

Samples of 1/6Ba₅Nb₄O₁₅·5/6BaNb₂O₆ along with the pure end members, Ba₅Nb₄O₁₅ and BaNb₂O₆, were sintered under low oxygen partial pressure. The degradation mechanisms of dielectric loss in this reducing atmosphere have been studied. We found that the degradation occurred primarily due to the formation of oxygen vacancies caused by the reduction of Nb⁵⁺. This was determined by measuring the electrical conductivity, and through X-ray photoelectron spectroscopy. More importantly, the dielectric loss of 1/6Ba₅Nb₄O₁₅·5/6BaNb₂O₆ samples with higher temperature stability was further decreased on sintering in a reducing atmosphere. This observation has been explained by considering the increased porosity and formation of a reduced second phase, Ba_0.65NbO₃.     

两种模具型芯结构的比较

对比两种高冲压开关件型芯拼块结构的优劣和设计要点。     

基于随机移动模型的移动sinks无线移动传感器网络性能分析与改进*

引入移动sinks节点是解决网络连通性、能耗平衡、提高网络生命周期和网络容量的有效方法。针对移动sinks节点的移动机制直接与网络性能相关,结合mWSNs体系结构,分析了基于随机移动模型的网络性能,提出了零数据包分片率的随机移动模型。理论分析与仿真结果表明,该模型能够保证数据零分片,提高了网络的时延性能和数据包传输成功率。     

用修正的Mann迭代算法求解分裂可行性问题

在Hilbert框架下借助于度量投影修正Mann迭代程序,证明了关于无限族非扩张映射的强收敛定理,并用于求解分裂可行性问题SFP.研究成果在很大程度上推广和改进了现有的结果.     

加权变分去噪模型的分裂Bregman算法

针对求解加权变分去噪模型时大量迭代导致计算速度缓慢的问题,为提高运算速度,在加权变分去噪模型中引入分裂Bregman算法.实验表明,与梯度下降法相比,该算法迭代次数少、处理过程快,极大地缩短了运算时间,并且保持了较好的去噪效果.     

开口谐振环结构负折射率材料对电磁波偏振特性的影响研究

电磁波在经过负折射率材料以后,偏振状态会有所改变.对开口谐振环电磁响应特性了解的基础上,采用时域有限积分方法,分别研究了方形、六边形和圆形开口谐振环负折射率材料在不同频率处以及斜入射时对电磁波偏振特性的影响.仿真结果表明,不同的结构、频率和入射角度,电磁波偏振翻转的程度有所不同.研究结果可为电磁波偏振状态的调控提供一定的理论依据和借鉴.     

CFD在调压室设计计算中的可行性研究

采用C FD方法对简单调压室和阻抗式调压室进行数值模拟,计算出不同分流比下,调压室的阻力系数值,将模拟结果同文献中的试验值进行对比分析。结果表明,模拟曲线和试验曲线的趋势基本一致,并且模拟数值和试验数值高度吻合,该方法可应用在调压室的阻力系数研究中。在此基础之上,该方法应用在实际电站调压室的模拟中,并通过水力过渡过程的计算,验证了该结果的准确性。最后得出结论, C FD方法可应用于调压室的设计计算。     

混合动力车制动工况分析与储能装置参数匹配

为提高混合动力系统整体性能,实现高效能量回收,分析某重型越野车辆驾驶循环工况中制动过程的功率与能量分布,从制动能量回收率与电机参数出发讨论对储能装置的性能要求. 提出电池组-超级电容复合储能装置的参数匹配方法,针对21 t级试验样车混合动力系统进行实例计算,论证锂离子电池组与超级电容组成的复合储能装置的性能. 实例计算与道路试验结果表明:匹配的复合储能装置符合车辆整体性能与制动能量回收的要求,体积、重量满足总体设计约束;匹配超级电容后,储能装置的瞬时功率能力大幅提升,可显著提高车辆的制动能力和制动能量回收率.     

基于RSV工艺装置提高乙烷收率的工艺技术北大核心CSCD

目的为研究大型天然气深冷工艺装置因膨胀机未投运、关键工艺参数未及时优化调整造成脱甲烷塔操作难度大等导致装置乙烷收率降低等问题,现采用适时投运膨胀机、优化液烃回收装置关键工艺参数等措施开展提高乙烷收率的工艺技术研究。方法基于Aspen HYSYS软件建立装置工艺计算模型,对比分析低温分离器温度、回流贫气和过冷原料气流量及温度等关键设计运行参数对提高乙烷收率的影响,考查上述关键工艺参数对装置乙烷收率的效果。结果经现场验证得出结论,低温分离器温度优化为-68.8~-68.0℃,回流贫气流量和温度分别调整为(7.38~7.60)×10^(4) m^(3)/h、-101.45~-100.05℃,过冷原料气流量和温度分别调整为(7.45~7.63)×10^(4) m^(3)/h、-101.48~-100.45℃,装置实现液烃产品年增产17.56×10^(4) t。结论该项目的应用可实现装置乙烷平均收率由30%提高至90%以上,每年可以获得较高的经济效益,具有较大的推广价值。