WorldWideScience

Sample records for calcite buffered solutions

  1. 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 rat

  2. Electrodialysis operation with buffer solution

    Science.gov (United States)

    Hryn, John N.; Daniels, Edward J.; Krumdick, Greg K.

    2009-12-15

    A new method for improving the efficiency of electrodialysis (ED) cells and stacks, in particular those used in chemical synthesis. The process entails adding a buffer solution to the stack for subsequent depletion in the stack during electrolysis. The buffer solution is regenerated continuously after depletion. This buffer process serves to control the hydrogen ion or hydroxide ion concentration so as to protect the active sites of electrodialysis membranes. The process enables electrodialysis processing options for products that are sensitive to pH changes.

  3. Single-contact pressure solution creep on calcite monocrystals

    CERN Document Server

    Zubtsov, Sergei; Gratier, Jean-Pierre; Dysthe, Dag; Traskine, Vladimir

    2005-01-01

    Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 degrees C for six weeks using ceramic indenters under stresses in the 50-200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter) is measured ex-situ at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0-100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calc...

  4. An AFM study of calcite dissolution in concentrated electrolyte solutions

    Science.gov (United States)

    Ruiz Agudo, E.; Putnis, C. V.; Putnis, A.; Rodriguez-Navarro, C.

    2009-04-01

    Calcite-solution interactions are of a paramount importance in a range of processes such as the removal of heavy metals, carbon dioxide sequestration, landscape modeling, weathering of building stone and biomineralization. Water in contact with minerals often carries significant amounts of solutes; additionally, their concentration may vary due to evaporation and condensation. It is well known that calcite dissolution is affected dramatically by the presence of such solutes. Here we present investigations on the dissolution of calcite in the presence of different electrolytes. Both bulk (batch reactors) experiments and nanoscale (in situ AFM) techniques are used to study the dissolution of calcite in a range of solutions containing alkaly cations balanced by halide anions. Previous works have indicated that the ionic strength has little influence in calcite dissolution rates measured from bulk experiments (Pokrovsky et al. 2005; Glendhill and Morse, 2004). Contrary to these results, our quantitative analyses of AFM observations show an enhancement of the calcite dissolution rate with increasing electrolyte concentration. Such an effect is concentration-dependent and it is most evident in concentrated solutions. AFM experiments have been carried out in a fluid cell using calcite cleavage surfaces in contact with solutions of simple salts of the alkaly metals and halides at different undersaturations with respect to calcite to try to specify the effect of the ionic strength on etch pit spreading rate and calcite dissolution rate. These results show that the presence of soluble salts may critically affect the weathering of carbonate rocks in nature as well as the decay of carbonate stone in built cultural heritage. References: Pokrosky, O.S.; Golubev, S.V.; Schott, J. Dissolution kinetics of calcite, dolomite and magnesite at 25°C and 0 to 50 atm pCO2. Chemical Geology, 2005, 217 (3-4) 239-255. Glendhill, D.K.; Morse, J.W. Dissolution kinetics of calcite in Na

  5. Buffer-free therapeutic antibody preparations provide a viable alternative to conventionally buffered solutions: from protein buffer capacity prediction to bioprocess applications.

    Science.gov (United States)

    Bahrenburg, Sven; Karow, Anne R; Garidel, Patrick

    2015-04-01

    Protein therapeutics, including monoclonal antibodies (mAbs), have significant buffering capacity, particularly at concentrations>50 mg/mL. This report addresses pH-related issues critical to adoption of self-buffered monoclonal antibody formulations. We evaluated solution conditions with protein concentrations ranging from 50 to 250 mg/mL. Samples were both buffer-free and conventionally buffered with citrate. Samples were non-isotonic or adjusted for isotonicity with NaCl or trehalose. Studies included accelerated temperature stability tests, shaking stability studies, and pH changes in infusion media as protein concentrate is added. We present averaged buffering slopes of capacity that can be applied to any mAb and present a general method for calculating buffering capacity of buffer-free, highly concentrated antibody liquid formulations. In temperature stability tests, neither buffer-free nor conventionally buffered solution conditions showed significant pH changes. Conventionally buffered solutions showed significantly higher opalescence than buffer-free ones. In general, buffer-free solution conditions showed less aggregation than conventionally buffered solutions. Shaking stability tests showed no differences between buffer-free and conventionally buffered solutions. "In-use" preparation experiments showed that pH in infusion bag medium can rapidly approximate that of self-buffered protein concentrate as concentrate is added. In summary, the buffer capacity of proteins can be predicted and buffer-free therapeutic antibody preparations provide a viable alternative to conventionally buffered solutions.

  6. Comparison of Dissolution and Surface Reactions Between Calcite and Aragonite in L-Glutamic and L-Aspartic Acid Solutions

    Directory of Open Access Journals (Sweden)

    Kwangsuk You

    2010-01-01

    Full Text Available We have investigated dissolution and surface reaction of calcite and aragonite in amino acid solutions of L-glutamic (L-glu and L-aspartic acid (L-asp at weak acidity of above pH 3. The surface reactions of calcite and aragonite were related with the dissolution. Calcite was dissolved in both solutions but the dissolution was limited by an adsorption of Ca-carboxylate salt. Aragonite was neither dissolved nor reacted in amino acid solutions because the crystal surface consisted of a hard to dissolve structure.

  7. 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

  8. The influence of solution composition and grain boundaries on the replacement of calcite by dolomite

    Science.gov (United States)

    Moraila Martinez, Teresita de Jesus; Putnis, Christine V.; Putnis, Andrew

    2016-04-01

    Dolomite formation is a mineral replacement reaction that affects extensive rock volumes and comprises a large fraction of oil and gas reservoirs [1,2]. The most accepted hypothesis is the 'dolomitization' of limestone by Mg-rich fluids [3]. The objective of this research is to study the replacement mechanism of calcite by dolomite, the role of grain boundaries, highlighted by Etschmann et al. (2014), and the possible influence of solutions in dolomite formation under the presence of ions that are normally in crustal aqueous fluids. To accomplish this purpose, we performed hydrothermal experiments using Carrara marble cubes of ~1.5 mm size and 7-9 mg weight as starting material, reacted with 1M (Mg,Ca)Cl2 aqueous solutions, with Mg/Ca ratios of 3 and 5 at 200°C, for different reaction times. Additional experiments were performed adding 1mM of Na2SO4, NaCl or NaF to the previous solutions. After the reaction, the product phases were identified using Raman spectroscopy, X-Ray powder diffraction (XRD), electron microprobe analysis (EMPA), and the textural evolution was studied by scanning electron microscopy (SEM). Samples reacted with aqueous solutions resulted in the replacements of the calcite rock into magnesite and dolomite. The amount and type of reaction strongly depends on the Mg/Ca ratio. Samples reacted with a Mg/Ca ratio of 5 resulted in an almost complete replacement reaction and more favorable for magnesite formation than for dolomite. When the Mg/Ca ratio was 3 dolomite formed but the replacement was located in the core of the sample. We show that grain boundaries are very important for the infiltration of solution and the progress of a replacement reaction, acting as fluid pathways. Solution composition controls the nature of the replacement product. Acknowledgment: This work is funded within a Marie Curie EU Initial Training Network- CO2-React. 1. Etschmann B., Brugger J., Pearce M.A., Ta C., Brautigan D., Jung M., Pring A. (2014). Grain boundaries as

  9. Advanced titania buffer layer architectures prepared by chemical solution deposition

    Science.gov (United States)

    Kunert, J.; Bäcker, M.; Brunkahl, O.; Wesolowski, D.; Edney, C.; Clem, P.; Thomas, N.; Liersch, A.

    2011-08-01

    Chemical solution deposition (CSD) was used to grow high-quality (100) oriented films of SrTiO3 (STO) on CSD CaTiO3 (CTO), Ba0.1Ca0.9TiO3 (BCT) and STO seed and template layers. These template films bridge the lattice misfit between STO and the nickel-tungsten (NiW) substrate, assisting in dense growth of textured STO. Additional niobium (Nb) doping of the STO buffer layer reduces oxygen diffusion which is necessary to avoid undesired oxidation of the NiW. The investigated templates offer suitable alternatives to established standard buffer systems like La2Zr2O7 (LZO) and CeO2 for coated conductors.

  10. Fabrication of calcite blocks from gypsum blocks by compositional transformation based on dissolution-precipitation reactions in sodium carbonate solution.

    Science.gov (United States)

    Ishikawa, Kunio; Kawachi, Giichiro; Tsuru, Kanji; Yoshimoto, Ayami

    2017-03-01

    Calcium carbonate (CaCO3) has been used as a bone substitute, and is a precursor for carbonate apatite, which is also a promising bone substitute. However, limited studies have been reported on the fabrication of artificial calcite blocks. In the present study, cylindrical calcite blocks (ϕ6×3mm) were fabricated by compositional transformation based on dissolution-precipitation reactions using different calcium sulfate blocks as a precursor. In the dissolution-precipitation reactions, both CaSO4·2H2O and CaSO4 transformed into calcite, a polymorph of CaCO3, while maintaining their macroscopic structure when immersed in 1mol/L Na2CO3 solution at 80°C for 1week. The diametral tensile strengths of the calcite blocks formed using CaSO4·2H2O and CaSO4 were 1.0±0.3 and 2.3±0.7MPa, respectively. The fabrication of calcite blocks using CaSO4·2H2O and CaSO4 proposed in this investigation may be a useful method to produce calcite blocks because of the self-setting ability and high temperature stability of gypsum precursors.

  11. 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.

  12. Surface Kinetic Model for the Fractionation of Trace Elements and Isotopes in Calcite Precipitated from Aqueous Solution

    Science.gov (United States)

    Depaolo, D. J.; Ryerson, F. J.; Watkins, J. M.; Bourg, I. C.; Yang, W.; Nielsen, L. C.; Druhan, J. L.

    2010-12-01

    The isotopic and trace element concentrations in calcite and other carbonate minerals form the basis for several paleoceanographic and paleoenvironmental indicators. The chemical and isotopic composition of natural calcites is determined by a combination of equilibrium partitioning and kinetic fractionations. Currently there is no general model that describes when equilibrium applies and how kinetic effects depend on the circumstances and rates of mineral growth. A useful approach is to separate the growth of calcite from aqueous solutions into forward (f) and backward (b) reactions, and to consider the mechanisms and fractionations that may be associated with each. We are evaluating a model where the net precipitation rate of calcite (Rp) is expressed as the difference between a forward rate (Rf) and a backward (dissolution) rate (Rb). Dissolution is approached only as Rp/Rb->0. Much natural calcite, including biogenic, forms under conditions where Rp ≫ Rb, hence the isotopic and trace element partitioning is strongly influenced by the kinetics of the forward reaction. Assuming that there are kinetic fractionations associated with the forward and backward reactions, a simple model can be developed for the dependence of calcite composition on precipitation rate. This model can explain most available experimental data on Ca and O isotopes, as well as Sr/Ca and Mn/Ca in calcite, and can be used to infer the behavior of other trace and minor elements. The critical parameter in applying the model is the value of Rb which to first order can be estimated from mineral dissolution rates, but apparently is not a constant, but instead varies with solution chemistry, especially at saturation conditions close to equilibrium. The surface kinetic model requires three parameters that are measureable experimentally and potentially also predictable from molecular dynamics simulation approaches. In this way it differs from the surface entrapment model of Watson (2004) which

  13. Buffer Sizing in Wireless Networks: Challenges, Solutions, and Opportunities

    KAUST Repository

    Showail, Ahmad

    2016-04-01

    Buffer sizing is an important network configuration parameter that impacts the Quality of Service (QoS) characteristics of data traffic. With falling memory costs and the fallacy that \\'more is better\\', network devices are being overprovisioned with large bu ers. This may increase queueing delays experienced by a packet and subsequently impact stability of core protocols such as TCP. The problem has been studied extensively for wired networks. However, there is little work addressing the unique challenges of wireless environment such as time-varying channel capacity, variable packet inter-service time, and packet aggregation, among others. In this paper we discuss these challenges, classify the current state-of-the-art solutions, discuss their limitations, and provide directions for future research in the area.

  14. Calcite precipitation from aqueous solution: transformation from vaterite and role of solution stoichiometry

    NARCIS (Netherlands)

    Nehrke, G.

    2007-01-01

    The morphology of vaterite precipitated by bubbling CO2 through a CaCl2 solution is framboidal aggregates. It is not possible, even when using the identical experimental setup and conditions, to reproduce aggregates having identical morphology. The density of the aggregates and crystallite size can

  15. Cobalt incorporation in calcite: thermochemistry of (Ca,Co)CO3 solid solutions from density functional theory simulations

    Science.gov (United States)

    González-López, Jorge; Ruiz-Hernández, Sergio E.; Fernández-González, Ángeles; Jiménez, Amalia; de Leeuw, Nora H.; Grau-Crespo, Ricardo

    2015-04-01

    The incorporation of cobalt in mixed metal carbonates is a possible route to the immobilization of this toxic element in the environment. However, the thermodynamics of (Ca,Co)CO3 solid solutions are still unclear due to conflicting data from experiment and from the observation of natural ocurrences. Atomistic computer simulations, which allow the evaluation of thermodynamic properties without the interference of unknown kinetic factors, have been increasingly used in recent years for the investigation of the thermodynamics of mixing and impurity incorporation in carbonate. We report here the results of a computer simulation study of the mixing of calcite (CaCO3) and spherocobaltite (CoCO3), using density functional theory calculations. Our simulations suggest that previously proposed thermodynamic models, based only on observed compositions, significantly overestimate the solubility between the two solids and therefore underestimate the extension of the miscibility gap under ambient conditions. The enthalpy of mixing of the disordered solid solution is strongly positive and moderately asymmetric: calcium incorporation in spherocobaltite is more endothermic than cobalt incorporation in calcite. Ordering of the impurities in (0001) layers is energetically favourable with respect to the disordered solid solution at low temperatures and intermediate compositions, but the ordered phase is still unstable to demixing. The solvus and spinodal lines in the phase diagram using a sub-regular solution model has been also calculated, and conclude that many Ca1-xCoxCO3 mineral solid solutions (with observed compositions of up to x=0.027, and above x=0.93) are metastable with respect to phase separation. The strong non-ideality of this solid solution has an important effect on the solid solution / aqueous solution thermodynamic partitioning: the equilibrium level of substitutional impurities in the endmember solids is always low, regardless of the composition of the aqueous

  16. What's in your buffer? Solute altered millisecond motions detected by solution NMR.

    Science.gov (United States)

    Wong, Madeline; Khirich, Gennady; Loria, J Patrick

    2013-09-17

    To date, little work has been conducted on the relationship between solute and buffer molecules and conformational exchange motion in enzymes. This study uses solution NMR to examine the effects of phosphate, sulfate, and acetate in comparison to MES- and HEPES-buffered references on the chemical shift perturbation and millisecond, chemical, or conformational exchange motions in the enzyme ribonuclease A (RNase A), triosephosphate isomerase (TIM) and HisF. The results indicate that addition of these solutes has a small effect on (1)H and (15)N chemical shifts for RNase A and TIM but a significant effect for HisF. For RNase A and TIM, Carr-Purcell-Meiboom-Gill relaxation dispersion experiments, however, show significant solute-dependent changes in conformational exchange motions. Some residues show loss of millisecond motions relative to the reference sample upon addition of solute, whereas others experience an enhancement. Comparison of exchange parameters obtained from fits of dispersion data indicates changes in either or both equilibrium populations and chemical shifts between conformations. Furthermore, the exchange kinetics are altered in many cases. The results demonstrate that common solute molecules can alter observed enzyme millisecond motions and play a more active role than what is routinely believed.

  17. 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

    The aim of this study is to illuminate how calcite precipitation depends on the identity and structure of the growth substrate. Calcite was precipitated at 25°C from supersaturated aqueous solutions in the presence of seeds of either calcite or one of six silicate materials: augite, enstatite......, 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......H equal to 9.1. Although the inlet fluid composition, flow rate, and temperature were identical for all experiments, the onset of calcite precipitation depended on the identity of the seeds present in the reactor. Calcite precipitated instantaneously and at a constant rate in the presence of calcite...

  18. Influence of phosphate-buffered sucrose solution on early graft function in feline renal autotransplantation.

    Science.gov (United States)

    Katayama, Masaaki; Okamura, Yasuhiko; Shimamura, Shunsuke; Katayama, Rieko; Kamishina, Hiroaki; Uzuka, Yuji

    2014-10-01

    Graft perfusion with cold heparinized saline has known to induce ischemia and reperfusion injury in feline kidney transplantation. In this study, the effects of phosphate-buffered sucrose solution and heparinized saline solution on early kidney graft function were compared in feline kidney autotransplantation. Perfusion of grafts with or without hypothermic storage with chilled phosphate-buffered sucrose solution prevented ischemia and reperfusion injury despite a very short ischemic time. The results of our study suggest that phosphate-buffered sucrose perfusion and storage solution should be effective to reduce ischemia and reperfusion injury despite a very short ischemic time in feline kidney transplantation.

  19. Impact of solute concentration on the electrocatalytic conversion of dissolved gases in buffered solutions

    KAUST Repository

    Shinagawa, Tatsuya

    2015-04-24

    To maintain local pH levels near the electrode during electrochemical reactions, the use of buffer solutions is effective. Nevertheless, the critical effects of the buffer concentration on electrocatalytic performances have not been discussed in detail. In this study, two fundamental electrochemical reactions, oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR), on a platinum rotating disk electrode are chosen as model gas-related aqueous electrochemical reactions at various phosphate concentrations. Our detailed investigations revealed that the kinetic and limiting diffusion current densities for both the ORR and HOR logarithmically decrease with increasing solute concentration (log|jORR|=-0.39c+0.92,log|jHOR|=-0.35c+0.73). To clarify the physical aspects of this phenomenon, the electrolyte characteristics are addressed: with increasing phosphate concentration, the gas solubility decrease, the kinematic viscosity of the solution increase and the diffusion coefficient of the dissolved gases decrease. The simulated limiting diffusion currents using the aforementioned parameters match the measured ones very well (log|jORR|=-0.43c+0.99,log|jHOR|=-0.40c+0.54), accurately describing the consequences of the electrolyte concentration. These alterations of the electrolyte properties associated with the solute concentration are universally applicable to other aqueous gas-related electrochemical reactions because the currents are purely determined by mass transfer of the dissolved gases. © 2015 The Authors.

  20. Effect of Solute Impurity of Mg on the Microstructure of Calcite

    Science.gov (United States)

    Xu, L.; Evans, B. J.; Renner, J.

    2006-12-01

    We produced synthetic marbles by hot isostatic pressing (HIPing) mixtures of calcite and dolomite powders for different intervals (2 to 30 hrs) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in macroscopically homogeneous calcite aggregates with Mg content ranging from 0.5 to 17 mol%. We performed creep tests on samples after HIP at differential stresses from ~ 20 to 170 MPa using constant strain rate and stress-stepping method. Microstructure of both HIPed and deformed samples were studied using both scanning electron microscope (SEM) and transmitted electron microscope (TEM). Both back- scattered electron images and chemical analysis using ion probe suggested that the dolomite phase is completely dissolved, and that the Mg distribution is homogeneous throughout the samples at a scale of a few microns. Grain sizes increase with HIP time and decrease with increasing Mg content (> 3.0 mol%). The growth exponent varies from 2.7 to 3.5 for samples containing 0.3 to 17.0 mol% Mg. Some HIPed samples have intragranular spherical pores, but the shape of the grain boundaries indicates pore drag. At stresses above 80 MPa, the stress sensitivity of strain, n, is greater than 3, indicating an increasing contribution of dislocation creep. The strength of calcite increases with the Mg content in the dislocation creep regime, but not when the rocks deform by diffusion creep. In some deformed samples (ɛ ~ 0.25), a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted..

  1. [Influence of buffer solutions on the performance of microbial fuel cell electricity generation].

    Science.gov (United States)

    Qiang, Lin; Yuan, Lin-jiang; Ding, Qing

    2011-05-01

    Microbial fuel cell (MFC) is a potential green technology due to its application in wastewater treatment and renewable energy generation. Phosphate buffer solution (PBS) has been commonly used in MFC studies to maintain a suitable pH for electricity generating bacteria and/or to increase the solution conductivity. However, it has some drawbacks using PBS in MFC: One is that the addition of a high concentration of phosphate buffer in MFCs is expensive, especially for the application in wastewater treatment; the other is that phosphates can contribute to the eutrophication conditions of water bodies if the effluents are discharged without the removal of phosphates. By adding PBS buffer as the comparison, the study investigated the effect of borax buffer and in the absence of buffer on the performance of electrical power, coulomb efficiency and effluent pH. 200 mmol/L PBS was the best, conductivity was 1.973 mS/cm,the maximum power density was 36.4 mW/m2 and the maximum coulomb efficiency was 2.92%, effluent pH was almost at (7.00 +/- 0.05). 100 mmol/L borax buffer solution, conductivity was 1.553 mS/cm; the maximum power density was 26.2 mW/m2 coulomb efficiency of 6.26%, which was 2.14 times to PBS and greatly increased the electron recovery efficiency with the effluent pH was (7.35 +/- 0.05). While free buffer solution conductivity was 0.314 mS/cm, maximum power density was 27.64 mW/m2; coulomb efficiency was 2.82% and the effluent pH of approximately 7.43. The electrolyte which in absence of buffer solution conductivity was 1/6 of adding PBS buffer, 1/5 of borax buffer, while its power density lower 8.76 mW/mr2 than adding PBS and higher 1.24 mW/m2 than borax buffer. The results showed that adding the suitable concentration of borax buffer may improve the electron recovery efficiency and under batch conditions, MFC run successfully without adding buffer solution to MFC.

  2. 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

  3. Side Effect of Good's Buffers on Optical Properties of Gold Nanoparticle Solutions

    DEFF Research Database (Denmark)

    Engelbrekt, Christian; Wagner, Michal; Undall-Behrend Christiansen, Mikkel

    2016-01-01

    In search of fluorescent nanoclusters (NCs) for bioimaging, several methods of synthesis have been attempted. Particularly, formation of gold NCs (AuNCs) during synthesis of gold nanoparticles (AuNPs) using Good's buffers was reported based on the optical properties of the reactions mixtures. Here...... we chose the Good's buffers 2-(N-morpholino)ethanesulfonic acid (MES), 3-(N-morpholino)propanesulfonic acid (MOPS) and 4-(N-morpholino)butanesulfonic acid (MOBS) as [AuCl4]- reducing agents. Resulting AuNP solutions were subjected to electrochemical investigations along with UV-vis and fluorescence...... spectroscopy. Distinct absorption features at ca. 290 and 360 nm and fluorescence emission in the 408-484 nm range are observed in filtered AuNP-free solutions. Electrochemical oxidation of these buffers generates similar optical properties, suggesting that the degradation products of the buffers contribute...

  4. Comparison of Ring-Buffer-Based Packet Capture Solutions

    Energy Technology Data Exchange (ETDEWEB)

    Barker, Steven Andrew [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

    2015-10-01

    Traditional packet-capture solutions using commodity hardware incur a large amount of overhead as packets are copied multiple times by the operating system. This overhead slows sensor systems to a point where they are unable to keep up with high bandwidth traffic, resulting in dropped packets. Incomplete packet capture files hinder network monitoring and incident response efforts. While costly commercial hardware exists to capture high bandwidth traffic, several software-based approaches exist to improve packet capture performance using commodity hardware.

  5. The effect of buffered solutions in corrosion testing of alloyed 13%Cr martensitic stainless steels for mildly sour applications

    Energy Technology Data Exchange (ETDEWEB)

    Drugli, J.M.; Rogne, T.; Svenning, M.; Axelsen, S. [SINTEF Materials Technology, Trondheim (Norway); Enerhaug, J. [Statoil, Trondheim (Norway)

    1999-11-01

    13% Cr stainless steels may suffer from sulfide stress corrosion cracking in sour environments if hydrogen enters the material. Hydrogen evolution is caused by the cathodic reaction in the corrosion process. As distinct from solutions without buffer, buffered solutions keep the pH stable at the surface almost independent of the electrochemical reactions. The most common initiation process for corrosion of stainless steels is break-down of the passive oxide by subsequent local acidification, which to a certain extent can be prevented in buffered solutions. For local corrosion the risk of corrosion therefore is higher in solutions without buffer than in buffered solutions at the same bulk pH. Hydrogen evolution may also be caused by general corrosion. For this type of corrosion the effect of buffer in the solution may be, contrary to the effect for local corrosion, that general corrosion of 13 Cr (with risk for cracking of loaded specimens) is more readily initiated in buffered solutions than in solutions without buffer at the same pH. With respect to corrosion on ground alloyed 13Cr base material by coupling to carbon steel, it is shown that general corrosion initiates both in strongly and moderately without buffer at pH 3.5, buffered solutions, but not in solution.

  6. Induction of Root Hair Growth in a Phosphorus-Buffered Culture Solution

    Institute of Scientific and Technical Information of China (English)

    LIU Guo-dong; James Dunlop; Thai Phung

    2006-01-01

    A system to control the release of phosphate in water was successfully established, based on solubility product of [Ca2+] and [PO43-] using tricalcium phosphate as P source in the hydroponic solution, and adding CaC12 for supplementing extra Ca2+. The system, similar to soil solutions, was a P nutrient buffer solution with very low bioavailable P. The buffer solution induced the roots of both monocotyledon and dicotyledon species to grow abundant root hairs, 3 mm in maximum length. The monocotyledons were corn (Zea mays L.) (var. Yellow Rose), wheat (Triticum aestivum L.) (var.Yanzhong 144), Triticale secale L. (var. Jingsong 5), and ryegrass (Lolium rigidum L.) (var. Ruanni), and the dicotyledons were Arabidopsis thaliana L. (var. Columbia), white clover (Trifolium repens) (var. Kopu), Lotus (Lotus peduncucatus Cav. Luliginosus Schkuhr) (var. Grasslands Maku). For these species we proved that the root environment controls the induction of root hair formation. However, the hydroponic buffer solution failed to induce root hairs on the roots of onion (Allium cepa L.). Other investigators have concluded that corn does not form root hairs in hydroponics, but abundant long root hairs on corn were induced by this buffer system. The roots with abundant long root hairs are called "hedgehog roots" because they have hairs everywhere just like a hedgehog.

  7. Dopamine-melanin film deposition depends on the used oxidant and buffer solution.

    Science.gov (United States)

    Bernsmann, Falk; Ball, Vincent; Addiego, Frédéric; Ponche, Arnaud; Michel, Marc; Gracio, José Joaquin de Almeida; Toniazzo, Valérie; Ruch, David

    2011-03-15

    The deposition of "polydopamine" films, from an aqueous solution containing dopamine or other catecholamines, constitutes a new and versatile way to functionalize solid-liquid interfaces. Indeed such films can be deposited on almost all kinds of materials. Their deposition kinetics does not depend markedly on the surface chemistry of the substrate, and the films can reach thickness of a few tens of nanometers in a single reaction step. Up to now, even if a lot is known about the oxidation mechanism of dopamine in solution, only little information is available to describe the deposition mechanism on surfaces either by oxidation in solution or by electrodeposition. The deposition kinetics of melanin was only investigated from dopamine solutions using oxygen or ammonium persulfate as an oxidant and from a tris(hydroxymethyl) aminomethane (Tris) containing buffer solutions at pH 8.5. Many other oxidants could be used, and the buffer agent containing a primary amine group may influence the deposition process. Herein we show that the deposition kinetics of melanin from dopamine containing buffers at pH 8.5 can be markedly modified using Cu(2+) instead of O2 as an oxidant: the deposition kinetics remains linear up to thicknesses of more than 70 nm, whereas the film growth stops at 45 ± 5 nm in the presence of 02. In addition, the films prepared from Cu(2+) containing solutions display an absorption spectrum with defined peaks at 320 and 370 nm, which are absent in the spectra of films prepared in oxygenated solutions. The replacement of Tris buffer by phosphate buffer also has a marked effect on the melanin deposition kinetics.

  8. Interaction mode and nanoparticle formation of bovine serum albumin and anthocyanin in three buffer solutions

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Rui; Dong, Xueyan; Song, Lanlan; Jing, Hao, E-mail: hao.haojing@gmail.com

    2014-11-15

    Investigation of interaction mode of bovine serum albumin (BSA) and anthocyanin (ACN) in different solutions will help us understand the interaction mechanism and functional change of bioactive small molecule and biomacromolecule. This study investigated the binding mode, including binding constant, number of binding sites, binding force of BSA and ACN interaction in three buffer solutions of phosphate (PBS), sodium chloride (NaCl), and PBS-NaCl, using fluorescence spectroscopy and synchronous fluorescence spectroscopy. Formation and characteristics of BSA–ACN complex were also investigated using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that ACN could interact with BSA at both tyrosine (Tyr) and tryptophan (Trp) residues through both hydrogen bonds and van der Waals force, and the same binding mode was seen in dH{sub 2}O and three buffer solutions. The value of binding constant K was decreased as the temperature increased from 298 K to 308 K, and the decreasing degree was in the order of dH{sub 2}O (9.0×10{sup 4})>NaCl (2.64×10{sup 4})/PBS (2.37×10{sup 4})>PBS-NaCl (0.88×10{sup 4}), which was inversely correlated with the ionic strength of the buffer solutions of PBS-NaCl>NaCl>PBS. It indicated that stability of BSA–ACN complex was affected most in dH{sub 2}O than in three buffer solutions. The BSA and ACN interaction led to formation of BSA–ACN nanoparticles. The sizes of BSA–ACN nanoparticles in dH{sub 2}O were smaller than that in three buffer solutions, which correlated with stronger binding force between BSA and ACN in dH{sub 2}O than in three buffer solutions at room temperature (25 °C, 298 K). - Highlights: • We report the influences of four solutions on the BSA–ACN interaction. • We report the relationship between BSA–ACN interaction and particle size of complex. • The stability of BSA–ACN complex was affected most in dH{sub 2}O than in buffer solutions.

  9. Microchannel electrokinetics of charged analytes in buffered solutions near floating electrodes

    DEFF Research Database (Denmark)

    Andersen, Mathias Bækbo; Wolfcale, Trevor; Gregersen, Misha Marie;

    We present both experimental and numerical studies of nonlinear electrokinetic flow of buffered solutions seeded with dilute analytes in a straight microchannel (0.6 μm high, 250 μm wide, and 9000 μm long) with a 0.15 μm high 60 μm wide electrode situated at the bottom center of the channel...

  10. Absorption of Sulphur Dioxide with Sodium Citrate Buffer Solution in a Rotating Packed Bed

    Institute of Scientific and Technical Information of China (English)

    JIANG Xiuping; LIU Youzhi; GU Meiduo

    2011-01-01

    Absorption of SO2 from a SO2/air mixture with sodium citrate buffer solution was investigated using a rotating packed bed(RPB) in laboratory scale.The effects of operating parameters,such as the rotation speed of RPB,liquid-gas ratio,inlet gas flow rate,inlet concentration of SO2 in flue gas,sodium citrate buffer concentration and initial pH of absorption solution,on the SO2 concentration in the absorption solution or removal efficiency of SO2 were examined.Incremental rate of sulfate radical ions in the absorption solution was also examined.Experimental results indicate that the efficiency of this regenerative process will be improved by using RPB under appropriate operating conditions,and the generation of SO2-4 will be restrained in the process in RPB.

  11. Differential effect of buffering agents on the crystallization of gemcitabine hydrochloride in frozen solutions.

    Science.gov (United States)

    Patel, Mehulkumar; Munjal, Bhushan; Bansal, Arvind K

    2014-08-25

    The purpose of this study was to evaluate the differential effect of buffering agents on the crystallization of gemcitabine hydrochloride (GHCl) in frozen solutions. Four buffering agents, viz. citric acid (CA), malic acid (MA), succinic acid (SA) and tartaric acid (TA) were selected and their effect on GHCl crystallization was monitored using standard DSC and low temperature XRD. Onset of GHCl crystallization during heating run in DSC was measured to compare the differential effect of buffering agents. Glass transition temperature (Tg'), unfrozen water content in the freeze concentrate and crystallization propensity of the buffering agents was also determined for mechanistic understanding of the underlying effects. CA and MA inhibited while SA facilitated crystallization of GHCl even at 25 mM concentration. Increasing the concentration enhanced their effect. However, TA inhibited GHCl crystallization at concentrations crystallization could be explained by consideration of two opposing factors: (i) their own crystallization tendency and (ii) unfrozen water content in the freeze concentrate. In conclusion, it was established that API crystallization in frozen solution is affected by the type and concentration of the buffering agents.

  12. Acanthamoeba encystment: multifactorial effects of buffers, biocides, and demulcents present in contact lens care solutions

    Directory of Open Access Journals (Sweden)

    Kovacs CJ

    2015-10-01

    Full Text Available Christopher J Kovacs, Shawn C Lynch, Marjorie J Rah, Kimberly A Millard, Timothy W Morris Bausch & Lomb Incorporated, Rochester, NY, USA Purpose: To determine whether agents which are purportedly capable of inducing encystment of Acanthamoeba can recapitulate the signal when tested in differing formulations. Methods: In accordance with the International Standard ISO 19045, Acanthamoeba castellanii ATCC 50370 trophozoites were cultured in antibiotic-free axenic medium, treated with test solutions, and encystment rates plus viability were measured via bright field and fluorescent microscopy. Test solutions included phosphate-buffered saline (PBS, borate-buffered saline, biguanide- and hydrogen peroxide (H2O2-based biocides, propylene glycol (PG and povidone (POV ophthalmic demulcents, and one-step H2O2-based contact lens disinfection systems. Results: Only PBS solutions with 0.25 ppm polyaminopropyl biguanide (PAPB and increasing concentrations of PG and POV stimulated A. castellanii encystment in a dose-dependent manner, whereas PBS solutions containing 3% H2O2 and increasing concentrations of PG and POV did not stimulate encystment. Borate-buffered saline and PBS/citrate solutions containing PG also did not stimulate encystment. In addition, no encystment was observed after 24 hours, 7 days, or 14 days of exposures of trophozoites to one-step H2O2 contact lens disinfection products or related solutions. Conclusion: The lack of any encystment observed when trophozoites were treated with existing or new one-step H2O2 contact lens care products, as well as when trophozoites were exposed to various related test solutions, confirms that Acanthamoeba encystment is a complex process which depends upon simultaneous contributions of multiple factors including buffers, biocides, and demulcents. Keywords: propylene glycol, contact lens care system, hydrogen peroxide disinfecting solution

  13. Effect of fluoride in phosphate buffer solution on bonding to artificially carious enamel.

    Science.gov (United States)

    Wang, Hao; Shimada, Yasushi; Tagami, Junji

    2007-09-01

    The purpose of the present study was to evaluate the effect of fluoride on resin bonding to artificially carious enamel. Specimens from demineralized human enamel sections were prepared using two commercially available adhesives (Clearfil SE Bond, Kuraray; Single Bond, 3M) and a composite resin (Clearfil AP-X, Kuraray) according to manufacturers' instructions. They were then immersed in phosphate buffered saline solution with varied fluoride concentrations at 0, 0.1, 0.5, 1, and 10 ppm. After immersion in each solution for one, three, or seven days, microshear bond strength was measured. The bond strengths of both adhesive systems to artificially carious enamel significantly increased after immersion in fluoride-phosphate buffer solution. Based on the findings obtained, we thus proposed not to remove the white enamel lesions for bonding in the clinic. They might be preserved and treated using fluoride applications.

  14. THE KINETICS OF SAPONIFICATION OF IODOACETIC ACID BY SODIUM HYDROXIDE AND BY CERTAIN ALKALINE BUFFER SOLUTIONS.

    Science.gov (United States)

    Brdicka, R

    1936-07-20

    1. The rate of the saponification of iodoacetic acid in sodium hydroxide and alkaline buffer solutions yielding glycollic acid was measured by means of Heyrovský's polarographic method. 2. From the bimolecular velocity constants, increasing with the ionic strength of the solution, the Brönsted factor, F, which characterizes the primary salt effect, was calculated. 3. In the borate buffer solutions the monomolecular constants of the saponification were determined which, at values above the pH of neutralization of boric acid, show a proportionality to the concentration of hydroxyl anions. Below the pH of neutralization of boric acid, they are proportional to the concentration of borate anions.

  15. Comparison of three buffer solutions for amino acid derivatization and following analysis by liquid chromatography electrospray mass spectrometry.

    Science.gov (United States)

    Rebane, Riin; Herodes, Koit

    2012-07-06

    For reversed phase separation amino acids are usually derivatized. Several derivatization reactions are carried out at basic pH. In the present work, influence of three basic buffer solutions on liquid chromatography electrospray ionization mass-spectrometric (LC-ESI-MS) analysis of amino acid derivatives was studied. Borate buffer--the most common derivatization buffer--was found to influence ESI ionization up to 23 min retention time. For 9-fluorenylmethylmethoxycarbonyl chloride (Fmoc-Cl derivatization) carbonate buffer should be preferred as it provides higher responses. Hexafluoroisopropanol (HFIP) buffer improves chromatographic peak shapes and responses for diethyl ethoxymethylenemalonate (DEEMM) derivatives.

  16. Hydrogen production in microbial reverse-electrodialysis electrolysis cells using a substrate without buffer solution.

    Science.gov (United States)

    Song, Young-Hyun; Hidayat, Syarif; Kim, Han-Ki; Park, Joo-Yang

    2016-06-01

    The aim of this work was to use substrate without buffer solution in a microbial reverse-electrodialysis electrolysis cell (MREC) for hydrogen production under continuous flow condition (10 cell pairs of RED stacks, HRT=5, 7.5, and 15h). Decreasing in the HRT (increasing in the organic matter) made cell current stable and increased. Hydrogen gas was produced at a rate of 0.61m(3)-H2/m(3)-Van/d in H-MREC, with a COD removal efficiency of 81% (1.55g/L/d) and a Coulombic efficiency of 41%. This MREC system without buffer solution could successfully produce hydrogen gas at a consistent rate.

  17. A new strategy to stabilize oxytocin in aqueous solutions: I. The effects of divalent metal ions and citrate buffer.

    Science.gov (United States)

    Avanti, Christina; Amorij, Jean-Pierre; Setyaningsih, Dewi; Hawe, Andrea; Jiskoot, Wim; Visser, Jan; Kedrov, Alexej; Driessen, Arnold J M; Hinrichs, Wouter L J; Frijlink, Henderik W

    2011-06-01

    In the current study, the effect of metal ions in combination with buffers (citrate, acetate, pH 4.5) on the stability of aqueous solutions of oxytocin was investigated. Both monovalent metal ions (Na(+) and K(+)) and divalent metal ions (Ca(2+), Mg(2+), and Zn(2+)) were tested all as chloride salts. The effect of combinations of buffers and metal ions on the stability of aqueous oxytocin solutions was determined by RP-HPLC and HP-SEC after 4 weeks of storage at either 4°C or 55°C. Addition of sodium or potassium ions to acetate- or citrate-buffered solutions did not increase stability, nor did the addition of divalent metal ions to acetate buffer. However, the stability of aqueous oxytocin in aqueous formulations was improved in the presence of 5 and 10 mM citrate buffer in combination with at least 2 mM CaCl(2), MgCl(2), or ZnCl(2) and depended on the divalent metal ion concentration. Isothermal titration calorimetric measurements were predictive for the stabilization effects observed during the stability study. Formulations in citrate buffer that had an improved stability displayed a strong interaction between oxytocin and Ca(2+), Mg(2+), or Zn(2+), while formulations in acetate buffer did not. In conclusion, our study shows that divalent metal ions in combination with citrate buffer strongly improved the stability of oxytocin in aqueous solutions.

  18. The effect of hemodialysis solution buffer on the control of blood pressure and efficacy of hemodialysis in chronic hemodialysis patients

    Directory of Open Access Journals (Sweden)

    Garevani H

    2007-11-01

    Full Text Available Background: The effect of kind of dialysis solution on the control of blood pressure and adequacy and efficacy of hemodialysis is a most debated and controversial issue.Methods: Twenty six chronic hemodialized patients in Ghaem hemodialysis center, Mashhad, Iran, in winter of the year 2004, enrolled this study for one month. The patients were dialyzed with bicarbonate buffer and were dialyzed in the next month with acetate. The kind of membranes and the dialysis machines were the same in both months. Systolic and diastolic pressures were measured before and after hemodialysis in at least three hemodialysis sessions, and he means recorded. The mean of the body weight were also recorded. In the same sessions of hemodialysis by measuring the urea, before and after hemodialysis, urea reduction ratio (URR, was also calculated. Statistical analysis was done with paired student t test for paired measurement, and independent t test for evaluating the effect of the kind of dialysate buffer on the measured parameters.Results: There were no significant statistical differences between acetate and bicarbonate dialysis solution buffers in the control of diastolic blood pressure. But use of acetate buffer resulted in more significant systolic blood pressure reduction compared with bicarbonate buffer (p=0.045. When adequacy of hemodialysis were compared between two kinds of buffers there were no significant statistical differences between them. When the effect of dialysate sodium concentration in the range utilized in two buffers, was evaluated on the systolic and diastolic pressure reduction, no significant differences, between two types of buffers attributable to the difference between dialysates sodium concentrations were found.Conclusion: Hemodialysis with both, acetate and bicarbonate buffers results in significant reductions in systolic and diastolic blood pressure, weight and urea ratio. Use of acetate buffer is more significantly associated with

  19. Study on the oxidation form of adenine in phosphate buffer solution.

    Science.gov (United States)

    Song, Yuan-Zhi; Zhou, Jian-Feng; Zhu, Feng-Xia; Ye, Yong; Xie, Ji-Min

    2010-07-01

    The oxidation of adenine in phosphate buffer solution is investigated using square-wave voltammetry and in situ UV spectroelectrochemistry. The geometry of adenine and the derivatives optimized at DFTB3LYP-6-31G (d, p)-PCM level is in agreement with the crystal structure, and the imitated UV spectra of adenine and the product at electrode are consistent with the in situ UV spectra. The relationship between the electrochemical property and the molecular structure is also discussed. The experimental and theoretical results show that the adenine oxidation origins from the neutral adenine.

  20. Cyclic growth and branching phenomena of calcite grown in Mg(2+) containing solutions and in natural systems

    Science.gov (United States)

    Wiethoff, Felix; Richter, Detlef K.; Neuser, Rolf D.; Immenhauser, Adrian; Gies, Hermann; Schreuer, Jürgen

    2016-04-01

    Undulosity in calcites (radiaxial fibrous calcite (RFC) and fascicular-optic fibrous calcite (FOFC)) is a common phenomenon in paleozoic and mesozoic limestones. Despite their importance as archives for climate reconstruction the underlying mechanisms and processes of their formation are still poorly understood [1]. To improve the application of such archives for climate reconstruction a better knowledge of their formation and possible alteration scenarios is necessary. In Mg2+ containing gel based growth experiments calcite crystals develop pathological morphologies. The morphology can be described as a product of a geometrical selective branching process at the rhombohedral crystal faces. Multiple sheet like building blocks evolve at the branching crystal face; each slightly tilted in respect to their substrate. The product is a crystal aggregate consisting out of several misoriented sub domains. In polarized light thin section microscopy the extinction behaviour of these sub units resemble the optical undulosity of radiaxial fibrous cements. In a multi method approach the local Mg2+ concentration was measured using EMPA and compared with maps of the local crystal orientation (via electron backscatter diffraction (EBSD)) and thin section microscopy. We found that Mg2+ is enriched at the sub-domain boundaries and deduced that lattice misfit as a consequence of impurity incorporation causes the crystal branching. We propose that this process is cyclic and each new misoriented sheet represents a growth period after a phase of inhibited growth caused by crystal faces covered by Mg2+-ions. In comparison to natural systems we found that radiaxial-fibrous cave cements show a pathological morphology based on the same formation principles. [1] Richter et al. (2011) Sediment. Geol. 239, 23-36 [2] Reeder & Paquette (1989) Sediment. Geol. 65, 239-247 [3] Davis et al. (2004) Am. Min. 89, 714-720

  1. Relation between etch-pit morphology and step retreat velocity on a calcite surface in aspartic acid solution

    Science.gov (United States)

    Yoshino, Toru; Kagi, Hiroyuki; Kamiya, Natsumi; Kokawa, Ryohei

    2010-04-01

    Effects of L-aspartic acid ( L-Asp) on dissolution of calcite were investigated. The step retreat velocity and dissolution rate of calcite were measured simultaneously using an AFM flow-through system. The etch-pit morphology of calcite was observed using confocal laser scanning microscopy. Results show that the etch-pit morphologies changed drastically depending on the L-Asp concentration ([ L-Asp]) in the order of rhomboidal, pentagonal, and triangular (not perfectly, but retaining an extra step). The change in obtuse step directions and appearance of the [0 1 0] step triggered these morphological changes. Addition of L-Asp accelerated all step retreats at [ L-Asp]0.01 M, L-Asp inhibited the retreats of obtuse steps and [0 1 0] step, although the retreat velocities of acute steps were constant irrespective of [ L-Asp]. These results suggest that the directional changes and the inhibition of retreat velocities of obtuse steps were attributed to the generation of [ 4 1 1] and [4 5 1] steps caused by L-Asp. Moreover, we confirmed the preferential effects of L-Asp on the [4 8 1] + to [ 4 4 1] ± step edge, and proposed the preferential effects of L-Asp on the [ 4 1 1] to [4 5 1] step edge.

  2. Simultaneous pollutant removal and electricity generation in denitrifying microbial fuel cell with boric acid-borate buffer solution.

    Science.gov (United States)

    Chen, Gang; Zhang, Shaohui; Li, Meng; Wei, Yan

    2015-01-01

    A double-chamber denitrifying microbial fuel cell (MFC), using boric acid-borate buffer solution as an alternative to phosphate buffer solution, was set up to investigate the influence of buffer solution concentration, temperature and external resistance on electricity generation and pollutant removal efficiency. The result revealed that the denitrifying MFC with boric acid-borate buffer solution was successfully started up in 51 days, with a stable cell voltage of 205.1 ± 1.96 mV at an external resistance of 50 Ω. Higher concentration of buffer solution favored nitrogen removal and electricity generation. The maximum power density of 8.27 W/m(3) net cathodic chamber was obtained at a buffer solution concentration of 100 mmol/L. An increase in temperature benefitted electricity generation and nitrogen removal. A suitable temperature for this denitrifying MFC was suggested to be 25 °C. Decreasing the external resistance favored nitrogen removal and organic matter consumption by exoelectrogens.

  3. Effect of pH on the Electrochemical Behavior of Tantalum in Borate Buffer Solutions

    Science.gov (United States)

    Attarzadeh, F. R.; Attarzadeh, N.; Vafaeian, S.; Fattah-Alhosseini, A.

    2016-10-01

    In this research, various electrochemical methods were used to investigate the electrochemical behavior of tantalum in borate buffer solutions of various pH values, ranging from 9.0 to 6.5. Potentiodynamic polarization curves revealed that tantalum showed excellent passive behavior in borate buffer solutions. The potentiodynamic polarization and electrochemical impedance spectroscopy results showed that the passive film formed on tantalum offered its best protective behavior when the pH is 8.0, with the passivity undergoing a drastic change as the pH moved toward higher values. The semiconductive behavior of the passive films formed on tantalum was investigated by employing Mott-Schottky analysis in conjunction with a point defect model. The results indicated that the passive film exhibited n-type semiconductive behavior and that donor densities were in the range of 1.958-7.242 × 1020 cm-3. Moreover, this analysis showed that the donor density and flat band potential were quite sensitive to the pH.

  4. Electrochemical passivation behaviour of nanocrystalline Fe80Si20 coating in borate buffer solution

    Indian Academy of Sciences (India)

    G Gupta; A P Moon; K Mondal

    2013-02-01

    Passivation behaviour of nanocrystalline coating (Fe80Si20) obtained by in situ mechanical alloying route is studied and compared with that of the commercial pure iron and cast Fe80Si20 in sodium borate buffer solution at two different pH values (7.7 and 8.4). The coating reveals single passivation at a pH of 7.7 and double stage passivity at a pH of 8.4. The first passive layer is due to the dissolution mechanism and second passivity is related to stable passivation. The cast sample shows single stage passivity in the solution of pH 8.4. The difference in the passivation behaviour for the cast alloy (Fe80Si20) and the coating is related to the presence of highly iron-enriched localized regions, formed during the processing stage of coating.

  5. Activity and stability of recombinant human superoxide dismutase in buffer solutions and hypothermic perfusates.

    Directory of Open Access Journals (Sweden)

    Senoo,Yoshimasa

    1988-06-01

    Full Text Available The stability of recombinant human superoxide dismutase (r-hSOD in buffer solutions was studied in solutions at various pH and temperatures. Additionally, we studied the effects of incubation with proteases, serum and two types of hypothermic perfusates. R-hSOD was stable in the pH range of 6-11 and at temperatures up to 80 degrees C for 30 min. R-hSOD activity was not affected by incubation with trypsin, aminopeptidase M or serum for 2 h. R-hSOD activity determined at various temperatures (4-37 degrees C did not vary remarkably. R-hSOD in hypothermic perfusates was stable at 4-37 degrees C for 24 h.

  6. Effect of phosphate buffer on photodegradation reactions of riboflavin in aqueous solution.

    Science.gov (United States)

    Ahmad, Iqbal; Fasihullah, Q; Vaid, Faiyaz H M

    2005-03-01

    The effect of phosphate buffer on aerobic photodegradation reactions of riboflavin (RF) at pH 7.0 has been studied. The photoproducts of the two major reactions, viz., intramolecular photoreduction and intramolecular photoaddition, have been determined by a specific multicomponent spectrophotometric method. The overall photodegradation of riboflavin in the presence of phosphate buffer involves the participation of both H2PO4-and HPO4(2-) species. The second-order rate constants for the H2PO4(-)-catalysed photodegradation of riboflavin (normal photolysis) to lumichrome (LC) and HPO4(2-)-catalysed photodegradation of riboflavin (photoaddition) to cyclodehydroriboflavin (CDRF) are 0.93 x 10(-4) and 4.0 x 10(-4) M(-1) s(-1), respectively. The addition of 0.25-2.00 M phosphate to RF solutions at pH 7.0 gives rise to RF-HPO4(2-) complex and hence the quenching of 4-36% fluorescence, respectively. This results in the suppression of normal photolysis leading to the formation of LC in favour of photoaddition to yield CDRF. The present study shows the involvement of H2PO4- anions in the base-catalysed degradation of riboflavin by normal photolysis vis-a-vis the involvement of HPO42- anions in photoaddition reactions of riboflavin suggested earlier [M. Schuman Jorns, G. Schollnhammer, P. Hemmerich, Intramolecular addition of the riboflavin side chain. Anion-catalysed neutral photochemistry, Eur. J. Biochem. 57 (1975) 35-48].

  7. Thermodynamic characteristics of the interaction between nicotinic acid and phenylalanine in an aqueous buffer solution at 298 K

    Science.gov (United States)

    Badelin, V. G.; Tyunina, E. Yu.; Mezhevoi, I. N.; Tarasova, G. N.

    2013-08-01

    The interaction between L-phenylalanine and nicotinic acid is studied by solution calorimetry in an aqueous buffer solution (pH 7.35) at different ratios of the reagents. Experimental data on the enthalpy of dissolution of amino acid in the buffer solution of nicotinic acid at 298.15 K are calculated. The values of thermodynamic parameters for the complexation of L-phenylalanine with nicotinic acid are calculated. It is shown that the formation of a 1: 2 molecular complex is stabilized by the entropy factor due to the dominant role of the dehydration effect of initial reagents.

  8. Photodegradation of Mercaptopropionic Acid- and Thioglycollic Acid-Capped CdTe Quantum Dots in Buffer Solutions.

    Science.gov (United States)

    Miao, Yanping; Yang, Ping; Zhao, Jie; Du, Yingying; He, Haiyan; Liu, Yunshi

    2015-06-01

    CdTe quantum dots (QDs) were synthesized by 3-mercaptopropionic acid (MPA) and thioglycollic acid (TGA) as capping agents. It is confirmed that TGA and MPA molecules were attached on the surface of the QDs using Fourier transform infrared (FT-IR) spectra. The movement of the QDs in agarose gel electrophoresis indicated that MPA-capped CdTe QDs had small hydrodynamic diameter. The photoluminescence (PL) intensity of TGA-capped QDs is higher than that of MPA-capped QDs at same QD concentration because of the surface passivation of TGA. To systemically investigate the photodegradation, CdTe QDs with various PL peak wavelengths were dispersed in phosphate buffered saline (PBS) and Tris-borate-ethylenediaminetetraacetic acid (TBE) buffer solutions. It was found that the PL intensity of the QDs in PBS decreased with time. The PL peak wavelengths of the QDs in PBS solutions remained unchanged. As for TGA-capped CdTe QDs, the results of PL peak wavelengths in TBE buffer solutions indicated that S(2-) released by TGA attached to Cd(2+) and formed CdS-like clusters layer on the surface of aqueous CdTe QDs. In addition, the number of TGA on the CdTe QDs surface was more than that of MPA. When the QDs were added to buffer solutions, agents were removed from the surface of CdTe QDs, which decreased the passivation of agents thus resulted in photodegradation of CdTe QDs in buffer solutions.

  9. Sulfate influx on band 3 protein of equine erythrocyte membrane (Equus caballus) using different experimental temperatures and buffer solutions.

    Science.gov (United States)

    Casella, S; Piccione, D; Ielati, S; Bocchino, E G; Piccione, G

    2013-06-01

    The aim of this study was to assess the anion transport in equine erythrocytes through the measurement of the sulfate uptake operating from band 3 using different experimental temperatures and buffer solutions. Blood samples of six clinically healthy horses were collected via jugular vein puncture, and an emochrome-citometric examination was performed. The blood was divided into four aliquots and by centrifugation and aspiration the plasma and buffy coat were carefully discarded. The red blood cells were washed with an isosmotic medium and centrifuged. The obtained cell suspensions were incubated with two different experimental buffer solutions (buffer A: 115 mM Na2SO4, 10 mM NaCl, 20 mM ethylenediaminetetraacetic acid, 30 mM glucose; and buffer B: 115 mM Na2SO4, 10 mM NaCl, 20 mM ethylenediaminetetraacetic acid, 30 mM MgCl2) in a water bath for 1 h at 25 °C and 37 °C. Normal erythrocytes, suspended at 3% hematocrit, were used to measure the SO4= influx by absorption spectrophotometry at 425 nm wavelength. Unpaired Student's t-test showed a statistically significant decrease (P buffer solutions. Comparing the buffer A with buffer B unpaired Student's t-test showed statistically lower values (P < 0.0001) for A solution versus B solution both at 25 °C and at 37 °C. The greater inhibition of SO4 (=) influx measured in equine erythrocytes indicates the increased formation of the sulfydryl bonds in band 3 and the modulation of the sulfydryl groups, culminating in the conformational changes in band 3.

  10. Transformation of nacre coatings into apatite coatings in phosphate buffer solution at low temperature.

    Science.gov (United States)

    Guo, Yaping; Zhou, Yu

    2008-08-01

    Nacre coatings were deposited on Ti6Al4V substrates by electrophoretic technique, and subsequently converted into apatite coatings with hierarchical porous structures by treatment with a phosphate buffer solution. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy (XPS), and N(2) adsorption-desorption isotherms. The results show that the nacre coatings are converted into the plate-like apatite coatings via a dissolution-precipitation reaction, while the organic components of the nacre are reserved. The mesopores with pore size of 4.4 nm are formed within the plate-like structure, and the macropores are formed among the plate-like structure. Simulated body fluid (SBF) immersion tests reveal that the apatite coatings have a good in vitro bioactivity. Bone-like apatite crystals are formed on the surfaces of the apatite coatings after soaking in SBF for 12 h, and fill up the macropores on the coatings with increasing the soaking time. In addition, XPS indicates that a TiO(x) layer and PO(4) (3-) ions appear on the substrate surfaces by pretreatment with a H(3)PO(4)/HF solution. The TiO(x) layer and PO(4) (3-) ions can induce the formation of apatite crystals, resulting in a composition gradient from the oxide layer to the external apatite layer.

  11. Sodium hydrosulfide improves the protective potential of the cardioplegic histidine buffer solution.

    Science.gov (United States)

    Alves, Marco G; Soares, Ana F; Carvalho, Rui A; Oliveira, Paulo J

    2011-03-01

    Since H(2)S has an emerging role as a cardioprotector, we hypothesized that NaHS addition to the new cardioplegic histidine buffer solution (HBS) could improve its cardioprotective potential. Male Wistar-Han rat hearts were divided in 4 groups: i) control, ii) perfusion control (perfusion only), iii) 6h ischemia in HBS or in a modified-HBS with 100 μM of NaHS, a H(2)S donor, (HBSM) and iv) as iii followed by 30 min reperfusion. During ischemia, aliquots of the cardioplegic solution were collected for NMR analysis. Heart mitochondria respiration and transmembrane potential were measured after ischemia or after ischemia followed by reperfusion. Proteins involved in the apoptotic signaling pathway were also quantified in both mitochondrial and tissue samples. Cardiac mechanic performance was evaluated by measuring the heart rate and the left ventricular pressure. In HBSM-preserved hearts, a) glucose consumption increased as well as lactate and alanine production during ischemia, b) heart mitochondria presented an improved phosphorylative efficiency, including decreased phosphorylative lag phase for complex I and complex II substrates, c) mitochondrial and tissue p53, Bax and caspase-9 were lower and d) there was a more positive atrial chronotropic response than in HBS-preserved hearts. We concluded that the addition of NaHS to HBS enhances glycolysis during ischemia, decreases mitochondrial dysfunction, especially by preserving the phosphorylative system, prevents apoptosis and during ischemia/reperfusion.

  12. Mixing MTA with phosphate buffered solution can improve its physical properties and increase favorable outcome

    Directory of Open Access Journals (Sweden)

    Naghmeh Meraji

    2014-01-01

    Full Text Available Introduction: Encountering environmental situations that have an adverse effect on the properties of Mineral Trioxide Aggregate (MTA is inevitable and unfortunately common. In many cases MTA does not set and the clinician is forced to apply this cement again. This occurrence may affect the outcome of endodontic treatments such as perforation repair. Therefore, strategies should be considered to overcome this matter. Various studies have been conducted that mixed several substances with MTA to reverse the adverse effects on this material but still we face this problem. The Hypothesis: In this paper, we propose a hypothesis that mixing MTA with phosphate buffered solution (PBS may reverse the adverse environmental effects and may help us overcome this clinical problem. Evaluation of the Hypothesis: PBS is a synthetic solution containing phosphate which is commonly used for mimicking in vivo situations in laboratory studies. Considering that some studies have shown that when MTA encounters tissue fluids containing phosphorous its properties improve, we suggest that mixing this cement with PBS can at least reverse the adverse effect of the environment. It should be noted that the better the properties of these cements, the better the outcome of treatment can be.

  13. A new strategy to stabilize oxytocin in aqueous solutions : I. The effects of divalent metal ions and citrate buffer

    NARCIS (Netherlands)

    Avanti, Christina; Amorij, Jean-Pierre; Setyaningsih, Dewi; Hawe, Andrea; Jiskoot, Wim; Visser, Jan; Kedrov, Alexej; Driessen, Arnold J. M.; Hinrichs, Wouter L. J.; Frijlink, Henderik W.

    2011-01-01

    In the current study, the effect of metal ions in combination with buffers (citrate, acetate, pH 4.5) on the stability of aqueous solutions of oxytocin was investigated. Both monovalent metal ions (Na+and K+) and divalent metal ions (Ca2+, Mg2+, and Zn2+) were tested all as chloride salts. The effec

  14. Substituent Effects on the Photodeprotection Reactions of Selected Ketoprofen Derivatives in Phosphate Buffered Aqueous Solutions

    Science.gov (United States)

    Liu, Mingyue; Li, Ming-De; Huang, Jinqing; Li, Tianlu; Liu, Han; Li, Xuechen; Phillips, David Lee

    2016-02-01

    Photodeprotection is an important reaction that has been attracting broad interest for use in a variety of applications. Recent advances in ultrafast and vibrational time-resolved spectroscopies can facilitate obtaining data to help unravel the reaction mechanisms involving in the photochemical reactions of interest. The kinetics and reaction mechanisms for the photodeprotection reactions of ketoprofen derivatives containing three different substituents (ibuprofen, Br and I) were investigated by femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy methods in phosphate buffered solutions (PBS). Fs-TA allows us to detect the decay kinetics of the triplet species as the key precursor for formation of a carbanion species for three different substituents attached to ketoprofen. To characterize the structural and electronic properties of the corresponding carbanion and triplet intermediates, TR3 spectroscopic experiments were conducted. The transient spectroscopy work reveals that the different substituents affect the photodecarboxylation reaction to produce carbon dioxide which in turn influences the generation of the carbanion species which determines the rate of the photorelease of the functional groups attached on the ketoprofen parent molecule. The fingerprint TR3 spectroscopy results suggest that ketoprofen derivatives may be deactivated to produce a triplet carbanion when increasing the atom mass of the halogen atoms.

  15. Corrosion behavior of pristine and added MgB2 in Phosphate Buffered Saline Solution

    Science.gov (United States)

    Batalu, D.; Bojin, D.; Ghiban, B.; Aldica, G.; Badica, P.

    2012-09-01

    We have obtained by Spark Plasma Sintering (SPS), dense samples of MgB2 added with Ho2O3. Starting composition was (MgB2)0.975(HoO1.5)0.025 and we used addition powders with an average particle size below and above 100 nm. For Mg, pristine and added MgB2 samples we measured potentiodynamic polarization curves in Phosphate Buffered Saline (PBS) solution media at room temperature. MgB2 based composites show corrosion/ degradation effects. This behavior is in principle similar to Mg based alloys in the same media. Our work suggests that the different morphologies and phase compositions of the SPS-ed samples influence the interaction with corrosion medium; hence additions can play an important role in controlling the corrosion rate. Pristine MgB2 show a significant improvement of the corrosion resistance, if compared with Mg. The best corrosion resistance is obtained for pristine MgB2, followed by MgB2 with nano-Ho2O3 and μ-Ho2O3 additions.

  16. Routing Flow-Shop with Buffers and Ready Times – Comparison of Selected Solution Algorithms

    Directory of Open Access Journals (Sweden)

    Józefczyk Jerzy

    2014-12-01

    Full Text Available This article extends the former results concerning the routing flow-shop problem to minimize the makespan on the case with buffers, non-zero ready times and different speeds of machines. The corresponding combinatorial optimization problem is formulated. The exact as well as four heuristic solution algorithms are presented. The branch and bound approach is applied for the former one. The heuristic algorithms employ known constructive idea proposed for the former version of the problem as well as the Tabu Search metaheuristics. Moreover, the improvement procedure is proposed to enhance the quality of both heuristic algorithms. The conducted simulation experiments allow evaluating all algorithms. Firstly, the heuristic algorithms are compared with the exact one for small instances of the problem in terms of the criterion and execution times. Then, for larger instances, the heuristic algorithms are mutually compared. The case study regarding the maintenance of software products, given in the final part of the paper, illustrates the possibility to apply the results for real-world manufacturing systems.

  17. Intracrystalline deformation of calcite

    NARCIS (Netherlands)

    de Bresser, Hans

    1991-01-01

    It is well established from observations on natural calcite tectonites that intracrystalline plastic mechanisms are important during the deformation of calcite rocks in nature. In this thesis, new data are presented on fundamental aspects of deformation behaviour of calcite under conditions where 'd

  18. The stability of DLC film on nitrided CoCrMo alloy in phosphate buffer solution

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, T.F.; Liu, B.; Wu, B.J.; Liu, J.; Sun, H.; Leng, Y.X., E-mail: yxleng@263.net; Huang, N.

    2014-07-01

    CoCrMo alloy is often used as the material for metal artificial joint, but metal debris and metal ions are the main concern on tissue inflammation or tissue proliferation for metal prosthesis. In this paper, nitrogen ion implantation and diamond like carbon (DLC) film composite treatment was used to reduce the wear and ion release of biomedical CoCrMo substrate. The mechanical properties and stability of N-implanted/DLC composite layer in phosphate buffer solution (PBS) was evaluated to explore the full potential of N-implanted/DLC composite layer as an artificial joint surface modification material. The results showed that the DLC film on N implanted CoCrMo (N-implanted/DLC composite layer) had the higher surface hardness and wear resistance than the DLC film on virgin CoCrMo alloy, which was resulted from the strengthen effect of the N implanted layer on CoCrMo alloy. After 30 days immersion in PBS, the structure of DLC film on virgin CoCrMo or on N implanted CoCrMo had no visible change. But the adhesion and corrosion resistance of DLC on N implanted CoCrMo (N-implanted/DLC composite layer) was weakened due to the dissolution of the N implanted layer after 30 days immersion in PBS. The adhesion reduction of N-implanted/DLC composite layer was adverse for in vivo application in long term. So researcher should be cautious to use N implanted layer as an inter-layer for increasing CoCrMo alloy load carrying capacity in vivo environment.

  19. Critical evaluation of buffering solutions for pKa determination by capillary electrophoresis.

    Science.gov (United States)

    Fuguet, Elisabet; Reta, Mario; Gibert, Carme; Rosés, Martí; Bosch, Elisabeth; Ràfols, Clara

    2008-07-01

    The performance of the most common and also some other less common CE buffers has been tested for the pKa determination of several types of compounds (pyridine, amines, and phenols). The selected buffers cover a pH ranging from 3.7 to 11.8. Whereas some buffers, like acetic acid/acetate, BisTrisH+/BisTris, TrisH+/Tris, CHES/CHES-, and CAPS/CAPS- can be used with all type of analytes, others like ammonium/ammonia, butylammonium/butylammonia, ethylammonium/ethylammonia, diethylammonium/diethylammonia, and hydrogenphosphate/phosphate are not recommended because they interact with a wide range of compounds. The rest of the tested buffers (dihydrogenphosphate/hydrogenphosphate, MES/MES-, HEPES/HEPES-, and boric acid/borate) can show specific interactions depending on the nature of the analytes, and their use in some applications should be restricted.

  20. 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

    for green, white and pink calcites were varied 0.087, 0.247 and 0.997 respectively. The low amounts of Eu anomaly for green and white calcites attributed to low rock/fluid ratio (Nesbitt et al., 1990 and relatively more pH value (Cheng et al., 2013, however, increasing the Eu anomaly may be due to high rock/fluid ratio and less pH value. Ce anomalies are 0.0241, 0.0113 and 0.0131 in pink, white and green calcites respectively. The most negative Ce anomaly values show that calcite have precipitated under reduction conditions (Nesbitt et al., 1990. Discussion Recently, multiple attributes decision-making techniques help scientist to solve decision-making problems related to various controlling factors (Zhijun et al., 2013. One of these techniques is a Technique for Order Preference by Similarity to Ideal Solution (TOPSIS which is a quantitative weighted method (Momenei 2006. The identified criteria are CaO abundant in solution (C1, Eu anomaly (C2, Ce anomaly (C3, Sr abundant (C4 and volume (C5. The Index-Rock matrix also includes A1, A2 and A3 alternatives; as pink, green and white calcite respectively. The weighted normalized decision matrix can be calculated by multiplying the normalized evaluation matrix with its associated weight to obtain the result. The result show that Eu anomaly, volume, Sr abundant and Ce anomaly in order have higher role to investigate the geochemical study of area. Calculation of the relative closeness to the ideal solution (Cl * for pink, green and white calcites are 0.837, 0.445 and 0.157 respectively. It can be deduced that the most preferable calcite to be sampled for investigating geochemically are pink and green calcites. References Cheng, D.L., Jiang-haob, L., Shou-pengc, Z., Lianga, L., Zhao-bina, Y., Guo-lina, G. and Tinga, L., 2013. Geochemical characteristics of calcite and dolomite in sandstone of Dongying Sinking, Shandong Province, China. Procedia Earth and Planetary Science, 7(4: 504 – 507. Eftekharnezhad, J., 1973

  1. Solution-processed In2S3 buffer layer for chalcopyrite thin film solar cells

    Directory of Open Access Journals (Sweden)

    Wang Lan

    2016-01-01

    Full Text Available We report a route to deposit In2S3 thin films from air-stable, low-cost molecular precursor inks for Cd-free buffer layers in chalcopyrite-based thin film solar cells. Different precursor compositions and processing conditions were studied to define a reproducible and robust process. By adjusting the ink properties, this method can be applied in different printing and coating techniques. Here we report on two techniques, namely spin-coating and inkjet printing. Active area efficiencies of 12.8% and 12.2% have been achieved for In2S3-buffered solar cells respectively, matching the performance of CdS-buffered cells prepared with the same batch of absorbers.

  2. Solution-processed In2S3 buffer layer for chalcopyrite thin film solar cells

    Science.gov (United States)

    Wang, Lan; Lin, Xianzhong; Ennaoui, Ahmed; Wolf, Christian; Lux-Steiner, Martha Ch.; Klenk, Reiner

    2016-02-01

    We report a route to deposit In2S3 thin films from air-stable, low-cost molecular precursor inks for Cd-free buffer layers in chalcopyrite-based thin film solar cells. Different precursor compositions and processing conditions were studied to define a reproducible and robust process. By adjusting the ink properties, this method can be applied in different printing and coating techniques. Here we report on two techniques, namely spin-coating and inkjet printing. Active area efficiencies of 12.8% and 12.2% have been achieved for In2S3-buffered solar cells respectively, matching the performance of CdS-buffered cells prepared with the same batch of absorbers.

  3. 磷酸盐改性方解石去除水中磷酸盐研究%Removal of phosphate from aqueous solution by phosphate-modified calcite

    Institute of Scientific and Technical Information of China (English)

    林建伟; 李佳; 詹艳慧

    2013-01-01

    Previous literatures have shown that calcite can be used to effectively remove phosphate from aqueous solution. In this study, the calcite-phosphate reaction product, i.e., phosphate-modified calcite was reused to remove phosphate from aqueous solution. The phosphate removal kinetics of natural calcite and phosphate-modified calcite were compared. The effect of various experimental conditions such as solution pH, initial phosphate concentration, temperature, Ca2+ and HCO3- on phosphate removal by phosphate-modified calcite was investigated. The phosphate removal efficiency of phosphate-modified calcite was much higher than that of natural calcite. When the reaction time was 2 h, the phosphate removal efficiency of phosphate-modified calcite was 72%under the experimental conditions, which was much higher than that of natural calcite (35%). The phosphate removal efficiency of phosphate-modified calcite was relatively high at pH 5-7, slightly decreased with increasing pH from 7 to 10, and significantly decreased with increasing pH from 10 to 12. The amount of phosphate removed by phosphate-modified calcite increased with increasing initial phosphate concentration. The phosphate removal efficiency of phosphate-modified calcite decreased with increasing initial phosphate concentration at a relatively high initial phosphate-phosphorus concentration (60-160 mg·L-1). The phosphate removal efficiency of phosphate-modified calcite increased with increasing temperature. The phosphate removal kinetics of phosphate-modified calcite followed a pseudo-second-order kinetic model. The removal of phosphate by phosphate-modified calcite occurred predominantly via the precipitation of calcium phosphate according to two consecutive phases:first, the dissolution of calcite produced an increase in the Ca2+concentration;then the Ca2+ions reacted with the phosphate ions to form the precipitate of calcium phosphate. The precipitation of calcium phosphate took place at the surface of

  4. Aspartate buffer and divalent metal ions affect oxytocin in aqueous solution and protect it from degradation

    NARCIS (Netherlands)

    Avanti, Christina; Oktaviani, Nur Alia; Hinrichs, Wouter L J; Frijlink, Henderik W; Mulder, Frans A A

    2013-01-01

    Oxytocin is a peptide drug used to induce labor and prevent bleeding after childbirth. Due to its instability, transport and storage of oxytocin formulations under tropical conditions is problematic. In a previous study, we have found that the stability of oxytocin in aspartate buffered formulation

  5. Nonclinical safety evaluation of boric acid and a novel borate-buffered contact lens multi-purpose solution, Biotrue™ multi-purpose solution.

    Science.gov (United States)

    Lehmann, David M; Cavet, Megan E; Richardson, Mary E

    2010-12-01

    Multipurpose solutions (MPS) often contain low concentrations of boric acid as a buffering agent. Limited published literature has suggested that boric acid and borate-buffered MPS may alter the corneal epithelium; an effect attributed to cytotoxicity induced by boric acid. However, this claim has not been substantiated. We investigated the effect of treating cells with relevant concentrations of boric acid using two cytotoxicity assays, and also assessed the impact of boric acid on corneal epithelial barrier function by measuring TEER and immunostaining for tight junction protein ZO-1 in human corneal epithelial cells. Boric acid was also assessed in an in vivo ocular model when administered for 28 days. Additionally, we evaluated Biotrue multi-purpose solution, a novel borate-buffered MPS, alone and with contact lenses for ocular compatibility in vitro and in vivo. Boric acid passed both cytotoxicity assays and did not alter ZO-1 distribution or corneal TEER. Furthermore, boric acid was well-tolerated on-eye following repeated administration in a rabbit model. Finally, Biotrue multi-purpose solution demonstrated good ocular biocompatibility both in vitro and in vivo. This MPS was not cytotoxic and was compatible with the eye when administered alone and when evaluated with contact lenses. We demonstrate that boric acid and a borate-buffered MPS is compatible with the ocular environment. Our findings provide evidence that ocular effects reported for some borate-buffered MPS may be incorrectly attributed to boric acid and are more likely a function of the unique combination of ingredients in the MPS formulation tested.

  6. Limitations when use chloramphenicol-bcyclodextrins complexes in ophtalmic solutions buffered with boric acid/borax system

    Directory of Open Access Journals (Sweden)

    Todoran Nicoleta

    2014-12-01

    Full Text Available Chloramphenicol eye drops are commonly prescribed in concentrations of 0.5-1% in the treatment of infectious conjunctivitis. In terms of ophthalmic solution preparation, the major disadvantage of chloramphenicol consists in its low solubility in water. The solubility is increased by substances that form chloramphenicol-complexes, for example: boric acid/borax or cyclodextrins. Objective: Experimental studies aimed to evaluate the potential advantages of enhancing the solubility and stability of chloramphenicol (API by molecular encapsulation in b-cyclodextrin (CD, in formulation of ophthalmic solutions buffered with boric acid/borax system. Methods and Results: We prepared four APIb- CD complexes, using two methods (kneading and co-precipitation and two molar ratio of API/b-cyclodextrin (1:1 and 1:2. The formation of complexes was proved by differential scanning calorimetry (DSC and the in vitro dissolution tests. Using these compounds, we prepared eight ophthalmic solutions, formulated in two variants of chloramphenicol concentrations (0.4% and 0.5%. Each solution was analyzed, by the official methods, at preparation and periodically during three months of storing in different temperature conditions (4°C, 20°C and 30°C. Conclusions: Inclusion of chloramphenicol in b-cyclodextrin only partially solves the difficulties due to the low solubility of chloramphenicol. The protection of chloramphenicol molecules is not completely ensured when the ophthalmic solutions are buffered with the boric acid/borax system.

  7. Matching phosphate and maleate buffer systems for dissolution of weak acids: Equivalence in terms of buffer capacity of bulk solution or surface pH?

    Science.gov (United States)

    Cristofoletti, Rodrigo; Dressman, Jennifer B

    2016-06-01

    The development of in vitro dissolution tests able to anticipate the in vivo fate of drug products has challenged pharmaceutical scientists over time, especially in the case of ionizable compounds. In the seminal model proposed by Mooney et al. thirty-five years ago, the pH at the solid-liquid interface (pH0) was identified as a key parameter in predicting dissolution rate. In the current work it is demonstrated that the in vitro dissolution of the weak acid ibuprofen in maleate and phosphate buffer systems is a function of the pH0, which in turn is affected by properties of the drug and the medium. The reported pH0 for ibuprofen dissolution in bicarbonate buffer, the predominant buffer species in the human small intestine under fasting conditions, can be achieved by reducing the phosphate buffer concentration to 5.0mM or the maleate buffer concentration to 2.2mM. Using this approach to identify the appropriate buffer/buffer capacity combination for in vitro experiments in FaSSIF-type media, it would be possible to increase the physiological relevance of this important biopharmaceutics tool. However, the necessity of monitoring and adjusting the bulk pH during the experiments carried out in 5.0mM phosphate or 2.2mM maleate buffers must also be taken into consideration.

  8. Strontium Titanate Buffer Layers on Cu/33%Ni Substrates using a Novel Solution Chemistry

    DEFF Research Database (Denmark)

    Pallewatta, Pallewatta G A P; Yue, Zhao; Hui, Tian;

    2013-01-01

    SrTiO3 is a widely studied perovskite material due to its advantages as a buffer template which can be simply applied between a metal substrate tape and a superconducting layer in 2G high temperature superconducting (HTS) tapes. In this study, heteroepitaxial SrTiO3 thin films were deposited on t......, suggesting that they are promising templates for further deposition of YBCO superconducting layers....

  9. The effect of undissociated acetic-acid concentration of buffer solutions on artificial caries-like lesion formation in human tooth enamel

    NARCIS (Netherlands)

    Groeneveld, A.; Theuns, H.M.; Dijk, J.W.E. van; Driessens, F.C.M.

    1984-01-01

    A chemical system for lesion production was used. The influence on lesion characteristics of the concentration of undissociated acetic acid in a calcium and phosphate-containing buffer solution was investigated. Artificial lesions obtained after demineralization in buffers with a pH of 4.0, 4.5, 5.0

  10. Simple solution-processed CuO{sub X} as anode buffer layer for efficient organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Wenfei [CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao 266101 (China); Institute of Hybrid Materials, The Growing Base for State Key Laboratory, Qingdao University, 308 Ningxia Road, Qingdao 266071 (China); Yang, Chunpeng [CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao 266101 (China); Bao, Xichang, E-mail: baoxc@qibebt.ac.cn [CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao 266101 (China); Sun, Liang; Wang, Ning [CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao 266101 (China); Tang, Jianguo [Institute of Hybrid Materials, The Growing Base for State Key Laboratory, Qingdao University, 308 Ningxia Road, Qingdao 266071 (China); Chen, Weichao [CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao 266101 (China); Yang, Renqiang, E-mail: yangrq@qibebt.ac.cn [CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao 266101 (China)

    2015-10-15

    Graphical abstract: - Highlights: • Simple solution-processed CuO{sub X} hole transport layer for efficient organic solar cell. • Good photovoltaic performances as hole transport layer in OSCs with P3HT and PBDTTT-C as donor materials. • The device with CuO{sub X} as hole transport layer shows great improved stability compared with that of device with PEDOT:PSS as hole transport layer. - Abstract: A simple, solution-processed ultrathin CuO{sub X} anode buffer layer was fabricated for high performance organic solar cells (OSCs). XPS measurement demonstrated that the CuO{sub X} was the composite of CuO and Cu{sub 2}O. The CuO{sub X} modified ITO glass exhibit a better surface contact with the active layer. The photovoltaic performance of the devices with CuO{sub X} layer was optimized by varying the thickness of CuO{sub X} films through changing solution concentration. With P3HT:PC{sub 61}BM as the active layer, we demonstrated an enhanced PCE of 4.14% with CuO{sub X} anode buffer layer, compared with that of PEDOT:PSS layer. The CuO{sub X} layer also exhibits efficient photovoltaic performance in devices with PBDTTT-C:PC{sub 71}BM as the active layer. The long-term stability of CuO{sub X} device is better than that of PEDOT:PSS device. The results indicate that the easy solution-processed CuO{sub X} film can act as an efficient anode buffer layer for high-efficiency OSCs.

  11. The solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3-CO2-H2O

    Science.gov (United States)

    Plummer, L. Niel; Busenberg, Eurybiades

    1982-01-01

    Calculations based on approximately 350 new measurements (CaT-PCO2) of the solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants KC, KA, and KV respectively, for the reaction CaCO3(s) = Ca2+ + CO2−3: 

  12. High-quality fiber fabrication in buffered hydrofluoric acid solution with ultrasonic agitation.

    Science.gov (United States)

    Zhong, Nianbing; Liao, Qiang; Zhu, Xun; Wang, Yongzhong; Chen, Rong

    2013-03-01

    An etching method for preparing high-quality fiber-optic sensors using a buffered etchant with ultrasonic agitation is proposed. The effects of etching conditions on the etch rate and surface morphology of the etched fibers are investigated. The effect of surface roughness is discussed on the fibers' optical properties. Linear etching behavior and a smooth fiber surface can be repeatedly obtained by adjusting the ultrasonic power and etchant pH. The fibers' spectral quality is improved as the ratio of the pit depth to size decreases, and the fibers with smooth surfaces are more sensitive to a bacterial suspension than those with rough surfaces.

  13. Antibacterial and photocatalytic activity of TiO2 and ZnO nanomaterials in phosphate buffer and saline solution.

    Science.gov (United States)

    Ng, Alan Man Ching; Chan, Charis May Ngor; Guo, Mu Yao; Leung, Yu Hang; Djurišić, Aleksandra B; Hu, Xu; Chan, Wai Kin; Leung, Frederick Chi Chung; Tong, Shuk Yin

    2013-06-01

    We studied antibacterial and photocatalytic activity of anatase TiO2 and ZnO in phosphate buffer and saline solution. We found that the different anions in the suspension medium (chloride and phosphate) significantly affected the following suspension properties: the stability of nanoparticle suspension, the release of metal ions from the nanoparticles, and the production of the reactive oxygen species by the nanoparticles. As a result, antibacterial activity and photocatalytic dye degradation were also affected. However, the effect of the suspension medium was different for ZnO and TiO2. Obtained results are discussed.

  14. Antigen retrieval using pH 3.5 glycine-HCl buffer or urea solution for immunohistochemical localization of Ki-67.

    Science.gov (United States)

    Shi, S R; Chaiwun, B; Young, L; Imam, A; Cote, R J; Taylor, C R

    1994-07-01

    A new antibody (MIB-1) has been described, permitting the demonstration of Ki-67 proliferation antigen in paraffin sections. However, satisfactory results were obtained only after subjecting tissue sections to microwave based antigen retrieval in citrate buffer solution. Other buffer solutions produce equivalent or better results and also permit use of the original Ki-67 antibody, which hitherto has been considered ineffective for paraffin sections.

  15. Formation Process and Thermodynamic Poperties of Calcite

    Institute of Scientific and Technical Information of China (English)

    NAN,Zhao-Dong; SHI,Zuo-Yi; QIN,Mei; HOU,Wan-Guo; TAN,Zhi-Cheng

    2007-01-01

    The fast mixing of aqueous solutions of calcium chloride and sodium carbonate resulted in crystalline forms of vaterite and calcite under vigorous stirring. Then, the vaterite was transformed to pure calcite within about 180 min.The crystalline forms all grew with experimental time increase. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction spectroscopy (XRD) techniques were employed to characterize the as-prepared samples. The heat capacity of the stable as-synthesized calcite was determined by means of an adiabatic calorimeter from 80 to 390 K. The thermodynamic functions of the calcite were derived based on the relationships among the thermodynamic functions and the function of the measured heat capacity with respect to temperature.

  16. All solution processable organic photovoltaic cells using DMDCNQI as an organic N-type buffer layer.

    Science.gov (United States)

    Yang, Eui Yeol; So, Byoung Min; Chung, Chan Moon; Oh, Se Young

    2012-01-01

    Organic photovoltaic cells consisting of ITO/PEDOT-PSS/P3HT:PCBM/TiO(x)/DMDCNQI/Al have been fabricated by using dip-coated DMDCNQI layer as a cathode buffer material. We have investigated the physical effects of charge transfer complex and wettability of DMDCNQI between TiO(x)/P3HT:PCBM layer and Al cathode electrode on the performance of organic photovoltaic cell. The photovoltaic cell fabricated with a dip-coated DMDCNQI layer exhibited almost similar performance compared to the device using conventional evaporated DMDCNQI layer. Especially, the power conversion efficiency of the prepared organic photovoltaic cell using TiO(x)/DMDCNQI layer was improved to 3.1%, which is mainly due to the decrease in the low contact resistance of organic-metal interface.

  17. Aspartate buffer and divalent metal ions affect oxytocin in aqueous solution and protect it from degradation

    DEFF Research Database (Denmark)

    Avanti, Christina; Oktaviani, Nur Alia; Hinrichs, Wouther L.J.

    2013-01-01

    is improved by the addition of divalent metal ions (unpublished results). The stabilizing effect of Zn2+ was by far superior compared to that of Mg2+. In addition, it was found that stabilization correlated well with the ability of the divalent metal ions to interact with oxytocin in aspartate buffer...... favorable. These interactions may explain the protection of the disulfide bridge against intermolecular reactions that lead to dimerization.Mg or Zn, using 2D NOESY, TOCSY, H-C HSQC and H- N HSQC NMR spectroscopy. Almost all H, C and N resonances of oxytocin could be assigned using HSQC spectroscopy...... that the carboxylate group of aspartate neutralizes the positive charge of the N-terminus of Cys, allowing the interactions with Zn to become more favorable. These interactions may explain the protection of the disulfide bridge against intermolecular reactions that lead to dimerization....

  18. Sorption and desorption of arsenate and arsenite on calcite

    DEFF Research Database (Denmark)

    Sø, Helle Ugilt; Postma, Diederik Jan; Jakobsen, Rasmus

    2008-01-01

    The adsorption and desorption of arsenate (As(V)) and arsenite (As(111)) oil calcite was investigated in a series of batch experiments in calcite-equilibrated solutions. The solutions covered a broad range of pH, alkalinity, calcium concentration and ionic strength. The initial arsenic...

  19. Physicochemistry of hexadecylammonium bromide and its methyl and ethanolic head group analogues in buffered aqueous and gelatin solution

    Indian Academy of Sciences (India)

    Debolina Mitra; Satya P Moul

    2010-05-01

    In this work, the interfacial and bulk behaviour of the amphiphiles hexadecylammonium bromide and its methyl and ethanolic head group analogues in buffered aqueous and gelatin solution has been examined. The analogues are of two categories: the methyl and the combined methyl and ethanolic head group representatives are considered as Group A compounds, and all non-methyl but ethanolic head group species are taken as Group B compounds. Different physical techniques have been employed to ascertain the amphiphilic behaviour in solution. The self-aggregation of these surfactants at different pH has been studied along with pH dependent interfacial activity of gelatin. The interaction of the two categories of the surfactants with gelatin at different pH has been investigated. A scheme for this interaction at various stages of the process has been proposed. The influence of the surfactant head groups on the interaction process has been assessed.

  20. Oxygen isotope analysis of carbonates in the calcite-dolomite-magnesite solid-solution by high-temperature pyrolysis: initial results.

    Science.gov (United States)

    Crowley, Stephen F; Spero, Howard J; Winter, David A; Sloane, Hilary J; Croudace, Ian W

    2008-06-01

    Accurate and efficient measurement of the oxygen isotope composition of carbonates (delta(C) (18)O) based on the mass spectrometric analysis of CO(2) produced by reacting carbonate samples with H(3)PO(4) is compromised by: (1) uncertainties associated with fractionation factors (alpha(CO)(2)C) used to correct measured oxygen isotope values of CO(2)(delta(CO(2)(18)O) to delta(C) (18)O; and (2) the slow reaction rates of many carbonates of geological and environmental interest with H(3)PO(4). In contrast, determination of delta(C) (18)O from analysis of CO produced by high-temperature (>1400 degrees C) pyrolytic reduction, using an elemental analyser coupled to continuous-flow isotope-ratio mass spectrometry (TC/EA CF-IRMS), offers a potentially efficient alternative that measures the isotopic composition of total carbonate oxygen and should, therefore, theoretically be free of fractionation effects. The utility of the TC/EA CF-IRMS technique was tested by analysis of carbonates in the calcite-dolomite-magnesite solid-solution and comparing the results with delta(C) (18)O measured by conventional thermal decomposition/fluorination (TDF) on the same materials. Initial results show that CO yields are dependent on both the chemical composition of the carbonate and the specific pyrolysis conditions. Low gas yields (+0.2 per thousand) deviations in delta(C(TC/EA) (18)O compared with delta(C(TDF) (18)O. At a pyrolysis temperature of 1420 degrees C the difference between delta(C) (18)O measured by TC/EA CF-IRMS and TDF (Delta(C(TC/EA,TDF) (18)O) was found to be negatively correlated with gas yield (r = -0.785) and this suggests that delta(C) (18)O values (with an estimated combined standard uncertainty of +/-0.38 per thousand) could be derived by applying a yield-dependent correction. Increasing the pyrolysis temperature to 1500 degrees C also resulted in a statistically significant correlation with gas yield (r = -0.601), indicating that delta(C) (18)O values (with an

  1. An evaluation of MES (2(N-Morpholino)ethanesulfonic acid) and Amberlite IRC-50 as pH buffers for nutrient solution studies

    Science.gov (United States)

    Bugbee, B. G.; Salisbury, F. B.

    1985-01-01

    All buffering agents used to stabilize pH in hydroponic research have disadvantages. Inorganic buffers are absorbed and may become phytotoxic. Solid carbonate salts temporarily mitigate decreasing pH but provide almost no protection against increasing pH, and they alter nutrient absorption. Exchange resins are more effective, but we find that they remove magnesium and manganese from solution. We have tested 2(N-Morpholino)ethanesulfonic acid (MES) as a buffering agent at concentrations of 1 and 10 mol m-3 (1 and 10 mM) with beans, corn, lettuce, tomatoes, and wheat. MES appears to be biologically inert and does not interact significantly with other solution ions. Relative growth rates among controls and MES treatments were nearly identical for each species during the trial period. The pH was stabilized by 1 mol m-3 MES. This buffer warrants further consideration in nutrient research.

  2. Aqueous Chemical Solution Deposition of Novel, Thick and Dense Lattice-Matched Single Buffer Layers Suitable for YBCO Coated Conductors: Preparation and Characterization

    Directory of Open Access Journals (Sweden)

    Isabel van Driessche

    2012-09-01

    Full Text Available In this work we present the preparation and characterization of cerium doped lanthanum zirconate (LCZO films and non-stoichiometric lanthanum zirconate (LZO buffer layers on metallic Ni-5% W substrates using chemical solution deposition (CSD, starting from aqueous precursor solutions. La2Zr2O7 films doped with varying percentages of Ce at constant La concentration (La0.5CexZr1−xOy were prepared as well as non-stoichiometric La0.5+xZr0.5−xOy buffer layers with different percentages of La and Zr ratios. The variation in the composition of these thin films enables the creation of novel buffer layers with tailored lattice parameters. This leads to different lattice mismatches with the YBa2Cu3O7−x (YBCO superconducting layer on top and with the buffer layers or substrate underneath. This possibility of minimized lattice mismatch should allow the use of one single buffer layer instead of the current complicated buffer architectures such as Ni-(5% W/LZO/LZO/CeO2. Here, single, crack-free LCZO and non-stoichiometric LZO layers with thicknesses of up to 140 nm could be obtained in one single CSD step. The crystallinity and microstructure of these layers were studied by XRD, and SEM and the effective buffer layer action was studied using XPS depth profiling.

  3. Effect of Phosphate-Buffered Solution Corrosion on the Ratcheting Fatigue Behavior of a Duplex Mg-Li-Al Alloy

    Science.gov (United States)

    Yuan, Xin; Yu, Dunji; Gao, Li-Lan; Gao, Hong

    2016-05-01

    This work reports the uniaxial ratcheting and fatigue behavior of a duplex Mg-Li-Al alloy under the influence of phosphate-buffered solution corrosion. Microstructural observations reveal pitting and filament corrosion defects, which impair the load-bearing capacity of the alloy and cause stress concentration, thus leading to an accelerated accumulation of ratcheting strain and shortened fatigue life under the same nominal loading conditions. Comparing Smith model, Smith-Watson-Topper model, and Paul-Sivaprasad-Dhar model, a ratcheting fatigue life prediction model based on the Broberg damage rule and the Paul-Sivaprasad-Dhar model was proposed, and the model yielded a superior prediction for the studied magnesium alloy.

  4. Electrochemical Behavior of Pure Copper in Phosphate Buffer Solutions: A Comparison Between Micro- and Nano-Grained Copper

    Science.gov (United States)

    Imantalab, O.; Fattah-alhosseini, A.; Keshavarz, M. K.; Mazaheri, Y.

    2016-02-01

    In this work, electrochemical behavior of annealed (micro-) and nano-grained pure copper (fabricated by accumulative roll bonding process) in phosphate buffer solutions of various pH values ranging from 10.69 to 12.59 has been studied. Before any electrochemical measurements, evaluation of microstructure was obtained by optical microscope and transmission electron microscopy. To investigate the electrochemical behavior of the samples, the potentiodynamic polarization, Mott-Schottky analysis, and electrochemical impedance spectroscopy (EIS) were carried out. Potentiodynamic polarization plots and EIS measurements revealed that as a result of grain refinement, the passive behavior of the nano-grained sample was improved compared to that of annealed pure copper. Also, Mott-Schottky analysis indicated that the passive films behaved as p-type semiconductors and grain refinement did not change the semiconductor type of passive films.

  5. Role of the buffer solution in the chemical deposition of CdS films for CIGS solar cell applications

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sooho; Kim, Donguk; Baek, Dohyun; Hong, Byoungyou; Yi, Junsin; Lee, Jaehyeong [Sungkyunkwan University, Suwon (Korea, Republic of); Park, Yongseob [Chosun College of Science and and Technology, Gwangju (Korea, Republic of); Choi, Wonseok [Hanbat National University, Daejeon (Korea, Republic of)

    2014-05-15

    In this work, the effects of NH{sub 4}Ac on the structural and the electro-optical properties of CdS films were investigated. CdS thin films were deposited on soda-lime glass and indium-tin-oxide (ITO) coated glass from a chemical bath containing 0.025 M cadmium acetate, 0 M ∼ 0.2 M ammonium acetate, 0.5 M thiourea, and ammonia. Cadmium acetate was the cadmium source, ammonium acetate served as a buffer, ammonia was the complexing agent, and thiourea was the source of sulfur. A commonly- available chemical bath deposition system was successfully modified to obtain precise control over the pH of the solution at 75 .deg. C during the deposition. Chemically deposited CdS films were studied by using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), optical transmittance, and electrical resistivity measurements.

  6. Defects in Calcite.

    Science.gov (United States)

    1991-05-13

    Interatomic Distances in Halides and Chalcogenides" Acta. Cryst. 32 (19-76) 751. 3 8 S.A. Marshall, J.A. McMillan, and R.A. Serway . "Electron Spin... Serway RA (1967) Electron Spin Resonance Absorption Spectrum of Y3 -Stabilized C0 3- Molecular-Ion in Single- Crystal Calcite. J. Chem. Phys. 48:5131-5137

  7. A Novel Solution for Discriminating Wormhole Attacks in MANETs from Congested Traffic using RTT and Transitory Buffer

    Directory of Open Access Journals (Sweden)

    Maria Sebastian

    2013-06-01

    Full Text Available Nowadays, the computing and communication services are accessed while on the move. Setting up of fixed access points and backbone infrastructure is not always viable. So in order to provide communication where there is lack of infrastructure or inconvenience in using the existing infrastructure, Mobile Adhoc Networks (MANETs are used. This inherent flexibility allows MANETs to be used for a wide range of applications such as rescue operations, military applications, vehicular communication, and business meetings. As there is no apriori trust relationship between the nodes of an ad hoc network and basic network functions like packet forwarding and routing are performed by the available nodes, security is an essential component in MANETs. Various attacks in MANETs are blackhole attack, byzantine attack, resource consumption attack, rushing attack, and wormhole attack. Wormhole attack is a severe threat among the other threats in MANET. Existing solutions to detect wormhole attacks include Packet Leashes, SECTOR, DelPHI, RTT-TC, TTM, etc. These solutions require special hardware or strict synchronized clocks or cause message overhead. Some solutions do not locate the wormhole, and some other may generate false alarms or does not consider network congestion into account. In this paper, wormhole attack detection is proposed based on RTT between successive nodes and congestion detection mechanism. If the RTT between two successive nodes is higher than the threshold value, a wormhole attack is suspected. If a wormhole is suspected, node's transitory buffer is probed to determine whether the long delay between the nodes is due to wormhole or not, as delays can be caused due to congestion or by queuing delays. The proposed method prevents both the hidden and the exposed attack. Advantage of our proposed solution is that it does not require any specialized hardware or synchronized clocks.

  8. Study on CexLa1-xO2 Buffer Layer used in Coated Conductors by Chemical Solution Method

    DEFF Research Database (Denmark)

    Zhao, Yue; Suo, Hongli; Grivel, Jean-Claude

    2009-01-01

    Developing multi-functional single buffer layer is one of the most important challenges for simplification of coated conductors configuration. Ladoped CeO2 films were prepared by chemical solution method. And surface morphology and texture quality of the La-doped CeO2 films were investigated...... method. It suggects that Ce0.9La0.1O2 film prepared by chemical solution route have a promising prospect for the simplification of coated conductors configuration....... in details. The results show that the as-obtained pore-free Ce0.9La0.1O2 film are epitaxially deposited on the textured NiW substrate. The 120nm thickness Ce0.9La0.1O2 film is obtained though multi-coating route. The YBCO film with Tco=90.5K, which is deposited on Ce0.9La0.1O2/NiW metallic template by PLD...

  9. 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 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.

  10. 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.

  11. Glassy carbon electrode modified by graphene–gold nanocomposite coating for detection of trace lead ions in acetate buffer solution

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Pui Mun [Interdisplinary Graduate School, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Environmental Chemistry and Materials Group (ECMG), Nanyang Environment and Water Research Institute (NEWRI), Nanyang Technological University, 1 Cleantech Loop, Singapore 637141 (Singapore); School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Wang, Zhaomeng [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Xiaoxu [Heilongjiang University of Science and Technology, Harbin 150027 (China); Chen, Zhong [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Erjia, E-mail: MEJLiu@ntu.edu.sg [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)

    2015-06-01

    Reduced graphene oxide (RGO) decorated with gold nanoparticles (AuNPs) was electrodeposited on glassy carbon electrode (GCE) using cyclic voltammetric method. The results of Raman spectroscopy confirmed the simultaneous formation of AuNPs and reduction of graphene oxide through the electrodeposition process. Scanning electron microscopic measurements showed a uniform distribution of the AuNPs on the RGO sheets. The RGO-AuNP nanocomposite coated GCE (G–Au/GCE) was used to detect lead ions (Pb{sup 2+}) contained in a 0.1 M acetate buffer solution (pH 5.3) using square wave anodic stripping voltammetry (SWASV). The G–Au/GCE demonstrated higher detection sensitivity and stronger SWASV signals than the bare GCE, with the limit of detection of about 0.8 nM. - Highlights: • Graphene with gold nanoparticles was electrodeposited on glassy carbon electrode. • The prepared electrode was able to detect trace lead ions at nM concentration. • Interference study against copper confirmed the selectivity of the electrode for lead. • The prepared electrode showed a promising recovery tested in tap water samples.

  12. Preparation of SmBiO3 buffer layer on YSZ substrate by an improved chemical solution deposition route

    Science.gov (United States)

    Zhu, Xiaolei; Pu, Minghua; Zhao, Yong

    2016-12-01

    A quick route for chemical solution deposition (CSD) has been developed to prepare SmBiO3 (SBO) layers on yttria stabilized zirconia (YSZ) substrates rapidly by using of solid state decomposition (SSD) technique. The proper conditions for volatilization of lactic acid, which as solvent in precursor coated layer, and SBO growth are 115°C for 30 min and 794°C for 60 min in flowing Ar gas. The coated layers are amorphous structure of mixture oxides and quasi-crystal structure of SBO before and after growth, respectively. The total time by this quick CSD route for organic solvent volatilization, salts decomposed and layer growth is not up to 2 h, which are much less than that needed for traditional CSD of over 10 h. SBO layer is directly epitaxial growth on YSZ substrate without any lattice rotation. SBO layer prepared by this quick route as well as that by traditional route are suitable for the growth of YBCO. The superconducting transition temperature and critical current density of the coated YBCO layer on SBO/YSZ obtained by this quick route are up to 90 K and 1.66 MA/cm2. These results may be the usable reference for continuous preparation of SBO buffer layer on IBAD-YSZ/Ni-based alloy tapes.

  13. Prediction for pitting corrosion of AISI type 403 stainless steel in chloride-containing borate buffer solution

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Yancheng [Pennsylvania State Univ. (United States); Macdonald, D.D. [Pennsylvania State Univ. (United States). Center for Electrochemical Science and Technology; Urquidi-Macdonald, M. [Pennsylvania State Univ. (United States). Engineering Science and Mechanics; Engelhardt, G.R. [OLI Systems, Inc. (United States); Dooley, R.B. [Electric Power Research Inst., Palo Alto, CA (United States). Materials and Chemistry Performance Dept.

    2007-07-15

    The prediction of pitting corrosion damage on low-pressure steam turbine (LPST) blade surfaces has been investigated experimentally and the results have been interpreted in terms of the Point Defect Model (PDM) for passivity breakdown and the nucleation of pits. Experimental relationships between the critical breakdown potential (Vc) and the chloride activity aCl- and pH have demonstrated the applicability of the PDM for describing passivity breakdown on AISI Type 403 stainless steel (SS), a commonly employed blade alloy in LPSTs, in chloride-containing borate buffer solutions. The model parameter values, as determined by optimization of the PDM on passivity breakdown data, may be used to predict the nucleation and accumulation of pitting damage on LPST blades under simulated turbine shutdown conditions. In order to evaluate the predictions, integral damage functions (IDFs) and extreme value distributions in pit depth have been measured on samples taken from failed blades recovered from the field (Texas Genco). These data are being used to test the predictions of Damage Function Analysis (DFA), which is based on the PDM and on deterministic models for pit growth and delayed repassivation. However, the success of this analysis critically depends on our ability to define the corrosion evolutionary path. (orig.)

  14. High Quality YBCO Film Growth on SrTiO3-Buffered LaAlO3 Substrate by Full Solution Method

    Institute of Scientific and Technical Information of China (English)

    Sansheng WANG; Lin WANG; Bingfu GU

    2008-01-01

    A full solution method has been developed as a low cost process of YBa2Cu3O7-x (YBCO) coated conductor fabrication.In this study,highly biaxially textured SrTiO3 (STO) buffer layers were fabricated on LaAlO3 (LAO) single crystal substrates by sol-gel method using metal alkoxides as the staring precursor materials.High quality YBCO superconducting film was then fabricated on STO-buffered LAO substrate by triflvoroacetic metalorganic deposition (TFA-MOD) method.For the YBCO superconducting film,only (001) diffraction peaks can be detected by XRD (X-ray diffraction) analysis with no other phases detectable.Especially,In-plane texture of YBCO film is improved compared to that of STO buffer layer from phi scans analysis,which indicates the self-epitaxy phenomenon explained by considering interfacial energy.STO and YBCO films both show c-axis oriented grains growt.h and have uniform surface microstructure.A critical transition temperature,Tc (R=0) of 89.5 K and a critical current density of 2 mA/cm2 (17 K,self-field) were obtained for a 0.2 μm thick YBCO film on STO-buffered LAO substrate.No reaction between YBCO and STO was detected by XRD analysis.This full solution process may provide a promising low cost fabrication route for YBCO coated conductors on metal tape.

  15. Influences of Temperature and pH Value on the Corrosion Behaviors of X80 Pipeline Steel in Carbonate/Bicarbonate Buffer Solution

    Institute of Scientific and Technical Information of China (English)

    LI,Jin-Bo; ZUO,Jian-E

    2008-01-01

    The joint effect of temperature and pH value on the corrosion behavior of X80 steel in carbonate/bicarbonate buffer solution was detected by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis. The results show that an unstable corrosion film will be formed on the X80 steel surface in low pH value solutions, and a better protective corrosion film can be formed on the X80 steel surface in high pH value solutions. On the whole, the corrosion film resistance and transfer resistance increase with the increment of pH value, and decrease with increase of solution temperature, which indicates that the protective effect of the corrosion film on X80 steel is enhanced with increasing pH value and decreasing the solution temperature. The corrosion film formed on X80 steel surface in carbonate/bicarbonate buffer solution has an n-type semi-conductive character, and the donor density decreases with increasing the pH value, and increases with increasing the solution temperature. The flat-band potential and pH value have a linear relationship with a positive slope.

  16. TES buffer-induced phase separation of aqueous solutions of several water-miscible organic solvents at 298.15 K: phase diagrams and molecular dynamic simulations.

    Science.gov (United States)

    Taha, Mohamed; Lee, Ming-Jer

    2013-06-28

    Water and the organic solvents tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, 1-propanol, 2-propanol, tert-butanol, acetonitrile, or acetone are completely miscible in all proportions at room temperature. Here, we present new buffering-out phase separation systems that the above mentioned organic aqueous solutions can be induced to form two liquid phases in the presence of a biological buffer 2-[[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]amino]ethanesulfonic acid (TES). The lower liquid phase is rich in water and buffer, and the upper phase is organic rich. This observation has both practical and mechanistic interests. The phase diagrams of these systems were constructed by experimental measurements at ambient conditions. Molecular dynamic (MD) simulations were performed for TES + water + THF system to understand the interactions between TES, water, and organic solvent at molecular level. Several composition-sets for this system, beyond and inside the liquid-liquid phase-splitting region, have been simulated. Interestingly, the MD simulation for compositions inside the phase separation region showed that THF molecules are forced out from the water network to start forming a new liquid phase. The hydrogen-bonds, hydrogen-bonds lifetimes, hydrogen-bond energies, radial distribution functions, coordination numbers, the electrostatic interactions, and the van der Waals interactions between the different pairs have been calculated. Additionally, MD simulations for TES + water + tert-butanol∕acetonitrile∕acetone phase separation systems were simulated. The results from MD simulations provide an explanation for the buffering-out phenomena observed in [TES + water + organic solvent] systems by a mechanism controlled by the competitive interactions of the buffer and the organic solvent with water. The molecular mechanism reported here is helpful for designing new benign separation materials.

  17. Activity of the Human Rhinovirus 3C Protease Studied in Various Buffers, Additives and Detergents Solutions for Recombinant Protein Production

    OpenAIRE

    2016-01-01

    Proteases are widely used to remove affinity and solubility tags from recombinant proteins to avoid potential interference of these tags with the structure and function of the fusion partner. In recent years, great interest has been seen in use of the human rhinovirus 3C protease owing to its stringent sequence specificity and enhanced activity. Like other proteases, activity of the human rhinovirus 3C protease can be affected in part by the buffer components and additives that are generally ...

  18. Mechanism of enhanced antibacterial activity of ultra-fine ZnO in phosphate buffer solution with various organic acids.

    Science.gov (United States)

    Yang, Lin; Kuang, Huijuan; Liu, Yingxia; Xu, Hengyi; Aguilar, Zoraida P; Xiong, Yonghua; Wei, Hua

    2016-11-01

    Ultra-fine-ZnO showed low toxicity in complex water matrix containing multiple components such as PBS buffer and the toxic mechanism of ultra-fine-ZnO has not been clearly elucidated. In present study, enhanced antibacterial activity of 200 nm diameter ultra-fine-ZnO in PBS buffer against Bacillus cereus and Escherichia coli were observed in the presence of several organic acids in comparison with ultra-fine-ZnO in PBS buffer alone. These findings indicated that the toxic effects of the ultra-fine-ZnO was dependent on the concentration of released Zn(2+) which was affected by organic acids. The production of reactive oxygen species (ROS) did not responsible to the toxic mechanism of ultra-fine-ZnO which was tested using the antioxidant N-Acetylcysteine (NAC). Indeed, ultra-fine-ZnO induced bacteria cell membrane leakages and cell morphology damages that eventually led to cell death, which were confirmed using propidium monoazide (PMA) in combination with PCR and scanning electron microscopy (SEM). All data gathered herein suggested that released Zn(2+) played a major role in the microbial toxicity of ultra-fine-ZnO.

  19. Grain coarsening of calcite: Fundamental mechanisms and biogenic inhibition

    DEFF Research Database (Denmark)

    Schultz, Logan Nicholas

    In a saturated solution, submicrometer calcite (CaCO3) crystals recrystallize and coarsen to minimize surface area. The thermodynamic driving force is described by the Gibbs-Thomson equation, but the rates and mechanism are poorly understood. Calcite grain coarsening has many implications...... in industry and nature, but the specific focus of this research project was to understand how small, biogenic calcite particles in chalk have resisted grain coarsening for over 60 million years in saturated reservoir fluids. A new method was developed to produce pure calcite powder that has submicrometer...... coarsening – small grains coarsen by aggregation at high temperatures, followed by Ostwald ripening. Alginate, a model for the acidic polysaccharides produced by coccolithiphores, inhibited coarsening at a steady rate. A Pseudomonas aeruginosa biofilm preserved particles for at least 60 days before...

  20. Calcite crystal growth rate inhibition by polycarboxylic acids

    Science.gov (United States)

    Reddy, M.M.; Hoch, A.R.

    2001-01-01

    Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

  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. 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.

  3. Interactions between cadmium and calcite

    OpenAIRE

    Van der Weijden, R.D.

    1995-01-01

    The thesis is composed of five chapters, some of which have been published or have been accepted for publication. The contents in some of the chapters may therefore slightly overlap, also because the subjects are closely related. The first two chapters focus mostly on the sorption of Cd on calcite, whereas the next two chapters are devoted to calcite growth and Cd incorporation during growth. In the fifth and final chapter, Cd sorption and incorporation is studied in an environment where calc...

  4. Corrosion behavior of Mg-3Zn/bioglass (45S5) composite in simulated body fluid (SBF) and phosphate buffered saline (PBS) solution

    Science.gov (United States)

    Ab llah, N.; Jamaludin, S. B.; Daud, Z. C.; Zaludin, M. A. F.; Jamal, Z. A. Z.; Idris, M. S.; Osman, R. A. M.

    2016-07-01

    Magnesium has emerged as promising materials in biomaterials research due to its good mechanical and physical properties closer to human bones. However, magnesium has poor corrosion resistance to chloride ions that exist in human blood plasma thus preventing its application in biomedical. The addition of zinc and bioglass can reduce magnesium corrosion rate. In this work, the effect of different solution media (Simulated Body Fluid and Phosphate Buffered Saline) to the corrosion behavior of Mg-Zn/bioglass (45S5) composites was investigated. The composites of Mg-3Zn added with 5, 10, 15, 20, 15 and 30 wt. % bioglass were fabricated by powder metallurgy. The composites were prepared by mixing at 140 rpm for 1 hour, pressing at 500 MPa and sintering in an argon environment at a temperature of 450°C for 3 hours. Sintered samples were immersed in Simulated Body Fluid (SBF) and Phosphate Buffered Saline (PBS) in order to investigate the corrosion behavior. Samples mass loss was determined after 3 days of immersion. Samples microstructure and corrosion products were analyzed using optical microscope and x-ray diffraction (XRD) respectively. The results revealed that the samples immersed in the Phosphate Buffered Saline (PBS) shows lower mass loss compare to the samples immersed in the Simulated Body Fluid (SBF) for all composition except for Mg-3Zn without bio-glass. The results indicated that the existence of high phosphate ions in PBS has retarded the corrosion rate of composite Mg-3Zn/45S5. The pH value of the PBS solution after immersion showed significant increase between 10.3 and 11.09. Diffraction pattern (XRD) showed the presence of Mg(OH)2 as the major corrosion product for samples immersed in the SBF and PBS solutions. The mass loss of samples decreased with the addition of bio-glass.

  5. Optimization of the Energy Level Alignment between the Photoactive Layer and the Cathode Contact Utilizing Solution-Processed Hafnium Acetylacetonate as Buffer Layer for Efficient Polymer Solar Cells.

    Science.gov (United States)

    Yu, Lu; Li, Qiuxiang; Shi, Zhenzhen; Liu, Hao; Wang, Yaping; Wang, Fuzhi; Zhang, Bing; Dai, Songyuan; Lin, Jun; Tan, Zhan'ao

    2016-01-13

    The insertion of an appropriate interfacial buffer layer between the photoactive layer and the contact electrodes makes a great impact on the performance of polymer solar cells (PSCs). Ideal interfacial buffer layers could minimize the interfacial traps and the interfacial barriers caused by the incompatibility between the photoactive layer and the electrodes. In this work, we utilized solution-processed hafnium(IV) acetylacetonate (Hf(acac)4) as an effective cathode buffer layer (CBL) in PSCs to optimize the energy level alignment between the photoactive layer and the cathode contact, with the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) all simultaneously improved with Hf(acac)4 CBL, leading to enhanced power conversion efficiencies (PCEs). Ultraviolet photoemission spectroscopy (UPS) and scanning Kelvin probe microscopy (SKPM) were performed to confirm that the interfacial dipoles were formed with the same orientation direction as the built-in potential between the photoactive layer and Hf(acac)4 CBL, benefiting the exciton separation and electron transport/extraction. In addition, the optical characteristics and surface morphology of the Hf(acac)4 CBL were also investigated.

  6. A study of the potentials achieved during mechanical abrasion and the repassivation rate of titanium and Ti6A14V in inorganic buffer solutions and bovine serum

    Energy Technology Data Exchange (ETDEWEB)

    Contu, F. [University of Mississippi Medical Center, Jackson, MS (United States); Elsener, B. [University of Cagliari (Italy). Dept. of Inorganic and Anlaytical Chemistry; Swiss Federal Institute of Technology, Zurich (Switzerland). Institute of Materials Chemistry; Boehni, H. [Swiss Federal Institute of Technology, Zurich (Switzerland). Institute of Materials Chemistry

    2004-11-15

    Titanium alloys in orthopaedic implants are susceptible to mechanical disruption of the passive film (fretting corrosion). To study this effect, open-circuit potential (ocp) measurements before, during and after mechanical disruption of the passive film in a tribo-electrochemical cell on commercial pure titanium, and Ti6Al4V alloy in inorganic buffer solutions in the pH range from 2.0 to 12.0 and calf bovine serum at pH 4.0 and 7.0 are reported. Additionally, the effect of pH, electrolyte and sample composition on the repassivation rate has been investigated. The potentials achieved during the abrasion of Ti6Al4V are the same as those characterizing pure titanium, which indicates that the corrosion current of both materials in the active state is due to the oxidation of titanium. However, commercial pure titanium displays a tendency to repassivate faster than Ti6Al4V in inorganic buffer solutions thanks to the lower critical current density and the higher catalytic activity towards the hydrogen evolution reaction observed on the pure metal in comparison with the alloy. Proteinaceous solutions like bovine serum, significantly slow down the anodic dissolution and the cathodic reactions both on titanium and the alloy. However, the repassivation rate of the Ti6Al4V is not affected by serum, while that of cp titanium significantly decreases both at pH 4.0 and 7.0. (author)

  7. Current characteristics of λ-DNA molecules/polystyrene nanoparticles in TBE buffer solution through micro/nanofluidic capillaries under DC electric field

    Science.gov (United States)

    Duan, Yifei; Zhao, Wei; Xue, Jing; Sun, Dan; Wang, Kaige; Wang, Guiren; Li, Junjie; Bai, Jintao; Gu, Changzhi

    2017-03-01

    In practical applications of biochips and bio-sensors, electrokinetic mechanisms are commonly employed to manipulate single bio-molecules and analyze their characteristics. To accurately and flexibly control the movement of single-molecule within micro/nanofluidic channels which are the basic components of Lab-chips, the current signals in micro/nanocapillaries filled with solutions of DNA molecules or polystyrene (PS) nanoparticles are systematically studied. Experimental results indicate that the current response along the micro/nanocapillaries can be significantly influenced by the diameter of the capillaries and the pH value of the solutions. Specifically, when there is only a pure (TBE) solution, the electric conductance does not monotonically decrease with decreasing the diameter of the capillaries, but slightly increases with decreasing the capillary diameter. When λ-DNA molecules or PS nanoparticles are added into the TBE buffer, the size effect on the electric conductance of the solutions are quite different. Although in the former, the electric conductance behaves differently from that in the pure TBE solution and decreases with the decreasing diameter, in the latter, the change is similar to that in the pure TBE solution. Besides, an abnormal ‘falling’ of the electric conductance is observed in a capillary with diameter of 200 nm. The investigation will significantly enhance the understanding on the electric properties of the solutions of biomolecules and particles in micro/nanofluidics. This is especially helpful for designing functional Lab-chip devices.

  8. Removal of organic magnesium in coccolithophore calcite

    Science.gov (United States)

    Blanco-Ameijeiras, S.; Lebrato, M.; Stoll, H. M.; Iglesias-Rodriguez, M. D.; Méndez-Vicente, A.; Sett, S.; Müller, M. N.; Oschlies, A.; Schulz, K. G.

    2012-07-01

    Coccolithophore calcite refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated calcite in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in calcite. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OH·HCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 ± 0.018, 0.220 ± 0.040, and 0.064 ± 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (protocol applicable to field and laboratory studies of trace elemental composition in

  9. The dissolution of monosodium urate monohydrate crystals: formulation of a biocompatible buffer solution with potential use in the treatment of gouty arthropathies

    Directory of Open Access Journals (Sweden)

    Gabriella Tamasi

    2013-04-01

    Full Text Available The dissolving abilities (DAs of several aqueous media for microcrystalline monosodium\turate\tmonohydrate\t(MSU, NaC5N4O3H3·H2O have been investigated using UV spectrophotometry for quantitative analytical determinations and X-ray diffraction, scanning electron microscopy and polarized light optical microscopy to assess structural aspects. High DAs were found for a buffer labeled TMT which contains tris(hydroxymethylaminomethane (TRIS, tris(hydroxymethylaminomethane\thydrochloride (TRIS·HCl, D-mannitol (MAN and taurine (TAU and gave DA30=1298(5 mg/L for synthetic MSU after 30 min incubation at 37°C and pH 7.4, most of the dissolution taking place within the first 5-10 min. Semiempirical molecular modelling techniques (ZINDO/1 show a favorable energy balance for the formation of a TRIS-urate-TRIS adduct which might explain the high DA values. Buffers containing linear or dendrimeric polyamines gave DA values which suggest that complex formation toward sodium cations is less important. An ex vivo MSU sample was found to have a significantly lower DA value (DA30=1124(5 mg/L in TMT as well as a lower crystallinity than its synthetic counterpart, possibly related to the presence of a non-crystalline impurity such as endogenous proteins. Cytotoxicity tests based on the MTT assay were used to check the biocompatibility of the TMT buffer and showed only moderate cell mortality after 24 h contact with the buffer solution.

  10. Growth of thick La{sub 2}Zr{sub 2}O{sub 7} buffer layers for coated conductors by polymer-assisted chemical solution deposition

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xin, E-mail: xzhang@my.swjtu.edu.cn [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, Superconductivity and New Energy Center (SNEC), Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); School of Electrical Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhao, Yong, E-mail: yzhao@swjtu.edu.cn [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, Superconductivity and New Energy Center (SNEC), Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); School of Materials Science and Engineering, University of New South Wales, Sydney, 2052 NSW (Australia); Xia, Yudong [State Key Lab of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Guo, Chunsheng [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, Superconductivity and New Energy Center (SNEC), Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Cheng, C.H. [School of Materials Science and Engineering, University of New South Wales, Sydney, 2052 NSW (Australia); Zhang, Yong [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, Superconductivity and New Energy Center (SNEC), Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhang, Han [Department of Physics, Peking University, Beijing 100871 (China)

    2015-06-15

    Highlights: • We develops a low-cost and high-efficient technology of fabricating LZO buffer layers. • Sufficient thickness LZO buffer layers have been obtained on NiW (2 0 0) alloy substrate. • Highly biaxially textured YBCO thin film has been deposited on LZO/NiW. - Abstract: La{sub 2}Zr{sub 2}O{sub 7} (LZO) epitaxial films have been deposited on LaAlO{sub 3} (LAO) (1 0 0) single-crystal surface and bi-axially textured NiW (2 0 0) alloy substrate by polymer-assisted chemical solution deposition, and afterwards studied with XRD, SEM and AFM approaches. Highly in-plane and out-of-plane oriented, dense, smooth, crack free and with a sufficient thickness (>240 nm) LZO buffer layers have been obtained on LAO (1 0 0) single-crystal surface; The films deposited on NiW (2 0 0) alloy substrate are also found with high degree in-plane and out-of-plane texturing, good density with pin-hole-free, micro-crack-free nature and a thickness of 300 nm. Highly epitaxial 500 nm thick YBa{sub 2}Cu{sub 3}O{sub 7−x} (YBCO) thin film exhibits the self-field critical current density (Jc) reached 1.3 MA/cm{sup 2} at 77 K .These results demonstrate the LZO epi-films obtained with current techniques have potential to be a buffer layer for REBCO coated conductors.

  11. Activity of the Human Rhinovirus 3C Protease Studied in Various Buffers, Additives and Detergents Solutions for Recombinant Protein Production.

    Science.gov (United States)

    Ullah, Raheem; Shah, Majid Ali; Tufail, Soban; Ismat, Fouzia; Imran, Muhammad; Iqbal, Mazhar; Mirza, Osman; Rhaman, Moazur

    2016-01-01

    Proteases are widely used to remove affinity and solubility tags from recombinant proteins to avoid potential interference of these tags with the structure and function of the fusion partner. In recent years, great interest has been seen in use of the human rhinovirus 3C protease owing to its stringent sequence specificity and enhanced activity. Like other proteases, activity of the human rhinovirus 3C protease can be affected in part by the buffer components and additives that are generally employed for purification and stabilization of proteins, hence, necessitate their removal by tedious and time-consuming procedures before proteolysis can occur. To address this issue, we examined the effect of elution buffers used for common affinity based purifications, salt ions, stability/solubility and reducing agents, and detergents on the activity of the human rhinovirus 3C protease using three different fusion proteins at 4°C, a temperature of choice for purification of many proteins. The results show that the human rhinovirus 3C protease performs better at 4°C than the frequently used tobacco etch virus protease and its activity was insensitive to most of the experimental conditions tested. Though number of fusion proteins tested is limited, we expect that these finding will facilitate the use of the human rhinovirus 3C protease in recombinant protein production for pharmaceutical and biotechnological applications.

  12. Activity of the Human Rhinovirus 3C Protease Studied in Various Buffers, Additives and Detergents Solutions for Recombinant Protein Production.

    Directory of Open Access Journals (Sweden)

    Raheem Ullah

    Full Text Available Proteases are widely used to remove affinity and solubility tags from recombinant proteins to avoid potential interference of these tags with the structure and function of the fusion partner. In recent years, great interest has been seen in use of the human rhinovirus 3C protease owing to its stringent sequence specificity and enhanced activity. Like other proteases, activity of the human rhinovirus 3C protease can be affected in part by the buffer components and additives that are generally employed for purification and stabilization of proteins, hence, necessitate their removal by tedious and time-consuming procedures before proteolysis can occur. To address this issue, we examined the effect of elution buffers used for common affinity based purifications, salt ions, stability/solubility and reducing agents, and detergents on the activity of the human rhinovirus 3C protease using three different fusion proteins at 4°C, a temperature of choice for purification of many proteins. The results show that the human rhinovirus 3C protease performs better at 4°C than the frequently used tobacco etch virus protease and its activity was insensitive to most of the experimental conditions tested. Though number of fusion proteins tested is limited, we expect that these finding will facilitate the use of the human rhinovirus 3C protease in recombinant protein production for pharmaceutical and biotechnological applications.

  13. Evolution and the Calcite Eye Lens

    CERN Document Server

    Williams, Vernon L

    2013-01-01

    Calcite is a uniaxial, birefringent crystal, which in its optically transparent form, has been used for animal eye lenses, the trilobite being one such animal. Because of the calcite birefringence there is a difficulty in using calcite as a lens. When the propagation direction of incoming light is not exactly on the c-axis, the mages blur. In this paper, calcite blurring is evaluated, and the non-blurring by a crystallin eye lens is compared to a calcite one.

  14. 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.

  15. Real-time HD Exchange Kinetics of Proteins from Buffered Aqueous Solution with Electrothermal Supercharging and Top-Down Tandem Mass Spectrometry

    Science.gov (United States)

    Going, Catherine C.; Xia, Zijie; Williams, Evan R.

    2016-06-01

    Electrothermal supercharging (ETS) with electrospray ionization produces highly charged protein ions from buffered aqueous solutions in which proteins have native folded structures. ETS increases the charge of ribonuclease A by 34%, whereas only a 6% increase in charge occurs for a reduced-alkylated form of this protein, which is unfolded and its structure is ~66% random coil in this solution. These results indicate that protein denaturation that occurs in the ESI droplets is the primary mechanism for ETS. ETS does not affect the extent of solution-phase hydrogen-deuterium exchange (HDX) that occurs for four proteins that have significantly different structures in solution, consistent with a droplet lifetime that is considerably shorter than observable rates of HDX. Rate constants for HDX of ubiquitin are obtained with a spatial resolution of ~1.3 residues with ETS and electron transfer dissociation of the 10+ charge-state using a single capillary containing a few μL of protein solution in which HDX continuously occurs. HDX protection at individual residues with ETS HDX is similar to that with reagent supercharging HDX and with solution-phase NMR, indicating that the high spray potentials required to induce ETS do not lead to HD scrambling.

  16. Low-Temperature Solution-Processed SnO2 Nanoparticles as a Cathode Buffer Layer for Inverted Organic Solar Cells.

    Science.gov (United States)

    Tran, Van-Huong; Ambade, Rohan B; Ambade, Swapnil B; Lee, Soo-Hyoung; Lee, In-Hwan

    2017-01-18

    SnO2 recently has attracted particular attention as a powerful buffer layer for organic optoelectronic devices due to its outstanding properties such as high electron mobility, suitable band alignment, and high optical transparency. Here, we report on facile low-temperature solution-processed SnO2 nanoparticles (NPs) in applications for a cathode buffer layer (CBL) of inverted organic solar cells (iOSCs). The conduction band energy of SnO2 NPs estimated by ultraviolet photoelectron spectroscopy was 4.01 eV, a salient feature that is necessary for an appropriate CBL. Using SnO2 NPs as CBL derived from a 0.1 M precursor concentration, P3HT:PC60BM-based iOSCs showed the best power conversion efficiency (PCE) of 2.9%. The iOSC devices using SnO2 NPs as CBL revealed excellent long-term device stabilities, and the PCE was retained at ∼95% of its initial value after 10 weeks in ambient air. These solution-processed SnO2 NPs are considered to be suitable for the low-cost, high throughput roll-to-roll process on a flexible substrate for optoelectronic devices.

  17. Environmental cadmium levels increase phytochelatin and glutathione in lettuce grown in a chelator-buffered nutrient solution.

    Science.gov (United States)

    Maier, Elizabeth A; Matthews, Rosalyn D; McDowell, Jennifer A; Walden, Rebecca R; Ahner, Beth A

    2003-01-01

    Phytochelatins are enzymatically synthesized peptides involved in metal detoxification and have been measured in plants grown at very high Cd concentrations, but few studies have examined the response of plants at lower environmentally relevant Cd concentrations. Using an ethylenediaminetetraacetic acid (EDTA)-buffered nutrient medium, we have varied Cd exposure and measured phytochelatin and glutathione concentrations in romaine lettuce (Lactuca sativa L. var. longifolia Lam. var. Parris Island) grown in a flow-through hydroponic (FTH) system. Very low free ionic Cd (10(-9.6) M) increased average phytochelatin concentrations above those of controls, and increasing Cd resulted in increased phytochelatin production, though increases were tissue dependent. Glutathione concentrations also increased with increasing Cd. In other standard hydroponic experiments, the media were manipulated to vary total Cd concentration while the ionic Cd was fixed. We found that the total amount of Cd (primarily EDTA bound) in the medium altered thiol production in roots, whereas thiols in leaves remained constant. The Cd uptake into roots and translocation to old leaves was also influenced by the total concentration in the medium. Cadmium in all tissues was lower and in some tissues thiol concentrations were higher than in FTH-grown plants grown in identical medium, suggesting that nutrient delivery technique is also an important variable. Though phytochelatin and glutathione production can be sensitive to changes in bioavailable Cd, thiol concentrations will not necessarily reflect the Cd content of the plant tissues.

  18. The use of ethylene glycol solution as the running buffer for highly efficient microchip-based electrophoresis in unmodified cyclic olefin copolymer microchips.

    Science.gov (United States)

    Wang, Qin; Zhang, Yuan; Ding, Hui; Wu, Jing; Wang, Lili; Zhou, Lei; Pu, Qiaosheng

    2011-12-30

    An ethylene glycol solution was used as the electrophoretic running buffer in unmodified cyclic olefin copolymer (COC) microchips to minimize the interactions between the analytes and the hydrophobic walls of the plastic microchannels, enhance the resolution of the analytes and eliminate the uncontrollable dispersion caused by uneven liquid levels and non-uniform surfaces of the separation channels. Five amino acids that were labeled with fluorescein isothiocyanate (FITC) were used as model analytes to examine the separation efficiency. The effects of ethylene glycol concentration, pH and sodium tetraborate concentration were systematically investigated. The five FITC-labeled amino acids were effectively resolved using a COC microchip with an effective length of 2.5 cm under optimum conditions, which included using a running buffer of 20 mmol/L sodium tetraborate in ethylene glycol:water (80:20, v/v), pH 6.7. A theoretical plate number of 4.8 × 10(5)/m was obtained for aspartic acid. The system exhibited good repeatability, and the relative standard deviations (n=5) of the peak areas and migration times were no more than 3.4% and 0.7%, respectively. Furthermore, the system was successfully applied to elucidate these five amino acids in human saliva.

  19. Interactions between cadmium and calcite

    NARCIS (Netherlands)

    van der Weijden, R.D.

    1995-01-01

    The thesis is composed of five chapters, some of which have been published or have been accepted for publication. The contents in some of the chapters may therefore slightly overlap, also because the subjects are closely related. The first two chapters focus mostly on the sorption of Cd on calcite,

  20. Buffer capacity of biologics--from buffer salts to buffering by antibodies.

    Science.gov (United States)

    Karow, Anne R; Bahrenburg, Sven; Garidel, Patrick

    2013-01-01

    Controlling pH is essential for a variety of biopharmaceutical process steps. The chemical stability of biologics such as monoclonal antibodies is pH-dependent and slightly acidic conditions are favorable for stability in a number of cases. Since control of pH is widely provided by added buffer salts, the current study summarizes the buffer characteristics of acetate, citrate, histidine, succinate, and phosphate buffers. Experimentally derived values largely coincide with values calculated from a model that had been proposed in 1922 by van Slyke. As high concentrated protein formulations become more and more prevalent for biologics, the self-buffering potential of proteins becomes of relevance. The current study provides information on buffer characteristics for pH ranges down to 4.0 and up to 8.0 and shows that a monoclonal antibody at 50 mg/mL exhibits similar buffer capacity as 6 mM citrate or 14 mM histidine (pH 5.0-6.0). Buffer capacity of antibody solutions scales linearly with protein concentration up to more than 200 mg/mL. At a protein concentration of 220 mg/mL, the buffer capacity resembles the buffer capacity of 30 mM citrate or 50 mM histidine (pH 5.0-6.0). The buffer capacity of monoclonal antibodies is practically identical at the process relevant temperatures 5, 25, and 40°C. Changes in ionic strength of ΔI=0.15, in contrast, can alter the buffer capacity up to 35%. In conclusion, due to efficient self-buffering by antibodies in the pH range of favored chemical stability, conventional buffer excipients could be dispensable for pH stabilization of high concentrated protein solutions.

  1. 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

    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...... of a high degree of super-saturation with respect to hydroxyapatite (SIHAP⩽7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the CO32- activity decreases (at constant pH) and as pH increases (at constant CO32- activity). The primary effect...

  2. CdS and Cd-Free Buffer Layers on Solution Phase Grown Cu2ZnSn(SxSe1- x)4 :Band Alignments and Electronic Structure Determined with Femtosecond Ultraviolet Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Haight, Richard; Barkhouse, Aaron; Wang, Wei; Yu, Luo; Shao, Xiaoyan; Mitzi, David; Hiroi, Homare; Sugimoto, Hiroki

    2013-12-02

    The heterojunctions formed between solution phase grown Cu2ZnSn(SxSe1- x)4(CZTS,Se) and a number of important buffer materials including CdS, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission spectroscopy (fs-UPS) and photovoltage spectroscopy. With this approach we extract the magnitude and direction of the CZTS,Se band bending, locate the Fermi level within the band gaps of absorber and buffer and measure the absorber/buffer band offsets under flatband conditions. We will also discuss two-color pump/probe experiments in which the band bending in the buffer layer can be independently determined. Finally, studies of the bare CZTS,Se surface will be discussed including our observation of mid-gap Fermi level pinning and its relation to Voc limitations and bulk defects.

  3. Graphene ultrathin film electrodes modified with bismuth nanoparticles and polyaniline porous layers for detection of lead and cadmium ions in acetate buffer solutions

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhaomeng; Li, Lin; Liu, Erjia, E-mail: mejliu@ntu.edu.sg

    2013-10-01

    Graphene ultrathin films were synthesized by means of solid-state carbon diffusion from amorphous carbon (a-C) thin layers deposited on silicon substrates, which was catalyzed by nickel layers coated on the top of the a-C layers. The graphene films were used as working electrodes that were modified by a polyaniline (PANI) porous layer together with in-situ deposited bismuth (Bi) nanoparticles for the detection of trace heavy metal ions (Pb{sup 2+} and Cd{sup 2+}) in acetate buffer solutions (pH 5.3) with square wave anodic stripping voltammetry. The graphene electrodes modified with PANI porous layers and Bi nanoparticles had excellent repeatability, ultrahigh sensitivity (as low as 0.33 nM) and good resistance to passivation caused by the surface active species adsorbed on the electrode surfaces. - Highlights: • Graphene fabricated by nickel-catalyzed carbon diffusion in solid state • Graphene electrodes modified by bismuth nanoparticles and polyaniline layers • High resistance of modified graphene electrodes to passivation in acetate solutions • Ultra-low detection limits of lead and cadmium ions by modified graphene electrodes.

  4. 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.

  5. 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

    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 View the MathML source. The results show that the adsorption...... 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...

  6. An improvement to the ligand optimisation method (LOM) for measuring the apparent dissociation constant and ligand purity in Ca2+ and Mg2+ buffer solutions.

    Science.gov (United States)

    McGuigan, John A S; Kay, James W; Elder, Hugh Y

    2014-01-01

    In Ca(2+)/Mg(2+) buffers the calculated ionised concentrations ([X(2+)]) can vary by up to a factor of seven. Since there are no defined standards it is impossible to check calculated [X(2+)], making measurement essential. The ligand optimisation method (LOM) is an accurate method to measure [X(2+)] in Ca(2+)/Mg(2+) buffers; independent estimation of ligand purity extends the method to pK(/) buffers, to calculate electrode and buffer characteristics as a function of Σ. Ca(2+)-electrodes have a Σ buffers. These results demonstrated that it is pK(/) that is normally distributed. Until defined standards are available, [X(2+)] in Ca(2+)/Mg(2+) buffers have to be measured. The most appropriate method is to use Ca(2+)/Mg(2) electrodes combined with the Excel programs SALE or AEC.

  7. Influence of heat treatment on microstructure and passivity of Cu–30Zn–1Sn alloy in buffer solution containing chloride ions

    Indian Academy of Sciences (India)

    U Tabrizi; R Parvizi; A Davoodi; M H Moayed

    2012-02-01

    Tin as an alloying element is of great interest in brasses for dezincification impediment. In this paper, Cu–30Zn–1Sn alloy was submitted to three different heat treatments, viz. A (heating up to 800 °C for 20 h, held at 200 °C for 20 h in salt bath and air cooled), B (heating up to 800 °C for 20 h and water quenched) and C (heating up to 600 °C for 20 h and water quenched). The influence of heat treatment on microstructure was evaluated by OM and SEM–EDS analysis. The corrosion resistance in buffer solution (pH 9), H3BO3/Na2B4O7.10H2O, with various concentrations of chloride ions was evaluated by potentiodynamic polarization curves and compared with multicomponent Pourbaix diagrams. A correlation between the heat treatment, microstructure and passivity of the heat treated samples was observed. The results indicated that all heat treatment procedures led to formation of , and -Sn-rich phases as microstructure constituents with a small fraction of ' phase in A. Sn-rich phase appears in grain boundaries and its morphology was slightly changed due to heat treatment. Beneficial influence of low concentration chloride ions on passivity was associated with the formation of copper oxides/hydroxide and chloride complexes. Deterioration was observed at concentrations higher than 0.05 M NaCl due to accelerated dissolution of copper by formation of CuCl$^{−}_{2}$. As a result of dezincification process, preferential corrosion attack and copper redeposition on phase (matrix) were observed. However, Sn-rich (1) phase in grain boundaries was not attacked due to SnO2 formation. In buffer solution, the higher passivity current density in A was related to the presence of small amount of ' phase. On the other hand, in 1 M NaCl, lower critical current density for passivation in B and A (about two times lower than C) was attributed to the grain size effect.

  8. Kinetic buffers.

    Science.gov (United States)

    Alibrandi, Giuseppe; Fabbrizzi, Luigi; Licchelli, Maurizio; Puglisi, Antonio

    2015-01-12

    This paper proposes a new type of molecular device that is able to act as an inverse proton sponge to slowly decrease the pH inside a reaction vessel. This makes the automatic monitoring of the concentration of pH-sensitive systems possible. The device is a composite formed of an alkyl chloride, which kinetically produces acidity, and a buffer that thermodynamically modulates the variation in pH value. Profiles of pH versus time (pH-t plots) have been generated under various experimental conditions by computer simulation, and the device has been tested by carrying out automatic spectrophotometric titrations, without using an autoburette. To underline the wide variety of possible applications, this new system has been used to realize and monitor HCl uptake by a di-copper(II) bistren complex in a single run, in a completely automatic experiment.

  9. Interactions of arsenic with calcite surfaces revealed by in-situ nanoscale imaging

    Science.gov (United States)

    Renard, Francois; Putnis, Christine; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hövelmann, Jörn; Sarret, Géraldine

    2015-04-01

    Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments calcite may play an important role in arsenic solubility and transfer in water. Arsenic-calcite interactions remain controversial, especially for As(III) which was proposed to be either incorporated as such, or as As(V) after oxidation. Here, we provide the first time-lapse in-situ study of calcite dissolution and growth in the presence of solutions with various amounts of As(III) or As(V). This was performed at room temperature and pH range 6-9 using a flow through cell connected to an atomic force microscope (AFM), to study the evolution of the (10-14) calcite cleavage surface morphology. Reaction products were then characterized by Raman spectroscopy. In parallel, co-precipitation experiments with either As(III) or As(V) were performed in batch reactors, and the speciation of arsenic in the resulting solids was studied by X-ray absorption spectroscopy (XAS). For As(V), AFM results showed that it interacts strongly with the calcite surface, and XAS results showed that As(V) was mostly incorporated in the calcite structure. For As(III), AFM results showed much less impact on calcite growth and dissolution and less incorporation was observed. This was confirmed by XAS results that indicate that As(III) was partly oxidized into As(V) before being incorporated into calcite and the resulting calcite contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with calcite than As(III) and that calcite may represent an important reservoir for arsenic in various geological environments.

  10. The Effect of Sintering Oxygen Partial Pressure on a SmBiO3 Buffer Layer for Coated Conductors via Chemical Solution Deposition

    Directory of Open Access Journals (Sweden)

    Xiaolei Zhu

    2016-10-01

    Full Text Available The application of high-temperature YBa2Cu3O7−δ (YBCO superconducting material is a considerable prospect for the growing energy shortages. Here, SmBiO3 (SBO films were deposited on (100-orientated yttrium-stabilized zirconia (YSZ simple crystal substrates via the chemical solution deposition (CSD approach for coated conductors, and the effects of sintering oxygen partial pressure on SBO films were studied. The crystalline structures and surface morphologies of SBO films were characterized by X-ray diffraction (XRD, scanning electron microscopy (SEM, and atomic force microscope (AFM. The optimized growth temperature, the intensity ratios of the SBO (200 peak to the SBO (111 peak, and the crystallinities of SBO films increased with the sintering oxygen partial pressure. The SEM and AFM images displayed a smooth and well-distributed surface in the argon atmosphere. The subsequent YBCO films with superconducting transition temperatures (Tc = 89.5 K, 90.2 K, and 86.2 K and critical current densities (Jc = 0.88 MA/cm2, 1.69 MA/cm2, and 0.09 MA/cm2; 77 K, self-field were deposited to further check the qualities of the SBO layer. These results indicated that sintering oxygen partial pressure had an effect on the epitaxial growth of the SBO buffer layer and YBCO superconducting properties. The experimental results may be a usable reference for the epitaxial growth of YBCO-coated conductors and other oxides.

  11. Effects of sodium hypochlorite and high pH buffer solution in electrokinetic soil treatment on soil chromium removal and the functional diversity of soil microbial community.

    Science.gov (United States)

    Cang, Long; Zhou, Dong-Mei; Alshawabkeh, Akram N; Chen, Hai-Feng

    2007-04-02

    Effects of sodium hypochlorite (NaClO), applied as an oxidant in catholyte, and high pH buffer solution on soil Cr removal and the functional diversity of soil microbial community during enhanced electrokinetic treatments of a chromium (Cr) contaminated red soil are evaluated. Using pH control system to maintain high alkalinity of soil together with the use of NaClO increased the electrical conductivities of soil pore liquid and electroosmotic flux compared with the control (Exp-01). The pH control and NaClO improved the removal of Cr(VI) and total Cr from the soil. The highest removal percentages of soil Cr(VI) and total Cr were 96 and 72%, respectively, in Exp-04 when the pH value of the anolyte was controlled at 10 and NaClO was added in the catholyte. The alkaline soil environment and introduction of NaClO in the soil enhanced the desorption of Cr(VI) from the soil and promoted Cr(III) oxidation to mobile Cr(VI), respectively. However, the elevated pH and introduction of NaClO in the soil, which are necessary for improving the removal efficiency of soil Cr, resulted in a significantly adverse impact on the functional diversity of soil microbial community. It suggests that to assess the negative impact of extreme conditions for enhancing the extraction efficiencies of Cr on the soil properties and function is necessary.

  12. Effects of sodium hypochlorite and high pH buffer solution in electrokinetic soil treatment on soil chromium removal and the functional diversity of soil microbial community

    Energy Technology Data Exchange (ETDEWEB)

    Cang Long [State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China); Zhou Dongmei [State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China)]. E-mail: dmzhou@issas.ac.cn; Alshawabkeh, Akram N. [Department of Civil and Environmental Engineering, Northeastern University, Boston, MA (United States); Chen Haifeng [State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China)

    2007-04-02

    Effects of sodium hypochlorite (NaClO), applied as an oxidant in catholyte, and high pH buffer solution on soil Cr removal and the functional diversity of soil microbial community during enhanced electrokinetic treatments of a chromium (Cr) contaminated red soil are evaluated. Using pH control system to maintain high alkalinity of soil together with the use of NaClO increased the electrical conductivities of soil pore liquid and electroosmotic flux compared with the control (Exp-01). The pH control and NaClO improved the removal of Cr(VI) and total Cr from the soil. The highest removal percentages of soil Cr(VI) and total Cr were 96 and 72%, respectively, in Exp-04 when the pH value of the anolyte was controlled at 10 and NaClO was added in the catholyte. The alkaline soil environment and introduction of NaClO in the soil enhanced the desorption of Cr(VI) from the soil and promoted Cr(III) oxidation to mobile Cr(VI), respectively. However, the elevated pH and introduction of NaClO in the soil, which are necessary for improving the removal efficiency of soil Cr, resulted in a significantly adverse impact on the functional diversity of soil microbial community. It suggests that to assess the negative impact of extreme conditions for enhancing the extraction efficiencies of Cr on the soil properties and function is necessary.

  13. The Kinetics of Anodic Dissolution and Repassivation on 316L Stainless Steel in Borate Buffer Solution Studied by Abrading Electrode Technique

    Energy Technology Data Exchange (ETDEWEB)

    Xu, H. S.; Sun, D. B.; Yu, H. Y.; Meng, H. M. [University of Science and Technology Beijing, Beijing (China)

    2015-12-15

    The capacity of passive metal to repassivate after film damage determines the development of local corrosion and the resistance to corrosion failures. In this work, the repassivation kinetics of 316L stainless steel (316L SS) was investigated in borate buffer solution (pH 9.1) using a novel abrading electrode technique. The repassivation kinetics was analyzed in terms of the current density flowing from freshly bare 316L SS surface as measured by a potentiostatic method. During the early phase of decay (t < 2 s), according to the Avrami kinetics-based film growth model, the transient current was separated into anodic dissolution (i{sub diss}) and film formation (i{sub film}) components and analyzed individually. The film reformation rate and thickness were compared according to applied potential. Anodic dissolution initially dominated the repassivation for a short time, and the amount of dissolution increased with increasing applied potential in the passive region. Film growth at higher potentials occurred more rapidly compared to at lower potentials. Increasing the applied potential from 0 V{sub SCE} to 0.8 V{sub SCE} resulted in a thicker passive film (0.12 to 0.52 nm). If the oxide monolayer covered the entire bare surface (θ=1), the electric field strength through the thin passive film reached 1.6 x 10{sup 7} V/cm.

  14. Synthesis, electrochemical, spectrophotometric and potentiometric studies of two azo-compounds derived from 4-amino-2-methylquinoline in ethanolic-aqueous buffered solutions

    Energy Technology Data Exchange (ETDEWEB)

    El-Attar, Mona A.; Ghoneim, Mohamed M. [Analytical Chemistry Research Unit, Chemistry Department, Tanta University (Egypt); Ismail, Iqbal M., E-mail: maema.2011@yahoo.com [Chemistry Department, Faculty of Science, King Abdul Aziz University, Jeddah (Saudi Arabia)

    2012-08-15

    Two azo-compounds, 2-methyl-4-(5-amino-2-hydroxy-phenylazo)-quinoline (2) and 2-methyl-4-(2-hydroxy-5-nitrophenylazo)-quinoline, derived from 4-amino-2-methylquinoline were synthesized. Their chemical structures were characterized and confirmed by means of elemental chemical analysis, infrared (IR) spectroscopy, {sup 1}H nuclear magnetic resonance (NMR) and mass spectrometry (MS). The electrochemical behavior of the starting compound (4-amino-2-methylquinoline) and of the two synthesized azo-derivatives was studied at the mercury electrode in the B-R universal buffer at various pH values (2-11.5) containing 40% (v/v) ethanol using dc-polarography, cyclic voltammetry and controlled-potential coulometry. Their electrode reaction pathways were elucidated and discussed. The dissociation constants (pKa) of the examined compounds, stability constants and stoichiometry of their complexes in solution with some transition metal ions (Co(II), Ni(II), Cu(II), La(III) and UO{sup 2+}{sub 2}) were determined. (author)

  15. Shock-induced devolatilization of calcite

    Science.gov (United States)

    Boslough, M. B.; Ahrens, T. J.; Vizgirda, J.; Becker, R. H.; Epstein, S.

    1982-01-01

    Experimental measurements of the release adiabats by Vizgirda (1981) indicate that substantial vaporization takes place upon release from shock pressures of 37 GPa for calcite and 14 GPa for aragonite. The present investigation includes the first controlled partial vaporization experiments on calcite. The experiments were conducted to test the predictions of the release adiabat experiments. The quantities of the gaseous species produced from shocked calcite and their carbon and oxygen isotopic compositions were determined, and the shock-induced effect on the Mn(2+) electron spin resonance spectrum in the shock-recovered calcite was observed. On the basis of the obtained results, it is concluded that shock stresses at the 17-18 GPa level give rise to volatilization of 0.03-0.3 (mole) percent of calcite to CO2 and CO. The devolatilization of calcite occurs at low pressure at significantly lower entropy densities than predicted on the basis of thermodynamic continuum models.

  16. Development of a four-zone carousel process packed with metal ion-imprinted polymer for continuous separation of copper ions from manganese ions, cobalt ions, and the constituent metal ions of the buffer solution used as eluent.

    Science.gov (United States)

    Jo, Se-Hee; Park, Chanhun; Yi, Sung Chul; Kim, Dukjoon; Mun, Sungyong

    2011-08-19

    A three-zone carousel process, in which Cu(II)-imprinted polymer (Cu-MIP) and a buffer solution were employed as adsorbent and eluent respectively, has been developed previously for continuous separation of Cu²⁺ (product) from Mn²⁺ and Co²⁺ (impurities). Although this process was reported to be successful in the aforementioned separation task, the way of using a buffer solution as eluent made it inevitable that the product stream included the buffer-related metal ions (i.e., the constituent metal ions of the buffer solution) as well as copper ions. For a more perfect recovery of copper ions, it would be necessary to improve the previous carousel process such that it can remove the buffer-related metal ions from copper ions while maintaining the previous function of separating copper ions from the other 2 impure heavy-metal ions. This improvement was made in this study by proposing a four-zone carousel process based on the following strategy: (1) the addition of one more zone for performing the two-step re-equilibration tasks and (2) the use of water as the eluent of the washing step in the separation zone. The operating conditions of such a proposed process were determined on the basis of the data from a series of single-column experiments. Under the determined operating conditions, 3 runs of carousel experiments were carried out. The results of these experiments revealed that the feed-loading time was a key parameter affecting the performance of the proposed process. Consequently, the continuous separation of copper ions from both the impure heavy-metal ions and the buffer-related metal ions could be achieved with a purity of 91.9% and a yield of 92.8% by using the proposed carousel process based on a properly chosen feed-loading time.

  17. Programmable pH buffers

    Science.gov (United States)

    Gough, Dara Van; Huber, Dale L.; Bunker, Bruce C.; Roberts, Mark E.

    2017-01-24

    A programmable pH buffer comprises a copolymer that changes pK.sub.a at a lower critical solution temperature (LCST) in water. The copolymer comprises a thermally programmable polymer that undergoes a hydrophobic-to-hydrophilic phase change at the LCST and an electrolytic polymer that exhibits acid-base properties that are responsive to the phase change. The programmable pH buffer can be used to sequester CO.sub.2 into water.

  18. Interactions of arsenic with calcite surfaces revealed by in situ nanoscale imaging

    Science.gov (United States)

    Renard, François; Putnis, Christine V.; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hovelmann, Jörn; Sarret, Géraldine

    2015-06-01

    Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments calcite may play an important role in arsenic solubility and transfer in water. Arsenic-calcite interactions remain controversial, especially for As(III) which was proposed to be either incorporated as such, or as As(V) after oxidation. Here, we provide the first time-lapse in situ study of the evolution of the (10-14) calcite cleavage surface morphology during dissolution and growth in the presence of solutions with various amounts of As(III) or As(V) at room temperature and pH range 6-11 using a flow-through cell connected to an atomic force microscope (AFM). Reaction products were then characterized by Raman spectroscopy. In parallel, co-precipitation experiments with either As(III) or As(V) were performed in batch reactors, and the speciation of arsenic in the resulting solids was studied by X-ray absorption spectroscopy (XAS). For As(V), AFM results showed that it interacts strongly with the calcite surface, and XAS results showed that As(V) was mostly incorporated in the calcite structure. For As(III), AFM results showed much less impact on calcite growth and dissolution and less incorporation was observed. This was confirmed by XAS results that indicate that As(III) was partly oxidized into As(V) before being incorporated into calcite and the resulting calcite contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with calcite than As(III) and that calcite may represent an important reservoir for arsenic in various geological environments.

  19. 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 calcite, the predicted pKa for deprotonation is 7.5, which is ∼3 pH units lower than in aqueous solution...

  20. The Effect of the Ca2+: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...

  1. 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...

  2. 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.

  3. Arsenite sorption and co-precipitation with calcite

    CERN Document Server

    Roman-Ross, Gabriela; Turrillas, Xavier; Fernandez-Martinez, Alejandro; Charlet, Laurent

    2008-01-01

    Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3 degrees is adsorbed by complexation to surface Ca surface sites, as previously described by the X-ray standing wave technique. The inflexion point of the isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST), yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this value, the amount of sorbed arsenic increases linearly with solution concentration, up to the saturation of arsenic with respect to the precipitation of CaHAsO3(s). The solid solutions formed in this concentration range were examined by X-ray and neutron diffraction. The doped calcite lattice parameters increase with arsenic content while c/a ratio remains constant. Our results made on bulk calcite on...

  4. Adaptively biased sequential importance sampling for rare events in reaction networks with comparison to exact solutions from finite buffer dCME method.

    Science.gov (United States)

    Cao, Youfang; Liang, Jie

    2013-07-14

    Critical events that occur rarely in biological processes are of great importance, but are challenging to study using Monte Carlo simulation. By introducing biases to reaction selection and reaction rates, weighted stochastic simulation algorithms based on importance sampling allow rare events to be sampled more effectively. However, existing methods do not address the important issue of barrier crossing, which often arises from multistable networks and systems with complex probability landscape. In addition, the proliferation of parameters and the associated computing cost pose significant problems. Here we introduce a general theoretical framework for obtaining optimized biases in sampling individual reactions for estimating probabilities of rare events. We further describe a practical algorithm called adaptively biased sequential importance sampling (ABSIS) method for efficient probability estimation. By adopting a look-ahead strategy and by enumerating short paths from the current state, we estimate the reaction-specific and state-specific forward and backward moving probabilities of the system, which are then used to bias reaction selections. The ABSIS algorithm can automatically detect barrier-crossing regions, and can adjust bias adaptively at different steps of the sampling process, with bias determined by the outcome of exhaustively generated short paths. In addition, there are only two bias parameters to be determined, regardless of the number of the reactions and the complexity of the network. We have applied the ABSIS method to four biochemical networks: the birth-death process, the reversible isomerization, the bistable Schlögl model, and the enzymatic futile cycle model. For comparison, we have also applied the finite buffer discrete chemical master equation (dCME) method recently developed to obtain exact numerical solutions of the underlying discrete chemical master equations of these problems. This allows us to assess sampling results objectively

  5. 缓冲液对微生物燃料电池产电性能影响研究%Influence of Buffer Solutions on the Performance of Microbial Fuel Cell Electricity Generation

    Institute of Scientific and Technical Information of China (English)

    强琳; 袁林江; 丁擎

    2011-01-01

    微生物燃料电池(microbial fuel cell,MFC)应用于废水处理是一项非常有潜力的除污产能的绿色技术.但MFC运行过程中采用磷酸盐缓冲液不符合除污产能要求,增加水体富营养化趋势且增加水处理成本.试验采用单极室微生物燃料电池处理模拟生活污水,以投加PBS(phosphate buffer solution)缓冲液为参比对象,讨论了投加硼砂缓冲液和无缓冲液对产电功率、库仑效率以及出水pH的影响.200 mmol/L的PBS缓冲液电导率为1.973 mS/cm,最大输出功率为36.4 mW/m2,最大库仑效率为2.92%,出水pH为(7.00±0.05).100 mmol/L的硼砂缓冲液的导电率为1.553 mS/cm,输出功率最大26.2 mW/m2,库仑效率为6.26%,是PBS缓冲液库仑效率的2.14倍,显著地提高了电子回收率,出水pH为7.35.无缓冲液电导率为0.314 mS/cm,最大输出功率为27.64 mW/m2,库仑效率为2.82%,出水pH约为7.43.不投加缓冲液的电导率仅为投加PBS缓冲液的1/6,硼砂缓冲液的1/5,功率比PBS低8.76 mW/m2,比硼砂缓冲液高1.24 mW/m2.试验结果表明投加适宜浓度的硼砂缓冲液可大大提高电子回收率,不投加缓冲液MFC在间歇运行模式下可成功运行.%Microbial fuel cell (MFC) is a potential green technology due to its application in wastewater treatment and renewable energy generation. Phosphate buffer solution (PBS) has been commonly used in MFC studies to maintain a suitable pH for electricity generating bacteria and/or to increase the solution conductivity. However, it has some drawbacks using PBS in MFC: One is that the addition of a high concentration of phosphate buffer in MFCs is expensive, especially for the application in wastewater treatment; the other is that phosphates can contribute to the eutrophication conditions of water bodies if the effluents are discharged without the removal of phosphates. By adding PBS buffer as the comparison , the study investigated the effect of borax buffer and in the absence of buffer on

  6. Calcite Formation in Soft Coral Sclerites Is Determined by a Single Reactive Extracellular Protein*

    Science.gov (United States)

    Rahman, M. Azizur; Oomori, Tamotsu; Wörheide, Gert

    2011-01-01

    Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called “calcite and aragonite seas.” Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce calcite despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form calcitic skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces calcite formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single crystals generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of calcite instead of aragonite in the biocalcification process and that –OH, secondary structures (e.g. α-helices and amides), and other necessary chemical groups are distributed over the center of the calcite crystals. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of crystal formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different calcite-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the crystal structure of calcite in nature. PMID:21768106

  7. Calcite formation in soft coral sclerites is determined by a single reactive extracellular protein.

    Science.gov (United States)

    Rahman, M Azizur; Oomori, Tamotsu; Wörheide, Gert

    2011-09-09

    Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called "calcite and aragonite seas." Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce calcite despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form calcitic skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces calcite formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single crystals generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of calcite instead of aragonite in the biocalcification process and that -OH, secondary structures (e.g. α-helices and amides), and other necessary chemical groups are distributed over the center of the calcite crystals. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of crystal formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different calcite-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the crystal structure of calcite in nature.

  8. Fracture-aperture alteration induced by calcite precipitation

    Science.gov (United States)

    Jones, T.; Detwiler, R. L.

    2013-12-01

    Mineral precipitation significantly alters the transport properties of fractured rock. Chemical solubility gradients that favor precipitation induce mineral growth, which decreases the local aperture and alters preferential flow paths. Understanding the resulting development of spatial heterogeneities is necessary to predict the evolution of transport properties in the subsurface. We present experimental results that quantify the relationship between mineral precipitation and aperture alteration in a transparent analog fracture, 7.62cm x 7.62cm, with a uniform aperture of ~200 μm. Prior to flow experiments, a pump circulated a super-saturated calcite solution over the bottom glass, coating the glass surface with calcite. This method of seeding resulted in clusters of calcite crystals with large reactive surface area and provided micro-scale variability in the aperture field. A continuous flow syringe pump injected a reactive fluid into the fracture at 0.5 ml/min. The fluid was a mixture of sodium bicarbonate (NaHCO3, 0.02M) and calcium chloride (CaCl2 0.0004M) with a saturation index, Ω, of 8.51 with respect to calcite. A strobed LED panel backlit the fracture and a high-resolution CCD camera monitored changes in transmitted light intensity. Light transmission techniques provided a quantitative measurement of fracture aperture over the flow field. Results from these preliminary experiments showed growth near the inlet of the fracture, with decreasing precipitation rates in the flow direction. Over a period of two weeks, the fracture aperture decreased by 17% within the first 4mm of the inlet. Newly precipitated calcite bridged individual crystal clusters and smoothed the reacting surface. This observation is an interesting contradiction to the expectation of surface roughening induced by mineral growth. Additionally, the aperture decreased uniformly across the width of the fracture due to the initial aperture distribution. Future experiments of precipitation

  9. 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.

  10. Properties of Pb(0.92)La(0.08)Zr(0.52)Ti(0.48)O(3) thin films grown on SrRuO(3) buffered nickel and silicon substrates by chemical solution deposition

    Energy Technology Data Exchange (ETDEWEB)

    Narayanan, M.; Ma, B.; Tong, S.; Koritala, R.; Balachandran, U. (Energy Systems); ( MSD)

    2012-01-01

    Ferroelectric film-on-foil capacitors are suitable to replace discrete passive components in the quest to develop electronic devices that show superior performance and are smaller in size. The film-on-foil approach is the most practical method to fabricate such components. Films of Pb{sub 0.92}La{sub 0.08}Zr{sub 0.52}Ti{sub 0.48}O{sub 3} (PLZT) were deposited on SrRuO{sub 3} (SRO) buffer films over nickel and silicon substrates. High-quality polycrystalline SRO thin-film electrodes were first deposited by chemical solution deposition. A phase pure, dense, uniform microstructure with grain size <100 nm was obtained in films crystallized at 700 C. The room-temperature resistivity of the SRO films crystallized at 700 C was {approx}800-900 {mu}{Omega}-cm. The dielectric properties of sol-gel derived PLZT capacitors on SRO-buffered nickel were evaluated as a function of temperature, bias field, and frequency, and the results were compared to those of the same films on silicon substrates. The comparison demonstrated the integrity of the buffer layer and its compatibility with nickel substrates. Device-quality dielectric properties were measured on PLZT films deposited on SRO-buffered nickel foils and found to be superior to those for PLZT on SRO-buffered silicon and expensive platinized silicon. These results suggest that SRO films can act as an effective barrier layer on nickel substrates suitable for embedded capacitor applications.

  11. Dependence of Device Characteristics of Bulk-Heterojunction Organic Thin-Film Solar Cells on Concentration of Glycerol and Sorbitol Addition in Pedot:. PSS Solutions for Fabricating Buffer Layers

    Science.gov (United States)

    Yamaki, Yusuke; Marumoto, Kazuhiro; Fujimori, Takuya; Mori, Tatsuo

    We have investigated the dependence of device characteristics of bulk-heterojunction organic thin-film solar cells on the concentration of glycerol and sorbitol addition in poly(3,4-ethylenedioxy thiophene):poly(4-styrene sulfonate) (PEDOT:PSS) solutions for fabricating buffer layers. The device structure is ITO/buffer/regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM)/Al. Glycerol addition is effective for increasing power conversion efficiency (PCE) from 1.25 to 1.41% because of the increase in short-circuit current density (Jsc) without decreasing open-circuit voltage (Voc). On the other hand, sorbitol addition decreases PCE from 1.25 to 1.04%, owing to the decrease in Voc. This difference in Voc behavior is ascribed to different work function of PEDOT:PSS with glycerol and sorbitol treatment.

  12. 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 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....... 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...... results show that approximately 99% of 2300 mg/L fluoride can be removed when CO2 is injected directly into the barrier. This can be compared to approximately 30-50% removal when the influent solution is equilibrated with atmospheric CO2 before contact with calcite....

  13. Optimization of buffer injection for the effective bioremediation of chlorinated solvents in aquifers

    Science.gov (United States)

    Brovelli, A.; Robinson, C.; Barry, A.; Kouznetsova, I.; Gerhard, J.

    2008-12-01

    Various techniques have been proposed to enhance biologically-mediated reductive dechlorination of chlorinated solvents in the subsurface, including the addition of fermentable organic substrate for the generation of H2 as an electron donor. One rate-limiting factor for enhanced dechlorination is the pore fluid pH. Organic acids and H+ ions accumulate in dechlorination zones, generating unfavorable conditions for microbial activity (pH Science of the Total Environment, submitted), which computes the amount of additional buffer required to maintain the pH at a level suitable for bacterial activity for batch systems. The batch model was coupled to a groundwater flow/solute transport/chemical reaction simulator to permit buffer optimization computations within the context of flowing systems exhibiting heterogeneous hydraulic, physical and chemical properties. A suite of simulations was conducted in which buffer optimization was examined within the bounds of the minimum concentration necessary to sustain a pH favorable to microbial activity and the maximum concentration to avoid excessively high pH values (also not suitable to bacterial activity) and mineral precipitation (e.g., calcite, which may lead to pore-clogging). These simulations include an examination of the sensitivity of this buffer concentration range to aquifer heterogeneity and groundwater velocity. This work is part of SABRE (Source Area BioREmediation), a collaborative international research project that aims to evaluate and improve enhanced bioremediation of chlorinated solvent source zones. In this context, numerical simulations are supporting the upscaling of the technique, including identifying the most appropriate buffer injection strategies for field applications

  14. Cryogenic and non-cryogenic pool calcites reflect alternating permafrost and interglacial periods (Breitscheid-Erdbach Cave, Germany

    Directory of Open Access Journals (Sweden)

    D. K. Richter

    2010-07-01

    Full Text Available Weichselian cryogenic calcites collected in what is referred to as the "Rätselhalle" of the Breitscheid-Erdbach Cave were structurally classified as rhombohedral crystal and spherulitic crystal sinters. The carbon and oxygen isotopic composition of these precipitates corresponds to those of known cryogenic calcites of slow genesis of Central European caves (δ13C=+0.6 and −7.3‰; δ18O=−6.9 to −18.0‰. The variant carbon and oxygen isotope pattern differing between different caves is attributed to cave specific ventilation. Particularly, Breitscheid cryogenic calcites reflect mean levels of cave ventilation. By petrographic and geochemical comparisons of Weichselian cryogenic calcite with recent to sub-recent precipitates as well as Weichselian non-cryogenic calcites of the same locality, a model for the precipitation of these calcites is proposed. While the recent and sub-recent pool-calcites isotopically match the geochemistry of interglacial speleothems (stalagmites, etc., isotope ratios of Weichselian non-cryogenic pool-calcites reflect cooler conditions. Weichselian cryogenic calcites show a trend towards 18O-depleted values with higher carbon isotope ratios reflecting slow freezing of the precipitating solution. In essence, the isotope geochemistry of the Weichselian calcites reflects the climate history changing from overall initial permafrost (glacial conditions to an interglacial and subsequently to renewed permafrost conditions. The last stage then grades into the present-day warm period. Judging from the data compiled here, the last permafrost stage is followed by only one interglacial. During this interglacial, the cave ice melted and non-cryogenic Weichselian calcite precipitates were deposited on the cave ground or on fallen blocks, respectively.

  15. Are buffers boring? Uniqueness and asymptotical stability of traveling wave fronts in the buffered bistable system.

    Science.gov (United States)

    Tsai, Je-Chiang; Sneyd, James

    2007-04-01

    Traveling waves of calcium are widely observed under the condition that the free cytosolic calcium is buffered. Thus it is of physiological interest to determine how buffers affect the properties of calcium waves. Here we summarise and extend previous results on the existence, uniqueness and stability of traveling wave solutions of the buffered bistable equation, which is the simplest possible model of the upstroke of a calcium wave. Taken together, the results show that immobile buffers do not change the existence, uniqueness or stability of the traveling wave, while mobile buffers can eliminate a traveling wave. However, if a wave exists in the latter case, it remains unique and stable.

  16. 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.

  17. Study of Biomass Calcite as Fine Aggregate of Concrete

    Institute of Scientific and Technical Information of China (English)

    WANG Jian; YU Yan

    2012-01-01

    The possibility of using crushed oyster shell to partly replace the fine aggregate of concrete was evaluated. The compressive strength and slump of concrete mixture with different amount of crushed oyster shell were tested and thus the appropriate dosage was determined. Additionally, the compatibility with super plasticizer and the stability in NazSO4 solution were also discussed to prove the feasibility of oyster shell as fine aggregate of concrete. The microstructure of concrete was observed with XRD and SEM techniques. This research provides the basis for the application of waste biomass calcite.

  18. Hydrothermal replacement of calcite by Mg-carbonates

    Science.gov (United States)

    Jonas, Laura; Mueller, Thomas; Dohmen, Ralf

    2014-05-01

    The transport of heat and mass through the Earth's crust is coupled to mineral reactions and the exchange of isotopes and elements between different phases. Carbonate minerals are a major constituent of the Earth's crust and play an important role in different physical, chemical and even biological processes. In this experimental study, the element exchange reaction between calcite (CaCO3) and a Mg-rich fluid phase is investigated under hydrothermal conditions. Single crystals of calcite (2x2x2 mm) react with 1 ml of a 1 M MgCl2 solution at 200° C in a Teflon-lined steel autoclave for different times between one day and four weeks. The reaction leads to the formation of a porous reaction front and the pseudomorphic replacement of calcite by dolomite [CaMg(CO3)2] and magnesite (MgCO3). Scanning electron microscopy revealed that the reaction rim consists of small Mg-carbonate rhombs closely attached to each other, suggesting that the replacement reaction takes place by a dissolution-precipitation mechanism. Typically, the observed reaction front can be divided into two different domains. The outer part of the reaction rim, i.e. from the mineral surface in contact to the fluid inwards, consists of magnesite, whereas the inner part of the rim surrounding the unreacted calcite core consists of Ca-rich dolomite. The formation of a porous microstructure that varies in different parts of the reaction rim is a direct result of the large molar volume change induced by the replacement of calcite by magnesite and dolomite. The developing porosity therefore creates fluid pathways that promote the progress of the reaction front towards the unreacted core of the single crystal. Compositional profiles measured perpendicular to the mineral surface across the reactions rims using electron microprobe (EMPA) further revealed a compositional gradient within the reaction rim with regard to the structure-forming elements Mg and Ca. Here, the amount of Mg incorporated in both product

  19. Interaction of alcohols with the calcite surface

    DEFF Research Database (Denmark)

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

    2015-01-01

    . Controlling their growth requires complex polysaccharides. Polysaccharide activity depends on the functionality of OH groups, so to simplify the system in order to get closer to a molecular level understanding, we investigated the interaction of OH from a suite of alcohols with clean, freshly cleaved calcite......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...... with the calcite surface through the OH group, with their carbon chains sticking away in a standing-up orientation. Alcohol molecules are closely packed and form a well-ordered monolayer on the surface....

  20. 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.

  1. Effect of Mg on the Grain Growth and Dislocation Creep of Calcite

    Science.gov (United States)

    Xu, L.

    2004-12-01

    We tested the effect of variations in the amount of the solute impurity (Mg) on grain growth and strength of calcite aggregate. Synthetic marbles were produced by hot isostatic pressing mixtures of powders of calcite and dolomite at 850° C and 300 MPa confining pressure for different intervals (2 to 30 hrs). The HIP treatment resulted in homogeneous aggregates of calcite with Mg content from 0.5 to 17 mol%. Stress stepping tests and constant strain rate tests were used to examine the effect of Mg content on the dislocation creep of calcite. The grain growth rate under static conditions was decreased with Mg content from 7 to 17 mol%, indicating perhaps that grain boundary mobility is suppressed by the solute drag effect. In the diffusion creep at stresses below 40 Mpa, the strength of calcite decreases with increasing Mg content owing to the difference in grain size at 800° C and 300 MPa confining pressure. The contribution of dislocation creep increases with increasing stress, and the transition between diffusion and dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. The creep data were fit assuming a composite flow law consisting of a linear combination of diffusion and dislocation creep and a single-valued grain size. The best agreement was obtained by using a dislocation creep law with exponential dependence of strain rate on stress (e.g. Peierls law). More evidence from microstructure is needed to identify the dominant deformation mechanism conclusively. Most of the samples were compressed up to strains of 0.25; small recrystallized grains are formed resulting in a bimodal grain size distribution in some of the deformed samples. Preliminary data shows that the recrystallized grain sizes are smaller for Mg-calcite compared with that of pure calcite. This study will help to understand the effect of impurities on grain-growth kinetics and strain weakening in localized shear zones.

  2. Cyclic Cratonic Carbonates and Phanerozoic Calcite Seas.

    Science.gov (United States)

    Wilkinson, Bruce H.

    1982-01-01

    Discusses causes of cyclicity in cratonic carbonate sequences and evidence for and potential significance of postulated primary calcite sediment components in past Paleozoic seas, outlining problems, focusing on models explaining existing data, and identifying background. Future sedimentary geologists will need to address these and related areas…

  3. 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.

  4. Heterogeneous growth of cadmium and cobalt carbonate phases at the (101¯4) calcite surface

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Man; Ilton, Eugene S.; Engelhard, Mark H.; Qafoku, Odeta; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.

    2015-03-01

    The ability of surface precipitates to form heteroepitaxially is an important factor that controls the extent of heterogeneous growth. In this work, the growth of cadmium and cobalt carbonate phases on (10-14) calcite surfaces is compared for a range of initial saturation states with respect to otavite (CdCO3) and sphaerocobaltite (CoCO3), two isostructural metal carbonates that exhibit different lattice misfits with respect to calcite. Calcite single crystals were reacted in static conditions for 16 hours with CdCl2 and CoCl2 aqueous solutions with initial concentrations 0.3 ≤ [Cd2+]0 ≤ 100 μM and 25 ≤ [Co2+]0 ≤ 200 μM. The reacted crystals were imaged in situ with atomic force microscopy (AFM) and analyzed ex situ with X-ray photoelectron spectroscopy (XPS). AFM images of Cd-reacted crystals showed the formation of large islands elongated along the direction, clear evidence of heteroepitaxial growth, whereas surface precipitates on Co-reacted crystals were small round islands. Deformation of calcite etch pits in both cases indicated the incorporation of Cd and Co at step edges. XPS analysis pointed to the formation of a Cd-rich (Ca,Cd)CO3 solid solution coating atop the calcite substrate. In contrast, XPS measurements of the Co-reacted crystals provided evidence for the formation of a mixed hydroxy-carbonate cobalt phase. The combined AFM and XPS results suggest that the lattice misfit between CoCO3 and CaCO3 ( 15% based on surface areas) is too large to allow for heteroepitaxial growth of a pure cobalt carbonate phase on calcite surfaces in aqueous solutions and at ambient conditions. The use of the satellite structure of the Co 2p3/2 photoelectron line as a tool for determining the nature of cobalt surface precipitates is also discussed.

  5. 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...... of the mineral particulate state (Xcryst) and, for calcite, have a 2nd order dependency (exponent n ¼ 2.05 ± 0.29) on thermodynamic supersaturation (s). Parameter analysis indicated that the model was more tolerant to a fast kinetic coefficient (kcryst) and so, in general, it is recommended that a large kcryst...

  6. Comparison of kinetic models to describe high pressure and gamma irradiation used to inactivate Vibrio vulnificus and Vibrio parahaemolyticus prepared in buffer solution and in whole oysters.

    Science.gov (United States)

    Hu, Xiaopei; Mallikarjunan, Parameswarakumar; Koo, Jaheon; Andrews, Linda S; Jahncke, Michael L

    2005-02-01

    Comparisons of different models in inactivation kinetics were conducted on data obtained from high-pressure and gamma-irradiation processing. Vibrio vulnificus (MO-624) and Vibrio parahaemolyticus (O3:K6 TX-2103) suspended in phosphate-buffered saline (pH 7.4, 10(7) CFU/ml) were exposed to pressures from 207 to 379 MPa for 1 to 20 min. Inoculated whole oysters (106 CFU/g) were exposed to pressure from 276 to 379 MPa for 1 to 15 min. Pure cultures and inoculated oysters (10(6) CFU/g) also were irradiated (gamma irradiation) at doses of less than 3 kGy. Four mathematical models, the Bigelow model, Arrhenius equation, Fermi equation, and Weibull frequency distributions, were applied to microbial survival data, and performances of the different kinetic models were compared. Weibull frequency distributions can predict the high-pressure inactivation of Vibrio spp. with more accuracy in both pure cultures and inoculated oyster samples. The Fermi model provided a better description of gamma-irradiation inactivation kinetics compared with the traditional Bigelow model.

  7. 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 presenc

  8. Trace concentration - Huge impact: Nitrate in the calcite/Eu(III) system

    Science.gov (United States)

    Hofmann, Sascha; Voïtchovsky, Kislon; Schmidt, Moritz; Stumpf, Thorsten

    2014-01-01

    The interactions of trivalent lanthanides and actinides with secondary mineral phases such as calcite is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially calcite has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of calcite crystals. NaNO3 causes serious modifications even in trace amounts (surface layer of low crystallinity on top of the calcite crystal. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in calcite must take into account the presence of nitrate in pore and ground waters.

  9. The passive oxide films growth on 316L stainless steel in borate buffer solution measured by real-time spectroscopic ellipsometry

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Haisong; Wang, Lu; Sun, Dongbai [National Center for Materials Service Safety (NCMS), University of Science and Technology Beijing, Beijing 100083 (China); Yu, Hongying, E-mail: hyyu@ustb.edu.cn [Institute of Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-10-01

    Highlights: • The optical properties of passive oxide films on 316L stainless steel were studied. • The thickness of the oxide films (1.5–2.6 nm) increased linearly with the potentials. • The growth of passive film followed high electric field ion conduction model. • Selective solubility of oxide induced compositional change of passive film. - Abstract: Passive film growth on 316L stainless steel was investigated in borate buffer electrolyte (pH = 9.1) by real-time spectroscopic ellipsometry (SE) and the composition was estimated by X-ray photoelectron spectroscopy (XPS). Anodic passivation of 316L SS was carried out in the potential range from 0 V{sub SCE} to 0.9 V{sub SCE}, after potentiostatic polarization for 1800s, the current density decayed from 10{sup −2} A cm{sup −2} to 10{sup −6} A cm{sup −2}. The passive film thickness was simulated from Frenel and Drude reflection equations, the average complex refractive index was assumed to be N = 2.3 − j0.445. The estimated thickness increased linearly with potential from 1.5 nm at 0 V to 2.6 nm at 0.8 V. The growth of passive film followed high electric field ion conduction model. The passive film mainly contained the oxide/hydroxide of iron and chromium. The selective solubility of oxide in passive film explained the change of iron and chromium content at different potentials. Few nickel and molybdenum also contributed to the passive film with a constant content.

  10. Common data buffer

    Science.gov (United States)

    Byrne, F.

    1981-01-01

    Time-shared interface speeds data processing in distributed computer network. Two-level high-speed scanning approach routes information to buffer, portion of which is reserved for series of "first-in, first-out" memory stacks. Buffer address structure and memory are protected from noise or failed components by error correcting code. System is applicable to any computer or processing language.

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

    Science.gov (United States)

    Reddy, Michael M.

    2012-01-01

    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.

  12. 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.

  13. Acceleration of calcite kinetics by abalone nacre proteins

    Energy Technology Data Exchange (ETDEWEB)

    Fu, G; Qiu, S R; Orme, C A; Morse, D E; De Yoreo, J J

    2005-06-09

    The fascinating shapes and hierarchical designs of biomineralized structures have long been an inspiration to materials scientists because of the potential they suggest for biomolecular control over synthesis of crystalline materials. One prevailing view is that mineral-associated macromolecules are responsible for initiating and stabilizing non-equilibrium crystal polymorphs and morphologies through interactions between anionic moieties and cations in solution or at mineral surfaces. Indeed, numerous studies have demonstrated that bio-organic additives can dramatically alter crystal shapes and growth-rates in vitro. However, previous molecular-scale studies revealing mechanisms of growth modification focused on small molecules such as amino acids or peptides and always observed growth inhibition. In contrast, studies using full proteins were non-quantitative and underlying sources of growth modification were ill-defined. Here we investigate interactions between proteins isolated from abalone shell nacre and growing surfaces of calcite. We find that these proteins significantly accelerate the molecular-scale kinetics and, though much larger than atomic steps, alter growth morphology through step-specific interactions that lower their free energies. We propose that these proteins act as surfactants to promote ion attachment at calcite surfaces.

  14. The role of background electrolytes on the kinetics and mechanism of calcite dissolution

    Science.gov (United States)

    Ruiz-Agudo, E.; Kowacz, M.; Putnis, C. V.; Putnis, A.

    2010-02-01

    The influence of background electrolytes on the mechanism and kinetics of calcite dissolution was investigated using in situ Atomic Force Microscopy (AFM). Experiments were carried out far from equilibrium by passing alkali halide salt (NaCl, NaF, NaI, KCl and LiCl) solutions over calcite cleavage surfaces. This AFM study shows that all the electrolytes tested enhance the calcite dissolution rate. The effect and its magnitude is determined by the nature and concentration of the electrolyte solution. Changes in morphology of dissolution etch pits and dissolution rates are interpreted in terms of modification in water structure dynamics (i.e. in the activation energy barrier of breaking water-water interactions), as well as solute and surface hydration induced by the presence of different ions in solution. At low ionic strength, stabilization of water hydration shells of calcium ions by non-paired electrolytes leads to a reduction in the calcite dissolution rate compared to pure water. At high ionic strength, salts with a common anion yield similar dissolution rates, increasing in the order Cl - salts with a common cation due to an increasing mobility of water around the calcium ion. Changes in etch pit morphology observed in the presence of F - and Li + are explained by stabilization of etch pit edges bonded by like-charged ions and ion incorporation, respectively. As previously reported and confirmed here for the case of F -, highly hydrated ions increased the etch pit nucleation density on calcite surfaces compared to pure water. This may be related to a reduction in the energy barrier for etch pit nucleation due to disruption of the surface hydration layer.

  15. 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.

  16. A parallel buffer tree

    DEFF Research Database (Denmark)

    Sitchinava, Nodar; Zeh, Norbert

    2012-01-01

    We present the parallel buffer tree, a parallel external memory (PEM) data structure for batched search problems. This data structure is a non-trivial extension of Arge's sequential buffer tree to a private-cache multiprocessor environment and reduces the number of I/O operations by the number...... of available processor cores compared to its sequential counterpart, thereby taking full advantage of multicore parallelism. The parallel buffer tree is a search tree data structure that supports the batched parallel processing of a sequence of N insertions, deletions, membership queries, and range queries...

  17. Development of One Meter Long Double-Sided CeO2 Buffered Ni-5at.%W Templates by Reel-to-Reel Chemical Solution Deposition Route

    DEFF Research Database (Denmark)

    Yue, Zhao; Konstantopoulou, K.; Wulff, Anders Christian

    2013-01-01

    High performance long-length coated conductors fabricated using various techniques have attracted a lot of interest recently. In this work, a reel-to-reel design for depositing double-sided coatings on long-length flexible metallic tapes via a chemical solution method is proposed and realized....... The major achievement of the design is to combine the dip coating and drying processes in order to overcome the technical difficulties of dealing with the wet films on both sides of the tape. We report the successful application of the design to fabricate a one-meterlong double side coated CeO2/Ni − 5at...... layer are 7.2◦ and 5.8◦ with standard deviation of 0.26◦ and 0.34◦, respectively, being indicative of the high quality epitaxial growth of the films prepared in the continuous manner. An all chemical solution derived YBCOLow−TFA/Ce0.9La0.1O2/Gd2Zr2O7/CeO2 structure is obtained on a short sample...

  18. Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the Calcite (101¯4) Surface

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10-14) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  19. Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the calcite (10 1bar 4) surface

    Science.gov (United States)

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10 1bar 4) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  20. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    Energy Technology Data Exchange (ETDEWEB)

    Gorman, Brian P [Colorado School of Mines, Golden, CO (United States)

    2015-09-02

    Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, pCO2, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of calcite precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO2, Ca2+, ionic strength and “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO2 in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable seed layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on calcite substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer

  1. Buffers more than buffering agent: introducing a new class of stabilizers for the protein BSA.

    Science.gov (United States)

    Gupta, Bhupender S; Taha, Mohamed; Lee, Ming-Jer

    2015-01-14

    In this study, we have analyzed the influence of four biological buffers on the thermal stability of bovine serum albumin (BSA) using dynamic light scattering (DLS). The investigated buffers include 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES), 4-(2-hydroxyethyl)-1-piperazine-propanesulfonic acid (EPPS), 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid sodium salt (HEPES-Na), and 4-morpholinepropanesulfonic acid sodium salt (MOPS-Na). These buffers behave as a potential stabilizer for the native structure of BSA against thermal denaturation. The stabilization tendency follows the order of MOPS-Na > HEPES-Na > HEPES ≫ EPPS. To obtain an insight into the role of hydration layers and peptide backbone in the stabilization of BSA by these buffers, we have also explored the phase transition of a thermoresponsive polymer, poly(N-isopropylacrylamide (PNIPAM)), a model compound for protein, in aqueous solutions of HEPES, EPPS, HEPES-Na, and MOPS-Na buffers at different concentrations. It was found that the lower critical solution temperatures (LCST) of PNIPAM in the aqueous buffer solutions substantially decrease with increase in buffer concentration. The mechanism of interactions between these buffers and protein BSA was probed by various techniques, including UV-visible, fluorescence, and FTIR. The results of this series of studies reveal that the interactions are mainly governed by the influence of the buffers on the hydration layers surrounding the protein. We have also explored the possible binding sites of BSA with these buffers using a molecular docking technique. Moreover, the activities of an industrially important enzyme α-chymotrypsin (α-CT) in 0.05 M, 0.5 M, and 1.0 M of HEPES, EPPS, HEPES-Na, and MOPS-Na buffer solutions were analyzed at pH = 8.0 and T = 25 °C. Interestingly, the activities of α-CT were found to be enhanced in the aqueous solutions of these investigated buffers. Based upon the Jones-Dole viscosity parameters, the

  2. Characterisation of passive films formed on low carbon steel in borate buffer solution (pH 9.2) by electrochemical impedance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hamadou, L. [Laboratoire de Materiaux, Electrochimie et Corrosion, Universite Mouloud MAMMERI de, Tizi-Ouzou, B.P. 17 (15000) (Algeria)]. E-mail: lamhama@yahoo.fr; Kadri, A. [Laboratoire de Materiaux, Electrochimie et Corrosion, Universite Mouloud MAMMERI de, Tizi-Ouzou, B.P. 17 (15000) (Algeria); Benbrahim, N. [Laboratoire de Materiaux, Electrochimie et Corrosion, Universite Mouloud MAMMERI de, Tizi-Ouzou, B.P. 17 (15000) (Algeria)

    2005-12-15

    The comprehension of passivity and its protective character against corrosion is closely connected with the electronic properties of passive films. Passive films formed anodically on carbon steel in borate/boric acid solution, pH 9.2, have been characterised by electrochemical impedance spectroscopy (EIS). Mott-Schottky plots and impedance measurements were made on films formed at different potentials and times. The investigation allowed the determination of the semiconductive properties of the films. The results of the capacitance response indicate that the passive films behave like highly doped n-type semiconductors, showing that the passive film properties are dominated by iron. The value of donors density (N {sub D}) for the passive film is of the order of 10{sup 21} cm{sup -3} and decreases with increasing formation time and potential, indicating that defects decrease with increasing film thickness. Based on the information about the physical phenomena, an equivalent circuit is proposed to fit the experimental data, leading to determination of anodic film capacitance and film resistance.

  3. 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.

  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.

  5. 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.

    2017-01-01

    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. PMID:28262764

  6. 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.

  7. Synthesis and characterization of spider silk calcite composite

    Directory of Open Access Journals (Sweden)

    Svetlana Dmitrović

    2016-03-01

    Full Text Available Spider silk poses excellent mechanical properties, tenacity and elasticity and it has been used as a template for calcite mineralization to improve load bearing strength of osteoconductive calcite. The samples were obtained by mimicking biomineralization for five days in order to follow formation and growth of calcite on the surface of spider silk. Crystal phase was detected by XRD and FTIR spectroscopy. Microstructure, crystal size and its morphology were studied by means of FESEM. After two days of processing, pure calcite phase was obtained, and a size of the formed crystals increased with prolongation of biomineralization.

  8. Biogenic and synthetic high magnesium calcite - a review.

    Science.gov (United States)

    Long, Xia; Ma, Yurong; Qi, Limin

    2014-01-01

    Systematic studies on the Mg distributions, the crystal orientations, the formation mechanisms and the mechanical properties of biogenic high-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites in the hard tissues of marine organisms mentioned generally own a few common features as follows. Firstly, the Mg distribution is not uniform in most of the minerals. Secondly, high-Mg calcite biominerals are usually composed of nanoparticles that own almost the same crystallographic orientations and thus they behave like single crystals or mesocrystals. Thirdly, the formation of thermodynamically unstable high-Mg calcites in marine organisms under mild conditions is affected by three key factors, that is, the formation of amorphous calcium (magnesium) carbonate precursor, the control of polymorph via biomolecules and the high Mg/Ca ratios in modern sea. Lastly, the existence of Mg ions in the Mg-containing calcite may improve the mechanical properties of biogenic minerals. Furthermore, the key progress in the synthesis of high-Mg calcites in the laboratory based on the formation mechanisms of the biogenic high-Mg calcites was reviewed. Many researchers have realized the synthesis of high-Mg calcites in the laboratory under ambient conditions with the help of intermediate amorphous phase, mixed solvents, organic/inorganic surfaces and soluble additives. Studies on the structural analysis and formation mechanisms of thermodynamically unstable biogenic high-Mg calcite minerals may shed light on the preparation of functional materials with enhanced mechanical properties.

  9. Towards Optimal Buffer Size in Wi-Fi Networks

    KAUST Repository

    Showail, Ahmad J.

    2016-01-19

    Buffer sizing is an important network configuration parameter that impacts the quality of data traffic. Falling memory cost and the fallacy that ‘more is better’ lead to over provisioning network devices with large buffers. Over-buffering or the so called ‘bufferbloat’ phenomenon creates excessive end-to-end delay in today’s networks. On the other hand, under-buffering results in frequent packet loss and subsequent under-utilization of network resources. The buffer sizing problem has been studied extensively for wired networks. However, there is little work addressing the unique challenges of wireless environment. In this dissertation, we discuss buffer sizing challenges in wireless networks, classify the state-of-the-art solutions, and propose two novel buffer sizing schemes. The first scheme targets buffer sizing in wireless multi-hop networks where the radio spectral resource is shared among a set of con- tending nodes. Hence, it sizes the buffer collectively and distributes it over a set of interfering devices. The second buffer sizing scheme is designed to cope up with recent Wi-Fi enhancements. It adapts the buffer size based on measured link characteristics and network load. Also, it enforces limits on the buffer size to maximize frame aggregation benefits. Both mechanisms are evaluated using simulation as well as testbed implementation over half-duplex and full-duplex wireless networks. Experimental evaluation shows that our proposal reduces latency by an order of magnitude.

  10. Crystalline order of a water/glycine film coadsorbed on the (104) calcite surface.

    Science.gov (United States)

    Magdans, Uta; Torrelles, Xavier; Angermund, Klaus; Gies, Hermann; Rius, Jordi

    2007-04-24

    For biomineralization processes, the interaction of the surface of calcite crystals with organic molecules is of particular importance. Especially, biologically controlled biomineralization as in exoskeletons of mollusks and echinoderms, e.g., sea urchin with single-crystal-like spines and shells,1-3 requires molecular control of seed formation and growth process. So far, experiments showing the obvious influence of organic molecules on the morphology and habit of calcite crystals have demonstrated the molecular dimension of the interaction.4-7 Details of the kinetics of growth and dissolution of mineral surfaces influenced by additives are available,8,9 but other experimental data about the structure of the organic/inorganic interface on the atomic scale are rare. On the other hand, complicated organic macromolecules which are involved in biomineralization are numerous, with only a small fraction solved in structure and function so far.10-13 Therefore, model systems have to be designed to provide a basic understanding for the interaction process.14 Using grazing incidence X-ray diffraction combined with molecular modeling techniques, we show that glycine molecules order periodically on the calcite (104) face in competition with the solvent water when exposed to an aqueous solution of the most simple amino acid. In contrast to the general concept of the charge-matching fit of organic molecules on mineral surfaces,4,14 glycine is not attached to the calcite surface directly but substitutes for water molecules in the second hydration layer.

  11. Dissolution and Sorption Processes on the Surface of Calcite in the Presence of High Co2+ Concentration

    Directory of Open Access Journals (Sweden)

    Jorge González-López

    2017-02-01

    Full Text Available The interaction of the calcite surface with Co2+-rich aqueous solutions ([Co2+aq]initial = 1000 ppm, i.e., ca. 17 mM was investigated by means of macroscopic experiments and surface spectroscopic techniques. In the case of the macroscopic experiments, calcite powder and monocrystals were immersed into solutions for different time periods (from 1 min to one month. The Ca concentrations in the filtrates was measured by means of atomic absorption spectrometry (AAS while the interacted solids were studied using a combination of X-ray photoelectron spectroscopy (XPS and 12C-rutherford backscattering spectrometry (12C-RBS. The macroscopic data showed a characteristic surface dissolution process, in parallel to the surface sorption processes. Adsorption and co-precipitation were seen for almost the entire immersion period for both calcite powder and monocrystals. The surface study by XPS (analyzed at a depth of approximately 12 nm suggested that adsorption takes place in the first hour of the interaction, followed by incorporation of Co2+ into calcite surface layers, leading to the formation of a Co2+-bearing surface (coprecipitate, which occurs over a period of hours and days. The 12C-RBS measurements on calcite { 10 1 ¯ 4 } indicated that the thickness of this surface co-precipitate was 270 nm after one day and then stabilized at 320 nm after more than a week.

  12. Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate.

    Science.gov (United States)

    Kim, Yi-Yeoun; Hetherington, Nicola B J; Noel, Elizabeth H; Kröger, Roland; Charnock, John M; Christenson, Hugo K; Meldrum, Fiona C

    2011-12-23

    Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product.

  13. Cryogenic and non-cryogenic pool calcites indicating permafrost and non-permafrost periods: a case study from the Herbstlabyrinth-Advent Cave system (Germany

    Directory of Open Access Journals (Sweden)

    D. K. Richter

    2010-11-01

    Full Text Available Weichselian cryogenic calcites collected in what is referred to as the Rätselhalle of the Herbstlabyrinth-Advent Cave system are structurally classified as rhombohedral crystals and spherulitic aggregates. The carbon and oxygen isotopic composition of these precipitates (δ13C = +0.6 to −7.3‰ δ18O = −6.9 to −18.0‰ corresponds to those of known slowly precipitated cryogenic cave calcites under conditions of isotopic equilibrium between water and ice of Central European caves. The carbon and oxygen isotopic composition varies between different caves which is attributed to the effects of cave air ventilation before the freezing started.

    By petrographic and geochemical comparisons of Weichselian cryogenic calcite with recent to sub-recent precipitates as well as Weichselian non-cryogenic calcites of the same locality, a model for the precipitation of these calcites is proposed. While the recent and sub-recent pool-calcites isotopically match the composition of interglacial speleothems (stalagmites, etc., isotope ratios of Weichselian non-cryogenic pool-calcites reflect cooler conditions. Weichselian cryogenic calcites show a trend towards low δ18O values with higher carbon isotope ratios reflecting slow freezing of the precipitating solution. In essence, the isotope geochemistry of the Weichselian calcites reflects the climate history changing from overall initial permafrost conditions to permafrost-free and subsequently to renewed permafrost conditions. Judging from the data compiled here, the last permafrost stage in the Rätselhalle is followed by a warm period (interstadial and/or Holocene. During this warmer period, the cave ice melted and cryogenic and non-cryogenic Weichselian calcite precipitates were deposited on the cave ground or on fallen blocks, respectively.

  14. Degradation of Fipronil in Aqueous Buffer Solutions

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    @@1 Introduction Currently there are as many pesticides as there are pests,but still some more chemical compounds are continuously being synthesized and introduced as new pesticides.Fipronil is one fo the recently developed pesticides and belongs to a relatively new phenylpyrazole class of insecticides that is active at the neuro-inhibitory

  15. Transformation of amorphous calcium carbonate to rod-like single crystal calcite via "copying" collagen template.

    Science.gov (United States)

    Xue, Zhonghui; Hu, Binbin; Dai, Shuxi; Du, Zuliang

    2015-10-01

    Collagen Langmuir films were prepared by spreading the solution of collagen over deionized water, CaCl2 solution and Ca(HCO3)2 solution. Resultant collagen Langmuir monolayers were then compressed to a lateral pressure of 10 mN/m and held there for different duration, allowing the crystallization of CaCO3. The effect of crystallization time on the phase composition and microstructure of CaCO3 was investigated. It was found that amorphous calcium carbonate (ACC) was obtained at a crystallization time of 6 h. The amorphous CaCO3 was transformed to rod-like single crystal calcite crystals at an extended crystallization time of 12 h and 24 h, via "copying" the symmetry and dimensionalities of collagen fibers. Resultant calcite crystallites were well oriented along the longitudinal axis of collagen fibers. The ordered surface structure of collagen fibers and electrostatic interactions played key roles in tuning the oriented nucleation and growth of the calcite crystallites. The mineralized collagen possessing both desired mechanical properties of collagen fiber and good biocompatibility of calcium carbonate may be assembled into an ideal biomaterial for bone implants.

  16. Emission polarization study on quartz and calcite.

    Science.gov (United States)

    Vincent, R. K.

    1972-01-01

    Calculation of the spectral emission polarization of quartz and calcite polished plates for observation angles of 20 and 70 deg by the substitution of complex index of refraction values for each mineral into Fresnel's equations. The emission polarization is shown to be quite wavelength-dependent, demonstrating that selected narrow or medium-width spectral bands exhibit a significantly higher percentage of polarization than a broad spectral band for these two minerals. Field measurements with a broadband infrared radiometer yield polarizations on the order of 2% for a coarse-grained granite rock and beach sand (both quartz-rich). This implies that a more sensitive detector with a selected medium-width filter may be capable of measuring emission polarization accurately enough to make this parameter useful as a remote sensing tool for discrimination among rocks on the basis of texture.

  17. 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

  18. 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. Fir

  19. Variations in calcite growth kinetics with surface topography: molecular dynamics simulations and process-based growth kinetics modelling

    NARCIS (Netherlands)

    Wolthers, M.; Di Tommaso, D.; Du, Zhimei; de Leeuw, Nora H.

    2013-01-01

    It is generally accepted that cation dehydration is the rate-limiting step to crystal growth from aqueous solution. Here we employ classical molecular dynamics simulations to show that the water exchange frequency at structurally distinct calcium sites in the calcite surface varies by about two orde

  20. 3-吗啉丙磺酸缓冲的生理盐溶液的配制及pH稳定性%Preparation and pH stability of a physiological salt solution buffered with 3-Morpholine propanesulfonic acid

    Institute of Scientific and Technical Information of China (English)

    平娜娜; 曹蕾; 黄燕茹; 米燕妮; 曹永孝

    2012-01-01

    目的 配制以3-吗啉丙磺酸和Na2HPO4为缓冲对的生理盐溶液(MOPS液),并观察其pH稳定性及对大鼠离体血管张力的影响.方法 配制MOPS液和Krebs液及其母液,分别给MOPS液或Krebs液通O2或950 mL/L O2+50 mL/L CO2,用pH计测定pH值,用张力描记仪记录大鼠离体血管的张力.结果 MOPS液和K+-MOPS液14d内的pH变化为(7.32±0.04)~(7.51±0.04),基本恒定;Krebs液和K+ -Krebs液随时间延长,pH由7.40±0.01逐渐升至8.41±0.04.通气速度对MOPS液的pH影响小,变化范围为(7.24±0.04)~(7.39±0.00);Krebs液对通气速度敏感,在15~60个气泡/min,pH的变化范围在(6.81±0.07)~(8.33±0.02)之间,波动范围较大.在相同通气速度下MOPS液和Krebs液体积的变化对其pH影响小.大鼠离体的肠系膜动脉、脑基底动脉和冠状动脉在MOPS液中能产生良好的收缩.结论 MOPS液具有pH稳定、放置时间长、通气容易掌握,并且应用成本低的优点,可用于哺乳动物离体组织、器官如血管等实验.%To prepare a normal saline solution buffered with 3-morpholine propanesulfonic acid (MOPS), and to study its pH stability and its influence on rat artery rings isometric tension. Methods The MOPS solution, Krebs solution and their stock solutions were prepared, and aerated with O2 or 95% O2 + 5% CO2. The solutions' pH was measured by pH meter, and an isometric tension of rat artery rings was recorded by a sensitive myograph in vitro. Results The pH value of MOPS solution and K+-MOPS solution ranged steadily from 7.32+ 0.04 to 7.51 ±0.04 in 14 days. The pH value of Krebs solution and K+ -Krebs solution increased gradually from 7.40 ±0.01 to 8.41±0.04 over time and extended, and its fluctuation range was large. Aerating velocity had little effect on the pH of MOPS solution, which ranged from 7.24±0.04 to 7.39±0.00; while the pH value of Krebs solution was sensitive to aerating velocity, ranging from 6. 81 ±0.07 to 8.33 + 0.02 with a velocity of 15

  1. CaCO{sub 3}/Ca-P biphasic materials prepared by microwave processing of natural aragonite and calcite

    Energy Technology Data Exchange (ETDEWEB)

    Pena, J.; LeGeros, R.Z.; Rohanizadeh, R.; LeGeros, J.P. [New York Univ., NY (United States). Coll. of Dentistry

    2001-07-01

    The purpose of this study was to prepare CaCO{sub 3}/Ca-P biphasic or composite materials using microwave technology. Particles of coral (natural aragonite) and a porous limestone (natural calcite) were suspended in phosphate solutions of different pH and concentrations and heated for different periods (up to 5 hrs) using a domestic microwave. Parallel experiments were carried out using hydrolysis method. Higher extents of transformation were observed with microwave processed materials. Depending on the reaction pH and reaction period, partial transformation of aragonite (coral) or calcite (limestone) to acidic calcium (monetite) or basic (carbonatehydroxyapatite, CHA) calcium phosphates was achieved (orig.)

  2. An assessment of calcite crystal growth mechanisms based on crystal size distributions

    Science.gov (United States)

    Kile, D.E.; Eberl, D.D.; Hoch, A.R.; Reddy, M.M.

    2000-01-01

    Calcite crystal growth experiments were undertaken to test a recently proposed model that relates crystal growth mechanisms to the shapes of crystal size distributions (CSDs). According to this approach, CSDs for minerals have three basic shapes: (1) asymptotic, which is related to a crystal growth mechanism having constant-rate nucleation accompanied by surface-controlled growth; (2) lognormal, which results from decaying-rate nucleation accompanied by surface-controlled growth; and (3) a theoretical, universal, steady-state curve attributed to Ostwald ripening. In addition, there is a fourth crystal growth mechanism that does not have a specific CSD shape, but which preserves the relative shapes of previously formed CSDs. This mechanism is attributed to supply-controlled growth. All three shapes were produced experimentally in the calcite growth experiments by modifying nucleation conditions and solution concentrations. The asymptotic CSD formed when additional reactants were added stepwise to the surface of solutions that were supersaturated with respect to calcite (initial Ω = 20, where Ω = 1 represents saturation), thereby leading to the continuous nucleation and growth of calcite crystals. Lognormal CSDs resulted when reactants were added continuously below the solution surface, via a submerged tube, to similarly supersaturated solutions (initial Ω = 22 to 41), thereby leading to a single nucleation event followed by surface-controlled growth. The Ostwald CSD resulted when concentrated reactants were rapidly mixed, leading initially to high levels of supersaturation (Ω >100), and to the formation and subsequent dissolution of very small nuclei, thereby yielding CSDs having small crystal size variances. The three CSD shapes likely were produced early in the crystallization process, in the nanometer crystal size range, and preserved during subsequent growth. Preservation of the relative shapes of the CSDs indicates that a supply-controlled growth mechanism

  3. Buffer Overflow Detection on Binary Code

    Institute of Scientific and Technical Information of China (English)

    ZHENG Yan-fei; LI Hui; CHEN Ke-fei

    2006-01-01

    Most solutions for detecting buffer overflow are based on source code. But the requirement for source code is not always practical especially for business software. A new approach was presented to detect statically the potential buffer overflow vulnerabilities in the binary code of software. The binary code was translated into assembly code without the lose of the information of string operation functions. The feature code abstract graph was constructed to generate more accurate constraint statements, and analyze the assembly code using the method of integer range constraint. After getting the elementary report on suspicious code where buffer overflows possibly happen, the control flow sensitive analysis using program dependence graph was done to decrease the rate of false positive. A prototype was implemented which demonstrates the feasibility and efficiency of the new approach.

  4. Calcite Supersaturation and Precipitation Kinetics in the Lower Colorado River, Ail-American Canal and East Highline Canal

    Science.gov (United States)

    Suarez, D. L.

    1983-06-01

    In situ pH determinations and analysis of major ions in solution indicated that the lower Colorado River is supersaturated with respect to calcite throughout the entire daily cycle, in both winter and summer. Although the ion activity product was 4 to 6 times greater than the calcite solubility product, there was no detectable precipitation. Chemical analyses of water samples taken along 350 km of the river and canals from Parker Dam to the Salton Sea also revealed no evidence of calcium carbonate precipitation despite the inflow of saline and highly supersaturated irrigation return flows. Laboratory kinetic studies indicated that calcite crystal growth rates with Colorado River water are about 30% of the rate for pure Ca-HCO3 waters and about 70% of that for synthetic Colorado River water. Calcite precipitation by crystal growth in the river is limited by the combination of short residence times and unavailability of reactive calcite. Critical supersaturation levels necessary for heterogeneous nucleation do not occur; a high suspended load limits algal photosynthesis and thus prevents large decreases in daytime H2CO3 levels.

  5. Workshop on moisture buffer capacity

    DEFF Research Database (Denmark)

    2003-01-01

    Summary report of a Nordtest workshop on moisture buffer capacity held at Copenhagen August 21-22 2003......Summary report of a Nordtest workshop on moisture buffer capacity held at Copenhagen August 21-22 2003...

  6. Temperature buffer test. Hydro-mechanical and chemical/ mineralogical characterizations

    Energy Technology Data Exchange (ETDEWEB)

    Aakesson, Mattias; Olsson, Siv; Dueck, Ann; Nilsson, Ulf; Karnland, Ola [Clay Technology AB, Lund (Sweden); Kiviranta, Leena; Kumpulainen, Sirpa [BandTech Oy, Helsinki (Finland); Linden, Johan [Aabo Akademi, Aabo (Finland)

    2012-01-15

    TEM), iron oxidation state (Moessbauer spectroscopy). The retention tests, the CEC-determinations, the chemical analyses by ICP, and the mineralogical analyses by XRD and FTIR were performed on bulk samples as well as on a Na-converted fine fraction (<0.5 {mu}m). The latter fraction was subjected also to TEM analyses. The hydro-mechanical characterizations of the bentonite resulted in the following observations: i) compared to the reference material no large deviation was seen in the retention curves for the Na converted fine fraction of the material from the innermost positions, and for the bulk material from the same positions a marked deviation was observed for equilibrium with RH = 97%; ii) a reduction in swelling pressure was observed on re-saturated samples from the field experiment, especially on those from the innermost part. Measured hydraulic conductivity values were generally scattered, but displayed a tendency with increased values on re-saturated specimens drilled from the innermost part, and a similar tendency was also observed on ground and re-compacted specimens and specimens prepared from dried material; iii) the triaxial test performed on the one specimen from the inner part demonstrated a brittle behaviour involving high stiffness, high shear strength, and low strain at failure; and iv) the unconfined compression tests demonstrated a reduced strain at failure on all specimens from the field material, and also a reduced maximum deviator stress on the re-saturated specimens from the innermost position. The chemical/mineralogical characterization indicated that: i) sulfate was redistributed under the thermal and hydration gradients that were prevalent during the test. Anhydrite accumulated at some distance from the heater, whereas gypsum was dissolved in the peripheral parts of the buffer where water was supplied; ii) cristobalite was dissolved at the bentonite/heater contact; iii) calcite was dissolved in the warmest parts of the block; iv

  7. The biocompatibility of titanium in a buffer solution: compared effects of a thin film of TiO2 deposited by MOCVD and of collagen deposited from a gel.

    Science.gov (United States)

    Popescu, Simona; Demetrescu, Ioana; Sarantopoulos, Christos; Gleizes, Alain N; Iordachescu, Dana

    2007-10-01

    This study aims at evaluating the biocompatibility of titanium surfaces modified according two different ways: (i) deposition of a bio-inert, thin film of rutile TiO(2) by chemical vapour deposition (MOCVD), and (ii) biochemical treatment with collagen gel, in order to obtain a bio-interactive coating. Behind the comparison is the idea that either the bio-inert or the bio-active coating has specific advantages when applied to implant treatment, such as the low price of the collagen treatment for instance. The stability in buffer solution was evaluated by open circuit potential (OCP) for medium time and cyclic voltametry. The OCP stabilized after 5.10(4) min for all the specimens except the collagen treated sample which presented a stable OCP from the first minutes. MOCVD treated samples stabilized to more electropositive values. Numeric results were statistically analysed to obtain the regression equations for long time predictable evolution. The corrosion parameters determined from cyclic curves revealed that the MOCVD treatment is an efficient way to improve corrosion resistance. Human dermal fibroblasts were selected for cell culture tests, taking into account that these cells are present in all bio-interfaces, being the main cellular type of connective tissue. The cells grew on either type of surface without phenotype modification. From the reduction of yellow, water-soluble 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT cytotoxicity test), MOCVD treated samples offer better viability than mechanically polished Ti and collagen treated samples as well. Cell spreading, as evaluated from microscope images processed by the program Sigma Scan, showed also enhancement upon surface modification. Depending on the experimental conditions, MOCVD deposited TiO(2) exhibits different nanostructures that may influence biological behaviour. The results demonstrate the capacity of integration in simulated physiologic liquids for an implant pretreated by

  8. Development and application of a green-chemistry solution deposition technique for buffer layer coating on cube-textured metal substrates in view of further deposition of rare-earth based superconductors

    DEFF Research Database (Denmark)

    Pallewatta, Pallewatta G A P

    , allowing the epitaxial growth of the superconducting layer. State-of-the-art coated conductor hetero structures are mainly based on CeO2 based buffer stacks that consist of a sequence of several different buffer layers. Buffer layers deposited by continuous chemical deposition techniques, which...... and hazardous chemicals such as 2-methoxyethanol, and trifluroacetic acid (TFA). Therefore, in our research the main focus was on the development of SrTiO3 single buffer layers based on environmentally safe chemicals, to reach the engineering requirements for continuous coating of long substrate tapes. A new......Superconductor based energy production has been thoroughly researched by many scientists all over the world, due to the advantage of zero electric resistance that will contribute to the energy saving capabilities. Recently successful developments have been reported in coated conductor architectures...

  9. 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

  10. Selective adsorption of L- and D-amino acids on calcite: Implications for biochemical homochirality

    Science.gov (United States)

    Hazen, R. M.; Filley, T. R.; Goodfriend, G. A.

    2001-01-01

    The emergence of biochemical homochirality was a key step in the origin of life, yet prebiotic mechanisms for chiral separation are not well constrained. Here we demonstrate a geochemically plausible scenario for chiral separation of amino acids by adsorption on mineral surfaces. Crystals of the common rock-forming mineral calcite (CaCO(3)), when immersed in a racemic aspartic acid solution, display significant adsorption and chiral selectivity of d- and l-enantiomers on pairs of mirror-related crystal-growth surfaces. This selective adsorption is greater on crystals with terraced surface textures, which indicates that d- and l-aspartic acid concentrate along step-like linear growth features. Thus, selective adsorption of linear arrays of d- and l-amino acids on calcite, with subsequent condensation polymerization, represents a plausible geochemical mechanism for the production of homochiral polypeptides on the prebiotic Earth.

  11. Functionalizing single crystals: incorporation of nanoparticles inside gel-grown calcite crystals.

    Science.gov (United States)

    Liu, Yujing; Yuan, Wentao; Shi, Ye; Chen, Xiaoqiang; Wang, Yong; Chen, Hongzheng; Li, Hanying

    2014-04-14

    Synthetic single crystals are usually homogeneous solids. Biogenic single crystals, however, can incorporate biomacromolecules and become inhomogeneous solids so that their properties are also extrinsically regulated by the incorporated materials. The discrepancy between the properties of synthetic and biogenic single crystals leads to the idea to modify the internal structure of synthetic crystals to achieve nonintrinsic properties by incorporation of foreign material. Intrinsically colorless and diamagnetic calcite single crystals are turned into colored and paramagnetic solids, through incorporation of Au and Fe3O4 nanoparticles without significantly disrupting the crystalline lattice of calcite. The crystals incorporate the nanoparticles and gel fibers when grown in agarose gel media containing the nanoparticles, whereas the solution-grown crystals do not. As such, our work extends the long-history gel method for crystallization into a platform to functionalize single-crystalline materials.

  12. Molecular ordering of ethanol at the calcite surface

    DEFF Research Database (Denmark)

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

    2012-01-01

    -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-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...

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

    Science.gov (United States)

    Kluge, Tobias; Haderlein, Astrid; Weißbach, Therese

    2016-04-01

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

  14. Universal buffers for use in biochemistry and biophysical experiments

    Directory of Open Access Journals (Sweden)

    Dewey Brooke

    2015-08-01

    Full Text Available The use of buffers that mimic biological solutions is a foundation of biochemical and biophysical studies. However, buffering agents have both specific and nonspecific interactions with proteins. Buffer molecules can induce changes in conformational equilibria, dynamic behavior, and catalytic properties merely by their presence in solution. This effect is of concern because many of the standard experiments used to investigate protein structure and function involve changing solution conditions such as pH and/or temperature. In experiments in which pH is varied, it is common practice to switch buffering agents so that the pH is within the working range of the weak acid and conjugate base. If multiple buffers are used, it is not always possible to decouple buffer induced change from pH or temperature induced change. We have developed a series of mixed biological buffers for protein analysis that can be used across a broad pH range, are compatible with biologically relevant metal ions, and avoid complications that may arise from changing the small molecule composition of buffers when pH is used as an experimental variable.

  15. Synthesis of Gold Nanoparticles with Buffer-Dependent Variations of Size and Morphology in Biological Buffers.

    Science.gov (United States)

    Ahmed, Syed Rahin; Oh, Sangjin; Baba, Rina; Zhou, Hongjian; Hwang, Sungu; Lee, Jaebeom; Park, Enoch Y

    2016-12-01

    The demand for biologically compatible and stable noble metal nanoparticles (NPs) has increased in recent years due to their inert nature and unique optical properties. In this article, we present 11 different synthetic methods for obtaining gold nanoparticles (Au NPs) through the use of common biological buffers. The results demonstrate that the sizes, shapes, and monodispersity of the NPs could be varied depending on the type of buffer used, as these buffers acted as both a reducing agent and a stabilizer in each synthesis. Theoretical simulations and electrochemical experiments were performed to understand the buffer-dependent variations of size and morphology exhibited by these Au NPs, which revealed that surface interactions and the electrostatic energy on the (111) surface of Au were the determining factors. The long-term stability of the synthesized NPs in buffer solution was also investigated. Most NPs synthesized using buffers showed a uniquely wide range of pH stability and excellent cell viability without the need for further modifications.

  16. Synthesis of Gold Nanoparticles with Buffer-Dependent Variations of Size and Morphology in Biological Buffers

    Science.gov (United States)

    Ahmed, Syed Rahin; Oh, Sangjin; Baba, Rina; Zhou, Hongjian; Hwang, Sungu; Lee, Jaebeom; Park, Enoch Y.

    2016-02-01

    The demand for biologically compatible and stable noble metal nanoparticles (NPs) has increased in recent years due to their inert nature and unique optical properties. In this article, we present 11 different synthetic methods for obtaining gold nanoparticles (Au NPs) through the use of common biological buffers. The results demonstrate that the sizes, shapes, and monodispersity of the NPs could be varied depending on the type of buffer used, as these buffers acted as both a reducing agent and a stabilizer in each synthesis. Theoretical simulations and electrochemical experiments were performed to understand the buffer-dependent variations of size and morphology exhibited by these Au NPs, which revealed that surface interactions and the electrostatic energy on the (111) surface of Au were the determining factors. The long-term stability of the synthesized NPs in buffer solution was also investigated. Most NPs synthesized using buffers showed a uniquely wide range of pH stability and excellent cell viability without the need for further modifications.

  17. Thermoluminescence glow curve of {gamma}-irradiated calcite

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S.D.; Ingotombi, S. [Manipur Univ. (India). Dept. of Physics

    1995-07-14

    The trapping parameters, namely the activation energy E, frequency factor s and b order of kinetics of the thermoluminescence (TL) peaks of calcites (brown and colourless varieties) irradiated with 4.08 kGy of {gamma}-rays, are determined using the least-squares curve-fitting technique. The electron lifetime {tau} of the peaks of calcite are calculated in order to estimate the upper limit of their utility in TL dating. (author).

  18. In-situ growth of calcite at Devils Hole, Nevada: Comparison of field and laboratory rates to a 500,000 year record of near-equilibrium calcite growth

    Science.gov (United States)

    Plummer, L.N.; Busenberg, E.; Riggs, A.C.

    2000-01-01

    Calcite grew continuously for 500,000 years on the submerged walls of an open fault plane (Devils Hole) in southern Nevada, U.S.A. at rates of 0.3 to 1.3 mm/ka, but ceased growing approximately 60,000 years ago, even though the fault plane remained open and was continuously submerged. The maximum initial in-situ growth rate on pre-weighed crystals of Iceland spar placed in Devils Hole (calcite saturation index, SI, is 0.16 to 0.21 at 33.7??C) for growth periods of 0.75 to 4.5 years was 0.22 mm/ka. Calcite growth on seed crystals slowed or ceased following initial contact with Devils Hole groundwater. Growth rates measured in synthetic Ca-HCO3 solutions at 34??C, CO2 partial pressures of 0.101, 0.0156 (similar to Devils Hole groundwater) and 0.00102 atm, and SI values of 0.2 to 1.9 were nearly independent of P(CO)(2), decreased with decreasing saturation state, and extrapolated through the historical Devils Hole rate. The results show that calcite growth rate is highly sensitive to saturation state near equilibrium. A calcite crystal retrieved from Devils Hole, and used without further treatment of its surface, grew in synthetic Devils Hole groundwater when the saturation index was raised nearly 10-fold that of Devils Hole water, but the rate was only 1/4 that of fresh laboratory crystals that had not contacted Devils Hole water. Apparently, inhibiting processes that halted calcite growth in Devils Hole 60,000 years ago continue today.

  19. 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.

  20. 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

  1. Variation of power generation at different buffer types and conductivities in single chamber microbial fuel cells.

    Science.gov (United States)

    Nam, Joo-Youn; Kim, Hyun-Woo; Lim, Kyeong-Ho; Shin, Hang-Sik; Logan, Bruce E

    2010-01-15

    Microbial fuel cells (MFCs) are operated with solutions containing various chemical species required for the growth of electrochemically active microorganisms including nutrients and vitamins, substrates, and chemical buffers. Many different buffers are used in laboratory media, but the effects of these buffers and their inherent electrolyte conductivities have not been examined relative to current generation in MFCs. We investigated the effect of several common buffers (phosphate, MES, HEPES, and PIPES) on power production in single chambered MFCs compared to a non-buffered control. At the same concentrations the buffers produced different solution conductivities which resulted in different ohmic resistances and power densities. Increasing the solution conductivities to the same values using NaCl produced comparable power densities for all buffers. Very large increases in conductivity resulted in a rapid voltage drop at high current densities. Our results suggest that solution conductivity at a specific pH for each buffer is more important in MFC studies than the buffer itself given relatively constant pH conditions. Based on our analysis of internal resistance and a set neutral pH, phosphate and PIPES are the most useful buffers of those examined here because pH was maintained close to the pK(a) of the buffer, maximizing the ability of the buffer to contribute to increase current generation at high power densities.

  2. Variation of power generation at different buffer types and conductivities in single chamber microbial fuel cells

    KAUST Repository

    Nam, Joo-Youn

    2010-01-15

    Microbial fuel cells (MFCs) are operated with solutions containing various chemical species required for the growth of electrochemically active microorganisms including nutrients and vitamins, substrates, and chemical buffers. Many different buffers are used in laboratory media, but the effects of these buffers and their inherent electrolyte conductivities have not been examined relative to current generation in MFCs. We investigated the effect of several common buffers (phosphate, MES, HEPES, and PIPES) on power production in single chambered MFCs compared to a non-buffered control. At the same concentrations the buffers produced different solution conductivities which resulted in different ohmic resistances and power densities. Increasing the solution conductivities to the same values using NaCl produced comparable power densities for all buffers. Very large increases in conductivity resulted in a rapid voltage drop at high current densities. Our results suggest that solution conductivity at a specific pH for each buffer is more important in MFC studies than the buffer itself given relatively constant pH conditions. Based on our analysis of internal resistance and a set neutral pH, phosphate and PIPES are the most useful buffers of those examined here because pH was maintained close to the pKa of the buffer, maximizing the ability of the buffer to contribute to increase current generation at high power densities. © 2009 Elsevier B.V. All rights reserved.

  3. Aluminum elution and precipitation in glass vials: effect of pH and buffer species.

    Science.gov (United States)

    Ogawa, Toru; Miyajima, Makoto; Wakiyama, Naoki; Terada, Katsuhide

    2015-02-01

    Inorganic extractables from glass vials may cause particle formation in the drug solution. In this study, the ability of eluting Al ion from borosilicate glass vials, and tendencies of precipitation containing Al were investigated using various pHs of phosphate, citrate, acetate and histidine buffer. Through heating, all of the buffers showed that Si and Al were eluted from glass vials in ratios almost the same as the composition of borosilicate glass, and the amounts of Al and Si from various buffer solutions at pH 7 were in the following order: citrate > phosphate > acetate > histidine. In addition, during storage after heating, the Al concentration at certain pHs of phosphate and acetate buffer solution decreased, suggesting the formation of particles containing Al. In citrate buffer, Al did not decrease in spite of the high elution amount. Considering that the solubility profile of aluminum oxide and the Al eluting profile of borosilicate glass were different, it is speculated that Al ion may be forced to leach into the buffer solution according to Si elution on the surface of glass vials. When Al ions were added to the buffer solutions, phosphate, acetate and histidine buffer showed a decrease of Al concentration during storage at a neutral range of pHs, indicating the formation of particles containing Al. In conclusion, it is suggested that phosphate buffer solution has higher possibility of forming particles containing Al than other buffer solutions.

  4. Modeling the evolution of complex conductivity during calcite precipitation on glass beads

    Science.gov (United States)

    Leroy, Philippe; Li, Shuai; Jougnot, Damien; Revil, André; Wu, Yuxin

    2017-01-01

    SUMMARYWhen pH and alkalinity increase, calcite frequently precipitates and hence modifies the petrophysical properties of porous media. The complex conductivity method can be used to directly monitor calcite precipitation in porous media because it is sensitive to the evolution of the mineralogy, pore structure and its connectivity. We have developed a mechanistic grain polarization model considering the electrochemical polarization of the Stern and diffuse layer surrounding calcite particles. Our complex conductivity model depends on the surface charge density of the Stern layer and on the electrical potential at the onset of the diffuse layer, which are computed using a basic Stern model of the calcite/water interface. The complex conductivity measurements of Wu et al. (2010) on a column packed with glass beads where calcite precipitation occurs are reproduced by our surface complexation and complex conductivity models. The evolution of the size and shape of calcite particles during the calcite precipitation experiment is estimated by our complex conductivity model. At the early stage of the calcite precipitation experiment, modeled particles sizes increase and calcite particles flatten with time because calcite crystals nucleate at the surface of glass beads and grow into larger calcite grains around glass beads. At the later stage of the calcite precipitation experiment, modeled sizes and cementation exponents of calcite particles decrease with time because large calcite grains aggregate over multiple glass beads, a percolation threshold is achieved, and small and discrete calcite crystals polarize.

  5. Hydrochemical controls on aragonite versus calcite precipitation in cave dripwaters

    Science.gov (United States)

    Rossi, Carlos; Lozano, Rafael P.

    2016-11-01

    Despite the paleoclimatic relevance of primary calcite to aragonite transitions in stalagmites, the relative role of fluid Mg/Ca ratio, supersaturation and CO32- concentration in controlling such transitions is still incompletely understood. Accordingly, we have monitored the hydrochemistry of 50 drips and 8 pools that are currently precipitating calcite and/or aragonite in El Soplao and Torca Ancha Caves (N. Spain), investigating the mineralogy and geochemistry of the CaCO3 precipitates on the corresponding natural speleothem surfaces. The data reveal that, apart from possible substrate effects, dripwater Mg/Ca is the only obvious control on CaCO3 polymorphism in the studied stalagmites and pools, where calcite- and aragonite-precipitating dripwaters are separated by an initial (i.e. at stalactite tips) Mg/Ca threshold at ≈1.1 mol/mol. Within the analyzed ranges of pH (8.2-8.6), CO32- concentration (1-6 mg/L), supersaturation (SIaragonite: 0.08-1.08; SIcalcite: 0.23-1.24), drip rate (0.2-81 drops/min) and dissolved Zn (6-90 μg/L), we observe no unequivocal influence of these parameters on CaCO3 mineralogy. Despite the almost complete overlapping supersaturations of calcite- and aragonite-precipitating waters, the latter are on average less supersaturated because the waters having Mg/Ca above ∼1.1 have mostly achieved such high ratios by previously precipitating calcite. Both calcite and aragonite precipitated at or near oxygen isotopic equilibrium, and Mg incorporation into calcite was consistent with literature-based predictions, indicating that in the studied cases CaCO3 precipitation was not significantly influenced by strong kinetic effects. In the studied cases, the calcites that precipitate at ∼11 °C from dripwaters with initial Mg/Ca approaching ∼1.1 incorporate ∼5 mol% MgCO3, close to the published value above which calcite solubility exceeds aragonite solubility, suggesting that aragonite precipitation in high-relative-humidity caves is

  6. Complexation of buffer constituents with neutral complexation agents: part I. Impact on common buffer properties.

    Science.gov (United States)

    Riesová, Martina; Svobodová, Jana; Tošner, Zdeněk; Beneš, Martin; Tesařová, Eva; Gaš, Bohuslav

    2013-09-17

    The complexation of buffer constituents with the complexation agent present in the solution can very significantly influence the buffer properties, such as pH, ionic strength, or conductivity. These parameters are often crucial for selection of the separation conditions in capillary electrophoresis or high-pressure liquid chromatography (HPLC) and can significantly affect results of separation, particularly for capillary electrophoresis as shown in Part II of this paper series (Beneš, M.; Riesová, M.; Svobodová, J.; Tesařová, E.; Dubský, P.; Gaš, B. Anal. Chem. 2013, DOI: 10.1021/ac401381d). In this paper, the impact of complexation of buffer constituents with a neutral complexation agent is demonstrated theoretically as well as experimentally for the model buffer system composed of benzoic acid/LiOH or common buffers (e.g., CHES/LiOH, TAPS/LiOH, Tricine/LiOH, MOPS/LiOH, MES/LiOH, and acetic acid/LiOH). Cyclodextrins as common chiral selectors were used as model complexation agents. We were not only able to demonstrate substantial changes of pH but also to predict the general complexation characteristics of selected compounds. Because of the zwitterion character of the common buffer constituents, their charged forms complex stronger with cyclodextrins than the neutral ones do. This was fully proven by NMR measurements. Additionally complexation constants of both forms of selected compounds were determined by NMR and affinity capillary electrophoresis with a very good agreement of obtained values. These data were advantageously used for the theoretical descriptions of variations in pH, depending on the composition and concentration of the buffer. Theoretical predictions were shown to be a useful tool for deriving some general rules and laws for complexing systems.

  7. 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.

  8. Mechanisms of buffer therapy resistance.

    Science.gov (United States)

    Bailey, Kate M; Wojtkowiak, Jonathan W; Cornnell, Heather H; Ribeiro, Maria C; Balagurunathan, Yoganand; Hashim, Arig Ibrahim; Gillies, Robert J

    2014-04-01

    Many studies have shown that the acidity of solid tumors contributes to local invasion and metastasis. Oral pH buffers can specifically neutralize the acidic pH of tumors and reduce the incidence of local invasion and metastatic formation in multiple murine models. However, this effect is not universal as we have previously observed that metastasis is not inhibited by buffers in some tumor models, regardless of buffer used. B16-F10 (murine melanoma), LL/2 (murine lung) and HCT116 (human colon) tumors are resistant to treatment with lysine buffer therapy, whereas metastasis is potently inhibited by lysine buffers in MDA-MB-231 (human breast) and PC3M (human prostate) tumors. In the current work, we confirmed that sensitive cells utilized a pH-dependent mechanism for successful metastasis supported by a highly glycolytic phenotype that acidifies the local tumor microenvironment resulting in morphological changes. In contrast, buffer-resistant cell lines exhibited a pH-independent metastatic mechanism involving constitutive secretion of matrix degrading proteases without elevated glycolysis. These results have identified two distinct mechanisms of experimental metastasis, one of which is pH-dependent (buffer therapy sensitive cells) and one which is pH-independent (buffer therapy resistant cells). Further characterization of these models has potential for therapeutic benefit.

  9. Geochemical and isotope aspects of calcite deposits and calcitic marbles hosts mineralizations, Serra do Carumbe, Vale do Ribeira, Parana state, Brazil; Aspectos geoquimicos e isotopicos das mineralizacoes de calcita e marmores calciticos encaixantes, Serra do Carumbe, Vale do Ribeira, estado do Parana

    Energy Technology Data Exchange (ETDEWEB)

    Venusso, Gerson Caetano; Andrade e Silva, Antonio C. Gondim de, E-mail: venusso@geologia.ufpr.br, E-mail: gondim@geologia.ufpr.br [Universidade Federal do Parana (UFPR), Curitiba, PR (Brazil)

    2011-07-01

    The calcite deposits and the calcitic marbles hosts occur in Serra do Carumbe, in the Vale do Ribeira region, Parana State, were studied in their geochemical and isotopic aspects viewing the gathering of information about their genesis and economical use. The calcite deposits are constituted by veins and lenses, being three of them concordant and one discordant in relation to the S{sub 0} from the hosting marbles. In these deposits four main types of calcite were recognized: rombohedrical, fibrous, banded and microcrystalline. The calcite reveal themselves having high purity, with CaO concentration above 55.30% and MgO below 0.42%. The lithogeochemical study of the marbles sequence was conducted in various suites revealing an uniformity in their composition, with high values of CaO (above 46.92%) in relation to the MgO values (below 3,37%), what favors their use for cement manufacture, except in sectors that suffered fault influences, where the marbles are impure (siliceous, magnesian, ferruginous and aluminous). Regarding their trace elements content, the hosting calcitic marbles have higher concentrations than the calcite, in the elements Sr, B, Ba and Mg, what makes evident their different formation environments. The δ{sup 13}C values from calcite range from –9,02 to –12,24 ‰ , referring to PDB, while the values δ{sup 18}O range from 24,48 to 25,23 ‰, referring to SMOW; meanwhile, for the calcitic marbles, the δ{sup 13}C values range from –4,03 to 1,42‰ and of δ{sup 18}O range from 20,71 to 23,00 ‰. The high δ{sup 18}O values would indicate enrichment referring to the interaction of the calcite's generator fluid with the carbonatic host rock. The δ{sup 13}C values indicate origin from hydrothermal solution for the calcite, although they would not allow to conclude if their sources would be superficial or profound. As for the hosting calcitic marbles, the isotopic values indicate genesis from pre-cambrian marine limestone. (author)

  10. Monoclinic deformation of calcite crystals at ambient conditions

    Science.gov (United States)

    Przeniosło, R.; Fabrykiewicz, P.; Sosnowska, I.

    2016-09-01

    High resolution synchrotron radiation powder diffraction shows that the average crystal structure of calcite at ambient conditions is described with the trigonal space group R 3 bar c but there is a systematic hkl-dependent Bragg peak broadening. A modelling of this anisotropic peak broadening with the microstrain model from Stephens (1999) [15] is presented. The observed lattice parameters' correlations can be described by assuming a monoclinic-type deformation of calcite crystallites. A quantitative model of this monoclinic deformation observed at ambient conditions is described with the space group C 2 / c . The monoclinic unit cell suggested at ambient conditions is related with the monoclinic unit cell reported in calcite at high pressure (Merrill and Bassett (1975) [10]).

  11. Shell microstructure and its inheritance in the calcitic helcionellid Mackinnonia

    Directory of Open Access Journals (Sweden)

    Michael J. Vendrasco

    2015-02-01

    Full Text Available Mackinnonia davidi from the Cambrian (Series 2 of Australia has a prismatic outer shell layer and, as newly described here, a calcitic semi-nacre inner layer. The pattern is the same as in stenothecids such as Mellopegma, providing more evidence for a strong phylogenetic signal in the shell microstructure of Cambrian molluscs. In addition, calcite now appears to have been common in helcionellids and other molluscs during the early and middle Cambrian, with many species exhibiting foliated calcite. This is surprising given the dominance of aragonite in molluscs, both modern and from post-Cambrian fossil deposits with exceptional shell microstructure preservation, including localities from the Ordovician of the Cincinnati region, USA.

  12. The equilibrium between diagenetic calcites and dolomites and its impact on reservoir quality in the sandstone reservoir of Kela 2 gas field

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the equilibrium theory of chemical reactions between water and rocks, this paper establishes a thermodynamic phase relationship diagram among calcites, dolomites and water solution under the condition of diagenesis based on the thermodynamic database of related minerals and fluids and dolomite's degree of order parameters. It has been discovered that the equilibrium between calcites and dolomites in the diagenetic environment is strongly impacted by temperature and the Ca/Mg ratios in groundwater, and that the dolomite's degree of order in the diagenetic environment is a function of crystallization temperature and time, not controlled by water solution. Hereby, the authors make a further analysis of the close relationship of chemical reaction between carbonate cements and pore water in the sandstone reservoirs of Kala 2 gas field in Kuche sag. It can be seen that there are different impacts on sandstone reservoir quality among the equilibrium system of calcites, dolomites and pore water at different depths of reservoirs.

  13. Small scale shear zone in calcite: AMS and microstructure

    Science.gov (United States)

    Roxerová, Zuzana; Machek, Matěj; Kusbach, Vladimír; Racek, Martin; Silva, Pedro F.

    2016-04-01

    Two structural profiles across thin shear zone in calcite from quarry in Estremoz (Portugal) were studied to find a relationship between AMS and strain in natural rocks. The mesoscopic fabric is characterized by the change from the subhorizontal coarse-grained foliation towards the ~2cm-wide shear zone center with subvertical fine-grained foliation. In microstructure, the shear zone records dynamic recrystallization of calcite aggregate which resulted in development of porphyroclastic microstructure with increasing proportion of fine-grained recrystallized matrix towards the shear zone center. Two distinct crystallographic preferred orientations of calcite were recorded. One related with porphyroclasts, characterized by subvertical orientation of calcite axes and another associated with recrystallized matrix showing subhorizontal calcite axes orientation. The magnetic susceptibility ranges from -8e-6SI to 9e-6SI, with the average -4e-6SI. The majority of the rock mass is diamagnetic, corresponding well with the thermomagnetic curves, with local paramagnetic accumulations in form of thin bands. The AMS of the both profiles exhibits stable subvertical foliation bearing vertical lineation which is locally alternated by the medium-angle foliation. We interpret the AMS fabric pattern which is perpendicular to the mineral one as a type of inverse AMS fabric, due to high iron content in major part of calcite grains The magnetic and microstructural description of the shear zone is accompanied by numerical modeling of AMS based on CPO and different proportion of porphyroclasts, matrix and mica for purposes of deciphering the influence of present microstructural features on AMS.

  14. ENVIRONMENTAL MANAGEMENT SCIENCE PROGRAM PROJECT NUMBER 87016 CO-PRECIPITATION OF TRACE METALS IN GROUNDWATER AND VADOSE ZONE CALCITE: IN SITU CONTAINMENT AND STABILIZATION OF STRONTIUM-90 AND OTHER DIVALENT METALS AND RADIONUCLIDES AT ARID WESTERN DOE SITES

    Energy Technology Data Exchange (ETDEWEB)

    Ferris, F. Grant; Fujita, Yoshiko; Smith, Robert W.

    2004-06-15

    Radionuclide and metal contaminants are present in the vadose zone and groundwater throughout the U.S. Department of Energy (DOE) weapons complex. In situ containment and stabilization of these contaminants in vadose zones or groundwater is a cost-effective treatment strategy. Our facilitated approach relies upon the hydrolysis of introduced urea to cause the acceleration of calcium carbonate precipitation (and trace metal coprecipitation) by increasing groundwater pH and alkalinity (Fujita et al., 2000; Warren et al., 2001). Subsurface urea hydrolysis is catalyzed by the urease enzyme, which may be either introduced with the urea or produced in situ by ubiquitous subsurface urea hydrolyzing microorganisms. Because the precipitation processes are irreversible and many western aquifers are saturated with respect to calcite, the co-precipitated metals and radionuclides will be effectively removed from groundwater. The rate at which trace metals are incorporated into calcite is a function of calcite precipitation kinetics, adsorption interactions between the calcite surface and the trace metal in solution (Zachara et al., 1991), solid solution properties of the trace metal in calcite (Tesoriero and Pankow, 1996), and also the surfaces upon which the calcite is precipitating. A fundamental understanding of the coupling of calcite precipitation and trace metal partitioning, and how this occurs in aquifers and vadose environments is lacking. This report summarizes work undertaken during the second year of this project.

  15. ENVIRONMENTALMANAGEMENT SCIENCE PROGRAM PROJECT NUMBER 87016 CO-PRECIPITATION OF TRACEMETALS INGROUNDWATER AND VADOSE ZONE CALCITE: IN SITU CONTAINMENT AND STABILIZATION OF STRONTIUM-90 ANDOTHER DIVALENT METALS AND RADIONUCLIDES AT ARIDWESTERN DOE SITES

    Energy Technology Data Exchange (ETDEWEB)

    Ferris, F. Grant; Fujita, Yoshiko; Smith, Robert W.; Cosgrove, Donna M.; Colwell, F. S.

    2004-06-15

    Radionuclide and metal contaminants are present in the vadose zone and groundwater throughout the U.S. Department of Energy (DOE) weapons complex. In situ containment and stabilization of these contaminants in vadose zones or groundwater is a cost-effective treatment strategy. Our facilitated approach relies upon the hydrolysis of introduced urea to cause the acceleration of calcium carbonate precipitation (and trace metal coprecipitation) by increasing groundwater pH and alkalinity (Fujita et al., 2000; Warren et al., 2001). Subsurface urea hydrolysis is catalyzed by the urease enzyme, which may be either introduced with the urea or produced in situ by ubiquitous subsurface urea hydrolyzing microorganisms. Because the precipitation processes are irreversible and many western aquifers are saturated with respect to calcite, the co-precipitated metals and radionuclides will be effectively removed from groundwater. The rate at which trace metals are incorporated into calcite is a function of calcite precipitation kinetics, adsorption interactions between the calcite surface and the trace metal in solution (Zachara et al., 1991), solid solution properties of the trace metal in calcite (Tesoriero and Pankow, 1996), and also the surfaces upon which the calcite is precipitating. A fundamental understanding of the coupling of calcite precipitation and trace metal partitioning, and how this occurs in aquifers and vadose environments is lacking. This report summarizes work undertaken during the second year of this project.

  16. Isotopic and elemental proxies in mollusc and brachiopod calcite

    DEFF Research Database (Denmark)

    Ullmann, Clemens Vinzenz

    This thesis summarizes the findings of studies conducted at the University of Copenhagen from September 2010 to September 2013, aiming at a better understanding of the geochemical signatures in marine, biogenic calcite. Throughout the history of the Earth, the climatic conditions and the chemical...... for a meaningful interpretation of isotopic and elemental ratios in shell materials. Without this knowledge the correct interpretation of the shell composition in terms of past environments is impossible. Calcite shells of brachiopods, bivalves and belemnites were analyzed here for shell ultra...

  17. Diagenetic alteration in low-Mg calcite from macrofossils

    DEFF Research Database (Denmark)

    Ullmann, Clemens Vinzenz; Korte, Christoph

    2015-01-01

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

  18. The Influence of Phosphate Buffer on the Formation of N-Nitrosodimethylamine from Dimethylamine Nitrosation

    Directory of Open Access Journals (Sweden)

    Long Xu

    2013-01-01

    Full Text Available Buffer solutions were widely used for almost all the investigations concerning N-nitrosodimethylamine (NDMA, a member of powerful mutagenic and carcinogenic compounds which are ubiquitous in the environment. However, whether or how the buffer matrixes influence NDMA formation is still unknown. The effect of buffer solutions on NDMA formation from the nitrosation of dimethylamine (DMA by nitrite (NaNO2 was investigated at pH 6.4 in four kinds of buffer solutions, that is, Na2HPO4/C6H8O7, Na3(C6H5O7/C6H8O7, NaH2PO4/NaOH, and NaH2PO4/Na2HPO4. Our observations demonstrate an unexpected inhibitory effect of the buffer solutions on NDMA formation and the phosphate buffer plays a more significant role in inhibiting NDMA formation compared to the citrate buffer. Moreover, the amount of the phosphate in the buffer was also found to greatly impact the formation of NDMA. A further investigation indicates that it is the interaction between NaH2PO4 and reactant NaNO2 rather than DMA that leads to the inhibitory effect of phosphate buffer during the DMA nitrosation reaction. This study expands the understanding of the influence of buffer solution on nitrosamines formation through the nitrosation pathway and further gives a hint for water plants to reduce the formation of nitrosamines.

  19. Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration

    OpenAIRE

    Lee, Martin R.; Lindgren, Paula; Sofe, Mahmood R.

    2014-01-01

    Carbonate minerals in CM carbonaceous chondrite meteorites, along with the silicates and sulphides with which they are intergrown, provide a detailed record of the nature and evolution of parent body porosity and permeability, and the chemical composition, temperature and longevity of aqueous solutions. Fourteen meteorites were studied that range in petrologic subtype from mildly aqueously altered CM2.5 to completely hydrated CM2.0. All of them contain calcite, whereas aragonite occurs only i...

  20. The Influence of Phosphate Buffer on the Formation of N-Nitrosodimethylamine from Dimethylamine Nitrosation

    OpenAIRE

    Long Xu; Zhi Sun; Qing Ming Liu; Yong Dong Liu; Ru Gang Zhong; Fengchang Wu

    2013-01-01

    Buffer solutions were widely used for almost all the investigations concerning N-nitrosodimethylamine (NDMA), a member of powerful mutagenic and carcinogenic compounds which are ubiquitous in the environment. However, whether or how the buffer matrixes influence NDMA formation is still unknown. The effect of buffer solutions on NDMA formation from the nitrosation of dimethylamine (DMA) by nitrite (NaNO2) was investigated at pH 6.4 in four kinds of buffer solutions, that is, Na2HPO4/C6H8O7, Na...

  1. The efficiency of buffer

    Directory of Open Access Journals (Sweden)

    Ahmed Aldammas

    2016-04-01

    This paper proposes an internal router architecture, for on chip communication, implementing flow-control mechanism for congestion avoidance with QoS consideration. It describes the internal functions of this router for optimal output flit scheduling and its capability to apply per-class service for inbound flows. The paper focuses mainly on the description and performance analysis of two proposed schemes for data flow control that can be used with the proposed router architecture. The results shown in this paper prove that the application of these proposed schemes in NoC achieves an interesting enhancement in the measured end to end QoS. We carried out an extensive comparison of the proposed solutions with the existing schemes published in the literature to show that the proposed solution outperforms these, maintaining an interesting tradeoff with the hardware characteristics when designed with 45 nm integration technology.

  2. SOLUTIONING

    Directory of Open Access Journals (Sweden)

    Maria de Hoyos Guajardo, Ph.D. Candidate, M.Sc., B.Eng.

    2004-11-01

    Full Text Available The theory that is presented below aims to conceptualise how a group of undergraduate students tackle non-routine mathematical problems during a problem-solving course. The aim of the course is to allow students to experience mathematics as a creative process and to reflect on their own experience. During the course, students are required to produce a written ‘rubric’ of their work, i.e., to document their thoughts as they occur as well as their emotionsduring the process. These ‘rubrics’ were used as the main source of data.Students’ problem-solving processes can be explained as a three-stage process that has been called ‘solutioning’. This process is presented in the six sections below. The first three refer to a common area of concern that can be called‘generating knowledge’. In this way, generating knowledge also includes issues related to ‘key ideas’ and ‘gaining understanding’. The third and the fourth sections refer to ‘generating’ and ‘validating a solution’, respectively. Finally, once solutions are generated and validated, students usually try to improve them further before presenting them as final results. Thus, the last section deals with‘improving a solution’. Although not all students go through all of the stages, it may be said that ‘solutioning’ considers students’ main concerns as they tackle non-routine mathematical problems.

  3. Clumped-Isotope Thermometry and Oxygen Isotope Systematics in Speleothem Calcite From a Near Cave-Entrance Environment

    Science.gov (United States)

    Carlson, P. E.; Banner, J.; Breecker, D.; Affek, H. P.

    2015-12-01

    Speleothems that grow in well-ventilated zones of caves have not been widely used in paleoclimate studies, yet may provide paleotemperature records. These zones are characterized by low CO2 concentrations year-round and, in temperate climates, large seasonal temperature fluctuations. They are typically avoided for paleoclimate reconstruction due to concerns about kinetic isotope effects (KIE). However, speleothems in general seem to be sensitive to KIE, even in non-ventilated areas and can nonetheless provide useful paleoclimate records. At Westcave Preserve (Westcave), a shallow, well-ventilated cave in central Texas, we have found seasonal temperature differences recorded in both the oxygen isotope and clumped isotope compositions of speleothem calcite grown on glass-plate substrates harvested from active drips. Although growth rates in this cave are relatively rapid, speleothem analogs in Westcave are growing near oxygen-isotopic equilibrium with their drip waters (between the calibrations of Kim and O'Neil, 1997 and Coplen, 2007). We have tested the compatibility of the Zaarur et al. (2013) clumped isotope bulk solution thermometer calibration to glass-substrate calcite in the cave collected during various months. This technique can provide absolute temperatures, but is sensitive to kinetic isotope effects, often significantly overestimating growth temperatures of speleothems. When this thermometer was applied to calcite collected from near where the plates were impacted by drip water, it overestimated measured temperatures by 7.7 ± 4.3°C, showing moderate KIE. When applied to calcite away from the drip impact, it overestimated temperatures by 18.7 ± 4.2°C, showing KIE increasing away from the drip. Measured monthly average temperatures in the cave ranged seasonally between 8 and 28°C, and daily temperatures vary significantly. At Westcave, calcite growth rates increase with temperature, and the calcite may therefore preferentially record warmer daily or

  4. The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+ partitioning

    Directory of Open Access Journals (Sweden)

    Gebrehiwet Tsigabu A

    2012-01-01

    Full Text Available Abstract Background A proposed strategy for immobilizing trace metals in the subsurface is to stimulate calcium carbonate precipitation and incorporate contaminants by co-precipitation. Such an approach will require injecting chemical amendments into the subsurface to generate supersaturated conditions that promote mineral precipitation. However, the formation of reactant mixing zones will create gradients in both the saturation state and ion activity ratios (i.e., aCO32-/aCa2+. To better understand the effect of ion activity ratios on CaCO3 precipitation kinetics and Sr2+ co-precipitation, experiments were conducted under constant composition conditions where the supersaturation state (Ω for calcite was held constant at 9.4, but the ion activity ratio (r=aCO32-/aCa2+ was varied between 0.0032 and 4.15. Results Calcite was the only phase observed, by XRD, at the end of the experiments. Precipitation rates increased from 41.3 ± 3.4 μmol m-2 min-1 at r = 0.0315 to a maximum rate of 74.5 ± 4.8 μmol m-2 min-1 at r = 0.306 followed by a decrease to 46.3 ± 9.6 μmol m-2 min-1 at r = 1.822. The trend was simulated using a simple mass transfer model for solute uptake at the calcite surface. However, precipitation rates at fixed saturation states also evolved with time. Precipitation rates accelerated for low r values but slowed for high r values. These trends may be related to changes in effective reactive surface area. The aCO32-/aCa2+ ratios did not affect the distribution coefficient for Sr in calcite (DPSr2+, apart from the indirect effect associated with the established positive correlation between DPSr2+ and calcite precipitation rate. Conclusion At a constant supersaturation state (Ω = 9.4, varying the ion activity ratio affects the calcite precipitation rate. This behavior is not predicted by affinity-based rate models. Furthermore, at the highest ion ratio tested, no precipitation was observed, while at the lowest ion ratio precipitation

  5. Comparison of Lactoperoxidase System in Saliva and Buffer Solution on the Inhibition of the Growth of Porphyromonas gingivalis and Fusobacterium nucleatum%不同溶液中乳过氧化物酶系统对Pg和Fn的影响

    Institute of Scientific and Technical Information of China (English)

    李红旭; 胡德渝

    2005-01-01

    比较唾液和缓冲液对含硫氰酸根离子(SCN -)或I -的乳过氧化物酶(LP)抗菌系统抑制牙龈卟啉单胞菌(Porphyromonas gingivalis,Pg)和具核梭杆菌(Fusobacterium nucleatum,Fn) 生长的影响.以Pg(6.0×10 8 /mL)为例,根据所含底物不同,将实验分 2 大组:第 1 大组(含SCN -),分 3 小组:Saliva(对照组),Saliva+(LP-SCN -)组,Buffer+(LP-SCN -)组;第 2 大组(含I -)分 3 小组:Saliva(对照组),Saliva+(LP-I -)组,Buffer+(LP-I -) 组;各组均含H 2O 2(对照组除外),Fn (1.0×10 8 /mL) 分组同Pg.将 2 大组分别在 37 ℃震荡水浴培养 30 min和 60 min,5 μL DTT终止反应,10 倍浓度系列稀释,接种于BHI-S琼脂培养基厌氧培养 4 d并记数CFU.反应至 30 min时,实验组抑制Pg和Fn生长的作用明显高于对照组(P<0.05),Buffer+(LP-I -) 组抑制Pg和Fn生长的作用明显高于Saliva+(LP-I -) 组,且持续到 60 min(P<0.05);反应 60 min时,Buffer+(LP-SCN -) 组抑制Pg生长的作用明显高于Saliva+(LP-SCN -) 组(P<0.05).LP系统在唾液和缓冲液中均能有效抑制Pg和Fn的生长,但是唾液的存在可削弱LP抗菌系统的抑菌作用.

  6. Epitaxial growth of YBa2Cu3O7−x films on Ce0.9La0.1O2−y buffered yttria-stabilized zirconia substrates by an all-chemical-solution route

    DEFF Research Database (Denmark)

    Yue, Zhao; Wu, Wei; Tang, Xiao;

    2014-01-01

    In view of high rate fabrication of coated conductors at low-cost, YBa2Cu3O7 (YBCO) films on Ce0.9La0.1O2−y buffered yttria-stabilized zirconia substrates were deposited by means of a novel low-fluorine metal–organic solution route. A high critical current density of 3 MA cm−2 (77 K, self field......) was achieved on such an all-chemical derived configuration. Structural characterization showed that the enhanced superconductivity performance of the YBCO films is mainly related to the defects induced by the interface....

  7. Incorporation of Eu(III) into Calcite under Recrystallization conditions.

    Science.gov (United States)

    Hellebrandt, S E; Hofmann, S; Jordan, N; Barkleit, A; Schmidt, M

    2016-09-13

    The interaction of calcite with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three calcite powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu(3+) occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different calcites. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na(+). These findings emphasize the different retention potential of calcite as a primary and secondary mineral e.g. in a nuclear waste disposal site.

  8. Incorporation of Eu(III) into Calcite under Recrystallization conditions

    Science.gov (United States)

    Hellebrandt, S. E.; Hofmann, S.; Jordan, N.; Barkleit, A.; Schmidt, M.

    2016-09-01

    The interaction of calcite with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three calcite powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu3+ occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different calcites. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na+. These findings emphasize the different retention potential of calcite as a primary and secondary mineral e.g. in a nuclear waste disposal site.

  9. Explanation for the enhanced dissolution of silica column packing in high pH phosphate and carbonate buffers.

    Science.gov (United States)

    Tindall, G W; Perry, R L

    2003-02-28

    It has been reported that at high pH, the rate of bonded phase packing degradation in methanol/water mobile phases is greater for carbonate and phosphate buffers than for amine buffers. This conclusion was based on buffer pH determined in the aqueous buffer before dilution with methanol. Changes in buffer species pKa, and therefore buffer pH, upon methanol dilution are consistent with the observed degradation results. Measurements of pH in the methanol/water solutions confirm that the carbonate and phosphate buffers were considerably more basic than the amine buffer, even though all the buffers were pH 10 before dilution with methanol. These results demonstrate that it can be misleading to extrapolate aqueous pH data to partially aqueous solutions. Measurements of pH in the mixed solvent provide more reliable predictions of column and sample stability.

  10. 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

  11. A Bicriteria Approximation for the Reordering Buffer Problem

    CERN Document Server

    Barman, Siddharth; Umboh, Seeun

    2012-01-01

    In the reordering buffer problem (RBP), a server is asked to process a sequence of requests lying in a metric space. To process a request the server must move to the corresponding point in the metric. The requests can be processed slightly out of order; in particular, the server has a buffer of capacity k which can store up to k requests as it reads in the sequence. The goal is to reorder the requests in such a manner that the buffer constraint is satisfied and the total travel cost of the server is minimized. The RBP arises in many applications that require scheduling with a limited buffer capacity, such as scheduling a disk arm in storage systems, switching colors in paint shops of a car manufacturing plant, and rendering 3D images in computer graphics. We study the offline version of RBP and develop bicriteria approximations. When the underlying metric is a tree, we obtain a solution of cost no more than 9OPT using a buffer of capacity 4k + 1 where OPT is the cost of an optimal solution with buffer capacit...

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

    OpenAIRE

    Vučinić Dušica R.; Jovanović Vladimir D.; Kolonja Božo M.; Sekulić Živko T.; Mihajlović Slavica R.

    2012-01-01

    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 breaki...

  13. Mechanical properties of polyvinyl chloride mixtures with the addition of modified calcite as filler

    OpenAIRE

    Mihajlović, Slavica R.; Sekulić, Živko T.; Vučinić, Dušica R.; Jovanović, Vladimir D.; Kolonja, Božo M.

    2012-01-01

    In this study, mechanical properties of PVC mixtures (PVC, stabilizer, lubricant and 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 had better mechanical properties compared to those with the calcite modified by the dry process. Tensile and breaking s...

  14. Structural incorporation of Neptunyl(V) into Calcite: Interfacial Reactions and Kinetics

    OpenAIRE

    Heberling, Frank

    2010-01-01

    In this experimental work the calcite-water interface is characterized by means of zetapotential and surface diffraction measurements. Based on the experimental results a new Basic Stern Surface Complexation model for calcite is developed. Neptunyl(V) adsorption at the calcite surface and incorporation into the calcite structure is studied by batch type adsorption- and mixed flow reactor experiments. Adsorption and incorporation species of Neptunyl are investigated by EXAFS spectroscopy.

  15. Deadlock-free Production Scheduling with Dynamic Buffers in MES

    Directory of Open Access Journals (Sweden)

    Taiping Mo

    2014-11-01

    Full Text Available In order to enable enterprises to change the production management mode and improve efficiency, MES provides overall solutions to information integration of manufacturing enterprises. Production scheduling is an important functional module in MES, and research of shop scheduling in MES has important significance. The concept deadlock is first put forward by computer science researchers who are engaged in resource allocation in the operation system. Modern manufacturing enterprises need to process complex workpieces with different processing step, so it is easy to produce a deadlock in the production process. A deadlock will bring many serious consequences for the system. Equipping with enough buffers can solve the problem of deadlock. However, it is costly and there is even no way to allocate buffers in some manufacturing industries. Considering the buffer cost and scheduling index, this paper puts forward the dynamic buffers deadlock-free scheduling to reduce cost and lower risk of the enterprise to a minimum.

  16. Sorption and catalytic oxidation of Fe(II) at the surface of calcite

    NARCIS (Netherlands)

    Mettler, S.; Wolthers, M.; Charlet, L.; Von Gunten, U.

    2009-01-01

    The effect of sorption and coprecipitation of Fe(II) with calcite on the kinetics of Fe(II) oxidation was investigated. The interaction of Fe(II) with calcite was studied experimentally in the absence and presence of oxygen. The sorption of Fe(II) on calcite occurred in two distinguishable steps: (a

  17. Buffer gas acquisition and storage

    Science.gov (United States)

    Parrish, Clyde F.; Lueck, Dale E.; Jennings, Paul A.

    2001-02-01

    The acquisition and storage of buffer gases (primarily argon and nitrogen) from the Mars atmosphere provides a valuable resource for blanketing and pressurizing fuel tanks and as a buffer gas for breathing air for manned missions. During the acquisition of carbon dioxide (CO2), whether by sorption bed or cryo-freezer, the accompanying buffer gases build up in the carbon dioxide acquisition system, reduce the flow of CO2 to the bed, and lower system efficiency. It is this build up of buffer gases that provide a convenient source, which must be removed, for efficient capture of CO2. Removal of this buffer gas barrier greatly improves the charging rate of the CO2 acquisition bed and, thereby, maintains the fuel production rates required for a successful mission. Consequently, the acquisition, purification, and storage of these buffer gases are important goals of ISRU plans. Purity of the buffer gases is a concern e.g., if the CO2 freezer operates at 140 K, the composition of the inert gas would be approximately 21 percent CO2, 50 percent nitrogen, and 29 percent argon. Although there are several approaches that could be used, this effort focused on a hollow-fiber membrane (HFM) separation method. This study measured the permeation rates of CO2, nitrogen (N2), and argon (Ar) through a multiple-membrane system and the individual membranes from room temperature to 193 K and 10 kPa to 300 kPa. Concentrations were measured with a gas chromatograph. The end result was data necessary to design a system that could separate CO2, N2, and Ar. .

  18. Buffer Gas Acquisition and Storage

    Science.gov (United States)

    Parrish, Clyde F.; Lueck, Dale E.; Jennings, Paul A.; Callahan, Richard A.; Delgado, H. (Technical Monitor)

    2001-01-01

    The acquisition and storage of buffer gases (primarily argon and nitrogen) from the Mars atmosphere provides a valuable resource for blanketing and pressurizing fuel tanks and as a buffer gas for breathing air for manned missions. During the acquisition of carbon dioxide (CO2), whether by sorption bed or cryo-freezer, the accompanying buffer gases build up in the carbon dioxide acquisition system, reduce the flow of CO2 to the bed, and lower system efficiency. It is this build up of buffer gases that provide a convenient source, which must be removed, for efficient capture Of CO2 Removal of this buffer gas barrier greatly improves the charging rate of the CO2 acquisition bed and, thereby, maintains the fuel production rates required for a successful mission. Consequently, the acquisition, purification, and storage of these buffer gases are important goals of ISRU plans. Purity of the buffer gases is a concern e.g., if the CO, freezer operates at 140 K, the composition of the inert gas would be approximately 21 percent CO2, 50 percent nitrogen, and 29 percent argon. Although there are several approaches that could be used, this effort focused on a hollow-fiber membrane (HFM) separation method. This study measured the permeation rates of CO2, nitrogen (ND, and argon (Ar) through a multiple-membrane system and the individual membranes from room temperature to 193K and 10 kpa to 300 kPa. Concentrations were measured with a gas chromatograph that used a thermoconductivity (TCD) detector with helium (He) as the carrier gas. The general trend as the temperature was lowered was for the membranes to become more selective, In addition, the relative permeation rates between the three gases changed with temperature. The end result was to provide design parameters that could be used to separate CO2 from N2 and Ar.

  19. Biosorption of divalent Pb, Cd and Zn on aragonite and calcite mollusk shells

    Energy Technology Data Exchange (ETDEWEB)

    Du Yang; Lian Fei [Key Laboratory of Pollution Process and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Urban Ecology Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071 (China); Zhu Lingyan, E-mail: zhuly@nankai.edu.cn [Key Laboratory of Pollution Process and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Urban Ecology Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071 (China)

    2011-07-15

    The potential of using mollusk shell powder in aragonite (razor clam shells, RCS) and calcite phase (oyster shells, OS) to remove Pb{sup 2+}, Cd{sup 2+} and Zn{sup 2+} from contaminated water was investigated. Both biogenic sorbents displayed very high sorption capacities for the three metals except for Cd on OS. XRD, SEM and XPS results demonstrated that surface precipitation leading to crystal growth took place during sorption. Calcite OS displayed a remarkably higher sorption capacity to Pb than aragonite RCS, while the opposite was observed for Cd. However, both sorbents displayed similar sorption capacities to Zn. These could be due to the different extent of matching in crystal lattice between the metal bearing precipitate and the substrates. The initial pH of the solution, sorbent's dosage and grain size affected the removal efficiency of the heavy meals significantly, while the organic matter in mollusk shells affected the removal efficiency to a lesser extent. - Highlights: > Mollusk shells display high removal efficiency to heavy metals in contaminated water. > Surface precipitation leading to crystal growth takes place during the sorption. > Crystal structure similarity between precipitates and substrates affects the sorption. > pH, sorbent dosage and grain size of adsorbent affects the removal efficiency. > Organic matter in mollusk shells affects the removal efficiency to a less extent. - Mollusk shells display high sorption ability to heavy metals and crystal structure similarity between precipitates and substrates affects the sorption.

  20. Thermophysical tests of buffer materials

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, H. [ITC, Tokyo (Japan); Taniguchi, Wataru

    1999-03-01

    Thermodynamic properties of buffer materials were measured for putting in order thermodynamic constants to be used in the near-field thermal analysis. The thermal diffusivity and thermal conductivity were measured as functions of the water content and temperature to deduce the specific heat. The thermal conductivity and specific heat varied significantly as the water content changed. Obtained values of the specific heat agreed well the expected values calculated based on the constituents of the buffer material. Temperature dependence of the thermodynamic constants was found small below 90degC. From the findings, the thermal conductivity and specific heat of the buffer material were formulated as functions of the water content. Thermodynamic study of powdery bentonite was carried out as well with a purpose of use for filling apertures in the artificial barrier. (H. Baba)

  1. Constitutive Response of Microbial Induced Calcite Precipitation Cemented Sands

    Science.gov (United States)

    Feng, Kai

    In the last decade, microbial induced calcite precipitation (MICP) emerged as a novel technique for implementing soil improvement in an environmentally-friendly and economically beneficial manner. However, the mechanical behavior and constitutive response of these materials are still not fully explored by researchers. In this dissertation, the characteristics of MICP cemented sands are investigated through numerical modelling and experimental tests, including macro and micro tests under both static and dynamic loading. In the first part, the mechanical behavior of MICP cemented sands were probed using monotonic load testing and the existence of calcite precipitation was verified by scanning electron microscopy, with this behavior compared to traditionally cemented soil and naturally cemented soil. Both MICP cementation and traditional cementation were verified to be effective in the increase of stiffness and strength, and unique characteristic of MICP cemented soil was highlighted.

  2. Tuning hardness in calcite by incorporation of amino acids

    Science.gov (United States)

    Kim, Yi-Yeoun; Carloni, Joseph D.; Demarchi, Beatrice; Sparks, David; Reid, David G.; Kunitake, Miki E.; Tang, Chiu C.; Duer, Melinda J.; Freeman, Colin L.; Pokroy, Boaz; Penkman, Kirsty; Harding, John H.; Estroff, Lara A.; Baker, Shefford P.; Meldrum, Fiona C.

    2016-08-01

    Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure-property relationships of even the simplest building unit--mineral single crystals containing embedded macromolecules--remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0-7 mol%) or aspartic acid (0-4 mol%), we elucidate the origin of the superior hardness of biogenic calcite. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.

  3. ACETIC ACID AND A BUFFER

    DEFF Research Database (Denmark)

    2009-01-01

    The present invention relates to a composition comprising : a) 0.01-20% wt/wt acetic acid and b) a physiologically tolerable buffer capable of maintaining acetic acid at a pH in the range of 2-7; and use of such a composition as an antimicrobial agent.......The present invention relates to a composition comprising : a) 0.01-20% wt/wt acetic acid and b) a physiologically tolerable buffer capable of maintaining acetic acid at a pH in the range of 2-7; and use of such a composition as an antimicrobial agent....

  4. Investigations into the stabilization of drugs by sugar glasses : III. The influence of various high-pH buffers

    NARCIS (Netherlands)

    Eriksson, Jonas H C; Hinrichs, Wouter L J; de Jong, Gerhardus J; Somsen, Govert W; Frijlink, Henderik W

    2003-01-01

    PURPOSE: To study the effect of the high-pH buffers ammediol, borax, CHES, TRIS, and Tricine on the glass transition temperature of the freeze concentrated fraction (Tg') of trehalose/buffer and inulin/buffer solutions at pH 6.0 and pH 9.8. Also, the glass transition temperature (Tg) of sugar glasse

  5. Adsorption of polar aromatic hydrocarbons on synthetic calcite

    DEFF Research Database (Denmark)

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

    1996-01-01

    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...... of magnitude of Delta G degrees for the adsorption process implies the formation of a strong bond between the calcite surface and the adsorbate molecules. Copyright (C) 1996 Elsevier Science Ltd....

  6. Magnesium-Calcite Crystal Formation Mediated by the Thermophilic Bacterium Geobacillus thermoglucosidasius Requires Calcium and Endospores.

    Science.gov (United States)

    Murai, Rie; Yoshida, Naoto

    2016-11-01

    Fresh Geobacillus thermoglucosidasius cells grown on soybean-casein digest nutrient agar were inoculated as a parent colony 1 cm in diameter on the surface of an agar gel containing acetate and calcium ions (calcite-promoting hydrogel) and incubated at 60 °C for 4 days, after which magnesium-calcite single crystals of 50-130 µm in size formed within the parent colony. Addition of EDTA, polyacrylic acid or N,N-dicyclohexylcarbodiimide to the calcite-forming hydrogel inhibited the parent colony from forming magnesium-calcite crystals. Inoculation of G. thermoglucosidasius on calcite-forming hydrogel containing 5 µM cadmium and 20 µM zinc resulted in a decrease in the sporulation rate from 55 to 7-8 %. Magnesium-calcite synthesis decreased relative to the sporulation rate. G. thermoglucosidasius exhibited higher adsorption/absorbance of calcium than other Geobacillus sp. that do not mediate calcite formation and higher levels of magnesium accumulation. Calcium ions contained in the calcite-promoting hydrogel and magnesium ions concentrated in G. thermoglucosidasius cells serve as the elements for magnesium-calcite synthesis. The observed decreases in sporulation rate and magnesium-calcite formation support the hypothesis that endospores act as nuclei for the synthesis of magnesium-calcite single crystals.

  7. Meteoric calcitization of magnesite in Miocene lacustrine deposits (Calatayud basin, NE Spain)

    Science.gov (United States)

    Cañaveras, J. C.; Sánchez-Moral, S.; Sanz-Rubio, E.; Hoyos, M.

    1998-08-01

    Sedimentary magnesite deposits are commonly present in evaporite successions in the Tertiary Calatayud basin (NE Spain). Outcropping evaporite sequences, mainly composed of secondary gypsum after anhydrite-glauberite, show centimetre-thick layers of magnesite passing laterally into calcite pseudospar. Petrographic and stable isotope data indicate that calcite pseudospar formed via late-stage calcitization of magnesite under near-surface conditions. Calcitization occurred by the interaction between magnesite and Ca-enriched waters derived from the dissolution of gypsum and/or glauberite. The geochemical simulation of this process, petrographic evidence, and the correlation between the magnesite/calcite ratio and the δ18O values of both magnesite and calcite samples across the reaction front are in agreement with the existence of neoformed 18O-depleted magnesite during the waning stages of the calcitization process.

  8. Interactions of salicylic acid derivatives with calcite crystals.

    Science.gov (United States)

    Ukrainczyk, Marko; Gredičak, Matija; Jerić, Ivanka; Kralj, Damir

    2012-01-01

    Investigation of basic interactions between the active pharmaceutical compounds and calcium carbonates is of great importance because of the possibility to use the carbonates as a mineral carrier in drug delivery systems. In this study the mode and extent of interactions of salicylic acid and its amino acid derivates, chosen as pharmaceutically relevant model compounds, with calcite crystals are described. Therefore, the crystal growth kinetics of well defined rhombohedral calcite seed crystals in the systems containing salicylic acid (SA), 5-amino salicylic acid (5-ASA), N-salicyloil-l-aspartic acid (N-Sal-Asp) or N-salicyloil-l-glutamic acid (N-Sal-Glu), were investigated. The precipitation systems were of relatively low initial supersaturation and of apparently neutral pH. The data on the crystal growth rate reductions in the presence of the applied salicylate molecules were analyzed by means of Cabrera & Vermileya's, and Kubota & Mullin's models of interactions of the dissolved additives and crystal surfaces. The crystal growth kinetic experiments were additionally supported with the appropriate electrokinetic, spectroscopic and adsorption measurements. The Langmuir adsorption constants were determined and they were found to be in a good correlation with values obtained from crystal growth kinetic analyses. The results indicated that salicylate molecules preferentially adsorb along the steps on the growing calcite surfaces. The values of average spacing between the adjacent salicylate adsorption active sites and the average distance between the neighboring adsorbed salicylate molecules were also estimated.

  9. The Uptake of Eu(III) and Th(IV) by Calcite under Hyperalkaline Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Tits, J.; Wieland, E.; Bradbury, M.H.; Eckert, P.; Schaible, A

    2002-10-01

    Calcite is an important component of Valanginian marl, a potential host rock for a low and intermediate level radioactive waste (L/ILW) repository in Switzerland. This mineral also forms an important component of the disturbed zone around a repository, as it remains largely unaffected by the hyperalkaline waters migrating out of the cementitious repository . The sorption behaviour of Eu(III) and Th(IV) on Merck calcite in an artificial cement pore water (ACW) at pH 13.3 has been studied in batch-type sorption experiments. In addition, the effect of {alpha}-isosaccharinic acid (ISA) and gluconic acid (GLU) on the sorption of these two cations has been investigated. In the absence of ISA and GLU, a strong interaction of Eu(III) and Th(IV) with Merck calcite was observed. Eu(III) and Th(IV) sorption kinetics were fast and the isotherms indicated a linear adsorption behaviour over the experimentally accessible concentration range. In the case of Eu(III), a decrease of the R{sub d} value with increasing solid to liquid (S:L) ratio was observed indicating that, along with adsorption, other processes might influence the immobilisation of this cation by Merck calcite under ACW conditions. In the case of Th(IV), however, changes in the S:L ratio had no effect on the sorption behaviour . High ISA and GLU concentrations in solution significantly affected the sorption of both Eu(III) and Th(IV): R{sub d} values for Eu(III) decreased significantly at ISA concentrations higher than 10{sup -5} M and at GLU concentrations higher than 10{sup -7} M. The sorption of Th(IV) was reduced at ISA concentrations above 2.10{sup -5} M and at GLU concentrations above 10{sup -6} M. The effects of ISA and GLU on the immobilisation of Eu(III) and Th(IV) were interpreted in terms of complex formation in solution. In the case of Eu(III) the metal ligand complexes were found to have a 1 : 1 stoichiometry. Complexation constants derived for the aqueous Eu(III)-ISA. and Eu(III)GLU complexes were

  10. Thermo-hydro-geochemical modelling of the bentonite buffer. LOT A2 experiment

    Energy Technology Data Exchange (ETDEWEB)

    Sena, Clara; Salas, Joaquin; Arcos, David (Amphos 21 Consulting S.L., Barcelona (Spain))

    2010-12-15

    /condensation process /Karnland et al. 2009/. Once bentonite is water saturated, the transport of solutes is driven by diffusion. Although Donnan equilibrium /Birgersson and Karnland 2009/ and anion exclusion /Muurinen et al. 2004/ are able to influence the mobility of chloride in the bentonite buffer, under the high temperature LOT A2 test conditions, measured data seem to indicate a relatively low influence of these processes on the transport of chloride. For this reason, the transport of chloride has been modelled taking into account advective, dispersive and diffusive fluxes that are believed to have occurred in the LOT A2 test. Numerical results were conducted at fixed thermal gradients for both heated and non-heated bentonite based on the temperatures recorded during the experiment for both heated and non-heated bentonite. The computed evolution of the bentonite saturation indicates that, within approximately one year, the bentonite blocks located at the depth of the heater are completely water saturated which agrees with measured data. The simulated transport of chloride is also in good agreement with data measured at the end of the LOT A2 test for the two cases considered, reflecting the reliability of the conceptual model defined for the LOT A2 test. Based on the geochemical data obtained at end of the LOT A2 test, and on previous modelling exercises /Arcos et al. 2006/, the main geochemical processes that are believed to have developed during the LOT A2 test are: (i) precipitation/dissolution of carbonate, sulphate and silica minerals and, (ii) cation exchange in the montmorillonite interlayer. Numerical results predict the dissolution - precipitation of anhydrite, calcite and silica in the heated bentonite in agreement with data measured at the end of the LOT A2 test

  11. A Capital Adequacy Buffer Model

    NARCIS (Netherlands)

    D.E. Allen (David); M.J. McAleer (Michael); R.J. Powell (Robert); A.K. Singh (Abhay)

    2013-01-01

    markdownabstract__Abstract__ In this paper, we develop a new capital adequacy buffer model (CABM) which is sensitive to dynamic economic circumstances. The model, which measures additional bank capital required to compensate for fluctuating credit risk, is a novel combination of the Merton structur

  12. ON OPTIMAL LOCAL BUFFER ALLOCATION IN FLEXIBLE MANUFACTURING SYSTEMS

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    An optimal design problem of local buffer allocation in the FMS is discussed in order to maximize a reward earned from processed jobs at all workstations. Structural properties of the optimal design problem are analyzed for the model with two job routing policies. Based on these properties, approaches to optimal solutions are given.

  13. Integrated optical buffers for packet-switched networks

    Science.gov (United States)

    Burmeister, Emily Frances

    Routers form the backbone of the Internet, directing data to the right locations with huge throughput capacity of terabits/second) and very few errors (1 error allowed in 1012 bits). However, as the Internet continues to grow rapidly, so must the capacity of electronic routers, thereby also growing in footprint and power consumption. The energy bill alone has developers looking for an alternate solution. Today's routers can only operate with electrical signals although Internet data is transmitted optically. This requires the data to be converted from the optical domain to the electrical domain and back again. Optical routers have the potential of saving in power by omitting these conversions, but have been held back in part by the lack of a practical optical memory device. This work presents the first integrated optical buffer for next generation optical packet-switched networks. Buffering is required in a router to move packets of data in order to avoid collisions between packets heading to the same destination at the same time. The device presented here uses an InP-based two-by-two switch with a silica waveguide delay to form a recirculating buffer. Packet storage was shown with 98% packet recovery for 5 circulations. Autonomous contention resolution was demonstrated with two buffered channels to show that the technology is a realistic solution for creating multiple element buffers on multiple router ports. This thesis proposes and demonstrates the first integrated optical random access memory, thereby making a great stride toward high capacity optical routers.

  14. Experimental acidification of two biogeochemically-distinct neotropical streams: Buffering mechanisms and macroinvertebrate drift

    Energy Technology Data Exchange (ETDEWEB)

    Ardón, Marcelo, E-mail: ardonsayaom@ecu.edu [Department of Biology and North Carolina Center for Biodiversity, East Carolina University, Greenville, NC 27858 (United States); Duff, John H. [U.S. Geological Survey, Menlo Park, CA 94025 (United States); Ramírez, Alonso [Department of Environmental Sciences, University of Puerto Rico, San Juan, PR 00931 (Puerto Rico); Small, Gaston E. [Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN 55108 (United States); Jackman, Alan P. [University of California, Davis, CA 95616 (United States); Triska, Frank J. [U.S. Geological Survey, Menlo Park, CA 94025 (United States); Pringle, Catherine M. [Odum School of Ecology, University of Georgia, Athens, GA 30602 (United States)

    2013-01-15

    Research into the buffering mechanisms and ecological consequences of acidification in tropical streams is lacking. We have documented seasonal and episodic acidification events in streams draining La Selva Biological Station, Costa Rica. Across this forested landscape, the severity in seasonal and episodic acidification events varies due to interbasin groundwater flow (IGF). Streams that receive IGF have higher concentrations of solutes and more stable pH (∼ 6) than streams that do not receive IGF (pH ∼ 5). To examine the buffering capacity and vulnerability of macroinvertebrates to short-term acidification events, we added hydrochloric acid to acidify a low-solute, poorly buffered (without IGF) and a high-solute, well buffered stream (with IGF). We hypothesized that: 1) protonation of bicarbonate (HCO{sub 3}{sup −}) would neutralize most of the acid added in the high-solute stream, while base cation release from the sediments would be the most important buffering mechanism in the low-solute stream; 2) pH declines would mobilize inorganic aluminum (Ali) from sediments in both streams; and 3) pH declines would increase macroinvertebrate drift in both streams. We found that the high-solute stream neutralized 745 μeq/L (96% of the acid added), while the solute poor stream only neutralized 27.4 μeq/L (40%). Protonation of HCO{sub 3}{sup −} was an important buffering mechanism in both streams. Base cation, Fe{sup 2+}, and Ali release from sediments and protonation of organic acids also provided buffering in the low-solute stream. We measured low concentrations of Ali release in both streams (2-9 μeq/L) in response to acidification, but the low-solute stream released double the amount Ali per 100 μeq of acid added than the high solute stream. Macroinvertebrate drift increased in both streams in response to acidification and was dominated by Ephemeroptera and Chironomidae. Our results elucidate the different buffering mechanisms in tropical streams and

  15. Geochemical signatures of fluid paleo-transfer in fracture filling calcite from low permeability rock masses: examples taken from Bure's and Tournemire's site in France and northern Switzerland; Signatures geochimiques de paleocirculations aqueuses dans la calcite de remplissage de fracture de massifs argileux peu permeables et de leurs encaissants: exemples pris sur les sites de Bure, Tournemire et Suisse du nord

    Energy Technology Data Exchange (ETDEWEB)

    Lecocq, D

    2002-12-15

    Fractures in rock masses represent preferential path for fluid transfer and, as such, are the most efficient way for migration of radionuclides at a regional scale. The impact of fracturing on hydrogeological system is a major challenge for underground radioactive waste storage projects. In this context, geochemistry of fracture-filling calcite is used to better understand physical and chemical properties of palaeo-fluids. A new methodology has been developed to analyze Mg, Mn, Fe, Sr and Rare Earth Elements REE (La, Ce, Nd, Sm, Eu, Dy and Yb) in calcite by Secondary Ion Mass Spectrometry. Analyses of calcite crystals have been performed in fractures from Jurassic clays and limestones in France (Bure and Tournemire sites) and northern Switzerland (Mt Terri's tunnel and deep borehole). On each case, several geochemical signatures are observed, according to REE partitioning and Mn and Fe concentrations. In the Bure site, a dependence of calcite geochemistry from fracture host rock has been evidenced. On the other hand, speciation of REE in solution equilibrated with clayey or calcareous rocks at circum-neutral pH (7 to 8) is not significantly influenced by the media: speciation is dominated by carbonate species in both cases and phosphate complexes can modify heavy REE availability in relatively to light REE. These results point out that in fractures in clays, calcite crystallizes at equilibrium with a fluid expulsed during diagenesis from clay minerals, recording the effect of clays and accessory phases. In limestone fractures, calcite records a later event related to the past functioning of the present aquifer, and the fluid has reached equilibrium with the rock minerals. In secondary filling calcite from Toarcian Argilites faults close to Tournemire's tunnel, three successive generations of calcite are observed in an extensive fault, and a fourth in a compressive one. In Aalenian Opalinus Clays veins, comparison between existing isotopic data and Mn, Fe

  16. Photoinduced synthesis of single-digit micrometer-size spheroidal calcite composites in the presence of partially hydrolyzed poly(vinyl alcohol)

    Science.gov (United States)

    Nishio, Takashi; Naka, Kensuke

    2015-06-01

    Photoinduced crystallization of calcium carbonate (CaCO3), which was based on the photodecarboxylation of ketoprofen (KP, 2-(3-benzoylphyenyl)propionic acid) under alkaline conditions of pH 8.4 and 10 was studied for preparation of CaCO3 composite particles in single-digit micrometer-sizes. In this method, a homogeneous solution comprising KP, calcium chloride, ammonia, and partially hydrolyzed poly(vinyl alcohol) (PVAPS, degree of saponification: 86.5-89.0 mol%) was used as a precursor solution and was exposed to ultraviolet (UV) irradiation for different time periods. After the UV irradiation for 50 min, calcite spheroids in single-digit micrometer-sizes were obtained as major products at pH 8.4. The obtained calcite spheroids contained organic components of about 10 wt%. The comparison of the characteristics of the CaCO3 obtained at pH 8.4 and 10 suggests that the nucleation and crystallization of both vaterite and calcite continuously took place in a moderated supersaturation owing to the CO2 hydration equilibrium as long as the photodecarboxylation of KP continued. Consequently, the aggregation-based crystal growth in the presence of PVAPS seemed to enable the formation of the spheroidal composites of calcite in single-digit micrometer-sizes.

  17. 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.

  18. PAM微球表面方解石晶体的制备与表征%Synthesis and characterization of calcite crystal on surface of PAM microgel

    Institute of Scientific and Technical Information of China (English)

    李红; 阮美茹

    2013-01-01

    The synthesis of calcium carbonate crystals (calcite) from aqueous solutions containing polyacrylamide(PAM) microgels was performed by the method of dipping of the solution of CaCl2 and Na2CO3 by turns.The formation of calcite in several laboratory experiments was discussed.The PAM-CaCO3 composite spheres were characterized by SEM,FFIR,EDX,TAG.It was demonstrated that rhombohedral calcite is produced on the surface of microgels.Increasing the concentration of dipping solution,reaction speed quickens,meanwhile rhombohedral calcite begins to cluster.But delaying alternation time and increasing microgels quantity,size of calcite particles and clusters change smaller.%将聚丙烯酰胺(PAM)微凝胶在CaCl2和Na2CO3溶液中交替浸渍,其表面发生碳酸钙沉积反应,研究不同实验条件对所形成碳酸钙晶体(方解石)形貌的影响.利用SEM、FFIR、EDX、TAG等分析手段对制备的PAM-CaCO3复合微球进行表征.结果表明,在PAM微凝胶表面形成了由菱形层状簇集的方解石形貌;随着浸渍的溶液浓度增大,反应速度加快,层数增加,堆积成串状;但浸渍交替时间的延长和PAM微凝胶量的加大,均会使所形成的方解石颗粒变大,簇集层数减少.

  19. Environmentally acceptable effect of hydrogen peroxide on cave 'lamp-flora', calcite speleothems and limestones

    Energy Technology Data Exchange (ETDEWEB)

    Faimon, Jiri; Stelcl, Jindrich; Kubesova, Svatava; Zimak, Jiri

    2003-04-01

    Hydrogen peroxide plus limestone fragments allows removal of organisms without corrosion of limestone and speleothem. - 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 Katerinska 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 3.77x10{sup -3} and 1.81x10{sup -3} mol m{sup -2} h{sup -1}, respectively. In the 15% peroxide solution, the limestone and speleothem dissolution rates were one order of magnitude higher, 2.00x10{sup -2} and 2.21x10{sup -2} mol m{sup -2} h{sup -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.

  20. New Proactive Time Buffer Heuristics for Robust Project Scheduling

    Science.gov (United States)

    Elshaer, Raafat; Yamamoto, Hidehiko

    Robust scheduling is aiming at constructing proactive schedules capable of dealing with multiple disruptions during project execution. Insertion a time buffer, before an activity start time, is a method to improve the robustness (stability) of a baseline schedule. In this paper, we introduce new heuristics for inserting time buffers in a given baseline schedule while the project due date is predefined and stochastic activity duration is considered. Computational results obtained from a set of benchmark projects show that the proposed heuristics capable of generating proactive schedules with acceptable quality and solution robustness.

  1. Influence of glyphosate on the copper dissolution in phosphate buffer

    Science.gov (United States)

    Coutinho, C. F. B.; Silva, M. O.; Machado, S. A. S.; Mazo, L. H.

    2007-01-01

    The electrochemical behavior of copper microelectrode in phosphate buffer in the presence of glyphosate was investigated by electrochemical techniques. It was observed that the additions of glyphosate in the phosphate buffer increased the anodic current of copper microelectrode and the electrochemical dissolution was observed. This phenomenon could be associated with the Cu(II) complexation by glyphosate forming a soluble complex. Physical characterization of the surface showed that, in absence of glyphosate, an insoluble layer covered the copper surface; on the other hand, in presence of glyphosate, it was observed a corroded copper surface with the formation of glyphosate complex in solution.

  2. Cell buffer with built-in test

    Science.gov (United States)

    Ott, William E. (Inventor)

    2004-01-01

    A cell buffer with built-in testing mechanism is provided. The cell buffer provides the ability to measure voltage provided by a power cell. The testing mechanism provides the ability to test whether the cell buffer is functioning properly and thus providing an accurate voltage measurement. The testing mechanism includes a test signal-provider to provide a test signal to the cell buffer. During normal operation, the test signal is disabled and the cell buffer operates normally. During testing, the test signal is enabled and changes the output of the cell buffer in a defined way. The change in the cell buffer output can then be monitored to determine if the cell buffer is functioning correctly. Specifically, if the voltage output of the cell buffer changes in a way that corresponds to the provided test signal, then the functioning of the cell buffer is confirmed. If the voltage output of the cell buffer does not change correctly, then the cell buffer is known not to be operating correctly. Thus, the built in testing mechanism provides the ability to quickly and accurately determine if the cell buffer is operating correctly. Furthermore, the testing mechanism provides this functionality without requiring excessive device size and complexity.

  3. Effect of airborne particle on SO 2-calcite reaction

    Science.gov (United States)

    Böke, Hasan; Göktürk, E. Hale; Caner-Saltık, Emine N.; Demirci, Şahinde

    1999-02-01

    In modern urban atmosphere, sulphur dioxide (SO 2) attacks calcite (CaCO 3) in calcareous stone-producing gypsum (CaSO 4·2H 2O) which forms crust at rain sheltered surfaces and accelerates erosion at areas exposed to rain. The airborne particles collected on stone surfaces have always been considered to enhance the gypsum crust formation and thus it is believed that they should be removed from the surface to decrease the effects of SO 2. In this study, our aim was to investigate this event by carrying out a series of experiments in laboratory using pure calcium carbonate powder to represent calcareous stone. Sodium montmorillonite, activated carbon, ferric oxide, vanadium pentoxide and cupric chloride were mixed in the pure calcium carbonate powder as substitutes of the airborne particles in the polluted atmosphere. The samples have been exposed at nearly 10 ppmv SO 2 concentrations at 90% relative humidity conditions in a reaction chamber for several days. The mineralogical composition of the exposed samples were determined by X-ray diffraction (XRD) analysis and infrared spectrometer (IR). Sulphation reaction products, calcium sulphite hemihydrate, gypsum and unreacted calcite, were determined quantitatively using IR. Exposed samples have also been investigated morphologically using a scanning electron microscope (SEM). Experimental results reveal that calcium sulphite hemihydrate is the main reaction product of the SO 2-calcite reaction. It turns out that airborne particles play an important catalytic role in the oxidation of calcium sulphite hemihydrate into gypsum, although their presence does not very significantly affect the extent of sulphation reaction. This behaviour of airborne particles is explained by the presence of liquid film on the calcium carbonate surface where a series of reactions in the gas-liquid-solid interfaces takes place.

  4. 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.

  5. 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.".

  6. Microscopic optical buffering in a harmonic potential

    CERN Document Server

    Sumetsky, M

    2015-01-01

    In the early days of quantum mechanics, Schr\\"odinger noticed that oscillations of a wave packet in a one-dimensional harmonic potential well are periodic and, in contrast to those in anharmonic potential wells, do not experience distortion over time. This original idea did not find applications up to now since an exact one-dimensional harmonic resonator does not exist in nature and has not been created artificially. However, an optical pulse propagating in a bottle microresonator (a dielectric cylinder with a nanoscale-high bump of the effective radius) can exactly imitate a quantum wave packet in the harmonic potential. Here, we propose a tuneable microresonator that can trap an optical pulse completely, hold it as long as the material losses permit, and release it without distortion. This result suggests the solution of the long standing problem of creating a microscopic optical buffer, the key element of the future optical signal processing devices.

  7. Simulating Succinate-Promoted Dissolution at Calcite {104} Steps

    Science.gov (United States)

    Mkhonto, D.; Sahai, N.

    2008-12-01

    Organic molecules of a wide range of molecular weights from small organic acids, amino-acids, acidic peptides and acidic proteins to humic and fulvic acids play a key role in modulating nucleation, crystal growth and dissolution of calcium carbonate polymorphs. In general, these acidic molecules inhibit calcite growth and, promote dissolution preferentially along specific crystallographic directions, in the process, regulating crystal shape and size, and even whether a metastable polymorph (e.g., vaterite or aragonite) is nucleated first. For example, chiral faces of calcite are selected by chiral amino-acids and the unusual {hk0} faces are expressed in the presence of amino-acids [Orme et al., 2001], and unusual heptagonal dissolution etch-pit are seen in the presence of succinate compared to the normal rhombohedral pits in water alone [Teng et al., 2006]. Thus, the presence of unusual crystal morphologies may indicate organic-mediated growth, thus serving as a biosignature. We have conducted the Molecular Dynamics (MD) simulations using the Consistent Valence Force Field (CVFF) as implemented in the FORCITE© module of the Materials Studio © software package (Accelrys, Inc. TM) to model the adsorption of succinate, a dicarboxylic acid, and charge- balancing Na+ ions on dry and hydrated steps in different directions on the {104} cleavage face of calcite [Mkhonto and Sahai, in prep.]. At the site of succinate adsorption, we find elongation of the interatomic distances (Ca-OCO3,i) between surface Ca2+ cation and the oxygen of the underlying inorganic CO32- anion the first surface layer of calcite, compared to the corresponding distances in the presence of water alone, suggesting greater ease of surface Ca2+ detachment. This result is consistent with the empirically observed increase in overall dissolution rate with succinate [Teng et al., 2006]. Furthermore, succinate adsorption lowers the step energies, which explains the appearance of steps in the unsusual [42

  8. Buffering agents modify the hydration landscape at charged interfaces.

    Science.gov (United States)

    Trewby, William; Livesey, Duncan; Voïtchovsky, Kislon

    2016-03-07

    Buffering agents are widely used to stabilise the pH of solutions in soft matter and biological sciences. They are typically composed of weak acids and bases mixed in an aqueous solution, and can interact electrostatically with charged surfaces such as biomembranes. Buffers can induce protein aggregation and structural modification of soft interfaces, but a molecular-level picture is still lacking. Here we use high-resolution atomic force microscopy to investigate the effect of five commonly used buffers, namely 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES), 2-(N-morpholino)ethanesulfonic acid (MES), monosodium phosphate, saline sodium citrate (SSC) and tris(hydroxymethyl)aminomethane (Tris) on the hydration landscape of Muscovite mica in solution. Mica is an ideal model substrate due to its negative surface charge and identical lattice parameter when compared with gel-phase lipid bilayers. We show that buffer molecules can produce cohesive aggregates spanning over tens of nanometres of the interface. SSC, Tris and monosodium phosphate tend to create an amorphous mesh layer several molecules thick and with no preferential ordering. In contrast, MES and HEPES adopt epitaxial arrangements commensurate with the underlying mica lattice, suggesting that they offer the most suitable solution for high-resolution studies. To confirm that this effect persisted in biologically-relevant interfaces, the experiments were repeated on a silica-supported lipid bilayer. Similar trends were observed for this system using atomic force microscopy as well as ellipsometry. The effect of the buffering agents can be mitigated by the inclusion of salt which helps displace them from the interface.

  9. Unusual calcite stromatolites and pisoids from a landfill leachate collection system

    Science.gov (United States)

    Maliva, Robert G.; Missimer, Thomas M.; Leo, Kevin C.; Statom, Richard A.; Dupraz, Christophe; Lynn, Matthew; Dickson, J. A. D.

    2000-10-01

    Low-magnesium calcite stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a Palm Beach County, Florida, landfill. The stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with calcite. The stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous crystals. The pisoids consist of concentric layers of radial fibrous and microcrystalline calcite. Bacteria, likely sulfate reducing, appear to have acted as catalysts for calcite crystal nucleation, and thus the formation of the stromatolites and pisoids. The leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation. By acting as catalysts for calcite nucleation, bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions. Rapid calcite precipitation catalyzed by bacteria has interfered with the operation of the Palm Beach County landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites.

  10. Effects of hypertonic buffer composition on lymph node uptake and bioavailability of rituximab, after subcutaneous administration.

    Science.gov (United States)

    Fathallah, Anas M; Turner, Michael R; Mager, Donald E; Balu-Iyer, Sathy V

    2015-03-01

    The subcutaneous administration of biologics is highly desirable; however, incomplete bioavailability after s.c. administration remains a major challenge. In this work we investigated the effects of excipient dependent hyperosmolarity on lymphatic uptake and plasma exposure of rituximab as a model protein. Using Swiss Webster (SW) mice as the animal model, we compared the effects of NaCl, mannitol and O-phospho-L-serine (OPLS) on the plasma concentration of rituximab over 5 days after s.c. administration. An increase was observed in plasma concentrations in animals administered rituximab in hypertonic buffer solutions, compared with isotonic buffer. Bioavailability, as estimated by our pharmacokinetic model, increased from 29% in isotonic buffer to 54% in hypertonic buffer containing NaCl, to almost complete bioavailability in hypertonic buffers containing high dose OPLS or mannitol. This improvement in plasma exposure is due to the improved lymphatic trafficking as evident from the increase in the fraction of dose trafficked through the lymph nodes in the presence of hypertonic buffers. The fraction of the dose trafficked through the lymphatics, as estimated by the model, increased from 0.05% in isotonic buffer to 13% in hypertonic buffer containing NaCl to about 30% for hypertonic buffers containing high dose OPLS and mannitol. The data suggest that hypertonic solutions may be a viable option for improving s.c. bioavailability.

  11. Electrodialytic membrane suppressors for ion chromatography make programmable buffer generators.

    Science.gov (United States)

    Chen, Yongjing; Srinivasan, Kannan; Dasgupta, Purnendu K

    2012-01-01

    The use of buffer solutions is immensely important in a great variety of disciplines. The generation of continuous pH gradients in flow systems plays an important role in the chromatographic separation of proteins, high-throughput pK(a) determinations, etc. We demonstrate here that electrodialytic membrane suppressors used in ion chromatography can be used to generate buffers. The generated pH, computed from first principles, agrees well with measured values. We demonstrate the generation of phosphate and citrate buffers using a cation-exchange membrane (CEM) -based anion suppressor and Tris and ethylenediamine buffers using an anion-exchange membrane (AEM) -based cation suppressor. Using a mixture of phosphate, citrate, and borate as the buffering ions and using a CEM suppressor, we demonstrate the generation of a highly reproducible (avg RSD 0.20%, n = 3), temporally linear (pH 3.0-11.9, r(2) > 0.9996), electrically controlled pH gradient. With butylamine and a large concentration (0.5 M) of added NaCl, we demonstrate a similar linear pH gradient of large range with a near-constant ionic strength. We believe that this approach will be of value for the generation of eluents in the separation of proteins and other biomolecules and in online process titrations.

  12. Doped LZO buffer layers for laminated conductors

    Science.gov (United States)

    Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

    2010-03-23

    A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

  13. 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.

  14. Calcite sealing in a fractured geothermal reservoir: Insights from combined EBSD and chemistry mapping

    Science.gov (United States)

    McNamara, David D.; Lister, Aaron; Prior, Dave J.

    2016-09-01

    Fractures play an important role as fluid flow pathways in geothermal resources hosted in indurated greywacke basement of the Taupo Volcanic Zone, New Zealand, including the Kawerau Geothermal Field. Over time, the permeability of such geothermal reservoirs can be degraded by fracture sealing as minerals deposit out of transported geothermal fluids. Calcite is one such fracture sealing mineral. This study, for the first time, utilises combined data from electron backscatter diffraction and chemical mapping to characterise calcite vein fill morphologies, and gain insight into the mechanisms of calcite fracture sealing in the Kawerau Geothermal Field. Two calcite sealing mechanisms are identified 1) asymmetrical syntaxial growth of calcite, inferred by the presence of single, twinned, calcite crystals spanning the entire fracture width, and 2) 3D, interlocking growth of bladed vein calcite into free space as determined from chemical and crystallographic orientation mapping. This study also identifies other potential uses of combined EBSD and chemical mapping to understand geothermal field evolution including, potentially informing on levels of fluid supersaturation from the study of calcite lattice distortion, and providing information on a reservoir's history of stress, strain, and deformation through investigation of calcite crystal deformation and twinning patterns.

  15. Molecular simulation of oligomer inhibitors for calcite scale

    Institute of Scientific and Technical Information of China (English)

    Qiuyu Zhang; Hua Ren; Wenwen Wang; Junping Zhang; Hepeng Zhang

    2012-01-01

    Molecular simulation was performed to study the interaction between CaCO3 crystal and several oligomer inhibitors,by using the equilibrium morphology method to calculate the growth morphology of CaCO3 without inhibitors.The calculated morphology agreed well with SEM photographs.Then,a double-layer model was built to investigate the interaction between calcite crystal and oligomer inhibitors containing maleic anhydride (MA) and acrylic acid (AA).Interaction energy per gram of an oligomer inhibitor was introduced as a scale of inhibition efficiency of different monomers.The results indicated that,for calcite scale inhibition,acrylamide (AM) and vinyl phosphonic acid (VPA) were the most efficient monomers,while allylsulfonic acid (AS) was the poorest.Increasing proportion of AM in dimer inhibitor molecule would improve the inhibition efficiency of MA,though,for a trimer,such as MA-AA-AM,certain sequence of monomers in the inhibitor molecule was necessary besides higher proportion of AM.

  16. 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.

  17. Environmental controls on the Emiliania huxleyi calcite mass

    Science.gov (United States)

    Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

    2013-06-01

    Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO32-], there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high CO2 world and improve interpretation of paleorecords.

  18. Temperature buffer test. Hydro-mechanical and chemical/ mineralogical characterizations

    Energy Technology Data Exchange (ETDEWEB)

    Aakesson, Mattias; Olsson, Siv; Dueck, Ann; Nilsson, Ulf; Karnland, Ola [Clay Technology AB, Lund (Sweden); Kiviranta, Leena; Kumpulainen, Sirpa [BandTech Oy, Helsinki (Finland); Linden, Johan [Aabo Akademi, Aabo (Finland)

    2012-01-15

    TEM), iron oxidation state (Moessbauer spectroscopy). The retention tests, the CEC-determinations, the chemical analyses by ICP, and the mineralogical analyses by XRD and FTIR were performed on bulk samples as well as on a Na-converted fine fraction (<0.5 {mu}m). The latter fraction was subjected also to TEM analyses. The hydro-mechanical characterizations of the bentonite resulted in the following observations: i) compared to the reference material no large deviation was seen in the retention curves for the Na converted fine fraction of the material from the innermost positions, and for the bulk material from the same positions a marked deviation was observed for equilibrium with RH = 97%; ii) a reduction in swelling pressure was observed on re-saturated samples from the field experiment, especially on those from the innermost part. Measured hydraulic conductivity values were generally scattered, but displayed a tendency with increased values on re-saturated specimens drilled from the innermost part, and a similar tendency was also observed on ground and re-compacted specimens and specimens prepared from dried material; iii) the triaxial test performed on the one specimen from the inner part demonstrated a brittle behaviour involving high stiffness, high shear strength, and low strain at failure; and iv) the unconfined compression tests demonstrated a reduced strain at failure on all specimens from the field material, and also a reduced maximum deviator stress on the re-saturated specimens from the innermost position. The chemical/mineralogical characterization indicated that: i) sulfate was redistributed under the thermal and hydration gradients that were prevalent during the test. Anhydrite accumulated at some distance from the heater, whereas gypsum was dissolved in the peripheral parts of the buffer where water was supplied; ii) cristobalite was dissolved at the bentonite/heater contact; iii) calcite was dissolved in the warmest parts of the block; iv

  19. Ultrasonic assisted arsenate adsorption on solvothermally synthesized calcite modified by goethite, α-MnO2 and goethite/α-MnO2.

    Science.gov (United States)

    Markovski, Jasmina S; Đokić, Veljko; Milosavljević, Milutin; Mitrić, Miodrag; Perić-Grujić, Aleksandra A; Onjia, Antonije E; Marinković, Aleksandar D

    2014-03-01

    A highly porous calcium carbonate (calcite; sorbent 1) was used as a support for modification with α-FeOOH (calcite/goethite; sorbent 2), α-MnO2 (calcite/α-MnO2; sorbent 3) and α-FeOOH/α-MnO2 (calcite/goethite/α-MnO2; sorbent 4) in order to obtain a cheap hybrid materials for simple and effective arsenate removal from aqueous solutions. The adsorption ability of synthesized adsorbents was studied as a function of functionalization methods, pH, contact time, temperature and ultrasonic treatment. Comparison of the adsorptive effectiveness of synthesized adsorbents for arsenate removal, under ultrasound treatment and classical stirring method, has shown better performance of the former one reaching maximum adsorption capacities of 1.73, 21.00, 10.36 and 41.94 mg g(-1), for sorbents 1-4, respectively. Visual MINTEQ equilibrium speciation modeling was used for prediction of pH and interfering ion influences on arsenate adsorption.

  20. Impact of Montmorillonite and Calcite on Release and Adsorption of Cyanobacterial Fatty Acids at Ambient Temperature

    Institute of Scientific and Technical Information of China (English)

    Liu Deng; Yang Xiaofen; Wang Hongmei; Li Jihong; Su Nian

    2008-01-01

    Minerals might act as important sorbents of sedimentary organic matter and reduce biodegradation, which favors the formation of hydrocarbon source rocks in the earth's history. Since most organic matter is degraded during the sinking process, at ambient temperature, it is important to investigate the adsorption capacity of different minerals during this process, to assess the organic loss from primary productivity to sedimentary organic matter. In this study, montmorillonite and calcite have been selected to study the impact of different minerals on the release, adsorption, and deposition of cyanobacterial (Synechococcus elonpata) fatty acids (FAs) at ambient temperature. Gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) have been utilized to detect the variation in fatty acids. Primary results suggest that minerals have a different impact on dissolved organic matter. Montmorillonite can specifically enhance the release of fatty acids from cyanobacterial cells by lowering the pH values of the solution. The adsorption of the dissolved organic matter by montmorillonite will also be enhanced under a lower pH value. Conjunction of fatty acids with montmorillonite to form a complex will favor the sinking and preservation of these organics. Selective adsorption is observed among fatty acids with different carbon numbers. In contrast, calcite does not show any impact on the release and adsorption of organic matter even though it is reportedly capable of acting as a catalyst during the transformation of organic matter at high temperature. The primary data bridge a link between primary productivity and sedimentary organic matter, suggesting the relative importance of claystoncs in the formation of hydrocarbon source rocks in the earth's history.

  1. Buffered Communication Analysis in Distributed Multiparty Sessions

    Science.gov (United States)

    Deniélou, Pierre-Malo; Yoshida, Nobuko

    Many communication-centred systems today rely on asynchronous messaging among distributed peers to make efficient use of parallel execution and resource access. With such asynchrony, the communication buffers can happen to grow inconsiderately over time. This paper proposes a static verification methodology based on multiparty session types which can efficiently compute the upper bounds on buffer sizes. Our analysis relies on a uniform causality audit of the entire collaboration pattern - an examination that is not always possible from each end-point type. We extend this method to design algorithms that allocate communication channels in order to optimise the memory requirements of session executions. From these analyses, we propose two refinements methods which respect buffer bounds: a global protocol refinement that automatically inserts confirmation messages to guarantee stipulated buffer sizes and a local protocol refinement to optimise asynchronous messaging without buffer overflow. Finally our work is applied to overcome a buffer overflow problem of the multi-buffering algorithm.

  2. Stability of buffer-free freeze-dried formulations: A feasibility study of a monoclonal antibody at high protein concentrations.

    Science.gov (United States)

    Garidel, Patrick; Pevestorf, Benjamin; Bahrenburg, Sven

    2015-11-01

    We studied the stability of freeze-dried therapeutic protein formulations over a range of initial concentrations (from 40 to 160 mg/mL) and employed a variety of formulation strategies (including buffer-free freeze dried formulations, or BF-FDF). Highly concentrated, buffer-free liquid formulations of therapeutic monoclonal antibodies (mAbs) have been shown to be a viable alternative to conventionally buffered preparations. We considered whether it is feasible to use the buffer-free strategy in freeze-dried formulations, as an answer to some of the known drawbacks of conventional buffers. We therefore conducted an accelerated stability study (24 weeks at 40 °C) to assess the feasibility of stabilizing freeze-dried formulations without "classical" buffer components. Factors monitored included pH stability, protein integrity, and protein aggregation. Because the protein solutions are inherently self-buffering, and the system's buffer capacity scales with protein concentration, we included highly concentrated buffer-free freeze-dried formulations in the study. The tested formulations ranged from "fully formulated" (containing both conventional buffer and disaccharide stabilizers) to "buffer-free" (including formulations with only disaccharide lyoprotectant stabilizers) to "excipient-free" (with neither added buffers nor stabilizers). We evaluated the impacts of varying concentrations, buffering schemes, pHs, and lyoprotectant additives. At the end of 24 weeks, no change in pH was observed in any of the buffer-free formulations. Unbuffered formulations were found to have shorter reconstitution times and lower opalescence than buffered formulations. Protein stability was assessed by visual inspection, sub-visible particle analysis, protein monomer content, charge variants analysis, and hydrophobic interaction chromatography. All of these measures found the stability of buffer-free formulations that included a disaccharide stabilizer comparable to buffer

  3. Buffered Electrochemical Polishing of Niobium

    Energy Technology Data Exchange (ETDEWEB)

    Ciovati, Gianluigi [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Tian, Hui [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); College of William and Mary, Williamsburg, VA (United States); Corcoran, Sean [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)

    2011-03-01

    The standard preparation of superconducting radio-frequency (SRF) cavities made of pure niobium include the removal of a 'damaged' surface layer, by buffered chemical polishing (BCP) or electropolishing (EP), after the cavities are formed. The performance of the cavities is characterized by a sharp degradation of the quality factor when the surface magnetic field exceeds about 90 mT, a phenomenon referred to as 'Q-drop.' In cavities made of polycrystalline fine grain (ASTM 5) niobium, the Q-drop can be significantly reduced by a low-temperature (? 120 °C) 'in-situ' baking of the cavity if the chemical treatment was EP rather than BCP. As part of the effort to understand this phenomenon, we investigated the effect of introducing a polarization potential during buffered chemical polishing, creating a process which is between the standard BCP and EP. While preliminary results on the application of this process to Nb cavities have been previously reported, in this contribution we focus on the characterization of this novel electrochemical process by measuring polarization curves, etching rates, surface finish, electrochemical impedance and the effects of temperature and electrolyte composition. In particular, it is shown that the anodic potential of Nb during BCP reduces the etching rate and improves the surface finish.

  4. Simulating speleothem growth in the laboratory: Determination of stable isotope fractionation factors during precipitation of speleothem calcite

    Science.gov (United States)

    Hansen, Maximilian; Schöne, Bernd R.; Spötl, Christoph; Scholz, Denis

    2016-04-01

    We present laboratory experiments aiming to understand the processes affecting the δ13C and δ18O values of speleothems during precipitation of calcite from a thin layer of solution. In particular, we determined the precipitation rates and the isotope fractionation factors in dependence of several parameters, such as temperature, cave pCO2 and supersaturation with respect to calcite. The experiments were performed in a climate box in order to simulate cave conditions and to control them during the experiments[1]. In the experiments, a thin film of a CaCO3-CO2-H2O-solution supersaturated with respect to calcite flew down an inclined marble surface or a sand-blasted borosilicate glass plate, and the drip water was sampled at different distances and, thus, residence times on the plate. Subsequently, pH, electrical conductivity and the δ13C and δ18O values of the dissolved inorganic carbon (DIC) as well as the precipitated CaCO3 were determined. In addition, we determined the stable isotope values of the drip water and the atmosphere inside the box during the experiments. This enabled the identification of carbon and oxygen isotope fractionation factors between all carbonate species. The experiments were conducted at 10, 20 and 30 ° C, a pCO2 of 1000 and 3000 ppmV and with a Ca2+ concentration of 2 and 5 mmol/l. We observed an exponential decay of conductivity with increasing distance of flow documenting progressive precipitation of calcite confirming previous observations[2]. The corresponding time constants of precipitation range from 180 to 660 s. Both the δ13C and δ18O values show a progressive increase along the flow path. The enrichment of the δ13C values seems to be strongly influenced by kinetic isotope fractionation, whereas the δ18O values are in the range of isotopic equilibrium. The fractionation between the precipitated CaCO3 and DIC is between -1 and - 6.5 ‰ for carbon isotopes (13ɛ) and between -1.5 and -3 ‰ for oxygen isotopes (18ɛ). The

  5. 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.

  6. Shock-induced effects in calcite from Cactus Crater

    Science.gov (United States)

    Vizgirda, J.; Ahrens, T. J.; Tsay, F.-D.

    1980-01-01

    The paper discusses shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.

  7. Elucidating low-frequency vibrational dynamics in calcite and water with time-resolved third-harmonic generation spectroscopy.

    Science.gov (United States)

    Wang, Liang; Liu, Weimin; Fang, Chong

    2015-07-14

    Low-frequency vibrations are foundational for material properties including thermal conductivity and chemical reactivity. To resolve the intrinsic molecular conformational dynamics in condensed phase, we implement time-resolved third-harmonic generation (TRTHG) spectroscopy to unravel collective skeletal motions in calcite, water, and aqueous salt solution in situ. The lifetime of three Raman-active modes in polycrystalline calcite at 155, 282 and 703 cm(-1) is found to be ca. 1.6 ps, 1.3 ps and 250 fs, respectively. The lifetime difference is due to crystallographic defects and anharmonic effects. By incorporating a home-built wire-guided liquid jet, we apply TRTHG to investigate pure water and ZnCl2 aqueous solution, revealing ultrafast dynamics of water intermolecular stretching and librational bands below 500 cm(-1) and a characteristic 280 cm(-1) vibrational mode in the ZnCl4(H2O)2(2-) complex. TRTHG proves to be a compact and versatile technique that directly uses the 800 nm fundamental laser pulse output to capture ultrafast low-frequency vibrational motion snapshots in condensed-phase materials including the omnipresent water, which provides the important time dimension to spectral characterization of molecular structure-function relationships.

  8. A global deglacial negative carbon isotope excursion in speleothem calcite

    Science.gov (United States)

    Breecker, D.

    2015-12-01

    δ13C values of speleothem calcite decreased globally during the last deglaciation defining a carbon isotope excursion (CIE) despite relatively constant δ13C values of carbon in the ocean-atmosphere system. The magnitude of the CIE varied with latitude, increasing poleward from ~2‰ in the tropics to as much as 7‰ at high latitudes. This recent CIE provides an interesting comparison with CIEs observed in deep time. A substantial portion of this CIE can be explained by the increase in atmospheric pCO2 that accompanied deglaciation. The dependence of C3 plant δ13C values on atmospheric pCO2 predicts a 2‰ δ13C decrease driven by the deglacial pCO2 increase. I propose that this signal was transferred to caves and thus explains nearly 100% of the CIE magnitude observed in the tropics and no less than 30% at the highest latitudes in the compilation. An atmospheric pCO2 control on speleothem δ13C values, if real, will need to be corrected for using ice core data before δ13C records can be interpreted in a paleoclimate context. The decrease in the magnitude of the equilibrium calcite-CO2 carbon isotope fractionation factor explains a maximum of 1‰ of the CIE at the highest northern latitude in the compilation, which experienced the largest deglacial warming. Much of the residual extratropical CIE was likely driven by increasing belowground respiration rates, which were presumably pronounced at high latitudes as glacial retreat exposed fresh surfaces and/or vegetation density increased. The largest increases in belowground respiration would have therefore occurred at the highest latitudes, explaining the meridional trend. This work supports the notion that increases in atmospheric pCO2 and belowground respiration rates can result in large CIEs recorded in terrestrial carbonates, which, as previously suggested, may explain the magnitude of the PETM CIE as recorded by paleosol carbonates.

  9. Unusual micrometric calcite-aragonite interface in the abalone shell Haliotis (Mollusca, Gastropoda).

    Science.gov (United States)

    Dauphin, Yannicke; Cuif, Jean-Pierre; Castillo-Michel, Hiram; Chevallard, Corinne; Farre, Bastien; Meibom, Anders

    2014-02-01

    Species of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which calcite and aragonite coexist at a microscale with small patches of aragonite embedded in larger calcitic zones. A detailed examination of the boundary between calcite and aragonite using analytical microscopies shows that the organic contents of calcite and aragonite differ. Moreover, changes in the chemical composition of the two minerals seem to be gradual and define a micrometric zone of transition between the two main layers. A similar transition zone has been observed between the layers in more classical and regularly structured mollusk shells. The imbrication of microscopic patches of aragonite within a calcitic zone suggests the occurrence of very fast physiological changes in these taxa.

  10. Influence of surface conductivity on the apparent zeta potential of calcite

    CERN Document Server

    Li, Shuai; Heberling, Frank; Devau, Nicolas; Jougnot, Damien; Chiaberge, Christophe

    2016-01-01

    Zeta potential is a physicochemical parameter of particular importance in describing the surface electrical properties of charged porous media. However, the zeta potential of calcite is still poorly known because of the difficulty to interpret streaming potential experiments. The Helmholtz-Smoluchowski (HS) equation is widely used to estimate the apparent zeta potential from these experiments. However, this equation neglects the influence of surface conductivity on streaming potential. We present streaming potential and electrical conductivity measurements on a calcite powder in contact with an aqueous NaCl electrolyte. Our streaming potential model corrects the apparent zeta potential of calcite by accounting for the influence of surface conductivity and flow regime. We show that the HS equation seriously underestimates the zeta potential of calcite, particularly when the electrolyte is diluted (ionic strength < 0.01 M) because of calcite surface conductivity. The basic Stern model successfully predicted ...

  11. The effect of dissolved magnesium on creep of calcite II: transition from diffusion creep to dislocation creep

    Science.gov (United States)

    Xu, Lili; Renner, Jörg; Herwegh, Marco; Evans, Brian

    2009-03-01

    We extended a previous study on the influence of Mg solute impurity on diffusion creep in calcite to include deformation under a broader range of stress conditions and over a wider range of Mg contents. Synthetic marbles were produced by hot isostatic pressing (HIP) mixtures of calcite and dolomite powders for different intervals (2-30 h) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in high-magnesian calcite aggregates with Mg content ranging from 0.5 to 17 mol%. Both back-scattered electron images and chemical analysis suggested that the dolomite phase was completely dissolved, and that Mg distribution was homogeneous throughout the samples at the scale of about two micrometers. The grain size after HIP varied from 8 to 31 μm, increased with time at temperature, and decreased with increasing Mg content (>3.0 mol%). Grain size and time were consistent with a normal grain growth equation, with exponents from 2.4 to 4.7, for samples containing 0.5-17.0 mol% Mg, respectively. We deformed samples after HIP at the same confining pressure with differential stresses between 20 and 200 MPa using either constant strain rate or stepping intervals of loading at constant stresses in a Paterson gas-medium deformation apparatus. The deformation tests took place at between 700 and 800°C and at strain rates between 10-6 and 10-3 s-1. After deformation to strains of about 25%, a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted in some samples loaded at higher stresses. The deformation data indicated a transition in mechanism from diffusion creep to dislocation creep. At stresses below 40 MPa, the strength was directly proportional to grain size and decreased with increasing Mg content due to the reductions in grain size. At about 40 MPa, the sensitivity of log strain rate to log stress, ( n), became greater than 1 and eventually exceeded 3 for stresses above 80 MPa. At a given strain rate and temperature, the stress at

  12. Melatonin: Buffering the Immune System

    Directory of Open Access Journals (Sweden)

    Juan M. Guerrero

    2013-04-01

    Full Text Available Melatonin modulates a wide range of physiological functions with pleiotropic effects on the immune system. Despite the large number of reports implicating melatonin as an immunomodulatory compound, it still remains unclear how melatonin regulates immunity. While some authors argue that melatonin is an immunostimulant, many studies have also described anti-inflammatory properties. The data reviewed in this paper support the idea of melatonin as an immune buffer, acting as a stimulant under basal or immunosuppressive conditions or as an anti-inflammatory compound in the presence of exacerbated immune responses, such as acute inflammation. The clinical relevance of the multiple functions of melatonin under different immune conditions, such as infection, autoimmunity, vaccination and immunosenescence, is also reviewed.

  13. EFFECT OF MAGNESIUM AS SUBSTITUTE MATERIAL IN ENZYME MEDIATED CALCITE PRECIPITATION (EMCP FOR SOIL IMPROVEMENT TECHNIQUE

    Directory of Open Access Journals (Sweden)

    Heriansyah ePutra

    2016-05-01

    Full Text Available 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 treated with concentration-controlled solutions composed of urea, urease, calcium, and magnesium chloride. The mechanical properties of the treated soil specimens were examined through unconfined compressive strength (UCS tests. A precipitation ratio of the carbonate up to 90% of the maximum theoretical precipitation was achieved by adding a small amount of magnesium chloride. Adding magnesium chloride as a delaying agent was indeed found to reduce the reaction rate of the precipitation, which may increase the volume of the treated soil if used in real fields because of the slower precipitation rate and the resulting higher injectivity. A mineralogical analysis revealed that magnesium chloride decreases the crystal size of the precipitated materials and that another carbonate of aragonite is newly formed. Mechanical test results indicated that carbonate precipitates within the soils and brings about a significant improvement in strength. A maximum UCS of 0.6 MPa was obtained from the treated samples.

  14. Buffer strips in composites at elevated temperature

    Science.gov (United States)

    Bigelow, C. A.

    1983-01-01

    The composite material 'buffer strip' concept is presently investigated at elevated temperatures for the case of graphite/polyimide buffer strip panels using a (45/0/45/90)2S layup, where the buffer strip material was 0-deg S-glass/polyimide. Each panel was loaded in tension until it failed, and radiographs and crack opening displacements were recorded during the tests to determine fracture onset, fracture arrest, and the extent of damage in the buffer strip after crack arrest. At 177 + or - 3 C, the buffer strips increased the panel strength by at least 40 percent in comparison with panels without buffer strips. Compared to similar panels tested at room temperature, those tested at elevated temperature had lower residual strengths, but higher failure strains.

  15. Density measurements of potassium phosphate buffer from 4 to 45 degrees C.

    Science.gov (United States)

    Schiel, John E; Hage, David S

    2005-01-30

    Potassium phosphate buffer is often used in methods such as equilibrium dialysis, high performance liquid chromatography (HPLC), and affinity capillary electrophoresis (ACE) for characterizing the binding of drugs and hormones with proteins or other ligands within the body. In these experiments, the buffer density is often approximated to be that of water and the concentrations of all reagents are assumed to be constant with temperature. However, some difference in density between phosphate buffer and water would be expected, and variations in this density could lead to significant changes in the concentrations of dissolved solutes with temperature. This, in turn, could affect the binding observed for a solute-ligand system in such a buffer. In this study, the densities of potassium phosphate buffers with concentrations up to 0.10M were measured at or near physiological pH for temperatures ranging from 4-45 degrees C. The general change in density versus temperature followed a quadratic equation, while the changes in density with concentration and pH followed a linear response. The results were used to formulate a general equation that could be used to calculate the density of potassium phosphate buffer at any pH, temperature, and concentration within the tested range. This equation and more specialized relationships developed in the temperature, concentration, and pH studies were found to give much greater accuracy in describing the density of these buffers versus a previous relationship developed for solutions containing only potassium dihydrogen phosphate.

  16. Signature-based store checking buffer

    Science.gov (United States)

    Sridharan, Vilas; Gurumurthi, Sudhanva

    2015-06-02

    A system and method for optimizing redundant output verification, are provided. A hardware-based store fingerprint buffer receives multiple instances of output from multiple instances of computation. The store fingerprint buffer generates a signature from the content included in the multiple instances of output. When a barrier is reached, the store fingerprint buffer uses the signature to verify the content is error-free.

  17. A Constant Factor Approximation Algorithm for Reordering Buffer Management

    CERN Document Server

    Avigdor-Elgrabli, Noa

    2012-01-01

    In the reordering buffer management problem (RBM) a sequence of $n$ colored items enters a buffer with limited capacity $k$. When the buffer is full, one item is removed to the output sequence, making room for the next input item. This step is repeated until the input sequence is exhausted and the buffer is empty. The objective is to find a sequence of removals that minimizes the total number of color changes in the output sequence. The problem formalizes numerous applications in computer and production systems, and is known to be NP-hard. We give the first constant factor approximation guarantee for RBM. Our algorithm is based on an intricate "rounding" of the solution to an LP relaxation for RBM, so it also establishes a constant upper bound on the integrality gap of this relaxation. Our results improve upon the best previous bound of $O(\\sqrt{\\log k})$ of Adamaszek et al. (STOC 2011) that used different methods and gave an online algorithm. Our constant factor approximation beats the super-constant lower b...

  18. Temperature buffer test. Dismantling operation

    Energy Technology Data Exchange (ETDEWEB)

    Aakesson, Mattias [Clay Technology AB, Lund (Sweden)

    2010-12-15

    The Temperature Buffer Test (TBT) is a joint project between SKB/ANDRA and supported by ENRESA (modelling) and DBE (instrumentation), which aims at improving the understanding and to model the thermo-hydro-mechanical behavior of buffers made of swelling clay submitted to high temperatures (over 100 deg C) during the water saturation process. The test has been carried out in a KBS-3 deposition hole at Aespoe HRL. It was installed during the spring of 2003. Two heaters (3 m long, 0.6 m diameter) and two buffer arrangements have been investigated: the lower heater was surrounded by bentonite in the usual way, whereas the upper heater was surrounded by a ring of sand. The test was dismantled and sampled during a period from the end of October 2009 to the end of April 2010, and this report describes this operation. Different types of samples have been obtained during this operation. A large number of diameter 50 mm bentonite cores have been taken for analysis of water content and density. Large pieces, so-called big sectors, have been taken for hydro-mechanical and chemical characterizations. Finally, there has been an interest to obtain different types of interface samples in which bentonite were in contact with sand, iron or concrete. One goal has been to investigate the retrievability of the upper heater, given the possibility to remove the surrounding sand shield, and a retrieval test has therefore been performed. The sand in the shield was first removed with an industrial vacuum cleaner after loosening the material through mechanical means (with hammer drill and core machine). A front loader was subsequently used for applying a sufficient lifting force to release the heater from the bentonite underneath. The experiment has been documented in different aspects: measurements of the coordinate (height or radius) of different interfaces (between bentonite blocks and between bentonite and sand); verification of sensor positions and retrieval of sensors for subsequent

  19. Kinetics of calcium phosphate nucleation and growth on calcite: implications for predicting the fate of dissolved phosphate species in alkaline soils.

    Science.gov (United States)

    Wang, Lijun; Ruiz-Agudo, Encarnación; Putnis, Christine V; Menneken, Martina; Putnis, Andrew

    2012-01-17

    Unraveling the kinetics of calcium orthophosphate (Ca-P) precipitation and dissolution is important for our understanding of the transformation and mobility of dissolved phosphate species in soils. Here we use an in situ atomic force microscopy (AFM) coupled with a fluid reaction cell to study the interaction of phosphate-bearing solutions with calcite surfaces. We observe that the mineral surface-induced formation of Ca-P phases is initiated with the aggregation of clusters leading to the nucleation and subsequent growth of Ca-P phases on calcite, at various pH values and ionic strengths relevant to soil solution conditions. A significant decrease in the dissolved phosphate concentration occurs due to the promoted nucleation of Ca-P phases on calcite surfaces at elevated phosphate concentrations and more significantly at high salt concentrations. Also, kinetic data analyses show that low concentrations of citrate caused an increase in the nucleation rate of Ca-P phases. However, at higher concentrations of citrate, nucleation acceleration was reversed with much longer induction times to form Ca-P nuclei. These results demonstrate that the nucleation-modifying properties of small organic molecules may be scaled up to analyze Ca-P dissolution-precipitation processes that are mediated by a more complex soil environment. This in situ observation, albeit preliminary, may contribute to an improved understanding of the fate of dissolved phosphate species in diverse soil systems.

  20. 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.

  1. Aragonite-calcite transformation in fossil snail shells of loess sequences in Loess Plateau, Central China

    Institute of Scientific and Technical Information of China (English)

    SHENG Xuefen; CHEN Jun; CAI Yuanfeng; CHEN Yang; JI Junfeng

    2005-01-01

    The methods of X-ray diffraction (XRD) and ICP-AES are applied to analyzing the mineral composition of modern and fossil snail shells in Luochuan section and Xifeng section. The results show that the mineral phase of calcium carbonate in modern snail shells is aragonite, but for some fossil snail shells in certain layers of loess sequences, a part of aragonite is transformed into calcite. In Luochuan and Xifeng sections, the stratigraphic borderline of aragonite-calcite transformation appearing obviously is between L5 and L6. Under the earth surface condition, the aragonite-calcite transformation is influenced by the factor of temperature only in a long time scale. It seems that the pressure is not the factor influencing the aragonite-calcite transformation. The results also show that existing age of snail shells is possibly the dominant and principal factor for the aragonite-calcite transformation. To a certain extent, the degree of aragonite-calcite transformation in snail shell is controlled by the content of trace element, such as Mg2+. The trace element can improve the stability of snail shell aragonite and impede the process of aragonite transforming into calcite.

  2. Influence of surface conductivity on the apparent zeta potential of calcite.

    Science.gov (United States)

    Li, Shuai; Leroy, Philippe; Heberling, Frank; Devau, Nicolas; Jougnot, Damien; Chiaberge, Christophe

    2016-04-15

    Zeta potential is a physicochemical parameter of particular importance in describing the surface electrical properties of charged porous media. However, the zeta potential of calcite is still poorly known because of the difficulty to interpret streaming potential experiments. The Helmholtz-Smoluchowski (HS) equation is widely used to estimate the apparent zeta potential from these experiments. However, this equation neglects the influence of surface conductivity on streaming potential. We present streaming potential and electrical conductivity measurements on a calcite powder in contact with an aqueous NaCl electrolyte. Our streaming potential model corrects the apparent zeta potential of calcite by accounting for the influence of surface conductivity and flow regime. We show that the HS equation seriously underestimates the zeta potential of calcite, particularly when the electrolyte is diluted (ionic strength ⩽ 0.01 M) because of calcite surface conductivity. The basic Stern model successfully predicted the corrected zeta potential by assuming that the zeta potential is located at the outer Helmholtz plane, i.e. without considering a stagnant diffuse layer at the calcite-water interface. The surface conductivity of calcite crystals was inferred from electrical conductivity measurements and computed using our basic Stern model. Surface conductivity was also successfully predicted by our surface complexation model.

  3. Uranium isotope fractionation during coprecipitation with aragonite and calcite

    Science.gov (United States)

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

    2016-09-01

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

  4. Analyses IR quantitatives des sédiments. Exemple du dosage du quartz et de la calcite Quantitative Ir Analysis of Sediments. Example of Quartz and Calcite Determination

    Directory of Open Access Journals (Sweden)

    Pichard C.

    2006-11-01

    Full Text Available Plus généralement utilisée pour l'étude des phases fluides, la spectrophotométrie d'absorption infrarouge a trouvé un important champ d'application dans l'analyse minéralogique quantitative globale des roches sédimentaires. En s'appuyant sur deux exemples précis de constituants importants des sédiments (quartz et calcite, on montre ici les différentes possibilités analytiques avec échantillon seul, compensation du diluant pur, compensation d'un minéral pur et compensation d'un minéral en mélange artificiel et naturel (roche sédimentaire. On décrit les modifications subies par les spectres et des courbes d'étalonnages sont dressées dans chaque cas. Les données recueillies permettent de vérifier l'utilisation légitime de la loi d'absorption pour ces analyses infrarouges de phases solides impliquant une compensation, et donc un traitement des spectres originaux, l'erreur relative maximale expérimentale ne dépassant pas quelques pourcents dans les cas les plus défavorables. Dans les limites du dosage de minéraux à composition chimique et structure cristalline fixes, l'analyse d'un minéral par sa compensation partielle peut être d'un grand intérêt pour des constituants majeurs de roches, car autorisant l'analyse là où une concentration trop élevée l'aurait interdite. Cette méthode de compensation est plus délicate, voire impossible, pour les solutions solides ou tout minéral à formule chimique variable. D'une manière générale, les principaux constituants des roches sédimentaires peuvent être ainsi quantifiés sur un seul spectre par l'analyse IR qui offre donc la possibilité d'une définition numérique des faciès. Although it is more generally used for analyzing fluid phases, infrared absorption spectrophotometry has found an important area of application in the bulk quantitative mineralogical analysis of sedimentary rocks. On the basis of two specific examples of important constituents of sediments

  5. 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

  6. 46 CFR 58.25-45 - Buffers.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 2 2010-10-01 2010-10-01 false Buffers. 58.25-45 Section 58.25-45 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING MAIN AND AUXILIARY MACHINERY AND RELATED SYSTEMS Steering Gear § 58.25-45 Buffers. For each vessel on an ocean, coastwise, or Great Lakes...

  7. Buffer Management Simulation in ATM Networks

    Science.gov (United States)

    Yaprak, E.; Xiao, Y.; Chronopoulos, A.; Chow, E.; Anneberg, L.

    1998-01-01

    This paper presents a simulation of a new dynamic buffer allocation management scheme in ATM networks. To achieve this objective, an algorithm that detects congestion and updates the dynamic buffer allocation scheme was developed for the OPNET simulation package via the creation of a new ATM module.

  8. Recurrent Pure Calcite Urolithiasis Confirmed by Endoscopic Removal and Infrared Spectroscopy in a Malnourished Anorectic Female

    Science.gov (United States)

    Andreassen, Kim Hovgaard; Sloth Osther, Palle Jörn

    2016-01-01

    Abstract Often when calcite is found as a component of urinary calculi, they are considered false calculi or artifacts. We present a case of true calcite urolithiasis. The stone material was removed percutaneously from a severely malnourished anorectic woman and analyzed by infrared spectroscopy (IRS). In addition, calcite urolithiasis was confirmed in several recurrent stone events by IRS. Laxative abuse with magnesium oxide was believed to be the underlying cause of stone formation, and ammonium chloride given as one weekly dose turned out to be effective for stone prevention. PMID:27579419

  9. Comparison of galvanic displacement and electroless methods for deposition of gold nanoparticles on synthetic calcite

    Indian Academy of Sciences (India)

    Chamarthi K Srikanth; P Jeevanandam

    2012-11-01

    Gold nanoparticles have been deposited on synthetic calcite substrate by galvanic displacement reaction and electroless deposition methods. A comparative study has shown that electroless deposition is superior compared to galvanic displacement reaction for uniform deposition of gold nanoparticles on calcite. Characterization of the samples, prepared by two different deposition methods, was carried out by X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy (FE–SEM) and diffuse reflectance spectroscopy (DRS) measurements. FE–SEM studies prove that smaller nanoparticles of gold are deposited uniformly on calcite if electroless deposition method was employed and DRS measurements show the characteristic surface plasmon resonance of gold nanoparticles.

  10. 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

    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...... 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...

  11. Buffer management in wireless full-duplex systems

    KAUST Repository

    Bouacida, Nader

    2015-10-19

    Wireless full-duplex radios can simultaneously transmit and receive using the same frequency. In theory, this can double the throughput. In fact, there is only little work addressing aspects other than throughput gains in full-duplex systems. Over-buffering in today\\'s networks or the so-called “bufferbloat” phenomenon creates excessive end-to-end delays resulting in network performance degradation. Our analysis shows that full-duplex systems may suffer from high latency caused by bloated buffers. In this paper, we address the problem of buffer management in full-duplex networks by using Wireless Queue Management (WQM), which is an active queue management technique for wireless networks. Our solution is based on Relay Full-Duplex MAC (RFD-MAC), an asynchronous media access control protocol designed for relay full-duplexing. We compare the performance of WQM in full-duplex environment to Drop Tail mechanism over various scenarios. Our solution reduces the end-to-end delay by two orders of magnitude while achieving similar throughput in most of the cases.

  12. Conceptual modeling coupled thermal-hydrological-chemical processes in bentonite buffer for high-level nuclear waste repository

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Byoung Young; Park, Jin Young [Korea Institute of Geoscience and Mineral Resources, Daejeon (Korea, Republic of); Ryu, Ji Hun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-03-15

    In this study, thermal-hydrological-chemical modeling for the alteration of a bentonite buffer is carried out using a simulation code TOUGHREACT. The modeling results show that the water saturation of bentonite steadily increases and finally the bentonite is fully saturated after 10 years. In addition, the temperature rapidly increases and stabilizes after 0.5 year, exhibiting a constant thermal gradient as a function of distance from the copper tube. The change of thermal-hydrological conditions mainly results in the alteration of anhydrite and calcite. Anhydrite and calcite are dissolved along with the inflow of groundwater. They then tend to precipitate in the vicinity of the copper tube due to its high temperature. This behavior induces a slight decrease in porosity and permeability of bentonite near the copper tube. Furthermore, this study finds that the diffusion coefficient can significantly affect the alteration of anhydrite and calcite, which causes changes in the hydrological properties of bentonite such as porosity and permeability. This study may facilitate the safety assessment of high-level radioactive waste repositories.

  13. Buffer sizing for multi-hop networks

    KAUST Repository

    Shihada, Basem

    2014-01-28

    A cumulative buffer may be defined for an interference domain in a wireless mesh network and distributed among nodes in the network to maintain or improve capacity utilization of network resources in the interference domain without increasing packet queuing delay times. When an interference domain having communications links sharing resources in a network is identified, a cumulative buffer size is calculated. The cumulative buffer may be distributed among buffers in each node of the interference domain according to a simple division or according to a cost function taking into account a distance of the communications link from the source and destination. The network may be monitored and the cumulative buffer size recalculated and redistributed when the network conditions change.

  14. Optimization of protein buffer cocktails using Thermofluor.

    Science.gov (United States)

    Reinhard, Linda; Mayerhofer, Hubert; Geerlof, Arie; Mueller-Dieckmann, Jochen; Weiss, Manfred S

    2013-02-01

    The stability and homogeneity of a protein sample is strongly influenced by the composition of the buffer that the protein is in. A quick and easy approach to identify a buffer composition which increases the stability and possibly the conformational homogeneity of a protein sample is the fluorescence-based thermal-shift assay (Thermofluor). Here, a novel 96-condition screen for Thermofluor experiments is presented which consists of buffer and additive parts. The buffer screen comprises 23 different buffers and the additive screen includes small-molecule additives such as salts and nucleotide analogues. The utilization of small-molecule components which increase the thermal stability of a protein sample frequently results in a protein preparation of higher quality and quantity and ultimately also increases the chances of the protein crystallizing.

  15. [Mechanical buffering characteristics of feline paw pads].

    Science.gov (United States)

    Zhang, Xiaopeng; Yang, Jialing; Yu, Hui

    2012-12-01

    In the long time of natural evolution, the bodies of some animals, such as feline, that live in the wild and complicate surroundings have evolved to possess outstanding buffering characteristics, which make the animals adapt to the environment perfectly. These animals generally have well-developed paw pads under their soles to play an important role in attenuating the intensity of impact when they land on the ground. Investigating the buffering characteristics of these animals' paw pads could help us to design "bionic" buffering and energy-absorption devices. In this paper, based on observations of animal jumping test, a simple mass-spring-buffer model was proposed to explore the buffering characteristics of the animals' paw pads. By analytically solving the differential equations of this model, the parameters concerned with paw pads functions were discussed and some significant results were obtained.

  16. Ultrasonic Observation of the Calcite-Aragonite Transition

    Science.gov (United States)

    Ahrens, T. J.; Katz, S.

    1963-01-01

    Elastic-wave velocities were measured as a function of pressure by ultrasonic pulse Interferometry in Solenhofen and Manilus limestone specimens to pressures of 27 and 38 kb. Longitudinal velocities decrease sharply from 5.3 km/sec at a mean pressure of 4 kb to a minimum of 4.8 km/sec at 8 kb. Transverse velocities decrease from 3.1 to 2.9 km/sec. At the minimum bulk and rigidity moduli are 25 and 20 per cent below their 4-kb values. A density increase of 1.7 per cent is associated with this minimum. The observed effects are attributed to the calcite-aragonite transition, and they may be due to an inherent property of the material, a component of which undergoes a polymorphic transition, the low- and high-pressure phases coexisting over a considerable pressure range. This may be an additional mechanism to account for low-velocity zones in the earth?s interior.

  17. Microbiologically Induced Calcite Precipitation Mediated by Sporosarcina pasteurii.

    Science.gov (United States)

    Bhaduri, Swayamdipta; Debnath, Nandini; Mitra, Sushanta; Liu, Yang; Kumar, Aloke

    2016-04-16

    The particular bacterium under investigation here (S. pasteurii) is unique in its ability, under the right conditions, to induce the hydrolysis of urea (ureolysis) in naturally occurring environments through secretion of an enzyme urease. This process of ureolysis, through a chain of chemical reactions, leads to the formation of calcium carbonate precipitates. This is known as Microbiologically Induced Calcite Precipitation (MICP). The proper culture protocols for MICP are detailed here. Finally, visualization experiments under different modes of microscopy were performed to understand various aspects of the precipitation process. Techniques like optical microscopy, Scanning Electron Microscopy (SEM) and X-Ray Photo-electron Spectroscopy (XPS) were employed to chemically characterize the end-product. Further, the ability of these precipitates to clog pores inside a natural porous medium was demonstrated through a qualitative experiment where sponge bars were used to mimic a pore-network with a range of length scales. A sponge bar dipped in the culture medium containing the bacterial cells hardens due to the clogging of its pores resulting from the continuous process of chemical precipitation. This hardened sponge bar exhibits superior strength when compared to a control sponge bar which becomes compressed and squeezed under the action of an applied external load, while the hardened bar is able to support the same weight with little deformation.

  18. Alkaline flocculation of Phaeodactylum tricornutum induced by brucite and calcite.

    Science.gov (United States)

    Vandamme, Dries; Pohl, Philip I; Beuckels, Annelies; Foubert, Imogen; Brady, Patrick V; Hewson, John C; Muylaert, Koenraad

    2015-11-01

    Alkaline flocculation holds great potential as a low-cost harvesting method for marine microalgae biomass production. Alkaline flocculation is induced by an increase in pH and is related to precipitation of calcium and magnesium salts. In this study, we used the diatom Phaeodactylum tricornutum as model organism to study alkaline flocculation of marine microalgae cultured in seawater medium. Flocculation started when pH was increased to 10 and flocculation efficiency reached 90% when pH was 10.5, which was consistent with precipitation modeling for brucite or Mg(OH)2. Compared to freshwater species, more magnesium is needed to achieve flocculation (>7.5mM). Zeta potential measurements suggest that brucite precipitation caused flocculation by charge neutralization. When calcium concentration was 12.5mM, flocculation was also observed at a pH of 10. Zeta potential remained negative up to pH 11.5, suggesting that precipitated calcite caused flocculation by a sweeping coagulation mechanism.

  19. 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.

  20. Buffer Effects in the Solubility, Nucleation and Growth of Chicken Egg White Lysozyme

    Science.gov (United States)

    Gibson, Ursula J.

    1999-01-01

    The growth of protein crystals is important for determination of their three-dimensional structure, which relates to their biochemical functions and to the practical goal of designing pharmaceuticals to modify that function. While many proteins have been successfully crystallized by a variety of methods, there is still limited understanding of the process of nucleation and growth of even the simplest proteins. Chicken egg-white lysozyme (CEWL) is readily crystallized under a variety of conditions, and studies underway at MSFC are designed to elucidate the mechanisms by which the crystals nucleate and grow. We have investigated the effect of buffer choice on the solubility, nucleation and growth of CEWL. CEWL was purified by dialysis against a .05M phosphate buffer and chromatographic separation from contaminants in a sepharose column. Solubility studies were made as a function of buffer concentration for phosphate and formate buffers, and the nucleation and growth of crystals at 10 C was studied as a function of pH for oxalate, succinate, formate, butyrate, carbonate, phosphate and acetate buffer solutions. The solubility data support the conclusion that there is a solubility minimum as a function of buffer concentration for amphiphilic molecules, while no minimum is observed for a phosphate buffer. Nucleation is suppressed at pH greater than pKa for all buffers except phosphate. The aspect ratio of the (110) faces is shown to be a function of crystal size, rather than pH.

  1. Buffer salt effects in off-line coupling of capillary electrophoresis and mass spectrometry.

    Science.gov (United States)

    Marák, Jozef; Stanová, Andrea

    2014-05-01

    In this work, the impact of buffer salts/matrix effects on the signal in direct injection MS with an electrospray interface (DI-ESI-MS) following pITP fractionation of the sample was studied. A range of buffers frequently used in CE analyses (pH 3-10) was prepared containing 10, 50, and 90% v/v of ACN, respectively. The sets of calibration solutions of cetirizine (an antihistaminic drug with an amphiprotic character) within a 0.05-2.0 mg/L concentration range were prepared in different buffers. The greatest enhancements in the MS signal (in terms of change in the slope of the calibration line) were obtained for the beta-alanine buffer (pH 3.5) in positive ionization and for the borate buffer (pH 9.2) in negative ionization, respectively. The procedure was successfully applied to the analysis of buserelin (a peptidic drug). The slope of the calibration line for solutions containing the beta-alanine buffer with 50% of ACN was 4 times higher than for water or urine, respectively. This study clearly demonstrates that the buffer salt/matrix effects in an offline combination of pITP and DI-ESI-MS can also play a positive role, as they can enhance the signal in MS. A similar influence of the above effects can also be presumed in the CE techniques combined on-line with ESI-MS.

  2. SYSTEM AGGREGATION METHOD FOR FAILURE PRONE PRODUCTION LINES WITH UNRELIABLE LIMITED BUFFERS

    Institute of Scientific and Technical Information of China (English)

    LIU Jun; RUI Zhiyuan; ZHAO Juntian; WEI Yaobing

    2008-01-01

    Different from traditional aggregation method, the unreliable buffers are originally considered and a more general aggregation method is offered, in which not only the unreliable buffers are considered, but also the probabilities of system states are obtained by a discrete model rather than the continuous flow model of unreliable manufacturing systems. The solution technique is offered to get the system sate probabilities. The method advances the traditional system aggregation techniques. Numerical results specify the extended aggregation method and also show that the unreliable limited buffers have a strong impact on the efficiency of the production lines.

  3. Design on Buffer Structure of Traction Running with a Constant Speed

    Directory of Open Access Journals (Sweden)

    Zeng Xianren

    2013-06-01

    Full Text Available This study mainly aims to study buffer structure design on the traction transport system when the traction transport boundary conditions are given. With such conditions as the maximum impact force, traction speed, maximum speed of alluvium, the elasticity coefficient and the mass of buffer structure, a mathematical model was established and the solution of differential equations was solved. At last, a program was compiled with MATLAB language. With this program the elasticity coefficient and the maximum impact force which meet the requirements in impact process can be solved as long as the boundary conditions are input. This provides a quick design basis of buffer structure for most mechanical engineers.

  4. Reactive transport modeling of leaking CO2-enriched brine through fault zones taking into account the physical and geochemical interactions with calcite formation and the effects of porosity variations on the flow field

    Science.gov (United States)

    Ahmad, Nawaz; Worman, Anders

    2014-05-01

    One of the concerns related to CO2 underground storage is the possibility of CO2 leakage from the injection formation. Although CO2 starts getting dissolved in brine after its injection in the reservoir there is risk of its leakage in dissolved form due to either increased reservoir pressure as a result of CO2 injection or large-scale groundwater motion. The flow of brine through weaker zones like faults may cause the leakage of dissolved CO2. The mobility and spreading of reactive solutes is however significantly affected by diffusion, sorption in the fault zone and the rock-matrix and geochemical reactions with the rock-forming minerals. This study presents the results of numerical modeling of leaking CO2-enriched brine through a fault zone with physical and geochemical interactions with the neighboring limestone rock matrix over a period of 1000 years for 10m long fault zone with 2.5m wide rock matrix domain. Coupled geochemical reactive transport modeling is performed using COMSOL Multiphysics and MATLAB. Calcite dissolution and precipitation are observed in the fault zone and the rock matrix, however, dissolution of calcite dominates the calcite precipitation in the rock matrix. Calcite dissolution/precipitation results in porosity variation in both the fault zone and the rock matrix mainly close to the bottom inlet boundary and along the fault zone. An intense dissolution of calcite is observed, in close vicinity of the fault inlet boundary, in the rock matrix which results in a cave like formation with porosity increasing to unity. A porosity decrease in the rock matrix is also observed due to calcite precipitation. In the fault zone, a cyclic porosity variation is observed due to a cyclic calcite dissolution and precipitation in the fault zone. Overall porosity increase is observed in the fault zone reaching to unity in some parts of the fault zone. The variation in porosity is observed as posing strong effects on the flow field in the fault and the rock

  5. Throughput and Latency in Finite-Buffer Line Networks

    CERN Document Server

    Vellambi, Badri N; Fekri, Faramarz

    2010-01-01

    This work investigates the effect of finite buffer sizes on the throughput capacity and packet delay of line networks with packet erasure links that have perfect feedback. These performance measures are shown to be linked to the stationary distribution of an underlying irreducible Markov chain that models the system exactly. Using simple strategies, bounds on the throughput capacity are derived. The work then presents two iterative schemes to approximate the steady-state distribution of node occupancies by decoupling the chain to smaller queueing blocks. These approximate solutions are used to understand the effect of buffer sizes on throughput capacity and the distribution of packet delay. Using the exact modeling for line networks, it is shown that the throughput capacity is unaltered in the absence of hop-by-hop feedback provided packet-level network coding is allowed. Finally, using simulations, it is confirmed that the proposed framework yields accurate estimates of the throughput capacity and delay dist...

  6. Temperature buffer test. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Aakesson, Mattias [Clay Technology AB, Lund (Sweden)

    2012-04-15

    The Temperature Buffer Test (TBT) is a joint project between SKB/ANDRA and supported by ENRESA (modelling) and DBE (instrumentation), which aims at improving the understanding and to model the thermo-hydro-mechanical behavior of buffers made of swelling clay submitted to high temperatures (over 100 deg C) during the water saturation process. The test has been carried out in a KBS-3 deposition hole at Aspo HRL. It was installed during the spring of 2003. Two steel heaters (3 m long, 0.6 m diameter) and two buffer arrangements have been investigated: the lower heater was surrounded by rings of compacted Wyoming bentonite only, whereas the upper heater was surrounded by a composite barrier, with a sand shield between the heater and the bentonite. The test was dismantled and sampled during the winter of 2009/2010. This report is the final report and a summary of all work performed within the TBT project. The design and the installation of the different components are summarized: the depositions hole, the heating system, the bentonite blocks with emphasis on the initial density and water content in these, the filling of slots with sand or pellets, the retaining construction with the plug, lid and nine anchor cables, the artificial saturation system, and finally the instrumentation. An overview of the operational conditions is presented: the power output from heaters, which was 1,500 W (and also 1,600 W) from each heater during the first {approx}1,700 days, and then changed to 1,000 and 2,000 W, for the upper and lower heater respectively, during the last {approx}600 days. From the start, the bentonite was hydrated with a groundwater from a nearby bore-hole, but this groundwater was replaced with de-ionized water from day {approx}1,500, due to the high flow resistance of the injections points in the filter, which implied that a high filter pressure couldn't be sustained. The sand shield around the upper heater was hydrated from day {approx}1,500 to day {approx}1

  7. Temperature buffer test. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Aakesson, Mattias [Clay Technology AB, Lund (Sweden)

    2012-04-15

    The Temperature Buffer Test (TBT) is a joint project between SKB/ANDRA and supported by ENRESA (modelling) and DBE (instrumentation), which aims at improving the understanding and to model the thermo-hydro-mechanical behavior of buffers made of swelling clay submitted to high temperatures (over 100 deg C) during the water saturation process. The test has been carried out in a KBS-3 deposition hole at Aspo HRL. It was installed during the spring of 2003. Two steel heaters (3 m long, 0.6 m diameter) and two buffer arrangements have been investigated: the lower heater was surrounded by rings of compacted Wyoming bentonite only, whereas the upper heater was surrounded by a composite barrier, with a sand shield between the heater and the bentonite. The test was dismantled and sampled during the winter of 2009/2010. This report is the final report and a summary of all work performed within the TBT project. The design and the installation of the different components are summarized: the depositions hole, the heating system, the bentonite blocks with emphasis on the initial density and water content in these, the filling of slots with sand or pellets, the retaining construction with the plug, lid and nine anchor cables, the artificial saturation system, and finally the instrumentation. An overview of the operational conditions is presented: the power output from heaters, which was 1,500 W (and also 1,600 W) from each heater during the first {approx}1,700 days, and then changed to 1,000 and 2,000 W, for the upper and lower heater respectively, during the last {approx}600 days. From the start, the bentonite was hydrated with a groundwater from a nearby bore-hole, but this groundwater was replaced with de-ionized water from day {approx}1,500, due to the high flow resistance of the injections points in the filter, which implied that a high filter pressure couldn't be sustained. The sand shield around the upper heater was hydrated from day {approx}1,500 to day {approx}1

  8. COMBINATIONS OF BUFFER-STOCKS AND BUFFER-FUNDS FOR WOOL PRICE STABILISATION IN AUSTRALIA

    OpenAIRE

    Moir, Brian; Piggott, Roley R.

    1991-01-01

    In this paper a preliminary analysis is presented of a combined buffer-fund and buffer-stock as an alternative to a pure buffer-fund or a pure buffer stock for stabilising wool prices. The alternatives analysed are designed so that each provides the same prices to producers as did the Reserve Price Scheme over the period of analysis. Least-cost combinations of policy instruments are derived. The results show that there is considerable potential for cost savings to be made by combining buffer-...

  9. High School Forum: "Invitations to Enquiry": The Calcite/Acid Reaction.

    Science.gov (United States)

    Herron, J. Dudley, Ed.; Driscoll, D. R.

    1979-01-01

    Describes a high school chemistry experiment which involves the reaction between calcite and hydrochloric and sulfuric acids. This reaction can be carried out as a projected demonstration and on an individual basis. (HM)

  10. Morphological changes of calcite single crystals induced by graphene-biomolecule adducts

    Science.gov (United States)

    Calvaresi, Matteo; Di Giosia, Matteo; Ianiro, Alessandro; Valle, Francesco; Fermani, Simona; Polishchuk, Iryna; Pokroy, Boaz; Falini, Giuseppe

    2017-01-01

    Calcite has the capability to interact with a wide variety of molecules. This usually induces changes in shape and morphology of crystals. Here, this process was investigated using sheets of graphene-biomolecule adducts. They were prepared and made dispersible in water through the exfoliation of graphite by tip sonication in the presence tryptophan or N-acetyl-D-glucosamine. The crystallization of calcium carbonate in the presence of these additives was obtained by the vapor diffusion method and only calcite formed. The analysis of the microscopic observations showed that the graphene-biomolecule adducts affected shape and morphology of rhombohedral {10.4} faced calcite crystals, due to their stabilization of additional {hk.0} faces. The only presence of the biomolecule affected minimally shape and morphology of calcite crystals, highlighting the key role of the graphene sheets as 2D support for the adsorption of the biomolecules.

  11. Calcium sulfoaluminate (Ye'elimite) hydration in the presence of gypsum, calcite, and vaterite

    Energy Technology Data Exchange (ETDEWEB)

    Hargis, Craig W. [Department of Civil and Environmental Engineering, University of California, Berkeley, CA (United States); Telesca, Antonio [School of Engineering, University of Basilicata, Potenza (Italy); Monteiro, Paulo J.M., E-mail: monteiro@ce.berkeley.edu [Department of Civil and Environmental Engineering, University of California, Berkeley, CA (United States)

    2014-11-15

    Six calcium sulfoaluminate-based cementitious systems composed of calcium sulfoaluminate, calcite, vaterite, and gypsum were cured as pastes and mortars for 1, 7, 28 and 84 days. Pastes were analyzed with X-ray diffraction, thermogravimetric and differential thermal analyses. Mortars were tested for compressive strength, dimensional stability and setting time. Furthermore, pastes with a water/cementitious material mass ratio of 0.80 were tested for heat evolution during the first 48 h by means of isothermal conduction calorimetry. It has been found that: (1) both calcite and vaterite reacted with monosulfoaluminate to give monocarboaluminate and ettringite, with vaterite being more reactive; (2) gypsum lowered the reactivity of both carbonates; (3) expansion was reduced by calcite and vaterite, irrespective of the presence of gypsum; and (4) both carbonates increased compressive strength in the absence of gypsum and decreased compressive strength less in the presence of gypsum, with vaterite's action more effective than that of calcite.

  12. Enhancing mechanical properties of calcite by Mg substitutions: An ab initio study

    Science.gov (United States)

    Elstnerova, Pavlina; Friak, Martin; Hickel, Tilmann; Fabritius, Helge Otto; Lymperakis, Liverios; Petrov, Michal; Raabe, Dierk; Neugebauer, Joerg; Nikolov, Svetoslav; Zigler, Andreas; Hild, Sabine

    2011-03-01

    Arthropoda representing a majority of all known animal species are protected by an exoskeleton formed by their cuticle. The cuticle represents a hierarchically structured multifunctional bio-composite based on chitin and proteins. Some groups like Crustacea reinforce the load-bearing parts of their cuticle with calcite. As the calcite sometimes contains Mg it was speculated that Mg may have a stiffening impact on the mechanical properties of the cuticle. We present a theoretical parameter-free quantum-mechanical study of thermodynamic, structural and elastic properties of Mg-substituted calcite. Our results show that substituting Ca by Mg causes an almost linear decrease in the crystal volume with Mg concentration and of substituted crystals. As a consequence the calcite crystals become stiffer giving rise e.g. to substantially increased bulk moduli.

  13. Calcite dissolution along a transect in the western tropical Indian Ocean: A multiproxy approach

    Digital Repository Service at National Institute of Oceanography (India)

    Naik, S.S.; Naidu, P.D.

    Three paleocarbonate ion proxies, size index, planktonic foraminifera shell weight, and calcite crystallinity, have been employed here to a set of core top samples from the western tropical Indian Ocean in the water depth ranges from 1086 to 4730 m...

  14. The Influence of Exotic Calcite on the Mechanical Behavior of Quartz Bearing Fault Gouge

    Science.gov (United States)

    Carpenter, B. M.; Di Stefano, G.; Collettini, C.

    2014-12-01

    The interseismic recovery of frictional strength is a fundamental part of the seismic cycle. This restrengthening, and related phenomena, plays a key role in determining the stability and mode of tectonic faulting. Recent experimental data has shown that gouge mineralogy has a strong influence on the rate of frictional healing, with calcite-dominated gouges showing the highest rates. Combining these data with widespread observations of calcite as cement or veins in non-carbonate hosted faults, indicates that the presence of calcite within a fault gouge could play an important role in shallow- and mid-crustal earthquakes. We report on laboratory experiments designed to explore the mechanical behavior of quartz/calcite mixtures as a means to better understand the evolution of fault behavior in faults where carbonate materials are present. We sheared mixtures of powdered Carrara marble (>98% CaCO3) and disaggregated Ottawa sand (99.8% SiO2) at constant normal stress of 5 MPa under saturated conditions at room temperature. We performed slide-hold-slide tests, 1-3,000 seconds, and velocity stepping tests, 0.1-1000 μm/s, to measure the amount of frictional healing and velocity dependence of friction respectively. Small subsets of experiments were conducted at different boundary conditions. Preliminary results show that the presence of calcite in quartz-based fault gouge has a hardening effect, both in overall frictional strength, where the strength of our mixtures increases with increasing calcite content, and in single experiments, where mixtures with low percentages of calcite show a consistent strain-hardening trend. We also observe that the rates of frictional healing and creep relaxation increase with increasing calcite content. Finally, our results show that the addition of as little as 2.5% calcite within a fault gouge results in a 30% increase in the rate of frictional healing, with further increases in calcite content resulting in larger increases in the rate

  15. Buffer-regulated biocorrosion of pure magnesium.

    Science.gov (United States)

    Kirkland, Nicholas T; Waterman, Jay; Birbilis, Nick; Dias, George; Woodfield, Tim B F; Hartshorn, Richard M; Staiger, Mark P

    2012-02-01

    Magnesium (Mg) alloys are being actively investigated as potential load-bearing orthopaedic implant materials due to their biodegradability in vivo. With Mg biomaterials at an early stage in their development, the screening of alloy compositions for their biodegradation rate, and hence biocompatibility, is reliant on cost-effective in vitro methods. The use of a buffer to control pH during in vitro biodegradation is recognised as critically important as this seeks to mimic pH control as it occurs naturally in vivo. The two different types of in vitro buffer system available are based on either (i) zwitterionic organic compounds or (ii) carbonate buffers within a partial-CO(2) atmosphere. This study investigated the influence of the buffering system itself on the in vitro corrosion of Mg. It was found that the less realistic zwitterion-based buffer did not form the same corrosion layers as the carbonate buffer, and was potentially affecting the behaviour of the hydrated oxide layer that forms on Mg in all aqueous environments. Consequently it was recommended that Mg in vitro experiments use the more biorealistic carbonate buffering system when possible.

  16. Electrophoretic mobilities of erythrocytes in various buffers

    Science.gov (United States)

    Plank, L. D.; Kunze, M. E.; Todd, P. W.

    1985-01-01

    The calibration of space flight equipment depends on a source of standard test particles, this test particle of choice is the fixed erythrocyte. Erythrocytes from different species have different electrophoretic mobilities. Electrophoretic mobility depends upon zeta potential, which, in turn depends upon ionic strength. Zeta potential decreases with increasing ionic strength, so cells have high electrophoretic mobility in space electrophoresis buffers than in typical physiological buffers. The electrophoretic mobilities of fixed human, rat, and rabbit erythrocytes in 0.145 M salt and buffers of varying ionic strength, temperature, and composition, to assess the effects of some of the unique combinations used in space buffers were characterized. Several effects were assessed: glycerol or DMSO (dimethylsulfoxide) were considered for use as cryoprotectants. The effect of these substances on erythrocyte electrophoretic mobility was examined. The choice of buffer depended upon cell mobility. Primary experiments with kidney cells established the choice of buffer and cryoprotectant. A nonstandard temperature of EPM in the suitable buffer was determined. A loss of ionic strength control occurs in the course of preparing columns for flight, the effects of small increases in ionic strength over the expected low values need to be evaluated.

  17. Molecular dynamics simulation of adsorption of an oil-water-surfactant mixture on calcite surface

    Institute of Scientific and Technical Information of China (English)

    Lu Guiwu; Zhang Xuefen; Shao Changjin; Yang Hong

    2009-01-01

    An interface super molecular structure model for oil-water-surfactant mixture and calcite was established. By using a molecular dynamics method, the effects of rhamnolipid, sodium dodecyl benzene sulfonate and sodium hexadecyl sulfonate on the interface adsorption behavior of oil molecules were investigated. It was found that these three surfactants could reduce oil-calcite interface binding energy, and play a role of oil-displacing agent.

  18. Accurate measurement of the main refractive indices and thermo-optical coefficients of the calcite crystal

    Institute of Scientific and Technical Information of China (English)

    Shuang Zhao; Fuquan Wu; Haifeng Wang; Weigang Zhong; Xiuzhen Li; Hengjing Tang; Meng Shi; Hongyan Deng

    2007-01-01

    The main refractive indices of calcite crystal are measured by the means of auto-collimation, and the thermo-optical coefficients are calculated. The coefficient expression of Sellmeier equation is obtained by solving Sellmeier equation strictly and the refractive indices of different wavelengths are calculated, which accord with experimental esultsery well. The measured main refractive indices of calcite at 488-nm wavelength are identical with the values obtained by Sellmeier equation.

  19. Origin of sulfate in barite and calcite cements in the Jebel Madar salt dome (Oman)

    Science.gov (United States)

    Vandeginste, V.; John, C. M.; Gilhooly, W. P.

    2012-12-01

    Jebel Madar is a 500-m high mountain rising in the desert at the Oman Foothills. The Jebel consists of Triassic to Cretaceous carbonate host rocks forming the carapace of a salt dome. Halokinesis caused major fracturing and faulting at Jebel Madar, and the resulting structures acted as the main pathways for fluids that generated diagenetic cements composed of both barite and calcite. The spatial distribution of calcite and barite occurrences shows that calcite is formed in large abundance along the three main faults, whereas barite is more concentrated along faults further away from the three main ones. The stable carbon and oxygen isotope composition of calcite and fluid inclusion data from both calcite and barite show a distinct evolution of the fluid with a highly saline component towards more mixing with meteoric water. This is in agreement with clumped isotopes data on calcite cements indicating an evolution towards lower temperatures, consistent with doming of the Jebel and greater input of lower-temperature descending meteoric fluids. Here, we present sulphur and oxygen isotopic data on barite that suggest a link between the barite formation and the Precambrian salt underlying Jebel Madar. The average δ34S measured in barite is 33‰ CDT (1σ = 5‰; n = 33), which falls at the lower end of the δ34S range reported for the Ara Group anhydrite. The average δ18O in the same barite samples is 23‰ VSMOW (1σ = 2‰; n = 33). Data from the barite will be compared with sulphur isotopes from the carbonate-associate sulfate in the calcite cements. The overall goal of our research is to gain a better insight in the formation process of barite and calcite in Jebel Madar and its link with salt tectonics. We would like to acknowledge the financial support of QCCSRC (funded jointly by Qatar Petroleum, Shell and the Qatar Science & Technology Park) and the GSA Laubach fund for this study.

  20. Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

    Directory of Open Access Journals (Sweden)

    S. Bindschedler

    2014-01-01

    Full Text Available Calcitic nanofibres are ubiquitous habits of secondary calcium carbonate (CaCO3 accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enigmatic. Three possible mechanisms fuel the debate: (i purely physicochemical processes, (ii mineralization of rod-shaped bacteria, and (iii crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic or organic in nature. They are very often observed in association with Needle Fibre Calcite (NFC, another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent association is likely to be an important fact to help understanding the origin of nanofibres. In this manuscript the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothesis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morphological resemblance when compared to their natural counterparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hypothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically-influenced mineralization process, generating calcitic nanofibres. This highlights the possible involvement of Fungi in CaCO3 biomineralization processes, a role still poorly documented at

  1. The coordination of sulfur in synthetic and biogenic Mg calcites: The red coral case

    Science.gov (United States)

    Perrin, J.; Rivard, C.; Vielzeuf, D.; Laporte, D.; Fonquernie, C.; Ricolleau, A.; Cotte, M.; Floquet, N.

    2017-01-01

    Sulfur has been recognized in biogenic calcites for a long time. However, its structural position is matter of debate. For some authors, sulfur is a marker of the organic matrix while it is part of the calcite structure itself for others. To better understand the place of sulfur in calcite, sulfated magnesian calcites (S-MgCalcite) have been synthetized at high pressure and temperature and studied by μ-XANES spectroscopy. S-MgCalcite XANES spectra show two different types of sulfur: sulfate (SO42-) as a predominant species and a small contribution of sulfite (SO32-), both substituting for carbonate ions in the calcite structure. To address the question of the position of sulfur in biogenic calcites, the oxidation states of sulfur in the skeleton and organic tissues of Corallium rubrum have been investigated by micro X-ray fluorescence (μ-XRF) and sulfur K-edge micro X-ray absorption near edge structure (μ-XANES) spectroscopy at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) on beamline ID21. In the skeleton, sulfur is mainly present as oxidized sulfur SO42- (+VI), plus a weak sulfite contribution. XANES spectra indicate that sulfur is inorganically incorporated as sulfur structurally substituted to carbonate ions (SSS). Although an organic matrix is present in the red coral skeleton, reduced organic sulfur could not be detected by μ-XANES spectroscopy in the skeleton probably due to low organic/inorganic sulfur ratio. In the organic tissues surrounding the skeleton, several sulfur oxidation states have been detected including disulfide (S-S), thioether (R-S-CH3), sulfoxide (SO2), sulfonate (SO2O-) and sulfate (SO42-). The unexpected occurrence of inorganic sulfate within the organic tissues suggests the presence of pre-organized organic/inorganic complexes in the circulatory system of the red coral, precursors to biomineralization ahead of the growth front.

  2. 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...

  3. Sturgeon and paddlefish (Acipenseridae) sagittal otoliths are composed of the calcium carbonate polymorphs vaterite and calcite.

    Science.gov (United States)

    Pracheil, B M; Chakoumakos, B C; Feygenson, M; Whitledge, G W; Koenigs, R P; Bruch, R M

    2017-02-01

    This study sought to resolve whether sturgeon (Acipenseridae) sagittae (otoliths) contain a non-vaterite fraction and to quantify how large a non-vaterite fraction is using neutron diffraction analysis. This study found that all otoliths examined had a calcite fraction that ranged from 18 ± 6 to 36 ± 3% by mass. This calcite fraction is most probably due to biological variation during otolith formation rather than an artefact of polymorph transformation during preparation.

  4. Buffer protection in the installation phase

    Energy Technology Data Exchange (ETDEWEB)

    Wimelius, Hans (Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden)); Pusch, Roland (Geodevelopment International AB, Lund (Sweden))

    2008-12-15

    The research and development of the design and construction of the SKB's repository for final disposal of spent reactor fuel is conducted along several paths ('lines'). Issues concerning the bedrock are dealt with in the 'rock line' and those related to buffer and backfill in deposition holes and tunnels are considered in the 'buffer line' and 'backfill line', respectively. These lines also deal with sub-activities that are coupled to several other lines. One of them includes development of techniques for protecting buffer blocks from moisture and water in the installation phase. Techniques and methods for placement and removal of the 'buffer protection sheet' are dealt with in the 'buffer line'. The removal is, however, considered as being part of the backfilling sequence. Since the performance of the sheet is of fundamental importance to the placement and function of the buffer it deserves particular attention. Thus, the removal of the rubber sheet that serves to protect the buffer blocks in the installation phase may be difficult and can cause significant problems that may require retrieval of already placed canister, buffer and backfill. These matters are in focus in the present report. Arrangements for protecting already placed buffer blocks from moist air and water have been tested in earlier large-scale experiments, i.e. the Prototype Repository project at Aespoe but the experience from them has called for more effective protection of the clay blocks as described in the present report. Focus is on the construction of foundation components at the bottom of the deposition holes required for establishing a tight seal between rock and buffer blocks, and on the protection sheet and arrangements for limiting water pressure on it. Special attention is paid to the drainage of the space between rock and protection sheet that is necessary for avoiding failure of the sheet and to systems for achieving

  5. Surface Water Protection by Productive Buffers

    DEFF Research Database (Denmark)

    Christen, Benjamin

    Vegetated riparian buffer zones are a widely recommended best management practice in agriculture for protecting surface and coastal waters from diffuse nutrient pollution. On the background of the EU funded research project NitroEurope (NEU; www.NitroEurope.eu), this study concentrates...... on the mitigation of nitrogen pollution in surface and groundwater, using riparian buffer zones for biomass production. The objectives are to map suitable areas for buffer implementation across the six NEU study landscapes, model tentative N-loss mitigation, calculate biomass production potential and economic...... designed for local conditions could be a way of protecting water quality attractive to many stakeholders....

  6. Reaction-induced fracturing in a hot pressed calcite-periclase aggregate

    Science.gov (United States)

    Kuleci, H.; Ulven, O. I.; Rybacki, E.; Wunder, B.; Abart, R.

    2017-01-01

    The chemo-mechanical feedbacks associated with hydration of periclase immersed in a calcite matrix were investigated experimentally. Dense calcite-periclase aggregates with calcite to periclase ratio of 90/10 and 95/5 by volume were prepared by hot isostatic pressing. Subsequent hydration experiments were performed in a hydrothermal apparatus at temperatures of 580-610 °C and a pressure of 200 MPa for run durations of 5-60 min. The rate of the periclase to brucite transformation was primarily controlled by the access of fluid. Where fluid was present, the reaction was too fast for the associated positive volume increase of the solids of about 100% to be accommodated by creep of the calcite matrix, and fracturing was induced. The newly formed cracks greatly enhanced the access of fluid leading to a positive feedback between hydration and fracturing. Mostly the newly formed cracks follow pre-existing grain boundaries in the calcite matrix. Comparison of experimental results with numerical 2D discrete element modelling (DEM) of crack formation revealed that the geometry of the crack pattern around a reacting particle depends on the shape of the original periclase particle, on the mechanical strength of the particle-matrix interface and on the mechanical strength and arrangement of grain boundaries in the calcite matrix in the immediate vicinity of the swelling particle.

  7. Sea urchin tooth mineralization: calcite present early in the aboral plumula.

    Science.gov (United States)

    Stock, Stuart R; Veis, Arthur; Xiao, Xianghui; Almer, Jonathan D; Dorvee, Jason R

    2012-11-01

    In both vertebrate bone, containing carbonated hydroxyapatite as the mineral phase, and in invertebrate hard tissue comprised of calcium carbonate, a popular view is that the mineral phase develops from a long-lived amorphous precursor which later transforms into crystal form. Important questions linked to this popular view are: when and where is the crystallized material formed, and is amorphous solid added subsequently to the crystalline substrate? Sea urchin teeth, in which the earliest mineral forms within isolated compartments, in a time and position dependent manner, allow direct investigation of the timing of crystallization of the calcite primary plates. Living teeth of the sea urchin Lytechinus variegatus, in their native coelomic fluid, were examined by high-energy synchrotron X-ray diffraction. The diffraction data show that calcite is present in the most aboral portions of the plumula, representing the very earliest stages of mineralization, and that this calcite has the same crystal orientation as in the more mature adoral portions of the same tooth. Raman spectroscopy of the aboral plumula confirms the initial primary plate mineral material is calcite and does not detect amorphous calcium carbonate; in the more mature adoral incisal flange, it does detect a broader calcite peak, consistent with two or more magnesium compositions. We hypothesize that some portion of each syncytial membrane in the plumula provides the information for nucleation of identically oriented calcite crystals that subsequently develop to form the complex geometry of the single crystal sea urchin tooth.

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

    Indian Academy of Sciences (India)

    E Venkateshwar Rao; M Ramakrishna Murthy

    2008-04-01

    Experimental investigations on the defect sub-structure and surface modifications, brought about by He+ ion-bombardment of calcite cleavages (100), have been carried out. Optical and scanning electron microscopic investigations revealed drastic modifications on the surface morphology, local symmetry and defect concentration. Additional structural defects on ion-bombardment of calcite surfaces also have been observed. Changes in shape and form of chemical etch pits are found to be a function of ion-beam energy, as studied by optical microscopy. Radiation damage in calcite has been attributed mainly due to desorption of CO$^{-2}_{3}$ ions from the calcite surfaces, on irradiation. Measurements of surface conductivity on irradiated calcite surfaces have been made employing a four-probe technique. Enhancement of surface conductivity has been considered to be due to an increase in concentration of CO$^{-2}_{3}$ ions formed, on ion irradiation and subsequent thermal stimulation. Planar plastic anisotropy has been studied on irradiated calcite cleavages by measurement of microhardness.

  9. NMR characterization of hydrocarbon adsorption on calcite surfaces: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Bevilaqua, Rochele C. A.; Miranda, Caetano R. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, UFABC, Santo André, SP (Brazil); Rigo, Vagner A. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, UFABC, Santo André, SP (Brazil); Universidade Tecnológica Federal do Paraná, UTFPR, Cornélio Procópio, PR (Brazil); Veríssimo-Alves, Marcos [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, UFABC, Santo André, SP (Brazil); Departamento de Física, ICEx, Universidade Federal Fluminense, UFF, Volta Redonda, RJ (Brazil)

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca{sup 2+}. Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO{sub 3} (101{sup ¯}4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for {sup 43}Ca, {sup 13}C, and {sup 17}O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated.

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

    Science.gov (United States)

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

    2005-01-01

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

  11. Low-Temperature Plasticity of Naturally Deformed Calcite Rocks

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Optical, cathodoluminescence and transmission electron microscope (TEM) analyses were conducted onfour groups of calcite fault rocks, a cataclastic limestone, cataclastic coarse-grained marbles from two fault zones, and afractured mylonite. These fault rocks show similar microstructural characteristics and give clues to similar processes ofrock deformation. They are characterized by the structural contrast between macroscopic cataclastic (brittle) andmicroscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e. deformation twins, kinkbands and microfractures) are well preserved in the deformed grains in clasts or in primary rocks. The matrix materials areof extremely fine grains with diffusive features. Dislocation microstructures for co-existing brittle deformation andcrystalline plasticity were revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformedclasts, while dislocation walls form in the transitions to the fine-grained matrix materials and free dislocations, dislocationloops and dislocation dipoles are observed both in the deformed clasts and in the fine-grained matrix materials. Dynamicrecrystallization grains from subgrain rotation recrystallization and subsequent grain boundary migration constitute themajor parts of the matrix materials. Statistical measurements of densities of free dislocations, grain sizes of subgrains anddynamically recrystallized grains suggest an unsteady state of the rock deformation. Microstructural andcathodoluminescence analyses prove that fluid activity is one of the major parts of faulting processes. Low-temperatureplasticity, and thereby induced co-existence of macroscopic brittle and microscopic ductile microstmctures are attributedto hydrolytic weakening due to the involvement of fluid phases in deformation and subsequent variation of rock rheology.During hydrolytic weakening, fluid phases, e.g. water, enhance the rate of dislocation slip and climb, and

  12. Effects of phosphate buffer in parenteral drugs on particle formation from glass vials.

    Science.gov (United States)

    Ogawa, Toru; Miyajima, Makoto; Wakiyama, Naoki; Terada, Katsuhide

    2013-01-01

    The characteristics of inorganic particles generated in glass vials filled with phosphate buffer solutions were investigated. During storage, particles were visually detected in the phosphate buffer solution in particular glass vials which pass compendial tests of containers for injectable drugs. These particles were considered to be different from ordinal glass delamination, which has been reported in a number of papers because the particles were mainly composed of Al, P and O, but not Si. The formation of the particles accelerated at higher storage temperatures. Among the surface treatments tested for the glass vials, sulfur treatment showed a protective effect on the particle formation in the vials, whereas the SiO(2) coating did not have any protective effects. It was found that the elution ratio of Al and Si in the solution stored in the glass vials after the heating was similar to the ratio of Al and Si in borosilicate glass. However, the Al concentration decreased during storage (5°C, 6 months), and consequently, particle formation was observed in the solution. Adding citrate, which is a chelating agent for Al, effectively suppressed the particle formation in the heated solution. When 50 ppb and higher concentrations of Al ion were added to the phosphate buffer solution, the formation of white particles containing Al, P and O was detected. It is suggested that a phosphate buffer solution in a borosilicate glass vial has the ability to form particles due to interactions with the Al that is eluted from the glass during storage.

  13. The buffer effect in neutral electrolyte supercapacitors

    DEFF Research Database (Denmark)

    Thrane Vindt, Steffen; Skou, Eivind M.

    2016-01-01

    to a change in the redox potential of water in opposite directions on the two electrodes, resulting in the wider stability window. The magnitude of this effect is suggested to be dependent on the buffer capacity, rather than the intrinsic pH value of the electrolyte. This is confirmed by studying the impact...... of addition of a buffer to such systems. It is shown that a 56 % higher dynamic storage capacity may be achieved, simply by controlling the buffer capacity of the electrolyte. The model system used, is based on a well-known commercial activated carbon (NORIT™ A SUPRA) as the electrode material, aqueous...... potassium nitrate as the electrolyte and potassium phosphates as the buffer system....

  14. Capture effeciency of a vegetative environmental buffer

    Science.gov (United States)

    Particulate matter emitted from tunnel-ventilated animal feeding operations (AFOs) is known to transport malodorous compounds. As a mitigation strategy, vegetative environmental buffers (VEBs) are often installed surrounding AFOs to capture particulates and induce lofting and dispersion. Currently, ...

  15. Buffer layer for thin film structures

    Science.gov (United States)

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

    2006-10-31

    A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

  16. Probabilistic Analysis of Buffer Starvation in Markovian Queues

    CERN Document Server

    Xu, Yuedong; El-Azouzi, Rachid; Haddad, Majed; Elayoubi, Salaheddine; Jimenez, Tania

    2011-01-01

    Our purpose in this paper is to obtain the exact distribution of the number of buffer starvations within a sequence of $N$ consecutive packet arrivals. The buffer is modeled as an M/M/1 queue, plus the consideration of bursty arrivals characterized by an interrupted Poisson process. When the buffer is empty, the service restarts after a certain amount of packets are prefetched. With this goal, we propose two approaches, one of which is based on Ballot theorem, and the other uses recursive equations. The Ballot theorem approach gives an explicit solution, but at the cost of the high complexity order in certain circumstances. The recursive approach, though not offering an explicit result, needs fewer computations. We further propose a fluid analysis of starvation probability on the file level, given the distribution of file size and the traffic intensity. The starvation probabilities of this paper have many potential applications. We apply them to optimize the quality of experience (QoE) of media streaming serv...

  17. Buffer regulation of calcium puff sequences.

    Science.gov (United States)

    Fraiman, Daniel; Dawson, Silvina Ponce

    2014-02-01

    Puffs are localized Ca(2 +) signals that arise in oocytes in response to inositol 1,4,5-trisphosphate (IP3). They are the result of the liberation of Ca(2 +) from the endoplasmic reticulum through the coordinated opening of IP3 receptor/channels clustered at a functional release site. The presence of buffers that trap Ca(2 +) provides a mechanism that enriches the spatio-temporal dynamics of cytosolic calcium. The expression of different types of buffers along the cell's life provides a tool with which Ca(2 +) signals and their responses can be modulated. In this paper we extend the stochastic model of a cluster of IP3R-Ca(2 +) channels introduced previously to elucidate the effect of buffers on sequences of puffs at the same release site. We obtain analytically the probability laws of the interpuff time and of the number of channels that participate of the puffs. Furthermore, we show that under typical experimental conditions the effect of buffers can be accounted for in terms of a simple inhibiting function. Hence, by exploring different inhibiting functions we are able to study the effect of a variety of buffers on the puff size and interpuff time distributions. We find the somewhat counter-intuitive result that the addition of a fast Ca(2 +) buffer can increase the average number of channels that participate of a puff.

  18. Effect of pH, buffer concentration and buffer composition on the absorption of theophylline from the small intestine of the rat

    NARCIS (Netherlands)

    Blaey, C.J. de; Schurgers, N.

    1984-01-01

    The absorption of theophylline from the small intestine of the rat was investigated using buffer solutions of different pH (3.0–9.2), composition and concentration. The technique used, encloses luminal perfusion of an intestinal loop with collection of the blood draining the perfused loop, which ena

  19. Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

    Energy Technology Data Exchange (ETDEWEB)

    Engel, Jesse H. [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Surendranath, Yogesh [Univ. of California, Berkeley, CA (United States); Alivisatos, Paul [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2013-07-20

    Semiconductor nanocrystal solids are attractive materials for active layers in next-generation optoelectronic devices; however, their efficient implementation has been impeded by the lack of precise control over dopant concentrations. Herein we demonstrate a chemical strategy for the controlled doping of nanocrystal solids under equilibrium conditions. Exposing lead selenide nanocrystal thin films to solutions containing varying proportions of decamethylferrocene and decamethylferrocenium incrementally and reversibly increased the carrier concentration in the solid by 2 orders of magnitude from their native values. This application of redox buffers for controlled doping provides a new method for the precise control of the majority carrier concentration in porous semiconductor thin films.

  20. Implementation of Input Block of Minimally Buffered Deflection NoC Router

    Directory of Open Access Journals (Sweden)

    Priti M. Shahane

    2016-08-01

    Full Text Available The traditional system on chip designs employ the shared bus architecture for data transfer in highly integrated Multiprocessor system on chips(MPSoC.Network on chip (NoCis a new paradigm for on chip communication for Multiprocessor systems on chips(MPSoCs. NoCs replace the traditional shared buses system with routing switches. Heart of the NoC is the router and it consists of an input buffer, arbiter, crossbar and an output port. The NoC router uses a buffer to store the incoming packets. These buffers improve the performance but they consume more power and area. Bufferless deflection routing is the solution for improvement in energy efficiency. In this method deflections of the packets take place to overcome the contention problem. But at high network load, deflection routing degrades the performance because of unnecessary hopping of data packets. The MinBD (minimally buffered deflection router is a new router design that uses a small buffer for bufferless deflection routing. In this paper the input block of MinBD router is implemented on FPGA which shows that a small buffer will help to reduce the network deflection rate. It also improves the performance and energy efficiency while buffering only deflected data packets.

  1. Thermal and Evolved Gas Behavior of Calcite Under Mars Phoenix TEGA Operating Conditions

    Science.gov (United States)

    Ming, D.W.; Niles, P.B.; Morris, R.V.; Boynton, W.V.; Golden, D.C.; Lauer, H.V.; Sutter, B.

    2009-01-01

    The Mars Phoenix Scout Mission with its diverse instrument suite successfully examined several soils on the Northern plains of Mars. The Thermal and Evolved Gas Analyzer (TEGA) was employed to detect organic and inorganic materials by coupling a differential scanning calorimeter (DSC) with a magnetic-sector mass spectrometer (MS). Martian soil was heated up to 1000 C in the DSC ovens and evolved gases from mineral decomposition products were examined with the MS. TEGA s DSC has the capability to detect endothermic and exothermic reactions during heating that are characteristic of minerals present in the Martian soil. Initial TEGA results indicated the presence of endothermic peaks with onset temperatures that ranged from 675 C to 750 C with corresponding CO2 release. This result suggests the presence of calcite (CaCO3. CaO + CO2). Organic combustion to CO2 is not likely since this mostly occurs at temperatures below 550 C. Fe-carbonate and Mg-carbonate are not likely because their decomposition temperatures are less than 600 C. TEGA enthalpy determinations suggest that calcite, may occur in the Martian soil in concentrations of approx.1 to 5 wt. %. The detection of calcite could be questioned based on previous results that suggest Mars soils are mostly acidic. However, the Phoenix landing site soil pH was measured at pH 8.3 0.5, which is typical of terrestrial soils where pH is controlled by calcite solubility. The range of onset temperatures and calcite concentration as calculated by TEGA is poorly con-strained in part because of limited thermal data of cal-cite at reduced pressures. TEGA operates at calcite literature thermal data was obtained at 1000 mbar or higher pressures.

  2. Low noise buffer amplifiers and buffered phase comparators for precise time and frequency measurement and distribution

    Science.gov (United States)

    Eichinger, R. A.; Dachel, P.; Miller, W. H.; Ingold, J. S.

    1982-01-01

    Extremely low noise, high performance, wideband buffer amplifiers and buffered phase comparators were developed. These buffer amplifiers are designed to distribute reference frequencies from 30 KHz to 45 MHz from a hydrogen maser without degrading the hydrogen maser's performance. The buffered phase comparators are designed to intercompare the phase of state of the art hydrogen masers without adding any significant measurement system noise. These devices have a 27 femtosecond phase stability floor and are stable to better than one picosecond for long periods of time. Their temperature coefficient is less than one picosecond per degree C, and they have shown virtually no voltage coefficients.

  3. The influence of final repository relevant electrolyte on the interaction of trivalent lanthanides and actinides with calcite; Der Einfluss endlagerrelevanter Elektrolyte auf die Wechselwirkung dreiwertiger Lanthanide und Actinide mit Calcit

    Energy Technology Data Exchange (ETDEWEB)

    Hofmann, Sascha

    2015-10-21

    Calcite, a naturally occurring and very abundant mineral, is considered a potential retentive geochemical barrier regarding nuclear waste disposal. In this work, the reactivity of calcite towards trivalent Ln and An has been determined by spectroscopic, microscopic and X-ray scattering techniques. This, in connection with the use of luminescent probes Eu(III) and Cm(III), allowed for the understanding of electrolyte influences on the retention potential of calcite.

  4. Temperature Buffer Test. Measurements of water content and density of the excavated buffer material

    Energy Technology Data Exchange (ETDEWEB)

    Johannesson, Lars-Erik [Clay Technology AB, Lund (Sweden)

    2010-12-15

    TBT (Temperature Buffer Test) is a joint project between SKB/ANDRA and supported by ENRESA (modeling) and DBE (instrumentation), which aims at understanding and modeling the thermo-hydromechanical behavior of buffers made of swelling clay submitted to high temperatures (over 100 deg C) during the water saturation process. The test was carried out at the - 420 m level in Aespoe HRL in a 8 meters deep and 1.76 m diameter deposition hole, with two heaters (3 m long, 0.6 m diameter), surrounded by a MX-80 bentonite buffer and a confining plug on top anchored with 9 rods. It was installed during spring 2003. The bentonite around upper heater was removed during the period October - December 2009 and the buffer around the lower heater was removed during January - Mars 2010. During dismantling of the buffer, samples were taken on which analyses were made. This report describes the work with the deteroemoeination of the water content and the density of the taken samples. Most of the samples were taken from the buffer by core drilling from the upper surface of each installed bentonite block. The cores had a diameter of about 50 mm and a maximum length equal to the original height of the bentonite blocks (about 500 mm). The water content of the buffer was determined by drying a sample at a temperature of 105 deg C for 24 h and the bulk density was determined by weighing a sample both in the air and immerged in paraffin oil with known density. The water content, dry density, degree of saturation and void ratio of the buffer were then plotted. The plots show that all parts of the buffer had taken up water and the degree of saturation of the buffer varied between 90 - 100%. Large variation in the dry density of the buffer was also observed.

  5. 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.

  6. The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite.

    Science.gov (United States)

    Rodriguez-Blanco, Juan Diego; Shaw, Samuel; Benning, Liane G

    2011-01-01

    The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.

  7. Phosphorus speciation in calcite speleothems determined from solid-state NMR spectroscopy

    Science.gov (United States)

    Mason, Harris E.; Frisia, Silvia; Tang, Yuanzhi; Reeder, Richard J.; Phillips, Brian L.

    2007-02-01

    Variations in speleothem P concentration show cyclic patterns that have important implications for high resolution palaeoclimate and palaeoenvironmental reconstructions. However, little is known about the speciation of P in calcite speleothems. Here we employ solid-state 31P and 1H magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopic techniques as a non-destructive method for analyzing the distribution of P in speleothems. The 31P MAS NMR results show three peaks indicating the presence of three primary types of phosphate species in samples from the Grotta di Ernesto (northeastern Italy): a broad peak at a chemical shift δP-31 = 3.1 to 3.7 ppm from individual phosphate ions incorporated within calcite, a narrow set of peaks near δP-31 = - 0.9 ppm from crystalline monetite and a narrow peak at δP-31 = 2.9 ppm from an unidentified crystalline phosphate phase. Essentially identical results were obtained for a synthetic calcite/phosphate coprecipitate. Spectra collected for a sample from Grotte de Clamouse (southern France) show only a broad peak near 3.5 ppm suggesting a possible limit for phosphate incorporation into the calcite structure. These data suggest that P in this system can interact to form calcium phosphate surface precipitates during infiltration events and are subsequently enclosed during calcite growth.

  8. 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.

  9. Restriction endonucleases digesting DNA in PCR buffer

    Institute of Scientific and Technical Information of China (English)

    LIU Xue-dong; ZHENG Dong; ZHOU Yan-na; MAO Wei-wei; MA Jian-zhang

    2005-01-01

    Six commonly used restriction endonucleases (Res) (Acc I, Ban II, EcoR I, Hind III, Sac I, Sca I) were tested for their ability to directly digest DNA completely in the Polymerase Chain Reaction (PCR) buffers. The results showed that: with the requirement for additional magnesium supplemented as activator, Res, except EcoR I appeared star activity, completely digested unmethylated lambda DNA after overnight incubation in PCR buffer and functioned as equally well as in recommended Restriction Enzyme Buffer provided with each enzyme; all Res tested completely digested PCR products in PCR buffer, it implied digestion of PCR products may often be performed directly in the PCR tube without the requirement for any precipitation or purification steps; and the concentration of MgCl2 from 2.5 mmol·L-1 to 10 mmol·L-1 did not significantly affect activity of Res in PCR buffer. This simplified method for RE digestion of PCR products could have applications in restriction fragment length polymorphism (RFLP) analysis and single-stranded conformational polymorphism (SSCP) analysis of large PCR products. However, usage of this procedure for cloning applications needs further data.

  10. The ability of contrasting ericaceous ecosystems to buffer nitrogen leaching

    Directory of Open Access Journals (Sweden)

    C.D. Field

    2013-08-01

    Full Text Available Much attention has been given to the carbon balance of peatland and heathland ecosystems and their role as global carbon stores. They are also important as buffers for atmospheric nitrogen (N pollution, locking N into the soil and vegetation through tight nutrient cycling and preventing the leaching of soluble N into freshwater ecosystems. We compared mean annual soil exchangeable N, mineralisation and soil solution nitrogen at three contrasting ericaceous-dominated ecosystems: a lowland heath, an upland heath and an ombrotrophic raised bog at intermediate altitude, all of which were sites of long-term N-manipulation experiments. We expected that soil leachate N would be associated with soil C/N and total soil C, and that sites with higher C % and soil C/N would have greater ability to buffer N deposition before N saturation and leaching began. However, although soil solution N responded to N deposition at all the sites, we found that only the heathland sites were consistent with this expectation. The bog, with the highest C/N and largest C pool, was not the most strongly buffered. The upland heath was most effective at retaining N (extractable NH4+-N +3900 % from control compared to the lowland heath (extractable NH4+-N +370 % from control and the bog (extractable NH4+-N, +140–240 % from control. We concluded that the absence of a definable Calluna litter layer at the lowland heath and the bog, and the anoxic conditions at the bog, explained the earlier onset of leaching and that carbon and nitrogen cycles appeared more closely coupled in the heathlands but became decoupled at the bog due to the strong controlling effect of hydrology.

  11. Redox buffered hydrofluoric acid etchant for the reduction of galvanic attack during release etching of MEMS devices having noble material films

    Science.gov (United States)

    Hankins, Matthew G.

    2009-10-06

    Etchant solutions comprising a redox buffer can be used during the release etch step to reduce damage to the structural layers of a MEMS device that has noble material films. A preferred redox buffer comprises a soluble thiophosphoric acid, ester, or salt that maintains the electrochemical potential of the etchant solution at a level that prevents oxidation of the structural material. Therefore, the redox buffer preferentially oxidizes in place of the structural material. The sacrificial redox buffer thereby protects the exposed structural layers while permitting the dissolution of sacrificial oxide layers during the release etch.

  12. Development of all chemical solution derived Ce0.9La0.1O2 − y/Gd2Zr2O7 buffer layer stack for coated conductors: influence of the post-annealing process on surface crystallinity

    DEFF Research Database (Denmark)

    Yue, Zhao; Li, Xiaofen; Khoryushin, Alexey

    2012-01-01

    Preparation and characterization of a biaxially textured Gd2Zr2O7 and Ce0.9La0.1O2 − y (CLO, cap)/Gd2Zr2O7 (GZO, barrier) buffer layer stack by the metal–organic deposition route are reported. YBa2Cu3O7 − d (YBCO) superconductor films were deposited by the pulsed-laser deposition (PLD) technique ......-field), demonstrating that the novel CLO/GZO stack is very promising for further development of low cost buffer layer architectures for coated conductors....

  13. Undergraduate Chemistry Students' Perceptions of and Misconceptions about Buffers and Buffer Problems

    Science.gov (United States)

    Orgill, MaryKay; Sutherland, Aynsley

    2008-01-01

    Both upper- and lower-level chemistry students struggle with understanding the concept of buffers and with solving corresponding buffer problems. While it might be reasonable to expect general chemistry students to struggle with this abstract concept, it is surprising that upper-level students in analytical chemistry and biochemistry continue to…

  14. Nonlinear spelling in graphemic buffer deficit.

    Science.gov (United States)

    Schubert, Teresa; Nickels, Lyndsey

    2015-01-01

    In this paper, we describe a case of nonlinear spelling and its implications for theories of the graphemic buffer. C.T.J., an individual with an acquired deficit of the graphemic buffer, often wrote the letters of his responses in a nonlinear temporal order when writing to dictation. The spatial ordering of the letters was maintained: Letters in the later positions of the words were written towards the right side of the response, even when written before letters in earlier positions. This unusual phenomenon has been briefly reported in three prior cases but this study provides the most detailed analysis of the phenomenon to date. We specifically contend that the decoupling of the temporal and spatial aspects of spelling is difficult to reconcile with competitive queuing accounts of the graphemic buffer.

  15. Labview virtual instruments for calcium buffer calculations.

    Science.gov (United States)

    Reitz, Frederick B; Pollack, Gerald H

    2003-01-01

    Labview VIs based upon the calculator programs of Fabiato and Fabiato (J. Physiol. Paris 75 (1979) 463) are presented. The VIs comprise the necessary computations for the accurate preparation of multiple-metal buffers, for the back-calculation of buffer composition given known free metal concentrations and stability constants used, for the determination of free concentrations from a given buffer composition, and for the determination of apparent stability constants from absolute constants. As implemented, the VIs can concurrently account for up to three divalent metals, two monovalent metals and four ligands thereof, and the modular design of the VIs facilitates further extension of their capacity. As Labview VIs are inherently graphical, these VIs may serve as useful templates for those wishing to adapt this software to other platforms.

  16. A Better Reduction Theorem for Store Buffers

    CERN Document Server

    Cohen, Ernie

    2009-01-01

    When verifying a concurrent program, it is usual to assume that memory is sequentially consistent. However, most modern multiprocessors depend on store buffering for efficiency, and provide native sequential consistency only at a substantial performance penalty. To regain sequential consistency, a programmer has to follow an appropriate programming discipline. However, na\\"ive disciplines, such as protecting all shared accesses with locks, are not flexible enough for building high-performance multiprocessor software. We present a new discipline for concurrent programming under TSO (total store order, with store buffer forwarding). It does not depend on concurrency primitives, such as locks. Instead, threads use ghost operations to acquire and release ownership of memory addresses. A thread can write to an address only if no other thread owns it, and can read from an address only if it owns it or it is shared and the thread has flushed its store buffer since it last wrote to an address it did not own. This dis...

  17. Buffer management optimization strategy for satellite ATM

    Institute of Scientific and Technical Information of China (English)

    Lu Rong; Cao Zhigang

    2006-01-01

    ECTD (erroneous cell tail drop), a buffer management optimization strategy is suggested which can improve the utilization of buffer resources in satellite ATM (asynchronous transfer mode) networks. The strategy, in which erroneous cells caused by satellite channel and the following cells that belong to the same PDU (protocol data Unit) are discarded, concerns non-real-time data services that use higher layer protocol for retransmission. Based on EPD (early packet drop) policy, mathematical models are established with and without ECTD. The numerical results show that ECTD would optimize buffer management and improve effective throughput (goodput), and the increment of goodput is relative to the CER (cell error ratio) and the PDU length. The higher their values are, the greater the increment. For example,when the average PDU length values are 30 and 90, the improvement of goodput are respectively about 4% and 10%.

  18. Temperature Buffer Test. Final THM modelling

    Energy Technology Data Exchange (ETDEWEB)

    Aakesson, Mattias; Malmberg, Daniel; Boergesson, Lennart; Hernelind, Jan [Clay Technology AB, Lund (Sweden); Ledesma, Alberto; Jacinto, Abel [UPC, Universitat Politecnica de Catalunya, Barcelona (Spain)

    2012-01-15

    The Temperature Buffer Test (TBT) is a joint project between SKB/ANDRA and supported by ENRESA (modelling) and DBE (instrumentation), which aims at improving the understanding and to model the thermo-hydro-mechanical behavior of buffers made of swelling clay submitted to high temperatures (over 100 deg C) during the water saturation process. The test has been carried out in a KBS-3 deposition hole at Aespoe HRL. It was installed during the spring of 2003. Two heaters (3 m long, 0.6 m diameter) and two buffer arrangements have been investigated: the lower heater was surrounded by bentonite only, whereas the upper heater was surrounded by a composite barrier, with a sand shield between the heater and the bentonite. The test was dismantled and sampled during the winter of 2009/2010. This report presents the final THM modelling which was resumed subsequent to the dismantling operation. The main part of this work has been numerical modelling of the field test. Three different modelling teams have presented several model cases for different geometries and different degree of process complexity. Two different numerical codes, Code{sub B}right and Abaqus, have been used. The modelling performed by UPC-Cimne using Code{sub B}right, has been divided in three subtasks: i) analysis of the response observed in the lower part of the test, by inclusion of a number of considerations: (a) the use of the Barcelona Expansive Model for MX-80 bentonite; (b) updated parameters in the vapour diffusive flow term; (c) the use of a non-conventional water retention curve for MX-80 at high temperature; ii) assessment of a possible relation between the cracks observed in the bentonite blocks in the upper part of TBT, and the cycles of suction and stresses registered in that zone at the start of the experiment; and iii) analysis of the performance, observations and interpretation of the entire test. It was however not possible to carry out a full THM analysis until the end of the test due to

  19. Temperature Buffer Test. Final THM modelling

    Energy Technology Data Exchange (ETDEWEB)

    Aakesson, Mattias; Malmberg, Daniel; Boergesson, Lennart; Hernelind, Jan [Clay Technology AB, Lund (Sweden); Ledesma, Alberto; Jacinto, Abel [UPC, Universitat Politecnica de Catalunya, Barcelona (Spain)

    2012-01-15

    The Temperature Buffer Test (TBT) is a joint project between SKB/ANDRA and supported by ENRESA (modelling) and DBE (instrumentation), which aims at improving the understanding and to model the thermo-hydro-mechanical behavior of buffers made of swelling clay submitted to high temperatures (over 100 deg C) during the water saturation process. The test has been carried out in a KBS-3 deposition hole at Aespoe HRL. It was installed during the spring of 2003. Two heaters (3 m long, 0.6 m diameter) and two buffer arrangements have been investigated: the lower heater was surrounded by bentonite only, whereas the upper heater was surrounded by a composite barrier, with a sand shield between the heater and the bentonite. The test was dismantled and sampled during the winter of 2009/2010. This report presents the final THM modelling which was resumed subsequent to the dismantling operation. The main part of this work has been numerical modelling of the field test. Three different modelling teams have presented several model cases for different geometries and different degree of process complexity. Two different numerical codes, Code{sub B}right and Abaqus, have been used. The modelling performed by UPC-Cimne using Code{sub B}right, has been divided in three subtasks: i) analysis of the response observed in the lower part of the test, by inclusion of a number of considerations: (a) the use of the Barcelona Expansive Model for MX-80 bentonite; (b) updated parameters in the vapour diffusive flow term; (c) the use of a non-conventional water retention curve for MX-80 at high temperature; ii) assessment of a possible relation between the cracks observed in the bentonite blocks in the upper part of TBT, and the cycles of suction and stresses registered in that zone at the start of the experiment; and iii) analysis of the performance, observations and interpretation of the entire test. It was however not possible to carry out a full THM analysis until the end of the test due to

  20. 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....... Two heating cycles allow us to differentiate the effects of thermal agitation and organic molecules. Single peak analysis and Rietveld refinement were combined to show significant differences resulting from the occluded biomolecules on the mineral phase in biogenic calcite in the mollusk shell....... This suggests that the interaction between biomolecules and calcite is not as tight in the coccoliths as in the shell. Although the shape of chalk has been preserved over millions of years, no major influence on the crystal lattice was observed in the chalk samples....

  1. Effects of L-Aspartic acid on the step retreat kinetics of calcite

    Science.gov (United States)

    Yoshino, Toru; Kagi, Hiroyuki

    2012-01-01

    Effects of L-Aspartic acid (L-Asp) on step retreat kinetics in the dissolution of calcite were investigated. The step retreat velocities under surface-controlled kinetics were determined from in-situ atomic force microscopic observations using an improved flow-through system. Comparison of the present results with those obtained under a mixed kinetics condition revealed that the addition of L-Asp promotes the transport process in the calcite dissolution through acid-base and/or complex forming reactions in the diffusion boundary layer. Additionally, promotion of the acute and obtuse step retreats by the L-Asp additive was observed under surface-controlled kinetics. This report is the first to clarify that L-Asp promotes surface processes in the dissolution of calcite.

  2. Moisture Buffer Value of Building Materials

    DEFF Research Database (Denmark)

    Rode, Carsten; Peuhkuri, Ruut; Time, Berit

    2007-01-01

    When building materials are in contact with indoor air they have some effect to moderate the variations of indoor humidity in occupied buildings. But so far there has been a lack of a standardized quantity to characterize the moisture buffering capability of materials. It has been the objective o...... is a test protocol which expresses how materials should be tested for determination of their Moisture Buffer Value. Finally, the paper presents some of the results of a Round Robin Test on various typical building materials that has been carried out in the project....

  3. Buffer of Events as a Markovian Process

    Energy Technology Data Exchange (ETDEWEB)

    Berdugo, J.; Casaus, J.; Mana, C.

    2001-07-01

    In Particle and Asro-Particle Physics experiments, the events which get trough the detectors are read and processes on-line before they are stored for a more detailed processing and future Physics analysis. Since the events are read and, usually, processed sequentially, the time involved in these operations can lead to a significant lose of events which is, to some extent, reduced by using buffers. We present an estimate of the optimum buffer size and the fraction of events lost for a simple experimental condition which serves as an introductory example to the use of Markow Chains.(Author)

  4. Coccolithophore responses to environmental variability in the South China Sea: species composition and calcite content

    Science.gov (United States)

    Jin, Xiaobo; Liu, Chuanlian; Poulton, Alex J.; Dai, Minhan; Guo, Xianghui

    2016-08-01

    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 influenced species composition and cellular levels of calcite content. Average coccolithophore abundance and their calcite concentration in the water column were 11.82 cells mL-1 and 1508.3 pg C mL-1, respectively, during the cruise. Water samples can be divided into three floral groups according to their distinct coccolithophore communities. The vertical structure of the coccolithophore community in the water column was controlled by the trophic conditions, which were regulated by mesoscale eddies across the SCS basin. The evaluation of coccolithophore-based calcite in the surface ocean also showed that three key species in the SCS (Emiliania huxleyi, Gephyrocapsa oceanica, Florisphaera profunda) and other larger, numerically rare species made almost equal contributions to total coccolith-based calcite in the water column. For Emiliania huxleyi biometry measurements, coccolith size positively correlated with nutrients (nitrate, phosphate), and it is suggested that coccolith length is influenced by light and nutrients through the regulation of growth rates. Larger-sized coccoliths were also linked statistically to low pH and calcite saturation states; however, it is not a simple cause and effect relationship, as carbonate chemistry was strongly co-correlated with the other key environmental factors (nutrients, light).

  5. Use of pH 9.5 Tris-HCl buffer containing 5% urea for antigen retrieval immunohistochemistry.

    Science.gov (United States)

    Shi, S R; Cote, R J; Young, L; Imam, S A; Taylor, C R

    1996-07-01

    Successful antigen retrieval (AR) immunohistochemistry is dependent on the temperature, heating time, and pH value of the AR solutions. There is no single standardized AR solution, however, that is suitable for all antibodies "routinely" used in surgical pathology for immunostaining archival tissue sections. We tested a variety of AR solutions varying in pH value, chemical composition, and molarity. Based upon preliminary results, we compared three AR solutions: 0.1 M Tris-HCl buffer, pH 9.5, containing 5% urea, 0.1 M Tris-HCl buffer pH 9.5 without urea, and citrate buffer, pH 6.0. Each AR solution was tested with a panel of 34 antibodies using microwave heating for antigen retrieval. The heating conditions were standardized at 10 min and an automated stainer was used to standardize the immunostaining method. The Tris-HCl containing urea was superior to pH 6.0 citrate buffer for 22 antibodies. In 12 cases, Tris-HCl with urea was also superior to Tris-HCl alone. In 12 cases, the intensity was similar for all three retrieval solutions. The staining obtained with Tris-HCl with urea was equal to or better than with pH 6.0 citrate buffer in all cases. The Tris-HCl with urea solution is satisfactory for AR of most antibodies employed in routine surgical pathology.

  6. EFFCTS OF pH AND Cl- CONCENTRATION ON THE CORROSION BEHAVIOR OF COPPER IN BORIC ACID BUFFER SOLUTION%硼酸缓冲溶液中pH值和Cl-浓度对Cu腐蚀行为的影响

    Institute of Scientific and Technical Information of China (English)

    王长罡; 董俊华; 柯伟; 陈楠

    2011-01-01

    The strategy for disposal of high-level radioactive waste in china is to enclose the spent nuclear fuel in sealed metal canisters which are embedded in bentonite clay hundreds meters deep in the bed-rock. The choice of container material depends largely on the redox conditions and the aqueous environment of the repository. One of the choices for the fabrication of waste canisters is copper, for it is thermodynamically stable under the saline, anoxic conditions over the large majority of the container lifetime. For this advantage, some other countries (Canada, Sweden) have selected copper as the material of nuclear waste container. However, in the early aerobic phase of the geological disposal the corrosion of copper could take place, and the corrosion behavior of copper would be influenced by the complex chemical conditions of groundwater markedly. Regularly, in atmosphere environment the semiconductor passive film which is constructed by Cu2O would generate on the surface of copper. On the one hand, the Cu2O film could protect copper from corrosion. On the other hand, the formation of Cu2O film is necessary to maintain the propagation of crack during the stress corrosion cracking. Therefore, the study of the effect of water chemistry conditions on the stability of Cu2O passive film makes great sense for the general corrosion and stress corrosion cracking of copper. For copper and copper alloy, Cl- is a highly aggressive ion. Lots of cases of failure and corrosion behavior of copper and copper alloy in Cl- environment have been studied. The immersion of Cl- would affect the semiconductor properties of Cu2O, therefore, we focused on the effect of pH and Cl- concentration on the corrosion behavior and semiconductor properties of Cu2O in this paper. The polarization behavior of Cu electrodes and the stability of passive film Cu2O in boric acid buffer solution have been investigated respectively by potentiodynamic polarization, electrochemical impedance spectroscopy

  7. 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...

  8. 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.

  9. Birefringence measurements in single crystal sapphire and calcite shocked along the a axis

    Science.gov (United States)

    Tear, Gareth R.; Chapman, David J.; Eakins, Daniel E.; Proud, William G.

    2017-01-01

    Calcite and sapphire were shock compressed along the direction (a axis) in a plate impact configuration. Polarimetery and Photonic Doppler Velocimetery (PDV) were used to measure the change in birefringence with particle velocity in the shock direction. Results for sapphire agree well with linear photoelastic theory and current literature showing a linear relationship between birefringence and particle velocity up to 310 m s-1. A maximum change in birefringence of 5% was observed. Calcite however showed anomolous behaviour with no detectable change in birefringence (less than 0.1%) over the range of particle velocities studied (up to 75 m s-1).

  10. Study on vibrational modes by group theory and infrared spectra by D FT for calcite crystal

    Institute of Scientific and Technical Information of China (English)

    Danhua Lou; Fengjiu Sun; Lijuan Li

    2007-01-01

    The factor group symmetry analysis (FSA) method and position symmetry analysis (PSA) method are used to analyze the vibrational modes of calcite (CaCO3) crystal, respectively. With the activated results of infrared and Raman spectra presented, strong points of each method are concluded. The infrared spectra are studied by using dynamics calculations based on density-functional theory (DFT) with the supercell model of calcite crystal. The frequencies of 27 normal modes are achieved, which are consistent with that by the group symmetry analysis very well, and fit with the experimental results better than the lattice dynamical methods.

  11. Galacturonomannan and Golgi-derived membrane linked to growth and shaping of biogenic calcite

    Science.gov (United States)

    Marsh, M. E.; Ridall, A. L.; Azadi, P.; Duke, P. J.

    2002-01-01

    The coccolithophores are valuable models for the design and synthesis of composite materials, because the cellular machinery controlling the nucleation, growth, and patterning of their calcitic scales (coccoliths) can be examined genetically. The coccoliths are formed within the Golgi complex and are the major CaCO(3) component in limestone sediments-particularly those of the Cretaceous period. In this study, we describe mutants lacking a sulfated galacturonomannan and show that this polysaccharide in conjunction with the Golgi-derived membrane is directly linked to the growth and shaping of coccolith calcite but not to the initial orientated nucleation of the mineral phase.

  12. Aqueous solution dispersement of carbon nanotubes

    Science.gov (United States)

    Kim, Jae-Woo (Inventor); Park, Cheol (Inventor); Choi, Sang H. (Inventor); Lillehei, Peter T. (Inventor); Harrison, Joycelyn S. (Inventor)

    2011-01-01

    Carbon nanotubes (CNTs) are dispersed in an aqueous buffer solution consisting of at least 50 weight percent water and a remainder weight percent that includes a buffer material. The buffer material has a molecular structure defined by a first end, a second end, and a middle disposed between the first and second ends. The first end is a cyclic ring with nitrogen and oxygen heteroatomes, the middle is a hydrophobic alkyl chain, and the second end is a charged group.

  13. Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates

    Directory of Open Access Journals (Sweden)

    K. Schmidt

    2013-09-01

    Full Text Available Correlation between particulate organic carbon (POC and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d−1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

  14. Acid-base buffer effect of fulvic acid and barium fulvate from weathered coal

    Energy Technology Data Exchange (ETDEWEB)

    Xiao-feng Guo; Xi-feng Li [Taiyuan University of Science and Technology, Taiyuan (China). Mining Engineering Institute

    2009-12-15

    The acid-base buffer characteristics of fulvic acid (FA) and barium fulvate (BaFA) were analyzed. Each share of the sample or model agents (phthalic acid and salicylic acid) were separately mixed into a series of shares of dilute solutions of HCl or NaOH with a series of concentration. The original pH values of the solutions were arranged from 2 to 13. Final balanced pH of each share was measured. The pH changes show that FA and BaFA possess buffer ability, whereas the model agents do not. The tendency of balanced pH values was 5.4 for FA and 7.4 for BaFA, whereas the original pH was 4.0-8.5; balanced pH changed little. At room temperature, the maximum buffer capacities were as follows: 18.11 mmol hydroxyl per gram FA, 11.25 mmol hydroxyl per gram BaFA, 1.19 mmol proton per gram FA, and 1.45 mmol proton per gram BaFA. Mathematics analysis shows that logarithm of buffer capacities of FA and BaFA is linearly dependent on original pH. Compared with BaFA and model agents, it is concluded that FA buffer capacity against hydroxyl relies not only on its acidic groups, BaFA buffer capacity against hydroxyl does not rely on its acidic groups, and FA buffer capacity against proton is not related with its carboxyl and phenolic hydroxyl group. The pH values of FA-water solutions with different concentrations from 1 to 10 grams per liter were measured. Their pH values were slightly affected by its concentration. Thus, FA possesses a much stronger buffer ability against water dilution than common buffer agent. All the pH values of FA water solutions were very nearly 5.4, just the same as the balanced pH tendency for adding FA. 10 refs., 5 figs., 2 tabs.

  15. Acid-base buffer effect of fulvic acid and barium fulvate from weathered coal

    Institute of Scientific and Technical Information of China (English)

    GUO Xiao-feng; LI Xi-feng

    2009-01-01

    The acid-base buffer characteristics of fulvic acid (FA) and barium fulvate (BaFA) were analyzed. Each share of the sample or model agents (phthalic acid and salicylic acid) were separately mixed into a series of shares of dilute solutions of HCI or NaOH with a series of concentration. The original pH values of the solutions were arranged from 2 to 13. Final balanced pH of each share was measured. The pH changes show that FA and BaFA possess buffer ability, whereas the model agents do not. The tendency of balanced pH values was 5.4 for FA and 7.4 for BaFA, whereas the original pH was 4.0-8.5; balanced pH changed little. At room temperature, the maximum buffer capacities were as follows:18.11 mmol hydroxyl per gram FA, 11.25 mmol hydroxyl per gram BaFA, 1.19 mmol proton per gram FA, and 1.45 mmol proton per gram BaFA. Mathematics analysis shows that logarithm of buffer capacities of FA and BaFA is linearly dependent on original pH. Compared with BaFA and model agents, it is concluded that FA buffer capacity against hydroxyl relies not only on its acidic groups, BaFA buffer capacity against hydroxyl does not rely on its acidic groups, and FA buffer capacity against proton is not related with its carboxyl and phenolic hydroxyl group. The pH values of FA-water solutions with different concentrations from 1 to 10 grams per liter were measured. Their pH values were slightly affected by its concentration. Thus, FA possesses a much stronger buffer ability against water dilution than common buffer agent. All the pH values of FA water solutions were very nearby 5.4,just the same as the balanced pH tendency for adding FA.

  16. Grass buffers for playas in agricultural landscapes: An annotated bibliography

    Science.gov (United States)

    Melcher, Cynthia P.; Skagen, Susan K.

    2005-01-01

    This bibliography and associated literature synthesis (Melcher and Skagen, 2005) was developed for the Playa Lakes Joint Venture (PLJV). The PLJV sought compilation and annotation of the literature on grass buffers for protecting playas from runoff containing sediments, nutrients, pesticides, and other contaminants. In addition, PLJV sought information regarding the extent to which buffers may attenuate the precipitation runoff needed to fill playas, and avian use of buffers. We emphasize grass buffers, but we also provide information on other buffer types.

  17. Improving phosphate buffer-free cathode performance of microbial fuel cell based on biological nitrification.

    Science.gov (United States)

    You, Shi-Jie; Ren, Nan-Qi; Zhao, Qing-Liang; Kiely, Patrick D; Wang, Jing-Yuan; Yang, Feng-Lin; Fu, Lei; Peng, Luo

    2009-08-15

    To reduce the amount of phosphate buffer currently used in Microbial Fuel Cell's (MFC's), we investigated the role of biological nitrification at the cathode in the absence of phosphate buffer. The addition of a nitrifying mixed consortia (NMC) to the cathode compartment and increasing ammonium concentration in the catholyte resulted in an increase of cell voltage from 0.3 V to 0.567 V (external resistance of 100 Omega) and a decrease of catholyte pH from 8.8 to 7.05. A large fraction of ammonium was oxidized to nitrite, as indicated by an increase of nitrate-nitrogen (NO(3)(-)-N). An MFC inoculated with an NMC and supplied with 94.2 mgN/l ammonium to the catholyte could generate a maximum power of 2.1+/-0.14 mW (10.94+/-0.73 W/m(3)). This compared favorably to an MFC supplied with either buffered or non-buffered solution. The buffer-free NMC inoculated cathodic chamber showed the smallest polarization resistance, suggesting that nitrification resulted in improved cathode performance. The improved performances of the phosphate buffer-free cathode and cell are positively related to biological nitrification, in which we suggest additional protons produced from ammonium oxidation facilitated electrochemical reduction of oxygen at cathode.

  18. Asparagine deamidation dependence on buffer type, pH, and temperature.

    Science.gov (United States)

    Pace, Amanda L; Wong, Rita L; Zhang, Yonghua Taylor; Kao, Yung-Hsiang; Wang, Y John

    2013-06-01

    The deamidation of asparagine into aspartate and isoaspartate moieties is a major pathway for the chemical degradation of monoclonal antibodies (mAbs). It can affect the shelf life of a therapeutic antibody that is not formulated or stored appropriately. A new approach to detect deamidation using ion exchange chromatography was developed that separates papain-digested mAbs into Fc and Fab fragments. From this, deamidation rates of each fragment can be calculated. To generate kinetic parameters useful in setting shelf life, buffers prepared at room temperature and then placed at the appropriate stability temperatures. Solution pH was not adjusted to the same at different temperatures. Deamidation rate at 40°C was faster in acidic buffers than in basic buffers. However, this trend is reversed at 5°C, attributed to the change in hydroxide ion concentration influenced by buffer and temperature. The apparent activation energy was higher for rates generated in an acidic buffer than in a basic buffer. The rate-pH profile for mAb1 can be deconvoluted to Fc and Fab. The Fc deamidation showed a V-shaped profile: deamidation of PENNY peptide is responsible for the rate at high-pH, whereas deamidation of a new site, Asn323, may be responsible for the rate at low-pH. The profile for Fab is a straight line without curvature.

  19. Comparative analyses of universal extraction buffers for assay of stress related biochemical and physiological parameters.

    Science.gov (United States)

    Han, Chunyu; Chan, Zhulong; Yang, Fan

    2015-01-01

    Comparative efficiency of three extraction solutions, including the universal sodium phosphate buffer (USPB), the Tris-HCl buffer (UTHB), and the specific buffers, were compared for assays of soluble protein, free proline, superoxide radical (O2∙-), hydrogen peroxide (H2O2), and the antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), and glutathione reductase (GR) in Populus deltoide. Significant differences for protein extraction were detected via sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2-DE). Between the two universal extraction buffers, the USPB showed higher efficiency for extraction of soluble protein, CAT, GR, O2∙-, GPX, SOD, and free proline, while the UTHB had higher efficiency for extraction of APX, POD, and H2O2. When compared with the specific buffers, the USPB showed higher extraction efficiency for measurement of soluble protein, CAT, GR, and O2∙-, parallel extraction efficiency for GPX, SOD, free proline, and H2O2, and lower extraction efficiency for APX and POD, whereas the UTHB had higher extraction efficiency for measurement of POD and H2O2. Further comparisons proved that 100 mM USPB buffer showed the highest extraction efficiencies. These results indicated that USPB would be suitable and efficient for extraction of soluble protein, CAT, GR, GPX, SOD, H2O2, O2∙-, and free proline.

  20. Analysis and Study of Buffer Overflow

    Institute of Scientific and Technical Information of China (English)

    Liu Sidong; Zen TaoYu; Yongquan

    2009-01-01

    Buffer overflow attack is one of the most threatening attack types and it jeopardizes security a lot. According to the principle of the attack, this paper demonstrates how it works, and emphasizes the importance of writing code that does not permit such attacks.

  1. Buffer layers on biaxially textured metal substrates

    Science.gov (United States)

    Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

    2001-01-01

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  2. Biochar contribution to soil pH buffer capacity

    Science.gov (United States)

    Tonutare, Tonu; Krebstein, Kadri; Utso, Maarius; Rodima, Ako; Kolli, Raimo; Shanskiy, Merrit

    2014-05-01

    Biochar as ecologically clean and stable form of carbon has complex of physical and chemical properties which make it a potentially powerful soil amendment (Mutezo, 2013). Therefore during the last decade the biochar application as soil amendment has been a matter for a great number of investigations. For the ecological viewpoint the trend of decreasing of soil organic matter in European agricultural land is a major problem. Society is faced with the task to find possibilities to stabilize or increase soil organic matter content in soil and quality. The availability of different functional groups (e.g. carboxylic, phenolic, acidic, alcoholic, amine, amide) allows soil organic matter to buffer over a wide range of soil pH values (Krull et al. 2004). Therefore the loss of soil organic matter also reduces cation exchange capacity resulting in lower nutrient retention (Kimetu et al. 2008). Biochar can retain elements in soil directly through the negative charge that develops on its surfaces, and this negative charge can buffer acidity in the soil. There are lack of investigations about the effect of biochar to soil pH buffering properties, The aim of our investigation was to investigate the changes in soil pH buffer capacity in a result of addition of carbonizated material to temperate region soils. In the experiment different kind of softwood biochars, activated carbon and different soil types with various organic matter and pH were used. The study soils were Albeluvisols, Leptosols, Cambisols, Regosols and Histosols . In the experiment the series of the soil: biochar mixtures with the biochar content 0 to 100% were used. The times of equiliberation between solid and liquid phase were from 1 to 168 hours. The suspension of soil: biochar mixtures was titrated with HCl solution. The titration curves were established and pH buffer capacities were calculated for the pH interval from 3.0 to 10.0. The results demonstrate the dependence of pH buffer capacity from soil type

  3. Influence of HEPES buffer on the local pH and formation of surface layer during in vitro degradation tests of magnesium in DMEM

    OpenAIRE

    Naddaf Dezfuli, S.; Zhigang Huan; Mol, J.M.C.; Leeflang, M. A.; Jiang Chang; Jie Zhou

    2014-01-01

    The human body is a buffered environment where pH is effectively maintained. HEPES is a biological buffer often used to mimic the buffering activity of the body in in vitro studies on the degradation behavior of magnesium. However, the influence of HEPES on the degradation behavior of magnesium in the DMEM pseudo-physiological solution has not yet been determined. The research aimed at elucidating the degradation mechanisms of magnesium in DMEM with and without HEPES. The morphologies and com...

  4. 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

    The Campanian-Maastrichtian limestones in the south of the Netherlands are well-sorted fine-grained mudstones and silt- to fine sand-sized bioclastic grainstones. These limestones show a distinct lithological cyclicity manifested by fining-upward grain-size cycles with calcite-cemented layers...... and differences in the degree of early diagenesis. Cemented layers and hardgrounds are the result of differential early marine calcite cementation. In these limestones early calcite cementation cannot be explained by the supply of cementing materials from saturated seawater, An alternative model for early marine...... 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...

  5. Origin of zoning within dedolomite and calcitized gypsum of the Mississippian Arroyo Penasco Group

    Energy Technology Data Exchange (ETDEWEB)

    Ulmer, D.S.

    1985-01-01

    The Mississippian Arroyo Penasco Group carbonates are the oldest Paleozoic rocks present in north-central New Mexico. These supratidal to shallow,subtidal sediments exhibit complex diagenetic fabrics produced by periods of pre-Pennsylvanian subaerial exposure. Both extensive recrystallization of the Espiritu Santo carbonates and brecciation of the overlying Macho Member of the Tererro Formation resulted from an extended period of Mississippian subaerial exposure of broad, low-relief tidal flats. Cathodoluminescent petrography indicates that the recrystallized limestones consist of calcite pseudomorphs of dolomite and gypsum. Dedolomite and calcitized gypsum crystals, with /sup 13/C//sup 12/C ratios of -2 to +1.5% PDB, range from highly zoned to uniformly luminescent. Electron microprobe analyses reveals variable Mn and Fe contents across the pseudomorphs which are responsible for differences in observed luminosity. These features are interpreted to reflect a period of subaerial exposure after deposition of Macho Member sediments, which caused dissolution of gypsum and dolomite by sulfate and Mg depleted meteoric fluids and produced the collapse breccia. Preservation of zoning within some pseudomorphs required simultaneous dissolution of gypsum and dolomite and precipitation of calcite. C-isotope data indicates a meteoric to mixed phreatic origin for pore fluids which precipitated calcite; repetitive zoning within dolomite and gypsum pseudomorphs is indicative of interactions between marine and meteoric phreatic fluids in the intertidal environment.

  6. Adsorption and migration of single metal atoms on the calcite (10.4) surface

    Science.gov (United States)

    Pinto, H.; Haapasilta, V.; Lokhandwala, M.; Öberg, S.; Foster, Adam S.

    2017-04-01

    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface.

  7. 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...

  8. Assembly Synthesis of Sheet-like Calcite Array and Stable-Vaterite by Supported Liquid Membrane

    Institute of Scientific and Technical Information of China (English)

    SUN,Dong-Mei(孙冬梅); WU,Qing-Sheng(吴庆生)

    2004-01-01

    Sheet-like calcite array and stable vaterite were synthesized by bio-mimetic supported liquid membrane system under different reaction conditions. Both of the FTIR spectra of products showed narrower peak at 1418 cm-1 than that of bulk CaCO3, and that of vaterite has a split in this peak.

  9. 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.

  10. Higher Order Elastic Constants, Gruneisen Parameters and Lattice Thermal Expansion of Trigonal Calcite

    Directory of Open Access Journals (Sweden)

    Thresiamma Phlip

    2005-01-01

    Full Text Available The second- and third-order elastic constants of trigonal calcite have been obtained using the deformation theory. The strain energy density derived using the deformation theory is compared with the strain dependent lattice energy obtained from the elastic continuum model approximation to get the expressions for the second- and third-order elastic constants. Higher order elastic constants are a measure of the anharmonicity of a crystal lattice. The seven second-order elastic constants and the fourteen non-vanishing third-order elastic constants of trigonal calcite are obtained. The second-order elastic constants C11, which corresponds to the elastic stiffness along the basal plane of the crystal is greater than C33, which corresponds to the elastic stiffness tensor component along the c-axis of the crystal. First order pressure derivatives of the second-order elastic constants of calcite are evaluated. The higher order elastic constants are used to find the generalized Gruneisen parameters of the elastic waves propagating in different directions in calcite. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with available reported values.

  11. 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 ha...

  12. 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 ha...

  13. Sorption of trace metals on calcite: Applicability of the surface precipitation model

    NARCIS (Netherlands)

    Comans, R.N.J.; Middelburg, J.J.

    1987-01-01

    Published Sorption isotherm data of Cd2+, Mn2+, Zn2+, and Co2+ on calcite are adequately described by the surface precipitation model which was originally developed by FArley et al. (1985) for the sorption of cations on metal oxides. In addition to monolayer adsorption, the model accounts for the fo

  14. 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.

  15. Elasticity and yielding of a calcite paste: scaling laws in a dense colloidal suspension.

    Science.gov (United States)

    Liberto, Teresa; Le Merrer, Marie; Barentin, Catherine; Bellotto, Maurizio; Colombani, Jean

    2017-03-08

    We address the mechanical characterization of a calcite paste as a model system to investigate the relation between the microstructure and macroscopic behavior of colloidal suspensions. The ultimate goal is to achieve control of the elastic and yielding properties of calcite which will prove valuable in several domains, from paper coating to paint manufacture and eventually in the comprehension and control of the mechanical properties of carbonate rocks. Rheological measurements have been performed on calcite suspensions over a wide range of particle concentrations. The calcite paste exhibits a typical colloidal gel behavior, with an elastic regime and a clear yield strain above which it enters a plastic regime. The yield strain shows a minimum when increasing the solid concentration, connected to a change in the power law scaling of the storage modulus. In the framework of the classical fractal elasticity model for colloidal suspensions proposed by Shih et al. [Phys. Rev. A, 1990, 42, 4772], we interpret this behavior as a switch with the concentration from the strong-link regime to the weak-link regime, which had never been observed so far in one well-defined system without external or chemical forcing.

  16. Modelling how incorporation of divalent cations affects calcite wettability–implications for biomineralisation and oil recovery

    Science.gov (United States)

    Andersson, M. P.; Dideriksen, K.; Sakuma, H.; Stipp, S. L. S.

    2016-06-01

    Using density functional theory and geochemical speciation modelling, we predicted how solid-fluid interfacial energy is changed, when divalent cations substitute into a calcite surface. The effect on wettability can be dramatic. Trace metal uptake can impact organic compound adsorption, with effects for example, on the ability of organisms to control crystal growth and our ability to predict the wettability of pore surfaces. Wettability influences how easily an organic phase can be removed from a surface, either organic compounds from contaminated soil or crude oil from a reservoir. In our simulations, transition metals substituted exothermically into calcite and more favourably into sites at the surface than in the bulk, meaning that surface properties are more strongly affected than results from bulk experiments imply. As a result of divalent cation substitution, calcite-fluid interfacial energy is significantly altered, enough to change macroscopic contact angle by tens of degrees. Substitution of Sr, Ba and Pb makes surfaces more hydrophobic. With substitution of Mg and the transition metals, calcite becomes more hydrophilic, weakening organic compound adsorption. For biomineralisation, this provides a switch for turning on and off the activity of organic crystal growth inhibitors, thereby controlling the shape of the associated mineral phase.

  17. Microstratigraphic logging of calcite fabrics in speleothems as tool for palaeoclimate studies

    Directory of Open Access Journals (Sweden)

    Silvia Frisia

    2015-01-01

    Full Text Available The systematic documentation of calcite fabrics in stalagmites and flowstones provides robustness to palaeoclimate interpretation based on geochemical proxies, but it has been neglected because it is difficult to transform crystal morphologies into numerical values, and construct fabric time series. Here, general criteria that allow for coding fabrics of calcite composing stalagmites and flowstones is provided. Being based on known models of fabric development, the coding ascribes sequential numbers to each fabric, which reflect climate-related parameters, such as changes in drip rate variability, bio-mediation or diagenetic modifications. Acronyms are proposed for Columnar types, Dendritic, Micrite, Microsparite and Mosaic fabrics, whose use could then render possible comparison of calcite fabrics in stalagmites and flowstones from diverse latitudinal and altitudinal settings. The climatic and environmental significance of similarities in the geochemical signals and trends analysed in coeval stalagmites and flowstones (or differences in the signals and trends will be more robust when compared with fabric time series. This is particularly true where, such as in the Holocene, changes in geochemical values may be subtle, yet fabrics may show changes related to variations in supersaturation, drip rate or input of detrital particles or organic compounds. The proposed microstratigraphic logging allows recognition of changes in stable isotope ratio or trace element values that can be ascribed to hydrology and diagenesis, with considerable improvement of reconstructions based on the chemical proxies of stalagmites and flowstones composed of calcite.

  18. Morphological and mechanical characterization of composite calcite/SWCNT-COOH single crystals.

    Science.gov (United States)

    Calvaresi, Matteo; Falini, Giuseppe; Pasquini, Luca; Reggi, Michela; Fermani, Simona; Gazzadi, Gian Carlo; Frabboni, Stefano; Zerbetto, Francesco

    2013-08-01

    A growing number of classes of organic (macro)molecular materials have been trapped into inorganic crystalline hosts, such as calcite single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite calcite/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite calcite/SWCNT-COOH single crystals was similar to that of pure calcite their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites.

  19. 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) 26 Mg ACC-Mg2+ = + 2.0 ‰) are consistent with the formation of a hydrated Ca nanoporous solid accommodating Mg bicarbonate/carbonate species in combination with hydrated magnesium. This material crossed by percolating channels filled with the

  20. 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

  1. Effect of glycine on pH changes and protein stability during freeze-thawing in phosphate buffer systems.

    Science.gov (United States)

    Pikal-Cleland, Katherine A; Cleland, Jeffrey L; Anchordoquy, Thomas J; Carpenter, John F

    2002-09-01

    Previous studies have established that the selective precipitation of a less soluble buffer component during freezing can induce a significant pH shift in the freeze concentrate. During freezing of sodium phosphate solutions, crystallization of the disodium salt can produce a pH decrease as great as 3 pH units which can dramatically affect protein stability. The objective of our study was to determine how the presence of glycine (0-500 mM), a commonly used bulking agent in pharmaceutical protein formulations, affects the pH changes normally observed during freezing in sodium phosphate buffer solutions and to determine whether these pH changes contribute to instability of model proteins in glycine/phosphate formulations. During freezing in sodium phosphate buffers, the presence of glycine significantly influenced the pH. Glycine at the lower concentrations (phosphate buffer, possibly by reducing the nucleation rate of salt and thereby decreasing the extent of buffer salt crystallization. The presence of glycine at higher concentration (> 100 mM) in the sodium phosphate buffer resulted in a more complete crystallization of the disodium salt as indicated by the frozen pH values closer to the equilibrium value (pH 3.6). Although high concentrations of glycine can facilitate more buffer salt crystallization and these pH shifts may prove to be potentially damaging to the protein, glycine, in its amorphous state, can also act to stabilize a protein via the preferential exclusion mechanism.

  2. Buffer layers on rolled nickel or copper as superconductor substrates

    Science.gov (United States)

    Paranthaman, Mariappan; Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /CeO.sub.2 /Ni, RE.sub.2 O.sub.3 /Ni (RE=Rare Earth), and Yb.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /CeO.sub.2 /Cu, RE.sub.2 O.sub.3 /Cu, and Yb.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approach, which includes chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

  3. HEAVY TRAFFIC LIMIT THEOREMS IN FLUID BUFFER MODELS

    Institute of Scientific and Technical Information of China (English)

    YIN Gang; ZHANG Hanqin

    2004-01-01

    A fluid buffer model with Markov modulated input-output rates is considered.When traffic intensity is near its critical value, the system is known as in heavy traffic.It is shown that a suitably scaled sequence of the equilibrium buffer contents has a weakor distributional limit under heavy traffic conditionsThis weak limit is a functional of adiffusion process determined by the Markov chain modulating the input and output rates.The first passage time of the reflected process is examinedIt is shown that the mean firstpassage time can be obtained via a solution of a Dirichlet problemThen the transitiondensity of the reflected process is derived by solving the Kolmogorov forward equation witha Neumann boundary conditionFurthermore, when the fast changing part of the generatorof the Markov chain is a constant matrix, the representation of the probability distributionof the reflected process is derivedUpper and lower bounds of the probability distributionare also obtained by means of asymptotic expansions of standard normal distribution.

  4. Diagenetic Mg-calcite overgrowths on foraminiferal tests in the vicinity of methane seeps

    Science.gov (United States)

    Panieri, Giuliana; Lepland, Aivo; Whitehouse, Martin J.; Wirth, Richard; Raanes, Morten P.; James, Rachael H.; Graves, Carolyn A.; Crémière, Antoine; Schneider, Andrea

    2017-01-01

    Methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera. Here, we present structural, geochemical, and stable carbon isotope data from single foraminiferal calcite tests and authigenic Mg-calcite overgrowths in a sediment core recovered from an area of active methane seepage in western Svalbard at ca. 340 m water depth. The foraminifera are from intervals in the core where conventional bulk foraminiferal δ13 C values are as low as -11.3 ‰. Mg/Ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain Mg-rich interlayers with Mg/Ca up to 220 mmol/mol. Transmission electron microscopy (TEM) of the contact point between the biogenic calcite and authigenic Mg-calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation. Secondary ion mass spectrometry (SIMS) analyses reveal that the Mg-rich layers are strongly depleted in 13C (δ13 C as low as -34.1 ‰). These very low δ13 C values indicate that the authigenic Mg-calcite precipitated from pore waters containing methane-derived dissolved inorganic carbon at the depth of the sulfate-methane transition zone (SMTZ). As the depth of the SMTZ can be located several meters below the sediment-seawater interface, interpretation of low foraminiferal δ13 C values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care.

  5. A buffer insertion and simultaneous sizing timing optimization algorithm

    Institute of Scientific and Technical Information of China (English)

    Yin Guoli; Lin Zhenghui

    2006-01-01

    A path-based timing optimization algorithm for buffer insertion and simultaneous sizing is proposed.Firstly, candidate buffer insertion location and buffer size for each branch in a given routing path were obtained via localized timing optimization. Then, through evaluating each potential insertion against design objectives, potential optimal buffer insertion locations and sizes for the whole routing tree were determined. At last, by removing redundant buffer insertion operations which do not maximize S ( so ), given timing requirements are finally fulfilled through minimum number of buffers.

  6. Time-resolved SAXS measurements facilitated by online HPLC buffer exchange

    DEFF Research Database (Denmark)

    Jensen, Malene Hillerup; Toft, Katrine Nørgaard; David, Gabriel

    2010-01-01

    be possible to separate contributions from individual species present in solution. Hence, time-resolved SAXS (TR-SAXS) data of processes in development can be analyzed. Many reported TR-SAXS results are initialized by a sudden change in buffer conditions facilitated by rapid mixing combined with either...... continuous or stopped flow. In this paper a method for obtaining TR-SAXS data from systems where the reaction is triggered by removal of a species is presented. This method is based on fast buffer exchange over a short desalting column facilitated by an online HPLC (high-performance liquid chromatography...

  7. MOISTURE-BUFFERING CHARACTERISTICS OF BUILDING MATERIALS

    Directory of Open Access Journals (Sweden)

    Young Cheol Choi

    2016-05-01

    Full Text Available The humidity level of indoor air is an important factor influencing the air quality and energy consumption of buildings, as well as the durability of building components. Indoor humidity levels depend on several factors, such as moisture sources, air flow, and the adsorption/desorption properties of materials. The moisture-buffering characteristics of building materials that are in contact with indoor air may help moderate the variations of indoor humidity, especially in the summer and winter. In this study, the moisture adsorption/desorption properties of building materials were investigated experimentally and numerically. These properties can be used to characterize the ability of building materials to exchange moisture with the indoor environment. This study indicates that a building material surface resistivity was the main factor creating variations of moisture buffering.

  8. Microbial activity in bentonite buffers. Literature study

    Energy Technology Data Exchange (ETDEWEB)

    Ratto, M.; Itavaara, M.

    2012-07-01

    The proposed disposal concept for high-level radioactive wastes involves storing the wastes underground in copper-iron containers embedded in buffer material of compacted bentonite. Hydrogen sulphide production by sulphate-reducing prokaryotes is a potential mechanism that could cause corrosion of waste containers in repository conditions. The prevailing conditions in compacted bentonite buffer will be harsh. The swelling pressure is 7-8 MPa, the amount of free water is low and the average pore and pore throat diameters are small. This literature study aims to assess the potential of microbial activity in bentonite buffers. Literature on the environmental limits of microbial life in extreme conditions and the occurrence of sulphatereducing prokaryotes in extreme environments is reviewed briefly and the results of published studies characterizing microbes and microbial processes in repository conditions or in relevant subsurface environments are presented. The presence of bacteria, including SRBs, has been confirmed in deep groundwater and bentonite-based materials. Sulphate reducers have been detected in various high-pressure environments, and sulphate-reduction based on hydrogen as an energy source is considered a major microbial process in deep subsurface environments. In bentonite, microbial activity is strongly suppressed, mainly due to the low amount of free water and small pores, which limit the transport of microbes and nutrients. Spore-forming bacteria have been shown to survive in compacted bentonite as dormant spores, and they are able to resume a metabolically active state after decompaction. Thus, microbial sulphide production may increase in repository conditions if the dry density of the bentonite buffer is locally reduced. (orig.)

  9. Isostatic compression of buffer blocks. Middle scale

    Energy Technology Data Exchange (ETDEWEB)

    Ritola, J.; Pyy, E. [VTT Technical Research Centre of Finland, Espoo (Finland)

    2012-01-15

    Manufacturing of buffer components using isostatic compression method has been studied in small scale in 2008 (Laaksonen 2010). These tests included manufacturing of buffer blocks using different bentonite materials and different compression pressures. Isostatic mould technology was also tested, along with different methods to fill the mould, such as vibration and partial vacuum, as well as a stepwise compression of the blocks. The development of manufacturing techniques has continued with small-scale (30 %) blocks (diameter 600 mm) in 2009. This was done in a separate project: Isostatic compression, manufacturing and testing of small scale (D = 600 mm) buffer blocks. The research on the isostatic compression method continued in 2010 in a project aimed to test and examine the isostatic manufacturing process of buffer blocks at 70 % scale (block diameter 1200 to 1300 mm), and the aim was to continue in 2011 with full-scale blocks (diameter 1700 mm). A total of nine bentonite blocks were manufactured at 70 % scale, of which four were ring-shaped and the rest were cylindrical. It is currently not possible to manufacture full-scale blocks, because there is no sufficiently large isostatic press available. However, such a compression unit is expected to be possible to use in the near future. The test results of bentonite blocks, produced with an isostatic pressing method at different presses and at different sizes, suggest that the technical characteristics, for example bulk density and strength values, are somewhat independent of the size of the block, and that the blocks have fairly homogenous characteristics. Water content and compression pressure are the two most important properties determining the characteristics of the compressed blocks. By adjusting these two properties it is fairly easy to produce blocks at a desired density. The commonly used compression pressure in the manufacturing of bentonite blocks is 100 MPa, which compresses bentonite to approximately

  10. Wintering bird response to fall mowing of herbaceous buffers

    Science.gov (United States)

    Blank, P.J.; Parks, J.R.; Dively, G.P.

    2011-01-01

    Herbaceous buffers are strips of herbaceous vegetation planted between working agricultural land and streams or wetlands. Mowing is a common maintenance practice to control woody plants and noxious weeds in herbaceous buffers. Buffers enrolled in Maryland's Conservation Reserve Enhancement Program (CREP) cannot be mowed during the primary bird nesting season between 15 April and 15 August. Most mowing of buffers in Maryland occurs in late summer or fall, leaving the vegetation short until the following spring. We studied the response of wintering birds to fall mowing of buffers. We mowed one section to 10-15 cm in 13 buffers and kept another section unmowed. Ninety-two percent of birds detected in buffers were grassland or scrub-shrub species, and 98% of all birds detected were in unmowed buffers. Total bird abundance, species richness, and total avian conservation value were significantly greater in unmowed buffers, and Savannah Sparrows (Passerculus sandwichensis), Song Sparrows (Melospiza melodia), and White-throated Sparrows (Zonotrichia albicollis) were significantly more abundant in unmowed buffers. Wintering bird use of mowed buffers was less than in unmowed buffers. Leaving herbaceous buffers unmowed through winter will likely provide better habitat for wintering birds. ?? 2011 by the Wilson Ornithological Society.

  11. Queueing analysis of some buffered random multiple access schemes

    Science.gov (United States)

    Sykas, E. D.; Karvelas, D. E.; Protonotarios, E. N.

    1986-08-01

    A queueing model appropriate for the analysis of multiple-access schemes with finite user buffer capacity is proposed. This model can be applied to several slotted random multiple-access schemes, such as the URN, ALOHA, random TDMA channels, etc. The examined system, in general, can be modeled as a multidimensional Markov chain. The enormous state space for its complete description makes numerical analysis intractable. Nevertheless, symmetry properties of the system can be exploited so that the state will be reduced. In particular, the queue length at one station and the number of busy stations are used to characterize the behavior of the system. In this way, a two-dimensional Markov chain can be constructed and an approximate solution is obtained which is in excellent agreement with simulation results.

  12. Evolution of a physiological pH 6.8 bicarbonate buffer system: application to the dissolution testing of enteric coated products.

    OpenAIRE

    Liu, Fang; Merchant, Hamid A.; Kulkarni, Rucha P.; Alkademi, Maram; Basit, Abdul W

    2011-01-01

    The use of compendial pH 6.8 phosphate buffer to assess dissolution of enteric coated products gives rise to poor in vitro-in vivo correlations because of the inadequacy of the buffer to resemble small intestinal fluids. A more representative and physiological medium, pH 6.8 bicarbonate buffer, was developed to evaluate the dissolution behaviour of enteric coatings. The bicarbonate system was evolved from pH7.4 Hanks balanced salt solution to produce a pH 6.8 bicarbonate buffer (modified Hank...

  13. Throughput maximization for buffer-aided hybrid half-/full-duplex relaying with self-interference

    KAUST Repository

    Khafagy, Mohammad Galal

    2015-06-01

    In this work, we consider a two-hop cooperative setting where a source communicates with a destination through an intermediate relay node with a buffer. Unlike the existing body of work on buffer-aided half-duplex relaying, we consider a hybrid half-/full-duplex relaying scenario with loopback interference in the full-duplex mode. Depending on the channel outage and buffer states that are assumed available at the transmitters, the source and relay may either transmit simultaneously or revert to orthogonal transmission. Specifically, a joint source/relay scheduling and relaying mode selection mechanism is proposed to maximize the end-to-end throughput. The throughput maximization problem is converted to a linear program where the exact global optimal solution is efficiently obtained via standard convex/linear numerical optimization tools. Finally, the theoretical findings are corroborated with event-based simulations to provide the necessary performance validation.

  14. Explicit filtering for large eddy simulation as use of a spectral buffer

    CERN Document Server

    Mathew, Joseph

    2016-01-01

    The explicit filtering method for large eddy simulation (LES,) which comprises integration of the governing equations without any added terms for sub-grid-scale modeling and the application of a low-pass filter to transported fields, is discussed. The shapes of filter response functions of numerical schemes for spatial derivatives and the explicit filter, that have been used for several LES, are examined. Generally, these are flat (no filtering) over a range of low wavenumbers, and then fall off over a small range of the highest represented wavenumbers. It is argued that this high wavenumber part can be viewed as a spectral buffer analogous to physical buffer (or sponge) zones used near outflow boundaries. The monotonic convergence of this approach to a direct numerical simulation, and the shifting of the spectral buffer to larger wavenumbers as the represented spectral range is increased, without altering the low wavenumber part of solutions, is demonstrated with LES of two sample flows. Connections to other...

  15. Influence of Alkylammonium Acetate Buffers on Protein-Ligand Noncovalent Interactions Using Native Mass Spectrometry

    Science.gov (United States)

    Zhuang, Xiaoyu; Gavriilidou, Agni F. M.; Zenobi, Renato

    2017-02-01

    We investigate the influence of three volatile alkylammonium acetate buffers on binding affinities for protein-ligand interactions determined by native electrospray ionization-mass spectrometry (ESI-MS). Four different types of proteins were chosen for this study. A charge-reduction effect was observed for all the cases studied, in comparison to the ions formed in ammonium acetate solution. When increasing the collision energy, the complexes of trypsin and the ligand were found to be more stable when sprayed from alkylammonium acetate buffers than from ammonium acetate. The determined dissociation constant (Kd) also exhibited a drop (up to 40%) when ammonium acetate was replaced by alkylammonium acetate buffers for the case of lysozyme and the ligand. The prospective uses of these ammonium acetate analogs in native ESI-MS are discussed in this paper as well.

  16. Impact of Physical Stress on Salivary Buffering Capacity

    OpenAIRE

    Yu Nakashima; Emi Nagata; Takahiko Oho

    2016-01-01

    Background: Saliva has many properties and the buffering capacity is important for the neutralization of oral fluids. It is unclear whether stressful conditions directly affect salivary buffering capacity, and we investigated the impact of physical stress on salivary buffering capacity. Methods: Twelve participants were subjected to the physical stress of jogging and running. The salivary buffering capacity and flow rate of the participants were measured before and after exposure to stressful...

  17. 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

  18. A preliminary study of the calcite beef found in the Cretaceous Jinju Formation, Gyeongsang Basin, South Korea

    Science.gov (United States)

    Ha, S.; Chae, Y. U.; Son, M.; Jeong, G. Y.; Paik, I. S.; Lim, H. S.

    2015-12-01

    The term "beef" refers to fibrous minerals in bedding-parallel veins, where the fibers are approximately perpendicular to the vein margins (Cobbold et al., 2013). It mostly appears within organic-rich black shale layers in sedimentary basin. Although the veins can consist of white gangue minerals, such as calcite, gypsum, or quartz, the commonest mineral in the fibers is calcite. According to the worldwide localities of calcite beef compiled by Cobbold et al (2012), they concentrated in some areas, especially around the Atlantic Ocean. However, they have been rarely reported in the western Pacific margin, except Australia and New Zealand. Recently, calcite beefs have been found in the Cretaceous Jinju Formation, Gyeongsang Basin, Korea. As far as we know, this is the first report of calcite beef in Korea. The lacustrine Jinju Formation is about 1,200 m thick, and made up mainly of lacustrine dark grey to black mudstones. In the study area, calcite beefs were commonly found in the organic-rich black shale layers. The vein thickness is anywhere between a few millimeters to maximum 3 centimeters, and their length ranges from a few centimeters to several tens of meters. The interval between successive veins is from a few centimeters to about 1 meter. Most of them occur parallel to the bedding planes, although some of them are developed along fault planes or within deformed layers. In case of relatively thick beefs, the center of veins often shows a dark grey to black central median line, defined by fine-grained calcite grains, fluid inclusion lines, or wall rock particles. Based on the orientation of fibrous calcite, they can be divided into two types: straight and sigmoidal types. The fibrous calcites are thought to have been symmetrically grown from the median lines to top and bottom of wall rock. The formation mechanism of horizontal fractures, and the formation temperature of beefs in the study area remain as a matter to be studied further.

  19. U-Th dating of calcite corals from the Gulf of Aqaba

    Science.gov (United States)

    Yehudai, Maayan; Lazar, Boaz; Bar, Neta; Kiro, Yael; Agnon, Amotz; Shaked, Yonathan; Stein, Mordechai

    2017-02-01

    Most of the fossil corals in the elevated reef terraces along the Gulf of Aqaba (GOA) were extensively altered to calcite. This observation indicates extensive interaction with freshwater, possibly when the terraces passed through a coastal aquifer that existed along the shores of the GOA, implying a wetter climate during the time of recrystallization from aragonite to calcite. Thus, dating of the recrystallization events should yield the timing of past wetter conditions in the current hyper-arid area of the GOA. In the present study, 18 aragonite and calcite corals were collected from several elevated coral reef terraces off the coast, south of the city of Aqaba. While aragonite corals were dated with the conventional closed system age equation (assuming zero initial Th), the dating of the calcite corals required the development of adequate equations to allow the calculation of both the initial formation age of the aragonite corals and the time of recrystallization to calcite. The two age calculations were based on the assumptions that each reef terrace went through a single and rapid recrystallization event and that the pristine aragonite corals were characterized by a rather uniform initial U concentration, typical for pristine modern corals. Two recrystallization events were identified at 104 ± 6 ka and 124 ± 8 ka. The ages coincide with the timing of sapropel events S4 and S5, respectively, when the African monsoon induced enhanced wetness in the desert area. Considering the age uncertainties, the times of formation of the two major reef terraces are estimated to be ∼124 ka (reef terrace R2) and ∼130 ka (reef terrace R3), matching the peaks in the global sea level during the last interglacial MIS 5e stage. Apparently, sea level of the GOA did not fluctuate a lot during the period between ∼130 ka and ∼104 ka and remained close to the Marine Isotopic stage (MIS) 5e highstand. The availability of freshwater (during the sapropel periods) and limited sea

  20. Environmental controls for the precipitation of different fibrous calcite cement fabrics

    Science.gov (United States)

    Ritter, Ann-Christine; Wiethoff, Felix; Neuser, Rolf D.; Richter, Detlev K.; Immenhauser, Adrian

    2016-04-01

    Abiogenic calcite cements are widely used as climate archives. They can yield information on environmental change and climate dynamics at the time when the sediment was lithified in a (marine) diagenetic environment. Radiaxial-fibrous (RFC) and fascicular-optic fibrous (FOFC) calcite cements are two very common and similar pore-filling cement fabrics in Palaeozoic and Mesozoic carbonate rocks (Richter et al., 2011) and in Holocene Mg-calcitic speleothems (Richter et al., 2015). Both fabrics are characterised by distinct crystallographic properties. Current research has shown that these fabrics are often underexplored and that a careful combination of conservative and innovative proxies allows for a better applicability of these carbonate archives to paleoenvironmental reconstructions (Ritter et al., 2015). A main uncertainty in this context is that it is still poorly understood which parameters lead to the formation of either RFC or FOFC and if differential crystallographic parameters affect proxy data from these fabrics. This study aims at a better understanding of the environmental factors that may control either RFC or FOFC precipitation. Therefore, suitable samples (a stalagmite and a Triassic marine cement succession), each with clearly differentiable layers of RFC and FOFC, were identified and analysed in high detail using a multi-proxy approach. Detailed thin section and cathodoluminescence analysis of the samples allowed for a precise identification of layers consisting solely of either RFC or FOFC. Isotopic (δ13C, δ18O) as well as trace elemental compositions have been determined and the comparison of data obtained from these different carbonate archives sheds light on changes in environmental parameters during RFC or FOFC precipitation. References: Richter, D.K., et al., 2011. Radiaxial-fibrous calcites: A new look at an old problem. Sedimentary Geology, 239, 26-36 Richter, D.K., et al., 2015. Radiaxial-fibrous and fascicular-optic Mg-calcitic cave

  1. Cathode buffer composed of fullerene-ethylenediamine adduct for an organic solar cell

    Science.gov (United States)

    Kimoto, Yoshinori; Akiyama, Tsuyoshi; Fujita, Katsuhiko

    2017-02-01

    We developed a fullerene-ethylenediamine adduct (C60P-DC) for a cathode buffer material in organic bulk heterojunction solar cells, which enhance the open-circuit voltage (V oc). The evaporative spray deposition using ultra dilute solution (ESDUS) technique was employed to deposit the buffer layer onto the organic active layer to avoid damage during the deposition. By the insertion of a C60P-DC buffer layer, V oc and power conversion efficiency (PCE) were increased from 0.41 to 0.57 V and from 1.65 to 2.10%, respectively. The electron-only device with the C60P-DC buffer showed a much lower current level than that without the buffer, indicating that the V oc increase is caused not by vacuum level shift but by hole blocking. The curve fitting of current density-voltage (J-V) characteristics to the equivalent circuit with a single diode indicated that the decrease in reversed saturation current by hole blocking increased caused the V oc.

  2. Kinetic Study of Photocatalytic Degradation of Tolonium Chloride Under High Pressure Irradiation in Aquatic Buffer Systems

    Directory of Open Access Journals (Sweden)

    M. Montazerozohori

    2011-01-01

    Full Text Available Anatase titanium dioxide catalyzed photodegradation of tolonium chloride at various bufferic pH of 2, 7, 9 and 12 in aqueous solution is presented. The effect of some physicochemical parameters such as initial concentration of dye, catalyst amount and reaction time on photocatalytic degradation has been investigated in a photo-reactor cell containing high pressure mercury lamp to obtain the optimum conditions in each bufferic pH at constant temperature. A complete spectrophotometric kinetic study of tolonium chloride under high pressure irradiation at buffer media was performed. The photocatalytic degradation observed rate constants (kobs were found to be 2.90×10-3, 3.30×10-3, 3.20×10-3 and 5.20×10-3 min-1 for buffer pH of 2-12 respectively. It was found that a pseudo-first-order kinetic model based on Langmuir-Hinshelwood one is usable to photodegradation of this compound at all considered buffer pH. In addition to these, the Langmuir-Hinshelwood rate constants, kr for the titled compound at various pH are reported.

  3. Managing Multiuser Database Buffers Using Data Mining Techniques

    NARCIS (Netherlands)

    Feng, L.; Lu, H.J.

    2004-01-01

    In this paper, we propose a data-mining-based approach to public buffer management for a multiuser database system, where database buffers are organized into two areas – public and private. While the private buffer areas contain pages to be updated by particular users, the public buffe

  4. The distribution of saliva buffer values in schoolchildren.

    Science.gov (United States)

    Wikner, S; Moum, I

    1986-01-01

    Buffer capacity of stimulated saliva was estimated by Dentobuff in 1596 7-15 years old schoolchildren. 39.7% of the children had a high, 39.9% a low and 20.4% an intermediate buffer capacity. No significant differences between the distributions in different ages were recorded and the mean buffer values did not differ significantly between the age-groups.

  5. CRACK2 - Modelling calcium carbonate deposition from bicarbonate solution in cracks in concrete

    Energy Technology Data Exchange (ETDEWEB)

    Brodersen, K

    2003-03-01

    The numerical CRACK2 model simulates precipitation of calcite from calcium bicarbonate solution (e.g. groundwater) passing through cracks in concrete or other cementitious materials. A summary of experimental work is followed by a detailed description of the model. Hydroxyl ions are transported by diffusion in pore systems in columns of cementitious materials. The hydroxyl is precipitating calcite from a flow of bicarbonate solution in a crack connecting the ends of a row of such columns. The cementitious material is simulated as calcium hydroxide mixed with inert material but with sodium hydroxide dissolved in the pore solution. Diffusive migration of cesium as radioactive isotope is also considered. Electrical interaction of the migrating ions is taken into account. Example calculations demonstrate effects of parameter variations on distribution of precipitated calcite in the crack and on the composition of the outflowing solution, which can be compared directly with experimental results. Leaching behavior of sodium can be used to tune the model to experimental observations. The calcite is mostly precipitated on top of the original crack surface and may under certain circumstances fill the crack. The produced thin layers of low porosity calcite act as a diffusion barrier limiting contact between cement and solution. Pore closure mechanisms in such layers are discussed. Implications for safety assessment of radioactive waste disposal are shortly mentioned. The model is also relevant for conventional uses of concrete. (au)

  6. Experimental Research on Microscopic Indicators of Temperature's Returning-to-Zero in Deformation of Calcite and Discussions of Correlation Problem

    Institute of Scientific and Technical Information of China (English)

    Yao Daquan; Zhai Hongtao

    2005-01-01

    In order to determine the degree of returning-to-zero of temperatures of deformed calcite, a series of rock-breaking experiments were designed to test calcite-rich limestone samples under fixed confining pressures and different temperatures. The consolidated deformed samples in their initial state were observed under a microscope and the microscopic indicators in different zero-returning states were put forward, thus providing a microscopic foundation for evaluation of reliability of dating values of deformation in calcite. At last, the correction of dating values of deformation for samples whose temperature has not yet returned to zero is discussed.

  7. Buffer for a gamma-insensitive optical sensor with gas and a buffer assembly

    Science.gov (United States)

    Kruger, Hans W.

    1994-01-01

    A buffer assembly for a gamma-insensitive gas avalanche focal plane array operating in the ultra-violet/visible/infrared energy wavelengths and using a photocathode and an avalanche gas located in a gap between an anode and the photocathode. The buffer assembly functions to eliminate chemical compatibility between the gas composition and the materials of the photocathode. The buffer assembly in the described embodiment is composed of two sections, a first section constructed of glass honeycomb under vacuum and a second section defining a thin barrier film or membrane constructed, for example, of Al and Be, which is attached to and supported by the honeycomb. The honeycomb section, in turn, is supported by and adjacent to the photocathode.

  8. 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

  9. 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.

    2016-06-01

    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.

  10. Deformation twinning and the role of amino acids and magnesium in calcite hardness from molecular simulation.

    Science.gov (United States)

    Côté, A S; Darkins, R; Duffy, D M

    2015-08-21

    We employ classical molecular dynamics to calculate elastic properties and to model the nucleation and propagation of deformation twins in calcite, both as a pure crystal and with magnesium and aspartate inclusions. The twinning is induced by applying uniaxial strain to the crystal and relaxing all stress components except the uniaxial component. A detailed analysis of the atomistic processes reveal that the twinning mechanism involves small displacements of the Ca ions and cooperative rotations of the CO3 ions. The volume of the twinned region expands under increased uniaxial strain via the propagation of steps along the twin boundaries. The energy cost of the twin boundaries is compensated by the reduced hydrostatic stress and strain energy. The presence of biogenic impurities is shown to decrease the strain required to induce twin formation in calcite and, thus, the yield stress. This increased propensity for twinning provides a possible explanation for the increased hardness and penetration resistance observed experimentally in biominerals.

  11. Arsenic uptake by gypsum and calcite: Modeling and probing by neutron and x-ray scattering

    CERN Document Server

    Fernandez-Martinez, Alejandro; Roman-Ross, Gabriela; Johnson, Mark R; Bardelli, Fabrizio; Turrillas, Xavier; Charlet, Laurent

    2006-01-01

    Here we report on two structural studies performed on As-doped gypsum (CaSO4 2H2O) and calcite (CaCO3), using neutron (D20-ILL) and x-ray (ID11-ESRF) diffraction data and EXAFS (BM8-ESRF). The aim of this study is to determine whether As gets into the bulk of gypsum and calcite structures or is simply adsorbed on the surface. Different mechanisms of substitution are used as hypotheses. The combined Rietveld analysis of neutron and x-ray diffraction data shows an expansion of the unit cell volume proportional to the As concentration within the samples. DFT-based simulations confirm the increase of the unit cell volume proportional to the amount of carbonate or sulphate groups substituted. Interpolation of the experimental Rietveld data allows us to distinguish As substituted within the structure from that adsorbed on the surface of both minerals.

  12. 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......, stable adsorption layer. In contrast, a single water molecule can only form one or other of these interactions and is thus less well bound, resulting in a more unstable adsorption layer. Consequently, when competitive adsorption is considered, ethanol dominates the adsorption layer that forms even when...... the starting configuration consists of a complete monolayer of water at the surface. The computational results are in good agreement with the results from atomic force microscopy experiments where it is observed that a layer of ethanol remains attached to the calcite surface, decreasing its ability to interact...

  13. k(+)-buffer: An Efficient, Memory-Friendly and Dynamic k-buffer Framework.

    Science.gov (United States)

    Vasilakis, Andreas-Alexandros; Papaioannou, Georgios; Fudos, Ioannis

    2015-06-01

    Depth-sorted fragment determination is fundamental for a host of image-based techniques which simulates complex rendering effects. It is also a challenging task in terms of time and space required when rasterizing scenes with high depth complexity. When low graphics memory requirements are of utmost importance, k-buffer can objectively be considered as the most preferred framework which advantageously ensures the correct depth order on a subset of all generated fragments. Although various alternatives have been introduced to partially or completely alleviate the noticeable quality artifacts produced by the initial k-buffer algorithm in the expense of memory increase or performance downgrade, appropriate tools to automatically and dynamically compute the most suitable value of k are still missing. To this end, we introduce k(+)-buffer, a fast framework that accurately simulates the behavior of k-buffer in a single rendering pass. Two memory-bounded data structures: (i) the max-array and (ii) the max-heap are developed on the GPU to concurrently maintain the k-foremost fragments per pixel by exploring pixel synchronization and fragment culling. Memory-friendly strategies are further introduced to dynamically (a) lessen the wasteful memory allocation of individual pixels with low depth complexity frequencies, (b) minimize the allocated size of k-buffer according to different application goals and hardware limitations via a straightforward depth histogram analysis and (c) manage local GPU cache with a fixed-memory depth-sorting mechanism. Finally, an extensive experimental evaluation is provided demonstrating the advantages of our work over all prior k-buffer variants in terms of memory usage, performance cost and image quality.

  14. Buffer layers and articles for electronic devices

    Science.gov (United States)

    Paranthaman, Mariappan P.; Aytug, Tolga; Christen, David K.; Feenstra, Roeland; Goyal, Amit

    2004-07-20

    Materials for depositing buffer layers on biaxially textured and untextured metallic and metal oxide substrates for use in the manufacture of superconducting and other electronic articles comprise RMnO.sub.3, R.sub.1-x A.sub.x MnO.sub.3, and combinations thereof; wherein R includes an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, and A includes an element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.

  15. Microcracking in calcite and dolomite marble: microstructural influences and effects on properties

    OpenAIRE

    Shushakova, Victoria; Fuller, Edwin; Siegesmund, Siegfried

    2012-01-01

    Microstructure‐based finite-element analysis with a microcracking algorithm was used to simulate an actual degradation phenomenon of marble structures, i.e., microcracking. Both microcrack initiation and crack propagation were characterized, as were their dependence on lattice preferred orientation (LPO), grain shape preferred orientation (SPO), grain size, marble composition (calcite and dolomite) and grain‐boundary fracture toughness. Two LPOs were analyzed: a random orientation distributio...

  16. Identification of spectrally similar materials using the USGS Tetracorder algorithm: The calcite-epidote-chlorite problem

    Science.gov (United States)

    Dalton, J.B.; Bove, D.J.; Mladinich, C.S.; Rockwell, B.W.

    2004-01-01

    A scheme to discriminate and identify materials having overlapping spectral absorption features has been developed and tested based on the U.S. Geological Survey (USGS) Tetracorder system. The scheme has been applied to remotely sensed imaging spectroscopy data acquired by the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) instrument. This approach was used to identify the minerals calcite, epidote, and chlorite in the upper Animas River watershed, Colorado. The study was motivated by the need to characterize the distribution of calcite in the watershed and assess its acid-neutralizing potential with regard to acidic mine drainage. Identification of these three minerals is difficult because their diagnostic spectral features are all centered at 2.3 ??m, and have similar shapes and widths. Previous studies overestimated calcite abundance as a result of these spectral overlaps. The use of a reference library containing synthetic mixtures of the three minerals in varying proportions was found to simplify the task of identifying these minerals when used in conjunction with a rule-based expert system. Some inaccuracies in the mineral distribution maps remain, however, due to the influence of a fourth spectral component, sericite, which exhibits spectral absorption features at 2.2 and 2.4 ??m that overlap the 2.3-??m absorption features of the other three minerals. Whereas the endmember minerals calcite, epidote, chlorite, and sericite can be identified by the method presented here, discrepancies occur in areas where all four occur together as intimate mixtures. It is expected that future work will be able to reduce these discrepancies by including reference mixtures containing sericite. ?? 2004 Elsevier Inc. All rights reserved.

  17. Higher Order Elastic Constants, Gruneisen Parameters and Lattice Thermal Expansion of Trigonal Calcite

    OpenAIRE

    Thresiamma Phlip; Menon, C S; Indulekha, K.

    2005-01-01

    The second- and third-order elastic constants of trigonal calcite have been obtained using the deformation theory. The strain energy density derived using the deformation theory is compared with the strain dependent lattice energy obtained from the elastic continuum model approximation to get the expressions for the second- and third-order elastic constants. Higher order elastic constants are a measure of the anharmonicity of a crystal lattice. The seven second-order elastic constants and the...

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

    OpenAIRE

    2016-01-01

    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...

  19. Rapid changes in water hardness and alkalinity: Calcite formation is lethal to Daphnia magna.

    Science.gov (United States)

    Bogart, Sarah J; Woodman, Samuel; Steinkey, Dylan; Meays, Cindy; Pyle, Greg G

    2016-07-15

    There is growing concern that freshwater ecosystems may be negatively affected by ever-increasing anthropogenic inputs of extremely hard, highly alkaline effluent containing large quantities of Ca(2+), Mg(2+), CO3(2-), and HCO3(-) ions. In this study, the toxicity of rapid and extreme shifts in water hardness (38-600mg/L as CaCO3) and alkalinity (30-420mg/L as CaCO3) to Daphnia magna was tested, both independently and in combination. Within these ranges, where no precipitation event occurred, shifts in water hardness and/or alkalinity were not toxic to D. magna. In contrast, 98-100% of D. magna died within 96h after exposure to 600mg/L as CaCO3 water hardness and 420mg/L as CaCO3 alkalinity (LT50 of 60h with a 95% CI of 54.2-66.0h). In this treatment, a CaCO3 (calcite) precipitate formed in the water column which was ingested by and thoroughly coated the D. magna. Calcite collected from a mining impacted stream contained embedded organisms, suggesting field streams may also experience similar conditions and possibly increased mortality as observed in the lab tests. Although further investigation is required to determine the exact fate of aquatic organisms exposed to rapid calcite precipitation in the field, we caution that negative effects may occur more quickly or at lower concentrations of water hardness and alkalinity in which we observed effects in D. magna, because some species, such as aquatic insects, are more sensitive than cladocerans to changes in ionic strength. Our results provide evidence that both calcite precipitation and the major ion balance of waters should be managed in industrially affected ecosystems and we support the development of a hardness+alkalinity guideline for the protection of aquatic life.

  20. 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.

  1. Shock Waves Trigger Fault Weakening in Calcite-bearing Rocks During Earthquakes

    Science.gov (United States)

    Spagnuolo, E.; Plumper, O.; Violay, M.; Cavallo, A.; Di Toro, G.

    2014-12-01

    The weakening mechanism of calcite-bearing rocks is still poorly understood though many major earthquakes stroke within carbonate sequences. Insights derive from the laboratory: in experiments performed on calcite-bearing gouges, up to 90% drop in friction is associated to grain size reduction to the nanoscale and the formation of crystal-plastic microstructures suggesting the activation of debated weakening mechanisms (e.g., grain boundary sliding and diffusion creep; nanopowder lubrication). Whatever the case, it is unclear how nanoparticles form and what their role is at the initiation of sliding. To investigate initial fault instability we sheared with a rotary shear apparatus SHIVA pre-cut ring-shaped solid cylinders (50/30 mm ext/int diameter) of Carrara marble (99.9% CaCO3). Rock cylinders were slid for few millimetres(0, 1.5 mm and 5mm) at accelerations (6.5 ms-2) and normal stresses (10 MPa) approaching seismic deformation conditions. Initial slip (nano-fracturing have occurred preserving the grain shape (pulverization) and (3) reaction products attributable to high pressure and high temperature conditions (i.e. calcite decomposition into amorphous carbon rimming the nanograins). All the above features are typical of shock-induced changes in minerals. We interpret the above observations as follows: pre-existing grain boundaries or newly formed defects are the nuclei for the generation of dislocations and for their pile-up; the fast release of those piles-up in avalanches under rapid stress loading (fast moving dislocations) may explain the origin of such a shock-like behaviour responsible for large initial frictional weakening. The passage of the shock wave induces pervasive nanofracturing with grain size reduction to the nano-scale and an abrupt temperature rise responsible for calcite decarbonation and formation of carbon amorphous material.

  2. Buffer Standards for the Biological pH of the Amino Acid N-[2 hydroxyethyl]piperazine-N'-[3-propanesulfonic acid], HEPPS, From (278.15 to 328.15) K.

    Science.gov (United States)

    Roy, Lakshmi N; Roy, Rabindra N; Wollen, Joshua T; Harmon, Meagan A; Stegner, Jessica M; Shah, Ankita A; Henson, Isaac B

    2011-01-01

    For the HEPPS buffer under investigation, there are seven buffer solutions without NaCl and eight buffer solutions that contain Cl(-) and have an ionic strength (I = 0.16 mol·kg(-1)), which is similar to that of blood plasma. These buffer solutions have been evaluated in the temperature range of (278.15 to 328.15) K using the extended Debye- Hückel equation and the Bates-Guggenheim convention. The previously determined E(j) values have been used to determine the operational pH values of HEPPS buffer solutions at (298.15 and 310.15) K. These are recommended as secondary standard reference solutions for pH measurements in saline media with an isotonic ionic strength of I = 0.16 mol·kg(-1).

  3. Buffer Standards for the Biological pH of the Amino Acid N-[2 hydroxyethyl]piperazine-N’-[3-propanesulfonic acid], HEPPS, From (278.15 to 328.15) K

    Science.gov (United States)

    Roy, Lakshmi N.; Roy, Rabindra N.; Wollen, Joshua T.; Harmon, Meagan A.; Stegner, Jessica M.; Shah, Ankita A.; Henson, Isaac B.

    2011-01-01

    For the HEPPS buffer under investigation, there are seven buffer solutions without NaCl and eight buffer solutions that contain Cl− and have an ionic strength (I = 0.16 mol·kg−1), which is similar to that of blood plasma. These buffer solutions have been evaluated in the temperature range of (278.15 to 328.15) K using the extended Debye- Hückel equation and the Bates-Guggenheim convention. The previously determined Ej values have been used to determine the operational pH values of HEPPS buffer solutions at (298.15 and 310.15) K. These are recommended as secondary standard reference solutions for pH measurements in saline media with an isotonic ionic strength of I = 0.16 mol·kg−1. PMID:22096257

  4. Microstructural Characterization of Calcite-Based Powder Materials Prepared by Planetary Ball Milling

    Directory of Open Access Journals (Sweden)

    Wen-Tien Tsai

    2013-08-01

    Full Text Available In this work, a planetary ball milling was used to modify the surface properties of calcite-based material from waste oyster shell under the rotational speed of 200–600 rpm, grinding time of 5–180 min and sample mass of 1–10 g. The milling significantly changed the microstructural properties of the calcite-based minerals (i.e., surface area, pore volume, true density, and porosity. The surface characterization of the resulting powder should be macroporous and/or nonporous based on the nitrogen adsorption/desorption isotherms. Under the optimal conditions at the rotational speed of 400 rpm, grinding time of 30 min and sample mass of 5 g, the resulting calcite-based powder had larger specific surface area (i.e., 10.64 m2·g−1 than the starting material (i.e., 4.05 m2·g−1. This finding was also consistent with the measurement of laser-diffraction (i.e., 9.7 vs. 15.0 μm of mean diameter. In addition, the results from the scanning electron microscope (SEM observation indicated that surface roughness can be enhanced as particle size decreases as a result of particle-particle attrition. Thus, grinding the aquacultural bioresource by a high-energy ball milling can create the fine materials, which may be applied in the fields of inorganic minerals like aggregate and construction material.

  5. Biomineralization processes of calcite induced by bacteria isolated from marine sediments.

    Science.gov (United States)

    Wei, Shiping; Cui, Hongpeng; Jiang, Zhenglong; Liu, Hao; He, Hao; Fang, Nianqiao

    2015-06-01

    Biomineralization is a known natural phenomenon associated with a wide range of bacterial species. Bacterial-induced calcium carbonate precipitation by marine isolates was investigated in this study. Three genera of ureolytic bacteria, Sporosarcina sp., Bacillus sp. and Brevundimonas sp. were observed to precipitate calcium carbonate minerals. Of these species, Sporosarcina sp. dominated the cultured isolates. B. lentus CP28 generated higher urease activity and facilitated more efficient precipitation of calcium carbonate at 3.24 ± 0.25 × 10(-4) mg/cell. X-ray diffraction indicated that the dominant calcium carbonate phase was calcite. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like crystals. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated calcite crystals through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored calcite precipitation at a higher level of 96 mg/L. The results of this research provide evidence that a variety of marine bacteria can induce calcium carbonate precipitation, and may influence the marine carbonate cycle in natural environments.

  6. Effects of limestone petrography and calcite microstructure on OPC clinker raw meals burnability

    Science.gov (United States)

    Galimberti, Matteo; Marinoni, Nicoletta; Della Porta, Giovanna; Marchi, Maurizio; Dapiaggi, Monica

    2016-12-01

    Limestone represents the main raw material for ordinary Portland cement clinker production. In this study eight natural limestones from different geological environments were chosen to prepare raw meals for clinker manufacturing, aiming to define a parameter controlling the burnability. First, limestones were characterized by X-Ray Fluorescence, X-Ray Powder Diffraction and Optical Microscopy to assess their suitability for clinker production and their petrographic features. The average domains size and the microstrain of calcite were also determined by X-Ray Powder Diffraction line profile analysis. Then, each limestone was admixed with clay minerals to achieve the adequate chemical composition for clinker production. Raw meals were thermally threated at seven different temperatures, from 1000 to 1450 °C, to evaluate their behaviour on heating by ex situ X-Ray Powder Diffraction and to observe the final clinker morphology by Scanning Electron Microscopy. Results indicate the calcite microstrain is a reliable parameter to predict the burnability of the raw meals, in terms of calcium silicates growth and lime consumption. In particular, mixtures prepared starting from high-strained calcite exhibit a better burnability. Later, when the melt appears this correlation vanishes; however differences in the early burnability still reflect on the final clinker composition and texture.

  7. Biomineralization processes of calcite induced by bacteria isolated from marine sediments

    Directory of Open Access Journals (Sweden)

    Shiping Wei

    2015-06-01

    Full Text Available Biomineralization is a known natural phenomenon associated with a wide range of bacterial species. Bacterial-induced calcium carbonate precipitation by marine isolates was investigated in this study. Three genera of ureolytic bacteria, Sporosarcina sp., Bacillus sp. and Brevundimonas sp. were observed to precipitate calcium carbonate minerals. Of these species, Sporosarcina sp. dominated the cultured isolates. B. lentus CP28 generated higher urease activity and facilitated more efficient precipitation of calcium carbonate at 3.24 ± 0.25 × 10−4 mg/cell. X-ray diffraction indicated that the dominant calcium carbonate phase was calcite. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like crystals. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated calcite crystals through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored calcite precipitation at a higher level of 96 mg/L. The results of this research provide evidence that a variety of marine bacteria can induce calcium carbonate precipitation, and may influence the marine carbonate cycle in natural environments.

  8. Numerical Simulations of Urea Hydrolysis and Calcite Precipitation in Porous Media Using STOMP

    Energy Technology Data Exchange (ETDEWEB)

    Luanjing Guo; Hai Huang; Bill X. Hu

    2010-11-01

    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 in situ immobilization approach of these contaminants is engineered mineral (co)precipitation of calcite driven by urea hydrolysis that is catalyzed by enzyme urease. The tight nonlinear coupling among flow, transport, reaction and reaction-induced property changes of media of this approach was studied by reactive transport simulations with systematically increasing level of complexities of reaction network and physical/chemical heterogeneities using a numerical simulator named STOMP. Sensitivity studies on the reaction rates of both urea hydrolysis and calcite precipitation are performed via controlling urease enzyme concentration and precipitation rate constant according to the rate models employed. We have found that the rate of ureolysis is a dominating factor in the amount of precipitated mineral; however, the spatial distribution of the precipitates depends on both rates of ureolysis and calcite precipitation. A maximum 5% reduction in the porosity was observed within the simulation time period of 6 pore volumes in our 1-dimensional (1D) column simulations. When a low permeability inclusion is considered in the 2D simulations, the altered flow fields redistribute mineral forming constituents, leading to a distorted precipitation reaction front. The simulations also indicate that mineral precipitation occurs along the boundary of the low permeability zone, which implies that contaminants in the low permeability zone could be encapsulated and isolated from the flow paths.

  9. Morphogenetic control of calcite crystal growth in sulfonic acid based hydrogels.

    Science.gov (United States)

    Grassmann, Olaf; Löbmann, Peer

    2003-03-17

    In this paper the mineralization of CaCO(3) in various hydrogel matrices is presented. Sulfonic acid based hydrogels were prepared by introduction of sulfonate-containing monomers into a polyacrylamide network. The sulfonate content of polyacrylamide-co-vinylsulfonate and polyacrylamide-co-allylsulfonate decreases during elution of the copolymers in demineralized water, indicating insufficient linking of the sulfonate-bearing monomers within the hydrogel. In contrast to this, acrylamidomethylpropanesulfonate (AMPS) effectively copolymerizes with acrylamide (AAm) monomers. To study the influence of spatial arrangement of ionic functional groups within hydrogel networks on the mineralization of CaCO(3), AMPS copolymers with different degrees of AMPS cross-linking were synthesized. For the mineralization experiments the copolymers were placed into a double-diffusion arrangement. Calcite as the thermodynamically stable modification of CaCO(3) was obtained with a particular morphology. The pseudocubic habitus resembles aggregates obtained by mineralization in pure polyacrylamide. However, closer examination of the aggregates by scanning electron microscopy (SEM) shows that the crystal growth in the AMPS copolymers is different from that observed in polyacrylamide. Whereas the morphology of the calcite aggregates could be fine-tuned by using copolymers with different sulfonate content, the spatial distribution of the ionic functional groups alters the course of crystallization. Calcium ions are locally accumulated due to the heterogeneous distribution of functional sulfonate groups within the copolymer network. Thereby the nucleation of calcite is triggered, resulting in enhanced mineralization.

  10. Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite.

    Science.gov (United States)

    Benzerara, Karim; Menguy, Nicolas; Guyot, Francois; Dominici, Christian; Gillet, Philippe

    2003-06-24

    Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.

  11. 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.

  12. 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.

  13. 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.

  14. Calcite crystal growth inhibition by humic substances with emphasis on hydrophobic acids from the Florida Everglades

    Science.gov (United States)

    Hoch, A.R.; Reddy, M.M.; Aiken, G.R.

    2000-01-01

    The crystallization of calcium carbonate minerals plays an integral role in the water chemistry of terrestrial ecosystems. Humic substances, which are ubiquitous in natural waters, have been shown to reduce or inhibit calcite crystal growth in experiments. The purpose of this study is to quantify and understand the kinetic effects of hydrophobic organic acids isolated from the Florida Everglades and a fulvic acid from Lake Fryxell, Antarctica, on the crystal growth of calcite (CaCO3). Highly reproducible calcite</