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921.
Magnetic reconnection induced by Kelvin Helmholtz instability 总被引:1,自引:0,他引:1
MHD simulation study is performed to investigate magnetic reconnection induced by the Kelvin Helmholtz instability in the initially sheared magnetic field geometry as well as in the uniform magnetic field geometry. Slow mode rarefaction structures seen in the uniform field case are not observed in the sheared field case. Dynamo action is less prominent and the conversion of plasma flow energy into the other forms of energy is also smaller in the sheared field case than in the uniform field case. Momentum transport is mostly due to the hydrodynamic stress in the sheared field case, while the electromagnetic stress is dominant in the uniform field case. The long term evolutions are also markedly different in the two cases. In the uniform field geometry, the magnetic field lines twisted due to the Kelvin Helmholtz instability become reconnected and flattened so that they resume the straight field line structure which resembles the initial field geometry. The magnetic field, however, is not uniform with smaller intensity in the central region where the pressure balance is partially maintained by the enhanced thermal pressure. In the initially sheared magnetic field geometry, magnetic reconnection continues to operate until the end of the simulation and the conversion of the flow energy into the thermal energy is still seen. 相似文献
922.
本文对大陆动力学研究中密切关注的问题,如大陆裂解和碰撞的经典、非经典、非威尔逊旋回;盆─山转换的多类型多阶段;大陆垂向增生与侧向增生──是拆沉还是抽拉?造山带结构的复杂性和多样性以及大陆岩石圈发展与演化的“力源”等问题进行了归纳分析和讨论,同时提出了笔者对上述问题的看法。 相似文献
923.
Solar Physics - A curved filament in a decaying active region (AR&;nbsp;8329) was observed on 9 September 1998 with a combination of several instruments. The main data base is a 4-hour long time... 相似文献
924.
925.
Guang-Zhong Xie Luo-En Chen Huai-Zhen Li Li-Sheng Mao Hong Dai Zhao-Hua Xie Li Ma Shu-Bai Zhou National Astronomical Observatories Yunnan Observatory Chinese Academy of Science Kunming Yunnan Astrophysics Center Yunnan University Kunming Physics Department Yunnan Normal University Kunming Physics Department Yuxi Normal College Yuxi Graduate University of Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(5):463-470
Black hole mass is one of the fundamental physical parameters of active galactic nuclei (AGNs), for which many methods of estimation have been proposed. One set of methods assumes that the broad-line region (BLR) is gravitationally bound by the central black hole potential, so the black hole mass can be estimated from the orbital radius and the Doppler velocity. Another set of methods assumes the observed variability timescale is determined by the orbital timescale near the innermost stable orbit around the Schwarzschild black hole or the Kerr black hole, or by the characteristic timescale of the accretion disk. We collect a sample of 21 AGNs, for which the minimum variability timescales have been obtained and their black hole masses (Mσ) have been well estimated from the stellar velocity dispersion or the BLR size-luminosity relation. Using the minimum variability timescales we estimated the black hole masses for 21 objects by the three different methods, the results are denoted by Ms, Mk and Md, respectively. We compared each of them with Mσindividually and found that: (1) using the minimum variability timescale with the Kerr black hole theory leads to small differences between Mσand Mk, none exceeding one order of magnitude, and the mean difference between them is about 0.53 dex; (2) using the minimum variability timescale with the Schwarzschild black hole theory leads to somewhat larger difference between Mσand Ms: larger than one order of magnitude for 6 of the 21 sources, and the mean difference is 0.74 dex; (3) using the minimum variability timescale with the accretion disk theory leads to much larger differences between Mσand Md, for 13 of the 21 sources the differences are larger than two orders of magnitude; and the mean difference is as high as about 2.01 dex. 相似文献
926.
927.
我们于1989年用北京天文台兴隆观测站的60/90/180厘米施密特望远镜及Thomson红敏CCD对14个PG候选激变变星进行光度观测.其光变曲线特性表明:PG0027+260,PG0818+513,和PC1030+590为激变食变星,PG1341—079 是一个可能的激变食变星,PG1551+719为SU UM_a型矮新星,此外还有6个天体的光变曲线有激变星特有的闪变特征.因此PG样本中,激变变星的成功率为79%.PG1030+590的轨道周期为3~h279,PG1717+413的闪变变幅在二个月内有明显变化,它与本身的亮度无明显相关,说明闪变变幅的变化可能是亮斑的局部效应. 相似文献
928.
用天文方法建立商后期甲骨文年代序列的新途径—解析殷历月法 总被引:8,自引:2,他引:6
利用对具有月龄特征的历谱规律的研究成果,以推定甲骨文的绝对年代,从而提供了建立商后期甲骨文年代序列的新方法,并给出了13版卜辞的例证,通过分析殷历月的结构,得出殷历中“二癸月”和“四癸月”的月首分别为首甲日和首癸日,初步归纳出殷历月法,月首为初三,月长等于逆望月周期,建立固定,且找到建立丑之例,置闰规律未知,已存在年终,年中置闰两种闰法。 相似文献
929.
中国古历定朔推步综述 总被引:10,自引:0,他引:10
“朔”简言之表日月黄经相等,先民对其认识经历了一个从平朔到定朔的过程,通过研究古历,文中分析并归纳了不同时期中国古历日制度的基本元素之一-朔的两种推步方法:“积年法”和“《授时历》法”,其中包括平朔,日躔,月离,及定朔的推步方法等;得出了由各历的基本历数直接推出的中国古历定朔计算的一般公式,同时亦给出了《授时历》的推朔法和部分算例。 相似文献
930.
It is apparent that there is a difference between mud coasts and sand coasts in such aspects as sediment components, hydrodynamics
of nearshore waters, and the formative process in configuration, and profile. The intensity distribution of waves affecting
the mud flats in Lianyungang, and the conditions determining tidal water levels, are discussed in this paper. A mathematical
model which describes the erosion process of mud flats has been derived on the basis of the results of tests for the mud process
in seawater. The model is satisfactory for the actual mud flat profile change in Lianyungang with artificial mud discharges. 相似文献