نتایج جستجو برای: isotopic
تعداد نتایج: 18280 فیلتر نتایج به سال:
Four crustal xenoliths from Scotland have been dissected in order to evaluate the effects of magma-xenolith interaction on Rb-Sr and Sm-Nd isotopic systematics, and hence the use of the xenoliths for accurate determination of source compositions. Each xenolith was sampled from the edge to the center, The Nd isotopic compositions are virtually uniform across each xenolith; however, there are sig...
Context Abstract: N2O has been identi®ed in the Kyoto Protocol as one of the six greenhouse gases for which anthropogenic emissions should be regulated, however, regulation procedures may not be implemented until a wellde®ned N2O budget has been established. The measurement of N2O isotopic fractionation provides a potential means for constraining the global budget since biological and anthropog...
Stable isotopes of carbon, nitrogen, and sulfur are used as ecological tracers for a variety of applications, such as studies of animal migrations, energy sources, and food web pathways. Yet uncertainty relating to the time period integrated by isotopic measurement of animal tissues can confound the interpretation of isotopic data. There have been a large number of experimental isotopic diet sh...
Seasonal O variations in precipitation, soil water, snowmelt, spring flow and stream baseflow were analyzed to characterize seasonal dynamics of groundwater recharge in three central Pennsylvania catchments. The catchments represented three common landscape types: Valley and Ridge-shale (Mahantango Creek), Valley and Ridge-carbonate (Buffalo Run), and Appalachian Plateau-sandstone (Benner Run)....
The development of the multi-collector ICP-MS has provided a wider range of isotopic systems (e.g. Li, Mg, Fe, Cu, Hf, Tl) that can used to place constraints on the timing of mantle metasomatism and better characterize metasomatic processes. Associated with the application of these isotopic systems has been the parallel development of in-situ isotope analysis using a laser ablation microprobe a...
[1] Recent experiments have shown that in the oxygen isotopic exchange reaction for O(D) + CO2 the elastic channel is approximately 50% that of the inelastic channel [Perri et al., 2003]. We propose an analogous oxygen atom exchange reaction for the isoelectronic O(D) + N2O system to explain the mass-independent isotopic fractionation (MIF) in atmospheric N2O. We apply quantum chemical methods ...
The isotopic composition of different materials can be imaged by secondary ion mass spectrometry. In biology, this method is mainly used to study cellular metabolism and turnover, by pulsing the cells with marker molecules such as amino acids labelled with stable isotopes ((15)N, (13)C). The incorporation of the markers is then imaged with a lateral resolution that can surpass 100 nm. However, ...
We report a new method for measurement of the isotopic composition of nitrate (NO3-) at the natural-abundance level in both seawater and freshwater. The method is based on the isotopic analysis of nitrous oxide (N20) generated from nitrate by denitrifying bacteria that lack N2O-reductase activity. The isotopic composition of both nitrogen and oxygen from nitrate are accessible in this way. In t...
Hydrogen-isotopic abundances of lipid biomarkers are emerging as important proxies in the study of ancient environments and ecosystems. A decade ago, pioneering studies made use of new analytical methods and demonstrated that the hydrogen-isotopic composition of individual lipids from aquatic and terrestrial organisms can be related to the composition of their growth (i.e., environmental) water...
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