Perihelion motion of small irregular dust particles due to radiation forces

Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust particles is investigated under the action of solar gravity and solar electromagnetic radiation. As for spherical particle [Kla?ka, J., 2004. Electromagnetic radiation and motion of a particle. Cel. Mech. Dynam. Astron. 89, 1-61]: (i) perihelion motion is of the order ( is heliocentric velocity of the meteoroid and c is the speed of light in vacuum), if a component of electromagnetic radiation acceleration is considered as a part of central acceleration; (ii) perihelion motion is of the first order in if the total electromagnetic radiation force is considered as a disturbing force. The new facts presented in this paper concern irregular dust particles. Detailed numerical calculations were performed for the grains ejected at aphelion of comet Encke. Perihelion motion for irregular interplanetary dust particles exists already in the first order in for both cases of central accelerations. Moreover, perihelion motion of irregular particles exhibits both positive and negative directions during the particle orbital motion. Irregularity of the grains causes not only perihelion motion, but also dispersion of the dust in various directions, also normal to the orbital plane of the parent body.     

中国古代中心日食记载与地球自转速率的变化

利用中国古代中心日食（全、环食）的观测记载研究近2千余年间地球自转速率长期变化的原理和方法,讨论了中国古代中心日食和近中心日食观测的记载资料,并利用其中可靠的记载和-26.0″/（100a）²的月球本征加速度值计算得到了表示地球自转长期变化的△T值系列,由此得到表示地球自转长期减慢的日长变化均值约为1.4ms/100a,该平均值相应的历元为A.D.1141。     

Recognition of the hydrogeological potential using electrical sounding in the Khemisset-Tiflet region,Morocco

The low recharge of reservoirs and the increasing demand for water limit the potential of mobilized resources, especially in arid to semi-arid areas like Morocco. Integrated management is essential to safeguard this resource. In respect with this perspective, this work provides the analysis of hydrogeological potential of Khemisset-Tiflet region, which falls within the action area of the Sebou Hydraulic Basin Agency. The basis of our studies was as follows:(1) The interpretation of the existing geoelectric data;(2) application of geophysical methods for non-destructive reconnaissance and their integration into a Geographic Information System(GIS). The analysis demonstrates that: The map of the isohypses and the geoelectric cross-section of the substratum of the superficial roof aquifer show clearly a plunge associated with development of the Paleozoic roof in the South and the direction of flow of the surface water is from south to north, from the upper zone to the north of the El Kansera dam. These conclusions constitute very useful contribution for any resource management projects in this area.     

Characterisation of the non-asphaltene products of mild chemical degradation of asphaltenes

The major steranes of the non-asphaltene fraction of Nigerian tar sand bitumen (maltene) are the c₂₇-c₂₉ diasteranes [13β(H),17α(H); 20R + S] and C₂₈-C₂₉ regular steranes [14β (H),17β (H); 20S]. The reducing metal reaction products of the corresponding asphaltenes (maltene-I) contain mainly C₂₇-C₂₉ regular steranes with the 14β(H),17β(H); 20R + S and 14α(H),17α(H); 20R + S configurations as well as the corresponding diasteranes having the 13β(H),17α(H); 20R + S configuration. These sterane distributions suggest that maltene-I corresponds to an unaltered oil whilst the maltene is equivalent to the product of severe biodegradation of maltene-I. This is consistent with maltene-I being the remnant of “original oil” trapped within the asphaltene matrix and protected from the effect of in-reservior biodégradation.Degradation of Nigerian asphaltenes by refluxing with ferric chloride-acetic anhydride or methanolic potassium hydroxide also releases soluble reaction products having the characteristics of unaltered oil such as the presence of n-alkanes having an unbiased distribution. These methods appear to be milder and more suitable than reducing metal reactions for releasing hydrocarbons occluded by asphaltenes.     

Detrital footprint of the Mozambique ocean: U–Pb SHRIMP and Pb evaporation zircon geochronology of metasedimentary gneisses in eastern Madagascar

The southern East African Orogen is a collisional belt where the identification of major suture zones has proved elusive. In this study, we apply U–Pb isotopic techniques to date detrital zircons from a key part of the East African Orogen, analyse their possible source region and discuss how this information can help in unravelling the orogen.U–Pb sensitive high-mass resolution ion microprobe (SHRIMP) and Pb evaporation analyses of detrital zircons from metasedimentary rocks in eastern Madagascar reveal that: (1) the protoliths of many of these rocks were deposited between 800 and 550 Ma; and (2) these rocks are sourced from regions with rocks that date back to over 3400 Ma, with dominant age populations of 3200–3000, 2650, 2500 and 800–700 Ma.The Dharwar Craton of southern India is a potential source region for these sediments, as here rocks date back to over 3400 Ma and include abundant gneissic rocks with protoliths older than 3000 Ma, sedimentary rocks deposited at 3000–2600 Ma and granitoids that crystallised at 2513–2552 Ma. The 800–700 Ma zircons could potentially be sourced from elsewhere in India or from the Antananarivo Block of central Madagascar in the latter stages of closure of the Mozambique Ocean. The region of East Africa adjacent to Madagascar in Gondwana reconstructions (the Tanzania craton) is rejected as a potential source as there are no known rocks here older than 3000 Ma, and no detrital grains in our samples sourced from Mesoproterozoic and early Neoproterozoic rocks that are common throughout central east Africa. In contrast, coeval sediments 200 km west, in the Itremo sheet of central Madagascar, have detrital zircon age profiles consistent with a central East African source, suggesting that two late Neoproterozoic provenance fronts pass through east Madagascar at approximately the position of the Betsimisaraka suture. These observations support an interpretation that the Betsimisaraka suture separates rocks that were derived from different locations within, or at the margins of, the Mozambique Ocean basin and therefore, that the suture is the site of subduction of a strand of Mozambique Ocean crust.     

地图代数在用地选址模拟中的应用——以大庆地区为例

在哈大齐工业走廊用地总体规划中,大庆市共开发340.9km2,其中盐碱地达320km2。本文利用GIS的空间分析(Spatial Analyst)模块建立选址模型,以地图代数为分析语言,在栅格数据(Grid)的环境下,用层次分析法(AHP)来确定权重,对大庆地区的工业用地选址情况进行模拟,当适宜度value≥8.38,我们已获得的土地面积达到362.07km2。结果表明在栅格数据的环境下,以GIS地图代数进行用地选址,科学性强、易于在计算机上实现,具有良好的效果。     

中高纬大气环流异常和低纬30～60天低频对流活动对南海夏季风爆发的影响

利用1979-2003年NCAR/NCEP-2再分析全球日平均资料,及1979～2003年全球候平均的CMAP降水和NOAA日平均的向外长波辐射资料,分析了中高纬大气环流异常和低纬30～60天低频对流的活动对南海夏季风爆发迟早的影响.分析结果表明,当5月1～15日期间乌拉尔山及其以西地区对流层出现位势高度负距平(低频气旋)、中纬度大陆为位势高度正距平(低频反气旋)、我国东部沿岸地区为位势高度负距平(低频气旋)、鄂霍次克海地区为位势高度正距平(低频反气旋)时,副热带高压脊较早撤出南海,与此同时,孟加拉湾东部低频对流活跃东传,菲律宾南部周围低频对流发展西移,华南地区低频对流活动南移以及加里曼丹低频对流活跃北移.在这种情况下,南海夏季风爆发偏早.相反,当5月1～15日期间乌拉尔山及其以西地区对流层出现位势高度正距平(低频反气旋)、中纬度大陆为位势高度负距平(低频气旋)、我国东部沿岸地区为位势高度正距平(低频反气旋)、鄂霍次克海地区为位势高度负距平(低频气旋)时,副热带高压脊撤出南海较迟; 与此同时,孟加拉湾东部低频对流不活跃、东传晚,菲律宾南部周围低频对流不活跃、其西移与孟加拉湾东部低频对流的东传反位相,华南地区低频对流活动也不活跃,加里曼丹低频对流较弱.在这种情况下,南海夏季风爆发偏迟.     

Contemporary Refugee‐Border Dynamics and the Legacies of the 1919 Paris Peace Conference

While the geopolitical legacies of the World War I peace negotiations are widely recognized, this article examines the often overlooked connection between the WWI Paris Peace Conference's spatial and geopolitical logics and contemporary refugee‐border dynamics. We argue that the spatial and geopolitical logics that framed the WWI Paris Peace Conference—the creation of new states, the propagation of the Western ideal of bounded sovereign states, the nationalist goals of self‐determination and homogeneous ethnic nations, and the establishment of a system of international governance—continue to impact refugee‐border dynamics and “crises” today. The categories, ideals, and practices of the international refugee regime that emerged over the last one‐hundred years stem in great part from these logics. In this paper, we urge critical contemplation about how these foundations—including the establishment of the post of High Commissioner for Refugees in 1921, the resultant Nansen Passports, the post‐WWI minority treaties, and lastly the 1933 Convention Relating to the International Status of Refugees—connect to contemporary human (im)mobility and border violence. We also introduce the articles in this special issue and highlight key themes and future directions for research in critical migration studies.     

柴达木盆地宗马海湖地区钾盐矿床成矿规律与成矿预测研究

研究区位于柴达木盆地北部边缘,属柴达木盆地中—新生代盐类成矿区。该次研究了浅部、中深部及深层储层特征、卤水钾盐的赋存规律及构造控矿理论。浅部卤水钾盐依据KCl含量,分为工业品位区、边界品位区、有浅层卤水区及无浅层卤水区。中深部卤水钾盐分布于山间古冲洪积平原(Ⅰ■)和马海湖次级洼陷(Ⅰ■)中,矿层厚度较大的区域在马海湖次级洼陷(Ⅰ■)北部,主要分布于全新统—更新统含盐系中,计算深度297.22m。深部卤水钾盐,厚度较薄者分布于冷湖六号、冷湖七号构造以北地区的一层至数层的砂岩及砂砾岩层中,自南东向北西由深变浅,分布于上新统,含卤水层段厚约50～250m。厚度较大者分布在赛什腾山山前冲洪积带,北至驼南断裂,南大致至ZK4012孔一线,孔隙卤水层累计深度达1265.14m,分布于全新统—上新统,是今后寻找深层卤水钾盐矿最重要的找矿区域。     

共轭伸展褶劈理夹角的定量解析

９０ 年代初以来,中国地质学者先后在浙、皖、赣、湘的“板溪群”及震旦系中发现了古生代的生物化石。因此,再次将“板溪群”是否是前震旦纪的一个变质地层单位、江南古陆是否存在以及华南大地构造格局是否需要重新厘定等问题提了出来。１９９３ 年笔者于赣东北蛇绿混杂岩带内的“双桥山群”岩块中,首次发现了含晚古生代的放射虫硅质岩。１９９６ 年又在该混杂岩带多处的“双桥山群”岩块和“下震旦统志棠组”中找到了含晚古生代的放射虫硅质岩,还首次在“登山群拔竹坑组”中发现了早古生代的几丁虫化石。经数年野外多次观察和对室内化石鉴定、岩石地球化学测试结果以及岩石学特征的综合分析表明,所发现的含晚古生代放射虫硅质岩及其岩石组合是一套洋盆深水相沉积;登山群拔竹坑组,是早古生代的一套浅水陆棚 深水陆棚 半深海相沉积。结合同行学者在邻区“板溪群”研究方面取得的新成果,笔者认为：“板溪群”不是前震旦纪的一个变质地层单位,而是一个复杂的构造岩带,江南古陆是不存在的,华南从早古生代到中生代早期还经历了一次洋盆演化过程,现在的构造格局是印支运动奠定的