WorldWideScience

Sample records for isotope effect study

  1. Uses of isotope effects in the study of enzymes.

    Science.gov (United States)

    Northrop, D B

    2001-06-01

    There have been few recent additions to the technical methods employed in the study of isotope effects, notable exceptions being the use of high pressure as an experimental variable and the measurement of heavy-atom isotope effects on maximal velocities using continuous-flow techniques. Most of the innovations are in the realm of new experimental designs that allow the asking of new questions. These designs include the use of isotope effects to: determine kinetic mechanisms, distinguish between changes in enzymatic activity and loss of active enzyme, distinguish between reactant-state origins and transition-state origins and quantify hydrogen tunneling, separate and quantify multiple origins of solvent isotope effects, distinguish between concerted and stepwise chemical mechanisms, characterize bond order changes in ligand binding, distinguish different pathways of inhibitor binding, and estimate intrinsic isotope effects. Copyright 2001 Academic Press.

  2. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    Science.gov (United States)

    Ni, Y.; Ma, Q.; Ellis, G.S.; Dai, J.; Katz, B.; Zhang, S.; Tang, Y.

    2011-01-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using ??D values in ethane from several basins in the world are in close agreement with similar predictions based on the ??13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that ??D values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that ??D values in ethane might be more suitable for modeling than comparable values in methane and propane. ?? 2011 Elsevier Ltd.

  3. Combining Solvent Isotope Effects with Substrate Isotope Effects in Mechanistic Studies of Alcohol and Amine Oxidation by Enzymes*

    Science.gov (United States)

    Fitzpatrick, Paul F.

    2014-01-01

    Oxidation of alcohols and amines is catalyzed by multiple families of flavin-and pyridine nucleotide-dependent enzymes. Measurement of solvent isotope effects provides a unique mechanistic probe of the timing of the cleavage of the OH and NH bonds, necessary information for a complete description of the catalytic mechanism. The inherent ambiguities in interpretation of solvent isotope effects can be significantly decreased if isotope effects arising from isotopically labeled substrates are measured in combination with solvent isotope effects. The application of combined solvent and substrate (mainly deuterium) isotope effects to multiple enzymes is described here to illustrate the range of mechanistic insights that such an approach can provide. PMID:25448013

  4. Combining solvent isotope effects with substrate isotope effects in mechanistic studies of alcohol and amine oxidation by enzymes.

    Science.gov (United States)

    Fitzpatrick, Paul F

    2015-11-01

    Oxidation of alcohols and amines is catalyzed by multiple families of flavin- and pyridine nucleotide-dependent enzymes. Measurement of solvent isotope effects provides a unique mechanistic probe of the timing of the cleavage of the OH and NH bonds, necessary information for a complete description of the catalytic mechanism. The inherent ambiguities in interpretation of solvent isotope effects can be significantly decreased if isotope effects arising from isotopically labeled substrates are measured in combination with solvent isotope effects. The application of combined solvent and substrate (mainly deuterium) isotope effects to multiple enzymes is described here to illustrate the range of mechanistic insights that such an approach can provide. This article is part of a Special Issue entitled: Enzyme Transition States from Theory and Experiment. Copyright © 2014 Elsevier B.V. All rights reserved.

  5. Isotope effects on nuclear shielding

    International Nuclear Information System (INIS)

    Hansen, P.E.

    1983-01-01

    This review concentrates upon empirical trends and practical uses of mostly secondary isotope effects, both of the intrinsic and equilibrium types. The text and the tables are arranged in the following fashion. The most 'popular' isotope effect is treated first, deuterium isotope effects on 13 C nuclear shielding, followed by deuterium on 1 H nuclear shieldings, etc. Focus is thus on the isotopes producing the effect rather than on the nuclei suffering the effect. After a brief treatment of each type of isotope effect, general trends are dealt with. Basic trends of intrinsic isotope effects such as additivity, solvent effects, temperature effects, steric effects, substituent effects and hyperconjugation are discussed. Uses of isotope effects for assignment purposes, in stereochemical studies, in hydrogen bonding and in isotopic tracer studies are dealt with. Kinetic studies, especially of phosphates, are frequently performed by utilizing isotope effects. In addition, equilibrium isotope effects are treated in great detail as these are felt to be new and very important and may lead to new uses of isotope effects. Techniques used to obtain isotope effects are briefly surveyed at the end of the chapter. (author)

  6. Stable isotope studies

    International Nuclear Information System (INIS)

    Ishida, T.

    1992-01-01

    The research has been in four general areas: (1) correlation of isotope effects with molecular forces and molecular structures, (2) correlation of zero-point energy and its isotope effects with molecular structure and molecular forces, (3) vapor pressure isotope effects, and (4) fractionation of stable isotopes. 73 refs, 38 figs, 29 tabs

  7. The isotope altitude effect reflected in groundwater: a case study from Slovenia.

    Science.gov (United States)

    Mezga, Kim; Urbanc, Janko; Cerar, Sonja

    2014-01-01

    This paper presents the stable isotope data of oxygen (δ(18)O) and hydrogen (δ(2)H) in groundwater from 83 sampling locations in Slovenia and their interpretation. The isotopic composition of water was monitored over 3 years (2009-2011), and each location was sampled twice. New findings on the isotopic composition of sampled groundwater are presented, and the data are also compared to past studies regarding the isotopic composition of precipitation, surface water, and groundwater in Slovenia. This study comprises: (1) the general characteristics of the isotopic composition of oxygen and hydrogen in groundwater in Slovenia, (2) the spatial distribution of oxygen isotope composition (δ(18)O) and d-excess in groundwater, (3) the groundwater isotope altitude effect, (4) the correlation between groundwater d-excess and the recharge area altitude of the sampling location, (5) the relation between hydrogen and oxygen isotopes in groundwater in comparison to the global precipitation isotope data, (6) the groundwater isotope effect of distance from the sea, and (7) the estimated relation between the mean temperature of recharge area and δ(18)O in groundwater.

  8. Isotope effects of neodymium in different ligands exchange systems studied by ion exchange displacement chromatography

    Directory of Open Access Journals (Sweden)

    Ibrahim Ismail

    2013-03-01

    Full Text Available The isotope effects of neodymium in Nd-glycolate ligand exchange system were studied by using ion exchange chromatography. The separation coefficients of neodymium isotopes, ε’s, were calculated from the observed isotopic ratios at the front and rear boundaries of the neodymium adsorption band. The values of separation coefficients of neodymium isotopes, ε’s, for the Nd-glycolate ligand exchange system were compared with those of Nd-malate and Nd-citrate, which indicated that the isotope effects of neodymium as studied by the three ligands takes the following direction Malate > Citrate > Glycolate. This order agrees with the number of available sites for complexation of each ligand. The values of the plate height, HETP of Nd in Nd-ligand exchange systems were also calculated.

  9. Secondary hydrogen isotope effects

    International Nuclear Information System (INIS)

    Melander, L.; Sonders, U.

    1983-01-01

    Secondary isotope effects can be produced by isotopes of elements heavier than hydrogen, but secondary isotope effects of hydrogen are of greater interest, because they are larger and can be measured easier. Such aspects of the problem as solvolytic reactions (in the case of α-position and β-position in organic compounds), reactions of compounds with deuterium remoted from reaction centre, with deuterium in nonsaturated compounds, participation of neighbouring groups in the reaction, are considered. Besides, steric isotope effects and inductive isotope effects are considered

  10. Isotope effects in gas-phase chemistry

    International Nuclear Information System (INIS)

    Various aspects of isotope effects in chemical reactions and photochemical reactions are presented. Most studies consider kinetic isotope effects with emphasis on hydrogen, deuterium, and muonium containing molecules and atoms. Theoretical origins of kinetic isotope effects are considered in several papers. A few of the latter papers consider atmospheric chemistry with respect to isotope effects

  11. Studies of isotopic effects in the excited electronic states of molecular systems

    International Nuclear Information System (INIS)

    1982-01-01

    Rare gas halogen (RGH) lasers serve as convenient tools for a range of photophysical processes which exhibit isotope effects. This document summarizes progress in the production of molecular systems in their electronic excited states with the aid of RGH lasers, and the various isotopic effects one can study under these conditions. We conclude that the basic physical mechanisms involved in the isotopically sensitive characteristics of excited molecular electronic states are sufficiently selective to be useful in both the detection and separation of many atomic materials

  12. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    Use of Isotopes for Studying Reaction. Mechanisms. 3. Secondary Kinetic Isotope Effect. Uday Maitra and. J Chandrasekhar are members of the Organic. Chemistry faculty in. Indian Institute of. Science at Bangalore. The previous articles of this series were: 1. Isotopes as markers, May. 1997. 2. Primary kinetic isotope effect.

  13. Isotope effect study of κ-(BEDT-TTF)2Cu(NCS)2: Labeling in the anion

    International Nuclear Information System (INIS)

    Kini, A.M.; Wang, H.H.; Schlueter, J.A.

    1995-01-01

    Since the initial discovery of organic superconductivity in 1979, a large number of organic superconductors have now been synthesized. However, the mechanism of electron-pairing in these novel superconductors has remained largely unresolved. Isotope effect studies constitute an important experimental tool for the investigation of whether or not the electron-pairing mechanism in organic superconductors is phonon-mediated, as in conventional superconductors. Recent isotope effect studies in the authors' laboratory, involving seven different isotopically labeled BEDT-TTF (or ET) derivatives, have demonstrated the following: (1) intramolecular phonon modes involving C double-bond C and Csingle bondS stretching vibrations in the ET donor molecule are not the dominant mediators of electron-pairing, and (2) in κ-(ET) 2 Cu(NCS) 2 , there exist two competing isotope effects--a normal mass effect, i.e., lowering of T c upon isotopic labeling, when the ET molecular mass is increased by concurrent 13 C and 34 S labeling, in addition to an inverse isotope effect upon deuterium labeling in ET. It is of great interest to investigate if there is an isotope effect when the charge-compensating anions, which are also located within the non-conducting layer in the superconducting cation-radical salts, are isotopically labeled. The existence of an isotope effect when the anions are labeled would be indicative of electron-pairing with the mediation of vibrational frequencies associated with the anions. In this paper, the authors present the results of the first isotope effect study in which isotopic labeling in the anion portion of κ-(ET) 2 Cu(NCS) 2 is carried out. The authors find no isotope effect when the carbon and nitrogen atoms of the thiocyanate groups in the anion are replaced with 13 C and 15 N isotopes

  14. A new cascade method for studying isotope effect in chemical exchange system without valance change

    International Nuclear Information System (INIS)

    Wen Xiaoning; Luo Wenzong

    1987-01-01

    A new cascade method for studying isotope effect in chemical exchange system without valance change is developed and described. This method is simple to use and consumes less extractant as compared with the commonly used Woodward method. It is also convenient for unstable systems

  15. A multielement isotopic study of refractory FUN and F CAIs: Mass-dependent and mass-independent isotope effects

    Science.gov (United States)

    Kööp, Levke; Nakashima, Daisuke; Heck, Philipp R.; Kita, Noriko T.; Tenner, Travis J.; Krot, Alexander N.; Nagashima, Kazuhide; Park, Changkun; Davis, Andrew M.

    2018-01-01

    Calcium-aluminum-rich inclusions (CAIs) are the oldest dated objects that formed inside the Solar System. Among these are rare, enigmatic objects with large mass-dependent fractionation effects (F CAIs), which sometimes also have large nucleosynthetic anomalies and a low initial abundance of the short-lived radionuclide 26Al (FUN CAIs). We have studied seven refractory hibonite-rich CAIs and one grossite-rich CAI from the Murchison (CM2) meteorite for their oxygen, calcium, and titanium isotopic compositions. The 26Al-26Mg system was also studied in seven of these CAIs. We found mass-dependent heavy isotope enrichment in all measured elements, but never simultaneously in the same CAI. The data are hard to reconcile with a single-stage melt evaporation origin and may require reintroduction or reequilibration for magnesium, oxygen and titanium after evaporation for some of the studied CAIs. The initial 26Al/27Al ratios inferred from model isochrons span a range from <1 × 10-6 to canonical (∼5 × 10-5). The CAIs show a mutual exclusivity relationship between inferred incorporation of live 26Al and the presence of resolvable anomalies in 48Ca and 50Ti. Furthermore, a relationship exists between 26Al incorporation and Δ17O in the hibonite-rich CAIs (i.e., 26Al-free CAIs have resolved variations in Δ17O, while CAIs with resolved 26Mg excesses have Δ17O values close to -23‰). Only the grossite-rich CAI has a relatively enhanced Δ17O value (∼-17‰) in spite of a near-canonical 26Al/27Al. We interpret these data as indicating that fractionated hibonite-rich CAIs formed over an extended time period and sampled multiple stages in the isotopic evolution of the solar nebula, including: (1) an 26Al-poor nebula with large positive and negative anomalies in 48Ca and 50Ti and variable Δ17O; (2) a stage of 26Al-admixture, during which anomalies in 48Ca and 50Ti had been largely diluted and a Δ17O value of ∼-23‰ had been achieved in the CAI formation region; and (3

  16. Laboratory study of nitrate photolysis in Antarctic snow. II. Isotopic effects and wavelength dependence

    Energy Technology Data Exchange (ETDEWEB)

    Berhanu, Tesfaye A.; Erbland, Joseph; Savarino, Joël [Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS, F-38041 Grenoble (France); Univ. Grenoble Alpes, LGGE, F-38041 Grenoble (France); Meusinger, Carl; Johnson, Matthew S. [Copenhagen Center for Atmospheric Research (CCAR), Department of Chemistry, University of Copenhagen, Copenhagen (Denmark); Jost, Rémy [Laboratoire de Interdisciplinaire de Physique (LIPHY) Univ. de Grenoble, Grenoble (France); Bhattacharya, S. K. [Research Center for Environmental Changes, Academia Sinica, Nangang, Taipei 115, Taiwan (China)

    2014-06-28

    Atmospheric nitrate is preserved in Antarctic snow firn and ice. However, at low snow accumulation sites, post-depositional processes induced by sunlight obscure its interpretation. The goal of these studies (see also Paper I by Meusinger et al. [“Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry,” J. Chem. Phys. 140, 244305 (2014)]) is to characterize nitrate photochemistry and improve the interpretation of the nitrate ice core record. Naturally occurring stable isotopes in nitrate ({sup 15}N, {sup 17}O, and {sup 18}O) provide additional information concerning post-depositional processes. Here, we present results from studies of the wavelength-dependent isotope effects from photolysis of nitrate in a matrix of natural snow. Snow from Dome C, Antarctica was irradiated in selected wavelength regions using a Xe UV lamp and filters. The irradiated snow was sampled and analyzed for nitrate concentration and isotopic composition (δ{sup 15}N, δ{sup 18}O, and Δ{sup 17}O). From these measurements an average photolytic isotopic fractionation of {sup 15}ε = (−15 ± 1.2)‰ was found for broadband Xe lamp photolysis. These results are due in part to excitation of the intense absorption band of nitrate around 200 nm in addition to the weaker band centered at 305 nm followed by photodissociation. An experiment with a filter blocking wavelengths shorter than 320 nm, approximating the actinic flux spectrum at Dome C, yielded a photolytic isotopic fractionation of {sup 15}ε = (−47.9 ± 6.8)‰, in good agreement with fractionations determined by previous studies for the East Antarctic Plateau which range from −40 to −74.3‰. We describe a new semi-empirical zero point energy shift model used to derive the absorption cross sections of {sup 14}NO{sub 3}{sup −} and {sup 15}NO{sub 3}{sup −} in snow at a chosen temperature. The nitrogen isotopic fractionations obtained by applying

  17. Isotopic effect giant resonances

    International Nuclear Information System (INIS)

    Buenerd, M.; Lebrun, D.; Martin, P.; Perrin, G.; Saintignon, P. de; Chauvin, J.; Duhamel, G.

    1981-10-01

    The systematics of the excitation energy of the giant dipole, monopole, and quadrupole resonances are shown to exhibit an isotopic effect. For a given element, the excitation energy of the transition decreases faster with the increasing neutron number than the empirical laws fitting the overall data. This effect is discussed in terms of the available models

  18. Relative extents of hydrogen-deuterium exchange of nitrosamines: relevance to biological isotope effect studies

    International Nuclear Information System (INIS)

    Singer, G.M.; Lijinsky, W.

    1979-01-01

    Relative extents of base-catalyzed, hydrogen-deuterium exchange have been determined for a number of nitrosamines. Observed trends in the exchanges are discussed in terms of substitution, ring size and conformation. The relevance of the exchanges to deuterium isotope effects in carcinogenesis tests is discussed. Those compounds which give pronounced biological isotope effects undergo exchange only to a small extent. No biological isotope effect is found for compounds which undergo extensive exchange. (author)

  19. Reaction kinetics: mechanisms and isotope effects

    International Nuclear Information System (INIS)

    Jones, J.R.

    1977-01-01

    This chapter emphasized how the isotope effects are obtained, and the factors that govern their magnitude. Most of the discussion concerned hydrogen isotope effects. Of the other isotopes much work has been done on carbon. Less extensive studies were reported using the isotopes of chlorine ( 35 Cl, 37 Cl), sulfur ( 32 S, 34 S), nitrogen ( 14 N, 15 N), and oxygen ( 16 O, 17 O). The customary way of altering the symmetry of the transition state is to vary the strength of the base B. Very large primary kinetic hydrogen isotope effects have also been observed for nitrocompounds. Some hydrogen alien reactions which may also be characterized by small solvation changes exhibit extremely large K/sup H//K/sup D/ values. Recently the main application of secondary hydrogen isotope effects has been in the study of the ability of neighboring groups to alter the energetics of organic reactions. 1 figure, 5 tables

  20. Isotope effects on chemical equilibria

    International Nuclear Information System (INIS)

    Golding, P.D.

    1974-01-01

    The thermodynamic equilibrium constants of three deuterated substituted acetic acids are reported. The calculation of secondary isotope effects of the second kind for the three isotopic acid pairs has been accomplished by the appropriate comparison of thermodynamic equilibrium constants, and by the comparison of isotopic slopes. The effect of substituent variation on the isotope effects reported here disqualifies the simple inductive model as a legitimate description of secondary isotope effects of the second kind. The correlation of diminishing isotope effect per deuterium atom with increasing acidity is also invalidated by the present results. The syntheses of 9-thia-9,10-dihydrophenanthrene-9-oxide and thioxanthene-10-oxide are described. These compounds have been partially deuterated at their respective methylene positions. Spectral evidence indicates stereoselectivity of the methylene protons in the exchange reactions of both compounds. (author)

  1. Mass-independent isotope effects.

    Science.gov (United States)

    Buchachenko, Anatoly L

    2013-02-28

    Three fundamental properties of atomic nuclei-mass, spin (and related magnetic moment), and volume-are the source of isotope effects. The mostly deserved and popular, with almost hundred-year history, is the mass-dependent isotope effect. The first mass-independent isotope effect which chemically discriminates isotopes by their nuclear spins and nuclear magnetic moments rather than by their masses was detected in 1976. It was named as the magnetic isotope effect because it is controlled by magnetic interaction, i.e., electron-nuclear hyperfine coupling in the paramagnetic species, the reaction intermediates. The effect follows from the universal physical property of chemical reactions to conserve angular momentum (spin) of electrons and nuclei. It is now detected for oxygen, silicon, sulfur, germanium, tin, mercury, magnesium, calcium, zinc, and uranium in a great variety of chemical and biochemical reactions including those of medical and ecological importance. Another mass-independent isotope effect was detected in 1983 as a deviation of isotopic distribution in reaction products from that which would be expected from the mass-dependent isotope effect. On the physical basis, it is in fact a mass-dependent effect, but it surprisingly results in isotope fractionation which is incompatible with that predicted by traditional mass-dependent effects. It is supposed to be a function of dynamic parameters of reaction and energy relaxation in excited states of products. The third, nuclear volume mass-independent isotope effect is detected in the high-resolution atomic and molecular spectra and in the extraction processes, but there are no unambiguous indications of its importance as an isotope fractionation factor in chemical reactions.

  2. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    In the previous articles of this series, we discussed the use of isotopes to trace the nature of reactive intermediates and also to obtain information about minima and transition states through quantitative measurements of equilibrium and kinetic isotope effects. In this part, we describe an ingenious way of studying dynamic ...

  3. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    In the previous articles of this series, we discussed the use of isotopes to trace the nature of reactive intermediates and also to obtain information about minima and transition states through quan- titative measurements of equilibrium and kinetic isotope effects. In this part, we describe an ingenious way of studying dynamic ...

  4. Study on the Effect of the Separating Unit Optimization on the Economy of Stable Isotope Separation

    Directory of Open Access Journals (Sweden)

    YANG Kun

    2015-01-01

    Full Text Available An economic criterion called as yearly net profit of single separating unit (YNPSSU was presented to evaluate the influence of structure optimization on the economy. Using YNPSSU as a criterion, economic analysis was carried out for the structure optimization of separating unit in the case of separating SiF4 to obtain the 28Si and 29Si isotope. YNPSSU was calculated and compared with that before optimization. The results showed that YNPSSU was increased by 12.3% by the structure optimization. Therefore, the structure optimization could increase the economy of the stable isotope separation effectively.

  5. Kinetic isotope effect studies of the S-adenosylmethionine synthetase reaction

    International Nuclear Information System (INIS)

    Markham, G.D.; Parkin, D.W.; Schramm, V.L.

    1986-01-01

    S-adenosylmethionine (AdoMet) synthetase catalyzes a unique substitution reaction at the 5' carbon of MgATP. Kinetic isotope effect (V/K) measurements have been used to investigate the mechanism of AdoMet synthetase from E. coli. Changes in 3 H/ 14 C ratios when AdoMet is formed from a mixture of either ([5'- 14 C]ATP and [5'- 12 C,1'- 3 H]ATP) or ([5'- 3 H]ATP and [5'- 1 H,1'- 14 C]ATP) were examined. The effects of varying the concentrations of the co-substrate methionine and the monovalent cation activator K + were investigated. Substitution of 14 C for 12 C at the 5' position of ATP yields a primary V/K kinetic isotope effect ( 12 C/ 14 C) of 1.128 +/- 0.004 at low K + and methionine concentrations. The observed isotope effect diminishes slightly to 1.107 +/- 0.003 when both K + and methionine are present at saturating concentrations, suggesting that MgATP has only a low commitment to catalysis from at conditions near Vmax. No secondary V/K 3 H isotope effect from [5'- 3 H]ATP was detected ( 1 H/ 3 H) = 0.997 +/- 0.003. The magnitude of the primary 14 C isotope effect and the small secondary 3 H effect demonstrate that AdoMet synthesis occurs with a S/sub N/ 2 transition state which is symmetric with respect to the sulfur nucleophile and the departing tripolyphosphate group

  6. Basic study on isotope separation using light induced drift effects (Progress report)

    Energy Technology Data Exchange (ETDEWEB)

    Suto, Osamu; Yamaguchi, Hiromi; Suzuki, M. [Japan Nuclear Cycle Development Inst., Tokai, Ibaraki (Japan). Tokai Works; Ishii, K.

    1999-03-01

    As a preliminary research on {sup 15}N-isotope separation on the basis of light induced drift (LID) effects in NH{sub 3}, the authors have confirmed the feasibility on {sup 13}C-isotope separation using LID effects in CH{sub 3}F for which all the necessary spectroscopic data are available and found that: (1) Concentration difference at the entrance and at the exit end of the drift tube {delta}n{sub a} (number/cm{sup 3}) was proportional to the energy density absorbed ({delta}W/cm{sup 2}), indicating the validity of theoretical LID equation. (2) Pressure dependence of {delta}n{sub a}/{delta}S was maximum at ca. 0.5 Torr. Lower {delta}n{sub a}/{delta}S values are due to power saturation effects at low pressures and due to absorption line broadening at high pressures. (3) Maximum isotopic selectivity was obtained at 0.5 Torr and to be 1.18. (4) Time needed for {delta}n{sub a} to attain the equilibrium increased with increasing pressure. They concluded that the possibility of {sup 15}N isotope separation using NH{sub 3}-LID effect was in principle confirmed. (S. Ohno)

  7. Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds

    DEFF Research Database (Denmark)

    Hansen, Poul Erik

    2015-01-01

    The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between “static” ...

  8. Isotope effects in photochemical rearrangements

    International Nuclear Information System (INIS)

    Sommer, F.

    1983-01-01

    Taking anthracene resp. 9-deuteroanthracene as the initial substance, different substitution products have been prepared. The products originating by direct photolysis have been characterized and their structure has been determined. By comparing the measured kinetic isotope effect and the quantum yield of the nondeuterated and the monodeuterated fluorenes formed it could been demonstrated that the isotope effect mainly is due to the reaction rates and the influence of the deuterium substitution upon the radiationless desactivation against that is small. (HBR) [de

  9. Study by photoelectron spectroscopy of isotopic effects in various polyatomic molecules. Comparison between experimental and calculated vibrational transitions probabilities

    International Nuclear Information System (INIS)

    Carlier, J.; Botter, R.

    1978-01-01

    Isotopic substitution of polyatomic molecules shift the spectrum in photoelectron spectroscopy. This effect is easier to detect with substitution of hydrogen by deuterium than with heavier elements. Hydrogen partially or totally substituted in ethylene by deuterium is studied by photoelectron spectroscopy for frequency attribution and experimental results are compared with frequency ratio calculated by the Teller-Redlich rule. Vibrational transition probabilities are also determined with a good precision. Ionization potentials are higher for molecules with heavy isotopes but for partially substituted molecules a variation of symetry could shift slightly potential curves [fr

  10. Isotope effect studies of the chemical mechanism of nicotinamide adenine dinucleotide malic enzyme from Crassula

    International Nuclear Information System (INIS)

    Grissom, C.B.; Willeford, O.; Wedding, R.T.

    1987-01-01

    The 13 C primary kinetic isotope effect on the decarboxylation of malate by nicotinamide adenine dinucleotide malic enzyme from Crassula argentea is 1.0199 +/- 0.0006 with proteo L-malate-2-H and 1.0162 +/- 0.0003 with malate-2-d. The primary deuterium isotope effect is 1.45 +/- 0.10 on V/K and 1.93 +/- 0.13 on V/sub max/. This indicates a stepwise conversion of malate to pyruvate and CO 2 with hydride transfer preceding decarboxylation, thereby suggesting a discrete oxaloacetate intermediate. This is in agreement with the stepwise nature of the chemical mechanism of other malic enzymes despite the Crassula enzyme's inability to reduce or decarboxylate oxaloacetate. Differences in morphology and allosteric regulation between enzymes suggest specialization of the Crassula malic enzyme for the physiology of crassulacean and acid metabolism while maintaining the catalytic events founds in malic enzymes from animal sources

  11. Sensitized charge carrier injection into organic crystals studied by isotope effects in weak magnetic fields

    International Nuclear Information System (INIS)

    Bube, W.; Michel-Beyerle, M.E.; Haberkorn, R.; Steffens, E.

    1977-01-01

    The magnetic field (H approximately 50 Oe) dependence of the rhodamine sensitized triplet exciton density in anthracene crystals is influenced by isotopic substitution. This confirms the hyperfine interaction as mechanism explaining the change of the spin multiplicity in the initially formed singlet state of the radical pair. The isotope effect occurs in the sensitizing dye ( 14 N/ 15 N) rather than at the molecular site of the injected charge within the crystal. This can be understood in terms of the high hopping frequency of the charge carriers as compared to the time constant of the hyperfine induced singlet-triplet transition. Since the dye molecules adsorb in an oriented fashion, the angular dependence of the magnetic field modulation of the triplet exciton density can be interpreted without assuming any additional interactions. (Auth.)

  12. Isotopic study of Karst water

    International Nuclear Information System (INIS)

    Leskovsek-Sefman, H.

    1985-01-01

    Measurement of the isotopic composition of water formed part of an extended investigation of the water drainage system in the Slovenian Karst. These studies were planned to complement geological and speleological investigations which are already being performed in this area, with the knowledge of the mechanism of changes in the isotopic composition of water in the natural environment on some smaller locations, Planina cave near Postojna where the vertical percolation of meteoric water through the karstified carbonate ceiling was studied and the water catchment areas of some small rivers, Ljubljanica, Rizana and Idrijca. Mass spectrometric investigations of the isotopic composition of some elements ( 18 O, D, 13 C and T) in water and in dissolved carbonates, as well as the isotopic composition of 18 O and 13 C in cave carbonates were performed. The results allow to conclude that the waters in karst aquifers in spite of producing the homogenisation to a great extent, qualitative determination of the retention time and of the prevailing sources for some springs and surface and underground water flows is nevertheless possible. The isotopic composition of 18 O in water and of 18 O and 13 C in dissolved carbonates depends on climatic conditions and on denudation processes. The investigation of cave carbonates revealed that they have different isotopic compositions of 18 O and 13 C because of different locations and also different ages

  13. Isotopic effect in high temperature superconductors

    International Nuclear Information System (INIS)

    Ohno, Takashi

    2000-01-01

    It is well-known that it essentially contributed to construct the BCB theory that a mechanism on formation of the Cooper pairs was dependent upon a lattice oscillation to change a critical temperature, T(sub c) of a superconductor with isotopic displacement. In this paper, here was, at first, described on an isotopic index actually measured to high temperature superconductors, and was introduced on a study on selective displacement of oxygen position. And then, a detailed measurement of 63-Cu(2) nuclear quadrupole resonance (NQR) at a plane position of YBa2Cu4O8 (Y1248) displaced with 18-O and 16-O, discussion of the isotopic effect on a base of 63-Cu(2) nuclear spin-lattice relaxation ratio, and consideration on the isotopic index according to the isotopic effect were described. As a result of the considerations, it could be concluded that the isotopic effect in a high temperature superconductor proved that antiferromagnetic spin fluctuation was an origin of Cooper pairs cohesive strength. (G.K.)

  14. Theoretical Study of H/D Isotope Effects on Nuclear Magnetic Shieldings Using an ab initio Multi-Component Molecular Orbital Method

    Directory of Open Access Journals (Sweden)

    Masanori Tachikawa

    2013-05-01

    Full Text Available We have theoretically analyzed the nuclear quantum effect on the nuclear magnetic shieldings for the intramolecular hydrogen-bonded systems of σ-hydroxy acyl aromatic species using the gauge-including atomic orbital technique combined with our multi-component density functional theory. The effect of H/D quantum nature for geometry and nuclear magnetic shielding changes are analyzed. Our study clearly demonstrated that the geometrical changes of hydrogen-bonds induced by H/D isotope effect (called geometrical isotope effect: GIE is the dominant factor of deuterium isotope effect on 13C chemical shift.

  15. Isotope effect and isotope separation. A chemist's view

    International Nuclear Information System (INIS)

    Ishida, Takanobu

    2002-01-01

    What causes the isotope effects (IE)? This presentation will be centered around the equilibrium isotope effects due to the differences in the nuclear masses. The occurrence of the equilibrium constant, K, of isotope exchange reactions which differ from the values predicted by the classical theory of statistical mechanics, K cl , is explored. The non-classical K corresponds to the unit-stage separation factor, α, that is different from unity and forms a basis of an isotope separation process involving the chemical exchange reaction. Here, the word 'chemical exchange' includes not only the isotope exchange chemical reactions between two or more chemical species but also the isotope exchanges involving the equilibria between liquid and vapor phases and liquid-gas, liquid solution-gas, liquid-liquid, and solid-liquid phases. In Section I, origins of the isotope effect phenomena will be explored and, in the process, various quantities used in discussions of isotope effect that have often caused confusions will be unambiguously defined. This Section will also correlate equilibrium constant with separation factor. In Section II, various forms of temperature-dependence of IE and separation factor will be discussed. (author)

  16. Non-linear Isotope Effects

    DEFF Research Database (Denmark)

    Schmidt, Johan Albrecht

    The isotopic fractionation associated with photodissociation of N2O, OCS and CO2, at different altitudes in Earth’s atmosphere, is investigated theoretically using constructed quantum mechanical models of the dissociation processes (i.e. potential energy surfaces and relevant coupling elements......’s stratosphere is nearly mass dependent, and only a small fraction of the observed anomalous oxygen-17 excess can be attributed to N2O photolysis. In contrast, stratospheric photolysis produces a significant inverse clumped isotope effect.(ii) Stratospheric OCS photolysis significantly enrich the remaining OCS...... in heavy carbon. The sulfur fractionation is weak and photolysis of OCS in the stratosphere produces only a small and mass dependent enrichment of heavy sulfur isotopes in the remaining OCS. Sulfur fractionation from the two remaining chemical sinks (oxidation by O(3P) and OH, respectively) is weak...

  17. Study of the effect of Chinese medicine on calcium absorption with isotopic tracer technique

    International Nuclear Information System (INIS)

    Hu, S.M.; Mao, X.Y.; Feng, W.Y.; OY, H.; Wang, M.; Xu, D.D.; Zhang, F.; Chai, Z.F.

    2005-01-01

    The present work was undertaken to study the effect of Chinese medicine on calcium absorption. Female Wistar rats, 3 months old, weighing 250-275 g, were randomly divided into ten groups of 5 rats each. The rats were individually housed in stainless steel metabolic cages in an environmentally controlled room (temperature, 20 degree C; relative humidity, 30%-60%; reversed light : dark cycle, 12:12 hr). Isotopic tracer technique was conducted to study the absorption of calcium acetate and calcium acetate + Chinese medicine in rats. The two calcium supplements were irradiated in a nuclear reactor for 4.95 d at neutron flux of φ=6.1 x 10 13 n/cm 2 ·s. Then they were prepared from concentrated 47 Ca solution (10 mg/ml) with cyclodextrin. The animals received oral doses of 25 mg calcium as calcium acetate or calcium acetate + Chinese medicine via an intragastric gavage. The animals were fasted overnight preceding and food was resumed 3 hrs after the gavage. Blood, heart, lung, liver, spleen, stomach, kidney, small intestine, large intestine and femur samples of the rats were taken upon sacrifice at 0.5, 1, 2, 4, 12, 24, 48, 72, 120, 168 hrs after dosing and assayed for 47 Ca. Urine and feces samples were collected separately after dosing and assayed for 47 Ca. The radioactivity of the samples was counted with a high pure Ge detector and a PC-based Ortec MCA. Its energy resolution was l.85 keV at 1332.5 keV and the relative detection efficiency was 30 %. The dead time was controlled within 10 % to reduce the count loss. Weighed 47 CaCO 3 was used as reference materials. A big distance between the samples and detector was kept to overcome the geometric effect caused by different shape and size of the samples. The gamma energy spectra were analyzed with a multipurpose gamma ray spectrum analysis software package. The parameters were evaluated by means of general linear model, using analysis of covariance with SAS 6.12 for Windows. The results showed that peroral 47 Ca was

  18. Isotopic effects in mechanistic studies of biotransformations of fluorine derivatives of L-alanine catalysed by L-alanine dehydrogenase

    International Nuclear Information System (INIS)

    Szymańska-Majchrzak, Jolanta; Pałka, Katarzyna; Kańska, Marianna

    2017-01-01

    Synthesis of 3-fluoro-[2- 2 H]-L-alanine (3-F-[ 2 H]-L-Ala) in reductive amination of 3-fluoropyruvic acid catalysed by L-alanine dehydrogenase (AlaDH) was described. Fluorine derivative was used to study oxidative deamination catalysed by AlaDH applied kinetic (for 3-F-L-Ala in H 2 O - KIE’s on V max : 1.1; on V max /K M : 1.2; for 3-F-L-Ala in 2 H 2 O – on V max : 1.4; on V max /K M : 2.1) and solvent isotope effect methods (for 3-F-L-Ala - SIE’s on V max : 1.0; on V max /K M : 0.87; for 3-F-[2- 2 H]-L-Ala – on V max : 1.4; on V max /K M : 1.5). Studies explain some details of reaction mechanism. - Highlights: • Synthesis of 3-fluoro-[2- 2 H]-L-alanine was performed. • The reactions were catalysed using the enzyme L-alanine dehydrogenase. • Performed reactions involved fluorinated analogues of L-alanine. • Solvent isotope effects of deuterium were determined. • Kinetic isotope effects were determined for obtained 3-fluoro-L-alanine. • The mechanism of reaction catalysed by L-alanine dehydrogenase was proposed.

  19. Non-linear Isotope Effects

    DEFF Research Database (Denmark)

    Schmidt, Johan Albrecht

    ’s stratosphere is nearly mass dependent, and only a small fraction of the observed anomalous oxygen-17 excess can be attributed to N2O photolysis. In contrast, stratospheric photolysis produces a significant inverse clumped isotope effect.(ii) Stratospheric OCS photolysis significantly enrich the remaining OCS...

  20. Modeling nuclear volume isotope effects in crystals

    Science.gov (United States)

    Schauble, Edwin A.

    2013-01-01

    Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac–Hartree–Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor–crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium

  1. Relative rate study of the kinetic isotope effect in the 13CH3D + Cl reaction

    DEFF Research Database (Denmark)

    Joelsson, Lars Magnus Torvald; Forecast, Roslyn; Schmidt, Johan Albrecht

    2014-01-01

    The 13CH3D/12CH4kinetic isotope effect, α13CH3D, of CH4 + Cl is determined for the first time, using the relative rate technique and Fourier transform infrared (FTIR) spectroscopy. α13CH3D is found to be 1.60 ± 0.04. In addition, a quantum chemistry/transition state theory model with tunneling...... correction is constructed and the primary cause for α13CH3D is found to be the substantially reduced reactivity of the D atom, which, in turn, can be explained by a significant increase in the reaction barrier due to changes in the vibrational zero point energy and to a lesser extent tunneling....

  2. Lithium isotopic separation: preliminary studies

    International Nuclear Information System (INIS)

    Macedo, Sandra Helena Goulart de

    1998-01-01

    In order to get the separation of natural isotopes of lithium by electrolytic amalgamation, an electrolytic cell with a confined mercury cathode was used to obtain data for the design of a separation stage. The initial work was followed by the design of a moving mercury cathode electrolytic cell and three experiments with six batches stages were performed for the determination of the elementary separation factor. The value obtained, 1.053, was ill agreement: with the specialized literature. It was verified in all experiments that the lithium - 6 isotope concentrated in the amalgam phase and that the lithium - 7 isotope concentrated in the aqueous phase. A stainless-steel cathode for the decomposition of the lithium amalgam and the selective desamalgamation were also studied. In view of the results obtained, a five stages continuous scheme was proposed. (author)

  3. The effect of dipolar interaction on the magnetic isotope effect

    DEFF Research Database (Denmark)

    Mojaza, Matin; Pedersen, Jørgen Boiden; Lukzen, Nikita

    2010-01-01

    A multi-channel kinetic description is used to study the magnetic isotope effect (MIE) in zero magnetic field. The maximal isotope effect is equal to the number of channels, two for the hyperfine interaction but four for the electron spin dipole–dipole interaction of the intermediate radical pair....... Quantum mechanical calculations agree with these conclusion and show that large MIE may be obtained even in the presence of a strong exchange interaction. The observed magnesium isotope effect on the rate of enzymatic synthesis of adenosine triphosphate (ATP) is approximately 3 implying that the dipolar...... interaction is responsible for the effect. Our calculations provide support for the proposed mechanism....

  4. The study on effect of zeolite on nitrogen use efficiency of corn by 15N-isotope dilution method

    International Nuclear Information System (INIS)

    Li Changhong; Li Huaxing; Zhang Xinming; Liu Yuanjin

    2002-01-01

    A pot experiment was carried out to study the effect of natural zeolite on nitrogen use efficiency of corn by using 15 N-isotope dilution method. The results showed that application of zeolite could improve the corn growth and enhance the biomass of the corn seedling. By using zeolite, nitrogen use efficiency (NUE) of corn was increased by 23.2%-33.1% as compared with no-zeolite treatment; and the residual nitrogen has no significant difference between zeolite treatment and no-zeolite treatment

  5. Isotope effect of glycinium phosphite NH3CH2COOH·H2PO3 studied by neutron diffraction

    International Nuclear Information System (INIS)

    Magome, Eisuke; Komukae, Masaru; Machida, Mitsuo; Tamura, Yuuki

    2007-01-01

    To study the isotope effect of glycinium phosphite (GPI), temperature dependences of the 5 0 6-bar and 3 0 1 0-bar structure factors of GPI and the 1 1 0 3-bar and 9 0 8-bar structure factors of deuterated GPI (DGPI) were analyzed in the ferroelectric phase by using the quasi-one-dimensional Ising model. The Ising model reproduces well the behavior of all the structure factors in the wide temperature region. The parameters for the intrachain and interchain interactions are determined to be 312 and 7.1 K for GPI, and 477 and 8.4 K for DGPI on average, respectively. (author)

  6. Forces in EDO-TTF: Theoretical study of isotope and charge effects on vibronic coupling

    Science.gov (United States)

    Tokunaga, Ken

    Isotope and charge effects on vibronic coupling constant (V) and energy gradient (g) of ethylenedioxy-tetrathiafulvalen (EDO-TTF) upon the electron injection into cation and electron removal from neutral molecule are investigated. It is found that normal modes which include C = C stretching motion generally have large V and g. For electron removal, three normal modes (v460, v470, and v480) have large Vi+ and gi+, and deuteration results in decrease of V46+ and increase of V47+. For electron injection, five normal modes (ν+42, ν+44, ν+45, ν+47, and ν+48) have large vi0 and gi0 deuteration results in increase of V045 and V048 and decrease of V047. From the analysis of vibronic coupling constants using vibronic coupling density (VCD), regional vibronic coupling constant (RVCC), and atomic vibronic coupling constant (AVCC), it is revealed that the change in normal mode vectors (d) due to the deuteration and electron removal (or injection) leads to the change in V.

  7. Isotope effects on desorption kinetics of hydrogen isotopes implanted into stainless steel by glow discharge

    International Nuclear Information System (INIS)

    Matsuyama, M.; Kondo, M.; Noda, N.; Tanaka, M.; Nishimura, K.

    2015-01-01

    In a fusion device the control of fuel particles implies to know the desorption rate of hydrogen isotopes by the plasma-facing materials. In this paper desorption kinetics of hydrogen isotopes implanted into type 316L stainless steel by glow discharge have been studied by experiment and numerical calculation. The temperature of a maximum desorption rate depends on glow discharge time and heating rate. Desorption spectra observed under various experimental conditions have been successfully reproduced by numerical simulations that are based on a diffusion-limited process. It is suggested, therefore, that desorption rate of a hydrogen isotope implanted into the stainless steel is limited by a diffusion process of hydrogen isotope atoms in bulk. Furthermore, small isotope effects were observed for the diffusion process of hydrogen isotope atoms. (authors)

  8. Using species-specific enriched stable isotopes to study the effect of fresh mercury inputs in soil-earthworm systems.

    Science.gov (United States)

    Álvarez, C Rodríguez; Jiménez-Moreno, M; Bernardo, F J Guzmán; Martín-Doimeadios, R C Rodríguez; Nevado, J J Berzas

    2018-01-01

    The fate of mercury (Hg) in the soil-earthworm system is still far from being fully understood, especially regarding recurrent and challenging questions about the importance of the reactivity of exogenous Hg species. Thus, to predict the potential effect of Hg inputs in terrestrial ecosystems, it is necessary to evaluate separately the reactivity of the endogenous and exogenous Hg species and, for this purpose, the use of enriched stable isotope tracers is a promising tool. In the present work, earthworms (Lumbricus terrestris) were exposed to historically Hg contaminated soils from the Almadén mining district, Spain. The soils were either non-spiked, which contain only endogenous or native Hg naturally occurring in the soil, or spiked with isotopically enriched inorganic Hg ( 199 IHg), representing exogenous or spiked Hg apart from the native one. The differential reactivity of endogenous and exogenous Hg in the soil conditioned the processes of methylation, mobilization, and assimilation of inorganic Hg by earthworms. Both endogenous and exogenous Hg species also behave distinctly regarding their bioaccumulation in earthworms, as suggested by the bioaccumulation factors, being the endogenous methylmercury (MeHg) the species more readily bioaccumulated by earthworms and in a higher extent. To the best of our knowledge, this work demonstrates for the first time the potential of enriched stable isotopes to study the effects of fresh Hg inputs in soil-earthworm systems. The findings of this work can be taken as a case study on the dynamics of Hg species in complex terrestrial systems and open a new door for future experiments. Copyright © 2017 Elsevier Inc. All rights reserved.

  9. Radiogenic age and isotopic studies

    International Nuclear Information System (INIS)

    1992-01-01

    This is one of an annual collection of reports presenting data from the Geochronology Section of the Continental Geoscience Division of the Geological Survey of Canada (GSC). The main purpose of this collection is to make geochronological and other radiogenic isotope data produced by the section available promptly to the geological community. Reports make full presentation of the data, relate these to field settings and make comparatively short interpretations. Other geochronological and isotope data produced in the laboratory but published in outside journals or separate GSC publications are summarized at the end of this report. Report 5 contains 24 papers from most regions of Canada, but particularly from British Columbia. The Geochronology Laboratory has, over the years, provided substantial U-Pb dating for the Cordilleran Division of the Geological Survey of Canada in Vancouver, and the results of a number of these studies are presented this year. A compilation of K-Ar ages is given. (figs., tabs., refs.)

  10. Radiogenic age and isotopic studies

    International Nuclear Information System (INIS)

    1991-01-01

    This is one of an annual collection of reports presenting data from the Geochronology Section of the Continental Geoscience Division of the Geological Survey of Canada (GSC). The main purpose of this collection is to make geochronological and other radiogenic isotope data produced by the section available promptly to the geological community. Reports make full presentation of the data, relate these to field settings and make comparatively short interpretations. Other geochronological and isotope data produced in the laboratory but published in outside journals or separate GSC publications are summarized at the end of this report. Reports in this issue give U-Pb zircon ages for rocks in Newfoundland, Yukon Territory, Manitoba, Ontario, and the Northwest Territories; present a compilation of K-Ar ages; and discuss Precambrian activity in New Brunswick, the geochronology of rock from the Northwest Territories, and reconnaissance Nd studies of rocks from the Northwest Territories. (figs., tabs., refs.)

  11. Structural and kinetic isotope effect studies of nicotinamidase (Pnc1) from Saccharomyces cerevisiae.

    Science.gov (United States)

    Smith, Brian C; Anderson, Mark A; Hoadley, Kelly A; Keck, James L; Cleland, W Wallace; Denu, John M

    2012-01-10

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD(+) salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from Saccharomyces cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction in which ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogues acting as inhibitors or substrates were examined, revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary (15)N and (13)C kinetic isotope effects (KIEs) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased, indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was indicative of a stronger commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid, is discussed. These results will aid in the design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity.

  12. Structural and Kinetic Isotope Effect Studies of Nicotinamidase (Pnc1) from Saccharomyces cerevisiae

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Brian C.; Anderson, Mark A.; Hoadley, Kelly A.; Keck, James L.; Cleland, W. Wallace; Denu, John M. (UW)

    2012-05-08

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD{sup +} salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from Saccharomyces cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction in which ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogues acting as inhibitors or substrates were examined, revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary {sup 15}N and {sup 13}C kinetic isotope effects (KIEs) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased, indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was indicative of a stronger commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid, is discussed. These results will aid in the design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity.

  13. Structural and Kinetic Isotope Effect Studies of Nicotinamidase (Pnc1) from S. cerevisiae†

    Science.gov (United States)

    Smith, Brian C.; Anderson, Mark A.; Hoadley, Kelly A.; Keck, James L.; Cleland, W. Wallace; Denu, John M.

    2011-01-01

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD+ salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from S. cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction where ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogs acting as inhibitors or substrates were examined revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary 15N and 13C kinetic isotope effects (KIE) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was observed indicative of a higher commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism is discussed involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid. These results will aid design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity. PMID:22229411

  14. Structural and Kinetic Isotope Effect Studies of Nicotinamidase (Pnc1) from Saccharomyces cerevisiae

    International Nuclear Information System (INIS)

    Smith, Brian C.; Anderson, Mark A.; Hoadley, Kelly A.; Keck, James L.; Cleland, W. Wallace; Denu, John M.

    2012-01-01

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD + salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from Saccharomyces cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction in which ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogues acting as inhibitors or substrates were examined, revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary 15 N and 13 C kinetic isotope effects (KIEs) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased, indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was indicative of a stronger commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid, is discussed. These results will aid in the design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity.

  15. Studies on fractionation of ytterbium isotopes in Yb(III)-acetate/Yb-amalgam system. Even-odd effect

    Energy Technology Data Exchange (ETDEWEB)

    Dembinski, W.; Poninski, M.; Fiedler, R.

    1997-12-31

    The fractionation of ytterbium isotopes with the even and odd numbers of neutrons was investigated in a Yb(III)-acetate/Yb-amalgam exchange systems. The light isotope was preferentially fractionated to the amalgam phase. The values of the unit separation gain per mass difference,{epsilon}, were found to be -0.00054 for {sup 176/171}Yb and -0.00069 for {sup 176/174}Yb The difference which amounted to 0.00015 is an evidence for the occurrence of the so called `even-odd` effect. It was also found that the chemical isotope shift of ytterbium was monitored by optical isotope shift its atomic spectra. (author). 23 refs, 7 figs, 4 tabs.

  16. A new scheme to calculate isotope effects.

    Science.gov (United States)

    Swiderek, Katarzyna; Dybala-Defratyka, Agnieszka; Rohr, Daniel R

    2011-09-01

    We present a new scheme to calculate isotope effects. Only selected frequencies at the target level of theory are calculated. The frequencies are selected by an analysis of the Hessian from a lower level of theory. We obtain accurate isotope effects without calculating the full Hessian at the target level of theory. The calculated frequencies are very accurate. The scheme converges to the correct isotope effect.

  17. Isotope effect studies of chicken liver NADP malic enzyme: role of the metal ion and viscosity dependence

    International Nuclear Information System (INIS)

    Grissom, C.B.; Cleland, W.W.

    1988-01-01

    The role of the metal ion in the oxidative decarboxylation of malate by chicken liver NADP malic enzyme and details of the reaction mechanism have been investigated by 13 C isotope effects. With saturating NADP and the indicated metal ion at a total concentration 10-fold higher than its K/sub m/, the following primary 13 C kinetic isotope effects at C 4 of malate [ 13 (VK/sub mal/)] were observed at pH 8.0: Mg 2+ , 1.0336; Mn 2+ , 1.0365; Cd 2+ , 1.0366; Zn 2+ , 1.0337; Co 2+ , 1.0283; Ni 2+ , 1.025. Knowing the partitioning of the intermediate oxalacetate between decarboxylation to pyuvate and reduction to malate allows calculation of the intrinsic carbon isotope effect for decarboxylation to pyuvate and reduction to malate allows calculation of the intrinsic carbon isotope effect for decarboxylation. For Mg 2+ as activator, this was 1.049 with NADP and 1.046 with 3-acetylpyridine adenine dinucleotide phosphate, although the intrinsic primary deuterium isotope effects on dehydrogenation were 5.6 and 4.2, and the partition ratios of the oxalacetate intermediate for decarboxylation as opposed to hydride transfer were 0.11 and 3.96. It was not possible to calculate reasonable intrinsic carbon isotope effects with the other metal ions by use of the partitioning ratio of oxalacetate because of decarboxylation by another mechanism. The variation of 13 (VK/sub mal/) with pH was used to dissect the total forward and external components. When the authors attempted to use the variation of 13 (VK/sub mal/) with solution viscosity to determine the internal and external commitments, incorrect values were obtained because of a specific effect of the viscosogen in decreasing the K/sub m/ for malate, so that VK/sub mal/ actually increased with viscosity instead of decreasing, as theory predicts

  18. Isotope studies on soil and fertilizer nitrogen

    International Nuclear Information System (INIS)

    Olson, R.A.

    1979-01-01

    Reductions in isotope cost in the 1960s and equipment innovations, have extended compared to 1940, the research of soil and plant scientists so that 15 N is now an indispensable tool when working with N. Leadership of FAO/IAEA coordinated research programmes and the Nitrogen Laboratory of the Tennessee Valley Authority helped greatly in bringing about this expanded usage. Recognized isotope effects are of insufficient magnitude to invalidate tracer measurements of field crop uptake in the treatment year if enrichment of 0.3 at.% excess 15 N or greater is employed. Thus, use of 15 N depleted tracer with potential of 0.366% 15 N differential from the standard isotope ratio of N in air is feasible. Its manufacture has allowed further economy in the isotope tag and ultimate treatment of field-scale plots. Interest in Δ 15 N measurements for predicting the NO - 3 contaminant source in surface and ground waters has depreciated. Variations in natural isotope ratio of soil N commonly exceed the differences in Δ 15 N values of the presumed source materials. 15 N provides the only correct measure of fertilizer N utilization efficiency. The field study examples of irrigated maize demonstrate that little or no fertilizer N is likely to escape the root zone where the rate applied does not exceed that required for maximum yield; also, that light and frequent irrigations afford higher yields than heavier, less frequent irrigations. Delaying fertilizer N applications until the crop is well established affords not only higher yields, but greater residual fertilizer N for future crops. Measured effective root activity for absorbing NO - 3 has been invaluable in estimating fertilizer requirements of a crop in relation to residual mineral N in soil at planting and projecting the depth at which the NO - 3 becomes an environmental hazard. The tag likewise is indispensable in determining symbiotic N fixation

  19. Bromine and carbon isotope effects during photolysis of brominated phenols.

    Science.gov (United States)

    Zakon, Yevgeni; Halicz, Ludwik; Gelman, Faina

    2013-12-17

    In the present study, carbon and bromine isotope effects during UV-photodegradation of bromophenols in aqueous and ethanolic solutions were determined. An anomalous relatively high inverse bromine isotope fractionation (εreactive position up to +5.1‰) along with normal carbon isotope effect (εreactive position of -12.6‰ to -23.4‰) observed in our study may be attributed to coexistence of both mass-dependent and mass-independent isotope fractionation of C-Br bond cleavage. Isotope effects of a similar scale were observed for all the studied reactions in ethanol, and for 4-bromophenol in aqueous solution. This may point out related radical mechanism for these processes. The lack of any carbon and bromine isotope effects during photodegradation of 2-bromophenol in aqueous solution possibly indicates that C-Br bond cleavage is not a rate-limiting step in the reaction. The bromine isotope fractionation, without any detectable carbon isotope effect, that was observed for 3-bromophenol photolysis in aqueous solution probably originates from mass-independent fractionation.

  20. Macrocyclic ligand decorated ordered mesoporous silica with large-pore and short-channel characteristics for effective separation of lithium isotopes: synthesis, adsorptive behavior study and DFT modeling.

    Science.gov (United States)

    Liu, Yuekun; Liu, Fei; Ye, Gang; Pu, Ning; Wu, Fengcheng; Wang, Zhe; Huo, Xiaomei; Xu, Jian; Chen, Jing

    2016-10-18

    Effective separation of lithium isotopes is of strategic value which attracts growing attention worldwide. This study reports a new class of macrocyclic ligand decorated ordered mesoporous silica (OMS) with large-pore and short-channel characteristics, which holds the potential to effectively separate lithium isotopes in aqueous solutions. Initially, a series of benzo-15-crown-5 (B15C5) derivatives containing different electron-donating or -withdrawing substituents were synthesized. Extractive separation of lithium isotopes in a liquid-liquid system was comparatively studied, highlighting the effect of the substituent, solvent, counter anion and temperature. The optimal NH 2 -B15C5 ligands were then covalently anchored to a short-channel SBA-15 OMS precursor bearing alkyl halides via a post-modification protocol. Adsorptive separation of the lithium isotopes was fully investigated, combined with kinetics and thermodynamics analysis, and simulation by using classic adsorption isotherm models. The NH 2 -B15C5 ligand functionalized OMSs exhibited selectivity to lithium ions against other alkali metal ions including K(i). Additionally, a more efficient separation of lithium isotopes could be obtained at a lower temperature in systems with softer counter anions and solvents with a lower dielectric constant. The highest value separation factor (α = 1.049 ± 0.002) was obtained in CF 3 COOLi aqueous solution at 288.15 K. Moreover, theoretical computation based on the density functional theory (DFT) was performed to elucidate the complexation interactions between the macrocyclic ligands and lithium ions. A suggested mechanism involving an isotopic exchange equilibrium was proposed to describe the lithium isotope separation by the functionalized OMSs.

  1. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    would help us optimize reaction conditions to effect higher yields, minimize reaction times, etc. The transformation ... effect of the isotope on the reaction rate. In the following. Uday Maitra and. J Chandrasekhar .... to the reaction, the rate of isotope exchange was unaltered, but the rate of racemization (of the reactant) became ...

  2. Platinum isotopes in iron meteorites: Galactic cosmic ray effects and nucleosynthetic homogeneity in the p-process isotope 190Pt and the other platinum isotopes

    Science.gov (United States)

    Hunt, Alison C.; Ek, Mattias; Schönbächler, Maria

    2017-11-01

    Platinum isotopes are sensitive to the effects of galactic cosmic rays (GCR), which can alter isotope ratios and mask nucleosynthetic isotope variations. Platinum also features one p-process isotope, 190Pt, which is very low abundance and therefore challenging to analyse. Platinum-190 is relevant for early solar-system chronology because of its decay to 186Os. Here, we present new Pt isotope data for five iron meteorite groups (IAB, IIAB, IID, IIIAB and IVA), including high-precision measurements of 190Pt for the IAB, IIAB and IIIAB irons, determined by multi-collector ICPMS. New data are in good agreement with previous studies and display correlations between different Pt isotopes. The slopes of these correlations are well-reproduced by the available GCR models. We report Pt isotope ratios for the IID meteorite Carbo that are consistently higher than the predicted effects from the GCR model. This suggests that the model predictions do not fully account for all the GCR effects on Pt isotopes, but also that the pre-atmospheric radii and exposure times calculated for Carbo may be incorrect. Despite this, the good agreement of relative effects in Pt isotopes with the predicted GCR trends confirms that Pt isotopes are a useful in-situ neutron dosimeter. Once GCR effects are accounted for, our new dataset reveals s- and r-process homogeneity between the iron meteorite groups studied here and the Earth. New 190Pt data for the IAB, IIAB and IIIAB iron meteorites indicate the absence of GCR effects and homogeneity in the p-process isotope between these groups and the Earth. This corresponds well with results from other heavy p-process isotopes and suggests their homogenous distribution in the inner solar system, although it does not exclude that potential p-process isotope variations are too diluted to be currently detectable.

  3. Molecular dynamics studies of irradiation effects on hydrogen isotope diffusion through nickel crystals and grain boundaries.

    Science.gov (United States)

    Zhou, X W; Dingreville, R; Karnesky, R A

    2017-12-20

    Experiments indicated that tritium permeation in 316 austenitic stainless steel is enhanced by a factor of ∼2-5 after irradiation as compared to the ex-reactor results. To understand this enhancement, we have performed extensive molecular dynamics simulations to study the effects of both the grain boundary structure (Σ3{111}, Σ5{100} and Σ11{311}) and the nature of point defects (vacancy, interstitial, and Frenkel pair) on hydrogen diffusivities in an exemplar fcc metal (nickel). By deriving diffusivities from mean square displacement, all possible atomic jump paths encountered during real diffusion are realistically sampled. By performing extremely long simulations, the statistical errors typically associated with this method are also significantly reduced. We found that within grains, interstitial defects increase diffusivity whereas vacancies have almost no effects. This mechanism might explain hydrogen permeation enhancements in irradiated materials with coarse grains. The largest increase in hydrogen diffusivity was found at a certain combination of grain boundary and point defect. This suggests that permeability of materials with finer grains can also be enhanced by irradiation depending on whether the grain boundary character is skewed. Our results shed new light on the enhancement of tritium permeation in 316 stainless steels during reactor operations.

  4. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 2; Issue 5. Use of Isotopes for Studying Reaction Mechanisms Isotopes as Markers. Uday Maitra J Chandrasekhar. Series Article Volume 2 Issue 5 May 1997 pp 23-28. Fulltext. Click here to view fulltext PDF. Permanent link:

  5. NMR studies of solid pentachlorophenol-4-methylpyridine complexes exhibiting strong OHN hydrogen bonds: geometric H/D isotope effects and hydrogen bond coupling cause isotopic polymorphism.

    Science.gov (United States)

    Ip, Brenda C K; Shenderovich, Ilya G; Tolstoy, Peter M; Frydel, Jaroslaw; Denisov, Gleb S; Buntkowsky, Gerd; Limbach, Hans-Heinrich

    2012-11-26

    We have studied the hydrogen bond interactions of (15)N labeled 4-methylpyridine (4-MP) with pentachlorophenol (PCP) in the solid state and in polar solution using various NMR techniques. Previous spectroscopic, X-ray, and neutron crystallographic studies showed that the triclinic 1:1 complex (4-MPPCP) exhibits the strongest known intermolecular OHN hydrogen bond in the solid state. By contrast, deuteration of the hydrogen bond gives rise to the formation of a monoclinic structure exhibiting a weaker hydrogen bond. By performing NMR experiments at different deuterium fractions and taking advantage of dipolar (1)H-(15)N recoupling under combined fast MAS and (1)H decoupling, we provide an explanation of the origin of the isotopic polymorphism of 4-MPPCP and improve previous chemical shift correlations for OHN hydrogen bonds. Because of anharmonic ground state vibrations, an ODN hydrogen bond in the triclinic form exhibits a shorter oxygen-hydron and a longer oxygen-nitrogen distance as compared to surrounding OHN hydrogen bonds, which also implies a reduction of the local dipole moment. The dipole-dipole interaction between adjacent coupled OHN hydrogen bonds which determines the structure of triclinic 4-MPPCP is then reduced by deuteration, and other interactions become dominant, leading to the monoclinic form. Finally, the observation of stronger OHN hydrogen bonds by (1)H NMR in polar solution as compared to the solid state is discussed.

  6. Medium Effects in Reactions with Rare Isotopes

    International Nuclear Information System (INIS)

    Bertulani, C A; Karakoç, M

    2012-01-01

    We discuss medium effects in knockout reactions with rare isotopes of weakly-bound nuclei at intermediate energies. We show that the poorly known corrections may lead to sizable modifications of knockout cross sections and momentum dsitributions.

  7. Spectroscopic and Quantum Mechanical Calculation Study of the Effect of Isotopic Substitution on NIR Spectra of Methanol.

    Science.gov (United States)

    Grabska, Justyna; Czarnecki, Mirosław A; Beć, Krzysztof B; Ozaki, Yukihiro

    2017-10-19

    In this work, we studied methanol and its deuterated derivatives (CH 3 OH, CH 3 OD, CD 3 OH, CD 3 OD) by NIR spectroscopy and anharmonic quantum chemical calculations. Vibrational bands corresponding to up to three quanta transitions (first and second overtones, binary and ternary combination modes) were predicted by the use of the VPT2 route. The accuracy of prediction of NIR modes was evaluated through density functional theory (DFT) with selected density functionals and basis sets. On the basis of the theoretical NIR spectra, detailed band assignments for all studied molecules were proposed. It was found that the pattern of bands in NIR spectra of deuterated methanols can be used for identification of isotopically equalized forms. Calculations of NIR spectra of all possible forms of CXXXOX (X = H, D) molecules demonstrated that the isotopic contamination can be identified due to a coexistence of bands specific to OH and OD groups. Also, bands from partially deuterated methyl groups can be distinguished in NIR spectra. Since the VPT2 framework is known to be sensitive to inaccuracy in the case of highly anharmonic modes, we obtained an independent insight by numerical solving of the time-independent Schrödinger equation corresponding to the O-X stretching mode scanned within -0.4 to 2.0 Å over a dense grid of 0.005 Å. This way the energies of vibrational levels of the CX1X2X3OX4 (X = H, D) isotopomers and the corresponding transition frequencies were obtained with high accuracy (<0.1 cm -1 ). The change in normal coordinate influences the reduced mass of the oscillator and thus its frequency. Our results lead to a conclusion that the effect of deuterization of the methyl group introduces a very specific and consistent frequency shift of the first overtone of the O-X stretching mode depending on the substitution of X1, X2, or X3 positions (<2 cm -1 ). However, the pattern of this shift is not reproduced accurately and is also largely overestimated by VPT2

  8. Solvent isotope effects in the complex formation of beryllium sulphate

    International Nuclear Information System (INIS)

    Boojj, M.

    1978-01-01

    The kinetics of complex formation and dissociation of BeSO 4 in D 2 O has been studied. The association constant and the inner sphere/outer sphere equilibrium constant were obtained. By comparing with the corresponding results in H 2 O(1) the solvent isotope effect could be evaluated for some of the involved thermodynamic and kinetic constants. The isotope effects can be understood in terms of Swain and Bader's statistical thermodynamical calculations (2). (orig.) [de

  9. Kinetic 15N-isotope effects on algal growth

    Science.gov (United States)

    Andriukonis, Eivydas; Gorokhova, Elena

    2017-03-01

    Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound changes in growth dynamics of the green alga Raphidocelis subcapitata grown in 15N-enriched media. With increasing 15N concentration (0.37 to 50 at%), the lag phase increased, whereas maximal growth rate and total yield decreased; moreover, there was a negative relationship between the growth and the lag phase across the treatments. The latter suggests that a trade-off between growth rate and the ability to adapt to the high 15N environment may exist. Remarkably, the lag-phase response at 3.5 at% 15N was the shortest and deviated from the overall trend, thus providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is particularly favorable for living organisms. These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies.

  10. Clumped isotope effects during OH and Cl oxidation of methane

    DEFF Research Database (Denmark)

    Whitehill, Andrew R.; Joelsson, Lars Magnus T.; Schmidt, Johan Albrecht

    2017-01-01

    A series of experiments were carried out to determine the clumped (13CH3D) methane kinetic isotope effects during oxidation of methane by OH and Cl radicals, the major sink reactions for atmospheric methane. Experiments were performed in a 100 L quartz photochemical reactor, in which OH...... was produced from the reaction of O(1D) (from O3 photolysis) with H2O, and Cl was from photolysis of Cl2. Samples were taken from the reaction cell and analyzed for methane (12CH4, 12CH3D, 13CH4, 13CH3D) isotopologue ratios using tunable infrared laser direct absorption spectroscopy. Measured kinetic isotope...... effects for singly substituted species were consistent with previous experimental studies. For doubly substituted methane, 13CH3D, the observed kinetic isotope effects closely follow the product of the kinetic isotope effects for the 13C and deuterium substituted species (i.e., 13,2KIE = 13KIE × 2KIE...

  11. Bibliography on vapour pressure isotope effects

    International Nuclear Information System (INIS)

    Illy, H.; Jancso, G.

    1976-03-01

    The bibliography of research on vapour pressure isotope effects from 1919 to December 1975 is presented in chronological order. Within each year the references are listed alphabetically according to the name of the first author of each work. The bibliography is followed by a Compound Index containing the names o compounds, but the type of isotopic substituation is not shown. The Author Index includes all authors of the papers. (Sz.N.Z.)

  12. Hydride Transfer in DHFR by Transition Path Sampling, Kinetic Isotope Effects, and Heavy Enzyme Studies

    Science.gov (United States)

    Wang, Zhen; Antoniou, Dimitri; Schwartz, Steven D.; Schramm, Vern L.

    2016-01-01

    Escherichia coli dihydrofolate reductase (ecDHFR) is used to study fundamental principles of enzyme catalysis. It remains controversial whether fast protein motions are coupled to the hydride transfer catalyzed by ecDHFR. Previous studies with heavy ecDHFR proteins labeled with 13C, 15N, and nonexchangeable 2H reported enzyme mass-dependent hydride transfer kinetics for ecDHFR. Here, we report refined experimental and computational studies to establish that hydride transfer is independent of protein mass. Instead, we found the rate constant for substrate dissociation to be faster for heavy DHFR. Previously reported kinetic differences between light and heavy DHFRs likely arise from kinetic steps other than the chemical step. This study confirms that fast (femtosecond to picosecond) protein motions in ecDHFR are not coupled to hydride transfer and provides an integrative computational and experimental approach to resolve fast dynamics coupled to chemical steps in enzyme catalysis. PMID:26652185

  13. Variation of kinetic isotope effect in multiple proton transfer reactions

    Indian Academy of Sciences (India)

    Proton transfer; promoter modes; kinetic isotope effect. 1. Introduction. Kinetic isotope effect (KIE) is the dependence of the rate constant on the mass of the isotope of the atom in a chemical reaction. The primary kinetic isotope effect is the KIE when the bonds connecting that atom to the rest of the molecular frame are broken ...

  14. Studies of control materials of isotope transformation

    Energy Technology Data Exchange (ETDEWEB)

    Noda, Tetsuji; Suzuki, Hiroshi; Araki, Hiroshi; Fujita, Mitsutane; Hirano, Toshiyuki; Abe, Fujio; Numazawa, Takenori [National Research Inst. for Metals, Tsukuba, Ibaraki (Japan)

    1999-02-01

    To control wavelength of laser, the physical properties of control materials of molecular excitation and isotope should be studied. We carried out isotopic enrichment, Si thin film growth, and preparation of boron isotope crystal and to make a calculation code of nuclear transmutation simulation. A gas circulation system for developing isotope laser was produced in order to control of molecular vibration excitation. We developed a single straight system of silicon isotope enrichment and silicon thin film preparation by infrared laser. When laser irradiated Si{sub 2}F{sub 6}, unreacted Si{sub 2}F{sub 6} contained 99.72% of {sup 28}Si at about 956 cm{sup -1} wavelength. When SiF{sub 4} or Si{sub 2}F{sub 6} with enriched isotope were directly decomposed by the plasma CVD method at about from 350 to 450degC, the yield of silicon crystal was about 28%. A homogeneous crystal with 10 mm diameter was obtained as the control material of boron isotope. The computer code for simulation of nuclear transmutation was improved to calculate the displacement damage, change of composition, induced radioactivity and decay heat. (S.Y.)

  15. Effect of temperature and salinity on stable isotopic composition of shallow water benthic foraminifera: A laboratory culture study

    Digital Repository Service at National Institute of Oceanography (India)

    Kurtarkar, S.R.; Linshy, V.N.; Saraswat, R.; Nigam, R.

    Quantitative estimation of past climatic parameters from stable isotopic composition of foraminifera relies on estimating the precise relationship between stable isotopic composition of the species analyzed and the physico-chemical factors...

  16. Stable isotope 'vital effects' in coccolith calcite

    NARCIS (Netherlands)

    Ziveri, P.; Stoll, H.; Probert, I.; Klaas, C.; Geisen, M.; Ganssen, G.M.; Young, J.

    2003-01-01

    Uncertainties about the origin of the many disequilibrium or 'vital effects' in a variety of calcifying organisms, and whether these effects are constant or variable, have hampered paleoceanographic application of carbon and oxygen isotopic ratios. Unraveling the source of these effects will improve

  17. Radiogenic age and isotopic studies

    International Nuclear Information System (INIS)

    Parrish, R.R.

    1990-01-01

    This is one of an annual collection of reports presenting data from the Geochronology Section of the Continental Geoscience Division of the Geological Survey of Canada (GSC). The main purpose of this collection is to make geochronological and other radiogenic isotope data produced by the section available promptly to the geological community. Reports make full presentation of the data, relate these to field settings and make comparatively short interpretations. Other geochronological and isotope data produced in the laboratory but published in outside journals or separate GSC publications are summarized at the end of this report. Reports in this issue cover methods for Rb-Sr and Sm-Nd isotopic analyses; 40 Ar- 39 Ar ages for the New Quebec Crater and for basaltic rocks; U-Pb ages for a differentiated mafic sill in the Ogilvie Mountains, plutonic rocks in the Contwoyto-Nose Lakes are, zircons from the Anton Complex, the Clinton-Colden gabbro-anorthosite intrusion, the Himag plutonic suite, the Campbell granite, the Central Gneiss Belt, Silurian granites, a metarhyolite, plagiogranite and gabbro, and the Wage shear zone; Rb-Sr ages for granitic rocks; K-Ar and Rb-Sr geochronology of granites; a compilation of K-Ar ages; ages of archean and proterozoic mylonites and pre-Misi granitoid domes; and reconnaissance geochronology of Baffin Island

  18. Metabolic studies in man using stable isotopes

    International Nuclear Information System (INIS)

    Faust, H.; Jung, K.; Krumbiegel, P.

    1993-01-01

    In this project, stable isotope compounds and stable isotope pharmaceuticals were used (with emphasis on the application of 15 N) to study several aspects of nitrogen metabolism in man. Of the many methods available, the 15 N stable isotope tracer technique holds a special position because the methodology for application and nitrogen isotope analysis is proven and reliable. Valid routine methods using 15 N analysis by emission spectrometry have been demonstrated. Several methods for the preparation of biological material were developed during our participation in the Coordinated Research Programme. In these studies, direct procedures (i.e. use of diluted urine as a samples without chemical preparation) or rapid isolation methods were favoured. Within the scope of the Analytical Quality Control Service (AQCS) enriched stable isotope reference materials for medical and biological studies were prepared and are now available through the International Atomic Energy Agency. The materials are of special importance as the increasing application of stable isotopes as tracers in medical, biological and agricultural studies has focused interest on reliable measurements of biological material of different origin. 24 refs

  19. Study of neutron-deficient Sn isotopes

    International Nuclear Information System (INIS)

    Auger, G.

    1982-05-01

    The formation of neutron deficient nuclei by heavy ion reactions is investigated. The experimental technique is presented, and the results obtained concerning Sn et In isotopes reported: first excited states of 106 Sn, high spin states in 107 Sn and 107 In; Yrast levels of 106 Sn, 107 Sn, 108 Sn; study of neutron deficient Sn and In isotopes formed by the desintegration of the compound nucleus 112 Xe. All these results are discussed [fr

  20. Field experimentation in isotope-aided studies

    International Nuclear Information System (INIS)

    Zapata, F.

    1990-01-01

    Isotopic-aided studies involve the application of isotopically labelled fertilizer as tracers for the quantitative and precise determination of the fate of specific nutrient elements in the soil/plant system. The planning of isotopic-aided studies requires a different approach from that followed in the design of normal fertilizer trials because of the cost and supply of isotopically labelled materials, the use of highly specialized equipment and the need for skillful trained staff in the use of isotope techniques both in the field/greenhouse and the laboratory. This report is intended to highlight the main points to be considered while applying those techniques in the field or greenhouse. It has been well established that nuclear techniques are a powerful tool in agricultural research. One should take advantage of the use of such techniques if the following criteria are met: The isotope method is the only way to solve a particular question or to obtain a specific piece of information. There are other methods available for such a purpose but the nuclear method provides a direct and quick means to obtain the needed information resulting in higher economic return

  1. Embryotoxicity of stable isotopes and use of stable isotopes in studies of teratogenetic mechanisms

    International Nuclear Information System (INIS)

    Spielmann, H.; Nau, H.

    1986-01-01

    Experiments on teratogenic effects of stable isotopes from our own and other laboratories are evaluated. In the first series of investigations, the enrichment of the stable isotope 13 C derived from U- 13 C-glucose was studied in mouse embryos at various stages of development, including limb buds in organ culture. Preimplantation mouse embryos incubated in vitro in 13 C-enriched medium for 48 hours showed normal development during subsequent differentiation in vitro and also in vivo after embryo transfer to faster mothers. These embryos were 15% to 20% enriched in 13 C. Administration of U-13-C-glucose to pregnant mice during organogenesis led to an increase of the absolute 13 C content of the embryo for several days after the end of isotope administration, whereas the enrichment in maternal tissue decreased. No alterations of embryonic development were detected due to stable isotope enrichment. Development of cultured mouse limb buds was unaffected by incubation with 82 mol% U- 13 C-glucose as judged from morphologic and biochemical criteria. The second part of the article describes the value of deuterium-labeled drugs as probes into the mechanism of activation of teratogenic metabolites. A comparison of the pharmacokinetics as well as the teratogenicity between cyclophosphamide and some specific deuterium-labeled analogues showed that the isotope effect observed can be related to a particular metabolic pathway crucial for teratogenic activation by this drug

  2. Isotopic effects on non-linearity, molecular radius and intermolecular ...

    Indian Academy of Sciences (India)

    study the isotopic effects on the non-linearity parameter and the physicochemical proper- ties of the liquids, which in turn has been used to study their effect on the intermolecular interactions produced thereof. Keywords. Non-linearity parameter; molecular radius; free length; intermolecular inter- actions. PACS Nos 43.25.

  3. Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition

    International Nuclear Information System (INIS)

    Zielinski, M.; Zielinska, A.; Papiernik-Zielinska, H.; McKenzie, J.A.; Bernasconi, S.; Paul, H.

    1998-01-01

    Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition above and below its melting temperature have been studied and compared with the primary (PKIE) and secondary kinetic isotope effects (SKIE) of 13 C and 18 O, respectively, in the decarboxylation of other heterocyclic acids. The temperature dependence of the secondary oxygen-18 isotope effects is negative in the total 221-255 deg C temperature interval investigated initially. The 13 C KIE measured above melting point of N.A. (temperature interval 235-270 deg C) are located in the range 1.007-1.009. Below melting point of nicotinic acid the 13 C KIE are larger and reveal the negative temperature dependence ( 13 C KIE decreases with decreasing the reaction temperature from 1.013/at 230 deg C to 1.0114/at 221 deg C). A discussion of the above isotopic results is presented. (author)

  4. Fundamental studies in isotope chemistry. Progress report, 1 July 1976--30 Jun 1977

    International Nuclear Information System (INIS)

    Bigeleisen, J.; Harris, T.H.

    1977-01-01

    The current thrust of the program is the use of isotope effects to study the fundamental properties of matter, measurement and calculation of isotope fractionation factors of systems of potential technological importance and the correlation of isotope effects with molecular structure. The first measurements of the isotopic fractionation factors for two components in a solution were completed by the study of argon-krypton mixtures. The measurements cover the range from pure argon to pure krypton and extrapolate very well to previous measurements on the pure components. The vapor pressure isotope effects between solid-vapor and liquid-vapor for the rare gases neon, argon, and krypton is given

  5. Stable isotope studies: Progress report, March 1985--August 1987

    International Nuclear Information System (INIS)

    Ishida, Takanobu.

    1987-01-01

    Studies have been carried out in the following areas: Stable Isotope Fractionation (1) Effects of chemical poisons and surface modifiers on polycrystalline platinum electrode surfaces have been investigated with a goal to develop a new form of heterogeneous catalyst for the hydrogen isotope exchange between dihydrogen and water. (2) A new nitrogen-15 fractionation process has been developed, based on the isotope exchange between liquid N 2 O 3 -N 2 O 4 mixture and their vapor phase at a subambient temperature and a raised pressure. (3) A closed chemical recycle process has been developed for use in connection with the refluxer in the Nitrox-type nitrogen-15 plant. Isotope Effects (1) The vapor pressure isotope effect (VPIE) study of liquid fluoromethanes have been completed. (2) The VPIE study of solid and liquid ammonia has been completed. (3) A theoretical foundation of the additivity for the vibrational zero-point energy (ZPE) has been developed. Studies of Liquid Ammonia. With an aim to study intermolecular interaction (and the inversion phenomenon, in particular) in liquid ammonia, and to further investigate various ammonia solutions, a molecular dynamics (MD) study has been initiated. An MD program has been completed, and force field functions have been developed for an ensemble of non-rigid ammonia molecules. 107 refs., 41 figs., 10 tabs

  6. Transport hysteresis and hydrogen isotope effect on confinement

    Science.gov (United States)

    Itoh, S.-I.; Itoh, K.

    2018-03-01

    A Gedankenexperiment on hydrogen isotope effect is developed, using the transport model with transport hysteresis. The transport model with hysteresis is applied to case where the modulational electron cyclotron heating is imposed near the mid-radius of the toroidal plasmas. The perturbation propagates either outward or inward, being associated with the clockwise (CW) hysteresis or counter-clockwise (CCW) hysteresis, respectively. The hydrogen isotope effects on the CW and CCW hysteresis are investigated. The local component of turbulence-driven transport is assumed to be the gyro-Bohm diffusion. While the effect of hydrogen mass number is screened in the response of CW hysteresis, it is amplified in CCW hysteresis. This result motivates the experimental studies to compare CW and CCW cases in order to obtain further insight into the physics of hydrogen isotope effects.

  7. Isotopic studies in soil and plant nutrition

    International Nuclear Information System (INIS)

    Pasricha, N.S.

    2001-01-01

    One of the most important peaceful applications of isotopes is in research for the enhancement of our understanding for increased crop production and better management of resources with higher economic efficiency and environmental safety. Nuclear techniques helped in generating useful information on such aspects as use-efficiency of fertilizer nutrients, quantifying their losses from soil and their biological transformations. Such information was, hitherto, obtained indirectly by conventional methods. Radio and stable isotopes have also been successfully employed for getting information in such diverse fields as soil erosion, turnover of soil organic matter, pesticide retention in soil ground water recharge etc. The property of 137 Cs adhering tightly to certain exchange surface in soil and its chemically inert nature has made it a useful tool for soil erosion studies. In this paper, applications of isotopes in the research and other such studies as degradation, movement and retention of pesticides, movement of nitrate in soil, biological and ammoniacal nitrogen fixation in soil is discussed

  8. The effects of α-cellulose extraction and blue-stain fungus on retrospective studies of carbon and oxygen isotope variation in live and dead trees†

    Science.gov (United States)

    English, N.B.; McDowell, N.G.; Allen, Craig D.; Mora, C.

    2011-01-01

    Tree-ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ13C and δ18O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α-cellulose from live and dead specimens of ponderosa pine (Pinus ponderosa), one-seed juniper (Juniperous monosperma), piñon pine (Pinus edulis) and white fir (Abies concolor), including those with fungal growth and beetle frass in the wood, to determine if α-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ13C or δ18O values of α-cellulose and whole wood was the same for both live and dead trees across a large range of inter-annual and regional climate differences. The method of α-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ13C (up to 0.4‰) and δ18O (up to 1.2‰) of α-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus (Ophiostoma) on the δ13C and δ18O of whole wood or α-cellulose. The relationships between whole wood and α-cellulose δ13C for ponderosa, piñon and juniper yielded slopes of ~1, while the relationship between δ18O of whole wood and α-cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States.

  9. Isotope and mixture effects on neoclassical transport in the pedestal

    Science.gov (United States)

    Pusztai, Istvan; Buller, Stefan; Omotani, John T.; Newton, Sarah L.

    2017-10-01

    The isotope mass scaling of the energy confinement time in tokamak plasmas differs from gyro-Bohm estimates, with implications for the extrapolation from current experiments to D-T reactors. Differences in mass scaling in L-mode and various H-mode regimes suggest that the isotope effect may originate from the pedestal. In the pedestal, sharp gradients render local diffusive estimates invalid, and global effects due to orbit-width scale profile variations have to be taken into account. We calculate neoclassical cross-field fluxes from a radially global drift-kinetic equation using the PERFECT code, to study isotope composition effects in density pedestals. The relative reduction to the peak heat flux due to global effects as a function of the density scale length is found to saturate at an isotope-dependent value that is larger for heavier ions. We also consider D-T and H-D mixtures with a focus on isotope separation. The ability to reproduce the mixture results via single-species simulations with artificial ``DT'' and ``HD'' species has been considered. These computationally convenient single ion simulations give a good estimate of the total ion heat flux in corresponding mixtures. Funding received from the International Career Grant of Vetenskapsradet (VR) (330-2014-6313) with Marie Sklodowska Curie Actions, Cofund, Project INCA 600398, and Framework Grant for Strategic Energy Research of VR (2014-5392).

  10. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 2; Issue 10. Use of Isotopes for Studying Reaction Mechanisms Distinguishing between Single Minima and Rapidly Equilibrating Structures. Uday Maitra J Chandrasekhar. Series Article Volume 2 Issue 10 October 1997 pp 29-37 ...

  11. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 16; Issue 12. Use of Isotopes for Studying Reaction Mechanisms - Distinguishing between Single Mimima and Rapidly Equilibrating Structures. Uday Maitra J Chandrasekhar. Volume 16 Issue 12 December 2011 pp 1315-1323 ...

  12. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    applications of isotopic substitution for studying reaction mechanisms and dynamic structures. Suggested Reading. • B K Carpenter. Determination of Organic Reaction Mechanisms. John. Wiley. New York, 1984. • F A Carey and R J Sundberg. Advanced Organic Chemistry. Part A. 3rd. Ed. Plenum Press. New York, 1990.

  13. H/D isotope effects in high temperature proton conductors

    NARCIS (Netherlands)

    Bonanos, N.; Huijser, Jannetje Maria; Poulsen, F.W.

    2015-01-01

    The atomic mass ratio of ca. 2 between deuterium and hydrogen is the highest for any pair of stable isotopes and results in significant and measurable H/D isotope effects in high temperature proton conductors containing these species. This paper discusses H/D isotope effects manifested in O–H/O–D

  14. NMR stratagems for the study of multiple kinetic hydrogen/deuterium isotope effects of proton exchange. Example: Di-p-fluorophenylformamidine/THF

    International Nuclear Information System (INIS)

    Limbach, H.H.; Meschede, L.; Scherer, G.

    1989-01-01

    Stratagems are presented for the determination of kinetic isotope effects of proton exchange reactions by dynamic NMR spectroscopy. In such experiments, lineshape analyses and/or polarization transfer experiments are performed on the exchanging protons or deuterons as well as on remote spins, as a function of the deuterium fraction in the mobile proton sites. These methods are NMR analogs of previous proton inventory techniques involving classical kinetic methods. A theory is developed in order to derive the kinetic isotope effects as well as the number of transferred protons from the experimental NMR spectra. The technique is then applied to the problem of proton exchange in the system 15 N, 15 N'-di-p-fluorophenylformamidine, a nitrogen analog of formic acid, dissolved in tetrahydrofuran-d 8 (THF). DFFA forms two conformers in THF to which s-trans and s-cis structures have been assigned. Only the s-trans conformer is able to dimerize and exchange protons. Lineshape simulations and magnetization transfer experiments were carried out at 189,2 K, at a concentration of 0.02 mol l -1 , as a function of the deuterium fraction D in the 1 H- 15 N sites. Using 1 H NMR spectroscopy, a linear dependence of the inverse proton lifetimes on D was observed. From this it was concluded that two protons are transported in the rate limiting step of the proton exchange. This result is expected for a double proton transfer in an s-trans dimer with a cyclic structure. The full kinetic HH/HD/DD isotope effects of 233:11:1 at 189 K were determined through 19 F NMR experiments on the same samples. The deviation from the rule of geometric mean, although substantial, is much smaller than found in previous studies of intramolecular HH transfer reactions. Possible causes of this effect are discussed. (orig.)

  15. Isotopic effects on the phonon modes in boron carbide.

    Science.gov (United States)

    Werheit, H; Kuhlmann, U; Rotter, H W; Shalamberidze, S O

    2010-10-06

    The effect of isotopes ((10)B-(11)B; (12)C-(13)C) on the infrared- and Raman-active phonons of boron carbide has been investigated. For B isotopes, the contributions of the virtual crystal approximation, polarization vector and isotopical disorder are separated. Boron and carbon isotope effects are largely opposite to one another and indicate the share of the particular atoms in the atomic assemblies vibrating in specific phonon modes. Some infrared-active phonons behave as expected for monatomic boron crystals.

  16. Charge state distribution studies of pure and oxygen mixed krypton ECR plasma - signature of isotope anomaly and gas mixing effect.

    Science.gov (United States)

    Kumar, Pravin; Mal, Kedar; Rodrigues, G

    2016-11-01

    We report the charge state distributions of the pure, 25% and 50% oxygen mixed krypton plasma to shed more light on the understanding of the gas mixing and the isotope anomaly [A. G. Drentje, Rev. Sci. Instrum. 63 (1992) 2875 and Y Kawai, D Meyer, A Nadzeyka, U Wolters and K Wiesemann, Plasma Sources Sci. Technol. 10 (2001) 451] in the electron cyclotron resonance (ECR) plasmas. The krypton plasma was produced using a 10 GHz all-permanent-magnet ECR ion source. The intensities of the highly abundant four isotopes, viz. 82 Kr (~11.58%), 83 Kr (~11.49%), 84 Kr (~57%) and 86 Kr (17.3%) up to ~ +14 charge state have been measured by extracting the ions from the plasma and analysing them in the mass and the energy using a large acceptance analyzer-cum-switching dipole magnet. The influence of the oxygen gas mixing on the isotopic krypton ion intensities is clearly evidenced beyond +9 charge state. With and without oxygen mixing, the charge state distribution of the krypton ECR plasma shows the isotope anomaly with unusual trends. The anomaly in the intensities of the isotopes having quite closer natural abundance, viz. 82 Kr, 86 Kr and 83 Kr, 86 Kr is prominent, whereas the intensity ratio of 86 Kr to 84 Kr shows a weak signature of it. The isotope anomaly tends to disappear with increasing oxygen mixing in the plasma. The observed trends in the intensities of the krypton isotopes do not follow the prediction of linear Landau wave damping in the plasma. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  17. Radiochemical studies of neutron deficient actinide isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Williams, K.E.

    1978-04-01

    The production of neutron deficient actinide isotopes in heavy ion reactions was studied using alpha, gamma, x-ray, and spontaneous fission detection systems. A new isotope of berkelium, /sup 242/Bk, was produced with a cross-section of approximately 10 ..mu..b in reactions of boron on uranium and nitrogen on thorium. It decays by electron capture with a half-life of 7.0 +- 1.3 minutes. The alpha-branching ratio for this isotope is less than 1% and the spontaneous fission ratio is less than 0.03%. Studies of (Heavy Ion, pxn) and (Heavy Ion, ..cap alpha..xn) transfer reactions in comparison with (Heavy ion, xn) compound nucleus reactions revealed transfer reaction cross-sections equal to or greater than the compound nucleus yields. The data show that in some cases the yield of an isotope produced via a (H.I.,pxn) or (H.I.,..cap alpha..xn) reaction may be higher than its production via an xn compound nucleus reaction. These results have dire consequences for proponents of the ''Z/sub 1/ + Z/sub 2/ = Z/sub 1+2/'' philosophy. It is no longer acceptable to assume that (H.I.,pxn) and (H.I.,..cap alpha..xn) product yields are of no consequence when studying compound nucleus reactions. No evidence for spontaneous fission decay of /sup 228/Pu, /sup 230/Pu, /sup 232/Cm, or /sup 238/Cf was observed indicating that strictly empirical extrapolations of spontaneous fission half-life data is inadequate for predictions of half-lives for unknown neutron deficient actinide isotopes.

  18. Solid state NMR of isotope labelled murine fur: a powerful tool to study atomic level keratin structure and treatment effects

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Wai Ching Veronica; Narkevicius, Aurimas; Chow, Wing Ying; Reid, David G.; Rajan, Rakesh [University of Cambridge, Department of Chemistry (United Kingdom); Brooks, Roger A. [University of Cambridge, Department of Trauma and Orthopaedic Surgery, Addenbrooke’s Hospital (United Kingdom); Green, Maggie [University of Cambridge, Central Biomedical Resources, School of Clinical Medicine (United Kingdom); Duer, Melinda J., E-mail: mjd13@cam.ac.uk [University of Cambridge, Department of Chemistry (United Kingdom)

    2016-10-15

    We have prepared mouse fur extensively {sup 13}C,{sup 15}N-labelled in all amino acid types enabling application of 2D solid state NMR techniques which establish covalent and spatial proximities within, and in favorable cases between, residues. {sup 13}C double quantum–single quantum correlation and proton driven spin diffusion techniques are particularly useful for resolving certain amino acid types. Unlike 1D experiments on isotopically normal material, the 2D methods allow the chemical shifts of entire spin systems of numerous residue types to be determined, particularly those with one or more distinctively shifted atoms such as Gly, Ser, Thr, Tyr, Phe, Val, Leu, Ile and Pro. Also the partial resolution of the amide signals into two signal envelopes comprising of α-helical, and β-sheet/random coil components, enables resolution of otherwise overlapped α-carbon signals into two distinct cross peak families corresponding to these respective secondary structural regions. The increase in resolution conferred by extensive labelling offers new opportunities to study the chemical fate and structural environments of specific atom and amino acid types under the influence of commercial processes, and therapeutic or cosmetic treatments.

  19. Solid state NMR of isotope labelled murine fur: a powerful tool to study atomic level keratin structure and treatment effects

    International Nuclear Information System (INIS)

    Wong, Wai Ching Veronica; Narkevicius, Aurimas; Chow, Wing Ying; Reid, David G.; Rajan, Rakesh; Brooks, Roger A.; Green, Maggie; Duer, Melinda J.

    2016-01-01

    We have prepared mouse fur extensively 13 C, 15 N-labelled in all amino acid types enabling application of 2D solid state NMR techniques which establish covalent and spatial proximities within, and in favorable cases between, residues. 13 C double quantum–single quantum correlation and proton driven spin diffusion techniques are particularly useful for resolving certain amino acid types. Unlike 1D experiments on isotopically normal material, the 2D methods allow the chemical shifts of entire spin systems of numerous residue types to be determined, particularly those with one or more distinctively shifted atoms such as Gly, Ser, Thr, Tyr, Phe, Val, Leu, Ile and Pro. Also the partial resolution of the amide signals into two signal envelopes comprising of α-helical, and β-sheet/random coil components, enables resolution of otherwise overlapped α-carbon signals into two distinct cross peak families corresponding to these respective secondary structural regions. The increase in resolution conferred by extensive labelling offers new opportunities to study the chemical fate and structural environments of specific atom and amino acid types under the influence of commercial processes, and therapeutic or cosmetic treatments.

  20. Identifying vital effects in Halimeda algae with Ca isotopes

    Directory of Open Access Journals (Sweden)

    C. L. Blättler

    2014-12-01

    Full Text Available Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater, resulting in experimental samples with somewhat malformed skeletons. The Ca-isotope fractionation of the algal calcite (−0.6‰ appears to be much smaller than that for the algal aragonite (−1.4‰, similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda has higher Ca-isotope ratios than inorganic forms by approximately 0.25‰, likely because of Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the marine Ca-isotope cycle.

  1. Malic enzyme: Tritium isotope effects with alternative dinucleotide substrates and divalent metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Karsten, W.E.; Harris, B.G.; Cook, P.F. (Texas College of Osteopathic Medicine, Fort Worth (United States))

    1992-01-01

    The NAD-malic enzyme from Ascaris suum catalyzes the divalent metal ion dependent oxidative decarboxylation of L-malate to yield pyruvate, carbon dioxide and NADH. Multiple isotope effect studies suggest a stepwise chemical mechanism with hydride transfer from L-malate to NAD occurring first to form oxalacetate, followed by decarboxylation. Utilizing L-malate-2-T, tritium V/K isotope effects have been determined for the hydride transfer step using a variety of alternative dinucleotide substrates and divalent metal ions. Combination of these data with deuterium isotope effects data and previously determined [sup 13]C isotope effects has allowed the calculation of intrinsic isotope effects for the malic enzyme catalyzed reaction. The identity of both the dinucleotide substrate and divalent metal ion has an effect of the size of the intrinsic isotope effect for hydride transfer.

  2. Malic enzyme: Tritium isotope effects with alternative dinucleotide substrates and divalent metal ions

    International Nuclear Information System (INIS)

    Karsten, W.E.; Harris, B.G.; Cook, P.F.

    1992-01-01

    The NAD-malic enzyme from Ascaris suum catalyzes the divalent metal ion dependent oxidative decarboxylation of L-malate to yield pyruvate, carbon dioxide and NADH. Multiple isotope effect studies suggest a stepwise chemical mechanism with hydride transfer from L-malate to NAD occurring first to form oxalacetate, followed by decarboxylation. Utilizing L-malate-2-T, tritium V/K isotope effects have been determined for the hydride transfer step using a variety of alternative dinucleotide substrates and divalent metal ions. Combination of these data with deuterium isotope effects data and previously determined 13 C isotope effects has allowed the calculation of intrinsic isotope effects for the malic enzyme catalyzed reaction. The identity of both the dinucleotide substrate and divalent metal ion has an effect of the size of the intrinsic isotope effect for hydride transfer

  3. Use of Isotopes for Studying Reaction Mechanisms -RE ...

    Indian Academy of Sciences (India)

    location and distribution of the label in the product(s). There is a more subtle effect ofisotopes which when studied quantitatively can give even greater details of chemical processes. Isotopic substitution can influence an equilibrium, sometimes dramatically. For example, the equilibria are shifted significantly to the right for ...

  4. Determination of underivatized amino acid delta(13)C by liquid chromatography/isotope ratio mass spectrometry for nutritional studies: the effect of dietary non-essential amino acid profile on the isotopic signature of individual amino acids in fish.

    Science.gov (United States)

    McCullagh, James; Gaye-Siessegger, Julia; Focken, Ulfert

    2008-06-01

    This study provides data for the effect of dietary non-essential amino acid composition on the delta(13)C values of individual amino acids in rainbow trout (Oncorhynchus mykiss) using liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS). In this experiment, trout were reared either on a control diet or on three experimental diets, differing in the composition of non-essential/conditionally essential amino acids, for a period of 6 weeks. The control diet was a commercial trout starter feed with fish meal as the main protein source. The experimental diets contained no protein, only synthetic amino acids. Diet 1 resembled the composition of fish meal in both essential and non-essential amino acids, Diet 2 had all essential amino acids, but cysteine, glycine, proline and tyrosine were replaced by the corresponding amounts of their precursors, and in Diet 3 all non-essential amino acids were replaced by glutamate. LC/IRMS was used for the determination of delta(13)C values of individual amino acids from diets and tissues without derivatization. Diet affected the delta(13)C of individual amino acids in fish. For fish on Diets 1-3 amino acid delta(13)C values showed a similar trend: phenylalanine showed very little change from diet to body tissue. Arginine, lysine, tyrosine and proline showed strong depletion from diet to body tissue and glycine, alanine, aspartate and serine all showed variable but strong enrichment in (13)C. Improvements are necessary before all amino acid delta(13)C values can be determined; however, this study demonstrates that measuring amino acid isotopic signatures by LC/IRMS is a promising new technique for nutritional physiologists.

  5. The electrooxidation mechanism of formic acid on platinum and on lead ad-atoms modified platinum studied with the kinetic isotope effect

    Science.gov (United States)

    Bełtowska-Brzezinska, M.; Łuczak, T.; Stelmach, J.; Holze, R.

    2014-04-01

    Kinetics and mechanism of formic acid (FA) oxidation on platinum and upd-lead ad-atoms modified platinum electrodes have been studied using unlabelled and deuterated compounds. Poisoning of the electrode surface by CO-like species was prevented by suppression of dissociative chemisorption of FA due to a fast competitive underpotential deposition of lead ad-atoms on the Pt surface from an acidic solution containing Pb2+ cations. Modification of the Pt electrode with upd lead induced a catalytic effect in the direct electrooxidation of physisorbed FA to CO2. With increasing degree of H/D substitution, the rate of this reaction decreased in the order: HCOOH > DCOOH ≥ HCOOD > DCOOD. HCOOH was oxidized 8.5-times faster on a Pt/Pb electrode than DCOOD. This primary kinetic isotope effect proves that the C-H- and O-H-bonds are simultaneously cleaved in the rate determining step. A secondary kinetic isotope effect was found in the dissociative chemisorption of FA in the hydrogen adsorption-desorption range on a bare Pt electrode after H/D exchange in the C-H bond, wherein the influence of deuterium substitution in the O-H group was negligibly small. Thus the C-H bond cleavage is accompanied by the C-OH and not the O-H bond split in the FA decomposition, producing CO-like species on the Pt surface sites.

  6. Mechanism of inactivation of human leukocyte elastase by a chloromethyl ketone: kinetic and solvent isotope effect studies

    International Nuclear Information System (INIS)

    Stein, R.L.; Trainor, D.A.

    1986-01-01

    The mechanism of inactivation of human leukocyte elastase (HLE) by the chloromethyl ketone MeOSuc-Ala-Ala-Pro-Val-CH 2 Cl was investigated. The dependence of the first-order rate constant for inactivation on concentration of chloromethyl ketone is hyperbolic and suggests formation of a reversible Michaelis complex prior to covalent interaction between the enzyme and inhibitor. However, the observed Ki value is 10 microM, at least 10-fold lower than dissociation constants for complexes formed from interaction of HLE with structurally related substrates or reversible inhibitors, and suggests that Ki is a complex kinetic constant, reflecting the formation and accumulation of both the Michaelis complex and a second complex. It is proposed that this second complex is a hemiketal formed from attack of the active site serine on the carbonyl carbon of the inhibitor. The accumulation of this intermediate may be a general feature of reactions of serine proteases and chloromethyl ketones derived from specific peptides and accounts for the very low Ki values observed for these reactions. The solvent deuterium isotope effect (SIE) on the inactivation step (ki) is 1.58 +/- 0.07 and is consistent with rate-limiting, general-catalyzed attack of the active site His on the methylene carbon of the inhibitor with displacement of chloride anion. The general catalyst is thought to be the active site Asp. In contrast, the SIE on the second-order rate constant for HLE inactivation, ki/Ki, is inverse and equals 0.64 +/- 0.05

  7. STABLE ISOTOPES IN ECOLOGICAL STUDIES: NEW DEVELOPMENTS IN MIXING MODELS

    Science.gov (United States)

    Stable isotopes are increasingly being used as tracers in ecological studies. One application uses isotopic ratios to quantify the proportional contributions of multiple sources to a mixture. Examples include food sources for animals, water sources for plants, pollution sources...

  8. Isotope studies on rice fertilization

    International Nuclear Information System (INIS)

    1978-01-01

    The aim of the report is to provide practical information on the efficient utilization of nitrogen fertilizers in rice production. Results obtained from field investigations during the years 1970 to 1974 in ten countries (Bangladesh, Burma, Indonesia, Republic of Korea, Sri Lanka, Taiwan, Thailand, Vietnam, India, Philippines), using 15 N-labelled nitrogen fertilizers (ammonium sulfate, urea) are given. The experiments, which were conducted both during the dry and wet seasons, included comparison of varieties, effect of placement, source and time of nitrogen fertilizer application on the yield and quality of rice. The data from the project is presented in table form. In most of the experiments, the addition of nitrogen increased the rice grain yield. The role of soil nitrogen vs. fertilizer nitrogen is compared, and it is concluded that the physiological growth stage at which fertilizer-derived nitrogen is absorbed is of great importance

  9. Stable isotope methods: The effect of gut contents on isotopic ratios of zooplankton

    Science.gov (United States)

    Hill, J. M.; McQuaid, C. D.

    2011-05-01

    In the past decade there has been an increased awareness of the potential for methodological bias resulting from multiple pre-analytical procedures in foodweb interpretations based on stable isotope techniques. In the case of small organisms, this includes the effect of gut contents on whole body signatures. Although gut contents may not reflect actual assimilation, their carbon and nitrogen values will be isotopically lighter than after the same material has been assimilated. The potential skewing of isotopic ratios in whole organism samples is especially important for aquatic environments as many studies involve trophic relationships among small zooplankton. This is particularly important in pelagic waters, where herbivorous zooplankton comprise small taxa. Hence this study investigated the effect of gut contents on the δ13C and δ15N ratios of three size classes of zooplankton (1.0-2.0, 2.0-4.0 and >4.0 mm) collected using bongo net tows in the tropical waters of the south-west Indian Ocean. Animals were collected at night, when they were likely to be feeding, sieved into size classes and separated into genera. We focused on Euphausia spp which dominated zooplankton biomass. Three treatment types were processed: bulk animals, bulk animals without guts and tail muscle from each size class at 10 bongo stations. The δ15N ratios were influenced by zooplankton size class, presumably reflecting ontogenetic changes in diet. ANOVA post hoc results and correlations in δ15N signatures among treatments suggest that gut contents may not affect overall nitrogen signatures of Euphausia spp., but that δ13C signatures may be significantly altered by their presence. Carbon interpretations however, were complicated by potential effects of variation in chitin, lipids and metabolism among tissues and the possibility of opportunistic omnivory. Consequently we advocate gut evacuation before sacrifice in euphausiids if specific tissue dissection is impractical and recommend

  10. Carbon-13 kinetic isotope effects in the decarbonylation of lactic acid of natural isotopic composition in phosphoric acid medium

    International Nuclear Information System (INIS)

    Zielinski, M.; Czarnota, G.; Papiernik-Zielinska, H.; Kasprzyk, G.; Gumolka, L.; Staedter, W.

    1993-01-01

    The 13 C kinetic isotope effect fractionation in the decarbonylation of lactic acid (LA) of natural isotopic composition by concentrated phosphoric acids (PA) and by 85% H 3 PO 4 has been studied in the temperature interval of 60-150 deg C. The values of the 13 C (1) isotope effects in the decarbonylation of lactic acid in 100% H 3 PO 4 , in pyrophosphoric acid and in more concentrated phosphoric acids are intermediate between the values calculated assuming that the C (1)- OH bond is broken in the rate-controlling step of dehydration and those calculated for rupture of the carbon-carbon bond in the transition state. In the temperature interval of 90-130 deg C the experimental 13 C fractionation factors determined in concentrated PA approach quite closely the 13 C fractionation corresponding to C (2)- C (1) bond scission. The 13 C (1) kinetic isotope effects in the decarbonylation of LA in 85% orthophosphoric acid in the temperature range of 110-150 deg C coincide with the 13 C isotope effects calculated assuming that the frequency corresponding to the C (1) -OH vibration is lost in the transition state of decarbonylation. A change of the mechanism of decarbonylation of LA in going from concentrated PA medium to 85% H 3 PO 4 has been suggested. A possible secondary 18 O and a primary 18 O kinetic isotope effect in decarbonylation of lactic acid in phosphoric acids media have been discussed, too. (author) 21 refs.; 3 tabs

  11. Expanding the isotopic toolbox: Applications of hydrogen and oxygen stable isotope ratios to food web studies

    OpenAIRE

    Hannah B Vander Zanden; David X Soto; Gabriel J Bowen; Keith A Hobson; Keith A Hobson

    2016-01-01

    The measurement of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H) and oxygen (δ18O) isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applicat...

  12. Expanding the Isotopic Toolbox: Applications of Hydrogen and Oxygen Stable Isotope Ratios to Food Web Studies

    OpenAIRE

    Vander Zanden, Hannah B.; Soto, David X.; Bowen, Gabriel J.; Hobson, Keith A.

    2016-01-01

    The measurement of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H) and oxygen (δ18O) isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applicatio...

  13. The effect of exposure to employees from mining and milling operations in a uranium mine on lead isotopes-a pilot study

    International Nuclear Information System (INIS)

    Gulson, Brian L.; Mizon, Karen J.; Dickson, Bruce L.; Korsch, Michael J.

    2005-01-01

    Potential exposure during mining and milling of uranium ore has resulted in the industry being highly regulated. Exposure can arise from inhalation of the daughter product radioactive gas radon ( 222 Rn), inhalation of radioactive dust particles from mining and milling, direct irradiation from outside the body, and ingestion of radionuclides (e.g. uranium or radium) in food or water. Making use of the highly unusual lead isotopic signature for uranium ores (high 206 Pb/ 204 Pb from the high uranium content, low 208 Pb/ 204 Pb from the low Th/U ratio), we undertook a pilot study of nine male mine employees and three controls from the Ranger uranium mine in the Northern Territory Australia to determine if it was feasible to use lead isotopes in blood to identify exposure to uranium-derived materials. The lead isotopic data for the mine employees and controls plot in two distinct fields which are consistent with predicted isotopic patterns. Assuming retention of 10% of the ingested lead, then the increases seen in 206 Pb represent intakes of between 0.9 and 15 mg, integrated over the years of exposure. The small amount of lead does not affect blood lead concentrations, but appears to be sufficient to be detectable with sensitive isotopic methods. Further studies, including those on urine, should be undertaken to confirm the veracity of the lead isotope method in monitoring exposure of uranium industry employees

  14. The effect of exposure to employees from mining and milling operations in a uranium mine on lead isotopes--a pilot study.

    Science.gov (United States)

    Gulson, Brian L; Mizon, Karen J; Dickson, Bruce L; Korsch, Michael J

    2005-03-01

    Potential exposure during mining and milling of uranium ore has resulted in the industry being highly regulated. Exposure can arise from inhalation of the daughter product radioactive gas radon (222Rn), inhalation of radioactive dust particles from mining and milling, direct irradiation from outside the body, and ingestion of radionuclides (e.g. uranium or radium) in food or water. Making use of the highly unusual lead isotopic signature for uranium ores (high 206Pb/204Pb from the high uranium content, low 208Pb/204Pb from the low Th/U ratio), we undertook a pilot study of nine male mine employees and three controls from the Ranger uranium mine in the Northern Territory Australia to determine if it was feasible to use lead isotopes in blood to identify exposure to uranium-derived materials. The lead isotopic data for the mine employees and controls plot in two distinct fields which are consistent with predicted isotopic patterns. Assuming retention of 10% of the ingested lead, then the increases seen in 206Pb represent intakes of between 0.9 and 15 mg, integrated over the years of exposure. The small amount of lead does not affect blood lead concentrations, but appears to be sufficient to be detectable with sensitive isotopic methods. Further studies, including those on urine, should be undertaken to confirm the veracity of the lead isotope method in monitoring exposure of uranium industry employees.

  15. Broadband non-selective excitation of plutonium isotopes for isotope ratio measurements in resonance ionization mass spectrometry: a theoretical study.

    Science.gov (United States)

    Sankari, M

    2012-10-15

    Making isotope ratio measurements with minimum isotope bias has always been a challenging task to mass spectrometrists, especially for the specific case of plutonium, owing to the strategic importance of the element. In order to use resonance ionization mass spectrometry (RIMS) as a tool for isotope ratio measurements, optimization of the various laser parameters and other atomic and system parameters is critical to minimize isotopic biases. Broadband simultaneous non-selective excitation of the isotopes of plutonium in the triple resonance excitation scheme with λ(1) = 420.77 nm, λ(2) = 847.28 nm, and λ(3) = 767.53 nm based on density matrix formalism has been theoretically computed for the determination of isotope ratios. The effects of the various laser parameters and other factors such as the atomization temperature and the dimensions of the atomic beam on the estimation of isotope ratios were studied. The effects of Doppler broadening, and time-dependent excitation parameters such as Rabi frequencies, ionization rate and the effect of non-Lorenztian lineshape have all been incorporated. The average laser powers and bandwidths for the three-excitation steps were evaluated for non-selective excitation. The laser intensity required to saturate the three-excitation steps were studied. The two-dimensional lineshape contour and its features were investigated, while the reversal of peak asymmetry of two-step and two-photon excitation peaks under these conditions is discussed. Optimized powers for the non-selective ionization of the three transitions were calculated as 545 mW, 150 mW and 545 mW and the laser bandwidth for all the three steps was ~20 GHz. The isotopic bias between the resonant and off-resonant isotope under the optimized conditions was no more than 9%, which is better than an earlier reported value. These optimized laser power and bandwidth conditions are better than in the earlier experimental work since these comprehensive calculations yield

  16. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    Isotopes are generally distinguished by three analytical means. The first ofthem makes use of radioactive isotopes, such as tritium PH), 14C,. 32p etc. This is a highly sensitive technique, but special facilities are required to handle radioactive material. Mass spectroscopy can also be used to detect isotopes. This is also a.

  17. Study on atmospheric hydrogen enrichment by cryopump method and isotope separation by gas chromatography

    International Nuclear Information System (INIS)

    Taniyama, Yuki; Momoshima, Noriyuki

    2001-01-01

    To obtain the information of source of atmospheric hydrogen tritium an analysis of tritium isotopes is thought to be effective. So an atmospheric hydrogen enrichment apparatus and a cryogenic gas chromatographic column were made. Experiments were carried out to study the performance of cryopump to enrich atmospheric hydrogen and the column to separate hydrogen isotopes that obtained by cryopump method. The cryopump was able to process about 1000 1 atmosphere and the column was able to separate hydrogen isotopes with good resolution. (author)

  18. 2015 Accomplishments-Tritium aging studies on stainless steel. Effects of hydrogen isotopes, crack orientation, and specimen geometry on fracture toughness

    Energy Technology Data Exchange (ETDEWEB)

    Morgan, Michael J. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2016-01-01

    This study reports on the effects of hydrogen isotopes, crack orientation, and specimen geometry on the fracture toughness of stainless steels. Fracture toughness variability was investigated for Type 21-6-9 stainless steel using the 7K0004 forging. Fracture toughness specimens were cut from the forging in two different geometric configurations: arc shape and disc shape. The fracture toughness properties were measured at ambient temperature before and after exposure to hydrogen gas and compared to prior studies. There are three main conclusions that can be drawn from the results. First, the fracture toughness properties of actual reservoir forgings and contemporary heats of steel are much higher than those measured in earlier studies that used heats of steel from the 1980s and 1990s and forward extruded forgings which were designed to simulate reservoir microstructures. This is true for as-forged heats as well as forged heats exposed to hydrogen gas. Secondly, the study confirms the well-known observation that cracks oriented parallel to the forging grain flow will propagate easier than those oriented perpendicular to the grain flow. However, what was not known, but is shown here, is that this effect is more pronounced, particularly after hydrogen exposures, when the forging is given a larger upset. In brick forgings, which have a relatively low amount of upset, the fracture toughness variation with specimen orientation is less than 5%; whereas, in cup forgings, the fracture toughness is about 20% lower than that forging to show how specimen geometry affects fracture toughness values. The American Society for Testing Materials (ASTM) specifies minimum specimen section sizes for valid fracture toughness values. However, sub-size specimens have long been used to study tritium effects because of the physical limitation of diffusing hydrogen isotopes into stainless steel at mild temperatures so as to not disturb the underlying forged microstructure. This study shows

  19. Isotope effects in photo dissociation of ozone with visible light

    Science.gov (United States)

    Früchtl, Marion; Janssen, Christof; Röckmann, Thomas

    2014-05-01

    Ozone (O3) plays a key role for many chemical oxidation processes in the Earth's atmosphere. In these chemical reactions, ozone can transfer oxygen to other trace gases. This is particularly interesting, since O3 has a very peculiar isotope composition. Following the mass dependent fractionation equation δ17O = 0.52 * δ18O, most fractionation processes depend directly on mass. However, O3 shows an offset to the mass dependent fractionation line. Processes, which show such anomalies, are termed mass independent fractionations (MIF). A very well studied example for a chemical reaction that leads to mass independent fractionation is the O3 formation reaction. To what degree O3 destruction reactions need to be considered in order to understand the isotope composition of atmospheric O3 is still not fully understood and an open question within scientific community. We set up new experiments to investigate the isotope effect resulting from photo dissociation of O3 in the Chappuis band (R1). Initial O3 is produced by an electric discharge. After photolysis O3 is collected in a cold trap at the triple point temperature of nitrogen (63K). O3 is then converted to O2 in order to measure the oxygen isotopes of O3 using isotope ratio mass spectrometry. To isolate O3 photo dissociation (R1) from O3 decomposition (R2) and secondary O3 formation (R3), we use varying amounts of carbon monoxide (CO) as O atom quencher (R4). In this way we suppress the O + O3 reaction (R3) and determine the isotope fractionation in R1 and R2 separately. We present first results on the isotope effects in O3 photo dissociation with visible light in the presence of different bath gases. Results are interpreted based on chemical kinetics modeling. (R1) O3 + hυ → O (3P) + O2 (R2) O3 + O (3P) → 2 O2 (R3) O + O2 + M → O3 + M (R4) O (3P) + CO + M → CO2 + M

  20. Study of groundwater recharge in Rechna Doab using isotope techniques

    International Nuclear Information System (INIS)

    Sajjad, M.I.; Tasneem, M.A.; Ahmed, M.; Hussain, S.D.; Khan, I.H.; Akram, W.

    1992-04-01

    Isotopic studies were performed in the Rechna Doab area to understand the recharge mechanism, investigate the relative contributions from various sources such as rainfall, rivers and canal system and to estimate the turn over times and replenishment rate of groundwater. The isotopic data suggest that the groundwater in the project area can be divided into different zones each having its own characteristic isotopic composition. The enriched isotopic values show rain recharge and depleted isotopic values are associated with river/canal system while the intermediate isotopic values show a mixing of two or more sources of water. The major contribution, however, comes from canal system. The isotopic data suggest that there is no quick movement of groundwater in the area. 18 figs. (author)

  1. Isotopic Analysis of Fingernails as a USGS Open House Demonstration of the Use of Stable Isotopes in Foodweb Studies

    Science.gov (United States)

    Silva, S. R.; Kendall, C.; Young, M. B.; Choy, D.

    2011-12-01

    The USGS Isotope Tracers Project uses stable isotopes and tritium to add a unique dimension of chemical information to a wide range of environmental investigations. The use and application of isotopes is usually an unfamiliar and even esoteric topic to the general public. Therefore during three USGS open house events, as a public outreach effort, we demonstrated the use of stable isotopes by analyzing nitrogen and carbon isotopes from very small fragments of fingernail from willing participants. We titled the exhibit "You Are What You Eat". The results from all participants were plotted on a graph indicating the general influence of different food groups on the composition of body tissues as represented by fingernails. All participants were assigned a number and no personal-identification information was collected. A subset of participants provided us with an estimate of the number of days a week various foods were eaten and if they were vegetarians, vegans or non-vegetarians. Volunteers from our research group were on hand to explain and discuss fundamental concepts such as how foods attain their isotopic composition, the difference between C3 and C4 plants, the effects of assimilation, trophic enrichment, and the various uses of stable isotopes in environmental studies. The results of the fingernail analyses showed the variation of the range of isotopic compositions among about 400 people at each event, the distinct influence of C4 plants (mainly corn and cane sugar) on our carbon isotopic composition, and the isotopic differences between vegetarians and non vegetarians among other details (http://wwwrcamnl.wr.usgs.gov/isoig/projects/fingernails/). A poll of visitors attending the open house event in 2006 indicated that "You Are What You Eat" was among the most popular exhibits. Following the first two open house events we were contacted by a group of researchers from Brazil who had completed a very similar study. Our collaboration resulted in a publication in

  2. Isotopic effect on thermal physical properties of isotopically modified boron single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Quanli [Japan Science and Technology Corporation, Kawaguchi, Saitama (Japan); Noda, Tetsuji; Suzuki, Hiroshi; Araki, Hiroshi; Numazawa, Takenori; Hirano, Toshiyuki [National Institute for Materials Science, Tsukuba, Ibaraki (Japan); Nogi, Naoyuki; Tanaka, Satoru [University of Tokyo, Department of Quantum Engineering and Systems Science, Tokyo (Japan)

    2002-04-01

    The measurement of specific heat and thermal conductivity at low temperature for isotopically modified boron single crystals was performed between 0.5 and 100K using relaxation method and steady heat flow method, respectively. The results indicate that the specific heat has obvious divergences at T<5K. At 40K, the thermal conductivity of {sup 10}B-enriched crystal is about 570 W/m{center_dot}K, which is 40% larger than that of natural boron crystal. The influence of lattice vibration modes and the isotopic effect on specific heat and thermal conductivity for isotopically modified boron are discussed. (author)

  3. Isotopic modeling of the sub-cloud evaporation effect in precipitation.

    Science.gov (United States)

    Salamalikis, V; Argiriou, A A; Dotsika, E

    2016-02-15

    In dry and warm environments sub-cloud evaporation influences the falling raindrops modifying their final stable isotopic content. During their descent from the cloud base towards the ground surface, through the unsaturated atmosphere, hydrometeors are subjected to evaporation whereas the kinetic fractionation results to less depleted or enriched isotopic signatures compared to the initial isotopic composition of the raindrops at cloud base. Nowadays the development of Generalized Climate Models (GCMs) that include isotopic content calculation modules are of great interest for the isotopic tracing of the global hydrological cycle. Therefore the accurate description of the underlying processes affecting stable isotopic content can improve the performance of iso-GCMs. The aim of this study is to model the sub-cloud evaporation effect using a) mixing and b) numerical isotope evaporation models. The isotope-mixing evaporation model simulates the isotopic enrichment (difference between the ground and the cloud base isotopic composition of raindrops) in terms of raindrop size, ambient temperature and relative humidity (RH) at ground level. The isotopic enrichment (Δδ) varies linearly with the evaporated raindrops mass fraction of the raindrop resulting to higher values at drier atmospheres and for smaller raindrops. The relationship between Δδ and RH is described by a 'heat capacity' model providing high correlation coefficients for both isotopes (R(2)>80%) indicating that RH is an ideal indicator of the sub-cloud evaporation effect. Vertical distribution of stable isotopes in falling raindrops is also investigated using a numerical isotope-evaporation model. Temperature and humidity dependence of the vertical isotopic variation is clearly described by the numerical isotopic model showing an increase in the isotopic values with increasing temperature and decreasing RH. At an almost saturated atmosphere (RH=95%) sub-cloud evaporation is negligible and the isotopic

  4. Isotopically sensitive branching and its effect on the observed intramolecular isotope effects in cytochrome P-450 catalyzed reactions: a new method for the estimation of intrinsic isotope effects

    International Nuclear Information System (INIS)

    Jones, J.P.; Korzekwa, K.R.; Rettie, A.E.; Trager, W.F.

    1986-01-01

    Two selectively deuterated n-octanes (octane-1- 2 H 3 and octane-1,2,3- 2 H 7 ) were synthesized and subjected to hydroxylation by phenobarbital-induced rat liver microsomes and purified cytochrome P-450b. The results of these experiments provide evidence which clarifies the interplay between a branched reaction pathway and the equilibration of an enzyme-substrate complex, in determining the magnitude of an observed isotope effect. An equation is derived that allows limits to placed on the intrinsic isotope effect. The equation is based on the observed isotope effect and the regioselectivity of a branch reaction pathway, catalyzed by an enzyme that forms two products via a single enzyme-substrate complex. The intrinsic isotope effect for the formation of 1-octanol was determined by this equation to lie between 9.5 and 9.8

  5. Stable isotope composition of atmospheric carbon monoxide. A modelling study

    International Nuclear Information System (INIS)

    Gromov, Sergey S.

    2014-01-01

    This study aims at an improved understanding of the stable carbon and oxygen isotope composition of the carbon monoxide (CO) in the global atmosphere by means of numerical simulations. At first, a new kinetic chemistry tagging technique for the most complete parameterisation of isotope effects has been introduced into the Modular Earth Submodel System (MESSy) framework. Incorporated into the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model, an explicit treatment of the isotope effects on the global scale is now possible. The expanded model system has been applied to simulate the chemical system containing up to five isotopologues of all carbon- and oxygen-bearing species, which ultimately determine the δ 13 C, δ 18 O and Δ 17 O isotopic signatures of atmospheric CO. As model input, a new stable isotope-inclusive emission inventory for the relevant trace gases has been compiled. The uncertainties of the emission estimates and of the resulting simulated mixing and isotope ratios have been analysed. The simulated CO mixing and stable isotope ratios have been compared to in-situ measurements from ground-based observatories and from the civil-aircraft-mounted CARIBIC-1 measurement platform. The systematically underestimated 13 CO/ 12 CO ratios of earlier, simplified modelling studies can now be partly explained. The EMAC simulations do not support the inferences of those studies, which suggest for CO a reduced input of the highly depleted in 13 C methane oxidation source. In particular, a high average yield of 0.94 CO per reacted methane (CH 4 ) molecule is simulated in the troposphere, to a large extent due to the competition between the deposition and convective transport processes affecting the CH 4 to CO reaction chain intermediates. None of the other factors, assumed or disregarded in previous studies, however hypothesised to have the potential in enriching tropospheric CO in 13 C, were found significant when explicitly simulated. The

  6. Stable carbon and oxygen isotope study on benthic foraminifera ...

    Indian Academy of Sciences (India)

    Ajoy K Bhaumik

    2017-07-24

    Jul 24, 2017 ... Stable isotopes of benthic foraminifera have widely been applied in micropalaeontological research to understand vital effects in foraminifera. Isotopic fractionations are mainly controlled by ontogeny, bottom/pore water chemistry, habitat preference, kinetic effect and respiration. Discontinuous abundance.

  7. Effect of Nutrient-limitation on the Microbial S-isotope Fractionation

    Science.gov (United States)

    Sim, M.; Bosak, T.; Ono, S.

    2011-12-01

    Microbial sulfate reduction (MSR) utilizes sulfate as an electron acceptor and produces sulfide that is depleted in heavy isotopes of sulfur relative to sulfate. This process controls much of the distribution of sulfur isotopes in sedimentary sulfides and sulfates, but the magnitude of S-isotope fractionations in natural environments often exceeds those in laboratory cultures. This difference may be due to many factors and environmental stresses, including the limitation by essential nutrients. However, none of the studies to date investigated the effect of nutrients such as nitrogen, iron, or phosphate, on sulfur isotope fractionation by sulfate reducing microbes. Here, we examine the influence of N and Fe limitation on multiple-S isotope fractionation by a marine sulfate reducing bacterium by reducing the concentrations of N and Fe in a defined medium by 10 to 1000 times. Nitrogen limitation reduces the growth rate and the cellular yield, but increases the respiration rate without altering the magnitude of isotope fractionation. In contrast, S-isotope fractionation was up to 40% larger in iron-limited than in iron-replete cultures. This increase in sulfur isotope fractionation is accompanied by a decrease in the growth rate, the cellular yield, the respiration rate, and the cytochrome c content. Thus, iron limitation increases the reversibility of microbial sulfate reduction pathway, possibly by affecting iron-containing respiratory complexes such as cytochromes and iron-sulfur proteins. The apparent influence of iron limitation on S-isotope fractionation is relevant to the interpretations of sulfur isotope data in modern and ancient environments. Some areas where iron limitation may lead to large observed S-isotope effects include iron-limited deep open ocean sediments, whereas smaller S-isotope effects would be expected where Fe is more bioavailable (e.g., in anoxic basins, where Fe enrichment occurs due to Fe shuttling).

  8. Some isotope hydrological studies in Southern Africa

    International Nuclear Information System (INIS)

    Verhagen, B.Th.

    2001-01-01

    Four case studies involving the use of the environmental isotopes 14 C and 3 H, in the and to semi-arid Kalahari region of Southern Africa are described and general conclusions regarding the qualitative aspects of recharge and discharge characteristics of the systems are based on these measurements. In each of the studies, diffuse, local recharge was found to be the dominant recharge mechanism. Recharge via river beds was found to be limited at the regional scale. The balancing discharge mechanism for groundwater was found to be via evapotranspiration. Groundwater salinity and mineralisation as well as the regional hydrogeology are controlled by geological structure rather than lithologies or residence times and the absence of hypersaline groundwaters indicates that the aquifers are periodically flushed during pluvial periods, thus pointing to long-term hydroclimatic controls over the observed present-day hydrology. (author)

  9. Isotopes in soil-plant nutrition studies

    International Nuclear Information System (INIS)

    1962-01-01

    Radioisotopes have greatly facilitated investigating the characteristics of plant nutrients in the soil, in measuring soil moisture, in studying the uptake of nutrients by plants and in devising efficient methods of fertilizer application, and are now being widely used in soil-plant nutrition research. A recent international symposium on the use of radioisotopes in soil-plant nutrition studies showed the varied ways in which isotopes can contribute to agricultural production by helping to investigate soil characteristics and soil-plant relationships. The symposium, jointly sponsored by the International Atomic Energy Agency and the Food and Agriculture Organization of the United Nations, was held in Bombay from 26 February to 2 March 1962, at the invitation of the Government of India

  10. Stable Chlorine Isotope Study: Application to Early Solar System Materials

    Science.gov (United States)

    Mala,ira. M/; Nyquist, L. E.; Reese, Y.; Shih, C-Y; Fujitani, T.; Okano, O.

    2010-01-01

    A significantly large mass fractionation between two stable chlorine isotopes is expected during planetary processes In addition, in view of the isotopic heterogeneity of other light elements, the chlorine isotopes can potentially be used as a tracer for the origins and evolutionary processes of early solar system materials. Due to analytical difficulties, however, current chlorine isotope studies on planetary materials are quite controversial among IRMS (gas source mass spectrometry) and/or TIMS (Thermal Ionization Mass Spectrometry) groups [i.e. 1-3]. Although a cross-calibration of IRMS and TIMS indicates that both techniques are sufficiently consistent with each other [4], some authors have claimed that the Cl-37/Cl-35 ratio of geological samples obtained by TIMS technique are, in general, misleadingly too high and variable compared to those of IRMS [3]. For example, almost no differences of Cl isotope composition were observed among mantle materials and carbonaceous meteorites by [3]. On the other hand, according to more recent IRMS work [2], significant Cl isotope variations are confirmed for mantle materials. Therefore, additional careful investigation of Cl isotope analyses are now required to confirm real chlorine isotope variations for planetary materials including carbonaceous chondrites [5]. A significantly large mass fractionation between two stable chlorine isotopes is expected during planetary processes In addition, in view of the isotopic heterogeneity of other light elements, the chlorine isotopes can potentially be used as a tracer for the origins and evolutionary processes of early solar system materials. Due to analytical difficulties, however, current chlorine isotope studies on planetary materials are quite controversial among IRMS (gas source mass spectrometry) and/or TIMS (Thermal Ionization Mass Spectrometry) groups [i.e. 1-3]. Although a cross-calibration of IRMS and TIMS indicates that both techniques are sufficiently consistent with each

  11. An experimental study on the effect of carbonic anhydrase on the oxygen isotope exchange kinetics and equilibrium in the carbonic acid system

    Science.gov (United States)

    Uchikawa, J.; Zeebe, R. E.

    2011-12-01

    Stable oxygen isotopes of marine biogenic carbonates are often depleted in 18O relative to the values expected for thermodynamic equilibrium with ambient seawater. One possibility is that 18O-depletion in carbonates is kinetically controlled. The kinetic isotope effect associated with the hydration of CO2 results in 18O-depleted HCO3-. If the HCO3- is utilized before re-establishing equilibrium with ambient water under rapid calcification, the 18O-depletion will be recorded in carbonates. But one caveat in this kinetic model is the fact that many marine calcifiers posses carbonic anhydrase, a zinc-bearing enzyme that catalyzes the CO2 hydration reaction. It is expected that this enzyme accelerates 18O-equilibration in the carbonic acid system by facilitating direct oxygen isotope exchange between HCO3- and H2O via CO2 hydration. Clearly this argues against the conceptual framework of the kinetic model. Yet the critical variable here is the effectiveness of the carbonic anhydrase, which is likely to depend on its concentration and the carbonate chemistry of the aqueous medium. It is also hitherto unknown whether the presence of carbonic anhydrase alters the equilibrium oxygen isotope fractionations between dissolved carbonate species and water. We performed a series of quantitative inorganic carbonate precipitation experiments to examine the changes in the oxygen isotope equilibration time as a function of carbonic anhydrase concentrations. We conducted experiments at pH 8.3 and 8.9. These pH values are similar to the average surface ocean pH and the elevated pH levels observed within calcification microenvironments of certain corals and planktonic foraminifera. A summary of our new experimental results will be presented.

  12. Great isotope effects in compounding of sodium isotopes by macrocyclic polyether

    International Nuclear Information System (INIS)

    Knoechel, A.; Wilken, R.D.

    1978-01-01

    Isotope effects appear in the compounding of the two sodium isotopes 24 Na + and 22 Na + with macrocyclic polyethers, whose value was determined for the 13 best known polyethers. A radiometric process was used for determining the different half life periods of the nuclides used. To separate the compound and non-compound types, these were distributed between water and chloroform. The isotope ratio in the chloroform phase was compared with the output isotope ratio and the separation facfor determined from this. When using crown ethers, there was enrichment of 24 Na + by a significant amount (large crown ether) up to 3.1 +- 0.4% for 18 crown 6. The remarkably high results can be correlated by Biegeleisen's theory with other chemical conditions. There is a report on the first results of transferring these conditions to the H + /T + system. (orig.) [de

  13. Isotope effect in the Knight shift of potassium

    International Nuclear Information System (INIS)

    Sahm, W.; Schwenk, A.

    1975-01-01

    The Knight shifts of the potassium isotopes 39 K and 41 K were determined with high accuracy: Ksup((39)) = 0.274 35(10)% and Ksup((41)) = 0.274 93(12)%. The relative isotope effect ΔK/K = -0.210 (20)% is in agreement with the hyperfine structure anomaly 39 Δ 41 . (orig.) [de

  14. Variation of kinetic isotope effect in multiple proton transfer reactions

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 124; Issue 1. Variation of kinetic isotope ... An extension of this to the concerted multiple proton transfer reactions implies that the kinetic isotope effect in such reaction depends exponentially on the number of protons that are being transferred. Computational evidence ...

  15. Carbon and hydrogen isotopic effects of stomatal density in Arabidopsis thaliana

    Science.gov (United States)

    Lee, Hyejung; Feakins, Sarah J.; Sternberg, Leonel da S. L.

    2016-04-01

    Stomata are key gateways mediating carbon uptake and water loss from plants. Varied stomatal densities in fossil leaves raise the possibility that isotope effects associated with the openness of exchange may have mediated plant wax biomarker isotopic proxies for paleovegetation and paleoclimate in the geological record. Here we use Arabidopsis thaliana, a widely used model organism, to provide the first controlled tests of stomatal density on carbon and hydrogen isotopic compositions of cuticular waxes. Laboratory grown wildtype and mutants with suppressed and overexpressed stomatal densities allow us to directly test the isotope effects of stomatal densities independent of most other environmental or biological variables. Hydrogen isotope (D/H) measurements of both plant waters and plant wax n-alkanes allow us to directly constrain the isotopic effects of leaf water isotopic enrichment via transpiration and biosynthetic fractionations, which together determine the net fractionation between irrigation water and n-alkane hydrogen isotopic composition. We also measure carbon isotopic fractionations of n-alkanes and bulk leaf tissue associated with different stomatal densities. We find offsets of +15‰ for δD and -3‰ for δ13C for the overexpressed mutant compared to the suppressed mutant. Since the range of stomatal densities expressed is comparable to that found in extant plants and the Cenozoic fossil record, the results allow us to consider the magnitude of isotope effects that may be incurred by these plant adaptive responses. This study highlights the potential of genetic mutants to isolate individual isotope effects and add to our fundamental understanding of how genetics and physiology influence plant biochemicals including plant wax biomarkers.

  16. The use of stable isotopes in drug metabolism studies.

    Science.gov (United States)

    Abramson, F P

    2001-06-01

    Although there is a long history of stable isotopes use in drug metabolism research, it is appropriate to evaluate them in pregnancy drug studies in which safety takes highest priority. It is well established through a number of human and animal experiments that stable isotopes themselves rarely generate additional toxicities beyond the molecules to which they are attached. For the analysis of stable isotopes involved in metabolism studies, mass spectrometry plays the predominant role. Several mass spectrometry-based techniques now exist that enable the selective quantitative detection of stable isotopes with better sensitivity and better retention of chromatographic resolution than do in-line radioactivity monitors for 14C. Even mass balance studies can be performed by using stable isotopes, a type of experiment that still predominantly uses radioisotopes. Some of the newest developments in the use of stable isotopes involve biopolymers, in which fully isotope-labeled species can be generated from cells grown in isotopically labeled growth media. Having shown safety, sensitivity, specificity, and versatility, stable isotopes should play an important role in drug metabolism studies in pregnancy.

  17. Studies of enzyme mechanism using isotopic probes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C.

    1987-01-01

    The isotope partitioning studies of the Ascaris suum NAD-malic enzyme reaction were examined with five transitory complexes including E:NAD, E:NAD:Mg, E:malate, E:Mg:malate, and E:NAD:malate. Three productive complexes, E:NAD, E:NAD:Mg, and E:Mg:malate, were obtained, suggesting a steady-state random mechanism. Data for trapping with E:/sup 14/C-NAD indicate a rapid equilibrium addition of Mg/sup 2 +/ prior to the addition of malate. Trapping with /sup 14/C-malate could only be obtained from the E:Mg/sup 2 +/:/sup 14/C-malate complex, while no trapping from E:/sup 14/C-malate was obtained under feasible experimental conditions. The equations for the isotope partitioning studies varying two substrates in the chase solution in an ordered terreactant reaction were derived, allowing a determination of the relative rates of substrate dissociation to the catalytic reaction for each of the productive transitory complexes. NAD and malate are released from the central complex at an identical rate, equal to the catalytic rate. The release of NAD from E:NAD and E:NAD:Mg complexes is 2- to 4-fold and 5- to 9-fold V/sub max//E/sub t/, respectively. The release of malate from the E:Mg:malate complex is 0.1- to 0.3-fold of V/sub max//E/sub t/. The individual rate constants for association and dissociation of the substrates, NAD and malate have been estimated.

  18. Studies of enzyme mechanism using isotopic probes

    International Nuclear Information System (INIS)

    Chen, C.

    1987-01-01

    The isotope partitioning studies of the Ascaris suum NAD-malic enzyme reaction were examined with five transitory complexes including E:NAD, E:NAD:Mg, E:malate, E:Mg:malate, and E:NAD:malate. Three productive complexes, E:NAD, E:NAD:Mg, and E:Mg:malate, were obtained, suggesting a steady-state random mechanism. Data for trapping with E: 14 C-NAD indicate a rapid equilibrium addition of Mg 2+ prior to the addition of malate. Trapping with 14 C-malate could only be obtained from the E:Mg 2+ : 14 C-malate complex, while no trapping from E: 14 C-malate was obtained under feasible experimental conditions. The equations for the isotope partitioning studies varying two substrates in the chase solution in an ordered terreactant reaction were derived, allowing a determination of the relative rates of substrate dissociation to the catalytic reaction for each of the productive transitory complexes. NAD and malate are released from the central complex at an identical rate, equal to the catalytic rate. The release of NAD from E:NAD and E:NAD:Mg complexes is 2- to 4-fold and 5- to 9-fold V/sub max//E/sub t/, respectively. The release of malate from the E:Mg:malate complex is 0.1- to 0.3-fold of V/sub max//E/sub t/. The individual rate constants for association and dissociation of the substrates, NAD and malate have been estimated

  19. Selected bibliography on deuterium isotope effects and heavy water

    International Nuclear Information System (INIS)

    Dave, S.M.; Donde, M.M.

    1983-01-01

    In recent years, there has been a great deal of interest in using deuterium and heavy water not only in nuclear industry but also in various fields of basic as well as applied research in physics, chemistry and biology. As a result, the literature is being enriched with a large number of research papers and technical reports published each year. Thus, to enable the scientists to have an easy reference to these works, an endeavour has been made in this selected bibliography, to enlist the publications related to these fields. Since the interest is concerned mainly with heavy water production processes, deuterium isotope effects etc., several aspects (e.g. nuclear) of deuterium have not been covered here. The material in this bibliography which cites 2388 references has been classified under six broad headings, viz. (1) Production of heavy water, (2) Study of deuterium isotope effects, (3) Analysis and Properties of heavy water, (4) Laser Separation of deuterium, (5) Isotopic exchange reactions, and (6) Miscellaneous. The sources of information used for this compilation are chemical abstracts, nuclear science abstracts, INIS Atomindex and also some scattered search through journals and reports available in the B.A.R.C. library. However, in spite of sincere attempts for a wide coverage, no claim is being made towards the exhaustiveness of this bibliography. (author)

  20. X-ray diffraction and inelastic neutron scattering study of 1:1 tetramethylpyrazine chloranilic acid complex: temperature, isotope, and pressure effects.

    Science.gov (United States)

    Prager, M; Pietraszko, A; Sobczyk, L; Pawlukojć, A; Grech, E; Seydel, T; Wischnewski, A; Zamponi, M

    2006-11-21

    The x-ray diffraction studies of the title complex were carried out at room temperature and 14 K for H/D (in hydrogen bridge) isotopomers. At 82 K a phase transition takes place leading to a doubling of unit cells and alternation of the hydrogen bond lengths linking tetramethylpyrazine (TMP) and chloranilic acid molecules. A marked H/D isotope effect on these lengths was found at room temperature. The elongation is much smaller at 14 K. The infrared isotopic ratio for O-H(D)...N bands equals to 1.33. The four tunnel splittings of methyl librational ground states of the protonated complex required by the structure are determined at a temperature T=4.2 K up to pressures P=4.7 kbars by high resolution neutron spectroscopy. The tunnel mode at 20.6 microeV at ambient pressure shifts smoothly to 12.2 microeV at P=3.4 kbars. This is attributed to an increase of the strength of the rotational potential proportional to r(-5.6). The three other tunnel peaks show no or weak shifts only. The increasing interaction with diminishing intermolecular distances is assumed to be compensated by a charge transfer between the constituents of deltae/e approximately 0.02 kbar(-1). The phase transition observed between 3.4 and 4.7 kbars leads to increased symmetry with only two more intense tunneling bands. In the isotopomer with deuterated hydrogen bonds and P=1 bar all tunnel intensities become equal in consistency with the low temperature crystal structure. The effect of charge transfer is confirmed by a weakening of rotational potentials for those methyl groups whose tunnel splittings were independent of pressure. Density functional theory calculations for the model TMP.(HF)2 complex and fully ionized molecule TMP+ point out that the intramolecular rotational potential of methyl groups is weaker in the charged species. They do not allow for the unequivocal conclusions about the role of the intermolecular charge transfer effect on the torsional frequencies.

  1. A first isotopic dietary study of the Greenlandic Thule Culture

    DEFF Research Database (Denmark)

    Nelson, D.E.; Lynnerup, Niels; Arneborg, J.

    2012-01-01

    The isotopic dietary method has been applied to samples of some 65 Thule Culture individuals from existing archaeological collections of Greenlandic human skeletal material. The aim was to use the Greenlandic Thule Culture as a test of the isotopic method, in that we know they were heavily...... dependent on marine resources, and should thus provide a direct measure of the isotopic values for humans consuming almost entirely marine protein. The sites from which the material was originally obtained encompass almost the entire periphery of Greenland. Isotopic data from a study of animals of Greenland...

  2. Biosynthetic effects on the stable carbon isotopic compositions of agal lipids: Implications for deciphering the carbon isotopic biomarker record

    NARCIS (Netherlands)

    Sinninghe Damsté, J.S.; Schouten, S.; Klein Breteler, W.C.M.; Blokker, P.; Schogt, N.; Rijpstra, W.I.C.; Grice, K.; Baas, M.

    1998-01-01

    Thirteen species of algae covering an extensive range of classes were cultured and stable carbon isotopic compositions of their lipids were analysed in order to assess carbon isotopic fractionation effects during their biosynthesis. The fatty acids were found to have similar stable carbon isotopic

  3. The effects of inhomogeneous isotope distribution on the vibrational properties of isotope enriched double walled carbon nanotubes

    International Nuclear Information System (INIS)

    Zolyomi, V.; Simon, F.; Rusznyak, A.; Kuerti, J.; Pfeiffer, R.; Peterlik, H.; Kuzmany, H.

    2007-01-01

    The radial breathing mode in the Raman spectrum of 13 C isotope enriched single walled carbon nanotubes is inhomogeneously broadened due to the random distribution of isotopes. We study this effect theoretically using density functional theory within the local density approximation and compare the result with experiments on isotope engineered double walled carbon nanotubes in which the inner tubes were grown from a mixture of 13 C enriched fullerenes and natural fullerenes. As explained by the calculations, this synthesis procedure leads to an increased inhomogeneity compared to a case when only enriched fullerenes are used. The good agreement between the measurements and calculations shows the absence of carbon diffusion along the tube axis during inner tube growth, and presents a strong support of the theory that inner tube growth is governed by Stone-Wales transformations following the interconnection of fullerenes. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Isotope effects in lithium hydride and lithium deuteride crystals by molecular dynamics simulations.

    Science.gov (United States)

    Dammak, Hichem; Antoshchenkova, Ekaterina; Hayoun, Marc; Finocchi, Fabio

    2012-10-31

    Molecular dynamics (MD) simulations have been carried out to study isotope effects in lithium hydride and lithium deuteride crystals. Quantum effects on nuclear motion have been included through a quantum thermal bath (QTB). The interatomic forces were described either within the density functional theory (DFT) in the generalized gradient approximation (GGA) or by the phenomenological approach using the shell model. For both models, the isotopic shift in the lattice parameter can be successfully predicted by QTB-MD simulations. The slope of the experimental isotopic shift in pressure is satisfactorily reproduced by QTB-MD within DFT-GGA, in contrast to both density functional perturbation theory and QTB-MD with the shell model. We have analyzed the reasons for these discrepancies through the vibrational densities of states and the isotopic shifts in bulk modulus. The results illustrate the importance of anharmonic contributions to vibrations and to the isotopic pressure shift between LiH and LiD.

  5. Biological isotopy. Introduction to the isotopic effects and to their applications in biology

    International Nuclear Information System (INIS)

    Tcherkez, G.

    2010-01-01

    Since their discovery in the beginning of the 20. century, the study of stable isotopes has considerably developed. This domain, which remained limited in its applications until the 1990's, has become particularly important thereafter thanks to its practical applications and in particular to its economical impacts. Many techniques used in fraud control, in drugs use control, in selection of high-yield plants etc are based on isotopic abundance measurements. This reference book gives a synthesis of our actual knowledge on the use of stable isotopes and of isotope fractionation in biology. It presents the basic notions of isotopic biochemistry and explains the origin of the isotopic effects. The application principles of these effects to metabolism, to organisms physiology, to environmental biology etc are explained and detailed using examples and exercises. The first chapters present the basic knowledge which defines, from a mathematical point-of-view, the isotopic effects of chemical reactions or of physical processes taking place in biology. The measurements principle of natural isotopes abundance is then synthesised. Finally, all these notions are applied at different scales: enzymes, physiology, metabolism, environment, ecosystems and fraud crackdown. (J.S.)

  6. Kinetic isotope effects significantly influence intracellular metabolite (13) C labeling patterns and flux determination.

    Science.gov (United States)

    Wasylenko, Thomas M; Stephanopoulos, Gregory

    2013-09-01

    Rigorous mathematical modeling of carbon-labeling experiments allows estimation of fluxes through the pathways of central carbon metabolism, yielding powerful information for basic scientific studies as well as for a wide range of applications. However, the mathematical models that have been developed for flux determination from (13) C labeling data have commonly neglected the influence of kinetic isotope effects on the distribution of (13) C label in intracellular metabolites, as these effects have often been assumed to be inconsequential. We have used measurements of the (13) C isotope effects on the pyruvate dehydrogenase enzyme from the literature to model isotopic fractionation at the pyruvate node and quantify the modeling errors expected to result from the assumption that isotope effects are negligible. We show that under some conditions kinetic isotope effects have a significant impact on the (13) C labeling patterns of intracellular metabolites, and the errors associated with neglecting isotope effects in (13) C-metabolic flux analysis models can be comparable in size to measurement errors associated with GC-MS. Thus, kinetic isotope effects must be considered in any rigorous assessment of errors in (13) C labeling data, goodness-of-fit between model and data, confidence intervals of estimated metabolic fluxes, and statistical significance of differences between estimated metabolic flux distributions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Kinetic isotope effects significantly influence intracellular metabolite 13C labeling patterns and flux determination

    Science.gov (United States)

    Wasylenko, Thomas M.; Stephanopoulos, Gregory

    2014-01-01

    Rigorous mathematical modeling of carbon-labeling experiments allows estimation of fluxes through the pathways of central carbon metabolism, yielding powerful information for basic scientific studies as well as for a wide range of applications. However, the mathematical models that have been developed for flux determination from 13C labeling data have commonly neglected the influence of kinetic isotope effects on the distribution of 13C label in intracellular metabolites, as these effects have often been assumed to be inconsequential. We have used measurements of the 13C isotope effects on the pyruvate dehydrogenase enzyme from the literature to model isotopic fractionation at the pyruvate node and quantify the modeling errors expected to result from the assumption that isotope effects are negligible. We show that under some conditions kinetic isotope effects have a significant impact on the 13C labeling patterns of intracellular metabolites, and the errors associated with neglecting isotope effects in 13C-metabolic flux analysis models can be comparable in size to measurement errors associated with GC–MS. Thus, kinetic isotope effects must be considered in any rigorous assessment of errors in 13C labeling data, goodness-of-fit between model and data, confidence intervals of estimated metabolic fluxes, and statistical significance of differences between estimated metabolic flux distributions. PMID:23828762

  8. Oxygen isotope studies of ordinary chondrites

    Science.gov (United States)

    Clayton, Robert N.; Mayeda, Toshiko K.; Olsen, Edward J.; Goswami, J. N.

    1991-01-01

    Several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components (chondrules, fragments, clasts, and matrix). The whole-rock isotopic compositions reflect the iron-group of the meteorite (H, L, or LL). Isotopic uniformity of H3 to H6 and L3 to L6 are consistent with closed-system metamorphism within each parent body. LL3 chondrites differ slightly from LL4 to LL6, implying a small degree of open-system aqueous alteration and carbon reduction. On the scale of individual chondrules, the meteorites are isotopically heterogeneous, allowing recognition of the solar-nebular processes of chondrule formation. Chondrules for all classes of ordinary chondrites are derived from a common population, which was separate from the population of chondrules in carbonaceous or enstatite chondrites. Chondrules define an isotopic mixing line dominated by exchange between (O - 16)-rich and (O - 16)-poor reservoirs. The oxygen isotopic compositions of chondrites serve as 'fingerprints' for identification of genetic association with other meteorite types (achondrites and iron) and for recognition of source materials in meteoritic breccias.

  9. Stable carbon and oxygen isotope study on benthic foraminifera ...

    Indian Academy of Sciences (India)

    The present study is pursued on isotopic values of different pairs of benthic foraminifera from the Krishna–Godavari basin and Peru offshore to understand habitat-wise isotopic variation and ... Department of Applied Geology, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand 826 004, India.

  10. A comparative study on isotopic composition of precipitation in wet ...

    Indian Academy of Sciences (India)

    A comparative study on isotopic composition of precipitation in wet tropic and semi-arid stations across southern India. C Unnikrishnan Warrier∗ and M Praveen Babu. Isotope Hydrology Division, Centre for Water Resources Development and Management,. Kunnamangalam P.O., Kozhikode 673 571, Kerala, India. ∗.

  11. Stable isotope methods in biological and ecological studies of arthropods

    NARCIS (Netherlands)

    Hood-Nowotny, R.C.; Knols, B.G.J.

    2007-01-01

    This is an eclectic review and analysis of contemporary and promising stable isotope methodologies to study the biology and ecology of arthropods. It is augmented with literature from other disciplines, indicative of the potential for knowledge transfer. It is demonstrated that stable isotopes can

  12. Medical applications of Cu, Zn, and S isotope effects.

    Science.gov (United States)

    Albarede, Francis; Télouk, Philippe; Balter, Vincent; Bondanese, Victor P; Albalat, Emmanuelle; Oger, Philippe; Bonaventura, Paola; Miossec, Pierre; Fujii, Toshiyuki

    2016-10-01

    This review examines recent applications of stable copper, zinc and sulfur isotopes to medical cases and notably cancer. The distribution of the natural stable isotopes of a particular element among coexisting molecular species varies as a function of the bond strength, the ionic charge, and the coordination, and it also changes with kinetics. Ab initio calculations show that compounds in which a metal binds to oxygen- (sulfate, phosphate, lactate) and nitrogen-bearing moieties (histidine) favor heavy isotopes, whereas bonds with sulfur (cysteine, methionine) favor light isotopes. Oxidized cations (e.g., Cu(ii)) and low coordination numbers are expected to favor heavy isotopes relative to their reduced counterparts (Cu(i)) and high coordination numbers. Here we discuss the first observations of Cu, Zn, and S isotopic variations, three elements closely related along multiple biological pathways, with emphasis on serum samples of healthy volunteers and of cancer patients. It was found that heavy isotopes of Zn and to an even greater extent Cu are enriched in erythrocytes relative to serum, while the difference is small for sulfur. Isotopic variations related to age and sex are relatively small. The 65 Cu/ 63 Cu ratio in the serum of patients with colon, breast, and liver cancer is conspicuously low relative to healthy subjects. The characteristic time over which Cu isotopes may change with disease progression (a few weeks) is consistent with both the turnover time of the element and albumin half-life. A parallel effect on sulfur isotopes is detected in a few un-medicated patients. Copper in liver tumor tissue is isotopically heavy. In contrast, Zn in breast cancer tumors is isotopically lighter than in healthy breast tissue. 66 Zn/ 64 Zn is very similar in the serum of cancer patients and in controls. Possible reasons for Cu isotope variations may be related to the cytosolic storage of Cu lactate (Warburg effect), release of intracellular copper from cysteine

  13. Isotope effects in ice Ih: A path-integral simulation

    Science.gov (United States)

    Herrero, Carlos P.; Ramírez, Rafael

    2011-03-01

    Ice Ih has been studied by path-integral molecular dynamics simulations, using the effective q-TIP4P/F potential model for flexible water. This has allowed us to analyze finite-temperature quantum effects in this solid phase from 25 to 300 K at ambient pressure. Among these effects we find a negative thermal expansion of ice at low temperatures, which does not appear in classical molecular dynamics simulations. The compressibility derived from volume fluctuations gives results in line with experimental data. We have analyzed isotope effects in ice Ih by considering normal, heavy, and tritiated water. In particular, we studied the effect of changing the isotopic mass of hydrogen on the kinetic energy and atomic delocalization in the crystal as well as on structural properties such as interatomic distances and molar volume. For D2O ice Ih at 100 K we obtained a decrease in molar volume and intramolecular O-H distance of 0.6% and 0.4%, respectively, as compared to H2O ice.

  14. Isotope effects in ice Ih: a path-integral simulation.

    Science.gov (United States)

    Herrero, Carlos P; Ramírez, Rafael

    2011-03-07

    Ice Ih has been studied by path-integral molecular dynamics simulations, using the effective q-TIP4P/F potential model for flexible water. This has allowed us to analyze finite-temperature quantum effects in this solid phase from 25 to 300 K at ambient pressure. Among these effects we find a negative thermal expansion of ice at low temperatures, which does not appear in classical molecular dynamics simulations. The compressibility derived from volume fluctuations gives results in line with experimental data. We have analyzed isotope effects in ice Ih by considering normal, heavy, and tritiated water. In particular, we studied the effect of changing the isotopic mass of hydrogen on the kinetic energy and atomic delocalization in the crystal as well as on structural properties such as interatomic distances and molar volume. For D(2)O ice Ih at 100 K we obtained a decrease in molar volume and intramolecular O-H distance of 0.6% and 0.4%, respectively, as compared to H(2)O ice. © 2011 American Institute of Physics.

  15. Entering chloride kinetic isotope effects in protic and aprotic solvents

    International Nuclear Information System (INIS)

    Cromartie, T.H.; Swain, C.G.

    1976-01-01

    Chlorine kinetic isotope effects for the reaction of ethylene oxide and chloride ion are normal ( 35 Cl/ 37 Cl greater than unity) in protic solvents and in acetone and dimethylformamide (DMF) in the presence of 1 equiv of 2,6-lutidinium ion. In the presence of 0.1 equiv of this cation (and 0.9 of Li + ) the isotope effect in DMF is inverse (0.9922). This is the first observation of an inverse entering-group heavy-atom isotope effect. The reaction of chloride ion with dimethyl sulfate is normal in water but inverse in DMF. The ''normal'' isotope effects are shown to be due in large measure to the dominance of changes in hydrogen bonding to chlorine over changes in carbon--chlorine bonding

  16. Preliminary economic feasibility study of MIP (Medical Isotopes Producer)

    International Nuclear Information System (INIS)

    Mon, G. H.; O, S. Y.

    2004-01-01

    Preliminary economic feasibility study of MIP (Medical Isotopes Producer), which is used liquid nuclear fuel to produce medical isotopes of Mo-99 and Sr-89, was performed. To do this, this study was estimated the IRR(Internal Rate of Return) and PBP(Pay-back Period) about optimistic and pessimistic cases for market penetration of Asia and U.S.A. isotope markets. And sensitivity analysis is also performed about capital cost and price of Mo-99 and Sr-89. According to the results, IRR was between 14.9% and 24.3%, and PBP was between 4.8 years and 7.8 years. These suggest that MIP has economic merits. MIP can produce other medical isotopes such as Sr-90, I-131, Xe-133, Cs-137. So, it is necessary to do cost-benefit analysis considering production of these other isotopes

  17. Absence of isotope effect of diffusion in a metallic glass

    International Nuclear Information System (INIS)

    Heesemann, A.; Raetzke, K.; Faupel, F.; Hoffmann, J.; Heinemann, K.

    1995-01-01

    The isotope effect E = d ln(D)/d ln (1/√m) of Co diffusion in structurally relaxed Co 86 Zr 14 and Co 81 Zr 19 glasses has been measured by means of a radiotracer technique. Within experimental accuracy no isotope effect was detected (E < 0.04). This suggests a highly cooperative diffusion mechanism. The connection between diffusion and collective low-frequency relaxations in glasses is discussed. (orig.)

  18. Hydrochemical and isotope study of Lake Titicaca

    International Nuclear Information System (INIS)

    Gonfiantini, R.; Cioni, R.; Paredes, M.

    2002-01-01

    The chemical and isotopic compositions of Lake Titicaca and its inflow waters (precipitation, tributaries, groundwater) were determined with the aim of establishing the lake chemical and isotope balance. The three main regions of the lake, i.e. the Lago Mayor, the eastern and the western basins of Lago Menor, connected in cascade, show significant chemical and isotopic differences. Chloride and sodium balance indicates that an average of about 92% of the inflow water evaporates, and the remaining 8 % is lost through Rio Desaguadero and infiltration. The balance of each basin is also obtained, including the inter-basin fluxes. The stable isotope balance in not possible because no data are available on the mean atmospheric vapour isotopic composition. However, this was tentatively computed using the fluxes obtained from chemistry. The vapour δ-values are slightly more negative than those of rainfall. Tritium, noble gases and chloro-fluoro-carbons in vertical profiles show that the lake is vertically well mixed and there is no water segregation at depth. (author)

  19. H/D Isotope Effects in Hydrogen Bonded Systems

    Directory of Open Access Journals (Sweden)

    Aleksander Filarowski

    2013-04-01

    Full Text Available An extremely strong H/D isotope effect observed in hydrogen bonded A-H…B systems is connected with a reach diversity of the potential shape for the proton/deuteron motion. It is connected with the anharmonicity of the proton/deuteron vibrations and of the tunneling effect, particularly in cases of short bridges with low barrier for protonic and deuteronic jumping. Six extreme shapes of the proton motion are presented starting from the state without possibility of the proton transfer up to the state with a full ionization. The manifestations of the H/D isotope effect are best reflected in the infra-red absorption spectra. A most characteristic is the run of the relationship between the isotopic ratio nH/nD and position of the absorption band shown by using the example of NHN hydrogen bonds. One can distinguish a critical range of correlation when the isotopic ratio reaches the value of ca. 1 and then increases up to unusual values higher than . The critical range of the isotope effect is also visible in NQR and NMR spectra. In the critical region one observes a stepwise change of the NQR frequency reaching 1.1 MHz. In the case of NMR, the maximal isotope effect is reflected on the curve presenting the dependence of Δd (1H,2H on d (1H. This effect corresponds to the range of maximum on the correlation curve between dH and ΔpKa that is observed in various systems. There is a lack in the literature of quantitative information about the influence of isotopic substitution on the dielectric properties of hydrogen bond except the isotope effect on the ferroelectric phase transition in some hydrogen bonded crystals.

  20. A first isotopic dietary study of the Greenlandic Thule Culture

    DEFF Research Database (Denmark)

    Nelson, D.E.; Lynnerup, Niels; Arneborg, J.

    2012-01-01

    The isotopic dietary method has been applied to samples of some 65 Thule Culture individuals from existing archaeological collections of Greenlandic human skeletal material. The aim was to use the Greenlandic Thule Culture as a test of the isotopic method, in that we know they were heavily...... dependent on marine resources, and should thus provide a direct measure of the isotopic values for humans consuming almost entirely marine protein. The sites from which the material was originally obtained encompass almost the entire periphery of Greenland. Isotopic data from a study of animals of Greenland...... was used as the basis for analysis. As expected, the results indicate that these people were almost entirely dependent on the marine biosphere for their protein. An exception is those from Northeast Greenland, whose isotopic signatures show evidence for consumption of terrestrial protein as well...

  1. Full-dimensional analytical potential energy surface describing the gas-phase Cl + C2H6 reaction and kinetics study of rate constants and kinetic isotope effects.

    Science.gov (United States)

    Rangel, Cipriano; Espinosa-Garcia, Joaquin

    2018-02-07

    Within the Born-Oppenheimer approximation a full-dimensional analytical potential energy surface, PES-2017, was developed for the gas-phase hydrogen abstraction reaction between the chlorine atom and ethane, which is a nine body system. This surface presents a valence-bond/molecular mechanics functional form dependent on 60 parameters and is fitted to high-level ab initio calculations. This reaction presents little exothermicity, -2.30 kcal mol -1 , with a low height barrier, 2.44 kcal mol -1 , and intermediate complexes in the entrance and exit channels. We found that the energetic description was strongly dependent on the ab initio level used and it presented a very flat topology in the entrance channel, which represents a theoretical challenge in the fitting process. In general, PES-2017 reproduces the ab initio information used as input, which is merely a test of self-consistency. As a first test of the quality of the PES-2017, a theoretical kinetics study was performed in the temperature range 200-1400 K using two approaches, i.e. the variational transition-state theory and quasi-classical trajectory calculations, with spin-orbit effects. The rate constants show reasonable agreement with experiments in the whole temperature range, with the largest differences at the lowest temperatures, and this behaviour agrees with previous theoretical studies, thus indicating the inherent difficulties in the theoretical simulation of the kinetics of the title reaction. Different sources of error were analysed, such as the limitations of the PES and theoretical methods, recrossing effects, and the tunnelling effect, which is negligible in this reaction, and the manner in which the spin-orbit effects were included in this non-relativistic study. We found that the variation of spin-orbit coupling along the reaction path, and the influence of the reactivity of the excited Cl( 2 P 1/2 ) state, have relative importance, but do not explain the whole discrepancy. Finally, the

  2. Isotope separation factor and kinetic isotope effect of the hydrogen evolution reaction

    International Nuclear Information System (INIS)

    Krishtalik, L.I.

    2001-01-01

    In the framework of junified approach the experimentally observed dependences of kinetic isotopic effects (KIE) of the reaction of hydrogen electrolytic evolution on the value of potential on electrode were explained. It is shown that hydrogen isotope separation factor depends on KIE for two stages of the reaction, i.e. discharge on the electrode and electrochemical desorption, moreover, decrease in KIE with potential for the desorption stage overbalances its growth for the discharge stage. The reason for KIE decrease is non-activation character of the process, therefore, there is no dependence on potential of relative contribution of the product vibration-excited states [ru

  3. D/H isotopic fractionation effects in the H2-H2O system: An in-situ experimental study at supercritical water conditions

    Science.gov (United States)

    Foustoukos, D.; Mysen, B. O.

    2011-12-01

    Understanding the effect of temperature on the relative distribution of volatiles in supercritical aqueous solutions is important to constrain elemental and isotopic partitioning/fractionation effects in systems applicable to planetary interiors where the temperature-pressure conditions are often beyond existing experimental or theoretical datasets. For example, very little exists for the fundamental equilibria between H2, D2 and HD (H2 + D2 = 2HD), which, in turn, constrains the internal D/H isotope exchange and the evolution of HD in H2-containing systems such as H2-CH4 and H2-H2O. Theoretical calculations considering the partition functions of the molecules predict that with temperature increase, the equilibrium constant of this reaction approximates values that correspond to the stochastic distribution of species. These calculations consider pure harmonic vibrational frequencies, which, however, do not apply to the diatomic molecule of hydrogen, especially because anharmonic oscillations are anticipated to become stronger at high temperatures. Published experimental data have been limited to conditions lower than 468°C with large uncertainties at elevated temperatures. To address the lack of experimental data, a series of hydrothermal diamond anvil experiments has been conducted utilizing vibrational spectroscopy as a novel quantitative method to explore the relative distribution of H- and D-bearing volatiles in the H2-D2-D2O-H2O-Ti-TiO2 system. The fundamentals of this methodology are based on the distinct Raman frequency shift resulting from deuterium substitution in the H-H and O-H bonds. In detail, H2O-D2O solutions (1:1) were reacted with Ti metal (for 3-9hrs) at 600-800°C and pressures of 0.5-1 GPa, leading to formation of H2, D2, HD and HDO species through Ti oxidation and H-D isotope exchange reactions. Experimental results obtained in-situ and in the quenched gas phase, indicate a significant deviation from the theoretical estimate of the equilibrium

  4. Bibliography on vapor pressure isotope effects

    International Nuclear Information System (INIS)

    Jancso, G.

    1980-04-01

    The first Bibliography on Vapour Pressure Isotope and covered the literature of the period from 1919 through December 1975. The present Supplement reviews the literature from January 1976 through December 1979. The bibliography is arranged in chronological order; within each year the references are listed alphabetically according to the name of the first author of each work. (author)

  5. Design study of fuel circulating system using Pd-alloy membrane isotope separation method

    International Nuclear Information System (INIS)

    Naito, T.; Yamada, T.; Yamanaka, T.; Aizawa, T.; Kasahara, T.; Nishikawa, M.; Asami, N.

    1980-01-01

    Design study on the fuel circulating system (FCS) for a tokamak experimental fusion reactor (JXFR) has been carried out to establish the system concept, to plan the development program, and to evaluate the feasibility of diffusion system. The FCS consists of main vacuum system, fuel gas refiners, isotope separators, fuel feeders, and auxiliary systems. In the system design, Pd-alloy membrane permeation method is adopted for fuel refining and isotope separating. All impurities are effectively removed and hydrogen isotopes are sufficiently separated by Pd-alloy membrane. The isotope separation system consists of 1st (47 separators) and 2nd (46 separators) cascades for removing protium and separating deuterium, respectively. In the FCS, while cryogenic distillation method appears to be practicable, Pd-alloy membrane diffusion method is attractive for isotope separation and refining of fuel gas. The choice will have to be based on reliability, economic, and safety analyses

  6. Multiple-sulfur isotope effects during photolysis of carbonyl sulfide

    Directory of Open Access Journals (Sweden)

    Y. Lin

    2011-10-01

    Full Text Available Laboratory experiments were carried out to determine sulfur isotope effects during ultraviolet photolysis of carbonyl sulfide (OCS to carbon monoxide (CO and elemental sulfur (S0. The OCS gas at 3.7 to 501 mbar was irradiated with or without a N2 bath gas using a 150 W Xe arc lamp. Sulfur isotope ratios for the product S0 and residual OCS were analyzed by an isotope ratio mass-spectrometer with SF6 as the analyte gas. The isotope fractionation after correction for the reservoir effects is −6.8‰ for the ratio 34S/32S, where product S0 is depleted in heavy isotopes. The magnitude of the overall isotope effect is not sensitive to the addition of N2 but increases to −9.5‰ when radiation of λ > 285 nm is used. The measured isotope effect reflects that of photolysis as well as the subsequent sulfur abstraction (from OCS reaction. The magnitude of isotope effects for the abstraction reaction is estimated by transition state theory to be between −18.9 and −3.1‰ for 34S which gives the photolysis isotope effect as −10.5 to +5.3‰. The observed triple isotope coefficients are ln(δ34S + 1/ln(δ34S + 1 = 0.534 ± 0.005 and ln(δ36S + 1/ln(δ34S + 1 = 1.980 ± 0.021. These values differ from canonical values for mass-dependent fractionation of 0.515 and 1.90, respectively. The result demonstrates that the OCS photolysis does not produce large isotope effects of more than about 10‰ for 34S/32S, and can be the major source of background stratospheric sulfate aerosol (SSA during volcanic quiescence.

  7. Evaluation of spurious results in the infrared measurement of CO2 isotope ratios due to spectral effects: a computer simulation study

    International Nuclear Information System (INIS)

    Mansfield, C.D.; Rutt, H.N.

    1999-01-01

    The application of infrared spectroscopy to the measurement of carbon isotope ratio breath tests is a promising alternative to conventional techniques, offering relative simplicity and lower costs. However, when designing such an instrument one should be conscious of several spectral effects that may be misinterpreted as changes in the isotope concentration and which therefore lead to spurious results. Through a series of computer simulations which model the behaviour of the CO 2 absorption spectrum, the risk these effects pose to reliable measurement of 13 CO 2 / 12 CO 2 ratios and the measures required to eliminate them are evaluated. The computer model provides a flexible high-resolution spectrum of the four main isotopomer fundamental transitions and fifteen of their most significant hotband transitions. It is demonstrated that the infrared source, infrared windows and breath sample itself all exhibit strong temperature-induced errors but pressure effects do not produce significant errors. We conclude that for reliable measurement of 13 CO 2 / 12 CO 2 ratios using infrared spectroscopy no pressure controls are required, window effects are eliminated using windows wedged at a minimum angle of 0.8-2.2 mrad, depending on the material, and the temperature sensitivity of source and gas cells necessitates stabilization to an accuracy of at least 0.2 K. (author)

  8. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    tionally low barrier. It remained an emotional debate. The contesting scientists devised several methods to prove their respective points of view. One such procedure developed specifically to solve the non- classical ion problem, but one which has general applicability, is the isotopic perturbation method of Martin Saunders.

  9. Enrichment and separation of isotopes utilizing a novel magnetic isotope effect. Final report

    International Nuclear Information System (INIS)

    Chung, C.J.; Turro, N.J.; Ruderman, W.

    1983-04-01

    Results are presented of a study undertaken to find a suitable isotope separation process for the 13 C- 12 C system that could be adapted to a multi-stage process for the commercial enrichment and separation of isotopes. Experiments reveal that solid porous silica provides an appropriate medium for the efficient enrichment of 13 C via the photolysis of dibenzyl ketones (and related ketones). It is concluded that a system can be designed for the practical separation of 13 C from 12 C based on the photolysis in a magnetic field of ketones absorbed on solid porous silica

  10. Thermal Conductivity of Nanotubes: Effects of Chirality and Isotope Impurity

    OpenAIRE

    Gang, Zhang; Li, Baowen

    2005-01-01

    We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality and isotope impurity by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also study the dependence of thermal conductivity on tube length for t...

  11. Effects of organic amendments on water use efficiency evaluated by a stable isotope technique. A case study in experimental mine restoration.

    Science.gov (United States)

    Luna Ramos, Lourdes; Delgado Huertas, Antonio; Miralles Mellado, Isabel; Solé Benet, Albert

    2017-04-01

    Water deficit and low infiltration reduce restoration success in semiarid post-mine soils, where high mortality of plants has been observed in early years of the restoration. Species that originate from arid and semi-arid regions are often considered appropriate for xeriscaping, but there have been relatively few direct measurements of main water related parameters as water use efficiency (WUE) in restoration strategies. In this respect, the goal of this study was to analyse the efficiency with which native plants use water when organic amendments and mulches are applied in mine soil restorations. The experimental design was established in a calcareous quarry in Almería (SE Spain), under arid climate. We tested two organic amendments (sewage sludge from water treatment plant and compost from vegetable residues) and gravel mulch. Three plant species were planted in 50 m2 experimental plots: Macrochloa tenacissima, Genista umbellata and Anthyllis cytisoides. Soil moisture was monitored at a depth of 0.1 m during 4 years and at the end of this period stable isotope of Carbon (δ13C), considered as an effective method to evaluate the plant intrinsic WUE, was measured. We did not observe significant differences in soil moisture among the different soil restoration treatments. With regard to WUE, species is the factor most important to establish differences. Anthyllis cytisoides showed the lowest mean δ13C values, indicating low WUE. On the contrary, Macrochloa tenacissima presented high δ13C values. Moreover, species showed higher δ13C values when gravel mulch was applied. To increase WUE in restored soils under arid conditions it is necessary to apply water conservation methods and to use the most appropriate species.

  12. A stable isotopic study of the diet of Potamonautes sidneyi ...

    African Journals Online (AJOL)

    Natal, South Africa. Recent flood events in the iSimangaliso Wetland Park have allowed a substantial range expansion of this species, including previously hypersaline and desiccated areas. A stable isotope study was conducted to examine ...

  13. Isotopic phonon effects in β-rhombohedral boron--non-statistical isotope distribution.

    Science.gov (United States)

    Werheit, H; Filipov, V; Kuhlmann, U; Schwarz, U; Armbrüster, M; Antadze, M

    2012-05-02

    On the basis of the spectra of IR- and Raman-active phonons, the isotopic phonon effects in β-rhombohedral boron are analysed for polycrystalline (10)B- and (11)B-enriched samples of different origin and high-purity (nat)B single crystals. Intra- and inter-icosahedral B-B vibrations are harmonic, hence meeting the virtual crystal approximation (VCA) requirements. Deviations from the phonon shift expected according to the VCA are attributed to the anharmonic share of the lattice vibrations. In the case of icosahedral vibrations, the agreement with calculations on α-rhombohedral boron by Shirai and Katayama-Yoshida is quite satisfactory. Phonon shifts due to isotopic disorder in (nat)B are separated and determined. Some phonon frequencies are sensitive to impurities. The isotopic phonon effects yield valuable specific information on the nature of the different phonon modes. The occupation of regular boron sites by isotopes deviates significantly from the random distribution. © 2012 IOP Publishing Ltd

  14. Isotope effects in hydrogen atom transfers. 9. Neighboring group participation

    International Nuclear Information System (INIS)

    Lewis, E.S.; Shen, C.C.

    1977-01-01

    The tritium isotope effects in hydrogen abstraction by bromine atoms from HC(Me) 2 CH 2 X have been measured in the photobromination reaction by a technique which measures the specific activity of the HBr product. At 1 0 C and with the reverse reaction suppressed or irrelevant the values for k/sub H//k/sub T/ are 3.9, 8.2, and 11.6 for X = CH 3 , Cl, and Br, respectively. An isotope effect of 3.5 for X = H was also measured, but the contribution of the reverse reaction was not established. The relatively large isotope effect for X = Br is interpreted in terms of a weakening of the CH bond by neighboring bromine participation. The smaller effect of chlorine may correspond to a minor participation, but the unfavorable inductive effect of the chlorine is also a factor. The case of X = Br is the microscopic reverse of the addition of HBr to 2-methylpropene, and the results are compared with isotope effects in the addition to HBr to olefins. The measurement of isotope effect is, within some described limitations, a convenient and general method for detecting neighboring group participation in hydrogen atom abstractions

  15. Stable isotopes in pharmacology studies: present and future

    International Nuclear Information System (INIS)

    Browne, T.R.

    1986-01-01

    Stable-isotope techniques offer advantages over older methods in safety, sensitivity, specificity, and reduction in numbers of subjects required and analytic determinations for some types of pharmacology studies. In addition to their use as internal standards in gas chromatography-mass spectrometry analytic methods, stable isotopes have been successfully employed in studies of absorption, bioavailability, distribution, biotransformation, excretion, metabolite identification, time-dependent and dose-dependent pharmacokinetic changes, drug interactions, pharmacologic changes during pregnancy, mutagenicity, and teratogenicity. 32 references

  16. Ionic conductivity in aqueous solutions: deuterium isotope effect

    International Nuclear Information System (INIS)

    Samanta, Alok; Ghosh, Swapan K.

    1997-01-01

    A simple theoretical investigation of the calculation of ionic conductivity in aqueous solution is presented. The dipolar hard sphere model for the solvent which has been successful elsewhere has been employed here and it has been possible to reproduce the experimental results quite accurately for both water and heavy water using only two parameters. In a more detailed theoretical approach one should employ better models for water with proper account of its vibrations, liberations and also hydrogen bonding. It is also of interest to study the temperature effect and the concentration dependence of the conductivity. The time-dependent friction can also be calculated from the present formalism and be used for the study of isotope effect in proton transfer reactions or other aspects of chemical dynamics

  17. Tightly bound soil water introduces isotopic memory effects on mobile and extractable soil water pools.

    Science.gov (United States)

    Newberry, Sarah L; Prechsl, Ulrich E; Pace, Matthew; Kahmen, Ansgar

    2017-08-01

    Cryogenic vacuum extraction is the well-established method of extracting water from soil for isotopic analyses of waters moving through the soil-plant-atmosphere continuum. We investigate if soils can alter the isotopic composition of water through isotope memory effects, and determined which mechanisms are responsible for it. Soils with differing physicochemical properties were re-wetted with reference water and subsequently extracted by cryogenic water distillation. Results suggest some reference waters bind tightly to the soil and not all of this tightly bound water is removed during cryogenic vacuum extraction. Kinetic isotopic fractionation occurring when reference water binds to the soil is likely responsible for the 18 O-depletion of re-extracted reference water, suggesting an enrichment of the tightly bound soil water pool. Further re-wetting of cryogenically extracted soils indicates an isotopic memory effect of tightly bound soil water on water added to the soil. The data suggest tightly bound soil water can influence the isotopic composition of mobile soil water. Findings show that soils influence the isotope composition of soil water by (i) kinetic fractionation when water is bound to the soil and (ii) equilibrium fractionation between different soil water pools. These findings could be relevant for plant water uptake investigations and complicate ecohydrological and paleohydrological studies.

  18. Thermal neutron beam modification studies using an isotope based neutron radiography facility

    International Nuclear Information System (INIS)

    Baheti, G.L.; Khatri, P.K.; Meghwal, L.R.; Meena, V.L.

    1996-01-01

    Neutron radiography has established itself as one of the advanced NDT technique. Isotope based facilities are being developed to make the technique available for inplant use. Quality of neutron radiograph obtained is a function of beam parameters like flux, Cd ratio and neutron to gamma ratio, scattered neutrons etc. These parameters can be modified using design features of the facility. Effect of modifications in these parameters on final image quality has been studied and were found to be useful in meeting the widely varying radiographic requirements, particularly through an isotope based facility. These modifications can also overcome some of the inherent limitations of isotope based neutron radiography facilities. (author)

  19. An anion-exchange chromatographic study on boron isotopic fractionation at 2 MPa at 293 K.

    Science.gov (United States)

    Musashi, Masaaki; Matsuo, Motoyuki; Oi, Takao; Nomura, Masao

    2006-10-27

    To study boron isotopic fractionation at high pressure, column chromatography operated in the breakthrough manner was performed at 2.0 MPa at 25.0 degrees C. The fractionation factor (S) between boron adsorbed onto strongly basic anion-exchange resin and boron in solution was obtained as 1.013, which was smaller than the values at 0.1 MPa (atmospheric pressure) found in literature. The pressure dependence of S was discussed based on the polymerization of boron in the solution and resin phases and on the occurrence of the pressure dependent isotope effect relating to the molar volume changes of boron species upon isotope substitution.

  20. A latitudinal study of oxygen isotopes within horsehair

    Science.gov (United States)

    Thompson, E.; Bronk Ramsey, C.; McConnell, J. R.

    2016-12-01

    This study aims to explore the hypothesis that 'if oxygen isotope ratios deplete with decreasing temperature then a study of oxygen isotope ratios within horsehair from Oxfordshire to Iceland will show a latitudinal depletion gradient'. By looking at oxygen isotope values at different geographical positions, we can track the relationship with latitude and with different regional climate features. This will provide a firmer understanding of how to compare climate records from different locations. Additionally, a comparison of the horse breeds from this study to those analysed within previous studies will create an even better understanding of the intra-species variation within the δ18O values of horsehair. A total of 24 horses were sampled on the 7th March from Thordale Stud in Shetland, the Icelandic Food And Veterinary Authority in Iceland, the Exmoor Pony Centre in Exmoor and the Pigeon House Equestrian Centre in Oxfordshire. By starting the sampling process from the most recent growth at the follicle, the sampling date becomes a chronological marker, temporally fixing the first sample within a sequential set of data points extending for one year or longer, depending on the length of each individual hair. The samples were analysed for oxygen isotope values using an IRMS coupled within a Sercon HTEA. Preliminary results show a latitudinal gradient is evident on comparison between the locations, consistent with the findings of Darling and Talbot's study of fresh water isotopes in the British Isles (2003). These results support the hypothesis, showing that a study of oxygen isotope ratios within horse hair from Oxfordshire to Iceland showing a latitudinal depletion gradient, consistent with a depletion of oxygen isotope ratios due to decreasing temperatures. Darling, W. and Talbot, J. (2003). The O and H stable isotope composition of freshwaters in the British Isles. 1. Rainfall. Hydrol. Earth System Science, 7(2), pp.163-181.

  1. Introducing fecal stable isotope analysis in primate weaning studies.

    Science.gov (United States)

    Reitsema, Laurie J

    2012-10-01

    This research investigates the potential of a new, noninvasive method for determining age of weaning among primates using stable carbon and nitrogen isotope ratios in feces. Analysis of stable isotope ratios in body tissues is a well-established method in archeology and ecology for reconstructing diet. This is the first study to investigate weaning in primates using fecal stable isotope ratios. Diets of a single François' langur (Trachypithecus francoisi) mother-infant pair at the Toledo Zoo are reconstructed using this technique to track changes in infant suckling behavior over the weaning period. Stable isotope ratios in feces are sampled instead of more traditional samples such as bone or hair to enable daily, noninvasive snapshots of weaning status. Isotopic assessments of weaning status are compared to visual assessments to identify any discordance between the two. Three measurements documented the transition from breast milk to solid foods: stable carbon isotope ratios (δ(13)C), stable nitrogen isotope ratios (δ(15)N), and nitrogen content of feces (%N). It appears that solid foods were introduced at approximately 2 months of infant age, but that nursing continued into the 12th month, when sample collection ceased. Stable isotope data exposed a much longer weaning period than what was expected based on previously published data for captive langurs, and clarified visual estimates of weaning status. This reflects the method's sensitivity to suckling at night and ability to distinguish actual nursing from comfort nursing. After testing this method with zoo animals, it can readily be applied among wild populations. An isotopic approach to weaning provides a new, accurate, and biologically meaningful assessment of interbirth intervals, and facilitates a better understanding of mother-infant interactions. Both of these outcomes are critical for developing successful conservation strategies for captive and wild primates. © 2012 Wiley Periodicals, Inc.

  2. Magnetic isotope and magnetic field effects on the DNA synthesis

    Science.gov (United States)

    Buchachenko, Anatoly L.; Orlov, Alexei P.; Kuznetsov, Dmitry A.; Breslavskaya, Natalia N.

    2013-01-01

    Magnetic isotope and magnetic field effects on the rate of DNA synthesis catalysed by polymerases β with isotopic ions 24Mg2+, 25Mg2+ and 26Mg2+ in the catalytic sites were detected. No difference in enzymatic activity was found between polymerases β carrying 24Mg2+ and 26Mg2+ ions with spinless, non-magnetic nuclei 24Mg and 26Mg. However, 25Mg2+ ions with magnetic nucleus 25Mg were shown to suppress enzymatic activity by two to three times with respect to the enzymatic activity of polymerases β with 24Mg2+ and 26Mg2+ ions. Such an isotopic dependence directly indicates that in the DNA synthesis magnetic mass-independent isotope effect functions. Similar effect is exhibited by polymerases β with Zn2+ ions carrying magnetic 67Zn and non-magnetic 64Zn nuclei, respectively. A new, ion–radical mechanism of the DNA synthesis is suggested to explain these effects. Magnetic field dependence of the magnesium-catalysed DNA synthesis is in a perfect agreement with the proposed ion–radical mechanism. It is pointed out that the magnetic isotope and magnetic field effects may be used for medicinal purposes (trans-cranial magnetic treatment of cognitive deceases, cell proliferation, control of the cancer cells, etc). PMID:23851636

  3. Mass independent isotope effects and their observations in nature

    International Nuclear Information System (INIS)

    Thiemens, M.H.

    2002-01-01

    In 1983, Thiemens and Heidenreich reported the first chemically produced mass independent isotope effect. A significant feature of the fractionation was that it identically produced the isotopic relation observed in the calcium-aluminum inclusions in the Allende meteorite. This δ 17 O=δ 18 O composition had previously been thought to represent a nucleosynthetic component as no chemical process was capable of producing a mass independent isotopic composition. It now appears nearly certain that the meteoritic oxygen isotopic anomalies were produced by chemical, rather than nuclear, processes. Since oxygen is the major element in stony planets this represents a major event in the formation of the solar system. In a recent review (Thiemens, 1999), it has been shown that mass independent isotopic compositions are pervasive in the Earth's atmosphere. Molecules which have been demonstrated to possess mass independent isotopic compositions include: O 2 , O 3 , CO 2 , CO, and N 2 O. In each case, the specific nature of the mass independent isotopic composition has provided details of their atmospheric chemistry that could not have been obtained by any other measurement technique. Most recently, solid materials have been observed to possess mass independent isotopic composition. In this paper, these observations are briefly discussed. These solid reservoirs include: 1) carbonates and sulphates from Mars, 2) terrestrial aerosol sulphate, 3) sulphides and sulphates from the Earth, ranging in time from 3.8 to 2.2 billion years before present, 4) sulphates from the Namibian desert and 5) the Antartic Dry Valleys. The information obtained from these measurements is extraordinarily wide ranging, extending from understanding the history of Martian atmosphereregolith interaction to the evolution of the oxygen in the Earth's earliest atmosphere. As was the case for gas phase species, this information and insight could not have been obtained by any other measurement technique

  4. Isotopic-tracer-aided studies on undesirable effects of heavy metals in the soil-plant system. Part of a coordinated programme on isotopic-tracer-aided studies of agrochemical residue - soil biota interactions

    International Nuclear Information System (INIS)

    Oberlaender, H.E.

    1982-07-01

    Uptake of isotopically labelled mercury (Hg-203), cadmium (Cd-115m) and zinc (Zn-65) from a calcareous chernozem and a podzolized brown earth by spring and winter varieties of wheat, rye and barley was investigated in pot experiments carried out until maturity of the plants. The labelled heavy metals, applied at concentrations innocuous to plant growth (0.5 ppm Hg or Cd, 50 ppm Zn) were determined radiometrically in the straw and in the grains of the harvested plants, as well as in the milling products (bran, semolina and flour) obtained by standard procedures of grain processing. Uptake of mercury was several hundred times smaller than the uptake of cadmium, if both metals were applied to the soil in equal amounts. Whereas the uptake of mercury from the acid soil was insignificant or not detectable, cadmium was taken up from this soil at a much higher rate than from the alkaline soil. Thus, not mercury, but cadmium imposes the greatest hazard on the food chain. Winter varieties of cereals took up more mercury and cadmium than did spring varieties. The content of heavy metals in the plants decreased considerably when plants approached maturity. During translocation through the plants the metals were gradually retained when passing from the stalks (''straw'') into the grains, and from the seed-cover (''bran'') into the endosperm (''flour''). The heavy metal contents of the grain fractions decreased in the order: bran > semolina > flour. Concentrations of heavy metals in flour were 3-8 times smaller than in straw, showing that flour is least affected by heavy metal pollution of cereals via the soil. The metal content of the various flour types was correlated with their percentage of bran and with their ash content. By adding an ion-exchanger to the soil the pattern of relative distribution of heavy metals in mature plants was not changed, but the cadmium content of all cereal products was considerably lowered

  5. Product study of 1-adamantyl and 1-bicyclo[2.2.2]octyl radicals in hydrocarbon solvents. An unusually large hydrogen isotope effect

    International Nuclear Information System (INIS)

    Engel, P.S.; Chae, W.K.; Baughman, S.A.; Marschke, G.E.; Lewis, E.S.; Timberlake, J.W.; Luedtke, A.E.

    1983-01-01

    1-Adamantyl (ada.) and 1-bicyclo[2.2.2]octyl (bo.) radicals have been generated by photolysis of the corresponding azoalkanes in various hydrocarbon solvents. Both radicals abstract hydrogen readily from saturated hydrocarbons and they add to aromatic rings much faster than tert-butyl. does. Despite its reactivity, ada. is remarkably selective in hydrogen atom abstraction, preferring a benzylic hydrogen 25:1 over a cyclohexane hydrogen. The effect of solvent viscosity indicates that formation of the radical dimers biada and bibo occurs in the solvent cage. The most striking result of this work is a deuterium isotope effect of 25 for hydrogen transfer from cyclohexane to ada. at 65 0 C. Steric compression in the transition state is postulated to cause an unusually large tunnel correction and hence a large k/sub H//k/sub D/. 6 tables

  6. Statistical analysis of lead isotope data in provenance studies

    International Nuclear Information System (INIS)

    Reedy, C.L.

    1991-01-01

    This paper reports on tracing artifacts to ore sources which is different from assigning ore samples to time epochs. Until now, archaeometrists working with lead isotopes have used the ratio methods developed by geochronologists. For provenance studies, however, the use of composition data (the fraction of each of the four isotopes) leads to fewer arbitrary choices, two standard types of plots (labelled ternary and canonical variable, and a consistent method of discriminant analysis for separating groups of samples from different sources

  7. Measurement of environmental tritium for isotope hydrology studies

    International Nuclear Information System (INIS)

    1973-01-01

    The Section of Isotope Hydrology of the IAEA Division of Research and Laboratories gains valuable hydrological information from studies of the concentration of environmental tritium in precipitation, surface and groundwater samples from various sites around the world. This photo story shows the steps in the measurement of these very low levels of tritium in water as performed in the Isotope Hydrology Laboratory of the Agency. (author)

  8. Expanding the isotopic toolbox: Applications of hydrogen and oxygen stable isotope ratios to food web studies

    Directory of Open Access Journals (Sweden)

    Hannah B Vander Zanden

    2016-03-01

    Full Text Available The measurement of stable carbon (δ13C and nitrogen (δ15N isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H and oxygen (δ18O isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applications using δ2H and, to a lesser extent, δ18O values have demonstrated potential for these elements to provide novel insights in modern food web studies. We explore the advantages and challenges associated with three applications of δ2H and δ18O values in food web studies. First, large δ2H differences between aquatic and terrestrial ecosystem end members can permit the quantification of energy inputs and nutrient fluxes between these two sources, with potential applications for determining allochthonous vs. autochthonous nutrient sources in freshwater systems and relative aquatic habitat utilization by terrestrial organisms. Next, some studies have identified a relationship between δ2H values and trophic position, which suggests that this marker may serve as a trophic indicator, in addition to the more commonly used δ15N values. Finally, coupled measurements of δ2H and δ18O values are increasing as a result of reduced analytical challenges to measure both simultaneously and may provide additional ecological information over single element measurements. In some organisms, the isotopic ratios of these two elements are tightly coupled, whereas the isotopic disequilibrium in other organisms may offer insight into the diet and physiology of individuals. Although a coherent framework for interpreting δ2H and δ18O data in the context of food web studies is emerging, many fundamental uncertainties remain. We highlight directions for targeted research that

  9. Isotope effect on band gap and radiative transitions properties of boron nitride nanotubes.

    Science.gov (United States)

    Han, Wei-Qiang; Yu, Hua-Gen; Zhi, Chunyi; Wang, Jianbin; Liu, Zhenxian; Sekiguchi, Takashi; Bando, Yoshio

    2008-02-01

    We have carried out an isotope study on the band gap and radiative transition spectra of boron nitride nanotubes (BNNTs) using both experimental and theoretical approaches. The direct band gap of BNNTs was determined at 5.38 eV, independent of the nanotube size and isotope substitution, by cathodoluminescences (CL) spectra. At lower energies, several radiative transitions were observed, and an isotope effect was revealed. In particular, we confirmed that the rich CL spectra between 3.0 and 4.2 eV reflect a phonon-electron coupling mechanism, which is characterized by a radiative transition at 4.09 eV. The frequency red shift and peak broadening due to isotopic effect have been observed. Our Fourier transform infrared spectra and density functional theory calculations suggest that those radiative transitions in BNNTs could be generated by a replacement of some nitrogen atoms with oxygen.

  10. Neutron-rich B isotopes studied with antisymmetrized molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Kanada-En`yo, Y.; Horiuchi, H. [Department of Physics, Kyoto University, Kyoto 606-01 (Japan)

    1995-08-01

    Structure of odd-even B isotopes up to the neutron dripline is studied systematically with the antisymmetrized molecular dynamics (AMD). The AMD method has already proved to be a powerful theoretical approach for the systematic study of nuclear structure in extensive region including exotic neutron-rich nuclei as well as ordinary nuclei. It is owing to its flexible nature free from any model assumptions such as the existence of clusters. The energies and other observed data of B isotopes are reproduced well. Especially very good reproduction of electromagnetic properties is obtained. The systematic behavior of the electromagnetic properties is explained in relation to the drastic change between clustering structure and shell-model-like structure. This explanation gives us an important indication that clustering structure in neutron-rich B nuclei is strongly suggested by the experimental data. It is shown that the structure change with increase of the neutron number is largely governed by the shell effect of neutron orbits. Exotic structure with new type of clustering is suggested to evolve in neutron-rich nuclei near the dripline.

  11. The status of applying stable isotope in the studies of environmental science

    International Nuclear Information System (INIS)

    Bai Zhipeng; Zhang Liwen; Zhu Tan; Feng Yinchang

    2007-01-01

    The stable isotope composition is characteristic in the pollution source, and it is relatively fixed in the process of transferring and reaction. At present the precise analysis result of stable isotope ratio can be obtained easily. So the stable isotopes can be applied to the pollution affair arbitration and source study. The concept and analytical method of stable isotopes are introduced. The research status of the stable isotopes in the field of environmental science and the isotope fractionation is reviewed. (authors)

  12. HPLC isotope effects and macrocycles: the case of Echinocandin B

    International Nuclear Information System (INIS)

    Jones, A.N.; Simpson, R.E.; Jenkins, H.J.

    1992-01-01

    Echinocandin B was catalytically reduced with hydrogen, deuterium, or tritium. HPLC analysis of the products showed that the labeled analogs exhibited a significant isotope effect relative to the unlabeled parent, with the elution order tritiated < deuterated < hydrogenated. Mass spectral data and specific activity measurements indicated label incorporation exceeded saturation of the double bonds. Proton nmr of the deuterated compound indicated labeling was confined to the aliphatic side chain. A model compound, anilonosteareamide, prepared from the linoleic precursor by reduction with hydrogen or deuterium, incorporated the label only in the aliphatic chain, and also exhibited an isotope effect. This helped confirm that label incorporation in only the fatty acid portion of tetrahydroechinocandin B was sufficient to cause the observed isotope effect. (Author)

  13. Contribution to the study of isotopic exchange of hydrogen in purine derivatives

    International Nuclear Information System (INIS)

    Valenta, V.

    1977-01-01

    The dependence was studied of the rate of hydrogen isotopic exchange in purine derivatives in aqueous media. The effect of pH and of temperature was investigated in adenosine, adenosine monophosphate and adenosine triphosphate, and of pH in guanosine, guanosine monophosphate and guanosine triphosphate. The isotopic exchange of hydrogen was studied in the system hexamethyl phosphotriamide - [ 3 H]water - purine derivative (adenine, adenosine, adenosine monophosphate). The reaction mechanism of hydrogen isotopic exchange is discussed. It may be inferred from the measured value of the kinetic isotopic effect. The ''reverse'' isotopic exchange of hydrogen was investigated in [8- 3 H]adenosine, [8- 3 H]adenosine-5'-monophosphate, and [8- 3 H]adenosine-5'-triphosphate. The possible use was verified of the hydrogen isotopic exchange in the system tritium gas - water - purine derivative, catalyzed by metal catalysts, for the preparation of purine derivatives labelled with tritium in position 8. The effect of pH of, the catalyst type and of quantity was studied. Adenosine-5'-triphosphate with a molar activity of 860 GBq/mmol was prepared using carrier-free tritium gas. (author)

  14. Quantum instanton evaluation of the kinetic isotope effects

    Energy Technology Data Exchange (ETDEWEB)

    Vanicek, Jiri; Miller, William H.; Castillo, Jesus F.; Aoiz, F.Javier

    2005-04-19

    A general quantum-mechanical method for computing kinetic isotope effects is presented. The method is based on the quantum instanton approximation for the rate constant and on the path integral Metropolis Monte-Carlo evaluation of the Boltzmann operator matrix elements. It computes the kinetic isotope effect directly, using a thermodynamic integration with respect to the mass of the isotope, thus avoiding the more computationally expensive process of computing the individual rate constants. The method is more accurate than variational transition-state theories or the semiclassical instanton method since it does not assume a single reaction path and does not use a semiclassical approximation of the Boltzmann operator. While the general Monte-Carlo implementation makes the method accessible to systems with a large number of atoms, we present numerical results for the Eckart barrier and for the collinear and full three-dimensional isotope variants of the hydrogen exchange reaction H+H{sub 2} {yields} H{sub 2}+H. In all seven test cases, for temperatures between 250 K and 600 K, the error of the quantum instanton approximation for the kinetic isotope effects is less than {approx}10%.

  15. Nuclear transformations studies in selenium isotopes

    International Nuclear Information System (INIS)

    Lopez M, B.E.

    1976-01-01

    A compilation is made with regard to the chemical effects produced by nuclear transformations, such as the chemical effects of the beta decay and the chemical effects of the reaction (n,γ) in selenium radioisotopes. As a particular case the chemical effect of the isomeric transition of sup(81m)Se(VI) in potassium selenate crystals marked with radioactive selenium is studied experimentally and the method of adsorption in activated carbon is applied for the analytical separation of the traces of the nuclear isomer tetravalent sup(81b)Se(IV) of one fraction which contains the mixture of the selenium radioisotopes. (author)

  16. An Experimental and Theoretical Study on the Kinetic Isotope Effect of C2H6 and C2D6 Reaction with OH

    KAUST Repository

    Khaled, Fathi

    2015-10-30

    We report experimental and theoretical results for the deuterated kinetic isotope effect (DKIE) of the reaction of OH with ethane (C2H6) and deuterated ethane (C2D6). The reactions were investigated behind reflected shock waves over 800–1350 K by monitoring OH radicals near 306.69 nm using laser absorption. In addition, high level CCSD(T)/cc-pV(T,Q)Z//MP2/cc-pVTZ quantum chemical and statistical rate theory calculations were performed which agreed very well with the experimental findings. The results reported herein provide the first experimental evidence that DKIE for alkanes asymptotes to a value of 1.4 at high temperatures.

  17. Contribution to optimisation of Environmental Isotopes tracing in Hydrogeology. Case study of Madagascar

    International Nuclear Information System (INIS)

    RAJAOBELISON, J.

    2003-01-01

    The aim of this work is to suggest some improvements on the theory of interpretation and on the methodological approach for the optimum use of environmental isotopes tracing applied to hydrogeological investigation. A review of the theory of environmental isotopes used in hydrogeology has been made. The main constraints have been highlighted and led to some comments and proposals of improvement, in particular with regard to the continental effect on stable isotopes, to the seasonal variation of groundwater 1 4C content, and to the appropriate model for fractured crystalline aquifers. A literature survey on ten specific scientific papers, dealing with isotopic hydrology in miscellaneous types of aquifers and catchments, allowed to draw a synthesis of the hydrogeological, geochemical and isotopic constraints. A proposal of optimum methodological approach, taking into account the above mentioned constraints, have been inferred. The results of an on-going hydrogeological investigation carried out in the Southern crystalline basement and coastal sedimentary aquifers of Madagascar highlights an unusual methodological approach based on the lack of initial basic hydrogeological data. Besides, it shows to what extent the experience of the above mentioned research works can apply in the specific case of the complex aquifers of Madagascar. The lessons gained from this study contribute to enrich the synthesis of environmental isotopes constraints in hydrogeology and lead to a more realistic methodological approach proposal wich is likely to better make profitable the isotope hydrology technology

  18. Neutron-rich polonium isotopes studied with in-source laser spectroscopy

    CERN Document Server

    Dexters, Wim; Cocolios, T E

    This work studies the unknown region of neutron rich polonium isotopes. The polonium isotopes, with Z=84, lie above the magic lead nuclei (Z=82). The motivation for this research can mainly be found in these lead nuclei. When looking at the changes in the mean square charge radii beyond the N=126 shell gap, a kink is observed. This kink is also found in the radon (Z=86) and radium (Z=88) isotopes. The observed effect cannot be reproduced with our current models. The polonium isotopes yield more information on the kink and they are also able to link the known charge radii in lead isotopes to those in radon and radium. Additionally, the nuclear moments of the odd-neutron isotope $^{211}$Po are investigated. This nucleus has two protons and one neutron more than the doubly magic nucleus $^{208}$Pb. Nuclear moments of isotopes close to this doubly magic nucleus are good tests for the theoretic models. Besides pushing the models to their limits, the nuclear moments of $^{211}$Po also yield new information on the f...

  19. Proceedings of the study of environmental change using isotope techniques

    International Nuclear Information System (INIS)

    2002-01-01

    Global warming is acknowledged as a major crisis facing society today, principally due to anticipated impacts on the environment, and availability and distribution of water resources. Scientific understanding of recent human-induced climate change, as well as evaluation of potential mitigation strategies, is progressively being developed through studies of atmospheric greenhouse gases and modern water energy carbon cycling processes. These efforts have been advanced through study of past global climate changes to understand mechanisms that play a role in determining natural climate fluctuations observed in ice cores, lake and sea sediments, corals, paleo-groundwater, cave deposits, tree rings, and other archives. Predictive models incorporating natural and human-induced climate change processes contribute to a better appreciation for the sensitivity of climate to specific anthropogenic perturbations. Increasingly, isotopes are being integrated in climate change studies. For example, isotope methodologies offer substantial improvements in the ability to label the origin and fate of greenhouse gases, and for studying the water and carbon cycle response to past climate changes, a high priority area for action identified by the Intergovernmental Panel on Climate Change (IPCC). Isotopes are also widely used as diagnostic variables for validation of models aimed at providing a prognosis of future environmental conditions. The International Atomic Energy Agency (IAEA) has long supported research and development of isotope applications for climate studies. The joint IAEA/WMO Global Network for Isotopes in Precipitation managed by the IAEA has for the last four decades provided the basic isotope data necessary for integrating stable oxygen and hydrogen isotopes in climate models. The IAEA has also sponsored co-ordinated research projects on Isotope Variations of Carbon Dioxide and other Trace Gases in the Atmosphere and Isotope-Aided Studies of Atmospheric Carbon Dioxide

  20. Molecular modeling study of lithium isotopic separation by crown-ethers in ethanol

    International Nuclear Information System (INIS)

    Dehez, F.

    2002-01-01

    The isotopic separation of lithium ion isotopes is studied at the CEA in Pierrelatte using a liquid chromatography technique. Exchange systems are composed by crown-ethers grafted on silica (12C4, 15C5, B15C5, DB15C5, 18C6, B18C6). Lithium is introduced as a salt melted in ethanol. This work concerns the theoretical study of lithium isotopic exchange reactions with those systems. After a brief presentation of isotope separation techniques and isotopic effects (Chap.I), we describe the methods of theoretical chemistry used in this work (Chap. II). In chapter III, we test AM1 and PM3 semi-empirical methods for the treatment of Li + /crown-ether species. Then, we calculate isotopic separation factors via ab initio and semi-empirical calculations for the exchange reactions in vacuum. The different crown-ethers are considered with and without graftings arms. Studies of exchange reactions in ethanol are presented in chapter IV. First, each species of the reaction are solvated by a few ethanol molecules. Isotopic separation factors calculated show a large effect of the solvent on the exchange reaction. The effect of the grafting arm has been investigated using hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics for species with the 12C4. Trajectories have been generated successively with 7 Li and 6 Li. Atomic velocity autocorrelation functions have allowed the access to vibrational frequencies necessary to calculate isotopic separation factors. The last chapter is devoted to methodological developments made during this Ph.D. We propose an approach to treat long range electrostatic interactions in hybrid QM/MM method, relying on a lattice summation technique. (author) [fr

  1. Low temperature isotope effects of hydrogen diffusion in metallic glasses

    International Nuclear Information System (INIS)

    Hofmann, A.; Kronmueller, H.

    1989-01-01

    Snoek-like relaxation peaks of Hydrogen and Deuterium in amorphous Fe 80 B 20 , Fe 40 Ni 40 P 14 B 6 and Fe 91 Zr 9 are detected. At low H, D concentrations the peaks are near 200 K and show small isotope effects of the average activation energies (anti Q H ≅ 0.6 eV, anti Q D - anti Q H ≤ 10 meV). For higher H, D-contents the peaks shift to lower temperatures around to 120 K and show distinct isotope effects in the activation energies (anti Q H ≅ 0.3 eV, anti Q D - anti Q H ≅ 30 meV) and in the amplitude of the low temperature tails of the relaxation peaks. This points to isotope mass dependent deviations from the Arrhenius law due to nonthermal tunneling processes. (orig.)

  2. Cl and C isotope analysis to assess the effectiveness of chlorinated ethene degradation by zero-valent iron: Evidence from dual element and product isotope values

    International Nuclear Information System (INIS)

    Audí-Miró, Carme; Cretnik, Stefan; Otero, Neus; Palau, Jordi; Shouakar-Stash, Orfan; Soler, Albert

    2013-01-01

    Highlights: ► TCE and cis-DCE Cl isotope fractionation was investigated for the first time with ZVI. ► A C–Cl bond is broken in the rate-limiting step during ethylene ZVI dechlorination. ► Dual C/Cl isotope plot is a promising tool to discriminate abiotic degradation. ► Product-related carbon isotopic fractionation gives evidence of abiotic degradation. ► Hydrogenolysis and β-dichloroelimination pathways occur simultaneously. - Abstract: This study investigated C and, for the first time, Cl isotope fractionation of trichloroethene (TCE) and cis-dichloroethene (cis-DCE) during reductive dechlorination by cast zero-valent iron (ZVI). Hydrogenolysis and β-dichloroelimination pathways occurred as parallel reactions, with ethene and ethane deriving from the β-dichloroelimination pathway. Carbon isotope fractionation of TCE and cis-DCE was consistent for different batches of Fe studied. Transformation of TCE and cis-DCE showed Cl isotopic enrichment factors (ε Cl ) of −2.6‰ ± 0.1‰ (TCE) and −6.2‰ ± 0.8‰ (cis-DCE), with Apparent Kinetic Isotope Effects (AKIE Cl ) for Cl of 1.008 ± 0.001 (TCE) and 1.013 ± 0.002 (cis-DCE). This indicates that a C–Cl bond breakage is rate-determining in TCE and cis-DCE transformation by ZVI. Two approaches were investigated to evaluate if isotope fractionation analysis can distinguish the effectiveness of transformation by ZVI as opposed to natural biodegradation. (i) Dual isotope plots. This study reports the first dual (C, Cl) element isotope plots for TCE and cis-DCE degradation by ZVI. The pattern for cis-DCE differs markedly from that reported for biodegradation of the same compound by KB-1, a commercially available Dehalococcoides-containing culture. The different trends suggest an expedient approach to distinguish abiotic and biotic transformation, but this needs to be confirmed in future studies. (ii) Product-related isotope fractionation. Carbon isotope ratios of the hydrogenolysis product cis

  3. Effectiveness of different pre-treatments in recovering pre-burial isotopic ratios of charred plants.

    Science.gov (United States)

    Brinkkemper, O; Braadbaart, F; van Os, B; van Hoesel, A; van Brussel, A A N; Fernandes, R

    2018-02-15

    Isotopic analysis of archaeological charred plant remains offers useful archaeological information. However, adequate sample pre-treatment protocols may be necessary to provide a contamination-free isotopic signal while limiting sample loss and achieving a high throughput. Under these constraints, research was undertaken to compare the performance of different pre-treatment protocols. Charred archaeological plant material was selected for isotopic analysis (δ 13 C and δ 15 N values) by isotope ratio mass spectrometry from a variety of plant species, time periods and soil conditions. Preservation conditions and the effectiveness of cleaning protocols were assessed through Fourier transform infrared spectroscopy and X-ray fluorescence (XRF) spectrometry. An acid-base-acid protocol, successfully employed in radiocarbon dating, was used to define a contamination-free isotopic reference. Acid-base-acid isotopic measurements were compared with those obtained from untreated material and an acid-only protocol. The isotopic signals of untreated material and the acid-only protocol typically did not differ more than 1‰ from those of the acid-base-acid reference. There were no significant isotopic offsets between acid-base-acid and acid-only or untreated samples. Sample losses in the acid-base-acid protocol were on average 50 ± 17% (maximum = 98.4%). Elemental XRF measurements showed promising results in the detection of more contaminated samples albeit with a high rate of false positives. For the large range of preservation conditions described in the study, untreated charred plant samples, water cleaned of sediments, provide reliable stable isotope ratios of carbon and nitrogen. The use of pre-treatments may be necessary under different preservation conditions or more conservative measurement uncertainties should be reported. Copyright © 2017 John Wiley & Sons, Ltd.

  4. Isotope effects in the evaporation of water: a status report of the Craig-Gordon model.

    Science.gov (United States)

    Horita, Juske; Rozanski, Kazimierz; Cohen, Shabtai

    2008-03-01

    The Craig-Gordon model (C-G model) [H. Craig, L.I. Gordon. Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperatures, E. Tongiorgi (Ed.), pp. 9-130, Laboratorio di Geologia Nucleare, Pisa (1965).] has been synonymous with the isotope effects associated with the evaporation of water from surface waters, soils, and vegetations, which in turn constitutes a critical component of the global water cycle. On the occasion of the four decades of its successful applications to isotope geochemistry and hydrology, an attempt is made to: (a) examine its physical background within the framework of modern evaporation models, (b) evaluate our current knowledge of the environmental parameters of the C-G model, and (c) comment on a general strategy for the use of these parameters in field applications. Despite its simplistic representation of evaporation processes at the water-air interface, the C-G model appears to be adequate to provide the isotopic composition of the evaporation flux. This is largely due to its nature for representing isotopic compositions (a ratio of two fluxes of different isotopic water molecules) under the same environmental conditions. Among many environmental parameters that are included in the C-G model, accurate description and calculations are still problematic of the kinetic isotope effects that occur in a diffusion-dominated thin layer of air next to the water-air interface. In field applications, it is of importance to accurately evaluate several environmental parameters, particularly the relative humidity and isotopic compositions of the 'free-atmosphere', for a system under investigation over a given time-scale of interest (e.g., hourly to daily to seasonally). With a growing interest in the studies of water cycles of different spatial and temporal scales, including paleoclimate and water resource studies, the importance and utility of the C-G model is also likely to

  5. Chemical Ligation and Isotope Labeling to Locate Dynamic Effects during Catalysis by Dihydrofolate Reductase.

    Science.gov (United States)

    Luk, Louis Y P; Ruiz-Pernía, J Javier; Adesina, Aduragbemi S; Loveridge, E Joel; Tuñón, Iñaki; Moliner, Vincent; Allemann, Rudolf K

    2015-07-27

    Chemical ligation has been used to alter motions in specific regions of dihydrofolate reductase from E. coli and to investigate the effects of localized motional changes on enzyme catalysis. Two isotopic hybrids were prepared; one with the mobile N-terminal segment containing heavy isotopes ((2) H, (13) C, (15) N) and the remainder of the protein with natural isotopic abundance, and the other one with only the C-terminal segment isotopically labeled. Kinetic investigations indicated that isotopic substitution of the N-terminal segment affected only a physical step of catalysis, whereas the enzyme chemistry was affected by protein motions from the C-terminal segment. QM/MM studies support the idea that dynamic effects on catalysis mostly originate from the C-terminal segment. The use of isotope hybrids provides insights into the microscopic mechanism of dynamic coupling, which is difficult to obtain with other studies, and helps define the dynamic networks of intramolecular interactions central to enzyme catalysis. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

  6. Constraints on the vital effect in coccolithophore and dinoflagellate calcite by oxygen isotopic modification of seawater

    Science.gov (United States)

    Hermoso, Michaël; Horner, Tristan J.; Minoletti, Fabrice; Rickaby, Rosalind E. M.

    2014-09-01

    In this study, we show that there are independent controls of 18O/16O and 13C/12C fractionation in coccolithophore and dinoflagellate calcite due to the contrasting kinetics of each isotope system. We demonstrate that the direction and magnitude of the oxygen isotope fractionation with respect to equilibrium is related to the balance between calcification rate and the replenishment of the internal pool of dissolved inorganic carbon (DIC). As such, in fast growing cells, such as those of Emiliania huxleyi and Gephyrocapsa oceanica (forming the so-called ;heavy group;), calcification of the internal carbon pool occurs faster than complete isotopic re-adjustment of the internal DIC pool with H2O molecules. Hence, coccoliths reflect the heavy oxygen isotope signature of the CO2 overprinting the whole DIC pool. Conversely, in large and slow growing cells, such as Coccolithus pelagicus ssp. braarudii, complete re-equilibration is achieved due to limited influx of CO2 leading to coccoliths that are precipitated in conditions close to isotopic equilibrium (;equilibrium group;). Species exhibiting the most negative oxygen isotope composition, such as Calcidiscus leptoporus (;light group;), precipitate coccolith under increased pH in the coccolith vesicle, as previously documented by the ;carbonate ion effect;. We suggest that, for the carbon isotope system, any observed deviation from isotopic equilibrium is only ;apparent;, as the carbon isotopic composition in coccolith calcite is controlled by a Rayleigh fractionation originating from preferential incorporation of 12C into organic matter. Therefore, species with low PIC/POC ratios as E. huxleyi and G. oceanica are shifted towards positive carbon isotope values as a result of predominant carbon fixation into the organic matter. By contrast, cells with higher PIC/POC as C. braarudii and C. leptoporus maintain, to some extent, the original negative isotopic composition of the CO2. The calcareous dinoflagellate

  7. The isotope effect in the thermodynamic parameters of polymerization of styrene

    International Nuclear Information System (INIS)

    Lebedev, B.V.; Kirillin, A.I.; Kozyreva, N.M.; Lebedev, N.K.; Smirnova, N.N.

    1985-01-01

    This paper studies the effect of substitution of hydrogen by deuterium on the thermodynamic criteria of polymerization processes. The isotope effects in the enthalpy, entropy, and Gibbs energy of the polymerization of styrene are studied by the methods of adiabatic and isothermal calorimetry. The heat capacity of polystyrenes and polydeuterostyrenes are shown

  8. Studies of carbon--isotope fractionation. Annual progress report, December 1, 1974--November 30, 1975

    Energy Technology Data Exchange (ETDEWEB)

    Ishida, T.

    1975-12-01

    The vapor pressure isotope effect of /sup 13/C//sup 12/C-substitution in CClF/sub 3/ was measured at temperatures between 169/sup 0/ and 206/sup 0/K by means of cryogenic distillation. The /sup 13/C//sup 12/C-vapor pressure isotope effect in CHF/sub 3/ was also studied at temperatures between 161/sup 0/ and 205/sup 0/K by a similar method. The construction of a cryostat has progressed as scheduled. The investigation of carbon isotope exchange equilibria between carbon dioxide and various carbamates dissolved in various organic solvents has continued. The five-stage system of Taylor-Ghate design was improved to shorten the transient time. A single stage apparatus was designed, built, and tested. These systems are used to measure the equilibrium constants and various phase equilibria involved in the carbon dioxide--carbamate system. The investigation of the explicit method of total isotope effect has made progress. A satisfactory approximation was found for the classical partition function of a Morse oscillator. The method gives a reasonable result at rho identical with /sup 1///sub 2/..sqrt..(u/sub e//x/sub e/) greater than 1.5. The medium cluster approach was applied to isotopic methanes to investigate the effects of intermolecular distance and mutual orientations of molecules in the liquid upon vapor pressure isotope effect. It was found that all geometrical effects studied tend to vanish as the size of clusters is increased. Isotope effect in the zero-point energy shifts on condensation was calculated on the basis of London dispersion forces in liquid and a semi-empirical molecular orbital theory, and was favorably compared with experimental results. (auth)

  9. The essential role of isotopes in studies of water resources

    International Nuclear Information System (INIS)

    1977-01-01

    In studies of surface water, isotope techniques are used to measure water runoff from rain and snow, flow rates of streams and rivers, leakage from lakes, reservoirs and canals and the dynamics of various bodies of water. Studies of groundwater resources (springs, wells) today are virtually unthinkable without isotope techniques. Basically, these techniques are simple and relatively quick. Among the many questions which may be asked of hydrologists about a given groundwater supply, often the most critical one concerns the safe yield so that the source will not run dry, or for a source to be 'mined', the total yield. Isotope techniques can be used to solve such problems as: identification of the origin of groundwater, determination of its age, flow velocity and direction, interrelations between surface waters and ground waters, possible connections between different aquifers, local porosity, transmissivity and dispersivity of an aquifer. The cost of such investigations is often small in comparison to the cost of classical hydrological techniques, and in addition they are able to provide information which sometimes cannot be obtained by other techniques. The IAEA provides assistance to countries in the application of isotope techniques in water resources studies and other hydrology field projects. The examples given of field studies are intended to give some idea of how these techniques are being applied to specific problems in various regions of the world. Most are discussed briefly, but in some cases a more detailed description has been given in order to demonstrate the application of environmental isotope techniques

  10. Fine print in isotope effects: the glucose anomeric equilibrium and binding of glucose to human brain hexokinase

    International Nuclear Information System (INIS)

    Lewis, B.E; Schramm, V.L.

    2002-01-01

    Binding isotope effects are a sensitive measure of changes in molecular vibrational character that occur during ligand-receptor binding. In this study, we have measured isotope effects on the binding of glucose to human brain hexokinase using the ultrafiltration method, with the following results: 0.991±0.001, 0.908±0.003, 1.010±0.001, 0.974±0.002, 1.022±0.002 for [ 14 C]-glucose mixed with [1- 3 H]-, [2- 3 H]-, [3- 3 H]-, [5- 3 H]-, [6,6- 3 H]-glucose, respectively. Comparing the observed data with isotope effects on the anomeric equilibrium in glucose reported previously proves the existence of binding isotope effects in this system. Preliminary computational results are presented to explain the observed binding isotope effects in terms of hydrogen bond patterns and molecular crowding found in the binary complex of sugar and enzyme. (author)

  11. Magic numbers and isotopic effect of ion clusters

    International Nuclear Information System (INIS)

    Wang Guanghou

    1989-04-01

    The magic numbers and isotopic effect as well as stable configurations in relation to the charge state of the clusters are discussed. Ionic (atomic) clusters are small atomic aggregates, a physical state between gas and solid states, and have many interesting properties, some of them are more or less similar to those in nuclei

  12. Kinetic Isotope Effects in the Reduction of Methyl Iodide

    DEFF Research Database (Denmark)

    Holm, Torkil

    1999-01-01

    a-Deuterium kinetic isotope effects (KIE's) have been determined for the reaction of methyl iodide with a series of reducing agents. Reagents which transfer hydride ion in an SN2 reaction show small inverse or small normal KIE's. Reagents which transfer an electron to methyl iodide to produce...

  13. Carbon-13 kinetic isotope effects in the decarbonylations of lactic acid containing 13C at the natural abundance level

    International Nuclear Information System (INIS)

    Zielinski, M.; Czarnota, G.; Papiernik-Zielinska, H.

    1992-01-01

    The 13 C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20-80 deg C. The 13 C (1) isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40 deg C. Below this temperature the 13 C isotope effect in the decarbonylation of lactic acid by concentrated sulfuric acid is normal similarly as has been found in the decarbonylation of lactic [1- 14 C] acid. The experimental values of k (12C) /k (13C) ratios of isotopic rate constants for 12 C and 13 C are close to, but slightly higher than theoretical 13 C-kinetic isotope effects calculated (neglecting tunneling) under the asumption that the C (1) -OH bond is broken in the rate-controlling step of the dehydration reaction. Dilution of concentrated sulfuric acid with water up to 1.4 molar (H 2 O)/(H 2 SO 4 ) ratio caused the increase of the 13 C isotope fractionation from 1.0273 found in concentrated sulfuric acid at 80.5 deg C to 1.0536±0.0008 (at 80.6 deg C). A discussion of the abnormally high temperature dependence of 14 C and 13 C isotope fractionation in this reaction and the discussion of the problem of relative 14 C/ 13 C kinetic isotope effects is given. (author) 18 refs.; 2 tabs

  14. The effect of the isotopic composition of oxygen on the non-mass-dependent isotopic fractionation in the formation of ozone by discharge of O2. [from meteorites

    Science.gov (United States)

    Yang, Jongmann; Epstein, Samuel

    1987-01-01

    Isotopic fractionation processes in the formation of O3 by 20-kV 60-kHz discharge of O2 in a fused silica container at 77 K are investigated experimentally, with a focus on the effects of changes in the isotopic composition of O2, the O2 pressure, the degree of O3 formation, and the discharge geometry on the isotope abundances in the postdischarge O2 and O3. The results are presented in tables and graphs and compared with the predictions of theoretical models involving vibrational anharmonicity and symmetry effects on O3 predissociation. In experiments using O2 enriched with O-17 and O-18, the heavy isotope is enriched in the residual O2 and not in the O3, whereas the opposite is true when atmospheric isotope abundances are used. It is inferred that the predissociation rate depends on the symmetry and mass of the O3 molecules and not on self-shielding or symmetry effects in the reactant O2. The potential value of the present findings for studies of anomalous isotope abundances in meteorites is indicated.

  15. Nitrogen and Oxygen Isotopic Studies of the Marine Nitrogen Cycle.

    Science.gov (United States)

    Casciotti, Karen L

    2016-01-01

    The marine nitrogen cycle is a complex web of microbially mediated reactions that control the inventory, distribution, and speciation of nitrogen in the marine environment. Because nitrogen is a major nutrient that is required by all life, its availability can control biological productivity and ecosystem structure in both surface and deep-ocean communities. Stable isotopes of nitrogen and oxygen in nitrate and nitrite have provided new insights into the rates and distributions of marine nitrogen cycle processes, especially when analyzed in combination with numerical simulations of ocean circulation and biogeochemistry. This review highlights the insights gained from dual-isotope studies applied at regional to global scales and their incorporation into oceanic biogeochemical models. These studies represent significant new advances in the use of isotopic measurements to understand the modern nitrogen cycle, with implications for the study of past ocean productivity, oxygenation, and nutrient status.

  16. Predictive Framework and Experimental Tests of the Kinetic Isotope Effect at Redox-Active Interfaces

    Science.gov (United States)

    Kavner, A.; John, S.; Black, J. R.

    2013-12-01

    Electrochemical reactions provide a compelling framework to study kinetic isotope effects because redox-related processes are important for a wide variety of geological and environmental processes. In the laboratory, electrochemical reaction rates can be electronically controlled and measured in the laboratory using a potentiostat. This enables variation of redox reactions rates independent of changes in chemistry and, and the resulting isotope compositions of reactants and products can be separated and analyzed. In the past years, a series of experimental studies have demonstrated a large, light, and tunable kinetic isotope effect during electrodeposition of metal Fe, Zn, Li, Cu, and Mo from a variety of solutions (e.g. Black et al., 2009, 2010, 2011). A theoretical framework based on Marcus kinetic theory predicts a voltage-dependent kinetic isotope effect (Kavner et al., 2005, 2008), however while this framework was able to predict the tunable nature of the effect, it was not able to simultaneously predict absolute reaction rates and relative isotope rates. Here we present a more complete development of a statistical mechanical framework for simple interfacial redox reactions, which includes isotopic behavior. The framework is able to predict a kinetic isotope effect as a function of temperature and reaction rate, starting with three input parameters: a single reorganization energy which describes the overall kinetics of the electron transfer reaction, and the equilibrium reduced partition function ratios for heavy and light isotopes in the product and reactant phases. We show the framework, elucidate some of the predictions, and show direct comparisons against isotope fractionation data obtained during laboratory and natural environment redox processes. A. Kavner, A. Shahar, F. Bonet, J. Simon and E. Young (2005) Geochim. Cosmochim. Acta, 69(12), 2971-2979. A. Kavner, S. G. John, S. Sass, and E. A. Boyle (2008), Geochim. Cosmochim. Acta, vol 72, pp. 1731

  17. Progress in isotope hydrological study at Olak Lempit, Selangor

    International Nuclear Information System (INIS)

    Md Shahid Ayub

    2002-01-01

    This case study ia an on going project. Initial results from environmental isotopes and CFCs suggested short circuit to the groundwater flow. Removal of confining layer (if any) by mining activities could be the cause. It is also suggested the existence of saltwater / fresh water interface at the south-western fringe of the study area. This study is not yet conclusive. (Author)

  18. Compound-specific Isotope Analysis of Cyanobacterial Pure cultures and Microbial Mats: Effects of Photorespiration?

    Science.gov (United States)

    Jahnke, L. L.; Summons, R. E.

    2006-01-01

    Microbial mats are considered modern homologs of Precambrian stromatolites. The carbon isotopic compositions of organic matter and biomarker lipids provide clues to the depositional environments of ancient mat ecosystems. As the source of primary carbon fixation for over two billion years, an understanding of cyanobacterial lipid biosynthesis, associated isotopic discriminations, and the influence of physiological factors on growth and isotope expression is essential to help us compare modern microbial ecosystems to their ancient counterparts. Here, we report on the effects of photorespiration (PR) on the isotopic composition of cyanobacteria and biomarker lipids, and on potential PR effects associated with the composition of various microbial mats. The high light, high O2 and limiting CO2 conditions often present at the surface of microbial mats are known to support PR in cyanobacteria. The oxygenase function of ribulose bisphosphate carboxylase/oxygenase can result in photoexcretion of glycolate and subsequent degration by heterotrophic bacteria. We have found evidence which supports an isotopic depletion (increased apparent E) scaled to O2 level associated with growth of Phormidium luridum at low CO2 concentrations (less than 0.04%). Similar to previous studies, isotopic differences between biomass and lipid biomarkers, and between lipid classes were positively correlated with overall fractionation, and should provide a means of estimating the influence of PR on overall isotopic composition of microbial mats. Several examples of microbial mats growing in the hydrothermal waters of Yellowstone National Park and the hypersaline marine evaporation ponds at Guerrero Negro, Baja Sur Mexico will be compared with a view to PR as a possible explanation of the relatively heavy C-isotope composition of hypersaline mats.

  19. Transient competitive complexation in biological kinetic isotope fractionation explains nonsteady isotopic effects: Theory and application to denitrification in soils

    Science.gov (United States)

    Maggi, Federico; Riley, William J.

    2009-12-01

    The theoretical formulation of biological kinetic isotope fractionation often assumes first-order or Michaelis-Menten kinetics, the latter solved under the quasi-steady state assumption. Both formulations lead to a constant isotope fractionation factor, therefore they may return incorrect estimations of isotopic effects and misleading interpretations of isotopic signatures when fractionation is not a steady process. We have analyzed the isotopic signature of denitrification in biogeochemical soil systems by Menyailo and Hungate (2006) in which high and variable 15N-N2O enrichment during N2O production and inverse isotope fractionation during N2O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with Michaelis-Menten kinetics. When Michaelis-Menten kinetics were coupled to Monod kinetics to describe biomass and enzyme dynamics, and the quasi-steady state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observed concentrations, and variable and inverse isotope fractionations. These results imply a substantial revision in modeling isotopic effects, suggesting that steady state kinetics such as first-order, Rayleigh, and classic Michaelis-Menten kinetics should be superseded by transient kinetics in conjunction with biomass and enzyme dynamics.

  20. Study of oxygen isotope ratio in accessory zircons

    International Nuclear Information System (INIS)

    Bibikova, E.V.; Ustinov, V.I.; Gracheva, T.V.; Kiselevskij, M.A.; Shukolyukov, Yu.A.

    1982-01-01

    The isotope ratio of oxygen has been studied in accessory zircons of ores predominantly of granite composition, of different age with a known contents and distribution of radioactive elements in the grain volume, which enabled one to calculate the integral dose of the mineral structure irradiation by alpha-particles. The degree of zircon structure metamict character has been also calculated from the data obtained with the use of infrared spectroscopy. It is shown that for the totally metamictous zircons the exchange between the structural oxygen and the oxygen of water is characteristic, the water easily penetrating into broken structure of the mineral and washing out the radiogenic lead. The prevailing role of the chemical processes is confirmed, but not of the diffusion ones resulting in the lead carry-over, break of the U-Pb isotope system, and appearance of discordant ages. The isotopically light zircon proves to be less suitable for geochronological studies

  1. Dew water effects on leaf water using a stable isotope approach

    Science.gov (United States)

    Kim, K.; Lee, X.

    2009-12-01

    The presence of dew is a common meteorological phenomenon in field conditions and takes into account for significant portion of hydrologic processes in terrestrial ecosystems. The isotope composition of leaf water plays an important role in the isotopic water and carbon fluxes between terrestrial plants and the atmosphere. However, the consequence of dew formation in the plant-atmosphere relations has been ignored in many studies. The objective of this study is to improve our understanding of environmental and biological controls on the leaf water in equilibrium with dew water through laboratory experiments. Five species of plants (soybean, corn, sorghum, wheat, cotton) were grown hydroponically with water of a known isotopic content in a greenhouse. On the day of the experiment, they were first moved to ambient environment in full sunlight for at least 6 hr and then into a dark container inside the lab for up to 48 hr in which water vapor isotope ratios, temperature, and humidity were controlled. This arrangement created a step change in the forcing on the plant isotopic exchange. Leaves were sampled prior to the transfer to the dark container and 6 more times every 4 - 12 hr over the experiment. Humidity inside the container was saturated to mimic dew events in field conditions. Water from the leaf samples was extracted by a vacuum line and was analyzed for both δD and δ18O. The dataset will allow us to evaluate leaf water isotopic theories by exploring the transitions of the isotopic ratio of leaf water in response to the step change. Specifically, we are interested in whether the stomatal opening is an effective pathway for gaseous exchange in total darkness and how the transitional behaviors of the isotopic ratio of leaf water differ between the C3 and C4 photosynthesis pathways.

  2. Ageing and structural effects on the sorption characteristics of Cd2+ by clinoptilolite and Y-type zeolite studied using isotope exchange technique

    International Nuclear Information System (INIS)

    Ahmed, I.A.M.; Young, S.D.; Crout, N.M.J.

    2010-01-01

    This research investigates the long-term kinetics of Cd 2+ sorption and desorption by calcium-exchanged clinoptilolite (CaCpt) and Y-type (CaY) zeolite using isotopic exchange with 109 Cd while maintaining pH at circumneutral values. The effects of Si/Al ratio and crystal structure of these zeolitic materials on intracrystalline transport of Cd are discussed. A first-order kinetic model was developed to describe the progressive transfer of Cd 2+ to a less reactive form within the zeolite structure, following initial sorption and subsequent desorption of Cd subject to different initial contact times. The kinetic model differentiates between two forms of sorbed Cd 2+ designated 'labile' and 'non-labile' in which the labile form is in immediate equilibrium with the free Cd 2+ ion activity in solution. A model combining diffusion and first-order kinetics for cation exchange was also employed to determine Cd 2+ diffusivity and intracrystalline exchange rates in CaY and CaCpt. The efficiency of Permeable Reactive Barriers (PRBs) containing zeolitic materials in protecting water systems against lateral flow of metal-contaminated leachate was simulated for three contrasting zeolites. The slow transfer of Cd between labile and non-labile forms was particularly important in moderating high concentration pulses of Cd traversing the PRB. In addition, the reversibility of Cd fixation effectively restored the sorption capability of the zeolite through slow leakage to drainage water.

  3. Protonation mechanism and location of rate-determining steps for the Ascaris suum nicotinamide adenine dinucleotide-malic enzyme reaction from isotope effects and pH studies

    Energy Technology Data Exchange (ETDEWEB)

    Kiick, D.M.; Harris, B.G.; Cook, P.F.

    1986-01-14

    The pH dependence of the kinetic parameters and the primary deuterium isotope effects with nicotinamide adenine dinucleotide (NAD) and also thionicotinamide adenine dinucleotide (thio-NAD) as the nucleotide substrates were determined in order to obtain information about the chemical mechanism and location of rate-determining steps for the Ascaris suum NAD-malic enzyme reaction. The maximum velocity with thio-NAD as the nucleotide is pH-independent from pH 4.2 to 9.6, while with NAD, V decreases below a pK of 4.8. V/K for both nucleotides decreases below a pK of 5.6 and above a pK of 8.9. Both the tartronate pKi and V/Kmalate decrease below a pK of 4.8 and above a pK of 8.9. Oxalate is competitive vs. malate above pH 7 and noncompetitive below pH 7 with NAD as the nucleotide. The oxalate Kis increases from a constant value above a pK of 4.9 to another constant value above a pK of 6.7. The oxalate Kii also increases above a pK of 4.9, and this inhibition is enhanced by NADH. In the presence of thio-NAD the inhibition by oxalate is competitive vs. malate below pH 7. For thio-NAD, both DV and D(V/K) are pH-independent and equal to 1.7. With NAD as the nucleotide, DV decreases to 1.0 below a pK of 4.9, while D(V/KNAD) and D(V/Kmalate) are pH-independent. Above pH 7 the isotope effects on V and the V/K values for NAD and malate are equal to 1.45, the pH-independent value of DV above pH 7. Results indicate that substrates bind to only the correctly protonated form of the enzyme. Two enzyme groups are necessary for binding of substrates and catalysis. Both NAD and malate are released from the Michaelis complex at equal rates which are equal to the rate of NADH release from E-NADH above pH 7. Below pH 7 NADH release becomes more rate-determining as the pH decreases until at pH 4.0 it completely limits the overall rate of the reaction.

  4. Protonation mechanism and location of rate-determining steps for the Ascaris suum nicotinamide adenine dinucleotide-malic enzyme reaction from isotope effects and pH studies

    International Nuclear Information System (INIS)

    Kiick, D.M.; Harris, B.G.; Cook, P.F.

    1986-01-01

    The pH dependence of the kinetic parameters and the primary deuterium isotope effects with nicotinamide adenine dinucleotide (NAD) and also thionicotinamide adenine dinucleotide (thio-NAD) as the nucleotide substrates were determined in order to obtain information about the chemical mechanism and location of rate-determining steps for the Ascaris suum NAD-malic enzyme reaction. The maximum velocity with thio-NAD as the nucleotide is pH-independent from pH 4.2 to 9.6, while with NAD, V decreases below a pK of 4.8. V/K for both nucleotides decreases below a pK of 5.6 and above a pK of 8.9. Both the tartronate pKi and V/Kmalate decrease below a pK of 4.8 and above a pK of 8.9. Oxalate is competitive vs. malate above pH 7 and noncompetitive below pH 7 with NAD as the nucleotide. The oxalate Kis increases from a constant value above a pK of 4.9 to another constant value above a pK of 6.7. The oxalate Kii also increases above a pK of 4.9, and this inhibition is enhanced by NADH. In the presence of thio-NAD the inhibition by oxalate is competitive vs. malate below pH 7. For thio-NAD, both DV and D(V/K) are pH-independent and equal to 1.7. With NAD as the nucleotide, DV decreases to 1.0 below a pK of 4.9, while D(V/KNAD) and D(V/Kmalate) are pH-independent. Above pH 7 the isotope effects on V and the V/K values for NAD and malate are equal to 1.45, the pH-independent value of DV above pH 7. Results indicate that substrates bind to only the correctly protonated form of the enzyme. Two enzyme groups are necessary for binding of substrates and catalysis. Both NAD and malate are released from the Michaelis complex at equal rates which are equal to the rate of NADH release from E-NADH above pH 7. Below pH 7 NADH release becomes more rate-determining as the pH decreases until at pH 4.0 it completely limits the overall rate of the reaction

  5. The effect of pressure, isotopic (H/D) substitution, and other variables on miscibility in polymer-solvent systems. The nature of the demixing process; dynamic light scattering and small angle neutron scattering studies. Final report

    International Nuclear Information System (INIS)

    Van Hook, W.A.

    2000-01-01

    A research program examining the effects of pressure, isotope substitution and other variables on miscibility in polymer solvent systems is described. The techniques employed included phase equilibrium measurements and dynamic light scattering and small angle neutron scattering

  6. Rubidium-strontium and uranium-lead isotopic age studies

    International Nuclear Information System (INIS)

    Loveridge, W.D.

    1981-01-01

    The results of five Rb-Sr isotopic age studies predominantly on whole-rock samples, and six U-Pb studies on zircon monazite concentrates are presented. Descriptions of the geological problems and interpretations of the measured ages are included. Laboratory age determination methods and techniques are described or referenced

  7. Stable isotopes in plant nutrition, soil fertility and environmental studies

    International Nuclear Information System (INIS)

    1991-01-01

    The individual contributions in these proceedings are indexed separately. Main topics covered include the measurement of biological nitrogen fixation, studies of soil organic matter, investigations of nutrient uptake and use by plants, studies of plant metabolism and new methodologies in the analysis of stable isotopes. Refs, figs and tabs

  8. Menopause effect on blood Fe and Cu isotope compositions.

    Science.gov (United States)

    Jaouen, Klervia; Balter, Vincent

    2014-02-01

    Iron (δ(56) Fe) and copper (δ(65) Cu) stable isotope compositions in blood of adult human include a sex effect, which still awaits a biological explanation. Here, we investigate the effect of menopause by measuring blood δ(56) Fe and δ(65) Cu values of aging men and women. The results show that, while the Fe and Cu isotope compositions of blood of men are steady throughout their lifetime, postmenopausal women exhibit blood δ(65) Cu values similar to men, and δ(56) Fe values intermediate between men and premenopausal women. The residence time of Cu and Fe in the body likely explains why the blood δ(65) Cu values, but not the δ(56) Fe values, of postmenopausal women resemble that of men. We suggest that the Cu and Fe isotopic fractionation between blood and liver resides in the redox reaction occurring during hepatic solicitation of Fe stores. This reaction affects the Cu speciation, which explains why blood Cu isotope composition is impacted by the cessation of menstruations. Considering that Fe and Cu sex differences are recorded in bones, we believe this work has important implications for their use as a proxy of sex or age at menopause in past populations. Copyright © 2013 Wiley Periodicals, Inc.

  9. Tritium conductivity and isotope effect in proton-conducting perovskites

    International Nuclear Information System (INIS)

    Mukundan, R.; Brosha, E.L.; Birdsell, S.A.; Costello, A.L.; Garzon, F.H.; Willms, R.S.

    1999-01-01

    The tritium ion conductivities of SrZr 0.9 Yb 0.1 O 2.95 and BaCe 0.9 Yb 0.1 O 2.95 have been measured by ac impedance analysis. The high tritium conductivity of these perovskites could potentially lead to their application as an electrochemical membrane for the recovery of tritium from tritiated gas streams. The conductivities of these perovskites, along with SrCe 0.95 Yb 0.05 O 2.975 , were also measured in hydrogen- and deuterium-containing atmospheres to illustrate the isotope effect. For the strontium zirconate and barium cerate samples, the impedance plot consists of two clearly resolved arcs, a bulk and a grain boundary arc, in the temperature range 50--350 C. However, for the strontium cerate sample, the clear resolution of the bulk conductivity was not possible and only the total conductivity was measurable. Thus, the isotope effect was clearly established only for the strontium zirconate and barium cerate samples. The decrease in bulk conductivity with increasing isotope mass was found to be a result of an increase in the activation energy for conduction accompanied by a decrease in the pre-exponential factor. Since the concentration of the mobile species (H+, D+, or T+) should remain relatively constant at T < 350 C, this increase in activation energy is directly attributable to the increased activation energy for the isotope mobility

  10. Bibliographical study on photochemical separation of uranium isotopes

    International Nuclear Information System (INIS)

    Bougon, Roland

    1975-01-01

    The objective of this report is to propose an overview of knowledge and current works on isotopic separation of uranium by means of selective excitation where this excitation is obtained by a light source with a wave length corresponding to a selective or preferential absorption by a molecule or by the atom itself of one of the isotopes. After a brief overview of principles and requirements of isotopic separation by selective excitation, the author reviews compounds which can be used for this process. These compounds are mainly considered in terms of spectroscopy, and the study focuses on the most volatile among them, the uranium hexafluoride, its spectra, and possible processes for extraction. Some much less volatile uranium compounds are also mentioned with, when available, their spectroscopic properties. The uranium vapour excitation process is described, and some orientations for further researches are proposed [fr

  11. Structure of potassium isotopes studied with collinear laser spectroscopy

    CERN Document Server

    AUTHOR|(CDS)2082445

    By exploring the structure of different nuclei, one can learn about the interaction between the nucleons, their building blocks. In this field of research, there is a strong interplay between experiment and theory. In particular, theory has a crucial role in the interpretation of the experimental results, while new experimental results provide testing ground and directions for theorists. In the light- and mid-mass regions of the nuclear chart, the shell model is very successful and widely used for calculations of the ground- as well as excited- states properties. It is based on associated larger energy gaps between single particle energy levels for isotopes with certain proton (Z) and neutron (N) numbers, which are called "magic numbers". It was believed that these numbers (8, 20, 28, ...) are preserved for all nuclei throughout the nuclear chart. However, during the last decades studies of the isotopes with an unbalanced number of protons and neutrons revealed that in these isotopes the shell gaps could chan...

  12. Oxygen-18 Isotopic Studies of HOOO and DOOO.

    Science.gov (United States)

    Barreau, Lou; Martinez, Oscar; Crabtree, Kyle N; Womack, Caroline C; Stanton, John F; McCarthy, Michael C

    2017-08-24

    Owing to questions that still persist regarding the length of the O-H and central O-O bond, and large-amplitude torsional motion of trans hydridotrioxygen HOOO, a weakly bound complex between OH and O 2 , new 18 O isotopic measurements of HOOO and DOOO were undertaken using Fourier transform microwave and microwave-millimeter-wave double resonance techniques. Rotational lines from three new 18 O species of DOOO (D 18 OOO, DO 18 O 18 O, and D 18 O 18 O 18 O) were detected, along with the two singly substituted 18 O isotopic species of HOOO (HO 18 OO and HOO 18 O) that were not measured in the previous isotopic investigation. From a least-squares fit, spectroscopic constants, including the three rotational constants, were precisely determined for all five species. The inertial defect of DOOO and its 18 O species is uniformly negative: of order -0.04 amu Å 2 , regardless of the number or location of the 18 O atoms, in contrast to that found for HOOO or its 18 O isotopic species. A reanalysis of the molecular structure was performed using either normal HOOO and its four singly substituted isotopic species, the new DOOO data, or all the isotopic species (10 in total). The differences between the purely experimental (r 0 ) structures are generally quite small, of order ±0.01 Å for the bond lengths and ±1° for the bond angle. The length of the O-H bond remains unrealistically short compared to free OH, and the central O-O bond length is consistently very close to 1.68 Å. On the basis of the effective O-H bond length derived from the experimental structure, the average displacement of the large amplitude torsional motion from planarity is estimated to be ∼22°.

  13. In situ NRA study of hydrogen isotope exchange in self-ion damaged tungsten exposed to neutral atoms

    Science.gov (United States)

    Markelj, S.; Založnik, A.; Schwarz-Selinger, T.; Ogorodnikova, O. V.; Vavpetič, P.; Pelicon, P.; Čadež, I.

    2016-02-01

    Isotope exchange was studied in-situ by Nuclear Reaction Analysis in the bulk of self-ion damaged tungsten at 600 K. Both variations of isotope exchange of H by D and of D by H were measured. The deuterium isothermal desorption was also studied and evaluated in order to be able to resolve the self-desorption from the isotope exchange at 600 K. The isotope exchange was also studied on the surface by Elastic Recoil Detection Analysis at 480 K and 380 K. The exchange mechanism was effective both on the surface and in the bulk of damaged tungsten. A simple model was introduced to describe the exchange efficiency on the surface and in the bulk obtaining the exchange cross sections on the surface and in bulk. In both cases an isotope effect was observed, where the exchange of H atoms by D atoms was more efficient than for the reverse sequence.

  14. Study on the meat isotopic composition for origin identification

    Directory of Open Access Journals (Sweden)

    Irina Chernukha

    2018-03-01

    Full Text Available Russian consumer and governmental authorities are equally concerned to know where food products come from. This requires more accurate and specialized methods for the evaluation of geographical location. The following methods are used: chemometrics, histological and histochemical, genomic and proteomic, microbiological, immunochemical and mass spectrometric. Method of stable isotope analysis is becoming increasingly promising nowadays for the identification of meat and meat products' place of origin. The isotope ratios of the four elements - carbon, nitrogen, oxygen and hydrogen, are mainly determined. The method is successfully used to identify a country of origin of wines, juices and water. The aim of the research was to study the stable isotope ratios for pork and beef samples purchased in Moscow supermarkets (Russian Federation. The country of production of meat samples was determined according to specifications and/or labels. The geography of countries of meat samples origin includes Europe, both America continents and Australia. Databases collected by the All-Russian Scientific Research Institute of the Brewing, Non-Alcoholic and Wine Industrywere used for the analysis and interpretation of the results. Values of 13С/12С, δ13С, 18О/16О, δ18О, 2Н/1Н, δ2Н for 30 pork and beef samples from 13 countries were obtained. Differences in stable isotope ratios were found depending on place of origin. The data correlated with the oxygen isotope characteristics for wine, which were in the range from 2.5 to 4.5 ppm. According to the 13С/12С, δ13С results, the assumption was made about a false indication of the region for the beef sample. Despite the fact that beef was labeled as a product of Lithuania, the region of origin was most probably defined as Germany. The studies carried out showed the possibility to identify the region of raw meat origin by the stable isotope ratio.

  15. Study of variations of stable isotopes in precipitation: case of Antananarivo

    International Nuclear Information System (INIS)

    Randrianarivola, M.

    2014-01-01

    The isotopic signature of precipitation is the input signal in any study of hydrological cycle. The scientific objective of this work is to better understand the isotopic variations in precipitation and identify their processes. We used the network of measurement GNIP (Global Network of Isotopes in Precipitation) in which data is acquired by the International Atomic Energy Agency through isotope hydrology laboratory at INSTN-Madagascar. Analyzes stable isotopes ( 18O and 2 H), were performed at a monthly time step. We were able to confirm the relative importance of different mechanisms governing the isotopic composition of precipitation. The spatial distribution of abundance ratios of Antananarivo rain is in fact dictated by the temperature which follow indirectly from the effects of altitude and seasonal variations. At the monthly scale, local meteoric water line δ 2 H versus δ 18 O shows the specificity of Antananarivo (deuterium excess of 17.5‰ ). Additionally, seasonal variations in precipitation is related to the temperature such that in summer (d=15‰) and winter (d=18‰) [fr

  16. Nitrogen and Oxygen Isotope Effects of Ammonia Oxidation by Thermophilic Thaumarchaeota from a Geothermal Water Stream.

    Science.gov (United States)

    Nishizawa, Manabu; Sakai, Sanae; Konno, Uta; Nakahara, Nozomi; Takaki, Yoshihiro; Saito, Yumi; Imachi, Hiroyuki; Tasumi, Eiji; Makabe, Akiko; Koba, Keisuke; Takai, Ken

    2016-08-01

    Ammonia oxidation regulates the balance of reduced and oxidized nitrogen pools in nature. Although ammonia-oxidizing archaea have been recently recognized to often outnumber ammonia-oxidizing bacteria in various environments, the contribution of ammonia-oxidizing archaea is still uncertain due to difficulties in the in situ quantification of ammonia oxidation activity. Nitrogen and oxygen isotope ratios of nitrite (δ(15)NNO2- and δ(18)ONO2-, respectively) are geochemical tracers for evaluating the sources and the in situ rate of nitrite turnover determined from the activities of nitrification and denitrification; however, the isotope ratios of nitrite from archaeal ammonia oxidation have been characterized only for a few marine species. We first report the isotope effects of ammonia oxidation at 70°C by thermophilic Thaumarchaeota populations composed almost entirely of "Candidatus Nitrosocaldus." The nitrogen isotope effect of ammonia oxidation varied with ambient pH (25‰ to 32‰) and strongly suggests the oxidation of ammonia, not ammonium. The δ(18)O value of nitrite produced from ammonia oxidation varied with the δ(18)O value of water in the medium but was lower than the isotopic equilibrium value in water. Because experiments have shown that the half-life of abiotic oxygen isotope exchange between nitrite and water is longer than 33 h at 70°C and pH ≥6.6, the rate of ammonia oxidation by thermophilic Thaumarchaeota could be estimated using δ(18)ONO2- in geothermal environments, where the biological nitrite turnover is likely faster than 33 h. This study extended the range of application of nitrite isotopes as a geochemical clock of the ammonia oxidation activity to high-temperature environments. Because ammonia oxidation is generally the rate-limiting step in nitrification that regulates the balance of reduced and oxidized nitrogen pools in nature, it is important to understand the biological and environmental factors underlying the regulation of

  17. Nitrogen and Oxygen Isotope Effects of Ammonia Oxidation by Thermophilic Thaumarchaeota from a Geothermal Water Stream

    Science.gov (United States)

    Sakai, Sanae; Konno, Uta; Nakahara, Nozomi; Takaki, Yoshihiro; Saito, Yumi; Imachi, Hiroyuki; Tasumi, Eiji; Makabe, Akiko; Koba, Keisuke; Takai, Ken

    2016-01-01

    ABSTRACT Ammonia oxidation regulates the balance of reduced and oxidized nitrogen pools in nature. Although ammonia-oxidizing archaea have been recently recognized to often outnumber ammonia-oxidizing bacteria in various environments, the contribution of ammonia-oxidizing archaea is still uncertain due to difficulties in the in situ quantification of ammonia oxidation activity. Nitrogen and oxygen isotope ratios of nitrite (δ15NNO2− and δ18ONO2−, respectively) are geochemical tracers for evaluating the sources and the in situ rate of nitrite turnover determined from the activities of nitrification and denitrification; however, the isotope ratios of nitrite from archaeal ammonia oxidation have been characterized only for a few marine species. We first report the isotope effects of ammonia oxidation at 70°C by thermophilic Thaumarchaeota populations composed almost entirely of “Candidatus Nitrosocaldus.” The nitrogen isotope effect of ammonia oxidation varied with ambient pH (25‰ to 32‰) and strongly suggests the oxidation of ammonia, not ammonium. The δ18O value of nitrite produced from ammonia oxidation varied with the δ18O value of water in the medium but was lower than the isotopic equilibrium value in water. Because experiments have shown that the half-life of abiotic oxygen isotope exchange between nitrite and water is longer than 33 h at 70°C and pH ≥6.6, the rate of ammonia oxidation by thermophilic Thaumarchaeota could be estimated using δ18ONO2− in geothermal environments, where the biological nitrite turnover is likely faster than 33 h. This study extended the range of application of nitrite isotopes as a geochemical clock of the ammonia oxidation activity to high-temperature environments. IMPORTANCE Because ammonia oxidation is generally the rate-limiting step in nitrification that regulates the balance of reduced and oxidized nitrogen pools in nature, it is important to understand the biological and environmental factors underlying

  18. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    DEFF Research Database (Denmark)

    Farver, O.; Zhang, Jingdong; Chi, Qijin

    2001-01-01

    -0' is also different, yielding entropy changes of -57 J K-1 mol-l in water and -84 J K-1 mol(-1) in deuterium oxide. The driving force difference of 10 mV is in keeping with the kinetic isotope effect, but the contribution to DeltaS(double dagger) from the temperature dependence of E-0' is positive......Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K-1 mol(-1...... entropy difference and to compensate for the different temperature dependencies of E-0'. Thus, differences in driving force and thermal expansion appear as the most straightforward rationale for the observed isotope effect....

  19. Isotope exchange reactions on ceramic breeder materials and their effect on tritium inventory

    International Nuclear Information System (INIS)

    Nishikawa, M.; Baba, A.; Kawamura, Y.; Nishi, M.

    1998-01-01

    Though lithium ceramic materials such as Li 2 O, LiAlO 2 , Li 2 ZrO 3 , Li 2 TiO 3 and Li 4 SiO 4 are considered as breeding materials in the blanket of a D-T fusion reactor, the release behavior of the bred tritium in these solid breeder materials has not been fully understood. The isotope exchange reaction rate between hydrogen isotopes in the purge gas and tritium on the surface of breeding materials have not been quantified yet, although helium gas with hydrogen or deuterium is planned to be used as the blanket purge gas in the recent blanket designs. The mass transfer coefficient representing the isotope exchange reaction between H 2 and D 2 O or that between D 2 and H 2 O in the ceramic breeding materials bed is experimentally obtained in this study. Effects of isotope exchange reactions on the tritium inventory in the bleeding blanket is discussed based on data obtained in this study where effects of diffusion of tritium in the grain, absorption of water in the bulk of grain, and adsorption of water on the surface of grain, together with two types of isotope exchange reactions are considered. The way to estimate the tritium inventory in a Li 2 ZrO 3 blanket used in this study shows a good agreement with data obtained in such in-situ experiments as MOZART, EXOTIC-5, 6 and TRINE experiments. (author)

  20. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    DEFF Research Database (Denmark)

    Farver, O.; Zhang, Jingdong; Chi, Qijin

    2001-01-01

    rather than negative. Isotope effects are, however, also inherent in the nuclear reorganization Gibbs free energy and in the tunneling factor for the electron transfer process. A slightly larger thermal protein expansion in H2O than in D2O (0.001 nm K-1) is sufficient both to account for the activation......Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K-1 mol(-1...

  1. Using stable isotope analysis to study the diet of Gilchristella ...

    African Journals Online (AJOL)

    Using stable isotope analysis to study the diet of Gilchristella aestuaria larvae: preliminary insights into the foodwebs of six South African estuaries. ... We found a high similarity among the Kariega, Gamtoos, Great Fish and Sundays estuaries in terms of consumers and potential sources for both δ13C and δ15N signatures.

  2. Experimental study of xenon isotopes production by gas centrifuge

    International Nuclear Information System (INIS)

    Zhou Mingsheng; Liang Xiongwen; Zhang Yonggang; Dong Jinping

    2006-01-01

    The gas centrifuge technology is studied for the separation of Xe isotopes. The nature Xe is chosen as processing gas. A four-state cascade is designed to separate 124 Xe to a concentration of being greater than 65% in three separation runs. 124 Xe can be enriched to a concentration 99% in more separation runs using a cascade of more gas centrifuges. (authors)

  3. Systematic study of neutron-rich Molybdenum isotopes

    International Nuclear Information System (INIS)

    Oudih, M.R.; Fellah, M.; Allal, N.H.; Benhamouda, N.

    2010-01-01

    The ground state properties of neutron-rich even-even Molybdenum isotopes are studied using Hartree-Fock-Bogoliubov mean-field theory. Quantities such as two-neutron separation energies and r.m.s radii have been investigated and compared with available experimental data. Deformations and shape coexistence for not yet observed nuclei are predicted.

  4. Gas cleaning with hot char beds studied by stable isotopes

    DEFF Research Database (Denmark)

    Egsgaard, Helge; Ahrenfeldt, Jesper; Ambus, Per

    2014-01-01

    The chemistry taking place in a high temperature char bed used for binding aromatic tar compounds has been studied in detail. 13C labelled tar compounds were used to trace the incorporation into the char bed using isotope ratio mass spectrometry (IRMS) and GC-MS. Furthermore, compounds labelled...

  5. The Enriched Background Isotope Study (EBIS)

    Energy Technology Data Exchange (ETDEWEB)

    Hanson, Paul J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Trumbore, Susan [Univ. of California, Irvine, CA (United States); Swanston, Chris [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Torn, Margaret [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Jastrow, Julie [Argonne National Lab. (ANL), Argonne, IL (United States); Parton, William A [Colorado State Univ., Fort Collins, CO (United States); Century Ecosystems, Inc. (United States); Post, Wilfred M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Froberg, Mats J [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hainsworth, Laura J [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kleber, Markus [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kramer, Christiane [Univ. of California, Irvine, CA (United States); Matamala-Paradeda, Roser [Argonne National Lab. (ANL), Argonne, IL (United States); Garten, Jr, Charles T. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2007-02-05

    A unique, large release of radiocarbon occurred near the Oak Ridge Reservation (ORR), Oak Ridge, TN in July/August 1999. Measurements of 14C in tree ring cellulose throughout the ORR area demonstrate that the 1999 release was unprecedented in its uptake by vegetation. We are taking advantage of the whole-ecosystem isotopic label generated by this release to address five outstanding issues in the terrestrial carbon cycle: (1) partitioning of soil respiration between autotrophic and heterotrophic sources, and quantification of that partitioning seasonally and inter-annually, (2) partitioning of heterotrophic respiration sources between above-ground litter decomposition and below-ground root detritus decomposition, (3) identification of pathways leading from leaf and root detritus to long-term stabilization of soil organic matter, including the role of soil fauna, (4) the role of dissolved organic carbon (DOC) transport in distributing carbon within the soil profile, and, (5) the longevity and turnover time of fine roots. The first four issues are being addressed through a reciprocal litter transplant experiment set up at four sites on the ORR encompassing two soil types and two levels of 14C exposure in 1999. The fifth issue, longevity and turnover of fine roots, is being addressed by tracing the radiocarbon label through the fine root pool over time. With a combination of incubation, soil surface chamber and soil CO2 profiles, and continuous measurements of soil temperature and moisture controls, we are tracking changes in soil respiration partitioning over several years. The nature and source of organic matter pools that reside in soils for years to decades are being tracked with differently labeled root and surface litter, and experiments to exclude soil fauna have been initiated to elucidate their role in vertical transport. Periodic sampling of soils and soil solutions and the use of inert tracers, allow us to investigate the chemical nature and form of DOC and

  6. Study of reversible ion-isotopic self diffusion reaction kinetics using 82Br as a radioactive tracer isotope

    International Nuclear Information System (INIS)

    Lokhande, R.S.; Singare, P.U.

    2003-01-01

    Radioactive tracers as a sensitive analytical technique have been used to study the reversible ion-isotopic self-diffusion reactions. In forward self-diffusion reactions, the ion exchangers in bromide form were equilibrated with bromide ion solution (labelled with 82B r as a radioactive tracer isotope) in the concentration range of 0.005-0.100 M. In reverse ion-isotopic self-diffusion reactions, the labelled ion exchangers in the range of 0.7500-1.2500 g were equilibrated with 0.0100 M bromide ion solution concentration. The results of reversible ion-isotopic self-diffusion reaction indicate that under identical experimental parameters, the reaction rates (min -1 ) are calculated to be nearly same, indicating that forward and reverse ion-isotopic self-diffusion reactions are complementary to each other. (author)

  7. Design study of fuel circulating system using Pd alloy membrane isotope separation method

    International Nuclear Information System (INIS)

    Naito, T.; Yamada, T.; Aizawa, T.; Kasahara, T.; Yamanaka, T.

    1981-01-01

    It is expected that the method of permeating through Pd-alloy membrances is effective for isotope separation and the refining of fuel gas. In this paper, the design study of the Fuel Circulating System (FCS) using Pb-alloy membranes is described. The study is mainly focused on the main vacuum, fuel gas refining, isotope separating, and tritium containment systems. In the fuel gas refining system, impurities are effectively removed by using Pd-alloy membranes. For the isotope separation system, the diffusion method through Pd-alloy membranes was adopted. From the standpoint of the safety and economy, a three-stage tritium containment system was adopted to control tritium release to the environment as low as possible. The principal conclusion drawn from the design study was as follows. In the FCS, while cryogenic distillation method appears to be practicable, Pd-alloy membrane method is attractive for isotope separation and the refining of fuel gas. For a large amount of tritium inventory, handling and control technologies should be completed by the experimental evaluation and development of the components and materials used for the FCS. A three-stage containment system was adopted to control tritium release to environment as low as possible. Consideration to prevent tritium escape will be necessary for fuel gas refiners and isotope separators. (Kato, T.)

  8. Stable isotope studies. Annual progress report, March 1, 1981-February 28, 1982

    International Nuclear Information System (INIS)

    Ishida, T.

    1981-01-01

    Our studies during the year consisted of cryogenic measurements of vapor pressure isotope effects (VPIE) in CHF 3 , CH 2 F 2 , CH 3 F, and ammonia, interpretations of the results of the VPIE studies of CHF 3 and CH 3 F by means of ab initio molecular orbital calculations and vibrational analyses, studies of nitrogen isotope fractionation by an exchange between nitric oxide and the liquid phase consisting of N 2 O 3 and N 2 O 4 under elevated pressures, an exploration of the concept of closed refluxer system for the Nitrox process for separating 15 N using a Fe(II)/Fe(III) system as reducing agent for nitric acid and the electrolysis for regeneration of Fe(II), and a theoretical study of approximation of the zero-point energy and its isotopic differences developed on the basis of Lanczos' tau-method

  9. Dynamical barrier and isotope effects in the simplest substitution reaction via Walden inversion mechanism

    Science.gov (United States)

    Zhao, Zhiqiang; Zhang, Zhaojun; Liu, Shu; Zhang, Dong H.

    2017-02-01

    Reactions occurring at a carbon atom through the Walden inversion mechanism are one of the most important and useful classes of reactions in chemistry. Here we report an accurate theoretical study of the simplest reaction of that type: the H+CH4 substitution reaction and its isotope analogues. It is found that the reaction threshold versus collision energy is considerably higher than the barrier height. The reaction exhibits a strong normal secondary isotope effect on the cross-sections measured above the reaction threshold, and a small but reverse secondary kinetic isotope effect at room temperature. Detailed analysis reveals that the reaction proceeds along a path with a higher barrier height instead of the minimum-energy path because the umbrella angle of the non-reacting methyl group cannot change synchronously with the other reaction coordinates during the reaction due to insufficient energy transfer from the translational motion to the umbrella mode.

  10. Aerodynamic effects in isotope separation by gaseous diffusion

    International Nuclear Information System (INIS)

    Bert, L.A.; Prosperetti, A.; Fiocchi, R.

    1978-01-01

    The turbulent flow of an isotopic mixture in a porous-walled pipe is considered in the presence of suction through the wall. A simple model is formulated for the evaluation of aerodynamic effects on the separation efficiency. The predictions of the model are found to compare very favourably with experiment. In the limit of small suction velocities, results obtained by other investigators for diffusion in a turbulent steam are recovered. (author)

  11. Isotope effect in thermodynamic parameters of styrene polymerization

    International Nuclear Information System (INIS)

    Lebedev, B.V.; Lebedev, N.K.; Smirnova, N.N.

    1985-01-01

    Isotope effects in the enthalpy, entropy and Gibbs energy of the styrene polymerization process are detected by adiabatic- and isothermal calorimetry methods. Thermodynamic parameters of styrene- and deuterostyrene polymerization are calculated in the range from 0 to 350 K. Differences in thermodynamic quantities of these processes are explained by the influence of hydrogen substitution by deuterium and constitute: for enthalpy and Gibbs energy 2-3 kJ/mol, for entropy - 2-3 J/(mol x k)

  12. Is the isotope effect a consequence of magnetic transport?

    International Nuclear Information System (INIS)

    Zurro, B.; Rodriguez-Rodrigo, L.; Castejon, F.

    1994-01-01

    The isotope effect, i.e. the improved confinement of deuterium fuelling compared with hydrogen fuelling, shows up in nearly all tokamaks with various type of wall conditioning and in various confinement regimes. Many empirical scalings for energy confinement include a dependence of the energy replacement time τ E ∝ A i α where α ∼ 1/2, and A i is the atomic mass of the plasma ion species. However, no convincing theoretical justification has so far been found for such a dependence; classical transport would lead us to expect α 1/2, as would some theories for anomalous transport (e.g. those based on drift wave turbulence). This empirical scaling effect has been reviewed along with other relevant theories in a recent paper. The main conclusion drawn therein was that this effect was an unsolved fundamental problem in tokamak transport theory. In this paper, we put forward the hypothesis that the isotope effect is a consequence of magnetic transport in the plasma which we can support by observed reductions in the magnetic turbulence level in deuterium operated plasmas. The proposition is supported by data which we claim give some information about the level of stochastic magnetic turbulence within the plasma. These data show a reduction for the deuterium in the difference between the apparent temperature of a central ion (C V) and that of the main ion, hydrogen or deuterium. This can account for the isotope enhancement factors. In addition, preliminary results from sawtooth propagation in both hard and soft X-ray monitors supports the former proposition. To outline this, firstly the isotope documentation in the TJ-I tokamak is reported and then a plausible interpretation within a magnetic transport model is discussed. (author) 6 refs., 4 figs

  13. Investigations of isotopic composition of foodstuff - basic study and applications

    International Nuclear Information System (INIS)

    Wierzchnicki, R.

    2005-01-01

    Study of food isotopic composition play actually an important role in food authenticity and origin control. In Institute of Nuclear Chemistry and technology the subject of study has been investigated for many years. In last time our work is concentrated on the implementation new methods for selected food and improves of our proficiency in laboratory work. The examples of our study results are presented. (author)

  14. Effect of Different Carbon Substrates on Nitrate Stable Isotope Fractionation During Microbial Denitrification

    DEFF Research Database (Denmark)

    Wunderlich, Anja; Meckenstock, Rainer; Einsiedl, Florian

    2012-01-01

    -labeled water and 18O-labeled nitrite were added to the microcosm experiments to study the effect of putative backward reactions of nitrite to nitrate on the stable isotope fractionation. We found no evidence for a reverse reaction. Significant variations of the stable isotope enrichment factor ε were observed......In batch experiments, we studied the isotope fractionation in N and O of dissolved nitrate during dentrification. Denitrifying strains Thauera aromatica and “Aromatoleum aromaticum strain EbN1” were grown under strictly anaerobic conditions with acetate, benzoate, and toluene as carbon sources. 18O...... of nitrate transport across the cell wall compared to the kinetics of the intracellular nitrate reduction step of microbial denitrification....

  15. The isotopic contamination in electromagnetic isotope separators

    International Nuclear Information System (INIS)

    Cassignol, Ch.

    1959-01-01

    In the early years of isotope separation, and in particular electromagnetic isotope separation, needs for rapid results have conducted to empiric research. This paper describes fundamental research on the electromagnetic isotope separation to a better understanding of isotope separators as well as improving the performances. Focus has been made on the study of the principle of isotope contamination and the remedial action on the separator to improve the isotope separation ratio. In a first part, the author come back to the functioning of an electromagnetic separator and generalities on isotope contamination. Secondly, it describes the two stages separation method with two dispersive apparatus, an electromagnetic separation stage followed by an electrostatic separation stage, both separated by a diaphragm. The specifications of the electrostatic stage are given and its different settings and their consequences on isotope separation are investigated. In a third part, mechanisms and contamination factors in the isotope separation are discussed: natural isotope contamination, contamination by rebounding on the collector, contamination because of a low resolution, contamination by chromatism and diffusion effect, breakdown of condenser voltage. Analysis of experimental results shows the diffusion as the most important contamination factor in electromagnetic isotope separation. As contamination factors are dependent on geometric parameters, sector angle, radius of curvature in the magnetic field and clearance height are discussed in a fourth part. The better understanding of the mechanism of the different contamination factors and the study of influential parameters as pressure and geometric parameters lead to define a global scheme of isotope contamination and determinate optima separator design and experimental parameters. Finally, the global scheme of isotope contamination and hypothesis on optima specifications and experimental parameters has been checked during a

  16. Isotope effects in addition reactions of importance in combustion: Theoretical studies of the reactions CH + H2 right-reversible CH3* right-reversible CH2 + H

    International Nuclear Information System (INIS)

    Wagner, A.F.; Harding, L.B.

    1992-01-01

    Ab initio electronic structure characterizations of the addition reaction path for the title reaction are described. Variational RRKM calculations employing the reaction path properties are then used to compute thermal rate constants for comparison to kinetics measurements on the acetyl radical reaction hydrogen and its isotopic variation

  17. Electronic isotope effects in the palladium-hydrogen system

    International Nuclear Information System (INIS)

    Oppeneer, P.M.

    1987-01-01

    The main objective of this investigation is the determination of the physical origin of the isotope effects measured in the de Haas-van Alphen quantities of dilute Pd(H), Pd(D) and Pd(T) alloys. A computational method for the numerical evaluation of interstitial Green functions, which are indispensable for the descriptions of interactions of conducting electrons with interstitial atoms, is presented. The Green functions are tested in ab initio calculations of the dHvA quantities for the frozen interstitial impurities H, B and C in Pd using a KKR-Green function formulation for interstitial effects. The results are in good agreement with the experimental data and it is concluded that the interstitial Green functions, in combination with the KKR-Green function approach, are applicable for the description of electron scattering by interstitial defects. The influence of zero-point motion of a light interstitial on the electron scattering is evaluated in a computational model. Computations show that the influence on the dHvA quantities is quite small. The anharmonicity of the octahedral potential well in a Pd lattice is considered because it can cause differences in the vibrational properties of hydrogen isotopes. The influence of resonant vibrations on the electron-defect scattering is investigated. It is shown that the occurrence of a resonant mode depends sensitively on the isotope's mass and force constants. It is concluded that the isotope effect in dHvA quantities can be explained by the occurrence of a low-frequency resonant vibration in the Pd(D) system. 264 refs.; 9 figs.; 10 tabs

  18. Unusual Atmospheric Processes: Implications for the Unusual Isotope Effect in Precipitation

    Science.gov (United States)

    Hurst, S.; Krishnamurthy, R. V.

    2016-12-01

    Several samples associated in particular with thunderstorms collected from Kalamazoo, Michigan reveal oxygen and hydrogen isotope ratios that are not compatible with known thermodynamic fractionation or the so-called Raleigh Distillation Effect. Data gathered from April 2014 to February 2016 can be separated into two categories: (1) samples with expected isotopic values based on previous work, (2) samples with unusually high δ18O and δ2H values. Values as high as 42‰ and 25‰ for δ2H and δ18O respectively are obtained. Recent studies suggest that precipitation produced by deep convection can produce moderately enriched oxygen isotopic values, although no hydrogen values for those precipitations are available. Moreover, no values have been recorded that are as high as some of those presented here. The unusual isotope values cannot be attributed to air mass contributions. It is argued that changes in atmospheric chemistry, most likely induced by lightning associated with thunderstorms are responsible. This is likely since temperatures associated with lightning can reach 40000°K. Several studies have indicated that lightning can significantly impact atmospheric chemistry producing, among other species, ozone and NOx. Atmospheric ozone has enriched isotopic values and likely contributes to enriched Oxygen-18 seen in precipitation. An explanation for enrichment in hydrogen is somewhat elusive, but a likely candidate is ion molecular reactions produced by extremely high temperatures in the corona of lightning.

  19. Measurements of Volatile Circumstellar Isotopes: Effects of Fractionation vs. Nucleosynthesis

    Science.gov (United States)

    Milam, Stefanie

    The origin, evolution, and fate of our Universe and/or Galaxy have puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolutionary state of a galaxy. In particular the volatile isotope ratios carry an imprint of stellar evolution and nucleosynthesis. Primitive materials, such as meteorites and IDPs, have revealed a component of ``atypical" isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive is essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to analyze data obtained from the Herschel Space Observatory of circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. This proposal augments data from the Herschel Space Observatory, primarily from the HIFISTARS program and MESS, though the entire Herschel archive will be searched for relevant data. The broader implications for this study include fundamental data necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace their natal, nucleosynthetic isotope ratios. We will analyze Herschel data obtained for a survey of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry (e.g. oxygen-rich vs. carbon-rich). A full circumstellar model will be developed for each source to address specific affects that may influence either the ratios or chemistry. The isotope ratios of 12C

  20. Isotopic effects in the neon fixed point: uncertainty of the calibration data correction

    Science.gov (United States)

    Steur, Peter P. M.; Pavese, Franco; Fellmuth, Bernd; Hermier, Yves; Hill, Kenneth D.; Seog Kim, Jin; Lipinski, Leszek; Nagao, Keisuke; Nakano, Tohru; Peruzzi, Andrea; Sparasci, Fernando; Szmyrka-Grzebyk, Anna; Tamura, Osamu; Tew, Weston L.; Valkiers, Staf; van Geel, Jan

    2015-02-01

    The neon triple point is one of the defining fixed points of the International Temperature Scale of 1990 (ITS-90). Although recognizing that natural neon is a mixture of isotopes, the ITS-90 definition only states that the neon should be of ‘natural isotopic composition’, without any further requirements. A preliminary study in 2005 indicated that most of the observed variability in the realized neon triple point temperatures within a range of about 0.5 mK can be attributed to the variability in isotopic composition among different samples of ‘natural’ neon. Based on the results of an International Project (EUROMET Project No. 770), the Consultative Committee for Thermometry decided to improve the realization of the neon fixed point by assigning the ITS-90 temperature value 24.5561 K to neon with the isotopic composition recommended by IUPAC, accompanied by a quadratic equation to take the deviations from the reference composition into account. In this paper, the uncertainties of the equation are discussed and an uncertainty budget is presented. The resulting standard uncertainty due to the isotopic effect (k = 1) after correction of the calibration data is reduced to (4 to 40) μK when using neon of ‘natural’ isotopic composition or to 30 μK when using 20Ne. For comparison, an uncertainty component of 0.15 mK should be included in the uncertainty budget for the neon triple point if the isotopic composition is unknown, i.e. whenever the correction cannot be applied.

  1. Isotope effect in the carbonyl sulfide reaction with O(3P)

    DEFF Research Database (Denmark)

    Hattori, Shohei; Schmidt, Johan Albrecht; Mahler, Denise W.

    2012-01-01

    The sulfur kinetic isotope effect (KIE) in the reaction of carbonyl sulfide (OCS) with O((3)P) was studied in relative rate experiments at 298 ± 2 K and 955 ± 10 mbar. The reaction was carried out in a photochemical reactor using long path FTIR detection, and data were analyzed using a nonlinear......; at 300 K, the isotopic fractionation was found to be (34)e = -14.8‰. The OCS sink reaction with O((3)P) cannot explain the large fractionation in (34)S, over +73‰, indicated by remote sensing data. In addition, (34)e in OCS photolysis and OH oxidation are not larger than 10‰, indicating that...

  2. Carbon-13 isotope effects on 199Hg nuclear shielding

    International Nuclear Information System (INIS)

    Sebald, Angelika; Wrackmeyer, Bernd

    1985-01-01

    Secondary 13 C/ 12 C isotope effects on 199 Hg nuclear shielding (Δdeltasup(i)( 199 Hg)) are of interest because of the unusual shift to high frequency which has been observed for a few alkyl mercury compounds. Continuing interest in the NMR parameters of mercury compounds prompted a search for the values Δdeltasup(i)( 199 Hg) in a greater variety of organomercurials. This should help to find out about the range of Δdeltasup(i)( 199 Hg) and to obtain a firmer basis for the discussion of the high-frequency shifts. The data and experimental conditions are given for chemical shifts delta 199 Hg, coupling constants sup(n)J( 199 Hg 13 C) and 13 C/ 12 C isotope shifts Δdeltasup(i)( 199 Hg) of fourteen 199 Hg organomercury compounds. The results are discussed. (author)

  3. Hydrodynamic and Environmental Controls on the Nitrogen Isotope Effect of Benthic N2 Production

    Science.gov (United States)

    Rooze, J.; Meile, C. D.

    2016-02-01

    Isotopic signatures of nitrogen (N) pools, together with knowledge on fractionation during the conversion between different forms of N, can be used to constrain marine N budgets. However, the reported extent of N isotope fractionation during benthic N2 production has differed substantially between studies, leading to uncertainty in the estimate of the global benthic N2 production rate. To assess the range and identify mechanisms underlying such observations, we developed a reactive transport model and ran simulations evaluating the impact of nitrification, denitrification, and anaerobic ammonium oxidation on the isotopic composition of in-situ N/2 production. Different hydrodynamic regimes were taken into account, including advective flow induced by bioirrigation and purely diffusive transport. The effects of the benthic mineralization rate and the composition of the overlying water were also quantified. The benthic redox conditions were found to control the N isotope effect, which under reducing conditions is driven by fractionation during nitrification and anaerobic ammonium oxidation and under oxidizing conditions by fractionation during denitrification. The mineralization rate, the bioirrigation intensity, and chemical composition of the overlying water affect the benthic redox zonation and therefore also the benthic N isotope effect. With increasing water-depth the mineralization rate and the advective nitrate supply to the sediment both decrease, constraining most benthic N cycling to the continental shelf. Simulations that reproduce observed trends of sediment O2 uptake and N2 fluxes with water depth, combined with ocean bathymetry yield an average benthic N isotope effect of -3‰, in line with independent estimates from global circulation models coupled to N cycle models (Somes et al., 2013. Biogeosciences 10, 5889-5910).

  4. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    Science.gov (United States)

    Green, C.T.; Böhlke, J.K.; Bekins, B.A.; Phillips, S.P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field-scale (apparent) estimated reaction rates and isotopic fractionations and local-scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O 2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample-based estimates of "apparent" parameters with "true" (intrinsic) values. For this aquifer, non-Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2 threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport. ?? 2010 by the American Geophysical Union.

  5. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    Science.gov (United States)

    Green, Christopher T.; Böhlke, John Karl; Bekins, Barbara A.; Phillips, Steven P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field‐scale (apparent) estimated reaction rates and isotopic fractionations and local‐scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample‐based estimates of “apparent” parameters with “true“ (intrinsic) values. For this aquifer, non‐Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport.

  6. Isotope geochemistry and the study of habitability and life on other planets (Invited)

    Science.gov (United States)

    Eiler, J.

    2010-12-01

    The question of life on other planets might be solved by a remarkable discovery — a martian coquina, or perhaps a tentacle print on a distant landscape. But, until this happens, evidence for life and, more generally, habitability will use indirect geochemical arguments such as isotope thermometers and biomarkers (molecular, isotopic, and elemental fingerprints of biology)., Understanding this evidence will also demand a quantitative planetary history based on isotopic dating. Laboratory study of samples derived from Mars or other solar-system bodies will be a focus of geochemical investigations aimed at such assessments. Examples of how this will be done can be found in studies of the Precambrian geologic record and Martian meteorites. Debates regarding environmental conditions and biogenicity of minerals and organic matter are common in the study of such materials. These controversies derive from simple but refractory problems with the geochemical principles we employ: Indicators of metabolism can be mimicked by abiologic reactions; paleo-environmental proxies generally require an understanding of related geochemical cycles (e.g., the isotopic budget of water); and, though many organic molecules are unambiguous biomarkers, diagenesis can transform them into compounds that resemble products of abiogenic organic synthesis. If planetary sample return is to produce definitive geochemical constraints on habitability and biology, we will require either luck or a new class of geochemical tools that explicitly address these problems. The spatial distribution of rare isotopes within molecular structures, including ‘clumping’ and position-specific isotope effects, offer new geochemical tools that could provide such solutions. For example, even a simple molecule like acetic acid (C2H4O2) has more than 200 distinct isotopic configurations when spatial distribution of isotopes is considered, and the proportions of these could reflect formation temperature, the nature of

  7. Effects of GC temperature and carrier gas flow rate on on-line oxygen isotope measurement as studied by on-column CO injection.

    Science.gov (United States)

    Chen, Zhi-Gang; Yin, Xi-Jie; Zhou, Youping

    2015-08-01

    Although deemed important to δ 18 O measurement by on-line high-temperature conversion techniques, how the GC conditions affect δ 18 O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO-N 2 mix onto the GC column by a six-port valve and examined the CO yield, CO peak shape, CO-N 2 separation, and δ 18 O value under different GC temperatures and carrier gas flow rates. The results show the CO peak area decreases when the carrier gas flow rate increases. The GC temperature has no effect on peak area. The peak width increases with the increase of CO injection volume but decreases with the increase of GC temperature and carrier gas flow rate. The peak intensity increases with the increase of GC temperature and CO injection volume but decreases with the increase of carrier gas flow rate. The peak separation time between N 2 and CO decreases with an increase of GC temperature and carrier gas flow rate. δ 18 O value decreases with the increase of CO injection volume (when half m/z 28 intensity is rate. On average, the δ 18 O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ 18 O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C 16 O or oxygen isotopic exchange between zeolite and CO. For practical application, a lower carrier gas flow rate is therefore recommended as it has the combined advantages of higher CO yield, better N 2 -CO separation, lower He consumption, and insignificant effect on δ 18 O value, while a higher-than-60 °C GC temperature and a larger-than-100 µl CO volume is also recommended. When no N 2 peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

  8. Kinetic isotope effects and how to describe them

    Directory of Open Access Journals (Sweden)

    Konstantin Karandashev

    2017-11-01

    Full Text Available We review several methods for computing kinetic isotope effects in chemical reactions including semiclassical and quantum instanton theory. These methods describe both the quantization of vibrational modes as well as tunneling and are applied to the ⋅H + H2 and ⋅H + CH4 reactions. The absolute rate constants computed with the semiclassical instanton method both using on-the-fly electronic structure calculations and fitted potential-energy surfaces are also compared directly with exact quantum dynamics results. The error inherent in the instanton approximation is found to be relatively small and similar in magnitude to that introduced by using fitted surfaces. The kinetic isotope effect computed by the quantum instanton is even more accurate, and although it is computationally more expensive, the efficiency can be improved by path-integral acceleration techniques. We also test a simple approach for designing potential-energy surfaces for the example of proton transfer in malonaldehyde. The tunneling splittings are computed, and although they are found to deviate from experimental results, the ratio of the splitting to that of an isotopically substituted form is in much better agreement. We discuss the strengths and limitations of the potential-energy surface and based on our findings suggest ways in which it can be improved.

  9. Neutron skin effect of some Mo isotopes in pre-equilibrium reactions

    Indian Academy of Sciences (India)

    The neutron skin effect has been investigated for even isotopes of molybdenum at 25.6. MeV 94−100Mo(p,xn) ... exciton numbers from different radii of even Mo isotopes were used to obtain the corresponding neutron ..... nical applications such as the isotope production alternatives (for producing medical ra- dioisotopes ...

  10. Detuning effect in multistep photo-ionization of atomic isotope of heavy element

    International Nuclear Information System (INIS)

    Wakaida, Ikuo; Akaoka, Katsuaki; Miyabe, Masabumi; Oba, Masaki; Arisawa, Takashi

    1995-01-01

    Detuning effect on the excitation wavelength in 3-step photoionization of atomic isotope of heavy element was experimentally obtained and the role of the isotope shift and hyperfine structure in each transition level was discussed. To achieve high selectivity, the combination of the HFS and isotope sift of upper and lower energy level including the autoionizing level was important. (author)

  11. Measurement of isotopic effects in photosynthetic fixation of CO2 by CO2 enriched in carbon 13 and oxygen 18

    International Nuclear Information System (INIS)

    Gerster, Richard

    The use of 13 C and 18 O enriched CO 2 allows to measure with accuracy isotopic effects, related to the carbon atoms, occuring during the diffusion of carbon dioxide between two phases. Photosynthesis experiments performed with algae suspensions (Euglena gracilis) or aerial leaves (Saccharum officinale, Lycopersicum esculantum, Platanus orientalis, Sinapis alba...) have led to determine an Isotopic Discrimination Factor between 12 C and 13 C very close to 1. The method can be applied to the study of isotopic effects in enzymatic reactions involving CO 2 [fr

  12. Heavy Atom Secondary Kinetic Isotope Effect on H-Tunneling.

    Science.gov (United States)

    Eckhardt, André K; Gerbig, Dennis; Schreiner, Peter R

    2018-02-08

    Although frequently employed, heavy atom kinetic isotope effects (KIE) have not been reported for quantum mechanical tunneling reactions. Here we examine the secondary KIE through 13 C-substitution of the carbene atom in methylhydroxycarbene (H 3 C-C̈-OH) in its [1,2]H-tunneling shift reaction to acetaldehyde (H 3 C-CHO). Our study employs matrix-isolation IR spectroscopy in various inert gases and quantum chemical computations. Depending on the choice of the matrix host gas, the KIE varies within a range of 1.0 in xenon to 1.4 in neon. A KIE of 1.1 was computed using the Wentzel-Kramers-Brillouin (WKB) CVT/SCT, and instanton approaches for the gas phase at the B3LYP/cc-pVTZ level of theory. Computations with explicit consideration of the noble gas environment indicate that the surrounding atoms influence the tunneling reaction barrier height and width. The tunneling half-lives computed with the WKB approach are in good agreement with the experimental results in the different noble gases.

  13. Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

    Science.gov (United States)

    Freiman, Yuri A.; Crespo, Yanier

    2017-12-01

    The multiple isotopic family of hydrogens (H2, HD, D2, HT, DT, T2) due to large differences in the de Boer quantum parameter and inertia moments displays a diversity of pronounced quantum isotopic solid-state effects. The homonuclear members of this family (H2, D2, T2) due to the permutation symmetry are subjects of the constraints of quantum mechanics which link the possible rotational states of these molecules to their total nuclear spin giving rise to the existence of two spin-nuclear modifications, ortho- and parahydrogens, possessing substantially different properties. Consequently, hydrogen solids present an unique opportunity for studying both isotope and spin-nuclear effects. The rotational spectra of heteronuclear hydrogens (HD, HT, DT) are free from limitations imposed by the permutation symmetry. As a result, the ground state of these species in solid state is virtually degenerate. The most dramatic consequence of this fact is an effect similar to the Pomeranchuk effect in 3He which in the case of the solid heteronuclear hydrogens manifests itself as the reentrant broken symmetry phase transitions. In this review article we discuss thermodynamic and kinetic effects pertaining to different isotopic and spin-nuclear species, as well as problems that still remain to be solved.

  14. Magnetic field and magnetic isotope effects on photochemical reactions

    International Nuclear Information System (INIS)

    Wakasa, Masanobu

    1999-01-01

    By at present exact experiments and the theoretical analysis, it was clear that the magnetic field less than 2 T affected a radical pair reaction and biradical reaction. The radical pair life and the dissipative radical yield showed the magnetic field effects on chemical reactions. The radical pair mechanism and the triplet mechanism were known as the mechanism of magnetic field effects. The radical pair mechanism consists of four mechanisms such as the homogeneous hyperfine interaction (HFC), the delta-g mechanism, the relaxation mechanism and the level cross mechanism. In order to observe the magnetic effects of the radical pair mechanism, two conditions need, namely, the recombination rate of singlet radical pair > the dissipation rate and the spin exchange rate > the dissipation rate. A nanosecond laser photo-decomposition equipment can observe the magnetic field effects. The inversion phenomena of magnetic field effect, isolation of the relaxation mechanism and the delta-g mechanism, the magnetic field effect of heavy metal radical reaction, the magnetic field effect in homogeneous solvent, saturation of delta-g mechanism are explained. The succeeded examples of isotope concentration by the magnetic isotope effect are 17 O, 19 Si, 33 S, 73 Ge and 235 U. (S.Y.)

  15. Experimental investigation of nitrogen isotopic effects associated with ammonia degassing at 0-70 °C

    Science.gov (United States)

    Deng, Yuying; Li, Yingzhou; Li, Long

    2018-04-01

    Ammonia degassing is a common process in natural alkaline waters and in the atmosphere. To quantitatively assess the nitrogen cycle in these systems, the essential parameter of nitrogen isotope fractionation factors associated with ammonia degassing is required, but still not constrained yet. In this study, we carried out laboratory experiments to examine the nitrogen isotope behavior during ammonia degassing in alkaline conditions. The experiments started with ammonium sulfate solution with excess sodium hydroxide. The reaction can be described as: NH4+ + OH- (excess) → NH3·nH2O → NH3 (g)↑. Two sets of experiments, one with ammonia degassing under static conditions and the other with ammonia degassing by bubbling of N2 gas, were carried out at 2, 21, 50, and 70 °C. The results indicate that kinetic isotopic effects are dominated during efficient degassing of ammonia in the bubbling experiments, which yielded kinetic nitrogen isotope fractionation factors αNH3(g)-NH3(aq) of 0.9898 at 2 °C, 0.9918 at 21 °C, 0.9935 at 50 °C and 0.9948 at 70 °C. These values show a good relationship with temperature as 103lnαNH3(g)-NH3(aq) = 14.6 - 6.8 × 1000/T. In contrast, isotopic effects during less efficient degassing of ammonia in the static experiments are more complicated. The results do not match either kinetic isotope fractionation or equilibrium isotope fractionation but sit between these two. The most likely cause is that back dissolution of the degassed ammonia occurred in these experiments and consequently shifted kinetic isotope fractionation toward equilibrium isotope fractionation. Our experimental results highlight complicated isotopic effects may occur in natural environments, and need to be fully considered in the interpretation of field data.

  16. In situ NRA study of hydrogen isotope exchange in self-ion damaged tungsten exposed to neutral atoms

    International Nuclear Information System (INIS)

    Markelj, S.; Založnik, A.; Schwarz-Selinger, T.; Ogorodnikova, O.V.; Vavpetič, P.; Pelicon, P.; Čadež, I.

    2016-01-01

    Isotope exchange was studied in-situ by Nuclear Reaction Analysis in the bulk of self-ion damaged tungsten at 600 K. Both variations of isotope exchange of H by D and of D by H were measured. The deuterium isothermal desorption was also studied and evaluated in order to be able to resolve the self-desorption from the isotope exchange at 600 K. The isotope exchange was also studied on the surface by Elastic Recoil Detection Analysis at 480 K and 380 K. The exchange mechanism was effective both on the surface and in the bulk of damaged tungsten. A simple model was introduced to describe the exchange efficiency on the surface and in the bulk obtaining the exchange cross sections on the surface and in bulk. In both cases an isotope effect was observed, where the exchange of H atoms by D atoms was more efficient than for the reverse sequence. - Highlights: • First study of isotope exchange on surface and in bulk of self-ion damaged tungsten by exposure to neutral atoms. • In situ study by ion beam techniques NRA and ERDA. • Modelling of the isotope exchange mechanism.

  17. A Tale of Two Gases: Isotope Effects Associated with the Enzymatic Production of H2 and N2O

    Science.gov (United States)

    Yang, H.; Gandhi, H.; Kreuzer, H. W.; Moran, J.; Hill, E. A.; McQuarters, A.; Lehnert, N.; Ostrom, N. E.; Hegg, E. L.

    2014-12-01

    Stable isotopes can provide considerable insight into enzymatic mechanisms and fluxes in various biological processes. In our studies, we used stable isotopes to characterize both enzyme-catalyzed H2 and N2O production. H2 is a potential alternative clean energy source and also a key metabolite in many microbial communities. Biological H2 production is generally catalyzed by hydrogenases, enzymes that combine protons and electrons to produce H2 under anaerobic conditions. In our study, H isotopes and fractionation factors (α) were used to characterize two types of hydrogenases: [FeFe]- and [NiFe]-hydrogenases. Due to differences in the active site, the α associated with H2 production for [FeFe]- and [NiFe]-hydrogenases separated into two distinct clusters (αFeFe > αNiFe). The calculated kinetic isotope effects indicate that hydrogenase-catalyzed H2 production has a preference for light isotopes, consistent with the relative bond strengths of O-H and H-H bonds. Interestingly, the isotope effects associated with H2 consumption and H2-H2O exchange reactions were also characterized, but in this case no specific difference was observed between the different enzymes. N2O is a potent greenhouse gas with a global warming potential 300 times that of CO2, and the concentration of N2O is currently increasing at a rate of ~0.25% per year. Thus far, bacterial and fungal denitrification processes have been identified as two of the major sources of biologically generated N2O. In this study, we measured the δ15N, δ18O, δ15Nα (central N atom in N2O), and δ15Nβ (terminal N atom in N2O) of N2O generated by purified fungal P450 nitric oxide reductase (P450nor) from Histoplasma capsulatum. We observed normal isotope effects for δ18O and δ15Nα, and inverse isotope effects for bulk δ15N (the average of Nα and Nβ) and δ15Nβ. The observed isotope effects have been used in conjunction with DFT calculations to provide important insight into the mechanism of P450nor. Similar

  18. Coulomb excitation of neutron-deficient polonium isotopes studied at ISOLDE

    CERN Document Server

    Neven, Michiel

    The polonium isotopes represent an interesting region of the nuclear chart having only two protons outside the Z = 82 closed shell. These isotopes have already been extensively studied theoretically and experimentally. The heavier isotopes (A > 200) seem to follow a "regular seniority-type regime" while for the lighter isotopes (A < 200) a more collective behavior is observed. Many questions remain regarding the transition between these two regimes and the configuration mixing between quantum states. Experiments in the lighter polonium isotopes point to the presence of shape coexistence, however the phenomenon is not fully understood. A Coulomb excitation study of the polonium isotopes whereby the dynamic properties are investigated can provide helpful insights in understanding the shape coexistence phenomena. In this thesis $^{202}$Po was studied via Coulomb excitation. The $^{202}$Po isotope was part of an experimental campaign in which the $^{196,198,200,206}$Po isotopes were studied as well via Coulomb...

  19. Applications of C and N stable isotopes to ecological and environmental studies in seagrass ecosystems

    Energy Technology Data Exchange (ETDEWEB)

    Lepoint, Gilles [Centre MARE, Laboratoire d' Oceanologie, Institut de Chimie, B6, Universite de Liege, B-4000 Liege (Belgium)]. E-mail: g.lepoint@ulg.ac.be; Dauby, Patrick [Centre MARE, Laboratoire d' Oceanologie, Institut de Chimie, B6, Universite de Liege, B-4000 Liege (Belgium); Institut Royal des Sciences Naturelles de Belgique, rue Vautier, B1000 Brussels (Belgium); Gobert, Sylvie [Centre MARE, Laboratoire d' Oceanologie, Institut de Chimie, B6, Universite de Liege, B-4000 Liege (Belgium)

    2004-12-01

    Stable isotopes of carbon and nitrogen are increasingly used in marine ecosystems, for ecological and environmental studies. Here, we examine some applications of stable isotopes as ecological integrators or tracers in seagrass ecosystem studies. We focus on both the use of natural isotope abundance as food web integrators or environmental tracers and on the use of stable isotopes as experimental tools. As ecosystem integrators, stable isotopes have helped to elucidate the general structure of trophic webs in temperate, Mediterranean and tropical seagrass ecosystems. As environmental tracers, stable isotopes have proven their utility in sewage impact measuring and mapping. However, to make such environmental studies more comprehensible, future works on understanding of basic reasons for variations of N and C stable isotopes in seagrasses should be encouraged. At least, as experimental tracers, stable isotopes allow the study of many aspects of N and C cycles at the scale of a plant or at the scale of the seagrass ecosystem.

  20. STABLE ISOTOPES IN ECOLOGICAL STUDIES: NEW DEVELOPMENTS IN MIXING MODELS (BRAZIL)

    Science.gov (United States)

    Stable isotopes are increasingly being used as tracers in ecological studies. One application uses isotopic ratios to quantify the proportional contributions of multiple sources to a mixture. Examples include pollution sources for air or water bodies, food sources for animals, ...

  1. STABLE ISOTOPES IN ECOLOGICAL STUDIES: NEW DEVELOPMENTS IN MIXING MODELS (URUGUAY)

    Science.gov (United States)

    Stable isotopes are increasingly being used as tracers in ecological studies. One application uses isotopic ratios to quantify the proportional contributions of multiple sources to a mixture. Examples include pollution sources for air or water bodies, food sources for animals, ...

  2. Paleoclimate studies in Brazil using carbon isotopes in soils

    Science.gov (United States)

    Pessenda, Luiz C. R.; Valencia, E. P. E.; Aravena, R.; Telles, E. C. C.; Boulet, R.

    This chapter presents carbon isotope data of soil organic matter (SOM), collected in natural forest ecosystems in different sites from Brazil. The studied areas are located in Londrina (Southern part of the country), Piracicaba (Southeast), Salitre (Central) and Altamira (Northern). This study is part of the research program on tropical and sub-tropical soils in Brazil, of which the main objective is to use carbon isotopes to provide information on vegetation changes and their relationships with climatic changes during the Holocene. 14C data of charcoal samples, the humin fraction and soil organic matter (SOM) contents, indicate that the organic matter of this area is at least of Holocene age. 13C data in SOM indicate that C4 plants were the dominant vegetation in Londrina and Piracicaba during the early and middle Holocene, while C3 plants were the dominant vegetation in Altamira and probably a mixture of C3 and C4 plants occurred in Salitre during the Holocene.

  3. Isotope techniques in lake water studies

    International Nuclear Information System (INIS)

    Gourcy, L.

    1999-01-01

    Freshwater lakes are among the most easily exploitable freshwater resources. Lakes are also recognized as major sedimentological features in which stored material can be used to study recent climate and pollution evolution. To adequately preserve these important landscape features, and to use them as climatic archives, an improved understanding of processes controlling their hydrologic and bio-geochemical environments if necessary. This article briefly describes the IAEA activities related to the study of lakes in such areas as lake budget, lake dynamics, water contamination, and paleolimnological investigations

  4. Stable Isotope Signatures of Middle Palaeozoic Ahermatypic Rugose Corals – Deciphering Secondary Alteration, Vital Fractionation Effects, and Palaeoecological Implications

    Science.gov (United States)

    Jakubowicz, Michal; Berkowski, Blazej; López Correa, Matthias; Jarochowska, Emilia; Joachimski, Michael; Belka, Zdzislaw

    2015-01-01

    This study investigates stable isotope signatures of five species of Silurian and Devonian deep-water, ahermatypic rugose corals, providing new insights into isotopic fractionation effects exhibited by Palaeozoic rugosans, and possible role of diagenetic processes in modifying their original isotopic signals. To minimize the influence of intraskeletal cements on the observed signatures, the analysed specimens included unusual species either devoid of large intraskeletal open spaces ('button corals': Microcyclus, Palaeocyclus), or typified by particularly thick corallite walls (Calceola). The corals were collected at four localities in the Holy Cross Mountains (Poland), Mader Basin (Morocco) and on Gotland (Sweden), representing distinct diagenetic histories and different styles of diagenetic alteration. To evaluate the resistance of the corallites to diagenesis, we applied various microscopic and trace element preservation tests. Distinct differences between isotopic compositions of the least-altered and most-altered skeleton portions emphasise a critical role of material selection for geochemical studies of Palaeozoic corals. The least-altered parts of the specimens show marine or near-marine stable isotope signals and lack positive correlation between δ13C and δ18O. In terms of isotopic fractionation mechanisms, Palaeozoic rugosans must have differed considerably from modern deep-water scleractinians, typified by significant depletion in both 18O and 13C, and pronounced δ13C-δ18O co-variance. The fractionation effects exhibited by rugosans seem similar rather to the minor isotopic effects typical of modern non-scleractinian corals (octocorals and hydrocorals). The results of the present study add to growing evidence for significant differences between Scleractinia and Rugosa, and agree with recent studies indicating that calcification mechanisms developed independently in these two groups of cnidarians. Consequently, particular caution is needed in using

  5. Isotope enrichment effect of gaseous mixtures in standing sound vibration

    International Nuclear Information System (INIS)

    Knesebeck, R.L.

    1984-01-01

    When standing acoustic waves are excited in a tube containing a mixture of two gases, a partial zonal fractioning of the components arises as consequence of mass transport by diffusion, driven by the thermal and pressure gradients which are associeted with the standing waves. This effect is present in each zone corresponding to a quarter wavelength, with the heavier component becoming enriched at the nodes fo the standing waves and deplected at the crests. The magnitude of the enrichment in one of the components of a binary gas mixture is given by Δω=ap 2 /lambda [b + (1-bω)] 2 . Where ω is the mass concentration of the component in the mixture, a and b are parameters which are related to molecular proprieties of the gases, p is the relative pressure amplitude of the standing wave and lambda is its wavelength. For a natural mixture of uranium hexafluorate, with 0.715% of the uranium isotope 340 an enrichment of about 2 x 10 -6 % in the concentration of this isotope is theorecticaly attainable per stage consisting of a quarter wavelenght, when a standing acoustical wave of relative pressure amplitude of 0,2 and wavelenght of 20 cm is used. Since standing acoustical waves are easely excited in gas columns, an isotope enrichment plant made of a cascade of tubes in which standing waves are excited, is presumably feasible with relatively low investment and operation costs. (Author) [pt

  6. Direct determination of equilibrium deuterium isotope effects at natural abundance

    International Nuclear Information System (INIS)

    Zhang, B.; Martin, M.L.

    1992-01-01

    A great variety of techniques has been used to study deuterium-protium partitioning in exchanging systems at equilibrium. In this context it is shown that the determination of site-specific isotope contents by 2 H-NMR at natural abundance provides simple and direct access to thermodynamic isotope fractionation factors. This method avoids the recourse to deuterated species and therefore the approximations inherent in the analysis of complex isotopomeric mixtures. A number of slowly exchanging systems involving OH, NH, or SH groups and water offer suitable conditions (large chemical shift differences, moderate line widths,hor-ellipsis) for the relatively accurate determination of thermodynamic fractionation factors. Moreover multiple fractionations can be observed and compared in ternary mixtures. 25 refs., 2 tabs

  7. Isotopic Studies of O-O Bond Formation During Water Oxidation (SISGR)

    Energy Technology Data Exchange (ETDEWEB)

    Roth, Justine P. [Johns Hopkins Univ., Baltimore, MD (United States)

    2015-03-03

    Isotopic Studies of O-O Bond Formation During Water Oxidation (SISGR) Research during the project period focused primarily on mechanisms of water oxidation by structurally defined transition metal complexes. Competitive oxygen isotope fractionation of water, mediated by oxidized precursors or reduced catalysts together with ceric, Ce(IV), ammonium nitrate in aqueous media, afforded oxygen-18 kinetic isotope effects (O-18 KIEs). Measurement, calculation, and interpretation of O-18 KIEs, described in the accompanying report has important ramifications for the production of electricity and solar hydrogen (as fuel). The catalysis division of BES has acknowledged that understanding mechanisms of transition metal catalyzed water oxidation has major ramifications, potentially leading to transformation of the global economy and natural environment in years to come. Yet, because of program restructuring and decreased availability of funds, it was recommended that the Solar Photochemistry sub-division of BES would be a more appropriate parent program for support of continued research.

  8. Study of oxalic acid effect on equilibrium and kinetics of isotopic exchange between penta- and hexavalent neptunium in nitric acid solutions

    International Nuclear Information System (INIS)

    Nikitenko, S.I.; Ionnikova, N.I.

    1989-01-01

    Spectrophotometry at 25 deg C and ionic force μ=1.0 mol/l (KNO 3 +HNO 3 ) was used to show that at HNO 3 concentration 0.1-1.0 mol/l H 2 C 2 O 4 introduction to nitric acid solutions of Np 5+ in the presence of nitrite-ion resulted in the shift of equilibrium between Np 5+ and Np 6+ to the side of Np 6+ accumulation. The presence of H 2 C 2 O 4 at HNO 3 concentration > 1.0 mol/l doesn't affect the equilibrium position. The values of nominal equilibrium constant at different HNO 3 and H 2 C 2 O 4 concentrations were calculated. It was found that isotope exchange ( 239 Np/ 237 Np) between Np 5+ and Np 6+ in oxalate solutions proceeded more slowly than in oxalate absence. Rate constants of isotope exchange calculated at 9 deg C, μ=1.0 mol/l (KNO 3 ), H 2 C 2 O 4 concentration 0.01 mol/l and pH=2.2 and 3.5 are equal to 0.49x10 3 and 0.67x10 2 l/mol·min respectively. Mechanism of isotope exchange including electron transport between Np 5+ and Np 6+ oxalate complexes is suggested

  9. Revisiting climate changes. Isotope studies open scientific windows to the past

    International Nuclear Information System (INIS)

    Gibson, John; Aggarwal, Pradeep

    2001-01-01

    present climate; Isotopes are being used to study the past climate from groundwater aquifers in Europe, Asia, Australia, Africa, and the Americas. Isotope-based research plays an important role in understanding past climate change. It is this understanding of past changes that holds the key to predicting future changes. These changes may not only influence global temperatures, but also energy needs, availability of drinking water, and adequate food supplies. In this sense, isotopes are invaluable tools that help scientists look 'back to the future' to develop options for minimizing adverse effects of the world's dynamic and changing climate

  10. On the Effect of Planetary Stable Isotope Compositions on Growth and Survival of Terrestrial Organisms.

    Directory of Open Access Journals (Sweden)

    Xueshu Xie

    Full Text Available Isotopic compositions of reactants affect the rates of chemical and biochemical reactions. Usually it is assumed that heavy stable isotope enrichment leads to progressively slower reactions. Yet the effect of stable isotopes may be nonlinear, as exemplified by the "isotopic resonance" phenomenon. Since the isotopic compositions of other planets of Solar system, including Mars and Venus, are markedly different from terrestrial (e.g., deuterium content is ≈5 and ≈100 times higher, respectively, it is far from certain that terrestrial life will thrive in these isotopic conditions. Here we found that Martian deuterium content negatively affected survival of shrimp in semi-closed biosphere on a year-long time scale. Moreover, the bacterium Escherichia coli grows slower at Martian isotopic compositions and even slower at Venus's compositions. Thus, the biological impact of varying stable isotope compositions needs to be taken into account when planning interplanetary missions.

  11. Isotopic study of water exchange between atmosphere and biosphere at Changa Manga site in Pakistan

    International Nuclear Information System (INIS)

    Fazil, M.; Ali, M.; Latif, Z.; Butt, S.

    2012-01-01

    Study of water exchange between atmosphere and biosphere was initiated to understand the ties between these two spheres. Samples of leaves and stems of 23 woody plants along with soil from the surface and from the depth of 7 cm were collected from Changa Manga forest. Moisture content from these samples was extracted using the vacuum distillation method and analyzed for stable isotopes (/sup 18/O and /sup 2/H). Air moisture was also collected in the field. Isotopic data plotted long with the Local Meteoric Water Line (LMWL) indicates that /sup 18/O and /sup 2/H contents of moisture in the leaves of woody plants are higher than their respective stems. This behavior is due to the evaporative enrichment trend originating from the soil moisture in active root zone and also from the leaf surface. The stem samples did not show any significant variation in gamma /sup 18/O suggesting no significant evaporation from stems of big trees. Degree of enrichment of leave samples of woody plants indicated the species-specific effects in isotopes during transpiration. Pine and Eucalyptus leaves showed more variation in the isotopic contents as compared to other species. Temporal variations of /sup 18/O and /sup 2/H in the leaves indicated enriched isotopic values during hot and dry periods as compared to those during wet period (monsoon and winter rains) mainly due to higher transpiration rates at high temperature and low humidity. (orig./A.B.)

  12. Effect of ecological conditions on migration of thorium isotopes isotopes in the soil-plant system

    International Nuclear Information System (INIS)

    Shuktomova, I.I.; Titaeva, N.A.; Kochan, I.G.

    1994-01-01

    Two territories (zones of central taiga and mountainous tundra) with a high natural content of thorium in soil forming rock and soil were examined in comparative analysis of fixed state and behavior of thorium isotopes ( 232 Th, 230 Th, 228 Th, 227 Th) in the soil layer and rock including evaluation and nature of distribution and forms of presence of isotopes in soil profiles; the extent of participance of isotopes in soil-forming processes is discussed and several conclusions are made regarding the role of genesis of isotopes and parameters of the migration medium for the direction and rate of migration processes. It was found that both climatic zones are characterized by the inclusion of all thorium isotopes in the biological cycle in the soil--plant systems. Characterizing as a whole the build up up thorium isotopes in all examined vegetation of the tundra, it may be noted that it is characterized by a slightly different dependence of mobility of these isotopes in comparison with the vegetation of the taiga zone. In addition, the intensity of inclusion of these thorium isotopes in the biological cycles of migration in the taiga zones is higher than in the tundra zone. 3 refs., 4 tabs

  13. Isotopic studies of the aquiferous of Lima

    International Nuclear Information System (INIS)

    Plata, A.; Rojas M, R.; Sebastian C, C.; Ruiz G, J.

    1993-01-01

    Filtrations from Rimac and Blanco rivers and Graton Tunnel (on the Rimac basin, 80 km from Lima city and 2500 m sea level) were studied using artificial tracers and superficial tracers and superficial water analysis. Graton tunnel has a 3 -5 m 3 /s volume. Domestic and industrial demand of Lima (7 millions inhabitants) is 22 m 3 /s . Preliminary results suggest that Graton tunnel filtrations do not originate on Rimac or Blanco rivers, but in regions at 4600 m sea level. Detected tritium suggests that water filtrated in Graton tunnel is modern. (authors) 10 refs., 2 figs

  14. Australis: AMS for ultra sensitive trace element and isotopic studies

    Energy Technology Data Exchange (ETDEWEB)

    Sie, S.H.; Suter, G.F. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), North Ryde, NSW (Australia). Div. of Exploration Geoscience

    1993-12-31

    The accelerator mass spectrometer (AMS) at the CSIRO HIAF laboratory is being upgraded to enable in-situ measurements of ultratraces and isotopic-ratios in mineralogical applications. The upgraded system will include a microbeam Cs ion source which is designed to produce better than 50 micrometre diameter Cs beam to enable analyses of monomineralic grains. The Cs primary beam will be mass analysed in order to minimize contamination of the sample. The detection system will be upgraded to enable analyses of elements up to U, at 2 MV terminal voltage for charge states 4 and 5. The system will be known as AUSTRALIS: A.M.S. for Ultra Sensitive TRAce eLement and Isotopic Studies. An overview of the system and the anticipated applications in minerals exploration and mining research are presented. 4 refs., 1 fig.

  15. Stable isotope biogeochemistry of seabird guano fertilization: results from growth chamber studies with maize (Zea mays).

    Science.gov (United States)

    Szpak, Paul; Longstaffe, Fred J; Millaire, Jean-François; White, Christine D

    2012-01-01

    Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ(15)N). Animal excrement is known to impact plant δ(15)N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint. This paper presents isotopic (δ(13)C and δ(15)N) and vital data for maize (Zea mays) fertilized with Peruvian seabird guano under controlled conditions. The level of (15)N enrichment in fertilized plants is very large, with δ(15)N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ(15)N values ranged between -0.3 and 5.7‰. Intraplant and temporal variability in δ(15)N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ(13)C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk. The results presented in this study demonstrate the very large impact of seabird guano on maize δ(15)N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data

  16. Stable Strontium Isotope (δ88/86Sr) Fractionation in the Marine Realm: A Pilot Study

    OpenAIRE

    Krabbenhöft, André

    2011-01-01

    The determination of the isotopic composition of natural substances is an important field of research within isotope geochemistry. Especially the investigation of the alkaline earth element strontium (Sr) plays an important role in geological and geochemical research. In order to quantify the degree of natural stable Sr isotope fractionation a double spike technique was developed in the frame of this study. This technique allows the precise determination of natural Sr isotope frac...

  17. Target and PADC Track Detectors for Rare Isotope Studies

    Directory of Open Access Journals (Sweden)

    J. Bermudez

    2011-01-01

    Full Text Available A higher yield of rare isotope production methods, for example, isotope separation on-line (ISOL, is expected to be developed for the EURISOL facility. In this paper as a part of the ongoing project, high power-target assembly and passive detector inclusion are given. Theoretical calculations of several configurations were done using Monte Carlo code FLUKA aimed to produce 1015 fiss/s on LEU-Cx target. The proposed radioactive ion beam (RIB production relies on a high-power (4 MW multibody target; a complete target design is given. Additionally we explore the possibility to employ PADC passive detector as a complementary system for RIB characterization, since these already demonstrated their importance in nuclear interactions phenomenology. In fact, information and recording rare and complex reaction product or short-lived isotope detection is obtained in an integral form through latent track formation. Some technical details on track formation and PADC detector etching conditions complete this study.

  18. Dose formation and hematologic effects with prolonged internal exposure of rats by isotope 131I

    International Nuclear Information System (INIS)

    Sova, O.A.; Drozd, Yi.P.

    2013-01-01

    Processes in single dose formation and long-term domestic revenue 131 I in rats was investigated. Original method of estimating absorbed doses in hemacyte for macro-dosemeters indicators was proposed. Dose factors for hemacyte and the dynamics of the blood-forming organs doses for prolonged two cases of prolonged exposure was calculated. Hematologic effects were studied for two variants of entry of the isotope. Peculiarities of doses formation and identified hematological effects are discussed

  19. Isotope effect in impure high T_c superconductors

    OpenAIRE

    Mierzynska, M.; Wysokinski, K. I.

    2003-01-01

    The influence of various kinds of impurities on the isotope shift exponent \\alpha of high temperature superconductors has been studied. In these materials the dopant impurities, like Sr in La_{2-x}Sr_xCuO_4, play different role and usually occupy different sites than impurities like Zn, Fe, Ni {\\it etc} intentionally introduced into the system to study its superconducting properties. In the paper the in-plane and out-of-plane impurities present in layered superconductors have been considered....

  20. Molybdenum isotope variations in calc-alkaline lavas from the Banda arc, Indonesia: Assessing the effect of crystal fractionation in creating isotopically heavy continental crust

    NARCIS (Netherlands)

    Wille, Martin; Nebel, Oliver; Pettke, Thomas; Vroon, Pieter Z.; König, Stephan; Schoenberg, Ronny

    2018-01-01

    Recent studies report a large Mo isotope variability of up to 1‰ (expressed in δ98/95MoNIST3134) in convergent margin lavas. These isotopic variations have been associated with subduction zone processes and ultimately may account for heavy and variable isotope signatures in evolved continental

  1. Preparation and purification of organic samples for selenium isotope studies.

    Science.gov (United States)

    Banning, Helena; Stelling, Monika; König, Stephan; Schoenberg, Ronny; Neumann, Thomas

    2018-01-01

    Selenium (Se) is an important micronutrient but also a strong toxin with a narrow tolerance range for many organisms. As such, a globally heterogeneous Se distribution in soils is responsible for various disease patterns (i.e. Se excess and deficiency) and environmental problems, whereby plants play a key role for the Se entrance into the biosphere. Selenium isotope variations were proved to be a powerful tracer for redox processes and are therefore promising for the exploration of the species dependent Se metabolism in plants and the Se cycling within the Critical Zone. Plant cultivation setups enable systematic controlled investigations, but samples derived from them-plant tissue and phytoagar-are particularly challenging and require specific preparation and purification steps to ensure precise and valid Se isotope analytics performed with HG-MC-ICP-MS. In this study, different methods for the entire process from solid tissue preparation to Se isotope measurements were tested, optimized and validated. A particular microwave digestion procedure for plant tissue and a vacuum filtration method for phytoagar led to full Se recoveries, whereby unfavorable organic residues were reduced to a minimum. Three purification methods predominantly described in the literature were systematically tested with pure Se solution, high concentrated multi-element standard solution as well as plant and phytoagar as target matrices. All these methods efficiently remove critical matrix elements, but differ in Se recovery and organic residues. Validation tests doping Se-free plant material and phytoagar with a reference material of known Se isotope composition revealed the high impact of organic residues on the accuracy of MC-ICP-MS measurements. Only the purification method with no detectable organic residues, hydride generation and trapping, results in valid mass bias correction for plant samples with an average deviation to true δ82/76Se values of 0.2 ‰ and a reproducibility (2 SD

  2. Isotope effects in gas-phase chemical reactions and photodissociation processes: Overview

    International Nuclear Information System (INIS)

    Kaye, J.A.

    1992-01-01

    The origins of isotope effects in equilibrium and non-equilibrium chemical processes are reviewed. In non-equilibrium processes, attention is given to isotope effects in simple bimolecular reactions, symmetry-related reactions, and photodissociation processes. Recent examples of isotope effects in these areas are reviewed. Some indication of other scientific areas for which measurements and/or calculations of isotope effects are used is also given. Examples presented focus on neutral molecule chemistry and in many cases complement examples considered in greater detail in the other chapters of this volume

  3. Studies on Separation Process and Production Technology of Boron Isotope

    OpenAIRE

    LI Jian-ping

    2014-01-01

    The boron isotopes separation test was performed by chemical exchange reaction in the benzene ether -three boron fluoride system, which resulted to the boron isotopic enrichment of -10 in the liquid phase, the boron isotopic enrichment of -11 in the gas phase. After then, boron isotope separation trial production has been finished. In this process, the exchange column and complex tower normal operating parameters and the complex tower technology have been obtained, the problems of material di...

  4. Isotope exchange reactions on ceramic breeder materials and their effect on tritium inventory

    Energy Technology Data Exchange (ETDEWEB)

    Nishikawa, M.; Baba, A. [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering; Kawamura, Y.; Nishi, M.

    1998-03-01

    Though lithium ceramic materials such as Li{sub 2}O, LiAlO{sub 2}, Li{sub 2}ZrO{sub 3}, Li{sub 2}TiO{sub 3} and Li{sub 4}SiO{sub 4} are considered as breeding materials in the blanket of a D-T fusion reactor, the release behavior of the bred tritium in these solid breeder materials has not been fully understood. The isotope exchange reaction rate between hydrogen isotopes in the purge gas and tritium on the surface of breeding materials have not been quantified yet, although helium gas with hydrogen or deuterium is planned to be used as the blanket purge gas in the recent blanket designs. The mass transfer coefficient representing the isotope exchange reaction between H{sub 2} and D{sub 2}O or that between D{sub 2} and H{sub 2}O in the ceramic breeding materials bed is experimentally obtained in this study. Effects of isotope exchange reactions on the tritium inventory in the bleeding blanket is discussed based on data obtained in this study where effects of diffusion of tritium in the grain, absorption of water in the bulk of grain, and adsorption of water on the surface of grain, together with two types of isotope exchange reactions are considered. The way to estimate the tritium inventory in a Li{sub 2}ZrO{sub 3} blanket used in this study shows a good agreement with data obtained in such in-situ experiments as MOZART, EXOTIC-5, 6 and TRINE experiments. (author)

  5. Shape coexistence in the lightest Tl isotopes studied by laser spectroscopy

    CERN Multimedia

    Herfurth, F; Antalic, S; Darby, I G; Venhart, M; Flanagan, K; Veselsky, M; Blaum, K; Radulov, D P; Beck, D; Kowalska, M; Schwarz, S; Chapman, R; Diriken, J V J; Lane, J; Rosenbusch, M

    This proposal aims at atomic spectroscopy studies of the very neutron-deficient isotopes $^{178-187}$Tl, at and far beyond the region of the neutron mid-shell at N=104, in which shape coexistence phenomena were investigated so far by particle and $\\gamma$-ray spectroscopy methods only. Our motivation for this proposal is as follows : \\\\\\\\ -These studies will provide direct data on magnetic dipole moment, spin, charge radii and deformations of these isotopes. The results will form a stringent test for our current understanding of the shape coexistence phenomena in the vicinity of the neutron mid-shell at N=104, where the relevant effects are expected to be the strongest (cf.shape staggering in the isotopes $^{181,183,185}$Hg). \\\\-The knowledge of the structure (configuration, spin, deformation) and whether one or two $\\beta$-decaying isomers are present in the parent isotopes $^{178,180,182}$Tl are crucial for understanding of the results of our recent studies of $\\beta$-delayed fission in the lightest thalli...

  6. Estimating Niche Width Using Stable Isotopes in the Face of Habitat Variability: A Modelling Case Study in the Marine Environment

    Science.gov (United States)

    Cummings, David O.; Buhl, Jerome; Lee, Raymond W.; Simpson, Stephen J.; Holmes, Sebastian P.

    2012-01-01

    Distributions of stable isotopes have been used to infer an organism's trophic niche width, the ‘isotopic niche’, and examine resource partitioning. Spatial variation in the isotopic composition of prey may however confound the interpretation of isotopic signatures especially when foragers exploit resources across numerous locations. In this study the isotopic compositions from marine assemblages are modelled to determine the role of variation in the signature of prey items and the effect of dietary breadth and foraging strategies on predator signatures. Outputs from the models reveal that isotopic niche widths can be greater for populations of dietary specialists rather than for generalists, which contravenes what is generally accepted in the literature. When a range of different mixing models are applied to determine if the conversion from δ to p-space can be used to improve model accuracy, predator signature variation is increased rather than model precision. Furthermore the mixing models applied failed to correctly identify dietary specialists and/or to accurately estimate diet contributions that may identify resource partitioning. The results presented illustrate the need to collect sufficiently large sample sizes, in excess of what is collected under most current studies, across the complete distribution of a species and its prey, before attempts to use stable isotopes to make inferences about niche width can be made. PMID:22876280

  7. Interim report on modeling studies of two-photon isotope separation

    International Nuclear Information System (INIS)

    Hwang, W.C.; Badcock, C.C.; Kamada, R.F.

    1975-01-01

    The two-photon or two-step dissociation method of laser induced isotope enrichment is being modeled for the HBrNO photochemical system. In the model, H 79 Br is selectively excited by resonance IR laser radiation and then dissociated by uv radiation. Selectively dissociated Br atoms are scavenged to form isotopically enriched BrNO and Br 2 . This model includes all kinetic and absorption processes found to be significant and the time-varying concentrations of any species involved in a significant process. Among these processes are vibrational energy transfer reactions (including isotopic exchange) involving HBr v = 0 - 3, rotational and translational (velocity) relaxation processes, dissociation of HBr in the v = 0 - 3 levels, and secondary chemical reactions of the dissociation products. The absorption and kinetic processes that are most important to 79 Br enrichment have been identified and the study of the effects on enrichment upon variation of external parameters (such as reactant pressure, ir or uv source intensity, and temperature) is in progress. Some preliminary results are: (1) intensity of the ir source is usually more important than the uv intensity; (2) chemical reactions are the dominant kinetic processes at lower pressures while energy transfer reactions dominate at higher pressures; (3) kinetic processes usually have greater effect on the absolute amount of enriched products; (4) isotopic abundance of 79 Br in the products can range from 0.55 to 0.80 for the conditions used in the model

  8. Effects of isotope selection on solution convergence in HZE transport

    Science.gov (United States)

    Kim, Myung-Hee Y.; Wilson, John W.; Kiefer, Richard L.; Thibeault, Sheila A.

    1994-01-01

    A fragmenting iron ion produces hundreds of isotopes during nuclear reactions. These isotopes are represented in the solution of the transport problem. A reduced set of isotopes is selected to minimize the computational burden but introduces error in the final result. A minimum list of 122 isotopes is required for adequate representation of the mass and charge distributions of the secondary radiation fields. A reduced set of 80 isotopes is sufficient to represent the charge distribution alone and represents reasonably well the linear energy transfer properties of the iron beam. Because iron fragmentation produces nearly every isotope lighter than iron, the resulting 122-isotope list should be adequate for ion beams with charges equal to or less than 26.

  9. Aragonite-Calcite Inversion During Biogenic Carbonate Sampling: Considerations for Interpreting Isotopic Measurements in Paleoclimate Studies

    Science.gov (United States)

    Waite, A. J.; Swart, P. K.

    2011-12-01

    As aragonite is the metastable polymorph of calcium carbonate, it lends itself to monotropic inversion to the more stable polymorph, calcite. This inversion is possible through an increase in the temperature and pressure conditions to which the sample is exposed and, although first noted nearly a century ago, has been primarily discussed in the context of sample roasting prior to analyses in paleoclimatological studies. Over the last several decades, however, researchers have found evidence to suggest that the friction associated with the sampling of biogenic carbonates via milling/drilling also induces inversion. Furthermore, this inversion may be associated with a shift in measured oxygen isotopic values and ultimately have significant implications for the interpretation of paleoclimatic reconstructions. Despite this, the isotopic heterogeneity of biogenic aragonite skeletons makes the effects of inversion challenging to test and the subject remains underrepresented in the literature. Here we present a first order study into the effects of milling on both the mineralogy and isotopic compositions measured in sclerosponges, corals, and molluscs. X-Ray diffraction analysis of samples hand ground with a mortar and pestle reveal 100% aragonitic skeletons. Conversely, samples milled with a computerized micromill show measurable inversion to calcite. On average, percent inversion of aragonite to calcite for individual specimens was 15% for sclerosponges, 16% for corals, and 9% for molluscs. Isotopic data from these specimens show that the higher the percentage of aragonite inverted to calcite, the more depleted the measured oxygen isotopic values. In the largest of the datasets (sclerosponges), it is evident that the range of oxygen isotope values from milled samples (-0.02 to +0.84%) exceeds the range in values for those samples which were hand ground and showed no inversion (+0.53 to +0.90%). This, coupled with the strong correlation between the two variables

  10. Isotope studies of hydrogen and oxygen in ground ice-experiences with the equilibration technique.

    Science.gov (United States)

    Meyer, H; Schönicke, L; Wand, U; Hubberten, H W; Friedrichsen, H

    2000-01-01

    Equilibration technique suitable for a large amount of samples is described for hydrogen and oxygen isotope analyses of ground ice, especially ice wedges, including the sampling strategy and the analytical procedure as well as the calibration of the Finnigan MAT Delta-S mass spectrometer in June, 1999. Since for future analyses of ice wedges, a higher sampling resolution with limited sample volume is required, the limit of the equilibration technique for small water sample sizes of between 0.05 and 5 ml was checked. For water samples smaller than 1 ml, corresponding to a molar ratio [H2O]/[H2] of smaller than 0.994, a balance correction has to be applied. The experimental errors due to partial evaporation during evacuation, the balance calculation of the isotope equilibration process, the linearity as well as memory effects of the mass spectrometer for samples with large differences in delta18O and deltaD are tackled in this paper. In the polar regions of Northern Siberia without Late Pleistocene and Holocene glaciation, ground ice is used as an archive for paleoclimate studies. First results of stable isotope measurements on ice wedges clearly show a shift towards heavier isotopes and thus warmer winter temperatures as well as a change in the source of the precipitation between Late Pleistocene and Holocene. These results indicate the high potential of ground ice for paleoclimate studies.

  11. Chemical and environmental isotopes study of precipitation in Syria

    International Nuclear Information System (INIS)

    Al-Charideh, A.; Abou Zakhem, B.

    2009-02-01

    Chemical and isotopic compositions of monthly precipitation were monitored at 12 stations distributed over the entire region in Syria for a period of 4 years from December 1999 to April 2003. Amount of precipitation and mean air temperature of rain monthly were also recorded. The conductivity of rain waters varies between 35 μ/cm in the mountainous stations and 336 μ/cm at Deir Az-Zor station. Excepted Tartous station, the mean value of Cl in the rainfall in all station is 3.8 mg/l. The seasonal variations in δ 18 O are smaller at west stations than to the east stations due to low seasonal temperature variations. All stations are characterized by water lines with slopes significantly lower than GMWL, except Bloudan, suggesting the influence of local factors on the isotopic composition of the precipitation. d-excess values decrease from 19% in the western part to 13% in the eastern part of Syria, indicating the influence of the precipitation generated by the air masses coming from the Mediterranean Sea over Syria. A reliable altitude effect represent by depletion of heavy stable isotopes of about -0.21, and -1.47, per 100 m elevation of 18 O and δ 2 H, respectively. Monthly tritium activity and seasonal variations pattern are low in the west stations than at the east stations. The weighted mean tritium values are between 3 to 9 TU during 2000-2003, and it is increasing with distance from the Syrian coast by 1 TU /100 Km. (author)

  12. Study of groundwater salinization in Chaj Doab using environmental isotopes

    International Nuclear Information System (INIS)

    Hussain, S.D.; Sajjid, M.I.; Akram, W.; Ahmad, M.; Rafiq, M.

    1991-09-01

    Environmental isotopes and chemical composition of water have been used to study the origin of groundwater salinity in Chaj Doab. Three important possible processes of salinization i.e. enrichment of salt content of water by evaopration, mixing with connate marine water and dissolution of salts from soil sediments have been investigated. No evidence for mixing with connate maine water could be found. The process of evaporation too does not seem to apply any significant role in salinization of groundwater. The dissolution of salts from soil sediments appears as dominant mechanism for increasing the salt content of water in this area. (author)

  13. Deuterium isotope effects on 13C chemical shifts of 10-Hydroxybenzo[h]quinolines

    DEFF Research Database (Denmark)

    Hansen, Poul Erik; Kamounah, Fadhil S.; Gryko, Daniel T.

    2013-01-01

    Deuterium isotope effects on 13C-NMR chemical shifts are investigated in a series of 10-hydroxybenzo[h]quinolines (HBQ’s) The OH proton is deuteriated. The isotope effects on 13C chemical shifts in these hydrogen bonded systems are rather unusual. The formal four-bond effects are found to be nega...

  14. Charge exchange effect on laser isotope separation of atomic uranium

    International Nuclear Information System (INIS)

    Niki, Hideaki; Izawa, Yasukazu; Otani, Hiroyasu; Yamanaka, Chiyoe

    1982-01-01

    Uranium isotope separating experiment was performed using the two-step photoionization technique with dye laser and nitrogen laser by heating uranium metal with electron beam and producing atomic beam using generated vapour. The experimental results are described after explaining the two-step photoionization by laser, experimental apparatus, the selection of exciting wavelength and others. Enrichment factor depends largely on the spectrum purity of dye laser which is the exciting source. A large enrichment factor of 48.3 times was obtained for spectrum width 0.03A. To put the uranium isotope separation with laser into practice, the increase of uranium atomic density is considered to be necessary for improving the yield. Experimental investigation was first carried out on the charge exchange effect that seems most likely to affect the decrease of enrichment factor, and the charge exchange cross-section was determined. The charge exchange cross-section depends on the relative kinetic energy between ions and atoms. The experimental result showed that the cross-section was about 5 x 10 -13 cm 2 at 1 eV and 10 -13 cm 2 at 90 eV. These values are roughly ten times as great as those calculated in Lawrence Livermore Laboratory, and it is expected that they become the greatest factor for giving the upper limit of uranium atomic density in a process of practical application. (Wakatsuki, Y.)

  15. Effect of Ca content on equilibrium Ca isotope fractionation between orthopyroxene and clinopyroxene

    Science.gov (United States)

    Wang, Wenzhong; Zhou, Chen; Qin, Tian; Kang, Jin-Ting; Huang, Shichun; Wu, Zhongqing; Huang, Fang

    2017-12-01

    -cpx can be used as an independent thermometer with a precision comparable to elemental thermometers. Because most naturally occurring minerals are solid solutions with variable chemical compositions, this study presents a guideline to explore the concentration effect on equilibrium isotope fractionation among minerals.

  16. Investigating the Direct Meltwater Effect in Terrestrial Oxygen-Isotope Paleoclimate Records Using an Isotope-Enabled Earth System Model

    Science.gov (United States)

    Zhu, Jiang; Liu, Zhengyu; Brady, Esther C.; Otto-Bliesner, Bette L.; Marcott, Shaun A.; Zhang, Jiaxu; Wang, Xianfeng; Nusbaumer, Jesse; Wong, Tony E.; Jahn, Alexandra; Noone, David

    2017-12-01

    Variations in terrestrial oxygen-isotope reconstructions from ice cores and speleothems have been primarily attributed to climatic changes of surface air temperature, precipitation amount, or atmospheric circulation. Here we demonstrate with the fully coupled isotope-enabled Community Earth System Model an additional process contributing to the oxygen-isotope variations during glacial meltwater events. This process, termed "the direct meltwater effect," involves propagating large amounts of isotopically depleted meltwater throughout the hydrological cycle and is independent of climatic changes. We find that the direct meltwater effect can make up 15-35% of the δ18O signals in precipitation over Greenland and eastern Brazil for large freshwater forcings (0.25-0.50 sverdrup (106 m3/s)). Model simulations further demonstrate that the direct meltwater effect increases with the magnitude and duration of the freshwater forcing and is sensitive to both the location and shape of the meltwater. These new modeling results have important implications for past climate interpretations of δ18O.

  17. Isotope separation

    International Nuclear Information System (INIS)

    Ravoire, Jean

    1978-11-01

    Separation of isotopes is treated in a general way, with special reference to the production of enriched uranium. Uses of separated isotopes are presented quickly. Then basic definitions and theoretical concepts are explained: isotopic effects, non statistical and statistical processes, reversible and irreversible processes, separation factor, enrichment, cascades, isotopic separative work, thermodynamics. Afterwards the main processes and productions are reviewed. Finally the economical and industrial aspects of uranium enrichment are resumed [fr

  18. Microscopic study of neutron-rich dysprosium isotopes

    International Nuclear Information System (INIS)

    Vargas, Carlos E.; Velazquez, Victor; Lerma, Sergio

    2013-01-01

    Microscopic studies in heavy nuclei are very scarce due to large valence spaces involved. This computational problem can be avoided by means of the use of symmetry-based models. Ground-state, γ and β bands, and their B(E2) transition strengths in 160-168 Dy isotopes, are studied in the framework of the pseudo-SU(3) model which includes the preserving symmetry Q . Q term and the symmetry-breaking Nilsson and pairing terms, systematically parametrized. Additionally, three rotor-like terms are considered, whose free parameters, fixed for all members of the chain, are used to fine tune the moment of inertia of rotational bands and the band head of γ and β bands. The model succesfully describes in a systematic way rotational features in these nuclei and allows to extrapolate toward the midshell nucleus 170 Dy. The results presented show that it is possible to study a full chain of isotopes or isotones in the region with the present model. (orig.)

  19. Microscopic study of neutron-rich dysprosium isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Vargas, Carlos E. [Universidad Veracruzana, Facultad de Fisica e Inteligencia Artificial, Xalapa (Mexico); Universidad Nacional Autonoma de Mexico, Facultad de Ciencias, Apartado Postal 70-542, Mexico D.F. (Mexico); Velazquez, Victor [Universidad Nacional Autonoma de Mexico, Facultad de Ciencias, Apartado Postal 70-542, Mexico D.F. (Mexico); Lerma, Sergio [Universidad Veracruzana, Facultad de Fisica e Inteligencia Artificial, Xalapa (Mexico)

    2013-01-15

    Microscopic studies in heavy nuclei are very scarce due to large valence spaces involved. This computational problem can be avoided by means of the use of symmetry-based models. Ground-state, {gamma} and {beta} bands, and their B(E2) transition strengths in {sup 160-168}Dy isotopes, are studied in the framework of the pseudo-SU(3) model which includes the preserving symmetry Q . Q term and the symmetry-breaking Nilsson and pairing terms, systematically parametrized. Additionally, three rotor-like terms are considered, whose free parameters, fixed for all members of the chain, are used to fine tune the moment of inertia of rotational bands and the band head of {gamma} and {beta} bands. The model succesfully describes in a systematic way rotational features in these nuclei and allows to extrapolate toward the midshell nucleus {sup 170}Dy. The results presented show that it is possible to study a full chain of isotopes or isotones in the region with the present model. (orig.)

  20. Laser-mass spectrometric studies on measurement of isotopic ratios Sm and Nd

    International Nuclear Information System (INIS)

    Manoravi, P.; Sajimol, R.; Joseph, M.; Sivakumar, N.

    2014-01-01

    Measurements of isotopic ratio is important in many areas of research such as nuclear technology, geochemistry etc. However, depending on the nature of application of such data, the required accuracy and precision will also vary. For instance, in geochemistry, with subnanogram foraminifera samples, one needs to measure the ratio to within a very small variation (± 50‰) compared to natural isotopic composition. Whereas, in the boron enrichment plant (20-90 atom %), the accuracy needed is about ± 1 atom %. In the former case, one needs to make measurements using an expensive instruments such as a magnetic sector mass spectrometer coupled with a suitable ionization method. For the latter application, one can use less expensive instruments such as, quadrupole mass filer (QMF) or time-of-flight mass spectrometer (TOF-MS) etc. In the present work the effect of pulse width of Nd-YAG laser on the measurement of isotopic ratio of Sm and Nd is studied using an in-house developed Laser Ionization Mass Spectrometer (LIMS) facility. The picosecond Cps) laser seems to provide better data compared to nanosecond (ns) laser. This LIMS method is a relatively simple method to measure the isotope ratios to within ± 1%. (author)

  1. Utilizing Stable Isotopes and Isotopic Anomalies to Study Early Solar System Formation Processes

    Science.gov (United States)

    Simon, Justin

    2017-01-01

    Chondritic meteorites contain a diversity of particle components, i.e., chondrules and calcium-, aluminum-rich refractory inclusions (CAIs), that have survived since the formation of the Solar System. The chemical and isotopic compositions of these materials provide a record of the conditions present in the protoplanetary disk where they formed and can aid our understanding of the processes and reservoirs in which solids formed in the solar nebula, an important step leading to the accretion of planetesimals. Isotopic anomalies associated with nucleosynthetic processes are observed in these discrete materials, and can be compared to astronomical observations and astrophysical formation models of stars and more recently proplyds. The existence and size of these isotopic anomalies are typically thought to reflect a significant state of isotopic heterogeneity in the earliest Solar System, likely left over from molecular cloud heterogeneities on the grain scale, but some could also be due to late stellar injection. The homogenization of these isotopic anomalies towards planetary values can be used to track the efficiency and timescales of disk wide mixing,

  2. Use of isotope effects in the elucidation of aliphatic oxidation as catalyzed by cytochrome P-450

    International Nuclear Information System (INIS)

    Jones, J.P.

    1987-01-01

    Two selectively deuterated n-octanes (octane-1- 2 H 3 and octane-1, 2, 3- 2 H 7 ) were synthesized and subjected to hydroxylation by phenobarbital-induced rat liver microsomes and purified cytochrome P-450b. The results of these experiments provide evidence which clarifies the interplay between a branched reaction pathway and the equilibration of an enzyme-substrate complex, in determining the magnitude of an observed isotope effect. An equation is derived that allows limits to be placed on the intrinsic isotope effect. The intrinsic isotope effect for the formation of 1-octanol was determined by this equation to lie between 9.5 and 9.8. The intramolecular isotope effect for octane-1- 2 H 3 was separated into its primary and secondary components using the method of Hanzlik. The primary effect was found to lie between 7.3 and 7.9 while the secondary effect was found to lie between 1.09-1.14. These data are consistent with a symmetrical reaction coordinate with 15% of the observed isotope effect being due to the secondary effects. A slight deviation from the rule of the geometric means was observed. An identical analysis was performed for ortho, meta and para-xylenes that contained deuterium in one methyl group. The secondary isotope effects varied dramatically, from between 0.93 to 1.19, due to violation of the rule of the geometric mean. The observed isotope effects appeared to vary as a function of the distance between the methyl groups in the various methyl groups of xylene with ortho having the largest isotope effect, meta a median isotope effect or an isotope effect similar in magnitude to ortho, and para the smallest effect

  3. Application of isotopic techniques for study of ground water from karstic areas. 1. Origin of waters

    International Nuclear Information System (INIS)

    Feurdean, Victor; Feurdean, Lucia

    2000-01-01

    Environmental stable isotope method was used for study of ground water from karst of NE Dobrogea. Study area is in the vicinity of Danube Delta (declared in 1990 by UNESCO the Reserve of Biosphere) and presents scientific and ecological interest. Measurements of deuterium content of ground water show that waters are meteoric in origin, but at the same time the results showed that the water from two sampling points could not originate from local ground water and have their recharge area at high altitude and a considerable distance. According to the δD values the following categories of waters were established: - waters depleted in deuterium (δD 0 / 00 ) relative to δD values of surface and ground water in the geographic area from which they were collected. They represent most probably the intrusion of isotopically light water from high altitude sites (higher than 1000 m) through network of highly permeable karst channels. The discharge of this component of aquifer occurs both by conduct flow and by diffuse flow; - Waters tributaries to the Danube River (δD > -75 0 / 00 ) that have a small time variability of δD values; - Local infiltration waters, situated in the West side of the investigated area towards the continental platform of the Dobrogea (δD > -70 0 / 00 ). They present high time variability of δD values, due to distinct seasonal effects; - Waters originated in mixing processes between the waters with different isotopic content. The endmember one is heavier isotopic water that belongs to local recharged waters (local infiltration waters and waters tributary to Danube river) while the other endmember is the isotopically light water. (authors)

  4. Water uptake in woody riparian phreatophytes of the southwestern United States: a stable isotope study

    International Nuclear Information System (INIS)

    Busch, D.E.; Ingraham, N.L.; Smith, S.D.

    1992-01-01

    Alluvial forest associations are often dominated by woody phreatophytes, plants that are tightly linked to aquifers for water uptake. Anthropogenic hydrological alterations (e.g., water impoundment or diversion) are of clear importance to riparian ecosystem function. Because decreased frequency of flooding and depression of water tables may, in effect, sever riparian plants from their natural water sources, research was undertaken to determine water uptake patterns for the dominant native and introduced woody taxa of riparian plant communities of the southwestern United States. At floodplain study sites along the Bill Williams and lower Colorado Rivers (Arizona, USA), naturally occurring D and 18 O were used to distinguish among potential water sources. Isotopic ratios from potential uptake locations were compared to water extracted from the dominant woody taxa of the study area (Populus fremontii, Salix gooddingii, and Tamarix ramosissima) to elucidate patterns of water absorption. Isotopic composition of water obtained from sapwood cores did not differ significantly from heartwood or branch water, suggesting that heartwood water exchange, stem capacitance, and phloem sap mixing may be inconsequential in actively transpiring Salix and Populus. There was evidence for close hydrologic linkage of river, ground, and soil water during the early part of the growing season. Surface soils exhibited D enrichment due to cumulative exposure to evaporation as the growing season progressed. Isotopic ratios of water extracted from Populus and Salix did not exhibit isotopic enrichment and were not significantly different from groundwater or saturated soil water sources, indicating a phreatophytic uptake pattern. Associations of isotopic ratios with water relations parameters indicated high levels of canopy evaporation and possible use of moisture from unsaturated alluvial soils in addition to groundwater in Tamarix. (author)

  5. Magnetic isotope effect of magnesium in phosphoglycerate kinase phosphorylation.

    Science.gov (United States)

    Buchachenko, Anatoly L; Kouznetsov, Dmitri A; Orlova, Marina A; Markarian, Artyom A

    2005-08-02

    Phosphoglycerate kinase (PGK) is found to be controlled by a (25)Mg(2+)-related magnetic isotope effect. Mg(2+) nuclear spin selectivity manifests itself in PGK-directed ADP phosphorylation, which has been clearly proven by comparison of ATP synthesis rates estimated in reaction mixtures with different Mg isotopy parameters. Both pure (25)Mg(2+) (nuclear spin 5/2, magnetic moment +0.85) and (24)Mg(2+) (spinless, nonmagnetic nucleus) species as well as their mixtures were used in experiments. In the presence of (25)Mg(2+), ATP production is 2.6 times higher compared with the yield of ATP reached in (24)Mg(2+)-containing PGK-based catalytic systems. The chemical mechanism of this phenomenon is discussed. A key element of the mechanism proposed is a nonradical pair formation in which (25)Mg(+) radical cation and phosphate oxyradical are involved.

  6. Kinetic Isotope Effects in the Reduction of Methyl Iodide

    DEFF Research Database (Denmark)

    Holm, Torkil

    1999-01-01

    a Grignard reagent to methyl iodide, and for reduction of methyl iodide with tributyltin hydride or with gaseous hydrogen iodide. Very small KIE's were found for electron transfer to methyl iodide from magnesium in ether or from sodium in ammonia. The reason may be that these reactions are transport......a-Deuterium kinetic isotope effects (KIE's) have been determined for the reaction of methyl iodide with a series of reducing agents. Reagents which transfer hydride ion in an SN2 reaction show small inverse or small normal KIE's. Reagents which transfer an electron to methyl iodide to produce...... methyl radical show large normal KIE's up to 20 % per a-D. Large KIE's were found for the reaction of methyl iodide with sodium, for Pd-catalyzed reaction of methyl iodide with hydrogen, for ET at a platinum cathode, for ET from benzophenone ketyl or from sodium naphthalenide, for iron catalyzed ET from...

  7. Research of biological isotope effect of deuterium in Anabaena azollae

    International Nuclear Information System (INIS)

    Zhang Yongbo; Wang Wenqing; Shi Dingji; Luo Shanggeng

    1996-01-01

    Anabaena azollae is cultured in BG-11 medium whose mass fraction of heavy water is 0%, 10%, 30%, 60% and 90%, respectively. During different time, activities of photosynthesis, respiration and nitrogenase are measured. In addition, growth-curve, absorption spectrum and low temperature fluorescence spectrum are given. The change of cellular morphology is observed with scanning electron microscope. The results show that the addition of heavy water causes lagging of the exponential period of growth, and inhibits the activities of photosynthesis respiration and nitrogenase markedly. Absorption spectrum shows that the ratio of phycobilins to carotenoid decreases with increasing percentage of heavy water. Low temperature fluorescence spectrum indicates that the ratio of F 733 /F 695 decreases and photo-energy distributed to system II is more than to system I. According to the maximum of net photosynthesis, the isotope effect is also discussed

  8. Delayed Particle Study of Neutron Rich Lithium Isotopes

    CERN Multimedia

    Marechal, F; Perrot, F

    2002-01-01

    We propose to make a systematic complete coincidence study of $\\beta$-delayed particles from the decay of neutron-rich lithium isotopes. The lithium isotopes with A=9,10,11 have proven to contain a vast information on nuclear structure and especially on the formation of halo nuclei. A mapping of the $\\beta$-strength at high energies in the daughter nucleus will make possible a detailed test of our understanding of their structure. An essential step is the comparison of $\\beta$-strength patterns in $^{11}$Li and the core nucleus $^{9}$Li, another is the full characterization of the break-up processes following the $\\beta$-decay. To enable such a measurement of the full decay process we will use a highly segmented detection system where energy and emission angles of both charged and neutral particles are detected in coincidence and with high efficiency and accuracy. We ask for a total of 30 shifts (21 shifts for $^{11}$Li, 9 shifts $^{9}$Li adding 5 shifts for setting up with stable beam) using a Ta-foil target...

  9. Isotopic Effects on Stereodynamics of the C+ + H2 → CH+ + H Reaction

    Science.gov (United States)

    Guo, Lu; Yang, Yun-Fan; Fan, Xiao-Xing; Ma, Feng-Cai; Li, Yong-Qing

    2017-05-01

    The effects of isotope substitution on stereodynamic properties for the reactions {C}++{H}2/{H D}/{H T}\\to {{C H}}++H/D/T have been studied applying a quasi classical trajectory method occurring on the new ground state {{C H}}2+ potential energy surface [J. Chem. Phys. 142 (2015) 124302]. In the center of mass coordinates applying the quasi classical trajectory method to investigate the orientation and the alignment of the product molecule. Differential cross section and three angle distribution functions P(θr), P(ϕr), P( {θ }r,{φ }r ) on the potential energy surface that fixed the collision energy with a value is 40 kcal/mol have been studied. The isotope effect becomes more and more important with the reagent molecules H 2 changing into HD and HT. P({θ }r,{φ }r) as the joint probability density function of both polar angles θ r and ϕ r , which can illustrate more detailed dynamics information. The isotope effect is obvious influence on the properties of stereodynamics in the reactions of {C}++{H}2/{H D}/{H T}\\to {{C H}}++H/D/T. Supported by the National Natural Science Foundation of China under Grant Nos. 11474141, 11274149, 11544015, the Program for Liaoning Excellent Talents in University under Grant No. LJQ2015040, and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (2014-1685)

  10. Quantum and thermal ionic motion, oxygen isotope effect, and superexchange distribution in La2CuO4

    DEFF Research Database (Denmark)

    Haefliger, P. S.; Gerber, S.; Pramod, R.

    2014-01-01

    We study the zero-point and thermal ionic motion in La2CuO4 by means of high-resolution neutron-diffraction experiments. Our results demonstrate anisotropic motion of O and, to a lesser extent, Cu ions, both consistent with the structure of coupled CuO6 octahedra, and quantify the relative effects...... of zero-point and thermal contributions to ionic motion. By substitution of O-18, we find that the oxygen isotope effect on the lattice dimensions is small and negative (-0.01%), while the isotope effect on the ionic displacement parameters is significant (-6 to 50%). We use our results as input...... for theoretical estimates of the distribution of magnetic interaction parameters, J, in an effective one-band model for the cuprate plane. We find that ionic motion causes only small (1%) effects on the average value , which vary with temperature and O isotope, but results in dramatic (10-20%) fluctuations...

  11. Effect of density of state on isotope effect exponent of two-band superconductors

    International Nuclear Information System (INIS)

    Udomsamuthirun, P.; Kumvongsa, C.; Burakorn, A.; Changkanarth, P.; Yoksan, S.

    2005-01-01

    The exact formula of T c 's equation and the isotope effect exponent of two-band s-wave superconductors in weak-coupling limit are derived by considering the influence of two kinds of density of state: constant and van Hove singularity. The paring interaction in each band consisted of two parts: the electron-phonon interaction and non-electron-phonon interaction are included in our model. We find that the interband interaction of electron-phonon show more effect on isotope exponent than the intraband interaction and the isotope effect exponent with constant density of state can fit to experimental data, MgB 2 and high-T c superconductor, better than van Hove singularity density of state

  12. Isotope studies on dynamics and sedimentation in Lake Naini, India

    International Nuclear Information System (INIS)

    Rao, S.M.; Kumar, U.S.; Shivanna, K.; Sinha, U.K.; Sharma, S.

    2001-01-01

    Understanding hydrodynamics of a water body like a lake is a prerequisite for planning and managing its use. In the present study, isotope techniques are employed to study the dynamics and sedimentation pattern of Lake Naini, in India. From the study a few observations are made: (i) the Lake is a warm monomictic one; (ii) the presence of a centrally submerged ridge in the Lake plays a vital role in the intermixing of the Lake's two sub-basins; (iii) the Lake-Groundwater system is a flow-through type and (iv) the Lake is not shallowing at a rate reported by earlier investigators and has different depositional zones with constant/varying sedimentation rates. A Tritium and Water Balance Model is developed to estimate the water retention time of the Lake and also the groundwater residence time between precipitation and input to the Lake. (author)

  13. Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

    Energy Technology Data Exchange (ETDEWEB)

    Pearson, Scott, F.; Levey, Douglas, J.; Greenberg, Catheryn, H.; Martinez del Rio, Carlos

    2003-02-28

    Pearson, S.F., D.J. Levey, C.H. Greenberg, and C.M. del Rio. 2003. Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird. Oecologia. 135:516-523. The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine d15N and d13C turnover rates for blood, d15N and d13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for d13C and from 0.5 to 1.7 days for d15N. Half-life did not differ among diets. Whole blood half-life for d13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7.3.6% for nitrogen isotopes and by 1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures

  14. Isotope effect and deuterium excess parameter revolution in ice and snow melt

    International Nuclear Information System (INIS)

    Yin Guan; Ni Shijun; Fan Xiao; Wu Hao

    2003-01-01

    The change of water isotope composition actually is a integrated reaction depending on the change of environment. The ice and snow melt of different seasons in high mountain can obviously influence the change of isotope composition and deuterium excess parameter of surface flow and shallow groundwater. To know the isotopic fractionation caused by this special natural background, explore its forming and evolvement, is unusually important for estimating, the relationship between the environment, climate and water resources in an area. Taking the example of isotope composition of surface flow and shallow groundwater in Daocheng, Sichuan, this paper mainly introduced the changing law of isotope composition and deuterium excess parameter of surface flow and hot-spring on conditions of ice and snow melt with different seasons in high mountain; emphatically discussed the isotope effect and deuterium excess parameter revolution in the process of ice and snow melting and its reason. (authors)

  15. Hydrodynamic influence on reservoir sustainability in semi-arid climate: A physicochemical and environmental isotopic study.

    Science.gov (United States)

    Ammar, Rawaa; Kazpard, Véronique; El Samrani, Antoine G; Amacha, Nabil; Saad, Zeinab; Chou, Lei

    2017-07-15

    Water scarcity and increasing water demand require the development of water management plans such as establishing artificial lakes and dams. Plans to meet water needs are faced by uprising challenges to improve water quality and to ensure the sustainability of hydro-projects. Environmental isotopes coupled to water physicochemical characteristics were investigated over a biennial cycle to assess both geomorphological and environmental impacts on the water quality of a reservoir situated in an intensively used agricultural watershed under a Mediterranean semi-arid climate. The particularity of the semi-arid climate and the diverse topography generate a continental and orographic rain effect on the isotopic composition of precipitation and the water recharged sources. The studied reservoir responds quickly to land-use activities and climatic changes as reflected by temporal and spatial variations of water chemistry and isotopic composition. Increasing changes in precipitation rate and dry periods significantly modified the water isotopic composition in the reservoir. During the first year, hydrogen (δD) and oxygen (δ 18 O) isotopes are depleted by 6 and 2‰ between dry and wet season, respectively. While a shift of -2‰ for δD and -1‰ for δ 18 O was detected during the second annual cycle. Environmental isotopic compositions demonstrate for the first time the occurrence of groundwater inflow to the central (Cz) and dam (Dz) zones of the Qaraaoun reservoir. The Cz and Dz can be considered as open water bodies subjected to dilution by groundwater inflow, which induces vertical mixing and reverse isotopic stratification of the water column. In the contrary, the river mouth zone acts as a closed system without groundwater intrusion, where heavy water accumulates and may act as a sink for contaminants during dry season. Groundwater influx acts as a dilution factor that renews the hypolimnion, and minimizes the perturbations induced by both internal

  16. Use of isotopes in root activities and distribution studies

    International Nuclear Information System (INIS)

    Nario M, Adriana; Pino N, Ines; Albornoz G, Maria Paz; Baherle V, Pedro

    2003-01-01

    Several studies shown the relevance of the plant's root activity pattern knowledge, across the profile, to determine the suitable zone to apply the nutrients and irrigation to the plant. In Chile, the studies with the isotopes 15 N and 32 P had been used to carry out applications in solution across the soil profile and in lateral distances from the plant in fruit trees and prairies to determine root activity pattern. In peaches, under furrow irrigation, the major root concentration was found at 20 cm depth and 1 m lateral distance from the trunk. Table grapes, under drip irrigation, presented more root activity at 40 cm depth and under the dripper line in lateral distance. In prairies, the root activity was found between 10 to 40 cm depth, depending on the root capacity to explore the profile (author)

  17. Isotope effect on charge transfer in collisions of H with He^+ and He2+

    Science.gov (United States)

    Vaeck, N.; Loreau, J.; Ryabchenko, S.

    2011-05-01

    Data on charge exchange mechanism between ions and neutral atoms or molecules are central to the interpretation of measurements of the chemical composition in several astrophysical environments. In this work, we study the charge transfer process in collisions of H with He^+ or He2+ ions at energies between 0.1 and 200 eV/amu. To calculate the cross section for these reactions, we use a quantal method which consists in a combination of ab initio and wave packet propagat ion methods, and compare our results with the use of the semi-classical eikonal method. We consider in particular the isotope effect that arises when hydrogen is replaced by deuterium or tritium. Indeed, it was demonstrated using semi-classical methods that the isotope effect could be important at energies as high as 100 eV/amu. This large isotopic effect would contradict the commun knowledge that hydrogen, deuterium and tritium could be interchangeable in charge exchange processes above 1 eV/amu.

  18. Magnetic field and magnetic isotope effects in organic photochemical reactions. A novel probe of reaction mechanisms and a method for enrichment of magnetic isotopes

    International Nuclear Information System (INIS)

    Turro, N.J.; Kraeutler, B.

    1980-01-01

    A brief qualitative description of the theory of intersystem crossing (ISC) in radical pairs is presented. It provides a simple unified theoretical basis for understanding chemically induced nuclear polarization (CIDNP), the magnetic spin isotope effect, and magnetic field effects on chemical reactions. Examples are given in which the magnetic spin isotope effect is employed to separate 13 C (a magnetic isotope) from 12 C (a nonmagnetic isotope) more efficiently than any mechanism involving a conventional mass isotope effect, and to separate selectively 17 O (a magnetic isotope) from 16 O and 18 O (nonmagnetic isotope), which is impossible via a conventional mass isotope effect. Examples are also provided for which the magnetic field effect is utilized to control the efficiency of cage reactions of radical pairs. The observation of magnetic isotope and magnetic field effects on the photolysis of dibenzyl ketone in micellar solution is not an isolated finding. Numerous other ketones (phenyl adamantyl ketone, phenyl benzyl ketone, etc.) have been found to exhibit analogous behavior. The ideas discussed may be employed in principle, to design chemical reactions that will separate magnetic isotopes from their nonmagnetic colleagues. The key features are the requirement of a singlet-triplet crossing along the reaction coordinate, the availability of a hyperfine hole at the molecular geometry corresponding to the hole, and sufficient time for the representative point to find the hole when it arrives in the region of phase space corresponding to the hole. Magnetic field and magnetic isotope effects provide a complement to CIDNP for probing mechanisms of radical reactions

  19. Silver diffusion and isotope effect in silver rubidium iodide

    International Nuclear Information System (INIS)

    Arzigian, J.S.

    1980-01-01

    The diffusion coefficient of silver in RbAg 4 I 5 was measured in both superionic phases using radiotracer Ag-110m and serial sectioning with a low temperature sectioning apparatus. The activation energies for diffusion in alpha-RbAg 4 I 5 and beta-RbAg 4 I 5 , respectively, are 0.11 +- 0.01 eV and 0.20 +- 0.04 eV. An isotope effect for diffusion was also measured in both superionic phases. Ag-105 and Ag-110m radioisotopes were used with gamma spectroscopy and energy discrimination. The effect is small, with no significant temperature variation, with the value at 333 0 K being 0.12 +- 0.01. The second-order phase transition at 208 0 K has a small effect, if any, on the magnitude of the effect. The data suggest that a highly cooperative transport mechanism is responsible for the unusually high values of both the conductivity and diffusion coefficient. Although it is not possible to deduce the particular mechanism involved, theories inolving ionic polarons, or cooperative motion, such as crowdions or solitons, seem consistent with the observed results

  20. Isotope Fractionation Studies in Prestellar Cores: The Case of Nitrogen

    Science.gov (United States)

    Milam, Stefanie N.; Charnley, Steven B.

    2011-01-01

    Isotopically fractionated material is found in many solar system objects, including meteorites and comets. It is considered, in some cases, to trace interstellar material that was incorporated into the solar system without undergoing significant processing, thus preserving the fractionation. In interstellar molecular clouds, ion-molecule chemistry continually cycles nitrogen between the two main reservoirs - N and N2 - leading to only minor N-15 enrichments. Charnley and Rodgers showed that depletion of CO removes oxygen from the gas and weakens this cycle such that significant N-15 fractionation can occur for N2 and other N-bearing species in such cores. Observations are being conducted at millimeter and submillimeter wavelengths employing various facilities in order to both spatially and spectrally, resolve emission from these cores. A preliminary study to obtain the N-14/N-15 ratio in nitriles (HCN and HNC) was conducted at the Arizona Radio Observatory's 12m telescope on Kitt Peak, AZ. Spectra were obtained at high resolution (0.08 km/s) in order to resolve dynamic properties of each source as well as to resolve hyperfine structure present in certain isotopologues. This study included four dark cloud cores, observed to have varying levels of molecular depletion: L1521E, L1498, L1544, and L1521F. Previous studies of the N-14/N-15 ratio towards LI544 were obtained with N2H+ and NIH3, yielding ratios of 446 and >700, respectively. The discrepancy observed in these two measurements suggests a strong chemical dependence on the fractionation of nitrogen. Ratios (C,N, and D) obtained from isotopologues for a particular molecule are likely tracing the same chemical heritage and are directly comparable within a given source. Results and comparisons between the protostellar evolutionary state and isomer isotope fractionation as well as between other N-bearing species will be presented.

  1. A first isotopic dietary study of the Greenlandic Thule Culture

    DEFF Research Database (Denmark)

    Nelson, D.E.; Lynnerup, Niels; Arneborg, J.

    2012-01-01

    The isotopic dietary method has been applied to samples of some 65 Thule Culture individuals from existing archaeological collections of Greenlandic human skeletal material. The aim was to use the Greenlandic Thule Culture as a test of the isotopic method, in that we know they were heavily depend...

  2. Diffusion related isotopic fractionation effects with one-dimensional advective–dispersive transport

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Bruce S. [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Lollar, Barbara Sherwood [Earth Sciences Department, University of Toronto, 22 Russell Street, Toronto, ON M5S 3B1 (Canada); Passeport, Elodie [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Chemical Engineering and Applied Chemistry Department, University of Toronto, 200 College Street, Toronto, ON M5S 3E5 (Canada); Sleep, Brent E., E-mail: sleep@ecf.utoronto.ca [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada)

    2016-04-15

    Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining “observable” DRIF based on constraints imposed by the scale of measurements in the field, and on standard limits of detection and analytical uncertainty. Specifically, constraints for the detection of DRIF were determined in terms of the diffusive fractionation factor, the initial concentration of contaminants (C{sub 0}), the method detection limit (MDL) for isotopic analysis, the transport time, and the ratio of the longitudinal mechanical dispersion coefficient to effective molecular diffusion coefficient (D{sub mech}/D{sub eff}). The results allow a determination of field conditions under which DRIF may be an important factor in the use of stable carbon isotope measurements for evaluation of contaminant transport and transformation for one-dimensional advective–dispersive transport. This study demonstrates that for diffusion-dominated transport of BTEX, MTBE, and chlorinated ethenes, DRIF effects are only detectable for the smaller molar mass compounds such as vinyl chloride for C{sub 0}/MDL ratios of 50 or higher. Much larger C{sub 0}/MDL ratios, corresponding to higher source concentrations or lower detection limits, are necessary for DRIF to be detectable for the higher molar mass compounds. The distance over which DRIF is observable for VC is small (less than 1 m) for a relatively young diffusive plume (< 100 years), and DRIF will not easily be detected by using the conventional sampling approach with “typical” well spacing (at least several meters). With contaminant transport by advection, mechanical dispersion, and molecular diffusion this study suggests that in field sites where D{sub mech}/D{sub eff} is

  3. The effects of fat loss after bariatric surgery on inflammation, serum hepcidin, and iron absorption: a prospective 6-mo iron stable isotope study.

    Science.gov (United States)

    Cepeda-Lopez, Ana C; Allende-Labastida, Javier; Melse-Boonstra, Alida; Osendarp, Saskia Jm; Herter-Aeberli, Isabelle; Moretti, Diego; Rodriguez-Lastra, Ramiro; Gonzalez-Salazar, Francisco; Villalpando, Salvador; Zimmermann, Michael B

    2016-10-01

    Iron deficiency is common in obese subjects. This may be due to an increase in serum hepcidin and a decrease in iron absorption from adiposity-related inflammation. We evaluated whether weight and fat loss in obese subjects would decrease inflammation and serum hepcidin and thereby improve iron absorption. We performed a 6-mo prospective study in obese [body mass index (in kg/m 2 ) ≥35 and deficient subjects (n = 17), geometric mean (95% CI) iron absorption increased by 28% [from 9.7% (6.5%, 14.6%) to 12.4% (7.7%, 20.1%); P = 0.03], whereas in iron-sufficient subjects (n = 21), absorption did not change [5.9% (4.0%, 8.6%) and 5.6% (3.9%, 8.2%); P = 0.81]. Adiposity-related inflammation is associated with a reduction in the normal upregulation of iron absorption in iron-deficient obese subjects, and this adverse effect may be ameliorated by fat loss. This protocol was approved by the ethics committees of Wageningen University, ETH Zurich, the University of Monterrey, and the Federal Commission for the Protection against Sanitary Risks, and registered at clinicaltrials.gov as NCT01347905. © 2016 American Society for Nutrition.

  4. Isotope study in the Alpine karst region of Rawil (Switzerland)

    International Nuclear Information System (INIS)

    Schotterer, U.; Siegenthaler, U.; Oeschger, H.; Wildberger, A.; Nabholz, W.

    1978-01-01

    An isotope study in the karst of the high Alps in Switzerland is described. From 1973 to 1978 discharge, 3 H, delta 18 O, conductivity and temperature were measured in representative springs. The springs are influenced by snowmelt in late spring and summer, by rain in late summer and autumn, and in the winter period, when infiltration stops, by reservoir water. Since tritium in precipitation in the last years scattered irregularly in time and space, the residence time of winter baseflow (2-4 years) could not be determined very precisely. The pronounced difference in delta 18 O between several springs allowed us to estimate the difference in mean altitude of their recharge areas. (orig.) [de

  5. Study on silicon isotope separation at FEL-SUT

    International Nuclear Information System (INIS)

    Nomaru, Keiji; Chernyshev, A.V; Nakajima, Noriaki; Kuroda, Haruo

    2002-01-01

    Aiming for the study of the isotope separation of silicon by the FEL, multi-photon dissociation of SiF 3 I by the irradiation with the light of TEA-CO 2 laser and by the co-irradiation with the lights from IR-FEL and TEA-CO 2 laser was investigated. By the irradiation of the FEL, the vibrational bands of SiF 3 I were red-shifted and the dissociation cross-section for the TEA-CO 2 laser increased. By the co-irradiation with FEL light at the frequency of 975 cm -1 , the maximum dissociation rate was enhanced up to three times. (author)

  6. Is there a stable isotope evidence for the CO 2 fertiliser effect

    Indian Academy of Sciences (India)

    Stable carbon and hydrogen isotope ratios of cellulose extracted from annual growth rings (covering the time period 1980-1993) in an oak tree from Kalamazoo, SW Michigan provide a basis to investigate at a physiological level how the fertilization effect may operate. The carbon isotope ratios show that the intercellular ...

  7. Determination of the variation of mercury isotope concentration based on spectral-phase effects

    International Nuclear Information System (INIS)

    Ganeev, A.A.; Man', D.D.; Turkin, Yu.I.

    1988-01-01

    A method of isotopic atomic-absorption analysis, based on spectral-phase effects in which there is no need to use several sources of radiation with pure isotopes of the analyte element, was developed. The method made it possible to simplify the analysis and to determine the variation of the concentration of mercury isotopes from one deposit to another with an accuracy several times higher that of traditional methods of spectral isotopic analysis. The method was tested on mercury 198 and mercury 202. The isotopic analyzer is diagramed and described. The mechanism of spectral-phase effects was determined by the difference in effective photon lifetimes, corresponding to different components of the hyperfine structure of the resonance line of mercury at 254 nm

  8. Water stable isotopes: application to the water cycle and climate variations study

    International Nuclear Information System (INIS)

    Risi, C.

    2009-12-01

    The stable isotopic composition of water (H 2 16 , HDO, H 2 18 , H 2 17 ) is a promising tracer of the present day water cycle and past climates. While the isotopic composition recorded in polar ice core have long been used to reconstruct past temperatures, however, what controls the isotopic composition of the tropical precipitation is more complex. The goal of this thesis is thus to better understand the processes that affect the isotopic composition of tropical precipitation and atmospheric water, more particularly in the tropics. Since most of the tropical precipitation arises from atmospheric convection, and most isotopic archives are on land, we focus more particularly on the impact of convective and land surface processes. In turn, what can be learned about convection and land surface processes using isotopic measurements? Can they help constrain their representation in models? At the inter-annual to climate change scale, what information about the tropical climate variability is recorded in isotopic signals observed in archives? First, we investigate the influence of convection on water stable isotopes. We use both (1) numerical modeling, with a hierarchy of models (single column model, two-dimensional model of squall lines, general circulation model) and (2) data analysis, using isotopic data from rain collected in the Sahel during the African Monsoon Multidisciplinary Analysis campaign, at the event and intra-event scales. These studies highlight the strong impact of convection on the precipitation composition, and stress the importance of rain evaporation and convective or meso-scale subsidence in controlling the rain isotopic composition. Convection also plays an important role on isotopic profiles in the upper troposphere-lower stratosphere. Second, we study what information about climatic variability is recorded by water stable isotopes in precipitation. We analyze simulations of present day and past climates with LMDZ, and evaluate to what extent

  9. Nuclear structure studies of rare francium isotopes using Collinear Resonance Ionization Spectroscopy (CRIS)

    CERN Document Server

    AUTHOR|(CDS)2084441

    It was known for many years that nuclei possessing certain numbers of protons (Z) and neutrons (N), called the magic numbers (8,20,28,50,82,126...), exhibit characteristic behavior and are in general more stable than their neighboring isotopes. As the capabilities of producing isotopes with more extreme values of Z and N increased, it was realized that those spherical nuclei only represent a small fraction of the total number of isotopes and that most isotopes are deformed. In order to study exotic isotopes and their deformation, it was necessary to develop new experimental techniques that would be powerful enough to be able to cope with very small production yields, but precise enough to measure the nuclear properties (such as radii and moments) with relatively small uncertainties. One technique that can measure nuclear properties of scarcely produced isotopes is in-source resonant ionization, but this technique does not allow for sufficient precision to deduce nuclear quadrupole moments. Furthermore, this t...

  10. Isotope tracers in global water and climate studies of the past and present

    International Nuclear Information System (INIS)

    Edwards, T.W.D.; Birks, S.J.; Gibson, J.J.

    2002-01-01

    To date the global distribution of isotopes in modern precipitation has been characterized almost exclusively from the IAEA/WMO GNIP database, although patchiness of GNIP station records in both time and space has limited the potential of isotope hydrology and climate applications in some areas. Herein, we discuss the prospect of utilizing GCMs for simulating global isotope distributions as a supplementary tool for modern and paleoclimate isotope studies to bridge this gap. Such models currently generate reliable zonal isotope fields, and it is anticipated that future enhancements in finescale resolution of GCMs, and incorporation of land-surface feedbacks and topography will allow for future development of a global reanalysis data set ground-truthed by GNIP. Compilation of time-slice maps of past isotope distribution in precipitation from archival records of meteoric waters also offers significant potential to ground-truth paleoclimate simulations extending back tens to hundreds of thousands of years. (author)

  11. Stable isotope biogeochemistry of seabird guano fertilization: results from growth chamber studies with maize (Zea mays.

    Directory of Open Access Journals (Sweden)

    Paul Szpak

    Full Text Available Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ(15N. Animal excrement is known to impact plant δ(15N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint.This paper presents isotopic (δ(13C and δ(15N and vital data for maize (Zea mays fertilized with Peruvian seabird guano under controlled conditions. The level of (15N enrichment in fertilized plants is very large, with δ(15N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ(15N values ranged between -0.3 and 5.7‰. Intraplant and temporal variability in δ(15N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ(13C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk.The results presented in this study demonstrate the very large impact of seabird guano on maize δ(15N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs. Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data

  12. Photon strength functions in Gd isotopes studied from radiative capture of resonance neutrons

    Directory of Open Access Journals (Sweden)

    Kroll J.

    2014-04-01

    Full Text Available The experimental spectra of γ rays following radiative neutron capture on isolated resonances of stable 152,154–158Gd targets were measured by the DANCE calorimeter installed at the Los Alamos Neutron Scattering Center in New Mexico, USA. These spectra were analyzed within the extreme statistical model to get new information on the photon strength functions. Special emphasis was put on study of the scissors vibrational mode present in these isotopes. Our data show that the scissors-mode resonances are built not only on the ground states but also on the excited levels of all studied Gd isotopes. The scissors mode strength observed in 157,159Gd products is significantly higher than in neighboring even-even nuclei 156,158Gd. Such a difference indicates the existence of an odd-even effect in the scissors mode strength. Moreover, there exists no universal parameter-free model of the electric dipole photon strength function describing the experimental data in all of the Gd isotopes studied. The results for the scissors mode are compared with the (γ, γ′ data for the ground-state transitions and with the results from 3He-induced reactions.

  13. Experimental study of relationship between average isotopic fractionation factor and evaporation rate

    Directory of Open Access Journals (Sweden)

    Tao Wang

    2010-12-01

    Full Text Available Isotopic fractionation is the basis of tracing the water cycle using hydrogen and oxygen isotopes. Isotopic fractionation factors in water evaporating from free water bodies are mainly affected by temperature and relative humidity, and vary significantly with these atmospheric factors over the course of a day. The evaporation rate (E can reveal the effects of atmospheric factors. Therefore, there should be a certain functional relationship between isotopic fractionation factors and E. An average isotopic fractionation factor (α* was defined to describe isotopic differences between vapor and liquid phases in evaporation with time intervals of days. The relationship between α* and E based on the isotopic mass balance was investigated through an evaporation pan experiment with no inflow. The experimental results showed that the isotopic compositions of residual water were more enriched with time; α* was affected by air temperature, relative humidity, and other atmospheric factors, and had a strong functional relation with E. The values of α* can be easily calculated with the known values of E, the initial volume of water in the pan, and isotopic compositions of residual water.

  14. Structure of Li, Be And B isotopes studied with quantum molecular dynamic model

    International Nuclear Information System (INIS)

    Abdel-Hafiez, A.; Saleh, Z.A.

    2000-01-01

    Quantum molecular dynamics (QMD) is applied to study the ground state properties of Li, Be and B isotopes. The model Hamiltonian includes both two-and three-body density dependent interactions, a Coulomb term, and a momentum dependent Pauli potential. With parameters which guarantee the infinite nuclear matter properties, the QMD model can only reproduce the binding energies for Be and B isotopes. The experimental root mean square radii of the Li, Be and B isotopes are not sufficiently reproduced by these parameters. It is shown, however, that the binding energies and root mean square radii of these isotopes can simultaneously be reproduced in the lower density limit of the potential parameters

  15. Stable isotope canopy effects for sympatric monkeys at Tai Forest, Cote d'Ivoire.

    Science.gov (United States)

    Krigbaum, John; Berger, Michael H; Daegling, David J; McGraw, W Scott

    2013-08-23

    This study tests the hypothesis that vertical habitat preferences of different monkey species inhabiting closed canopy rainforest are reflected in oxygen isotopes. We sampled bone from seven sympatric cercopithecid species in the Taï forest, Côte d'Ivoire, where long-term study has established taxon-specific patterns of habitat use and diet. Modern rib samples (n = 34) were examined for oxygen (δ(18)Oap) and carbon (δ(13)Cap) from bone apatite ('bioapatite'), and carbon (δ(13)Cco) and nitrogen (δ(15)Nco) from bone collagen. Results are consistent for C3 feeders in a closed canopy habitat. Low irradiance and evapotranspiration, coupled with high relative humidity and recycled CO2 in forest understory, contribute to observed isotopic variability. Both δ(13)Cco and δ(13)Cap results reflect diet; however, δ(13)C values are not correlated with species preference for canopy height. By contrast, δ(18)Oap results are correlated with mean observed height and show significant vertical partitioning between taxa feeding at ground, lower and upper canopy levels. This oxygen isotope canopy effect has important palaeobiological implications for reconstructing vertical partitioning among sympatric primates and other species in tropical forests.

  16. Isotopic studies of Yucca Mountain soil fluids and carbonate pedogenesis

    International Nuclear Information System (INIS)

    McConnaughey, T.A.; Whelan, J.F.; Wickland, K.P.; Moscati, R.J.

    1994-01-01

    Secondary carbonates occurring within the soils, faults, and subsurface fractures of Yucca Mountain contain some of the best available records of paleoclimate and palehydrology for the potential radioactive waste repository site. This article discusses conceptual and analytical advances being made with regard to the interpretation of stable isotope data from pedogenic carbonates, specifically related to the 13 C content of soil CO 2 , CaCO 3 , precipitation mechanisms, and isotopic fractionations between parent fluids and precipitating carbonates. The 13 C content of soil carbon dioxide from Yucca Mountain and vicinity shows most of the usual patterns expected in such contexts: Decreasing 13 C content with depth decreasing 13 C with altitude and reduced 13 C during spring. These patterns exist within the domain of a noisy data set; soil and vegetational heterogeneities, weather, and other factors apparently contribute to isotopic variability in the system. Several soil calcification mechanisms appear to be important, involving characteristic physical and chemical environments and isotopic fractionations. When CO 2 loss from thin soil solutions is an important driving factor, carbonates may contain excess heavy isotopes, compared to equilibrium precipitation with soil fluids. When root calcification serves as a proton generator for plant absorption of soil nutrients, heavy isotope deficiencies are likely. Successive cycles of dissolution and reprecipitation mix and redistribute pedogenic carbonates, and tend to isotopically homogenize and equilibrate pedogenic carbonates with soil fluids

  17. Isotope effect of impurity diffusion of cadmium in silver

    International Nuclear Information System (INIS)

    Rockosch, H.J.; Herzig, C.

    1984-01-01

    The isotope effect of impurity diffusion of cadmium in silver single crystals was measured with the radioisotopes 115 Cd/ 109 Cd by gamma spectrometry. As a mean value E = 0.37 at T = 1060 K was obtained. The correlation factor f /SUB Cd/ = 0.41 is in disagreement with previous results of other investigators due to their unfavourable experimental approach. The present value of f /SUB Cd/ , however, is consistent with those of In and Sn in Ag. A comparison with the corresponding correlation factors in the copper solvent reveals a distinct influence of lattice perturbations because of the different atomic volumes of the solvents. Since the size effect is neglected in the electrostatic diffusion model, the agreement with this model is only qualitative. The frequency ratios for vacancy jumps were calculated. The free binding enthalpy of the vacancy-impurity complex was estimated to be Δg /SUB Cd/ = -0.064 eV. This value is smaller than those for In and Sn in Ag and complies with the relative diffusivities of these impurities in Ag

  18. Effect of interband interaction on isotope effect exponent of MgB2 ...

    Indian Academy of Sciences (India)

    Abstract. The exact formula of Tc's equation and the isotope effect exponent of two- band s-wave superconductors in the weak-coupling limit are derived by considering the influence of interband interaction. In each band, our model consists of two pairing inter- actions: the electron–phonon interaction and ...

  19. Ion beam production and study of radioactive isotopes with the laser ion source at ISOLDE

    Science.gov (United States)

    Fedosseev, Valentin; Chrysalidis, Katerina; Day Goodacre, Thomas; Marsh, Bruce; Rothe, Sebastian; Seiffert, Christoph; Wendt, Klaus

    2017-08-01

    At ISOLDE the majority of radioactive ion beams are produced using the resonance ionization laser ion source (RILIS). This ion source is based on resonant excitation of atomic transitions by wavelength tunable laser radiation. Since its installation at the ISOLDE facility in 1994, the RILIS laser setup has been developed into a versatile remotely operated laser system comprising state-of-the-art solid state and dye lasers capable of generating multiple high quality laser beams at any wavelength in the range of 210-950 nm. A continuous programme of atomic ionization scheme development at CERN and at other laboratories has gradually increased the number of RILIS-ionized elements. At present, isotopes of 40 different elements have been selectively laser-ionized by the ISOLDE RILIS. Studies related to the optimization of the laser-atom interaction environment have yielded new laser ion source types: the laser ion source and trap and the versatile arc discharge and laser ion source. Depending on the specific experimental requirements for beam purity or versatility to switch between different ionization mechanisms, these may offer a favourable alternative to the standard hot metal cavity configuration. In addition to its main purpose of ion beam production, the RILIS is used for laser spectroscopy of radioisotopes. In an ongoing experimental campaign the isotope shifts and hyperfine structure of long isotopic chains have been measured by the extremely sensitive in-source laser spectroscopy method. The studies performed in the lead region were focused on nuclear deformation and shape coexistence effects around the closed proton shell Z = 82. The paper describes the functional principles of the RILIS, the current status of the laser system and demonstrated capabilities for the production of different ion beams including the high-resolution studies of short-lived isotopes and other applications of RILIS lasers for ISOLDE experiments. This article belongs to the Focus on

  20. Investigation of the feeding effect on the 13C/12C isotope ratio of the hormones in bovine urine using gas chromatography/combustion isotope ratio mass spectrometry

    NARCIS (Netherlands)

    Balizs, Gabor; Jainz, Annett; Horvatovich, Peter

    2005-01-01

    The effect of the feeding on the 13C/12C isotope ratio of four endogenous steroid hormones testosterone (T), epi-testosterone (epi-T), dehydroepiandrosterone (DHEA) and etiocholanolone (ETIO) in bovine urine was investigated. An analytical method to determine the accurate isotope ratio was developed

  1. Transient competitive complexation in biological kinetic isotope fractionation explains non-steady isotopic effects: Theory and application to denitrification in soils

    Energy Technology Data Exchange (ETDEWEB)

    Maggi, F.M.; Riley, W.J.

    2009-06-01

    The theoretical formulation of biological kinetic reactions in isotopic applications often assume first-order or Michaelis-Menten-Monod kinetics under the quasi-steady-state assumption to simplify the system kinetics. However, isotopic e ects have the same order of magnitude as the potential error introduced by these simpli cations. Both formulations lead to a constant fractionation factor which may yield incorrect estimations of the isotopic effect and a misleading interpretation of the isotopic signature of a reaction. We have analyzed the isotopic signature of denitri cation in biogeochemical soil systems by Menyailo and Hungate [2006], where high {sup 15}N{sub 2}O enrichment during N{sub 2}O production and inverse isotope fractionation during N{sub 2}O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with the quasi-steady-state Michaelis-Menten-Monod kinetics. When the quasi-steady-state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observations and aided in interpretation of experimental isotopic signatures. These results may imply a substantial revision in using the Rayleigh equation for interpretation of isotopic signatures and in modeling biological kinetic isotope fractionation with first-order kinetics or quasi-steady-state Michaelis-Menten-Monod kinetics.

  2. A theoretical study of the chiroptical properties of molecules with isotopically engendered chirality

    Science.gov (United States)

    Dierksen, Marc; Grimme, Stefan

    2006-05-01

    There has been a considerable interest in the chiroptical properties of molecules whose chirality is exclusively due to an isotopic substitution and numerous examples for the electronic circular dichroism (CD) spectra of isotopically chiral systems have been reported in literature. Four different explanations have been proposed for the mechanism as to how the isotopic substitution induces a chiral perturbation of the otherwise achiral electronic wave function; however, up to now no conclusive answer has been given about the dominating effect responsible for the experimental observations. In this study we will present, for the first time, fully quantum-mechanical calculations of the CD spectra of three different molecular systems with isotopically engendered chirality. As examples, we consider the spectra of organic molecules with ketone and α-diketone carbonyl and diene chromophores. The effect of vibronic couplings for the reorientation of the electric and magnetic transition dipole moments is taken into account within the Herzberg-Teller approximation. The ground and excited state geometries and vibrational normal modes are obtained with (time-dependent) density functional theory [(TD)DFT], while the vibronic coupling effects are calculated at the TDDFT and density functional theory/multireference configuration interaction (DFT/MRCI) levels of theory. Generally, the band shapes of the experimental CD spectra are reproduced very well, and also the absolute CD intensities from the simulations are of the right order of magnitude. The sign and the intensity of the CD band are determined by a delicate balance of the contributions of a large number of individual vibronic transitions, and it is found that the vibrational normal modes with a large displacement are dominant. The separation of the calculated CD spectrum into the different contributions due to the overlap of the in-plane and out-of-plane components (regarding the symmetry plane of the unsubstituted

  3. Effect of amino acids on the precipitation kinetics and Ca isotopic composition of gypsum

    Science.gov (United States)

    Harouaka, Khadouja; Kubicki, James D.; Fantle, Matthew S.

    2017-12-01

    frequency calculations of clusters derived from DFT structures vary by as much as 1.4‰. This suggests that the equilibrium fractionation factor for the bulk crystal can vary substantially, and that surface sorption can induce changes in αeq associated with gypsum precipitation. While we do not rule out the influence of kinetic isotope effects, our results clearly demonstrate that the mode of crystal growth can have a sizeable effect on the bulk fractionation factor (αs-f). Ultimately, our results suggest that the same mechanism by which organic molecules affect the morphology of a mineral can also impact the isotopic composition of the mineral. The results of our study provide valuable insight into the mechanism of Ca isotopic fractionation during gypsum precipitation. Our results are also important for establishing a framework for accurate interpretations of mineral-hosted Ca isotope records of the past, as we demonstrate a mechanistic pathway by which the biological and chemical environment can impact Ca isotopic fractionation during mineral precipitation.

  4. The effect of natural weathering on the chemical and isotopic composition of biotites

    International Nuclear Information System (INIS)

    Clauer, N.; Bonnot-Courtois, C.

    1982-01-01

    The effect of progressive natural weathering on the isotopic (Rb-Sr, K-Ar, deltaD, delta 18 O) and chemical (REE, H 2 O + ) compositions of biotite has been studied on a suite of migmatitic biotites from the Chad Republic. During the early stages of weathering the Rb-Sr system is strongly affected, the hydrogen and oxygen isotope compositions change markedly, the minerals are depleted in light REE, the water content increases by a factor of two, and the K-Ar system is relatively little disturbed. During intensive weathering the K-Ar system is more strongly disturbed than the Rb-Sr system. Most of the isotopic and chemical modifications take place under nonequilibrium conditions and occur before newly formed kaolinite and/or smectite can be detected. These observations suggest that (a) 'protominerals' may form within the biotite structure during the initial period of weathering, and (b) only when chemical equilibrium is approached in the weathering profile are new minerals able to form. (author)

  5. Triple Isotope Water Analyzer for Extraplanetary Studies, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — Los Gatos Research (LGR) proposes to employ Off-Axis ICOS to develop triple-isotope water analyzers for lunar and other extraplanetary exploration. This instrument...

  6. Isotopic study of some fossil and actual hydrothermal systems

    International Nuclear Information System (INIS)

    Demont, J.M.

    1981-07-01

    Oxygen and hydrogen isotopic compositions of rocks from the INAG no 1 drillhole provide evidence of a fossil hydrothermal system in the Ceyssat region of the Massif Central. Oxygen isotope temperatures for the mineral paragenesis are about 275 0 C and the water is of marine origin. Measurements have also been made of delta 13 C values of dissolved carbon and gaseous CO 2 from several hot springs in the Pyrenees and Massif Central. The carbon isotopic composition of the total systems have been calculated from the gas-liquid ratios at the emergence sites and these results are discussed in terms of the origin of the carbon. Most of the hydrothermal carbon is of deep origin. The observed variations in isotopic compositions may be explained by the behavior of the fluids during their ascent to the surface [fr

  7. Triple Isotope Water Analyzer for Extraplanetary Studies Project

    Data.gov (United States)

    National Aeronautics and Space Administration — In this Small Business Innovative Research (SBIR) effort, Los Gatos Research (LGR) proposes to develop a miniature, high-resolution, low power, triple-isotope water...

  8. ISOTOPE METHODS IN HOMOGENEOUS CATALYSIS.

    Energy Technology Data Exchange (ETDEWEB)

    BULLOCK,R.M.; BENDER,B.R.

    2000-12-01

    The use of isotope labels has had a fundamentally important role in the determination of mechanisms of homogeneously catalyzed reactions. Mechanistic data is valuable since it can assist in the design and rational improvement of homogeneous catalysts. There are several ways to use isotopes in mechanistic chemistry. Isotopes can be introduced into controlled experiments and followed where they go or don't go; in this way, Libby, Calvin, Taube and others used isotopes to elucidate mechanistic pathways for very different, yet important chemistries. Another important isotope method is the study of kinetic isotope effects (KIEs) and equilibrium isotope effect (EIEs). Here the mere observation of where a label winds up is no longer enough - what matters is how much slower (or faster) a labeled molecule reacts than the unlabeled material. The most careti studies essentially involve the measurement of isotope fractionation between a reference ground state and the transition state. Thus kinetic isotope effects provide unique data unavailable from other methods, since information about the transition state of a reaction is obtained. Because getting an experimental glimpse of transition states is really tantamount to understanding catalysis, kinetic isotope effects are very powerful.

  9. Biological isotopy. Introduction to the isotopic effects and to their applications in biology; Isotopie biologique. Introduction aux effets isotopiques et a leurs applications en biologie

    Energy Technology Data Exchange (ETDEWEB)

    Tcherkez, G.

    2010-07-01

    Since their discovery in the beginning of the 20. century, the study of stable isotopes has considerably developed. This domain, which remained limited in its applications until the 1990's, has become particularly important thereafter thanks to its practical applications and in particular to its economical impacts. Many techniques used in fraud control, in drugs use control, in selection of high-yield plants etc are based on isotopic abundance measurements. This reference book gives a synthesis of our actual knowledge on the use of stable isotopes and of isotope fractionation in biology. It presents the basic notions of isotopic biochemistry and explains the origin of the isotopic effects. The application principles of these effects to metabolism, to organisms physiology, to environmental biology etc are explained and detailed using examples and exercises. The first chapters present the basic knowledge which defines, from a mathematical point-of-view, the isotopic effects of chemical reactions or of physical processes taking place in biology. The measurements principle of natural isotopes abundance is then synthesised. Finally, all these notions are applied at different scales: enzymes, physiology, metabolism, environment, ecosystems and fraud crackdown. (J.S.)

  10. Deformation effects in the alpha accompanied cold ternary fission of even-even {sup 244-260}Cf isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Santhosh, K.P.; Krishnan, Sreejith [Kannur University, School of Pure and Applied Physics, Payyanur, Kerala (India)

    2016-04-15

    Within the unified ternary fission model (UTFM), the alpha accompanied ternary fission of even-even {sup 244-260}Cf isotopes has been studied by taking the interacting barrier as the sum of Coulomb and proximity potential. For the alpha accompanied ternary fission of the {sup 244}Cf isotope, the highest yield is obtained for the fragment combination {sup 108}Ru + {sup 4}He + {sup 132}Te, which contains the near doubly magic nucleus {sup 132}Te (N = 80, Z = 52). In the case of {sup 246}Cf and {sup 248}Cf isotopes, the highest yield is obtained for the fragment combinations with the near doubly magic nucleus {sup 134}Te (N = 82, Z = 52) as the heaviest fragment. The highest yield obtained for {sup 250}Cf, {sup 252}Cf, {sup 254}Cf, {sup 256}Cf, {sup 258}Cf and {sup 260}Cf isotopes is for the fragment combination with the doubly magic nucleus {sup 132}Sn (N = 82), Z = 50 as the heaviest fragment. We have included the effect of deformation and orientation of fragments and this has revealed that in addition to the closed shell effect, ground-state deformation also plays an important role in the calculation of the relative yield of favorable fragment combinations. The computed isotopic yields for the alpha accompanied ternary fission of the {sup 252}Cf isotope are found to be in agreement with the experimental data. The emission probability and kinetic energy of the long-range alpha particle is calculated for the various isotopes of Cf and are found to be in good agreement with the experimental data. (orig.)

  11. Decay studies of neutron deficient astatine isotopes, ch. 3

    International Nuclear Information System (INIS)

    Lingeman, E.W.A.

    1975-01-01

    The neutron deficient astatine isotopes were produced using 209 Bi( 3 He, xn) reactions; excitation functions were measured. Singles gamma-ray measurements and level schemes are presented for 207 At, 208 At and 209 At. Energies and relative intensities of gamma-rays belong to decays to Po isotopes are also reported. A special investigation on 206 Po decay was performed. (V.J.C.)

  12. Trace element and isotopic studies of Permo-Carboniferous

    Indian Academy of Sciences (India)

    Several nodules were collected from Gondwana basins of east-central India and analyzed for stable carbon and oxygen isotope ratios, REE and trace element composition, and Sr isotope ratio. The mean 18O and 13C values of the calcites in the nodules are — 19.5‰ and -9.7‰ (w.r.t. PDB) respectively suggesting a ...

  13. Effect of Calcium Oxide Microstructure on the Diffusion of Isotopes

    CERN Document Server

    Fernandes Ramos, João Pedro; Stora, T

    2012-01-01

    Calcium oxide (CaO) powder targets have been successfully used at CERN-ISOLDE to produce neutron deficient exotic argon and carbon isotopes under proton irradiation at high temperatures (>1000°C). These targets outperform the other related targets for the production of the same beams. However, they presented either slow release rates (yields) from the beginning or a rapid decrease over time. This problem was believed to come from the target microstructure degradation, justifying the material investigation. In order to do so, the synthesis, reactivity in ambient air and sintering kinetics of CaO were studied, through surface area determination by N2 adsorption, X-ray diffraction for crystalline phase identification and crystallite size determination, and scanning and transmission electron microscopy to investigate the microstructure. The synthesis studies revealed that a nanometric material is obtained from the decarbonation of CaCO3 in vacuum at temperatures higher than 550°C, which is very reactive in air....

  14. Covariance of oxygen and hydrogen isotopic compositions in plant water: species effects

    International Nuclear Information System (INIS)

    Cooper, L.W.; DeNiro, M.J.

    1989-01-01

    Leaf water becomes enriched in the heavy isotopes of oxygen and hydrogen during evapotranspiration. The magnitude of the enrichment has been shown to be influenced by temperature and humidity, but the effects of species—specific factors on leaf water enrichment of D and 18 O have not been studied for different plants growing together. Accordingly, to learn whether leaf water enrichment patterns and processes for D and 18 O are different for individual species growing under the same environmental conditions we tested the proposal that leaf waters in plants with crassulacean acid metabolism (CAM) show higher slopes (m in the leaf water equation °D = m ° 18 O + b) than in C 3 plants. We determined the relationships between the stable hydrogen (°D) and oxygen (° 18 O) isotope ratios of leaf waters collected during the diurnal cycle of evapotranspiration for Yucca schidigera, Ephedra aspera, Agave deserti, Prunus ilicifolia, Yucca whipplei, Heteromeles arbutifolia, Dyckia fosteriana, Simmondsia chinensis, and Encelia farinosa growing at two sites in southern California. Slopes (m in the above leaf water equation) ranged from 1.50 to 3.21, compared to °8 for meteoric water, but differences in slope could not be attributed to carboxylation pathway (CAM vs. C 3 ) nor climate (coastal California vs. Sonoran Desert). Higher slopes were correlated with greater overall ranges of leaf water enrichment of D and 18 O. Water in plants with higher slopes also differed most from unaltered meteoric water. Leaf water isotope ratios in plants with lower slopes were better correlated with temperature and humidity. The findings indicate that m in the aforementioned equation is related to the overall residence time for water in the leaf and proportions of water subjected to repeated evapotranspiration enrichments of heavy isotopes

  15. Advisory group meeting on stable isotope labelled compounds in biomedical studies

    International Nuclear Information System (INIS)

    Vera Ruiz, H.; Parr, R.M.

    1985-11-01

    The programme of the meeting was restricted to topics involving applications of stable isotopes of the lighter elements (H, C, N, O). The current status of stable isotope techniques and applications in nutritional and biomedical studies, the applicability of these techniques in developing countries and the IAEA's future programmes on this topic were discussed

  16. Contribution of stable isotopes to the study of pharmacokinetics of magnesium salts

    International Nuclear Information System (INIS)

    Benech, H.

    1999-01-01

    The use of stable isotopes as labels is becoming an attractive tool for the study of magnesium behavior in humans. It has been used two stable isotopes of magnesium, 25 Mg and 26 Mg, to measure the absolute bioavailability of a pharmaceutical form of magnesium. (N.C.)

  17. STABLE ISOTOPES IN ECOLOGICAL STUDIES: EXPANDING THE SCOPE OF MIXING MODELS

    Science.gov (United States)

    Stable isotopes are increasingly being used as tracers in ecological studies. One common application uses isotopic ratios to quantify the proportional contributions of multiple sources to a mixture. Examples include pollution sources for air or water bodies, food sources for an...

  18. Isotopic studies of nitrogen balance in a cracking clay

    International Nuclear Information System (INIS)

    Craswell, E.T.; Martin, A.E.

    1975-01-01

    The stable isotope 15 N was used to study the fate of nitrogen fertilizers applied to a black earth growing wheat. In a glasshouse experiment using soil packed at 56 per cent moisture (pF 2) into pots, added nitrate was almost completely recovered (mean, 98.8 +- 2.3 per cent) by soil and plant analysis. This experiment was repeated using 15 N-labelled ammonium as well as nitrate; mean recoveries at 15 weeks were 96.8 and 97 per cent respectively (+- 2.2 per cent at P 15 N measured, 97 and 96.8 per cent at 56 and 63 per cent moisture respectively. Fallow and planted systems were then studied in a gas lysimeter. During experiments lasting up to 14 weeks, gaseous losses as 15 N-labelled denitrification products were less than the equivalent of 0.2 μg nitrogen/g soil (the lower limit of detection with a mass spectrometer). Although analysis of plant and soil from the lysimeter in two experiments showed virtually quantitative recovery (99.7 and 97.05 per cent), small (0.16 per cent) losses of labelled ammonia into the lysimeter atmosphere were detected. The significance of these results is discussed in relation to the common finding of large deficits in nitrogen balance studies. (author)

  19. Photochemically induced hydrogen isotope exchange between anthracene and aliphatic amines

    International Nuclear Information System (INIS)

    Gebicki, J.; Reimschuessel, W.; Nowicki, T.

    1978-01-01

    The kinetics of photochemically induced deuterium and tritium isotope exchange between anthracene and diethylamine labelled in NH group or triethylamine-labelled water mixture was studied in acetonitrile and n-heptane. The rate constants of isotope exchange were calculated and ksub(D)/ksub(T) isotope effect was found. A mechanism for isotope exchange involving exciplex formation was proposed. (Auth.)

  20. Oxygen isotope studies of the Salton Sea geothermal field

    International Nuclear Information System (INIS)

    Olson, E.R.

    1978-01-01

    Interbedded shales and sandstones were drilled to a depth of 1588 metres in Sinclair Number Four Well, Salton Sea Geothermal Field. Bottom hole temperatures are approximately 290 0 C. The oxygen dels of hydrothermal and detrital calcite have a systematic relationship at any depth in the geothermal reservoir. Typical values are: vein calcite, +6 0 / 00 ; calcite in white sandstone, +10 0 / 00 ; calcite in dark gray shale, +11 0 / 00 ; calcite in light gray shale, +17 0 / 00 ; calcite in red-brown shale, +20 0 / 00 . This succession represents decreasing water-rock interaction that is also indicated by the clay mineralogy of the shales. Permeability has a marked effect on the equilibration of water and rocks at any given temperature. Original differences in permeability have resulted in partial preservation of original detrital sedimentary compositions. The fluids in the Salton Sea Geothermal Field are probabaly partially evaporated Colorado River water, and their oxygen del values vary as much as 4 0 / 00 throughout the field. Truesdell's (1974) data suggest that dissolved salts may make the water oxygen activity del as much as 6 0 / 00 greater than the concentration del in the geothermal reservoir. Such an uncertainty is a serious impediment to precise isotope geothermometry in this system.(auth.)

  1. Comparative study on ion-isotopic exchange reaction kinetics by application of tracer technique

    International Nuclear Information System (INIS)

    Lokhande, R.S.; Singare, P.U.

    2007-01-01

    The radioactive isotopes 131 I and 82 Br were used to trace the ion-isotopic exchange reactions using industrial grade ion exchange resins Amberlite IRA-400. The experiments were performed to understand the effect of temperature and concentration of ionic solution on kinetics of exchange reactions. Both the exchange reactions were greatly influenced by rise in temperature, which result in higher percentage of ions exchanged. For bromide ion-isotopic exchange reactions, the calculated values of specific reaction rate/min -1 , and amount of ions exchanged/mmol were obtained higher than that for iodide ion-isotopic exchange reactions under identical experimental conditions. The observed variation in the results for two ion-isotopic exchange reactions was due to the difference in the ionic size of bromide and iodide ions. (orig.)

  2. Heavy-atom isotope effects on binding of reactants to lactate dehydrogenase and pyruvate kinase

    International Nuclear Information System (INIS)

    Gawlita, E.

    1993-04-01

    18 O and 13 C kinetic isotope effects have been measured on the reaction of pyruvate kinase with phospho-enol-pyruvate and ADP using a remote label technique. The magnitude of both investigated isotope effects showed a dependence on the concentration of ADP. However, while the carbon effect was simply 'washed out' to unity at high ATP concentration, the oxygen effect becomes inverse and reached 0.9928 at the highest used concentration of ADP. Such a result testifies that the assumption of the negligible effect of isotopic substitution on enzyme-substrate associations remains correct only for carbon effects. An equilibrium 18 O isotope effect on association of oxalate with lactate dehydrogenase in the presence of NADHP has been evaluated by both experimental and theoretical means. Experimental methods, which involved equilibrium dialysis and gas chromatographic/mass spectrometric measurement of isotopic ration, yielded an inverse value of 0.9840. Semiempirical methods involved vibrational analysis of oxalate in two different environments. The comparison of calculated values with the experimentally determined isotope effect indicated that the AM 1 Hamiltonian proved superior to its PM 3 counterpart in this modelling. 160 refs, 8 figs, 18 tabs

  3. Herschel Studies of Circumstellar Volatile Isotopes: Supporting Observations from the Ground and SOFIA

    Science.gov (United States)

    Milam, Stefanie

    The long standing question of ''What are the origin, evolution, and fate of our Universe and/or Galaxy?" has puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolution of a galaxy. Stars are the factories of heavy elements, including carbon, nitrogen, and oxygen, that are fundamental in chemical complexity associated with planetary systems. Primitive materials have revealed a component of “atypical” isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive are essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to perform a comprehensive program of radioastronomical and infrared observations in circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. These data augment current programs underway with the Herschel Space Observatory. The broad implications for this study include fundamental values necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace the natal, nucleosynthetic isotope ratio. We will survey a sample of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry (e.g. oxygen-rich vs. carbon-rich). The isotope ratios of 12C/13C, 14N/15N, 16O/17O, and 16O/18O will be obtained and compared to previous studies conducted on species now considered to be affected by chemical effects in the circumstellar shell

  4. Application of carbon and oxygen stable isotopes to the study of Brazilian precambrian

    International Nuclear Information System (INIS)

    Torquato, J.R.F.

    1980-01-01

    Samples of carbonated rocks of precambrian age are studied. The stable carbon and oxygen isotopes are applied to the study of terrestrial materials considering the variations of some element isotopic composition in function of the environment of sedimentation. The isotopic analysis was done using mass spectrometers. The analytical results and the description of region geology of the site of each sample are presented. The isotopic data are interpreted aiming to the environment of sedimentation. New techniques for better improvement of carbon and oxygen ratios, are proposed, such as: to use the analysis of surface trend and the isotopic logging in mapping of surface and subsurface. A new method for approximated determination of the ages of precambrian carbonated rocks, considering the limitations of their new technique, is also presented. (M.C.K.) [pt

  5. Isotope effects associated with the anaerobic oxidation of sulfide by the purple photosynthetic bacterium, Chromatium vinosum

    International Nuclear Information System (INIS)

    Fry, B.; Gest, H.; Hayes, J.M.

    1984-01-01

    Small inverse isotope effects of 1-3 per thousand were consistently observed for the oxidation of sulfide to elemental sulfur during anaerobic photometabolism by Chromatium vinosum. The inverse fractionation can be accounted for by an equilibrium isotope effect between H 2 S and HS - , and may indicate that C. vinosum (and other photosynthetic bacteria) utilizes H 2 S rather than HS - as the substrate during sulfide oxidation. (Auth.)

  6. Use of intermediate partitioning to calculate intrinsic isotope effects for the reaction catalyzed by malic enzyme

    International Nuclear Information System (INIS)

    Grissom, C.B.; Cleland, W.W.

    1985-01-01

    For those enzymes that proceed via a stepwise reaction mechanism with a discrete chemical intermediate and where deuterium and 13 C isotope effects are on separate steps, a new method has been developed to solve for the intrinsic deuterium and 13 C kinetic isotope effects that relies on directly observing the partitioning of the intermediate between the forward and reverse directions. This observed partitioning ratio, along with the values of the primary deuterium, tritium, and 13 C kinetic isotope effects on V/K for the substrate with the label being followed, allows an exact solution for the intrinsic deuterium and 13 C isotope effects, the forward commitment for the deuterium-sensitive step, and the partition ratio for the intermediate in the reaction. This method allows portions of the reaction coordinate diagram to be defined precisely and the relative energy levels of certain activation barriers to be assigned exactly. With chicken liver triphosphopyridine nucleotide (TPN) malic enzyme activated by Mg 2+ , the partitioning of oxalacetate to pyruvate vs. malate in the presence of TPNH, 0.47, plus previously determined isotope effects gives an intrinsic deuterium isotope effect of 5.7 on hydride transfer and a 13 C isotope effect of 1.044 on decarboxylation. Reverse hydride transfer is 10 times faster than decarboxylation, and the forward commitment for hydride transfer is 3.3. The 13 C isotope effect is not significantly different with reduced acetylpyridine adenine dinucleotide phosphate replacing TPNH (although the pyruvate/malate partitioning ratio for oxalactate is now 9.9), but replacement of Mg 2+ by Mn 2+ raises the value to 1.065 (partition ratio 0.99)

  7. Stable isotope analysis as an early monitoring tool for community-scale effects of rat eradication

    Science.gov (United States)

    Nigro, Katherine M.; Hathaway, Stacie A.; Wegmann, Alex; Miller-ter Kuile, Ana; Fisher, Robert N.; Young, Hillary S.

    2017-01-01

    Invasive rats have colonized most of the islands of the world, resulting in strong negative impacts on native biodiversity and on ecosystem functions. As prolific omnivores, invasive rats can cause local extirpation of a wide range of native species, with cascading consequences that can reshape communities and ecosystems. Eradication of rats on islands is now becoming a widespread approach to restore ecosystems, and many native island species show strong numerical responses to rat eradication. However, the effect of rat eradication on other consumers can extend beyond direct numerical effects, to changes in behavior, dietary composition, and other ecological parameters. These behavioral and trophic effects may have strong cascading impacts on the ecology of restored ecosystems, but they have rarely been examined. In this study, we explore how rat eradication has affected the trophic ecology of native land crab communities. Using stable isotope analysis of rats and crabs, we demonstrate that the diet or trophic position of most crabs changed subsequent to rat eradication. Combined with the numerical recovery of two carnivorous land crab species (Geograpsus spp.), this led to a dramatic widening of the crab trophic niche following rat eradication. Given the established importance of land crabs in structuring island communities, particularly plants, this suggests an unappreciated mechanism by which rat eradication may alter island ecology. This study also demonstrates the potential for stable isotope analysis as a complementary monitoring tool to traditional techniques, with the potential to provide more nuanced assessments of the community- and ecosystem-wide effects of restoration.

  8. Isotope hydrology study of Kato Nevrokopi of Dramas

    International Nuclear Information System (INIS)

    Leontiadis, I.L.; Payne, B.R.; Letsios, A.; Papagianni, N.; Kakarelis, D.; Chadjiagorakis, D.

    1984-01-01

    The isotopic composition of the water was used in order to define the mechanism of recharge of the high plateau of Kato Nevrokopi of Dramas. The results of this study indicate that there are two main sources of recharge to groundwater. One is infiltration of water from the network of irrigation canals which carry water from the Vathitopos stream. The other source of recharge originates in the mountains to the east of the plain. Infiltration from the Nevrokopi stream does occur, but is believed to be minor in this part of the plain. Recharge by infiltration of local precipitation is considered to be minor in comparison with the two main sources of recharge. An underground barrier prevents draining of the groundwater through the sinkhole, resulting in a very big reservoir under the whole central and southern parts of the high plateau. The exploitation of the groundwater of this reservoir very probably offers a low-cost solution to satisfy all needs of the area for irrigation water. (author)

  9. Feasibility study of medical isotope production at Sandia National Laboratories

    International Nuclear Information System (INIS)

    Massey, C.D.; Miller, D.L.; Carson, S.D.

    1995-12-01

    In late 1994, Sandia National Laboratories in Albuquerque, New Mexico, (SNL/NM), was instructed by the Department of Energy (DOE) Isotope Production and Distribution Program (IPDP) to examine the feasibility of producing medically useful radioisotopes using the Annular Core Research Reactor (ACRR) and the Hot Cell Facility (HCF). Los Alamos National Laboratory (LANL) would be expected to supply the targets to be irradiated in the ACRR. The intent of DOE would be to provide a capability to satisfy the North American health care system demand for 99 Mo, the parent of 99m Tc, in the event of an interruption in the current Canadian supply. 99m Tc is used in 70 to 80% of all nuclear medicine procedures in the US. The goal of the SNL/NM study effort is to determine the physical plant capability, infrastructure, and staffing necessary to meet the North American need for 99 Mo and to identify and examine all issues with potential for environmental impact

  10. Isotope hydrology study of Molai area in Laconia

    International Nuclear Information System (INIS)

    Leontiadis, J.L.

    1981-04-01

    The isotopic composition of the groundwater was used in order to investigate the mechanism of recharge of the Molai plain (Laconia) and of the coastal brackish springs of the area. The results of this study have shown that the Tripolitza carbonates, northeast of the plain, do not form a unique aquifer nor contribute to the recharge of the plain which is mainly fed by the local rainwater. The brackish springs at Glyfada are fed by the Tripolitza carbonates, northeast of the Mavrovouni-Koupia fault, through an isolated from the neogene aquifer of the plain conduit. The water content of the corresponding reservoir is estimated in the range of 2318 to 3091 hm 3 . The brackish springs at Plytra are fed by the marbles of Chavallas and Skardolakka mountains through the bedrock of Assopos river and the neogene aquifer of that part of the plain. The water content of the corresponding reservoir is estimated to be more than 284 hm 3 . The brackish coastal springs between Palea Monemvasia and Hierax are fed by the Tripolitza limestones southeast of the Mavrovouni-Koupia fault. (T.A.)

  11. Feasibility study of medical isotope production at Sandia National Laboratories

    Energy Technology Data Exchange (ETDEWEB)

    Massey, C.D.; Miller, D.L.; Carson, S.D. [Sandia National Labs., Albuquerque, NM (United States). Environmental Regulatory Assessment Dept.] [and others

    1995-12-01

    In late 1994, Sandia National Laboratories in Albuquerque, New Mexico, (SNL/NM), was instructed by the Department of Energy (DOE) Isotope Production and Distribution Program (IPDP) to examine the feasibility of producing medically useful radioisotopes using the Annular Core Research Reactor (ACRR) and the Hot Cell Facility (HCF). Los Alamos National Laboratory (LANL) would be expected to supply the targets to be irradiated in the ACRR. The intent of DOE would be to provide a capability to satisfy the North American health care system demand for {sup 99}Mo, the parent of {sup 99m}Tc, in the event of an interruption in the current Canadian supply. {sup 99m}Tc is used in 70 to 80% of all nuclear medicine procedures in the US. The goal of the SNL/NM study effort is to determine the physical plant capability, infrastructure, and staffing necessary to meet the North American need for {sup 99}Mo and to identify and examine all issues with potential for environmental impact.

  12. Isotopic study of oxygen diffusion in oxide coatings

    Science.gov (United States)

    Gulino, Daniel A.; Kren, Lawrence A.; Dever, Therese M.

    1989-01-01

    Diffusion of oxygen in thin films of silicon dioxide was studied using oxygen isotopically enriched in oxygen of atomic mass 18 (O-18). This subject is of interest because thin films of dielectrics such as SiO2 are proposed for use as a protective coatings for solar mirrors in low Earth orbit, which is a strongly oxidizing environment. Films of this material were prepared with a direct current magnetron using reactive sputtering techniques. To produce (O-18)- enriched SiO2, a standard 3.5-in.-diameter silicon wafer was reactively sputtered using (O-18)-enriched (95 percent) oxygen as the plasma feed gas. The films were characterized using Rutherford backscattering and Secondary Ion Mass Spectrometer (SIMS) to establish stoichiometry and purity. Subsequently, the films were exposed to an air-derived oxygen plasma in a standard laboratory plasma reactor for durations of up to 10 hr. The concentration ratio of O-16 as a function of depth was determined using SIMS profiling and compared to a baseline, nonplasma exposed sample. A value for the diffusivity of oxygen near the surface of these films was obtained and found to be about 10(-15)sq cm/sec.

  13. Contribution of stable isotopes to the study of pharmacokinetics of magnesium salts; Apport des isotopes stables a l'etude de la pharmacocinetique de sels de magnesium

    Energy Technology Data Exchange (ETDEWEB)

    Benech, H

    1999-05-28

    The use of stable isotopes as labels is becoming an attractive tool for the study of magnesium behavior in humans. It has been used two stable isotopes of magnesium, {sup 25}Mg and {sup 26}Mg, to measure the absolute bioavailability of a pharmaceutical form of magnesium. (N.C.)

  14. Stable isotope ratio measurements in atmospheric sulfate studies

    Energy Technology Data Exchange (ETDEWEB)

    Cunningham, P.T.; Holt, B.D.

    1976-01-01

    The isotopic composition of atmospheric sulfate has been determined by a number of workers and the results interpreted in terms of contributing sources and mechanisms of origin. A correlation between the /sup 18/O enrichment of atmospheric water and airborne particulate sulfate has been observed. Laboratory preparations of sulfate made from sulfur dioxide by two sets of sequential reactions, hydrolysis followed by oxidation and oxidation followed by hydrolysis, yielded products of distinguishable oxygen-isotope composition. Oxygen isotopic analysis of simultaneously collected field samples of ambient sulfate, sulfur dioxide, and water vapor indicated seasonal trends for all of the major constituents of atmospheric sulfation processes. Some isotopic data were also obtained on precipitation and precipitation sulfates. Field results suggest that ambient sulfates collected in the area of Argonne correpond more closely in oxygen isotope composition to a sulfate molecule containing two oxygens originating from sulfur dioxide, one oxygen from air and one oxygen from condensed-phased atmospheric water, SO/sub s/O/sub s/O/sub cw/O/sup 2 -//sub a/, than to the molecule SO/sub s/O/sub s/O/sub wv/O/sup 2//sub a/ in which one oxygen originates from vapor-phase atmospheric water.

  15. Stable isotope ratio measurements in atmospheric sulfate studies

    International Nuclear Information System (INIS)

    Cunningham, P.T.; Holt, B.D.

    1976-01-01

    The isotopic composition of atmospheric sulfate has been determined by a number of workers and the results interpreted in terms of contributing sources and mechanisms of origin. A correlation between the 18 O enrichment of atmospheric water and airborne particulate sulfate has been observed. Laboratory preparations of sulfate made from sulfur dioxide by two sets of sequential reactions, hydrolysis followed by oxidation and oxidation followed by hydrolysis, yielded products of distinguishable oxygen-isotope composition. Oxygen isotopic analysis of simultaneously collected field samples of ambient sulfate, sulfur dioxide, and water vapor indicated seasonal trends for all of the major constituents of atmospheric sulfation processes. Some isotopic data were also obtained on precipitation and precipitation sulfates. Field results suggest that ambient sulfates collected in the area of Argonne correpond more closely in oxygen isotope composition to a sulfate molecule containing two oxygens originating from sulfur dioxide, one oxygen from air and one oxygen from condensed-phased atmospheric water, SO/sub s/O/sub s/O/sub cw/O 2- /sub a/, than to the molecule SO/sub s/O/sub s/O/sub wv/O 2 /sub a/ in which one oxygen originates from vapor-phase atmospheric water

  16. Study of elastic and inelastic scattering of 16O on even-even Sm isotopes

    International Nuclear Information System (INIS)

    Talon, Pascal.

    1979-01-01

    The recent equipment of tandem accelerators devoted to the study of heavy ion interactions with high-resolution magnetic spectrometers has enabled long-range effects to be observed during elastic scattering on deformed nuclei. These phenomena were studied as a function of energy around the Coulomb barrier and of Sm isotope deformation. Analyses by simple analytical formulae or using the optical model with an effective potential introducing an imaginary part into the Coulomb potential have fully confirmed that these long-range effects are induced by Coulomb excitation. A coupled channel analysis is shown to give access to nuclear deformation parameters. High resolution studies on the elastic scattering of heavy ions opens up a very interesting field of application for the study of deformed nuclei. The Coulomb barrier was seen to be lowered by the angular behavior of the Q opt of transfer reactions ( 16 O, 14 C) and ( 16 O, 12 C) on deformed Sm isotopes. It is now well known that the transfer of some nucleons induced by heavy ions can proceed from a two-stage mechanism. It may be supposed that the strong Coulomb excitation of a level can create the wave function overlapping conditions necessary to a nuclear transfer [fr

  17. Effects of inorganic anions on carbon isotope fractionation during Fenton-like degradation of trichloroethene

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yunde [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Laboratory of Basin Hydrology and Wetland Eco-restoration, China University of Geosciences, Wuhan 430074 (China); Zhou, Aiguo, E-mail: aiguozhou@cug.edu.cn [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Gan, Yiqun; Li, Xiaoqian [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China)

    2016-05-05

    Highlights: • The effect of inorganic anions on carbon isotope fractionation was evaluated. • The enrichment factors was independent concentration of NO{sub 3}{sup −}, or SO{sub 4}{sup 2−}. • Cl{sup −} significantly influenced the carbon isotope fractionation. - Abstract: Understanding the magnitude and variability in isotope fractionation with respect to specific processes is crucial to the application of stable isotopic analysis as a tool to infer and quantify transformation processes. The variability of carbon isotope fractionation during Fenton-like degradation of trichloroethene (TCE) in the presence of different inorganic ions (nitrate, sulfate, and chloride), was investigated to evaluate the potential effects of inorganic anions on carbon isotope enrichment factor (ε value). A comparison of ε values obtained in deionized water, nitrate solution, and sulfate solution demonstrated that the ε values were identical and not affected by the presence of nitrate and sulfate. In the presence of chloride, however, the ε values (ranging from −6.3 ± 0.8 to 10 ± 1.3‰) were variable and depended on the chloride concentration, indicating that chloride could significantly affect carbon isotope fractionation during Fenton-like degradation of TCE. Thus, caution should be exercised in selecting appropriate ε values for the field application of stable isotope analysis, as various chloride concentrations may be present due to naturally present or introduced with pH adjustment and iron salts during Fenton-like remediation. Furthermore, the effects of chloride on carbon isotope fractionation may be able to provide new insights about reaction mechanisms of Fenton-like processes.

  18. Isotope study of impact of climatic changes on hydrological cycle in Central Asian and Caspian arid region

    International Nuclear Information System (INIS)

    Ferronsky, V.I.; Polyakov, V.A.; Lobov, A.L.; Batov, V.I.

    2001-01-01

    The problem of replenishment of groundwater and lakes in the Central Asian and Caspian and region during the Late Pleistocene-Holocene transition time on the basis of isotope studies is discussed. Interpretation of the oxygen and carbon isotope record from the palaeogroundwaters and lake sediments shows that during climate cooling over the Eurasian continent its humid zone was extended towards the and regions. In addition, voluminous glaciers were accumulated in the northern and southern mountain regions. Intensive melting of the glaciers during the transition time provided effective replenishment of the aquifers and lakes in the and zone by fresh water. (author)

  19. Ab Initio Calculation of the Zn Isotope Effect in Phosphates, Citrates, and Malates and Applications to Plants and Soil

    OpenAIRE

    Fujii, Toshiyuki; Albar?de, Francis

    2012-01-01

    International audience; Stable Zn isotopes are fractionated in roots and leaves of plants. Analyses demonstrate that the heavy Zn isotopes are enriched in the root system of plants with respect to shoots and leaves as well as the host soil, but the fractionation mechanisms remain unclear. Here we show that the origin of this isotope fractionation is due to a chemical isotope effect upon complexation by Zn malates and citrates in the aerial parts and by phosphates in the roots. We calculated t...

  20. Radioactive isotope and isomer separation with using light induced drift effect

    International Nuclear Information System (INIS)

    Hradecny, C.; Slovak, J.; Tethal, T.; Ermolaev, I.M.; Shalagin, A.M.

    1991-01-01

    The isotope separation with using light induced drift (LID) is discussed. The basic theoretical characteristics of the method are deduced: separation simultaneously with an arbitrary high enrichment and without significant losses; separation productivity up to 100 μg/h. These characteristics are sufficient and very convenient for separation of expensive radioactive isotopes and isomers which are applied in medicine and science. The first experimental separation of the radioactive isotopes ( 22,24 Na) by using the LID effect is reported. 13 refs.; 5 figs

  1. Theory and Application of the Relationship between Steady-State Isotope Effects on Enzyme Intermediate Concentrations and Net Rate Constants☆

    Science.gov (United States)

    Ruszczycky, Mark W.; Liu, Hung-wen

    2018-01-01

    Steady-state kinetic isotope effects on enzyme catalyzed reactions are often interpreted in terms of the microscopic rate constants associated with the elementary reactions of interest. Unfortunately, this approach can lead to confusion, especially when more than one elementary reaction is isotopically sensitive, because it forces one to consider the full catalytic cycle one step at a time rather than as a complete whole. Herein we argue that shifting focus from intrinsic effects to net rate constants and enzyme intermediate concentrations provides a more natural and holistic interpretation by which the effects of partial rate-limitation are more easily understood. In doing so, we demonstrate how the experimental determination of isotope effects on enzyme intermediate concentrations allows a direct determination of isotope effects on net rate constants. The chapter is divided into three main sections. The first outlines the basic theory and its interpretation. The second discusses an application of the theory in the study of the radical SAM enzyme DesII. The final section then provides the complete mathematical treatment. PMID:28911781

  2. 13C Kinetic isotopic effect of polymerization on monomers with multiple bond

    International Nuclear Information System (INIS)

    Berman, E.L.; Polyakov, V.B.; Makovetskij, K.L.; Golenko, T.G.; Galimov, Eh.M.; AN SSSR, Moscow. Inst. Organicheskoj Khimii; AN SSSR, Moscow. Inst. Geokhimii i Analiticheskoj Khimii)

    1988-01-01

    13 C kinetic isotopic effect (KIE) of anionic and radical polymerization and metathesis reaction of monomers with multiple bonds are studied and correlation between the found KIE values of polymerization and the structure of transition state is established. 13 C KIE of polymerization reactions are investigated using monomers with natural content of the isotope. Polymerization was carried out using high-vacuum equipment: radical polymerization of methyl acrylate (MA) and vinyl acetate in benzene solution under the effect of benzoyl peroxide (60 deg C); anionic polymerization of MA, initiated by potassium butyl cellosolvolate, was realized in mass at 25 deg C; cyclopentene metathesis reaction was conducted in benzene under the effect of initiating system WCl 6 - (C 3 H 5 ) 2 Si(CH 3 ) 2 at -30 deg C; phenylacetylene polymers were prepared by polymerization in benzene solution at 20 deg C under the effect of WCl 6 . It is ascertained that 13 C KIE of radical and anionic polymerization of olefins and cycloolefin metathesis constitutes 2.0 -2.4%. Polymerization of compound with ternary bond is accompanied by a lower value of 13 C KIE (<1%), which is explained by double bond of reacting bond in transition state

  3. Kinetic isotope effects in the CH4 + H→CH3 + H2 system. Predictions of the LMR six-body potential-energy reaction hypersurface

    International Nuclear Information System (INIS)

    Marriott, T.D.

    1976-01-01

    Scope of Study: The purpose of this study was two-fold. First, it served to test, in part, the usefulness of the LMR six-body potential-energy surface (LMR-PES) for transition-state theory predictions of the kinetic isotope effects for both the forward and reverse reactions of CH 4 + H reversible CH 3 + H 2 . In this regard the agreement between experimental and theoretical isotope effects, assuming the former to be accurate, provides information about the accuracy of the curvature of the potential energy surface for motion both parallel and perpendicular to the reaction coordinate. Second, these isotope effects were used to assess the validity of a number of qualitative and semi-quantitative interpretations of kinetic isotope effects developed in physical organic chemistry with regard to this reaction system. The force constants and geometries obtained numerically from the LMR-PES were found to produce reasonable harmonic approximations to the reactant normal mode frequencies. Neglecting tunneling, the LMR-PES reasonably reproduces the experimental k/sub H//k/sub D/ values for the reactions CH 4 + H(D), CH 3 + HD(DH) and CD 2 + HD(DH). Since previous theoretical treatments of primary deuterium kinetic isotope effects have neglected the bending normal mode frequencies, a semi-quantitative study of the effect of neglecting bending frequencies on the VP, EXC, and ZPE elements as well as the transition-state theory kinetic isotope effects was performed. The Swain-Schaad relationship between primary deuterium and tritium kinetic isotope effects was shown to hold to a reasonable degree of accuracy for the LMR-PES reaction system. A relationship between 13-carbon and 14-carbon kinetic isotope effects similar to the Swain-Schaad relationship was derived

  4. Effects of preservation methods of muscle tissue from upper-trophic level reef fishes on stable isotope values (δ13C and δ15N

    Directory of Open Access Journals (Sweden)

    Christopher D. Stallings

    2015-03-01

    Full Text Available Research that uses stable isotope analysis often involves a delay between sample collection in the field and laboratory processing, therefore requiring preservation to prevent or reduce tissue degradation and associated isotopic compositions. Although there is a growing literature describing the effects of various preservation techniques, the results are often contextual, unpredictable and vary among taxa, suggesting the need to treat each species individually. We conducted a controlled experiment to test the effects of four preservation methods of muscle tissue from four species of upper trophic-level reef fish collected from the eastern Gulf of Mexico (Red Grouper Epinephelus morio, Gag Mycteroperca microlepis, Scamp Mycteroperca phenax, and Red Snapper Lutjanus campechanus. We used a paired design to measure the effects on isotopic values for carbon and nitrogen after storage using ice, 95% ethanol, and sodium chloride (table salt, against that in a liquid nitrogen control. Mean offsets for both δ13C and δ15N values from controls were lowest for samples preserved on ice, intermediate for those preserved with salt, and highest with ethanol. Within species, both salt and ethanol significantly enriched the δ15N values in nearly all comparisons. Ethanol also had strong effects on the δ13C values in all three groupers. Conversely, for samples preserved on ice, we did not detect a significant offset in either isotopic ratio for any of the focal species. Previous studies have addressed preservation-induced offsets in isotope values using a mass balance correction that accounts for changes in the isotope value to that in the C/N ratio. We tested the application of standard mass balance corrections for isotope values that were significantly affected by the preservation methods and found generally poor agreement between corrected and control values. The poor performance by the correction may have been due to preferential loss of lighter isotopes

  5. Isotope mixtures of hydrogen in vanadium

    International Nuclear Information System (INIS)

    Mecking-Schloetensack, P.

    1982-03-01

    The properties of isotope-mixtures of Protium and Deuterium stored in Vanadium have been studied. Protium and Deuterium are existing as interstitial-atoms on tetrahedral sites as well as on octahedral sites in this system. This feature leads to large isotopic-effects between the two isotopes. The dependence of the thermodynamic functions like heat of solution, nonconfigurational entropy, specific heat and ordering temperatures from the composition of the isotope-mixture has been determined. (orig.)

  6. Study of hydrogen isotopes super permeation through vanadium membrane on 'Prometheus' setup

    International Nuclear Information System (INIS)

    Musyaev, R. K.; Yukhimchuk, A. A.; Lebedev, B. S.; Busnyuk, A. O.; Notkin, M. E.; Samartsev, A. A.; Livshits, A. I.

    2008-01-01

    To develop the membrane pumping technology by means of superpermeable membranes at RFNC-VNIIEF in the 'Prometheus' setup, the experiments on superpermeation of hydrogen isotopes through metal membranes were carried out. The experimental results on superpermeation of thermal atoms of hydrogen isotopes including tritium through a cylindrical vanadium membrane are presented. The possibility of effective pumping, compression and recuperation of hydrogen isotopes by means of superpermeable membrane was demonstrated. The evaluation of membrane pumping rates and asymmetry degree of pure vanadium membrane was given. The work was performed under the ISTC-2854 project. (authors)

  7. Electrochemical H-D isotope effect at metal-perovskite proton conductor interfaces

    DEFF Research Database (Denmark)

    Kek, D.; Bonanos, N.

    1999-01-01

    The H-D isotope effect on the electrode kinetics of a metal-proton conductor interface has been investigated. The current-voltage behaviour depends on the nature of the electrode (Ni, Ag), the atmosphere (H(2), D(2)), the partial pressures of the gases, and the temperature. The isotope effect...... was manifested by a reduction in anodic current densities when H(2) was replaced by D(2). For both nickel and silver, the anodic part of the polarisation curves displayed limiting current behaviour, due to concentration polarisation. The empirical reaction order was not influenced by isotope replacement....... The empirical activation energy of the limiting current was affected by both the isotope used and the nature of the electrode. For both metals, a higher activation energy was observed with deuterium than with hydrogen. (C) 1999 Elsevier Science B.V. All rights reserved....

  8. Neutronic and thermal-hydraulic studies of aqueous homogeneous reactor for medical isotopes production

    Energy Technology Data Exchange (ETDEWEB)

    Perez, Daniel Milian; Lorenzo, Daniel E. Milian; Lira, Carlos A. Brayner de Oliveira; Garcia, Lorena P. Rodríguez, E-mail: milianperez89@gmail.com, E-mail: dmilian@instec.cu, E-mail: lorenapilar1109@gmail.com, E-mail: cabol@ufpe.br [Higher Institute of Technologies and Applied Sciences (InSTEC), Havana (Cuba); Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil). Departamento de Energia Nuclear

    2017-11-01

    The use of Aqueous Homogenous Reactors (AHR) is one of the most promissory alternatives to produce medical isotopes, mainly {sup 99}Mo. Compare to multipurpose research reactors, an AHR dedicated for {sup 99}Mo production has advantages because of their low cost, small critical mass, inherent passive safety, and simplified fuel handling, processing, and purification characteristics. This article presents the current state of research in our working group on this topic. Are presented and discussed the group validation efforts with benchmarking exercises that include neutronic and thermal-hydraulic results of two solution reactors, the SUPO and ARGUS reactors. Neutronic and thermal-hydraulic results of 75 kWth AHR based on the ARGUS reactor LEU configuration are presented. The neutronic studies included the determination of parameters such as reflector thickness, critical height, medical isotopes production and others. Thermal-hydraulics studies were focused on demonstrating that sufficient cooling capacity exists to prevent fuel overheating. In addition, the effects of some calculation parameters on the computational modeling of temperature, velocity and gas volume fraction during steady-state operation of an AHR are discussed. The neutronic and thermal-hydraulics studies have been performed with the MCNPX version 2.6e computational code and the version 14 of ANSYS CFX respectively. Our group studies and the results obtained contribute to demonstrate the feasibility of using AHR for the production of medical isotopes, however additional studies are still necessary to confirm these results and contribute to development and demonstration of their technical, safety, and economic viability. (author)

  9. Gyrokinetic characterization of the isotope effect in turbulent transport at the FT-2 tokamak

    Science.gov (United States)

    Niskala, P.; Gurchenko, A. D.; Gusakov, E. Z.; Altukhov, A. B.; Esipov, L. A.; Kantor, M. Yu; Kiviniemi, T. P.; Kouprienko, D.; Korpilo, T.; Lashkul, S. I.; Leerink, S.; Perevalov, A. A.; Rochford, R.

    2017-04-01

    Isotope effect allows fusion devices to perform better when heavier hydrogen isotopes are used as fuel, but the reason for this improvement is not yet understood. We present the first direct evidence of the isotope effect on particle confinement in the FT-2 tokamak and investigate it via gyrokinetic simulations. Experimental measurements for comparable hydrogen and deuterium discharges show that the particle confinement time increases by 40% for the heavier isotope species. The isotope effect on particle flux is reproduced in global and local gyrokinetic simulations. Global ELMFIRE simulations demonstrate a systemic reduction in particle fluxes across the radial range, showing a ratio of fluxes {{{Γ }}}{{H}}/{{{Γ }}}{{D}}=1.3 at the edge and {{{Γ }}}{{H}}/{{{Γ }}}{{D}}=1.4 at r/a=0.6. Local GENE simulations agree qualitatively with the result. Besides the fluctuation level, smaller scales and a favorable shift in the cross-phase between the turbulent fluctuations are found to contribute to the isotope effect in the simulations.

  10. Therapeutic use of radioactive isotopes

    CERN Multimedia

    Caroline Duc

    2013-01-01

    In December, researchers from ISOLDE-CERN, the Paul Scherrer Institute (PSI) and the Institut Laue-Langevin (ILL) published the results of an in vivo study which successfully proved the effectiveness of four terbium isotopes for diagnosing and treating cancerous tumours.   Four terbium isotopes suitable for clinical purposes. “ISOLDE is the only installation capable of supplying terbium isotopes of such purity and intensity in the case of three out of the four types used in this study,” explains Karl Johnson, a physicist at ISOLDE.  “Producing over a thousand different isotopes, our equipment offers the widest choice of isotopes in the world!” Initially intended for fundamental physics research, ISOLDE has diversified its activities over time to invest in various projects in the materials science, biochemistry and nuclear medicine fields. The proof-of-concept study has confirmed that the four terbium isotopes 149Tb, 152Tb, 155Tb produ...

  11. Utility of stable isotope analysis in studying foraging ecology of herbivores: Examples from moose and caribou

    Science.gov (United States)

    Ben-David, M.; Shochat, E.; Adams, L.

    2001-01-01

    Recently, researchers emphasized that patterns of stable isotope ratios observed at the individual level are a result of an interaction between ecological, physiological, and biochemical processes. Isotopic models for herbivores provide additional complications because those mammals consume foods that have high variability in nitrogen concentrations. In addition, distribution of amino acids in plants may differ greatly from that required by a herbivore. At northern latitudes, where the growing season of vegetation is short, isotope ratios in herbivore tissues are expected to differ between seasons. Summer ratios likely reflect diet composition, whereas winter ratios would reflect diet and nutrient recycling by the animals. We tested this hypothesis using data collected from blood samples of caribou (Rangifer tarandus) and moose (Alces alces) in Denali National Park and Preserve, Alaska, USA. Stable isotope ratios of moose and caribou were significantly different from each other in late summer-autumn and winter. Also, late summer-autumn and winter ratios differed significantly between seasons in both species. Nonetheless, we were unable to evaluate whether differences in seasonal isotopic ratios were a result of diet selection or a response to nutrient recycling. We believe that additional studies on plant isotopic ratios as related to ecological factors in conjunction with investigations of diet selection by the herbivores will enhance our understanding of those interactions. Also, controlled studies investigating the relation between diet and physiological responses in herbivores will increase the utility of isotopic analysis in studying foraging ecology of herbivores.

  12. Study of the stability of the gallium isotopes beyond the N = 50 neutron shell closure

    CERN Multimedia

    We propose to study the stability of the nuclear structure beyond N = 50 and Z = 28 with beams of neutron-rich gallium isotopes at the CRIS experiment at ISOLDE. The study of their hyperne structure and isotope shift will provide spins, magnetic dipole moments, electric quadrupole moments and changes in the mean-square charge radii. The $\\beta$-decay of $^{80}$Ga will be unambiguously measured using the technique of Laser Assisted Nuclear Decay Spectroscopy (LANDS). The half-lives of the very neutron-rich isotopes with N > 54 will be measured for their impact on the astrophysical ${r}$-process.

  13. International conference on isotopes in environmental studies - Aquatic Forum 2004. Book of extended synopses

    International Nuclear Information System (INIS)

    2004-01-01

    The International Conference on Isotopes in Environmental Studies: AQUATIC FORUM 2004, organized by the International Atomic Energy Agency (IAEA) was held in Monte-Carlo, Monaco, 25-29 October 2004. The principal objective of the Conference was to review recent achievements in the use of isotopic techniques to study marine and terrestrial environmental processes, transport of contaminants in the aquatic environment, climate change, computer modelling of environmental processes, present state of the art of isotopic techniques, data validation and syntheses, and the development of geographical information systems. This publication contains the extended synopses of presentations at the Conference

  14. Growth of adlayers studied by fluorination of isotopically engineered graphene

    Czech Academy of Sciences Publication Activity Database

    Ek Weis, Johan; da Costa, Sara; Frank, Otakar; Kalbáč, Martin

    2014-01-01

    Roč. 251, č. 12 (2014), s. 2505-2508 ISSN 0370-1972 R&D Projects: GA MŠk LH13022 Institutional support: RVO:61388955 Keywords : chemical vapor deposition * graphene * isotope labeling Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.489, year: 2014

  15. Heating Isotopically Labeled Bernal Stacked Graphene: A Raman Spectroscopy Study

    Czech Academy of Sciences Publication Activity Database

    Ek Weis, Johan; da Costa, Sara; Frank, Otakar; Kalbáč, Martin

    2014-01-01

    Roč. 5, č. 3 (2014), s. 549-554 ISSN 1948-7185 R&D Projects: GA MŠk LL1301 Institutional support: RVO:61388955 Keywords : Bernal * graphene * isotopic labeling Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 7.458, year: 2014

  16. Hydrologic and isotopic study of the Quito aquifer

    International Nuclear Information System (INIS)

    Villalba, Fabio; Benalcazar, Julio; Garcia, Marco; Altamirano, Cesar; Altamirano, Homero; Sarasti, Santiago; Mancero, Maria; Leiva, Eduardo; Pino, Jose; Alulema, Rafael; Cedeno, Alberto; Burbano, Napoleon; Paquel, Efren; Becerra, Simon; Andrade, Graciela

    2000-10-01

    The dynamics of the Quito basin and surrounding area aquifers were determined through the use of stable and radioactive isotopes, and the monitoring of the freatic levels and of the bacteriological and physico-chemical quality of the water. A conceptual hydrodynamic model of the Quito aquifer was also proposed in order to establish in the future a sustainable management system

  17. Crystal-plastic deformation of zircon : effects on microstructures, textures, microchemistry and the retention of radiogenic isotopes

    International Nuclear Information System (INIS)

    Kovaleva, E.

    2015-01-01

    Dating of deep-crustal deformation events potentially can be achieved by using plastically-deformed accessory minerals found in high-temperature shear zones. Deformation microstructures, such as dislocations and low-angle boundaries, form due to plastic deformation in the crystal lattice and act as fluid migration pathways and trace element (e.g. Pb, Ti, U, Th, REE) diffusion pathways through so-called “pipe diffusion”. Deformation microstructures can alter the chemical and isotopic composition of certain grain parts and may lead to complete or partial isotopic resetting of certain geochronometers (e.g. U/Th/Pb, K/Ar, Rb/Sr) in the mineral domains. This work aims to better understand the processes of crystal-plastic deformation and associated trace element redistribution and the resetting of isotopic systems in zircon. This study finds that: a) there are three general finite deformation patterns in deformed zircons; b) suggests that it is possible to reconstruct the macroscopic kinematic framework of the shear zone based on the orientation of deformed zircon grains and the operating misorientation axes; c) and demonstrates the effect of deformation microstructures on trace elements and Pb isotopes in zircon. The final goal of this project is to develop a tool for isotopic dating of high-temperature deformation events in the deep crust. In addition to these results, zircon grains with planar deformation bands have been discovered in paleo-seismic zones; these deformation features have been described in detail and a possible mechanism of their origin and formation is suggested. The effect of planar deformation bands on trace element and isotopic behavior has also been investigated. (author) [de

  18. Carbon Isotopes of Alkanes in Hydrothermal Abiotic Organic Synthesis Processes at High Temperatures and Pressures: An Experimental Study

    Science.gov (United States)

    Fu, Qi; Socki, Richard A.; Niles, Paul B.

    2010-01-01

    Observation of methane in the Martian atmosphere has been reported by different detection techniques [1-4]. With more evidence showing extensive water-rock interaction in Martian history [5-7], abiotic formation by Fischer-Tropsch Type (FTT) synthesis during serpentization reactions may be one possible process responsible for methane generation on Mars [8, 9]. While the experimental studies performed to date leave little doubt that chemical reactions exist for the abiotic synthesis of organic compounds by mineral surface-catalyzed reactions [10-12], little is known about the reaction pathways by which CO2 and/or CO are reduced under hydrothermal conditions. Carbon and hydrogen isotope measurements of alkanes have been used as an effective tool to constrain the origin and reaction pathways of hydrocarbon formation. Alkanes generated by thermal breakdown of high molecular weight organic compounds have carbon and hydrogen isotopic signatures completely distinct from those formed abiotically [13-15]. Recent experimental studies, however, showed that different abiogenic hydrocarbon formation processes (e.g., polymerization vs. depolymerization) may have different carbon and hydrogen isotopic patterns [16]. Results from previous experiments studying decomposition of higher molecular weight organic compounds (lignite) also suggested that pressure could be a crucial factor affecting fractionation of carbon isotopes [17]. Under high pressure conditions, no experimental data are available describing fractionation of carbon isotope during mineral catalyzed FTT synthesis. Thus, hydrothermal experiments present an excellent opportunity to provide the requisite carbon isotope data. Such data can also be used to identify reaction pathways of abiotic organic synthesis under experimental conditions.

  19. Dynamic isotope power system (DIPS) applications study. Volume I. Summary. Final report

    International Nuclear Information System (INIS)

    1979-11-01

    The Nuclear Integrated Multimission Spacecraft (NIMS) is designed for communications, surveillance, navigation and meteorelogical missions. This study assesses th attributes of the Dynamic Isotope Power System (DIPS) for this spacecraft. These attributes include cost, system and mission compatibility, and survivability

  20. Lithium isotope effect in the extraction systems of polyethers: effect of salt concentration

    International Nuclear Information System (INIS)

    Fang Shengqiang; Fu Lian

    1991-01-01

    Separation factors of lithium isotopes at 20 deg C were determined in the extraction systems of B15C5-CHCl 3 /LiBr-H 2 O. The initial concentration of LiBr was controlled in the extent of more than 2 mol/l. It may be established that the increase of LiBr concentration causes a remarkable increase of the separation factor. The essence of this effect due to the change in salt concentration was discussed in connection with examination of relevant phenomena in literature. It can be concluded that the relationship between α and Cm, the concentration of lithium salt, is dependent on K Q and K P express respectively, lithium isotope exchange equilibrium constants between Li-crownether complex and hydrated lithium ion for lithium concentration less than 1-2 mol/l, and between lithium salt ion pair and hydrated lithium ion for lithium concentration more than 2 mol/l in aqueous phase

  1. Disentangling effects of growth and nutritional status on seabird stable isotope ratios

    Science.gov (United States)

    Sears, J.; Hatch, Shyla A.; O'Brien, D. M.

    2009-01-01

    A growing number of studies suggest that an individual's physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather ??15N and ??13C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing ??15N and ??13C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in ??15N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC ??15N, with chicks exhibiting lower ??15N when they were growing the fastest. As growth slowed, ??15N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted ??15N in chick RBCs by 0.92???. We propose that increased nitrogen-use efficiency is responsible for 15N depletion in both growing and food-restricted chicks. ??15N values in RBCs of free-ranging auklets fell within a range of only 1.03???, while feather ??15N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue. ?? 2008 Springer-Verlag.

  2. Multiple isotope effects with alternative dinucleotide substrates as a probe of the malic enzyme reaction

    International Nuclear Information System (INIS)

    Weiss, P.M.; Urbauer, J.L.; Cleland, W.W.; Gavva, S.R.; Harris, B.G.; Cook, P.F.

    1991-01-01

    Deuterium isotope effects and 13 C isotope effects with deuterium- and protium-labeled malate have been obtained for both NAD- and NADP-malic enzymes by using a variety of alternative dinucleotide substrates. With nicotinamide-containing dinucleotides as the oxidizing substrate, the 13 C effect decreases when deuterated malate is the substrate compared to the value obtained with protium-labeled malate. These data are consistent with a stepwise chemical mechanism in which hydride transfer precedes decarboxylation of the oxalacetate intermediate as previously proposed. When dinucleotide substrates such as thio-NAD, 3-nicotinamide rings are used, the 13 C effect increases when deuterated malate is the substrate compared to the value obtained with protium-labeled malate. These data, at face value, are consistent with a change in mechanism from stepwise to concerted for the oxidative decarboxylation portion of the mechanism. However, the increase in the deuterium isotope effect from 1.5 to 3 with a concomitant decrease in the 13 C isotope effect from 1.034 to 1.003 as the dinucleotide substrate is changed suggests that the reaction may still be stepwise with the non-nicotinamide dinucleotides. A more likely explanation is that a β-secondary 13 C isotope effect accompanies hydride transfer as a result of hyperconjugation of the β-carboxyl of malate as the transition state for the hydride transfer step is approached

  3. Parameter study on Japanese proposal of ITER hydrogen isotope separation system

    International Nuclear Information System (INIS)

    Yoshida, Hiroshi; Enoeda, Mikio; Tanaka, Shigeru; Ohokawa, Yoshinao; Ohara, Atsushi; Nagakura, Masaaki; Naito, Taisei; Nagashima, Kazuhiro.

    1991-01-01

    As part of Japanese design contribution in the ITER activity, conceptual design of an entire ITER tritium system and their safety analysis have been carried out through the three-year period since 1988. The tritium system includes the following subsystems; - Fuelling (gas puffing and pellet injection) subsystem, - Torus vacuum pumping subsystem, - Plasma exhaust gas purification subsystem, - Hydrogen isotope separation subsystem, - NBI gas processing subsystem, - Blanket tritium recovery subsystem, - Tritiated water processing subsystem, - Tritium safety subsystem. Hydrogen isotope separation system is a key subsystem in the ITER tritium system because it is connected to all above subsystems. This report describes an analytical study on the Japanese concept of hydrogen isotope separation system. (author)

  4. Isotopic studies of rare gases in terrestrial samples and in natural nucleosynthesis

    International Nuclear Information System (INIS)

    1987-07-01

    This project is concerned with research in rare gas mass spectrometry. The broad objective is to read the natural record that isotopes of the rare gases comprise as trace constituents of natural gases, rocks, and meteorites. In past years, these interests have led to the study of such diverse problems as the dating of rocks, the early chronology and isotopic structure of the solar system as revealed by extinct radioactivities, and the elemental and isotopic composition of trapped primordial rare gases in meteorites. In recent years, the project has focused progressively more on terrestrial problems

  5. Isotopic studies of rare gases in terrestrial samples and in natural nucleosynthesis

    International Nuclear Information System (INIS)

    Reynolds, J.H.

    1988-08-01

    This project is concerned with research in rare gas mass spectrometry. The broad objective is to read the natural record that isotopes of the rare gases comprise as trace constituents of natural gases, rocks, and meteorites. In past years, these interests have led to the study of such diverse problems as the dating of rocks, the early chronology and isotopic structure of the solar system as revealed by extinct radioactivities, and the elemental and isotopic composition of trapped primordial rare gases in meteorites. In recent years, the project has focused progressively more on terrestrial problems

  6. Radioactive Emissions from Fission-Based Medical Isotope Production and Their Effect on Global Nuclear Explosion Detection

    International Nuclear Information System (INIS)

    Bowyer, T.; Saey, P.

    2015-01-01

    The use of medical isotopes, such as Tc-99m, is widespread with over 30 million procedures being performed every year, but the fission-based production of isotopes used for medical procedures causes emissions into the environment. This paper will show that gaseous radioactive isotopes of xenon, such as Xe-133, are released in high quantities, because they have a high fission cross section and they are difficult to scrub from the processes used to produce the medical isotopes due to their largely unreactive nature. Unfortunately, the reasons that large amounts of radioactive xenon isotopes are emitted from isotope production are the same as those that make these isotopes the most useful isotopes for the detection of underground nuclear explosions. Relatively recently, the nuclear explosion monitoring community has established a provisional monitoring network for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) that includes radioactive xenon monitoring as a major component. This community has discovered that emissions from medical isotope production present a more serious problem to nuclear explosion monitoring than thought when the network was first conceived. To address the growing problem, a group of scientists in both the monitoring and the isotope production communities have come together to attempt to find scientific and pragmatic ways to address the emissions problems, recognizing that medical isotope production should not be adversely affected, while monitoring for nuclear explosions should remain effective as isotope production grows, changes, and spreads globally. (author)

  7. Stable isotope variations in benthic primary producers along the Bosphorus (Turkey): A preliminary study

    International Nuclear Information System (INIS)

    Calizza, Edoardo; Aktan, Yelda; Costantini, Maria Letizia; Rossi, Loreto

    2015-01-01

    Highlights: • Nitrogen pollution along the Bosphorus Strait was investigated. • C and N isotopic and elemental analyses on benthic primary producers were performed. • δ 15 N decreased, while δ 13 C and N% increased from north to south along the Strait. • Ulva lactuca was more useful than epiphytes as indicator of nitrogen pollution. • Preliminary isotopic analyses on resident organisms are useful monitoring tools. - Abstract: The Bosphorus Strait is a dynamic and complex system. Recent evidences showed nitrogen and heavy metal concentrations to follow opposite patterns across the Strait, suggesting a complex spatial organisation of the anthropogenic disturbance in this system. Here, we provide isotopic information on the origin and transportation of dissolved nitrogen along the Bosphorus. C and N isotopic and elemental analyses were performed on specimens of Ulva lactuca and associated epiphytes sampled in five locations across the Strait. Variations in C and N isotopic signatures were observed in U. lactuca, pointing to a decrease in the availability of anthropogenic organic dissolved nitrogen along a north-south direction. Conversely, epiphytes did not show isotopic or elemental patterns across the Strait. These results suggest that preliminary stable isotope surveys in extended costal systems basing on U. lactuca can represent a valuable tool to focus meaningful targets and hypotheses for pollution studies in the Mediterranean region

  8. Lead isotope ratios as a tracer for lead contamination sources: A lake Andong case study

    Directory of Open Access Journals (Sweden)

    Kim Y. H

    2013-04-01

    Full Text Available The objective of this study was to evaluate stable Pb isotope signatures as a tracer for Pb contamination in Lake Andong. For Pb isotope analysis, we collected water and sediment from Lake Andong, particles in the air, soils, and stream water, mine tailings, sludge and wastewater from zinc smelting around lake Andong watershed. The results showed that Pb isotope ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb for zinc concentrate were 18.809 ± 0.322, 15.650 ± 0.062, and 38.728 ± 0.421, respectively. In wastewater, isotopic ratio values (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb were 17.363 ± 0.133, 15.550 ± 0.025, and 37.217 ± 0.092, respectively. Additionally, isotopic ratio values (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb for sludge were 17.515 ± 0.155, 15.537 ± 0.018, and 37.357 ± 0.173, respectively. These values were similar to those in zinc and lead concentrate originated from Canada and South America. In contrast, Pb isotope ratios of soil, tailings and sediment from Lake Andong were similar to those of Korean ore. Atmospheric particles showed different patterns of Pb isotope ratios from sediments, soils, and zinc smelting and this needs further investigation in order to identify atmospheric Pb sources.

  9. Study of polonium isotopes ground state properties by simultaneous atomic- and nuclear-spectroscopy

    CERN Multimedia

    Koester, U H; Kalaninova, Z; Imai, N

    2007-01-01

    We propose to systematically study the ground state properties of neutron deficient $^{192-200}$Po isotopes by means of in-source laser spectroscopy using the ISOLDE laser ion source coupled with nuclear spectroscopy at the detection setup as successfully done before by this collaboration with neutron deficient lead isotopes. The study of the change in mean square charge radii along the polonium isotope chain will give an insight into shape coexistence above the mid-shell N = 104 and above the closed shell Z = 82. The hyperfine structure of the odd isotopes will also allow determination of the nuclear spin and the magnetic moment of the ground state and of any identifiable isomer state. For this study, a standard UC$_{x}$ target with the ISOLDE RILIS is required for 38 shifts.

  10. Evidence of a kinetic isotope effect in nanoaluminum and water combustion.

    Science.gov (United States)

    Tappan, Bryce C; Dirmyer, Matthew R; Risha, Grant A

    2014-08-25

    The normally innocuous combination of aluminum and water becomes violently reactive on the nanoscale. Research in the field of the combustion of nanoparticulate aluminum has important implications in the design of molecular aluminum clusters, hydrogen storage systems, as well as energetic formulations which could use extraterrestrial water for space propulsion. However, the mechanism that controls the reaction speed is poorly understood. While current models for micron-sized aluminum water combustion reactions place heavy emphasis on diffusional limitations, as reaction scales become commensurate with diffusion lengths (approaching the nanoscale) reaction rates have long been suspected to depend on chemical kinetics, but have never been definitely measured. The combustion analysis of nanoparticulate aluminum with H2O or D2O is presented. Different reaction rates resulting from the kinetic isotope effect are observed. The current study presents the first-ever observed kinetic isotope effect in a metal combustion reaction and verifies that chemical reaction kinetics play a major role in determining the global burning rate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Isotopic effects in the interaction of O- with D2 and H2 at low temperatures

    Science.gov (United States)

    Plašil, Radek; Tran, Thuy Dung; Roučka, Štěpán; Jusko, Pavol; Mulin, Dmytro; Zymak, Illia; Rednyk, Serhiy; Kovalenko, Artem; Dohnal, Petr; Glosík, Juraj; Houfek, Karel; Táborský, Jiří; Čížek, Martin

    2017-12-01

    The isotopic effects in reactions of O- ions with H2 and D2 have been studied experimentally using a cryogenic 22-pole radio-frequency ion trap. The rate coefficients for associative detachment leading to H2O +e- and to D2O +e- and for atom transfer reactions leading to formation of OH- and OD- ions were determined at temperatures ranging from 15 to 300 K. The measured temperature dependencies of the rate coefficients for both channels of reactions of O- with H2 and D2 are compared with the results of the classical trajectory Monte Carlo simulation of the O-+H2 and O-+D2 collisions using the newly calculated potential energy surfaces. The measured temperature dependencies of the reaction rate coefficients for associative detachment are in very good agreement with the calculated ones. Agreement between experimental and calculated temperature dependencies of the rate coefficients of atom transfer reactions is off at most by a factor of 3 and the isotope effect is reproduced.

  12. Prediction of isotope effects for anticipated intermediate structures in the course of bacterial denitrification

    International Nuclear Information System (INIS)

    Morgenstern, M.A.; Schowen, R.L.

    1989-01-01

    Vibrational-analysis methods have been used to estimate the equilibrium 14 N/ 15 N isotope effects to be expected for conversion of nitrite anion to thirteen possible intermediate-state and product-state structures [HONO, NO + , NO, NO - , FeNO, ON * NO 2 , O * NNO 2 , O 2 NNO 2 , ONO * N, O * NON, ONNO, * NNO, N * NO] in the reduction of nitrite ion to nitrous oxide denitrifying bacteria. The results, taken in combination with previous experimental isotope-effect and tracer studies of the Pseudomonas stutzeri and related systems, are consistent with a suggestion that a second nitrite anion enters the enzyme-catalytic cycle at the stage of a nitrosyl-ion intermediate but re-emerges after entry of the reducing electrons; the product nitrous oxide is then formed by disproportionation of enzymically generated hyponitrous acid. The calculations are consistent with contributions, under different experimental conditions, of several different transition states to limiting the rate of the enzymic reaction. These transition states (and the corresponding experimental conditions) are the transition states for N-O fission in the generation of a mononitrogen electrophilic species from nitrite anion (high reductant, high nitrite concentrations), for attack of nitrite on this electrophile (high reductant, low nitrite concentrations) and for electron transfer to a dinitrogen-trioxide-like species (low reductant concentration). (orig.)

  13. How Trees Interact with Their Hydrologic Environment: a Stable Isotope Study

    Science.gov (United States)

    Gierke, C.; Newton, T.

    2012-12-01

    The Sacramento Mountains of southeast New Mexico serve as the primary recharge area to adjacent regional aquifers, including the Roswell Artesian Basin, the Tularosa Basin and the Salt Basin. Under pressures of population growth and climate change, land and water managers are interested in identifying land management and forest restoration methods that may increase local and regional groundwater recharge in the high mountains. The Sacramento Mountain Watershed Study is designed to assess the effects of tree thinning in mountain watersheds as an effective method of increasing groundwater recharge. The project employs a soil water balance to quantify the partitioning of local precipitation before and after tree thinning. This study was designed to determine the role that trees play in the hydrologic cycle by using the stable isotopes of oxygen and hydrogen to identify tree water sources. The study is being conducted in a 1st order watershed with no perennial outflow stream where vegetation is dominated by Douglas Fir (Pseudotsuga Menziesii). Ridges are capped with San Andres Limestone while lower slopes and the valley bottom are underlain by the Yeso Formation which is composed of sandstones, mudstones and interbedded carbonate layers. The area has thin soils covering shallow fractured bedrock or epikarst features. Some of the fractures within the epikarst zone provide direct conduits to the larger groundwater system while others are isolated rendering the reservoir inactive. From March 2011 to February 2012, we collected soil and twig samples from which water was extracted by cryogenic vacuum distillation. Soil water was also sampled with passive capillary samplers (PCAPS). The isotopic composition of bulk soil water appears to be controlled by evaporation of snowmelt stored within the soil matrix. The isotopic composition of soil water sampled by wick samplers reflects mixing of non-evaporated rainfall with evaporated bulk soil water. As the monsoon season

  14. Use of water stable isotopes in climatology and paleoclimatology illustrated from polar ice cores studies

    International Nuclear Information System (INIS)

    Jouzel, J.; Lorius, C.

    1994-01-01

    The isotopic content of ancient waters (deuterium and oxygen 18) gives a key access to past climatic changes. An essentially linear relationship exists between the isotopic content of a precipitation and the temperature of the site (at least for medium and high latitudes). This link between water isotope atmospheric cycle and climate is presented through various isotopic models and illustrated from the deuterium profile obtained along the Vostok ice core in East Antarctica. This 2 km record which covers a full glacial-interglacial cycle (160000 years) confirms the existence of a link between insolation changes and climate (Milankovitch theory). It shows also that the greenhouse effect has played a role in glacial-interglacial changes in amplifying this orbital forcing. (authors). 10 figs., 23 refs

  15. Ab Initio Calculations of Deuterium Isotope Effects on Chemical Shifts of Salt-Bridged Lysines

    DEFF Research Database (Denmark)

    Ullah, Saif; Ishimoto, Takayoshi; Williamson, Mike P.

    2011-01-01

    Deuterium isotope effects measure the change in chemical shift on substitution of a proton by deuterium. They have been calculated by direct treatment of the H/D nuclear quantum effect using a multicomponent ab initio molecular orbital method based on a non-Born−Oppenheimer approximation. This me......Deuterium isotope effects measure the change in chemical shift on substitution of a proton by deuterium. They have been calculated by direct treatment of the H/D nuclear quantum effect using a multicomponent ab initio molecular orbital method based on a non-Born−Oppenheimer approximation...

  16. Contrasting Effects of Carbon and Sulfur on Fe-Isotope Fractionation between Metal and Silicate Melt during Planetary Core Formation

    Science.gov (United States)

    Elardo, S. M.; Shahar, A.

    2015-12-01

    There are numerous studies that show well-resolved Fe isotope fractionations in igneous materials from different planetary bodies. Potential explanations for these fractionations include a non-chondritic bulk planetary Fe isotopic composition, and equilibrium fractionation between Fe-alloys or minerals and silicate melts during planetary differentiation, mantle melting, or fractional crystallization. This is further complicated by the fact that these processes are not mutually exclusive, making the interpretation of Fe isotope data a complex task. Here we present new experimental results investigating the effect of C on Fe isotope fractionation between molten peridotite and an Fe-alloy. Experiments were conducted at 1 GPa and 1850° C for 0.5 - 3 hours on a mixture of an 54Fe-spiked peridotite and Fe-metal with and without Ni metal in an end-loaded piston cylinder at the Geophysical Laboratory. Carbon saturation was achieved with a graphite capsule, and resulted in C contents of the Fe-alloy in our experiments ranging from 3.8 - 4.9 wt. %. The metal and silicate phases from half of each experiment were separated manually and dissolved in concentrated acids. Iron was separated from matrix elements by anion exchange chromatagraphy. Iron-isotopic compositions were determined with the Nu Plasma II MC-ICP-MS at GL. The other half of each experiment was used for quantitative microbeam analysis. Equilibrium was assessed with a time series and the three-isotope exchange method. The Ni-free experiments resulted in no resolvable Fe isotope fractionation between the Fe-C-alloy and molten silicate. This is in contrast to the results of Shahar et al. (2015) which showed a fractionation for Δ57Fe of ~0.18 ‰ between a peridotite and an Fe-alloy with a similar S abundance to C in these experiments. The one experiment thus far that contained Ni (~4 wt. % in the alloy) showed a resolvable fractionation between the Fe-Ni-C alloy and silicate of ~0.10 ‰. Shahar et al. found a

  17. Thermal Conductivity of Nanotubes Revisited: Effects of Chirality, Isotope Impurity, Tube Length, and Temperature

    OpenAIRE

    Zhang, Gang; Li, Baowen

    2004-01-01

    We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality, isotope impurity, tube length and temperature by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also found that the tube length dependence o...

  18. Evaluation of the residual effect of P fertilizer's on plant P nutrition using isotopic techniques

    International Nuclear Information System (INIS)

    Fardeau, J.C.; Zapata, F.

    1994-01-01

    The residual effect of P fertilizers previously applied to a soil on plant P nutrition was examined by both the isotopic dilution method (pot experiment) and isotopic exchange method (laboratory test) using 32 p as a tracer. The fraction of P derived from a fertilizer in plant (%Pdff in plant) was compared with the fraction of P derived from fertilizer in soil solution (%Pdff in soil solution) which is a new laboratory index proposed by Morel and Fardeau to predict %Pdff in plant. Four soil samples of a Humic Andosol from long-term experimental plots, which received no fertilizer (A1 soil), a readily soluble fertilizer (A2 soil), the same readily soluble fertilizer (RSF) plus a fused magnesium phosphate (A3 soil), and combination of RSF with Florida phosphate rock (A4 soil), were tested. In the pot experiment, maize (Zea mays) was grown during 38 days and dry shoot weight, P uptake and specific radioactivity were measured. Dry shoot weight, P uptake and L-value were the highest in A3 soil, followed by A4, A2 and A1 soils. %Pdff in plant were 71,9%, 51,9% and 15,4% in A3, A4 and A2 soils respectively. A laboratory study using 32 p isotopic exchange kinetics was carried out to examine three status parameters of soil P, intensity, quantity and capacity factors. Goof agreement was obtained between quantity factor (E 1 -value), and the pot experimental data; i.e. P uptake and L-value. %Pdff in soil solution were similar to those %Pdff in plant except for A4 soil. The enhancement of P uptake by the plant from the phosphate rock obtained in A4 soil could be attributed to specific plant factors and soil moisture conditions. (authors)

  19. Metabolism and transport studies of exogenous compounds thanks to 13C uniform isotopic enrichment

    International Nuclear Information System (INIS)

    Bravin, F.

    2008-12-01

    The study of many exogenous compounds does not raise difficulties when they are isolated, purified and in quantities sufficient for the usual detection methods used in biology (Chromatography, NMR, Mass Spectrometry, etc). When they are found in a biological fluid (blood, urines,..), they are often in infinitesimal amount such as the effect of their biological matrices or the background noise that make their detection and their quantification very delicate. The use of internal standards uniformly enriched with carbon 13 and/or nitrogen 15 makes it possible to obtain a signal more easily recognizable and identifiable thanks to the presence of the isotopes (peaks shifted in a mass spectrum for example). This is why, complementary to the analytical and biochemical studies of zearalenone (ZEN) metabolism, we were interested in building mass spectra of molecules enriched (rates between 0 and 1) by various isotopes ( 13 C, 15 N, 18 O and 2 H). In parallel we studied the influence of the 13 C enrichment on the reactivity of a given molecule, from a theoretical and an experimental point of view. (author)

  20. Use of stable isotopes of selenium in human metabolic studies: development of analytical methodology

    International Nuclear Information System (INIS)

    Janghorbani, M.; Ting, B.T.; Young, V.R.

    1981-01-01

    Use of stable isotopes of selenium in relation to enrichment of diets for studies of selenium absorption and metabolism in human subjects is discussed. A method based on radiochemical neutron activation analysis is described which allows accurate measurement of stable isotopes 74Se, 76Se, and 80Se in matrices (feces, plasma, red blood cells, and urine) of interest in metabolic studies. We show that these isotopes can routinely be measured with analytical precision and accuracy of 10% in samples of available size. This precision and accuracy is satisfactory for conduct of many nutritional experiments concerned with gastrointestinal absorption, plasma and red cell selenium turnover, and urinary excretion of the element, using an oral dose of 74Se. Original, experimental data are presented to illustrate the degree of enrichment of 74Se in feces, plasma, and urine after a single oral ingestion of 50 micrograms of the isotope with a breakfast meal in healthy young men

  1. Aspartate beta-decarboxylase from Alcaligenes faecalis: carbon-13 kinetic isotope effect and deuterium exchange experiments

    International Nuclear Information System (INIS)

    Rosenberg, R.M.; O'Leary, M.H.

    1985-01-01

    The authors have measured the 13 C kinetic isotope effect at pH 4.0, 5.0, 6.0, and 6.5 and in D 2 O at pH 5.0 and the rate of D-H exchange of the alpha and beta protons of aspartic acid in D 2 O at pH 5.0 for the reaction catalyzed by the enzyme aspartate beta-decarboxylase from Alcaligenes faecalis. The 13 C kinetic isotope effect, with a value of 1.0099 +/- 0.0002 at pH 5.0, is less than the intrinsic isotope effect for the decarboxylation step, indicating that the decarboxylation step is not entirely rate limiting. The authors have been able to estimate probable values of the relative free energies of the transition states of the enzymatic reaction up to and including the decarboxylation step from the 13 C kinetic isotope effect and the rate of D-H exchange of alpha-H. The pH dependence of the kinetic isotope effect reflects the pKa of the pyridine nitrogen of the coenzyme pyridoxal 5'-phosphate but not that of the imine nitrogen. A mechanism is proposed for the exchange of aspartate beta-H that is consistent with the stereochemistry suggested earlier

  2. Coordinated programme on isotopic tracer-aided studies of the biological side effects of foreign chemical residues in food and agriculture. Study of sulfur dioxide effects on phosphorus metabolism in plants using 32-P as indicator

    International Nuclear Information System (INIS)

    Plesnicar, M.

    1977-07-01

    Exposure of bean plants to low sulphur dioxide concentrations (0.02-0.32 ppm, up to 72 hours) stimulated the incorporation of 32 P into RNA, DNA, phospholipids and the acid soluble fraction, without altering the total phosphorus content. Statistically significant 32 P increases were only observed with RNA. Uptake of 35 SO 2 (14 ppm) by bean leaves was shown to be fairly rapid and the radioactivity was translocated in the roots within 1 to 6 hours following exposure. Subcellular leaf fractions showed that the supernatant contained 60-90% of the absorbed radioactivity. The chloroplasts and microsomes showed higher 35 S content than the mitochondrial fraction. In vitro studies on pea-derived chloroplasts included photosynthetic phosphorylation and electron transport. Phosphorylation was found to be inhibited in presence of SO 2 (I 50 =3.7 mM). The nature of inhibition seems to be of the reversible-competitive type with an apparent inhibitor constant (Ki) of 1.5 mM. The electron transport system remained unaffected. It is maintained that the identification of some lesions in this study would contribute to a better understanding of the nature of the complex interactions between cultivated plants and sulphur dioxide

  3. Ions, isotopes, and metal cyanides: Observational and laboratory studies

    Science.gov (United States)

    Savage, Chandra Shannon

    2004-11-01

    Chemistry in the interstellar medium is very different from the processes which take place in terrestrial settings. Environments such as circumstellar envelopes, molecular clouds, and comets contain diverse and complex chemical networks. The low temperatures (10 50 K) and densities (1 10 6 cm-3) allow normally unstable molecules to exist in significant quantities. At these temperatures, the rotational energy levels of molecules are populated, and thus these species can be detected by millimeter-wave radio astronomy. The detection and quantification of interstellar molecules, including metal cyanides and molecular ions, is the basis of this dissertation work. While conducting observations of CN and 13CN to determine the 12C/13C ratio throughout the Galaxy, it was found that the ratios in photon- dominated regions (PDRs) were much higher than those in nearby molecular clouds. This can be explained by isotope-selective photodissociation, in which the 12CN molecules are self-shielded. However, the chemistry in these regions is poorly understood, and other processes may be occurring. In order to understand one of the chemical networks present in PDRs, observations of HCO+, HOC +, and CO+ were made toward several of these sources. Previous studies indicated that the HCO+/HOC+ ratio was much lower in PDRs, due to the presence of CO+. The new observations indicate that there is a strong correlation between CO + and HOC+ abundances, which suggests that other molecular ions which have not been detected in molecular clouds may be present in PDRs. There is a significant obstacle to the detection of new interstellar molecular ions, however. The laboratory spectra are virtually unknown for many of these species, due to their inherent instability. Thus, techniques which can selectively detect ionic spectra must be utilized. One such method is velocity modulation, which incorporates an AC electrical discharge to produce and detect ions. Previously, velocity modulation spectroscopy

  4. Studies on separation of lithium isotopes by solvent extraction: Pt.1

    International Nuclear Information System (INIS)

    Chen Yaohuan; Yan Jinying; Wu Fubing

    1987-01-01

    The separation effects of lithium isotopes on the extraction with Sudan I(1-phenylazo-2-naphthol)-neutral ligand synergetic extraction systems are reported in this paper. Different separation effects are observed when different kinds of neutral ligands are used. Among them, the separation coefficient (α) of Sudan I-TOPO-xylene/LiCl-LiOH is found to be 1.009 ± 0.001. The heavy isotope 7 Li is enriched in the organic phase. The contributions of different structural chelating agents, synergetic agents and diluents to the separation effect are discussed. It is shown that the chelating agent played an important role in the separation effect, and the synergetic agent also exhibited obvious effect, while the shift of diluent didn't affect the separation coefficient significantly. The rates of extraction and isotope exchange equilibrium are high and these systems are shown to be diffusion-controlled ones

  5. Alternate substrates and isotope effects as a probe of the malic enzyme reaction

    Energy Technology Data Exchange (ETDEWEB)

    Gavva, S.R.

    1988-01-01

    Dissociation constants for alternative dinucleotide substrates and competitive inhibitors suggest that the dinucleotide binding site of the Ascaris suum NAD-malic enzyme is hydrophobic in the vicinity of the nicotinamide ring. Changes in the divalent metal ion activator from Mg{sup 2+} to Mn{sup 2+} or Cd{sup 2+} results in a decrease in the dinucleotide affinity and an increase in the affinity for malate. Primary deuterium and {sup 13}C isotope effects obtained with the different metal ions suggest either a change in the transition state structure for the hydride transfer or decarboxylation steps or both. Deuterium isotope effects are finite whether reactants are maintained at saturating or limiting concentrations with all the metal ions and dinucleotide substrates used. For the native enzyme, primary deuterium isotope effects increase with a concomitant decrease in the {sup 13}C effects when NAD is replaced by an alternate dinucleotide substrate different in redox potential.

  6. Alternate substrates and isotope effects as a probe of the malic enzyme reaction

    International Nuclear Information System (INIS)

    Gavva, S.R.

    1988-01-01

    Dissociation constants for alternative dinucleotide substrates and competitive inhibitors suggest that the dinucleotide binding site of the Ascaris suum NAD-malic enzyme is hydrophobic in the vicinity of the nicotinamide ring. Changes in the divalent metal ion activator from Mg 2+ to Mn 2+ or Cd 2+ results in a decrease in the dinucleotide affinity and an increase in the affinity for malate. Primary deuterium and 13 C isotope effects obtained with the different metal ions suggest either a change in the transition state structure for the hydride transfer or decarboxylation steps or both. Deuterium isotope effects are finite whether reactants are maintained at saturating or limiting concentrations with all the metal ions and dinucleotide substrates used. For the native enzyme, primary deuterium isotope effects increase with a concomitant decrease in the 13 C effects when NAD is replaced by an alternate dinucleotide substrate different in redox potential

  7. Use of isotopes in organic matter studies: a discussion illustrated by recent applications

    International Nuclear Information System (INIS)

    Warembourg, F.R.

    1982-01-01

    After a presentation of the various concepts leading to the advantageous use of isotope tracers in soil organic matter and related studies, a discussion is proposed around three main types of methods which are related to the time scale of the processes occurring in the soil organic matter transformations. Examples help to illustrate the purpose. Static methods describing the state of soil organic matter such as carbon dating. Long term dynamic studies involving the use of labelled plant materials and their applications in situ. Short term dynamic studies as an insight into the short term lived processes such as biotic and abiotic energetic activivation, flushes, priming effect, nitrogen fixation. More than an exhaustive enumeration of the litterature, the main objective of this presentation will tend to be a comprehensive analysis of the many problems arising from the study of soil activities and of the modern approaches of investigation. (Author) [pt

  8. Isotopes in environmental research

    International Nuclear Information System (INIS)

    Bowen, G.; Rozanski, K.; Vose, P.

    1990-01-01

    Radioactive and stable isotopes have long been considered a very efficient tool for studying physical and biological aspects of how the global ecosystem functions. Their applications in environmental research are numerous, embracing research at all levels. This article looks at only a few of the approaches to environmental problems that involve the use of isotopes. Special attention is given to studies of the Amazon Basin. Environmental isotopes are very efficient tools in water cycle studies. Tritium, a radioactive tracer, is especially useful in studying dynamics of water movement in different compartments of the hydrosphere, both on the local and global scales. Heavy stable isotopes of hydrogen and oxygen (deuterium and oxygen-18) provide information about steady-state characteristics of the water cycle. Isotope methods, some relatively new, have a major role in site-specific studies. Some indicative examples include: Studying turnover of organic matter. Changes in the carbon-13/carbon-12 isotopic ratio of organic matter were used to determine the respective contributions of organic carbon derived from forest and pasture. Studying biological nitrogen fixation. One of the ways nitrogen levels in soil can be maintained for productivity is by biological nitrogen fixation. Studying nitrogen availability and losses. The experimental use of nitrogen-15 is invaluable for defining losses of soil nitrogen to the atmosphere and to groundwater. Studies can similarly be done with stable and radioactive sulphur isotopes. This article indicates some potential uses of isotopes in environmental research. While the major problem of global climate change has not been specifically addressed here, the clearing of the Amazon forest, one focus of the IAEA's environmental programme, may have serious consequences for the global climate. These include substantial reduction of the amount of latent heat transported to the regions outside the tropics and acceleration of the greenhouse

  9. 2. Workshop 'Isotopes in Nature'. 1

    International Nuclear Information System (INIS)

    1979-11-01

    The workshop was aimed at discussing in detail the following problems: (1) distribution of stable and radioactive isotopes in nature, (2) theoretical and experimental studies of isotopic effects in natural processes, (3) problems of sample preparation and sample measurement in determining the relative abundance of stable isotopes or radioactive isotopes in nature, (4) age estimations of samples from different areas of the geosphere, (5) contributions to the specification of global and regional substance cycles in nature with the aid of isotopic and geochemical studies. 75 summaries are included

  10. Isotope effects upon translational diffusion as a probe for translation-rotation coupling in molecular liquids

    International Nuclear Information System (INIS)

    Holz, M.; Weingaertner, H.; Sacco, A.

    1990-01-01

    Mass changes of molecules caused by isotopic substitution (e.g. H-D substitution) can change the dynamic properties of a molecular liquid. Up to now, these dynamic isotope effects have been investigated only for a very small number of liquids. In the present paper we report on isotope effects upon self-diffusion coefficients, upon limiting tracer diffusion coefficients and upon viscosities of methanol, dimithylsulphoxide, dimethylformamide and nitromethane at 25deg C. It is shown that the square-root of mass dependence, which follows from a first theoretical approach, cannot predict the observed dynamic isotope effects. The experimental data correlate much better with the square root of the moments of inertia. Thus we establish a strong coupling between translational and rotational motion in these liquids. These results demonstrate that the dynamic isotope effects may serve as a sensitive probe for translation-rotation coupling in molecular liquids. The experimental finding of translation-rotation coupling is in agreement with recent computer simulations and has far consequences for the correct interpretation of liquid-state spectra as e.g. far-infrared absorption spectra. (orig.)

  11. Effect of channel coupling on the elastic scattering of lithium isotopes

    Science.gov (United States)

    Furumoto, T.; Suhara, T.; Itagaki, N.

    2018-04-01

    Herein, we investigated the channel coupling (CC) effect on the elastic scatterings of lithium (Li) isotopes (A =6 -9) for 12C and 28Si targets at E /A =50 -60 MeV. The wave functions of the Li isotopes were obtained using the stochastic multi-configuration mixing method based on the microscopic-cluster model. The proton radii of the 7Li, 8Li, and 9Li nuclei became smaller as the number of valence neutrons increased. The valence neutrons in the 8Li and 9Li nuclei exhibited a glue-like behavior, thereby attracting the α and t clusters. Based on the transition densities derived from these microscopic wave functions, the elastic-scattering cross section was calculated using a microscopic coupled-channel method with a complex G -matrix interaction. The existing experimental data for the elastic scatterings of the Li isotopes and 10Be nuclei were well reproduced. The Li isotope elastic cross sections were demonstrated for the 12C and 28Si targets at E /A =53 MeV. The glue-like effect of the valence neutrons on the Li isotope was clearly demonstrated by the CC effect on elastic scattering. Finally, we realize that the valence neutrons stabilized the bindings of the core parts and the CC effect related to core excitation was indeed reduced.

  12. Studies on the separation of hydrogen isotopes and spin isomers by gas chromatography

    International Nuclear Information System (INIS)

    Pushpa, K.K.; Annaji Rao, K.

    2000-08-01

    Separation and analysis of mixture of hydrogen isotopes has gained considerable importance because of various applications needing different isotopes in lasers, nuclear reactions and tracer or labelled compounds. In the literature gas chromatographic methods are reported using columns packed with partly dehydrated or thoroughly dehydrated alumina/molecular sieve stationary phase at 77 deg K with helium, neon and even hydrogen or deuterium as carrier gas. In the present study an attempt is made to compare the chromatographic behaviour of these two stationary phases using virgin and Fe doped form in partly dehydrated and thoroughly dehydrated state, using helium, neon, hydrogen and deuterium as carrier gas. The results of this study show that helium or neon carrier gas behave similarly broad peaks with some tailing. Sharp symmetric peaks are obtained with hydrogen or deuterium carrier gas. This is attributed to large hold up capacity for H 2 or D 2 at 77 deg K in these materials as compared to helium or neon. Spin isomers of H 2 or D 2 are separated on Fe free stationary phases, though ortho H 2 and HD are not resolved. Using a combination of Fe doped short column and plain alumina column, both maintained in dehydrated form, the effect of Fe doping on thermal equilibrium of ortho/para forms at 77 deg K is clearly demonstrated. (author)

  13. Isotopic studies of rare gases in terrestrial samples and natural nucleosynthesis

    International Nuclear Information System (INIS)

    1990-07-01

    This project is concerned with research in rare gas mass spectrometry. We read the natural record that isotopes of the rare gases provide. We study fluids using a system (RARGA) that is sometimes deployed in the field. In 1990 there was a strong effort to reduce the backlog of RARGA samples on hand, so that it was a year of intensive data gathering. Samples from five different areas in the western United States and samples from Guatemala and Australia were analyzed. In a collaborative study we also began analyzing noble gases from rocks associated with the fluids. An important objective, continuing in 1991, is to understand better the reasons for somewhat elevated 3 He/ 4 He ratios in regions where there is no contemporary volcanism which could produce the effect by addition of mantle helium. Our helium data have given us and our collaborators some insights, which are to be followed up, into gold mineralization in geothermal regions. Our DOE work in calibrating a sensitive laser microprobe mass spectrometer for noble gases in fluid inclusions continues. Having completed a series of papers on noble gases in diamonds, we next will attempt to make precise isotopic measurements on xenon from mantle sources, in search of evidence for terrestrially elusive 244 Pu decay

  14. Study of yrast bands and electromagnetic properties in neutron-rich 114-128Cd isotopes

    Science.gov (United States)

    Chaudhary, Ritu; Pandit, Rakesh K.; Devi, Rani; Khosa, S. K.

    2018-02-01

    The projected shell model framework has been employed to carry out a systematic study on the deformation systematics of E (21+) and E (41+) / E (21+) values, BCS subshell occupation numbers, yrast spectra, backbending phenomena and electromagnetic quantities in 114-128Cd isotopes. Present calculations reproduce the observed systematics of the E (21+), R42 and B (E 2 ;2+ →0+) values for 114-128Cd isotopic mass chain and give the evidence that deformation increases as one moves from 114Cd to 118Cd, thereafter it decreases up to 126Cd. This in turn confirms 118Cd to be the most deformed nucleus in this set of isotopic mass chain. The emergence of backbending, decrease in B (E 2) values and change in g-factors in all these isotopes are intimately related to the crossing of g-band by 2-qp bands.

  15. The study of trace metal absoption using stable isotopes and mass spectrometry

    Science.gov (United States)

    Fennessey, P. V.; Lloyd-Kindstrand, L.; Hambidge, K. M.

    1991-12-01

    The absorption and excretion of zinc stable isotopes have been followed in more than 120 human subjects. The isotope enrichment determinations were made using a standard VG 7070E HF mass spectrometer. A fast atom gun (FAB) was used to form the ions from a dry residue on a pure silver probe tip. Isotope ratio measurements were found to have a precision of better than 2% (relative standard deviation) and required a sample size of 1-5 [mu]g. The average true absorption of zinc was found to be 73 ± 12% (2[sigma]) when the metal was taken in a fasting state. This absorption figure was corrected for tracer that had been absorbed and secreted into the gastrointestinal (GI) tract over the time course of the study. The average time for a majority of the stable isotope tracer to pass through the GI tract was 4.7 ± 1.9 (2[sigma]) days.

  16. Study on pH conditions in deep underground by using isotopic analysis of carbonate minerals

    International Nuclear Information System (INIS)

    Iwatsuki, Teruki; Yoshida, Hidekazu; Hama, Katsuhiro; Metcalfe, R.

    2000-01-01

    This study was undertaken to develop a method for evaluating geochemical environments in deep granitic basement rocks. The method involves analyzing fracture-filling minerals to determine their isotopic compositions. A preliminary isotopic investigation (δ 13 C, δ 18 O, 14 C activity) of the groundwater and fracture-filling calcite in granite at the Tono research site, central Japan, was conducted. The isotopic compositions were used, together with geological evidence for the history of the Tono area, to infer the origins of the waters from which the calcite precipitated. These waters were:1. hydrothermal solutions, 2. relatively 'old' fresh water, 3. seawater, and 4. present groundwater. The investigation methods were very valuable for evaluating the temporal variations of geochemical conditions deep underground. The isotopic evidence for seawater is so far the most direct evidence that seawater penetrated into the granite in this area in the past. (author)

  17. Isotope Effects Associated with N2O Production by Fungal and Bacterial Nitric Oxide Reductases: Implications for Enzyme Mechanisms

    Science.gov (United States)

    Hegg, E. L.; Yang, H.; Gandhi, H.; McQuarters, A.; Lehnert, N.; Ostrom, N. E.

    2014-12-01

    Nitrous oxide (N2O) is both a powerful greenhouse gas and a key participant in ozone destruction. Microbial activity accounts for over 70% of the N2O produced annually, and the atmospheric concentration of N2O continues to rise. Because the fungal and bacterial denitrification pathways are major contributors to microbial N2O production, understanding the mechanism by which NO is reduced to N2O will contribute to both N2O source tracing and quantification. Our strategy utilizes stable isotopes to probe the enzymatic mechanism of microbial N2O production. Although the use of stable isotopes to study enzyme mechanisms is not new, our approach is distinct in that we employ both measurements of isotopic preferences of purified enzyme and DFT calculations, thereby providing a synergistic combination of experimental and computational approaches. We analyzed δ18O, δ15Nα (central N atom in N2O), and δ15Nβ (terminal N atom) of N2O produced by purified fungal cytochrome P450 nitric oxide reductase (P450nor) from Histoplasma capsulatum as well as bacterial cytochrome c dependent nitric oxide reductase (cNOR) from Paracoccus denitrificans. P450nor exhibits an inverse kinetic isotope effect for Nβ (KIE = 0.9651) but a normal isotope effect for both Nα (KIE = 1.0127) and the oxygen atom (KIE = 1.0264). These results suggest a mechanism where NO binds to the ferric heme in the P450nor active site and becomes Nβ. Analysis of the NO-binding step indicated a greater difference in zero point energy in the transition state than the ground state, resulting in the inverse KIE observed for Nβ. Following protonation and rearrangement, it is speculated that this complex forms a FeIV-NHOH- species as a key intermediate. Our data are consistent with the second NO (which becomes Nα and O in the N2O product) attacking the FeIV-NHOH- species to generate a FeIII-N2O2H2 complex that enzymatically (as opposed to abiotically) breaks down to release N2O. Conversely, our preliminary data

  18. Effect of 2H and 18O water isotopes in kinesin-1 gliding assay

    Directory of Open Access Journals (Sweden)

    Andy Maloney

    2014-03-01

    Full Text Available We show for the first time the effects of heavy-hydrogen water (2H2O and heavy-oxygen water (H218O on the gliding speed of microtubules on kinesin-1 coated surfaces. Increased fractions of isotopic waters used in the motility solution decreased the gliding speed of microtubules by a maximum of 21% for heavy-hydrogen and 5% for heavy-oxygen water. We also show that gliding microtubule speed returns to its original speed after being treated with heavy-hydrogen water. We discuss possible interpretations of these results and the importance for future studies of water effects on kinesin and microtubules. We also discuss the implication for using heavy waters in biomolecular devices incorporating molecular motors.

  19. The nitrogen isotope effect of benthic remineralization-nitrification-denitrification coupling in an estuarine environment

    Science.gov (United States)

    Alkhatib, M.; Lehmann, M. F.; del Giorgio, P. A.

    2012-05-01

    The nitrogen (N) stable isotopic composition of pore water nitrate and total dissolved N (TDN) was measured in sediments of the St. Lawrence Estuary and the Gulf of St. Lawrence. The study area is characterized by gradients in organic matter reactivity, bottom water oxygen concentrations, as well as benthic respiration rates. N isotope effects on the water column associated with the benthic exchange of nitrate (ϵapp) and TDN (ϵsed) during benthic nitrification-denitrification coupling were investigated. The sediments were a major sink for nitrate and a source of reduced dissolved N (RDN = DON + NH4+). We observed that both the pore water nitrate and RDN pools were enriched in 15N relative to the water column, with increasing δ15N downcore in the sediments. As in other marine environments, the biological nitrate isotope fractionation of net fixed N loss was barely expressed at the scale of sediment-water exchange, with ϵapp values denitrification zone, bottom water oxygen concentrations and the organic matter reactivity can modulate ϵapp. For the first time, actual measurements of δ15N of pore water RDN were included in the calculations of ϵsed. We argue that large fractions of the sea-floor-derived DON are reactive and, hence, involved in the development of the δ15N of dissolved inorganic N (DIN) in the water column. In the St. Lawrence sediments, the combined benthic N transformations yield a flux of 15N-enriched RDN that can significantly elevate ϵsed above ϵapp. Calculated ϵsed values were within the range of 4.6 ± 2‰ and were related to organic matter reactivity and oxygen penetration depth in the sediments. ϵsed reflects the δ15N of the N2 lost from marine sediments and thus best describes the isotopic impact of fixed N loss from sediments on the oceanic fixed N pool. Our mean value for ϵsed is larger than assumed by earlier work, questioning

  20. Pre-steady state transients in the Drosophila alcohol dehydrogenase catalyzed reaction: isotope effects and stereospecificity

    International Nuclear Information System (INIS)

    Place, A.R.; Eccleston, J.F.

    1987-01-01

    The alcohol dehydrogenase (ADH) isolated from Drosophila is unique among alcohol metabolizing enzymes by not requiring metals for catalysis, by showing 4-pro-S (B-sided) hydride transfer stereospecificity, and by possessing a greater catalytic turnover rate for secondary alcohols than for primary alcohols. They have extended their studies on the kinetic mechanism for this enzyme by examining the pre-steady state transients of ternary complex interconversion using stopped-flow fluorescence methods. When enzyme and a 30-fold molar excess of NADH is mixed with excess acetadehyde, methyl ethyl ketone (MEK), or cyclohexanone a rapid (> 100 s -1 ) transient is observe before the steady-state. The rates are insensitive to isotope substitution. With the substrate MEK, the rate and amplitude suggests a single turnover of the enzyme. Similar pre-steady state transients are observed when enzyme and a 50-fold molar excess of NAD + is mixed with ethanol, 2-propanol, and cyclohexanol. The rates show a hyperbolic concentration dependence and a deuterium isotope effect. With d 6 -deuteroethanol the transient no longer occurs in the pre-steady state. When the optical isomers of secondary alcohols are used as substrates, transients are observed only in the R-(-) isomers for all chain lengths. With 2-S(+)-heptanol and 2-S(+)-octanol no transients occur

  1. A comparative study on isotopic composition of precipitation in wet ...

    Indian Academy of Sciences (India)

    Deuterium, D) in water are useful, to investigate groundwater recharge (Fontes. 1980; IAEA 1981; Mazor 1991; Mathieu and Bariac. 1996; Clark and Fritz 1997), to study the effects of evaporation on groundwater systems(Gonfiantini. 1986; Hendry ...

  2. Application of Stable Isotope-Assisted Metabolomics for Cell Metabolism Studies

    Directory of Open Access Journals (Sweden)

    Le You

    2014-03-01

    Full Text Available The applications of stable isotopes in metabolomics have facilitated the study of cell metabolisms. Stable isotope-assisted metabolomics requires: (1 properly designed tracer experiments; (2 stringent sampling and quenching protocols to minimize isotopic alternations; (3 efficient metabolite separations; (4 high resolution mass spectrometry to resolve overlapping peaks and background noises; and (5 data analysis methods and databases to decipher isotopic clusters over a broad m/z range (mass-to-charge ratio. This paper overviews mass spectrometry based techniques for precise determination of metabolites and their isotopologues. It also discusses applications of isotopic approaches to track substrate utilization, identify unknown metabolites and their chemical formulas, measure metabolite concentrations, determine putative metabolic pathways, and investigate microbial community populations and their carbon assimilation patterns. In addition, 13C-metabolite fingerprinting and metabolic models can be integrated to quantify carbon fluxes (enzyme reaction rates. The fluxome, in combination with other “omics” analyses, may give systems-level insights into regulatory mechanisms underlying gene functions. More importantly, 13C-tracer experiments significantly improve the potential of low-resolution gas chromatography-mass spectrometry (GC-MS for broad-scope metabolism studies. We foresee the isotope-assisted metabolomics to be an indispensable tool in industrial biotechnology, environmental microbiology, and medical research.

  3. Stable isotope methodology in the pharmacokinetic studies of androgenic steroids in humans

    International Nuclear Information System (INIS)

    Shinohara, Y.; Baba, S.

    1990-01-01

    The use of stable isotopically labeled steroids combined with gas chromatography/mass spectrometry (GC/MS) has found a broad application in pharmacologic studies. Initially, stable isotopically labeled steroids served as the ideal analytic internal standard for GC/MS analysis; however, their in vivo use has expanded and has proven to be a powerful pharmacokinetic tool. We have successfully used stable isotope methodology to study the pharmacokinetic/bioavailability of androgens. The primary advantage of the technique is that endogenous and exogenous steroids with the same basic structure can be differentiated by using stable isotopically labeled analogs. The method was used to examine the pharmacokinetics of testosterone and testosterone propionate, and to clarify the influence of endogenous testosterone. Another advantage of the isotope methods is that steroidal drugs can be administered concomitantly in two formulations (e.g., solution and solid dosage). A single set of blood samples serves to describe the time course of the formulations being compared. This stable isotope coadministration technique was used to estimate the relative bioavailability of 17 alpha-methyltestosterone. 35 references

  4. Application of Stable Isotope-Assisted Metabolomics for Cell Metabolism Studies

    Science.gov (United States)

    You, Le; Zhang, Baichen; Tang, Yinjie J.

    2014-01-01

    The applications of stable isotopes in metabolomics have facilitated the study of cell metabolisms. Stable isotope-assisted metabolomics requires: (1) properly designed tracer experiments; (2) stringent sampling and quenching protocols to minimize isotopic alternations; (3) efficient metabolite separations; (4) high resolution mass spectrometry to resolve overlapping peaks and background noises; and (5) data analysis methods and databases to decipher isotopic clusters over a broad m/z range (mass-to-charge ratio). This paper overviews mass spectrometry based techniques for precise determination of metabolites and their isotopologues. It also discusses applications of isotopic approaches to track substrate utilization, identify unknown metabolites and their chemical formulas, measure metabolite concentrations, determine putative metabolic pathways, and investigate microbial community populations and their carbon assimilation patterns. In addition, 13C-metabolite fingerprinting and metabolic models can be integrated to quantify carbon fluxes (enzyme reaction rates). The fluxome, in combination with other “omics” analyses, may give systems-level insights into regulatory mechanisms underlying gene functions. More importantly, 13C-tracer experiments significantly improve the potential of low-resolution gas chromatography-mass spectrometry (GC-MS) for broad-scope metabolism studies. We foresee the isotope-assisted metabolomics to be an indispensable tool in industrial biotechnology, environmental microbiology, and medical research. PMID:24957020

  5. Some measurements of H/D polarizability isotope effects using differential refractometry

    International Nuclear Information System (INIS)

    Foster Smith, M.; Van Hook, W.A.

    1989-01-01

    Refractive index differences between the H and D isomers of some common molecules in the liquid phase were measured between 404.7 and 690.0 nm. The data are combined with information on molar volume isotope effects to yield values for H/D isotope effects on the static polarizability, the vibrational contribution to the static and frequency dependent parts of the polarizability, and the H/D isotope effect on the second moment of the electronic charge distribution. The present results suffice to demonstrate the practicability of this technique to measure the components of the polarizability listed above. However for accurate resolution of the vibrational and second moment contributions, refractive index data of still greater precision will be required. (orig.)

  6. Zinc absorption study using an enriched stable isotope (70Zn)

    International Nuclear Information System (INIS)

    Li Gongpan.

    1990-04-01

    A weaning food from fermented soybean was prepared for increasing the bioavailability of zinc. The zinc absorption was compared with that of a weaning food from non-fermented soybean and normal staple food. A stable isotope tracer technique ( 70 Zn) and neutron activation were used for determining the absorption of zinc. Nine children aged 7 to 18 months were tested. Zinc bioavailability of weaning food from fermented soybean is higher than that of normal weaning food. The weight increment and zinc nutrition of children having weaning food from fermented soybean are improved by this diet. 5 tabs

  7. Effects of different water storage procedures on the dissolved Fe concentration and isotopic composition of chemically contrasted waters from the Amazon River Basin.

    Science.gov (United States)

    Mulholland, Daniel S; Poitrasson, Franck; Boaventura, Geraldo R

    2015-11-15

    Although recent studies have investigated the Fe isotopic composition of dissolved, colloidal and particulate phases from continental and oceanic natural waters, few efforts have been made to evaluate whether water sample storage and the separation of different pore-size fractions through filtration can cause any change to the Fe isotopic compositions. The present study investigates the possible biases introduced by different water storage conditions on the dissolved Fe concentration and isotopic composition of chemically different waters. Water samples were collected from an organic-rich river and from mineral particulate-rich rivers. Filtered and unfiltered water samples were stored either at room temperature or frozen at -18°C in order to assess possible biases due to (i) different water storage temperature, and (ii) storage of bulk (unfiltered) vs filtered water. Iron isotope measurements were performed by Multicollector Inductively Coupled Plasma Mass Spectrometry with a Thermo Electron Neptune instrument, after Fe purification using anion-exchange resins. Our data reveal that bulk water storage at room temperature without filtration produces minor changes in the dissolved Fe isotopic composition of mineral particulate-rich waters, but significant isotopic composition changes in organic-rich waters. In both cases, however, the impact of the different procedures on the Fe concentrations was strong. On the other hand, the bulk water stored frozen without filtration produced more limited changes in the dissolved Fe concentrations, and also on isotopic compositions, relative to the samples filtered in the field. The largest effect was again observed for the organic-rich waters. These findings suggest that a time lag between water collection and filtration may cause isotopic exchanges between the dissolved and particulate Fe fractions. When it is not possible to filter the samples in the field immediately after collection, the less detrimental approach is to

  8. Studying of isotope structure of uranium by alpha-spectrometric method

    International Nuclear Information System (INIS)

    Sattarov, G.S.; Muzafarov, A.M.; Petukhov, O.F.; Petrenko, V.Z.

    2004-01-01

    Full text: The knowledge of isotope structure of uranium in waters, in minerals and in finished goods gives the helpful information on the radiation and nuclear-physical processes occurring in natural environments. Besides, customers put a question before uranium producing enterprises on the control of limiting concentration of an isotope 234 U in finished goods (uranium protoxide-oxide). For these reasons studying and development of techniques of definition of isotope structure of uranium is an actual task. In this connection for researches alpha - spectrometers 'PROGRESS-ALPHA' produced by R and D 'DOZE' Russia and firms 'Canberra' the USA were used. The isotope structure of uranium ( 234 U, 235 U, 238 U) was determined on a known ratio 234 U/ 238 U, which is equal to 53,41micrograms/gram. Identification of isotopes carried out by 4198 keV ( 235 U), 4395 keV ( 234 U) and 4773 keV ( 238 U). The technique of radiochemical preparation of samples to the analysis included: clearing of organic chemistry and preventing natural isotopes; drawing by a method electrolytic sedimentation on a metal substrate (d=24mm) an active stain, the area 4,5 cm 2 , with isotropy distribution of ions 234 U, 235 U, 238 U. As standards, the international and All-Russian standards with known contents 234 U were used. The isotope structure of uranium in uranium protoxide-oxide, chemical concentrates, technological solutions is determined. Infringements of isotope balance 234 U/ 238 U on separate sites of fulfilled uranium deposits and in technological products are found out

  9. Isotope effects in ice Ih: A path-integral simulation

    OpenAIRE

    Herrero, Carlos P.; Ramirez, Rafael

    2011-01-01

    Ice Ih has been studied by path-integral molecular dynamics simulations, using the effective q-TIP4P/F potential model for flexible water. This has allowed us to analyze finite-temperature quantum effects in this solid phase from 25 to 300 K at ambient pressure. Among these effects we find a negative thermal expansion of ice at low temperatures, which does not appear in classical molecular dynamics simulations. The compressibility derived from volume fluctuations gives results in line with ex...

  10. Studies on separation of lithium isotopes by solvent extraction: Pt. 2

    International Nuclear Information System (INIS)

    Chen Yaohuan; Yan Jinying; Li Yongkun

    1987-01-01

    The effect of the struture of chelating agent and synergetic agent on the extraction separation of lithium isotopes by Sudan I-neutral ligand synergetic extraction systems were discussed in this paper. In order to obtain higher isotopic effect, the chelating agent must possess weaker acidity (pK a > 11), stronger intramolecular hydrogen bonding and a greater tendency to form a six-membered chelating ring. In the synergetic agent, there must be a functional group possessing strong coordination ability without steric hindrance. The separation effect (α) increased with the increase in the basicity of the coordinating group. The increase of the number of chelating rings in the extractable complex was of benefit to the enhancement of α. Further discussions are also made on the enrichment direction of extraction systems and the prospects of different systems to be used for isotope separation

  11. Laser Spectroscopy Study on the Neutron-Rich and Neutron-Deficient Te Isotopes

    CERN Multimedia

    2002-01-01

    We propose to perform laser spectroscopy measurements on the Te isotopes. This will give access to fundamental properties of the ground and rather long-lived isomeric states such as the change in the mean square charge radius ($\\delta\\langle$r$^2_c\\rangle$) and the nuclear moments. For these medium-mass isotopes, at this moment the optical resolution obtained with RILIS is not high enough to perform isotope shift measurements. Thus we will use the COMPLIS experimental setup which allows Resonant Ionization Spectroscopy (RIS) on laser desorbed atoms. The 5p$^{4}$ $^{3}$P$_{2} \\rightarrow$ 5p$^{3}$ 6s $^{3}$S$_{1}$ and 5p$^{4}$ $^{3}$P$_{2} \\rightarrow$ 5p$^{3}$ 6s $^{5}$S$_{2}$ optical transitions have been used to perform, on the stable Te isotopes, the tests required by the INTC committee. For this purpose stable-ion sources have been built and Te isotopes have been delivered as stable beams by the injector coupled to the COMPLIS setup. ISOLDE offers the opportunity for studying the Te isotope series over a ...

  12. Study of Neutron-Deficient $^{202-205}$Fr Isotopes with Collinear Resonance Ionization Spectroscopy

    CERN Document Server

    De Schepper, Stijn; Cocolios, Thomas; Budincevic, Ivan

    The scope of this master’s thesis is the study of neutron-deficient $^{202−205}$Fr isotopes. These isotopes are inside the neutron-deficient lead region, a region that has shown evidence of shape coexistence. For this thesis, this discussion is limited to the phenomenon where a low lying excited state has a different shape than the ground state. Shape coexistence is caused by intruder states. These are single-particle Shell Model states that are perturbed in energy due to the interaction with a deformed core. In the neutron-deficient lead region the main proton intruder orbit is the 3s$_{1/2}$orbit. When going towards more neutron-deficient isotopes, deformation increases. The $\\pi3s_{1/2}$orbit will rise in energy and will eventually become the ground state in odd- A bismuth (Z=83) isotopes. It is also observed in odd-A astatine (Z=85) isotopes, already in less neutron-deficient nuclei. The same phenomenon is expected to be present francium (Z=87) isotopes already at $^{199}$Fr. Although it is currently ...

  13. Solvent isotope effects on the rates of alkylation of thiolamine models of papain

    International Nuclear Information System (INIS)

    Wandinger, A.; Creighton, D.J.

    1980-01-01

    As a test of whether it is chemically reasonable to attribute any or all of the observed kinetic solvent deuterium isotope effects reported on papain to the fundamental properties of the tautomerization equilibrium, the magnitudes of the solvent deuterium isotope effects on the rates of alkylation of the tautomeric forms of cysteine and β-mercaptoethylamine were determined for bromo- and chloroacetate, bromo- and chloroacetamide, as well as for methylbromoacetate. These thiolamines are viewed as elementary chemical models of the sulfhydryl group tautomerization equilibrium envisioned in the active site of papain. (Auth.)

  14. The kinetic deuterium isotope effect in the thermal dehydration of boric acid

    International Nuclear Information System (INIS)

    Tanaka, H.; Ohshima, S.; Ichiba, S.; Negita, H.

    1981-01-01

    The kinetic deuterium isotope effect in the thermal dehydration process from H 3 BO 3 to HBO 2 (III) was determined using simultaneous TG and DSC. The rate constant ratio of H 3 BO 3 to D 3 BO 3 obtained by the analysis of isothermal TG and DSC curves was found to be smaller than unity. Both activation energy, E, and frequency factor, A, for the dehydration of H 3 BO 3 proved to be larger than those of D 3 BO 3 , using non-isothermal TG and DSC. The origin of the deuterium kinetic isotope effect in the thermal dehydration of boric acid is also briefly discussed. (orig.)

  15. Studies of isotopic hydrology in Latin America 2006

    International Nuclear Information System (INIS)

    2009-04-01

    Policies for the exploitation of groundwater as a complement to surface water resources are frequently based on short term planning and may not be sustainable over time. The objective of sustainable groundwater management is to use groundwater in conjunction with surface waters in such a way that a state of equilibrium is reached in terms of both quantity and quality of water. This type of management allows these underground resources to be preserved for future generations. Conventional and isotope techniques allow information to be obtained on the most important hydrogeological parameters such as identification and evaluation of recharge and discharge area and rates, the available volume of groundwater to be estimated, hydrological interconnections between aquifers and surface waters, direction and velocity of groundwater flows, etc., which allow mathematical flow models to be established and validated. Mathematical models are indispensable tools for sustainable water resource management. The objective of the IAEA technical cooperation project RLA/8/031 was to contribute to improve the hydrogeological understanding of the aquifers through the use of isotopic and conventional techniques, with the final aim of improving groundwater resource management in several countries in Latin America. The present paper briefly summarizes the technical results obtained during the four years of the regional project [es

  16. Calculation of turnover rates in stable-isotope studies

    International Nuclear Information System (INIS)

    Wootton, R.; Ford, G.C.; Cheng, K.N.; Halliday, D.

    1985-01-01

    In a comparison of glucose turnover measured with 2 H-glucose and with 13 C-glucose Tserng and Kalhan used five apparently different equations and obtained conflicting answers. There is, however, no difference in principle between the use of a stable isotope as a tracer and the use of a radioactive isotope, and the rate of appearance of tracee in a steady-state system (the turnover) can therefore be shown to be proportional to the equilibrium dilution of the infused tracer. Because the sensitivity of measurement of this dilution made using a gas chromatograph-mass spectrometer is lower than that made by radioactivity measurement, the contribution to the measured turnover rate due to the infusate cannot be neglected, as it usually is in radioisotope work. A convenient calibration curve to establish this dilution is the mole ratio of the pure infusate against the area ratio for the relevant ions. Tserng and Kalhan's apparently conflicting results for glucose-turnover using 13 C-glucose as the tracer can all be shown to amount to approximately 11.6 μmol min -1 kg -1 . This value is only slightly lower (0.05 2 H-glucose as the tracer and supports the use of 13 C-glucose as an alternative. (author)

  17. The effect of warming on grassland evapotranspiration partitioning using laser-based isotope monitoring techniques

    KAUST Repository

    Wang, Lixin

    2013-06-01

    The proportion of transpiration (T) in total evapotranspiration (ET) is an important parameter that provides insight into the degree of biological influence on the hydrological cycles. Studies addressing the effects of climatic warming on the ecosystem total water balance are scarce, and measured warming effects on the T/ET ratio in field experiments have not been seen in the literature. In this study, we quantified T/ET ratios under ambient and warming treatments in a grassland ecosystem using a stable isotope approach. The measurements were made at a long-term grassland warming site in Oklahoma during the May-June peak growing season of 2011. Chamber-based methods were used to estimate the δ2H isotopic composition of evaporation (δE), transpiration (δT) and the aggregated evapotranspiration (δET). A modified commercial conifer leaf chamber was used for δT, a modified commercial soil chamber was used for δE and a custom built chamber was used for δET. The δE, δET and δT were quantified using both the Keeling plot approach and a mass balance method, with the Craig-Gordon model approach also used to calculate δE. Multiple methods demonstrated no significant difference between control and warming plots for both δET and δT. Though the chamber-based estimates and the Craig-Gordon results diverged by about 12‰, all methods showed that δE was more depleted in the warming plots. This decrease in δE indicates that the evaporation flux as a percentage of total water flux necessarily decreased for δET to remain constant, which was confirmed by field observations. The T/ET ratio in the control treatment was 0.65 or 0.77 and the ratio found in the warming treatment was 0.83 or 0.86, based on the chamber method and the Craig-Gordon approach. Sensitivity analysis of the Craig-Gordon model demonstrates that the warming-induced decrease in soil liquid water isotopic composition is the major factor responsible for the observed δE depletion and the temperature

  18. Correlation of the vapor pressure isotope effect with molecular force fields in the liquid state

    Energy Technology Data Exchange (ETDEWEB)

    Pollin, J.S.; Ishida, T.

    1976-07-01

    The present work is concerned with the development and application of a new model for condensed phase interactions with which the vapor pressure isotope effect (vpie) may be related to molecular forces and structure. The model considers the condensed phase as being represented by a cluster of regularly arranged molecules consisting of a central molecule and a variable number of molecules in the first coordination shell. The methods of normal coordinate analysis are used to determine the modes of vibration of the condensed phase cluster from which, in turn, the isotopic reduced partition function can be calculated. Using the medium cluster model, the observed vpie for a series of methane isotopes has been successfully reproduced with better agreement with experiment than has been possible using the simple cell model. We conclude, however, that insofar as the medium cluster model provides a reasonable picture of the liquid state, the vpie is not sufficiently sensitive to molecular orientation to permit an experimental determination of intermolecular configuration in the condensed phase through measurement of isotopic pressure ratios. The virtual independence of vapor pressure isotope effects on molecular orientation at large cluster sizes is a demonstration of the general acceptability of the cell model assumptions for vpie calculations.

  19. Effects of trace element concentration on enzyme controlled stable isotope fractionation during aerobic biodegradation of toluene.

    Science.gov (United States)

    Mancini, Silvia A; Hirschorn, Sarah K; Elsner, Martin; Lacrampe-Couloume, Georges; Sleep, Brent E; Edwards, Elizabeth A; Lollar, Barbara Sherwood

    2006-12-15

    The effects of iron concentration on carbon and hydrogen isotopic fractionation during aerobic biodegradation of toluene by Pseudomonas putida mt-2 were investigated using a low iron medium and two different high iron media. Mean carbon enrichment factors (epsilonc) determined using a Rayleigh isotopic model were smaller in culture grown under high iron conditions (epsilonc = -1.7+/-0.1%) compared to low iron conditions (epsilonc = -2.5+/-0.3%). Mean hydrogen enrichment factors (epsilonH) were also significantly smaller for culture grown under high iron conditions (epsilonH = -77 +/-4%) versus low iron conditions (EpsilonH = -159+/-11%). A mechanistic model for enzyme kinetics was used to relate differences in the magnitude of isotopic fractionation for low iron versus high iron cultures to the efficiency of the enzymatic transformation. The increase of carbon and hydrogen enrichment factors at low iron concentrations suggests a slower enzyme-catalyzed substrate conversion step (k2) relative to the enzyme-substrate binding step (k-l) at low iron concentration. While the observed differences were subtle and, hence, do not significantly impact the ability to use stable isotope analysis in the field, these results demonstrated that resolvable differences in carbon and hydrogen isotopic fractionation were related to low and high iron conditions. This novel result highlights the need to further investigate the effects of other trace elements known to be key components of biodegradative enzymes.

  20. Environmental isotope-aided studies on water resources in the region of Cheju(v)

    International Nuclear Information System (INIS)

    Ahn, Jong Sung; Kim, Chun Soo; Kim, Jong Hun; Yun, Si Tae; Kim, Kae Nam; Jeong, Chan Ho

    1988-12-01

    In order to provide effective remedial-measure for the groundwater contamination from sea water environmental isotope characteristics and groundwater composition were studied. The study area was selected in Pyoson and Namwon regions of the Cheju island, to ascertain whether the existing wells and springs are affected by sea water intrusion. The salt contents and electrical conductivity of groundwater sampled below 50 m altitude in these areas were 2∼30 times higher than those of groundwater above 50 m altitude and those of Cheju and Sogwipo cities. The groundwater in the coastal area has higher ratios (3.00∼97.2) of chloride / bicarbonate than those in the inland area, and it was classified as a Na-Cl type water. It is concluded that the groundwater in the coastal area is already contaminated. But it can be used for agricultural purpose because the SAR ratio is relatively low. (Author)

  1. The effectiveness of using carbonate isotope measurements of body tissues to infer diet in human evolution: Evidence from wild western chimpanzees (Pan troglodytes verus).

    Science.gov (United States)

    Fahy, Geraldine E; Boesch, Christophe; Hublin, Jean-Jacques; Richards, Michael P

    2015-11-01

    Changes in diet throughout hominin evolution have been linked with important evolutionary changes. Stable carbon isotope analysis of inorganic apatite carbonate is the main isotopic method used to reconstruct fossil hominin diets; to test its effectiveness as a paleodietary indicator we present bone and enamel carbonate carbon isotope data from a well-studied population of modern wild western chimpanzees (Pan troglodytes verus) of known sex and age from Taï, Cote d'Ivoire. We found a significant effect of age class on bone carbonate values, with adult chimpanzees being more (13)C- and (18)O-depleted compared to juveniles. Further, to investigate habitat effects, we compared our data to existing apatite data on eastern chimpanzees (P. troglodytes schweinfurthii) and found that the Taï chimpanzees are significantly more depleted in enamel δ(13)Cap and δ(18)Oap compared to their eastern counterparts. Our data are the first to present a range of tissue-specific isotope data from the same group of wild western chimpanzees and, as such, add new data to the growing number of modern non-human primate comparative isotope datasets providing valuable information for the interpretation of diet throughout hominin evolution. By comparing our data to published isotope data on fossil hominins we found that our modern chimpanzee bone and enamel data support hypotheses that the trend towards increased consumption of C4 foods after 4 Ma (millions of years ago) is unique to hominins. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. The effects of Porapak™ trap temperature on δ(18)O, δ(13)C, and Δ47 values in preparing samples for clumped isotope analysis.

    Science.gov (United States)

    Petersen, Sierra V; Winkelstern, Ian Z; Lohmann, Kyger C; Meyer, Kyle W

    2016-01-15

    The clumped isotope paleothermometer, a new proxy widely applicable in studies of paleoclimate, tectonics, and paleontology, relates the abundance of doubly substituted isotopologues of carbonate-derived CO2 to the temperature of formation of the carbonate phase. As this technique becomes more widely used, more is discovered about the effects of everyday laboratory procedures on the clumped isotopic composition of CO2 gas. Preparation of CO2 for clumped isotope analysis requires the removal of isobaric contaminants prior to measurement, achieved dynamically by passing the CO2 through a gas chromatography column using a helium carrier gas or cryogenically pumping CO2 through a static trap filled with Porapak™ Q (PPQ) material. The stable and clumped isotopic compositions of carbonate standards prepared at PPQ trap temperatures between -40°C and -10°C were measured by isotope ratio mass spectrometry to evaluate potential artifacts introduced by the static PPQ trap method. The stable isotopic composition of carbonates run at temperatures below -20°C was fractionated, despite achieving >99% retrieval of gas at temperatures as cold as -30°C. The δ(13)C and δ(18)O values decreased by ~0.01 and ~0.03 ‰/(°C below -20°C). The raw Δ47 values decreased by 0.003-0.005 ‰/(°C below -20°C), but the final reference-frame-corrected values (Δ47-RFAC ) were unaffected as long as the carbonate samples and standard gases were prepared identically. Preparing carbonate samples for clumped isotope analysis using a PPQ trap that is too cold can result in erroneous stable isotopic compositions. New and existing labs using the static PPQ trap cleaning procedure should determine the ideal PPQ trap temperature for their particular system through monitoring not only yield through the PPQ trap, but also stable isotopic composition at various PPQ trap temperatures. Copyright © 2015 John Wiley & Sons, Ltd.

  3. Ab initio calculation of the Zn isotope effect in phosphates, citrates, and malates and applications to plants and soil.

    Science.gov (United States)

    Fujii, Toshiyuki; Albarède, Francis

    2012-01-01

    Stable Zn isotopes are fractionated in roots and leaves of plants. Analyses demonstrate that the heavy Zn isotopes are enriched in the root system of plants with respect to shoots and leaves as well as the host soil, but the fractionation mechanisms remain unclear. Here we show that the origin of this isotope fractionation is due to a chemical isotope effect upon complexation by Zn malates and citrates in the aerial parts and by phosphates in the roots. We calculated the Zn isotope effect in aqueous citrates, malates, and phosphates by ab initio methods. For pHphosphates, with respect to leaves, which concentrate malates and citrates, by about one permil. It is proposed that Zn isotope fractionation represents a useful tracer of Zn availability and mobility in soils.

  4. Hydrogen isotope effect on storage behavior of U{sub 2}Ti and UZr{sub 2.3}

    Energy Technology Data Exchange (ETDEWEB)

    Jat, Ram Avtar; Sawant, S.G.; Rajan, M.B.; Dhanuskar, J.R. [Product Development Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India); Kaity, Santu [Radiometallurgy Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India); Parida, S.C., E-mail: sureshp@barc.gov.in [Product Development Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)

    2013-11-15

    U{sub 2}Ti and UZr{sub 2.3} alloys were prepared by arc melting method, vacuum annealed and characterized by XRD, SEM and EDX methods. Hydrogen isotope effect on the storage behavior of these alloys were studied by measuring the hydrogen/deuterium desorption pressure–composition–temperature (PCT) profiles in the temperature range of 573–678 K using a Sievert’s type volumetric apparatus. It was observed that, in the temperature and pressure range of investigation, all the isotherms show a single desorption plateau. The PCT data reveals that both U{sub 2}Ti and UZr{sub 2.3} alloys had normal isotope effects on hydrogen/deuterium desorption at all experimental temperatures. Thermodynamic parameters for dehydrogenation and dedeuteration reactions of the corresponding hydrides and deuterides of the above alloys were deduced from the PCT data.

  5. Strong isotope effects on melting dynamics and ice crystallisation processes in cryo vitrification solutions.

    Directory of Open Access Journals (Sweden)

    Oleg Kirichek

    Full Text Available The nucleation and growth of crystalline ice during cooling, and further crystallization processes during re-warming are considered to be key processes determining the success of low temperature storage of biological objects, as used in medical, agricultural and nature conservation applications. To avoid these problems a method, termed vitrification, is being developed to inhibit ice formation by use of high concentration of cryoprotectants and ultra-rapid cooling, but this is only successful across a limited number of biological objects and in small volume applications. This study explores physical processes of ice crystal formation in a model cryoprotective solution used previously in trials on vitrification of complex biological systems, to improve our understanding of the process and identify limiting biophysical factors. Here we present results of neutron scattering experiments which show that even if ice crystal formation has been suppressed during quench cooling, the water molecules, mobilised during warming, can crystallise as detectable ice. The crystallisation happens right after melting of the glass phase formed during quench cooling, whilst the sample is still transiting deep cryogenic temperatures. We also observe strong water isotope effects on ice crystallisation processes in the cryoprotectant mixture. In the neutron scattering experiment with a fully protiated water component, we observe ready crystallisation occurring just after the glass melting transition. On the contrary with a fully deuteriated water component, the process of crystallisation is either completely or substantially supressed. This behaviour might be explained by nuclear quantum effects in water. The strong isotope effect, observed here, may play an important role in development of new cryopreservation strategies.

  6. Study of the isotope separation of uranium by extraction method with crown ether

    International Nuclear Information System (INIS)

    Han Yande; Luo Wenzong; Gao Shuqin

    1993-01-01

    This paper presents two-phase isotope chemical exchange systems for isotope separation of uranium. The equilibrated phases consisted of an aqueous solution of a uranium salt and a 1.2-dichloroethane solution of uranium-crown ether complex. Significant uranium isotope effect can be obtained without a valence change of uranium in isotope exchanging between the aqua and crown ether complexes in these systems, and uranium-235 was concentrated in the organic phase in all cases, and the uranium isotope exchange rate with crown ether was rapid. By means of a stepwise enriching and depleting cascade process, the equilibrium single-stage separation factors α were determined in several liquid-liquid extraction systems, in which uranyl chloride is extracted by DCH18C6(Dicyclohexyl-18-Crown-6), the values α were found to be 1.0010 ± 0.0002 and 1.0012 ± 0.0004 for initial U(VI) concentrations of 5 mg u/ml and 100 mg u/ml in the aqueous phase, respectively, for an enriching cascade process. The average values of α were found to be 1.0014 ± 0.0007 for initial U(VI) concentration of 75 mg u/ml in aqueous phase for a stepwise depleting cascade process. The mean single-stage separation factors were determined as α = 1.00061 ± 0.00009 and α = 1.00066± 0.00019 for four independent cascade processes of the stepwise enriching and stepwise depleting, respectively, for the isotope chemical exchange systems in which uranyl chloride is extracted by DCH24C8 (Dicyclohexy 1-24-Crown-8). The value of separation factor was found to be α = 1.0007 ± 0.0001 in the isotope chemical exchange system in which UCI 4 is extracted by DCH18C6, for initial 0.1012 mol u/l in the aqueous phase

  7. Isotopic techniques to study phosphorus cycling in soils

    International Nuclear Information System (INIS)

    Manjaiah, K.M.; Sreenivasa Chari, M.; Sachdev, P.; Sachdev, M.S.

    2008-01-01

    A sound understanding of phosphorus cycling in soil system is essential in order to manage this system in a sustainable manner. Phosphorus transformations are characterized by physico-chemical (sorption-desorption) and biological processes . The transformation rates need to be taken into account while developing nutrient management strategies for economical and sustainable production. One of the important tools and the method gaining popularity for determining the gross transformation rates of nutrients in the soil is the isotopic dilution technique. The major processes in the soil-plant system which determine the distribution and bioavailability of phosphorus in various inorganic and organic soil components consist of: (1) the dissolution of soil mineral phosphates, (2) retention of phosphorus by inorganic soil constituents, (3) decomposition of organic phosphorus contained in plant, animal and microbial detritus and (4) Immobilization of phosphorus via the soil microbial biomass and plan uptake

  8. Calculation of isotope selective excitation of uranium isotopes using spectral simulation method

    International Nuclear Information System (INIS)

    Al-Hassanieh, O.

    2009-06-01

    Isotope ratio enhancement factor and isotope selectivity of 235 U in five excitation schemes (I: 0→10069 cm - 1 →IP, II: 0 →10081 cm - 1 →IP, III: 0 →25349 cm - 1→ IP, IV: 0→28650 cm - 1 →IP, V: 0→16900 cm - 1 →34659 cm - 1 →IP), were computed by a spectral simulation approach. The effect of laser bandwidth and Doppler width on the isotope ratio enhancement factor and isotope selectivity of 235 U has been studied. The photoionization scheme V gives the highest isotope ratio enhancement factor. The main factors which effect the separation possibility are the isotope shift and the relative intensity of the transitions between hyperfine levels. The isotope ratio enhancement factor decreases exponentially by increasing the Doppler width and the laser bandwidth, where the effect of Doppler width is much greater than the effect of the laser bandwidth. (author)

  9. Deuterium isotope effects on drug pharmacokinetics. I. System-dependent effects of specific deuteration with aldehyde oxidase cleared drugs.

    Science.gov (United States)

    Sharma, Raman; Strelevitz, Timothy J; Gao, Hongying; Clark, Alan J; Schildknegt, Klaas; Obach, R Scott; Ripp, Sharon L; Spracklin, Douglas K; Tremaine, Larry M; Vaz, Alfin D N

    2012-03-01

    The pharmacokinetic properties of drugs may be altered by kinetic deuterium isotope effects. With specifically deuterated model substrates and drugs metabolized by aldehyde oxidase, we demonstrate how knowledge of the enzyme's reaction mechanism, species differences in the role played by other enzymes in a drug's metabolic clearance, and differences in systemic clearance mechanisms are critically important for the pharmacokinetic application of deuterium isotope effects. Ex vivo methods to project the in vivo outcome using deuterated carbazeran and zoniporide with hepatic systems demonstrate the importance of establishing the extent to which other metabolic enzymes contribute to the metabolic clearance mechanism. Differences in pharmacokinetic outcomes in guinea pig and rat, with the same metabolic clearance mechanism, show how species differences in the systemic clearance mechanism can affect the in vivo outcome. Overall, to gain from the application of deuteration as a strategy to alter drug pharmacokinetics, these studies demonstrate the importance of understanding the systemic clearance mechanism and knowing the identity of the metabolic enzymes involved, the extent to which they contribute to metabolic clearance, and the extent to which metabolism contributes to the systemic clearance.

  10. Coordinated Oxygen Isotopic and Petrologic Studies of CAIS Record Varying Composition of Protosolar

    Science.gov (United States)

    Simon, Justin I.; Matzel, J. E. P.; Simon, S. B.; Weber, P. K.; Grossman, L.; Ross, D. K.; Hutcheon, I. D.

    2012-01-01

    Ca-, Al-rich inclusions (CAIs) record the O-isotope composition of Solar nebular gas from which they grew [1]. High spatial resolution O-isotope measurements afforded by ion microprobe analysis across the rims and margin of CAIs reveal systematic variations in (Delta)O-17 and suggest formation from a diversity of nebular environments [2-4]. This heterogeneity has been explained by isotopic mixing between the O-16-rich Solar reservoir [6] and a second O-16-poor reservoir (probably nebular gas) with a "planetary-like" isotopic composition [e.g., 1, 6-7], but the mechanism and location(s) where these events occur within the protoplanetary disk remain uncertain. The orientation of large and systematic variations in (Delta)O-17 reported by [3] for a compact Type A CAI from the Efremovka reduced CV3 chondrite differs dramatically from reports by [4] of a similar CAI, A37 from the Allende oxidized CV3 chondrite. Both studies conclude that CAIs were exposed to distinct, nebular O-isotope reservoirs, implying the transfer of CAIs among different settings within the protoplanetary disk [4]. To test this hypothesis further and the extent of intra-CAI O-isotopic variation, a pristine compact Type A CAI, Ef-1 from Efremovka, and a Type B2 CAI, TS4 from Allende were studied. Our new results are equally intriguing because, collectively, O-isotopic zoning patterns in the CAIs indicate a progressive and cyclic record. The results imply that CAIs were commonly exposed to multiple environments of distinct gas during their formation. Numerical models help constrain conditions and duration of these events.

  11. The effects of biomanipulation on the biogeochemistry, carbon isotopic composition and pelagic food web relations of a shallow lake

    Directory of Open Access Journals (Sweden)

    B. M. Bontes

    2006-01-01

    Full Text Available In this study we investigated the effects of experimental biomanipulation on community structure, ecosystem metabolism, carbon biogeochemistry and stable isotope composition of a shallow eutrophic lake in the Netherlands. Three different biomanipulation treatments were applied. In two parts of the lake, isolated from the rest, fish was removed and one part was used as a reference treatment in which no biomanipulation was applied. Stable isotopes have proved useful to trace trophic interactions at higher food web levels but until now methodological limitations have restricted species specific isotope analysis in the plankton community. We applied a new approach based on the combination of fluorescence activated cell sorting (FACS and isotope ratio mass spectrometry (IRMS to trace carbon flow through the planktonic food web. With this method we aimed at obtaining group specific δ13C signatures of phytoplankton and to trace possible shifts in δ13C resulting from fish removal. Biomanipulation led to an increase in transparency and macrophyte biomass and decrease in phytoplankton abundance, but zooplankton numbers did not increase. Fish removal also resulted in high pH, high O2, low CO2 and more negative δ13CDIC values than expected, which is attributed to chemical enhanced diffusion with large negative fractionation. Despite high temporal variation we detected differences between the isotopic signatures of the primary producers and between the different treatments. The fractionation values of green algae (~21 and diatoms (~23 were similar and independent of treatment, while fractionation factors of filamentous cyanobacteria were variable between the treatments that differed in CO2 availability. 13C-labeling of the phytoplankton groups showed that biomanipulation led to increased growth rates of green algae and diatoms at the expense of cyanobacteria. Finally, consumers seemed generalists to the available food sources.

  12. Groundwater recharge studies using isotope-chemical techniques in wadi gharandal, sinai peninsula(E G))

    International Nuclear Information System (INIS)

    Awad, M.A.A.; Salem, W.M.; Ezzeldin

    1999-01-01

    Wadi Gharandal lies on southwestern part of sinai peninsula with its outlets into the Gulf of suez. Eight groundwater samples were collected from quaternary aquifer in wadi gharandal to identify the sources of replenishment and evaluation of its water quality. The variation in chemical composition of water samples is due to water-rock interaction and the effect of sea spray. The distribution of chemical species in the examined groundwater samples is controlled by geography and climate conditions prevailing in the area of study. The salinity increase towards the gulf of suez. The isotopic data indicate that precipitation and floods are considered to be the main sources of recharge in this area. The investigated groundwater samples are found to be suitable for irrigation purposes based on sodium adsorption ratio (SAR) and unsuitable for domestic usages due to high salinity and hardness values

  13. Geochemical monitoring using noble gases and carbon isotopes: study of a natural reservoir

    International Nuclear Information System (INIS)

    Jeandel, E.

    2008-12-01

    To limit emissions of greenhouse gases in the atmosphere, CO 2 geological sequestration appears as a solution in the fight against climate change. The development of reliable monitoring tools to ensure the sustainability and the safety of geological storage is a prerequisite for the implementation of such sites. In this framework, a geochemical method using noble gas and carbon isotopes geochemistry has been tested on natural and industrial analogues. The study of natural analogues from different geological settings showed systematic behaviours of the geochemical parameters, depending on the containment sites, and proving the effectiveness of these tools in terms of leak detection and as tracers of the behaviour of CO 2 . Moreover, an experience of geochemical tracing on a natural gas storage has demonstrated that it is possible to identify the physical-chemical processes taking place in the reservoir to a human time scale, increasing interest in the proposed tool and providing general information on its use. (author)

  14. Note on isotopic effects in range calculations of high-energy ion beams

    International Nuclear Information System (INIS)

    Dominguez-Vazquez, Javier; Perez-Martin, A.M.C.; Jimenez-Rodriguez, J.J.; Konoplev, Vladimir; Gras-Marti, Albert; Castella-Mayor, Javier

    1995-01-01

    A simple analytical model that allows the calculation of the percent-level differences of the average ranges of isotopic ion beams slowing down in solid targets is extended to energies in the MeV region and to investigate isotopic effects due to small variations in the mass of the target species. The various contributions to the range in terms of ion stopping, both nuclear and electronic, and angular scattering, can be investigated separately. The model agrees with available experimental data, and predictions are made for a range of cases of interest. (orig.)

  15. An experimental investigation of the isotope effect in the CVD growth of diamonds

    International Nuclear Information System (INIS)

    Vakil, H.B.; Banholzer, W.F.; Kehl, R.J.; Spiro, C.L.

    1989-01-01

    An experimental investigation of the effect of isotopic substitution of hydrogen by deuterium was carried out for the chemical vapor deposition (CVD) of diamond films to determine whether the rate determining step involves a C-H or a C-C bond. Results show that if such a comparison is carried out in a proper manner the growth rate with deuterium is slower by the expected isotopic factor of the square root of 2, indicating that most likely a C-H bond is involved in the rate limiting step. Additionally, it is found that the kinetics of the atomic species generation were equally affected by the isotopic switch, strongly suggesting that the rate limiting step for that process involves the metal-H bond

  16. Dual Isotope SPECT Study With Epilepsy Patients Using Semiconductor SPECT System.

    Science.gov (United States)

    Shiga, Tohru; Suzuki, Atsuro; Sakurai, Kotarou; Kurita, Tsugiko; Takeuchi, Wataru; Toyonaga, Takuya; Hirata, Kenji; Kobashi, Keiji; Katoh, Chietsugu; Kubo, Naoki; Tamaki, Nagara

    2017-09-01

    We developed a prototype CdTe SPECT system with 4-pixel matched collimator for brain study. This system provides high-energy-resolution (6.6%), high-sensitivity (220 cps/MBq/head), and high-spatial-resolution images. The aim of this study was to evaluate dual-isotope study of CBF and central benzodiazepine receptor (BZR) images using Tc-ECD and I-IMZ with the new SPECT system in patients with epilepsy comparing with single-isotope study using the conventional scintillation gamma camera. This study included 13 patients with partial epilepsy. The BZR images were acquired at 3 hours after I-IMZ injection for 20 minutes. The images of IMZ were acquired with a conventional 3-head scintillation gamma camera. After BZR image acquisition with the conventional camera, Tc-ECD was injected, and CBF and BZR images were acquired simultaneously 5 minutes after ECD injection with the new SPECT system. The CBF images were also acquired with the conventional camera on separate days. The findings were visually analyzed, and 3D-SSP maximum Z scores of lesions were compared between the 2 studies. There were 47 abnormal lesions on BZR images and 60 abnormal lesions on CBF images in the single-isotope study with the conventional camera. Dual-isotope study with the new system showed concordant abnormal findings of 46 of 47 lesions on BZR and 54 of 60 lesions on CBF images with the single-isotope study with the conventional camera. There was high agreement between the 2 studies in both BZR and CBF findings (Cohen κ values = 0.96 for BZR and 0.78 for CBF). In semiquantitative analysis, maximum Z scores of dual-isotope study with the new system strongly correlated with those of single-isotope study with the conventional camera (BZR: r = 0.82, P isotope study for pixel-by-pixel analysis of CBF and BZR information with the same pathophysiological condition in patients with epilepsy.

  17. Studies of rotational structures in the neutron-rich niobium isotopes 101-103

    International Nuclear Information System (INIS)

    Paffrath, U.

    1989-08-01

    The aim of this thesis was to study rotational structures in the low-lying levels of the niobium isotopes 101, 102, and 103. This was performed at the recoil separator JOSEF of the Nuclear Research Facility Juelich by studies of the β-decays of the zirconium isotopes 101-103 into their niobium daughters. By γ-γ respectively X-γ coincidence measurements the already existing term schemes of the niobium isotopes should be verified respectively extended and by γ-γ angular-correlation measurements the rotational structures should be studied. The term schemes of the niobium isotopes 101 and 102 could be confirmed in the framework of the performed experiments while the level scheme of the 103 Nb could be essentially extended. From the X-γ coincidence measurement for a plurality of γ transitions the conversion coefficients and by this the dominant multipolarities could be determined. With these conversion coefficients then also the mixing parameters were calculated. These data together with the results from the γ-γ angular-correlation experiments led to a fixing concerning the spins and parities at a series of levels in all three niobium isotopes. (orig./HSI) [de

  18. Iron absorption studies from Philippine meals using isotope techniques. 1. Double isotope extrinsic tag method

    International Nuclear Information System (INIS)

    Marzan, A.M.; Morck, T.A.; Cook, J.D.

    1980-01-01

    Two different complete test meals extrinsically tagged with Fe-55 and Fe-59 together with a reference dose of iron were administered to 17 normal American volunteers. Serial iron absorption was determined from the whole blood levels of individual subjects as well as to the nutrient composition of the test meal. The results of the study indicate the presence of an optimum proportion of nutrients favouring high iron absorption. (author)

  19. Isotopic evidence of the effects of herbivory and landscape position on plant nitrogen sources in a riparian ecosystem.

    Science.gov (United States)

    Menezes, Rômulo S C

    2009-03-01

    This study used (15)N natural abundance techniques to investigate whether elk herbivory affects the capability of willow (Salix spp.) and reed-grass (Carex spp.) to access N from groundwater in upper and lower landscape positions within riparian areas of the Rocky Mountain National Park. For this, delta(15)N values of plant, soil, rainfall and groundwater samples were measured within a replicated field experiment. Despite the relatively high variability in the (15)N data, it provided evidence of the effects of grazing and lanscape position on plant N sources. Carex seemed to acquire less groundwater N in upper landscape positions compared to Salix, maybe due to the deeper willow rooting system. However, grazed willows in upper landscape positions seemed to acquire less groundwater N as compared to willows protected from herbivory. These findings were in accordance with other isotopic and non-isotopic studies conducted in the same experimental site.

  20. Isotopes in environmental studies - Aquatic Forum 2004. Proceedings of an international conference. Unedited papers

    International Nuclear Information System (INIS)

    2006-01-01

    A better understanding of key processes in the aquatic environment, responsible for its future development and its protection, were at the forefront of the IAEA's International Conference on Isotopes in Environmental Studies - AQUATIC FORUM 2004 convened in Monaco from 25 to 29 October 2004, which was the most important gathering of the year of isotope environmental scientists. Over 320 experts from 60 IAEA Member States and 6 international organizations delivered 185 oral presentations in 6 plenary and 31 parallel sessions and made 130 poster presentations. The conference reviewed the present state of the art isotopic methods for investigation of the aquatic environment. The main conference subjects considered were: (i) behaviour, transport and distribution of isotopes in the aquatic environment; (ii) climate change studies using isotopic records in the marine environment; (iii) groundwater dynamics, modelling and management of freshwater sources; (iv) important global projects, such as WOCE, WOMARS, SHOTS, GEOTRACES; (v) joint IAEA-UNESCO submarine groundwater investigations in the Mediterranean Sea, the Southwest Atlantic and Pacific Oceans; (vi) new trends in radioecological investigations, concentrating on the protection of marine biota against radioactive contamination; (vii) transfers in analytical technologies from bulk analyses to particle and compound specific analyses of environmental samples; (viii) development of new isotopic techniques, such as AMS and ICPMS, and their successful applications in environmental studies; and many other exciting topics which were presented and discussed during the Conference. Four workshops were held simultaneously: - ATOMS-Med Workshop - development of a project proposal for oceanographic investigations in the Eastern Mediterranean. - El Nino - Research Co-ordination Meeting of the new IAEA Coordinated Research Project investigating climate change using isotopic records in the marine environment. - CELLAR Workshop