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The partitioning of stable carbon isotopes between calcite, graphite and CO2 was experimentally determined at temperatures from 500 to 1200 °C and 1 to 15 kbar pressure. Attainment of carbon isotope equilibrium in CO2-calcite runs was proven by achieving the same fractionation from isotopically opposite directions. The resultant CO2-calcite fractionation curve for carbon differs from Bottinga's calculation by 1.2 and confirms recent experiments of Chacko et al. and Mattey et al. In CO2-graphite experiments equilibrium fractions were extrapolated by applying the partial-exchange technique of Northrop and Clayton and by optimizing the contribution of surface reaction in graphite. CO2-graphite fractionations at temperatures up to 800 °C are in fair agreement with Bottinga's calculation, but yield a surprisingly high fractionation of 5 at upper mantle temperatures. The combination of CO2-calcite (carbon) and CO2-graphite fractionation results in a new experimentally determined calcite-grapite fractionation curve, expressed by the equation:
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Williams James H. Wilson Thomas M. Horspool Nick Lane Emily M. Hughes Matthew W. Davies Tim Le Lina Scheele Finn 《Natural Hazards》2019,96(3):1167-1211
Natural Hazards - Tsunamis can have severe impacts on society. In addition to casualties and damage to buildings, they can also damage and disrupt critical infrastructure. To support effective risk... 相似文献
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Yuhan Ji Song Gao Tam Huynh Chris Scheele James Triveri Jacob Kruse Collin Bennett Yicheng Wen 《Transactions in GIS》2023,27(3):663-685
Large-scale trajectory data offer a finer lens into the regularity in individual mobility choices. Previous studies have exerted efforts to measure the regularity in people's location visiting patterns. However, the complexity of travel behavior at different spatial and temporal scales has not been adequately considered. To capture regularity in a more comprehensive manner, we construct human mobility profiles with interpretable features at three levels, that is, location, motif, and route, on personal vehicle drivers. A feature engineering approach is designed to analyze the extent to which individuals exhibit multi-level regularity. The analysis pipeline includes feature selection, user segmentation and profiling, and feature importance evaluation. Our empirical study analyzed over 4 million trips of 3743 personal vehicle drivers collected over a month in six metropolitan areas in the United States. The weak correlations between features confirm the validity of quantifying regularity from different aspects. We discovered five clusters of drivers (i.e., gig drivers, homebodies, movers, typical drivers, and work-focused commuters) that differ in their regularity to commute to the workplace and the inclination to participate in non-work activities. A similar driver segmentation and profiling pattern is found in all of the studied metro areas. The minor differences are interpreted from the distribution of mobility features and urban features. The proposed method using multi-level feature engineering provides a generic framework to study regularity and can be readily adapted to other mobility data sources by customizing the features. The improved understanding of mobility patterns within the built environment is valuable for innovating urban transportation solutions. 相似文献
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Ikaite crystals (CaCO3×6H2O) have been found at 232- to 238-cm sediment depth in R/V Polarstern core PS2460-4 from the Laptev Sea continental margin in a water depth of 204 m. δ13C values of this phase average −36.3±0.4‰ PDB (N=2), which is significantly outside the range of normal marine carbonates. The CO2 involved in the precipitation of the ikaite is most probably derived from methane, which has extremely depleted 13C isotope values. Two possible sources of methane in these sediments are: (1) methanogenesis (decomposition of organic matter
under anaerobic conditions); and (2) gas hydrates, which are known to occur in the Siberian shelf regions.
Received: 20 March 1996 / Revision received: 22 July 1996 相似文献
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