Modelling methodology for thermal analysis of hot solder dip process

The shift of electronics industry towards the use of lead-free solders in components manufacturing brought also the challenge of addressing the problem of tin whiskers. Manufacturers of high reliability and safety critical equipment in sectors such as defence and aerospace rely increasingly on the use of commercial-of-the-shelf (COTS) electronic components for their products and systems. The use of COTS components with lead-free solder plated terminations comes with the risks for their long term reliability associated with tin whisker growth related failures. In the case of leaded type electronic components such as Quad Flat Package (QFP) and Small Outline Package (SOP), one of the promising solutions to this problem is to “re-finish” the package terminations by replacing the lead-free solder coatings on the leads with conventional tin–lead solder. This involves subjecting the electronic components to a post-manufacturing process known as Hot Solder Dip (HSD). One of the main concerns for adopting HSD (refinishing) as a strategy to the tin whisker problem is the potential risk for thermally induced damage in the components when subjected to this process.     

城市应急联动系统GEIS

GEIS（Grid Based Emergency Inter-Act System）是一个基于主体网格的城市应急联动与社会综合服务系统，通过主体网格和通信系统将治安、消防、卫生急救、交通、公共设施，自然灾害等突发事件的应急联动与综合服务，调度集成在一个管理平台中，通过共享指挥平台和基础信息，实现统一接处警，统一指挥，联合行动，快速反应，为市民提供更加便捷的紧急救援及相关服务，为政府科学决策和处置各种紧急与灾害事件提供技术支持为城市公共安全提供技术保障。GEIS的一个突出优势是将范例推理（Case Base Reasoning,CBR）与规则推理（Rule Base Reasoning,RBR）两种人工智能技术相结合，实现了快速预案支持，为科学决策打下良好基础，目前，GEIS已经应用到抗洪抢险和交通事故处理中，效果表明它具有跨平台性好，稳定性强，响应速度快，易操作的独特优势。     

高功率激光装置中的鬼点反射分析

介绍了高功率激光装置中的鬼点反射及其带来的破坏影响 ,分析并计算了神光 Ⅱ装置中主放大器部分的鬼点反射 ,给出了避开鬼点反射损伤的方法。     

MPLS的原理与应用

MPLS是一个可以在多种第二层媒质上进行标记交换的网络技术.本文主要介绍了MPLS的工作流程,在实践中的应用,MPLS技术的意义,最后指出了MPLS还存在的一些问题.     

多级缓存架构CDN在融合媒体互动直播中的时延分析及应用

网络互动直播、4K高清视频的大规模应用导致传输流量需求急速增加,现有网络流量的局限性有时无法保证直播流的稳定传输,画面延迟抖动问题造成用户不良体验.基于此,本文提出了多级缓存CDN架构模型,研究了其上的时延变量因素,并通过设计优化实验,推导出时延变量最优值,用在实际的互动直播活动,传输质量提升显著,在一定程度上满足了直...     

Si(111)衬底上GaN外延材料的应力分析

对Si(111)衬底上GaN外延材料的应力随着低温AlN插入层数的变化进行了分析研究。通过喇曼散射谱在高频E2(TO)模式下的测试分析发现,随着低温AlN插入层数的增加,GaN材料的E2(TO)峰位逐渐接近体GaN材料的E2(TO)峰位(无应力体GaN材料的E2(TO)峰位为568cm-1),计算得出GaN材料的应力从1.09GPa减小到0.42GPa。同时,使用室温光荧光谱进行了分析验证。结果表明,Si衬底上GaN外延材料受到的是张应力,通过低温AlN插入层技术可以有效降低GaN材料的应力,并且最终实现了表面光亮的厚层无裂纹GaN材料。     

Polarity Analysis of Self-Seeded Aluminum Nitride Crystals Grown by Sublimation

Self-seeded aluminum nitride (AlN) crystals were successfully grown in a tungsten crucible by the sublimation method. The polarities along the growth direction of these AlN samples were characterized by chemical etching, combined with high-resolution transmission electronic microscopy (HRTEM) and Raman spectroscopy. It has been proven by our experimental results that etching in KOH solution and in molten KOH-NaOH can be a reliable method to determine the surfaces with different polarities. Chemically active N-polar (0001) AlN surfaces were removed appreciably, while only etch pits related to threading dislocations were observed on Al-polar surfaces after chemical etching. HRTEM images revealed that there are noticeable inversion domain boundaries in the samples. Raman spectrum measurements showed the vibration mode change before and after etching in the same geometrical arrangement.     

Modeling of elastic modulus evolution of cirrhotic human liver

A micromechanics-based composite model is developed for the elastic behavior and its modulus evolution of cirrhotic human liver correlated with different pathological stages. Microstructurally, the cirrhotic liver is hypothesized to be pathologically elastic nodules embedded in the soft tissue matrix whose hyperelastic behavior is controlled by the Veronda-Westmann model. Under finite deformation, the total strain energy of the liver is collected through the combination of that in nodule particles and that in the tissue matrix. The overall constitutive relation of the pathological liver can further be established through the nonlinear hyperelasticity theory. Predictions of the elastic modulus and its pathological evolution are compared with available experimental data.     

中波发射台自动化监控系统的实践和完善

为了加快推动发射台管理模式现代化的进程．2004年国家广电总局科技委会议明确提出,加大发射台自动化监控程序．以先进的科学技术完善发射台的管理,代替以往的“人管机器”的管理模式,以先进的监测设备为基础,科学的管理理念为平台,有效地提高发射台安全播出的成功率。随着广电总局关于发射台自动化改造精神的进一步落实．发射台自动播出监测技术的运用已成为台站管理的发展方向。本文通过详细介绍肇庆中波转播台的播出自动化监控系统,探讨了利用先进的计算机控制和科学的管理模式实现对中波发射机的自动控制,     

Fast mode dependent directional transform via butterfly-style transform and integer lifting steps

Mode dependent directional transform (MDDT) can improve the coding efficiency of H.264/AVC but it also brings high computation complexity. In this paper we present a new design for implementing fast MDDT transform through integer lifting steps. We first approximate the optimal MDDT by a proper transform matrix that can be implemented with butterfly-style operation. We further factorize the butterfly-style transform into a series of integer lifting steps to eliminate the need of multiplications. Experimental results show that the proposed fast MDDT can significantly reduce the computation complexity while introducing negligible loss in the coding efficiency. Due to the merit of integer lifting steps, the proposed fast MDDT is reversible and can be implemented on hardware very easily.