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Showing 1 to 20 of 74 for “"natural abundance"”.
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Natural abundance of ¹⁵N as a tool for assessing patterns of nitrogen loss from forest ecosystems
… nitrate losses. An underlying assumption in natural abundance isotope studies is that soil [delta]15 N is at steady-state over time. I found that [delta]15 N was not at steady state in either the Oie or Oa horizon for the period 1969 t[delta]1992 for the reference watershed (W6) at the …
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Investigating the ecology of partial and full myco-heterotrophy among Orchidaceae and Ericaceae using the stable isotope natural abundance analysis approach
… early development. The use of stable isotope natural abundance analyses recently revealed that some adult green and hence putatively autotrophic Orchidaceae and Pyroleae gain organic carbon and nitrogen from their fungal partners in addition to the carbon obtained through photosynthesis and …
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Palladium-Catalyzed Alkenylsilanol Cross -Coupling Reactions: Method Development and Mechanistic Analysis
… mechanism was examined through the natural abundance 13C NMR kinetic isotope effect (KIE) studies. This provided evidence for either palladium-olefin complexation or a Heck-type carbometalation as the turnover-limiting step for these cross-coupling reactions.
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Lewis Base Catalyzed Enantioselective Aldol Additions: Preparative and Mechanistic Studies
… formation of an activated complex. Finally, natural abundance 13C NMR kinetic isotope effect (KIE) studies have determined aldolization to be rate limiting.
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Multinuclear Solid-State Nuclear Magnetic Resonance Spectroscopy of Microporous Materials
… processes of CPO-27-Mg were examined by natural abundance 25Mg SSNMR at an ultrahigh magnetic field of 21.1 T. The dynamics of several guest molecules inside of CPO-27-M were monitored by variable-temperature 2H SSNMR. The structures of a-Mg3(HCOO)6, before and after guest adsorption, …
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Applications of Nuclear Quadrupole Double Resonance Spectroscopy
… and ('17)O) and, in the case of ('17)O, the low natural abundance, the contribution of NQR spectroscopy to our understanding of chemical bonding has been small. Only recently have nuclear quadrupole double resonance techniques been developed to facilitate observation of NQR spectra of the light …
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In Situ Enrichment and Epitaxial Growth of 28Si Films via Ion Beam Deposition
… the roughly 4.7 % 29Si isotopes present in natural abundance Si, which possesses nuclear spin I = 1/2 that is disruptive to qubit operation. However, high-quality 28Si is scarce and the degree to which it improves the performance of a qubit is not well understood. This leads to an important …
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Karakterisering van Grubbs-tipe prekatalisatore met behulp van kernmagnetiese resonansspektroskopie
… of 1H, 31P, COSY and rarely 13C. Due to the high natural abundance of 1H and 31P (99.98% and 100%), these experiments could be carried out quickly and easily. The only change that had to be made was to the spectral width, to accommodate the carbene signal (Ru=CH) between δ 20.02 and δ 17.32 ppm. …
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Synthesis and catalytic structure activity relations of hydrophobic zeolites with isolated framework metals that act as water tolerant Lewis acids
… nuclear polarization (DNP) NMR to characterize natural-abundance Sn-Beta. An indirect use of proton spin diffusion resulted in a 50-fold signal increase and the ability to observe natural-abundance ¹¹⁹Sn-Beta in <24 h. Since DNP NMR only enables efficient detection of spin-1/2 nuclei, a …
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Synthesis, characterisation, and properties of powder metallurgy transition metal-based high entropy alloys for electrocatalytic application
… electrocatalysts for OER, however their natural abundance is minuscule, hence they are expensive. Transition metal based electrocatalysts are emerging materials for OER applications due to their high natural abundance and low cost. However, these materials exhibit poor conductivity and …
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Isotopic constraints on the sources and associations of organic compounds in marine sediments
To provide a new perspective on the fate of both natural organic matter and hydrophobic organic contaminants (HOCs) in marine sediments, we have investigated the relationship between radiocarbon (14C) age and the different modes of association in aquatic sediments and soils. Radiocarbon is a …
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The biogeochemistry of marine nitrous oxide
… by marine nitrification as well as the natural abundance stable isotopic signatures of N2O produced by marine nitrifiers. This thesis shows that in addition to chemical controls on N2O production rates such as oxygen (O2) and nitrite (NO-2) concentrations, there are also biological …
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Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments
… which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing …
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The biogeochemistry of marine nitrous oxide
… by marine nitrification as well as the natural abundance stable isotopic signatures of N₂O produced by marine nitrifiers. This thesis shows that in addition to chemical controls on N₂O production rates such as oxygen (O₂) and nitrite (NO₂- ) concentrations, there are also biological …
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Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments
… which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing …
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Isotopic constraints on the sources and associations of organic compounds in marine sediments
To provide a new perspective on the fate of both natural organic matter and hydrophobic organic contaminants (HOCs) in marine sediments, we have investigated the relationship between radiocarbon (14C) age and the different modes of association in aquatic sediments and soils. Radiocarbon is a …
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Surfactants in nonpolar oils: agents of electric charging and nanogel templates
… liquids. Unlike aqueous media with their natural abundance of charged species, liquids of low dielectric constant do not readily accommodate charges, but can do so in the presence of certain surfactant additives. Surfactant-mediated charging in nonpolar oils has long been exploited …
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Part 1. Lewis Base-Catalyzed Cross-Aldol Reactions of Aldehydes: Preparative and Mechanistic Studies. Part 2. Initial Studies on Lewis Base-Catalyzed Reactions of Silyl Ynol Ethers With Aldehydes
… and 12C/13C kinetic isotope effects at natural abundance indicated that no significant change in mechanism occurs up on changing the electronic nature of aldehydes. The divergent trends in selectivity were interpreted according to the Hammond postulate and the Curtin-Hammett principle. …
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Some aspects of the nitrogen nutrition and growth of Gracilaria gracilis grown by suspended cultivation in Saldanha Bay, South Africa
… Nitrogen content, C:N ratio and stable isotope abundances of C and N were obtained for material grown for varying lengths of time, material grown at various depths and material that had been fertilized prior to placement on the raft. The relationship between thallus colour and nitrogen content …
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The Expression and Characterization of Human Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) in Tobacco
… superfamily of transporter proteins. Due to low natural abundance of CFTR and difficulties producing sufficient amounts in heterologous systems, the exact protein function/structure relationship is unknown. Expression of CFTR in E. coli is lethal and mammalian culture systems are expensive and …
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