Alfvénic Electron Acceleration in Aurora Occurs in Global Alfvén Resonosphere Region

Auroral emission caused by electron precipitation (Hardy et al., 1987, J. Geophys. Res. 92, 12275–12294) is powered by magnetospheric driving processes. It is not yet fully understood how the energy transfer mechanisms are responsible for the electron precipitation. It has been proposed (Hasegawa, 1976, J. Geophys. Res. 81, 5083–5090) that Alfvén waves coming from the magnetosphere play some role in powering the aurora (Wygant et al., 2000, J. Geophys. Res. 105, 18675–18692, Keiling et al., 2003, Science 299, 383–386). Alfvén-wave-induced electron acceleration is shown to be confined in a rather narrow radial distance range of 4–5 R _E (Earth radii) and its importance, relative to other electron acceleration mechanisms, depends strongly on the magnetic disturbance level so that it represents 10% of all electron precipitation power during quiet conditions and increased to 40% during disturbed conditions. Our observations suggest that an electron Landau resonance mechanism operating in the “Alfvén resonosphere” is responsible for the energy transfer.     

Dynamic analysis of C/C composite finger seal

A seal device as an important component of aeroengines has decisive influence on per- formance, reliability, and working life of aeroengines. With the development of aeroengines, demands on the performance characteristics of seal devices are made strictly. Finger seal as a novel kind of sealing device, recently attracts more and more attentions in academic circles and engineer- ing fields at home and abroad. Research on finger seals has been extensively developed, especially on leakage and wear performances under dynamic conditions. However, it is a pity that the work on finger seals has been limited with a single approach that is improving the performance by structural optimization; in addition, the technology of dynamic analysis on finger seals is weak. Aiming at the problems mentioned above, a distributed mass equivalent dynamic model of finger seals considering the coupling effect of overlaid laminates is established in the present paper, the dynamic perfor- mance of 2.5 dimension C/C composite finger seal is analyzed with the model, and then the effects of fiber bundle density and fiber bundle preparation direction on finger seal＇s dynamic performance are discussed, as well as compared with those of Co-based alloy finger seal. The current work is about dynamic analysis of finger seals and application of C/C composite in this paper may have much academic significance and many engineering values for improving research level of finger seal dynamics and exploring feasibility of C/C composite being used for finger seals.     

Probing the first stars and black holes in the early Universe with the Dark Ages Radio Explorer (DARE)

A concept for a new space-based cosmology mission called the Dark Ages Radio Explorer (DARE) is presented in this paper. DARE’s science objectives include: (1) When did the first stars form? (2) When did the first accreting black holes form? (3) When did Reionization begin? (4) What surprises does the end of the Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted hyperfine 21-cm transition from neutral hydrogen to track the formation of the first luminous objects by their impact on the intergalactic medium during the end of the Dark Ages and during Cosmic Dawn (redshifts z = 11–35). It will measure the sky-averaged spin temperature of neutral hydrogen at the unexplored epoch 80–420 million years after the Big Bang, providing the first evidence of the earliest stars and galaxies to illuminate the cosmos and testing our models of galaxy formation. DARE’s approach is to measure the expected spectral features in the sky-averaged, redshifted 21-cm signal over a radio bandpass of 40–120 MHz. DARE orbits the Moon for a mission lifetime of 3 years and takes data above the lunar farside, the only location in the inner solar system proven to be free of human-generated radio frequency interference and any significant ionosphere. The science instrument is composed of a low frequency radiometer, including electrically-short, tapered, bi-conical dipole antennas, a receiver, and a digital spectrometer. The smooth frequency response of the antennas and the differential spectral calibration approach using a Markov Chain Monte Carlo technique will be applied to detect the weak cosmic 21-cm signal in the presence of the intense solar system and Galactic foreground emissions.     

基于起落架参数设计的某直升机地面共振及参数影响分析

建立了某直升机地面共振分析力学模型,计算了起落架在桨毂中心处的等效刚度和阻尼,针对某直升机进行了地面共振分析,同时分析了摆振铰外伸量、质量静距、桨毂中心有效刚度等对地面共振的影响,为避免地面共振及参数改进提供依据。     

一种便携式多通道精密测温仪

介绍了利用数字式温度传感器 DS1 6 2 4构成的多路温度测量仪器。它具有线路简单 ,测量精度高的优点 (在 - 5 5～ 1 2 5°C内 ,精度优于 0 .0 5°C) ;带有计算机接口 ,能够实现长时间连续测量。     

面向新世纪的粒子图像测速

一种综述粒子图像测速(Particle Image Velocimetry)的非接触、瞬时、动态、全流场的和本质上是直接的速度场测量技术,成为当今最实用和非常有潜力的流体力学全流场观测(Full Flow Field Observation & Measurement)技术.回顾和展望PIV(包括DPIV,SPIV,HPIV等)及其应用的进展和前景.面临新世纪,PIV技术有望最终攻克一个容积的三维速度场时间历程(3Dt-3C)的观测和推动流体力学进入十分活跃的新时期.     

利用Visual C++实现流量计自动检定

介绍了利用Visual C 控制数据采集卡、数字多用表等,完成流量计的自动检定,结合Office嵌入式编成,实现一定格式的证书打印、数据保存、数据查询等功能.     

基于通用数字信号处理器的雷达坐标测量系统

介绍了由PC机主CPU与TMS320C32(以下简称C32)DSP构成的多目标雷达坐标测量系统，并将任务合理分配给PC机主CPU及C32负担，从而使PC机主CPU和C32在低价位下提供最佳性能。     

Analysis of total visual and CCD V-broadband observations of Comet C/1995 O1 (Hale-Bopp): 1995–2001

We developed a general method for determination of water production rates from groundbased visual observations and applied it to Comet Hale–Bopp. Our main objective is to extend the method to include total visual magnitude observations obtained with CCD detector and V filter in the analysis of total visual magnitudes. We compare the CCD V-broadband careful observations of Liller [Liller, W. Pre-perihelion CCD photometry of Comet 1995 O1 (Hale-Bopp). Planet. Space Sci. 45, 1505–1513, 1997; Liller, W. CCD photometry of Comet C/1995 O1 (Hale-Bopp): 1995–2000. Int. Comet Quart. 23(3), 93–97, 2001] with the total visual magnitude observations from experienced international observers found in the International Comet Quarterly (ICQ) archive. A data set of ∼400 CCD observations covering about the same 6 years time span of the ∼12,000 ICQ selected total visual magnitude observations were used in the analysis. A least-square method applied to the water production rates, yields power laws as a function of the heliocentric distances for the pre- and post-perihelion phases. The average dimension of the nucleus as well as its effective active area is determined and compared with values published in the literature.     

导航计算机应用软件快速更新方法研究

目前,大多数嵌入式开发系统的软件更新必须通过硬件仿真器来实现,不便于系统的维护.良好的可维护性是嵌入式系统性能的一个重要方面,在一定程度上决定系统能否被广泛应用.本文针对南航导航研究中心自主开发的微小型导航计算机,研究了利用串行通信的方式实现应用软件快速更新的方法,解决了程序的定位、代码传输等问题,提高了系统的可维护性,体现了方法研究的实用价值.