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1.
The presence and compositions of atmospheres on the terrestrial planets do not follow directly from condensation models which would have Earth accreting near 500°K. No single mechanism yet proposed adequately accounts for the abundances of noble gases and carbon and nitrogen in the atmospheres. We show that the composition of clathrates forming at low temperatures in cold regions of the nebula can be predicted. Addition of about 1 ppm clathrate material to the Earth can explain observed abundances of Ar, Kr, and Xe. Condensation and adsorption processes occuring at 400–500°K are necessary to explain the observed abundances of Ne, H2O, C, and N. Possible sources of clathrates could be cometary bodies formed in the outer solar system. 相似文献
2.
Godfrey D. Mudimu 《Singapore journal of tropical geography》1997,17(2):179-194
The growing of crops on open and undeveloped spaces within urban zones in eastern and southern African cities has become an important source of food security. Urban populations have expanded without a corresponding increase in economic opportunities for employment. Economic reforms have led to the removal of subsidies on food commodities and retrenchments in the formal employment sectors. It is reported that a result of this is that vulnerable households have resorted to urban agriculture to sustain their livelihoods. Though a widespread practice, urban agriculture is not planned for or supported by urban planners and managers as a legitimate form of urban land use in Harare, Zimbabwe. As women are the main participants in urban agriculture, their activities come into direct conflict with planning provisions for urban space. This study examines the role of women in urban agriculture and views and perceptions of the use of urban space for agricultural activities in Harare. It shows that urban agriculture is useful in meeting household food needs by those who undertake it. The study offers empirical insight on the perceptions of the use of space in an urban tropical environment for agriculture, where conflicts can arise as a result of different perceptions and alternative uses. 相似文献
3.
中国东南大陆晚侏罗世地层普遍缺失,仅零星见于个别地区,香港新界东北的荔枝庄组即为其一。荔枝庄组出露于香港世界地质公园沉积岩园区的荔枝庄地区,自下往上由火山岩—沉积岩—火山岩组合而成,沉积岩中发育大型包卷层理和滑塌构造等典型沉积构造,是香港地区最具代表性的晚侏罗世火山—沉积岩系。通过实测地层剖面研究,确定其成岩过程大体上可划分为早期普林尼式火山爆发、中期破火山口湖相沉积和晚期普林尼式火山爆发三个阶段,以湖相沉积作用为主、火山喷发作用为辅;受晚期火山岩浆活动的影响,沉积岩层普遍发生硅化或炭化。荔枝庄组独特的岩石组合与形成的古地理环境,为探讨中国东南大陆中生代火山活动—沉积作用方式与成岩过程,提供了难得的研究实例。 相似文献
4.
Rob M. Ellam Brian G. J. Upton J. Godfrey Fitton 《Contributions to Mineralogy and Petrology》1998,133(1-2):51-59
The Myggbukta caldera complex and a swarm of basic dykes constitute the latest Tertiary magmatism in the Hold with Hope region,
East Greenland. The Sr and Nd isotope ratios of these rocks show coherent variations which extend to high 87Sr/86Sr and low 143Nd/144Nd values and require a contribution from continental lithosphere. Broad correlations with major element differentiation indices
suggest that the continental component was incorporated during magmatic differentiation thereby favouring a crustal contamination
process. Trace element concentrations are strongly correlated with isotopic compositions but display ranges for many incompatible
elements which extend beyond likely crustal contaminant compositions. This is readily modelled by AFC processes in which the
dominant cause of trace element enrichment is the concentration effect of fractional crystallisation rather than the composition
of the contaminant. The simplest such models still require unrealistically high degrees of fractional crystallisation to explain
the ten-fold enrichment of some trace elements. This can be overcome if the primary magmas entering the crust already had
highly variable trace element compositions. Such variability is readily achieved if melts from different parts of the melting
column escape without thorough homogenization. An AFC model which incorporates variability in parental magma composition is
then able to simulate the range of compositions observed at Hold with Hope. This carries the implication that the variations
observed are more readily attributed to changes in uncontaminated parental magma than to variations in the composition or
amount of contaminant.
Received: 5 March 1998 / Accepted: 16 June 1998 相似文献
5.
Andrew E. Godfrey 《Environmental Geology》1977,2(1):43-50
Physiography has been studied in the United States for more than 75 years, but only recently has it been applied to land use
planning. Advantages of a physiographic approach are that it 1) focuses on the problems at the proper scale and conserves
energy, effort, and time by selecting the critical parameters, 2) stresses geologic structure and process as factors which
should control land use, and 3) presents data in a form which the non-geologically trained planner can easily understand.
In 1928 Fenneman delineated and described the provinces and sections of the United States. This paper proposes a classification
of smaller physiographic units and presents two examples of how they can be used for planning purposes. Below the section,
the units used in this paper are the subsection, the land type, and the topographic element. Subsections delineate areas of
distinct geologic structure or process whereas land types delineate ranges in the intensity of those processes. Topographic
elements delineate units with distinct ranges of slopes or shapes of slopes, such as concave or convex. 相似文献
6.
An Overview of Nowcasting Development, Applications, and Services in the Hong Kong Observatory 下载免费PDF全文
The Hong Kong Observatory (HKO) has been developing a suite of nowcasting systems to support op- erations of the forecasting center and to provide a variety of nowcasting services for the general public and specialized users. The core system is named the Short-range Warnings of Intense Rainstorm of Localized Systems (SWIRLS), which is a radar-based nowcasting system mainly for the automatic tracking of the movement of radar echoes and the short-range Quantitative Precipitation Forecast (QPF). The differential, integral (or variational), and object-oriented tracking algorithms were developed and integrated into the nowcasting suite. In order to predict severe weather associated with intense thunderstorms, such as high gust, hail, and lightning, SWIRLS was enhanced to SWIRLS-II by introduction of a number of physical models, especially the icing physics as well as the thermodynamics of the atmosphere. SWIRLS-Ⅱ was further enhanced with non-hydrostatic, high resolution numerical models for extending the forecast range up to 6h ahead. Meanwhile, SWIRLS was also modified for providing nowcasting services for aviation community and specialized users. To take into account the rapid development of lightning events, ensemble nowcasting techniques such as time-lagged and weighted average ensemble approaches were also adopted in the nowcasting system. Apart from operational uses in Hong Kong, SWIRLS/SWIRLS-Ⅱ was also exported to other places to participate in several international events such as the WMO/WWRP Forecast Demon- stration Project (FDP) during the Beijing 2008 Olympics Games and the Shanghai Expo 2010. Meanwhile, SWIRLS has also been transferred to various regional meteorological organizations for establishing their nowcasting infrastructure. This paper summarizes the history and the technologies of SWIRLS/SWIRLS-Ⅱ and its variants and the associated nowcasting applications and services provided by the HKO since the mid 1990s. 相似文献
7.
8.
Andrei M. Sobolev Edmund C. Sutton Dinah M. Cragg Peter D. Godfrey 《Astrophysics and Space Science》2005,295(1-2):189-196
In studies of the environment of massive young stellar objects, recent progress in both observations and theory allows a unified treatment of data for maser and quasi-thermal lines. Interferometric maser images provide information on the distribution and kinematics of masing gas on small spatial scales. Observations of multiple masing transitions provide constraints on the physical parameters.Interferometric data on quasi-thermal molecular lines permits an investigation of the overall distribution and kinematics of the molecular gas in the vicinity of young stellar objects, including those which are deeply embedded. Using multiple transitions of different molecules, one can obtain good constraints on the physical and chemical parameters. Combining these data enables the construction of unified models, which take into account spatial scales differing by orders of magnitude.Here, we present such a combined analysis of the environment around the ultracompact HII region in W3(OH). This includes the structure of the methanol masing region, physical structure of the near vicinity of W3(OH), detection of new masers in the large-scale shock front and embedded sources in the vicinity of the TW young stellar object. 相似文献
9.
收缩情境下城市用地结构时空格局演变及动力机制——以中国东北地区为例 总被引:3,自引:1,他引:2
构建城市用地结构时空格局演变分析框架,引入信息熵和偏移份额模型定量剖析2000—2017年中国东北地区城市用地结构时空格局演变特征,通过计量经济模型分阶段对比分析收缩情境下东北地区城市用地结构演变的动力机制。结果表明:东北地区城市用地总面积持续增长,用地结构信息熵整体呈现先上升、后下降的趋势。2011年以后,城市用地结构有序性、多样性不断提升,单一优势地类主导作用显著下降。公共设施用地、道路交通用地及绿地与广场用地为增长型地类,是东北地区城市用地规模扩张和结构演变的主要动因。用地结构竞争性偏移量具有显著的空间非均衡性,总体与辽中南和哈长两大城市群空间格局基本吻合,新增城市用地的集聚效应不断凸显。城市人口规模变迁、城市经济发展水平提升、产业结构升级与城市居住条件改善对城市用地结构演变具有显著的正向驱动作用。收缩情境下,各因素的拉动作用逐渐减弱,国家宏观政策的约束力不断增强,城市公共服务水平改善的强需求成为驱动用地结构演变的外在动力。 相似文献
10.
进入21世纪以来,全球生产网络(Global Production Net-work,GPN)研究非常深刻地展现了 Peter Dicken所描绘的"全球-地方矛盾".这个概念由Dicken在1994年发表于《Economic Geography》上的Roepke Lecture特邀文章中首次提出[1].作为过去20多年经济地理学的一个主要学术支柱,GPN研究经历了两个重要的理论发展阶段,即从早期的广泛而一般的GPN框架2-4]过渡到更加具备解释性的GPN 2.0理论[5-7].在GPN研究理论快速发展的这个时期里,Coe等首先提出了"战略耦合"这一关键而新颖的概念[4],并由Yeung对其进行了完善[8-10]. 相似文献