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21.
22.
M. Hajduková Jr. 《Earth, Moon, and Planets》2008,102(1-4):67-71
The hyperbolic meteor orbits among the 4,581 photographic and 62,906 radar meteors of the IAU MDC have been analysed using
statistical methods. It was shown that the vast majority of hyperbolic orbits has been caused by the dispersion of determined
velocities. The large proportion of hyperbolic orbits among the known meteor showers strongly suggests the hyperbolicity of
the meteors is not real. The number of apparent hyperbolic orbits increases inversely proportional to the difference between
the mean heliocentric velocity of meteor shower and the parabolic velocity limit. The number of hyperbolic meteors in the
investigated catalogues does not, in any case, represent the number of interstellar meteors in observational data. The apparent
hyperbolicity of these orbits is caused by a high spread in velocity determination, shifting a part of the data through the
parabolic limit. 相似文献
23.
在回顾电视传媒市场化改革的基础上,结合时空分析、标准距离法和决策树C5.0演算法,研究了2005―2015年4个直辖市和26个省会城市电视市场结构的空间格局演变及其影响因素。结果发现:电视市场空间格局存在3阶段变化特征,市场化发展期为南北差异格局,市场化推进期为东西差异格局,市场化深化期东西差异格局进一步细化;文化差异、电视传媒发展、市场的“马太效应”分别是3个市场化阶段电视市场结构空间格局演变的主要原因,市场化使电视市场结构从文化差异主导的空间格局演变为经济差异主导的空间格局。 相似文献
24.
《Geoforum》2017
In the current environment of austerity, social justice concerns are increasingly permeating the food security agenda. However, there is a need to clarify what it means to create socially just food systems conceptually and practically. To address this gap, this paper proposes an analytical framework to embed a more complex conceptualisation of justice in food security debates that also serves as a bridging device across competing narratives. This framework is mobilised to analyse the framing process of the UK media, which plays a key role in developing narratives that provide audiences with schemas for interpreting events. Results show the emergence of eleven frames which highlight different solutions to deliver food security. The application of the justice analytical framework evidences the contingent relationship between food security and justice claims and discusses how these food security frames address differently what counts as a matter of justice (including economic, socio-cultural and political dimensions) and who counts as a subject of justice, tackling issues around delimitation of scales and sites of justice. The analysis reveals polarised positions between whether the sites subject to justice should be individuals or structures and uncovers how political and global elements of justice are largely by-passed in food security debates. These conceptualisations of justice and associated policy recommendations neglect the potential for people to participate fully in the conditions and decisions that give rise to particular distributions of goods and bads in the first place; limiting the construction of shared responsibilities to deliver global and participative food justices. 相似文献
25.
Chicgoua Noubactep 《洁净——土壤、空气、水》2013,41(7):702-710
Water treatment with metallic iron (Fe0) is still based on the premise that Fe0 is a reducing agent. An alternative concept stipulates that contaminants are removed by adsorption, co‐precipitation, and size‐exclusion in a reactive filtration process. This article underlines the universal validity of the alternative concept. It is shown that admixing non‐expansive material to Fe0 as a pre‐requisite for sustainable Fe0‐based filtration systems. Fe0‐based filters are demonstrated an affordable, appropriate, and efficient decentralized water treatment technology. 相似文献
26.
高温高压岩石力学—历史,现状,展望 总被引:30,自引:2,他引:30
高温高压岩石力学是岩石力学的分支学科,它以固体地球介质(材料)的变形行为和机制为研究对象,与一般变形固体力学相比较,具有高温、高压、强约束、宽时域、大变形、以及固-液相互作用、物理效应-化学效应并存等特点。高温高压岩石力学是在经典连续介质力学的基础上,针对自身的特殊性,运用破裂学、摩擦学和流变学的研究成果,经过相当长时期的酝酿和积累,大致于本世纪七十年代建立并逐步发展起来的。它在岩石破裂、摩质力学 相似文献
27.
Gail Davies 《Geoforum》2000,31(4)
This paper develops a conceptualisation of institutional geographies through participation observation and interviews in the BBC’s Natural History Unit (NHU), and the approach of actor network theory. The methodological and theoretical tenets of actor network theory are examined for the insights they offer for understanding the achievements of this pre-eminent centre for the production of natural history films. The scope, scale and longevity of the NHU are analysed through the means by which localised institutional modes of ordering extend through space and over time. Drawing on empirical material, the paper outlines three different modes of ordering, which organise relations between actors in the film-making processes in different ways: prioritising different kinds of institutional arrangements, material resources and spatial strategies in the production of natural history films. Through these three modes of ordering, and through the topological insights of actor network theory, a series of overlapping and interlinked institutional geographies are revealed, through which the identity of the Unit as a centre of excellence for wildlife film-making is performed. 相似文献
28.
继本文作者对星际A型CH3CN与H2含超精细能级的碰撞过程的研究之后,又计算了星际分子云条件下E型CH3CN与H2的碰撞跃迁速率系数。为研究分子云与恒星形成区的物理、化学性质提供了有用的基础分子数据。 相似文献
29.
The evolution of the different chemical species are followed in a model of contracting interstellar cloud. The central density increases from n = 10 cm–3 diffuse initial cloud model to a dense cloud with central density number of n >- 105 cm–3 after a time of 1.2 × 107 yr. A network of 622 reactions has been involved. The chemistry of the cloud is integrated simultaneously with the hydrodynamic equations of contraction.The results predict that the different molecular species increase in abundance as the contraction proceeds. The species which enhance significantly are CO, HCO, CS and NO. The fractional abundances of many of the other molecular species increase distinctly with contraction, e.g. CH, C2H, CN, SO2, CO2, H2O, C2, NH3, HCN, SO, OCS and SN. The transformation of the initial diffuse cloud model with small abundances of molecular species to a dense molecular cloud with enhancement of the different molecular species is confirmed. The results predict good agreements of our results with both the observations and other theoretical studies. 相似文献
30.
L. Viktor Tóth András Horváth Jr. Lauri K. Haikala 《Astrophysics and Space Science》1995,233(1-2):175-179
We report on a comparative study of nearby shocked clouds with and without star formation, based on IRAS, HI(21cm), CO(1-0) NH3 (and other molecular line) observations. The dark clouds L1780 (no star formation) and L1251 (high SFE) are discussed here. Their density and velocity structure are compared with the predictions of the HD model of Horváth & Tóth (1995), Paper I. 相似文献