Sample records for mg isotopic equilibrium

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

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


    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.

  2. Corrigendum to "Equilibrium magnesium isotope fractionation between aqueous Mg2+ and carbonate minerals: Insights from path integral molecular dynamics" [Geochim. Cosmochim. Acta 163 (2015) 126-139

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


    The theoretical 26Mg/24Mg β-factor of aqueous Mg2+ of Schauble (2011) has been reported with an error in Pinilla et al. (2015). The corresponding value in Table 7 is incorrect and should read 25.5‰ at 298 K. In Section 3.6 (page 133), one sentence is affected and should be rephrased as: "It is noteworthy that the estimate of the Mg(aq)β-factor from a set of salts containing the Mg(H20)62+ complex leads to a value ∼2‰ higher than the other estimates at 298 K." Finally, the curves in Fig. 8 corresponding to the calculations of Schauble (2011) have been corrected in the figure below.

  3. Calculation of individual isotope equilibrium constants for geochemical reactions

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


    Theory is derived from the work of Urey (Urey H. C. [1947] The thermodynamic properties of isotopic substances. J. Chem. Soc. 562-581) 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 ?? = (Kex)1/n, where n is the number of atoms exchanged. This relation is extended to include species containing multiple isotopes, for example 13C16O18O and 1H2H18O. The equilibrium constants of the isotope exchange reactions can be expressed as ratios of individual isotope equilibrium constants for geochemical reactions. Knowledge of the equilibrium constant for the dominant isotopic species can then be used to calculate the individual isotope equilibrium constants. Individual isotope equilibrium constants are calculated for the reaction CO2g = CO2aq for all species that can be formed from 12C, 13C, 16O, and 18O; for the reaction between 12C18 O2aq and 1H218Ol; and among the various 1H, 2H, 16O, and 18O species of H2O. This is a subset of a larger number of equilibrium constants calculated elsewhere (Thorstenson D. C. and Parkhurst D. L. [2002] Calculation of individual isotope equilibrium constants for implementation in geochemical models. Water-Resources Investigation Report 02-4172. U.S. Geological Survey). Activity coefficients, activity-concentration conventions for the isotopic variants of H2O in the solvent 1H216Ol, and salt effects on isotope fractionation have been included in the derivations. The effects of nonideality are small because of the chemical similarity of different isotopic species of the same molecule or ion. The temperature dependence of the individual isotope equilibrium constants can be calculated from the temperature dependence of the fractionation

  4. Preparation of Metallic Isotope 26Mg

    WuXiaolei; ZhangFuming; GanZaiguo; GuoJunsheng; QinZhi


    Some special isotope material is usually used in nuclear experiments. It can be served as ion beam or target. When new superheavy nuclide 265Bh (Z=107) is synthesized, a reaction of 243Am target with 26Mg ion beamis selected to produce new isotope 265Bh. The preparation and production of this rare and extremely expensive isotope 26 Mg used for ion beam substance will be a key problem in synthesizing experiment of 265Bh. Theavailable chemical form of isotope 26Mg in commercial product usually is oxide or other compound, which are not required in our experiment. They need to be transformed to metal form as a proper working substance in ion source.

  5. Phase equilibrium in Mg-Cu-Y

    Mezbahul-Islam, Mohammad; Medraj, Mamoun


    Magnesium-based bulk metallic glasses (BMG) have potential in applications ranging from biomedical to sports equipment and the Mg-Cu-Y system offers some of the most promising alloys. Phase relations and ternary solubility of the binary and ternary compounds of this system have been experimentally investigated. The Isothermal section of Mg-Cu-Y system at 673 K for the entire composition range has been constructed. Phase relations in the Cu-rich (>66 at.% Cu) region of the Mg-Cu-Y system has been determined for the first time. The homogeneity range of three ternary compounds has been determined. Solidifications behavior of several key alloys have been discussed based on the differential scanning calorimetry (DSC) experiments and thermodynamic calculations. Extensive analysis of the DSC curves has been carried out to relate them to the corresponding phase transformation reactions and temperatures. Some of the most promising metallic glass forming regions have been analyzed using thermodynamic calculations.

  6. A Review of Mg Isotope Analytical Methods by MC-ICP-MS

    Yajun An; Fang Huang


    Application of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has led to big breakthrough of analytical methods for metal stable isotopes, resulting in rapid progresses in non-traditional stable isotope geochemistry. As a new geological tracer, Mg isotopes have been widely applied in studies of almost all important disciplines of geochemistry. High precision Mg isotope data measured by MC-ICP-MS are now available with precision about 0.05‰ amu-1 (2SD) or better. Because mass bias caused by chemical procedure and instrument can easily cause significant analytical error, it is still a challenge to obtain accurate Mg isotope data for natural samples. In this paper, we systematically review the development of analytical technique of Mg isotopes, with a detailed description of a series of important techniques used in the measurement process, including calibration of instrumental mass-bias, chemical purification process, matrix effect, and pitfalls for high precision isotope analyses. We compare standard data from different labs and establish a guideline for Mg iso-tope analysis procedure. Additionally, we briefly discuss the behaviors of Mg isotopes during geological processes including equilibrium and kinetic Mg isotope fractionations, such as magma differentiation, chemical and thermal diffusion, and continental weathering. Finally, we propose some future prospects for Mg isotope geochemistry in both high and low temperature geological processes.

  7. Impact of amorphous precursor phases on magnesium isotope signatures of Mg-calcite

    Mavromatis, Vasileios; Purgstaller, Bettina; Dietzel, Martin; Buhl, Dieter; Immenhauser, Adrian; Schott, Jacques


    Various marine calcifiers form exoskeletons via an amorphous calcium carbonate (ACC) precursor phase and magnesium plays an important role in the temporary stabilization of this metastable phase. Thus, the use of Mg isotope ratios of marine biogenic carbonates as a proxy to reconstruct past seawater chemistry calls for a detailed understanding of the mechanisms controlling Mg isotope signatures during the formation and transformation of ACC to the final crystalline carbonate mineral. For this purpose we have investigated the Mg isotope fractionation between (Ca,Mg)CO3 solids and aqueous fluids at 25 °C and pH = 8.3 during (i) the direct precipitation of crystalline Mg-calcite and (ii) the formation of Mg-rich ACC (Mg-ACC) and its transformation to Mg-calcite. The outcome documents that the small Mg isotope fractionation between Mg-ACC and reactive fluid (ΔMg26ACC-fluid = - 1.0 ± 0.1 ‰) is not preserved during the transformation of the ACCs into Mg-calcite. Following a pronounced isotopic shift accompanying the transformation of Mg-ACC into Mg-calcite, Δ26Mgcalcite-fluid progressively decreases with reaction progress from ∼ - 3.0 ‰ to - 3.6 ‰, reflecting both the approach of isotopic equilibrium and the increase of calcite Mg content (to near 20 mol % Mg). In contrast the crystalline Mg-calcite precipitated directly from the reacting fluid, i.e. lacking a discernable formation of an amorphous precursor, exhibits only small temporal variations in Δ26Mgcalcite-fluid which overall is affected by the precipitation kinetics. The values found in this study at the onset of Mg-ACC precipitation for Mg isotope fractionation between Mg-ACC and the fluid (ΔMg26ACC-fluid = - 1.0 ‰) and between Mg-ACC and Mg2+(aq) (Δ(aq) 26 Mg ACC-Mg2+ = + 2.0 ‰) are consistent with the formation of a hydrated Ca nanoporous solid accommodating Mg bicarbonate/carbonate species in combination with hydrated magnesium. This material crossed by percolating channels filled with the

  8. The three-isotope method for equilibrium isotope fractionation factor determination: Unfounded optimism

    Cao, X.; Hayles, J. A.; Bao, H.


    The equilibrium isotope fractionation factor α is a fundamental parameter in stable isotope geochemistry. Although equilibrium α can be determined by theoretical calculation or by measurement of natural samples, direct laboratory experiments are ultimately required to verify those results. The attainment of a true exchange equilibrium in experiments is often difficult, but three methods have been devised and used to ensure that an equilibrium α has been obtained in an isotope exchange experiment. These are the two-directional method, partial-exchange method, and three-isotope method. Of these, the three-isotope method is thought to be the most rigorous. Using water-water exchange as a basic unit, we have developed a set of complex exchange models to study when and why the three-isotope method may work well or not. We found that the method cannot promise to lead to an equilibrium α before the kinetic complexity of the specific exchange experiment is known. An equilibrium point in δ17O-δ18O space can be reached only when all of the isotope exchange pathways are fully reversible, i.e. there is no mass loss at any instant, and the forward and backward reactions share the same pathway. If the exchange pathways are not fully reversible, steady state may be reached, but a steady state α can be very different from the equilibrium α. Our results validated the earlier warning that the trajectory for three-isotope evolution in δ17O-δ18O space may be a distinctly curved line or contain more than one straight line due to the non-fully reversible isotope exchange reactions. The three-isotope method for equilibrium α determination is not as rigorous or as promising as it may seem. Instead, the trajectory of three-isotope evolution provides detailed insights into the kinetics of isotope exchange between compounds. If multiple components exist in the exchange system, the δ17O-δ18O evolving trajectory would be more complex.

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

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


    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.

  10. Resetting of Mg isotopes between calcite and dolomite during burial metamorphism: Outlook of Mg isotopes as geothermometer and seawater proxy

    Hu, Zhongya; Hu, Wenxuan; Wang, Xiaomin; Lu, Yizhou; Wang, Lichao; Liao, Zhiwei; Li, Weiqiang


    Magnesium isotopes are an emerging tool to study the geological processes recorded in carbonates. Calcite, due to its ubiquitous occurrence and the large Mg isotope fractionation associated with the mineral, has attracted great interests in applications of Mg isotope geochemistry. However, the fidelity of Mg isotopes in geological records of carbonate minerals (e.g., calcite and dolomite) against burial metamorphism remains poorly constrained. Here we report our investigation on the Mg isotope systematics of a dolomitized Middle Triassic Geshan carbonate section in eastern China. Magnesium isotope analysis was complemented by analyses of Sr-C-O isotopic compositions, major and trace element concentrations, and petrographic and mineralogical features. Multiple lines of evidence consistently indicated that post-depositional diagenesis of carbonate minerals occurred to the carbonate rocks. Magnesium isotope compositions of the carbonate rocks closely follow a mixing trend between a high δ26Mg dolomite end member and a low δ26Mg calcite end member, irrespective of sample positions in the section and calcite/dolomite ratio in the samples. By fitting the measured Mg isotope data using a two-end member mixing model, an inter-mineral Δ26Mgdolomite-calcite fractionation of 0.72‰ was obtained. Based on the experimentally derived Mg isotope fractionation factors for dolomite and calcite, a temperature of 150-190 °C was calculated to correspond to the 0.72‰ Δ26Mgdolomite-calcite fractionation. Such temperature range matches with the burial-thermal history of the local strata, making a successful case of Mg isotope geothermometry. Our results indicate that both calcite and dolomite had been re-equilibrated during burial metamorphism, and based on isotope mass balance of Mg, the system was buffered by dolomite in the section. Therefore, burial metamorphism may reset Mg isotope signature of calcite, and Mg isotope compositions in calcite should be dealt with caution in

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

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


    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.

  12. Boron isotope effect in superconducting MgB2.

    Bud'ko, S L; Lapertot, G; Petrovic, C; Cunningham, C E; Anderson, N; Canfield, P C


    We report the preparation method of and boron isotope effect for MgB2, a new binary intermetallic superconductor with a remarkably high superconducting transition temperature T(c)(10B) = 40.2 K. Measurements of both temperature dependent magnetization and specific heat reveal a 1.0 K shift in T(c) between Mg11B2 and Mg10B2. Whereas such a high transition temperature might imply exotic coupling mechanisms, the boron isotope effect in MgB2 is consistent with the material being a phonon-mediated BCS superconductor.

  13. Mg isotope fractionation during microbe-mineral interactions

    Kim, Insu; Ryu, Jong-sik; Lee, Kwang-sik; Lee, Dongho


    Magnesium is involved in various biogeochemical processes important to the global climate change over geological time-scale. Mg isotopes allow us to directly trace the Mg cycle in the Earth's surface but the factors controlling Mg isotopic compositions have not fully understood yet. Here, we conducted a batch experiment using two bacterial species (Shewanella putrefaciens and Burkholderia fungorum) and three major Mg-bearing minerals (biotite, dolomite and hornblende). All elemental concentrations increased by 336 h and then reached to steady-state values, of which Mg concentrations varied depending on minerals and bacterial species. This result indicates that the mineral dissolution is affect by the presence of microbes, which either provide organic acids or attach onto mineral surface. The Mg isotopic compositions of initial minerals biotite, dolomite and hornblende are -0.35o of biotite, -0.99o of dolomite, and -0.24o of hornblende, in δ26Mg. Similarly, δ26Mg values increased by 336 h and reached to steady-state values, which also varied with minerals and microbes. During dissolution of three minerals, the light isotope of Mg is preferentially incorporated into the dissolved phases and then the dissolved δ26Mg values become consistent with those of minerals with the time.

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

    Agrinier, Pierre; Javoy, Marc


    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

  15. Mg Isotope Fractionation Between E. coli and Growth Medium

    Basset, R.; Lemelle, L.; Albalat, E.; Telouk, P.; Albarède, F.


    Magnesium is a major element in both microbial cells and minerals, immune to redox conditions and atmospheric interactions. In organic cells, Mg can be associated with membranes, with cytoplasm (either as an isolated ion or bound to proteins). Its isotope composition can be used to constrain the contribution of organic material to carbonate fluxes and the overall cycle of this element in the exogenous environment [1, 2]. Cells of DH5α E. coli strain were grown in Luria Broth medium and the Mg isotope fractionation between the cells and their growth medium determined after calcination in Pt crucibles, chemical purification by cation exchange chemistry in HCl medium [3] and isotopic analysis on a Nu HR MC-ICPMS. The yield is better than 96%. The Mg contents of 2.19 ± 0.08 mg per g DW in cells and 0.117 ± 0.001 mg per g DW in Luria Broth medium are consistent with literature data [4]. About half of the Mg initially present in the LB medium is taken up by the growing cells. At high cellular concentrations (OD600 = 3.5), cells are enriched in 26Mg by 0.97 ± 0.14 ‰ with respect to the culture medium. Although E. coli may not be a good proxy for oceanic plankton, such a substantial fractionation of Mg isotopes suggests that incorporation of even a few percent organic matter into oceanic oozes depletes oceanic Mg in its heavy isotopes and therefore accounts for the isotopic difference between riverine and marine Mg. [1] Drever, The Sea 5 (1974) 337-357 [2] Tipper et al., EPSL 250 (2006) 241-253 [3] Chang et al., JAAS 18 (2003) 296-301 [4] Outten et al., Science 292 (2001), 2488-2492




    Experiments were performed to determine the equilibrium as well as kinetic stable nitrogen and oxygen isotope fractionations between aqueous dissolved and gaseous N2O. The equilibrium fractionations, defined as the ratio of the isotopic abundance ratios (15R and 18R, respectively) of gaseous and

  17. First-principles models of equilibrium tellurium isotope fractionation

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


    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

  18. High-precision Mg isotopic systematics of bulk chondrites

    Schiller, Martin; Handler, Monica R.; Baker, Joel A.


    Variations of the mass-independent abundance of 26Mg ( δ26Mg*) and stable Mg ( δ25Mg) isotope composition of chondrites are important because they constrain the homogeneity of 26Al and Mg isotopes in the proto-planetary disc and the validity of the short-lived 26Al-to- 26Mg chronometer applied to meteorites. We present high-precision Mg isotope data and Al/Mg ratios of chondrites representing nearly all major chondrite classes, including a step-leaching experiment on the CM2 chondrite Murchison. δ26Mg* variations in leachates of Murchison representing acid soluble material are ≤ 30 times smaller than reported for neutron-rich isotopes of Ti and Cr and do not reveal resolvable deficits in δ26Mg* (-0.002 to + 0.118‰). Very small variations in δ26Mg* anomalies in bulk chondrites (-0.006 to + 0.019‰) correlate with increasing 27Al/ 24Mg ratios and δ50Ti, reflecting the variable presence of calcium-aluminium-rich inclusions (CAIs) in some types of carbonaceous chondrites. Similarly, release of radiogenic 26Mg produced by 26Al decay from CAI material in the step-leaching of Murchison best explains the high δ26Mg* observed in the last, aggressive, leaching steps of this experiment. Overall, the observed variations in δ26Mg* are small and potential differences beyond that which result from the presence of CAI-like material cannot be detected within the analytical uncertainties of this study (± 0.004‰). The results do not allow radical heterogeneity of 26Al (≥±30%) or measurable Mg nucleosynthetic heterogeneity (≥±0.005‰) to have existed on a planetesimal scale in the proto-planetary disc. Combined with published δ26Mg* data for CAIs, the bulk chondrite data yield a precise initial ( 26Al/ 27Al) 0 = (5.21 ± 0.06) × 10 -5 and δ26Mg* = -0.0340 ± 0.0016‰ for the Solar System. However, it is not possible with the currently available data to determine with certainty whether CAIs and the material from which planetesimals accreted including

  19. Equilibrium between (Li,Na,K,Mg)-carbonate melt, gaseous CO

    Velden, P.F. van


    Considerable amounts of MgCO3 may appear in alkali metal carbonate melts in contact with MgO and carbon dioxide gas. The equilibrium between dissolved MgCO3, MgO and carbon dioxide gas has been studied. The results satisfactorily obey thermodynamic theory based upon a melt mode

  20. Predicting equilibrium uranium isotope fractionation in crystals and solution

    Schauble, E. A.


    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

  1. Ground-state properties of neutron-rich Mg isotopes

    Watanabe, Shin; Shimada, Mitsuhiro; Tagami, Shingo; Kimura, Masaaki; Takechi, Maya; Fukuda, Mitsunori; Nishimura, Daiki; Suzuki, Takeshi; Matsumoto, Takuma; Shimizu, Yoshifumi R; Yahiro, Masanobu


    We analyze recently-measured total reaction cross sections for 24-38Mg isotopes incident on 12C targets at 240 MeV/nucleon by using the folding model and antisymmetrized molecular dynamics(AMD). The folding model well reproduces the measured reaction cross sections, when the projectile densities are evaluated by the deformed Woods-Saxon (def-WS) model with AMD deformation. Matter radii of 24-38Mg are then deduced from the measured reaction cross sections by ?ne-tuning the parameters of the def-WS model. The deduced matter radii are largely enhanced by nuclear deformation. Fully-microscopic AMD calculations with no free parameter well reproduce the deduced matter radii for 24-36Mg, but still considerably underestimate them for 37,38Mg. The large matter radii suggest that 37,38Mg are candidates for deformed halo nucleus. AMD also reproduces other existing measured ground-state properties (spin-parity, total binding energy, and one-neutron separation energy) of Mg isotopes. Neutron-number (N) dependence of defor...

  2. Isotopic fractionation of Mg 2+(aq), Ca 2+(aq), and Fe 2+(aq) with carbonate minerals

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.


    Density-functional electronic structure calculations are used to compute the equilibrium constants for 26Mg/ 24Mg and 44Ca/ 40Ca isotope exchange between carbonate minerals and uncomplexed divalent aquo ions. The most reliable calculations at the B3LYP/6-311++G(2d,2p) level predict equilibrium constants K, reported as 10 3ln ( K) at 25 °C, of -5.3, -1.1, and +1.2 for 26Mg/ 24Mg exchange between calcite (CaCO 3), magnesite (MgCO 3), and dolomite (Ca 0.5Mg 0.5CO 3), respectively, and Mg 2+(aq), with positive values indicating enrichment of the heavy isotope in the mineral phase. For 44Ca/ 40Ca exchange between calcite and Ca 2+(aq) at 25 °C, the calculations predict values of +1.5 for Ca 2+(aq) in 6-fold coordination and +4.1 for Ca 2+(aq) in 7-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO)610- and M(HO)62+ embedded in a set of fixed atoms representing the second-shell (and greater) coordination environment. We find that the aqueous cluster representing the aquo ion is much more sensitive to improvements in the basis set than the calculations on the mineral systems, and that fractionation factors should be computed using the best possible basis set for the aquo complex, even if the reduced partition function ratio calculated with the same basis set is not available for the mineral system. The new calculations show that the previous discrepancies between theory and experiment for Fe 3+-hematite and Fe 2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe 3+(aq) and Fe 2+(aq) species.

  3. Isotopic Fractionation of Mg2+(aq), Ca2+(aq), and Fe2+(aq) with Carbonate Minerals

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.


    Density functional electronic structure calculations are used to compute the equilibrium constant (the isotope fractionation factor) for 26Mg/24Mg and 44Ca/40Ca isotope exchange between carbonate minerals and uncomplexed divalent aquo ions. The most reliable calculations at the B3LYP/6-311++G(2d,2p) level predict equilibrium constants K, reported as 103ln(K) at 25 °C, of -5.3, -1.1, and +1.1 for 26Mg/24Mg exchange between calcite (CaCO3), magnesite (MgCO3), and dolomite (Ca0.5Mg0.5CO3), respectively, and Mg2+(aq), with positive values indicating enrichment in the mineral phase. For 44Ca/40Ca exchange between calcite and Ca2+(aq), the calculations predict values of +1.5 for Ca2+(aq) in six-fold coordination and +4.1 for Ca2+(aq) in seven-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO3)610- and M2+(H2O)6 embedded in a set of fixed atoms representing the 2nd shell (and greater) coordination environment. We find that the aqueous cluster representing the aquo ion is much more sensitive to improvements in the basis set than the calculations on the mineral systems, and that fractionation factors should be computed using 2 the best possible basis set for the aquo complex, even if the reduced partition function ratio calculated with the same basis set is not available for the mineral system. The new calculations show that the previous discrepancies between theory and experiment for Fe3+-hematite and Fe2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe3+(aq) and Fe2+(aq) species.

  4. Resolving the stellar sources of isotopically rare presolar silicate grains through Mg and Fe isotopic analyses

    Nguyen, Ann N.; Messenger, Scott, E-mail: [Robert M. Walker Laboratory for Space Science, Astromaterials Research and Exploration Science Directorate, NASA Johnson Space Center, Houston, TX 77058 (United States)


    We conducted multi-element isotopic analyses of 11 presolar silicate grains from the Acfer 094 meteorite having unusual O isotopic compositions. Eight grains are {sup 18}O-rich, one is {sup 16}O-rich, and two are extremely {sup 17}O-rich. We constrained the grains' stellar sources by measuring their Si and Mg isotopic ratios, and also the {sup 54}Fe/{sup 56}Fe and {sup 57}Fe/{sup 56}Fe ratios for five grains. The Mg and Fe isotopic measurements were conducted after surrounding matrix grains were removed for more accurate ratios. Most of the {sup 18}O-rich silicates had anomalous Mg isotopic ratios, and their combined isotopic constraints are consistent with origins in low-mass Type II supernovae (SNe II) rather than high-metallicity stars. The isotopic ratios of the {sup 16}O-rich silicate are also consistent with an SN origin. Mixing small amounts of interior stellar material with the stellar envelope replicated all measured isotopic ratios except for {sup 29}Si/{sup 28}Si and {sup 54}Fe/{sup 56}Fe in some grains. The {sup 29}Si/{sup 28}Si ratios of all SN-derived grains are matched by doubling the {sup 29}Si yield in the Ne- and Si-burning zones. The {sup 54}Fe/{sup 56}Fe ratios of the grains imply elemental fractionation in the Si/S zone, or introduction of isotopically solar Fe by secondary processing. The two highly {sup 17}O-rich silicates exhibited significant {sup 25}Mg and/or {sup 26}Mg enrichments and their isotopic ratios are best explained by strong dilution of 1.15 M {sub ☉} CO nova matter. We estimate that ∼12% and 1% of presolar silicates have SN and nova origins, respectively, similar to presolar SiC and oxides. This implies that asymptotic giant branch stars are the dominant dust producers in the galaxy.

  5. Equilibrium and kinetic Si isotope fractionation factors and their implications on Si isotope distributions in the Earth's surface environments

    Tang, M.; Zhang, S.; Liu, Y.


    Several important equilibrium Si isotope fractionation factors among minerals, organic molecules and the H4SiO4 solution are complemented to facilitate explanation of distributions of Si isotope in the Earth's surface environments. The results reveal that heavy Si isotopes will be significantly enriched in the secondary silicate minerals in comparison to aqueous H4SiO4. On the contrary, quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution. The extent of 28Si-enrichment in hyper-coordinated organosilicon complexes is found the largest. In addition, the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer is calculated and the result supports previous statement that highly 28Si-enrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations. With equilibrium Si isotope fractionation factors provided here, Si isotope distributions in many surface systems of the Earth can be explained. For example, the change of bulk soil δ30Si can be predicted as a concave pattern with respect to weathering degree, with the minimum value where allophane completely dissolves and the total amount of sesqui-oxides and poorly crystalline minerals reaches its maximum. When well-crystallized clays start to precipitate from pore solutions under equilibrium conditions, the bulk soil δ30Si will increase again and reach a constant value. Similarly, the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain δ30Si variations in the ground water profile. Equilibrium Si isotope fractionations among quadra-coordinated organosilicon complexes and the H4SiO4 solution may also shed the light on the Si isotope distributions in Si-accumulating plants.

  6. Determination of the Fe(II)aq-magnetite equilibrium iron isotope fractionation factor using the three-isotope method and a multi-direction approach to equilibrium

    Frierdich, Andrew J.; Beard, Brian L.; Scherer, Michelle M.; Johnson, Clark M.


    Magnetite is ubiquitous in the Earth's crust and its presence in modern marine sediments has been taken as an indicator of biogeochemical Fe cycling. Magnetite is also the most abundant Fe oxide in banded iron formations (BIFs) that have not been subjected to ore-forming alteration. Magnetite is therefore an important target of stable Fe isotope studies, and yet interpretations are currently difficult because of large uncertainties in the equilibrium stable Fe isotope fractionation factors for magnetite relative to fluids and other minerals. In this study, we utilized the three-isotope method (57Fe-56Fe-54Fe) to explore isotopic exchange via an enriched-57Fe tracer, and natural mass-dependent fractionation using 56Fe/54Fe variations, during reaction of aqueous Fe(II) (Fe(II)aq) with magnetite. Importantly, we employed a multi-direction approach to equilibrium by reacting four 57Fe-enriched Fe(II) solutions that had distinct 56Fe/54Fe ratios, which identifies changes in the instantaneous Fe isotope fractionation factor and hence identifies kinetic isotope effects. We find that isotopic exchange can be described by two 56Fe/54Fe fractionations, where an initial rapid exchange (∼66% isotopic mixing within 1 day) involved a relatively small Fe(II)aq-magnetite 56Fe/54Fe fractionation, followed by slower exchange (∼25% isotopic mixing over 50 days) that was associated with a larger Fe(II)aq-magnetite 56Fe/54Fe fractionation; this later fractionation is interpreted to approach isotopic equilibrium between Fe(II)aq and the total magnetite. All four Fe(II) solutions extrapolate to the same final equilibrium 56Fe/54Fe fractionation for Fe(II)aq-magnetite of -1.56±0.20‰ (2σ) at 22 °C. Additional experiments that synthesized magnetite via conversion of ferrihydrite by reaction with aqueous Fe(II) yield final 56Fe/54Fe fractionations that are identical to those of the exchange experiments. Our experimental results agree well with calculated fractionation factors using

  7. The behaviour of Li and Mg isotopes during primary phase dissolution and secondary mineral formation in basalt

    Wimpenny, Josh; Gíslason, Sigurður R.; James, Rachael H.; Gannoun, Abdelmouhcine; Pogge Von Strandmann, Philip A. E.; Burton, Kevin W.


    This study presents lithium (Li) and magnesium (Mg) isotope data from experiments designed to assess the effects of dissolution of primary phases and the formation of secondary minerals during the weathering of basalt. Basalt glass and olivine dissolution experiments were performed in mixed through-flow reactors under controlled equilibrium conditions, at low pH (2-4) in order to keep solutions undersaturated (i.e. far-from equilibrium) and inhibit the formation of secondary minerals. Combined dissolution-precipitation experiments were performed at high pH (10 and 11) increasing the saturation state of the solutions (moving the system closer to equilibrium) and thereby promoting the formation of secondary minerals. At conditions far from equilibrium saturation state modelling and solution stoichiometry suggest that little secondary mineral formation has occurred. This is supported by the similarity of the dissolution rates of basalt glass and olivine obtained here compared to those of previous experiments. The δ 7Li isotope composition of the experimental solution is indistinguishable from that of the initial basalt glass or olivine indicating that little fractionation has occurred. In contrast, the same experimental solutions have light Mg isotope compositions relative to the primary phases, and the solution becomes progressively lighter with time. In the absence of any evidence for secondary mineral formation the most likely explanation for these light Mg isotope compositions is that there has been preferential loss of light Mg during primary phase dissolution. For the experiments undertaken at close to equilibrium conditions the results of saturation state modelling and changes in solution chemistry suggest that secondary mineral formation has occurred. X-ray diffraction (XRD) measurements of the reacted mineral products from these experiments confirm that the principal secondary phase that has formed is chrysotile. Lithium isotope ratios of the experimental

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

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


    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.

  9. Ice-vapor equilibrium fractionation factor of hydrogen and oxygen isotopes

    Ellehøj, Mads Dam; Steen-Larsen, Hans Christian; Johnsen, Sigfus Johann;


    RATIONALE: The equilibrium fractionation factors govern the relative change in the isotopic composition during phase transitions of water. The commonly used results, which were published more than 40 years ago, are limited to a minimum temperature of -33 degrees C. This limits the reliability...

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

    Williams, Kathryn R.; Lipford, Levin C.


    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…

  11. Magnesium isotopic composition of the oceanic mantle and oceanic Mg cycling

    Liu, Ping-Ping; Teng, Fang-Zhen; Dick, Henry J. B.; Zhou, Mei-Fu; Chung, Sun-Lin


    To constrain the Mg isotopic composition of the oceanic mantle, investigate Mg isotope fractionation of abyssal peridotites during seafloor alteration, and assess Mg budget in the oceans, a suite of 32 abyssal peridotite samples from the Gakkel Ridge and Southwest Indian Ridge (SWIR) was, for the first time, selected for high-precision Mg isotope analyses. Although most of these samples are extensively altered, largely by serpentinization and weathering, primary olivine, diopside and enstatite grains are preserved in some samples. Olivine grains from the least altered samples have δ26Mg varying from -0.30 to -0.12‰ (n = 7), whereas enstatite and diopside have δ26Mg varying from -0.27 to -0.16‰ (n = 7), and from -0.23 to -0.09‰ (n = 6), respectively. Whole-rock δ26Mg values range from -0.24 to 0.03‰ with an average of -0.12 ± 0.13‰ (2SD, n = 32). Strongly serpentinized peridotites have lower average δ26Mg values (δ26Mg = -0.19 ± 0.07‰, 2SD, n = 7) than weathering-dominated ones (δ26Mg = -0.10 ± 0.12‰, 2SD, n = 25). Calculated Mg isotopic compositions of fresh mantle peridotites vary from -0.29 to -0.13‰, beyond the previously reported range of the subcontinental lithospheric mantle (-0.25 ± 0.04‰) and the analytical uncertainty (±0.07‰, 2SD). Our study therefore indicates that the oceanic mantle may have similar but slightly heterogeneous Mg isotopic compositions to that of subcontinental lithospheric mantle. Secondary serpentinization does not fractionate Mg isotopes of abyssal peridotites, whereas low-T weathering and formation of clay can result in the enrichment of heavy Mg isotopes in abyssal peridotites. This study also demonstrates that fluid-rock interaction does not necessarily produce rocks with intermediate Mg isotopic compositions. Magnesium isotopes of the rocks thereafter are dependent on the secondary minerals formed. We also conclude that the release of light Mg isotopes into the ocean during alteration of abyssal

  12. Measurement of fatty acid oxidation: validation of isotopic equilibrium extrapolation

    Robin, A.P.; Jeevanandam, M.; Elwyn, D.H.; Askanazi, J.; Kinney, J.M.


    Measurement of whole body substrate oxidation requires prolonged isotope infusion to attain plateau specific activity (SA) of expired CO/sub 2/. We have investigated in 13 hospitalized patients a technique whereby plateau /sup 14/CO/sub 2/ SA is extrapolated using computer curve fitting based upon the early exponential rise. A primed-constant infusion of albumin-bound 1-/sup 14/C-palmitate was continued for 260 minutes with isotope priming of the secondary bicarbonate pool at 70 minutes. Plasma free fatty acid (FFA) SA reached steady state by 40 minutes and was 91% +/- 4% (SE) of values obtained at 190 to 260 minutes. At 70 minutes /sup 14/CO/sub 2/ SA reached only 44% +/- 1% of the 190 to 260 minute values, which were consistently at plateau. The predicted steady state /sup 14/CO/sub 2/ SA from the 40 to 70 minute curves and the FFA oxidation rates calculated from those values were 94% +/- 2% and 102% +/- 4%, respectively, of values measured at steady state (190 to 260 minutes). The relationship between predicted and measured values approximated the line of identity for /sup 14/CO/sub 2/ SA (y = 0.90x + 0.14, r = .98, P less than .001) and FFA oxidation (y = 1.02x, r = .98, P less than .001). The results suggest that FFA oxidation can be accurately calculated using a short infusion of labeled FFA without bicarbonate pool priming, thus avoiding overpriming or underpriming and possibly allowing multiple studies and diminished radioisotope exposure.

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

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


    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.

  14. Equilibrium simulations of Marine Isotope Stage 3 interstadial climate

    Guo, Chuncheng; Nisancioglu, Kerim; Bentsen, Mats; Bethke, Ingo


    Marine Isotope Stage 3 (MIS3) was a period between approximately 60 ka to 30 ka BP that is characterised by abrupt climate transitions between cold, stadial and mild, interstadial climate conditions. The fluctuations are known as Dansgaard-Oeschger (D-O) events featured by a rapid warming from stadial to interstadial in a matter of a few decades, followed by a gradual cooling to stadial. We present fully coupled climate simulations of a pre-industrial control run and a MIS3 experiment at 38 ka, both integrated for 2000 years using the Norwegian Earth System Model (NorESM). With the recent model developments in the Bjerknes Centre for Climate Research (Norway), a new and efficient NorESM version (BCCR fast version) with 2 degrees atmosphere and 1 degree ocean is configured for paleo-modelling. BCCR fast version is capable of simulating Arctic sea ice and North Atlantic inflow well. We will present the large scale climate features in the MIS3 interstadial relative to today, such as the Atlantic Meridional Overturning Circulation, surface air temperature, etc. We also focus on the climate conditions in the Arctic and discuss the ocean circulations and sea ice conditions. In addition, sensitivity experiments with freshwater input into different regions (e.g., along the Norwegian coast, in the Nordic Seas, in the Labrador Sea, and in the region between 50 and 70 N) are performed; we will show the response of Arctic sea ice and Greenland temperature change from the freshwater perturbations and their implications for D-O events.

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

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


    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.

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

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


    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

  17. Mg isotope ratios in giant stars of the globular clusters M 13 and M 71

    Yong, D; Lambert, D L; Yong, David; Aoki, Wako; Lambert, David L.


    We present Mg isotope ratios in 4 red giants of the globular cluster M 13 and 1 red giant of the globular cluster M 71 based on spectra obtained with HDS on the Subaru Telescope. We confirm earlier results by Shetrone that for M 13, the ratio varies from (25+26)Mg/24Mg = 1 in stars with the highest Al abundance to (25+26)Mg/24Mg = 0.2 in stars with the lowest Al abundance. However, we separate the contributions of all three isotopes and find a spread in the ratio 24Mg:25Mg:26Mg with values ranging from 48:13:39 to 78:11:11. As in NGC 6752, we find a positive correlation between 26Mg and Al, an anticorrelation between 24Mg and Al, and no correlation between 25Mg and Al. In M 71, our one star has a ratio 70:13:17. For both clusters, the lowest ratios of 25Mg/24Mg and 26Mg/24Mg exceed those observed in field stars at the same metallicity, a result also found in NGC 6752. The contribution of 25Mg to the total Mg abundance is constant within a given cluster and between clusters with 25Mg/(24+25+26)Mg = 0.13. For M...

  18. Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

    Pogge von Strandmann, P. A. E.; Forshaw, J.; Schmidt, D. N.


    Magnesium is an element critically involved in the carbon cycle, because weathering of Ca-Mg silicates removes atmospheric CO2 into rivers, and formation of Ca-Mg carbonates in the oceans removes carbon from the ocean-atmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and isotopically heavy Mg during calcification, show no correlation between the Mg isotope composition (δ26Mg, relative to DSM-3) and temperature, Mg / Ca or other parameters such as carbonate saturation (ΔCO3). However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ26Mg inferred from the foraminiferal record decreased from ~0‰ at 15 Ma, to -0.83‰ at the present day, which coincides with increases in seawater lithium and oxygen isotope ratios. It strongly suggests that neither Mg concentrations nor isotope ratios are at steady state in modern oceans, given its ~10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers) and Mg sinks (dolomitisation and hydrothermal alteration). Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ26Mg of seawater, while hydrothermal Mg removal and the δ26Mg of rivers are more minor controls. Using Mg riverine flux and isotope ratios inferred from the 87Sr / 86Sr record, the modelled Mg removal by dolomite formation shows minima in the Oligocene and at the present day (with decreasing trends from 15 Ma

  19. Solubility measurement and solid-liquid equilibrium model for the ternary system MgBr2 + MgSO4 + H2O at 288.15 K

    Li Dan


    Full Text Available The solubility of magnesium minerals and the refractive index of the ternary system MgBr2 + MgSO4 + H2O at 288.15 K were investigated using an isothermal dissolution method. It was found that there are two invariant points in the phase diagram and the solubility isotherm of this ternary system consists of three branches, corresponding to equilibrium crystallization of Epsomite (MgSO4·7H2O, Eps, hexahydrite (MgSO4·6H2O, Hex and magnesium bromide hexahydrate (MgBr2·6H2O, Mb. Neither solid solutions nor double salts were found. The refractive indices calculated from empirical equation are in good agreement with the experimental data. Combining the results from solubility measurements with the single-salt parameters for MgBr2 and MgSO4, and the mixed ion-interaction parameter θBr,S0(4, the parameter ψMg,Br,S0(4 at 288.15 K was fitted using the Pitzer theory and Harvie-Weare (HW approach. In addition, the average equilibrium constants of the stable equilibrium solids at 288.15 K were obtained by a method using the activity product constant. A chemical model, which combined the Pitzer parameters and the average equilibrium constants, was constructed to calculate the solid + liquid equilibria in the ternary system MgBr2 + MgSO4 + H2O at 288.15 K. The model agreed well with the equilibrium solubility data for the magnesium salts.

  20. Isotope Effect on Electron-Phonon Coupling in Multiband Superconductor MgB2

    Mou, Daixiang; Taufour, Valentin; Wu, Yun; Huang, Lunan; Bud'Ko, Serguei; Canfield, Paul; Kaminski, Adam

    We systematically investigate the isotope effect of electron-phonon coupling in multi-band superconductor MgB2 by laser based Angle Resolved Photoemission Spectroscopy. The kink structure around 70 meV on two σ bands, which is caused by electron coupling to E2 g phonon mode, is shifted to higher binding energy in Mg10B2 than that in Mg11B2. The measured shifting energy of 3.5 meV is consistent with theoretical calculation based on harmonic phonon in MgB2. Our temperature dependent measurement also indicates the isotope effect of kink structure is not dependent on superconducting transition.

  1. Mg Isotope Evolution During Water-Rock Interaction in a Carbonate Aquifer

    Zhang, Z.; Jacobson, A. D.; Lundstrom, C. C.; Huang, F.


    To better understand how Mg isotopes behave during weathering and aqueous transport, we used a Nu Plasma MC-ICP-MS to measure δ26Mg values (relative to DSM-3) in water samples along a 236 km flow path in the Madison aquifer of South Dakota, a confined carbonate aquifer recharging in the igneous Black Hills. We also analyzed local granite and dolomite samples to characterize the Mg isotope composition of source rocks constituting the recharge zone and aquifer, respectively. Repeated analyses of Mg standard solutions yielded external precisions (2σ) better than 0.1 permil for δ26Mg(CAM-1, - 2.584±0.071, n=13; UIMg-1, -2.217±0.087, n=9.). The Madison aquifer provides a unique opportunity to quantify Mg isotope effects during water-rock interaction because (1) fluids and rock have chemically equilibrated over a much longer timescale (up to ~15 kyr) than can be simulated in laboratory experiments and (2) previous studies have determined the rates and mass-balances of de- dolomitization and other geochemical reactions controlling solute evolution along the flow path. Reactions important for changing the concentration and isotope composition of Mg include dolomite dissolution, Mg-for- Na ion exchange, calcite precipitation, and isotope exchange. δ26Mg values within the recharge region (0-17 km along flow path) vary between -1.08 and -1.63 permil, and then remain essentially constant at -1.408±0.010 permil(1σ, 5 samples) from 17 to 189 km. A final sample at 236 km shows an increase to -1.09 permil. Either mixing between different recharge waters or rapid isotope exchange between infiltrating waters and dolomite could control δ26Mg variability between 0 and 17 km. Likewise, reactive transport modeling suggests that preferential uptake of 24Mg during Mg-for-Na ion exchange might cause an increase in δ26Mg between 189 and 236 km. However, unchanging δ26Mg values observed throughout most of the aquifer clearly demonstrate that Mg isotopes are not fractionated during

  2. Modern and Cenozoic records of magnesium behaviour from foraminiferal Mg isotopes

    P. A. E. Pogge von Strandmann


    Full Text Available Magnesium is an element critically involved in the carbon cycle, because weathering of Ca–Mg silicates removes atmospheric CO2 into rivers, and formation of Ca–Mg carbonates in the oceans removes carbon from the ocean–atmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and isotopically heavy Mg during calcification, show no correlation between the Mg isotope composition (δ26Mg and temperature, Mg / Ca or other parameters such as carbonate saturation (Δ CO3. However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ26Mg inferred from the foraminiferal record decreased from ~ 0‰ at 15 Ma, to −0.83‰ at the present day, which coincides with increases in seawater lithium and oxygen isotope ratios. It strongly suggests that neither Mg concentrations nor isotope ratios are at steady-state in modern oceans, given its ~ 10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers and Mg sinks (dolomitisation and hydrothermal alteration. Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ26Mg of seawater, while hydrothermal Mg removal and the δ26Mg of rivers are more minor controls. Using riverine flux and isotope ratios inferred from the 87Sr / 86Sr record, the modelled Mg removal by dolomite formation shows minima in the Oligocene and at the present day (with decreasing trends from 15

  3. Theoretical calculation of equilibrium copper (I) isotope fractionations in ore-forming fluid

    Seo, J.; Lee, I.; Lee, S.


    Equilibrium isotope fractionation of Cu (I) complexes in hydrothermal ore-forming fluid is calculated. Ab-initio quantum calculation of molecular structures and vibrational frequencies is conducted by Density Functional Theory (DFT) and Hartree-Fock Self Consistent Field (HF-SCF) method. Cu isotope (65Cu, 63Cu) exchange is expressed as reduced partition function ratios, 103·ln(β65-63), for liquid phase complexes (copper chlorides, copper hydrosulfides), and vapor phase complexes (hydrated copper chloride). Isodensity Polarizable Continuum Model (IPCM) is applied to the liquid complexes, whereas the vapor complexes are calculated in vacuo. Large fractionation (more than 2‰ at 25°C) is predicted between coexisting phases without changing oxidation state. CuCl(H2O)2 (vapor phase) is enriched in 65Cu better than any other studied complexes, whereas [CuCl3]2- (liquid phase) is mostly depleted. Heavy copper isotope is favor to partition into vapor phase complexes than coexisting liquid phase complexes. In the sea-floor hydrothermal system, after separation of phases into vapor and brine, vapor phase (CuCl(H2O)2) and chlorine-rich brine ([CuCl3]2-) will show +0.418‰ and -0.688‰ deviation from [CuCl2]1- at 150°C, respectively. However, most of the dominant copper-bearing species in hydrothermal condition, [CuCl2]1- and [Cu(HS)2]1-, fractionate at almost the same degree. Possible ranges of copper isotope ratio, δ65Cu, can be constrained from the calculated equilibrium isotope fractionation. Changes of oxidation state in low-temperature (e.g. supergene formation) have been thought to trigger most copper isotope fractionations, so far. However, measurable Cu isotope fractionation (1.106‰ at 150°C and 0.615‰ at 300°C) in hydrothermal ore-forming fluid is predicted within +1 valence state by theoretical study. Molecular structures and vibrational frequencies are compared with measured data. However, there is no experimental or theoretical work of some molecules

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

    M H Bölükdemir; E Tel; S Okuducu; N N Akti


    The neutron skin effect has been investigated for even isotopes of molybdenum at 25.6 MeV 94−100Mo(, ) reaction using the geometry-dependent hybrid model of pre-equilibrium nuclear reactions. Here the initial neutron/proton exciton numbers were calculated from the neutron/proton densities obtained from an effective nucleon–nucleon interaction of the Skyrme type. Initial exciton numbers from different radii of even Mo isotopes were used to obtain the corresponding neutron emission spectra. In this investigation the calculated results are compared with the experimental data as also with each other. The results using central densities in the geometry-dependent hybrid model are in better agreement with the experimental data.

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

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


    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

  6. Coherent phonon decay and the boron isotope effect for MgB2.

    Alarco, Jose A; Talbot, Peter C; Mackinnon, Ian D R


    Ab initio DFT calculations for the phonon dispersion (PD) and the phonon density of states (PDOS) of the two isotopic forms ((10)B and (11)B) of MgB2 demonstrate that use of a reduced symmetry super-lattice provides an improved approximation to the dynamical, phonon-distorted P6/mmm crystal structure. Construction of phonon frequency plots using calculated values for these isotopic forms gives linear trends with integer multiples of a base frequency that change in slope in a manner consistent with the isotope effect (IE). Spectral parameters inferred from this method are similar to that determined experimentally for the pure isotopic forms of MgB2. Comparison with AlB2 demonstrates that a coherent phonon decay down to acoustic modes is not possible for this metal. Coherent acoustic phonon decay may be an important contributor to superconductivity for MgB2.

  7. Theoretical prediction for several important equilibrium Ge isotope fractionation factors and geological implications

    Li, Xuefang; Zhao, Hui; Tang, Mao; Liu, Yun


    This study estimates equilibrium fractionation factors in the Ge isotope system, including the dominant aqueous Ge(OH) 4 and GeO(OH) 3- species in seawater, Ge-bearing organic complexes (e.g. Ge-catechol, Ge-oxalic acid and Ge-citric acid), and Ge in quartz- (or opal-), albite-, K-feldspar-, olivine- and sphalerite-like structures. Estimations are based on Urey model (or Bigeleisen-Mayer equation) and high level quantum chemistry calculations. All calculations are made at B3LYP/6-311 + G(d,p) theory level. Solvation effects are treated by explicit solvent model ("water-droplet" method), and mineral structures are simulated using cluster models, in which the clusters are cut from the X-ray structures of those minerals. In addition, a number of different conformers are used for aqueous complexes in order to reduce the possible errors coming from the differences of configurations in solution. The "salt effect" on GeO(OH) 3-(aq) species is also carefully evaluated. We estimate the accuracy of these fractionation calculations at about ± 0.3‰. Excitedly, very large isotope fractionations are found between many Ge isotope systems. The Ge-containing sulfides (e.g. sphalerite) can extremely enrich light Ge isotopes (more than 10‰) compared with 4-coordinated Ge-O compounds (e.g. Ge(OH) 4(aq) or quartz). The fractionations between Ge(OH) 4(aq) and 6-coordinated Ge-bearing organic complexes can be also up to 4‰ at 25 °C. These results give a good explanation for the experimental observations of Rouxel et al. (2006). It also suggests a great potential for broad application of Ge isotope method in various geological systems.

  8. Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite

    Mavromatis, Vasileios; Immenhauser, Adrian; Buhl, Dieter; Purgstaller, Bettina; Baldermann, Andre; Dietzel, Martin


    Calcite growth experiments have been performed at 25 oC and 1 bar pCO2 in the presence of aqueous Mg and six organic ligands in the concentration range from 10-5 to 10-3 M. These experiments were performed in order to quantify the effect of distinct organic ligands on the Mg partitioning and Mg stable isotope fractionation during its incorporation in calcite at similar growth rates normalized to total surface area. The organic ligands used in this study comprise of (i) acetate acid, (ii) citrate, (iii) glutamate, (iv) salicylate, (v) glycine and (vi) ethylenediaminetetraacetic acid (EDTA), containing carboxyl- and amino-groups. These fuctional groups are required for bacterial activity and growth as well as related to biotic and abiotic mineralization processes occurring in sedimentary and earliest diagenetic aquatic environments (e.g. soil, cave, lacustrine, marine). The results obtained in this study indicate that the presence of organic ligands promotes an increase in the partition coefficient of Mg in calcite (DMg = (Mg/Ca)calcite (Mg/Ca)fluid). This behaviour can be explained by the temporal formation of aqueous Mg-ligand complexes that are subsequently adsorbed on the calcite surfaces and thereby reducing the active growth sites of calcite. The increase of DMg values as a function of the supersaturation degree of calcite in the fluid phase can be described by the linear equation LogDMg =0.3694 (±0.0329)×SIcalcite - 1.9066 (±0.0147); R2=0.92 In contrast, the presence of organic ligands, with exception of citrate, does not significantly affect the Mg isotope fractionation factor between calcite and reactive fluid (Δ26Mgcalcite-fluid = -2.5 ±0.1). Citrate likely exhibits larger fractionation between the Mg-ligand complexes and free aqueous Mg2+, compared to the other organic ligands studied in this work, as evidenced by the smaller Δ26Mgcalcite-fluid values. These results indicate that in Earth's surface calcite precipitating environments that are

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

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


    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

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

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


    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.

  11. Effect of interband interaction on isotope effect exponent of MgB2 superconductors

    P Udomsamuthirun; C Kumvongsa; A Burakorn; P Changkanarth


    The exact formula of c's equation and the isotope effect exponent of two-band s-wave superconductors in the weak-coupling limit are derived by considering the influence of interband interaction. In each band, our model consists of two pairing interactions: the electron-phonon interaction and non-electron-phonon interaction. We find that the isotope effect exponent of MgB2, = 0.3 with c ≈ 40 K can be found in the weak coupling regime and interband interaction of electron-phonon shows more effect on the isotope effect exponent than on the interband interaction of non-phonon.

  12. Mg isotopes in biocarbonates: new insight into vital effects associated to echinoderms and bivalves calcification

    Planchon, F.; Hermans, J.; Borremans, C.; Dubois, P.; Poulain, C.; Paulet, Y.; Andre, L.


    Mg isotopes can be helpful tracers to reveal the fundamental pathways of Mg incorporation during biomineralisation. We report in this study a detailed characterisation of the Mg isotopic signatures of different biominerals: high magnesium calcitic skeletons of selected echinoderms (sea urchins and starfish) and low magnesium aragonitic shells of a bivalve species (clam). State of the art analytical procedures were applied including sample purification step followed by high precision measurements using MC-ICP-MS (Nu instrument) in dry plasma conditions. 26Mg/24Mg and 25Mg/24Mg are expressed as per mil deviations from the DSM3 (Dead Sea Metal 3) reference standard in delta notation (d26Mg and d25Mg). For echinoderms, we considered: (a) adult specimens of six starfish species (Asteria r., Marthasterias g., Anseropoda p., Asterina g., Echinaster s. and Henricia o.), sampled in Brittany (France); (b) a sea urchin species (Paracentrotus lividus) with field samples (Mediterranean Sea, Marseille, France) and culture specimen under T and S controlled conditions. In vivo endoskeletons display negative, but different d26Mg values of -3.06 for starfish (with uniform interspecies signatures) and -2.65 for sea urchin. Relative to seawater signature (-0.82), all echinoderms favour the incorporation of light isotopes during biocalcification. The d26Mg depletion is lower than theoretically expected from a inorganic calcite precipitation from seawater (at -3.5). These differences suggest that on its route from seawater to the shell, Mg isotopes are partly biologically fractionationated through "vital effects" leaving heavier Mg isotopic signatures. Taken into account that calcification in echinoderms is an intra- cellular process involving transient amorphous calcium carbonate (ACC) phase, the observed bio-fractionation factors can be related to: (1) changes in the isotopic composition of the precipitating intracellular fluids due to active pumping in and out of the cell; (2) a

  13. Can Mg isotopes be used to trace cyanobacteria-mediated magnesium carbonate precipitation in alkaline lakes?

    Shirokova, L. S.; Mavromatis, V.; Bundeleva, I.; Pokrovsky, O. S.; Bénézeth, P.; Pearce, C.; Gérard, E.; Balor, S.; Oelkers, E. H.


    The fractionation of Mg isotopes was determined during the cyanobacterial mediated precipitation of hydrous magnesium carbonate precipitation in both natural environments and in the laboratory. Natural samples were obtained from Lake Salda (SE Turkey), one of the few modern environments on the Earth's surface where hydrous Mg-carbonates are the dominant precipitating minerals. This precipitation was associated with cyanobacterial stromatolites which were abundant in this aquatic ecosystem. Mg isotope analyses were performed on samples of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments. Laboratory Mg carbonate precipitation experiments were conducted in the presence of purified Synechococcus sp cyanobacteria that were isolated from the lake water and stromatolites. The hydrous magnesium carbonates nesquehonite (MgCO3·3H2O) and dypingite (Mg5(CO3)4(OH)25(H2O)) were precipitated in these batch reactor experiments from aqueous solutions containing either synthetic NaHCO3/MgCl2 mixtures or natural Lake Salda water, in the presence and absence of live photosynthesizing Synechococcus sp. Bulk precipitation rates were not to affected by the presence of bacteria when air was bubbled through the system. In the stirred non-bubbled reactors, conditions similar to natural settings, bacterial photosynthesis provoked nesquehonite precipitation, whilst no precipitation occurred in bacteria-free systems in the absence of air bubbling, despite the fluids achieving a similar or higher degree of supersaturation. The extent of Mg isotope fractionation (Δ26Mgsolid-solution) between the mineral and solution in the abiotic experiments was found to be identical, within uncertainty, to that measured in cyanobacteria-bearing experiments, and ranges from -1.4 to -0.7 ‰. This similarity refutes the use of Mg isotopes to validate microbial mediated precipitation of hydrous Mg carbonates.

  14. Isotope effect on electron-phonon interaction in the multiband superconductor MgB2

    Mou, Daixiang; Manni, Soham; Taufour, Valentin; Wu, Yun; Huang, Lunan; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam


    We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the σ band, which is caused by electron coupling to the E2 g phonon mode, is shifted to higher binding energy by ˜3.5 meV in Mg 10B2 and the shift is not affected by superconducting transition. These results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown.

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

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


    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.

  16. New candidate for deformed halo nucleus in Mg isotopes through analysis of reaction cross sections

    Watanabe S.


    Full Text Available The total reaction cross sections of Mg isotopes on a 12C target at 240 MeV/nucleon have been analyzed with a fully microscopic framework, i.e., the double folding model with the density calculated by antisymmetrized molecular dynamics. Our results well reproduce the latest experimental data except 37Mg as a new candidate for a deformed halo nucleus.

  17. Nuclear Structure and Reaction Properties of Ne, Mg and Si Isotopes with RMF Densities

    Panda, R N; Patra, S K


    We have studied nuclear structure and reaction properties of Ne, Mg and Si isotopes, using relativistic mean field densities, in the frame work of Glauber model. Total reaction cross section $\\sigma_R$ for Ne isotopes on 12C target have been calculated at incident energy 240 MeV. The results are compared with the experimental data and with the recent theoretical study [W. Horiuchi et al., Phys. Rev. C, 86, 024614 (2012)]. Study of $\\sigma_R$ using deformed densities have shown a good agreement with the data. We have also predicted total reaction cross section $\\sigma_R$ for Ne, Mg and Si isotopes as projectiles and 12C as target at different incident energies.

  18. Core correlation effects in multiconfiguration calculations of isotope shifts in Mg I

    Filippin, Livio; Ekman, Jörgen; Jönsson, Per


    The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of isotope shifts for several well-known transitions in neutral magnesium. Relativistic normal and specific mass shift factors as well as the electronic probability density at the origin are calculated. Combining these electronic quantities with available nuclear data, energy and transition level shifts are determined for the $^{26}$Mg$-^{24}$Mg pair of isotopes. Different models for electron correlation are adopted. It is shown that although valence and core-valence models provide accurate values for the isotope shifts, the inclusion of core-core excitations in the computational strategy significantly improves the accuracy of the transition energies and normal mass shift factors.

  19. Can Mg isotopes be used to trace cyanobacteria-mediated magnesium carbonate precipitation in alkaline lakes?

    L. S. Shirokova


    Full Text Available The fractionation of Mg isotopes was determined during the cyanobacterial mediated precipitation of hydrous magnesium carbonate precipitation in both natural environments and in the laboratory. Natural samples were obtained from Lake Salda (SE Turkey, one of the few modern environments on the Earth's surface where hydrous Mg-carbonates are the dominant precipitating minerals. This precipitation was associated with cyanobacterial stromatolites which were abundant in this aquatic ecosystem. Mg isotope analyses were performed on samples of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments. Laboratory Mg carbonate precipitation experiments were conducted in the presence of purified Synechococcus sp cyanobacteria that were isolated from the lake water and stromatolites. The hydrous magnesium carbonates nesquehonite (MgCO3·3H2O and dypingite (Mg5(CO34(OH25(H2O were precipitated in these batch reactor experiments from aqueous solutions containing either synthetic NaHCO3/MgCl2 mixtures or natural Lake Salda water, in the presence and absence of live photosynthesizing Synechococcus sp. Bulk precipitation rates were not to affected by the presence of bacteria when air was bubbled through the system. In the stirred non-bubbled reactors, conditions similar to natural settings, bacterial photosynthesis provoked nesquehonite precipitation, whilst no precipitation occurred in bacteria-free systems in the absence of air bubbling, despite the fluids achieving a similar or higher degree of supersaturation. The extent of Mg isotope fractionation (Δ26Mgsolid-solution between the mineral and solution in the abiotic experiments was found to be identical, within uncertainty, to that measured in cyanobacteria-bearing experiments, and ranges from −1.4 to −0.7 ‰. This similarity refutes

  20. Ca and Mg isotope constraints on the origin of Earth's deepest δ13 C excursion

    Husson, Jon M.; Higgins, John A.; Maloof, Adam C.; Schoene, Blair


    Understanding the extreme carbon isotope excursions found in carbonate rocks of the Ediacaran Period (635-541 Ma), where δ13 C of marine carbonates (δ13 Ccarb) reach their minimum (- 12 ‰) for Earth history, is one of the most vexing problems in Precambrian geology. Known colloquially as the 'Shuram' excursion, the event has been interpreted by many as a product of a profoundly different Ediacaran carbon cycle. More recently, diagenetic processes have been invoked, with the very negative δ13 C values of Ediacaran carbonates explained via meteoric alteration, late-stage burial diagenesis or growth of authigenic carbonates in the sediment column, thus challenging models which rely upon a dramatically changing redox state of the Ediacaran oceans. Here we present 257 δ 44 / 40 Ca and 131 δ26 Mg measurements, along with [Mg], [Mn] and [Sr] data, from carbonates of the Ediacaran-aged Wonoka Formation (Fm.) of South Australia to bring new isotope systems to bear on understanding the 'Shuram' excursion. Data from four measured sections spanning the basin reveal stratigraphically coherent trends, with variability of ∼1.5‰ in δ26 Mg and ∼1.2‰ in δ 44 / 40 Ca. This Ca isotope variability dwarfs the 0.2-0.3 ‰ change seen coeval with the Permian-Triassic mass extinction, the largest recorded in the rock record, and is on par with putative changes in the δ 44 / 40 Ca value of seawater seen over the Phanerozoic Eon. Changes in both isotopic systems are too large to explain with changes in the isotopic composition of Ca and Mg in global seawater given modern budgets and residence times, and thus must be products of alternative processes. Relationships between δ 44 / 40 Ca and [Sr] and δ26 Mg and [Mg] are consistent with mineralogical control (e.g., aragonite vs. calcite, limestone vs. dolostone) on calcium and magnesium isotope variability. The most pristine samples in the Wonoka dataset, preserving Sr concentrations (in the 1000s of ppm range) and δ 44 / 40

  1. Precise calibration of equilibrium oxygen isotope fractionations between dissolved phosphate and water from 3 to 37 °C

    Chang, Sae Jung; Blake, Ruth E.


    The stable oxygen isotope composition of orthophosphate (δ18OPO4) is a widely used (paleo)temperature indicator and more recently, a useful tracer of phosphorus-cycling. In natural aqueous systems (e.g., oceans, rivers, soil/ground water) the largest reactive phosphorus pool is dissolved inorganic phosphate. Here, we present a new experimentally-determined equation for thermodynamic equilibrium O-isotope fractionations between dissolved phosphate and water, catalyzed by the enzyme inorganic pyrophosphatase (PPase) between 3 and 37 °C;

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

    Walters, Wendell W.; Michalski, Greg


    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.

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

    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.


    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.

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

    Nevinitsa, V. A., E-mail:; Dudnikov, A. A.; Blandinskiy, V. Yu.; Balanin, A. L.; Alekseev, P. N. [National Research Centre Kurchatov Institute (Russian Federation); Titarenko, Yu. E.; Batyaev, V. F.; Pavlov, K. V.; Titarenko, A. Yu., E-mail: [Institute for Theoretical and Experimental Physics (Russian Federation)


    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.

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

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


    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.

  6. Oxygen isotopic constraints on the origin of Mg-rich olivines from chondritic meteorites

    Libourel, Guy; Chaussidon, Marc


    Chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system, the calcium-aluminum-rich inclusions, were condensed from the nebula gas. Chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk. Petrographic, compositional and isotopic arguments allowed the identification of metal-bearing Mg-rich olivine aggregates among the precursors of magnesian type I chondrules. Two very different settings can be considered for the formation of these Mg-rich olivines: either a nebular setting corresponding mostly to condensation-evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal. An ion microprobe survey of Mg-rich olivines of a set of type I chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the ∆17O values and the presence of a large range of mass fractionation (several ‰) within each mode. The chemistry and the oxygen isotopic compositions indicate that Mg-rich olivines are unlikely to be of nebular origin (i.e., solar nebula condensates) but are more likely debris of broken differentiated planetesimals (each of them being characterized by a given ∆17O). Mg-rich olivines could have crystallized from magma ocean-like environments on partially molten planetesimals undergoing metal-silicate differentiation processes. Considering the very old age of chondrules, Mg-rich olivine grains or aggregates might be considered as millimeter-sized fragments from disrupted first-generation differentiated planetesimals. Finally, the finding of only a small number of discrete ∆17O modes for Mg-rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and

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

    Dideriksen, Knud; Baker, Joel A.; Stipp, Susan Louise Svane


    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, Fedesferrioxamine B (at pH 2). The two......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...... for the slower stage, indicating that approximately 40% reequilibration 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...

  8. Evolution of Single Particle and Collective properties in the Neutron-Rich Mg Isotopes

    Reiter, P; Wiens, A; Fitting, J; Lauer, M; Van duppen, P L E; Finke, F


    We propose to study the single particle and collective properties of the neutron-rich Mg isotopes in transfer reactions and Coulomb excitation using REX-ISOLDE and MINIBALL. From the Coulomb excitation measurement precise and largely model independent B( E2 ; 0$^{+}_{g.s.}\\rightarrow$ 2$^{+}_{1}$ ) will be determined for the even-even isotopes. For the odd isotopes the distribution of the E2 strength over a few low-lying states will be measured. The sign of the M1/E2 mixing ratio, extracted from angular distributions, is characteristic of the sign of the deformation, as is the resulting level scheme. The neutron-pickup channel in the transfer reactions will allow for a determination of the single particle properties (spin, parity, spectroscopic factors) of these nuclei. This information will give new insights in changes of nuclear structure in the vicinity of the island of deformation around $^{32}$Mg. A total of 24 shifts of REX beam time is requested.

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

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


    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.

  10. The calcite → aragonite transformation in low-Mg marble: Equilibrium relations, transformations mechanisms, and rates

    Hacker, Bradley R.; Rubie, David C.; Kirby, Stephen H.; Bohlen, Steven R.


    Experimental transformation of a rather pure natural calcite marble to aragonite marble did not proceed via the expected straightforward polymorphic replacement. Instead, the small amount of Mg in the starting material (0.36 wt %) was excluded from the growing aragonite and diffused preferentially into the remaining calcite grains, producing Mg-rich calcite rods that persisted as relicts. Nucleation of aragonite occurred exclusively on grain boundaries, with aragonite [001] oriented subparallel to calcite [0001]. The aragonite crystals preferentially consumed the calcite crystal on which they nucleated, and the reaction fronts developed preferentially along the {010} and {110} planes of aragonite. Each aragonite neoblast that grew was nearly free of Mg (typically growth rates are approximately linear and range from ∼3 × 10−11 m s−1 at 600°C to ∼9 × 10−9 m s−1 at 850°C, with an apparent activation enthalpy of 166 ± 91 kJ mol−1. This reaction mechanism and the resultant texture are akin to cellular precipitation reactions in metals. Similar transformation textures have been reported from high-Mg marbles in Japan and China that disproportionated to low-Mg calcite and dolomite.

  11. Prediction of equilibrium Li isotope fractionation between minerals and aqueous solutions at high P and T: an efficient ab initio approach

    Kowalski, Piotr M


    The mass-dependent equilibrium stable isotope fractionation between different materials is an important geochemical process. Here we present an efficient method to compute the isotope fractionation between complex minerals and fluids at high pressure, P, and temperature, T, representative for the Earth's crust and mantle. The method is tested by computation of the equilibrium fractionation of lithium isotopes between aqueous fluids and various Li bearing minerals such as staurolite, spodumene and mica. We are able to correctly predict the direction of the isotope fractionation as observed in the experiments. On the quantitative level the computed fractionation factors agree within 1.0 permil with the experimental values indicating predictive power of ab initio methods. We show that with ab initio methods we are able to investigate the underlying mechanisms driving the equilibrium isotope fractionation process, such as coordination of the fractionating elements, their bond strengths to the neighboring atoms, c...

  12. High-precision Mg isotope measurements of terrestrial and extraterrestrial material by HR-MC-ICPMS—implications for the relative and absolute Mg isotope composition of the bulk silicate Earth

    Bizzarro, Martin; Paton, Chad; Larsen, Kirsten Kolbjørn


    shergottite and sea water samples. Repeated analyses of terrestrial and extraterrestrial samples demonstrate that it is possible to routinely measure the relative Mg-isotope composition of silicate materials with an external reproducibility of 2.5 and 20 ppm for the m26Mg* and m25Mg values, respectively (m......-isotope composition for Earth’s mantle – and hence that of the bulk silicate Earth – to be 25Mg/24Mg 1/4 0.126896 ¿ 0.000025 and 26Mg/24Mg 1/4 0.139652 ¿ 0.000033. Given the restricted range of m25Mg obtained for bulk planetary material by the sample-standard bracketing technique and the excellent agreement between...

  13. The nucleosynthesis of heavy elements in Stars: the key isotope 25Mg

    Massimi C.


    Full Text Available We have measured the radiative neutron-capture cross section and the total neutron-induced cross section of one of the most important isotopes for the s process, the 25Mg. The measurements have been carried out at the neutron time-of-flight facilities n_TOF at CERN (Switzerland and GELINA installed at the EC-JRC-IRMM (Belgium. The cross sections as a function of neutron energy have been measured up to approximately 300 keV, covering the energy region of interest to the s process. The data analysis is ongoing and preliminary results show the potential relevance for the s process.

  14. The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment

    Chapela Lara, María; Buss, Heather L.; Pogge von Strandmann, Philip A. E.; Schuessler, Jan A.; Moore, Oliver W.


    In order to assess the effects of critical zone processes on Mg concentrations and isotopic signatures of tropical streams, we studied a well constrained, highly weathered andesitic volcaniclastic catchment in the Luquillo Critical Zone Observatory, Puerto Rico. Our results indicate that dissolved Mg concentrations and isotope ratios in the regolith pore water are mainly controlled by rain input, with weathering inputs being more important at sites with thinner regolith (2.7-0.9 m deep) and at depth (>8 m) on a thick ridgetop regolith (∼10 m). In addition to mixing of precipitation and weathering-sourced Mg, an isotopic fractionation process is taking place between dissolved Mg and the regolith, likely during dissolution or recrystallisation of Fe(III)-(hydro)oxides under alternating redox conditions. Bulk regolith is isotopically heavier than both the bedrock and the exchangeable fraction (δ26Mgregolith-bedrock = +0.03 to +0.47‰), consistent with the preferential incorporation of heavy 26Mg into secondary minerals with some exchange of sorbed Mg with isotopically lighter pore water. Magnesium concentrations in the stream show a typical dilution behaviour during a storm event, but the [Mg] - δ26Mg pattern cannot be explained by mixing of rain and pore water; the data are best explained by a steady-state fractionation model with α = 1.00115. During baseflow the stream has δ26Mg = +0.01‰, higher than any of the water samples or the bedrock. In-situ analysis of the Mg isotopic composition of bedrock minerals points at the dissolution of Mg-rich chlorite (δ26Mg = +0.19‰) as the most likely source of this isotopically heavy Mg, with mass balance calculations indicating chlorite dissolution is also the main source of Mg to the stream. Overall, our study highlights the importance of atmospheric input of nutrients to the vegetation in tropical areas covered by thick, highly leached regolith, whereas the Mg flux and Mg isotopic signature of watershed exports

  15. The effects of diagenesis and dolomitization on Ca and Mg isotopes in marine platform carbonates: Implications for the geochemical cycles of Ca and Mg

    Fantle, Matthew S.; Higgins, John


    The Ca, Mg, O, and C isotopic and trace elemental compositions of marine limestones and dolostones from ODP Site 1196A, which range in depth (∼58 to 627 mbsf) and in depositional age (∼5 and 23 Ma), are presented. The objectives of the study are to explore the potential for non-traditional isotope systems to fingerprint diagenesis, to quantify the extent to which geochemical proxies are altered during diagenesis, and to investigate the importance of diagenesis within the global Ca and Mg geochemical cycles. The data suggest that Ca, which has a relatively high solid to fluid mass ratio, can be isotopically altered during diagenesis. In addition, the alteration of Ca correlates with the alteration of Mg in such a way that both can serve as useful tools for deciphering diagenesis in ancient rocks. Bulk carbonate δ44Ca values vary between 0.60 and 1.31‰ (SRM-915a scale); the average limestone δ44Ca is 0.97 ± 0.24‰ (1SD), identical within error to the average dolostone (1.03 ± 0.15 1SD ‰). Magnesium isotopic compositions (δ26Mg, DSM-3 scale) range between -2.59‰ and -3.91‰, and limestones (-3.60 ± 0.25‰) and dolostones (-2.68 ± 0.07‰) are isotopically distinct. Carbon isotopic compositions (δ13C, PDB scale) vary between 0.86‰ and 2.47‰, with average limestone (1.96 ± 0.31‰) marginally offset relative to average dolostone (1.68 ± 0.57‰). The oxygen isotopic compositions (δ18O, PDB scale) of limestones (-1.22 ± 0.94‰) are substantially lower than the dolostones measured (2.72 ± 1.07‰). The isotopic data from 1196A suggest distinct and coherent trends in isotopic and elemental compositions that are interpreted in terms of diagenetic trajectories. Numerical modeling supports the contention that such trends can be interpreted as diagenetic, and suggests that the appropriate distribution coefficient (KMg) associated with limestone diagenesis is ∼1 to 5 × 10-3, distinctly lower than those values (>0.015) reported in laboratory

  16. Is my C isotope excursion global, local, or both? Insights from the Mg and Ca isotopic composition of primary, diagenetic, and authigenic carbonates

    Higgins, J. A.; Blättler, C. L.; Husson, J. M.


    The C isotopic composition of ancient limestones and dolomites is a widely used proxy for the global geochemical cycles of carbon and oxygen in the ocean-atmosphere system and a critical tool for chemostratigraphy in Precambrian rocks. Although relatively robust to diagenesis, the C isotopic composition of bulk carbonates can be reset when conditions favor high water-to-rock ratios or fluids with high C concentrations and distinct isotopic compositions. Authigenic carbonates and different pools of primary carbonate (e.g. calcite vs. aragonite) may also bias the C isotopic composition of bulk carbonates if they are both abundant and isotopically distinct. New approaches to quantifying contributions from diagenesis, authigenesis, and mixing of primary carbonates to the C isotopic composition of bulk sedimentary carbonates are needed. Here we present preliminary Mg and Ca isotope data sets of primary, diagenetic, and authigenic carbonates, both modern and ancient. We show that recrystallization, dolomitization, and authigenesis produce Mg and Ca isotope fingerprints that may be used to identify and characterize these processes in ancient carbonate sediments.

  17. Constraining dolomitization by Mg isotopes: A case study from partially dolomitized limestones of the middle Cambrian Xuzhuang Formation, North China

    Peng, Yang; Shen, Bing; Lang, Xian-Guo; Huang, Kang-Jun; Chen, Ji-Tao; Yan, Zhen; Tang, Wen-bo; Ke, Shan; Ma, Hao-Ran; Li, Fang-Bing


    The "dolomite problem" refers to the rare dolomite formation in modern oceans that is in sharp contrast to the widespread ancient dolostone in rock record, as well as failure of laboratory inorganic dolomite precipitation at near Earth-surface temperature. Novel Mg isotope systematics provides a promising tool in resolving the "dolomite problem". Here, we develop a protocol to place constraints on the dolomitization process by using Mg isotopes. In this study, we measured Mg isotopic compositions (δ26Mg) of two batches of partially dolomitized limestone samples from the middle Cambrian Xuzhuang Formation in North China. δ26Mg varies between -0.55‰ and -3.18‰, and shows a negative linear correlation with 1>/[Mg>], suggesting that δ26Mg can be described by a binary mixing between the calcite and dolomite components. Mg isotopic composition of the dolomite component (δ26Mgdol) for the lower sample set that is collected from a 4 m stratigraphic interval containing three high-frequency ribbon rock-packstone cycles is -1.6‰, while δ26Mgdol for the upper sample set (from a thick sequence of ribbon rock) is significantly higher (-0.3‰). However, neither mineralogical and elemental compositions, carbon and oxygen isotopes, nor crystal morphologies of dolomite provides diagnostic criteria to differentiate these two batches of samples. δ26Mgdol of the Xuzhuang limestone is simulated by the Advective Flow (AF) and the Diffusion-Advection-Reaction (DAR) models. The AF model assumes that Mg is transported by advective fluid flows, while the DAR model simulates a contemporaneous seawater dolomitization process, in which Mg is delivered by diffusion. The AF modeling result indicates that δ26Mg of the dolomitization fluid is +0.4‰ and +1.7‰ for the lower and upper sample sets, respectively. These values are significantly higher than modern and Cenozoic seawater Mg isotopic composition, suggesting that the dolomitization fluid is not contemporaneous seawater. The

  18. Mg/Ca and isotopic high resolution record of deep-sea hydrothermal barnacles

    Bojar, A.-V.; Bojar, H.-P.; Tufar, W.


    Barnacles are crustaceans adapted to a sessile existence and cemented to a substrate by a protein complex. Most of the known species inhabit shallow marine environment, less than 2% of the species are found at depths between 100 and 2500 m. The shell of barnacles has a great adaptive significance, the shell of some barnacle species have been already investigated for microstructure. In this study we investigated the shell microstructure as well as the Mg/Ca and stable isotope distribution of barnacles found at a depth of around 2500m at a black smoker from the Manus Spreading centre, north-east of Papua New Guinea. The shell consists of three substructures: an outer layer with pores and aragonite crystals, a massive interior mass and an inner layer with pores. The shell shows grown lines and the outer layer exhibits longitudinal striation from base to apex. The pores have a medium size of 0.8 microns. The size of the calcitic microcrystals are in the range of 0.2 to 0.5 microns, beside, larger aragonite crystals, with size of c. 10 microns are present. The massive interior mass has a compact structure, no pores or channels could be observed. Oxygen stable isotope data of barnacle shell were performed from the centre to the border of the calcitic shells, along profiles. Within one shell, the isotope values show variations of max. 0.6 ‰. The calculated temperatures from the stable isotope data consistently indicate that the barnacles populate sites with low temperature values, up to a few °C. The calculated temperatures from the isotope data are also in agreement with the reported habitat from the North Fiji and Lau Basins, where temperatures of max. 6°C were measured at sites populated by barnacles. Both calculated and measured temperatures of a few degrees indicate that at the sites where barnacles live, hydrothermal fluid input is present, as ambient temperature is around 1.5°C. Electron-microbeam analyses were done along the interior layer of the shell. The

  19. Doping-Induced Isotopic Mg11B2 Bulk Superconductor for Fusion Application

    Qi Cai


    Full Text Available Superconducting wires are widely used for fabricating magnetic coils in fusion reactors. Superconducting magnet system represents a key determinant of the thermal efficiency and the construction/operating costs of such a reactor. In consideration of the stability of 11B against fast neutron irradiation and its lower induced radioactivation properties, MgB2 superconductor with 11B serving as the boron source is an alternative candidate for use in fusion reactors with a severe high neutron flux environment. In the present work, the glycine-doped Mg11B2 bulk superconductor was synthesized from isotopic 11B powder to enhance the high field properties. The critical current density was enhanced (103 A·cm−2 at 20 K and 5 T over the entire field in contrast with the sample prepared from natural boron.

  20. Photodissociation spectroscopy of the Mg + -CO2 complex and its isotopic analogs

    Yeh, C. S.; Willey, K. F.; Robbins, D. L.; Pilgrim, J. S.; Duncan, M. A.


    Mg+-CO2 ion-molecule cluster complexes are produced by laser vaporization in a pulsed nozzle cluster source. The vibronic spectroscopy in these complexes is studied with mass-selected photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer. Two excited electronic states are observed (2) 2Σ+ and 2Π. The 2Π state has a vibrational progression in the metal-CO2 stretching mode (ωe'=381.8 cm-1). The complexes are linear (Mg+-OCO) and are bound by the charge-quadrupole interaction. The dissociation energy (D0`) is 14.7 kcal/mol. Corresponding spectra are measured for each of the 24, 25, and 26 isotopes of magnesium. These results are compared to theoretical predictions made by Bauschlicher and co-workers.

  1. The complex nature of superconductivity in MgB2 as revealed by the reduced total isotope effect.

    Hinks, D G; Claus, H; Jorgensen, J D


    Magnesium diboride, MgB2, was recently observed to become superconducting at 39 K, which is the highest known transition temperature for a non-copper-oxide bulk material. Isotope-effect measurements, in which atoms are substituted by isotopes of different mass to systematically change the phonon frequencies, are one of the fundamental tests of the nature of the superconducting mechanism in a material. In a conventional Bardeen-Cooper-Schrieffer (BCS) superconductor, where the mechanism is mediated by electron-phonon coupling, the total isotope-effect coefficient (in this case, the sum of both the Mg and B coefficients) should be about 0.5. The boron isotope effect was previously shown to be large and that was sufficient to establish that MgB2 is a conventional superconductor, but the Mg effect has not hitherto been measured. Here we report the determination of the Mg isotope effect, which is small but measurable. The total reduced isotope-effect coefficient is 0.32, which is much lower than the value expected for a typical BCS superconductor. The low value could be due to complex materials properties, and would seem to require both a large electron-phonon coupling constant and a value of mu* (the repulsive electron-electron interaction) larger than found for most simple metals.

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

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


    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

  3. Pivaloylmetals (tBu-COM: M = Li, MgX, K) as equilibrium components.

    Knorr, R; Böhrer, G; Schubert, B; Böhrer, P


    Short-lived pivaloylmetals, (H(3)C)(3)C-COM, were established as the reactive intermediates arising through thermal heterolytic expulsion of O=CtBu(2) from the overcrowded metal alkoxides tBuC(=O)-C(-OM)tBu(2) (M = MgX, Li, K). In all three cases, this fission step is counteracted by a faster return process, as shown through the trapping of tBu-COM by O=C(tBu)-C(CD(3))(3) with formation of the deuterated starting alkoxides. If generated in the absence of trapping agents, all three tBu-COM species "dimerize" to give the enediolates MO-C(tBu)=C(tBu)-OM along with O=CtBu(2) (2 equiv). A common-component rate depression by surplus O=CtBu(2) proves the existence of some free tBu-COM (separated from O=CtBu(2)); but companion intermediates with the traits of an undissociated complex such as tBu-COM & O=CtBu(2) had to be postulated. The slow fission step generating tBu-COMgX in THF levels the overall rates of dimerization, ketone addition, and deuterium incorporation. Formed by much faster fission steps, both tBu-COLi and tBu-COK add very rapidly to ketones and dimerize somewhat slower (but still fairly fast, as shown through trapping of the emerging O=CtBu(2) by H(3)CLi or PhCH(2)K, respectively). At first sight surprisingly, the rapid fission, return, and dimerization steps combine to very slow overall decay rates of the precursor Li and K alkoxides in the absence of trapping agents: A detailed study revealed that the fast fission step, generating tBu-COLi in THF, is followed by a kinetic partitioning that is heavily biased toward return and against the product-forming dimerization. Both tBu-COLi and tBu-COK form tBu-CH=O with HN(SiMe(3))(3), but only tBu-COK is basic enough for being protonated by the precursor acyloin tBuC(=O)-C(-OH)tBu(2) .

  4. Pygmy dipole mode in deformed neutron-rich Mg isotopes close to the drip line

    Yoshida, Kenichi


    We investigate the microscopic structure of the low-lying isovector-dipole excitation mode in neutron-rich Mg36,38,40 close to the drip line by means of the deformed quasiparticle random-phase approximation employing the Skyrme and the local pairing energy-density functionals. It is found that the low-lying bump structure above the neutron emission-threshold energy develops when the drip line is approached, and that the isovector dipole strength at ExThomas-Reiche-Kuhn dipole sum rule in Mg40. We obtained the collective dipole modes at around 8-10 MeV in Mg isotopes, that consist of many two-quasiparticle excitations of the neutron. The transition density clearly shows an oscillation of the neutron skin against the isoscalar core. We found significant coupling effects between the dipole and octupole excitation modes due to the nuclear deformation. It is also found that the responses for the compressional dipole and isoscalar octupole excitations are much enhanced in the lower energy region.

  5. Mg++ and K+ Distribution in Frog Muscle and Egg: A Disproof of the Donnan Theory of Membrane Equilibrium Applied to the Living Cells,


    ELECTE! Mg++ and K+ Distribution in Frog Muscle and Egg: B A Disproof of the Donnan Theory of Membrane B Equilibrium Applied to the Living Cells GILBERT...19107 J ABSTRACT 1. We studied the equilibrium distribution of Mg** in the form of chlo- ride and pulfate at two temperatures (5* and 25°C) in frog ...vicinity of 90 jmoles/g/ fresh muscle cells. 4. We observed a similar rectilinear distribution of Mg** in frog ovarian eggs. As in muscle tissues, no major

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

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


    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. Copyright © 2014 Wiley Periodicals, Inc.

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

    Tang, M.; Liu, Y.


    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

  8. Ground-state properties and symmetry energy of neutron-rich and neutron-deficient Mg isotopes

    Gaidarov, M K; Antonov, A N; de Guerra, E Moya


    A comprehensive study of various ground-state properties of neutron-rich and neutron-deficient Mg isotopes with $A$=20-36 is performed in the framework of the self-consistent deformed Skyrme-Hartree-Fock plus BCS method. The correlation between the skin thickness and the characteristics related with the density dependence of the nuclear symmetry energy is investigated for this isotopic chain following the theoretical approach based on the coherent density fluctuation model and using the Brueckner energy-density functional. The results of the calculations show that the behavior of the nuclear charge radii and the nuclear symmetry energy in the Mg isotopic chain is closely related to the nuclear deformation. We also study, within our theoretical scheme, the emergence of an "island of inversion" at neutron-rich $^{32}$Mg nucleus, that was recently proposed from the analyses of spectroscopic measurements of $^{32}$Mg low-lying energy spectrum and the charge rms radii of all magnesium isotopes in the $sd$ shell.

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

    Polyakov, Veniamin B.


    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.

  10. Temperature dependency of the triple isotope fractionation relationship for equilibrium processes

    Hayles, J. A.; Cao, X.; Bao, H.


    The use of an approximation to the Bigeleisen-Mayer-Urey model for isotope fractionation has led to the concept of a constant, and later constrained, mass fractionation law for multiple isotopes of the same element. This concept has brought new insights to investigation in photochemistry, radical chemistry, or the contribution of quantum tunneling to chemical and biological processes. Despite previous work indicating that these mass fractionation laws can be highly variable, the concept of a constant relationship remains common in these fields. Using the diatomic case as a first-order approximation, we demonstrate generically that the mass fractionation exponent, θ, can take any value for small fractionations but is less variable for large fractionations. The predicted variability is larger than both theoretical and analytical precision. These deviations from the traditional range of mass-dependence exponents are the largest under cross-over scenarios, but can occur for any scenario with small fractionations. We advocate the use of ∆∆‡M or "change in cap-delta", defined strictly with a slope of at the high-temperature limit, as a necessary, more reliable and more useful descriptor of mass-dependent fractionation. This work can bring new insights and a conventional explanation to low temperature experiments yielding traditionally unusual mass fractionation laws.

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


    Goldman S. D. et a ..., Geochim. Cosmochim. Acta (2008), doi:10.1016/j.gca.2008.09tions of Urey (1947). First, we predicted the equilibrium constants...11623–11627. Urey H. C. (1947) The thermodynamic properties of isotopic substances. J. Chem. Soc., 562–581. Walker J. C. G., Klein C., Schidlowski M

  12. Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite in the absence of growth rate effects

    Mavromatis, Vasileios; Immenhauser, Adrian; Buhl, Dieter; Purgstaller, Bettina; Baldermann, Andre; Dietzel, Martin


    Calcite growth rate has been previously shown to be the dominating parameter controlling both Mg partitioning and Mg isotope fractionation during calcite growth. In natural calcite precipitation environments - characterized by abundant organic material - the presence of dissolved organic molecules may affect these two parameters. In order to assess the role of organic molecules, steady state calcite growth experiments have been performed at 25 °C, 1 bar pCO2 and constant, within analytical uncertainty growth rate (rp = 10-7.4 mol m-2 s-1) in the presence of aqueous Mg and six organic ligands in the concentration range from 0.01 to 10 mM. The organic ligands used in this study are: (i) acetic acid, (ii) citric acid, (iii) glutamic acid, (iv) salycilic acid, (v) glycine, and (vi) ethylenediaminetetraacetic acid (EDTA). These contain one or more carboxyl- and amino-groups that are commonly present in natural organic substances found in lacustrine, fluvial, soil, cave, as well as in marine and earliest diagenetic porewater environments. Results shown here indicate that the presence of these carboxyl- and amino-groups promotes an increase in the partition coefficient of Mg in calcite (DMg = (Mg/Ca)calcite/(Mg/Ca)fluid) that can be attributed to their adsorption onto the calcite surfaces and the subsequent reduction of the active sites of growth. This increase of DMg values as a function of the supersaturation degree of calcite in the fluid phase can be described by the linear equation:

  13. Experimental study of the Mg and Sr isotopic evolution of seawater interacting with basalt between 150 and 300 ° C.

    Voigt, Martin; Pearce, Christopher R.; Oelkers, Eric H.


    The chemical exchange of material between seawater and the oceanic crust plays a major role in marine geochemical cycles [1]. Isotopic signatures provide an important means of tracing elemental transfer in hydrothermal environments, yet only a limited amount of experimental data on the extent of isotopic fractionation under these conditions is currently available. This study consequently investigated the extent of δ26/24Mg and 87Sr/86Sr isotopic variation during a seawater-basalt interaction experiments at 150, 250 and 290 ° C. A suite of closed system experiments were run for several months at each temperature under saturated water pressure, using either crystalline or glassy basalt as the starting material and a water/rock ratio of 10 or 25. Our results demonstrate that the dissolution of basaltic material in hydrothermal environments occurs at the same time as the precipitation of alteration minerals (mainly smectite and anhydrite), which is consistent with results from similar studies in the past (e.g. [2]). As expected, the rate of reaction using crystalline basalt was slower than with basaltic glass, and both sample types reacted faster at higher temperatures. The 87Sr/86Sr composition of the experimental fluids decreased from the initial seawater value (0.70916) towards the lower basaltic signature during the experiments (0.70317), demonstrating the progressive release of Sr during basalt dissolution. Magnesium was steadily removed from the fluid via the precipitation of clay minerals, with the residual fluids having progressively lighter δ26/24Mg compositions. The mean Mg isotope fractionation factor (αsolid-solution) observed at 250 oC was 1.0005±0.0002, supporting low-temperature evidence that clay minerals preferentially incorporate isotopically heavy magnesium [3]. These experiments provide quantitative information on the extent of Mg isotopic fractionation between fluids and secondary silicate minerals in hydrothermal systems, and demonstrate the

  14. Effect of pressure on the metastable phase formation of equilibrium immiscible Ti-Mg system studied by ab initio technique and mechanical milling

    Phasha, MJ


    Full Text Available on the metastable phase formation of equilibrium immiscible Ti-Mg system studied by ab initio technique and mechanical milling MJ PHASHA1,2, M KASONDE1, P E NGOEPE1,2 1CSIR Materials Science and Manufacturing, PO Box 395, Pretoria, 0001 2Materials Modelling... to predict the possible metastable phases of A3B, AB and AB3 type in the Ti-Mg system, which has no alloy phase over the entire composition range. RESULTS CONCLUSION 1 The hypothetical crystalline structures of Ti-Mg system were successfully cal...

  15. Chemical and isotopic kinship of iron in the Earth and Moon deduced from the lunar Mg-Suite

    Sossi, Paolo A.; Moynier, Frédéric


    The Moon and the Earth's mantle share many chemical and isotopic traits, leading to the prevailing theory that they were formed from similar material. Iron is one element that shows apparent differences between the two bodies, with models for the composition of the Moon having ≈1.5 times more FeO (12-14 wt.%), relative to the Earth's mantle (8 wt.%). This difference is mirrored in their isotope compositions, where lunar mare basalts have δ57Fe (per mille deviation of the 57Fe/54Fe ratio from the IRMM-014 standard) 0.1-0.2‰ higher than peridotitic rocks representative of Earth's mantle, a feature initially attributed to loss of isotopically light Fe following a giant impact. However, whether basaltic rocks are suitable analogues for the Moon's composition is debatable in the light of their distinct source regions that reflect the extensive lithological stratification of the lunar mantle. Here, we evaluate the iron isotope composition of the bulk Moon through the study of igneous cumulate rocks of the lunar highlands Magnesium Suite (Mg Suite). The δ57Fe of Mg Suite rocks spans a limited range, from 0.05‰ to 0.10‰, with an average (+ 0.07 ± 0.02 ‰) that overlaps with Earth's mantle (+ 0.05 ± 0.01 ‰), similarities that extend to their Mg#s, where both reach 0.9. Numerical modelling of iron isotope fractionation during lunar magma ocean crystallisation shows that the Mg Suite should accurately reflect the composition of the bulk Moon, which is therefore + 0.07 ± 0.02 ‰, indistinguishable from Earth's mantle but heavier than chondrites (- 0.01 ± 0.01 ‰). Iron thus behaves coherently with other elements that condense at temperatures higher than Li in showing no isotopic difference between the Earth and Moon, suggesting element depletion on the Moon affected only the more volatile elements. Therefore, there is no cosmochemical basis for iron enrichment or depletion in the bulk Moon relative to the Earth's mantle, whose composition is an analogue for

  16. The effect of permafrost, vegetation, and lithology on Mg and Si isotope composition of the Yenisey River and its tributaries at the end of the spring flood

    Mavromatis, Vasileios; Rinder, Thomas; Prokushkin, Anatoly S.; Pokrovsky, Oleg S.; Korets, Mikhail A.; Chmeleff, Jérôme; Oelkers, Eric H.


    This work focuses on the behavior of the stable Mg and Si isotope compositions of the largest Arctic river, the Yenisey River and 28 of its major and minor tributaries during the spring flood period. Samples were collected along a 1500 km latitudinal profile covering a wide range of permafrost, lithology, and vegetation. Despite significant contrasts in the main physico-geographical, climate, and lithological parameters of the watersheds, the isotope composition of both dissolved Mg and Si was found to be only weakly influenced by the degree of the permafrost coverage, type of vegetation (forest vs. tundra), and lithology (granites, basalts, carbonates or terrigenous rocks). This observation is generally consistent with the lack of chemical uptake of Mg and Si by soil mineral formation and vegetation during the early spring. The radiogenic Sr isotope composition of the Yenisey and its tributaries varied within a narrow range (0.708 ⩽ 87Sr/86Sr ⩽ 0.711) reflecting the dominance of Phanerozoic rock weathering and/or atmospheric deposition on these compositions. The Mg and Si isotopic compositions of riverine samples reflect two main processes with distinct isotopic signatures. First, isotopically heavier Mg (δ26Mg = -1.0 ± 0.2‰) and isotopically lighter Si (δ30Si = 1.0 ± 0.25‰) are added to the waters by river suspended matter dissolution and leaching from vegetation biomass/topsoil litter. Second, isotopically lighter Mg (δ26Mg = -1.5 to -1.75‰) and isotopically heavier Si (δ30Si = 1.75-2.0‰) are delivered to the Yenisey's tributaries from deep underground water feeding the rivers via taliks. This lighter Mg and heavier Si isotopic composition is interpreted to originate from Precambrian dolomite dissolution and aluminosilicate dissolution coupled with authigenic mineral precipitation, respectively, in deep underground water reservoirs. Taking account of the isotopic composition evolution over the course of the year established earlier on mono

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

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


    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.

  18. Importance of a Fully Anharmonic Treatment of Equilibrium Isotope Fractionation Properties of Dissolved Ionic Species As Evidenced by Li(+)(aq).

    Dupuis, Romain; Benoit, Magali; Tuckerman, Mark E; Méheut, Merlin


    Equilibrium fractionation of stable isotopes is critically important in fields ranging from chemistry, including medicinal chemistry, electrochemistry, geochemistry, and nuclear chemistry, to environmental science. The dearth of reliable estimates of equilibrium fractionation factors, from experiment or from natural observations, has created a need for accurate computational approaches. Because isotope fractionation is a purely quantum mechanical phenomenon, exact calculation of fractionation factors is nontrivial. Consequently, a severe approximation is often made, in which it is assumed that the system can be decomposed into a set of independent harmonic oscillators. Reliance on this often crude approximation is one of the primary reasons that theoretical prediction of isotope fractionation has lagged behind experiment. A class of problems for which one might expect the harmonic approximation to perform most poorly is the isotopic fractionation between solid and solution phases. In order to illustrate the errors associated with the harmonic approximation, we have considered the fractionation of Li isotopes between aqueous solution and phyllosilicate minerals, where we find that the harmonic approximation overestimates isotope fractionation factors by as much as 30% at 25 °C. Lithium is a particularly interesting species to examine, as natural lithium isotope signatures provide information about hydrothermal processes, carbon cycle, and regulation of the Earth's climate by continental alteration. Further, separation of lithium isotopes is of growing interest in the nuclear industry due to a need for pure (6)Li and (7)Li isotopes. Moving beyond the harmonic approximation entails performing exact quantum calculations, which can be achieved using the Feynman path integral formulation of quantum statistical mechanics. In the path integral approach, a system of quantum particles is represented as a set of classical-like ring-polymer chains, whose interparticle

  19. A Fast Numerical Method for the Calculation of the Equilibrium Isotopic Composition of a Transmutation System in an Advanced Fuel Cycle

    F. Álvarez-Velarde


    Full Text Available A fast numerical method for the calculation in a zero-dimensional approach of the equilibrium isotopic composition of an iteratively used transmutation system in an advanced fuel cycle, based on the Banach fixed point theorem, is described in this paper. The method divides the fuel cycle in successive stages: fuel fabrication, storage, irradiation inside the transmutation system, cooling, reprocessing, and incorporation of the external material into the new fresh fuel. The change of the fuel isotopic composition, represented by an isotope vector, is described in a matrix formulation. The resulting matrix equations are solved using direct methods with arbitrary precision arithmetic. The method has been successfully applied to a double-strata fuel cycle with light water reactors and accelerator-driven subcritical systems. After comparison to the results of the EVOLCODE 2.0 burn-up code, the observed differences are about a few percents in the mass estimations of the main actinides.

  20. Impact of the carbon pore size and topology on the equilibrium quantum sieving of hydrogen isotopes at zero coverage and finite pressures.

    Kowalczyk, Piotr; Gauden, Piotr A; Terzyk, Artur P; Furmaniak, Sylwester


    Carbonaceous slit-shaped and square-shaped pores efficiently differentiate adsorbed hydrogen isotopes at 77 and 33 K. Extensive path integral Monte Carlo simulations revealed that the square-shaped carbon pores enhanced the selectivity of deuterium over hydrogen in comparison to equivalent slit-shaped carbon pores at zero coverage as well as at finite pressures (i.e. quantum sieving of hydrogen isotopes is pore-topology-dependent). We show that this enhancement of the D(2)/H(2) equilibrium selectivity results from larger localization of hydrogen isotopes in square-shaped pores. The operating pressures for efficient quantum sieving of hydrogen isotopes are strongly dependent on the topology as well as on the size of the carbon pores. However, for both considered carbon pore topologies the highest D(2)/H(2) separation factor is observed at zero-coverage limit. Depending on carbon pore size and topology we predicted monotonic decreasing and non-monotonic shape of the D(2)/H(2) equilibrium selectivity at finite pressures. For both kinds of carbonaceous pores of molecular sizes we predict high compression of hydrogen isotopes at 77 and 33 K (for example, the pore density of compressed hydrogen isotopes at 77 K and 0.25 MPa in a square-shaped carbon pore of size 2.6 Å exceeds 60 mmol cm(-3); for comparison, the liquid density of para-H(2) at 30 K and 30 MPa is 42 mmol cm(-3)). Finally, by direct comparison of simulation results with experimental data it is explained why 'ordinary' carbonaceous materials are not efficient quantum sieves.

  1. A ternary linear compound T{sub 2} and its phase equilibrium relationships in Mg-Zn-Nd system at 400 {sup o}C

    Huang, M.L. [Department of Materials Science and Engineering, Northeastern University at Qinhuangdao, 066004 (China); School of Materials and Metallurgy, Northeastern University, Shenyang, Liaoning 110004 (China); Li, H.X., E-mail: [School of Materials and Metallurgy, Northeastern University, Shenyang, Liaoning 110004 (China); Ding, H.; Tang, Z.Y. [School of Materials and Metallurgy, Northeastern University, Shenyang, Liaoning 110004 (China); Mei, R.B.; Zhou, H.T. [Department of Materials Science and Engineering, Northeastern University at Qinhuangdao, 066004 (China); School of Materials and Metallurgy, Northeastern University, Shenyang, Liaoning 110004 (China); Ren, R.P.; Hao, S.M. [School of Materials and Metallurgy, Northeastern University, Shenyang, Liaoning 110004 (China)


    The composition and the crystal structure of the phases in the alloys of Mg-Zn-Nd system at 400 {sup o}C have been studied by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD) and selected area electron diffraction (SAED) of transmission electron microscopy (TEM). The phase equilibrium relationships have been identified. As a result, a linear ternary compound T{sub 2} phase has been identified. The general chemical formula of T{sub 2} phase is (Mg, Zn){sub 11.5}Nd and the crystal structure of that is C-centered orthorhombic. As the results, the other three ternary compounds T{sub 1} phase, T{sub 3} phase and T{sub 4} phase have also been identified. The partial isothermal section of phase diagram of Mg-Zn-Nd system at 400 {sup o}C has been established.

  2. Modelling Equilibrium and Fractional Crystallization in the System MgO-FeO-CaO-Al2O3-SiO2

    Herbert, F.


    A mathematical modelling technique for use in petrogenesis calculations in the system MgO-FeO-CaO-Al2O3-SiO2 is reported. Semiempirical phase boundary and elemental distribution information was combined with mass balance to compute approximate equilibrium crystallization paths for arbitrary system compositions. The calculation is applicable to a range of system compositions and fractionation calculations are possible. The goal of the calculation is the computation of the composition and quantity of each phase present as a function of the degree of solidification. The degree of solidification is parameterized by the heat released by the solidifying phases. The mathematical requirement for the solution of this problem is: (1) An equation constraining the composition of the magma for each solid phase in equilibrium with the liquidus phase, and (2) an equation for each solid phase and each component giving the distribution of that element between that phase and the magma.

  3. Extraction Equilibrium of Mn2+, Ca2+, and Mg2+ from Chloride Solutions by Di(2-ethylhexyl)phosphoric Acid Dissolved in Kerosene

    Zhang, Chuanfu; Cao, Wenxin; Zhan, Jing; Ding, Fenghua; Hwang, Jiann-Yang


    The presence of calcium and magnesium affects the purity of the final product MnCl2 in hydrometallurgical treatment processes. The solvent extraction method can be used to separate Ca2+ and Mg2+ from Mn2+ solutions containing impurity ions such as Ca2+ and Mg2+. This article aims to investigate the single-stage extraction equilibrium of Ca2+, Mg2+, and Mn2+ in chloride medium using di(2-ethylhexyl)phosphoric acid in kerosene (O:A = 1:1). The results show that the pH0.5 values are 1.11, 1.56, and 2.18 for Ca2+, Mn2+, and Mg2+, respectively. The mechanism of extraction and stoichiometries of metal-containing extracted species were illustrated based on a slope analysis. The composition of the extracted species in the organic phase is proposed to be MnR2·R2H2, CaR2·R2H2, and MgR2·(R2H2)2, respectively.

  4. Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

    Ingram, B.L.; De Deckker, P.; Chivas, A.R.; Conrad, M.E.; Byrne, A.R.


    Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma Marsh over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10-35 {per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5 {per_thousand} between 500 yr BR and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3-4 {per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100-300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600-700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.

  5. Investigation of the Mg isotopes using the shell-model-like approach in relativistic mean field theory

    Bai, Hong-Bo; Zhang, Zhen-Hua; Li, Xiao-Wei


    Ground state properties for Mg isotopes, including binding energies, one- and two-neutron separation energies, pairing energies, nuclear matter radii and quadrupole deformation parameters, are obtained from the self-consistent relativistic mean field (RMF) model with the pairing correlations treated by a shell-mode-like approach (SLAP), in which the particle-number is conserved and the blocking effects are treated exactly. The experimental data, including the binding energies and the one- and two-neutron separation energies, which are sensitive to the treatment of pairing correlations and block effects, are well reproduced by the RMF+SLAP calculations. Supported by NSFC (11465001,11275098, 11275248, 11505058,11165001) and Natural Science Foundation of Inner Mongolia of China (2016BS0102)

  6. Isotope shifts of the (3s3p) 3P0,1,2-(3s4s) 3S1 Mg I transitions

    He, Ming; Therkildsen, Kasper T.; Jensen, Brian B.;


    We report measurements of the isotope shifts of the (3s3p)P30,1,2-(3s4s)S31 Mg I transitions for the stable isotopes M24g (I=0) , M25g (I=5/2) , and M26g (I=0) . Furthermore, the M25g S31 hyperfine coefficient A(S31)=(-321.6±1.5)MHz is extracted and found to be in excellent agreement with state...

  7. Variations of oceanic oxygen isotopes at the present day and the LGM: equilibrium simulations with an oceanic general circulation model

    X. Xu


    Full Text Available The isotope-enabled oceanic general circulation model, MPI-OM, is used to simulate the oxygen isotope compositions of sea waters in the oceans under preindustrial and last glacial maximum climate conditions. Simulated oceanic isotope distributions at the last glacial maximum (21 000 yr ago show features similar to the preindustrial in most basins but the Northern North Atlantic. With the exception of the ice sheet impact, the oxygen-18 content variations at sea surface during the last glacial maximum are mainly controlled by the changes in boundary isotopic fluxes in most regions, while the changes from subsurface to bottom waters are mostly due to the differences in the water mass circulations. The changes in topography at the northern high latitudes have a remarkable influence on the isotopic composition in the Arctic Ocean. The pre-industrial and the last glacial maximum calcite oxygen isotope compositions in the surface water and their difference are also calculated. These results are compared with the observed values from different foraminifera species and are in agreement with the observations in most regions.

  8. Calibration of the dolomite clumped isotope thermometer from 25 to 350 °C, and implications for a universal calibration for all (Ca, Mg, Fe)CO3 carbonates

    Bonifacie, Magali; Calmels, Damien; Eiler, John M.; Horita, Juske; Chaduteau, Carine; Vasconcelos, Crisogono; Agrinier, Pierre; Katz, Amandine; Passey, Benjamin H.; Ferry, John M.; Bourrand, Jean-Jacques


    Carbonate clumped isotope thermometry is based on the temperature-dependent formation of 13C18O16O22- ion groups within the lattice of solid carbonate minerals. At low temperatures the bonds between rare, heavy 13C and 18O isotopes are thermodynamically favored, and thus at equilibrium they are present in higher than random abundances. Here we calibrate the use of this temperature proxy in a previously uncalibrated carbonate phase - dolomite [CaMg(CO3)2] - over a temperature range that extends to conditions typical of shallow crustal environments, by determining the Δ47 values of CO2 extracted from synthetic or natural (proto)dolomites grown at known temperatures from 25 to 350 °C and analyzed in two different laboratories using different procedures for sample analysis, purification and post-measurement data treatment. We found that the Δ47-1/T2 dependence for (proto)dolomite is linear between 25 and 350 °C, independent of their Mg/Ca compositions or cation order (or the laboratory in which they were analyzed), and offset from, but parallel to, the theoretical predictions of the Δ63 dependence to temperature of the abundance of the 13C18O16O2 isotopologue inside the dolomite and calcite mineral lattices as expected from ab-initio calculations (Schauble et al., 2006). This suggests that neither the equilibrium constant for 13C-18O clumping in (proto)dolomite lattice, nor the experimental fractionation associated with acid digestion to produce CO2, depend on their formation mechanism, degree of cation order and/or stoichiometry (i.e., Mg/Ca ratio) and/or δ18O and δ13C compositions (at least over the range we explored). Thus, we suggest the following single Δ47-1/T2 linear regression for describing all dolomite minerals:

  9. Mg/Casea surface temperatures during the Marine Isotope Stage 31 collapse of the Ross Ice Shelf

    Dunbar, G. B.


    The recovery of the AND-1b and CRP-1 drill cores from the Southwest Ross Sea highlighted the potential instability in of the Ross Ice Shelf and the West Antarctic Ice Sheet it buttresses. Both cores recovered a few individuals of the planktonic foraminifera Neogloboquadrina pachyderma from marine isotope stage (MIS) 31. This interval is significant because it marks the youngest occurrence of open ocean diatom sediment at AND-1b, which is now situated under the McMurdo Ice Shelf, indicating a substantial retreat of the Ross Ice Shelf occurred during this interglacial. However, sediment deposited after MIS 31 at both sites is represented only by glacial-dominated sediment, suggesting a critical environmental threshold had been crossed enabling the Ross Ice Shelf to form and persist. Numerical modeling by Pollard and DeConto (Nature, 2009) suggested that sub-ice oceanic melting is a critical element in the stability of ice shelves and that "WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5°C." Laser ablation ICPMS measurement of the Mg/Ca content of N. pachyderma shows that although there is considerable heterogeneity in the distribution of Mg in their tests the mean Mg/Ca of a sample population appears proportional to calcification temperature. By empirically calibrating Mg/Ca in CRP-1 N. pachyderma against values measured in modern populations collected from Ross Sea and Southern Ocean sites with SSTs ranging from 1.2°C to 14°C it is concluded that SST during MIS 31 was warmer than today by 5-9°C, consistent with model projections.

  10. Characterizing the Effect of Shock on Isotopic Ages. 2; Mg-Suite Troctolite Major Elements

    Edmunson, Jennifer; Cohen, Barbara


    Two troctolites from the lunar magnesium suite (Mg-suite), 76335 and 76535, have Sm-147-ND-143 and Rb-87- Sr-87 ages that do not indicate the same age for their respective sample. In the case of 76335, the Sm-147-ND-143 age is 4278 +/- 60 Ma, but the Rb-87-Sr-87 data does not reveal an isochron]. For 76535, the Sm-147-ND-143 age is significantly younger (4260 +/- 60 Ma) than the Rb-87- Sr-87 age (4570 +/- 70 Ma, Lambda = 1.402x10(exp -11)). This study was designed to discover why the Sm-147-ND-143 and Rb-87-Sr-87 ages did not match for each individual sample.

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

    Larsen, Kirsten Kolbjørn; Wielandt, Daniel Kim Peel; Schiller, Martin;


    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 ...

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

    Dideriksen, Knud; Baker, Joel A.; Stipp, Susan Louise Svane


    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...... differently complexed Fe(III) pools were separated by addition of Na2CO3, 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......(III)-bearing environments, such as soils and rivers, and may, for example, largely control the Fe isotope composition of marine Fe–Mn crusts....

  13. A method for combined Sr-Nd-Hf isotopic analysis of <10 mg dust samples: implication for ice core science

    Ujvari, Gabor; Wegner, Wencke; Klötzli, Urs


    Aeolian mineral dust particles below the size of 10-20 μm often experience longer distance transport in the atmosphere, and thus Aeolian dust is considered an important tracer of large-scale atmospheric circulation. Since ice core dust is purely Aeolian in origin, discrimination of its potential source region(s) can contribute to a better understanding of past dust activity and climatic/environmental causes. Furthermore, ice core dust source information provides critical experimental constraints for model simulations of past atmospheric circulation patterns [1,2]. However, to identify dust sources in past dust archives such as ice cores, the mineralogy and geochemistry of the wind-blown dust material must be characterized. While the amount of dust in marine cores or common terrestrial archives is sufficient for different types of analyses and even for multiple repeat measurements, dust content in ice cores is usually extremely low even for the peak dusty periods such as the Last Glacial Maximum (LGM) (5-8 mg dust/kg ice; [3]). Since the most powerful dust fingerprinting methods, such as REE composition and Sr-Nd-Pb isotopic analyses are destructive there is a clear need to establish sequential separation techniques of Sr, Nd, Pb and other REEs to get the most information out of small (5-10 mg) dust samples recovered from ice cores. Although Hf isotopes have recently been added as a robust tool of aerosol/dust source discrimination (e.g. [4,5,6,7]), precise Hf isotopic measurements of small (Central Europe (NUS), China (BEI) and the US (JUD) were processed (all acetic acid treated for carbonate removal, i.e. aluminosilicate fractions were analysed). Sr isotopic compositions varied between the aliquots within a range of ˜0.00007 for the three samples. Comparison of these values with previously obtained 87Sr/86Sr isotopic ratios from the same samples (different acid/sample amounts) reveals that these values are very sensitive to the acetic acid treatment (acid

  14. A DFT-based comparative equilibrium study of thermal dehydration and hydrolysis of CaCl₂ hydrates and MgCl₂ hydrates for seasonal heat storage.

    Pathak, Amar Deep; Nedea, Silvia; Zondag, Herbert; Rindt, Camilo; Smeulders, David


    Salt hydrates store solar energy in chemical form via a reversible dehydration-hydration reaction. However, as a side reaction to dehydration, hydrolysis (HCl formation) may occur in chloride based salt hydrates (specially in MgCl2 hydrates), affecting the durability of the storage system. The mixture of CaCl2 and MgCl2 hydrates has been shown experimentally to have exceptional cycle stability and improved kinetics. However, the optimal operating conditions for the mixture are unknown. To understand the appropriate balance between dehydration and hydrolysis kinetics in the mixtures, it is essential to gain in-depth insight into the mixture components. We present a GGA-DFT level study to investigate the various gaseous structures of CaCl2 hydrates and to understand the relative stability of their conformers. The hydration strength and relative stability of conformers are dominated by electrostatic interactions. A wide network of intramolecular homonuclear and heteronuclear hydrogen bonds is observed in CaCl2 hydrates. Equilibrium product concentrations are obtained during dehydration and hydrolysis reactions under various temperature and pressure conditions. The trend of the dehydration curve with temperature in CaCl2 hydrates is similar to the experiments. Comparing these results to those of MgCl2 hydrates, we find that CaCl2 hydrates are more resistant towards hydrolysis in the temperature range of 273-800 K. Specifically, the present study reveals that the onset temperatures of HCl formation, a crucial design parameter for MgCl2 hydrates, are lower than for CaCl2 hydrates except for the mono-hydrate.

  15. Search for halo nucleus in Mg isotopes through the measurements of reaction cross sections towards the vicinity of neutron drip line

    Takechi M.


    Full Text Available Reaction cross sections (σR for 24–38Mg on C targets at the energies of around 240 MeV/nucleon have been measured precisely at RIBF, RIKEN for the purpose of obtaining the crucial information on the changes of nuclear structure in unstable nuclei, especially around the so-called “island of inversion” region. In the island of inversion region, which includes neutron-rich Ne, Na, and Mg isotopes, the vanishing of the N = 20 magic number for neutrons have been discussed along with nuclear deformation. The present result suggest deformation features of Mg isotopes and shows a large cross section of weakly-bound nucleus 37Mg, which could be caused by a neutron halo formation.

  16. Evolution of the South African mantle — A case study of garnet peridotites from the Finsch diamond mine (Kaapvaal craton); part 1: Inter-mineral trace element and isotopic equilibrium

    Lazarov, Marina; Brey, Gerhard P.; Weyer, Stefan


    A thorough assessment of inter-mineral equilibrium is essential for the understanding of trace element partitioning and also for the interpretation of isotopic data. Here we investigated high temperature (~ 1200 °C and 6 GPa) garnet peridotite xenoliths from the Kaapvaal craton (Finsch mine, South Africa), with exceptionally well equilibrated mineral major element compositions, for their trace element and isotopic inter-mineral equilibrium. Trace element compositions for all major mineral phases, i.e. olivine, orthopyroxene (opx), clinopyroxene (cpx) and garnet, were analysed by laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Garnet, cpx and opx of selected samples were analysed for their Sm-Nd and Lu-Hf isotope compositions by multi collector ICP-MS. Most important mineral characteristics include: a) olivines from most samples are enriched in high-field-strength elements relative to other incompatible trace elements. Their lithium content correlates negatively with Mg#, indicating a depletion signature; b) all other minerals are depleted in heavy and middle rare earth elements (H- and M-REE) and enriched in light REE and large ion lithophile elements. This implies a complex history of depletion and metasomatic overprint for the Finsch cratonic mantle; c) orthopyroxene has similarly shaped trace element patterns as cpx, with one to two orders of magnitude lower abundances; and d) both, garnet and cpx, display variable, mostly positive ɛHf coupled with moderate variations in ɛNd. Trace element partitioning between garnet/cpx, cpx/opx and garnet/opx, displays only a weak pressure and temperature dependency. However, equilibrium partitioning of most trace elements between garnet and cpx shows a strong compositional dependency, i.e. on the Cr- (and Ca-) content of the garnets. Garnet-cpx partition coefficients follow a second grade polynomial correlation with Cr2O3 of garnet, whereby high chromium garnets (Cr2O3 > 6 wt.%) have generally higher

  17. Ground state properties of neutron-rich Mg isotopes the "island of inversion" studied with laser and $\\beta$-NMR spectroscopy

    Kowalska, M


    Studies in regions of the nuclear chart in which the model predictions of properties of nuclei fail can bring a better understanding of the strong interaction in the nuclear medium. To such regions belongs the so called "island of inversion" centered around Ne, Na and Mg isotopes with 20 neutrons in which unexpected ground-state spins, large deformations and dense low-energy spectra appear. This is a strong argument that the magic N=20 is not a closed shell in this area. In this thesis investigations of isotope shifts of stable $^{24-26}$Mg, as well as spins and magnetic moments of short-lived $^{29,31}$Mg are presented. The successful studies were performed at the ISOLDE facility at CERN using collinear laser and $\\beta$-NMR spectroscopy techniques. The isotopes were investigated as single-charged ions in the 280 nm transition from the atomic ground state $^2\\!$S$_{1/2}$ to one of the two lowest excited states $^2\\!$P$_{1/2 ,\\,3/2}$ using continuous wave laser beams. The isotope-shift measurements with fluor...

  18. Assessment of surface reactivity of thorium oxide in conditions close to chemical equilibrium by isotope exchange {sup 229}Th/{sup 232}Th method

    Suzuki-Muresan, Tomo; Perrigaud, Katy; Vandenborre, Johan; Ribet, Solange; Grambow, Bernd [Nantes Univ., CNRS/IN2P3 (France). SUBATECH Unite Mixte de Recherche 6457; Takamasa, Inai [TOKAI Univ., Kanagawa (Japan)


    This work aims to assess the solubility and the surface reactivity of crystallized thorium at pH 3.0 in presence of three types of solids: synthesized powder at 1300 C, crushed kernel, and intact kernel. In this study, the kernel is composed by the core solid from high temperature reactors (HTR) sphere particles. The originality of this work consisted in following in a sequential order the kinetic of dissolution, the surface reactivity in presence of isotope tracer {sup 229}Th, and its desorption process. Long time experiments (634 days) allowed to get deeper understanding on the behavior of the surface reactivity in contact with the solution. Solubility values are ranging from 0.3 x 10{sup -7} mol.L{sup -1} to 3 x 10{sup -7} mol.L{sup -1} with a dissolution rate of 10{sup -6}-10{sup -4} g.m{sup -2} day{sup -1}. PHREEQC modeling showed that crystallized ThO{sub 2}(cr, 20 nm) phase controls the equilibrium in solution. Isotope exchange between {sup 229}Th and {sup 232}Th indicated that well-crystallized phase exist as an inert surface regarding to the absence of exchange between surface solid and solution.

  19. Petrologic and Al-Mg isotopic clues to the accretion of two refractory inclusions onto the Leoville parent body - One was hot, the other wasn't

    Caillet, Catherine; MacPherson, Glenn J.; Zinner, Ernst K.


    A detailed petrologic and magnesium isotopic study of two Ca-Al-rich inclusions from the foliated Leoville meteorite is presented. The two type B refractory inclusions found within several centimeters of each other differ greatly in their styles of deformation, textures, and Mg-Al isotopic characteristics. One is a subspheroidal type B1 with textures similar to those observed previously in many type B1s from other CV3 meteorites, and whose deformation (fracturing, some granulation) has been almost entirely brittle in nature. Its isotopic composition shows Mg-26/Mg-24 correlated with Al-27/Mg-24 which, although disturbed, indicates a lower limit for initial Al-26/Al-27 of around 4.9 x 10 to the -5. The other inclusion is a highly elongate object whose long axis lies in the plane of foliation. It has a predominantly metamorphic texture, but relict islands of an earlier and more 'normal' type B precursor are preserved in its core. The most likely origin for the deformed and recrystallized features of the elongate inclusion is that it accreted onto the Leoville parent body while still very hot, and deformed into its present state at the moment of impact.

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

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


    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

  1. Improvement in the transport critical current density and microstructure of isotopic Mg11B2 monofilament wires by optimizing the sintering temperature

    Qiu, Wenbin; Jie, Hyunseock; Patel, Dipak; Lu, Yao; Luzin, Vladimir; Devred, Arnaud; Somer, Mehmet; Shahabuddin, Mohammed; Kim, Jung Ho; Ma, Zongqing; Dou, Shi Xue; Hossain, Md. Shahriar Al


    Superconducting wires are widely used in fabricating magnetic coils in fusion reactors. In consideration of the stability of 11B against neutron irradiation and lower induced radio-activation properties, MgB2 superconductor with 11B serving as boron source is an alternative candidate to be used in fusion reactor with severe irradiation environment. In present work, a batch of monofilament isotopic Mg11B2 wires with amorphous 11B powder as precursor were fabricated using powder-in-tube (PIT) process at different sintering temperature, and the evolution of their microstructure and corresponding superconducting properties was systemically investigated. Accordingly, the best transport critical current density (Jc) = 2 × 104 A/cm2 was obtained at 4.2 K and 5 T, which is even comparable to multi-filament Mg11B2 isotope wires reported in other work. Surprisingly, transport Jc vanished in our wire which was heat-treated at excessively high temperature (800 °C). Combined with microstructure observation, it was found that lots of big interconnected microcracks and voids that can isolate the MgB2 grains formed in this whole sample, resulting in significant deterioration in inter-grain connectivity. The results can be a constructive guide in fabricating Mg11B2 wires to be used as magnet coils in fusion reactor systems such as ITER-type tokamak magnet.

  2. Thermodynamics Behavior of Germanium During Equilibrium Reactions between FeOx-CaO-SiO2-MgO Slag and Molten Copper

    Shuva, M. A. H.; Rhamdhani, M. A.; Brooks, G. A.; Masood, S.; Reuter, M. A.


    The distribution ratio of germanium (Ge), L_{{Ge}}^{s/m} during equilibrium reactions between magnesia-saturated FeOx-CaO-SiO2 (FCS) slag and molten copper has been measured under oxygen partial pressures from 10-10 to 10-7 atm and at temperatures 1473 to 1623 K (1200 to 1350 °C). It was observed that the Ge distribution ratio increases with increasing oxygen partial pressure, and with decreasing temperature. It was also observed that the distribution ratio is strongly dependent on slag basicity. The distribution ratio was observed to increase with increasing optical basicity. At fixed CaO concentration in the slag, the distribution ratio was found to increase with increasing Fe/SiO2 ratio, tending to a plateau at L_{{Ge}}^{s/m} = 0.8. This behavior is consistent with the assessment of ionic bond fraction carried out in this study, and suggested the acidic nature of germanium oxide (GeO2) in the slag system studied. The characterisation results of the quenched slag suggested that Ge is present in the FeOx-CaO-SiO2-MgO slag predominantly as GeO2. At 1573 K (1300 °C) and p_{{{{O}}2 }} = 10-8 atm, the activity coefficient of GeO2 in the slag was calculated to be in the range of 0.24 to 1.50. The results from the current study suggested that less-basic slag, high operating temperature, and low oxygen partial pressure promote a low Ge distribution ratio. These conditions are desired for maximizing Ge recovery, for example, during pyrometallurgical processing of Ge-containing e-waste through secondary copper smelting. Overall, the thermodynamics data generated from this study can be used for process modeling purposes for improving recovery of Ge in primary and secondary copper smelting processes.

  3. A combined Sm-Nd, Rb-Sr, and U-Pb isotopic study of Mg-suite norite 78238: Further evidence for early differentiation of the Moon

    Edmunson, J; E.Borg, L; Nyquist, L E; Asmerom, Y


    Lunar Mg-suite norite 78238 was dated using the Sm-Nd, Rb-Sr, and U-Pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of Mg-suite magmatism, as well as to provide a direct comparison between the three isotopic systems. The Sm-Nd isotopic system yields a crystallization age for 78238 of 4334 {+-} 37 Ma and an initial {var_epsilon}{sub Nd}{sup 143} value of -0.27 {+-} 0.74. The age-initial {var_epsilon}{sub Nd}{sup 143} (T-I) systematics of a variety of KREEP-rich samples, including 78238 and other Mg-suite rocks, KREEP basalts, and olivine cumulate NWA 773, suggest that lunar differentiation was completed by 4492 {+-} 61 Ma assuming a Chondritic Uniform Reservoir bulk composition for the Moon. The Rb-Sr isotopic systematics of 78238 were disturbed by post-crystallization processes. Nevertheless, selected data points yield two Rb-Sr isochrons. One is concordant with the Sm-Nd crystallization age, 4366 {+-} 53 Ma. The other is 4003 {+-} 95 Ma and is concordant with an Ar-Ar age for 78236. The {sup 207}Pb-{sup 206}Pb age of 4333 {+-} 59 Ma is concordant with the Sm-Nd age. The U-Pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the Pb-Pb system, and may reflect fractionation of U and Pb during sample handling. Despite the disturbed nature of the U-Pb systems, a time-averaged {mu} ({sup 238}U/{sup 204}Pb) value of the source can be estimated at 27 {+-} 30 from the Pb-Pb isotopic systematics. Because KREEP-rich samples are likely to be derived from source regions with the highest U/Pb ratios, the relatively low {mu} value calculated for the 78238 source suggests the bulk Moon does not have an exceedingly high {mu} value.

  4. The Rise of the AGB in the Galactic Halo: Mg Isotopic Ratios and High Precision Elemental Abundances in M71 Giants

    Melendez, Jorge


    High-resolution (R ~ 100 000), high signal-to-noise spectra of M71 giants have been obtained with HIRES at the KeckI Telescope in order to measure their Mg isotopic ratios, as well as elemental abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Ni, Zr and La. We demonstrate that M71 has two populations, the first having weak CN, normal O, Na, Mg, and Al, and a low ratio of 26Mg/Mg (~4%) consistent with models of galactic chemical evolution with no contribution from AGB stars. The Galactic halo could have been formed from the dissolution of globular clusters prior to their intermediate mass stars reaching the AGB. The second population has enhanced Na and Al accompanied by lower O and by higher 26Mg/Mg (~8%), consistent with models which do incorporate ejecta from AGB stars via normal stellar winds. All the M71 giants have identical [Fe/H], [Si/Fe], [Ca/Fe], [Ti/Fe] and [Ni/Fe] to within sigma = 0.04 dex (10%). We therefore infer that the timescale for formation of the first generation of stars we see today in thi...

  5. Investigating the hydrological significance of stalagmite geochemistry (Mg, Sr) using Sr isotope and particulate element records across the Late Glacial-to-Holocene transition

    Belli, R.; Borsato, A.; Frisia, S.; Drysdale, R.; Maas, R.; Greig, A.


    The trace element and Sr isotope records in two coeval stalagmites characterized by different growth rates and flow regimes at Savi cave (Grotta Savi, NE Italy) reveal different sources and incorporation mechanisms for Mg and Sr. Mg is sourced primarily from dissolved cave host rock while particulate Mg derived from soil plays a subordinate role. The presence of particulate-borne Mg is inferred from the co-variation of Mg and particle-associated elements (Th, Al and Mn) which are preferentially concentrated in open columnar calcite layers. Variation in Mg concentrations corrected for particle-influenced components, the Mgc parameter, is controlled by water-rock interaction, with higher and lower Mgc during dry and wet phases, respectively. This is thought to reflect incongruent dissolution of Mg-rich phases. Correction of Sr concentrations for contributions from airborne exogenic Sr, based on 87Sr/86Sr ratios, yields the bedrock-only contribution (Src). Src variation in stalagmite calcite is influenced by speleothem growth rate and by variation of the calcite-water Sr partitioning in wet and dry phases, and only to a minor extent by incongruent dissolution of Mg-rich phases. Concentration profiles for Mgc and Srcg (corrected for growth rate effects) show inverse correlations and are inferred to show hydrological significance which is captured in a hydrological index, HI. We suggest HI provides robust information on water-rock interaction related to hydrological changes and can be utilized in both wet and semi-arid environments, provided the corrections for soil Mg and exogenic Sr can be applied with confidence. Application of the HI index allows correction of Grotta Savi oxygen isotope data, to yield a δ18Oc time series that shows when changes in moisture sources and atmospheric reorganization, or changes in moisture amount, were significant. This is especially evident during the Younger Dryas (YD). The Savi record supports the concept of a two-phase YD, marked by



    1 A New Therapeutic Agent for Radiation Synovectomy: Preparation of 166Ho-EDTMP-HA Bai Hongsheng Jin Xiaohai Du Jin Wang Fan Chen Daming Fan Hongqiang Cheng Zhen In order to treat the patient with inflammatory synovial disease, HA particle is labeled with 166Ho by EDTMP under the condition of pH6.0-8.0 and vibration time 15 min, its labeling efficiency is more than 98%, the size of particle is mainly in the range of 2-5 μm. The absorbed capacity is 5 mg Ho per 1g HA. Study on stability of 166Ho-EDTMP-HA in vitro shows that loss of 166Ho is less than 2% for166Ho-EDTMP-HA incubated 72 h in the 0.9% saline and 1% BSA solution at 37 ℃ .Biodistribution in vivo and extra articular leakage are investigated following injection of 166Ho-EDTMP-HA into knee of normal rabbits. The experimental results show that the extra leakage of 166Ho-EDTMP-HA is 0.32% at 48 h post-injection, most of 166Ho radioactivity leaked from the knee joint is excreted in the urine. 99% of 166Ho radioactivity is retained in the knee joint of rabbits. Thereby 166Ho-EDTMP-HA, as a new therapeutical agent of radiation synovectomy, had a value of further clinical study.

  7. Contribution of local thyroxine monodeiodination to intracellular 3,5, 3'-triiodothyronine in several tissues of hyperthyroid rats at isotopic equilibrium

    van Doorn, J.; van der Heide, D.; Roelfsema, F.


    The local conversion of T4 as a source of intracellular T3 in several organs of both hypothyroid and euthyroid rats has recently been recognized to be an important phenomenon. In the present study the source and quantity of T3 in various peripheral tissues of hyperthyroid rats were investigated. Athyreotic rats received a continuous iv infusion of T4 over a prolonged period in order to attain hyperthyroid conditions. At the same time, the animals also received a continuous iv infusion of (/sup 125/I)T4 and (/sup 131/I)T3 until isotopic equilibrium was achieved. After the animals were bled and perfused, the source and quantity of T3 in various tissue homogenates and subcellular preparations of liver, kidney, and the anterior pituitary gland were analyzed. In spite of the elevated plasma T3 and T4 levels, the concentration of T3 in the cerebral cortex and cerebellum was within the normal range. The contribution of T3 derived from local T4 to T3 conversion (Lc T3(T4)) was rather low in both parts of the brain when compared with values previously determined for euthyroid rats. Whereas previous studies revealed that Lc T3(T4) contributes significantly to the T3 in the pituitary glands of both hypothyroid and euthyroid rats, this was not the case for the hyperthyroid animals; virtually all T3 was derived from plasma. It was found that the T3 in muscle was derived exclusively from plasma. Both the liver and kidney showed high concentrations of T3. Whereas Lc T3(T4) was the main source of T3 in the liver, it contributed only a minor fraction of the total T3 content in the kidney.

  8. Cryogenic separation of hydrogen isotopes in single-walled carbon and boron-nitride nanotubes: insight into the mechanism of equilibrium quantum sieving in quasi-one-dimensional pores.

    Kowalczyk, Piotr; Gauden, Piotr A; Terzyk, Artur P


    Quasi-one-dimensional cylindrical pores of single-walled boron nitride and carbon nanotubes efficiently differentiate adsorbed hydrogen isotopes at 33 K. Extensive path integral Monte Carlo simulations revealed that the mechanisms of quantum sieving for both types of nanotubes are quantitatively similar; however, the stronger and heterogeneous external solid-fluid potential generated from single-walled boron nitride nanotubes enhanced the selectivity of deuterium over hydrogen both at zero coverage and at finite pressures. We showed that this enhancement of the D(2)/H(2) equilibrium selectivity results from larger localization of hydrogen isotopes in the interior space of single-walled boron nitride nanotubes in comparison to that of equivalent single-walled carbon nanotubes. The operating pressures for efficient quantum sieving of hydrogen isotopes are strongly depending on both the type as well as the size of the nanotube. For all investigated nanotubes, we predicted the occurrence of the minima of the D(2)/H(2) equilibrium selectivity at finite pressure. Moreover, we showed that those well-defined minima are gradually shifted upon increasing of the nanotube pore diameter. We related the nonmonotonic shape of the D(2)/H(2) equilibrium selectivity at finite pressures to the variation of the difference between the average kinetic energy computed from single-component adsorption isotherms of H(2) and D(2). In the interior space of both kinds of nanotubes hydrogen isotopes formed solid-like structures (plastic crystals) at 33 K and 10 Pa with densities above the compressed bulk para-hydrogen at 30 K and 30 MPa.

  9. Origin and Distribution of 26Al and Mg Isotopes in the Solar Protoplanetary Disk

    Larsen, Kirsten Kolbjørn

    birth environment of our Sun and a unique time-window into the very earliest history of our solar system. Ever since the discovery of its decay product, 26Mg, in primitive solar system objects more than 30 years ago, the short-lived radioactive nuclide, 26Al (t1/2 = 0.73 Myr), has been the optimal...... and differentiation within the large planetesimals that eventually served as building blocks for our planetary system. As such, our interpretations require a re-evaluation of our current understanding of solar system chronology....

  10. SIMS analyses of Mg, Cr, and Ni isotopes in primitive meteorites and short-lived radionuclides in the early solar system

    Guan, Y.; Huss, G.R.; Leshin, L.A


    SIMS analyses of {sup 26}Al-{sup 26}Mg, {sup 60}Fe-{sup 60}Ni, and {sup 53}Mn-{sup 53}Cr systems in unequilibrated enstatite chondrites provide evidence for the former existence of {sup 26}Al, {sup 60}Fe, and {sup 53}Mn in this highly reduced meteorite group, suggesting the widespread of these short-lived radionuclides in the early solar system. Calcium-aluminum-rich inclusions and Al-rich chondrules in enstatite chondrites show {sup 26}Al-{sup 26}Mg characteristics similar to their counterparts in other types of chondrites. Assuming its homogenous distribution, fine-scale {sup 26}Al relative chronology can be obtained for different components in meteorites. Well-defined isochrons yield initial {sup 60}Fe/{sup 56}Fe ratios of (0.3-1)x10{sup -6} in sulfides from enstatite chondrites. The former presence of {sup 60}Fe suggests a stellar source and its possible high abundance points to a supernova origin. {sup 26}Al and {sup 60}Fe could be important heat sources for the early planetary processes. The large variations of initial {sup 60}Fe/{sup 56}Fe and {sup 53}Mn/{sup 55}Mn ratios and the discordance between {sup 60}Fe-{sup 60}Ni and {sup 53}Mn-{sup 53}Cr systems observed in sulfides indicate later disturbance of the two isotopic systems, and therefore, bear no strict chronological significance. SIMS isotopic analysis can be utilized to attain important information about the early evolution of the solar system.

  11. 26Al-26Mg deficit dating ultramafic meteorites and silicate planetesimal differentiation in the early Solar System?

    Baker, J.A.; Schiller, M.; Bizzarro, Martin


    sequentially from cation exchange separation columns with fractionated stable Mg isotope compositions; (4) Mg separated from samples that was bracketed by analyses of both DSM-3 and Mg separated from a natural olivine sample subjected to the same chemical processing as the samples. These tests confirm...... it is possible to resolve differences in d Mg from the terrestrial materials that are =0.005‰. However, if Mg yields from chemical separation are low or an inappropriate equilibrium-isotopically fractionated standard is used this will generate analytical artefacts on d Mg when this is calculated with the kinetic...

  12. Origin and Distribution of 26Al and Mg Isotopes in the Solar Protoplanetary Disk

    Larsen, Kirsten Kolbjørn

    birth environment of our Sun and a unique time-window into the very earliest history of our solar system. Ever since the discovery of its decay product, 26Mg, in primitive solar system objects more than 30 years ago, the short-lived radioactive nuclide, 26Al (t1/2 = 0.73 Myr), has been the optimal...... and differentiation, however, relies on the critical assumption that the parent nuclide, 26Al, was uniformly distributed throughout the protoplanetary disk at the time of formation of the first solar system solids. Therefore, we have focused our research on evaluating the initial distribution of 26Al in early...... with higher 26Al abundance. Moreover, our results suggest that the formation of the solar systems oldest solids was brief and recurrent, possibly associated with the earliest evolutionary stages of the proto-Sun. Finally, we propose that physico-chemical mixing and unmixing of presolar dust components...

  13. An equilibrium model for the Mg(2+)-linked self-assembly of FtsZ in the presence of GTP or a GTP analogue.

    Monterroso, Begoña; Rivas, Germán; Minton, Allen P


    The concerted formation of a narrow distribution of oligomeric FtsZ species in the presence of GTP or a GTP analogue under close to physiological conditions (neutral pH and 0.5 M K(+)) has been characterized recently by various biophysical methods [Monterroso, B., et al. (2012) Biochemistry 51, 4541-4550]. An equilibrium model may semiquantitatively account for the results of this study; in the model, FtsZ self-associates in a noncooperative fashion to form linear fibrils, that upon increasing to a certain size exhibit an increasing tendency to form closed cyclic fibrils, as previously suggested [González, J. M., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 1895-1900]. The closed cyclic fibrils are formed when the natural curvature and flexibility of a linear oligomer bring the ends of a linear fiber sufficiently close to overcome the entropic barrier to loop closure. The size distribution of cyclic oligomers is thus a reflection of the tendency toward curvature of linear fibrils of FtsZ under the conditions used in these experiments.

  14. An Equilibrium Model for the Mg2+-Linked Self-Assembly of FtsZ in the Presence of GTP or a GTP Analogue

    Monterroso, Begoña; Rivas, Germán; Minton, Allen P.


    The concerted formation of a narrow distribution of oligomeric FtsZ species in the presence of GTP or a GTP analogue under close to physiological conditions (neutral pH and 0.5 M K+) has been characterized recently by various biophysical methods [Monterroso, B., et al. (2012) Biochemistry 51, 4541–4550]. An equilibrium model may semiquantitatively account for the results of this study; in the model, FtsZ self-associates in a noncooperative fashion to form linear fibrils, that upon increasing to a certain size exhibit an increasing tendency to form closed cyclic fibrils, as previously suggested [González, J. M., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 1895–1900]. The closed cyclic fibrils are formed when the natural curvature and flexibility of a linear oligomer bring the ends of a linear fiber sufficiently close to overcome the entropic barrier to loop closure. The size distribution of cyclic oligomers is thus a reflection of the tendency toward curvature of linear fibrils of FtsZ under the conditions used in these experiments. PMID:22809122

  15. The origin of high-Mg magmas in Mt Shasta and Medicine Lake volcanoes, Cascade Arc (California): higher and lower than mantle oxygen isotope signatures attributed to current and past subduction

    Martin, E.; Bindeman, I.; Grove, T. L.


    We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ18O (δ18OOl) values of 5.9-6.1‰, which are about 1‰ higher than those observed in olivine from normal mantle-derived magmas. In contrast, HAOT lavas from Medicine Lake have δ18OOl values ranging from 4.7 to 5.5‰, which are similar to or lower than values for olivine in equilibrium with mantle-derived magmas. Other magma types from both volcanoes show intermediate δ18OOl values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace element composition of olivine phenocrysts precludes a pyroxenitic mantle source. Therefore, the high and variable δ18OOl signature of the most magnesian samples studied (HAOT and BA) comes from the peridotitic mantle wedge itself. As HAOT magma is generated by anhydrous adiabatic partial melting of the shallow mantle, its 1.4‰ range in δ18OOl reflects a heterogeneous composition of the shallow mantle source that has been influenced by subduction fluids and/or melts sometime in the past. Magmas generated in the mantle wedge by flux melting due to modern subduction fluids, as exemplified by BA and probably PMA, display more homogeneous composition with only 0.5‰ variation. The high-δ18O values observed in magnesian lavas, and principally in the HAOT, are difficult to explain by a single-stage flux-melting process in the mantle wedge above the modern subduction zone and require a mantle source enriched in 18O. It is here explained by flow of older, pre-enriched portions of the mantle through the slab window beneath the South Cascades.


    Monique Florenzano


    Full Text Available General equilibrium is a central concept of economic theory. Unlike partial equilibrium analysis which study the equilibrium of a particular market under the clause “ceteris paribus” that revenues and prices on the other markets stay approximately unaffected, the ambition of a general equilibrium model is to analyze the simultaneous equilibrium in all markets of a competitive economy. Definition of the abstract model, some of its basic results and insights are presented. The important issues of uniqueness and local uniqueness of equilibrium are sketched; they are the condition for a predictive power of the theory and its ability to allow for statics comparisons. Finally, we review the main extensions of the general equilibrium model. Besides the natural extensions to infinitely many commodities and to a continuum of agents, some examples show how economic theory can accommodate the main ideas in order to study some contexts which were not thought of by the initial model

  17. Application of nano-magnesso ferrite (n-MgFe{sub 2}O{sub 4}) for the removal of Co{sup 2+} ions from synthetic wastewater: Kinetic, equilibrium and thermodynamic studies

    Srivastava, Varsha, E-mail: [Laboratory of Green Chemistry, Faculty of Technology, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Sharma, Y.C. [Department of Chemistry, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005 (India); Sillanpää, Mika [Laboratory of Green Chemistry, Faculty of Technology, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland)


    Graphical abstract: - Highlights: • The removal efficiency of n-MgFe{sub 2}O{sub 4} for Co(II) ions was investigated. • Rapid removal efficiency was observed within 60 min of contact time. • The kinetic data of Co(II) followed the pseudo-second-order model. • Thermodynamic studies revealed that the adsorption reaction was spontaneous. • Desorption study demonstrated its reusability upto three adsorption–desorption cycles. - Abstract: The aim of this research is to investigate the adsorption characteristics of nano-magnesso ferrite (n-MgFe{sub 2}O{sub 4}) for the removal of Co(II) ions from aqueous solution. n-MgFe{sub 2}O{sub 4} was synthesized by precipitation method. XRD of synthesized particles reveals the formation of single-phase n-MgFe{sub 2}O{sub 4} nanoparticles. TEM confirms the formation of particle size in the range of 25–35 nm. AFM and SEM analysis also support the TEM result. BET surface area of nanoparticles was determined to be 53.83 m{sup 2}/g. The adsorption of Co(II) onto n-MgFe{sub 2}O{sub 4} was found to be dependent on pH and the removal increased in alkaline medium. Co(II) adsorption followed pseudo-second-order model. Thermodynamic study showed that the adsorption process was endothermic and spontaneous. The equilibrium adsorption data was analyzed by two parameters and three parameters isotherm. Langmuir adsorption capacity was determined to be 67.41 mg/g. Chi-square test, standard deviations and the sum of squares of the errors (SSE) were evaluated to find out the better isotherm model. Desorption and reusability test suggested that n-MgFe{sub 2}O{sub 4} can be efficiently used up to three adsorption–desorption cycles. The findings of the present study suggest that n-MgFe{sub 2}O{sub 4} is very efficient for the adsorption of Co(II) ions. Adsorption efficiency of n-MgFe{sub 2}O{sub 4} for Co(II) has not yet been studied, so this study can be helpful for the treatment of Co(II) rich wastewater in near future.

  18. Influence of isotopic re-equilibration on speleothem and fluid inclusion isotope ratios after primary calcite precipitation

    Kluge, Tobias; Haderlein, Astrid; Weißbach, Therese


    Oxygen isotope ratios in speleothems (notably stalagmites) have been used since decades to successfully infer paleotemperatures and deduce paleo-environmental information. In addition, recent technical developments allow to increasingly use fluid inclusions as an archive for drip-water and together with the surrounding calcite as paleothermometer. A basic requirement for isotope data interpretation is the complete knowledge of the fractionation between calcite and fluid. Most laboratory and in-situ cave experiments focus on calcite growth and the isotope fractionation between calcite and feed solution. Potential isotope exchange and re-equilibration processes after the initial deposition have mostly been neglected. However, experiments of Oelkers et al. (2015) showed that the isotope exchange between minerals and fluid can proceed rapidly (within days), even at chemical equilibrium. In hydrous Mg carbonates a similar process of continuous isotope exchange between carbonate and fluid was observed after the carbonate precipitation was completed (Mavromatis et al., 2015). These observations suggest that the isotope ratios of speleothem calcite may be affected by this continuous exchange, likely driving the isotope composition continuously towards equilibrium at the respective cave conditions. In addition, fluid inclusions are suspected to be sensitive to an isotope exchange with the surrounding carbonate highlighting the need to precisely understand and quantify this effect. We assessed the oxygen isotope exchange between calcite and solution at chemical equilibrium conditions with theoretical estimates and laboratory experiments over an intermediate time scale (hours-weeks). A large isotope gradient (~20 ‰)) between solution and calcite was prepared in the experiment to investigate the dynamics of this re-equilibration process. We used a theoretical model based on a Rayleigh fractionation approach and the direct comparison with the experiment to determine

  19. Western Indian Ocean circulation and climate variability on different time scales. A study based on stable oxygen and carbon isotopes, benthic foraminiferal assemblages and Mg/Ca paleothermometry

    Romahn, Sarah


    In order to understand the Earth's climate evolution it is crucial to evaluate the role of low-latitude oceans in the global climate system, as they are connected to both hemispheres via atmospheric and oceanic circulation and thus hold the potential to disentangle the asynchronicity of short-term Pleistocene climate variability. However, the potential of low latitude oceans to respond to and force large-scale changes of the climate system is still debated. The aim of this thesis is to examine and to understand the causal relationship of both atmospheric and oceanic changes in the tropical western Indian Ocean on centennial-, millennial and glacial-interglacial timescales. For this purpose I investigated stable oxygen and carbon isotope compositions of both planktic and benthic foraminiferal tests, Mg/Ca ratios of planktic foraminiferal tests as well as benthic foraminiferal assemblages and sedimentary geochemical parameters on two sediment cores (GeoB12615-4, 446 m and GeoB12616-4, 1449 m) from the continental slope off Tanzania, East Africa.

  20. Phase Equilibria of ``Cu2O''-``FeO''-CaO-MgO-Al2O3 Slags at PO2 of 10-8.5 atm in Equilibrium with Metallic Copper for a Copper Slag Cleaning Production

    Henao, Hector M.; Pizarro, Claudio; Font, Jonkion; Moyano, Alex; Hayes, Peter C.; Jak, Evgueni


    Limited data are available on phase equilibria of the multicomponent slag system at the oxygen partial pressures used in the copper smelting, converting, and slag-cleaning processes. Recently, experimental procedures have been developed and have been applied successfully to characterize several complex industrial slags. The experimental procedures involve high-temperature equilibration on a substrate and quenching followed by electron probe X-ray microanalysis. This technique has been used to construct the liquidus for the “Cu2O”-“FeO”-SiO2-based slags with 2 wt pct of CaO, 0.5 wt pct of MgO, and 4.0 wt pct of Al2O3 at controlled oxygen partial pressures in equilibrium with metallic copper. The selected ranges of compositions and temperatures are directly relevant to the copper slag-cleaning processes. The new experimental equilibrium results are presented in the form of ternary sections and as a liquidus temperature vs Fe/SiO2 weight ratio diagram. The experimental results are compared with the FactSage thermodynamic model calculations.

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

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


    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.

  2. Equilibrium Modeling for Hydrogen Isotope Separation by Cryogenic Adsorption%氢同位素低温吸附分离的平衡吸附模型

    张东辉; 周理; 苏伟; 孙艳


    The separation of hydrogen and deuterium by cryogenic adsorption was conducted, using the molecular sieve 5A as adsorbent, helium as the carrier gas in a fixed column. The breakthrough curves of hydrogen, deuterium and the mixture of two components in helium carrier gas were measured, a separation factor, approximately 2, for the hydrogen-deuterium binary mixture was obtained. The equilibrium model was built for simulation of the concentration distribution for single hydrogen, deuterium and their mixture with helium carrier in the fixed column, and the simulation compared well with the experimental results.

  3. ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K+─Ca²+─Mg²+─NH4+─Na+─SO4²-─NO3-─Cl-─H2O aerosols

    C. Fountoukis


    Full Text Available This study presents ISORROPIA II, a thermodynamic equilibrium model for the K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl−–H2O aerosol system. A comprehensive evaluation of its performance is conducted against water uptake measurements for laboratory aerosol and predictions of the SCAPE2 thermodynamic module over a wide range of atmospherically relevant conditions. The two models agree well, to within 13% for aerosol water content and total PM mass, 16% for aerosol nitrate and 6% for aerosol chloride and ammonium. Largest discrepancies were found under conditions of low RH, primarily from differences in the treatment of water uptake and solid state composition. In terms of computational speed, ISORROPIA II was more than an order of magnitude faster than SCAPE2, with robust and rapid convergence under all conditions. The addition of crustal species does not slow down the thermodynamic calculations (compared to the older ISORROPIA code because of optimizations in the activity coefficient calculation algorithm. Based on its computational rigor and performance, ISORROPIA II appears to be a highly attractive alternative for use in large scale air quality and atmospheric transport models.

  4. Scleractinian Fossil Corals as Archives of Seawater δ26Mg

    Gothmann, A. O.; Higgins, J. A.; Adkins, J. F.; Stolarski, J.; Bender, M. L.


    The recovery of environmental signatures from coral skeletons is often made difficult by 'vital effects', which cause skeletal chemistry to deviate from the expected composition of aragonite in equilibrium with seawater. Recent studies show that Mg isotopes in scleractinian corals are subject to vital effects, which appear as a departure of the δ26Mg coral temperature dependence from that of inorganic aragonite [1]. However, different from the case for Mg/Ca or δ44Ca in coral, the magnitude of the observed Mg-isotope vital effect is small (on the order of 0.1 ‰ or less). In addition, measurements of different species of modern coral show similar fractionations, suggesting that coral δ26Mg is not species dependent [2]. Together, these observations indicate that corals should faithfully record the seawater Mg-isotope composition, and that vital effects will not bias reconstructions. We measured Mg isotopes in a set of extremely well-preserved fossil scleractinian corals, ranging in age from Jurassic through Recent, to reconstruct past seawater δ26Mg. Well-preserved fossil corals of similar age show a range in δ26Mg of ~0.2 ‰, pointing to the presence of vital effects. However, our results show little variability in the δ26Mg of fossil corals across different geologic ages, suggesting that seawater δ26Mg has remained relatively constant throughout the Cenozoic and Mesozoic. This pattern has implications for our understanding of the mechanisms driving secular variations in seawater Mg/Ca. In particular, our data imply that dolomitization rates have not changed enough during the Mesozoic and Cenozoic to account for secular variations in seawater Mg/Ca. Our coral δ26Mg record agrees with a Cenozoic record from bulk foraminifera, further supporting the faithfulness of the coral archive. However, both of these records disagree with a third Cenozoic Mg-isotope record, derived from species-specific planktic forams [3]. [1] Saenger, C. et al. (2014) Chem. Geol

  5. Reflective equilibrium

    van der Burg, W.; van Willigenburg, T.


    The basic idea of reflective equilibrium, as a method for theory construction and decision making in ethics, is that we should bring together a broad variety of moral and non-moral beliefs and, through a process of critical scrutiny and mutual adjustment, combine these into one coherent belief syste

  6. Reflective equilibrium

    van der Burg, W.; van Willigenburg, T.


    The basic idea of reflective equilibrium, as a method for theory construction and decision making in ethics, is that we should bring together a broad variety of moral and non-moral beliefs and, through a process of critical scrutiny and mutual adjustment, combine these into one coherent belief syste

  7. Sweatshop Equilibrium

    Chau, Nancy H.


    This paper presents a capability-augmented model of on the job search, in which sweatshop conditions stifle the capability of the working poor to search for a job while on the job. The augmented setting unveils a sweatshop equilibrium in an otherwise archetypal Burdett-Mortensen economy, and reconciles a number of oft noted yet perplexing features of sweatshop economies. We demonstrate existence of multiple rational expectation equilibria, graduation pathways out of sweatshops in complete abs...

  8. Conditions of stichtite (Mg6Cr2(OH)16[CO3]·4H2O) formation and its geochemical and isotope record of early phanerozoic serpentinizing environments

    Melchiorre, Erik B.; Bottrill, Ralph; Huss, Gary R.; Lopez, Amanda


    Stichtite is a magnesium-chromium hydroxycarbonate mineral found in association with early Phanerozoic chromite-rich serpentinite rocks of Tasmania, Australia and Tehuitzingo, Mexico. Elemental analysis of stichtite shows a range of compositions within the Cr-Fe-Al hydrotalcite group, with compositional trends associated with each discrete serpentinite host body. Elemental and textural analysis of stichtite-associated chromite indicates that stichtite forms in fore-arc setting rocks through interaction of chromite and methane-rich serpentinizing fluids. The degree to which chromite is replaced by stichtite is inferred to correlate with the length of time that the host rocks spent within the ;stichtite window.; Carbon stable-isotope analyses of stichtite suggest carbon sourcing from marine kerogen with a minor marine carbonate component in some samples. The carbon and hydrogen stable isotope profile of stichtite ranges from the field of methane from active serpentinizing zones, to organic thermogenic methane. The association of the stichtite 2H polytype (nee barbertonite) with aragonite ± antigorite suggests this is a higher pressure/temperature polytype of stichtite. Reaction completion textures, isotopic values, and qualitative mineral thermobarometric indicators indicate that stichtite forms during serpentinization of fore-arc setting rocks in a methane/H2-rich environment within fluid conduits, ranging from low temperatures and pressures near the surface, to depths where pressure is up to 0.8-1.2 GPa and temperature is up to ∼300 °C. These unique chemical, isotopic, and textural properties of stichtite from distinct serpentinite bodies likely record the duration of serpentinization at specific thermobarometric conditions, and provide a window into the conditions associated with a potentially habitable environment on early Earth and other bodies of the solar system.

  9. High-precision 27Al/24Mg ratio determination using a modified isotope-dilution approach

    Paton, Chad; Schiller, Martin; Ulfbeck, David Garf


    The precision of the 26Al–26Mg system—one of the most widely used chronometers for constraining the relative timing of events in the early solar system—is presently limited by methods for the determination of 27Al/24Mg ratios, which have seen little improvement in the last decade. We present a no...... on multiple measurements of a ∼2.7 gram piece of the Ivuna CI chondrite, we present a new estimate for the 27Al/24Mg ratio of this meteorite of 0.09781 ± 0.00029....

  10. Equilibrium thermodynamics

    de Oliveira, Mário J


    This textbook provides an exposition of equilibrium thermodynamics and its applications to several areas of physics with particular attention to phase transitions and critical phenomena. The applications include several areas of condensed matter physics and include also a chapter on thermochemistry. Phase transitions and critical phenomena are treated according to the modern development of the field, based on the ideas of universality and on the Widom scaling theory. For each topic, a mean-field or Landau theory is presented to describe qualitatively the phase transitions. These theories include the van der Waals theory of the liquid-vapor transition, the Hildebrand-Heitler theory of regular mixtures, the Griffiths-Landau theory for multicritical points in multicomponent systems, the Bragg-Williams theory of order-disorder in alloys, the Weiss theory of ferromagnetism, the Néel theory of antiferromagnetism, the Devonshire theory for ferroelectrics and Landau-de Gennes theory of liquid crystals. This new edit...

  11. Equilibrium thermodynamics

    Oliveira, Mário J


    This textbook provides an exposition of equilibrium thermodynamics and its applications to several areas of physics with particular attention to phase transitions and critical phenomena. The applications include several areas of condensed matter physics and include also a chapter on thermochemistry. Phase transitions and critical phenomena are treated according to the modern development of the field, based on the ideas of universality and on the Widom scaling theory. For each topic, a mean-field or Landau theory is presented to describe qualitatively the phase transitions.  These theories include the van der Waals theory of the liquid-vapor transition, the Hildebrand-Heitler theory of regular mixtures, the Griffiths-Landau theory for multicritical points in multicomponent systems, the Bragg-Williams theory of order-disorder in alloys, the Weiss theory of ferromagnetism, the Néel theory of antiferromagnetism, the Devonshire theory for ferroelectrics and Landau-de Gennes theory of liquid crystals. This textbo...


    李雪芳; 唐茂; 刘耘


    This study provided a number of theoretical equilibrium isotope fractionations between several Ge species, including quartz- (or opal-), albite-, K-feldspar- and olivine-like structures, as well as the dominant Ge(OH)4 and GeO(OH)3- species in aqueous solutions. They are basic parameters for exploring the unknown application of Ge isotope in the field of geochemistry. Our method is based on the Urey model (or the Bigeleisen-Mayer equation) and quantum chemistry calculation. We estimated that the accuracy of the parameters could be around 0.3‰, with the calculations made at B3LYP/6-311+G(d,p) level. Solvent effect was handled using explicit solvent model ("water droplet" method), and the minerals were simulated by cluster model. Our results showed that quartz- or opal-like structure can enrich most heavy Ge isotopes, and at 25℃, the fractionations are around Δquartz-Ge(OH)4=0.9‰, ΔGe(OH)4-GeO(OH)3-=0.3‰ (in seawaters), Δquartz-albite=0.6‰, Δquartz-K-feldspar=0.4‰, Δolivine-Ge(OH)4=-1.2‰ and Δquartz-olivine=2.1‰. These data could give better explanations to the experimental observations of Siebert et al. (2006) and Rouxel et al. (2006), suggesting that our theoretical prediction is accurate and important for real geochemical problems.%本研究基于Urey模型(或称Bigeleisen和Mayer公式),结合量子化学计算的方法,在B3LYP/6-311+G(d, p)理论水平下,计算了Ge在类似石英(包括蛋白石)、钠长石、钾长石、橄榄石结构以及水溶液(包括海水)中Ge(OH)4和GeO(OH)3-之间的Ge同位素平衡分馏系数.其中,溶液效应用"水滴法"处理,矿物结构用簇合物方法模拟.结果显示这些基本分馏参数的精度约±0.3‰;类石英(或蛋白石)结构最可能富集重Ge同位素,在25 ℃,几个Ge同位素分馏系数分别约为:Δ石英-Ge(OH)4=0.9‰、ΔGe(OH)4-GeO(OH)3-=0.3‰(海水中)、Δ石英-钠长石=0.6‰、Δ石英-钾长石=0.4‰、Δ橄榄石-Ge(OH)4=-1.2‰.类石英与类橄榄



    <正>20040631 Chen Jiangfeng (School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui) ; Xie Zhi Relationships Between Rb-Sr, Ar - Ar Geochronometers and Oxygen Isotopic Equilibrium of Intrusions from Eastern Anhui Province, China (Geological Journal of China Universities, ISSN 1006 - 7493, CN 32 -

  14. Surface area dependence of calcium isotopic reequilibration in carbonates: Implications for isotopic signatures in the weathering zone

    Fernandez, N. M.; Druhan, J. L.; Potrel, A.; Jacobson, A. D.


    The concept of dynamic equilibrium carries the implicit assumption of continued isotopic exchange between a mineral and the surrounding fluid. While this effect has received much attention in the marine paleoproxy literature, it has been relatively overlooked in application to the terrestrial environment. In weathering systems, a potential consequence is that rapid reequilibration may alter or erase isotopic signatures generated during secondary mineral formation. The extent and timescale over which isotopic signatures are reset in these hydrologic systems is unknown. Using reactive transport modeling, we show isotopic reequilibration under conditions reflecting terrestrial hydrologic settings to be significant and dependent on the reactive surface area of the solid. In particular, we suggest that the non-traditional stable isotopes commonly used in application to carbonates (e.g., Ca, Mg, Sr) are sensitive to these effects due to their rapid reaction rates. We aim to characterize the dependence of Ca isotopic reequilibration on surface area during calcite precipitation via batch experiments conducted at ambient temperature over 48-hour time periods. Calcite precipitation was performed in a closed batch reactor utilizing a controlled free-drift method. The batch reactors contained mixed supersaturated solutions of CaCl2 and NaHCO3 at an initial pH of 8.54. Precipitation was initiated by seed inoculation of calcite crystals with two distinct, pre-constrained surface areas. All experiments achieved the same final state of chemical equilibrium, but as expected, the fastest approach to equilibrium occurred for experiments employing calcite seeds with the highest surface area. This implies that differences in equilibrated Ca isotope ratios (δ44/40Ca) should reflect differences in surface area. This prediction is upheld by models of the experiments, indicating a measureable difference in δ44Ca during calcite precipitation where the higher surface area corresponds to

  15. Density functional theory study of small X-doped Mg(n) (X = Fe, Co, Ni, n = 1-9) bimetallic clusters: equilibrium structures, stabilities, electronic and magnetic properties.

    Kong, Fanjie; Hu, Yanfei


    The geometries, stabilities, and electronic and magnetic properties of Mg(n) X (X = Fe, Co, Ni, n = 1-9) clusters were investigated systematically within the framework of the gradient-corrected density functional theory. The results show that the Mg(n)Fe, Mg(n)Co, and Mg(n)Ni clusters have similar geometric structures and that the X atom in Mg(n)X clusters prefers to be endohedrally doped. The average atomic binding energies, fragmentation energies, second-order differences in energy, and HOMO-LUMO gaps show that Mg₄X (X = Fe, Co, Ni) clusters possess relatively high stability. Natural population analysis was performed and the results showed that the 3s and 4s electrons always transfer to the 3d and 4p orbitals in the bonding atoms, and that electrons also transfer from the Mg atoms to the doped atoms (Fe, Co, Ni). In addition, the spin magnetic moments were analyzed and compared. Several clusters, such as Mg₁,₂,₃,₄,₅,₆,₈,₉Fe, Mg₁,₂,₄,₅,₆,₈,₉Co, and Mg₁,₂,₅,₆,₇,₉Ni, present high magnetic moments (4 μ(B), 3 μ(B), and 2 μ(B), respectively).

  16. Simultaneous analysis of matter radii, transition probabilities, and excitation energies of Mg isotopes by angular-momentum-projected configuration-mixing calculations

    Shimada, Mitsuhiro; Tagami, Shingo; Matsumoto, Takuma; Shimizu, Yoshifumi R; Yahiro, Masanobu


    We perform simultaneous analysis of (1) matter radii, (2) $B(E2; 0^+ \\rightarrow 2^+ )$ transition probabilities, and (3) excitation energies, $E(2^+)$ and $E(4^+)$, for $^{24-40}$Mg by using the beyond mean-field (BMF) framework with angular-momentum-projected configuration mixing with respect to the axially symmetric $\\beta_2$ deformation with infinitesimal cranking. The BMF calculations successfully reproduce all of the data for $r_{\\rm m}$, $B(E2)$, and $E(2^+)$ and $E(4^+)$, indicating that it is quite useful for data analysis, particularly for low-lying states. We also discuss the absolute value of the deformation parameter $\\beta_2$ deduced from measured values of $B(E2)$ and $r_{\\rm m}$. This framework makes it possible to investigate the effects of $\\beta_2$ deformation, the change in $\\beta_2$ due to restoration of rotational symmetry, $\\beta_2$ configuration mixing, and the inclusion of time-odd components by infinitesimal cranking. Under the assumption of axial deformation and parity conservation,...

  17. Simultaneous analysis of matter radii, transition probabilities, and excitation energies of Mg isotopes by angular-momentum-projected configuration-mixing calculations

    Shimada, Mitsuhiro; Watanabe, Shin; Tagami, Shingo; Matsumoto, Takuma; Shimizu, Yoshifumi R.; Yahiro, Masanobu


    We perform simultaneous analysis of (1) matter radii, (2) B (E 2 ;0+→2+) transition probabilities, and (3) excitation energies, E (2+) and E (4+) , for Mg-4024 by using the beyond-mean-field (BMF) framework with angular-momentum-projected configuration mixing with respect to the axially symmetric β2 deformation with infinitesimal cranking. The BMF calculations successfully reproduce all of the data for rm,B (E 2 ) , and E (2+) and E (4+) , indicating that it is quite useful for data analysis; particularly for low-lying states. We also discuss the absolute value of the deformation parameter β2 deduced from measured values of B (E 2 ) and rm. This framework makes it possible to investigate the effects of β2 deformation, the change in β2 due to restoration of rotational symmetry, β2 configuration mixing, and the inclusion of time-odd components by infinitesimal cranking. Under the assumption of axial deformation and parity conservation, we clarify which effect is important for each of the three measurements and propose the kinds of BMF calculations that are practical for each of the three kinds of observables.

  18. A Decrease in NiO-MgO Phase Through Its Solid Solution Equilibrium with Tetragonal (La1−zSrz2Ni1−yMgyO4−δ: Effect on Catalytic Partial Oxidation of Methane

    Xiong Yin


    Full Text Available Calcination of an oxide mixture consisting of 0.4 La2O3, 0.2 SrCO3, (1−xNiO, and xMgO at 800∘C results in an equilibrium between tetragonal (La1−zSrz2Ni1−yMgyO4−δ phase and NiO-MgO phase. Forming rock-salt NiO-MgO facilitates the NiO to join the tetragonal phase. The size of the NiO-MgO phase in the resulting composite is reduced with the increase in MgO (the x value. The composite thus obtained is used to catalyze partial oxidation of methane, and the maximum methane conversion of ca. 93% is achieved when x=0.2. A further rise in x value results in a monotonic decrease in the methane conversion. X-ray diffraction, electron microscopy, and chemosorption all confirm a decrease in both size and amount of the supported Ni0 clusters with the increase in MgO dosage. The reduction in size promotes the dispersion of Ni0 sites and gives rise to both high activity and strong coking resistance.

  19. Uranium isotope fractionation during coprecipitation with aragonite and calcite

    Chen, Xinming; Romaniello, Stephen J.; Herrmann, Achim D.; Wasylenki, Laura E.; Anbar, Ariel D.


    Natural variations in 238U/235U of marine calcium carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ∼7.5 and ∼8.5 to study possible U isotope fractionation during incorporation into these minerals. Small but significant U isotope fractionation was observed in aragonite experiments at pH ∼8.5, with heavier U isotopes preferentially enriched in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007 + 0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ∼7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3(aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism. These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2 , Ca2+, or Mg2+ concentrations. In general, these effects are likely to be small (<0.13‰), but are nevertheless potentially significant because of the small natural range of

  20. Phase Equilibrium Studies of CaO-SiO2-MgO-Al2O3 System with Binary Basicity of 1.5 Related to Blast Furnace Slag

    Kou, Mingyin; Wu, Shengli; Ma, Xiaodong; Wang, Laixin; Chen, Mao; Cai, Qingwu; Zhao, Baojun


    Slags play an important role in blast furnace operation, and their compositions are based on the CaO-SiO2-MgO-Al2O3 quaternary system in many steel companies. The binary basicity (CaO/SiO2 weight ratio) of blast furnace slags, especially primary slag and bosh slag, can be as high as 1.5 or higher. Phase equilibria and liquidus temperatures in the CaO-SiO2-MgO-Al2O3 system with binary basicity of 1.50 are experimentally determined for temperatures in the range 1723 K to 1823 K (1450 °C to 1550 °C). High temperature equilibration, quenching, and electron probe X-ray microanalysis techniques have been used in the present study. The isotherms are obtained in the primary phase fields of Ca2SiO4, melilite, spinel, periclase, and merwinite related to blast furnace slags. Effects of Al2O3, MgO, and binary basicity on liquidus temperatures have been discussed. In addition, extensive solid solutions have been measured for different primary phases and will be used for development and optimization of the thermodynamic database.

  1. Concurrent fractional and equilibrium crystallisation

    Sha, Lian-Kun


    This paper proposes the concept of concurrent fractional and equilibrium crystallisation (CFEC) in a multi-phase magmatic system in light of experimental results on diffusivities of elements and other species in minerals and melts. A group of equations are presented to describe how the concentrations of an element or isotope change in fractionated solid, equilibrated solid, melt, liquid, and gas phases, as well as in magma, as a function of distribution coefficients and mass fractions during the CFEC process. CFEC model is a generalised and unified formulation that is valid, not only for pure fractional crystallisation (FC) and perfect equilibrium crystallisation (EC) singly, as two of its limiting end-member cases, but also for the geologically more important process of concurrent fractional and equilibrium crystallisation. The concept that both fractional and equilibrium crystallisation can operate concurrently in a magmatic system, for a given element, among different minerals, and even within different-sized crystal grains of the very same mineral phase, is of fundamental importance in deepening our current understanding of magmatic differentiation processes. CFEC probably occurs more frequently in the natural world than either pure fractional or perfect equilibrium crystallisation alone, as a result of the interplay of varying diffusivities of elements under diverse physicochemical conditions, different residence time and growth rates of mineral phases in magmas, and varying grain sizes within each phase and among different phases. The marked systematic variations in trace element concentrations in the melts of the Bishop Tuff have long been perplexing and difficult to reconcile with existing models of differentiation. CFEC, which is able to better explain the scatter trends in a systematic way than fractional crystallisation, is considered to be the cause.

  2. Hydrologic Cycle Response to the Paleocene-Eocene Thermal Maximum at Austral, High-Latitude Site 690 as Revealed by In Situ Measurements of Foraminiferal Oxygen Isotope and Mg/Ca Ratios

    Kozdon, R.; Kelly, D.; Fournelle, J.; Valley, J. W.


    Earth surface temperatures warmed by ~5°C during an ancient (~55.5 Ma) global warming event termed the Paleocene-Eocene thermal maximum (PETM). This transient (~200 ka) "hyperthermal" climate state had profound consequences for the planet's surficial processes and biosphere, and is widely touted as being an ancient analog for climate change driven by human activities. Hallmarks of the PETM are pervasive carbonate dissolution in the ocean basins and a negative carbon isotope excursion (CIE) recorded in variety of substrates including soil and marine carbonates. Together these lines of evidence signal the rapid (≤30 ka) release of massive quantities (≥2000 Gt) of 13C-depleted carbon into the exogenic carbon cycle. Paleoenvironmental reconstructions based on pedogenic features in paleosols, clay mineralogy and sedimentology of coastal and continental deposits, and land-plant communities indicate that PETM warmth was accompanied by a major perturbation to the hydrologic cycle. Micropaleontological evidence and n-alkane hydrogen isotope records indicate that increased poleward moisture transport reduced sea-surface salinities (SSSs) in the central Arctic Ocean during the PETM. Such findings are broadly consistent with predictions of climate model simulations. Here we reassess a well-studied PETM record from the Southern Ocean (ODP Site 690) in light of new δ18O and Mg/Ca data obtained from planktic foraminiferal shells by secondary ion mass spectrometry (SIMS) and electron microprobe analysis (EMPA), respectively. The unparalleled spatial resolution of these in situ techniques permits extraction of more reliable δ18O and Mg/Ca data by targeting of minute (≤10 μm spots), biogenic domains within individual planktic foraminifera that retain the original shell chemistry (Kozdon et al. 2011, Paleocean.). In general, the stratigraphic profile and magnitude of the δ18O decrease (~2.2‰) delimiting PETM warming in our SIMS-generated record are similar to those of

  3. Ion exchange equilibrium constants

    Marcus, Y


    Ion Exchange Equilibrium Constants focuses on the test-compilation of equilibrium constants for ion exchange reactions. The book first underscores the scope of the compilation, equilibrium constants, symbols used, and arrangement of the table. The manuscript then presents the table of equilibrium constants, including polystyrene sulfonate cation exchanger, polyacrylate cation exchanger, polymethacrylate cation exchanger, polysterene phosphate cation exchanger, and zirconium phosphate cation exchanger. The text highlights zirconium oxide anion exchanger, zeolite type 13Y cation exchanger, and




    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.

  5. What is the Role of the Transition State in Soret and Chemical Diffusion Induced Isotopic Fractionation?

    Dominguez, G.


    For over six decades, Urey's (1) statistical mechanical model of isotopic fractionation based on partition functions with quantized energy levels have enjoyed enormous success in quantitatively explaining equilibrium isotopic fractionation in a wide variety of geochemical systems For example, the interpretation of oxygen isotopic variations in carbonate systems (e.g. foraminiferas), in terms of partition functions with quantized energy levels, forms the basis for paleothermometry (2). Recent observations of isotopic fractionation from chemical and thermal (Soret) diffusion (3-7) appear to challenge our theoretical understanding of mass-transport and isotopic fractionation (8, 9). For example, a recently proposed quantum mechanical model of Soret diffusion, which correctly predicts the isotopic fractionation in thermal gradients for isotopes of Mg, Ca, Fe, Si, and possibly oxygen, was critiqued as being unphysical. First, it was argued that the zero point energies needed to explain the magnitude of isotopic fractionation in basalt melts were unrealistically high based on infrared spectra of these melts. Second, it was argued that the chemical diffusion isotopic fractionation (beta) factors expected from these zero-point energies were also unphysical (10). A recently proposed collision-momentum transfer model partially explains observed fractionation factors, although it fails miserably (by a factor of 3) to account for the isotopic fractionation of Mg isotopes (11). In this presentation, I will review recent observations and models of isotopic fractionation in geochemical melts with thermal gradients and expand upon previous work (8, 12) to show how transition state theory can simultaneously explain mass-transport induced isotopic fractionation, including kinetic, equilibrium, and Soret isotopic fractionation. I show this by providing a few example calculations of the kinetic fractionation factors (a.k.a. beta factors) expected in chemical diffusion as well as

  6. TRPM6 forms the Mg2+ influx channel involved in intestinal and renal Mg2+ absorption.

    Voets, T.; Nilius, B.; Hoefs, S.J.G.; Kemp, J.W.C.M. van der; Droogmans, G.; Bindels, R.J.M.; Hoenderop, J.G.J.


    Mg2+ is an essential ion involved in a multitude of physiological and biochemical processes and a major constituent of bone tissue. Mg2+ homeostasis in mammals depends on the equilibrium between intestinal Mg2+ absorption and renal Mg2+ excretion, but little is known about the molecular nature of

  7. A new method for studying iodine metabolism; the isotopic equilibrium method - kinetic and quantitative aspects of measurements made on rats; Une nouvelle methode d'etude du metabolisme de l'iode: la methode d'equilibre isotopique - aspects cinetiques et quantitatifs obtenus chez le rat

    Simon, C. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires


    The isotopic equilibrium method which has been developed in the case of the rat has made it possible to measure the absolute values of the principal parameters of iodine metabolism in this animal. The quantities and concentrations of iodine have been measured in the thyroid gland and in the plasma with a sensitivity of 0.001 {mu}g of {sup 127}I. This sensitivity has made it possible to measure pools as small as the iodide and the free iodotyrosines of the thyroid and to demonstrate the absence of free iodotyrosines in the plasma of the normal rat. In vivo, the isotopic equilibrium method has made it possible to measure the iodine content of the thyroid gland and to calculate the intensity of this gland's secretion without removing it. By double labelling with {sup 125}I and {sup 131}I the isotopic equilibrium method has made it possible to measure the flux, intensity of the intrathyroidal recycling as well as the turnover rates of all the iodine containing compounds of the thyroid gland. For this gland no precursor-product relationship has been found between The iodotyrosines (MIT and DIT) and the iodothyronines (T{sub 4} and T{sub 3}). The absence of this relationship is due to the heterogeneity of the thyroglobulin turnover. It has been shown furthermore that there exists in the plasma an organic fraction of the iodine which is different to thyroglobulin and which is renewed more rapidly than the circulating hormones T{sub 3} and T{sub 4}. The isotopic equilibrium method is very useful for series measurements of iodine. It makes it possible furthermore to improve the biochemical fractionations by adding carriers without affecting the subsequent {sup 127}I measurements. (author) [French] La methode d'equilibre isotopique, mise au point chez le rat, a permis de mesurer en valeur absolue les principaux parametres du metabolisme de l'iode chez cet animal. Les quantites ou les concentrations d'iode ont ete mesurees pour la thyroide et pour le

  8. Planetary and meteoritic Mg/Si and d30Si variations inherited from solar nebula chemistry

    Dauphas, Nicolas; Burkhardt, Christoph; Kobayashi, Hiroshi; Kurosawa, Kosuke


    The bulk chemical compositions of planets are uncertain, even for major elements such as Mg and Si. This is due to the fact that the samples available for study all originate from relatively shallow depths. Comparison of the stable isotope compositions of planets and meteorites can help overcome this limitation. Specifically, the non-chondritic Si isotope composition of the Earth's mantle was interpreted to reflect the presence of Si in the core, which can also explain its low density relative to pure Fe-Ni alloy. However, we have found that angrite meteorites display a heavy Si isotope composition similar to the lunar and terrestrial mantles. Because core formation in the angrite parent-body (APB) occurred under oxidizing conditions at relatively low pressure and temperature, significant incorporation of Si in the core is ruled out as an explanation for this heavy Si isotope signature. Instead, we show that equilibrium isotopic fractionation between gaseous SiO and solid forsterite at 1370 K in the solar neb...


    Guangya CHEN


    In this paper we define a concept of weak equilibrium for vector network equilibrium problems.We obtain sufficient conditions of weak equilibrium points and establish relation with vector network equilibrium problems and vector variational inequalities.

  10. Phase equilibrium engineering

    Brignole, Esteban Alberto


    Traditionally, the teaching of phase equilibria emphasizes the relationships between the thermodynamic variables of each phase in equilibrium rather than its engineering applications. This book changes the focus from the use of thermodynamics relationships to compute phase equilibria to the design and control of the phase conditions that a process needs. Phase Equilibrium Engineering presents a systematic study and application of phase equilibrium tools to the development of chemical processes. The thermodynamic modeling of mixtures for process development, synthesis, simulation, design and

  11. Intrinsic Conductivity in Magnesium-Oxygen Battery Discharge Products: MgO and MgO2

    Smith, Jeffrey G.; Naruse, Junichi; Hiramatsu, Hidehiko


    O, the equilibrium concentration of carriers in MgO2 is low, and moderate-to-poor mobility further limits conductivity. If equilibrium behavior is realized, then we conclude that (i) sluggish charge transport in MgO or MgO2 will limit battery performance when these compounds cover the cathode support and (ii) what...

  12. Magnesium isotope geochemistry in arc volcanism

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  13. Magnesium isotope geochemistry in arc volcanism.

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ(26)Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ(26)Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  14. Stable isotope utilization methodology; Methodologie de l`emploi des isotopes stables

    Roth, E. [Conservatoire National des Arts et Metiers (CNAM), 75 - Paris (France)


    The various applications of stable isotope utilization are reviewed, as a function of their specific properties: poly-isotopic abundance modification is used for tracer applications; the accurate measurement of the stable isotope abundance may be applied to isotopic dilution for ultra-trace measurement, physical constant determination, fluid volume and concentration measurement; isotopic effects, such as reaction equilibrium differences are used for separation and identification of molecule active centers (pharmacology, paleoclimatology, hydrogeological studies) while reaction rate differences (competitive and non competitive methods) are used for the study of reaction mechanisms, such as enzymatic reactions. Analysis techniques (mass spectrometry, nuclear magnetic resonance, optical methods) are reviewed. 2 figs., 18 refs.

  15. Copper isotope signatures in modern marine sediments

    Little, Susan H.; Vance, Derek; McManus, James; Severmann, Silke; Lyons, Timothy W.


    The development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling. To date, no Cu isotope data has been published for modern sediments deposited under low oxygen conditions. We present data encompassing a broad spectrum of hydrographic and redox regimes, including continental margin and euxinic (sulphide-containing) settings. Taken together with previously published data from oxic settings, these data indicate that the modern oceanic sink for Cu has a surprisingly homogeneous isotopic composition of about +0.3‰ (δ65Cu, relative to NIST SRM976). We suggest that this signature reflects one of two specific water-column processes: (1) an equilibrium isotope fractionation between soluble, isotopically heavy, Cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver Cu to the sediment, or (2) an equilibrium isotope fractionation between the same isotopically heavy ligand-bound pool and the particle reactive free Cu2+ species, with the latter being scavenged by particulates and thereby delivered to the sediment. An output flux of about +0.3‰ into sediments is isotopically light relative to the known inputs to the ocean (at around +0.6‰) and the seawater value of +0.6 to +0.9‰, suggesting the presence of an as yet unidentified isotopically light source of Cu to the oceans. We hypothesize that this source may be hydrothermal, or may result from the partial dissolution of continentally derived particles.

  16. Heavy atom isotope effects on enzymatic reactions

    Paneth, Piotr


    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.

  17. Quantification of Labile Soil Mercury by Stable Isotope Dilution Techniques

    Shetaya, Waleed; Huang, Jen-How; Osterwalder, Stefan; Alewell, Christine


    Mercury (Hg) is a toxic element that can cause severe health problems to humans. Mercury is emitted to the atmosphere from both natural and anthropogenic sources and can be transported over long distances before it is deposited to aquatic and terrestrial environments. Aside from accumulation in soil solid phases, Hg deposited in soils may migrate to surface- and ground-water or enter the food chain, depending on its lability. There are many operationally-defined extraction methods proposed to quantify soil labile metals. However, these methods are by definition prone to inaccuracies such as non-selectivity, underestimation or overestimation of the labile metal pool. The isotopic dilution technique (ID) is currently the most promising method for discrimination between labile and non-labile metal fractions in soil with a minimum disturbance to soil-solid phases. ID assesses the reactive metal pool in soil by defining the fraction of metal both in solid and solution phases that is isotopically-exchangeable known as the 'E-value'. The 'E-value' represents the metal fraction in a dynamic equilibrium with the solution phase and is potentially accessible to plants. This is carried out by addition of an enriched metal isotope to soil suspensions and quantifying the fraction of metal that is able to freely exchange with the added isotope by measuring the equilibrium isotopic ratio by ICP-MS. E-value (mg kg-1) is then calculated as follows: E-Value = (Msoil/ W) (CspikeVspike/ Mspike) (Iso1IAspike -Iso2IAspikeRss / Iso2IAsoil Rss - Iso1IAsoil) where M is the average atomic mass of the metal in the soil or the spike, W is the mass of soil (kg), Cspike is the concentration of the metal in the spike (mg L-1), Vspike is the volume of spike (L), IA is isotopic abundance, and Rss is the equilibrium ratio of isotopic abundances (Iso1:Iso2). Isotopic dilution has been successfully applied to determine E-values for several elements. However, to our knowledge, this method has not yet

  18. Beat the equilibrium

    Berty, J.M.; Krishnan, C.; Elliott, J.R. Jr. (Berty Reaction Engineers, Ltd. (USA))


    Methanol is synthesised catalytically from H{sub 2}, CO and CO{sub 2}. Equilibrium considerations dictated the use of high pressures until the advent of copper-based catalysts. But equilibrium problems still exist; single pass conversions of CO and H{sub 2} are low, typically 30-40%. A solvent methanol process (SMP) is proposed to overcome existing problems. A high-boiling inert solvent is introduced with the synthesis gas. The solvent selectively absorbs CH{sub 3}OH, thus shifting the equilibrium towards the product. The strongest solvent identified and tested is tetraethyleneglycol dimethyl ether (tetraglyme). 24 refs., 4 figs., 2 tabs.

  19. Chemical Principles Revisited: Chemical Equilibrium.

    Mickey, Charles D.


    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)

  20. The magnesium isotope record of cave carbonate archives

    S. Riechelmann


    Full Text Available Here we explore the potential of time-series magnesium (δ26Mg isotope data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco, the warm-temperate (Germany, the equatorial-humid (Peru and the cold-humid (Austria climate zones. Changes in the calcite magnesium isotope signature with time are placed against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and non-equilibrium processes governs the δ26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rain water or snow as well as soil and hostrock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean δ26Mg values (GDA: −4.26 ± 0.07 ‰ and HK3: −4.17 ± 0.15 ‰ and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value (NC-A and NC-B δ26Mg: −3.96 ± 0.04 ‰ but only minor variations in Mg-isotope composition, which is in concert with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean δ26Mg: −4.01 ± 0.07 ‰; BU 4 mean δ26Mg: −4.20 ± 0.10 ‰ record changes in outside air temperature as driving factor rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: −3.00 ± 0.73 ‰; SPA 59: −3.70 ± 0.43 ‰ are affected by glacial versus interglacial climate change with outside air temperature affecting soil zone activity

  1. Isotope and chemical geothermometry and its applications



    The Na-K-Mg Geoindicator created by Giggenbach (1988) is convenient to use but it is still based on the empirical geothermometry equations and discrepancy for different cation geo-thermometers is observed. In fact, the location of the curve of "full equilibrium" is different if a different Na-K geothermometry equation is used. The difference is pronounced for temperatures lower than about 220℃. A case study on the Zhangzhou geothermal field of SE China resulted in a reliable estimate of reservoir temperature of 150℃ by the SO4-H2O pair Oxygen-18 isotope geothermometer. This has provided an example of attained equilibrium of the marine sulphate in the geothermal system in the low-medium temperature range (<150℃). A recent refinement of the theoretical geothermometry was achieved by the FixAl method, which provides the possibility to identify and solve problems such as an erroneous analytical value of Aluminium, and influence of processes such as mixing and degassing, and therefore makes it possible to

  2. Thermodynamics "beyond" local equilibrium

    Vilar, Jose; Rubi, Miguel


    Nonequilibrium thermodynamics has shown its applicability in a wide variety of different situations pertaining to fields such as physics, chemistry, biology, and engineering. As successful as it is, however, its current formulation considers only systems close to equilibrium, those satisfying the so-called local equilibrium hypothesis. Here we show that diffusion processes that occur far away from equilibrium can be viewed as at local equilibrium in a space that includes all the relevant variables in addition to the spatial coordinate. In this way, nonequilibrium thermodynamics can be used and the difficulties and ambiguities associated with the lack of a thermodynamic description disappear. We analyze explicitly the inertial effects in diffusion and outline how the main ideas can be applied to other situations. [J.M.G. Vilar and J.M. Rubi, Proc. Natl. Acad. Sci. USA 98, 11081-11084 (2001)].

  3. Non-equilibrium Economics

    Katalin Martinás


    Full Text Available A microeconomic, agent based framework to dynamic economics is formulated in a materialist approach. An axiomatic foundation of a non-equilibrium microeconomics is outlined. Economic activity is modelled as transformation and transport of commodities (materials owned by the agents. Rate of transformations (production intensity, and the rate of transport (trade are defined by the agents. Economic decision rules are derived from the observed economic behaviour. The non-linear equations are solved numerically for a model economy. Numerical solutions for simple model economies suggest that the some of the results of general equilibrium economics are consequences only of the equilibrium hypothesis. We show that perfect competition of selfish agents does not guarantee the stability of economic equilibrium, but cooperativity is needed, too.

  4. Response reactions: equilibrium coupling.

    Hoffmann, Eufrozina A; Nagypal, Istvan


    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.

  5. The evolution of Carbon isotopes in calcite in the presence of cyanobacteria

    Grimm, Christian; Mavromatis, Vasileios; Pokrovsky, Oleg S.; Oelkers, Eric H.


    Stable isotopic compositions in carbonates are widely used as indicators of environmental conditions prevailing during mineral formation. This reconstruction is substantially based on the assumption that there is no change in the mineral composition over geological time. However, recent experimental studies have shown that carbon and magnesium isotopes in hydrous Mg-carbonates undergo continuous re-equilibration with the ambient solution even after mineral precipitation stopped ([1] and [2], respectively). To verify whether this holds true for anhydrous Ca-bearing carbonates which readily form at earth's surface environments, a series of batch system calcite precipitation experiments were performed in the presence of actively growing cyanobacteria Synechococcus sp. The bacteria were grown at ambient temperature in a BG11 culture medium (SIGMA C3061) and continuous stirring, air-bubbling and illumination. Calcite precipitation was initiated by the addition of 8.5mM CaCl2 and 0-50 mM NaHCO3 or NaHCO3-Na2CO3 mixtures. The presence of cyanobacteria is on one hand promoting CaCO3 formation due to increasing pH resulting from photosynthesis. On the other hand, actively growing cyanobacteria drastically change carbon isotope signature of the aqueous fluid phase by preferably incorporating the lighter 12C isotope into biomass [1]. This study explores the effect of continuously changing carbon isotope compositions in dissolved inorganic carbon (DIC) on precipitated calcite which is in chemical equilibrium with the ambient fluid phase. [1] Mavromatis et al. (2015). The continuous re-equilibration of carbon isotope compositions of hydrous Mg-carbonates in the presence of cyanobacteria. Chem. Geol. 404, 41-51 [2] Mavromatis et al. (2012). Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria. Geochim. Cosmochim. Acta 76, 161-174

  6. Equilibrium statistical mechanics

    Mayer, J E


    The International Encyclopedia of Physical Chemistry and Chemical Physics, Volume 1: Equilibrium Statistical Mechanics covers the fundamental principles and the development of theoretical aspects of equilibrium statistical mechanics. Statistical mechanical is the study of the connection between the macroscopic behavior of bulk matter and the microscopic properties of its constituent atoms and molecules. This book contains eight chapters, and begins with a presentation of the master equation used for the calculation of the fundamental thermodynamic functions. The succeeding chapters highlight t

  7. Quaternary equilibrium diagrams ZrO{sub 2}-Al{sub 2}O{sub 3}-SiO{sub 2}-(CaO, MgO, TiO{sub 2}). A powerful tool for the development of new materials by reaction sintering; Diagramas de equilibrio cuaternarios ZrO{sub 2}-Al{sub 2}O{sub 3}-SiO{sub 2}- (CaO, MgO, TiO{sub 2}). Una poderosa herramienta para el desarrollo de nuevos materiales por sinterizacion reactiva

    Moya, J. S.; Bartolome, J. F.; Pena, P.


    In this paper we set out, discuss and evaluate the work on Mullite-zirconia composites obtained by reaction sintering led and inspired by Salvador de Aza on the basis of ZrO{sub 2}-Al{sub 2}O{sub 3}-SiO{sub 2}-(CaO, MgO, TiO{sub 2}) multicomponent phase equilibrium diagrams. We analyze their impact on different areas of ceramic science and technology such as refractory grogs, aluminum industry, etc. The possible fields of future applications such as dental prosthesis replacing partially stabilized zirconia materials with rare earths are also reported. (Author) 42 refs.

  8. Magnesium isotope fractionation during carbonatite magmatism at Oldoinyo Lengai, Tanzania

    Li, Wang-Ye; Teng, Fang-Zhen; Halama, Ralf; Keller, Jörg; Klaudius, Jurgis


    To investigate the behaviour of Mg isotopes during carbonatite magmatism, we analyzed Mg isotopic compositions of natrocarbonatites and peralkaline silicate rocks from Oldoinyo Lengai, Tanzania. The olivine melilitites from the vicinity of Oldoinyo Lengai have homogeneous and mantle-like Mg isotopic compositions (δ26Mg of -0.30 to -0.26‰), indicating limited Mg isotope fractionation during mantle melting. The highly evolved peralkaline silicate rocks not related to silicate-carbonatite liquid immiscibility, including phonolites from the unit Lengai I, combeite-wollastonite nephelinites (CWNs) from the unit Lengai II A and carbonated combeite-wollastonite-melilite nephelinites (carbCWMNs), have δ26Mg values (from -0.25 to -0.10‰) clustered around the mantle value. By contrast, the CWNs from the unit Lengai II B, which evolved from the silicate melts that were presumably generated by silicate-carbonatite liquid immiscibility, have heavier Mg isotopes (δ26Mg of -0.06 to +0.09‰). Such a difference suggests Mg isotope fractionation during liquid immiscibility and implies, based on mass-balance calculations, that the original carbonatite melts at Lengai were isotopically light. The variable and positive δ26Mg values of natrocarbonatites (from +0.13 to +0.37‰) hence require a change of their Mg isotopic compositions subsequent to liquid immiscibility. The negative correlations between δ26Mg values and contents of alkali and alkaline earth metals of natrocarbonatites suggest Mg isotope fractionation during fractional crystallization of carbonatite melts, with heavy Mg isotopes enriched in the residual melts relative to fractionated carbonate minerals. Collectively, significant Mg isotope fractionation may occur during both silicate-carbonatite liquid immiscibility and fractional crystallization of carbonatite melts, making Mg isotopes a potentially useful tracer of these processes relevant to carbonatite petrogenesis.

  9. Equilibrium games in networks

    Li, Angsheng; Zhang, Xiaohui; Pan, Yicheng; Peng, Pan


    It seems a universal phenomenon of networks that the attacks on a small number of nodes by an adversary player Alice may generate a global cascading failure of the networks. It has been shown (Li et al., 2013) that classic scale-free networks (Barabási and Albert, 1999, Barabási, 2009) are insecure against attacks of as small as O(logn) many nodes. This poses a natural and fundamental question: Can we introduce a second player Bob to prevent Alice from global cascading failure of the networks? We proposed a game in networks. We say that a network has an equilibrium game if the second player Bob has a strategy to balance the cascading influence of attacks by the adversary player Alice. It was shown that networks of the preferential attachment model (Barabási and Albert, 1999) fail to have equilibrium games, that random graphs of the Erdös-Rényi model (Erdös and Rényi, 1959, Erdös and Rényi, 1960) have, for which randomness is the mechanism, and that homophyly networks (Li et al., 2013) have equilibrium games, for which homophyly and preferential attachment are the underlying mechanisms. We found that some real networks have equilibrium games, but most real networks fail to have. We anticipate that our results lead to an interesting new direction of network theory, that is, equilibrium games in networks.

  10. On equilibrium structures of the water molecule

    Császár, Attila G.; Czakó, Gábor; Furtenbacher, Tibor; Tennyson, Jonathan; Szalay, Viktor; Shirin, Sergei V.; Zobov, Nikolai F.; Polyansky, Oleg L.


    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

  11. Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber.

    Zhu, Dan; Bao, Huiming; Liu, Yun


    Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ(57)Fe difference often less than 0.2 per mil). However, an increasing number of data has revealed a puzzling observation, e.g., the δ(57)Fe for silicic magmas ranges from 0‰ up to 0.6‰, with the most positive δ(57)Fe almost exclusively found in A-type granitoids. Several interpretations have been proposed by different research groups, but these have so far failed to explain some aspects of the observations. Here we propose a dynamic, diffusion-induced isotope fractionation model that assumes Si-melts are growing and ascending immiscibly in a Fe-rich bulk magma chamber. Our model offers predictions on the behavior of non-traditional stable isotope such as Fe, Mg, Si, and Li that are consistent with observations from many A-type granitoids, especially those associated with layered intrusions. Diffusion-induced isotope fractionation may be more commonly preserved in magmatic rocks than was originally predicted.

  12. Immunity by equilibrium.

    Eberl, Gérard


    The classical model of immunity posits that the immune system reacts to pathogens and injury and restores homeostasis. Indeed, a century of research has uncovered the means and mechanisms by which the immune system recognizes danger and regulates its own activity. However, this classical model does not fully explain complex phenomena, such as tolerance, allergy, the increased prevalence of inflammatory pathologies in industrialized nations and immunity to multiple infections. In this Essay, I propose a model of immunity that is based on equilibrium, in which the healthy immune system is always active and in a state of dynamic equilibrium between antagonistic types of response. This equilibrium is regulated both by the internal milieu and by the microbial environment. As a result, alteration of the internal milieu or microbial environment leads to immune disequilibrium, which determines tolerance, protective immunity and inflammatory pathology.

  13. The magnesium isotope record of cave carbonate archives

    S. Riechelmann


    Full Text Available Here we explore the potential of magnesium (δ26Mg isotope time-series data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco, the warm-temperate (Germany, the equatorial-humid (Peru and the cold-humid (Austria climate zones. Changes in the calcite magnesium isotope signature with time are compared against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and disequilibrium processes governs the δ26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rainwater or snow as well as soil and host rock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean δ26Mg values (GDA: −4.26 ± 0.07‰ and HK3: −4.17 ± 0.15‰, and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value of all stalagmites (NC-A and NC-B δ26Mg: −3.96 ± 0.04‰ but only minor variations in Mg-isotope composition, which is consistent with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean δ26Mg: −4.01 ± 0.07‰; BU 4 mean δ26Mg: −4.20 ± 0.10‰ suggest changes in outside air temperature was the principal driver rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: −3.00 ± 0.73‰; SPA 59: −3.70 ± 0.43‰ are affected by glacial versus interglacial climate change with outside air temperature

  14. Blood: bone equilibrium

    Neuman, M.W.


    The conundrum of blood undersaturation with respect to bone mineralization and its supersaturation with respect to bone's homeostatic function has acquired a new equation. On the supply side, Ca/sup 2 +/ is pumped in across bone cells to provide the needed Ca/sup 2 +/ x P/sub i/ for brushite precipitation. On the demand side, blood is in equilibrium with bone fluid, which is in equilibrium with a mineral more soluble than apatite. The function of potassium in this equation is yet to be found.

  15. Carbonate "clumped" isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

    Kimball, Justine; Eagle, Robert; Dunbar, Robert


    Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near-constant temperature, salinity, and pH and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop "clumped" isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate-related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and high-Mg calcitic gorgonian (Isididae and Coralliidae) deep-sea corals and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures, and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than high-Mg calcitic gorgonian corals and the two groups of coral produce statistically different relationships between Δ47-temperature calibrations. These data are significant in the interpretation of all carbonate clumped isotope calibration data as they show that distinct Δ47-temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset

  16. Equilibrium CO bond lengths

    Demaison, Jean; Császár, Attila G.


    Based on a sample of 38 molecules, 47 accurate equilibrium CO bond lengths have been collected and analyzed. These ultimate experimental (reEX), semiexperimental (reSE), and Born-Oppenheimer (reBO) equilibrium structures are compared to reBO estimates from two lower-level techniques of electronic structure theory, MP2(FC)/cc-pVQZ and B3LYP/6-311+G(3df,2pd). A linear relationship is found between the best equilibrium bond lengths and their MP2 or B3LYP estimates. These (and similar) linear relationships permit to estimate the CO bond length with an accuracy of 0.002 Å within the full range of 1.10-1.43 Å, corresponding to single, double, and triple CO bonds, for a large number of molecules. The variation of the CO bond length is qualitatively explained using the Atoms in Molecules method. In particular, a nice correlation is found between the CO bond length and the bond critical point density and it appears that the CO bond is at the same time covalent and ionic. Conditions which permit the computation of an accurate ab initio Born-Oppenheimer equilibrium structure are discussed. In particular, the core-core and core-valence correlation is investigated and it is shown to roughly increase with the bond length.

  17. A theoretical model of isotopic fractionation by thermal diffusion and its implementation on silicate melts

    Xuefang, L.; Liu, Y.


    Huang et al (2010) found that Fe, Ca and Mg isotope fractionations of high-temperature silicate melts are only associated with the temperature gradients in thermal diffusion processes and are independent of compositions and mean temperatures [1]. Richter et al (2010) doubted that the existing data are sufficient to obtain such conclusion [2]. A few theoretical models have been proposed for explaining isotopic fractionations in these processes under high temperatures [3, 4]. However, molecular-level mechanisms and theoretical treatments of these processes are still under debating. Here we provide a unified theory based on the local thermodynamic equilibrium treatment (LTE) of statistical mechanics for evaluating thermal isotopic fractionations under a wide range of temperatures. Under high temperatures, our theory however can be reasonably approximated to this equation: where A and B are constants which are related to specific isotope systems and chemical compositions of silicate melts. If the thermal gradient is not very large and the mean temperature is high, the second part of the above equation can be safely neglected and obtain an extremely simple equation which is linearly depended on temperatures, agreeing with what Huang et al (2010) concluded. Based on this terse equation, we can not only easily provide isotope fractionation data for almost all kinds of isotope systems, but also can provide the mechanisms of isotope fractionation in thermal diffusion processes. [1] Huang et al (2010) Nature 464, 396-400. [2] Richter et al (2010) Nature 472, E1-E1. [3] Dominguez et al (2011) Nature 473, 70-73.

  18. Towards Non-Equilibrium Dynamics with Trapped Ions

    Silbert, Ariel; Jubin, Sierra; Doret, Charlie


    Atomic systems are superbly suited to the study of non-equilibrium dynamics. These systems' exquisite isolation from environmental perturbations leads to long relaxation times that enable exploration of far-from-equilibrium phenomena. One example of particular relevance to experiments in trapped ion quantum information processing, metrology, and precision spectroscopy is the approach to thermal equilibrium of sympathetically cooled linear ion chains. Suitable manipulation of experimental parameters permits exploration of the quantum-to-classical crossover between ballistic transport and diffusive, Fourier's Law conduction, a topic of interest not only to the trapped ion community but also for the development of microelectronic devices and other nanoscale structures. We present progress towards trapping chains of multiple co-trapped calcium isotopes geared towards measuring thermal equilibration and discuss plans for future experiments in non-equilibrium statistical mechanics. This work is supported by Cottrell College Science Award from the Research Corporation for Science Advancement and by Williams College.

  19. Problems in equilibrium theory

    Aliprantis, Charalambos D


    In studying General Equilibrium Theory the student must master first the theory and then apply it to solve problems. At the graduate level there is no book devoted exclusively to teaching problem solving. This book teaches for the first time the basic methods of proof and problem solving in General Equilibrium Theory. The problems cover the entire spectrum of difficulty; some are routine, some require a good grasp of the material involved, and some are exceptionally challenging. The book presents complete solutions to two hundred problems. In searching for the basic required techniques, the student will find a wealth of new material incorporated into the solutions. The student is challenged to produce solutions which are different from the ones presented in the book.

  20. Bounded Computational Capacity Equilibrium

    Hernandez, Penelope


    We study repeated games played by players with bounded computational power, where, in contrast to Abreu and Rubisntein (1988), the memory is costly. We prove a folk theorem: the limit set of equilibrium payoffs in mixed strategies, as the cost of memory goes to 0, includes the set of feasible and individually rational payoffs. This result stands in sharp contrast to Abreu and Rubisntein (1988), who proved that when memory is free, the set of equilibrium payoffs in repeated games played by players with bounded computational power is a strict subset of the set of feasible and individually rational payoffs. Our result emphasizes the role of memory cost and of mixing when players have bounded computational power.

  1. General Search Market Equilibrium

    Albrecht, James W.; Axell, Bo


    In this paper we extend models of “search market equilibrium” to incorporate general equilibrium considerations. The model we treat is one with a single product market and a single labor market. Imperfectly informed individuals follow optimal strategies in searching for a suitably low price and high wage. For any distribution of price and wage offers across firms these optimal strategies generate product demand and labor supply schedules. Firms then choose prices and wages to maximize expecte...

  2. Equilibrium statistical mechanics

    Jackson, E Atlee


    Ideal as an elementary introduction to equilibrium statistical mechanics, this volume covers both classical and quantum methodology for open and closed systems. Introductory chapters familiarize readers with probability and microscopic models of systems, while additional chapters describe the general derivation of the fundamental statistical mechanics relationships. The final chapter contains 16 sections, each dealing with a different application, ordered according to complexity, from classical through degenerate quantum statistical mechanics. Key features include an elementary introduction t

  3. Volatility in Equilibrium

    Bollerslev, Tim; Sizova, Natalia; Tauchen, George

    Stock market volatility clusters in time, carries a risk premium, is fractionally inte- grated, and exhibits asymmetric leverage effects relative to returns. This paper develops a first internally consistent equilibrium based explanation for these longstanding empirical facts. The model is cast......, and the dynamic cross-correlations of the volatility measures with the returns calculated from actual high-frequency intra-day data on the S&P 500 aggregate market and VIX volatility indexes....

  4. Tourism Equilibrium Price Trends

    Mohammad Mohebi


    Full Text Available Problem statement: A review of the tourism history shows that tourism as an industry was virtually unknown in Malaysia until the late 1960s. Since then, it has developed and grown into a major industry, making an important contribution to the country's economy. By allocating substantial funds to the promotion of tourism and the provision of the necessary infrastructure, the government has played an important role in the impressive progress of the Malaysian tourism industry. One of the important factors which can attract tourists to Malaysia is the tourism price. Has the price of tourism decreased? To answer this question, it is necessary to obtain the equilibrium prices as well as the yearly trend for Malaysia during the sample period as it will be useful for analysis of the infrastructure situation of the tourism industry in this country. The purpose of the study is to identify equilibrium tourism price trends in Malaysian tourism market. Approach: We use hotel room as representative of tourism market. Quarterly data from 1995-2009 are used and a dynamic model of simultaneous equation is employed. Results: Based on the result during the period of 1995 until 2000, the growth rate of the equilibrium price was greater than consumer price index and producer price index. Conclusion: In the Malaysian tourism market, new infrastructure during this period had not been developed to keep pace with tourist arrivals.

  5. Leatherback Isotopes

    National Oceanic and Atmospheric Administration, Department of Commerce — SWFSC is currently working on a project identifying global marine isotopes using leatherback turtles (Dermochelys coriacea) as the indicator species. We currently...

  6. Isotopic chirality

    Floss, H.G. [Univ. of Washington, Seattle, WA (United States)


    This paper deals with compounds that are chiral-at least in part, due to isotope substitution-and their use in tracing the steric course of enzyme reaction in vitro and in vivo. There are other applications of isotopically chiral compounds (for example, in analyzing the steric course of nonenzymatic reactions and in probing the conformation of biomolecules) that are important but they will not be discussed in this context.

  7. Isotopic Paleoclimatology

    Bowen, R.

    Paleotemperature scales were calculated by H. C. Urey and others in the 1950s to assess past temperatures, and later work using the stable isotopes of oxygen, hydrogen, and carbon employed standards such as Peedee belemnite (PDB) and Standard Mean Ocean Water (SMOW). Subsequently, subjects as diverse as ice volume and paleotemperatures, oceanic ice and sediment cores, Pleistocene/Holocene climatic changes, and isotope chronostratigraphy extending back to the Precambrian were investigated.

  8. Magnesium isotope geochemistry in arc volcanism

    Teng, Fang-Zhen; Hu, Yan


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from −0.25 to −0.10, in contrast to the narrow range that characterizes the mantle (−0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid−mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. PMID:27303032

  9. Redefining the utility of the three-isotope method

    Cao, Xiaobin; Bao, Huiming


    The equilibrium isotope fractionation factor αeq is a fundamental parameter in the study of stable isotope effects. Experimentally, it has been difficult to establish that a system has attained equilibrium. The three-isotope method, using the initial trajectory of changing isotope ratios (e.g. 16O, 17O, and 18O) to deduce the final equilibrium point of isotope exchange, has long been hailed as the most rigorous experimental approach. However, over the years some researchers have cautioned on the limitations of this method, but the foundation of three-isotope method has not been properly examined and the method is still widely used in calibrating αeq for both traditional and increasingly non-traditional isotope systems today. Here, using water-water and dissolved CO2-water oxygen exchange as model systems, we conduct an isotopologues-specific kinetic analysis of the exchange processes and explore the underlying assumptions and validity of the three-isotope method. We demonstrate that without knowing the detailed exchange kinetics a priori the three-isotope method cannot lead to a reliable αeq. For a two-reservoir exchanging system, α determined by this method may be αeq, kinetic isotope effect, or apparent kinetic isotope effect, which can all bear different values. When multiple reservoirs exist during exchange, the evolving trajectory can be complex and hard to predict. Instead of being a tool for αeq determination, three-isotope method should be used as a tool for studying kinetic isotope effect, apparent kinetic isotope effect, and detailed exchange kinetics in diverse systems.

  10. Noncompact Equilibrium Points and Applications

    Zahra Al-Rumaih


    Full Text Available We prove an equilibrium existence result for vector functions defined on noncompact domain and we give some applications in optimization and Nash equilibrium in noncooperative game.

  11. Magnesium isotope systematics in Martian meteorites

    Magna, Tomáš; Hu, Yan; Teng, Fang-Zhen; Mezger, Klaus


    Magnesium isotope compositions are reported for a suite of Martian meteorites that span the range of petrological and geochemical types recognized to date for Mars, including crustal breccia Northwest Africa (NWA) 7034. The δ26Mg values (per mil units relative to DSM-3 reference material) range from -0.32 to -0.11‰; basaltic shergottites and nakhlites lie to the heavier end of the Mg isotope range whereas olivine-phyric, olivine-orthopyroxene-phyric and lherzolitic shergottites, and chassignites have slightly lighter Mg isotope compositions, attesting to modest correlation of Mg isotopes and petrology of the samples. Slightly heavier Mg isotope compositions found for surface-related materials (NWA 7034, black glass fraction of the Tissint shergottite fall; δ26Mg > -0.17‰) indicate measurable Mg isotope difference between the Martian mantle and crust but the true extent of Mg isotope fractionation for Martian surface materials remains unconstrained. The range of δ26Mg values from -0.19 to -0.11‰ in nakhlites is most likely due to accumulation of clinopyroxene during petrogenesis rather than garnet fractionation in the source or assimilation of surface material modified at low temperatures. The rather restricted range in Mg isotope compositions between spatially and temporally distinct mantle-derived samples supports the idea of inefficient/absent major tectonic cycles on Mars, which would include plate tectonics and large-scale recycling of isotopically fractionated surface materials back into the Martian mantle. The cumulative δ26Mg value of Martian samples, which are not influenced by late-stage alteration processes and/or crust-mantle interactions, is - 0.271 ± 0.040 ‰ (2SD) and is considered to reflect δ26Mg value of the Bulk Silicate Mars. This value is robust taking into account the range of lithologies involved in this estimate. It also attests to the lack of the Mg isotope variability reported for the inner Solar System bodies at current

  12. Extended Mixed Vector Equilibrium Problems

    Mijanur Rahaman


    Full Text Available We study extended mixed vector equilibrium problems, namely, extended weak mixed vector equilibrium problem and extended strong mixed vector equilibrium problem in Hausdorff topological vector spaces. Using generalized KKM-Fan theorem (Ben-El-Mechaiekh et al.; 2005, some existence results for both problems are proved in noncompact domain.

  13. Non-equilibrium thermodynamics

    De Groot, Sybren Ruurds


    The study of thermodynamics is especially timely today, as its concepts are being applied to problems in biology, biochemistry, electrochemistry, and engineering. This book treats irreversible processes and phenomena - non-equilibrium thermodynamics.S. R. de Groot and P. Mazur, Professors of Theoretical Physics, present a comprehensive and insightful survey of the foundations of the field, providing the only complete discussion of the fluctuating linear theory of irreversible thermodynamics. The application covers a wide range of topics: the theory of diffusion and heat conduction, fluid dyn

  14. Geochemical evidence for repetitive intracrystal recrystallization during the mineralogical stabilization of some biogenic Mg calcites

    Budd, D.A. (Univ. of Colorado, Boulder, CO (United States). Dept. of Geological Sciences)


    Mineralogical stabilization of porcellaneous foraminifera is unique relative to other types of bioclasts in that these foraminifera is unique relative to other types of bioclasts in that these foraminifera can undergo stabilization to low-Mg calcite without any textural change. Holocene porcellaneous foraminifer from the freshwater diagenetic zone of the Schooner Cays, Bahamas, are in the midst of this alteration and thus provide a rare insight into the stabilization process. These bioclasts exhibit Mg loss and oxygen isotopic changes with no textural alteration at any scale. The mineralogical stabilization, or recrystallization, is a repetitive intracrystal process. Each recrystallization produces a calcite with a slightly lower Mg content than its predecessor. The stabilization rate is dependent on time and hydrologic flux; older phreatic-zone material is the most altered and younger vadose-zone material is the least altered. Numerical modeling of the chemical diagenesis suggests that the molar water:rock ratio of a single recrystallization is about 1:100 and that the resultant precipitate is not in equilibrium with the ambient pore waters. Repetitive recrystallizations, however, eventually yield a mineralogically stable low-Mg calcite that can be in equilibrium with the bulk pore waters. Complete mineralogical stabilization to LMC should occur at cumulative molar water:rock ratios of about 16 and requires hundreds to thousands of recrystallizations, each reducing Mg content by less than 0.01 mole %. The large number of recrystallizations with incrementally small chemical changes per recrystallization makes alteration of these foraminifera significantly different from single-step recrystallization of other types of bioclasts.

  15. 镁同位素地球化学研究新进展及其应用%Advances and application in magnesium isotope geochemistry

    柯珊; 刘盛遨; 李王晔; 杨蔚; 滕方振


    Mg isotopes retained in the weathered products and light Mg isotopes released into the hydrosphere; (2) equilibrium Mg isotope fractionation during magma differentiation is limited; (3) significant kinetic Mg isotope fractionation occurs during chemical and thermal diffusion at high temperatures. Based on these studies, Mg isotopes have been used to trace accretion of the Earth and recycling of crustal materials, and, in the near future, may potentially be applied to tracing chemical evolution of the continental crust and be used as geological thermometers.

  16. Thermal equilibrium of goats.

    Maia, Alex S C; Nascimento, Sheila T; Nascimento, Carolina C N; Gebremedhin, Kifle G


    The effects of air temperature and relative humidity on thermal equilibrium of goats in a tropical region was evaluated. Nine non-pregnant Anglo Nubian nanny goats were used in the study. An indirect calorimeter was designed and developed to measure oxygen consumption, carbon dioxide production, methane production and water vapour pressure of the air exhaled from goats. Physiological parameters: rectal temperature, skin temperature, hair-coat temperature, expired air temperature and respiratory rate and volume as well as environmental parameters: air temperature, relative humidity and mean radiant temperature were measured. The results show that respiratory and volume rates and latent heat loss did not change significantly for air temperature between 22 and 26°C. In this temperature range, metabolic heat was lost mainly by convection and long-wave radiation. For temperature greater than 30°C, the goats maintained thermal equilibrium mainly by evaporative heat loss. At the higher air temperature, the respiratory and ventilation rates as well as body temperatures were significantly elevated. It can be concluded that for Anglo Nubian goats, the upper limit of air temperature for comfort is around 26°C when the goats are protected from direct solar radiation.

  17. Statistical physics ""Beyond equilibrium

    Ecke, Robert E [Los Alamos National Laboratory


    The scientific challenges of the 21st century will increasingly involve competing interactions, geometric frustration, spatial and temporal intrinsic inhomogeneity, nanoscale structures, and interactions spanning many scales. We will focus on a broad class of emerging problems that will require new tools in non-equilibrium statistical physics and that will find application in new material functionality, in predicting complex spatial dynamics, and in understanding novel states of matter. Our work will encompass materials under extreme conditions involving elastic/plastic deformation, competing interactions, intrinsic inhomogeneity, frustration in condensed matter systems, scaling phenomena in disordered materials from glasses to granular matter, quantum chemistry applied to nano-scale materials, soft-matter materials, and spatio-temporal properties of both ordinary and complex fluids.

  18. General equilibrium without utility functions

    Balasko, Yves; Tvede, Mich


    How far can we go in weakening the assumptions of the general equilibrium model? Existence of equilibrium, structural stability and finiteness of equilibria of regular economies, genericity of regular economies and an index formula for the equilibria of regular economies have been known not to re......How far can we go in weakening the assumptions of the general equilibrium model? Existence of equilibrium, structural stability and finiteness of equilibria of regular economies, genericity of regular economies and an index formula for the equilibria of regular economies have been known...... and the diffeomorphism of the equilibrium manifold with a Euclidean space; (2) the diffeomorphism of the set of no-trade equilibria with a Euclidean space; (3) the openness and genericity of the set of regular equilibria as a subset of the equilibrium manifold; (4) for small trade vectors, the uniqueness, regularity...

  19. Equilibrium models and variational inequalities

    Konnov, Igor


    The concept of equilibrium plays a central role in various applied sciences, such as physics (especially, mechanics), economics, engineering, transportation, sociology, chemistry, biology and other fields. If one can formulate the equilibrium problem in the form of a mathematical model, solutions of the corresponding problem can be used for forecasting the future behavior of very complex systems and, also, for correcting the the current state of the system under control. This book presents a unifying look on different equilibrium concepts in economics, including several models from related sciences.- Presents a unifying look on different equilibrium concepts and also the present state of investigations in this field- Describes static and dynamic input-output models, Walras, Cassel-Wald, spatial price, auction market, oligopolistic equilibrium models, transportation and migration equilibrium models- Covers the basics of theory and solution methods both for the complementarity and variational inequality probl...

  20. On the Local Equilibrium Principle

    Hessling, H


    A physical system should be in a local equilibrium if it cannot be distinguished from a global equilibrium by ``infinitesimally localized measurements''. This seems to be a natural characterization of local equilibrium, however the problem is to give a precise meaning to the qualitative phrase ``infinitesimally localized measurements''. A solution is suggested in form of a {\\em Local Equilibrium Condition} (LEC) which can be applied to non-interacting quanta. The Unruh temperature of massless quanta is derived by applying LEC to an arbitrary point inside the Rindler Wedge. Massless quanta outside a hot sphere are analyzed. A stationary spherically symmetric local equilibrium does only exist according to LEC if the temperature is globally constant. Using LEC a non-trivial stationary local equilibrium is found for rotating massless quanta between two concentric cylinders of different temperatures. This shows that quanta may behave like a fluid with a B\\'enard instability.

  1. Equilibrium states of homogeneous sheared compressible turbulence

    Riahi, M.; Lili, T.


    Equilibrium states of homogeneous compressible turbulence subjected to rapid shear is studied using rapid distortion theory (RDT). The purpose of this study is to determine the numerical solutions of unsteady linearized equations governing double correlations spectra evolution. In this work, RDT code developed by authors solves these equations for compressible homogeneous shear flows. Numerical integration of these equations is carried out using a second-order simple and accurate scheme. The two Mach numbers relevant to homogeneous shear flow are the turbulent Mach number Mt, given by the root mean square turbulent velocity fluctuations divided by the speed of sound, and the gradient Mach number Mg which is the mean shear rate times the transverse integral scale of the turbulence divided by the speed of sound. Validation of this code is performed by comparing RDT results with direct numerical simulation (DNS) of [A. Simone, G.N. Coleman, and C. Cambon, Fluid Mech. 330, 307 (1997)] and [S. Sarkar, J. Fluid Mech. 282, 163 (1995)] for various values of initial gradient Mach number Mg0. It was found that RDT is valid for small values of the non-dimensional times St (St 10) in particular for large values of Mg0. This essential feature justifies the resort to RDT in order to determine equilibrium states in the compressible regime.

  2. Equilibrium states of homogeneous sheared compressible turbulence

    M. Riahi


    Full Text Available Equilibrium states of homogeneous compressible turbulence subjected to rapid shear is studied using rapid distortion theory (RDT. The purpose of this study is to determine the numerical solutions of unsteady linearized equations governing double correlations spectra evolution. In this work, RDT code developed by authors solves these equations for compressible homogeneous shear flows. Numerical integration of these equations is carried out using a second-order simple and accurate scheme. The two Mach numbers relevant to homogeneous shear flow are the turbulent Mach number Mt, given by the root mean square turbulent velocity fluctuations divided by the speed of sound, and the gradient Mach number Mg which is the mean shear rate times the transverse integral scale of the turbulence divided by the speed of sound. Validation of this code is performed by comparing RDT results with direct numerical simulation (DNS of [A. Simone, G.N. Coleman, and C. Cambon, Fluid Mech. 330, 307 (1997] and [S. Sarkar, J. Fluid Mech. 282, 163 (1995] for various values of initial gradient Mach number Mg0. It was found that RDT is valid for small values of the non-dimensional times St (St 10 in particular for large values of Mg0. This essential feature justifies the resort to RDT in order to determine equilibrium states in the compressible regime.

  3. Dentine oxygen isotopes (δ 18O) as a proxy for odontocete distributions and movements

    Matthews, Cory J. D.; Longstaffe, Fred J.; Ferguson, Steven H


    Abstract Spatial variation in marine oxygen isotope ratios (δ 18O) resulting from differential evaporation rates and precipitation inputs is potentially useful for characterizing marine mammal distributions and tracking movements across δ 18O gradients. Dentine hydroxyapatite contains carbonate and phosphate that precipitate in oxygen isotopic equilibrium with body water, which in odontocetes closely tracks the isotopic composition of ambient water. To test whether dentine oxygen isotope comp...

  4. Determination of the 36Mg(n ,γ )37Mg reaction rate from Coulomb dissociation of 37Mg

    Shubhchintak; Chatterjee, R.; Shyam, R.


    We use the Coulomb dissociation (CD) method to calculate the rate of the 36Mg(n ,γ )37Mg radiative capture reaction. The CD cross sections of the 37Mg nucleus on a 208Pb target at the beam energy of 244 MeV/nucleon, for which new experimental data have recently become available, were calculated within the framework of a finite-range distorted-wave Born approximation theory that is extended to include the projectile deformation effects. Invoking the principle of detailed balance, these cross sections are used to determine the excitation function and subsequently the rate of the 36Mg(n ,γ )37Mg reaction. We compare these rates to those of the 36Mg(α ,n )39Si reaction calculated within a Hauser-Feshbach model. We find that for T9 as large as up to 1.0 (in units of 109 K) the 36Mg(n ,γ )37Mg reaction is much faster than the 36Mg(α ,n )39Si one. The inclusion of the effects of 37Mg projectile deformation in the breakup calculations enhances the (n ,γ ) reaction rate even further. Therefore, it is highly unlikely that the (n ,γ )β -decay r -process flow will be broken at the 36Mg isotope by the α process.

  5. Measurement of isotope abundance variations in nature by gravimetric spiking isotope dilution analysis (GS-IDA).

    Chew, Gina; Walczyk, Thomas


    Subtle variations in the isotopic composition of elements carry unique information about physical and chemical processes in nature and are now exploited widely in diverse areas of research. Reliable measurement of natural isotope abundance variations is among the biggest challenges in inorganic mass spectrometry as they are highly sensitive to methodological bias. For decades, double spiking of the sample with a mix of two stable isotopes has been considered the reference technique for measuring such variations both by multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS) and multicollector-thermal ionization mass spectrometry (MC-TIMS). However, this technique can only be applied to elements having at least four stable isotopes. Here we present a novel approach that requires measurement of three isotope signals only and which is more robust than the conventional double spiking technique. This became possible by gravimetric mixing of the sample with an isotopic spike in different proportions and by applying principles of isotope dilution for data analysis (GS-IDA). The potential and principle use of the technique is demonstrated for Mg in human urine using MC-TIMS for isotopic analysis. Mg is an element inaccessible to double spiking methods as it consists of three stable isotopes only and shows great potential for metabolically induced isotope effects waiting to be explored.

  6. Paleoproxies: Heavy Stable Isotope Perspectives

    Nagler, T. F.; Hippler, D.; Siebert, C.; Kramers, J. D.


    Recent advances in isotope ratio mass spectrometry, namely multiple collector ICP-MS and refined TIMS techniques, will significantly enhance the ability to measure heavy stable isotope fractionation, which will lead to the development of a wide array of process-identifying (bio)-geochemical tools. Thus far research in this area is not easily assessable to scientists outside the isotope field. This is due to the fact that analyzing heavy stable isotopes does not provide routine numbers which are per se true (the preciser the truer) but is still a highly experimental field. On the other hand resolving earth science problems requires specialists familiar with the environment being studied. So what is in there for paleoceanographers? In a first order approach, relating isotope variations to physical processes is straightforward. A prominent example are oxygen isotope variations with temperature. The total geological signal is of course far more complicated. At low temperatures, heavy stable isotopes variations have been reported for e.g. Ca, Cr, Fe, Cu, Zn, Mo and Tl. Fractionation mechanisms and physical parameters responsible for the observed variations are not yet resolved for most elements. Significant equilibrium isotope fractionation is expected from redox reactions of transition metals. However a difference in coordination number between two coexisting speciations of an element in the same oxidation state can also cause fractionation. Protonation of dissolved Mo is one case currently discussed. For paleoceanography studies, a principal distinction between transition metals essential for life (V to Zn plus Mo) or not will be helpful. In case of the former group, distinction between biogenic and abiogenic isotope fractionation will remain an important issue. For example, abiotic Fe redox reactions result in isotope fractionations indistinguishable in direction and magnitude from microbial effects. Only a combination of different stable isotope systems bears the

  7. Napoleon Is in Equilibrium

    Phillips, Rob


    It has been said that the cell is the test tube of the twenty-first century. If so, the theoretical tools needed to quantitatively and predictively describe what goes on in such test tubes lag sorely behind the stunning experimental advances in biology seen in the decades since the molecular biology revolution began. Perhaps surprisingly, one of the theoretical tools that has been used with great success on problems ranging from how cells communicate with their environment and each other to the nature of the organization of proteins and lipids within the cell membrane is statistical mechanics. A knee-jerk reaction to the use of statistical mechanics in the description of cellular processes is that living organisms are so far from equilibrium that one has no business even thinking about it. But such reactions are probably too hasty given that there are many regimes in which, because of a separation of timescales, for example, such an approach can be a useful first step. In this article, we explore the power of statistical mechanical thinking in the biological setting, with special emphasis on cell signaling and regulation. We show how such models are used to make predictions and describe some recent experiments designed to test them. We also consider the limits of such models based on the relative timescales of the processes of interest.

  8. On the progress in stable isotope separation

    Prusakov, V.N. [Kurchatov Institute, Moscow (Russian Federation)


    The principles and process of centrifuge isotope separation are reviewed; the fundamental advantage of the centrifuge over gaseous diffusion arises from the fact that the primary isotope separation effect occurs at thermodynamic equilibrium; thus, gas centrifuge enrichment uses only about 1/20 to 1/30 of the electricity per SWU (separation work unit) consumed by gaseous diffusion. The various substances that can be used in centrifuge isotope separation are listed (fluorides, oxyfluorides, {pi}-complexes, boron hydrides, metal-organic compounds, halides...). The centrifuge method productivity is much greater than with the electromagnetic separation technique; examples of centrifuge stable and radioactive isotope separation are given; the method of the residue reduction is also presented with the example of separating radioactive krypton-85 out of a nuclear reactor krypton blend. 4 figs.


    Poitrasson, F.; Zambardi, T.; Magna, T.; Neal, C. R.


    It is difficult to estimate the bulk chemical and isotopic properties of planets, especially for the Moon for which our sampling is far more limited than for the Earth. As a result, there is currently a debate on the bulk Fe isotope composition of the Moon: Whereas in a first study we proposed that the bulk lunar Fe isotope composition (δ57Fe ~0.2‰) was twice as heavy as that of the Earth (δ57Fe ~0.1‰) relative to chondrites (δ57Fe ~0‰), normalized to IRMM-14, others proposed that there is no difference between Earth and Moon. This question is of crucial importance because the first case may track the Moon-forming giant interplanetary impact, whereas the alternative situation may also result from a very high pressure metal-silicate fractionation during the Earth’s core formation, assuming that the Moon subsequently inherited the Earth Fe isotope composition. To reassess this question, we analyzed a suite of 18 mare basalts (both high- and low-Ti) by MC-ICP-MS using the nickel doping technique developed at LMTG. Combined with our previous measurements of lunar rocks, we obtained a mean δ57Fe of 0.138±0.035‰ (2SE, n=11) for low-Ti basalts, 0.269±0.026‰ (2SE, n=16) for high-Ti ones and 0.177±0.036‰ (2SE, n=6) for highland rocks. T-tests confirm that averages of low- and high-Ti basalts are significantly different at the 95% confidence level. Similarly, t-tests indicate that highland rocks are significantly different from high-Ti basalts, but not from low-Ti ones. These new data therefore confirm suggestion from previous groups that low- and high-Ti basalts contain distinct Fe isotope signatures. This shows that on the Moon, high temperature processes can significantly change the Fe isotope composition of bulk mafic rocks at the planetary scale. This cannot result from simple equilibrium magmatic fractionation or assimilation of ilmenite given its Fe isotope fractionation factor, however. We conclude that another process, yet to be identified, is

  10. Si isotope homogeneity of the solar nebula

    Pringle, Emily A.; Savage, Paul S.; Moynier, Frédéric [Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130 (United States); Jackson, Matthew G. [Department of Earth Science, University of California, Santa Barbara, CA 93109 (United States); Barrat, Jean-Alix, E-mail:, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [Université Européenne de Bretagne, Université de Brest, CNRS UMR 6538 (Domaines Océaniques), I.U.E.M., Place Nicolas Copernic, F-29280 Plouzané Cedex (France)


    The presence or absence of variations in the mass-independent abundances of Si isotopes in bulk meteorites provides important clues concerning the evolution of the early solar system. No Si isotopic anomalies have been found within the level of analytical precision of 15 ppm in {sup 29}Si/{sup 28}Si across a wide range of inner solar system materials, including terrestrial basalts, chondrites, and achondrites. A possible exception is the angrites, which may exhibit small excesses of {sup 29}Si. However, the general absence of anomalies suggests that primitive meteorites and differentiated planetesimals formed in a reservoir that was isotopically homogenous with respect to Si. Furthermore, the lack of resolvable anomalies in the calcium-aluminum-rich inclusion measured here suggests that any nucleosynthetic anomalies in Si isotopes were erased through mixing in the solar nebula prior to the formation of refractory solids. The homogeneity exhibited by Si isotopes may have implications for the distribution of Mg isotopes in the solar nebula. Based on supernova nucleosynthetic yield calculations, the expected magnitude of heavy-isotope overabundance is larger for Si than for Mg, suggesting that any potential Mg heterogeneity, if present, exists below the 15 ppm level.

  11. Fundamental functions in equilibrium thermodynamics

    Horst, H.J. ter


    In the standard presentations of the principles of Gibbsian equilibrium thermodynamics one can find several gaps in the logic. For a subject that is as widely used as equilibrium thermodynamics, it is of interest to clear up such questions of mathematical rigor. In this paper it is shown that using

  12. Rapid-Equilibrium Enzyme Kinetics

    Alberty, Robert A.


    Rapid-equilibrium rate equations for enzyme-catalyzed reactions are especially useful because if experimental data can be fit by these simpler rate equations, the Michaelis constants can be interpreted as equilibrium constants. However, for some reactions it is necessary to use the more complicated steady-state rate equations. Thermodynamics is…

  13. Non-equilibrium phase transitions

    Henkel, Malte; Lübeck, Sven


    This book describes two main classes of non-equilibrium phase-transitions: (a) static and dynamics of transitions into an absorbing state, and (b) dynamical scaling in far-from-equilibrium relaxation behaviour and ageing. The first volume begins with an introductory chapter which recalls the main concepts of phase-transitions, set for the convenience of the reader in an equilibrium context. The extension to non-equilibrium systems is made by using directed percolation as the main paradigm of absorbing phase transitions and in view of the richness of the known results an entire chapter is devoted to it, including a discussion of recent experimental results. Scaling theories and a large set of both numerical and analytical methods for the study of non-equilibrium phase transitions are thoroughly discussed. The techniques used for directed percolation are then extended to other universality classes and many important results on model parameters are provided for easy reference.

  14. A Multiperiod Equilibrium Pricing Model

    Minsuk Kwak


    Full Text Available We propose an equilibrium pricing model in a dynamic multiperiod stochastic framework with uncertain income. There are one tradable risky asset (stock/commodity, one nontradable underlying (temperature, and also a contingent claim (weather derivative written on the tradable risky asset and the nontradable underlying in the market. The price of the contingent claim is priced in equilibrium by optimal strategies of representative agent and market clearing condition. The risk preferences are of exponential type with a stochastic coefficient of risk aversion. Both subgame perfect strategy and naive strategy are considered and the corresponding equilibrium prices are derived. From the numerical result we examine how the equilibrium prices vary in response to changes in model parameters and highlight the importance of our equilibrium pricing principle.

  15. Equilibrium with arbitrary market structure

    Grodal, Birgit; Vind, Karl


    Fifty years ago Arrow [1] introduced contingent commodities and Debreu [4] observed that this reinterpretation of a commodity was enough to apply the existing general equilibrium theory to uncertainty and time. This interpretation of general equilibrium theory is the Arrow-Debreu model. The compl......Fifty years ago Arrow [1] introduced contingent commodities and Debreu [4] observed that this reinterpretation of a commodity was enough to apply the existing general equilibrium theory to uncertainty and time. This interpretation of general equilibrium theory is the Arrow-Debreu model....... The complete market predicted by this theory is clearly unrealistic, and Radner [10] formulated and proved existence of equilibrium in a multiperiod model with incomplete markets. In this paper the Radner result is extended. Radner assumed a specific structure of markets, independence of preferences...

  16. Investigation of Stable C and Cl Isotope Effects of Trichloroethene and Tetrachloroethylene during Evaporation at Different Temperatures

    Tingting Yu; Yiqun Gan; Aiguo Zhou; Kai Yu; Yunde Liu


    There are variations of reported isotope enrichment factors of chlorinated organic contaminants in evaporation processes. Trichloroethene (TCE) and tetrachloroethylene (PCE) were chosen to study carbon and chlorine isotope effects during evaporation at different temperatures. Equilibrium vapor-liquid carbon and chlorine isotope effects experiments were also conducted. In the equilibrium liquid-vapor system, the 13C was enriched but 37Cl was depleted in the vapor phase, being consistent with previous results. For evaporation average carbon isotope enrichment factor εC were +0.28‰± 0.01‰ for TCE and +0.56‰±0.09‰ for PCE at temperature from 20 to 26 ºC. Meanwhile, average chlorine isotope enrichment factor εCl were -1.33‰±0.21‰ for TCE and -1.00‰±0.00‰ for PCE. The results indicate that during evaporation the equilibrium isotope effect attenuates the magnitude of carbon isotope fractionation whereas enhances the chlorine isotope effect. Isotope fractionation during evaporation is determined by both equilibrium and kinetic factors. Chlorine isotope fractionation is influenced by the evaporation rate which is linked to temperature. When using stable isotope to investigate the behavior of chlorinated organic contaminants in groundwater with slow biodegradation rate, the isotope fractionation resulted from evaporation should be taken into consideration. Furthermore, the environment conditions such as temperature are also factors to be considered.

  17. Stable isotope deltas: Tiny, yet robust signatures in nature

    Brand, Willi A.; Coplen, Tyler B.


    Although most of them are relatively small, stable isotope deltas of naturally occurring substances are robust and enable workers in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic science, geochemistry, geology, oceanography, and paleoclimatology to study a variety of topics. Two fundamental processes explain the stable isotope deltas measured in most terrestrial systems: isotopic fractionation and isotope mixing. Isotopic fractionation is the result of equilibrium or kinetic physicochemical processes that fractionate isotopes because of small differences in physical or chemical properties of molecular species having different isotopes. It is shown that the mixing of radioactive and stable isotope end members can be modelled to provide information on many natural processes, including 14C abundances in the modern atmosphere and the stable hydrogen and oxygen isotopic compositions of the oceans during glacial and interglacial times. The calculation of mixing fractions using isotope balance equations with isotope deltas can be substantially in error when substances with high concentrations of heavy isotopes (e.g. 13C, 2H, and 18O ) are mixed. In such cases, calculations using mole fractions are preferred as they produce accurate mixing fractions. Isotope deltas are dimensionless quantities. In the International System of Units (SI), these quantities have the unit 1 and the usual list of prefixes is not applicable. To overcome traditional limitations with expressing orders of magnitude differences in isotope deltas, we propose the term urey (symbol Ur), after Harold C. Urey, for the unit 1. In such a manner, an isotope delta value expressed traditionally as−25 per mil can be written as−25 mUr (or−2.5 cUr or−0.25 dUr; the use of any SI prefix is possible). Likewise, very small isotopic differences often expressed in per meg ‘units’ are easily included (e.g. either+0.015 ‰ or+15 per meg

  18. Stable isotope deltas: tiny, yet robust signatures in nature.

    Brand, Willi A; Coplen, Tyler B


    Although most of them are relatively small, stable isotope deltas of naturally occurring substances are robust and enable workers in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic science, geochemistry, geology, oceanography, and paleoclimatology to study a variety of topics. Two fundamental processes explain the stable isotope deltas measured in most terrestrial systems: isotopic fractionation and isotope mixing. Isotopic fractionation is the result of equilibrium or kinetic physicochemical processes that fractionate isotopes because of small differences in physical or chemical properties of molecular species having different isotopes. It is shown that the mixing of radioactive and stable isotope end members can be modelled to provide information on many natural processes, including (14)C abundances in the modern atmosphere and the stable hydrogen and oxygen isotopic compositions of the oceans during glacial and interglacial times. The calculation of mixing fractions using isotope balance equations with isotope deltas can be substantially in error when substances with high concentrations of heavy isotopes (e.g. (13)C, (2)H, and (18)O ) are mixed. In such cases, calculations using mole fractions are preferred as they produce accurate mixing fractions. Isotope deltas are dimensionless quantities. In the International System of Units (SI), these quantities have the unit 1 and the usual list of prefixes is not applicable. To overcome traditional limitations with expressing orders of magnitude differences in isotope deltas, we propose the term urey (symbol Ur), after Harold C. Urey, for the unit 1. In such a manner, an isotope delta value expressed traditionally as-25 per mil can be written as-25 mUr (or-2.5 cUr or-0.25 dUr; the use of any SI prefix is possible). Likewise, very small isotopic differences often expressed in per meg 'units' are easily included (e.g. either+0.015 ‰ or+15 per meg

  19. Combinatorial effects on clumped isotopes and their significance in biogeochemistry

    Yeung, Laurence Y.


    The arrangement of isotopes within a collection of molecules records their physical and chemical histories. Clumped-isotope analysis interrogates these arrangements, i.e., how often rare isotopes are bound together, which in many cases can be explained by equilibrium and/or kinetic isotope fractionation. However, purely combinatorial effects, rooted in the statistics of pairing atoms in a closed system, are also relevant, and not well understood. Here, I show that combinatorial isotope effects are most important when two identical atoms are neighbors on the same molecule (e.g., O2, N2, and D-D clumping in CH4). When the two halves of an atom pair are either assembled with different isotopic preferences or drawn from different reservoirs, combinatorial effects cause depletions in clumped-isotope abundance that are most likely between zero and -1‰, although they could potentially be -10‰ or larger for D-D pairs. These depletions are of similar magnitude, but of opposite sign, to low-temperature equilibrium clumped-isotope effects for many small molecules. Enzymatic isotope-pairing reactions, which can have site-specific isotopic fractionation factors and atom reservoirs, should express this class of combinatorial isotope effect, although it is not limited to biological reactions. Chemical-kinetic isotope effects, which are related to a bond-forming transition state, arise independently and express second-order combinatorial effects related to the abundance of the rare isotope. Heteronuclear moeties (e.g., Csbnd O and Csbnd H), are insensitive to direct combinatorial influences, but secondary combinatorial influences are evident. In general, both combinatorial and chemical-kinetic factors are important for calculating and interpreting clumped-isotope signatures of kinetically controlled reactions. I apply this analytical framework to isotope-pairing reactions relevant to geochemical oxygen, carbon, and nitrogen cycling that may be influenced by combinatorial

  20. Equilibrium relationships for non-equilibrium chemical dependencies

    Yablonsky, Gregory S.; Constales, Denis; Marin, Guy B.


    In contrast to common opinion, it is shown that equilibrium constants determine the time-dependent behavior of particular ratios of concentrations for any system of reversible first-order reactions. Indeed, some special ratios actually coincide with the equilibrium constant at any moment in time. This is established for batch reactors, and similar relations hold for steady-state plug-flow reactors, replacing astronomic time by residence time. Such relationships can be termed time invariants o...

  1. On Generalized Vector Equilibrium Problems

    An-hua Wan; Jun-yi Fu; Wei-hua Mao


    A new generalized vector equilibrium problem involving set-valued mappings and the proper quasi-concavity of set-valued mappings in topological vector spaces are introduced; its existence theorems and the convexity of the solution sets are established.

  2. Equilibrium and Orientation in Cephalopods.

    Budelmann, Bernd-Ulrich


    Describes the structure of the equilibrium receptor system in cephalopods, comparing it to the vertebrate counterpart--the vestibular system. Relates the evolution of this complex system to the competition of cephalopods with fishes. (CS)

  3. Equilibrium Electro-osmotic Instability

    Rubinstein, Isaak


    Since its prediction fifteen years ago, electro-osmotic instability has been attributed to non-equilibrium electro-osmosis related to the extended space charge which develops at the limiting current in the course of concentration polarization at a charge-selective interface. This attribution had a double basis. Firstly, it has been recognized that equilibrium electro-osmosis cannot yield instability for a perfectly charge-selective solid. Secondly, it has been shown that non-equilibrium electro-osmosis can. First theoretical studies in which electro-osmotic instability was predicted and analyzed employed the assumption of perfect charge-selectivity for the sake of simplicity and so did the subsequent numerical studies of various time-dependent and nonlinear features of electro-osmotic instability. In this letter, we show that relaxing the assumption of perfect charge-selectivity (tantamount to fixing the electrochemical potential in the solid) allows for equilibrium electro-osmotic instability. Moreover, we s...

  4. Magnesium Isotopic Composition of Subducting Marine Sediments

    Hu, Y.; Teng, F. Z.; Plank, T. A.; Huang, K. J.


    Subducted marine sediments have recently been called upon to explain the heterogeneous Mg isotopic composition (δ26Mg, ‰) found in mantle wehrlites (-0.39 to +0.09 [1]) in the context of a homogeneous mantle (-0.25 ± 0.07 [2]). However, no systematic measurements of δ26Mg on marine sediments are currently available to provide direct support to this model. To characterize the Mg inputs to global subduction zones, we measured δ26Mg data for a total of 90 marine sediments collected from 12 drill sites outboard of the world's major subduction zones. These sediments span a 1.73‰ range in δ26Mg. The detritus-dominated sediments have δ26Mg (-0.59 to +0.53) comparable to those of weathered materials on continents (e.g. -0.52 to +0.92 [3]), while the calcareous oozes yield δ26Mg (as light as -1.20) more similar to the seawater value (-0.83 [4]). The negative correlation between δ26Mg and CaO/Al2O3 in these sediments indicates the primary control of mineralogy over the Mg isotopic distribution among different sediment types, as carbonates are enriched in light Mg isotopes (-5.10 to -0.40 [5]) whereas clay-rich weathering residues generally have heavier δ26Mg (e.g. up to +0.65 in saprolite [6]). In addition, chemical weathering and grain-size sorting drive sediments to a heavier δ26Mg, as indicated by the broad positive trends between δ26Mg with CIA (Chemical Index of Alteration [7]) and Al2O3/SiO2, respectively. Collectively, the arc systems sampled in this study represent ~30% of global arc length and the extrapolated global Mg flux of subducting marine sediments accounts for ~9% of the yearly Mg riverine input with a flux-weighted average δ26Mg at -0.26. Subduction of these heterogeneous sediments may not cause significant mantle heterogeneity on a global scale, but the highly variable Mg fluxes and δ26Mg of sediments delivered to different trenches are capable of producing local mantle variations. Volcanic rocks sourced from these mantle domains are thus

  5. Errors in the isotopic estimations of hepatic glycogen synthesis and glucose output

    Rognstad, R.


    Ignoring the reality of glucose in equilibrium glucose-6P cycling in the liver in vivo produces large potential errors in the isotopic quantitation of percentage contributions of direct and indirect pathways of glycogen synthesis and of hepatic glucose output.

  6. A Strategic-Equilibrium Based

    Gabriel J. Turbay


    Full Text Available The strategic equilibrium of an N-person cooperative game with transferable utility is a system composed of a cover collection of subsets of N and a set of extended imputations attainable through such equilibrium cover. The system describes a state of coalitional bargaining stability where every player has a bargaining alternative against any other player to support his corresponding equilibrium claim. Any coalition in the sable system may form and divide the characteristic value function of the coalition as prescribed by the equilibrium payoffs. If syndicates are allowed to form, a formed coalition may become a syndicate using the equilibrium payoffs as disagreement values in bargaining for a part of the complementary coalition incremental value to the grand coalition when formed. The emergent well known-constant sum derived game in partition function is described in terms of parameters that result from incumbent binding agreements. The strategic-equilibrium corresponding to the derived game gives an equal value claim to all players.  This surprising result is alternatively explained in terms of strategic-equilibrium based possible outcomes by a sequence of bargaining stages that when the binding agreements are in the right sequential order, von Neumann and Morgenstern (vN-M non-discriminatory solutions emerge. In these solutions a preferred branch by a sufficient number of players is identified: the weaker players syndicate against the stronger player. This condition is referred to as the stronger player paradox.  A strategic alternative available to the stronger players to overcome the anticipated not desirable results is to voluntarily lower his bargaining equilibrium claim. In doing the original strategic equilibrium is modified and vN-M discriminatory solutions may occur, but also a different stronger player may emerge that has eventually will have to lower his equilibrium claim. A sequence of such measures converges to the equal

  7. Electronic structure of MgB2

    P Modak; R S Rao; B K Godwal; S K Sikka


    Results of ab initio electronic structure calculations on the compound MgB2 using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated (F) and the experimental specific heat data. The c is found to be 24.7 K.

  8. Sr isotopic constraints on the process of glauconitization

    Clauer, Norbert; Keppens, Eddy; Stille, Peter


    Sr isotopic data of Holocene glauconitic pellets suggest a twofold glauconitization process that is strongly linked to the detrital clay minerals from surrounding mud which act as precursors until the K2O content of the glauconitic material reaches 4%. Above that, a detectable sea-water influence becomes progressively predominant. The process seems to start with a dissolution-crystallization reaction in equilibrium with the precursor, which is followed by a maturation process in isotopic equilibrium with sea-water Sr, while the K2O content increases further. This chemical evolutionary process may also occur for other types of clay minerals.

  9. Simulation of cloud microphysical effects on water isotope fractionation in a frontal system

    Chen, J. P.; Tsai, I. C.; Chen, W. Y.; Liang, M. C.


    The stable water isotopic composition changes due to fractionation during phase changes. This information is useful for understanding the water cycle, such as the water vapor source, transport and cloud microphysical processes. In conventional atmospheric models, the isotope exchange between liquid and gas phase is usually assumed to be in an equilibrium state, which is not sufficient to describe the highly kinetic phase transformation processes in clouds. In this study, a two-moment microphysical scheme incorporated into the NCAR Weather Research and Forecasting (WRF) model is modified to simulate the isotope fractionations. Experimentally determined stable water isotope thermal equilibrium data are converted into isotope saturation vapor pressure, which is then put into the two-stream Maxwellian kinetic equation to calculate the fractionation during vapor condensation/evaporation or deposition/sublimation. Isotope mass transfer between liquid- and ice-phase hydrometeors during freezing/melting are also considered explicitly. The simulation results were compared with rainwater isotope measurements and showed fairly good agreement. Sensitivity tests were also conducted to quantify the contribution of rainwater isotopic due to water vapor source and transport, condensation environment conditions, and cloud microphysical processes. The results show that isotopic water vapor source dominates the stable isotope concentration in rainwater but the cloud microphysical processes including the ice-phase processes are also quite important. The results also showed that the two-stream Maxwellian kinetic method would cause significantly more deuterium to be transported into higher altitudes during convection than the thermal equilibrium method.

  10. Isotopic Fingerprint for Phosphorus in Drinking Water Supplies.

    Gooddy, Daren C; Lapworth, Dan J; Ascott, Matthew J; Bennett, Sarah A; Heaton, Timothy H E; Surridge, Ben W J


    Phosphate dosing of drinking water supplies, coupled with leakage from distribution networks, represents a significant input of phosphorus to the environment. The oxygen isotope composition of phosphate (δ(18)OPO4), a novel stable isotope tracer for phosphorus, offers new opportunities to understand the importance of phosphorus derived from sources such as drinking water. We report the first assessment of δ(18)OPO4 within drinking water supplies. A total of 40 samples from phosphate-dosed distribution networks were analyzed from across England and Wales. In addition, samples of the source orthophosphoric acid used for dosing were also analyzed. Two distinct isotopic signatures for drinking water were identified (average = +13.2 or +19.7‰), primarily determined by δ(18)OPO4 of the source acid (average = +12.4 or +19.7‰). Dependent upon the source acid used, drinking water δ(18)OPO4 appears isotopically distinct from a number of other phosphorus sources. Isotopic offsets from the source acid ranging from -0.9 to +2.8‰ were observed. There was little evidence that equilibrium isotope fractionation dominated within the networks, with offsets from temperature-dependent equilibrium ranging from -4.8 to +4.2‰. While partial equilibrium fractionation may have occurred, kinetic effects associated with microbial uptake of phosphorus or abiotic sorption and dissolution reactions may also contribute to δ(18)OPO4 within drinking water supplies.

  11. Computing Equilibrium Free Energies Using Non-Equilibrium Molecular Dynamics

    Christoph Dellago


    Full Text Available As shown by Jarzynski, free energy differences between equilibrium states can be expressed in terms of the statistics of work carried out on a system during non-equilibrium transformations. This exact result, as well as the related Crooks fluctuation theorem, provide the basis for the computation of free energy differences from fast switching molecular dynamics simulations, in which an external parameter is changed at a finite rate, driving the system away from equilibrium. In this article, we first briefly review the Jarzynski identity and the Crooks fluctuation theorem and then survey various algorithms building on these relations. We pay particular attention to the statistical efficiency of these methods and discuss practical issues arising in their implementation and the analysis of the results.

  12. 26Al- 26Mg deficit dating ultramafic meteorites and silicate planetesimal differentiation in the early Solar System?

    Baker, Joel A.; Schiller, Martin; Bizzarro, Martin


    Meteorites with significantly sub-chondritic Al/Mg that formed in the first 2 million years of the Solar System should be characterised by deficits in the abundance of 26Mg (δ26Mg∗) due to the absence of in-growth of 26Mg from the decay of short-lived 26Al (t1/2 = 0.73 Myr). However, these 26Mg deficits will be small (δ26Mg∗ >-0.037‰) even for material that formed at the same time as the Solar System’s oldest solids - calcium-aluminium-rich inclusions - and thus measurement of these deficits is analytically challenging. Here, we report on a search for 26Mg deficits in three types of ultramafic meteorites (pallasites, ureilites and aubrites) by multiple-collector inductively coupled plasma mass spectrometry. A range of analytical tests were carried out including analysis of: (1) a range of synthetic Mg solution standards; (2) Mg gravimetrically doped with a high purity 26Mg spike; (3) Mg cuts collected sequentially from cation exchange separation columns with fractionated stable Mg isotope compositions; (4) Mg separated from samples that was bracketed by analyses of both DSM-3 and Mg separated from a natural olivine sample subjected to the same chemical processing as the samples. These tests confirm it is possible to resolve differences in δ26Mg∗ from the terrestrial materials that are ⩽0.005‰. However, if Mg yields from chemical separation are low or an inappropriate equilibrium-isotopically fractionated standard is used this will generate analytical artefacts on δ26Mg∗ when this is calculated with the kinetic/exponential mass fractionation law as is the case when correcting for instrumental mass bias during mass spectrometric analysis. Olivine from four different main group pallasites and four bulk ureilites have small deficits in the abundance of 26Mg with δ26MgDSM-3∗=-0.0120±0.0018‰ and δ26MgDSM-3∗=-0.0062±0.0023‰, respectively, relative to terrestrial olivine (δ26MgDSM-3∗=+0.0029±0.0028‰). Six aubrites have δ26MgDSM-3

  13. Stable isotope studies

    Ishida, T.


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

  14. Evaporation in equilibrium, in vacuum, and in hydrogen gas

    Nagahara, Hiroko


    Evaporation experiments were conducted for SiO2 in three different conditions: in equilibrium, in vacuum, and in hydrogen gas. Evaporation rate in vacuum is about two orders of magnitude smaller than that in equilibrium, which is consistent with previous works. The rate in hydrogen gas changes depending on hydrogen pressure. The rate at 10 exp -7 bar of hydrogen pressure is as small as that of free evaporation, but at 10 exp -5 bar of hydrogen pressure it is larger than that in equilibrium. In equilibrium and in vacuum, the evaporation rate is limited by decomposition of SiO2 on the crystal surface, but it is limited by a diffusion process for evaporation in hydrogen gas. Therefore, evaporation rate of minerals in the solar nebula can be shown neither by that in equilibrium nor by that in vacuum. The maximum temperature of the solar nebula at the midplane at 2-3 AU where chondrites are believed to have originated is calculated to be as low as 150 K, 1500 K, or in between them. The temperature is, in any case, not high enough for total evaporation of the interstellar materials. Therefore, evaporation of interstellar materials is one of the most important processes for the origin and fractionation of solid materials. The fundamental process of evaporation of minerals has been intensively studied for these several years. Those experiments were carried out either in equilibrium or in vacuum; however, evaporation in the solar nebula is in hydrogen (and much smaller amount of helium) gas. In order to investigate evaporation rate and compositional (including isotopic) fractionation during evaporation, vaporization experiments for various minerals in various conditions are conducted. At first, SiO2 was adopted for a starting material, because thermochemical data and its nature of congruent vaporization are well known. Experiments were carried out in a vacuum furnace system.

  15. Diagenetic alteration in low-Mg calcite from macrofossils

    Ullmann, Clemens Vinzenz; Korte, Christoph


    microscopy) and chemical (trace element abundances, isotopic ratios) screening techniques used to assess the alteration degree of low-Mg calcite macrofossils and summarize the findings on diagenetic trends observed for elemental and isotopic systems in such materials. For a robust evaluation...... of the preservation state of biogenic calcite, it is advisable to combine a set of complementary techniques. Absolute limiting values of element and isotope ratios for discarding diagenetically altered materials cannot be universally applied, but should rather be evaluated on a case to case basis. The evaluation can...

  16. Calcium isotopic composition of mantle xenoliths and minerals from Eastern China

    Kang, Jin-Ting; Zhu, Hong-Li; Liu, Yu-Fei; Liu, Fang; Wu, Fei; Hao, Yan-Tao; Zhi, Xia-Chen; Zhang, Zhao-Feng; Huang, Fang


    This study presents calcium isotope data for co-existing clinopyroxenes (cpx), orthopyroxenes (opx), and olivine (ol) in mantle xenoliths to investigate Ca isotopic fractionation in the upper mantle. δ44/40Ca (δ44/40Ca (‰) = (44Ca/40Ca)SAMPLE/(44Ca/40Ca)SRM915a - 1) in opx varies from 0.95 ± 0.05‰ to 1.82 ± 0.01‰ and cpx from 0.71 ± 0.06‰ to 1.03 ± 0.12‰ (2se). δ44/40Ca in ol (P-15) is 1.16 ± 0.08‰, identical to δ44/40Ca of the co-existing opx (1.12 ± 0.09‰, 2se). The Δ44/40Caopx-cpx (Δ44/40Caopx-cpx = δ44/40Caopx-δ44/40Cacpx) shows a large variation ranging from -0.01‰ to 1.11‰ and it dramatically increases with decreasing of Ca/Mg (atomic ratio) in opx. These observations may reflect the effect of opx composition on the inter-mineral equilibrium fractionation of Ca isotopes, consistent with the theoretical prediction by first-principles theory calculations (Feng et al., 2014). Furthermore, Δ44/40Caopx-cpx decreases when temperature slightly increases from 1196 to 1267 K. However, the magnitude of such inter-mineral isotopic fractionation (1.12‰) is not consistent with the value calculated by the well-known correlation between inter-mineral isotope fractionation factors and 1/T2 (Urey, 1947). Instead, it may reflect the temperature control on crystal chemistry of opx (i.e., Ca content), which further affects Δ44/40Caopx-cpx. The calculated δ44/40Ca of bulk peridotites and pyroxenites range from 0.76 ± 0.06‰ to 1.04 ± 0.12‰ (2se). Notably, δ44/40Ca of bulk peridotites are positively correlated with CaO and negatively with MgO content. Such correlations can be explained by mixing between a fertile mantle end-member and a depleted one with low δ44/40Ca, indicating that Ca isotopes could be a useful tool in studying mantle evolution.

  17. Equilibrium Temperature Profiles within Fission Product Waste Forms

    Kaminski, Michael D. [Argonne National Lab. (ANL), Argonne, IL (United States)


    We studied waste form strategies for advanced fuel cycle schemes. Several options were considered for three waste streams with the following fission products: cesium and strontium, transition metals, and lanthanides. These three waste streams may be combined or disposed separately. The decay of several isotopes will generate heat that must be accommodated by the waste form, and this heat will affect the waste loadings. To help make an informed decision on the best option, we present computational data on the equilibrium temperature of glass waste forms containing a combination of these three streams.

  18. Proliferation-resistant stable isotope separation based on optical pumping

    Kim, Cheol-Jung; Park, Hyunmin; Ko, Kwang-Hoon; Lim, Gwon; Kim, Taek-Soo; Rho, Sipyo; Cha, Yong-Ho; Han, Jamin; Jeong, Do-Young [Korea Atomic Energy Research Institute, Deajeon (Korea, Republic of). Quantum Optics Division


    Korea Atomic Energy Research Institute (KAERI) has developed the laser stable isotope separation based on optical pumping which can be applied to isotopes with small isotopic shift, provides high enrichment, is economical owing to high efficiency, and is proliferation-resistant. KAERI's laser isotope separation is based on isotope-selective optical pumping by very narrow bandwidth continuous wave laser followed by efficient infrared photo-ionization. KAERI demonstrated the pilot production of Tl-203 enriching over 97 % and separating 100 mg/hr. KAERI also demonstrated the separation of Yb-168 over 30 % and Yb- 176 over 97 % with tens of mg/hr. KAERI plans to scale up the production of Tl-203 up to 500 mg/hr and apply it to separation of Zn-67, Zn-70, Ba-130 and Ca-48 which are very important in medical industry and basic sciences. (author)

  19. Pressure-induced structural transitions in MgH2.

    Vajeeston, P; Ravindran, P; Kjekshus, A; Fjellvåg, H


    The stability of MgH2 has been studied up to 20 GPa using density-functional total-energy calculations. At ambient pressure alpha-MgH2 takes a TiO2-rutile-type structure. alpha-MgH2 is predicted to transform into gamma-MgH2 at 0.39 GPa. The calculated structural data for alpha- and gamma-MgH2 are in very good agreement with experimental values. At equilibrium the energy difference between these modifications is very small, and as a result both phases coexist in a certain volume and pressure field. Above 3.84 GPa gamma-MgH2 transforms into beta-MgH2, consistent with experimental findings. Two further transformations have been identified at still higher pressure: (i) beta- to delta-MgH2 at 6.73 GPa and (ii) delta- to epsilon-MgH2 at 10.26 GPa.

  20. Physicochemical Perturbations of Phase Equilibriums

    Dobruskin, Vladimir Kh


    The alternative approach to the displacement of gas/liquid equilibrium is developed on the basis of the Clapeyron equation. The phase transition in the system with well-established properties is taken as a reference process to search for the parameters of phase transition in the perturbed equilibrium system. The main equation, derived in the framework of both classical thermodynamics and statistical mechanics, establishes a correlation between variations of enthalpies of evaporation, \\Delta (\\Delta H), which is induced by perturbations, and the equilibrium vapor pressures. The dissolution of a solute, changing the surface shape, and the effect of the external field of adsorbents are considered as the perturbing actions on the liquid phase. The model provides the unified method for studying (1) solutions, (2) membrane separations (3) surface phenomena, and (4) effect of the adsorption field; it leads to the useful relations between \\Delta (\\Delta H), on the one hand, and the osmotic pressures, the Donnan poten...

  1. General equilibrium of an ecosystem.

    Tschirhart, J


    Ecosystems and economies are inextricably linked: ecosystem models and economic models are not linked. Consequently, using either type of model to design policies for preserving ecosystems or improving economic performance omits important information. Improved policies would follow from a model that links the systems and accounts for the mutual feedbacks by recognizing how key ecosystem variables influence key economic variables, and vice versa. Because general equilibrium economic models already are widely used for policy making, the approach used here is to develop a general equilibrium ecosystem model which captures salient biological functions and which can be integrated with extant economic models. In the ecosystem model, each organism is assumed to be a net energy maximizer that must exert energy to capture biomass from other organisms. The exerted energies are the "prices" that are paid to biomass, and each organism takes the prices as signals over which it has no control. The maximization problem yields the organism's demand for and supply of biomass to other organisms as functions of the prices. The demands and supplies for each biomass are aggregated over all organisms in each species which establishes biomass markets wherein biomass prices are determined. A short-run equilibrium is established when all organisms are maximizing and demand equals supply in every biomass market. If a species exhibits positive (negative) net energy in equilibrium, its population increases (decreases) and a new equilibrium follows. The demand and supply forces in the biomass markets drive each species toward zero stored energy and a long-run equilibrium. Population adjustments are not based on typical Lotka-Volterra differential equations in which one entire population adjusts to another entire population thereby masking organism behavior; instead, individual organism behavior is central to population adjustments. Numerical simulations use a marine food web in Alaska to

  2. Calcium isotopes in wine

    Holmden, C. E.


    The δ 44/40Ca values of bottled wine vary between -0.76% to -1.55% on the seawater scale and correlate weakly with inverse Ca concentration and Mg/Ca ratio, such that the lowest δ 44/40Ca values have the highest Ca concentrations and lowest Mg/Ca ratios. The correlation is notable in the sense that the measured wines include both whites and reds sampled from different wine growing regions of the world, and cover a wide range of quality. Trends among the data yield clues regarding the cause of the observed isotopic fractionation. White wines, and wines generally perceived to be of lower quality, have lower δ 44/40Ca values compared to red wines and wines of generally perceived higher quality. Quality was assessed qualitatively through sensory evaluation, price, and scores assigned by critics. The relationship between δ 44/40Ca and wine quality was most apparent when comparing wines of one varietal from one producer from the same growing region. In the vineyard, wine quality is related to factors such as the tonnage of the crop and the ripeness of the grapes at the time of harvesting, the thickness of the skins for reds, the age of the vines, as well as the place where the grapes were grown (terroir). Quality is also influenced by winemaking practices such as fermentation temperature, duration of skin contact, and barrel ageing. Accordingly, the relationship between δ 44/40Ca and wine quality may originate during grape ripening in the vineyard or during winemaking in the cellar. We tested the grape ripening hypothesis using Merlot grapes sampled from a vineyard in the Okanagan, British Columbia, using sugar content (degrees Brix) as an indicator of ripeness. The grapes were separated into pulp, skin, and pip fractions and were analyzed separately. Thus far, there is no clear evidence for a systematic change in δ 44/40Ca values associated with progressive ripening of grapes in the vineyard. On the day of harvesting, the δ 44/40Ca value of juice squeezed from

  3. Incentives in Supply Function Equilibrium

    Vetter, Henrik


    The author analyses delegation in homogenous duopoly under the assumption that the firm-managers compete in supply functions. In supply function equilibrium, managers’ decisions are strategic complements. This reverses earlier findings in that the author finds that owners give managers incentives...... to act in an accommodating way. As a result, optimal delegation reduces per-firm output and increases profits to above-Cournot profits. Moreover, in supply function equilibrium the mode of competition is endogenous. This means that the author avoids results that are sensitive with respect to assuming...

  4. Incentives in Supply Function Equilibrium

    Vetter, Henrik


    to act in an accommodating way. As a result, optimal delegation reduces per-firm output and increases profits to above-Cournot profits. Moreover, in supply function equilibrium the mode of competition is endogenous. This means that the author avoids results that are sensitive with respect to assuming......The author analyses delegation in homogenous duopoly under the assumption that the firm-managers compete in supply functions. In supply function equilibrium, managers’ decisions are strategic complements. This reverses earlier findings in that the author finds that owners give managers incentives...

  5. Equilibrium in a Production Economy

    Chiarolla, Maria B., E-mail: [Universita di Roma ' La Sapienza' , Dipartimento di Metodi e Modelli per l' Economia, il Territorio e la Finanza, Facolta di Economia (Italy); Haussmann, Ulrich G., E-mail: [University of British Columbia, Department of Mathematics (Canada)


    Consider a closed production-consumption economy with multiple agents and multiple resources. The resources are used to produce the consumption good. The agents derive utility from holding resources as well as consuming the good produced. They aim to maximize their utility while the manager of the production facility aims to maximize profits. With the aid of a representative agent (who has a multivariable utility function) it is shown that an Arrow-Debreu equilibrium exists. In so doing we establish technical results that will be used to solve the stochastic dynamic problem (a case with infinite dimensional commodity space so the General Equilibrium Theory does not apply) elsewhere.

  6. Magnesium isotope fractionation during differentiation of Harney Peak granite

    Ke, S.; Teng, F.; Walker, R. J.


    Although numerous studies have sought to constrain the Mg isotopic composition of mantle rocks, few studies have focused on the Mg isotopic compositions of crustal rocks, particularly evolved igneous rocks, such as granites. Granites are a major component of the upper continental crust and can be produced by partial melting of the deep continental crust. Studies of granites, therefore, can potentially provide important constraints on Mg isotopic composition variations in the continental crust as related to sources and petrogenetic processes. In order to explore the behavior of Mg isotopes during partial melting of continental crust, as well as granite differentiation, we have begun a study of a set of well-characterized samples from S-type Harney Peak granite, its potential source rocks and associated Tin Mountain pegmatite from Black Hills, South Dakota, USA. δ26Mg values of Harney Peak granites and Tin Mountain pegmatite vary significantly (from -0.69 to +0.11), well beyond the range of their potential source rocks (from -0.40 to +0.15) — early Proterozoic schists and late Archean metagranites. The large Mg isotopic variations within the granite suite likely, in part, reflect heterogeneities in source rocks, as previously shown for oxygen and Nd isotopes. A greater cause of the variations may be fractionations that occur during partial melting and subsequent differentiation of granitic melts, as suggested by the correlations between δ26Mg with SiO2, Al2O3, Na2O and Sr.

  7. Diffusion of Ca and Mg in Calcite

    Cygan, R.T.; Fisler, D.K.


    The self-diffusion of Ca and the tracer diffusion of Mg in calcite have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single crystals of calcite were coated with a thermally-sputtered oxide thin film and then annealed in a CO{sub 2} gas at one atmosphere total pressure and temperatures from 550 to 800 C. Diffusion coefficient values were derived from the depth profiles obtained by ion microprobe analysis. The resultant activation energies for Mg tracer diffusion and Ca self-diffusion are respectively: E{sub a}(Mg) = 284 {+-} 74 kJ/mol and E{sub a}(Ca) = 271 {+-} 80 kJ/mol. For the temperature ranges in these experiments, the diffusion of Mg is faster than Ca. The results are generally consistent in magnitude with divalent cation diffusion rates obtained in previous studies and provide a means of interpreting the thermal histories of carbonate minerals, the mechanism of dolomitization, and other diffusion-controlled processes. The results indicate that cation diffusion in calcite is relatively slow and cations are the rate-limiting diffusing species for the deformation of calcite and carbonate rocks. Application of the calcite-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in calcite indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.

  8. Precise measurement of chromium isotopes by MC-ICPMS

    Schiller, Martin; Van Kooten, Elishevah; Holst, Jesper Christian


    of the neutron-rich isotope 54Cr. Because nitride and oxide interferences are a major obstacle to precise and accurate 54Cr measurements by MC-ICPMS, our approach is designed to minimize these interferences. Based on repeat measurements of standards, we show that the mass-independent 53Cr and 54Cr compositions......We report novel analytical procedures allowing for the concurrent determination of the stable and mass-independent Cr isotopic composition of silicate materials by multiple collector inductively coupled mass spectrometry (MC-ICPMS). In particular, we focus on improved precision of the measurement...... by equilibrium processes during production of the synthetic standards. The stable isotope data concurrently obtained have a precision of 0.05‰ Da-1, which is comparable to earlier studies. Comparison of the measured isotopic composition of four meteorites with published data indicates that Cr isotope data...

  9. Fractionation of Boron Isotopes in Icelandic Hydrothermal Systems

    Aggarwal, J.K.; Palmer, M.R.


    Boron isotope ratios have been determined in a variety of different geothermal waters from hydrothermal systems across Iceland. Isotope ratios from the high temperature meteoric water recharged systems reflect the isotope ratio of the host rocks without any apparent fractionation. Seawater recharged geothermal systems exhibit more positive {delta}{sup 11}B values than the meteoric water recharged geothermal systems. Water/rock ratios can be assessed from boron isotope ratios in the saline hydrothermal systems. Low temperature hydrothermal systems also exhibit more positive {delta}{sup 11}B than the high temperature systems, indicating fractionation of boron due to adsorption of the lighter isotope onto secondary minerals. Fractionation of boron in carbonate deposits may indicate the level of equilibrium attained within the systems.

  10. Equilibrium and thermodynamics of azo dyes biosorption onto Spirulina platensis

    G. L. Dotto


    Full Text Available The equilibrium and thermodynamics of azo dye (tartrazine and allura red biosorption onto Spirulina platensis biomass were investigated. The equilibrium curves were obtained at 298, 308, 318 and 328 K, and four isotherm models were fitted the experimental data. Biosorption thermodynamic parameters (ΔG, ΔH and ΔS were estimated. The results showed that the biosorption was favored by a temperature decrease. For both dyes, the Sips model was the best to represent the equilibrium experimental data (R²>0.99 and ARE<5.0% and the maximum biosorption capacities were 363.2 and 468.7 mg g-1 for tartrazine and allura red, respectively, obtained at 298 K. The negative values of ΔG and ΔH showed that the biosorption of both dyes was spontaneous, favorable and exothermic. The positive values of ΔS suggested that the system disorder increases during the biosorption process.

  11. Contribution of stable isotopes to the study of pharmacokinetics of magnesium salts; Apport des isotopes stables a l'etude de la pharmacocinetique de sels de magnesium

    Benech, H


    The use of stable isotopes as labels is becoming an attractive tool for the study of magnesium behavior in humans. It has been used two stable isotopes of magnesium, {sup 25}Mg and {sup 26}Mg, to measure the absolute bioavailability of a pharmaceutical form of magnesium. (N.C.)

  12. Quantifying mixing using equilibrium reactions

    Wheat, Philip M.; Posner, Jonathan D.


    A method of quantifying equilibrium reactions in a microchannel using a fluorometric reaction of Fluo-4 and Ca2+ ions is presented. Under the proper conditions, equilibrium reactions can be used to quantify fluid mixing without the challenges associated with constituent mixing measures such as limited imaging spatial resolution and viewing angle coupled with three-dimensional structure. Quantitative measurements of CaCl and calcium-indicating fluorescent dye Fluo-4 mixing are measured in Y-shaped microchannels. Reactant and product concentration distributions are modeled using Green's function solutions and a numerical solution to the advection-diffusion equation. Equilibrium reactions provide for an unambiguous, quantitative measure of mixing when the reactant concentrations are greater than 100 times their dissociation constant and the diffusivities are equal. At lower concentrations and for dissimilar diffusivities, the area averaged fluorescence signal reaches a maximum before the species have interdiffused, suggesting that reactant concentrations and diffusivities must be carefully selected to provide unambiguous, quantitative mixing measures. Fluorometric equilibrium reactions work over a wide range of pH and background concentrations such that they can be used for a wide variety of fluid mixing measures including industrial or microscale flows.

  13. Understanding Thermal Equilibrium through Activities

    Pathare, Shirish; Huli, Saurabhee; Nachane, Madhura; Ladage, Savita; Pradhan, Hemachandra


    Thermal equilibrium is a basic concept in thermodynamics. In India, this concept is generally introduced at the first year of undergraduate education in physics and chemistry. In our earlier studies (Pathare and Pradhan 2011 "Proc. episteme-4 Int. Conf. to Review Research on Science Technology and Mathematics Education" pp 169-72) we…

  14. Financial equilibrium with career concerns

    Amil Dasgupta


    Full Text Available What are the equilibrium features of a financial market where a sizeable proportion of traders face reputational concerns? This question is central to our understanding of financial markets, which are increasingly dominated by institutional investors. We construct a model of delegated portfolio management that captures key features of the US mutual fund industry and embed it in an asset pricing framework. We thus provide a formal model of financial equilibrium with career concerned agents. Fund managers differ in their ability to understand market fundamentals, and in every period investors choose a fund. In equilibrium, the presence of career concerns induces uninformed fund managers to churn, i.e., to engage in trading even when they face a negative expected return. Churners act as noise traders and enhance the level of trading volume. The equilibrium relationship between fund return and net fund flows displays a skewed shape that is consistent with stylized facts. The robustness of our core results is probed from several angles.

  15. Equilibrium theory : A salient approach

    Schalk, S.


    Whereas the neoclassical models in General Equilibrium Theory focus on the existence of separate commodities, this thesis regards 'bundles of trade' as the unit objects of exchange. Apart from commodities and commodity bundles in the neoclassical sense, the term `bundle of trade' includes, for

  16. Experimental determination of magnesium isotope fractionation during higher plant growth

    Bolou-Bi, Emile B.; Poszwa, Anne; Leyval, Corinne; Vigier, Nathalie


    Two higher plant species (rye grass and clover) were cultivated under laboratory conditions on two substrates (solution, phlogopite) in order to constrain the corresponding Mg isotope fractionations during plant growth and Mg uptake. We show that bulk plants are systematically enriched in heavy isotopes relative to their nutrient source. The Δ 26Mg plant-source range from 0.72‰ to 0.26‰ for rye grass and from 1.05‰ to 0.41‰ for clover. Plants grown on phlogopite display Mg isotope signatures (relative to the Mg source) ˜0.3‰ lower than hydroponic plants. For a given substrate, rye grass display lower δ 26Mg (by ˜0.3‰) relative to clover. Magnesium desorbed from rye grass roots display a δ 26Mg greater than the nutrient solution. Adsorption experiments on dead and living rye grass roots also indicate a significant enrichment in heavy isotopes of the Mg adsorbed on the root surface. Our results indicate that the key processes responsible for heavy isotope enrichment in plants are located at the root level. Both species also exhibit an enrichment in light isotopes from roots to shoots (Δ 26Mg leaf-root = -0.65‰ and -0.34‰ for rye grass and clover grown on phlogopite respectively, and Δ 26Mg leaf-root of -0.06‰ and -0.22‰ for the same species grown hydroponically). This heavy isotope depletion in leaves can be explained by biological processes that affect leaves and roots differently: (1) organo-Mg complex (including chlorophyll) formation, and (2) Mg transport within plant. For both species, a positive correlation between δ 26Mg and K/Mg was observed among the various organs. This correlation is consistent with the link between K and Mg internal cycles, as well as with formation of organo-magnesium compounds associated with enrichment in heavy isotopes. Considering our results together with the published range for δ 26Mg of natural plants and rivers, we estimate that a significant change in continental vegetation would induce a change of

  17. Coupled extremely light Ca and Fe isotopes in peridotites

    Zhao, Xinmiao; Zhang, Zhaofeng; Huang, Shichun; Liu, Yufei; Li, Xin; Zhang, Hongfu


    Large metal stable isotopic variations have been observed in both extraterrestrial and terrestrial samples. For example, Ca exhibits large mass-dependent isotopic variation in terrestrial igneous rocks and mantle minerals (on the order of ∼2‰ variation in 44Ca/40Ca). A thorough assessment and understanding of such isotopic variations in peridotites provides important constraints on the evolution and compositon of the Earth's mantle. In order to better understand the Ca and Fe isotopic variations in terrestrial silicate rocks, we report Ca isotopic compositions in a set of peridotitic xenoliths from North China Craton (NCC), which have been studied for Fe isotopes. These NCC peridotites have large Ca and Fe isotopic variations, with δ44/40Ca ranging from -0.08 to 0.92 (delta value relative to SRM915a) and δ57/54Fe (delta value relative to IRMM-014) ranging from -0.61 to 0.16, and these isotopic variations are correlated with large Mg# (100 × Mg/(Mg + Fe) molar ratio) variation, ranging from 80 to 90. Importantly, NCC Fe-rich peridotites have the lowest 44Ca/40Ca and 57Fe/54Fe ratios in all terrestrial silicate rocks. In contrast, although ureilites, mantle rocks from a now broken differentiated asteroid(s), have large Mg# variation, from 70 to 92, they have very limited δ57Fe/54Fe variation (0.03-0.21, delta value relative to IRMM-014). Our model calculations show that the coupled extremely light Ca-Fe isotopic signatures in NCC Fe-rich peridotites most likely reflect kinetic isotopic fractionation during melt-peridotite reaction on a timescale of several to 104 years. In addition, our new data and compiled literature data show a possible compositional effect on the inter-mineral Ca isotopic fractionation between co-existing clinopyroxene and orthopyroxene pairs.

  18. Isotopic fractionation between seawater and the shell of

    Santos, S.; Cardoso, J.F.M.F.; Borges, V.; Luttikhuizen, P.C.; van der Veer, H.W.


    This study analyzed the isotopic profiles of four aragonitic shells of Scrobicularia plana in conjunction with measured seawater temperatures and salinities. Comparison of delta O-18(SHELL) with expected values revealed fractionation of delta O-18 in near equilibrium with the ambient environment. Gr

  19. Non-Equilibrium Properties from Equilibrium Free Energy Calculations

    Pohorille, Andrew; Wilson, Michael A.


    Calculating free energy in computer simulations is of central importance in statistical mechanics of condensed media and its applications to chemistry and biology not only because it is the most comprehensive and informative quantity that characterizes the eqUilibrium state, but also because it often provides an efficient route to access dynamic and kinetic properties of a system. Most of applications of equilibrium free energy calculations to non-equilibrium processes rely on a description in which a molecule or an ion diffuses in the potential of mean force. In general case this description is a simplification, but it might be satisfactorily accurate in many instances of practical interest. This hypothesis has been tested in the example of the electrodiffusion equation . Conductance of model ion channels has been calculated directly through counting the number of ion crossing events observed during long molecular dynamics simulations and has been compared with the conductance obtained from solving the generalized Nernst-Plank equation. It has been shown that under relatively modest conditions the agreement between these two approaches is excellent, thus demonstrating the assumptions underlying the diffusion equation are fulfilled. Under these conditions the electrodiffusion equation provides an efficient approach to calculating the full voltage-current dependence routinely measured in electrophysiological experiments.

  20. On generalized operator quasi-equilibrium problems

    Kum, Sangho; Kim, Won Kyu


    In this paper, we will introduce the generalized operator equilibrium problem and generalized operator quasi-equilibrium problem which generalize the operator equilibrium problem due to Kazmi and Raouf [K.R. Kazmi, A. Raouf, A class of operator equilibrium problems, J. Math. Anal. Appl. 308 (2005) 554-564] into multi-valued and quasi-equilibrium problems. Using a Fan-Browder type fixed point theorem in [S. Park, Foundations of the KKM theory via coincidences of composites of upper semicontinuous maps, J. Korean Math. Soc. 31 (1994) 493-519] and an existence theorem of equilibrium for 1-person game in [X.-P. Ding, W.K. Kim, K.-K. Tan, Equilibria of non-compact generalized games with L*-majorized preferences, J. Math. Anal. Appl. 164 (1992) 508-517] as basic tools, we prove new existence theorems on generalized operator equilibrium problem and generalized operator quasi-equilibrium problem which includes operator equilibrium problems.

  1. Silicon burning; 1, neutronization and the physics of quasi-equilibrium

    Hix, W R


    As the ultimate stage of stellar nucleosynthesis, and the source of the iron peak nuclei, silicon burning is important to our understanding of the evolution of massive stars and supernovae. Our reexamination of silicon burning, using results gleaned from simulation work done with a large nuclear network (299 nuclei and more than 3000 reactions) and from independent calculations of equilibrium abundance distributions, offers new insights into the quasi-equilibrium mechanism and the approach to nuclear statistical equilibrium. We find that the degree to which the matter has been neutronized is of great importance, not only to the final products but also to the rate of energy generation and the membership of the quasi-equilibrium groups. A small increase in the global neutronization results in much larger free neutron fluences, increasing the abundances of more neutron-rich nuclei. As a result, incomplete silicon burning results in neutron richness among the isotopes of the iron peak much larger than the global ...

  2. Combinatorial search for hydrogen storage alloys: Mg-Ni and Mg-Ni-Ti

    Oelmez, Rabia; Cakmak, Guelhan; Oeztuerk, Tayfur [Dept. of Metallurgical and Materials Engineering, Middle East Technical University, 06531 Ankara (Turkey)


    A combinatorial study was carried out for hydrogen storage alloys involving processes similar to those normally used in their fabrication. The study utilized a single sample of combined elemental (or compound) powders which were milled and consolidated into a bulk form and subsequently deformed to heavy strains. The mixture was then subjected to a post annealing treatment, which brings about solid state reactions between the powders, yielding equilibrium phases in the respective alloy system. A sample, comprising the equilibrium phases, was then pulverized and screened for hydrogen storage compositions. X-ray diffraction was used as a screening tool, the sample having been examined both in the as processed and the hydrogenated state. The method was successfully applied to Mg-Ni and Mg-Ni-Ti yielding the well known Mg{sub 2}Ni as the storage composition. It is concluded that a partitioning of the alloy system into regions of similar solidus temperature would be required to encompass the full spectrum of equilibrium phases. (author)

  3. Protonation Equilibrium of Linear Homopolyacids

    Požar J.


    Full Text Available The paper presents a short summary of investigations dealing with protonation equilibrium of linear homopolyacids, in particularly those of high charge density. Apart from the review of experimental results which can be found in the literature, a brief description of theoretical models used in processing the dependence of protonation constants on monomer dissociation degree and ionic strength is given (cylindrical model based on Poisson-Boltzmann equation, cylindrical Stern model, the models according to Ising, Högfeldt, Mandel and Katchalsky. The applicability of these models regarding the polyion charge density, electrolyte concentration and counterion type is discussed. The results of Monte Carlo simulations of protonation equilibrium are also briefly mentioned. In addition, frequently encountered errors connected with calibration of of glass electrode and the related unreliability of determined protonation constants are pointed out.


    Spevack, J.S.


    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.

  5. Holding Costs and Equilibrium Arbitrage

    Tuckman, Bruce; Vila, Jean-Luc


    This paper constructs a dynamic model of the equilibrium determination of relative prices when arbitragers face holding costs. The major findings are that 1) models based on riskless arbitrage arguments alone may not provide usefully tight bounds on observed prices, 2) arbitragers are often most effective in eliminating the mispricings of shorter-term assets, 3) arbitrage activity increases the mean reversion of changes in the mispricing process and reduces their conditional volatility, and 4...

  6. Monetary policy as equilibrium selection

    Gaetano Antinolfi; Costas Azariadis; Bullard, James B.


    Can monetary policy guide expectations toward desirable outcomes when equilibrium and welfare are sensitive to alternative, commonly held rational beliefs? This paper studies this question in an exchange economy with endogenous debt limits in which dynamic complementarities between dated debt limits support two Pareto-ranked steady states: a suboptimal, locally stable autarkic state and a constrained optimal, locally unstable trading state. The authors identify feedback policies that reverse ...

  7. Korshunov instantons out of equilibrium

    Titov, M.; Gutman, D. B.


    Zero-dimensional dissipative action possesses nontrivial minima known as Korshunov instantons. They have been known so far only for imaginary time representation that is limited to equilibrium systems. In this work we reconstruct and generalise Korshunov instantons using real-time Keldysh approach. This allows us to formulate the dissipative action theory for generic nonequilibrium conditions. Possible applications of the theory to transport in strongly biased quantum dots are discussed.

  8. An introduction to equilibrium thermodynamics

    Morrill, Bernard; Hartnett, James P; Hughes, William F


    An Introduction to Equilibrium Thermodynamics discusses classical thermodynamics and irreversible thermodynamics. It introduces the laws of thermodynamics and the connection between statistical concepts and observable macroscopic properties of a thermodynamic system. Chapter 1 discusses the first law of thermodynamics while Chapters 2 through 4 deal with statistical concepts. The succeeding chapters describe the link between entropy and the reversible heat process concept of entropy; the second law of thermodynamics; Legendre transformations and Jacobian algebra. Finally, Chapter 10 provides a

  9. Mesoscopic non-equilibrium thermodynamics

    Rubi, Jose' Miguel


    Full Text Available Basic concepts like energy, heat, and temperature have acquired a precise meaning after the development of thermodynamics. Thermodynamics provides the basis for understanding how heat and work are related and with the general rules that the macroscopic properties of systems at equilibrium follow. Outside equilibrium and away from macroscopic regimes most of those rules cannot be applied directly. In this paper we present recent developments that extend the applicability of thermodynamic concepts deep into mesoscopic and irreversible regimes. We show how the probabilistic interpretation of thermodynamics together with probability conservation laws can be used to obtain kinetic equations describing the evolution of the relevant degrees of freedom. This approach provides a systematic method to obtain the stochastic dynamics of a system directly from the knowledge of its equilibrium properties. A wide variety of situations can be studied in this way, including many that were thought to be out of reach of thermodynamic theories, such as non-linear transport in the presence of potential barriers, activated processes, slow relaxation phenomena, and basic processes in biomolecules, like translocation and stretching.

  10. Local equilibrium in bird flocks

    Mora, Thierry; Walczak, Aleksandra M.; Del Castello, Lorenzo; Ginelli, Francesco; Melillo, Stefania; Parisi, Leonardo; Viale, Massimiliano; Cavagna, Andrea; Giardina, Irene


    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.

  11. Statistical clumped isotope signatures

    Röckmann, T.; Popa, M. E.; Krol, M. C.; Hofmann, M. E. G.


    High precision measurements of molecules containing more than one heavy isotope may provide novel constraints on element cycles in nature. These so-called clumped isotope signatures are reported relative to the random (stochastic) distribution of heavy isotopes over all available isotopocules of a m

  12. Lithium Isotopic Fractionation in Subduction Zones: Clues From Clays

    Williams, L. B.; Hervig, R. L.


    Lithium isotope ratios show such large variations in nature (>30 per mil), that many areas of geosciences are exploring the usefulness of this system in explaining the evolution of particular rocks. Here we show how the lithium isotope ratios change during the transformation of smectite clay minerals to illite during burial metamorphism. Such a transition may be a common feature in the shallow regions of subduction zones and may ultimately affect the Li isotope compositions of fluids contributing to arc magmatism. Lithium is a ubiquitous trace element in natural formation waters that, like B, shows large isotopic fractionation especially during interactions with clay minerals. Lithium is adsorbed in the interlayer region of expandable clay minerals but is easily exchanged. Lithium is also incorporated into the octahedral sites. The substitutions of Li in two crystallographic sites of clay minerals may complicate interpretations of bulk Li-isotope ratios. We suggest that the magnitude of the isotopic fractionation of Li between fluid and clay is different in the interlayer sites of clay minerals than in the octahedral sites of clay minerals. Examination of Li contents and isotope variations in experimental reactions of smectite to illite (300C, 100MPa) shows changes with structural re-arrangement of the clay layers. The Li-isotope trend declines (from ~+6 to -13 per mil, expressed as ratios of 7/6) throughout R1-ordering of the mixed-layered illite smectite (I/S). However, the equilibrium end products of the reaction have R3-ordering and show a heavier isotope ratio (~0 per mil). This observation is very similar to the trends we observed for B-isotopes, where the interlayer B initially overprinted the tetrahedral-layer B isotope composition, but as the interlayer sites were collapsed during illitization, the equilibrium isotope composition was approached. The significant Li and B isotopic changes that occur during ordering of I/S coincides with the temperatures

  13. Magnesium and chromium isotope evidence for initial melting by radioactive decay of 26Al and late stage impact-melting of the ureilite parent body

    van Kooten, Elishevah M. M. E.; Schiller, Martin; Bizzarro, Martin


    Polymict ureilites are meteoritic breccias that provide insights into the differentiation history of the ureilite parent body. We have sampled a total of 24 clasts from the polymict ureilite Dar al Gani 319, representing a variety of lithologies such as mantle residues, cumulates and crustal fragments that are genetically related to monomict ureilites. In addition, we sampled four non-indigenous dark clasts and two chondrule-containing clasts from the same meteorite. We report on the petrology and the bulk mass-dependent and mass-independent magnesium and chromium isotope systematics of these clasts. The DaG 319 polymict ureilite consists predominantly of clasts related to Main Group ureilite residues (MG clasts) with varying Mg#s (0.74-0.91), as well as a significant fraction of olivine-orthopyroxene clasts related to Hughes Type ureilites (HT clasts) with consistently high Mg#s (∼0.89). In addition, DaG 319 contains less abundant feldspathic clasts that are thought to represent melts derived from the ureilite mantle. A significant mass-dependent Mg-isotope fractionation totaling Δμ25 Mg = ∼450 ppm was found between isotopically light feldspathic clasts (μ25 Mg = -305 ± 25 to 15 ± 12 ppm), MG clasts (μ25 Mg = -23 ± 51 ppm) and HT clasts (μ25 Mg = 157 ± 21 ppm). We suggest that this isotopic offset is the result of equilibrium isotope fractionation during melting in the presence of an isotopically light magnesite component. We propose Mg-carbonates to be stable in the upper ureilite mantle, and pure carbon phases such as graphite to be stable at higher pressures. This is consistent with HT clasts lacking carbon-related phases, whereas MG clasts contain abundant carbon. The timing of differentiation events for the ureilitic clasts are constrained by high precision 53Mn-53Cr systematics and 26Al-26Mg model ages. We show that a dichotomy of ages exist between the differentiation of main group ureilite residues and HT cumulates rapidly after CAI formation

  14. Geochronological and isotopic records of crustal storage and assimilation in the Wolverine Creek-Conant Creek system, Heise eruptive centre, Snake River Plain

    Szymanowski, D.; Ellis, B. S.; Wotzlaw, J. F.; Buret, Y.; von Quadt, A.; Peytcheva, I.; Bindeman, I. N.; Bachmann, O.


    Understanding the processes of differentiation of the Yellowstone-Snake River Plain (YSRP) rhyolites is typically impeded by the apparent lack of erupted intermediate compositions as well as the complex nature of their shallow interaction with the surrounding crust responsible for their typically low O isotopic ratios. A pair of normal-δ18O rhyolitic eruptions from the Heise eruptive centre in eastern Idaho, the Wolverine Creek Tuff and the Conant Creek Tuff, represent unique magmatic products of the Yellowstone hotspot preserving abundant vestiges of the intermediate differentiation steps leading to rhyolite generation. We address both shallow and deep processes of magma generation and storage in the two units by combining high-precision ID-TIMS U-Pb zircon geochronology, trace element, O and Hf isotopic studies of zircon, and Sr isotopic analyses of individual high-Mg# pyroxenes inherited from lower- to mid-crustal differentiation stages. The zircon geochronology confirms the derivation of both tuffs from the same rhyolitic magma reservoir erupted at 5.5941 ± 0.0097 Ma, preceded by at least 92 ± 14 ky of continuous or intermittent zircon saturation approximating the length of pre-eruptive magma accumulation in the upper crust. Some low-Mg# pyroxenes enclosing zircons predate the eruption by at least 45 ± 27 ky, illustrating the co-crystallisation of major and accessory phases in the near-liquidus rhyolitic melts of the YSRP over a significant period of time. Coeval zircon crystals are isotopically heterogeneous (two populations at ɛHf -5 and -13), requiring the assembly of isotopically distinct melt pockets directly prior to, or during, the eruption. The primitive Mg# 60-90 pyroxenes are out of isotopic equilibrium with the host rhyolitic melt (87Sr/86Sri = 0.70889), covering a range of 87Sr/86Sri = 0.70705-0.70883 corresponding to ratios typical of the most radiogenic YSRP basalts to the least radiogenic YSRP rhyolites. Together with the low ɛHf in zircon

  15. Morphodynamic equilibrium of alluvial estuaries

    Tambroni, Nicoletta; Bolla Pittaluga, Michele; Canestrelli, Alberto; Lanzoni, Stefano; Seminara, Giovanni


    The evolution of the longitudinal bed profile of an estuary, with given plan-form configuration, subject to given tidal forcing at the mouth and prescribed values of water and sediment supply from the river is investigated numerically. Our main goal is to ascertain whether, starting from some initial condition, the bed evolution tends to reach a unique equilibrium configuration asymptotically in time. Also, we investigate the morphological response of an alluvial estuary to changes in the tidal range and hydrologic forcing (flow and sediment supply). Finally, the solution helps characterizing the transition between the fluvially dominated region and the tidally dominated region of the estuary. All these issues play an important role also in interpreting how the facies changes along the estuary, thus helping to make correct paleo-environmental and sequence-stratigraphic interpretations of sedimentary successions (Dalrymple and Choi, 2007). Results show that the model is able to describe a wide class of settings ranging from tidally dominated estuaries to fluvially dominated estuaries. In the latter case, the solution is found to compare satisfactory with the analytical asymptotic solution recently derived by Seminara et al. (2012), under the hypothesis of fairly 'small' tidal oscillations. Simulations indicate that the system always moves toward an equilibrium configuration in which the net sediment flux in a tidal cycle is constant throughout the estuary and equal to the constant sediment flux discharged from the river. For constant width, the bed equilibrium profile of the estuarine channel is characterized by two distinct regions: a steeper reach seaward, dominated by the tide, and a less steep upstream reach, dominated by the river and characterized by the undisturbed bed slope. Although the latter reach, at equilibrium, is not directly affected by the tidal wave, however starting from an initial uniform stream with the constant 'fluvial' slope, the final

  16. On static equilibrium and balance puzzler

    Dey, Samrat; Saikia, Dipankar; Kalita, Deepjyoti; Debbarma, Anamika; Wahab, Shaheen Akhtar; Sarma, Saurabh


    The principles of static equilibrium are of special interest to civil engineers. For a rigid body to be in static equilibrium the condition is that net force and net torque acting on the body should be zero. That clearly signifies that if equal weights are placed on either sides of a balance, the balance should be in equilibrium, even if its beam is not horizontal (we have considered the beam to be straight and have no thickness, an ideal case). Thus, although the weights are equal, they will appear different which is puzzling. This also shows that the concept of equilibrium is confusing, especially neutral equilibrium is confused to be stable equilibrium. The study not only throws more light on the concept of static equilibrium, but also clarifies that a structure need not be firm and steady even if it is in static equilibrium.

  17. Equilibrium thermodynamics - Callen’s postulational approach

    Jongschaap, Robert J.J.; Öttinger, Hans Christian


    In order to provide the background for nonequilibrium thermodynamics, we outline the fundamentals of equilibrium thermodynamics. Equilibrium thermodynamics must not only be obtained as a special case of any acceptable nonequilibrium generalization but, through its shining example, it also elucidates

  18. Generation of Radixenon Isotopes

    McIntyre, Justin I.; Bowyer, Ted W.; Hayes, James C.; Heimbigner, Tom R.; Morris, Scott J.; Panisko, Mark E.; Pitts, W. K.; Pratt, Sharon L.; Reeder, Paul L.; Thomas, Charles W.


    Pacific Northwest National Laboratory has developed an automated system for separating Xe from air and can detect the following radioxenon isotopes, 131mXe, 133mXe, 133Xe, and 135Xe. This report details the techniques used to generate the various radioxenon isotopes that are used for the calibration of the detector as well as other isotopes that have the potential to interfere with the fission produced radioxenon isotopes. Fission production is covered first using highly enriched uranium followed by a description and results from an experiment to produce radioxenon isotopes from neutron activation of ambient xenon.

  19. Isotopes in heterogeneous catalysis

    Hargreaves, Justin SJ


    The purpose of this book is to review the current, state-of-the-art application of isotopic methods to the field of heterogeneous catalysis. Isotopic studies are arguably the ultimate technique in in situ methods for heterogeneous catalysis. In this review volume, chapters have been contributed by experts in the field and the coverage includes both the application of specific isotopes - Deuterium, Tritium, Carbon-14, Sulfur-35 and Oxygen-18 - as well as isotopic techniques - determination of surface mobility, steady state transient isotope kinetic analysis, and positron emission profiling.

  20. Natural gas at thermodynamic equilibrium. Implications for the origin of natural gas.

    Mango, Frank D; Jarvie, Daniel; Herriman, Eleanor


    It is broadly accepted that so-called 'thermal' gas is the product of thermal cracking, 'primary' thermal gas from kerogen cracking, and 'secondary' thermal gas from oil cracking. Since thermal cracking of hydrocarbons does not generate products at equilibrium and thermal stress should not bring them to equilibrium over geologic time, we would not expect methane, ethane, and propane to be at equilibrium in subsurface deposits. Here we report compelling evidence of natural gas at thermodynamic equilibrium. Molecular compositions are constrained to equilibrium, [Formula in text] and isotopic compositions are also under equilibrium constraints: [Formula in text].The functions [(CH4)*(C3H8)] and [(C2H6)2] exhibit a strong nonlinear correlation (R2 = 0.84) in which the quotient Q progresses to K as wet gas progresses to dry gas. There are striking similarities between natural gas and catalytic gas generated from marine shales. A Devonian/Mississippian New Albany shale generates gas with Q converging on K over time as wet gas progresses to dry gas at 200 degrees C. The position that thermal cracking is the primary source of natural gas is no longer tenable. It is challenged by its inability to explain the composition of natural gas, natural gases at thermodynamic equilibrium, and by the existence of a catalytic path to gas that better explains gas compositions.

  1. Natural gas at thermodynamic equilibrium Implications for the origin of natural gas

    Jarvie Daniel


    Full Text Available Abstract It is broadly accepted that so-called 'thermal' gas is the product of thermal cracking, 'primary' thermal gas from kerogen cracking, and 'secondary' thermal gas from oil cracking. Since thermal cracking of hydrocarbons does not generate products at equilibrium and thermal stress should not bring them to equilibrium over geologic time, we would not expect methane, ethane, and propane to be at equilibrium in subsurface deposits. Here we report compelling evidence of natural gas at thermodynamic equilibrium. Molecular compositions are constrained to equilibrium, and isotopic compositions are also under equilibrium constraints: The functions [(CH4*(C3H8] and [(C2H62] exhibit a strong nonlinear correlation (R2 = 0.84 in which the quotient Q progresses to K as wet gas progresses to dry gas. There are striking similarities between natural gas and catalytic gas generated from marine shales. A Devonian/Mississippian New Albany shale generates gas with Q converging on K over time as wet gas progresses to dry gas at 200°C. The position that thermal cracking is the primary source of natural gas is no longer tenable. It is challenged by its inability to explain the composition of natural gas, natural gases at thermodynamic equilibrium, and by the existence of a catalytic path to gas that better explains gas compositions.

  2. The geometry of finite equilibrium sets

    Balasko, Yves; Tvede, Mich


    We investigate the geometry of finite datasets defined by equilibrium prices, income distributions, and total resources. We show that the equilibrium condition imposes no restrictions if total resources are collinear, a property that is robust to small perturbations. We also show that the set...... of equilibrium datasets is pathconnected when the equilibrium condition does impose restrictions on datasets, as for example when total resources are widely noncollinear....

  3. Thermodynamic re-optimization of the Cu-Mg-Sn system at the Cu-Mg side

    Miettinen J.


    Full Text Available Thermodynamic description of the ternary Cu-Mg-Sn system at its Cu-Mg side is presented. The thermodynamic parameters of the binary sub-systems, Cu-Mg, Cu-Sn and Mg-Sn, are taken from the earlier SGTE-based assessments (modifying the Mg-Sn description slightly and those of the Cu-Mg-Si system are optimized in this study using the experimental thermodynamic and phase equilibrium data. The solution phases of the systems are described with the substitutional solution model and the intermetallic Cu2Mg compound (Laves C15, treated as simple semi-stoichiometric phases of the (A,BpCq type, is described with the twosublattice model. The present ternary description is valid for tin contents up to 45 wt% (xSn≈0.30.

  4. Oxygen isotope systematics in the aragonite-CO2-H2O-NaCl system up to 0.7 mol/kg ionic strength at 25 °C

    Kim, Sang-Tae; Gebbinck, Christa Klein; Mucci, Alfonso; Coplen, Tyler B.


    To investigate the oxygen isotope systematics in the aragonite-CO2-H2O-NaCl system, witherite (BaCO3) was precipitated quasi-instantaneously and quantitatively from Na-Cl-Ba-CO2 solutions of seawater-like ionic strength (I = 0.7 mol/kg) at two pH values (~7.9 and ~10.6) at 25 °C. The oxygen isotope composition of the witherite and the dissolved inorganic carbon speciation in the starting solution were used to estimate the oxygen isotope fractionations between HCO3¯ and H2O as well as between CO3 2 and H2O. Given the analytical error on the oxygen isotope composition of the witherite and uncertainties of the parent solution pH and speciation, oxygen isotope fractionation between NaHCO3° and HCO3¯, as well as between NaCO3¯ and CO3 2, is negligible under the experimental conditions investigated. The influence of dissolved NaCl concentration on the oxygen isotope fractionation in the aragonite-CO2-H2O-NaCl system also was investigated at 25 °C. Aragonite was precipitated from Na-Cl-Ca-Mg-(B)-CO2 solutions of seawater-like ionic strength using passive CO2 degassing or constant addition methods. Based upon our new experimental observations and published experimental data from lower ionic strength solutions by Kim et al. (2007b), the equilibrium aragonite-water oxygen isotope fractionation factor is independent of the ionic strength of the parent solution up to 0.7 mol/kg. Hence, our study also suggests that the aragonite precipitation mechanism is not affected by the presence of sodium and chloride ions in the parent solution over the range of concentrations investigated.

  5. Open problems in non-equilibrium physics

    Kusnezov, D.


    The report contains viewgraphs on the following: approaches to non-equilibrium statistical mechanics; classical and quantum processes in chaotic environments; classical fields in non-equilibrium situations: real time dynamics at finite temperature; and phase transitions in non-equilibrium conditions.

  6. The concept of equilibrium in organization theory

    Gazendam, Henk W.M.


    Many organization theories consist of an interpretation frame and an idea about the ideal equilibrium state. This article explains how the equilibrium concept is used in four organization theories: the theories of Fayol, Mintzberg, Morgan, and Volberda. Equilibrium can be defined as balance, fit or

  7. The concept of equilibrium in organization theory

    Gazendam, Henk W.M.


    Many organization theories consist of an interpretation frame and an idea about the ideal equilibrium state. This article explains how the equilibrium concept is used in four organization theories: the theories of Fayol, Mintzberg, Morgan, and Volberda. Equilibrium can be defined as balance, fit or

  8. Equilibrium figures of dwarf planets

    Rambaux, Nicolas; Chambat, Frederic; Castillo-Rogez, Julie; Baguet, Daniel


    Dwarf planets including transneptunian objects (TNO) and Ceres are >500 km large and display a spheroidal shape. These protoplanets are left over from the formation of the solar System about 4.6 billion years ago and their study could improve our knowledge of the early solar system. They could be formed in-situ or migrated to their current positions as a consequence of large-scale solar system dynamical evolution. Quantifying their internal composition would bring constraints on their accretion environment and migration history. That information may be inferred from studying their global shapes from stellar occultations or thermal infrared imaging. Here we model the equilibrium shapes of isolated dwarf planets under the assumption of hydrostatic equilibrium that forms the basis for interpreting shape data in terms of interior structure. Deviations from hydrostaticity can shed light on the thermal and geophysical history of the bodies. The dwarf planets are generally fast rotators spinning in few hours, so their shape modeling requires numerically integration with Clairaut's equations of rotational equilibrium expanded up to third order in a small parameter m, the geodetic parameter, to reach an accuracy better than a few kilometers depending on the spin velocity and mean density. We also show that the difference between a 500-km radius homogeneous model described by a MacLaurin ellipsoid and a stratified model assuming silicate and ice layers can reach several kilometers in the long and short axes, which could be measurable. This type of modeling will be instrumental in assessing hydrostaticity and thus detecting large non-hydrostatic contributions in the observed shapes.

  9. Risk premia in general equilibrium

    Posch, Olaf

    This paper shows that non-linearities can generate time-varying and asymmetric risk premia over the business cycle. These (empirical) key features become relevant and asset market implications improve substantially when we allow for non-normalities in the form of rare disasters. We employ explicit...... solutions of dynamic stochastic general equilibrium models, including a novel solution with endogenous labor supply, to obtain closed-form expressions for the risk premium in production economies. We find that the curvature of the policy functions affects the risk premium through controlling the individual......'s effective risk aversion....

  10. Seasonal dynamics of stable isotopes and element ratios in authigenic calcites during their precipitation and dissolution, Sacrower See (northeastern Germany



    Full Text Available The seasonal evolution of chemical and physical water properties as well as particle fluxes was monitored in Sacrower See (northeastern Germany during two consecutive years (Oct 2003 - Oct 2005. Additonally, we measured δ18O and δ13C as well as Sr:Ca and Mg:Ca ratios of authigenic calcites that were collected in sequencing sediment traps in order to disentangle environmental and climatic factors controlling these parameters. In particular, our aim was to find out if element ratios and the isotopic composition of calcites reflect changes in water and air temperatures. Lake water is highly enriched in 18O (-1.3 to -2.5‰ VSMOW with an evaporative increase of 0.6‰ during summer. Values are 5-6‰ more positive than groundwater values and 4-5‰ more positive than long-term weighted annual means of precipitation. During spring and summer, high amounts of dissolved phosphate cause eutrophic conditions and calcite precipitation in isotopic disequilibrium. Measured values are depleted in 18O by 2 to 10‰ compared to calculated equilibrium values. Resuspension and partial dissolution of calcite in the water column contribute to this isotopic divergence in summer and autumn as δ18Oca and δ13C values increased in the hypolimnion during this time. Mg:Ca and Sr:Ca ratios are altered by dissolution as well. In the hypolimnion these ratios were higher than in the epilimnion. Another reason for the huge deviation between measured and theoretical δ18Oca values during summer is the occurrence of large amounts of Phacotus lenticularis in the carbonate fraction. High amounts of Phacotus lead to more negative δ18Oca and more positive δ13C values. Several characteristics of δ18Oca and δ13C are also reflected by Mg:Ca and Sr:Ca ratios and isotopic composition of oxygen and carbon were influenced by the onset and stability of stratification. Especially the earlier onset of stratification in 2005 caused higher sediment fluxes and more positive carbon and

  11. Silicon isotope evidence against an enstatite chondrite Earth.

    Fitoussi, Caroline; Bourdon, Bernard


    The compositions of Earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems. Although this suggests that Earth largely accreted from enstatite chondrites, definitive proof of this model has been lacking. By comparing the silicon (Si) isotope signatures of several extraterrestrial materials with terrestrial samples, we show that they cannot be explained by core-formation scenarios involving a bulk Earth of enstatite chondrite composition. Si isotope similarities between the bulk silicate Earth and the Moon preclude the existence of a hidden reservoir in the lower mantle, a necessary condition of the enstatite chondrite model, and require an equilibrium process after the Moon-forming impact. A three-end-member chondritic mixing model for Earth reconciles the Si isotope similarities between enstatite chondrites and Earth.

  12. Lithium isotope effect accompanying electrochemical intercalation of lithium into graphite

    Yanase, S; Oi, T


    Lithium has been electrochemically intercalated from a 1:2 (v/v) mixed solution of ethylene carbonate (EC) and methylethyl carbonate (MEC) containing 1 M LiClO sub 4 into graphite, and the lithium isotope fractionation accompanying the intercalation was observed. The lighter isotope was preferentially fractionated into graphite. The single-stage lithium isotope separation factor ranged from 1.007 to 1.025 at 25 C and depended little on the mole ratio of lithium to carbon of the lithium-graphite intercalation compounds (Li-GIC) formed. The separation factor increased with the relative content of lithium. This dependence seems consistent with the existence of an equilibrium isotope effect between the solvated lithium ion in the EC/MEC electrolyte solution and the lithium in graphite, and with the formation of a solid electrolyte interfaces on graphite at the early stage of intercalation. (orig.)

  13. Isotope separation of the Yb-168 stable isotope for low energy gamma ray sources

    Park, Hyun Min; Kwon, Duck Hee; Cha, Yong Ho; Lee, Ki Tae; Nam, Sung Mo; Yoo, Jaek Won; Han, Jae Min; Rhee, Yong Joo [Lab. of Quantum Optics, Korea Atomic Energy Research Institute, Taejeon (Korea, Republic of)


    We developed laser isotope separation technology of stable isotope of low melting point metals. Yb-168 can be effectively used in non-destructive testing (NDT) after it is transformed to Yb-168 by neutron irradiation in a nuclear reactor. For this application of Yb-168, the isotope purity of it should be enhanced to more than 15% from the natural abundance of 0.135%. Our isotope separation system consist of laser system, Yb vapor generating system, and photoionized particle extraction system. For the system, we developed a diode-pumped slid-state laser of high-repetition rate and 3-color dye lasers. Yb vapor was generated by heating solid Yb sample resistively. The photo-ion produced by resonance ionization were extracted by a devised extractor. We produced enriched Yb metal more than 20 mg with the abundance of 25.8% of Yb-168 in the Yb (NO{sub 3}){sub 3}.

  14. Thermochemistry of MgCr2O4, MgAl2O4, MgFe2O4 spinels in SO2-O2-SO3 atmosphere

    Anna Gerle


    Full Text Available The present paper investigates high-temperature sulphate corrosion of basic refractory ceramics containing magnesium spinels (MgAl2O4, MgFe2O4, MgCr2O4 and their solid solutions widely used in metallurgy, chemical, ceramic and glass industry. This group of refractories are exposed to a number of destructive factors during a working campaign. One of such factors is gas corrosion caused by sulphur oxides. However, gas sulphate corrosion of basic refractory materials containing magnesium spinels, which has a great practical meaning for the corrosion resistance of the material main components, is not sufficiently examined. This work presents a thermodynamic analysis of (MgCr2O4, MgAl2O4, MgFe2O4−SO2−O2−SO3 system aimed to calculate: i the standard free enthalpy of chemical reactions, ii the equilibrium composition of the gas mixture initially containing SO2 and O2 and iii sulphates equilibrium dissociation pressure and equilibrium partial pressure for the reaction of SO3 with the spinels to predict the temperature range of corrosion products’ stability. A thermochemical calculation provides information about equilibrium state in the analysed system. In real conditions the state of equilibrium does not have to be achieved. For this reason, the results of calculations were compared with experimental data. The experiment results were consistent with the theoretical predictions.

  15. Are the Concepts of Dynamic Equilibrium and the Thermodynamic Criteria for Spontaneity, Nonspontaneity, and Equilibrium Compatible?

    Silverberg, Lee J.; Raff, Lionel M.


    Thermodynamic spontaneity-equilibrium criteria require that in a single-reaction system, reactions in either the forward or reverse direction at equilibrium be nonspontaneous. Conversely, the concept of dynamic equilibrium holds that forward and reverse reactions both occur at equal rates at equilibrium to the extent allowed by kinetic…

  16. Evidence for beta -delayed neutron emission from /sup 31/Mg and /sup 32/Mg

    Zaidins, C S; De Saint-Simon, M; Détraz, C; Epherre-Rey-Campagnolle, Marcelle; Guillemaud, D; Klapisch, Robert; Langevin, M; Naulin, F; Thibault, C; Touchard, F


    Investigates the time spectrum of beta -delayed neutron emission from /sup 30-34/Na and their descendants using beta -neutron coincidence detection. The authors have been able to assign an upper limit of 0,4% to the probability of beta -delayed neutron emission, p/sub n/, from the /sup 30/Na daugher isotope /sup 30/Mg. In fitting the time spectra of beta -delayed neutrons from /sup 31/Na and /sup 32/Na, we find a definitive component from subsequent daughter decay as well. This provides evidence for beta -delayed neutron emission from /sup 31/Mg and /sup 32/Mg with P/sub n/ values of the order of 2% for each. (7 refs).

  17. Pre-equilibrium plasma dynamics

    Heinz, U.


    Approaches towards understanding and describing the pre-equilibrium stage of quark-gluon plasma formation in heavy-ion collisions are reviewed. Focus is on a kinetic theory approach to non-equilibrium dynamics, its extension to include the dynamics of color degrees of freedom when applied to the quark-gluon plasma, its quantum field theoretical foundations, and its relationship to both the particle formation stage at the very beginning of the nuclear collision and the hydrodynamic stage at late collision times. The usefulness of this approach to obtain the transport coefficients in the quark-gluon plasma and to derive the collective mode spectrum and damping rates in this phase are discussed. Comments are made on the general difficulty to find appropriated initial conditions to get the kinetic theory started, and a specific model is given that demonstrates that, once given such initial conditions, the system can be followed all the way through into the hydrodynamical regime. 39 refs., 7 figs. (LEW)

  18. A Simple Procedure for the Synthesis of [32P]Phosphoenol Pyruvate via the Pyruvate Kinase Exchange Reaction at Equilibrium

    Roossien, F.F.; Brink, J.; Robillard, G.T.


    A one step procedure is presented for the preparation of [32P]phosphoenolpyruvate from [γ-32P]ATP using pyruvate kinase. The reaction is carried out at chemical equilibrium and involves only an exchange of isotope between ATP and phosphoenolpyruvate. The initial phosphoenolpyruvate/ATP ratio in the

  19. Characterization of calcium isotopes in natural and synthetic barite

    Griffith, E.M.; Schauble, E.A.; Bullen, T.D.; Paytan, A.


    The mineral barite (BaSO4) accommodates calcium in its crystal lattice, providing an archive of Ca-isotopes in the highly stable sulfate mineral. Holocene marine (pelagic) barite samples from the major ocean basins are isotopically indistinguishable from each other (??44/40Ca = -2.01 ?? 0.15???) but are different from hydrothermal and cold seep barite samples (??44/40Ca = -4.13 to -2.72???). Laboratory precipitated (synthetic) barite samples are more depleted in the heavy Ca-isotopes than pelagic marine barite and span a range of Ca-isotope compositions, ??44/40Ca = -3.42 to -2.40???. Temperature, saturation state, a Ba2 + / a SO42 -, and aCa2+/aBa2+ each influence the fractionation of Ca-isotopes in synthetic barite; however, the fractionation in marine barite samples is not strongly related to any measured environmental parameter. First-principles lattice dynamical modeling predicts that at equilibrium Ca-substituted barite will have much lower 44Ca/40Ca than calcite, by -9??? at 0 ??C and -8??? at 25 ??C. Based on this model, none of the measured barite samples appear to be in isotopic equilibrium with their parent solutions, although as predicted they do record lower ??44/40Ca values than seawater and calcite. Kinetic fractionation processes therefore most likely control the extent of isotopic fractionation exhibited in barite. Potential fractionation mechanisms include factors influencing Ca2+ substitution for Ba2+ in barite (e.g. ionic strength and trace element concentration of the solution, competing complexation reactions, precipitation or growth rate, temperature, pressure, and saturation state) as well as nucleation and crystal growth rates. These factors should be considered when investigating controls on isotopic fractionation of Ca2+ and other elements in inorganic and biogenic minerals. ?? 2008 Elsevier Ltd.

  20. Thermodynamic modeling of the Ba - Mg binary system

    Ren, Xin; Li, Changrong; Du, Zhenmin; Guo, Cuiping; Chen, Sicheng [Univ. of Science and Technology, Beijing (China). School of Materials Science and Engineering


    On the basis of the thermochemical and phase equilibrium experimental data, the phase diagram of the Ba - Mg binary system has been assessed by means of the calculation of phase diagrams technique. The liquid phase is of unlimited solubility and modeled as a solution phase using the Redlich-Kister equation. The intermetallic compounds, Mg{sub 17}Ba{sub 2}, Mg{sub 23}Ba{sub 6} and Mg{sub 2}Ba, with no solubility ranges are treated as strict stoichiometric compounds with the formula Mg{sub m} Ba{sub n}. Two terminal phases, BccBa and HcpMg, are kept as solution phases, since the solubilities of the two phases are of considerable importance. After optimization, a set of self-consistent thermodynamic parameters has been obtained. The calculated values agree well with the available experimental data.

  1. Thermodynamic assessment of the Bi-Mg binary system

    Chunju NIU; Changrong LI; Zhenmin DU; Cuiping GUO; Yongjuan JING


    The Bi-Mg binary system had been assessed by adopting the ionic melt and the modified quasi-chemical models to describe the liquid phase with short range ordering behavior.In general considerations of the development of the thermodynamic database of the multi-component Mg-based alloys and the consistency of the thermodynamic models of the related phases,the Gibbs energy descriptions of all the phases in the Bi-Mg binary system were reasonably re-modeled and critically re-assessed in the present work.Especially for the liquid phase,the associate model was used with the constituent species Bi,Mg and Bi2Mg3.The Mg-rich terminal phase hcp_A3 was modeled as a substitutional solution following Redlich-Kister equation and the Bi-rich terminal phase Rhombohedral_A7 was treated as a pure Bi substance since the extremely small solubility of Mg in Bi. The low and high temperature nonstoichiometric compounds β-Bi2Mg3 and α-Bi2Mg3 were described by the sublattice models (Bi,Va)2Mg3 and (Bi)1 (Bi,Va)aMg6 respectively based on their structure features.A set of self-consistent thermodynamic parameters of the Bi-Mg system was obtained and the experimental thermodynamic and phase equilibrium data were well reproduced by the optimized thermodynamic data.

  2. Time-series analysis of ion and isotope geochemistry of selected springs of the Nevada Test Site, Nye County, Nevada

    Lyles, B.F.; Edkins, J.; Jacobson, R.L.; Hess, J.W.


    The temporal variations of ion and isotope geochemistry were observed at six selected springs on the Nevada Test Site, Nye County, Nevada and included: Cane, Whiterock, Captain Jack, Topopah, Tippipah, and Oak Springs. The sites were monitored from 1980 to 1982 and the following parameters were measured: temperature, pH, electrical conductance, discharge, cations (Ca{sup 2+}, Mg{sup 2+}. Na{sup +}, K{sup +}), anions Cl{sup {minus}}, SO{sub 4}{sup 2{minus}}. HCO{sub 3}{sup {minus}}, silica, stable isotopes ({delta}{sup 18}O, {delta}D, {delta}{sup 13}C), and radioactive isotopes ({sup 3}H, {sup 14}C). A more detailed study was continued from 1982 to 1988 at Cane and Whiterock Springs. Field microloggers were installed at these sites in 1985 to measure the high frequency response of temperature, electrical conductance, and discharge to local precipitation. Stage fluctuations near the discharge point dissolve minerals/salts as groundwater inundates the mineralized zone immediately above the equilibrium water table. This phenomena was most noticeable at Whiterock Spring and lagged the discharge response by several hours. Stable isotope analysis of precipitation and groundwater suggests a 1.5 to 2 month travel time for meteoric water to migrate from the recharge area to the discharge point. Groundwater age determinations suggest a mean age of approximately 30 years at Whiterock Spring and possibly older at Cane Spring. However, the short travel time and geochemical integrity of recharge pulses suggest that the waters are poorly mixed along the flow paths. 25 refs., 25 figs., 24 tabs.

  3. MgCo2-D2 and MgCoNi-D2 systems synthesized at high pressures and interaction mechanism during the HDDR processing

    Chubin Wan


    MgCo2 is a new example of the hydrogen storage alloy, in which a successful HDDR processing results in the reversible formation of the initial intermetallic at much lower temperatures than in the equilibrium phase diagram of the Mg-Co system.

  4. Equilibrium calculations of firework mixtures

    Hobbs, M.L. [Sandia National Labs., Albuquerque, NM (United States); Tanaka, Katsumi; Iida, Mitsuaki; Matsunaga, Takehiro [National Inst. of Materials and Chemical Research, Tsukuba, Ibaraki (Japan)


    Thermochemical equilibrium calculations have been used to calculate detonation conditions for typical firework components including three report charges, two display charges, and black powder which is used as a fuse or launch charge. Calculations were performed with a modified version of the TIGER code which allows calculations with 900 gaseous and 600 condensed product species at high pressure. The detonation calculations presented in this paper are thought to be the first report on the theoretical study of firework detonation. Measured velocities for two report charges are available and compare favorably to predicted detonation velocities. However, the measured velocities may not be true detonation velocities. Fast deflagration rather than an ideal detonation occurs when reactants contain significant amounts of slow reacting constituents such as aluminum or titanium. Despite such uncertainties in reacting pyrotechnics, the detonation calculations do show the complex nature of condensed phase formation at elevated pressures and give an upper bound for measured velocities.

  5. Equilibrium Analysis in Cake Cutting

    Branzei, Simina; Miltersen, Peter Bro


    Cake cutting is a fundamental model in fair division; it represents the problem of fairly allocating a heterogeneous divisible good among agents with different preferences. The central criteria of fairness are proportionality and envy-freeness, and many of the existing protocols are designed...... to guarantee proportional or envy-free allocations, when the participating agents follow the protocol. However, typically, all agents following the protocol is not guaranteed to result in a Nash equilibrium. In this paper, we initiate the study of equilibria of classical cake cutting protocols. We consider one...... of the simplest and most elegant continuous algorithms -- the Dubins-Spanier procedure, which guarantees a proportional allocation of the cake -- and study its equilibria when the agents use simple threshold strategies. We show that given a cake cutting instance with strictly positive value density functions...

  6. Neoclassical equilibrium in gyrokinetic simulations

    Garbet, X.; Dif-Pradalier, G.; Nguyen, C.; Sarazin, Y.; Grandgirard, V.; Ghendrih, Ph.


    This paper presents a set of model collision operators, which reproduce the neoclassical equilibrium and comply with the constraints of a full-f global gyrokinetic code. The assessment of these operators is based on an entropy variational principle, which allows one to perform a fast calculation of the neoclassical diffusivity and poloidal velocity. It is shown that the force balance equation is recovered at lowest order in the expansion parameter, the normalized gyroradius, hence allowing one to calculate correctly the radial electric field. Also, the conventional neoclassical transport and the poloidal velocity are reproduced in the plateau and banana regimes. The advantages and drawbacks of the various model operators are discussed in view of the requirements for neoclassical and turbulent transport.

  7. Local non-equilibrium thermodynamics.

    Jinwoo, Lee; Tanaka, Hajime


    Local Shannon entropy lies at the heart of modern thermodynamics, with much discussion of trajectory-dependent entropy production. When taken at both boundaries of a process in phase space, it reproduces the second law of thermodynamics over a finite time interval for small scale systems. However, given that entropy is an ensemble property, it has never been clear how one can assign such a quantity locally. Given such a fundamental omission in our knowledge, we construct a new ensemble composed of trajectories reaching an individual microstate, and show that locally defined entropy, information, and free energy are properties of the ensemble, or trajectory-independent true thermodynamic potentials. We find that the Boltzmann-Gibbs distribution and Landauer's principle can be generalized naturally as properties of the ensemble, and that trajectory-free state functions of the ensemble govern the exact mechanism of non-equilibrium relaxation.

  8. Ringed accretion disks: equilibrium configurations

    Pugliese, D


    We investigate a model of ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the General Relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can be then determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We pr...

  9. Isotopic studies of Yucca Mountain soil fluids and carbonate pedogenesis

    McConnaughey, T.A.; Whelan, J.F.; Wickland, K.P.; Moscati, R.J.


    Secondary carbonates occurring within the soils, faults, and subsurface fractures of Yucca Mountain contain some of the best available records of paleoclimate and palehydrology for the potential radioactive waste repository site. This article discusses conceptual and analytical advances being made with regard to the interpretation of stable isotope data from pedogenic carbonates, specifically related to the {sup 13}C content of soil CO{sub 2}, CaCO{sub 3}, precipitation mechanisms, and isotopic fractionations between parent fluids and precipitating carbonates. The {sup 13}C content of soil carbon dioxide from Yucca Mountain and vicinity shows most of the usual patterns expected in such contexts: Decreasing {sup 13}C content with depth decreasing {sup 13}C with altitude and reduced {sup 13}C during spring. These patterns exist within the domain of a noisy data set; soil and vegetational heterogeneities, weather, and other factors apparently contribute to isotopic variability in the system. Several soil calcification mechanisms appear to be important, involving characteristic physical and chemical environments and isotopic fractionations. When CO{sub 2} loss from thin soil solutions is an important driving factor, carbonates may contain excess heavy isotopes, compared to equilibrium precipitation with soil fluids. When root calcification serves as a proton generator for plant absorption of soil nutrients, heavy isotope deficiencies are likely. Successive cycles of dissolution and reprecipitation mix and redistribute pedogenic carbonates, and tend to isotopically homogenize and equilibrate pedogenic carbonates with soil fluids.

  10. Probing isotope effects in chemical reactions using single ions

    Staanum, Peter F; Wester, Roland; Drewsen, Michael


    Isotope effects in reactions between Mg+ in the 3p 2P3/2 excited state and molecular hydrogen at thermal energies are studied through single reaction events. From only ~250 reactions with HD, the branching ratio between formation of MgD+ and MgH+ is found to be larger than 5. From additional 65 reactions with H2 and D2 we find that the overall decay probability of the intermediate MgH2+, MgHD+ or MgD2+ complexes is the same. Our study shows that few single ion reactions can provide quantitative information on ion-neutral reactions. Hence, the method is well-suited for reaction studies involving rare species, e.g., rare isotopes or short-lived unstable elements.

  11. Chemical and Isotopic Composition of Waters and Dissolved Gases in Some Thermal Springs of Sicily and Adjacent Volcanic Islands, Italy

    Grassa, Fausto; Capasso, Giorgio; Favara, Rocco; Inguaggiato, Salvatore


    Hydrochemical (major and some minor constituents), stable isotope ([InlineMediaObject not available: see fulltext.] and [InlineMediaObject not available: see fulltext.], δ13CTDIC total dissolved inorganic carbon) and dissolved gas composition have been determined on 33 thermal discharges located throughout Sicily (Italy) and its adjacent islands. On the basis of major ion contents, four main water types have been distinguished: (1) a Na-Cl type; (2) a Ca-Mg > Na-SO4-Cl type; (3) a Ca-Mg-HCO3 type and (4) a Na-HCO3 type water. Most waters are meteoric in origin or resulting from mixing between meteoric water and heavy-isotope end members. In some samples, δ 18O values reflect the effects of equilibrium processes between thermal waters and rocks (positive 18O-shift) or thermal waters and CO2 (negative 18O-shift). Dissolved gas composition indicates the occurrence of gas/water interaction processes in thermal aquifers. N2/O2 ratios higher than air-saturated water (ASW), suggest the presence of geochemical processes responsible for dissolved oxygen consumption. High CO2 contents (more than 3000 cc/litre STP) dissolved in the thermal waters indicate the presence of an external source of carbon dioxide-rich gas. TDIC content and δ 13C TDIC show very large ranges from 4.6 to 145.3 mmol/Kg and from 10.0‰ and 2.8‰, respectively. Calculated values indicate the significant contribution from a deep source of carbon dioxide inorganic in origin. Interaction with Mediterranean magmatic CO2 characterized by heavier carbon isotope ratios ([InlineMediaObject not available: see fulltext.] value from -3 to 0‰ vs V-PDB (CAPASSO et al., 1997, GIAMMANCO et al., 1998; INGUAGGIATO et al., 2000) with respect to MORB value and/or input of CO2-derived from thermal decomposition of marine carbonates have been inferred.

  12. Controls on the stable isotope compositions of travertine from hyperalkaline springs in Oman: Insights from clumped isotope measurements

    Falk, E. S.; Guo, W.; Paukert, A. N.; Matter, J. M.; Mervine, E. M.; Kelemen, P. B.


    Carbonate formation at hyperalkaline springs is typical of serpentinization in peridotite massifs worldwide. These travertines have long been known to exhibit large variations in their carbon and oxygen isotope compositions, extending from apparent equilibrium values to highly depleted values. However, the exact causes of these variations are not well constrained. We analyzed a suite of well-characterized fresh carbonate precipitates and travertines associated with hyperalkaline springs in the peridotite section of the Samail ophiolite, Sultanate of Oman, and found their clumped isotope compositions vary systematically with formation environments. Based on these findings, we identified four main processes controlling the stable isotope compositions of these carbonates. These include hydroxylation of CO2, partial isotope equilibration of dissolved inorganic carbon, mixing between isotopically distinct carbonate end-members, and post-depositional recrystallization. Most notably, in fresh crystalline films on the surface of hyperalkaline springs and in some fresh carbonate precipitates from the bottom of hyperalkaline pools, we observed large enrichments in Δ47 (up to ∼0.2‰ above expected equilibrium values) which accompany depletions in δ18O and δ13C, yielding about 0.01‰ increase in Δ47 and 1.1‰ decrease in δ13C for every 1‰ decrease in δ18O, relative to expected equilibrium values. This disequilibrium trend, also reflected in preserved travertines ranging in age from modern to ∼40,000 years old, is interpreted to arise mainly from the isotope effects associated with the hydroxylation of CO2 in high-pH fluids and agrees with our first-order theoretical estimation. In addition, in some fresh carbonate precipitates from the bottom of hyperalkaline pools and in subsamples of one preserved travertine terrace, we observed additional enrichments in Δ47 at intermediate δ13C and δ18O, consistent with mixing between isotopically distinct carbonate end

  13. A combined radio- and stable-isotopic study of a California coastal aquifer system

    Swarzenski, Peter W.; Baskaran, Mark; Rosenbauer, Robert J.; Edwards, Brian D.; Land, Michael


    Stable and radioactive tracers were utilized in concert to characterize geochemical processes in a complex coastal groundwater system and to provide constraints on the kinetics of rock/water interactions. Groundwater samples from wells within the Dominguez Gap region of Los Angeles County, California were analyzed for a suite of major cations (Na+, K+, Mg2+, Ca2+) and anions (Cl−, SO42−), silica, alkalinity, select trace elements (Ba, B, Sr), dissolved oxygen, stable isotopes of hydrogen (δD), oxygen (δ18O), dissolved inorganic carbon (δ13CDIC), and radioactive isotopes (3H, 222Rn and 223,224,226,228Ra). In the study area, groundwater may consist of a complex mixture of native groundwater, intruded seawater, non-native injected water, and oil-field brine water. In some wells, Cl− concentrations attained seawater-like values and in conjunction with isotopically heavier δ18O values, these tracers provide information on the extent of seawater intrusion and/or mixing with oil-field brines. Groundwater 3H above 1 tritium unit (TU) was observed only in a few select wells close to the Dominguez Gap area and most other well groundwater was aged pre-1952. Based on an initial 14C value for the study site of 90 percent modern carbon (pmc), groundwater age estimates likely extend beyond 20 kyr before present and confirm deep circulation of some native groundwater through multiple aquifers. Enriched values of groundwater δ13CDIC in the absence of SO42− imply enhanced anaerobic microbial methanogenesis. While secular equilibrium was observed for 234U/238U (activity ratios ~1) in host matrices, strong isotopic fractionation in these groundwater samples can be used to obtain information of adsorption/desorption kinetics. Calculated Ra residence times are short, and the associated desorption rate constant is about three orders of magnitude slower than that of the adsorption rate constant. Combined stable- and radio-isotopic results provide unique insights into aquifer

  14. Elemental and Isotopic Incorporation into the Aragonitic Shells of Arctica Islandica: Insights from Temperature Controlled Experiments

    Wanamaker, A. D.; Gillikin, D. P.


    The long-lived ocean quahog, Arctica islandica, is a fairly well developed and tested marine proxy archive, however, the utility of elemental ratios in A. islandica shell material as environmental proxies remains questionable. To further evaluate the influence of seawater temperature on elemental and isotopic incorporation during biomineralization, A. islandica shells were grown at constant temperatures under two regimes during a 16-week period from March 27 to July 21, 2011. Seawater from the Darling Marine Center in Walpole, Maine was pumped into temperature and flow controlled tanks that were exposed to ambient food and salinity conditions. A total of 20 individual juvenile clams with an average shell height of 36 mm were stained with calcein (a commonly used biomarker) and cultured at 10.3 ± 0.3 °C for six weeks. After this, shell heights were measured and the clams were again stained with calcein and cultured at 15.0 ± 0.4 °C for an additional 9.5 weeks. The average shell growth during the first phase of the experiment was 2.4 mm with a linear extension rate of 0.40 mm/week. The average shell growth during the second phase of the experiment was 3.2 mm with an extension rate of 0.34 mm/week. Average salinity values were 30.2 ± 0.7 and 30.7 ±0.7 in the first and second phases of the experiment, respectively. Oxygen isotopes from the cultured seawater were collected throughout the experiment and provide the basis for establishing if shells grew in oxygen isotopic equilibrium. Elemental ratios (primarily Ba/Ca, Mg/Ca, Sr/Ca) in the aragonitic shells were determined via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), while stable oxygen and carbon isotope ratios were measured using continuous flow isotope ratio mass spectrometry. Continuous sampling within and across the temperature conditions (from 10 °C to 15 °C) coupled with the calcein markings provides the ability to place each sample into a precise temporal framework. The

  15. A Combined Radio- and Stable-Isotopic Study of a California Coastal Aquifer System

    Michael Land


    Full Text Available Stable and radioactive tracers were utilized in concert to characterize geochemical processes in a complex coastal groundwater system and to provide constraints on the kinetics of rock/water interactions. Groundwater samples from wells within the Dominguez Gap region of Los Angeles County, California were analyzed for a suite of major cations (Na+, K+, Mg2+, Ca2+ and anions (Cl−, SO42−, silica, alkalinity, select trace elements (Ba, B, Sr, dissolved oxygen, stable isotopes of hydrogen (δD, oxygen (δ18O, dissolved inorganic carbon (δ13CDIC, and radioactive isotopes (3H, 222Rn and 223,224,226,228Ra. In the study area, groundwater may consist of a complex mixture of native groundwater, intruded seawater, non-native injected water, and oil-field brine water. In some wells, Cl− concentrations attained seawater-like values and in conjunction with isotopically heavier δ18O values, these tracers provide information on the extent of seawater intrusion and/or mixing with oil-field brines. Groundwater 3H above 1 tritium unit (TU was observed only in a few select wells close to the Dominguez Gap area and most other well groundwater was aged pre-1952. Based on an initial 14C value for the study site of 90 percent modern carbon (pmc, groundwater age estimates likely extend beyond 20 kyr before present and confirm deep circulation of some native groundwater through multiple aquifers. Enriched values of groundwater δ13CDIC in the absence of SO42− imply enhanced anaerobic microbial methanogenesis. While secular equilibrium was observed for 234U/238U (activity ratios ~1 in host matrices, strong isotopic fractionation in these groundwater samples can be used to obtain information of adsorption/desorption kinetics. Calculated Ra residence times are short, and the associated desorption rate constant is about three orders of magnitude slower than that of the adsorption rate constant. Combined stable- and radio-isotopic results provide unique insights

  16. Mineral composition control on inter-mineral iron isotopic fractionation in granitoids

    Wu, Hongjie; He, Yongsheng; Bao, Leier; Zhu, Chuanwei; Li, Shuguang


    This study reports elemental and iron isotopic compositions of feldspar and its coexisting minerals from four Dabie I-type granitoids to evaluate the factors that control inter-mineral Fe isotopic fractionation in granitoids. The order of heavy iron isotope enrichment is feldspar > pyrite > magnetite > biotite ≈ hornblende. Feldspar has heavier iron isotopic compositions than its co-existing magnetite (Δ56Feplagioclase-magnetite = +0.376‰ to +1.084‰, Δ56Fealkali-feldspar-magnetite = +0.516‰ to +0.846‰), which can be attributed to its high Fe3+/Fetot ratio and low coordination number (tetrahedrally-coordinated) of Fe3+. Δ56Femagnetite-biotite of coexisting magnetite and biotite ranges from 0.090‰ to 0.246‰. Based on homogeneous major and iron isotopic compositions of mineral replicates, the inter-mineral fractionation in this study should reflect equilibrium fractionation. The large variations of inter-mineral fractionation among feldspar, magnetite and biotite cannot be simply explained by temperature variation, but strongly depend on mineral compositions. The Δ56Feplagioclase-magnetite and Δ56Fealkali-feldspar-magnetite are positively correlated with albite mode in plagioclase and orthoclase mode in alkali-feldspar, respectively. This could be explained by different Fe-O bond strength in feldspar due to different Fe3+/∑Fe or different crystal parameters. The Δ56Femagnetite-biotite increases with decreasing Fe3+/∑Febiotite and increasing mole (Na + K)/Mgbiotite, indicating a decrease of β factor in low Fe3+/∑Fe and high (Na + K)/Mg biotite. High-silica leucosomes from Dabie migmatites with a feldspar accumulation petrogenesis have higher δ56Fe values (δ56Fe = 0.42-0.567‰) than leucosome that represents pristine partial melt (δ56Fe = 0.117 ± 0.016‰), indicating that accumulation of feldspar could account for high δ56Fe values of these rocks. High δ56Fe values are also predicted for other igneous rocks that are mainly composed of

  17. An Approach to Analysis of Stable Isotopes in Microsamples

    韩友科; 安娜


    A new aproach to isotopic analysis of carbon,oxygen,sulfur and nitrogen in microsamples has been established.Samples were conventionally prepared by mixing microsamples to be analyzed with reference samples with known δ values in a proper proportion,and then analyzed for their stable isotopes as those at ordinary levels.According to the equilibrium relationships before and after mixing,the δvalues of unknown microsamples were calculated.The δ15N of the atmosphere was estimated at zero by this approach,which is concordant with the internationally recommended value.

  18. Stable isotopes (δ 18O and δ 13C), trace and minor element compositions of Recent scleractinians and Last Glacial bivalves at the Santa Maria di Leuca deep-water coral province, Ionian Sea

    Correa, Matthias López; Montagna, Paolo; Vendrell-Simón, Begoña; McCulloch, Malcolm; Taviani, Marco


    The aragonitic skeletons of bathyal cold-water corals have a high potential as geochemical in situ archives for paleoceanography. Oxygen isotopes and stable carbon isotopes (δ 18O and δ 13C) have been analyzed, as well as trace and minor element compositions (e.g. Mg/Ca, Sr/Ca, U/Ca, B/Ca and P/Ca) in Lophelia pertusa, one of the most important frame-builders at the Santa Maria di Leuca (SML) deep-water coral hotspot in the Central Mediterranean. The Apulian Bank is swept by strong currents of the Adriatic Deep Water Outflow. The temperature of 13.9 °C is the highest temperature recorded for L. pertusa and provides an important end-member of environmental conditions for geochemical analyses on living Atlantic and Mediterranean cold-water corals. Temperature and salinity (38.77 PSU) are stable throughout the year, and thus virtually no changes should be observed in the stable oxygen isotope signal—if the coral precipitates its skeleton in equilibrium with seawater. We measured various marine properties, such as the seawater oxygen isotope composition (δ 18O sw), stable carbon isotope composition (δ 13C DIC) of dissolved inorganic carbon (DIC), and dissolved inorganic nutrient concentrations (PO 4, NO 3, NO 2, NH 3 and SiO 2). Bottom water at the coral sites shows a mean oxygen isotope composition of 1.47‰ δ 18O sw-VSMOW, and δ 13C DIC showed a mean of 1.1‰ VPDB. A section of a living L. pertusa with a thick theca calcification was probed with a Merchantek MicroMill at a high spatial sampling resolution with 10 samples per 1 mm. This reduced the signal-smoothing inherent to conventional sampling. The δ 18O ag of coral aragonite ranges between -2.0‰ and +2.8‰ VPDB and the δ 13C ag ranges between -7.77‰ and +1.47‰ VPDB. The Gaussian data distribution for both parameters, including heavy equilibrium values, suggests the completeness of the captured isotopic variability. The strict linear correlation of δ 13C and δ 18O displays a strong 'kinetic

  19. Discovery of the Cobalt Isotopes

    Szymanski, T.; Thoennessen, M.


    Twenty-six cobalt isotopes have so far been observed; the discovery of these isotopes is discussed. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

  20. Discovery of the Arsenic Isotopes

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


    Twenty-nine arsenic isotopes have so far been observed; the discovery of these isotopes is discussed. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

  1. Intracellular Cadmium Isotope Fractionation

    Horner, T. J.; Lee, R. B.; Henderson, G. M.; Rickaby, R. E.


    Recent stable isotope studies into the biological utilization of transition metals (e.g. Cu, Fe, Zn, Cd) suggest several stepwise cellular processes can fractionate isotopes in both culture and nature. However, the determination of fractionation factors is often unsatisfactory, as significant variability can exist - even between different organisms with the same cellular functions. Thus, it has not been possible to adequately understand the source and mechanisms of metal isotopic fractionation. In order to address this problem, we investigated the biological fractionation of Cd isotopes within genetically-modified bacteria (E. coli). There is currently only one known biological use or requirement of Cd, a Cd/Zn carbonic anhydrase (CdCA, from the marine diatom T. weissfloggii), which we introduce into the E. coli genome. We have also developed a cleaning procedure that allows for the treating of bacteria so as to study the isotopic composition of different cellular components. We find that whole cells always exhibit a preference for uptake of the lighter isotopes of Cd. Notably, whole cells appear to have a similar Cd isotopic composition regardless of the expression of CdCA within the E. coli. However, isotopic fractionation can occur within the genetically modified E. coli during Cd use, such that Cd bound in CdCA can display a distinct isotopic composition compared to the cell as a whole. Thus, the externally observed fractionation is independent of the internal uses of Cd, with the largest Cd isotope fractionation occurring during cross-membrane transport. A general implication of these experiments is that trace metal isotopic fractionation most likely reflects metal transport into biological cells (either actively or passively), rather than relating to expression of specific physiological function and genetic expression of different metalloenzymes.

  2. Physical Equilibrium Evaluation in Parkinson Disease

    Schmidt, Paula da Silva


    Full Text Available Introduction: The Parkinson disease can be among the multiple causes of alterations in the physical equilibrium. Accordingly, this study has the objective to evaluate Parkinson patients' physical equilibrium. Method: Potential study in which 12 Parkinson individuals were evaluated by way of tests of static and dynamic equilibrium, dynamic posturography and vectoelectronystagmograph. To compare the dynamic posturography results a group of gauged control was used. Results: Alterations in Romberg-Barré, Unterberger and Walk tests were found. The vestibular exam revealed 06 normal cases, 04 central vestibular syndrome and 02 cases of peripheral vestibular syndrome. In the dynamic posturography, an equilibrium alteration has been verified, when compared to the control group in all Sensorial Organization Tests, in average and in the utilization of vestibular system. Conclusion: Parkinson patients present a physical equilibrium alteration. The dynamic posturography was more sensitive to detect the equilibrium alterations than vectoelectronystagmograph.

  3. A Constructive Generalization of Nash Equilibrium

    Huang, Xiaofei


    In a society of multiple individuals, if everybody is only interested in maximizing his own payoff, will there exist any equilibrium for the society? John Nash proved more than 50 years ago that an equilibrium always exists such that nobody would benefit from unilaterally changing his strategy. Nash Equilibrium is a central concept in game theory, which offers the mathematical foundation for social science and economy. However, the original definition is declarative without including a solution to find them. It has been found later that it is computationally difficult to find a Nash equilibrium. Furthermore, a Nash equilibrium may be unstable, sensitive to the smallest variation of payoff functions. Making the situation worse, a society with selfish individuals can have an enormous number of equilibria, making it extremely hard to find out the global optimal one. This paper offers a constructive generalization of Nash equilibrium to cover the case when the selfishness of individuals are reduced to lower level...

  4. Equilibrium Solubility of CO2 in Alkanolamines

    Waseem Arshad, Muhammad; Fosbøl, Philip Loldrup; von Solms, Nicolas


    Equilibrium solubility of CO2 were measured in aqueous solutions of Monoethanolamine (MEA) and N,N-diethylethanolamine(DEEA). Equilibrium cells are generally used for these measurements. In this study, the equilibrium data were measured from the calorimetry. For this purpose a reaction calorimeter...... (model CPA 122 from ChemiSens AB, Sweden) was used. The advantage of this method is being the measurement of both heats of absorption and equilibrium solubility data of CO2 at the same time. The measurements were performed for 30 mass % MEA and 5M DEEA solutions as a function of CO2 loading at three...... different temperatures 40, 80 and 120 ºC. The measured 30 mass % MEA and 5M DEEA data were compared with the literature data obtained from different equilibrium cells which validated the use of calorimeters for equilibrium solubility measurements....

  5. Mathematical models and equilibrium in irreversible microeconomics

    Anatoly M. Tsirlin


    Full Text Available A set of equilibrium states in a system consisting of economic agents, economic reservoirs, and firms is considered. Methods of irreversible microeconomics are used. We show that direct sale/purchase leads to an equilibrium state which depends upon the coefficients of supply/demand functions. To reach the unique equilibrium state it is necessary to add either monetary exchange or an intermediate firm.

  6. Characteristics of equilibrium reaction of zolazepam.

    Hong, W H; Szulczewski, D H


    The equilibrium reaction of zolazepam, a pyrazolodiazepinone, was studied and analyzed using the approach used previously for other pyrazolodiazepinone derivatives. The intrinsic ring closure equilibrium constant for this reaction was approximately 100 times larger than that observed for pyrazolodiazepinones studied previously. This study illustrates that the diazepinone ring can dominate in equilibrium mixtures formed at pH values far below the pKa of the corresponding form.




    We present a new hybrid Monte Carlo method for 1-D equilibrium diffusion problems in which the radiation field coexists with matter in local thermodynamic equilibrium. This method, the Equilibrium Discrete Diffusion Monte Carlo (EqDDMC) method, combines Monte Carlo particles with spatially discrete diffusion solutions. We verify the EqDDMC method with computational results from three slab problems. The EqDDMC method represents an incremental step toward applying this hybrid methodology to non-equilibrium diffusion, where it could be simultaneously coupled to Monte Carlo transport.

  8. Kinetic Isotopic Fractionation During Diffusion of Ionic Speciesin Water

    Richter, Frank M.; Mendybaev, Ruslan A.; Christensen, John; Hutcheon, Ian D.; Williams, Ross W.; Sturchio, Neil C.; Beloso Jr.,Abelardo D.


    Experiments specifically designed to measure the ratio of the diffusivities of ions dissolved in water were used to determine D{sub Li}/D{sub K}, D{sub 7{sub Li}}/D{sub 6{sub Li}}, D{sub 25{sub Mg}}/D{sub 24{sub Mg}}, D{sub 26{sub Mg}}/D{sub 25{sub Mg}}, and D{sub 37{sub Cl}}/D{sub 35{sub Cl}}. The measured ratio of the diffusion coefficients for Li and K in water (D{sub Li}/D{sub K} = 0.6) is in good agreement with published data, providing evidence that the experimental design being used resolves the relative mobility of ions with adequate precision to also be used for determining the fractionation of isotopes by diffusion in water. In the case of Li we found measurable isotopic fractionation associated with the diffusion of dissolved LiCl (D{sub 7{sub Li}}/D{sub 6{sub Li}} = 0.99772 {+-} 0.00026). This difference in the diffusion coefficient of {sup 7}Li compared to {sup 6}Li is significantly less than reported in an earlier study, a difference we attribute to the fact that in the earlier study Li diffused through a membrane separating the water reservoirs. Our experiments involving Mg diffusing in water found no measurable isotopic fractionation (D{sub 25{sub Mg}}/D{sub 24{sub Mg}} = 1.00003 {+-} 0.00006). Cl isotopes were fractionated during diffusion in water (D{sub 37{sub Cl}}/D{sub 35{sub Cl}} = 0.99857 {+-} 0.00080) whether or not the co-diffuser (Li or Mg) was isotopically fractionated. The isotopic fractionation associated with the diffusion of ions in water is much smaller than values we found previously for the isotopic fractionation of Li and Ca isotopes by diffusion in molten silicate liquids. A major distinction between water and silicate liquids is that water, being a polar liquid, surrounds dissolved ions with hydration shells, which very likely play an important but still poorly understood role in reducing isotopic fractionation associated with diffusion.

  9. Equilibrium structure and rotational constant of HCC/sup +/

    Montgomery, J.A. Jr.; Dykstra, C.E.


    Using ab initio electronic structure techniques, the equilibrium structure of HCC/sup +/ has been predicted and the resulting equilibrium rotational constant (B/sub e/) is 44.3 GHz. Through comparison of the experimentally determined J=1..-->..0 transition frequency with a similarly calculated B/sub e/ for HNN/sup +/, the J=1..-->..0 transition in HCC/sup +/ is predicted to occur at 88.2 GHz. Isotopic substitution gives a rotational constant (B/sub e/) for DCC/sup +/ of 36.3 GHz. An estimate of the hyperfine interaction leads to the prediction that the rotational spectrum of DCC/sup +/ will consist of three lines around 72.6 GHz with separations of 0.09 and 0.06 MHz. While error limits from theoretical determinations are not clear cut, the use of a large basis set and careful treatment of electron correlation suggest that an experimentally determined transition frequency for HCC/sup +/ is most likely to be within +- 0.3 GHz of 88.2 GHz.

  10. Chromium isotope variations

    D'Arcy, Joan Mary

    is incorporated into carbonates. Hence, ancient carbonates can potentially record the Cr isotopic composition (δ53Cr ‰) of seawater in the geological past. Reliable application and interpretation of this proxy requires a detailed knowledge about processes that fractionate Cr on the Earth’s surface...... deposited during the Early Ordovician — a time of known redox instability in ancient oceans – exhibit a significant positive Cr isotope excursion of +0.5‰. This excursion is interpreted as the reductive drawn down of dissolved Cr in seawater in response to the development of a proximal anoxic sink......, and the quantification the Cr isotope composition of major Cr fluxes into and out of ocean. This thesis adds to the current knowledge of the Cr isotope system and is divided into two studies. The focus of the first study was to determine what processes control the Cr isotopic compositionof river water and to quantify...

  11. Isotopes in Greenland Precipitation

    Faber, Anne-Katrine

    Greenland ice cores offer a unique opportunity to investigate the climate system behaviour. The objective of this PhD project is to investigate isotope modelling of present- day conditions and conduct model-data comparison using Greenland ice cores. Thus this thesis investigates how the integration...... of model and data can be used to improve the understanding of climate changes. This is done through analysis of isotope modelling, observations and ice core measurements. This dissertation comprises three projects: (1) Modelling the isotopic response to changes in Arctic sea surface conditions, (2......) Constructing a new Greenland database of observations and present-day ice core measurements, and (3) Performance test of isotope-enabled CAM5 for Greenland. The recent decades of rapid Arctic sea ice decline are used as a basis for an observational-based model experiment using the isotope-enabled CAM model 3...

  12. Sulfur isotope effects associated with protonation of HS- and volatilization of H2S

    Fry, B.; Gest, H.; Hayes, J. M.


    The isotope effects associated with: (1) formation of H2S from HS- by protonation in aqueous solution; and (2) volatilization of H2S have been experimentally determined. Both isotopic distributions in closed systems at equilibrium and differential rates of volatilization of isotopic species in open systems were measured at 22 +/- 1 degrees C. It was found that, at equilibrium aqueous H2S is enriched in 34S by 2.0 - 2.7% relative to HS- and that H2S volatilized from solution is depleted in 34S by 0.5% relative to dissolved H2S. A small kinetic isotope effect accompanying volatilization of H2S was observed in the open-system experiments.

  13. Iron isotope characteristics of Hot Springs at Chocolate Pots, Yellowstone National Park.

    Wu, Lingling; Brucker, Rebecca Poulson; Beard, Brian L; Roden, Eric E; Johnson, Clark M


    Chocolate Pots Hot Springs in Yellowstone National Park is a hydrothermal system that contains high aqueous ferrous iron [∼0.1 mM Fe(II)] at circumneutral pH conditions. This site provides an ideal field environment in which to test our understanding of Fe isotope fractionations derived from laboratory experiments. The Fe(III) oxides, mainly produced through Fe(II) oxidation by oxygen in the atmosphere, have high ⁵⁶Fe/⁵⁴Fe ratios compared with the aqueous Fe(II). However, the degree of fractionation is less than that expected in a closed system at isotopic equilibrium. We suggest two explanations for the observed Fe isotope compositions. One is that light Fe isotopes partition into a sorbed component and precipitate out on the Fe(III) oxide surfaces in the presence of silica. The other explanation is internal regeneration of isotopically heavy Fe(II) via dissimilatory Fe(III) reduction farther down the flow path as well as deeper within the mat materials. These findings provide evidence that silica plays an important role in governing Fe isotope fractionation factors between reduced and oxidized Fe. Under conditions of low ambient oxygen, such as may be found on early Earth or Mars, significantly larger Fe isotope variations are predicted, reflecting the more likely attainment of Fe isotope equilibrium associated with slower oxidation rates under low-O₂ conditions.

  14. Reflective Equilibrium: Epistemological or Political?

    Andrew Lister


    Full Text Available One of the reasons for ongoing interest in the work of political philosopher John Rawls is that he developed novel methods for thinking systematically about the nature of justice. This paper examines the moral and epistemological motivations for Rawls’s method of “reflective equilibrium,” and the tension between them in Kai Nielsen’s use of “wide reflective equilibrium” in the service of critical and emancipatory social theory. Une des raisons de l’intérêt soutenu pour l’oeuvre du philosophe politique John Rawls est qu’il a développé de nouvelles méthodes de réflexion systématique au sujet de la nature de la justice. Cet article étudie les motifs moraux et épistémologiques soutenant la méthode d’ «équilibre réflectif» de Rawls, et les tensions entre eux dans l’utilisation par Kai Nielsen d’ «équilibre réflectif étendu» au service de la théorie sociale critique et émancipatrice.

  15. Colin Rowe and ' Dynamic Equilibrium'

    Pablo López Marín


    Full Text Available AbstractIn 1944 Gyorgy Kepes published what undoubtless will be his most influential text, "The language of vision". What Kepes tried to do was a guide of grammar and syntax of vision, which allows to face art as purely sensory experience or just visual, devisted of any literary , semantic or sentimental meaning.Among all the concepts that Kepes developes in his essay perhaps the most decisive one is the so called dynamic equilibrium, which is introduced in this work for fi rst time, verbalizing something that was in the air, orbiting around the entire modern plastic but far only explained in an empirical way.Colin Rowe reverberates the recent readed kepesian ideas on his own writings Transparency: Literal and Phenomenal and Neo-'Classicism' and Modern Architecture I and II, when the author tries to highlight the founding principles of the modern movement refusing the plastic  dimension of the discipline . The article will try to expose and explain this influence.


    Pugliese, D.; Stuchlík, Z., E-mail:, E-mail: [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)


    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  17. Equilibrium avalanches in spin glasses

    Le Doussal, Pierre; Müller, Markus; Wiese, Kay Jörg


    We study the distribution of equilibrium avalanches (shocks) in Ising spin glasses which occur at zero temperature upon small changes in the magnetic field. For the infinite-range Sherrington-Kirkpatrick (SK) model, we present a detailed derivation of the density ρ(ΔM) of the magnetization jumps ΔM. It is obtained by introducing a multicomponent generalization of the Parisi-Duplantier equation, which allows us to compute all cumulants of the magnetization. We find that ρ(ΔM)˜ΔM-τ with an avalanche exponent τ=1 for the SK model, originating from the marginal stability (criticality) of the model. It holds for jumps of size 1≪ΔMmodel. For finite-range models, using droplet arguments, we obtain the prediction τ=(df+θ)/dm where df,dm, and θ are the fractal dimension, magnetization exponent, and energy exponent of a droplet, respectively. This formula is expected to apply to other glassy disordered systems, such as the random-field model and pinned interfaces. We make suggestions for further numerical investigations, as well as experimental studies of the Barkhausen noise in spin glasses.

  18. Magnesium stable isotope composition of Earth's upper mantle

    Handler, Monica R.; Baker, Joel A.; Schiller, Martin; Bennett, Vickie C.; Yaxley, Gregory M.


    The mantle is Earth's largest reservoir of Mg containing > 99% of Earth's Mg inventory. However, no consensus exists on the stable Mg isotope composition of the Earth's mantle or how variable it is and, in particular, whether the mantle has the same stable Mg isotope composition as chondrite meteorites. We have determined the Mg isotope composition of olivine from 22 mantle peridotites from eastern Australia, west Antarctica, Jordan, Yemen and southwest Greenland by pseudo-high-resolution MC-ICP-MS on Mg purified to > 99%. The samples include fertile lherzolites, depleted harzburgites and dunites, cryptically metasomatised ('dry') peridotites and modally metasomatised apatite ± amphibole-bearing harzburgites and wehrlites. Olivine from these samples of early Archaean through to Permian lithospheric mantle have δ25Mg DSM-3 = - 0.22 to - 0.08‰. These data indicate the bulk upper mantle as represented by peridotite olivine is homogeneous within current analytical uncertainties (external reproducibility ≤ ± 0.07‰ [2 sd]). We find no systematic δ25Mg variations with location, lithospheric age, peridotite fertility, or degree or nature of mantle metasomatism. Although pyroxene may have slightly heavier δ25Mg than coexisting olivine, any fractionation between mantle pyroxene and olivine is also within current analytical uncertainties with a mean Δ25Mg pyr-ol = +0.06 ± 0.10‰ (2 sd; n = 5). Our average mantle olivine δ25Mg DSM-3 = - 0.14 ± 0.07‰ and δ26Mg DSM-3 = - 0.27 ± 0.14‰ (2 sd) are indistinguishable from the average of data previously reported for terrestrial basalts, confirming that basalts have stable Mg isotope compositions representative of the mantle. Olivine from five pallasite meteorites have δ25Mg DSM-3 = - 0.16 to - 0.11‰ that are identical to terrestrial olivine and indistinguishable from the average δ25Mg previously reported for chondrites. These data provide no evidence for measurable heterogeneity in the stable Mg isotope

  19. The use of the uranium isotopic model on the study of aquifers at Morro do Ferro, Pocos de Caldas, Minas Gerais State, Brazil; Utilizacao de modelo isotopico de uranio no estudo de aquiferos do Morro do Ferro, Pocos de Caldas (MG)

    Bonotto, Daniel M. [UNESP, Rio Claro, SP (Brazil). Inst. de Geociencias e Ciencias Exatas


    Uranium isotopic analyses were performed in groundwaters from several boreholes drilled at the thorium and rare earth deposit located at Morro do Ferro, near the centre of the Pocos de Caldas Plateau, Minas Gerais State, Brazil. The samples were collected during dry and wet periods, proceeding from aquifers developed in the weathered mantle due to in situ intense alteration, with the weathered zone establishing an argillaceous laterite greater than 100 m thick. The {sup 234} U/{sup 238} U activity ratio and U content measured for each sample by alpha spectrometry were used to evaluate the applicability in the area of the model developed to deduce proportions of groundwaters in a mixture. The influence of the rainfall on the utilization of the uranium isotopic model was considered, and also it was possible to suggest which boreholes would be able to supply samples representing different systems of circulation of groundwaters. (author). 5 figs., 2 tabs.

  20. Reaction dynamics of {sup 34-38}Mg projectile with carbon target using Glauber model

    Shama, Mahesh K., E-mail: [School of Physics and Material Sciences, Thapar University Patiala-147004 (India); Department of Applied Sciences, Chandigarh Engineering College, Landran Mohali-140307 (India); Panda, R. N. [Department of Physics, ITER, Shiksha O Anusandhan University, Bhubaneswar-751030 (India); Sharma, Manoj K. [School of Physics and Material Sciences, Thapar University Patiala-147004 (India); Patra, S. K. [Institute of Physics, Sachivalaya marg Bhubneswar-751005 (India)


    We have studied nuclear reaction cross-sections for {sup 34-38}Mg isotopes as projectile with {sup 12}C target at projectile energy 240AMeV using Glauber model with the conjunction of densities from relativistic mean filed formalism. We found good agreement with the available experimental data. The halo status of {sup 37}Mg is also investigated.

  1. Filling the gap in Ca input-output budgets in base-poor forest ecosystems: The contribution of non-crystalline phases evidenced by stable isotopic dilution

    van der Heijden, Gregory; Legout, Arnaud; Mareschal, Louis; Ranger, Jacques; Dambrine, Etienne


    In terrestrial ecosystems, plant-available pools of magnesium and calcium are assumed to be stored in the soil as exchangeable cations adsorbed on the surface of mineral and/or organic particles. The pools of exchangeable magnesium and calcium are measured by ion-exchange soil extractions. These pools are sustained in the long term by the weathering of primary minerals in the soil and atmospheric inputs. This conceptual model is the base of input-output budgets from which soil acidification and the sustainability of soil chemical fertility is inferred. However, this model has been questioned by data from long-term forest ecosystem monitoring sites, particularly for calcium. Quantifying the contribution of atmospheric inputs, ion exchange and weathering of both primary, secondary and non-crystalline phases to tree nutrition in the short term is challenging. In this study, we developed and applied a novel isotopic dilution technique using the stable isotopes of magnesium and calcium to study the contribution of the different soil phases to soil solution chemistry in a very acidic soil. The labile pools of Mg and Ca in the soil (pools in equilibrium with the soil solution) were isotopically labeled by spraying a solution enriched in 26Mg and 44Ca on the soil. Labeled soil columns were then percolated with a dilute acid solution during a 3-month period and the isotopic dilution of the tracers was monitored in the leaching solution, in the exchangeable (2 sequential 1 mol L-1 ammonium acetate extractions) and non-crystalline (2 sequential soil digestions: oxalic acid followed by nitric acid) phases. Significant amounts of Mg and Ca isotope tracer were recovered in the non-crystalline soil phases. These phases represented from 5% to 25% and from 24% to 50%, respectively, of the Mg and Ca labile pools during the experiment. Our results show that non-crystalline phases act as both a source and a sink of calcium and magnesium in the soil, and contribute directly to soil

  2. Non-equilibrium modelling of distillation

    Wesselingh, JA; Darton, R


    There are nasty conceptual problems in the classical way of describing distillation columns via equilibrium stages, and efficiencies or HETP's. We can nowadays avoid these problems by simulating the behaviour of a complete column in one go using a non-equilibrium model. Such a model has phase

  3. Approximate Equilibrium Problems and Fixed Points

    H. Mazaheri


    Full Text Available We find a common element of the set of fixed points of a map and the set of solutions of an approximate equilibrium problem in a Hilbert space. Then, we show that one of the sequences weakly converges. Also we obtain some theorems about equilibrium problems and fixed points.

  4. The Geometry of Finite Equilibrium Datasets

    Balasko, Yves; Tvede, Mich

    We investigate the geometry of finite datasets defined by equilibrium prices, income distributions, and total resources. We show that the equilibrium condition imposes no restrictions if total resources are collinear, a property that is robust to small perturbations. We also show that the set...

  5. Equilibrium Tail Distribution Due to Touschek Scattering

    Nash,B.; Krinsky, S.


    Single large angle Coulomb scattering is referred to as Touschek scattering. In addition to causing particle loss when the scattered particles are outside the momentum aperture, the process also results in a non-Gaussian tail, which is an equilibrium between the Touschek scattering and radiation damping. Here we present an analytical calculation for this equilibrium distribution.

  6. Zeroth Law, Entropy, Equilibrium, and All That

    Canagaratna, Sebastian G.


    The place of the zeroth law in the teaching of thermodynamics is examined in the context of the recent discussion by Gislason and Craig of some problems involving the establishment of thermal equilibrium. The concept of thermal equilibrium is introduced through the zeroth law. The relation between the zeroth law and the second law in the…

  7. System of Operator Quasi Equilibrium Problems

    Suhel Ahmad Khan


    Full Text Available We consider a system of operator quasi equilibrium problems and system of generalized quasi operator equilibrium problems in topological vector spaces. Using a maximal element theorem for a family of set-valued mappings as basic tool, we derive some existence theorems for solutions to these problems with and without involving Φ-condensing mappings.

  8. Zeroth Law, Entropy, Equilibrium, and All That

    Canagaratna, Sebastian G.


    The place of the zeroth law in the teaching of thermodynamics is examined in the context of the recent discussion by Gislason and Craig of some problems involving the establishment of thermal equilibrium. The concept of thermal equilibrium is introduced through the zeroth law. The relation between the zeroth law and the second law in the…

  9. 高温下非传统稳定同位素分馏%Non-traditional stable isotope fractionation at high temperatures



    The last ten years have seen big progress and wide applications of a novel field, non-traditional stable isotope (NTSI) geochemistry, to high temperature geo-science studies. Invention of multi-collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) led to the big breakthrough of analytical methods for heavy stable isotopes. This contribution summarizes Ii, Fe, and Mg isotope studies on igneous rocks and minerals, as representative of NTSI geochemistry. Ii isotopes have been widely applied to the studies of mantle geochemistry, recycling of subducted materials, and metamorphism to constrain the source of magma and kinetic diffusion process. Fe isotope fractionation is related to partitioning of multi-valent Fe between Fe-bearing phases, which can occur in the course of mantle metasomatism, partial melting, and fractional crystallization. Mg isotopic compositions of igneous rocks most likely reflect the source signatures. Variation of Mg isotopic ratios of mantle peridotites is trivial and this provides a homogenous background for Mg isotope fractionation in low temperature processes. Furthermore, Cl, Si, Cu, Ca, and U isotopes are also promising in the future geochemical studies. Experimental studies and theoretical simulation for the mechanisms of isotope fractionation provide important guidances for understanding the NTIS data. Experimental studies show that light and heavy isotopes have different migration velocity at high temperature processes such as chemical diffusion, evaporation, and desublimation, which could produce significant kinetic isotope fractionation. Equilibrium isotopic fractionation could occur among mineral, melt, and fluid when chemical environment of the isotopes are different between the phases. Recent thermal diffusion and migration experiments on silicate material reveal a " new" mechanism of magma differentiation and isotope fractionation. Along a temperature gradient in silicate magma, large elemental variation and isotopic

  10. Implementing an Equilibrium Law Teaching Sequence for Secondary School Students to Learn Chemical Equilibrium

    Ghirardi, Marco; Marchetti, Fabio; Pettinari, Claudio; Regis, Alberto; Roletto, Ezio


    A didactic sequence is proposed for the teaching of chemical equilibrium law. In this approach, we have avoided the kinetic derivation and the thermodynamic justification of the equilibrium constant. The equilibrium constant expression is established empirically by a trial-and-error approach. Additionally, students learn to use the criterion of…

  11. Implementing an Equilibrium Law Teaching Sequence for Secondary School Students to Learn Chemical Equilibrium

    Ghirardi, Marco; Marchetti, Fabio; Pettinari, Claudio; Regis, Alberto; Roletto, Ezio


    A didactic sequence is proposed for the teaching of chemical equilibrium law. In this approach, we have avoided the kinetic derivation and the thermodynamic justification of the equilibrium constant. The equilibrium constant expression is established empirically by a trial-and-error approach. Additionally, students learn to use the criterion of…

  12. Economic networks in and out of equilibrium

    Squartini, Tiziano


    Economic and financial networks play a crucial role in various important processes, including economic integration, globalization, and financial crises. Of particular interest is understanding whether the temporal evolution of a real economic network is in a (quasi-)stationary equilibrium, i.e. characterized by smooth structural changes rather than abrupt transitions. Smooth changes in quasi-equilibrium networks can be generally controlled for, and largely predicted, via an appropriate rescaling of structural quantities, while this is generally not possible for abrupt transitions in non-stationary networks. Here we study whether real economic networks are in or out of equilibrium by checking their consistency with quasi-equilibrium maximum-entropy ensembles of graphs. As illustrative examples, we consider the International Trade Network (ITN) and the Dutch Interbank Network (DIN). We show that, despite the globalization process, the ITN is an almost perfect example of quasi-equilibrium network, while the DIN ...

  13. Cosmological particle production and generalized thermodynamic equilibrium

    Zimdahl, W


    With the help of a conformal, timelike Killing-vector we define generalized equilibrium states for cosmological fluids with particle production. For massless particles the generalized equilibrium conditions require the production rate to vanish and the well known ``global'' equilibrium of standard relativistic thermodynamics is recovered as a limiting case. The equivalence between the creation rate for particles with nonzero mass and an effective viscous fluid pressure follows as a consequence of the generalized equilibrium properties. The implications of this equivalence for the cosmological dynamics are discussed, including the possibility of a power-law inflationary behaviour. For a simple gas a microscopic derivation for such kind of equilibrium is given on the basis of relativistic kinetic theory.

  14. Equilibrium and Sudden Events in Chemical Evolution

    Weinberg, David H; Freudenburg, Jenna


    We present new analytic solutions for one-zone (fully mixed) chemical evolution models and explore their implications. In contrast to existing analytic models, we incorporate a realistic delay time distribution for Type Ia supernovae (SNIa) and can therefore track the separate evolution of $\\alpha$-elements produced by core collapse supernovae (CCSNe) and iron peak elements synthesized in both CCSNe and SNIa. In generic cases, $\\alpha$ and iron abundances evolve to an equilibrium at which element production is balanced by metal consumption and gas dilution, instead of continuing to increase over time. The equilibrium absolute abundances depend principally on supernova yields and the outflow mass loading parameter $\\eta$, while the equilibrium abundance ratio [$\\alpha$/Fe] depends mainly on yields and secondarily on star formation history. A stellar population can be metal-poor either because it has not yet evolved to equilibrium or because high outflow efficiency makes the equilibrium abundance itself low. Sy...

  15. Disturbances in equilibrium function after major earthquake

    Honma, Motoyasu; Endo, Nobutaka; Osada, Yoshihisa; Kim, Yoshiharu; Kuriyama, Kenichi


    Major earthquakes were followed by a large number of aftershocks and significant outbreaks of dizziness occurred over a large area. However it is unclear why major earthquake causes dizziness. We conducted an intergroup trial on equilibrium dysfunction and psychological states associated with equilibrium dysfunction in individuals exposed to repetitive aftershocks versus those who were rarely exposed. Greater equilibrium dysfunction was observed in the aftershock-exposed group under conditions without visual compensation. Equilibrium dysfunction in the aftershock-exposed group appears to have arisen from disturbance of the inner ear, as well as individual vulnerability to state anxiety enhanced by repetitive exposure to aftershocks. We indicate potential effects of autonomic stress on equilibrium function after major earthquake. Our findings may contribute to risk management of psychological and physical health after major earthquakes with aftershocks, and allow development of a new empirical approach to disaster care after such events.

  16. Conjectural Equilibrium in Water-filling Games

    Su, Yi


    This paper considers a non-cooperative game in which competing users sharing a frequency-selective interference channel selfishly optimize their power allocation in order to improve their achievable rates. Previously, it was shown that a user having the knowledge of its opponents' channel state information can make foresighted decisions and substantially improve its performance compared with the case in which it deploys the conventional iterative water-filling algorithm, which does not exploit such knowledge. This paper discusses how a foresighted user can acquire this knowledge by modeling its experienced interference as a function of its own power allocation. To characterize the outcome of the multi-user interaction, the conjectural equilibrium is introduced, and the existence of this equilibrium for the investigated water-filling game is proved. Interestingly, both the Nash equilibrium and the Stackelberg equilibrium are shown to be special cases of the generalization of conjectural equilibrium. We develop...

  17. The three shapes of 32Mg

    Poves A.


    Full Text Available The N=20 and N=28 “islands of inversion” are described by large scale shell model calculations which mix configurations with different Nħω or equivalently with different number of particles promoted from the sd-shell to the pf -shell. We pay particular attention to the properties of the states at fix Nħω which turn out to be the real protagonists of the physics at N=20. In particular we study the appearance of spherical, deformed and superdeformed structures in 32Mg at fixed 0p-0h, 2p-2h and 4p-4h configurations. Finally we submit that the islands of deformation at N=20 and N=28 merge in the Magnesium isotopes

  18. Mass transfer and carbon isotope evolution in natural water systems

    Wigley, T.M.L.; Plummer, L.N.; Pearson, F.J.


    This paper presents a theoretical treatment of the evolution of the carbon isotopes C13 and C14 in natural waters and in precipitates which derive from such waters. The effects of an arbitrary number of sources (such as dissolution of carbonate minerals and oxidation of organic material) and sinks (such as mineral precipitation, CO2 degassing and production of methane), and of equilibrium fractionation between solid, gas and aqueous phases are considered. The results are expressed as equations relating changes in isotopic composition to changes in conventional carbonate chemistry. One implication of the equations is that the isotopic composition of an aqueous phase may approach a limiting value whenever there are simultaneous inputs and outputs of carbonate. In order to unambiguously interpret isotopic data from carbonate precipitates and identify reactants and products in reacting natural waters, it is essential that isotopic changes are determined chiefly by reactant and product stoichiometry, independent of reaction path. We demonstrate that this is so by means of quantitative examples. The evolution equations are applied to: 1. (1) carbon-14 dating of groundwaters; 2. (2) interpretation of the isotopic composition of carbonate precipitates, carbonate cements and diagenetically altered carbonates; and 3. (3) the identification of chemical reaction stoichiometry. These applications are illustrated by examples which show the variation of ??C13 in solutions and in precipitates formed under a variety of conditions involving incongruent dissolution, CO2 degassing, methane production and mineral precipitation. ?? 1978.

  19. The chemical composition of red giants in 47 Tucanae. II. Magnesium isotopes and pollution scenarios

    Thygesen, A O; Ludwig, H -G; Ventura, P; Yong, D; Collet, R; Christlieb, N; Melendez, J; Zaggia, S


    The phenomenon of multiple populations in globular clusters is still far from understood, with several proposed mechanisms to explain the observed behaviour. The study of elemental and isotopic abundance patterns are crucial for investigating the differences among candidate pollution mechanisms. We derive magnesium isotopic ratios for 13 stars in the globular cluster 47 Tucanae (NGC 104) to provide new, detailed information about the nucleosynthesis that has occurred within the cluster. For the first time, the impact of 3D model stellar atmospheres on the derived Mg isotopic ratios is investigated. Using both tailored 1D atmospheric models and 3D hydrodynamical models, we derive magnesium isotopic ratios from four features of MgH near 5135{\\AA} in 13 giants near the tip of the RGB, using high signal-to-noise, high-resolution spectra. We derive the magnesium isotopic ratios for all stars and find no significant offset of the isotopic distribution between the pristine and the polluted populations. Furthermore, ...

  20. Assessing the biomineralization processes in the shell microstructure of modern brachiopods: variations in the oxygen isotope composition and minor element ratios

    Milner Garcia, Sara Ana; Rollion-Bard, Claire; Burckel, Pierre; Tomašových, Adam; Angiolini, Lucia; Henkel, Daniela


    Brachiopods have been extensively used to reconstruct physicochemical conditions of ancient oceans due to their extensive fossil record and shells made of stable low-Mg calcite. In this context, it is important to assess the impact of brachiopod shell biomineralization processes on geochemical proxies. Six modern species of brachiopod specimen representing the three low-Mg calcite orders (i.e. Terebratulida, Rhynchonellida and Thecideida) were selected, in order to identify the most reliable taxa and the best shell portions to use for measurements of proxies. Three main different shell structures were identified: (1) only primary layer, (2) primary and secondary fibrous layers and (3) same as (2) with also a tertiary columnar layer. Oxygen isotope composition was measured at the micrometre scale with high-resolution ion microprobe. Generally, O isotope values of shells composed of primary and secondary layers show a progression towards more positive values from the outer primary layer to the inner secondary layer. The columnar tertiary shell layer, when present, has the most positive isotopic O values, the closest to the isotopic equilibrium. Variations at the micrometre scale are higher than those measured by conventional bulk techniques, as already shown by Cusack et al. (2012). Trace elements ratios (Li/Ca, B/Ca, Na/Ca, Mg/Ca, and Sr/Ca) were determined by laser ablation coupled to an ICP-MS. The trace element points define profiles parallel to the O isotope ion probe spots. The elemental ratio profiles of species composed by primary and secondary shell layers (Terebratalia transversa, Magasella sanguinea and Magellania venosa) show different behaviours depending on the elements. Mg/Ca and Sr/Ca values are constant throughout all profiles, even Mg/Ca values are more variable. The values of both ratios are in good agreement with previous studies (Perez-Huerta et al., 2008; Butler et al., 2015). Li/Ca values are also constant among the different profiles. In

  1. Oxygen Isotope Study of the Suzhou Granite

    王汝成; 沈渭洲; 等


    Oxygen isotope studies of the Suzhou granite have been made based on drill-hole samples.In the inner part,the δ18 O values are less variable either in the whole-rock,quartz or in feldspar.Oxygen isotopic compositions are in equilibrium between coexisting quartz and feldspar.Data points from the inner part are plotted in a small area in the δ18 OQ-δ18Of diagram,indicating that this part has not been affected by meteoric hydrothermal fluids.But the whole-rock δ18 O values of the marginal part vary greatly.Oxygen isotopic compositions are in extreme disequilibrium between quartz and feldspar.Data points from the marginal part are displayed with a nearly vertical slope in the δ18OQ-δ18 Of diagram,implying that rocks of this part are affected by the meteoric hydrothermal fluids.Extreme water-rock interactions lead to mineralizations of rare-elements(Nb,Ta,as well as Zr,Hf,Th)in the marginal part.Source materials of the Suzhou granite are also discussed in this paper.

  2. Myths of Isotopic Reference Materials Busted

    Coplen, T.


    During the past several years, the determination of the isotopic abundances of elements including H, Li, B, C, N, O, Mg, Si, S, Cl, Ca, Cr, Fe, Cu, Zn, Tl, and Se has substantially increased because of expanded use in hydrology, environmental studies, microbiology, forensic investigations, atmospheric investigations, oceanography, etc. Improvements in instrumentation enable increasingly precise isotope-amount-ratio measurements in these fields, but these improvements in precision commonly do not lead to improvements in accuracy because of the lack or improper use of isotopic reference materials. When properly used, these critically important materials enable any laboratory worldwide to measure the same homogeneous sample and report the same isotopic abundance within analytical uncertainty. For example, for stable isotopic analysis of gaseous hydrogen samples, the agreement among 36 laboratories worldwide before normalization to any hydrogen gas reference material was 11.8 per mill. After normalization to anchors (gaseous H isotopic reference materials) at each end of the delta H-2 scale, the agreement was 0.85 per mill, an improvement of more than an order of magnitude. Consistency of delta C-13 measurements often can be improved by nearly 50 percent by anchoring the delta C-13 scale with two isotopic reference materials differing substantially in C-13 mole fraction, namely NBS 19 calcite and L-SVEC lithium carbonate. Agreement of delta C-13 values of four expert laboratories analyzing USGS40 L- glutamic acid by CF-IRMS methods improved from 0.084 to 0.015 per mill with use of the two scale anchors (NBS 19 and L-SVEC). Solid oxygen isotopic reference materials (IAEA-600 caffeine, IAEA-601 and IAEA-602 benzoic acids, IAEA-NO-3, USGS32, USGS34, and USGS35 nitrates, NBS-127, IAEA-SO-5, and IAEA-SO-6 barium sulfates) are poorly calibrated. Calibrating these solids to the VSMOW-SLAP reference water scale has been very difficult because both the solids and reference

  3. Cryogenic Calcite: A Morphologic and Isotopic Analog to the ALH84001 Carbonates

    Niles, P. B.; Leshin, L. A.; Socki, R. A.; Guan, Y.; Ming, D. W.; Gibson, E. K.


    Martian meteorite ALH84001 carbonates preserve large and variable microscale isotopic compositions, which in some way reflect their formation environment. These measurements show large variations (>20%) in the carbon and oxygen isotopic compositions of the carbonates on a 10-20 micron scale that are correlated with chemical composition. However, the utilization of these data sets for interpreting the formation conditions of the carbonates is complex due to lack of suitable terrestrial analogs and the difficulty of modeling under non-equilibrium conditions. Thus, the mechanisms and processes are largely unknown that create and preserve large microscale isotopic variations in carbonate minerals. Experimental tests of the possible environments and mechanisms that lead to large microscale isotopic variations can help address these concerns. One possible mechanism for creating large carbon isotopic variations in carbonates involves the freezing of water. Carbonates precipitate during extensive CO2 degassing that occurs during the freezing process as the fluid s decreasing volume drives CO2 out. This rapid CO2 degassing results in a kinetic isotopic fractionation where the CO2 gas has a much lighter isotopic composition causing an enrichment of 13C in the remaining dissolved bicarbonate. This study seeks to determine the suitability of cryogenically formed carbonates as analogs to ALH84001 carbonates. Specifically, our objective is to determine how accurately models using equilibrium fractionation factors approximate the isotopic compositions of cryogenically precipitated carbonates. This includes determining the accuracy of applying equilibrium fractionation factors during a kinetic process, and determining how isotopic variations in the fluid are preserved in microscale variations in the precipitated carbonates.

  4. Interpretation of isotopic data in groundwater-rock systems: Model development and application to Sr isotope data from Yucca Mountain

    Johnson, Thomas M.; Depaolo, Donald J.


    A model enabling extraction of hydrologic information from spatial and temporal patterns in measurements of isotope ratios in water-rock systems is presented. The model describes the evolution of isotope ratios in response to solute transport and water-rock interaction. In advective systems, a single dimensionless parameter (a Damköhler number, ND) dominates in determining the distance over which isotopic equilibrium between the water and rock is approached. Some isotope ratios act as conservative tracers (ND ≪ 1), while others reflect only interaction with the local host rock (ND ≫ 1). If ND is close to one (i.e., the distance for equilibration is close to the length scale of observation), isotope ratio measurements can be used to determine ND, which in turn may yield information concerning reaction rates, or spatial variations in water velocity. Zones of high velocity (e.g., as a result of greater fracture density), or less reactive zones, may be identified through observation of their lower ND values. The model is applied to paleohydrologic interpretations of Sr isotope data from calcite fracture fillings in drill cores from Yucca Mountain, Nevada (Marshall et al., 1992). The results agree with other studies suggesting "fast path" transport in the unsaturated zone. Also, we find that the data do not give a conclusive indication of paleowater table elevation because of the effects of water-rock interaction.

  5. Silicon Burning, Quasi-Equilibrium and the formation of the Iron Peak

    Hix, William Raphael; Thielemann, Friedrich-Karl


    As the most tightly bound nuclei, the 'Iron Peak' nuclei result from Nuclear Statistical Equilibrium (NSE) and are the culmination of nuclear energy generation in astrophysical environments. Our re-examination of silicon burning, the mechanism by which the nuclei of the iron peak are produced, has revealed a number of potential improvements in the treatment of this ultimate stage of astrophysical nuclear energy generation. We will discuss results gleaned from simulation work done with a large nuclear network (300 nuclei and 3000 reactions) and from independent calculations of equilirium abundance distributions, which offer new insights into the quasi-equilibrium mechanism and the approach to NSE. We find that the degree to which the matter has been neutronized is of great importance, not only to the final products, but also to the rate of energy generation and the membership of the quasi-equilibrium groups. Furthermore, we find that, as a result of quasi-equilibrium, incomplete silicon burning results in neutron richness among the isotopes of the iron group much larger than the global neutronization would indicate. We will discuss methods which use this quasi-equilibrium mechanism to preserve the most important features of the large nuclear network calculations at a significant improvement in computational speed. Such improved methods are ideally suited for hydrodynamic calculations which involve the production of iron peak nuclei, where the larger network calculation proves unmanageable.

  6. Silicon Burning I: The Importance of Neutronization to the Physics of Quasi-Equilibrium

    Hix, W. R.; Thielemann, F.-K.


    As the most tightly bound nuclei, the `Iron Peak' nuclei are the culmination of nuclear energy generation in astrophysical environments and the result of Nuclear Statistical Equilibrium (NSE). Our re-examination of silicon burning, the mechanism by which the nuclei of the iron peak are produced, has revealed a number of potential improvements to our understanding of this ultimate stage of astrophysical nuclear energy generation. We will discuss results gleaned from simulation work done with a large nuclear network (300 nuclei and 3000 reactions) and from independent calculations of equilibrium abundance distributions, which offer new insights into the quasi-equilibrium mechanism and the approach to NSE. We find that the degree to which the matter has been neutronized is of great importance, not only to the final products, but also to the rate of energy generation and the membership of the quasi-equilibrium groups. Furthermore, we find that, as a result of quasi-equilibrium, incomplete silicon burning results in neutron richness among the isotopes of the iron group much larger than the global neutronization would indicate. In light of our findings, we will also discuss the applicability of approximations for silicon burning commonly employed in hydrodynamic simulations.

  7. Fractionation of Stable Isotopes in Atmospheric Aerosol Reactions

    Meusinger, Carl

    reactions and undergo complex chemical and physical changes during their lifetimes. In order to assess processes that form and alter aerosols, information provided by stable isotopes can be used to help constrain estimates on the strength of aerosol sources and sinks. This thesis studies (mass......-independent) fractionation processes of stable isotopes of C, N, O and S in order to investigate three different systems related to aerosols: 1. Post-depositional processes of nitrate in snow that obscure nitrate ice core records 2. Formation and aging of secondary organic aerosol generated by ozonolysis of X...... as required. The kndings provide important results for the studies' respective felds, including a description of the isotopic fractionation and quantum yield of nitrate photolysis in snow, equilibrium fractionation in secondary organic aerosol and fractionation constants of different oxidation pathways of SO2....

  8. Kinetic secondary deuterium isotope effects for substituted benzaldehyde cyanohydrin formation

    Okano, V.; do Amaral, L.; Cordes, E.H.


    ..cap alpha.. secondary deuterium isotope effects have been measured for the observed rate constants for addition of cyanide ion to a series of substituted benzaldehydes in aqueous solution at 25/sup 0/C. Under the experimental conditions employed, these reactions did not proceed to completion, and the observed isotope effects were corrected to account for the influence of the reverse reaction employing measured equilibrium constants for cyanohydrin formation and previously determined secondary deuterium isotope effect for the equilibrium constant for 4-methoxybenzaldehyde cyanohydrin formation. In the four cases studied, values of k/sub D//k/sub H/ varied from 1.15 to 1.20, only slightly lower than the calculated maximal value for complete formation of the anionic tetrahedral species which is the immediate product of the rate-determining step, 1.21. A trend in isotope effect as a function of substrate reactivity could not be definitively established. The results suffice to establish that addition of cyanide to benzaldehydes proceeds via transition states in which rehybridization of carbonyl carbon to the tetrahedral geometry is nearly complete.

  9. LP Well-Posedness for Bilevel Vector Equilibrium and Optimization Problems with Equilibrium Constraints

    Phan Quoc Khanh


    Full Text Available The purpose of this paper is introduce several types of Levitin-Polyak well-posedness for bilevel vector equilibrium and optimization problems with equilibrium constraints. Base on criterion and characterizations for these types of Levitin-Polyak well-posedness we argue on diameters and Kuratowski’s, Hausdorff’s, or Istrǎtescus measures of noncompactness of approximate solution sets under suitable conditions, and we prove the Levitin-Polyak well-posedness for bilevel vector equilibrium and optimization problems with equilibrium constraints. Obtain a gap function for bilevel vector equilibrium problems with equilibrium constraints using the nonlinear scalarization function and consider relations between these types of LP well-posedness for bilevel vector optimization problems with equilibrium constraints and these types of Levitin-Polyak well-posedness for bilevel vector equilibrium problems with equilibrium constraints under suitable conditions; we prove the Levitin-Polyak well-posedness for bilevel equilibrium and optimization problems with equilibrium constraints.

  10. Isotopes in Greenland Precipitation

    Faber, Anne-Katrine

    the Arctic Ocean. A comprehensive database is created based on ice core and weather station data from Greenland within the period 1890-2014. Present day annual and seasonal mean values are computed for 326 locations in Greenland. Parameterization of the spatial distribution of temperature and δ18O are used...... of model and data can be used to improve the understanding of climate changes. This is done through analysis of isotope modelling, observations and ice core measurements. This dissertation comprises three projects: (1) Modelling the isotopic response to changes in Arctic sea surface conditions, (2......) Constructing a new Greenland database of observations and present-day ice core measurements, and (3) Performance test of isotope-enabled CAM5 for Greenland. The recent decades of rapid Arctic sea ice decline are used as a basis for an observational-based model experiment using the isotope-enabled CAM model 3...

  11. Perchlorate isotope forensics

    Böhlke, J.K.; Sturchio, N.C.; Gu, B.; Horita, J.; Brown, G.M.; Jackson, W.A.; Batista, J.; Hatzinger, P.B.


    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.

  12. Isotope Production Facility (IPF)

    Federal Laboratory Consortium — The Los Alamos National Laboratory has produced radioactive isotopes for medicine and research since the mid 1970s, when targets were first irradiated using the 800...

  13. Calcium stable isotope geochemistry

    Gausonne, Nikolaus [Muenster Univ. (Germany). Inst. fuer Mineralogie; Schmitt, Anne-Desiree [Strasbourg Univ. (France). LHyGeS/EOST; Heuser, Alexander [Bonn Univ. (Germany). Steinmann-Inst. fuer Geologie, Mineralogie und Palaeontologie; Wombacher, Frank [Koeln Univ. (Germany). Inst. fuer Geologie und Mineralogie; Dietzel, Martin [Technische Univ. Graz (Austria). Inst. fuer Angewandte Geowissenschaften; Tipper, Edward [Cambridge Univ. (United Kingdom). Dept. of Earth Sciences; Schiller, Martin [Copenhagen Univ. (Denmark). Natural History Museum of Denmark


    This book provides an overview of the fundamentals and reference values for Ca stable isotope research, as well as current analytical methodologies including detailed instructions for sample preparation and isotope analysis. As such, it introduces readers to the different fields of application, including low-temperature mineral precipitation and biomineralisation, Earth surface processes and global cycling, high-temperature processes and cosmochemistry, and lastly human studies and biomedical applications. The current state of the art in these major areas is discussed, and open questions and possible future directions are identified. In terms of its depth and coverage, the current work extends and complements the previous reviews of Ca stable isotope geochemistry, addressing the needs of graduate students and advanced researchers who want to familiarize themselves with Ca stable isotope research.

  14. Isotopically controlled semiconductors

    Haller, E.E.


    A review of recent research involving isotopically controlled semiconductors is presented. Studies with isotopically enriched semiconductor structures experienced a dramatic expansion at the end of the Cold War when significant quantities of enriched isotopes of elements forming semiconductors became available for worldwide collaborations. Isotopes of an element differ in nuclear mass, may have different nuclear spins and undergo different nuclear reactions. Among the latter, the capture of thermal neutrons which can lead to neutron transmutation doping, can be considered the most important one for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples. Manuel Cardona, the longtime editor-in-chief of Solid State Communications has been and continues to be one of the major contributors to this field of solid state physics and it is a great pleasure to dedicate this review to him.

  15. Isotopic fractionation of alkali earth metals during carbonate precipitation

    Yotsuya, T.; Ohno, T.; Muramatsu, Y.; Shimoda, G.; Goto, K. T.


    The alkaline earth metals such as magnesium, calcium and strontium play an important role in a variety of geochemical and biological processes. The element ratios (Mg/Ca and Sr/Ca) in marine carbonates have been used as proxies for reconstruction of the past environment. Recently several studies suggested that the study for the isotopic fractionation of the alkaline earth metals in marine carbonates has a potentially significant influence in geochemical research fields (e.g. Eisenhauer et al., 2009). The aim of this study is to explore the influence of carbonate polymorphs (Calcite and Aragonite) and environmental factors (e.g., temperature, precipitation rate) on the level of isotopic fractionation of the alkaline earth metals. We also examined possible correlations between the level of isotopic fractionation of Ca and that of other alkaline earth metals during carbonate precipitation. In order to determine the isotope fractionation factor of Mg, Ca and Sr during carbonate precipitation, calcite and aragonite were synthesized from calcium bicarbonate solution in which the amount of magnesium was controlled based on Kitano method. Calcium carbonates were also prepared from the mixture of calcium chlorite and sodium hydrogen carbonate solutions. The isotope fractionation factors were measured by MC-ICPMS. Results suggested that the level of isotopic fractionation of Mg during carbonate precipitation was correlated with that of Sr and that the change of the carbonate crystal structure could make differences of isotopic fractionations of Mg and Ca, however no difference was found in the case of Sr. In this presentation, the possible mechanism will be discussed.

  16. Isotopes through the looking glass

    Mårtensson Pendrill, Ann Marie


    Nuclear distributions affect many aspects of atomic spectra. As an example, recent experimental results for the hyperfine anomaly in Fr isotopes are considered. These depend on nuclear charge and magnetization distributions. The variations in charge radii for these isotopes were studied earlier by measuring optical isotope shifts. The hyperfine anomalies for the odd-odd isotopes involve the neutron distributions, of interest for studies of parity nonconserving effects along a chain of isotopes.

  17. Evidence for equilibrium conditions during the partitioning of nickel between olivine and komatiite liquids.

    Budahn, J.R.


    Olivine-liquid partition coefficients for Ni(DNi), calculated from Ni vs MgO abundance variations in komatiite series basalts, compare favourably with experimentally determined values, if Ni variations in olivine-controlled basalts can be modelled with an equation that assumes equilibrium between the entire olivine crystal and its coexisting liquid.-J.A.Z.

  18. Methods of isotopic geochronology

    Gorokhov, I. M.; Levchenkov, O. A.

    Papers are presented on such topics as the age of the chemical elements; the age of meteorites, the moon, and the earth; isotopic ages of the most ancient terrestrial formations; and the Archean evolution of Enderby Land in the Antarctic as evidenced by isotopic dating. Consideration is also given to a uranium-lead geochronology technique for investigating Precambrian ore deposits, a Pb-Pb technique of zircon dating, and the potentials and limitations of Sm-Nd geochronology.

  19. Magnesium stable isotope ecology using mammal tooth enamel.

    Martin, Jeremy E; Vance, Derek; Balter, Vincent


    Geochemical inferences on ancient diet using bone and enamel apatite rely mainly on carbon isotope ratios (δ(13)C) and to a lesser extent on strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) elemental ratios. Recent developments in nontraditional stable isotopes provide an unprecedented opportunity to use additional paleodietary proxies to disentangle complex diets such as omnivory. Of particular relevance for paleodietary reconstruction are metals present in large quantity in bone and enamel apatite, providing that biologically mediated fractionation processes are constrained. Calcium isotope ratios (δ(44)Ca) meet these criteria but exhibit complex ecological patterning. Stable magnesium isotope ratios (δ(26)Mg) also meet these criteria but a comprehensive understanding of its variability awaits new isotopic data. Here, 11 extant mammal species of known ecology from a single locality in equatorial Africa were sampled for tooth enamel and, together with vegetation and feces, analyzed for δ(26)Mg, δ(13)C, Sr/Ca, and Ba/Ca ratios. The results demonstrate that δ(26)Mg incorporated in tooth enamel becomes heavier from strict herbivores to omnivores/faunivores. Using data from experimentally raised sheep, we suggest that this (26)Mg enrichment up the trophic chain is due to a (26)Mg enrichment in muscle relative to bone. Notably, it is possible to distinguish omnivores from herbivores, using δ(26)Mg coupled to Ba/Ca ratios. The potential effects of metabolic and dietary changes on the enamel δ(26)Mg composition remain to be explored but, in the future, multiproxy approaches would permit a substantial refinement of dietary behaviors or enable accurate trophic reconstruction despite specimen-limited sampling, as is often the case for fossil assemblages.

  20. Iron isotope fractionation between aqueous ferrous iron and goethite

    Beard, Brian L.; Handler, Robert M.; Scherer, Michelle M.; Wu, Lingling; Czaja, Andrew D.; Heimann, Adriana; Johnson, Clark M.


    The equilibrium Fe isotope fractionation factor between aqueous Fe(II) and goethite has been experimentally measured to be - 1.05 ± 0.08‰ in 56Fe/54Fe (2σ) at 22 °C, using the three-isotope method. Experiments were done using two sizes of goethite (81 × 11 nm and 590 × 42 nm), and the experimental products were subjected to serial extraction using acid partial dissolution techniques to determine if surface Fe(III) atoms have different isotopic properties than the bulk goethite. These experiments indicate that the interaction of Fe(II)aq and goethite is dynamic and results in complete or near-complete Fe isotope exchange over 30 days, involving at least four components: Fe(II)aq, goethite, sorbed Fe(II), and Fe(III)surface. The equilibrium fractionation factor between Fe(II)aq and Fe(II)sorb is the same for both sizes of goethite, at Δ56FeFe(II)aq-Fe(II)sorb = - 1.24 ± 0.14‰; this fractionation factor is significantly different than the results of previous studies on Fe(II) sorption to goethite. The proportion of the Fe(III)surface component is greatest in the experiments that used the smallest goethite, and the Fe(III)surface-Fe(II)aq fractionation is estimated to be at least + 2.1‰. The high Fe(III)surface-Fe(II)aq fractionation may exert a significant influence on the Fe isotope compositions of aqueous Fe(II) in natural systems that contain nanoparticulate goethite, including those involving bacterial iron reduction. These results demonstrate that the isotopic properties of nano-scale minerals may be distinct from micron-scale or larger minerals, as is the case for other thermodynamic properties of nanoparticles.

  1. Oxygen Isotopes in Meteorites

    Clayton, R. N.


    Oxygen isotope abundance variations in meteorites are very useful in elucidating chemical and physical processes that occurred during the formation of the solar system (Clayton, 1993). On Earth, the mean abundances of the three stable isotopes are 16O: 99.76%, 17O: 0.039%, and 18O: 0.202%. It is conventional to express variations in abundances of the isotopes in terms of isotopic ratios, relative to an arbitrary standard, called SMOW (for standard mean ocean water), as follows:The isotopic composition of any sample can then be represented by one point on a "three-isotope plot," a graph of δ17O versus δ18O. It will be seen that such plots are invaluable in interpreting meteoritic data. Figure 1 shows schematically the effect of various processes on an initial composition at the center of the diagram. Almost all terrestrial materials lie along a "fractionation" trend; most meteoritic materials lie near a line of "16O addition" (or subtraction). (4K)Figure 1. Schematic representation of various isotopic processes shown on an oxygen three-isotope plot. Almost all terrestrial materials plot along a line of "fractionation"; most primitive meteoritic materials plot near a line of "16O addition." The three isotopes of oxygen are produced by nucleosynthesis in stars, but by different nuclear processes in different stellar environments. The principal isotope, 16O, is a primary isotope (capable of being produced from hydrogen and helium alone), formed in massive stars (>10 solar masses), and ejected by supernova explosions. The two rare isotopes are secondary nuclei (produced in stars from nuclei formed in an earlier generation of stars), with 17O coming primarily from low- and intermediate-mass stars (shielding in the UV photodissociation of CO (van Dishoeck and Black, 1988). This process results from the large differences in abundance between C16O, on the one hand, and C17O and C18O on the other. Photolysis of CO occurs by absorption of stellar UV radiation in the

  2. Electric Current Equilibrium in the Corona

    Filippov, Boris


    A hyperbolic flux-tube configuration containing a null point below the flux rope is considered as a pre-eruptive state of coronal mass ejections that start simultaneously with flares. We demonstrate that this configuration is unstable and cannot exist for a long time in the solar corona. The inference follows from general equilibrium conditions and from analyzing simple models of the flux-rope equilibrium. A direct consequence of the stable flux-rope equilibrium in the corona are separatrices in the horizontal-field distribution in the chromosphere. They can be recognized as specific "herring-bone structures" in a chromospheric fibril pattern.

  3. Electric Current Equilibrium in the Corona

    Filippov, Boris


    A hyperbolic flux-tube configuration containing a null point below the flux rope is considered as a pre-eruptive state of coronal mass ejections that start simultaneously with flares. We demonstrate that this configuration is unstable and cannot exist for a long time in the solar corona. The inference follows from general equilibrium conditions and from analyzing simple models of the flux-rope equilibrium. A direct consequence of the stable flux-rope equilibrium in the corona are separatrices in the horizontal-field distribution in the chromosphere. They can be recognized as specific "herring-bone structures" in a chromospheric fibril pattern.

  4. A Multi Period Equilibrium Pricing Model

    Pirvu, Traian A


    In this paper, we propose an equilibrium pricing model in a dynamic multi-period stochastic framework with uncertain income streams. In an incomplete market, there exist two traded risky assets (e.g. stock/commodity and weather derivative) and a non-traded underlying (e.g. temperature). The risk preferences are of exponential (CARA) type with a stochastic coefficient of risk aversion. Both time consistent and time inconsistent trading strategies are considered. We obtain the equilibriums prices of a contingent claim written on the risky asset and non-traded underlying. By running numerical experiments we examine how the equilibriums prices vary in response to changes in model parameters.




    For the evaporation of the pure liquid under the condition of constant temperature and constant external pressure, the phase equilibrium of the liquid vapor in the bubble and the liquid outside the bubble is always a kind of stable equilibrium whether there is air or not in the bubble. If there is no air in the bubble, the bubble and liquid cannot coexist in the mechanical equilibrium when the vapor pressure of the liquid in the bubble is less than or equal to the external pressure; the bubbl...

  6. Interpreting the Mg IIh andk Line Profiles of Mira Variables

    Wood, B. E.; Karovska, M.


    We use radiative transfer calculations to reproduce the basic appearance of Mg II lines observed from Mira variables. These lines have centroids that are blueshifted by at least 30 km s-1 from the stellar rest frame. It is unlikely that flow velocities in the stellar atmospheres are this fast, so radiative transfer effects must be responsible for this behavior. Published hydrodynamic models predict the existence of cool, downflowing material above the shocked material responsible for the Mg II emission, and we demonstrate that scattering in this layer can result in Mg II profiles as highly blueshifted as those that are observed. However, our models also show that scattering within the shock plays an equally strong role in shaping the Mg II profiles, and our calculations illustrate the importance of partial redistribution and the effects of being out of ionization equilibrium.

  7. Oxygen Isotope Composition of Nitrate Produced by Freshwater Nitrification

    Boshers, D.; Granger, J.; Bohlke, J. K.


    Measurements of the naturally occurring nitrogen and oxygen stable isotope ratios of nitrate (NO3-), δ15N and δ18O, can be used to determine the source, dispersal, and fate of natural and contaminant NO3- in aquatic environments. To this end, it is necessary to know the extent to which NO3- isotopologues are modified by biological reactions, as heavy and light isotopes have different reaction rates. The purpose of this study was to determine the influence of the δ18O of ambient water on the isotope composition of NO3- produced during nitrification, the biological oxidation of ammonium (NH4+) to nitrite (NO2-) and then NO3-, which is poorly constrained in freshwater systems. To determine the δ18O of NO3- produced by nitrification in freshwater, we collected water from a stream in New England, which we amended with NH4+ and with increments of 18O-enriched water, to monitor the isotope composition of NO3- produced by a natural consortium of nitrifiers. Added NH4+ was completely oxidized to NO3- over 26 days. The final δ18O of nitrified NO3- revealed sensitivity to the δ18O of water mediated by (a) isotopic equilibration between water and NO2- and (b) kinetic isotope fractionation during O-atom incorporation from water into NO2- and NO3-. Our results concur with nitrifying culture experiments that have demonstrated analogous sensitivity of the δ18O of nitrified NO3- to equilibrium and kinetic O isotope effects (Buchwald et al. 2012), as well as show that these dynamics need to be considered to interpret NO3- isotope distribution in freshwater environments.

  8. Solubility of hydrogen and its isotopes in metals from mixed gases

    San Marchi, C.; Somerday, B. P.; Larson, R. S.; Rice, S. F.


    This short communication reviews the classical thermodynamics governing dissolution of hydrogen in metals. Classical thermodynamics is then applied to equilibrium dissolution of hydrogen and its isotopes in metals from mixtures of their diatomic gases. For simplicity in presentation, we use the specific example of H 2 and D 2 gas mixtures to demonstrate the general principles of equilibrium solubility; however, other systems may be treated analogously. The formation of HD gas is shown to have a significant effect on equilibrium solubility since it affects the chemical potentials of the H 2 and D 2 gases. Finally, we compare this thermodynamic analysis with empirical solutions from the literature.

  9. Adsorption of dyes using peat: equilibrium and kinetic studies.

    Sepúlveda, L; Fernández, K; Contreras, E; Palma, C


    In recent years, adsorption has been accepted as one of the most appropriate processes for decolorization of wastewaters. This paper presents experimental results on application of peat for removal of structurally diverse dyes (azo, oxazine, triphenylmethane, thiazine and others) with emphasis on relevant factors such as the adsorbate-adsorbent chemical properties and chemical interaction as well as adsorption conditions. The equilibrium experimental results were fitted to Langmuir and Freundlich isotherms to obtain the characteristic parameters of each model. According to the evaluation using the Langmuir equation, the maximum sorption capacity of basic dyes at 22 degrees C was 667 (mg g(-1)) for Basic Blue 24, 526 (mg g(-1)) for Basic Green 4 and 714 (mg g(-1)) for Basic Violet 4. On the other hand for Acid Black 1 it was only 25 (mg g(-1)). Batch kinetics studies were undertaken and the data evaluated in compliance with chemical sorption mechanisms. For all of the systems studied the pseudo-second order model provided the best correlation of the kinetic experimental data. A film-pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, Deff, for the adsorption of basic dyes in to peat.

  10. Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates

    Hippler, Dorothee; Buhl, Dieter; Witbaard, Rob; Richter, Detlev K.; Immenhauser, Adrian


    This study presents magnesium stable-isotope compositions of various biogenic carbonates of several marine calcifying organisms and an algae species, seawater samples collected from the western Dutch Wadden Sea, and reference materials. The aim of this study is to explore the influence of mineralogy, taxonomy and environmental factors (e.g., seawater isotopic composition, temperature, salinity) on magnesium-isotopic (δ 26Mg) ratios of skeletal carbonates. Using high-precision multi-collector inductively coupled plasma mass spectrometry, we observed that the magnesium-isotopic composition of seawater from the semi-enclosed Dutch Wadden Sea is identical to that of open marine seawater. We further found that a considerable component of the observed variability in δ 26Mg values of marine skeletal carbonates can be attributed to differences in mineralogy. Furthermore, magnesium-isotope fractionation is species-dependent, with all skeletal carbonates being isotopically lighter than seawater. While δ 26Mg values of skeletal aragonite and high-magnesium calcite of coralline red algae indicate the absence or negligibility of metabolic influences, the δ 26Mg values of echinoids, brachiopods and bivalves likely result from a taxon-specific level of control on Mg-isotope incorporation during biocalcification. Moreover, no resolvable salinity and temperature effect were observed for coralline red algae and echinoids. In contrast, Mg-isotope data of bivalves yield ambiguous results, which require further validation. The data presented here, point to a limited use of Mg isotopes as temperature proxy, but highlight the method's potential as tracer of seawater chemistry through Earth's history.

  11. Modelling oxygen isotopes in the University of Victoria Earth System Climate Model

    C. E. Brennan


    Full Text Available Implementing oxygen isotopes (H218O, H216O in coupled climate models provides both an important test of the individual model's hydrological cycle, and a powerful tool to mechanistically explore past climate changes while producing results directly comparable to isotope proxy records. Here we describe the addition of oxygen isotopes in the University of Victoria Earth System Climate Model (UVic ESCM. Equilibrium simulations are performed for preindustrial and Last Glacial Maximum conditions. The oxygen isotope content in the model preindustrial climate is compared against observations for precipitation and seawater. The distribution of oxygen isotopes during the LGM is compared against available paleo-reconstructions.

  12. Stable isotopes of transition and post-transition metals as tracers in environmental studies

    Bullen, Tomas D.; Baskaran, Mark


    The transition and post-transition metals, which include the elements in Groups 3–12 of the Periodic Table, have a broad range of geological and biological roles as well as industrial applications and thus are widespread in the environment. Interdisciplinary research over the past decade has resulted in a broad understanding of the isotope systematics of this important group of elements and revealed largely unexpected variability in isotope composition for natural materials. Significant kinetic and equilibrium isotope fractionation has been observed for redox sensitive metals such as iron, chromium, copper, molybdenum and mercury, and for metals that are not redox sensitive in nature such as cadmium and zinc. In the environmental sciences, the isotopes are increasingly being used to understand important issues such as tracing of metal contaminant sources and fates, unraveling metal redox cycles, deciphering metal nutrient pathways and cycles, and developing isotope biosignatures that can indicate the role of biological activity in ancient and modern planetary systems.

  13. Stochastic approach to equilibrium and nonequilibrium thermodynamics.

    Tomé, Tânia; de Oliveira, Mário J


    We develop the stochastic approach to thermodynamics based on stochastic dynamics, which can be discrete (master equation) and continuous (Fokker-Planck equation), and on two assumptions concerning entropy. The first is the definition of entropy itself and the second the definition of entropy production rate, which is non-negative and vanishes in thermodynamic equilibrium. Based on these assumptions, we study interacting systems with many degrees of freedom in equilibrium or out of thermodynamic equilibrium and how the macroscopic laws are derived from the stochastic dynamics. These studies include the quasiequilibrium processes; the convexity of the equilibrium surface; the monotonic time behavior of thermodynamic potentials, including entropy; the bilinear form of the entropy production rate; the Onsager coefficients and reciprocal relations; and the nonequilibrium steady states of chemical reactions.

  14. Effect of Ultrasound on Desorption Equilibrium

    秦炜; 原永辉; 戴猷元


    Effects of ultrasound on intensification of separation process were investigated through the experiment of desorption equilibrium behavior. Tri-butyl phosphate (TBP) on NKA-X resin and phenol on a solvent impregnated resin, CL-TBP resin, were used for desorption processes. The desorption rate was measured with and without ultrasound. Desorption equilibrium was studied under various ultrasonic power densities or thermal infusion. Results showed that the desorption rate with ultrasound was much higher than that with normal thermal infusion. Both ultrasound and thermal infusion broke the desorption equilibrium existed at room temperature. However, after the systems were cooled down, the amount of solute desorbed in the liquid phase in the presence of ultrasound was much higher than that at the temperature corresponding to the same ultrasound power. It is proved that the initial desorption equilibrium was broken as a result of the spot energy effect of ultrasound.

  15. Equilibrium Analysis for Anycast in WDM Networks

    唐矛宁; 王汉兴


    In this paper, the wavelength-routed WDM network, was analyzed for the dynamic case where the arrival of anycast requests was modeled by a state-dependent Poisson process. The equilibrium analysis was also given with the UWNC algorithm.



    The author studies semilinear parabolic equations with initial and periodic boundary value conditions. In the presence of non-well-ordered sub- and super-solutions:"subsolution (≤) supersolution", the existence and stability/instability of equilibrium solutions are obtained.

  17. A comprehensive metabolic profile of cultured astrocytes using isotopic transient metabolic flux analysis and 13C-labeled glucose

    Ana I Amaral


    Full Text Available Metabolic models have been used to elucidate important aspects of brain metabolism in recent years. This work applies for the first time the concept of isotopic transient 13C metabolic flux analysis (MFA to estimate intracellular fluxes of cultured astrocytes. This methodology comprehensively explores the information provided by 13C labeling time-courses of intracellular metabolites after administration of a 13C labeled substrate. Cells were incubated with medium containing [1-13C]glucose for 24 h and samples of cell supernatant and extracts collected at different time-points were then analyzed by mass spectrometry and/or HPLC. Metabolic fluxes were estimated by fitting a carbon labeling network model to isotopomer profiles experimentally determined. Both the fast isotopic equilibrium of glycolytic metabolite pools and the slow labeling dynamics of TCA cycle intermediates are described well by the model. The large pools of glutamate and aspartate which are linked to the TCA cycle via reversible aminotransferase reactions are likely to be responsible for the observed delay in equilibration of TCA cycle intermediates. Furthermore, it was estimated that 11% of the glucose taken up by astrocytes was diverted to the pentose phosphate pathway. In addition, considerable fluxes through pyruvate carboxylase (PC (PC/pyruvate dehydrogenase (PDH ratio = 0.5, malic enzyme (5% of the total pyruvate production and catabolism of branched-chained amino acids (contributing with ~40% to total acetyl-CoA produced confirmed the significance of these pathways to astrocytic metabolism. Consistent with the need of maintaining cytosolic redox potential, the fluxes through the malate-aspartate shuttle and the PDH pathway were comparable. Finally, the estimated glutamate/α-ketoglutarate exchange rate (~0.7 µ prot-1.h-1 was similar to the TCA cycle flux. In conclusion, this work demonstrates the potential of isotopic transient MFA for a comprehensive analysis of

  18. Isotopic and chemical analyses of a temperate firn core from a Chinese alpine glacier and its regional climatic significance


    Mt. Yulong is the southernmost currently glacier-covered area in Eurasia, including China. There are 19 sub-tropical temperate glaciers on the mountain, controlled by the south-western monsoon climate. In the summer of 1999, a firn core, 10. 10 m long, extending down to glacier ice, was recovered in the accumulation area of the largest glacier, Baishui No. 1. Periodic variations of climatic signals above 7. 8 m depth were apparent, and net accumulation of four years was identified by the annual oscillations of isotopic and ionic composition. The boundaries of annual accumulation were confirmed by higher values of electrical conductivity and pH, and by dirty refreezing ice layers at the levels of summer surfaces. Calculated mean annual net accumulation from 1994/1995 to 1997/1998 was about 900 mm water equivalent. The amplitude of isotopic variations in the profile decreased with increasing depth, and isotopic homogenization occurred below 7. 8 m as a result of meltwater percolation. Variations of δ18O above 7. 8 m showed an approximate correlation with the winter climatic trend at Li Jiang Station, 25 km away. Concentrations of Ca2+ and Mg2+ were much higher than those of Na+ and K+ , indicating that the air masses for precipitation were mainly from a continental source, and that the core material accumulated during the winter period. The close correspondence of C1- and Na+ indicated their common origin. Very low concentrations of SO2-4 and NO3- suggest that pollution caused by human activities is quite low in the area. The mean annual net accumulation in the core and the estimated ablation indicate that the average annual precipitation above the glacier's equilibrium line is 2400 - 3150 mm, but this needs to be confirmed by long term observation of mass balance.

  19. Two Proton Knockout from ^32Mg

    Fallon, P.; Rodriguez-Vieitez, E.; Macchiavelli, A. O.; Clark, R. M.; Lee, I.-Y.; Wiedeking, M.; Gade, A.; Adrich, P.; Bazin, D.; Bowen, M.; Campbell, C. M.; Cook, J. M.; Dinca, D. C.; Glasmacher, T.; McDaniel, S.; Mueller, W. F.; Ratiewicz, A. F.; Siwek, K.; Terry, J. R.; Wiesshaar, D.; Yoneda, K.; Brown, B. A.; Otsuka, T.; Tostevin, J. A.; Utsuno, Y.


    We present data and calculations on the near-dripline nucleus ^30Ne. Gamma-ray decays from excited states as well as inclusive and exclusive cross-sections were measured in the ^9Be(^32Mg,^30Ne γ)X two-proton knockout reaction at incident beam energies of 99.7 and 86.7 MeV/A. The measured inclusive cross section sigma = 0.22(4)mb is suppressed compared to calculation and is indicative of a reduced overlap of initial and final state wavefunctions. We interpret this reduction as a result of large 4p4h intruder components present in ^30Ne, but not ^32Mg. Large 4p4h amplitudes are predicted to generate increased T=1 paring strengths and to help stabilize the heavier fluorine isotopes against neutron decay. A new gamma-ray transition at 1443 keV is assigned to the decay of the 4^+ state based on the spin dependent sigma for 2 proton knockout from the (d5/2)^4 configuration.

  20. The cycle of stable isotopes and tritium in water

    Hunziker, J.C. [Inst. de Mineralogie, Lausanne (Switzerland)


    In hydrology, meteorology, climatology and environmental research natural hydrogen and oxygen isotopes of water increasingly replace radioactive or chemical tracers used in the past to track fluid paths through nature. This evolution has made possible through the network of precipitation data established since 1961 by the International Atomic Energy Agency (IAEA) in Vienna, that provides the necessary data base for the stable isotope interpretations. Evaporation and condensation and, at higher temperatures, water-rock interaction are the main mechanisms responsible for changing the isotopic ratio of water. These data provide insight into mean residence time of a water body and/or mean altitude of a catchment area. They also yield climatological information and allow the mass transfer quantification because of the temperature dependence of equilibrium fractionation. As the acquired isotopic ratio of a water is generally conserved during flow and percolation through geologic bodies, admixing of water showing different histories can easily be monitored, and when the end members are known or can be measured, mixtures can be calculated. Including isotopic measurements of certain anions, often dissolved in remarkable quantities in groundwaters e.g. nitrates, sulfates or phosphates, increases the reliability and the possibility to trace fluid paths through geologic bodies. In addition in environmental studies, oxygen, nitrogen and sulfur isotopes allow for source determination studies, again providing a possibility of quantification, which can not be obtained by any other method. Recent advances in the specific determination of organic molecules by means of GC-IRMS (gas-chromatography-isotope ratio mass spectrometry) has considerably enlarged our possibilities in detection and quantification of organic water pollution. These organic compounds (debris of macromolecules) increasingly deteriorate the quality of our drinking water; unfortunately they are normally not

  1. Thermodynamics and fluctuations far from equilibrium

    Ross, John


    This book deals with the formulation of the thermodynamics of chemical and other systems far from equilibrium, including connections to fluctuations. It contains applications to non-equilibrium stationary states and approaches to such states, systems with multiple stationary states, stability and equi-stability conditions, reaction diffusion systems, transport properties, and electrochemical systems. The theoretical treatment is complemented by experimental results to substantiate the formulation. Dissipation and efficiency are analyzed in autonomous and externally forced reactions, including several biochemical systems.

  2. Equilibrium fluctuation energy of gyrokinetic plasma

    Krommes, J.A.; Lee, W.W.; Oberman, C.


    The thermal equilibrium electric field fluctuation energy of the gyrokinetic model of magnetized plasma is computed, and found to be smaller than the well-known result (k)/8..pi.. = 1/2T/(1 + (klambda/sub D/)/sup 2/) valid for arbitrarily magnetized plasmas. It is shown that, in a certain sense, the equilibrium electric field energy is minimum in the gyrokinetic regime. 13 refs., 2 figs.

  3. Information equilibrium as an economic principle


    A general information equilibrium model in the case of ideal information transfer is defined and then used to derive the relationship between supply (information destination) and demand (information source) with the price as the detector of information exchange between demand and supply. We recover the properties of the traditional economic supply-demand diagram. Information equilibrium is then applied to macroeconomic problems, recovering some common macroeconomic models in particular limits...

  4. The Theory of Variances in Equilibrium Reconstruction

    Zakharov, Leonid E.; Lewandowski, Jerome; Foley, Elizabeth L.; Levinton, Fred M.; Yuh, Howard Y.; Drozdov, Vladimir; McDonald, Darren


    The theory of variances of equilibrium reconstruction is presented. It complements existing practices with information regarding what kind of plasma profiles can be reconstructed, how accurately, and what remains beyond the abilities of diagnostic systems. The σ-curves, introduced by the present theory, give a quantitative assessment of quality of effectiveness of diagnostic systems in constraining equilibrium reconstructions. The theory also suggests a method for aligning the accuracy of measurements of different physical nature.


    Ervik, Inger Sommerfelt; Soegaard, Christian


    Conventional economic theory stipulates that output in Cournot competition is too low relative to that which is attained in perfect competition. We revisit this result in a General Cournot-competitive Equilibrium model with two industries that di er only in terms of productivity. We show that in general equilibrium, the more ecient industry produces too little and the less ecient industry produces too much compared to an optimal scenario with perfect competition.

  6. Isotope and multiband effects in layered superconductors.

    Bussmann-Holder, Annette; Keller, Hugo


    In this review we consider three classes of superconductors, namely cuprate superconductors, MgB(2) and the new Fe based superconductors. All of these three systems are layered materials and multiband compounds. Their pairing mechanisms are under discussion with the exception of MgB(2), which is widely accepted to be a 'conventional' electron-phonon interaction mediated superconductor, but extending the Bardeen-Cooper-Schrieffer (BCS) theory to account for multiband effects. Cuprates and Fe based superconductors have higher superconducting transition temperatures and more complex structures. Superconductivity is doping dependent in these material classes unlike in MgB(2) which, as a pure compound, has the highest values of T(c) and a rapid suppression of superconductivity with doping takes place. In all three material classes isotope effects have been observed, including exotic ones in the cuprates, and controversial ones in the Fe based materials. Before the area of high-temperature superconductivity, isotope effects on T(c) were the signature for phonon mediated superconductivity-even when deviations from the BCS value to smaller values were observed. Since the discovery of high T(c) materials this is no longer evident since competing mechanisms might exist and other mediating pairing interactions are discussed which are of purely electronic origin. In this work we will compare the three different material classes and especially discuss the experimentally observed isotope effects of all three systems and present a rather general analysis of them. Furthermore, we will concentrate on multiband signatures which are not generally accepted in cuprates even though they are manifest in various experiments, the evidence for those in MgB(2), and indications for them in the Fe based compounds. Mostly we will consider experimental data, but when possible also discuss theoretical models which are suited to explain the data.

  7. Isotope analytics for the evaluation of the feeding influence on the isotope ratio in beef samples; Isotopenanalytik zur Bestimmung des Einflusses der Ernaehrung auf die Isotopenzusammensetzung in Rinderproben

    Herwig, Nadine


    Information about the origin of food and associated production systems has a high significance for food control. An extremely promising approach to obtain such information is the determination of isotope ratios of different elements. In this study the correlation of the isotope ratios C-13/C-12, N-15/N-14, Mg-25/Mg-24, and Sr-87/Sr-86 in bovine samples (milk and urine) and the corresponding isotope ratios in feed was investigated. It was shown that in the bovine samples all four isotope ratios correlate with the isotope composition of the feed. The isotope ratios of strontium and magnesium have the advantage that they directly reflect the isotope ratios of the ingested feed since there is no isotope fractionation in the bovine organism which is in contrast to the case of carbon and nitrogen isotope ratios. From the present feeding study it is evident, that a feed change leads to a significant change in the delta C-13 values in milk and urine within 10 days already. For the deltaN-15 values the feed change was only visible in the bovine urine after 49 days. Investigations of cows from two different regions (Berlin/Germany and Goestling/Austria) kept at different feeding regimes revealed no differences in the N-15/N-14 and Mg-26/Mg-24 isotope ratios. The strongest correlation between the isotope ratio of the bovine samples and the kind of ingested feed was observed for the carbon isotope ratio. With this ratio even smallest differences in the feed composition were traceable in the bovine samples. Since different regions usually coincide with different feeding regimes, carbon isotope ratios can be used to distinguish bovine samples from different regions if the delta C-13 values of the ingested feed are different. Furthermore, the determination of strontium isotope ratios revealed significant differences between bovine and feed samples of Berlin and Goestling due to the different geologic realities. Hence the carbon and strontium isotope ratios allow the best

  8. An analytical model of crater count equilibrium

    Hirabayashi, Masatoshi; Minton, David A.; Fassett, Caleb I.


    Crater count equilibrium occurs when new craters form at the same rate that old craters are erased, such that the total number of observable impacts remains constant. Despite substantial efforts to understand this process, there remain many unsolved problems. Here, we propose an analytical model that describes how a heavily cratered surface reaches a state of crater count equilibrium. The proposed model formulates three physical processes contributing to crater count equilibrium: cookie-cutting (simple, geometric overlap), ejecta-blanketing, and sandblasting (diffusive erosion). These three processes are modeled using a degradation parameter that describes the efficiency for a new crater to erase old craters. The flexibility of our newly developed model allows us to represent the processes that underlie crater count equilibrium problems. The results show that when the slope of the production function is steeper than that of the equilibrium state, the power law of the equilibrium slope is independent of that of the production function slope. We apply our model to the cratering conditions in the Sinus Medii region and at the Apollo 15 landing site on the Moon and demonstrate that a consistent degradation parameterization can successfully be determined based on the empirical results of these regions. Further developments of this model will enable us to better understand the surface evolution of airless bodies due to impact bombardment.

  9. Modelling and interpreting the isotopic composition of water vapour in convective updrafts

    M. Bolot


    Full Text Available The isotopic compositions of water vapour and its condensates have long been used as tracers of the global hydrological cycle, but may also be useful for understanding processes within individual convective clouds. We review here the representation of processes that alter water isotopic compositions during processing of air in convective updrafts and present a unified model for water vapour isotopic evolution within undiluted deep convective cores, with a special focus on the out-of-equilibrium conditions of mixed-phase zones where metastable liquid water and ice coexist. We use our model to show that a combination of water isotopologue measurements can constrain critical convective parameters, including degree of supersaturation, supercooled water content and glaciation temperature. Important isotopic processes in updrafts include kinetic effects that are a consequence of diffusive growth or decay of cloud particles within a supersaturated or subsaturated environment; isotopic re-equilibration between vapour and supercooled droplets, which buffers isotopic distillation; and differing mechanisms of glaciation (droplet freezing vs. the Wegener–Bergeron–Findeisen process. As all of these processes are related to updraft strength, particle size distribution and the retention of supercooled water, isotopic measurements can serve as a probe of in-cloud conditions of importance to convective processes. We study the sensitivity of the profile of water vapour isotopic composition to differing model assumptions and show how measurements of isotopic composition at cloud base and cloud top alone may be sufficient to retrieve key cloud parameters.

  10. Stable isotopes of authigenic minerals in variably-saturated fractured tuff

    Weber, D.S.; Evans, D.D.


    Identifying stable isotope variation and mineralogical changes in fractured rock may help establish the history of climatic and geomorphological processes that might affect the isolation properties of a waste repository site. This study examines the use of the stable isotope ratios of oxygen ({sup 18}O/{sup 16}O) and carbon ({sup 13}C/{sup 12}C) in authigenic minerals as hydrogeochemical tools tracing low-temperature rock-water interaction in variably-saturated fractured stuff. Isotopic compositions of fracture-filling and rock matrix minerals in the Apache Leap tuff, near Superior, Arizona were concordant with geothermal temperatures and in equilibrium with water isotopically similar to present-day meteoric water and groundwater. Oxygen and carbon isotope ratios of fracture-filling, in unsaturated fractured tuff, displayed an isotopic gradient believed to result from near-surface isotopic enrichment due to evaporation rather than the effects of rock-water interaction. Oxygen isotope ratios of rock matrix opal samples exhibited an isotopic gradient believed to result from, leaching and reprecipitation of silica at depth. Methods and results can be used to further define primary flowpaths and the movement of water in variably-saturated fractured rock. 71 refs., 23 figs., 3 tabs.

  11. Oxygen isotopes as a tracer of phosphate sources and cycling in aquatic systems (Invited)

    Young, M. B.; Kendall, C.; Paytan, A.


    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

  12. Comparison of rizatriptan 5 mg and 10 mg tablets and sumatriptan 25 mg and 50 mg tablets.

    Kolodny, A; Polis, A; Battisti, W P; Johnson-Pratt, L; Skobieranda, F


    This randomized, double-blind, two-attack, placebo-controlled, crossover study explored the efficacy and tolerability of rizatriptan 10 mg compared with sumatriptan 50 mg as well as rizatriptan 5 mg compared with sumatriptan 25 mg in the acute treatment of migraine. Following randomization to one of six possible treatment sequences, patients (n = 1447) treated two sequential attacks, of moderate or severe intensity, separated by at least 5 days. Patients assessed pain severity, migraine-associated symptoms, and functional disability at 0.5, 1, 1.5, and 2 h post treatment. Compared with placebo, all treatments were effective. On the primary endpoint of time to pain relief, rizatriptan 10 mg was not statistically different from sumatriptan 50 mg [odds ratio (OR) 1.10, P = 0.161], and rizatriptan 5 mg was statistically superior to sumatriptan 25 mg (OR 1.22, P = 0.007). In general, rizatriptan 10 mg and 5 mg treatment resulted in improvement compared with the corresponding doses of sumatriptan on measures of pain severity, migraine symptoms, and functional disability and the 5-mg dose reached statistical significance on almost all measures. All treatments were generally well tolerated.

  13. Thermodynamic assessment of the Mg-Pb and Mg-Bi systems using substitutional solution and associate models for the liquid phase

    Zhang F.


    Full Text Available By means of CALPHAD approach, thermodynamic assessments of the Mg-Pb and Mg-Bi systems were carried out based on the available experimental data including thermodynamic properties and phase equilibrium data. The liquid phase was described with both the substitutional solution model and the associate model, and two sets of self-consistent thermodynamic parameters for the Mg-Pb and Mg-Bi systems were obtained, respectively. It was found that the associate model can account for the experimental data more satisfactorily than the substitutional solution one, especially for the liquid phase with the short-range order behavior.

  14. Metal stable isotope signatures as tracers in environmental geochemistry.

    Wiederhold, Jan G


    The biogeochemical cycling of metals in natural systems is often accompanied by stable isotope fractionation which can now be measured due to recent analytical advances. In consequence, a new research field has emerged over the last two decades, complementing the traditional stable isotope systems (H, C, O, N, S) with many more elements across the periodic table (Li, B, Mg, Si, Cl, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ge, Se, Br, Sr, Mo, Ag, Cd, Sn, Sb, Te, Ba, W, Pt, Hg, Tl, U) which are being explored and potentially applicable as novel geochemical tracers. This review presents the application of metal stable isotopes as source and process tracers in environmental studies, in particular by using mixing and Rayleigh model approaches. The most important concepts of mass-dependent and mass-independent metal stable isotope fractionation are introduced, and the extent of natural isotopic variations for different elements is compared. A particular focus lies on a discussion of processes (redox transformations, complexation, sorption, precipitation, dissolution, evaporation, diffusion, biological cycling) which are able to induce metal stable isotope fractionation in environmental systems. Additionally, the usefulness and limitations of metal stable isotope signatures as tracers in environmental geochemistry are discussed and future perspectives presented.

  15. Growth of high Mg content wurtzite MgZnO epitaxial films via pulsed metal organic chemical vapor deposition

    Alema, Fikadu; Ledyaev, Oleg; Miller, Ross; Beletsky, Valeria; Osinsky, Andrei; Schoenfeld, Winston V.


    We report on the growth of high Mg content, high quality, wurtzite MgxZn1-xO (MgZnO) epitaxial films using a pulsed metal organic chemical vapor deposition (PMOCVD) method. Series of MgZnO films with variable Mg concentration were deposited on bare and AlN coated sapphire substrates. The band gap of the films estimated using UV-visible transmission spectra ranges from 3.24 eV to 4.49 eV, corresponding to fraction of Mg between x=0.0 and x=0.51, as determined by Rutherford backscattering spectroscopy. The cathodoluminescence (CL) measurement has shown a blue-shift in the peak position of MgZnO with an increasing Mg content. No multi-absorption edges and CL band splitting were observed, suggesting the absence of phase segregation in the as grown films. The crystal structure and phase purity of the films were also confirmed by XRD analysis. Hall effect measurement in van der Pauw configuration was employed to evaluate the electrical properties of the films. With a rise in Mg incorporation into the ZnO lattice, the films became very resistive, consistent with the widening of the band gap. The AFM measurement on the films has shown a decreasing surface roughness with an Mg content. To the best of our knowledge, the current result shows the highest Mg content (x=0.51), high quality, wurtzite MgZnO epitaxial film ever grown by MOCVD. The high Mg incorporation without phase separation is believed to be due to the non-equilibrium behavior of the PMOCVD in which the kinetic processes dominate the thermodynamic one.

  16. Preequilibrium and statistical model calculations for neutron activation cross sections on titanium isotopes

    Ivascu, M.; Avrigeanu, M.; Avrigeanu, V.


    Calculated data are presented on (n,p), (n,n'p) and (n,2n) reaction cross sections for stable titanium isotopes in the energy range from threshold up to 20 MeV. An improved preequilibrium approach, allowing a unitary use of preequilibrium and equilibrium emission parameters, has increased the agreement between calculated and experimental cross sections.

  17. Substitution of Mn for Mg in MgB_2*

    Fitzpatrick, Michael D.; Johnston, David C.; Miller, Lance L.; Hill, Julienne M.


    The study of solid solutions in which the Mg in MgB2 is partially replaced by magnetic 3d or 4f atoms can potentially reveal important information on the superconducting state of MgB_2. As an end-member of the hypothetical Mg_1-xMn_xB2 system, MnB2 is isostructural with MgB2 and is an antiferromagnet below TN = 760 K which becomes canted at 157 K. A previous study by Moritomo et al.[1] examined the structure and properties of multi-phase samples with 0.01J. Phys. Soc. Japan b70, 1889 (2001).; “Effects of transition metal doping in MgB2 superconductor", Y. Moritomo at al. arXiv:cond-mat/0104568.

  18. Chromium and zinc uptake by algae Gelidium and agar extraction algal waste: kinetics and equilibrium.

    Vilar, Vítor J P; Botelho, Cidália M S; Boaventura, Rui A R


    Biosorption of chromium and zinc ions by an industrial algal waste, from agar extraction industry has been studied in a batch system. This biosorbent was compared with the algae Gelidium itself, which is the raw material for agar extraction, and the industrial waste immobilized with polyacrylonitrile (composite material). Langmuir and Langmuir-Freundlich equilibrium models describe well the equilibrium data. The parameters of Langmuir equilibrium model at pH 5.3 and 20 degrees C were for the algae, q(L)=18 mg Cr(III)g(-1) and 13 mgZn(II)g(-1), K(L) = 0.021l mg(-1)Cr(III) and 0.026l mg(-1) Zn(II); for the algal waste, q(L)=12 mgCr(III)g(-1) and 7mgZn(II)g(-1), K(L)=0.033lmg(-1) Cr(III) and 0.042l mg(-1) Zn(II); for the composite material, q(L) = 9 mgCr(III)g(-1) and 6 mgZn(II)g(-1), K(L)=0.032l mg(-1)Cr(III) and 0.034l mg(-1)Zn(II). The biosorbents exhibited a higher preference for Cr(III) ions and algae Gelidium is the best one. The pseudo-first-order Lagergren and pseudo-second-order models fitted well the kinetic data for the two metal ions. Kinetic constants and equilibrium uptake concentrations given by the pseudo-second-order model for an initial Cr(III) and Zn(II) concentration of approximately 100 mgl(-1), at pH 5.3 and 20 degrees C were k(2,ads)=0.04 g mg(-1)Cr(III)min(-1) and 0.07 g mg(-1)Zn(II)min(-1), q(eq)=11.9 mgCr(III)g(-1) and 9.5 mgZn(II)g(-1) for algae; k(2,ads)=0.17 g mg(-1)Cr(III)min(-1) and 0.19 g mg(-1)Zn(II)min(-1), q(eq)=8.3 mgCr(III)g(-1) and 5.6 mgZn(II)g(-1) for algal waste; k(2,ads)=0.01 g mg(-1)Cr(III)min(-1) and 0.18 g mg(-1)Zn(II)min(-1), q(eq)=8.0 mgCr(III)g(-1) and 4.4 mgZn(II)g(-1) for composite material. Biosorption was modelled using a batch adsorber mass transfer kinetic model, which successfully predicts Cr(III) and Zn(II) concentration profiles. The calculated average homogeneous diffusivities, D(h), were 4.2 x 10(-8), 8.3 x 10(-8) and 1.4 x 10(-8)cm(2)s(-1) for Cr(III) and 4.8 x 10(-8), 9.7 x 10(-8) and 6.2 x 10(-8)cm(2)s(-1

  19. Freezeouts from neutron-rich nuclear statistical equilibrium

    Meyer, B. S.


    The correlated isotopic anomalies in Ca-48, Ti-50, and Cr-54 in Ca-Al rich inclusions suggest that these isotopes were coproduced in a neutron-rich Nuclear Statistical Equilibrium (NSE) environment. Nucleosynthesis theory had already reached that conclusion, largely through the NSE calculations. The astrophysical setting for this nucleosynthesis was envisioned to be near the mass cut of a type II (core-collapse) supernova. Work on supernova theory in the past several years has shown that the conditions assumed are not appropriate for the type II mass cut environment. In particular, the densities at given temperatures in the realistic supernova models are about 10x lower than those assumed for the NSE calculations. The lower density in the realistic supernova models means that more free nucleons and alpha particles are present at the time of NSE freezeout, and capture of these light particles on heavier nuclei can substantially alter the NSE abundance pattern. Do such modifications alter the NSE pattern enough to destroy the coproduction of the neutron-rich iron-group nuclei? In order to answer this question, it is necessary to make calculations with a large nucleosynthesis network. I have performed such network calculations for material expanding from an initial density of 3.4 x 107 g/cu cm and temperature 1010 K on an expansion timescale of 0.2 s. These are fairly realistic conditions in light of the supernova models. Freezeout calculations with realistic parameters confirm co-production of the neutron-rich iron-group nuclei. Further calculations are underway to explore the sensitivity of these results to the initial density and the expansion timescale.

  20. Sorption mechanisms of arsenate on Mg-Fe layered double hydroxides: A combination of adsorption modeling and solid state analysis.

    Hudcová, Barbora; Veselská, Veronika; Filip, Jan; Číhalová, Sylva; Komárek, Michael


    Layered double hydroxides have been proposed as effective sorbents for As(V), but studies investigating adsorption mechanisms usually lack a comprehensive mechanistic/modeling approach. In this work, we propose coupling surface complexation modeling with various spectroscopic techniques. To this end, a series of batch experiments at different pH values were performed. Kinetic data were well fitted by a pseudo-second order kinetic model, and the equilibrium data were fitted by the Freundlich model. Moreover, the pH-dependent As(V) sorption data were satisfactorily fitted by a diffuse layer model, which described the formation of >SOAsO3H(-) monodentate and >(SO)2AsO2(-) bidentate inner-sphere complexes (">S" represents a crystallographically-bound group on the surface). Additionally, XPS analyses confirmed the adsorption mechanisms. The sorption mechanisms were affected by anion exchange, which was responsible for the formation of outer sphere complexes, as identified by XRD and FTIR analyses. Furthermore, a homogenous distribution of As(V) was determined by HR-TEM with elemental mapping. Using low-temperature Mössbauer spectroscopy on isotope (57)Fe, a slight shift of the hyperfine parameters towards higher values following As(V) sorption was measured, indicating a higher degree of structural disorder. In general, mechanistic adsorption modeling coupled with solid state analyses presents a powerful approach for investigating the adsorption mechanism of As(V) on Mg-Fe LDH or other sorbents.

  1. Contamination risk of stable isotope samples during milling.

    Isaac-Renton, M; Schneider, L; Treydte, K


    Isotope analysis of wood is an important tool in dendrochronology and ecophysiology. Prior to mass spectrometry analysis, wood must be homogenized, and a convenient method involves a ball mill capable of milling samples directly in sample tubes. However, sample-tube plastic can contaminate wood during milling, which could lead to biological misinterpretations. We tested possible contamination of whole wood and cellulose samples during ball-mill homogenization for carbon and oxygen isotope measurements. We used a multi-factorial design with two/three steel milling balls, two sample amounts (10 mg, 40 mg), and two milling times (5 min, 10 min). We further analyzed abrasion by milling empty tubes, and measured the isotope ratios of pure contaminants. A strong risk exists for carbon isotope bias through plastic contamination: the δ(13) C value of polypropylene deviated from the control by -6.77‰. Small fibers from PTFE filter bags used during cellulose extraction also present a risk as the δ(13) C value of this plastic deviated by -5.02‰. Low sample amounts (10 mg) showed highest contamination due to increased abrasion during milling (-1.34‰), which is further concentrated by cellulose extraction (-3.38‰). Oxygen isotope measurements were unaffected. A ball mill can be used to homogenize samples within test tubes prior to oxygen isotope analysis, but not prior to carbon or radiocarbon isotope analysis. There is still a need for a fast, simple and contamination-free sample preparation procedure. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  2. Fe isotope fractionation between chalcopyrite and dissolved Fe during hydrothermal recrystallization: An experimental study at 350 °C and 500 bars

    Syverson, Drew D.; Luhmann, Andrew J.; Tan, Chunyang; Borrok, David M.; Ding, Kang; Seyfried, William E.


    Equilibrium Fe isotope fractionation between chalcopyrite and dissolved Fe was determined in acidic chloride-bearing fluid at 350 °C and 500 bars. The study utilized deformable gold-cell technology, which allowed time-series sampling of solution during chalcopyrite recrystallization and isotope exchange. A key element of the experimental design involved the addition of anomalous dissolved 57Fe to an on-going experiment as a means of determining the degree and rate of isotope exchange. Taking explicit account of imposed chemical and isotopic mass balance constraints of Fe in fluid and mineral (chalcopyrite) reservoirs, these data indicate that no more than 1000 h is required for the isotopically anomalous dissolved Fe reservoir to exchange completely with the coexisting chalcopyrite. The experimental calibration of the rate of Fe isotope exchange for the δ57Fe-spiked experiment provides critical insight for the time necessary to achieve Fe isotope exchange in two non-spiked, but otherwise identical experiments. The Fe isotope data indicate that the equilibrium fractionation between chalcopyrite and dissolved Fe, Δ56FeCpy-Fe (aq), at 350 °C is small, 0.09 ± 0.17‰ (2σ), and is in good agreement with recent theoretical equilibrium predictions. Owing to the apparent rate of Fe isotope exchange at 350 °C, it is likely that chalcopyrite formed at high temperature deep-sea vents (black smoker systems) achieves isotopic equilibrium, and effectively records the Fe isotopic composition of the coexisting end-member hydrothermal fluid. Comparison of the experimental mineral-fluid equilibrium fractionation factors with conjugate chalcopyrite and dissolved Fe pairs sampled from high temperature hydrothermal vent systems at Axial Caldera and Main Endeavour Field (Juan de Fuca Ridge) are in agreement with this inference. The experimental data were further used to determine the mineral-mineral equilibrium Fe isotope fractionation between pyrite-chalcopyrite, Δ56Fe

  3. General Equilibrium Theory with Market Frictions. Part I. Quantity Equilibrium with Rational Expectations.


    general equilibrium model of an economy with market fritions. A market is said to have frictions if buyers and sellers have trouble finding each other, if it is costly for them to search for each other, and if it is costly to wait to buy or sell. Equilibrium is a stationary probability distribution over the set of possible time paths of states of the economy. This equilibrium reflects rational expectations if all agents know the stationary distribution of the variables they observe and if they exploit this information. Prices are fixed and are not necessarily equilibrium

  4. Kinetic control on Zn isotope signatures recorded in marine diatoms

    Köbberich, Michael; Vance, Derek


    Marine diatoms dominate the oceanic cycle of the essential micronutrient zinc (Zn). The stable isotopes of zinc and other metals are increasingly used to understand trace metal micronutrient cycling in the oceans. One clear feature of the early isotope data is the heavy Zn isotope signature of the average oceanic dissolved pool relative to the inputs, potentially driven by uptake of light isotopes into phytoplankton cells and export to sediments. However, despite the fact that diatoms strip Zn from surface waters across the Antarctic polar front in the Southern Ocean, the local upper ocean is not isotopically heavy. Here we use culturing experiments to quantify the extent of Zn isotope fractionation by diatoms and to elucidate the mechanisms driving it. We have cultured two different open-ocean diatom species (T. oceanica and Chaetoceros sp.) in a series of experiments at constant medium Zn concentration but at bioavailable medium Fe ranging from limiting to replete. We find that T. oceanica can maintain high growth rates and Zn uptake rates over the full range of bioavailable iron (Fe) investigated, and that the Zn taken up has a δ66Zn that is unfractionated relative to that of the bioavailable free Zn in the medium. The studied representative of the genus Chaetoceros, on the other hand, shows more significantly reduced Zn uptake rates at low Fe and records more variable biomass δ66Zn signatures, of up to 0.85‰ heavier than the medium. We interpret the preferential uptake of heavy isotopes at extremely low Zn uptake rates as potentially due to either of the following two mechanisms. First, the release of extracellular polymeric substances (EPS), at low Fe levels, may preferentially scavenge heavy Zn isotopes. Second, the Zn uptake rate may be slow enough to establish pseudo-equilibrium conditions at the transporter site, with heavy Zn isotopes forming more stable surface complexes. Thus we find that, in our experiments, Fe-limitation exerts a key control that

  5. Mg/Ca and δ18O in the calcite of benthic foraminifera: does size matter?

    de Nooijer, Lennart; Bijma, Jelle; -Jan Reichart, Gert; Hathorne, Ed


    Mg/Ca and del-18O are popular proxies for past sea water temperatures, ice volume and, together, salinity. The biological control that foraminifera have over calcification results in precipitation of calcium carbonate that has an isotope and element composition that is very different from those of inorganically precipitated calcium carbonates. Indications for an effect of ontogeny (i.e. size of a specimen) on the fractionation of oxygen isotopes are contradictory, while for the incorporation of most (trace) elements, data are lacking. The causes of size-based variability in element incorporation and isotope fractionation need to be understood and quantified in order to reliably use them as paleoproxies. In this study, we present Mg/Ca and oxygen isotope data from cultured specimens of the benthic foraminifer Ammonia tepida. When asexual reproduction takes place in this species, 50-300 genetically identical juveniles (i.e. clones) are produced. These juveniles are cultured at constant temperature, carbonate chemistry, salinity, etc to determine inter- and intra-specimen variability in Mg/Ca, Ba/Ca and Sr/Ca. From the same groups of clones, del-18O was determined from specimens with different sizes. Results show that the variability differs greatly between the analysed elements (e.g. relatively constant for Sr and Ba, variable for Mg) and isotopes, underscoring the need for a biological understanding of foraminiferal calcification pathways.

  6. Iron isotope systematics in planetary reservoirs

    Sossi, Paolo A.; Nebel, Oliver; Foden, John


    Iron is the only polyvalent major element, and controls reduction-oxidation (redox) reactions in a host of geologic processes and reservoirs, from the mineral- to planetary-scale, on Earth and in space. Mass transfer of Fe is often accompanied by changes in bonding environment, meaning the resultant variation in bond-strength in crystals, liquids and gases induces stable isotope fractionation, even at high temperatures. In the absence of iron exchange, electron transfer can also affect iron's valence state and calculated oxygen fugacity (fO2), however its isotope composition remains unchanged. Thus, iron isotopes are a powerful tool to investigate processes that involve mass transfer, redox reactions and changes in bonding environment in planetary systems. Primitive chondritic meteorites show remarkable isotopic homogeneity, δ57 Fe = - 0.01 ± 0.01 ‰ (2SE), over a wide range of Fe/Mg vs Ni/Mg, a proxy for fO2 in the solar nebula. In chondrites, there are iron isotope differences between metal and silicates that become more pronounced at higher metamorphic grades. However, on a planetary scale, Mars and Vesta overlap with chondrites, preserving no trace of core formation or volatile depletion on these bodies. Upon assessment of pristine lherzolites, the Bulk Silicate Earth is heavier than chondrites (δ57 Fe = + 0.05 ± 0.01 ‰; 2SE), and similar to or slightly lighter than the Moon. That the mantles of some differentiated inner solar system bodies extend to heavier compositions (+ 0.2 ‰) than chondrites may principally result from volatile depletion either at a nebular or late accretion stage. Within terrestrial silicate reservoirs, iron isotopes provide insight into petrogenetic and geodynamic processes. Partial melting of the upper mantle produces basalts that are heavier than their sources, scaling with degree of melting and driving the increasingly refractory peridotite to lighter compositions. Mid-Ocean Ridge Basalts (MORBs) are homogeneous to δ57 Fe

  7. Stable isotopes. Applications and production; Les isotopes stables. Applications - production

    Goldstein, S.; Louvet, P.; Soulie, E. [eds.


    This conference presents 46 communications concerning stable isotope production, utilization and application, grouped in 6 sessions and posters. The various themes are: biological applications (pharmacology, medical diagnosis, metabolism and protein studies, toxicity and response studies, labelled compounds), analysis procedures (NMR analysis for macromolecules, tracer studies), nuclear applications (utilization of stable isotopes in nuclear reactors), biological, physical and chemical applications (mass transfer, mobility, crystallography, isotopic exchange), stable isotope production (ion chromatography, ion cyclotron resonance, cryogenic distillation).

  8. Characterization of groundwater in the Ejina Basin,northwest China:hydrochemical and environmental isotopes approaches


    To characterize the groundwater in the Ejina Basin,surface and groundwater samples were collected in May and October of 2002.On-site analyses included temperature,electrical conductance(EC),total alkalinity(as HCO 3) by titration,and pH.Chemical analyses were undertaken at the Geochemistry Laboratory of the Cold and Arid Region Environmental and Engineering Institute,Chinese Academy of Sciences,Lanzhou,China.The pH of the groundwater ranged from 7.18 to 8.90 with an average value of 7.72,indicating an alkaline nature.The total dissolved solids(TDS) of the groundwater ranged from 567.5 to 5,954.4 mg/L with an average of 1,543.1 mg/L and a standard deviation of 1,471.8 mg/L.According to the groundwater salinity classification of Robinove et al.(1958),47.4 percent of the samples were brackish and the remainder were fresh water.The ion concentration of the groundwater along the riverbed and near the southern margin of the basin were lower than those farther away from the riverbed.The groundwater in the study area was of Na +-HCO 3 type near the bank of the Heihe River and in the southern margin of the basin,while Na +-SO 4 2-Cl type samples were observed in the terminal lake region.In the desert area the groundwater reached a TDS of 3,000-6,000 mg/L and was predominantly by a Na +-Cl chemistry.Br/Cl for the water of Ejina Basin indicates an evaporite origin for the groundwater with a strongly depleted Br/Cl ratio(average 0.000484).The surface water was slightly enriched in Br/Cl(average 0.000711) compared with groundwater.The calculated saturation index(SI) for calcite and dolomite of the groundwater samples range from 0.89 to 1.31 and 1.67 to 2.67 with averaged 0.24 and 0.61,respectively.About 97 percent of the groundwater samples were kinetically oversaturated with respect to calcite and dolomite,and all the samples were below the equilibrium state with gypsum.Using isotope and hydrochemical analyses,this study investigated the groundwater evolution and its residence

  9. Oxygen isotope fractionation between analcime and water - An experimental study

    Karlsson, Haraldur R.; Clayton, Robert N.


    The oxygen isotope fractionation between analcime and water is studied to test the feasibility of using zeolites as low-temperature thermometers. The fractionation of oxygen isotopes between natural analcime and water is determined at 300, 350, and 400 C, and at fluid pressures ranging from 1.5 to 5.0 kbar. Also, isotope ratios for the analcime framework, the channel water, and bulk water are obtained. The results suggest that the channel water is depleted in O-18 relative to bulk water by a constant value of about 5 percent, nearly independent of temperature. The analcime-water fractionation curve is presented, showing that the exchange has little effect on grain morphology and does not involve recrystallization. The exchange is faster than any other observed for a silicate. The exchange rates suggest that zeolites in active high-temperature geothermal areas are in oxygen isotopic equilibrium with ambient fluids. It is concluded that calibrated zeolites may be excellent low-temperature oxygen isotope geothermometers.

  10. Impact of hydrogen isotope species on microinstabilities in helical plasmas

    Nakata, Motoki; Nunami, Masanori; Sugama, Hideo; Watanabe, Tomo-Hiko


    The impact of isotope ion mass on ion-scale and electron-scale microinstabilities such as ion temperature gradient (ITG) mode, trapped electron mode (TEM), and electron temperature gradient (ETG) mode in helical plasmas are investigated by using gyrokinetic Vlasov simulations with a hydrogen isotope and real-mass kinetic electrons. Comprehensive scans for the equilibrium parameters and magnetic configurations clarify the transition from ITG mode to TEM instability, where a significant TEM enhancement is revealed in the case of inward-shifted plasma compared to that in the standard configuration. It is elucidated that the ion-mass dependence on the ratio of the electron-ion collision frequency to the ion transit one, i.e. {ν\\text{ei}}/{ω\\text{ti}}\\propto {{≤ft({{m}\\text{i}}/{{m}\\text{e}}\\right)}1/2} , leads to a stabilization of the TEM for heavier isotope ions. The ITG growth rate indicates a gyro-Bohm-like ion-mass dependence, where the mixing-length estimate of diffusivity yields γ /k\\bot2\\propto m\\text{i}1/2 . On the other hand, a weak isotope dependence of the ETG growth rate is identified. A collisionality scan also reveals that the TEM stabilization by the isotope ions becomes more significant for relatively higher collisionality in a banana regime.

  11. Deformation of C isotopes

    Kanada-Enyo, Y


    Systematic analysis of the deformations of proton and neutron densities in even-even C isotopes was done based on the method of antisymmetrized molecular dynamics. The $E2$ transition strength was discussed in relation to the deformation. We analyze the $B(E2;2^+_1\\to 0^+_1)$ in $^{16}$C, which has been recently measured to be abnormally small. The results suggest the difference of the deformations between proton and neutron densities in the neutron-rich C isotopes. It was found that stable proton structure in C isotopes plays an important role in the enhancement the neutron skin structure as well as in the systematics of $B(E2)$ in the neutron-rich C.

  12. Adsorption equilibrium of citric acid from supercritical carbon dioxide/ethanol on cyano column

    Huisheng L; Guoqing Wang; Minhua Zhang; Zhongfeng Geng; Miao Yang; Yanpeng Sun


    Supercritical adsorption equilibrium has a significant role in defining supercritical adsorption behavior. In this paper, the adsorption equilibrium of citric acid from supercritical CO2/ethanol on a cyano column was systemat-ical y investigated with the elution by characteristic point method. Equilibrium loading was obtained at 313.15 K and 321.15 K with supercritical CO2/ethanol densities varying from 0.7068 g·cm−3 to 0.8019 g·cm−3. The exper-imental results showed that the adsorption capacity of citric acid decreased with increasing temperature and in-creasing density of the supercritical CO2/ethanol mobile phase. The adsorption equilibrium data were fitted wel by the Quadratic Hill isotherm model and the isotherms showed anti-Langmuir behavior. The monolayer satura-tion adsorption capacity of citric acid is in the range of 44.54 mg·cm−3 to 64.66 mg·cm−3 with an average value of 56.86 mg·cm−3.

  13. Influence of liquid structure on diffusive isotope separation in molten silicates and aqueous solutions

    Watkins, James M.; DePaolo, Donald J.; Ryerson, Frederick J.; Peterson, Brook T.


    Molecular diffusion in natural volcanic liquids discriminates between isotopes of major ions (e.g., Fe, Mg, Ca, and Li). Although isotope separation by diffusion is expected on theoretical grounds, the dependence on mass is highly variable for different elements and in different media. Silicate liquid diffusion experiments using simple liquid compositions were carried out to further probe the compositional dependence of diffusive isotopic discrimination and its relationship to liquid structure. Two diffusion couples consisting of the mineral constituents anorthite (CaAl 2Si 2O 8; denoted AN), albite (NaAlSi 3O 8; denoted AB), and diopside (CaMgSi 2O 6; denoted DI) were held at 1450 °C for 2 h and then quenched to ambient pressure and temperature. Major-element as well as Ca and Mg isotope profiles were measured on the recovered quenched glasses. In both experiments, Ca diffuses rapidly with respect to Si. In the AB-AN experiment, D Ca/ D Si ≈ 20 and the efficiency of isotope separation for Ca is much greater than in natural liquid experiments where D Ca/ D Si ≈ 1. In the AB-DI experiment, D Ca/ D Si ≈ 6 and the efficiency of isotope separation is between that of the natural liquid experiments and the AB-AN experiment. In the AB-DI experiment, D Mg/ D Si ≈ 1 and the efficiency of isotope separation for Mg is smaller than it is for Ca yet similar to that observed for Mg in natural liquids. The results from the experiments reported here, in combination with results from natural volcanic liquids, show clearly that the efficiency of diffusive separation of Ca isotopes is systematically related to the solvent-normalized diffusivity - the ratio of the diffusivity of the cation ( D Ca) to the diffusivity of silicon ( D Si). The results on Ca isotopes are consistent with available data on Fe, Li, and Mg isotopes in silicate liquids, when considered in terms of the parameter D cation/ D Si. Cations diffusing in aqueous solutions display a similar relationship

  14. Diffusion-driven magnesium and iron isotope fractionation in Hawaiian olivine

    Teng, F.-Z.; Dauphas, N.; Helz, R.T.; Gao, S.; Huang, S.


    Diffusion plays an important role in Earth sciences to estimate the timescales of geological processes such as erosion, sediment burial, and magma cooling. In igneous systems, these diffusive processes are recorded in the form of crystal zoning. However, meaningful interpretation of these signatures is often hampered by the fact that they cannot be unambiguously ascribed to a single process (e.g., magmatic fractionation, diffusion limited transport in the crystal or in the liquid). Here we show that Mg and Fe isotope fractionations in olivine crystals can be used to trace diffusive processes in magmatic systems. Over sixty olivine fragments from Hawaiian basalts show isotopically fractionated Mg and Fe relative to basalts worldwide, with up to 0.4??? variation in 26Mg/24Mg ratios and 1.6??? variation in 56Fe/54Fe ratios. The linearly and negatively correlated Mg and Fe isotopic compositions [i.e., ??56Fe=(??3.3??0.3)????26Mg], co-variations of Mg and Fe isotopic compositions with Fe/Mg ratios of olivine fragments, and modeling results based on Mg and Fe elemental profiles demonstrate the coupled Mg and Fe isotope fractionation to be a manifestation of Mg-Fe inter-diffusion in zoned olivines during magmatic differentiation. This characteristic can be used to constrain the nature of mineral zoning in igneous and metamorphic rocks, and hence determine the residence times of crystals in magmas, the composition of primary melts, and the duration of metamorphic events. With improvements in methodology, in situ isotope mapping will become an essential tool of petrology to identify diffusion in crystals. ?? 2011 Elsevier B.V.

  15. Isotopes in Condensed Matter

    G Plekhanov, Vladimir


    This book provides a concise introduction to the newly created sub-discipline of solid state physics isotopetronics. The role of isotopes in materials and their properties are describe  in this book. The problem of the enigma of the atomic mass in microphysics is briefly discussed.  The range of the applications of isotopes is wide: from biochemical process in living organisms to modern technical applications in quantum information. Isotopetronics promises to improve nanoelectronic and optoelectronic devices. With numerous illustrations this book is useful to researchers, engineers and graduate students.

  16. Atomic Weights and Isotopic Compositions

    SRD 144 Atomic Weights and Isotopic Compositions (Web, free access)   The atomic weights are available for elements 1 through 111, and isotopic compositions or abundances are given when appropriate.

  17. The Application of Methane Clumped Isotope Measurements to Determine the Source of Large Methane Seeps in Alaskan Lakes

    Douglas, P. M.; Stolper, D. A.; Eiler, J. M.; Sessions, A. L.; Walter Anthony, K. M.


    Natural methane emissions from the Arctic present an important potential feedback to global warming. Arctic methane emissions may come from either active microbial sources or from deep fossil reservoirs released by the thawing of permafrost and melting of glaciers. It is often difficult to distinguish between and quantify contributions from these methane sources based on stable isotope data. Analyses of methane clumped isotopes (isotopologues with two or more rare isotopes such as 13CH3D) can complement traditional stable isotope-based classifications of methane sources. This is because clumped isotope abundances (for isotopically equilibrated systems) are a function of temperature and can be used to identify pathways of methane generation. Additionally, distinctive effects of mixing on clumped isotope abundances make this analysis valuable for determining the origins of mixed gasses. We find large variability in clumped isotope compositions of methane from seeps in several lakes, including thermokarst lakes, across Alaska. At Lake Sukok in northern Alaska we observe the emission of dominantly thermogenic methane, with a formation temperature of at least 100° C. At several other lakes we find evidence for mixing between thermogenic methane and biogenic methane that forms in low-temperature isotopic equilibrium. For example, at Eyak Lake in southeastern Alaska, analysis of three methane samples results in a distinctive isotopic mixing line between a high-temperature end-member that formed between 100-170° C, and a biogenic end-member that formed in isotopic equilibrium between 0-20° C. In this respect, biogenic methane in these lakes resembles observations from marine gas seeps, oil degradation, and sub-surface aquifers. Interestingly, at Goldstream Lake in interior Alaska, methane with strongly depleted clumped-isotope abundances, indicative of disequilibrium gas formation, is found, similar to observations from methanogen culture experiments.

  18. Bringing organic carbon isotopes and phytoliths to the table as additional constraints on paleoelevation

    Sheldon, N. D.; Cotton, J. M.; Hren, M. T.; Hyland, E. G.; Smith, S. Y.; Strömberg, C. A. E.


    A commonly used tool in paleotectonic and paleoaltimetry studies is the oxygen isotopic composition of authigenic carbonates formed that formed in lakes or soils, with both spatial (e.g., shoreline to mountain top) or temporally resolved records potentially providing constraints. However, in many cases there is a substantial spread in the oxygen isotope data for a given time period, often to the point of allowing for essentially any interpretation of the data depending upon how they have been used by the investigator. One potential way of distinguishing between different potential paleotectonic or paleoaltimetric interpretations is to use carbon isotope and plant microfossil (phytolith) analyses from the same paleosols to screen the oxygen isotope data by looking for evidence of evaporative enrichment. For example, if both inorganic (carbonate) and organic carbon isotopes are measured from the same paleosol, then in it possible to determine if the two isotope record equilibrium conditions or if they record disequilibrium driven by kinetic effects. In the former case, the oxygen isotope results can be considered reliable whereas in the latter case, the oxygen isotope results can be considered unreliable and could be culled from the interpretation. Similarly, because the distribution of C4 plants varies as a function of temperature and elevation, the presence/absence or abundance of C4 plant phytoliths, or of carbon isotope compositions that require a component of C4 vegetation can also be used to constrain paleoelevation by providing a maximum elevation constraint. Worked examples will include the late Miocene-Pliocene of Catamarca, Argentina, where phytoliths and organic carbon isotopes provide a maximum elevation constraint and can be used to demonstrate that oxygen isotopes do not provide a locally useful constraint on paleoelevation, and Eocene-Miocene of southwestern Montana where organic matter and phytoliths can be used to select between different potential

  19. Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

    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


    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

  20. Non-Equilibrium Transitions of Heliospheric plasma

    Livadiotis, G.; McComas, D. J.


    Recent advances in Space Physics theory have established the connection between non-extensive Statistical Mechanics and space plasmas by providing a theoretical basis for the empirically derived kappa distributions commonly used to describe the phase space distribution functions of these systems [1]. The non-equilibrium temperature and the kappa index that govern these distributions are the two independent controlling parameters of non-equilibrium systems [1-3]. The significance of the kappa index is primarily given by its role in identifying the non-equilibrium stationary states, and measuring their "thermodynamic distance" from thermal equilibrium [4], while its physical meaning is connected to the correlation between the system's particles [5]. For example, analysis of the IBEX high Energetic Neutral Atom spectra [6] showed that the vast majority of measured kappa indices are between ~1.5 and ~2.5, consistent with the far-equilibrium "cavity" of minimum entropy discovered by Livadiotis & McComas [2]. Spontaneous procedures that can increase the entropy, move the system gradually toward equilibrium, that is the state with the maximum (infinite) kappa index. Other external factors that may decrease the entropy, move the system back to states further from equilibrium where the kappa indices are smaller. Newly formed pick-up ions can play this critical role in the solar wind and other space plasmas. We have analytically shown that their highly ordered motion can reduce the average entropy in the plasma beyond the termination shock, inside the inner heliosheath [7]. Non-equilibrium transitions have a key role in understanding the governing thermodynamical processes of space plasmas. References 1. Livadiotis, G., & McComas, D. J. 2009, JGR, 114, 11105. 2. Livadiotis, G., & McComas, D. J. 2010a, ApJ, 714, 971. 3. Livadiotis, G., & McComas, D. J. 2010c, in AIP Conf. Proc. 9, Pickup Ions Throughout the Heliosphere and Beyond, ed. J. LeRoux, V. Florinski, G. P. Zank, & A

  1. Overview of Uranium Isotopic Reference Materials at IRMM

    Alonso-Munoz, A.; Richter, S.; Eykens, R.; Aregbe, Y.; Kuehn, H.; Verbruggen, A.


    For many applications in the geological sciences, in particular in geochemistry research, isotope ratio measurements play a significant role. For instance, in geochronology isotope abundances of uranium and its daughter products thorium and lead have been used since more than five decades to determine the age of various samples of geological interest. However, in order to validate mass spectrometric measurement procedures and to calibrate detector systems, suitable isotope reference materials are needed. IRMM is a well recognized provider for nuclear isotope reference materials to the nuclear industry and nuclear safeguards authorities, which can also be used for geological applications. This paper gives an overview of isotope reference materials for uranium prepared and certified at IRMM. These materials are synthetic isotope reference materials prepared based on proven methods of purifying and mixing highly enriched oxides. Firstly, a set of 10 mixtures of 233U, 235U and 238U was made in which the 235U/238U ratios were kept at 1:1 and the 233U/235U ratios varied from 1.0 to 10-6 (IRMM-072). This set is ideal for checking the linearity response of detectors used in isotope mass spectrometry. Recently, after the IRMM-072 series was exhausted, it has been replaced by the IRMM-073 and IRMM-074 series. Secondly the double spike IRMM-3636 with a 233U/236U ratio of 1:1 was prepared which allows internal mass fractionation correction for high precision 235U/238U ratio measurements. The 234U abundance of this double spike material is low enough to allow an accurate and precise correction of 234U/238U ratios, even for measurements of close to equilibrium uranium samples.

  2. Isotopic studies of Yucca Mountain soil fluids and carbonate pedogenesis

    McConnaughey, T.A.; Whelan, J.F.; Wickland, K.P.; Moscati, R.J. [Geological Survey, Denver, CO (United States)


    Secondary carbonates occurring within the soils, faults, and subsurface fractures of Yucca Mountain contain some of the best available records of paleoclimate and paleohydrology for the potential radioactive waste repository site. This article discusses conceptual and analytical advances being made with regard to the interpretation of stable isotope data from pedogenic carbonates, specifically related to the {sup 13}C content of soil CO{sub 2}, CaCO{sub 3} precipitation mechanisms, and isotopic fractionations between parent fluids and precipitating carbonates. The {sup 13}C content of soil carbon dioxide from Yucca Mountain and vicinity shows most of the usual patterns expected in such contexts: decreasing {sup 13}C content with depth (due mainly to increased importance of respired CO{sub 2}), decreasing {sup 13}C with altitude (partially due to relatively more C-3 vegetation), and reduced {sup 13}C during spring (due again to higher rates of respiration, and reduced gas permeability of wet soils). These patterns exist within the domain of a noisy data set; soil and vegetational heterogeneities, weather, and other factors apparently contribute to isotopic variability in the system. Several soil calcification mechanisms appear to be important, involving characteristic physical and chemical environments and isotopic fractionations. When CO{sub 2} loss from thin soil solutions is an important driving factor, carbonates may contain excess heavy isotopes, compared to equilibrium precipitation with soil fluids. When root calcification serves as a proton generator for plant absorption of soil nutrients, heavy isotope deficiencies are likely. Successive cycles of dissolution and reprecipitation mix and redistribute pedogenic carbonates, and tend to isotopically homogenize and equilibrate pedogenic carbonates with soil fluids.

  3. Aerospace Applications of Non-Equilibrium Plasma

    Blankson, Isaiah M.


    Nonequilibrium plasma/non-thermal plasma/cold plasmas are being used in a wide range of new applications in aeronautics, active flow control, heat transfer reduction, plasma-assisted ignition and combustion, noise suppression, and power generation. Industrial applications may be found in pollution control, materials surface treatment, and water purification. In order for these plasma processes to become practical, efficient means of ionization are necessary. A primary challenge for these applications is to create a desired non-equilibrium plasma in air by preventing the discharge from transitioning into an arc. Of particular interest is the impact on simulations and experimental data with and without detailed consideration of non-equilibrium effects, and the consequences of neglecting non-equilibrium. This presentation will provide an assessment of the presence and influence of non-equilibrium phenomena for various aerospace needs and applications. Specific examples to be considered will include the forward energy deposition of laser-induced non-equilibrium plasmoids for sonic boom mitigation, weakly ionized flows obtained from pulsed nanosecond discharges for an annular Hall type MHD generator duct for turbojet energy bypass, and fundamental mechanisms affecting the design and operation of novel plasma-assisted reactive systems in dielectric liquids (water purification, in-pipe modification of fuels, etc.).

  4. Low-temperature, non-stoichiometric oxygen isotope exchange coupled to Fe(II)-goethite interactions

    Frierdich, Andrew J. [Univ. of Wisconsin, Madison, WI (United States); Univ. of Iowa, Iowa City, IA (United States); Beard, Brian L. [Univ. of Wisconsin, Madison, WI (United States); Rosso, Kevin M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Scherer, Michelle M. [Univ. of Iowa, Iowa City, IA (United States); Spicuzza, Michael J. [Univ. of Wisconsin, Madison, WI (United States); Valley, John W. [Univ. of Wisconsin, Madison, WI (United States); Johnson, Clark M. [Univ. of Wisconsin, Madison, WI (United States)


    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

  5. Monitoring climatological, hydrological and geochemical parameters in the Père Noël cave (Belgium: implication for the interpretation of speleothem isotopic and geochemical time-series

    Verheyden Sophie


    Full Text Available Père Noël cave climatology (air and water temperature, PCO2, hydrology (drip rate, conductivity and geochemistry of water and calcite deposits (δ18O, δ13C, Mg/Ca and Sr/Ca where studied to better interpret stable isotopic and trace element variations of speleothems. Results of an automated monitoring station and of manual sampling between 1991 and 1998 have demonstrated the highly seasonal signal of drip rate, its control by water excess and rainfall, and, at a shorter scale to air pressure changes.The modern calcite deposit study suggests a relationship between cave calcite isotopic composition (δ18O and δ13C and drip rate likely due to variations in degree of isotopic equilibrium during calcite precipitation. δ18O and δ13C of the calcite are therefore, through drip rate, linked to water recharge. Mg/Ca and Sr/Ca ratios of Père Noël cave calcite, depend closely on the residence time of the water, and therefore are also linked to drip rate and therefore to water recharge. This crossed link of δ18O and δ13C as of Mg/Ca and Sr/Ca to water recharge may explain the very similar variations of these four parameters along the longitudinal axis of a Holocene stalagmite, but it may also be the consequence of kinetic effects during calcite precipitation as suggested by similar variations of the four parameters along a single layer of the Holocene stalagmite.

  6. Equilibrium chemical vapor deposition growth of Bernal-stacked bilayer graphene.

    Zhao, Pei; Kim, Sungjin; Chen, Xiao; Einarsson, Erik; Wang, Miao; Song, Yenan; Wang, Hongtao; Chiashi, Shohei; Xiang, Rong; Maruyama, Shigeo


    Using ethanol as the carbon source, self-limiting growth of AB-stacked bilayer graphene (BLG) has been achieved on Cu via an equilibrium chemical vapor deposition (CVD) process. We found that during this alcohol catalytic CVD (ACCVD) a source-gas pressure range exists to break the self-limitation of monolayer graphene on Cu, and at a certain equilibrium state it prefers to form uniform BLG with a high surface coverage of ∼94% and AB-stacking ratio of nearly 100%. More importantly, once the BLG is completed, this growth shows a self-limiting manner, and an extended ethanol flow time does not result in additional layers. We investigate the mechanism of this equilibrium BLG growth using isotopically labeled (13)C-ethanol and selective surface aryl functionalization, and results reveal that during the equilibrium ACCVD process a continuous substitution of graphene flakes occurs to the as-formed graphene and the BLG growth follows a layer-by-layer epitaxy mechanism. These phenomena are significantly in contrast to those observed for previously reported BLG growth using methane as precursor.

  7. Exploration Of Activity Measurements And Equilibrium Checks For Sediment Dating Using Thick-Window Germanium Detectors

    Warner, Jacob A.; Fitzsimmons, Kathryn E.; Reynolds, Eva M.; Gladkis, Laura G.; Timmers, Heiko


    Activity measurements on sediment samples for trapped-charge geological dating using gamma-ray spectroscopy are an important verification of the field-site dose rate determination. Furthermore gamma-ray spectroscopy can check if the natural decay series are in secular equilibrium which is a crucial assumption in such dating. Typically the activities of leading members of the Thorium and Uranium decay series are measured, which requires Germanium detectors with thin windows and good energy resolution in order to effectively detect the associated low energy gamma-rays. Such equipment is not always readily available. The potential of conventional Germanium detectors with thick entrance window has been explored towards routine gamma-ray spectroscopy of sediment samples using higher energy gamma-rays. Alternative isotopes, such as Ac-228 and Pb-212 for the Thorium series, and Pa-234m, Ra-226 and Bi-214 for the Uranium series, have been measured in order to determine the mass-specific activity for the respective series and possibly provide a check of secular equilibrium. In addition to measurements of the K-40 activity, with the alternative approach, the activities of both decay series can be accurately determined. The secular equilibrium condition may be tested for the Thorium series. Measurement accuracy for Pa-234m is, however, not sufficient to permit also a reliable check of equilibrium for the Uranium series.

  8. Silicon Isotopic Fractionation of CAI-like Vacuum Evaporation Residues

    Knight, K; Kita, N; Mendybaev, R; Richter, F; Davis, A; Valley, J


    Calcium-, aluminum-rich inclusions (CAIs) are often enriched in the heavy isotopes of magnesium and silicon relative to bulk solar system materials. It is likely that these isotopic enrichments resulted from evaporative mass loss of magnesium and silicon from early solar system condensates while they were molten during one or more high-temperature reheating events. Quantitative interpretation of these enrichments requires laboratory determinations of the evaporation kinetics and associated isotopic fractionation effects for these elements. The experimental data for the kinetics of evaporation of magnesium and silicon and the evaporative isotopic fractionation of magnesium is reasonably complete for Type B CAI liquids (Richter et al., 2002, 2007a). However, the isotopic fractionation factor for silicon evaporating from such liquids has not been as extensively studied. Here we report new ion microprobe silicon isotopic measurements of residual glass from partial evaporation of Type B CAI liquids into vacuum. The silicon isotopic fractionation is reported as a kinetic fractionation factor, {alpha}{sub Si}, corresponding to the ratio of the silicon isotopic composition of the evaporation flux to that of the residual silicate liquid. For CAI-like melts, we find that {alpha}{sub Si} = 0.98985 {+-} 0.00044 (2{sigma}) for {sup 29}Si/{sup 28}Si with no resolvable variation with temperature over the temperature range of the experiments, 1600-1900 C. This value is different from what has been reported for evaporation of liquid Mg{sub 2}SiO{sub 4} (Davis et al., 1990) and of a melt with CI chondritic proportions of the major elements (Wang et al., 2001). There appears to be some compositional control on {alpha}{sub Si}, whereas no compositional effects have been reported for {alpha}{sub Mg}. We use the values of {alpha}Si and {alpha}Mg, to calculate the chemical compositions of the unevaporated precursors of a number of isotopically fractionated CAIs from CV chondrites whose

  9. Magnesium isotopic fractionation in chondrules from the Murchison and Murray CM2 carbonaceous chondrites

    Bouvier, Audrey; Wadhwa, Meenakshi; Simon, Steven B.; Grossman, Lawrence


    We present high-precision measurements of the Mg isotopic compositions of a suite of types I and II chondrules separated from the Murchison and Murray CM2 carbonaceous chondrites. These chondrules are olivine- and pyroxene-rich and have low 27Al/24Mg ratios (0.012-0.316). The Mg isotopic compositions of Murray chondrules are on average lighter (δ26Mg ranging from -0.95‰ to -0.15‰ relative to the DSM-3 standard) than those of Murchison (δ26Mg ranging from -1.27‰ to +0.77‰). Taken together, the CM2 chondrules exhibit a narrower range of Mg isotopic compositions than those from CV and CB chondrites studied previously. The least-altered CM2 chondrules are on average lighter (average δ26Mg = -0.39 ± 0.30‰, 2SE) than the moderately to heavily altered CM2 chondrules (average δ26Mg = -0.11 ± 0.21‰, 2SE). The compositions of CM2 chondrules are consistent with isotopic fractionation toward heavy Mg being associated with the formation of secondary silicate phases on the CM2 parent body, but were also probably affected by volatilization and recondensation processes involved in their original formation. The low-Al CM2 chondrules analyzed here do not exhibit any mass-independent variations in 26Mg from the decay of 26Al, with the exception of two chondrules that show only small variations just outside of the analytical error. In the case of the chondrule with the highest Al/Mg ratio (a type IAB chondrule from Murchison), the lack of resolvable 26Mg excess suggests that it either formed >1 Ma after calcium-aluminum-rich inclusions, or that its Al-Mg isotope systematics were reset by secondary alteration processes on the CM2 chondrite parent body after the decay of 26Al.

  10. Unusually large spin polarization and magnetoresistance in a FeMg8-FeMg8 superatomic dimer

    Zhu, Lin; Qian, Meichun; Khanna, Shiv N.


    Electronic transport across a FeMg8 magnetic superatom and its dimer has been investigated using a density functional theory combined with Keldysh nonequilibrium Green's-function formalism. For a single cluster, our studies for the cluster supported in various orientations on a Au(100) surface show that the transport is sensitive to the contact geometry. Investigations covering the cases where the axes of Mg square antiprism are 45°, perpendicular, and parallel to the transport direction, show that the equilibrium conductance, transferred charge, and current polarizations can all change significantly with orientation. Our studies on the transport across a magnetic superatom dimer FeMg8-FeMg8 focus on the effect of electrode contact distance and the support. The calculated I-V curves show negative differential resistance behavior at larger electrode-cluster contact distances. Further, the equilibrium conductance in ferromagnetic state shows an unusually high spin polarization that is about 81.48% for specific contact distance, and a large magnetoresistance ratio exceeding 500% is also found. The results show that the superatom assemblies can provide unusual transport characteristics, and that the spin polarization and magnetoresistance can be controlled via the contact geometry.

  11. Discoveries of isotopes by fission

    M Thoennessen


    Of the about 3000 isotopes presently known, about 20% have been discovered in fission. The history of fission as it relates to the discovery of isotopes as well as the various reaction mechanisms leading to isotope discoveries involving fission are presented.

  12. Communication: Microphase equilibrium and assembly dynamics

    Zhuang, Yuan; Charbonneau, Patrick


    Despite many attempts, ordered equilibrium microphases have yet to be obtained in experimental colloidal suspensions. The recent computation of the equilibrium phase diagram of a microscopic, particle-based microphase former [Zhuang et al., Phys. Rev. Lett. 116, 098301 (2016)] has nonetheless found such mesoscale assemblies to be thermodynamically stable. Here, we consider their equilibrium and assembly dynamics. At intermediate densities above the order-disorder transition, we identify four different dynamical regimes and the structural changes that underlie the dynamical crossovers from one disordered regime to the next. Below the order-disorder transition, we also find that periodic lamellae are the most dynamically accessible of the periodic microphases. Our analysis thus offers a comprehensive view of the dynamics of disordered microphases and a route to the assembly of periodic microphases in a putative well-controlled, experimental system.

  13. Regret Theory and Equilibrium Asset Prices

    Jiliang Sheng


    Full Text Available Regret theory is a behavioral approach to decision making under uncertainty. In this paper we assume that there are two representative investors in a frictionless market, a representative active investor who selects his optimal portfolio based on regret theory and a representative passive investor who invests only in the benchmark portfolio. In a partial equilibrium setting, the objective of the representative active investor is modeled as minimization of the regret about final wealth relative to the benchmark portfolio. In equilibrium this optimal strategy gives rise to a behavioral asset priciting model. We show that the market beta and the benchmark beta that is related to the investor’s regret are the determinants of equilibrium asset prices. We also extend our model to a market with multibenchmark portfolios. Empirical tests using stock price data from Shanghai Stock Exchange show strong support to the asset pricing model based on regret theory.

  14. Relativistic perfect fluids in local thermal equilibrium

    Coll, Bartolomé; Sáez, Juan Antonio


    The inverse problem for conservative perfect fluid energy tensors provides a striking result. Namely that, in spite of its name, its historic origin or its usual conceptualization, the notion of {\\em local thermal equilibrium} for a perfect fluid is a {\\em purely hydrodynamic}, not thermodynamic, notion. This means that it may be thought, defined and detected using exclusively hydrodynamic quantities, without reference to temperature or any other thermodynamic concept, either of equilibrium or irreversible: a relativistic perfect fluid evolves in local thermal equilibrium if, and only if, its hydrodynamic variables evolve keeping a certain relation among them. This relation fixes, but only fixes, a precise fraction of the thermodynamics of the fluid, namely that relating the speed of its sound waves to the hydrodynamic variables. All thermodynamic schemes (sets of thermodynamic variables and their mutual relations) compatible with such a relation on the sole hydrodynamic variables are obtained. This hydrodyna...

  15. Non-equilibrium quantum heat machines

    Alicki, Robert; Gelbwaser-Klimovsky, David


    Standard heat machines (engine, heat pump, refrigerator) are composed of a system (working fluid) coupled to at least two equilibrium baths at different temperatures and periodically driven by an external device (piston or rotor) sometimes called the work reservoir. The aim of this paper is to go beyond this scheme by considering environments which are stationary but cannot be decomposed into a few baths at thermal equilibrium. Such situations are important, for example in solar cells, chemical machines in biology, various realizations of laser cooling or nanoscopic machines driven by laser radiation. We classify non-equilibrium baths depending on their thermodynamic behavior and show that the efficiency of heat machines powered by them is limited by the generalized Carnot bound.

  16. Non-Equilibrium Thermodynamics in Multiphase Flows

    Mauri, Roberto


    Non-equilibrium thermodynamics is a general framework that allows the macroscopic description of irreversible processes. This book introduces non-equilibrium thermodynamics and its applications to the rheology of multiphase flows. The subject is relevant to graduate students in chemical and mechanical engineering, physics and material science. This book is divided into two parts. The first part presents the theory of non-equilibrium thermodynamics, reviewing its essential features and showing, when possible, some applications. The second part of this book deals with how the general theory can be applied to model multiphase flows and, in particular, how to determine their constitutive relations. Each chapter contains problems at the end, the solutions of which are given at the end of the book. No prior knowledge of statistical mechanics is required; the necessary prerequisites are elements of transport phenomena and on thermodynamics. “The style of the book is mathematical, but nonetheless it remains very re...

  17. Module description of TOKAMAK equilibrium code MEUDAS

    Suzuki, Masaei; Hayashi, Nobuhiko; Matsumoto, Taro; Ozeki, Takahisa [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment


    The analysis of an axisymmetric MHD equilibrium serves as a foundation of TOKAMAK researches, such as a design of devices and theoretical research, the analysis of experiment result. For this reason, also in JAERI, an efficient MHD analysis code has been developed from start of TOKAMAK research. The free boundary equilibrium code ''MEUDAS'' which uses both the DCR method (Double-Cyclic-Reduction Method) and a Green's function can specify the pressure and the current distribution arbitrarily, and has been applied to the analysis of a broad physical subject as a code having rapidity and high precision. Also the MHD convergence calculation technique in ''MEUDAS'' has been built into various newly developed codes. This report explains in detail each module in ''MEUDAS'' for performing convergence calculation in solving the MHD equilibrium. (author)

  18. Oxygen isotope exchange in rocks and minerals from the Cerro Prieto geothermal system: Indicators of temperature distribution and fluid flow

    Williams, A. E.; Elders, W. A.


    Paleotemperatures different from the present thermal regime were studied by examining coexisting mineral systems which exchanged their oxygen with the geothermal brines at different rates. Oxygen isotopic compositions were measured in drill cuttings and core and core samples from more than 40 wells. Oxygen isotopic profiles of pore filling calcites in sandstones are a measure of the recent equilibrium temperature distribution. A three dimensional map was developed, showing the equilibrium temperatures in the geothermal field. A mass balance calculation was performed using measured 18O enrichment of the geothermal brine. This calculation implies an overall water; rock volume ratio of approximately 3:1 during the history of the Cerro Prieto system.

  19. Disturbances of ionic equilibrium in mosses of contaminated areas

    Piotr Kosiba


    Full Text Available Mosses are sensitive and precise bioindicators of heavy metals contamination of the environment. They accumulate in their tissues large amounts of these elements than do higher plants. The aim of this study was to present the influence of environmental pollution on quantitative relations of heavy metals and cationic equilibrium in tissues of mosses: Pleurozium schreberi, Hylocomium splendens and Hypnum cupressiforme. Twelve sampling sites were selected in the area of Lower Silesia (Poland, diverse in respect of pollution degree determined for dust fall and contents of metals in dust. The contents of Ca, K, Na, Mg, Al, Mn, Fe, Cu, Pb, Ni, Cd, and Zn have been examined in the mosses. Significant differences in the elements contents of mosses between the examined sites, and between moss species were found. This differentiation affects the cationic equilibrium. It is expressed by weighed sum of square roots of relative cation concentrations. The quantitative relations between contents of elements in mosses depended on species and pollution level. These relations and accumulation of metals in moss tissues is the indicator of environmental pollution, which influences the ecological condition of mosses and their occurrence in the given area. The air contaminated by heavy metals causes stress and the decline of moss populations, and can be of significance for their survival. The results of this type of investigations are of importance for the active protection of mosses and their biotopes.

  20. Beyond temperature: Clumped isotope signatures in dissolved inorganic carbon species and the influence of solution chemistry on carbonate mineral composition

    Tripati, Aradhna K.; Hill, Pamela S.; Eagle, Robert A.; Mosenfelder, Jed L.; Tang, Jianwu; Schauble, Edwin A.; Eiler, John M.; Zeebe, Richard E.; Uchikawa, Joji; Coplen, Tyler B.; Ries, Justin B.; Henry, Drew


    “Clumped-isotope” thermometry is an emerging tool to probe the temperature history of surface and subsurface environments based on measurements of the proportion of 13C and 18O isotopes bound to each other within carbonate minerals in 13C18O16O22- groups (heavy isotope “clumps”). Although most clumped isotope geothermometry implicitly presumes carbonate crystals have attained lattice equilibrium (i.e., thermodynamic equilibrium for a mineral, which is independent of solution chemistry), several factors other than temperature, including dissolved inorganic carbon (DIC) speciation may influence mineral isotopic signatures. Therefore we used a combination of approaches to understand the potential influence of different variables on the clumped isotope (and oxygen isotope) composition of minerals.We conducted witherite precipitation experiments at a single temperature and at varied pH to empirically determine 13C-18O bond ordering (Δ47) and δ18O of CO32- and HCO3- molecules at a 25 °C equilibrium. Ab initio cluster models based on density functional theory were used to predict equilibrium 13C-18O bond abundances and δ18O of different DIC species and minerals as a function of temperature. Experiments and theory indicate Δ47 and δ18O compositions of CO32- and HCO3- ions are significantly different from each other. Experiments constrain the Δ47-δ18O slope for a pH effect (0.011 ± 0.001; 12 ⩾ pH ⩾ 7). Rapidly-growing temperate corals exhibit disequilibrium mineral isotopic signatures with a Δ47-δ18O slope of 0.011 ± 0.003, consistent with a pH effect.Our theoretical calculations for carbonate minerals indicate equilibrium lattice calcite values for Δ47 and δ18O are intermediate between HCO3− and CO32−. We analyzed synthetic calcites grown at temperatures ranging from 0.5 to 50 °C with and without the enzyme carbonic anhydrase present. This enzyme catalyzes oxygen isotopic exchange between DIC species and is present in many



    <正>20090432 Zhou Shuqing (School of Energy Resources, China University of Geosciences Beijing 100083, China); Huang Haiping Stable Isotopic Records vs. Important Events in Life Evolution and the Concurrent Environment (Geological Review, ISSN0371-5736, CN11-1952, 54(2), 2008, p.225-231, 3 illus., 1 table, 77 refs.)



    <正>20141014Wang Hairan(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an710069,China);Zhao Hongge Theory and Application of Zircon U-Pb Isotope Dating Technique(Geology and Resources,ISSN1671-1947,CN21-1458/P,22(3),2013,p.229



    <正>20072750 Huang Sijing(State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China);Pei Changrong Age Calibration for the Boundary between Lower and Middle Triassic by Strontium Isotope Stratigraphy in Eastern Sichuan Province



    <正>20070454 Bao Zengkuan (Institute of High Energy Physics, CAS, Beijing 100049, China); Yuan Wanming Apatite (U-Th)/He Dating and Its Application (Acta Petrologica et Mineralogica, ISSN1000-6524, CN11-1966/P, 24(2), 2005, p.126-132, 2 illus., 25 refs.) Key words: isotopic geochronology

  5. Isotopic Implicit Surface Meshing

    Boissonnat, Jean-Daniel; Cohen-Steiner, David; Vegter, Gert


    This paper addresses the problem of piecewise linear approximation of implicit surfaces. We first give a criterion ensuring that the zero-set of a smooth function and the one of a piecewise linear approximation of it are isotopic. Then, we deduce from this criterion an implicit surface meshing algor

  6. Isotope hydrograph separation

    Fritz, P. [UFZ-Umweltforschungszentrum, Centre of Environmental Research Leipzig-Halle, Leipzig (Germany)


    Storm-runoff thus reflects the complex hydraulic behaviour of drainage basins and water-links of such systems. Water of different origin may participate in the events and in this lecture, the application of isotope techniques to separate storm hydrographs into different components will be presented.

  7. Forensic Stable Isotope Biogeochemistry

    Cerling, Thure E.; Barnette, Janet E.; Bowen, Gabriel J.; Chesson, Lesley A.; Ehleringer, James R.; Remien, Christopher H.; Shea, Patrick; Tipple, Brett J.; West, Jason B.


    Stable isotopes are being used for forensic science studies, with applications to both natural and manufactured products. In this review we discuss how scientific evidence can be used in the legal context and where the scientific progress of hypothesis revisions can be in tension with the legal expectations of widely used methods for measurements. Although this review is written in the context of US law, many of the considerations of scientific reproducibility and acceptance of relevant scientific data span other legal systems that might apply different legal principles and therefore reach different conclusions. Stable isotopes are used in legal situations for comparing samples for authenticity or evidentiary considerations, in understanding trade patterns of illegal materials, and in understanding the origins of unknown decedents. Isotope evidence is particularly useful when considered in the broad framework of physiochemical processes and in recognizing regional to global patterns found in many materials, including foods and food products, drugs, and humans. Stable isotopes considered in the larger spatial context add an important dimension to forensic science.

  8. The transformation dynamics towards equilibrium in non-equilibrium w/w/o double emulsions

    Chao, Youchuang; Mak, Sze Yi; Shum, Ho Cheung


    We use a glass-based microfluidic device to generate non-equilibrium water-in-water-in-oil (w/w/o) double emulsions and study how they transform into equilibrium configurations. The method relies on using three immiscible liquids, with two of them from the phase-separated aqueous two-phase systems. We find that the transformation is accompanied by an expansion rim, while the characteristic transformation speed of the rim mainly depends on the interfacial tension between the innermost and middle phases, as well as the viscosity of the innermost phase when the middle phase is non-viscous. Remarkably, the viscosity of the outermost phase has little effect on the transformation speed. Our results account for the dynamics of non-equilibrium double emulsions towards their equilibrium structure and suggest a possibility to utilize the non-equilibrium drops to synthesize functional particles.

  9. Retention of phosphorous ions on natural and engineered waste pumice: Characterization, equilibrium, competing ions, regeneration, kinetic, equilibrium and thermodynamic study

    Karimaian, Kamal Aldin [Department of Environmental Health Engineering, Faculty of Health, Kurdistan University of Medical Sciences, Sannandaj (Iran, Islamic Republic of); Amrane, Abdeltif [Ecole Nationale Supérieure de Chimie de Rennes, Université Rennes 1, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7 (France); Kazemian, Hossein [Department of Chemical and Biochemical Engineering, Western University, London, ON, Canada N6A 5B9 (Canada); Panahi, Reza [Department of Biotechnology, Faculty of Chemical Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Zarrabi, Mansur, E-mail: [Department of Environmental Health Engineering, Faculty of Health, Alborz University of Medical Sciences, Karaj (Iran, Islamic Republic of)


    Natural and Mg{sup 2+} modified pumice were used for the removal of phosphorous. The adsorbents were characterized using XRF, XRD, SEM and FTIR instrumental techniques. In the optimal conditions, namely at equilibrium time (30 min), for a phosphorus concentration of 15 mg/L and pH 6, 69 and 97% phosphorus removals were achieved using 10 g/L of natural and modified pumice adsorbents, respectively. Maximum adsorption capacities were 11.88 and 17.71 mg/g by natural and modified pumice, respectively. Pseudo-second order kinetic model was the most relevant to describe the kinetic of phosphorus adsorption. External mass transfer coefficient decreased for increasing phosphorous concentration and film diffusion was found to be the rate-controlling step. Only a very low dissolution of the adsorbent was observed, leading to a low increase in conductivity and turbidity. Removal efficiency decreased for increasing ionic strength. It also decreased in the presence of competing ions; however modified pumice remained effective, since 67% of phosphorus was removed, versus only 17% for the natural pumice. The efficiency of the modified pumice was confirmed during the regeneration tests, since 96% regeneration yield was obtained after 510 min experiment, while only 22% was observed for the raw pumice.

  10. Return to equilibrium in the XY model

    Hume, L.; Robinson, D.W.


    We prove that the locally perturbed XY model returns to equilibrium under the unperturbed evolution but the unperturbed model does not necessarily approach equilibrium under the perturbed evolution. In fact this latter property is false for perturbation by a local magnetization. The failure is directly attributable to the formation of bound states. If the perturbation is quadratic these problems are reduced to spectral analysis of the one-particle Hamiltonian. We demonstrate that the perturbed Hamiltonian has a finite set of eigenvalues of finite multiplicity together with some absolutely continuous spectrum. Eigenvalues can occur in the continuum if, and only if, the perturbation dislocates the system. Singular continuous spectrum cannot occur.

  11. Unconstrained Optimization Reformulations of Equilibrium Problems

    Li Ping ZHANG; Ji Ye HAN


    We generalize the D-gap function developed in the literature for variational inequalities to a general equilibrium problem (EP). Through the D-gap function,the equilibrium problem is cast as an unconstrained minimization problem. We give conditions under which any stationary point of the D-gap function is a solution of EP and conditions under which it provides a global error bound for EP. Finally,these results are applied to box-constrained EP and then weaker conditions are established to obtain the desired results for box-constrained EP.

  12. Equilibrium-torus bifurcation in nonsmooth systems

    Zhusubahyev, Z.T.; Mosekilde, Erik


    Considering a set of two coupled nonautonomous differential equations with discontinuous right-hand sides describing the behavior of a DC/DC power converter, we discuss a border-collision bifurcation that can lead to the birth of a two-dimensional invariant torus from a stable node equilibrium...... linear approximation to our system in the neighbourhood of the border. We determine the functional relationships between the parameters of the normal form map and the actual system and illustrate how the normal form theory can predict the bifurcation behaviour along the border-collision equilibrium......-torus bifurcation curve....

  13. Asymptotic stability estimates near an equilibrium point

    Dumas, H. Scott; Meyer, Kenneth R.; Palacián, Jesús F.; Yanguas, Patricia


    We use the error bounds for adiabatic invariants found in the work of Chartier, Murua and Sanz-Serna [3] to bound the solutions of a Hamiltonian system near an equilibrium over exponentially long times. Our estimates depend only on the linearized system and not on the higher order terms as in KAM theory, nor do we require any steepness or convexity conditions as in Nekhoroshev theory. We require that the equilibrium point where our estimate applies satisfy a type of formal stability called Lie stability.

  14. Putting A Human Face on Equilibrium

    Glickstein, Neil


    A short biography of chemist Fritz Haber is used to personalize the abstract concepts of equilibrium chemistry for high school students in an introductory course. In addition to giving the Haber Bosch process an historic, an economic, and a scientific background the reading and subsequent discussion allows students for whom the human perspective is of paramount importance a chance to investigate the irony of balance or equilibrium in Haber's life story. Since the inclusion of the Haber biography, performance in the laboratory and on examinations for those students who are usually only partially engaged has dramatically improved.

  15. Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks

    García del Real, Pablo; Maher, Kate; Kluge, Tobias; Bird, Dennis K.; Brown, Gordon E.; John, Cédric M.


    mineralization at shallow crustal depths in the presence of meteoric water. Hydrous magnesium carbonates from a 400-km latitudinal transect along the serpentinized-peridotite bodies of the California Coast Ranges record clumped-isotope temperatures between 14.2 and 22.7 ± 2.8 °C, in agreement with historical maximum temperatures during the rainy season for California. Talc-carbonate alteration of ultramafic rocks in Greenland (Isua Supracrustal Belt) and Vermont (Ludlow) yields clumped-isotope alteration temperatures of magnesite and dolomite between 326 and 490 °C, broadly consistent with paragenesis and thermodynamic analysis for CO2 metasomatism of ultramafic rocks. These metamorphic carbonates extend the applicability of clumped-isotope thermometry to high-temperature magnesium carbonate systems and indicate equilibrium blocking temperatures for magnesite of ∼490 °C. Our study demonstrates the applicability of the clumped isotope approach to provide information on the formation of magnesium carbonates as ore resources, surface records of climate, and metamorphic assemblages.

  16. Heterogeneous distribution of Zn stable isotopes in mice and applications to medical sciences

    Moynier, F.; Fujii, T.; Shaw, A.; Le Borgne, M.


    Zinc is required for the function of more than 300 enzymes involved in many metabolic pathways, and is a vital micronutrient for living organisms. To investigate if Zn isotopes could be used to better understand metal homeostasis, as well as a biomarker for diseases, we assessed the distribution of natural Zn isotopes in various mouse tissues. We found that, with respect to Zn isotopes, most mouse organs are isotopically distinct and that the total range of variation within one mouse encompasses the variations observed in the Earth's crust. Therefore, biological activity must have a major impact on the distribution of Zn isotopes in inorganic materials. The most striking aspect of the data is that red blood cells and bones are enriched by ~0.5 per mil in 66Zn relative to 64Zn when compared to serum, and up to ~1 per mil when compared to the brain and liver. This fractionation is well explained by the equilibrium distribution of isotopes between different bonding environments of Zn in different organs. Differences in gender and genetic background did not appear to affect the isotopic distribution of Zn. Together, these results suggest that potential use of Zn isotopes as a tracer for dietary Zn, and for detecting disturbances in Zn metabolism due to pathological conditions.

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

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


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

  18. 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

    Zheng, Xin-Yuan; Beard, Brian L.; Reddy, Thiruchelvi R.; Roden, Eric E.; Johnson, Clark M.


    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

  19. Copper adsorption on magnetite-loaded chitosan microspheres: A kinetic and equilibrium study

    Podzus, P.E., E-mail: [Grupo de Aplicaciones de Materiales Biocompatibles, Departamento de Quimica, Facultad de Ingenieria, Universidad de Buenos Aires, Paseo Colon 850, C1063ACV Buenos Aires (Argentina); Debandi, M.V. [Grupo de Aplicaciones de Materiales Biocompatibles, Departamento de Quimica, Facultad de Ingenieria, Universidad de Buenos Aires, Paseo Colon 850, C1063ACV Buenos Aires (Argentina); Daraio, M.E., E-mail: [Grupo de Aplicaciones de Materiales Biocompatibles, Departamento de Quimica, Facultad de Ingenieria, Universidad de Buenos Aires, Paseo Colon 850, C1063ACV Buenos Aires (Argentina)


    A composite of Fe{sub 3}O{sub 4} nanoparticles and the biopolymer chitosan, chemically crosslinked, was prepared as microspheres and used to adsorb copper ions, which were chosen as a model of contaminant metal in water. The adsorption of copper on the magnetic microspheres was studied in a batch process, with different aqueous solutions of Cu (II) at concentrations ranging from 40 to 1100 ppm. Kinetic and equilibrium aspects of the adsorption process were studied. The time-dependent Cu (II) adsorption data were well described by a pseudo-second-order kinetic model. It was found that the equilibrium data follow the Langmuir isotherm, with a maximum adsorption capacity of around 500 mg Cu/g chitosan. The used microspheres were removed and after desorption the material was able to be reused as an adsorbent. The prepared microspheres proved efficient in the removal of copper ions through an adsorption process whose kinetic and equilibrium characteristics were analyzed.

  20. Water isotopes in desiccating lichens

    Cuntz, Matthias; Máguas, Cristina; Lakatos, Michael


    The stable isotopic composition of water is routinely used as a tracer to study water exchange processes in vascular plants and ecosystems. To date, no study has focussed on isotope processes in non-vascular, poikilohydric organisms such as lichens and bryophytes. To understand basic isotope exchange processes of non-vascular plants, thallus water isotopic composition was studied in various green-algal lichens exposed to desiccation. The study indicates that lichens equilibrate with the isotopic composition of surrounding water vapour. A model was developed as a proof of concept that accounts for the specific water relations of these poikilohydric organisms. The approach incorporates first their variable thallus water potential and second a compartmentation of the thallus water into two isotopically distinct but connected water pools. Moreover, the results represent first steps towards the development of poikilohydric organisms as a recorder of ambient vapour isotopic composition. PMID:19888598