排序方式： 共有51条查询结果，搜索用时 15 毫秒
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Nikos Prantzos 《Astrophysics and Space Science》2003,284(2):675-684
We develop a detailed model of the Milky Way (a `prototypical' disk galaxy) and extend it to other disks with the help of
some simple scaling relations, obtained in the framework of Cold Dark Matter models. This phenomenological (`hybrid') approach
to the study of disk galaxy evolution allows us to reproduce successfully a large number of observed properties of disk galaxies
in the local Universe and up to redshift z ∼ 1. The important conclusion is that, on average, massive disks have formed the bulk of their stars earlier than their lower
mass counterparts: the `star formation hierarchy' has been apparently opposite to the `dark matter assembly' hierarchy. It
is not yet clear whether `feedback' (as used in semi-analytical models of galaxy evolution) can explain that discrepancy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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M. A. P. Torres J. Casares I. G. Martínez-Pais P. A. Charles 《Monthly notices of the Royal Astronomical Society》2002,334(1):233-240
We present a library of 47 open-cluster integrated spectra, mostly obtained at CASLEO (San Juan, Argentina) in the range 3600 < λ < 7400 Å , which are made available at CDS. The data are combined with previous spectra to obtain 10 high signal-to-noise ratio basic templates in the young and intermediate-age domains, which are also provided in the library. These Galactic disc templates represent the increased time resolution spectral evolution of a stellar population unit around the Solar metallicity level. The improved signal-to-noise ratio of the present templates with respect to previous template lists, together with their increased time resolution, allowed us to improve the fundamental parameters of some open clusters. The present spectral library will be useful for several astrophysical applications, particularly for population syntheses of star-forming giant galaxies. 相似文献
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The present-day chemical and dynamical properties of the Milky Way are signatures of the Galaxy's formation and evolution.
Using a self consistent chemodynamical evolution code we examine these properties within the currently favoured paradigm for
galaxy formation – hierarchical clustering within a CDM cosmology. Our Tree N-body/Smoothed Particle Hydrodynamics code includes
a self-consistent treatment of gravity, hydrodynamics, radiative cooling, star formation, supernova feedback and chemical
enrichment. Two models are described which explore the role of small-scale density perturbations in driving the evolution
of structure within the Milky Way. The relationship between metallicity and kinematics of halo stars are quantified and the
implications for galaxy formation discussed. While high-eccentricity halo stars have previously been considered a signature
of `rapid collapse', we suggest that many such stars may have come from recently accreted satellites.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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恒星的Al元素丰度可以为探索星团和星系的化学演化提供重要线索.通过系统分析银河系薄盘、厚盘、核球、银晕以及M4、M5等球状星团中恒星的[Al/Fe]随恒星金属丰度[Fe/H]的变化趋势,得出银河系薄盘、厚盘和核球恒星的[Al/Fe]随着[Fe/H]的增加而缓慢下降,而球状星团M4和M5恒星的[Al/Fe]随[Fe/H]增加没有下降趋势,这暗示Ia超新星对M4和M5恒星元素丰度的贡献比较小.详细研究了银河系恒星[Al/Fe]与[Mg/Fe]、[Na/Fe]的相关性,结果表明银河系场星的[Al/Fe]与[Mg/Fe]正相关,但在球状星团M4和M5恒星中未见此相关性;银河系盘星及M4和M5等球状星团恒星的[Al/Fe]与[Na/Fe]都存在正相关. 相似文献
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灾害是人类面临的最严重的威胁。本文简要列述了各类灾害对国民经济建设和人类生存的危害性,论述了灾害的分类和体系特征,探讨了灾害形成的科学机理,强调了开展多学科、大体系研究的重要意义。同时结合国土环境遥感调查,提出了开展灾害学研究、监测防御、减灾抗祸的对策和建议,以期发挥现代地球科学理论与遥感技术的潜力,为促进灾害学的研究、保障人类更好地生存与发展作出贡献。 相似文献
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Chigurupati Murali & Scott Tremaine 《Monthly notices of the Royal Astronomical Society》1998,296(3):749-762
We determine the response of a self-similar isothermal stellar system to small adiabatic gravitational perturbations. For odd spherical harmonics the response is identical to the response of the analogous isothermal fluid system. For even spherical harmonics the response can be regarded as an infinite series of wavetrains in log r , implying alternating compression and rarefaction in equal logarithmic radius intervals. Partly because of the oscillatory nature of the solutions, tidal fields from external sources are not strongly amplified by an intervening isothermal stellar system, except at radii ≲10−3.5 times the satellite radius; at some radii the stellar system can even screen the external tidal field in a manner analogous to Debye screening. As Weinberg has pointed out, individual resonances in a stellar system can strongly amplify external tidal fields over a limited radial range, but we cannot address this possibility because we examine only adiabatic perturbations. We also discuss the application of our method to the halo response caused by the slow growth of an embedded thin disc. 相似文献
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直接测量恒星形成区的距离;从而确定银河系的旋臂结构以及银河系运动学的工作正在逐步展开.通过对恒星形成区脉泽的多历元VLBI观测,利用类星体和脉泽相位参考技术,精确地测定脉泽的位置、自行和视差.精确的距离能够确定旋臂的位置,从而建立银河系旋臂结构的新模型;运用绝对自行确定该处天体的三维运动,由此精确测定银河系的旋转曲线,... 相似文献
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对银河系内卫星星系进行全面的"人口普查"具有重要的意义。目前已经发现了二十几个卫星星系,其光度范围分布很广,最暗的矮星系比球状星体还暗。叙述了卫星星系的光度分布、空间分布和动力学性质。总结了观测和理论研究进展,并讨论了星流和伽玛射线在研究银河系结构和暗物质性质方面的贡献。表明了卫星星系的统计分布能用来很好地限制冷暗物质理论和星系形成的相关物理过程,同时指出当前研究的局限性和可能的发展方向。 相似文献
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Parama Roy 《Geoforum》2010,41(2):337-348
Arguments regarding citizen involvement and empowerment within neoliberal urban politics are ample in geographic literature. Existing discussions often define and evaluate empowerment as either some social, political, or economic end-product of a specific event. Such singular conceptualization is problematic. First, different kinds of social, political, and economic changes can simultaneously empower/disempower communities in contradictory ways. In addition, the view of empowerment as an end-product of a present event obscures a more nuanced understanding of empowerment as an ongoing process of state-civil society relation-building. An in-depth assessment of such a process is only possible with reference to the past and the potential future occurrences. Elwood’s (2002) multi-dimensional conceptualization of empowerment recognizes the limitations of a singular definition of empowerment. However, it falls short of operationalizing empowerment as a temporal process with a historically and geographically contingent past, dynamic present, and future in the making. Therefore, in this paper I expand on Elwood’s framework to show how a process-based view as opposed to a narrow end-product-based or event-based one can provide a deeper understanding of state-civil society interaction and community empowerment. This paper analyzes the interaction between the City of Milwaukee, the residents of a predominantly black inner-city neighborhood, the Walnut Way, and their community organization, the Walnut Way Conservation Corp. within a land-use dispute related to the development of a park space into a housing project. Using data collected through semi-structured in-depth interviews, archival research, and participant observation, this paper emphasizes that despite methodological limitations of collecting long-term data, community empowerment can and should be studied as a process with reference to the past, present, and potential future state-civil society interactions. 相似文献