供测量高阻率材料电压、电流和电阻用的前置放大器

本文介绍一种供测量高阻率材料直流电压、电流和电阻用的前置放大器,其测量范围分别为:电压:30μv～10v;电流:10~(-2)～10~(-13)A;电阻:10~3～10~(13)Ω。若在反馈回路中接入适当的电容器还可测量电荷。本前置放大器采用市场上供应的运算放大器制成,其体积较小,并可与市场上大量供应的电压表或记录器联合使用,适用于无定形的(非晶体的)半导体薄膜电气性能的就地测量。     

欧空局通信卫星监视设施的现状

欧空局通信卫星监视设施(CSMF)可为参与和负责卫星研制和生产的工程师们提供跟踪卫星在轨运行情况的手段。该设施可为这些工程师们提供与制造卫星过程一样的卫星接口。这种用户接口是用“欧洲试验操作语言”(ETOL)提供的。在卫星的射前、射后操作中,这种语言允许重复使用卫星控制系统的软件。     

激光熔覆制备金属间化合物抗冲蚀涂层

采用同轴送粉方法,激光熔覆制备了WC增强Ni3Al金属间化合物基复合涂层,通过试验,优化了工艺参数,对激光熔覆涂层的成分、组织和硬度进行了测试和分析.结果表明,激光熔覆涂层无裂纹和气孔,与基体形成良好的冶金结合,WC颗粒的添加显著提高了涂层硬度.     

发动机维修企业开始探索零部件修理能力

<正>在售后服务市场竞争日趋激烈、航空公司不断挤压发动机维修成本以期节约成本,以及OEM对原厂件不断提价的大环境下,众多发动机维修服务供应商开始探索发展零部件自修能力,以代替换件修理。本文介绍了几家大型MRO发展发动机零部件修理能力的经验,供业内参考。     

A380结构的先进材料和技术--未来发展的技术平台

A380超大型客机是目前仅有的采用全机身长度双层客舱的4通道客机、能容纳555名乘客。本文简要介绍了A380机体结构所采用的先进材料和制造技术。     

用高阶信号处理方法处理UWB雷达数据提取目标材料特性

本文介绍了用两种高阶信号处理方法处理ＵＨＦ波段（３００￣９００ＭＨｚ）超宽带（ＵＷＢ）雷达数据（在专门设计的收发分置的测试场内收集的ＵＷＢ雷达数据）所得到的初步结果。我们用四种类型的ＵＷＢ信号来测试金属板（参照物）和五种不同的有金属衬片的雷达波吸收材料的商品样品（ＲＡＭ）以及５种普通材料（散射）样品。该项研究的目的是评估我们的几种ＵＷＢ信号形式和相关的信号处理方法可靠提取不同目标材料的雷达散射特性     

关于S形进气道中的旋流研究

本文给出了具有典型飞机进气道比例的S形管道在不同攻角下,压力分布和旋流的实验结果。为了减小大攻角下的旋流,研究了两种方法:一是通过扰流板改变管道内气流的压力分布,二是通过辅助进气门引入自由流空气,向分离流补充能量。结果表明,在低攻角下旋流很弱并呈现为典型的反向旋转对涡二次流动,而在高攻角下则为一个很强的单涡旋转流动。至于反旋流措施,扰流板的效果最好,通过变化其尺寸不仅能改变旋流方向,而且还可完全消除旋流。本文建议用一个旋流系数,SC_(60),来描述名义发动机进口处的旋流。其值对原设计模型在30°攻角时为0.188,而通过辅助进气门引入自由流空气向分离流补充能量后为0.068,当采用一个0.15倍喉道宽度的扰流板时,旋流系数变为-0.039。本研究使S形进气道中旋流的产生、发展和性质得到进一步的认识。     

Isothermal study of effusion cooling flows using a large eddy simulation approach

An isothermal numerical study of effusion cooling flow is conducted using a large eddy simulation(LES) approach.Two main types of cooling are considered,namely tangential film cooling and oblique patch effusion cooling.To represent tangential film cooling,a simplified model of a plane turbulent wall jet along a flat plate in quiescent surrounding fluid is considered.In contrast to a classic turbulent boundary layer flow,the plane turbulent wall jet possesses an outer free shear flow region,an inner near wall region and an interaction region,characterised by substantial levels of turbulent shear stress transport.These shear stress characteristics hold significant implications for RANS modelling,implications that also apply to more complex tangential film cooling flows with non-zero free stream velocities.The LES technique used in the current study provides a satisfactory overall prediction of the plane turbulent wall jet flow,including the initial transition region,and the characteristic separation of the zero turbulent shear stress and zero shear strain locations.Oblique effusion patch cooling is modelled using a staggered array of 12 rows of effusion holes,drilled at 30° to the flat plate surface.The effusion holes connect two channels separated by the flat plate.Specifically,these comprise of a channel representing the combustion chamber flow and a cooling air supply channel.A difference in pressure between the two channels forces air from the cooling supply side,through the effusion holes,and into the combustion chamber side.Air from successive effusion rows coalesces to form an aerodynamic film between the combustion chamber main flow and the flat plate.In practical applications,this film is used to separate the hot combustion gases from the combustion chamber liner.The numerical model is shown to be capable of accurately predicting the injection,penetration,downstream decay,and coalescence of the effusion jets.In addition,the numerical model captures entrainment of the combustion chamber mainstream flow towards the wall by the presence of the effusion jets.Two contra-rotating vortices,with axes of rotation along the stream-wise direction,are predicted as a result of this entrainment.The presence and characteristics of these vortices are in good agreement with previous published research.      

Endolithic cyanobacteria in halite rocks from the hyperarid core of the Atacama Desert

In the driest parts of the Atacama Desert there are no visible life forms on soil or rock surfaces. The soil in this region contains only minute traces of bacteria distributed in patches, and conditions are too dry for cyanobacteria that live under translucent stones. Here we show that halite evaporite rocks from the driest part of the Atacama Desert are colonized by cyanobacteria. This colonization takes place just a few millimeters beneath the rock surface, occupying spaces among salt crystals. Our work reveals that these communities are composed of extremely resistant Chroococcidiopsis morphospecies of cyanobacteria and associated heterotrophic bacteria. This newly discovered endolithic environment is an extremely dry and, at the same time, saline microbial habitat. Photosynthetic microorganisms within dry evaporite rocks could be an important and previously unrecognized target for the search for life within our Solar System.     

今后十年的卫星遥感

1978年,航宇局将发射陆地卫星-C、海洋卫星-A和热容量绘图卫星。大约在1981年,还要发射陆地卫星-D。陆地卫星-D可能携带七个光谱段的主题绘图仪,也许还要装多光谱扫描器。美国地质勘探局提出了一种三个谱段的线性列阵遥感器。在出击式飞行的航天飞机上、在欧洲空间实验室和由航天飞机发射和维修的某些不载人飞行器上,都将带有大幅面测绘相机。到八十年代中期,可能会出现地球同步实时观测系统。