The early history of pulse compression radar-the development ofAN/FPS-17 coded-pulse radar at Lincoln Laboratory

The development of pulse compression radar at MIT Lincoln Laboratory is related on the basis of the author's personal recollections. He describes the formation of the Radar Techniques Group, the development of the concept, the first system constructed, and the selection of an appropriate code for the transmitted waveform     

Detection of polyphase pulse compression waveforms using the radon-ambiguity transform

The recently developed Radon-ambiguity transform (RAT) detects unknown linear frequency modulated (LFM) signals by computing line integrals through the origin of the signal's ambiguity function (AF) magnitude. It is shown that this method also detects the step LFM and frequency-derived polyphase pulse compression waveforms with varying performance degradation. Simulations are provided to estimate the detection loss relative to the LFM.     

Design and analysis of new p(n,k) polyphase pulse compression codes

P(n,k) codes as a new class of polyphase pulse compression codes are introduced and analyzed in detail. The P(n,k) codes are conceptually derived by step approximation of the phase function of a nonlinear-frequency modulated (NLFM) Chirp signal with a favorable energy density spectrum. The significant advantages of P(n,k) codes over conventional polyphase codes are lower autocorrelation sidelobes and an improved tolerance of low Doppler shifts and precompression bandwidth limitations. The primary disadvantage of the P(n,k) codes over conventional codes is a loss in range resolution. The uniform P(n,k) codes are especially attractive for radars employing digital signal professing because their favorable correlation properties also remain when quantization effects are taken into account     

Numerical simulation of compression corner flows at Mach number 9

A hypersonic vehicle encounters a wide range of conditions during its complete flight regime.These flight conditions may vary from low to high Mach numbers with varying angles of attack.The near-wall viscous dissipation associated with flows at combined high Mach and Reynolds numbers leads to significant wall heat transfer rates and shear stresses.The shock wave/boundary-layer interaction results in a flow separation region,which commonly augments total pressure losses in the flow and lowers the efficiency of aerodynamic control surfaces such as fins installed on a vehicle.The standard turbulence models,when used to resolve such flows,result in incorrect separation bubble size for large separated flows.Therefore,it results in an inaccurate aerodynamic load,such as the wall pressures,skin friction distribution,and heat transfer rate.In previous studies,the application of the shock-unsteadiness correction to the standard two-equation k-ω turbulence model improved the separation bubble size leading to an accurate pressure prediction and shock definition with the assumption of constant Prandtl number.In the present work,the new shock-unsteadiness modification to the k-ω turbulence model is applied to the hypersonic compression corner flows.This new model with variable Prandtl number is based on the model parameter,which depends upon the local density ratio.The computed wall pressures,heat flux and flow field are compared to the experimental data.A parametric study is carried out by varying compression deflection angles,free stream Reynolds number and wall temperatures to compute the flow field and wall data accurately,particularly in the shock boundary layer interaction region.The new shockunsteadiness modified k-ω model with variable Prandtl number shows an accurate prediction of initial pressure rise location,pressure distribution in the plateau region and heat flux in comparison to the standard k-ω model.     

The history of communications-from cave drawings to mail messages

The considerations that shaped human communication over time are identified and used as a framework for discussing the early history of communication. The communication means examined include voice, drumbeat, horn and whistle, fire, and letters     

统计过程控制在西飞公司波音737-700垂尾上的应用

基于对美国波音公司先进质量体系和美国通用电器公司的六西格玛管理的研究,建立了适用于西飞公司的统计过程控制管理体系,并将该体系应用于西飞公司波音737-700垂尾的生产过程控制。实践表明,该体系的应用完善了现有统计过程控制的管理体系,同时提高了产品质量,增加了公司效益。     

论证券公司的风险管理及内部控制

我国证券公司在从事证券经纪、证券承销、自营、资产管理等业务时均面临着经营风险，因此，必须充分认识防范和控制市场风险的必要性，从体制上、技术上以及全体员工的意识上加强风险管理并完善内部控制机制，这对于保证证券市场的健康、有序和持续发展也具有重要意义。     

苏宁电器收购日本LAOX公司估价与整合成本问题研究

通过苏宁电器收购日本LAOX公司的案例,用现金流法对日本LAOX公司的收购价值进行估值。通过现金流的估算发现日本LAOX公司从财务角度上,不论其资产还是现金流都具有很强的收购价值,而且通过增长率的方差统计来看,LAOX公司经营的持续性比较稳定,是一个很好的收购目标。但从长远来看,收购后所面临的整合成本是巨大而又不可估算的,所以这次收购是否能够达到预期目标还有待时间的检验,总体上收购还是成功的。苏宁电器收购日本LAOX公司加快了中国企业国际化战略的实施步伐,提醒企业在跨国并购时要注重风险的有效控制,而收购后的成功整合则是企业收购的关键。     

一种新运行方式脉冲燃烧风洞研制及初步应用

介绍了一座喷管口径为600mm、利用氢与富氧空气混合燃烧产生高焓试验气流的脉冲风洞。风洞首次采用了活塞挤压为加热器供应燃料和路德维希管供应富氧空气的工作方式，实现了风洞试验过程中需多少燃料就供多少燃料，消除了采用路德维希管供燃料存在的弊端。自主研制的大通径快速阀取代了膜片，提高了设备运行效率。风洞在吸气式高超声速技术研究中得到了成功应用。     

中国民航危险品运输发展史及管理现状

航空运输所管控的危险品是指能对人体健康、飞行安全、财产或者环境构成危害,且在国际民航组织(ICAO)所颁布的《危险物品安全航空运输技术细则》(Technical Instructions for the Safe Transport of Dangerous Goods     

岁晚,一灯如豆

<正><岁晚>当寒风穿过地平线,在北半球停留的时候,这一年的冬天便悄然而至了。经过了立冬的节气,冷冽的感觉就十分明显,这也预告着,十二月的降临,一年又走向了岁晚。时间真是一件很勤快的事情,从来都不落下任何一秒,精确准时,像一列火车,突突地进站,又准时离去,从来都不会误点。任凭岁月里有春花秋     

目前我国宏观经济状况及其调控

2007年12月5日落幕的中央经济工作会议提出,防止经济转向过热和明显通胀是2008年中国宏观调控的首要任务。2008年4月16日,国家统计局发布了一季度我国国民经济运行的主要数据,文章以此研究中央经济工作会议确立的目标能否实现,在一季度数据背景下,应采取哪些宏观调控政策来保证经济平稳运行和健康发展。     

络阴离子在阴极放电中的推动力

众所周知,“简单金属离子”可在电极上放电。而络阴离子,如:Zn(oH)_4~(2-),CU(CN)_4~(2-),Ag(CN)_2~-,等等,能逆电场力跑到阴极表面去放电,这似乎是不可思议的事。本文扼要阐述引起此现象的原因所在。     

The Low-Latitude Boundary Layer at the Flanks of the Magnetopause

This is a brief overview on what we know and do not know about the low-latitude boundary layer (LLBL) at the flanks of the magnetotail. On the basis of recent observations, simulations and theories we conclude that reconnection is the dominant process in generating the LLBL and its structure probably even under northward IMF conditions. Part of the LLBL always seems to be on open field lines. Possibly the LLBL possesses a double structure with its outer part open and inner part closed. Anomalous diffusive processes cannot sustain the LLBL but provide sufficient diffusivity for reconnection. Strong diffusion is only expected in narrow localized regions and can make the transition to superdiffusion. Kelvin-Helmholtz instability (KHI) is favoured for northward IMF, producing vortices at the tail flanks. Its contribution to efficient mass transport still remains questionable. Coupling of the LLBL to the ionosphere can strongly affect the internal structure of the LLBL, causing turbulent eddies and detachments of plasma blobs as also field-aligned currents and electron heating. The structure and dynamics of the LLBL are affected by field-aligned electric potentials that decouple the LLBL from the ionosphere. Non-ideal coupling simulations suggest that the dusk flank is decoupled, favouring KHI, while the dawn flank is dominated by currents and turbulence.     

The Chemical Composition of Interstellar Matter at the Solar Location

The Local Interstellar Cloud (LIC) surrounds the Solar System and sets the boundary conditions for the heliosphere. Using both in situ and absorption line data towards ε CMa we are able to constrain both the ionization and the gas phase abundances of the LIC gas at the Solar Location. We find that the abundances are consistent with all of the carbonaceous dust grains having been destroyed, and in fact with a supersolar abundance of C. The constituents of silicate grains, Si, Mg, and Fe, appear to be sub-solar, indicating that silicate dust is present in the LIC. N, O and S are close to the solar values.     

某型机飞机典型构件失效分析

本文较详细的分析了某型飞机典型构件的失效原因 ,并对关键部件作了深入细致的腐蚀失效分析。针对分析结果 ,提出了较为具体的腐蚀控制措施 ,为飞机的设计维护提供了依据     

“鹰”“龙”啸神州国产新型作战飞机集萃

近年来,以“飞豹”、“枭龙”、歼10、“猎鹰”、“山鹰”、“翼龙”为代表的一系列新型国产作战飞机陆续面世,标志着中国航空工业在军用飞机的研发能力迈上了新的台阶。