MASINGA RESERVOIR IN KENYA：SEDIMENT DISCHARGE AND IMPLICATIONS FOR ITS CAPACITY     

F.A.O. Otieno 《国际泥沙研究》1996,(3)

ＭＡＳＩＮＧＡＲＥＳＥＲＶＯＩＲＩＮＫＥＮＹＡ：ＳＥＤＩＭＥＮＴＤＩＳＣＨＡＲＧＥＡＮＤＩＭＰＬＩＣＡＴＩＯＮＳＦＯＲＩＴＳＣＡＰＡＣＩＴＹ￥Ｆ．Ａ．Ｏ．Ｏｔｉｅｎｏ（ＳｅｎｉｏｒＬｅｃｔｕｒｅｒｉｎＣｉｖｉｌＥｎｇｉｎｅｅｒｉｎｇ，Ｕｎｉｖｅｒｓｉ...  相似文献   

Isotopic analyses of nitrogenous compounds from the Murchison meteorite: ammonia, amines, amino acids, and polar hydrocarbons     

Pizzarello S  Feng X  Epstein S  Cronin JR 《Geochimica et cosmochimica acta》1994,58(24):5579-5587

The combined volatile bases (ammonia, aliphatic amines, and possibly other bases), ammonia, amino acids, and polar hydrocarbons were prepared from the Murchison meteorite for isotopic analyses. The volatile bases were obtained by cryogenic transfer after acid-hydrolysis of a hot-water extract and analyzed by combined gas chromatography-mass spectrometry of pentafluoropropionyl derivatives. The aliphatic amines present in this preparation comprise a mixture that includes both primary and secondary isomers through C5 at a total concentration of > or = 100 nmoles g-1. As commonly observed for meteoritic organic compounds, almost all isomers through C5 are present, and the concentrations within homologous series decrease with increasing chain length. Ammonia was chromatographically separated from the other volatile bases and found at a concentration of 1.1-1.3 micromoles g-1 meteorite. The ammonia analyzed includes contributions from ammonium salts and the hydrolysis of extractable organic compounds, e.g., carboxamides. Stable isotope analyses showed the volatile bases to be substantially enriched in the heavier isotopes, relative to comparable terrestrial compounds delta D < or = +1221%; delta 13C = +22%; delta 15N = +93%). Ammonia, per se, was found to have a somewhat lower delta 15N value (+69%) than the total volatile bases; consequently, a higher delta 15N (>93%) can be inferred for the other bases, which include the amines. Solvent-extractable polar hydrocarbons obtained separately were found to be enriched in 15N (delta 15N = +104%). Total amino acids, prepared from a hydrolyzed hot-water extract by cation exchange chromatography, gave a delta 15N of +94%, a value in good agreement with that obtained previously. Nitrogen isotopic data are also given for amino acid fractions separated chromatographically. The delta 15N values of the Murchison soluble organic compounds analyzed to date fall within a rather narrow range (delta 15N = +94 +/- 8%), an observation consistent with their formation, or formation of their precursors, by interstellar chemistry.  相似文献   

基于随机有限断层模型的中国北京延怀地区1720年沙城地震(Ms7.0)强震动的三维有限差分模拟     

G.Q.Wang  X.Y.Zhou  李奇 《地球与行星物理论评》2020,51(5)

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亚洲岩石层是否俯冲到了青藏高原东北缘之下?从远震接收函数得到的启示     

X.Z.Shen  X.H.Yuan  M.Liu  李敏娟  钱银苹 《世界地震译丛》2018,(2)

亚洲岩石层是否俯冲到了青藏高原之下?这对于理解高原生长机制非常重要。我们使用来自青藏高原东北缘固定台站的地震波数据,利用P波和S波接收函数研究了青藏高原东北缘岩石层和上地幔的结构特征。P波和S波接收函数偏移成像结果显示,在青藏高原下面有一个厚的地壳和一个模糊的岩石层—软流圈边界(LAB),这与亚洲块体下方相对来说较薄的地壳和尖锐且清晰的岩石层—软流圈边界形成了鲜明对比。亚洲块体下清晰的岩石层—软流圈边界向青藏高原倾斜,但并没有显著延伸到青藏高原之下;这与俯冲到青藏高原之下的亚洲岩石层地幔模型是不一致的。相反,我们的结果表明亚洲岩石层的变形对于正在生长的青藏高原的响应是有限、被动的。  相似文献   

黄河上游盆地重组所导致的快速侵蚀下切     

W.H.Craddock  E.Kirby  N.W.Harkins  H.P.Zhang  X.H.Shi  J.H.Liu  贾伟 《世界地震译丛》2019,(4)

高起伏的造山高原边缘的快速剥蚀常被用来指代区域地表隆升~(1～3)。然而,诸如岩体隆升的空间差异~4,降雨的地形效应以及冰川~5、滑坡导致的河道堵塞~(6,7)等阻碍河流下切的因素,可能会使剥蚀作用严重滞后于地表抬升~8。本文中,我们通过研究青藏高原东北缘黄河沿岸沉积盆地的地层学、年代学和地貌学特征,重建黄河上游侵蚀下切的时间、速率以及模式。我们发现河流下切的起始时间明显晚于山体开始隆升的时间(14～8Ma)~9。高原边缘的河流下切始于1.8Ma~(10),然后以大约350km/Ma的速度向上游传递~(11)。我们认为该地区在气候驱动下的湖泊扩张并溢出作用是黄河上游快速下切的主要原因,并最终导致了现代黄河地貌的形成。  相似文献   

对《中国国家自然地图集》的评价     

O.A.叶夫捷耶夫  T.B.科托娃  B.C.吉库诺夫  JI.X.延瓦烈娃 《地球信息科学学报》2000,2(3):70-71

1999年出版了中国国家自然地图集,它是反映中国自然、社会、历史、经济和文化系列国家地图集的一部分。该图集用中(2500册)英(1000册)文出版。中国国家自然地图集的工作在1956年由周恩来总理直接领导编制的“科学发展十二年规划”中就开始了。于1958年开始图集的设计工作。按设计要求,图集由四卷组成:即普通地图集、自然地图集、历史地图集、经济地图集。1965年出版了中华人民共和国自然地图集。普通地图集没有全部完成,于1969年出版了“中华人民共和国分省地图”。  相似文献   

Risks posed by trace organic contaminants in coastal sediments in the Pearl River Delta, China   总被引：8，自引：0，他引：8  

Fung CN  Zheng GJ  Connell DW  Zhang X  Wong HL  Giesy JP  Fang Z  Lam PK 《Marine pollution bulletin》2005,50(10):1036-1049

Local marine environments in China's Pearl River Delta (PRD), the most rapidly developing region in one of the world's fastest growing economies, have been experiencing significant environmental stress during the past decades. This investigation was conducted to determine the status and trends of persistence organic pollutants (POPs) such as polycyclic aromatic hydrocarbons (PAHs), petroleum hydrocarbons (PHCs), polychlorinated biphenyls (PCBs), organochlorine (OC) pesticides and dioxin-related compounds in marine sediments collected from sixteen coastal stations in the Pearl River Delta (PRD) in March 2003. Elevated concentrations of PAHs (94-4300 ng/g), PCBs (6.0-290 ng/g), PHCs (14-150 microg/g), and DDTs (1.4-600 ng/g) were detected in sediment samples. In addition, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like activities in the sediment samples were estimated to range from 0.3 to 440 pg TCDD-EQ/g. Sediments collected from Xiashan contained the greatest concentrations of trace organic contaminations amongst all the sampling stations in the present study. The degree of trace organic contamination was, in general, more severe at stations situated along the west shores of the PRD than their counterparts in the east. A preliminary assessment was performed to examine the probable risks to the marine ecosystem due to POPs. The results showed that OC pesticide contamination in the PRD was particularly serious and might pose a threat to the health of the marine inhabitants.  相似文献   

Bioenergetic responses in green lipped mussels (Perna viridis) as indicators of pollution stress in Xiamen coastal waters, China     

Wang S  Hong H  Wang X 《Marine pollution bulletin》2005,51(8-12):738-743

Samples of green lipped mussels (Perna viridis) were collected from three sites (Huoshao, I’Maluan and Tong’an) around Xiamen coastal waters, where levels of various trace organic pollutants have been studied. Samples were also collected at a “cleaner” reference site near Dongshan Island for comparison. Clearance rate, absorption efficiency and oxygen consumption of the mussels were measured under controlled laboratory condition; organic pollutants in their tissues were also analyzed. Scope for growth (SFG) was employed as a general biomarker to evaluate the stress of pollutants. Specimens from Tong’an site had the lowest SFG values (1.14 J/h/g); while specimens from the I’Maluan site and Huoshao site had SFG values of 5.01 and 6.72 J/h/g, respectively. Specimens from Dongshan (reference site) had a relatively high SFG value of 10.96 J/h/g. There was a significant negative correlation between the SFG of the different populations of green lipped mussels and the concentration of DDT in their tissues.  相似文献   

Porphyry and Skarn Cu-Mo-Pb-Zn-Ag-Au Metallogeny of the Gangdise Plutonic-Volcanic Arc, Tibet     

Gu X. X.  Tang J. X.  Wang C. S. WT  ”BX 《地学前缘》2000,(Z1)

PORPHYRY AND SKARN Cu-Mo-Pb-Zn-Ag-Au METALLOGENY OF THE GANGDISE PLUTONIC -VOLCANIC ARC, TIBETtheNational973Project“MetallogenicBackgroundandProspectiveEvaluationoftheGangdiseBelt”  相似文献   

The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data     

Tsvetanov ZI  Golimowski DA  Zheng W  Geballe TR  Leggett SK  Ford HC  Davidsen AF  Uomoto A  Fan X  Knapp GR  Strauss MA  Brinkmann J  Lamb DQ  Newberg HJ  Rechenmacher R  Schneider DP  York DG  Lupton RH  Pier JR  Annis J  Csabai I  Hindsley RB  Ivesic Z  Munn JA  Thakar AR  Waddell P 《The Astrophysical journal》2000,531(1):L61-L65

We report the discovery of a second field methane brown dwarf from the commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS J134646.45-003150.4 (hereafter SDSS 1346-00), was selected because of its very red color and stellar appearance. Its spectrum between 0.8 and 2.5 μm is dominated by strong absorption bands of H2O and CH4 and closely mimics those of Gliese 229B and SDSS 162414.37+002915.6 (hereafter SDSS 1624+00), two other known methane brown dwarfs. SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that it lies about 11 pc from the Sun. The ratio of flux at 2.1 μm to that at 1.27 μm is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which suggests that SDSS 1346-00 has a slightly higher effective temperature than the others. Based on a search area of 130 deg2 and a detection limit of z*=19.8, we estimate a space density of 0.05 pc-3 for methane brown dwarfs with Teff approximately 1000 K in the 40 pc3 volume of our search. This estimate is based on small-sample statistics and should be treated with appropriate caution.  相似文献