PULSED Nd-YAG LASER WELDING OF AN AI-SiC_p METAL MATRIX COMPOSITE

SupportedbytheNationalNaturalScienceFoundationofChinaThefewweldingtechniques,includinggastungstenarcwelding,gasmetalarcweldingandelectronbeamwelding,whichhavebeenexploredforjoiningofMMCs,werefoundtobeunsatisfactorymainlyduetotheformationofexcessivebrittleAl-carbidephase["2'J.Never-theless,limitedsuccesshasbeenachievedinusingCO,laserstoweldcertaintypesofAl-Si/SiCMMCs[s'J.Themeritsoflaserweldingareapparent:theintrinsicfocusingabilityandtheca-pabilityofhavingprecisecontroloverthelaserpro…     

混合解析/数值方法在含高频振荡点源项的欧拉方程数值计算上的应用

 通过模型方程分析看到了一个重要的现象, 如果源项涉及的时间尺度远小于对流项的时间尺度, 那么基于对流时间尺度作为步长的传统数值方法, 即使源项相对于墩流项是个小量, 也会导致平均尺度上错误的结果。为了克服这种困难, 采用时间分裂方法, 把方程分裂成含对流项部分的偏微分方程( PDE) 和包含源项的常微分方程(ODE) 基础上, PDE 使用传统的数值方法, ODE 用解析的方法求解。该混合方法在数值格式时间步长小于平均流动时间尺度时, 得到正确解, 而与点源所隐含的时间尺度无关。把这个方法应用在含源流动的Euler 方程的计算中, 计算了翼型振荡问题, 取得了理想的结果。     

铸造碳纤维增强铝基复合材料

 用铸造法制备抗拉强度达800MPa的连续碳纤维增强铝基复合材料。将国产PAN 1碳纤维经SiC+Ni复合涂层处理后,以束状分布于铸模内,用调压铸造设备在0.75MPa的空气压力和4000Pa的真空度条件下,将铝合金液浸渗入铸模纤维内而获得C/Al复合材料。讨论了碳纤维复合涂层的作用和纤维的束状分布在浸渗动力学过程中的有利影响。     

XILINX的FPGA芯片架构剖析

从芯片结构原理上分析了XILINX的Virtex系列芯片.结合微电子学相关知识,详细分析了芯片的基本结构、可配置功能逻辑、输入输出模块、可编程内连等方面.最后将该芯片与XILINX其它系列芯片相关内容进行了比较分析,给出了该芯片与其它各类不同芯片之间结构与性能上的差异.     

基于气/固耦合非定常流动的叶栅颤振分析

采用二维N-S方程／结构振动方程组耦合数值方法，分析计算了二维非定常气动力强迫振动条件下振动能量及气动力对叶栅所做的功，分别根据振动能量和气动力做功分析了叶栅的颤振特性。NACA0012和PROF叶栅在不同折合频率下气动参数随时间的变化表明，折合频率是影响叶栅颤振的重要因素。气固耦合方法得到的NA-CA0012叶栅颤振折合频率比非耦合的结果高，而对PROF叶栅则相反。这表明叶栅结构动力参数对其发生颤振时的折合频率影响很大且很复杂，要准确预测颤振应该考虑叶栅结构动力与气动力的耦合因素。     

基于Client/Server模式的敏捷制造信息系统方法

客户/服务器(Client/Server)采用并发服务器和socket编程方法,巧妙地解决了网络通信的同步问题。基于Client/Server模式,根据动态联盟的组织原则,提出了开放性的敏捷制造信息系统结构。这种结构实现了动态联盟中分散的制造资源的共享;维护了联盟单元在解决问题时的自主性;通过联盟单元间的双向委托协议,可以保证信息数据的一致性;保证了联盟单元组织不同结构的兼容性。解决了在组织动态联盟时的几个关键问题,为进一步开展敏捷制造方法奠定了基础。     

飞机配电系统中交流模拟固态功率控制器设计

主要介绍了一种交流模拟固态功率控制器（SSPC）的设计和实现。它主要使用了在嵌入式系统中广泛应用的单片机，来实现SSPC的基本功能。从核心器件到对负载电流通断控制以及对采入信号的调理都进行了详细的介绍与说明。     

浅析Blob在S3C44B0上的移植

嵌入式Linux系统通常由三部份组成:Bootloader、Kernel和File System,其中Bootloader的任务是为调用Kernel准备必要的软硬件环境。Blob是一款功能强大的Bootloader,本文介绍了Blob的运行过程和整体结构,同时给出将Blob移植到基于S3C44B0目标板的过程,并对移植过程中的关键代码进行了分析,为项目的后续开发打下基础。     

The Coma of Comet 9P/Tempel 1

As comet 9P/Tempel 1 approaches the Sun in 2004–2005, a temporary atmosphere, or “coma,” will form, composed of molecules and dust expelled from the nucleus as its component icy volatiles sublimate. Driven mainly by water ice sublimation at surface temperatures T > 200 K, this coma is a gravitationally unbound atmosphere in free adiabatic expansion. Near the nucleus (≤ 10² km), it is in collisional equilibrium, at larger distances (≥10⁴ km) it is in free molecular flow. Ultimately the coma components are swept into the comet’s plasma and dust tails or simply dissipate into interplanetary space. Clues to the nature of the cometary nucleus are contained in the chemistry and physics of the coma, as well as with its variability with time, orbital position, and heliocentric distance. The DI instrument payload includes CCD cameras with broadband filters covering the optical spectrum, allowing for sensitive measurement of dust in the comet’s coma, and a number of narrowband filters for studying the spatial distribution of several gas species. DI also carries the first near-infrared spectrometer to a comet flyby since the VEGA mission to Halley in 1986. This spectrograph will allow detection of gas emission lines from the coma in unprecedented detail. Here we discuss the current state of understanding of the 9P/Tempel 1 coma, our expectations for the measurements DI will obtain, and the predicted hazards that the coma presents for the spacecraft. An erratum to this article is available at .     

Deep Impact Mission Design

The Deep Impact mission is designed to provide the first opportunity to probe below the surface of a comet nucleus by a high-speed impact. This requires finding a suitable comet with launch and encounter conditions that allow a meaningful scientific experiment. The overall design requires the consideration of many factors ranging from environmental characteristics of the comet (nucleus size, dust levels, etc.), to launch dates fitting within the NASA Discovery program opportunities, to launch vehicle capability for a large impactor, to the observational conditions for the two approaching spacecraft and for telescopes on Earth.