光纤固定软钎焊焊点的三维形态模拟

本文在建立光纤固定软钎焊焊点模型及能量边界条件的基础上,利用有限元方法对焊点三维形态进行数值模拟并分析材料及结构等参数对焊点形态的影响规律.基于能量最小原理并利用形态模拟数据,得出钎料量及焊盘尺寸对光纤与焊盘间隙高度的影响规律,以及光纤横向偏移量对回复力的影响规律.研究结果表明:针对一定的焊盘相对尺寸,当钎料量大于临界值,最小间隙高度随着钎料量的增加而成线性增加;光纤横向偏移量小于一定值时,回复力随着偏移量的增加成线性增加.研究结果对于通过调整结构及工艺参数来控制光纤对准偏移具有指导意义.     

高强铝合金T型接头激光焊接的研究现状

分析总结了高强铝合金T型接头激光焊接存在的几个主要问题,从工艺的优劣性方面介绍了当前高强铝合金T型接头激光焊接常用的几种工艺,通过实验论证了采用填充粉末焊接高强铝合金T型接头焊接的可行性。并提出了激光加工专用粉末制粉工艺的一个新的研究方向。     

信源信道联合编码技术用于AVS传输的研究

针对误码信道和信源编码的统计特性,提出了一种基于AVS视频序列的联合编码技术,按照重要性对AVS视频层序列码流进行分组重排,信道编码器根据码流信息对其进行比重不等的保护措施,以较低复杂度的运算实现了码率的优化分配.实验表明,与现有的等差错保护相比,在高误码信道中能有效提高AVS码流抗误码性能.     

直埋光缆接头盒浸水防治的措施

直埋光缆线路接头盒浸水问题是一直困扰光缆线路维护的一个难题,本文通过对凡士林规格及性能的分析,利用凡士林对光缆接头盒进行密封安装实验.实验表明凡士林防水性能良好,适合作预防光缆接头盒浸水材料.     

Joint optimization of spectrum sensing and accessing in multiuser multiple‐input single‐output cognitive networks

In this paper, a joint spectrum sensing and accessing optimization framework for a multiuser cognitive network is proposed to significantly improve spectrum efficiency. For such a cognitive network, there are two important and limited resources that should be distributed in a comprehensive manner, namely feedback bits and time duration. First, regarding the feedback bits, there are two components: sensing component (used to convey various users' sensing results) and accessing component (used to feedback channel state information). A large sensing component can support more users to perform cooperative sensing, which results in high sensing precision. However, a large accessing component is preferred as well, as it has a direct impact on the performance in the multiuser cognitive network when multi‐antenna technique, such as zero‐forcing beamforming, is utilized. Second, the tradeoff of sensing and accessing duration in a transmission interval needs to be determined, so that the sum transmission rate is optimized while satisfying the interference constraint. In addition, the aforementioned two resources are interrelated and inversive under some conditions. Specifically, sensing time can be saved by utilizing more sensing feedback bits for a given performance objective. Hence, the resources should be allocation in a jointly manner. Based on the joint optimization framework and the intrinsic relationship between the two resources, we propose two joint resource allocation schemes by maximizing the average sum transmission rate in a multiuser multi‐antenna cognitive network. Simulation results show that, by adopting the joint resource allocation schemes, obvious performance gain can be obtained over the traditional fixed strategies.Copyright © 2014 John Wiley & Sons, Ltd.     

基于物联网的联合训练导控系统框架

为了更好地开展联合训练,利用物联网技术搭建联合训练的导控系统。在分析功能需求的基础上,探讨了导控系统的总体结构,并将该系统的各功能模块融入到物联网的感知层、网络层和应用层3层体系结构中,使整个导控系统被物联网覆盖,成为物联网的一个特定实体。通过对系统分层讨论,给出了基于物联网技术进行系统设计的总体思路。研究分析了系统的总体框架和技术架构,可为日后系统开发奠定理论基础。     

Suppression of void coalescence in thermal aging of tin-silver-copper-X solder joints

Addressing the potential for drop impact failure of Pb-free interconnects, the shear ductility after extensive aging of Sn-Ag-Cu (SAC) solders has been improved radically by Co or Fe modifications. Several other SAC+X candidates (X=Mn, Ni, Ge, Ti, Si, Cr, and Zn) now have been tested. Solder joint microstructures and shear strength results show that new SAC+X alloys also suppress void formation and coalescence at the Cu (substrate)/Cu₃Sn interface (and embrittlement) after aging at 150°C for up to 1,000 h. Microprobe measurements of 1,000 h aged samples suggest that Cu substitution by X is usually accentuated in the intermetallic layers, consistent with X=Co and Fe results.     

无铅焊点的电阻应变温度迟滞回线特性

在焊点热可靠性研究过程中,发现无铅焊点在313.15～398.15K循环热载荷条件下电阻应变与温度存在滞后效应,以力学分析方法对该效应的迟滞回线进行了分析讨论。结果表明:塑性电阻应变是引起迟滞回线变化的主要原因;稳定期内一个循环的最大塑性电阻应变量是0.00158,电阻应变滞后于温度变化18.31s;高温迟滞回线变化较低温更明显,二者相差0.0036749,反映了高温下焊点内部损伤程度更快。随着循环次数的增多,迟滞回线从不稳定趋向稳定,最后趋向不闭合,且斜率降低。     

QFP焊点塑性应变的数值模拟

元素铅既对人体存在神经毒性也对环境产生重金属污染,因此,无铅焊料的研究倍受封装业的重视。文章采用温度循环下有限元数值模拟方法,针对4种焊料5种配比包括SnPb（60／40,10／90）、SnPbAg（5／92．5／2．5）、SnAg（96．5／3．5）和SnAgCu（95．5／3．8／0．7）,定量评估QFP焊点的塑性应变。给出焊料各参数对于焊点塑性应变的影响程度,第一主元分析显式为△Ps≈-2．56△（Q／R）,相应的Y向塑性应变均值降低为优化前的11％。所得的结果可为QFP封装时的焊料选择提供新的设计参考。     

美军联合电子战消除频率冲突方式

为在作战、通信和情报活动中协调地使用电磁频谱,对美军联合电子战消除频率冲突的方式进行研究。研究美军联合电子战消除频率冲突的程序和内容,介绍美军在联合电子战中分析频率冲突的2种方式,并分析美军联合部队各相关部门的职责。该研究可为提升我军电子战水平提供参考。