热仿真设计在陶瓷封装中的应用研究

热仿真设计可以对封装产品进行散热性能评估,对缩短产品设计周期、提高产品热可靠性有着重要的意义。采用有限元方法对陶瓷封装器件进行了结壳热阻(θJC)的仿真分析。仿真结果显示,当采用两种不同方法进行边界条件处理时,所得仿真结果产生一定的差异。分析认为,陶瓷基板散热条件的变化会对最终的热阻值造成一定的影响。热电测试法被用来进行实物封装的热阻测量,测试时采用的导热胶会对最终的测试结果产生影响。仿真与测试结果对比显示,仿真方法可以获得较精确的结果。     

国产基茨系列中压变频器在煤矿皮带机变频改造中的应用

本文叙述了国产基茨系列中压变频器在煤炭矿井采煤作业面输送皮带机变频改造中的应用；详细地叙述了输煤皮带机的工作原理和变频改造的方法。分析了置相异步电动机在四个象限的工作状态，介绍了采用IGBT垂直串联技术的国产基茨系列中压变频器。本改造案例是国产基茨系列高压变频器在煤炭矿井输送机上的典型应用实例，为国内各煤矿企业类似的改造提供了范例。     

利用2-D射影变换实现多视图下元素的预报

在描述多视图的几何元素对应关系方面,2-D射影变换是一种有力工具。该文把求解2-D射影变换矩阵的方法从单纯的四点对应扩展到多种组合形式的四元素对应当中,如:4点、4线、3点1线、3线1点和2点2线等。基于2-D射影对应所描述的视图关系,可以有效解决双视图和三视图条件下的点元素或线元素的预报问题。由于没有任何估计因素的介入,提高了预报结果的准确性。灵活组合点线多种元素建立视图关系使得预报环境适应面广泛。实验结果验证了方法的有效性。     

利用信息技术由二维切片图重建三视图

利用计算机对某一管道的二维层状切片图形进行分析处理.利用多媒体著作工具MultimediaToolBook[1～3]找出图形中最大的内切圆,内切圆圆心的轨迹就是管道中心轴线的轨迹,编制程序计算出半径数值,在确定管道中心轴过程中,采用圆弧上两点的角平分线与圆弧的交点进行插值;运用Origin工具作出管道的三维图和三视图;使用Visio工具将三视图修改成光滑的曲线.     

A tool for the automatic generation and analysis of regular analog layout modules

This paper describes the characteristics of a new CAD tool that enables the creation of layout libraries of selected analog modules. This Analog Modules Generator (AMG) automatically creates multiple layout versions of two commonly used analog structures: the differential pair and arrays of series-connected or stacked devices, for the subsequent generation of layout libraries. Based on the number of devices and rows defined by the user for the layout implementation, the tool validates all possible implementations, which are later saved in a database. Additionally, an extraction process can be optionally executed over all the layout views saved in the database. The AMG generates several reports with all the characteristics of the implemented layouts, including area and parasitic components, facilitating further statistical processing. We describe the features and capabilities of the proposed AMG tool, and several test cases are presented. Results show that suitable layout implementations can be achieved by layout and circuit designers in a very reduced amount of time.     

一种基于网络的入侵检测系统的研究与实现

网络入侵检．测系统作为重要的安全工具已经成为研究的热点。本文首先介绍了IDS的基本概念及其组成和分类，然后重点介绍了一种基于网络的入侵检测系统的框架和具体实现，最后对IDS的当前研究情况和发展提出了看法。     

JC型转矩转速传感器输出信号的处理方法

为从JC型传感器获得较准确的转矩转速信号,根据其工作原理寻找合理的信号处理方法,获得电信号和转矩转速信号的转换。采用PIC18F458单片机,通过对传感器输出两路正弦电信号进行放大、滤波及整形处理后并获得两个同频信号的方波,应用RS触发电路将两路正弦信号的相位差变为触发器输出脉冲的宽度。通过脉冲计数法测量方波信号的频率获得转速,利用等精度法检测RS触发器的输出脉冲宽度求取转矩,同时运用滑动平均提高信号的准确性和稳定性。实验结果表明,该方法可有效地测量转矩转速信号,且在电动汽车和机械动力装置仪器中具有实用价值。     

Comprehensive classification of collaboration approaches in E-learning

There are a number of approaches to learning such as traditional approaches (teacher-centered) and collaborative approaches (learner-centered). Nowadays, the concepts of collaboration and social interactions are the major trends in education. Therefore, many researchers embrace these concepts to offer the educational field enhanced learning environments which are supported by communication and collaboration techniques. The adaptation causes the existence of varied approaches which are addressing the collaborative learning techniques. As a result, there is a need for a mechanism to study those approaches and highlight their eminence. The aim of this paper is to give a comprehensive overview about the state-of-art in collaborative learning, especially by integrating social media tools. To do so, the study adopts a classification framework based on four different views (subject, purpose, method, and tool). The framework has been used to compare ten collaborative e-learning approaches. The finding indicates the potential of all approaches in developing an online learning environment for remote collaborative learning despite the lack of fulfilling all the requirements highlighted in the four views.     

Understanding and restructuring Web sites with ReWeb

The authors investigated automatic and semiautomatic Web site analysis with our tool ReWeb, focusing on a site's architecture and evolution. A case study demonstrates how ReWeb addresses the need to support Web site maintenance and evolution while retaining and possibly improving quality. Although not definitive, the case study described confirms that an automatic or semiautomatic tool can help developers understand and maintain Web sites. High-level views, describing the overall site architecture, are very useful, and detailed analyses can help with a site's enclosed subparts. Specifically, we based restructuring on the reaching frames, dominators, and shortest path analyses. In fact, they highlight structural and navigation problems before restructuring and their absence after the intervention. We devote future work to improving the ReWeb's robustness, widening the spectrum of analyzable sites, and enriching its set of analyses and facilities. We would also like to add abstraction techniques to support a high-level view of the site and to partially automate input selection in the presence of dynamic pages     

A model for mobile code using interacting automata

The Internet supports migration of code from node to node. A number of paradigms exist for distributed computing and mobile code, including client/server, remote evaluation, code-on-demand, and mobile agents. We find them overly-restrictive views of reality. We propose a model that can express previous paradigms as special cases. We derive a model using cellular automata (CA) abstractions to study relations between local node behavior and global system behavior. Example mobile code systems are provided and existing paradigms are expressed in terms of the model. These examples include network attacks such as viruses, worms, and distributed denial of service (DDoS). A distributed system simulation tool based on the model is described. Simulation results provide insights gained from this work.     

NetScope: traffic engineering for IP networks

Managing large IP networks requires an understanding of the current traffic flows, routing policies, and network configuration. However, the state of the art for managing IP networks involves manual configuration of each IP router, and traffic engineering based on limited measurements. The networking industry is sorely lacking in software systems that a large Internet service provider can use to support traffic measurement and network modeling, the underpinnings of effective traffic engineering. This article describes the AT&T Labs NetScope, a unified set of software tools for managing the performance of IP backbone networks. The key idea behind NetScope is to generate global views of the network on the basis of configuration and usage data associated with the individual network elements. Having created an appropriate global view, we are able to infer and visualize the networkwide implications of local changes in traffic, configuration, and control. Using NetScope, a network provider can experiment with changes in network configuration in a simulated environment rather than the operational network. In addition, the tool provides a sound framework for additional modules for network optimization and performance debugging. We demonstrate the capabilities of the tool through an example traffic engineering exercise of locating a heavily loaded link, identifying which traffic demands flow on the link, and changing the configuration of intradomain routing to reduce the congestion     

Surface Leakage in GaN/InGaN Double Heterojunction Bipolar Transistors

We report a study on the surface-leakage current in GaN/InGaN double heterojunction bipolar transistors (DHBTs) that are grown on a sapphire substrate. Surface-leakage-current densities on an unpassivated DHBT are 9.6 times 10^-5 - 5.8 times 10^-4 A/cm for JC = 0.5-50 A/cm². A fabricated n-p-n GaN/InGaN DHBT shows the common-emitter dc current gain of 42, the collector-current density of 5.2 kA/cm², and the common-emitter breakdown voltage (BV_CEO) of 75 V.     

Fast synthesized and predicted just noticeable distortion maps for perceptual multiview video coding

The just noticeable distortion (JND) map is a useful tool for perceptual video coding. However, direct calculation of the JND map incurs high complexity, and the problem is aggravated in multiview video coding. In this paper, two fast methods are proposed to generate the JND maps of multiview videos. In the first method, the JND maps of some anchor views are used to synthesize the JND maps of other views via the depth image based rendering (DIBR), which can be much faster than direct JND computation. In the second method, the motion and disparity vectors obtained during the video coding are employed to predict the JND maps. If the prediction is not satisfactory, the JND block will be refreshed by calculating the JND directly. This method does not need any camera parameters and depth maps. The performances of the two fast JND map generation methods are evaluated in a perceptual MVC framework, where the residuals after spatial, temporal, or inter-view prediction are tuned according to the JND thresholds to save the bits without affecting the perceptual quality. Experimental results show that the JND prediction method has better accuracy and lower complexity. In addition, both fast JND methods lead to negligible degradation of the coding performance, compared to the direct JND method.     

基于Microsoft网络的DNS命名结构设计策略研究

AD是Microsoft网络中的一项重要服务和网络管理的重要工具，是当今计算机网络的主流技术。正确的设计DNS系统结构是规划基于AD网络的重要前提。在系统分析DNS系统的基础上，总结归纳了DNS命名结构的4个设计策略：单一DNS结构；子域；单独的同名DNS结构；单独的DNS结构。同时针对这4种设计策略提出了一些观点和意见。     

Incremental backprojection algorithm: modification of the searching flow scheme and utilization of the relationship among projection views

A two-dimensional (2-D) search flow scheme is proposed for the incremental backprojection algorithm. In this scheme, the searching direction in a beam is determined only by the distance from the current pixel to the corresponding ray; no pixels outside the beam are involved in the procedure. In addition, the geometrical relationships between the image grids and the projection rays in different views are fully exploited to further reduce the search operations. It is found that backprojection of four views can be performed at the same time, and the search operation is only required for one of them if the number of views is even. Thus, backprojection is accomplished on a quartet-by-quartet of views basis as well as on beam-by-beam basis. These approaches not only minimize the number of search operations but also possess a simple algorithm structure. Implementation results obtained with an AST-386 computer for the incremental backprojection algorithm using this search flow scheme and the relationship among projection views show that the processing time can be reduced by a factor of about 2.     

Integration of Ground-Penetrating Radar and Laser Position Sensors for Real-Time 3-D Data Fusion

Full-resolution 3-D ground-penetrating radar (GPR) imaging of the near surface should be simple and efficient. Geoscientists, archeologists, and engineers need a tool capable of generating interpretable subsurface views at centimeter-to-meter resolution of field sites ranging from smooth parking lots to rugged terrain. The authors have integrated novel rotary laser positioning technology with GPR into such a 3-D imaging system. The laser positioning enables acquisition of centimeter accurate x, y, and z coordinates from multiple small detectors attached to moving GPR antennas. Positions streaming with 20 updates/s from each detector are fused in real time with the GPR data. The authors developed software for automated data acquisition and real time 3-D GPR data quality control on slices at selected depths. Industry standard (SEGY) format data cubes and animations are generated within an hour after the last trace has been acquired. Such instant 3-D GPR can be used as an on-site imaging tool supporting field work, hypothesis testing, and optimized excavation and sample collection in the exploration of the static and dynamic nature of the shallow subsurface     

Incentive analysis for cooperative interactive multiview video streaming

In interactive multiview video streaming (IMVS), users can periodically select one out of many captured views available for observation. In single-view video streaming, cooperative strategies where peers share received packets of the same video have proven to be effective in reducing server׳s upload burden, and incentive mechanisms are designed to stimulate user cooperation. However, exploiting user cooperation in higher dimensional IMVS is difficult, since users watching different views makes it difficult to establish partnership, and users switching views frequently and independently makes it difficult to maintain partnership over time. In this paper, we use a multiview video frame structure for IMVS to support cooperative view-switching, where peers may help each other even if they are observing different views. We then model peers׳ interaction as an indirect reciprocity game, where each user is assigned a reputation level. To gain a higher reputation level, users help others, which in turn leads to a higher likelihood to receive others׳ help later. In this work, we focus on how view switching, the key feature of IMVS, affects user cooperation. By modeling users׳ decision making as a Markov decision process, our analysis shows that users tend to cooperate at some views but not others: given peers can predict their future view navigation paths probabilistically, for a peer who is likely to enter a view-switching path not requiring others׳ help, he also has less incentive to cooperate. Furthermore, we observe that the game may have multiple Nash Equilibria corresponding to different cooperation levels, e.g., users cooperate at all views in the full cooperation equilibrium, while users only cooperate at certain views in the partial cooperation equilibrium. The particular equilibrium the game will converge to depends on the initial cooperation level of the game. To stimulate user cooperation at all views, we propose a Pay-for-Cooperation (PfC) scheme at the beginning of the game to drive the game to the full cooperation equilibrium to improve system efficiency. Our simulation results show the effectiveness of PfC.