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Sample records for isotopic equilibrium method

  1. Technical Note: A simple method for vaterite precipitation in isotopic equilibrium: implications for bulk and clumped isotope analysis

    NASA Astrophysics Data System (ADS)

    Kluge, T.; John, C. M.

    2014-12-01

    Calcium carbonate (CaCO3) plays an important role in the natural environment as a major constituent of the skeleton and supporting structure of marine life and has high economic importance as additive in food, chemicals and medical products. Pure CaCO3 occurs in the three different polymorphs calcite, aragonite and vaterite, whereof calcite is the most abundant and best characterized mineral. In contrast, little is known about the rare polymorph vaterite, in particular with regard to the oxygen isotope fractionation between H2O and the mineral. Synthetic precipitation of vaterite in the laboratory typically involves rapid processes and isotopic non-equilibrium, which excludes isotope studies focused on characterization of vaterite at equilibrium conditions. Here, we used a new experimental approach that enables vaterite mineral formation from an isotopically equilibrated solution. The solution consists of a ~ 0.007 mol L-1 CaCO3 solution that is saturated with NaCl at room temperature (up to 6.5 mol L-1). Vaterite precipitated as single phase or major phase (≥ 94%) in experiments performed between 23 and 91 °C. Only at 80 °C was vaterite a minor phase with a relative abundance of 27%. The high mineral yield of up to 235 mg relative to a total dissolved CaCO3 amount of 370 mg enables an investigation of the oxygen isotope fractionation between mineral and water, and the determination of clumped isotope values in vaterite.

  2. Calculation of individual isotope equilibrium constants for geochemical reactions

    USGS Publications Warehouse

    Thorstenson, D.C.; Parkhurst, D.L.

    2004-01-01

    factors. The derivations can be extended to calculation of individual isotope equilibrium constants for ion pairs and equilibrium constants for isotopic species of other chemical elements. The individual isotope approach calculates the same phase isotopic compositions as existing methods, but also provides concentrations of individual species, which are needed in calculations of mass-dependent effects in transport processes. The equilibrium constants derived in this paper are used to calculate the example of gas-water equilibrium for CO2 in an acidic aqueous solution. ?? 2004 Elsevier Ltd.

  3. Calculation of individual isotope equilibrium constants for implementation in geochemical models

    USGS Publications Warehouse

    Thorstenson, Donald C.; Parkhurst, David L.

    2002-01-01

    Theory is derived from the work of Urey to calculate equilibrium constants commonly used in geochemical equilibrium and reaction-transport models for reactions of individual isotopic species. Urey showed that equilibrium constants of isotope exchange reactions for molecules that contain two or more atoms of the same element in equivalent positions are related to isotope fractionation factors by , where is n the number of atoms exchanged. This relation is extended to include species containing multiple isotopes, for example and , and to include the effects of nonideality. The equilibrium constants of the isotope exchange reactions provide a basis for calculating the individual isotope equilibrium constants for the geochemical modeling reactions. The temperature dependence of the individual isotope equilibrium constants can be calculated from the temperature dependence of the fractionation factors. Equilibrium constants are calculated for all species that can be formed from and selected species containing , in the molecules and the ion pairs with where the subscripts g, aq, l, and s refer to gas, aqueous, liquid, and solid, respectively. These equilibrium constants are used in the geochemical model PHREEQC to produce an equilibrium and reaction-transport model that includes these isotopic species. Methods are presented for calculation of the individual isotope equilibrium constants for the asymmetric bicarbonate ion. An example calculates the equilibrium of multiple isotopes among multiple species and phases.

  4. Theoretical prediction for several important equilibrium Ge isotope fractionation factors

    NASA Astrophysics Data System (ADS)

    Tang, M.; Li, X.; Liu, Y.

    2008-12-01

    As a newly emerging field, the stable isotope geochemistry of germanium (Ge) needs basic equilibrium fractionation factors to explore its unknown world. In this study, the Ge isotope fractionations between systems including the aqueous Ge(OH)4 and GeO(OH)3- which are the dominant Ge species in seawater, the Ge-bearing organic complexes (e.g. Ge-catechol, Ge-oxalic acid and Ge-citric acid), the quartz- (or opal- ), albite-, K-feldspar- and olivine- like mineral structures are studied. It is the first time that some geologically important equilibrium Ge isotope fractionation factors are reported. Surprisingly, up to 5 per mil large isotopic fractionations between these Ge isotope systems are found at 25 degree. These results suggest a potentially broad application for the Ge isotope geochemistry. Our theoretical calculations are based on the Urey model (or Bigeleisen-Mayer equation) and high level quantum chemistry calculations. The B3LYP/6-311+G(d,p) level quantum chemistry method and the explicit solvent model ("water droplet" method) are used. Many different conformers are also used for the aqueous complexes in order to reduce the possible errors coming from the differences of configurations in solution. The accuracy of our calculation of the Ge isotopic fractionations is estimated about 0.2 per mil. Our results show quartz-like or opal-like structure can enrich most heavy Ge isotopes. Relative to quartz (or opal), some Ge isotopic fractionations are (at 25 C): quartz-organic Ge = 4-5,quartz-Ge(OH)4 =0.9,quartz-GeO(OH)3- =1.5,quartz-albite=0.6,quartz-K-feldspar=0.4 and quartz-olivine=3.9 per mil. The large fractionations between inorganic Ge complexes and organic Ge ones could be used to distinguish the possible bio-involving processes. Our results suggest a good explanation to the experimental observations of Siebert et al. (2006) and Rouxel et al. (2006) and provide important constraints to the study of Ge cycle in ocean.

  5. Unbiased isotope equilibrium factors from partial isotope exchange experiments in 3-exchange site systems

    NASA Astrophysics Data System (ADS)

    Agrinier, Pierre; Javoy, Marc

    2016-09-01

    Two methods are available in order to evaluate the equilibrium isotope fractionation factors between exchange sites or phases from partial isotope exchange experiments. The first one developed by Northrop and Clayton (1966) is designed for isotope exchanges between two exchange sites (hereafter, the N&C method), the second one from Zheng et al. (1994) is a refinement of the first one to account for a third isotope exchanging site (hereafter, the Z method). In this paper, we use a simple model of isotope kinetic exchange for a 3-exchange site system (such as hydroxysilicates where oxygen occurs as OH and non-OH groups like in muscovite, chlorite, serpentine, or water or calcite) to explore the behavior of the N&C and Z methods. We show that these two methods lead to significant biases that cannot be detected with the usual graphical tests proposed by the authors. Our model shows that biases originate because isotopes are fractionated between all these exchanging sites. Actually, we point out that the variable mobility (or exchangeability) of isotopes in and between the exchange sites only controls the amplitude of the bias, but is not essential to the production of this bias as previously suggested. Setting a priori two of the three exchange sites at isotopic equilibrium remove the bias and thus is required for future partial exchange experiments to produce accurate and unbiased extrapolated equilibrium fractionation factors. Our modeling applied to published partial oxygen isotope exchange experiments for 3-exchange site systems (the muscovite-calcite (Chacko et al., 1996), the chlorite-water (Cole and Ripley, 1998) and the serpentine-water (Saccocia et al., 2009)) shows that the extrapolated equilibrium fractionation factors (reported as 1000 ln(α)) using either the N&C or the Z methods lead to bias that may reach several δ per mil in a few cases. These problematic cases, may be because experiments were conducted at low temperature and did not reach high

  6. ISOTOPE METHODS IN HOMOGENEOUS CATALYSIS.

    SciTech Connect

    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.

  7. Nuclear Volume Effects in Equilibrium Stable Isotope Fractionations of Hg, Tl and Pb Isotope Systems

    NASA Astrophysics Data System (ADS)

    Yang, S.; Liu, Y.

    2014-12-01

    Many evidences showed that heavy isotope systems could be significantly fractionated as the consequence of the nuclear volume effect (NVE) or so-called nuclear field shift effect. Here we investigate NVEs of Hg, Tl and Pb isotope systems by using quantum chemistry computational methods with careful evaluation on quantum relativistic effects via the Dirac's formalism of full-electron wavefunction. Our results generally agree with previous studies but with noticeable differences in many cases. With the unique NVE driving force, equilibrium 202Hg/198Hg and 205Tl/203Tl isotopes can be fractionated up to 3.94‰ and 2.78‰ at 0℃, respectively, showing potentially large equilibrium isotope fractionations can be expected for future studies of these two isotope systems. Moreover, the NVE causes large mass-independent fractionations (MIF) for odd-mass isotopes (e.g., ∆199NVHg and ∆201NVHg) and small MIFs for even-mass isotopes (e.g., ∆200NVHg). For Pb isotope system, NVEs induce isotope fractionations up to 1.62‰ (207Pb/206Pb) and 4.06‰ (208Pb/206Pb) at 0℃. However, contributions from classical mass-dependent driving force are small, about 0.1-0.5‰ for 207Pb/206Pb and 0.2-0.9‰ for 208Pb/206Pb. We find that Pb4+-bearing species can be significantly enriched heavy isotopes than Pb2+-bearing species. Comparing to Pb0, Pb2+-bearing species even enrich lighter Pb isotopes. A very strange and interesting thing is that the beta value of Pb2+-bearing species can be smaller than the unity (1.000). Similar thing has been found on Tl+-bearing species. This is an impossible and unexplained situation if only based on classical mass-dependent isotope fractionation theory (e.g., Bigeleisen-Mayer equation). The consequence is that the different direction of beta values of Pb2+-bearing species will let the Pb isotope fractionation even larger when they fractionate with Pb4+-bearing species. Moreover, NVEs also cause mass-independent fractionation (MIF) of odd 207Pb

  8. Devils Hole paleotemperatures and implications for oxygen isotope equilibrium fractionation

    NASA Astrophysics Data System (ADS)

    Kluge, Tobias; Affek, Hagit P.; Dublyansky, Yuri; Spötl, Christoph

    2014-08-01

    Subaqueous calcite in Devils Hole, Nevada, was growing continuously from slightly super-saturated groundwater, providing a 570 kyr-long δO18 paleoclimate record. Due to its very slow growth it has been assumed to have grown under conditions of isotopic equilibrium. However, its Holocene δO18 value is 1.5‰ higher than predicted by laboratory-precipitation-based oxygen isotope thermometer calibrations. The suggestion that Devils Hole calcite anchors the isotope thermometer to more 18O-enriched values has stirred a debate as to which paleothermometer calibration is relevant for paleoclimate and casts doubt on the validity of δO18-based paleotemperatures. We used clumped isotopes to test the assumptions of the Devils Hole alternative 18O-thermometer. Carbonate clumped isotopes are a temperature proxy that measures the abundance of 13Csbnd 18O bonds in CaCO3. This proxy is independent of the water composition and therefore gives independent estimates of temperatures when calcite forms at thermodynamic and isotopic equilibrium. We find that Devils Hole water paleotemperatures were constant at 30.6±2.6 °C between 27 and 180 ka, similarly to the modern groundwater temperature of 32.8-34.3 °C. The proximity of the Devils Hole clumped isotope data to values expected based on modern groundwater temperatures supports the notion that Devils Hole calcite grew under equilibrium conditions. Therefore, the commonly used laboratory-based δO18-temperature calibrations should be reconsidered. The constant water temperature over the glacial-interglacial cycles indicates that the long Devils Hole δO18 record reflects only variations in the groundwater δO18 values and as such, represents a valuable archive of paleoclimate and isotope paleohydrology.

  9. First Principles Calculation on Equilibrium Si Isotope Fractionation Factors and its Implementation on Si Isotope Distributions in Earth Surface Environments

    NASA Astrophysics Data System (ADS)

    Liu, Y.; He, H. T.; Zhu, C.

    2014-12-01

    Several important equilibrium Si isotope fractionation factors are calculated here. We use a so-called volume-variable-cluster-model (VVCM) method for solids and the "water-droplet" method for aqueous species for isotope fractionation calculation at the same quantum chemistry level. The calculation results show that several silicate minerals, such as quartz, feldspar, kaolinite, etc., all enrich heavy Si isotopes relative to aqueous H4SiO4 and can be up to 3.3‰ at 25°C, different from most field observations. Meanwhile stable organosilicon complexes can enrich even lighter Si isotopes than aqueous H4SiO4. For explaining the difference between the calculation results and field observations, we calculate the kinetic isotope effect (KIE) associated with the formation of amorphous silica, and find that amorphous silica will enrich extremely light Si isotopes. From amorphous silica to crystalline quartz, the structural adjustment & transition needs getting rid of small amount of Si to re-organize the structure. Light Si isotopes will be preferentially lost and let the final crystalline quartz with a little bit more heavy Si isotopes. However, such late-stage Si heavy isotope enrichment cannot erase the total isotopic signal, crystalline quartz still inherit much light Si isotopic composition from amorphous quartz. That is the reason for the discrepancy between the calculation results and the field observations, because the formation of amorphous quartz is under a non-equilibrium process but theoretical calculations are for equilibrium isotope fractionations. With accurate equilibrium fractionation factors provided here, Si isotope distributions in earth surface environments including soil, groundwater and plants can be further interpreted. We find that δ30Si variations in soil are mainly driven by secondary minerals precipitation and adsorption. Also, bulk soil δ30Si maybe have a parabolic distribution with soil age, with a minimum value at where allophane is

  10. The oxygen isotope equilibrium fractionation between sulfite species and water

    NASA Astrophysics Data System (ADS)

    Müller, Inigo A.; Brunner, Benjamin; Breuer, Christian; Coleman, Max; Bach, Wolfgang

    2013-11-01

    Sulfite is an important sulfoxy intermediate in oxidative and reductive sulfur cycling in the marine and terrestrial environment. Different aqueous sulfite species exist, such as dissolved sulfur dioxide (SO2), bisulfite (HSO3-), pyrosulfite (S2O52-) and sulfite sensu stricto (SO32-), whereas their relative abundance in solution depends on the concentration and the pH. Conversion of one species into another is rapid and involves in many cases incorporation of oxygen from, or release of oxygen to, water (e.g. SO2 + H2O ↔ HSO3- + H+), resulting in rapid oxygen isotope exchange between sulfite species and water. Consequently, the oxygen isotope composition of sulfite is strongly influenced by the oxygen isotope composition of water. Since sulfate does not exchange oxygen isotopes with water under most earth surface conditions, it can preserve the sulfite oxygen isotope signature that it inherits via oxidative and reductive sulfur cycling. Therefore, interpretation of δO values strongly hinges on the oxygen isotope equilibrium fractionation between sulfite and water which is poorly constrained. This is in large part due to technical difficulties in extraction of sulfite from solution for oxygen isotope analysis.

  11. Predicting equilibrium uranium isotope fractionation in crystals and solution

    NASA Astrophysics Data System (ADS)

    Schauble, E. A.

    2015-12-01

    Despite the rapidly growing interest in using 238U/235U measurements as a proxy for changes in oxygen abundance in surface and near-surface environments, the present theoretical understanding of uranium isotope fractionation is limited to a few simple gas-phase molecules and analogues of dissolved species (e.g., 1,2,3). Understanding uranium isotope fractionation behavior in more complicated species, such as crystals and adsorption complexes, will help in the design and interpretation of experiments and field studies, and may suggest other uses for 38U/235U measurements. In this study, a recently developed first-principles method for estimating the nuclear volume component of field shift fractionation in crystals and complex molecular species (4) is combined with mass-dependent fractionation theory to predict equilibrium 38U/235U fractionations in aqueous and crystalline uranium compounds, including uraninite (UO2). The nuclear field shift effect, caused by the interaction of electrons with the finite volume of the positive charge distribution in uranium nuclei, is estimated using Density Functional Theory and the Projector Augmented Wave method (DFT-PAW). Tests against relativistic electronic structure calculations and Mössbauer isomer shift data indicate that the DFT-PAW method is reasonably accurate, while being much better suited to models of complex and crystalline species. Initial results confirm previous predictions that the nuclear volume effect overwhelms mass depdendent fractionation in U(VI)-U(IV) exchange reactions, leading to higher 238U/235U in U(IV) species (i.e., for UO2 xtal vs. UO22+aq, ln αNV ≈ +1.8‰ , ln αMD ≈ -0.8‰, ln αTotal ≈ +1.0‰ at 25ºC). UO2 and U(H2O)94+, are within ~0.4‰ of each other, while U(VI) species appear to be more variable. This suggests that speciation is likely to significantly affect natural uranium isotope fractionations, in addition to oxidation state. Tentatively, it appears that uranyl-type (UO22

  12. On the equilibrium isotopic composition of the thorium-uranium-plutonium fuel cycle

    NASA Astrophysics Data System (ADS)

    Marshalkin, V. Ye.; Povyshev, V. M.

    2016-12-01

    The equilibrium isotopic compositions and the times to equilibrium in the process of thorium-uranium-plutonium oxide fuel recycling in VVER-type reactors using heavy water mixed with light water are estimated. It is demonstrated thEhfat such reactors have a capacity to operate with self-reproduction of active isotopes in the equilibrium mode.

  13. Quantum-mechanical equilibrium isotopic fractionation correction to radiocarbon dating: a theory study.

    PubMed

    Yuan, Jie; Liu, Yun

    This paper relates the quantum-mechanical equilibrium isotopic fractionation correction to the radiocarbon dating method by Eq. 9, and also shows the significant influence of temperature on the method. It is suggested that the correction is a function of the frequencies and temperature of a specific sample and these two variables can be evaluated theoretically by the ab initio quantum calculations and experimentally by analyzing the clumped-isotope ratios in it, respectively. This paper also suggests that the (14)C/(12)C ratio in the atmosphere in geological time can be calculated by Eq. 10.

  14. Equilibrium clumped-isotope effects in doubly substituted isotopologues of ethane

    NASA Astrophysics Data System (ADS)

    Webb, Michael A.; Wang, Yimin; Braams, Bastiaan J.; Bowman, Joel M.; Miller, Thomas F.

    2017-01-01

    We combine path-integral Monte Carlo methods with a new intramolecular potential energy surface to quantify the equilibrium enrichment of doubly substituted ethane isotopologues due to clumped-isotope effects. Ethane represents the simplest molecule to simultaneously exhibit 13C-13C, 13C-D, and D-D clumped-isotope effects, and the analysis of corresponding signatures may provide useful geochemical and biogeochemical proxies of formation temperatures or reaction pathways. Utilizing path-integral statistical mechanics, we predict equilibrium fractionation factors that fully incorporate nuclear quantum effects, such as anharmonicity and rotational-vibrational coupling which are typically neglected by the widely used Urey model. The magnitude of the calculated fractionation factors for the doubly substituted ethane isotopologues indicates that isotopic clumping can be observed if rare-isotope substitutions are separated by up to three chemical bonds, but the diminishing strength of these effects suggests that enrichment at further separations will be negligible. The Urey model systematically underestimates enrichment due to 13C-D and D-D clumped-isotope effects in ethane, leading to small relative errors in the apparent equilibrium temperature, ranging from 5 K at 273.15 K to 30 K at 873.15 K. We additionally note that the rotameric dependence of isotopologue enrichment must be carefully considered when using the Urey model, whereas the path-integral calculations automatically account for such effects due to configurational sampling. These findings are of direct relevance to future clumped-isotope studies of ethane, as well as studies of 13C-13C, 13C-D, and D-D clumped-isotope effects in other hydrocarbons.

  15. Method for separating isotopes

    DOEpatents

    Jepson, B.E.

    1975-10-21

    Isotopes are separated by contacting a feed solution containing the isotopes with a cyclic polyether wherein a complex of one isotope is formed with the cyclic polyether, the cyclic polyether complex is extracted from the feed solution, and the isotope is thereafter separated from the cyclic polyether.

  16. Equilibrium Strontium Isotope Fractionation in Minerals and Solution

    NASA Astrophysics Data System (ADS)

    Schauble, E. A.; Griffith, E. M.

    2011-12-01

    Recent interest in stable strontium isotope fractionation highlights our lack of understanding of the processes separating the isotopes of heavy elements in nature. Here we present thermodynamic calculations of equilibrium strontium isotope (88Sr/86Sr) fractionation in minerals and aqueous solution (by analogy to crystalline strontium hydrates). Strontium is among the ten most abundant dissolved ions seawater, and is unique in this group because it encompasses an extensively studied, long-lived radiogenic tracer (87Sr/86Sr) as well as three stable isotopes. Strontium is also widely distributed as a trace element in sedimentary minerals (especially carbonates and sulfates) and more broadly as a substituent for the major elements calcium, sodium and/or potassium in high-temperature igneous and metamorphic assemblages. However, we are aware of only a few theoretical or experimental studies of fractionation of strontium isotopes in crystals or solution (1). An important goal of our work is to provide a baseline for determining whether equilibrium isotope partitioning is important for generating observed signatures, which can be particularly difficult to establish experimentally in solid materials at ambient temperatures. Mass dependent fractionations are estimated for stoichiometric strontium-bearing crystals, including strontianite (SrCO3), celestine (SrSO4), strontia (SrO), and strontiofluorite (SrF2), as well as crystals with hydrated Sr2+-ions (e.g., SrCl2.6H2O, which contains a [Sr(H2O)9]2+ substructure) and strontium-substituted barite (Sr:BaSO4). Calculations are based on density functional perturbation theory models of the vibrational (phonon) densities of states of 86Sr- and 88Sr-substituted crystals. Most of the models of celestine indicate instability in the known orthorhombic structure - possibly because of shortcomings in pseudopotentials or density functionals. The models predict that fractionations between crystals tend to be small; strontia

  17. Spinel-olivine-pryoxene equilibrium iron isotopic fractionation and applications to natural peridotites

    SciTech Connect

    Roskosz, Mathieu; Sio, Corliss K. I.; Dauphas, Nicolas; Bi, Wenli; Tissot, Francois L. H.; Hu, Michael Y.; Zhao, Jiyong; Alp, Esen E.

    2015-11-15

    Eight spinel-group minerals were synthesized by a flux-growth method producing spinels with varying composition and Fe3+/Fe-tot ratios. The mean force constants of iron bonds in these minerals were determined by synchrotron nuclear resonant inelastic X-ray scattering (NRIXS) in order to determine the reduced isotopic partition function ratios (beta-factors) of these spinels. The mean force constants are strongly dependent on the Fe3+/Fe-tot of the spinel but are independent, or weakly dependent on other structural and compositional parameters. From our spectroscopic data, it is found that a single redox-dependent calibration line accounts for the effects of Fe3+/Fe-tot on the beta-factors of spinels. This calibration successfully describes the equilibrium Fe isotopes fractionation factors between spinels and silicates (olivine and pyroxenes). Our predictions are in excellent agreement with independent determinations for the equilibrium Fe isotopic fractionations for the magnetite- fayalite and the magnetite-hedenbergite couples. Our calibration applies to the entire range of Fe3+/Fe-tot ratios found in natural spinels and provides a basis for interpreting iron isotopic variations documented in mantle peridotites. Except for a few exceptions, most of the samples measured so far are in isotopic disequilibrium, reflecting metasomatism and partial melting processes.

  18. First-principles models of equilibrium tellurium isotope fractionation

    NASA Astrophysics Data System (ADS)

    Haghnegahdar, M. A.; Schauble, E. A.; Fornadel, A. P.; Spry, P. G.

    2013-12-01

    In this study, equilibrium mass-dependent isotopic fractionation among representative Te-bearing species is estimated with first-principles thermodynamic calculations. Tellurium is a group 16 element (along with O, S, and Se) with eight stable isotopes ranging in mass from 120Te to 130Te, and six commonly-occurring oxidation states: -II, -I, 0, +II, +IV, and +VI. In its reduced form, Te(-II), tellurium has a unique crystal-chemical role as a bond partner for gold and silver in epithermal and orogenic gold deposits, which likely form when oxidized Te species (e.g., H2TeO3, TeO32-) or perhaps polytellurides (e.g., Te22-) interact with precious metals in hydrothermal solution. Te(IV) is the most common oxidation state at the Earth's surface, including surface outcrops of telluride ore deposits, where tellurite and tellurate minerals form by oxidation. In the ocean, dissolved tellurium tends to be scavenged by particulate matter. Te(VI) is more abundant than Te(IV) in the ocean water (1), even though it is thought to be less stable thermodynamically. This variety of valence states in natural systems and range of isotopic masses suggest that tellurium could exhibit geochemically useful isotope abundance variations. Tellurium isotope fractionations were determined for representative molecules and crystals of varying complexity and chemistry. Gas-phase calculations are combined with supermolecular cluster models of aqueous and solid species. These in turn are compared with plane-wave density functional theory calculations with periodic boundary conditions. In general, heavyTe/lightTe is predicted to be higher for more oxidized species, and lower for reduced species, with 130Te/125Te fractionations as large as 4‰ at 100οC between coexisting Te(IV) and Te(-II) or Te(0) compounds. This is a much larger fractionation than has been observed in naturally occurring redox pairs (i.e., Te (0) vs. Te(IV) species) so far, suggesting that disequilibrium processes may control

  19. Method for separating boron isotopes

    DOEpatents

    Rockwood, Stephen D.

    1978-01-01

    A method of separating boron isotopes .sup.10 B and .sup.11 B by laser-induced selective excitation and photodissociation of BCl.sub.3 molecules containing a particular boron isotope. The photodissociation products react with an appropriate chemical scavenger and the reaction products may readily be separated from undissociated BCl.sub.3, thus effecting the desired separation of the boron isotopes.

  20. METHOD OF ISOTOPE CONCENTRATION

    DOEpatents

    Spevack, J.S.

    1957-04-01

    An isotope concentration process is described which consists of exchanging, at two or more different temperature stages, two isotopes of an element between substances that are physically separate from each other and each of which is capable of containing either of the isotopes, and withdrawing from a point between at least two of the temperatare stages one of the substances containing an increased concentration of the desired isotope.

  1. Equilibrium isotopic fractionation and isotopic exchange kinetics between Cr(III) and Cr(VI)

    NASA Astrophysics Data System (ADS)

    Wang, Xiangli; Johnson, Thomas M.; Ellis, Andre S.

    2015-03-01

    We determined the equilibrium isotope fractionation between Cr(III) and Cr(VI), defined as Δ53CrVI-III = δ53Cr(VI) - δ53Cr(III), and the rates of isotopic exchange between the two redox species under different conditions. In high Cr concentration, low-pH experiments we determined the Δ53CrV-III between CrO42- and Cr(H2O)63+ to be 5.2 ± 0.3‰ and 5.5 ± 0.3‰ at 60 °C and 40 °C, respectively. At 25 °C, the system only progressed 25% toward isotopic equilibrium after 684 days. By extrapolating from the 60 °C and 40 °C experiments we estimated the Δ53CrVI-III between CrO42- and Cr(H2O)63+ to be 5.8 ± 0.5‰ at 25 °C. Isotope exchange rates between dissolved Cr(III) and dissolved Cr(VI) at 25 °C, 40 °C, and 60 °C were determined to be 3.13 × 10-5 M day-1, 6.83 × 10-4 M day-1, and 8.37 × 10-3 M day-1, respectively. In low concentration, neutral-pH experiments we determined the isotopic exchange rates between dissolved Cr(VI) and solid Cr(III) oxyhydroxide at 25 °C. In these experiments, significant isotopic exchange was found on time scales of months, though the magnitude of isotopic shifts was limited by the small mass of Cr(III) available for exchange on the surfaces of Cr(III) oxyhydroxide particles. Exchange rates were relatively fast, compared to rates obtained from high concentration, low-pH experiments. This faster isotopic exchange is attributed to adsorption of Cr(VI) to Cr(III) particle surfaces, which keeps Cr(III) and Cr(VI), and potentially intermediate species Cr(V), in close proximity long enough to allow multiple electron transfers. The isotopic exchange rate at neutral-pH was found to conform to the rate law R = k·[Cr(VI)]adsorbed, in which R is the isotopic exchange rate (M day-1); k is the rate constant, determined to be 0.00047 day-1; [CrO42-]adsorbed is the concentration of Cr(VI) adsorbed to Cr(III) oxyhydroxide (M). The impact of isotopic exchange on the 53Cr/52Cr ratio of the dissolved Cr(VI) depends on the relative masses

  2. Equilibrium carbon and hydrogen isotope fractionation in iron

    NASA Astrophysics Data System (ADS)

    Schauble, E. A.

    2009-12-01

    Recent theoretical and experimental studies (e.g., [1-3]) have suggested that Si- and Fe-isotopic signatures can be used to characterize the compositions and conditions of segregation of metallic cores in planetary interiors. This study expands the theoretical framework to include carbon and hydrogen, which may also be alloying elements. Hydrogen (D/H) and carbon (13C/12C) fractionations in iron-rich metallic melts are estimated by modeling analogous iron-rich crystals, i.e., dhcp-FeH and η-Fe2C. C- and H-atoms in these crystals are completely coordinated by iron. The driving energy for equilibrium fractionation is assumed to come from the reduction of vibrational frequencies when heavy isotopes are substituted for light ones; vibrations are assumed to be harmonic. This treatment is crude at high temperature, and for the relatively anharmonic vibrations typical of hydrogen-bearing substances, but may provide a reasonably accurate, semi-quantitative approximation of real fractionation behavior. Vibrational frequencies of all crystals are modeled with density functional theory, using gradient-corrected functionals and ultrasoft pseudopotentials. For both carbon and hydrogen, the models suggest that the metal phase will be strongly depleted in heavy isotopes. At 2000 K, 1 atm, η-Fe2C will have 3‰ lower 13C/12C than coexisting diamond. Combining this result with previous high-temperature theoretical and experimental studies (e.g., [4]), metal-graphite fractionation is expected to be very similar, while metal-CO2 fractionation will be almost twice as large, ca. -5‰. Deuterium/hydrogen fractionations are expected to be an order of magnitude larger, with 50-70‰ lower D/H in dhcp-FeH than in coexisting H2 gas at 2000 K, and approximately 100‰ lower D/H than water vapor. These fractionations are much larger than those inferred for silicon and iron, as expected given the differences in atomic mass. References: 1. Georg et al. (2007) Nature 447:1102; 2. Rustad & Yin

  3. A process-based model for non-equilibrium clumped isotope effects in carbonates

    NASA Astrophysics Data System (ADS)

    Watkins, J. M.; Hunt, J. D.

    2015-12-01

    The equilibrium clumped isotope composition of carbonate minerals is independent of the composition of the aqueous solution. However, many carbonate minerals grow at rates that place them in a non-equilibrium regime with respect to carbon and oxygen isotopes with unknown consequences for clumped isotopes. We develop a process-based model that allows one to calculate the oxygen, carbon, and clumped isotope composition of calcite as a function of temperature, crystal growth rate, and solution pH. In the model, carbon and oxygen isotope fractionation occurs through the mass-dependent attachment/detachment kinetics of the isotopologues of HCO-3 and CO2-3 to and from the calcite surface, which in turn, influence the clumped isotope composition of calcite. At experimental and biogenic growth rates, the mineral is expected to inherit a clumped isotopic composition that is similar to that of the DIC pool, which helps to explain (1) why different organisms share the same clumped isotope versus temperature calibration curves, (2) why many inorganic calibration curves are slightly different from one another, and (3) why foraminifera, coccoliths, and deep sea corals can have near-equilibrium clumped isotope compositions but far-from-equilibrium carbon and oxygen isotope compositions. Some aspects of the model can be generalized to other mineral systems and should serve as a useful reference in future efforts to quantify kinetic clumped isotope effects.

  4. Theoretical calculation of nitrogen isotope equilibrium exchange fractionation factors for various NOy molecules

    NASA Astrophysics Data System (ADS)

    Walters, Wendell W.; Michalski, Greg

    2015-09-01

    The nitrogen stable isotope ratio (15N/14N) of nitrogen oxides (NOx = NO + NO2) and its oxidation products (NOy = NOx + PAN (peroxyacetyl nitrate = C2H3NO5) + HNO3 + NO3 + HONO + N2O5 + ⋯ + particulate nitrates) has been suggested as a tool for partitioning NOx sources; however, the impact of nitrogen (N) equilibrium isotopic fractionation on 15N/14N ratios during the conversion of NOx to NOy must also be considered, but few fractionation factors for these processes have been determined. To address this limitation, computational quantum chemistry calculations of harmonic frequencies, reduced partition function ratios (15β), and N equilibrium isotope exchange fractionation factors (αA/B) were performed for various gaseous and aqueous NOy molecules in the rigid rotor and harmonic oscillator approximations using the B3LYP and EDF2 density functional methods for the mono-substitution of 15N. The calculated harmonic frequencies, 15β, and αA/B are in good agreement with available experimental measurements, suggesting the potential to use computational methods to calculate αA/B values for N isotope exchange processes that are difficult to measure experimentally. Additionally, the effects of solvation (water) on 15β and αA/B were evaluated using the IEF-PCM model, and resulted in lower 15β and αA/B values likely due to the stabilization of the NOy molecules from dispersion interactions with water. Overall, our calculated 15β and αA/B values are accurate in the rigid rotor and harmonic oscillator approximations and will allow for the estimation of αA/B involving various NOy molecules. These calculated αA/B values may help to explain the trends observed in the N stable isotope ratio of NOy molecules in the atmosphere.

  5. Method of separating boron isotopes

    SciTech Connect

    Jensen, R.J.; Cluff, C.L.; Hayes, J.K.; Thorne, J.M.

    1984-05-08

    A method of boron isotope enrichment involving the isotope preferential photolysis of (2-chloroethenyl)dichloroborane as the feed material. The photolysis can readily be achieved with CO/sub 2/ laser radiation and using fluences significantly below those required to dissociate BCl/sub 3/.

  6. Method of separating boron isotopes

    DOEpatents

    Jensen, R.J.; Thorne, J.M.; Cluff, C.L.

    1981-01-23

    A method of boron isotope enrichment involving the isotope preferential photolysis of (2-chloroethenyl)-dichloroborane as the feed material. The photolysis can readily by achieved with CO/sub 2/ laser radiation and using fluences significantly below those required to dissociate BCl/sub 3/.

  7. Method of separating boron isotopes

    DOEpatents

    Jensen, Reed J.; Thorne, James M.; Cluff, Coran L.; Hayes, John K.

    1984-01-01

    A method of boron isotope enrichment involving the isotope preferential photolysis of (2-chloroethenyl)dichloroborane as the feed material. The photolysis can readily be achieved with CO.sub.2 laser radiation and using fluences significantly below those required to dissociate BCl.sub.3.

  8. Oxygen isotope equilibrium between eclogite minerals and its constraints on mineral Sm-Nd chronometer

    NASA Astrophysics Data System (ADS)

    Zheng, Yong-Fei; Wang, Zheng-Rong; Li, Shu-Guang; Zhao, Zi-Fu

    2002-02-01

    Sm-Nd and oxygen isotope analyses were carried out for mineral separates of ultrahigh pressure eclogites from the Sulu terrane in eastern China. The results show a direct correspondence in equilibrium or disequilibrium state between the oxygen and Sm-Nd isotope systems of eclogite minerals. The omphacite-garnet pairs of oxygen isotope equilibrium at eclogite-facies conditions yield meaningful Triassic Sm-Nd isochron ages, whereas those of oxygen isotope disequilibrium give non-Triassic ages of geological meaninglessness. This can be reasonably interpreted by the fact that the rates of oxygen diffusion in garnet and pyroxene are lower than, or close to, those of Nd diffusion, and thus attainment of isotopic equilibrium in the omphacite-garnet O system suggests achievement of Nd isotope equilibrium in the same mineral pairs. The presence or absence of fluid in the eclogite protoliths is a major rate-controlling factor for isotopic equilibration during high-grade metamorphism. It appears that the state of oxygen isotope equilibrium between cogenetic minerals can provide a critical test for the validity of the Sm-Nd mineral chronometer. In addition, the exact timing of the ultrahigh pressure metamorphism in the Dabie-Sulu terranes is constrained at Early Triassic rather than Late Triassic.

  9. Group Contribution Methods for Phase Equilibrium Calculations.

    PubMed

    Gmehling, Jürgen; Constantinescu, Dana; Schmid, Bastian

    2015-01-01

    The development and design of chemical processes are carried out by solving the balance equations of a mathematical model for sections of or the whole chemical plant with the help of process simulators. For process simulation, besides kinetic data for the chemical reaction, various pure component and mixture properties are required. Because of the great importance of separation processes for a chemical plant in particular, a reliable knowledge of the phase equilibrium behavior is required. The phase equilibrium behavior can be calculated with the help of modern equations of state or g(E)-models using only binary parameters. But unfortunately, only a very small part of the experimental data for fitting the required binary model parameters is available, so very often these models cannot be applied directly. To solve this problem, powerful predictive thermodynamic models have been developed. Group contribution methods allow the prediction of the required phase equilibrium data using only a limited number of group interaction parameters. A prerequisite for fitting the required group interaction parameters is a comprehensive database. That is why for the development of powerful group contribution methods almost all published pure component properties, phase equilibrium data, excess properties, etc., were stored in computerized form in the Dortmund Data Bank. In this review, the present status, weaknesses, advantages and disadvantages, possible applications, and typical results of the different group contribution methods for the calculation of phase equilibria are presented.

  10. Equilibrium mercury isotope fractionation between dissolved Hg(II) species and thiol-bound Hg.

    PubMed

    Wiederhold, Jan G; Cramer, Christopher J; Daniel, Kelly; Infante, Ivan; Bourdon, Bernard; Kretzschmar, Ruben

    2010-06-01

    Stable Hg isotope ratios provide a new tool to trace environmental Hg cycling. Thiols (-SH) are the dominant Hg-binding groups in natural organic matter. Here, we report experimental and computational results on equilibrium Hg isotope fractionation between dissolved Hg(II) species and thiol-bound Hg. Hg(II) chloride and nitrate solutions were equilibrated in parallel batches with varying amounts of thiol resin resulting in different fractions of thiol-bound and free Hg. Mercury isotope ratios in both fractions were analyzed by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). Theoretical equilibrium Hg isotope effects by mass-dependent fractionation (MDF) and nuclear volume fractionation (NVF) were calculated for 14 relevant Hg(II) species. The experimental data revealed that thiol-bound Hg was enriched in light Hg isotopes by 0.53 per thousand and 0.62 per thousand (delta(202)Hg) relative to HgCl(2) and Hg(OH)(2), respectively. The computational results were in excellent agreement with the experimental data indicating that a combination of MDF and NVF was responsible for the observed Hg isotope fractionation. Small mass-independent fractionation (MIF) effects (<0.1 per thousand) were observed representing one of the first experimental evidences for MIF of Hg isotopes by NVF. Our results indicate that significant equilibrium Hg isotope fractionation can occur without redox transition, and that NVF must be considered in addition to MDF to explain Hg isotope variations.

  11. Isotope separation apparatus and method

    DOEpatents

    Feldman, Barry J.

    1985-01-01

    The invention relates to an improved method and apparatus for laser isotope separation by photodeflection. A molecular beam comprising at least two isotopes to be separated intersects, preferably substantially perpendicular to one broad side of the molecular beam, with a laser beam traveling in a first direction. The laser beam is reflected back through the molecular beam, preferably in a second direction essentially opposite to the first direction. Because the molecules in the beam occupy various degenerate energy levels, if the laser beam comprises chirped pulses comprising selected wavelengths, the laser beam will very efficiently excite substantially all unexcited molecules and will cause stimulated emission of substantially all excited molecules of a selected one of the isotopes in the beam which such pulses encounter. Excitation caused by first direction chirped pulses moves molecules of the isotope excited thereby in the first direction. Stimulated emission of excited molecules of the isotope is brought about by returning chirped pulses traveling in the second direction. Stimulated emission moves emitting molecules in a direction opposite to the photon emitted. Because emitted photons travel in the second direction, emitting molecules move in the first direction. Substantial molecular movement of essentially all the molecules containing the one isotope is accomplished by a large number of chirped pulse-molecule interactions. A beam corer collects the molecules in the resulting enriched divergent portions of the beam.

  12. Low temperature equilibrium isotope fractionation and isotope exchange kinetics between U(IV) and U(VI)

    NASA Astrophysics Data System (ADS)

    Wang, Xiangli; Johnson, Thomas M.; Lundstrom, Craig C.

    2015-06-01

    Measurements of the uranium (U) isotope ratio 238U/235U provide an emerging redox proxy in environmental and paleoredox studies, but many key parameters concerning U isotope fractionation are still poorly constrained. Here we report the equilibrium isotopic fractionation between dissolved U(IV) and dissolved U(VI), and rates of isotope exchange between solid-phase U(IV) and dissolved U(VI). We conducted one experiment at high concentration [35 mM U(IV) and 32 mM U(VI)] and low pH (0.2) in hydrochloric acid media at room temperature to determine the equilibrium isotopic fractionation between dissolved U(IV) and dissolved U(VI). Isotopic equilibrium was reached in about 19 days under such experimental conditions. The equilibrium isotope fractionation was determined to be 1.64 ± 0.16‰, with U(IV) being enriched in 238U relative to U(VI). Applicability of the determined equilibrium fractionation is discussed. We also conducted a set of experiments to determine isotopic exchange rates between dissolved U(VI) and nanouraninite U(IV) under conditions closer to those in natural system, with lower concentrations and neutral pH. The exchange rate was found to conform to the rate law R = k[U(VI)]adsorbed, in which R is the isotopic exchange rate (μM day-1); k is the rate constant determined to be 0.21 day-1; and [U(VI)]adsorbed is the concentration of U(VI) adsorbed to nanouraninite (μM). Our results, combined with consideration of the variables controlling U(VI)-U(IV) contact in natural settings, indicate that the timescale for significant isotope equilibration varies depending on environmental conditions, mostly uranium concentrations. In natural uncontaminated sediments with low uranium concentrations, equilibration is expected to occur on a timescale of hundreds to thousands of years. In contrast, in U-contaminated aquifers with high U concentrations, significant equilibration could occur on timescales of weeks to years.

  13. Isotope separation apparatus and method

    DOEpatents

    Cotter, Theodore P.

    1982-12-28

    The invention relates to a method and apparatus for laser isotope separation by photodeflection. A molecular beam comprising at least two isotopes to be separated intersects, preferable substantially perpendicular to one broad side of the molecular beam, with a laser beam traveling in a first direction. The laser beam is reflected back through the molecular beam, preferably in a second direction essentially opposite to the first direction. The laser beam comprises .pi.-pulses of a selected wavelength which excite unexcited molecules, or cause stimulated emission of excited molecules of one of the isotopes. Excitation caused by first direction .pi.-pulses moves molecules of the isotope excited thereby in the first direction. Stimulated emission of excited molecules of the isotope is brought about by returning .pi.-pulses traveling in the second direction. Stimulated emission moves emitting molecules in a direction opposite to the photon emitted. Because emitted photons travel in the second direction, emitting molecules move in the first direction. Substantial molecular movement is accomplished by a large number of .pi.-pulse-molecule interactions. A beam corer collects the molecules in the resulting enriched divergent portions of the beam.

  14. Isotopic equilibrium between mantle peridotite and melt: Evidence from the Corsica ophiolite

    NASA Astrophysics Data System (ADS)

    Rampone, Elisabetta; Hofmann, Albrecht W.; Raczek, Ingrid

    2009-11-01

    A widely used assumption of mantle geochemistry and the theory of partial melting at oceanic settings is the existence of isotopic equilibrium between mantle source and melt. Yet, recent diffusion studies and isotopic investigations of ophiolites, abyssal peridotites and associated MORBs have cast doubts on this assumption, by providing evidence for isotopic disequilibrium between residual peridotites and MORBs. Here we present Sr and Sm-Nd isotope data on mantle peridotites and gabbroic intrusions from the Mt. Maggiore (Alpine Corsica, France) Tethyan ophiolite, which document Nd isotopic homogeneity, implying isotopic equilibrium, on a 1-kilometer scale. The peridotites record multi-stage melt-rock interaction and melt intrusion occurring at different lithospheric depths. Samples studied are residual cpx-poor spinel lherzolites, reactive spinel harzburgites, impregnated plagioclase peridotites and related gabbronoritic veinlets, later gabbroic dykes. Strontium isotopes in peridotites and gabbros are highly variable, due to interaction with sea-water derived fluids, and cannot be used to test melt-residue isotopic equilibrium. In contrast, Nd isotopes are unaffected by sea-water alteration. Peridotites display present-day high 147Sm/ 144Nd (0.49-0.59) and 143Nd/ 144Nd (0.513367-0.513551) ratios, with no appreciable differences between residual and reactive spinel peridotites, and between spinel and plagioclase peridotites. Gabbroic dykes have present-day Nd isotopic compositions typical of MORB ( 143Nd/ 144Nd = 0.513122-0.513138). Internal (plag-whole rock-cpx) Sm-Nd isochrons for olivine gabbro dykes and a gabbronoritic veinlet yield Jurassic ages (162 ± 10 and 159 ± 15 Ma in ol-gabbros, 155 ± 6 Ma in gabbronorite), and initial ɛNd = 8.9-9.7 indicative of a MORB-type source. Sm-Nd isotopic compositions of peridotites conform to the linear array defined by the gabbroic rocks, and yield initial (160 Ma) ɛNd values of 7.6-8.9, again consistent with a MORB

  15. METHOD OF ISOTOPE CONCENTRATION

    DOEpatents

    Taylor, T.I.; Spindel, W.

    1960-02-01

    A method of concentrating N/sup 15/ in a liquid is described. Gaseous nitric oxide and at least one liquid selected from the group consisting of the aqueous oxyacids and oxides of nitrogen, wherein the atomic ratio of oxygen to nitrogen is greater than unity, are brought into intimate contact to cause an enrichment of the liquid and a depletion of the gas in N/sup 15/. The liquid is, thereafter, reacted with sulfur dioxide to produce a gas contuining nitric oxide. The gas contuining nitric oxide is then continuously passed in countercurrent contact with the liquid to cause further enrichment of the liquid.

  16. Method for laser induced isotope enrichment

    DOEpatents

    Pronko, Peter P.; Vanrompay, Paul A.; Zhang, Zhiyu

    2004-09-07

    Methods for separating isotopes or chemical species of an element and causing enrichment of a desired isotope or chemical species of an element utilizing laser ablation plasmas to modify or fabricate a material containing such isotopes or chemical species are provided. This invention may be used for a wide variety of materials which contain elements having different isotopes or chemical species.

  17. Barium isotope fractionation during witherite (BaCO3) dissolution, precipitation and at equilibrium

    NASA Astrophysics Data System (ADS)

    Mavromatis, Vasileios; van Zuilen, Kirsten; Purgstaller, Bettina; Baldermann, Andre; Nägler, Thomas F.; Dietzel, Martin

    2016-10-01

    This study examines the behavior of Ba isotope fractionation between witherite and fluid during mineral dissolution, precipitation and at chemical equilibrium. Experiments were performed in batch reactors at 25 °C in 10-2 M NaCl solution where the pH was adjusted by continuous bubbling of a water saturated gas phase of CO2 or atmospheric air. During witherite dissolution no Ba isotope fractionation was observed between solid and fluid. In contrast, during witherite precipitation, caused by a pH increase, a preferential uptake of the lighter 134Ba isotopomer in the solid phase was observed. In this case, the isotope fractionation factor αwitherite-fluid is calculated to be 0.99993 ± 0.00004 (or Δ137/134Bawitherite-fluid ≈ -0.07 ± 0.04‰, 2 sd). The most interesting feature of this study, however, is that after the attainment of chemical equilibrium, the Ba isotope composition of the aqueous phase is progressively becoming lighter, indicating a continuous exchange of Ba2+ ions between witherite and fluid. Mass balance calculations indicate that the detachment of Ba from the solid is not only restricted to the outer surface layer of the solid, but affects several (∼7 unit cells) subsurface layers of the crystal. This observation comes in excellent agreement with the concept of a dynamic system at chemical equilibrium in a mineral-fluid system, denoting that the time required for the achievement of isotopic equilibrium in the witherite-fluid system is longer compared to that observed for chemical equilibrium. Overall, these results indicate that the isotopic composition of Ba bearing carbonates in natural environments may be altered due to changes in fluid composition without a net dissolution/precipitation to be observed.

  18. Evidence for equilibrium iron isotope fractionation by nitrate-reducing iron(II)-oxidizing bacteria

    PubMed Central

    Kappler, A.; Johnson, C.M.; Crosby, H.A.; Beard, B.L.; Newman, D.K.

    2010-01-01

    Iron isotope fractionations produced during chemical and biological Fe(II) oxidation are sensitive to the proportions and nature of dissolved and solid-phase Fe species present, as well as the extent of isotopic exchange between precipitates and aqueous Fe. Iron isotopes therefore potentially constrain the mechanisms and pathways of Fe redox transformations in modern and ancient environments. In the present study, we followed in batch experiments Fe isotope fractionations between Fe(II)aq and Fe(III) oxide/hydroxide precipitates produced by the Fe(III) mineral encrusting, nitrate-reducing, Fe(II)-oxidizing Acidovorax sp. strain BoFeN1. Isotopic fractionation in 56Fe/54Fe approached that expected for equilibrium conditions, assuming an equilibrium Δ56FeFe(OH)3 – Fe(II)aq fractionation factor of +3.0 ‰. Previous studies have shown that Fe(II) oxidation by this Acidovorax strain occurs in the periplasm, and we propose that Fe isotope equilibrium is maintained through redox cycling via coupled electron and atom exchange between Fe(II)aq and Fe(III) precipitates in the contained environment of the periplasm. In addition to the apparent equilibrium isotopic fractionation, these experiments also record the kinetic effects of initial rapid oxidation, and possible phase transformations of the Fe(III) precipitates. Attainment of Fe isotope equilibrium between Fe(III) oxide/hydroxide precipitates and Fe(II)aq by neutrophilic, Fe(II)-oxidizing bacteria or through abiologic Fe(II)aq oxidation is generally not expected or observed, because the poor solubility of their metabolic product, i.e. Fe(III), usually leads to rapid precipitation of Fe(III) minerals, and hence expression of a kinetic fractionation upon precipitation; in the absence of redox cycling between Fe(II)aq and precipitate, kinetic isotope fractionations are likely to be retained. These results highlight the distinct Fe isotope fractionations that are produced by different pathways of biological and

  19. Clumped-isotope signatures at equilibrium of CH4, NH3, H2O, H2S and SO2

    NASA Astrophysics Data System (ADS)

    Liu, Qi; Liu, Yun

    2016-02-01

    High precision Δi values at equilibrium determined by theoretical methods are imperatively needed as references for the development of new clumped-isotope thermometers (or tracers). In this study, quantum chemistry methods with corrections beyond the harmonic approximation are used to obtain the clumped-isotope signatures at equilibrium of several gas-phase molecules (i.e., CH4, NH3, H2O, H2S, and SO2). Here, we consider as many corrections to the traditional Bigeleisen-Mayer equation as possible to obtain accurate Δi values at equilibrium and their temperature dependences. The corrections include anharmonic correction for zero-point energy, anharmonic correction for vibrational excited states, vibration-rotation coupling correction for zero-point energy, vibration-rotation coupling correction for vibrational excited states, quantum mechanical correction to rotation, and centrifugal distortion correction, which are important for theoretical understanding of clumped-isotope signals. Specifically, molecular constants are calculated via second-order perturbative analysis at the MP2/aug-cc-pVTZ level. The CCSD/6-311+G(3df,3pd) and CCSD/aug-cc-pVTZ levels are further employed to ensure the precision of harmonic frequencies of methane. For methane, a polynomial fit of ΔCH133D values over the temperature range of from 273.15 to 1000 K is obtained:

  20. Isotopic Dilution Analysis and Secular Equilibrium Study: Two Complementary Radiochemistry Experiments.

    ERIC Educational Resources Information Center

    Williams, Kathryn R.; Lipford, Levin C.

    1985-01-01

    Describes a complementary pair of radiochemistry experiments for instruction of isotopic dilution analysis and secular equilibrium. Both experiments use the readily available cesium-137 nuclide and the simple precipitation technique for cesium with the tetraphenylborate anion. Procedures used and typical results obtained are provided and…

  1. Ab initio calculations of Li and B equilibrium isotope fractionation between high -P and -T minerals and aqueous fluids

    NASA Astrophysics Data System (ADS)

    Kowalski, P.; Jahn, S.; Wunder, B.

    2011-12-01

    Stable isotopes are excellent geochemical tracers widely used in petrology. Among them the isotopes of light elements such as Li or B strongly fractionate between minerals and aqueous fluids during fluid-rock interaction processes, which makes them excellent tracers of mass transfer processes in the subduction cycle. In order to use the full power of isotopes tracing methods the isotope fractionation mechanisms and fractionation factors between minerals and fluids of interest must be well known and characterized. One of the most important mechanisms leading to the formation of isotopic signatures is the equilibrium isotope fractionation, which nowadays can be modeled on the atomic scale by modern computational methods. However, due to high computational requirements the current works have been limited to calculations of simple materials only. In order to overcome these limitations we develop an efficient ab initio based computational approach for prediction of the equilibrium isotope fractionation factors between high pressure and temperature materials, including fluids, which would allow for efficient calculations of the isotope fractionation factors of complex minerals and fluids containing even hundreds of atoms in the supercell. We will show our results for the Li and B stable equilibrium isotope fractionation factors between complex Li/B-bearing crystalline solids (staurolite, spodumene, tourmaline, olenite and micas) and aqueous fluids. The fractionation factors were obtained in an efficient way by simplifying the consideration to calculations of the properties of fractionating atoms only. The comparison of the calculated fractionation factors, on the qualitative and quantitative levels, with the existing experimental data show the comparable to the in situ experimental techniques, predictive power of the computations. We show that with the atomistic scale modelling we are able to reproduce correctly the experimental isotope fractionation sequences

  2. Equilibrium magnesium isotope fractionation between aqueous Mg2+ and carbonate minerals: Insights from path integral molecular dynamics

    NASA Astrophysics Data System (ADS)

    Pinilla, Carlos; Blanchard, Marc; Balan, Etienne; Natarajan, Suresh K.; Vuilleumier, Rodolphe; Mauri, Francesco

    2015-08-01

    The theoretical determination of the isotopic fractionation between an aqueous solution and a mineral is of utmost importance in Earth sciences. While for crystals, it is well established that equilibrium isotopic fractionation factors can be calculated using a statistical thermodynamic approach based on the vibrational properties, several theoretical methods are currently used to model ions in aqueous solution. In this work, we present a systematic study to determine the reduced partition function ratio (β-factor) of aqueous Mg2+ using several levels of theory within the simulations. In particular, using an empirical force field, we compare and discuss the performance of the exact results obtained from path integral molecular dynamics (PIMD) simulations, with respect to the more traditional methods based on vibrational properties and the cluster approximation. The results show the importance of including configurational disorder for the estimation of the equilibrium isotope fractionation factor. We also show that using the vibrational frequencies computed from snapshots taken from equilibrated classical molecular dynamics represents a good approximation for the study of aqueous ions. Based on these conclusions, the β-factor of aqueous Mg2+ have been estimated from a Car-Parrinello molecular dynamics (CPMD) simulation with an ab initio force field, and combined with the β-factors of carbonate minerals (magnesite, dolomite, calcite and aragonite). Mg β-factor of Mg-bearing aragonite, calculated here for the first time, displays a lower value than the three other carbonate minerals. This is explained by a strong distortion of the cationic site leading to a decrease of the coordination number during Ca-Mg substitution. Overall, the equilibrium magnesium isotope fractionation factors between aqueous Mg2+ and carbonate minerals that derive from this methodological study support the previous theoretical results obtained from embedded cluster models.

  3. Theoretical estimation of equilibrium sulfur isotope fractionations among aqueous sulfite species: Implications for isotope models of microbial sulfate reduction

    NASA Astrophysics Data System (ADS)

    Eldridge, D. L.; Farquhar, J.; Guo, W.

    2015-12-01

    Sulfite (sensu lato), an intermediate in a variety sulfur redox processes, plays a particularly important role in microbial sulfate reduction. It exists intracellularly as multiple species between sets of enzymatic reactions that transform sulfate to sulfide, with the exact speciation depending on pH, T, and ionic strength. However, the complex speciation of sulfite is ignored in current isotope partitioning models of microbial sulfate reduction and simplified solely to the pyramidal SO32- (sulfite sensu stricto), due to a lack of appropriate constraints. We theoretically estimated the equilibrium sulfur isotope fractionations (33S/32S, 34S/32S, 36S/32S) among all documented sulfite species in aqueous solution, including sulfite (SO32-), bisulfite isomers and dimers ((HS)O3-, (HO)SO2-, S2O52-), and SO2(aq), through first principles quantum mechanical calculations. The calculations were performed at B3LYP/6-31+G(d,p) level using cluster models with 30-40 water molecules surrounding the solute. Our calculated equilibrium fractionation factors compare well to the available experimental constraints and suggest that the minor and often-ignored tetrahedral (HS)O3- isomer of bisulfite strongly influences isotope partitioning behavior in the sulfite system under most environmentally relevant conditions, particularly fractionation magnitudes and unusual temperature dependence. For example, we predict that sulfur isotope fractionation between sulfite and bulk bisulfite in solution should have an apparent inverse temperature dependence due to the influence of (HS)O3- and its increased stability at higher temperatures. Our findings highlight the need to appropriately account for speciation/isomerization of sulfur species in sulfur isotope studies. We will also present similar calculation results of other aqueous sulfur compounds (e.g., H2S/HS-, SO42-, S2O32-, S3O62-, and poorly documented SO22- species), and discuss the implication of our results for microbial sulfate

  4. A reassessment of isotopic equilibrium (Δ47 and δ18O) in the Laghetto Basso pool carbonates

    NASA Astrophysics Data System (ADS)

    Daëron, M.; Drysdale, R.; Blamart, D.; Genty, D.; Zanchetta, G.

    2013-12-01

    To the best of our current knowledge, the overwhelming majority of modern speleothems have Δ47 values which differ significantly from those predicted for thermodynamic equilibrium. The extent to which these differences may vary temporally and spatially is still an open issue, precluding a straightforward application of clumped isotopes paleothermometry to speleothem records. Here we report on the recent results of a reassessment of isotopic equilibrium in the Laghetto Basso pool carbonates (Antro del Corchia cave, NW Italy), which offer excellent a priori conditions for equilibrium carbonate precipitation and provide a continuous or quasi-continuous isotopic record of the past million years.

  5. Carbon-isotopic composition of soil-respired carbon dioxide in static closed chambers at equilibrium.

    PubMed

    Mora, Germán; Raich, James W

    2007-01-01

    The carbon-isotopic composition (delta13C) of soil-respired CO2 has been employed to evaluate soil carbon-cycling processes and the contribution of soil CO2 emissions to canopy and tropospheric air. These evaluations can be successful only when accurate isotope values of soil-respired CO2 are available. Here, we tested the robustness of delta13C values of soil-respired CO2 obtained after long incubations in static closed chambers that were initially flushed with soil air. The rationale of this approach is that the equilibrium carbon-isotope values of chamber-headspace CO2 are theoretically equal to those of CO2 produced within the soil. Static closed chambers were installed in replicated grass monocultures, and measurements of headspace CO2 concentrations and delta13C values were performed at regular time intervals for 24 h in July 2005. The results revealed no significant effects of grass species on headspace CO2 concentrations or delta13C values (repeated measures analysis of variance (ANOVA), P>0.1). As predicted by theory, isotope values asymptotically approached equilibrium conditions, which in our experimental setting occurred after 10 h. This good match between model predictions and our results suggests that an accurate determination of delta13C values of CO2 produced within soils is obtained through the isotopic measurement of chamber-headspace CO2 once equilibrium conditions have been reached with the underlying soils. An additional advantage of this approach is that only one sample per chamber is required, which, combined with the low uncertainties of these measurements, facilitates the investigation of the spatial (landscape) variability of soil-respired CO2.

  6. Computational and Experimental Evidence of Emergent Equilibrium Isotope Effects in Anion Receptor Complexes

    PubMed Central

    2017-01-01

    The measurement of a deuterium equilibrium isotope effect (EIE) for the aryl CH···Cl– interaction of anion receptor 1H/1D is reported. Computations corroborate the results of solution measurements for a small, normal EIE in the full complex (KaH/KaD = 1.019 ± 0.010). Interestingly, isotope effects involving fragments of the anion receptor (urea, aryl ring, etc.) are predicted to produce an inverse effect. This points to an unusual and subtle structural organization effect of the anion receptor complex that changes the nature of the combined interactions to a normal isotope effect. The reversal of EIE values suggests that overall architecture of the anion receptor can dramatically impact the nature of bonding in these complexes. PMID:28282134

  7. Transesterification thio effects of phosphate diesters: free energy barriers and kinetic and equilibrium isotope effects from density-functional theory.

    PubMed

    Liu, Yun; Gregersen, Brent A; Hengge, Alvan; York, Darrin M

    2006-08-22

    Primary and secondary kinetic and equilibrium isotope effects are calculated with density-functional methods for the in-line dianionic methanolysis of the native (unsubstituted) and thio-substituted cyclic phosphates. These reactions represent reverse reaction models for RNA transesterification under alkaline conditions. The effect of solvent is treated with explicit (single and double) water molecules and self-consistently with an implicit (continuum) solvation model. Singly substituted reactions at the nonbridging O(P1) position and bridging O(2)('), O(3)('), and O(5)(') positions and a doubly substituted reaction at the O(P1) and O(P2) positions were considered. Aqueous free energy barriers are calculated, and the structures and bond orders of the rate-controlling transition states are characterized. The results are consistent with available experimental data and provide useful information for the interpretation of measured isotope and thio effects used to probe mechanism in phosphoryl transfer reactions catalyzed by enzymes and ribozymes.

  8. Equilibrium fractionation of H and O isotopes in water from path integral molecular dynamics

    NASA Astrophysics Data System (ADS)

    Pinilla, Carlos; Blanchard, Marc; Balan, Etienne; Ferlat, Guillaume; Vuilleumier, Rodolphe; Mauri, Francesco

    2014-06-01

    The equilibrium fractionation factor between two phases is of importance for the understanding of many planetary and environmental processes. Although thermodynamic equilibrium can be achieved between minerals at high temperature, many natural processes involve reactions between liquids or aqueous solutions and solids. For crystals, the fractionation factor α can be theoretically determined using a statistical thermodynamic approach based on the vibrational properties of the phases. These calculations are mostly performed in the harmonic approximation, using empirical or ab-initio force fields. In the case of aperiodic and dynamic systems such as liquids or solutions, similar calculations can be done using finite-size molecular clusters or snapshots obtained from molecular dynamics (MD) runs. It is however difficult to assess the effect of these approximate models on the isotopic fractionation properties. In this work we present a systematic study of the calculation of the D/H and 18O/16O equilibrium fractionation factors in water for the liquid/vapour and ice/vapour phases using several levels of theory within the simulations. Namely, we use a thermodynamic integration approach based on Path Integral MD calculations (PIMD) and an empirical potential model of water. Compared with standard MD, PIMD takes into account quantum effects in the thermodynamic modeling of systems and the exact fractionation factor for a given potential can be obtained. We compare these exact results with those of modeling strategies usually used, which involve the mapping of the quantum system on its harmonic counterpart. The results show the importance of including configurational disorder for the estimation of isotope fractionation in liquid phases. In addition, the convergence of the fractionation factor as a function of parameters such as the size of the simulated system and multiple isotope substitution is analyzed, showing that isotope fractionation is essentially a local effect in

  9. Nuclear volume effects in equilibrium stable isotope fractionations of mercury, thallium and lead

    NASA Astrophysics Data System (ADS)

    Yang, Sha; Liu, Yun

    2015-07-01

    The nuclear volume effects (NVEs) of Hg, Tl and Pb isotope systems are investigated with careful evaluation on quantum relativistic effects via the Dirac’s formalism of full-electron wave function. Equilibrium 202Hg/198Hg, 205Tl/203Tl, 207Pb/206Pb and 208Pb/206Pb isotope fractionations are found can be up to 3.61‰, 2.54‰, 1.48‰ and 3.72‰ at room temperature, respectively, larger than fractionations predicted by classical mass-dependent isotope fractionations theory. Moreover, the NVE can cause mass-independent fractionations (MIF) for odd-mass isotopes and even-mass isotopes. The plot of vs. for Hg-bearing species falls into a straight line with the slope of 1.66, which is close to previous experimental results. For the first time, Pb4+-bearing species are found can enrich heavier Pb isotopes than Pb2+-bearing species to a surprising extent, e.g., the enrichment can be up to 4.34‰ in terms of 208Pb/206Pb at room temperature, due to their NVEs are in opposite directions. In contrast, fractionations among Pb2+-bearing species are trivial. Therefore, the large Pb fractionation changes provide a potential new tracer for redox conditions in young and closed geologic systems. The magnitudes of NVE-driven even-mass MIFs of Pb isotopes (i.e., ) and odd-mass MIFs (i.e., ) are almost the same but with opposite signs.

  10. Nuclear volume effects in equilibrium stable isotope fractionations of mercury, thallium and lead.

    PubMed

    Yang, Sha; Liu, Yun

    2015-07-30

    The nuclear volume effects (NVEs) of Hg, Tl and Pb isotope systems are investigated with careful evaluation on quantum relativistic effects via the Dirac's formalism of full-electron wave function. Equilibrium (202)Hg/(198)Hg, (205)Tl/(203)Tl, (207)Pb/(206)Pb and (208)Pb/(206)Pb isotope fractionations are found can be up to 3.61‰, 2.54‰, 1.48‰ and 3.72‰ at room temperature, respectively, larger than fractionations predicted by classical mass-dependent isotope fractionations theory. Moreover, the NVE can cause mass-independent fractionations (MIF) for odd-mass isotopes and even-mass isotopes. The plot of [formula in text] for Hg-bearing species falls into a straight line with the slope of 1.66, which is close to previous experimental results. For the first time, Pb(4+)-bearing species are found can enrich heavier Pb isotopes than Pb(2+)-bearing species to a surprising extent, e.g., the enrichment can be up to 4.34‰ in terms of (208)Pb/(206)Pb at room temperature, due to their NVEs are in opposite directions. In contrast, fractionations among Pb(2+)-bearing species are trivial. Therefore, the large Pb fractionation changes provide a potential new tracer for redox conditions in young and closed geologic systems. The magnitudes of NVE-driven even-mass MIFs of Pb isotopes (i.e., [formula in text]) and odd-mass MIFs (i.e., [formula in text) are almost the same but with opposite signs.

  11. Method for isotope separation by photodeflection

    DOEpatents

    Bernhardt, Anthony F.

    1977-01-01

    In the method of separating isotopes wherein a desired isotope species is selectively deflected out of a beam of mixed isotopes by irradiating the beam with a directed beam of light of narrowly defined frequency which is selectively absorbed by the desired species, the improvement comprising irradiating the deflected beam with light from other light sources whose frequencies are selected to cause the depopulation of any metastable excited states.

  12. METHOD AND APPARATUS FOR COLLECTING ISOTOPES

    DOEpatents

    Leyshon, W.E.

    1957-08-01

    A method and apparatus for collecting isotopes having a high vapor pressure, such as isotopes of mercury, in a calutron are described. Heretofore, the collected material would vaporize and escape from the ion receiver as fast as it was received. By making the receiver of pure silver, the mercury isotopes form a nonvolatile amalgam with the silver at the water cooled temperature of the receiver, and the mercury is thus retained.

  13. [Dichotomizing method applied to calculating equilibrium constant of dimerization system].

    PubMed

    Cheng, Guo-zhong; Ye, Zhi-xiang

    2002-06-01

    The arbitrary trivariate algebraic equations are formed based on the combination principle. The univariata algebraic equation of equilibrium constant kappa for dimerization system is obtained through a series of algebraic transformation, and it depends on the properties of monotonic functions whether the equation is solvable or not. If the equation is solvable, equilibrium constant of dimerization system is obtained by dichotomy and its final equilibrium constant of dimerization system is determined according to the principle of error of fitting. The equilibrium constants of trisulfophthalocyanine and biosulfophthalocyanine obtained with this method are 47,973.4 and 30,271.8 respectively. The results are much better than those reported previously.

  14. Chromatographic speciation of Cr(III)-species, inter-species equilibrium isotope fractionation and improved chemical purification strategies for high-precision isotope analysis.

    PubMed

    Larsen, K K; Wielandt, D; Schiller, M; Bizzarro, M

    2016-04-22

    Chromatographic purification of chromium (Cr), which is required for high-precision isotope analysis, is complicated by the presence of multiple Cr-species with different effective charges in the acid digested sample aliquots. The differing ion exchange selectivity and sluggish reaction rates of these species can result in incomplete Cr recovery during chromatographic purification. Because of large mass-dependent inter-species isotope fractionation, incomplete recovery can affect the accuracy of high-precision Cr isotope analysis. Here, we demonstrate widely differing cation distribution coefficients of Cr(III)-species (Cr(3+), CrCl(2+) and CrCl2(+)) with equilibrium mass-dependent isotope fractionation spanning a range of ∼1‰/amu and consistent with theory. The heaviest isotopes partition into Cr(3+), intermediates in CrCl(2+) and the lightest in CrCl2(+)/CrCl3°. Thus, for a typical reported loss of ∼25% Cr (in the form of Cr(3+)) through chromatographic purification, this translates into 185 ppm/amu offset in the stable Cr isotope ratio of the residual sample. Depending on the validity of the mass-bias correction during isotope analysis, this further results in artificial mass-independent effects in the mass-bias corrected (53)Cr/(52)Cr (μ(53)Cr* of 5.2 ppm) and (54)Cr/(52)Cr (μ(54)Cr* of 13.5 ppm) components used to infer chronometric and nucleosynthetic information in meteorites. To mitigate these fractionation effects, we developed strategic chemical sample pre-treatment procedures that ensure high and reproducible Cr recovery. This is achieved either through 1) effective promotion of Cr(3+) by >5 days exposure to HNO3H2O2 solutions at room temperature, resulting in >∼98% Cr recovery for most types of sample matrices tested using a cationic chromatographic retention strategy, or 2) formation of Cr(III)-Cl complexes through exposure to concentrated HCl at high temperature (>120 °C) for several hours, resulting in >97.5% Cr recovery using a

  15. Chromatographic speciation of Cr(III)-species, inter-species equilibrium isotope fractionation and improved chemical purification strategies for high-precision isotope analysis

    PubMed Central

    Larsen, K.K.; Wielandt, D.; Schiller, M.; Bizzarro, M.

    2016-01-01

    Chromatographic purification of chromium (Cr), which is required for high-precision isotope analysis, is complicated by the presence of multiple Cr-species with different effective charges in the acid digested sample aliquots. The differing ion exchange selectivity and sluggish reaction rates of these species can result in incomplete Cr recovery during chromatographic purification. Because of large mass-dependent inter-species isotope fractionation, incomplete recovery can affect the accuracy of high-precision Cr isotope analysis. Here, we demonstrate widely differing cation distribution coefficients of Cr(III)-species (Cr3+, CrCl2+ and CrCl2+) with equilibrium mass-dependent isotope fractionation spanning a range of ~1‰/amu and consistent with theory. The heaviest isotopes partition into Cr3+, intermediates in CrCl2+ and the lightest in CrCl2+/CrCl3°. Thus, for a typical reported loss of ~25% Cr (in the form of Cr3+) through chromatographic purification, this translates into 185 ppm/amu offset in the stable Cr isotope ratio of the residual sample. Depending on the validity of the mass-bias correction during isotope analysis, this further results in artificial mass-independent effects in the mass-bias corrected 53Cr/52Cr (μ53 Cr* of 5.2 ppm) and 54Cr/52Cr (μ54Cr* of 13.5 ppm) components used to infer chronometric and nucleosynthetic information in meteorites. To mitigate these fractionation effects, we developed strategic chemical sample pre-treatment procedures that ensure high and reproducible Cr recovery. This is achieved either through 1) effective promotion of Cr3+ by >5 days exposure to HNO3 —H2O2 solutions at room temperature, resulting in >~98% Cr recovery for most types of sample matrices tested using a cationic chromatographic retention strategy, or 2) formation of Cr(III)-Cl complexes through exposure to concentrated HCl at high temperature (>120 °C) for several hours, resulting in >97.5% Cr recovery using a chromatographic elution strategy that

  16. Isotopic equilibrium between precipitation and water vapor: evidence from continental rains in central Kenya

    NASA Astrophysics Data System (ADS)

    Soderberg, K.; Gerlein, C.; Kemeny, P. C.; Caylor, K. K.

    2013-12-01

    An accurate understanding of the relationships between the isotopic composition of liquid water and that of water vapor in the environment can help describe hydrologic processes across many scales. One such relationship is the isotopic equilibrium between falling raindrops and the surrounding vapor. The degree of equilibration is used to model the isotopic composition of precipitation in isotope-enable general circulation models and land-atmosphere exchange models. Although this equilibrium has been a topic of isotope hydrology research for more than four decades, few studies have included vapor measurements to validate modeling efforts. Recent advances in laser technology have allowed for in situ vapor measurements at high temporal resolution (e.g., >1 Hz). Here we present concomitant rain and vapor measurements for a series of 17 rain events during the 'Continental' rainy season (June through August) at Mpala Research Center in central Kenya. Rain samples (n=218) were collected at intervals of 2 to 35 minutes (median of 3 minutes) depending on the rain rate (0.4 to 10.5 mm/hr). The volume-weighted mean rain values for δ18O, δ2H and D-excess (δ2H - 8* δ18O) were 0.1 ‰, 10.7 ‰, and 10.1 ‰. These values are more enriched than the annual weighted means reported for the area (-2.2 ‰, -7.6 ‰, and 11.0 ‰, respectively). Vapor was measured continuously at ~2Hz (DLT-100, Los Gatos Research), with an inverted funnel intake 4m above the ground surface. The mean vapor isotopic composition during the rain events was -10.0 +/- 1.2 ‰ (1 σ) for δ18O and -73.9 +/- 7.0 ‰ for δ2H. The difference between the rain sample isotopic composition and that of liquid in isotopic equilibrium with the corresponding vapor at the ambient temperature was 0.8 +/- 2.2 ‰ for δ18O and 6.2 +/- 7.0 ‰ for δ2H. This disequilibrium was found to correlate with the natural log of rain rate (R2 of 0.26 for δ18O and 0.46 for δ2H), with lower rain rates having larger

  17. Equilibrium-disequilibrium relations in the Monte Rosa Granite, Western Alps: Petrological, Rb-Sr and stable isotope data

    USGS Publications Warehouse

    Frey, M.; Hunziker, J.C.; O'Neil, J.R.; Schwander, H.W.

    1976-01-01

    Nine samples from the Monte Rosa Granite have been investigated by microscopic, X-ray, wet chemical, electron microprobe, stable isotope and Rb-Sr and K-Ar methods. Two mineral assemblages have been distinguished by optical methods and dated as Permian and mid-Tertiary by means of Rb-Sr age determinations. The Permian assemblage comprises quartz, orthoclase, oligoclase, biotite, and muscovite whereas the Alpine assemblage comprises quartz, microcline, albite+epidote or oligoclase, biotite, and phengite. Disequilibrium between the Permian and Alpine mineral assemblages is documented by the following facts: (i) Two texturally distinguishable generations of white K-mica are 2 M muscovite (Si=3.1-3.2) and 2 M or 3 T phengite (Si=3.3-3.4). Five muscovites show Permian Rb-Sr ages and oxygen isotope fractionations indicating temperatures between 520 and 560 ?? C; however, K-Ar ages are mixed or rejuvenated. Phengite always shows mid-Tertiary Rb-Sr ages, (ii) Two biotite generations can be recognized, although textural evidence is often ambiguous. Three out of four texturally old biotites show mid-Tertiary Rb-Sr cooling ages while the oxygen isotopic fractionations point to Permian, mixed or Alpine temperatures, (iii) Comparison of radiogenic and stable isotope relations indicates that the radiogenic isotopes in the interlayer positions of the micas were mobilized during Alpine time without recrystallization, that is, without breaking Al-O or Si-O bonds. High Ti contents in young muscovites and biotites also indicate that the octahedral (and tetrahedral) sites remained undisturbed during rejuvenation. (iv) 'Isotopic reversals' in the order of O18 enrichment between K-feldspar and albite exist. Arguments for equilibrium during Permian time are meagre because of Alpine overprinting effects. Texturally old muscovites show high temperatures and Permian Rb-Sr ages in concordancy with Rb-Sr whole rock ages. For the tectonically least affected samples, excellent concordance

  18. Determination and application of the equilibrium oxygen isotope effect between water and sulfite

    NASA Astrophysics Data System (ADS)

    Wankel, Scott D.; Bradley, Alexander S.; Eldridge, Daniel L.; Johnston, David T.

    2014-01-01

    The information encoded by the two stable isotope systems in sulfate (δ34SSO4 and δ18OSO4) has been widely applied to aid reconstructions of both modern and ancient environments. Interpretation of δ18OSO4 records has been complicated by rapid oxygen isotope equilibration between sulfoxyanions and water. Specifically, the apparent relationship that develops between δ18OSO4 and δ18Owater during microbial sulfate reduction is thought to result from rapid oxygen isotope equilibrium between intracellular water and aqueous sulfite - a reactive intermediate of the sulfate reduction network that can back-react to produce sulfate. Here, we describe the oxygen equilibrium isotope effect between water and sulfite (referring to all the sum of all S(IV)-oxyanions including sulfite and both isomers and the dimer of bisulfite). Based on experiments conducted over a range of pH (4.5-9.8) and temperature (2-95 °C), where ε = 1000 * (α - 1), we find εSO3-H2O=13.61-0.299∗pH-0.081∗T °C. Thus, at a pH (7.0) and temperature (25 °C) typifying commonly used experimental conditions for sulfate reducing bacterial cultures, sulfite is enriched in 18O by 9.5‰ (±0.8‰) relative to ambient water. We examine the implication of these results in a sulfate reduction network that has been revised to reflect our understanding of the reactions involving oxygen. By evaluating previously published data within this new architecture, our results are consistent with previous suggestions of high reversibility of the sulfate reduction biochemical network. We also demonstrate that intracellular exchange rates between SO32- and water must be on average 1-3 orders of magnitude more rapid than intracellular fluxes of sulfate reduction intermediates and that kinetic isotope effects upstream of SO32- are required to explain previous laboratory and environmental studies of δ18OSO4 resulting as a consequence of sulfate reduction.

  19. Density Functional Theory Study of Controls on Equilibrium Fe Isotope Fractionation

    NASA Astrophysics Data System (ADS)

    Domagal-Goldman, S. D.; Kubicki, J. D.

    2006-12-01

    Previous molecular orbital/density functional theory (MO/DFT) calculations of Fe(III) and Fe(II) complexed with oxalate and catechol was used to predict and compare the equilibrium Fe isotope fractionation factors associated with changes to ligands bound to Fe and those associated with changes to the oxidation state of Fe. The predicted fractionation factors between Fe bound by different ligands was < 1.7‰ in vacuo and < 1.2‰ in solution. These values were consistently and significantly smaller than those for equilibrium between different oxidation states of Fe, predicted to be > 2.8‰ in vacuo and > 2.2‰ in solution. Curiously, a trend was originally found where 56Fe is partitioned into smaller ligands with lower Fe affinities and presumably weaker Fe-O bonds. This was the case for the ligands water, oxalate, and catechol, which show respectively increasing Fe affinities yet decreasing predicted 56Fe/^{54}Fe. Current research is using a model of a full siderophore to calculate the Fe isotope fractionation associated with organic complexation. Fractionation is more complicated upon the inclusion of the siderophore desferrioxamine B (DFOB). The high affinity of DFOB for Fe(III) results in the highest predicted fractionation for 56Fe of all the complexes studied, reversing the unexpected fractionation trend mentioned above. We present the results of a detailed analysis of the bonding between Fe(III) and the ligands bound to it. We use natural bond order (NBO) analysis to show why the smaller ligands result in a larger partitioning of 56Fe to smaller ligands, and why DFOB has the highest 56Fe partitioning. This study will help elucidate the molecular controls on Fe isotope fractionation, and as such will be useful in placing experimental work in theoretical context and in helping drive future research questions. Accordingly, the implications of our results for the use of Fe isotopes as a biomarker and as a tracer of ocean redox history will be discussed, as

  20. The early bird gets the shrimp: Confronting assumptions of isotopic equilibrium and homogeneity in a wild bird population

    USGS Publications Warehouse

    Wunder, Michael B.; Jehl, Joseph R.; Stricker, Craig A.

    2012-01-01

    1. Because stable isotope distributions in organic material vary systematically across energy gradients that exist in ecosystems, community and population structures, and in individual physiological systems, isotope values in animal tissues have helped address a broad range of questions in animal ecology. It follows that every tissue sample provides an isotopic profile that can be used to study dietary or movement histories of individual animals. Interpretations of these profiles depend on the assumption that metabolic pools are isotopically well mixed and in equilibrium with dietary resources prior to tissue synthesis, and they extend to the population level by assuming isotope profiles are identically distributed for animals using the same proximal dietary resource. As these assumptions are never fully met, studying structure in the variance of tissue isotope values from wild populations is informative. 2. We studied variation in δ13C, δ15N, δ2H and δ18O data for feathers from a population of eared grebes (Podiceps nigricollis) that migrate to Great Salt Lake each fall to moult feathers. During this time, they cannot fly and feed almost exclusively on superabundant brine shrimp (Artemia franciscana). The ecological simplicity of this situation minimized the usual spatial and trophic complexities often present in natural studies of feather isotope values. 3. Ranges and variances of isotope values for the feathers were larger than those from previously published studies that report feather isotopic variance, but they were bimodally distributed in all isotope dimensions. Isotope values for proximal dietary resources and local surface water show that some of the feathers we assumed to have been grown locally must have been grown before birds reached isotopic equilibrium with local diet or immediately prior to arrival at Great Salt Lake. 4. Our study provides novel insights about resource use strategies in eared grebes during migration. More generally, it

  1. The early bird gets the shrimp: confronting assumptions of isotopic equilibrium and homogeneity in a wild bird population.

    PubMed

    Wunder, Michael B; Jehl, Joseph R; Stricker, Craig A

    2012-11-01

    1. Because stable isotope distributions in organic material vary systematically across energy gradients that exist in ecosystems, community and population structures, and in individual physiological systems, isotope values in animal tissues have helped address a broad range of questions in animal ecology. It follows that every tissue sample provides an isotopic profile that can be used to study dietary or movement histories of individual animals. Interpretations of these profiles depend on the assumption that metabolic pools are isotopically well mixed and in equilibrium with dietary resources prior to tissue synthesis, and they extend to the population level by assuming isotope profiles are identically distributed for animals using the same proximal dietary resource. As these assumptions are never fully met, studying structure in the variance of tissue isotope values from wild populations is informative. 2. We studied variation in δ(13) C, δ(15) N, δ(2) H and δ(18) O data for feathers from a population of eared grebes (Podiceps nigricollis) that migrate to Great Salt Lake each fall to moult feathers. During this time, they cannot fly and feed almost exclusively on superabundant brine shrimp (Artemia franciscana). The ecological simplicity of this situation minimized the usual spatial and trophic complexities often present in natural studies of feather isotope values. 3. Ranges and variances of isotope values for the feathers were larger than those from previously published studies that report feather isotopic variance, but they were bimodally distributed in all isotope dimensions. Isotope values for proximal dietary resources and local surface water show that some of the feathers we assumed to have been grown locally must have been grown before birds reached isotopic equilibrium with local diet or immediately prior to arrival at Great Salt Lake. 4. Our study provides novel insights about resource use strategies in eared grebes during migration. More generally

  2. Device and method for separating oxygen isotopes

    DOEpatents

    Rockwood, Stephen D.; Sander, Robert K.

    1984-01-01

    A device and method for separating oxygen isotopes with an ArF laser which produces coherent radiation at approximately 193 nm. The output of the ArF laser is filtered in natural air and applied to an irradiation cell where it preferentially photodissociates molecules of oxygen gas containing .sup.17 O or .sup.18 O oxygen nuclides. A scavenger such as O.sub.2, CO or ethylene is used to collect the preferentially dissociated oxygen atoms and recycled to produce isotopically enriched molecular oxygen gas. Other embodiments utilize an ArF laser which is narrowly tuned with a prism or diffraction grating to preferentially photodissociate desired isotopes. Similarly, desired mixtures of isotopic gas can be used as a filter to photodissociate enriched preselected isotopes of oxygen.

  3. Ab initio path-integral calculations of kinetic and equilibrium isotope effects on base-catalyzed RNA transphosphorylation models.

    PubMed

    Wong, Kin-Yiu; Xu, Yuqing; York, Darrin M

    2014-06-30

    Detailed understandings of the reaction mechanisms of RNA catalysis in various environments can have profound importance for many applications, ranging from the design of new biotechnologies to the unraveling of the evolutionary origin of life. An integral step in the nucleolytic RNA catalysis is self-cleavage of RNA strands by 2'-O-transphosphorylation. Key to elucidating a reaction mechanism is determining the molecular structure and bonding characteristics of transition state. A direct and powerful probe of transition state is measuring isotope effects on biochemical reactions, particularly if we can reproduce isotope effect values from quantum calculations. This article significantly extends the scope of our previous joint experimental and theoretical work in examining isotope effects on enzymatic and nonenzymatic 2'-O-transphosphorylation reaction models that mimic reactions catalyzed by RNA enzymes (ribozymes), and protein enzymes such as ribonuclease A (RNase A). Native reactions are studied, as well as reactions with thio substitutions representing chemical modifications often used in experiments to probe mechanism. Here, we report and compare results from eight levels of electronic-structure calculations for constructing the potential energy surfaces in kinetic and equilibrium isotope effects (KIE and EIE) computations, including a "gold-standard" coupled-cluster level of theory [CCSD(T)]. In addition to the widely used Bigeleisen equation for estimating KIE and EIE values, internuclear anharmonicity and quantum tunneling effects were also computed using our recently developed ab initio path-integral method, that is, automated integration-free path-integral method. The results of this work establish an important set of benchmarks that serve to guide calculations of KIE and EIE for RNA catalysis.

  4. Feasibility of Isotopic Measurements: Graphite Isotopic Ratio Method

    SciTech Connect

    Wood, Thomas W.; Gerlach, David C.; Reid, Bruce D.; Morgan, W. C.

    2001-04-30

    This report addresses the feasibility of the laboratory measurements of isotopic ratios for selected trace constituents in irradiated nuclear-grade graphite, based on the results of a proof-of-principal experiment completed at Pacific Northwest National Laboratory (PNNL) in 1994. The estimation of graphite fluence through measurement of isotopic ratio changes in the impurity elements in the nuclear-grade graphite is referred to as the Graphite Isotope Ratio Method (GIRM). Combined with reactor core and fuel information, GIRM measurements can be employed to estimate cumulative materials production in graphite moderated reactors. This report documents the laboratory procedures and results from the initial measurements of irradiated graphite samples. The irradiated graphite samples were obtained from the C Reactor (one of several production reactors at Hanford) and from the French G-2 Reactor located at Marcoule. Analysis of the irradiated graphite samples indicated that replicable measurements of isotope ratios could be obtained from the fluence sensitive elements of Ti, Ca, Sr, and Ba. While these impurity elements are present in the nuclear-grade graphite in very low concentrations, measurement precision was typically on the order of a few tenths of a percent to just over 1 percent. Replicability of the measurements was also very good with measured values differing by less than 0.5 percent. The overall results of this initial proof-of-principal experiment are sufficiently encouraging that a demonstration of GIRM on a reactor scale basis is planned for FY-95.

  5. In Equilibrium Stable Isotope Chemistry of The Deep Water Coral Stylaster Sp. From Rockall Trough: Paleoceanographic Implications

    NASA Astrophysics Data System (ADS)

    Mienis, F.

    Living corals, molluscs and associated water samples were collected from deep sea coral reefs along the margins of Rockall Trough (N. Atlantic). Oxygen (d18O) and carbon (d13C) isotope analyses of seawater and skeletal CaCO3 indicate that vari- ous organisms do not precipitate CaCO3 in isotopic equilibrium with host water. Par- ticularly the most abundant coral genera Lophelia sp and Madrepora sp fractionate markedly, as was already observed by a number of previous studies. However, our new data shows that the coral genus Stylaster, occuring in small numbers in the Rock- all Trough area, is in isotopic equilibrium with seawater. Like for the aragonitic bi- valves and gastropods inhabiting the same deep water reefs, microsampling of growth banded Stylaster specimens can be applied to obtain high resolution time series of in-equilibrium d13C and d18O data covering the life span of individual specimens.

  6. Equilibrium Fe isotope fractionation between inorganic aqueous Fe(III) and the siderophore complex, Fe(III)-desferrioxamine B

    NASA Astrophysics Data System (ADS)

    Dideriksen, K.; Baker, J. A.; Stipp, S. L. S.

    2008-05-01

    In oxic oceans, most of the dissolved iron (Fe) exists as complexes with siderophore-like, strongly coordinating organic ligands. Thus, the isotope composition of the little amount of free inorganic Fe that is available for precipitation and preservation in the geological record may largely be controlled by isotope fractionation between the free and complexed iron. We have determined the equilibrium Fe isotope fractionation induced by organic ligand activity in experiments with solutions having co-existing inorganic Fe(III) species and siderophore complexes, Fe-desferrioxamine B (at pH 2). The two differently complexed Fe(III) pools were separated by addition of Na 2CO 3, which led to immediate precipitation of the inorganic Fe without causing significant dissociation of Fe-desferrioxamine complexes. Experiments using enriched 57Fe tracer showed that isotopic equilibration between the 57Fe-labelled inorganic species and the isotopically "normal" siderophore-bound Fe was rapid during the first few seconds and then became slower. Consequently, the data fitted poorly to first and second order reaction equations. However, with a two-stage reaction, the data fit perfectly with a first order equation for the slower stage, indicating that approximately 40% re-equilibration may take place during the separation of the two pools. To further test if the induced precipitation leads to experimental artefacts, the fractionation during precipitation of inorganic Fe was determined. Assuming a Rayleigh-type fractionation during precipitation, this experiment yielded an isotope fractionation factor of α56Fe solution-solid = 1.00027. Calculations based on these results indicate that isotopic re-equilibration is unlikely to significantly affect our determined equilibrium Fe isotope fractionation between inorganically and organically complexed Fe. To determine the equilibrium Fe isotope fractionation between inorganically and organically bound Fe(III), experiments with variable

  7. Explicit Integration of Extremely Stiff Reaction Networks: Partial Equilibrium Methods

    SciTech Connect

    Guidry, Mike W; Billings, J. J.; Hix, William Raphael

    2013-01-01

    In two preceding papers [1,2] we have shown that, when reaction networks are well removed from equilibrium, explicit asymptotic and quasi-steady-state approximations can give algebraically stabilized integration schemes that rival standard implicit methods in accuracy and speed for extremely stiff systems. However, we also showed that these explicit methods remain accurate but are no longer competitive in speed as the network approaches equilibrium. In this paper we analyze this failure and show that it is associated with the presence of fast equilibration timescales that neither asymptotic nor quasi-steady-state approximations are able to remove efficiently from the numerical integration. Based on this understanding, we develop a partial equilibrium method to deal effectively with the new partial equilibrium methods, give an integration scheme that plausibly can deal with the stiffest networks, even in the approach to equilibrium, with accuracy and speed competitive with that of implicit methods. Thus we demonstrate that algebraically stabilized explicit methods may offer alternatives to implicit integration of even extremely stiff systems, and that these methods may permit integration of much larger networks than have been feasible previously in a variety of fields.

  8. Autoinduced catalysis and inverse equilibrium isotope effect in the frustrated Lewis pair catalyzed hydrogenation of imines.

    PubMed

    Tussing, Sebastian; Greb, Lutz; Tamke, Sergej; Schirmer, Birgitta; Muhle-Goll, Claudia; Luy, Burkhard; Paradies, Jan

    2015-05-26

    The frustrated Lewis pair (FLP)-catalyzed hydrogenation and deuteration of N-benzylidene-tert-butylamine (2) was kinetically investigated by using the three boranes B(C6F5)3 (1), B(2,4,6-F3-C6H2)3 (4), and B(2,6-F2-C6H3)3 (5) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol(-1)) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect.

  9. Stark broadening for diagnostics of the electron density in non-equilibrium plasma utilizing isotope hydrogen alpha lines

    SciTech Connect

    Yang, Lin; Tan, Xiaohua; Wan, Xiang; Chen, Lei; Jin, Dazhi; Qian, Muyang; Li, Gongping

    2014-04-28

    Two Stark broadening parameters including FWHM (full width at half maximum) and FWHA (full width at half area) of isotope hydrogen alpha lines are simultaneously introduced to determine the electron density of a pulsed vacuum arc jet. To estimate the gas temperature, the rotational temperature of the C{sub 2} Swan system is fit to 2500 ± 100 K. A modified Boltzmann-plot method with b{sub i}-factor is introduced to determine the modified electron temperature. The comparison between results of atomic and ionic lines indicates the jet is in partial local thermodynamic equilibrium and the electron temperature is close to 13 000 ± 400 K. Based on the computational results of Gig-Card calculation, a simple and precise interpolation algorithm for the discrete-points tables can be constructed to obtain the traditional n{sub e}-T{sub e} diagnostic maps of two Stark broadening parameters. The results from FWHA formula by the direct use of FWHM = FWHA and these from the diagnostic map are different. It can be attributed to the imprecise FWHA formula form and the deviation between FWHM and FWHA. The variation of the reduced mass pair due to the non-equilibrium effect contributes to the difference of the results derived from two hydrogen isotope alpha lines. Based on the Stark broadening analysis in this work, a corrected method is set up to determine n{sub e} of (1.10 ± 0.08) × 10{sup 21} m{sup −3}, the reference reduced mass μ{sub 0} pair of (3.30 ± 0.82 and 1.65 ± 0.41), and the ion kinetic temperature of 7900 ± 1800 K.

  10. Theoretical estimation for equilibrium Mo isotope fractionations between dissolved Mo species and the adsorbed complexes on (Fe,Mn)-oxyhydroxides

    NASA Astrophysics Data System (ADS)

    Tang, M.; Liu, Y.

    2009-12-01

    Although Mo isotopes have been increasingly used as a paleoredox proxy in the study of paleo-oceanographic condition changes (Barling et al., 2001; Siebert et al., 2003, 2005,2006; Arnold et al., 2004; Poulson et al., 2006), some very basic aspects of Mo isotopes geochemistry have not been obtained yet. First, although there are several previous studies on equilibrium Mo isotope fractionation factors(Tossell,2005; Weeks et al.,2007; Wasylenki et al.,2008), these studies were dealing with situations in vacuum and we find unfortunately the solvation effects for Ge species in solution cannot be ignored. Therefore, accurate Ge fractionation factors are actually not determined yet. Second, except the dominant dissolved Mo species in seawater which is known as molybdate ion (MoO42-), the forms of possible other minor species remain elusive. Third, the Mo removal mechanisms from seawater are only known for the anoxia and euxinic conditions (e.g. Helz et al., 1996; Zheng et al., 2000), the Mo removal mechanism under oxic condition are still arguing. Fourth, the adsorption effects on Mo isotope fractionation are almost completely unknown. Especially, without the adsorption fractionation knowledge, it is difficult to understand many distinct fractionations found in a number of geologic systems and it is difficult to explain the exceptionally long residence time of Mo in seawater. Urey model or Bigeleisen-Mayer equation based theoretical method and the super-molecule clusters are used to precisely evaluate the fractionation factors. The B3LYP/(6-311+G(2df,p),LANL2DZ) level method is used for frequencies calculation. 24 water molecules are used to form the supermolecues surrounding the Mo species. At least 4 different conformers for each supermolecule are used to prevent the errors from the diversity of configurations in solution. This study provides accurate equilibrium Mo isotope fractionation factors between possible dissolved Mo species and the adsorbed Mo species on the

  11. A Straightforward Method to Determine Equilibrium Constants from Spectrophotometric Data

    NASA Astrophysics Data System (ADS)

    Keszei, E.; Takács, M. G.; Vizkeleti, B.

    2000-07-01

    Spectrophotometry provides reliable information on the equilibrium concentration in chemically reacting mixtures. However, the widely used traditional linearized models to determine the equilibrium constant from spectrophotometric data do not provide optimal information and unnecessarily complicate data evaluation for students. In this paper we show an easy and straightforward inference method, which makes use only of Beer's Law and an elementary mathematical treatment of the problem. Though the resulting parameter estimation is nonlinear with respect to the equilibrium constant, the commercial availability of many nonlinear parameter estimation software packages eliminates the need for the student to bother with either mathematical or numerical details. Adding a suitable spectral shape function to the model describing equilibrium further facilitates the use of the proposed method and makes it an easy task to determine the components' spectra from equilibrium measurements. Three practical examples are treated in detail in the online version. They illustrate how the method works at different complexity levels and are easy to install in undergraduate physical chemistry labs.

  12. Calculation of equilibrium stable isotope partition function ratios for aqueous zinc complexes and metallic zinc

    NASA Astrophysics Data System (ADS)

    Black, Jay R.; Kavner, Abby; Schauble, Edwin A.

    2011-02-01

    The goal of this study is to determine reduced partition function ratios for a variety of species of zinc, both as a metal and in aqueous solutions in order to calculate equilibrium stable isotope partitioning. We present calculations of the magnitude of Zn stable-isotope fractionation ( 66,67,68Zn/ 64Zn) between aqueous species and metallic zinc using measured vibrational spectra (fit from neutron scattering studies of metallic zinc) and a variety of electronic structure models. The results show that the reduced metal, Zn(0), will be light in equilibrium with oxidized Zn(II) aqueous species, with the best estimates for the Zn(II)-Zn(0) fractionation between hexaquo species and metallic zinc being Δ 66/64Zn aq-metal ˜ 1.6‰ at 25 °C, and Δ 66/64Zn aq-metal ˜ 0.8‰ between the tetrachloro zinc complex and metallic zinc at 25 °C using B3LYP/aug-cc-pVDZ level of theory and basis set. To examine the behavior of zinc in various aqueous solution chemistries, models for Zn(II) complex speciation were used to determine which species are thermodynamically favorable and abundant under a variety of different conditions relevant to natural waters, experimental and industrial solutions. The optimal molecular geometries for [Zn(H 2O) 6] 2+, [Zn(H 2O) 6]·SO 4, [ZnCl 4] 2- and [Zn(H 2O) 3(C 3H 5O(COO) 3)] - complexes in various states of solvation, protonation and coordination were calculated at various levels of electronic structure theory and basis set size. Isotopic reduced partition function ratios were calculated from frequency analyses of these optimized structures. Increasing the basis set size typically led to a decrease in the calculated reduced partition function ratios of ˜0.5‰ with values approaching a plateau using the aug-cc-pVDZ basis set or larger. The widest range of species were studied at the B3LYP/LAN2DZ/6-31G ∗ level of theory and basis-set size for comparison. Aqueous zinc complexes where oxygen is bound to the metal center tended to have the

  13. Stellarator expansion methods for MHD equilibrium and stability calculations

    SciTech Connect

    Lynch, V.E.; Charlton, L.A.; Hicks, H.R.; Holmes, J.A.; Carreras, B.A.; Hender, T.C.; Garcia, L.

    1986-03-01

    Two methods for performing stellarator expansion, or average method, MHD calculations are described. The first method includes the calculation of vacuum, equilibrium, and stability, using the Greene and Johnson stellarator expansion in which the equilibrium is reduced to a 2-D problem by averaging over the geometric toroidal angle in real space coordinates. In the second method, the average is performed in a system of vacuum magnetic coordinates. Both methods are implemented to utilize realistic vacuum field information, making them applicable to configuration studies and machine design, as well as to basic research. Illustrative examples are presented to detail the sensitivities of the calculations to physical parameters and to show numerical convergence and the comparison of these methods with each other and with other methods.

  14. EQUILIBRIUM AND NONEQUILIBRIUM FOUNDATIONS OF FREE ENERGY COMPUTATIONAL METHODS

    SciTech Connect

    C. JARZYNSKI

    2001-03-01

    Statistical mechanics provides a rigorous framework for the numerical estimation of free energy differences in complex systems such as biomolecules. This paper presents a brief review of the statistical mechanical identities underlying a number of techniques for computing free energy differences. Both equilibrium and nonequilibrium methods are covered.

  15. Hybrid Method for Tokamak MHD Equilibrium Configuration Reconstruction

    NASA Astrophysics Data System (ADS)

    He, Hong-Da; Dong, Jia-Qi; Zhang, Jin-Hua; Jiang, Hai-Bin

    2007-02-01

    A hybrid method for tokamak MHD equilibrium configuration reconstruction is proposed and employed in the modified EFIT code. This method uses the free boundary tokamak equilibrium configuration reconstruction algorithm with one boundary point fixed. The results show that the position of the fixed point has explicit effects on the reconstructed divertor configurations. In particular, the separatrix of the reconstructed divertor configuration precisely passes the required position when the hybrid method is used in the reconstruction. The profiles of plasma parameters such as pressure and safety factor for reconstructed HL-2A tokamak configurations with the hybrid and the free boundary methods are compared. The possibility for applications of the method to swing the separatrix strike point on the divertor target plate is discussed.

  16. Meshless method for solving fixed boundary problem of plasma equilibrium

    NASA Astrophysics Data System (ADS)

    Imazawa, Ryota; Kawano, Yasunori; Itami, Kiyoshi

    2015-07-01

    This study solves the Grad-Shafranov equation with a fixed plasma boundary by utilizing a meshless method for the first time. Previous studies have utilized a finite element method (FEM) to solve an equilibrium inside the fixed separatrix. In order to avoid difficulties of FEM (such as mesh problem, difficulty of coding, expensive calculation cost), this study focuses on the meshless methods, especially RBF-MFS and KANSA's method to solve the fixed boundary problem. The results showed that CPU time of the meshless methods was ten to one hundred times shorter than that of FEM to obtain the same accuracy.

  17. Study report on a double isotope method of calcium absorption

    NASA Technical Reports Server (NTRS)

    1978-01-01

    Some of the pros and cons of three methods to study gastrointestinal calcium absorption are briefly discussed. The methods are: (1) a balance study; (2) a single isotope method; and (3) a double isotope method. A procedure for the double isotope method is also included.

  18. ISOTOPE CONVERSION DEVICE AND METHOD

    DOEpatents

    Wigner, E.P.; Ohlinger, L.A.

    1958-11-11

    Homogeneous nuclear reactors are discussed, and an apparatus and method of operation are descrlbed. The apparatus consists essentially of a reaction tank, a heat exchanger connected to the reaction tank and two separate surge tanks connected to the heat exchanger. An oscillating differential pressure is applied to the surge tanks so that a portion of the homogeneous flssionable solution is circulated through the heat exchanger and reaction tank while maintaining sufficient solution in the reaction tank to sustain a controlled fission chain reaction. The reaction tank is disposed within another tank containing a neutron absorbing material through which coolant fluid is circulated, the outer tank being provided with means to permit and cause rotation thereof due to the circulation of the coolant therethrough.

  19. High-Temperature Fractionation of Iron Isotopes During Metal Segregation From a Silicate Melt: Experimental Study of Kinetic and Equilibrium Fractionation

    NASA Astrophysics Data System (ADS)

    Roskosz, M.; Luais, B.; Watson, H.; Toplis, M. J.; Alexander, C. M.; Mysen, B. O.

    2005-12-01

    Advances in mass spectrometry make it possible to measure isotopic variations of iron in meteoritic and igneous materials. However, interpreting these data is hampered by a lack of theoretical and experimental knowledge concerning how Fe isotopes fractionate during magmatic processes. As a first step in this direction we have performed experiments in which metallic iron was reduced and segregated from a silicate melt at one bar as a function of f(O2) and time. The starting material was a glass of anorthite-diopside eutectic composition, to which 9 wt% Fe2O3 was added. Experiments were performed at 1500 circC and f(O2) in the range 10-0.7 to 10-8 bars. A proportion of this iron is extracted through formation of an alloy with the Pt-capsule in which the melt was held. The silicate and metallic portions were physically separated and bulk analyses of each fraction performed using standard MC-ICP-MS methods. Furthermore, a Cameca 6f ion microprobe was used to measure isotopic profiles in metallic samples, such that kinetic and equilibrium effects may be disentangled and quantified. Large isotopic variations are observed and attributed to kinetic fractionation during incorporation of iron into the initially Fe-free Pt-capsule. This process leads to the formation of isotopically light metal and a heavy silicate. For instance, in samples heat-treated for 24 hours, metal fractions have δ56Fe/54Fe from 0 to -2‰, whereas silicate fractions have δ56Fe/54Fe from 0 to 4.8‰. These values are positively correlated with the fraction of iron lost to the platinum. Ion-probe analyses and time-series experiments confirm that Fe isotopes are strongly fractionated during diffusion of Fe in the Pt,Fe alloy, and the observed profiles are used to calculate the diffusion coefficients of individual iron isotopes. With increasing time at fixed oxygen fugacity, iron in the alloy reaches a constant isotopic composition. At these conditions, assumed to represent equilibrium, iron in the

  20. Theoretical calculation of oxygen equilibrium isotope fractionation factors involving various NOy molecules, radOH, and H2O and its implications for isotope variations in atmospheric nitrate

    NASA Astrophysics Data System (ADS)

    Walters, Wendell W.; Michalski, Greg

    2016-10-01

    The oxygen stable isotope composition (δ18O) of nitrogen oxides [NOx = nitric oxide (NO) + nitrogen dioxide (NO2)] and their oxidation products (NOy = NOx + nitric acid (HNO3) + particulate nitrate (p-NO3-) + nitrate radical (NO3) + dinitrogen pentoxide (N2O5) + nitrous acid (HONO) + …) have been shown to be a useful tool for inferring the proportion of NOx that is oxidized by ozone (O3). However, isotopic fractionation processes may have an influence on δ18O of various NOy molecules and other atmospheric O-bearing molecules pertinent to NOx oxidation chemistry. Here we have evaluated the impacts of O isotopic exchange involving NOy molecules, the hydroxyl radical (radOH), and water (H2O) using reduced partition function ratios (xβ) calculated by hybrid density functional theory. Assuming atmospheric isotopic equilibrium is achieved between NO and NO2 during the daytime, and NO2, NO3, and N2O5 during the nighttime, δ18O-δ15N compositions were predicted for the major atmospheric nitrate formation pathways using our calculated exchange fractionation factors and isotopic mass-balance. Our equilibrium model predicts that various atmospheric nitrate formation pathways, including NO2 + radOH → HNO3, N2O5 + H2O + surface → 2HNO3, and NO3 + R → HNO3 + Rrad will yield distinctive δ18O-δ15N compositions. Our calculated δ18O-δ15N compositions match well with previous atmospheric nitrate measurements, and will potentially help better understand the role oxidation chemistry plays on the N and O isotopic composition of atmospheric nitrate.

  1. The procedure and results of calculations of the equilibrium isotopic composition of a demonstration subcritical molten salt reactor

    NASA Astrophysics Data System (ADS)

    Nevinitsa, V. A.; Dudnikov, A. A.; Blandinskiy, V. Yu.; Balanin, A. L.; Alekseev, P. N.; Titarenko, Yu. E.; Batyaev, V. F.; Pavlov, K. V.; Titarenko, A. Yu.

    2015-12-01

    A subcritical molten salt reactor with an external neutron source is studied computationally as a facility for incineration and transmutation of minor actinides from spent nuclear fuel of reactors of VVER-1000 type and for producing 233U from 232Th. The reactor configuration is chosen, the requirements to be imposed on the external neutron source are formulated, and the equilibrium isotopic composition of heavy nuclides and the key parameters of the fuel cycle are calculated.

  2. The procedure and results of calculations of the equilibrium isotopic composition of a demonstration subcritical molten salt reactor

    SciTech Connect

    Nevinitsa, V. A. Dudnikov, A. A.; Blandinskiy, V. Yu.; Balanin, A. L.; Alekseev, P. N.; Titarenko, Yu. E.; Batyaev, V. F.; Pavlov, K. V.; Titarenko, A. Yu.

    2015-12-15

    A subcritical molten salt reactor with an external neutron source is studied computationally as a facility for incineration and transmutation of minor actinides from spent nuclear fuel of reactors of VVER-1000 type and for producing {sup 233}U from {sup 232}Th. The reactor configuration is chosen, the requirements to be imposed on the external neutron source are formulated, and the equilibrium isotopic composition of heavy nuclides and the key parameters of the fuel cycle are calculated.

  3. First-principles investigation of equilibrium isotopic fractionation of Si and O isotopes among quartz, albite, anthorite, orthoenstatite, clinoenstatite, olivine, and zircon

    NASA Astrophysics Data System (ADS)

    Qin, T.; Wu, F.; Huang, F.; Wu, Z.

    2013-12-01

    Silicon is one of the most abundant elements in the crust and mantle. Because of advance of high precision analytical technique, Si isotope geochemistry has been widely applied into studies of a variety of important processes including planetary formation, core-mantle segregation, magmatism, and weathering of the crust. In order to better understanding Si isotope data in high temperature rock and mineral samples, it is critical to obtain equilibrium fractionation factors of Si isotopes among silicate minerals. However, experimental studies on calibrating Si isotope fractionation factors are still no available in literature. Here we used first-principles calculation based on density functional theory to investigate Si isotope fractionation factors among silicate minerals commonly occurring in magmatism in crustal level. These minerals include quartz, albite, anthorite, orthoenstatite, clinoenstatite, olivine, and zircon. We also calculated oxygen isotope fractionation factors among these minerals. Our results indicate the 18O-enrichment order among these minerals follows sequence of quartz > albite > anorthite > enstatite> zircon > olivine, showing good agreement with the data from previous experiments or natural sample measurement. For Si isotopes, our work shows that the 30Si-enrichment order in these minerals follows sequence of quartz > albite > anorthite > olivine ~ zircon > enstatite > diopside. These results are consistent with previous calculation [1] and observation from natural minerals. For example, Δ30Sianorthite-olivine = 0.2‰ at 1000oC based on our calculation, well consistent with value from the study of Skaergaard Intrusion (Δ30Siplagioclase-olivine = 0.24-27‰) [2] at same temperature. Our calculation indicates that Si isotopes can be significantly fractionated among silicate minerals during high temperature geochemical processes. References: [1] M. Méheut et al (2007), GCA 71:3170-3180. [2] P. S. Savage et al (2011), GCA 75:6124-6139.

  4. Effect of parent body evolution on equilibrium and kinetic isotope fractionation: a combined Ni and Fe isotope study of iron and stony-iron meteorites

    NASA Astrophysics Data System (ADS)

    Chernonozhkin, Stepan M.; Goderis, Steven; Costas-Rodríguez, Marta; Claeys, Philippe; Vanhaecke, Frank

    2016-08-01

    resolvable differences, similar in magnitude but opposite in sign (Δ56/54Femet-oliv of +0.178 ± 0.092‰ and Δ60/58Nimet-oliv of -0.212 ± 0.082‰, 2SD). As such, the heavier Fe isotope ratios for the metal (δ56/54Fe = +0.023‰ to +0.247‰) and lighter values for the corresponding olivines (δ56/54Fe = -0.155‰ to -0.075‰) are interpreted to reflect later-stage Fe isotopic re-equilibration between these phases, rather than a pristine record of mantle-core differentiation. In the case of mesosiderites, the similarly lighter Ni and Fe isotopic signatures found for the silicate phase (-0.149‰ to +0.023‰ for δ60/58Ni, -0.214‰ to -0.149‰ for δ56/54Fe) compared to the metal phase (+0.168‰ to +0.191‰ for δ60/58Ni, +0.018‰ to +0.120‰ for δ56/54Fe) likely result from Fe and Ni diffusion. Overall, the Fe and Ni isotopic compositions of iron-rich meteorites reflect multiple, often superimposed, processes of equilibrium or kinetic nature, illustrating convoluted parent body histories and late-stage interaction between early-formed planetesimal reservoirs.

  5. Method for production of an isotopically enriched compound

    DOEpatents

    Watrous, Matthew G.

    2012-12-11

    A method is presented for producing and isolating an isotopically enriched compound of a desired isotope from a parent radionuclide. The method includes forming, or placing, a precipitate containing a parent radionuclide of the desired daughter isotope in a first reaction zone and allowing sufficient time for the parent to decay into the desired gaseous daughter radioisotope. The method further contemplates collecting the desired daughter isotope as a solid in a second reaction zone through the application of temperatures below the freezing point of the desired isotope to a second reaction zone that is connected to the first reaction zone. Specifically, a method is presented for producing isotopically enriched compounds of xenon, including the radioactive isotope Xe-131m and the stable isotope Xe-131.

  6. Bayesian methods for examining Hardy-Weinberg equilibrium.

    PubMed

    Wakefield, Jon

    2010-03-01

    Testing for Hardy-Weinberg equilibrium is ubiquitous and has traditionally been carried out via frequentist approaches. However, the discreteness of the sample space means that uniformity of p-values under the null cannot be assumed, with enumeration of all possible counts, conditional on the minor allele count, offering a computationally expensive way of p-value calibration. In addition, the interpretation of the subsequent p-values, and choice of significance threshold depends critically on sample size, because equilibrium will always be rejected at conventional levels with large sample sizes. We argue for a Bayesian approach using both Bayes factors, and the examination of posterior distributions. We describe simple conjugate approaches, and methods based on importance sampling Monte Carlo. The former are convenient because they yield closed-form expressions for Bayes factors, which allow their application to a large number of single nucleotide polymorphisms (SNPs), in particular in genome-wide contexts. We also describe straightforward direct sampling methods for examining posterior distributions of parameters of interest. For large numbers of alleles at a locus we resort to Markov chain Monte Carlo. We discuss a number of possibilities for prior specification, and apply the suggested methods to a number of real datasets.

  7. Gravitational stability computed through the limit equilibrium method revisited

    NASA Astrophysics Data System (ADS)

    Tinti, Stefano; Manucci, Anna

    2006-01-01

    The stability of slopes is a problem of great relevance for geologists and geophysicists as well as for geotechnical and geoenvironmental engineers. The classical approaches are the method of limit equilibrium, and the finite-element and finite-difference analyses of deformations. Since the former is computationally simpler and less expensive, it is more widely used in common practice, though it has some weakness points from a theoretical point of view. Essential in this technique is the definition and computation of the factor of safety F for the slope, a parameter indicating that the slope is stable, if it is larger than unity. The method is known to have not a unique solution, but it is common belief that the safety factors associated with all the solutions fulfilling the basic equilibrium equations do not differ more than 5-10 per cent from each other, which is a range of variability considered acceptable by most. Here the non-uniqueness of the solution is discussed, and it is shown that the magnitude range of F can be so large as to undermine the meaning of the safety factor criterion. The classical limit equilibrium methods based on the assumptions of cutting the sliding body into a set of vertical slices are revised, and the new concept of minimum lithostatic deviation (MLD) is introduced as a means to mitigate the effect of non-uniqueness. The paper suggests that the proper solution to the problem is the one that satisfies the equilibrium equations and minimizes the lithostatic deviation that is defined here as the ratio of the average intensity of the interslice forces and the total weight of the body. Accordingly, the factor of safety F associated with such a solution is suggested to be the value appropriate to evaluate the stability of the slope. Remarkably, the MLD principle gives us the means to introduce a completely revolutionary approach to study stability. We derive expressions that account for gravitational loading, and for additional effects such

  8. A Variational Method in Out-of-Equilibrium Physical Systems

    PubMed Central

    Pinheiro, Mario J.

    2013-01-01

    We propose a new variational principle for out-of-equilibrium dynamic systems that are fundamentally based on the method of Lagrange multipliers applied to the total entropy of an ensemble of particles. However, we use the fundamental equation of thermodynamics on differential forms, considering U and S as 0-forms. We obtain a set of two first order differential equations that reveal the same formal symplectic structure shared by classical mechanics, fluid mechanics and thermodynamics. From this approach, a topological torsion current emerges of the form , where Aj and ωk denote the components of the vector potential (gravitational and/or electromagnetic) and where ω denotes the angular velocity of the accelerated frame. We derive a special form of the Umov-Poynting theorem for rotating gravito-electromagnetic systems. The variational method is then applied to clarify the working mechanism of particular devices. PMID:24316718

  9. Minimizing the Free Energy: A Computer Method for Teaching Chemical Equilibrium Concepts.

    ERIC Educational Resources Information Center

    Heald, Emerson F.

    1978-01-01

    Presents a computer method for teaching chemical equilibrium concepts using material balance conditions and the minimization of the free energy. Method for the calculation of chemical equilibrium, the computer program used to solve equilibrium problems and applications of the method are also included. (HM)

  10. Method of enhancing selective isotope desorption from metals

    DOEpatents

    Knize, Randall J.; Cecchi, Joseph L.

    1984-01-01

    A method of enhancing the thermal desorption of a first isotope of a diatomic gas from a metal comprises the steps of (a) establishing a partial pressure of a second isotope of the diatomic gas in vicinity of the metal; heating the metal to a temperature such that the first isotope is desorbed from the metal; and reducing the partial pressure of the desorbed first isotope while maintaining the partial pressure of the second isotope substantially constant. The method is especially useful for enhancing the desorption of tritium from the Zr-Al getter in a plasma confinement device.

  11. Effect of magnesium ions on the stable oxygen isotope equilibrium between dissolved inorganic carbon species and water.

    NASA Astrophysics Data System (ADS)

    Uchikawa, Joji; Zeebe, Richard

    2010-05-01

    Stable oxygen isotope (δ18O) values of foraminiferal calcites, which represent one of the most fundamental paleoceanographic tools to reconstruct ancient seawater temperatures, are influenced by seawater pH variations. Understanding the driving mechanism for such phenomenon requires precise knowledge of the equilibrium 18O fractionation factors between dissolved inorganic carbon (DIC) species and water. An experimental study by Beck et al. (2005) successfully refined the 18O fractionation factors between DIC components and water. Based on these results, the overall 18O fractionation between total DIC and water as a function of pH can be readily calculated (e.g., Zeebe, 2007). However, these calculations may not be applicable to seawater because the fractionation factors were measured in freshwater. Natural seawater contains numerous ionic species and other dissolved constituents, which may affect the fractionation factors. For example, it has been experimentally demonstrated that the presence of magnesium ions (Mg2+) in solutions affect equilibrium carbon isotope (13C) fractionation between aqueous CO2 and carbonate ions presumably due to the enrichment of 13C isotopes in Mg-CO30 complexes (Thode et al., 1965). This suggests that the presence of Mg2+ in solutions similarly affects the 18O fractionation factors between DIC species and water. On the other hand, Beck et al. (2005) concluded that the effect of ion pairs on the δ18O equilibrium appears to be negligible. However, this conclusion may not apply to ion paring in general, because experiments were not conducted for metal ions other than Na+. Given that Mg2+ has a marked effect on the equilibrium δ13C fractionation factors and Mg-CO30 is the most abundant form of metal-CO3-complexes in natural seawater, the potential effect of Mg2+ on the 18O fractionation factors between DIC components and water needs to be examined. Here, we will present preliminary results from quantitative carbonate precipitation

  12. Method for isotope enrichment by photoinduced chemiionization

    DOEpatents

    Dubrin, James W.

    1985-01-01

    Isotope enrichment, particularly .sup.235 U enrichment, is achieved by irradiating an isotopically mixed vapor feed with radiant energy at a wavelength or wavelengths chosen to selectively excite the species containing a desired isotope to a predetermined energy level. The vapor feed if simultaneously reacted with an atomic or molecular reactant species capable of preferentially transforming the excited species into an ionic product by a chemiionization reaction. The ionic product, enriched in the desired isotope, is electrostatically or electromagnetically extracted from the reaction system.

  13. Doubly labeled water method: in vivo oxygen and hydrogen isotope fractionation

    SciTech Connect

    Schoeller, D.A.; Leitch, C.A.; Brown, C.

    1986-12-01

    The accuracy and precision of the doubly labeled water method for measuring energy expenditure are influenced by isotope fractionation during evaporative water loss and CO/sub 2/ excretion. To characterize in vivo isotope fractionation, we collected and isotopically analyzed physiological fluids and gases. Breath and transcutaneous water vapor were isotopically fractionated. The degree of fractionation indicated that the former was fractionated under equilibrium control at 37/sup 0/C, and the latter was kinetically fractionated. Sweat and urine were unfractionated. By use of isotopic balance models, the fraction of water lost via fractionating routes was estimated from the isotopic abundances of body water, local drinking water, and dietary solids. Fractionated water loss averaged 23% (SD = 10%) of water turnover, which agreed with our previous estimates based on metabolic rate, but there was a systematic difference between the results based on O/sub 2/ and hydrogen. Corrections for isotopic fractionation of water lost in breath and (nonsweat) transcutaneous loss should be made when using labeled water to measure water turnover or CO/sub 2/ production.

  14. Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures

    PubMed Central

    Loyd, S. J.; Sample, J.; Tripati, R. E.; Defliese, W. F.; Brooks, K.; Hovland, M.; Torres, M.; Marlow, J.; Hancock, L. G.; Martin, R.; Lyons, T.; Tripati, A. E.

    2016-01-01

    Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings. PMID:27447820

  15. Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures.

    PubMed

    Loyd, S J; Sample, J; Tripati, R E; Defliese, W F; Brooks, K; Hovland, M; Torres, M; Marlow, J; Hancock, L G; Martin, R; Lyons, T; Tripati, A E

    2016-07-22

    Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.

  16. Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures

    NASA Astrophysics Data System (ADS)

    Loyd, S. J.; Sample, J.; Tripati, R. E.; Defliese, W. F.; Brooks, K.; Hovland, M.; Torres, M.; Marlow, J.; Hancock, L. G.; Martin, R.; Lyons, T.; Tripati, A. E.

    2016-07-01

    Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ~0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.

  17. Wide reflective equilibrium as a method of justification in bioethics.

    PubMed

    Nichols, Peter

    2012-10-01

    Carson Strong has recently argued that wide reflective equilibrium (WRE) is an unacceptable method of justification in bioethics. In its place, Strong recommends a methodology in which certain foundational moral judgments play a central role in the justification of moral beliefs, and coherence plays a limited justificatory role in that the rest of our judgments are made to cohere with these foundational judgments. In this paper, I argue that Strong's chief criticisms of WRE are unsuccessful and that his proposed alternative is in fact just another version of WRE. In the course of doing so, I specify which theses are central to WRE and which are not, and thus, provide a response to an additional objection, advanced by Peter Singer, that WRE is vacuous. I conclude by arguing that there may be better prospects for advancing the debate regarding methodology in bioethics if we focus on restricted epistemic and methodological theses rather than broad approaches, such as WRE, that come in many different varieties.

  18. Method of isotope separation by chemi-ionization

    DOEpatents

    Wexler, Sol; Young, Charles E.

    1977-05-17

    A method for separating specific isotopes present in an isotopic mixture by aerodynamically accelerating a gaseous compound to form a jet of molecules, and passing the jet through a stream of electron donor atoms whereby an electron transfer takes place, thus forming negative ions of the molecules. The molecular ions are then passed through a radiofrequency quadrupole mass filter to separate the specific isotopes. This method may be used for any compounds having a sufficiently high electron affinity to permit negative ion formation, and is especially useful for the separation of plutonium and uranium isotopes.

  19. Simultaneous determination of equilibrium constants and enthalpy changes by titration calorimetry: Methods, instruments, and uncertainties.

    PubMed

    Hansen, Lee D; Fellingham, Gilbert W; Russell, Donald J

    2011-02-15

    Calorimetric methods have been used to determine equilibrium constants since 1937, but no comprehensive review of the various calorimeters and methods has been done previously. This article reports methods for quantitative comparison of the capabilities of calorimeters for simultaneous determination of equilibrium constants and enthalpy changes, for determining optimal experimental conditions, and for assessing the effects of systematic and random errors on the accuracy and precision of equilibrium constants and enthalpy changes determined by this method.

  20. Research and application of method of oxygen isotope of inorganic phosphate in Beijing agricultural soils.

    PubMed

    Tian, Liyan; Guo, Qingjun; Zhu, Yongguan; He, Huijun; Lang, Yunchao; Hu, Jian; Zhang, Han; Wei, Rongfei; Han, Xiaokun; Peters, Marc; Yang, Junxing

    2016-12-01

    Phosphorus (P) in agricultural ecosystems is an essential and limited element for plants and microorganisms. However, environmental problems caused by P accumulation as well as by P loss have become more and more serious. Oxygen isotopes of phosphate can trace the sources, migration, and transformation of P in agricultural soils. In order to use the isotopes of phosphate oxygen, appropriate extraction and purification methods for inorganic phosphate from soils are necessary. Here, we combined two different methods to analyze the oxygen isotopic composition of inorganic phosphate (δ(18)OP) from chemical fertilizers and different fractions (Milli-Q water, 0.5 mol L(-1) NaHCO3 (pH = 8.5), 0.1 mol L(-1) NaOH and 1 mol L(-1) HCl) of agricultural soils from the Beijing area. The δ(18)OP results of the water extracts and NaHCO3 extracts in most samples were close to the calculated equilibrium value. These phenomena can be explained by rapid P cycling in soils and the influence of chemical fertilizers. The δ(18)OP value of the water extracts and NaHCO3 extracts in some soil samples below the equilibrium value may be caused by the hydrolysis of organic P fractions mediated by extracellular enzymes. The δ(18)OP values of the NaOH extracts were above the calculated equilibrium value reflecting the balance state between microbial uptake of phosphate and the release of intracellular phosphate back to the soil. The HCl extracts with the lowest δ(18)OP values and highest phosphate concentrations indicated that the HCl fraction was affected by microbial activity. Hence, these δ(18)Op values likely reflected the oxygen isotopic values of the parent materials. The results suggested that phosphate oxygen isotope analyses could be an effective tool in order to trace phosphate sources, transformation processes, and its utilization by microorganisms in agricultural soils.

  1. A new nonlocal thermodynamical equilibrium radiative transfer method for cool stars. Method and numerical implementation

    NASA Astrophysics Data System (ADS)

    Lambert, J.; Josselin, E.; Ryde, N.; Faure, A.

    2015-08-01

    Context. The solution of the nonlocal thermodynamical equilibrium (non-LTE) radiative transfer equation usually relies on stationary iterative methods, which may falsely converge in some cases. Furthermore, these methods are often unable to handle large-scale systems, such as molecular spectra emerging from, for example, cool stellar atmospheres. Aims: Our objective is to develop a new method, which aims to circumvent these problems, using nonstationary numerical techniques and taking advantage of parallel computers. Methods: The technique we develop may be seen as a generalization of the coupled escape probability method. It solves the statistical equilibrium equations in all layers of a discretized model simultaneously. The numerical scheme adopted is based on the generalized minimum residual method. Results: The code has already been applied to the special case of the water spectrum in a red supergiant stellar atmosphere. This demonstrates the fast convergence of this method, and opens the way to a wide variety of astrophysical problems.

  2. On anharmonic and pressure corrections to the equilibrium isotopic constants for minerals

    NASA Astrophysics Data System (ADS)

    Polyakov, Veniamin B.

    1998-09-01

    Specifies of the calculations of the reduced isotopic partition function ratios (β-factor) of minerals are discussed. Comparative calculations in the framework of the fully harmonic, quasi-harmonic, and intrinsic anharmonic approximations show minor anharmonic corrections to the harmonic values of the β-factor. In the case of calcite, the difference between the fully harmonic and intrinsic anharmonic values of 10 3lnβ varies from 0.60 at 300 K to 0.37 at 1200 K and is close to typical values of the anharmonic correction in gas molecules. A new treatment for calculating isotopic effects in molar volumes of minerals and pressure effects on their β-factors is developed on the basis of the Mie-Grüneisen equation of state. There is no significant difference between the quasi-harmonic and intrinsic harmonic values of (∂lnβ/∂ P) T. For calcite, the pressure derivative of the β-factor is positive, decreases monotonically with temperature, and becomes small at T ˜ 1000 K (10 3(∂lnβ/ ∂P) T ≈ 0.1-0.15 GPa -1). These results contradict the large anharmonic and pressure effects to the β-factor of calcite calculated by Gillet et al. (1996) as well as their conclusion that the pressure correction to the β-factor of calcite is negative at higher temperatures and increases in its absolute value with increasing temperature.

  3. Reconciling Empirical Carbonate Clumped Isotope Calibrations: A Comparison of Calcite Precipitation and Acid Digestion Methods

    NASA Astrophysics Data System (ADS)

    Kelson, J.; Huntington, K. W.; Schauer, A. J.; Saenger, C.; Lechler, A. R.

    2015-12-01

    An accurate empirical calibration is necessary to confidently apply the carbonate clumped isotope (Δ47) thermometer. Previous synthetic carbonate calibrations disagree in temperature sensitivity, with one group of calibrations displaying a shallow Δ47-temperature slope (e.g., Dennis & Schrag, GCA, 2010), and the other a steep slope (e.g., Zaarur et al., EPSL, 2013). These calibrations differ in both the method of mineral precipitation and the temperature of the phosphoric acid used to digest carbonates for analysis, making it difficult to isolate the cause of the discrepancy. Here, we precipitate synthetic carbonates at temperatures of 6-80ºC using 4 different precipitation methods, and analyze the samples using both 90 and 25°C acid digestion. Precipitation experiments varied the use of salts (NaHCO3 and CaCl2) vs. dissolved CaCO3 as a starting solution, the use of carbonic anhydrase to promote isotopic equilibrium among dissolved inorganic carbon species in solution, and the method by which CO2 degasses to force carbonate precipitation. Carbonates precipitated by using salts and allowing CO2 to passively degas produce a shallow calibration slope that we hypothesize to approach isotopic equilibrium. Precipitation methods that bubble CO2 into solution then degas that CO2 (either passively or actively by bubbling N2) produce carbonates with consistently lower Δ47 and higher δ18O values for a given growth temperature. We infer that these carbonates grew in disequilibrium during rapid CO2 degassing. Varying acid digestion temperature does not change the results; acid fractionation factor is not correlated with grain size, Δ47, or d47 values. No precipitation method produces a steep calibration slope. Our large sample set of >60 carbonates lend confidence to a shallow slope calibration, and inform interpretations of Δ47 and δ18O values of natural carbonates that grow under conditions of isotopic disequilibrium.

  4. Method for isotopic analysis of chlorinated organic compounds

    DOEpatents

    Holt, Ben D.; Sturchio, Neil C.

    1999-01-01

    The present invention provides a method for preparing a VOC sample for carbon and chlorine isotope ratio analysis by mass spectrometer. A VOC sample is placed in a combustion tube and reacted with CuO to form CO.sub.2 and CuCl. The CO.sub.2 is then extracted and analyzed for the carbon isotope ratio. The CuCl is separated from the excess CuO and reacted with CH.sub.3 I to form CH.sub.3 Cl, extracted and analyzed for chlorine isotope ratio.

  5. Method for isotopic analysis of chlorinated organic compounds

    DOEpatents

    Holt, B.D.; Sturchio, N.C.

    1999-08-24

    The present invention provides a method for preparing a VOC sample for carbon and chlorine isotope ratio analysis by mass spectrometer. A VOC sample is placed in a combustion tube and reacted with CuO to form CO{sub 2} and CuCl. The CO{sub 2} is then extracted and analyzed for the carbon isotope ratio. The CuCl is separated from the excess CuO and reacted with CH{sub 3}I to form CH{sub 3}Cl, extracted and analyzed for chlorine isotope ratio. 9 figs.

  6. [Progress in stable isotope labeled quantitative proteomics methods].

    PubMed

    Zhou, Yuan; Shan, Yichu; Zhang, Lihua; Zhang, Yukui

    2013-06-01

    Quantitative proteomics is an important research field in post-genomics era. There are two strategies for proteome quantification: label-free methods and stable isotope labeling methods which have become the most important strategy for quantitative proteomics at present. In the past few years, a number of quantitative methods have been developed, which support the fast development in biology research. In this work, we discuss the progress in the stable isotope labeling methods for quantitative proteomics including relative and absolute quantitative proteomics, and then give our opinions on the outlook of proteome quantification methods.

  7. Revised method for calculating cloud densities in equilibrium models

    NASA Astrophysics Data System (ADS)

    Wong, M. H.; Atreya, S. K.; Kuhn, W. R.

    2013-12-01

    Models of cloud condensation under thermodynamic equilibrium in planetary atmospheres are simple but still useful for several reasons. They calculate the wet adiabatic lapse rate, they determine saturation-limited mixing ratios of condensing species, and they calculate the stabilizing effect of latent heat release and molecular weight stratification. Equilibrium cloud condensation models (ECCMs) also calculate a type of condensate density---a condensate "unit density"---that only equates to cloud density under specific circumstances, because microphysics and dynamics are not considered in ECCMs. Unit densities are calculated for every model altitude by requiring that condensed material remains at the level where it condenses. Many ECCMs in use trace their heritage to Weidenschilling and Lewis (1973; Icarus 20, 465--476; hereafter WL73), which contains an error that affects only the calculation of condensate unit density. The error led to densities too high by a factor of the atmospheric scale height divided by unit length, which is about 3x10^6 at Jupiter's ammonia cloud level. We will describe the condensate unit density calculation error in WL73, and provide a new algorithm based on the local change in vapor mixing ratio, rather than the difference between integrated column masses as in WL73. The new algorithm satisfies conservation of mass. Using a simple scaling law to parameterize dynamics in terms of updraft speed and duration, condensate unit densities from ECCMs can be converted to cloud densities. We validate the technique for the terrestrial case, by comparing model predictions with representative densities of cirrus and cumulus clouds. For cirrus and cumulus updraft parameters, respectively, we find cloud densities of 0.01--0.2 g m-3 and 0.8--7 g m-3, in excellent agreement with observations and models of terrestrial clouds of these types. Implications for models of planetary and exoplanetary atmospheres will be discussed. [This material is based upon

  8. Out-of-equilibrium finite-size method for critical behavior analyses.

    PubMed

    Lulli, Matteo; Parisi, Giorgio; Pelissetto, Andrea

    2016-03-01

    We present a dynamic off-equilibrium method for the study of continuous transitions, which represents a dynamic generalization of the usual equilibrium cumulant method. Its main advantage is that critical parameters are derived from numerical data obtained much before equilibrium has been attained. Therefore, the method is particularly useful for systems with long equilibration times, like spin glasses. We apply it to the three-dimensional Ising spin-glass model, obtaining accurate estimates of the critical exponents and of the critical temperature with a limited computational effort.

  9. Out-of-equilibrium finite-size method for critical behavior analyses

    NASA Astrophysics Data System (ADS)

    Lulli, Matteo; Parisi, Giorgio; Pelissetto, Andrea

    2016-03-01

    We present a dynamic off-equilibrium method for the study of continuous transitions, which represents a dynamic generalization of the usual equilibrium cumulant method. Its main advantage is that critical parameters are derived from numerical data obtained much before equilibrium has been attained. Therefore, the method is particularly useful for systems with long equilibration times, like spin glasses. We apply it to the three-dimensional Ising spin-glass model, obtaining accurate estimates of the critical exponents and of the critical temperature with a limited computational effort.

  10. Original isotopic composition of water in precipitation by different methods

    NASA Astrophysics Data System (ADS)

    Singh, B. P.

    2016-11-01

    Stable isotopes of 2H and 18O in precipitation are different globally and carry all information about water molecules movement in hydrosphere cycles. Isotopic composition is a function of temperature, relative humidity, and speed of evaporation at different latitudes, longitudes, and altitudes. On the basis of this, we observe local meteoric water line measurements in the plot of δ2H versus δ18O. It will be interesting to know the original isotopic composition (without any modification) in a transition from cloud down to earth in different environmental conditions. This had been done by plotting of slope versus intercept of Local Meteoric Water Line (LMWL) at different altitudes in different years of observations. Intercept of LMWL with Global Meteoric Water Line (GMWL) data taken from the hydrology frame work of Corsica was plotted and it was found that the isotopic composition of water in precipitation by all these methods is same.

  11. Estimating of equilibrium formation temperature by curve fitting method and it's problems

    SciTech Connect

    Kenso Takai; Masami Hyodo; Shinji Takasugi

    1994-01-20

    Determination of true formation temperature from measured bottom hole temperature is important for geothermal reservoir evaluation after completion of well drilling. For estimation of equilibrium formation temperature, we studied non-linear least squares fitting method adapting the Middleton Model (Chiba et al., 1988). It was pointed out that this method was applicable as simple and relatively reliable method for estimation of the equilibrium formation temperature after drilling. As a next step, we are studying the estimation of equilibrium formation temperature from bottom hole temperature data measured by MWD (measurement while drilling system). In this study, we have evaluated availability of nonlinear least squares fitting method adapting curve fitting method and the numerical simulator (GEOTEMP2) for estimation of the equilibrium formation temperature while drilling.

  12. A rapid method for the computation of equilibrium chemical composition of air to 15000 K

    NASA Technical Reports Server (NTRS)

    Prabhu, Ramadas K.; Erickson, Wayne D.

    1988-01-01

    A rapid computational method has been developed to determine the chemical composition of equilibrium air to 15000 K. Eleven chemically reacting species, i.e., O2, N2, O, NO, N, NO+, e-, N+, O+, Ar, and Ar+ are included. The method involves combining algebraically seven nonlinear equilibrium equations and four linear elemental mass balance and charge neutrality equations. Computational speeds for determining the equilibrium chemical composition are significantly faster than the often used free energy minimization procedure. Data are also included from which the thermodynamic properties of air can be computed. A listing of the computer program together with a set of sample results are included.

  13. Quantum Chemical Study of the Fe(III)-Desferrioxamine B Siderophore Complex-Electronic Structure, Vibrational Frequencies, and Equilibrium Fe-Isotope Fractionation

    DTIC Science & Technology

    2008-09-19

    chemical study of the Fe(III)-desferrioxamine B siderophore complex—Electronic structure, vibrational frequencies, and equilibrium Fe-isotope fractionation...Fitzwater, 1988). Siderophores , an important class of organic acids with large complexation constants for Fe, are produced by sev- eral organisms in order...to overcome iron deficiencies (Wie- derhold et al., 2006). Due to their exceptionally high affinity for Fe, siderophores complex Fe(III) by extracting

  14. Predicting equilibrium vapour pressure isotope effects by using artificial neural networks or multi-linear regression - A quantitative structure property relationship approach.

    PubMed

    Parinet, Julien; Julien, Maxime; Nun, Pierrick; Robins, Richard J; Remaud, Gerald; Höhener, Patrick

    2015-09-01

    We aim at predicting the effect of structure and isotopic substitutions on the equilibrium vapour pressure isotope effect of various organic compounds (alcohols, acids, alkanes, alkenes and aromatics) at intermediate temperatures. We attempt to explore quantitative structure property relationships by using artificial neural networks (ANN); the multi-layer perceptron (MLP) and compare the performances of it with multi-linear regression (MLR). These approaches are based on the relationship between the molecular structure (organic chain, polar functions, type of functions, type of isotope involved) of the organic compounds, and their equilibrium vapour pressure. A data set of 130 equilibrium vapour pressure isotope effects was used: 112 were used in the training set and the remaining 18 were used for the test/validation dataset. Two sets of descriptors were tested, a set with all the descriptors: number of(12)C, (13)C, (16)O, (18)O, (1)H, (2)H, OH functions, OD functions, CO functions, Connolly Solvent Accessible Surface Area (CSA) and temperature and a reduced set of descriptors. The dependent variable (the output) is the natural logarithm of the ratios of vapour pressures (ln R), expressed as light/heavy as in classical literature. Since the database is rather small, the leave-one-out procedure was used to validate both models. Considering higher determination coefficients and lower error values, it is concluded that the multi-layer perceptron provided better results compared to multi-linear regression. The stepwise regression procedure is a useful tool to reduce the number of descriptors. To our knowledge, a Quantitative Structure Property Relationship (QSPR) approach for isotopic studies is novel.

  15. Hg stable isotope analysis by the double-spike method.

    PubMed

    Mead, Chris; Johnson, Thomas M

    2010-06-01

    Recent publications suggest great potential for analysis of Hg stable isotope abundances to elucidate sources and/or chemical processes that control the environmental impact of mercury. We have developed a new MC-ICP-MS method for analysis of mercury isotope ratios using the double-spike approach, in which a solution containing enriched (196)Hg and (204)Hg is mixed with samples and provides a means to correct for instrumental mass bias and most isotopic fractionation that may occur during sample preparation and introduction into the instrument. Large amounts of isotopic fractionation induced by sample preparation and introduction into the instrument (e.g., by batch reactors) are corrected for. This may greatly enhance various Hg pre-concentration methods by correcting for minor fractionation that may occur during preparation and removing the need to demonstrate 100% recovery. Current precision, when ratios are normalized to the daily average, is 0.06 per thousand, 0.06 per thousand, 0.05 per thousand, and 0.05 per thousand (2sigma) for (202)Hg/(198)Hg, (201)Hg/(198)Hg, (200)Hg/(198)Hg, and (199)Hg/(198)Hg, respectively. This is slightly better than previously published methods. Additionally, this precision was attained despite the presence of large amounts of other Hg isotopes (e.g., 5.0% atom percent (198)Hg) in the spike solution; substantially better precision could be achieved if purer (196)Hg were used.

  16. Non-Equilibrium Allele Frequency Spectra Via Spectral Methods

    PubMed Central

    Hey, Jody; Chen, Kevin

    2011-01-01

    A major challenge in the analysis of population genomics data consists of isolating signatures of natural selection from background noise caused by random drift and gene flow. Analyses of massive amounts of data from many related populations require high-performance algorithms to determine the likelihood of different demographic scenarios that could have shaped the observed neutral single nucleotide polymorphism (SNP) allele frequency spectrum. In many areas of applied mathematics, Fourier Transforms and Spectral Methods are firmly established tools to analyze spectra of signals and model their dynamics as solutions of certain Partial Differential Equations (PDEs). When spectral methods are applicable, they have excellent error properties and are the fastest possible in high dimension; see [15]. In this paper we present an explicit numerical solution, using spectral methods, to the forward Kolmogorov equations for a Wright-Fisher process with migration of K populations, influx of mutations, and multiple population splitting events. PMID:21376069

  17. An aquaculture-based method for calibrated bivalve isotope paleothermometry

    NASA Astrophysics Data System (ADS)

    Wanamaker, Alan D.; Kreutz, Karl J.; Borns, Harold W.; Introne, Douglas S.; Feindel, Scott; Barber, Bruce J.

    2006-09-01

    To quantify species-specific relationships between bivalve carbonate isotope geochemistry (δ18Oc) and water conditions (temperature and salinity, related to water isotopic composition [δ18Ow]), an aquaculture-based methodology was developed and applied to Mytilus edulis (blue mussel). The four-by-three factorial design consisted of four circulating temperature baths (7, 11, 15, and 19°C) and three salinity ranges (23, 28, and 32 parts per thousand (ppt); monitored for δ18Ow weekly). In mid-July of 2003, 4800 juvenile mussels were collected in Salt Bay, Damariscotta, Maine, and were placed in each configuration. The size distribution of harvested mussels, based on 105 specimens, ranged from 10.9 mm to 29.5 mm with a mean size of 19.8 mm. The mussels were grown in controlled conditions for up to 8.5 months, and a paleotemperature relationship based on juvenile M. edulis from Maine was developed from animals harvested at months 4, 5, and 8.5. This relationship [T°C = 16.19 (±0.14) - 4.69 (±0.21) {δ18Oc VPBD - δ18Ow VSMOW} + 0.17 (±0.13) {δ18Oc VPBD - δ18Ow VSMOW}2; r2 = 0.99; N = 105; P < 0.0001] is nearly identical to the Kim and O'Neil (1997) abiogenic calcite equation over the entire temperature range (7-19°C), and it closely resembles the commonly used paleotemperature equations of Epstein et al. (1953) and Horibe and Oba (1972). Further, the comparison of the M. edulis paleotemperature equation with the Kim and O'Neil (1997) equilibrium-based equation indicates that M. edulis specimens used in this study precipitated their shell in isotopic equilibrium with ambient water within the experimental uncertainties of both studies. The aquaculture-based methodology described here allows similar species-specific isotope paleothermometer calibrations to be performed with other bivalve species and thus provides improved quantitative paleoenvironmental reconstructions.

  18. A method of solid-solid phase equilibrium calculation by molecular dynamics

    NASA Astrophysics Data System (ADS)

    Karavaev, A. V.; Dremov, V. V.

    2016-12-01

    A method for evaluation of solid-solid phase equilibrium curves in molecular dynamics simulation for a given model of interatomic interaction is proposed. The method allows to calculate entropies of crystal phases and provides an accuracy comparable with that of the thermodynamic integration method by Frenkel and Ladd while it is much simpler in realization and less intense computationally. The accuracy of the proposed method was demonstrated in MD calculations of entropies for EAM potential for iron and for MEAM potential for beryllium. The bcc-hcp equilibrium curves for iron calculated for the EAM potential by the thermodynamic integration method and by the proposed one agree quite well.

  19. Teasing Cellulose Isotopic Signals Apart by Chemical Methods

    NASA Astrophysics Data System (ADS)

    Sternberg, L. D.; Anderson, W. T.; Morrison, K.

    2002-12-01

    The δ18O and δD values of precipitation water correlates with changes in atmospheric circulation patterns and temperature. This has been the basis of many attempts to use fossil tree ring cellulose as a proxy for paleoclimate. Ideally by measuring δ18O and δD values of tree ring cellulose one would infer isotopic composition of water available for plant uptake, which presumably is the least isotopically altered from precipitation. Subsequently, paleo-temperatures or atmospheric circulation patterns at the time of cellulose formation could then be inferred. However, this goal is confounded by isotopic exchange processes occurring in the leaf. Our current understanding of the physiological/biochemical mechanisms operating during the labeling of carbohydrates by water during tree ring cellulose synthesis indicates that the isotopic composition of tree ring cellulose is a mixture of isotopic signals coming from source (CA 35 to 45%) and leaf (CA 55 to 65%) water. The isotopic composition of the latter component is radically modified from that of the original source water by factors such as relative humidity and leaf properties. Here we present a chemical method of derivatizing cellulose to tease these two signals apart. We analyze the isotopic composition of cellulose and its derivative and calculate the δ18O value of the oxygen attached to the second carbon of the glucose moieties in cellulose (2C-OH). A one to one relationship between δ18O values of this oxygen and that of water available for cellulose synthesis in seeds germinated in the presence of water having different δ18O values was observed. Indicating that 2C-OH undergoes complete exchange with water during the synthesis of cellulose from sucrose. This technique can potentially be an analytical tool in paleo-climatic and ecological studies, once the analytical techniques are refined so as to increase precision.

  20. Raman scattering method and apparatus for measuring isotope ratios and isotopic abundances

    DOEpatents

    Harney, Robert C.; Bloom, Stewart D.

    1978-01-01

    Raman scattering is used to measure isotope ratios and/or isotopic abundances. A beam of quasi-monochromatic photons is directed onto the sample to be analyzed, and the resulting Raman-scattered photons are detected and counted for each isotopic species of interest. These photon counts are treated mathematically to yield the desired isotope ratios or isotopic abundances.

  1. Generator Coordinate Method Analysis of Xe and Ba Isotopes

    NASA Astrophysics Data System (ADS)

    Higashiyama, Koji; Yoshinaga, Naotaka; Teruya, Eri

    Nuclear structure of Xe and Ba isotopes is studied in terms of the quantum-number projected generator coordinate method (GCM). The GCM reproduces well the energy levels of high-spin states as well as low-lying states. The structure of the low-lying states is analyzed through the GCM wave functions.

  2. Method of enhancing selective isotope desorption from metals

    DOEpatents

    Knize, R.J.; Cecchi, J.L.

    1983-07-26

    This invention relates generally to the field of gas desorption from metals; and, more particularly, to a method of enhancing the selective desorption of a particular isotope of a gas from metals. Enhanced selective desorption is especially useful in the operation of fusion devices.

  3. RECTIFIED ABSORPTION METHOD FOR THE SEPARATION OF HYDROGEN ISOTOPES

    DOEpatents

    Hunt, C.D.; Hanson, D.N.

    1961-10-17

    A method is described for separating and recovering heavy hydrogen isotopes from gaseous mixtures by multiple stage cyclic absorption and rectification from an approximate solvent. In particular, it is useful for recovering such isoteoes from ammonia feedstock streams containing nitrogen solvent. Modifications of the process ranging from isobaric to isothermal are provided. Certain impurities are tolerated, giving advantages over conventional fractional distillation processes. (AEC)

  4. METHOD TO TEST ISOTOPIC SEPARATION EFFICIENCY OF PALLADIUM PACKED COLUMNS

    SciTech Connect

    Heung, L; Gregory Staack, G; James Klein, J; William Jacobs, W

    2007-06-27

    The isotopic effect of palladium has been applied in different ways to separate hydrogen isotopes for many years. At Savannah River Site palladium deposited on kieselguhr (Pd/k) is used in a thermal cycling absorption process (TCAP) to purify tritium for over ten years. The need to design columns for different throughputs and the desire to advance the performance of TCAP created the need to evaluate different column designs and packing materials for their separation efficiency. In this work, columns with variations in length, diameter and metal foam use, were tested using an isotope displacement method. A simple computer model was also developed to calculate the number of theoretical separation stages using the test results. The effects of column diameter, metal foam and gas flow rate were identified.

  5. Three applications of path integrals: equilibrium and kinetic isotope effects, and the temperature dependence of the rate constant of the [1,5] sigmatropic hydrogen shift in (Z)-1,3-pentadiene.

    PubMed

    Zimmermann, Tomáš; Vaníček, Jiří

    2010-11-01

    Recent experiments have confirmed the importance of nuclear quantum effects even in large biomolecules at physiological temperature. Here we describe how the path integral formalism can be used to describe rigorously the nuclear quantum effects on equilibrium and kinetic properties of molecules. Specifically, we explain how path integrals can be employed to evaluate the equilibrium (EIE) and kinetic (KIE) isotope effects, and the temperature dependence of the rate constant. The methodology is applied to the [1,5] sigmatropic hydrogen shift in pentadiene. Both the KIE and the temperature dependence of the rate constant confirm the importance of tunneling and other nuclear quantum effects as well as of the anharmonicity of the potential energy surface. Moreover, previous results on the KIE were improved by using a combination of a high level electronic structure calculation within the harmonic approximation with a path integral anharmonicity correction using a lower level method.

  6. Quantum chemical study of the Fe(III)-desferrioxamine B siderophore complex—Electronic structure, vibrational frequencies, and equilibrium Fe-isotope fractionation

    NASA Astrophysics Data System (ADS)

    Domagal-Goldman, S. D.; Paul, K. W.; Sparks, D. L.; Kubicki, J. D.

    2009-01-01

    This study presents molecular orbital/density functional theory (MO/DFT) calculations of the electronic structure, vibrational frequencies, and equilibrium isotope fractionation factors for iron desferrioxamine B (Fe-DFO-B) complexes in aqueous solution. In general, there was good agreement between the predicted properties of Fe(III)-DFO-B and previously published experimental and theoretical results. The predicted fractionation factor for equilibrium between Fe(III)-DFO-B and Fe(III)-catecholate at 22 °C, 0.68 ± 0.25‰, was in good agreement with a previously measured isotopic difference between bacterial cells and solution during the bacterial-mediated dissolution of hornblende [Brantley S. L., Liermann L. and Bullen T. D. (2001) Fractionation of Fe isotopes by soil microbes and organic acids. Geology29, 535-538]. Conceptually, this agreement is consistent with the notion that Fe is first removed from mineral surfaces via complexation with small organic acids (e.g., oxalate), subsequently sequestered by DFO-B in solution, and ultimately delivered to bacterial cells by Fe(III)-DFO-B complexes. The ability of DFO-B to discriminate between Fe(III) and Fe(II)/Al(III) was investigated with Natural Bond Orbital (NBO) analysis and geometry calculations of each metal-DFO-B complex. The results indicated that higher affinity for Fe(III) is not strictly a function of bond length but also the degree of Fe-O covalent bonding.

  7. Multigrid method for the equilibrium equations of elasticity using a compact scheme

    NASA Technical Reports Server (NTRS)

    Taasan, S.

    1986-01-01

    A compact difference scheme is derived for treating the equilibrium equations of elasticity. The scheme is inconsistent and unstable. A multigrid method which takes into account these properties is described. The solution of the discrete equations, up to the level of discretization errors, is obtained by this method in just two multigrid cycles.

  8. Distance, Dialogue and Reflection: Interpersonal Reflective Equilibrium as Method for Professional Ethics Education

    ERIC Educational Resources Information Center

    van den Hoven, Mariëtte; Kole, Jos

    2015-01-01

    The method of reflective equilibrium (RE) is well known within the domain of moral philosophy, but hardly discussed as a method in professional ethics education. We argue that an interpersonal version of RE is very promising for professional ethics education. We offer several arguments to support this claim. The first group of arguments focus on a…

  9. Opening opportunities for high-resolution isotope analysis - quantification of δ(15)NNO3 and δ(18)ONO3 in Diffusive Equilibrium in Thin-film passive samplers.

    PubMed

    Comer-Warner, Sophie A; Krause, Stefan; Gooddy, Daren C; Bennett, Sarah A; Wexler, Sarah Katrina; Kaiser, Jan

    2017-03-01

    The fate of nitrate transported across groundwater-surface water interfaces has been intensively studied in recent decades. The interfaces between aquifers and rivers or lakes have been identified as biogeochemical hotspots with steep redox gradients. However, a detailed understanding of the spatial heterogeneity and potential temporal variability of these hotspots, and the consequences for nitrogen processing, is still hindered by a paucity of adequate measurement techniques. A novel methodology is presented here, using Diffusive Equilibrium in Thin-film (DET) gels as high-spatial-resolution passive-samplers of The fate of nitrate transported across groundwater-surface water interfaces has been intensively studied in recent decades. The interfaces between aquifers and rivers or lakes have been identified as biogeochemical hotspots with steep redox gradients. However, a detailed understanding of the spatial heterogeneity and potential temporal variability of these hotspots, and the consequences for nitrogen processing, is still hindered by a paucity of adequate measurement techniques. A novel methodology is presented here, using Diffusive Equilibrium in Thin-film (DET) gels as high-spatial-resolution passive-samplers of δ(15)NNO3 and δ(18)ONO3 to investigate nitrogen cycling. Fractionation of δ(15)NNO3 and δ(18)ONO3 during diffusion of nitrate through the DET gel was determined using varying equilibrium times and nitrate concentrations. This demonstrated that nitrate isotopes of δ(15)NNO3 and δ(18)ONO3 do not fractionate when sampled with a DET gel. δ(15)NNO3 values from the DET gels ranged between 2.3±0.2 and 2.7±0.3‰ for a NO3- stock solution value of 2.7±0.4‰, and δ(18)ONO3 values ranged between 18.3±1.0 and 21.5±0.8‰ for a NO3- stock solution of 19.7±0.9‰. Nitrate recovery and isotope values were independent of equilibrium time and nitrate concentration. Additionally, an in-situ study showed that nitrate concentration and isotopes, provide

  10. Technical Note: A simple method for vaterite precipitation for isotopic studies: implications for bulk and clumped isotope analysis

    NASA Astrophysics Data System (ADS)

    Kluge, T.; John, C. M.

    2015-06-01

    Calcium carbonate (CaCO3) plays an important role in the natural environment as a major constituent of the skeleton and supporting structure of marine life and has high economic importance as an additive in food, chemicals and medical products. Anhydrous CaCO3 occurs in the three different polymorphs calcite, aragonite and vaterite, whereof calcite is the most abundant and best characterized mineral. In contrast, little is known about the rare polymorph vaterite, in particular with regard to the oxygen isotope fractionation between H2O and the mineral. Synthetic precipitation of vaterite in the laboratory typically involves rapid processes and isotopic non-equilibrium, which excludes isotope studies focused on the characterization of vaterite under equilibrium conditions. Here, we used a new experimental approach that enables vaterite mineral formation from an isotopically equilibrated solution. The solution consists of a ~0.007 mol L-1 CaCO3 solution that is saturated with NaCl at room temperature (up to 6.4 mol L-1). Vaterite precipitated as single phase or major phase (≥94%) in experiments performed between 23 and 91 °C. Only at 80 °C was vaterite a minor phase with a relative abundance of 27%. The high mineral yield per experiment of up to 235 mg relative to the initially dissolved CaCO3 amount of on average 360 mg enables an investigation of the oxygen isotope fractionation between the mineral and water, and the determination of clumped isotope values in vaterite.

  11. METHOD FOR PRODUCING ISOTOPIC METHANES AND PARTIALLY HALOGENATED DERIVATIVES THEROF

    DOEpatents

    Frazer, J.W.

    1959-08-18

    A method is given for producing isotopic methanes and/ or partially halogenated derivatives. Lithium hydride, deuteride, or tritide is reacted with a halogenated methane or with a halogenated methane in combination with free halogen. The process is conveniently carried out by passing a halogenated methane preferably at low pressures or in an admixture with an inert gas through a fixed bed of finely divided lithium hydride heated initially to temperatures of 100 to 200 deg C depending upon the halogenated methane used.

  12. Computational methods for multiphase equilibrium and kinetics calculations for geochemical and reactive transport applications

    NASA Astrophysics Data System (ADS)

    Leal, Allan; Saar, Martin

    2016-04-01

    Computational methods for geochemical and reactive transport modeling are essential for the understanding of many natural and industrial processes. Most of these processes involve several phases and components, and quite often requires chemical equilibrium and kinetics calculations. We present an overview of novel methods for multiphase equilibrium calculations, based on both the Gibbs energy minimization (GEM) approach and on the solution of the law of mass-action (LMA) equations. We also employ kinetics calculations, assuming partial equilibrium (e.g., fluid species in equilibrium while minerals are in disequilibrium) using automatic time stepping to improve simulation efficiency and robustness. These methods are developed specifically for applications that are computationally expensive, such as reactive transport simulations. We show how efficient the new methods are, compared to other algorithms, and how easy it is to use them for geochemical modeling via a simple script language. All methods are available in Reaktoro, a unified open-source framework for modeling chemically reactive systems, which we also briefly describe.

  13. Isotope correlations for safeguards surveillance and accountancy methods

    SciTech Connect

    Persiani, P.J.; Kalimullah

    1982-01-01

    Isotope correlations corroborated by experiments, coupled with measurement methods for nuclear material in the fuel cycle have the potential as a safeguards surveillance and accountancy system. The ICT allows the verification of: fabricator's uranium and plutonium content specifications, shipper/receiver differences between fabricator output and reactor input, reactor plant inventory changes, reprocessing batch specifications and shipper/receiver differences between reactor output and reprocessing plant input. The investigation indicates that there exist predictable functional relationships (i.e. correlations) between isotopic concentrations over a range of burnup. Several cross-correlations serve to establish the initial fuel assembly-averaged compositions. The selection of the more effective correlations will depend not only on the level of reliability of ICT for verification, but also on the capability, accuracy and difficulty of developing measurement methods. The propagation of measurement errors through the correlations have been examined to identify the sensitivity of the isotope correlations to measurement errors, and to establish criteria for measurement accuracy in the development and selection of measurement methods. 6 figures, 3 tables.

  14. First-principles calculations of equilibrium fractionation of O and Si isotopes in quartz, albite, anorthite, and zircon

    NASA Astrophysics Data System (ADS)

    Qin, Tian; Wu, Fei; Wu, Zhongqing; Huang, Fang

    2016-11-01

    In this study, we used first-principles calculations based on density functional theory to investigate silicon and oxygen isotope fractionation factors among the most abundant major silicate minerals in granites, i.e., quartz and plagioclase (including albite and anorthite), and an important accessory mineral zircon. Combined with previous results of minerals commonly occurring in the crust and upper mantle (orthoenstatite, clinoenstatite, garnet, and olivine), our study reveals that the Si isotope fractionations in minerals are strongly correlated with SiO4 tetrahedron volume (or average Si-O bond length). The 30Si enrichment order follows the sequence of quartz > albite > anorthite > olivine ≈ zircon > enstatite > diopside, and the 18O enrichment follows the order of quartz > albite > anorthite > enstatite > zircon > olivine. Our calculation predicts that measurable fractionation of Si isotopes can occur among crustal silicate minerals during high-temperature geochemical processes. This work also allows us to evaluate Si isotope fractionation between minerals and silicate melts with variable compositions. Trajectory for δ30Si variation during fractional crystallization of silicate minerals was simulated with our calculated Si isotope fractionation factors between minerals and melts, suggesting the important roles of fractional crystallization to cause Si isotopic variations during magmatic differentiation. Our study also predicts that δ30Si data of ferroan anorthosites of the Moon can be explained by crystallization and aggregation of anorthite during lunar magma ocean processes. Finally, O and Si isotope fractionation factors between zircon and melts were estimated based on our calculation, which can be used to quantitatively account for O and Si isotope composition of zircons crystallized during magma differentiation.

  15. Fixed-point methods for computing the equilibrium composition of complex biochemical mixtures.

    PubMed Central

    Kuzmic, P

    1998-01-01

    The fixed-point algebraic method [Storer and Cornish-Bowden (1976) Biochem. J. 159, 1-5] for computing the concentrations at equilibrium of complex biochemical mixtures fails for many binding stoichiometries, especially those that include molecular self-association. A typical example is the monomer-dimer-tetramer equilibrium. This paper reports two main results. First, the above algorithm is analysed theoretically to predict for which binding stoichiometries it succeeds and for which it will fail. Secondly, an alternative algorithm is described for self-associating biochemical systems. Illustrative examples are based on the dimeric proteinase from HIV. PMID:9531499

  16. Semiexperimental equilibrium structure of the lower energy conformer of glycidol by the mixed estimation method.

    PubMed

    Demaison, Jean; Craig, Norman C; Conrad, Andrew R; Tubergen, Michael J; Rudolph, Heinz Dieter

    2012-09-13

    Rotational constants were determined for (18)O-substituted isotopologues of the lower energy conformer of glycidol, which has an intramolecular inner hydrogen bond from the hydroxyl group to the oxirane ring oxygen. Rotational constants were previously determined for the (13)C and the OD species. These rotational constants have been corrected with the rovibrational constants calculated from an ab initio cubic force field. The derived semiexperimental equilibrium rotational constants have been supplemented by carefully chosen structural parameters, including those for hydrogen atoms, from medium level ab initio calculations. The combined data have been used in a weighted least-squares fit to determine an equilibrium structure for the glycidol H-bond inner conformer. This work shows that the mixed estimation method allows us to determine a complete and reliable equilibrium structure for large molecules, even when the rotational constants of a number of isotopologues are unavailable.

  17. A new method of tree xylem water extraction for isotopic analysis

    NASA Astrophysics Data System (ADS)

    Gierke, C.; Newton, B. T.

    2011-12-01

    waters (IW), allowing diffusive processes to proceed to equilibrium, measuring the composition of the resulting mixture or final water (FW) then, solving a simple mixing equation. To evaluate this method, we collected several twig samples from Douglas Firs in the Sacramento Mountains. Twig water was prepared for isotopic analysis both by cryogenic distillation and the mixing method. Soil in close proximity to these trees was also sampled and water was extracted by cryogenic distillation. Preliminary results show that the isotopic composition of distilled twig water and soil waters plot to the right of the local meteoric water line (LMWL) suggesting that trees are extracting shallow evaporated soil water. Twig water obtained from the mixing method plot near the LMWL within the range expected for local snow melt, suggesting a possibly deeper non-evaporated source. In general, distillation values are approximately 4% heavier with respect to delta 18O than waters obtained from the mixing method. It is possible that this difference is due to the contribution of the fractionated water of the twig phloem that is released during the distillation process. This difference is quite significant and can lead to very different interpretations. These results are being addressed with additional experiments.

  18. Calculation of equilibrium constants by matrix method for complexes of gold(III).

    PubMed

    Kudrev, A G

    2008-04-15

    A new matrix approach is proposed to calculate the equilibrium constants of ligands substitution in a metal ion inner coordination sphere with fixed binding sites positions. The proposed method allows to reduce the number of independent variables, necessary for the titration curves fitting without deterioration in the description accuracy. The square planar complexes [MY(4-n)X(n)] n=0-4 formation in solution model includes three independent variables K , omega(cis) and omega(trans) (K -equilibrium constant of replacement of first ligand, omega(cis), omega(trans)-parameters of mutual influence) as an alternative to four stepwise equilibrium constants and two microconstants. In the present investigation experimental spectrophotometric data published in the literature for system {Au(3+)-Cl(-)-Br(-)} were analysed. With the help of the proposed method the equilibrium constants of chloride by bromide ion substitution in internal coordination sphere of Au(III) are calculated K =50; omega(cis)=1.3; omega(trans)=0.7.

  19. A method for obtaining three-dimensional computation equilibrium of non-neutral plasmas using WARP

    SciTech Connect

    Wurtele, J.; Wurtele, J.; Friedman, A.; Grote, D.P.; Vay, J-L.; Gomberoff, K.

    2006-03-25

    Computer simulation studies of the stability and transport properties of trapped non-neutral plasmas require the numerical realization of a three-dimensional plasma distribution. This paper presents a new numerical method for obtaining, without an explicit model for physical collisions in the code, a low noise three-dimensional computational equilibrium distribution. This requires both the loading of particles into an idealized distribution and the relaxation from that distribution toward an approximate numerical equilibrium. The equilibrium can then be modified through a slow change of system parameters, to generate other equilibria. In the present work we apply this method to a UC Berkeley experiment on electron confinement in magnetic geometries appropriate for the ALPHA anti-hydrogen experiment, using the three-dimensional Particle-In-Cell code WARP. WARP's guiding center mover and its option to switch between different solvers during a simulation are highly valuable because they speed up the simulations; they enable the practical use of the new technique for generating numerical equilibrium states of trapped nonneutral plasmas.

  20. A method for obtaining three-dimensional computational equilibrium of non-neutral plasmas using WARP

    SciTech Connect

    Gomberoff, K. . E-mail: katia@physics.technion.ac.il; Wurtele, J.; Friedman, A.; Grote, D.P.; Vay, J.-L.

    2007-08-10

    Computer simulation studies of the stability and transport properties of trapped non-neutral plasmas require the numerical realization of a three-dimensional plasma distribution. This paper presents a new numerical method for obtaining, without an explicit model for physical collisions in the code, a low noise three-dimensional computational equilibrium distribution. This requires both the loading of particles into an idealized distribution and the relaxation from that distribution toward an approximate numerical equilibrium. The equilibrium can then be modified through a slow change of system parameters, to generate other equilibria. In the present, work we apply this method to a UC Berkeley experiment on electron confinement in magnetic geometries appropriate for the ALPHA anti-hydrogen experiment, using the three-dimensional particle-in-cell code WARP. WARP's guiding center mover and its option to switch between different solvers during a simulation are highly valuable because they speed up the simulations; they enable the practical use of the new technique for generating numerical equilibrium states of trapped non-neutral plasmas.

  1. Method for enriching a middle isotope using vibration-vibration pumping

    DOEpatents

    Rich, Joseph W.; Homicz, Gregory F.; Bergman, Richard C.

    1989-01-01

    Method for producing isotopically enriched material by vibration-vibration excitation of gaseous molecules wherein a middle mass isotope of an isotopic mixture including lighter and heavier mass isotopes preferentially populates a higher vibrational mode and chemically reacts to provide a product in which it is enriched. The method can be used for vibration-vibration enrichment of .sup.17 O in a CO reactant mixture.

  2. LBM-DSMC Hybrid Method for Complex Out-of-Equilibrium Flows

    NASA Astrophysics Data System (ADS)

    di Staso, Gianluca; Clercx, Herman J. H.; Succi, Sauro; Toschi, Federico

    2016-11-01

    Many complex flows are characterized by the simultaneous presence of a range of non-equilibrium and rarefaction effects in different regions of the flow field. We recently developed a Direct Simulation Monte Carlo (DSMC)-Lattice Boltzmann Method (LBM) hybrid scheme, based on domain decomposition technique and on Grad's moments method, able to accurately and efficiently simulate such flows. While DSMC is employed to compute the flow field only where large non-equilibrium effects are present, the more computationally efficient LBM is employed wherever the non-equilibrium effects can be dealt with perturbatively, i.e. according to Navier-Stokes hydrodynamics. Here we present the results on the application of the hybrid method to complex three-dimensional flows, in particular to the flow around a microsphere and through a disk-shaped expansion channel. The solutions provided by the hybrid method are compared against full DSMC simulations and the computational gain guaranteed by the application of the hybrid method over the full DSMC is also demonstrated.

  3. A refined method for calculating paleotemperatures from linear correlations in bamboo coral carbon and oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Saenger, Casey; Watkins, James M.

    2016-06-01

    Bamboo corals represent an emerging paleoclimate archive with the potential to record variability at intermediate depths throughout much of the global ocean. Realizing this potential has been complicated by biologically mediated vital effects, which are evident in linear correlations of skeletal carbon (δ13C) and oxygen (δ18O) isotope composition. Previous efforts to develop a bamboo coral δ18O paleothermometer by accounting for such vital effects have not been completely successful as they still rely on empirical calibrations that are offset from the temperature dependence of abiogenic experiments. Here we describe an approach that better corrects for bamboo coral vital effects and allows paleotemperatures to be calculated directly from the abiogenic temperature dependence. The success of the method lies in calculating apparent equilibrium carbon and oxygen isotope fractionation at the temperature, pH, and growth rate of each coral, as well as in the use of model II regressions. Rigorous propagation of uncertainty suggests typical errors of ±2-3°C, but in select cases errors as low as ±0.65°C can be achieved for densely sampled and strongly correlated data sets. This lower limit approaches the value attributed to uncertainty in pH and growth rate estimates alone, as predicted by a series of pseudoproxy experiments. The incorporation of isotopically light metabolic CO2 appears to be negligible in most Pacific corals, but may be significant in Atlantic specimens, potentially requiring an additional correction. The success of the method therefore hinges on how well complex environmental systems and biomineralization strategies are constrained, with the most reliable temperatures occurring when calcifying fluid pH, growth rate, and incorporation of metabolic carbon into skeletal calcite are constrained using multiple geochemical proxies.

  4. Methods for separating medical isotopes using ionic liquids

    DOEpatents

    Luo, Huimin; Boll, Rose Ann; Bell, Jason Richard; Dai, Sheng

    2014-10-21

    A method for extracting a radioisotope from an aqueous solution, the method comprising: a) intimately mixing a non-chelating ionic liquid with the aqueous solution to transfer at least a portion of said radioisotope to said non-chelating ionic liquid; and b) separating the non-chelating ionic liquid from the aqueous solution. In preferred embodiments, the method achieves an extraction efficiency of at least 80%, or a separation factor of at least 1.times.10.sup.4 when more than one radioisotope is included in the aqueous solution. In particular embodiments, the method is applied to the separation of medical isotopes pairs, such as Th from Ac (Th-229/Ac-225, Ac-227/Th-227), or Ra from Ac (Ac-225 and Ra-225, Ac-227 and Ra-223), or Ra from Th (Th-227 and Ra-223, Th-229 and Ra-225).

  5. Development of a non-equilibrium quantum transport calculation method based on constrained density functional

    NASA Astrophysics Data System (ADS)

    Kim, Han Seul; Kim, Yong-Hoon

    2015-03-01

    We report on the development of a novel first-principles method for the calculation of non-equilibrium quantum transport process. Within the scheme, non-equilibrium situation and quantum transport within the open-boundary condition are described by the region-dependent Δ self-consistent field method and matrix Green's function theory, respectively. We will discuss our solutions to the technical difficulties in describing bias-dependent electron transport at complicated nanointerfaces and present several application examples. Global Frontier Program (2013M3A6B1078881), Basic Science Research Grant (2012R1A1A2044793), EDISON Program (No. 2012M3C1A6035684), and 2013 Global Ph.D fellowship program of the National Research Foundation. KISTI Supercomputing Center (KSC-2014-C3-021).

  6. INSTRUMENTS AND METHODS OF INVESTIGATION: Plasma isotope separation based on ion cyclotron resonance

    NASA Astrophysics Data System (ADS)

    Dolgolenko, Dmitrii A.; Muromkin, Yurii A.

    2009-04-01

    Experiments that have been conducted in the USA, France, and Russia to investigate isotopically selective ion cyclotron resonance (ICR) as a tool for plasma isotope separation are analyzed. Because this method runs into difficulties at low values of the relative isotope mass difference ΔM/M, for some elements (for gadolinium, as an example) isotope separation still remains a problem. There are ways to solve it, however, as experimental results and theoretical calculations suggest.

  7. An Analytical Investigation of Three General Methods of Calculating Chemical-Equilibrium Compositions

    NASA Technical Reports Server (NTRS)

    Zeleznik, Frank J.; Gordon, Sanford

    1960-01-01

    The Brinkley, Huff, and White methods for chemical-equilibrium calculations were modified and extended in order to permit an analytical comparison. The extended forms of these methods permit condensed species as reaction products, include temperature as a variable in the iteration, and permit arbitrary estimates for the variables. It is analytically shown that the three extended methods can be placed in a form that is independent of components. In this form the Brinkley iteration is identical computationally to the White method, while the modified Huff method differs only'slightly from these two. The convergence rates of the modified Brinkley and White methods are identical; and, further, all three methods are guaranteed to converge and will ultimately converge quadratically. It is concluded that no one of the three methods offers any significant computational advantages over the other two.

  8. Method of rapid determination of MHD equilibrium properties with the modified version of the SURFAS code

    SciTech Connect

    Lee, D.K.; Hirshman, S.P.; Okabayashi, M.; Reusch, M.F.; Sun, Y.C.

    1993-09-01

    Rapid determination of MHD eqilibrium properties of tokamak plasmas is carried out by means of an approximation method based on the use of database files. These are computed a priori from MHD equilibrium solutions obtained by performing reconstruction to match experimental measurements, which include motional Stark effect (MSE) data. The procedure carries out a single iteration of Newton`s method to determine the poloidal variation of the toroidal plasma current density in the equilibrium form j{sub {phi}} = {minus}2{pi}({mu}{sub 0}Rp{prime} + FF{prime}/R) by representing p{prime}({psi}) and F({psi})F{prime}({psi}) in series expansions of Chebyshev polynomials. The polynominal expansion coefficients are obtained through a least-squares data fitting process similar to that used in the equilibrium reconstruction. Knowing the current density j{phi} allows the determination of the internal q-profile from the MSE data. This important stability parameter is generally unavailable from a current filament model. Numerical results calculated in this approach are compared with those determined from an accurate solution of the Grad-Shafranov equation, subject to a similar set of magnetic and pressure measurement constraints.

  9. Real-time extraction of plasma equilibrium parameters in KSTAR tokamak using statistical methods

    NASA Astrophysics Data System (ADS)

    Na, Yong-Su; Jeon, Young-Mu; Hong, S. H.; Hwang, Y. S.

    2001-02-01

    To improve inherent shortcomings of statistical methods and apply them to the extraction of plasma equilibrium parameters in a fast timescale for real-time plasma control, new concepts of statistical methods such as principal component analysis-based neural network (NN), functional parametrization (FP)-based NN and double network are introduced by modifying NN and FP. These new methods are benchmarked and compared with the conventional techniques of NN and FP in a simple single-filament system. As a result of their applications to identification of plasma equilibrium parameters in the Korea Superconducting Tokamak Advanced Research tokamak, particularly, the double network concept among them has successfully achieved the improvement of drawbacks in the conventional methods. It is shown that more reliable results from the double network method can be obtained by combining several different statistical treatments as a primary network. Even in the case of nonoptimized methods united as a primary network, quite acceptable results can be achieved in the double network method.

  10. Rotational spectra of rare isotopic species of fluoroiodomethane: Determination of the equilibrium structure from rotational spectroscopy and quantum-chemical calculations

    NASA Astrophysics Data System (ADS)

    Puzzarini, Cristina; Cazzoli, Gabriele; López, Juan Carlos; Alonso, José Luis; Baldacci, Agostino; Baldan, Alessandro; Stopkowicz, Stella; Cheng, Lan; Gauss, Jürgen

    2012-07-01

    Supported by accurate quantum-chemical calculations, the rotational spectra of the mono- and bi-deuterated species of fluoroiodomethane, CHDFI and CD2FI, as well as of the 13C-containing species, 13CH2FI, were recorded for the first time. Three different spectrometers were employed, a Fourier-transform microwave spectrometer, a millimeter/submillimter-wave spectrometer, and a THz spectrometer, thus allowing to record a huge portion of the rotational spectrum, from 5 GHz up to 1.05 THz, and to accurately determine the ground-state rotational and centrifugal-distortion constants. Sub-Doppler measurements allowed to resolve the hyperfine structure of the rotational spectrum and to determine the complete iodine quadrupole-coupling tensor as well as the diagonal elements of the iodine spin-rotation tensor. The present investigation of rare isotopic species of CH2FI together with the results previously obtained for the main isotopologue [C. Puzzarini, G. Cazzoli, J. C. López, J. L. Alonso, A. Baldacci, A. Baldan, S. Stopkowicz, L. Cheng, and J. Gauss, J. Chem. Phys. 134, 174312 (2011);, 10.1063/1.3583498 G. Cazzoli, A. Baldacci, A. Baldan, and C. Puzzarini, Mol. Phys. 109, 2245 (2011)], 10.1080/00268976.2011.609142 enabled us to derive a semi-experimental equilibrium structure for fluoroiodomethane by means of a least-squares fit procedure using the available experimental ground-state rotational constants together with computed vibrational corrections. Problems related to the missing isotopic substitution of fluorine and iodine were overcome thanks to the availability of an accurate theoretical equilibrium geometry (computed at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations).

  11. Rotational spectra of rare isotopic species of fluoroiodomethane: determination of the equilibrium structure from rotational spectroscopy and quantum-chemical calculations.

    PubMed

    Puzzarini, Cristina; Cazzoli, Gabriele; López, Juan Carlos; Alonso, José Luis; Baldacci, Agostino; Baldan, Alessandro; Stopkowicz, Stella; Cheng, Lan; Gauss, Jürgen

    2012-07-14

    Supported by accurate quantum-chemical calculations, the rotational spectra of the mono- and bi-deuterated species of fluoroiodomethane, CHDFI and CD(2)FI, as well as of the (13)C-containing species, (13)CH(2)FI, were recorded for the first time. Three different spectrometers were employed, a Fourier-transform microwave spectrometer, a millimeter/submillimter-wave spectrometer, and a THz spectrometer, thus allowing to record a huge portion of the rotational spectrum, from 5 GHz up to 1.05 THz, and to accurately determine the ground-state rotational and centrifugal-distortion constants. Sub-Doppler measurements allowed to resolve the hyperfine structure of the rotational spectrum and to determine the complete iodine quadrupole-coupling tensor as well as the diagonal elements of the iodine spin-rotation tensor. The present investigation of rare isotopic species of CH(2)FI together with the results previously obtained for the main isotopologue [C. Puzzarini, G. Cazzoli, J. C. López, J. L. Alonso, A. Baldacci, A. Baldan, S. Stopkowicz, L. Cheng, and J. Gauss, J. Chem. Phys. 134, 174312 (2011); G. Cazzoli, A. Baldacci, A. Baldan, and C. Puzzarini, Mol. Phys. 109, 2245 (2011)] enabled us to derive a semi-experimental equilibrium structure for fluoroiodomethane by means of a least-squares fit procedure using the available experimental ground-state rotational constants together with computed vibrational corrections. Problems related to the missing isotopic substitution of fluorine and iodine were overcome thanks to the availability of an accurate theoretical equilibrium geometry (computed at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations).

  12. Method of preparing mercury with an arbitrary isotopic distribution

    DOEpatents

    Grossman, M.W.; George, W.A.

    1986-12-16

    This invention provides for a process for preparing mercury with a predetermined, arbitrary, isotopic distribution. In one embodiment, different isotopic types of Hg[sub 2]Cl[sub 2], corresponding to the predetermined isotopic distribution of Hg desired, are placed in an electrolyte solution of HCl and H[sub 2]O. The resulting mercurous ions are then electrolytically plated onto a cathode wire producing mercury containing the predetermined isotopic distribution. In a similar fashion, Hg with a predetermined isotopic distribution is obtained from different isotopic types of HgO. In this embodiment, the HgO is dissolved in an electrolytic solution of glacial acetic acid and H[sub 2]O. The isotopic specific Hg is then electrolytically plated onto a cathode and then recovered. 1 fig.

  13. Method of preparing mercury with an arbitrary isotopic distribution

    DOEpatents

    Grossman, Mark W.; George, William A.

    1986-01-01

    This invention provides for a process for preparing mercury with a predetermined, arbitrary, isotopic distribution. In one embodiment, different isotopic types of Hg.sub.2 Cl.sub.2, corresponding to the predetermined isotopic distribution of Hg desired, are placed in an electrolyte solution of HCl and H.sub.2 O. The resulting mercurous ions are then electrolytically plated onto a cathode wire producing mercury containing the predetermined isotopic distribution. In a similar fashion, Hg with a predetermined isotopic distribution is obtained from different isotopic types of HgO. In this embodiment, the HgO is dissolved in an electrolytic solution of glacial acetic acid and H.sub.2 O. The isotopic specific Hg is then electrolytically plated onto a cathode and then recovered.

  14. Methods and limitations of 'clumped' CO2 isotope (Delta47) analysis by gas-source isotope ratio mass spectrometry.

    PubMed

    Huntington, K W; Eiler, J M; Affek, H P; Guo, W; Bonifacie, M; Yeung, L Y; Thiagarajan, N; Passey, B; Tripati, A; Daëron, M; Came, R

    2009-09-01

    The geochemistry of multiply substituted isotopologues ('clumped-isotope' geochemistry) examines the abundances in natural materials of molecules, formula units or moieties that contain more than one rare isotope (e.g. (13)C(18)O(16)O, (18)O(18)O, (15)N(2), (13)C(18)O(16)O(2) (2-)). Such species form the basis of carbonate clumped-isotope thermometry and undergo distinctive fractionations during a variety of natural processes, but initial reports have provided few details of their analysis. In this study, we present detailed data and arguments regarding the theoretical and practical limits of precision, methods of standardization, instrument linearity and related issues for clumped-isotope analysis by dual-inlet gas-source isotope ratio mass spectrometry (IRMS). We demonstrate long-term stability and subtenth per mil precision in 47/44 ratios for counting systems consisting of a Faraday cup registered through a 10(12) ohm resistor on three Thermo-Finnigan 253 IRMS systems. Based on the analyses of heated CO(2) gases, which have a stochastic distribution of isotopes among possible isotopologues, we document and correct for (1) isotopic exchange among analyte CO(2) molecules and (2) subtle nonlinearity in the relationship between actual and measured 47/44 ratios. External precisions of approximately 0.01 per thousand are routinely achieved for measurements of the mass-47 anomaly (a measure mostly of the abundance anomaly of (13)C-(18)O bonds) and follow counting statistics. The present technical limit to precision intrinsic to our methods and instrumentation is approximately 5 parts per million (ppm), whereas precisions of measurements of heterogeneous natural materials are more typically approximately 10 ppm (both 1 s.e.). These correspond to errors in carbonate clumped-isotope thermometry of +/-1.2 degrees C and +/-2.4 degrees C, respectively.

  15. Spectrophotometric and thermodynamic study on the dimerization equilibrium of ionic dyes in water by chemometrics method

    NASA Astrophysics Data System (ADS)

    Niazi, Ali; Yazdanipour, Ateesa; Ghasemi, Jahanbakhsh; Kubista, Mikael

    2006-09-01

    The monomer-dimer equilibrium and thermodynamic of several ionic dyes (Neutral Red, Nile Blue A, Safranine T and Thionine) has been investigated by means of spectrophotometric and chemometrics methods. The dimerization constants of these ionic dyes have been determined by studying the dependence of their absorption spectra on the temperature in the range 20-75 °C at concentrations of Neutral Red (1.73 × 10 -5 M), Nile Blue A (3.94 × 10 -5 M), Safranine (6.59 × 10 -5 M) and Thionine (6.60 × 10 -5 M). The monomer-dimer equilibrium of these dyes has been determined by chemometrics refinement of the absorption spectra obtained by thermometric titrations performed. The processing of the data carried out for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. The enthalpy and entropy of the dimerization reactions were determined from the dependence of the equilibrium constants to the temperature (van't Hoff equation).

  16. Quantification of metabotropic glutamate subtype 5 receptors in the brain by an equilibrium method using 18F-SP203.

    PubMed

    Kimura, Yasuyuki; Siméon, Fabrice G; Zoghbi, Sami S; Zhang, Yi; Hatazawa, Jun; Pike, Victor W; Innis, Robert B; Fujita, Masahiro

    2012-02-01

    A new PET ligand, 3-fluoro-5-(2-(2-(18)F-(fluoromethyl)-thiazol-4-yl)ethynyl)benzonitrile (18F-SP203) can quantify metabotropic glutamate subtype 5 receptors (mGluR5) in human brain by a bolus injection and kinetic modeling. As an alternative approach to a bolus injection, binding can simply be measured as a ratio of tissue to metabolite-corrected plasma at a single time point under equilibrium conditions achieved by administering the radioligand with a bolus injection followed by a constant infusion. The purpose of this study was to validate the equilibrium method as an alternative to the standard kinetic method for measuring 18F-SP203 binding in the brain. Nine healthy subjects were injected with 18F-SP203 using a bolus plus constant infusion for 300 min. A single ratio of bolus-to-constant infusion (the activity of bolus equaled to that of infusion over 219 min) was applied to all subjects to achieve equilibrium in approximately 120 min. As a measure of ligand binding, we compared total distribution volume (VT) calculated by the equilibrium and kinetic methods in each scan. The equilibrium method calculated VT by the ratio of radioactivity in the brain to the concentration of 18F-SP203 in arterial plasma at 120 min, and the kinetic method calculated VT by a two-tissue compartment model using brain and plasma dynamic data from 0 to 120 min. VT obtained via the equilibrium method was highly correlated with VT obtained via kinetic modeling. Inter-subject variability of VT obtained via the equilibrium method was slightly smaller than VT obtained via the kinetic method. VT obtained via the equilibrium method was ~10% higher than VT obtained via the kinetic method, indicating a small difference between the measurements. Taken together, the results of this study show that using the equilibrium method is an acceptable alternative to the standard kinetic method when using 18F-SP203 to measure mGluR5. Although small differences in the measurements obtained via the

  17. Equilibrium Iron Isotope Fractionation Factors of Minerals: Reevaluation from the Data of Nuclear Inelastic Resonant X-ray Scattering and Mossbauer Spectroscopy

    SciTech Connect

    Polyakov, Dr. V. B.; Clayton, R. N.; Horita, Juske; Mineev, S. D.

    2007-01-01

    We have critically reevaluated equilibrium iron isotope fractionation factors for oxide and sulfide minerals using recently acquired data obtained by Moessbauer spectroscopy and inelastic nuclear resonant X-ray scattering (INRXS) synchrotron radiation. Good agreement was observed in the iron {beta}-factors of metallic iron ({alpha}-Fe) and hematite calculated using both Moessbauer- and INRXS-derived data, which supports the validity and reliability of the calculations. Based on this excellent agreement, we suggest the use of the present data on the iron {beta}-factors of hematite as a reference. The previous Moessbauer-derived iron {beta}-factor for magnetite has been modified significantly based on the Fe-sublattice density of states obtained from the INRXS experiments. This resolves the disagreement between naturally observed iron isotope fractionation factors for mineral pairs involving magnetite and those obtained from the calculated {beta}-factors. The correctness of iron {beta}-factor for pyrite has been corroborated by the good agreement with experimental data of sulfur isotope geothermometers of pyrite-galena and pyrite-sphalerite. A good correlation between the potential energy of the cation site, the oxidation state of iron and the iron {beta}-factor value has been established. Specifically, ferric compounds, which have a higher potential energy of iron than ferrous compounds, have higher {beta}-factors. A similar dependence of b-factors on the oxidation state and potential energy could be extended to other transition metals. Extremely low values of INRXS-derived iron {beta}-factors for troilite and Fe{sub 3}S significantly widen the range of iron b-factors for covalently bonded compounds.

  18. Thermodynamic equilibrium solubility measurements in simulated fluids by 96-well plate method in early drug discovery.

    PubMed

    Bharate, Sonali S; Vishwakarma, Ram A

    2015-04-01

    An early prediction of solubility in physiological media (PBS, SGF and SIF) is useful to predict qualitatively bioavailability and absorption of lead candidates. Despite of the availability of multiple solubility estimation methods, none of the reported method involves simplified fixed protocol for diverse set of compounds. Therefore, a simple and medium-throughput solubility estimation protocol is highly desirable during lead optimization stage. The present work introduces a rapid method for assessment of thermodynamic equilibrium solubility of compounds in aqueous media using 96-well microplate. The developed protocol is straightforward to set up and takes advantage of the sensitivity of UV spectroscopy. The compound, in stock solution in methanol, is introduced in microgram quantities into microplate wells followed by drying at an ambient temperature. Microplates were shaken upon addition of test media and the supernatant was analyzed by UV method. A plot of absorbance versus concentration of a sample provides saturation point, which is thermodynamic equilibrium solubility of a sample. The established protocol was validated using a large panel of commercially available drugs and with conventional miniaturized shake flask method (r(2)>0.84). Additionally, the statistically significant QSPR models were established using experimental solubility values of 52 compounds.

  19. Isotope-ratio-monitoring gas chromatography-mass spectrometry: methods for isotopic calibration

    NASA Technical Reports Server (NTRS)

    Merritt, D. A.; Brand, W. A.; Hayes, J. M.

    1994-01-01

    In trial analyses of a series of n-alkanes, precise determinations of 13C contents were based on isotopic standards introduced by five different techniques and results were compared. Specifically, organic-compound standards were coinjected with the analytes and carried through chromatography and combustion with them; or CO2 was supplied from a conventional inlet and mixed with the analyte in the ion source, or CO2 was supplied from an auxiliary mixing volume and transmitted to the source without interruption of the analyte stream. Additionally, two techniques were investigated in which the analyte stream was diverted and CO2 standards were placed on a near-zero background. All methods provided accurate results. Where applicable, methods not involving interruption of the analyte stream provided the highest performance (sigma = 0.00006 at.% 13C or 0.06% for 250 pmol C as CO2 reaching the ion source), but great care was required. Techniques involving diversion of the analyte stream were immune to interference from coeluting sample components and still provided high precision (0.0001 < or = sigma < or = 0.0002 at.% or 0.1 < or = sigma < or = 0.2%).

  20. System and method for high precision isotope ratio destructive analysis

    DOEpatents

    Bushaw, Bruce A; Anheier, Norman C; Phillips, Jon R

    2013-07-02

    A system and process are disclosed that provide high accuracy and high precision destructive analysis measurements for isotope ratio determination of relative isotope abundance distributions in liquids, solids, and particulate samples. The invention utilizes a collinear probe beam to interrogate a laser ablated plume. This invention provides enhanced single-shot detection sensitivity approaching the femtogram range, and isotope ratios that can be determined at approximately 1% or better precision and accuracy (relative standard deviation).

  1. Using (18)O/(16)O exchange to probe an equilibrium space-charge layer at the surface of a crystalline oxide: method and application.

    PubMed

    De Souza, Roger A; Martin, Manfred

    2008-05-07

    The use of an (18)O/(16)O exchange experiment as a means for probing surface space-charge layers in oxides is examined theoretically and experimentally. On the basis of a theoretical treatment, isotope penetration profiles are calculated for (18)O/(16)O exchange across a gas-solid interface and subsequent diffusion of the labelled isotope through an equilibrium space-charge layer depleted of mobile oxygen vacancies and into a homogeneous bulk phase. Profiles calculated for a range of conditions all have a characteristic shape: a sharp drop in isotope fraction close to the surface followed by a normal bulk diffusion profile. Experimental (18)O profiles in an exchanged (001) oriented single crystal of Fe-doped SrTiO(3) were measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). By extracting the space-charge potential from such profiles, we demonstrate that this method allows the spatially resolved characterization of space-charge layers at the surfaces of crystalline oxides under thermodynamically well-defined conditions.

  2. Theoretical estimates of equilibrium sulfur isotope effects in aqueous sulfur systems: Highlighting the role of isomers in the sulfite and sulfoxylate systems

    NASA Astrophysics Data System (ADS)

    Eldridge, D. L.; Guo, W.; Farquhar, J.

    2016-12-01

    We present theoretical calculations for all three isotope ratios of sulfur (33S/32S, 34S/32S, 36S/32S) at the B3LYP/6-31+G(d,p) level of theory for aqueous sulfur compounds modeled in 30-40H2O clusters spanning the range of sulfur oxidation state (Sn, n = -2 to +6) for estimating equilibrium fractionation factors in aqueous systems. Computed 34β values based on major isotope (34S/32S) reduced partition function ratios (RPFRs) scale to a first order with sulfur oxidation state and coordination, where 34β generally increase with higher oxidation state and increasing coordination of the sulfur atom. Exponents defining mass dependent relationships based on β values (x/34κ = ln(xβ)/ln(34β), x = 33 or 36) conform to tight ranges over a wide range of temperature for all aqueous compounds (33/34κ ≈ 0.5148-0.5159, 36/34κ ≈ 1.89-1.90 from T ⩾ 0 °C). The exponents converge near a singular value for all compounds at the high temperature limit (33/34κT→∞ = 0.51587 ± 0.00003 and 36/34κT→∞ = 1.8905 ± 0.0002; 1 s.d. of all computed compounds), and typically follow trends based on oxidation state and coordination similar to those seen in 34β values at lower temperatures. Theoretical equilibrium fractionation factors computed from these β-values are compared to experimental constraints for HSO3-T(aq)/SO2(g, aq), SO2(aq)/SO2(g), H2S(aq)/H2S(g), H2S(aq)/HS-(aq), SO42-(aq)/H2ST(aq), S2O32-(aq) (intramolecular), and S2O32-(aq)/H2ST(aq), and generally agree within a reasonable estimation of uncertainties. We make predictions of fractionation factors where other constraints are unavailable. Isotope partitioning of the isomers of protonated compounds in the sulfite and sulfoxylate systems depend strongly on whether protons are bound to either sulfur or oxygen atoms. The magnitude of the HSO3-T/SO32- major isotope (34S/32S) fractionation factor is predicted to increase with temperature from 0 to 70 °C due to the combined effects of the large magnitude (HS)O3

  3. Meshless Method for Solving Fixed Boundary Problem of Axisymmetric Plasma Equilibrium

    NASA Astrophysics Data System (ADS)

    Imazawa, Ryota; Kawano, Yasunori; Itami, Kiyoshi

    2013-10-01

    This study is to solve Grad-Shafranov (GS) equation with the fixed plasma boundary by utilizing the meshless method for the first time. The previous studies have utilized the finite element method (FEM) to solve the equilibrium inside the fixed separatrix. In order to avoid the difficulty of FEM (e.g. mesh problem, difficulty of coding, expensive calculation cost, etc.), this study proposes the new method to apply the meshless methods, especially RBF-MFS and Kansa's method to inhomogeneous and nonlinear partial differential equations (PDE). Although the RBF-MFS and Kansa's method are applicable to the inhomogeneous PDE, the application of these methods to the GS equation is not straight-forward. Since the current profile is usually parameterized by the normalized poloidal flux, the inhomogeneous term of the GS equation contains the normalized poloidal flux, not just a poloidal flux. This is the difficulty for solving the GS equation. Accuracy and calculation time of the meshless method and FEM are compared in the condition of the same total number of nodes. The results show that the error of magnetic field obtained by the meshless methods is one hundredth of that by FEM and that the calculation time of the meshless method is one tenth of that of FEM. Moreover, this study shows that the meshless methods can be easily accelerated by parallel computing.

  4. Fast convergence to equilibrium for long-chain polymer melts using a MD/continuum hybrid method.

    PubMed

    Senda, Yasuhiro; Fujio, Miyuki; Shimamura, Shuji; Blomqvist, Janne; Nieminen, Risto M

    2012-10-21

    Effective and fast convergence toward an equilibrium state for long-chain polymer melts is realized by a hybrid method coupling molecular dynamics and the elastic continuum. The required simulation time to achieve the equilibrium state is reduced compared with conventional equilibration methods. The polymers move on a wide range phase space due to large-scale fluctuation generated by the elastic continuum. A variety of chain structures is generated in the polymer melt which results in the fast convergence to the equilibrium state.

  5. An innovative method for extracting isotopic information from low-resolution gamma spectra

    SciTech Connect

    Miko, D.; Estep, R.J.; Rawool-Sullivan, M.W.

    1998-12-01

    A method is described for the extraction of isotopic information from attenuated gamma ray spectra using the gross-count material basis set (GC-MBS) model. This method solves for the isotopic composition of an unknown mixture of isotopes attenuated through an absorber of unknown material. For binary isotopic combinations the problem is nonlinear in only one variable and is easily solved using standard line optimization techniques. Results are presented for NaI spectrum analyses of various binary combinations of enriched uranium, depleted uranium, low burnup Pu, {sup 137}Cs, and {sup 133}Ba attenuated through a suite of absorbers ranging in Z from polyethylene through lead. The GC-MBS method results are compared to those computed using ordinary response function fitting and with a simple net peak area method. The GC-MBS method was found to be significantly more accurate than the other methods over the range of absorbers and isotopic blends studied.

  6. Non-equilibrium simulation of CH4 production through the depressurization method from gas hydrate reservoirs

    NASA Astrophysics Data System (ADS)

    Qorbani, Khadijeh; Kvamme, Bjørn

    2016-04-01

    as non-equilibrium processes under local constraint of mass and heat fluxes. In this work, we have extended RCB by adding another route for dissociation or reformation of CH4-hydrate towards CH4 into the aqueous phase and water. CH4-hydrate formation and dissociation is resolved by looking at supersaturation and undersaturation with respect to thermodynamics variables. Hydrate instability due to undersaturation of CH4 in the contacting water phase is also considered. A complete non-equilibrium thermodynamic package, developed in-house, was combined with RCB to account for competing phase transitions by considering the minimization of Gibb's free energy. The energy differences were calculated from variations in chemical potentials of hydrate and hydrate formers. Mass transport, heat transport and non-equilibrium thermodynamic effects were implemented through classical nucleation theory to model the kinetic rate of hydrate phase transitions. To illustrate our implementations we ran simulations covering time-spans in the order of hundred years. CH4 production was modelled using the depressurization method, where we employed the Messoyakha field data. We discuss our implementations, as well as results obtained from simulations utilizing our modifications.

  7. Non-equilibrium Green's functions method: Non-trivial and disordered leads

    NASA Astrophysics Data System (ADS)

    He, Yu; Wang, Yu; Klimeck, Gerhard; Kubis, Tillmann

    2014-11-01

    The non-equilibrium Green's function algorithm requires contact self-energies to model charge injection and extraction. All existing approaches assume infinitely periodic leads attached to a possibly quite complex device. This contradicts today's realistic devices in which contacts are spatially inhomogeneous, chemically disordered, and impacting the overall device characteristics. This work extends the complex absorbing potentials method for arbitrary, ideal, or non-ideal leads in atomistic tight binding representation. The algorithm is demonstrated on a Si nanowire with periodic leads, a graphene nanoribbon with trumpet shape leads, and devices with leads of randomly alloyed Si0.5Ge0.5. It is found that alloy randomness in the leads can reduce the predicted ON-state current of Si0.5Ge0.5 transistors by 45% compared to conventional lead methods.

  8. Non-equilibrium Green function method: theory and application in simulation of nanometer electronic devices

    NASA Astrophysics Data System (ADS)

    Do, Van-Nam

    2014-09-01

    We review fundamental aspects of the non-equilibrium Green function method in the simulation of nanometer electronic devices. The method is implemented into our recently developed computer package OPEDEVS to investigate transport properties of electrons in nano-scale devices and low-dimensional materials. Concretely, we present the definition of the four real-time Green functions, the retarded, advanced, lesser and greater functions. Basic relations among these functions and their equations of motion are also presented in detail as the basis for the performance of analytical and numerical calculations. In particular, we review in detail two recursive algorithms, which are implemented in OPEDEVS to solve the Green functions defined in finite-size opened systems and in the surface layer of semi-infinite homogeneous ones. Operation of the package is then illustrated through the simulation of the transport characteristics of a typical semiconductor device structure, the resonant tunneling diodes.

  9. Phases, periphases, and interphases equilibrium by molecular modeling. I. Mass equilibrium by the semianalytical stochastic perturbations method and application to a solution between (120) gypsum faces

    NASA Astrophysics Data System (ADS)

    Pedesseau, Laurent; Jouanna, Paul

    2004-12-01

    The SASP (semianalytical stochastic perturbations) method is an original mixed macro-nano-approach dedicated to the mass equilibrium of multispecies phases, periphases, and interphases. This general method, applied here to the reflexive relation Ck⇔μk between the concentrations Ck and the chemical potentials μk of k species within a fluid in equilibrium, leads to the distribution of the particles at the atomic scale. The macroaspects of the method, based on analytical Taylor's developments of chemical potentials, are intimately mixed with the nanoaspects of molecular mechanics computations on stochastically perturbed states. This numerical approach, directly linked to definitions, is universal by comparison with current approaches, DLVO Derjaguin-Landau-Verwey-Overbeek, grand canonical Monte Carlo, etc., without any restriction on the number of species, concentrations, or boundary conditions. The determination of the relation Ck⇔μk implies in fact two problems: a direct problem Ck⇒μk and an inverse problem μk⇒Ck. Validation of the method is demonstrated in case studies A and B which treat, respectively, a direct problem and an inverse problem within a free saturated gypsum solution. The flexibility of the method is illustrated in case study C dealing with an inverse problem within a solution interphase, confined between two (120) gypsum faces, remaining in connection with a reference solution. This last inverse problem leads to the mass equilibrium of ions and water molecules within a 3 Å thick gypsum interface. The major unexpected observation is the repulsion of SO42- ions towards the reference solution and the attraction of Ca2+ ions from the reference solution, the concentration being 50 times higher within the interphase as compared to the free solution. The SASP method is today the unique approach able to tackle the simulation of the number and distribution of ions plus water molecules in such extreme confined conditions. This result is of prime

  10. Phases, periphases, and interphases equilibrium by molecular modeling. I. Mass equilibrium by the semianalytical stochastic perturbations method and application to a solution between (120) gypsum faces.

    PubMed

    Pedesseau, Laurent; Jouanna, Paul

    2004-12-22

    The SASP (semianalytical stochastic perturbations) method is an original mixed macro-nano-approach dedicated to the mass equilibrium of multispecies phases, periphases, and interphases. This general method, applied here to the reflexive relation C(k)<=>mu(k) between the concentrations C(k) and the chemical potentials mu(k) of k species within a fluid in equilibrium, leads to the distribution of the particles at the atomic scale. The macroaspects of the method, based on analytical Taylor's developments of chemical potentials, are intimately mixed with the nanoaspects of molecular mechanics computations on stochastically perturbed states. This numerical approach, directly linked to definitions, is universal by comparison with current approaches, DLVO Derjaguin-Landau-Verwey-Overbeek, grand canonical Monte Carlo, etc., without any restriction on the number of species, concentrations, or boundary conditions. The determination of the relation C(k)<=>mu(k) implies in fact two problems: a direct problem C(k)=>mu(k) and an inverse problem mu(k)=>C(k). Validation of the method is demonstrated in case studies A and B which treat, respectively, a direct problem and an inverse problem within a free saturated gypsum solution. The flexibility of the method is illustrated in case study C dealing with an inverse problem within a solution interphase, confined between two (120) gypsum faces, remaining in connection with a reference solution. This last inverse problem leads to the mass equilibrium of ions and water molecules within a 3 A thick gypsum interface. The major unexpected observation is the repulsion of SO(4) (2-) ions towards the reference solution and the attraction of Ca(2+) ions from the reference solution, the concentration being 50 times higher within the interphase as compared to the free solution. The SASP method is today the unique approach able to tackle the simulation of the number and distribution of ions plus water molecules in such extreme confined conditions

  11. Solute transport with multisegment, equilibrium-controlled reactions: A feed forward simulation method

    USGS Publications Warehouse

    Rubin, Jacob

    1990-01-01

    The feed forward method (FF method) is one of the ways of formulating operational equations which simulate transport of solutes influenced by equilibrium-controlled reaction networks. The FF method provides increased solution efficiency by adapting its formulations to some of the network's fundamental features. In this study the FF method is further developed by adapting and testing it for a variety of network conditions. Classes of homogeneous, classical heterogeneous, and ion exchange network segments are studied. Networks may contain only a single class of segments or they may involve two or three segment classes. The FF method is found applicable to all the cases tested. In only one of these cases, for the more complex configurations of network segments, the FF method does not attain all of its objectives. A systematic, stepwise approach to method development is employed. It reveals, for certain subnetworks, an a priori inadmissibility, irrespective of the method used, and, for some other networks, an a priori irrelevance to transport dynamics. It also demonstrates that when certain subnetworks, belonging to different segment classes, form a single network, synergism (or antagonism) may occasionally arise and decrease (or increase) the difficulty of solving the transport problem.

  12. VELOCITY SELECTOR METHOD FOR THE SEPARATION OF ISOTOPES

    DOEpatents

    Britten, R.J.

    1957-12-31

    A velocity selector apparatus is described for separating and collecting an enriched fraction of the isotope of a particular element. The invention has the advantage over conventional mass spectrometers in that a magnetic field is not used, doing away with the attendant problems of magnetic field variation. The apparatus separates the isotopes by selectively accelerating the ionized constituents present in a beam of the polyisotopic substance that are of uniform kinetic energy, the acceleration being applied intermittently and at spaced points along the beam and in a direction normal to the direction of the propagation of the uniform energy beam whereby a transverse displacement of the isotopic constituents of different mass is obtained.

  13. Multiple temperature kinetic model and gas-kinetic method for hypersonic non-equilibrium flow computations

    NASA Astrophysics Data System (ADS)

    Xu, Kun; He, Xin; Cai, Chunpei

    2008-07-01

    It is well known that for increasingly rarefied flowfields, the predictions from continuum formulation, such as the Navier-Stokes equations lose accuracy. For the high speed diatomic molecular flow in the transitional regime, the inaccuracies are partially attributed to the single temperature approximations in the Navier-Stokes equations. Here, we propose a continuum multiple temperature model based on the Bhatnagar-Gross-Krook (BGK) equation for the non-equilibrium flow computation. In the current model, the Landau-Teller-Jeans relaxation model for the rotational energy is used to evaluate the energy exchange between the translational and rotational modes. Due to the multiple temperature approximation, the second viscosity coefficient in the Navier-Stokes equations is replaced by the temperature relaxation term. In order to solve the multiple temperature kinetic model, a multiscale gas-kinetic finite volume scheme is proposed, where the gas-kinetic equation is numerically solved for the fluxes to update the macroscopic flow variables inside each control volume. Since the gas-kinetic scheme uses a continuous gas distribution function at a cell interface for the fluxes evaluation, the moments of a gas distribution function can be explicitly obtained for the multiple temperature model. Therefore, the kinetic scheme is much more efficient than the DSMC method, especially in the near continuum flow regime. For the non-equilibrium flow computations, i.e., the nozzle flow and hypersonic rarefied flow over flat plate, the computational results are validated in comparison with experimental measurements and DSMC solutions.

  14. Investigation of the Photochemical Method for Uranium Isotope Separation

    DOE R&D Accomplishments Database

    Urey, H. C.

    1943-07-10

    To find a process for successful photochemical separation of isotopes several conditions have to be fulfilled. First, the different isotopes have to show some differences in the spectrum. Secondly, and equally important, this difference must be capable of being exploited in a photochemical process. Parts A and B outline the physical and chemical conditions, and the extent to which one might expect to find them fulfilled. Part C deals with the applicability of the process.

  15. The invariant constrained equilibrium edge preimage curve method for the dimension reduction of chemical kinetics

    NASA Astrophysics Data System (ADS)

    Ren, Zhuyin; Pope, Stephen B.; Vladimirsky, Alexander; Guckenheimer, John M.

    2006-03-01

    This work addresses the construction and use of low-dimensional invariant manifolds to simplify complex chemical kinetics. Typically, chemical kinetic systems have a wide range of time scales. As a consequence, reaction trajectories rapidly approach a hierarchy of attracting manifolds of decreasing dimension in the full composition space. In previous research, several different methods have been proposed to identify these low-dimensional attracting manifolds. Here we propose a new method based on an invariant constrained equilibrium edge (ICE) manifold. This manifold (of dimension nr) is generated by the reaction trajectories emanating from its (nr-1)-dimensional edge, on which the composition is in a constrained equilibrium state. A reasonable choice of the nr represented variables (e.g., nr "major" species) ensures that there exists a unique point on the ICE manifold corresponding to each realizable value of the represented variables. The process of identifying this point is referred to as species reconstruction. A second contribution of this work is a local method of species reconstruction, called ICE-PIC, which is based on the ICE manifold and uses preimage curves (PICs). The ICE-PIC method is local in the sense that species reconstruction can be performed without generating the whole of the manifold (or a significant portion thereof). The ICE-PIC method is the first approach that locally determines points on a low-dimensional invariant manifold, and its application to high-dimensional chemical systems is straightforward. The "inputs" to the method are the detailed kinetic mechanism and the chosen reduced representation (e.g., some major species). The ICE-PIC method is illustrated and demonstrated using an idealized H2/O system with six chemical species. It is then tested and compared to three other dimension-reduction methods for the test case of a one-dimensional premixed laminar flame of stoichiometric hydrogen/air, which is described by a detailed mechanism

  16. The invariant constrained equilibrium edge preimage curve method for the dimension reduction of chemical kinetics.

    PubMed

    Ren, Zhuyin; Pope, Stephen B; Vladimirsky, Alexander; Guckenheimer, John M

    2006-03-21

    This work addresses the construction and use of low-dimensional invariant manifolds to simplify complex chemical kinetics. Typically, chemical kinetic systems have a wide range of time scales. As a consequence, reaction trajectories rapidly approach a hierarchy of attracting manifolds of decreasing dimension in the full composition space. In previous research, several different methods have been proposed to identify these low-dimensional attracting manifolds. Here we propose a new method based on an invariant constrained equilibrium edge (ICE) manifold. This manifold (of dimension nr) is generated by the reaction trajectories emanating from its (nr-1)-dimensional edge, on which the composition is in a constrained equilibrium state. A reasonable choice of the nr represented variables (e.g., nr "major" species) ensures that there exists a unique point on the ICE manifold corresponding to each realizable value of the represented variables. The process of identifying this point is referred to as species reconstruction. A second contribution of this work is a local method of species reconstruction, called ICE-PIC, which is based on the ICE manifold and uses preimage curves (PICs). The ICE-PIC method is local in the sense that species reconstruction can be performed without generating the whole of the manifold (or a significant portion thereof). The ICE-PIC method is the first approach that locally determines points on a low-dimensional invariant manifold, and its application to high-dimensional chemical systems is straightforward. The "inputs" to the method are the detailed kinetic mechanism and the chosen reduced representation (e.g., some major species). The ICE-PIC method is illustrated and demonstrated using an idealized H2O system with six chemical species. It is then tested and compared to three other dimension-reduction methods for the test case of a one-dimensional premixed laminar flame of stoichiometric hydrogen/air, which is described by a detailed mechanism

  17. A bacterial method for the nitrogen isotopic analysis of nitrate in seawater and freshwater

    USGS Publications Warehouse

    Sigman, D.M.; Casciotti, K.L.; Andreani, M.; Barford, C.; Galanter, M.; Böhlke, J.K.

    2001-01-01

    We report a new method for measurement of the isotopic composition of nitrate (NO3-) at the natural-abundance level in both seawater and freshwater. The method is based on the isotopic analysis of nitrous oxide (N2O) generated from nitrate by denitrifying bacteria that lack N2O-reductase activity. The isotopic composition of both nitrogen and oxygen from nitrate are accessible in this way. In this first of two companion manuscripts, we describe the basic protocol and results for the nitrogen isotopes. The precision of the method is better than 0.2‰ (1 SD) at concentrations of nitrate down to 1 μM, and the nitrogen isotopic differences among various standards and samples are accurately reproduced. For samples with 1 μM nitrate or more, the blank of the method is less than 10% of the signal size, and various approaches may reduce it further.

  18. LC-MS determination of bioactive molecules based upon stable isotope-coded derivatization method.

    PubMed

    Toyo'oka, Toshimasa

    2012-10-01

    Liquid chromatography (LC) coupled with mass spectrometry (MS) has been widely used for the analyses of various molecules in many research fields. The electrospray ionization of MS has contributed to the advancement of the LC-MS and LC-MS/MS methods. However, the detection sensitivity is not always sufficient in biological samples, in spite of the highly sensitive ionization method. To increase the sensitivity, chemical derivatization, providing ionization enhancement and avoiding the matrix effect, is effective for various functional groups in the target molecules. However, the accuracy and precision by the determination is sometimes insufficient, especially in complex matrices. In such a case, stable isotope-labeled analogs are often used as the internal standards for the determination of the analytes. When the target compound in samples is limited, a high accuracy and precision is usually obtained by the isotope dilution method. However, the use of individual isotope standards is very difficult for the analyses of multiple molecules in complex matrices. Instead of the use of an isotope analog of the analytes, the differential isotope labeling method based upon chemical derivatization (stable isotope-coded derivatization) (ICD) by both reagents possessing different isotopes is realized. The ICD technique utilizing mass-different isotope tags is known to be an efficient means for metabolite profiling analyses. Thus, the present paper reviews the ICD method reported in the past 10 years. The species of the ICD reagents, their features and the applications to biological specimens are also described in this review.

  19. Improvement of 2,4-dinitrophenylhydrazine derivatization method for carbon isotope analysis of atmospheric acetone.

    PubMed

    Wen, Sheng; Yu, Yingxin; Guo, Songjun; Feng, Yanli; Sheng, Guoying; Wang, Xinming; Bi, Xinhui; Fu, Jiamo; Jia, Wanglu

    2006-01-01

    Through simulation experiments of atmospheric sampling, a method via 2,4-dinitrophenylhydrazine (DNPH) derivatization was developed to measure the carbon isotopic composition of atmospheric acetone. Using acetone and a DNPH reagent of known carbon isotopic compositions, the simulation experiments were performed to show that no carbon isotope fractionation occurred during the processes: the differences between the predicted and measured data of acetone-DNPH derivatives were all less than 0.5 per thousand. The results permitted the calculation of the carbon isotopic compositions of atmospheric acetone using a mass balance equation. In this method, the atmospheric acetone was collected by a DNPH-coated silica cartridge, washed out as acetone-DNPH derivatives, and then analyzed by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Using this method, the first available delta13C data of atmospheric acetone are presented.

  20. Reducing the matrix effects in chemical analysis: fusion of isotope dilution and standard addition methods

    NASA Astrophysics Data System (ADS)

    Pagliano, Enea; Meija, Juris

    2016-04-01

    The combination of isotope dilution and mass spectrometry has become an ubiquitous tool of chemical analysis. Often perceived as one of the most accurate methods of chemical analysis, it is not without shortcomings. Current isotope dilution equations are not capable of fully addressing one of the key problems encountered in chemical analysis: the possible effect of sample matrix on measured isotope ratios. The method of standard addition does compensate for the effect of sample matrix by making sure that all measured solutions have identical composition. While it is impossible to attain such condition in traditional isotope dilution, we present equations which allow for matrix-matching between all measured solutions by fusion of isotope dilution and standard addition methods.

  1. Liquid-phase thermal diffusion isotope separation apparatus and method having tapered column

    DOEpatents

    Rutherford, W.M.

    1985-12-04

    A thermal diffusion counterflow method and apparatus for separating isotopes in solution in which the solution is confined in a long, narrow, vertical slit which tapers from bottom to top. The variation in the width of the slit permits maintenance of a stable concentration distribution with relatively long columns, thus permitting isotopic separation superior to that obtained in the prior art.

  2. Liquid-phase thermal diffusion isotope separation apparatus and method having tapered column

    DOEpatents

    Rutherford, William M.

    1988-05-24

    A thermal diffusion counterflow method and apparatus for separating isotopes in solution in which the solution is confined in a long, narrow, vertical slit which tapers from bottom to top. The variation in the width of the slit permits maintenance of a stable concentration distribution with relatively long columns, thus permitting isotopic separation superior to that obtainable in the prior art.

  3. Method for separating different isotopes in compounds by means of laser radiation

    SciTech Connect

    Meyer-Kretschmer, G.; Jetter, H.; Toennies, P.

    1984-05-29

    A method is claimed for separating isotopes of a compound having molecules in the gaseous state which comprises exciting the gas with laser radiation having a frequency capable of exciting a selected isotope thereof, interacting the excited gas with electrons having an energy sufficient to form position ions therein and separating the ionized molecules from the other molecules in the gas.

  4. An efficient monte carlo method for calculating the equilibrium properties for a quantum system coupled strongly to a classical one

    NASA Astrophysics Data System (ADS)

    Carmeli, Benny; Metiu, Horia

    1987-02-01

    We calculate the equilibrium properties of a system consisting of two strongly interacting quantum and classical subsystems, by using a fast Fourier transform method to evaluate the quantum contribution and a Monte Carlo method to evaluate the contribution of the classical part. The method is applied to a model relevant to tunneling problems.

  5. General methods for sensitivity analysis of equilibrium dynamics in patch occupancy models

    USGS Publications Warehouse

    Miller, David A.W.

    2012-01-01

    Sensitivity analysis is a useful tool for the study of ecological models that has many potential applications for patch occupancy modeling. Drawing from the rich foundation of existing methods for Markov chain models, I demonstrate new methods for sensitivity analysis of the equilibrium state dynamics of occupancy models. Estimates from three previous studies are used to illustrate the utility of the sensitivity calculations: a joint occupancy model for a prey species, its predators, and habitat used by both; occurrence dynamics from a well-known metapopulation study of three butterfly species; and Golden Eagle occupancy and reproductive dynamics. I show how to deal efficiently with multistate models and how to calculate sensitivities involving derived state variables and lower-level parameters. In addition, I extend methods to incorporate environmental variation by allowing for spatial and temporal variability in transition probabilities. The approach used here is concise and general and can fully account for environmental variability in transition parameters. The methods can be used to improve inferences in occupancy studies by quantifying the effects of underlying parameters, aiding prediction of future system states, and identifying priorities for sampling effort.

  6. A moving mesh finite difference method for equilibrium radiation diffusion equations

    SciTech Connect

    Yang, Xiaobo; Huang, Weizhang; Qiu, Jianxian

    2015-10-01

    An efficient moving mesh finite difference method is developed for the numerical solution of equilibrium radiation diffusion equations in two dimensions. The method is based on the moving mesh partial differential equation approach and moves the mesh continuously in time using a system of meshing partial differential equations. The mesh adaptation is controlled through a Hessian-based monitor function and the so-called equidistribution and alignment principles. Several challenging issues in the numerical solution are addressed. Particularly, the radiation diffusion coefficient depends on the energy density highly nonlinearly. This nonlinearity is treated using a predictor–corrector and lagged diffusion strategy. Moreover, the nonnegativity of the energy density is maintained using a cutoff method which has been known in literature to retain the accuracy and convergence order of finite difference approximation for parabolic equations. Numerical examples with multi-material, multiple spot concentration situations are presented. Numerical results show that the method works well for radiation diffusion equations and can produce numerical solutions of good accuracy. It is also shown that a two-level mesh movement strategy can significantly improve the efficiency of the computation.

  7. Non-Condon equilibrium Fermi's golden rule electronic transition rate constants via the linearized semiclassical method.

    PubMed

    Sun, Xiang; Geva, Eitan

    2016-06-28

    In this paper, we test the accuracy of the linearized semiclassical (LSC) expression for the equilibrium Fermi's golden rule rate constant for electronic transitions in the presence of non-Condon effects. We do so by performing a comparison with the exact quantum-mechanical result for a model where the donor and acceptor potential energy surfaces are parabolic and identical except for shifts in the equilibrium energy and geometry, and the coupling between them is linear in the nuclear coordinates. Since non-Condon effects may or may not give rise to conical intersections, both possibilities are examined by considering: (1) A modified Garg-Onuchic-Ambegaokar model for charge transfer in the condensed phase, where the donor-acceptor coupling is linear in the primary mode coordinate, and for which non-Condon effects do not give rise to a conical intersection; (2) the linear vibronic coupling model for electronic transitions in gas phase molecules, where non-Condon effects give rise to conical intersections. We also present a comprehensive comparison between the linearized semiclassical expression and a progression of more approximate expressions. The comparison is performed over a wide range of frictions and temperatures for model (1) and over a wide range of temperatures for model (2). The linearized semiclassical method is found to reproduce the exact quantum-mechanical result remarkably well for both models over the entire range of parameters under consideration. In contrast, more approximate expressions are observed to deviate considerably from the exact result in some regions of parameter space.

  8. Non-Condon equilibrium Fermi's golden rule electronic transition rate constants via the linearized semiclassical method

    NASA Astrophysics Data System (ADS)

    Sun, Xiang; Geva, Eitan

    2016-06-01

    In this paper, we test the accuracy of the linearized semiclassical (LSC) expression for the equilibrium Fermi's golden rule rate constant for electronic transitions in the presence of non-Condon effects. We do so by performing a comparison with the exact quantum-mechanical result for a model where the donor and acceptor potential energy surfaces are parabolic and identical except for shifts in the equilibrium energy and geometry, and the coupling between them is linear in the nuclear coordinates. Since non-Condon effects may or may not give rise to conical intersections, both possibilities are examined by considering: (1) A modified Garg-Onuchic-Ambegaokar model for charge transfer in the condensed phase, where the donor-acceptor coupling is linear in the primary mode coordinate, and for which non-Condon effects do not give rise to a conical intersection; (2) the linear vibronic coupling model for electronic transitions in gas phase molecules, where non-Condon effects give rise to conical intersections. We also present a comprehensive comparison between the linearized semiclassical expression and a progression of more approximate expressions. The comparison is performed over a wide range of frictions and temperatures for model (1) and over a wide range of temperatures for model (2). The linearized semiclassical method is found to reproduce the exact quantum-mechanical result remarkably well for both models over the entire range of parameters under consideration. In contrast, more approximate expressions are observed to deviate considerably from the exact result in some regions of parameter space.

  9. Simple, rapid method for the preparation of isotopically labeled formaldehyde

    SciTech Connect

    Hooker, Jacob Matthew; Schonberger, Matthias; Schieferstein, Hanno; Fowler, Joanna S.

    2011-10-04

    Isotopically labeled formaldehyde (*C.sup..sctn.H.sub.2O) is prepared from labeled methyl iodide (*C.sup..sctn.H.sub.3I) by reaction with an oxygen nucleophile having a pendant leaving group. The mild and efficient reaction conditions result in good yields of *C.sup..sctn.H.sub.2O with little or no *C isotopic dilution. The simple, efficient production of .sup.11CH.sub.2O is described. The use of the .sup.11CH.sub.2O for the formation of positron emission tomography tracer compounds is described. The reaction can be incorporated into automated equipment available to radiochemistry laboratories. The isotopically labeled formaldehyde can be used in a variety of reactions to provide radiotracer compounds for imaging studies as well as for scintillation counting and autoradiography.

  10. Laboratory and field methods for stable isotope analysis in human biology.

    PubMed

    Reitsema, Laurie J

    2015-01-01

    Stable isotope analysis (SIA; carbon, hydrogen, nitrogen, sulfur, and oxygen) of human tissues offers a means for assessing diet among living humans. Stable isotope ratios of broad categories of food and drink food vary systematically, and stable isotope ratios in consumer tissues represent a composite of the isotopic ratios of food and drink consumed during an individual's life. Isotopic evidence for diet is independent of errors in informant recall, and accrues during time periods when researchers are absent. Beyond diet reconstruction, tissue stable isotope ratios are sensitive to excursions from homeostasis, such as starvation and rapid growth. Because of their relationship to diet, geographic location, hydration, and nutritional status, stable isotope signatures in human tissues offer a window into human biocultural adaptations, past and present. This article describes methods for SIA that may be usefully applied in studies of living humans, with emphasis placed on carbon and nitrogen. Some of the ecological, physiological, and evolutionary applications of stable isotope data among living humans are discussed. By incorporating SIA in research, human biologists facilitate a productive dialog with bioarchaeologists, who routinely use stable isotope evidence, mingling different perspectives on human biology and behavior.

  11. Equilibrium and dynamic methods when comparing an English text and its Esperanto translation

    NASA Astrophysics Data System (ADS)

    Ausloos, M.

    2008-11-01

    A comparison of two English texts written by Lewis Carroll, one (Alice in Wonderland), also translated into Esperanto, the other (Through the Looking Glass) are discussed in order to observe whether natural and artificial languages significantly differ from each other. One dimensional time series like signals are constructed using only word frequencies (FTS) or word lengths (LTS). The data is studied through (i) a Zipf method for sorting out correlations in the FTS and (ii) a Grassberger-Procaccia (GP) technique based method for finding correlations in LTS. The methods correspond to an equilibrium and a dynamic approach respectively to human texts features. There are quantitative statistical differences between the original English text and its Esperanto translation, but the qualitative differences are very minutes. However different power laws are observed with characteristic exponents for the ranking properties, and the phase space attractor dimensionality. The Zipf exponent can take values much less than unity (∼0.50 or 0.30) depending on how a sentence is defined. This variety in exponents can be conjectured to be an intrinsic measure of the book style or purpose, rather than the language or author vocabulary richness, since a similar exponent is obtained whatever the text. Moreover the attractor dimension r is a simple function of the so called phase space dimension n, i.e., r=nλ, with λ=0.79. Such an exponent could also be conjectured to be a measure of the author style versatility, - here well preserved in the translation.

  12. A numerical method for retrieving high oxygen isotope temperatures from plutonic igneous rocks: An example from the Laramie Anorthosite Complex, Wyoming, USA

    SciTech Connect

    Farquhar, J.; Chacko, T. . Dept. of Geology); Frost, B.R. )

    1992-01-01

    The Sybille Pit is a late-stage magnetite-ilmenite-plagioclase-bearing differentiate of the Laramie Anorthosite with a wide range of grain sizes and modal mineralogy. This variability makes Sybille an ideal locality in which to study the factors that affect isotopic thermometry in plutonic environments. The authors have developed a numerical model based on isotope exchange trajectories that retrieves close to magmatic temperatures for samples from Sybille. This method is based on the premise that hand sample-scale sub-systems close to exchange with each other at temperatures that exceed those of the constituent minerals. The temperature of hand-sample scale closure is retrieved by back calculating the isotope exchange trajectories to the temperature at which two samples with widely different model compositions are in isotopic equilibrium. Application of these methods to samples from Sybille provides promising results. Whereas conventional isotopic thermometry of individual samples yields a wide range of temperatures ([approximately]600 to > 1000 C) depending on the mineral-pair chosen, application of this numerical model to multiple samples yields temperatures of 1,070 [+-] 100 C which corresponds closely to the inferred solidus for these rocks.

  13. COMBINING SOURCES IN STABLE ISOTOPE MIXING MODELS: ALTERNATIVE METHODS

    EPA Science Inventory

    Stable isotope mixing models are often used to quantify source contributions to a mixture. Examples include pollution source identification; trophic web studies; analysis of water sources for soils, plants, or water bodies; and many others. A common problem is having too many s...

  14. Apparatus and method for monitoring of gas having stable isotopes

    DOEpatents

    Clegg, Samuel M; Fessenden-Rahn, Julianna E

    2013-03-05

    Gas having stable isotopes is monitored continuously by using a system that sends a modulated laser beam to the gas and collects and transmits the light not absorbed by the gas to a detector. Gas from geological storage, or from the atmosphere can be monitored continuously without collecting samples and transporting them to a lab.

  15. Accurate Ab Initio Calculation of the Isotopic Exchange Equilibrium 10B(OH)3 + 11B(OH)4- = 11B(OH)3 + 10B(OH)4- In Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Tossell, J. A.

    2005-12-01

    For more than a decade the B isotopic compositions of marine carbonates have been used as paleo-pH proxies for seawater and to reconstruct paleo-[CO2] concentrations in the atmosphere. A necessary step is this process is the accurate determination of the equilibrium constant, K, for the reaction shown in the title above. This equilibrium constant has been recently calculated using ab initio quantum chemical methods applied to nanoclusters containing the solutes B(OH)3 and B(OH)4- coordinated by large numbers of explicit solvent molecules, a computationally difficult procedure. To obtain the most accurate possible value for K the calculated vibrational frequencies were scaled to best fit the limited experimental data available. The value of K obtained (@ 25°C) was 1.027 (significantly larger than the long used value of 1.0194). Even more recently a purely experimental value of K= 1.0265 ± 0.0015 has been obtained through an accurate spectrophotometric determination of the difference of pKa's of commercially available bulk samples of >99% enriched 10B(OH)3(s) and 11B(OH)3 (s). Since we now know the correct experimental value and have a calculation, admittedly a difficult and slightly parameterized one, which matches the experimental result (which was obtained after the calculation), it is worthwhile to analyze the steps in the theoretical calculation of K in more detail. We need to establish a general procedure which can yield accurate K values for other similar aqueous species even if we have no accurate experimental value for K and no vibrational spectral data. To this end we will examine the dependence of the calculated values of vibrational frequencies, isotopomer frequency differences and K values on a number of factors, including (a) the quantum mechanical level (basis set and treatment of electron correlation) used for the free solutes, (b) the incorporation of aqueous medium effects, (c) the effects of vibrational anharmonicity, (d) incorporation of the

  16. Some Developments of the Equilibrium Particle Simulation Method for the Direct Simulation of Compressible Flows

    NASA Technical Reports Server (NTRS)

    Macrossan, M. N.

    1995-01-01

    The direct simulation Monte Carlo (DSMC) method is the established technique for the simulation of rarefied gas flows. In some flows of engineering interest, such as occur for aero-braking spacecraft in the upper atmosphere, DSMC can become prohibitively expensive in CPU time because some regions of the flow, particularly on the windward side of blunt bodies, become collision dominated. As an alternative to using a hybrid DSMC and continuum gas solver (Euler or Navier-Stokes solver) this work is aimed at making the particle simulation method efficient in the high density regions of the flow. A high density, infinite collision rate limit of DSMC, the Equilibrium Particle Simulation method (EPSM) was proposed some 15 years ago. EPSM is developed here for the flow of a gas consisting of many different species of molecules and is shown to be computationally efficient (compared to DSMC) for high collision rate flows. It thus offers great potential as part of a hybrid DSMC/EPSM code which could handle flows in the transition regime between rarefied gas flows and fully continuum flows. As a first step towards this goal a pure EPSM code is described. The next step of combining DSMC and EPSM is not attempted here but should be straightforward. EPSM and DSMC are applied to Taylor-Couette flow with Kn = 0.02 and 0.0133 and S(omega) = 3). Toroidal vortices develop for both methods but some differences are found, as might be expected for the given flow conditions. EPSM appears to be less sensitive to the sequence of random numbers used in the simulation than is DSMC and may also be more dissipative. The question of the origin and the magnitude of the dissipation in EPSM is addressed. It is suggested that this analysis is also relevant to DSMC when the usual accuracy requirements on the cell size and decoupling time step are relaxed in the interests of computational efficiency.

  17. Equilibrium isotherms of methane onto activated carbons using a static volumetric method.

    PubMed

    Kavitha, T; Kaliappan, S

    2009-07-01

    The aim of this research is to develop a technology for the storage of biogas. The present work pertains to the measurement of the adsorption capacity of methane onto activated carbons at room temperature at pressure range varying from 1 atm to 10 atm. The results were obtained with a static volumetric method. Adsorption isotherms for methane on Sorbonorit 4, Norit SX Plus, Sorbonorit B3, Norit PAC 200 XC were plotted. The equilibrium pressure data were analysed using Langmuir, Dubinin-Astakhov's (DA) and Dubinin-Radushkevich (DR) equations. The DA equation described the isotherm behavior better with the exponent n equals to 1.0 for Sorbonorit 4, Sorbonorit B3, Norit PAC 200 XC and 1.7 for Norit SX Plus than the other equations. The order of the adsorption capacity is as follows: Sorbonorit 4 (4.6 mmol/g) > Norit PAC 200 XC (3.81 mmol/g) > Sorbonorit B3 (3.52 mmol/g) > Norit SX Plus (3.51 mmol/g).

  18. Isotope methods for management of shared aquifers in northern Africa.

    PubMed

    Wallin, Bill; Gaye, Cheikh; Gourcy, Laurence; Aggarwal, Pradeep

    2005-01-01

    Access to fresh water is one of the major issues of northern and sub-Saharan Africa. The majority of the fresh water used for drinking and irrigation is obtained from large ground water basins where there is minor contemporary recharge and the aquifers cross national borders. These aquifers include the Nubian Aquifer System shared by Chad, Egypt, Libya, and Sudan; the Iullemeden Aquifer System, extending over Niger, Nigeria, Mali, Benin, and Algeria; and the Northwest Sahara Aquifer System shared by Algeria, Libya, and Tunisia. These resources are subject to increased exploitation and may be severely stressed if not managed properly as witnessed already by declining water levels. In order to make appropriate decisions for the sustainable management of these shared water resources, planners and managers in different countries need an improved knowledge base of hydrological information. Three technical cooperation projects related to aquifer systems will be implemented by the International Atomic Energy Agency, in collaboration with the United Nations Educational, Scientific and Cultural Organization and United Nations Development Programme/Global Environmental Facility. These projects focus on isotope hydrology studies to better quantify ground water recharge and dynamics. The multiple isotope approach combining commonly used isotopes 18O and 2H together with more recently developed techniques (chlorofluorocarbons, 36Cl, noble gases) will be applied to improve the conceptual model to study stratification and ground water flows. Moreover, the isotopes will be an important indicator of changes in the aquifer due to water abstraction, and therefore they will assist in the effort to establish a sustainable ground water management.

  19. A Computational Method for Determining the Equilibrium Composition and Product Temperature in a LH2/LOX Combustor

    NASA Technical Reports Server (NTRS)

    Sozen, Mehmet

    2003-01-01

    In what follows, the model used for combustion of liquid hydrogen (LH2) with liquid oxygen (LOX) using chemical equilibrium assumption, and the novel computational method developed for determining the equilibrium composition and temperature of the combustion products by application of the first and second laws of thermodynamics will be described. The modular FORTRAN code developed as a subroutine that can be incorporated into any flow network code with little effort has been successfully implemented in GFSSP as the preliminary runs indicate. The code provides capability of modeling the heat transfer rate to the coolants for parametric analysis in system design.

  20. Inverse methods for estimating primary input signals from time-averaged isotope profiles

    NASA Astrophysics Data System (ADS)

    Passey, Benjamin H.; Cerling, Thure E.; Schuster, Gerard T.; Robinson, Todd F.; Roeder, Beverly L.; Krueger, Stephen K.

    2005-08-01

    Mammalian teeth are invaluable archives of ancient seasonality because they record along their growth axes an isotopic record of temporal change in environment, plant diet, and animal behavior. A major problem with the intra-tooth method is that intra-tooth isotope profiles can be extremely time-averaged compared to the actual pattern of isotopic variation experienced by the animal during tooth formation. This time-averaging is a result of the temporal and spatial characteristics of amelogenesis (tooth enamel formation), and also results from laboratory sampling. This paper develops and evaluates an inverse method for reconstructing original input signals from time-averaged intra-tooth isotope profiles. The method requires that the temporal and spatial patterns of amelogenesis are known for the specific tooth and uses a minimum length solution of the linear system Am = d, where d is the measured isotopic profile, A is a matrix describing temporal and spatial averaging during amelogenesis and sampling, and m is the input vector that is sought. Accuracy is dependent on several factors, including the total measurement error and the isotopic structure of the measured profile. The method is shown to accurately reconstruct known input signals for synthetic tooth enamel profiles and the known input signal for a rabbit that underwent controlled dietary changes. Application to carbon isotope profiles of modern hippopotamus canines reveals detailed dietary histories that are not apparent from the measured data alone. Inverse methods show promise as an effective means of dealing with the time-averaging problem in studies of intra-tooth isotopic variation.

  1. A Stochastic Method for Estimating the Effect of Isotopic Uncertainties in Spent Nuclear Fuel

    SciTech Connect

    DeHart, M.D.

    2001-08-24

    This report describes a novel approach developed at the Oak Ridge National Laboratory (ORNL) for the estimation of the uncertainty in the prediction of the neutron multiplication factor for spent nuclear fuel. This technique focuses on burnup credit, where credit is taken in criticality safety analysis for the reduced reactivity of fuel irradiated in and discharged from a reactor. Validation methods for burnup credit have attempted to separate the uncertainty associated with isotopic prediction methods from that of criticality eigenvalue calculations. Biases and uncertainties obtained in each step are combined additively. This approach, while conservative, can be excessive because of a physical assumptions employed. This report describes a statistical approach based on Monte Carlo sampling to directly estimate the total uncertainty in eigenvalue calculations resulting from uncertainties in isotopic predictions. The results can also be used to demonstrate the relative conservatism and statistical confidence associated with the method of additively combining uncertainties. This report does not make definitive conclusions on the magnitude of biases and uncertainties associated with isotopic predictions in a burnup credit analysis. These terms will vary depending on system design and the set of isotopic measurements used as a basis for estimating isotopic variances. Instead, the report describes a method that can be applied with a given design and set of isotopic data for estimating design-specific biases and uncertainties.

  2. The variability of standard artificial soils: cadmium and phenanthrene sorption measured by a batch equilibrium method.

    PubMed

    Bielská, Lucie; Hovorková, Ivana; Kuta, Jan; Machát, Jiří; Hofman, Jakub

    2017-01-01

    Artificial soil (AS) is used in soil ecotoxicology as a test medium or reference matrix. AS is prepared according to standard OECD/ISO protocols and components of local sources are usually used by laboratories. This may result in significant inter-laboratory variations in AS properties and, consequently, in the fate and bioavailability of tested chemicals. In order to reveal the extent and sources of variations, the batch equilibrium method was applied to measure the sorption of 2 model compounds (phenanthrene and cadmium) to 21 artificial soils from different laboratories. The distribution coefficients (Kd) of phenanthrene and cadmium varied over one order of magnitude: from 5.3 to 61.5L/kg for phenanthrene and from 17.9 to 190L/kg for cadmium. Variations in phenanthrene sorption could not be reliably explained by measured soil properties; not even by the total organic carbon (TOC) content which was expected. Cadmium logKd values significantly correlated with cation exchange capacity (CEC), pHH2O and pHKCl, with Pearson correlation coefficients of 0.62, 0.80, and 0.79, respectively. CEC and pHH2O together were able to explain 72% of cadmium logKd variability in the following model: logKd=0.29pHH2O+0.0032 CEC -0.53. Similarly, 66% of cadmium logKd variability could be explained by CEC and pHKCl in the model: logKd=0.27pHKCl+0.0028 CEC -0.23. Variable cadmium sorption in differing ASs could be partially treated with these models. However, considering the unpredictable variability of phenanthrene sorption, a more reliable solution for reducing the variability of ASs from different laboratories would be better harmonization of AS preparation and composition.

  3. Semiexperimental Equilibrium Structures for the Equatorial Conformers of N-Methylpiperidone and Tropinone by the Mixed Estimation Method

    NASA Astrophysics Data System (ADS)

    Demaison, Jean; Craig, Norman C.; Cocinero, Emilio J.; Grabow, Jens-Uwe; Lesarri, Alberto; Rudolph, H. D.

    2012-06-01

    N-methylpiperidone and tropinone, which contain a structural motif found in numerous alkaloids, are too large for determining an accurate equilibrium structure either by ab initio methods or by experiment. However, the ground state rotational constants of the parent species and of all isotopologues with a substituted heavy atom (13C, 15N, 18O) are known from microwave spectroscopy. These constants have been corrected for the rovibrational contribution calculated from an ab initio cubic force field. These semiexperimental equilibrium rotational constants have been supplemented by carefully chosen structural parameters from medium level ab initio calculations. In the mixed estimation method, the two sets of data have been used in a weighted least-squares fit to determine a reliable equilibrium structure for both molecules. This work shows that it is possible to determine reliable equilibrium structures for large molecules (34 degrees of freedom in the case of tropinone). The method could be applied without too much difficulty to still larger molecules. L. Evangelisti, A. Lesarri, M. K. Jahn, E. J. Cocinero, W. Caminati, J.-U. Grabow J. Phys. Chem. A 115, 9545-9551 (2011) E. J. Cocinero, A. Lesarri, P. Écija, J.-U. Grabow, J. A. Fernández, F. Castaño PCCP 12, 6076-6083 (2010)

  4. Nash equilibrium in differential games and the construction of the programmed iteration method

    SciTech Connect

    Averboukh, Yurii V

    2011-05-31

    This work is devoted to the study of nonzero-sum differential games. The set of payoffs in a situation of Nash equilibrium is examined. It is shown that the set of payoffs in a situation of Nash equilibrium coincides with the set of values of consistent functions which are fixed points of the program absorption operator. A condition for functions to be consistent is given in terms of the weak invariance of the graph of the functions under a certain differential inclusion. Bibliography: 18 titles.

  5. A General Method for Automatic Computation of Equilibrium Compositions and Theoretical Rocket Performance of Propellants

    NASA Technical Reports Server (NTRS)

    Gordon, Sanford; Zeleznik, Frank J.; Huff, Vearl N.

    1959-01-01

    A general computer program for chemical equilibrium and rocket performance calculations was written for the IBM 650 computer with 2000 words of drum storage, 60 words of high-speed core storage, indexing registers, and floating point attachments. The program is capable of carrying out combustion and isentropic expansion calculations on a chemical system that may include as many as 10 different chemical elements, 30 reaction products, and 25 pressure ratios. In addition to the equilibrium composition, temperature, and pressure, the program calculates specific impulse, specific impulse in vacuum, characteristic velocity, thrust coefficient, area ratio, molecular weight, Mach number, specific heat, isentropic exponent, enthalpy, entropy, and several thermodynamic first derivatives.

  6. A method for obtaining equilibrium tautomeric mixtures of reducing sugars via glycosylamines using nonaqueous media.

    PubMed

    Allavudeen, Sikkander Sulthan; Kuberan, Balagurunathan; Loganathan, Duraikkannu

    2002-05-13

    Equilibrium tautomeric mixtures of several mono- and disaccharides are obtained in anhydrous form, without the use of water, by reacting the commercially available reducing sugars with ammonia gas in dry methanol, followed by the concentration of the resultant solution to dryness. Mutarotation and hydrolysis of the initially formed glycosylamine in the resultant medium account for the transformation. Equilibrium anomeric mixtures enriched in the beta-form of commercially available sugars such as alpha-D-glucose and alpha-lactose have not only vastly increased solubility, but are also synthetically valuable as these can be readily converted to the methyl/benzyl/trimethylsilyl ether and other derivatives for further transformations.

  7. A new method of snowmelt sampling for water stable isotopes

    USGS Publications Warehouse

    Penna, D.; Ahmad, M.; Birks, S. J.; Bouchaou, L.; Brencic, M.; Butt, S.; Holko, L.; Jeelani, G.; Martinez, D. E.; Melikadze, G.; Shanley, J.B.; Sokratov, S. A.; Stadnyk, T.; Sugimoto, A.; Vreca, P.

    2014-01-01

    We modified a passive capillary sampler (PCS) to collect snowmelt water for isotopic analysis. Past applications of PCSs have been to sample soil water, but the novel aspect of this study was the placement of the PCSs at the ground-snowpack interface to collect snowmelt. We deployed arrays of PCSs at 11 sites in ten partner countries on five continents representing a range of climate and snow cover worldwide. The PCS reliably collected snowmelt at all sites and caused negligible evaporative fractionation effects in the samples. PCS is low-cost, easy to install, and collects a representative integrated snowmelt sample throughout the melt season or at the melt event scale. Unlike snow cores, the PCS collects the water that would actually infiltrate the soil; thus, its isotopic composition is appropriate to use for tracing snowmelt water through the hydrologic cycle. The purpose of this Briefing is to show the potential advantages of PCSs and recommend guidelines for constructing and installing them based on our preliminary results from two snowmelt seasons.

  8. A hydrogen gas-water equilibration method produces accurate and precise stable hydrogen isotope ratio measurements in nutrition studies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Stable hydrogen isotope methodology is used in nutrition studies to measure growth, breast milk intake, and energy requirement. Isotope ratio MS is the best instrumentation to measure the stable hydrogen isotope ratios in physiological fluids. Conventional methods to convert physiological fluids to ...

  9. Novel methods for estimating 3D distributions of radioactive isotopes in materials

    NASA Astrophysics Data System (ADS)

    Iwamoto, Y.; Kataoka, J.; Kishimoto, A.; Nishiyama, T.; Taya, T.; Okochi, H.; Ogata, H.; Yamamoto, S.

    2016-09-01

    In recent years, various gamma-ray visualization techniques, or gamma cameras, have been proposed. These techniques are extremely effective for identifying "hot spots" or regions where radioactive isotopes are accumulated. Examples of such would be nuclear-disaster-affected areas such as Fukushima or the vicinity of nuclear reactors. However, the images acquired with a gamma camera do not include distance information between radioactive isotopes and the camera, and hence are "degenerated" in the direction of the isotopes. Moreover, depth information in the images is lost when the isotopes are embedded in materials, such as water, sand, and concrete. Here, we propose two methods of obtaining depth information of radioactive isotopes embedded in materials by comparing (1) their spectra and (2) images of incident gamma rays scattered by the materials and direct gamma rays. In the first method, the spectra of radioactive isotopes and the ratios of scattered to direct gamma rays are obtained. We verify experimentally that the ratio increases with increasing depth, as predicted by simulations. Although the method using energy spectra has been studied for a long time, an advantage of our method is the use of low-energy (50-150 keV) photons as scattered gamma rays. In the second method, the spatial extent of images obtained for direct and scattered gamma rays is compared. By performing detailed Monte Carlo simulations using Geant4, we verify that the spatial extent of the position where gamma rays are scattered increases with increasing depth. To demonstrate this, we are developing various gamma cameras to compare low-energy (scattered) gamma-ray images with fully photo-absorbed gamma-ray images. We also demonstrate that the 3D reconstruction of isotopes/hotspots is possible with our proposed methods. These methods have potential applications in the medical fields, and in severe environments such as the nuclear-disaster-affected areas in Fukushima.

  10. RAPID FUSION METHOD FOR DETERMINATION OF PLUTONIUM ISOTOPES IN LARGE RICE SAMPLES

    SciTech Connect

    Maxwell, S.

    2013-03-01

    A new rapid fusion method for the determination of plutonium in large rice samples has been developed at the Savannah River National Laboratory (Aiken, SC, USA) that can be used to determine very low levels of plutonium isotopes in rice. The recent accident at Fukushima Nuclear Power Plant in March, 2011 reinforces the need to have rapid, reliable radiochemical analyses for radionuclides in environmental and food samples. Public concern regarding foods, particularly foods such as rice in Japan, highlights the need for analytical techniques that will allow very large sample aliquots of rice to be used for analysis so that very low levels of plutonium isotopes may be detected. The new method to determine plutonium isotopes in large rice samples utilizes a furnace ashing step, a rapid sodium hydroxide fusion method, a lanthanum fluoride matrix removal step, and a column separation process with TEVA Resin cartridges. The method can be applied to rice sample aliquots as large as 5 kg. Plutonium isotopes can be determined using alpha spectrometry or inductively-coupled plasma mass spectrometry (ICP-MS). The method showed high chemical recoveries and effective removal of interferences. The rapid fusion technique is a rugged sample digestion method that ensures that any refractory plutonium particles are effectively digested. The MDA for a 5 kg rice sample using alpha spectrometry is 7E-5 mBq g{sup -1}. The method can easily be adapted for use by ICP-MS to allow detection of plutonium isotopic ratios.

  11. An automated method for 'clumped-isotope' measurements on small carbonate samples.

    PubMed

    Schmid, Thomas W; Bernasconi, Stefano M

    2010-07-30

    Clumped-isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped-isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of earth sciences. Clumped-isotope thermometry allows reconstructing the temperature of formation of carbonate minerals without knowing the isotopic composition of the water from which they were formed. This feature enables new approaches in paleothermometry. The currently published method is, however, limited by sample weight requirements of 10-15 mg and because measurements are performed manually. In this paper we present a new method using an automated sample preparation device coupled to an isotope ratio mass spectrometer. The method is based on the repeated analysis (n = 6-8) of 200 microg aliquots of sample material and completely automated measurements. In addition, we propose to use precisely calibrated carbonates spanning a wide range in Delta(47) instead of heated gases to correct for isotope effects caused by the source of the mass spectrometer, following the principle of equal treatment of the samples and standards. We present data for international standards (NBS 19 and LSVEC) and different carbonates formed at temperatures exceeding 600 degrees C to show that precisions in the range of 10 to 15 ppm (1 SE) can be reached for repeated analyses of a single sample. Finally, we discuss and validate the correction procedure based on high-temperature carbonates instead of heated gases.

  12. A Simple Method to Calculate the Temperature Dependence of the Gibbs Energy and Chemical Equilibrium Constants

    ERIC Educational Resources Information Center

    Vargas, Francisco M.

    2014-01-01

    The temperature dependence of the Gibbs energy and important quantities such as Henry's law constants, activity coefficients, and chemical equilibrium constants is usually calculated by using the Gibbs-Helmholtz equation. Although, this is a well-known approach and traditionally covered as part of any physical chemistry course, the required…

  13. A time-accurate implicit method for chemical non-equilibrium flows at all speeds

    NASA Technical Reports Server (NTRS)

    Shuen, Jian-Shun

    1992-01-01

    A new time accurate coupled solution procedure for solving the chemical non-equilibrium Navier-Stokes equations over a wide range of Mach numbers is described. The scheme is shown to be very efficient and robust for flows with velocities ranging from M less than or equal to 10(exp -10) to supersonic speeds.

  14. Validation of a method for prediction of isotopic concentrations in burnup credit applications

    SciTech Connect

    DeHart, M.D.; Hermann, O.W.; Parks, C.V.

    1995-09-01

    Unlike fresh fuel assumptions typically employed in the criticality safety analysis of spent fuel configurations, burnup credit applications rely on depletion and decay calculations to predict the isotopic composition of spent fuel. These isotopics are used in subsequent criticality calculations to assess the reduced worth of the spent fuel. To validate the codes and data used in depletion approaches, experimental measurements are compared with numerical predictions for relevant spent fuel samples. This paper describes a set of experimentally characterized pressurized-water-reactor (PWR) fuel samples and provides a comparison to results of SCALE-4 depletion calculations. An approach to determine biases and uncertainties between calculated and measured isotopic concentrations is discussed, together with a method to statistically combine these terms to obtain a conservative estimate of spent fuel isotopic concentrations.

  15. Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater using the denitrifier method

    USGS Publications Warehouse

    Casciotti, K.L.; Sigman, D.M.; Hastings, M. Galanter; Böhlke, J.K.; Hilkert, A.

    2002-01-01

    We report a novel method for measurement of the oxygen isotopic composition (18O/16O) of nitrate (NO3-) from both seawater and freshwater. The denitrifier method, based on the isotope ratio analysis of nitrous oxide generated from sample nitrate by cultured denitrifying bacteria, has been described elsewhere for its use in nitrogen isotope ratio (15N/14N) analysis of nitrate.1Here, we address the additional issues associated with 18O/16O analysis of nitrate by this approach, which include (1) the oxygen isotopic difference between the nitrate sample and the N2O analyte due to isotopic fractionation associated with the loss of oxygen atoms from nitrate and (2) the exchange of oxygen atoms with water during the conversion of nitrate to N2O. Experiments with 18O-labeled water indicate that water exchange contributes less than 10%, and frequently less than 3%, of the oxygen atoms in the N2O product for Pseudomonas aureofaciens. In addition, both oxygen isotope fractionation and oxygen atom exchange are consistent within a given batch of analyses. The analysis of appropriate isotopic reference materials can thus be used to correct the measured 18O/16O ratios of samples for both effects. This is the first method tested for 18O/16O analysis of nitrate in seawater. Benefits of this method, relative to published freshwater methods, include higher sensitivity (tested down to 10 nmol and 1 μM NO3-), lack of interference by other solutes, and ease of sample preparation.

  16. Using stable isotopes to monitor forms of sulfur during desulfurization processes: A quick screening method

    USGS Publications Warehouse

    Liu, Chao-Li; Hackley, Keith C.; Coleman, D.D.; Kruse, C.W.

    1987-01-01

    A method using stable isotope ratio analysis to monitor the reactivity of sulfur forms in coal during thermal and chemical desulfurization processes has been developed at the Illinois State Geological Survey. The method is based upon the fact that a significant difference exists in some coals between the 34S/32S ratios of the pyritic and organic sulfur. A screening method for determining the suitability of coal samples for use in isotope ratio analysis is described. Making these special coals available from coal sample programs would assist research groups in sorting out the complex sulfur chemistry which accompanies thermal and chemical processing of high sulfur coals. ?? 1987.

  17. Method and apparatus for maintaining equilibrium in a helical axis stellarator

    DOEpatents

    Reiman, A.; Boozer, A.

    1984-10-31

    Apparatus for maintaining three-dimensional MHD equilibrium in a plasma contained in a helical axis stellarator includes a resonant coil system, having a configuration such that current therethrough generates a magnetic field cancelling the resonant magnetic field produced by currents driven by the plasma pressure on any given flux surface resonating with the rotational transform of another flux surface in the plasma. Current through the resonant coil system is adjusted as a function of plasma beta.

  18. Method and apparatus for maintaining equilibrium in a helical axis stellarator

    DOEpatents

    Reiman, Allan; Boozer, Allen

    1987-01-01

    Apparatus for maintaining three-dimensional MHD equilibrium in a plasma contained in a helical axis stellerator includes a resonant coil system, having a configuration such that current therethrough generates a magnetic field cancelling the resonant magnetic field produced by currents driven by the plasma pressure on any given flux surface resonating with the rotational transform of another flux surface in the plasma. Current through the resonant coil system is adjusted as a function of plasma beta.

  19. Development of safe mechanism for surgical robots using equilibrium point control method.

    PubMed

    Park, Shinsuk; Lim, Hokjin; Kim, Byeong-sang; Song, Jae-bok

    2006-01-01

    This paper introduces a novel mechanism for surgical robotic systems to generate human arm-like compliant motion. The mechanism is based on the idea of the equilibrium point control hypothesis which claims that multi-joint limb movements are achieved by shifting the limbs' equilibrium positions defined by neuromuscular activity. The equilibrium point control can be implemented on a robot manipulator by installing two actuators at each joint of the manipulator, one to control the joint position, and the other to control the joint stiffness. This double-actuator mechanism allows us to arbitrarily manipulate the stiffness (or impedance) of a robotic manipulator as well as its position. Also, the force at the end-effector can be estimated based on joint stiffness and joint angle changes without using force transducers. A two-link manipulator and a three-link manipulator with the double-actuator units have been developed, and experiments and simulation results show the potential of the proposed approach. By creating the human arm-like behavior, this mechanism can improve the performance of robot manipulators to execute stable and safe movement in surgical environments by using a simple control scheme.

  20. Viscosity-Projection Method for a Family of General Equilibrium Problems and Asymptotically Strict Pseudocontractions in the Intermediate Sense

    PubMed Central

    Wen, Dao-Jun

    2013-01-01

    In this paper, a Meir-Keeler contraction is introduced to propose a viscosity-projection approximation method for finding a common element of the set of solutions of a family of general equilibrium problems and the set of fixed points of asymptotically strict pseudocontractions in the intermediate sense. Strong convergence of the viscosity iterative sequences is obtained under some suitable conditions. Results presented in this paper extend and unify the previously known results announced by many other authors. PMID:24285937

  1. A coupled isotope tracer method to characterize input water to lakes

    NASA Astrophysics Data System (ADS)

    Yi, Yi; Brock, Bronwyn E.; Falcone, Matthew D.; Wolfe, Brent B.; Edwards, Thomas W. D.

    2008-02-01

    SummaryWe develop a new coupled isotope tracer method for characterizing the isotopic composition of input water to lakes, and apply it in the context of ongoing hydrological process studies in the Peace-Athabasca Delta, a large, remote, riparian ecosystem in the boreal region of western Canada. The region has a highly seasonal climate, with floodplain lakes typically receiving input only during the 4-6 month open-water season from varying proportions of spring snowmelt, summer rains and river flooding. These possible input sources have distinct ranges of isotopic compositions that are strongly constrained to a well-defined local meteoric water line, thus affording the opportunity to derive lake-specific estimates of the integrated isotopic composition of input waters after accounting for the effects of secondary evaporative isotopic enrichment. As shown by comparison of the results of isotopic surveys of delta lakes prior to freeze-up in 2000 and 2005, this isotopic characterization of input waters can be combined with other data and field observations to provide new insight into spatial and temporal variability in delta lake recharge processes. This includes evidence that summer rainfall in 2000 played an important role in replenishing shallow basins delta-wide, especially in the central low-lying region, compensating for below-average snow accumulation during the previous winter. In contrast, 2005 was marked by greater relative contributions from both snowmelt and river flooding because of high winter snow accumulation and a spring ice-jam that caused river floodwaters to enter some basins in the southern part of the delta. The method is readily transferable to investigations in other remote regions that are sparsely monitored by conventional hydrometric networks.

  2. A stable isotope dilution method for measuring bioavailability of organic contaminants

    PubMed Central

    Delgado-Moreno, Laura; Gan, Jay

    2014-01-01

    Methods for determining bioavailability of organic contaminants suffer various operational limitations. We explored the use of stable isotope labeled references in developing an isotope dilution method (IDM) to measure the exchangeable pool (E) of pyrene and bifenthrin as an approximation of their bioavailability in sediments. The exchange of deuterated bifenthrin or pyrene with its native counterpart was completed within 48 h. The derived E was 38–82% for pyrene and 28–59% for bifenthrin. Regression between E and the sum of rapid and slow desorption fractions obtained from sequential desorption showed a slope close to 1.0. The ability of IDM to predict bioavailability was further shown from a strong relationship (r2 > 0.93) between E and bioaccumulation into Chironomus tentans. Given the abundance of stable isotope labeled references and their relatively easy analysis, the IDM has the potential to become a readily adoptable tool for estimating organic contaminants bioaccessibility in various matrices. PMID:23434573

  3. Oxygen isotopes in nitrite: Analysis, calibration, and equilibration

    USGS Publications Warehouse

    Casciotti, K.L.; Böhlke, J.K.; McIlvin, M.R.; Mroczkowski, S.J.; Hannon, J.E.

    2007-01-01

    Nitrite is a central intermediate in the nitrogen cycle and can persist in significant concentrations in ocean waters, sediment pore waters, and terrestrial groundwaters. To fully interpret the effect of microbial processes on nitrate (NO3-), nitrite (NO2-), and nitrous oxide (N2O) cycling in these systems, the nitrite pool must be accessible to isotopic analysis. Furthermore, because nitrite interferes with most methods of nitrate isotopic analysis, accurate isotopic analysis of nitrite is essential for correct measurement of nitrate isotopes in a sample that contains nitrite. In this study, nitrite salts with varying oxygen isotopic compositions were prepared and calibrated and then used to test the denitrifier method for nitrite oxygen isotopic analysis. The oxygen isotopic fractionation during nitrite reduction to N2O by Pseudomonas aureofaciens was lower than for nitrate conversion to N2O, while oxygen isotopic exchange between nitrite and water during the reaction was similar. These results enable the extension of the denitrifier method to oxygen isotopic analysis of nitrite (in the absence of nitrate) and correction of nitrate isotopes for the presence of nitrite in "mixed" samples. We tested storage conditions for seawater and freshwater samples that contain nitrite and provide recommendations for accurate oxygen isotopic analysis of nitrite by any method. Finally, we report preliminary results on the equilibrium isotope effect between nitrite and water, which can play an important role in determining the oxygen isotopic value of nitrite where equilibration with water is significant. ?? 2007 American Chemical Society.

  4. The use of isotope effects to determine enzyme mechanisms.

    PubMed

    Cleland, W W

    2005-01-01

    Isotope effects are one of the most powerful kinetic tools for determining enzyme mechanisms. There are three methods of measurement. First, one can compare reciprocal plots with labeled and unlabeled substrates. The ratio of the slopes is the isotope effect on V/K, and the ratio of the vertical intercepts is the isotope effect on V(max). This is the only way to determine V(max) isotope effects, but is limited to isotope effects of 5% or greater. The second method is internal competition, where the labeled and unlabeled substrates are present at the same time and the change in their ratio in residual substrate or in product is used to calculate an isotope effect, which is that on V/K of the labeled reactant. This is the method used for tritium or (14)C, or with the natural abundances of (13)C, (15)N, or (18)O. The third method involves perturbations from equilibrium when a labeled substrate and corresponding unlabeled product are present at chemical equilibrium. This also gives just an isotope effect on V/K for the labeled reactant. The chemistry is typically not fully rate limiting, so that the isotope effect on V/K is given by: (x)(V/K)=((x)k+c(f)+c(r)(x)K(eq))/(1+c(f)+c(r)) where x defines the isotope (D, T, 13, 15, 18 for deuterium, tritium, (13)C, (15)N, or (18)O), and (x)(V/K), (x)k, and (x)K(eq) are the observed isotope effect, the intrinsic one on the chemical step, and the isotope effect on the equilibrium constant, respectively. The constants c(f) and c(r) are commitments in forward and reverse directions, and are the ratio of the rate constant for the chemical reaction and the net rate constant for release from the enzyme of the varied substrate (direct comparison) or labeled substrate (internal competition and equilibrium perturbation) for c(f), or the first product released or the one involved in the perturbation for c(r). The intrinsic isotope effect, (x)k, can be estimated by comparing deuterium and tritium isotope effects on V/K, or by comparing the

  5. Computational methods for reactive transport modeling: An extended law of mass-action, xLMA, method for multiphase equilibrium calculations

    NASA Astrophysics Data System (ADS)

    Leal, Allan M. M.; Kulik, Dmitrii A.; Kosakowski, Georg; Saar, Martin O.

    2016-10-01

    We present an extended law of mass-action (xLMA) method for multiphase equilibrium calculations and apply it in the context of reactive transport modeling. This extended LMA formulation differs from its conventional counterpart in that (i) it is directly derived from the Gibbs energy minimization (GEM) problem (i.e., the fundamental problem that describes the state of equilibrium of a chemical system under constant temperature and pressure); and (ii) it extends the conventional mass-action equations with Lagrange multipliers from the Gibbs energy minimization problem, which can be interpreted as stability indices of the chemical species. Accounting for these multipliers enables the method to determine all stable phases without presuming their types (e.g., aqueous, gaseous) or their presence in the equilibrium state. Therefore, the here proposed xLMA method inherits traits of Gibbs energy minimization algorithms that allow it to naturally detect the phases present in equilibrium, which can be single-component phases (e.g., pure solids or liquids) or non-ideal multi-component phases (e.g., aqueous, melts, gaseous, solid solutions, adsorption, or ion exchange). Moreover, our xLMA method requires no technique that tentatively adds or removes reactions based on phase stability indices (e.g., saturation indices for minerals), since the extended mass-action equations are valid even when their corresponding reactions involve unstable species. We successfully apply the proposed method to a reactive transport modeling problem in which we use PHREEQC and GEMS as alternative backends for the calculation of thermodynamic properties such as equilibrium constants of reactions, standard chemical potentials of species, and activity coefficients. Our tests show that our algorithm is efficient and robust for demanding applications, such as reactive transport modeling, where it converges within 1-3 iterations in most cases. The proposed xLMA method is implemented in Reaktoro, a

  6. A method for carbon stable isotope analysis of methyl halides and chlorofluorocarbons at pptv concentrations.

    PubMed

    Archbold, Marie E; Redeker, Kelly R; Davis, Simon; Elliot, Trevor; Kalin, Robert M

    2005-01-01

    A pre-concentration system has been validated for use with a gas chromatography/mass spectrometry/isotope ratio mass spectrometer (GC/MS/IRMS) to determine ambient air (13)C/(12)C ratios for methyl halides (MeCl and MeBr) and chlorofluorocarbons (CFCs). The isotopic composition of specific compounds can provide useful information on their atmospheric budgets and biogeochemistry that cannot be ascertained from abundance measurements alone. Although pre-concentration systems have been previously used with a GC/MS/IRMS for atmospheric trace gas analysis, this is the first study also to report system validation tests. Validation results indicate that the pre-concentration system and subsequent separation technologies do not significantly alter the stable isotopic ratios of the target methyl halides, CFC-12 (CCl(2)F(2)) and CFC-113 (C(2)Cl(3)F(3)). Significant, but consistent, isotopic shifts of -27.5 per thousand to -25.6 per thousand do occur within the system for CFC-11 (CCl(3)F), although the shift is correctible. The method presented has the capacity to separate these target halocarbons from more than 50 other compounds in ambient air samples. Separation allows for the determination of stable carbon isotope ratios of five of these six target trace atmospheric constituents within ambient air for large volume samples (isotope results similar to published values for (13)C/(12)C analysis of MeCl (-39.1 per thousand) and CFC-113 (-28.1 per thousand). However, this is the first paper reporting stable carbon isotope signatures for CFC-11 (-29.4 per thousand) and CFC-12 (-37.0 per thousand).

  7. RAPID AND PRECISE METHOD FOR MEASURING STABLE CARBON ISOTOPE RATIOS OF DISSOLVED INORGANIC CARBON

    EPA Science Inventory

    We describe a method for rapid preparation, concentration and stable isotopic analysis of dissolved inorganic carbon (d13C-DIC). Liberation of CO2 was accomplished by placing 100 ?l phosphoric acid and 0.9 ml water in an evacuated 1.7-ml gas chromatography (GC) injection vial. Fo...

  8. Method for the purification of polybrominated diphenyl ethers in sediment for compound-specific isotope analysis.

    PubMed

    Zeng, Yan-Hong; Luo, Xiao-Jun; Chen, Hua-Shan; Chen, She-Jun; Wu, Jiang-Ping; Mai, Bi-Xian

    2013-07-15

    A purification method for lower polybrominated diphenyl ethers (PBDEs, from tri- to hexa-BDE) in sediment for compound-specific isotope analysis (CSIA) was developed in this study. The compounds were extracted using a Soxhlet apparatus with addition of activated alumina and Florisil in the paper tube during the Soxhlet extraction provided for less complex extracts. Then, the extract was isolated from polar compounds using a multi-layer silica gel column, separated into different fractions using alumina/silica (Al/Si) gel columns and finally purified using a Florisil column. The mean recoveries of the major PBDE congeners in the spiked samples ranged from 76.2% to 82.4%. The purity of the samples was verified by GC-MS in full scan mode. The stable isotopic integrity of the spiked samples after the purification was tested by comparing the stable carbon isotope ratios (δ(13)C) of the processed and the unprocessed standard materials. The differences in the δ(13)C values for each compound between the processed and unprocessed standards were less than 0.5‰, with the exception of BDE100 (0.54‰). Finally, the purification and isotope analysis method was successfully applied to measure the δ(13)C of PBDEs in sediments. This application of the method indicated that CSIA seems to be a promising method for providing intrinsic characteristics for further environmental fate studies of PBDEs.

  9. A simplified method for obtaining high-purity perchlorate from groundwater for isotope analyses.

    SciTech Connect

    vonKiparski, G; Hillegonds, D

    2011-04-04

    Investigations into the occurrence and origin of perchlorate (ClO{sub 4}{sup -}) found in groundwater from across North America have been sparse until recent years, and there is mounting evidence that natural formation mechanisms are important. New opportunities for identifying groundwater perchlorate and its origin have arisen with the utilization of improved detection methods and sampling techniques. Additionally, application of the forensic potential of isotopic measurements has begun to elucidate sources, potential formation mechanisms and natural attenuation processes. Procedures developed appear to be amenable to enable high precision stable isotopic analyses, as well as lower precision AMS analyses of {sup 36}Cl. Immediate work is in analyzing perchlorate isotope standards and developing full analytical accuracy and uncertainty expectations. Field samples have also been collected, and will be analyzed when final qa/qc samples are deemed acceptable.

  10. An equilibrium method for prediction of transverse shear stresses in a thick laminated plate

    NASA Technical Reports Server (NTRS)

    Chaudhuri, R. Z.

    1986-01-01

    First two equations of equilibrium are utilized to compute the transverse shear stress variation through thickness of a thick laminated plate after in-plane stresses have been computed using an assumed quadratic displacement triangular element based on transverse inextensibility and layerwise constant shear angle theory (LCST). Centroid of the triangle is the point of exceptional accuracy for transverse shear stresses. Numerical results indicate close agreement with elasticity theory. An interesting comparison between the present theory and that based on assumed stress hybrid finite element approach suggests that the latter does not satisfy the condition of free normal traction at the edge. Comparison with numerical results obtained by using constant shear angle theory suggests that LCST is close to the elasticity solution while the CST is closer to classical (CLT) solution. It is also demonstrated that the reduced integration gives faster convergence when the present theory is applied to a thin plate.

  11. System and method of adjusting the equilibrium temperature of an inductively-heated susceptor

    DOEpatents

    Matsen, Marc R; Negley, Mark A; Geren, William Preston

    2015-02-24

    A system for inductively heating a workpiece may include an induction coil, at least one susceptor face sheet, and a current controller coupled. The induction coil may be configured to conduct an alternating current and generate a magnetic field in response to the alternating current. The susceptor face sheet may be configured to have a workpiece positioned therewith. The susceptor face sheet may be formed of a ferromagnetic alloy having a Curie temperature and being inductively heatable to an equilibrium temperature approaching the Curie temperature in response to the magnetic field. The current controller may be coupled to the induction coil and may be configured to adjust the alternating current in a manner causing a change in at least one heating parameter of the susceptor face sheet.

  12. Effect of deviation from local thermodynamic equilibrium on the Goldberg-Unno method. [turbulence effects on optical density in the solar photosphere

    NASA Technical Reports Server (NTRS)

    Troyan, V. I.

    1974-01-01

    The dependence of turbulent velocity on optical depth was studied by use of the Goldberg-Unno method, with allowance made for the influence of deviation from the local thermodynamic equilibrium. It was found that allowance for deviation from local thermodynamic equilibrium displaces the curve of dependence of turbulent velocity on optical depth along two axes.

  13. Experimental evaluation of the isotopic exchange equilibrium 10B(OH) 3+ 11B(OH) 4-= 11B(OH) 3+ 10B(OH) 4- in aqueous solution

    NASA Astrophysics Data System (ADS)

    Byrne, Robert H.; Yao, Wensheng; Klochko, Kateryna; Tossell, John A.; Kaufman, Alan J.

    2006-04-01

    The precision of spectrophotometric measurements of indicator absorbance ratios is sufficient to allow evaluation of small isotopically induced differences in the dissociation constant of boric acid ( KB). The quotient of 11KB and 10KB, obtained using isotopically ⩾99% pure borate/boric acid buffers, provides an equilibrium constant for the reaction 10B(OH) 3+ 11B(OH) 4-⇔ 11B(OH) 3+ 10B(OH) 4- which heretofore had not been experimentally determined. Previous theoretical and semi-empirical evaluations of this equilibrium, which is important for assessments of the paleo-pH of seawater and the paleo- pCO 2 of the atmosphere, have yielded constants, 11-10KB= 10KB/ 11KB, that have ranged between 1.0194 and approximately 1.033. The experimentally determined value 11-10KB=1.028 5±0.001 6 (mean±95% confidence interval) obtained at 25 °C and 0.63 molal (mol kg -1 H 2O) ionic strength is in much better agreement with recent theoretical assessments of 11-10KB that have ranged between 1.026 and 1.033, than the much-cited original estimate (1.0194) of Kakihana et al. (1977) [Fundamental studies on the ion-exchange separation of boron isotopes. Bulletin of Chemical Society of Japan 50, 158-163]. Since the activity quotient for the fractionation reaction is almost equal to unity, it is expected that the 11-10KB value obtained in this study will be applicable over a wide range of solution compositions and ionic strengths.

  14. Structural design using equilibrium programming

    NASA Technical Reports Server (NTRS)

    Scotti, Stephen J.

    1992-01-01

    Multiple nonlinear programming methods are combined in the method of equilibrium programming. Equilibrium programming theory has been appied to problems in operations research, and in the present study it is investigated as a framework to solve structural design problems. Several existing formal methods for structural optimization are shown to actually be equilibrium programming methods. Additionally, the equilibrium programming framework is utilized to develop a new structural design method. Selected computational results are presented to demonstrate the methods.

  15. A Study of Interactions between Mixing and Chemical Reaction Using the Rate-Controlled Constrained-Equilibrium Method

    NASA Astrophysics Data System (ADS)

    Hadi, Fatemeh; Janbozorgi, Mohammad; Sheikhi, M. Reza H.; Metghalchi, Hameed

    2016-10-01

    The rate-controlled constrained-equilibrium (RCCE) method is employed to study the interactions between mixing and chemical reaction. Considering that mixing can influence the RCCE state, the key objective is to assess the accuracy and numerical performance of the method in simulations involving both reaction and mixing. The RCCE formulation includes rate equations for constraint potentials, density and temperature, which allows taking account of mixing alongside chemical reaction without splitting. The RCCE is a dimension reduction method for chemical kinetics based on thermodynamics laws. It describes the time evolution of reacting systems using a series of constrained-equilibrium states determined by RCCE constraints. The full chemical composition at each state is obtained by maximizing the entropy subject to the instantaneous values of the constraints. The RCCE is applied to a spatially homogeneous constant pressure partially stirred reactor (PaSR) involving methane combustion in oxygen. Simulations are carried out over a wide range of initial temperatures and equivalence ratios. The chemical kinetics, comprised of 29 species and 133 reaction steps, is represented by 12 RCCE constraints. The RCCE predictions are compared with those obtained by direct integration of the same kinetics, termed detailed kinetics model (DKM). The RCCE shows accurate prediction of combustion in PaSR with different mixing intensities. The method also demonstrates reduced numerical stiffness and overall computational cost compared to DKM.

  16. A method to extract soil water for stable isotope analysis

    USGS Publications Warehouse

    Revesz, K.; Woods, P.H.

    1990-01-01

    A method has been developed to extract soil water for determination of deuterium (D) and 18O content. The principle of this method is based on the observation that water and toluene form an azeotropic mixture at 84.1??C, but are completely immiscible at ambient temperature. In a specially designed distillation apparatus, the soil water is distilled at 84.1??C with toluene and is separated quantitatively in the collecting funnel at ambient temperature. Traces of toluene are removed and the sample can be analyzed by mass spectrometry. Kerosene may be substituted for toluene. The accuracy of this technique is ?? 2 and ?? 0.2???, respectively, for ??D and ??18O. Reduced accuracy is obtained at low water contents. ?? 1990.

  17. Isobaric molecular dynamics version of the generalized replica exchange method (gREM): Liquid–vapor equilibrium

    DOE PAGES

    Malolepsza, Edyta; Secor, Maxim; Keyes, Tom

    2015-09-23

    A prescription for sampling isobaric generalized ensembles with molecular dynamics is presented and applied to the generalized replica exchange method (gREM), which was designed for simulating first-order phase transitions. The properties of the isobaric gREM ensemble are discussed and a study is presented of the liquid-vapor equilibrium of the guest molecules given for gas hydrate formation with the mW water model. As a result, phase diagrams, critical parameters, and a law of corresponding states are obtained.

  18. Statistical equilibrium in simple exchange games I. Methods of solution and application to the Bennati-Dragulescu-Yakovenko (BDY) game

    NASA Astrophysics Data System (ADS)

    Scalas, E.; Garibaldi, U.; Donadio, S.

    2006-09-01

    Simple stochastic exchange games are based on random allocation of finite resources. These games are Markov chains that can be studied either analytically or by Monte Carlo simulations. In particular, the equilibrium distribution can be derived either by direct diagonalization of the transition matrix, or using the detailed balance equation, or by Monte Carlo estimates. In this paper, these methods are introduced and applied to the Bennati-Dragulescu-Yakovenko (BDY) game. The exact analysis shows that the statistical-mechanical analogies used in the previous literature have to be revised.

  19. Development of an identification method of pressure anisotropy based on equilibrium analysis and magnetics

    SciTech Connect

    Asahi, Y.; Suzuki, Y.; Watanabe, K. Y.; Cooper, W. A.

    2013-02-15

    We evaluate the fluxes measured by the magnetic flux loops installed in LHD by using a three dimensional MHD equilibrium analysis code, ANIMEC, which enable us to directly determine the calibration function between the anisotropic pressure and the measured fluxes for the non-axisymmetric plasmas for the first time. The result indicates that the diamagnetic flux represents a nearly single-valued function of the beta perpendicular with respect to the field, and the saddle loop flux represents a nearly single-valued function of an equally weighted average of the beta values parallel and perpendicular to the field, regardless of the pressure anisotropy or the amount of energetic trapped particles. The values of the beta perpendicular to the field and the equal weighting averaged beta estimated by the single-valued functions (calibration functions) are investigated in order to clarify the magnitude of deviation from those original values, and the range of anisotropy where the beta value evaluated by the magnetic flux measurement is calculated within a 10% error.

  20. Toroidal figures of equilibrium from a second-order accurate, accelerated SCF method with subgrid approach

    NASA Astrophysics Data System (ADS)

    Huré, J.-M.; Hersant, F.

    2017-02-01

    We compute the structure of a self-gravitating torus with polytropic equation of state (EOS) rotating in an imposed centrifugal potential. The Poisson solver is based on isotropic multigrid with optimal covering factor (fluid section-to-grid area ratio). We work at second order in the grid resolution for both finite difference and quadrature schemes. For soft EOS (i.e. polytropic index n ≥ 1), the underlying second order is naturally recovered for boundary values and any other integrated quantity sensitive to the mass density (mass, angular momentum, volume, virial parameter, etc.), i.e. errors vary with the number N of nodes per direction as ˜1/N2. This is, however, not observed for purely geometrical quantities (surface area, meridional section area, volume), unless a subgrid approach is considered (i.e. boundary detection). Equilibrium sequences are also much better described, especially close to critical rotation. Yet another technical effort is required for hard EOS (n < 1), due to infinite mass density gradients at the fluid surface. We fix the problem by using kernel splitting. Finally, we propose an accelerated version of the self-consistent field (SCF) algorithm based on a node-by-node pre-conditioning of the mass density at each step. The computing time is reduced by a factor of 2 typically, regardless of the polytropic index. There is a priori no obstacle to applying these results and techniques to ellipsoidal configurations and even to 3D configurations.

  1. Method and apparatus for noble gas atom detection with isotopic selectivity

    DOEpatents

    Hurst, G. Samuel; Payne, Marvin G.; Chen, Chung-Hsuan; Parks, James E.

    1984-01-01

    Apparatus and methods of operation are described for determining, with isotopic selectivity, the number of noble gas atoms in a sample. The analysis is conducted within an evacuated chamber which can be isolated by a valve from a vacuum pumping system capable of producing a pressure of 10.sup.-8 Torr. Provision is made to pass pulses of laser beams through the chamber, these pulses having wavelengths appropriate for the resonance ionization of atoms of the noble gas under analysis. A mass filter within the chamber selects ions of a specific isotope of the noble gas, and means are provided to accelerate these selected ions sufficiently for implantation into a target. Specific types of targets are discussed. An electron measuring device produces a signal relatable to the number of ions implanted into the target and thus to the number of atoms of the selected isotope of the noble gas removed from the gas sample. The measurement can be continued until a substantial fraction, or all, of the atoms in the sample have been counted. Furthermore, additional embodiments of the apparatus are described for bunching the atoms of a noble gas for more rapid analysis, and for changing the target for repetitive cycling of the gas in the chamber. The number of repetitions of the cyclic steps depend upon the concentration of the isotope of interest, the separative efficiency of the mass filter, etc. The cycles are continued until a desired selectivity is achieved. Also described are components and a method of operation for a pre-enrichment operation for use when an introduction of a total sample would elevate the pressure within the chamber to levels in excess of those for operation of the mass filter, specifically a quadrupole mass filter. Specific examples of three noble gas isotope analyses are described.

  2. A METHOD FOR THE MEASUREMENT OF SITE-SPECIFIC TAUTOMERIC AND ZWITTERIONIC MICROSPECIES EQUILIBRIUM CONSTANTS

    EPA Science Inventory

    We describe a method for the individual measurement of simultaneously occurring, unimolecular, site-specific "microequilibrium" constants as in, for example, prototropic tautomerism and zwitterionic equilibria. Our method represents an elaboration of that of Nygren et al. (Anal. ...

  3. METHOD FOR THE MEASUREMENT OF SITE-SPECIFIC TAUTOMERIC AND ZWITTERIONIC MICROSPECIES EQUILIBRIUM CONSTANTS

    EPA Science Inventory

    We describe a method for the individual measurement of simultaneously occurring, unimolecular, site-specific “microequilibrium” constants as in, for example, prototropic tautomerism and zwitterionic equilibria. Our method represents an elaboration of that of Nygren et al. (Anal. ...

  4. A method to predict the equilibrium solubility of drugs in solid polymers near room temperature using thermal analysis.

    PubMed

    Bellantone, Robert A; Patel, Piyush; Sandhu, Harpreet; Choi, Duk Soon; Singhal, Dharmendra; Chokshi, H; Malick, A Waseem; Shah, Navnit

    2012-12-01

    A method is presented for determining the equilibrium solubility of a drug in a solid polymer at or near room temperature, which represents a typical storage temperature. The method is based on a thermodynamic model to calculate the Gibbs energy change ΔG(SS) associated with forming a binary drug-polymer solid solution from the unmixed polymer and solid drug. The model includes contributions from heat capacity differences between the solid solution and the corresponding unmixed components, breaking up of the solid drug structure, and drug-polymer mixing. Calculation of ΔG(SS) from thermal analysis data is demonstrated, and it is shown that minima of plots of ΔG(SS) versus the dissolved drug concentration represent the equilibrium drug solubility in the polymer. Solid solutions were produced for drug-polymer systems (griseofulvin, indomethacin, itraconazole; PVP K30, Eudragit L100, Eudragit E100) in drug weight fractions up to ∼25%. At 25°C, it was seen that heat capacity effects were important in determining the drug solubility. It was concluded that drug solubilities in solid polymers can be determined using thermal analysis, and must include heat capacity effects when evaluated near room temperature.

  5. A new method for calibrating a boron isotope paleo-pH proxy using massive Porites corals

    NASA Astrophysics Data System (ADS)

    Kubota, Kaoru; Yokoyama, Yusuke; Ishikawa, Tsuyoshi; Suzuki, Atsushi

    2015-09-01

    The boron isotope ratio (δ11B) of marine biogenic carbonates can reconstruct pH and pCO2 of seawater, and potentially CO2 concentration in the atmosphere. To date, δ11B-pHSW calibration has been proposed via culturing experiments, where calcifying organisms are cultured under artificially acidified seawater. However, in scleractinian corals, reconstructed pH values using culture-based calibrations do not agree well with actual observations of seawater CO2 chemistry. Thus, another approach is needed to establish a more reliable calibration method. In this study, we established field-based calibrations for Chichijima and Tahiti, both located in subtropical gyres where surface seawater is close to CO2 equilibrium. We suggest a new approach to calibration of δ11B-pH in which the long-term δ11B variation of massive Porites corals is compared with the decreasing pH trend (i.e., ocean acidification) that has occurred since the Industrial Revolution. This calibration will offer a new avenue for studying seawater CO2 chemistry using coral δ11B in diverse settings, such as upwelling regions, coral reefs, and coastal areas.

  6. Partition Equilibrium

    NASA Astrophysics Data System (ADS)

    Feldman, Michal; Tennenholtz, Moshe

    We introduce partition equilibrium and study its existence in resource selection games (RSG). In partition equilibrium the agents are partitioned into coalitions, and only deviations by the prescribed coalitions are considered. This is in difference to the classical concept of strong equilibrium according to which any subset of the agents may deviate. In resource selection games, each agent selects a resource from a set of resources, and its payoff is an increasing (or non-decreasing) function of the number of agents selecting its resource. While it has been shown that strong equilibrium exists in resource selection games, these games do not possess super-strong equilibrium, in which a fruitful deviation benefits at least one deviator without hurting any other deviator, even in the case of two identical resources with increasing cost functions. Similarly, strong equilibrium does not exist for that restricted two identical resources setting when the game is played repeatedly. We prove that for any given partition there exists a super-strong equilibrium for resource selection games of identical resources with increasing cost functions; we also show similar existence results for a variety of other classes of resource selection games. For the case of repeated games we identify partitions that guarantee the existence of strong equilibrium. Together, our work introduces a natural concept, which turns out to lead to positive and applicable results in one of the basic domains studied in the literature.

  7. DoE optimization of a mercury isotope ratio determination method for environmental studies.

    PubMed

    Berni, Alex; Baschieri, Carlo; Covelli, Stefano; Emili, Andrea; Marchetti, Andrea; Manzini, Daniela; Berto, Daniela; Rampazzo, Federico

    2016-05-15

    By using the experimental design (DoE) technique, we optimized an analytical method for the determination of mercury isotope ratios by means of cold-vapor multicollector ICP-MS (CV-MC-ICP-MS) to provide absolute Hg isotopic ratio measurements with a suitable internal precision. By running 32 experiments, the influence of mercury and thallium internal standard concentrations, total measuring time and sample flow rate was evaluated. Method was optimized varying Hg concentration between 2 and 20 ng g(-1). The model finds out some correlations within the parameters affect the measurements precision and predicts suitable sample measurement precisions for Hg concentrations from 5 ng g(-1) Hg upwards. The method was successfully applied to samples of Manila clams (Ruditapes philippinarum) coming from the Marano and Grado lagoon (NE Italy), a coastal environment affected by long term mercury contamination mainly due to mining activity. Results show different extents of both mass dependent fractionation (MDF) and mass independent fractionation (MIF) phenomena in clams according to their size and sampling sites in the lagoon. The method is fit for determinations on real samples, allowing for the use of Hg isotopic ratios to study mercury biogeochemical cycles in complex ecosystems.

  8. New optimization method for intermolecular potentials: Optimization of a new anisotropic united atoms potential for olefins: Prediction of equilibrium properties

    NASA Astrophysics Data System (ADS)

    Bourasseau, Emeric; Haboudou, Mehalia; Boutin, Anne; Fuchs, Alain H.; Ungerer, Philippe

    2003-02-01

    In this study, we propose a new global procedure to perform optimization of semiempirical intermolecular potential parameters on the basis of a large reference database. To obtain transferable parameters, we used the original method proposed by Ungerer [Ungerer et al., J. Chem. Phys. 112, 5499 (2000)], based on the minimization of a dimensionless error criterion. This method allows the simultaneous optimization of several parameters from a large set of reference data. However, the computational cost of such a method limits its application, because it implies the calculation of an important number of partial derivatives, calculated by finite differences between the results of several different simulations. In this work, we propose a new method to evaluate partial derivatives, in order to reduce the computing time and to obtain more consistent derivatives. This method is based on the analysis of statistical fluctuations during a single simulation. To predict equilibrium properties of olefins, we optimize the Lennard-Jones potential parameters of the unsaturated hydrocarbon groups using the anisotropic united atoms description. The resulting parameters are consistent with those previously determined for linear and branched alkanes. Test simulations have been performed at temperatures ranging from 150 to 510 K for several α-olefins (ethylene, propene, 1-butene, 1-pentene, 1-hexene, 1-octene), several β-olefins (trans-2-butene, cis-2-butene, trans-2-pentene), isobutene, and butadiene. Equilibrium properties are well predicted, and critical properties can be evaluated with a good accuracy, despite the fact that most of the results constitute pure predictions. It is concluded that the AUA potential, due to a relevant physical meaning, can be transferred to a large range of olefins with good success.

  9. Treatment methods for the determination of delta2H and delta18O of hair keratin by continuous-flow isotope-ratio mass spectrometry.

    PubMed

    Bowen, Gabriel J; Chesson, Lesley; Nielson, Kristine; Cerling, Thure E; Ehleringer, James R

    2005-01-01

    The structural proteins that comprise approximately 90% of animal hair have the potential to record environmentally and physiologically determined variation in delta2H and delta18O values of body water. Broad, systematic, geospatial variation in stable hydrogen and oxygen isotopes of environmental water and the capacity for rapid, precise measurement via methods such as high-temperature conversion elemental analyzer/isotope ratio mass spectrometry (TC/EA-IRMS) make these isotope systems particularly well suited for applications requiring the geolocation of hair samples. In order for such applications to be successful, however, methods must exist for the accurate determination of hair delta2H and delta18O values reflecting the primary products of biosynthesis. Here, we present the results of experiments designed to examine two potential inaccuracies affecting delta2H and delta18O measurements of hair: the contribution of non-biologic hydrogen and oxygen to samples in the form of sorbed molecular water, and the exchange of hydroxyl-bound hydrogen between hair keratin and ambient water vapor. We show that rapid sorption of molecular water from the atmosphere can have a substantial effect on measured delta2H and delta18O values of hair (comprising approximately 7.7% of the measured isotopic signal for H and up to approximately 10.6% for O), but that this contribution can be effectively removed through vacuum-drying of samples for 6 days. Hydrogen exchange between hair keratin and ambient vapor is also rapid (reaching equilibrium within 3-4 days), with 9-16% of the total hydrogen available for exchange at room temperature. Based on the results of these experiments, we outline a recommended sample treatment procedure for routine measurement of delta2H and delta18O in mammal hair.

  10. Isotopic Dilution GC/MS Method for Methionine Determination in Biological Media

    NASA Astrophysics Data System (ADS)

    Horj, Elena; Iordache, Andreea; Culea, Monica

    2011-10-01

    The isotopic dilution mass spectrometry technique is the method of choice for sensitive and accurate determination of analytes in biological samples. The aim of this work was to establish a sensitive analytical method for the determination of methionine in different biological media. Quantitation of methionine from the resultant tracer spectrum requires deconvolution of the enrichment of the isotopomers. Deconvolution of the ion abundance ratios to yield tracer-to-tracee ratio for the isotopomer was done using Brauman's least squares approach. Comparison with regression curve calculation method is presented. The method was applied for amino-acids determination in beef, pork and fish meat.

  11. A new method to track seed dispersal and recruitment using 15N isotope enrichment.

    PubMed

    Carlo, Tomás A; Tewksbury, Joshua J; Martínez Del Río, Carlos

    2009-12-01

    Seed dispersal has a powerful influence on population dynamics, genetic structuring, evolutionary rates, and community ecology. Yet, patterns of seed dispersal are difficult to measure due to methodological shortcomings in tracking dispersed seeds from sources of interest. Here we introduce a new method to track seed dispersal: stable isotope enrichment. It consists of leaf-feeding plants with sprays of 15N-urea during the flowering stage such that seeds developed after applications are isotopically enriched. We conducted a greenhouse experiment with Solanum americanum and two field experiments with wild Capsicum annuum in southern Arizona, USA, to field-validate the method. First, we show that plants sprayed with 15N-urea reliably produce isotopically enriched progeny, and that delta 15N (i.e., the isotopic ratio) of seeds and seedlings is a linear function of the 15N-urea concentration sprayed on mothers. We demonstrate that three urea dosages can be used to distinctly enrich plants and unambiguously differentiate their offspring after seeds are dispersed by birds. We found that, with high urea dosages, the resulting delta 15N values in seedlings are 10(3) - 10(4) times higher than the delta 15N values of normal plants. This feature allows tracking not only where seeds arrive, but in locations where seeds germinate and recruit, because delta 15N enrichment is detectable in seedlings that have increased in mass by at least two orders of magnitude before fading to normal delta 15N values. Last, we tested a mixing model to analyze seed samples in bulk. We used the delta 15N values of batches (i.e., combined seedlings or seeds captured in seed traps) to estimate the number of enriched seeds coming from isotopically enriched plants in the field. We confirm that isotope enrichment, combined with batch-sampling, is a cheap, reliable, and user-friendly method for bulk-processing seeds and is thus excellent for the detection of rare dispersal events. This method could

  12. Trigonometric and hyperbolic functions method for constructing analytic solutions to nonlinear plane magnetohydrodynamics equilibrium equations

    SciTech Connect

    Moawad, S. M.

    2015-02-15

    In this paper, we present a solution method for constructing exact analytic solutions to magnetohydrodynamics (MHD) equations. The method is constructed via all the trigonometric and hyperbolic functions. The method is applied to MHD equilibria with mass flow. Applications to a solar system concerned with the properties of coronal mass ejections that affect the heliosphere are presented. Some examples of the constructed solutions which describe magnetic structures of solar eruptions are investigated. Moreover, the constructed method can be applied to a variety classes of elliptic partial differential equations which arise in plasma physics.

  13. Method for correcting for isotope burn-in effects in fission neutron dosimeters

    DOEpatents

    Gold, Raymond; McElroy, William N.

    1988-01-01

    A method is described for correcting for effect of isotope burn-in in fission neutron dosimeters. Two quantities are measured in order to quantify the "burn-in" contribution, namely P.sub.Z',A', the amount of (Z', A') isotope that is burned-in, and F.sub.Z', A', the fissions per unit volume produced in the (Z', A') isotope. To measure P.sub.Z', A', two solid state track recorder fission deposits are prepared from the very same material that comprises the fission neutron dosimeter, and the mass and mass density are measured. One of these deposits is exposed along with the fission neutron dosimeter, whereas the second deposit is subsequently used for observation of background. P.sub.Z', A' is then determined by conducting a second irradiation, wherein both the irradiated and unirradiated fission deposits are used in solid state track recorder dosimeters for observation of the absolute number of fissions per unit volume. The difference between the latter determines P.sub.Z', A' since the thermal neutron cross section is known. F.sub.Z', A' is obtained by using a fission neutron dosimeter for this specific isotope, which is exposed along with the original threshold fission neutron dosimeter to experience the same neutron flux-time history at the same location. In order to determine the fissions per unit volume produced in the isotope (Z', A') as it ingrows during the irradiation, B.sub.Z', A', from these observations, the neutron field must generally be either time independent or a separable function of time t and neutron energy E.

  14. 2D Quantum Simulation of MOSFET Using the Non Equilibrium Green's Function Method

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexel; Anantram, M. P.; Govindan, T. R.; Yan, Jerry (Technical Monitor)

    2000-01-01

    The objectives this viewgraph presentation summarizes include: (1) the development of a quantum mechanical simulator for ultra short channel MOSFET simulation, including theory, physical approximations, and computer code; (2) explore physics that is not accessible by semiclassical methods; (3) benchmarking of semiclassical and classical methods; and (4) study other two-dimensional devices and molecular structure, from discretized Hamiltonian to tight-binding Hamiltonian.

  15. Evaluation of Isotope 32P Method to Mark Culex pipiens (Diptera: Culicidae) in a Laboratory

    PubMed Central

    Zhang, Chongxing; Shi, Guihong; Zhao, Yuqiang; Yan, Dongmei; Li, Huaiju; Liu, Hongmei; Wiwatanaratanabutr, Itsanun; Gong, Maoqing

    2016-01-01

    Background: The aim of the current study was to develop a marking technique as an internal marker to mark post blood meal mosquitoes by using stable phosphate isotope 32P and determine the optimal concentration of it. Methods: An isotonic physiological saline solution, containing different concentration of radioactive isotope 32P-labeled disodium phosphate (Na2H32PO4) was injected into rabbits via the jugular vein in the laboratory. Emerged Cx. pipiens were marked after feeding on rabbit. At the same time, the labeled conditions of emerged Cx. pipiens were also measured by placing feces of No. 6 rabbit into containers with mosquito larvae and pupae inside. Results: According to the label condition of Cx. pipiens after taking blood and the effect of different dosage Na2H32PO4 on rabbit health, the optimal concentration of radioactive isotope was determined, that is, 0.1211 mCi/kg. By placing feces of No. 6 rabbit into containers with mosquito larvae and pupae inside, the emerged mosquitoes were also labeled. Therefore, feeding mosquitoes on the animal injected with radioactive Na2H32PO4 was more practical for detecting and tracing mosquitoes. Conclusion: The method was less time-consuming, more sensitive and safer. This marking method will facilitate post-bloodmeal studies of mosquitoes and other blood-sucking insects. PMID:27308279

  16. General method and thermodynamic tables for computation of equilibrium composition and temperature of chemical reactions

    NASA Technical Reports Server (NTRS)

    Huff, Vearl N; Gordon, Sanford; Morrell, Virginia E

    1951-01-01

    A rapidly convergent successive approximation process is described that simultaneously determines both composition and temperature resulting from a chemical reaction. This method is suitable for use with any set of reactants over the complete range of mixture ratios as long as the products of reaction are ideal gases. An approximate treatment of limited amounts of liquids and solids is also included. This method is particularly suited to problems having a large number of products of reaction and to problems that require determination of such properties as specific heat or velocity of sound of a dissociating mixture. The method presented is applicable to a wide variety of problems that include (1) combustion at constant pressure or volume; and (2) isentropic expansion to an assigned pressure, temperature, or Mach number. Tables of thermodynamic functions needed with this method are included for 42 substances for convenience in numerical computations.

  17. Isotope geochemistry. Biological signatures in clumped isotopes of O₂.

    PubMed

    Yeung, Laurence Y; Ash, Jeanine L; Young, Edward D

    2015-04-24

    The abundances of molecules containing more than one rare isotope have been applied broadly to determine formation temperatures of natural materials. These applications of "clumped" isotopes rely on the assumption that isotope-exchange equilibrium is reached, or at least approached, during the formation of those materials. In a closed-system terrarium experiment, we demonstrate that biological oxygen (O2) cycling drives the clumped-isotope composition of O2 away from isotopic equilibrium. Our model of the system suggests that unique biological signatures are present in clumped isotopes of O2—and not formation temperatures. Photosynthetic O2 is depleted in (18)O(18)O and (17)O(18)O relative to a stochastic distribution of isotopes, unlike at equilibrium, where heavy-isotope pairs are enriched. Similar signatures may be widespread in nature, offering new tracers of biological and geochemical cycling.

  18. Evaluating gull diets: A comparison of conventional methods and stable isotope analysis

    USGS Publications Warehouse

    Weiser, E.L.; Powell, A.N.

    2011-01-01

    Samples such as regurgitated pellets and food remains have traditionally been used in studies of bird diets, but these can produce biased estimates depending on the digestibility of different foods. Stable isotope analysis has been developed as a method for assessing bird diets that is not biased by digestibility. These two methods may provide complementary or conflicting information on diets of birds, but are rarely compared directly. We analyzed carbon and nitrogen stable isotope ratios of feathers of Glaucous Gull (Larus hyperboreus) chicks from eight breeding colonies in northern Alaska, and used a Bayesian mixing model to generate a probability distribution for the contribution of each food group to diets. We compared these model results with probability distributions from conventional diet samples (pellets and food remains) from the same colonies and time periods. Relative to the stable isotope estimates, conventional analysis often overestimated the contributions of birds and small mammals to gull diets and often underestimated the contributions of fish and zooplankton. Both methods gave similar estimates for the contributions of scavenged caribou, miscellaneous marine foods, and garbage to diets. Pellets and food remains therefore may be useful for assessing the importance of garbage relative to certain other foods in diets of gulls and similar birds, but are clearly inappropriate for estimating the potential impact of gulls on birds, small mammals, or fish. However, conventional samples provide more species-level information than stable isotope analysis, so a combined approach would be most useful for diet analysis and assessing a predator's impact on particular prey groups. ?? 2011 Association of Field Ornithologists.

  19. Physical and Mathematical Methods for Removing Organic Interference from Optical Isotope Measurements

    NASA Astrophysics Data System (ADS)

    Hsiao, G.; Chappellet-Volini, L.; Vu, D.

    2012-12-01

    Portable high precision isotope analyzers using CRDS technology have greatly increased the use of stable isotopes in hydrological, oceanographic, and ecological studies over the past five years. However studies of some water samples yielded incorrect isotopic values indicating some form of spectroscopic interference. Subsequent work has shown that waters derived from some plants containing interfering alcohols but meteoric waters are not affected. The initial approach to handling such samples was to use spectroscopic anomalies to identify and flag affected samples for later analysis by non-optical methods. This presentation will examine the approaches developed within the past year to allow for accurate analysis of such samples by optical methods. The first approach uses an advanced spectroscopic model to identify and quantify alcohols present in the sample. The alcohol signal is incorporated into the overall fit of the measure spectra to calculate the concentration of the individual isotopes. It was found that the δ18O value could be calculated with high accuracy, the result for the δ2H value was sufficient for many applications. The second approach uses physical treatment of the sample to break down the organic molecules into non-interfering species. The liquid sample is injected into a flash vaporizer then the vapor travels through a cartridge for physical treatment prior to analysis by CRDS. Inside the cartridge the organic molecules undergo oxidation at high temperature in the air carrier gas when exposed to the catalyst. This approach is highly effective for ethanol solutions as high as 5% as well as for the complex mixtures of alcohols found in plants. Comparison of the results of both of these methods will be compared with tertiary techniques such as IRMS where possible.

  20. RAPID SEPARATION METHOD FOR 237NP AND PU ISOTOPES IN LARGE SOIL SAMPLES

    SciTech Connect

    Maxwell, S.; Culligan, B.; Noyes, G.

    2010-07-26

    A new rapid method for the determination of {sup 237}Np and Pu isotopes in soil and sediment samples has been developed at the Savannah River Site Environmental Lab (Aiken, SC, USA) that can be used for large soil samples. The new soil method utilizes an acid leaching method, iron/titanium hydroxide precipitation, a lanthanum fluoride soil matrix removal step, and a rapid column separation process with TEVA Resin. The large soil matrix is removed easily and rapidly using this two simple precipitations with high chemical recoveries and effective removal of interferences. Vacuum box technology and rapid flow rates are used to reduce analytical time.

  1. A method for the rapid radiochemical analysis of uranium and thorium isotopes in impure carbonates.

    PubMed

    Elyahyaoui, A; Zarki, R; Chiadli, A

    2003-01-01

    A simple method combining solvent extraction and electrodeposition procedures is described for the determination of the isotopic composition and content of uranium and thorium in travertine samples. The actinide elements are extracted with diethyl ether from a calcium nitrate solution. The isolation of the elements and the alpha source preparation are performed in two steps after the sample digestion. The acid leaching of samples is performed using both partial and total dissolution methods. High recoveries of both uranium and thorium and good alpha-spectra are obtained with both partial and total dissolution methods.

  2. Non-Equilibrium Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Ciccotti, Giovanni; Kapral, Raymond; Sergi, Alessandro

    Statistical mechanics provides a well-established link between microscopic equilibrium states and thermodynamics. If one considers systems out of equilibrium, the link between microscopic dynamical properties and non-equilibrium macroscopic states is more difficult to establish [1,2]. For systems lying near equilibrium, linear response theory provides a route to derive linear macroscopic laws and the microscopic expressions for the transport properties that enter the constitutive relations. If the system is displaced far from equilibrium, no fully general theory exists to treat such systems. By restricting consideration to a class of non-equilibrium states which arise from perturbations (linear or non-linear) of an equilibrium state, methods can be developed to treat non-equilibrium states. Furthermore, non-equilibrium molecular dynamics (NEMD) simulation methods can be devised to provide estimates for the transport properties of these systems.

  3. A New Method of Separating 210Pb from Ra-DEF for a Radioactive Equilibrium Experiment.

    ERIC Educational Resources Information Center

    Wai, C. M.; Lo, J. M.

    1984-01-01

    Background information, procedures, and results are provided for an experiment in which lead-210 is separated from bismuth-210 and polonium-210 by means of solvent extraction of their diethyldithiocarbamate complexes. The method involves a simple extraction procedure which allows complete separation of lead-210 from commercially available…

  4. Finite-Temperature Non-equilibrium Quasicontinuum Method based on Langevin Dynamics

    SciTech Connect

    Marian, J; Venturini, G; Hansen, B; Knap, J; Ortiz, M; Campbell, G

    2009-05-08

    The concurrent bridging of molecular dynamics and continuum thermodynamics presents a number of challenges, mostly associated with energy transmission and changes in the constitutive description of a material across domain boundaries. In this paper, we propose a framework for simulating coarse dynamic systems in the canonical ensemble using the Quasicontinuum method (QC). The equations of motion are expressed in reduced QC coordinates and are strictly derived from dissipative Lagrangian mechanics. The derivation naturally leads to a classical Langevin implementation where the timescale is governed by vibrations emanating from the finest length scale occurring in the computational cell. The equations of motion are integrated explicitly via Newmark's ({beta} = 0; {gamma} = 1/2) method, leading to a robust numerical behavior and energy conservation. In its current form, the method only allows for wave propagations supported by the less compliant of the two meshes across a heterogeneous boundary, which requires the use of overdamped dynamics to avoid spurious heating due to reflected vibrations. We have applied the method to two independent crystallographic systems characterized by different interatomic potentials (Al and Ta) and have measured thermal expansion in order to quantify the vibrational entropy loss due to homogenization. We rationalize the results in terms of system size, mesh coarseness, and nodal cluster diameter within the framework of the quasiharmonic approximation. For Al, we find that the entropy loss introduced by mesh coarsening varies linearly with the element size, and that volumetric effects are not critical in driving the anharmonic behavior of the simulated systems. In Ta, the anomalies of the interatomic potential employed result in negative and zero thermal expansion at low and high temperatures, respectively.

  5. Preservation Methods Alter Carbon and Nitrogen Stable Isotope Values in Crickets (Orthoptera: Grylloidea)

    PubMed Central

    Jesus, Fabiene Maria; Pereira, Marcelo Ribeiro; Rosa, Cassiano Sousa; Moreira, Marcelo Zacharias; Sperber, Carlos Frankl

    2015-01-01

    Stable isotope analysis (SIA) is an important tool for investigation of animal dietary habits for determination of feeding niche. Ideally, fresh samples should be used for isotopic analysis, but logistics frequently demands preservation of organisms for analysis at a later time. The goal of this study was to establish the best methodology for preserving forest litter-dwelling crickets for later SIA analysis without altering results. We collected two cricket species, Phoremia sp. and Mellopsis doucasae, from which we prepared 70 samples per species, divided among seven treatments: (i) freshly processed (control); preserved in fuel ethanol for (ii) 15 and (iii) 60 days; preserved in commercial ethanol for (iv) 15 and (v) 60 days; fresh material frozen for (vi) 15 and (vii) 60 days. After oven drying, samples were analyzed for δ15N, δ13C values, N(%), C(%) and C/N atomic values using continuous flow isotope ratio mass spectrometry. All preservation methods tested, significantly impacted δ13C and δ15N and C/N atomic values. Chemical preservatives caused δ13C enrichment as great as 1.5‰, and δ15N enrichment as great as 0.9‰; the one exception was M. doucasae stored in ethanol for 15 days, which had δ15N depletion up to 1.8‰. Freezing depleted δ13C and δ15N by up to 0.7 and 2.2‰, respectively. C/N atomic values decreased when stored in ethanol, and increased when frozen for 60 days for both cricket species. Our results indicate that all preservation methods tested in this study altered at least one of the tested isotope values when compared to fresh material (controls). We conclude that only freshly processed material provides adequate SIA results for litter-dwelling crickets. PMID:26390400

  6. Preservation Methods Alter Carbon and Nitrogen Stable Isotope Values in Crickets (Orthoptera: Grylloidea).

    PubMed

    Jesus, Fabiene Maria; Pereira, Marcelo Ribeiro; Rosa, Cassiano Sousa; Moreira, Marcelo Zacharias; Sperber, Carlos Frankl

    2015-01-01

    Stable isotope analysis (SIA) is an important tool for investigation of animal dietary habits for determination of feeding niche. Ideally, fresh samples should be used for isotopic analysis, but logistics frequently demands preservation of organisms for analysis at a later time. The goal of this study was to establish the best methodology for preserving forest litter-dwelling crickets for later SIA analysis without altering results. We collected two cricket species, Phoremia sp. and Mellopsis doucasae, from which we prepared 70 samples per species, divided among seven treatments: (i) freshly processed (control); preserved in fuel ethanol for (ii) 15 and (iii) 60 days; preserved in commercial ethanol for (iv) 15 and (v) 60 days; fresh material frozen for (vi) 15 and (vii) 60 days. After oven drying, samples were analyzed for δ15N, δ13C values, N(%), C(%) and C/N atomic values using continuous flow isotope ratio mass spectrometry. All preservation methods tested, significantly impacted δ13C and δ15N and C/N atomic values. Chemical preservatives caused δ13C enrichment as great as 1.5‰, and δ15N enrichment as great as 0.9‰; the one exception was M. doucasae stored in ethanol for 15 days, which had δ15N depletion up to 1.8‰. Freezing depleted δ13C and δ15N by up to 0.7 and 2.2‰, respectively. C/N atomic values decreased when stored in ethanol, and increased when frozen for 60 days for both cricket species. Our results indicate that all preservation methods tested in this study altered at least one of the tested isotope values when compared to fresh material (controls). We conclude that only freshly processed material provides adequate SIA results for litter-dwelling crickets.

  7. Detection of Human Sewage in Urban Stormwater Using DNA Based Methods and Stable Isotope Analysis

    NASA Astrophysics Data System (ADS)

    McLellan, S. L.; Malet, N.; Sauer, E.; Mueller-Spitz, S.; Borchardt, M.

    2008-12-01

    related to the mixed organic matter sources in polluted stormwater runoff, and that this signal will distinct from untreated sanitary sewage. Stable isotope signatures of stormwater and untreated sewage were determined and compared with the rivers. Isotopic values of stormwater was delta 15N = 1.1 ± 2 %; delta 13C = -25.5 ± 3 % and sewage was delta 15N = -1.9 ± 0.2 %; delta 13C = -23.6 ± 0.3. Suspended particular organic matter (SPOM) of Milwaukee River showed depleted delta 13C (-28.6 ± 1.6 %) and enriched delta 15N (7.7 ± 1.9 %) values. SPOM of the KK River exhibited the most depleted delta 15N (0.2 ± 1.6 %) and enriched delta 13C (-24.8 ± 1.8 %) isotopic values. Menomonee River SPOM showed intermediate isotopic values. The delta 13C values of each river and the estuary enriched significantly throughout the summer storm periods. The isotope signals in the KK and Menomonee were indicative of stormwater runoff and sewage contamination. These results suggest that unrecognized sewage inputs are chronically present and may be delivered through urban stormwater systems. DNA based methods combined with isotope analysis may provide a useful tool for urban watershed assessments and to identify sewage inputs. Delineating the relative contribution of stormwater and sewage to overall degraded water quality might give the first indication of the impact of these sources on the Michigan Lake waters.

  8. Model for determining vapor equilibrium rates in the hanging drop method for protein crystal growth

    NASA Technical Reports Server (NTRS)

    Baird, James K.; Frieden, Richard W.; Meehan, E. J., Jr.; Twigg, Pamela J.; Howard, Sandra B.; Fowlis, William A.

    1987-01-01

    An engineering analysis of the rate of evaporation of solvent in the hanging drop method of protein crystal growth is presented. Results are applied to 18 drop and well arrangements commonly encountered in the laboratory. The chemical nature of the salt, drop size and shape, drop concentration, well size, well concentration, and temperature are taken into account. The rate of evaporation increases with temperature, drop size, and the salt concentration difference between the drop and the well. The evaporation in this model possesses no unique half-life. Once the salt in the drop achieves 80 percent of its final concentration, further evaporation suffers from the law of diminishing returns.

  9. Uranium and Calcium Isotope Ratio Measurements using the Modified Total Evaporation Method in TIMS

    NASA Astrophysics Data System (ADS)

    Richter, S.; Kuehn, H.; Berglund, M.; Hennessy, C.

    2010-12-01

    A new version of the "modified total evaporation" (MTE) method for isotopic analysis by multi-collector thermal ionization mass spectrometry (TIMS), with high analytical performance and designed in a more user-friendly and routinely applicable way, is described in detail. It is mainly being used for nuclear safeguards measurements of U and Pu and nuclear metrology, but can readily be applied to other scientific tasks in geochemistry, e.g. for Sr, Nd and Ca, as well. The development of the MTE method was organized in collaboration of several "key nuclear mass spectrometry laboratories", namely the New Brunswick Laboratory (NBL), the Institute for Transuranium Elements (ITU), the Safeguards Analytical Laboratory (now Safeguards Analytical Services, SGAS) of the International Atomic Energy Agency (IAEA) and the Institute for Reference Materials and Measurements (IRMM), with IRMM taking the leading role. The manufacturer of the TRITON TIMS instrument, Thermo Fisher Scientific, integrated this method into the software of the instrument. The development has now reached its goal to become a user-friendly and routinely useable method for uranium isotope ratio measurements with high precision and accuracy. Due to the use of the “total evaporation” (TE) method the measurement of the "major" uranium isotope ratio 235U/238U is routinely being performed with a precision of 0.01% to 0.02%. The use of a (certified) reference material measured under comparable conditions is emphasized to achieve an accuracy at a level of 0.02% - depending on the stated uncertainty of the certified value of the reference material. In contrast to the total evaporation method (TE), in the MTE method the total evaporation sequence is interrupted on a regular basis to allow for correction for background from peak tailing, internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, and ion source re-focusing. Therefore, the most significant improvement using the

  10. EPA Method EMSL-33: Isotopic Determination of Plutonium, Uranium, and Thorium in Water, Soil, Air, and Biological Tissue

    EPA Pesticide Factsheets

    SAM lists this method to provide for the analysis of isotopic plutonium, uranium and thorium, together or individually, in drinking water, aqueous/liquid, soil/sediment, surface wipe and/or air filter samples by alpha spectrometry.

  11. A numerical method for generating rapidly rotating bipolytropic structures in equilibrium

    NASA Astrophysics Data System (ADS)

    Kadam, Kundan; Motl, Patrick M.; Frank, Juhan; Clayton, Geoffrey C.; Marcello, Dominic C.

    2016-10-01

    We demonstrate that rapidly rotating bipolytropic (composite polytropic) stars and toroidal discs can be obtained using Hachisu's self-consistent field technique. The core and the envelope in such a structure can have different polytropic indices and also different average molecular weights. The models converge for high T/|W| cases, where T is the kinetic energy and W is the gravitational energy of the system. The agreement between our numerical solutions with known analytical as well as previously calculated numerical results is excellent. We show that the uniform rotation lowers the maximum core mass fraction or the Schönberg-Chandrasekhar limit for a bipolytropic sequence. We also discuss the applications of this method to magnetic braking in low-mass stars with convective envelopes.

  12. When stable-stage equilibrium is unlikely: integrating transient population dynamics improves asymptotic methods

    PubMed Central

    Tremblay, Raymond L.; Raventos, Josep; Ackerman, James D.

    2015-01-01

    Background and Aims Evaluation of population projection matrices (PPMs) that are focused on asymptotically based properties of populations is a commonly used approach to evaluate projected dynamics of managed populations. Recently, a set of tools for evaluating the properties of transient dynamics has been expanded to evaluate PPMs and to consider the dynamics of populations prior to attaining the stable-stage distribution, a state that may never be achieved in disturbed or otherwise ephemeral habitats or persistently small populations. This study re-evaluates data for a tropical orchid and examines the value of including such analyses in an integrative approach. Methods Six small populations of Lepanthes rubripetala were used as a model system and the R software package popdemo was used to produce estimates of the indices for the asymptotic growth rate (lambda), sensitivities, reactivity, first-time step attenuation, maximum amplification, maximum attenuation, maximal inertia and maximal attenuation. The response in lambda to perturbations of demographic parameters using transfer functions and multiple perturbations on growth, stasis and fecundity were also determined. The results were compared with previously published asymptotic indices. Key Results It was found that combining asymptotic and transient dynamics expands the understanding of possible population changes. Comparison of the predicted density from reactivity and first-time step attenuation with the observed change in population size in two orchid populations showed that the observed density was within the predicted range. However, transfer function analysis suggests that the traditional approach of measuring perturbation of growth rates and persistence (inertia) may be misleading and is likely to result in erroneous management decisions. Conclusions Based on the results, an integrative approach is recommended using traditional PPMs (asymptotic processes) with an evaluation of the diversity of dynamics

  13. A rapid method for the sampling of atmospheric water vapour for isotopic analysis.

    PubMed

    Peters, Leon I; Yakir, Dan

    2010-01-01

    Analysis of the stable isotopic composition of atmospheric moisture is widely applied in the environmental sciences. Traditional methods for obtaining isotopic compositional data from ambient moisture have required complicated sampling procedures, expensive and sophisticated distillation lines, hazardous consumables, and lengthy treatments prior to analysis. Newer laser-based techniques are expensive and usually not suitable for large-scale field campaigns, especially in cases where access to mains power is not feasible or high spatial coverage is required. Here we outline the construction and usage of a novel vapour-sampling system based on a battery-operated Stirling cycle cooler, which is simple to operate, does not require any consumables, or post-collection distillation, and is light-weight and highly portable. We demonstrate the ability of this system to reproduce delta(18)O isotopic compositions of ambient water vapour, with samples taken simultaneously by a traditional cryogenic collection technique. Samples were collected over 1 h directly into autosampler vials and were analysed by mass spectrometry after pyrolysis of 1 microL aliquots to CO. This yielded an average error of < +/-0.5 per thousand, approximately equal to the signal-to-noise ratio of traditional approaches. This new system provides a rapid and reliable alternative to conventional cryogenic techniques, particularly in cases requiring high sample throughput or where access to distillation lines, slurry maintenance or mains power is not feasible.

  14. Spectral-Lagrangian methods for collisional models of non-equilibrium statistical states

    SciTech Connect

    Gamba, Irene M. Tharkabhushanam, Sri Harsha

    2009-04-01

    We propose a new spectral Lagrangian based deterministic solver for the non-linear Boltzmann transport equation (BTE) in d-dimensions for variable hard sphere (VHS) collision kernels with conservative or non-conservative binary interactions. The method is based on symmetries of the Fourier transform of the collision integral, where the complexity in its computation is reduced to a separate integral over the unit sphere S{sup d-1}. The conservation of moments is enforced by Lagrangian constraints. The resulting scheme, implemented in free space, is very versatile and adjusts in a very simple manner to several cases that involve energy dissipation due to local micro-reversibility (inelastic interactions) or elastic models of slowing down process. Our simulations are benchmarked with available exact self-similar solutions, exact moment equations and analytical estimates for the homogeneous Boltzmann equation, both for elastic and inelastic VHS interactions. Benchmarking of the simulations involves the selection of a time self-similar rescaling of the numerical distribution function which is performed using the continuous spectrum of the equation for Maxwell molecules as studied first in Bobylev et al. [A.V. Bobylev, C. Cercignani, G. Toscani, Proof of an asymptotic property of self-similar solutions of the Boltzmann equation for granular materials, Journal of Statistical Physics 111 (2003) 403-417] and generalized to a wide range of related models in Bobylev et al. [A.V. Bobylev, C. Cercignani, I.M. Gamba, On the self-similar asymptotics for generalized non-linear kinetic Maxwell models, Communication in Mathematical Physics, in press. URL: ()]. The method also produces accurate results in the case of inelastic diffusive Boltzmann equations for hard spheres (inelastic collisions under thermal bath), where overpopulated non-Gaussian exponential tails have been conjectured in computations by stochastic methods [T.V. Noije, M. Ernst

  15. A new method for stable carbon isotope analysis of chlorofluorocarbons in contaminated groundwater

    NASA Astrophysics Data System (ADS)

    Horst, Axel; Lacrampe-Couloume, Georges; Sherwood Lollar, Barbara

    2015-04-01

    Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been widely used as refrigerants, propellants, solvents, foaming agents and are important intermediates in the production of anesthetics and other fluorinated compounds. Due to their ozone depletion potential, production was banned for most uses under the Montreal Protocol (1987) and its amendments and atmospheric mixing ratios have started to decrease. In addition to the atmosphere, CFCs and HCFCs have been detected in groundwater, and emissions from various sources such as landfill sites are still ongoing. Previous studies have shown that both abiotic and biotic transformation of CFCs may occur under certain conditions. To investigate degradation that may take place in soils and groundwaters, a purge and trap method (P&T) has been developed to measure the stable carbon isotopic composition of CFCs and HCFCs extracted from waters. A set of pure phase working standards (HCFC-22, CFC-11, CFC-113) has been prepared offline and characterized by sealed tube combustion dual inlet mass spectrometry. Comparison between isotopic standards and CFCs extracted by our method demonstrates the sample P&T extraction steps do not induce significant δ13C fractionation (lt;0.5 per mill). Standards characterized by continuous flow CSIA (compound specific isotope analysis) after extraction agree with offline characterized values. Evaporation experiments were carried out to investigate any isotope effects due to volatile loss that might occur either due to sampling methods or sample handling in the lab. Monitoring δ13C values during progressive evaporation showed small isotopic fractionation associated with evaporation. Enrichment factors, obtained from Rayleigh plots, showed inverse isotope fractionation i.e depletion in 13C in the remaining compound. Notably, this effect is in the opposite direction to the fractionation (13C enrichment) that is likely to be associated with abiotic or biotic transformation effects

  16. Growth of 18O isotopically enriched ZnO nanorods by two novel VPT methods

    NASA Astrophysics Data System (ADS)

    Gray, Ciarán; Trefflich, Lukas; Röder, Robert; Ronning, Carsten; Henry, Martin O.; McGlynn, Enda

    2017-02-01

    We have developed two novel vapour phase transport methods to grow ZnO nanorod arrays isotopically enriched with 18O. Firstly, a three-step process used to grow natural and Zn-enriched ZnO nanorods has been further modified, by replacing the atmospheric O2 with enriched 18O2, in order to grow 18O-enriched ZnO nanorods using this vapour-solid method on chemical bath deposited buffer layers. In addition, 18O-enriched ZnO nanorods were successfully grown using 18O isotopically enriched ZnO source powders in a vapour-liquid-solid growth method. Scanning electron microscopy studies confirmed the success of both growth methods in terms of nanorod morphology, although in the case of the vapour-liquid-solid samples, the nanorods' c-axes were not vertically aligned due to the use of a non-epitaxial substrate. Raman and PL studies indicated clearly that O-enrichment was successful in both cases, although the results indicate that the enrichment is at a lower level in our samples compared to previous reports with the same nominal enrichment levels. The results of our studies also allow us to comment on both levels of enrichment achieved and on novel effects of the high temperature growth environment on the nanorod growth, as well as suggesting possible mechanisms for such effects. Very narrow photoluminescence line widths, far narrower than those reported previously in the literature for isotopically enriched bulk ZnO, are seen in both the vapour-solid and vapour-liquid-solid nanorod samples demonstrating their excellent optical quality and their potential for use in detailed optical studies of defects and impurities using low temperature photoluminescence.

  17. Accelerated radiation damping for increased spin equilibrium (ARISE): a new method for controlling the recovery of longitudinal magnetization.

    PubMed

    Huang, Susie Y; Witzel, Thomas; Wald, Lawrence L

    2008-11-01

    Control of the longitudinal magnetization in fast gradient-echo (GRE) sequences is an important factor in enabling the high efficiency of balanced steady-state free precession (bSSFP) sequences. We introduce a new method for accelerating the return of the longitudinal magnetization to the +z-axis that is independent of externally applied RF pulses and shows improved off-resonance performance. The accelerated radiation damping for increased spin equilibrium (ARISE) method uses an external feedback circuit to strengthen the radiation damping (RD) field. The enhanced RD field rotates the magnetization back to the +z-axis at a rate faster than T(1) relaxation. The method is characterized in GRE phantom imaging at 3T as a function of feedback gain, phase, and duration, and compared with results from numerical simulations of the Bloch equations incorporating RD. A short period of feedback (10 ms) during a refocused interval of a crushed GRE sequence allowed greater than 99% recovery of the longitudinal magnetization when very little T(2) relaxation had time to occur. An appropriate application might be to improve navigated sequences. Unlike conventional flip-back schemes, the ARISE "flip-back" is generated by the spins themselves, thereby offering a potentially useful building block for enhancing GRE sequences.

  18. Isotope separation

    DOEpatents

    Bartlett, Rodney J.; Morrey, John R.

    1978-01-01

    A method and apparatus is described for separating gas molecules containing one isotope of an element from gas molecules containing other isotopes of the same element in which all of the molecules of the gas are at the same electronic state in their ground state. Gas molecules in a gas stream containing one of the isotopes are selectively excited to a different electronic state while leaving the other gas molecules in their original ground state. Gas molecules containing one of the isotopes are then deflected from the other gas molecules in the stream and thus physically separated.

  19. Installations for separation of hydrogen isotopes by the method of chemical isotopic exchange in the `water-hydrogen` system

    SciTech Connect

    Andreev, B.M.; Sakharovsky, Y.A.; Rozenkevich, M.B.; Magomedbekov, E.P.; Park, Y.S.; Uborskiy, V.V.; Trenin, V.D.; Alekseev, I.A.; Fedorchenko, O.A.; Karpov, S.P.; Konoplev, K.A.

    1995-10-01

    The paper presents the results of more than a year of running a pilot setup for separation of hydrogen isotopes using catalytic isotopic exchange between hydrogen and liquid water. The setup is 5 m high, has the inner diameter of 28 mm, and is equipped with upper and lower reflux devices. The experimental values of HETP vary from 15 cm at T=333 K to 38 cm at T=293 K. The setup is capable of upgrading diluted heavy water with 85-90% deuterium content up to [D{sub 2}O] > 99.95 at.%, yielding daily 4 kg of the product. We also report on the progress in constructing a similar setup for eliminating tritium and an industrial setup, for which the one reported is a prototype. 10 refs., 1 fig., 3 tabs.

  20. Rapid fusion method for the determination of refractory thorium and uranium isotopes in soil samples

    SciTech Connect

    Maxwell, Sherrod L.; Hutchison, Jay B.; McAlister, Daniel R.

    2015-02-14

    Recently, approximately 80% of participating laboratories failed to accurately determine uranium isotopes in soil samples in the U.S Department of Energy Mixed Analyte Performance Evaluation Program (MAPEP) Session 30, due to incomplete dissolution of refractory particles in the samples. Failing laboratories employed acid dissolution methods, including hydrofluoric acid, to recover uranium from the soil matrix. The failures illustrate the importance of rugged soil dissolution methods for the accurate measurement of analytes in the sample matrix. A new rapid fusion method has been developed by the Savannah River National Laboratory (SRNL) to prepare 1-2 g soil sample aliquots very quickly, with total dissolution of refractory particles. Soil samples are fused with sodium hydroxide at 600 ºC in zirconium crucibles to enable complete dissolution of the sample. Uranium and thorium are separated on stacked TEVA and TRU extraction chromatographic resin cartridges, prior to isotopic measurements by alpha spectrometry on cerium fluoride microprecipitation sources. Plutonium can also be separated and measured using this method. Batches of 12 samples can be prepared for measurement in <5 hours.

  1. Rapid fusion method for the determination of refractory thorium and uranium isotopes in soil samples

    DOE PAGES

    Maxwell, Sherrod L.; Hutchison, Jay B.; McAlister, Daniel R.

    2015-02-14

    Recently, approximately 80% of participating laboratories failed to accurately determine uranium isotopes in soil samples in the U.S Department of Energy Mixed Analyte Performance Evaluation Program (MAPEP) Session 30, due to incomplete dissolution of refractory particles in the samples. Failing laboratories employed acid dissolution methods, including hydrofluoric acid, to recover uranium from the soil matrix. The failures illustrate the importance of rugged soil dissolution methods for the accurate measurement of analytes in the sample matrix. A new rapid fusion method has been developed by the Savannah River National Laboratory (SRNL) to prepare 1-2 g soil sample aliquots very quickly, withmore » total dissolution of refractory particles. Soil samples are fused with sodium hydroxide at 600 ºC in zirconium crucibles to enable complete dissolution of the sample. Uranium and thorium are separated on stacked TEVA and TRU extraction chromatographic resin cartridges, prior to isotopic measurements by alpha spectrometry on cerium fluoride microprecipitation sources. Plutonium can also be separated and measured using this method. Batches of 12 samples can be prepared for measurement in <5 hours.« less

  2. Application of the generator coordinate method to neutron-rich Se and Ge isotopes

    NASA Astrophysics Data System (ADS)

    Higashiyama, Koji; Yoshinaga, Naotaka

    2014-03-01

    The quantum-number projected generator coordinate method (GCM) is applied to the neutron-rich Se and Ge isotopes, where the monopole and quadrupole pairing plus quadrupole-quadrupole interaction is employed as an effective interaction. The energy spectra obtained by the GCM are compared to both the shell model results and the experimental data. The GCM reproduces well the energy levels of high-spin states as well as the low-lying states. The structure of the low-lying collective states is analyzed through the GCM wave functions.

  3. Method and apparatus for storing hydrogen isotopes. [stored as uranium hydride in a block of copper

    DOEpatents

    McMullen, J.W.; Wheeler, M.G.; Cullingford, H.S.; Sherman, R.H.

    1982-08-10

    An improved method and apparatus for storing isotopes of hydrogen (especially tritium) are provided. The hydrogen gas is stored as hydrides of material (for example uranium) within boreholes in a block of copper. The mass of the block is critically important to the operation, as is the selection of copper, because no cooling pipes are used. Because no cooling pipes are used, there can be no failure due to cooling pipes. And because copper is used instead of stainless steel, a significantly higher temperature can be reached before the eutectic formation of uranium with copper occurs, (the eutectic of uranium with the iron in stainless steel forms at a significantly lower temperature).

  4. Independent Verification of Research Reactor Operation (Analysis of the Georgian IRT-M Reactor by the Isotope Ratio Method)

    SciTech Connect

    Cliff, John B.; Frank, Douglas P.; Gerlach, David C.; Gesh, Christopher J.; Little, Winston W.; Reid, Bruce D.; Tsiklauri, Georgi V.; Abramidze, Sh; Rostomashvili, Z.; Kiknadze, G.; Dzhavakhishvily, O.; Nabakhtiani, G.

    2010-08-11

    The U.S. Department of Energy’s Office of Nonproliferation and International Security (NA-24) develops technologies to aid in implementing international nuclear safeguards. The Isotope Ratio Method (IRM) was successfully developed in 2005 – 2007 by Pacific Northwest National Laboratory (PNNL) and the Republic of Georgia’s Andronikashvili Institute of Physics as a generic technology to verify the declared operation of water-moderated research reactors, independent of spent fuel inventory. IRM estimates the energy produced over the operating lifetime of a fission reactor by measuring the ratios of the isotopes of trace impurity elements in non-fuel reactor components.The Isotope Ratio Method is a technique for estimating the energy produced over the operating lifetime of a fission reactor by measuring the ratios of the isotopes of impurity elements in non-fuel reactor components.

  5. Clumped isotope thermometry and catagenesis

    NASA Astrophysics Data System (ADS)

    Eiler, J. M.; Clog, M. D.; Dallas, B.; Douglas, P. M.; Piasecki, A.; Sessions, A. L.; Stolper, D. A.

    2014-12-01

    Clumped- and site-specific isotopic compositions of organic compounds can constrain their formation temperatures, sources, and chemical reaction histories. The large number of isotopologues of organic molecules may allow for the isotopic composition of a single compound to illuminate many processes. For example, it is possible that clumping or site specific effects in different parts of the same molecule will differ in blocking temperature, such that a molecule's full isotopic structure could simultaneously constrain conditions of biosynthesis, catagenic 'cracking', and storage in the crust. Recent innovations in high-resolution mass spectrometry and methods of IR and NMR spectroscopy make it possible to explore these questions. Methane is the first organic molecule to have its clumped isotope geochemistry analyzed in a variety of natural environments and controlled experiments. Methane generated through catagenic cracking of kerogen and other organic matter forms in equilibrium with respect to isotopic clumping, and preserves that state through later storage or migration, up to temperatures of ~250 ˚C. This kinetic behavior permits a variety of useful geological applications. But it is unexpected because the bulk stable isotope composition of thermogenic methane is thought to reflect kinetic isotope effects on irreversible reactions. Our observations imply a new interpretation of the chemical physics of catagenic methane formation. Additional instrument and methods developments are currently extending the measurement of isotopic clumping and position specific effects to larger alkanes, other hydrocarbon compounds, and amino acids. These measurements will ultimately expand our capacity to understand the formational conditions and fates of organic molecules in high- and low-temperature environments through geological time.

  6. EPA Method: Rapid Radiochemical Method for Americium-241, Radium-226, Plutonium-238/-239, Radiostronium, and Isotopic Uranium in Water for Environmental Restoration Following Homeland Security Events

    EPA Pesticide Factsheets

    SAM lists this method for the qualitative determination of Americium-241, Radium-226, Plutonium-238, Plutonium-239 and isotopic uranium in drinking water samples using alpha spectrometry and radiostrontium using beta counting.

  7. Adaptation of the doubly labeled water method for subjects consuming isotopically enriched water.

    PubMed

    Gretebeck, R J; Schoeller, D A; Socki, R A; Davis-Street, J; Gibson, E K; Schulz, L O; Lane, H W

    1997-02-01

    The use of doubly labeled water (DLW) to measure energy expenditure is subject to error if the background abundance of the oxygen and hydrogen isotope tracers changes during the test period. This study evaluated the accuracy and precision of different methods by which such background isotope changes can be corrected, including a modified method that allows prediction of the baseline that would be achieved if subjects were to consume water from a given source indefinitely. Subjects in this study were eight women (4 test subjects and 4 control subjects) who consumed for 28 days water enriched to resemble drinking water aboard the United States space shuttle. Test subjects and control subjects were given a DLW dose on days 1 and 15, respectively. The change to an enriched water source produced a bias in expenditure calculations that exceeded 2.9 MJ/day (35%), relative to calculations from intake-balance. The proposed correction based on the predicted final abundance of 18O and deuterium after equilibration to the new water source eliminated this bias, as did the traditional use of a control group. This new modified correction method is advantageous under field conditions when subject numbers are limited.

  8. Isotope dilution gas chromatography/mass spectrometry method for determination of pyrethroids in apple juice.

    PubMed

    Wong, Siu-kay; Yu, Kwok-chiu; Lam, Chi-ho

    2010-03-01

    This paper presents the development of a highly precise and accurate analytical method for the determination of three matrix-bound pyrethroids, namely, cypermethrin, permethrin, and bifenthrin, using an isotope dilution gas chromatography/mass spectrometry technique. Identification of the analytes was confirmed under selective ion monitoring mode by the presence of two dominant ion fragments within specific time windows and matching of relative ion intensities of the ions concerned in samples and calibration standards. Quantitation was based on the measurement of concentration ratios of the natural and isotope analogues in the sample and calibration blends. Intraday and interday repeatabilities of replicate analyses of the pyethroids in an apple juice sample were below 0.5%. The expanded relative uncertainty ranged from 3 to 6%, which was significantly lower than the range obtained using internal or external calibration methods. As a labeled analogue is not available for bifenthrin, bifenthrin was determined using labeled cis-permethrin as the internal standard. The results were counterchecked by a gas chromatography-electron capture detection technique using PCB 209 as the internal standard. The method developed was applied to a recent pilot study organized by CCQM and the results were consistent with those of other participants.

  9. Rapid Method for the Determination of the Stable Oxygen Isotope Ratio of Water in Alcoholic Beverages.

    PubMed

    Wang, Daobing; Zhong, Qiding; Li, Guohui; Huang, Zhanbin

    2015-10-28

    This paper demonstrates the first successful application of an online pyrolysis technique for the direct determination of oxygen isotope ratios (δ(18)O) of water in alcoholic beverages. Similar water concentrations in each sample were achieved by adjustment with absolute ethyl alcohol, and then a fixed GC split ratio can be used. All of the organic ingredients were successfully separated from the analyte on a CP-PoraBond Q column and subsequently vented out, whereas water molecules were transferred into the reaction furnace and converted to CO. With the system presented, 15-30 μL of raw sample was diluted and can be analyzed repeatedly; the analytical precision was better than 0.4‰ (n = 5) in all cases, and more than 50 injections can be made per day. No apparent memory effect was observed even if water samples were injected using the same syringe; a strong correlation (R(2) = 0.9998) was found between the water δ(18)O of measured sample and that of working standards. There was no significant difference (p > 0.05) between the mean δ(18)O value and that obtained by the traditional method (CO2-water equilibration/isotope ratio mass spectrometry) and the newly developed method in this study. The advantages of this new method are its rapidity and straightforwardness, and less test portion is required.

  10. A robust method for ammonium nitrogen isotopic analysis in freshwater and seawater at natural abundance levels

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Altabet, M. A.; Wu, T.; Hadas, O.

    2006-12-01

    Natural ammonium N isotopic abundance has been increasingly used in studies of marine and freshwater biogeochemistry. However, current methods are time-consuming, subject to interference from DON, and not reliable at low concentrations. Our new method for determining the δ15N of ammonium overcomes these difficulties by employing the oxidation of ammonium to nitrite followed by conversion of nitrite to nitrous oxide. In the first step, ammonium is quantitatively oxidized by hypobromite at pH~12. After the addition of sodium arsenite to consume excess hypobromite, yield is verified by colorimetric NO2-measurement using sulfanilamide and naphthyl ethylenediamine (NED). Nitrite is further reduced to N2O by a 1:1 sodium azide and acetic acid buffer solution using previously established procedures. Buffer concentration can be varied according to sample matrix to ensure that a reaction pH between 2 and 4 is reached. The product nitrous oxide is then isotopically analyzed using a continuous flow purge and cryogenic trap system coupled to an isotope ratio mass spectrometer. Reliable δ15N values (±0.31‰) are obtained over a concentration range of 0.5 μM to 20 μM using 20 ml volumes of either fresh or seawater samples. Reagent blanks are very low, about 0.05 μM. There is no interference from any of the nitrogen containing compounds tested except short chain aliphatic amino acid (i.e. glycine) which typically are not present at sufficiently high environmental concentrations to pose a problem.

  11. Use of Isotope Dilution Method To Predict Bioavailability of Organic Pollutants in Historically Contaminated Sediments

    PubMed Central

    2015-01-01

    Many cases of severe environmental contamination arise from historical episodes, where recalcitrant contaminants have resided in the environment for a prolonged time, leading to potentially decreased bioavailability. Use of bioavailable concentrations over bulk chemical levels improves risk assessment and may play a critical role in determining the need for remediation or assessing the effectiveness of risk mitigation operations. In this study, we applied the principle of isotope dilution to quantify bioaccessibility of legacy contaminants DDT and PCBs in marine sediments from a Superfund site. After addition of 13C or deuterated analogues to a sediment sample, the isotope dilution reached a steady state within 24 h of mixing. At the steady state, the accessible fraction (E) derived by the isotope dilution method (IDM) ranged from 0.28 to 0.89 and was substantially smaller than 1 for most compounds, indicating reduced availability of the extensively aged residues. A strong linear relationship (R2 = 0.86) was found between E and the sum of rapid (Fr) and slow (Fs) desorption fractions determined by sequential Tenax desorption. The IDM-derived accessible concentration (Ce) was further shown to correlate closely with tissue residue in the marine benthic polychaete Neanthes arenaceodentata exposed in the same sediments. As shown in this study, the IDM approach involves only a few simple steps and may be readily adopted in laboratories equipped with mass spectrometers. This novel method is expected to be especially useful for historically contaminated sediments or soils, for which contaminant bioavailability may have changed significantly due to aging and other sequestration processes. PMID:24946234

  12. Effect of cohesion and fill amplification on seismic stability of municipal solid waste landfills using limit equilibrium method.

    PubMed

    Savoikar, Purnanand; Choudhury, Deepankar

    2010-12-01

    Municipal solid waste (MSW) landfills in seismic zones are subjected to the seismic forces both in the horizontal and vertical directions. The stability of landfills against these seismic forces was evaluated by computing the factor of safety of landfills with different modes of failure among which failures of landfills due to translation are very common. Conventionally, the seismic stability of landfill is evaluated by using pseudo-static limit equilibrium method. In the present study, seismic stability of landfills is evaluated by both the conventional pseudo-static and modern pseudo-dynamic method. The pseudo-dynamic method is superior as it takes into account the effect of duration and frequency of earthquake motion and corresponding body waves in addition to the variation of earthquake accelerations along depth and time. In the present study, the effects of cohesion and fill amplification on seismic stability of landfill are also taken into account. It was noticed that, neglecting cohesion of fill material as well as liner material, results in a lower factor of safety and, hence, a very conservative/uneconomic design. Also, fill amplification is found to reduce the factor of safety values computed only by using the pseudo-dynamic method, showing its advantage. Generalized expressions are developed for factor of safety and yield acceleration against translational failure, which can be used for evaluating the seismic stability of MSW landfills. Comparisons of results under static condition with existing, similar methodology show a very good agreement. However, the present study seems to provide unique results for the seismic case.

  13. Comparison of methods for separating small quantities of hydrogen isotopes from an inert gas

    SciTech Connect

    Willms, R.S.; Tuggle, D.; Birdsell, S.; Parkinson, J.; Price, B.; Lohmeir, D.

    1998-03-01

    It is frequent within tritium processing systems that a small amount of hydrogen isotopes (Q{sub 2}) must be separated from an inert gas such as He, Ar and N{sub 2}. Thus, a study of presently available technologies for effecting such a separation was performed. A base case and seven technology alternatives were identified and a simple design of each was prepared. These technologies included oxidation-adsorption-metal bed reduction, oxidation-adsorption-palladium membrane reactor, cryogenic adsorption, cryogenic trapping, cryogenic distillation, hollow fiber membranes, gettering and permeators. It was found that all but the last two methods were unattractive for recovering Q{sub 2} from N{sub 2}. Reasons for technology rejection included (1) the method unnecessarily turns the hydrogen isotopes into water, resulting in a cumbersome and more hazardous operation, (2) the method would not work without further processing, and (3) while the method would work, it would only do so in an impractical way. On the other hand, getters and permeators were found to be attractive methods for this application. Both of these methods would perform the separation in a straightforward, essentially zero-waste, single step operation. The only drawback for permeators was that limited low-partial Q{sub 2} pressure data is available. The drawbacks for getters are their susceptibility to irreversible and exothermic reaction with common species such as oxygen and water, and the lack of long-term operation of such beds. More research is envisioned for both of these methods to mature these attractive technologies.

  14. Hydrogen isotope exchange in tungsten: Discussion as removal method for tritium

    NASA Astrophysics Data System (ADS)

    Roth, J.; Schwarz-Selinger, T.; Alimov, V. Kh.; Markina, E.

    2013-01-01

    Hydrogen isotope exchange in re-crystallized polycrystalline tungsten was investigated at 320 and 450 K. In a first step the tungsten samples were loaded with deuterium to a fluence of 1024 D/m2 from a low-temperature plasma at 200 eV/D particle energy. In a second step, H was implanted at the same particle energy and similar target temperature with a mass-separated ion beam at different ion fluences ranging from 2 × 1020 to 7.5 × 1023 H/m2. The analytic methods used were nuclear reaction analysis with D(3He,p)α reaction and elastic recoil detection analysis with 4He. In order to determine the D concentration at depths of up to 7.4 μm the 3He energy was varied from 0.5 to 4.5 MeV. It was found that already at an H fluence of 2 × 1020 H/m2, i.e. at 1/5000 of the initial D fluence, about 30% of the retained D was released. Depth profiling of D without and with subsequent H implantation shows strong replacement close to the surface at 320 K, but extending to all analyzable depths at 450 K especially at high fluences, leading to higher release efficiency. The reverse sequence of hydrogen isotopes allowed the analysis of the replacing isotope and showed that the release of D is balanced by the uptake of H. It also shows that hydrogen does not diffuse through a region of filled traps into a region were unfilled traps can be encounter but transport is rather a dynamic process of trapping and de-trapping even at 320 K. Initial D retention in H loaded W is an order of magnitude higher than in pristine W, indicating that every H-containing trap is a potential trap for D. In consequence, hydrogen isotope exchange is not a viable method to significantly enhance the operation time before the tritium inventory limit is reached but should be considered an option to reduce the tritium inventory in ITER before major interventions at the end of an operation period.

  15. Nonlinear Boltzmann equation for the homogeneous isotropic case: Some improvements to deterministic methods and applications to relaxation towards local equilibrium

    NASA Astrophysics Data System (ADS)

    Asinari, P.

    2011-03-01

    Boltzmann equation is one the most powerful paradigms for explaining transport phenomena in fluids. Since early fifties, it received a lot of attention due to aerodynamic requirements for high altitude vehicles, vacuum technology requirements and nowadays, micro-electro-mechanical systems (MEMs). Because of the intrinsic mathematical complexity of the problem, Boltzmann himself started his work by considering first the case when the distribution function does not depend on space (homogeneous case), but only on time and the magnitude of the molecular velocity (isotropic collisional integral). The interest with regards to the homogeneous isotropic Boltzmann equation goes beyond simple dilute gases. In the so-called econophysics, a Boltzmann type model is sometimes introduced for studying the distribution of wealth in a simple market. Another recent application of the homogeneous isotropic Boltzmann equation is given by opinion formation modeling in quantitative sociology, also called socio-dynamics or sociophysics. The present work [1] aims to improve the deterministic method for solving homogenous isotropic Boltzmann equation proposed by Aristov [2] by two ideas: (a) the homogeneous isotropic problem is reformulated first in terms of particle kinetic energy (this allows one to ensure exact particle number and energy conservation during microscopic collisions) and (b) a DVM-like correction (where DVM stands for Discrete Velocity Model) is adopted for improving the relaxation rates (this allows one to satisfy exactly the conservation laws at macroscopic level, which is particularly important for describing the late dynamics in the relaxation towards the equilibrium).

  16. Integrated use of soil physical and water isotope methods for ecohydrological characterization of desertified areas

    NASA Astrophysics Data System (ADS)

    Külls, Christoph; Nunes, Alice; Köbel-Batista, Melanie; Branquinho, Cristina; Bianconi, Nadja; Costantini, Eduardo

    2014-05-01

    marked decrease in water permeability at 0.04, 0.20, or 0.40 m depth. Soil isotope profiles indicated that percolation beneath the root zone and groundwater recharge ranges from 21.7 mm/y to 29.7 mm/y. The recharge rate was positively related to mean annual rainfall and soil organic matter, and interestingly, increased with aridity and desertification. The difference between mean annual rainfall and percolation was positively related to plant cover and in inverse proportion to the aridity index. Our results highlight the importance of combining different methods of site characterization by soil physics, soil water isotopes and soil water chemistry (chloride) with vegetation data, providing a more specific analysis of ecohydrological conditions and their relation to ecosystem functioning and recovery potential. The field protocol applied can provide relevant information for guiding restoration strategies. Costantini, E. A. C., Urbano, F., Aramini, G., Barbetti, R., Bellino, F., Bocci, M., & Tascone, F. (2009). Rationale and methods for compiling an atlas of desertification in Italy. Land Degradation & Development, 20(3), 261-276. Garvelmann, J., Külls, C., & Weiler, M. (2012). A porewater-based stable isotope approach for the investigation of subsurface hydrological processes. Hydrology and Earth System Sciences, 16(2), 631-640.

  17. An isotope-dilution standard GC/MS/MS method for steroid hormones in water

    USGS Publications Warehouse

    Foreman, William T.; Gray, James L.; ReVello, Rhiannon C.; Lindley, Chris E.; Losche, Scott A.

    2013-01-01

    An isotope-dilution quantification method was developed for 20 natural and synthetic steroid hormones and additional compounds in filtered and unfiltered water. Deuterium- or carbon-13-labeled isotope-dilution standards (IDSs) are added to the water sample, which is passed through an octadecylsilyl solid-phase extraction (SPE) disk. Following extract cleanup using Florisil SPE, method compounds are converted to trimethylsilyl derivatives and analyzed by gas chromatography with tandem mass spectrometry. Validation matrices included reagent water, wastewater-affected surface water, and primary (no biological treatment) and secondary wastewater effluent. Overall method recovery for all analytes in these matrices averaged 100%; with overall relative standard deviation of 28%. Mean recoveries of the 20 individual analytes for spiked reagent-water samples prepared along with field samples analyzed in 2009–2010 ranged from 84–104%, with relative standard deviations of 6–36%. Detection levels estimated using ASTM International’s D6091–07 procedure range from 0.4 to 4 ng/L for 17 analytes. Higher censoring levels of 100 ng/L for bisphenol A and 200 ng/L for cholesterol and 3-beta-coprostanol are used to prevent bias and false positives associated with the presence of these analytes in blanks. Absolute method recoveries of the IDSs provide sample-specific performance information and guide data reporting. Careful selection of labeled compounds for use as IDSs is important because both inexact IDS-analyte matches and deuterium label loss affect an IDS’s ability to emulate analyte performance. Six IDS compounds initially tested and applied in this method exhibited deuterium loss and are not used in the final method.

  18. A validated method for the quantitation of 1,1-difluoroethane using a gas in equilibrium method of calibration.

    PubMed

    Avella, Joseph; Lehrer, Michael; Zito, S William

    2008-10-01

    1,1-Difluoroethane (DFE), also known as Freon 152A, is a member of a class of compounds known as halogenated hydrocarbons. A number of these compounds have gained notoriety because of their ability to induce rapid onset of intoxication after inhalation exposure. Abuse of DFE has necessitated development of methods for its detection and quantitation in postmortem and human performance specimens. Furthermore, methodologies applicable to research studies are required as there have been limited toxicokinetic and toxicodynamic reports published on DFE. This paper describes a method for the quantitation of DFE using a gas chromatography-flame-ionization headspace technique that employs solventless standards for calibration. Two calibration curves using 0.5 mL whole blood calibrators which ranged from A: 0.225-1.350 to B: 9.0-180.0 mg/L were developed. These were evaluated for linearity (0.9992 and 0.9995), limit of detection of 0.018 mg/L, limit of quantitation of 0.099 mg/L (recovery 111.9%, CV 9.92%), and upper limit of linearity of 27,000.0 mg/L. Combined curve recovery results of a 98.0 mg/L DFE control that was prepared using an alternate technique was 102.2% with CV of 3.09%. No matrix interference was observed in DFE enriched blood, urine or brain specimens nor did analysis of variance detect any significant differences (alpha = 0.01) in the area under the curve of blood, urine or brain specimens at three identical DFE concentrations. The method is suitable for use in forensic laboratories because validation was performed on instrumentation routinely used in forensic labs and due to the ease with which the calibration range can be adjusted. Perhaps more importantly it is also useful for research oriented studies because the removal of solvent from standard preparation eliminates the possibility for solvent induced changes to the gas/liquid partitioning of DFE or chromatographic interference due to the presence of solvent in specimens.

  19. A Robust and Fully-Automated Chromatographic Method for the Quantitative Purification of Ca and Sr for Isotopic Analysis

    NASA Astrophysics Data System (ADS)

    Smith, H. B.; Kim, H.; Romaniello, S. J.; Field, P.; Anbar, A. D.

    2014-12-01

    High throughput methods for sample purification are required to effectively exploit new opportunities in the study of non-traditional stable isotopes. Many geochemical isotopic studies would benefit from larger data sets, but these are often impractical with manual drip chromatography techniques, which can be time-consuming and demand the attention of skilled laboratory staff. Here we present a new, fully-automated single-column method suitable for the purification of both Ca and Sr for stable and radiogenic isotopic analysis. The method can accommodate a wide variety of sample types, including carbonates, bones, and teeth; silicate rocks and sediments; fresh and marine waters; and biological samples such as blood and urine. Protocols for these isotopic analyses are being developed for use on the new prepFAST-MCTM system from Elemental Scientific (ESI). The system is highly adaptable and processes up to 24-60 samples per day by reusing a single chromatographic column. Efficient column cleaning between samples and an all Teflon flow path ensures that sample carryover is maintained at the level of background laboratory blanks typical for manual drip chromatography. This method is part of a family of new fully-automated chromatographic methods being developed to address many different isotopic systems including B, Ca, Fe, Cu, Zn, Sr, Cd, Pb, and U. These methods are designed to be rugged and transferrable, and to allow the preparation of large, diverse sample sets via a highly repeatable process with minimal effort.

  20. Informational Equilibrium.

    DTIC Science & Technology

    1982-09-01

    that for variouis standard types of equilibria* they hold. In particular, if one uses the teaporary equilibrium framework one can use the standard ...T, the integral converges toward f’ia(da) f fU(b~dc)6(a,b,c)T( asdm ) A B C which is fR (da) f d(lib,c) U0 T (cab) A BxC Me converse Is obvious

  1. Methods for the separation of rhenium, osmium and molybdenum applicable to isotope geochemistry

    USGS Publications Warehouse

    Morgan, J.W.; Golightly, D.W.; Dorrzapf, A.F.

    1991-01-01

    Effective methods are described for the chemical separation of rhenium, osmium and molybdenum. The methods are based on distillation and anion-exchange chromatography, and have been the basis for rhenium-osmium isotope studies of ore deposits and meteorites. Successful anion-exchange separation of osmium requires both recognition and careful control of the osmium species in solution; thus, distillation of osmium tetroxide from a mixture of sulfuric acid and hydrogen peroxide is preferred to anion-exchange. Distribution coefficients measured for perrhenate in sulfuric acid media are sufficiently high (Kd > 500) for rhenium to be directly loaded onto an ion-exchange column from a distillation residue and subsequently eluted with nitric acid. Polymerization of molybdenum species during elution is prevented by use of a solution that is 1M in hydrochloric acid and 1M in sodium chloride. ?? 1991.

  2. Assay of tyrosol and hydroxytyrosol in olive oil by tandem mass spectrometry and isotope dilution method.

    PubMed

    Mazzotti, Fabio; Benabdelkamel, Hicham; Di Donna, Leonardo; Maiuolo, Loredana; Napoli, Anna; Sindona, Giovanni

    2012-12-01

    Hydroxytyrosol and tyrosol, the strong antioxidant present in large amount in virgin olive oil have been assayed by LC-MS/MS under MRM condition and isotope dilution method, using d(2)-labelled internal standards obtained by simple synthetic procedures. The assay has been performed under MRM condition monitoring two transitions for each analyte to improve the specificity. This paper deals with a modern approach for assaying the content of this polyphenols in virgin olive oil down to a limit of a few hundreds of parts per billion. Tyrosol and hydroxytyrosol ranged from 10 to 47ppm and from 5 to 25ppm in commercial olive oil, respectively. The accuracy (98-107%) and analytical parameters values confirm the reliability of the proposed approach. The method can be extended to any natural matrices, including mill wastes, after a simple step of sample preparation.

  3. Method and apparatus for isotope-selectively exciting gaseous or vaporous uranium hexafluoride molecules

    SciTech Connect

    Fill, E.E.; Jetter, H.L.; Volk, R.

    1981-06-09

    A method of isotope-selectively exciting gaseous or vaporous uranium hexafluoride molecules by subjecting them to the action of a monochromatic iodine laser beam, the frequency of which can be adjusted and tuned to an absorption band of the molecules to be excited, the laser beam being scattered by liquid and/or solid nitrogen to obtain a triple raman-scattering. In a preferred embodiment, the laser has an emission frequency of 7600 to 7610 cm-1 and the tuning is effected by means of a magnetic field. An apparatus suitable for carrying out such a method comprises a high-performance iodine laser and an optical resonator into which the emission beam or pulses of the laser are focused, one or more dewar vessels filled with liquid or solid nitrogen being located within the optical resonator. In a preferred embodiment, the laser beam tube is located between the poles of an electromagnet.

  4. METHOD FOR REMOVAL OF LIGHT ISOTOPE PRODUCT FROM LIQUID THERMAL DIFFUSION UNITS

    DOEpatents

    Hoffman, J.D.; Ballou, J.K.

    1957-11-19

    A method and apparatus are described for removing the lighter isotope of a gaseous-liquid product from a number of diffusion columns of a liquid thermal diffusion system in two stages by the use of freeze valves. The subject liquid flows from the diffusion columns into a heated sloping capsule where the liquid is vaporized by the action of steam in a heated jacket surrounding the capsule. When the capsule is filled the gas flows into a collector. Flow between the various stages is controlled by freeze valves which are opened and closed by the passage of gas and cool water respectively through coils surrounding portions of the pipes through which the process liquid is passed. The use of the dual stage remover-collector and the freeze valves is an improvement on the thermal diffusion separation process whereby the fraction containing the lighter isotope many be removed from the tops of the diffusion columns without intercolumn flow, or prior stage flow while the contents of the capsule is removed to the final receiver.

  5. Isotope separation by photochromatography

    DOEpatents

    Suslick, K.S.

    1975-10-03

    A photochromatographic method for isotope separation is described. An isotopically mixed molecular species is adsorbed on an adsorptive surface, and the adsorbed molecules are irradiated with radiation of a predetermined wavelength which will selectively excite desired isotopic species. Sufficient energy is transferred to the excited molecules to desorb them from the surface and thus separate them from the undesired isotopic species. The method is particularly applicable to the separation of hydrogen isotopes. (BLM)

  6. Isotope separation by photochromatography

    DOEpatents

    Suslick, Kenneth S.

    1977-01-01

    An isotope separation method which comprises physically adsorbing an isotopically mixed molecular species on an adsorptive surface and irradiating the adsorbed molecules with radiation of a predetermined wavelength which will selectively excite a desired isotopic species. Sufficient energy is transferred to the excited molecules to desorb them from the surface and thereby separate them from the unexcited undesired isotopic species. The method is particularly applicable to the separation of hydrogen isotopes.

  7. Tooth enamel maturation reequilibrates oxygen isotope compositions and supports simple sampling methods

    NASA Astrophysics Data System (ADS)

    Trayler, Robin B.; Kohn, Matthew J.

    2017-02-01

    Oxygen isotope and major element zoning patterns of several disparate ungulate teeth were collected to evaluate the timing and geometry of enamel formation, records of isotope zoning, and tooth enamel sampling strategies. Isotopic zoning in mammalian tooth enamel encodes a sub-annual time series of isotopic variation of an animal's body water composition, with a damping factor that depends on the specifics of how enamel mineralizes. Enamel formation comprises two stages: precipitation of appositional enamel with a high CO3:PO4 ratio, followed by precipitation of maturational enamel with a lower CO3:PO4. If appositional and maturational enamel both contribute to isotope compositions (but with different CO3:PO4), and if isotope compositions vary seasonally, paired δ18O values from CO3 and PO4 profiles should show a spatial separation. CO3 isotope patterns should be shifted earlier seasonally than PO4 isotope patterns. Such paired profiles for new and published data show no resolvable shifts, i.e. CO3 and PO4 δ18O profiles show coincident maxima and minima. This coincidence suggests that enamel maturation reequilibrates appositional isotope compositions. If enamel maturation establishes enamel isotope compositions, the geometry of maturation, not apposition, should be considered when devising sampling protocols. X-ray maps of Ca zoning show that the majority of enamel (inner and middle layers) mineralizes heavily at a high angle to the external tooth surface and the enamel-dentine junction over length scales of 2-4 mm, while the outer enamel surface mineralizes more slowly. These data suggest that isotopic sampling strategies should parallel maturational geometry and focus on interior enamel to improve data fidelity. The magnitude of isotopic damping is also smaller than implied in previous studies, so tooth enamel zoning more closely reflects original body water isotopic variations than previously assumed.

  8. Comparison of isotope dilution and excretion methods for determining the half-life of ascorbic acid in the guinea pig

    SciTech Connect

    Kipp, D.E.; Rivers, J.M.

    1984-08-01

    The half-life of ascorbic acid (AA) in guinea pigs was investigated by the isotope dilution and excretion methods. The dilution method measures (1-14C)AA disappearance from the plasma, whereas the excretion method measures the elimination of (1-14C)AA and the metabolites from the body. Two groups of animals underwent both isotope studies in reverse order. Animals were conditioned to the experimental procedures and fed 2.5 mg AA/100 g body weight orally to maintain a daily intake of the vitamin independent of food consumption. The two isotope procedures imposed similar stress on the animals, as determined by plasma cortisol levels and body weight changes. The AA half-life calculations of the rapidly exchangeable pool by the isotope dilution method yielded values of 1.23 and 0.34 hours for the two groups, respectively. The half-life of the slowly exchangeable pool for the two groups was 60.2 and 65.8 hours, respectively. The half-life of AA in the rapidly exchangeable pool, as measured by the excretion studies, was 4.57-8.75 hours. For the slowly exchangeable pool, it was 146-149 hours. The longer half-life of both pools obtained with the excretion method indicates that the isotope is disappearing from the plasma more rapidly than it is being excreted. This suggests that a portion of the (1-14C)AA leaving the plasma is removed to a body pool that is not sampled by the isotope excretion method.

  9. Methods for the stable isotopic analysis of chlorine in chlorate and perchlorate compounds.

    PubMed

    Ader, M; Coleman, M L; Doyle, S P; Stroud, M; Wakelin, D

    2001-10-15

    Chlorate and perchlorate compounds, used as herbicides, solid fuel propellants, and explosives, are increasingly recognized as pollutants in groundwater. Stable isotope characterization would permit both environmental monitoring of extent of remediation and forensic characterization. Stoichiometric reduction to chloride (greater than 98% yield), by Fe(II) for chlorate and alkaline fusion-decomposition for perchlorate, allows analysis by standard methods to give highly reproducible and accurate delta37Cl results (0.05/1000, 2 x standard error). Analysis of various compounds from different suppliers yielded delta37Cl values for chlorate samples near to +0.2/1000 (SMOC), but one has within-sample heterogeneity of 0.5/1000, possibly due to crystallization processes during manufacture. Results for perchlorate samples also are generally near +0.2/1000, but one is +2.3/1000 (SMOC). The initial results suggest that both forensic and environmental applications might be feasible.

  10. Radiometric method for determining concentration of naturally occurring isotopes and device therefor

    SciTech Connect

    Yakubovich, S.L.; Gerling, V.E.; Golubnichy, V.V.; Kotsen, M.E.; Stepanov, J.N.

    1984-10-09

    The proposed method essentially consists in that a sample of a substance is placed between two scintillators in immediate contact therewith whereupon said sample is hermetically sealed. Arranged in close proximity to each scintillator is a photomultiplier tube recording ionizing ..cap alpha..- and b-radiation. A selector is utilized to select pulses corresponding to ..cap alpha..- and b-particles, and delayed coincidence circuits of a recording element separate and record b-..cap alpha.. and ..cap alpha..-..cap alpha.. cascade pairs of delayed coincidences of RaC, ThC, and AcA radionuclides. Flows are measured twice at a predetermined time interval to account for emanation build-up tendency and concentration of isotopes of radium is determined from a formula.

  11. Boundary-layer isotope dilution/mass balance methods for measurement of nocturnal methane emissions from grazing sheep

    NASA Astrophysics Data System (ADS)

    Harvey, M. J.; Brailsford, G. W.; Bromley, A. M.; Lassey, K. R.; Mei, Z.; Kristament, I. S.; Reisinger, A. R.; Walker, C. F.; Kelliher, F. M.

    Following advances with methods for 13C/ 12C isotopic analysis of methane in small (⩽4 L) air samples, new isotope dilution techniques are proposed for measurement of methane emissions at the paddock scale from grazing ruminant animals. These techniques combine measurement of the isotopic δ13CH 4 composition of air samples with a non-intrusive mass balance method applied in the nocturnal boundary layer. Flux estimates from trials using the isotope dilution techniques are compared with estimates based on scaling up individual animal emission measurements using a rumen gas tracer technique. The methane flux assessed by the latter technique ranged from 35 to 70 mg (CH 4) m -2 d -1 with a stocking density between 10 and 20 sheep ha -1. The isotope dilution based nocturnal boundary-layer estimates generally agreed to better than a factor of 2 and usually to within 20% of the average of individual animal emission rate per unit area of paddock. Both static and advecting mass balance methods are developed. In the advecting case, the upwind/downwind contrast in δ13C was typically 0.2-0.5‰. Care was necessary with air sampling to avoid error in this small contrast contributing to error in the flux. Agreement between concentration- and isotope-based nocturnal boundary layer methods and the sheep breath measurements indicated that sample representativeness was generally good. Factors which affect the accuracy of the method are examined and include variability in nocturnal mixing height, the assumed δ13CH 4 composition of the source sheep breath and diurnal patterns in sheep emission. This paper establishes new techniques useful in the paddock to landscape scale although widespread application awaits further development of technology for rapid and repeatable field analysis of δ13CH 4 in small samples.

  12. Subjective Well-Being: Revisions to Dynamic Equilibrium Theory Using National Panel Data and Panel Regression Methods

    ERIC Educational Resources Information Center

    Headey, Bruce

    2006-01-01

    This paper partly revises the dynamic equilibrium (DE) theory of subjective well-being (SWB), sometimes termed set point theory. Results from four national panel surveys show that correlations among measures of SWB diminish over time, and that the SWB set points of a minority of individuals substantially change. These results mean that DE theory…

  13. Better characterization of young and old groundwater systems through improved groundwater dating by isotope methods

    NASA Astrophysics Data System (ADS)

    Aggarwal, Pradeep; Suckow, Axel; Newman, Brent; Araguas, Luis; Groening, Manfred; Voss, Clifford; Vitvar, Tomas; Froehlich, Klaus; Kurttas, Turker

    2010-05-01

    . The combined use of radioactive tracers such as carbon-14, chlorine-36 and krypton-81, and numerical hydrodynamic modelling showed inconsistencies in residence time estimates made before the extensive use of accelerator mass spectrometry (AMS) dating methods. Most of the inconsistencies in the use of radiocarbon were the result of contamination with atmospheric CO2 during sampling by the conventional precipitation method. Duplicate analysis of radiocarbon by both sampling methods in selected large aquifers showed consistent differences, up to 10 pMC. The lack of radiocarbon in some deep groundwaters has been confirmed by other long-lived radioisotopes. We have re-evaluated groundwater ages of several of these aquifers coupled with 3-D groundwater models. Our study has demonstrated the usefulness of conservative long-lived radioisotopes for assessing groundwater dynamics of large aquifers containing fossil groundwaters, such as the Nubian Sandstone Aquifer System in Africa and the Guarani aquifer in South America. This presentation will discuss these and related IAEA initiatives in the field of isotope age dating of both young and old groundwaters under various climatic conditions.

  14. Evaluation of a Stable Isotope Method to Mark Naturally-Breeding Larval Mosquitoes for Adult Dispersal Studies

    PubMed Central

    HAMER, GABRIEL L.; DONOVAN, DANIELLE J.; HOOD-NOWOTNY, REBECCA; KAUFMAN, MICHAEL G.; GOLDBERG, TONY L.; WALKER, EDWARD D.

    2014-01-01

    Understanding mosquito dispersal is critically important for vector-borne disease control and prevention. Mark–release–recapture methods using various marking techniques have made substantial contributions to the study of mosquito biology. However, the ability to mark naturally breeding mosquitoes noninvasively and with life-long retention has remained problematic. Here, we describe a method to mark naturally breeding mosquitoes with stable isotopes. Culexpipiens f. molestus mosquitoes were provisioned as larvae in laboratory experiments with 15N-labeled potassium nitrate and 13C-labeled glucose. Larval enrichment was sufficient to differentiate marked adult mosquitoes from unmarked control mosquitoes and the natural source population from Chicago Illinois, using either δ15N or δ13C. Isotopic retention lasted for at least 55 d for adult male and females mosquitoes. There were no consistent effects of isotopic enrichment on immature mosquito survival or adult mosquito body size. We then applied this marking technique to naturally breeding Culex pipiens mosquitoes in suburban Chicago, IL, and for the first time, report successful isotopic enrichment of mosquitoes in the field. This stable isotope marking technique will facilitate studies of mosquito dispersal. PMID:22308772

  15. Multi-mycotoxin stable isotope dilution LC-MS/MS method for Fusarium toxins in cereals.

    PubMed

    Habler, Katharina; Rychlik, Michael

    2016-01-01

    A multi-mycotoxin stable isotope dilution LC-MS/MS method was developed for 14 Fusarium toxins including modified mycotoxins in cereals (deoxynivalenol, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, HT2-toxin, T2-toxin, enniatin B, enniatin B1, enniatin A1, enniatin A, beauvericin, fusarenone X, nivalenol, deoxynivalenol-3-glucoside, and zearalenone). The chromatographic separation of the toxins with particular focus on deoxynivalenol and deoxynivalenol-3-glucoside was achieved using a C18-hydrosphere column. An expedient sample preparation method was developed that uses solid-phase extraction for the purification of trichothecenes combined with zearalenone, enniatins, and beauvericin and provides excellent validation data. Linearity, intra-day precision, inter-day precision, and recoveries were ≥0.9982, 1-6%, 5-12%, and 79-117%, respectively. Method accuracy was verified by analyzing certified reference materials for deoxynivalenol, HT2-toxin, and T2-toxin with deviations below 7%. The results of this method found barley malt samples from 2012, 2013, and 2014 frequently contaminated with high concentrations of enniatin B, deoxynivalenol, and its modified mycotoxin deoxynivalenol-3-glucoside. Samples from 2012 were especially contaminated. Fusarenone X was not detected in any of the analyzed samples.

  16. Accurate Hf isotope determinations of complex zircons using the "laser ablation split stream" method

    NASA Astrophysics Data System (ADS)

    Fisher, Christopher M.; Vervoort, Jeffery D.; DuFrane, S. Andrew

    2014-01-01

    The "laser ablation split stream" (LASS) technique is a powerful tool for mineral-scale isotope analyses and in particular, for concurrent determination of age and Hf isotope composition of zircon. Because LASS utilizes two independent mass spectrometers, a large range of masses can be measured during a single ablation, and thus, the same sample volume can be analyzed for multiple geochemical systems. This paper describes a simple analytical setup using a laser ablation system coupled to a single-collector (for U-Pb age determination) and a multicollector (for Hf isotope analyses) inductively coupled plasma mass spectrometer (MC-ICPMS). The ability of the LASS for concurrent Hf + age technique to extract meaningful Hf isotope compositions in isotopically zoned zircon is demonstrated using zircons from two Proterozoic gneisses from northern Idaho, USA. These samples illustrate the potential problems associated with inadvertently sampling multiple age and Hf components in zircons, as well as the potential of LASS to recover meaningful Hf isotope compositions. We suggest that such inadvertent sampling of differing age and Hf components can be a significant cause of excess scatter in Hf isotope analyses and demonstrate that the LASS approach offers a robust solution to these issues. The veracity of the approach is demonstrated by accurate analyses of 10 reference zircons with well-characterized age and Hf isotopic composition, using laser spot diameters of 30 and 40 µm. In order to expand the database of high-precision Lu-Hf isotope analyses of reference zircons, we present 27 new isotope dilution-MC-ICPMS Lu-Hf isotope measurements of five U-Pb zircon standards: FC1, Temora, R33, QGNG, and 91500.

  17. A field and laboratory method for monitoring the concentration and isotopic composition of soil CO2.

    PubMed

    Breecker, Dan; Sharp, Zachary D

    2008-01-01

    The stable isotope composition of nmol size gas samples can be determined accurately and precisely using continuous flow isotope ratio mass spectrometry (IRMS). We have developed a technique that exploits this capability in order to measure delta13C and delta18O values and, simultaneously, the concentration of CO2 in sub-mL volume soil air samples. A sampling strategy designed for monitoring CO2 profiles at particular locations of interest is also described. This combined field and laboratory technique provides several advantages over those previously reported: (1) the small sample size required allows soil air to be sampled at a high spatial resolution, (2) the field setup minimizes sampling times and does not require powered equipment, (3) the analytical method avoids the introduction of air (including O2) into the mass spectrometer thereby extending filament life, and (4) pCO2, delta13C and delta18O are determined simultaneously. The reproducibility of measurements of CO2 in synthetic tank air using this technique is: +/-0.08 per thousand (delta13C), +/-0.10 per thousand (delta18O), and +/-0.7% (pCO2) at 5550 ppm. The reproducibility for CO2 in soil air is estimated as: +/-0.06 per thousand (delta13C), +/-0.06 per thousand (delta18O), and +/-1.6% (pCO2). Monitoring soil CO2 using this technique is applicable to studies concerning soil respiration and ecosystem gas exchange, the effect of elevated atmospheric CO2 (e.g. free air carbon dioxide enrichment) on soil processes, soil water budgets including partitioning evaporation from transpiration, pedogenesis and weathering, diffuse solid-earth degassing, and the calibration of speleothem and pedogenic carbonate delta13C values as paleoenvironmental proxies.

  18. Uranium isotopes quantitatively determined by modified method of atomic absorption spectrophotometry

    NASA Technical Reports Server (NTRS)

    Lee, G. H.

    1967-01-01

    Hollow-cathode discharge tubes determine the quantities of uranium isotopes in a sample by using atomic absorption spectrophotometry. Dissociation of the uranium atoms allows a large number of ground state atoms to be produced, absorbing the incident radiation that is different for the two major isotopes.

  19. Stable isotope ratio method for the characterisation of the poultry house environment.

    PubMed

    Skipitytė, Raminta; Mašalaitė, Agnė; Garbaras, Andrius; Mickienė, Rūta; Ragažinskienė, Ona; Baliukonienė, Violeta; Bakutis, Bronius; Šiugždaitė, Jūratė; Petkevičius, Saulius; Maruška, Audrius Sigitas; Remeikis, Vidmantas

    2017-06-01

    Stable isotope analysis was applied to describe the poultry house environment. The poultry house indoor environment was selected for this study due to the relevant health problems in animals and their caretakers. Air quality parameters including temperature, relative humidity, airflow rate, NH3, CO2 and total suspended particles, as well as mean levels of total airborne bacteria and fungi count, were measured. Carbon isotope ratios ((13)C/(12)C) were obtained in size-segregated aerosol particles. The carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) isotope ratios were measured in feed, litter, scrapings from the ventilation system, feathers and eggs. Additionally, the distribution of δ(13)C and δ(15)N values in different tissues of the chicken was examined. The airborne bacteria and fungi extracted from the air filters collected from poultry farms were grown in the laboratory in media with known isotope values and measured for stable isotope ratios. Analysis of isotope fractionation between microorganisms and their media indicated the applicability of stable isotope analysis in bulk samples for the identification of source material. The analysed examples imply that stable isotope analysis can be used to examine the indoor environment along with its biology and ecology, and serve as an informative bioanalytical tool.

  20. Equilibrium Fermi's Golden Rule Charge Transfer Rate Constants in the Condensed Phase: The Linearized Semiclassical Method vs Classical Marcus Theory.

    PubMed

    Sun, Xiang; Geva, Eitan

    2016-05-19

    In this article, we present a comprehensive comparison between the linearized semiclassical expression for the equilibrium Fermi's golden rule rate constant and the progression of more approximate expressions that lead to the classical Marcus expression. We do so within the context of the canonical Marcus model, where the donor and acceptor potential energy surface are parabolic and identical except for a shift in both the free energies and equilibrium geometries, and within the Condon region. The comparison is performed for two different spectral densities and over a wide range of frictions and temperatures, thereby providing a clear test for the validity, or lack thereof, of the more approximate expressions. We also comment on the computational cost and scaling associated with numerically calculating the linearized semiclassical expression for the rate constant and its dependence on the spectral density, temperature, and friction.

  1. Applications of the two-photon doppler-free method: Hyperfine interactions and isotope shift measurements

    NASA Astrophysics Data System (ADS)

    Cagnac, B.

    1985-08-01

    The hyperfine structures are generally of the same order of magnitude as the Doppler broadening of optical transitions and so are the isotopic shifts in the case of heavy elements. When these structures are too small, one must use Doppler-free methods. Among these methods, the two-photon spectroscopy has obtained good results in highly excited levels. In our laboratory in Paris, we did measurements on neon and helium by two-photon excitation from metastable levels. The precision of the measurements is of the order of one MHz, which permits a precise comparison with theory. We compare the measurements on neon with the theory by Liberman and we obtain a good fit in the first approximation, but must introduce mixing of wave functions for an exact explanation. In the case of helium, we obtain a good fit with the theoretical values obtained from the wave functions by Accad, Pekeris and Schiff. We also give an example where another technique by polarization measurements permits us to obtain experimentally a hyperfine structure smaller than the natural width. We also present a short review of the measurements done by the two-photon method in other laboratories on other elements, Pb, Tl, In and alkaline earths Ca, Sr. Ba.

  2. LC/MS Method for the Determination of Stable Isotope Labeled Promethazine in Human Plasma

    NASA Technical Reports Server (NTRS)

    Zuwei, Wang; Boyd, Jason; Berens, Kurt L.; Putcha, Lakshmi

    2004-01-01

    Promethazine (PMZ) is taken by astronauts orally (PO), intramuscularly (IM) or rectally (PR) for space motion sickness. LC/MS method was developed with off-line solid phase extraction to measure plasma concentrations of PMZ given as stable isotope-labeled (SIL) formulations by the three different routes of administration simultaneously. Samples (0.5ml) were loaded on to Waters Oasis HLB co-polymer cartridges and eluted with 1.0 mL methanol. HPLC separation of the eluted sample was performed using an Agilent Zorbax SB-CN column (50 x 2.1 mm) at a flow rate of 0.2 mL/min for 6 min. Acetonitrile/ ammonium acetate (30 mM) in water (3:2, v/v), pH 5.6 plus or minus 0.1, was used as the mobile phase for separation. Concentrations of PMZ, PMZ-d4 and PMZ-d7 and chlorpromazine (internal standard) were determined using a Micromass ZMD single quadrupole mass spectrometer with Electrospray Ionization (ESI). ESI mass spectra were acquired in positive ion mode with selected ion monitoring of [M+ H]dot plus. The method is rapid, reproducible and the assay specific parameters are listed in a table. A novel, sensitive and specific method for the measurement of PMZ and SIL PMZ in human plasma is reported.

  3. Multi-mycotoxin stable isotope dilution LC-MS/MS method for Fusarium toxins in beer.

    PubMed

    Habler, Katharina; Gotthardt, Marina; Schüler, Jan; Rychlik, Michael

    2017-03-01

    A stable isotope dilution LC-MS/MS multi-mycotoxin method was developed for 12 different Fusarium toxins including modified mycotoxins in beer (deoxynivalenol-3-glucoside, deoxynivalenol, 3-acetyldeoxynivalenol, 15-acetyl-deoxynivalenol, HT2-toxin, T2-toxin, enniatin B, B1, A1, A, beauvericin and zearalenone). As sample preparation and purification of beer a combined solid phase extraction for trichothecenes, enniatins, beauvericin and zearalenone was firstly developed. The validation of the new method gave satisfying results: intra-day and inter-day precision and recoveries were 1-5%, 2-8% and 72-117%, respectively. In total, 61 different organic and conventional beer samples from Germany and all over the world were analyzed by using the newly developed multi-mycotoxin method. In summary, deoxynivalenol, deoxynivalenol-3-glucoside, 3-acetyldeoxynivaleneol and enniatin B were quantified in rather low contents in the investigated beer samples. None of the other monitored Fusarium toxins like 15-acetyldeoxynivalenol, HT2- and T2-toxin, zearalenone, enniatin B1, A1, A or beauvericin were detectable.

  4. High-Throughput Method for Strontium Isotope Analysis by Multi-Collector-Inductively Coupled Plasma-Mass Spectrometer

    SciTech Connect

    Hakala, Jacqueline Alexandra

    2016-11-22

    This technical report presents the details of the Sr column configuration and the high-throughput Sr separation protocol. Data showing the performance of the method as well as the best practices for optimizing Sr isotope analysis by MC-ICP-MS is presented. Lastly, this report offers tools for data handling and data reduction of Sr isotope results from the Thermo Scientific Neptune software to assist in data quality assurance, which help avoid issues of data glut associated with high sample throughput rapid analysis.

  5. Online induction heating for determination of isotope composition of woody stem water with laser spectrometry: A methods assessment

    USGS Publications Warehouse

    Lazarus, Brynne E.; Germino, Matthew; Vander Veen, Jessica L.

    2016-01-01

    Application of stable isotopes of water to studies of plant–soil interactions often requires a substantial preparatory step of extracting water from samples without fractionating isotopes. Online heating is an emerging approach for this need, but is relatively untested and major questions of how to best deliver standards and assess interference by organics have not been evaluated. We examined these issues in our application of measuring woody stem xylem of sagebrush using a Picarro laser spectrometer with online induction heating. We determined (1) effects of cryogenic compared to induction-heating extraction, (2) effects of delivery of standards on filter media compared to on woody stem sections, and (3) spectral interference from organic compounds for these approaches (and developed a technique to do so). Our results suggest that matching sample and standard media improves accuracy, but that isotopic values differ with the extraction method in ways that are not due to spectral interference from organics.

  6. Online induction heating for determination of isotope composition of woody stem water with laser spectrometry: a methods assessment.

    PubMed

    Lazarus, Brynne E; Germino, Matthew J; Vander Veen, Jessica L

    2016-06-01

    Application of stable isotopes of water to studies of plant-soil interactions often requires a substantial preparatory step of extracting water from samples without fractionating isotopes. Online heating is an emerging approach for this need, but is relatively untested and major questions of how to best deliver standards and assess interference by organics have not been evaluated. We examined these issues in our application of measuring woody stem xylem of sagebrush using a Picarro laser spectrometer with online induction heating. We determined (1) effects of cryogenic compared to induction-heating extraction, (2) effects of delivery of standards on filter media compared to on woody stem sections, and (3) spectral interference from organic compounds for these approaches (and developed a technique to do so). Our results suggest that matching sample and standard media improves accuracy, but that isotopic values differ with the extraction method in ways that are not due to spectral interference from organics.

  7. A simple method for estimating equilibrium constants for serum testosterone binding resulting in an optimal free testosterone index for use in elderly men.

    PubMed

    Ross, H Alec; Meuleman, Eric J; Sweep, Fred C G J

    2005-01-01

    An algorithm was developed to evaluate equilibrium constants for testosterone (Te) and sex hormone-binding globulin (SHBG) or albumin from serum free testosterone (FTe) measurements performed in a panel of 30 healthy elderly men by means of a near-reference method, i.e., symmetric dialysis (affinity constants: SHBG-Te, 1.13 x 10(9) L/mol; albumin-Te, 4.4 x 10(4) L/mol). Using these estimates, a free testosterone index (FTeI) was calculated from total Te and SHBG concentrations in a further 35 elderly men. This FTeI perfectly matches with actually measured free testosterone concentrations by symmetric dialysis in this second group, with a mean ratio index/measurement of 0.998+/-0.016 (SEM). The efficacy of the algorithm, which represents a simple alternative to previous cumbersome methods for estimation of equilibrium constants, is thereby demonstrated.

  8. Source apportionment of methane using a triple isotope approach - Method development and application in the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Steinbach, Julia; Holmstrand, Henry; Semiletov, Igor; Shakhova, Natalia; Shcherbakova, Kseniia; Kosmach, Denis; Sapart, Célia J.; Gustafsson, Örjan

    2015-04-01

    We present a method for measurements of the stable and radiocarbon isotope systems of methane in seawater and sediments. The triple isotope characterization of methane is useful in distinguishing different sources and for improving our understanding of biogeochemical processes affecting methane in the water column. D14C-CH4 is an especially powerful addition to stable isotope analyses in distinguishing between thermogenic and biogenic origins of the methane. Such measurements require large sample sizes, due to low natural abundance of the radiocarbon in CH4. Our system for sample collection, methane extraction and purification builds on the approach by Kessler and Reeburgh (Limn. & Ocean. Meth., 2005). An in-field system extracts methane from 30 -120 l water or 1-2 l sediment (depending on the in-situ methane concentration) by purging the samples with Helium to transfer the dissolved methane to the headspace and circulating it through cryogenically cooled absorbent traps where methane is collected. The in-field preparation eliminates the risks of storage and transport of large seawater quantities and subsequent leakage of sample gas as well as ongoing microbial processes and chemical reactions that may alter the sample composition. In the subsequent shore-based treatment, a laboratory system is used to purify and combust the collected CH4 to AMS-amenable CO2. Subsamples from the methane traps are analyzed for stable isotopes and compared to stable isotope measurements directly measured from small water samples taken in parallel, to correct for any potential fractionation occurring during this process. The system has been successfully tested and used on several shorter shipboard expeditions in the Baltic Sea and on a long summer expedition across the Arctic Ocean. Here we present the details of the method and testing, as well as first triple isotope field data from two cruises to the Landsort Deep area in the Central Baltic Sea.

  9. A routine high-precision method for Lu-Hf isotope geochemistry and chronology

    USGS Publications Warehouse

    Patchett, P.J.; Tatsumoto, M.

    1981-01-01

    A method for chemical separation of Lu and Hf from rock, meteorite and mineral samples is described, together with a much improved mass spectrometric running technique for Hf. This allows (i) geo- and cosmochronology using the176Lu???176Hf+??- decay scheme, and (ii) geochemical studies of planetary processes in the earth and moon. Chemical yields for the three-stage ion-exchange column procedure average 90% for Hf. Chemical blanks are <0.2 ng for Lu and Hf. From 1 ??g of Hf, a total ion current of 0.5??10-11 Ampere can be maintained for 3-5 h, yielding 0.01-0.03% precision on the ratio176Hf/177Hf. Normalisation to179Hf/177Hf=0.7325 is used. Extensive results for the Johnson Matthey Hf standard JMC 475 are presented, and this sample is urged as an international mass spectrometric standard; suitable aliquots, prepared from a single batch of JMC 475, are available from Denver. Lu-Hf analyses of the standard rocks BCR-1 and JB-1 are given. The potential of the Lu-Hf method in isotope geochemistry is assessed. ?? 1980 Springer-Verlag.

  10. Discovery of the krypton isotopes

    SciTech Connect

    Heim, M.; Fritsch, A.; Schuh, A.; Shore, A.; Thoennessen, M.

    2010-07-15

    Thirty-two krypton isotopes have been observed so far and the discovery of these isotopes is discussed here. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

  11. A New Method for Evaluating the Carbon Isotope Characteristics of Carbonate Formed Under Cryogenic Conditions Analogous to Mars

    NASA Technical Reports Server (NTRS)

    Niles, P. B.; Socki, R. A.; Hredzak, P. L.

    2007-01-01

    soil or dust. This study demonstrates an innovative new method for measuring the isotopic composition of gas evolved from the freezing of carbonate solutions in real time, which allows for a much clearer view of the chemical processes involved. This method now sets the stage for detailed analysis of the chemical and isotopic mechanisms that produce cryogenic carbonates.

  12. Chemical and isotopic methods for quantifying ground-water recharge in a regional, semiarid environment

    USGS Publications Warehouse

    Wood, Warren W.; Sanford, Ward E.

    1995-01-01

    The High Plains aquifer underlying the semiarid Southern High Plains of Texas and New Mexico, USA was used to illustrate solute and isotopic methods for evaluating recharge fluxes, runoff, and spatial and temporal distribution of recharge. The chloride mass-balance method can provide, under certain conditions, a time-integrated technique for evaluation of recharge flux to regional aquifers that is independent of physical parameters. Applying this method to the High Plains aquifer of the Southern High Plains suggests that recharge flux is approximately 2% of precipitation, or approximately 11 ± 2 mm/y, consistent with previous estimates based on a variety of physically based measurements. The method is useful because long-term average precipitation and chloride concentrations in rain and ground water have less uncertainty and are generally less expensive to acquire than physically based parameters commonly used in analyzing recharge. Spatial and temporal distribution of recharge was evaluated by use of δ2H, δ18O, and tritium concentrations in both ground water and the unsaturated zone. Analyses suggest that nearly half of the recharge to the Southern High Plains occurs as piston flow through playa basin floors that occupy approximately 6% of the area, and that macropore recharge may be important in the remaining recharge. Tritium and chloride concentrations in the unsaturated zone were used in a new equation developed to quantify runoff. Using this equation and data from a representative basin, runoff was found to be 24 ± 3 mm/y; that is in close agreement with values obtained from water-balance measurements on experimental watersheds in the area. Such geochemical estimates are possible because tritium is used to calculate a recharge flux that is independent of precipitation and runoff, whereas recharge flux based on chloride concentration in the unsaturated zone is dependent upon the amount of runoff. The difference between these two estimates yields the amount

  13. Fast methods for determination of antropogenic actinides and U/Th-series isotopes in aqueous samples.

    PubMed

    Eikenberg, J; Bajo, S; Beer, H; Hitz, J; Ruethi, M; Zumsteg, I; Letessier, P

    2004-01-01

    Rapid and simple methods are applied at the PSI radioanalytical laboratory for determining anthropogenic actinides in waste and nuclear reactor waters (U, Pu, Am, Cm) as well as for analysis of naturally occurring alpha-emitters in continental river and ground water. Anion exchange chromatography followed by alpha-spectrometry as well as alpha/beta-LSC is applied for the reactor coolant waters. To avoid alpha-spectrum interference between 238Pu and 241Am at 5.5 MeV, the Pu-fraction is purified using anion exchange resin. Prior to the separation of the Pu-fraction, all actinides (U, Pu, Am, Cm) are adsorbed batch-wise under stirring onto Actinide Resin and subsequent decomposition of the reagent. The residue is then re-dissolved in a sulfate buffer solution for electrolytic deposition. In tabular water samples isotopes of Ra and Po are analyzed additionally via sorption onto manganese coated discs (Ra) and deposition on silver discs (Po). For counting times of 1 day and use of 0.1-1l sample aliquots, detection limits of a few mBql(-1) can be obtained easily.

  14. A comparison of force fields and calculation methods for vibration intervals of isotopic H3(+) molecules

    NASA Astrophysics Data System (ADS)

    Carney, G. D.; Adler-Golden, S. M.; Lesseski, D. C.

    1986-04-01

    This paper reports (1) improved values for low-lying vibration intervals of H3(+), H2D(+), D2H(+), and D3(+) calculated using the variational method and Simons-Parr-Finlan (1973) representations of the Carney-Porter (1976) and Dykstra-Swope (1979) ab initio H3(+) potential energy surfaces, (2) quartic normal coordinate force fields for isotopic H3(+) molecules, (3) comparisons of variational and second-order perturbation theory, and (4) convergence properties of the Lai-Hagstrom internal coordinate vibrational Hamiltonian. Standard deviations between experimental and ab initio fundamental vibration intervals of H3(+), H2D(+), D2H(+), and D3(+) for these potential surfaces are 6.9 (Carney-Porter) and 1.2/cm (Dykstra-Swope). The standard deviations between perturbation theory and exact variational fundamentals are 5 and 10/cm for the respective surfaces. The internal coordinate Hamiltonian is found to be less efficient than the previously employed 't' coordinate Hamiltonian for these molecules, except in the case of H2D(+).

  15. Isotope geochemistry in 1990s

    SciTech Connect

    Billo, S.M.

    1995-12-31

    The intense interest in radioactive minerals as a source of atomic energy, and their application in searching for ore deposits and also in gamma-ray and neutron logging oil wells, have opened new vistas in every science. Many minerals containing elements of high atomic weight are radioactive, and emit a radiation which affects a photographic plate and may be detected by means of a sensitive phosphorescent screen. Most of the elements as found in nature are a mixture of isotopes. isotopes are atoms of one element which have different masses. Uranium, thorium, potassium, and rubidium isotopes are also used to date minerals and rocks. Organic materials that have been in equilibrium with CO{sub 2}-photosynthetic cycle during the past 50,000 years are dated by carbon-14 method. The stable isotopes of H{sub 2}, C, N{sub 2}, O{sub 2}, and S are intimately associated with the atmosphere, hydrosphere, and lithosphere and are used in probing water resources.

  16. Artifactual responses of mesophyll conductance to CO2 and irradiance estimated with the variable J and online isotope discrimination methods

    SciTech Connect

    Gu, Lianhong; Sun, Ying

    2013-01-01

    Studies with the variable J method have reported that mesophyll conductance (gm) rapidly decreases with increasing intercellular CO2 partial pressures (Ci) or decreasing irradiance. Similar responses have been suggested with the online isotope discrimination method, although with less consistency. Here we show that even when the true gm is constant, the variable J method can produce an artifactual dependence of gm on Ci or irradiance similar to those reported in previous studies for any of the following factors: day respiration and chloroplastic CO2 photocompensation point are estimated with Laisk method; Ci or electron transport rate is positively biased; net photosynthetic rate is negatively biased; insufficient NADPH is assumed while insufficient ATP limits RuBP regeneration. The isotopic method produces similar artifacts if fractionation of carboxylation or Ci are positively biased or 13 negatively biased. A nonzero chloroplastic resistance to CO2 movement results in a qualitatively different dependence of gm on Ci or irradiance and this dependence is only sensitive at low Ci. We thus cannot rule out the possibility that previously reported dependence of gm on Ci or irradiance is a methodological artifact. Recommendations are made to take advantage of sensitivities of the variable J and isotopic methods for estimating gm.

  17. Forebody and base region real gas flow in severe planetary entry by a factored implicit numerical method. II - Equilibrium reactive gas

    NASA Technical Reports Server (NTRS)

    Davy, W. C.; Green, M. J.; Lombard, C. K.

    1981-01-01

    The factored-implicit, gas-dynamic algorithm has been adapted to the numerical simulation of equilibrium reactive flows. Changes required in the perfect gas version of the algorithm are developed, and the method of coupling gas-dynamic and chemistry variables is discussed. A flow-field solution that approximates a Jovian entry case was obtained by this method and compared with the same solution obtained by HYVIS, a computer program much used for the study of planetary entry. Comparison of surface pressure distribution and stagnation line shock-layer profiles indicates that the two solutions agree well.

  18. Determining origin in a migratory marine vertebrate: a novel method to integrate stable isotopes and satellite tracking.

    PubMed

    Zanden, Hannah B Vander; Tucker, Anton D; Hart, Kristen M; Lamont, Margaret M; Fuisaki, Ikuko; Addison, David; Mansfield, Katherine L; Phillips, Katrina F; Wunder, Michael B; Bowen, Gabriel J; Pajuelo, Mariela; Bolten, Alan B; Bjorndal, Karen A

    2015-03-01

    Stable isotope analysis is a useful tool to track animal movements in both terrestrial and marine environments. These intrinsic markers are assimilated through the diet and may exhibit spatial gradients as a result of biogeochemical processes at the base of the food web. In the marine environment, maps to predict the spatial distribution of stable isotopes are limited, and thus determining geographic origin has been reliant upon integrating satellite telemetry and stable isotope data. Migratory sea turtles regularly move between foraging and reproductive areas. Whereas most nesting populations can be easily accessed and regularly monitored, little is known about the demographic trends in foraging populations. The purpose of the present study was to examine migration patterns of loggerhead nesting aggregations in the Gulf of Mexico (GoM), where sea turtles have been historically understudied. Two methods of geographic assignment using stable isotope values in known-origin samples from satellite telemetry were compared: (1) a nominal approach through discriminant analysis and (2) a novel continuous-surface approach using bivariate carbon and nitrogen isoscapes (isotopic landscapes) developed for this study. Tissue samples for stable isotope analysis were obtained from 60 satellite-tracked individuals at five nesting beaches within the GoM. Both methodological approaches for assignment resulted in high accuracy of foraging area determination, though each has advantages and disadvantages. The nominal approach is more appropriate when defined boundaries are necessary, but up to 42% of the individuals could not be considered in this approach. All individuals can be included in the continuous-surface approach, and individual results can be aggregated to identify geographic hotspots of foraging area use, though the accuracy rate was lower than nominal assignment. The methodological validation provides a foundation for future sea turtle studies in the region to

  19. New online method for water isotope analysis of speleothem fluid inclusions using laser absorption spectroscopy (WS-CRDS)

    NASA Astrophysics Data System (ADS)

    Affolter, S.; Fleitmann, D.; Leuenberger, M.

    2014-07-01

    A new online method to analyse water isotopes of speleothem fluid inclusions using a wavelength scanned cavity ring down spectroscopy (WS-CRDS) instrument is presented. This novel technique allows us simultaneously to measure hydrogen and oxygen isotopes for a released aliquot of water. To do so, we designed a new simple line that allows the online water extraction and isotope analysis of speleothem samples. The specificity of the method lies in the fact that fluid inclusions release is made on a standard water background, which mainly improves the δ D robustness. To saturate the line, a peristaltic pump continuously injects standard water into the line that is permanently heated to 140 °C and flushed with dry nitrogen gas. This permits instantaneous and complete vaporisation of the standard water, resulting in an artificial water background with well-known δ D and δ18O values. The speleothem sample is placed in a copper tube, attached to the line, and after system stabilisation it is crushed using a simple hydraulic device to liberate speleothem fluid inclusions water. The released water is carried by the nitrogen/standard water gas stream directly to a Picarro L1102-i for isotope determination. To test the accuracy and reproducibility of the line and to measure standard water during speleothem measurements, a syringe injection unit was added to the line. Peak evaluation is done similarly as in gas chromatography to obtain &delta D; and δ18O isotopic compositions of measured water aliquots. Precision is better than 1.5 ‰ for δ D and 0.4 ‰ for δ18O for water measurements for an extended range (-210 to 0 ‰ for δ D and -27 to 0 ‰ for δ18O) primarily dependent on the amount of water released from speleothem fluid inclusions and secondarily on the isotopic composition of the sample. The results show that WS-CRDS technology is suitable for speleothem fluid inclusion measurements and gives results that are comparable to the isotope ratio mass

  20. New on-line method for water isotope analysis of speleothem fluid inclusions using laser absorption spectroscopy (WS-CRDS)

    NASA Astrophysics Data System (ADS)

    Affolter, S.; Fleitmann, D.; Leuenberger, M.

    2014-01-01

    A new online method to analyse water isotopes of speleothem fluid inclusions using a wavelength scanned cavity ring down spectroscopy (WS-CRDS) instrument is presented. This novel technique allows us to simultaneously measure hydrogen and oxygen isotopes for a released aliquot of water. To do so, we designed a new simple line that allows the on-line water extraction and isotope analysis of speleothem samples. The specificity of the method lies in the fact that fluid inclusions release is made on a standard water background, which mainly improves the δD reliability. To saturate the line, a peristaltic pump continuously injects standard water into the line that is permanently heated to 140 °C and flushed with dry nitrogen gas. This permits instantaneous and complete vaporisation of the standard water resulting in an artificial water background with well-known δD and δ18O values. The speleothem sample is placed into a copper tube, attached to the line and after system stabilisation is crushed using a simple hydraulic device to liberate speleothem fluid inclusions water. The released water is carried by the nitrogen/standard water gas stream directly to a Picarro L1102-i for isotope determination. To test the accuracy and reproducibility of the line and to measure standard water during speleothem measurements a syringe injection unit was added to the line. Peak evaluation is done similarly as in gas chromatography to obtain δD and δ18O isotopic composition of measured water aliquots. Precision is better than 1.5‰ for δD and 0.4‰ for δ18O for water measurement for an extended range (-210 to 0‰ for δD and -27 to 0‰ for δ18O) primarily dependent on the amount of water released from speleothem fluid inclusions and secondarily on the isotopic composition of the sample. The results show that WS-CRDS technology is suitable for speleothem fluid inclusion measurements and gives results that are comparable to Isotope Ratio Mass Spectrometry (IRMS) technique.

  1. Determining origin in a migratory marine vertebrate: a novel method to integrate stable isotopes and satellite tracking

    USGS Publications Warehouse

    Vander Zanden, Hannah B.; Tucker, Anton D.; Hart, Kristen M.; Lamont, Margaret M.; Fujisaki, Ikuko; Addison, David S.; Mansfield, Katherine L.; Phillips, Katrina F.; Wunder, Michael B.; Bowen, Gabriel J.; Pajuelo, Mariela; Bolten, Alan B.; Bjorndal, Karen A.

    2015-01-01

    Stable isotope analysis is a useful tool to track animal movements in both terrestrial and marine environments. These intrinsic markers are assimilated through the diet and may exhibit spatial gradients as a result of biogeochemical processes at the base of the food web. In the marine environment, maps to predict the spatial distribution of stable isotopes are limited, and thus determining geographic origin has been reliant upon integrating satellite telemetry and stable isotope data. Migratory sea turtles regularly move between foraging and reproductive areas. Whereas most nesting populations can be easily accessed and regularly monitored, little is known about the demographic trends in foraging populations. The purpose of the present study was to examine migration patterns of loggerhead nesting aggregations in the Gulf of Mexico (GoM), where sea turtles have been historically understudied. Two methods of geographic assignment using stable isotope values in known-origin samples from satellite telemetry were compared: 1) a nominal approach through discriminant analysis and 2) a novel continuous-surface approach using bivariate carbon and nitrogen isoscapes (isotopic landscapes) developed for this study. Tissue samples for stable isotope analysis were obtained from 60 satellite-tracked individuals at five nesting beaches within the GoM. Both methodological approaches for assignment resulted in high accuracy of foraging area determination, though each has advantages and disadvantages. The nominal approach is more appropriate when defined boundaries are necessary, but up to 42% of the individuals could not be considered in this approach. All individuals can be included in the continuous-surface approach, and individual results can be aggregated to identify geographic hotspots of foraging area use, though the accuracy rate was lower than nominal assignment. The methodological validation provides a foundation for future sea turtle studies in the region to inexpensively

  2. Thermal equilibrium and prehydration processes of electrons injected into liquid water calculated by dynamic Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Kai, Takeshi; Yokoya, Akinari; Ukai, Masatoshi; Fujii, Kentaro; Watanabe, Ritsuko

    2015-10-01

    The thermalization length and spatial distribution of electrons in liquid water were simulated for initial electron energies ranging from 0.1 eV to 100 keV using a dynamic Monte Carlo code. The results showed that electrons were decelerated for thermalization over a longer time period than was previously predicted. This long thermalization time significantly contributed to the series of processes from initial ionization to hydration. We further studied the particular deceleration process of electrons at an incident energy of 1 eV, focusing on the temporal evolution of total track length, mean traveling distance, and energy distributions of decelerating electrons. The initial prehydration time and thermalization periods were estimated to be approximately 50 and 220 fs, respectively, indicating that the initial prehydration began before or contemporaneously with the thermal equilibrium. Based on these results, the prehydrated electrons were suggested to play an important role during multiple DNA damage induction.

  3. Isotopic evidence for lateral flow and diffusive transport, but not sublimation, in a sloped seasonal snowpack, Idaho, USA

    NASA Astrophysics Data System (ADS)

    Evans, Samantha L.; Flores, Alejandro N.; Heilig, Achim; Kohn, Matthew J.; Marshall, Hans-Peter; McNamara, James P.

    2016-04-01

    Oxygen and hydrogen isotopes in snow were measured in weekly profiles during the growth and decline of a sloped subalpine snowpack, southern Idaho, 2011-2012. Isotopic steps (10‰, δ18O; 80‰, δD) were preserved relative to physical markers throughout the season, albeit with some diffusive smoothing. Melting stripped off upper layers without shifting isotopes within the snowpack. Meltwater is in isotopic equilibrium with snow at the top but not with snow at each respective collection height. Transport of meltwater occurred primarily along pipes and lateral flow paths allowing the snowpack to melt initially in reverse stratigraphic order. Isotope diffusivities are ~2 orders of magnitude faster than estimated from experiments but can be explained by higher temperature and porosity. A better understanding of how snowmelt isotopes change during meltout improves hydrograph separation methods, whereas constraints on isotope diffusivities under warm conditions improve models of ice core records in low-latitude settings.

  4. Bird Migration and Avian Influenza: A Comparison of Hydrogen Stable Isotopes and Satellite Tracking Methods.

    PubMed

    Bridge, Eli S; Kelly, Jeffrey F; Xiao, Xiangming; Takekawa, John Y; Hill, Nichola J; Yamage, Mat; Haque, Enam Ul; Islam, Mohammad Anwarul; Mundkur, Taej; Yavuz, Kiraz Erciyas; Leader, Paul; Leung, Connie Y H; Smith, Bena; Spragens, Kyle A; Vandegrift, Kurt; Hosseini, Parviez R; Saif, Samia; Mohsanin, Samiul; Mikolon, Andrea; Islam, Ausrafal; George, Acty; Sivananinthaperumal, Balachandran; Daszak, Peter; Newman, Scott H

    2014-10-01

    Satellite-based tracking of migratory waterfowl is an important tool for understanding the potential role of wild birds in the long-distance transmission of highly pathogenic avian influenza. However, employing this technique on a continental scale is prohibitively expensive. This study explores the utility of stable isotope ratios in feathers in examining both the distances traveled by migratory birds and variation in migration behavior. We compared the satellite-derived movement data of 22 ducks from 8 species captured at wintering areas in Bangladesh, Turkey, and Hong Kong with deuterium ratios (δD) of these and other individuals captured at the same locations. We derived likely molting locations from the satellite tracking data and generated expected isotope ratios based on an interpolated map of δD in rainwater. Although δD was correlated with the distance between wintering and molting locations, surprisingly, measured δD values were not correlated with either expected values or latitudes of molting sites. However, population-level parameters derived from the satellite-tracking data, such as mean distance between wintering and molting locations and variation in migration distance, were reflected by means and variation of the stable isotope values. Our findings call into question the relevance of the rainfall isotope map for Asia for linking feather isotopes to molting locations, and underscore the need for extensive ground truthing in the form of feather-based isoscapes. Nevertheless, stable isotopes from feathers could inform disease models by characterizing the degree to which regional breeding populations interact at common wintering locations. Feather isotopes also could aid in surveying wintering locations to determine where high-resolution tracking techniques (e.g. satellite tracking) could most effectively be employed. Moreover, intrinsic markers such as stable isotopes offer the only means of inferring movement information from birds that have died

  5. Bird migration and avian influenza: a comparison of hydrogen stable isotopes and satellite tracking methods

    USGS Publications Warehouse

    Bridge, Eli S.; Kelly, Jeffrey F.; Xiao, Xiangming; Takekawa, John Y.; Hill, Nichola J.; Yamage, Mat; Haque, Enam Ul; Islam, Mohammad Anwarul; Mundkur, Taej; Yavuz, Kiraz Erciyas; Leader, Paul; Leung, Connie Y.H.; Smith, Bena; Spragens, Kyle A.; Vandegrift, Kurt J.; Hosseini, Parviez R.; Saif, Samia; Mohsanin, Samiul; Mikolon, Andrea; Islam, Ausrafal; George, Acty; Sivananinthaperumal, Balachandran; Daszak, Peter; Newman, Scott H.

    2014-01-01

    Satellite-based tracking of migratory waterfowl is an important tool for understanding the potential role of wild birds in the long-distance transmission of highly pathogenic avian influenza. However, employing this technique on a continental scale is prohibitively expensive. This study explores the utility of stable isotope ratios in feathers in examining both the distances traveled by migratory birds and variation in migration behavior. We compared the satellite-derived movement data of 22 ducks from 8 species captured at wintering areas in Bangladesh, Turkey, and Hong Kong with deuterium ratios (δD) in the feathers of these and other individuals captured at the same locations. We derived likely molting locations from the satellite tracking data and generated expected isotope ratios based on an interpolated map of δD in rainwater. Although δD was correlated with the distance between wintering and molting locations, surprisingly, measured δD values were not correlated with either expected values or latitudes of molting sites. However, population-level parameters derived from the satellite-tracking data, such as mean distance between wintering and molting locations and variation in migration distance, were reflected by means and variation of the stable isotope values. Our findings call into question the relevance of the rainfall isotope map for Asia for linking feather isotopes to molting locations, and underscore the need for extensive ground truthing in the form of feather-based isoscapes. Nevertheless, stable isotopes from feathers could inform disease models by characterizing the degree to which regional breeding populations interact at common wintering locations. Feather isotopes also could aid in surveying wintering locations to determine where high-resolution tracking techniques (e.g. satellite tracking) could most effectively be employed. Moreover, intrinsic markers such as stable isotopes offer the only means of inferring movement information from

  6. METHOD FOR PRODUCING ISOTOPIC METHANES FROM LITHIUM CARBONATE AND LITHIUM HYDRIDE

    DOEpatents

    Frazer, J.W.

    1959-10-27

    A process is descrlbed for the production of methane and for the production of methane containing isotopes of hydrogen and/or carbon. Finely divided lithium hydrlde and litldum carbonate reactants are mixed in intimate contact and subsequently compacted under pressures of from 5000 to 60,000 psl. The compacted lithium hydride and lithium carbenate reactunts are dispised in a gas collecting apparatus. Subsequently, the compact is heated to a temperature in the range 350 to 400 deg C whereupon a solid-solid reaction takes place and gaseous methane is evolved. The evolved methane is contaminated with gaseous hydrogen and a very small amount of CO/sub 2/; however, the desired methane product is separated from sald impurities by well known chemical processes, e.g., condensation in a cold trap. The product methane contalns isotopes of carbon and hydrogen, the Isotopic composition being determined by the carbon isotopes originally present In the lithium carbonate and the hydrogen isotopes originally present in the lithium hydride.

  7. Torque equilibrium attitude control for Skylab reentry

    NASA Technical Reports Server (NTRS)

    Glaese, J. R.; Kennel, H. F.

    1979-01-01

    All the available torque equilibrium attitudes (most were useless from the standpoint of lack of electrical power) and the equilibrium seeking method are presented, as well as the actual successful application during the 3 weeks prior to Skylab reentry.

  8. A method of calculating of the thermodynamic properties and the composition of the explosion products of hydrocarbons and air under partial chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Shargatov, V. A.

    2016-11-01

    We examined the approximate method to calculate composition and thermodynamic parameters of hydrocarbons-air nonequilibrium explosion products based on the assumption of the existence of a partial chemical equilibrium. With excellent accuracy of calculating thermodynamic properties and species mass fraction the respective stiff system of detailed kinetics differential equations can be replaced by the one differential equation or the two differential equations and a system of algebraic equations. This method is always consistent with the detailed kinetic mechanism. The constituent equations of the method were derived and the respective computer code written. We examine the applicability of the method by solving the test problem. The proposed method simulation results are in excellent agreement with the detailed kinetics model results corresponding the stiff ordinary differential equation solver including NO time histories.

  9. The molecular yo-yo method: Live jump detection improves throughput of single-molecule force spectroscopy for out-of-equilibrium transitions

    NASA Astrophysics Data System (ADS)

    Mack, A. H.; Schlingman, D. J.; Kamenetska, M.; Collins, R.; Regan, L.; Mochrie, S. G. J.

    2013-08-01

    By monitoring multiple molecular transitions, force-clamp, and trap-position-clamp methods have led to precise determinations of the free energies and free energy landscapes for molecular states populated in equilibrium at the same or similar forces. Here, we present a powerful new elaboration of the force-clamp and force-jump methods, applicable to transitions far from equilibrium. Specifically, we have implemented a live jump detection and force-clamp algorithm that intelligently adjusts and maintains the force on a single molecule in response to the measured state of that molecule. We are able to collect hundreds of individual molecular transitions at different forces, many times faster than previously, permitting us to accurately determine force-dependent lifetime distributions and reaction rates. Application of our method to unwinding and rewinding the nucleosome inner turn, using optical tweezers reveals experimental lifetime distributions that comprise a statistically meaningful number of transitions, and that are accurately single exponential. These measurements significantly reduce the error in the previously measured rates, and demonstrate the existence of a single, dominant free energy barrier at each force studied. A key benefit of the molecular yo-yo method for nucleosomes is that it reduces as far as possible the time spent in the tangentially bound state, which minimizes the loss of nucleosomes by dissociation.

  10. The molecular yo-yo method: live jump detection improves throughput of single-molecule force spectroscopy for out-of-equilibrium transitions.

    PubMed

    Mack, A H; Schlingman, D J; Kamenetska, M; Collins, R; Regan, L; Mochrie, S G J

    2013-08-01

    By monitoring multiple molecular transitions, force-clamp, and trap-position-clamp methods have led to precise determinations of the free energies and free energy landscapes for molecular states populated in equilibrium at the same or similar forces. Here, we present a powerful new elaboration of the force-clamp and force-jump methods, applicable to transitions far from equilibrium. Specifically, we have implemented a live jump detection and force-clamp algorithm that intelligently adjusts and maintains the force on a single molecule in response to the measured state of that molecule. We are able to collect hundreds of individual molecular transitions at different forces, many times faster than previously, permitting us to accurately determine force-dependent lifetime distributions and reaction rates. Application of our method to unwinding and rewinding the nucleosome inner turn, using optical tweezers reveals experimental lifetime distributions that comprise a statistically meaningful number of transitions, and that are accurately single exponential. These measurements significantly reduce the error in the previously measured rates, and demonstrate the existence of a single, dominant free energy barrier at each force studied. A key benefit of the molecular yo-yo method for nucleosomes is that it reduces as far as possible the time spent in the tangentially bound state, which minimizes the loss of nucleosomes by dissociation.

  11. Uniform deposition of uranium hexafluoride (UF6): Standardized mass deposits and controlled isotopic ratios using a thermal fluorination method

    SciTech Connect

    McNamara, Bruce K.; O’Hara, Matthew J.; Casella, Andrew M.; Carter, Jennifer C.; Addleman, R. Shane; MacFarlan, Paul J.

    2016-07-01

    Abstract: We report a convenient method for the generation of volatile uranium hexafluoride (UF6) from solid uranium oxides and other uranium compounds, followed by uniform deposition of low levels of UF6 onto sampling coupons. Under laminar flow conditions, UF6 is shown to interact with surfaces within the chamber to a highly predictable degree. We demonstrate the preparation of uranium deposits that range between ~0.01 and 470±34 ng∙cm-2. The data suggest the method can be extended to creating depositions at the sub-picogram∙cm-2 level. Additionally, the isotopic composition of the deposits can be customized by selection of the uranium source materials. We demonstrate a layering technique whereby two uranium solids, each with a different isotopic composition, are employed to form successive layers of UF6 on a surface. The result is an ultra-thin deposit of UF6 that bears an isotopic signature that is a composite of the two uranium sources. The reported deposition method has direct application to the development of unique analytical standards for nuclear safeguards and forensics.

  12. New method for the measurement of osmium isotopes applied to a New Zealand Cretaceous/Tertiary boundary shale

    USGS Publications Warehouse

    Lichte, F.E.; Wilson, S.M.; Brooks, R.R.; Reeves, R.D.; Holzbecher, J.; Ryan, D.E.

    1986-01-01

    The determination of osmium content and isotopic abundances in geological materials has received increasing attention in recent years following the proposal of Alvarez et al.1 that mass extinctions at the end of the Cretaceous period were caused by the impact of a large (???10km) meteorite which left anomalously high iridium levels as a geochemical signature in the boundary shales. Here we report a new and simple method for measuring osmium in geological materials, involving fusion of the sample with sodium peroxide, distillation of the osmium as the tetroxide using perchloric acid, extraction into chloroform, and absorption of the chloroform extract onto graphite powder before instrumental neutron activation analysis. In a variant of this technique, the chloroform extract is back-extracted into an aqueous phase and the osmium isotopes are determined by plasma-source mass spectrometry (ICPMS). We have used this method on the Woodside Creek (New Zealand) Cretaceous/Tertiary boundary clay and have obtained the first osmium content (6g ng g-1) for this material. The 187Os/186Os ratio is 1.12??0.16, showing a typical non-crustal signature. This combined distillation-extraction- ICPMS method will prove to be useful for measuring osmium isotopes in other geological materials. ?? 1986 Nature Publishing Group.

  13. An upwind, kinetic flux-vector splitting method for flows in chemical and thermal non-equilibrium

    NASA Technical Reports Server (NTRS)

    Eppard, W. M.; Grossman, B.

    1993-01-01

    We have developed new upwind kinetic difference schemes for flows with non-equilibrium thermodynamics and chemistry. These schemes are derived from the Boltzmann equation with the resulting Euler schemes developed as moments of the discretized Boltzmann scheme with a locally Maxwellian velocity distribution. Splitting the velocity distribution at the Boltzmann level is seen to result in a flux-split Euler scheme and is called Kinetic Flux Vector Splitting (KFVS). Extensions to flows with finite-rate chemistry and vibrational relaxation is accomplished utilizing nonequilibrium kinetic theory. Computational examples are presented comparing KFVS with the schemes of Van Leer and Roe for a quasi-one-dimensional flow through a supersonic diffuser, inviscid flow through two-dimensional inlet, and viscous flow over a cone at zero angle-of-attack. Calculations are also shown for the transonic flow over a bump in a channel and the transonic flow over an NACA 0012 airfoil. The results show that even though the KFVS scheme is a Riemann solver at the kinetic level, its behavior at the Euler level is more similar to the existing flux-vector splitting algorithms than to the flux-difference splitting scheme of Roe.

  14. Quantifying the ion atmosphere of unfolded, single-stranded nucleic acids using equilibrium dialysis and single-molecule methods

    PubMed Central

    Jacobson, David R.; Saleh, Omar A.

    2016-01-01

    To form secondary structure, nucleic acids (NAs) must overcome electrostatic strand–strand repulsion, which is moderated by the surrounding atmosphere of screening ions. The free energy of NA folding therefore depends on the interactions of this ion atmosphere with both the folded and unfolded states. We quantify such interactions using the preferential ion interaction coefficient or ion excess: the number of ions present near the NA in excess of the bulk concentration. The ion excess of the folded, double-helical state has been extensively studied; however, much less is known about the salt-dependent ion excess of the unfolded, single-stranded state. We measure this quantity using three complementary approaches: a direct approach of Donnan equilibrium dialysis read out by atomic emission spectroscopy and two indirect approaches involving either single-molecule force spectroscopy or existing thermal denaturation data. The results of these three approaches, each involving an independent experimental technique, are in good agreement. Even though the single-stranded NAs are flexible polymers that are expected to adopt random-coil configurations, we find that their ion atmosphere is quantitatively described by rod-like models that neglect large-scale conformational freedom, an effect that we explain in terms of the competition between the relevant structural and electrostatic length scales. PMID:27036864

  15. The equilibrium shape of fluid-fluid interfaces: derivation and a new numerical method for Young's and Young-Laplace equations.

    PubMed

    Soligno, Giuseppe; Dijkstra, Marjolein; van Roij, René

    2014-12-28

    Many physical problems require explicit knowledge of the equilibrium shape of the interface between two fluid phases. Here, we present a new numerical method which is simply implementable and easily adaptable for a wide range of problems involving capillary deformations of fluid-fluid interfaces. We apply a simulated annealing algorithm to find the interface shape that minimizes the thermodynamic potential of the system. First, for completeness, we provide an analytical proof that minimizing this potential is equivalent to solving the Young-Laplace equation and the Young law. Then, we illustrate our numerical method showing two-dimensional results for fluid-fluid menisci between vertical or inclined walls and curved surfaces, capillary interactions between vertical walls, equilibrium shapes of sessile heavy droplets on a flat horizontal solid surface, and of droplets pending from flat or curved solid surfaces. Finally, we show illustrative three-dimensional results to point out the applicability of the method to micro- or nano-particles adsorbed at a fluid-fluid interface.

  16. The equilibrium shape of fluid-fluid interfaces: Derivation and a new numerical method for Young’s and Young-Laplace equations

    SciTech Connect

    Soligno, Giuseppe; Roij, René van; Dijkstra, Marjolein

    2014-12-28

    Many physical problems require explicit knowledge of the equilibrium shape of the interface between two fluid phases. Here, we present a new numerical method which is simply implementable and easily adaptable for a wide range of problems involving capillary deformations of fluid-fluid interfaces. We apply a simulated annealing algorithm to find the interface shape that minimizes the thermodynamic potential of the system. First, for completeness, we provide an analytical proof that minimizing this potential is equivalent to solving the Young-Laplace equation and the Young law. Then, we illustrate our numerical method showing two-dimensional results for fluid-fluid menisci between vertical or inclined walls and curved surfaces, capillary interactions between vertical walls, equilibrium shapes of sessile heavy droplets on a flat horizontal solid surface, and of droplets pending from flat or curved solid surfaces. Finally, we show illustrative three-dimensional results to point out the applicability of the method to micro- or nano-particles adsorbed at a fluid-fluid interface.

  17. Continuous flow stable isotope methods for study of δ13C fractionation during halomethane production and degradation

    USGS Publications Warehouse

    Kalin, Robert M.; Hamilton, John T.G.; Harper, David B.; Miller, Laurence G.; Lamb, Clare; Kennedy, James T.; Downey, Angela; McCauley, Sean; Goldstein, Allen H.

    2001-01-01

    Gas chromatography/mass spectrometry/isotope ratio mass spectrometry (GC/MS/IRMS) methods for δ13C measurement of the halomethanes CH3Cl, CH3Br, CH3I and methanethiol (CH3SH) during studies of their biological production, biological degradation, and abiotic reactions are presented. Optimisation of gas chromatographic parameters allowed the identification and quantification of CO2, O2, CH3Cl, CH3Br, CH3I and CH3SH from a single sample, and also the concurrent measurement of δ13C for each of the halomethanes and methanethiol. Precision of δ13C measurements for halomethane standards decreased (±0.3, ±0.5 and ±1.3‰) with increasing mass (CH3Cl, CH3Br, CH3I, respectively). Given that carbon isotope effects during biological production, biological degradation and some chemical (abiotic) reactions can be as much as 100‰, stable isotope analysis offers a precise method to study the global sources and sinks of these halogenated compounds that are of considerable importance to our understanding of stratospheric ozone destruction. 

  18. Method for the isolation of citric acid and malic acid in Japanese apricot liqueur for carbon stable isotope analysis.

    PubMed

    Akamatsu, Fumikazu; Hashiguchi, Tomokazu; Hisatsune, Yuri; Oe, Takaaki; Kawao, Takafumi; Fujii, Tsutomu

    2017-02-15

    A method for detecting the undeclared addition of acidic ingredients is required to control the authenticity of Japanese apricot liqueur. We developed an analytical procedure that minimizes carbon isotope discrimination for measurement of the δ(13)C values of citric and malic acid isolated from Japanese apricot liqueur. Our results demonstrated that freeze-drying is preferable to nitrogen spray-drying, because it does not significantly affect the δ(13)C values of citric acid and results in smaller isotope discrimination for malic acid. Both 0.1% formic acid and 0.2% phosphoric acid are acceptable HPLC mobile phases for the isolation of citric and malic acid, although the δ(13)C values of malic acid exhibited relatively large variation compared with citric acid following isolation using either mobile phase. The developed procedure allows precise δ(13)C measurements of citric and malic acid isolated from Japanese apricot liqueur.

  19. Site-Specific Carbon Isotopes in Organics

    NASA Astrophysics Data System (ADS)

    Piasecki, A.; Eiler, J. M.

    2012-12-01

    Natural organic molecules exhibit a wide range of internal site-specific isotope variation (i.e., molecules with same isotopic substitution type but different site). Such variations are generally unconstrained by bulk isotopic measurements. If known, site-specific variations might constrain temperatures of equilibrium, mechanisms of formation or consumption reactions, and possibly other details. For example, lipids can exhibit carbon isotope differences of up to 30‰ between adjacent carbon sites as a result of fractionations arising during decarboxylation of pyruvate and other steps in lipid biosynthesis(1). We present a method for site-specific carbon isotope analysis of propane, based on high-resolution, multi-collector gas source mass spectrometry, using a novel prototype instrument - the Thermo MAT 253 Ultra. This machine has an inlet system and electron bombardment ion source resembling those in conventional stable isotope gas source mass spectrometers, and the energy filter, magnet, and detector array resembling those in multi-collector ICPMS and TIMS. The detector array has 7 detector positions, 6 of which are movable, and each of which can collect ions with either a faraday cup (read through amplifiers ranging from 107-1012 ohms) or an SEM. High mass resolving power (up to 27,000, MRP = M/dM definition) is achieved through a narrow entrance slit, adjustable from 250 to 5 μm. Such resolution can cleanly separate isobaric interferences between isotopologues of organic molecules having the same cardinal mass (e.g., 13CH3 and 12CH2D). We use this technology to analyze the isotopologues and fragments of propane, and use such data to solve for the site-specific carbon isotope fractionation. By measuring isotopologues of both the one-carbon (13CH3) and the two-carbon (13C12CH4) fragment ion, we can solve for both bulk δ13C and the difference in δ13C between the terminal and central carbon position. We tested this method by analyzing mixtures between natural

  20. Organic Tank Safety Project: development of a method to measure the equilibrium water content of Hanford organic tank wastes and demonstration of method on actual waste

    SciTech Connect

    Scheele, R.D.; Bredt, P.R.; Sell, R.L.

    1996-09-01

    Some of Hanford`s underground waste storage tanks contain Organic- bearing high level wastes that are high priority safety issues because of potentially hazardous chemical reactions of organics with inorganic oxidants in these wastes such as nitrates and nitrites. To ensure continued safe storage of these wastes, Westinghouse Hanford Company has placed affected tanks on the Organic Watch List and manages them under special rules. Because water content has been identified as the most efficient agent for preventing a propagating reaction and is an integral part of the criteria developed to ensure continued safe storage of Hanford`s organic-bearing radioactive tank wastes, as part of the Organic Tank Safety Program the Pacific Northwest National Laboratory developed and demonstrated a simple and easily implemented procedure to determine the equilibrium water content of these potentially reactive wastes exposed to the range of water vapor pressures that might be experienced during the wastes` future storage. This work focused on the equilibrium water content and did not investigate the various factors such as @ ventilation, tank surface area, and waste porosity that control the rate that the waste would come into equilibrium, with either the average Hanford water partial pressure 5.5 torr or other possible water partial pressures.

  1. Improved curve fits for the thermodynamic properties of equilibrium air suitable for numerical computation using time-dependent or shock-capturing methods, part 1

    NASA Technical Reports Server (NTRS)

    Tannehill, J. C.; Mugge, P. H.

    1974-01-01

    Simplified curve fits for the thermodynamic properties of equilibrium air were devised for use in either the time-dependent or shock-capturing computational methods. For the time-dependent method, curve fits were developed for p = p(e, rho), a = a(e, rho), and T = T(e, rho). For the shock-capturing method, curve fits were developed for h = h(p, rho) and T = T(p, rho). The ranges of validity for these curves fits were for temperatures up to 25,000 K and densities from 10 to the minus 7th power to 10 to the 3d power amagats. These approximate curve fits are considered particularly useful when employed on advanced computers such as the Burroughs ILLIAC 4 or the CDC STAR.

  2. Modification of a method-of-characteristics solute-transport model to incorporate decay and equilibrium-controlled sorption or ion exchange

    USGS Publications Warehouse

    Goode, D.J.; Konikow, L.F.

    1989-01-01

    The U.S. Geological Survey computer model of two-dimensional solute transport and dispersion in ground water (Konikow and Bredehoeft, 1978) has been modified to incorporate the following types of chemical reactions: (1) first-order irreversible rate-reaction, such as radioactive decay; (2) reversible equilibrium-controlled sorption with linear, Freundlich, or Langmuir isotherms; and (3) reversible equilibrium-controlled ion exchange for monovalent or divalent ions. Numerical procedures are developed to incorporate these processes in the general solution scheme that uses method-of- characteristics with particle tracking for advection and finite-difference methods for dispersion. The first type of reaction is accounted for by an exponential decay term applied directly to the particle concentration. The second and third types of reactions are incorporated through a retardation factor, which is a function of concentration for nonlinear cases. The model is evaluated and verified by comparison with analytical solutions for linear sorption and decay, and by comparison with other numerical solutions for nonlinear sorption and ion exchange.

  3. Determination of (241)Pu by the method of disturbed radioactive equilibrium using 2πα-counting and precision gamma-spectrometry.

    PubMed

    Alekseev, I; Kuzmina, T

    2016-04-01

    A simple technique is proposed for the determination of the content of (241)Pu, which is based on disturbance of radioactive equilibrium in the genetically related (237)U←(241)Pu→(241)Am decay chain of radionuclides, with the subsequent use of 2πα-counting and precision gamma-spectroscopy for monitoring the process of restoration of that equilibrium. It has been shown that the data on dynamics of accumulation of the daughter (241)Am, which were obtained from the results of measurements of α- and γ-spectra of the samples, correspond to the estimates calculated for the chain of two genetically related radionuclides, the differences in the estimates of (241)Pu radioactivity not exceeding 2%. Combining the different methods of registration (2πα-counting, semiconductor alpha- and gamma-spectrometry) enables the proposed method to be efficiently applied both for calibration of (241)Pu-sources (from several hundreds of kBq and higher) and for radioisotopic analysis of plutonium mixtures. In doing so, there is a deep purification of (241)Pu from its daughter decay products required due to unavailability of commercial detectors that could make it possible, based only on analysis of alpha-spectra, to conduct quantitative analysis of the content of (238)Pu and (241)Am.

  4. Scaled effective solvent method for predicting the equilibrium ensemble of structures with analysis of thermodynamic properties of amorphous polyethylene glycol-water mixtures.

    PubMed

    Shin, Hyeyoung; Pascal, Tod A; Goddard, William A; Kim, Hyungjun

    2013-01-24

    Water-soluble polymers such as polyethylene glycol (PEG) are critical components of industrial processes ranging from drug delivery to water purification. However, the understanding of the microscopic structure of these polymers in water and of the thermodynamics of the mixtures is limited because available experimental techniques (such as SLS and SANS) give little information about conformations and provide even the radius of gyration only in the dilute limit (<~5 wt % PEG). Computer simulations employing Monte Carlo (MC) and molecular dynamics (MD) techniques can provide an atomistic molecular structure; however, such approaches have difficulties in predicting the equilibrium polymer configurations of high-molecular-weight polymers at normal densities and in obtaining entropies and free energies directly from the MD. Here, we develop the scaled effective solvent (SES) method to predict the equilibrium ensemble of polymer configurations, which we illustrate for the case of a 20 kDa PEG (455 monomers) at a 25 wt % PEG aqueous solution (3339 waters per PEG chain). We evaluate the free energy and entropy of the members of this ensemble including explicit water, validating that it leads to average sizes (R(g)) observed experimentally and that all members of the ensemble have favorable free energies. With the SES method validated to provide well-equilibrated polymer chains in water, it should be useful for predicting ensembles of polymer chains in polymer melts and in solvents.

  5. New treatment method for boron in aqueous solutions using Mg-Al layered double hydroxide: Kinetics and equilibrium studies.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2015-08-15

    Mg-Al layered double hydroxides (LDHs) intercalated with NO3(-) (NO3 · Mg - Al LDHs) and with Cl(-) (Cl · Mg - Al LDHs) were found to take up boron from aqueous solutions. Boron was removed by anion exchange of B(OH)4(-) in solution with NO3(-) and Cl(-) intercalated in the interlayer of the LDH. Using three times the stoichiometric quantity of NO3 · Mg-Al LDH, the residual concentration of B decreased from 100 to 1.9 mg L(-1) in 120 min. Using five times the stoichiometric quantity of Cl · Mg - Al LDH, the residual concentration of B decreased from 100 to 5.6 mg L(-1) in 120 min. It must be emphasized that, in both cases, the residual concentration of B was less than the effluent standards in Japan (10 mg L(-1)). The rate-determining step of B removal by the NO3 · Mg - Al and Cl · Mg - Al LDHs was found to be chemical adsorption involving anion exchange of B(OH)4(-) with intercalated NO3(-) and Cl(-). The removal of B was well described by a pseudo second-order kinetic equation. The adsorption of B by NO3 · Mg - Al LDH and Cl · Mg - Al LDH followed a Langmuir-type adsorption. The values of the maximum adsorption and the equilibrium adsorption constant were 3.6 mmol g(-1) and 1.7, respectively, for NO3 · Mg - Al LDH, and 3.8 mmol g(-1) and 0.7, respectively, for Cl · Mg-Al LDH. The B(OH)4(-) in B(OH)4 · Mg - Al LDH produced by removal of B was found to undergo anion exchange with NO3(-) and Cl(-) in solution. The NO3 · Mg - Al and Cl · Mg - Al LDHs obtained after this regeneration treatment were able to remove B from aqueous solutions, indicating the possibility of recycling NO3 · Mg - Al and Cl · Mg - Al LDHs for B removal.

  6. Thermochemical parameters of minerals from oxygen-buffered hydrothermal equilibrium data: Method, application to annite and almandine

    USGS Publications Warehouse

    Zen, E.-A.

    1973-01-01

    Reversed univariant hydrothermal phase-equilibrium reactions, in which a redox reaction occurs and is controlled by oxygen buffers, can be used to extract thermochemical data on minerals. The dominant gaseous species present, even for relatively oxidizing buffers such as the QFM buffer, are H2O and H2; the main problem is to calculate the chemical potentials of these components in a binary mixture. The mixing of these two species in the gas phase was assumed by Eugster and Wones (1962) to be ideal; this assumption allows calculation of the chemical potentials of the two components in a binary gas mixture, using data in the literature. A simple-mixture model of nonideal mixing, such as that proposed by Shaw (1967), can also be combined with the equations of state for oxygen buffers to permit derivation of the chemical potentials of the two components. The two mixing models yield closely comparable results for the more oxidizing buffers such as the QFM buffer. For reducing buffers such as IQF, the nonideal-mixing correction can be significant and the Shaw model is better. The procedure of calculation of mineralogical thermochemical data, in reactions where hydrogen and H2O simultaneously appear, is applied to the experimental data on annite, given by Wones et al. (1971), and on almandine, given by Hsu (1968). For annite the results are: Standard entropy of formation from the elements, Sf0 (298, 1)=-283.35??2.2 gb/gf, S0 (298, 1) =+92.5 gb/gf. Gf0 (298, 1)=-1148.2??6 kcal, and Hf0 (298, 1)=-1232.7??7 kcal. For almandine, the calculation takes into account the mutual solution of FeAl2O4 (Hc) in magnetite and of Fe3O4 (Mt) in hercynite and the temperature dependence of this solid solution, as given by Turnock and Eugster (1962); the calculations assume a regular-solution model for this binary spinel system. The standard entropy of formation of almandine, Sf,A0 (298, 1) is -272.33??3 gb/gf. The third law entropy, S0 (298, 1) is +68.3??3 gb/gf, a value much less than the

  7. KHF2-CoF3 Method For Determining Oxygen Triple Isotopic Compositions Of Quartz And Biogenic Silica

    NASA Astrophysics Data System (ADS)

    Morimoto, M.; Abe, O.; Kawai, T.

    2006-12-01

    The oxygen isotopic composition in quartz and biogenic silica is an important tracer for investigating past environmental information. Quartz has been measured to clarify its origin and process that has experienced, and biogenic silica in marine or lacustrine sediments has been used as a paleoclimatic indicator of temperature and isotopic composition of water. Major extraction methods of oxygen from silicates for isotopic analysis can be classified into two methods; (1) oxidation by some fluorine compounds to yield oxygen as O2 and often followed by conversion to CO2 for conventional mass spectrometric analysis, and (2) reduction by carbon at high temperature to yield CO for introducing mass spectrometer. For fluorination, a batch method by heating an individual sample in the metallic reaction vessel has been conventionally used, then laser-based fluorination techniques have been rapidly developed recently. Commonly used reagents for the fluorination are fluorine, BrF5 and ClF3, however, they require particular attention for safety handling to avoid gas leakage. Here we have developed an alternative batch method for the fluorination using solid oxidizing reagents (fused flux of KHF2 and CoF3), and it is relatively safer for handling. In this study, required sample amount can be reduced from the original method proposed by Sakai and Honma (1967), and δ17O can be determined together with δ18O by direct O2 introduction into the mass spectrometer, without conversion to CO2. We report the system configuration and experimental procedures as well as the results on assessments of blank, precision and application to natural quartz and biogenic silica samples.

  8. INSTRUMENTS AND METHODS OF INVESTIGATION: Dynamic compression of hydrogen isotopes at megabar pressures

    NASA Astrophysics Data System (ADS)

    Trunin, Ryurik F.; Urlin, Vitalii D.; Medvedev, Aleksandr B.

    2010-09-01

    We review the results of shock compression of solid protium to the pressure 66 GPa, of liquid deuterium to 110 GPa, and of solid deuterium to 123 GPa in explosive devices of spherical geometry. The results are compared with data obtained by US scientists using traditional energy sources (explosives and light-gas guns), striker acceleration in a strong magnetic field (Z facility at Sandia), and powerful lasers (Nova at Lawrence Livermore National Laboratory (LLNL) and Omega at the Laboratory for Laser Energetics, University of Rochester). Results of density measurements of hydrogen isotopes under quasi-isentropic compression are analyzed. The absence of an anomalous increase in density under shock and quasi-isentropic compression of hydrogen isotopes is demonstrated. On the other hand, both processes exhibit a sharp change in the compression curve slopes, at the respective pressures 45 and 300 GPa.

  9. Sulfide isotope ratios as a method for examining environmental conditions leading up to the Permian-Triassic extinction

    NASA Astrophysics Data System (ADS)

    Holmes, S. E.; Stebbins, A.; Fernandes, G.; Williams, J. C.; Hannigan, R.

    2013-12-01

    The Permian-Triassic (P-T) extinction that occurred 250 million years ago has an air of mystery surrounding it. One hypothesis for this event is widespread ocean anoxia. This study focuses on using sulfide isotope ratio values (δ34S) as a method for investigating changes in the sulfur cycle leading up to the P-T boundary. The sample site for this study, Lingti 2, was deposited in the Neo-Tethys ocean, now located in the Spiti Valley region of Himichal Pradesh, India. The section consists of Permian black shale (Gungri Formation) and was sampled along strike from the base of the P-T Boundary to the base of the exposed shale at this location. Sulfide was extracted from these shales using chromium reduction. A Costech 4010 Elemental Analyzer (EA) and Isotope Ratio Mass Spectrometer (IRMS) were used to measure the δ34S values in each sample. A chemostratigraphic profile of δ34S and the variations in isotopic composition was evaluated in the context of redox state at the time of sulfide formation. Based on the idea that, under anoxic conditions, bacterial sulfate reducers fractionate sulfur isotopes (reducing 32S preferentially over 34S) and therefore depleting the 32S (and enriching 34S) in the surrounding pore waters. Episodic shifts in δ34S were seen over time. These trends, coupled with degree of pyritization and iron speciation data, suggest periods of low sulfate with intervals euxinia prior to the P-T boundary. The low organic carbon content in these shales coupled with periodic "non-marine" S/C suggest that fluctuations in redox conditions combined with low organic matter content and reduced sulfate availability limited pyrite formation.

  10. Sources of groundwater nitrate revealed using residence time and isotope methods

    SciTech Connect

    Moore, K B; Ekwurzel, B; Esser, B K; Hudson, G B; Moran, J E

    2004-10-07

    Nitrate concentrations approaching and greater than the maximum contaminant level (MCL) are impairing the viability of many groundwater basins as drinking water sources. Nitrate isotope data are effective in determining contaminant sources, especially when combined with other isotopic tracers such as stable isotopes of water and tritium-helium ages to give insight into the routes and timing of nitrate inputs to the flow system. This combination of techniques is demonstrated in Livermore, CA, where it is determined that low nitrate reclaimed wastewater predominates in the northwest, while two flowpaths with distinct nitrate sources originate in the southeast. Along the eastern flowpath, {delta}{sup 15}N values greater than 10{per_thousand} indicate that animal waste is the primary source. Diminishing concentrations over time suggest that contamination results from historical land use practices. The other flowpath begins in an area where rapid recharge, primarily of low-nitrate imported water (identified by stable isotopes of water and a tritium-helium residence time of less than 1 year), mobilizes a significant local nitrate source, bringing groundwater concentrations up to 53 mg NO{sub 3} L{sup -1}. In this area, artificial recharge of imported water via local arroyos increases the flux of nitrate to the regional aquifer. The low {delta}{sup 15}N value (3.1{per_thousand}) in this location implicates synthetic fertilizer. In addition to these anthropogenic sources, natural nitrate background levels between 15 and 20 mg NO{sub 3} L{sup -1} are found in deep wells with residence times greater than 50 years.

  11. Modeling nuclear volume isotope effects in crystals.

    PubMed

    Schauble, Edwin A

    2013-10-29

    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 (119)Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium.

  12. Modeling nuclear volume isotope effects in crystals

    NASA Astrophysics Data System (ADS)

    Schauble, Edwin A.

    2013-10-01

    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.

  13. Modeling nuclear volume isotope effects in crystals

    PubMed Central

    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

  14. Capture and isotopic exchange method for water and hydrogen isotopes on zeolite catalysts up to technical scale for pre-study of processing highly tritiated water

    SciTech Connect

    Michling, R.; Braun, A.; Cristescu, I.; Dittrich, H.; Gramlich, N.; Lohr, N.; Glugla, M.; Shu, W.; Willms, S.

    2015-03-15

    Highly tritiated water (HTW) may be generated at ITER by various processes and, due to the excessive radio toxicity, the self-radiolysis and the exceedingly corrosive property of HTW, a potential hazard is associated with its storage and process. Therefore, the capture and exchange method for HTW utilizing Molecular Sieve Beds (MSB) was investigated in view of adsorption capacity, isotopic exchange performance and process parameters. For the MSB, different types of zeolite were selected. All zeolite materials were additionally coated with platinum. The following work comprised the selection of the most efficient zeolite candidate based on detailed parametric studies during the H{sub 2}/D{sub 2}O laboratory scale exchange experiments (about 25 g zeolite per bed) at the Tritium Laboratory Karlsruhe (TLK). For the zeolite, characterization analytical techniques such as Infrared Spectroscopy, Thermogravimetry and online mass spectrometry were implemented. Followed by further investigation of the selected zeolite catalyst under full technical operation, a MSB (about 22 kg zeolite) was processed with hydrogen flow rates up to 60 mol*h{sup -1} and deuterated water loads up to 1.6 kg in view of later ITER processing of arising HTW. (authors)

  15. Effects of preservation methods of muscle tissue from upper-trophic level reef fishes on stable isotope values (δ (13)C and δ (15)N).

    PubMed

    Stallings, Christopher D; Nelson, James A; Rozar, Katherine L; Adams, Charles S; Wall, Kara R; Switzer, Theodore S; Winner, Brent L; Hollander, David J

    2015-01-01

    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 δ (13)C and δ (15)N 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 δ (15)N values in nearly all comparisons. Ethanol also had strong effects on the δ (13)C 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 and

  16. Improved methods for achieving the equilibrium number of phases in mixtures suitable for use in battery electrodes e. g. , for lithiating FeS/sub 2/

    DOEpatents

    Guidotti, R.A.

    1986-06-10

    A method is disclosed for preparing lithiated, particulate FeS/sub 2/ useful as a catholyte material in a lithium thermal battery, whereby the latter's voltage regulation properties are improved. The method comprises admixing FeS/sub 2/ and an amount of a lithium-containing compound, whereby the resultant total composition falls in an invariant region of the metallurgical phase diagram of its constituent components. Said lithium-containing compound and FeS/sub 2/ are admixed together with a solid electrolyte compatible with said catholyte, and the mixture is heated at a temperature above the melting point of said electrolyte and at which said mixture reaches its thermodynamic equilibrium number of phases.

  17. Edge equilibrium code for tokamaks

    SciTech Connect

    Li, Xujing; Drozdov, Vladimir V.

    2014-01-15

    The edge equilibrium code (EEC) described in this paper is developed for simulations of the near edge plasma using the finite element method. It solves the Grad-Shafranov equation in toroidal coordinate and uses adaptive grids aligned with magnetic field lines. Hermite finite elements are chosen for the numerical scheme. A fast Newton scheme which is the same as implemented in the equilibrium and stability code (ESC) is applied here to adjust the grids.

  18. Non-equilibrium supramolecular polymerization.

    PubMed

    Sorrenti, Alessandro; Leira-Iglesias, Jorge; Markvoort, Albert J; de Greef, Tom F A; Hermans, Thomas M

    2017-03-28

    Supramolecular polymerization has been traditionally focused on the thermodynamic equilibrium state, where one-dimensional assemblies reside at the global minimum of the Gibbs free energy. The pathway and rate to reach the equilibrium state are irrelevant, and the resulting assemblies remain unchanged over time. In the past decade, the focus has shifted to kinetically trapped (non-dissipative non-equilibrium) structures that heavily depend on the method of preparation (i.e., pathway complexity), and where the assembly rates are of key importance. Kinetic models have greatly improved our understanding of competing pathways, and shown how to steer supramolecular polymerization in the desired direction (i.e., pathway selection). The most recent innovation in the field relies on energy or mass input that is dissipated to keep the system away from the thermodynamic equilibrium (or from other non-dissipative states). This tutorial review aims to provide the reader with a set of tools to identify different types of self-assembled states that have been explored so far. In particular, we aim to clarify the often unclear use of the term "non-equilibrium self-assembly" by subdividing systems into dissipative, and non-dissipative non-equilibrium states. Examples are given for each of the states, with a focus on non-dissipative non-equilibrium states found in one-dimensional supramolecular polymerization.

  19. Accuracy of some routine method used in clinical chemistry as judged by isotope dilution-mass spectrometry

    SciTech Connect

    Bjoerkhem, I.; Bergman, A.; Falk, O.; Kallner, A.; Lantto, O.; Svensson, L.; Akerloef, E.; Blomstrand, R.

    1981-05-01

    Serum from patients was pooled, filtered, dispensed, and frozen. This pooled specimen was used for accuracy control in 64 participating laboratories in Sweden. Mean values (state-of-the-art values) were obtained for creatinine, cholesterol, glucose, urea, uric acid, and cortisol. These values were compared with values obtained with highly accurate reference methods based on isotope dilution-mass spectrometry. Differences were marked in the case of determination of creatinine and cortisol. Concerning the other components, the differences between the state-of-the-art value and the values obtained with the reference methods were negligible. Moreover, the glucose oxidase and the oxime methods for determination of glucose and urea were found to give significantly lower values than the hexokinase and urease methods, respectively. Researchers conclude that methods with a higher degree of accuracy are required for routine determination of creatinine and cortisol.

  20. Equilibrium state of anatase to rutile transformation for nano-structured Titanium Dioxide powder using polymer template method.

    NASA Astrophysics Data System (ADS)

    Dam, Tapabrata; Jena, Sidhartha S.; Pradhan, Dillip K.

    2016-02-01

    In this work we report the novel synthesis procedure of phase-pure nano-structured titania in anatase phase using polyacrylamide gel based polymer template method. The evolution of rutile phased titania with increasing temperature has also been investigated. The synthesized nano-materials are characterized using X-ray diffraction, Brunauer - Emmett - Teller surface analysis technique and Scanning electron microscopy. We have used dual phase Rietveld refinement method to analyse the X-Ray diffraction data to get clear picture of crystallographic information of the prepared samples.

  1. Adsorption and isotopic fractionation of Xe

    NASA Technical Reports Server (NTRS)

    Bernatowicz, T. J.; Podosek, F. A.

    1986-01-01

    A theoretical description of the mechanisms of isotopic fractionation arising during adsorption of noble gases in a Henry's Law pressure regime is given. Experimental data on the isotopic composition of Xe adsorbed on activated charcoal in the temperature range 220 K to 350 K are presented. Both theoretical considerations and the experimental data indicate that equilibrium adsorption does not significantly alter the isotopic structure of adsorbed structure of adsorbed noble gases. Therefore, if adsorption is responsible for the elemental noble gas pattern in meteorites and the earth, the heavy noble gas isotopic fractionation between them must have been produced prior to and by a different process than equilibrium adsorption.

  2. Stable Isotope Phenotyping via Cluster Analysis of NanoSIMS Data As a Method for Characterizing Distinct Microbial Ecophysiologies and Sulfur-Cycling in the Environment

    PubMed Central

    Dawson, Katherine S.; Scheller, Silvan; Dillon, Jesse G.; Orphan, Victoria J.

    2016-01-01

    Stable isotope probing (SIP) is a valuable tool for gaining insights into ecophysiology and biogeochemical cycling of environmental microbial communities by tracking isotopically labeled compounds into cellular macromolecules as well as into byproducts of respiration. SIP, in conjunction with nanoscale secondary ion mass spectrometry (NanoSIMS), allows for the visualization of isotope incorporation at the single cell level. In this manner, both active cells within a diverse population as well as heterogeneity in metabolism within a homogeneous population can be observed. The ecophysiological implications of these single cell stable isotope measurements are often limited to the taxonomic resolution of paired fluorescence in situ hybridization (FISH) microscopy. Here we introduce a taxonomy-independent method using multi-isotope SIP and NanoSIMS for identifying and grouping phenotypically similar microbial cells by their chemical and isotopic fingerprint. This method was applied to SIP experiments in a sulfur-cycling biofilm collected from sulfidic intertidal vents amended with 13C-acetate, 15N-ammonium, and 33S-sulfate. Using a cluster analysis technique based on fuzzy c-means to group cells according to their isotope (13C/12C, 15N/14N, and 33S/32S) and elemental ratio (C/CN and S/CN) profiles, our analysis partitioned ~2200 cellular regions of interest (ROIs) into five distinct groups. These isotope phenotype groupings are reflective of the variation in labeled substrate uptake by cells in a multispecies metabolic network dominated by Gamma- and Deltaproteobacteria. Populations independently grouped by isotope phenotype were subsequently compared with paired FISH data, demonstrating a single coherent deltaproteobacterial cluster and multiple gammaproteobacterial groups, highlighting the distinct ecophysiologies of spatially-associated microbes within the sulfur-cycling biofilm from White Point Beach, CA. PMID:27303371

  3. Lifetimes in neutron-rich Nd isotopes measured by Doppler profile method

    SciTech Connect

    Ahmad, I.; Lister, C.J.; Morss, L.R.

    1995-08-01

    Lifetimes of the rotational levels in neutron-rich even-even Nd isotopes were deduced from the analysis of the Doppler broadened line shapes. The experiment was performed at Daresbury with the Eurogam array, which at that time consisted of 45 Compton-suppressed Ge detectors and 5 Low-Energy Photon Spectrometers. The source was in the form of a 7-mm pellet which was prepared by mixing 5-mg; {sup 248}Cm and 65-mg KCl and pressing it under high pressure. Events for which three or more detectors fired were used to construct a cubic data array whose axes represented the {gamma}-ray energies and the contents of each channel the number of events with that particular combination of {gamma}-ray energies. From this cubic array, one-dimensional spectra were generated by placing gates on peaks on the other two axes. Gamma-ray spectra of even-even Nd isotopes were obtained by gating on the transitions in the complimentary Kr fragments. The gamma peaks de-exciting states with I {>=} 12 h were found to be broader than the instrumental line width due to the Doppler effect. The line shapes of they-ray peaks were fitted separately with a simple model for the feeding of the states and assuming a rotational band with constant intrinsic quadruple moment and these are shown in Fig. I-27. The quadrupole moments thus determined were found to be in good agreement with the quadrupole moments measured previously for lower spin states. Because of the success of this technique for the Nd isotopes, we intend to apply this technique to the new larger data set collected with the Eurogam II array. The results of this study were published.

  4. Calcium isotopic composition of mantle peridotites

    NASA Astrophysics Data System (ADS)

    Huang, F.; Kang, J.; Zhang, Z.

    2015-12-01

    Ca isotopes are useful to decipher mantle evolution and the genetic relationship between the Earth and chondrites. It has been observed that Ca isotopes can be fractionated at high temperature [1-2]. However, Ca isotopic composition of the mantle peridotites and fractionation mechanism are still poorly constrained. Here, we report Ca isotope composition of 12 co-existing pyroxene pairs in 10 lherzolites, 1 harzburgite, and 1 wehrlite xenoliths collected from Hainan Island (South Eastern China). Ca isotope data were measured on a Triton-TIMS using the double spike method at the Guangzhou Institute of Geochemistry, CAS. The long-term external error is 0.12‰ (2SD) based on repeated analyses of NIST SRM 915a and geostandards. δ44Ca of clinopyroxenes except that from the wehrlite ranges from 0.85‰ to 1.14‰, while opx yields a wide range from 0.98‰ up to 2.16‰. Co-existing pyroxene pairs show large ∆44Caopx-cpx (defined as δ44Caopx-δ44Cacpx) ranging from 0 to 1.23‰, reflecting equilibrium fractionation controlled by variable Ca contents in the opx. Notably, clinopyroxene of wehrlite shows extremely high δ44Ca (3.22‰). δ44Ca of the bulk lherzolites and harzburgites range from 0.86‰ to 1.14‰. This can be explained by extracting melts with slightly light Ca isotopic compositions. Finally, the high δ44Ca of the wehrlite (3.22‰) may reflect metasomatism by melt which has preferentially lost light Ca isotopes due to chemical diffusion during upwelling through the melt channel. [1] Amini et al (2009) GGR 33; [2] Huang et al (2010) EPSL 292.

  5. Practically convenient and industrially-aligned methods for iridium-catalysed hydrogen isotope exchange processes.

    PubMed

    Cochrane, A R; Idziak, C; Kerr, W J; Mondal, B; Paterson, L C; Tuttle, T; Andersson, S; Nilsson, G N

    2014-06-14

    The use of alternative solvents in the iridium-catalysed hydrogen isotope exchange reaction with developing phosphine/NHC Ir(I) complexes has identified reaction media which are more widely applicable and industrially acceptable than the commonly employed chlorinated solvent, dichloromethane. Deuterium incorporation into a variety of substrates has proceeded to deliver high levels of labelling (and regioselectivity) in the presence of low catalyst loadings and over short reaction times. The preparative outputs have been complemented by DFT studies to explore ligand orientation, as well as solvent and substrate binding energies within the catalyst system.

  6. METHOD OF AND APPARATUS FOR WITHDRAWING LIGHT ISOTOPIC PRODUCT FROM A LIQUID THERMAL DIFFUSION PLANT

    DOEpatents

    Dole, M.

    1959-09-22

    An improved process and apparatus are described for removing enriched product from the columns of a thermal diffusion plant for separation of isotopes. In the removal cycle, light product at the top cf the diffusion columns is circulated through the column tops and a shipping cylinder connected thereto unttl the concertation of enriched product in the cylinder reaches the desired point. During the removal, circulation through the bottoms is blocked bv freezing. in the diffusion cycle, the bottom portion is unfrozen, fresh feed is distributed to the bottoms of the columns, ard heavy product is withdrawn from the bottoms, while the tops of the columns are blocked by freezing.

  7. Novel Stable Isotope Methods for Assessing Changes in Seasonality of Precipitation from Sediments of Ombrotrophic Peatlands

    NASA Astrophysics Data System (ADS)

    Nichols, J. E.; Booth, R. K.; Jackson, S. T.; Pendall, E. G.; Walcott, M.; Bradley, R.; Pilcher, J.; Huang, Y.

    2007-12-01

    The seasonality of precipitation is a key but often elusive climate parameter in paleoclimate reconstructions. Sediments from ombrotrophic peatlands are excellent archives of past changes in precipitation/evaporation balance. Here we show that these peatland sediments can also be used to assess changes in the seasonality of precipitation. We have recently determined that distributions of Sphagnum and vascular plant biomarkers sensitively record changes in hydrologic balance (Nichols et al., 2006, Org. Geochem. 37, 1505-1513), but biomarker distributions alone do not offer detailed information for the changes in seasonal precipitation. In this study, we combine biomarker and compound-specific H and C isotope ratios to create a more comprehensive picture of the changing climate affecting these sensitive ombrotrophic systems. We present here two sets of downcore data from sites in Arctic Europe as well as Eastern North America. Basic paleohydrology is established using a ratio of Sphagnum to vascular plant biomarkers (C23 and C29 n-alkanes, respectively. We further describe paleohydrology using novel stable isotope proxies based on δD and δ13C measurements of Sphagnum and vascular plant biomarkers. Because Sphagnum has no vascular system and loses water directly by evaporation, Sphagnum biomarkers enriched in deuterium indicate an evaporative growing season (summer). Vascular plants use their root systems to take up water stored within the peatland, so deuterium-depleted vascular plant biomarkers should indicate increased winter recharge of the peatland. A methanotrophic symbiont living inside the Sphagnum's hyaline (water-holding) cells is more active when the Sphagnum is wet and therefore provides more 13C depleted (methane- derived) carbon dioxide for biomass production when the growing season is less evaporative. Hence, 13C depleted Sphagnum biomarkers indicate increased methanotrophy and therefore a wetter summer. We corroborate our stable isotope proxies by

  8. Methods for achieving the equilibrium number of phases in mixtures suitable for use in battery electrodes, e.g., for lithiating FeS.sub.2

    DOEpatents

    Guidotti, Ronald A.

    1988-01-01

    In a method for preparing lithiated, particulate FeS.sub.2 useful as a catholyte material in a lithium thermal battery, whereby the latter's voltage regulation properties are improved, comprising admixing FeS.sub.2 and an amount of a lithium-containing compound whereby the resultant total composition falls in an invariant region of the metallurgical phase diagram of its constituent components, an improvement comprises admixing said lithium-containing compound and FeS.sub.2 together with a solid electrolyte compatible with said catholyte, and heating the mixture at a temperature above the melting point of said electrolyte and at which said mixture reaches its thermodynamic equilibrium number of phases.

  9. Method optimization for non-equilibrium solid phase microextraction sampling of HAPs for GC/MS analysis

    NASA Astrophysics Data System (ADS)

    Zawadowicz, M. A.; Del Negro, L. A.

    2010-12-01

    Hazardous air pollutants (HAPs) are usually present in the atmosphere at pptv-level, requiring measurements with high sensitivity and minimal contamination. Commonly used evacuated canister methods require an overhead in space, money and time that often is prohibitive to primarily-undergraduate institutions. This study optimized an analytical method based on solid-phase microextraction (SPME) of ambient gaseous matrix, which is a cost-effective technique of selective VOC extraction, accessible to an unskilled undergraduate. Several approaches to SPME extraction and sample analysis were characterized and several extraction parameters optimized. Extraction time, temperature and laminar air flow velocity around the fiber were optimized to give highest signal and efficiency. Direct, dynamic extraction of benzene from a moving air stream produced better precision (±10%) than sampling of stagnant air collected in a polymeric bag (±24%). Using a low-polarity chromatographic column in place of a standard (5%-Phenyl)-methylpolysiloxane phase decreased the benzene detection limit from 2 ppbv to 100 pptv. The developed method is simple and fast, requiring 15-20 minutes per extraction and analysis. It will be field-validated and used as a field laboratory component of various undergraduate Chemistry and Environmental Studies courses.

  10. Temperature method for measuring the concentration of {sup 127}I and {sup 129}I isotopes based on laser-induced fluorescence

    SciTech Connect

    Kireev, S.V.; Shnyrev, S.L.

    1995-05-01

    A method for measuring the concentration of {sup 129}I and {sup 127}I isotopes are based on differences in the temperature behavior of the fluorescence intensity of molecular iodine isotopes is proposed. The {sup 129}I: {sup 127}I ratio, obtained with a He{sup 3}-Ne{sup 22} (633 nm) laser, was found to be not worse than 10{sup -2}. 10 refs., 2 figs.

  11. On the Use of Biomineral Oxygen Isotope Data to Identify Human Migrants in the Archaeological Record: Intra-Sample Variation, Statistical Methods and Geographical Considerations

    PubMed Central

    Lightfoot, Emma; O’Connell, Tamsin C.

    2016-01-01

    Oxygen isotope analysis of archaeological skeletal remains is an increasingly popular tool to study past human migrations. It is based on the assumption that human body chemistry preserves the δ18O of precipitation in such a way as to be a useful technique for identifying migrants and, potentially, their homelands. In this study, the first such global survey, we draw on published human tooth enamel and bone bioapatite data to explore the validity of using oxygen isotope analyses to identify migrants in the archaeological record. We use human δ18O results to show that there are large variations in human oxygen isotope values within a population sample. This may relate to physiological factors influencing the preservation of the primary isotope signal, or due to human activities (such as brewing, boiling, stewing, differential access to water sources and so on) causing variation in ingested water and food isotope values. We compare the number of outliers identified using various statistical methods. We determine that the most appropriate method for identifying migrants is dependent on the data but is likely to be the IQR or median absolute deviation from the median under most archaeological circumstances. Finally, through a spatial assessment of the dataset, we show that the degree of overlap in human isotope values from different locations across Europe is such that identifying individuals’ homelands on the basis of oxygen isotope analysis alone is not possible for the regions analysed to date. Oxygen isotope analysis is a valid method for identifying first-generation migrants from an archaeological site when used appropriately, however it is difficult to identify migrants using statistical methods for a sample size of less than c. 25 individuals. In the absence of local previous analyses, each sample should be treated as an individual dataset and statistical techniques can be used to identify migrants, but in most cases pinpointing a specific homeland should

  12. On the Use of Biomineral Oxygen Isotope Data to Identify Human Migrants in the Archaeological Record: Intra-Sample Variation, Statistical Methods and Geographical Considerations.

    PubMed

    Lightfoot, Emma; O'Connell, Tamsin C

    2016-01-01

    Oxygen isotope analysis of archaeological skeletal remains is an increasingly popular tool to study past human migrations. It is based on the assumption that human body chemistry preserves the δ18O of precipitation in such a way as to be a useful technique for identifying migrants and, potentially, their homelands. In this study, the first such global survey, we draw on published human tooth enamel and bone bioapatite data to explore the validity of using oxygen isotope analyses to identify migrants in the archaeological record. We use human δ18O results to show that there are large variations in human oxygen isotope values within a population sample. This may relate to physiological factors influencing the preservation of the primary isotope signal, or due to human activities (such as brewing, boiling, stewing, differential access to water sources and so on) causing variation in ingested water and food isotope values. We compare the number of outliers identified using various statistical methods. We determine that the most appropriate method for identifying migrants is dependent on the data but is likely to be the IQR or median absolute deviation from the median under most archaeological circumstances. Finally, through a spatial assessment of the dataset, we show that the degree of overlap in human isotope values from different locations across Europe is such that identifying individuals' homelands on the basis of oxygen isotope analysis alone is not possible for the regions analysed to date. Oxygen isotope analysis is a valid method for identifying first-generation migrants from an archaeological site when used appropriately, however it is difficult to identify migrants using statistical methods for a sample size of less than c. 25 individuals. In the absence of local previous analyses, each sample should be treated as an individual dataset and statistical techniques can be used to identify migrants, but in most cases pinpointing a specific homeland should not

  13. [Hardy-Weinberg equilibrium in genetic epidemiology].

    PubMed

    Liu, Hong; Hu, Yonghua

    2010-01-01

    Hardy-Weinberg equilibrium test is the base of genetic epidemiology. The new methods for Hardy-Weinberg equilibrium test involve: X chromosome-linked single nucleotide polymorphism Hardy-Weinberg test, inbreeding coefficient (F) test, an incomplete enumeration algorithm for an exact test of Hardy-Weinberg proportions with multiple alleles, and graphical tests for Hardy-Weinberg equilibrium based on the ternary plot. It is necessary to conduct Hardy-Weinberg equilibrium test in genetic epidemiology studies and adjust the associations as deviation of Hardy-Weinberg equilibrium occurs.

  14. Development of an enantiomer-specific stable carbon isotope analysis (ESIA) method for assessing the fate of α-hexachlorocyclo-hexane in the environment.

    PubMed

    Badea, Silviu-Laurentiu; Vogt, Carsten; Gehre, Matthias; Fischer, Anko; Danet, Andrei-Florin; Richnow, Hans-Hermann

    2011-05-30

    α-Hexachlorocyclohexane (α-HCH) is the only chiral isomer of the eight 1,2,3,4,5,6-HCHs and we have developed an enantiomer-specific stable carbon isotope analysis (ESIA) method for the evaluation of its fate in the environment. The carbon isotope ratios of the α-HCH enantiomers were determined for a commercially available α-HCH sample using a gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) system equipped with a chiral column. The GC-C-IRMS measurements revealed δ-values of -32.5 ± 0.8‰ and -32.3 ± 0.5‰ for (-) α-HCH and (+) α-HCH, respectively. The isotope ratio of bulk α-HCH was estimated to be -32.4 ± 0.6‰ which was in accordance with the δ-values obtained by GC-C-IRMS (-32.7 ± 0.2‰) and elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) of the bulk α-HCH (-32.1 ± 0.1‰). The similarity of the isotope ratio measurements of bulk α-HCH by EA-IRMS and GC-C-IRMS indicates the accuracy of the chiral GC-C-IRMS method. The linearity of the α-HCH ESIA method shows that carbon isotope ratios can be obtained for a signal size above 100 mV. The ESIA measurements exhibited standard deviations (2σ) that were mostly < ± 0.5‰. In order to test the chiral GC-C-IRMS method, the isotope compositions of individual enantiomers in biodegradation experiments of α-HCH with Clostridium pasteurianum and samples from a contaminated field site were determined. The isotopic compositions of the α-HCH enantiomers show a range of enantiomeric and isotope patterns, suggesting that enantiomeric and isotope fractionation can serve as an indicator for biodegradation and source characterization of α-HCH in the environment.

  15. A new method for collection of nitrate from fresh water and the analysis of nitrogen and oxygen isotope ratios

    USGS Publications Warehouse

    Silva, S.R.; Kendall, C.; Wilkison, D.H.; Ziegler, A.C.; Chang, Cecily C.Y.; Avanzino, R.J.

    2000-01-01

    A new method for concentrating nitrate from fresh waters for ??15N and ??18O analysis has been developed and field-tested for four years. The benefits of the method are: (1) elimination of the need to transport large volumes of water to the laboratory for processing; (2) elimination of the need for hazardous preservatives; and (3) the ability to concentrate nitrate from fresh waters. Nitrate is collected by, passing the water-sample through pre-filled, disposable, anion exchanging resin columns in the field. The columns are subsequently transported to the laboratory where the nitrate is extracted, converted to AgNO3 and analyzed for its isotope composition. Nitrate is eluted from the anion exchange columns with 15 ml of 3 M HCl. The nitrate-bearing acid eluant is neutralized with Ag2O, filtered to remove the AgCl precipitate, then freeze-dried to obtain solid AgNO3, which is then combusted to N2 in sealed quartz tubes for ?? 15N analysis. For ?? 18O analysis, aliquots of the neutralized eluant are processed further to remove non-nitrate oxygen-bearing anions and dissolved organic matter. Barium chloride is added to precipitate sulfate and phosphate; the solution is then filtered, passed through a cation exchange column to remove excess Ba2+, re-neutralized with Ag2O, filtered, agitated with activated carbon to remove dissolved organic matter and freeze-dried. The resulting AgNO3 is combusted with graphite in a closed tube to produce CO2, which is cryogenically purified and analyzed for its oxygen isotope composition. The 1?? analytical precisions for ??15N and ??18O are ?? 0.05%o and ??0.5???, respectively, for solutions of KNO3 standard processed through the entire column procedure. High concentrations of anions in solution can interfere with nitrate adsorption on the anion exchange resins, which may result in isotope fractionation of nitrogen and oxygen (fractionation experiments were conducted for nitrogen only; however, fractionation for oxygen is expected

  16. A new method for collection of nitrate from fresh water and the analysis of nitrogen and oxygen isotope ratios

    NASA Astrophysics Data System (ADS)

    Silva, S. R.; Kendall, C.; Wilkison, D. H.; Ziegler, A. C.; Chang, C. C. Y.; Avanzino, R. J.

    2000-02-01

    A new method for concentrating nitrate from fresh waters for δ15N and δ18O analysis has been developed and field-tested for four years. The benefits of the method are: (1) elimination of the need to transport large volumes of water to the laboratory for processing; (2) elimination of the need for hazardous preservatives; and (3) the ability to concentrate nitrate from fresh waters. Nitrate is collected by, passing the water-sample through pre-filled, disposable, anion exchanging resin columns in the field. The columns are subsequently transported to the laboratory where the nitrate is extracted, converted to AgNO 3 and analyzed for its isotope composition. Nitrate is eluted from the anion exchange columns with 15 ml of 3 M HCl. The nitrate-bearing acid eluant is neutralized with Ag 2O, filtered to remove the AgCl precipitate, then freeze-dried to obtain solid AgNO 3, which is then combusted to N 2 in sealed quartz tubes for δ15N analysis. For δ18O analysis, aliquots of the neutralized eluant are processed further to remove non-nitrate oxygen-bearing anions and dissolved organic matter. Barium chloride is added to precipitate sulfate and phosphate; the solution is then filtered, passed through a cation exchange column to remove excess Ba 2+, re-neutralized with Ag 2O, filtered, agitated with activated carbon to remove dissolved organic matter and freeze-dried. The resulting AgNO 3 is combusted with graphite in a closed tube to produce CO 2, which is cryogenically purified and analyzed for its oxygen isotope composition. The 1 σ analytical precisions for δ15N and δ18O are ±0.05‰ and ±0.5‰, respectively, for solutions of KNO 3 standard processed through the entire column procedure. High concentrations of anions in solution can interfere with nitrate adsorption on the anion exchange resins, which may result in isotope fractionation of nitrogen and oxygen (fractionation experiments were conducted for nitrogen only; however, fractionation for oxygen is

  17. Equilibrium cycle pin by pin transport depletion calculations with DeCART

    SciTech Connect

    Kochunas, B.; Downar, T.; Taiwo, T.

    2012-07-01

    As the Advanced Fuel Cycle Initiative (AFCI) program has matured it has become more important to utilize more advanced simulation methods. The work reported here was performed as part of the AFCI fellowship program to develop and demonstrate the capability of performing high fidelity equilibrium cycle calculations. As part of the work here, a new multi-cycle analysis capability was implemented in the DeCART code which included modifying the depletion modules to perform nuclide decay calculations, implementing an assembly shuffling pattern description, and modifying iteration schemes. During the work, stability issues were uncovered with respect to converging simultaneously the neutron flux, isotopics, and fluid density and temperature distributions in 3-D. Relaxation factors were implemented which considerably improved the stability of the convergence. To demonstrate the capability two core designs were utilized, a reference UOX core and a CORAIL core. Full core equilibrium cycle calculations were performed on both cores and the discharge isotopics were compared. From this comparison it was noted that the improved modeling capability was not drastically different in its prediction of the discharge isotopics when compared to 2-D single assembly or 2-D core models. For fissile isotopes such as U-235, Pu-239, and Pu-241 the relative differences were 1.91%, 1.88%, and 0.59%), respectively. While this difference may not seem large it translates to mass differences on the order of tens of grams per assembly, which may be significant for the purposes of accounting of special nuclear material. (authors)

  18. 25 years (1981-2005) of equilibrium-line altitude and mass-balance reconstruction on Glacier Blanc, French Alps, using remote-sensing methods and meteorological data

    NASA Astrophysics Data System (ADS)

    Rabatel, Antoine; Dedieu, Jean-Pierre; Thibert, Emmanuel; Letréguilly, Anne; Vincent, Christian

    Annual equilibrium-line altitude (ELA) and surface mass balance of Glacier Blanc, Ecrins region, French Alps, were reconstructed from a 25 year time series of satellite images (1981-2005). The remote-sensing method used was based on identification of the snowline, which is easy to discern on optical satellite images taken at the end of the ablation season. In addition, surface mass balances at the ELA were reconstructed for the same period using meteorological data from three nearby weather stations. A comparison of the two types of series reveals a correlation of r > 0.67 at the 0.01 level of significance. Furthermore, the surface mass balances obtained from remote-sensing data are consistent with those obtained from field measurements on five other French glaciers (r = 0.76, p < 0.01). Also consistent for Glacier Blanc is the total mass loss (10.8 m w.e.) over the studied period. However, the surface mass balances obtained with the remote-sensing method show lower interannual variability. Given that the remote-sensing method is based on changes in the ELA, this difference probably results from the lower sensitivity of the surface mass balance to climate parameters at the ELA.

  19. Method for detecting and correcting for isotope burn-in during long-term neutron dosimetry exposure

    DOEpatents

    Ruddy, Francis H.

    1988-01-01

    A method is described for detecting and correcting for isotope burn-in during-long term neutron dosimetry exposure. In one embodiment, duplicate pairs of solid state track recorder fissionable deposits are used, including a first, fissionable deposit of lower mass to quantify the number of fissions occuring during the exposure, and a second deposit of higher mass to quantify the number of atoms of for instance .sup.239 Pu by alpha counting. In a second embodiment, only one solid state track recorder fissionable deposit is used and the resulting higher track densities are counted with a scanning electron microscope. This method is also applicable to other burn-in interferences, e.g., .sup.233 U in .sup.232 Th or .sup.238 Pu in .sup.237 Np.

  20. Method for ultra-trace cesium isotope ratio measurements from environmental samples using thermal ionization mass spectrometry

    SciTech Connect

    Snow, Mathew S.; Snyder, Darin C.; Mann, Nick R.; White, Byron M.

    2015-05-01

    135Cs/137Cs isotope ratios can provide the age, origin and history of environmental Cs contamination. Relatively high precision 135Cs/137Cs isotope ratio measurements from samples containing femtogram quantities of 137Cs are needed to accurately track contamination resuspension and redistribution following environmental 137Cs releases; however, mass spectrometric analyses of environmental samples are limited by the large quantities of ionization inhibitors and isobaric interferences which are present at relatively high concentrations in the environment. We report a new approach for Cs purification from environmental samples. An initial ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) column provides a robust method for extracting Cs under a wide variety of sample matrices and mass loads. Cation exchange separations using a second AMP-PAN column result in more than two orders of magnitude greater Cs/Rb separation factors than commercially available strong cation exchangers. Coupling an AMP-PAN cation exchanging step to a microcation column (AG50W resin) enables consistent 2-4% (2σ) measurement errors for samples containing 3-6,000 fg 137Cs, representing the highest precision 135Cs/137Cs ratio measurements currently reported for soil samples at the femtogram level.

  1. The Sm-Nd isotopic method in the geochronology laboratory of the University of Brasília.

    PubMed

    Gioia; Pimentel

    2000-06-01

    Nd isotopes represent one of the best tools to investigate the processes involved in the evolution of the continental crust and mantle. This is due mainly to the similar geochemical behaviour of Sm and Nd, both light rare earth elements, which inhibits their fractionation during most varied geological processes. In order to carry out crustal evolution studies in central Brazil, the Sm-Nd isotopic method was implanted at the Geochronology Laboratory of the University of Brasília. The Sm-Nd separation methodology is basically that described in Richard et al. (1976), with the addition of some improvements. In this study we describe in detail the methodology used in Brasília. Precision and accuracy were checked with the international standards such as JB-3, BCR-1, BHVO-1 and La Jolla, and the following results were found: JB-3 (Nd=15.74 ppm and Sm=4.28 ppm), BCR-1 (143Nd/144Nd=0.512647+/-8, Nd=28.73 ppm and Sm=6.66 ppm), BHVO-1 (Nd=24.83 ppm and Sm=6.2 ppm) and La Jolla (143Nd/144Nd=0.511835+/-14).

  2. Solvent-based dissolution method to sample gas-phase volatile organic compounds for compound-specific isotope analysis.

    PubMed

    Bouchard, Daniel; Hunkeler, Daniel

    2014-01-17

    An investigation was carried out to develop a simple and efficient method to collect vapour samples for compound specific isotope analysis (CSIA) by bubbling vapours through an organic solvent (methanol or ethanol). The compounds tested were benzene and trichloroethylene (TCE). The dissolution efficiency was tested for different air volume injections, using flow rates ranging from 25ml/min to 150ml/min and injection periods varying between 10 and 40min. Based on the results, complete mass recovery for benzene and TCE in both solvents was observed for the flow rates of 25 and 50ml/min. However, small mass loss was observed at increased flow rate. At 150ml/min, recovery was on average 80±17% for benzene and 84±10% for TCE, respectively in methanol and ethanol. The δ(13)C data measured for benzene and TCE dissolved in both solvents were reproducible and were stable independently of the volume of air injected (up to 6L) or the flow rate used. The stability of δ(13)C values hence underlines no isotopic fractionation due to compound-solvent interaction or mass loss. The development of a novel and simple field sampling technique undertaken in this study will facilitate the application of CSIA to diverse gas-phase volatile organic compound studies, such as atmospheric emissions, soil gas or vapour intrusion.

  3. A facile method for expression and purification of 15N isotope-labeled human Alzheimer's β-amyloid peptides from E. coli for NMR-based structural analysis

    PubMed Central

    Armand, Tara; Ball, K. Aurelia; Chen, Anna; Pelton, Jeffrey G.; Wemmer, David E.; Head-Gordon, Teresa

    2016-01-01

    Alzheimer's disease (AD) is a progressive neurodegenerative disease affecting millions of people worldwide. AD is characterized by the presence of extracellular plaques composed of aggregated/oligomerized β-amyloid peptides with Aβ42 peptide representing a major isoform in the senile plaques. Given the pathological significance of Aβ42 in the progression of AD, there is considerable interest in understanding the structural ensembles for soluble monomer and oligomeric forms of Aβ42. This report describes an efficient method to express and purify high quality 15N isotope-labeled Aβ42 for structural studies by NMR. The protocol involves utilization of an auto induction system with 15N isotope labeled medium, for high-level expression of Aβ42 as a fusion with IFABP. After the over-expression of the 15N isotope-labeled IFABP-Aβ42 fusion protein in the inclusion bodies, pure 15N isotope-labeled Aβ42 peptide is obtained following a purification method that is streamlined and improved from the method originally developed for the isolation of unlabeled Aβ42 peptide (Garai et al., 2009). We obtain a final yield of ∼6 mg/L culture for 15N isotope-labeled Aβ42 peptide. Mass spectrometry and 1H–15N HSQC spectra of monomeric Aβ42 peptide validate the uniform incorporation of the isotopic label. The method described here is equally applicable for the uniform isotope labeling with 15N and 13C in Aβ42 peptide as well as its other variants including any Aβ42 peptide mutants. PMID:26231074

  4. A novel method for the quantitation of gingerol glucuronides in human plasma or urine based on stable isotope dilution assays.

    PubMed

    Schoenknecht, Carola; Andersen, Gaby; Schieberle, Peter

    2016-11-15

    The bio-active compounds of ginger (Zingiber officinale Roscoe), the gingerols, are gaining considerable attention due to their numerous beneficial health effects. In order to elucidate the physiological relevance of the ascribed effects their bioavailability has to be determined taking their metabolization into account. To quantitate in vivo generated [6]-, [8]- and [10]-gingerol glucuronides in human plasma and urine after ginger tea consumption, a simultaneous and direct liquid chromatography-tandem mass spectrometry method based on stable isotope dilution assays was established and validated. The respective references as well as the isotopically labeled substances were synthesized and characterized by mass spectrometry and NMR. Selective isolation of gingerol glucuronides from human plasma and urine by a mixed-phase anion-exchange SPE method led to recovery rates between 80.8 and 98.2%. LC-MS/MS analyses in selected reaction monitoring modus enabled a highly sensitive quantitation of gingerol glucuronides with LoQs between 3.9-9.8nmol/L in plasma and 39.3-161.1nmol/L in urine. The method precision in plasma and urine varied in the range±15%, whereas the intra-day accuracy in plasma and urine showed values between 78 and 122%. The developed method was then applied to a pilot study in which two volunteers consumed one liter ginger tea. Pharmacokinetic parameters like the maximum concentration (cmax), the time to reach cmax (tmax), area under the curve (AUC), elimination rate constant (kel) and elimination half-life (t1/2) were calculated from the concentration-time curve of each gingerol glucuronide. The obtained results will enable more detailed investigation of gingerol glucuronides as bioactives in their physiologically relevant concentrations.

  5. Isotopic Biogeochemistry

    NASA Technical Reports Server (NTRS)

    Hayes, J. M.

    1985-01-01

    An overview is provided of the biogeochemical research. The funding, productivity, personnel and facilities are reviewed. Some of the technical areas covered are: carbon isotopic records; isotopic studies of banded iron formations; isotope effects in microbial systems; studies of organic compounds in ancient sediments; and development in isotopic geochemistry and analysis.

  6. Hybrid isotope separation scheme

    DOEpatents

    Maya, J.

    1991-06-18

    A method is described for yielding selectively a desired enrichment in a specific isotope including the steps of inputting into a spinning chamber a gas from which a scavenger, radiating the gas with a wave length or frequency characteristic of the absorption of a particular isotope of the atomic or molecular gas, thereby inducing a photochemical reaction between the scavenger, and collecting the specific isotope-containing chemical by using a recombination surface or by a scooping apparatus. 2 figures.

  7. Hybrid isotope separation scheme

    DOEpatents

    Maya, Jakob

    1991-01-01

    A method of yielding selectively a desired enrichment in a specific isotope including the steps of inputting into a spinning chamber a gas from which a scavenger, radiating the gas with a wave length or frequency characteristic of the absorption of a particular isotope of the atomic or molecular gas, thereby inducing a photochemical reaction between the scavenger, and collecting the specific isotope-containing chemical by using a recombination surface or by a scooping apparatus.

  8. Development of particle induced gamma-ray emission methods for nondestructive determination of isotopic composition of boron and its total concentration in natural and enriched samples.

    PubMed

    Chhillar, Sumit; Acharya, Raghunath; Sodaye, Suparna; Pujari, Pradeep K

    2014-11-18

    We report simple particle induced gamma-ray emission (PIGE) methods using a 4 MeV proton beam for simultaneous and nondestructive determination of the isotopic composition of boron ((10)B/(11)B atom ratio) and total boron concentrations in various solid samples with natural isotopic composition and enriched with (10)B. It involves measurement of prompt gamma-rays at 429, 718, and 2125 keV from (10)B(p,αγ)(7)Be, (10)B(p, p'γ)(10)B, and (11)B(p, p'γ)(11)B reactions, respectively. The isotopic composition of boron in natural and enriched samples was determined by comparing peak area ratios corresponding to (10)B and (11)B of samples to natural boric acid standard. An in situ current normalized PIGE method, using F or Al, was standardized for total B concentration determination. The methods were validated by analyzing stoichiometric boron compounds and applied to samples such as boron carbide, boric acid, carborane, and borosilicate glass. Isotopic compositions of boron in the range of 0.247-2.0 corresponding to (10)B in the range of 19.8-67.0 atom % and total B concentrations in the range of 5-78 wt % were determined. It has been demonstrated that PIGE offers a simple and alternate method for total boron as well as isotopic composition determination in boron based solid samples, including neutron absorbers that are important in nuclear technology.

  9. Oxygen isotopes as a tracer of phosphate sources and cycling in aquatic systems (Invited)

    NASA Astrophysics Data System (ADS)

    Young, M. B.; Kendall, C.; Paytan, A.

    2013-12-01

    The oxygen isotopic composition of phosphate can provide valuable information about sources and processes affecting phosphorus as it moves through hydrologic systems. Applications of this technique in soil and water have become more common in recent years due to improvements in extraction methods and instrument capabilities, and studies in multiple aquatic environments have demonstrated that some phosphorus sources may have distinct isotopic compositions within a given system. Under normal environmental conditions, the oxygen-phosphorus bonds in dissolved inorganic phosphate (DIP) can only be broken by enzymatic activity. Biological cycling of DIP will bring the phosphate oxygen into a temperature-dependent equilibrium with the surrounding water, overprinting any existing isotopic source signals. However, studies conducted in a wide range of estuarine, freshwater, and groundwater systems have found that the phosphate oxygen is often out of biological equilibrium with the water, suggesting that it is common for at least a partial isotopic source signal to be retained in aquatic systems. Oxygen isotope analysis on various potential phosphate sources such as synthetic and organic fertilizers, animal waste, detergents, and septic/wastewater treatment plant effluents show that these sources span a wide range of isotopic compositions, and although there is considerable overlap between the source groups, sources may be isotopically distinct within a given study area. Recent soil studies have shown that isotopic analysis of phosphate oxygen is also useful for understanding microbial cycling across different phosphorus pools, and may provide insights into controls on phosphorus leaching. Combining stable isotope information from soil and water studies will greatly improve our understanding of complex phosphate cycling, and the increasing use of this isotopic technique across different environments will provide new information regarding anthropogenic phosphate inputs and

  10. Hybrid quantum and classical methods for computing kinetic isotope effects of chemical reactions in solutions and in enzymes.

    PubMed

    Gao, Jiali; Major, Dan T; Fan, Yao; Lin, Yen-Lin; Ma, Shuhua; Wong, Kin-Yiu

    2008-01-01

    A method for incorporating quantum mechanics into enzyme kinetics modeling is presented. Three aspects are emphasized: 1) combined quantum mechanical and molecular mechanical methods are used to represent the potential energy surface for modeling bond forming and breaking processes, 2) instantaneous normal mode analyses are used to incorporate quantum vibrational free energies to the classical potential of mean force, and 3) multidimensional tunneling methods are used to estimate quantum effects on the reaction coordinate motion. Centroid path integral simulations are described to make quantum corrections to the classical potential of mean force. In this method, the nuclear quantum vibrational and tunneling contributions are not separable. An integrated centroid path integral-free energy perturbation and umbrella sampling (PI-FEP/UM) method along with a bisection sampling procedure was summarized, which provides an accurate, easily convergent method for computing kinetic isotope effects for chemical reactions in solution and in enzymes. In the ensemble-averaged variational transition state theory with multidimensional tunneling (EA-VTST/MT), these three aspects of quantum mechanical effects can be individually treated, providing useful insights into the mechanism of enzymatic reactions. These methods are illustrated by applications to a model process in the gas phase, the decarboxylation reaction of N-methyl picolinate in water, and the proton abstraction and reprotonation process catalyzed by alanine racemase. These examples show that the incorporation of quantum mechanical effects is essential for enzyme kinetics simulations.

  11. Accurate Equilibrium Structures for trans-HEXATRIENE by the Mixed Estimation Method and for the Three Isomers of Octatetraene from Theory; Structural Consequences of Electron Delocalization

    NASA Astrophysics Data System (ADS)

    Craig, Norman C.; Demaison, Jean; Groner, Peter; Rudolph, Heinz Dieter; Vogt, Natalja

    2015-06-01

    An accurate equilibrium structure of trans-hexatriene has been determined by the mixed estimation method with rotational constants from 8 deuterium and carbon isotopologues and high-level quantum chemical calculations. In the mixed estimation method bond parameters are fit concurrently to moments of inertia of various isotopologues and to theoretical bond parameters, each data set carrying appropriate uncertainties. The accuracy of this structure is 0.001 Å and 0.1°. Structures of similar accuracy have been computed for the cis,cis, trans,trans, and cis,trans isomers of octatetraene at the CCSD(T) level with a basis set of wCVQZ(ae) quality adjusted in accord with the experience gained with trans-hexatriene. The structures are compared with butadiene and with cis-hexatriene to show how increasing the length of the chain in polyenes leads to increased blurring of the difference between single and double bonds in the carbon chain. In trans-hexatriene r(“C_1=C_2") = 1.339 Å and r(“C_3=C_4") = 1.346 Å compared to 1.338 Å for the “double" bond in butadiene; r(“C_2-C_3") = 1.449 Å compared to 1.454 Å for the “single" bond in butadiene. “Double" bonds increase in length; “single" bonds decrease in length.

  12. High Atomic Weight Isotope Separator.

    DTIC Science & Technology

    This patent discusses a method of separating one isotopic species of a given element from a mixture. Collisionless plasma instabilities slow down the ions and oppositely charged electrodes separate the isotopes.

  13. Laser Ablation Molecular Isotopic Spectrometry: Strontium and its isotopes

    NASA Astrophysics Data System (ADS)

    Mao, Xianglei; Bol'shakov, Alexander A.; Choi, Inhee; McKay, Christopher P.; Perry, Dale L.; Sorkhabi, Osman; Russo, Richard E.

    2011-11-01

    The experimental details are reported of Laser Ablation Molecular Isotopic Spectrometry (LAMIS) and its application for performing optical isotopic analysis of solid strontium-containing samples in ambient atmospheric air at normal pressure. The LAMIS detection method is described for strontium isotopes from samples of various chemical and isotopic compositions. The results demonstrate spectrally resolved measurements of the three individual 86Sr, 87Sr, and 88Sr isotopes that are quantified using multivariate calibration of spectra. The observed isotopic shifts are consistent with those calculated theoretically. The measured spectra of diatomic oxide and halides of strontium generated in laser ablation plasmas demonstrate the isotopic resolution and capability of LAMIS. In particular, emission spectra of SrO and SrF molecular radicals provided clean and well resolved spectral signatures for the naturally occurring strontium isotopes. A possibility is discussed of using LAMIS of strontium isotopes for radiogenic age determination.

  14. Isotope dilution/mass spectrometry of serum cholesterol with (3,4-/sup 13/C)cholesterol: proposed definitive method

    SciTech Connect

    Pelletier, O.; Wright, L.A.; Breckenridge, W.C.

    1987-08-01

    We describe a new gas-chromatographic/mass-spectrometric (GC/MS) isotope-dilution method for determination of serum cholesterol. The method has been fully optimized and documented to provide the high accuracy and precision expected for a Definitive Method. In the presence of (3,4-/sup 13/C)cholesterol, cholesteryl esters in serum are hydrolyzed under optimum conditions and the entire cholesterol pool is extracted and derivatized to silyl ethers. The cholesterol derivatives are resolved from other sterols by gas-liquid chromatography on a fused silica column, and selected ions characteristic of cholesterol and the (3,4-/sup 13/C)cholesterol are monitored with a GC/MS quandrupole system. We estimated the cholesterol content of samples by bracketing each sample with standards of comparable cholesterol concentration that also contained the (3,4-/sup 13/C)cholesterol. The procedure was highly reproducible (CV less than 0.5%), better accuracy and precision being obtained with (3,4-/sup 13/C)cholesterol than with heptadeuterated cholesterol. Mean values per gram of dry serum for one serum pool assayed by this method and that of the National Bureau of Standards differed by 0.5%. We conclude that the method satisfies the criteria for a Definitive Method.

  15. Impact-induced devolatilization and hydrogen isotopic fractionation of serpentine: Implications for planetary accretion

    NASA Technical Reports Server (NTRS)

    Tyburczy, James A.; Krishnamurthy, R. V.; Epstein, Samuel; Ahrens, Thomas J.

    1988-01-01

    Impact-induced devolatilization of porous serpentine was investigated using two independent experimental methods, the gas recovery and the solid recovery method, each yielding nearly identical results. For shock pressures near incipient devolatilization, the hydrogen isotopic composition of the evolved H2O is very close to that of the starting material. For shock pressures at which up to 12 percent impact-induced devolatilization occurs, the bulk evolved gas is significantly lower in deuterium than the starting material. There is also significant reduction of H2O to H2 in gases recovered at these higher shock pressures, probably caused by reaction of evolved H2O with the metal gas recovery fixture. Gaseous H2O-H2 isotopic fractionation suggests high temperature isotopic equilibrium between the gaseous species, indicating initiation of devolatilization at sites of greater than average energy deposition. Bulk gas-residual solid isotopic fractionations indicate nonequilibrium, kinetic control of gas-solid isotopic ratios. Impact-induced hydrogen isotopic fractionation of hydrous silicates during accretion can strongly affect the long-term planetary isotopic ratios of planetary bodies, leaving the interiors enriched in deuterium. Depending on the model used for extrapolation of the isotopic fractionation to devolatilization fractions greater than those investigated experimentally can result from this process.

  16. Shape characteristics of equilibrium and non-equilibrium fractal clusters.

    PubMed

    Mansfield, Marc L; Douglas, Jack F

    2013-07-28

    It is often difficult in practice to discriminate between equilibrium and non-equilibrium nanoparticle or colloidal-particle clusters that form through aggregation in gas or solution phases. Scattering studies often permit the determination of an apparent fractal dimension, but both equilibrium and non-equilibrium clusters in three dimensions frequently have fractal dimensions near 2, so that it is often not possible to discriminate on the basis of this geometrical property. A survey of the anisotropy of a wide variety of polymeric structures (linear and ring random and self-avoiding random walks, percolation clusters, lattice animals, diffusion-limited aggregates, and Eden clusters) based on the principal components of both the radius of gyration and electric polarizability tensor indicates, perhaps counter-intuitively, that self-similar equilibrium clusters tend to be intrinsically anisotropic at all sizes, while non-equilibrium processes such as diffusion-limited aggregation or Eden growth tend to be isotropic in the large-mass limit, providing a potential means of discriminating these clusters experimentally if anisotropy could be determined along with the fractal dimension. Equilibrium polymer structures, such as flexible polymer chains, are normally self-similar due to the existence of only a single relevant length scale, and are thus anisotropic at all length scales, while non-equilibrium polymer structures that grow irreversibly in time eventually become isotropic if there is no difference in the average growth rates in different directions. There is apparently no proof of these general trends and little theoretical insight into what controls the universal anisotropy in equilibrium polymer structures of various kinds. This is an obvious topic of theoretical investigation, as well as a matter of practical interest. To address this general problem, we consider two experimentally accessible ratios, one between the hydrodynamic and gyration radii, the other

  17. Experimental assessment of the purity of α-cellulose produced by variations of the Brendel method: Implications for stable isotope (δ13C, δ18O) dendroclimatology

    NASA Astrophysics Data System (ADS)

    Brookman, Tom; Whittaker, Thomas

    2012-09-01

    Stable isotope dendroclimatology using α-cellulose has unique potential to deliver multimillennial-scale, sub-annually resolved, terrestrial climate records. However, lengthy processing and analytical methods often preclude such reconstructions. Variants of the Brendel extraction method have reduced these limitations, providing fast, easy methods of isolating α-cellulose in some species. Here, we investigate application of Standard Brendel (SBrendel) variants to resinous soft-woods by treating samples of kauri (Agathis australis), ponderosa pine (Pinus ponderosa) and huon pine (Lagarastrobus franklinii), varying reaction vessel, temperature, boiling time and reagent volume. Numerous samples were visibly `under-processed' and Fourier Transform infrared spectroscopic (FTIR) investigation showed absorption peaks at 1520 cm-1 and ˜1600 cm-1 in those fibers suggesting residual lignin and retained resin respectively. Replicate analyses of all samples processed at high temperature yielded consistent δ13C and δ18O despite color and spectral variations. Spectra and isotopic data revealed that α-cellulose δ13C can be altered during processing, most likely due to chemical contamination from insufficient acetone removal, but is not systematically affected by methodological variation. Reagent amount, temperature and extraction time all influence δ18O, however, and our results demonstrate that different species may require different processing methods. FTIR prior to isotopic analysis is a fast and cost effective way to determine α-cellulose extract purity. Furthermore, a systematic isotopic test such as we present here can also determine sensitivity of isotopic values to methodological variables. Without these tests, isotopic variability introduced by the method could obscure or `create' climatic signals within a data set.

  18. A Computer Simulation Method for the Calculation of Equilibrium Constants for the Formation of Physical Clusters of Molecules: Application to Small Water Clusters.

    DTIC Science & Technology

    1981-08-01

    areas of chemical physics. First, the values of K 2and K 3are related to the second and third virial coefficients of the substance. Second , the theory of...equilibrium constants for dimer and trimer formation are simply related to the second and third virial coefficients . Here we discuss our choice of the Rn and...containment sphere at low temperatures. The equilibrium constant for dimer formation can be related to the second virial coefficient for the gas under

  19. Methods for modeling non-equilibrium degenerate statistics and quantum-confined scattering in 3D ensemble Monte Carlo transport simulations

    NASA Astrophysics Data System (ADS)

    Crum, Dax M.; Valsaraj, Amithraj; David, John K.; Register, Leonard F.; Banerjee, Sanjay K.

    2016-12-01

    Particle-based ensemble semi-classical Monte Carlo (MC) methods employ quantum corrections (QCs) to address quantum confinement and degenerate carrier populations to model tomorrow's ultra-scaled metal-oxide-semiconductor-field-effect-transistors. Here, we present the most complete treatment of quantum confinement and carrier degeneracy effects in a three-dimensional (3D) MC device simulator to date, and illustrate their significance through simulation of n-channel Si and III-V FinFETs. Original contributions include our treatment of far-from-equilibrium degenerate statistics and QC-based modeling of surface-roughness scattering, as well as considering quantum-confined phonon and ionized-impurity scattering in 3D. Typical MC simulations approximate degenerate carrier populations as Fermi distributions to model the Pauli-blocking (PB) of scattering to occupied final states. To allow for increasingly far-from-equilibrium non-Fermi carrier distributions in ultra-scaled and III-V devices, we instead generate the final-state occupation probabilities used for PB by sampling the local carrier populations as function of energy and energy valley. This process is aided by the use of fractional carriers or sub-carriers, which minimizes classical carrier-carrier scattering intrinsically incompatible with degenerate statistics. Quantum-confinement effects are addressed through quantum-correction potentials (QCPs) generated from coupled Schrödinger-Poisson solvers, as commonly done. However, we use these valley- and orientation-dependent QCPs not just to redistribute carriers in real space, or even among energy valleys, but also to calculate confinement-dependent phonon, ionized-impurity, and surface-roughness scattering rates. FinFET simulations are used to illustrate the contributions of each of these QCs. Collectively, these quantum effects can substantially reduce and even eliminate otherwise expected benefits of considered In0.53Ga0.47 As FinFETs over otherwise identical

  20. Sediment-air equilibrium partitioning of semi-volatile hydrophobic organic compounds. Part 1. Method development and water vapor sorption isotherm.

    PubMed

    de Seze, G; Valsaraj, K T; Reible, D D; Thibodeaux, L J

    2000-05-15

    Contaminated sediments that become exposed to air as a result of dredging and disposal in confined disposal facilities are potential sources of air pollution. A critical parameter to develop emission estimation models is the equilibrium partition coefficient of contaminants, between sediment and air. In this first of two articles, we present a method, based on gas saturation in a flowing stream, to study both the adsorption of water and semi-volatile organic compounds on a sediment from the Campus Lake, Baton Rouge, LA, USA. The experimental set-up was used to determine the adsorption isotherm for water partitioning between sediment and pore-air. A detailed characterization of the sediment surface area and pore volume was used to develop an adsorption-condensation model for predicting water sorption on sediment. The model was used to estimate the importance of water adsorption on mineral surfaces and condensation in pores. This information serves, in the accompanying second article in the series, as the basis for the modeling of the partitioning of phenanthrene, and dibenzofuran.

  1. Entropy generation for an axisymmetric MHD flow under thermal non-equilibrium in porous micro duct using a modified lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Rabhi, Raja; Amami, Bayssain; Dhahri, Hacen; Mhimid, Abdallah

    2016-12-01

    The present paper centered on a numerical investigation of irreversibility within a porous micro duct subjected to an external oriented magnetic field. At the wall, slip velocity and temperature jump are used as types of boundary conditions. The flow is described by Darcy-Brinkman-Forchheimer model. The Local Thermal Non Equilibrium (LTNE) is adopted including viscous dissipation effects into the energy equation of fluid phase. The study has been carried out for slip-flow regime for wide range of Knudsen numbers, 10-3 ≤ Kn ≤ 10-1 . The obtained governing system equations are solved using the modified Lattice Boltzmann Method (LBM). Efforts are focused on identifying the influence of magnetic field on the entropy generation and Bejan number with a change of various parameters such as Knudsen, Eckert, Biot, Darcy numbers and thermal conductivity ratio. The obtained results show that the irreversibility and the contribution of heat transfer irreversibility and fluid flow irreversibility are strongly affected by the presence of magnetic field.

  2. Kinetic and equilibrium studies for the adsorption process of cadmium(II) and copper(II) onto Pseudomonas aeruginosa using square wave anodic stripping voltammetry method.

    PubMed

    Kong, Bo; Tang, Biyu; Liu, Xiaoying; Zeng, Xiandong; Duan, Haiyan; Luo, Shenglian; Wei, Wanzhi

    2009-08-15

    A novel method for the simultaneous determination of cadmium(II) and copper(II) during the adsorption process onto Pseudomonas aeruginosa was developed. The concentration of the free metal ions was successfully detected by square wave anodic stripping voltammetry (SWASV) on the mercaptoethane sulfonate (MES) modified gold electrode, while the P. aeruginosa was efficiently avoided approaching to the electrode surface by the MES monolayer. And the anodic stripping peaks of Cd(2+) and Cu(2+) appear at -0.13 and 0.34V respectively, at the concentration range of 5-50 microM, the peak currents of SWASV present linear relationships with the concentrations of cadmium and copper respectively. As the determination of Cd(2+) and Cu(2+) was in real time and without pretreatment, the kinetic characteristics of the adsorption process were studied and all the corresponding regression parameters were obtained by fitting the electrochemical experimental data to the pseudo-second-order kinetic model. Moreover, Langmuir and Freundlich models well described the biosorption isotherms. And there were some differences in the amount of metal ion adsorbed at equilibrium (q(e)) and other kinetics parameters when the two ions coexisted were compared with the unaccompanied condition, which were also discussed in this paper. The proposed electrode system provides excellent platform for the simultaneous determination of trace metals in complex biosorption process.

  3. A validated LC-MS/MS method of total and unbound lenvatinib quantification in human serum for protein binding studies by equilibrium dialysis.

    PubMed

    Mano, Yuji; Kusano, Kazutomi

    2015-10-10

    A sensitive method for the determination of total and unbound lenvatinib (Lenvima™), a novel tyrosine kinase inhibitor, in human serum was developed for protein binding studies using an equilibrium dialysis and liquid chromatography with tandem mass spectrometry. Serum samples (0.8 mL) were dialyzed against phosphate buffered saline (PBS) in dialyzer for 18 h at 37 °C to obtain dialysate and serum for unbound and total lenvatinib, respectively. After extraction by organic solvent, separation was achieved on a Symmetry Shield RP8 column with isocratic elution of 2 mM ammonium acetate (pH 4.0)-acetonitrile (3:2, v/v) at the flow rate of 0.2 mL/min. Detection was performed using API4000 with multiple reaction monitoring mode using positive electrospray ionization. The standard curve ranged from 0.0400 to 16.0 ng/mL and 0.0800 to 400 ng/mL as lenvatinib free base in PBS and serum, respectively. Accuracy and precision in the intra- and inter-batch reproducibility study were within the acceptance criteria. Various stability assessments including bench-top, freeze/thaw, processed samples, and frozen stability confirmed that lenvatinib was stable in serum and PBS. Application to in vivo protein binding studies in clinical studies was successfully performed and results showed that lenvatinib was highly protein bound in serum.

  4. (Carbon isotope fractionation inplants)

    SciTech Connect

    O'Leary, M.H.

    1990-01-01

    The objectives of this research are: To develop a theoretical and experimental framework for understanding isotope fractionations in plants; and to develop methods for using this isotope fractionation for understanding the dynamics of CO{sub 2} fixation in plants. Progress is described.

  5. A Method for Analyzing A+2 Isotope Patterns for Use in Undergraduate Organic Courses

    ERIC Educational Resources Information Center

    Gross, Ray A.

    2007-01-01

    A novel ratio method is developed and automated for finding the bromine-chlorine-sulfur stoichiometry in the molecular formula of an unknown. This method is also useful in spectrometric analysis or beginning organic chemistry.

  6. Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

    NASA Astrophysics Data System (ADS)

    Casado, Mathieu; Landais, Amaelle; Masson-Delmotte, Valérie; Genthon, Christophe; Kerstel, Erik; Kassi, Samir; Arnaud, Laurent; Picard, Ghislain; Prie, Frederic; Cattani, Olivier; Steen-Larsen, Hans-Christian; Vignon, Etienne; Cermak, Peter

    2016-07-01

    Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require one to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow. Here, we target the isotopic composition of water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for 1 month in December 2014-January 2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading

  7. An Investigation Into the Molecular and Isotopic Composition of Diatom Frustule-Bound Organic Matter: Method Development for New Proxies

    NASA Astrophysics Data System (ADS)

    Bridoux, M. C.; Ingalls, A. E.

    2009-12-01

    Diatoms are single cell phytoplankton that are ubiquitous in marine ecosystems and are responsible for up to 40% of the carbon fixed annually in the ocean. Their intricately nanopatterned siliceous frustules are formed under the control of template organic molecules, some of which are incorporated into the frustule during growth. Several diatom frustule-based paleoproxies have been developed to exploit these microfossils because they are from a known phytoplankton source that is relatively unaltered from diagenesis. Among these proxies, diatom frustule-bound organic matter (OM) is recognized as a potentially important material for use in paleoreconstructions of past productivity (13C/12C), nutrient utilization (15N/14N) as well as to determine the radiocarbon age of sedimentary frustules (Δ14C). Despite numerous advances, diatom frustule-bound OM remains poorly characterized. Here we focus on the chemical characterization of diatom frustule-bound OM with the goal of developing molecular and compound-specific isotope methods to better reconstruct the past environments of diatom rich regions such as the Southern Ocean and the North Pacific. To do this, we 1) chemically cleaned diatom frustules, 2) dissolve them in HF to release organic compounds embedded in the frustules and 3) unambiguously characterized this organic matter by ion pairing reversed phase liquid chromatography coupled to diode array, electrospray ionization - ion trap mass spectrometry (ESI/IT-MSn) and accurate mass quadrupole time of flight mass spectrometry (Q-TOF). These analyses reveal the presence of low molecular weight, UV light absorbing compounds called mycosporine-like amino acids (MAAs) and a series of long chain polyamines (LCPAs) consisting of N-methylated derivatives of polypropyleneimine units attached to putrescine. LCPAs are known to direct silicification, while MAAs are thought to provide sunscreen to many marine organisms. The presence of these specific biomarkers in sediment

  8. Equilibrium sampling by reweighting nonequilibrium simulation trajectories.

    PubMed

    Yang, Cheng; Wan, Biao; Xu, Shun; Wang, Yanting; Zhou, Xin

    2016-03-01

    Based on equilibrium molecular simulations, it is usually difficult to efficiently visit the whole conformational space of complex systems, which are separated into some metastable regions by high free energy barriers. Nonequilibrium simulations could enhance transitions among these metastable regions and then be applied to sample equilibrium distributions in complex systems, since the associated nonequilibrium effects can be removed by employing the Jarzynski equality (JE). Here we present such a systematical method, named reweighted nonequilibrium ensemble dynamics (RNED), to efficiently sample equilibrium conformations. The RNED is a combination of the JE and our previous reweighted ensemble dynamics (RED) method. The original JE reproduces equilibrium from lots of nonequilibrium trajectories but requires that the initial distribution of these trajectories is equilibrium. The RED reweights many equilibrium trajectories from an arbitrary initial distribution to get the equilibrium distribution, whereas the RNED has both advantages of the two methods, reproducing equilibrium from lots of nonequilibrium simulation trajectories with an arbitrary initial conformational distribution. We illustrated the application of the RNED in a toy model and in a Lennard-Jones fluid to detect its liquid-solid phase coexistence. The results indicate that the RNED sufficiently extends the application of both the original JE and the RED in equilibrium sampling of complex systems.

  9. Equilibrium sampling by reweighting nonequilibrium simulation trajectories

    NASA Astrophysics Data System (ADS)

    Yang, Cheng; Wan, Biao; Xu, Shun; Wang, Yanting; Zhou, Xin

    2016-03-01

    Based on equilibrium molecular simulations, it is usually difficult to efficiently visit the whole conformational space of complex systems, which are separated into some metastable regions by high free energy barriers. Nonequilibrium simulations could enhance transitions among these metastable regions and then be applied to sample equilibrium distributions in complex systems, since the associated nonequilibrium effects can be removed by employing the Jarzynski equality (JE). Here we present such a systematical method, named reweighted nonequilibrium ensemble dynamics (RNED), to efficiently sample equilibrium conformations. The RNED is a combination of the JE and our previous reweighted ensemble dynamics (RED) method. The original JE reproduces equilibrium from lots of nonequilibrium trajectories but requires that the initial distribution of these trajectories is equilibrium. The RED reweights many equilibrium trajectories from an arbitrary initial distribution to get the equilibrium distribution, whereas the RNED has both advantages of the two methods, reproducing equilibrium from lots of nonequilibrium simulation trajectories with an arbitrary initial conformational distribution. We illustrated the application of the RNED in a toy model and in a Lennard-Jones fluid to detect its liquid-solid phase coexistence. The results indicate that the RNED sufficiently extends the application of both the original JE and the RED in equilibrium sampling of complex systems.

  10. Low-temperature, non-stoichiometric oxygen isotope exchange coupled to Fe(II)-goethite interactions

    SciTech Connect

    Frierdich, Andrew J.; Beard, Brian L.; Rosso, Kevin M.; Scherer, Michelle M.; Spicuzza, Michael J.; Valley, John W.; Johnson, Clark M.

    2015-07-01

    The oxygen isotope composition of natural iron oxide minerals has been widely used as a paleoclimate proxy. Interpretation of their stable isotope compositions, however, requires accurate knowledge of isotopic fractionation factors and an understanding of their isotopic exchange kinetics, the latter of which informs us how diagenetic processes may alter their isotopic compositions. Prior work has demonstrated that crystalline iron oxides do not significantly exchange oxygen isotopes with pure water at low temperature, which has restricted studies of isotopic fractionation factors to precipitation experiments or theoretical calculations. Using a double three-isotope method (¹⁸O-¹⁷O-¹⁶O and ⁵⁷Fe-⁵⁶Fe-⁵⁴Fe) we compare O and Fe isotope exchange kinetics, and demonstrate, for the first time, that O isotope exchange between structural O in crystalline goethite and water occurs in the presence of aqueous Fe(II) (Fe(II)aq) at ambient temperature (i.e., 22–50 °C). The three-isotope method was used to extrapolate partial exchange results to infer the equilibrium, mass-dependent isotope fractionations between goethite and water. In addition, this was combined with a reversal approach to equilibrium by reacting goethite in two unique waters that vary in composition by about 16‰ in ¹⁸O/¹⁶O ratios. Our results show that interactions between Fe(II)aq and goethite catalyzes O isotope exchange between the mineral and bulk fluid; no exchange (within error) is observed when goethite is suspended in ¹⁷O-enriched water in the absence of Fe(II)aq. In contrast, Fe(II)-catalyzed O isotope exchange is accompanied by significant changes in ¹⁸O/¹⁶O ratios. Despite significant O exchange, however, we observed disproportionate amounts of Fe versus O exchange, where Fe isotope exchange in goethite was roughly three times that of O. This disparity provides novel insight into the reactivity of oxide minerals in aqueous

  11. Recoil distance transmission method: Measurement of interaction cross sections of excited states with fast rare-isotope beams

    NASA Astrophysics Data System (ADS)

    Kobayashi, N.; Whitmore, K.; Iwasaki, H.

    2016-09-01

    The possible appearance of nuclear halos in ground and excited states close to the particle-decay threshold is of great importance in the investigation of nuclear structure and few-body correlations at the limit of stability. In order to obtain direct evidence of the halo structure manifested in nuclear excited states, we have considered a new method to measure the interaction cross sections of excited states. The combination of the transmission method and the recoil distance Doppler-shift method with a plunger device enables us to measure the number of interactions of the excited states in a target. Formulae to determine the interaction cross section are derived, and key issues to realize measurements are discussed. Dominant sources of errors are uncertainties in the excited-state lifetimes and γ-ray yields. We examine prototype experiments and perform simulations to study the impact of each uncertainty on the final result. This method provides a novel opportunity to perform cross section measurements on the excited states of rare isotopes.

  12. Dual-isotope method for determination of human zinc absorption: the use of a test meal of turkey meat

    SciTech Connect

    Flanagan, P.R.; Cluett, J.; Chamberlain, M.J.; Valberg, L.S.

    1985-01-01

    The percentage of /sup 65/Zn taken up (absorbed) from extrinsically labeled turkey meat was calculated from the amounts of /sup 65/Zn and a nonabsorbed /sup 51/Cr marker present in the body or in a single stool specimen after 1-2 d. /sup 51/CrCl/sub 3/ proved to be a suitable marker for unabsorbed /sup 65/Zn and so the early determination of /sup 65/Zn absorption was possible. With stool counting, /sup 65/Zn absorption data from first stool samples after 1-2 d were accurate as judged by correlation with the amount of /sup 65/Zn in the body 7-10 d later (retention); results from subsequent stools gave lower absorption values due to the early excretion of some absorbed /sup 65/Zn. The dual-isotope method gave reproducible results when four successive tests of zinc absorption were carried out in a group of six subjects. The average (mean +/- SD) /sup 65/Zn absorption from turkey meals containing 31 mumol (2 mg) and 46 mumol (3 mg) of zinc was 39 +/- 8% and 29 +/- 6%, respectively, measured by stool counting; /sup 65/Zn absorption and retention correlated well in both studies. A series of different beverages was given in place of water with the turkey meal. Orange juice significantly reduced /sup 65/Zn absorption and milk also showed this tendency, but tea, whiskey, wine or beer had no significant effect on the absorption of /sup 65/Zn from the turkey meal. In groups of subjects the mean ratio of /sup 65/Zn absorption from extrinsically labeled turkey meat on two occasions (1.06) was not significantly different from that of the absorption of extrinsic to intrinsic /sup 65/Zn labels (1.16). The dual-isotope technique with either stool or body counting is suitable for the rapid determination of /sup 65/Zn absorption from extrinsically labeled turkey within 2 d.

  13. Evaluating the fate of chlorinated ethenes in streambed sediments by combining stable isotope, geochemical and microbial methods

    NASA Astrophysics Data System (ADS)

    Abe, Yumiko; Aravena, Ramon; Zopfi, Jakob; Parker, Beth; Hunkeler, Daniel

    2009-06-01

    The occurrence of chlorinated ethene transformation in a streambed was investigated using concentration and carbon isotope data from water samples taken at different locations and depths within a 15 × 25 m study area across which a tetrachloroethene (PCE) plume discharges. Furthermore, it was evaluated how the degree of transformation is related to groundwater discharge rates, redox conditions, solid organic matter content (SOM) and microbial factors. Groundwater discharge rates were quantified based on streambed temperatures, and redox conditions using concentrations of dissolved redox-sensitive species. The degree of chlorinated ethene transformation was highly variable in space from no transformation to transformation beyond ethene. Complete reductive dechlorination to ethane and ethene occurred at locations with at least sulfate-reducing conditions and with a residence time in the samples streambed zone (80 cm depth) of at least 10 days. Among these locations, Dehalococcoides was detected using a PCR method where SOM contents were > 2% w/w and where transformation proceeded beyond ethene. However, it was not detected at locations with low SOM, which may cause an insufficient H 2 supply to sustain a detectably dense Dehalococcoides population. Additionally, it is possible that other organisms are responsible for the biodegradation. A microcosm study with streambed sediments demonstrated the potential of VC oxidation throughout the site even at locations without a pre-exposure to VC, consistent with the detection of the epoxyalkane:coenzyme M transferase (EaCoMT) gene involved in the degradation of chlorinated ethenes via epoxidation. In contrast, no aerobic transformation of cDCE in microcosms over a period of 1.5 years was observed. In summary, the study demonstrated that carbon isotope analysis is a sensitive tool to identify the degree of chlorinated ethene transformation even in hydrologically and geochemically complex streambed systems. In addition, it was

  14. INTERLABORATORY COMPARISON OF MASS SPECTROMETRIC METHODS FOR LEAD ISOTOPES AND TRACE ELEMENTS IN NIST SRM 1400 BONE ASH

    EPA Science Inventory

    The results of an interlaboratory comparison are reported for he lead isotope composition and for trace element concentrations in NIST SRM 1400 Bone Ash obtained using quadrupole and magnetic-sector inductively coupled plasma mass spectrometry (ICP-MS) and (for the Pb isotopes on...

  15. Including the spatial variability of metal speciation in the effect factor in life cycle impact assessment: Limits of the equilibrium partitioning method.

    PubMed

    Tromson, Clara; Bulle, Cécile; Deschênes, Louise

    2017-03-01

    In life cycle assessment (LCA), the potential terrestrial ecotoxicity effect of metals, calculated as the effect factor (EF), is usually extrapolated from aquatic ecotoxicological data using the equilibrium partitioning method (EqP) as it is more readily available than terrestrial data. However, when following the AMI recommendations (i.e. with at least enough species that represents three different phyla), there are not enough terrestrial data for which soil properties or metal speciation during ecotoxicological testing are specified to account for the influence of soil property variations on metal speciation when using this approach. Alternatively, the TBLM (Terrestrial Biotic Ligand Model) has been used to determine an EF that accounts for speciation, but is not available for metals; hence it cannot be consistently applied to metals in an LCA context. This paper proposes an approach to include metal speciation by regionalizing the EqP method for Cu, Ni and Zn with a geochemical speciation model (the Windermere Humic Aqueous Model 7.0), for 5213 soils selected from the Harmonized World Soil Database. Results obtained by this approach (EF(EqP)regionalized) are compared to the EFs calculated with the conventional EqP method, to the EFs based on available terrestrial data and to the EFs calculated with the TBLM (EF(TBLM)regionalized) when available. The spatial variability contribution of the EF to the overall spatial variability of the characterization factor (CF) has been analyzed. It was found that the EFs(EqP)regionalized show a significant spatial variability. The EFs calculated with the two non-regionalized methods (EqP and terrestrial data) fall within the range of the EFs(EqP)regionalized. The EFs(TBLM)regionalized cover a larger range of values than the EFs(EqP)regionalized but the two methods are not correlated. This paper highlights the importance of including speciation into the terrestrial EF and shows that using the regionalized EqP approach is not an

  16. Getting Freshman in Equilibrium.

    ERIC Educational Resources Information Center

    Journal of Chemical Education, 1983

    1983-01-01

    Various aspects of chemical equilibrium were discussed in six papers presented at the Seventh Biennial Conference on Chemical Education (Stillwater, Oklahoma 1982). These include student problems in understanding hydrolysis, helping students discover/uncover topics, equilibrium demonstrations, instructional strategies, and flaws to kinetic…

  17. Achieving comparability with IFCC reference method for the measurement of hemoglobin A1c by use of an improved isotope-dilution mass spectrometry method.

    PubMed

    Liu, Hong; Wong, Lingkai; Yong, Sharon; Liu, Qinde; Lee, Tong Kooi

    2015-10-01

    The development of reference measurement methods for hemoglobin A1c (HbA1c) is important for quality assurance in diabetes management. The IFCC reference method using purified proteins as calibration standards is the recommended accuracy-based reference method for the standardization of HbA1c measurement. We developed a highly precise and accurate liquid chromatography-isotope-dilution tandem mass spectrometry (LC-IDMS/MS) procedure, which can serve as an alternative accuracy-based method for HbA1c measurement. In this method, enzymatic proteolysis was applied to sample preparation, followed by LC-IDMS/MS measurement of hemoglobin A0 (HbA0) and HbA1c, using two "signature" hexapeptides for calibration. The concentrations of the signature hexapeptide calibration solutions were, in turn, determined using a hydrolysis method with HCl, followed by LC-IDMS/MS measurement using amino acid solutions as calibration standards. These solutions were gravimetrically prepared from pure amino acid certified reference materials (CRMs). The developed LC-IDMS/MS method was used in participation in an IFCC ring trial for reference laboratories (RELA 2013 and 2014) for HbA1c, where our results were compared with those using the IFCC reference method. The deviations were found to be 0.4-1.7 mmol mol(-1) [or 0.04-0.16% in National Glygohemoglobin Standardization Program (NGSP) units], revealing good comparability with the IFCC reference method. The relative expanded uncertainty of the LC-IDMS/MS was in the range of 2.6% to 2.8% (1.6% to 2.2% after converting to NGSP units). With excellent method precision, good comparability with the IFCC reference method, and a small measurement uncertainty, the developed LC-IDMS/MS method may be used as an alternative accuracy-based reference method for HbA1c measurement.

  18. A novel method of carbon dioxide clumped isotope analysis with tunable infra-red laser direct absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Prokhorov, Ivan; Kluge, Tobias; Janssen, Christof

    2016-04-01

    Precise clumped isotopes analysis of carbon dioxide opens up new horizons of atmospheric and biogeochemical research. Recent advances in laser and spectroscopic techniques provides us necessary instrumentation to access extremely low sub-permill variations of multiply-substituted isotopologues. We present an advanced analysis method of carbon dioxide clumped isotopes using direct absorption spectroscopy. Our assessments predict the ultimate precision of the new method on the sub-permill level comparable to state of the art mass spectrometry. Among the most auspicious intrinsic properties of this method we highlight genuine Δ16O13C18O and Δ16O13C18O measurements without isobaric interference, measurement cycle duration of several minutes versus hours for mass spectrometric analysis, reduced sample size of ˜ 10 μmol and high flexibility, allowing us to perform in-situ measurements. The pilot version of the instrument is being developed in an international collaboration framework between Heidelberg University, Germany and Pierre and Marie Curie University, Paris, France. It employs two continuous interband quantum cascade lasers tuned at 4.439 μm and 4.329 μm to measure doubly ( 16O13C18O, 16O13C17O) and singly ( 16O12C16O, 16O13C16O, 16O12C17O, 16O12C18O) substituted isotopologues, respectively. Two identical Herriot cells are filled with dry pure CO2 sample and reference gas at working pressure of 1 - 10 mbar. Cells provide optical path lengths of ˜ 17 m for the laser tuned at doubly substituted isotopologues lines and use a single pass for the laser tuned at the stronger lines of singly substituted isotopologues. Light outside of the gas cells is coupled into optical fiber to avoid absorption by ambient air CO2. Simulations predict sub-permill precision at working pressure of 1 mbar and room temperature stabilised at the ±10 mK level. Our prime target is to apply the proposed method for continuous in-situ analysis of CO2. We are foreseeing potential

  19. Equilibrium of KSTAR Plasma

    NASA Astrophysics Data System (ADS)

    You, K.-I.; Lee, D.-K.; Lee, S. G.; Bak, J. G.; Hahn, S. H.; Lao, L.; Kstar Team

    2011-10-01

    We have installed the EFIT code on our computing system and made some modification to reconstruct the plasma equilibrium of KSTAR (Korea Superconducting Tokamak Advanced Research). KSTAR PF and TF coil systems use a CICC (Cable-In-Conduit Conductor) type superconductor. The CICC jacket material for most PF and all TF coils is Incoloy 908, which is a magnetic material with relative magnetic permeability greater than 10 in low external field. We newly introduced Diamagnetic Loop and variational Motion Stark Effect signals to equilibrium reconstruction. In this paper, we present some results of equilibrium reconstruction with the EFIT code, assess the effects of newly introduced diagnsotics signal on the equilibrium reconstruction and compare the EFIT results with the various diagnostics data in various plasma conditions including H- and L- modes. In addition, we will show the Incoloy908 effects on the plasma equilibrium.

  20. Isotopic Methods for Determining the Relative Importance of Bioavailability Versus Trophic Position in Controlling Mercury Concentrations in Everglades Mosquitofish

    NASA Astrophysics Data System (ADS)

    Bemis, B. E.; Kendall, C.

    2007-12-01

    The concentration of mercury in fish tissues is widely used as an indicator of the magnitude of mercury contamination in aquatic ecosystems. Eastern mosquitofish (Gambusia holbrookii) is an important sentinel species used for this purpose in the varied environments of the Florida Everglades, because mosquitofish are abundant, have a short lifespan, and migrate little. Like other freshwater fish, the primary route of mercury uptake into mosquitofish tissues is through diet as bioavailable methylmercury. Yet, it is unclear whether variations in mosquitofish mercury observed across the Everglades are due primarily to differences in bioaccumulation (i.e., trophic position) or abundance of methylmercury available to the food web base. We use isotopic methods to investigate the importance of these two controls on mosquitofish mercury at the landscape scale. As part of the USEPA REMAP project, mosquitofish and periphyton were collected during September 1996 from over one hundred sites throughout the Everglades and analyzed for mercury concentration. The USGS analyzed splits of the samples for nitrogen (d15N), carbon (d13C), and sulfur (d34S) isotopic composition, to investigate the causes of mercury variations. The d15N value of tissues is often used to estimate the relative trophic positions of organisms in a food web, and should correlate positively with tissue mercury if bioaccumulation is an important control on mosquitofish mercury concentration. The d13C value can be useful for detecting differences in food web base (e.g., algal versus detrital), and thus the entry point of contaminants. Tissue d34S potentially indicates the extent of dissimilatory sulfate reduction in sediments, a process used by sulfate-reducing bacteria (SRB) during conversion of inorganic Hg(II) to bioavailable methylmercury. Because this process increases the d34S value of remaining sulfate, which enters the food web base, mosquitofish sulfur isotopes should show positive correlations with SRB

  1. Online determination of copper in aluminum alloy by microchip solvent extraction using isotope dilution ICP-MS method.

    PubMed

    Kagawa, Tsuyoshi; Ohno, Masashi; Seki, Tatsuya; Chikama, Katsumi

    2009-09-15

    Isotope dilution mass spectroscopy (IDMS)/ICP-MS combined with microchip solvent extraction was successfully applied for the online determination of copper in an aluminum alloy. The microchip solvent extraction was developed for the separation of Cu from major element, and optimal pH range was wider than that of the batchwise extraction method. The dimensions of the microchip were 30 mm x 70 mm and that of micro-channel on the microchip was 180 microm wide and 40 microm deep. The copper complex with 8-hydroxyquinoline was extracted into o-xylene at pH 5.5 and back extracted with 0.1 mol l(-1) nitric acid at flow rate of 20 microl min(-1). The total extraction efficiency (water/organic solvent/nitric acid) was around 40%. IDMS/ICP-MS was coupled with solvent extraction for precise determination of Cu. The extraction and back-extraction on the microchip took about 1s and the total measurement time for the IDMS/ICP-MS was about 40s/sample. The blank value of this method was 0.1 ng g(-1). The proposed method was used for the determination of Cu in Al standard materials (JSAC 0121-C, The Japan Society for Analytical Chemistry and 7074 Al alloy, Nippon Light Metal Co. Ltd.). The obtained analytical results are in good agreement with the certified values.

  2. An inexpensive, fast, and reliable method for vacuum extraction of soil and plant water for stable isotope analyses by mass spectrometry.

    PubMed

    Koeniger, Paul; Marshall, John D; Link, Timothy; Mulch, Andreas

    2011-10-30

    The stable isotopes of water (hydrogen and oxygen isotopes) are of utmost interest in ecology and the geosciences. In many cases water has to be extracted directly from a matrix such as soil or plant tissue before isotopes can be analyzed by mass spectrometry. Currently, the most widely used technique for water is cryogenic vacuum extraction. We present a simple and inexpensive modification of this method and document tests conducted with soils of various grain size and tree core replicates taken on four occasions during 2010. The accuracies for sandy soils are between 0.4‰ and 3‰ over a range of 21‰ and 165‰ for δ(18)O and δ(2)H, respectively. Spiking tests with water of known isotope composition were conducted with soil and tree core samples; they indicate reliable precision after an extraction time of 15 min for sandy soils. For clayey soils and tree cores, the deviations were up to 0.63‰ and 4.7‰ for δ(18)O and δ(2)H, respectively. This indicates either that the extraction time should be extended or that mechanisms different from Rayleigh fractionation play a role. The modified protocol allows a fast and reliable extraction of large numbers of water samples from soil and plant material in preparation for stable isotope analyses.

  3. Impact-induced devolatilization and hydrogen isotopic fractionation of serpentine: implications for planetary accretion.

    PubMed

    Tyburczy, J A; Krishnamurthy, R V; Epstein, S; Ahrens, T J

    1990-05-01

    The degree of impact-induced devolatilization of nonporous serpentine, porous serpentine, and deuterium-enriched serpentine was investigated using two independent experimental methods, the gas recovery method and the solid recovery method, yielding consistent results. The gas recovery method enables determination of the chemical and hydrogen isotopic composition of the recovered gases. Experiments on deuterium-enriched serpentine unambiguously identify the samples as the source of the recovered gases, as opposed to other possible contaminants. For shock pressures near incipient devolatilization (Pinitial = 5.0 GPa), the hydrogen isotopic composition of the evolved gas is similar to that of the starting material. For higher shock pressures the bulk evolved gas is significantly lower in deuterium than the starting material. There is also significant reduction of H2O to H2 in gases recovered at higher shock pressures, probably caused by reaction of evolved H2O with the metal gas recovery fixture. The hydrogen isotopic fractionation between the evolved gas and the residual solid indicates nonequilibrium, kinetic control of gas-solid isotopic ratios. In contrast, gaseous H2O-H2 isotopic fractionation suggests high temperature (800-1300 K) isotopic equilibrium between the gaseous species, indicating initiation of devolatilization at sites of greater than average energy deposition (i.e., shear bands). Impact-induced hydrogen isotopic fractionation of hydrous silicates during accretion can affect the distribution of hydrogen isotopes of planetary bodies during accretion, leaving the interiors enriched in deuterium. The significance of this process for planetary development depends on the models used for extrapolation of the observed isotopic fractionation to devolatilizations greater than those investigated experimentally and assumptions about timing and rates of protoatmosphere loss, frequency of multiple impacts, and rates of gas-solid or gas-melt isotopic re

  4. Compound-Specific Chlorine Isotope Analysis of Tetrachloromethane and Trichloromethane by Gas Chromatography-Isotope Ratio Mass Spectrometry vs Gas Chromatography-Quadrupole Mass Spectrometry: Method Development and Evaluation of Precision and Trueness.

    PubMed

    Heckel, Benjamin; Rodríguez-Fernández, Diana; Torrentó, Clara; Meyer, Armin; Palau, Jordi; Domènech, Cristina; Rosell, Mònica; Soler, Albert; Hunkeler, Daniel; Elsner, Martin

    2017-03-21

    Compound-specific chlorine isotope analysis of tetrachloromethane (CCl4) and trichloromethane (CHCl3) was explored by both, gas chromatography-isotope ratio mass spectrometry (GC-IRMS) and GC-quadrupole MS (GC-qMS), where GC-qMS was validated in an interlaboratory comparison between Munich and Neuchâtel with the same type of commercial GC-qMS instrument. GC-IRMS measurements analyzed CCl isotopologue ions, whereas GC-qMS analyzed the isotopologue ions CCl3, CCl2, CCl (of CCl4) and CHCl3, CHCl2, CHCl (of CHCl3), respectively. Lowest amount dependence (good linearity) was obtained (i) in H-containing fragment ions where interference of (35)Cl- to (37)Cl-containing ions was avoided; (ii) with tuning parameters favoring one predominant rather than multiple fragment ions in the mass spectra. Optimized GC-qMS parameters (dwell time 70 ms, 2 most abundant ions) resulted in standard deviations of 0.2‰ (CHCl3) and 0.4‰ (CCl4), which are only about twice as large as 0.1‰ and 0.2‰ for GC-IRMS. To compare also the trueness of both methods and laboratories, samples from CCl4 and CHCl3 degradation experiments were analyzed and calibrated against isotopically different reference standards for both CCl4 and CHCl3 (two of each). Excellent agreement confirms that true results can be obtained by both methods provided that a consistent set of isotopically characterized reference materials is used.

  5. Magnetospheric equilibrium with anisotropic pressure

    SciTech Connect

    Cheng, C.Z.

    1991-07-01

    Self-consistent magnetospheric equilibrium with anisotropic pressure is obtained by employing an iterative metric method for solving the inverse equilibrium equation in an optimal flux coordinate system. A method of determining plasma parallel and perpendicular pressures from either analytic particle distribution or particle distribution measured along the satellite's path is presented. The numerical results of axisymmetric magnetospheric equilibrium including the effects of finite beta, pressure anisotropy, and boundary conditions are presented for a bi-Maxwellian particle distribution. For the isotropic pressure cases, the finite beta effect produces an outward expansion of the constant magnetic flux surfaces in relation to the dipole field lines, and along the magnetic field the toroidal ring current is maximum at the magnetic equator. The effect of pressure anisotropy is found to further expand the flux surfaces outward. Along the magnetic field lines the westward ring current can be peak away from the equator due to an eastward current contribution resulting from pressure anisotropy. As pressure anisotropy increases, the peak westward current can become more singular. The outer boundary flux surface has significant effect on the magnetospheric equilibrium. For the outer flux boundary resembling dayside compressed flux surface due to solar wind pressure, the deformation of the magnetic field can be quite different from that for the outer flux boundary resembling the tail-like surface. 23 refs., 17 figs.

  6. A method for the routine determination of methylmercury in marine tissue by GC isotope dilution-ICP-MS.

    PubMed

    Valdersnes, Stig; Maage, Amund; Fliegel, Daniel; Julshamn, Kåre

    2012-01-01

    Currently, there is no legal limit for methyl mercury (MeHg) in food; thus, no standardized method for the determination of MeHg in seafood exists within the European jurisdiction. In anticipation of a future legislative limit an inductively coupled plasma isotope dilution mass spectrometry (GC-ICP-ID-MS) method was developed in collaboration with the European Standardization Organization (CEN). The method comprises spiking the tissue sample with Me201Hg, followed by decomposition with tetramethylammonium hydroxide, pH adjustment and derivatization with sodium tetraethylborate, and finally organic extraction of the derivatized MeHg in a hexane phase. Subsequently, the sample is analyzed via GC-ICP-MS and the result calculated using the ID equation. The working range of the method was 0.0005-1.321 mg/kg MeHg in marine tissue, with an internal reproducibility (RSD) of 12-1%. The method was validated based on statistical measures, such as the z-scores, using the commercially available reference materials from National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1566b, NIST SRM 2977 and National Research Council of Canada (NRCC) TORT 2, NRCC, DORM 3, NRCC DOLT 4, and European Reference Material (ERM) CE 464. Z-scores for all standard reference materials, except for NIST SRM 1566b, were better than 11.51. The wide range of marine tissues used during the validation ensures that the method will be applicable for measuring of MeHg in seafood matrixes of all kinds.

  7. Labile pools of Pb in vegetable-growing soils investigated by an isotope dilution method and its influence on soil pH.

    PubMed

    Xie, Hong; Huang, Zhi-Yong; Cao, Ying-Lan; Cai, Chao; Zeng, Xiang-Cheng; Li, Jian

    2012-08-01

    Pollution of Pb in the surface of agricultural soils is of increasing concern due to its serious impact on the plant growth and the human health through the food chain. However, the mobility, activity and bioavailability of Pb rely mainly on its various chemical species in soils. In the present study, E and L values, the labile pools of isotopically exchangeable Pb, were estimated using the method of isotope dilution in three vegetable-growing soils. The experiments involved adding a stable enriched isotope ((206)Pb > 96%) to a soil suspension and to soils in which plants are subsequently grown, the labile pools of Pb were then estimated by measuring the isotopic composition of Pb in soil solutions and in the plant tissues, respectively. In addition, the correlation of E values and soil pH was investigated at the ranges of pH 4.5-7.0. The amount of labile Pb in soils was also estimated using different single chemical extractants and a modified BCR approach. The results showed that after spiking the enriched isotopes of (206)Pb (>96%) for 24 hours an equilibration of isotopic exchanges in soil suspensions was achieved, and the isotope ratios of (208)Pb/(206)Pb measured at that time was used for calculating the E(24 h) values. The labile pools of Pb by %E(24 h) values, ranging from 53.2% to 61.7% with an average 57%, were found to be significantly higher (p < 0.05) than the values estimated with L values, single chemical extractants and the Σ(BCR) values obtained with the BCR approach, respectively. A strong negative correlation (R(2) = 0.984) between E(24 h) values and soil pH was found in the tested soil sample. The results indicate that the %E(24 h) value can more rapidly and easily predict the labile pools of Pb in soils compared with L values, but it might be readily overestimated because of the artificial soil acidity derived from the spiked isotopic tracer and the excess of spiked enriched isotopes. The results also suggest that the amounts of Pb extracted

  8. Technical considerations for the use of passive samplers to quantify the isotopic composition of NOx and NO2 using the denitrifier method

    NASA Astrophysics Data System (ADS)

    Dahal, Bigyan; Hastings, Meredith G.

    2016-10-01

    The isotopic composition of nitrogen oxides (NOx = NO + NO2) hold potential to trace emissions sources, as well as chemistry in the atmosphere. Passive samplers that collect NOx and NO2 as nitrite could provide a simple and inexpensive means by which to collect samples in a variety of environments, and we report here on several methodological considerations when using Ogawa passive collectors of NOx and NO2 for concentration analysis via colorimetric methods and isotopic analysis via the denitrifier method. Using Ogawa samplers, NOx and NO2 were collected in Providence, RI, USA (41.8°N, 71.4°W) with exposure times of seven, fourteen, twenty-one, and twenty-eight days during summer and winter in an area dominated by vehicle emissions, particularly diesel delivery trucks. Average values were -9.7 ± 0.7‰ for δ15N-NOx and -8.3 ± 0.9‰ for δ15N-NO2 based on duplicate seven, fourteen, twenty-one, and twenty-eight day exposures (n = 8) in summertime, and -11.9 ± 0.7‰ for δ15N-NOx and -6.4 ± 1.4‰ for δ15N-NO2 based on seven, fourteen, twenty-one, and twenty-eight day exposures (n = 7) in wintertime. The oxygen isotopic composition (δ18O, Δ17O) was also determined with averages of: 36.3 ± 2.4‰ for δ18O-NOx (n = 8), 50.5 ± 3.2‰ for δ18O-NO2 (n = 8), 6.2 ± 0.8‰ for Δ17O-NOx and 10.8 ± 0.6‰ for Δ17O-NO2 (n = 4) in summer; and 38.7 ± 2.9‰ for δ18O-NOx and 47.4 ± 1.2‰ for δ18O-NO2 (n = 7), 7.7 ± 1.5‰ for Δ17O-NO2 (n = 4) and 5.3 ± 1.2‰ for Δ17O-NOx (n = 5), in winter. Our isotopic results differ from previous studies that utilized passive samplers and suggest specific nitrogen and oxygen isotopic signatures associated with vehicular emissions. To collect sufficient sample for multiple isotopic analyses (e.g., 10 nmol N for δ15N and δ18O; 50 nmol N for Δ17O) the exposure time for the samplers, even in urban areas, is at least days. This necessarily results in collection of a mixture of local emissions sources, as well as

  9. A novel method to measure isotopic labeled gas-phase nitrous acid (HO15NO) in biogeochemical studies

    NASA Astrophysics Data System (ADS)

    Wu, Dianming; Kampf, Christopher; Pöschl, Ulrich; Oswald, Robert; Cui, Junfang; Ermel, Michael; Hu, Chunsheng; Trebs, Ivonne; Sörgel, Matthias

    2014-05-01

    We developed a new method (gas-phase stripping-derivatization coupled to LC-MS) to measure the 15N atom percent excess (APE) of HONO in the gas-phase. Gaseous HONO is quantitatively collected and transferred to an azo dye by the well-known Griess reaction in the Long Path Absorption Photometer (LOPAP). The reaction solutions containing the dye are collected at the outflow of the LOPAP, purified by solid-phase extraction and analyzed using high performance liquid chromatography coupled to mass spectrometry (HPLC-MS). The unlabeled azo dye (C18H19O2N5S) with a monoisotopic molecular mass of 369.41 g mol-1 can be detected as its protonated molecular ion ([M+H+], M) by HPLC-MS at a retention time of 2.8 min. Due to the natural isotope distribution M + 0, M + 1, M + 2, and M + 3 ions were considered for the calculation of the 15N APE. The optimal working range was found to be between 20 and 50% for the 15N/14N ratio. The optimum pH and solvents for extraction by SPE and potential interferences are discussed. The method has been applied for the measurement of HO15NO emissions from soil in a dynamic chamber with and without spiking 15N labeled urea. Our results confirm biogenic HONO emissions from soil as HO15NO was measured after addition of 15N urea.

  10. Detection of adulteration in honey samples added various sugar syrups with 13C/12C isotope ratio analysis method.

    PubMed

    Tosun, Murat

    2013-06-01

    Honey can be adulterated in various ways. One of the adulteration methods is the addition of different sugar syrups during or after honey production. Starch-based sugar syrups, high fructose corn syrup (HFCS), glucose syrup (GS) and saccharose syrups (SS), which are produced from beet or canes, can be used for adulterating honey. In this study, adulterated honey samples were prepared with the addition of HFCS, GS and SS (beet sugar) at a ratio of 0%, 10%, 20%, 40% and 50% by weight. (13)C/(12)C analysis was conducted on these adulterated honey samples using an isotope ratio mass spectrometer in combination with an elemental analyser (EA-IRMS). As a result, adulteration using C(4) sugar syrups (HFCS and GS) could be detected to a certain extent while adulteration of honey using C(3) sugar syrups (beet sugar) could not be detected. Adulteration by using SS (beet sugar) still has a serious detection problem, especially in countries in which beet is used in manufacturing sugar. For this reason, practice and analysis methods are needed to meet this deficit and to detect the adulterations precisely in the studies that will be conducted.

  11. Nitrogen isotopes determination in natural gas: analytical method and first results on magmatic, hydrothermal and soil gas samples.

    PubMed

    Grassa, Fausto; Capasso, Giorgio; Oliveri, Ygor; Sollami, Aldo; Carreira, Paula; Rosario Carvalho, M; Marques, Jose M; Nunes, Joao C

    2010-06-01

    A continuous-flow GC/IRMS technique has been developed to analyse delta(15)N values for molecular nitrogen in gas samples. This method provides reliable results with accuracy better than 0.15 per thousand and reproducibility (1sigma) within+/-0.1 per thousand for volumes of N(2) between 1.35 (about 56 nmol) and 48.9 muL (about 2 mumol). The method was tested on magmatic and hydrothermal gases as well as on natural gas samples collected from various sites. Since the analysis of nitrogen isotope composition may be prone to atmospheric contamination mainly in samples with low N(2) concentration, we set the instrument to determine also N(2) and (36)Ar contents in a single run. In fact, based on the simultaneously determined N(2)/(36)Ar ratios and assuming that (36)Ar content in crustal and mantle-derived fluids is negligible with respect to (36)Ar concentration in the atmosphere, for each sample, the degree of atmospheric contamination can be accurately evaluated. Therefore, the measured delta(15)N values can be properly corrected for air contamination.

  12. Sequential injection method for rapid and simultaneous determination of 236U, 237Np, and Pu isotopes in seawater.

    PubMed

    Qiao, Jixin; Hou, Xiaolin; Steier, Peter; Golser, Robin

    2013-11-19

    An automated analytical method implemented in a novel dual-column tandem sequential injection (SI) system was developed for simultaneous determination of (236)U, (237)Np, (239)Pu, and (240)Pu in seawater samples. A combination of TEVA and UTEVA extraction chromatography was exploited to separate and purify target analytes, whereupon plutonium and neptunium were simultaneously isolated and purified on TEVA, while uranium was collected on UTEVA. The separation behavior of U, Np, and Pu on TEVA-UTEVA columns was investigated in detail in order to achieve high chemical yields and complete purification for the radionuclides of interest. (242)Pu was used as a chemical yield tracer for both plutonium and neptunium. (238)U was quantified in the sample before the separation for deducing the (236)U concentration from the measured (236)U/(238)U atomic ratio in the separated uranium target using accelerator mass spectrometry. Plutonium isotopes and (237)Np were measured using inductively coupled plasma mass spectrometry after separation. The analytical results indicate that the developed method is robust and efficient, providing satisfactory chemical yields (70-100%) of target analytes and relatively short analytical time (8 h/sample).

  13. Determination of niobium in rocks by an isotope dilution spectrophotometric method

    USGS Publications Warehouse

    Greenland, L.P.; Campbell, E.Y.

    1970-01-01

    Rocks and minerals are fused with sodium peroxide in the presence of carrierfree 95Nb. The fusion cake is leached with water and the precipitate dissolved in hydrofluoric-sulfuric acid mixture. Niobium is extracted into methyl isobutyl ketone and further purified by ion exchange. The amount of niobium is determined spectrophotometrically with 4-(2-pyridylazo)-resorcinol, and the chemical yield of the separations determined by counting 95Nb. This procedure is faster and less sensitive to interferences than previously proposed methods for determining niobium in rocks.The high purity of the separated niobium makes the method applicable to nearly all matrices. ?? 1970.

  14. Mass spectrometric methods for the direct elemental and isotopic analysis of solid material

    NASA Astrophysics Data System (ADS)

    Ganeev, A. A.; Gubal, A. R.; Potapov, S. V.; Agafonova, N. N.; Nemets, V. M.

    2016-04-01

    Methods for the direct analysis of solids have a number of undeniable advantages over the methods that require preliminary dissolution of samples. High sensitivity and selectivity make the direct mass spectrometric techniques the most in-demand. The review concerns spark source mass spectrometry, laser ionization mass spectrometry, laser ablation inductively coupled plasma mass spectrometry, secondary ion mass spectrometry, secondary neutral mass spectrometry and glow discharge mass spectrometry. Basic principles, analytical characteristics and trends in the development of these techniques are discussed. Particular attention is given to applications of the techniques as well as to their competitive advantages and drawbacks. The bibliography includes 123 references.

  15. Heavy atom isotope effects on enzymatic reactions

    NASA Astrophysics Data System (ADS)

    Paneth, Piotr

    1994-05-01

    The theory of isotope effects, which has proved to be extremely useful in providing geometrical details of transition states in a variety of chemical reactions, has recently found an application in studies of enzyme-catalyzed reactions. These reactions are multistep in nature with few steps being partially rate-limiting, thus interpretation of these isotope effects is more complex. The theoretical framework of heavy-atom isotope effects on enzymatic reactions is critically analyzed on the basis of recent results of: carbon kinetic isotope effects on carbonic anhydrase and catalytic antibodies; multiple carbon, deuterium isotope effects on reactions catalyzed by formate decarboxylase; oxygen isotope effects on binding processes in reactions catalyzed by pyruvate kinase; and equilibrium oxygen isotope effect on binding an inhibitor to lactate dehydrogenase. The advantages and disadvantages of reaction complexity in learning details of formal and molecular mechanisms are discussed in the examples of reactions catalyzed by phosphoenolpyruvate carboxylase, orotidine decarboxylase and glutamine synthetase.

  16. Stable water isotope simulation by current land-surface schemes:Results of IPILPS phase 1

    SciTech Connect

    Henderson-Sellers, A.; Fischer, M.; Aleinov, I.; McGuffie, K.; Riley, W.J.; Schmidt, G.A.; Sturm, K.; Yoshimura, K.; Irannejad, P.

    2005-10-31

    Phase 1 of isotopes in the Project for Intercomparison of Land-surface Parameterization Schemes (iPILPS) compares the simulation of two stable water isotopologues ({sup 1}H{sub 2} {sup 18}O and {sup 1}H{sup 2}H{sup 16}O) at the land-atmosphere interface. The simulations are off-line, with forcing from an isotopically enabled regional model for three locations selected to offer contrasting climates and ecotypes: an evergreen tropical forest, a sclerophyll eucalypt forest and a mixed deciduous wood. Here we report on the experimental framework, the quality control undertaken on the simulation results and the method of intercomparisons employed. The small number of available isotopically-enabled land-surface schemes (ILSSs) limits the drawing of strong conclusions but, despite this, there is shown to be benefit in undertaking this type of isotopic intercomparison. Although validation of isotopic simulations at the land surface must await more, and much more complete, observational campaigns, we find that the empirically-based Craig-Gordon parameterization (of isotopic fractionation during evaporation) gives adequately realistic isotopic simulations when incorporated in a wide range of land-surface codes. By introducing two new tools for understanding isotopic variability from the land surface, the Isotope Transfer Function and the iPILPS plot, we show that different hydrological parameterizations cause very different isotopic responses. We show that ILSS-simulated isotopic equilibrium is independent of the total water and energy budget (with respect to both equilibration time and state), but interestingly the partitioning of available energy and water is a function of the models' complexity.

  17. Chemical Principles Revisited: Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Mickey, Charles D.

    1980-01-01

    Describes: (1) Law of Mass Action; (2) equilibrium constant and ideal behavior; (3) general form of the equilibrium constant; (4) forward and reverse reactions; (5) factors influencing equilibrium; (6) Le Chatelier's principle; (7) effects of temperature, changing concentration, and pressure on equilibrium; and (8) catalysts and equilibrium. (JN)

  18. An Isotope Dilution Method for High-frequency Measurements of Dissolved Inorganic Carbon concentration in the Surface Ocean

    NASA Astrophysics Data System (ADS)

    Huang, K.; Bender, M. L.; Wanninkhof, R. H.; Cassar, N.

    2013-12-01

    Dissolved inorganic carbon (DIC) is one of the most important species in the ocean carbon system. An autonomous system using isotope dilution as its core method has been developed to obtain high-frequency measurements of dissolved inorganic carbon (DIC) concentrations in the surface ocean. This system accurately mixes a seawater sample and a 13C-labeled sodium bicarbonate solution (spike). The mixed solution is then acidified and sent through a gas permeable membrane contactor. CO2 derived from DIC in the mixture is extracted by a CO2-free gas stream, and is sent to a cavity ring-down spectrometer to analyze its 13C/12C ratio. [DIC] of the seawater can then be derived from the measured 13C/12C, the known mixing ratio and the [DI13C] of the spike. The method has been tested under a wide [DIC] range (1800-2800 μmol/kg) in the laboratory. It has also been deployed on a cruise that surveyed ocean waters to the south of Florida. At a sampling resolution of 4 minutes (15 samples per hour), the relative standard deviation of DIC determined from the laboratory tests and the field deployment is ×0.07% and ×0.09%, respectively. The accuracy of the method is better than 0.1% except where [DIC] varies faster than 5 μmol/kg per minute. Based on the laboratory and field evaluations, we conclude that this method can provide accurate underway [DIC] measurements at high resolution in most oceanic regions. Schematic illustration of the work flow.

  19. Response reactions: equilibrium coupling.

    PubMed

    Hoffmann, Eufrozina A; Nagypal, Istvan

    2006-06-01

    It is pointed out and illustrated in the present paper that if a homogeneous multiple equilibrium system containing k components and q species is composed of the reactants actually taken and their reactions contain only k + 1 species, then we have a unique representation with (q - k) stoichiometrically independent reactions (SIRs). We define these as coupling reactions. All the other possible combinations with k + 1 species are the coupled reactions that are in equilibrium when the (q - k) SIRs are in equilibrium. The response of the equilibrium state for perturbation is determined by the coupling and coupled equilibria. Depending on the circumstances and the actual thermodynamic data, the effect of coupled equilibria may overtake the effect of the coupling ones, leading to phenomena that are in apparent contradiction with Le Chatelier's principle.

  20. The Isotope-Coded Affinity Tag Method for Quantitative Protein Profile Comparison and Relative Quantitation of Cysteine Redox Modifications.

    PubMed

    Chan, James Chun Yip; Zhou, Lei; Chan, Eric Chun Yong

    2015-11-02

    The isotope-coded affinity tag (ICAT) technique has been applied to measure pairwise changes in protein expression through differential stable isotopic labeling of proteins or peptides followed by identification and quantification using a mass spectrometer. Changes in protein expression are observed when the identical peptide from each of two biological conditions is identified and a difference is detected in the measurements comparing the peptide labeled with the heavy isotope to the one with a normal isotopic distribution. This approach allows the simultaneous comparison of the expression of many proteins between two different biological states (e.g., yeast grown on galactose versus glucose, or normal versus cancer cells). Due to the cysteine-specificity of the ICAT reagents, the ICAT technique has also been applied to perform relative quantitation of cysteine redox modifications such as oxidation and nitrosylation. This unit describes both protein quantitation and profiling of cysteine redox modifications using the ICAT technique.

  1. An instrumental and numerical method to determine the hydrogenic ratio in isotopic experiments in the TJ-II stellarator

    SciTech Connect

    Baciero, A. Zurro, B.; Martínez, M.

    2014-11-15

    The isotope effect is an important topic that is relevant for future D-T fusion reactors, where the use of deuterium, rather than hydrogen, may lean to improved plasma confinement. An evaluation of the ratio of hydrogen/deuterium is needed for isotope effect studies in current isotopic experiments. Here, the spectral range around H{sub α} and D{sub α} lines, obtained with an intensified multi-channel detector mounted to a 1-m focal length spectrometer, is analyzed using a fit function that includes several Gaussian components. The isotopic ratio evolution for a single operational day of the TJ-II stellarator is presented. The role of injected hydrogen by Neutral Beam Injection heating is also studied.

  2. Computing Equilibrium Chemical Compositions

    NASA Technical Reports Server (NTRS)

    Mcbride, Bonnie J.; Gordon, Sanford

    1995-01-01

    Chemical Equilibrium With Transport Properties, 1993 (CET93) computer program provides data on chemical-equilibrium compositions. Aids calculation of thermodynamic properties of chemical systems. Information essential in design and analysis of such equipment as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical-processing equipment. CET93/PC is version of CET93 specifically designed to run within 640K memory limit of MS-DOS operating system. CET93/PC written in FORTRAN.

  3. Automated method for simultaneous lead and strontium isotopic analysis applied to rainwater samples and airborne particulate filters (PM10).

    PubMed

    Beltrán, Blanca; Avivar, Jessica; Mola, Montserrat; Ferrer, Laura; Cerdà, Víctor; Leal, Luz O

    2013-09-03

    A new automated, sensitive, and fast system for the simultaneous online isolation and preconcentration of lead and strontium by sorption on a microcolumn packed with Sr-resin using an inductively coupled plasma mass spectrometry (ICP-MS) detector was developed, hyphenating lab-on-valve (LOV) and multisyringe flow injection analysis (MSFIA). Pb and Sr are directly retained on the sorbent column and eluted with a solution of 0.05 mol L(-1) ammonium oxalate. The detection limits achieved were 0.04 ng for lead and 0.03 ng for strontium. Mass calibration curves were used since the proposed system allows the use of different sample volumes for preconcentration. Mass linear working ranges were between 0.13 and 50 ng and 0.1 and 50 ng for lead and strontium, respectively. The repeatability of the method, expressed as RSD, was 2.1% and 2.7% for Pb and Sr, respectively. Environmental samples such as rainwater and airborne particulate (PM10) filters as well as a certified reference material SLRS-4 (river water) were satisfactorily analyzed obtaining recoveries between 90 and 110% for both elements. The main features of the LOV-MSFIA-ICP-MS system proposed are the capability to renew solid phase extraction at will in a fully automated way, the remarkable stability of the column which can be reused up to 160 times, and the potential to perform isotopic analysis.

  4. On the Equilibrium States of Interconnected Bubbles or Balloons.

    ERIC Educational Resources Information Center

    Weinhaus, F.; Barker, W.

    1978-01-01

    Describes the equilibrium states of a system composed of two interconnected, air-filled spherical membranes of different sizes. The equilibrium configurations are determined by the method of minimization of the availability of the system at constant temperature. (GA)

  5. Testing of an automated online EA-IRMS method for fast and simultaneous carbon content and stable isotope measurement of aerosol samples

    NASA Astrophysics Data System (ADS)

    Major, István; Gyökös, Brigitta; Túri, Marianna; Futó, István; Filep, Ágnes; Hoffer, András; Molnár, Mihály

    2016-04-01

    Comprehensive atmospheric studies have demonstrated that carbonaceous aerosol is one of the main components of atmospheric particulate matter over Europe. Various methods, considering optical or thermal properties, have been developed for quantification of the accurate amount of both organic and elemental carbon constituents of atmospheric aerosol. The aim of our work was to develop an alternative fast and easy method for determination of the total carbon content of individual aerosol samples collected on prebaked quartz filters whereby the mass and surface concentration becomes simply computable. We applied the conventional "elemental analyzer (EA) coupled online with an isotope ratio mass spectrometer (IRMS)" technique which is ubiquitously used in mass spectrometry. Using this technique we are able to measure simultaneously the carbon stable isotope ratio of the samples, as well. During the developing process, we compared the EA-IRMS technique with an off-line catalytic combustion method worked out previously at Hertelendi Laboratory of Environmental Studies (HEKAL). We tested the combined online total carbon content and stable isotope ratio measurement both on standard materials and real aerosol samples. Regarding the test results the novel method assures, on the one hand, at least 95% of carbon recovery yield in a broad total carbon mass range (between 100 and 3000 ug) and, on the other hand, a good reproducibility of stable isotope measurements with an uncertainty of ± 0.2 per mill. Comparing the total carbon results obtained by the EA-IRMS and the off-line catalytic combustion method we found a very good correlation (R2=0.94) that proves the applicability of both preparation method. Advantages of the novel method are the fast and simplified sample preparation steps and the fully automated, simultaneous carbon stable isotope ratio measurement processes. Furthermore stable isotope ratio results can effectively be applied in the source apportionment

  6. Electron linac for medical isotope production with improved energy efficiency and isotope recovery

    DOEpatents

    Noonan, John; Walters, Dean; Virgo, Matt; Lewellen, John

    2015-09-08

    A method and isotope linac system are provided for producing radio-isotopes and for recovering isotopes. The isotope linac is an energy recovery linac (ERL) with an electron beam being transmitted through an isotope-producing target. The electron beam energy is recollected and re-injected into an accelerating structure. The ERL provides improved efficiency with reduced power requirements and provides improved thermal management of an isotope target and an electron-to-x-ray converter.

  7. Copper isotope fractionation between aqueous compounds relevant to low temperature geochemistry and biology

    NASA Astrophysics Data System (ADS)

    Fujii, Toshiyuki; Moynier, Frédéric; Abe, Minori; Nemoto, Keisuke; Albarède, Francis

    2013-06-01

    Isotope fractionation between the common Cu species present in solution (Cu+, Cu2+, hydroxide, chloride, sulfide, carbonate, oxalate, and ascorbate) has been investigated using both ab initio methods and experimental solvent extraction techniques. In order to establish unambiguously the existence of equilibrium isotope fractionation (as opposed to kinetic isotope fractionation), we first performed laboratory-scale liquid-liquid distribution experiments. Upon exchange between HCl medium and a macrocyclic complex, the 65Cu/63Cu ratio fractionated by -1.06‰ to -0.39‰. The acidity dependence of the fractionation was appropriately explained by ligand exchange reactions between hydrated H2O and Cl- via intramolecular vibrations. The magnitude of the Cu isotope fractionation among important Cu ligands was also estimated by ab initio methods. The magnitude of the nuclear field shift effect to the Cu isotope fractionation represents only ˜3% of the mass-dependent fractionation. The theoretical estimation was expanded to chlorides, hydroxides, sulfides, sulfates, and carbonates under different conditions of pH. Copper isotope fractionation of up to 2‰ is expected for different forms of Cu present in seawater and for different sediments (carbonates, hydroxides, and sulfides). We found that Cu in dissolved carbonates and sulfates is isotopically much heavier (+0.6‰) than free Cu. Isotope fractionation of Cu in hydroxide is minimal. The relevance of these new results to the understanding of metabolic processes was also discussed. Copper is an essential element used by a large number of proteins for electron transfer. Further theoretical estimates of δ65Cu in hydrated Cu(I) and Cu(II) ions, Cu(II) ascorbates, and Cu(II) oxalate predict Cu isotope fractionation during the breakdown of ascorbate into oxalate and account for the isotopically heavy Cu found in animal kidneys.

  8. Evaluation of sample pretreatment methods for analysis of polonium isotopes in herbal medicines.

    PubMed

    Sreejith, Sathyapriya R; Nair, Madhu G; Rao, D D

    2014-12-01

    Herbal infusions like ayurvedic aristas are widely consumed by Indian population for good health. With increasing awareness about radiological assessment, an effort was made to assess the radioactivity concentration of naturally occurring radionuclides in herbal medicines. (210)Po is an important alpha particle emitter contributing to internal dose to man from ingestion. Though (210)Po can be spontaneously deposited on silver disk for alpha spectrometric measurements with less radiochemical step, great care has to be taken during the sample pretreatment step owing to the high volatility of polonium even at low temperatures. Aim of the study was to evaluate an appropriate sample pretreatment method for estimation of polonium in herbal medicines. (209)Po was used for radiochemical yield calculation. Conventional open vessel wet ashing, physical evaporation, freeze-drying and microwave digestion in a Teflon vessel were examined. The recovery ranged between 9 and 79%. The lowest recovery was obtained for the samples that were processed by open vessel digestion without any volume reduction. The recoveries were comparable for those samples that were freeze dried and subjected to HNO3 + HClO4 + H2O2 + HF acid digestion and microwave digested samples. (210)Po concentration in the samples ranged from 11.3 to 39.6 mBq/L.

  9. A Facile Stable-Isotope Dilution Method for Determination of Sphingosine Phosphate Lyase Activity

    PubMed Central

    Suh, Jung H.; Eltanawy, Abeer; Rangan, Apoorva; Saba, Julie D.

    2015-01-01

    A new technique for quantifying sphingosine phosphate lyase activity in biological samples is described. In this procedure, 2-hydrazinoquinoline is used to convert (2E)-hexadecenal into the corresponding hydrazone derivative to improve ionization efficiency and selectivity of detection. Combined utilization of liquid chromatographic separation and multiple reaction monitoring-mass spectrometry allows for simultaneous quantification of the substrate S1P and product (2E)-hexadecenal. Incorporation of (2E)-d5-hexadecenal as an internal standard improves detection accuracy and precision. A simple one-step derivatization procedure eliminates the need for further extractions. Limits of quantification for (2E)-hexadecenal and sphingosine-1-phosphate are 100 and 50 fmol, respectively. The assay displays a wide dynamic detection range useful for detection of low basal sphingosine phosphate lyase activity in wild type cells, SPL-overexpressing cell lines, and wild type mouse tissues. Compared to current methods, the capacity for simultaneous detection of sphingosine-1-phosphate and (2E)-hexadecenal greatly improves the accuracy of results and shows excellent sensitivity and specificity for sphingosine phosphate lyase activity detection. PMID:26408264

  10. Easy Extraction Method To Evaluate δ13C Vanillin by Liquid Chromatography-Isotopic Ratio Mass Spectrometry in Chocolate Bars and Chocolate Snack Foods.

    PubMed

    Bononi, Monica; Quaglia, Giancarlo; Tateo, Fernando

    2015-05-20

    An easy extraction method that permits the use of a liquid chromatography-isotopic ratio mass spectrometry (LC-IRMS) system to evaluate δ(13)C of vanillin in chocolate products and industrial flavorings is presented. The method applies the determination of stable isotopes of carbon to discriminate between natural vanillin from vanilla beans and vanillin from other sources (mixtures from beans, synthesis, or biotechnology). A series of 13 chocolate bars and chocolate snack foods available on the Italian market and 8 vanilla flavorings derived from industrial quality control processes were analyzed. Only 30% of products considered in this work that declared "vanilla" on the label showed data that permitted the declaration "vanilla" according to European Union (EU) Regulation 1334/2008. All samples not citing "vanilla" or "natural flavoring" on the label gave the correct declaration. The extraction method is presented with data useful for statistical evaluation.

  11. Method for determination of uranium isotopes in environmental samples by liquid-liquid extraction with triisooctylamine/xylene in hydrochloric media and alpha spectrometry.

    PubMed

    Popov, L

    2012-10-01

    Alternative method for determination of uranium isotopes in various environmental samples is presented. The method is based on total decomposition of the solid materials and preconcentration of liquid samples. The separation of uranium from interfering radionuclides and stable matrix elements is attained by liquid-liquid extraction with triisooctylamine/xylene in hydrochloric media. After the additional removal of stable iron by extraction with diisopropyl ether, purified uranium is electrodeposited on stainless steel disks and measured by alpha spectrometry. The analytical method has been successfully applied to the determination of uranium isotopes in water and bottom sediments from the rivers Danube, Ogosta and Tzibritza in Northwestern Bulgaria. The analytical quality was checked by analyzing reference materials with different matrices.

  12. Chromatographic hydrogen isotope separation

    DOEpatents

    Aldridge, Frederick T.

    1981-01-01

    Intermetallic compounds with the CaCu.sub.5 type of crystal structure, particularly LaNiCo.sub.4 and CaNi.sub.5, exhibit high separation factors and fast equilibrium times and therefore are useful for packing a chromatographic hydrogen isotope separation colum. The addition of an inert metal to dilute the hydride improves performance of the column. A large scale mutli-stage chromatographic separation process run as a secondary process off a hydrogen feedstream from an industrial plant which uses large volumes of hydrogen can produce large quantities of heavy water at an effective cost for use in heavy water reactors.

  13. Chromatographic hydrogen isotope separation

    DOEpatents

    Aldridge, F.T.

    Intermetallic compounds with the CaCu/sub 5/ type of crystal structure, particularly LaNiCo/sub 4/ and CaNi/sub 5/, exhibit high separation factors and fast equilibrium times and therefore are useful for packing a chromatographic hydrogen isotope separation column. The addition of an inert metal to dilute the hydride improves performance of the column. A large scale multi-stage chromatographic separation process run as a secondary process off a hydrogen feedstream from an industrial plant which uses large volumes of hydrogen cn produce large quantities of heavy water at an effective cost for use in heavy water reactors.

  14. Abiologic silicon isotope fractionation between aqueous Si and Fe(III)-Si gel in simulated Archean seawater: Implications for Si isotope records in Precambrian sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Zheng, Xin-Yuan; Beard, Brian L.; Reddy, Thiruchelvi R.; Roden, Eric E.; Johnson, Clark M.

    2016-08-01

    Precambrian Si-rich sedimentary rocks, including cherts and banded iron formations (BIFs), record a >7‰ spread in 30Si/28Si ratios (δ30Si values), yet interpretation of this large variability has been hindered by the paucity of data on Si isotope exchange kinetics and equilibrium fractionation factors in systems that are pertinent to Precambrian marine conditions. Using the three-isotope method and an enriched 29Si tracer, a series of experiments were conducted to constrain Si isotope exchange kinetics and fractionation factors between amorphous Fe(III)-Si gel, a likely precursor to Precambrian jaspers and BIFs, and aqueous Si in artificial Archean seawater under anoxic conditions. Experiments were conducted at room temperature, and in the presence and absence of aqueous Fe(II) (Fe(II)aq). Results of this study demonstrate that Si solubility is significantly lower for Fe-Si gel than that of amorphous Si, indicating that seawater Si concentrations in the Precambrian may have been lower than previous estimates. The experiments reached ˜70-90% Si isotope exchange after a period of 53-126 days, and the highest extents of exchange were obtained where Fe(II)aq was present, suggesting that Fe(II)-Fe(III) electron-transfer and atom-exchange reactions catalyze Si isotope exchange through breakage of Fe-Si bonds. All experiments except one showed little change in the instantaneous solid-aqueous Si isotope fractionation factor with time, allowing extraction of equilibrium Si isotope fractionation factors through extrapolation to 100% isotope exchange. The equilibrium 30Si/28Si fractionation between Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -2.30 ± 0.25‰ (2σ) in the absence of Fe(II)aq. In the case where Fe(II)aq was present, which resulted in addition of ˜10% Fe(II) in the final solid, creating a mixed Fe(II)-Fe(III) Si gel, the equilibrium fractionation between Fe(II)-Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -3.23 ± 0.37‰ (2σ). Equilibrium

  15. Selective IR multiphoton dissociation of molecules in a pulsed gas-dynamically cooled molecular flow interacting with a solid surface as an alternative to low-energy methods of molecular laser isotope separation

    NASA Astrophysics Data System (ADS)

    Makarov, G. N.; Petin, A. N.

    2016-03-01

    We report the results of studies on the isotope-selective infrared multiphoton dissociation (IR MFD) of SF6 and CF3I molecules in a pulsed, gas-dynamically cooled molecular flow interacting with a solid surface. The productivity of this method in the conditions of a specific experiment (by the example of SF6 molecules) is evaluated. A number of low-energy methods of molecular laser isotope separation based on the use of infrared lasers for selective excitation of molecules are analysed and their productivity is estimated. The methods are compared with those of selective dissociation of molecules in the flow interacting with a surface. The advantages of this method compared to the low-energy methods of molecular laser isotope separation and the IR MPD method in the unperturbed jets and flows are shown. It is concluded that this method could be a promising alternative to the low-energy methods of molecular laser isotope separation.

  16. An Improved Method for TIMS High Precision Nd Isotopic Analysis of Very Small Aliquots (1- 10ng) With Example Application in Garnet Sm/Nd Geochronology

    NASA Astrophysics Data System (ADS)

    Baxter, E. F.; Harvey, J.; Mehl, L. Y.; Peterman, E. M.

    2007-12-01

    Technological and scientific developments have demonstrated both the attainability and the utility of very high precision (i.e. 5-20ppm 2 σ) Nd isotopic measurements with TIMS. However such high precision has been limited to relatively large aliquots of Nd, on the order of several hundred nanograms. Several potential applications of precise Nd isotopic measurements, including garnet Sm/Nd geochronology, do not always permit such large samples, instead yielding only a few nanograms of Nd. We have explored and tested an improved method for Nd isotopic analysis of such small (1-10ng) aliquots of Nd using the NdO+ method with a Triton TIMS at Boston University. Analyzing Nd isotopes as the oxide is a well known technique, frequently involving an oxygen bleed valve. Instead, we forego the bleed valve and load samples with a TaO slurry which provides the oxygen source. Using an in-house Nd isotopic standard solution, 4ng loads easily yield stable 2.0-2.5 volt beams resulting in internal precisions of 10ppm 2 σ RSE. Within barrel external precision of 4ng loads of the Nd standard is 13ppm 2 σ RSD (n=20). Long term (6 months, six analysts) external precision of 4ng loads of the standard is currently 23ppm 2 σ RSD (n=55) suggesting that further improvements are possible. As a further test of this method, we dissolved a natural rock sample (a metapelite), separated the Nd using TRU- spec and MLA column chemistry, and loaded nineteen 4ng loads in one barrel. Within barrel external precision was 21ppm 2 σ RSD (n=18). This precision represents a significant advance over previous NdO+ analyses of small samples using an oxygen bleed valve. The TaO loading method for small Nd aliquots is useful in Sm/Nd garnet geochronology as exemplified by two case studies. Garnets from eclogite facies gneisses from Norway ran very well with 2.4-18ng loads and yielded age precision as good as 0.8 million years 2 σ. Conversely, garnets from blueschist facies rocks from Sifnos, Greece, ran

  17. A universal SI-traceable isotope dilution mass spectrometry method for protein quantitation in a matrix by tandem mass tag technology.

    PubMed

    Li, Jiale; Wu, Liqing; Jin, Youxun; Su, Ping; Yang, Bin; Yang, Yi

    2016-05-01

    Isotope dilution mass spectrometry (IDMS), an important metrological method, is widely used for absolute quantification of peptides and proteins. IDMS employs an isotope-labeled peptide or protein as an internal standard although the use of a protein provides improved accuracy. Generally, the isotope-labeled protein is obtained by stable isotope labeling by amino acids in cell culture (SILAC) technology. However, SILAC is expensive, laborious, and time-consuming. To overcome these drawbacks, a novel universal SI-traceable IDMS method for absolute quantification of proteins in a matrix is described with human transferrin (hTRF). The hTRF and a human serum sample were labeled with different tandem mass tags (TMTs). After mixing the TMT-labeled hTRF and serum sample together followed by digestion, the peptides were separated by nano-liquid chromatography and analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Using the signature peptides, we calculated the ratios of reporter ions from the TMT-labeled peptides which, in turn, allowed determination of the mass fraction of hTRF. The recovery ranged from 97% to 105% with a CV of 3.9%. The LOD and LOQ were 1.71 × 10(-5) g/g and 5.69 × 10(-5) g/g of hTRF in human serum, respectively, and the relative expanded uncertainty was 4.7% with a mass fraction of 2.08 mg/g. For comparison, an enzyme-linked immunosorbent assay (ELISA) method for hTRF yielded a mass fraction of 2.03 mg/g. This method provides a starting point for establishing IDMS technology to accurately determine the mass fractions of protein biomarkers in a matrix with traceability to SI units. This technology should support the development of a metrological method useful for quantification of a wide variety of proteins.

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

    PubMed

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

    2017-03-23

    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.

  19. Position-specific and clumped stable isotope studies: comparison of the Urey and path-integral approaches for carbon dioxide, nitrous oxide, methane, and propane.

    PubMed

    Webb, Michael A; Miller, Thomas F

    2014-01-16

    We combine path-integral Monte Carlo methods with high-quality potential energy surfaces to compute equilibrium isotope effects in a variety of systems relevant to 'clumped' isotope analysis and isotope geochemistry, including CO2, N2O, methane, and propane. Through a systematic study of heavy-atom isotope-exchange reactions, we quantify and analyze errors that arise in the widely used Urey model for predicting equilibrium constants of isotope-exchange reactions using reduced partition function ratios. These results illustrate that the Urey model relies on a nontrivial cancellation of errors that can shift the apparent equilibrium temperature by as much as 35 K for a given distribution of isotopologues. The calculations reported here provide the same level of precision as the best existing analytical instrumentation, resolving the relative enrichment of certain isotopologues to as little as 0.01‰. These findings demonstrate path-integral methods to be a rigorous and viable alternative to more approximate methods for heavy-atom geochemical applications.

  20. On equilibrium structures of the water molecule

    NASA Astrophysics Data System (ADS)

    Császár, Attila G.; Czakó, Gábor; Furtenbacher, Tibor; Tennyson, Jonathan; Szalay, Viktor; Shirin, Sergei V.; Zobov, Nikolai F.; Polyansky, Oleg L.

    2005-06-01

    Equilibrium structures are fundamental entities in molecular sciences. They can be inferred from experimental data by complicated inverse procedures which often rely on several assumptions, including the Born-Oppenheimer approximation. Theory provides a direct route to equilibrium geometries. A recent high-quality ab initio semiglobal adiabatic potential-energy surface (PES) of the electronic ground state of water, reported by Polyansky et al. [Polyansky et al.Science 299, 539 (2003)] and called CVRQD here, is analyzed in this respect. The equilibrium geometries resulting from this direct route are deemed to be of higher accuracy than those that can be determined by analyzing experimental data. Detailed investigation of the effect of the breakdown of the Born-Oppenheimer approximation suggests that the concept of an isotope-independent equilibrium structure holds to about 3×10-5Å and 0.02° for water. The mass-independent [Born-Oppenheimer (BO)] equilibrium bond length and bond angle on the ground electronic state PES of water is reBO=0.95782Å and θeBO=104.485°, respectively. The related mass-dependent (adiabatic) equilibrium bond length and bond angle of H2O16 is read=0.95785Å and θead=104.500°, respectively, while those of D2O16 are read=0.95783Å and θead=104.490°. Pure ab initio prediction of J =1 and 2 rotational levels on the vibrational ground state by the CVRQD PESs is accurate to better than 0.002cm-1 for all isotopologs of water considered. Elaborate adjustment of the CVRQD PESs to reproduce all observed rovibrational transitions to better than 0.05cm-1 (or the lower ones to better than 0.0035cm-1) does not result in noticeable changes in the adiabatic equilibrium structure parameters. The expectation values of the ground vibrational state rotational constants of the water isotopologs, computed in the Eckart frame using the CVRQD PESs and atomic masses, deviate from the experimentally measured ones only marginally, especially for A0 and B0. The

  1. Novel hybrid isotope separation scheme and apparatus

    DOEpatents

    Maya, Jakob

    1991-01-01

    A method of yielding selectively a desired enrichment in a specific isotope including the steps of inputting into a spinning chamber a gas from which the specific isotope is to be isolated, radiating the gas with frequencies characteristic of the absorption of a particular isotope of the atomic or molecular gas, thereby inducing a photoionization reaction of the desired isotope, and collecting the specific isotope ion by suitable ion collection means.

  2. Novel hybrid isotope separation scheme and apparatus

    DOEpatents

    Maya, J.

    1991-06-18

    A method is described for yielding selectively a desired enrichment in a specific isotope including the steps of inputting into a spinning chamber a gas from which the specific isotope is to be isolated, radiating the gas with frequencies characteristic of the absorption of a particular isotope of the atomic or molecular gas, thereby inducing a photoionization reaction of the desired isotope, and collecting the specific isotope ion by suitable ion collection means. 3 figures.

  3. An assessment of geochemical preparation methods prior to organic carbon concentration and carbon isotope ratio analyses of fine-grained sedimentary rocks

    NASA Astrophysics Data System (ADS)

    KöNitzer, Sven F.; Leng, Melanie J.; Davies, Sarah J.; Stephenson, Michael H.

    2012-09-01

    This study summarizes organic carbon isotope (δ13C) and total organic carbon (TOC) data from a series of tests undertaken to provide an appropriate methodology for pre-analysis treatment of mudstones from an Upper Carboniferous sedimentary succession, in order to develop a consistent preparation procedure. The main treatments involved removing both inorganic carbonate and hydrocarbons (which might be extraneous) before δ13C and TOC analysis. The results show that decarbonating using hydrochloric acid causes significant reduction in δ13C and total carbon (TC) of the bulk material due to the removal of inorganic carbonate. These changes are most pronounced where soluble calcium carbonate (rather than Ca-Mg-Fe carbonate) is present. Deoiled samples show only slightly higher mean δ13C where visible bitumen was extracted from the bulk sample. Moreover, the isotopic signatures of the extracts are closely correlated to those of their respective bulk samples, suggesting that small yields of hydrocarbons were generated in situ with no isotopic fractionation. In addition, further δ13C and TC analyses were performed on samples where mixing of oil-based drilling mud with brecciated core material had been undertaken. Brecciated mudstone material did not display distinct isotopic signals compared to the surrounding fine-grained material. Overall we show that the most accurate assessment of bulk organic carbon isotopes and concentration in these samples can be achieved through decarbonating the material prior to measurement via the `rinse method'. However, our results support recent findings that pre-analysis acid treatments can cause variable and unpredictable errors in δ13C and TOC values. We believe that, despite these uncertainties, the findings presented here can be applied to paleoenvironmental studies on organic matter contained within sedimentary rocks over a range of geological ages and compositions.

  4. New Method for Determining Isotopic Values of Glutamic Acid and Phenylalanine for Estimation of Precise Trophic Position in Food Web Studies

    NASA Astrophysics Data System (ADS)

    Kamath, T.; Broek, T.; McCarthy, M.

    2012-12-01

    Compound Specific Isotope Analysis of Amino Acids (CSI-AA) has emerged as a highly precise new method of determining trophic levels of both aquatic and terrestrial organisms. Multiple studies have now shown that δ15N values for glutamic acid (Glu) and phenylalanine (Phe) can be coupled to provide extremely precise estimates of trophic position in diverse food web studies. The standard gas chromatography—isotope ratio mass spectrometer (GC-IRMS) approach is presently limited to a select number of labs since necessary equipment is both expensive and not widely accessible. Furthermore, typical GC-IRMS δ15N precision (±1‰) is significantly lower than usual bulk δ15N values (±0.1‰), thus presenting a considerable setback for precise trophic level calculations. In this study, we develop a new dual-column method to purify Glu and Phe using high performance liquid chromatography (HPLC). Phe is purified using an analytical scale reverse phase column embedded with anionic ion-pairing reagents and collected using automated fraction collection. Glu is separated from the non-polar amino acids using the same column and further purified using a hydrophilic interaction liquid chromatography (HILIC) cation and anion-exchange column and collected via automated fraction collection. Isotopic analysis of the purified AAs is then conducted on an elemental analyzer—isotope ratio mass spectrometer (EA-IRMS). As a test of this method, we present and compare the trophic position of five marine organisms—cyanobacteria, deep-sea bamboo coral, juvenile and adult white sea bass, and harbor seal, calculated using Glu and Phe δ15N values produced by both GC-IRMS and our HPLC-EA-IRMS approach. The preliminary results of this study suggest that the HPLC-EA-IRMS method is a viable alternative to GC-IRMS, which should allow accurate trophic position estimates to be made by more researchers using more readily available instrumentation.

  5. Determination of nonaxisymmetric equilibrium

    SciTech Connect

    Elkin, D.

    1980-01-01

    The Princeton Equilibrium Code is modified to determine the equilibrium surfaces for a large aspect ratio toroidal system with helical magnetic fields. The code may easily be made to include any variety of modes. Verification of the code is made by comparison with an analytic solution for l = 3. Previously observed shifting of the magnetic axis with increasing pressure or with a changed externally applied vertical field is obtained. The case l = 0, a bumpy torus, gives convergence only for the lenient convergence tolerance of epsilon/sub b/ = 1.0 x 10-/sup 2/.

  6. Beyond Equilibrium Thermodynamics

    NASA Astrophysics Data System (ADS)

    Öttinger, Hans Christian

    2005-01-01

    Beyond Equilibrium Thermodynamics fills a niche in the market by providing a comprehensive introduction to a new, emerging topic in the field. The importance of non-equilibrium thermodynamics is addressed in order to fully understand how a system works, whether it is in a biological system like the brain or a system that develops plastic. In order to fully grasp the subject, the book clearly explains the physical concepts and mathematics involved, as well as presenting problems and solutions; over 200 exercises and answers are included. Engineers, scientists, and applied mathematicians can all use the book to address their problems in modelling, calculating, and understanding dynamic responses of materials.

  7. A simple isotopic labeling method to study cysteine oxidation in Alzheimer's disease: oxidized cysteine-selective dimethylation (OxcysDML).

    PubMed

    Gu, Liqing; Robinson, Renã A S

    2016-04-01

    Cysteine is widely involved in redox signaling pathways through a number of reversible and irreversible modifications. Reversible modifications (e.g., S-glutathionylation, S-nitrosylation, disulfide bonds, and sulfenic acid) are used to protect proteins from oxidative attack and maintain cellular homeostasis, while irreversible oxidations (e.g., sulfinic acid and sulfonic acid) serve as hallmarks of oxidative stress. Proteomic analysis of cysteine-enriched peptides coupled with reduction of oxidized thiols can be used to measure the oxidation states of cysteine, which is helpful for elucidating the role that oxidative stress plays in biology and disease. As an extension of our previously reported cysDML method, we have developed oxidized cysteine-selective dimethylation (OxcysDML), to investigate the site-specific total oxidation of cysteine residues in biologically relevant samples. OxcysDML employs (1) blocking of free thiols by a cysteine-reactive reagent, (2) enrichment of peptides containing reversibly oxidized cysteine by a solid phase resin, and (3) isotopic labeling of peptide amino groups to quantify cysteine modifications arising from different biological conditions. On-resin enrichment and labeling minimizes sample handing time and improves efficiency in comparison with other redox proteomic methods. OxcysDML is also inexpensive and flexible, as it can accommodate the exploration of various cysteine modifications. Here, we applied the method to liver tissues from a late-stage Alzheimer's disease (AD) mouse model and wild-type (WT) controls. Because we have previously characterized this proteome using the cysDML approach, we are able here to probe deeper into the redox status of cysteine in AD. OxcysDML identified 1129 cysteine sites (from 527 proteins), among which 828 cysteine sites underwent oxidative modifications. Nineteen oxidized cysteine sites had significant alteration levels in AD and represent proteins involved in metabolic processes. Overall

  8. 3D quantification of dynamic fluid-fluid interfaces in porous media with fast x-ray microtomography: A comparison with quasi-equilibrium methods

    NASA Astrophysics Data System (ADS)

    Meisenheimer, D.; Brueck, C. L.; Wildenschild, D.

    2015-12-01

    X-ray microtomography imaging of fluid-fluid interfaces in three-dimensional porous media allows for the testing of thermodynamically derived predictions that seek a unique relationship between capillary pressure, fluid saturation, and specific interfacial area (Pc-Sw-Anw). Previous experimental studies sought to test this functional dependence under quasi-equilibrium conditions (assumed static on the imaging time-scale); however, applying predictive models developed under static conditions for dynamic scenarios can lead to substantial flaws in predicted outcomes. Theory and models developed using dynamic data can be verified using fast x-ray microtomography which allows for the unprecedented measurement of developing interfacial areas, curvatures, and trapping behaviors of fluid phases in three-dimensional systems. We will present results of drainage and imbibition experiments of air and water within a mixture of glass beads. The experiments were performed under both quasi-equilibrium and dynamic conditions at the Advanced Photon Source (APS) at Argonne National Laboratory. Fast x-ray microtomography was achieved by utilizing the high brilliance of the x-ray beam at the APS under pink-beam conditions where the white beam is modified with a 4 mm Al absorber and a 0.8 mrad Pt-coated mirror to eliminate low and high-energy photons, respectively. We present a comparison of the results from the quasi-equilibrium and dynamic experiments in an effort to determine if the Pc-Sw-Anw relationship is comparable under either experimental condition and to add to the discussion on whether the Pc-Sw-Anw relationship is unique as hypothesized by existing theory.

  9. Laser Ablation Molecular Isotopic Spectrometry

    NASA Astrophysics Data System (ADS)

    Russo, Richard E.; Bol'shakov, Alexander A.; Mao, Xianglei; McKay, Christopher P.; Perry, Dale L.; Sorkhabi, Osman

    2011-02-01

    A new method of performing optical isotopic analysis of condensed samples in ambient air and at ambient pressure has been developed: Laser Ablation Molecular Isotopic Spectrometry (LAMIS). The technique uses radiative transitions from molecular species either directly vaporized from a sample or formed by associative mechanisms of atoms or ions in a laser ablation plume. This method is an advanced modification of a known atomic emission technique called laser-induced breakdown spectroscopy (LIBS). The new method — LAMIS — can determine not only chemical composition but also isotopic ratios of elements in the sample. Isotopic measurements are enabled by significantly larger isotopic shifts found in molecular spectra relative to atomic spectra. Analysis can be performed from a distance and in real time. No sample preparation or pre-treatment is required. Detection of the isotopes of hydrogen, boron, carbon, and oxygen are discussed to illustrate the technique.

  10. Towards breaking temperature equilibrium in multi-component Eulerian schemes

    SciTech Connect

    Grove, John W; Masser, Thomas

    2009-01-01

    We investigate the effects ofthermal equilibrium on hydrodynamic flows and describe models for breaking the assumption ofa single temperature for a mixture of components in a cell. A computational study comparing pressure-temperature equilibrium simulations of two dimensional implosions with explicit front tracking is described as well as implementation and J-D calculations for non-equilibrium temperature methods.

  11. An Updated Equilibrium Machine

    ERIC Educational Resources Information Center

    Schultz, Emeric

    2008-01-01

    A device that can demonstrate equilibrium, kinetic, and thermodynamic concepts is described. The device consists of a leaf blower attached to a plastic container divided into two chambers by a barrier of variable size and form. Styrofoam balls can be exchanged across the barrier when the leaf blower is turned on and various air pressures are…

  12. Local equilibrium in bird flocks

    NASA Astrophysics Data System (ADS)

    Mora, Thierry; Walczak, Aleksandra M.; Del Castello, Lorenzo; Ginelli, Francesco; Melillo, Stefania; Parisi, Leonardo; Viale, Massimiliano; Cavagna, Andrea; Giardina, Irene

    2016-12-01

    The correlated motion of flocks is an example of global order emerging from local interactions. An essential difference with respect to analogous ferromagnetic systems is that flocks are active: animals move relative to each other, dynamically rearranging their interaction network. This non-equilibrium characteristic has been studied theoretically, but its impact on actual animal groups remains to be fully explored experimentally. Here, we introduce a novel dynamical inference technique, based on the principle of maximum entropy, which accommodates network rearrangements and overcomes the problem of slow experimental sampling rates. We use this method to infer the strength and range of alignment forces from data of starling flocks. We find that local bird alignment occurs on a much faster timescale than neighbour rearrangement. Accordingly, equilibrium inference, which assumes a fixed interaction network, gives results consistent with dynamical inference. We conclude that bird orientations are in a state of local quasi-equilibrium over the interaction length scale, providing firm ground for the applicability of statistical physics in certain active systems.

  13. What are the instrumentation requirements for measuring the isotopic composition of net ecosystem exchange of CO2 using eddy covariance methods?

    PubMed

    Saleska, Scott R; Shorter, Joanne H; Herndon, Scott; Jiménez, Rodrigo; McManus, J Barry; Munger, J William; Nelson, David D; Zahniser, Mark S

    2006-06-01

    Better quantification of isotope ratios of atmosphere-ecosystem exchange of CO2 could substantially improve our ability to probe underlying physiological and ecological mechanisms controlling ecosystem carbon exchange, but the ability to make long-term continuous measurements of isotope ratios of exchange fluxes has been limited by measurement difficulties. In particular, direct eddy covariance methods have not yet been used for measuring the isotopic composition of ecosystem fluxes. In this article, we explore the feasibility of such measurements by (a) proposing a general criterion for judging whether a sensor's performance is sufficient for making such measurements (the criterion is met when the contribution of sensor error to the flux measurement error is comparable to or less than the contribution of meteorological noise inherently associated with turbulence flux measurements); (b) using data-based numerical simulations to quantify the level of sensor precision and stability required to meet this criterion for making direct eddy covariance measurements of the 13C/12C ratio of CO2 fluxes above a specific ecosystem (a mid-latitude temperate forest in central Massachusetts, USA); (c) testing whether the performance of a new sensor-a prototype pulsed quantum cascade laser (QCL) based isotope-ratio absorption spectrometer (and plausible improvements thereon)-is sufficient for meeting the criterion in this ecosystem. We found that the error contribution from a prototype sensor (approximately 0.2 per thousand, 1 SD of 10 s integrations) to total isoflux measurement error was comparable to (1.5 to 2x) the irreducible 'meteorological' noise inherently associated with turbulent flux measurements above this ecosystem (daytime measurement error SD of approximately 60% of flux versus meteorological noise of 30-40% for instantaneous half-hour fluxes). Our analysis also shows that plausible instrument improvements (increase of sensor precision to approximately 0.1 per

  14. Fractional absorption of active absorbable algal calcium (AAACa) and calcium carbonate measured by a dual stable-isotope method

    Technology Transfer Automated Retrieval System (TEKTRAN)

    With the use of stable isotopes, this study aimed to compare the bioavailability of active absorbable algal calcium (AAACa), obtained from oyster shell powder heated to a high temperature, with an additional heated seaweed component (Heated Algal Ingredient, HAI), with that of calcium carbonate. In ...

  15. Method and means of reducing erosion of components of plasma devices exposed to helium and hydrogen isotope radiation

    DOEpatents

    Kaminsky, Manfred S.; Das, Santosh K.; Rossing, Thomas D.

    1977-01-25

    Surfaces of components of plasma devices exposed to radiation by atoms or ions of helium or isotopes of hydrogen can be protected from damage due to blistering by shielding the surfaces with a structure formed by sintering a powder of aluminum or beryllium and its oxide or by coating the surfaces with such a sintered metal powder.

  16. Calcium ion binding of three different types of oligo/polysialic acids as studied by equilibrium dialysis and circular dichroic methods.

    PubMed

    Shimoda, Y; Kitajima, K; Inoue, S; Inoue, Y

    1994-02-08

    Ca2+ binding properties of three different types of oligo/polysialic acid chains, i.e., oligo/poly(Neu5Ac), oligo/poly(Neu5Gc), and oligo/poly(KDN), were studied by equilibrium dialysis and circular dichroism. Colominic acid, high molecular weight polysialoglycoprotein (H-PSGP), low molecular weight polysialoglycoprotein (L-PSGP), and 3-deoxy-D-glycero-D-galacto-2-nonulosonic acid (KDN) glycoprotein were found to bind calcium ions with about 8-100 times the affinity of sialic acid monomer. Analysis by equilibrium dialysis of the binding of Ca2+ to colominic acid was biphasic, and the high-affinity interaction was shown to change with the degree of polymerization. Specific binding of Ca2+ to polysialic acid (polySia) caused characteristic effects in the circular dichroism spectrum. A pronounced decrease in the circular dichroism of polySia at 205 nm was observed upon addition of calcium. H-PSGP was found to bind calcium ions with 3-fold higher affinity than L-PSGP.

  17. Teaching Chemical Equilibrium with the Jigsaw Technique

    NASA Astrophysics Data System (ADS)

    Doymus, Kemal

    2008-03-01

    This study investigates the effect of cooperative learning (jigsaw) versus individual learning methods on students’ understanding of chemical equilibrium in a first-year general chemistry course. This study was carried out in two different classes in the department of primary science education during the 2005-2006 academic year. One of the classes was randomly assigned as the non-jigsaw group (control) and other as the jigsaw group (cooperative). Students participating in the jigsaw group were divided into four “home groups” since the topic chemical equilibrium is divided into four subtopics (Modules A, B, C and D). Each of these home groups contained four students. The groups were as follows: (1) Home Group A (HGA), representin g the equilibrium state and quantitative aspects of equilibrium (Module A), (2) Home Group B (HGB), representing the equilibrium constant and relationships involving equilibrium constants (Module B), (3) Home Group C (HGC), representing Altering Equilibrium Conditions: Le Chatelier’s principle (Module C), and (4) Home Group D (HGD), representing calculations with equilibrium constants (Module D). The home groups then broke apart, like pieces of a jigsaw puzzle, and the students moved into jigsaw groups consisting of members from the other home groups who were assigned the same portion of the material. The jigsaw groups were then in charge of teaching their specific subtopic to the rest of the students in their learning group. The main data collection tool was a Chemical Equilibrium Achievement Test (CEAT), which was applied to both the jigsaw and non-jigsaw groups The results indicated that the jigsaw group was more successful than the non-jigsaw group (individual learning method).

  18. Perchlorate isotope forensics

    USGS Publications Warehouse

    Böhlke, J.K.; Sturchio, N.C.; Gu, B.; Horita, J.; Brown, G.M.; Jackson, W.A.; Batista, J.; Hatzinger, P.B.

    2005-01-01

    Perchlorate has been detected recently in a variety of soils, waters, plants, and food products at levels that may be detrimental to human health. These discoveries have generated considerable interest in perchlorate source identification. In this study, comprehensive stable isotope analyses ( 37Cl/35Cl and 18O/17O/ 16O) of perchlorate from known synthetic and natural sources reveal systematic differences in isotopic characteristics that are related to the formation mechanisms. In addition, isotopic analyses of perchlorate extracted from groundwater and surface water demonstrate the feasibility of identifying perchlorate sources in contaminated environments on the basis of this technique. Both natural and synthetic sources of perchlorate have been identified in water samples from some perchlorate occurrences in the United States by the isotopic method. ?? 2005 American Chemical Society.

  19. New method for GC/FID and GC-C-IRMS analysis of plasma free fatty acid concentration and isotopic enrichment.

    PubMed

    Kangani, Cyrous O; Kelley, David E; Delany, James P

    2008-09-15

    A simple, direct and accurate method for the determination of concentration and enrichment of free fatty acids (FFAs) in human plasma was developed. The validation and comparison to a conventional method are reported. Three amide derivatives, dimethyl, diethyl and pyrrolidide, were investigated in order to achieve optimal resolution of the individual fatty acids. This method involves the use of dimethylamine/Deoxo-Fluor to derivatize plasma free fatty acids to their dimethylamides. This derivatization method is very mild and efficient, and is selective only towards FFAs so that no separation from a total lipid extract is required. The direct method gave lower concentrations for palmitic acid and stearic acid and increased concentrations for oleic acid and linoleic acid in plasma as compared to methyl ester derivative after thin-layer chromatography. The [(13)C]palmitate isotope enrichment measured using direct method was significantly higher than that observed with the BF(3)/MeOH-TLC method. The present method provided accurate and precise measures of concentration as well as enrichment when analyzed with gas chromatography combustion-isotope ratio-mass spectrometry.

  20. Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks

    NASA Astrophysics Data System (ADS)

    García del Real, Pablo; Maher, Kate; Kluge, Tobias; Bird, Dennis K.; Brown, Gordon E.; John, Cédric M.

    2016-11-01

    Magnesium carbonate minerals produced by reaction of H2O-CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic methods to infer temperatures of mineralization, the nature of mineralizing fluids, and the mechanisms controlling the transformation of dissolved CO2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved. Clumped-isotope compositions of magnesium carbonates provide a means to determine primary mineralization or (re)equilibration temperature, which permits the reconstruction of geologic processes that govern magnesium carbonate formation. We first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite, along with natural metamorphic magnesite and low-temperature hydromagnesite precipitated within a mine adit. We show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error. In addition, we employ carbonate clumped-isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings. Cryptocrystalline magnesite vein deposits from California (Red Mountain magnesite mine), Austria (Kraubath locality), Turkey (Tutluca mine, Eskişehir district) and Iran (Derakht-Senjed deposit) exhibit broadly uniform Δ47 compositions that yield apparent clumped-<