Heavy ion observations by MARIE in cruise phase and Mars orbit

The charged particle spectrum for nuclei from protons to neon, (charge Z=10) was observed during the cruise phase and orbit around Mars by the MARIE charged particle spectrometer on the Odyssey spacecraft. The cruise data were taken between April 23, 2001 and mid-August 2001. The Mars orbit data were taken March 5, 2002 through May 2002 and are scheduled to continue until August 2004. Charge peaks are clearly separated for charges up to Z=10. Especially prominent are the carbon and oxygen peaks, with boron and nitrogen also clearly visible. Although heavy ions are much less abundant than protons in the cosmic ray environment, it is important to determine their abundances because their ionization energy losses (proportional to Z²) are far more dangerous to humans and to instruments. Thus the higher charged nuclei make a significant contribution to dose and dose equivalent received in space. Results of the charged particle spectrum measurements will be reported.     

发动机燃气喷流红外辐射场的数值模拟

在高温流动中热辐射与流场是耦合的,但在发动机燃气喷流流场的温度范围内可以在流场计算中忽略热辐射的影响,于是流场与辐射场的模型方程可解耦.为此提出了模拟飞行器绕流流场红外辐射的解耦模型以及相应的算法.该算法首先采用总变差减小TVD(Total Variation Diminishing)格式对流场进行模拟,再引入有限体积概念,应用所取得的流场参数,在同一组网格上计算流场中的红外辐射特征.以轴对称喷管内N₂,O₂,CO₂,H₂O,CO,HCl,H₂等7组分高度欠膨胀冻结流与均匀绕流干扰流场为算例进行了验证性的模拟计算,并与已有试验和计算数据进行了对比,表明该算法是可靠的,可在较大幅度地降低计算量的情况下给出满足工程需要的结果.     

快速大时间步长熵条件格式的分辨率研究

提出了高分辨率快速大时间步长熵条件格式的构造方法.用激波管问题对一族熵条件格式进行研究.在精度、步长、限制器方面进行了详细的数值实验,研究了同样计算量下各种格式的表现品质.从理论上保证了大时间步长格式的无振荡性质,从具体的数值实验分析中确定了大时间步长格式的分辨率问题.      

Onset study of impulsive solar energetic particleevents

Impulsive solar energetic particle (SEP) events are associated with impulsive X-ray flares, energetic electrons,and enhanced heavy ion abundances. Using instruments on ACE, we have examined the composition and origin of twelve impulsive SEP events from November 1997 to June 2000. All selected impulsive SEP events have enhanced ³He/⁴He ratios compared with the solar wind values. The range of ³He/⁴He ratios varies from 0.01 to 7.8. By assuming scatter-free propagation at zero degree pitch-angle, we fitted the minimum particle path lengths (from 1.2 to 1.4 AU, as expected), and estimated the ion event release time back at the Sun to within better than 30 minutes in most cases. We found only four events in which the release times agree for both 38–50 keV electrons and <1 MeV/nucleon ions. Five of our events have significant differences (>40 minutes) between the electron and ion onset times, all with ions injected later. Three impulsive ion events have no association with any impulsive electron event. Seven events have associated solar electromagnetic signatures (Type III radio bursts and/or X-ray flares).     

高超声速飞行器尾喷管的优化设计

以喷管上壁折转角、下壁长度、舵面长度及其折转角为设计变量,结合遗传算法和特征线法对高超声速飞行器尾喷管进行了优化设计,并对设计变量进行了参数研究.结果表明,所采用的优化设计方法计算效率高且比较准确,特别适合于高超声速飞行器尾喷管的优化设计;所采用的4个设计参数均能有效地影响尾喷管的气动性能,其中喷管上壁折转角和舵面折转角分别对喷管的升力和推力的影响相对明显,对其进行均衡选择方能得到最优的结果.      

CME Theory and Models

This chapter provides an overview of current efforts in the theory and modeling of CMEs. Five key areas are discussed: (1) CME initiation; (2) CME evolution and propagation; (3) the structure of interplanetary CMEs derived from flux rope modeling; (4) CME shock formation in the inner corona; and (5) particle acceleration and transport at CME driven shocks. In the section on CME initiation three contemporary models are highlighted. Two of these focus on how energy stored in the coronal magnetic field can be released violently to drive CMEs. The third model assumes that CMEs can be directly driven by currents from below the photosphere. CMEs evolve considerably as they expand from the magnetically dominated lower corona into the advectively dominated solar wind. The section on evolution and propagation presents two approaches to the problem. One is primarily analytical and focuses on the key physical processes involved. The other is primarily numerical and illustrates the complexity of possible interactions between the CME and the ambient medium. The section on flux rope fitting reviews the accuracy and reliability of various methods. The section on shock formation considers the effect of the rapid decrease in the magnetic field and plasma density with height. Finally, in the section on particle acceleration and transport, some recent developments in the theory of diffusive particle acceleration at CME shocks are discussed. These include efforts to combine self-consistently the process of particle acceleration in the vicinity of the shock with the subsequent escape and transport of particles to distant regions.     

Unsteady aerodynamics and flow control for flapping wing flyers

The creation of micro air vehicles (MAVs) of the same general sizes and weight as natural fliers has spawned renewed interest in flapping wing flight. With a wingspan of approximately 15 cm and a flight speed of a few meters per second, MAVs experience the same low Reynolds number (10⁴–10⁵) flight conditions as their biological counterparts. In this flow regime, rigid fixed wings drop dramatically in aerodynamic performance while flexible flapping wings gain efficacy and are the preferred propulsion method for small natural fliers. Researchers have long realized that steady-state aerodynamics does not properly capture the physical phenomena or forces present in flapping flight at this scale. Hence, unsteady flow mechanisms must dominate this regime. Furthermore, due to the low flight speeds, any disturbance such as gusts or wind will dramatically change the aerodynamic conditions around the MAV. In response, a suitable feedback control system and actuation technology must be developed so that the wing can maintain its aerodynamic efficiency in this extremely dynamic situation; one where the unsteady separated flow field and wing structure are tightly coupled and interact nonlinearly. For instance, birds and bats control their flexible wings with muscle tissue to successfully deal with rapid changes in the flow environment. Drawing from their example, perhaps MAVs can use lightweight actuators in conjunction with adaptive feedback control to shape the wing and achieve active flow control. This article first reviews the scaling laws and unsteady flow regime constraining both biological and man-made fliers. Then a summary of vortex dominated unsteady aerodynamics follows. Next, aeroelastic coupling and its effect on lift and thrust are discussed. Afterwards, flow control strategies found in nature and devised by man to deal with separated flows are examined. Recent work is also presented in using microelectromechanical systems (MEMS) actuators and angular speed variation to achieve active flow control for MAVs. Finally, an explanation for aerodynamic gains seen in flexible versus rigid membrane wings, derived from an unsteady three-dimensional computational fluid dynamics model with an integrated distributed control algorithm, is presented.     

CIR Morphology, Turbulence, Discontinuities, and Energetic Particles

Corotating interaction regions (CIRs) in the middle heliosphere have distinct morphological features and associated patterns of turbulence and energetic particles. This report summarizes current understanding of those features and patterns, discusses how they can vary from case to case and with distance from the Sun and possible causes of those variations, presents an analytical model of the morphological features found in earlier qualitative models and numerical simulations, and identifies aspects of the features and patterns that have yet to be resolved. This revised version was published online in August 2006 with corrections to the Cover Date.     

发动机维护服务的现状与未来

航空发动机大修业务开始企稳,而且预计未来还将有所增加. 据MRO Prospector统计,目前在役的窄体飞机机队数量约是宽体飞机的3倍,2011年窄体飞机的发动机返厂维修量将会有大幅增加.     

Frequency-hopping signal detection using partial band coverage

The performance of a channelized radiometer in detecting a frequency-hopping signal is analyzed for a variable number of parallel radiometers not necessarily covering the entire hopping band. The full band may not be covered because of an attempt to avoid interfering signals, limited radiometer resources, lack of knowledge of the band frequency location, or combinations of these factors. The analysis provides for calculation of the value of the signal-to-noise ratio (SNR) required to achieve a given probability of detection for a specified false-alarm rate, assuming an observation interval equivalent to N hops using either a fixed or a moving observation window. The dependence of the probability of detection on a misalignment of the detector observation intervals with the hop transitions is also analyzed. Numerical results are presented and discussed. Applied to a typical slow-hopping VHF radio, the results imply that a 150-hop transmission can be detected by a channelized radiometer covering half the hopping band when the SNR is about 2 dB