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Dynamic environment near heterogeneous asteroids is worth studying since many small bodies have varied internal structures. In this paper, we investigated the effect of temporary resonance with the heterogeneous Itokawa. Zero-power curves divide the space into four regions. The test particle experiences orbital energy-enhancing in the Region I and Region III, but receding in the Region II and Region IV. Moreover, there are differences in zero-power curves between the heterogeneous and homogeneous cases. The absolute values of gravity power in the gravitational field of heterogeneous Itokawa are more significant than those of the homogeneous one. It means the particle suffers from stronger energy change near the heterogeneous body. Numerical simulations conducted in Region II and Region III verify the difference. Thus, vicinal ejecta is easier to run away from a heterogeneous Itokawa, which may lead to a more frequent exchange of materials on the surface. These results give a better understanding of dust’s motion near a heterogeneous body. Moreover, the performance of temporary resonance near a heterogeneous body might serve as a guiding principle for probe orbiting an asteroid with a varied internal structure. 相似文献
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Stalagmites are good archives for paleoecological change, as they are easy to date, and contain multiple environmental proxy records, including climatic records from oxygen isotopes. Lipid biomarkers preserved within stalagmites have recently been used to investigate changes in the overlying soil and vegetation. However, the understanding of lipid records from stalagmites is still at an early stage, and is hindered by the low abundances of lipids preserved and the complexity of the organic matter signal. Here the first results of a sequential extraction procedure are presented, that enables examination of the distribution patterns of “free” (solvent extraction) and “bound” (including physically bound within the calcite matrix and chemically bound to macromolecules) lipids in a stalagmite from southern China. In both groups the dominant compounds are saturated fatty acids, which are an order of magnitude more abundant in the “bound” phase. n-alkanes and n-alcohols chiefly appear in the “free” lipids. In contrast, 3-hydroxy acids are predominantly released under strong acid reflux conditions, suggesting a principal input from bacterial membrane compounds. A direct comparison between the present results and the published data from an Ethiopian stalagmite shows significant differences in the lipid signals from separate sites, with a stronger microbial signal in the Chinese sample. This preliminary investigation of lipid distributions in different modes highlights the importance of microbial geochemical processes in karst systems and supports the use of stalagmites in paleoecological reconstruction. 相似文献
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以三峡库区秭归-巴东段为例,将地理加权回归(GWR)模型引入到研究区的空间尺度分割方法中,利用粒子群优化(PSO)算法对支持向量机(SVM)模型参数进行优化,构建GWR-PSO-SVM耦合模型,完成研究区滑坡易发性评价,并与传统的PSO-SVM耦合模型结果进行对比。结果表明,在特定类别精度分析、总体预测精度分析和曲线下面积分析中,本文方法评价效果均优于传统方法。 相似文献
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Xianyu Xue Jonathan F. Stebbins Masami Kanzaki 《Physics and Chemistry of Minerals》1993,19(7):480-485
Stishovite, a high-pressure SiO2 polymorph in which each Si is coordinated by six O atoms, transforms to an amorphous phase when undergoing heat treatment below the glass transition temperature at ambient pressure. We have applied 29Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) to study this amorphization process. We found that the amorphous phase generated after heating stishovite for up to 3 days at around 600 ° C consisted exclusively of four-coordinate Si, similar to glasses quenched from melts at ambient pressure. Furthermore, our data suggest that there are subtle structural differences between the amorphous phase transformed from stishovite at 600 ° C and glasses quenched from melts at ambient pressure: the amorphous phase from stishovite had a smaller mean Si-O-Si angle initially, and it gradually relaxed toward the latter with increasing heating time. There was no detectable change in the stishovite structure even after about 80% of it had been converted to the amorphous phase. The mechanism of the amorphization of stishovite is discussed in light of these results. 相似文献
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Yin Hongfu Feng Qinglai Xie Shucheng Yu Jianxin He Weihong Liang Handong Lai Xulong Huang Xianyu 《Frontiers of Earth Science》2007,1(2):129-141
This is a review of research achievements on the Permian-Triassic transition in South China. It comprises of five parts: (1)
advances on the biostratigraphy and eventostratigraphy of the Meishan Section, the Global Stratotype Section and Point (GSSP)
of the Permian-Triassic boundary (PTB); (2) advances on the PTB research of deep water facies, especially the Dongpan Section
in Guangxi; (3) advances on the PTB research of terrestrial facies, especially the Chahe Section in Guizhou; (4) correlation
of the global change and biotic extinction between the PTB and modern times and its revelation to the status and future of
the earth and mankind; and (5) the pattern and causality of the Permian-Triassic extinction. In the last part, it is concluded
that the Permian-Triassic transitional interval constitutes a prolonged crisis period ranging from end-Guadalupian extinction
to the end of Early Triassic, totaling 14 Ma. The environmental crisis and mass extinction peaked at the PTB, which displayed
multiphase extinction rather than just one phase. Commencement of an extinctions prelude prior to the postulated bolide impact
implies that the causes of PTB extinction largely lie in the intrinsic developments of the earth, especially those related
with the integration of Pangea. 相似文献
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湖北清江和尚洞洞穴滴水脂肪酸分布特征及其古生态意义 总被引：5，自引：4，他引：5
对采自湖北省清江和尚洞滴水样品,采用XAD大孔径树脂吸附法及气相色谱-质谱联用仪(GC-MS)检测出种类丰富的脂肪酸,包括直链(nC12:0～nC30:0)与支链(iC14:0～iC26:0,及aC15:0和aC17:0)饱和脂肪酸,直链单不饱和脂肪酸(nC15:1,nC16:1,nC17:1和nC18:1),多不饱和脂肪酸(nC18:2)及微量的支链不饱和脂肪酸(iC17:1).滴水脂肪酸分布特征显示有机质以微生物来源为主,兼有高等植物贡献.占优势的偶碳直链饱和脂肪酸(主要是nC16:0,nC18:0和nC14:0),含量相对较高的单不饱和脂肪酸及多不饱和脂肪酸可能主要来源于地下水微藻.滴水中还检出含量较高的nC17:1和nC15:1及微量的iC17:1和iC15:1,它们很可能来自洞顶土壤厌氧层中的硫酸盐还原菌.洞顶土壤、滴水与现代石笋碳酸钙沉积脂肪酸分布对比揭示,石笋有机质主要来源于土壤,也有地下水微生物及洞穴原地微生物贡献. 相似文献
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TIAN Jian XIN Houtian TENG Xuejian DUAN Xiaolong CHENG Xianyu ZHANG Yong REN Bangfan 《《地质学报》英文版》2020,94(4):1256-1275
The tectonic attributes of different blocks within orogenic belts are of great significance for the study of accretionary processes and the evolution of Earth. The Hongliuhe-Niujianzi-Baiyunshan-Xichangjing ophiolitic mélange belt(HXOMB) is distributed in the heart of the Beishan Orogen, the Shuangyingshan and Minshui-Hanshan blocks being distributed in the south and north of the HXOMB respectively, and a large number of Early Paleozoic geological units are exposed on the blocks. According to the zircon age populations of the metasandstones in the Baiyunshan area recovered in this paper, when compared with the zircon age populations of the Paleozoic metasandstones reported in the Niujuanzi and Hanshan areas, we found that the metasandstones of the Shuangyingshan Block have age peaks at c. 598 Ma, 742 Ma, 828 Ma, 941 Ma, 990 Ma, 1168 Ma, 1636 Ma, 2497 Ma with non-significant age populations of 1500–1300 Ma, showing a possible affinity with the Tarim Craton; the metasandstones of the Minshui-Hanshan Block have age peaks at c. 606 Ma, 758 Ma, 914 Ma, 1102 Ma, 1194 Ma, 1304 Ma, 1672 Ma with significant age populations of 1500-1300 Ma, showing a possible affinity with the Chinese Central Tianshan Block. Therefore, the HXOMB of the Beishan Orogen is of great significance in plate segmentation, which separates the Tarim Craton in the south and the Chinese Central Tianshan Block in the north. Based on the evolutionary process of the Hongliuhe-Xichangjing ocean in the Beishan Orogen, we believe that break-up and convergence can be recognized as having occurred twice between the Chinese Central Tianshan Block and the Tarim Craton since the Mesoproterozoic in the Beishan area. This was related firstly to the break-up of the Columbia Supercontinent and the convergence of the Rodinia Supercontinent, mainly during the Middle Mesoproterozoic to Early Neoproterozoic, and secondly to the opening and closing of the Hongliuhe-Xichangjing ocean, mainly during the Early Paleozoic. 相似文献