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901.
GPS无线电掩星技术能提供高精度、高分辨率、全球覆盖的地球电离层和中性层大气剖面。它具有全天候、低费用、无系统长期漂移等优点。从1995年4月至1997年3月,首次GPS/MET试验的成功显示了GPS掩星技术对监测全球大气能够发挥重要的作用,从而成为当前空间探测技术的研究热点之一。该文主要叙述了无线电掩星技术的数据处理系统的有关情况,并介绍了美国UCAR的掩星数据处理系统CDAAC的概况,可作为我国开展无线电掩星计划有关工作的借鉴。 相似文献
902.
Dong Han Shuang-Nan Zhang Department of Engineering Physics & Center for Astrophysics Tsinghua University Beijing Department of Physics & Center for Astrophysics Tsinghua University Beijing Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2006,6(4)
Hilbert-Huang Transform (HHT) is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated light curves and an X-ray burst from the X-ray burster 4U 1702-429 with both the HHT and the Windowed Fast Fourier Transform (WFFT) methods. Our results show that the HHT method has failed in all cases for light curves with Poissonian fluctuations which are typical for all photon counting instruments used in astronomy, whereas the WFFT method can sensitively detect the periodic signals in the presence of Poissonian fluctuations; the only drawback of the WFFT method is that it cannot detect sharp frequency variations accurately. 相似文献
903.
Qi-Rong Yuan Peng-Fei Yan Yan-Bin Yang Xu Zhou Department of Physics Nanjing Normal University Nanjing yuanqirong@njnu. edu. cn National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Mathematics Physics Qingdao University of Science Technology Qingdao 《中国天文和天体物理学报》2005,5(2):126-136
Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of 5.4h-1 Mpc are currently expanding at 583 km s-1 along a direction with a projection angle of 67.5°, and they will reach a maximum extent of 5.65 h-1 Mpc in about 1.0 h-1 Gyr. 相似文献
904.
We present results of photometric observations of the young eclipsing system KH 15D made during two observational seasons, 2002–2004. A comparison of our data with the earlier results of Hamilton et al. and Herbst et al. reveals the existence of a multiyear photometric trend in the brightness: over a period of 5 years the brightness of the system in the Ic band decreased by almost 1 stellar magnitude. It is also shown that the systematic variations in the eclipse parameters reported by Herbst et al. continue to the present. The shape of the light curve has not changed significantly and, as before, it is characterized by a slight brightening in the central portion of the eclipses. These results are discussed in the context of current models for KH 15D.Translated from Astrofizika, Vol. 48, No. 1, pp. 5–14 (February 2005). 相似文献
905.
为了观测太阳耀斑高速电子轰击色球,紫金山天文台赣榆观测站将原精细结构望远镜改造为高速CCD精细结构望远镜,拍摄到局部H_α活动区.在光学系统里增加缩焦器,引进干涉偏振滤光片后,高速CCD就能记录H_α各波段的单色像.经过1999年至2004年的反复试验和改进,目前H_α图像的空间分辨率己达1个角秒,时间分辨率为每秒钟30至40帧图像.2004年11月观测到一个M1.1级耀斑,我们将H_α紫移(H_α-0.5(?))高速图像和硬X-射线暴、射电微波暴比较,结果发现:初始的耀斑成对亮点在上升相相互靠近,特别是微波暴源也显出类似的靠近运动,以前从未观测到这种现象,它可解释为磁弧脚根沿中性线的剪切运动. 相似文献
906.
随着数字技术的发展,数字信号处理芯片的速度越来越快,这为高速数字滤波的实时实现提供了可能。简要阐述了数字滤波的原理,并对两种数字滤波的实现方法进行了分析;给出了数字滤波较模拟滤波的优势;介绍了数字滤波在射电天文测量中的各种应用。 相似文献
907.
For the analysis of non‐linear problems, the displacement‐controlled method (DCM) has a more extensive application scope and more powerful abilities than the load‐controlled method (LCM). However, difficulties of the DCM's procedure not amenable to most finite element implementations of the conventional LCM have restricted its applications in geomechanics. By means of Sherman–Morrison's theorem, the solution of DCM is improved. The improved procedure is characterized by high efficiency, good numerical stability and a programme structure similar to LCM. Two aspects of applications of DCM are illustrated. The first application is to compute the response of a structure under a given load level like the conventional finite element analysis. The second application is to trace the equilibrium path of a structure under a given load distribution type. A simple but effective algorithm is presented for automatically adjusting the step length in tracing the equilibrium path. Examples illustrate that the proposed procedures are suited for modelling complicated non‐linear problems in geomechanics. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
908.
909.
910.
Patrizia A. Caraveo Giovanni F. Bignami Joachim E. Trümper 《Astronomy and Astrophysics Review》1996,7(3):209-216
Summary. As of today, seven X-ray sources have been tentatively identified as radio-quiet, isolated neutron stars. The family appears
to be a rapidly growing one, although not all the objects have been identified with the same degree of certainty. The most
convincing example of radio quiet pulsar is certainly Geminga, the neutron star nature of which, proposed in 1983 on the basis
of its similarity with the Vela pulsar, has been firmly established with the discovery of its X and pulsation. Four more neutron star candidates, originally found in the Einstein data, have been confirmed by ROSAT, which
has added to the list two more entries. All this is not the result of an unbiased search. The seven sources were not selected
at random: four are inside supernova remnants, an obvious place to search for isolated neutron stars, while the remaining
three were singled out because of some peculiarity. Intense -ray emission in the case of Geminga, very high X-ray counting rate for RXJ185635-3754, or being the brightest unidentified
source in the Einstein medium sensitivity survey, MS 0317-6647. In spite of the limited number of objects and of the observational
biases, these seven radio quiet neutron star candidates add valuable pieces of information to the observational panorama of
known pulsars. Their properties, inferred from the X-ray emission, offer a coherent picture, pointing towards thermally emitting,
cooling neutron stars.
Received: April 1, 1996 相似文献