Resonant Cavity Measurements of Ionized Wakes

A transmission resonant cavity technique, which is suitable for making measurements of electron line densities and collision frequencies in the ionized wakes of hypervelocity projectiles, is described. With this method electron density measurements can be made over six orders of magnitude. Resonant cavity design requirements and limitations of the method are discussed. Typical data from measurements behind projectiles traveling at speeds up to 6.5 km/s are given.     

Radar Doppler Spectra of Turbulent Ionized Wakes

The evaluation of the double convolution integrat involved in the expression of the radar response to scattering from a turbulent ionized wake is simplified by the approximation technique presented here, so that the Doppler spectrum parameters can be explicitly expressed in terms of the wake characteristics.     

Absolute Radiometer for the Flow Field of a Hypervelocity Projectile

As part of a hypervelocity instrumentation development program, it was desirable to include a radiometer system for measuring absolute radiation from projectile flow fields. A system employing a photomultiplier tube was designed, and laboratory and range experiments were conducted to investigate its performance characteristics. The laboratory experiments show that the linearity, saturation, and noise characteristics are suitable for this measurement; the system bandwidth is adequate to allow low frequency calibrations to be applied to high frequency measurements; and a derived expression for radiometer sensitivity variation as a function of photomultiplier supply voltage is reasonably correct. The results of the range experiments imply that the system response is sufficient to reproduce accurately input pulses as narrow as one microsecond and that a particular analytical technique for calculating the form of the radiative input to the radiometer from the projectile stagnation region is valid. Principles involved in the design of photomultiplier radiometer circuits of this type are discussed in detail.     

Shock Tube Instrumentation Techniques for Study of Hypervelocity Entry Problems

Shock tube instrumentation techniques developed for the study of convective heat transfer and the radiative properties of high temperature gases at conditions simulating hypervelocity entry into planetary atmospheres are described. An electrically heated helium driven shock tube is used; measurement methods suitable for conventional shock tubes must be modified before they can be used in the hypervelocity shock tube. Extremely high shock velocities necessary for proper simulation are associated with very short test times imposing requirements for fast response instrumentation systems. Methods for evaluating test gas quality are illustrated. Techniques described have been applied to several studies; typical results are shown and instrumentation requirements for the extension of aerothermodynamic investigation in the hypervelocity regime are outlined.     

Absolute Electron Density Measurement Techniques in Hypersonic Wakes

New techniques have been evolved for the application of Langmuir probes to the measurement of electron densities in the wakes of hypersonic projectiles flown in ballistic ranges. These techniques concern probe cleanliness, minimization of flow disturbance, minimization of reflected shocks, and the effect of plasma potential. Electron density level estimates obtained with the probes in sphere wakes were in good agreement with electron density estimates derived from simultaneous measurements with a microwave interferometer.     

静止圆柱尾迹的稳定性分析

采用二维非平行流的整体线性不稳定性分析和基于局部平行假设的绝对／对流不稳定性分析两种方法研究静止圆柱尾迹的稳定性，基本流场由相同的低维Ｇａｌｅｒｋｉｎ方法计算得到。结果证实，随着Ｒｅ数的增加直至Ｋａｒｍａｎ涡街形成，先后发生了两次整体模太的跳跃和一次Ｈｏｐｒ分叉，并首次用绝对／对流不稳定性理论解释了这一现象。     

基于多元极值Copula的尾流飞行风险概率评估

在尾流问题日益突出的背景之下,结合人-机-环复杂系统建模与多元极值理论,评估遭遇近距近地尾流情形下的飞行风险概率。基于蒙特卡罗法提取尾流极值参数,验证了一维极值参数符合广义极值（GEV）分布;在此基础上提出了二维极值参数的双参数变权重（DPAVW） Copula模型,利用自适应区间粒子群优化（ARPSO）算法对目标函数中的未知参数进行了辨识,拟合优度检验的结果表明DPAVW Copula模型具有比其他Copula模型更高的精度;在利用Copula模型对尾流三维空间中所有二维极值参数进行描述的基础上,求出了每个网格节点上对应的飞行风险概率值,构建了尾流场内二维及三维可视化风险概率图。所提方法是对飞机系统安全性评估理论与方法的有效补充,对于尾流场内的导航控制与风险规避、机场起降的尾流安全间隔改进、环境风险可视化等研究方向有一定的参考价值;同时也适用于不同状况下飞行风险概率的横向对比分析。     

高超声速钝体尾流光电特性的计算

本文提出了一个高超声速非烧蚀钝体尾流全流场的简化模型和简化的空气化学模型。该模型用于化学非平衡尾流积分电子密度与NO_2化学发光辐射等参数的计算。对于NO_2化学发光辐射既求得了整个频谱范围内的总辐射,也求得了分谱辐射强度。计算结果与弹道靶测量数据进行了比较,它们之间的一致性良好。     

Langmuir Turbulence and Suprathermal Electrons

Charged particle acceleration takes place ubiquitously in the Universe including the near-Earth heliospheric environment. Typical in situ spacecraft measurements made in the solar wind show that the charged particle velocity distribution contains energetic components with quasi scale-free power-law velocity dependence, f～v ^?α , for high velocity range. In this Review a theory of quiet-time solar-wind electrons that contain a suprathermal component is discussed, in which these electrons are taken to be in dynamical equilibrium with Langmuir turbulence. This Review includes an overview of the Langmuir turbulence theory, as well as a discussion on asymptotic equilibrium solution of Langmuir turbulence/suprathermal electron system. Theoretical predictions of high-energy electron velocity power-law distribution index is then compared against the recent observations of the superhalo electron velocity distribution made by instruments onboard WIND and STEREO spacecraft. It is shown that the theoretical prediction of velocity power-law index is intermediate to the observed range.     

温度传感器动态校准研究

介绍了传感器动态校准的现状,包括概念、特点、数据处理方法等.特别是针对温度传感器动态校准的方法进行了研究,给出了校准装置的选择和校准结果的一些评定方法.     

Doppler Spectral Moments of Radar Scattering from Turbulent Ionized Wakes

The Doppler frequency shift, and spectral spread, of the radar scattering return from turbulent underdense ionized wakes are explicitly related here to the wake mean velocity, and to the wake turbulent velocity fluctuations and mean velocity gradients, respectively, via spectral moments of the matched-filter receiver response.     

轴流压缩机粘性尾迹噪声研究

本文研究了微弯机翼在正弦阵风作用下的脉动升力,并导出计算公式,分析了动、静叶栅几何及气动参数对转子脉动升力及噪声级的影响。     

Galaxy Clusters as Probes for Matter in the Universe

Galaxy clusters are ideal tracers of the large-scale structure and evolution of the universe. They are thus good probes for the matter content of the universe, the existence of dark matter, and for the statistics of the large-scale structure of the matter distribution. X-ray observations provide a very effective tool to characterize individual galaxy clusters as well as the cluster population. With the detailed analysis of X-ray observations of galaxy clusters the matter composition of clusters is obtained which can be taken as representative of the matter composition of the universe. Based on galaxy cluster surveys in X-rays a census of the galaxy cluster population and statistical measures of the spatial distribution of clusters is obtained. Comparison of the results with predictions from cosmological models yields interesting cosmological model constraints and in particular favours a low density universe.     

世界深空探测最新报道

从2004年到2005年的3月,世界深空探测取得了不少喜人成就,新一轮探月热潮、火星探测重大发现、土星探测器成功入轨和彗星探测器发射成功是其中的四大亮点     

Langmuir Turbulence and Solar Radio Bursts

Langmuir waves and turbulence resulting from an electron beam-plasma instability play a fundamental role in the generation of solar radio bursts. We report recent theoretical advances in nonlinear dynamics of Langmuir waves. First, starting from the generalized Zakharov equations, we study the parametric excitation of solar radio bursts at the fundamental plasma frequency driven by a pair of oppositely propagating Langmuir waves with different wave amplitudes. Next, we briefly discuss the emergence of chaos in the Zakharov equations. We point out that chaos can lead to turbulence in the source regions of solar radio emissions. This revised version was published online in August 2006 with corrections to the Cover Date.     

钝体尾迹的稳定性研究及流动控制探讨

系统地回顾了研究钝尾尾迹稳定性的主要方法，并利用局部绝对／对流稳定性分析及整体稳定性分析两种方法，研究了圆柱绕流定常和时均尾迹流场的稳定性。采用低维Ｇａｌｅｒｋｉｎ方法研究了尾迹对圆柱流向振动的响应问题，揭示了频率锁定，涡街的激发和抑制等现象。     

Mission Overview for the Radiation Belt Storm Probes Mission

Provided here is an overview of Radiation Belt Storm Probes (RBSP) mission design. The driving mission and science requirements are presented, and the unique engineering challenges of operating in Earth’s radiation belts are discussed in detail. The implementation of both the space and ground segments are presented, including a discussion of the challenges inherent with operating multiple observatories concurrently and working with a distributed network of science operation centers. An overview of the launch vehicle and the overall mission design will be presented, and the plan for space weather data broadcast will be introduced.     

大偏心率火星探测器轨道外推的近似方法

对于快自转天体,如地球和火星,由于其非球形引力位中田谐项的振动频率与卫星运动频率相当,会给构造大偏心率环绕型探测器轨道分析解带来无法克服的困难。本文以轨道偏心率e≈0.9的＂萤火虫一号＂（YH-1）火星环绕探测器为例,探讨在精度要求不高的情况下,给出近似分析解和计算效率与其相当的数值解计算方案,以满足在计算资源有限的制约下快速轨道外推的要求。