Coma Morphology of Three Non-periodic Comets     

R. Schulz  J. A. Stüwe  C. Erd 《Earth, Moon, and Planets》2005,97(3-4):387-397

The coma morphology and short-term evolution was investigated of three non-periodic comets in retrograde orbits, C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), and C/2003 K4 (LINEAR). All three comets display distinct coma features, which were very different from one comet to the next and remained rather constant in shape during the observational period. A single, broad feature perpendicular to the sun-tail direction dominated the coma of C/2003 K4 in all used filters (B,V,R,I), whereas the coma of Comet C/2002 T7 exhibited different features in blue and red filters. C/2001 Q4 showed rather complex coma morphology with clear short-term variability in coma brightness. Therefore, these non-periodic comets neither show a featureless coma nor any similarities of the features detected. The overall distribution of coma material was investigated from the shape of radial coma profiles averaged around the comet nucleus. For C/2001 Q4 and C/2002 T7, the slopes fitted to the linear part of these profiles are flatter in the blue than in the red, which can be explained by the presence of coma gas. For C/2003 K4 no such difference is indicated in the May observations (r = 2.3 AU), while in July (r = 1.7 AU) the profiles in the B-filter are flatter than in V, R, and I, hence gas contamination was relevant at least in the B filter. The R and I filter images were used to determine approximate Afρ values of each comet as a function of time.  相似文献   

The Variabilities of the Soft and Hard X—ray Components of NGC 7314 and NGC 7582 and the Distribution of Absorbing Matter in Type Ⅱ AGNs     

Xiang－HuaZou  Sui－JianXue 《中国天文和天体物理学报》2002,2(4):352-360

ASCA observations of the two Type Ⅱ AGNs,NGC7314 and NGC 7582,show clear variations in the broad X-ray band(0.4-10keV)on short timescales-10^4s.Spectral analysis indicates that they bot have an absorbed hard X-ray component and an unabsorbed soft“excess” component.To clarify the origin of the latter,we made a cross-correlation analysis of the two components.The results show that,for NGC7314,the soft X-ray variability is proportional to that of the hard X-ray component.This indicates that the active nucleus of NGC 7314 must be partially covered and so the soft emission is a “leaking” of the variable hard component.For NGC 7582,there is no detectable variability in the soft component, although there is a definite one in the hard component.This indicates that the variable nucleus of NGC 7582 must be fully blocked by absorbing matter,and the soft emission is most likely the scattered component predicted by the AGN unified model.  相似文献   

图形软件在编辑出版专题地图中的应用研究     

王大新 《地球信息科学学报》2001,3(2):25-28

计算机制图(CAC)和电子出版系统的普及和推广,从根本上改变了传统的地图生产工艺。本文结合制图实践,讨论了应用Coreldraw图形软件编辑出版专题地图的适应性、系统条件和工艺流程,并总结了一些制图经验和应该注意的若干问题。  相似文献   

Morphology of subglacial conduit deposits: control by bedrock topography, discharge flow variation, or both? A cautionary case study: Axelsberg, Nynäshamn, south central Sweden     

Amir Mokhtari Fard   《Global and Planetary Change》2001,28(1-4)

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The age of the Geminids: a constraint from the spin-up time-scale     

Martin Beech 《Monthly notices of the Royal Astronomical Society》2002,336(2):559-563

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The intermediate-age open cluster NGC 2112     

Giovanni Carraro  Roberto Barbon  Carla S. Boschetti 《Monthly notices of the Royal Astronomical Society》2002,336(1):259-264

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The influence of a non‐associated flow rule on the calculation of the factor of safety of soil slopes     

Yu‐Jie Wang  Jian‐Hua Yin  C. F. Lee 《国际地质力学数值与分析法杂志》2001,25(13):1351-1359

This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

胜利油气区有机包裹体研究及其在油气勘探中的应用     

李荣西  金奎励  廖永胜 《地球科学与环境学报》1997,(4)

应用显微光度术、显微傅立叶红外光谱（Ｍｉｃｒｏ－ＦＴ．ＩＲ）和飞行时间二次离子质谱（ＴＯＦ－ＳＩＭＳ）等原位微分析技术并结合均一温度测量对胜利油气区下第三系沙河街组沙三段中有机包裹体进行了研究。区分出两类有机包裹体，即原生有机包裹体和次生有机包裹体。结果表明两类有机包裹体特征不同，二者物质组成、有机质成分及化学结构、热演化程度等差别也较大。结合地质分析表明原生有机包裹体是沙三段烃源岩生成烃类运移产物，具“自生自储”特点，而次生有机包裹体是沙四段烃源岩生成的烃类二次运移的产物。沙三段是沙河街组油气运移和聚集的主要层位，因而是寻找油气资源的主要目标层。研究表明，有机包裹体是研究油气生成、运移、聚集和演化等成藏系统最有效的手段之一，在油气勘探中有重要的应用意义。  相似文献   

The β Cephei instability strip     

L. Deng  D.R. Xiong 《Monthly notices of the Royal Astronomical Society》2001,327(3):881-887

We carried out a series of linear stability analyses of the radial and low-degree non-radial p modes for stellar models with initial masses of     . The stellar models were computed by using convective overshoot distance     , 0.25 and 0.40  H _P. Our numerical results show that the β Cephei instability strip forms a horn-shaped region pointing upwards near the main sequence on the Hertzsprung–Russell diagram (HRD). The lower part of the instability strip for the radial modes join the zero-age main-sequence (ZAMS) at     , while the top of the instability strip extends up to     . The instability strip for the non-radial modes is even wider. The overall instability strip is dominated by the radial and non-radial fundamental modes. The first overtone (the radial-order index     is also pulsationally unstable. We have shown that the β Cephei stability is almost independent of the overshoot parameter d _over used for the stellar models, while it depends critically on the metal abundance. With decreasing metal abundance, the instability region shrinks and eventually disappears for     .  相似文献   

卫星激光测距的新进展   总被引：6，自引：0，他引：6  

张忠萍  杨福民 《天文学进展》2001,19(2):283-288

扼要综述了近几年国际上卫星激光测距的进展，介绍了国内激光测距网的现状，展望了未来卫星激光测距的发展。  相似文献