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991.
M. Yan A. Dalgarno W. Klemperer A. E. S. Miller 《Monthly notices of the Royal Astronomical Society》2000,313(2):L17-L18
The origin of the strong CO Cameron band emission in the Red Rectangle is investigated. From a comparison of laboratory spectroscopic data and astronomical observations in combination with chemical modelling, it is concluded that the Cameron band emission of CO originates from the dissociative recombination of HCO+ , and its intensity provides a measure of the product of the density of HCO+ ions and the electron density, integrated along the line of sight. 相似文献
992.
The possibility of nitrogen isotopic fractionation owing to ion–molecule exchange reactions involving the most abundant N-containing species in dense interstellar clouds has been explored. We find that exchange reactions between N atoms and N-containing ions have most influence on the fractionation, although the extent of fractionation is too small to be readily detectable. 相似文献
993.
Totally 2472 grains of Radiolaria belonging to 36 Genera and 45 species are distinguished from 12 surface sediments in the Bering Sea. The distribution characteristics of Radiolaria fossils in the surface sediments are as follows: (1) From the shelf of shallow water to the upper of continental slope, there are a few Radiolaria fossils and monotonous genus and species; (2) In the lower of continental slope, Radiolaria fossils are poor in the volcanic cinders and turbidite; (3) The abundance and diversity of Radiolaria fossils are high in clay of the basin. The dominant species of Radiolaria is Spongotrochus glacialis on the continental shelf. Current, topography, water depth, and temperature etc. are key factors influencing Radiolaria distribution. The sources of sediments mainly are terrigenous, biogenic and volcanic sediments in the survey area and they are mostly from the Kamchatka peninsula in the east of Russia and the Aleutian Islands. 相似文献
994.
995.
Ewa Kolaczkowska Nacer-Eddine Slougui David S. Watt Robert E. Maruca J. Michael Moldowan 《Organic Geochemistry》1990,16(4-6)
The thermodynamic stability of selected alkylated, dealkylated and rearranged 17α- and 17β-hopane isomers in the C27, C28, C29, C30 and C31 families were calculated using molecular mechanics (MM2) methods and, where possible, calculated equilibrium ratios of certain isomers were compared with observed ratios of isomers in thermally mature crude oil samples. Those calculated and observed ratios having similar values include: (1) the relative distributions among 17β(H)/17α(H) and 21β(H)/21α(H)-hopanes including the absence of the 17β(H),21β(H)- and 17α(H),21α(H)-hopanes; (2) the 22R/22S ratios in 30-methyl-17α-hopane and 30-methyl-17β-moretane; (3) the relative distributions among 17α(H)/17β(H)- and 21α(H)/21β(H)-28,30-bisnorhopanes and among 25,28,30-trisnorhopanes, including the relatively greater stability of 17β(H) isomers in contrast to the regular hopane series; and (4) the ratios of 28(18−17S)abeo hopanes with respect to their unrearranged counterparts including the C27 compounds, Ts/Tm. 相似文献
996.
997.
Based on experimental and observational evidence, a mode of origin involving evaporative fractionation is proposed for a class of petroleums enriched in light aromatic and naphthenic hydrocarbons (benzene, toluene, meta-xylene, para-xylene, methylcyclopentane, cyclohexane, and methylcyclohexane). Progressive gas loss from gas-saturated oil is suggested as the causal mechanism, with simultaneous loss of light ends in gaseous solution, and accompanying fractionation. These processes were simulated experimentally.Residual oils exhibit the following changes in their remaining light hydrocarbons, <C9: (1) increase in aromaticity (in aromatic hydrocarbons relative to normal alkanes of molecular weight); (2) increase in “normality” (in unbranched alkanes and naphthenes relative to branched isomers), and (3) decrease in paraffinicity (in paraffins relative to naphthenes). Retrogressive changes in maturity indicators take place leading to spurious evidence of immaturity in residual oils and the derived evaporative condensates.The phenomena occur in many basins, and are a key to understanding major aspects of petroleum variability. On the basis of aromaticity and paraffinicity relationships, evaporative gas-condensates are distinguishable from those generated by thermal cracking. Unfractionated thermal gas-condensates are rare. Evaporative condensates are the daughter products of oils which have suffered evaporative fractionation. 相似文献
998.
在周家油房等地采集到披毛犀(Coelodonta antiquitatis Blumenbach),猛犸象(Mammuthus),野牛(Bison),鼢鼠(Myspalax)等化石。并在二级阶地觅到这一动物群的主要成员——野马(Equus)化石。证实这一动物群埋藏于松花江第二级阶地松散堆积物中。通过C~(14)同位素年龄测定,测得猛犸象门齿年龄距今39400±250年,猛犸象肢骨年龄距今30810±1385年,进一步说明这一动物群生存于晚更新世晚期,与化石产出地层时代吻合。发现的旧石器石片,原料为黑矅岩,从石片的形态、打击特点,都表明当时人具有较高的打片水平。这是迄今该区发现的最好的石片。 相似文献
999.
1000.
安徽休宁陡山沱期后生植物化石的新认识 总被引:11,自引:3,他引:8
本文对中国安徽省休宁地区震旦纪陡山沱期蓝田组的化石资料进行了综述,报道了类似现代某些高等藻类的生殖托化石结构和类似孢子囊裂开的化石结构,以及可能是合子萌发成胚,再发育成底栖固着的藻类成体的个体发育现象,这一现象为进一步探讨高等藻类世代交替的生活历史提供了有益的线索,是后生藻类植物性别分化的宏观化石证据。 相似文献