Evaluation and testing of a fracture critical bridge

The I-40 bridges over the Rio Grande in Albuquerque, New Mexico were due to be razed in the fall of 1993 due to geometry and traffic safety considerations, thus providing a unique opportunity for testing them. These medium span steel bridges represent a common design in the US and are classified by AASHTO as non-redundant ‘fracture critical’ two girder steel bridges (fracture critical classification means that failure of a primary member would probably cause collapse of the bridge). The subject bridge, built in 1963, is a 1275 foot (600m) bridge, and consists of three medium span continuous units with spans of 131′-163'−131′ each. The bridge was field tested to determine the impact of a near full depth girder fracture on the redistribution of loads, the load capacity, and the potential for collapse. Four levels of damage were introduced in the middle span of the north plate girder by making various cuts in the web and the flange of the girder. The final cut resulted in a six foot deep crack in the 10ft deep girder, extending from the bottom flange to the floor beam to girder connection. Data was taken under dead load and under a static live load consisting of an 82 000 lb truck. The after fracture response and the load redistribution in the fractured bridge were evaluated. The contribution of the different members to the redundancy of the structure was assessed.     

Characteristics of copper oxide films deposited by PBII&D

Copper oxide films were deposited by plasma based ion implantation and deposition using a copper antenna as rf sputtering ion source. A gas mixture of Ar + O₂ was used as working gas. During the process, copper that was sputtered from the rf antenna reacted with oxygen and was deposited on a silicon substrate. The composition and the chemical state of the deposited films were analyzed by XPS. The structure of the films was detected by XRD. It is observed that Cu₂O film has been prepared on the Si substrate. It is found that the microstructure of the deposited film is amorphous for the applied voltage of − 5 kV. The surface layer of the deposited films is CuO. This is because the surface layer absorbs the oxygen from ambient air after the treated sample was removed from the vacuum chamber. An appropriate applied voltage, 2 kV under the present conditions, brings the lowest resistance. It is also seen that the maximum absorbance of the deposited films moves to a lower wavelength with increased applied voltage.     

离子渗碳层中的晶间脆性SCIEI

本文对20Cr2Ni4A钢离子渗碳层出现的沿晶断裂的原因进行了分析,结果表明,渗碳层中的残余奥氏体与在该区域产生的沿晶脆断无关。TEM分析和Auger电子能谱分析表明,形成沿晶断裂的主要原因是S,P等杂质元素在原奥氏体晶界的偏聚。采用二次加热淬火可以消除这种现象。     

卫星遥感技术在海洋倾废中的应用进展

海洋污染始终是全球热议问题,人为倾废活动是引起该类问题的主要原因,利用监测手段研究海洋倾废活动可以更好地掌握海洋环境的变化及污染程度。重点总结了传统监测方法及遥感技术在海洋倾废监测中的研究进展,进一步分析了传统方法和极轨卫星在研究中的局限性,探讨了地球同步轨道卫星在实际应用中的进步和优势,结合实际应用结果指出地球同步轨道水色卫星在目前研究过程中存在的问题,并对今后的研究方向进行了展望。     

基于MotionView整车虚拟试验场仿真的后转向节强度分析

由于车辆行驶状况复杂多样,传统静态工况无法复现各类恶劣路况下后底盘转向节真实应力,因此在利用MotionView建立整车刚柔耦合多体动力学模型的基础上,将后转向节利用柔性体进行模拟;在进行虚拟试验场仿真分析的同时采用模态综合法计算结构动应力,得到后转向节最高应力位置及发生时刻.仿真结果与整车道路试验结果的对比表明仿真方法准确.     

基于世界大学城空间的计算机课程教学探讨

传统的课堂教学已经无法满足当前的教育教学需要,世界大学城空间的出现,有效改变了传统的教学模式,提供了一种新的教学、交流和学习模式。介绍了世界大学城空间的应用,并且设计了世界大学城空间下的计算机课程教学环节,最后提出来世界大学城空间的计算机课程教学的几点思考。     

Fractional Order Modeling of Human Operator Behavior with Second Order Controlled Plant and Experiment Research

Modeling human operator's dynamics plays a very important role in the manual closed-loop control system, and it is an active research area for several decades. Based on the characteristics of human brain and behavior, a new kind of fractional order mathematical model for human operator in single-input single-output (SISO) systems is proposed. Compared with the traditional models based on the commonly used quasilinear transfer function method or the optimal control theory method, the proposed fractional order model has simpler structure with only few parameters, and each parameter has explicit physical meanings. The actual data and experiment results with the second-order controlled plant illustrate the effectiveness of the proposed method.      

基于双焦单目立体视觉的多层次特征检测算法

特征检测是立体视觉技术的重要组成部分;与传统的Canny或Harris等边缘与角点检测相分离的算法不同,采用相位一致性特征检测算法可以同时检测出边缘和角点;相位一致性特征检测在频域进行,与特征点形状及图像的对比度无关,定位效果好,所得角点是边缘点的子集;在特征检测过程中,利用四叉树将图像分割为与图像特征分布相关的多个区域,在各个区域内分别进行处理;同时,通过控制四叉树的分解级数及特征检测的阈值实现了图像的多层次特征检测,实现结果表明,与传统的特征检测算法相比,该算法效果更为理想,且能更好地适用于单目立体视觉系统。     

Performance evaluation of dynamic probabilistic broadcasting for flooding in mobile ad hoc networks

In mobile ad hoc networks (MANETs), flooding is a required message dissemination technique for network-wide broadcast. The conventional blind flooding algorithm causes broadcast storm problem, a high number of unnecessary packet rebroadcasts thus resulting in high contention and packet collisions. This paper proposes a new probabilistic approach that dynamically fine-tunes the rebroadcasting probability of a node for routing request packets (RREQs) according to the number of neighbour nodes. We evaluate the performance of the proposed approach for the ad hoc on demand distance vector (AODV) routing protocol and compared against the blind flooding, fixed probabilistic and adjusted probabilistic flooding [L.M.M.M. Bani-Yassein, M. Ould-Khaoua et al., Performance analysis of adjusted probabilistic broadcasting in mobile ad hoc networks, International Journal of Wireless Information Networks 13(2) (2006) 127–140; M.B. Yassein, M.O. Khaoua et al., Improving route discovery in on-demand routing protocols using local topology information in MANETs, Proceedings of the ACM international workshop on Performance Monitoring, Measurement, and Evaluation of Heterogeneous Wireless and Wired Networks, Terromolinos, Spain, ACM Press, 2006, pp. 95–99.] approaches. The simulation results show that our proposed approach demonstrates better performance than blind flooding, fixed probabilistic and adjusted flooding approaches.     

可编程数据平面技术综述

在软件定义网络中,可编程数据平面提供的编程能力是网络功能虚拟化的基石。可编程数据平面技术的核心是可编程能力与数据包处理性能。首先从数据平面的可编程性出发,探讨现有数据平面的数据包处理抽象。然后,分别对数据平面实施的目标平台与对应平台上的主要流表算法进行介绍,详细论述现有数据平面技术。最后,探讨了高性能数据平面技术存在的关键挑战。