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Sample records for calcite surfaces implications

  1. High surface area calcite

    Science.gov (United States)

    Schultz, L. N.; Andersson, M. P.; Dalby, K. N.; Müter, D.; Okhrimenko, D. V.; Fordsmand, H.; Stipp, S. L. S.

    2013-05-01

    Calcite (CaCO3) is important in many fields—in nature, because it is a component of aquifers, oil reservoirs and prospective CO2 storage sites, and in industry, where it is used in products as diverse as paper, toothpaste, paint, plastic and aspirin. It is difficult to obtain high purity calcite with a high surface area but such material is necessary for industrial applications and for fundamental calcite research. Commercial powder is nearly always contaminated with growth inhibitors such as sugars, citrate or pectin and most laboratory synthesis methods deliver large precipitates, often containing vaterite or aragonite. To address this problem, we (i) adapted the method of carbonating a Ca(OH)2 slurry with CO2 gas to develop the first simple, cheap, safe and reproducible procedure using common laboratory equipment, to obtain calcite that reproducibly had a surface area of 14-17 m2/g and (ii) conducted a thorough characterization of the product. Scanning electron microscopy (SEM) revealed nanometer scale, rhombohedral crystals. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) confirmed highly crystalline, pure calcite that more closely resembles the dimensions of the biogenic calcite produced by algae in coccoliths than other methods for synthesizing calcite. We suggest that this calcite is useful when purity and high surface area are important.

  2. Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs

    KAUST Repository

    Yutkin, Maxim P.

    2017-08-25

    Low-salinity waterflooding (LSW) is ineffective when reservoir rock is strongly water-wet or when crude oil is not asphaltenic. Success of LSW relies heavily on the ability of injected brine to alter surface chemistry of reservoir crude-oil brine/rock (COBR) interfaces. Implementation of LSW in carbonate reservoirs is especially challenging because of high reservoir-brine salinity and, more importantly, because of high reactivity of the rock minerals. Both features complicate understanding of the COBR surface chemistries pertinent to successful LSW. Here, we tackle the complex physicochemical processes in chemically active carbonates flooded with diluted brine that is saturated with atmospheric carbon dioxide (CO2) and possibly supplemented with additional ionic species, such as sulfates or phosphates. When waterflooding carbonate reservoirs, rock equilibrates with the injected brine over short distances. Injected-brine ion speciation is shifted substantially in the presence of reactive carbonate rock. Our new calculations demonstrate that rock-equilibrated aqueous pH is slightly alkaline quite independent of injected-brine pH. We establish, for the first time, that CO2 content of a carbonate reservoir, originating from CO2-rich crude oil and gas, plays a dominant role in setting aqueous pH and rock-surface speciation. A simple ion-complexing model predicts the calcite-surface charge as a function of composition of reservoir brine. The surface charge of calcite may be positive or negative, depending on speciation of reservoir brine in contact with the calcite. There is no single point of zero charge; all dissolved aqueous species are charge determining. Rock-equilibrated aqueous composition controls the calcite-surface ion-exchange behavior, not the injected-brine composition. At high ionic strength, the electrical double layer collapses and is no longer diffuse. All surface charges are located directly in the inner and outer Helmholtz planes. Our evaluation of

  3. Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale

    Directory of Open Access Journals (Sweden)

    Cubillas Pablo

    2009-06-01

    Full Text Available Abstract Lateral Force Microscopy (LFM studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3 or calcite-otavite solid solutions (SS as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0–40 nN, a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

  4. Relative wettability alteration of calcite surfaces

    Science.gov (United States)

    Prabhakar, Sanjay; Liu, Jian; Pantelides, Sokrates

    Enhancement of crude oil recovery from calcite reservoirs remains a major challenge in the oil industry. Crude oil recovery can be enhanced by modifying the relative wettability of calcite reservoirs by injecting sea water. In this work, we consider acetic acid as a model component of crude oil and use the changes of adsorption energies of oil and water molecules induced by additives as a measure of relative wettability alteration of the calcite surface. More specifically, we investigate the influence of Na+, Mg2+, Ca2+, SO42- and Cl- ions on the adsorption energies of water and acetic acid. It is expected that crude oil recovery is enhanced if the modified acetic acid molecule binds weaker than acetic acid. We use density functional theory calculations and show that the presence of Na+ ions reduces oil recovery whereas the presence of Mg and SO4 ions enhance oil recovery. Additionally, we propose a novel possibility of lifting two oil molecules by one Mg2+ ion, which yields enhanced oil recovery, as observed. We also found that Cl merely binds to the surface and has no effect on the adsorption energy of acetic acid, which means that Cl has no effect on oil recovery. This work was supported by a Grant from the Petroleum Institute of Abu Dhabi.

  5. Calcite surface structure and reactivity: molecular dynamics simulations and macroscopic surface modelling of the calcite-water interface

    NARCIS (Netherlands)

    Wolthers, M.; Di Tommaso, D.; Du, Z.; de Leeuw, N.H.

    2012-01-01

    Calcite–water interactions are important not only in carbon sequestration and the global carbon cycle, but also in contaminant behaviour in calcite-bearing host rock and in many industrial applications. Here we quantify the effect of variations in surface structure on calcite surface reactivity.

  6. Atomistic simulations of calcium uranyl(VI) carbonate adsorption on calcite and stepped-calcite surfaces.

    Science.gov (United States)

    Doudou, Slimane; Vaughan, David J; Livens, Francis R; Burton, Neil A

    2012-07-17

    Adsorption of actinyl ions onto mineral surfaces is one of the main mechanisms that control the migration of these ions in environmental systems. Here, we present computational classical molecular dynamics (MD) simulations to investigate the behavior of U(VI) in contact with different calcite surfaces. The calcium-uranyl-carbonate [Ca(2)UO(2)(CO(3))(3)] species is shown to display both inner- and outer-sphere adsorption to the flat {101̅4} and the stepped {314̅8} and {31̅2̅16} planes of calcite. Free energy calculations, using the umbrella sampling method, are employed to simulate adsorption paths of the same uranyl species on the different calcite surfaces under aqueous condition. Outer-sphere adsorption is found to dominate over inner-sphere adsorption because of the high free energy barrier of removing a uranyl-carbonate interaction and replacing it with a new uranyl-surface interaction. An important binding mode is proposed involving a single vicinal water monolayer between the surface and the sorbed complex. From the free energy profiles of the different calcite surfaces, the uranyl complex was also found to adsorb preferentially on the acute-stepped {314̅8} face of calcite, in agreement with experiment.

  7. Interaction of alcohols with the calcite surface

    DEFF Research Database (Denmark)

    Bovet, Nicolas Emile; Yang, Mingjun; Javadi, Meshkat Sadat

    2015-01-01

    A clearer understanding of calcite interactions with organic molecules would contribute to a range of fields including harnessing the secrets of biomineralisation where organisms produce hard parts, increasing oil production from spent reservoirs, remediating contaminated soils and drinking water...... aquifers and improving manufacturing methods for industrial products such as pigments, soft abrasives, building materials and optical devices. Biomineralisation by some species of blue green algae produces beautifully elaborate platelets of calcite where the individual crystals are of nanometer scale...

  8. Molecular ordering of ethanol at the calcite surface

    DEFF Research Database (Denmark)

    Pasarín, I. S.; Yang, M.; Bovet, Nicolas Emile

    2012-01-01

    dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH 3-CH2-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol...... molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH3 ends form a new surface, about 6 Å from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three...... ethanol molecules thick, about 14 Å, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems. © 2012 American Chemical Society....

  9. Surface tension alteration on calcite, induced by ion substitution

    DEFF Research Database (Denmark)

    Sakuma, Hiroshi; Andersson, Martin Peter; Bechgaard, Klaus

    2014-01-01

    The interaction of water and organic molecules with mineral surfaces controls many processes in nature and industry. The thermodynamic property, surface tension, is usually determined from the contact angle between phases, but how does one understand the concept of surface tension at the nanoscale...... in the pore water. Incorporation of MgSO4 into calcite, which is energetically favored, decreases surface tension and releases polar oil compounds......., where particles are smaller than the smallest droplet? We investigated the energy required to exchange Mg2+ and SO4 2- from aqueous solution into calcite {10.4} surfaces using density functional theory. Mg2+ substitution for Ca2+ is favored but only when SO4 2- is also present and MgSO4 incorporates...

  10. Molecular ordering of ethanol at the calcite surface.

    Science.gov (United States)

    Pasarín, I S; Yang, M; Bovet, N; Glyvradal, M; Nielsen, M M; Bohr, J; Feidenhans'l, R; Stipp, S L S

    2012-02-07

    To produce biominerals, such as shells, bones, and teeth, living beings create organic compounds that control the growth of the solid phase. Investigating the atomic scale behavior of individual functional groups at the mineral-fluid interface provides fundamental information that is useful for constructing accurate predictive models for natural systems. Previous investigations of the activity of coccolith-associated polysaccharides (CAP) on calcite, using atomic force microscopy (AFM) [Henriksen, K., Young, J. R., Bown, P. R., and Stipp, S. L. S. Palentology 2004, 43 (Part 3), 725-743] and molecular dynamics (MD) modeling [Yang, M., Stipp, S. L. S., and Harding, J. H. Cryst. Growth Des. 2008, 8 (11), 4066-4074], have suggested that OH functional groups control polysaccharide attachment. The purpose of this work was to characterize, using X-ray reflectivity (XR) combined with molecular dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH(3)-CH(2)-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH(3) ends form a new surface, about 6 Å from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three ethanol molecules thick, about 14 Å, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems.

  11. Is bicarbonate stable in and on the calcite surface?

    DEFF Research Database (Denmark)

    Andersson, Martin Peter; Rodriguez Blanco, Juan Diego; Stipp, Susan Louise Svane

    2016-01-01

    We have used density functional theory with the COSMO-RS implicit solvent model to predict the pKa for the deprotonation of bicarbonate to carbonate, i.e. HCO3− CO32− + H+, when HCO3− is included in, and adsorbed on, a calcite surface. We have used cluster models (80–100 atoms) to represent...... the flat {10.4} surface, acute steps, obtuse steps, two types of kinks on the acute step and two types of kinks on the obtuse steps. Based on the predicted pKa values, which range from −6.0 to 2.4 depending on the surface site, we conclude that bicarbonate deprotonates to carbonate when it is in calcite...... even when pH in solution is very low. This is true for all surface sites, even for solutions where 2.4 bicarbonate is adsorbed on calcite, the predicted pKa for deprotonation is 7.5, which is ∼3 pH units lower than in aqueous solution...

  12. Effect of Mica and Hematite (001 Surfaces on the Precipitation of Calcite

    Directory of Open Access Journals (Sweden)

    Huifang Xu

    2018-01-01

    Full Text Available The substrate effect of mica and hematite on the nucleation and crystallization of calcite was investigated using scanning electron microscope (SEM, X-ray diffraction (XRD, and electron backscatter diffraction (EBSD methods. On mica, we found, in the absence of Mg2+, the substrates’ (001 surfaces with hexagonal and pseudo-hexagonal two-dimensional (2-D structure can affect the orientation of calcite nucleation with calcite (001 ~// mica (001 and calcite (010 ~// mica (010 to be the major interfacial relationship. On hematite, we did not observe frequent twinning relationship between adjacent calcite gains, but often saw preferentially nucleation of calcite at surface steps on hematite substrate. We suggest that calcite crystals initially nucleate from the Ca2+ layers adsorbed on the surfaces. The pseudo-hexagonal symmetry on mica (001 surface also leads to the observed calcite (001 twinning. A second and less common orientation between calcite {104} and mica (001 was detected but could be due to local structure damage of the mica surface. Results in the presence of Mg2+ show that the substrate surfaces can weaken Mg toxicity to calcite nucleation and lead to a higher level of Mg incorporation into calcite lattice.

  13. The role of silicate surfaces on calcite precipitation kinetics

    DEFF Research Database (Denmark)

    Stockmann, Gabrielle J.; Wolff-Boenisch, Domenik; Bovet, Nicolas Emile

    2014-01-01

    , labradorite, olivine, basaltic glass and peridotite rock. Calcite saturation was achieved by mixing a CaCl2-rich aqueous solution with a NaHCO3-Na2CO3 aqueous buffer in mixed-flow reactors containing 0.5-2g of mineral, rock, or glass seeds. This led to an inlet fluid calcite saturation index of 0.6 and a p...

  14. Structure of the (1014) Surfaces of Calcite, Dolomite, and Magnesite under Wet and Dry Conditions

    Energy Technology Data Exchange (ETDEWEB)

    WRIGHT,KATE; CYGAN,RANDALL T.; SLATER,BEN

    2000-06-12

    Atomistic computer simulation methods have been employed to model the structure of the (10{bar 1}4) surfaces of calcite, dolomite and magnesite. The authors calculations show that under vacuum conditions, calcite undergoes the greatest degree of surface relaxation with rotation and distortion of the carbonate group accompanied by movement of the calcium ion. The magnesite surface is the least distorted of the three carbonates, with dolomite being intermediate to the two end members. When water molecules are placed on the surface to produce complete monolayer coverage, the calcite surface is stabilized and the amount of relaxation is substantially reduced. In contrast, the dolomite and magnesite surfaces are destabilized by hydration as indicated by a significant increase in the surface energies relative to the dry surface.

  15. Ethanol adsorption on the {10(1)over-bar4} calcite surface

    DEFF Research Database (Denmark)

    Sand, Karina Krarup; Stipp, Susan Louise Svane; Hassenkam, Tue

    2008-01-01

    Preliminary atomic force microscopy investigations of the {10 (1) over bar4} calcite Surface cleaved in ethanol indicate a different surface behaviour than that of the {10 (1) over bar4} surface cleaved in air. The results are consistent with recent theoretical studies and suggest strong ordering...

  16. Thickness and structure of the water film deposited from vapour on calcite surfaces

    DEFF Research Database (Denmark)

    Bohr, Jakob; Wogelius, Roy A.; Morris, Peter M.

    2010-01-01

    Synchrotron X-ray reflectivity (SXR) was used to measure the thickness of the water film that adsorbs on a {10¯14} cleavage surface of calcite (CaCO3) in a sample chamber where relative humidity could be controlled within the range from......Synchrotron X-ray reflectivity (SXR) was used to measure the thickness of the water film that adsorbs on a {10¯14} cleavage surface of calcite (CaCO3) in a sample chamber where relative humidity could be controlled within the range from...

  17. Impact of trace metals on the water structure at the calcite surface

    Science.gov (United States)

    Wolthers, Mariette; Di Tommaso, Devis; De Leeuw, Nora

    2014-05-01

    Carbonate minerals play an important role in regulating the chemistry of aquatic environments, including the oceans, aquifers, hydrothermal systems, soils and sediments. Through mineral surface processes such as dissolution, precipitation and sorption, carbonate minerals affect the biogeochemical cycles of not only the constituent elements of carbonates, such as Ca, Mg, Fe and C, but also H, P and trace elements. Surface charging of the calcite mineral-water interface, and its reactivity towards foreign ions can be quantified using a surface structural model that includes, among others, the water structure at the interface (i.e. hydrogen bridging) [1,2] in accordance with the CD-MUSIC formalism [3]. Here we will show the impact of foreign metals such as Mg and Sr on the water structure around different surface sites present in etch pits and on growth terraces at the calcite (10-14) surface. We have performed Molecular Dynamics simulations of metal-doped calcite surfaces, using different interatomic water potentials. Results show that the local environment around the structurally distinct sites differs depending on metal presence, suggesting that metal substitutions in calcite affect its reactivity. The information obtained in this study will help in improving existing macroscopic surface model for the reactivity of calcite [2] and give more general insight in mineral surface reactivity in relation to crystal composition. [1] Wolthers, Charlet, & Van Cappellen (2008). Am. J. Sci., 308, 905-941. [2] Wolthers, Di Tommaso, Du, & de Leeuw (2012). Phys. Chem. Chem. Phys. 14, 15145-15157. [3] Hiemstra and Van Riemsdijk (1996) J. Colloid Interf. Sci. 179, 488-508.

  18. Adsorption of arsenic and phosphate onto the surface of calcite as revealed by batch experiments and surface complexation modelling

    DEFF Research Database (Denmark)

    Sø, Helle Ugilt

    is complete after 1 and 2-3 hours, respectively). Also desorption is fast and complete for both ions within 0.5 h. The reversibility of the sorption process indicates that neither arsenate nor phosphate is readily incorporated into the calcite crystal lattice under our experimental conditions. The phosphate....... The primary effect of the ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. For the adsorption of arsenate onto calcite, the effect of the ionic strength is more pronounced and cannot fully be accounted for by changes in the aqueous...... and sequential addition (3 hours apart) yields the same reduction in adsorption, underlining the high reversibility of the system. The reduction in adsorption of both arsenate and phosphate is most likely due to competition for the same sorption sites at the calcite surface, considering the similarity...

  19. Adsorption Behavior and Mechanism of SCA-1 on a Calcite Surface: A Molecular Dynamics Study.

    Science.gov (United States)

    Xue, Zhengyang; Shen, Qiying; Liang, Lijun; Shen, Jia-Wei; Wang, Qi

    2017-10-24

    The crystallization mechanism for natural mineral, especially the role of biological molecules in biomineralization, is still under debate. Protein adsorption on material surfaces plays a key role in biomineralization. In this article, molecular dynamics (MD) simulations were performed to systematically investigate the adsorption behavior of struthio camelus eggshell protein struthiocalcin-1 (SCA-1) on the calcite (104) surface with several different starting orientations in an explicit water environment. For each binding configuration, detailed adsorption behaviors and a mechanism were presented with the analysis of interaction energy, binding residues, hydrogen bonding, and structures (such as DSSP, dipole moment, and the electrostatic potential calculation). The results indicate that the positively charged and polar residues are the dominant residues for protein adsorption on the calcite (104) surface, and the strong electrostatic interaction drives the binding of model protein to the surface. The hydrogen bond bridge was found to play an important role in surface interactions as well. These results also demonstrate that SCA-1 is relatively rigid in spite of strong adsorption with few structural changes in α-helix and β-sheet contents. The results of the orientation calculation suggest that the dipole moment of the protein tends to remain parallel to calcite in most stable cases, which was confirmed by electrostatic potential isosurfaces analysis.

  20. The surface interactions of a near-neutral carbon nanoparticle tracer with calcite

    KAUST Repository

    Li, Yan Vivian

    2016-03-02

    A new class of nearly charge-neutral carbon-cored nanoparticle tracers are remarkably non-interactive with solid surfaces and could provide a valuable baseline for diverse hydrological and environmental studies of subsurface flow and particle transport. We investigate the causes of inertness by studying the interactions with calcite of a nanoparticle of this class synthesized from malic acid and ethanolamine (M-dots) dispersed in brine (NaCl, CaCl2, and MgCl2) solutions. None of the M-dots are retained in calcite sand-packed columns when dispersed in DI water. Dispersed in the NaCl and mixed brine solutions, 5.6 % of and 7.3 % of the M-dots are initially retained, but 65 and 13 % of these retained particles are subsequently released when the column is flushed with DI water. When dispersed in the CaCl2 and MgCl2 solutions, 65 and 54 % of the M-dots are initially retained, and 28 and 26 % subsequently released in the DI water flush. The M-dots have a small negative zeta potential in all solutions, but the calcite zeta potential changes from strongly negative to strongly positive across the solution series, and the particle retention tracks this change. Derjaguin–Landau–Verwey–Overbeek (DLVO) modeling of the force between a calcite probe and an M-dot coated surface shows that hydration forces repel the particles in the DI water, NaCl, and mixed solutions, but not in the CaCl2 and MgCl2 solutions. These results show that near-zero charge and strongly hydrophilic decoration are the causes of the remarkable inertness of carbon-cored nanoparticles, and also suggest that nanoparticles could be useful in solute-surface interaction studies.

  1. The surface interactions of a near-neutral carbon nanoparticle tracer with calcite

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yan Vivian, E-mail: yan.li@colostate.edu [Colorado State University, Department of Design and Merchandising (United States); Cathles, Lawrence M., E-mail: lmc19@cornell.edu [Cornell University, Earth and Atmospheric Sciences (United States)

    2016-03-15

    A new class of nearly charge-neutral carbon-cored nanoparticle tracers are remarkably non-interactive with solid surfaces and could provide a valuable baseline for diverse hydrological and environmental studies of subsurface flow and particle transport. We investigate the causes of inertness by studying the interactions with calcite of a nanoparticle of this class synthesized from malic acid and ethanolamine (M-dots) dispersed in brine (NaCl, CaCl{sub 2}, and MgCl{sub 2}) solutions. None of the M-dots are retained in calcite sand-packed columns when dispersed in DI water. Dispersed in the NaCl and mixed brine solutions, 5.6 % of and 7.3 % of the M-dots are initially retained, but 65 and 13 % of these retained particles are subsequently released when the column is flushed with DI water. When dispersed in the CaCl{sub 2} and MgCl{sub 2} solutions, 65 and 54 % of the M-dots are initially retained, and 28 and 26 % subsequently released in the DI water flush. The M-dots have a small negative zeta potential in all solutions, but the calcite zeta potential changes from strongly negative to strongly positive across the solution series, and the particle retention tracks this change. Derjaguin–Landau–Verwey–Overbeek (DLVO) modeling of the force between a calcite probe and an M-dot coated surface shows that hydration forces repel the particles in the DI water, NaCl, and mixed solutions, but not in the CaCl{sub 2} and MgCl{sub 2} solutions. These results show that near-zero charge and strongly hydrophilic decoration are the causes of the remarkable inertness of carbon-cored nanoparticles, and also suggest that nanoparticles could be useful in solute-surface interaction studies.Graphical Abstract.

  2. Interaction of ethanol and water with the {1014} surface of calcite

    DEFF Research Database (Denmark)

    Cooke, David; Gray, R J; Sand, K K

    2010-01-01

    Molecular dynamics simulations have been used to model the interaction between ethanol, water, and the {1014} surface of calcite. Our results demonstrate that a single ethanol molecule is able to form two interactions with the mineral surface (both Ca-O and O-H), resulting in a highly ordered...... with water and for growth at the {1014} surface to occur. This observation, and its corresponding molecular explanation, may give some insight into the ability to control crystal form using mixtures of different organic solvents....

  3. Investigating the Physical Basis of Amorphous Precursor Transformation to Calcite Using Patterned Alkanethiol Surfaces

    Science.gov (United States)

    Wang, D.; Wallace, A.; Han, T. Y.; Lee, J. R.; Hailey, P. D.; de Yoreo, J. J.; Dove, P. M.

    2007-12-01

    Increasing evidence from X-ray Absorption Spectroscopy and Environmental Scanning Electron Microscopy (ESEM) studies of biominerals extracted from calcifying organisms show that amorphous calcium carbonate (ACC) plays a key role in the initial formation of carbonate minerals and in shaping them into complex morphologies. Echinoderms and possibly a wide variety of other organisms, use ACC as a precursor phase. The ACC is first formed within spatial and temporally controlled environments such as vesicles, followed by a subsequent onset of mineralization that transforms the precursor into a fully crystalline material. Recent studies on sea urchin embryos have shown that during this transformation, ACC develops short-range order that resembles calcite before fully crystallizing. While this "non-traditional" process is recognized, the mechanisms and factors that govern this transformation remain poorly understood. Of particular interest are the roles of water, and the functional group chemistry of surfaces and macromolecules within mineralization environments. To investigate these questions, we have developed an experimental approach using ESEM that allows us to control impurity concentration, surface functionality and water content through the degree of water condensation. Patterned self-assembled monolayers (SAM) of hydrophilic moieties with domains of approximately 25 microns in diameter are used to form an array of micro-reactors. ACC particles with known composition are then deposited on the patterns. Condensing water in the ESEM initializes the transformation of ACC to calcite. Our results show that in saturated water vapor, ACC swells, but no obvious faceting of the material occurs. It is only in bulk water, via dissolution/crystallization, where the calcite grown on carboxyl-terminated surfaces is found with the often-observed \\{013\\} nucleation face. We use this insight to understand the role of the different chemical moieties on ACC to calcite transformation

  4. Molecular modeling studies of interactions between sodium polyacrylate polymer and calcite surface

    Science.gov (United States)

    Ylikantola, A.; Linnanto, J.; Knuutinen, J.; Oravilahti, A.; Toivakka, M.

    2013-07-01

    The interactions between calcite pigment and sodium polyacrylate dispersing agent, widely used in papermaking as paper coating components, were investigated using classical force field and quantum chemical approaches. The objective was to understand interactions between the calcite surface and sodium polyacrylate polymer at 300 K using molecular dynamics simulations. A quantum mechanical ab initio Hartree-Fock method was also used to obtain detailed information about the sodium polyacrylate polymer structure. The effect of water molecules (moisture) on the interactions was also examined. Calculations showed that molecular weight, branching and the orientation of sodium polyacrylate polymers influence the interactions between the calcite surface and the polymer. The force field applied, and also water molecules, were found to have an impact on all systems studied. Ab initio Hartree-Fock calculations indicated that there are two types of coordination between sodium atoms and carboxylate groups of the sodium polyacrylate polymer, inter- and intra-carboxylate group coordination. In addition, ab initio Hartree-Fock calculations of the structure of the sodium polyacrylate polymer produced important information regarding interactions between the polymers and carboxylated styrene-butadiene latex particles.

  5. Molecular modeling studies of interactions between sodium polyacrylate polymer and calcite surface

    Energy Technology Data Exchange (ETDEWEB)

    Ylikantola, A. [University of Jyväskylä, Department of Chemistry, P.O. Box 35, University of Jyväskylä, FI-40014 (Finland); Linnanto, J., E-mail: juha.m.linnanto@gmail.com [University of Jyväskylä, Department of Chemistry, P.O. Box 35, University of Jyväskylä, FI-40014 (Finland); University of Tartu, Institute of Physics, Riia 142, EE-51014 Tartu (Estonia); Knuutinen, J.; Oravilahti, A. [University of Jyväskylä, Department of Chemistry, P.O. Box 35, University of Jyväskylä, FI-40014 (Finland); Toivakka, M. [Åbo Akademi University, Laboratory of Paper Coating and Converting and Center for Functional Materials, FI-20500 Turku/Åbo (Finland)

    2013-07-01

    The interactions between calcite pigment and sodium polyacrylate dispersing agent, widely used in papermaking as paper coating components, were investigated using classical force field and quantum chemical approaches. The objective was to understand interactions between the calcite surface and sodium polyacrylate polymer at 300 K using molecular dynamics simulations. A quantum mechanical ab initio Hartree–Fock method was also used to obtain detailed information about the sodium polyacrylate polymer structure. The effect of water molecules (moisture) on the interactions was also examined. Calculations showed that molecular weight, branching and the orientation of sodium polyacrylate polymers influence the interactions between the calcite surface and the polymer. The force field applied, and also water molecules, were found to have an impact on all systems studied. Ab initio Hartree–Fock calculations indicated that there are two types of coordination between sodium atoms and carboxylate groups of the sodium polyacrylate polymer, inter- and intra-carboxylate group coordination. In addition, ab initio Hartree–Fock calculations of the structure of the sodium polyacrylate polymer produced important information regarding interactions between the polymers and carboxylated styrene-butadiene latex particles.

  6. Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solution

    Energy Technology Data Exchange (ETDEWEB)

    DePaolo, D.

    2010-10-15

    A surface reaction kinetic model is developed for predicting Ca isotope fractionation and metal/Ca ratios of calcite as a function of rate of precipitation from aqueous solution. The model is based on the requirements for dynamic equilibrium; i.e. proximity to equilibrium conditions is determined by the ratio of the net precipitation rate (R{sub p}) to the gross forward precipitation rate (R{sub f}), for conditions where ionic transport to the growing crystal surface is not rate-limiting. The value of R{sub p} has been experimentally measured under varying conditions, but the magnitude of R{sub f} is not generally known, and may depend on several factors. It is posited that, for systems with no trace constituents that alter the surface chemistry, R{sub f} can be estimated from the bulk far-from-equilibrium dissolution rate of calcite (R{sub b} or k{sub b}), since at equilibrium R{sub f} = R{sub b}, and R{sub p} = 0. Hence it can be inferred that R{sub f} {approx} R{sub p} + R{sub b}. The dissolution rate of pure calcite is measureable and is known to be a function of temperature and pH. At given temperature and pH, equilibrium precipitation is approached when R{sub p} (= R{sub f} - R{sub b}) << R{sub b}. For precipitation rates high enough that R{sub p} >> R{sub b}, both isotopic and trace element partitioning are controlled by the kinetics of ion attachment to the mineral surface, which tend to favor more rapid incorporation of the light isotopes of Ca and discriminate weakly between trace metals and Ca. With varying precipitation rate, a transition region between equilibrium and kinetic control occurs near R{sub p} {approx} R{sub b} for Ca isotopic fractionation. According to this model, Ca isotopic data can be used to estimate R{sub f} for calcite precipitation. Mechanistic models for calcite precipitation indicate that the molecular exchange rate is not constant at constant T and pH, but rather is dependent also on solution saturation state and hence R{sub p

  7. Structure and dynamics of microbe-exuded polymers and their interactions with calcite surfaces.

    Energy Technology Data Exchange (ETDEWEB)

    Cygan, Randall Timothy; Mitchell, Ralph (Harvard University, Cambridge, MA); Perry, Thomas D. (Harvard University, Cambridge, MA)

    2005-12-01

    Cation binding by polysaccharides is observed in many environments and is important for predictive environmental modeling, and numerous industrial and food technology applications. The complexities of these organo-cation interactions are well suited to predictive molecular modeling studies for investigating the roles of conformation and configuration of polysaccharides on cation binding. In this study, alginic acid was chosen as a model polymer and representative disaccharide and polysaccharide subunits were modeled. The ability of disaccharide subunits to bind calcium and to associate with the surface of calcite was investigated. The findings were extended to modeling polymer interactions with calcium ions.

  8. Fluoride removal by calcite: evidence for fluorite precipitation and surface adsorption.

    Science.gov (United States)

    Turner, Brett D; Binning, Philip; Stipp, S L S

    2005-12-15

    Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide. In this study, fluoride removal by crushed limestone (99% pure calcite) was investigated by batch studies and surface-sensitive techniques from solutions with fluoride concentrations from 150 micromol/L (3 mg/L) to 110 mM (approximately 2100 mg/L). Surface-sensitive techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as zeta potential measurements, confirm that, in addition to precipitation reactions, adsorption of fluoride also occurs. Results indicate that fluoride adsorption occurs immediately over the entire calcite surface with fluorite precipitating at step edges and kinks, where dissolved Ca2+ concentration is highest. The PHREEQ geochemical model was applied to the observed data and indicates that existing models, especially at low fluoride concentrations and high pH (>7.5) are not equipped to describe this complex system, largely because the PHREEQ model includes only precipitation reactions, whereas a combination of adsorption and precipitation parameters are required.

  9. Nanometer-Scale Chemistry of a Calcite Biomineralization Template: Implications for Skeletal Composition and Nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Branson, Oscar; Bonnin, Elisa A.; Perea, Daniel E.; Spero, Howard J.; Zhu, Zihua; Winters, Maria; Hönisch, Bärbel; Russell, Ann D.; Fehrenbacher, Jennifer S.; Gagnon, Alexander C.

    2016-10-28

    Biomineralizing organisms exhibit exquisite control over skeletal morphology and composition. The promise of understanding and harnessing this feat of natural engineering has motivated an intense search for the mechanisms that direct in vivo mineral self-assembly. We used atom probe tomography, a sub-nanometer 3D chemical mapping technique, to examine the chemistry of a buried organic-mineral interface in biomineral calcite from a marine foraminifer. The chemical patterns at this interface capture the processes of early biomineralization, when the shape, mineralogy, and orientation of skeletal growth are initially established. Sodium is enriched by a factor of nine on the organic side of the interface. Based on this pattern, we suggest that sodium plays an integral role in early biomineralization, potentially altering interfacial energy to promote crystal nucleation, and that interactions between organic surfaces and electrolytes other than calcium or carbonate could be a crucial aspect of CaCO3 biomineralization.

  10. Anisotropic Growth of Otavite on Calcite: Implications for Heteroepitaxial Growth Mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Riechers, Shawn L. [Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States; Kerisit, Sebastien N. [Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States

    2017-12-18

    Elucidating how cation intermixing can affect the mechanisms of heteroepitaxial growth in aqueous media has remained a challenging endeavor. Toward this goal, in situ atomic force microscopy was employed to image the heteroepitaxial growth of otavite (CdCO3) at the (10-14) surface of calcite (CaCO3) single crystals in static aqueous conditions. Heteroepitaxial growth proceeded via spreading of three-dimensional (3D) islands and two-dimensional (2D) atomic layers at low and high initial saturation levels, respectively. Experiments were carried out as a function of applied force and imaging mode thus enabling determination of growth mechanisms unaltered by imaging artifacts. This approach revealed the significant anisotropic nature of heteroepitaxial growth on calcite in both growth modes and its dependence on supersaturation, intermixing, and substrate topography. The 3D islands not only grew preferentially along the [42-1] direction relative to the [010] direction, resulting in rod-like surface precipitates, but also showed clear preference for growth from the island end rich in obtuse/obtuse kink sites. Pinning to step edges was observed to often reverse this tendency. In the 2D growth mode, the relative velocities of acute and obtuse steps were observed to switch between the first and second atomic layers. This phenomenon stemmed from the significant Cd-Ca intermixing in the first layer, despite bulk thermodynamics predicting the formation of almost pure otavite. Composition effects were also responsible for the inability of 3D islands to grow on 2D layers in cases where both modes were observed to occur simultaneously. Overall, the AFM images highlighted the effects of intermixing on heteroepitaxial growth, particularly how it can induce thickness-dependent growth mechanisms at the nanoscale.

  11. Three-dimensional hydration layer mapping on the (10.4) surface of calcite using amplitude modulation atomic force microscopy

    Science.gov (United States)

    Marutschke, Christoph; Walters, Deron; Cleveland, Jason; Hermes, Ilka; Bechstein, Ralf; Kühnle, Angelika

    2014-08-01

    Calcite, the most stable modification of calcium carbonate, is a major mineral in nature. It is, therefore, highly relevant in a broad range of fields such as biomineralization, sea water desalination and oil production. Knowledge of the surface structure and reactivity of the most stable cleavage plane, calcite (10.4), is pivotal for understanding the role of calcite in these diverse areas. Given the fact that most biological processes and technical applications take place in an aqueous environment, perhaps the most basic—yet decisive—question addresses the interaction of water molecules with the calcite (10.4) surface. In this work, amplitude modulation atomic force microscopy is used for three-dimensional (3D) mapping of the surface structure and the hydration layers above the surface. An easy-to-use scanning protocol is implemented for collecting reliable 3D data. We carefully discuss a comprehensible criterion for identifying the solid-liquid interface within our data. In our data three hydration layers form a characteristic pattern that is commensurate with the underlying calcite surface.

  12. Molecular dynamics simulations of the calcite/solution interface as a means to explore surface modifications induced by nitrate

    Energy Technology Data Exchange (ETDEWEB)

    Hofmann, Sascha; Schmidt, Moritz [Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden (Germany). Div. Surface Processes; Spijker, P. [Aalto Univ., Helsinki (Finland). Dept. of Applied Physics; Voitchovsky, K. [Durham Univ. (United Kingdom). Physics Dept.

    2016-07-01

    The reactivity of calcite, one of the most abundant minerals in the earth's crust, is determined by the molecular details of its interface with the contacting solution. Recently, it has been found that trace concentrations of NaNO{sub 3} severely affect calcite's (104) surface and its reactivity. Molecular dynamics (MD) simulations reveal density profiles of different ions near calcite's surface, with NO{sub 3}{sup -} able to reach closer to the surface than CO{sub 3}{sup 2-} and in higher concentrations. Additionally, incorporation of NO{sub 3}{sup -} into the surface significantly disturbs the water structure at the interface.

  13. The surface reactivity of chalk (biogenic calcite) with hydrophilic and hydrophobic functional groups

    Science.gov (United States)

    Okhrimenko, D. V.; Dalby, K. N.; Skovbjerg, L. L.; Bovet, N.; Christensen, J. H.; Stipp, S. L. S.

    2014-03-01

    The surface properties of calcium carbonate minerals play an important role in a number of industrial and biological processes. Properties such as wettability and adsorption control liquid-solid interface behaviour and thus have a strong influence on processes such as biomineralisation, remediation of aquifers and oil recovery. We investigated how two model molecules of different polarity, namely water and ethanol, interact with reservoir and outcrop chalk samples and we compared their behaviour with that of pure, inorganically precipitated calcite. Thermodynamic quantities, such as the work of wetting, surface energy and isosteric adsorption enthalpy, were determined from vapour adsorption isotherms. The chalks were studied fresh and after extraction of organic residues that were originally present in these samples. The work of wetting correlates with the amount of organic matter present in the chalk samples but we observed a fundamental difference between the adsorption properties of chalk and pure, inorganically precipitated calcite toward the less polar, ethanol molecule. Further analysis of the chemical composition of the organic matter extracted from the chalk samples was made by gas chromatography (GC-MS). Monitoring surface composition by X-ray photoelectron spectroscopy (XPS) before and after extraction of the organic material, and with atomic force microscopy (AFM), showed that nanometer sized clay crystals observed on the chalk particle surfaces could be an important part of the reason for the differences. Removal of the extractable portion of the hydrocarbons liberates adsorption sites that have different wetting properties than the rest of the chalk and these have an energy distribution that is similar to clays. Thus, the results exemplify the complexity of biogenic calcite adsorption behaviour and demonstrate that chalk wetting in drinking water aquifers as well as oil reservoirs is controlled partly by the nanoparticles of clay that have grown on the

  14. Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling

    DEFF Research Database (Denmark)

    Sø, Helle Ugilt; Postma, Dieke; Jakobsen, Rasmus

    2011-01-01

    . Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.......The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3h) and low concentrations of phosphate (⩽50μM). Sorption of phosphate on calcite...... was studied in 11 different calcite-equilibrated solutions that varied in pH, PCO2, ionic strength and activity of Ca2+, CO32- and HCO3-. Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2–3h while desorption...

  15. A model for trace metal sorption processes at the calcite surface: Adsorption of Cd2+ and subsequent solid solution formation

    Science.gov (United States)

    Davis, J.A.; Fuller, C.C.; Cook, A.D.

    1987-01-01

    The rate of Cd2+ sorption by calcite was determined as a function of pH and Mg2+ in aqueous solutions saturated with respect to calcite but undersaturated with respect to CdCO3. The sorption is characterized by two reaction steps, with the first reaching completion within 24 hours. The second step proceeded at a slow and nearly constant rate for at least 7 days. The rate of calcite recrystallization was also studied, using a Ca2+ isotopic exchange technique. Both the recrystallization rate of calcite and the rate of slow Cd2+ sorption decrease with increasing pH or with increasing Mg2+. The recrystallization rate could be predicted from the number of moles of Ca present in the hydrated surface layer. A model is presented which is consistent with the rates of Cd2+ sorption and Ca2+ isotopic exchange. In the model, the first step in Cd2+ sorption involves a fast adsorption reaction that is followed by diffusion of Cd2+ into a surface layer of hydrated CaCO3 that overlies crystalline calcite. Desorption of Cd2+ from the hydrated layer is slow. The second step is solid solution formation in new crystalline material, which grows from the disordered mixture of Cd and Ca carbonate in the hydrated surface layer. Calculated distribution coefficients for solid solutions formed at the surface are slightly greater than the ratio of equilibrium constants for dissolution of calcite and CdCO3, which is the value that would be expected for an ideal solid solution in equilibrium with the aqueous solution. ?? 1987.

  16. Comparative study of nanoscale surface structures of calcite microcrystals using FE-SEM, AFM, and TEM.

    Science.gov (United States)

    Chien, Yung-Ching; Mucci, Alfonso; Paquette, Jeanne; Sears, S Kelly; Vali, Hojatollah

    2006-08-01

    The bulk morphology and surface features that developed upon precipitation on micrometer-size calcite powders and millimeter-size cleavage fragments were imaged by three different microscopic techniques: field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) of Pt-C replicas, and atomic force microscopy (AFM). Each technique can resolve some nanoscale surface features, but they offer different ranges of magnification and dimensional resolutions. Because sample preparation and imaging is not constrained by crystal orientation, FE-SEM and TEM of Pt-C replicas are best suited to image the overall morphology of microcrystals. However, owing to the decoration effect of Pt-C on the crystal faces, TEM of Pt-C replicas is superior at resolving nanoscale surface structures, including the development of new faces and the different microtopography among nonequivalent faces in microcrystals, which cannot be revealed by FE-SEM. In conjunction with SEM, Pt-C replica provides the evidence that crystals grow in diverse and face-specific modes. The TEM imaging of Pt-C replicas has nanoscale resolution comparable to AFM. AFM yielded quantitative information (e.g., crystallographic orientation and height of steps) of microtopographic features. In contrast to Pt-C replicas and SEM providing three-dimensional images of the crystals, AFM can only image one individual cleavage or flat surface at a time.

  17. Study of wettability of calcite surfaces using oil-brine-enzyme systems for enhanced oil recovery applications

    DEFF Research Database (Denmark)

    Khusainova, Alsu; Nielsen, Sidsel Marie; Pedersen, Hanne Høst

    2015-01-01

    action has been found to be replacement of oil at the solid surface by the enzyme. Other mechanisms (modification of the surface tension or catalytic modification of hydrocarbons resulting in reducing the oil viscosity) have shown to be much less pronounced from the measurements reported here.......Enzymes have recently been considered as possible agents for enhanced oil recovery (EOR) acting at the liquid-solid interface. One way to assess this is via measuring the wettability of calcite surfaces, important for EOR methods in carbonaceous reservoirs. In the present work, we have...... experimentally investigated the effect of enzymes on the wettability of calcite mineral surfaces with oil-brine systems. The action of various enzymes, including esterases/lipases, carbohydrases, proteases and oxidoreductases (along with two commercial mixtures) was studied by contact angle measurements...

  18. Nanoscale observations of the effect of citrate on calcium oxalate precipitation on calcite surfaces.

    Science.gov (United States)

    Burgos-Cara, Alejandro; Ruiz-Agudo, Encarnacion; Putnis, Christine V.

    2016-04-01

    Calcium oxalate (CaC2O4ṡxH2O) minerals are naturally occurring minerals found in fossils, plants, kidney stones and is a by-product in some processes such as paper, food and beverage production [1,2]. In particular, calcium oxalate monohydrate phase (COM) also known as whewellite (CaC2O4ṡH2O), is the most frequently reported mineral phase found in urinary and kidney stones together with phosphates. Organic additives are well known to play a key role in the formation of minerals in both biotic and abiotic systems, either facilitating their precipitation or hindering it. In this regard, recent studies have provided direct evidence demonstrating that citrate species could enhance dissolution of COM and inhibit their precipitation. [3,4] The present work aims at evauate the influence of pH, citrate and oxalic acid concentrations in calcium oxalate precipitation on calcite surfaces (Island Spar, Chihuahua, Mexico) through in-situ nanoscale observation using in situ atomic force microscopy (AFM, Multimode, Bruker) in flow-through experiments. Changes in calcium oxalate morphologies and precipitated phases were observed, as well as the inhibitory effect of citrate on calcium oxalate precipitation, which also lead to stabilization an the amorphous calcium oxalate phase. [1] K.D. Demadis, M. Öner, Inhibitory effects of "green"additives on the crystal growth of sparingly soluble salts, in: J.T. Pearlman (Ed.), Green Chemistry Research Trends, Nova Science Publishers Inc., New York, 2009, pp. 265-287. [2] M. Masár, M. Zuborová, D. Kaniansky, B. Stanislawski, Determination of oxalate in beer by zone electrophoresis on a chip with conductivity detection, J. Sep. Sci. 26 (2003) 647-652. [3] Chutipongtanate S, Chaiyarit S, Thongboonkerd V. Citrate, not phosphate, can dissolve calcium oxalate monohydrate crystals and detach these crystals from renal tubular cells. Eur J Pharmacol 2012;689:219-25. [4] Weaver ML, Qiu SR, Hoyer JR, Casey WH, Nancollas GH, De Yoreo JJ

  19. Aragonite-calcite precipitation in vertical fractures of the "Erzberg" siderite deposit (Austria): Hydrogeochemical and neotectonic implications

    Science.gov (United States)

    Boch, Ronny; Wang, Xianfeng; Kluge, Tobias; Kurz, Walter; Leis, Albrecht; Lin, Ke; Pluch, Hannes; Mittermayr, Florian; Dietzel, Martin

    2017-04-01

    significant proportion from soil CO2. Prominently high δ13C in DIC (≤+3.8 ‰) were also measured in modern fracture waters next to elevated sulfate (up to 226 mg/l) and high total dissolved solid contents (up to 1273 mg/l). These results suggest intense water-rock interaction based on sulfide oxidation and sulfuric acid evolution providing an efficient mechanism for host rock dissolution, mobilization and typically rapid aragonite-calcite mineralization. Sulfide accessories are widespread at Erzberg and the brownish Fe-rich layers within erzbergite could be explained by corrosion of Fe-sulfides and/or Fe-carbonates. The aragonite-calcite lamination is interpreted as an event lamination (not annual), i.e. variable aqueous Mg2+/Ca2+ ratios and CaCO3 supersaturation states triggering the polymorphism. U-Th analyses yielded surprisingly young ages for erzbergite dated so far, i.e. late Pleistocene and mostly younger than the last glacial maximum. A 4 cm thick sample composed of aragonite exclusively and filling a tenths of meters extending fracture formed 10.4 ±0.2 (sample base, initiation) to 1.03 ±0.04 kyr BP (top, fracture filled). Another 25 cm laminated aragonite-calcite precipitate covers 14.2 ±0.2 to 5.0 ±0.2 kyr. Thus, the precipitates support geologically young and rather short time intervals of infilling and we consider it unlikely that the fractures are much older. An intimate connection with neotectonic activity entailing new vadose water flow routes and fresh reaction surfaces in fractures would be in accordance with our hydrogeochemical and field observations.

  20. Infrared spectroscopy and density functional theory investigation of calcite, chalk, and coccoliths-do we observe the mineral surface?

    DEFF Research Database (Denmark)

    Andersson, Martin Peter; Hem, Caroline Piper; Schultz, Logan Nicholas

    2014-01-01

    We have measured infrared spectra from several types of calcite: chalk, freshly cultured coccoliths produced by three species of algae, natural calcite (Iceland Spar), and two types of synthetic calcite. The most intense infrared band, the asymmetric carbonate stretch vibration, is clearly asymme...

  1. The radiogenic and stable Sr isotope geochemistry of basalt weathering in Iceland: Role of hydrothermal calcite and implications for long-term climate regulation

    Science.gov (United States)

    Andrews, M. Grace; Jacobson, Andrew D.

    2017-10-01

    volcanic C flux introduced to the atmosphere-ocean system as HCO3- after subsurface silicate weathering does not regulate long-term climate. Because hydrothermal calcite simply sequesters some of this HCO3- and delays its transmission to the atmosphere-ocean system until it dissolves at the surface later in time, it can be concluded the weathering of hydrothermal calcite bearing non-atmospheric C also has no effect on long-term climate regulation. Icelandic riverine HCO3- fluxes should be corrected for the hydrothermal calcite weathering contribution prior to quantifying atmospheric CO2 consumption rates by basalt weathering at the Earth's surface.

  2. Interactions of the Calcite {10.4} Surface with Organic Compounds: Structure and Behaviour at Mineral – Organic Interfaces

    DEFF Research Database (Denmark)

    Hakim, S. S.; Olsson, M. H. M.; Sørensen, H. O.

    2017-01-01

    that control crystal growth with organic macromolecules. Carbonate rocks, composed almost exclusively of calcite, host drinking water aquifers and oil reservoirs. In this study, we examined the ordering behaviour of several organic compounds and the thickness of the adsorbed layers formed on calcite {10...

  3. Nanometer-Scale Chemistry of a Calcite Biomineralization Template: Implications for Skeletal Composition and Nucleation

    Science.gov (United States)

    Bonnin, Elisa A.; Perea, Daniel E.; Spero, Howard J.; Zhu, Zihua; Winters, Maria; Hönisch, Bärbel; Russell, Ann D.; Fehrenbacher, Jennifer S.; Gagnon, Alexander C.

    2016-01-01

    Plankton, corals, and other organisms produce calcium carbonate skeletons that are integral to their survival, form a key component of the global carbon cycle, and record an archive of past oceanographic conditions in their geochemistry. A key aspect of the formation of these biominerals is the interaction between organic templating structures and mineral precipitation processes. Laboratory-based studies have shown that these atomic-scale processes can profoundly influence the architecture and composition of minerals, but their importance in calcifying organisms is poorly understood because it is difficult to measure the chemistry of in vivo biomineral interfaces at spatially relevant scales. Understanding the role of templates in biomineral nucleation, and their importance in skeletal geochemistry requires an integrated, multiscale approach, which can place atom-scale observations of organic-mineral interfaces within a broader structural and geochemical context. Here we map the chemistry of an embedded organic template structure within a carbonate skeleton of the foraminifera Orbulina universa using both atom probe tomography (APT), a 3D chemical imaging technique with Ångström-level spatial resolution, and time-of-flight secondary ionization mass spectrometry (ToF-SIMS), a 2D chemical imaging technique with submicron resolution. We quantitatively link these observations, revealing that the organic template in O. universa is uniquely enriched in both Na and Mg, and contributes to intraskeletal chemical heterogeneity. Our APT analyses reveal the cation composition of the organic surface, offering evidence to suggest that cations other than Ca2+, previously considered passive spectator ions in biomineral templating, may be important in defining the energetics of carbonate nucleation on organic templates. PMID:27794119

  4. Diagenesis associated with subaerial exposure of Miocene strata, southeastern Spain: Implications for sea-level change and preservation of low-temperature fluid inclusions in calcite cement

    Science.gov (United States)

    Goldstein, R.H.; Franseen, E.K.; Mills, M.S.

    1990-01-01

    Many ancient carbonate rocks contain calcite cements that precipitated from shallow, fresh groundwater that entered strata during events of subaerial exposure. Such low-temperature cementation may be difficult to interpret from fluid inclusion studies because some of the inclusions may reequilibrate during later thermal events. Miocene rocks of southeast Spain provide an example of the utility of fluid inclusion studies in rocks that have not been subjected to significant heating. In the Mesa Roldan area, one type of calcite cement occurs exclusively below a regional stratigraphic surface of enigmatic origin. The cement has petrographic characteristics indicative of cementation in the vadose zone (generally thought to be a zone of oxidation) but has cathodoluminescent bands containing reduced manganese and iron. Primary fluid inclusions contain mostly fresh water, have variable ratios of vapor to liquid, and are at one atmosphere of pressure. Our observations indicate that calcite precipitated from a freshwater vadose zone, which was subjected to local or repetitive saturation, and minor brackish water. The fluid inclusion data indicate that low-temperature fluid inclusions can be preserved in ancient sequences despite a later history of different pore fluids. This indication of subaerial diagenesis of distal slope deposits suggests a relative sea-level drop of at least 50-55 m during the Late Miocene. Similar petrographic and fluid inclusion observations can be used to interpret sea-level changes in other areas. ?? 1990.

  5. Early diagenetic high-magnesium calcite and dolomite indicate that coal balls formed in marine or brackish water: Stratigraphic and paleoclimatic implications

    Science.gov (United States)

    Raymond, Anne

    2016-04-01

    Coal balls are carbonate and pyrite permineralizations of peat that contain three-dimensional plant fossils preserved at the cellular level. Coal balls, which occur in Pennsylvanian and earliest Permian equatorial coals, provide a detailed record of terrestrial ecology and tropical climate during the Late Paleozoic Ice Age; yet their depositional environment remains controversial. The exquisite preservation of some coal-ball fossils, e.g. pollen with pollen tubes and leaves with mesophyll, indicates rapid formation. The presence of abundant, cement-filled, void spaces within and between the plant debris in most coal balls indicates that they formed in uncompacted peat, near the surface of the mire. Botanical, taphonomic and isotopic evidence point to a freshwater origin for coal balls. The nearest living relatives of coal ball plants (modern lycopsids, sphenopsids, marratialean ferns and conifers) grow in fresh water. Coal-ball peat contains a high percentage of aerial debris, similar to modern freshwater peat. The stable oxygen isotopes of coal-ball carbonate (δ18O = 16 to 3 per mil) suggest a freshwater origin. However, the widespread occurrence of marine invertebrates and early diagenetic framboidal pyrite in coal balls suggests that many formed in close proximity to marine water. Indeed, carbonate petrology points to a marine or brackish water origin for the first-formed carbonate cements in coal balls. Petrographic and geochemical (microprobe) analysis of coal-ball carbonates in Pennsylvanian coals from the midcontinent of North America (Western Interior Basin, West Pangaea) and the Ruhr and Donets Basins (East Pangaea) indicate that the first formed carbonate is either radaxial, nonstochiometric dolomite or high magnesium calcite (9 - 17 mol % MgCO3, indicating precipitation in marine or brackish water. Although both primary dolomite and high magnesium calcite can form in lacustrine settings, the lakes in which these minerals form occur in carbonate terranes

  6. Stratigraphic implications of trace element and strontium-isotope analyses of Kimmeridgian shell calcite from the Lower Saxony Basin, Germany

    Science.gov (United States)

    Zuo, Fanfan; Heimhofer, Ulrich; Huck, Stefan; Erbacher, Jochen; Bodin, Stephane

    2017-04-01

    Stratigraphic uncertainties due to the lack of open marine marker fossils (e.g. ammonites) hamper the precise age assignment and stratigraphic correlation of Kimmeridgian strata found in the Lower Saxony Basin of Northern Germany. Correlation of these deposits with the Jurassic standard ammonite zonation is still difficult, since the existing ostracod biostratigraphy is facies-controlled and of only limited stratigraphic precision. In this study, a chemostratigraphic approach has been chosen and biogenic shell material produced by brachiopods, oysters and lithiotids is evaluated for its reliability to act as proxy of the original Jurassic seawater strontium isotope composition. Low-Mg calcite shells have been collected from three stratigraphic sections accessible in open-cast quarries located in the Lower Saxony Basin of Northern Germany. In order to identify diagenetically altered shell calcite, trace element and stable isotope analysis of 227 calcite samples (oysters=101; brachiopods=60; Trichites=52) has been carried out. The geochemical results reveal that (1) concentration of different trace elements varies between the different groups of shell-forming organisms, which may be related to vital effects and (2) high strontium contents, low Mn and Fe contents and the lack of correlation between these elements indicate near-pristine calcite shells, and therefore shells are supposed to record the ambient sea water composition during the Late Jurassic. Strontium-isotope (87Sr/86Sr) analysis of diagenetically screened samples indicates an Early Kimmeridgian age of the studied deposits, which is in accordance with ostracod biostratigraphic data. An increasing trend in 87Sr/86Sr with stratigraphic height fits well with the global strontium-isotope curve. Besides, similar 87Sr/86Sr ratios derived from different organisms from a single stratigraphic level highlight the suitability of the shells for strontium-isotope stratigraphy. Despite the shallow-marine character of

  7. Zircon-quartz-calcite segregations in carbonate-alkaline metasomatic rocks of the western Baikal region and their petrogenetic implications

    Science.gov (United States)

    Savelyeva, V. B.; Bazarova, E. P.; Sharygin, V. V.; Karmanov, N. S.

    2015-12-01

    Fine-grained segregations up to 5 mm in size composed of graphic intergrowths of zircon, quartz, calcite and containing up to 0.8 wt % SrO have been found in albite-riebeckite and dolomite-biotite metasomatic rocks formed after alaskite granite. They contain magnetite, titanomagnetite (25.4 wt % TiO2), cerite-(Ce,Nd), rutile (up to 1.2 wt % Nb2O5), as well as rare micrograins of monazite-(Ce), bastnaesite-(Ce), and barite (up to 5.7 wt % SrO). The fine-grained structure of mineral aggregates suggests a metacolloidal nature. It is assumed that the zircon-quartz-calcite assemblage was formed due to exchange decomposition reaction between the salt phase of hydrothermal solution with predominant Na2CO3, elevated Zr and, to a lesser extent, Fe, Ti, LREE, Nb contents and dissolved calcium and silica compounds of a Na2SiO3 type.

  8. A Non-Electrostatic Surface Complexation Approach to Modeling Radionuclide Migration at the Nevada Test Site: I. Iron Oxides and Calcite

    Energy Technology Data Exchange (ETDEWEB)

    Zavarin, M; Bruton, C J

    2004-12-17

    Reliable quantitative prediction of contaminant transport in subsurface environments is critical to evaluating the risks associated with radionuclide migration. As part of the Underground Test Area (UGTA) project, radionuclide transport away from various underground nuclear tests conducted in the saturated zone at the Nevada Test Site (NTS) is being examined. In the near-field environment, reactive transport simulations must account for changes in water chemistry and mineralogy as a function of time and their effect on radionuclide migration. Unlike the K{sub d} approach, surface complexation (SC) reactions, in conjunction with ion exchange and precipitation, can be used to describe radionuclide reactive transport as a function of changing environmental conditions. They provide a more robust basis for describing radionuclide retardation in geochemically dynamic environments. The interaction between several radionuclides considered relevant to the UGTA project and iron oxides and calcite are examined in this report. The interaction between these same radionuclides and aluminosilicate minerals is examined in a companion report (Zavarin and Bruton, 2004). Selection criteria for radionuclides were based on abundance, half-life, toxicity to human and environmental health, and potential mobility at NTS (Tompson et al., 1999). Both iron oxide and calcite minerals are known to be present at NTS in various locations and are likely to affect radionuclide migration from the near-field. Modeling the interaction between radionuclides and these minerals was based on surface complexation. The effectiveness of the most simplified SC model, the one-site Non-Electrostatic Model (NEM), to describe sorption under various solution conditions is evaluated in this report. NEM reactions were fit to radionuclide sorption data available in the literature, as well as sorption data recently collected for the UGTA project, and a NEM database was developed. For radionuclide-iron oxide sorption

  9. Investigating the Basis of Biogenic Calcium Carbonate Formation from an Amorphous Precursor: Nature of the Transformation to Calcite on Hydroxyl Functionalized Surfaces

    Science.gov (United States)

    Wang, D.; Lee, J. R.; Talley, C. E.; Murphy, K. E.; Han, T. Y.; Deyoreo, J. J.; Dove, P. M.

    2006-12-01

    Calcium carbonate biominerals are particularly significant because of their direct role in regulating the global carbon cycle, as well as their ubiquitous occurrence across earth environments. Biogenic carbonates are further distinguished by their broad phlyogenetic distribution; hence it has been suggested that unrelated eukaryotes must have used similar biochemical strategies to control mineralization. Recent studies have shown that an amorphous calcium carbonate (ACC) phase potentially plays a key role in the initial formation of carbonate minerals and in "shaping" them into complex morphologies widely seen in biominerals. Echinoderms, mollusks, and possibly many other organisms use ACC as a precursor phase that is first nucleated in cellularly controlled environments such as vesicles and subsequently transforms into a fully crystalline material. Recent studies on sea urchin embryos have shown that during transformation ACC develops short range that resembles calcite before fully crystallizing and serve as inspiration for our studies in synthetic systems. Self-assembled monolayers (SAM) on gold and silver have been used as simple model systems that approximate biological surfaces. Many studies have shown that thiol monolayers with hydroxyl termination stabilize a transitory ACC film that with prolonged exposure to aqueous solution transforms into calcite nucleated on {104} faces. Using Near Edge X-ray Absorption Fine Structure (NEXAFS) we studied SAM/mineral interactions with well ordered mercaptophenol monolayers showed that when these films are first exposed to calcium carbonate solutions, they become disordered and remain so after subsequent deposition of an ACC over-layer. Yet calcite nucleates and grows from the surface bound ACC with predominantly {104} orientation, which suggests a dynamic structural relationship between the SAMs and the mineral phase. While the monolayer/mineral phase interaction has been characterized, the mechanism for nucleating

  10. Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation

    Science.gov (United States)

    Reddy, Michael M.

    2012-08-01

    Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (Ωc). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and Ωc=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10-4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10-4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

  11. Calcite Twinning in the Ordovician Martinsburg Formation, Delaware Water Gap, New Jersey, USA: Implications for Cleavage Formation and Tectonic Shortening in the Appalachian Piedmont Province

    Directory of Open Access Journals (Sweden)

    John P. Craddock

    2016-02-01

    Full Text Available A traverse across the Stone Church syncline in the Ordovician Martinsburg turbidites reveals an axial planar cleavage (N40°E, SE dips in regional thrust-related folds (N40°E, shallow plunges and five phases of sparry calcite. Calcite fillings are bedding-parallel, cleavage-parallel, and one vein set cross-cuts both earlier phases; the youngest calcite filling is a bedding-parallel fault gouge that crosscuts the cleavage and preserves top-down-to-the-southeast normal fault kinematics. Calcite veins unique to disharmonically-folded calcareous siltstones (Maxwell, 1962 were also analyzed. Stable isotopic analysis (O, C of all of the calcite phases indicates a uniform fluid source (δ13C −2.0, δ18O −13.3 VPDB and, potentially, a similar precipitation and mechanical twinning age. The twinning strains (n = 1341; average Δσ = −32 MPa; average ε1 = −2.9% in the calcite suite are consistent with SE-NW thrust shortening, and sub-horizontal shortening perpendicular to evolving axial planar cleavage planes in the Stone Church syncline. Calcareous siltstone layers within the Martinsburg Fm. turbidites share concordant bedding planes and are unique, chemically (XRF, but folded and cleaved differently than the surrounding clay-rich Martinsburg turbidites. Neither sediment type yielded detrital zircons. Electron backscatter X-ray diffraction (EBSD and calcite twinning results in a folded calcareous siltstone layer preserving a layer-normal SE-NW shortening strain and Lattice Preferred Orientation (LPO. Shortening axes for the five-phase calcite suite trends ~N40°W, consistent with tectonic transport associated with crystalline nappe emplacement of the Reading Prong within the Piedmont province.

  12. Differences in the rheological properties of calcitic and dolomitic lime slurries: influence of particle characteristics and practical implications in lime-based mortar manufacturing

    Directory of Open Access Journals (Sweden)

    Arizzi, A.

    2012-06-01

    Full Text Available The study of the rheological properties of lime suspensions is a useful means to evaluate the workability of lime mortars. In this work, we studied the flow behaviour of two industrial hydrated limes, one of calcitic and the other of dolomitic composition, by means of two types of rheometer with different geometry and setup mode. The obtained results were interpreted taking into account the differences in microstructure and surface properties of the suspended particles. Calcitic lime dry particles are formed by angular and polydisperse clusters and, once dispersed in water, they behave like thixotropic materials. On the other hand, the dolomitic lime is formed by nanoparticles and small round cluster and it shows a pronounced plastic behaviour in suspension. This fundamental difference between the two materials explains the traditional preference for dolomitic lime mortars for plastering and rendering applications.

    El estudio de las propiedades reológicas de suspensiones de cal es una herramienta muy útil para evaluar la trabajabilidad de morteros de cal. En este trabajo se ha estudiado el comportamiento en suspensión de dos cales hidratadas, de composición calcítica y dolomítica, mediante dos tipos de reómetros con geometría y modalidades distintas de medida. Los resultados obtenidos se han interpretado teniendo en cuenta las diferencias en la microestructura y las propiedades de superficie de las partículas en suspensión. Las partículas de cal calcítica están formadas por aglomerados angulares y polidispersos y, una vez dispersadas en agua, presentan un comportamiento tixotrópico. Por su parte, la cal dolomítica está formada por nanopartículas y pequeños agregados redondeados y muestra en suspensión un pronunciado comportamiento plástico. Esta importante diferencia entre las dos cales explica la preferencia tradicional de morteros de cal dolomítica para aplicaciones en revocos.

  13. Mechanisms of Subcritical Cracking in Calcite

    Science.gov (United States)

    Royne, A.; Dysthe, D. K.; Bisschop, J.

    2008-12-01

    Brittle materials are characterized by a critical stress intensity factor above which they will fail catastrophically by dynamic cracking. However, it has been observed that materials can also fail at much lower stresses, through slow crack growth, often referred to as subcritical cracking. This phenomenon can take place even in vacuum, but is greatly enhanced by water and other reactive species in the environment. For a given material and environmental condition there is a systematic relationship between the crack tip velocity and the stress intensity factor. The presence of a lower stress limit to subcritical cracking has been predicted from thermodynamics but has not been firmly demonstrated experimentally. This parameter would control the long- term strength of geological materials. Subcritical cracking must necessarily be important in controlling the rock strength in near-surface processes where water and other active species are present and the displacements and stresses are low. Weathering is one example of such a process. Modelling has shown that fracture networks generated by a high degree of subcritical cracking will percolate at much lower fracture densities than purely stochastical fracture networks. This has important implications for how water can move through the crust. Understanding the mechanisms for subcritical crack growth in geological materials is also important in assessing the stability and long term performance of sequestration reservoirs for CO2 or nuclear waste. The mechanism for stress corrosion is well known for glasses and quartz. For carbonate minerals, the mechanism for subcritical crack growth has not been identified, and the only experimental studies on calcitic materials have been on polycrystalline rocks such as marble. Suggested mechanisms include stress corrosion (weakening reactions at the crack tip), preferential dissolution at the crack tip with rapid removal of dissolved species, and environmentally controlled

  14. The origin of carbon isotope vital effects in coccolith calcite

    Science.gov (United States)

    McClelland, H. L. O.; Bruggeman, J.; Hermoso, M.; Rickaby, R. E. M.

    2017-03-01

    Calcite microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved calcite plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith calcite exhibits large and enigmatic departures from the isotopic composition of abiogenic calcite, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith calcite is isotopically heavier or lighter than abiogenic calcite, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2 paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive.

  15. Calcite Dissolution Kinetics

    Science.gov (United States)

    Berelson, W.; Subhas, A.; Dong, S.; Naviaux, J.; Adkins, J. F.

    2016-12-01

    A geological buffer for high atmospheric CO2 concentrations is neutralization via reaction with CaCO3. We have been studying the dissolution kinetics of carbonate minerals using labeled 13C calcite and Picarro-based measurements of 13C enrichments in solution DIC. This methodology has greatly facilitated our investigation of dissolution kinetics as a function of water carbonate chemistry, temperature and pressure. One can adjust the saturation state Omega by changing the ion activity product (e.g. adjusting carbonate ion concentration), or by changing the solubility product (e.g. adjusting temperature or pressure). The canonical formulation of dissolution rate vs. omega has been refined (Subhas et al. 2015) and shows distinct non-linear behavior near equilibrium and rates in sea water of 1-3 e-6 g/cm2day at omega = 0.8. Carbonic anhydrase (CA), an enzyme that catalyzes the hydration of dissolved CO2 to carbonic acid, was shown (in concentrations rate at low degrees of undersaturation by >500x. This result points to the importance of carbonic acid in enhancing dissolution at low degrees of undersaturation. CA activity and abundance in nature must be considered regarding the role it plays in catalyzing dissolution. We also have been investigating the role of temperature on dissolution kinetics. An increase of 16C yields an order of magnitude increase in dissolution rate. Temperature (and P) also change Omega critical, the saturation state where dissolution rates change substantially. Increasing pressure (achieved in a pressure reaction chamber we built) also shifts Omega critical closer to equilibrium and small pressure increases have large impact on dissolution kinetics. Dissolution rates are enhanced by an order of magnitude for a change in pressure of 1500 psi relative to the dissolution rate achieved by water chemistry effects alone for an omega of 0.8. We've shown that the thermodynamic determination of saturation state does not adequately describe the kinetics

  16. Calcite dissolution kinetics at the interface between a calcite-rich simulated sediment and natural seawater.

    Science.gov (United States)

    Sulpis, O.; Lix, C.; Mucci, A.; Boudreau, B. P.

    2016-12-01

    Over the past decades, numerous studies of CaCO3 mineral dissolution kinetics have been performed in seawater. Despite this continuous effort, the mechanisms controlling the dissolution are still poorly understood and large discrepancies exist between results of in-situ and laboratory studies, most of which have been carried out under conditions (e.g., mineral suspensions) that are not representative of processes taking place at the seafloor. In this study, we addressed this issue by using a synthetic sediment disk composed of a mixture of calcite and montmorillonite, in a thermostated, stirred-flow reactor over a range of seawater undersaturations in an attempt to simulate conditions encountered at the seafloor. We show that, unlike the higher reaction orders reported in previous studies, the dissolution kinetics of calcite are almost linearly dependent on the seawater undersaturation with respect to calcite when normalized to the exposed surface area of the disks, with a rate constant similar to that derived by Keir (1983) using reagent calcite. Even under quiescent conditions, the calcite dissolution appears to extend well below the sediment-water interface of our synthetic sediment disks. When normalized to the geometric surface area of calcite within the apparent reaction volume, the dissolution kinetics are also nearly linear, with a dissolution rate constant whose value is orders of magnitude lower than previously reported. Keir, R. S. (1983), Variation in the carbonate reactivity of deep-sea sediments: determination from flux experiments, Deep Sea Res., Part A, 30, 279-296.

  17. Elastic constants of calcite

    Science.gov (United States)

    Peselnick, L.; Robie, R.A.

    1962-01-01

    The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.

  18. Acidization of shales with calcite cemented fractures

    Science.gov (United States)

    Kwiatkowski, Kamil; Szymczak, Piotr; Jarosiński, Marek

    2017-04-01

    Investigation of cores drilled from shale formations reveals a relatively large number of calcite-cemented fractures. Usually such fractures are reactivated during fracking and can contribute considerably to the permeability of the resulting fracture network. However, calcite coating on their surfaces effectively excludes them from production. Dissolution of the calcite cement by acidic fluids is investigated numerically with focus on the evolution of fracture morphology. Available surface area, breakthrough time, and reactant penetration length are calculated. Natural fractures in cores from Pomeranian shale formation (northern Poland) were analyzed and classified. Representative fractures are relatively thin (0.1 mm), flat and completely sealed with calcite. Next, the morphology evolution of reactivated natural fractures treated with low-pH fluids has been simulated numerically under various operating conditions. Depth-averaged equations for fracture flow and reactant transport has been solved by finite-difference method coupled with sparse-matrix solver. Transport-limited dissolution has been considered, which corresponds to the treatment with strong acids, such as HCl. Calcite coating in reactivated natural fractures dissolves in a highly non-homogeneous manner - a positive feedback between fluid transport and calcite dissolution leads to the spontaneous formation of wormhole-like patterns, in which most of the flow is focused. The wormholes carry reactive fluids deeper inside the system, which dramatically increases the range of the treatment. Non-uniformity of the dissolution patterns provides a way of retaining the fracture permeability even in the absence of the proppant, since the less dissolved regions will act as supports to keep more dissolved regions open. Evolution of fracture morphology is shown to depend strongly on the thickness of calcite layer - the thicker the coating the more pronounced wormholes are observed. However the interaction between

  19. The effect of the Ca2+ to CO32- activity ratio on spiral growth at the calcite {1014} surface

    DEFF Research Database (Denmark)

    Larsen, Kirsten Kolbjørn; Bechgaard, Klaus; Stipp, Susan Louise Svane

    2010-01-01

    Variation in the Ca2+ to CO 2¿ activity ratio of natural waters is rarely considered in models intended to describe calcite 3 growth. Atomic force microscopy (AFM) and differential interference contrast (DIC) microscopy were used to examine spiral growth on calcite f10¿14g surfaces from solutions...... steps grow faster 3 than acute steps but this trend reverses at low activity ratios. This is reflected in the morphology of growth pyramids. The reversal in the inequivalent step growth velocity indicates that the hydrated carbonate ion preferentially incorporates at kink sites along the more...... structurally open obtuse step edges, whereas the hydrated calcium ion is more easily accommodated at the more confined acute step kink sites. Furthermore, the experimental data demonstrate that velocity is maximum for obtuse steps when the activities of Ca2+ and CO 2¿ are equal, whereas maximum acute step...

  20. Binding of ethanol on calcite: the role of the OH bond and its relevance to biomineralization.

    Science.gov (United States)

    Sand, K K; Yang, M; Makovicky, E; Cooke, D J; Hassenkam, T; Bechgaard, K; Stipp, S L S

    2010-10-05

    The interaction of OH-containing compounds with calcite, CaCO(3), such as is required for the processes that control biomineralization, has been investigated in a low-water solution. We used ethanol (EtOH) as a simple, model, OH-containing organic compound, and observed the strength of its adsorption on calcite relative to OH from water and the consequences of the differences in interaction on crystal growth and dissolution. A combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations showed that EtOH attachment on calcite is stronger than HOH binding and that the first adsorbed layer of ethanol is highly ordered. The strong ordering of the ethanol molecules has important implications for mineral growth and dissolution because it produces a hydrophobic layer. Ethanol ordering is disturbed along steps and at defect sites, providing a bridge from the bulk solution to the surface. The strong influence of calcite in structuring ethanol extends further into the liquid than expected from electrical double-layer theory. This suggests that in fluids where water activity is low, such as in biological systems optimized for biomineralization, organic molecules can control ion transport to and from the mineral surface, confining it to specific locations, thus providing the organism with control for biomineral morphology.

  1. Evaluation of Surface and Transport Limitations to the Rate of Calcite Dissolution Using Pore Scale Modeling of a Capillary Tube Experiment at pCO2 4 bar

    Science.gov (United States)

    Molins, S.; Trebotich, D.; Yang, L.; Ajo Franklin, J. B.; Ligocki, T.; Shen, C.; Steefel, C. I.

    2013-12-01

    Mineral trapping is generally considered to account for most of the long-term trapping of CO2 in the subsurface. Prediction of mineral trapping at the reservoir scale requires knowledge of continuum-scale mineral dissolution and precipitation rates. However, processes that take place at the pore scale (e.g., transport limitation to reactive surfaces) affect rates applicable at the continuum scale. To explore the pore scale processes that result in the discrepancy between rates measured in laboratory experiments and those calibrated from continuum-scale models, we have developed a high-resolution pore scale model of a capillary tube experiment. The capillary tube (L=0.7-cm, D=500-μm) is packed with crushed calcite (Iceland spar) and the resulting 3D pore structure is imaged by X-ray computed microtomography (XCMT) at Berkeley Lab's Advanced Light Source at a 0.899-μm resolution. A solution in equilibrium with a partial pressure of CO2 of 4 bars is injected at a rate of 5 microliter/min and the effluent concentrations of calcium are measured to ensure steady state conditions are achieved. A simulation domain is constructed from the XCMT image using implicit functions to represent the mineral surface locally on a grid. The pore-scale reactive transport model is comprised of high performance simulation tools and algorithms for incompressible Navier-Stokes flow, advective-diffusive transport and multicomponent geochemical reactions. Simulations are performed using 6,144 processors on NERSC's Cray XE6 Hopper to achieve a grid resolution of 2.32 μm. Equivalent continuum scale simulations are also performed to evaluate the effect of pore scale processes. Comparison of results is performed based on flux-averaged effluent calcium concentrations, which are used as indicator of effective rates in the capillary tube. Results from both pore- and continuum-scale simulations overestimate the calcium effluent concentrations, suggesting that the TST rate expression parameters

  2. Calcite growth rates as a function of aqueous calcium-to-carbonate ratio, saturation index and strontium concentration

    Energy Technology Data Exchange (ETDEWEB)

    Bracco, Jacquelyn N [ORNL; Grantham, Ms. Meg [Georgia Institute of Technology; Stack, Andrew G [ORNL

    2012-01-01

    Using in situ atomic force microscopy, the growth rates of the obtuse and acute step orientations on the calcite surface were measured at two saturation indices as a function of the aqueous calcium-to-carbonate ratio and aqueous strontium concentration. The amount of strontium required to inhibit growth was found to correlate with the aqueous calcium concentration, but did not correlate with carbonate. This suggests that strontium inhibits attachment of calcium ions to the reactive sites on the calcite surface. Strontium/calcium cation exchange selectivity coefficients for those sites, Kex, of 1.09 0.09 and 1.44 0.19 are estimated for the obtuse and acute step orientations, respectively. The implication of this finding is that to avoid poisoning calcite growth, the concentration of calcium should be higher than the quotient of the strontium concentration and Kex, regardless of saturation state. Additionally, analytical models of nucleation and propagation of steps are expanded from previous work to capture growth rates of these steps at multiple saturation indices and the effect of strontium. This work will have broader implications for naturally occurring or engineered calcite growth, such as to sequester subsurface strontium contamination.

  3. Life Sciences Implications of Lunar Surface Operations

    Science.gov (United States)

    Chappell, Steven P.; Norcross, Jason R.; Abercromby, Andrew F.; Gernhardt, Michael L.

    2010-01-01

    The purpose of this report is to document preliminary, predicted, life sciences implications of expected operational concepts for lunar surface extravehicular activity (EVA). Algorithms developed through simulation and testing in lunar analog environments were used to predict crew metabolic rates and ground reaction forces experienced during lunar EVA. Subsequently, the total metabolic energy consumption, the daily bone load stimulus, total oxygen needed, and other variables were calculated and provided to Human Research Program and Exploration Systems Mission Directorate stakeholders. To provide context to the modeling, the report includes an overview of some scenarios that have been considered. Concise descriptions of the analog testing and development of the algorithms are also provided. This document may be updated to remain current with evolving lunar or other planetary surface operations, assumptions and concepts, and to provide additional data and analyses collected during the ongoing analog research program.

  4. A comparative study of surface energies and water adsorption on Ce-bastnäsite, La-bastnäsite, and calcite via density functional theory and water adsorption calorimetry.

    Science.gov (United States)

    Goverapet Srinivasan, Sriram; Shivaramaiah, Radha; Kent, Paul R C; Stack, Andrew G; Riman, Richard; Anderko, Andre; Navrotsky, Alexandra; Bryantsev, Vyacheslav S

    2017-03-15

    Bastnäsite, a fluoro-carbonate mineral, is the single largest mineral source of light rare earth elements (REE), La, Ce and Nd. Enhancing the efficiency of separation of the mineral from gangue through froth flotation is the first step towards meeting an ever increasing demand for REE. To design and evaluate collector molecules that selectively bind to bastnäsite, a fundamental understanding of the structure and surface properties of bastnäsite is essential. In our earlier work (J. Phys. Chem. C, 2016, 120, 16767), we carried out an extensive study of the structure, surface stability and water adsorption energies of La-bastnäsite. In this work, we make a comparative study of the surface properties of Ce-bastnäsite, La-bastnäsite, and calcite using a combination of density functional theory (DFT) and water adsorption calorimetry. Spin polarized DFT+U calculations show that the exchange interaction between the electrons in Ce 4f orbitals is negligible and that these orbitals do not participate in bonding with the oxygen atom of the adsorbed water molecule. In agreement with calorimetry, DFT calculations predict larger surface energies and stronger water adsorption energies on Ce-bastnäsite than on La-bastnäsite. The order of stabilities for stoichiometric surfaces is as follows: [101[combining macron]0] > [101[combining macron]1] > [101[combining macron]2] > [0001] > [112[combining macron]2] > [101[combining macron]4] and the most favorable adsorption sites for water molecules are the same as for La-bastnäsite. In agreement with water adsorption calorimetry, at low coverage water molecules are strongly stabilized via coordination to the surface Ce3+ ions, whereas at higher coverage they are adsorbed less strongly via hydrogen bonding interaction with the surface anions. Due to similar water adsorption energies on bastnäsite [101[combining macron]1] and calcite [101[combining macron]4] surfaces, the design of collector molecules that selectively bind to

  5. Arsenic uptake in bacterial calcite

    Science.gov (United States)

    Catelani, Tiziano; Perito, Brunella; Bellucci, Francesco; Lee, Sang Soo; Fenter, Paul; Newville, Matthew; Rimondi, Valentina; Pratesi, Giovanni; Costagliola, Pilario

    2018-02-01

    Bio-mediated processes for arsenic (As) uptake in calcite were investigated by means of X-ray Diffraction (XRD) and X-ray Absorption Spectroscopy (XAS) coupled with X-ray Fluorescence measurements. The environmental bacterial strain Bacillus licheniformis BD5, sampled at the Bullicame Hot Springs (Viterbo, Central Italy), was used to synthesize calcite from As-enriched growth media. Both liquid and solid cultures were applied to simulate planktonic and biofilm community environments, respectively. Bacterial calcite samples cultured in liquid media had an As enrichment factor (Kd) 50 times higher than that from solid media. The XRD analysis revealed an elongation of the crystal lattice along the c axis (by 0.03 Å) for biogenic calcite, which likely resulted from the substitution of larger arsenate for carbonate in the crystal. The XAS data also showed a clear difference in the oxidation state of sorbed As between bacterial and abiotic calcite. Abiotic chemical processes yielded predominantly As(V) uptake whereas bacterial precipitation processes led to the uptake of both As(III) and As(V). The presence of As(III) in bacterial calcite is proposed to result from subsequent reduction of arsenate to arsenite by bacterial activities. To the best of our knowledge, this is the first experimental observation of the incorporation of As(III) in the calcite crystal lattice, revealing a critical role of biochemical processes for the As cycling in nature.

  6. Arsenic uptake in bacterial calcite

    Energy Technology Data Exchange (ETDEWEB)

    Catelani, Tiziano; Perito, Brunella; Bellucci, Francesco; Lee, Sang Soo; Fenter, Paul; Newville, Matthew G.; Rimondi, Valentina; Pratesi, Giovanni; Costagliola, Pilario

    2018-02-01

    Bio-mediated processes for arsenic (As) uptake in calcite were investigated by means of X-ray Diffraction (XRD) and Xray Absorption Spectroscopy (XAS) coupled with X-ray Fluorescence measurements. The environmental bacterial strain Bacillus licheniformis BD5, sampled at the Bullicame Hot Springs (Viterbo, Central Italy), was used to synthesize calcite from As-enriched growth media. Both liquid and solid cultures were applied to simulate planktonic and biofilm community environments, respectively. Bacterial calcite samples cultured in liquid media had an As enrichment factor (Kd) 50 times higher than that from solid media. The XRD analysis revealed an elongation of the crystal lattice along the c axis (by 0.03Å) for biogenic calcite, which likely resulted from the substitution of larger arsenate for carbonate in the crystal. The XAS data also showed a clear difference in the oxidation state of sorbed As between bacterial and abiotic calcite. Abiotic chemical processes yielded predominantly As(V) uptake whereas bacterial precipitation processes led to the uptake of both As(III) and As(V). The presence of As(III) in bacterial calcite is proposed to result from subsequent reduction of arsenate to arsenite by bacterial activities. To the best of our knowledge, this is the first experimental observation of the incorporation of As(III) in the calcite crystal lattice, revealing a critical role of biochemical processes for the As cycling in nature.

  7. Zinc isotope fractionation during adsorption on calcite

    Science.gov (United States)

    Dong, S.; Wasylenki, L. E.

    2013-12-01

    Zinc is an important element as a nutrient in the marine biosphere. However, our understanding of its biogeochemical cycling in the oceans is relatively limited. The Zn stable isotope system holds the promise of providing novel insights, since published Zn isotopic values for various natural samples reveal significant fractionations in the marine environment. Surface seawater, basalts, shales, deep-sea clay sediments, sediment trap material, bulk plankton and zooplankton samples, and eolian dust fall within a tight range (δ66/64Zn from -0.1 to 0.5‰), but modern ferromanganese crusts (δ66/64Zn from 0.5 to 1.2‰), as well as carbonates (δ66/64Zn from 0.3 to 1.4‰), are notably enriched in heavy Zn isotopes [1-4]. In this study we seek to constrain the mechanism by which carbonates are enriched in heavier isotopes. In particular, we have conducted experiments to quantify isotope fractionation during adsorption of Zn onto the surfaces of calcite crystals that are in equilibrium with solution. The adsorption experiments were carried out in a series of small-volume batch reactions in a clean laboratory environment, using high-purity reagents and calcite seed crystals. The calcite was equilibrated with the solution prior to addition of Zn at atmospheric CO2 pressure (i.e., in air) for 5 days until a stable pH of 8.3 was reached. Later, a small aliquot of dissolved ZnCl2 was added such that the solution remained undersaturated with respect to hydrozincite. Experimental duration varied among the replicates from 6 to 144 hours, and then all solids and solutions were separated by filtration, purified by ion exchange chromatography, and analyzed by MC-ICP-MS. Zn adsorbed on calcite is isotopically heavier than in the co-existing solutions, with Δ68/66Zncalcite-solution of approximately 0.3‰. The variation of Δ68/66Zncalcite-solution beyond 24 hours is insignificant, so we infer that isotopic equilibrium is reached by this time. Previous work strongly suggests that a

  8. Ion beam modifications of defect sub-structure of calcite cleavages

    Indian Academy of Sciences (India)

    WINTEC

    Planar plastic anisotropy has been studied on irradiated calcite cleavages by measurement of micro- hardness. Keywords. Calcite crystals; ion-bombardment; optical microscopy; ... in the near surface composition (Arnold and Peercy 1980). The ultimate physical properties depend on the inherent defects together with those ...

  9. Fabrication of Single-Crystalline Calcite Needle-Like Particles Using the Aragonite–Calcite Phase Transition

    Directory of Open Access Journals (Sweden)

    Yuki Kezuka

    2017-08-01

    Full Text Available Calcium carbonate (CaCO3 occurs in two major polymorphs: rhombohedral calcite and orthorhombic aragonite, the latter is thermodynamically metastable. In this study, we first prepared aragonite needle-like particles by introducing CO2-containing gas into Ca(OH2 aqueous slurry. Then, the resulted aragonite particles were heat treated at 500 °C for 1 h, in order to induce the aragonite–calcite phase transition. Particle structures before and after the heat treatment were characterized mainly by powder X-ray diffractometry (XRD, field emission-scanning electron microscopy (FE-SEM and transmission electron microscopy (TEM. We found that single-crystalline calcite needle-like particles with zigzag surface structures can be fabricated using the phase transition.

  10. Neptunium(V) adsorption to calcite.

    Science.gov (United States)

    Heberling, Frank; Brendebach, Boris; Bosbach, Dirk

    2008-12-12

    The migration behavior of the actinyl ions U(VI)O2(2+), Np(V)O2+ and Pu(V,VI)O2(+,2+) in the geosphere is to a large extend controlled by sorption reactions (inner- or outer-sphere adsorption, ion-exchange, coprecipitation/structural incorporation) with minerals. Here NpO2+ adsorption onto calcite is studied in batch type experiments over a wide range of pH (6.0-9.4) and concentration (0.4 microM-40 microM) conditions. pH is adjusted by variation of CO2 partial pressure. Adsorption is found to be pH dependent with maximal adsorption at pH 8.3 decreasing with increasing and decreasing pH. pH dependence of adsorption decreases with increasing Np(V) concentration. EXAFS data of neptunyl adsorbed to calcite and neptunyl in the supernatant shows differences in the Np(V)-O-yl distance, 1.85+/-0.01 angstroms for the adsorbed and 1.82+/-0.01 angstroms for the solution species. The equatorial environment of the neptunyl in solution shows about 5 oxygen neighbours at 2.45+/-0.02 angstroms. For adsorbed neptunyl there are also about 5 oxygen neighbours at 2.46+/-0.01 angstroms. An additional feature in the adsorbed species' R-space spectrum can be related to carbonate neighbours, 3 to 6 carbon backscatterers (C-eq) at 3.05+/-0.03 angstroms and 3 to 6 oxygen backscatterers (O-eq2) at 3.31+/-0.02 angstroms. The differences in the Np(V)-O-yl distance and the C-eq and O-eq2 backscatterers which are only present for the adsorbed species indicate inner-sphere bonding of the adsorbed neptunyl species to the calcite surface. Experiments on adsorption kinetics indicate that after a fast surface adsorption process a continuous slow uptake occurs which may be explained by incorporation via surface dissolution and reprecipitation processes. This is also indicated by the part irreversibility of the adsorption as shown by increased KD values after desorption compared to adsorption.

  11. Adhesion of CO2 on hydrated mineral surfaces and its implications to geologic carbon sequestration

    Science.gov (United States)

    Wang, S.; Clarens, A. F.; Tao, Z.; Persily, S. M.

    2013-12-01

    Most mineral surfaces are water wetting, which has important implications for the transport of non-aqueous phase liquids, such as CO2, through porous media. In this work, contact angle experiments were carried out wherein unusual wetting behavior was observed between mineral surfaces and liquid or supercritical CO2 under certain geochemical conditions. This behavior can be understood in the context of adhesion between the CO2 and the mineral surface. When adhesion occurs, the wettability characteristics of the surfaces are significantly altered. More importantly, the CO2 exhibits a strong affinity for the surface and is highly resistant to shear forces in the aqueous phase. A static pendant drop method was used on a variety of polished mineral surfaces to measure contact angles. The composition of the aqueous phase (e.g., pH, ionic strength) and the characteristics of the mineral surface (e.g., composition, roughness), were evaluated to understand their impact on the prevalence of adhesion. Pressure and temperature conditions were selected to represent those that would be prevalent in geologic carbon sequestration (GCS) or during leakage from target repositories. Adhesion was widely observed on phlogopite mica, silica, and calcite surfaces with roughness on the order of ~10 nanometers. CO2 exhibited no adhesion on mineral surfaces with higher roughness (e.g., quartz). On smoother surfaces, the CO2 is thought to have more effective contact area with the mineral, enabling the weak van der Waals forces that drive most adhesion processes. Brine chemistry also had an important role in controlling CO2 adhesion. Increases in CO2 partial pressure and ionic strength both increased the incidence of adhesion. The addition of strong acid or strong base permanently inhibited the development of adhesion. These results suggest that the development of adhesion between the CO2 and the mineral surface is dependent on the integrity and thickness of the hydration layer between the CO2

  12. The quantitative determination of calcite associated with the carbonate-bearing apatites

    Science.gov (United States)

    Silverman, Sol R.; Fuyat, Ruth K.; Weiser, Jeanne D.

    1951-01-01

    The CO2 combined as calcite in carbonate-bearing apatites as been distinguished from that combined as carbonate-apatite, or present in some form other than calcite, by use of X-ray powder patterns, differential thermal analyses, and differential solubility tests. These methods were applied to several pure apatite minerals, to one fossil bone, and to a group of phosphorites from the Phosphoria formation of Permian age from Trail Canyon and the Conda mine, Idaho, and the Laketown district, Utah. With the exceptions of pure fluorapatite, pure carbonate-flueorapatite, and one phosphorite from Trail Canyon, these substances contain varying amounts of calcite, but in all the samples an appreciable part of the carbonite content is not present as calcite. The results of solubility tests, in which the particle size of sample and the length of solution time were varied, imply that the carbonate content is not due to shielded calcite entrapped along an internal network of surfaces.

  13. Cretaceous joints in southeastern Canada: dating calcite-filled fractures

    Science.gov (United States)

    Schneider, David; Spalding, Jennifer; Gautheron, Cécile; Sarda, Philippe; Davis, Donald; Petts, Duane

    2017-04-01

    To resolve the timing of brittle tectonism is a challenge since the classical chronometers required for analyses are not often in equilibrium with the surrounding material or simply absent. In this study, we propose to couple LA-ICP-MS U-Pb and (U-Th)/He dating with geochemical proxies in vein calcite to tackle this dilemma. We examined intracratonic Middle Ordovician limestone bedrock that overlies Mesoproterozoic crystalline basement, which are cut by NE-trending fault zones that have historic M4-5 earthquakes along their trace. E-W to NE-SW vertical joint sets, the relatively youngest stress recorded in the bedrock, possess 1-7 mm thick calcite veins that seal fractures or coat fracture surfaces. The veins possess intragranular calcite that are lined with fine-grained calcite along the vein margin and can exhibit µm- to mm-scale offset (e.g. displaced fossil fragments in host rock). Calcite d18O and d13C values are analogous to the bulk composition of Middle to Late Ordovician limestones, and suggest vein formation from a source dominated by connate fluids. The calcite contain trails of fluid inclusions commonly along fractures, and 3He/4He analyses indicate a primitive, deep fluid signature (R/Ra: 0.5-2.7). Trace element geochemistry of the calcite is highly variable, generally following the elevated HREE and lower LREE of continental crust trends but individual crystals from a single vein may vary by three orders of magnitude. LA-ICP-MS geochemical traverse across veins show elevated concentrations along (sub)grain boundaries and the vein-host rock contact. Despite abundant helium concentrations, (U-Th)/He dating was unsuccessful yielding highly dispersed dates likely from excess helium derived from the fluid inclusions. However, LA-ICP-MS U-Pb dating on calcite separated from the veins yielded model ages of 110.7 ± 6.8 Ma (MSWD: 0.53; n: 16) to 81.4 ± 8.3 Ma (MSWD: 2.6; n: 17). Since all veins are from the same ENE-trend, we regressed all the calcite dates

  14. Removal of Pb(II from aqueous solution by natural and synthetic calcites

    Directory of Open Access Journals (Sweden)

    Ayomadewa Mercy Adesola

    2012-08-01

    Full Text Available A comparative evaluation of the adsorption capacity and kinetics of Pb(II uptake by both synthetic and natural calcites has been undertaken using batch equilibration technique. The originality of the calcite materials was confirmed by XRD and elemental composition by XRF. The point of zero charge values of 9.57 and 8.20 were obtained by mass titration method for synthetic and natural calcite, respectively. The maximum adsorption capacities of 200 mg/g and 150 mg/g Pb(II of synthetic calcite and natural calcite were obtained at initial lead loading of 1200 mg/L at 25±2 °C, respectively. The study showed a very slight dependence of sorption capacity on the ionic strength and pH, but a strong dependence on the particle size and contact time. The sorption data results fitted better the Langmuir than the Freundlich isotherms. The kinetic data fitted well to pseudo-first order sorption kinetic model with a regression coefficient value of 0.96 and 0.94 for synthetic and natural calcites, respectively. Desorption of Pb(II from calcite surface was achieved with efficiency of 95% using 4 M HNO3. The extent of reversibility of sorption reaction was a function of the equilibrium pH of calcite-Pb(II solution suspension.DOI: http://dx.doi.org/10.4314/bcse.v26i2.4

  15. The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass?

    National Research Council Canada - National Science Library

    Albert Le Floch; Guy Ropars; Jacques Lucas; Steve Wright; Trevor Davenport; Michael Corfield; Michael Harrisson

    2013-01-01

    ... the crystal by inducing roughness of its surface. Although both phenomena have reduced the transparency of the Alderney calcite crystal, we demonstrate that Alderney-like crystals could really have been used as an accurate optical sun compass...

  16. Direct nanoscale observations of the coupled dissolution of calcite and dolomite and the precipitation of gypsum.

    Science.gov (United States)

    Offeddu, Francesco Giancarlo; Cama, Jordi; Soler, Josep Maria; Putnis, Christine V

    2014-01-01

    In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (calcite and dolomite) and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C). The dissolution of the carbonate minerals took place at the (104) cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to calcite. The calculated dissolution rates of calcite at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with calcite dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the calcite surface, forming arrow-like forms parallel to the crystallographic orientations of the calcite etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of calcite, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours.

  17. Direct nanoscale observations of the coupled dissolution of calcite and dolomite and the precipitation of gypsum

    Directory of Open Access Journals (Sweden)

    Francesco G. Offeddu

    2014-08-01

    Full Text Available In-situ atomic force microscopy (AFM experiments were performed to study the overall process of dissolution of common carbonate minerals (calcite and dolomite and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C. The dissolution of the carbonate minerals took place at the (104 cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to calcite. The calculated dissolution rates of calcite at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with calcite dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the calcite surface, forming arrow-like forms parallel to the crystallographic orientations of the calcite etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of calcite, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours.

  18. Catalytic peptide hydrolysis by mineral surface: Implications for prebiotic chemistry

    Science.gov (United States)

    Marshall-Bowman, Karina; Ohara, Shohei; Sverjensky, Dimitri A.; Hazen, Robert M.; Cleaves, H. James

    2010-10-01

    The abiotic polymerization of amino acids may have been important for the origin of life, as peptides may have been components of the first self-replicating systems. Though amino acid concentrations in the primitive oceans may have been too dilute for significant oligomerization to occur, mineral surface adsorption may have provided a concentration mechanism. As unactivated amino acid polymerization is thermodynamically unfavorable and kinetically slow in aqueous solution, we studied mainly the reverse reaction of polymer degradation to measure the impact of mineral surface catalysis on peptide bonds. Aqueous glycine (G), diglycine (GG), diketopiperazine (DKP), and triglycine (GGG) were reacted with minerals (calcite, hematite, montmorillonite, pyrite, rutile, or amorphous silica) in the presence of 0.05 M, pH 8.1, KHCO 3 buffer and 0.1 M NaCl as background electrolyte in a thermostatted oven at 25, 50 or 70 °C. Below 70 °C, reaction kinetics were too sluggish to detect catalytic activity over amenable laboratory time-scales. Minerals were not found to have measurable effects on the degradation or elongation of G, GG or DKP at 70 °C in solution. At 70 °C pyrite was the most catalytic mineral with detectible effects on the degradation of GGG, although several others also displayed catalytic behavior. GGG degraded ˜1.5-4 times faster in the presence of pyrite than in control reactions, depending on the ratio of solution concentration to mineral surface area. The rate of pyrite catalysis of GGG hydrolysis was found to be saturable, suggesting the presence of discrete catalytic sites on the mineral surface. The mineral-catalyzed degradation of GGG appears to occur via a GGG → DKP + G mechanism, rather than via GGG → GG + G, as in solution-phase reactions. These results are compatible with many previous findings and suggest that minerals may have assisted in peptide synthesis in certain geological settings, specifically by speeding the approach to equilibrium

  19. Critical surface albedo and its implications to aerosol remote sensing

    Directory of Open Access Journals (Sweden)

    F. C. Seidel

    2012-07-01

    Full Text Available We analyse the critical surface albedo (CSA and its implications to aerosol remote sensing. CSA is defined as the surface albedo where the reflectance at top-of-atmosphere (TOA does not depend on aerosol optical depth (AOD. AOD retrievals are therefore inaccurate at the CSA. The CSA is obtained by derivatives of the TOA reflectance with respect to AOD using a radiative transfer code. We present the CSA and the effect of surface albedo uncertainties on AOD retrieval and atmospheric correction as a function of aerosol single-scattering albedo, illumination and observation geometry, wavelength and AOD. In general, increasing aerosol absorption and increasing scattering angles lead to lower CSA. In contrast to the strict definition of the CSA, we show that the CSA can also slightly depend on AOD and therefore rather represent a small range of surface albedo values. This was often neglected in previous studies. The following implications to aerosol remote sensing applications were found: (i surface albedo uncertainties result in large AOD retrieval errors, particularly close to the CSA; (ii AOD retrievals of weakly or non-absorbing aerosols require dark surfaces, while strongly absorbing aerosols can be retrieved more accurately over bright surfaces; (iii the CSA may help to estimate aerosol absorption; and (iv the presented sensitivity of the reflectance at TOA to AOD provides error estimations to optimise AOD retrieval algorithms.

  20. Rheological characterization of the influence of PVOH on calcite suspensions.

    Science.gov (United States)

    Eriksson, Rasmus; Kokko, Annaleena; Rosenholm, Jarl B

    2010-06-01

    Flow properties of the calcite/poly(vinyl alcohol) (PVOH) system were studied and related to the microstructure of the suspension. Adsorption of PVOH on calcite was confirmed, and it results in a shift of the slipping plane out from the surface. The charge density at the surface is assumed to remain unchanged. Since the PVOH used is only partially hydrolyzed, the most likely adsorption conformation consists of residual acetate groups adsorbed to the surface and vinylalcohol groups extending outward from the surface as loops and tails. The microstructure and flow properties of the calcite/PVOH system was found to go through several different stages as a function of PVOH concentration. At low PVOH concentrations a gradual weakening of the initially formed floc network is observed as a function of PVOH concentration. Further addition of PVOH eventually leads to breakdown of the flocs which results in a sterically stabilized suspension with a very low viscosity. This state persists for a narrow concentration range of PVOH, and increasing the PVOH concentration over a certain limit leads to a second gradual increase in viscosity. The system is believed not to undergo reflocculation at high PVOH concentrations as judged from the nonelastic nature of the suspensions. Instead, the polymers form a viscous matrix in the solution while the particles remain well-dispersed. At high enough PVOH concentration, the free volume available for the particles is greatly reduced, and the viscosity increases sharply.

  1. Surface history of Mercury - Implications for terrestrial planets

    Science.gov (United States)

    Murray, B. C.; Strom, R. G.; Trask, N. J.; Gault, D. E.

    1975-01-01

    A plausible surface history of Mercury is presented which is suggested by Mariner 10 television pictures. Five periods are postulated which are delineated by successive variations in the modification of the surface by external and internal processes: accretion and differentiation, terminal heavy bombardment, formation of the Caloris basin, flooding of that basin and other areas, and light cratering accumulated on the smooth plains. Each period is described in detail; the overall history is compared with the surface histories of Venus, Mars, and the moon; and the implications of this history for earth are discussed. It is tentatively concluded that: Mercury is a differentiated planet most likely composed of a large iron core enclosed by a relatively thin silicate layer; heavy surface bombardment occurred about four billion years ago, which probably affected all the inner planets, and was followed by a period of volcanic activity; no surface modifications caused by tectonic, volcanic, or atmospheric processes took place after the volcanic period.

  2. The effect of water on strain localization in calcite fault gouge sheared at seismic slip rates

    Science.gov (United States)

    Rempe, Marieke; Smith, Steven; Mitchell, Thomas; Hirose, Takehiro; Di Toro, Giulio

    2017-04-01

    Strain localization during coseismic slip in fault gouges is a critical mechanical process that has implications for understanding frictional heating, the earthquake energy budget and the evolution of fault rock microstructure. To assess the nature of strain localization during shearing of calcite fault gouges, high-velocity (vmax = 1m /s) rotary-shear experiments at normal stresses of 3-20 MPa were conducted under room-dry and wet conditions on synthetic calcite gouges containing dolomite gouge strain markers. When sheared at 1 m/s, the room-dry gouges showed a prolonged strengthening phase prior to dynamic weakening, whereas the wet gouges weakened nearly instantaneously. Microstructural analysis revealed that a thin (<600 μm) high-strain layer and through-going principal slip surface (PSS) developed after several centimeters of slip in both dry and wet gouges, and that strain localization at 1 m/s occurred progressively and rapidly. The strain accommodated in the bulk gouge layer did not change significantly with increasing displacement indicating that, once formed, the high-strain layer and PSS accommodated most of the displacement. Thus, a substantial strain gradient is present in the gouge layer. In water-dampened gouges, localization likely occurs during and after dynamic weakening. Our results suggest that natural fault zones in limestone are more prone to rapid dynamic weakening if water is present in the granular slipping zones.

  3. Seawater-softening process through formation of calcite ooids

    Directory of Open Access Journals (Sweden)

    A.A. Bakr

    2015-03-01

    Full Text Available Conventional water-softening processes usually involve the exchange of Na+ ions for Ca2+ and Mg2+ using commercial or synthesized ion exchangers. The differences in chemical compositions of the ooids can be attributed to the formation in different environments. In this paper, ooid grains form inside assembled semi-pilot softening unit through a continuous chemical process involving reaction between bicarbonate ions and added lime using natural seawater. Our sample of Mediterranean seawater has low Mg2+/Ca2+ ratio (1.98% within the range chemically favorable for precipitation of low-Mg calcite ooids. Precipitation of calcite occurs around pure quartz sand grains which act as nucleation points (the bed required for sand vessel is 1.65 l. The shape of the sand grains controls the overall external morphology of the resulting ooids; they vary in size from 0.5 to 3.0 mm and have a high degree of polish due to surface abrasion caused by continuous agitation inside the softening system. Calcite ooid grains (1.53 kg formed within the seawater-softening unit every 18 days have many of the ooid features formed in marine environments. Ooids grow to a significant size, at a rate of about 0.17 mm of one layer thickness per day inside the softening unit. The average weight percent of calcite precipitate is 35.48% after 18 days, at 10 °C, 60 l/min and pH 9.0. The pellets comprise mainly CaCO3 and SiO2 and some metal ions which may substitute for calcium ions in calcite are present only in trace amounts of the total composition.

  4. Calcite biomineralization in coccoliths: Evidence from atomic force microscopy (AFM)

    DEFF Research Database (Denmark)

    Henriksen, Karen; Stipp, S.L.S.

    2002-01-01

    geochemistry, crystal orientation, coccolith function, biomineralization, biological calcite, atomic force microscopy......geochemistry, crystal orientation, coccolith function, biomineralization, biological calcite, atomic force microscopy...

  5. Fabrication of porous calcite using chopped nylon fiber and its evaluation using rats.

    Science.gov (United States)

    Ishikawa, Kunio; Tram, Nguyen Xuan Thanh; Tsuru, Kanji; Toita, Riki

    2015-02-01

    Although porous calcite has attracted attention as bone substitutes, limited studies have been made so far. In the present study, porous calcite block was fabricated by introducing chopped nylon fiber as porogen. Ca(OH)2 powder containing 10 wt% chopped nylon fiber was compacted at 150 MPa, and sintered to burn out the fiber and to carbonate the Ca(OH)2 under stream of 1:2 O2-CO2. Sintering of Ca(OH)2 at 750 °C or lower temperature resulted in incomplete burning out of the fiber whereas sintering at 800 °C or higher temperature resulted in the formation of CaO due to the thermal decomposition of Ca(OH)2. However, sintering at 770 °C resulted in complete burning out of the fiber and complete carbonation of Ca(OH)2 to calcite without forming CaO. Macro- and micro-porosities of the porous calcite were approximately 23 and 16%, respectively. Diameter of the macropores was approximately 100 μm which is suitable for bone tissue penetration. Porous calcite block fabricated by this method exhibited good tissue response when implanted in the bone defect in femur of 12-weeks-old rat. Four weeks after implantation, bone bonded on the surface of calcite. Furthermore, bone tissue penetrated interior to the macropore at 8 weeks. These results demonstrated the good potential value of porous calcite as artificial bone substitutes.

  6. Diffusion of Ca and Mg in Calcite

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-02-10

    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.

  7. Do organic ligands affect calcite dissolution rates?

    Science.gov (United States)

    Oelkers, Eric H.; Golubev, Sergey V.; Pokrovsky, Oleg S.; Bénézeth, Pascale

    2011-04-01

    Steady state Iceland-spar calcite dissolution rates were measured at 25 °C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO 2 sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA 4-, succinate, D-glucosaminate, L-glutamate, D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change calcite dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.

  8. Direct observation of microbial inhibition of calcite dissolution.

    Science.gov (United States)

    Lüttge, Andreas; Conrad, Pamela G

    2004-03-01

    Vertical scanning interferometry (VSI) provides a method for quantification of surface topography at the angstrom to nanometer level. Time-dependent VSI measurements can be used to study the surface-normal retreat across crystal and other solid surfaces during dissolution or corrosion processes. Therefore, VSI can be used to directly and nondestructively measure mineral dissolution rates with high precision. We have used this method to compare the abiotic dissolution behavior of a representative calcite (CaCO(3)) cleavage face with that observed upon addition of an environmental microbe, Shewanella oneidensis MR-1, to the crystal surface. From our direct observations, we have concluded that the presence of the microbes results in a significant inhibition of the rate of calcite dissolution. This inhibition appears to be a 2nd-order effect that is related to the formation of etch pits. The opening of etch pits was greatly inhibited in the presence of added bacteria, suggesting that the bacterial cells exert their effect by inhibiting the formation of etch pits at high-energy sites at the crystal surface caused by lattice defects, e.g., screw or point dislocations. The experimental methodology thus provides a nondestructive, directly quantifiable, and easily visualized view of the interactions of microbes and minerals during weathering (or corrosion) processes or during mineral precipitation.

  9. Gallium isotope fractionation during Ga adsorption on calcite and goethite

    Science.gov (United States)

    Yuan, Wei; Saldi, Giuseppe D.; Chen, JiuBin; Vetuschi Zuccolini, Marino; Birck, Jean-Louis; Liu, Yujie; Schott, Jacques

    2018-02-01

    Gallium (Ga) isotopic fractionation during its adsorption on calcite and goethite was investigated at 20 °C as a function of the solution pH, Ga aqueous concentration and speciation, and the solid to solution ratio. In all experiments Ga was found to be enriched in light isotopes at the solid surface with isotope fractionation △71Gasolid-solution up to -1.27‰ and -0.89‰ for calcite and goethite, respectively. Comparison of Ga isotopic data of this study with predictions for 'closed system' equilibrium and 'Rayleigh fractionation' models indicates that the experimental data are consistent with a 'closed system' equilibrium exchange between the fluid and the solid. The results of this study can be interpreted based on Ga aqueous speciation and the structure of Ga complexes formed at the solid surfaces. For calcite, Ga isotope fractionation is mainly triggered by increased Ga coordination and Ga-O bond length, which vary respectively from 4 and 1.84 Å in Ga(OH)4- to 6 and 1.94 Å in the >Ca-O-GaOH(OH2)4+ surface complex. For goethite, despite the formation of Ga hexa-coordinated >FeOGa(OH)20 surface complexes (Ga-O distances of 1.96-1.98 Å) both at acid and alkaline pH, a similar extent of isotope fractionation was found at acid and alkaline pH, suggesting that Ga(OH)4- is preferentially adsorbed on goethite for all investigated pH conditions. In addition, the observed decrease of Ga isotope fractionation magnitude observed with increasing Ga surface coverage for both calcite and goethite is likely related to the formation of Ga surface polymers and/or hydroxides with reduced Ga-O distances. This first study of Ga isotope fractionation during solid-fluid interactions suggests that the adsorption of Ga by oxides, carbonates or clay minerals could yield significant Ga isotope fractionation between secondary minerals and surficial fluids including seawater. Ga isotopes thus should help to better characterize the surficial biogeochemical cycles of gallium and its

  10. Selective Separation of Fluorite, Barite and Calcite with Valonea Extract and Sodium Fluosilicate as Depressants

    Directory of Open Access Journals (Sweden)

    Zijie Ren

    2017-02-01

    Full Text Available Fluorite, barite and calcite are important industry minerals. However, they often co-exist, presenting difficulty in selectively separating them due to their similar surface properties. In this study, valonea extract and sodium fluosilicate were used as depressants to selectively separate them by flotation, with sodium oleate as the collector. The single mineral flotation results showed that valonea extract displayed the strongest depression on calcite, while sodium fluosilicate displayed the strongest depression on barite. These two depressants allowed selective separation of the three minerals through sequential flotation. The flotation of mixed minerals showed that 94% of the calcite was successfully depressed by the valonea extract, and 95% recovery of the fluorite was achieved in the subsequent flotation with sodium fluosilicate depressing barite. The different depressant–mineral interactions were investigated via electro-kinetic studies and molecular dynamics (MD simulations using the Materials Studio 6.0 program. The valonea extract exhibited the strongest adsorption on the calcite surface, and sodium fluosilicate exhibited the strongest adsorption on the barite surface, which prevented oleate species from reacting with Ca2+ or Ba2+ surface sites. This study provides useful guidance for how to process fluorite, barite and calcite resources.

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

    Science.gov (United States)

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

    2016-12-01

    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

  12. Calcite Biohybrids as Microenvironment for Stem Cells

    Directory of Open Access Journals (Sweden)

    Razi Vago

    2012-04-01

    Full Text Available A new type of composite 3D biomaterial that provides extracellular cues that govern the differentiation processes of mesenchymal stem cells (MSCs has been developed. In the present study, we evaluated the chondrogenecity of a biohybrid composed of a calcium carbonate scaffold in its calcite polymorph and hyaluronic acid (HA. The source of the calcite scaffolding is an exoskeleton of a sea barnacle Tetraclita rifotincta (T. rifotincta, Pilsbry (1916. The combination of a calcium carbonate-based bioactive scaffold with a natural polymeric hydrogel is designed to mimic the organic-mineral composite of developing bone by providing a fine-tuned microenvironment. The results indicate that the calcite-HA interface creates a suitable microenvironment for the chondrogenic differentiation of MSCs, and therefore, the biohybrid may provide a tool for tissue-engineered cartilage.

  13. Structure and reactivity of the calcite-water interface.

    Science.gov (United States)

    Heberling, Frank; Trainor, Thomas P; Lützenkirchen, Johannes; Eng, Peter; Denecke, Melissa A; Bosbach, Dirk

    2011-02-15

    The zetapotential of calcite in contact with aqueous solutions of varying composition is determined for pre-equilibrated suspensions by means of electrophoretic measurements and for non-equilibrium solutions by means of streaming potential measurements. Carbonate and calcium are identified as charge determining ions. Studies of the equilibrium solutions show a shift of isoelectric point with changing CO(2) partial pressure. Changes in pH have only a weak effect in non-equilibrium solutions. The surface structure of (104)-faces of single crystal calcite in contact to solutions corresponding to those of the zetapotential investigations is determined from surface diffraction measurements. The results reveal no direct indication of calcium or carbonate inner-sphere surface species. The surface ions are found to relax only slightly from their bulk positions; the most significant relaxation is a ∼4° tilt of the surface carbonate ions towards the surface. Two ordered layers of water molecules are identified, the first at 2.35±0.05Å above surface calcium ions and the second layer at 3.24±0.06Å above the surface associated with surface carbonate ions. A Basic-Stern surface complexation model is developed to model observed zetapotentials, while only considering outer-sphere complexes of ions other than protons and hydroxide. The Basic-Stern SCM successfully reproduces the zetapotential data and gives reasonable values for the inner Helmholtz capacitance, which are in line with the Stern layer thickness estimated from surface diffraction results. Copyright © 2010 Elsevier Inc. All rights reserved.

  14. Two-phase flow and calcite deposition

    Energy Technology Data Exchange (ETDEWEB)

    Gudmudsson, J.S.; Granadso-G, E.; Ortiz-R, J.

    1984-04-01

    The literature on two-phase flow in geothermal wells shows that the Orkiszewski method has found wide application in state-of-the-art wellbore simulators. Such a simulator was developed and then used for the problem of wellbore deposition of calcite in the Miravalles geothermal field in Costa Rica. The output of wells suffering calcite deposition decreases slowly at early time but rapidly at late time. The simulator was also used to estimate the deliverability curve for a large diameter well in the Svartsengi geothemal field in Iceland. The view is presented that more accurate wellbore simulators will make new reservoir engineering studies possible in geothermal fields.

  15. Calcite growth-rate inhibition by fulvic acids isolated from Big Soda Lake, Nevada, USA, The Suwannee River, Georgia, USA and by polycarboxylic acids

    Science.gov (United States)

    Reddy, Michael M.; Leenheer, Jerry

    2011-01-01

    Calcite crystallization rates are characterized using a constant solution composition at 25°C, pH=8.5, and calcite supersaturation (Ω) of 4.5 in the absence and presence of fulvic acids isolated from Big Soda Lake, Nevada (BSLFA), and a fulvic acid from the Suwannee River, Georgia (SRFA). Rates are also measured in the presence and absence of low-molar mass, aliphatic-alicyclic polycarboxylic acids (PCA). BSLFA inhibits calcite crystal-growth rates with increasing BSLFA concentration, suggesting that BSLFA adsorbs at growth sites on the calcite crystal surface. Calcite growth morphology in the presence of BSLFA differed from growth in its absence, supporting an adsorption mechanism of calcite-growth inhibition by BSLFA. Calcite growth-rate inhibition by BSLFA is consistent with a model indicating that polycarboxylic acid molecules present in BSLFA adsorb at growth sites on the calcite crystal surface. In contrast to published results for an unfractionated SRFA, there is dramatic calcite growth inhibition (at a concentration of 1 mg/L) by a SRFA fraction eluted by pH 5 solution from XAD-8 resin, indicating that calcite growth-rate inhibition is related to specific SRFA component fractions. A cyclic PCA, 1, 2, 3, 4, 5, 6-cyclohexane hexacarboxylic acid (CHXHCA) is a strong calcite growth-rate inhibitor at concentrations less than 0.1 mg/L. Two other cyclic PCAs, 1, 1 cyclopentanedicarboxylic acid (CPDCA) and 1, 1 cyclobutanedicarboxylic acid (CBDCA) with the carboxylic acid groups attached to the same ring carbon atom, have no effect on calcite growth rates up to concentrations of 10 mg/L. Organic matter ad-sorbed from the air onto the seed crystals has no effect on the measured calcite crystal-growth rates.

  16. Novel Determination of the Orientation of Calcite on Mineral Substrates

    Science.gov (United States)

    Zhao, L.; Ji, X.; Teng, H.

    2016-12-01

    In the threat of global warming, the transformation from CO2 to stable carbonate minerals is significant to geological CO2 sequestration in the long term.Previous efforts have found that when carbonate minerals nucleate on some mineral substrates ,the time of carbon capture can be shorted .Many efforts have been focused on the dynamics when carbonate minerals nucleate on mineral substrates, but few have studied the orientation of carbonate minerals on mineral substrates. In our experiment, we mainly focused on the orientation of calcite on mineral substrates.We mixed NaHCO3 and CaCl2 to nucleate when mineral substrates were added and a multi-parameter analyzer was used to monitor in real time to determine the induction time for nucleation. On the basis of classical nucleation theory, we got a brand new formula to decide the orientation of calcite on mineral substrates. lntind=(2-cosθ+cos3θ)*16πγ3vm2(12*(kBT)3*(lnS)2)+ln(1/N0v)+ ΔEa/(kBT)where θ is the angle between the substrate and the nuclei, tind is the induction time for nucleation, γ is he average surface free energy, N0 is the total number of particles per unit volume of solution, ΔEa is the activation energy for molecular motion across the embryo-matrix interface, S is the supersaturation index ,kB is the Boltzmann constant. Using the new formula above , when biotite was used as substrate mineral ,we found that the angle between the biotite and the nuclei was 119°. Angle measured on SEM images also supported our conclusion above. Combined with SEM and Debye ring analysed by Rigaku 2D data processing software, we only found one point of (006) in Debye ring, unlike (104)(many points in one ring and it meant that the orientation of (104) is random ). That meant (001) of calcite was first formed on biotite (001). In that case we inferred that 119° was formed by (001) of botite and (012) of calcite for the intersection angle of (001) and (012) was 120°. Future research will focus on the orientation of

  17. Adsorption of polar aromatic hydrocarbons on synthetic calcite

    DEFF Research Database (Denmark)

    Madsen, Lene; Grahl-Madsen, Laila; Grøn, Christian

    1996-01-01

    The wettability of hydrocarbon reservoirs depends on how and to what extent the organic compounds are adsorbed onto the surfaces of calcite, quartz and clay. A model system of synthetic call cite, cyclohexane and the three probe molecules: benzoic acid, benzyl alcohol and benzylamine, have been...... studied by adsorption experiments. The results clearly demonstrate the differences in the adsorption behaviour between probes with different functional groups of varying polarity and acidity. The maximum adsorption decreases in the order: benzoic acid, benzyl alcohol and benzylamine. The order...

  18. Interaction of europium and nickel with calcite studied by Rutherford Backscattering Spectrometry and Time-Resolved Laser Fluorescence Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sabau, A. [Agence Nationale pour la gestion des Déchets RAdioactifs, 1-7 rue J. Monnet, Parc de la Croix Blanche, 92298 Châtenay-Malabry Cedex (France); Université de Nice Sophia Antipolis, Ecosystèmes Côtiers Marins et Réponses aux Stress (ECOMERS), 28 avenue Valrose, 06108 Nice Cedex 2 (France); Pipon, Y., E-mail: pipon@ipnl.in2p3.fr [Institut de Physique Nucléaire de Lyon (IPNL), Université Lyon 1, CNRS/IN2P3, 4 rue Enrico Fermi, 69 622 Villeurbanne Cedex (France); Institut Universitaire de Technologie (IUT) Lyon-1, Université Claude Bernard Lyon 1, 69 622 Villeurbanne Cedex (France); Toulhoat, N. [Institut de Physique Nucléaire de Lyon (IPNL), Université Lyon 1, CNRS/IN2P3, 4 rue Enrico Fermi, 69 622 Villeurbanne Cedex (France); CEA/DEN, Saclay, 91191 Gif sur Yvette (France); Lomenech, C. [Université de Nice Sophia Antipolis, Ecosystèmes Côtiers Marins et Réponses aux Stress (ECOMERS), 28 avenue Valrose, 06108 Nice Cedex 2 (France); Jordan, N. [Helmholtz Zentrum Dresden Rossendorf (HZDR), Institute of Resource Ecology (IRE) (Germany); Moncoffre, N. [Institut de Physique Nucléaire de Lyon (IPNL), Université Lyon 1, CNRS/IN2P3, 4 rue Enrico Fermi, 69 622 Villeurbanne Cedex (France); Barkleit, A. [Helmholtz Zentrum Dresden Rossendorf (HZDR), Institute of Resource Ecology (IRE) (Germany); and others

    2014-08-01

    This study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO{sub 3}). Calcite powders or single crystals (some mm sized) were put into contact with Eu or Ni solutions at concentrations ranging from 10{sup −3} to 10{sup −5} mol L{sup −1} for Eu and 10{sup −3} mol L{sup −1} for Ni. The sorption durations ranged from 1 week to 1 month. Rutherford Backscattering Spectrometry (RBS) well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance), has been carried out. Moreover, using the fluorescence properties of europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage were also performed. Results showed that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.

  19. Calcite growth kinetics: Modeling the effect of solution stoichiometry

    NARCIS (Netherlands)

    Wolthers, M.; Nehrke, G.; Gustafsson, J.P.; Van Cappellen, P.

    2012-01-01

    Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth

  20. High-Magnesian Calcite Mesocrystals : A Coordination Chemistry Approach

    NARCIS (Netherlands)

    Lenders, Jos J. M.; Dey, Archan; Bomans, Paul H. H.; Spielmann, Jan; Hendrix, Marco M. R. M.; de With, Gijsbertus; Meldrum, Fiona C.; Harder, Sjoerd; Sommerdijk, Nico A. J. M.

    2012-01-01

    While biogenic calcites frequently contain appreciable levels of magnesium, the pathways leading to such high concentrations remain unclear. The production of high-magnesian calcites in vitro is highly challenging, because Mg-free aragonite, rather than calcite, is the favored product in the

  1. in situ Calcite Precipitation for Contaminant Immobilization

    Energy Technology Data Exchange (ETDEWEB)

    Yoshiko Fujita; Robert W. Smith

    2009-08-01

    in situ Calcite Precipitation for Contaminant Immobilization Yoshiko Fujita (Yoshiko.fujita@inl.gov) (Idaho National Laboratory, Idaho Falls, Idaho, USA) Robert W. Smith (University of Idaho-Idaho Falls, Idaho Falls, Idaho, USA) Subsurface radionuclide and trace metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of DOE’s greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide strontium-90, is co-precipitation in calcite. Calcite, a common mineral in the arid western U.S., can form solid solutions with trace metals. The rate of trace metal incorporation is susceptible to manipulation using either abiotic or biotic means. We have previously demonstrated that increasing the calcite precipitation rate by stimulating the activity of urea hydrolyzing microorganisms can result in significantly enhanced Sr uptake. Urea hydrolysis causes the acceleration of calcium carbonate precipitation (and trace metal co-precipitation) by increasing pH and alkalinity, and also by liberating the reactive cations from the aquifer matrix via exchange reactions involving the ammonium ion derived from urea: H2NCONH2 + 3H2O ? 2NH4+ + HCO3- + OH- urea hydrolysis >X:2Ca + 2NH4+ ? 2>X:NH4 + Ca2+ ion exchange Ca2+ + HCO3- + OH- ? CaCO3(s) + H2O calcite precipitation where >X: is a cation exchange site on the aquifer matrix. This contaminant immobilization approach has several attractive features. Urea hydrolysis is catalyzed by the urease enzyme, which is produced by many indigenous subsurface microorganisms. Addition of foreign microbes is unnecessary. In turn the involvement of the native microbes and the consequent in situ generation of reactive components in the aqueous phase (e.g., carbonate and Ca or Sr) can allow dissemination of the reaction over a larger volume and/or farther away from an amendment injection point, as compared to direct addition of the reactants at

  2. Isotopic analysis for degradation diagnosis of calcite matrix in mortar.

    Science.gov (United States)

    Dotsika, E; Psomiadis, D; Poutoukis, D; Raco, B; Gamaletsos, P

    2009-12-01

    Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (delta(13)C and delta(18)O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO(2) and water during calcite formation and degradation processes. Isotopic change of the initial delta(13)C and delta(18)O in carbonate matrix was caused by alteration of the primary source of CO(2) and H(2)O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO(2) from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter delta(18)O and delta(13)C in lime mortar.

  3. Effect of inorganic anions on the morphology and structure of magnesium calcite.

    Science.gov (United States)

    Kralj, Damir; Kontrec, Jasminka; Brecević, Ljerka; Falini, Giuseppe; Nöthig-Laslo, Vesna

    2004-04-02

    Calcium carbonate was precipitated from calcium hydroxide and carbonic acid solutions at 25 degrees C, with and without addition of different magnesium (MgSO(4), Mg(NO(3))(2) and MgCl(2)) and sodium salts (Na(2)SO(4), NaNO(3) and NaCl) of identical anions, in order to study the mode of incorporation of magnesium and inorganic anions and their effect on the morphology of calcite crystals over a range of initial reactant concentrations and limited c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios. The morphology, crystal size distribution, composition, structure, and specific surface area of the precipitated crystals, as well as the mode of cation and anion incorporation into the calcite crystal lattice, were studied by a combination of optical and scanning electron microscopy (SEM), electronic counting, a multiple BET method, thermogravimetry, FT-IR spectroscopy, X-ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. In the systems of high initial relative supersaturation, precipitation of an amorphous precursor phase preceded the formation of calcite, whereas in those of lower supersaturation calcite was the first and only polymorphic modification of calcium carbonate that appeared in the system. The magnesium content in calcite increased with the magnesium concentration in solution and was correlated with the type of magnesium salt used. Mg incorporation caused the formation of crystals elongated along the calcite c axis and, in some cases, the appearance of new [011] faces. Polycrystalline aggregates were formed when the c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios in solution were increased. Addition of sulfate ions, alone, caused formation of spherical calcite polycrystalline aggregates.

  4. 3D Mapping of calcite and a demonstration of its relevance to permeability evolution in reactive fractures

    Science.gov (United States)

    Ellis, Brian R.; Peters, Catherine A.

    2016-09-01

    There is a need to better understand reaction-induced changes in fluid transport in fractured shales, caprocks and reservoirs, especially in the context of emerging energy technologies, including geologic carbon sequestration, unconventional natural gas, and enhanced geothermal systems. We developed a method for 3D calcite mapping in rock specimens. Such information is critical in reactive transport modeling, which relies on information about the locations and accessible surface area of reactive minerals. We focused on calcite because it is a mineral whose dissolution could lead to substantial pathway alteration because of its high solubility, fast reactivity, and abundance in sedimentary rocks. Our approach combines X-ray computed tomography (XCT) and scanning electron microscopy. The method was developed and demonstrated for a fractured limestone core containing about 50% calcite, which was 2.5 cm in diameter and 3.5 cm in length and had been scanned using XCT. The core was subsequently sectioned and energy dispersive X-ray spectroscopy was used to determine elemental signatures for mineral identification and mapping. Back-scattered electron microscopy was used to identify features for co-location. Finally, image analysis resulted in characteristic grayscale intensities of X-ray attenuation that identify calcite. This attenuation mapping ultimately produced a binary segmented 3D image of the spatial distribution of calcite in the entire core. To demonstrate the value of this information, permeability changes were investigated for hypothetical fractures created by eroding calcite from 2D rock surfaces. Fluid flow was simulated using a 2D steady state model. The resulting increases in permeability were profoundly influenced by the degree to which calcite is contiguous along the flow path. If there are bands of less reactive minerals perpendicular to the direction of flow, fracture permeability may be an order of magnitude smaller than when calcite is contiguous

  5. Neptunium(V) coprecipitation with calcite.

    Science.gov (United States)

    Heberling, Frank; Denecke, Melissa A; Bosbach, Dirk

    2008-01-15

    Coprecipitation experiments of Np(V) and U(VI) with calcite were performed in mixed-flow reactors under steady state conditions at room temperature for up to 400 h at precipitation rates of 1.0 x 10(-8) to 6.8 x 10(-8) mol/(m2 s). The saturation index with respect to calcite varied between 0.04 and 0.95. Initial Np(V) or U(VI) concentrations were 1 micromol/L, 0.01 mol/L NaCl was used as background electrolyte, and pH ranged from 7.8 to 12.8. Partition coefficients for Np(V) were in the range of 0.5-10.3, compared to 0.02 for U(VI). Np L(III) and U L(III) EXAFS were used to characterize the local structural environment of the incorporated actinides. In the case of U(VI), the structural environment is not unambiguously characterized. Our data suggest that Np(V) ions occupy calcium lattice sites. The two axial oxygen atoms of the linear neptunyl moiety substitute two calcite carbonate groups in the first coordination sphere. Thus, four carbonate groups coordinate the neptunyl-ion in a monodentate fashion with four equatorial oxygen atoms (Oeq) at 2.4 A and associated carbon atoms (C) at 3.2 A. The interatomic distances indicate slight structural relaxation of the carbonate groups from their ideal sites. A similar structural model has been reported for U(VI) incorporated into natural calcite.

  6. Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve Pecten maximus

    Science.gov (United States)

    Lorrain, Anne; Gillikin, David P.; Paulet, Yves-Marie; Chauvaud, Laurent; Le Mercier, Alain; Navez, Jacques; André, Luc

    2005-12-01

    Although Sr/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report Sr/Ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve Pecten maximus (age class I). Ratios of Sr/Ca were found to be variable among individuals that grew at the same location, illustrating that vital effects dominate over environmental controls. Although daily growth rate was correlated with shell Sr/Ca ratios, it explained only half of the Sr/Ca variations. However, daily shell surface area increment, an estimation of the total quantity of carbonate precipitated for a given time, explained 74% of the Sr/Ca variability in the shells of P. maximus. This proves, for the first time in a calcitic bivalve, that shell Sr/Ca partitioning is mainly controlled by kinetic effects. The Sr/Ca ratio should therefore be tested as a potential proxy of calcification rate in modern or fossil calcitic biocarbonates.

  7. The Influence of Kinetic Growth Factors on the Clumped Isotope Composition of Calcite

    Science.gov (United States)

    Hunt, J. D.; Watkins, J. M.; Tripati, A.; Ryerson, F. J.; DePaolo, D. J.

    2014-12-01

    into calcite under non-equilibrium conditions. Adaptation of the model for clumped isotope uptake under non-equilibrium conditions requires knowledge of the clumped isotopic compositions of DIC species and any mass-dependent kinetic fractionation that arises during ion transport to or from the mineral surface.

  8. Cigarette smoke toxins deposited on surfaces: implications for human health.

    Directory of Open Access Journals (Sweden)

    Manuela Martins-Green

    Full Text Available Cigarette smoking remains a significant health threat for smokers and nonsmokers alike. Secondhand smoke (SHS is intrinsically more toxic than directly inhaled smoke. Recently, a new threat has been discovered - Thirdhand smoke (THS - the accumulation of SHS on surfaces that ages with time, becoming progressively more toxic. THS is a potential health threat to children, spouses of smokers and workers in environments where smoking is or has been allowed. The goal of this study is to investigate the effects of THS on liver, lung, skin healing, and behavior, using an animal model exposed to THS under conditions that mimic exposure of humans. THS-exposed mice show alterations in multiple organ systems and excrete levels of NNAL (a tobacco-specific carcinogen biomarker similar to those found in children exposed to SHS (and consequently to THS. In liver, THS leads to increased lipid levels and non-alcoholic fatty liver disease, a precursor to cirrhosis and cancer and a potential contributor to cardiovascular disease. In lung, THS stimulates excess collagen production and high levels of inflammatory cytokines, suggesting propensity for fibrosis with implications for inflammation-induced diseases such as chronic obstructive pulmonary disease and asthma. In wounded skin, healing in THS-exposed mice has many characteristics of the poor healing of surgical incisions observed in human smokers. Lastly, behavioral tests show that THS-exposed mice become hyperactive. The latter data, combined with emerging associated behavioral problems in children exposed to SHS/THS, suggest that, with prolonged exposure, they may be at significant risk for developing more severe neurological disorders. These results provide a basis for studies on the toxic effects of THS in humans and inform potential regulatory policies to prevent involuntary exposure to THS.

  9. Fracture calcites at Olkiluoto. Evidence from quaternary infills for palaeohydrogeology

    Energy Technology Data Exchange (ETDEWEB)

    Gehoer, S.; Kaerki, A.; Taikina-aho, O. [Kivitieto Oy (Finland); Karhu, J. [Helsinki Univ. (Finland); Loefman, J. [VTT Processes, Espoo (Finland); Pitkaenen, P. [VTT Building and Transport, Espoo (Finland); Ruotsalainen, P. [TUKES, Helsinki (Finland)

    2002-02-01

    Recently formed secondary minerals, predominantly calcite, occur in varying amounts as fracture infills, and the calcite types, their chemical compositions and isotope ratios reflect the compositions and physicochemical factors of the groundwater system in which they were formed. Fluid inclusions trapped in calcites give direct evidence of trapping temperatures and past salinities and of the chemical compositions of the palaeo fluids. A wide range of mineralogical and geochemical examinations were carried out within the EQUIP project to examine features of this kind. The fracture calcites at the Olkiluoto site are of various origins and represent several textural types. The exact number of calcite-producing events is unknown, but the duration of the period that was appropriate for the precipitation of low temperature calcite is estimated to have exceeded 1000 Ma. Thus the number of genetically related calcite units is assumed to be considerable. This study was focused on the petrogenesis of calcites crystallized in fractures of high water conductivity during the latest stages of geological evolution. The majority of these late stage calcites form physically homogeneous, scaly layers, and in a few cases thin layers composed of idiomorphic crystals. Chemically these are almost stoichiometric calcites (CaCO{sub 3}). The MnO content may exceed 1%, while the amounts of other elements present are minor, although the trace element concentrations, particularly those of large ionic trace elements, can be used as distinguishing features for the recognition of individual precipitates representing different calcite generations. Evidence from fluid inclusions, or more correctly from the absence of these in the late stage calcites, can be interpreted as an indication of slow rates of crystallization under cool conditions. Many chemical variables, e.g. oxygen isotope ratios, demonstrate an equilibrium between the latest calcites and water similar to the present groundwater. Older

  10. A High-Pressure Phase Transition of Calcite-III

    Science.gov (United States)

    Catalli, K. C.; Williams, Q.

    2005-12-01

    We document the presence of a high-pressure phase transition in metastable calcite-III using infrared spectroscopy. The post-calcite-III transition initiates at a pressure of 15.5 (±2) GPa, and is completed between 25 and 30 GPa. The transition is particularly apparent in the ν4-in-plane bending vibration of the carbonate group, in which two new peaks gradually supplant the doublet associated with calcite-III. Furthermore, both the ν3-asymmetric and ν1-symmetric stretches of the carbonate group in the high-pressure phase appear at considerably lower frequencies than the extrapolated positions of the corresponding calcite-III peaks. The geometry of the carbonate unit within the high-pressure phase is likely closer to trigonal symmetry than in the calcite-III structure, and the C-O bond is probably longer than in the lower pressure calcite-III phase.

  11. Unusual biogenic calcite structures in two shallow lakes, James Ross Island, Antarctica

    Science.gov (United States)

    Elster, J.; Nedbalová, L.; Vodrážka, R.; Láska, K.; Haloda, J.; Komárek, J.

    2016-01-01

    The floors of two shallow endorheic lakes, located on volcanic surfaces on James Ross Island, are covered with calcareous organosedimentary structures. Their biological and chemical composition, lake water characteristics, and seasonal variability of the thermal regime are introduced. The lakes are frozen down to the bottom for 8-9 months a year and their water chemistry is characterised by low conductivity and neutral to slightly alkaline pH. The photosynthetic microbial mat is composed of filamentous cyanobacteria and microalgae that are considered to be Antarctic endemic species. The mucilaginous black biofilm is covered by green spots formed by a green microalga and the macroscopic structures are packed together with fine material. Thin sections consist of rock substrate, soft biofilm, calcite spicules and mineral grains originating from different sources. The morphology of the spicules is typical of calcium carbonate monocrystals having a layered structure and specific surface texture, which reflect growth and degradation processes. The spicules' chemical composition and structure correspond to pure calcite. The lakes' age, altitude, morphometry, geomorphological and hydrological stability, including low sedimentation rates, together with thermal regime predispose the existence of this community. We hypothesise that the precipitation of calcite is connected with the photosynthetic activity of the green microalgae that were not recorded in any other lake in the region. This study has shown that the unique community producing biogenic calcite spicules is quite different to any yet described.

  12. Origin of calcite in the glacigenic Virttaankangas complex

    Directory of Open Access Journals (Sweden)

    Nina M. Kortelainen

    2007-01-01

    Full Text Available Groundwaters of the glacigenic Virttaankangas complex in southern Finland are characterized by high pH values ranging up to 9.5. These values are significantly higher than those observed in silicate-rich shallow groundwater formations in crystalline bedrock areas. TheVirttaankangas sediments were discovered to contain small amounts of fine grained, dispersed calcite, which has a high tendency to increase the pH of local groundwaters. The primary goal of this study was to determine the mode of occurrence of calcite and to identifyits sources. The mineralogy of the glacigenic Virttaankangas complex was studied using material from 21 sediment drill cores. Fine-grained calcite is present in trace amounts (<< 1.4 % in the glaciofluvial and glaciolacustrine depositional units of the Virttaankangas complex. The topmost littoral sands were practically devoid of calcite. The isotope records of carbon and oxygen, the angular morphology of the grains and the uniform dispersion of calcite in the complex suggest a clastic origin for calcite, with no evidence for in-situ precipitation. In order to constrain the source of calcite, the isotopic composition of carbon and oxygen in five calcite samples was compared to the isotopic data from five carbonate rock erratics and eight crystalline bedrock samples from the region. Based on carbon and oxygen isotope ratios and chemical compositions, the dispersed calcite grains of the Virttaankangas complex appear to have been derived from the Mesoproterozoic Satakunta Formation, some 30 km NW from the Virttaankangas area. In sandstone, calcite is predominantly present as diagenetic cement in grain interspaces, concretions and interlayers. The source of detrital calcite was unexpected, as prior to this study the Satakunta sandstone hasnot been known to contain calcite.

  13. Controlling the size and morphology of precipitated calcite particles by the selection of solvent composition

    Science.gov (United States)

    Konopacka-Łyskawa, Donata; Kościelska, Barbara; Karczewski, Jakub

    2017-11-01

    Precipitated calcium carbonate is used as an additive in the manufacture of many products. Particles with specific characteristics can be obtained by the selection of precipitation conditions, including temperature and the composition of solvent. In this work, calcium carbonate particles were obtained in the reaction of calcium hydroxide with carbon dioxide at 65 °C. Initial Ca(OH)2 suspensions were prepared in pure water and aqueous solutions of ethylene glycol or glycerol of the concentration range up to 20% (vol.). The course of reaction was monitored by conductivity measurements. Precipitated solids were analyzed by FTIR, XRD, SEM and the particles size distribution was determined by a laser diffraction method. The adsorption of ethylene glycol or glycerol on the surface of scalenohedral and rhombohedral calcite was testes by a normal-phase high-performance liquid chromatography. The addition of organic solvents changed the viscosity of reaction mixtures, the rate of carbon dioxide absorption and the solubility of inorganic components and therefore influence calcium carbonate precipitation conditions. All synthesized calcium carbonate products were in a calcite form. Scalenohedral calcite crystals were produced when water was a liquid phase, whereas addition of organic solvents resulted in the formation of rhombo-scalenohedral particles. The increase in organic compounds concentration resulted in the decrease of mean particles size from 2.4 μm to 1.7 μm in ethylene glycol solutions and to 1.4 μm in glycerol solutions. On the basis of adsorption tests, it was confirm that calcite surface interact stronger with glycerol than ethylene glycol. The interaction between scalenohedral calcite and used organic additives was higher in comparison to the pure rhombohedral form applied as a stationary phase.

  14. Surface activity, lipid profiles and their implications in cervical cancer.

    Directory of Open Access Journals (Sweden)

    Preetha A

    2005-01-01

    Full Text Available Background: The profiles of lipids in normal and cancerous tissues may differ revealing information about cancer development and progression. Lipids being surface active, changes in lipid profiles can manifest as altered surface activity profiles. Langmuir monolayers offer a convenient model for evaluating surface activity of biological membranes. Aims: The aims of this study were to quantify phospholipids and their effects on surface activity of normal and cancerous human cervical tissues as well as to evaluate the role of phosphatidylcholine (PC and sphingomyelin (SM in cervical cancer using Langmuir monolayers. Methods and Materials: Lipid quantification was done using thin layer chromatography and phosphorus assay. Surface activity was evaluated using Langmuir monolayers. Monolayers were formed on the surface of deionized water by spreading tissue organic phase corresponding to 1 mg of tissue and studying their surface pressure-area isotherms at body temperature. The PC and SM contents of cancerous human cervical tissues were higher than those of the normal human cervical tissues. Role of PC and SM were evaluated by adding varying amounts of these lipids to normal cervical pooled organic phase. Statistical analysis: Student′s t-test (p < 0.05 and one-way analysis of variance (ANOVA was used. Results: Our results reveals that the phosphatidylglycerol level in cancerous cervical tissue was nearly five folds higher than that in normal cervical tissue. Also PC and sphingomyelin SM were found to be the major phospholipid components in cancerous and normal cervical tissues respectively. The addition of either 1.5 µg DPPC or 0.5 µg SM /mg of tissue to the normal organic phase changed its surface activity profile to that of the cancerous tissues. Statistically significant surface activity parameters showed that PC and SM have remarkable roles in shifting the normal cervical lipophilic surface activity towards that of cancerous lipophilic

  15. Automatic Crater Detection and Implications for Surface Age Estimation

    Science.gov (United States)

    Salih, A. L.; Boukercha, A.; Grumpe, A.; Wöhler, C.; Hiesinger, H.

    2014-04-01

    Crater size-distribution measurements (CFSDs) are an important tool for the assessment of the ages of surface regions [1,2]. The freely available software Craterstats2 [3] allows for the determination of the absolute model ages (AMA) of the surface if the number and diameters of the craters within the count area of a certain size are known. In this context, manual counting and measuring of craters is a timeconsuming process while automatic crater detection may lead to increased false positive detections, missed craters and possibly inaccurate diameter determination. However, the influence of such recognition errors of automated crater detection systems on the estimated model age has not yet been fully investigated. Current automatic crater detection algorithms depend on either optical images or digital elevation models (DEM) [4]. In this study, we compare different crater detectors and their behaviour in the context of surface age determination.

  16. Implication of surface modified NZVI particle retention in the porous ...

    Indian Academy of Sciences (India)

    Retention of surface-modified nanoscale zero-valent iron (NZVI) particles in the porous media near the point of injection has been reported in the recent studies. Retention of excess particles in porous media can alter the media properties. The main objectives of this study are, therefore, to evaluate the effect of particle ...

  17. Growing spherulitic calcite grains in saline, hyperalkaline lakes: experimental evaluation of the effects of Mg-clays and organic acids

    Science.gov (United States)

    Mercedes-Martín, R.; Rogerson, M. R.; Brasier, A. T.; Vonhof, H. B.; Prior, T. J.; Fellows, S. M.; Reijmer, J. J. G.; Billing, I.; Pedley, H. M.

    2016-04-01

    that this morphology is not a universal consequence of having organic acids dissolved in the solution, but rather spherulite development requires specific binding behaviour. Finally, we found that the location of calcite precipitation was altered from the air:water interface to the surface of the glassware when organic acids were present, implying that attached calcite precipitates reflect precipitation via metal-organic intermediaries, rather than direct forcing via gas exchange.

  18. Influence of water on clumped-isotope bond reordering kinetics in calcite

    Science.gov (United States)

    Brenner, Dana C.; Passey, Benjamin H.; Stolper, Daniel A.

    2018-03-01

    Oxygen self-diffusion in calcite and many other minerals is considerably faster under wet conditions relative to dry conditions. Here we investigate whether this "water effect" also holds true for solid-state isotope exchange reactions that alter the abundance of carbonate groups with multiple rare isotopes ('clumped' isotope groups) via the process of solid-state bond reordering. We present clumped-isotope reordering rates for optical calcite heated under wet, high-pressure (100 MPa) conditions. We observe only modest increases in reordering rates under such conditions compared with rates for the same material reacted in dry CO2 under low-pressure conditions. Activation energies under wet, high-pressure conditions are indistinguishable from those for dry, low-pressure conditions, while rate constants are resolvably higher (up to ∼3 times) for wet, high-pressure relative to dry, low-pressure conditions in most of our interpretations of experimental results. This contrasts with the water effect for oxygen self-diffusion in calcite, which is associated with lower activation energies, and diffusion coefficients that are ≥103 times higher compared with dry (pure CO2) conditions in the temperature range of this study (385-450 °C). The water effect for clumped-isotopes leads to calculated apparent equilibrium temperatures ("blocking temperatures") for typical geological cooling rates that are only a few degrees higher than those for dry conditions, while O self-diffusion blocking temperatures in calcite grains are ∼150-200 °C lower in wet conditions compared with dry conditions. Since clumped-isotope reordering is a distributed process that occurs throughout the mineral volume, our clumped-isotope results support the suggestion of Labotka et al. (2011) that the water effect in calcite does not involve major changes in bulk (volume) diffusivity, but rather is primarily a surface phenomenon that facilitates oxygen exchange between the calcite surface and external

  19. Competitive adsorption of arsenate and phosphate onto calcite; experimental results and modeling with CCM and CD-MUSIC

    Science.gov (United States)

    Sø, Helle Ugilt; Postma, Dieke; Jakobsen, Rasmus; Larsen, Flemming

    2012-09-01

    The competitive adsorption of arsenate and phosphate onto calcite was studied in batch experiments using calcite-equilibrated solutions. The solutions had circum-neutral pH (7-8.3) and covered a wide span in the activity of Ca2+ and CO32-. The results show that the adsorption of arsenate onto calcite is strongly reduced by the presence of phosphate, whereas phosphate adsorption is only slightly reduced by arsenate addition. Simultaneous and sequential addition (3 h apart) yields the same reduction in adsorption, underlining the high reversibility of the system. The reduction in adsorption of both arsenate and phosphate is most likely due to competition for the same sorption sites at the calcite surface, considering the similarity in sorption edges, pKa's and geometry of the two anions. The strong reduction in arsenate adsorption by competition with phosphate suggests that adsorption of arsenate onto calcite is of minor importance in most groundwater aquifers, as phosphate is often present at concentration levels sufficient to significantly reduce arsenate adsorption. The CD-MUSIC model for calcite was used successfully to model adsorption of arsenate and phosphate separately. By combining the models for single sorbate systems the competitive adsorption of phosphate and arsenate onto calcite in the binary system could be predicted. This is in contrast to the constant capacitance model (CCM) which under-predicted the competition when combining the models for single sorbate systems. This study clearly shows the importance of performing competitive adsorption studies for validation of multi-component models and for estimating the mobility of an ion in the environment.

  20. Mn and Zn incorporation into calcite as a function of chloride aqueous concentration

    Science.gov (United States)

    Temmam, M.; Paquette, J.; Vali, H.

    2000-07-01

    During spiral growth of the calcite rhombohedron {10 overline14}, divalent metals substituting for Ca 2+ are differentially incorporated due to steric differences inherent to the asymmetric kink sites exposed at nonequivalent growth steps. Hence, ions "larger" than Ca 2+ (e.g., Sr 2+ and Ba 2+) exhibit an incorporation trend opposite to that of "smaller" ions (e.g., Mn 2+ and Co 2+). However, Zn 2+ exhibits the same incorporation trend as large ions in coprecipitation experiments conducted from strong NH 4Cl electrolytes. In this study we compared the incorporation trends of Zn and Mn from solutions with various chloride content to test the possibility that the adsorption of "large" ZnCl n2-n aqueous complexes influences the site preference of Zn. The incorporation trends of Mn and Zn were opposite at the symmetrically nonequivalent growth steps. From a 0.4 M NH 4Cl solution, where Zn aqueous speciation was thermodynamically dominated by the "free" aquo ion, Zn maintained its site preference for the geometrically less constrained surface sites. Thus, Zn exhibits a particular interaction with surface sites and its incorporation trend is not controlled by the prevalence of ZnCl n2-n complexes. Other factors like the electronic configuration must be considered. The surface microtopography of calcite was found to be sensitive to changes in the aqueous concentrations of NH 4Cl and Zn. Decreases in NH 4Cl concentration resulted in an increase of the density of growth hillocks. The strong adsorbing behaviour of Zn increased the surface roughness, decreased the rate of growth, perturbed the spiral growth mechanism, and triggered the nucleation of discrete surface precipitates (˜0.2 μm) along macrosteps. An increase of Cl incorporation, despite the decrease of its aqueous concentration by dilutions of the parent solution, suggests that surface roughness at the calcite-solution interface is another factor involved in the nonequilibrium process of impurity element

  1. Surface air quality implications of volcanic injection heights

    Science.gov (United States)

    Thomas, Manu Anna; Brännström, Niklas; Persson, Christer; Grahn, Håkan; von Schoenberg, Pontus; Robertson, Lennart

    2017-10-01

    Air quality implications of volcanic eruptions have gained increased attention recently in association with the 2010 Icelandic eruption that resulted in the shut-down of European air space. The emission amount, injection height and prevailing weather conditions determine the extent of the impact through the spatio-temporal distribution of pollutants. It is often argued that in the case of a major eruption in Iceland, like Laki in 1783-1784, that pollutants injected high into the atmosphere lead to substantially increased concentrations of sulfur compounds over continental Europe via long-range transport in the jet stream and eventual large-scale subsidence in a high-pressure system. Using state-of-the-art simulations, we show that the air quality impact of Icelandic volcanoes is highly sensitive to the injection height. In particular, it is the infinitesimal injections into the lower half of the troposphere, rather than the substantial injections into the upper troposphere/lower stratosphere that contribute most to increased pollutant concentrations, resulting in atmospheric haze over mainland Europe/Scandinavia. Besides, the persistent high pressure system over continental Europe/Scandinavia traps the pollutants from dispersing, thereby prolonging the haze.

  2. Effect of fluid salinity on subcritical crack propagation in calcite

    Science.gov (United States)

    Rostom, Fatma; Røyne, Anja; Dysthe, Dag Kristian; Renard, François

    2013-01-01

    The slow propagation of cracks, also called subcritical crack growth, is a mechanism of fracturing responsible for a ductile deformation of rocks under crustal conditions. In the present study, the double-torsion technique was used to measure the effect of fluid chemistry on the slow propagation of cracks in calcite single crystals at room temperature. Time-lapse images and measurements of force and load-point displacement allowed accurate characterization of crack velocities in a range of 10- 8 to 10- 4 m/s. Velocity curves as a function of energy-release rates were obtained for different fluid compositions, varying NH4Cl and NaCl concentrations. Our results show the presence of a threshold in fluid composition, separating two regimes: weakening conditions where the crack propagation is favored, and strengthening conditions where crack propagation slows down. We suggest that electrostatic surface forces that modify the repulsion forces between the two surfaces of the crack may be responsible for this behavior.

  3. Messinian Erosional Surface in the Levantin margins: geodynamic implications.

    Science.gov (United States)

    Mocochain, L.; Clauzon, G.; Robinet, J.; Blanpied, C.; Suc, J. P.; Gorini, C.; Abdalla, A. Al; Azki, F.

    2012-04-01

    During the Messinian salinity crisis (5.96-5.33 Ma), the Mediterranean Sea was disconnected from the Atlantic Ocean. As a consequence, a dramatic sea-level fall occurred during part of the crisis and deep erosion has been observed on the Mediterranean margins as well as on the continent. The origin and evolution of the Messinian Salinity Crisis (MSC) and associated deposits beneath the Mediterranean seafloor is still subject of considerable debate, mainly focused on their depositional environment, age and correlation from the basinal to marginal series. One of the key problems concerns the lack of biostratigraphy data and 3D geometrical control of main stratigraphic surfaces. Recent studies in three areas in the Eastern Mediterranean basins, Hatay (Turkey), Lattakie (Syria), and Psematismenos (Cyprus) basins confirm the presence of the Messinian Erosional Surface which separates the uppermost Miocene deposits from the Pliocene, clearly encased in incises valleys. Systematic cartography of this unconformity shows fluvial erosion in relation with the peak of the Messinian Salinity Crisis. On the edges of the Psematismenos incised valleys or subareal canyons, the Messinian Erosional Surface impacts the previously deposited Messinian marginal evaporites linked to a first step of the Messinian Salinity Crisis. Huge Mass Transport Deposits are often locally preserved along the canyons edges and made of breccias with blocks of variable size and nature, gypsum and other pre-Messinian rocks. Fan delta complexes infilled the Messinian canyons flooded during the Zanclean. The most spectacular is described in the Nahr El Khabir Valley in northern Syria. These observations consists in distinct steps of the Messinian Salinity Crisis: 1- circum-Mediterranean deposition of marginal evaporite between 5.96 and 5.6 Ma in suspended basins, and 2- the downcutting of the Messinian fluvial canyons between 5.6 and 5.32Ma ending with the complex Pliocene marine reflooding, caracterised by

  4. Ocean Surface Circulation with Implication for Marine Debris Distribution

    Science.gov (United States)

    Hafner, Jan; Maximenko, Nikolai; Niiler, Peter

    2010-05-01

    Modern, multi-instrumental Global Ocean Observing System (GOOS) includes satellites and in situ observations, monitoring the ocean state at the highest accuracy and resolution ever. By combining data of satellite altimetry, surface drifters, wind and gravity, ocean currents can be assessed globally and at research quality. The map of the mean surface currents shows a complex pattern of oceanic fronts and gyres. Distinct are the convergences of Ekman currents in subtropical gyres that, through the Sverdrup mechanism, are feeding anticyclonic circulation in the gyres. Drifter trajectories can also be utilized to simulate the evolution of the marine debris. Main problem is the inhomogeneous drifter data density, both due to convergence/divergence of the ocean currents and due to the drifter deployment scheme. A model constructed from statistics of the drifters exchange between small bins corrects this bias and was run from the uniform initial condition to study the fate of debris in the ocean. In addition to such actively studied debris accumulation areas as the Great Garbage Patch in the North Pacific, a new so far unrecognized, the world-strongest convergence is discovered in the South Pacific from the model solution. The same model reveals a complex pattern of convergence/divergence on the cold/warm flanks of major oceanic fronts. This pattern is studied in the framework of nonlinear interaction between Ekman drift and geostrophic baroclinic fronts outcropping at the sea surface. Results are generalized to assess the dynamics of internal Ekman layer distributed along the thermocline and controlling the secondary circulation at the fronts.

  5. Calcite/aragonite-biocoated artificial coral reefs for marine parks

    Directory of Open Access Journals (Sweden)

    Volodymyr Ivanov

    2017-08-01

    Full Text Available Natural formation of the coral reefs is complicated by slow biomediated precipitation of calcium carbonate from seawater. Therefore, manufactured artificial coral reefs can be used for the formation of “underwater gardens” in marine parks for the recreational fishing and diving that will protect natural coral reefs from negative anthropogenic effects. Additionally, the coating of the concrete, plastic or wooden surfaces of artificial coral reef with calcium carbonate layer could promote attachment and growth of coral larvae and photosynthetic epibiota on these surfaces. Three methods of biotechnological coating of the artificial coral reefs have been tested: (1 microbially induced calcium carbonate precipitation from concentrated calcium chloride solution using live bacterial culture of Bacillus sp. VS1 or dead but urease-active cells of Yaniella sp. VS8; (2 precipitation from calcium bicarbonate solution; (3 precipitation using aerobic oxidation of calcium acetate by bacteria Bacillus ginsengi strain VSA1. The thickness of biotechnologically produced calcium carbonate coating layer was from 0.3 to 3 mm. Biocoating using calcium salt and urea produced calcite in fresh water and aragonite in seawater. The calcium carbonate-coated surfaces were colonized in aquarium with seawater and hard corals as inoculum or in aquarium with fresh water using cyanobacteria Chlorella sorokiana as inoculum. The biofilm on the light-exposed side of calcium carbonate-coated surfaces was formed after six weeks of incubation and developed up to the average thickness of 250 µm in seawater and about 150 µm in fresh water after six weeks of incubation. The biotechnological manufacturing of calcium carbonate-coated concrete, plastic, or wooden surfaces of the structures imitating natural coral reef is technologically feasible. It could be commercially attractive solution for the introduction of aesthetically pleasant artificial coral reefs in marine parks and

  6. Biocementation of Concrete Pavements Using Microbially Induced Calcite Precipitation.

    Science.gov (United States)

    Jeong, Jin-Hoon; Jo, Yoon-Soo; Park, Chang-Seon; Kang, Chang-Ho; So, Jae-Seong

    2017-07-28

    In this study, the feasibility of introducing calcite-forming bacteria into concrete pavements to improve their mechanical performance was investigated. Lysinibacillus sphaericus WJ-8, which was isolated in a previous study and is capable of exhibiting high urease activity and calcite production, was used. When analyzed via scanning electron microscopy (SEM) and X-ray diffraction, WJ-8 showed a significant amount of calcite precipitation. The compressive strength of cement mortar mixed with WJ-8 cells and nutrient medium (urea with calcium lactate) increased by 10% compared with that of the controls. Energy dispersive x-ray spectroscopy analyses confirmed that the increase in strength was due to the calcite formed by the WJ-8 cells.

  7. Fluid inclusion studies of calcite veins from Yucca Mountain, Nevada, Tuffs: Environment of formation

    Energy Technology Data Exchange (ETDEWEB)

    Roedder, E. [Harvard Univ., Cambridge, MA (United States); Whelan, J.F. [Geological Survey, Denver, CO (United States); Vaniman, D.T. [Los Alamos National Lab., NM (United States)

    1994-12-31

    Calcite vein and vug fillings at four depths (130-314m), all above the present water table in USW G-1 bore hole at Yucca Mountain, Nevada, contain primary fluid inclusions with variable vapor/liquid raitos: Most of these inclusions are either full of liquid or full of vapor. The liquid-filled inclusions show that most of the host calcite crystallized from fluids at <100{degrees}C. The vapor-filled inclusions provide evidence that a separate vapor phase was present in the fluid during crystallization. Studies of these vapor-filled inclusions on the microscope crushing stage were interpreted in an earlier paper as indicating trapping of an air-water-CO{sub 2} vapor phase at ``<100{degrees}C``. Our new studies reveal the additional presence of major methane in the vapor-filled inclusion, indicating even lower temperatures of trapping, perhaps at near-surface temperatures. They also show that the host calcite crystals grew from a flowing film of water on the walls of fractures open to the atmosphere, the vapor-filled inclusions representing bubbles that exsolved from this film onto the crystal surface.

  8. Immobilization of nanoparticles by occlusion into microbial calcite

    DEFF Research Database (Denmark)

    Skuce, Rebecca L.; Tobler, Dominique Jeanette; MacLaren, Ian

    2017-01-01

    systems. In this study, the ureolytic bacteria Sporosarcina pasteurii was used to induce calcium carbonate precipitation in the presence of organo-metallic manufactured nanoparticles. As calcite crystals grew the nanoparticles in the solution became trapped inside these crystals. Capture of NPs within...... not influence calcite precipitation at the concentrations used here. Overall, these findings demonstrate that microbially driven mineral precipitation has potential to immobilize nanoparticles in the environment via occlusion....

  9. Annual 18O/16O composition of authigenic calcite in varved lake sediments reflects regional air temperature

    Science.gov (United States)

    Wirth, Stefanie; Gilli, Adrian

    2015-04-01

    The oxygen isotopic composition (18O/16O) of authigenic calcite in lake sediments reflects the temperature and the isotopic composition of the lake water from which the calcite is precipitated and thus contains information about the climatic conditions at the time of calcite formation. Varved lake sediments containing laminae of authigenically precipitated calcite provide the possibility to analyze the 18O/16O composition at an annual resolution, thus yielding high-resolution climatic information. Yet, despite this high potential the number of studies having used this approach is relatively low. Reasons for this are probably sampling challenges, the scarceness of suitable varved sediments, missing instrumental records to compare with, as well as uncertainties regarding the factors influencing the calcite isotopic composition (water/air temperature, precipitation, lake-internal factors). Still, annually resolved data of the 18O/16O composition of calcite seems a promising climate proxy and we therefore investigated the 18O/16O pattern of the authigenic calcite in the varved sediments of Lake Zurich. Lake Zurich is a pre-alpine lake with a surface area of 88 km2, a maximal water depth of 137 m and a theoretical water residence time of 1.4 years. Sediments are varved since the late 19th century due to anthropogenic lake eutrophication. For this calibration study, we analyzed the 18O/16O composition of the authigenic calcite for the time period 1960-2010 at annual resolution. The δ18O values range from -10.8 to -13.4 o; and the pattern is dominated by a conspicuous shift to more enriched values between 1985 and 1987. The same shift has been observed for local to large-scale climatic parameters such as lake, river, and groundwater temperatures throughout Switzerland, the mean air temperature for Switzerland, and the NAO index. The consistency of the instrumental temperature data sets with the 18O/16O composition of the authigenic calcite emphasizes the high potential

  10. Selective Flotation of Calcite from Fluorite: A Novel Reagent Schedule

    Directory of Open Access Journals (Sweden)

    Zhiyong Gao

    2016-10-01

    Full Text Available Fluorite is an important strategic mineral. In general, fluorite ores will contain a certain amount of calcite gangue mineral. Thus, they need to be separated from each other. For an economic separation, a reverse flotation process is used to float calcite gangue from fluorite. However, little information on the separation is available. In this study, a novel reagent schedule using citric acid (CA as the depressant, sodium fluoride (NaF as the regulator and sulfoleic acid (SOA as the collector, was developed to separate calcite from fluorite. The results demonstrated a high selectivity for the flotation of calcite from fluorite using this new reagent schedule. The best selective separation for a single mineral and mixed binary minerals was obtained when 200 mg/L of NaF, 50 mg/L of CA, and 6 mg/L of SOA were used at pH 9. In addition, a batch flotation experiment was carried out using a run-of-mine feed material. Selective separation was achieved with 85.18% calcite removal while only 11.2% of fluorite was lost. An attempt was made to understand the effect of the new reagent schedule on the flotation of calcite. The results from both microflotation and bench scale flotation demonstrated a great potential for industrial application using this novel reagent schedule to upgrade fluorite ore.

  11. Surface activity of thymol: implications for an eventual pharmacological activity.

    Science.gov (United States)

    Sánchez, Mariela E; Turina, Anahí del V; García, Daniel A; Nolan, M Verónica; Perillo, María A

    2004-03-15

    In the present work, we studied the ability of thymol to affect the organization of model membranes and the activity of an intrinsic membrane protein, the GABA(A) receptor (GABA(A)-R). In this last aspect, we tried to elucidate if the action mechanism of this terpene at the molecular level, involves its binding to the receptor protein, changes in the organization of the receptor molecular environment, or both. The self-aggregation of thymol in water with a critical micellar concentration approximately = 4 microM and its ability to penetrate in monomolecular layers of soybean phosphatidylcholine (sPC) at the air-water interface, even at surface pressures above the equilibrium, lateral pressure of natural bilayers were demonstrated. Thymol affected the self-aggregation of Triton X-100 and the topology of sPC vesicles. It also increased the polarity of the membrane environment sensed by the electrochromic dye merocyanine. A dipolar moment of 1.341 Debye was calculated from its energy-minimized structure. Its effect on the binding of [3H]-flunitrazepam ([3H]-FNZ) to chick brain synaptosomal membranes changed qualitatively from a tendency to the inhibition to a clear activatory regime, up on changing the phase state of the terpene (from a monomeric to a self-aggregated state). Above its CMC, thymol increased the affinity of the binding of [3H]-FNZ (K(d-control)= 2.9, K(d-thymol)= 1.7 nM) without changing the receptor density (B(max-control)= 910, B(max-thymol)= 895 fmol/mg protein). The activatory effect of thymol on the binding of [ [3H]-FNZ was observed even in the presence of the allosteric activator gamma-aminobutyric acid (GABA) at a concentration of maximal activity, and was blocked by the GABA antagonist bicuculline. Changes in the dipolar arrangement and in the molecular packing of GABA(A)-R environment are discussed as possible mediators of the action mechanism of thymol.

  12. Sea Urchin Spine Calcite Forms via a Transient Amorphous Calcium Carbonate Phase

    Science.gov (United States)

    Politi, Yael; Arad, Talmon; Klein, Eugenia; Weiner, Steve; Addadi, Lia

    2004-11-01

    The skeletons of adult echinoderms comprise large single crystals of calcite with smooth convoluted fenestrated morphologies, raising many questions about how they form. By using water etching, infrared spectroscopy, electron diffraction, and environmental scanning electron microscopy, we show that sea urchin spine regeneration proceeds via the initial deposition of amorphous calcium carbonate. Because most echinoderms produce the same type of skeletal material, they probably all use this same mechanism. Deposition of transient amorphous phases as a strategy for producing single crystals with complex morphology may have interesting implications for the development of sophisticated materials.

  13. Calcite Farming at Hollow Ridge Cave: Calibrating Net Rainfall and Cave Microclimate to Dripwater and Calcite Chemical Variability

    Science.gov (United States)

    Tremaine, D. M.; Kilgore, B. P.; Froelich, P. N.

    2012-04-01

    Stable isotope (δ18O and δ13C) and trace element records in cave speleothems are often interpreted as climate changes in rainfall amount or source, cave air temperature, overlying vegetation and atmospheric pCO2. However, these records are difficult to verify without in situ calibration of changes in cave microclimate (e.g., net rainfall, interior ventilation changes) to contemporaneous variations in dripwater and speleothem chemistry. In this study at Hollow Ridge Cave (HRC) in Marianna, Florida (USA), cave dripwater, bedrock, and modern calcite (farmed in situ) were collected in conjunction with continuous cave air pCO2, temperature, barometric pressure, relative humidity, radon-222 activity, airflow velocity and direction, rainfall amount, and drip rate data [1]. We analyzed rain and dripwater δD and δ18O, dripwater Ca2+, pH, δ13C and TCO2, cave air pCO2 and δ13C, and farmed calcite δ18O and δ13C to examine the relationships among rainwater isotopic composition, cave air ventilation, cave air temperature, calcite growth rate and seasonal timing, and calcite isotopic composition. Farmed calcite δ13C decreases linearly with distance from the front entrance to the interior of the cave during all seasons, with a maximum entrance-to-interior gradient of Δδ13C = -7‰ . A whole-cave "Hendy test" at distributed contemporaneous farming sites reveals that ventilation induces a +1.9 ± 0.96‰ δ13C offset between calcite precipitated in a ventilation flow path and out of flow paths. Farmed calcite δ18O exhibits a +0.82 ± 0.24‰ offset from values predicted by both theoretical calcite-water calculations and by laboratory-grown calcite [2]. Unlike calcite δ13C, oxygen isotopes show no ventilation effects and are a function only of temperature. Combining our data with other speleothem studies, we find a new empirical relationship for cave-specific water-calcite oxygen isotope fractionation across a range of temperatures and cave environments: 1000 ln α = 16

  14. Calcium and strontium isotope fractionation in aqueous solutions as a function of temperature and reaction rate; I. Calcite

    Science.gov (United States)

    AlKhatib, Mahmoud; Eisenhauer, Anton

    2017-07-01

    In order to study Strontium (Sr) partitioning and isotope fractionation of Sr and Calcium (Ca) in calcite we performed precipitation (T) experiments decoupling temperature and precipitation rate (R∗). Calcite was precipitated at 12.5, 25.0 and 37.5 °C by diffusing NH3 and CO2 gases into aqueous solutions closely following the experimental setup of Lemarchand et al. (2004). The precipitation rate (R∗) for every sample was determined applying the initial rate method and from the specific surface area of almost all samples for each reaction. The order of reaction with respect to Ca2+ ions was determined to be one and independent of T. However, the order of reaction with respect to HCO3- changed from three to one as temperature increases from 12.5, 25 °C and 37.5 °C. Strontium incorporated into calcite (expressed as DSr = [Sr/Ca]calcite/[Sr/Ca]solution) was found to be R∗ and T dependent. As a function of increasing R∗ the Δ88/86Sr-values become more negative and as temperature increases the Δ88/86Sr values also increase at constant R∗. The DSr and Δ88/86Sr-values are correlated to a high degree and depend only on R∗ being independent of temperature, complexation and varying initial ratios. Latter observation may have important implications for the study of diagenesis, the paleo-sciences and the reconstruction of past environmental conditions. Calcium isotope fractionation (Δ44/40Ca) was also found to be R∗ and T dependent. For 12.5 and 25.0 °C we observe a general increase of the Δ44/40Ca values as a function of R∗ (Lemarchand et al. type behavior, Lemarchand et al. (2004)). Whereas at 37.5 °C a significant decreasing Δ44/40Ca is observed relative to increasing R∗ (Tang et al. type behavior, Tang et al. (2008)). In order to reconcile the discrepant observations we suggest that the temperature triggered change from a Ca2+-NH3-aquacomplex covalent controlled bonding to a Ca2+-H2O-aquacomplex van-der-Waals controlled bonding caused the change

  15. Ice sintering timescales at the surface of Europa and implications for surface properties

    Science.gov (United States)

    Molaro, Jamie; Phillips, Cynthia B.; Meirion-Griffith, Gareth

    2017-10-01

    The planned exploration of Europa by NASA’s Europa Clipper Mission and the possibility of a future Europa lander have driven the need to characterize its surface strength, roughness, porosity, thermal conductivity, and regolith depth in order to accurately interpret remote sensing data and develop appropriate spacecraft landing systems. Many processes contribute to Europa’s landscape evolution, such as sputtering, mass wasting, thermal segregation, and impact gardening, driving the creation and distribution of icy regolith across the surface. While the efficacy of these processes are not well constrained, any amount of regolith emplaced at the surface will undergo subsequent processing due to sintering. Ice sintering is a form of frost metamorphism whereby contacting ice grains experience the diffusion of material into their contact region, forming a “neck” between them and densifying over time. Over long enough timescales, ice aggregates will sinter into solid material, which may contribute to the incorporation of non-ice material into Europa’s subsurface and help to drive subsurface chemistry. Sintering also interacts with other processes, adding to the complexity of icy surface evolution. For example, sputtering preferentially removes larger grains and may enhance sintering rates, and changes in ice porosity may affect the response of the surface to micrometeorite impacts.Quantifying the effects of ice sintering will allow us to predict the microstructural properties of Europa’s surface at spacecraft scales. To this end, we have modeled pressure-less (no overburden) sintering of spherical water-ice grains and validated the results with a laboratory experiment. We also modeled ice at the surface of Europa to obtain a first-order approximation of the sintering timescale and surface properties. Preliminary results indicate that ice grains will experience neck growth but not significant densification over Europa’s surface age, suggesting that loose

  16. Nickel adsorption on chalk and calcite

    DEFF Research Database (Denmark)

    Belova, Dina Alexandrovna; Lakshtanov, Leonid; Carneiro, J.F.

    2014-01-01

    and chalk and pH ranging from 7.7 to 8.8, explored the influence of initial concentration and the amount and type of sorbent on Ni uptake. Adsorption increases with increased surface area and pH. A surface complexation model describes the data well. Stability constants for the Ni surface complex are log KNi...

  17. On the complex conductivity signatures of calcite precipitation

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Yuxin; Hubbard, Susan; Williams, Kenneth Hurst; Ajo-Franklin, Jonathan

    2009-11-01

    Calcite is a mineral phase that frequently precipitates during subsurface remediation or geotechnical engineering processes. This precipitation can lead to changes in the overall behavior of the system, such as flow alternation and soil strengthening. Because induced calcite precipitation is typically quite variable in space and time, monitoring its distribution in the subsurface is a challenge. In this research, we conducted a laboratory column experiment to investigate the potential of complex conductivity as a mean to remotely monitor calcite precipitation. Calcite precipitation was induced in a glass bead (3 mm) packed column through abiotic mixing of CaCl{sub 2} and Na{sub 2}CO{sub 3} solutions. The experiment continued for 12 days with a constant precipitation rate of {approx}0.6 milimole/d. Visual observations and scanning electron microscopy imaging revealed two distinct phases of precipitation: an earlier phase dominated by well distributed, discrete precipitates and a later phase characterized by localized precipitate aggregation and associated pore clogging. Complex conductivity measurements exhibited polarization signals that were characteristic of both phases of calcite precipitation, with the precipitation volume and crystal size controlling the overall polarization magnitude and relaxation time constant. We attribute the observed responses to polarization at the electrical double layer surrounding calcite crystals. Our experiment illustrates the potential of electrical methods for characterizing the distribution and aggregation state of nonconductive minerals like calcite. Advancing our ability to quantify geochemical transformations using such noninvasive methods is expected to facilitate our understanding of complex processes associated with natural subsurface systems as well as processes induced through engineered treatments (such as environmental remediation and carbon sequestration).

  18. Defluoridation of drinking water by boiling with brushite and calcite.

    Science.gov (United States)

    Larsen, M J; Pearce, E I F

    2002-01-01

    Existing methods for defluoridating drinking water involve expensive high technology or are slow, inefficient and/or unhygienic. A new method is now suggested, encompassing brushite and calcite suspension followed by boiling. Our aim was to examine the efficiency of the method and the chemical reactions involved. Brushite, 0.3-0.5 g, and an equal weight of calcite were suspended in 1 litre water containing 5-20 ppm fluoride. The suspensions were boiled in an electric kettle, left to cool and the calcium salts to sediment. Solution ion concentrations were determined and sediments were examined by X-ray diffraction. In distilled water initially containing 5, 10 and 20 ppm fluoride the concentration was reduced to 0.06, 0.4 and 5.9 ppm, respectively. Using Aarhus tap water which contained 2.6 mmol/l calcium the final concentrations were 1.2, 2.5 and 7.7 ppm, respectively, and runs without calcite gave results similar to those with calcite. Without boiling the fluoride concentration remained unaltered, as did the brushite and calcite salts, despite occasional agitation by hand. All solutions were supersaturated with respect to fluorapatite and hydroxyapatite and close to saturation with respect to brushite. Boiling produced well-crystallised apatite and traces of calcite, while boiling of brushite alone left a poorly crystallised apatite. We conclude that boiling a brushite/calcite suspension rapidly converts the two salts to apatite which incorporates fluoride if present in solution, and that this process may be exploited to defluoridate drinking water. Copyright 2002 S. Karger AG, Basel

  19. An efficient phosphorus scavenging from aqueous solution using magnesiothermally modified bio-calcite.

    Science.gov (United States)

    Ahmad, Munir; Ahmad, Mahtab; Usman, Adel R A; Al-Faraj, Abdullah S; Ok, Yong Sik; Hussain, Qaiser; Abduljabbar, Adel S; Al-Wabel, Mohammad I

    2017-06-09

    Bio-calcite (BC) derived from waste hen eggshell was subjected to thermal treatments (calcined bio-calcite (CBC)). The BC and CBC were further modified via magnesiothermal treatments to produce modified bio-calcite (MBC) and modified calcined bio-calcite (MCBC), respectively, and evaluated as a novel green sorbent for P removal from aqueous solutions in the batch experiments. Modified BC exhibited improved structural and chemical properties, such as porosity, surface area, thermal stability, mineralogy and functional groups, than pristine material. Langmuir and Freundlich models well described the P sorption onto both thermally and magnesiothermally sorbents, respectively, suggesting mono- and multi-layer sorption. Langmuir predicted highest P sorption capacities were in the order of: MCBC (43.33 mg g -1 ) > MBC (35.63 mg g- 1 ) > CBC (34.38 mg g -1 ) > BC (30.68 mg g -1 ). The MBC and MCBC removed 100% P up to 50 mg P L -1 , which reduced to 35.43 and 39.96%, respectively, when P concentration was increased up to 1000 mg L -1 . Dynamics of P sorption was well explained by the pseudo-second-order rate equation, with the highest sorption rate of 4.32 mg g -1  min -1 for the MCBC. Hydroxylapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] and brushite [CaH(PO 4 )·2H 2 O] were detected after P sorption onto the modified sorbents by X-ray diffraction analysis, suggesting chemisorption as the operating sorption mechanism.

  20. Orientation and Mg Incorporation of Calcite Grown on Functionalized Self-Assembled Monolayers: A Synchrotron X-ray Study

    Energy Technology Data Exchange (ETDEWEB)

    Kwak,S.; DiMasi, E.; Han, Y.; Aizenberg, J.; Kuzmenko, I.

    2005-01-01

    Calcite crystals were nucleated from MgCl2/CaCl2 solutions onto functionalized self-assembled monolayers adsorbed onto E-beam evaporated Au films. Synchrotron X-ray scattering studies of the crystals reveal new information about preferred orientation and Mg incorporation. The Au [111] axis is distributed within 2.6 degrees of the film surface normal, but the oriented crystals may be tilted up to 6 degrees away from this axis. For low Mg{sup 2+} content, SO{sub 3}--functionalized films nucleated primarily near the (106) calcite face, odd-chain-length carboxylic acid terminated alkanethiol films nucleated near the (012) face, and even-chain-length carboxylic acid terminated alkanethiol films nucleated near the (113) face. [Mg{sup 2+}]/[Ca{sup 2+}] concentration ratios (n) of 2 and greater defeated this preferred orientation and created a powder texture. Diffraction patterns within the layer plane from the coarse calcite powders indicated a shift to higher 2 accompanied by peak broadening with increasing n. For 0.5 < n < 3.5, a double set of calcite peaks is observed, showing that two distinct Mg calcite phases form: one of comparatively lower Mg content, derived from the templated crystals, and a Mg-rich phase derived from amorphous precursor particles. According to the refinement of lattice parameters, Mg incorporation of up to 18 mol % occurs for n = 4, independent of film functionality. We discuss the differences between the differently functionalized monolayers and also introduce the hypothesis that two separate routes to Mg calcite formation occur in this system.

  1. A Raman spectroscopic comparison of calcite and dolomite.

    Science.gov (United States)

    Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L

    2014-01-03

    Raman spectroscopy was used to characterize and differentiate the two minerals calcite and dolomite and the bands related to the mineral structure. The (CO3)(2-) group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the calcite and dolomite were observed at 1440, 1088, 715 and 278 cm(-1). The significant differences between the minerals calcite and dolomite are observed by Raman spectroscopy. Calcite shows the typical bands observed at 1361, 1047, 715 and 157 cm(-1), and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm(-1) for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. Calcite has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral. Copyright © 2013 Elsevier B.V. All rights reserved.

  2. Nuclear anomalies in the buccal cells of calcite factory workers.

    Science.gov (United States)

    Diler, Songül Budak; Ergene, Serap

    2010-04-01

    The micronucleus (MN) assay on exfoliated buccal cells is a useful and minimally invasive method for monitoring genetic damage in humans. To determine the genotoxic effects of calcite dust that forms during processing, MN assay was carried out in exfoliated buccal cells of 50 (25 smokers and 25 non-smokers) calcite factory workers and 50 (25 smokers and 25 non-smokers) age- and sex-matched control subjects. Frequencies of nuclear abnormalities (NA) other than micronuclei, such as binucleates, karyorrhexis, karyolysis and 'broken eggs', were also evaluated. Micronuclei and the other aforementioned anomalies were analysed by two way analysis of covariance. The linear correlations between the types of micronucleus and nuclear abnormalities were determined by Spearman's Rho. There was a positive correlation between micronuclei and other types of nuclear abnormalities in accordance with the Spearman's Rho test. Results showed statistically significant difference between calcite fabric workers and control groups. MN and NA frequencies in calcite fabric workers were significantly higher than those in control groups (p < 0.05). The results of this study indicate that calcite fabric workers are under risk of significant cytogenetic damage.

  3. Nuclear anomalies in the buccal cells of calcite factory workers

    Directory of Open Access Journals (Sweden)

    Songül Budak Diler

    2010-01-01

    Full Text Available The micronucleus (MN assay on exfoliated buccal cells is a useful and minimally invasive method for monitoring genetic damage in humans. To determine the genotoxic effects of calcite dust that forms during processing, MN assay was carried out in exfoliated buccal cells of 50 (25 smokers and 25 non-smokers calcite factory workers and 50 (25 smokers and 25 non-smokers age- and sex-matched control subjects. Frequencies of nuclear abnormalities (NA other than micronuclei, such as binucleates, karyorrhexis, karyolysis and 'broken eggs', were also evaluated. Micronuclei and the other aforementioned anomalies were analysed by two way analysis of covariance. The linear correlations between the types of micronucleus and nuclear abnormalities were determined by Spearman's Rho. There was a positive correlation between micronuclei and other types of nuclear abnormalities in accordance with the Spearman's Rho test. Results showed statistically significant difference between calcite fabric workers and control groups. MN and NA frequencies in calcite fabric workers were significantly higher than those in control groups (p < 0.05. The results of this study indicate that calcite fabric workers are under risk of significant cytogenetic damage.

  4. Influence of solution chemistry on the boron content in inorganic calcite grown in artificial seawater

    Science.gov (United States)

    Uchikawa, Joji; Harper, Dustin T.; Penman, Donald E.; Zachos, James C.; Zeebe, Richard E.

    2017-12-01

    The ratio of boron to calcium (B/Ca) in marine biogenic carbonates has been proposed as a proxy for properties of seawater carbonate chemistry. Applying this proxy to planktic foraminifera residing in the surface seawater largely in equilibrium with the atmosphere may provide a valuable handle on past atmospheric CO2 concentrations. However, precise controls on B/Ca in planktic foraminifera remain enigmatic because it has been shown to depend on multiple physicochemical seawater properties. To help establish a firm inorganic basis for interpreting the B/Ca records, we examined the effect of a suite of chemical parameters ([Ca2+], pH, [DIC], salinity and [PO43-]) on B/Ca in inorganic calcite precipitated in artificial seawater. These parameters were primarily varied individually while keeping all others constant, but we also tested the influence of pH and [DIC] at a constant calcite precipitation rate (R) by concurrent [Ca2+] adjustments. In the simple [Ca2+], pH and [DIC] experiments, both R and B/Ca increased with these parameters. In the pH-[Ca2+] and [DIC]-[Ca2+] experiments at constant R, on the other hand, B/Ca was invariant at different pH and decreased with [DIC], respectively. These patterns agree with the behavior of solution [BTotal/DIC] ratio such that, at a fixed [BTotal], it is independent of pH but decreases with [DIC]. Based on these results, R and [BTotal/DIC] ratio appear to be the primary controls on B/Ca in inorganic calcite, suggesting that both B(OH)4- and B(OH)3 are possibly involved in B incorporation. Moreover, B/Ca modestly increased with salinity and [PO43-]. Inorganic calcite precipitated at higher R and in the presence of oxyanions such as SO42- and PO43- in growth solutions often undergoes surface roughening due to formation of crystallographic defects, vacancies and, occasionally, amorphous/hydrous CaCO3. These non-lattice sites may provide additional space for B, particularly B(OH)3. Consequently, besides the macroscopic influence of

  5. THE BUFFER ROLE OF GROUNDWATER WHEN SURFACE WATER SUPPLIES ARE UNCERTAIN: THE IMPLICATIONS FOR GROUNDWATER DEVELOPMENT

    OpenAIRE

    Tsur, Yacov

    1988-01-01

    When used in conjunction with surface water for irrigation, groundwater serves two roles: to increase water supply; and to mitigate fluctuations in the supply of water. The later is the buffer role. This paper identifies and evaluates the economic benefit associated with the buffer role of ground water. Implications for the development of groundwater resources are investigated. An estimate is given of the buffer benefit to wheat growers of the fossil water aquifer underlying the Israeli Negev...

  6. Catalysis and chemical mechanisms of calcite dissolution in seawater.

    Science.gov (United States)

    Subhas, Adam V; Adkins, Jess F; Rollins, Nick E; Naviaux, John; Erez, Jonathan; Berelson, William M

    2017-07-18

    Near-equilibrium calcite dissolution in seawater contributes significantly to the regulation of atmospheric [Formula: see text] on 1,000-y timescales. Despite many studies on far-from-equilibrium dissolution, little is known about the detailed mechanisms responsible for calcite dissolution in seawater. In this paper, we dissolve (13)C-labeled calcites in natural seawater. We show that the time-evolving enrichment of [Formula: see text] in solution is a direct measure of both dissolution and precipitation reactions across a large range of saturation states. Secondary Ion Mass Spectrometer profiles into the (13)C-labeled solids confirm the presence of precipitated material even in undersaturated conditions. The close balance of precipitation and dissolution near equilibrium can alter the chemical composition of calcite deeper than one monolayer into the crystal. This balance of dissolution-precipitation shifts significantly toward a dissolution-dominated mechanism below about [Formula: see text] Finally, we show that the enzyme carbonic anhydrase (CA) increases the dissolution rate across all saturation states, and the effect is most pronounced close to equilibrium. This finding suggests that the rate of hydration of [Formula: see text] is a rate-limiting step for calcite dissolution in seawater. We then interpret our dissolution data in a framework that incorporates both solution chemistry and geometric constraints on the calcite solid. Near equilibrium, this framework demonstrates a lowered free energy barrier at the solid-solution interface in the presence of CA. This framework also indicates a significant change in dissolution mechanism at [Formula: see text], which we interpret as the onset of homogeneous etch pit nucleation.

  7. TEM study of Pt-C replicas of calcite overgrowths precipitated from electrolyte solutions

    Science.gov (United States)

    Paquette, Jeanne; Vali, Hojatollah; Mucci, Alfonso

    1996-12-01

    The surface microtopography of synthetic magnesian calcite overgrowths on calcite powders was imaged on Pt-C replicas by transmission electron microscopy. The overgrowths were precipitated at room temperature under steady-state conditions from seawater-like solutions, in the presence and absence of Mg2+, SO42- and PO43- ions, and over a range of saturation states. Overgrowths produced from the Mg-free electrolyte show smooth coverage of the substrate with a few hillocks suggestive of spiral growth. Electrolytes containing Mg consistently produced patchy overgrowths on the {1014} faces of the seed crystals and differential inhibition of growth at their corners and edges. The patchy over-growths consist of flat-topped islands whose morphology is consistent with two-dimensional surface nucleation rather than spiral growth. The density of islands, their rounding, and their degree of coalescence increased with the saturation state of the precipitating solution. The effect of SO42- on the surface topography was imperceptible. Soluble reactive phosphate (SRP), on the other hand, clearly inhibited growth and dissolution along specific crystallographic directions. The development of irregular surfaces along specific edges and corners of the seed crystals shows that foreign ions promote the development of complex crystal morphology even at high saturation states.

  8. Rapid high temperature field test method for evaluation of geothermal calcite scale inhibitors

    Energy Technology Data Exchange (ETDEWEB)

    Asperger, R.G.

    1982-08-01

    A test method is described which allows the rapid field testing of calcite scale inhibitors in high- temperature geothermal brines. Five commercial formulations, chosen on the basis of laboratory screening tests, were tested in brines with low total dissolved solids at ca 500 F. Four were found to be effective; of these, 2 were found to be capable of removing recently deposited scale. One chemical was tested in the full-flow brine line for 6 wks. It was shown to stop a severe surface scaling problem at the well's control valve, thus proving the viability of the rapid test method. (12 refs.)

  9. Formation of a ternary neptunyl(V) biscarbonato inner-sphere sorption complex inhibits calcite growth rate.

    Science.gov (United States)

    Heberling, Frank; Scheinost, Andreas C; Bosbach, Dirk

    2011-06-01

    Neptunyl, Np(V)O(2)(+), along with the other actinyl ions U(VI)O(2)(2+) and Pu(V,VI)O(2)((+,2+)), is considered to be highly mobile in the geosphere, while interaction with mineral surfaces (inner- or outer-sphere adsorption, ion-exchange, and coprecipitation/structural incorporation) may retard its migration. Detailed information about the exact interaction mechanisms including the structure and stoichiometry of the adsorption complexes is crucial to predict the retention behavior in diverse geochemical environments. Here, we investigated the structure of the neptunyl adsorption complex at the calcite-water interface at pH 8.3 in equilibrium with air by means of low-temperature (15K) EXAFS spectroscopy at the Np-L(III) edge. The coordination environment of neptunyl consists of two axial oxygen atoms at 1.87(±0.01)Å, and an equatorial oxygen shell of six atoms at 2.51(±0.01)Å. Two oxygen backscatterers at 3.50(±0.04)Å along with calcium backscatterers at 3.95(±0.03)Å suggest that neptunyl is linked to the calcite surface through two monodentate bonds towards carbonate groups of the calcite surface. Two additional carbon backscatterers at 2.94(±0.02)Å are attributed to two carbonate ions in bidentate coordination. This structural environment is conclusively interpreted as a ternary surface complex, where a neptunyl biscarbonato complex sorbs through two monodentate carbonate bonds to steps at the calcite (104) face, while the two bidentately coordinated carbonate groups point away from the surface. This structural information is further supported by Mixed Flow Reactor (MFR) experiments. They show a significant decrease of the calcite growth rate in the presence of neptunyl(V), in line with blockage of the most active crystal growth sites, step and kink sites, by adsorption of neptunyl. Formation of this sorption complex constitutes an important retention mechanism for neptunyl in calcite-rich environments. Copyright © 2011 Elsevier B.V. All rights

  10. Surface modification of mineral dust particles by sulphuric acid processing: implications for ice nucleation abilities

    Directory of Open Access Journals (Sweden)

    P. Reitz

    2011-08-01

    Full Text Available The ability of coated mineral dust particles to act as ice nuclei (IN was investigated at LACIS (Leipzig Aerosol Cloud Interaction Simulator during the FROST1- and FROST2-campaigns (Freezing of dust. Sulphuric acid was condensed on the particles which afterwards were optionally humidified, treated with ammonia vapour and/or heat. By means of aerosol mass spectrometry we found evidence that processing of mineral dust particles with sulphuric acid leads to surface modifications of the particles. These surface modifications are most likely responsible for the observed reduction of the IN activation of the particles. The observed particle mass spectra suggest that different treatments lead to different chemical reactions on the particle surface. Possible chemical reaction pathways and products are suggested and the implications on the IN efficiency of the treated dust particles are discussed.

  11. Adsorption of pesticides onto quartz, calcite, kaolinite, and α-alumina

    DEFF Research Database (Denmark)

    Clausen, Liselotte; Fabricius, Ida Lykke; Madsen, L.

    2001-01-01

    The fate of pesticides in aquifers is influenced by the small but not insignificant adsorption of pesticides to mineral surfaces. Batch experiments with five pesticides and four minerals were conducted to quantify the contributions to adsorption from different mineral surfaces and compare...... adsorption characteristics of selected pesticides. Investigated mineral phases included quartz, calcite, kaolinite, and alpha -alumina. Selected pesticides comprised atrazine (6-chloro-N-2-ethyl-N-4-isopropyl-1,3,5-triazine-2,4-diamine isoproturon [3-(4-isopropyl-phenyl)-1,1-dimethylurea)], mecoprop [(RS)-2......-(4-chloro-2-methyl phenoxy)propionic acid], 2,4-D (2,4-dichlorophenoxyacetic acid), and bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide]. Specific surface area and mineral surface charge proved to be important for the adsorption of these pesticides. Detectable adsorption...

  12. Copper incorporation in foraminiferal calcite: results from culturing experiments

    NARCIS (Netherlands)

    Nooijer, L.J. de; Reichart, G.-J.; Dueñas Bohórquez, A.D.B.; Wolthers, M.; Ernst, S.R.; Mason, P.R.D.; Zwaan, G.J. van der

    2007-01-01

    A partition coefficient for copper (DCu) in foraminiferal calcite has been determined by culturing individuals of two benthic species under controlled laboratory conditions. The partition coefficient of a trace element (TE) is an emperically determined relation between the TE/Ca ratio in seawater

  13. An explanation for the 18O excess in Noelaerhabdaceae coccolith calcite

    Science.gov (United States)

    Hermoso, M.; Minoletti, F.; Aloisi, G.; Bonifacie, M.; McClelland, H. L. O.; Labourdette, N.; Renforth, P.; Chaduteau, C.; Rickaby, R. E. M.

    2016-09-01

    Coccoliths have dominated the sedimentary archive in the pelagic environment since the Jurassic. The biominerals produced by the coccolithophores are ideally placed to infer sea surface temperatures from their oxygen isotopic composition, as calcification in this photosynthetic algal group only occurs in the sunlit surface waters. In the present study, we dissect the isotopic mechanisms contributing to the ;vital effect;, which overprints the oceanic temperatures recorded in coccolith calcite. Applying the passive diffusion model of carbon acquisition by the marine phytoplankton widely used in biogeochemical and palaeoceanographic studies, our results suggest that the oxygen isotope offsets from inorganic calcite in fast dividing species Emiliania huxleyi and Gephyrocapsa oceanica originates from the legacy of assimilated 18O-rich CO2 that induces transient isotopic disequilibrium to the internal dissolved inorganic carbon (DIC) pool. The extent to which this intracellular isotopic disequilibrium is recorded in coccolith calcite (1.5 to +3‰ over a 10 to 25 °C temperature range) is set by the degree of isotopic re-equilibration between CO2 and water molecules before intracellular mineralisation. We show that the extent of re-equilibration is, in turn, set by temperature through both physiological (dynamics of the utilisation of the DIC pool) and thermodynamic (completeness of the re-equilibration of the relative 18O-rich CO2 influx) processes. At the highest temperature, less ambient aqueous CO2 is present for algal growth, and the consequence of carbon limitation is exacerbation of the oxygen isotope vital effect, obliterating the temperature signal. This culture dataset further demonstrates that the vital effect is variable for a given species/morphotype, and depends on the intricate relationship between the environment and the physiology of biomineralising algae.

  14. NMR spectroscopic study of organic phosphate esters coprecipitated with calcite

    Science.gov (United States)

    Phillips, Brian L.; Zhang, Zelong; Kubista, Laura; Frisia, Silvia; Borsato, Andrea

    2016-06-01

    Organic phosphorus incorporated in calcite during laboratory precipitation experiments and in natural cave deposits was investigated by solid-state NMR spectroscopy. For calcite precipitated in the presence of organic phosphoesters of varying size and functionality, solid-state 31P{1H} CP/MAS NMR shows that the phosphoesters were incorporated intact into the solid. Systematic changes in the 31P NMR chemical shift of the phosphate group were observed between the solid phosphoester and that incorporated in the solid precipitate, yielding 31P NMR chemical shifts of the coprecipitates in the range of +1.8 to -2.2 ppm. These chemical shifts are distinct from that of similarly prepared calcite coprecipitated with inorganic phosphate, 3.5 ppm. Only minor changes were noted in the phosphoester 31P chemical shift anisotropy (CSA) which suggests no significant change in the local structure of the phosphate group, which is dominated by C-O-P bonding. Close spatial proximity of the organic phosphate group to calcite structural components was revealed by 31P/13C rotational echo double resonance (REDOR) experiments for coprecipitates prepared with 13C-labeled carbonate. All coprecipitates showed significant 31P dephasing effects upon 13C-irradiation, signaling atomic-scale proximity to carbonate carbon. The dephasing rate for smaller organophosphate molecules is similar to that observed for inorganic phosphate, whereas much slower dephasing was observed for larger molecules having long and/or bulky side-chains. This result suggests that small organic molecules can be tightly enclosed within the calcite structure, whereas significant structural disruption required to accommodate the larger organic molecules leads to longer phosphate-carbonate distances. Comparison of 31P NMR spectroscopic data from the synthetic coprecipitates with those from calcite moonmilk speleothems indicates that phosphorus occurs mainly as inorganic orthophosphate in the natural deposits, although small

  15. Temperature limits for preservation of primary calcite clumped isotope paleotemperatures

    Science.gov (United States)

    Henkes, Gregory A.; Passey, Benjamin H.; Grossman, Ethan L.; Shenton, Brock J.; Pérez-Huerta, Alberto; Yancey, Thomas E.

    2014-08-01

    Solid-state reordering of C-O bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations, metrics commonly used to gauge preservation quality. To correctly interpret the paleoenvironmental significance of clumped isotope-derived paleotemperatures, it is necessary to understand the temperature-time domain in which solid-state C-O bond reordering is important. We address this question using a combination of laboratory and natural geological experiments on Paleozoic brachiopod shells. The laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13C-18O bond reordering. The resulting Arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions. We develop an alternative kinetic model for reordering that accounts for non-first-order reaction progress observed during the initial several hundred minutes of laboratory heating experiments, and show that the simplified first-order approximation model (Passey and Henkes, 2012) predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins. We evaluate our laboratory-based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories. Specifically, we use the laboratory-derived Arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million-year time steps reflecting the burial and exhumation temperature paths of each basin. While this exercise is limited by the relatively large uncertainties in the temperature histories of these basins, we find general correspondence, within error, between predicted and observed clumped isotope values

  16. Uranium Isotope Fractionation During Coprecipitation with Aragonite and Calcite

    Science.gov (United States)

    Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Wasylenki, L. E.; Anbar, A. D.

    2014-12-01

    Natural variations in the 238U/235U ratio of marine carbonates may provide a useful way of constraining past variations in ocean redox conditions. However, before applying this novel redox proxy, it is essential to explore possible isotopic fractionation during U coprecipitation with aragonite and calcite. We investigated these effects in laboratory experiments. Aragonite and calcite coprecipitation experiments were conducted at pH 8.5±0.1 using a constant addition method [1]. More than 90% of the U was incorporated into the solid phase at the end of each experiment. Samples were purified using UTEVA chemistry and δ238/235U was measured using 233U-236U double-spike MC-ICP-MS with a precision of ±0.10‰ [2]. The aragonite experiment demonstrated a 238U/235U Rayleigh fractionation factor of α=1.00008±0.00002 with the 238U preferentially incorporated. In contrast, the calcite experiment demonstrated no resolvable U isotope fractionation (α=1.00001±0.00003). To determine if U isotopes are affected during the early diagenetic conversion of aragonite to calcite, natural carbonate samples were collected along an aragonite-calcite transition across a single coral head in the Key Largo limestone, and characterized for U concentration and δ238/235U [3]. We found that the mean δ238/235U in aragonite (-0.33±0.07‰ 2se) was slightly heavier than that in calcite (-0.37±0.02‰ 2se). Further work is needed to address the mechanisms leading to differential isotopic fractionation of U(VI) during incorporation into aragonite and calcite. Possible drivers include differences in coordination in the crystal structure or equilibrium isotopic fractionation between various aqueous U(VI) species prior to incorporation. [1] Reeder et al. (2001) GCA 65, 3491-3503. [2] Weyer et al., (2008) GCA 72, 345-359. [3] Gill et al., (2008) GCA 72, 4699-4722.

  17. A quantitative analysis of microbially-induced calcite precipitation employing artificial and naturally-occurring sediments

    Science.gov (United States)

    Lokier, Stephen; Krieg Dosier, Ginger

    2013-04-01

    Microbially-induced calcite precipitation is a strong candidate for the production of sustainable construction materials. The process employs the microbe Sporosarcina pasteurii as an agent to microbially mediate the precipitation of calcium carbonate to bind unconsolidated sediment. As this process can be achieved under ambient temperature conditions and can utilise a wide variety of easily-available sediments, potentially including waste materials, it is envisioned that this procedure could significantly reduce carbon-dioxide emissions in the construction industry. This study describes and quantifies the precipitation of calcite cement in a range of naturally-occurring sediments compared with a control matrix. The study establishes the optimum treatment time for effective cement precipitation in order to produce a material that meets the standards required for construction whilst keeping economic and environmental outlays at a minimum. The 'control sediment' employed industrial-grade glass beads with a grain size range of 595-1180 microns (16-30 US mesh). Sporosarcina pasteurii were mixed in a solution of urea and calcium chloride and then inoculated into the control sediment. The microbes attach to the surface of the sediment grains and employ urea as a source of energy to produce ammonia and carbon dioxide. By so doing, they increase the pH of the solution allowing calcium carbonate to precipitate at the cell walls to act as nucleation points facilitating the precipitation of cements as a grain-coating and biocementing the unconsolidated sediment. The solution treatment was repeated at eight hour intervals with samples removed for detailed analysis after each every five consecutive treatments (i.e. 40 hours). The process was repeated to produce 20 samples with treatment times between 40 and 800 hours. Cemented samples were impregnated with blue epoxy and examined petrographically to monitor cement development. Modal analysis was undertaken on each cemented

  18. The spectral nature of various Titan surface units: implications on the composition

    Science.gov (United States)

    Solomonidou, A.

    2017-09-01

    We investigate both the surface and the atmospheric contributions on Titan from Visual and Infrared Mapping Spectrometer (VIMS) spectro-imaging near-infrared data by use of a radiative transfer code [1-3]. We focus here on the geological and albedo major units identified in [4-7]: mountains, plains, labyrinths, maculae, impact craters, dune fields, alluvial fans, and possible cryovolcanic and/or evaporite features. We find that, for some of the regions classified as the same geomorphological unit in SAR, there are significantly differences in spectral responses (albedo) from VIMS, depending on location. Conversely, some regions classified from SAR as different geomorphological units show very similar spectral responses in VIMS. The surface albedo differences and similarities among the various units constrain the implications for the geological processes that govern Titan's surface (i.e. aeolian, fluvial, sedimentary, lacustrine etc). Hence, we are able to report the differences and similarities among the various regions, monitor their temporal evolution, and provide implications on their chemical composition, which lead us to constrain specific processes of origin.

  19. Modeling Np and Pu transport with a surface complexation model and spatially variant sorption capacities: Implications for reactive transport modeling and performance assessments of nuclear waste disposal sites

    Science.gov (United States)

    Glynn, P.D.

    2003-01-01

    One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciation and sorption reactions on the ground-water transport of Np and Pu, two redox-sensitive elements. Earlier 1D simulations (Reardon, 1981) considered the kinetically limited dissolution of calcite and its effect on ion-exchange reactions (involving 90Sr, Ca, Na, Mg and K), and documented the spatial variation of a 90Sr partition coefficient under both transient and steady-state chemical conditions. In contrast, the simulations presented here assume local equilibrium for all reactions, and consider sorption on constant potential, rather than constant charge, surfaces. Reardon's (1981) seminal findings on the spatial and temporal variability of partitioning (of 90Sr) are reexamined and found partially caused by his assumption of a kinetically limited reaction. In the present work, sorption is assumed the predominant retardation process controlling Pu and Np transport, and is simulated using a diffuse-double-layer-surface-complexation (DDLSC) model. Transport simulations consider the infiltration of Np- and Pu-contaminated waters into an initially uncontaminated environment, followed by the cleanup of the resultant contamination with uncontaminated water. Simulations are conducted using different spatial distributions of sorption capacities (with the same total potential sorption capacity, but with different variances and spatial correlation structures). Results obtained differ markedly from those that would be obtained in transport simulations using constant Kd, Langmuir or Freundlich sorption models. When possible, simulation results (breakthrough curves) are fitted to a constant K d advection-dispersion transport model and compared. Functional differences often are great enough that they prevent a meaningful fit of the simulation results with a constant K d (or even a Langmuir or Freundlich) model, even in the case of Np, a weakly sorbed radionuclide under the

  20. An escort for GPCRs: implications for regulation of receptor density at the cell surface.

    Science.gov (United States)

    Achour, Lamia; Labbé-Jullié, Catherine; Scott, Mark G H; Marullo, Stefano

    2008-10-01

    G-protein-coupled receptors (GPCRs) are dynamically regulated by various mechanisms that tune their response to external stimuli. Modulation of their plasma membrane density, via trafficking between subcellular compartments, constitutes an important process in this context. Substantial information has been accumulated on cellular pathways that remove GPCRs from the cell surface for subsequent degradation or recycling. In comparison, much less is known about the mechanisms controlling trafficking of neo-synthesized GPCRs from intracellular compartments to the cell surface. Although GPCR export to the plasma membrane is commonly considered to mostly implicate the default, unregulated secretory pathway, an increasing number of observations indicate that trafficking to the plasma membrane from the endoplasmic reticulum might be tightly regulated and involve specific protein partners. Moreover, a new paradigm is emerging in some cellular contexts, in which stocks of functional receptors retained within intracellular compartments can be rapidly mobilized to the plasma membrane to maintain sustained physiological responsiveness.

  1. Testing Novel pH Proxies through Inorganic Calcite Precipitations and K/Pg Foraminifera

    Science.gov (United States)

    Super, J. R.; Pagani, M.; Wang, Z.

    2013-12-01

    Ocean pH proxies help constrain the carbon system in the paleocean and can be used to infer atmospheric CO2 when coupled with estimates of total alkalinity, aqueous pCO2 or dissolved inorganic carbon. This project investigates two novel pH proxies (cerium abundance and kinetically-controlled oxygen isotopes) through a series of precipitations of inorganic calcite, as well as the previously established boron isotope pH proxy. Precipitations are performed using varied pH and carbonate saturation states that span the range of typical ocean values as well as a 'free drift' that allows pH and saturation state to vary. The light rare earth element cerium speciates, depending on local oxidation-reduction conditions, between the soluble Ce3+ and highly insoluble Ce4+ ions, causing a relative depletion of cerium in ocean water. This project demonstrates how a suite rare earth elements, including cerium, partitions into inorganic calcite and how partitioning varies with changing pH and carbonate saturation state. Oxygen isotope fractionation is primarily controlled by temperature, but this project examines how pH and carbonate saturation state correlate with oxygen isotope values under kinetic conditions during the initial stage of precipitation. The effect of diagenesis on each proxy is simulated by dissolution of precipitated calcite in a pressure vessel. Results from the precipitations are used to inform a record of well-preserved benthic and planktonic foraminifera from DSDP Site 356 that range in age from the K/Pg boundary to the period when the δ13C gradient between the surface and deep ocean returned to pre-event levels. The pH record is used to infer the magnitude and length of the perturbation to the oceanic carbon system following the extinction event, particularly in terms of export productivity.

  2. Calcite/opal deposits at Yucca Mountain, Nevada: Pedogenic or hypogene?

    Energy Technology Data Exchange (ETDEWEB)

    Hill, C.A.; Schluter, C.M.; Harmon, R.S. [and others

    1994-01-01

    This study is part of the research program of the Yucca Mountain Project intended to provide the State of Nevada with a detailed assessment of the geology and geochemistry of Yucca Mountain and adjacent regions. The purpose of this paper is to consider all of the geological and geochemical data available for the calcite/opal deposits at Yucca Mountain and to ascertain whether this data favors a pedogenic or hyogene origin for these deposits. Far from being of esoteric concern, this subject is of paramount importance to the debate which rages around the suitability of Yucca Mountain as a high-level radioactive waste repository site. It is also the purpose of this paper to serve as a foundation for a lengthy feature article to be submitted for publication in 1994. In addition, a stand has been taken by the National Research Council of the National Academy of Sciences against the upwelling-water model (a vote of 17 to 0 against), and this same panel report has concluded that {open_quotes}there is no compelling evidence for the repetitive flooding of the environment by expulsion of groundwater{close_quotes} and that {open_quotes}instead, the evidence strongly supports the idea that the near-surface mineral deposits resulted from percolating rainwater, which carried soil minerals down into rock fractures{close_quotes}. Based on such information the Department of Energy has stated that it {open_quotes}finds no basis to continue to study the origin of these specific deposits{close_quotes}. This study, based upon many different independent lines of evidence, reaches the opposite conclusion and instead favors a hypogene spring-travertine origin for the controversial calcite/opal deposits at Yucca Mountain. This study recognizes a pedogenic carbonate component at Yucca Mountain, but argues that this component is distinct from, and sometimes intermixed with, the calcite/opal deposits.

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

    Science.gov (United States)

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

    2016-04-01

    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

  4. Adsorption of sulfide ions on cerussite surfaces and implications for flotation

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Qicheng [State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093 (China); Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Wen, Shuming, E-mail: fqckmust@126.com [State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093 (China); Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Zhao, Wenjuan [Kunming Metallurgical Research Institute, Kunming 650031 (China); Deng, Jiushuai; Xian, Yongjun [State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093 (China); Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

    2016-01-01

    Highlights: • A new discussion on the lead sulfide species is introduced. • The Na{sub 2}S concentration determines cerussite sulfidization. • The activity of lead sulfide species also determines cerussite sulfidization. • Disulfide and polysulfide in lead sulfide species affect its activity. - Abstract: The adsorption of sulfide ions on cerussite surfaces and implications for flotation were studied by X-ray photoelectron spectroscopy (XPS) analysis, micro-flotation tests, and surface adsorption experiments. The XPS analysis results indicated that lead sulfide species formed on the mineral surface after treatment by Na{sub 2}S, and the increase in the Na{sub 2}S concentration was beneficial for sulfidization. In addition to the content of lead sulfide species, its activity, which was determined by the proportion of sulfide, disulfide and polysulfide, also played an important role in cerussite sulfidization. Micro-flotation tests results demonstrated that insufficient or excessive addition of Na{sub 2}S in pulp solutions has detrimental effects on flotation performance, which was attributed to the dosage of Na{sub 2}S and the activity of lead sulfide species formed on the mineral surface. Surface adsorption experiments of sulfide ions determined the residual S concentrations in pulp solutions and provided a quantitative illustration for the inhibition of cerussite flotation by excessive sulfide ions. Moreover, it also revealed that sulfide ions in the pulp solution were transformed onto the mineral surface and formed lead sulfide species. These results showed that both of lead sulfide species and its activity acted as an important role in sulfidization flotation process of cerussite.

  5. Copper incorporation in foraminiferal calcite: results from culturing experiments

    Directory of Open Access Journals (Sweden)

    G. J. van der Zwaan

    2007-07-01

    Full Text Available A partition coefficient for copper (DCu in foraminiferal calcite has been determined by culturing individuals of two benthic species under controlled laboratory conditions. The partition coefficient of a trace element (TE is an emperically determined relation between the TE/Ca ratio in seawater and the TE/Ca ratio in foraminiferal calcite and has been established for many divalent cations. Despite its potential to act as a tracer of human-induced, heavy metal pollution, data is not yet available for copper. Since partition coefficients are usually a function of multiple factors (seawater temperature, pH, salinity, metabolic activity of the organism, etc., we chose to analyze calcite from specimens cultured under controlled laboratory conditions. They were subjected to different concentrations of Cu2+ (0.1–20 µmol/l and constant temperature (10 and 20°C, seawater salinity and pH. We monitored the growth of new calcite in specimens of the temperate, shallow-water foraminifer Ammonia tepida and in the tropical, symbiont-bearing Heterostegina depressa. Newly formed chambers were analyzed for Cu/Ca ratios by laser ablation-ICP-MS. The estimated partition coefficient (0.1–0.4 was constant to within experimental error over a large range of (Cu/Caseawater ratios and was remarkably similar for both species. Neither did the presence or absence of symbionts affect the DCu, nor did we find a significant effect of temperature or salinity on Cu-uptake.

  6. Controls on the precipitation of barite (BaSO 4) crystals in calcite travertine at Twitya Spring, a warm sulphur spring in Canada's Northwest Territories

    Science.gov (United States)

    Bonny, Sandy M.; Jones, Brian

    2008-01-01

    Twitya Spring discharges warm (24 °C), anoxic, sulphide-, calcium- (65 ppm) and barium- (≥ 0.78 ppm) rich spring water to a steep flow path that is inhabited by streamer and mat-forming microbes ( Thiothrix, Beggiatoa, Oscillatoria, Spirulina, diatoms, rod shaped bacteria). Oxidation and CO 2 degassing drive precipitation of elemental sulphur, barite, opaline silica, and calcite. A mound of travertine at the base of the flow path, dominantly composed of bedded barium-enriched crystallographic and noncrystallographic dendritic calcite crystals and calcite cements, hosts three types of barite crystals: type 1 (T1) intergrown tabular crystals that formed in solution, type 2 (T2) tabular and rhombic crystals that nucleated on calcite, and type 3 (T3) subhedral and anhedral microcrystals that nucleated on microbial cell surfaces and in microbial extracellular polymeric substances. The formation and distribution of T1, T2, and T3 barite in the Twitya Spring flow path are controlled by physiochemical gradients, calcite precipitation rates, and adsorption of barium to microbial biomass, all of which vary seasonally and episodically at Twitya Spring. The complex physiochemical and biological controls on barite formation at Twitya Spring both suggest that the classification of biogenic or inorganic sedimentary barite on the basis of crystal size and morphology may be oversimplified. There is also the potential that primary and authigenic barite crystals hosted in carbonates may yield information about the microbial ecology and ambient physiochemistry of their depositional environments.

  7. Rate of radiocarbon retention onto calcite by isotope exchange

    Energy Technology Data Exchange (ETDEWEB)

    Lempinen, Janne; Lehto, Jukka [Helsinki Univ. (Finland). Lab. of Radiochemistry

    2016-11-01

    Radiocarbon ({sup 14}C) is a top priority class radionuclide associated with the long-term safety of spent nuclear fuel disposal. Dissolved inorganic radiocarbon can be retained in bedrock via isotope exchange with calcite (CaCO{sub 3}) at solubility equilibrium with groundwater. In the present study, the rate of the isotope exchange process was investigated on synthetic calcite using batch experiments. Experiments were performed in solutions with a calcium concentration of 0.0002-0.1 M, including two synthetic reference groundwaters. The radiocarbon activity in the solutions decreased exponentially as a function of time, thus following first-order kinetics. The rate of isotope exchange was quantified from an exponential fit to the activity data over time. The rate of radiocarbon retention increased as a function of the calcium activity. The isotope exchange half-life was only 4.3 days at calcium ion activities over 0.01. This half-life is very much shorter than the half-life of {sup 14}C or the time scale of groundwater movements; consequently calcite can effectively retain radiocarbon from brackish and saline groundwaters.

  8. Beef and cone-in-cone calcite fibrous cements associated with the end-Permian and end-Triassic mass extinctions: Reassessment of processes of formation

    Directory of Open Access Journals (Sweden)

    Stephen Kershaw

    2016-01-01

    Based on the above evidence, our opinion is that B-CIC calcite is best explained as a later diagenetic feature unrelated to rapid Earth-surface environmental change associated with mass extinctions; thus a novel carbonate factory is highly unlikely.

  9. PVC mixtures’ mechanical properties with the addition of modified calcite as filler

    Directory of Open Access Journals (Sweden)

    Vučinić Dušica R.

    2012-01-01

    Full Text Available In this study mechanical properties of PVC mixtures (PVC, stabilizer, lubricant, filler such as tensile strength, tensile elongation, breaking strength, and breaking elongation were investigated. Unmodified calcite, as well as calcite modified by stearic acid, were used as fillers in wet and dry processes. The PVC mixtures containing the calcite modified by wet procedure have better mechanical properties compared to those with the calcite modified by the dry process. Tensile and breaking strength of the PVC mixture containing the calcite modified with 1.5% stearic acid using wet process, are higher for 2.8% and 5.2%, respectively, compared to the PVC mixture containing the calcite modified with the same amount of acid used in the dry process. The tensile strength difference between the mixtures increases with the increase of the concentration of used stearic acid up to 3%. The strength of PVC mixture with the calcite modified by wet process is 3.1% higher compared to the mixture containing calcite modified by dry process. The results showed that the bonding strength between calcite and the adsorbed organic component affected tensile strength, tensile elongation and breaking strength of the PVC mixtures. The best filler was obtained by wet modification using 1.5% stearic acid solution that provided the formation of a stearate monolayer chemisorbed on calcite. The PVC mixtures containing the calcite modified by wet process using 1.5% stearic acid solution exhibited the best mechanical properties. This calcite was completely hydrophobic with dominant chemically adsorbed surfactant, which means that stearate chemisorbed on calcite provided stronger interaction in the calcite-stearic acid-PVC system.

  10. Adhesion and friction force coupling of gecko setal arrays: implications for structured adhesive surfaces.

    Science.gov (United States)

    Zhao, Boxin; Pesika, Noshir; Rosenberg, Kenny; Tian, Yu; Zeng, Hongbo; McGuiggan, Patricia; Autumn, Kellar; Israelachvili, Jacob

    2008-02-19

    The extraordinary climbing ability of geckos is partially attributed to the fine structure of their toe pads, which contain arrays consisting of thousands of micrometer-sized stalks (setae) that are in turn terminated by millions of fingerlike pads (spatulae) having nanoscale dimensions. Using a surface forces apparatus (SFA), we have investigated the dynamic sliding characteristics of setal arrays subjected to various loading, unloading, and shearing conditions at different angles. Setal arrays were glued onto silica substrates and, once installed into the SFA, brought toward a polymeric substrate surface and then sheared. Lateral shearing of the arrays was initiated along both the "gripping" and "releasing" directions of the setae on the foot pads. We find that the anisotropic microstructure of the setal arrays gives rise to quite different adhesive and tribological properties when sliding along these two directions, depending also on the angle that the setae subtend with respect to the surface. Thus, dragging the setal arrays along the gripping direction leads to strong adhesion and friction forces (as required during contact and attachment), whereas when shearing along the releasing direction, both forces fall to almost zero (as desired during rapid detachment). The results and analysis provide new insights into the biomechanics of adhesion and friction forces in animals, the coupling between these two forces, and the specialized structures that allow them to optimize these forces along different directions during movement. Our results also have practical implications and criteria for designing reversible and responsive adhesives and articulated robotic mechanisms.

  11. Surface charges and interfaces: implications for mineral roles in prebiotic chemistry

    Directory of Open Access Journals (Sweden)

    MILA PONTES-BUARQUE

    2000-09-01

    Full Text Available There exists an extensive literature on the possible roles of minerals in the prebiotic stages of the chemical evolution of life (Bernal 1951, Cairns-Smith 1982, Wächtershäuser 1992, Vieyra et al. 1995, Tessis et al. 1999, see Lahav (1994 for a review. Among the original proposals, minerals have been considered in: (a processes that would discriminate molecular chirality; (b condensation reactions of biomolecular precursors; (c prebiotic catalysis; (d biochemical templates; and (e autocatalytic metabolism. In this communication it is emphazised the complex properties of both surface reactions and interfaces between minerals and aqueous solutions simulating Archean scenarios. The properties of pyrite surface net charge and of its interface with a solution simulating primitive seawater are discussed and their implications to the autocatalytic model (Wächtershäuser 1988a 1992 are presented in order to demonstrate their relevance. The proposed roles of iron-sulfide minerals (mainly pyrite as physical support for primitive bidimensional metabolism and chiral discriminator (Wächtershäuser 1988a, Huber & Wächtershäuser 1998 are revised. It is shown that: (a the net surface charge can be modulated by the pyrite-aqueous solution interface; (b mononucleotides attachment to pyrite require a cationic bridge; and (c direct absorption of acetate - a molecule proposed as carbon source in primitive aqueous environments - also modulates the interface properties and would have masked pyrite's bulk structure. These results indicate that physicochemical changes of mineral surfaces - caused by environments simulating Archean aqueous scenarios - should be taken into account in the proposals of mineral prebiotic roles.

  12. Incorporation of Mg and Sr in calcite of cultured benthic foraminifera: impact of calcium concentration and associated calcite saturation state

    Directory of Open Access Journals (Sweden)

    M. Raitzsch

    2010-03-01

    Full Text Available We investigated the effect of the calcium concentration in seawater and thereby the calcite saturation state (Ω on the magnesium and strontium incorporation into benthic foraminiferal calcite under laboratory conditions. For this purpose individuals of the shallow-water species Heterostegina depressa (precipitating high-Mg calcite, symbiont-bearing and Ammonia tepida (low-Mg calcite, symbiont-barren were cultured in media under a range of [Ca2+], but similar Mg/Ca ratios. Trace element/Ca ratios of newly formed calcite were analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS and normalized to the seawater elemental composition using the equation DTE=(TE/Cacalcite/(TE/Caseawater. The culturing study shows that DMg of A. tepida significantly decreases with increasing Ω at a gradient of −4.3×10−5 per Ω unit. The DSr value of A. tepida does not change with Ω, suggesting that fossil Sr/Ca in this species may be a potential tool to reconstruct past variations in seawater Sr/Ca. Conversely, DMg of H. depressa shows only a minor decrease with increasing Ω, while DSr increases considerably with Ω at a gradient of 0.009 per Ω unit. The different responses to seawater chemistry of the two species may be explained by a difference in the calcification pathway that is, at the same time, responsible for the variation in the total Mg incorporation between the two species. Since the Mg/Ca ratio in H. depressa is 50–100 times higher than that of A. tepida, it is suggested that the latter exhibits a mechanism that decreases the Mg/Ca ratio of the calcification fluid, while the high-Mg calcite forming species may not have this physiological tool. If the dependency of Mg incorporation on seawater [Ca2+] is also valid for deep

  13. Evolution of the isotope composition of C and O in the DIC in a water film during precipitation of calcite to the surface of a stalagmite in the presence of isotope exchange with the CO2 of the cave atmosphere and evaporation of the water

    Science.gov (United States)

    Dreybrodt, Wolfgang; Romanov, Douchko

    2016-04-01

    In a thin water layer, super saturated with respect to calcite with pH of about 8, where the aqueous CO2 is in equilibrium with the pCO2 of the cave atmosphere, the following processes determine the temporal evolution of the isotope composition of carbon and oxygen in the dissolved inorganic carbon ( DIC). a) Precipitation of calcite driven by super saturation, whereby deposition rates Between the heavy and light isotopes are slightly different. b) Evaporation of water reducing the depth of the water layer and changing the isotope composition of oxygen in the water by Rayleigh-distillation. c) Isotope exchange between the CO2 in the cave atmosphere and the DIC for both carbon and oxygen. d) Isotope exchange between the oxygen in the water molecules and that in the DIC. All these processes can be described by a differential equation, which can be solved numerically. For small times a simple solution can be given. Δ_DIC(T_drip) = [ ( (⪉mbda + ɛ) C_eq/C0 - ɛ ) T_drip/τ + (δ^atm_eq - δ0 ) T_drip/τ^atm + (δ^water_eq-δ_0-ɛ_wT_drip/T_ev) T_drip/τ^water] Δ_DIC(T_drip) is the change of the δ13C and δ18O (given here as small numbers and not in the ‰ notation) after the drip time T_drip. ⪉mbda, ɛ are kinetic parameters of precipitation on the order of 10-2 and τ is the time scale of precipitation, typically about 1000 s. (δ^atm_eq - δ_0) and (δ^water_eq - δ_0) are the differences between the corresponding initial δ-value and that when DIC is in isotope equilibrium with the atmosphere or in the case of oxygen with the water. τ^atm and τ^water, both on the order of 10,000 s, are the time scales of the exchange reactions to approach isotope equilibrium. For carbon the last term (exchange with water) must be deleted. C_eq is the concentration of DIC in chemical equilibrium with the CO2 in the cave atmosphere and C0 is the initial concentration, when the water drips to the stalagmite. T_ev is the time needed to fully evaporate the water layer and

  14. Effects of Citrate and Arginine on Sorption of Nickel to Yazd Sepiolite and Calcite

    Directory of Open Access Journals (Sweden)

    Ahmadreza Sheikhhosseini

    2017-03-01

    Full Text Available Introduction: Pollution of soil and water environment by release of heavy metals is of great concerns of the last decades. Sorption of heavy metals by low cost materials is considered as an inexpensive and efficient method used for removal of heavy metals from soil-water systems. The presence of different ligands with various complexing abilities can change the sorption properties of heavy metals and their fate in the environment as well. In order to assess the effect of citrate and arginine as natural organic ligands in soil environment, in a batch study we investigated the effects of these ligands on equilibrium sorption of nickel to sepiolite and calcite minerals and also kinetics of Ni sorption by these minerals. Materials and Methods: Minerals used in this study included sepiolite from Yazd (Iran and pure calcite (Analytical grade, Merck, Germany. Sepiolite was purified, saturated with Ca using 0.5 M CaCl2, powdered in a mortar and sieved by non-metal 230 mesh standard wire sieve. For equilibrium sorption study, in a 50-mL polyethylene centrifuge tube,0.3 g sample of each mineral was suspended in 30 mL of a 0.01 M CaCl2 solution containing 0, 5, 10, 20, 40, 60, 80 and 100 mg L-1 Ni (NiCl2 and containing zero (as control or 0.1mmol L-1 citrate or arginine ligands. The applied concentrationsfor each ligand can naturally occur in soils. Preparedtubes were shaken (180±2 rpm, 25±1oC for 24 h using an orbital shaker and centrifuged (4000×g for 10 min and the supernatants were analyzed for Ni concentration using an atomic absorption spectrophotometer (AAnalyst 200 Perkin-Elmer at a wavelength of 232 nm and a detection limit of 0.05 mg L-1. The quantity of Ni retained by each mineral at equilibrium was calculated using equation qe = (Ci - CeV/W where qe was the amount of nickel retained by mineral surface at equilibrium. Ci and Ce were the initial and the equilibrium concentrations (mg L-1 of Ni, respectively, V was the volume (L of the solution

  15. Utilization of calcite produced in Turkey for paper coating

    Directory of Open Access Journals (Sweden)

    Hüdaverdi Eroğlu

    2002-03-01

    Full Text Available Calcium carbonate is one of the coating pigments widely used in paper industry. Especially, in recent years calcium carbonate filler has gained high importance in alkaline pulping. In Turkey industry actually imports calcium carbonate; whereas, there are rich calcite reservoirs in the country. In this study two different types of domestic ground (GCC calcite samples were used. Physical and chemical properties of calcite samples were tested firstly. CaCO3 percentages of both samples were 97.3 % and 97.6 % (min. 95 % CaCO3. MgCO3 and Fe2O3 percentages were within the desired limits. Brightness values were 95.5 % and 94.5 % and yellowness 1.1 % and 1.5 % elrepho. These values also were within the requested limits. Under 2 microns particle size and over 10 microns particle size fractions were 95 % and 89 % (min. 80 and 1 % and 2 % (max. 2 respectively. Dry matter rates were between 40 %-65 %, for the pilot plant-coating machine. During the preparation of coating color calcium carbonate has been used together with kaolin. The ratios of calcium carbonate to kaolin were 30/70, 40/60, 50/50, 60/40, 70/30, 100/0. In coating color preparation latex was used as a binder because of its wide applications. Latex percentages were 11, 12, and 13 %. Coated papers were glossed and physically tested. As a result, both calcium carbonate samples were found suitable for using in coating color preparation. By the utilization of domestic calcium carbonate in coated paper production, there will be foreign currencies saving.

  16. The sensitized luminescence of manganese-activated calcite

    Science.gov (United States)

    Schulman, J.H.; Evans, L.W.; Ginther, R.J.; Murata, K.J.

    1947-01-01

    Synthetic manganese-activated calcites are shown to be practically inert to ultraviolet excitation in the range 2000-3500A, while they are luminescent under cathode-ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural calcites is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave-length ultraviolet-excited luminescence of all natural calcites to the action of an auxiliary impurity. The essential identity of the cathode-ray excited luminescence spectra of CaCO 3:Mn, CaCO3: (Pb+Mn), CaCO3:(Tl+Mn), and CaCO3:(Ce+Mn) with the 2537A-excited spectra of the latter three is evidence that the luminescent center in all cases is the manganese ion or the MnO6 group. It is shown that a "cascade" mechanism for the action of the auxiliary impurities, lead, thallium, and cerium, is incorrect; and that the phenomenon must be considered as a case of sensitized luminescence. Owing to the nature of cathode-ray excitation, the manganese activator can be excited by this agent even in the absence of a second impurity. For optical excitation, however, an absorption band for the ultraviolet must be established by building into the CaCO3:Mn a second impurity or "sensitizer.".

  17. Principles of calcite dissolution in human and artificial otoconia.

    Directory of Open Access Journals (Sweden)

    Leif Erik Walther

    Full Text Available Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV. The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic otoconia (calcite gelatin nanocomposits and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM. Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV.

  18. Calcite production by coccolithophores in the south east Pacific Ocean

    Directory of Open Access Journals (Sweden)

    L. Beaufort

    2008-08-01

    Full Text Available BIOSOPE cruise covered an oceanographic transect through the centre of the South Pacific Gyre (SPG from the Marquesas archipelago to the Peru-Chile upwelling (PCU. Water samples from 6 depths in the euphotic zone were collected at 20 stations. The concentrations of suspended calcite particles, coccolithophores cells and detached coccoliths were estimated together with size and weight using an automatic polarizing microscope, a digital camera, and a collection of softwares performing morphometry and pattern recognition. Some of these softwares are new and described here for the first time. The coccolithophores standing stocks were usually low and reached maxima west of the PCU. The coccoliths of Emiliania huxleyi, Gephyrocapsa spp. and Crenalithus spp. (Order Isochrysidales represented more than 30% of all the suspended calcite particles detected in the size range 0.1–46 μm (22% of PIC in term of calcite weight. These species grew preferentially in the Chlorophyll maximum zone. In the SPG their maximum cell concentrations were recorded between depth of 150 and 200 m, which is unusually deep for these taxa. The weight of coccoliths and coccospheres were correlated to their size. Large and heavy coccoliths and coccospheres were found in regions with relatively high fertility in the Marquises Island and in the PCU. Small and light coccoliths and coccospheres were found west of the PCU. This distribution is strongly related to ocean chemistry in particular to alkalinity and to carbonate ions concentration. The biotic (coccolithophores production influence on calcification is mainly driven at the local scale (depth whereas the abiotic (carbonate chemistry plays its most important role at the regional (horizontal level. Here 94% of the variability of coccolith and coccosphere weight can be explained by a change in 7 environmental variables.

  19. Tectonically driven organic fluid migration in the Dabashan Foreland Belt: Evidenced by geochemistry and geothermometry of vein-filling fibrous calcite with organic inclusions

    Science.gov (United States)

    Li, Rongxi; Dong, Shuwen; Lehrmann, Dan; Duan, Lizhi

    2013-10-01

    Fibrous calcite veins with organic inclusions have been widely considered as indicators of oil and gas generation and migration under overpressure. Abundant fibrous calcite veins containing organic-bearing inclusions occur in faulted Lower Paleozoic through Triassic hydrocarbon source rocks in the Dabashan Foreland Belt (DBF). δ13CPDB and δ18OPDB values of the fibrous calcite range from -4.8‰ to -1.9‰ and -12.8‰ to -8.4‰ respectively, which is lighter than that of associated carbonate host rocks ranging from -1.7‰ to +3.1‰ and -8.7‰ to -4.5‰. A linear relationship between δ13CPDB and δ18OPDB indicates that the calcite veins were precipitated from a mixture of basinal and surface fluids. The fibrous calcite contains a variety of inclusions, such as solid bitumen, methane-bearing all-liquid inclusions, and vapor-liquid aqueous inclusions. Homogenization temperatures of aqueous inclusions range from 140 to 196 °C with an average of 179 °C. Salinities of aqueous inclusions average 9.7 wt% NaCl. Independent temperatures from bitumen reflectance and inclusion phase relationships of aqueous and methane-bearing inclusions were used to determine fluid pressures. Results indicate high pressures, elevated above typical lithostatic confining pressure, from 150 to 200 MPa. The elevated salinity and high temperature and pressure conditions of the fibrous calcite veins argue against an origin solely from burial overpressure resulting from clay transformation and dehydration reactions. Instead fluid inclusion P-T data and geochemistry results and regional geology indicate abnormally high pressures during fluid migration. These findings indicate that tectonic stress generated fracture and fault fluid pathways and caused migration of organic-bearing fluids from the DBF during the Yanshan orogeny.

  20. Incorporation of Eu(III) into calcite under recrystallization conditions

    Energy Technology Data Exchange (ETDEWEB)

    Hellebrandt, S.E. [Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden (Germany). Inst. of Resource Ecology; Jordan, Norbert [Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden (Germany). Surface Processes; Barkleit, Astrid [Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden (Germany). Chemistry of the F-Elements; Schmidt, Moritz [Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden (Germany). HGF Young Investigator Group; Hofmann, S.

    2017-06-01

    The interaction of three calcite powders with Eu(III) under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). Batch contact studies with reaction times from 1 week up to 3 years revealed that the speciation differs from that observed previously in co-precipitation experiments and is dominated by a newly identified species ''γ''. The speed of formation of this species was found to depend greatly on the recrystallization rate of the studied minerals.

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

    Science.gov (United States)

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

    2014-09-01

    Thoracosphaera heimii exhibits different behaviour for both isotopic systems, in particular with respect to its very negative carbon isotope composition, owing to coeval intra and extracellular biomineralisation in this group. In this study, we also investigate the sensitivity of 18O/16O fractionation to varying ambient oxygen isotope composition of the medium for inorganic, coccolithophore, and dinoflagellate calcite precipitated under controlled laboratory conditions. The varying responses of different taxa to increased oxygen isotope composition of the growth medium may point to a potential bias in sea surface temperature reconstructions that are based on the oxygen isotopic compositions of sedimentary calcite, especially during times of changing seawater oxygen isotopic composition. Overall, this study represents an important step towards establishing a mechanistic understanding of the ;vital effect; in coccolith and dinoflagellate calcite, and provides valuable information for interpreting the geochemistry of the calcareous nannofossils in the sedimentary record, at both monospecific and interspecies levels.

  2. Calcite Precipitation at an Arctic Geothermal Spring Leads to Endolith Colonization and Ecological Succession

    Science.gov (United States)

    Starke, V.; Fogel, M. L.; Steele, A.

    2012-12-01

    increase with decreasing temperature across the aquatic samples, and all decrease with decreasing water content across the terrestrial samples. We attribute the trends in evenness to the balance of competition, with evenness limited in the most calcite-free environments by competition with photosynthetic eukaryotes, and in the driest endolith by competition for water and possibly nutrients. We suggest that the trends in richness result from the availability of physical niches, with availability first increasing as calcite grain surfaces become available for colonization, and later decreasing as pore volume becomes scares and potentially limiting. We suggest that microbial community structure at Troll can be understood as a consequence of ecological succession. It begins at the spring source with a few dominant phylotypes, progressing as conditions change into a more stable and even community. The succession is characterized by gradual changes in environmental parameters that produce a sequence of small, incremental and cumulative environmental disturbances. Disturbances change resource availability, and alter diversity by affecting growth, reproduction and competition, leading to successional transitions.

  3. Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve

    OpenAIRE

    Lorrain, Anne; Gillikin, David Paul; Paulet, Yves-Marie; Chauvaud, L.; Le Mercier, Alain; Navez, Jacques; André, Luc

    2005-01-01

    International audience; Although Sr/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report Sr/Ca ratios together with daily growth rates in the calcitic shells of 4 individuals of the bivalve Pecten maximus (age class I). Ratios of Sr/Ca were found to be variable among individuals that grew at the same location, illustrating that vital effects dominate over environmental ...

  4. Seasonal and Interannual Variability of Calcite in the Sub-Polar North Atlantic

    Science.gov (United States)

    Signorini, S. R.; McClain, C. R.

    2008-12-01

    Coccolithophores, among which Emiliania huxleyi (E. huxleyi) is the most abundant and widespread species, are considered to be the most productive calcifying organisms on Earth. They inhabit the surface layer (MLD ~20m) in highly stratified waters where light intensity is high. E. huxleyi often forms massive blooms in temperate and sub-polar oceans. Coupling of the coccolithophore organic carbon and carbonate pumps interact to consume (photosynthesis) and produce (calcification) CO2. The so-called Rain Ratio, defined as the ratio of particulate inorganic carbon (PIC) to particulate organic carbon (POC) in exported biogenic matter, determines the relative strength of the two biological carbon pumps and influences the flux of CO2 across the surface ocean - atmosphere interface. Here we use a combination of satellite ocean color algorithms and numerical model products to describe the seasonal and interannual variability of PIC in the sub-polar North Atlantic. Phytoplankton and calcite production have strong spatial variability. Nutrient supply, biomass and calcite concentrations are modulated by light and MLD seasonal cycle. The size, intensity, and location of coccolithophore blooms vary from year to year, but the peak bloom is always in June in the Central Basin (45°W - 10°W, 50°N - 65°N) and August in the Barents Sea. Calcification rates range from 5% to 27% of net primary production. The Barents Sea PIC production is about twice that of the Central Basin. Predicted freshening and warming of polar seas may increase stratification, thus favoring an increase in coccolithophore bloom development. However, although significant interannual changes were identified, there were no obvious trends in the satellite-derived PIC concentrations over the past 10 years.

  5. Prediction of calcite Cement Distribution in Shallow Marine Sandstone Reservoirs using Seismic Data

    Energy Technology Data Exchange (ETDEWEB)

    Bakke, N.E.

    1996-12-31

    This doctoral thesis investigates how calcite cemented layers can be detected by reflection seismic data and how seismic data combined with other methods can be used to predict lateral variation in calcite cementation in shallow marine sandstone reservoirs. Focus is on the geophysical aspects. Sequence stratigraphy and stochastic modelling aspects are only covered superficially. Possible sources of calcite in shallow marine sandstone are grouped into internal and external sources depending on their location relative to the presently cemented rock. Well data and seismic data from the Troll Field in the Norwegian North Sea have been analysed. Tuning amplitudes from stacks of thin calcite cemented layers are analysed. Tuning effects are constructive or destructive interference of pulses resulting from two or more closely spaced reflectors. The zero-offset tuning amplitude is shown to depend on calcite content in the stack and vertical stack size. The relationship is found by regression analysis based on extensive seismic modelling. The results are used to predict calcite distribution in a synthetic and a real data example. It is found that describing calcite cemented beds in shallow marine sandstone reservoirs is not a deterministic problem. Hence seismic inversion and sequence stratigraphy interpretation of well data have been combined in a probabilistic approach to produce models of calcite cemented barriers constrained by a maximum amount of information. It is concluded that seismic data can provide valuable information on distribution of calcite cemented beds in reservoirs where the background sandstones are relatively homogeneous. 63 refs., 78 figs., 10 tabs.

  6. Alternative origins for nannobacteria-like objects in calcite

    Science.gov (United States)

    Kirkland, Brenda L.; Lynch, F. Leo; Rahnis, Michael A.; Folk, Robert L.; Molineux, Ian J.; McLean, Robert J. C.

    1999-04-01

    More than 40 calcite-precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical-, rod-, and ovoid-shaped objects that have been widely interpreted as evidence of nanometer-scale life (i.e., nannobacteria). Individual experiments included the addition of soluble organic compounds, common species of eubacteria, or phage-induced eubacterial lysates. These experiments indicate that many of the nanometer-scale objects have inorganic or nonnannobacterial origins. In the precipitation experiments, calcite formed euhedral crystals 50 800 nm in diameter and smaller (Bacterial fragments occur as rounded to irregularly shaped particles that included cell-wall fragments, expulsed cytoplasm, and relict capsules that also closely resembled nannobacteria. Acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer-scale features that resembled nannobacteria in natural carbonates. The shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching. Much caution is advisable in interpreting the origin of rounded features <50 nm.

  7. Angle-dependent rotation of calcite in elliptically polarized light

    Science.gov (United States)

    Herne, Catherine M.; Cartwright, Natalie A.; Cattani, Matthew T.; Tracy, Lucas A.

    2017-08-01

    Calcite crystals trapped in an elliptically polarized laser field exhibit intriguing rotational motion. In this paper, we show measurements of the angle-dependent motion, and discuss how the motion of birefringent calcite can be used to develop a reliable and efficient process for determining the polarization ellipticity and orientation of a laser mode. The crystals experience torque in two ways: from the transfer of spin angular momentum (SAM) from the circular polarization component of the light, and from a torque due to the linear polarization component of the light that acts to align the optic axis of the crystal with the polarization axis of the light. These torques alternatingly compete with and amplify each other, creating an oscillating rotational crystal velocity. We model the behavior as a rigid body in an angle-dependent torque. We experimentally demonstrate the dependence of the rotational velocity on the angular orientation of the crystal by placing the crystals in a sample solution in our trapping region, and observing their behavior under different polarization modes. Measurements are made by acquiring information simultaneously from a quadrant photodiode collecting the driving light after it passes through the sample region, and by imaging the crystal motion onto a camera. We finish by illustrating how to use this model to predict the ellipticity of a laser mode from rotational motion of birefringent crystals.

  8. The effects of steam on the surface properties of palygorskite: Implications for palygorskite-water interactions

    Science.gov (United States)

    Kadakia, Abhy

    decreased by 40-50% after steam treatment. The reduced affinity for water and EGME may represent a reduced affinity for polar molecules in general. These results, particularly the XPS spectra and the observed large changes in rheological properties, suggest that steam altered the H + ion environment and/or concentration on palygorskite's surface. Exposing palygorskite to steam may have significant implications for its industrial applications, adversely affecting some applications and enhancing others.

  9. Calcite dissolution rate spectra measured by in situ digital holographic microscopy.

    Science.gov (United States)

    Brand, Alexander S; Feng, Pan; Bullard, Jeffrey W

    2017-09-01

    Digital holographic microscopy in reflection mode is used to track in situ, real-time nanoscale topography evolution of cleaved (104) calcite surfaces exposed to flowing or static deionized water. The method captures full-field holograms of the surface at frame rates of up to 12.5 s(-1). Numerical reconstruction provides 3D surface topography with vertical resolution of a few nanometers and enables measurement of time-dependent local dissolution fluxes. A statistical distribution, or spectrum, of dissolution rates is generated by sampling multiple area domains on multiple crystals. The data show, as has been demonstrated by Fischer et al. (2012), that dissolution is most fully described by a rate spectrum, although the modal dissolution rate agrees well with published mean dissolution rates (e.g., 0.1 µmol m(-2) s(-1) to 0.3 µmol m(-2) s(-1)). Rhombohedral etch pits and other morphological features resulting from rapid local dissolution appear at different times and are heterogeneously distributed across the surface and through the depth. This makes the distribution in rates measured on a single crystal dependent both on the sample observation field size and on time, even at nominally constant undersaturation. Statistical analysis of the inherent noise in the DHM measurements indicates that the technique is robust and that it likely can be applied to quantify and interpret rate spectra for the dissolution or growth of other minerals.

  10. Manganese-calcium intermixing facilitates heteroepitaxial growth at the 101¯4 calcite-water interface

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Man; Riechers, Shawn L.; Ilton, Eugene S.; Du, Yingge; Kovarik, Libor; Varga, Tamas; Arey, Bruce W.; Qafoku, Odeta; Kerisit, Sebastien

    2017-10-01

    In situ atomic force microscopy (AFM) measurements were performed to probe surface precipitates that formed on the (10-14) surface of calcite (CaCO3) single crystals following reaction with Mn2+-bearing aqueous solutions with a range of initial concentrations. Three-dimensional epitaxial islands were observed to precipitate and grow on the surfaces and in situ time-sequenced measurements demonstrated that their growth rates were commensurate with those obtained for epitaxial islands formed on calcite crystals reacted with Cd2+-bearing aqueous solutions of the same range in supersaturation with respect to the pure metal carbonate phase. This finding was unexpected as rhodochrosite (MnCO3) and calcite display a 10% lattice mismatch, based on the area of their (10-14) surface unit cells, whereas the lattice mismatch is only 4% for otavite (CdCO3) and calcite. Coatings of varying thicknesses were therefore synthesized by reacting calcite single crystals with calcite-equilibrated aqueous solutions with concentrations of up to 250 µM MnCl2 and analyzed to determine the composition of the surface precipitates. Ex situ X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR), and AFM measurements of the reacted crystals demonstrated the formation of an epitaxial (Mn,Ca)CO3 solid solution with a spatially complex composition atop the calcite surface, whereby the first few nanometers were rich in Ca and the Mn content increased with distance from the original calcite surface, culminating in a topmost region of almost pure MnCO3 for the thickest coatings. These findings explain the measured growth rates (the effective lattice mismatch was much smaller than nominal mismatch) and highlight the strong influence played by the substrate on the composition of surface precipitates in aqueous conditions.

  11. Biotic control of skeletal growth by scleractinian corals in aragonite-calcite seas.

    Directory of Open Access Journals (Sweden)

    Tomihiko Higuchi

    Full Text Available Modern scleractinian coral skeletons are commonly composed of aragonite, the orthorhombic form of CaCO3. Under certain conditions, modern corals produce calcite as a secondary precipitate to fill pore space. However, coral construction of primary skeletons from calcite has yet to be demonstrated. We report a calcitic primary skeleton produced by the modern scleractinian coral Acropora tenuis. When uncalcified juveniles were incubated from the larval stage in seawater with low mMg/Ca levels, the juveniles constructed calcitic crystals in parts of the primary skeleton such as the septa; the deposits were observable under Raman microscopy. Using scanning electron microscopy, we observed different crystal morphologies of aragonite and calcite in a single juvenile skeleton. Quantitative analysis using X-ray diffraction showed that the majority of the skeleton was composed of aragonite even though we had exposed the juveniles to manipulated seawater before their initial crystal nucleation and growth processes. Our results indicate that the modern scleractinian coral Acropora mainly produces aragonite skeletons in both aragonite and calcite seas, but also has the ability to use calcite for part of its skeletal growth when incubated in calcite seas.

  12. Accessory neurovascular foramina on the lingual surface of mandible: Incidence, topography, and clinical implications

    Directory of Open Access Journals (Sweden)

    B V Murlimanju

    2012-01-01

    Full Text Available Context: It was suggested that the accessory neurovascular foramina of the mandible might be of significance in relation to the effectiveness of local anesthesia following the routine inferior alveolar nerve block. Aims: To investigate the incidence of neurovascular foramina over the lingual surface of the mandible in South Indian population. Settings and Design: The study was conducted at the department of anatomy. Materials and Methods: The study included 67 human adult dry mandibles, the exact ages and sexes of which were not known. The location and number of neurovascular foramina were topographically analyzed. Statistical Analysis Used: Descriptive statistics. Results: The foramina were observed in 64 mandibles (95.5% and were often multiple in most of the cases. They were located between the two medial incisors in 8 mandibles (1.9%, between the medial and lateral incisor in 34 mandibles (50.7%; 25-bilateral; 7-right; 2-left, between the lateral incisor and canine in 7 mandibles (10.4%; 2-bilateral; 3-right; 2-left, between the canine and first premolar in 6 cases (8.9%; 3 on each side. Foramina were also present around the genial tubercle in 56 mandibles (83.6%. Among them, 52 mandibles showed a single foramen just above the genial tubercle, 34 mandibles had foramina below the tubercles, 13 mandibles had foramina on the right side of genial tubercle and 17 were having on the left side. Conclusion: Since the anatomical details of these foramina are important to various fields of dentistry and oncology, the present investigation was undertaken. The clinical significance and implications are emphasized.

  13. Calcite Dissolution Kinetics and Solubility in NaCl-CaCl2-MgCl2 Brines up to 1 bar pCO2 and 80\\deg C

    Science.gov (United States)

    Gledhill, D. K.; Morse, J. W.

    2004-12-01

    increase in rate was measured at 80\\deg C relative to 25\\deg C. The relatively high activation energy (Ea = 20 kJ mol-1) along with a stirring rate independence suggest the dissolution is dominated by surface controlled processes. These findings may offer important implications to reaction-transport models in carbonate bearing saline reservoirs.

  14. Investigating calcite growth rates using a quartz crystal microbalance with dissipation (QCM-D)

    Science.gov (United States)

    Cao, Bo; Stack, Andrew G.; Steefel, Carl I.; DePaolo, Donald J.; Lammers, Laura N.; Hu, Yandi

    2018-02-01

    Calcite precipitation plays a significant role in processes such as geological carbon sequestration and toxic metal sequestration and, yet, the rates and mechanisms of calcite growth under close to equilibrium conditions are far from well understood. In this study, a quartz crystal microbalance with dissipation (QCM-D) was used for the first time to measure macroscopic calcite growth rates. Calcite seed crystals were first nucleated and grown on sensors, then growth rates of calcite seed crystals were measured in real-time under close to equilibrium conditions (saturation index, SI = log ({Ca2+}/{CO32-}/Ksp) = 0.01-0.7, where {i} represent ion activities and Ksp = 10-8.48 is the calcite thermodynamic solubility constant). At the end of the experiments, total masses of calcite crystals on sensors measured by QCM-D and inductively coupled plasma mass spectrometry (ICP-MS) were consistent, validating the QCM-D measurements. Calcite growth rates measured by QCM-D were compared with reported macroscopic growth rates measured with auto-titration, ICP-MS, and microbalance. Calcite growth rates measured by QCM-D were also compared with microscopic growth rates measured by atomic force microscopy (AFM) and with rates predicted by two process-based crystal growth models. The discrepancies in growth rates among AFM measurements and model predictions appear to mainly arise from differences in step densities, and the step velocities were consistent among the AFM measurements as well as with both model predictions. Using the predicted steady-state step velocity and the measured step densities, both models predict well the growth rates measured using QCM-D and AFM. This study provides valuable insights into the effects of reactive site densities on calcite growth rate, which may help design future growth models to predict transient-state step densities.

  15. Mapping surface-modified titania nanoparticles with implications for activity and facet control

    National Research Council Canada - National Science Library

    Yung-Kang Peng; Yichen Hu; Hung-Lung Chou; Yingyi Fu; Ivo F Teixeira; Li Zhang; Heyong He; Shik Chi Edman Tsang

    2017-01-01

    The use of surface-directing species and surface additives to alter nanoparticle morphology and physicochemical properties of particular exposed facets has recently been attracting significant attention...

  16. Effects of DNP on the cell surface properties of marine bacteria and its implication for adhesion to surfaces

    Digital Repository Service at National Institute of Oceanography (India)

    Jain, A.; Nishad, K.K.; Bhosle, N.B.

    and the Environment (D Almorza C A, Brebbia D Sales & V Popov) (Editors),ISBN 1-85312-907- 0. Min Seok chae, Heidi Schraft, Lisbeth Truelstrup Hansen & Robet Mackereth (2006) Effect of physiochemical surface characteristic of Listeria monocytogenes strains...

  17. Response of the global surface ozone distribution to Northern Hemisphere sea surface temperature changes: implications for long-range transport

    Science.gov (United States)

    Yi, Kan; Liu, Junfeng; Ban-Weiss, George; Zhang, Jiachen; Tao, Wei; Cheng, Yanli; Tao, Shu

    2017-07-01

    The response of surface ozone (O3) concentrations to basin-scale warming and cooling of Northern Hemisphere oceans is investigated using the Community Earth System Model (CESM). Idealized, spatially uniform sea surface temperature (SST) anomalies of ±1 °C are individually superimposed onto the North Pacific, North Atlantic, and North Indian oceans. Our simulations suggest large seasonal and regional variability in surface O3 in response to SST anomalies, especially in the boreal summer. The responses of surface O3 associated with basin-scale SST warming and cooling have similar magnitude but are opposite in sign. Increasing the SST by 1 °C in one of the oceans generally decreases the surface O3 concentrations from 1 to 5 ppbv. With fixed emissions, SST increases in a specific ocean basin in the Northern Hemisphere tend to increase the summertime surface O3 concentrations over upwind regions, accompanied by a widespread reduction over downwind continents. We implement the integrated process rate (IPR) analysis in CESM and find that meteorological O3 transport in response to SST changes is the key process causing surface O3 perturbations in most cases. During the boreal summer, basin-scale SST warming facilitates the vertical transport of O3 to the surface over upwind regions while significantly reducing the vertical transport over downwind continents. This process, as confirmed by tagged CO-like tracers, indicates a considerable suppression of intercontinental O3 transport due to increased tropospheric stability at lower midlatitudes induced by SST changes. Conversely, the responses of chemical O3 production to regional SST warming can exert positive effects on surface O3 levels over highly polluted continents, except South Asia, where intensified cloud loading in response to North Indian SST warming depresses both the surface air temperature and solar radiation, and thus photochemical O3 production. Our findings indicate a robust linkage between basin-scale SST

  18. Response of the global surface ozone distribution to Northern Hemisphere sea surface temperature changes: implications for long-range transport

    Directory of Open Access Journals (Sweden)

    K. Yi

    2017-07-01

    Full Text Available The response of surface ozone (O3 concentrations to basin-scale warming and cooling of Northern Hemisphere oceans is investigated using the Community Earth System Model (CESM. Idealized, spatially uniform sea surface temperature (SST anomalies of ±1 °C are individually superimposed onto the North Pacific, North Atlantic, and North Indian oceans. Our simulations suggest large seasonal and regional variability in surface O3 in response to SST anomalies, especially in the boreal summer. The responses of surface O3 associated with basin-scale SST warming and cooling have similar magnitude but are opposite in sign. Increasing the SST by 1 °C in one of the oceans generally decreases the surface O3 concentrations from 1 to 5 ppbv. With fixed emissions, SST increases in a specific ocean basin in the Northern Hemisphere tend to increase the summertime surface O3 concentrations over upwind regions, accompanied by a widespread reduction over downwind continents. We implement the integrated process rate (IPR analysis in CESM and find that meteorological O3 transport in response to SST changes is the key process causing surface O3 perturbations in most cases. During the boreal summer, basin-scale SST warming facilitates the vertical transport of O3 to the surface over upwind regions while significantly reducing the vertical transport over downwind continents. This process, as confirmed by tagged CO-like tracers, indicates a considerable suppression of intercontinental O3 transport due to increased tropospheric stability at lower midlatitudes induced by SST changes. Conversely, the responses of chemical O3 production to regional SST warming can exert positive effects on surface O3 levels over highly polluted continents, except South Asia, where intensified cloud loading in response to North Indian SST warming depresses both the surface air temperature and solar radiation, and thus photochemical O3 production. Our findings indicate a robust linkage

  19. Incorporation of water vapor transfer in the JULES Land Surface Model: implications for key soil variables and land surface fluxes

    OpenAIRE

    Garcia Gonzalez, R.; Verhoef, A.; Luigi Vidale, P.; I. Braud

    2012-01-01

    This study focuses on the mechanisms underlying water and heat transfer in upper soil layers, and their effects on soil physical prognostic variables and the individual components of the energy balance. The skill of the JULES (Joint UK Environment Simulator) land surface model (LSM) to simulate key soil variables, such as soil moisture content and surface temperature, and fluxes such as evaporation, is investigated. The Richards equation for soil water transfer, as used in most LSMs, was upda...

  20. Absorption mechanism study of benzoic acid on calcite. Influence on the wettability; Etude du mecanisme d`absorption de l`acide benzoique sur la calcite. Incidence sur la mouillabilite

    Energy Technology Data Exchange (ETDEWEB)

    Legens, Ch.

    1997-12-03

    A pure carbonate rock is strongly water-wet whereas oil accumulations study shows that most of carbonate reservoirs are oil-wet or of mixed-wettability. This is one of the main difficulties to extract crude oil. This change of behavior is due to the adsorption of some crude oil compounds on the mineral surface. We have mainly studied the interactions between acid molecules by adsorption on a calcite powder in an organic phase (benzoic acid and lauric acid) and in an aqueous phase (benzoic acid and lauric sodium salt). The technics which enabled us to define and characterize adsorption are thermogravimetry infrared diffuse reflection and thermal analysis with controlled kinetic linked to a mass spectrometer. Molecular modelling calculations have completed these analysis. It has been showed that when crude oil fills the biggest pores of the reservoir rock, the aqueous film is unstable and acids adsorb via ionic bonds on mineral calcium ions. Wettability is evaluated thanks to contact angle measurements of a water droplet deposited on a compacted powder pellet. Calcite wettability changes were all the greater as hydro-carbonated chains were longer, as it confers molecule hydrophobia. It has been also investigated acid molecules diffusion from the organic to the aqueous phase which saturates the smallest pores. Molecules which are able to diffuse from the first to the second medium do not adsorb on the surface. As a consequence, carbonate rock wettability changes require a direct contact between crude oil and mineral that involves aqueous film instability. (author) 128 refs.

  1. Quantitative roughness characterization of geological surfaces and implications for radar signature analysis

    DEFF Research Database (Denmark)

    Dierking, Wolfgang

    1999-01-01

    Stochastic surface models are useful for analyzing in situ roughness profiles and synthetic aperture radar (SAR) images of geological terrain. In this paper, two different surface models are discussed: surfaces with a stationary random roughness (conventional model) and surfaces with a power-law ......-law roughness spectrum (fractal model). In the former case, it must be considered that for short profiles (L...

  2. Evaluation of Various Synthesis Methods for Calcite-Precipitated Calcium Carbonate (PCC) Formation

    Energy Technology Data Exchange (ETDEWEB)

    Ramakrishna, Chilakala [Hanil Cement Corporation, Danyang (Korea, Republic of); Thenepalli, Thriveni; Ahn, Ji Whan [Korea Institute of Geoscience and Mineral Resources, Daejeon (Korea, Republic of)

    2017-06-15

    This review paper evaluates different kinds of synthesis methods for calcite precipitated calcium carbonates by using different materials. The various processing routes of calcite with different compositions are reported and the possible optimum conditions required to synthesize a desired particle sizes of calcite are predicted. This paper mainly focuses on that the calcite morphology and size of the particles by carbonation process using loop reactors. In this regard, we have investigated various parameters such as CO{sub 2} flow rate, Ca (OH){sub 2} concentration, temperature, pH effect, reaction time and loop reactor mechanism with orifice diameter. The research results illustrate the formation of well-defined and pure calcite crystals with controlled crystal growth and particle size, without additives or organic solvents. The crystal growth and particle size can be controlled, and smaller sizes are obtained by decreasing the Ca (OH){sub 2} concentration and increasing the CO{sub 2} flow rate at lower temperatures with suitable pH. The crystal structure of obtained calcite was characterized by using X-ray diffraction method and the morphology by scanning electron microscope (SEM). The result of x-ray diffraction recognized that the calcite phase of calcium carbonate was the dominating crystalline structure.

  3. Stable carbon isotopes and lipid biomarkers provide new insight into the formation of calcite and siderite concretions in organic-matter rich deposits

    Science.gov (United States)

    Baumann, Lydia; Birgel, Daniel; Wagreich, Michael; Peckmann, Jörn

    2015-04-01

    composition of the host sediment differs significantly from the siderite concretions. The δ13C values of the Gosau host sediment reflect marine conditions, whereas the oxygen isotope values are best explained by meteoric overprint. Lipid biomarkers have been extracted before and after dissolution of the concretions in order to assess their authenticity and to exclude recent surface contamination. In the following, only the biomarkers extracted after dissolution are discussed, since they are thought to be related to concretion formation. The calcite concretions comprise abundant plant wax derived long-chain n-alkanes, reflecting high terrestrial input. Bacterial, terminally-branched fatty acids were found, but in overall low abundance. The siderite concretions did not yield biomarkers due to their high maturity. No archaeal biomarkers were found in any of the concretions. Considering the presence of framboidal pyrite, the moderately low δ13C values, and the biomarker inventory, bacterial sulfate reduction apparently contributed to the formation of the calcite concretions in a brackish environment. In contrast, ongoing sulfate reduction and resultant hydrogen sulfide production inhibit siderite precipitation. Therefore, the low δ13C values of the siderite concretions are best explained by bacterial iron reduction.

  4. The potential for phosphorus pollution remediation by calcite precipitation in UK freshwaters

    Directory of Open Access Journals (Sweden)

    C. Neal

    2001-01-01

    Full Text Available This paper examines the potential for calcium carbonate to reduce phosphate pollution in freshwaters by co-precipitation, a process known as a "self cleansing mechanism". Calcium carbonate saturation levels and phosphate concentrations (SRP - soluble reactive phosphate across the major eastern UK river basins are examined to test for solubility controls. The study shows that calcite saturation varies for each catchment as a function of flow and biological activity rather than by direct regulation by SRP. Indeed, there is no evidence, for any of the rivers studied, that calcite solubility controls hold. However, for groundwater and groundwater-fed springs in the Chalk of the Thames basin, calcite saturation is observed with associated low SRP levels. A self-cleansing mechanism may well be operative within the Chalk due to two factors. Firstly, there is a high potential for nucleation on the calcite micro-crystals in the aquifer. Secondly, there are within aquifer reactions that remove the calcite nucleating inhibitors (SRP and dissolved organic carbon, DOC to levels lower than those occurring within the rivers do. These inhibitors enter the catchment at very high concentrations in association with agricultural pollution (fertilizer application and animal slurry and household contamination (e.g. sewage sources from septic tanks. Under low flow conditions, when the saturation index for calcite is at its highest, so too is the concentration of the nucleation inhibitor SRP. Companion work shows that calcite precipitation can occur at the water-sediment interface of the river and this may involve SRP removal. The data, as a whole, define an apparent bound for calcite solubility control where in the presence of nucleating centres, SRP must be less than 4 mM-P l-1 and DOC must be less than 150 mM-C l-1: a condition that does not seem to pertain within most UK rivers. Keywords: calcite, calcium carbonate, phosphate, soluble reactive phosphate, dissolved

  5. Yeast expressing hepatitis B virus surface antigen determinants on its surface: Implications for a possible oral vaccine

    NARCIS (Netherlands)

    Schreuder, M.P.; Deen, C.; Boersma, W.J.A.; Pouwels, P.H.; Klis, F.M.

    1996-01-01

    The two major hydrophilic regions of the hepatitis B virus surface antigen (HBsAg) have been expressed in the outer mannoprotein layer of the cell wall of 'Bakers Yeast', Saccharomyces cerevisiae, by fusing them between the yeast invertase signal sequence and the yeast α-agglutinin carboxyterminal

  6. Measuring Carbon and Oxygen Isotope Uptake into Inorganic Calcite using Crystal Growth Experiments

    Science.gov (United States)

    Baker, E. B.; Watkins, J. M.

    2014-12-01

    Carbon and oxygen isotopes measured on natural calcite crystals provide a record of paleo-environment conditions. Despite the importance of measuring stable isotopes in calcite for paleo-environment reconstructions, there is neither a general theory nor an experimental data set that fully separates the effects of pH, temperature, and precipitation rate on isotope discrimination during calcite growth. Many stable isotope studies of calcite have focused on either carbon or oxygen isotope compositions individually, but few have measured both carbon and oxygen isotope uptake in the same set of crystals. We are precipitating inorganic calcite across a range in temperature, pH, and precipitation rate to guide the development of a general theory for combined carbon and oxygen isotope uptake into calcite crystals grown on laboratory timescales. In our experiments, dissolved inorganic carbon (DIC) is added to an aqueous solution (15 mM CaCl2 + 5 mM NH4Cl) by CO2 bubbling. Once a critical supersaturation is reached, calcite crystals nucleate spontaneously and grow on the beaker walls. A key aspect of this experimental approach is that the δ13C of DIC is relatively constant throughout the crystal growth period, because there is a continuous supply of DIC from the CO2-bearing bubbles. Carbonic anhydrase, an enzyme promoting rapid equilibration of isotopes between DIC and water, was added to ensure that the solution remained isotopically equilibrated during calcite growth. We have conducted experiments at T = 25°C and pH = 8.3 - 9.0. We observe that the fractionation of oxygen isotopes between calcite and water decreases with increasing pH, consistent with available data from experiments in which the enzyme carbonic anhydrase was used. Our results for carbon isotopes extend the available data set, which previously ranged from pH 6.62 to 7.75, to higher pH. At pH 8.3, we observe that calcite is isotopically heavier than DIC with respect to carbon isotopes by about 0.25‰. At

  7. Monitoring of Calcite Precipitation in Hardwater Lakes with Multi-Spectral Remote Sensing Archives

    Directory of Open Access Journals (Sweden)

    Iris Heine

    2017-01-01

    Full Text Available Calcite precipitation is a common phenomenon in calcium-rich hardwater lakes during spring and summer, but the number and spatial distribution of lakes with calcite precipitation is unknown. This paper presents a remote sensing based method to observe calcite precipitation over large areas, which are an important prerequisite for a systematic monitoring and evaluation of restoration measurements. We use globally archived satellite remote sensing data for a retrospective systematic assessment of past multi-temporal calcite precipitation events. The database of this study consists of 205 data sets that comprise freely available Landsat and Sentinel 2 data acquired between 1998 and 2015 covering the Northeast German Plain. Calcite precipitation is automatically identified using the green spectra and the metric BGR area, the triangular area between the blue, green and red reflectance value. The validation is based on field measurements of CaCO3 concentrations at three selected lakes, Feldberger Haussee, Breiter Luzin and Schmaler Luzin. The classification accuracy (0.88 is highest for calcite concentrations ≥0.7 mg/L. False negative results are caused by the choice of a conservative classification threshold. False positive results can be explained by already increased calcite concentrations. We successfully transferred the developed method to 21 other hardwater lakes in Northeast Germany. The average duration of lakes with regular calcite precipitation is 37 days. The frequency of calcite precipitation reaches from single time detections up to detections nearly every year. False negative classification results and gaps in Landsat time series reduce the accuracy of frequency and duration monitoring, but in future the image density will increase by acquisitions of Sentinel-2a (and 2b. Our study tested successfully the transfer of the classification approach to Sentinel-2 images. Our study shows that 15 of the 24 lakes have at least one phase of

  8. 88Sr/86Sr fractionation and calcite accumulation rate in the Sea of Galilee

    Science.gov (United States)

    Fruchter, N.; Lazar, B.; Nishri, A.; Almogi-Labin, A.; Eisenhauer, A.; Be'eri Shlevin, Y.; Stein, M.

    2017-10-01

    This study used the Sea of Galilee (Lake Kinneret, northern Israel) as a ;natural laboratory; to investigate the fractionation of the stable Sr isotope ratio (88Sr/86Sr) during precipitation of inorganic (primary) calcite from the lake's water. It was found that the absolute value of the 88Sr/86Sr fractionation factor, Δ88/86Sr, increases as a function of calcite accumulation rate (Δ88/86Sr [‰] = -0.05 to 0.042·log(R) [μmol·m-2·d-1], where R is the accumulation rate). Furthermore, the 87Sr/86Sr and 88Sr/86Sr ratios in the freshwater and brines that enter the lake were used to calculate the contributions of these sources to the lake Sr budget. The 87Sr/86Sr and 88Sr/86Sr ratios were measured in primary calcite, aragonite shells of live Melanopsis, lake water and various water sources to the lake. While the lake's 87Sr/86Sr ratios are determined by the mixture of freshwater of the Jordan River and saline springs, the 88Sr/86Sr ratios of the lake reflect a more complex mass balance that includes the effect of isotopic fractionation associated with the precipitation of primary calcite. Data analysis suggests that long-term accumulation of inorganic calcite depleted in the heavy isotope 88Sr, results in an increase of the δ88/86Sr value of the lake water by 0.05‰. In contrast to the primary inorganic calcite, biogenic aragonite of the Melanopsis shells show a rather constant 88Sr/86Sr water-CaCO3 fractionation of Δ88/86Sr = -0.21‰. Similar Δ88/86Sr values were reported for the precipitation of coralline and inorganic aragonite from seawater and the precipitation of inorganic calcite from various continental waters. The Δ88/86Sr value of inorganic calcite is modulated by the rate of carbonate precipitation, as noted above and shown by precipitation experiments. Massive precipitation of primary calcite with a wide spread of accumulation rates occurs during the spring phytoplankton bloom in Lake Kinneret. The bloom dictates the degree of calcite saturation

  9. Time-lapse 3D imaging of calcite precipitation in a microporous column

    Science.gov (United States)

    Godinho, Jose R. A.; Withers, Philip J.

    2018-02-01

    Time-lapse X-ray computed tomography is used to image the evolution of calcite precipitation during flow through microporous quartz over the course of 400 h. The growth rate decreases by more than seven times, which is linked to the clogging of flow paths that restricts flow to some regions of the column. Fewer precipitates are observed as a function of column depth, which is found to be related to a differential nucleation density along the sample. A higher nucleation density closer to the inlet implies more crystal volume increase per unit of time without affecting the rate if normalized to the surface area of crystals. Our overall growth rates measured in porous media are orders of magnitude slower than growth rates derived from traditional precipitation experiments on free surfaces. Based on our time-lapse results we hypothesize a scenario where the evolving distribution of precipitates within a pore structure during precipitation progressively modifies the local transport through the pores. Within less permeable regions the saturation index may be lower than along the main flow paths. Therefore, the reactive crystal surfaces within those regions grow at a slower rate than that expected from the bulk fluid composition. Since the amount of reactive surface area within these less permeable regions increases over time, the overall growth rate decreases without a necessary significant change of the bulk fluid composition along more permeable flow paths. In conclusion, the overall growth rates in an evolving porous media expected from bulk fluid compositions alone can be overestimated due to the development of stagnant sub-regions where the reactive surface area is bath by a solution with lower saturation index. In this context we highlight the value of time-lapse 3D studies for understanding the dynamics of mineral precipitation in porous media.

  10. Calcite-forming bacteria for compressive strength improvement in mortar.

    Science.gov (United States)

    Park, Sung-Jin; Park, Yu-Mi; Chun, Woo-Young; Kim, Wha-Jung; Ghim, Sa-Youl

    2010-04-01

    Microbiological calcium carbonate precipitation (MCP) has been investigated for its ability to improve the compressive strength of concrete mortar. However, very few studies have been conducted on the use of calcite-forming bacteria (CFB) to improve compressive strength. In this study, we discovered new bacterial genera that are capable of improving the compressive strength of concrete mortar. We isolated 4 CFB from 7 environmental concrete structures. Using sequence analysis of the 16S rRNA genes, the CFB could be partially identified as Sporosarcina soli KNUC401, Bacillus massiliensis KNUC402, Arthrobacter crystallopoietes KNUC403, and Lysinibacillus fusiformis KNUC404. Crystal aggregates were apparent in the bacterial colonies grown on an agar medium. Stereomicroscopy, scanning electron microscopy, and x-ray diffraction analyses illustrated both the crystal growth and the crystalline structure of the CaCO3 crystals. We used the isolates to improve the compressive strength of concrete mortar cubes and found that KNUC403 offered the best improvement in compressive strength.

  11. Carbonate saturation state of surface waters in the Ross Sea and Southern Ocean: controls and implications for the onset of aragonite undersaturation

    Science.gov (United States)

    DeJong, H. B.; Dunbar, R. B.; Mucciarone, D. A.; Koweek, D.

    2016-02-01

    Predicting when surface waters of the Ross Sea and Southern Ocean will become undersaturated with respect to biogenic carbonate minerals is challenging in part due to the lack of baseline high resolution carbon system data. Here we present 1700 surface total alkalinity measurements from the Ross Sea and along a transect between the Ross Sea and southern Chile from the austral autumn (February-March 2013). We calculate the saturation state of aragonite (ΩAr) and calcite (ΩCa) using measured total alkalinity and pCO2. In the Ross Sea and south of the Polar Front, variability in carbonate saturation state (Ω) is mainly driven by algal photosynthesis. Freshwater dilution and calcification have minimal influence on Ω variability. We estimate an early spring surface water ΩAr value of 1.2 for the Ross Sea using a total alkalinity-salinity relationship and historical pCO2 measurements. Our results suggest that the Ross Sea is not likely to become undersaturated with respect to aragonite until the year 2070.

  12. Atomic Resolution of Calcium and Oxygen Sublattices of Calcite in Ambient Conditions by Atomic Force Microscopy Using qPlus Sensors with Sapphire Tips.

    Science.gov (United States)

    Wastl, Daniel S; Judmann, Michael; Weymouth, Alfred J; Giessibl, Franz J

    2015-01-01

    Characterization and imaging at the atomic scale with atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomically resolved imaging of the calcite (101̅4) surface plane using stiff quartz cantilevers ("qPlus sensors", stiffness k = 1280 N/m) equipped with sapphire tips in ambient conditions without any surface preparation. With 10 atoms in one surface unit cell, calcite has a highly complex surface structure comprising three different chemical elements (Ca, C, and O). We obtain true atomic resolution of calcite in air at relative humidity ranging from 20% to 40%, imaging atomic steps and single atomic defects. We observe a great durability of sapphire tips with their Mohs hardness of 9, only one step below diamond. Depending on the state of the sapphire tip, we resolve either the calcium or the oxygen sublattice. We determine the tip termination by comparing the experimental images with simulations and discuss the possibility of chemical tip identification in air. The main challenges for imaging arise from the presence of water layers, which form on almost all surfaces and have the potential to dissolve the crystal surface. Frequency shift versus distance spectra show the presence of at least three ordered hydration layers. The measured height of the first hydration layer corresponds well to X-ray diffraction data and molecular dynamic simulations, namely, ∼220 pm. For the following hydration layers we measure ∼380 pm for the second and third layer, ending up in a total hydration layer thickness of at least 1 nm. Understanding the influence of water layers and their structure is important for surface segregation, surface reactions including reconstructions, healing of defects, and corrosion.

  13. Biogenic calcite particles from microalgae-Coccoliths as a potential raw material.

    Science.gov (United States)

    Jakob, Ioanna; Chairopoulou, Makrina Artemis; Vučak, Marijan; Posten, Clemens; Teipel, Ulrich

    2017-06-01

    Synthetic calcite (CaCO3) particles are found in a broad range of applications. The geometry of particles produced from limestone or precipitation are versatile but limited to basic shapes. The microalga Emiliania huxleyi produces micro-structured calcite platelets, called coccoliths. This article presents the results of an application-orientated study, which includes characteristic values also used in the calcite industry for particle evaluation. It is demonstrated that coccoliths are significantly different from all industrial particles produced so far. Coccoliths are porous particles, mainly consisted of calcium carbonate, with further elements such as Mg, Si, Sr, and Fe often embedded in their structure. Their structure is extremely sophisticated, while the overall particle morphology and particle size distribution are homogeneous. This study gives a first inside into the potential of these exceptional objects and may set further impulses for their utilization in specific calcite particle applications.

  14. Machine learning approach for predicting the effect of CO2 solubility on dissolution rate of calcite

    Science.gov (United States)

    Nomeli, Mohammad

    2017-11-01

    A machine learning-assisted model is developed to predict the dissolution rate of calcite in saline solutions that are imbibed with dissolved CO2 over a broad range of both subcritical and supercritical conditions. This study focuses on determining the rate of calcite dissolution within a temperature range of 50-100 C and pressures up to 600 bar, relevant for CO2 sequestration in saline aquifers. A general reaction kinetic model is used that is based on the extension of the standard Arrhenius equation with an added, solubility dependent, pH term to account for the saturated concentration of dissolved CO2. The kinetic model helps to obtain a predictive rate equation using machine learning methods to determine the dissolution of calcite as a function of temperature, pressure and salinity. The new rate equation helps us obtain good agreement with experimental data, and it is applied to study the geochemically induced alterations of fracture geometry due to calcite dissolution.

  15. Atomic modifications by synchrotron radiation at the calcite-ethanol interface

    DEFF Research Database (Denmark)

    Pasarín, I. S.; Bovet, Nicolas Emile; Glyvradal, Magni

    2012-01-01

    -mineral interfaces where the polar OH group, as present in ethanol, plays a key role in their molecular structure and bonding. Also, the chemical evolution observed in the interface provides new insight into the behavior of some complex organic molecules involved in biomineralization processes.......This article reports on studies of the chemical alterations induced by synchrotron radiation at the calcite-ethanol interface, a simple model system for interfaces between minerals and more complex organic molecules containing OH groups. A combination of X-ray reflectivity and X-ray photoelectron...... spectroscopy of natural calcite, cleaved in distilled ethanol to obtain new clean interfaces, indicated that, during a 5 h period, the two top atomic layers of calcite, CaCO3, transform into calcium oxide, CaO, by releasing CO2. Also, the occupation of the first ordered layer of ethanol attached to calcite...

  16. Total alignment of calcite at acidic polydiacetylene films: cooperativity at the organic-inorganic interface.

    Science.gov (United States)

    Berman, A; Ahn, D J; Lio, A; Salmeron, M; Reichert, A; Charych, D

    1995-07-28

    Biological matrices can direct the absolute alignment of inorganic crystals such as calcite. Cooperative effects at an organic-inorganic interface resulted in similar co-alignment of calcite at polymeric Langmuir-Schaefer films of 10,12-pentacosadiynoic acid (p-PDA). The films nucleated calcite at the (012) face, and the crystals were co-aligned with respect to the polymer's conjugated backbone. At the same time, the p-PDA alkyl side chains reorganized to optimize the stereochemical fit to the calcite structure, as visualized by changes in the optical spectrum of the polymer. These results indicate the kinds of interactions that may occur in biological systems where large arrays of crystals are co-aligned.

  17. Kinetic and thermodynamic factors controlling the distribution of SO 32- and Na + in calcites and selected aragonites

    Science.gov (United States)

    Busenberg, Eurybiades; Niel Plummer, L.

    1985-03-01

    Significant amounts of SO 42-, Na +, and OH - are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO 42-. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na +, but very low concentrations of SO 42-. The SO 42- content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na + and SO 42- increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO 42- beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO 42- is the same as that of aragonite. Na + appears to have very little effect on the solubility product of calcites. The amounts of Na + and SO 42- incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient ( D) of SO 42- in calcite at 25.0°C and 0.50 molal NaCl is described by the equation D = k 0 + k 1R where k 0 and k 1 are constants equal to 6.16 × 10 -6 and 3.941 × 10 -6, respectively, and R is the rate of crystal growth of calcite in mg·min -1·g -1 of seed. The data on Na + are consistent with the hypothesis that a significant amount of Na + occupies interstitial positions in the calcite structure. The distribution of Na + follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na + distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na + contents of calcites are not very accurate indicators of environmental salinities.

  18. Surface dose measurements in and out of field: Implications for breast radiotherapy with megavoltage photon beams.

    Science.gov (United States)

    Lonski, Peta; Ramachandran, Prabhakar; Franich, Rick; Kron, Tomas

    2017-12-01

    This study examines the difference in surface dose between flat and flattening filter free (FFF) photon beams in the context of breast radiotherapy. The surface dose was measured for 6MV, 6MV FFF, 10MV, 10MV FFF and 18MV photon beams using a thin window ionisation chamber for various field sizes. Profiles were acquired to ascertain the change in surface dose off-axis. Out-of-field measurements were included in a clinically representative half beam block tangential breast field. In the field centres of FFF beams the surface dose was found to be increased for small fields and decreased for large fields compared to flat beams. For FFF beams, surface dose was found to decrease off-axis and resulted in lower surface dose out-of-field compared to flat beams. Copyright © 2017. Published by Elsevier GmbH.

  19. The mechanical and microstructural behaviour of calcite-dolomite composites: An experimental investigation

    OpenAIRE

    Kushnir, Alexandra R. l.; Kennedy, L. A.; Misra, Santanu; Benson, Philip; White, J. C.

    2015-01-01

    The styles and mechanisms of deformation associated with many variably dolomitized limestone shear systems are strongly controlled by strain partitioning between dolomite and calcite. Here, we present experimental results from the deformation of four composite materials designed to address the role of dolomite on the strength of limestone. Composites were synthesized by hot isostatic pressing mixtures of dolomite (Dm) and calcite powders (% Dm: 25%-Dm, 35%-Dm, 51%-Dm, and 75%-Dm). In all comp...

  20. Precipitation of Calcite during the Deposition of Paleogene Sangkarewang Oil Shale, Ombilin Basin, West Sumatra, Indonesia

    Directory of Open Access Journals (Sweden)

    Agus Haris Widayat

    2015-09-01

    Full Text Available DOI: 10.17014/ijog.2.3.185-197Geochemical and petrographical analyses were carried out to investigate the occurrence of calcite in theformer Ombilin lacustrine lake. The study involves eight samples taken from a 56 m long drill core of Sangkarewangoil shale. Geochemical investigation showed that the samples consist of varied terrigenous input represented by Si, Al, K, and Ti, and autochthonous input represented by S, total organic carbon (TOC, and d13C of bulk organic matter. Along the drill core profile the abundance of autochthonous input decreases upwards, while that of terrigenous input oppositely increases upwards. Petrographical analysis revealed that calcite is a major mineral in the samples. In this study, the abundance of calcite could be represented by the abundance of Ca, as calcite is the only significant Ca containing mineral. Ca is abundant in the samples (8.4% in average and its concentration varies similarly with those of S, TOC, and d13C, suggesting that the element as well as calcite incorporates the autochthonous input. Thevariation of calcite abundance in the drill core profile is considered to be related with primary productivity changes during the development of the former lake. Higher primary productivity represented by more positive of d13C value(-24.8‰ during the deposition of the lower part of the drill core profile promoted the higher amount of deposited organic matter. In such environment, the supersaturation of carbonate ion in lake water was also reached and significant precipitation of authigenic calcite occurred. As the lake developed, the primary productivity decreased as indicated by more negative of d13C value (eventually -26.8‰. This condition led to the decreases of deposited organic matterand calcite in the lake sediments.

  1. Climate change and water table fluctuation: Implications for raised bog surface variability

    Science.gov (United States)

    Taminskas, Julius; Linkevičienė, Rita; Šimanauskienė, Rasa; Jukna, Laurynas; Kibirkštis, Gintautas; Tamkevičiūtė, Marija

    2018-03-01

    Cyclic peatland surface variability is influenced by hydrological conditions that highly depend on climate and/or anthropogenic activities. A low water level leads to a decrease of peatland surface and an increase of C emissions into the atmosphere, whereas a high water level leads to an increase of peatland surface and carbon sequestration in peatlands. The main aim of this article is to evaluate the influence of hydrometeorological conditions toward the peatland surface and its feedback toward the water regime. A regional survey of the raised bog water table fluctuation and surface variability was made in one of the largest peatlands in Lithuania. Two appropriate indicators for different peatland surface variability periods (increase and decrease) were detected. The first one is an 200 mm y- 1 average net rainfall over a three-year range. The second one is an average annual water depth of 25-30 cm. The application of these indicators enabled the reconstruction of Čepkeliai peatland surface variability during a 100 year period. Processes of peatland surface variability differ in time and in separate parts of peatland. Therefore, internal subbasins in peatland are formed. Subbasins involve autogenic processes that can later affect their internal hydrology, nutrient status, and vegetation succession. Internal hydrological conditions, surface fluctuation, and vegetation succession in peatland subbasins should be taken into account during evaluation of their state, nature management projects, and other peatland research works.

  2. Chromium isotopic fractionation in aquatic systems and foraminiferal calcite

    Science.gov (United States)

    Wang, X.; Wu, W.; Reinhard, C. T.; Planavsky, N.

    2016-12-01

    The stable chromium (Cr) isotope system is an emerging proxy for studying the reduction/oxidation (redox) state of the early earth. However, the distribution and isotopic composition of Cr in many modern environments is still poorly known. For this reason, Cr isotope fractionation during biological processes, in rivers, estuaries, seawaters, and modern sediments need to be constrained to calibrate this potentially very useful paleoredox proxy. Here we report concentrations and isotope systematics of dissolved and suspended Cr in the Connecticut River system, and from core-top planktonic foraminiferal calcite from the global ocean. In the Connecticut River system, soil profile samples are unfractionated from bulk silicate Earth (BSE) values. River waters range from -0.2‰ to 0.9‰ (δ53Cr expressed as 53Cr/52Cr relative to NIST SRM 979 standard), with some, but not all tributaries showing seasonal differences. Suspended particulate samples range from -0.1 to 0‰ in autumn and from 0 to 0.1‰ in spring. Modern planktonic foraminifera show a wide range of δ53Cr values, from 0.2‰ to 2.2‰. Such variability seems to be controlled by both seawater heterogeneity and biological fractionation. In summary, weathering environments studied so far suggest wide variability of δ53Cr in rivers and weathered rocks, but with indiscernible correlation with climate types (temperate vs. tropical). In addition, large spatial variability has been detected in the modern seawater and large biological fractionation has been observed during marine biological calcification. These observations provide important guidelines for interpreting the ancient Cr isotope record.

  3. Surface/bulk partitioning and acid/base speciation of aqueous decanoate: direct observations and atmospheric implications

    Directory of Open Access Journals (Sweden)

    N. L. Prisle

    2012-12-01

    Full Text Available Dilute aqueous solutions of the atmospheric organic surfactant sodium decanoate have been studied using surface sensitive X-ray photoelectron spectroscopy combined with synchrotron radiation. We studied the decanoate/decanoic acid speciation and preferential adsorption at the vapor–liquid interface, and the responses to mixing in solution with some of the most common atmospheric inorganic ions, Na+, NH4+, Cl, and SO42−. We observe little or no influence of Na+, Cl, or SO42− ions, on neither the relative speciation nor the individual adsorption properties of decanoate and decanoic acid. In particular, no significant salting-out effect due to common Na+ cations of the organic and inorganic salts was observed for these solutions. On the other hand, mixing with NH4+ cations resulted in a pronounced surface enhancement of decanoic acid, which is attributed to surface specific acid–base chemistry. These changes in surface/bulk partitioning and surface speciation may significantly affect properties of aqueous droplets containing decanoate/decanoic acid, and potential implications for several processes critical to the climate effects of atmospheric aerosols are discussed.

  4. Factors regulating the Great Calcite Belt in the Southern Ocean and its biogeochemical significance

    Science.gov (United States)

    Balch, William M.; Bates, Nicholas R.; Lam, Phoebe J.; Twining, Benjamin S.; Rosengard, Sarah Z.; Bowler, Bruce C.; Drapeau, Dave T.; Garley, Rebecca; Lubelczyk, Laura C.; Mitchell, Catherine; Rauschenberg, Sara

    2016-08-01

    The Great Calcite Belt (GCB) is a region of elevated surface reflectance in the Southern Ocean (SO) covering 16% of the global ocean and is thought to result from elevated, seasonal concentrations of coccolithophores. Here we describe field observations and experiments from two cruises that crossed the GCB in the Atlantic and Indian sectors of the SO. We confirm the presence of coccolithophores, their coccoliths, and associated optical scattering, located primarily in the region of the subtropical, Agulhas, and Subantarctic frontal regions. Coccolithophore-rich regions were typically associated with high-velocity frontal regions with higher seawater partial pressures of CO2 (pCO2) than the atmosphere, sufficient to reverse the direction of gas exchange to a CO2 source. There was no calcium carbonate (CaCO3) enhancement of particulate organic carbon (POC) export, but there were increased POC transfer efficiencies in high-flux particulate inorganic carbon regions. Contemporaneous observations are synthesized with results of trace-metal incubation experiments, 234Th-based flux estimates, and remotely sensed observations to generate a mandala that summarizes our understanding about the factors that regulate the location of the GCB.

  5. Mineral Surface Rearrangement at High Temperatures: Implications for Extraterrestrial Mineral Grain Reactivity.

    Science.gov (United States)

    King, Helen E; Plümper, Oliver; Putnis, Christine V; O'Neill, Hugh St C; Klemme, Stephan; Putnis, Andrew

    2017-04-20

    Mineral surfaces play a critical role in the solar nebula as a catalytic surface for chemical reactions and potentially acted as a source of water during Earth's accretion by the adsorption of water molecules to the surface of interplanetary dust particles. However, nothing is known about how mineral surfaces respond to short-lived thermal fluctuations that are below the melting temperature of the mineral. Here we show that mineral surfaces react and rearrange within minutes to changes in their local environment despite being far below their melting temperature. Polished surfaces of the rock and planetary dust-forming silicate mineral olivine ((Mg,Fe) 2 SiO 4 ) show significant surface reorganization textures upon rapid heating resulting in surface features up to 40 nm in height observed after annealing at 1200 °C. Thus, high-temperature fluctuations should provide new and highly reactive sites for chemical reactions on nebula mineral particles. Our results also may help to explain discrepancies between short and long diffusion profiles in experiments where diffusion length scales are of the order of 100 nm or less.

  6. Stable calcium isotope composition of a pedogenic carbonate in forested ecosystem: the case of the needle fibre calcite (NFC).

    Science.gov (United States)

    Milliere, Laure; Verrecchia, Eric; Gussone, Nikolaus

    2014-05-01

    Calcium (Ca), carbon (C) and oxygen (O) are important elements in terrestrial environment, as their biogeochemical cycles are directly related to the storage of atmospheric carbon. Nevertheless, contrarily to C and O, Ca isotope composition has been only poorly studied in the terrestrial carbonates. Needle Fibre Calcite (NFC) is one of the most common pedogenic carbonates, unless its origin is still under debate. Recent studies explain its formation by precipitation inside fungal hyphae. Due to this possible biogenic origin, NFC can be considered as a potential bridge between the biochemistry (precipitation inside organic structure) and geochemistry (pedogenic carbonate related to soil conditions) of the Ca. Thus, the study of the Ca isotope composition of NFC seem to be of first interest in order to shed light on the behaviour of Ca in terrestrial environment, especially when precipitation of secondary carbonates is involved. The sampling site is situated in the Swiss Jura Mountains and has been chosen due to a previous complete study of the C and O isotope composition of NFC in relation to the ecosystem, which represent a good precondition for the understanding of the NFC Ca isotope signatures in this context. In this study, the implication of the fungi in the origin of NFC is investigated, by comparing the Ca isotope composition of NFC and a purely physicochemical calcite cement (LCC), both precipitated in the same environment. The δ44Ca signature of NFC and LCC crystals were used to determine possible differences of the precipitation rate during their formation. NFC and LCC have similar δ18O composition and are supposed to precipitate at the same temperature (Milliere et al., 2011a). Thus the study of Ca isotope composition of NFC seems to demonstrate that the elongated shape of the calcite needle can be explained by different precipitation processes than the rhombohedric calcite crystals precipitated in the same environment; and more precisely, the specific

  7. Implications of surface noise for the motional coherence of trapped ions

    Science.gov (United States)

    Talukdar, I.; Gorman, D. J.; Daniilidis, N.; Schindler, P.; Ebadi, S.; Kaufmann, H.; Zhang, T.; Häffner, H.

    2016-04-01

    Electric noise from metallic surfaces is a major obstacle towards quantum applications with trapped ions due to motional heating of the ions. Here, we discuss how the same noise source can also lead to pure dephasing of motional quantum states. The mechanism is particularly relevant at small ion-surface distances, thus imposing a constraint on trap miniaturization. By means of a free induction decay experiment, we measure the dephasing time of the motion of a single ion trapped 50 μ m above a Cu-Al surface. From the dephasing times we extract the integrated noise below the secular frequency of the ion. We find that none of the most commonly discussed surface noise models for ion traps describes both the observed heating as well as the measured dephasing satisfactorily. Thus, our measurements provide a benchmark for future models for the electric noise emitted by metallic surfaces.

  8. Contrasting the surface ocean distribution of bromoform and methyl iodide; implications for boundary layer physics, chemistry and climate

    Energy Technology Data Exchange (ETDEWEB)

    Palmer, C J, E-mail: carl.j.palmer@gmail.co [Department of Oceanography, University of Cape Town, 7701 (South Africa)

    2010-08-15

    Bromoform and methyl iodide are both methane-like hydrocarbons with a halogen atom replacing one or more of the hydrogen atoms. Both of these compounds occur naturally in the environment as a result of their production from seaweed and kelp. They are of interest to climate science as a result of their catalytic destruction of boundary layer ozone (a potent greenhouse gas) and, specifically for methyl iodide, the proposed role in the formation of new cloud condensation nuclei with implications for climate. In this paper, the currently available data on the distribution of bromoform and methyl iodide are analysed and contrasted to show that the concentrations of bromoform and methyl iodide do not correlate, that, in contrast to bromoform, the parameterization of sea surface methyl iodide concentrations demands only the sea surface temperature, and that the pelagic distribution of methyl iodide appears to follow the solar zenith angle. These three observations together suggest that, while the pelagic source of bromoform is mostly biogenic, the source of methyl iodide is photochemical. This has implications for the understanding of planetary boundary layer chemistry and potential organohalogen mediated feedbacks to climate.

  9. Microimpact phenomena on Australasian microtektites: Implications for ejecta plume characteristics and lunar surface processes

    Digital Repository Service at National Institute of Oceanography (India)

    ShyamPrasad, M.; Sudhakar, M.

    and dust, craters generated by projectiles defining an oblique trajectory, high-velocity "pitless" craters, and the conventional hypervelocity craters with well-defined central pits and radial and concentric cracks-found commonly on lunar surface materials...

  10. Soil Surface Sealing Effect on Soil Moisture at a Semiarid Hillslope: Implications for Remote Sensing Estimation

    OpenAIRE

    Shai Sela; Tal Svoray; Shmuel Assouline

    2014-01-01

    Robust estimation of soil moisture using microwave remote sensing depends on extensive ground sampling for calibration and validation of the data. Soil surface sealing is a frequent phenomenon in dry environments. It modulates soil moisture close to the soil surface and, thus, has the potential to affect the retrieval of soil moisture from microwave remote sensing and the validation of these data based on ground observations. We addressed this issue using a physically-based modeling approach...

  11. Anisotropic surface physicochemical properties of spodumene and albite crystals: Implications for flotation separation

    Science.gov (United States)

    Xu, Longhua; Peng, Tiefeng; Tian, Jia; Lu, Zhongyuan; Hu, Yuehua; Sun, Wei

    2017-12-01

    Aluminosilicate minerals (e.g., spodumene, albite) have complex crystal structures and similar surface chemistries, but they have poor selectivity compared to traditional fatty acid collectors, making flotation separation difficult. Previous research has mainly considered the mineral crystal structure as a whole. In contrast, the surface characteristics at the atomic level and the effects of different crystal interfaces on the flotation behavior have rarely been investigated. This study focuses on investigating the surface anisotropy quantitatively, including the chemical bond characteristics, surface energies, and broken bond densities, using density functional theory and classical theoretical calculations. In addition, the anisotropy of the surface wettability and adsorption characteristics were examined using contact angle, zeta potential, and Fourier-transform infrared measurements. Finally, these surface anisotropies with different flotation behaviors were investigated and interpreted using molecular dynamics simulations, scanning electron microscopy, and X-ray photoelectron spectroscopy. This systematic research offers new ideas concerning the selective grinding and stage flotation of aluminosilicate minerals based on the crystal characteristics.

  12. Implications of Adhesion Studies for Dust Mitigation on Thermal Control Surfaces

    Science.gov (United States)

    Gaier, James R.; Berkebile, Stephen P.

    2012-01-01

    Experiments measuring the adhesion forces under ultrahigh vacuum conditions (10 (exp -10) torr) between a synthetic volcanic glass and commonly used space exploration materials have recently been described. The glass has a chemistry and surface structure typical of the lunar regolith. It was found that Van der Waals forces between the glass and common spacecraft materials was negligible. Charge transfer between the materials was induced by mechanically striking the spacecraft material pin against the glass plate. No measurable adhesion occurred when striking the highly conducting materials, however, on striking insulating dielectric materials the adhesion increased dramatically. This indicates that electrostatic forces dominate over Van der Waals forces under these conditions. The presence of small amounts of surface contaminants was found to lower adhesive forces by at least two orders of magnitude, and perhaps more. Both particle and space exploration material surfaces will be cleaned by the interaction with the solar wind and other energetic processes and stay clean because of the extremely high vacuum (10 (exp -12) torr) so the atomically clean adhesion values are probably the relevant ones for the lunar surface environment. These results are used to interpret the results of dust mitigation technology experiments utilizing textured surfaces, work function matching surfaces and brushing. They have also been used to reinterpret the results of the Apollo 14 Thermal Degradation Samples experiment.

  13. Biological implications of the hydrodynamics of swimming at or near the surface and in shallow water

    Energy Technology Data Exchange (ETDEWEB)

    Blake, R W [Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4 (Canada)], E-mail: blake@zoology.ubc.ca

    2009-03-01

    The origins and effects of wave drag at and near the surface and in shallow water are discussed in terms of the dispersive waves generated by streamlined technical bodies of revolution and by semi-aquatic and aquatic animals with a view to bearing on issues regarding the design and function of autonomous surface and underwater vehicles. A simple two-dimensional model based on energy flux, allowing assessment of drag and its associated wave amplitude, is applied to surface swimming in Lesser Scaup ducks and is in good agreement with measured values. It is argued that hydrodynamic limitations to swimming at speeds associated with the critical Froude number ({approx}0.5) and hull speed do not necessarily set biological limitations as most behaviours occur well below the hull speed. From a comparative standpoint, the need for studies on the hull displacement of different forms is emphasized. For forms in surface proximity, drag is a function of both Froude and Reynolds numbers. Whilst the depth dependence of wave drag is not particularly sensitive to Reynolds number, its magnitude is, with smaller and slower forms subject to relatively less drag augmentation than larger, faster forms that generate additional resistance due to ventilation and spray. A quasi-steady approach to the hydrodynamics of swimming in shallow water identifies substantial drag increases relative to the deeply submerged case at Froude numbers of about 0.9 that could limit the performance of semi-aquatic and aquatic animals and autonomous vehicles. A comparative assessment of fast-starting trout and upside down catfish shows that the energy losses of fast-starting fish are likely to be less for fish in surface proximity in deep water than for those in shallow water. Further work on unsteady swimming in both circumstances is encouraged. Finally, perspectives are offered as to how autonomous surface and underwater vehicles in surface proximity and shallow water could function to avoid prohibitive

  14. Calcite veining and feeding conduits in a hydrothermal system: Insights from a natural section across the Pleistocene Gölemezli travertine depositional system (western Anatolia, Turkey)

    Science.gov (United States)

    Capezzuoli, Enrico; Ruggieri, Giovanni; Rimondi, Valentina; Brogi, Andrea; Liotta, Domenico; Alçiçek, Mehmet Cihat; Alçiçek, Hülya; Bülbül, Ali; Gandin, Anna; Meccheri, Marco; Shen, Chuan-Chou; Baykara, Mehmet Oruç

    2018-02-01

    Linking the architecture of structural conduits with the hydrothermal fluids migrating from the reservoir up to the surface is a key-factor in geothermal research. A contribution to this achievement derives from the study of spring-related travertine deposits, but although travertine depositional systems occur widely, their feeding conduits are only rarely exposed. The integrated study carried out in the geothermal Gölemezli area, nearby the well-known Pamukkale area (Denizli Basin, western Anatolia, Turkey), focused on onyx-like calcite veins (banded travertine) and bedded travertine well exposed in a natural cross-section allowing the reconstruction of the shallower part of a geothermal system. The onyx-like veins represent the thickest vein network (> 150 m) so far known. New field mapping and structural/kinematic analyses allowed to document a partially dismantled travertine complex (bedded travertine) formed by proximal fissure ridges and distal terraced/pools depositional systems. The banded calcite veins, WNW-trending and up to 12 m thick, developed within a > 200 m thick damaged rock volume produced by parallel fault zones. Th/U dating indicates a long lasting (middle-late Pleistocene) fluids circulation in a palaeo-geothermal system that, due to its location and chemical characteristics, can be considered the analogue of the nearby, still active, Pamukkale system. The isotopic characteristics of the calcite veins together with data from fluid inclusions analyses, allow the reconstruction of some properties (i.e. temperature, salinity and isotopic composition) and processes (i.e. temperature variation and intensity of degassing) that characterized the parent fluids and the relation between degassing intensity and specific microfabric of calcite crystals (elongated/microsparite-micrite bands), controlled by changes/fluctuations of the physico-chemical fluid characteristics.

  15. Driven by excess? Climatic implications of new global mapping of near-surface water-equivalent hydrogen on Mars

    Science.gov (United States)

    Pathare, Asmin V.; Feldman, William C.; Prettyman, Thomas H.; Maurice, Sylvestre

    2018-02-01

    We present improved Mars Odyssey Neutron Spectrometer (MONS) maps of near-surface Water-Equivalent Hydrogen (WEH) on Mars that have intriguing implications for the global distribution of "excess" ice, which occurs when the mass fraction of water ice exceeds the threshold amount needed to saturate the pore volume in normal soils. We have refined the crossover technique of Feldman et al. (2011) by using spatial deconvolution and Gaussian weighting to create the first globally self-consistent map of WEH. At low latitudes, our new maps indicate that WEH exceeds 15% in several near-equatorial regions, such as Arabia Terra, which has important implications for the types of hydrated minerals present at low latitudes. At high latitudes, we demonstrate that the disparate MONS and Phoenix Robotic Arm (RA) observations of near surface WEH can be reconciled by a three-layer model incorporating dry soil over fully saturated pore ice over pure excess ice: such a three-layer model can also potentially explain the strong anticorrelation of subsurface ice content and ice table depth observed at high latitudes. At moderate latitudes, we show that the distribution of recently formed impact craters is also consistent with our latest MONS results, as both the shallowest ice-exposing crater and deepest non-ice-exposing crater at each impact site are in good agreement with our predictions of near-surface WEH. Overall, we find that our new mapping is consistent with the widespread presence at mid-to-high Martian latitudes of recently deposited shallow excess ice reservoirs that are not yet in equilibrium with the atmosphere.

  16. Surface emission from neutron stars and implications for the physics of their interiors.

    Science.gov (United States)

    Ozel, Feryal

    2013-01-01

    Neutron stars are associated with diverse physical phenomena that take place in conditions characterized by ultrahigh densities as well as intense gravitational, magnetic and radiation fields. Understanding the properties and interactions of matter in these regimes remains one of the challenges in compact object astrophysics. Photons emitted from the surfaces of neutron stars provide direct probes of their structure, composition and magnetic fields. In this review, I discuss in detail the physics that governs the properties of emission from the surfaces of neutron stars and their various observational manifestations. I present the constraints on neutron star radii, core and crust composition, and magnetic field strength and topology obtained from studies of their broadband spectra, evolution of thermal luminosity, and the profiles of pulsations that originate on their surfaces.

  17. Evolution of permeability and microstructure of tight carbonates due to numerical simulation of calcite dissolution

    Science.gov (United States)

    Miller, Kevin; Vanorio, Tiziana; Keehm, Youngseuk

    2017-06-01

    The current study concerns fundamental controls on fluid flow in tight carbonate rocks undergoing CO2 injection. Tight carbonates exposed to weak carbonic acid exhibit order of magnitude changes in permeability while maintaining a nearly constant porosity with respect to the porosity of the unreacted sample. This study aims to determine—if not porosity—what are the microstructural changes that control permeability evolution in these rocks? Given the pore-scale nature of chemical reactions, we took a digital rock physics approach. Tight carbonate mudstone was imaged using X-ray microcomputed tomography. We simulated calcite dissolution using a phenomenological numerical model that stands from experimental and microstructural observations under transport-limited reaction conditions. Fluid flow was simulated using the lattice-Boltzmann method, and the pore wall was adaptively eroded at a rate determined by the local surface area and velocity magnitude, which we use in place of solvent flux. We identified preexisting, high-conductivity fluid pathways imprinted in the initial microstructure. Though these pathways comprise a subset of the total connected porosity, they accommodated 80 to 99% of the volumetric flux through the digital sample and localized dissolution. Porosity-permeability evolution exhibited two stages: selective widening of narrow pore throats that comprised preferential pathways and development and widening of channels. We quantitatively monitored attributes of the pore geometry, namely, porosity, specific surface area, tortuosity, and average hydraulic diameter, which we qualitatively linked to permeability. This study gives a pore-scale perspective on the microstructural origins of laboratory permeability-porosity trends of tight carbonates undergoing transport-limited reaction with CO2-rich fluid.

  18. Subsurface Emission Effects in AMSR-E Measurements: Implications for Land Surface Microwave Emissivity Retrieval

    Science.gov (United States)

    Galantowicz, John F.; Moncet, Jean-Luc; Liang, Pan; Lipton, Alan E.; Uymin, Gennady; Prigent, Catherine; Grassotti, Christopher

    2011-01-01

    An analysis of land surface microwave emission time series shows that the characteristic diurnal signature associated with subsurface emission in sandy deserts carry over to arid and semi-arid region worldwide. Prior work found that diurnal variation of Special Sensor Microwave/Imager (SSM/I) brightness temperatures in deserts was small relative to International Satellite Cloud Climatology Project land surface temperature (LST) variation and that the difference varied with surface type and was largest in sand sea regions. Here we find more widespread subsurface emission effects in Advanced Microwave Scanning Radiometer-EOS (AMSR-E) measurements. The AMSR-E orbit has equator crossing times near 01:30 and 13 :30 local time, resulting in sampling when near-surface temperature gradients are likely to be large and amplifying the influence of emission depth on effective emitting temperature relative to other factors. AMSR-E measurements are also temporally coincident with Moderate Resolution Imaging Spectroradiometer (MODIS) LST measurements, eliminating time lag as a source of LST uncertainty and reducing LST errors due to undetected clouds. This paper presents monthly global emissivity and emission depth index retrievals for 2003 at 11, 19, 37, and 89 GHz from AMSR-E, MODIS, and SSM/I time series data. Retrieval model fit error, stability, self-consistency, and land surface modeling results provide evidence for the validity of the subsurface emission hypothesis and the retrieval approach. An analysis of emission depth index, emissivity, precipitation, and vegetation index seasonal trends in northern and southern Africa suggests that changes in the emission depth index may be tied to changes in land surface moisture and vegetation conditions

  19. Cell surface reactivity of Synechococcus sp. PCC 7002: Implications for metal sorption from seawater

    Science.gov (United States)

    Liu, Yuxia; Alessi, D. S.; Owttrim, G. W.; Petrash, D. A.; Mloszewska, A. M.; Lalonde, S. V.; Martinez, R. E.; Zhou, Qixing; Konhauser, K. O.

    2015-11-01

    The past two decades have seen a significant advancement in our understanding of bacterial surface chemistry and the ability of microbes to bind metals from aqueous solutions. Much of this work has been aimed at benthic, mat-forming species in an effort to model the mechanisms by which microbes may exert control over metal contaminant transport in soils and groundwater. However, there is a distinct paucity of information pertaining to the surface chemistry of marine planktonic species, and their ability to bind trace metals from the ocean's photic zone. To this end, the surface properties of the cyanobacterium Synechococcus sp. PCC 7002 were studied as this genus is one of the dominant marine phytoplankton, and as such, contributes significantly to metal cycling in the ocean's photic zone. Zeta potential measurement indicates that the cell surfaces display a net negative charge. This was supported by potentiometric titration and Fourier transform infrared spectroscopy analyses demonstrating that the cells are dominated by surface proton releasing ligands, including carboxyl, phosphoryl and amino functional groups, with a total ligand density of 34.18 ± 1.62 mmol/g (dry biomass). Cd adsorption experiments further reveal that carboxyl groups play a primary role in metal adsorption, with 1.0 g of dry biomass binding an equivalent of 7.05 × 10-5 M of Cd from solution at pH = 8. To put this value into context, in 1 L of seawater, and with an open-ocean population of Synechococcus of 105 cells/mL in the photic zone, approximately 10 nmol of Cd could potentially be adsorbed by the cyanobacteria; an amount equivalent to seawater Cd concentrations. Although we have only focused on one microbial species and one metal cation, and we have not considered trace element assimilation, our results highlight the potential role of surface sorption by phytoplankton in the cycling of metals in the ocean.

  20. Tailoring biomaterial surface properties to modulate host-implant interactions: implication in cardiovascular and bone therapy.

    Science.gov (United States)

    Pacelli, Settimio; Manoharan, Vijayan; Desalvo, Anna; Lomis, Nikita; Jodha, Kartikeya Singh; Prakash, Satya; Paul, Arghya

    Host body response to a foreign medical device plays a critical role in defining its fate post implantation. It is thus important to control host-material interactions by designing innovative implant surfaces. In the recent years, biochemical and topographical features have been explored as main target to produce this new type of bioinert or bioresponsive implants. The review discusses specific biofunctional materials and strategies to achieve a precise control over implant surface properties and presents possible solutions to develop next generation of implants, particularly in the fields of bone and cardiovascular therapy.

  1. Ozone-surface interactions: Investigations of mechanisms, kinetics, mass transport, and implications for indoor air quality

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, Glenn Charles [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    In this dissertation, results are presented of laboratory investigations and mathematical modeling efforts designed to better understand the interactions of ozone with surfaces. In the laboratory, carpet and duct materials were exposed to ozone and measured ozone uptake kinetics and the ozone induced emissions of volatile organic compounds. To understand the results of the experiments, mathematical methods were developed to describe dynamic indoor aldehyde concentrations, mass transport of reactive species to smooth surfaces, the equivalent reaction probability of whole carpet due to the surface reactivity of fibers and carpet backing, and ozone aging of surfaces. Carpets, separated carpet fibers, and separated carpet backing all tended to release aldehydes when exposed to ozone. Secondary emissions were mostly n-nonanal and several other smaller aldehydes. The pattern of emissions suggested that vegetable oils may be precursors for these oxidized emissions. Several possible precursors and experiments in which linseed and tung oils were tested for their secondary emission potential were discussed. Dynamic emission rates of 2-nonenal from a residential carpet may indicate that intermediate species in the oxidation of conjugated olefins can significantly delay aldehyde emissions and act as reservoir for these compounds. The ozone induced emission rate of 2-nonenal, a very odorous compound, can result in odorous indoor concentrations for several years. Surface ozone reactivity is a key parameter in determining the flux of ozone to a surface, is parameterized by the reaction probability, which is simply the probability that an ozone molecule will be irreversibly consumed when it strikes a surface. In laboratory studies of two residential and two commercial carpets, the ozone reaction probability for carpet fibers, carpet backing and the equivalent reaction probability for whole carpet were determined. Typically reaction probability values for these materials were 10

  2. The influence of surface area, porous structure, and surface state on the supercapacitor performance of titanium oxynitride: implications for a nanostructuring strategy.

    Science.gov (United States)

    Lee, Eun Joo; Lee, Lanlee; Abbas, Muhammad Awais; Bang, Jin Ho

    2017-08-09

    A recent surge of interest in metal (oxy)nitride materials for energy storage devices has given rise to the rapid development of various nanostructuring strategies for these materials. In supercapacitor applications, early transition metal (oxy)nitrides have been extensively explored, among which titanium oxynitride stands out due to its great potential for charge storage. Despite recent advances in supercapacitors based on titanium oxynitride, many underlying factors governing their capacitive performance remain elusive. In this work, nanostructured titanium oxynitride is prepared by firing an organic-inorganic hybrid precursor under a hot ammonia atmosphere, and the influence of its physical characteristics on the supercapacitor performance is investigated. New insights into the effects of surface area, porous structure, and surface state of titanium oxynitride on the supercapacitor performance are revealed through which a comprehensive understanding about the capacitive behavior of titanium oxynitride is provided. In addition, the implications of these insights for a nanostructuring strategy striving for higher capacitance and improved stability are discussed.

  3. Characterizing heavy metal build-up on urban road surfaces: Implication for stormwater reuse

    Energy Technology Data Exchange (ETDEWEB)

    Liu, An [Research Centre of Environmental Engineering and Management, Graduate School at Shenzhen, Tsinghua University, 518055 Shenzhen (China); Cooperative Research and Education Centre for Environmental Technology, Kyoto University–Tsinghua University, 518055 Shenzhen (China); Liu, Liang; Li, Dunzhu [Research Centre of Environmental Engineering and Management, Graduate School at Shenzhen, Tsinghua University, 518055 Shenzhen (China); Guan, Yuntao, E-mail: guanyt@tsinghua.edu.cn [Research Centre of Environmental Engineering and Management, Graduate School at Shenzhen, Tsinghua University, 518055 Shenzhen (China); School of Environment, Tsinghua University, Beijing 100084 (China)

    2015-05-15

    Stormwater reuse is increasingly popular in the worldwide. In terms of urban road stormwater, it commonly contains toxic pollutants such as heavy metals, which could undermine the reuse safety. The research study investigated heavy metal build-up characteristics on urban roads in a typical megacity of South China. The research outcomes show the high variability in heavy metal build-up loads among different urban road sites. The degree of traffic congestion and road surface roughness was found to exert a more significant influence on heavy metal build-up rather than traffic volume. Due to relatively higher heavy metal loads, stormwater from roads with more congested traffic conditions or rougher surfaces might be suitable for low-water-quality required activities while the stormwater from by-pass road sections could be appropriate for relatively high-water-quality required purposes since the stormwater could be relatively less polluted. Based on the research outcomes, a decision-making process for heavy metals based urban road stormwater reuse was proposed. The new finding highlights the importance to undertaking a “fit-for-purpose” road stormwater reuse strategy. Additionally, the research results can also contribute to enhancing stormwater reuse safety. - Highlights: • Heavy metal (HM) build-up varies with traffic and road surface conditions. • Traffic congestion and surface roughness exert a higher impact on HM build-up. • A “fit-for-purpose” strategy could suit urban road stormwater reuse.

  4. THE TULLY-FISHER RELATION FOR LOW SURFACE BRIGHTNESS GALAXIES - IMPLICATIONS FOR GALAXY EVOLUTION

    NARCIS (Netherlands)

    Zwaan, M.A.; VAN DER HULST, JM; DE BLOK, WJG; MCGAUGH, SS

    1995-01-01

    We present the B-band Tully-Fisher relation for low surface brightness (LSB) galaxies. These LSB galaxies follow the same Tully-Fisher relation as normal spiral galaxies. This implies that the mass-to-light ratio (M/L) of LSB galaxies is typically a factor of 2 larger than that of normal galaxies of

  5. IMPLICATIONS OF MICROBIAL ADHESION TO HYDROCARBONS FOR EVALUATING CELL-SURFACE HYDROPHOBICITY .2. ADHESION MECHANISMS

    NARCIS (Netherlands)

    VANDERMEI, HC; VANDEBELTGRITTER, B; BUSSCHER, HJ

    1995-01-01

    Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. Recent observations that the zeta potentials of hydrocarbons can be highly negative in the various solutions commonly used in MATH, have suggested that MATH may measure a

  6. Microbial dissolution of calcite at T = 28 °C and ambient pCO 2

    Science.gov (United States)

    Jacobson, Andrew D.; Wu, Lingling

    2009-04-01

    This study used batch reactors to quantify the mechanisms and rates of calcite dissolution in the presence and absence of a single heterotrophic bacterial species ( Burkholderia fungorum). Experiments were conducted at T = 28°C and ambient pCO 2 over time periods spanning either 21 or 35 days. Bacteria were supplied with minimal growth media containing either glucose or lactate as a C source, NH 4+ as an N source, and H 2PO 4- as a P source. Combining stoichiometric equations for microbial growth with an equilibrium mass-balance model of the H 2O-CO 2-CaCO 3 system demonstrates that B. fungorum affected calcite dissolution by modifying pH and alkalinity during utilization of ionic N and C species. Uptake of NH 4+ decreased pH and alkalinity, whereas utilization of lactate, a negatively charged organic anion, increased pH and alkalinity. Calcite in biotic glucose-bearing reactors dissolved by simultaneous reaction with H 2CO 3 generated by dissolution of atmospheric CO 2 (H 2CO 3 + CaCO 3 → Ca 2+ + 2HCO 3-) and H + released during NH 4+ uptake (H + + CaCO 3 → Ca 2+ + HCO 3-). Reaction with H 2CO 3 and H + supplied ˜45% and 55% of the total Ca 2+ and ˜60% and 40% of the total HCO 3-, respectively. The net rate of microbial calcite dissolution in the presence of glucose and NH 4+ was ˜2-fold higher than that observed for abiotic control experiments where calcite dissolved only by reaction with H 2CO 3. In lactate bearing reactors, most H + generated by NH 4+ uptake reacted with HCO 3- produced by lactate oxidation to yield CO 2 and H 2O. Hence, calcite in biotic lactate-bearing reactors dissolved by reaction with H 2CO 3 at a net rate equivalent to that calculated for abiotic control experiments. This study suggests that conventional carbonate equilibria models can satisfactorily predict the bulk fluid chemistry resulting from microbe-calcite interactions, provided that the ionic forms and extent of utilization of N and C sources can be constrained. Because

  7. 88Sr/86Sr fractionation and calcite accumulation rate in the Sea of Galilee

    Science.gov (United States)

    Fruchter, Noa; Lazar, Boaz; Nishri, Aminadav; Almogi-Labin, Ahuva; Eisenhauer, Anton; Beeri-Shlevin, Yaron; Stein, Mordechai

    2017-04-01

    This study uses Lake Kinneret (Sea of Galilee, northern Israel) as a natural laboratory to investigate the fractionation of the stable Sr isotope ratio (88Sr/86Sr) during precipitation of authigenic calcite in the water column, and evaluates the dependence of the fractionation 87Sr/86Sr and 88Sr/86Sr ratios in the freshwater and brines that enter the lake are used to calculate the relative contributions of these sources to the Sr budget of the modern lake. The 87Sr/86Sr and 88Sr/86Sr ratios were measured in authigenic calcite, living Melanopsis shells, lake water and various water sources to the lake. While the lake's 87Sr/86Sr ratios are determined by the mixture of freshwater supplied mainly by the Jordan River and saline springs, the 88Sr/86Sr ratios of the lake reflect a more complex mass balance that includes the effect of isotopic fractionation during the precipitation of authigenic calcite. The data show a significant long-term effect of calcite accumulation on the stable Sr isotope ratio of the lake, increasing the 88Sr/86Sr of the water by 0.04 ‰. In contrast to the authigenic calcite, biogenic aragonite shells are shown to have a rather constant 88Sr/86Sr water-CaCO3 fractionation of precipitation of coralline and chemical aragonite from seawater and the precipitation of authigenic calcite from various continental waters. The field data of the present study suggests that the fractionation of 88Sr/86Sr in authigenic calcite represents a kinetic fractionation that varies with precipitation rate, in addition to the constant thermodynamic property. Massive precipitation of authigenic calcite occurs in Lake Kinneret during the spring phytoplankton bloom as the latter increases considerably the degree of calcite saturation. The correlation between accumulation rate can be therefore used as a tool to reconstruct paleo-environmental variations by analyzing the 88Sr/86Sr ratio in authigenic CaCO3 in core sections.

  8. Saturn's Titan: Surface change, ammonia, and implications for atmospheric and tectonic activity

    Science.gov (United States)

    Nelson, R.M.; Kamp, L.W.; Matson, D.L.; Irwin, P.G.J.; Baines, K.H.; Boryta, M.D.; Leader, F.E.; Jaumann, R.; Smythe, W.D.; Sotin, Christophe; Clark, R.N.; Cruikshank, D.P.; Drossart, P.; Pearl, J.C.; Hapke, B.W.; Lunine, J.; Combes, M.; Bellucci, G.; Bibring, J.-P.; Capaccioni, F.; Cerroni, P.; Coradini, A.; Formisano, V.; Filacchione, G.; Langevin, R.Y.; McCord, T.B.; Mennella, V.; Nicholson, P.D.; Sicardy, B.

    2009-01-01

    Titan is known to have a young surface. Here we present evidence from the Cassini Visual and Infrared Mapping Spectrometer that it is currently geologically active. We report that changes in the near-infrared reflectance of a 73,000 km2 area on Titan (latitude 26° S, longitude 78° W) occurred between July 2004 and March of 2006. The reflectance of the area increased by a factor of two between July 2004 and March–April 2005; it then returned to the July 2004 level by November 2005. By late December 2005 the reflectance had surged upward again, establishing a new maximum. Thereafter, it trended downward for the next three months. Detailed spectrophotometric analyses suggest these changes happen at or very near the surface. The spectral differences between the region and its surroundings rule out changes in the distribution of the ices of reasonably expected materials such as H2O, CO2, and CH4 as possible causes. Remarkably, the change is spectrally consistent with the deposition and removal of NH3 frost over a water ice substrate. NH3 has been proposed as a constituent of Titan's interior and has never been reported on the surface. The detection of NH3 frost on the surface might possibly be explained by episodic effusive events occur which bring juvenile ammonia from the interior to the surface. If so, its decomposition would feed nitrogen to the atmosphere now and in the future. The lateral extent of the region exceeds that of active areas on the Earth (Hawaii) or Io (Loki).

  9. Nickel Alloy Primary Water Bulk Surface and SCC Corrosion Film Analytical Characterization and SCC Mechanistic Implications

    Energy Technology Data Exchange (ETDEWEB)

    Morton, D.; Lewis, N.; Hanson, M.; Rice, S.; Sanders, P.

    2007-04-18

    Alloy 600 corrosion coupon tests were performed: (1) to quantify the temperature dependency of general corrosion and (2) to characterize the composition and structure of bulk surface corrosion films for comparison with ongoing primary water SCC (PWSCC) crack tip corrosion film analyses. Results suggest that the thermal activation energy of Alloy 600 corrosion is consistent with the thermal activation energy of nickel alloy PWSCC. Analytical investigations of the structure and composition of Alloy 600 bulk surface corrosion oxides revealed a duplex (inner and outer) oxide layer structure. The outer layer is discontinuous and comprised of relatively large (1 to 3 {micro}m) nickel ferrite crystals and smaller ({approx}0.1 {micro}m) chromium containing nickel ferrite crystals. The inner layer consists of a relatively continuous chromite spinel (major phase) and chromia (Cr{sub 2}O{sub 3} minor phase) which formed through non-selective oxidation. Chromia and dealloyed Alloy 600 (highly Ni enriched metal) were only observed at 337 C (640 F) and only along the boundaries of deformation induced fine grains and subcells. Specimens having deformation free surfaces exhibited continuous uniform inner chromite spinel oxide layers. Specimens with machining induced surface deformation produced non-uniform inner layer oxides (chromite spinel, Cr{sub 2}O{sub 3} and unoxidized material). PWSCC crack tip oxides, in contrast, were fine grain (no duplex structure) and consisted of both chromium rich spinels and ''NiO'' structure oxides. Generally, nickel rich oxides were more abundant under more oxidized conditions (reduced coolant hydrogen) and spinel rich crack tip oxides were favored under more reducing conditions (increased coolant hydrogen). Bulk surface corrosion film thickness did not correlate with observed SCC growth rates. These results suggest that corrosion is not the rate controlling step of PWSCC but rather that PWSCC and corrosion have a common rate

  10. Soil Surface Sealing Effect on Soil Moisture at a Semiarid Hillslope: Implications for Remote Sensing Estimation

    Directory of Open Access Journals (Sweden)

    Shai Sela

    2014-08-01

    Full Text Available Robust estimation of soil moisture using microwave remote sensing depends on extensive ground sampling for calibration and validation of the data. Soil surface sealing is a frequent phenomenon in dry environments. It modulates soil moisture close to the soil surface and, thus, has the potential to affect the retrieval of soil moisture from microwave remote sensing and the validation of these data based on ground observations. We addressed this issue using a physically-based modeling approach that accounts explicitly for surface sealing at the hillslope scale. Simulated mean soil moisture at the respective layers corresponding to both the ground validation probe and the radar beam’s typical effective penetration depth were considered. A cyclic pattern was found in which, as compared to an unsealed profile, the seal layer intensifies the bias in validation during rainfall events and substantially reduces it during subsequent drying periods. The analysis of this cyclic pattern showed that, accounting for soil moisture dynamics at the soil surface, the optimal time for soil sampling following a rainfall event is a few hours in the case of an unsealed system and a few days in the case of a sealed one. Surface sealing was found to increase the temporal stability of soil moisture. In both sealed and unsealed systems, the greatest temporal stability was observed at positions with moderate slope inclination. Soil porosity was the best predictor of soil moisture temporal stability, indicating that prior knowledge regarding the soil texture distribution is crucial for the application of remote sensing validation schemes.

  11. Modeling results of calcium-containing minerals precipitation in the alkaline hydrotherms of Baikal Rift Zone: calcite and dolomite

    OpenAIRE

    Tokarenko, Olga Grigorievna; Zippa, E. V.

    2015-01-01

    The calculation modeling results of the nitric hydrotherms saturation in Baikal Rift Zone with calcite and dolomite are presented. The calcite and dolomite make the carbonate barrier to thermal waters equilibrium with primary minerals of igneous rocks. In the research territory, there are three main types of geochemical thermal waters which are characterized by the saturation degree with the calcite and dolomite and the proportion of precipitating minerals phases. It has been established that...

  12. Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve Pecten maximus

    OpenAIRE

    A. Lorrain; Gillikin, D. P.; Paulet, Y.-M.; Chauvaud, L.; Le Mercier, A.; Navez, J.; André, L.

    2005-01-01

    Although Sr/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report Sr/Ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve Pecten maximus (age class I). Ratios of Sr/Ca were found to be variable among individuals that grew at the same location, illustrating that vital effects dominate over environmental controls. Although da...

  13. Oxygen isotope fractionation processes in the water-calcite-aragonite system

    Science.gov (United States)

    Fohlmeister, Jens; Spötl, Christoph; Plessen, Birgit; Tjallingii, Rik; Schröder-Ritzrau, Andrea; Frank, Norbert; Arps, Jennifer; Leutz, Kathrin; Vollweiler, Nicole; Trüssel, Martin

    2017-04-01

    The O isotopic composition of speleothems in their pure calcite or pure aragonite polymorphs provides valuable insight into past climate variability. However, robust climatic interpretations become difficult when both polymorphs are present either in different growth layers or as intergrown fabrics. Experimental studies show that the O isotope fractionation between the dissolved carbonate species and CaCO3 is about 0.75‰ (at 10°C) larger for aragonite than for calcite (e.g., Kim et al., 2007, Kim and O'Neil, 1997). The temperature dependence of this offset is negligible for temperature variations typical of most cave systems. However, cave analogue experiments examining this offset are still lacking. Here, we present stable O isotope measurements of a Holocene speleothem from the Swiss Alps, which shows exactly one calcite-aragonite transition along individual growth layers. Oxygen isotope measurements along 'Hendy test'-like traverses across those transitions provide insight into the fractionation behavior of the water-calcite vs. water-aragonite system. We observed a fractionation offset smaller than predicted by laboratory experiments that varies by at least a factor of two. In addition, the observed variations correlate positively with growth rate and negatively with the isotopic composition of the calcite precipitating at the growth axis. The reason for this behavior is still unclear. Trace element analyses across the transitions of growth layers are planned to help understanding this pattern.

  14. Mechanism of Calcite Co-Orientation in the Sea Urchin Tooth

    Energy Technology Data Exchange (ETDEWEB)

    Killian, Christopher; Metzler, Rebecca; Gong, Y. U. T.; Olson, Ian; Aizenberg, Joanna; Politi, Yael; Wilt, Fred; Scholl, Andreas; Young, Anthony; Doran, Andrew; Kunz, Martin; Tamura, Nobumichi; Coppersmith, Susan; Gilbert, P. U. P. A.

    2009-12-01

    Sea urchin teeth are remarkable and complex calcite structures, continuously growing at the forming end and self-sharpening at the mature grinding tip. The calcite (CaCO{sub 3}) crystals of tooth components, plates, fibers, and a high-Mg polycrystalline matrix, have highly co-oriented crystallographic axes. This ability to co-orient calcite in a mineralized structure is shared by all echinoderms. However, the physico-chemical mechanism by which calcite crystals become co-oriented in echinoderms remains enigmatic. Here, we show differences in calcite c-axis orientations in the tooth of the purple sea urchin (Strongylocentrotus purpuratus), using high-resolution X-ray photoelectron emission spectromicroscopy (X-PEEM) and microbeam X-ray diffraction ({mu}XRD). All plates share one crystal orientation, propagated through pillar bridges, while fibers and polycrystalline matrix share another orientation. Furthermore, in the forming end of the tooth, we observe that CaCO{sub 3} is present as amorphous calcium carbonate (ACC). We demonstrate that co-orientation of the nanoparticles in the polycrystalline matrix occurs via solid-state secondary nucleation, propagating out from the previously formed fibers and plates, into the amorphous precursor nanoparticles. Because amorphous precursors were observed in diverse biominerals, solid-state secondary nucleation is likely to be a general mechanism for the co-orientation of biomineral components in organisms from different phyla.

  15. Influence of calcite on uranium(VI) reactive transport in the groundwater-river mixing zone.

    Science.gov (United States)

    Ma, Rui; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John; Zheng, Chunmiao

    2014-01-01

    Calcite is an important, relatively soluble mineral phase that can affect uranium reactive transport in subsurface sediments. This study was conducted to investigate the distribution of calcite and its influence on uranium adsorption and reactive transport in the groundwater-river mixing zone of the Hanford 300A site, Washington State. Simulations using a two-dimensional (2D) reactive transport model under field-relevant hydrological and hydrogeochemical conditions revealed the development of a calcite reaction front through the mixing zone as a result of dynamic groundwater-river interactions. The calcite concentration distribution, in turn, affected the concentrations of aqueous carbonate and calcium, and pH through dissolution, as river waters intruded and receded from the site at different velocities in response to stage changes. The composition variations in groundwater subsequently influenced uranium mobility and discharge rates into the river in a complex fashion. The results implied that calcite distribution and concentration are important variables that need to be quantified for accurate reactive transport predictions of uranium, especially in dynamic groundwater-river mixing zones. © 2013.

  16. Extenstional terrain formation in icy satellites: Implications for ocean-surface interaction

    Science.gov (United States)

    Howell, Samuel M.; Pappalardo, Robert T.

    2017-10-01

    Europa and Ganymede, Galilean satellites of Jupiter, exhibit geologic activity in their outer H2O ice shells that might convey material from water oceans within the satellites to their surfaces. Imagery from the Voyager and Galileo spacecraft reveal surfaces rich with tectonic deformation, including dilational bands on Europa and groove lanes on Ganymede. These features are generally attributed to the extension of a brittle ice lithosphere overlaying a possibly convecting ice asthenosphere. To explore band formation and interaction with interior oceans, we employ fully visco-elasto-plastic 2-D models of faulting and convection with complex, realistic pure ice rheologies. In these models, material entering from below is tracked and considered to be “fossilized ocean,” ocean material that has frozen into the ice shell and evolves through geologic time. We track the volume fraction of fossil ocean material in the ice shell as a function of depth, and the exposure of both fresh ice and fossil ocean material at the ice shell surface. To explore the range in extensional terrains, we vary ice shell thickness, fault localization, melting-temperature ice viscosity, and the presence of pre-existing weaknesses. Mechanisms which act to weaken the ice shell and thin the lithosphere (e.g. vigorous convection, thinner shells, pre-existing weaknesses) tend to plastically yield to form smooth bands at high strains, and are more likely to incorporate fossil ocean material in the ice shell and expose it at the surface. In contrast, lithosphere strengthened by rapid fault annealing or increased viscosity, for example, exhibits large-scale tectonic rifting at low strains superimposed over pre-existing terrains, and inhibits the incorporation and delivery of fossil ocean material to the surface. Thus, our results identify a spectrum of extensional terrain formation mechanisms as linked to lithospheric strength, rather than specific mechanisms that are unique to each type of band

  17. Electrolyte layering at the calcite(104)-water interface indicated by Rb+- and Se(VI) K-edge resonant interface diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Heberling, F.; Eng, P.; Denecke, M. A.; Lützenkirchen, J.; Geckeis, H. [Karlsruher; (Manchester); (UC)

    2014-09-22

    Calcite–water interface reactions are of major importance in various environmental settings as well as in industrial applications. Here we present resonant interface diffraction results on the calcite(104)–aqueous solution interface, measured in solutions containing either 10 mmol L-1 RbCl or 0.5 mmol L-1 Se(VI). Results indicate that Rb+ ions enter the surface adsorbed water layers and adsorb at the calcite(104)–water interface in an inner-sphere fashion. A detailed analysis based on specular and off-specular resonant interface diffraction data reveals three distinct Rb+ adsorption species: one 1.2 Å above the surface, the second associated with surface adsorbed water molecules 3.2 Å above the surface, and the third adsorbed in an outer-sphere fashion 5.6 Å above the surface. A peak in resonant amplitude between L = 1.5 and L = 3.0 is interpreted as signal from a layered electrolyte structure. The presence of a layered electrolyte structure seems to be confirmed by data measured in the presence of Se(VI).

  18. Modeling results of calcium-containing minerals precipitation in the alkaline hydrotherms of Baikal Rift Zone: calcite and dolomite

    Science.gov (United States)

    Tokarenko, O. G.; Zippa, E. V.

    2015-11-01

    The calculation modeling results of the nitric hydrotherms saturation in Baikal Rift Zone with calcite and dolomite are presented. The calcite and dolomite make the carbonate barrier to thermal waters equilibrium with primary minerals of igneous rocks. In the research territory, there are three main types of geochemical thermal waters which are characterized by the saturation degree with the calcite and dolomite and the proportion of precipitating minerals phases. It has been established that nitric thermal waters-rock system has equilibrium with these minerals, which leads to bonding migrated from the rocks calcium and magnesium by the secondary formed minerals - calcite and dolomite.

  19. Use of multiple attributes decision-making Technique for Order Preference by Similarity to Ideal Solution (TOPSIS for Ghare-Gheshlagh calcite in determination of optimum geochemical sampling sites

    Directory of Open Access Journals (Sweden)

    Mansour Rezaei Azizi

    2015-04-01

    Full Text Available Introduction Several valuable calcite deposits are located in Ghare-Gheshlagh, south basin of Urmia Lake, NW Iran. Ghare-Gheshlagh area is situated in the northern part of tectono-sedimentary unit, forming NW part of Tertiary Sanandaj-Sirjan geological belt (Stocklin and Nabavi, 1972. The predominant rock types of the area include light color limestones (Qom Formation and Quaternary alluviums and underlined dolomite in depth (Eftekharnejhad, 1973. The thickness of these units varies between 10 cm and 6 meters and up to some hundred meters in length. In the present study, the effect of geochemical parameters responsible for precipitating calcite from the carbonate aqueous fluids is interpreted by the TOPSIS method to find the most preferable sampling sites and geochemical data. Materials and Methods A total of 20 samples were taken from a NE-SW trending profile including 15 calcites of fresh surface outcrops (5 samples per each colored calcite units in order to determine the nature of the rocks. The mineral assemblages were analyzed by optical methods in combination with XRD powder diffraction analysis. Major elements were determined by X-Ray Fluorescence Spectrometry (XRF, trace and rare earth elements were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS in Geological Survey of Iran. Results The abundances of trace elements were normalized to the continental crust values (Taylor and McLennan, 1981. The green calcite revealed enrichment in Rb and Sr, while green and white calcite were enriched in U. The U enrichment in the green calcite indicates the reduction condition of deposition. Incompatible elements such as Ba, Th, Nb and P depleted in all calcites. Varying the Sr/Ba value between 3.18 and 5.21% indicates the continental deposition environment and non-magmatic waters as well (Cheng et al., 2013. The Sr2+ content of calcites varies from 123 to 427 ppm, indicates suitable condition for calcite precipitation. Eu anomalies

  20. Surface properties of the Orgueil meteorite - Implications for the early history of solar system volatiles

    Science.gov (United States)

    Fanale, F. P.; Cannon, W. A.

    1974-01-01

    The Kr and H2O adsorption properties of Orgueil were studied. Dehydration by stepwise calcination produced a tenfold change in its B.E.T. surface area, which increased to 120 and then fell to 40 square meters per gram. Water exchangeability was measured by water regain from lab air between calcination cycles. Dehydration at room temperature showed that Orgueil contained 6 per cent by weight of water adsorbed on free surfaces. These results are consistent with an identification of Orgueil as montmorillonite, although chemical data conflict with this. High D/H ratios in CI carbonaceous chondrites may result from D enrichment in OH- groups during equilibration of dispersed phyllosilicate dust with preplanetary nebula gas at temperatures much less than 0 C.

  1. Horizontal transfer of antibiotic resistance genes on abiotic touch surfaces: implications for public health.

    Science.gov (United States)

    Warnes, Sarah L; Highmore, Callum J; Keevil, C William

    2012-11-27

    Horizontal gene transfer (HGT) is largely responsible for increasing the incidence of antibiotic-resistant infections worldwide. While studies have focused on HGT in vivo, this work investigates whether the ability of pathogens to persist in the environment, particularly on touch surfaces, may also play an important role. Escherichia coli, virulent clone ST131, and Klebsiella pneumoniae harboring extended-spectrum-β-lactamase (ESBL) bla(CTX-M-15) and metallo-β-lactamase bla(NDM-1), respectively, exhibited prolonged survival on stainless steel, with approximately 10(4) viable cells remaining from an inoculum of 10(7) CFU per cm(2) after 1 month at 21°C. HGT of bla to an antibiotic-sensitive but azide-resistant recipient E. coli strain occurred on stainless steel dry touch surfaces and in suspension but not on dry copper. The conjugation frequency was approximately 10 to 50 times greater and occurred immediately, and resulting transconjugants were more stable with ESBL E. coli as the donor cell than with K. pneumoniae, but bla(NDM-1) transfer increased with time. Transconjugants also exhibited the same resistance profile as the donor, suggesting multiple gene transfer. Rapid death, inhibition of respiration, and destruction of genomic and plasmid DNA of both pathogens occurred on copper alloys accompanied by a reduction in bla copy number. Naked E. coli DNA degraded on copper at 21°C and 37°C but slowly at 4°C, suggesting a direct role for the metal. Persistence of viable pathogenic bacteria on touch surfaces may not only increase the risk of infection transmission but may also contribute to the spread of antibiotic resistance by HGT. The use of copper alloys as antimicrobial touch surfaces may help reduce infection and HGT. Horizontal gene transfer (HGT) conferring resistance to many classes of antimicrobials has resulted in a worldwide epidemic of nosocomial and community infections caused by multidrug-resistant microorganisms, leading to suggestions that we

  2. Modelling interstellar physics and chemistry: implications for surface and solid-state processes.

    Science.gov (United States)

    Williams, David; Viti, Serena

    2013-07-13

    We discuss several types of regions in the interstellar medium of the Milky Way and other galaxies in which the chemistry appears to be influenced or dominated by surface and solid-state processes occurring on or in interstellar dust grains. For some of these processes, for example, the formation of H₂ molecules, detailed experimental and theoretical approaches have provided excellent fundamental data for incorporation into astrochemical models. In other cases, there is an astrochemical requirement for much more laboratory and computational study, and we highlight these needs in our description. Nevertheless, in spite of the limitations of the data, it is possible to infer from astrochemical modelling that surface and solid-state processes play a crucial role in astronomical chemistry from early epochs of the Universe up to the present day.

  3. Monthly summaries of merchant ship surface marine observations and implications for climate variability studies

    Science.gov (United States)

    Michaud, Réjean; Lin, Charles A.

    1992-02-01

    We compute the interannual fluctuations of the surface heat budget of the North Atlantic using the trimmed monthly summaries of the Comprehensive Ocean-Atmosphere DataSet (COADS) for the period 1950 1979. The presence of long-period trends in the heat budget imply large variations of the northward cross-equatorial heat transport over the years. To assess the reliability of these variations, we compare the COADS climate signal to that derived from the ocean weather stations (OWSs) of the North Atlantic. The sea surface temperature, air temperature and sea level pressure show good correlation between the anomaly time series derived from the merchant ship monthly summaries of COADS, and those derived from OWS monthly summaries, except for northernmost locations during winter. In contrast, the sensible and latent heat parameters, which require simultaneous measurements of various variables, have merchant ships and ocean weather stations anomaly time series that are poorly correlated. Only in heavily travelled latitudes and during winter, when the air-sea heat exchange anomalies are large, are the merchant ship measurements able to reproduce the interannual fluctuations of the heat fluxes. The long-period trends in the surface heat budget of North Atlantic equatorward of 40° N implied by COADS thus appear unrepresentative of true climate trends. The COADS trends result from a gradual increase in the magnitude of the reported winds over the years due probably to variations in the ratio of measured to estimated winds, as well as from long period fluctuations in the near surface vertical temperature and humidity gradients.

  4. Surface Electrical Potentials of Root Cell Plasma Membranes: Implications for Ion Interactions, Rhizotoxicity, and Uptake

    Directory of Open Access Journals (Sweden)

    Yi-Min Wang

    2014-12-01

    Full Text Available Many crop plants are exposed to heavy metals and other metals that may intoxicate the crop plants themselves or consumers of the plants. The rhizotoxicity of heavy metals is influenced strongly by the root cell plasma membrane (PM surface’s electrical potential (ψ0. The usually negative ψ0 is created by negatively charged constituents of the PM. Cations in the rooting medium are attracted to the PM surface and anions are repelled. Addition of ameliorating cations (e.g., Ca2+ and Mg2+ to the rooting medium reduces the effectiveness of cationic toxicants (e.g., Cu2+ and Pb2+ and increases the effectiveness of anionic toxicants (e.g., SeO42− and H2AsO4−. Root growth responses to ions are better correlated with ion activities at PM surfaces ({IZ}0 than with activities in the bulk-phase medium ({IZ}b (IZ denotes an ion with charge Z. Therefore, electrostatic effects play a role in heavy metal toxicity that may exceed the role of site-specific competition between toxicants and ameliorants. Furthermore, ψ0 controls the transport of ions across the PM by influencing both {IZ}0 and the electrical potential difference across the PM from the outer surface to the inner surface (Em,surf. Em,surf is a component of the driving force for ion fluxes across the PM and controls ion-channel voltage gating. Incorporation of {IZ}0 and Em,surf into quantitative models for root metal toxicity and uptake improves risk assessments of toxic metals in the environment. These risk assessments will improve further with future research on the application of electrostatic theory to heavy metal phytotoxicity in natural soils and aquatic environments.

  5. Atmosphere-Surface Exchange of Reactive Nitrogen and its Implications for PM2.5

    Science.gov (United States)

    Wentworth, G.; Murphy, J. G.; Gregoire, P.; Tevlin, A.; Hems, R.; Cheyne, C.

    2012-12-01

    Recently it has been suggested that the surface-atmosphere exchange of both ammonia (NH3) and nitrous acid (HONO) can occur in a bidirectional fashion governed by a compensation point (i.e. the atmospheric mixing ratio where the flux changes direction). The compensation point corresponds to the gas phase mixing ratio that is in equilibrium with the dissolved constituents at the surface (soil water, plant tissue), governed by solubility and acid dissociation constants. Direct calculation of compensation point values is not trivial, because of the dependence on soil temperature, moisture, pH and the nitrogen distribution in the system. The presence of atmospheric particulate matter can further influence surface flux by providing a reactive sink for trace gases in the atmosphere. An accurate understanding of the factors governing bidirectional flux is required in order for air quality models to accurately predict trace gas mixing ratios, aerosol composition and spatial patterns of nitrogen deposition. A field study was conducted in southwestern Ontario during the summer of 2012 to measure the atmospheric and surface components of the system to provide observational constraints to test our understanding of the bi-directional exchange of reactive nitrogen. An Ambient Ion Monitor Ion Chromatograph (AIM-IC) was used to quantify the water-soluble trace gases (NH3, SO2, HNO3, HCl, and HONO) as well as water-soluble ions in PM2.5 with hourly time resolution. The same IC methods were used in an offline fashion to monitor soil ammonium, nitrite and nitrate composition. Challenges in selecting sampling and extraction protocols that can provide representative soil pH and nitrogen content are discussed.

  6. Plasma sterilization of poly lactic acid ultrasound contrast agents: surface modification and implications for drug delivery.

    Science.gov (United States)

    Eisenbrey, John R; Hsu, Jennifer; Wheatley, Margaret A

    2009-11-01

    Poly lactic acid (PLA) ultrasound contrast agents (CA) have been developed previously in our laboratory for ultrasound (US) imaging, as well as surface coated with doxorubicin to create a potential targeted platform of chemotherapeutic delivery using focused US. However, we have previously found it impossible to sterilize these agents while at the same time maintaining their acoustic properties, a task that would probably require fabrication within a clean facility. The purpose of this paper is to investigate the feasibility of using plasma to sterilize these CA while maintaining maximum echogenicity, a step that would greatly facilitate in vivo investigations. Effects of plasma exposure time (1, 3 and 6 min) and intensity (low-10 mA, 6.8 W; medium-15 mA, 10.5 W; and high-25 mA, 18 W) on the CAs' acoustic properties, surface morphology, zeta potential, capacity to carry chemotherapeutics and overall sterility are described. Both increases in plasma intensity and exposure time increased CA zeta potential and also significantly increased drug payload. High-intensity plasma exposure for 3 min was found to be an optimal sterilization protocol for maximal (100%) preservation of CA echogenicity. Plasma exposure resulted in sterile samples and maintained original CA enhancement of 20 dB and acoustic half-life over 75 min, while increasing CA zeta potential by 11 mV and doxorubicin loading efficiency by 10%. This study not only shows how a highly temperature- and pressure-sensitive agent can be sterilized using plasma, but also that surface modification can be used to increase surface binding of the drug.

  7. Range and geophysical corrections in coastal regions: and implications for mean sea surface determination

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Scharroo, Remko

    2011-01-01

    The determination of sea surface height from the altimeter range measurement involves a number of corrections: those expressing the behavior of the radar pulse through the atmosphere, and those correcting for sea state and other geophysical signals. A number of these corrections need special atte...... attention when reaching the coast: either because the signal is much larger or the correction is less accurate in coastal regions....

  8. The footprint of Alaskan tundra fires during the past half-century: implications for surface properties and radiative forcing

    Science.gov (United States)

    Rocha, Adrian V.; Loranty, Michael M.; Higuera, Phil E.; Mack, Michelle C.; Hu, Feng Sheng; Jones, Benjamin M.; Breen, Amy L.; Rastetter, Edward B.; Goetz, Scott J.; Shaver, Gus R.

    2012-01-01

    Recent large and frequent fires above the Alaskan arctic circle have forced a reassessment of the ecological and climatological importance of fire in arctic tundra ecosystems. Here we provide a general overview of the occurrence, distribution, and ecological and climate implications of Alaskan tundra fires over the past half-century using spatially explicit climate, fire, vegetation and remote sensing datasets for Alaska. Our analyses highlight the importance of vegetation biomass and environmental conditions in regulating tundra burning, and demonstrate that most tundra ecosystems are susceptible to burn, providing the environmental conditions are right. Over the past two decades, fire perimeters above the arctic circle have increased in size and importance, especially on the North Slope, indicating that future wildfire projections should account for fire regime changes in these regions. Remote sensing data and a literature review of thaw depths indicate that tundra fires have both positive and negative implications for climatic feedbacks including a decadal increase in albedo radiative forcing immediately after a fire, a stimulation of surface greenness and a persistent long-term (>10 year) increase in thaw depth. In order to address the future impact of tundra fires on climate, a better understanding of the control of tundra fire occurrence as well as the long-term impacts on ecosystem carbon cycling will be required.

  9. Conjunctive Surface and Groundwater Management in Utah. Implications for Oil Shale and Oil Sands Development

    Energy Technology Data Exchange (ETDEWEB)

    Keiter, Robert [Univ. of Utah, Salt Lake City, UT (United States); Ruple, John [Univ. of Utah, Salt Lake City, UT (United States); Tanana, Heather [Univ. of Utah, Salt Lake City, UT (United States); Holt, Rebecca [Univ. of Utah, Salt Lake City, UT (United States)

    2011-12-01

    Unconventional fuel development will require scarce water resources. In an environment characterized by scarcity, and where most water resources are fully allocated, prospective development will require minimizing water use and seeking to use water resources in the most efficient manner. Conjunctive use of surface and groundwater provides just such an opportunity. Conjunctive use includes two main practices: First, integrating surface water diversions and groundwater withdrawals to maximize efficiency and minimize impacts on other resource users and ecological processes. Second, conjunctive use includes capturing surplus or unused surface water and injecting or infiltrating that water into groundwater aquifers in order to increase recharge rates. Conjunctive management holds promise as a means of addressing some of the West's most intractable problems. Conjunctive management can firm up water supplies by more effectively capturing spring runoff and surplus water, and by integrating its use with groundwater withdrawals; surface and groundwater use can be further integrated with managed aquifer recharge projects. Such integration can maximize water storage and availability, while simultaneously minimizing evaporative loss, reservoir sedimentation, and surface use impacts. Any of these impacts, if left unresolved, could derail commercial-scale unconventional fuel development. Unconventional fuel developers could therefore benefit from incorporating conjunctive use into their development plans. Despite its advantages, conjunctive use is not a panacea. Conjunctive use means using resources in harmony to maximize and stabilize long-term supplies it does not mean maximizing the use of two separate but interrelated resources for unsustainable short-term gains and it cannot resolve all problems or provide water where no unappropriated water exists. Moreover, conjunctive use may pose risks to ecological values forgone when water that would otherwise remain in a stream

  10. Observation of surface features on an active landslide, and implications for understanding its history of movement

    Directory of Open Access Journals (Sweden)

    M. Parise

    2003-01-01

    Full Text Available Surface features are produced as a result of internal deformation of active landslides, and are continuously created and destroyed by the movement. Observation of their presence and distribution, and surveying of their evolution may provide insights for the zonation of the mass movement in sectors characterized by different behaviour. The present study analyses and describes some example of surface features observed on an active mass movement, the Slumgullion earthflow, in the San Juan Mountains of southwestern Colorado. The Slumgullion earthflow is one of the most famous and spectacular landslides in the world; it consists of a younger, active part which moves on and over an older, much larger, inactive part. Total length of the earthflow is 6.8 km, with an estimated volume of 170 × 10 6 m 3 . Its nearly constant rate of movement (ranging from about 2 m per year at the head, to a maximum of 6–7 m per year at its narrow and central part, to values between 1.3 and 2 m per year at the active toe, and the geological properties of moving material, are well suited for the observation of the development and evolution of surface features. In the last 11 years, repeated surveying at the Slumgullion site has been performed through recognition of surface features, measurements of their main characteristics, and detailed mapping. In this study, two sectors of the Slumgullion earthflow are analysed through comparison of the features observed in this time span, and evaluation of the changes occurred: they are the active toe and an area located at the left flank of the landslide. Choice of the sectors was dictated in the first case, by particular activity of movement and the nearby presence of elements at risk (highway located only 250 m downhill from the toe; and in the second case, by the presence of many surface features, mostly consisting of several generations of flank ridges. The active toe of the landslide is characterized by continuous movement

  11. Nano sized clay detected on chalk particle surfaces

    DEFF Research Database (Denmark)

    Skovbjerg, Lone; Hassenkam, Tue; Makovicky, Emil

    2012-01-01

    adsorption takes place, are largely unknown. In this study, we have used atomic force microscopy (AFM) to show that the grain surfaces in offshore and onshore chalk are more heterogeneous than previously assumed. The particles are not simply calcite surfaces but are partially covered by clay that is only 1...... that in calcite saturated water, both the polar and the nonpolar functional groups adhere to the nano sized clay particles but not to calcite. This is fundamentally important information for the development of conceptual and chemical models to explain wettability alterations in chalk reservoirs...

  12. Titan’s mid-latitude surface region from Cassini/VIMS data: Implications on the composition

    Science.gov (United States)

    Solomonidou, Anezina; Coustenis, Athena; M. C Lopes, Rosaly; Malaska, Michael; Rodriguez, Sebastien; Drossart, Pierre; Elachi, Charles; Schmitt, Bernard; Philippe, Sylvain; Janssen, Michael A.; Hirtzig, Mathieu; Wall, Stephen D.; Lawrence, Kenneth J.; Altobelli, Nicolas; Bratsolis, Emmanuel; Radebaugh, Jani; Stephan, Katrin; Brown, Robert H.; Le Mouélic, Stephane; Le Gall, Alice; Villanueva, Edward; Bloom, Anthony; Witasse, Olivier; Matsoukas, Christos; Schoenfeld, Ashley

    2017-10-01

    We investigate the surface of Titan using spectro-imaging near-infrared data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We apply a radiative transfer code to first determine the contributions of atmospheric haze to the Titan spectrum and then derive the surface albedo (Solomonidou et al. 2014; 2016). We focus here on the geological major units identified in Lopes et al. (2010, 2016), Malaska et al. (2016) and Radebaugh et al. (2016) from Synthetic Aperture Radar (SAR), data including mountains, different types of plains, labyrinths, impact craters, dune fields, and alluvial fans. We find that all regions classified as being the same geomorphological unit in SAR exhibit a coherent spectral response after the VIMS data analysis, thus suggesting a good correlation in the classification between SAR and VIMS. The Huygens landing site appears to be compositionally similar to one type of plains unit (variable plains), suggesting similar plain formation mechanisms. We have sub-categorized the VIMS data into three albedo categories (high, medium, low). By matching the extracted albedos with candidate materials for Titan’s surface (GhoSST database), we find that all regions of interest fall into one out of three main types of major candidate constituents: water ice, tholin-like material, or an unknown, very dark material. This suggests that Titan’s surface is possibly dominated by tholin-like material and a very dark unknown (most likely organic) material, and that most of the surface is covered by atmospheric/organic deposits. Water ice is also present at a number of regions as major constituent at latitudes higher than 30N and 30S. The surface albedo differences and similarities among the various geomorphological units constrain the implications for the geological processes that govern Titan’s surface and interior (e.g. aeolian, fluvial, sedimentary, lacustrine, cryovolcanic, tectonic).References: Lopes et al.: Icarus, 205, 540-558, 2010; Lopes

  13. The Effect of Global Change on Surface Ozone and Reactive Nitrogen Concentrations: Implications for the Biosphere

    Science.gov (United States)

    Hess, P. G.; Murazaki, K.; Emmons, L.; Lamarque, J.

    2005-12-01

    We simulated two ten year periods using the global chemical transport model MOZART-2 (Model of Ozone and Related chemical Tracers version 2): 1990-2000 and 2090-2100. In each case MOZART-2 is driven by meteorology from the National Center for Atmospheric Research (NCAR) coupled Climate Systems Model (CSM) 1.0 forced with the (SRES) A1 scenario. Profound future changes in the summertime climate over the U.S. are found including changes in temperature, water vapor and clouds and the frequency of synoptic venting of the boundary layer. Even allowing for no changes in emissions in the future, the changes in climate alone drive a significant increase in the ozone concentration over the eastern U.S. (up to 5 ppbv on average) and an increase in the persistence of pollution events. Implications of these changes on the biosphere are assessed with and without allowing for the impact of climate on biogenic emissions. Furthermore the changes in climate alone cause large changes in the partitioning of NOy, decreasing PAN by over 20% over the U.S. Coupled with changes in precipitation; this induces significant changes in the deposition of nitrogen species to the biosphere in a future climate.

  14. Ca and S K-edge XANES studies of calcite-acid mine water interactions

    Energy Technology Data Exchange (ETDEWEB)

    Myneni, S.C.B.; Perera, R.C.C. [Lawrence Berkeley National Lab., CA (United States)

    1997-04-01

    Heavy metal-rich acidic waters (SO{sub 4}{sup 2{minus}}, AsO{sub 4}{sup 3{minus}}, SeO{sub 4}{sup 2{minus}}, Fe{sup 2+}, Fe{sup 3+}, Al{sup 3+}, Cu{sup 2+}, Zn{sup 2+}, Cd{sup 2+}) and related ochreous coatings are common around abandoned sulfide and coal mine sites. This is mainly caused by the natural weathering of pyrite (FeS{sub 2}), arsenopyrite (FeAsS), and other metal sulfide containing shales. Acid generation in the case of pyrite can be explained by a general reaction: FeS{sub 2} + 3.5 O{sub 2} + H{sub 2}O {leftrightarrow} Fe{sup 2+} + SO{sub 4}{sup 2{minus}} + 2H{sup +}. Also, these low pH waters interact with the soils, and mobilize their soluble elements. One of the common remediation strategies is to allow these acid waters to react with limestone (CaCO{sub 3}-rich rock) and neutralize the pH and precipitate out soluble metals. Yet, the associated problem is the precipitation of Fe and Al oxides and hydroxy sulfate coatings on limestone surfaces, which block calcite reactive sites, and make them ineffective a few hours after initiation of treatment. The main objectives of this research are to examine: (1) the chemistry of limestone surface coatings, and (2) their toxic metal uptake and the conditions that inhibit their formation. Previous molecular studies using X-ray diffraction, and vibrational spectroscopy on limestone surface coatings (sampled from Athens, OH) indicate that the surface-most layer (the layer in contact with water) is composed of schwertmannite (Fe(III)-hydroxy sulfate) like phases. However, white, X-ray amorphous; Al-, sulfate- and carbonate-rich; and Ca-poor phases appeared at the interface between the limestone and the iron oxide coatings. The structure, morphology, and coordination chemistry of component major and trace elements of these white precipitate phases have not previously been examined.

  15. Photoluminescence Imaging of Polyfluorene Surface Structures on Semiconducting Carbon Nanotubes: Implications for Thin Film Exciton Transport.

    Science.gov (United States)

    Hartmann, Nicolai F; Pramanik, Rajib; Dowgiallo, Anne-Marie; Ihly, Rachelle; Blackburn, Jeffrey L; Doorn, Stephen K

    2016-12-27

    Single-walled carbon nanotubes (SWCNTs) have potential to act as light-harvesting elements in thin film photovoltaic devices, but performance is in part limited by the efficiency of exciton diffusion processes within the films. Factors contributing to exciton transport can include film morphology encompassing nanotube orientation, connectivity, and interaction geometry. Such factors are often defined by nanotube surface structures that are not yet well understood. Here, we present the results of a combined pump-probe and photoluminescence imaging study of polyfluorene (PFO)-wrapped (6,5) and (7,5) SWCNTs that provide additional insight into the role played by polymer structures in defining exciton transport. Pump-probe measurements suggest exciton transport occurs over larger length scales in films composed of PFO-wrapped (7,5) SWCNTs, compared to those prepared from PFO-bpy-wrapped (6,5) SWCNTs. To explore the role the difference in polymer structure may play as a possible origin of differing transport behaviors, we performed a photoluminescence imaging study of individual polymer-wrapped (6,5) and (7,5) SWCNTs. The PFO-bpy-wrapped (6,5) SWCNTs showed more uniform intensity distributions along their lengths, in contrast to the PFO-wrapped (7,5) SWCNTs, which showed irregular, discontinuous intensity distributions. These differences likely originate from differences in surface coverage and suggest the PFO wrapping on (7,5) nanotubes produces a more open surface structure than is available with the PFO-bpy wrapping of (6,5) nanotubes. The open structure likely leads to improved intertube coupling that enhances exciton transport within the (7,5) films, consistent with the results of our pump-probe measurements.

  16. Assessing metaldehyde concentrations in surface water catchments and implications for drinking water abstraction

    Science.gov (United States)

    Asfaw, Alemayehu; Shucksmith, James; Smith, Andrea; Cherry, Katherine

    2015-04-01

    Metaldehyde is an active ingredient in agricultural pesticides such as slug pellets, which are heavily applied to UK farmland during the autumn application season. There is current concern that existing drinking water treatment processes may be inadequate in reducing potentially high levels of metaldehyde in surface waters to below the UK drinking water quality regulation limit of 0.1 µg/l. In addition, current water quality monitoring methods can miss short term fluctuations in metaldehyde concentration caused by rainfall driven runoff, hampering prediction of the potential risk of exposure. Datasets describing levels, fate and transport of metaldehyde in river catchments are currently very scarce. This work presents results from an ongoing study to quantify the presence of metaldehyde in surface waters within a UK catchment used for drinking water abstraction. High resolution water quality data from auto-samplers installed in rivers are coupled with radar rainfall, catchment characteristics and land use data to i) understand which hydro-meteorological characteristics of the catchment trigger the peak migration of metaldehyde to surface waters; ii) assess the relationship between measured metaldehyde levels and catchment characteristics such as land use, topographic index, proximity to water bodies and runoff generation area; iii) describe the current risks to drinking water supply and discuss mitigation options based on modelling and real-time control of water abstraction. Identifying the correlation between catchment attributes and metaldehyde generation will help in the development of effective catchment management strategies, which can help to significantly reduce the amount of metaldehyde finding its way into river water. Furthermore, the effectiveness of current water quality monitoring strategy in accurately quantifying the generation of metaldehyde from the catchment and its ability to benefit the development of effective catchment management practices

  17. Implications of polar ocean surface stratification changes on a warming climate

    Science.gov (United States)

    Bauch, Henning; Kandiano, Evgenia; Thibodeau, Benoit; Pedersen, Thomas

    2017-04-01

    In the North Polar oceans surface properties have a significant influence on regional climate development. Stratification and salinity in this area are not just strongly coupled, they directly affect North Atlantic deepwater production and, thus, the ventilation of the deep sea and global ocean circulation. Besides a direct feedback on surface heat transfer to the Polar North, the response of upper stratification in a crucial region such as the Nordic Seas to near-future hydrologic forcing as surface water in the polar ocean warms and freshens due to global temperature rise and glacier demise, is still largely unresolved. We paired bulk sediment δ15N isotopic signatures with planktic foraminiferal assemblages across three major interglacials, each of which could be viewed as an analogue of the present. The isotope vs. foraminifer comparison defines stratification-induced variations in nitrate utilization between and within all of these warm periods and signifies changes in the thickness of the mixed-layer throughout the previous interglacials. As the thickness directly controls the depth-level of Atlantic water inflow, the changes recorded here suggest that drastic variations in freshwater water input associated with each preceding glacial terminations caused the Atlantic water to flow at greater depth. Backed up by independent salinity reconstructions using hydrogen isotope composition in alkenones, an active involvement of both glacial ice sheet size and subsequent specific melting history on interglacial climate development is suggested. Although the results also call for caution when using older interglacials as future climate analogues, they do help to better understand the effect of freshwater input on climate-sensitive ocean sites. It is further indicated that any future increase in freshwater flux into the polar oceans would not necessarily stop by itself the poleward advection of Atlantic water.

  18. Implications of atmospheric conditions for analysis of surface temperature variability derived from landscape-scale thermography.

    Science.gov (United States)

    Hammerle, Albin; Meier, Fred; Heinl, Michael; Egger, Angelika; Leitinger, Georg

    2017-04-01

    Thermal infrared (TIR) cameras perfectly bridge the gap between (i) on-site measurements of land surface temperature (LST) providing high temporal resolution at the cost of low spatial coverage and (ii) remotely sensed data from satellites that provide high spatial coverage at relatively low spatio-temporal resolution. While LST data from satellite (LSTsat) and airborne platforms are routinely corrected for atmospheric effects, such corrections are barely applied for LST from ground-based TIR imagery (using TIR cameras; LSTcam). We show the consequences of neglecting atmospheric effects on LSTcam of different vegetated surfaces at landscape scale. We compare LST measured from different platforms, focusing on the comparison of LST data from on-site radiometry (LSTosr) and LSTcam using a commercially available TIR camera in the region of Bozen/Bolzano (Italy). Given a digital elevation model and measured vertical air temperature profiles, we developed a multiple linear regression model to correct LSTcam data for atmospheric influences. We could show the distinct effect of atmospheric conditions and related radiative processes along the measurement path on LSTcam, proving the necessity to correct LSTcam data on landscape scale, despite their relatively low measurement distances compared to remotely sensed data. Corrected LSTcam data revealed the dampening effect of the atmosphere, especially at high temperature differences between the atmosphere and the vegetated surface. Not correcting for these effects leads to erroneous LST estimates, in particular to an underestimation of the heterogeneity in LST, both in time and space. In the most pronounced case, we found a temperature range extension of almost 10 K.

  19. Surface water δ18O in the marginal China seas and its hydrological implications

    Science.gov (United States)

    Ye, Feng; Deng, Wenfeng; Xie, Luhua; Wei, Gangjian; Jia, Guodong

    2014-06-01

    Surface water δ18O distribution in the marginal China seas (including the south Yellow and East China Seas, YECS, and the northern South China Sea, NSCS) and its relationship with salinity were investigated to gain insight into the surface hydrological processes in these seas. In the YECS where δ18O and salinity varied in relatively large ranges, seasonally different slopes of δ18O-salinity linear fits, i.e. 0.26 ± 0.02 in summer and 0.23 ± 0.01 in winter, were observed. In the NSCS, δ18O and salinity ranged narrower than in the YECS, and exhibited a similar linear relationship in winter but a poor correlation in summer. The saline surface water end-members were nearly identical in δ18O and salinity in both the YECS and NSCS and showed different values between summer and winter. These saline end-members were distinct from the reported values of the Kuroshio water (KW), which might be related to modification of KW mainly by atmospheric forcing. Using a simple mixing model, we showed that the observed significant linear δ18O-salinity relationships in the YECS were caused mainly by great terrestrial freshwater influx. The observed poor correlation between δ18O and salinity in the summer NSCS was likely associated with the relatively minor runoff contribution, although in wet period, to the freshwater end-member. The still good relationship in the NSCS during the dry wintertime, however, was attributable to the strong China Coastal Current flowing from the ECS to the NSCS through the Taiwan Strait driven by the prevailing northeast monsoon.

  20. Health risk implications of potentially toxic metals in street dust and surface soil of Tehran, Iran.

    Science.gov (United States)

    Dehghani, Sharareh; Moore, Farid; Keshavarzi, Behnam; Hale, Beverley A

    2017-02-01

    In this study a total of 30 street dusts and 10 surface soils were collected in the central district of Tehran and analyzed for major potentially toxic metals. Street dust was found to be greatly enriched in Sb, Pb, Cu and Zn and moderately enriched in Cr, Mn, Mo and Ni. Contamination of Cu, Sb, Pb and Zn was clearly related to anthropogenic sources such as brake wear, tire dust, road abrasion and fossil fuel combustion. Spatial distribution of pollution load index in street dust suggested that industries located south-west of the city intensify street dust pollution. Microscopic studies revealed six dominant group of morphological structures in calculation of the exposurethe street dusts and surface soils, with respect to different geogenic and anthropogenic sources. The BCR (the European Community Bureau of Reference) sequential extraction results showed that Sb, Ni, Mo, As and Cr bonded to silicates and sulfide minerals were highly resistant to dissolution. In contrast, Zn, Cd, and Mn were mostly associated with the exchangeable phase and thus would be easily mobilized in the environment. Cu was the most abundant metal in the reducible fraction, indicating its adsorption to iron and manganese oxy-hydroxides. Pb was equally extracted from exchangeable and reducible fractions. Anthropogenic sources related to traffic apparently play a small role in Cr, Ni and Mo contamination and dispersed them as bioavailable forms but with reduced mobility and bioavailablity due to high potential of complexation and adsorption to organic matter and iron and manganese oxy-hydroxides. Calculated Hazard Index (HI) suggests ingestion as the most important pathway for the majority of PTMs in children and dermal contact as the main exposure route for Cr, Cd and Sb for adults. The HIs and fractionation pattern of elements revealed Pb as the sole element that bears potential health risk in street dust and surface soil. Copyright © 2016 Elsevier Inc. All rights reserved.

  1. Implications of atmospheric conditions for analysis of surface temperature variability derived from landscape-scale thermography

    Science.gov (United States)

    Hammerle, Albin; Meier, Fred; Heinl, Michael; Egger, Angelika; Leitinger, Georg

    2017-04-01

    Thermal infrared (TIR) cameras perfectly bridge the gap between (i) on-site measurements of land surface temperature (LST) providing high temporal resolution at the cost of low spatial coverage and (ii) remotely sensed data from satellites that provide high spatial coverage at relatively low spatio-temporal resolution. While LST data from satellite (LSTsat) and airborne platforms are routinely corrected for atmospheric effects, such corrections are barely applied for LST from ground-based TIR imagery (using TIR cameras; LSTcam). We show the consequences of neglecting atmospheric effects on LSTcam of different vegetated surfaces at landscape scale. We compare LST measured from different platforms, focusing on the comparison of LST data from on-site radiometry (LSTosr) and LSTcam using a commercially available TIR camera in the region of Bozen/Bolzano (Italy). Given a digital elevation model and measured vertical air temperature profiles, we developed a multiple linear regression model to correct LSTcam data for atmospheric influences. We could show the distinct effect of atmospheric conditions and related radiative processes along the measurement path on LSTcam, proving the necessity to correct LSTcam data on landscape scale, despite their relatively low measurement distances compared to remotely sensed data. Corrected LSTcam data revealed the dampening effect of the atmosphere, especially at high temperature differences between the atmosphere and the vegetated surface. Not correcting for these effects leads to erroneous LST estimates, in particular to an underestimation of the heterogeneity in LST, both in time and space. In the most pronounced case, we found a temperature range extension of almost 10 K.

  2. Importance of initial buoyancy field on evolution of mantle thermal structure: Implications of surface boundary conditions

    Directory of Open Access Journals (Sweden)

    Petar Glišović

    2015-01-01

    Full Text Available Although there has been significant progress in the seismic imaging of mantle heterogeneity, the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models. To address this question, we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns. A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow, without imposing prescribed surface velocities (i.e., plate-like boundary condition. As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip (rigid boundary condition. A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved, and its geographical location is fixed during the evolution of mantle flow. Considering the impact of different assumed surface boundary conditions (rigid and plate-like on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure. Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term, stable pattern of thermal heterogeneity in the lowermost mantle that resembles the present-day Large Low Shear Velocity Provinces (LLSVPs, especially below the Pacific. The evolution of subduction zones may be, however, influenced by the mantle-wide flow driven by deeply-rooted and long-lived superplumes since Archean times. These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique

  3. Experimental and simulated scattering matrices of small calcite particles at 647nm

    Science.gov (United States)

    Dabrowska, D. D.; Muñoz, O.; Moreno, F.; Nousiainen, T.; Zubko, E.; Marra, A. C.

    2013-07-01

    We present measurements of the complete scattering matrix as a function of the scattering angle of a sample of calcite particles. The measurements are performed at 647nm in the scattering angle range from 3° to 177°. To facilitate the use of the experimental data we present a synthetic scattering matrix based on the measurements and defined in the full range from 0° to 180°. The scattering matrix of the calcite sample is modeled using the discrete-dipole approximation. Two sets of shapes, flake-like and rhomboid-like particles giving a total of 15 different targets are considered since both types of shapes have been found in our calcite sample. In our computations we use the measured size distribution of the calcite sample truncated at 1.2μm. We present a theoretical study of the impact of birefringence on the computed scattering matrix elements for both sets of shapes. Four different cases regarding the composition of the calcite particles are considered: two isotropic cases corresponding to the ordinary and extraordinary refractive index of calcite, respectively; one equivalent isotropic case analogous to internal mixing; and birefringence fully accounted for. Numerical simulations are compared with the experimental data. We find that birefringence has little impact on the calculated phase functions but it has a significant effect on the polarization-related elements of the scattering matrix. Moreover, we conclude that the shape of the targets (flakes or irregular rhomboids) has a much stronger effect on the computed scattering matrix elements than birefringence.

  4. Experimental determination of acetylene and ethylene solubility in liquid methane and ethane: Implications to Titan's surface

    Science.gov (United States)

    Singh, S.; Combe, J.-Ph.; Cordier, D.; Wagner, A.; Chevrier, V. F.; McMahon, Z.

    2017-07-01

    In this study, the solubility of acetylene (or ethyne, C2H2) and ethylene (or ethene, C2H4) in liquid methane (CH4) and ethane (C2H6) has been experimentally determined at Titan surface temperature (90 K) and pressure (1.5 bars). As predicted by theoretical models, the solubilities of acetylene and ethylene are very large at Titan temperature and these species are most likely to be abundantly present in the lakes and as evaporites on the shores or dry lake beds. Our results indicate the solubility of 4.9 × 10-2 mole fraction for acetylene in methane and 48 × 10-2 mole fraction in ethane; for ethylene, 5.6 × 10-1 mole fraction in methane and 4.8 × 10-1 mole fraction in ethane. Assuming the mole fractions from atmospheric models in the lower stratosphere and equilibrium with the surface, we determined that the lakes on Titan that cover ∼400,000 km2 are not saturated. The liquid lakes on Titan act as an important reservoir for both acetylene and ethylene. Assuming difference of methane and ethane content in the lakes at different latitudes, the difference in solubility in liquid methane and ethane, solutes in lakes may change with the temporal evolution (such as; evaporation and condensation) over seasons and geological time scales.

  5. C-terminal domains implicated in the functional surface expression of potassium channels

    Science.gov (United States)

    Jenke, Marc; Sánchez, Araceli; Monje, Francisco; Stühmer, Walter; Weseloh, Rüdiger M.; Pardo, Luis A.

    2003-01-01

    A short C-terminal domain is required for correct tetrameric assembly in some potassium channels. Here, we show that this domain forms a coiled coil that determines not only the stability but also the selectivity of the multimerization. Synthetic peptides comprising the sequence of this domain in Eag1 and other channels are able to form highly stable tetrameric coiled coils and display selective heteromultimeric interactions. We show that loss of function caused by disruption of this domain in Herg1 can be rescued by introducing the equivalent domain from Eag1, and that this chimeric protein can form heteromultimers with Eag1 while wild-type Erg1 cannot. Additionally, a short endoplasmic reticulum retention sequence closely preceding the coiled coil plays a crucial role for surface expression. Both domains appear to co-operate to form fully functional channels on the cell surface and are a frequent finding in ion channels. Many pathological phenotypes may be attributed to mutations affecting one or both domains. PMID:12554641

  6. Health initiatives to target obesity in surface transport industries: Review and implications for action

    Directory of Open Access Journals (Sweden)

    Anjum Naweed

    2015-06-01

    Full Text Available Lifestyle-related chronic diseases pose a considerable burden to the individual and the wider society, with correspondingly negative effects on industry. Obesity is a particular problem for the Australasian road and rail industries where it is associated with specific cardiac and fatigue-related safety risks, and levels are higher than those found in the general population. Despite this recognition, and the introduction of National Standards, very little consensus exists regarding approaches to preventative health for surface transport workers. A review of evidence regarding effective health promotion initiatives is urgently needed to inform best practice in this cohort. This review draws together research informing the scope and effectiveness of health promotion programs, initiatives and interventions targeting overweight and obesity in safety critical surface transport domains including the truck, bus and rail industries. A number of health interventions demonstrated measurable successes, including incentivising, peer mentoring, verbal counselling, development of personalised health profiles, and offer of healthier on-site food choices – some of which also resulted in sizeable return on investment over the long term.

  7. Chemical functionalization of ceramic tile surfaces by silane coupling agents: polymer modified mortar adhesion mechanism implications

    Directory of Open Access Journals (Sweden)

    Alexandra Ancelmo Piscitelli Mansur

    2008-09-01

    Full Text Available Adhesion between tiles and mortars are crucial to the stability of ceramic tile systems. From the chemical point of view, weak forces such as van der Waals forces and hydrophilic interactions are expected to be developed preferably at the tiles and polymer modified Portland cement mortar interface. The main goal of this paper was to use organosilanes as primers to modify ceramic tile hydrophilic properties to improve adhesion between ceramic tiles and polymer modified mortars. Glass tile surfaces were treated with several silane derivatives bearing specific functionalities. Contact angle measurements and Fourier Transform Infrared Spectroscopy (FTIR were used for evaluating the chemical changes on the tile surface. In addition, pull-off tests were conducted to assess the effect on adhesion properties between tile and poly(ethylene-co-vinyl acetate, EVA, modified mortar. The bond strength results have clearly shown the improvement of adherence at the tile-polymer modified mortar interface, reflecting the overall balance of silane, cement and polymer interactions.

  8. Neuronal Surface Autoantibodies in Neuropsychiatric Disorders: Are There Implications for Depression?

    Directory of Open Access Journals (Sweden)

    Shenghua Zong

    2017-07-01

    Full Text Available Autoimmune diseases are affecting around 7.6–9.4% of the general population. A number of central nervous system disorders, including encephalitis and severe psychiatric disorders, have been demonstrated to associate with specific neuronal surface autoantibodies (NSAbs. It has become clear that specific autoantibodies targeting neuronal surface antigens and ion channels could cause severe mental disturbances. A number of studies have focused or are currently investigating the presence of autoantibodies in specific mental conditions such as schizophrenia and bipolar disorders. However, less is known about other conditions such as depression. Depression is a psychiatric disorder with complex etiology and pathogenesis. The diagnosis criteria of depression are largely based on symptoms but not on the origin of the disease. The question which arises is whether in a subgroup of patients with depression, the symptoms might be caused by autoantibodies targeting membrane-associated antigens. Here, we describe how autoantibodies targeting membrane proteins and ion channels cause pathological effects. We discuss the physiology of these antigens and their role in relation to depression. Finally, we summarize a number of studies detecting NSAbs with a special focus on cohorts that include depression diagnosis and/or show depressive symptoms.

  9. Ray craters on Ganymede: Implications for cratering apex-antapex asymmetry and surface modification processes

    Science.gov (United States)

    Xu, Luyuan; Hirata, Naoyuki; Miyamoto, Hideaki

    2017-10-01

    As the youngest features on Ganymede, ray craters are useful in revealing the sources of recent impactors and surface modification processes on the satellite. We examine craters with D > 10 km on Ganymede from images obtained by the Voyager and Galileo spacecraft to identify ray craters and study their spatial distributions. Furthermore, we carefully select images of appropriate solar and emission angles to obtain unbiased ray crater densities. As a result, we find that the density of large ray craters (D > 25 km) on the bright terrain exhibits an apex-antapex asymmetry, and its degree of asymmetry is much lower than the theoretical estimation for ecliptic comets. For large craters (D > 25 km), ecliptic comets ought to be less important than previously assumed, and a possible explanation is that nearly isotropic comets may play a more important role on Ganymede than previously thought. We also find that small ray craters (10 km 10 km) on the dark terrain show no apex-antapex asymmetry. We interpret that the distribution difference between the terrain types comes from preferential thermal sublimation on the dark terrain, while the distribution difference between large and small ray craters suggests that rays of small craters are more readily erased by some surface modification processes, such as micrometeorite gardening.

  10. Modelling Groundwater-Surface water Exchange and its Implications on Groundwater Quality

    Science.gov (United States)

    Maier, Uli; Wiesner, Victoria; Trauth, Nico; Musolff, Andreas; Fleckenstein, Jan

    2014-05-01

    Hydrogeochemical interactions are still posing a significant challenge for the assessment of water quality at the catchment scale. Numerical modelling of water quality is still restricted by computer power and parameter uncertainty at larger scales and is demanding further research regarding the influence of surface water on groundwater resources. The Selke river is a tributary to the larger Bode river in the surroundings of the Harz mountains in northern Germany. Hydrology and water quality is monitored at a well-equipped field investigation site, which is accompanied by numerical modeling work at different scales. The site consists of approximately two km2 of river, alluvial sediments and gently inclined hillslopes. River stage, water levels and saturation in surface water, unsaturated zone and groundwater were simulated for quasi steady state conditions and a transient, climate-data driven run over the course of a year. Of particular interest are the observed model results for the hotspots of hydraulic and geochemical interaction, between the river, its alluvial plain and the hyporheic zone. Model results will be used to guide the further instrumentation of the field investigation. Such hotspots of interaction between environmental compartments are discussed, as well as travel time distributions from particle tracking and dispersive approaches. Groundwater nitrate contamination and its removal potential will be linked to the water exchange behavior.

  11. Surface Crystallization of Cloud Droplets: Implications for Climate Change and Ozone Depletion

    Science.gov (United States)

    Tabazadeh, A.; Djikaev, Y. S.; Reiss, H.; Gore, Warren J. (Technical Monitor)

    2002-01-01

    The process of supercooled liquid water crystallization into ice is still not well understood. Current experimental data on homogeneous freezing rates of ice nucleation in supercooled water droplets show considerable scatter. For example, at -33 C, the reported freezing nucleation rates vary by as much as 5 orders of magnitude, which is well outside the range of measurement uncertainties. Until now, experimental data on the freezing of supercooled water has been analyzed under the assumption that nucleation of ice took place in the interior volume of a water droplet. Here, the same data is reanalyzed assuming that the nucleation occurred "pseudoheterogeneously" at the air (or oil)-liquid water interface of the droplet. Our analysis suggest that the scatter in the nucleation data can be explained by two main factors. First, the current assumption that nucleation occurs solely inside the volume of a water droplet is incorrect. Second, because the nucleation process most likely occurs on the surface, the rates of nuclei formation could differ vastly when oil or air interfaces are involved. Our results suggest that ice freezing in clouds may initiate on droplet surfaces and such a process can allow for low amounts of liquid water (approx. 0.002 g per cubic meters) to remain supercooled down to -40 C as observed in the atmosphere.

  12. Surface temperatures of the Mid-Pliocene North Atlantic Ocean: Implications for future climate

    Science.gov (United States)

    Dowsett, Harry J.; Chandler, Mark A.; Robinson, Marci M.

    2009-01-01

    The Mid-Pliocene is the most recent interval in the Earth's history to have experienced warming of the magnitude predicted for the second half of the twenty-first century and is, therefore, a possible analogue for future climate conditions. With continents basically in their current positions and atmospheric CO2 similar to early twenty-first century values, the cause of Mid-Pliocene warmth remains elusive. Understanding the behaviour of the North Atlantic Ocean during the Mid-Pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change. Under the framework of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) sea surface reconstruction, we synthesize Mid-Pliocene North Atlantic studies by PRISM members and others, describing each region of the North Atlantic in terms of palaeoceanography. We then relate Mid-Pliocene sea surface conditions to expectations of future warming. The results of the data and climate model comparisons suggest that the North Atlantic is more sensitive to climate change than is suggested by climate model simulations, raising the concern that estimates of future climate change are conservative.

  13. Characterizing heavy metal build-up on urban road surfaces: implication for stormwater reuse.

    Science.gov (United States)

    Liu, An; Liu, Liang; Li, Dunzhu; Guan, Yuntao

    2015-05-15

    Stormwater reuse is increasingly popular in the worldwide. In terms of urban road stormwater, it commonly contains toxic pollutants such as heavy metals, which could undermine the reuse safety. The research study investigated heavy metal build-up characteristics on urban roads in a typical megacity of South China. The research outcomes show the high variability in heavy metal build-up loads among different urban road sites. The degree of traffic congestion and road surface roughness was found to exert a more significant influence on heavy metal build-up rather than traffic volume. Due to relatively higher heavy metal loads, stormwater from roads with more congested traffic conditions or rougher surfaces might be suitable for low-water-quality required activities while the stormwater from by-pass road sections could be appropriate for relatively high-water-quality required purposes since the stormwater could be relatively less polluted. Based on the research outcomes, a decision-making process for heavy metals based urban road stormwater reuse was proposed. The new finding highlights the importance to undertaking a "fit-for-purpose" road stormwater reuse strategy. Additionally, the research results can also contribute to enhancing stormwater reuse safety. Copyright © 2015 Elsevier B.V. All rights reserved.

  14. Characteristics of a calcite "limestone"-marble from Macedonia, used as flux material

    Directory of Open Access Journals (Sweden)

    Hristova E.

    2003-01-01

    Full Text Available The phase characteristics of calcite "limestone"-marble from Banjany area village (near Skopje, Macedonia were examined by means of XRD, SEM microscope in polarizing and reflected lights, chemical, DT/TG-analyses. It was concluded as follows: - calcite (CaCO3 is a major mineral component (cca 80-90 % prevailing in the marble over the other minerals - dolomite is generally of minor importance (cca 10-20 % in the rock - quartz, micas graphite, pyrite represent typical accessories. As result of the mentioned phase characteristics, this raw materials was for a long time (more than 30 years used as flux in the iron and steel metallurgy in Macedonia.

  15. Field Experiment to Stimulate Microbial Urease Activity in Groundwater for in situ Calcite Precipitation

    Science.gov (United States)

    Fujita, Y.; Taylor, J. L.; Tyler, T. L.; Banta, A. B.; Reysenbach, A. L.; Delwiche, M. E.; McLing, T. L.; Colwell, F. S.; Smith, R. W.

    2003-12-01

    Groundwater contamination by radionuclides and metals from past weapons processing activities is a significant problem for the United States Department of Energy. Removal of these pollutants from the subsurface can be prohibitively expensive and result in worker exposure, and therefore in situ containment and stabilization is an attractive remediation alternative. One potential approach for the immobilization of certain radionuclides and metals (e.g., 90Sr, 60Co, Pb, Cd) is to induce geochemical conditions that promote co-precipitation in calcite. Many aquifers in the arid western US are calcite-saturated, and calcite precipitated under an engineered remediation scheme in such aquifers should remain stable even after return to ambient conditions. We have proposed that an effective way to promote calcite precipitation is to utilize native microorganisms that hydrolyze urea. Urea hydrolysis results in carbonate and ammonium production, and an increase in pH. The increased carbonate alkalinity favors calcite precipitation, and the ammonium serves the additional role of promoting desorption of sorbed metal ions from the aquifer matrix by ion exchange. The desorbed metals are then accessible to co-precipitation in calcite, which can be a longer-term immobilization mechanism than sorption. The ability to hydrolyze urea is common among environmental microorganisms, and we have shown in the laboratory that microbial urea hydrolysis can be linked to calcite precipitation and co-precipitation of the trace metal strontium. As a next step in the development of our remediation approach, we aimed to demonstrate that we can stimulate the native microbial community to express urease in the field. In 2002 we conducted a preliminary field trial of our approach, using a well in the Eastern Snake River Plain Aquifer in Idaho Falls, Idaho, USA. A dilute molasses solution (0.00075%) was injected to promote overall biological growth, and then urea (50 mM) was added to the aquifer

  16. New Shocked Calcite and Fe Grains from Noerdlingen Ries Impact Crater

    Science.gov (United States)

    Miura, Y.

    1995-09-01

    Shocked minerals with simple chemical composition of silica, carbon or iron material reveal high-pressure phase during compression process [1]. As calcite mineral shows high-pressure phase of aragonite it should have the "shocked phase" formed from high-pressure phase mixed with quenched materials of gas-melt reaction [2,3,4]. The main purposes of this paper are (1) to discuss new shocked materials of calcite found in the Noerdlingen Ries impact crater. Germany and artificial impact phases. and (2) to show new findings of fine Fe-grains and anomalous plagioclase in suevite. Single grains of anomalous calcite for X-ray analysis were selected from limestone with wormy or bubble-included texture in Buschelberg Ries impact crater (sample R8) [3 4]. Powdered and single grain samples of anomalous calcites show low X-ray intensity and high Bragg angle shift. compared with standard calcite of Akiyoshi limestone as listed in Table 1 [2.3.4]. The unit-cell dimensions of the single grain measured with the four-axes X-ray diffractometer in Yamaguchi University were determined by the least square calculation from the "highest X-ray intensity peak" of each crystal plane which is the same data of the powdered X-ray diffraction sample as an average structure . Both powdered and single grain data reveal high density of 2.76 g/cm^3 (between aragonite of density: rho=2.8g/cm^3, and normal calcite: rho=2.71g/cm^3) of the calcite cell which is the same characters of shocked phases of quartz or graphite [1,2,3,4] (Table 1). Anomalous calcite contains minor amount of Si Fe Ti, though major cation is Ca of 99.4% in cation content. These foreign elements are mixed with during the formation in vapor plume [5]. Table 1, showing the x-ray density and unit-cell parameters of anomalous shocked calcite with high density from Ries and artificial impact craters, appears here in the hard copy. Two types of shocked calcites are found in artificial impact experiments of railgun of the ISAS. Japan. (a

  17. Width of surface rupture zone for thrust earthquakes: implications for earthquake fault zoning

    Directory of Open Access Journals (Sweden)

    P. Boncio

    2018-01-01

    Full Text Available The criteria for zoning the surface fault rupture hazard (SFRH along thrust faults are defined by analysing the characteristics of the areas of coseismic surface faulting in thrust earthquakes. Normal and strike–slip faults have been deeply studied by other authors concerning the SFRH, while thrust faults have not been studied with comparable attention. Surface faulting data were compiled for 11 well-studied historic thrust earthquakes occurred globally (5.4 ≤ M ≤ 7.9. Several different types of coseismic fault scarps characterize the analysed earthquakes, depending on the topography, fault geometry and near-surface materials (simple and hanging wall collapse scarps, pressure ridges, fold scarps and thrust or pressure ridges with bending-moment or flexural-slip fault ruptures due to large-scale folding. For all the earthquakes, the distance of distributed ruptures from the principal fault rupture (r and the width of the rupture zone (WRZ were compiled directly from the literature or measured systematically in GIS-georeferenced published maps. Overall, surface ruptures can occur up to large distances from the main fault ( ∼ 2150 m on the footwall and  ∼  3100 m on the hanging wall. Most of the ruptures occur on the hanging wall, preferentially in the vicinity of the principal fault trace ( >   ∼  50 % at distances  <   ∼  250 m. The widest WRZ are recorded where sympathetic slip (Sy on distant faults occurs, and/or where bending-moment (B-M or flexural-slip (F-S fault ruptures, associated with large-scale folds (hundreds of metres to kilometres in wavelength, are present. A positive relation between the earthquake magnitude and the total WRZ is evident, while a clear correlation between the vertical displacement on the principal fault and the total WRZ is not found. The distribution of surface ruptures is fitted with probability density functions, in order to define a criterion to

  18. Color variations on Ceres derived by Dawn/VIR: Implications for the surface composition

    Science.gov (United States)

    Zambon, F.; De Sanctis, M. C.; Tosi, F.; Longobardo, A.; Palomba, E.; Carrozzo, G.; Combe, J.-Ph.; Li, J.-Y.; McFadden, L. A.; Marchi, S.; Jaumann, R.; Schoeder, S.; Ciarniello, M.; Raponi, A.; Frigeri, A.; Ammannito, E.; Russell, C. T.; Raymond, C. A.

    2015-10-01

    Ceres, the second target of the Dawn mission [1], with a diameter of ˜952 km, is the largest object in the main asteroid belt [2], and classified as a dwarf planet. More than two years after departure from Vesta, Dawn finally arrived to Ceres. During the approach phase, the spacecraft acquired data with unprecedented spatial resolution. Previous work based on Hubble Space Telescope (HST) data, highlight regions with different albedo variation in the UV-VIS range [3] (Fig. 1). The Visible and InfraRed (VIR) mapping spectrometer onboard Dawn covers the overall wavelength range between 0.25 and 5.1 μm [4]. VIR will enable the first comprehensive compositional mapping of Ceres, focusing on the possible presence of water ice, salts, organics and volatiles, and surface thermal properties [5].

  19. Radioactive elements on Mercury's surface from MESSENGER: implications for the planet's formation and evolution.

    Science.gov (United States)

    Peplowski, Patrick N; Evans, Larry G; Hauck, Steven A; McCoy, Timothy J; Boynton, William V; Gillis-Davis, Jeffery J; Ebel, Denton S; Goldsten, John O; Hamara, David K; Lawrence, David J; McNutt, Ralph L; Nittler, Larry R; Solomon, Sean C; Rhodes, Edgar A; Sprague, Ann L; Starr, Richard D; Stockstill-Cahill, Karen R

    2011-09-30

    The MESSENGER Gamma-Ray Spectrometer measured the average surface abundances of the radioactive elements potassium (K, 1150 ± 220 parts per million), thorium (Th, 220 ± 60 parts per billion), and uranium (U, 90 ± 20 parts per billion) in Mercury's northern hemisphere. The abundance of the moderately volatile element K, relative to Th and U, is inconsistent with physical models for the formation of Mercury requiring extreme heating of the planet or its precursor materials, and supports formation from volatile-containing material comparable to chondritic meteorites. Abundances of K, Th, and U indicate that internal heat production has declined substantially since Mercury's formation, consistent with widespread volcanism shortly after the end of late heavy bombardment 3.8 billion years ago and limited, isolated volcanic activity since.

  20. Earthing: Health Implications of Reconnecting the Human Body to the Earth's Surface Electrons

    Science.gov (United States)

    Chevalier, Gaétan; Sinatra, Stephen T.; Oschman, James L.; Sokal, Karol; Sokal, Pawel

    2012-01-01

    Environmental medicine generally addresses environmental factors with a negative impact on human health. However, emerging scientific research has revealed a surprisingly positive and overlooked environmental factor on health: direct physical contact with the vast supply of electrons on the surface of the Earth. Modern lifestyle separates humans from such contact. The research suggests that this disconnect may be a major contributor to physiological dysfunction and unwellness. Reconnection with the Earth's electrons has been found to promote intriguing physiological changes and subjective reports of well-being. Earthing (or grounding) refers to the discovery of benefits—including better sleep and reduced pain—from walking barefoot outside or sitting, working, or sleeping indoors connected to conductive systems that transfer the Earth's electrons from the ground into the body. This paper reviews the earthing research and the potential of earthing as a simple and easily accessed global modality of significant clinical importance. PMID:22291721

  1. Earthing: Health Implications of Reconnecting the Human Body to the Earth's Surface Electrons

    Directory of Open Access Journals (Sweden)

    Gaétan Chevalier

    2012-01-01

    Full Text Available Environmental medicine generally addresses environmental factors with a negative impact on human health. However, emerging scientific research has revealed a surprisingly positive and overlooked environmental factor on health: direct physical contact with the vast supply of electrons on the surface of the Earth. Modern lifestyle separates humans from such contact. The research suggests that this disconnect may be a major contributor to physiological dysfunction and unwellness. Reconnection with the Earth's electrons has been found to promote intriguing physiological changes and subjective reports of well-being. Earthing (or grounding refers to the discovery of benefits—including better sleep and reduced pain—from walking barefoot outside or sitting, working, or sleeping indoors connected to conductive systems that transfer the Earth's electrons from the ground into the body. This paper reviews the earthing research and the potential of earthing as a simple and easily accessed global modality of significant clinical importance.

  2. Multichannel surface recordings on the visual cortex: implications for a neuroprosthesis

    Science.gov (United States)

    Chelvanayagam, D. K.; Vickery, R. M.; Kirkcaldie, M. T. K.; Coroneo, M. T.; Morley, J. W.

    2008-06-01

    Using a multi-channel platinum surface electrode array, recordings from cat primary visual cortex were obtained in response to visual stimuli, and electrical stimuli delivered using the elements of the array itself. Neural responses to electrical stimuli were consistent, regardless of stimulus polarity or leading phase (biphasic), although thresholds were lower for monophasic than biphasic pulses. Both visual and electrical stimuli reliably evoked responses with characteristic components, which interacted with each other in a nonlinear summation showing first facilitation then suppression during the window of interaction. The chronaxie for eliciting threshold cortical responses was about 100 µs, and the charge density with a pulse width of 50-100 µs was around 55 µC cm-2. These data form the basis of understanding the types of cortical responses to stimuli delivered by devices suitable for chronic implantation.

  3. Advection and diffusion in random media implications for sea surface temperature anomalies

    CERN Document Server

    Piterbarg, Leonid I

    1997-01-01

    The book presents the foundations of the theory of turbulent transport within the context of stochastic partial differential equations. It serves to establish a firm connection between rigorous and non-rigorous results concerning turbulent diffusion. Mathematically all of the issues addressed in this book are concentrated around a single linear equation: stochastic advection-diffusion (transport) equation. There is no attempt made to derive universal statistics for turbulent flow. Instead emphasis is placed on a statistical description of a passive scalar (tracer) under given velocity statistics. An application concerning transport of sea surface temperature anomalies reconciles the developed theory and a highly practical issue of modern physical oceanography by using the newly designed inversion techniques which take advantage of powerful maximum likelihood and autoregressive estimators. Audience: Graduate students and researchers in mathematics, fluid dynamics, and physical oceanography.

  4. The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt

    Science.gov (United States)

    Smith, Helen E. K.; Poulton, Alex J.; Garley, Rebecca; Hopkins, Jason; Lubelczyk, Laura C.; Drapeau, Dave T.; Rauschenberg, Sara; Twining, Ben S.; Bates, Nicholas R.; Balch, William M.

    2017-11-01

    The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Samples for phytoplankton enumeration were collected from the upper mixed layer (30 m) during two cruises, the first to the South Atlantic sector (January-February 2011; 60° W-15° E and 36-60° S) and the second in the South Indian sector (February-March 2012; 40-120° E and 36-60° S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Subtropical, Polar, and Subantarctic fronts. The influence of environmental parameters, such as sea surface temperature (SST), salinity, carbonate chemistry (pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macronutrients (nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB was assessed statistically. Nanophytoplankton (cells 2-20 µm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, with the coccolithophore Emiliania huxleyi and diatoms Fragilariopsis nana, F. pseudonana, and Pseudo-nitzschia spp. as the most numerically dominant and widely distributed. A combination of SST, macronutrient concentrations, and pCO2 provided the best statistical descriptors of the biogeographic variability in biomineralizing species composition between stations. Emiliania huxleyi occurred in silicic acid-depleted waters between the Subantarctic Front and the Polar Front, a favorable environment for this species after spring diatom blooms remove silicic acid

  5. Contrasting optical properties of surface waters across the Fram Strait and its potential biological implications

    DEFF Research Database (Denmark)

    Pavlov, Alexey K.; Granskog, Mats A.; Stedmon, Colin A.

    2015-01-01

    Underwater light regime is controlled by distribution and optical properties of colored dissolved organic matter (CDOM) and particulate matter. The Fram Strait is a region where two contrasting water masses are found. Polar water in the East Greenland Current (EGC) and Atlantic water in the West...... Spitsbergen Current (WSC) differ with regards to temperature, salinity and optical properties. We present data on absorption properties of CDOM and particles across the Fram Strait (along 79° N), comparing Polar and Atlantic surface waters in September 2009 and 2010. CDOM absorption of Polar water in the EGC...... with higher absorption found in the eastern part of the Fram Strait. Average values of particle absorption (aP(440), m-1) were 0.016±0.013 (in 2009) and 0.014±0.011 (in 2010), and 0.047±0.012 (in 2009) and 0.016±0.014 (in 2010), respectively for Polar and Atlantic water. Thus absorption of light in eastern...

  6. A review of the clinical implications of anti-infective biomaterials and infection-resistant surfaces.

    Science.gov (United States)

    Campoccia, Davide; Montanaro, Lucio; Arciola, Carla Renata

    2013-11-01

    Infection is currently regarded as the most severe and devastating complication associated to the use of biomaterials. The important social, clinical and economic impacts of implant-related infections are promoting the efforts to obviate these severe diseases. In this context, the development of anti-infective biomaterials and of infection-resistant surfaces is being regarded as the main strategy to prevent the establishment of implant colonisation and biofilm formation by bacteria. In this review, the attention is focused on the biomaterial-associated infections, from which the need for anti-infective biomaterials originates. Biomaterial-associated infections differ markedly for epidemiology, aetiology and severity, depending mainly on the anatomic site, on the time of biomaterial application, and on the depth of the tissues harbouring the prosthesis. Here, the diversity and complexity of the different scenarios where medical devices are currently utilised are explored, providing an overview of the emblematic applicative fields and of the requirements for anti-infective biomaterials. © 2013 Elsevier Ltd. All rights reserved.

  7. Temperature dependence of Fe/++/ crystal field spectra - Implications to mineralogical mapping of planetary surfaces

    Science.gov (United States)

    Sung, C.-M.; Singer, R. B.; Parkin, K. M.; Burns, R. G.; Osborne, M.

    1977-01-01

    Results are reported of Fe(++) crystal field spectral measurements for olivines and pyroxenes up to 400 C. The results are correlated with crystal structure data at elevated temperatures, and the validity of remote-sensed identifications of minerals on hot surfaces of the moon and Mercury is assessed. Two techniques were used to obtain spectra of minerals at elevated temperatures using a spectrophotometer. One employed a diamond cell assembly or a specially designed sample holder to measure polarized absorption spectra of heated single crystals. For the other technique, a sample holder was designed to attach to a diffuse reflectance accessory to produce reflectance spectra of heated powdered samples. Polarized absorption spectra of forsterite at 20-400 C are shown in a graph. Other graphs show the temperature dependence of Fe(++) crystal field bands in olivines, the diffuse reflectance spectra of olivine at 40-400 C, the polarization absorption spectra of orthopyroxene at 30-400 C, the diffuse reflectance spectra of pigeonite at 40-400 C, and unpolarized absorption spectra of lunar pyroxene from Apollo 15 rock 15058.

  8. Continuous cover forestry: possible implications for surface water acidification in the UK uplands

    Directory of Open Access Journals (Sweden)

    B. Reynolds

    2004-01-01

    Full Text Available The effects of widespread conifer afforestation on the acidity of lakes and streams in the acid sensitive uplands of the UK has been researched extensively and has contributed to the development and implementation of national forest management guidelines (e.g. Forest and Water Guidelines; Forestry Commission, 1993. However, a recent policy document (Woodlands for Wales; National Assembly for Wales, 2000 has proposed a major shift in the management of 50% of the Forestry Commission estate in Wales from the current system of patch clearfelling to Continuous Cover Forestry (CCF. This scale of change is without precedent in the UK; no studies in the UK forest environment have examined the likely environmental impacts of CCF. However, the wealth of environmental data from studies of UK forests managed by patch clearfelling enables an assessment of the impact of a change to CCF on three issues of particular relevance to surface water acidification in the uplands; forest harvesting, soil base cation depletion and atmospheric pollutant deposition. Whilst there is uncertainty as to how even-aged stands will be transformed to CCF in the UK, guiding principles for CCF on acidic and acid sensitive sites should focus on those aspects of management which minimise nitrate leaching, encourage base cation retention within the soil-plant system and enhance base cation inputs from external (atmospheric and internal sources (weathering. CCF may provide opportunities to achieve this by reducing the scale of clearfelling, increasing species diversity, changing the structure of plantation forests and maintaining uninterrupted woodland cover. Keywords: acidification, forestry, continuous cover forestry, clearfelling

  9. Illumination Conditions at Phobos: Implications for Surface Processes, Volatiles and Exploration

    Science.gov (United States)

    Stubbs, T. J.; Wang, Y.; Glenar, D. A.

    2016-12-01

    Illumination conditions at airless bodies, such as Phobos, control or significantly influence many aspects of their environment, including temperature of the surface and subsurface, volatile sequestration and transport. In this study we simulate the average present-day illumination conditions at Phobos and assess whether locations exist where water ice could be either thermally stable in the near subsurface on billion year timescales, or accumulated by the "thermal ice pump" effect. Previous investigations of Phobos temperature and volatile sequestration have assumed a sphere or triaxial ellipsoid shape for Phobos. Here we use more realistic shape models in order to capture the shadowing caused by both its global-scale irregular shape and smaller scale structures, such as craters, that can have a crucial role in determining illumination conditions. Phobos is frequently eclipsed by Mars, especially around equinoxes, and this important effect is accounted for in the shadowing simulations. Preliminary predictions for the average incident solar flux using the Thomas [1993] shape model reveal many interesting features, such as high fluxes around crater rims (e.g., Stickney), doubly-shadowed craters (e.g., Limtoc) and strong asymmetries between poleward- and equatorward-facing crater walls (e.g., Drunlo). Perhaps most significantly, there are regions (most likely small craters) that are predicted to receive very low average solar flux ( 40-50 Wm-2). These will likely be, on average, the coldest places on Phobos. Should water ice, or other volatiles, be present at relatively shallow depths at certain locations on Phobos, then this could serve as a witness plate to the history of the Mars system, as well as provide valuable resources to future explorers.

  10. Impact And Thermal Treatment Of Clays: Implications For The Surface Properties Of Mars

    Science.gov (United States)

    Gavin, Patricia; Chevrier, V.

    2007-10-01

    CRISM has recently confirmed OMEGA's previous detection of clays on the surface of Mars, mainly in the Nili Fossae and Mawrth Vallis regions in the Noachian terrains. It has been proposed that transformations of clays through meteoritic impacts and thermal metamorphism may be responsible for Mars’ red color. We thermally treated several samples of nontronite (Fe-rich clay) and montmorillonite (Al-rich clay) in both air and in a CO2 atmosphere to various temperatures (from 500°C to 1100°C) for various durations (4 to 24 hrs) and impacted each clay sample at 2.5 km/s. X-Ray Diffraction (XRD), infrared spectrometry (FT-IR), ESEM, TEM, and magnetic properties analyses were performed on each sample. XRD of heated samples showed the formation of hematite, sillimanite, and cristobalite in high temperature samples. The same phases with corundum and quartz formed in the medium temperature samples. ESEM and EDX analyses confirmed these results. No secondary phase was observed on the XRD spectra of the impacted samples. Magnetic analyses showed properties of hematite at high temperature, spinel only in the CO2 atmosphere at 850°C and the systematic formation of a distinct unknown magnetic phase around 900-1000°C, also observed in TEM. FT-IR analysis in the MIR range showed the loss of interlayer water and a quartz/silica-forming phase. NIR spectra of the shocked samples were of particular interest because of the formation of a pair of unidentified peaks at 3.4 and 3.5 μm. These two peaks did not appear in any other spectrum, indicating they are the result of the shock treatment only. Such result, combined with XRD results, suggests potential amorphisation of the impacted clays. Such a specific feature could help determine if clays were affected by shock on Mars.

  11. Binding of ethanol on calcite: the role of the OH bond and its relevance to biomineralization

    DEFF Research Database (Denmark)

    Sand, K K; Yang, M; Makovicky, E

    2010-01-01

    The interaction of OH-containing compounds with calcite, CaCO(3), such as is required for the processes that control biomineralization, has been investigated in a low-water solution. We used ethanol (EtOH) as a simple, model, OH-containing organic compound, and observed the strength of its...

  12. Morphology and formation mechanism in precipitation of calcite induced by Curvibacter lanceolatus strain HJ-1

    Science.gov (United States)

    Zhang, Chonghong; Li, Fuchun; Lv, Jiejie

    2017-11-01

    Precipitation of calcium carbobate induced by microbial activities is common occurrence in controlled solution, but the formation mechanism and morphology in precipitation of calcite in solution systems is unclear, and the role of microbes is disputed. Here, culture experiment was performed for 50 days using the Curvibacter lanceolatus strain HJ-1 in a M2 culture medium, and the phase composition and morphology of the precipitates were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM) techniques. We show that the precipitation processes in our experiment lead to unusual morphologies of crystals corresponding to different growth stages, and the morphologies of the precipitated crystal aggregates ranging from the main rod-, cross-, star-, cauliflower-like morphologies to spherulitic structure. The complex and unusual morphologies of the precipitated calcite by strain HJ-1 may provide a reference point for better understanding the biomineralization mechanism of calcite, moreover, morphological transition of minerals revealed that the multi-ply crystals-aggregation mechanism for calcite growth in crystallisation media.

  13. Simple, simultaneous gravimetric determination of calcite and dolomite in calcareous soils

    Science.gov (United States)

    Literature pertaining to determination of calcite and dolomite is not modern and describes slow methods that require expensive specialized apparatus. The objective of this paper was to describe a new method that requires no specialized equipment. Linear regressions and correlation coefficients for...

  14. Impacts of pH and [CO32-] on the incorporation of Zn in foraminiferal calcite

    NARCIS (Netherlands)

    van Dijk, Inge; de Nooijer, Lennart J.; Wolthers, Mariëtte; Reichart, Gert-Jan

    2017-01-01

    The trace elemental composition of foraminiferal shell calcite is known to reflect the environment in which the shell was precipitated. Whereas conservative elements incorporated in foraminiferal shell carbonate reflect factors such as temperature (Mg), carbonate chemistry (B) and salinity (Na), the

  15. Fulvic acid-like organic compounds control nucleation of marine calcite under suboxic conditions

    NARCIS (Netherlands)

    Neuweiler, F.; D'Orazio, M.; Immenhauser, A.M.; Geipel, G.; Heise, K.H.; Cocozza, C.; Miano, T.M.

    2003-01-01

    Intracrystalline organic compounds, enclosed within in situprecipitated marine microcrystalline calcite (automicrite), might represent either an inclusion or the catalyst of such precipitation. We use evidence from a Lower Cretaceous deep-water carbonate mound to show (1) the original source, (2)

  16. DC CONDUCTIVITY OF CERAMICS WITH CALCITE WASTE IN THE TEMPERATURE RANGE 20 - 1050C

    Directory of Open Access Journals (Sweden)

    Jan Ondruska

    2015-06-01

    Full Text Available The temperature dependences of the electrical DC conductivity of calcite waste, kaolinite and illite based ceramics were measured in the temperature range of 20 - 1050oC. The ceramic mass that was used was a mixture of 60 wt. % kaolinitic-illitic clay, 20 - 40 wt. % of this clay was fired at 1000oC for 90 min and 0, 10 and 20 wt. % of calcite waste. During heating, several processes take place - the release of the physically bound water, the burning of organic impurities, the dehydroxylation of kaolinite and illite, the decomposition of calcite, and the creation of anorthite and mullite. All of these processes were checked by means of differential thermal analysis (DTA, derivative thermogravimetry (DTG and thermodilatometry (TDA. At low temperatures (20 - 200oC, due to the release and decomposition of physically bound water, H+ and OH- are dominant charge carriers. After completion of release of physically bound water, up to the start of dehydroxylation at the temperature of ~ 450oC, the DC conductivity is dominated by a transport of Na+, K+, and Ca2+ ions. During dehydroxylation, H+ and OH- ions, which are released from kaolinite and illite lattices, contribute to the DC conductivity. Decomposition of calcite runs between ~ 700oC and 900oC. The glassy phase has a dominant influence on the DC conductivity in the fired ceramics. Its high conductivity is determined by the high mobility of Na+, K+, and Ca2+ ions.

  17. A generalised chemical precipitation modelling approach in wastewater treatment applied to calcite

    DEFF Research Database (Denmark)

    Mbamba, Christian Kazadi; Batstone, Damien J.; Flores Alsina, Xavier

    2015-01-01

    , the present study aims to identify a broadly applicable precipitation modelling approach. The study uses two experimental platforms applied to calcite precipitating from synthetic aqueous solutions to identify and validate the model approach. Firstly, dynamic pH titration tests are performed to define...

  18. Carbonates in thrust faults: High temperature investigations into deformation processes in calcite-dolomite systems

    Science.gov (United States)

    Kushnir, A.; Kennedy, L.; Misra, S.; Benson, P.

    2012-04-01

    The role of dolomite on the strength and evolution of calcite-dolomite fold and thrust belts and nappes (as observed in the Canadian Rockies, the Swiss Alps, the Italian Apennines, and the Naukluft Nappe Complex) is largely unknown. Field investigations indicate that strain in natural systems is localized in calcite, resulting in a ductile response, while dolomite deforms in a dominantly brittle manner. To date, experimental studies on polymineralic carbonate systems are limited to homogeneous, fine-grained, calcite-dolomite composites of relatively low dolomite content. The effect of dolomite on limestone rheology, the onset of crystal-plastic deformation in dolomite in composites, and the potential for strain localization in composites have not yet been fully quantified. Constant displacement rate (3x10-4 s-1and 10-4 s-1), high confining pressure (300 MPa) and high temperature (750° C and 800° C) torsion experiments were conducted to address the role of dolomite on the strength of calcite-dolomite composites. Experiments were performed on samples produced by hot isostatic pressing (HIP) amalgams of a natural, pure dolomite and a reagent, pure calcite. We performed experiments on the following mixtures (given as dolomite%): 25%, 35%, 50%, and 75%. These synthetic HIP products eliminated concerns of mineralogical impurities and textural anomalies due to porosity, structural fabrics (e.g., foliation) and fossil content. The samples were deformed up to a maximum finite shear strain of 5.0 and the experimental set up was unvented to inhibit sample decarbonation. Mechanical data shows a considerable increase in sample yield strength with increasing dolomite content. Experimental products with low starting dolomite content (dol%: 25% and 35%) display macroscopic strain localization along compositionally defined foliation. Experimental products with high dolomite content (dol%: 50% and 75%) demonstrate no macroscopic foliation. Post-deformation microstructure analysis

  19. Tracing formation and durability of calcite in a Punic-Roman cistern mortar (Pantelleria Island, Italy).

    Science.gov (United States)

    Dietzel, Martin; Schön, Frerich; Heinrichs, Jens; Deditius, Artur P; Leis, Albrecht

    2016-01-01

    Ancient hydraulic lime mortar preserves chemical and isotopic signatures that provide important information about historical processing and its durability. The distribution and isotopic composition of calcite in a mortar of a well-preserved Punic-Roman cistern at Pantelleria Island (Italy) was used to trace the formation conditions, durability, and individual processing periods of the cistern mortar. The analyses of stable carbon and oxygen isotopes of calcite revealed four individual horizons, D, E, B-1 and B-2, of mortar from the top to the bottom of the cistern floor. Volcanic and ceramic aggregates were used for the production of the mortar of horizons E/D and B-1/B-2, respectively. All horizons comprise hydraulic lime mortar characterized by a mean cementation index of 1.5 ± 1, and a constant binder to aggregate ratio of 0.31 ± 0.01. This suggests standardized and highly effective processing of the cistern. The high durability of calcite formed during carbonation of slaked lime within the matrix of the ancient mortar, and thus the excellent resistance of the hydraulic lime mortar against water, was documented by (i) a distinct positive correlation of δ(18)Ocalcite and δ(13)Ccalcite; typical for carbonation through a mortar horizon, (ii) a characteristic evolution of δ(18)Ocalcite and δ(13)Ccalcite through each of the four mortar horizons; lighter follow heavier isotopic values from upper to lower part of the cistern floor, and (iii) δ(18)Ocalcite varying from -10 to -5 ‰ Vienna Pee Dee belemnite (VPDB). The range of δ(18)Ocalcite values rule out recrystallization and/or neoformation of calcite through chemical attack of water stored in cistern. The combined studies of the chemical composition of the binder and the isotopic composition of the calcite in an ancient mortar provide powerful tools for elucidating the ancient techniques and processing periods. This approach helps to evaluate the durability of primary calcite and demonstrates the

  20. The influence of mineralization pathways on the Mg content and fractionation patterns in calcite

    Science.gov (United States)

    Dove, P. M.; Wang, D.; DeYoreo, J.

    2011-12-01

    Chemical proxy models are based upon the long-standing assumption that the uptake of minor and trace elements into a growing mineral reflects equilibrium fractionation processes. This picture is rooted in fundamental assumptions from BCF crystal growth theory- the thermodynamic-based model that was derived for step growth at very near equilibrium conditions. However, the original assumptions of this theory have been lost. Moreover, the applicability of step growth processes to biomineralization is being called into question with the realization that many carbonate biominerals form by non-classical processes. Here, mineralization begins with the accumulation of an amorphous calcium carbonate (ACC) in a localized environment that subsequently transforms to the complex mesocrystal/organic composites we know as skeletal structures. This study investigates the Mg content of calcites that form from ACC over a range of Mg/Ca ratios. At low Mg/Ca levels where Mg content is insufficient to inhibit step growth, the ACC transforms into crystallites of Mg calcites with 0-20 mol % MgCO3. These calcites exhibit the expected linear fractionation with Mg/Ca of the initial solution. In contrast, when initial Mg levels are above the threshold where step growth is prohibited, ACC transforms to nanoparticle aggregates of very high Mg calcite (30-50 mol% MgCO3). The Mg content of calcites formed by this process is approximately independent of solution composition- without evidence of fractionation. Mineralization is biased to this alternative pathway when the Mg content of the local environment is too high for calcite growth and saturation increases rapidly to reach ACC solubility before aragonite precipitation can occur. The pathway is allowed because high levels of supersaturation render thermodynamic barriers to nucleation less significant than kinetic barriers, which are apparently larger for the crystalline phases. Thus, the alternative pathway is a consequence of interplays

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

    Science.gov (United States)

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

    2017-04-01

    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) 26Mg 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

  2. Aggregation and surface properties of F-specific RNA phages: implication for membrane filtration processes.

    Science.gov (United States)

    Langlet, Jérémie; Gaboriaud, Fabien; Duval, Jérôme F L; Gantzer, Christophe

    2008-05-01

    illustrative examples. The determination and qualitative interpretation of the surface properties of the viral particles as reported in the current study are commented within the context of water treatment especially concerning viral removal by membrane filtration processes.

  3. Temperature dependence of oxygen isotope fractionation in coccolith calcite: A culture and core top calibration of the genus Calcidiscus

    Science.gov (United States)

    Candelier, Yaël; Minoletti, Fabrice; Probert, Ian; Hermoso, Michaël

    2013-01-01

    Reconstructions of seawater temperature based on measurement of oxygen isotopes in carbonates mostly derive from analyses of bulk sediment samples or manually picked foraminifera. The temperature dependence of 18O fractionation in biogenic calcite was first established in the 1950s and the objective of the present study is to re-evaluate this temperature dependence in coccolith calcite with a view to developing a robust proxy for reconstructing "vital effect"-free δ18O values. Coccoliths, the micron-sized calcite scales produced by haptophyte algae that inhabit surface mixed-layer waters, are a dominant component of pelagic sediments. Despite their small size, recent methodological developments allow species-specific separation (and thus isotopic analysis) of coccoliths from bulk sediments. This is especially the case for Calcidiscus spp. coccoliths that are relatively easy to separate out from other sedimentary carbonate grains including other coccolith taxa. Three strains of coccolithophores belonging to the genus Calcidiscus and characterised by distinct cell and coccolith diameters were grown in the laboratory under controlled temperature conditions over a range from 15 to 26 °C. The linear relationship that relates 18O fractionation to the temperature of calcification is here calibrated by the equation: T [°C] = -5.83 × (δ18OCalcidiscus - δ18Omedium) + 4.83 (r = 0.98). The slope of the regression is offset of ˜-1.1‰ from that of equilibrium calcite. This offset corresponds to the physiologically induced isotopic effect or "vital effect". The direction of fractionation towards light isotopic values is coherent with previous reports, but the intensity of fractionation in our dilute batch cultures was significantly closer to equilibrium compared to previously reported offset values. No significant isotopic difference was found between the three Calcidiscus coccolithophores, ruling out a control of the cell geometry on oxygen isotope fractionation within

  4. Review of aragonite and calcite crystal morphogenesis in thermal spring systems

    Science.gov (United States)

    Jones, Brian

    2017-06-01

    Aragonite and calcite crystals are the fundamental building blocks of calcareous thermal spring deposits. The diverse array of crystal morphologies found in these deposits, which includes monocrystals, mesocrystals, skeletal crystals, dendrites, and spherulites, are commonly precipitated under far-from-equilibrium conditions. Such crystals form through both abiotic and biotic processes. Many crystals develop through non-classical crystal growth models that involve the arrangement of nanocrystals in a precisely controlled crystallographic register. Calcite crystal morphogenesis has commonly been linked to a ;driving force;, which is a conceptual measure of the distance of the growth conditions from equilibrium conditions. Essentially, this scheme indicates that increasing levels of supersaturation and various other parameters that produce a progressive change from monocrystals and mesocrystals to skeletal crystals to crystallographic and non-crystallographic dendrites, to dumbbells, to spherulites. Despite the vast amount of information available from laboratory experiments and natural spring systems, the precise factors that control the driving force are open to debate. The fact that calcite crystal morphogenesis is still poorly understood is largely a reflection of the complexity of the factors that influence aragonite and calcite precipitation. Available information indicates that variations in calcite crystal morphogenesis can be attributed to physical and chemical parameters of the parent water, the presence of impurities, the addition of organic or inorganic additives to the water, the rate of crystal growth, and/or the presence of microbes and their associated biofilms. The problems in trying to relate crystal morphogenesis to specific environmental parameters arise because it is generally impossible to disentangle the controlling factor(s) from the vast array of potential parameters that may act alone or in unison with each other.

  5. Green technological approach to synthesis hydrophobic stable crystalline calcite particles with one-pot synthesis for oil-water separation during oil spill cleanup.

    Science.gov (United States)

    Wu, Min-Nan; Maity, Jyoti Prakash; Bundschuh, Jochen; Li, Che-Feng; Lee, Chin-Rong; Hsu, Chun-Mei; Lee, Wen-Chien; Huang, Chung-Ho; Chen, Chien-Yen

    2017-10-15

    The process of separating oil and water from oil/water mixtures is an attractive strategy to answer the menace caused by industrial oil spills and oily wastewater. In addition, water coproduced during hydrocarbon exploitation, which can be an economic burden and risk for freshwater resources, can become an important freshwater source after suitable water-oil separation. For oil-water separation purposes, considerable attention has been paid to the preparation of hydrophobic-oleophilic materials with modified surface roughness. However, due to issues of thermodynamic instability, costly and complex methods as well as lack of ecofriendly compounds, most of hydrophobic surface modified particles are of limited practical application. The study presents a facile procedure, to synthesize crystalline particles of calcite, which is the most stable polymorph of CaCO 3 from industrial CaCO 3 using oleic acid as an additive in a one-pot synthesis method. The XRD results show that the synthesized particles were a well-crystallized form of calcite. The FTIR results reflect the appearance of the alkyl groups from the oleic acid in synthesized particles which promotes the production of calcite with 'rice shape' (1.64 μm) (aggregated by spherical nanoparticle of 19.56 nm) morphology with concomitant changes in its surface wettability from hydrophilic to hydrophobic. The synthesized particles exhibited near to super hydrophobicity with ∼99% active ratio and a contact angle of 143.8°. The synthesized hydrophobic calcite particles had an oleophilic nature where waste diesel oil adsorption capacity of synthesized calcium carbonate (HCF) showed a very high (>99%) and fast (7 s) oil removal from oil-water mixture. The functional group of long alkyl chain including of CO bounds may play critical roles for adsorption of diesel oils. Moreover, the thermodynamically stable crystalline polymorph calcite (compared to vaterite) exhibited excellent recyclability. The isothermal study

  6. Strong sea surface cooling in the eastern equatorial Pacific and implications for Galápagos Penguin conservation

    Science.gov (United States)

    Karnauskas, K. B.; Jenouvrier, S.; Brown, C. W.; Murtugudde, R.

    2015-08-01

    The Galápagos is a flourishing yet fragile ecosystem whose health is particularly sensitive to regional and global climate variations. The distribution of several species, including the Galápagos Penguin, is intimately tied to upwelling of cold, nutrient-rich water along the western shores of the archipelago. Here we show, using reliable, high-resolution sea surface temperature observations, that the Galápagos cold pool has been intensifying and expanding northward since 1982. The linear cooling trend of 0.8°C/33 yr is likely the result of long-term changes in equatorial ocean circulation previously identified. Moreover, the northward expansion of the cold pool is dynamically consistent with a slackening of the cross-equatorial component of the regional trade winds—leading to an equatorward shift of the mean position of the Equatorial Undercurrent. The implied change in strength and distribution of upwelling has important implications for ongoing and future conservation measures in the Galápagos.

  7. Calcite dissolution by Brevibacterium sp. SOTI06: A futuristic approach for the reclamation of calcareous sodic soils

    Directory of Open Access Journals (Sweden)

    Tamilselvi S.M

    2016-12-01

    Full Text Available Assessing the ability of soil microorganisms to dissolute poorly soluble native calcite to supply Ca2+ is a new area to be explored in reclaiming sodic soils by supplying adequate Ca2+ and reducing the recurrent sodicity. Hence, the present study aimed to isolate a calcite dissolving bacteria (CDB from calcareous sodic soils and to understand the mechanism of calcite dissolution. Of the thirty three CDB isolates recovered from the calcareous sodic soils of Tamil Nadu (Coimbatore, Ramnad and Trichy, eleven isolates were screened for calcite dissolution based on titratable acidity. 16S rRNA gene sequence analysis of the three best isolates viz., SORI09, SOTI05 and SOTI06 revealed 99 % similarity to Bacillus aryabhattai, 100 % to B. megaterium and 93 % to Brevibacterium sp., respectively. Among them, Brevibacterium sp. SOTI06 released more Ca2+ (3.6 g.l-1 by dissolving 18.6 % of the native calcite. The spectral data of FTIR also showed reduction in the intensity of calcite (55.36 to 41.27 by the isolate at a wave number of 1636 cm-1 which confirmed the dissolution. Besides producing organic acids (gluconic acid and acetic acid, Brevibacterium sp. SOTI06 also produced siderophore (91.6 % and extracellular polysaccharides (EPS, 13.3 µg. ml-1 which might have enhanced the calcite dissolution.

  8. Calcite Dissolution by Brevibacterium sp. SOTI06: A Futuristic Approach for the Reclamation of Calcareous Sodic Soils.

    Science.gov (United States)

    Tamilselvi, S M; Thiyagarajan, Chitdeshwari; Uthandi, Sivakumar

    2016-01-01

    Assessing the ability of soil microorganisms to dissolute poorly soluble native calcite to supply Ca2+ is a new area to be explored in reclaiming sodic soils by supplying adequate Ca2+ and reducing the recurrent sodicity. Hence, the present study aimed to isolate a calcite dissolving bacteria (CDB) from calcareous sodic soils and to understand the mechanism of calcite dissolution. Of the 33 CDB isolates recovered from the calcareous sodic soils of Tamil Nadu (Coimbatore, Ramnad, and Trichy), 11 isolates were screened for calcite dissolution based on titratable acidity. 16S rRNA gene sequence analysis of the three best isolates viz., SORI09, SOTI05, and SOTI06 revealed 99% similarity to Bacillus aryabhattai, 100% to B. megaterium, and 93% to Brevibacterium sp., respectively. Among them, Brevibacterium sp. SOTI06 released more Ca2+ (3.6 g.l-1) by dissolving 18.6% of the native calcite. The spectral data of FTIR also showed reduction in the intensity of calcite (55.36-41.27) by the isolate at a wave number of 1636 cm-1 which confirmed the dissolution. Besides producing organic acids (gluconic acid and acetic acid), Brevibacterium sp. SOTI06 also produced siderophore (91.6%) and extracellular polysaccharides (EPS, 13.3 μg. ml-1) which might have enhanced the calcite dissolution.

  9. Microstructure of calcite deformed by high-pressure torsion: An X-ray line profile study

    Science.gov (United States)

    Schuster, Roman; Schafler, Erhard; Schell, Norbert; Kunz, Martin; Abart, Rainer

    2017-11-01

    Calcite aggregates were deformed to high strain using high-pressure torsion and applying confining pressures of 1-6 GPa and temperatures between room temperature and 450 °C. The run products were characterized by X-ray diffraction, and key microstructural parameters were extracted employing X-ray line profile analysis. The dominant slip system was determined as r { 10 1 bar 4 } ⟨ 2 bar 021 ⟩ with edge dislocation character. The resulting dislocation density and the size of the coherently scattering domains (CSD) exhibit a systematic dependence on the P-T conditions of deformation. While high pressure generally impedes recovery through reducing point defect mobility, the picture is complicated by pressure-induced phase transformations in the CaCO3 system. Transition from the calcite stability field to those of the high-pressure polymorphs CaCO3-II, CaCO3-III and CaCO3-IIIb leads to a change of the microstructural evolution with deformation. At 450 °C and pressures within the calcite stability field, dislocation densities and CSD sizes saturate at shear strains exceeding 10 in agreement with earlier studies at lower pressures. In the stability field of CaCO3-II, the dislocation density exhibits a more complex behavior. Furthermore, at a given strain and strain rate, the dislocation density increases and the CSD size decreases with increasing pressure within the stability fields of either calcite or of the high-pressure polymorphs. There is, however, a jump from high dislocation densities and small CSDs in the upper pressure region of the calcite stability field to lower dislocation densities and larger CSDs in the low-pressure region of the CaCO3-II stability field. This jump is more pronounced at higher temperatures and less so at room temperature. The pressure influence on the deformation-induced evolution of dislocation densities implies that pressure variations may change the rheology of carbonate rocks. In particular, a weakening is expected to occur at

  10. Survival of endospores of Bacillus subtilis on spacecraft surfaces under simulated martian environments: implications for the forward contamination of Mars

    Science.gov (United States)

    Schuerger, Andrew C.; Mancinelli, Rocco L.; Kern, Roger G.; Rothschild, Lynn J.; McKay, Christopher P.

    2003-01-01

    Experiments were conducted in a Mars simulation chamber (MSC) to characterize the survival of endospores of Bacillus subtilis under high UV irradiation and simulated martian conditions. The MSC was used to create Mars surface environments in which pressure (8.5 mb), temperature (-80, -40, -10, or +23 degrees C), gas composition (Earth-normal N2/O2 mix, pure N2, pure CO2, or a Mars gas mix), and UV-VIS-NIR fluence rates (200-1200 nm) were maintained within tight limits. The Mars gas mix was composed of CO2 (95.3%), N2 (2.7%), Ar (1.7%), O2 (0.2%), and water vapor (0.03%). Experiments were conducted to measure the effects of pressure, gas composition, and temperature alone or in combination with Mars-normal UV-VIS-NIR light environments. Endospores of B. subtilis, were deposited on aluminum coupons as monolayers in which the average density applied to coupons was 2.47 x 10(6) bacteria per sample. Populations of B. subtilis placed on aluminum coupons and subjected to an Earth-normal temperature (23 degrees C), pressure (1013 mb), and gas mix (normal N2/O2 ratio) but illuminated with a Mars-normal UV-VIS-NIR spectrum were reduced by over 99.9% after 30 sec exposure to Mars-normal UV fluence rates. However, it required at least 15 min of Mars-normal UV exposure to reduce bacterial populations on aluminum coupons to non-recoverable levels. These results were duplicated when bacteria were exposed to Mars-normal environments of temperature (-10 degrees C), pressure (8.5 mb), gas composition (pure CO2), and UV fluence rates. In other experiments, results indicated that the gas composition of the atmosphere and the temperature of the bacterial monolayers at the time of Mars UV exposure had no effects on the survival of bacterial endospores. But Mars-normal pressures (8.5 mb) were found to reduce survival by approximately 20-35% compared to Earth-normal pressures (1013 mb). The primary implications of these results are (a) that greater than 99.9% of bacterial populations on

  11. Ocean acidification: Towards a better understanding of calcite dissolution

    Science.gov (United States)

    Wilhelmus, Monica M.; Adkins, Jess; Menemenlis, Dimitris

    2016-11-01

    The drastic increase of anthropogenic CO2 emissions over the past two centuries has altered the chemical structure of the ocean, acidifying upper ocean waters. The net impact of this pH decrease on marine ecosystems is still unclear, given the unprecedented rate at which CO2 is being released into the atmosphere. As part of the carbon cycle, calcium carbonate dissolution in sediments neutralizes CO2: phytoplankton at the surface produce carbonate minerals, which sink and reach the seafloor after the organisms die. On time scales of thousands of years, the calcium carbonate in these shells ultimately reacts with CO2 in seawater. Research in this field has been extensive; nevertheless, the dissolution rate law, the impact of boundary layer transport, and the feedback with the global ocean carbon cycle remain controversial. Here, we (i) develop a comprehensive numerical framework via 1D modeling of carbonate dissolution in sediments, (ii) approximate its impact on water column properties by implementing a polynomial approximation to the system's response into a global ocean biogeochemistry general circulation model (OBGCM), and (iii) examine the OBGCM sensitivity response to different formulations of sediment boundary layer properties. We find that, even though the burial equilibration time scales of calcium carbonate are in the order of thousands of years, the formulation of a bottom sediment model along with an improved description of the dissolution rate law can have consequences on multi-year to decadal time scales.

  12. Experimental fractionation of stable carbon isotopes during degassing of carbon dioxide and precipitation of calcite from aqueous solutions

    Science.gov (United States)

    Müller, K.; Winde, V.; Escher, P.; von Geldern, R.; Böttcher, M. E.

    2012-04-01

    Processes in the carbonate system of surface waters are in particular sensitive to variations of boundary conditions as, for instance, the partial pressure of carbon dioxide in the atmosphere and the aqueous solution. Examples range from streams, rivers, to coastal marine waters. The flux of carbon dioxide from continental flowing waters was recently included into calculations of the global carbon budget (Butman & Raymond, 2011, Nature Geo.). These solutions, are often supersaturated in carbon dioxide with respect to the atmosphere. The degassing of carbon dioxide is associated with a kinetically controlled fractionation of the stable carbon isotopes, which has to be considered in balancing water-air carbon dioxide fluxes. The degassing process additionally leads to the super-saturation of the aqueous solution with respect to calcium carbonate. Stable isotope fractionation is of particular value to identify and quantify processes at the water-gas phase interface and link these non-equilibrium processes to the formation mechanisms of calcite and the hydrodynamics of surface waters. Experiments were carried out with or without inert N2 gas flow to degas carbon dioxide from initially supersaturated solutions. Natural solutions used are from different stations of the Elbe estuary, the Jade Bay, the backbarrier tidal area of Spiekeroog Island, carbonate springs of Rügen Island, and the Baltic Sea coastline. Results are compared experiments using bottled mineral waters. By following the (physico) chemical changes in the solutions (pH, TA, Ca PHREEQC modeling) it was found, that two evolutionary stages can be differentiated. Reaction progress led to the preferential liberation of carbon dioxide containing the light carbon isotope, following a Rayleigh-type process. After an induction period, where only degassing of carbon dioxide took place, a second stage was observed where calcite began to form from the highly supersaturated solutions. In this stage the carbonate

  13. Thermodynamics of magnesian calcite solid-solutions at 25°C and 1 atm total pressure

    Science.gov (United States)

    Busenberg, Eurybiades; Plummer, L. Niel

    1989-01-01

    The stability of magnesian calcites was reexamined, and new results are presented for 28 natural inorganic, 12 biogenic, and 32 synthetic magnesian calcites. The magnesian calcite solid-solutions were separated into two groups on the basis of differences in stoichiometric solubility and other physical and chemical properties. Group I consists of solids of mainly metamorphic and hydrothermal origin, synthetic calcites prepared at high temperatures and pressures, and synthetic solids prepared at low temperature and very low calcite supersaturations () from artificial sea water or NaClMgCl2CaCl2solutions. Group I solids are essentially binary s of CaCO2 and MgCO2, and are thought to be relatively free of structural defects. Group II solid-solutions are of either biogenic origin or are synthetic magnesian calcites and protodolomites (0–20 and ∼ 45 mole percent MgCO3) prepared at high calcite supersaturations () from NaClNa2SO4MgCl2CaCl2 or NaClMgCl2CaCl2 solutions. Group II solid-solutions are treated as massively defective solids. The defects include substitution foreign ions (Na+ and SO42−) in the magnesian calcite lattice (point defects) and dislocations (~2 · 109 cm−2). Within each group, the excess free energy of mixing, GE, is described by the mixing model , where x is the mole fraction of the end-member Ca0.5Mg0.5CO3 in the solid-solution. The values of A0and A1 for Group I and II solids were evaluated at 25°C. The equilibrium constants of all the solids are closely described by the equation ln , where KC and KD are the equilibrium constants of calcite and Ca0.5Mg0.5CO3. Group I magnesian calcites were modeled as sub-regular solid-solutions between calcite and dolomite, and between calcite and “disordered dolomite”. Both models yield almost identical equilibrium constants for these magnesian calcites. The Group II magnesian calcites were modeled as sub-regular solid-solutions between defective calcite and

  14. Uranium immobilization by sulfate-reducing biofilms grown on hematite, dolomite, and calcite.

    Science.gov (United States)

    Marsili, Enrico; Beyenal, Haluk; Di Palma, Luca; Merli, Carlo; Dohnalkova, Alice; Amonette, James E; Lewandowski, Zbigniew

    2007-12-15

    Biofilms of sulfate-reducing bacteria Desulfovibrio desulfuricans G20 were used to reduce dissolved U(VI) and subsequently immobilize U(IV) in the presence of uranium-complexing carbonates. The biofilms were grown in three identically operated fixed bed reactors, filled with three types of minerals: one noncarbonate-bearing mineral (hematite) and two carbonate-bearing minerals (calcite and dolomite). The source of carbonates in the reactors filled with calcite and dolomite were the minerals, while in the reactor filled with hematite it was a 10 mM carbonate buffer, pH 7.2, which we added to the growth medium. Our five-month study demonstrated that the sulfate-reducing biofilms grown in all reactors were able to immobilize/reduce uranium efficiently, despite the presence of uranium-complexing carbonates.

  15. Geochemistry of speleothems affected by aragonite to calcite recrystallization - Potential inheritance from the precursor mineral

    Science.gov (United States)

    Domínguez-Villar, David; Krklec, Kristina; Pelicon, Primož; Fairchild, Ian J.; Cheng, Hai; Edwards, Lawrence R.

    2017-03-01

    Formerly aragonite speleothems recrystallized to calcite result from solutions subsaturated in aragonite and supersaturated in calcite that infiltrate into the speleothem through the interconnected porosity. In most cases, the crystal replacement takes place through a thin solution film. This diagenetic process can occur under open or semi-closed geochemical conditions. Thus, secondary calcite crystals record the composition of the fluid at the time of diagenesis affected by calcite partition coefficients and fractionation factors (open system) or partly inherit the composition of the primary aragonite (semi-closed system). So, whether or not recrystallized aragonite speleothems can record reliable geochemical signals from the time of speleothem primary deposition still is an open debate. We studied a stalagmite from Eagle Cave (Spain) predominantly composed of secondary calcite that replaced aragonite, although a core of primary aragonite extending 45 mm along the growth direction was preserved at the base of the sample. We obtained Mg and Sr compositional maps, paired U-Th dating and δ18O and δ13C profiles across the diagenetic front. Additionally, two parallel isotope records were obtained along the speleothem growth direction in the aragonite and calcite sectors. Our results support that recrystallization of this speleothem took place in open system conditions for δ18O, δ13C, Mg and Sr, but in semi-closed system conditions for U and Th. The recrystallization of this sample took place during one or several events, likely after the Younger Dryas as a result of climate change influencing drip water composition. Based on compositional zoned patterns, we suggest that the advance of diagenetic fronts in this speleothem had an average rate of 50 ± 45 μm/yr. Such recrystallization rate can transform any aragonite speleothem into calcite within a few centuries. We suggest that the volume of water interacting with the speleothem at the time of recrystallization is

  16. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers.

    Science.gov (United States)

    Ihli, Johannes; Clark, Jesse N; Côté, Alexander S; Kim, Yi-Yeoun; Schenk, Anna S; Kulak, Alexander N; Comyn, Timothy P; Chammas, Oliver; Harder, Ross J; Duffy, Dorothy M; Robinson, Ian K; Meldrum, Fiona C

    2016-06-15

    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. Here we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. This work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates.

  17. Calcite and dolomite in intrusive carbonatites. II. Trace-element variations

    Science.gov (United States)

    Chakhmouradian, Anton R.; Reguir, Ekaterina P.; Couëslan, Christopher; Yang, Panseok

    2016-04-01

    The composition of calcite and dolomite from several carbonatite complexes (including a large set of petrographically diverse samples from the Aley complex in Canada) was studied by electron-microprobe analysis and laser-ablation inductively-coupled-plasma mass-spectrometry to identify the extent of substitution of rare-earth and other trace elements in these minerals and the effects of different igneous and postmagmatic processes on their composition. Analysis of the newly acquired and published data shows that the contents of rare-earth elements (REE) and certain REE ratios in magmatic calcite and dolomite are controlled by crystal fractionation of fluorapatite, monazite and, possibly, other minerals. Enrichment in REE observed in some samples (up to ~2000 ppm in calcite) cannot be accounted for by coupled substitutions involving Na, P or As. At Aley, the REE abundances and chondrite-normalized (La/Yb)cn ratios in carbonates decrease with progressive fractionation. Sequestration of heavy REE from carbonatitic magma by calcic garnet may be responsible for a steeply sloping "exponential" pattern and lowered Ce/Ce* ratios of calcite from Magnet Cove (USA) and other localities. Alternatively, the low levels of Ce and Mn in these samples could result from preferential removal of these elements by Ce4+- and Mn3+-bearing minerals (such as cerianite and spinels) at increasing f(O2) in the magma. The distribution of large-ion lithophile elements (LILE = Sr, Ba and Pb) in rock-forming carbonates also shows trends indicative of crystal fractionation effects (e.g., concomitant depletion in Ba + Pb at Aley, or Sr + Ba at Kerimasi), although the phases responsible for these variations cannot be identified unambiguously at present. Overall, element ratios sensitive to the redox state of the magma and its complexing characteristics (Eu/Eu*, Ce/Ce* and Y/Ho) are least variable and in both primary calcite and dolomite, approach the average chondritic values. In consanguineous

  18. The kinetics of the ordering of 13C-18O bonds in calcite and apatite

    Science.gov (United States)

    Stolper, D. A.; Halevy, I.; Eiler, J. M.

    2011-12-01

    Eiler and Schauble (2004) showed that the isotopes of C and O are not randomly distributed within single phases such as CO2 gas and carbonates, and in particular, that heavy isotopes of C and O tend to bond preferentially (clump) at lower temperatures. Consequently, the measurement of the deviation from a random distribution of C and O isotope distributions in a single phase can be used as a thermometer. As with other geothermometers based on homogeneous or heterogeneous equilibria, the clumped-isotope thermometer is susceptible to resetting (e.g., if the phase is reheated or experiences slow cooling). Thus, clumped-isotope "temperatures" of phases that have experienced complex thermal histories may, in fact, be closure temperatures, the interpretation of which requires quantification of the kinetics of redistribution of C and O isotopes as a function of temperature. These kinetics have received increasing attention (Dennis and Schrag, 2010; Passey 2010), and are likely to be critical for understanding clumped-isotope temperatures of samples that have been buried for long periods of time. To better constrain these kinetics we performed experiments on natural optical calcite from Mexico and carbonate-bearing apatite from the Siilinjarvi carbonatite (Finland). For each experiment, multiple single crystal grains (~2 mm in diameter) of calcite or apatite were loaded in open Pt capsules, pressurized with Ar gas, and held at 400-700 °C, 550 bars using a rapid quench TZM apparatus for 5 min to 520 hrs. After quenching, 13C-18O clumping was measured in the samples; the change from the initial Δ47 with time for each phase at each temperature was fit to simple mechanistic models of isotope exchange between sites in these phases. One conclusion of the experimental study is that resetting the internal ordering of carbonate groups proceeds more rapidly in calcites than in apatites. For example, heating apatite at 400 °C results in no change in clumping over a 24 hr period

  19. A calcite permeable reactive barrier for the remediation of Fluoride from spent potliner (SPL) contaminated groundwater

    DEFF Research Database (Denmark)

    Turner, B.D.; Binning, Philip John; Sloan, S.W.

    2008-01-01

    . The paper focuses on two issues in the implementation of calcite permeable reactive barriers for remediating fluoride contaminated water: the impact of the groundwater chemical matrix and CO2 addition on fluoride removal. Column tests comparing pure NaF solutions, synthetic SPL solutions, and actual SPL......The use of calcite (CaCO3) as a substrate for a permeable reactive barrier (PRB) for removing fluoride from contaminated groundwater is proposed and is illustrated by application to groundwater contaminated by spent potliner leachate (SPL), a waste derived from the aluminium smelting process...... leachate indicate that the complex chemical matrix of the SPL leachate can impact fluoride removal significantly. For SPL contaminant mixtures, fluoride removal is initially less than expected from idealized, pure, solutions. However, with time, the effect of other contaminants on fluoride removal...

  20. Commentary on the state of knowledge of the origins of the Yucca Mountain calcite veins. Special report number 17, Contract number 94/96.0003

    Energy Technology Data Exchange (ETDEWEB)

    Archambeau, C.

    1994-08-01

    This report is a compilation of papers and a letter providing technical information on the origin and geochemistry of calcite veins and calcretes in the vicinity of the Yucca Mountain repository. The information is presented to demonstrate that these deposits may be ``thermogenic`` in origin with some alteration by pedogenic processes. The papers present isotope ratios of uranium, strontium, and carbon to support the claims for a hydrothermal source. The letter provides a critical review of a previous paper presented at the 64th Advisory Committee on Nuclear Waste. The report makes an attempt to emphasize the need to review this possible origin because it has dramatic implications on the geologic history, paleo-ground water levels, and integrity of the repository.

  1. Aragonite→calcite transformation studied by EPR of Mn 2+ ions

    Science.gov (United States)

    Lech, J.; Śl|zak, A.

    1989-05-01

    The irreversible transformation aragonite→calcite has been studied both at different fixed heating rates (5, 10, 15 and 20 K/min) and at different fixed temperatures. Apparent progression rates of the transformation were observed above 685 K. At 730 K the transformation became sudden and violent. Time developments of the transformation at fixed temperatures have been discussed in terms of Avrami-Lichti's approach to transitions involving nucleation processes.

  2. EFFECT OF MAGNESIUM AS SUBSTITUTE MATERIAL IN ENZYME MEDIATED CALCITE PRECIPITATION (EMCP) FOR SOIL IMPROVEMENT TECHNIQUE

    OpenAIRE

    Heriansyah ePutra; Heriansyah ePutra; Hideaki eYasuhara; Naoki eKinoshita; Debendra eNeupane

    2016-01-01

    The optimization of enzyme-mediated calcite precipitation (EMCP) was evaluated as a soil improvement technique. In our previous works, purified urease was utilized to bio-catalyze the hydrolysis of urea, which causes the supplied Ca2+ to precipitate with CO32- as calcium carbonate. In the present work, magnesium chloride was newly added to the injecting solutions to delay the reaction rate and to enhance the amount of carbonate precipitation. Soil specimens were prepared in PVC cylinders and ...

  3. Coccolithophore responses to environmental variability in the South China Sea: species composition and calcite content

    OpenAIRE

    Jin, Xiaobo; Liu, Chuanlian; Poulton, Alex J.; Dai, Minhan; Guo, Xianghui

    2016-01-01

    Coccolithophore contributions to the global marine carbon cycle are regulated by the calcite content of their scales (coccoliths) and the relative cellular levels of photosynthesis and calcification rates. All three of these factors vary between coccolithophore species and with response to the growth environment. Here, water samples were collected in the northern basin of the South China Sea (SCS) during summer 2014 in order to examine how environmental variability influence...

  4. Epr of Mn2+ Impurities in Calcite: A Detailed Study Pertinent to Marble Provenance Determination

    DEFF Research Database (Denmark)

    Weihe, H.; Piligkos, S.; Barra, A.L.

    2009-01-01

    We demonstrate that the electron paramagnetic resonance spectrum of Mn2+ impurities in calcite, and therefore also in marble, may be accurately reproduced by a traditional spin Hamiltonian formalism. The success of such a treatment, however, very much depends on the spin Hamiltonian parameters...... having the correct signs as well as magnitudes. We present data that determine the sign of the axial anisotropy parameter and thereby facilitate future quantum mechanical characterizations of marble electron paramagnetic resonance spectra that supplement provenance determination...

  5. EPR OF Mn2+ IMPURITIES IN CALCITE: A DETAILED STUDY PERTINENT TO MARBLE PROVENANCE DETERMINATION

    DEFF Research Database (Denmark)

    Weihe, H.; Piligkos, S.; Barra, A.L.

    2009-01-01

    We demonstrate that the electron paramagnetic resonance spectrum of Mn2+ impurities in calcite, and therefore also in marble, may be accurately reproduced by a traditional spin Hamiltonian formalism. The success of such a treatment, however, very much depends on the spin Hamiltonian parameters...... having the correct signs as well as magnitudes. We present data that determine the sign of the axial anisotropy parameter and thereby facilitate future quantum mechanical characterizations of marble electron paramagnetic resonance spectra that supplement provenance determination....

  6. Quantitative laboratory measurements of biogeochemical processes controlling biogenic calcite carbon sequestration.

    Energy Technology Data Exchange (ETDEWEB)

    Zendejas, Frank; Lane, Todd W.; Lane, Pamela D.

    2011-01-01

    The purpose of this LDRD was to generate data that could be used to populate and thereby reduce the uncertainty in global carbon cycle models. These efforts were focused on developing a system for determining the dissolution rate of biogenic calcite under oceanic pressure and temperature conditions and on carrying out a digital transcriptomic analysis of gene expression in response to changes in pCO2, and the consequent acidification of the growth medium.

  7. Smaller calcite lattice deformation caused by occluded organic material in coccoliths than in mollusk shell

    DEFF Research Database (Denmark)

    Frølich, Simon; Sørensen, Henning Osholm; Hakim, Sepideh Sadat

    2015-01-01

    The growth and nucleation of biominerals are directed and affected by associated biological molecules. In this paper, we investigate the influence of occluded biomolecules on biogenic calcite from the coccolithophorid Pleurochrysis carterae and from chalk, a rock composed predominantly of fossil...... and the coccolithophorids. These differences were reflected in lattice deformation (macrostrain), structure (microstrain), and atomic disorder distributions (δorganic). The influence of the biological macromolecules on the inorganic phase was consistently smaller in the P. carterae compared to P. nobilis...

  8. Quantifying small-scale temporal surface change on glaciers and salt pans using terrestrial laser scanning: implications for modelling ablation and dust emission

    Science.gov (United States)

    Nield, J. M.; Wiggs, G. F. S.; Leyland, J.; Darby, S. E.; King, J.; Eckardt, F. D.; Chiverrell, R. C.; Vircavs, L. H.; Jacobs, B.

    2012-04-01

    Physical surface roughness is important in glacial and desert environments as it influences aerodynamic roughness, which in turn determines the ability of the wind to contribute to the turbulent heat flux component of the energy balance for glacial ice ablation or the likelihood of a surface emitting dust. Surface microtopography has traditionally been quantified by single 2D transects, but little is known about how these surfaces vary over time and the feedback between surface properties and other geomorphic processes. Terrestrial laser scanning (TLS) is the perfect tool to examine geomorphic microtopography over large spatial areas relatively quickly with the opportunity for repeat temporal measurements. Here we present examples of daily and weekly surface change measured on the Sua Pan, Botswana and the Svínafellsjökull, Iceland with mm accuracy using TLS. For the first time it is possible to quantify salt crust plucking and extrusion events and elucidate links between surface and wind shear interactions, as well as possible changes in aerodynamic roughness over time as surfaces evolve. Clear patterning is evident, with crust expansion limited to topographic highs. Likewise, we illustrate examples of measured daily ablation rates and patterns, and allude to implications for energy balance modelling by improving estimates of aerodynamic roughness. Specific ice patterning includes melt water eroding channels, the unique interactions of surface debris (volcanic ash from the 21 - 30 May 2011 eruption of Grímsvötn) melting out from the glacier and surface water forming a diverse microtopography of debris cones, cryoconite holes and perched blocks. However, whilst TLS represents a step-change in our ability to move from small transect derived roughness measurements to complete 3D surface change, detecting change on mobile surfaces through time is challenging, and linking surface properties to other point-based process measurements can be problematic.

  9. Intermediate-scale tests of sodium interactions with calcite and dolomite aggregate concretes. [LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Randich, E.; Acton, R.U.

    1983-09-01

    Two intermediate-scale tests were performed to compare the behavior of calcite and dolomite aggregate concretes when attacked by molten sodium. The tests were performed as part of an interlaboratory comparison between Sandia National Laboratories and Hanford Engineering Development Laboratories. Results of the tests at Sandia National Laboratories are reported here. The results show that both concretes exhibit similar exothermic reactions with molten sodium. The large difference in reaction vigor suggested by thermodynamic considerations of CO/sub 2/ release from calcite and dolomite was not realized. Penetration rates of 1.4 to 1.7 mm/min were observed for short periods of time with reaction zone temperatures in excess of 800/sup 0/C during the energetic attack. The penetration was not uniform over the entire sodium-concrete contact area. Rapid attack may be localized due to inhomogeneities in the concrete. The chemical reaction zone is less then one cm thick for the calcite concrete but is about seven cm thick for the dolomite concrete.

  10. Sulfur in foraminiferal calcite as a potential proxy for seawater carbonate ion concentration

    Science.gov (United States)

    van Dijk, I.; de Nooijer, L. J.; Boer, W.; Reichart, G.-J.

    2017-07-01

    Sulfur (S) incorporation in foraminiferal shells is hypothesized to change with carbonate ion concentration [CO32-], due to substitution of sulfate for carbonate ions in the calcite crystal lattice. Hence S/Ca values of foraminiferal carbonate shells are expected to reflect sea water carbonate chemistry. To generate a proxy calibration linking the incorporation of S into foraminiferal calcite to carbonate chemistry, we cultured juvenile clones of the larger benthic species Amphistegina gibbosa and Sorites marginalis over a 350-1200 ppm range of pCO2 values, corresponding to a range in [CO32-] of 93 to 211 μmol/kg. We also investigated the potential effect of salinity on S incorporation by culturing juvenile Amphistegina lessonii over a large salinity gradient (25-45). Results show S/CaCALCITE is not impacted by salinity, but increases with increasing pCO2 (and thus decreasing [CO32-] and pH), indicating S incorporation may be used as a proxy for [CO32-]. Higher S incorporation in high-Mg species S. marginalis suggests a superimposed biomineralization effect on the incorporation of S. Microprobe imaging reveals co-occurring banding of Mg and S in Amphistegina lessonii, which is in line with a strong biological control and might explain higher S incorporation in high Mg species. Provided a species-specific calibration is available, foraminiferal S/Ca values might add a valuable new tool for reconstructing past ocean carbonate chemistry.

  11. Ternary iron, magnesium, calcium carbonates; a thermodynamic model for dolomite as an ordered derivative of calcite-structure solutions

    National Research Council Canada - National Science Library

    Davidson, Paula M

    1994-01-01

      The simplest solution model that can account for dolomite as an ordered derivative structure of the disordered calcite structure solution, based on a ternary extension of the generalized point approximation given by C...

  12. Differential early diagenetic low-Mg calcite cementation and rhythmic hardground development in Campanian-Maastrichtian chalk

    DEFF Research Database (Denmark)

    Molenaar, Nicolaas; J.J.P., Zijlstra

    1997-01-01

    calcite cementation is proposed, in which early calcite cementation occurred within the sediment at some distance below the seafloor as a result of organic matter degradation and internal redistribution of bioclastic carbonate. Bacterial organic matter degradation caused dissolution of relatively unstable...... older burrowed sediment with a more advanced stage of organic matter degradation, in particular iron reduction. Cementation also occurred when redox boundaries repeatedly moved through the same layers during periods with low nett sedimentation and increased storm activity and erosion. The differences...... in the degree of early diagenetic calcite cementation were further enhanced during Paleocene karstification and development of secondary porosity by dissolution of remaining unstable carbonate grains and by associated meteoric water calcite cementation....

  13. Growing spherulitic calcite grains in saline, hyperalkaline lakes: Experimental evaluation of the effects of Mg-clays and organic acids

    NARCIS (Netherlands)

    Mercedes-Martín, R.; Rogerson, M.R.; Brasier, A.T.; Vonhof, H.B.; Prior, T.; Fellows, S.M.; Reijmer, J.J.G.; Billing, I.; Pedley, H.M.

    2016-01-01

    The origin of spherical-radial calcite bodies - spherulites - in sublacustrine, hyperalkaline and saline systems is unclear, and therefore their palaeoenvironmental significance as allochems is disputed. Here, we experimentally investigate two hypotheses concerning the origin of spherulites. The

  14. Competitive adsorption of arsenate and phosphate onto calcite; experimental results and modeling with CCM and CD-MUSIC

    DEFF Research Database (Denmark)

    Sø, Helle Ugilt; Postma, Dieke; Jakobsen, Rasmus

    2012-01-01

    that adsorption of arsenate onto calcite is of minor importance in most groundwater aquifers, as phosphate is often present at concentration levels sufficient to significantly reduce arsenate adsorption. The CD-MUSIC model for calcite was used successfully to model adsorption of arsenate and phosphate separately....... This study clearly shows the importance of performing competitive adsorption studies for validation of multi-component models and for estimating the mobility of an ion in the environment....

  15. Dissolution Processes at Step Edges of Calcite in Water Investigated by High-Speed Frequency Modulation Atomic Force Microscopy and Simulation.

    Science.gov (United States)

    Miyata, Kazuki; Tracey, John; Miyazawa, Keisuke; Haapasilta, Ville; Spijker, Peter; Kawagoe, Yuta; Foster, Adam S; Tsukamoto, Katsuo; Fukuma, Takeshi

    2017-07-12

    The microscopic understanding of the crystal growth and dissolution processes have been greatly advanced by the direct imaging of nanoscale step flows by atomic force microscopy (AFM), optical interferometry, and X-ray microscopy. However, one of the most fundamental events that govern their kinetics, namely, atomistic events at the step edges, have not been well understood. In this study, we have developed high-speed frequency modulation AFM (FM-AFM) and enabled true atomic-resolution imaging in liquid at ∼1 s/frame, which is ∼50 times faster than the conventional FM-AFM. With the developed AFM, we have directly imaged subnanometer-scale surface structures around the moving step edges of calcite during its dissolution in water. The obtained images reveal that the transition region with typical width of a few nanometers is formed along the step edges. Building upon insight in previous studies, our simulations suggest that the transition region is most likely to be a Ca(OH)2 monolayer formed as an intermediate state in the dissolution process. On the basis of this finding, we improve our understanding of the atomistic dissolution model of calcite in water. These results open up a wide range of future applications of the high-speed FM-AFM to the studies on various dynamic processes at solid-liquid interfaces with true atomic resolution.

  16. The Early Morphological Development of the Near Surface Region of Pickled Grade 91 Tubing Exposed to Steam and Its Long Term Implications

    Directory of Open Access Journals (Sweden)

    David M. Gorman

    2016-03-01

    Full Text Available To improve intra-laboratory consistency and experimental repeatability during high temperature oxidation testing, metallic coupons undergo a standardised surface preparation. It is stipulated in international testing standards that grinding of a coupons surface acceptably replicates surface conditions encountered in industrial settings whilst ensuring that each coupons surface is chemically and topographically homogenised [1,2]. Grade 91 steel tubing exposed in the laboratory to flowing steam at 650 °C and 1 bar for up to 3000 h has been compared with Grade 91 tubing exposed in a commercially operated boiler system at elevated pressures at temperatures in the range of 500 to 650 °C for 91 kh. It has been found that a pre-existing surface structure dissimilar from that of the bulk alloy and that of a ground surface, is present on the inside surface of the tubing. The presence of pre-existing surface features in commercially exposed material has implications on the long term morphological development of the oxidation region and may account for some of the discrepancies between observations made in laboratory and service exposures.

  17. Clumped isotope thermometry of calcite and dolomite in a contact metamorphic environment

    Science.gov (United States)

    Lloyd, Max K.; Eiler, John M.; Nabelek, Peter I.

    2017-01-01

    Clumped isotope compositions of slowly-cooled calcite and dolomite marbles record apparent equilibrium temperatures of roughly 150-200 °C and 300-350 °C, respectively. Because clumped isotope compositions are sensitive to the details of T-t path within these intervals, measurements of the Δ47 values of coexisting calcite and dolomite can place new constraints on thermal history of low-grade metamorphic rocks over a large portion of the upper crust (from ∼5 to ∼15 km depth). We studied the clumped isotope geochemistry of coexisting calcite and dolomite in marbles from the Notch Peak contact metamorphic aureole, Utah. Here, flat-lying limestones were intruded by a pluton, producing a regular, zoned metamorphic aureole. Calcite Δ47 temperatures are uniform, 156 ± 12 °C (2σ s.e.), across rocks varying from high-grade marbles that exceeded 500 °C to nominally unmetamorphosed limestones >5 km from the intrusion. This result appears to require that the temperature far from the pluton was close to this value; an ambient temperature just 20 °C lower would not have permitted substantial re-equilibration, and should have preserved depositional or early diagenetic Δ47 values several km from the pluton. Combining this result with depth constraints from overlying strata suggests the country rock here had an average regional geotherm of 22.3-27.4 °C/km from the late Jurassic Period until at least the middle Paleogene Period. Dolomite Δ47 in all samples above the talc + tremolite-in isograd record apparent equilibrium temperatures of 328-12+13 °C (1σ s.e.), consistent with the apparent equilibrium blocking temperature we expect for cooling from peak metamorphic conditions. At greater distances, dolomite Δ47 records temperatures of peak (anchi)metamorphism or pre-metamorphic diagenetic conditions. The interface between these domains is the location of the 330 °C isotherm associated with intrusion. Multiple-phase clumped isotope measurements are complemented by

  18. Simulated oxygen isotopes in cave drip water and speleothem calcite in European caves

    Directory of Open Access Journals (Sweden)

    A. Wackerbarth

    2012-11-01

    Full Text Available Interpreting stable oxygen isotope (δ18O records from stalagmites is still one of the complex tasks in speleothem research. Here, we present a novel model-based approach, where we force a model describing the processes and modifications of δ18O from rain water to speleothem calcite (Oxygen isotope Drip water and Stalagmite Model – ODSM with the results of a state-of-the-art atmospheric general circulation model enhanced by explicit isotope diagnostics (ECHAM5-wiso. The approach is neither climate nor cave-specific and allows an integrated assessment of the influence of different varying climate variables, e.g. temperature and precipitation amount, on the isotopic composition of drip water and speleothem calcite.

    First, we apply and evaluate this new approach under present-day climate conditions using observational data from seven caves from different geographical regions in Europe. Each of these caves provides measured δ18O values of drip water and speleothem calcite to which we compare our simulated isotope values. For six of the seven caves modeled δ18O values of drip water and speleothem calcite are in good agreement with observed values. The mismatch of the remaining caves might be caused by the complexity of the cave system, beyond the parameterizations included in our cave model.

    We then examine the response of the cave system to mid-Holocene (6000 yr before present, 6 ka climate conditions by forcing the ODSM with ECHAM5-wiso results from 6 ka simulations. For a set of twelve European caves, we compare the modeled mid-Holocene-to-modern difference in speleothem calcite δ18O to available measurements. We show that the general European changes are simulated well. However, local discrepancies are found, and might be explained either by a too low model resolution, complex local soil-atmosphere interactions affecting evapotranspiration or by cave specific factors

  19. Calcite as a bone substitute. Comparison with hydroxyapatite and tricalcium phosphate with regard to the osteoblastic activity

    Energy Technology Data Exchange (ETDEWEB)

    Monchau, F., E-mail: Francine.monchau@univ-artois.fr [Laboratoire Genie Civil et geo-Environnement (EA 4515, Universite Lille Nord de France), Equipe Biomateriaux Artois (Universite d' Artois), IUT/GMP, 1230, rue de l' Universite, BP 819, 62408 Bethune cedex (France); Hivart, Ph.; Genestie, B. [Laboratoire Genie Civil et geo-Environnement (EA 4515, Universite Lille Nord de France), Equipe Biomateriaux Artois (Universite d' Artois), IUT/GMP, 1230, rue de l' Universite, BP 819, 62408 Bethune cedex (France); Chai, F. [Laboratoire Medicaments et Biomateriaux a Liberation Controlee (INSERM U 1008, Universite Lille Nord de France), Groupe de Recherche sur les Biomateriaux (Universite Lille-2), Faculte de Medecine, 1, place de Verdun, 59045 Lille cedex (France); and others

    2013-01-01

    Close to the bone mineral phase, the calcic bioceramics, such as hydroxyapatite (HA) and {beta}-tricalcium phosphate ({beta}-TCP), are commonly used as substitutes or filling materials in bone surgery. Besides, calcium carbonate (CaCO{sub 3}) is also used for their excellent biocompatibility and bioactivity. However, the problem with the animal-origin aragonite demands the new technique to synthesize pure calcite capable of forming 3D bone implant. This study aims to manufacture and evaluate a highly-pure synthetic crystalline calcite with good cytocompatibility regarding to the osteoblasts, comparing to that of HA and {beta}-TCP. After the manufacture of macroporous bioceramic scaffolds with the identical internal architecture, their cytocompatibility is studied through MC3T3-E1 osteoblasts with the tests of cell viability, proliferation, vitality, etc. The results confirmed that the studied process is able to form a macroporous material with a controlled internal architecture, and this synthesized calcite is non-cytotoxic and facilitate the cell proliferation. Indeed requiring further improvement, the studied calcite is definitely an interesting alternative not only to coralline aragonite but also to calcium phosphate ceramics, particularly in bone sites with the large bone remodelling. Highlights: Black-Right-Pointing-Pointer Macroporous calcite manufacturing with controlled architecture as bone substitute Black-Right-Pointing-Pointer Cytotoxicity: adaptation of the colony-forming method with the target cells: MC3T3-E1 osteoblasts Black-Right-Pointing-Pointer Study of osteoblast proliferation and activity on calcite, HA and TCP.

  20. The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt

    Directory of Open Access Journals (Sweden)

    H. E. K. Smith

    2017-11-01

    Full Text Available The Great Calcite Belt (GCB of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Samples for phytoplankton enumeration were collected from the upper mixed layer (30 m during two cruises, the first to the South Atlantic sector (January–February 2011; 60° W–15° E and 36–60° S and the second in the South Indian sector (February–March 2012; 40–120° E and 36–60° S. The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Subtropical, Polar, and Subantarctic fronts. The influence of environmental parameters, such as sea surface temperature (SST, salinity, carbonate chemistry (pH, partial pressure of CO2 (pCO2, alkalinity, dissolved inorganic carbon, macronutrients (nitrate + nitrite, phosphate, silicic acid, ammonia, and mixed layer average irradiance, on species composition across the GCB was assessed statistically. Nanophytoplankton (cells 2–20 µm were the numerically abundant size group of biomineralizing phytoplankton across the GCB, with the coccolithophore Emiliania huxleyi and diatoms Fragilariopsis nana, F. pseudonana, and Pseudo-nitzschia spp. as the most numerically dominant and widely distributed. A combination of SST, macronutrient concentrations, and pCO2 provided the best statistical descriptors of the biogeographic variability in biomineralizing species composition between stations. Emiliania huxleyi occurred in silicic acid-depleted waters between the Subantarctic Front and the Polar Front, a favorable environment for this species

  1. Detecting Microbially Induced Calcite Precipitation in a Model Well-Bore Using Downhole Low-Field NMR.

    Science.gov (United States)

    Kirkland, Catherine M; Zanetti, Sam; Grunewald, Elliot; Walsh, David O; Codd, Sarah L; Phillips, Adrienne J

    2017-02-07

    Microbially induced calcite precipitation (MICP) has been widely researched recently due to its relevance for subsurface engineering applications including sealing leakage pathways and permeability modification. These applications of MICP are inherently difficult to monitor nondestructively in time and space. Nuclear magnetic resonance (NMR) can characterize the pore size distributions, porosity, and permeability of subsurface formations. This investigation used a low-field NMR well-logging probe to monitor MICP in a sand-filled bioreactor, measuring NMR signal amplitude and T2 relaxation over an 8 day experimental period. Following inoculation with the ureolytic bacteria, Sporosarcina pasteurii, and pulsed injections of urea and calcium substrate, the NMR measured water content in the reactor decreased to 76% of its initial value. T2 relaxation distributions bifurcated from a single mode centered about approximately 650 ms into a fast decaying population (T2 less than 10 ms) and a larger population with T2 greater than 1000 ms. The combination of changes in pore volume and surface minerology accounts for the changes in the T2 distributions. Destructive sampling confirmed final porosity was approximately 88% of the original value. These results indicate the low-field NMR well-logging probe is sensitive to the physical and chemical changes caused by MICP in a laboratory bioreactor.

  2. Variability in Bias of Gridded Sea Surface Temperature Data Products: Implications for Seasonally Resolved Marine Proxy Reconstructions

    Science.gov (United States)

    Ouellette, G., Jr.; DeLong, K. L.

    2016-12-01

    Seasonally resolved reconstructions of sea surface temperature (SST) are commonly produced using isotopic ratios and trace elemental ratios within the skeletal material of marine organisms such as corals, coralline algae, and mollusks. Using these geochemical proxies to produce paleoclimate reconstructions requires using regression methods to calibrate the proxy to observed SST, ideally with in situ SST records that span many years. Unfortunately, the few locations with in situ SST records rarely coincide with the time span of the marine proxy archive. Therefore, SST data products are often used for calibration and they are based on MOHSST or ICOADS SST observations as their main SST source but use different algorithms to produce globally gridded data products. These products include the Hadley Center's HADSST (5º) and interpolated HADISST (1º), NOAA's extended reconstructed SST (ERSST; 2º), optimum interpolation SST (OISST; 1º), and the Kaplan SST (5º). This study assessed the potential bias in these data products at marine archive sites throughout the tropical Atlantic using in situ SST where it was available, and a high-resolution (4 km) satellite-based SST data product from NOAA Pathfinder that has been shown to closely reflect in situ SST for our locations. Bias was assessed at each site, and then within each data product across the region for spatial homogeneity. Our results reveal seasonal biases in all data products, but not for all locations and not of a uniform magnitude or season among products. We found the largest differences in mean SST on the order of 1-3°C for single sites in the Gulf of Mexico, and differences for regional mean SST bias were 0.5-1°C when sites in the Gulf of Mexico were compared to sites in the Caribbean Sea within the same data product. No one SST data product outperformed the others and no systematic bias was found. This analysis illustrates regional strengths and weaknesses of these data products, and serves as a

  3. Origin and significance of postore dissolution collapse breccias cemented with calcite and barite at the Meikle gold deposit, Northern Carlin trend, Nevada

    Science.gov (United States)

    Emsbo, P.; Hofstra, A.H.

    2003-01-01

    The final event in a complicated hydrothermal history at the Meikle gold deposit was gold deficient but caused extensive postore dissolution of carbonate, collapse brecciation, and precipitation of calcite and barite crystals in the resulting cavities. Although previously interpreted to be part of the Carlin-type hydrothermal system, crosscutting relationships and U-Th-Pb geochronology constrain this hydrothermal event to late Pliocene time (ca. 2 Ma), nearly 36 Ma after ore formation. Mineralogic, fluid inclusion, and stable isotope data indicate that postore hydrothermal fluids were reduced, H2S-rich, unevolved meteoric waters ((??18O = -17???) of low temperature (ca. 65??C). The ??18O values of barite and calcite indicate that these minerals were in isotopic equilibrium, requiring that barite SO4 was derived from the oxidation of reduced sulfur; however, preexisting sulfides in breccia cavities were not oxidized. The ??34S (15???) values of barite are higher than those of local bulk sulfide and supergene alunite indicating that SO4 was not derived from supergene oxidation of local sulfide minerals. The 15 per mil ??34S value suggests that the H2S in the fluids may have been leached from sulfur-rich organic matter in the local carbonaceous sedimentary rocks. A reduced H2S-rich fluid is also supported by the bright cathodoluminescence of calcite which indicates that it is Mn rich and Fe poor. Calcite has a narrow range of ??13C values (0.3-1.8???) that are indistinguishable from those of the host Bootstrap limestone, indicating that CO2 in the fluid was from dissolution of the local limestone. These data suggest that dissolution and brecciation of the Bootstrap limestone occurred where H2S-rich fluids encountered more oxidizing fluids and formed sulfuric acid (H2SO4). Intense fracturing in the mine area by previous structural and hydrothermal events probably provided conduits for the descent of oxidized surface water which mixed with the underlying H2S-rich waters

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

    Science.gov (United States)

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

    2017-07-01

    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

  5. The surface chemistry of carbonates, a new approach

    NARCIS (Netherlands)

    Wolthers, M.; Charlet, L.; Van Cappellen, P.

    2004-01-01

    The Charge Distribution-MUltiSite Ion Complexation (CD-MUSIC) model was applied to describe the surface chemistry of calcite. Protonation reactions and proton affinity constants were predicted and the resulting surface model was compared to the existing Surface Complexation (SC) model. The

  6. Adsorption and diffusion of atomic oxygen and sulfur at pristine and doped Ni surfaces with implications for stress corrosion cracking

    Energy Technology Data Exchange (ETDEWEB)

    Alexandrov, Vitaly; Sushko, Maria L.; Schreiber, Daniel K.; Bruemmer, Stephen M.; Rosso, Kevin M.

    2016-12-01

    A density-functional-theory modeling study of atomic oxygen/sulfur adsorption and diffusion at pristine and doped Ni(111) and (110) surfaces is presented. We find that oxygen and sulfur feature comparable adsorption energies over the same surface sites, however, the surface diffusion of sulfur is characterized by an activation barrier about one half that of oxygen. Calculations with different alloying elements at Ni surfaces show that Cr strongly enhances surface binding of both species in comparison to Al. These results in combination with previous modeling studies help explain the observed differences in selective grain boundary oxidation mechanisms of Ni-Cr and Ni-Al alloys.

  7. Subglacial Calcites from Northern Victoria Land: archive of Antarctic volcanism in the Last Glacial Maximum

    Science.gov (United States)

    Frisia, Silvia; Weirich, Laura; Hellstrom, John; Borsato, Andrea; Golledge, Nicholas R.; Anesio, Alexandre M.; Bajo, Petra; Drysdale, Russell N.; Augustinus, Paul C.; Barbante, Carlo; Cooper, Alan

    2017-04-01

    Subglacial carbonates bear similarities to stalagmites in their fabrics and the potential to obtain precise chronologies using U-series methods. Their chemical properties also reflect those of their parent waters, which, in contrast to stalagmites, are those of subglacial meltwaters. In analogy to speleothems, stable Carbon isotope ratios and trace elements such as Uranium, Iron and Manganese provide the opportunity to investigate ancient extreme environments without the need to drill through thousands of metres of ice. Sedimentological, geochemical and microbial evidence preserved in LGM subglacial calcites from Northern Victoria Land, close to the East Antarctic Ice Sheet margin, allow us to infer that subglacial volcanism was active in the Trans Antarctic Mountain region and induced basal ice melting. We hypothesize that a meltwater reservoir was drained and injected into interconnected basal pore systems where microbial processes enhanced bedrock weathering and, thus, released micronutrients. Volcanic influence is supported by the presence of fluorine (F) and sulphur in sediment-laden calcite layers containing termophilic species. Notably, calcite δ13C points to dissolved inorganic carbon evolved from subglacial metabolic processes. Once transported to the sea, soluble iron likely contributed to fertilizing the Southern Ocean and CO2 drawdown. This is the first well-dated evidence for LGM volcanism in Antarctica, which complements the record of volcanic eruptions retrieved from Talos Dome ice core, and supports the hypothesis of large-scale volcanism as an important driver of climate change. We conclude that subglacial carbonates are equivalent to speleothems in their palaeoclimate potential and may become a most useful source of information of ecosystems and processes at peak glacials in high altitude/high latitude settings.

  8. Timescale for hygroscopic conversion of calcite mineral particles through heterogeneous reaction with nitric acid.

    Science.gov (United States)

    Sullivan, Ryan C; Moore, Meagan J K; Petters, Markus D; Kreidenweis, Sonia M; Roberts, Greg C; Prather, Kimberly A

    2009-09-28

    Atmospheric heterogeneous reactions can potentially change the hygroscopicity of atmospheric aerosols as they undergo chemical aging processes in the atmosphere. A particle's hygroscopicity influences its cloud condensation nuclei (CCN) properties with potential impacts on cloud formation and climate. In this study, size-selected calcite mineral particles were reacted with controlled amounts of nitric acid vapour over a wide range of relative humidities in an aerosol flow tube to study the conversion of insoluble and thus apparently non-hygroscopic calcium carbonate into soluble and hygroscopic calcium nitrate. The rate of hygroscopic change particles undergo during a heterogeneous reaction is derived from experimental measurements for the first time. The chemistry of the reacted particles was determined using an ultrafine aerosol time-of-flight mass spectrometer (UF-ATOFMS) while the particles' hygroscopicity was determined through measuring CCN activation curves fit to a single parameter of hygroscopicity, kappa. The reaction is rapid, corresponding to atmospheric timescales of hours. At low to moderate HNO3 exposures, the increase in the hygroscopicity of the particles is a linear function of the HNO3(g) exposure. The experimentally observed conversion rate was used to constrain a simple but accurate kinetic model. This model predicts that calcite particles will be rapidly converted into hygroscopic particles (kappa>0.1) within 4 h for low HNO3 mixing ratios (10 pptv) and in less than 3 min for 1000 pptv HNO3. This suggests that the hygroscopic conversion of the calcite component of atmospheric mineral dust aerosol will be controlled by the availability of nitric acid and similar reactants, and not by the atmospheric residence time.

  9. Scattering matrix measurements and light-scattering calculations of calcite particles

    Directory of Open Access Journals (Sweden)

    D. D. Dabrowska

    2011-09-01

    Full Text Available We present measurements of the complete scattering matrix as a function of the scattering angle of a sample of calcite particles collected near Lecce, Italy. The measurements are done at a wavelength of 647 nm in the scattering angle range 3°−177°. FESEM and SEM images show that the sample consists largely of flake-like particles. Ten different flake-like geometries are randomly generated and their scattering properties are simulated with DDA for sizes from 0.1 μm to 1 μm. Some preliminary comparisons of the simulations and the measurements are shown.

  10. Pulsed cathodoluminescence of diamond, calcite, spodumene, and fluorite under the action of subnanosecond electron beam

    Science.gov (United States)

    Baksht, E. Kh.; Burachenko, A. G.; Tarasenko, V. F.

    2010-11-01

    Amplitude and temporal characteristics of pulsed cathodoluminescence (PCL) of diamond (natural and synthetic), calcite, spodumene, and fluorite have been studied at a temporal resolution of ˜0.3 ns. The PCL was generated by electron beam pulses with a full width at half maximum (FWHM) of 0.1, 0.25, and 0.65 ns. The PCL spectra have been measured for the emission induced by 0.1- and 0.25-ns pulses at a beam current density of ˜90 A/cm2.

  11. Metal cation/anion adsorption on calcium carbonate: Implications to metal ion concentrations in groundwater

    Energy Technology Data Exchange (ETDEWEB)

    Zachara, J.M.; Cowan, C.E.; Resch, C.T.

    1990-05-01

    This chapter evaluates the sorption behavior of metallic ions on specimen calcite as a basis for determining the importance of calcite relative to other subsurface sorbents, such as layer silicates and oxides, in controlling metal ion concentration in calcareous groundwaters. A review of the literature shows the sorption of both metallic cations and anions on calcite over ranges in pH and CO{sub 2} partial pressure to be consistent with a surface-exchange process where cations exchange with surface Ca and anions exchange with surface CO{sub 3}. A general surface-exchange model was developed to account for the effects of Ca and CO{sub 3} concentrations, pH, and calcite surface area on cation and anion sorption onto calcite. The model was applied to recently developed experimental sorption data of Zn and SeO{sub 3} on specimen calcite in equilibrium CaCO{sub 3}(aq) suspensions. The surface-exchange model was able to describe the effects of pH on both cation and anion sorption, and provided good predictions of the effects of variable CO{sub 2}(g) pressure on Zn sorption and of PO{sub 4} on SeO{sub 3} sorption. The surface-exchange model, combined with sorption constants for other phases, was used to calculate Cd sorption to a hypothetical aquifer material containing a mixture of sorbents. The sorbent concentrations were fixed to those expected in groundwater zones. The multi-sorbent calculation documented the importance of calcite as a sorbent for metallic ions in groundwater.93 refs., 18 figs., 5 tabs.

  12. Modification of calcite crystal morphology by designed phosphopeptides and primary structures and substrate specifities of the cysteine proteases mexicain and chymomexicain

    Science.gov (United States)

    Lian, Zhirui

    In order to better understand the mechanism of biomineralization, we have undertaken to synthesize polypeptide model compounds of well-defined structure that can interact with specific faces of calcite and alter its crystal morphology. These peptides were designed based on the structure of alpha-helical winter flounder antifreeze polypeptide HPLC-6. In these peptides, from one to three of the threonine residues in HPLC-6 were substituted by phosphoserine or phosphotyrosine. CD spectra show that all the peptides have virtually the same alpha-helicity, i.e., about 90% at 4°C and 50% at 25°C. However, only peptides which contain at least two phosphate groups spaced 16.8-A apart can modify the crystal morphology of the calcite. The newly developed surface has been tentatively identified as the (001) basal face. Molecular modeling indicates that the spacing of phosphate groups allows for a good match with crystal lattice ions on the (001) plane. Another peptide, CBP-3D, in which the three threonine residues in HPLC-6 were substituted by aspartic acids, appears to bind only to {104} rhombohedral faces of calcite. These experiments suggest that conformation and orientation of the binding ligands in the peptide are important factors governing the mutual recognition of crystal surface and proteins. The complete amino acid sequences of the cysteine proteases mexicain and chymomexicain, isolated from the latex of the plant Pileus mexicanus , were determined by Edman degradation of proteolytic fragments. Mexicain and chymomexicain show-high sequence homology to the papain family of cysteine protease. Mexicain and chymomexicain are monomeric polypeptides, with molecular masses of 23,762 Da and 23,694 Da, respectively, and both contain three deduced disulfide bonds. The proteolytic substrate specificities of mexicain and chymomexicain were studied by digesting a series of synthetic peptides and analyzing the fragments by mass spectrometry. The two proteases showed virtually

  13. Surface morphology of caldera-forming eruption deposits revealed by lidar mapping of Crater Lake National Park, Oregon- Implications for emplacement and surface modification

    Science.gov (United States)

    Robinson, Joel E.; Bacon, Charles R.; Major, Jon J.; Wright, Heather M.; Vallance, James W.

    2017-01-01

    Large explosive eruptions of silicic magma can produce widespread pumice fall, extensive ignimbrite sheets, and collapse calderas. The surfaces of voluminous ignimbrites are rarely preserved or documented because most terrestrial examples are heavily vegetated, or severely modified by post-depositional processes. Much research addresses the internal sedimentary characteristics, flow processes, and depositional mechanisms of ignimbrites, however, surface features of ignimbrites are less well documented and understood, except for comparatively small-volume deposits of historical eruptions. The ~7,700 calendar year B.P. climactic eruption of Mount Mazama, USA vented ~50 km3 of magma, deposited first as rhyodacite pumice fall and then as a zoned rhyodacite-to-andesite ignimbrite as Crater Lake caldera collapsed. Lidar collected during summer 2010 reveals the remarkably well-preserved surface of the Mazama ignimbrite and related deposits surrounding Crater Lake caldera in unprecedented detail despite forest cover. The ±1 m lateral and ±4 cm vertical resolution lidar allows surface morphologies to be classified. Surface morphologies are created by internal depositional processes and can point to the processes at work when pyroclastic flows come to rest. We describe nine surface features including furrow-ridge sets and wedge-shaped mounds in pumice fall eroded by high-energy pyroclastic surges, flow- parallel ridges that record the passage of multiple pyroclastic flows, perched benches of marginal deposits stranded by more-mobile pyroclastic-flow cores, hummocks of dense clasts interpreted as lag deposit, transverse ridges that mark the compression and imbrication of flows as they came to rest, scarps indicating ignimbrite remobilization, fields of pit craters caused by phreatic explosions, fractures and cracks caused by extensional processes resulting from ignimbrite volume loss, and stream channels eroded in the newly formed surface. The nine morphologies presented

  14. Differential displacement and rotation in thrust fronts: A magnetic, calcite twinning and palinspastic study of the Jones Valley thrust, Alabama, US Appalachians

    Science.gov (United States)

    Hnat, James S.; van der Pluijm, Ben A.; Van der Voo, Rob; Thomas, William A.

    2008-06-01

    To test whether a displacement gradient along a curved fault structure requires rotation, we studied the northeast-striking, northwest-verging, large-displacement Jones Valley thrust fault of the Appalachian thrust belt in Alabama. Paleomagnetism, anisotropy of magnetic susceptibility (AMS) and calcite twinning analysis, complemented by balanced cross-sections, were used to evaluate the presence and magnitude of any rotation. Remanence directions from the Silurian Red Mountain Formation reveal a prefolding magnetization acquired in the Pennsylvanian, whereas magnetic analysis shows a strong, bedding-parallel compaction fabric with a tectonic lineation. Paleomagnetic directions and magnetic lineations reveal no relative rotation between the hanging wall and footwall of the thrust fault. Rather than rotation, therefore, we interpret the Jones Valley thrust sheet as a structure that developed in a self-similar fashion, with lateral growth of the fault surface occurring coincident with growth into the foreland.

  15. Unraveling the Formation of Large Amounts of Calcite Scaling in Geothermal Wells in the Bavarian Molasse Basin: A Reactive Transport Modeling Approach

    OpenAIRE

    Wanner, Christoph; Eichinger, Florian; Jahrfeld, Thomas; Diamond, Larryn W.

    2017-01-01

    Results from reactive transport simulations performed for the geothermal plant in Kirchstockach, located in the Bavarian Molasse Basin in southern Germany, are presented to unravel the formation of calcite scaling. Simulation results successfully predict the calcite scaling profile observed along the production well if supersaturation with respect to calcite is specified for the model water leaving the pump at 800 m depth. This observation is in good agreement with a previous study suggesting...

  16. A Remote Sensing Analysis on the Spatiotemporal Variation of Land Surface Albedo and Emissivity in South Florida: An Implication for Surface-Atmosphere Energy and Water Exchange

    Science.gov (United States)

    Kandel, H. P.; Melesse, A. M.

    2016-12-01

    Land use /land cover has wide range of impacts from surface energy budget to radiative forcing of climate change. This study aims to analyze the variation in two radiative properties, albedo and emissivity in South Florida landscape to investigate how radially distinct surfaces lead to a energy and moisture contrast on the near-surface atmosphere and eventually to surface-induced climate. Maps of land surface albedo and emissivity were prepared using algorithms that convert narrow-band spectral reflectance to total short-wave albedo, and vegetation index to emissivity from Landsat -5 TM images of several different summer dates. A comparative analysis was made using the zonal statistics in ArcGIS. Relatively higher albedos were found over cultivated and developed lands (0.17 - 0.21) than in forests and herbaceous wetland (0.09 - 0.16). The emissivities, on the other hand, are lower for developed and drained lands. Average albedo exhibits a slight increase whereas emissivity is found to be decreasing through time. Urban areas showing higher albedos, a unique occurrence in this landscape, store less short-wave radiation, however, their lower emissivities points to increased storage of long-wave radiation. The results imply that the emissivity perhaps play a dominant role in heat island development and initiation of local circulation in urbanized South Florida.

  17. Iodate in calcite and vaterite: Insights from synchrotron X-ray absorption spectroscopy and first-principles calculations

    Science.gov (United States)

    Podder, J.; Lin, J.; Sun, W.; Botis, S. M.; Tse, J.; Chen, N.; Hu, Y.; Li, D.; Seaman, J.; Pan, Y.

    2017-02-01

    Calcium carbonates such as calcite are the dominant hosts of inorganic iodine in nature and are potentially important for the retention and removal of radioactive iodine isotopes (129I and 131I) in contaminated water. However, little is known about the structural environment of iodine in carbonates. In this study, iodate (IO3-) doped calcite and vaterite have been synthesized using the gel-diffusion method at three NaIO3 concentrations (0.002; 0.004; 0.008 M) and a pH value of 9.0, under ambient temperature and pressure. Inductively coupled plasma mass spectrometry (ICP-MS) analyses show that iodine is preferentially incorporated into calcite over vaterite. Synchrotron iodine K-edge X-ray absorption near-edge structure (XANES) spectra confirm that IO3- is the dominant iodine species in synthetic calcite and vaterite. Analyses of iodine K-edge extended X-ray absorption fine structure (EXAFS) data, complemented by periodic first-principles calculations at the density functional theory (DFT) levels, demonstrate that the I5+ ion of the IO3- group in calcite and vaterite is bonded by three and two additional O atoms (i.e., coordination numbers = 6 and 5), respectively, and is incorporated via the charged coupled substitution I5+ + Na+ ↔ C4+ + Ca2+, with the Na+ cation at a nearest Ca2+ site being the most energetically favorable configuration.

  18. Electric field dependent structural and vibrational properties of the Si(100)-H(2 x 1) surface and its implications for STM induced hydrogen desorption

    DEFF Research Database (Denmark)

    Stokbro, Kurt

    1999-01-01

    We report a first principles study of the structure and the vibrational properties of the Si(100)-H(2 x 1) surface in an electric field. The calculated vibrational parameters are used to model the vibrational modes in the presence of the electric field corresponding to a realistic scanning...... at room temperature). We calculate the implications for current induced desorption of H using a recently developed first principles model of electron inelastic scattering. The calculations show that inelastic scattering events with energy transfer n (h) over bar omega, where n>1, play an important role...

  19. The effect of amorphous silicon surface hydrogenation on morphology, wettability and its implication on the adsorption of proteins

    Energy Technology Data Exchange (ETDEWEB)

    Filali, Larbi, E-mail: larbifilali5@gmail.com [Laboratoire de Physique des Couches Minces et Matériaux pour l' Electronique, Université d' Oran 1, Ahmed Ben Bella, BP 1524, El M' naouar 31100 Oran (Algeria); Brahmi, Yamina; Sib, Jamal Dine [Laboratoire de Physique des Couches Minces et Matériaux pour l' Electronique, Université d' Oran 1, Ahmed Ben Bella, BP 1524, El M' naouar 31100 Oran (Algeria); Bouhekka, Ahmed [Laboratoire de Physique des Couches Minces et Matériaux pour l' Electronique, Université d' Oran 1, Ahmed Ben Bella, BP 1524, El M' naouar 31100 Oran (Algeria); Département de Physique, Université Hassiba Ben Bouali, 02000 Chlef (Algeria); Benlakehal, Djamel; Bouizem, Yahya; Kebab, Aissa; Chahed, Larbi [Laboratoire de Physique des Couches Minces et Matériaux pour l' Electronique, Université d' Oran 1, Ahmed Ben Bella, BP 1524, El M' naouar 31100 Oran (Algeria)

    2016-10-30

    Highlights: • Hydrogenation of the surfaces had the effect of reducing the roughness by way of shadow etching. • Roughness was the driving factor affecting the wettability of the hydrogenated surfaces. • Bovine Serum Albumin proteins favored the surfaces with highest hydrogen content. • Surface modification induced secondary structure change of adsorbed proteins. - Abstract: We study the effect of amorphous silicon (a-Si) surface hydrogenation on Bovine Serum Albumin (BSA) adsorption. A set of (a-Si) films was prepared by radio frequency magnetron sputtering (RFMS) and after deposition; they were treated in molecular hydrogen ambient at different pressures (1–3 Pa). Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy and spectroscopic ellipsometry (SE) were used to study the hydrogenation effect and BSA adsorption. Atomic force microscopy (AFM) was used to evaluate morphological changes caused by hydrogenation. The wettability of the films was measured using contact angle measurement, and in the case of the hydrogenated surfaces, it was found to be driven by surface roughness. FTIR-ATR spectroscopy and SE measurements show that proteins had the strongest affinity toward the surfaces with the highest hydrogen content and their secondary structure was affected by a significant decrease of the α-helix component (-27%) compared with the proteins adsorbed on the un-treated surface, which had a predominantly α-helix (45%) structure. The adsorbed protein layer was found to be densely packed with a large thickness (30.9 nm) on the hydrogen-rich surfaces. The most important result is that the surface hydrogen content was the dominant factor, compared to wettability and morphology, for protein adsorption.

  20. Adjustment errors of sunstones in the first step of sky-polarimetric Viking navigation: studies with dichroic cordierite/ tourmaline and birefringent calcite crystals

    National Research Council Canada - National Science Library

    Száz, Dénes; Farkas, Alexandra; Blahó, Miklós; Barta, András; Egri, Ádám; Kretzer, Balázs; Hegedüs, Tibor; Jäger, Zoltán; Horváth, Gábor

    2016-01-01

    According to an old but still unproven theory, Viking navigators analysed the skylight polarization with dichroic cordierite or tourmaline, or birefringent calcite sunstones in cloudy/foggy weather...

  1. Calcite Wettability in the Presence of Dissolved Mg2+ and SO42-

    DEFF Research Database (Denmark)

    Generosi, Johanna; Ceccato, Marcel; Andersson, Martin Peter

    2017-01-01

    with calcite even after rinsing with CaCO3-saturated deionized water, suggesting sorption on or in calcite. When the calcite-saturated solution of MgSO4 was replaced by calcite-saturated NaCl at the same ionic strength, adhesion force increased again, indicating that the effect is reversible and suggesting Mg...... replacement by Ca. Experiments with solutions of Na2SO4 and MgCl2 suggest that Mg2+ uptake is favored when SO42– is also present...

  2. Environmentally acceptable effect of hydrogen peroxide on cave "lamp-flora", calcite speleothems and limestones.

    Science.gov (United States)

    Faimon, Jirí; Stelcl, Jindrich; Kubesová, Svatava; Zimák, Jirí

    2003-01-01

    Mosses, algae, and cyanobacteria (lamp-flora) colonize illuminated areas in show caves. This biota is commonly removed by a sodium hypochlorite solution. Because chlorine and other deleterious compounds are released into a cave environment during lamp-flora cleansing, hydrogen peroxide was tested as an alternative agent. In a multidisciplinary study conducted in the Kateinská Cave (Moravian Karst, Czech Republic), 12 algae- and cyanobacteria taxons and 19 moss taxons were detected. The threshold hydrogen peroxide concentration for the destruction of this lamp-flora was found to be 15 vol.%. Based on laboratory experiments in stirred batch reactors, the dissolution rates of limestones and calcite speleothems in water were determined as 3.77 x 10-3 and 1.81 x 10-3 mol m-2 h-1, respectively. In the 15% peroxide solution, the limestone and speleothem dissolution rates were one order of magnitude higher, 2.00 x 10-2 and 2.21 x 10-2 mol m-2 h-1, respectively. So, the peroxide solution was recognised to attack carbonates somewhat more aggressively than karst water. In order to prevent the potential corrosion of limestone and speleothems, the reaching of preliminary peroxide saturation with respect to calcite is recommended, for example, by adding of few limestone fragments into the solution at least 10 h prior to its application.

  3. Remineralization of permeate water by calcite bed in the Daoura's plant (south of Morocco)

    Science.gov (United States)

    Biyoune, M. G.; Atbir, A.; Bari, H.; Hassnaoui, L.; Mongach, E.; Khadir, A.; Boukbir, L.; Bellajrou, R.; Elhadek, M.

    2017-04-01

    To face water shortage and to fight drought, the National office of Water and Electricity (ONEE) carried out a program aiming at constructing several desalination stations of seawater in the South of Morocco. However, the final product water after desalination (osmosis water) has turned out to be unbalanced and has an aggressive character. Therefore, a post-treatment of remineralization is necessary to recover the calco-carbonic equilibrium of water and to protect the distribution network from corrosion degradation. Thereby, our work aims to examine the performance of the remineralization used in Daoura plant by the calcite bed in the absence of carbon dioxide CO2 (without acidification), we have followed many parameters indicating the performance of this technique adopted such as pH, TAC (hydroxide, carbonate and bicarbonate content), Ca content, Langelier saturation index (LSI), Larson index (LR). The results obtained show that this technique adopted in Daoura plant brings to water back its entire calco-carbonic balance to measure up to the Moroccan standards of drinking water. Generally, the exploitation of the calcite bed technique for remineralization is simple, easy and it does not require any major efforts or precautions.

  4. Genesis and microstratigraphy of calcite coralloids analysed by high resolution imaging and petrography

    Science.gov (United States)

    Vanghi, V.; Frisia, S.; Borsato, A.

    2017-08-01

    The genesis of calcite coralloid speleothems from Lamalunga cave (Southern Italy) is here investigated from a purely petrographic perspective, which constitutes the basis for any subsequent chemical investigation. Lamalunga cave coralloids formed on bones and debris on the floor of the cave. They consist of elongated columnar crystals whose elongation progressively increases from the flanks to the tips of the coralloid, forming a succession of lens-shaped layers, which may be separated by micrite or impurity-rich layers. Organic molecules are preferentially concentrated toward the centre of convex lenses as highlighted by epifluorescence. Their occurrence on cave floor, lens-shaped morphology and concentration of impurities toward the apex of the convex lenses supports the hypothesis that their water supply was hydroaerosol, generated by the fragmentation of cave drips. Evaporation and degassing preferentially occurred on tips, enhancing the digitated morphology and trapping the organic molecules and impurities, carried by the hydroaerosol, between the growing crystals which became more elongated. Micrite layers, that cap some coralloid lenses, likely identify periods when decreasing in hydroaerosol resulted in stronger evaporation and higher supersaturation with respect to calcite of the parent film of fluid. This interpretation of coralloid formation implies that these speleothems can be used to extract hydroclimate information.

  5. Characterization of urease and carbonic anhydrase producing bacteria and their role in calcite precipitation.

    Science.gov (United States)

    Achal, Varenyam; Pan, Xiangliang

    2011-03-01

    Urease and carbonic anhydrase (CA) are key enzymes in the chemical reaction of living organisms and have been found to be associated with calcification in a number of microorganisms and invertebrates. Three bacterial strains designated as AP4, AP6, and AP9 were isolated from highly alkaline soil samples using the enrichment culture technique. On the basis of various physiological tests and 16S rRNA sequence analysis, these three bacteria were identified as Bacillus sp., B. megaterium, and B. simplex. Further, these Bacillus species have been characterized for the production of urease and CA in the process of biocalcification. One of the isolates, AP6 produced 553 U/ml of urease and 5.61 EU/ml CA. All the strains were able to produce significant amount of exopolymeric substances and biofilm. Further, efficacy of these strains was tested for calcite production ability and results were correlated with urease and CA. Isolate AP6 precipitated 2.26 mg calcite/cell dry mass (mg). Our observations strongly suggest that it is not only urease but CA also plays an important role in microbially induced calcium carbonate precipitation process. The current work demonstrates that urease and CA producing microbes can be utilized in biocalcification as a sealing agent for filling the gaps or cracks and fissures in constructed facilities and natural formations alike.

  6. Study on effect of Microbial Induced Calcite Precipitates on strength of fine grained soils

    Directory of Open Access Journals (Sweden)

    Animesh Sharma

    2016-09-01

    Full Text Available For construction purposes, it is very essential to provide a strong foundation for the structure. If required, the suitability of soil has to be improved; this process of improving properties of soil is called Soil Stabilisation. This study intends to experimentally analyse the effectiveness of use of an unorthodox liquid soil stabiliser, Microbial Induced Calcite Precipitates (MICP for improving the shear strength parameters of two different types of fine grained soils. For this process, a species of Bacillus group, B. pastuerii was used to activate and catalyse the calcite precipitation caused by reaction between urea and calcium chloride. Two types of soils, i.e. intermediate compressible clay and highly compressible clay were used for the study. Parameters included concentration of B. pasteurii, concentration of the cementation reagent and duration of treatment. These parameters were applied on both the soils in a specified range in order to optimise their usage. The results proved that with the use of MICP, there was a noticeable improvement (1.5–2.9 times in the unconfined compressive strength of both type of soils. It was also found that the strength increased with an increase in duration of treatment. Based on this study, optimum quantity and concentration of liquid additive to be added for different soil types for better strength increments were established.

  7. Climatic variability of near-surface turbulent kinetic energy over the United States: implications for fire-weather predications

    Science.gov (United States)

    Warren E. Heilman; Xindi. Bain

    2013-01-01

    Recent research suggests that high levels of ambient near-surface atmospheric turbulence are often associated with rapid and sometimes erratic wildland fire spread that may eventually lead to large burn areas. Previous research has also examined the feasibility of using near-surface atmospheric turbulent kinetic energy (TKEs) alone or in...

  8. Amphotericin B channels in phospholipid membrane-coated nanoporous silicon surfaces: implications for photovoltaic driving of ions across membranes.

    Science.gov (United States)

    Yilma, Solomon; Liu, Nangou; Samoylov, Alexander; Lo, Ting; Brinker, C Jeffrey; Vodyanoy, Vitaly

    2007-03-15

    The antimycotic agent amphotericin B (AmB) functions by forming complexes with sterols to form ion channels that cause membrane leakage. When AmB and cholesterol mixed at 2:1 ratio were incorporated into phospholipid bilayer membranes formed on the tip of patch pipettes, ion channel current fluctuations with characteristic open and closed states were observed. These channels were also functional in phospholipid membranes formed on nanoporous silicon surfaces. Electrophysiological studies of AmB-cholesterol mixtures that were incorporated into phospholipid membranes formed on the surface of nanoporous (6.5 nm pore diameter) silicon plates revealed large conductance ion channels ( approximately 300 pS) with distinct open and closed states. Currents through the AmB-cholesterol channels on nanoporous silicon surfaces can be driven by voltage applied via conventional electrical circuits or by photovoltaic electrical potential entirely generated when the nanoporous silicon surface is illuminated with a narrow laser beam. Electrical recordings made during laser illumination of AmB-cholesterol containing membrane-coated nanoporous silicon surfaces revealed very large conductance ion channels with distinct open and closed states. Our findings indicate that nanoporous silicon surfaces can serve as mediums for ion-channel-based biosensors. The photovoltaic properties of nanoporous silicon surfaces show great promise for making such biosensors addressable via optical technologies.

  9. Diffuse scattering of radar on the surface of Venus - Origin and implications for the distribution of soils

    Science.gov (United States)

    Bindschadler, D. L.; Head, J. W.

    1988-01-01

    Pioneer Venus (PV) altimeter data have been analyzed in order to study tectonic, volcanic, and degradational processes on Venus. Analysis of a corrected reflectivity data set in combination with the PV data indicates that no more than 5 percent of the Venusian surface is covered by soils more than several to tens of cm in depth. It is suggested that most regions of apparent low reflectivity are due to the presence of small roughness elements on the surface. These regions are correlated with tessera, and models show that the diffuse scatterers in the tessera are rock fragments originating as part of tectonic deformation of the surface.

  10. An integrated geophysical survey of Kilbourne Hole, southern New Mexico: Implications for near surface exploration of Mars and the Moon

    Science.gov (United States)

    Maksim, Nisa

    Features such as the Home Plate plateau on Mars, a suspected remnant of an ancient phreatomagmatic eruption, can reveal important information about paleohydrologic conditions. The eruption intensity of a phreatomagmatic volcano is controlled mainly by the quantity of water and magma, the internal geometry of the volcano, and the depth of the interaction zone between magma and water. In order to understand the paleohydrologic conditions at the time of eruption, we must understand all the factors that influenced the phreatomagmatic event. I conducted an integrated geophysical survey, which are magnetic and gravity surveys, and a ground-penetrating radar (GPR) surveys at Kilbourne Hole, a phreatomagmatic crater in southern New Mexico. These investigations serve an analog paleo-hydrogeological study that could be conducted on Mars and the Moon with an implication for planetary exploration. These geophysical surveys are designed to delineate the internal structure of a phreatomagmatic volcano and to define the volumes and masses of volcanic dikes and excavation unit, the depth of feeder dikes, and impacted velocity of the volcanic blocks. For the gravity and magnetic surveys at Kilbourne Hole, I collected data at a total of 171 gravity survey stations and 166 magnetics survey stations. A 2D gravity and magnetic inverse model was developed jointly to map the body of the magma intrusions and the internal structure of Kilbourne Hole. A total of 6 GPR surveys lines were also completed at Kilbourne Hole to image and to define locations of pyroclastic deposits, volcanic sags and blocks, the sizes distribution of volcanic blocks, and the impact velocity of the volcanic blocks. Using the size distribution and impact velocity of volcanic blocks from our GPR data, I derived the initial gas expansion velocity and the time duration of the gas expansion phase of the Kilbourne Hole eruption. These obtained parameters (volumes, masses, and depths of the feeder dikes and the excavation

  11. Common Ion Effects In Zeoponic Substrates: Dissolution And Cation Exchange Variations Due to Additions of Calcite, Dolomite and Wollastonite

    Science.gov (United States)

    Beiersdorfer, R. E.; Ming, D. W.; Galindo, C., Jr.

    2003-01-01

    c1inoptilolite-rich tuff-hydroxyapatite mixture (zeoponic substrate) has the potential to serve as a synthetic soil-additive for plant growth. Essential plant macro-nutrients such as calcium, phosphorous, magnesium, ammonium and potassium are released into solution via dissolution of the hydroxyapatite and cation exchange on zeolite charged sites. Plant growth experiments resulting in low yield for wheat have been attributed to a Ca deficiency caused by a high degree of cation exchange by the zeolite. Batch-equilibration experiments were performed in order to determine if the Ca deficiency can be remedied by the addition of a second Ca-bearing, soluble, mineral such as calcite, dolomite or wollastonite. Variations in the amount of calcite, dolomite or wollastonite resulted in systematic changes in the concentrations of Ca and P. The addition of calcite, dolomite or wollastonite to the zeoponic substrate resulted in an exponential decrease in the phosphorous concentration in solution. The exponential rate of decay was greatest for calcite (5.60 wt. % -I), intermediate for wollastonite (2.85 wt.% -I) and least for dolomite (1.58 wt.% -I). Additions of the three minerals resulted in linear increases in the calcium concentration in solution. The rate of increase was greatest for calcite (3.64), intermediate for wollastonite (2.41) and least for dolomite (0.61). The observed changes in P and Ca concentration are consistent with the solubilities of calcite, dolomite and wollastonite and with changes expected from a common ion effect with Ca. Keywords: zeolite, zeoponics, common-ion effect, clinoptilolite, hydroxyapatite

  12. Late-stage anhydrite-gypsum-siderite-dolomite-calcite assemblages record the transition from a deep to a shallow hydrothermal system in the Schwarzwald mining district, SW Germany

    Science.gov (United States)

    Burisch, Mathias; Walter, Benjamin F.; Gerdes, Axel; Lanz, Maximilian; Markl, Gregor

    2018-02-01

    Tertiary) Pb-Zn-fluorite-quartz-barite assemblages in the same specific vein systems, albeit involving different fluid compositions. Late-stage hydrothermal (∼20-70 °C) vein assemblages reported in this study record the transition from deep (>2 km) to very shallow (0-1 km) crustal conditions. As a consequence of successive uplift, increasing proportions of shallower and cooler (∼50-70 °C) fluids could take part in such mixing processes. Associated changes in the fluid composition caused the vein mineralogy to change from sulphide-quartz-fluorite-barite to calcite-anhydrite/gypsum-siderite-dolomite, as the system passively ascended closer to the surface.

  13. Atomic Force Microscopy of Coccoliths: Implications for Biomineralisation and Diagenesis

    DEFF Research Database (Denmark)

    Henriksen, Karen; Young, Jette F.; Bown, P.R.

    2002-01-01

    geochemistry, diagenesis, coccoliths, biomineralization, biological calcite, atomic force microscopy......geochemistry, diagenesis, coccoliths, biomineralization, biological calcite, atomic force microscopy...

  14. Sea Surface Temperatures in the Eastern Equatorial Pacific and Surface Temperatures in the Eastern Cordillera of Colombia During El Niño: Implications for Pliocene Conditions

    Science.gov (United States)

    Pérez-Angel, Lina C.; Molnar, Peter

    2017-11-01

    Regressions of surface temperatures in the Eastern Cordillera of Colombia with sea surface temperatures (SSTs) in the equatorial Pacific, and specifically with Niño1+2 and Niño3 temperature anomalies, show that the Eastern Cordillera warms or cools by approximately half of the amplitude of the variation of SSTs in the eastern tropical Pacific. Because Pliocene SSTs in the eastern tropical Pacific resemble those during major El Niño events, when SSTs warm by 4°C, these regressions suggest that the Pliocene Eastern Cordillera was warmer by 2°C at both high and low elevations. Such post-Pliocene cooling is smaller than the 9-12°C inferred from fossil pollen assemblages, but comparable to recent estimates of Anderson et al. of 3 ± 1°C (1σ) since 8 Ma. This change in surface temperature could be explained by a change in regional climate associated with a different tropical Pacific SST distribution and therefore would require neither an elevation change of the Eastern Cordillera since that time nor a change between Pliocene and present-day temperatures in the tropics that is as large as estimates of the global change of 2.5-4°C.

  15. Relative Shock Effects in Mixed Powders of Calcite, Gypsum, and Quartz: A Calibration Scheme from Shock Experiments

    Science.gov (United States)

    Bell, Mary S.

    2009-01-01

    The shock behavior of calcite and gypsum is important in understanding the Cretaceous/Tertiary event and other terrestrial impacts that contain evaporite sediments in their targets. Most interest focuses on issues of devolatilization to quantify the production of CO2 or SO2 to better understand their role in generating a temporary atmosphere and its effects on climate and biota [e.g., papers in 1,2,3,4]. Devolatilization of carbonate is also important because the dispersion and fragmentation of ejecta is strongly controlled by the expansion of large volumes of gas during the impact process as well [5,6]. Shock recovery experiments for calcite yield seemingly conflicting results: early experimental devolatilization studies [7,8,9] suggested that calcite was substantially outgassed at 30 GPa (> 50%). However, the recent petrographic work of [10,11,12] presented evidence that essentially intact calcite is recovered from 60 GPa experiments. [13] reported results of shock experiments on anhydrite, gypsum, and mixtures of those phases with silica. Their observations indicate little or no devolatilization of anhydrite shocked to 42 GPa and that the fraction of sulfur, by mass, that degassed is approx.10(exp -2) of theoretical prediction. In another (preliminary) report of shock experiments on calcite, anhydrite, and gypsum, [14] observe calcite recrystallization when shock loaded at 61 GPa, only intensive plastic deformation in anhydrite shock loaded at 63 GPa, and gypsum converted to anhydrite when shock loaded at 56 GPa. [15] shock loaded anhydrite and quartz to a peak pressure of 60 GPa. All of the quartz grains were trans-formed to glass and the platy anhydrite grains were completely pseudomorphed by small crystallized anhydrite grains. However, no evidence of interaction between the two phases could be observed and they suggest that recrystallization of anhydrite grains is the result of a solid state transformation. [16] reanalyzed the calcite and anhydrite shock

  16. BET surface area distributions in polar stream sediments: Implications for silicate weathering in a cold-arid environment

    Science.gov (United States)

    Marra, Kristen R.; Elwood Madden, Megan E; Soreghan, Gerilyn S.; Hall, Brenda L

    2014-01-01

    BET surface area values are critical for quantifying the amount of potentially reactive sediments available for chemical weathering and ultimately, prediction of silicate weathering fluxes. BET surface area values of fine-grained (processes in the weathering environment. The remaining transects exhibit a range in variability in surface area distributions along the length of the channel, likely related to variations in eolian input to exposed channel beds, adjacent snow drifts, and to glacier surfaces, where dust is trapped and subsequently liberated during summer melting. Additionally, variations in stream discharge rate, which mobilizes sediment in pulses and influences water:rock ratios, the origin and nature of the underlying drift material, and the contribution of organic acids may play significant roles in the production and mobilization of high-surface area sediment. This study highlights the presence of sediments with high surface area in cold-based glacier systems, which influences models of chemical denudation rates and the impact of glacial systems on the global carbon cycle.

  17. Noncontact methods for measuring water-surface elevations and velocities in rivers: Implications for depth and discharge extraction

    Science.gov (United States)

    Nelson, Jonathan M.; Kinzel, Paul J.; McDonald, Richard R.; Schmeeckle, Mark

    2016-01-01

    Recently developed optical and videographic methods for measuring water-surface properties in a noninvasive manner hold great promise for extracting river hydraulic and bathymetric information. This paper describes such a technique, concentrating on the method of infrared videog- raphy for measuring surface velocities and both acoustic (laboratory-based) and laser-scanning (field-based) techniques for measuring water-surface elevations. In ideal laboratory situations with simple flows, appropriate spatial and temporal averaging results in accurate water-surface elevations and water-surface velocities. In test cases, this accuracy is sufficient to allow direct inversion of the governing equations of motion to produce estimates of depth and discharge. Unlike other optical techniques for determining local depth that rely on transmissivity of the water column (bathymetric lidar, multi/hyperspectral correlation), this method uses only water-surface information, so even deep and/or turbid flows can be investigated. However, significant errors arise in areas of nonhydrostatic spatial accelerations, such as those associated with flow over bedforms or other relatively steep obstacles. Using laboratory measurements for test cases, the cause of these errors is examined and both a simple semi-empirical method and computational results are presented that can potentially reduce bathymetric inversion errors.

  18. Ζ potential evidences silanol heterogeneity induced by metal contaminants at the quartz surface: Implications in membrane damage.

    Science.gov (United States)

    Pavan, Cristina; Turci, Francesco; Tomatis, Maura; Ghiazza, Mara; Lison, Dominique; Fubini, Bice

    2017-09-01

    Among the physico-chemical features responsible for the so-called "variability of quartz hazard", a key role has been assigned to the silica surface charge, evaluated by means of ζ potential measurement. The ζ potential of silica describes the protonation state of silanols which, in turn, determine interactions with cell membranes. To gain a molecular understanding of the role of silanols in silica pathogenicity, we conducted a systematic investigation of the variation of the ζ potential as a function of pH (ζ plot titration curve) on a large set of respirable quartz particles with different levels of metal contaminants. The membranolytic activity of the particles on red blood cells, used as a readout of pathogenic activity, was assessed in parallel. Pure quartz surfaces showed sigmoid-shaped ζ plots suggesting the presence of silanol families with similar acidity, whereas contaminated dusts exhibited convex-shaped ζ plots, indicating a higher silanol heterogeneity on contaminated surfaces with respect to the pure ones. The quartz particles with a higher surface heterogeneity related to metal contamination showed a higher membranolytic activity. By removing structural defects and chemical heterogeneity, the ζ plot shifted towards the typical shape of pure quartz and the membranolytic activity was reduced. We conclude that the ζ plot is a useful readout to measure the acid-base behavior of quartz surfaces and to describe the chemical heterogeneity of quartz silanols. Surface heterogeneity, here induced by metal contamination, is proposed as the main cause of quartz membranolytic activity, further supporting the hypothesis that surface silanol disorganization determines silica pathogenicity. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. Effect of annealing on natural calcitic crystals-A thermostimulated luminescence (TSL) study

    Energy Technology Data Exchange (ETDEWEB)

    Ponnusamy, V., E-mail: ponnu@mitindia.edu [Department of Physics, Division of Applied Sciences and Humanities, M.I.T. Campus, Anna University, Chennai 600044, Tamilnadu (India); Ramasamy, V. [Department of Physics, Annamalai University, Annamalainagar 608002, Tamilnadu (India); Jose, M.T. [Radiological Safety Division, IGCAR, Kalpakkam, Tamilnadu (India); Anandalakshmi, K. [Department of Physics, Annamalai University, Annamalainagar 608002, Tamilnadu (India)

    2012-04-15

    The quality crystals (Calcitic limestone) were selected using the UV-visible methylene blue adsorption method. The thermostimulated luminescence (TSL) glow curve characteristics of six well crystallized limestone samples were analyzed. The glow curves of unannealed sample show only one peak in the range 320-330 Degree-Sign C. The sample irradiated with a gamma dose of 100 Gy shows two additional peaks in the range of 113-125 Degree-Sign C and 242-260 Degree-Sign C when recorded with linear heating rate of 10 Degree-Sign C/s. The annealed sample also shows the same trend as that of irradiated sample. Annealing treatment above 250 Degree-Sign C increases the sensitivity of all TSL peaks except 320 Degree-Sign C. On the other hand, annealing at 750 Degree-Sign C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 650 Degree-Sign C for 4 h followed by quenching in air is the optimum condition for TSL sensitization. The response to gamma irradiation is linear in the range from 0.5 Gy to 10{sup 4} Gy. The emission spectra of all the samples show an emission at around 610 nm but with different intensities for each TSL peak. With reference to earlier work, it may be assumed that the recombination site always involves Mn{sup 2+} ions. The observation made through infra-red (IR) and X-ray diffraction (XRD) studies with thermal treatment shows the structural changes of calcite from D{sub 3h} to C{sub s} symmetry at 750 Degree-Sign C. The Thermogravimetric-Differential Thermal Analysis (TG-DTA) analysis shows the calcite gets disordered at 760 Degree-Sign C. Hence, the collapse in the TSL sensitivity at 750 Degree-Sign C is due to structural change or structural disorderedness. - Highlights: Black-Right-Pointing-Pointer Normally, the synthetic material was used as radiation dosimeter but the natural material can also be used for the same application. Black

  20. Calcitic sclerites at base of malacostracan pleopods (Crustacea)--part of a coxa.

    Science.gov (United States)

    Kutschera, Verena; Maas, Andreas; Mayer, Gerd; Waloszek, Dieter

    2015-06-19

    Cuticular specialisations such as joints and membranes play an important role in the function of arthropod limbs. This includes sclerotisations and mineral incrustations of cuticular areas to achieve either more rigidity or flexibility. The anterior eight thoracopods of Malacostraca have limb stems comprising a coxa and a basipod, which carries the two rami. Their pleopods, the limbs of the posterior trunk part, have for long been regarded to lack a coxa. Several calcitic sclerites occur in the area between ventral body and limb stem. This raises the questions: do these elements represent specialisations of the membrane due to functional requirements, and do they originate from an originally larger limb portion, i.e., the coxa, or in fact represent it. We investigated 16 species of selected malacostracan taxa from all major in-groups. Calcitic sclerites occur in constant numbers and position within a species (no individual variation, and independent of specific modification such as in genital appendages). These are even constant within a supra-specific taxon, which facilitates comparisons. In general the sclerites connect via two pivot joints to the sternite medially and the tergopleura laterally, and two more to the limb stem. Based on this, we reconstructed putative ground-pattern conditions for the sclerites of the examined taxa of Malacostraca. The pattern of sclerites is characteristic for each monophyletic malacostracan taxon. The highest number of sclerites most likely represents the plesiomorphic state. Reduction of sclerite numbers occurs in Caridoida and its in-groups. Sclerite arrangement in these taxa provides an important character complex for phylogenetic studies. The presence of pivot joints to the body proximally and basipod distally demonstrates the existence of a coxa, which is just slightly less sclerotised, particularly on its posterior side. This can be explained by enhanced flexibility of the pleopods evolved in the course to their major role

  1. An initial assessment of the impact of Australian aerosols on surface ultraviolet radiation and implications for human health

    Energy Technology Data Exchange (ETDEWEB)

    Chee, C Y [Medical School, Australian National University, Canberra, ACT, 0200 (Australia); Mills, F P, E-mail: Frank.Mills@anu.edu.a [Research School of Physics and Engineering and Fenner School of Environment and Society, Australian National University, Canberra, ACT, 0200 (Australia)

    2010-08-15

    Aerosols can have significant influence on surface radiation, and the intense surface ultraviolet radiation Australia experiences contributes to Australia's high incidence rates for related human diseases. Aerosol properties, such as total column aerosol optical depth, have been measured over several years for varying lengths of time at sites across Australia using sunphotometers. Statistical analysis of the average daily aerosol optical depth over sites near Alice Springs, Canberra, Darwin, and Perth provides one measure of the annual atmospheric loading of aerosols over these sites. The sunphotometers used at these sites do not make measurements in the UV-B spectral region and have only one channel in the UV-A spectral region, the regions of most interest for assessing human health impact. Consequently, model calculations using standard aerosol types have been used to make an initial estimate of the impact of the aerosols found over these four sites on surface ultraviolet radiation. The aerosol loading is at times sufficient to significantly reduce the surface ultraviolet radiation, but few such days occur each year. The annual average effect of aerosols on surface ultraviolet radiation, thus, appears to be small compared to lifestyle factors, such as clothing and use of sunscreen.

  2. Interaction of fullerene (C60) nanoparticles with humic acid and alginate coated silica surfaces: measurements, mechanisms, and environmental implications.

    Science.gov (United States)

    Chen, Kai Loon; Elimelech, Menachem

    2008-10-15

    The deposition kinetics of fullerene (C60) nanoparticles onto bare silica surfaces and surfaces precoated with humic acid and alginate are investigated over a range of monovalent (NaCI) and divalent (CaCl2) salt concentrations using a quartz crystal microbalance. Because simultaneous aggregation of the fullerene nanoparticles occurs, especially at higher electrolyte concentrations, we normalize the observed deposition rates by the corresponding favorable (transport-limited) deposition rates to obtain the attachment efficiencies, alpha. The deposition kinetics of fullerene nanoparticles onto bare silica surfaces are shown to be controlled by electrostatic interactions and van der Waals attraction, consistent with the classical particle deposition behavior where both favorable and unfavorable deposition regimes are observed. The presence of dissolved humic acid and alginate in solution leads to significantly slower deposition kinetics due to steric repulsion. Precoating the silica surfaces with humic acid and alginate exerts similar steric stabilization in the presence of NaCl. In the presence of CaCl2, the deposition kinetics of fullerene nanoparticles onto both humic acid- and alginate-coated surfaces are relatively high, even at relatively low (0.3 mM) calcium concentration. This behavior is attributed to the macromolecules undergoing complex formation with calcium ions, which reduces the charge and steric influences of the adsorbed macromolecular layers.

  3. First principles study on the adsorption of Au dimer on metal-oxide surfaces: The implications for Au growing

    Science.gov (United States)

    Dong, Shan; Zhang, Yanxing; Zhang, Xilin; Mao, Jianjun; Yang, Zongxian

    2017-12-01

    The adsorption of Au dimer on MgO(100), CaO(100), BaO(100), TiO2(110) and YSZ(100) surfaces is comparatively studied using ab initio density functional theory calculations. It is found that Au dimer prefers upright adsorption on MgO(100), CaO(100), BaO(100) surfaces and parallel adsorption on TiO2(110) and YSZ(111) surfaces. According to the analysis of the metal-metal cohesive energy (EAu-Au) and the metal-substrate adhesion energy (EAu-Support), we find that Au adatoms prefer 2D cluster on BaO(100) and TiO2(110) surfaces and 3D cluster on MgO(100), CaO(100) and YSZ(111) surfaces. We also find a linear relationship between EAu-Support/EAu-Au and Eb (binding energy of metal atom on the substrate). Furthermore, an interesting correlation between association energies and the amount of transferred charge is found. The findings may help to gain further insight into the structure-property correlation and provide valuable information on crucial parameters in catalyst design.

  4. An initial assessment of the impact of Australian aerosols on surface ultraviolet radiation and implications for human health

    Science.gov (United States)

    Chee, C. Y.; Mills, F. P.

    2010-08-01

    Aerosols can have significant influence on surface radiation, and the intense surface ultraviolet radiation Australia experiences contributes to Australia's high incidence rates for related human diseases. Aerosol properties, such as total column aerosol optical depth, have been measured over several years for varying lengths of time at sites across Australia using sunphotometers. Statistical analysis of the average daily aerosol optical depth over sites near Alice Springs, Canberra, Darwin, and Perth provides one measure of the annual atmospheric loading of aerosols over these sites. The sunphotometers used at these sites do not make measurements in the UV-B spectral region and have only one channel in the UV-A spectral region, the regions of most interest for assessing human health impact. Consequently, model calculations using standard aerosol types have been used to make an initial estimate of the impact of the aerosols found over these four sites on surface ultraviolet radiation. The aerosol loading is at times sufficient to significantly reduce the surface ultraviolet radiation, but few such days occur each year. The annual average effect of aerosols on surface ultraviolet radiation, thus, appears to be small compared to lifestyle factors, such as clothing and use of sunscreen.

  5. Adsorption of Oligo-DNA on Magnesium Aluminum-Layered Double-Hydroxide Nanoparticle Surfaces: Mechanistic Implication in Gene Delivery.

    Science.gov (United States)

    Andrea, Kori A; Wang, Li; Carrier, Andrew J; Campbell, Melanie; Buhariwalla, Margaret; Mutch, MacKenzi; MacQuarrie, Stephanie L; Bennett, Craig; Mkandawire, Martin; Oakes, Ken; Lu, Mingsheng; Zhang, Xu

    2017-04-25

    Magnesium aluminum-layered double-hydroxide nanoparticles (LDH NPs) are promising drug-delivery vehicles for gene therapy, particularly for siRNA interference; however, the interactions between oligo-DNA and LDH surfaces have not been adequately elucidated. Through a mechanistic study, oligo-DNA initially appears to rapidly bind strongly to the LDH outer surfaces through interactions with their phosphate backbones via ligand exchange with OH - on Mg 2+ centers and electrostatic forces with Al 3+ . These initial interactions might precede diffusion into interlayer spaces, and this knowledge can be used to design better gene therapy delivery systems.

  6. Quantum decoherence of near-surface nitrogen-vacancy centers in diamond and implications for nanoscale imaging

    Science.gov (United States)

    Myers, Bryan Andrew

    Nitrogen-vacancy (NV) centers in diamond excel as room-temperature quantum sensors by virtue of their long-lived spin coherence and experimental addressability at the single-spin level. When isolated deep within bulk diamond, NVs' spin coherence times and relaxation times are limited to several milliseconds by internal nuclear and electronic spin baths and vibrations in the crystal structure. However, when NVs are placed just nanometers from the diamond surface, which is necessary for nanoscale imaging of external fields, NV spin properties are impacted by a host of new decoherence sources that must be understood and mitigated to optimize the utility of the NV as a magnetometer. This dissertation addresses the questions: 1) What is the length scale over which near-surface NV spins experience decoherence due to the diamond surface? 2) What are the physical noise sources, and their frequency spectra, that cause surface-induced decoherence in NV centers? In addressing these questions, we also develop a NV on a scanning probe tip platform and use it to perform nanoscale imaging based on the NV spin-relaxation rate in the presence of magnetic and electric field fluctuations. First, we develop a method of nitrogen delta-doping during single-crystal diamond growth to create near-surface NV centers localized at multiple few-nanometer layers. Through a technique of scanning probe magnetic resonance imaging, we measure the depths of these shallow NVs with nanoscale precision. We correlate these depths to spin coherence times measured with dynamical decoupling and model this depth dependence with a combined model of surface-related and bulk magnetic noise. We find that significant discrepancies between the maximum measured coherence time and its maximum theoretical limit - twice the spin relaxation time - necessitate further study of the relaxation rates of near-surface NV centers. We develop a method to measure relaxation rates between all three NV spin-triplet ground state

  7. Two-dimensional X-ray diffraction as a tool for the rapid, nondestructive detection of low calcite quantities in aragonitic corals

    Science.gov (United States)

    Smodej, Jörg; Reuning, Lars; Wollenberg, Uwe; Zinke, Jens; Pfeiffer, Miriam; Kukla, Peter A.

    2015-10-01

    Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alteration. Secondary calcite can significantly affect paleotemperature reconstructions at very low amounts of ˜1%. X-ray powder diffraction is routinely used to detect diagenetic calcite in aragonitic corals. This procedure has its limitations as single powder samples might not represent the entire coral heterogeneity. A conventional and a 2-D X-ray diffractometer were calibrated with gravimetric powder standards of high and low magnesium calcite (0.3% to 25% calcite). Calcite contents slabs. The calcite detection performance of the 2-D-XRD setup was tested on thin sections from fossil Porites sp. samples that, based on powder XRD measurements, showed analysis showed very similar results. This enables spot measurements with diameters of ˜4 mm, as well as systematic line scans along potential tracks previous to geochemical proxy sampling. In this way, areas affected by diagenetic calcite can be avoided and alternative sampling tracks can be defined. Alternatively, individual sampling positions that show dubious proxy results can later be checked for the presence of calcite. The presented calibration and quantification method can be transferred to any 2-D X-ray diffractometer.

  8. Morphology of calcite crystals in clast coatings from four soils in the Mojave desert region

    Science.gov (United States)

    Chadwick, Oliver A.; Sowers, Janet M.; Amundson, Ronald G.

    1989-01-01

    Pedogenic calcite-crystal coatings on clasts were examined in four soils along an altitudinal gradient on Kyle Canyon alluvium in southern Nevada. Clast coatings were studied rather than matrix carbonate to avoid the effects of soil matrix on crystallization. Six crystal sizes and shapes were recognized and distinguished. Equant micrite was the dominant crystal form with similar abundance at all elevations. The distributions of five categories of spar and microspar appear to be influenced by altitudinally induced changes in effective moisture. In the drier, lower elevation soils, crystals were equant or parallel prismatic with irregular, interlocking boundaries while in the more moist, higher elevation soils they were randomly oriented, euhedral, prismatic, and fibrous. There was little support for the supposition that Mg(+2) substitution or increased (Mg + Ca)/HCO3 ratios in the precipitating solution produced crystal elongation.

  9. Impact of the distribution of calcite concretions on performance of SAGD

    Energy Technology Data Exchange (ETDEWEB)

    Gates, Ian [University of Calgary (Canada)

    2011-07-01

    In the heavy oil industry, the steam assisted gravity drainage (SAGD) process is often used to enhance oil recovery. In Grand Rapids oil sands reservoirs, carbonate cemented concretions can be found. In terms of SAGD process, these concretions can have an impact on the growth of steam chambers and thus on the method's performance. Calcite concretions are non productive rock but this can also enhance heat transfer through thermal dispersion depending on the length scales of its spatial distribution, sizes and shapes. The aim of this paper is then to study the effects of the concretion's spatial distributions and size on the performance of SAGD. Tests were conducted to assess several parameters of the steam chamber and results showed that steam chamber conformance depends on the heterogeneity of the concretions. This paper highlighted that SAGD performance can be optimized by deciding length scales for placement of well pairs and provided a means to do it.

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

    Science.gov (United States)

    Kimball, Justine; Eagle, Robert; Dunbar, Robert

    2016-12-01

    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

  11. Calcite-impregnated defluidization structures in littoral sands of mono lake, california.

    Science.gov (United States)

    Cloud, P; Lajoie, K R

    1980-11-28

    Associated locally with well-known tufa mounds and towers of Mono Lake, California, are subvertical, concretionary sand structures through which fresh calcium-containing artesian waters moved up to sites of calcium carbonate precipitation beneath and adjacent to the lake. The structures include closely spaced calcite-impregnated columns, tubes, and other configurations with subcylindrical to bizarre cross sections and predominantly vertical orientation in coarse, barely coherent pumice sands along the south shore of the lake. Many structures terminate upward in extensive calcareous layers of caliche and tufa. Locally they enter the bases of tufa mounds and towers. A common form superficially resembles root casts and animal burrows except that branching is mostly up instead of down. Similar defluidization structures in ancient sedimentary rocks have been mistakenly interpreted as fossil burrows.

  12. Multi-scale Geophysical Signatures of Biogenic Calcite and FeS Precipitation Using Rifle as a Model Site

    Science.gov (United States)

    Wu, Y.; Ajo-Franklin, J.; Williams, K. H.; Hubbard, S. S.; Nico, P. S.

    2008-12-01

    structure evolution in response to the remediation treatment. At the column scale, we collected time- lapse seismic, complex resistivity, and radar measurements to investigate the geophysical responses to biogeochemical transformations. Due to the contrast of electric conductivity, polarizability, density and elastic modulus between the two phases, the combined use of multiple and complementary geophysical methods across scales offers the potential to distinguish between the two mineral phases.Here, we present results that compare the microtomographic and column-scale geophysical signatures of the precipitation of the two phases. Our study suggests that: (1) Iron sulfide precipitation increases the polarization of the bulk material as well as the seismic and radar velocities due to its high electrical conductivity, high density and elastic modulus nature; (2) In comparison to iron sulfide, the effect of calcite precipitation on polarization is smaller, primarily due to the formation of nano- to micron-size precipitates that increase the surface area of the bulk material; (3) Dynamic microtomographic imagery clearly delineated the spatial distribution of precipitates in 3D and provided insights about solid phase speciation and separation at the level of grain coatings and contacts. Our results illustrate the potential of using geophysical methods for monitoring the evolution of and distinguishing between in-situ precipitates induced through remedial treatments.

  13. First-principles study of boron speciation in calcite and aragonite

    Science.gov (United States)

    Balan, Etienne; Pietrucci, Fabio; Gervais, Christel; Blanchard, Marc; Schott, Jacques; Gaillardet, Jérome

    2016-11-01

    Despite the importance of boron as a proxy of past ocean pH, the crystal-chemical factors controlling its incorporation in the structure of calcium carbonates are still poorly understood. This is partly linked to an imperfect knowledge of the coordination, protonation state and local environment of boron species in these minerals. In the present study, we use first-principles quantum mechanical tools to model selected trigonal and tetragonal boron species in calcite and aragonite. The stable geometry of the models is obtained from standard energy minimization schemes or using a more advanced metadynamics exploration of their configurational space. The computation of 11B NMR chemical shifts and quadrupolar coupling parameters enables a straightforward comparison of the models to existing experimental NMR data. The results show that B in calcium carbonates does occur as structural species substituted for CO32- anions. The B speciation depends on the polymorph considered. In calcite, structural boron is present as partially deprotonated trigonal BO2(OH)2- species coexisting with a fraction of substituted B(OH)4- groups. In aragonite, the B(OH)4- substitution for CO32- anions is dominant. Different species, including entrapped B(OH)3 molecules and substituted BO33- groups also occur in biogenic samples. The diversity of B speciation reflects a diversity of B incorporation mechanisms and sheds light on previous studies confronting B isotopic composition determination with NMR observations. The mechanisms of boron incorporation in calcium carbonates are probably more complex than usually assumed in the literature using boron isotopes as a proxy of paleo-atmospheric CO2 reconstructions. Although not invalidating the empirical paleo-pH proxy, these results call for a better understanding of the fundamental mechanisms of boron incorporation in carbonates.

  14. Altervalent substitution of sodium for calcium in biogenic calcite and aragonite

    Science.gov (United States)

    Yoshimura, Toshihiro; Tamenori, Yusuke; Suzuki, Atsushi; Kawahata, Hodaka; Iwasaki, Nozomu; Hasegawa, Hiroshi; Nguyen, Luan T.; Kuroyanagi, Azumi; Yamazaki, Toshitsugu; Kuroda, Junichiro; Ohkouchi, Naohiko

    2017-04-01

    Sodium concentrations in biogenic CaCO3 are several thousands of parts per million, and, on a molar basis, Na is among the most abundant constituent minor element in these carbonates. Nevertheless, the chemical form of Na in CaCO3 is not well constrained. We used synchrotron X-ray spectroscopy to identify the dominant molecular host sites for Na in biogenic calcite and aragonite precipitated by corals, bivalves, and foraminifera. We also used the K-edge X-ray absorption near-edge structure to investigate the chemical environment of Na in biogenic calcium carbonates and identify the altervalent substitution of Na into Ca sites in the lattice structures of calcite and aragonite. Minor cation and anion concentrations in biogenic CaCO3 suggest that the principal substitution mechanism involves charge compensation through the creation of CO32- vacancies. The mostly homogeneous Na concentrations in the skeletal microstructures of the various biota we examined indicate that environmental and biological controls, such as temperature, skeletal microstructure, and calcification rates, have only minor influences on skeletal Na concentrations. A decrease of Na:Ca ratios with increasing age of foraminiferal shells picked from a Quaternary sediment core, indicates progressive release of Na, which suggests that structurally-substituted Na in biogenic CaCO3 is readily leached during burial diagenesis. Whereas the sediment that undergo diagenesis release some Na back to the water column, sodium co-precipitation in biogenic CaCO3 serves as a potential sink of Na for the ocean.

  15. IMPLICATIONS OF MICROBIAL ADHESION TO HYDROCARBONS FOR EVALUATING CELL-SURFACE HYDROPHOBICITY .1. ZETA-POTENTIALS OF HYDROCARBON DROPLETS

    NARCIS (Netherlands)

    BUSSCHER, HJ; VANDEBELTGRITTER, B; VANDERMEI, HC

    1995-01-01

    Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. As microbial adhesion is a complicated interplay of long-range van der Waals and electrostatic forces and various short-range interactions, the above statement only holds

  16. Scale-dependency of the global mean surface temperature trend and its implication for the recent hiatus of global warming.

    Science.gov (United States)

    Lin, Yong; Franzke, Christian L E

    2015-08-11

    Studies of the global mean surface temperature trend are typically conducted at a single (usually annual or decadal) time scale. The used scale does not necessarily correspond to the intrinsic scales of the natural temperature variability. This scale mismatch complicates the separation of externally forced temperature trends from natural temperature fluctuations. The hiatus of global warming since 1999 has been claimed to show that human activities play only a minor role in global warming. Most likely this claim is wrong due to the inadequate consideration of the scale-dependency in the global surface temperature (GST) evolution. Here we show that the variability and trend of the global mean surface temperature anomalies (GSTA) from January 1850 to December 2013, which incorporate both land and sea surface data, is scale-dependent and that the recent hiatus of global warming is mainly related to natural long-term oscillations. These results provide a possible explanation of the recent hiatus of global warming and suggest that the hiatus is only temporary.

  17. Unintentional consequences of dual mode plasma reactors: Implications for upscaling lab-record silicon surface passivation by silicon nitride

    Science.gov (United States)

    Tong, Jingnan; To, Alexander; Lennon, Alison; Hoex, Bram

    2017-08-01

    Silicon nitride (SiN x ) synthesised by low-temperature plasma enhanced chemical vapour deposition (PECVD) is the most extensively used antireflection coating for crystalline silicon solar cells because of its tunable refractive index in combination with excellent levels of surface and bulk passivation. This has attracted a significant amount of research on developing SiN x films towards an optimal electrical and optical performance. Typically, recipes are first optimised in lab-scale reactors and subsequently, the best settings are transferred to high-throughput reactors. In this paper, we show that for one particular, but widely used, PECVD reactor configuration this upscaling is severely hampered by an important experimental artefact. Specifically, we report on the unintentional deposition of a dual layer structure in a dual mode AK 400 plasma reactor from Roth & Rau which has a significant impact on its surface passivation performance. It is found that the radio frequency (RF) substrate bias ignites an unintentional depositing plasma before the ignition of the main microwave (MW) plasma. This RF plasma deposits a Si-rich intervening SiN x layer (refractive index = 2.4) while using a recipe for stoichiometric SiN x . This layer was found to be 18 nm thick in our case and had an extraordinary impact on the Si surface passivation, witnessed by a reduction in effective surface recombination velocity from 22.5 to 6.2 cm/s. This experimental result may explain some “out of the ordinary” excellent surface passivation results reported recently for nearly stoichiometric SiN x films and has significant consequences when transferring these results to high-throughput deposition systems.

  18. Bay breeze climatology at two sites along the Chesapeake bay from 1986-2010: Implications for surface ozone.

    Science.gov (United States)

    Stauffer, Ryan M; Thompson, Anne M

    Hourly surface meteorological measurements were coupled with surface ozone (O3) mixing ratio measurements at Hampton, Virginia and Baltimore, Maryland, two sites along the Chesapeake Bay in the Mid-Atlantic United States, to examine the behavior of surface O3 during bay breeze events and quantify the impact of the bay breeze on local O3 pollution. Analyses were performed for the months of May through September for the years 1986 to 2010. The years were split into three groups to account for increasingly stringent environmental regulations that reduced regional emissions of nitrogen oxides (NOx): 1986-1994, 1995-2002, and 2003-2010. Each day in the 25-year record was marked either as a bay breeze day, a non-bay breeze day, or a rainy/cloudy day based on the meteorological data. Mean eight hour (8-h) averaged surface O3 values during bay breeze events were 3 to 5 parts per billion by volume (ppbv) higher at Hampton and Baltimore than on non-bay breeze days in all year periods. Anomalies from mean surface O3 were highest in the afternoon at both sites during bay breeze days in the 2003-2010 study period. In conjunction with an overall lowering of baseline O3 after the 1995-2002 period, the percentage of total exceedances of the Environmental Protection Agency (EPA) 75 ppbv 8-h O3 standard that occurred on bay breeze days increased at Hampton for 2003-2010, while remaining steady at Baltimore. These results suggest that bay breeze circulations are becoming more important to causing exceedance events at particular sites in the region, and support the hypothesis of Martins et al. (2012) that highly localized meteorology increasingly drives air quality events at Hampton.

  19. Halogen and Cl isotopic systematics in Martian phosphates: Implications for the Cl cycle and surface halogen reservoirs on Mars

    Science.gov (United States)

    Bellucci, J. J.; Whitehouse, M. J.; John, T.; Nemchin, A. A.; Snape, J. F.; Bland, P. A.; Benedix, G. K.

    2017-01-01

    The Cl isotopic compositions and halogen (Cl, F, Br, and I) abundances in phosphates from eight Martian meteorites, spanning most rock types and ages currently available, have been measured in situ by Secondary Ion Mass Spectrometry (SIMS). Likewise, the distribution of halogens has been documented by x-ray mapping. Halogen concentrations range over several orders of magnitude up to some of the largest concentrations yet measured in Martian samples or on the Martian surface, and the inter-element ratios are highly variable. Similarly, Cl isotope compositions exhibit a larger range than all pristine terrestrial igneous rocks. Phosphates in ancient (>4 Ga) meteorites (orthopyroxenite ALH 84001 and breccia NWA 7533) have positive δ37Cl anomalies (+1.1 to + 2.5 ‰). These samples also exhibit explicit whole rock and grain scale evidence for hydrothermal or aqueous activity. In contrast, the phosphates in the younger basaltic Shergottite meteorites (Phosphates with the largest negative δ37Cl anomalies display zonation in which the rims of the grains are enriched in all halogens and have significantly more negative δ37Cl anomalies suggestive of interaction with the surface of Mars during the latest stages of basalt crystallization. The phosphates with no textural, major element, or halogen enrichment evidence for mixing with this surface reservoir have an average δ37Cl of - 0.6 ‰, supporting a similar initial Cl isotope composition for Mars, the Earth, and the Moon. Oxidation and reduction of chlorine are the only processes known to strongly fractionate Cl isotopes, both positively and negatively, and perchlorate has been detected in weight percent concentrations on the Martian surface. The age range and obvious mixing history of the phosphates studied here suggest perchlorate formation and halogen cycling via brines, which have been documented on the Martian surface, has been active throughout Martian history.

  20. Distribution of tetraether lipids in surface sediments of the northern South China Sea: Implications for TEX86 proxies

    Directory of Open Access Journals (Sweden)

    Huangmin Ge

    2013-03-01

    Full Text Available Archaea have unique glycerol dialkyl glycerol tetraether (GDGT lipids that can be used to develop paleotemperature proxies such as TEX86. This research is to validate proposed GDGT-proxies for paleotemperature determination in the South China Sea (SCS. Samples were collected from core-top sediments (0–5 cm in the northern SCS. Total lipids were extracted to obtain core GDGTs, which were identified and quantified using liquid chromatography-mass spectrometry (LC-MS. The abundance of isoprenoidal GDGTs (iGDGTs ranged from 271.5 ng/g dry sediment to 1266.3 ng/g dry sediment, whereas the branched GDGTs (bGDGTs, supposedly derived from terrestrial sources, ranged from 22.2 ng/g dry sediment to 56.7 ng/g dry sediment. The TEX86-derived sea surface temperatures ranged from 20.9 °C in the coast (water depth  1000 m. TEX86-derived temperatures near shore (<160 m water depth averaged 23.1 ± 2.5 °C (n = 4, which were close to the satellite-derived winter mean sea surface temperature (average 22.6 ± 1.0 °C, n = 4; whereas the TEX86-derived temperatures offshore averaged 27.4 ± 0.3 °C (n = 7 and were consistent with the satellite mean annual sea surface temperature (average 26.8 ± 0.4 °C, n = 7. These results suggest that TEX86 may record the sea surface mean annual temperature in the open ocean, while it likely records winter sea surface temperature in the shallower water.

  1. Surface multiheme c-type cytochromes from Thermincola potens: Implications for dissimilatory metal reduction by Gram-positive bacteria

    Science.gov (United States)

    Carlson, H. K.; Iavarone, A. T.; Gorur, A.; Yeo, B. S.; Tran, R.; Melnyk, R. A.; Mathies, R. A.; Auer, M.; Coates, J. D.

    2011-12-01

    Almost nothing is known about the mechanisms of dissimilatory metal reduction by Gram-positive bacteria, although they have been shown to be the dominant species in some environments. Thermincola potens strain JR was isolated from the anode of a microbial fuel cell inoculated with anaerobic digester sludge and operated at 55 °C. Preliminary characterization revealed that T. potens coupled acetate oxidation to the reduction of hydrous ferric oxides (HFO) or the humic substances analog, anthraquinone-2,6-disulfonate (AQDS). The genome of T. potens was recently sequenced, and the abundance of multiheme c-type cytochromes (MHCs) is unusual for a Gram-positive bacterium. We present evidence from trypsin shaving LC-MS/MS experiments and surface-enhanced Raman spectroscopy (SERS) that indicates the expression of a number of MHCs during T. potens growth on either HFO or AQDS and that several MHCs are localized to the cell wall or cell surface of T. potens. Furthermore, one of the MHCs can be extracted from cells with low pH or denaturants suggesting a loose association with the cell wall or cell surface. Electron microscopy does not reveal an S-layer, and the precipitation of silver metal on the cell surface is inhibited by cyanide, supporting the involvement of surface-localized redox-active heme proteins in dissimilatory metal reduction. These results are the first direct evidence for cell-wall associated cytochromes and MHC involvement in conducting electrons across the cell envelope of a Gram-positive bacterium.

  2. An Exercise on Calibration: DRIFTS Study of Binary Mixtures of Calcite and Dolomite with Partially Overlapping Spectral Features

    Science.gov (United States)

    De Lorenzi Pezzolo, Alessandra

    2013-01-01

    Unlike most spectroscopic calibrations that are based on the study of well-separated features ascribable to the different components, this laboratory experience is especially designed to exploit spectral features that are nearly overlapping. The investigated system consists of a binary mixture of two commonly occurring minerals, calcite and…

  3. Early- to late-Holocene contrast in productivity, OMZ intensity and calcite dissolution in the eastern Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Naik, S.S.; Godad, S.P.; Naidu, P.D.; Tiwari, M.; Paropkari, A.L.

    , vol.24(6); 2014; 749-755 Early to Late Holocene Contrast in productivity, OMZ Intensity and Calcite Dissolution in the Eastern Arabian Sea Sushant S. Naik*,1, Shital P. Godad2, P. Divakar Naidu3, Manish Tiwari4, A. L. Paropkari5 1,2,3,5 CSIR...

  4. Evaluation of sediment capping with active barrier systems (ABS) using calcite/zeolite mixtures to simultaneously manage phosphorus and ammonium release.

    Science.gov (United States)

    Lin, Jianwei; Zhan, Yanhui; Zhu, Zhiliang

    2011-01-01

    The efficiency and mechanism of sediment capping with an active barrier system (ABS) using calcite/zeolite mixtures to simultaneously prevent phosphorus (P) and ammonium (NH(4)(+)) release from eutrophic lake sediments under anaerobic conditions was investigated through a series of batch and sediment incubation experiments. For this, natural calcite and various zeolites (natural, NaCl-pretreated and CaCl(2)-pretreated zeolites) were applied. Batch tests showed that the calcite was efficient for the removal of phosphate in aqueous solution and the zeolite was an efficient adsorbent for the removal of NH(4)(+) from aqueous solution. Sediment incubation experiments showed that the P and NH(4)(+) fluxes from the anaerobic sediments were significantly reduced by the ABS using the mixture of calcite and natural zeolite. Higher calcite dosage was found to be favorable for the prevention of P release from the sediments using the ABS. For controlling the P release from the sediments, the mixture of calcite and CaCl(2)-pretreated zeolite as a capping material was more efficient than that of calcite and natural zeolite, whereas the mixture of calcite and NaCl-pretreated zeolite was less efficient than that of calcite and natural zeolite. Batch and sediment incubation experiments proved that the zeolite as a component of the ABS using the mixture of calcite and CaCl(2)-pretreated zeolite has a dual function: (i) preventing NH(4)(+) release from the sediments; and (ii) supplying Ca(2+) through a Ca(2+)/NH(4)(+) exchange to improve the ability of the capping material to immobilize P release from the sediments. Copyright © 2010 Elsevier B.V. All rights reserved.

  5. Field Investigation of Surface Deformation Induced by the 2016 Meinong Earthquake and its Implications to Regional Geological Structures

    Science.gov (United States)

    Yi, De-Cheng; Chuang, Ray Y.; Lin, Ching-Weei

    2017-04-01

    We demonstrate mapping results of a newly-identified active folding-associated fault in southwestern Taiwan, which was triggered by the distant ML 6.6 Meinong earthquake in 2016. The 14.6-km-deep main shock occurred in Meinong at 3:57 (GMT +08) on February 6th while a series of 21-27 km deep aftershocks were induced after 160 seconds in Guanmiao, where is 25km NW away from the epicenter of the main shock. The focal mechanism of the Meinong main shock shows a westward oblique thrust with the fault plane of 275°/42°/17° (strike/dip/rake) but Guanmiao aftershocks show the N-S striking eastward normal movement. The study area locates at an on-going fold-and-thrust belt close to the deformation front of Taiwan orogeny with high rates of convergence, uplift and erosion. The geology of SW Taiwan is characterized by the 3-km-thick mudstones with high fluid pressure underlying the loose sedimentary rocks forming mud diapirs or mud-core anticlines. The significance of the Meinong earthquake is (1) aftershocks are far away from the main shock, and (2) the surface cracks partially distributed systematically along lineaments observed from InSAR, which has never been recognized as geological structures before. This study aims to establish possible kinematic processes of shallow deformation induced by the Meinong earthquake. We mapped surface cracks around the lineaments by using hand-held GPS and measured surface cracks by the compass and vernier. Among 249 kinematic data measured from 244 observed surface cracks and ruptures, the type of deformation was mostly identified as dilation or lateral translation and only 4 data were compressional deformation. The overall surface displacement moved to the northwest and west, consistent with the regional coseismic movement. The opening of the surface cracks range from 0.5 to 105 mm and 85% of them are less than 10 mm. Preseismic deformed features such as failure of the retaining wall were also observed along the western and eastern

  6. Changes in Surface Wind Speed over North America from CMIP5 Model Projections and Implications for Wind Energy

    Directory of Open Access Journals (Sweden)

    Sujay Kulkarni

    2014-01-01

    Full Text Available The centennial trends in the surface wind speed over North America are deduced from global climate model simulations in the Climate Model Intercomparison Project—Phase 5 (CMIP5 archive. Using the 21st century simulations under the RCP 8.5 scenario of greenhouse gas emissions, 5–10 percent increases per century in the 10 m wind speed are found over Central and East-Central United States, the Californian Coast, and the South and East Coasts of the USA in winter. In summer, climate models projected decreases in the wind speed ranging from 5 to 10 percent per century over the same coastal regions. These projected changes in the surface wind speed are moderate and imply that the current estimate of wind power potential for North America based on present-day climatology will not be significantly changed by the greenhouse gas forcing in the coming decades.

  7. The influence of surface and incorporated lime and gypsiferous by-products on surface and subsurface soil acidity. II. Root growth and agronomic implications

    Energy Technology Data Exchange (ETDEWEB)

    Wang, H.L.; Hedley, M.J.; Bolan, N.S.; Horne, D.J. [New Zealand Forest Research Institute, Rotorua (New Zealand)

    1999-04-01

    Lucerne (Medicago sativa. L) root elongation in acid soils amended by gypsiferous coal combustion by-products was investigated in a glasshouse study. Lime, fluidised bed boiler ash (FBA), and flue gas desulfurisation gypsum (FGDG) were mixed into the surface 50 mm of either an Allophanic (the Patua sand loam) or an Ultic (the Kaawa clay loam) soil column, at rates containing calcium equivalent to 5000 kg/ha of CaCO{sub 3}. Lucerne was grown on each column after it was leached with 400 mm of water. Whereas the lime treatment had no effect on root elongation in the acidic subsurface of the Patua soil, the FBA and FGDG treatments significantly improved lucerne root penetration into the subsurface soil. This was due to the `self liming effect` induced by sulfate adsorption. In contrast, topsoil incorporated amendments did not influence root penetration into the acidic subsurface of the Kaawa soil, which is dominated by permanently charged clay minerals. The `self-liming erect` caused by gypsum application is not a sustainable practice. Lime should be applied to neutralise the topsoil acidity, when gypsum is used as subsurface soil acidity ameliorant. FBA, which contains both lime and gypsum, can meet these requirements.

  8. Nitrogen-deficient microalgae are rich in cell-surface mannose: potential implications for prey biorecognition by phagotrophic protozoa

    Science.gov (United States)

    Martel, Claire M.

    2009-01-01

    Flow cytometry was used to quantify the abundance of mannose-linked glycoconjugates on microalgae precultured using low- or high-nitrate media. Nitrogen-deficient microalgae were richer in cell-surface mannose than nitrogen-sufficient. Findings are discussed in view of recent research which reveals mannose-specific ‘feeding receptors’ assist prey biorecognition by phagotrophic protozoa that ingest microalgae. PMID:24031323

  9. Constraining MODIS snow albedo at large solar zenith angles: Implications for the surface energy budget in Greenland

    OpenAIRE

    Wang, Xianwei; Zender, Charles S

    2010-01-01

    An understanding of the surface albedo of high latitudes is crucial for climate change studies. MODIS albedo retrievals flagged as high-quality compare well with in situ Greenland Climate Network (GC-Net) measurements but cover too small an area to fully characterize Greenland's albedo in nonsummer months. In contrast, poor quality MODIS retrievals provide adequate spatiotemporal coverage, but are not recommended for use at large solar zenith angles (SZAs) where they have a systematic low bia...

  10. Scale-dependency of the global mean surface temperature trend and its implication for the recent hiatus of global warming

    OpenAIRE

    Yong Lin; Christian L. E. Franzke

    2015-01-01

    Studies of the global mean surface temperature trend are typically conducted at a single (usually annual or decadal) time scale. The used scale does not necessarily correspond to the intrinsic scales of the natural temperature variability. This scale mismatch complicates the separation of externally forced temperature trends from natural temperature fluctuations. The hiatus of global warming since 1999 has been claimed to show that human activities play only a minor role in global warming. Mo...

  11. Structural features and seismotectonic implications of coseismic surface ruptures produced by the 2016 M w 7.1 Kumamoto earthquake

    Science.gov (United States)

    Lin, Aiming

    2017-09-01

    Field investigations and analyses of satellite images and aerial photographs reveal that the 2016 M w 7.1 (Mj 7.3) Kumamoto earthquake produced a ˜40-km surface rupture zone striking NE-SW on central Kyushu Island, Japan. Coseismic surface ruptures were characterized by shear faults, extensional cracks, and mole tracks, which mostly occurred along the pre-existing NE-SW-striking Hinagu-Futagawa fault zone in the southwest and central segments, and newly identified faults in the northeast segment. This study shows that (i) the Hinagu-Futagawa fault zone triggered the 2016 Kumamoto earthquake and controlled the spatial distribution of coseismic surface ruptures; (ii) the southwest and central segments were dominated by right-lateral strike-slip movement with a maximum in-site measured displacement of up to 2.5 m, accompanied by a minor vertical component. In contrast, the northeast segment was dominated by normal faulting with a maximum vertical offset of up to 1.75 m with a minor horizontal component that formed graben structures inside Aso caldera; (iii) coseismic rupturing initiated at the jog area between the Hinagu and Futagawa faults, then propagated northeastward into Aso caldera, where it terminated. The 2016 M w 7.1 Kumamoto earthquake therefore offers a rare opportunity to study the relationships between coseismic rupture processes and pre-existing active faults, as well as the seismotectonics of Aso volcano.

  12. High-pressure deformation of calcite marble and its transformation to aragonite under non-hydrostatic conditions

    Science.gov (United States)

    Hacker, B.R.; Kirby, S.H.

    1993-01-01

    We conducted deformation experiments on Carrara marble in the aragonite and calcite stability fields to observe the synkinematic transformation of calcite to aragonite, and to identify any relationships between transformation and deformation or sample strength. Deformation-induced microstructures in calcite crystals varied most significantly with temperature, ranging from limited slip and twinning at 400??C, limited recrystallization at 500??C, widespread recrystallization at 600 and 700??C, to grain growth at 800-900??C. Variations in confining pressure from 0.3 to 2.0 GPa have no apparent effect on calcite deformation microstructures. Aragonite grew in 10-6-10-7 s-1strain rate tests conducted for 18-524 h at confining pressures of 1.7-2.0 GPa and temperatures of 500-600??C. As in our previously reported hydrostatic experiments on this same transformation, the aragonite nucleated on calcite grain boundaries. The extent of transformation varied from a few percent conversion near pistons at 400??C, 2.0 GPa and 10-4 s-1 strain rate in a 0.8 h long experiment, to 98% transformation in a 21-day test at a strain rate of 10-7 s-7, a temperature of 600??C and a pressure of 2.0 GPa. At 500??C, porphyroblastic 100-200 ??m aragonite crystals grew at a rate faster than 8 ?? 10-1m s-1. At 600??C, the growth of aragonite neoblasts was slower, ???6 ?? 10-1 m s -1, and formed 'glove-and-finger' cellularprecipitation-like textures identical to those observed in hydrostatic experiments. The transformation to aragonite is not accompanied by a shear instability or anisotropic aragonite growth, consistent with its relatively small volume change and latent heat in comparison with compounds that do display those features. ?? 1993.

  13. Air Quality Investigation by Mobile Surface In Situ, Mobile Surface Remote Sensing, and Airborne Remote Sensing: Southern California Agricultural and Husbandry Inputs and Implication

    Science.gov (United States)

    Leifer, I.; Melton, C.; Tratt, D. M.; Buckland, K. N.; Fladeland, M. M.; Frash, J.; Hall, J. L.; Johnson, P. D.; Leen, J. B.; Vigil, S. A.

    2016-12-01

    There is strong interest in mitigating husbandry impacts on the environment, climate change, and health by improving real-world husbandry practices; however, this requires characterization on sub-facility length scales. Airborne thermal infrared (TIR) hyperspectral imagery and mobile surface-based TIR column spectroscopy were collected in the Los Angeles Basin and the San Joaquin Valley of the radiatively important husbandry gases, CH4 and NH3, by the Mako and MISTIR instruments, respectively. These gases, respectively, impact climate directly and indirectly by aerosol production. Supporting mobile in situ observations were collected by AMOG (AutoMObile trace Gas) Surveyor, a commuter car upgraded into a mobile air quality lab for use at up to highway speeds, and developed for satellite validation. AMOG Surveyor measures 12 gases (CO2, CH4, H2O, OCS, CO, NH3, H2S, O3, NO, NOX, SO2, combined sulfur) at sub-ppb levels using a combination of Cavity Enhanced Absorption Spectroscopy and Fluorescence analyzers, solar spectra (for column O3), and high accuracy 2D winds and meteorology. AMOG Surveyor integrates data in real-time to allow adaptive surveying. Derived O3 columns were compared with observed vertical O3 profiles collected in support of the California Air Resources Board's, CABOTS campaign, and mapped large spatial O3 column trends. In situ data agreed well spatially with NH3 and CH4 retrievals and derived fluxes. In situ data also showed downwind oxidant suppression. In situ plume transects for a wide range of husbandry gases were used to derive fluxes and estimate herd size based on literature emission rates. Agreement between head-estimates from multiple gases gave confidence to derived fluxes. Analysis showed that CH4 mitigation practice changes could increase NH3 emissions. Additionally, in situ NH3 and H2S data were used to map the strength of fertilizer applications between different fields in the San Joaquin Valley, and assess their relative importance.

  14. Multiscale Local Forcing of the Arabian Desert Daytime Boundary Layer, and Implications for the Dispersion of Surface-Released Contaminants.

    Science.gov (United States)

    Warner, Thomas T.; Sheu, Rong-Shyang

    2000-05-01

    Four 6-day simulations of the atmospheric conditions over the Arabian Desert during the time of the 1991 detonation and release of toxic material at the Khamisiyah, Iraq, weapons depot were performed using a mesoscale model run in a data-assimilation mode. These atmospheric simulations are being employed in a forensic analysis of the potential contribution of the toxic material to so-called Gulf War illness. The transport and concentration of such surface-released contaminants are related strongly to the planetary boundary layer (PBL) depth and the horizontal wind speed in the PBL. The product of the PBL depth and the mean wind speed within it is referred to as the ventilation and is used as a metric of the horizontal transport within the PBL. Thus, a corollary study to the larger forensic analysis involves employing the model solutions and available data in an analysis of the multiscale spatial variability of the daytime desert PBL depth and ventilation as they are affected by surface forcing from terrain elevation variations, coastal circulations, and contrasts in surface physical properties.The coarsest computational grid spanned the entire northern Arabian Desert and surrounding areas of the Middle East, and represented the large-scale PBL modulation by the orography. The PBL depths were greatest over the high elevations of the western Arabian Peninsula and over the Zagros Mountains in western Iran and were shallowest over water bodies and the lower elevations in the Tigris-Euphrates Valley. Higher-resolution grids in the nest (the smallest grid increment was 3.3 km) showed that the PBL depth minimum in the Tigris-Euphrates Valley was likely a consequence of compensating subsidence associated with the thermally forced daytime upward motion over the Zagros Mountains to the east in Iran, with possible contributions from an elevated mixed layer. Further local modulation of the daytime desert PBL occurred as a result of the inland penetration of the coastal sea

  15. Spectral characteristics of rocks: Effects of composition and texture and implications for the interpretation of planet surface compositions

    Science.gov (United States)

    Carli, Cristian; Sgavetti, Maria

    2011-02-01

    In spectroscopic remote sensing for the exploration of the surface compositions of Earth and terrestrial planets, reflectance spectra with very low spectral contrast and even devoid of diagnostic absorption bands can be observed, which make the interpretation of the component minerals ambiguous. Using selected examples of terrestrial rock samples from intrusive and effusive geologic systems, we discuss compositional and textural properties related to these particular spectral shapes. We show that: (1) this spectral behaviour is common for coarse grains of multimineral rocks, where the optical coupling is expected to occur between welded mineral particles; (2) it is emphasised by the presence of opaque minerals with various compositions, such as ulvospinel, magnetite and chromite in effusive rock groundmass and in intrusive rocks; (3) it is controlled by the number of silicate phases within which the FeO is distributed, irrespective of the total iron content in the rock: a rock composition with a high number of iron-bearing minerals producing this kind of low contrast, almost featureless spectra is indicated here as "critical mode"; (4) it is also strongly intensified by aqueous alteration of silicates. These observations suggest unpredictable combinations of several different petrographic variables affecting the spectra of some compact rocks, and stimulate both targeted studies to quantitatively relate spectral and petrographic parameters, and the development of appropriate methods of spectral decomposition. Our ongoing work is at present focused on the spectroscopic effects of the FeO concentration in transparent neutral plagioclase, the different compositions of the opaque neutral minerals, and the iron bearing amorphous phases. We also discuss the analogy between the rocks used in the analysis reported here and the crustal rock compositions observed on Mars and inferred for Mercury as well as the compatibility of the factors responsible for the low spectral

  16. Reflectance spectroscopy of palagonite and iron-rich montmorillonite clay mixtures - Implications for the surface composition of Mars

    Science.gov (United States)

    Orenberg, James; Handy, Jonathan

    1992-01-01

    The diffuse reflectance spectra of Hawaiian palagonite mixtures with an Fe-rich montmorillonite have prompted their present use as spectral analogs of the Martian surface. Like the Mars spectrum and unlike clays, the 2.2-micron reflectance spectrum absorption band is not present in the palagonite sample; neither is the 2.2-micron Al-OH clay lattice band seen in palagonite-montmorillonite mixtures, where the latter component remains below 15 wt pct. Fe-rich montmorillonite clay may therefore be present in Mars, in combination with palagonite, while remaining undetected in remotely sensed spectra.

  17. Differential proteomics analysis of the surface heterogeneity of dextran iron oxide nanoparticles and the implications for their in vivo clearance.

    Science.gov (United States)

    Simberg, Dmitri; Park, Ji-Ho; Karmali, Priya P; Zhang, Wan-Ming; Merkulov, Sergei; McCrae, Keith; Bhatia, Sangeeta N; Sailor, Michael; Ruoslahti, Erkki

    2009-08-01

    In order to understand the role of plasma proteins in the rapid liver clearance of dextran-coated superparamagnetic iron oxide (SPIO) in vivo, we analyzed the full repertoire of SPIO-binding blood proteins using novel two-dimensional differential mass spectrometry approach. The identified proteins showed specificity for surface domains of the nanoparticles: mannan-binding lectins bound to the dextran coating, histidine-rich glycoprotein and kininogen bound to the iron oxide part, and the complement lectin and contact clotting factors were secondary binders. Nanoparticle clearance studies in knockout mice suggested that these proteins, as well as several previously identified opsonins, do not play a significant role in the SPIO clearance. However, both the dextran coat and the iron oxide core remained accessible to specific probes after incubation of SPIO in plasma, suggesting that the nanoparticle surface could be available for recognition by macrophages, regardless of protein coating. These data provide guidance to rational design of bioinert, long-circulating nanoparticles.

  18. Observed and modeled surface Lagrangian transport between coastal regions in the Adriatic Sea with implications for marine protected areas

    Science.gov (United States)

    Carlson, Daniel F.; Griffa, Annalisa; Zambianchi, Enrico; Suaria, Giuseppe; Corgnati, Lorenzo; Magaldi, Marcello G.; Poulain, Pierre-Marie; Russo, Aniello; Bellomo, Lucio; Mantovani, Carlo; Celentano, Paolo; Molcard, Anne; Borghini, Mireno

    2016-04-01

    Surface drifters and virtual particles are used to investigate transport between seven coastal regions in the central and southern Adriatic Sea to estimate the degree to which these regions function as a network. Alongshore coastal currents and cyclonic gyres are the primary circulation features that connected regions in the Adriatic Sea. The historical drifter observations span 25 years and, thus, provide estimates of transport between regions realized by the mean surface circulation. The virtual particle trajectories and a dedicated drifter experiment show that southeasterly Sirocco winds can drive eastward cross-Adriatic transport from the Italian coast near the Gargano Promontory to the Dalmatian Islands in Croatia. Southeasterly winds disrupt alongshore transport on the west coast. Northwesterly Mistral winds enhanced east-to-west transport and resulted in stronger southeastward coastal currents in the western Adriatic current (WAC) and export to the northern Ionian Sea. The central Italian regions showed strong connections from north to south, likely realized by alongshore transport in the WAC. Alongshore, downstream transport was weaker on the east coast, likely due to the more complex topography introduced by the Dalmatian Islands of Croatia. Cross-Adriatic connection percentages were higher for east-to-west transport. Cross-Adriatic transport, in general, occurred via the cyclonic sub-gyres, with westward (eastward) transport observed in the northern (southern) arms of the central and southern gyres.

  19. Regulation of Pannexin 1 Surface Expression by Extracellular ATP: Potential Implications for Nervous System Function in Health and Disease

    Directory of Open Access Journals (Sweden)

    Leigh A. Swayne

    2017-08-01

    Full Text Available Pannexin 1 (Panx1 channels are widely recognized for their role in ATP release, and as follows, their function is closely tied to that of ATP-activated P2X7 purinergic receptors (P2X7Rs. Our recent work has shown that extracellular ATP induces clustering of Panx1 with P2X7Rs and their subsequent internalization through a non-canonical cholesterol-dependent mechanism. In other words, we have demonstrated that extracellular ATP levels can regulate the cell surface expression of Panx1. Here we discuss two situations in which we hypothesize that ATP modulation of Panx1 surface expression could be relevant for central nervous system function. The first scenario involves the development of new neurons in the ventricular zone. We propose that ATP-induced Panx1 endocytosis could play an important role in regulating the balance of cell proliferation, survival, and differentiation within this neurogenic niche in the healthy brain. The second scenario relates to the spinal cord, in which we posit that an impairment of ATP-induced Panx1 endocytosis could contribute to pathological neuroplasticity. Together, the discussion of these hypotheses serves to highlight important outstanding questions regarding the interplay between extracellular ATP, Panx1, and P2X7Rs in the nervous system in health and disease.

  20. Microbial Diversity in Surface Iron-Rich Aqueous Environments: Implications for Seeking Signs of Life on Mars

    Science.gov (United States)

    Brown, I. I.; Allen, C. C.; Tringe, S. G.; Klatt, C. G.; Bryant, D. A.; Sarkisova, S. A.; Garrison, D. H.; McKay, D. S.

    2010-01-01

    The success of selecting future landing sites on Mars to discover extinct and/or extant extraterrestrial life is dependent on the correct approximation of available knowledge about terrestrial paleogeochemistry and life evolution to Martian (paleo) geology and geochemistry. It is well known that both Earth and Mars are Fe rich. This widespread occurrence suggests that Fe may have played a key role in early life forms, where it probably served as a key constituent in early prosthetic moieties in many proteins of ancient microbes on Earth and likely Mars. The second critical idea is the premise that Life on Mars could most likely have developed when Mars experienced tectonic activity [1] which dramatically decreased around 1 bin years after Martian creation. After that Martian life could have gone extinct or hibernated in the deep subsurface, which would be expensive to reach in contrast to the successful work of Martian surface rovers. Here we analyze the diversity of microbes in several terrestrial Fe rich surface environments in conjunction with the phylogeny and molecular timing of emergence of those microbes on Earth. Anticipated results should help evaluate future landing sites on Mars in searches for biosignatures.

  1. Proteomics Analysis Reveals Distinct Corona Composition on Magnetic Nanoparticles with Different Surface Coatings: Implications for Interactions with Primary Human Macrophages.

    Directory of Open Access Journals (Sweden)

    Carmen Vogt

    Full Text Available Superparamagnetic iron oxide nanoparticles (SPIONs have emerged as promising contrast agents for magnetic resonance imaging. The influence of different surface coatings on the biocompatibility of SPIONs has been addressed, but the potential impact of the so-called corona of adsorbed proteins on the surface of SPIONs on their biological behavior is less well studied. Here, we determined the composition of the plasma protein corona on silica-coated versus dextran-coated SPIONs using mass spectrometry-based proteomics approaches. Notably, gene ontology (GO enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG pathway analysis revealed distinct protein corona compositions for the two different SPIONs. Relaxivity of silica-coated SPIONs was modulated by the presence of a protein corona. Moreover, the viability of primary human monocyte-derived macrophages was influenced by the protein corona on silica-coated, but not dextran-coated SPIONs, and the protein corona promoted cellular uptake of silica-coated SPIONs, but did not affect internalization of dextran-coated SPIONs.

  2. Effects of spatial pattern of green space on land surface temperature: implications for sustainable urban planning and climate change adaptation

    Science.gov (United States)

    Maimaitiyiming, M.; Ghulam, A.

    2013-12-01

    The urban heat island (UHI) refers to the phenomenon of higher atmospheric and surface temperatures occurring in urban areas than in the surrounding rural areas. Numerous studies have shown that increased percent cover of green space (PLAND) can significantly decrease land surface temperatures (LST). Fewer studies, however, have investigated the effects of configuration of green space on LST. This paper aims at to fill this gap using oasis city Aksu in northwestern China as a case study. PLAND along with two configuration metrics are used to measure the composition and configuration of green space. The metrics are calculated by moving window method based on a green space map derived from Landsat Thematic Mapper (TM) imagery, and LST data are retrieved from Landsat TM thermal band. Normalized mutual information measure is employed to investigate the relationship between LST and the spatial pattern of green space. The results show that while the PLAND is the most important variable that elicits LST dynamics, spatial configuration of green space also has significant effect on LST. In addition, the variance of LST is largely explained by both composition and configuration of green space. Results from this study can expand our understanding of the relationship between LST and vegetation, and provide insights for sustainable urban planning and management under changing climate.

  3. Dynamical Orientation of Large Molecules on Oxide Surfaces and its Implications for Dye-Sensitized Solar Cells

    KAUST Repository

    Brennan, Thomas P.

    2013-11-12

    A dual experimental-computational approach utilizing near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory-molecular dynamics (DFT-MD) is presented for determining the orientation of a large adsorbate on an oxide substrate. A system of interest in the field of dye-sensitized solar cells is studied: an organic cyanoacrylic acid-based donor-π-acceptor dye (WN1) bound to anatase TiO2. Assessment of nitrogen K-edge NEXAFS spectra is supported by calculations of the electronic structure that indicate energetically discrete transitions associated with the two π systems of the C-N triple bond in the cyanoacrylic acid portion of the dye. Angle-resolved NEXAFS spectra are fitted to determine the orientation of these two orbital systems, and the results indicate an upright orientation of the adsorbed dye, 63 from the TiO2 surface plane. These experimental results are then compared to computational studies of the WN1 dye on an anatase (101) TiO2 slab. The ground state structure obtained from standard DFT optimization is less upright (45 from the surface) than the NEXAFS results. However, DFT-MD simulations, which provide a more realistic depiction of the dye at room temperature, exhibit excellent agreement - within 2 on average - with the angles determined via NEXAFS, demonstrating the importance of accounting for the dynamic nature of adsorbate-substrate interactions and DFT-MD\\'s powerful predictive abilities. © 2013 American Chemical Society.

  4. Mixing heights and surface fluxes over Galveston Bay and the Gulf of Mexico: Implications for modeling of pollution episodes

    Science.gov (United States)

    Angevine, W. M.; Tucker, S. C.; Fairall, C.; Bariteau, L.; Wolfe, D.; Zagar, M.; Brewer, A.

    2007-12-01

    During the 2006 Texas Air Quality Study, boundary layer measurements were made by in-situ instruments, lidars, and rawinsondes on the NOAA RV Ronald H. Brown as well as by radar wind profilers on land. Brown also carried instruments to measure surface heat and momentum fluxes. This presentation will emphasize measurements made in Galveston Bay and in the Gulf of Mexico near the Houston area. Details of boundary layer depth and turbulence intensity over these waters have not been well known previously, but are quite important to the understanding of high ozone episodes in Houston. One somewhat surprising result is that the boundary layer over water was almost always slightly unstable, with positive surface heat flux. Mixing depths were moderate, although mixing was generally weak compared to that over land. Boundary layer heights over the water were substantially shallower than daytime heights over land. Experiments in modeling ozone episodes with WRF at 1.5-km grid spacing will be shown and compared with the measurements.

  5. Detection of snow surface thawing and refreezing in the Eurasian Arctic with QuikSCAT: implications for reindeer herding.

    Science.gov (United States)

    Bartsch, Annett; Kumpula, Timo; Forbes, Bruce C; Stammler, Florian

    2010-12-01

    Snow conditions play an important role for reindeer herding. In particular, the formation of ice crusts after rain-on-snow (ROS) events or general surface thawing with subsequent refreezing impedes foraging. Such events can be monitored using satellite data. A monitoring scheme has been developed for observation at the circumpolar scale based on data from the active microwave sensor SeaWinds on QuikSCAT (Ku-band), which is sensitive to changes on the snow surface. Ground observations on Yamal Peninsula were used for algorithm development. Snow refreezing patterns are presented for northern Eurasia above 60 degrees N from autumn 2001 to spring 2008. Western Siberia is more affected than Central and Eastern Siberia in accordance with climate data, and most events occur in November and April. Ice layers in late winter have an especially negative effect on reindeer as they are already weakened. Yamal Peninsula is located within a transition zone between high and low frequency of events. Refreezing was observed more than once a winter across the entire peninsula during recent years. The southern part experienced refreezing events on average four times each winter. Currently, herders can migrate laterally or north-south, depending on where and when a given event occurs. However, formation of ice crusts in the northern part of the peninsula may become as common as they are now in the southern part. Such a development would further constrain the possibility to migrate on the peninsula.

  6. Proteomics Analysis Reveals Distinct Corona Composition on Magnetic Nanoparticles with Different Surface Coatings: Implications for Interactions with Primary Human Macrophages.

    Science.gov (United States)

    Vogt, Carmen; Pernemalm, Maria; Kohonen, Pekka; Laurent, Sophie; Hultenby, Kjell; Vahter, Marie; Lehtiö, Janne; Toprak, Muhammet S; Fadeel, Bengt

    2015-01-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) have emerged as promising contrast agents for magnetic resonance imaging. The influence of different surface coatings on the biocompatibility of SPIONs has been addressed, but the potential impact of the so-called corona of adsorbed proteins on the surface of SPIONs on their biological behavior is less well studied. Here, we determined the composition of the plasma protein corona on silica-coated versus dextran-coated SPIONs using mass spectrometry-based proteomics approaches. Notably, gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed distinct protein corona compositions for the two different SPIONs. Relaxivity of silica-coated SPIONs was modulated by the presence of a protein corona. Moreover, the viability of primary human monocyte-derived macrophages was influenced by the protein corona on silica-coated, but not dextran-coated SPIONs, and the protein corona promoted cellular uptake of silica-coated SPIONs, but did not affect internalization of dextran-coated SPIONs.

  7. Proteomics Analysis Reveals Distinct Corona Composition on Magnetic Nanoparticles with Different Surface Coatings: Implications for Interactions with Primary Human Macrophages

    Science.gov (United States)

    Vogt, Carmen; Pernemalm, Maria; Kohonen, Pekka; Laurent, Sophie; Hultenby, Kjell; Vahter, Marie; Lehtiö, Janne; Toprak, Muhammet S.; Fadeel, Bengt

    2015-01-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) have emerged as promising contrast agents for magnetic resonance imaging. The influence of different surface coatings on the biocompatibility of SPIONs has been addressed, but the potential impact of the so-called corona of adsorbed proteins on the surface of SPIONs on their biological behavior is less well studied. Here, we determined the composition of the plasma protein corona on silica-coated versus dextran-coated SPIONs using mass spectrometry-based proteomics approaches. Notably, gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed distinct protein corona compositions for the two different SPIONs. Relaxivity of silica-coated SPIONs was modulated by the presence of a protein corona. Moreover, the viability of primary human monocyte-derived macrophages was influenced by the protein corona on silica-coated, but not dextran-coated SPIONs, and the protein corona promoted cellular uptake of silica-coated SPIONs, but did not affect internalization of dextran-coated SPIONs. PMID:26444829

  8. Trends in Downward Solar Radiation at the Surface over North America from Climate Model Projections and Implications for Solar Energy

    Directory of Open Access Journals (Sweden)

    Gerardo Andres Saenz

    2015-01-01

    Full Text Available The projected changes in the downward solar radiation at the surface over North America for late 21st century are deduced from global climate model simulations with greenhouse-gas (GHG forcing. A robust trend is found in winter over the United States, which exhibits a simple pattern of a decrease of sunlight over Northern USA. and an increase of sunlight over Southern USA. This structure was identified in both the seasonal mean and the mean climatology at different times of the day. It is broadly consistent with the known poleward shift of storm tracks in winter in climate model simulations with GHG forcing. The centennial trend of the downward shortwave radiation at the surface in Northern USA. is on the order of 10% of the climatological value for the January monthly mean, and slightly over 10% at the time when it is midday in the United States. This indicates a nonnegligible influence of the GHG forcing on solar energy in the long term. Nevertheless, when dividing the 10% by a century, in the near term, the impact of the GHG forcing is relatively minor such that the estimate of solar power potential using present-day climatology will remain useful in the coming decades.

  9. Effects of slope orientation on fine surface fuel moisture content: implications for ignition probabilities and connectivity of fuels

    Science.gov (United States)

    Nyman, Petter; Metzen, Daniel; Noske, Phil; Duff, Thomas; Sheridan, Gary

    2015-04-01

    This study quantifies topographic effects on microclimate and moisture dynamics in litter and near surface soil with the aim to improve spatial representation of fine surface fuel moisture content (FFMC) in mountainous terrain where forest fires typically operate. FFMC was monitored at 30-minute intervals using a novel field method for measuring moisture content of litter, providing unique data on the spatial-temporal variation in FFMC throughout a fire season. Moisture sensors were inserted into litter packs at sites on different slope aspects (North, South, West and East) and paired with manual measurement of gravimetric water content to relate sensor output to water content. Hydrochron sensors (or iButtons) were placed within the litter packs, measuring temperature at the interface between the litter layer and the soil. During the monitoring period the mean daily moisture content in the litter layer ranged from 0.07-1.30 kg kg-1 on the north-facing slope and from 0.11-1.83 kg kg-1 on the south-facing slope. The number of days during the fire season when the litter was below the fiber saturation point (~0.35 kg kg -1) was 49 and 128 on the south and north aspects, respectively, highlighting the very large aspect-driven variation in FFMC and the need for spatially explicit data on microclimate. Differences in moisture content were caused by aspect-related variation in incoming radiation which resulted in large temperature differences within the litter layer. On the warmest day of the monitoring period (38.9° C on 17 January), for example, the difference in litter temperature between North and South aspect was 14° C. Differences in surface temperature were driven mainly by the systematic variation in vegetation cover, and hence shading, which emerge as a result of aspect (i.e. eco-hydrologic effect) and partly by the effects of slope orientation (i.e. geometric effect) on incoming radiation. Furthermore, the differences in FFMC due to evaporative demand were

  10. Immunophenotyping of Waldenstroms macroglobulinemia cell lines reveals distinct patterns of surface antigen expression: potential biological and therapeutic implications.

    Directory of Open Access Journals (Sweden)

    Aneel Paulus

    Full Text Available Waldenströms macroglobulinemia (WM is a subtype of Non-Hodgkin's lymphoma in which the tumor cell population is markedly heterogeneous, consisting of immunoglobulin-M secreting B-lymphocytes, plasmacytoid lymphocytes and plasma cells. Due to rarity of disease and scarcity of reliable preclinical models, many facets of WM molecular and phenotypic architecture remain incompletely understood. Currently, there are 3 human WM cell lines that are routinely used in experimental studies, namely, BCWM.1, MWCL-1 and RPCI-WM1. During establishment of RPCI-WM1, we observed loss of the CD19 and CD20 antigens, which are typically present on WM cells. Intrigued by this observation and in an effort to better define the immunophenotypic makeup of this cell line, we conducted a more comprehensive analysis for the presence or absence of other cell surface antigens that are present on the RPCI-WM1 model, as well as those on the two other WM cell lines, BCWM.1 and MWCL-1. We examined expression of 65 extracellular and 4 intracellular antigens, comprising B-cell, plasma cell, T-cell, NK-cell, myeloid and hematopoietic stem cell surface markers by flow cytometry analysis. RPCI-WM1 cells demonstrated decreased expression of CD19, CD20, and CD23 with enhanced expression of CD28, CD38 and CD184, antigens that were differentially expressed on BCWM.1 and MWCL-1 cells. Due to increased expression of CD184/CXCR4 and CD38, RPCI-WM1 represents a valuable model in which to study the effects anti-CXCR4 or anti-CD38 targeted therapies that are actively being developed for treatment of hematologic cancers. Overall, differences in surface antigen expression across the 3 cell lines may reflect the tumor clone population predominant in the index patients, from whom the cell lines were developed. Our analysis defines the utility of the most commonly employed WM cell lines as based on their immunophenotype profiles, highlighting unique differences that can be further studied for

  11. Reflectance Spectroscopy of Palagonite and Iron-Rich Montmorillonite Clay Mixtures: Implications for the Surface Composition of Mars

    Science.gov (United States)

    Orenberg, James; Handy, Jonathan

    1992-01-01

    Mixtures of a Hawaiian palagonite and an iron-rich, montmorillonite clay (15.8 +/- 0.4 wt% Fe as Fe2O3) were evaluated as Mars surface spectral analogs from their diffuse reflectance spectra. The presence of the 2.2 microns absorption band in the reflectance spectrum of clays and its absence in the Mars spectrum have been interpreted as indicating that highly crystalline aluminous hydroxylated clays cannot be a major mineral component of the soil on Mars. The palagonite sample used in this study does not show this absorption feature in its spectrum. In mixtures of palagonite and iron-rich montmorillonite, the 2.2 microns Al-OH clay lattice band is not seen below 15 wt% montmorillonite. This suggests the possibility that iron-rich montmorillonite clay may be present in the soil of Mars at up to 15 wt% in combination with palagonite, and remain undetected in remotely sensed spectra of Mars.

  12. Photogeneration of reactive transient species upon irradiation of natural water samples: Formation quantum yields in different spectral intervals, and implications for the photochemistry of surface waters.

    Science.gov (United States)

    Marchisio, Andrea; Minella, Marco; Maurino, Valter; Minero, Claudio; Vione, Davide

    2015-04-15

    Chromophoric dissolved organic matter (CDOM) in surface waters is a photochemical source of several transient species such as CDOM triplet states ((3)CDOM*), singlet oxygen ((1)O2) and the hydroxyl radical (OH). By irradiation of lake water samples, it is shown here that the quantum yields for the formation of these transients by CDOM vary depending on the irradiation wavelength range, in the order UVB > UVA > blue. A possible explanation is that radiation at longer wavelengths is preferentially absorbed by the larger CDOM fractions, which show lesser photoactivity compared to smaller CDOM moieties. The quantum yield variations in different spectral ranges were definitely more marked for (3)CDOM* and OH compared to (1)O2. The decrease of the quantum yields with increasing wavelength has important implications for the photochemistry of surface waters, because long-wavelength radiation penetrates deeper in water columns compared to short-wavelength radiation. The average steady-state concentrations of the transients ((3)CDOM*, (1)O2 and OH) were modelled in water columns of different depths, based on the experimentally determined wavelength trends of the formation quantum yields. Important differences were found between such modelling results and those obtained in a wavelength-independent quantum yield scenario. Copyright © 2015 Elsevier Ltd. All rights reserved.

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

    Science.gov (United States)

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

    2015-12-01

    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.

  14. Seasonal and annual variations of mountain glaciers surface velocity, implications for ice dynamic. Case study: Karakorum and Pamir.

    Science.gov (United States)

    Nanni, Ugo; Scherler, Dirk; Ayoub, Francois; Malatesta, Luca; Herman, Frederic; Avouac, Jean-Philippe

    2017-04-01

    The Pamir and Karakorum regions are heavily glaciated and contain some of the largest and fastest mountain glaciers on Earth. Satellite imagery is key to constrain ice dynamics, in particular glacier surface velocities, and sub glacial processes, e.g., basal sliding or glacier erosion, in such large and remote regions. Significant velocity variations have previously been observed in this area and related to forcing by seasonal meltwater and surges mechanisms. However, the details of surges sequences, in particular their initiation and termination, and multiyear seasonal patterns are still poorly documented. Here we study 26 glaciers and quantify surface velocity variations at high temporal resolution from remote sensing. We present a processing strategy to exploit the large archives of optical satellite imagery available for the study area to obtain more than 500 velocity fields with a 16-day temporal resolution from April 2013 to July 2016. Glacier displacement is measured with a 1.5-meter resolution using sub-pixel correlation (COSI-Corr software) of Landsat-8 images. 14 out of the 26 studied glaciers show seasonal velocity variations with inter-annual variability. These glaciers typically accelerate in early spring, up to 150% of the winter velocity, starting in the ablation zone and occasionally propagating upstream. This behaviour supports a meteorological/hydrological forcing with higher velocities caused by an increase in water pressure due to melt water input during spring time. 12 out of the 26 glaciers underwent one sub-annual or multiyear surging event during the study period. The surging events do not follow a unique pattern. Velocity can increase by up 700% over a month, and with an acceleration that initiate anytime of the year. This suggests that surges are initiated by an internal process, e.g., shear heating or basal hydrology, rather than by an external seasonal forcing.

  15. The Geomorphic Expression and Surface Patterns of Ash-flow Deposits on Earth: Implications for the Presence of Ash Deposits on Mars.

    Science.gov (United States)

    de Silva, S. L.; Bailey, J.

    2011-12-01

    The presence of ash deposits and explosive volcanism on Mars has been debated for over three decades. If correct this has implications for the style of volcanism, the evolution of magmas and volatiles in the mantle and crust, the presence of water, and the evolution of the atmosphere. Critical evidence supporting the ash hypotheses is the geomorphic expression and surface expression of the deposits. Sheet-like aspect, columnar jointing, yardangs, and differential induration in the Medusa Fossae Formation have led to an origin as ash flow tuffs (or ignimbrites) as the most likely origin. Ongoing work on the surface patterns of terrestrial ignimbrites in the Central Andes may help further our understanding. The ignimbrites in this region provide the best terrestrial analog for Martian regions because of their scale and exposure. The regions arid climate allows capture of high resolution satellite views of the surface morphology largely unhindered by vegetation and atmospheric filtering. While the most prominent geomorphic expressions are produced by fluvial and aeolian processes, these are superimposed on features that are the result of post-depositional thermal and degassing history. Evidence of the latter includes indurated ridges that control yardang development, polygonal fractures that appear to be the intersection of dominant joint directions and concentric radiating "rosettes" that appear to the focus of jointing in the ignimbrites. Field observations show that all these geomorphic features are clearly associated with extensive high temperature vapor phase alteration of the deposit visible in the field. The presence of the regularly spaced vapor phase altered rosettes is consistent with post depositional fumarolic gas rise. This coupled with joint spacing as a proxy for cooling rate suggests the rosettes are associated with rapid cooling associated with vapor fluxing. The location and spacing of rosettes implicates external water suggesting that formation of

  16. Central surface curvatures of postmortem- extracted intact human crystalline lenses: implications for understanding the mechanism of accommodation.

    Science.gov (United States)

    Schachar, Ronald A

    2004-09-01

    To measure the radii of curvature of postmortem, whole, encapsulated human crystalline lenses, free of all zonular attachments, and to calculate their corresponding optical powers. Experimental study. Thirty human crystalline lenses from donors with a mean age of 33.6+/-14.4 years. Intact clear human crystalline lenses were obtained within an average of 21 hours of death. The lenses were removed from the eye b