Results 241 to 250 of about 3,681,214 (292)
Some of the next articles are maybe not open access.
Stable Carbon and Nitrogen Isotopic
Aquatic Geochemistry, 2004The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate ...
Jennifer Lawson +4 more
openaire +1 more source
Carbon stable isotopes as indicators of coastal eutrophication
Ecological Applications, 2014Coastal ecologists and managers have frequently used nitrogen stable isotopes (δ15N) to trace and monitor sources of anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of δ15N data can often be challenging, as the isotope values fractionate substantially due to preferential retention and uptake by biota.
Autumn, Oczkowski +3 more
openaire +2 more sources
The cycle of carbon and the stable carbon isotopes
Geochimica et Cosmochimica Acta, 1956The following estimates are used: carbonate carbon (A) 2420 ± 560 grammes, C12C13 = 88·55 ± 0·05; organic sedimentary carbon (B) between 0·1–0·5 per cent C in shales, C12C13 = 91·00 ± 0·1θ. The concept “crustal carbon” is defined, and based on the measurements of the isotope ratios of thirty-seven diamonds, nineteen carbonates from Ivigtut, some other ...
openaire +1 more source
Stable carbon isotopic composition of biogenic carbonates
Geochimica et Cosmochimica Acta, 1965Abstract The geology and sulfur isotopic composition of epigenetic pyrite of the Gas Hills district, Wyoming, indicate a bacterial origin for these sandstone-type uranium deposits. The δC13 value of epigenetic calcite associated with organic materials, however, is heavier than the isotopic composition of calcite of biogenic native sulfur deposits ...
E.S Cheney, M.L Jensen
openaire +1 more source
The geochemistry of the stable carbon isotopes
Geochimica et Cosmochimica Acta, 1953Abstract Several hundred samples of carbon from various geologic sources have been analyzed in a new survey of the variation of the ratio C13/C12 in nature. Mass spectrometric determinations were made on the instruments developed by H. C. Urey and his co-workers utilizing two complete feed systems with magnetic switching to determine small ...
openaire +1 more source
Stable carbon isotopic characteristics of fossil fuels in China
Science of The Total Environment, 2022Good knowledge on the stable carbon isotopic composition (δ13C) of fossil fuels is critical for the estimation of atmospheric CO2 sources. Here, we complied a comprehensive δ13C database including 336 coal, 580 oil, and 1160 natural gas data based on the extensive literature search, and conducted field measurements in two megacities, to characterize ...
Peng, Wang +7 more
openaire +2 more sources
Synthesis of carbon‐14 and stable isotope labeled Censavudine
Journal of Labelled Compounds and Radiopharmaceuticals, 2022Censavudine is a nucleoside reverse transcriptase inhibitor (NRTI) explored clinically by Bristol Myers Squibb for the treatment of human immunodeficiency virus‐1 (HIV‐1). As part of the development process, a carbon‐14 labeled analog was synthesized for use in a human absorption, distribution, metabolism, and excretion (ADME) study.
Richard C. Burrell +4 more
openaire +2 more sources
Stable carbon isotopes in marine porewaters
Earth and Planetary Science Letters, 1985Abstract We present centimeter-scale porewater δ 13 C profiles from four sites in the Central Equatorial Pacific Ocean, which reveal steep porewater δ 13 C gradients (up to −1.0‰ cm −1 ) at the deep-sea sediment—water interface. We describe the processes controlling porewater carbon isotopic composition and incorporate them into a model of the deep ...
Daniel C. McCorkle +2 more
openaire +1 more source
Journal of Forensic Sciences, 2008
Abstract: There remains significant uncertainty in illicit marijuana cultivation. We analyzed the δ13C and δ15N of 508 domestic samples from known U.S.A. counties, 31 seized from a single location, 5 samples grown in Mexico and Colombia, and 10 northwest border seizures. For a subset, inflorescences and leaves were analyzed separately.
Jason B, West +2 more
openaire +2 more sources
Abstract: There remains significant uncertainty in illicit marijuana cultivation. We analyzed the δ13C and δ15N of 508 domestic samples from known U.S.A. counties, 31 seized from a single location, 5 samples grown in Mexico and Colombia, and 10 northwest border seizures. For a subset, inflorescences and leaves were analyzed separately.
Jason B, West +2 more
openaire +2 more sources
Assessment of Carbon Allocation with Stable Carbon Isotope Labeling
Agronomy Journal, 1990AbstractLabeling plants with isotopic forms of C allows many processes important to agriculture and/or natural resource management to be studied. Most C‐labelling experiments have employed radioactive 14C, but in recent years regulatory constraints associated with use of radioactive materials appear to have curtailed studies which may have benefited ...
Tony J. Svejcar +2 more
openaire +1 more source