检索结果-南通市图书馆

An Efficient High-Resolution Shock-Capturing Scheme for Multi-Dimensional Flows I. Hydrodynamics

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2006年第6期6卷 680-688页

作者： Cong Yu national astronomical observatories / Yunnan astronomical Observatory, Chinese Academy of {2., Kunming 650011 Graduate School of Chinese Academy of {2., beijing 100049 Graduate School of Chinese Academy of sciences Beijing 100049

Many problems at the forefront of theoretical astrophysics require a treatment of dynamical fluid behavior. We present an efficient high-resolution shock-capturing hydrodynamic scheme designed to study such phenomena. We have implemented a weighted, essentially non-oscillatory （WENO） scheme to fifth order accuracy in space, lILLE approximate Riemann solver is used for the flux computation at cell interface, which does not require spectral decomposition into characteristic waves and so is computationally friendly. For time integration we apply a third order total variation diminishing （TVD） Runge-Kutta scheme. Extensive testing and comparison with schemes that *** characteristic decomposition are carried out demonstrating the ability of our scheme to address challenging open questions in astrophysics.

关键词： accretion - hydrodynamics- method numerical - shock waves

Entropy of Dilatonic Black Hole due to Arbitrary Spin Fields

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2001年第4期1卷 357-364页

作者： You-Gen Shen and Chang-Jun Gao (Shanghai astronomical Observatory, Chinese Academy of sciences, Shanghai 2.003. {2., Chinese Academy of sciences, beijing 100012 Institute of Theoretical Physics, Chinese Academy of Scienc Institute of Theoretical Physics Chinese Academy of Sciences Beijing 100080

Using the membrane model based on the brick-wall model, we calculate the free energy and entropy of dilatonic black hole due to arbitrary spin fields. The result shows that the entropy of scalar field and the entropy ... 详细信息

关键词： black hole physics - entropy - spin

Entropy of three-dimensional BTZ black holes

在线全文

学校读者我要写书评

暂无评论

中国科学：物理学、力学、天文学英文版 2004年第3期47卷 277-283页

作者： GAO Changjun1,2.& SHEN Yougen1,2.3.4 1.Shanghai astronomical Observatory,Chinese Academy of {3.,Shanghai 2.003.,China(mailing address) 2.{2.,Chinese Academy of {3.,beijing 100012,China 3.Institute of Theoretical Physics,Chinese academy of {3.,beijing 100080,China 4.Shanghai United Center for Astrophysics,Shanghai 2.02.4,China 1. Shanghai astronomical Observatory Chinese Academy of Sciences 200030 Shanghai China 2. national astronomical observatories Chinese Academy of Sciences 100012 Beijing China 3. Institute of Theoretical Physics Chinese Academy of Sciences 100080 Beijing China 4. Shanghai United Center for Astrophysics 200234 Shanghai China

The entropies of scalar field and neutrino field are calculated in the background of three-dimensional BTZ black hole. Considering statistical physics,we propose not to consider the superraradiant modes for bosons (Fermion fields do not display supperradiance).In fact,the nonsuperradiant modes do contribute exactly the area entropy for both bosons and fermions. The result shows that the neutrino field entropy is 3.2.times the scalar one.

关键词： BTZ black holes, entropy, supperradiant modes.

k-Nearest Neighbors for automated classification of celestial objects

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2008年第7期51卷 916-922页

作者： LI LiLi1,2.3. ZHANG YanXia1 & ZHAO YongHeng1 1 national astronomical observatories, Chinese Academy of sciences,{2., China 2.Department of Physics, Hebei Normal University, Shijiazhuang 050016, China 3.Weishanlu Middle School, Tianjin 3.02.2. China 1. national astronomical observatories Chinese Academy of Sciences Beijing 100012 China 2. Department of Physics Hebei Normal University Shijiazhuang 050016 China 3. Weishanlu Middle School Tianjin 300222 China

The nearest neighbors (NNs) classifiers, especially the k-Nearest Neighbors (kNNs) algorithm, are among the simplest and yet most efficient classification rules and widely used in practice. It is a nonparametric method of pattern recognition. In this paper, k-Nearest Neighbors, one of the most commonly used machine learning methods, work in automatic classification of multi-wavelength astronomical objects. Through the experiment, we conclude that the running speed of the kNN classier is rather fast and the classification accuracy is up to 97.73.. As a result, it is efficient and applicable to discriminate active objects from stars and normal galaxies with this method. The classifiers trained by the kNN method can be used to solve the automated classification problem faced by astronomy and the virtual observatory (VO).

关键词： k-Nearest Neighbors data analysis classification astronomical catalogues

Possible triggering of solar activity to big earthquakes (Ms ≥ 8) in faults with near west-east strike in China

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2004年第2期47卷 173-181页

作者： HAN Yanben1, GUO Zengjian1,2. WU Jinbing1,2.& MA Lihua1 1. national astronomical observatories, Chinese Academy of {3.,{2., China 2. Earthquake Research Institute of Lanzhou, CSB, Lanzhou 73.00, China Correspondence should be addressed to Han Yanben (email: hyb@***) 1. national astronomical observatories Chinese Academy of Sciences 100012 Beijing China 2. Earthquake Research Institute of Lanzhou CSB 73000 Lanzhou China

This paper studies the relationship between solar activity and big earthquakes (Ms≥8) that occurred in China and western Mongolia. It is discovered that the occurrence dates of most of the big earthquakes in and near faults with west-east strike are close to the maximum years of sunspot numbers, whereas dates of some big earthquakes which are not in such faults are not close to the maximum years. We consider that it is possibly because of the appearance of many magnetic storms in the maximum years of solar activity. The magnetic storms result in anomalies of geomagnetic field and then produce eddy current in the faults gestating earthquake with near west-east strike. Perhaps the gestated big earthquakes occur easily since the eddy current heats the rocks in the faults and therefore decreases the shear resistant intensity and the static friction limit of the rocks .

关键词： earthquake, solar activity, magnetic storm, eddy current.

A new method of ionospheric-free hybrid differential positioning based on a double-antenna CAPS receiver

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2009年第3期52卷 368-375页

作者： GUO JinYun1,2. HAN YanBen1 & CHANG XiaoTao3.1 national astronomical observatories, Chinese Academy of sciences,{2., China 2.College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao 2.6510, China 3.Chinese Academy of Surveying and Mapping, beijing 10003., China 1. national astronomical observatories Chinese Academy of Sciences Beijing 100012 China 2. College of Geodesy and Geomatics Shandong University of Science and Technology Qingdao 266510 China 3. Chinese Academy of Surveying and Mapping Beijing 100039 China

Chinese Area Positioning System (CAPS) is a transmitted satellite navigation system moved by the Chinese Academy of sciences. Three basic modes of navigation and positioning with CAPS are given, and then a comparative analysis is made in this paper. In terms of the principle that the ionospheric delay is at an inverse ratio to the frequency square, a new ionospheric-free positioning method based on a double-antenna CAPS receiver is put forward. Then the hybrid differential observations and the solving equations and algorithms for one epoch and multi epochs are deduced according to the basic principle of the method. The method may remove the global errors in signal emission, propagation, transmission and receiving (e.g., ionospheric delay, hardware delay, and clock error). So it is very convenient for the single-epoch solution and multi-epoch navigation and positioning, and may efficiently improve the precision of real time CAPS navigation. Furthermore, the method can be used not only for the geometric orbit determination of CAPS GEO and IGSO satellites and the navigation and positioning, but also for the estimation of the tropospheric zenith delay, which is useful for the study of water vapor changes in the atmosphere. Polynomials are used in this method to express the tropospheric zenith delay and CAPS satellite orbits within the limited time interval, which reduces the num- ber of unknown parameters and thus speeds the computation.

关键词： Chinese Area Positioning System (CAPS) ionospheric-free linear combination double-antenna receiver hybrid differential positioning method

Analysis on the positioning precision of CAPS

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2009年第3期52卷 328-332页

作者： JI YuanFa1,2.& SUN XiYan1,2.1 national astronomical observatories, Chinese Academy of {3.,{2., China 2.Applied Science and Technology College, Guilin University of Electronic Technology, Guilin 541004, China 1. national astronomical observatories Chinese Academy of Sciences Beijing 100012 China 2. Applied Science and Technology College Guilin University of Electronic Technology Guilin 541004 China

As a newly developed satellite positioning system, the Chinese Area Positioning System (CAPS) is a typical direct sequence spread spectrum ranging system like GPS. The positioning precision of such navigation signals depends on many factors, including the pseudo-code rate, the signal to noise ratio, the processing methods for tracking loops and so on. This paper describes the CAPS link budget, the solution approach for CAPS positioning, focusing on the autocorrelation function feature of C/A code signals. The CAPS signal measurement precision is studied by the software approach together with theoretical analysis of the range resolution. Because the conventional Delay Lock Loop (DLL) is vul- nerable to the impact of noise, a narrow correlator and multiple correlators as well as the corresponding discrimination methods of phases are proposed, which improves the robustness of DLL and the code-phase resolution of the measurement. The results show that the improvement of the DLL structure and the discrimination method are the most important way to improve the ranging resolution. Theoretical analysis and experimental results show that a CAPS receiver could reach a 2.-m positioning precision by using three satellites with a supported height from an altimeter.

关键词： satellite navigation receiver narrow correlation tracking loop

Discrepancy between infrared and optical emission in some Be stars

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2002年第18期47卷 1511-1513页

作者： LIU Qingzhong & WEI JianyanPurple Mountain Observatory, Chinese Academy of sciences, Nanjing2.0008, China national astronomical observatories, Chinese Academy of sciences, beijing 100012, China Purple Mountain Observatory Chinese Academy of Sciences Nanjing China national astronomical observatories Chinese Academy of Sciences Beijing China

An expanding ring model is put forward to investigate the original regions of Ha line emission and infrared excess emission in Be stars, by taking optical depth into account. We find that the two regions depend strongly on the physical properties of the envelope of Be stars such as the initial density and density structure. This model can be used to qualitatively interpret the disagreement between the near infrared excess and the equivalent width (EW) of Ha emission line, as observed in some Be stars.

关键词： Be star emission line near infrared excess.

1RXS J2.2.53.9+062.14: a New SU UMa Dwarf Nova below the Period Minimum

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2001年第6期1卷 483-486页

作者： Jian-Yan Wei, Xiao-Jun Jiang, Da-Wei Xu, Ai-Ying Zhou and Jing-Yao Hu national astronomical observatories, Chinese Academy of sciences,{2. national astronomical observatories Chinese Academy of Sciences Beijing 100012

RXS 12.2.53.9+062.14 was identified as a cataclysmic variable by Wei et al. (1999). Four low-resolution spectra of 1RXS J2.2.53.9+062.14 were obtained with the 2.16-rn telescope of the national astronomical observatories, of which two were at outburst, and two were at quiescence. The system is about 16.8 B and 16.5 V at quiescence, and 12.6 B and 12.6 V at outburst. The quiescent spectra were dominated by double-peaked Balmer emissions, which indicates a hydrogen-rich system with a high-inclination accretion disc. MgH and TiO absorption bands appeared in the quiescent spectrum which implies a companion with a spectral type of early M dwarf. If we take it as a MO dwarf, then the system is located at a distance of 3.0 pc with a proper motion velocity 150 km s-1. The superhump period of 0.0463.1 days was confirmed by our V photometry. The short period and the hydrogen-rich nature reveal that this system is another SU Ursae Majoris-type dwarf nova below the period minimum after V485 Centauri. 1RXS J2. 2.53.9+062.14 is one of the most important systems for studying the evolutionary scenario of cataclysmic variables since it is much brighter than V485 Cen.

关键词： stars: dwarf novae - stars: cataclysmic variables: individual: 1RXS J2.2.53.9 +062.14