Scalability in Global Mobile Information Systems (GloMo): Issues,Evaluation Methodology and Experiences

The GloMo (Global Mobile Information Systems) project¹ has focused on developing new wireless ad hoc networking technologies. These new technologies rely on a broad and varied set of techniques to help cope with the problems inherent in the wireless environment. One of the most critical design elements of all the various technologies is their applicability in large scale deployments. The main objective of our work is to develop and implement a simulation methodology to help evaluate the scalability of these new ad hoc networking technologies and gain some insight into the various aspects of ad hoc network performance scalability issues. To achieve that we have developed a scalability performance evaluation framework and plan, that spans all the various dimensions of scalability: size (number of nodes and density), traffic, operational environment (i.e. propagation models, terrain etc.), mobility. For demonstration purposes we have applied this process on a representative integrated protocol suite designed to provide communication services in mobile ad hoc wireless networks. The corresponding results of the two most critical aspects of scalability properties in tactical networks (i.e. network initialization time and traffic scalability) are also presented here, and demonstrate that a very extensive evaluation of the corresponding scalability metrics under a combination of the various scalability dimensions defined in this paper, is necessary in order to provide an in-depth analysis of the scalability properties in wireless mobile ad hoc networking environments.     

Processor Utilization Bounds for Real-Time Systems With Precedence Constraints

This paper presents a novel approach to computing tight upper bounds on the processor utilization for general real-time systems where tasks are composed of subtasks and precedence constraints may exist among subtasks of the same task. By careful analysis of preemption effects among tasks, the problem is formulated as a set of linear programming (LP) problems. Observations are made to reduce the number of LP problem instances required to be solved, which greatly improves the computation time of the utilization bounds. Furthermore, additional constraints are allowed to be included under certain circumstances to improve the quality of the bounds.     

声光效应拉曼-内斯方程矩阵级数解法及声光调制器优化设计

提出一种求解正常声光相互作用拉曼 内斯 (Raman Nath)方程的矩阵级数解法 ,该解法直观方便且具有普遍性。计算结果表明 ,对Q =4 1π ,Bragg衍射的效率只有 97 5 % ;对非对称入射 ,以往的Raman Nath近似解误差较大 ;指出提高Bragg衍射效率的有效途径在于提高声光频率比并给出计算声光器件最优长度的计算公式。     

全20CrMnTi表面激光重熔的组织与性能研究

本文对激光重熔20CrMnTi材料表明改性层显微组织分布特征、表面硬度分布规律以及残余应力状态作了研究,结果表明,表面改性层由熔融层、相变硬化层及过渡层组成,且材料表面显微硬度得到大幅度提高,表面硬度达到HV841,约提高4倍。硬化层深度约1mm。残余应力测试得出最大残余应力出现在熔凝带中心,表现为压应力。随着离中心距离的增大,残余应力逐步降低,到熔化带边缘,表现为低幅值压应力;而熔池的外边缘应力在热影响区则转变为拉应力状态。     

Effect of substrate flexibility on solder joint reliability

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint thermal fatigue lifetime significantly. The reliability of solder joint in flip chip assembly for both rigid and compliant substrates was evaluated by accelerated temperature cycling test. Experimental results strongly showed that the thermal fatigue lifetime of solder joints in flip chip on flex assembly was much improved over that in flip chip on rigid substrate assembly. Debonding area of solder joints in flip chip on rigid board and flip chip on flex assemblies were investigated, and it was found that flex substrate could slow down solder joint crack propagation rate. The mechanism of substrate flexibility on improving solder joint thermal fatigue was investigated by thermal mechanical analysis (TMA) technique. TMA results showed that flex substrate buckles or bends during temperature cycling and this phenomenon was discussed from the point of view of mechanics of the flip chip assembly during temperature cycling process. It was indicated that the thermal strain and stress in solder joints could be reduced by flex buckling or bending and flex substrates could dissipate energy that otherwise would be absorbed by solder joints. It was concluded that substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during temperature cycling.     

1.25Gb/s InP基多量子阱激光器与HBT驱动电路的单片集成

描述了一种基于InP材料沿[011]晶向湿法化学腐蚀形成平滑侧壁实现的InP基多量子阱激光器和异质结双极晶体管驱动电路单片集成.通过一个横向缓冲台面结构,降低了激光器阳极和晶体管集电极互连工艺的难度,改善了光发射单片光电集成电路的可制造性.采用该方法制作的光发射单片直流功耗为120mW,在码长223-1传输速率1.5Gb/s伪随机码信号调制下有清晰的眼图,光输出功率为2dBm.     

利用直接隧穿弛豫谱技术对超薄栅MOS结构中栅缺陷的研究

给出了超薄栅MOS结构中直接隧穿弛豫谱(DTRS)技术的细节描述,同时在超薄栅氧化层(＜3nm)中给出了该技术的具体应用.通过该技术,超薄栅氧化层中明显的双峰现象被发现,这意味着在栅氧化层退化过程中存在着两种陷阱.更进一步的研究发现,直接隧穿应力下超薄栅氧化层(＜3nm)中的界面/氧化层陷阱的密度以及俘获截面小于FN 应力下厚氧化层(＞4nm)中界面/氧化层陷阱的密度和俘获截面,同时发现超薄氧化层中氧化层陷阱的矩心更靠近阳极界面.     

基于神经网络与专家系统的压路机智能故障诊断

针对压路机发生故障时,故障原因与故障征兆之间复杂的对应关系,提出了一种基于神经网络与专家系统相结合的新方法,充分发挥了神经网络与专家系统各自的特点。介绍了系统的构成、功能及实现。利用该系统可大大提高压路机故障诊断的准确性和实时性。     

高山微波站防雷技术研究及探讨

从现代防雷理论及福建省无线通信局开展的防雷改造实际效果方面,论述了高山微波站防雷改造中采用的“高压电缆埋地”、“双向多级分流”两项措施具有的科学性、先进性、经济性和可推广性。     

铁电电容模型及其在铁电存储器中的应用

近年来,集成铁电学（integrated ferroelectrics)迅速发展。铁电体是一种特殊的电介质,在不存在外场的情况下,它仍然可以保持一个自发的极化强度。其极化方向在外电场的作用下可以发生反转,表现出特殊的非线性介电行为,即电滞回线。文章讨论了铁电电容模型的SPICE实现。首先介绍电容模型的实现,然后结合2T－2C铁电存储单元的工作原理,验证了该模型。最后,给出了一个完整的32位铁电存储器的电路仿真结果。该结果可以非常容易地推广到更大容量的铁电存储器中。