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Isotopic Effects (isotopic + effects)

Distribution by Scientific Domains
Physics and Astronomy40%

Selected Abstracts

Stable water isotope simulation in different reservoirs of Manaus, Brazil, by Community Land Model incorporating stable isotopic effect

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2009
Xin-Ping Zhang
Abstract The daily and monthly variations of stable water isotopes in different reservoirs at Manaus, Brazil, are simulated and inter-compared in an equilibrium year, using the Community Land Model (CLM) involving the stable isotopic effects as a diagnostic tool for an in-depth understanding of the hydrometeorological processes. On the daily scale, the ,18O in precipitation, vapour and surface runoff have clear seasonality, with marked negative correlations with the corresponding water amount. However, the ,18O in surface dew displays marked positive correlation with dew amount. On the diurnal time scale, the ,18O in precipitation displays an unclear diurnal variation and an unmarked correlation with the precipitation amount. However, the ,18O in vapour keeps consistency with specific humidity. On the monthly time scale, the ,18O in precipitation and surface runoff displays distinct bimodal seasonality, with two maxima in January and in July, and two minima in April and in October; Vapor displays a similar bimodal pattern, two maxima appear in January and August, and two minima in April and November. The amount effect simulated on the monthly time scale has consistency with the actual survey result at the Manaus station, from 1965 to 1990, set up by International Atomic Energy Agency (IAEA)/World Meteorological Organization (WMO). In addition, the slope (7.49) and the intercept (6.25) of the simulated meteoric water line (MWL) are all smaller than those of the actual mean MWL. However, compared with the annual MWL, the simulated MWL lies within the variation range of actual MWLs. Copyright © 2008 Royal Meteorological Society [source]

EPR study of nitroxides formed from the reaction of nitric oxide with photolyzed amides

MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2003
Fan Wang
Abstract Free radicals generated from UV irradiation of simple aliphatic amides in anaerobic and nitric oxide (NO)-saturated liquid mixtures or solutions gave EPR spectra of nitroxides. The application of isotopic effects to EPR spectra and the generation of radicals by transient radical attack on substrate molecules or by photolysing amine or acetoin were used to help identify photochemically produced radicals from the amides. The aliphatic amides used were formamide, acetamide and their N -methyl- or deuterium-substituted derivatives. Transient radicals used to attack the amides via hydrogen-atom abstraction were generated from the initiator AIBN or AAPH. The observation of various nitroxides indicates the reactivity of NO for trapping acyl, carbamoyl and other carbon-centered radicals. Possibly mechanistic pathways diagnosed with this trap are proposed. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Photoluminescence studies of isotopically enriched silicon

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2003
D. Karaiskaj
Abstract We report the first high resolution photoluminescence studies of isotopically pure silicon. New information is obtained on isotopic effects on the indirect band gap energy, phonon energies, and phonon broadenings, which is in good agreement with previous results obtained in germanium and diamond. Remarkably, the line widths of the no-phonon boron and phosphorus bound exciton transitions in the 28Si sample (99.896% 28Si) are much sharper than in natural Si, revealing new fine structure in the boron bound exciton luminescence. Most surprisingly, the small splittings of the neutral acceptor ground state in natural Si are absent in the photoluminescence spectra of acceptor bound excitons in isotopically purified 28Si, demonstrating conclusively that they result from the randomness of the Si isotopic composition. [source]

Electron-phonon interaction in Er and Dy doped YAl3(BO3)4 single crystals

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
M. Mazzera
Abstract In the present work high resolution Fourier Transform spectroscopy is applied to monitor the electron-phonon (e, -ph) interaction in YAB single crystals doped with trivalent Er and Dy ions. The electron-phonon coupling is analysed by monitoring the shape, width, and position of the zero-phonon lines induced by Er3+. The shift and broadening with temperature increasing are discussed in the framework of the two-phonon Raman scattering. The e, -ph interaction is revealed even by the presence, in the absorption spectra of Er and Dy doped YAB crystals, of new weak lines attributed to vibronic transitions. The energy separations between the vibronic and the ZP lines are compared with IR-active modes measured on YAB crystals. Boron isotopic effects are also put in evidence. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Variation in oxygen isotope fractionation during cellulose synthesis: intramolecular and biosynthetic effects

PLANT CELL & ENVIRONMENT, Issue 10 2006
LEONEL STERNBERG
ABSTRACT The oxygen isotopic composition of plant cellulose is commonly used for the interpretations of climate, ecophysiology and dendrochronology in both modern and palaeoenvironments. Further applications of this analytical tool depends on our in-depth knowledge of the isotopic fractionations associated with the biochemical pathways leading to cellulose. Here, we test two important assumptions regarding isotopic effects resulting from the location of oxygen in the carbohydrate moiety and the biosynthetic pathway towards cellulose synthesis. We show that the oxygen isotopic fractionation of the oxygen attached to carbon 2 of the glucose moieties differs from the average fractionation of the oxygens attached to carbons 3,6 from cellulose by at least 9%, for cellulose synthesized within seedlings of two different species (Triticum aestivum L. and Ricinus communis L.). The fractionation for a given oxygen in cellulose synthesized by the Triticum seedlings, which have starch as their primary carbon source, is different than the corresponding fractionation in Ricinus seedlings, within which lipids are the primary carbon source. This observation shows that the biosynthetic pathway towards cellulose affects oxygen isotope partitioning, a fact heretofore undemonstrated. Our findings may explain the species-dependent variability in the overall oxygen isotope fractionation during cellulose synthesis, and may provide much-needed insight for palaeoclimate reconstruction using fossil cellulose. [source]