Canonical theory of perturbations using eccentric anomaly as independent variable     

Janis Britals 《Celestial Mechanics and Dynamical Astronomy》1992,54(4):305-316

It is shown in this paper how to build a canonical transformation of variables, so that the eccentric anomaly becomes the new independent variable. In the case of eccentric elliptical orbits it changes the equations of motion so, that they can be integrated analytically to any order of approximation comparatively easy.  相似文献   

太阳发电机理论研究进展     

姜杰  汪景琇 《天文学进展》2005,23(2):121-134

太阳发电机理论主要解释太阳磁场的起源和演化，是太阳物理中最基本、最重要的问题之一．对它的研究不仅具有重要的科学价值，而且对空间天气的预测和空间技术的发展有一定的影响．随着日震学的发展，该理论也得到了很大改进。从相关观测入手，综述了发电机理论需解释的观测事实，以及为发电机理论提供约束的太阳内部动力学结构；介绍了基本理论和近来的主流模型，并指出尚待解决的问题和进一步的努力方向。  相似文献   

Application of micropolar plasticity to post failure analysis in geomechanics     

Majid T. Manzari 《国际地质力学数值与分析法杂志》2004,28(10):1011-1032

A micropolar elastoplastic model for soils is formulated and a series of finite element analyses are employed to demonstrate the use of a micropolar continuum in overcoming the numerical difficulties encountered in application of finite element method in standard Cauchy–Boltzmann continuum. Three examples of failure analysis involving a deep excavation, shallow foundation, and a retaining wall are presented. In all these cases, it is observed that the length scale introduced in the polar continuum regularizes the incremental boundary value problem and allows the numerical simulation to be continued until a clear collapse mechanism is achieved. The issue of grain size effect is also discussed. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Numerical calculations in the orbital determination of an artificial satellite for a long arc     

Lin Liu  Xinhao Liao 《Celestial Mechanics and Dynamical Astronomy》1994,59(3):221-235

Numerical methods are usually used for the computation of ephemerides with perturbations for the precise orbital determination of an artificial satellite. But their numerical stability will be encountered in a long arc. In this case the use the improved Encke special perturbation methods has been suggested. The results of this paper show that Encke's method does indeed have a certain effectiveness, but cannot yet completely resolve the numerical stability, and the more efficient method is to use the energy integral or its variational relation to control the growth of the along-track error in general numerical calculations so that the aim of stabilization can be achieved.  相似文献   

The Hubble constant from the gravitational lens CLASS B0218+357 using the Advanced Camera for Surveys     

T. York  N. Jackson  I. W. A. Browne  O. Wucknitz  J. E. Skelton † 《Monthly notices of the Royal Astronomical Society》2005,357(1):124-134

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FITS、BMP和SCR图象格式及相互转换   总被引：1，自引：0，他引：1  

季凯帆  曹文达  宋谦 《天文研究与技术》1996,(2)

本文详细介绍图象的ＦＩＴＳ格式、ＢＭＰ格式和ＳＣＲ格式。ＦＩＴＳ格式已经是天文界的通用格式，几乎所有的天文软件包都支持这一格式，而ＢＭＰ格式在ＰＣ计算机上有广泛的运用，有大量ＰＣ软件支持ＢＭＰ图象的显示，处理和打印。云南天文台的ＳＣＲ格式是ＰＣ机采集ＣＣＤ图象所使用的格式。实现这三种格式的相互转换，就可以自由的将ＣＣＤ图象在ＰＣ机和工作站上进行各种处理。转换的包括图象头和图象数据的转换，其关键在于交换数据的高低字节。  相似文献   

River sediments,great floods and centennial‐scale Holocene climate change     

Mark G. Macklin  John Lewin 《第四纪科学杂志》2003,18(2):101-105

A new analysis of all 346 published ¹⁴C dated Holocene alluvial units in Britain offers a unique insight into the regional impacts of global change and shows how surprisingly sensitive British rivers have been to relatively modest but repeated changes in climate. Fourteen major but probably brief periods of flooding are identified bracketed within the periods 400–1070, 1940–3940, 7520–8100 and at ca. 10 420 cal. yr BP. There is a strong correspondence between climatic deteriorations inferred from mire wet shifts and major periods of flooding, especially at ca. 8000 cal. yr BP and since ca. 4000 cal. yr BP. The unusually long and complete British record also demonstrates that alterations in land cover have resulted in a step change in river basin sensitivity to variations in climate. This has very important implications for assessing and mitigating the impact of increasing severe flooding. In small and medium‐sized river basins land use is likely to play a key role in either moderating or amplifying the climatic signal. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Does time dilation tell us the distance to gamma-ray bursts?     

Ralph A. M. J. Wijers 《Astrophysics and Space Science》1995,231(1-2):399-402

Since the discovery that dim gamma-ray bursts last longer on average than bright ones (time dilation) the cosmological origin of this effect has been contested by various researchers. I discuss the current status of this issue and conclude that current models for a non-cosmological time dilation only explain part of the observed phenomenon, and even then betray themselves by distinct signatures in the data. As those signatures have not been seen, the cosmological origin remains the favoured explanation of the time dilation.  相似文献   

Church-based social capital, networks and geographical scale: Katrina evacuation, relocation, and recovery in a New Orleans Vietnamese American community     

Christopher A. Airriess  Wei Li  Karen J. Leong  Angela Chia-Chen Chen  Verna M. Keith 《Geoforum》2008,39(3):1333-1346

This research examines the role of social capital and networks to explain the evacuation, relocation, and recovery experiences of a Vietnamese American community in New Orleans, Louisiana in the aftermath of Hurricane Katrina. As the single largest community institution, the parish church’s complex bonding and bridging social capital and networks proved particularly critical in part because of its historically based ontological security. The process of evacuation, but especially relocation and recovery, was dependent on deploying co-ethnic social capital and networks at a variety of geographical scales. Beyond the local or community scale, extra-local, regional, and national scales of social capital and networks reproduced a spatially redefined Vietnamese American community. Part of the recovery process included constructing discursive place-based collective-action frames to successfully contest a nearby landfill that in turn engendered social capital and networks crossing ethnic boundaries to include the extra-local African American community. Engaging social capital and networks beyond the local geographical scale cultivated a Vietnamese American community with an emergent post-Katrina cultural and political identity.  相似文献   

Fate of the verde: Water, environmental conflict, and the politics of scale in Arizona’s central highlands     

Bob Bolin  Timothy Collins  Kate Darby   《Geoforum》2008,39(3):1494-1511

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