Reflection and transmission of waves near the localization threshold

A theory is presented for propagation of waves in bounded media near the mobility edge, based on the self-consistent theory for localization. It predicts a spatially inhomogeneous diffusion constant that leads to scale dependence in enhanced backscattering and transmission.     

基于TINI平台的嵌入式互联网接入技术研究

随着网络技术的发展,将各种设备接人互联网,利用互联网实现数据传输与远程监控成为当今电子设备发展的必然趋势.文中介绍了DS80OC400芯片以及基于此芯片的TINI系统.提出了采用TINI系统来实现非网络设备接入互联网的方法,包括硬件结构、软件设计以及开发流程等,并以RS-232接口为例,给出了此方法的具体实现.与传统的通过PC机转接的方法相比,此方法具有开发成本低、效率高、运行稳定、低功耗、体积小等特点.     

基于自适应锁相环的高动态GPS信号载波跟踪算法

提出了一种基于四维卡尔曼滤波的自适应锁相环算法,并将该算法用于高动态GPS信号的载波跟踪.详细推导了卡尔曼滤波与数字锁相环之间的等效性,并给出了相应的环路更新步骤.仿真结果表明,该算法相对于采用固定增益数字锁相环的算法明显地降低了载波跟踪过程的均方根频率误差,提高了接收机的测速精度.     

Microstructural considerations for ultrafine lead free solder joints

As solder joints become increasingly miniaturised to meet the challenging demands of future electronic packaging, it is vitally important to consider whether the solder joint size and geometry could become a reliability issue and thereby affect the implementation of the Pb-free solders. In this study, different bumping techniques, e.g., solder dipping, stencil printing followed by solder reflow, and electroplating of solders and subsequent reflow, were used to investigate the microstructure and interfacial interactions of molten Sn and Sn-based Pb-free solders on different metallizations, e.g., copper and electroless nickel immersion gold (ENIG). The resultant microstructures from a variety of pad sizes, ranging from 1 mm down to 25 μm, and representing different solder bump geometries have been investigated. In addition, thermodynamic and combined thermodynamic-kinetic modelling has been used in order to understand the microstructure of Pb-free solders, the kinetics of dissolution of the metallizations and the formation of interfacial intermetallic compounds (IMCs). Both the experimental results and theoretical predictions suggest that the solder bump size and geometry can influence the as-soldered microstructure. In the light of the increasing importance of the microstructural features of the ultrafine solder joint in determining its long term reliability, a novel computational interface between software for thermodynamic calculations, high-level scientific computing and multiphysics modelling, is introduced. This modelling methodology provides a potential platform for microstructure-based Finite Element (FE) reliability modelling of ultrafine interconnects for future microelectronic products.     

两种气液两相流模型的应用和比较

本文应用MUSIG模型[1]和均一直径模型对某溶液堆台架模型堆芯内气液流动传热进行了数值模拟.在MUSIG模型中堆芯内离散相气泡被分为5组不同直径的气泡,用于分析堆芯内气泡的流动变化和大小分布,采用Luo and Svendsen[2]和Prince and Blanch[3]模型描述不同直径气泡组间的破裂和聚合.在均一直径模型中,堆芯内的气体被考虑为同一直径的组分,并且不考虑其破裂与聚合现象.计算得到采用两个模型的模拟结果并且对其进行了对比研究.结果显示应用MUSIG模型的计算结果与台架实验结果吻合更好.     

Six-Fold Degenerate Dark States in a Four-Level Atomic System

With all driving fields on Raman resonance, a tripod-type atomic system quickly evolves into a dark state decoupled from the lossy excited level. The dark state depends strongly on field Rabi frequencies, spontaneous decay rates, and the initial atomic population in a complicated way. Analytical results reveal that it is a sixfold degenerate dark state with its three components superposed both coherently and incoherently due to population redistribution from spontaneous emission.     

A Method for Quantification of the Effects of Size and Geometry on the Microstructure of Miniature Interconnects

Because the heterogeneity of microstructure has significant effects on the material properties of ultrafine interconnects, it should be quantified, to facilitate high-fidelity prediction of reliability. To address this challenge, a method based on autocorrelation and singular value decomposition is proposed for quantitative characterization of microstructure. The method was validated by developing a quantitative relationship between reported microstructure and tensile strength for SnAgCuRE solders reported in the literature. The method was used to study the effects of size and geometry in ultrafine Sn37Pb interconnects on microstructure and von Mises stress, which were obtained simultaneously by coupling a phase-field model with an elastic mechanical model. By use of this method the degree of heterogeneity of the microstructure in relation to preferred growth directions of the phases was quantified by use of a scalar microstructure index. It was found that microstructure heterogeneity increases with decreasing standoff height, and is higher for hourglass-shaped solder joints. The average von Mises stress was found to be positively related to the microstructure index. The strong correlation between microstructure index and average von Mises stress was confirmed by nonlinear regression analysis using an artificial neural network. This indicates that the mechanical behavior of ultrafine interconnects can be predicted more accurately on the basis of the microstructure index.