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41.
卫星编队飞行的难点之一是在干扰力环境下控制队形。采用了一种基于线性二次调节器(LQR)的最优控制方法,对低轨道地球卫星所受的地球扁率摄动(J2力)加以模拟,并在模拟的地球低轨道J2力环境中。对几种卫星编队进行了模拟控制,从控制精度和能量消耗的角度对控制方法进行了分析,提出了卫星编队飞行中相对距离控制和绝对距离控制需要注意的问题。 相似文献
42.
首先介绍传统考试方法的现状及其发展方向,并根据目前学校考试的实际需要,提出一个新的基于B/S模式考试方式.接着介绍了相关的技术,并对其实现的可行性、可靠性、高效性等做了进一步分析,同时给出系统解决方案.最后,阐述了整个系统安全性以及需要完善和改进之处. 相似文献
43.
R.L.C. Starling E.M. Puchnarewicz E. Romero-Colmenero K.O. Mason 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2588-2593
We present a series of monitoring observations of the ultrasoft broad-line Seyfert galaxy RE J2248-511 with XMM-Newton. Previous X-ray observations showed a transition from a very soft state to a harder state five years later. We find that the ultrasoft X-ray excess has re-emerged, yet there is no change in the hard power-law. Reflection models with a reflection fraction of 15, and Comptonisation models with two components of different temperatures and optical depths (kT1 = 83 keV, T1 = 30 eV, τ1 = 0.8; KT2 = 3.5 keV, T2 = 60 eV, τ2 = 2.8) can be fit to the spectrum, but cannot be constrained. The best representation of the spectrum is a model consisting of two blackbodies (kT1 = 0.09 ± 0.01 keV, kT2 = 0.21 ± 0.03 keV) plus a power-law (Γ = 1.8 ± 0.08). We also present simultaneous optical and infrared data showing that the optical spectral slope also changes dramatically on timescales of years. If the optical to X-ray flux comes primarily from a Comptonised accretion disk we obtain estimates for the black hole mass , accretion rate and inclination cos(i) 0.8 of the disk. 相似文献
44.
B.C. Joshi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2725-2727
The double pulsar system, J0737–3039, provides a unique probe of a pulsar magnetosphere due to its edge-on viewing geometry, a tight orbit and a significant rate of advance of the angle of periastron. In this paper, we report on the changes in radio emission from the long period pulsar in this system, J0737–3039B, over a period of 9 months. Observations of this system with Giant Metrewave Radio Telescope (GMRT) show that the duration of the first bright phase of the pulsar centered at 210° orbital longitude from the ascending node is shrinking. These observations will be useful to constrain the proposed models for this system. 相似文献
45.
基于J-积分半经验公式建立了构件表面裂纹在其长度和深度方向上的疲劳扩展速率表达式,用来预计模拟SUS304钢构件在550℃高温环境中受弯曲载荷作用下表面裂纹的疲劳扩展寿命.并在相同条件下进行了疲劳裂纹扩展试验.结果表明,预测曲线与实验数据基本一致,证明了本文预测方法的有效性. 相似文献
46.
47.
G. Facskó J.G. Trotignon I. Dandouras E.A. Lucek P.W. Daly 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Hot flow anomalies (HFAs) were first discovered in the early 1980s at the bow shock of the Earth. In the 1990s these features were studied, observed and simulated very intensively and many new missions (Cluster, THEMIS, Cassini and Venus Express) focused the attention to this phenomenon again. Many basic features and the HFA formation mechanism were clarified observationally and using hybrid simulation techniques. We described previous observational, theoretical and simulation results in the research field of HFAs. We introduced HFA observations performed at the Earth, Mars, Venus and Saturn in this paper. We share different observation results of space mission to give an overview to the reader. 相似文献
48.
Larmor size transient structures with density depletions as large as 99% of ambient solar wind density levels occur commonly upstream of Earth's collisionless bow shock. These "density holes" have a me... 相似文献
49.
Julien Malzac 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2872-2876
We interpret the rapid correlated UV/optical/X-ray variability of XTE J1118+480 as a signature of the coupling between the X-ray corona and a jet emitting synchrotron radiation in the optical band. We propose a scenario in which the jet and the X-ray corona are fed by the same energy reservoir where large amounts of accretion power are stored before being channelled into either the jet or the high energy radiation. This time-dependent model reproduces the main features of the rapid multi-wavelength variability of XTE J1118+480. A strong requirement of the model is that the total jet power should be at least a few times larger than the observed X-ray luminosity, implying a radiative efficiency for the jet j 3 × 10−3. This would be consistent with the overall low radiative efficiency of the source. We present independent arguments showing that the jet probably dominates the energetic output of all accreting black holes in the low-hard state. 相似文献
50.
M.T. Menna A. Papitto L. Burderi T. Di Salvo F. DAntona N.R. Robba 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2704-2706
We analyze the three outbursts of the X-ray millisecond pulsar SAX J1808.4-3658 that occurred in 1998, 2000, and 2002 observed with RXTE. With a technique based on epoch folding search we find an unique orbital solution valid over the five years of high temporal resolution data available. We revise the estimate of the orbital period, Porb = 7249.1569(1) s and of its error, which we decrease by one order of magnitude. We also give the first constraint on the orbital period derivative, . We find that in 2002 the pulse profile shape is clearly asymmetric, showing a secondary peak at about 145° from the main pulse, which is different from the sinusoidal shape reported at the beginning of the 1998 outburst. 相似文献