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1

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1) Adsorption of dilute PFOS(aq) and PFOA(aq) to acoustically cavitating bubble interfaces was greater than equilibrium expectations due to high-velocity bubble radial oscillations; 2) Relative ozone oxidation kinetics of aqueous iodide, sulfite, and thiosulfate were at variance with previously reported bulk aqueous kinetics; 3) Organics that directly chelated with the anode surface were oxidized by direct electron transfer, resulting in immediate carbon dioxide production but slower overall oxidation kinetics. Chemical reactions at aqueous interfaces can be the rate-limiting step of a reaction network and often display novel mechanisms and kinetics as compared to homogeneous chemistry.

Vecitis, Chad David

2

Aqueous chemical wash compositions  

SciTech Connect

This patent describes an aqueous, substantially unfoamed chemical wash composition having properties making it suitable for use as a pre-flush in well cementing operations and/or for removal of drilling mud from a borehole at a temperature of from about 150/sup 0/F to about 270/sup 0/F, the wash a. being predominantly composed of water, b. containing an active surfactant component comprising a combination of (1) from about 0.1 to about 1.5 weight percent (total weight basis) of a water soluble anionic surfactant; (2) from about 0.1 to about 1.5 weight percent (total weight basis) of a nonionic surfactant; and (3) from about 0.05 to about 0.54 weight percent (total weight basis) of at least one water soluble amphoteric surfactant, and c. having dispersed therein a heterogeneous mixture of distinct particles comprising both a first particulate oil soluble resin which is friable and a second particulate oil soluble resin which is pliable and where the size of the friable resin particles ranges from about 0.5 to about 300 microns and the size of the pliable resin particles ranges from about 0.05 to about 30 microns. The amount of the friable-pliable resin mixture is sufficient to impart effective fluid loss control to the chemical wash composition.

Bannister, C.E.

1987-07-21

3

Explosivity Conditions of Aqueous Solutions  

Microsoft Academic Search

This paper focuses on the conditions for explosive boiling and gas exsolution of aqueous solutions from a thermodynamic point\\u000a of view. Indeed, the kinetic nature of these processes, hence their explosivity, can be assessed by considering their relation\\u000a with the spinodal curve of these liquids. First, the concepts of mechanical and diffusion spinodals are briefly described,\\u000a which allows us to

R. Thiéry; L. Mercury

2009-01-01

4

Chemical Constraints Governing the Origin of Metabolism: The Thermodynamic Landscape of Carbon Group Transformations under Mild Aqueous Conditions  

NASA Astrophysics Data System (ADS)

The thermodynamics of organic chemistry under mild aqueous conditions was examined in order to begin to understand its influence on the structure and operation of metabolism and its antecedents. Free energies (?G) were estimated for four types of reactions of biochemical importance - carbon-carbon bond cleavage and synthesis, hydrogen transfer between carbon groups, dehydration of alcohol groups, and aldo-keto isomerization. The energies were calculated for mainly aliphatic groups composed of carbon, hydrogen, and oxygen. The energy values showed (1) that generally when carbon-carbon bond cleavage involves groups from different functional group classes (i.e., carboxylic acids, carbonyl groups, alcohols, and hydrocarbons), the transfer of the shared electron-pair to the more reduced carbon group is energetically favored over transfer to the more oxidized carbon group, and (2) that the energy of carbon-carbon bond transformation is primarily determined by the functional group class of the group that changes oxidation state in the reaction (i.e., the functional group class of the group that donates the shared electron-pair during cleavage, or that accepts the incipient shared electron-pair during synthesis). In contrast, the energy of hydrogen transfer between carbon groups is determined by the functional group class of both the hydrogen-donor group and the hydrogen-acceptor group. From these and other observations we concluded that the chemistry involved in the origin of metabolism (and to a lesser degree modern metabolism) was strongly constrained by (1) the limited redox-based transformation energy of organic substrates that is readily dissipated in a few energetically favorable irreversible reactions; (2) the energy dominance of a few transformation half-reactions that determines whether carbon-carbon bond transformation (cleavage or synthesis) is energetically favorable (?G < -3.5 kcal/mol), reversible (?G between +/-3.5 kcal/mol), or unfavorable (?G > +3.5 kcal/mol); and (3) the dependence of carbon group transformation energy on the functional group class (i.e., oxidation state) of participating groups that in turn is contingent on prior reactions and precursors in the synthetic pathway.

Weber, Arthur L.

2002-08-01

5

Chemical constraints governing the origin of metabolism: the thermodynamic landscape of carbon group transformations under mild aqueous conditions  

NASA Technical Reports Server (NTRS)

The thermodynamics of organic chemistry under mild aqueous conditions was examined in order to begin to understand its influence on the structure and operation of metabolism and its antecedents. Free energies (deltaG) were estimated for four types of reactions of biochemical importance carbon-carbon bond cleavage and synthesis, hydrogen transfer between carbon groups, dehydration of alcohol groups, and aldo-keto isomerization. The energies were calculated for mainly aliphatic groups composed of carbon, hydrogen, and oxygen. The energy values showed (1) that generally when carbon-carbon bond cleavage involves groups from different functional group classes (i.e., carboxylic acids, carbonyl groups, alcohols, and hydrocarbons), the transfer of the shared electron-pair to the more reduced carbon group is energetically favored over transfer to the more oxidized carbon group, and (2) that the energy of carbon-carbon bond transformation is primarily determined by the functional group class of the group that changes oxidation state in the reaction (i.e., the functional group class of the group that donates the shared electron-pair during cleavage, or that accepts the incipient shared electron-pair during synthesis). In contrast, the energy of hydrogen transfer between carbon groups is determined by the functional group class of both the hydrogen-donor group and the hydrogen-acceptor group. From these and other observations we concluded that the chemistry involved in the origin of metabolism (and to a lesser degree modern metabolism) was strongly constrained by (1) the limited redox-based transformation energy of organic substrates that is readily dissipated in a few energetically favorable irreversible reactions; (2) the energy dominance of a few transformation half-reactions that determines whether carbon-carbon bond transformation (cleavage or synthesis) is energetically favorable (deltaG < -3.5 kcal/mol), reversible (deltaG between +/-3.5 kcal/mol), or unfavorable (deltaG > +3.5 kcal/mol); and (3) the dependence of carbon group transformation energy on the functional group class (i.e., oxidation state) of participating groups that in turn is contingent on prior reactions and precursors in the synthetic pathway.

Weber, Arthur L.

2002-01-01

6

Plasmon-driven sequential chemical reactions in an aqueous environment.  

PubMed

Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H(+) in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight. PMID:24958029

Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

2014-01-01

7

Plasmon-driven sequential chemical reactions in an aqueous environment  

PubMed Central

Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.

Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

2014-01-01

8

CHEMICAL TRANSFORMATIONS USING NON-TRADITIONAL APPROACHES: MICROWAVE-ASSISTED GREENER SYNTHESES IN AQUEOUS MEDIA OR UNDER SOLVENT-FREE CONDITIONS  

EPA Science Inventory

Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a 'greener' chemical approach for expeditious N -alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N...

9

Quinone methide phosphodiester alkylations under aqueous conditions.  

PubMed

A detailed analysis of the alkylation of phosphodiesters with a p-quinone methide under aqueous conditions has been accomplished. The relative rates of phosphodiester alkylation and hydrolysis have been examined by (1)H NMR analysis of the reaction of 2,6-dimethyl-p-quinone methide in a buffered diethyl phosphate/acetonitrile solution (1:9 v/v, pH 4.0). The rate of hydrolysis of the quinone methide was confirmed by UV analysis in 28.5% solutions of aqueous inorganic phosphate in acetonitrile at pH 4.0 and 7.0. Similarly, the rate of phosphodiester alkylations by the quinone methide was also confirmed by UV analysis in 28.5% solutions of aqueous dibenzyl, dibutyl, or diethyl phosphate in acetonitrile at pH 4.0 and 7.0. These kinetic studies further establish that the phosphodiester alkylation reactions are acid-catalyzed, second-order processes. The rate constant for phosphodiester alkylation was found to range from approximately 370-3700 times the rate constant of quinone methide hydrolysis with diethyl and dibenzyl phosphate, respectively (pH 4.0, 28.5% aqueous acetonitrile). PMID:11597232

Zhou, Q; Turnbull, K D

2001-10-19

10

THE MECHANISM OF AQUEOUS HUMOR FORMATION INFERRED FROM CHEMICAL STUDIES ON BLOOD-AQUEOUS HUMOR DYNAMICS  

PubMed Central

The importance of considering the effect of a possible flow out of the anterior chamber before inferring any mechanism of aqueous humor formation from the relative concentration of a substance in the aqueous humor and plasma under equilibrium conditions has been stressed. Several processes to account for the chemical equilibria between aqueous humor and blood based on the ultrafiltration and secretion hypotheses with a possible simultaneous loss of aqueous humor by flow have been outlined. On the basis of these processes, equations were formulated which would relate the rates of transfer into and out of the anterior chamber to the ratio of concentration of a substance in the aqueous to that in the blood at various intervals after its introduction into the blood. The explanation of equilibrium ratios above and below one for aqueous constituents is made apparent from the mathematical formulations. For each substance tested a determination was made of the best fit when the concentration in the aqueous humor is plotted against time. This fit was obtained by plotting the rate of transfer in against the rate of transfer out of the anterior chamber for all of the experimentally found concentration ratios on the basis of both the ultrafiltration and secretory hypotheses. Two sets of values were obtained from these calculations, one set for each hypothesis. The substantial agreement of all the experimental data with an assumed rate of leakage out of the anterior chamber of approximately 4 c. mm. per minute was shown to be compatible only with the idea that all the monovalent electrolytes tested entered the anterior chamber as a result of secretory process. It could not be decided from these chemical studies whether the non-electrolytes and the one multivalent electrolyte tested enter the anterior chamber by ultrafiltration or secretion. Experimental findings from other sources were cited which would suggest that non-electrolytes enter the anterior chamber as a result of ultrafiltration. The implications of the mechanism outlined in the paper with respect to intraocular pressure have been discussed. Supplementary evidence from the literature has been given in support of the conclusions presented here.

Kinsey, V. Everett; Grant, W. Morton

1942-01-01

11

Interphase mass transfer during chemical oxidation of TCE DNAPL in an aqueous system  

Microsoft Academic Search

The chemical oxidation of trichloroethene dense non-aqueous phase liquid by permanganate was studied in an aqueous system using micro-reaction\\/extraction vessels in a novel approach. Experiments were conducted at ambient temperature (?20 °C) under static and mixed conditions to evaluate the rate of TCEDNAPL dissolution as a function of permanganate concentration. Chemical oxidation by permanganate was shown to increase the rate

Michael A. Urynowicz; Robert L. Siegrist

2005-01-01

12

Dynamics of a photochromic spiropyran under aqueous conditions  

NASA Astrophysics Data System (ADS)

The dynamics of a water soluble spiropyran is investigated by means of femtosecond transient absorption spectroscopy in the visible and infrared spectral range revealing an ultrafast reversible switching behavior under aqueous conditions with a high fatigue resistance.

Kohl-Landgraf, J.; Braun, M.; Özçoban, C.; Goncalves, D. P. N.; Heckel, A.; Wachtveitl, J.

2013-03-01

13

Modeling SOA formation in the aqueous phase - Comparing chemical processes in aqueous aerosol particles and cloud droplets  

NASA Astrophysics Data System (ADS)

Recent laboratory, field and model studies have suggested that low-volatility organic compounds can be efficiently formed in the atmospheric aqueous phase that is associated with aerosol particles or cloud droplets. A key species in these chemical transformations is glyoxal that is formed from the oxidation of numerous hydrocarbons, and is ubiquitous in the atmosphere. Whereas in the dilute aqueous phase (cloud droplets) glyoxal is successively oxidized to oxalic acid, i.e. retaining the carbon structure, additional pathways are occuring in the concentrated aerosol aqueous phase. These small water volumes are highly concentrated in terms of inorganic solutes (sulfate, ammonium) and organics, and triggers the formation of low-volatility products in form of oligomeric structures and/or combinations of inorganic and glyoxal molecules. This difference in chemical reactivity and product distribution has not been considered in models yet. Based on available laboratory measurements, we have derived reaction parameters for various processes (photochemical, reversible, and reactions between ammonium and related compounds with glyoxal). These parameters have been compiled into a new aerosol module that describes in detail the formation of SOA from glyoxal in aqueous particles. This module has been implemented into a cloud chemistry/microphysics model that has been used previously to predict SOA yields in clouds. Using trajectories that describe air parcels in subsaturated (~45% < RH < 100%) up to supersaturated conditions for different cloud types (cumulus, stratocumulus), we compare the efficiency of SOA formation in cloud droplets and aqueous particles and highlight conditions under which these SOA sources will significantly contribute to the total SOA budget. We show that despite the small water volume on aqueous particles as compared to clouds, chemical processes in particles can lead to significant amounts of SOA (up to several microg m-3 per day) due to enhanced reaction rates of mostly photochemical pathways but also other pathways that form unique aqueous phase products. Our results highlight the role of aerosol water as a chemical reactor for SOA formation particular under high relative humidity conditions and/or high loading of aqueous particles.

Ervens, B.; Volkamer, R.

2009-12-01

14

CHEMICAL SYNTHESES IN AQUEOUS MEDIA USING MICROWAVES  

EPA Science Inventory

The development of efficient, selective and eco-friendly synthetic methods has remained a major focus of our research group. Microwave (MW) irradiation as alternative energy source in conjunction with water as reaction media has proven to be a successful 'greener' chemical appro...

15

REDEQL.EPAK: AQUEOUS CHEMICAL EQUILIBRIUM COMPUTER PROGRAM  

EPA Science Inventory

This user's guide is a companion to the previously published report A User's Guide for REDEQL.EPA which explains the use of a computerized chemical equilibrium program for metals and ligands in aqueous systems. Changes in this guide include temperature correction for equilibrium ...

16

Wetting under chemical equilibrium and nonequilibrium conditions  

Microsoft Academic Search

The thermodynamics of a solid-liquid-vapor system both under chemical equilibrium and nonequilibrium conditions, based on the model of Gibbs, is discussed. Under chemical equilibrium conditions, the degree of wetting or nonwetting of a flat and nondeformable solid by the liquid is defined by Young's equation in terms of the static interfacial tensions. Under chemical nonequilibrium conditions, mass transfer across an

I. A. Aksay; Carl E. Hoge; Joseph A. Pask

1974-01-01

17

Attenuation of Aqueous Benzene in Soils under Saturated Flow Conditions  

Microsoft Academic Search

The fate of aqueous benzene in subsurface was investigated in this study, focusing on the role of sorption and biodegradation on the benzene attenuation under dynamic flow conditions. Two sets of column tests were conducted in Plexiglass flow cells packed uniformly with sandy aquifer materials. The first set of the experiment was conducted with a step-type injection of benzene with

S.-B. Kim; D.-J. Kim; S.-T. Yun

2006-01-01

18

FBX aqueous chemical dosimeter for measurement of dosimetric parameters.  

PubMed

We investigated the ferrous sulphate-benzoic acid-xylenol orange (FBX) aqueous chemical dosimeter for measurement of dosimetric parameters such as the output factor, backscatter factor and lateral beam profiles for different square fields sizes for (60)Co ?-rays. A water phantom was employed to measure these parameters. An ionization chamber (IC) was used for calibration and comparison. A comparison of the resulting measurements with an ionization chamber's measured parameters showed good agreement. We thus believe that the tissue equivalent FBX dosimetry system can measure the dosimetric parameters for (60)Co with reasonable accuracy. PMID:21036054

Moussous, O; Medjadj, T; Benguerba, M

2011-02-01

19

Aqueous photolysis of the organic ultraviolet filter chemical octyl methoxycinnamate.  

PubMed

Organic UV filter chemicals are the active ingredients in personal care products designed to protect the skin from UV radiation, and hundreds of tons are estimated to be produced annually. Despite their entrance into the aquatic environment by both direct and indirect routes and their detection in surface waters and fish, little is known about their environmental fate. UV filter chemicals are designed to be photostable, but some undergo transformation upon exposure to UV light. Octyl methoxycinnamate (OMC), a commonly used UV filter chemical, degrades rapidly by direct photolysis; previous studies have focused on its photoisomerization, and a few investigators have reported the formation of cyclodimers. Here, we present the kinetics and quantum efficiency of the direct photolysis of OMC and confirm that dimerization occurs as a result of direct photolysis in aqueous solution. Likely identities of the dimers are offered based on comparison to reported results for other cinnamate derivatives. We have identified additional products of direct photolysis that have not been previously reported and investigated their photostability, as well as the mechanism of product formation. There is also some evidence of indirect photolysis in the presence of dissolved natural organic matter. PMID:21476541

MacManus-Spencer, Laura A; Tse, Monica L; Klein, Jacob L; Kracunas, Alison E

2011-05-01

20

First experimental determination of iron isotope fractionation between hematite and aqueous solution at hydrothermal conditions  

NASA Astrophysics Data System (ADS)

Although iron isotopes provide a new powerful tool for tracing a variety of geochemical processes, the unambiguous interpretation of iron isotope ratios in natural systems and the development of predictive theoretical models require accurate data on equilibrium isotope fractionation between fluids and minerals. We investigated Fe isotope fractionation between hematite (Fe 2O 3) and aqueous acidic NaCl fluids via hematite dissolution and precipitation experiments at temperatures from 200 to 450 °C and pressures from saturated vapor pressure ( Psat) to 600 bar. Precipitation experiments at 200 °C and Psat from aqueous solution, in which Fe aqueous speciation is dominated by ferric iron (Fe III) chloride complexes, show no detectable Fe isotope fractionation between hematite and fluid, ? 57Fe fluid-hematite = ? 57Fe fluid - ? 57Fe hematite = 0.01 ± 0.08‰ (2 × standard error, 2SE). In contrast, experiments at 300 °C and Psat, where ferrous iron chloride species (FeCl 2 and FeCl +) dominate in the fluid, yield significant fluid enrichment in the light isotope, with identical values of ? 57Fe fluid-hematite = -0.54 ± 0.15‰ (2SE) both for dissolution and precipitation runs. Hematite dissolution experiments at 450 °C and 600 bar, in which Fe speciation is also dominated by ferrous chloride species, yield ? 57Fe fluid-hematite values close to zero within errors, 0.15 ± 0.17‰ (2SE). In most experiments, chemical, redox, and isotopic equilibrium was attained, as shown by constancy over time of total dissolved Fe concentrations, aqueous Fe II and Fe III fractions, and Fe isotope ratios in solution, and identical ? 57Fe values from dissolution and precipitation runs. Our measured equilibrium ? 57Fe fluid-hematite values at different temperatures, fluid compositions and iron redox state are within the range of fractionations in the system fluid-hematite estimated using reported theoretical ?-factors for hematite and aqueous Fe species and the distribution of Fe aqueous complexes in solution. These theoretical predictions are however affected by large discrepancies among different studies, typically ±1‰ for the ? 57Fe Fe(aq)-hematite value at 200 °C. Our data may thus help to refine theoretical models for ?-factors of aqueous iron species. This study provides the first experimental calibration of Fe isotope fractionation in the system hematite-saline aqueous fluid at elevated temperatures; it demonstrates the importance of redox control on Fe isotope fractionation at hydrothermal conditions.

Saunier, Gaëlle; Pokrovski, Gleb S.; Poitrasson, Franck

2011-11-01

21

Prediction of contaminant persistence in aqueous phase: a quantum chemical approach.  

PubMed

At contaminated field sites where active remediation measures are not feasible, monitored natural attenuation is sometimes the only alternative for surface water or groundwater decontamination. However, due to slow degradation rates of some contaminants under natural conditions, attenuation processes and their performance assessment can take several years to decades to complete. Here, we apply quantum chemical calculations to predict contaminant persistence in the aqueous phase. For the test compound hexamethylphosphoramide (HMPA), P-N bond hydrolysis is the only thermodynamically favorable reaction that may lead to its degradation under reducing conditions. Through calculation of aqueous Gibbs free energies of activation for all potential reaction mechanisms, it is predicted that HMPA hydrolyzes via an acid-catalyzed mechanism at pH < 8.2, and an uncatalyzed mechanism at pH 8.2-8.5. The estimated half-lives of thousands to hundreds of thousands of years over the groundwater-typical pH range of 6.0 to 8.5 indicate that HMPA will be persistent in the absence of suitable oxidants. At pH 0, where the hydrolysis reaction is rapid enough to enable measurement, the experimentally determined rate constant and half-life are in excellent agreement with the predicted values. Since the quantum chemical methodology described herein can be applied to virtually any contaminant or reaction of interest, it is especially valuable for the prediction of persistence when slow reaction rates impede experimental investigations and appropriate QSARs are unavailable. PMID:21332222

Blotevogel, Jens; Mayeno, Arthur N; Sale, Tom C; Borch, Thomas

2011-03-15

22

Effects of extraction conditions on the chemical structure and biological activity of white cabbage pectin  

Microsoft Academic Search

The purpose of this study was to isolate and perform chemical analyzes as well as biological testing of pectic material from white cabbage isolated by sequential aqueous ionic solutions (SEQAIS) or a simple pure water extraction (PW). Water extraction was aimed at yielding water-soluble pectins only, while the harsher conditions in SEQAIS aimed at extracting proto pectin as well. The

B. Westereng; T. E. Michaelsen; A. B. Samuelsen; S. H. Knutsen

2008-01-01

23

Evaluation of an evanescent fiber optic chemical sensor for monitoring aqueous volatile organic compounds.  

National Technical Information Service (NTIS)

Linear chemometric algorithms were used to model the quantitative response of an evanescent fiber optic chemical sensor in aqueous mixtures with concentrations between 20 and 300 ppm. Four data sets were examined with two different experimental arrangemen...

D. S. Blair

1997-01-01

24

Dermal Absorption of Chemicals: Effect of Application of Chemicals as a Solid, Aqueous Paste, Suspension, or in Volatile Vehicle.  

National Technical Information Service (NTIS)

The purpose of the study was to investigate the dermal absorption of chemicals applied to female F344 rats in different physical forms. These forms included chemical as a solid, aqueous paste, suspension or dissolved in the volatile vehicle ethanol. The c...

M. F. Hughes S. P. Shrivastava M. R. Sumler B. C. Edwards J. H. Goodwin

1992-01-01

25

MINEQL-EIR. Chemical Equilibrium Composition of Aqueous Systems  

SciTech Connect

MINEQL is a subroutine package to calculate equilibrium composition of an aqueous system, accounting for mass transfer. MINEQL-EIR contains an additional base on enthalpy and heat capacity data and has the option to do calculations at temperatures different from 25 degrees C.

Westall, J.C.; Zachary, J.L.; Morel, F.M.M [Massachusetts Institute of Technology, Cambridge (United States); Schweingruber, M. [Eidgenoessisches Institut for Reaktorforschung, Wuerenlingen (Switzerland)

1986-11-21

26

Biosorption of heavy metal ions from aqueous solutions by short hemp fibers: Effect of chemical composition  

Microsoft Academic Search

Sorption potential of waste short hemp fibers for Pb2+, Cd2+ and Zn2+ ions from aqueous media was explored. In order to assess the influence of hemp fiber chemical composition on their heavy metals sorption potential, lignin and hemicelluloses were removed selectively by chemical modification. The degree of fiber swelling and water retention value were determined in order to evaluate the

Biljana Pejic; Marija Vukcevic; Mirjana Kostic; Petar Skundric

2009-01-01

27

A physical chemical UNIFAC model for aqueous solutions of sugars  

Microsoft Academic Search

A new physical chemical model is proposed to describe the thermodynamic properties of binary water-carbohydrate mixtures. The chemical part of the model takes into account the conformational equilibria of sugars and the solvation equilibria between water and sugars. The physical part of the model is a modified UNIFAC model where three new main groups (pyranose ring, furanose ring and osidic

Marianne Catté; Claude-Gilles Dussap; Jean-Bernard Gros

1995-01-01

28

Oxygen Tension in the Aqueous Humor of Human Eyes under Different Oxygenation Conditions  

PubMed Central

Purpose To measure oxygen tension in the aqueous humor of human eyes under different oxygenation conditions. Methods This prospective comparative interventional case series consisted of two parts. In the first part, 120 consecutive patients scheduled for cataract surgery were randomized into group I (control group) in which surgery was performed under local anesthesia inhaling 21% oxygen; group II in whom general anesthesia using 50% oxygen was employed; and group III receiving general anesthesia with 100% oxygen. After aspirating 0.2 ml aqueous humor under sterile conditions, the aqueous sample and a simultaneously drawn arterial blood sample were immediately analyzed using a blood gas analyzer. In part II the same procedures were performed in 10 patients after fitting a contact lens and patching the eye for 20 minutes (group IV) and in 10 patients after transcorneal delivery of oxygen at a flow rate of 5 L/min (group V). Results Mean aqueous PO2 in groups I, II and III was 112.3±6.2, 141.1±20.4, and 170.1±27 mmHg, respectively (P values <0.001) and mean arterial PO2 was 85.7±7.9, 184.6±46, and379.1±75.9 mmHg, respectively (P values <0.001). Aqueous PO2 was 77.2±9.2 mmHg in group IV and 152.3±10.9 mmHg in group V (P values <0.001). There was a significant correlation between aqueous and blood PO2 (r=0.537, P<0.001). The contribution of atmospheric oxygen to aqueous PO2 was 23.7%. Conclusion Aqueous oxygen tension is mostly dependent on the systemic circulation and in part on the atmosphere. Increasing inspiratory oxygen and transcorneal oxygen delivery both increase aqueous PO2 levels.

Sharifipour, Farideh; Idani, Esmaeil; Zamani, Mitra; Helmi, Toktam; Cheraghian, Bahman

2013-01-01

29

FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

30

Effect of adsorbents and chemical treatments on the removal of strontium from aqueous solutions.  

PubMed

In the present investigation, three different solid wastes namely almond green hull, eggplant hull, and moss were initially treated and used as adsorbents for the adsorption of strontium ion from aqueous solutions. Adsorbent types and chemical treatments are proved to have effective roles on the adsorption of Sr(II) ion. Among the three adsorbents, almond green hull demonstrated strong affinity toward strontium ion in different solutions. The effectiveness of this new adsorbent was studied in batch adsorption mode under a variety of experimental conditions such as: different chemical treatments, various amounts of adsorbent, and initial metal-ion concentration. The optimum doses of adsorbent for the maximum Sr(II) adsorption were found to be 0.2 and 0.3 g for 45 and 102 mg L(-1) solutions, respectively. High Sr(II) adsorption efficiencies were achieved only in the first 3 min of adsorbent's contact time. The kinetics of Sr(II) adsorption on almond green hull was also examined and it was observed that it follows the pseudo second-order behavior. Both Langmuir and Freundlich models well predicted the experimental adsorption isotherm data. The maximum adsorption capacity on almond green hull was found to be 116.3 mg g(-1). The present study also confirmed that these low cost agriculture byproducts could be used as efficient adsorbents for the removal of strontium from wastewater streams. PMID:20633988

Ahmadpour, A; Zabihi, M; Tahmasbi, M; Bastami, T Rohani

2010-10-15

31

GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

Green chemical synthesis through catalysis and alternate reaction conditions Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

32

Aqueous alteration of VHTR fuels particles under simulated geological conditions  

NASA Astrophysics Data System (ADS)

Very High Temperature Reactor (VHTR) fuels consist of the bistructural-isotropic (BISO) or tristructural-isotropic (TRISO)-coated particles embedded in a graphite matrix. Management of the spent fuel generated during VHTR operation would most likely be through deep geological disposal. In this framework we investigated the alteration of BISO (with pyrolytic carbon) and TRISO (with SiC) particles under geological conditions simulated by temperatures of 50 and 90 °C and in the presence of synthetic groundwater. Solid state (scanning electron microscopy (SEM), micro-Raman spectroscopy, electron probe microanalyses (EPMA) and X-ray photoelectron spectroscopy (XPS)) and solution analyses (ICP-MS, ionique chromatography (IC)) showed oxidation of both pyrolytic carbon and SiC at 90 °C. Under air this led to the formation of SiO2 and a clay-like Mg-silicate, while under reducing conditions (H2/N2 atmosphere) SiC and pyrolytic carbon were highly stable after a few months of alteration. At 50 °C, in the presence and absence of air, the alteration of the coatings was minor. In conclusion, due to their high stability in reducing conditions, HTR fuel disposal in reducing deep geological environments may constitute a viable solution for their long-term management.

Ait Chaou, Abdelouahed; Abdelouas, Abdesselam; Karakurt, Gökhan; Grambow, Bernd

2014-05-01

33

Biosorption of Pb(II) from aqueous solutions using chemically modified Moringa oleifera tree leaves  

Microsoft Academic Search

Moringa oleifera leaves (MOL); an agro-waste material has been used as a precursor to prepare a new biosorbent. The leaves were washed with base and citric acid, and obtained new chemically modified MOL biosorbent (CAMOL) for sequestration of Pb(II) from aqueous solution. The biosorbent was characterized by SEM, FTIR spectral and elemental analyses. The effect of experimental parameters such as

D. Harikishore Kumar Reddy; Y. Harinath; K. Seshaiah; A. V. R. Reddy

2010-01-01

34

A USER'S GUIDE FOR REDEQL.EPA. A COMPUTER PROGRAM FOR CHEMICAL EQUILIBRIA IN AQUEOUS SYSTEMS  

EPA Science Inventory

This user's guide explains the use of the computerized chemical equilibrium program REDEQL.EPA. This program computes aqueous equilibria for up to 20 metals and 30 ligands in a system. The metals and ligands are selected from a list of 35 metals and 59 ligands for which thermodyn...

35

Aqueous polyaniline suspensions: Chemical oxidative polymerization of dodecylbenzene-sulfonic acid aniline salt  

Microsoft Academic Search

Chemical oxidative polymerization of dodecylbenzenesulfonic acid aniline salt in water using ammonium peroxydisulfate as oxidant was found to give an homogeneous polyaniline suspension. An aqueous transparent and green uniform suspension containing polyaniline complexed and doped with dodecylbenzenesulfonic acid was obtained to show a typical emeraldine salt spectrum. The polyaniline suspension was quite stable without any precipitation for several months and

Noriyuki Kuramoto; Atsuro Tomita

1997-01-01

36

ENDOCRINE DISRUPTING CHEMICALS - DEVELOPING LRPCD SOPS FOR AQUEOUS, BIOSOLIDS, AND SOLID SAMPLES  

EPA Science Inventory

As part of research in the risk management of Endocrine Disrupting Chemicals (EDCs), analytical techniques to measure EDCs are needed. This project will result in 6 LRPCD SOPs: analysis of steroid hormones in aqueous samples, analysis of alkylphenol ethoxylates and bisphenol A i...

37

Chemical transport in silicone rubber membranes from pure powders and saturated aqueous solutions  

Microsoft Academic Search

In this study membrane permeation was measured from finely divided pure powder and saturated aqueous solutions of two test chemicals with low vapor pressure, methyl paraben and 4-cyanophenol, through silicone rubber (polydimethylsiloxane) using diffusion cells operated to insure the concentration was negligible at the interface between the membrane and the receptor solution. The steady-state flux from the pure powder was

Eugene E. Ley; Annette L. Bunge

2007-01-01

38

Morphological and chemical features of nano and macroscale carbons affecting hydrogen peroxide decomposition in aqueous media  

Microsoft Academic Search

Chemical and structural factors of carbon materials affect their activity in adsorption and surface reactions in aqueous media. Decomposition of hydrogen peroxide studied is a probe reaction for exploring parameters of carbons that might be involved, such as specific surface area, nitrogen and oxygen doping and conformational changes. To date, a detailed comparison of the behavior of carbon nanoscale (Carbon

Kateryna V. Voitko; Raymond L. D. Whitby; Vladimir M. Gun’ko; Olga M. Bakalinska; Mykola T. Kartel; Krisztina Laszlo; Andrew B. Cundy; Sergey V. Mikhalovsky

2011-01-01

39

Polyelectrolyte brushes: a novel stable lubrication system in aqueous conditions.  

PubMed

Surface-initiated controlled radical copolymerizations of 2-dimethylaminoethyl methacrylate (DMAEMA), 2-(methacryloyloxy)ethyl phosphorylcholine (MPC), 2-(methacryloyloxy)ethyltrimethylammonium chloride) (MTAC), and 3-sulfopropyl methacrylate potassium salt (SPMK) were carried out on a silicon wafer and glass ball to prepare polyelectrolyte brushes with excellent water wettability. The frictional coefficient of the polymer brushes was recorded on a ball-on-plate type tribometer by linear reciprocating motion of the brush specimen at a selected velocity of 1.5 x 10(-3) m s-1 under a normal load of 0.49 N applied to the stationary glass ball (d = 10 mm) at 298 K. The poly(DMAEMA-co-MPC) brush partially cross-linked by bis(2-iodoethoxy)ethane maintained a relatively low friction coefficient around 0.13 under humid air (RH > 75%) even after 200 friction cycles. The poly(SPMK) brush revealed an extremely low friction coefficient around 0.01 even after 450 friction cycles. We supposed that the abrasion of the brush was prevented owing to the good affinity of the poly(SPMK) brush for water forming a water lubrication layer, and electrostatic repulsive interactions among the brushes bearing sulfonic acid groups. Furthermore, the poly(SPMK-co-MTAC) brush with a chemically cross-linked structure showed a stable low friction coefficient in water even after 1400 friction cycles under a normal load of 139 MPa, indicating that the cross-linking structure improved the wear resistance of the brush layer. PMID:23285641

Kobayashi, Motoyasu; Terada, Masami; Takahara, Atsushi

2012-01-01

40

Preparation of amino-functionalized silica in aqueous conditions  

NASA Astrophysics Data System (ADS)

Silica particle surfaces were modified with 3-aminopropyltriethoxysilane (APTES) for the fabrication under mild conditions of amino-functionalized silica particles which can be applied in a number of processes, e.g. chromatography. Surface activation was carried out in water at natural pH and in toluene on non-preheated silica in order to compare the grafting efficiency in these two solvents. No successive thermal treatments were carried out after grafting. Grafting extents were then calculated using solid state TOC measurements. Grafting extents of APTES in water and anhydrous solvent were surprisingly found to be the same after a simple rinsing step (i.e. 2.10 ± 0.09 ?mol/m2). Thus, in our case, the use of anhydrous solvent is an unnecessary precaution if the silica is further used in water since equivalent grafting extents of APTES are obtained with a simple and eco-friendly grafting process.

Cuoq, Fabrice; Masion, Armand; Labille, Jérôme; Rose, Jérôme; Ziarelli, Fabio; Prelot, Benedicte; Bottero, Jean-Yves

2013-02-01

41

Pad conditioning in chemical mechanical polishing  

Microsoft Academic Search

As circuits become increasingly complex and device sizes shrink, the demands placed on manufacturing processes increases. For successful manufacture of such circuits, high levels of wafer planarity are required. Chemical mechanical polishing (CMP) is a manufacturing process used to achieve global planarity. Studies have shown that the degree of planarity achieved is influenced by the pad properties. During polishing, the

B. J Hooper; G Byrne; S Galligan

2002-01-01

42

Ammonium sorption from aqueous solutions by the natural zeolite Transcarpathian clinoptilolite studied under dynamic conditions  

Microsoft Academic Search

The scope of this study is ammonium-ion uptake from synthetic aqueous solutions onto raw and pretreated forms of the natural zeolite Transcarpathian clinoptilolite under dynamic conditions. Hydrogen ions displaced exchangeable cations on the clinoptilolite in distilled water (sodium ions) and hydrochloric acid (sodium, potassium, and calcium ions) and destroyed the zeolite framework structure in the last case. Ammonium uptake onto

Myroslav Sprynskyy; Mariya Lebedynets; Artur P. Terzyk; Piotr Kowalczyk; Jacek Namie?nik; Bogus?aw Buszewski

2005-01-01

43

Single step signal group-imidazole labeling of organic phosphate groups under aqueous conditions  

DOEpatents

Compounds and methods for single step, covalent labeling of the phosphate group of an organic substance under aqueous conditions are described. The labeling compound includes any kind of detectable signal group covalently bound to an imidazole moiety, which can be imidazole or a substituted imidazole. A preferred labeling compound has the formula ##STR1##

Giese, Roger W. (Quincy, MA); Wang, Poguang (Medford, MA)

1996-01-01

44

Single step signal group-imidazole labeling of organic phosphate groups under aqueous conditions  

DOEpatents

Compounds and methods for single step, covalent labeling of the phosphate group of an organic substance under aqueous conditions are described. The labeling compound includes any kind of detectable signal group covalently bound to an imidazole moiety, which can be imidazole or a substituted imidazole. A preferred labeling compound has the formula shown in the accompanying diagram. 4 figs.

Giese, R.W.; Wang, P.

1996-04-30

45

Selection among aqueous and off-gas treatment technologies for synthetic organic chemicals  

SciTech Connect

A methodology for selecting the least-cost treatment technology for waters contaminated by organic wastes was developed using performance and cost models. This methodology simplifies the selection of the least expensive treatment process(es) for a given set of conditions. Two aqueous-phase treatment options were considered: air stripping and liquid-phase adsorption (granular activated carbon). When the off-gases from air stripping must be treated, four off-gas treatment options were considered: gas-phase adsorption (with both on- and off-site regeneration of the granular activated carbon), thermal incineration, and catalytic oxidation. Methodologies were developed for rapidly selecting the least-cost off-gas treatment option [for volatile organic compound (VOC) sources such as an air stripping tower], for selecting the least-cost overall (liquid and gas phase treatment) system, and for selecting the least-cost overall system for a multicomponent mixture. The comparison methodology is based on physical parameters of the target chemical: Henry`s constant and the solute distribution parameter. The results are a set of diagrams and heuristics for rapid identification of cases for which one treatment option is significantly less expensive than the other.

Dvorak, B.I. [Univ. of Nebraska, Lincoln, NE (United States). Dept. of Civil Engineering; Herbeck, C.J. [County Sanitation District of Los Angeles County, Whittier, CA (United States); Meurer, C.P. [Bee County Coll., Beeville, TX (United States); Lawler, D.F.; Speitel, G.E. Jr. [Univ. of Texas, Austin, TX (United States). Dept. of Civil Engineering

1996-07-01

46

Phytotoxic Activity and Chemical Composition of Aqueous Volatile Fractions from Eucalyptus Species  

PubMed Central

The essential oils from four Eucalyptus species (E. spathulata, E. salubris, E. brockwayii and E. dundasii) have been previously confirmed to have stronger inhibitory effects on germination and seedling growth of silverleaf nightshade (Solanum elaeagnifolium Cav.). The aqueous volatile fractions (AVFs) were the water soluble volatile fractions produced together with the essential oils (water insoluble fractions) during the steam distillation process. The aim of this study was to further assess the phytotoxicity of AVFs from the four Eucalyptus species and their chemical composition. The fresh leaves of the four Eucalyptus species were used for the extraction of AVFs. The AVFs were tested for their phytotoxic effects on the perennial weed, silverleaf nightshade under laboratory conditions. The chemical compositions of the AVFs were determined by gas chromatograph–mass spectrometry (GC-MS). Our results showed that the AVFs had strong inhibition on the germination and seedling growth of silverleaf nightshade. The inhibition index increased with the increasing concentrations of AVFs. The inhibitory effects of the AVFs varied between different Eucalyptus species. The AVF from E. salubris demonstrated the highest inhibitory activity on the weed tested, with complete inhibition on germination and seedling growth at a concentration of 75%. The GC-MS analysis revealed that 1,8-cineole, isopentyl isovalerate, isomenthol, pinocarvone, trans-pinocarveol, alpha-terpineol and globulol were the main compounds in the AVFs. These results indicated that all AVFs tested had differential inhibition on the germination and seedling growth of silverleaf nightshade, which could be due to the joint effects of compounds present in the AVFs as these compounds were present in different quantities and ratio between Eucalyptus species.

Zhang, Jinbiao; An, Min; Wu, Hanwen; Liu, De Li; Stanton, Rex

2014-01-01

47

Phytotoxic activity and chemical composition of aqueous volatile fractions from eucalyptus species.  

PubMed

The essential oils from four Eucalyptus species (E. spathulata, E. salubris, E. brockwayii and E. dundasii) have been previously confirmed to have stronger inhibitory effects on germination and seedling growth of silverleaf nightshade (Solanum elaeagnifolium Cav.). The aqueous volatile fractions (AVFs) were the water soluble volatile fractions produced together with the essential oils (water insoluble fractions) during the steam distillation process. The aim of this study was to further assess the phytotoxicity of AVFs from the four Eucalyptus species and their chemical composition. The fresh leaves of the four Eucalyptus species were used for the extraction of AVFs. The AVFs were tested for their phytotoxic effects on the perennial weed, silverleaf nightshade under laboratory conditions. The chemical compositions of the AVFs were determined by gas chromatograph-mass spectrometry (GC-MS). Our results showed that the AVFs had strong inhibition on the germination and seedling growth of silverleaf nightshade. The inhibition index increased with the increasing concentrations of AVFs. The inhibitory effects of the AVFs varied between different Eucalyptus species. The AVF from E. salubris demonstrated the highest inhibitory activity on the weed tested, with complete inhibition on germination and seedling growth at a concentration of 75%. The GC-MS analysis revealed that 1,8-cineole, isopentyl isovalerate, isomenthol, pinocarvone, trans-pinocarveol, alpha-terpineol and globulol were the main compounds in the AVFs. These results indicated that all AVFs tested had differential inhibition on the germination and seedling growth of silverleaf nightshade, which could be due to the joint effects of compounds present in the AVFs as these compounds were present in different quantities and ratio between Eucalyptus species. PMID:24681490

Zhang, Jinbiao; An, Min; Wu, Hanwen; Liu, De Li; Stanton, Rex

2014-01-01

48

Chemical coal beneficiation with aqueous hydrogen peroxide\\/sulfuric acid solutions  

Microsoft Academic Search

The removal of sulfur and ash from coal treated with aqueous hydrogen peroxide\\/sulfuric acid solutions at ambient temperature was studied under a variety of experimental conditions. Almost complete elimination of the sulfate and the pyritic sulfur was observed in most cases, as well as substantial reduction in the ash content. The rest of the organic coal matrix was not affected

N. P. Vasilakos; C. S. Clinton

1983-01-01

49

Chemical coal beneficiation with aqueous hydrogen peroxide\\/sulfuric acid solution  

Microsoft Academic Search

The removal of sulfur and ash from coal treated with aqueous hydrogen peroxide\\/sulfuric acid solutions at ambient temperature was studied under a variety of experimental conditions. Almost complete elimination of the sulfate and the pyritic sulfur was observed in most cases, along with substantial reduction in ash content. The remainder of the coal matrix was not affected significantly, thus indicating

N. P. Vasilakos; C. S. Clinton

1983-01-01

50

The effect of chemical pretreatment on the aerobic microbial degradation of PCB congeners in aqueous systems  

Microsoft Academic Search

A series of experiments was conducted to examine the effects of chemical pretreatment on biodegradation of14C-labeled PCB congeners in aqueous systems. Fenton's reagent was used to generate hydroxyl radicals (OH) which were successful in partially oxidizing\\/transforming otherwise recalcitrant molecules of tetrachlorinated PCB, but had little or no impact on the biodegradation of a monochlorinated congener. Application of Fenton's reagent (1%

B N Aronstein; J R Paterek; R L Kelley; L E Rice

1995-01-01

51

Efficiency of Cd(II) removal from aqueous media using chemically modified polystyrene foam  

Microsoft Academic Search

The removal of Cd(II) using polystyrene foam chemically modified with 2,2?-bipyridine has been investigated. The modified polystyrene foam has been characterized by FT-IR spectroscopy, thermogravimetry, elemental analysis and scanning electron microscopy. The solid was employed as a Cd(II) adsorption from aqueous solutions at room temperature. The effects of several variables (pH, shaking speed, agitation time, metal concentration and presence of

Jamil R. Memon; Saima Q. Memon; M. I. Bhanger; M. Y. Khuhawar; Geoffrey C. Allen; G. Zuhra Memon; A. G. Pathan

2008-01-01

52

Chemical characterization of some aqueous leachates from crop residues in 'CELSS'  

NASA Technical Reports Server (NTRS)

Aqueous leachate samples prepared from crop residues that are produced as a component of the Controlled Ecological Life Support System program designed to support long duration space missions have been compared and general chemical characterization has been accomplished. Solid phase extraction and high performance liquid chromatography were used to accomplish comparisons based on chromatographic and ultraviolet absorption properties of the components that are present. Specific compounds were not identified, however, general composition related to the presence of phenol-like compounds was explored.

Madsen, Brooks C.

1992-01-01

53

Kinetics of the chemical oxidation of polysulfide anions in aqueous solution  

Microsoft Academic Search

The kinetic properties of the chemical oxidation of aqueous polysulfide solutions have been studied in phosphate-buffered systems at pH 7–12, at temperatures between 20 and 40°C, and ionic strength between 0.05 and 0.50M. Polysulfide solutions were mixed with a buffer solution of known dissolved oxygen concentration, after which the decrease in the oxygen concentration of the solution was measured in

Wilfred E. Kleinjan; Arie de Keizer; Albert J. H. Janssen

2005-01-01

54

Chemical disinfection under conditions of microgravity  

NASA Astrophysics Data System (ADS)

There is enormous potential for point-of-use water purifiers where central water treatment does not exist or distribution systems are faulty and allow incursion of pathogenic organisms after primary treatment. Manned space missions on the Space Shuttle and planned missions on the Space Station also employ point-of-use water purifiers termed microbial check valves (MCVs). Polyiodide resin materials in use on the Space Shuttle within the MCV and in terrestrial water purifiers, silver and copper chelex resins, zirconium peroxide chelex resin, and a quaternary ammonium compound-Dow Corning 5700-polymerized to carbon and polystyrene beads, were compared for disinfection ability. Experiments were conducted in fluid processing apparatus (FPAs) at unit gravity and in microgravity conditions aboard seven STS missions. These new materials may have applications in both space and terrestrial water treatment devices.

Marchin, George L.

1997-01-01

55

Asian dust particles converted into aqueous droplets under remote marine atmospheric conditions  

PubMed Central

The chemical history of dust particles in the atmosphere is crucial for assessing their impact on both the Earth’s climate and ecosystem. So far, a number of studies have shown that, in the vicinity of strong anthropogenic emission sources, Ca-rich dust particles can be converted into aqueous droplets mainly by the reaction with gaseous HNO3 to form Ca(NO3)2. Here we show that other similar processes have the potential to be activated under typical remote marine atmospheric conditions. Based on field measurements at several sites in East Asia and thermodynamic predictions, we examined the possibility for the formation of two highly soluble calcium salts, Ca(NO3)2 and CaCl2, which can deliquesce at low relative humidity. According to the results, the conversion of insoluble CaCO3 to Ca(NO3)2 tends to be dominated over urban and industrialized areas of the Asian continent, where the concentrations of HNO3 exceed those of HCl ([HNO3/HCl] >  ? 1). In this regime, CaCl2 is hardly detected from dust particles. However, the generation of CaCl2 becomes detectable around the Japan Islands, where the concentrations of HCl are much higher than those of HNO3 ([HNO3/HCl] <  ? 0.3). We suggest that elevated concentrations of HCl in the remote marine boundary layer are sufficient to modify Ca-rich particles in dust storms and can play a more important role in forming a deliquescent layer on the particle surfaces as they are transported toward remote ocean regions.

Tobo, Yutaka; Zhang, Daizhou; Matsuki, Atsushi; Iwasaka, Yasunobu

2010-01-01

56

Formation of sulfur and nitrogen cross-linked macromolecules under aqueous conditions  

NASA Astrophysics Data System (ADS)

Polysulfides and ammonia are abundant in young depositional environments and play an important role in the formation of macromolecular structures such as protokerogen and humics. In this work, we study the co-incorporation of polysulfides and ammonia into simple carbonyl model compounds, octanal and trans 2-octenal, in order to study their effect on the formation of a cross-linked macromolecule and suggest a feasible mechanism. The reactions, performed in aqueous solutions at ambient temperature and pH ˜6 to 9, simulate formation of S and N cross-linked polymers in the natural environment. The complex S and N containing polymer was studied by 15N enrichment coupled to 2D NMR ( 1H, 13C, 15N) techniques and chemical degradation of S-S bonds followed by deuterium labeling and GC-MS analyses. In addition, molecular modeling techniques were used to provide theoretical interpretations and important insights at the molecular level. The results indicate that polysulfide out competes ammonia in the formation of Michael adducts while ammonia is equally competitive with polysulfides when the reaction is addition to the carbonyl position. The co-incorporation of ammonia and polysulfides into carbonyls rapidly forms N and S cross-linked polymers. The effects of ammonia and amines on the polymerization processes are by two means: (i) reaction with carbonyls through an imine functionality to form oligomers and polymers and (ii) catalysis of sulfur nucleophiles onto carbonyls by transfer of a proton which enhances the rate of polymerization. A similar catalytic effect is observed when glycine is used instead of ammonia. This mechanism is especially important under basic to neutral conditions like those that prevail in marine environments. The results show that ammonia and glycine or possibly other amino acids and/or peptides are intimately involved with sulfur nucleophiles throughout the polymerization processes that occur at low temperatures and thus are suggested as key reactants in diagenetic formation of protokerogen and humics.

Amrani, Alon; Turner, Jeffrey W.; Ma, Qisheng; Tang, Yongchun; Hatcher, Patrick G.

2007-09-01

57

Phyto-chemical evaluation of dried aqueous extract of Jivanti [Leptadenia reticulata (Retz.) Wt. et Arn  

PubMed Central

Jivanti (Leptadenia reticulata (Retz.) Wt. et Arn) is a well known climber used for its innumerable therapeutic properties like antioxidant, antibacterial, vasodilator, galactogogue, Jivaniya, etc., Its use in veterinary practice is tremendous due to its lactogenic effect. The Ghana (dried aqueous extract) of the whole plant was prepared and evaluated phyto-chemically by subjecting it to various tests like physico-chemical, qualitative analysis; TLC and HPTLC. Qualitative tests revealed the presence of flavonoids and TLC also inferred positive Rf value (0.30), indicating the presence of quercetin in the Ghana.

Pal, Atanu; Sharma, Parmeshwar P.; Pandya, Tarulata N.; Acharya, Rabinarayan; Patel, Bhupesh R.; Shukla, Vinay J.; Ravishankar, B.

2012-01-01

58

Phyto-chemical evaluation of dried aqueous extract of Jivanti [Leptadenia reticulata (Retz.) Wt. et Arn].  

PubMed

Jivanti (Leptadenia reticulata (Retz.) Wt. et Arn) is a well known climber used for its innumerable therapeutic properties like antioxidant, antibacterial, vasodilator, galactogogue, Jivaniya, etc., Its use in veterinary practice is tremendous due to its lactogenic effect. The Ghana (dried aqueous extract) of the whole plant was prepared and evaluated phyto-chemically by subjecting it to various tests like physico-chemical, qualitative analysis; TLC and HPTLC. Qualitative tests revealed the presence of flavonoids and TLC also inferred positive Rf value (0.30), indicating the presence of quercetin in the Ghana. PMID:23723676

Pal, Atanu; Sharma, Parmeshwar P; Pandya, Tarulata N; Acharya, Rabinarayan; Patel, Bhupesh R; Shukla, Vinay J; Ravishankar, B

2012-10-01

59

Methods and additives for delaying the release of chemicals in aqueous fluids  

SciTech Connect

Additives are provided for bringing about the delayed release of a chemical such as a gel breaker or demulsifier in an aqueous fluid such as a gelled oil well hydraulic fracturing or fracture-acidizing fluid. The additives are pelletized solids consisting of the chemical to be released such as sodium laryl sulfate. A gelling agent capable of being hydrated such as a polysaccharide, and a breaker for the gel produced by the gelling agent when hydrated such as a persulfate or an enzyme. 33 claims.

Burnham, J.W.; Briscoe, J.E.; Elphingstone, E.A.

1980-05-13

60

The Physical and Chemical Conditions of Chesapeake Bay; An Evaluation.  

National Technical Information Service (NTIS)

An assessment of the physical and chemical conditions of the Chesapeake Bay estuarine system indicates: (1) that there are marked natural spatial and temporal variations of temperature, that man has in local areas, had a measurable effect on the temperatu...

J. R. Schubel

1972-01-01

61

Kinetics of carbonate dissolution in CO2-saturated aqueous system at reservoir conditions  

NASA Astrophysics Data System (ADS)

In recent years, carbon capture and storage (CCS) has emerged as a key technology for limiting anthropogenic CO2 emissions while allowing the continued utilisation of fossil fuels. The most promising geological storage sites are deep saline aquifers because the capacity, integrity and injection economics are most favourable, and the environmental impact can be minimal. Many rock-fluid chemical reactions are known to occur both during and after CO2 injection in saline aquifers. The importance of rock-fluid reactions in the (CO2 + H2O) system can be understood in terms of their impact on the integrity and stability of both the formation rocks and cap rocks. The chemical interactions between CO2-acidified brines and the reservoir minerals can influence the porosity and permeability of the formations, resulting in changes in the transport processes occurring during CO2 storage. Since carbonate minerals are abundant in sedimentary rocks, one of the requirements to safely implement CO2 storage in saline aquifers is to characterise the reactivity of carbonate minerals in aqueous solutions at reservoir conditions. In this work, we reported measurements of the intrinsic rate of carbonate dissolution in CO2-saturated water under high-temperature high-pressure reservoir conditions extending up to 373 K and 14 MPa. The rate of carbonate dissolution in CO2-free HCl(aq) was also measured at ambient pressure at temperatures up to 353 K. Various pure minerals and reservoir rocks were investigated in this study, including single-crystals of calcite and magnesite, and samples of dolomite, chalks and sandstones. A specially-designed batch reactor system, implementing the rotating disc technique, was used to obtain the intrinsic reaction rate at the solid/liquid interface, free of mass transfer effects. The effective area and mineralogy of the exposed surface was determined by a combination of surface characterisation techniques including XRD, SEM, EDX and optical microscopy. The results of the study indicate that the rotating disc technique can allow accurate measurement of the carbonate dissolution rate under surface-reaction-controlled conditions, and that the carbonate dissolution rate typically increases with the increase of temperature, CO2 partial pressure and solution acidity. The study shows that the dissolution of carbonate in CO2-free acidic solutions can be described as a first order heterogeneous reaction; however, this model is not sufficient to describe the reaction kinetics of carbonate minerals in the (CO2 + H2O) system, particularly for high reactivity carbonates, such as calcite, at reservoir conditions. For these systems, both pH and the activity of CO2(aq) influence the dissolution rate. Based on the experimental results, kinetic models have been developed and parameterised to describe the dissolution of different carbonate minerals. The results of this study should facilitate more rigorous modelling of mineral dissolution in deep saline aquifers used for CO2 storage. We gratefully acknowledge the funding of QCCSRC provided jointly by Qatar Petroleum, Shell, and the Qatar Science & Technology Park. Keywords: Carbon Dioxide, Carbonate, High Pressure, High Temperature, Reaction Kinetics.

Peng, Cheng; Crawshaw, John P.; Maitland, Geoffrey; Trusler, J. P. Martin

2014-05-01

62

Removal of polycyclic aromatic hydrocarbons in aqueous environment by chemical treatments: a review.  

PubMed

Due to their carcinogenic, mutagenic and teratogenic potential, the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous environment using physical, biological and chemical processes has been studied by several researchers. This paper reviews the current state of knowledge concerning PAHs including their physico-chemical properties, input sources, occurrence, adverse effects and conventional and alternative chemical processes applied for their removal from water. The mechanisms and reactions involved in each treatment method are reported, and the effects of various variables on the PAH degradation rate as well as the extent of degradation are also discussed. Extensive literature analysis has shown that an effective way to perform the conversion and mineralization of this type of substances is the application of advanced oxidation processes (AOPs). Furthermore, combined processes, particularly AOPs coupled with biological treatments, seem to be one of the best solutions for the treatment of effluents containing PAHs. PMID:24552655

Rubio-Clemente, Ainhoa; Torres-Palma, Ricardo A; Peñuela, Gustavo A

2014-04-15

63

The 13 C chemical shifts of amino acids in aqueous solution containing organic solvents: Application to the secondary structure characterization of peptides in aqueous trifluoroethanol solution  

Microsoft Academic Search

The 13C chemical shifts for all of the protonated carbons of the 20 common amino acid residues in the protected linear pentapeptide Gly-Gly-X-Gly-Gly have been obtained in water at low pH as well as in aqueous solution containing 10, 20 and 30% acetonitrile or trifluoroethanol. Dioxane was used as an internal reference and its carbon chemical shift value was found

Venkataraman Thanabal; Diana O. Omecinsky; Michael D. Reily; Wayne L. Cody

1994-01-01

64

Biosorption of heavy metal ions from aqueous solutions by short hemp fibers: Effect of chemical composition.  

PubMed

Sorption potential of waste short hemp fibers for Pb(2+), Cd(2+) and Zn(2+) ions from aqueous media was explored. In order to assess the influence of hemp fiber chemical composition on their heavy metals sorption potential, lignin and hemicelluloses were removed selectively by chemical modification. The degree of fiber swelling and water retention value were determined in order to evaluate the change in accessibility of the cell wall components to aqueous solutions due to the fiber modification. The effects of initial ion concentration, contact time and cosorption were studied in batch sorption experiments. The obtained results show that when the content of either lignin or hemicelluloses is progressively reduced by chemical treatment, the sorption properties of hemp fibers are improved. Short hemp fibers are capable of sorbing metal ions (Pb(2+), Cd(2+) and Zn(2+)) from single as well as from ternary metal ion solutions. The maximum total uptake capacities for Pb(2+), Cd(2+) and Zn(2+) ions from single solutions are the same, i.e. 0.078mmol/g, and from ternary mixture 0.074, 0.035 and 0.035mmol/g, respectively. PMID:18778893

Pejic, Biljana; Vukcevic, Marija; Kostic, Mirjana; Skundric, Petar

2009-05-15

65

Homogeneous ice freezing temperatures and ice nucleation rates of aqueous ammonium sulfate and aqueous levoglucosan particles for relevant atmospheric conditions.  

PubMed

Homogeneous ice nucleation from micrometre-sized aqueous (NH4)2SO4 and aqueous levoglucosan particles is studied employing the optical microscope technique. A new experimental method is introduced that allows us to control the initial water activity of the aqueous droplets. Homogeneous ice freezing temperatures and ice melting temperatures of these aqueous solution droplets, 10 to 80 microm in diameter, are determined. Homogeneous ice nucleation from aqueous (NH4)2SO4 particles 5-39 wt% in concentration and aqueous levoglucosan particles with initial water activities of 0.85-0.99 yield upper limits of the homogeneous ice nucleation rate coefficients of up to 1x10(10) cm(-3) s(-1). The experimentally derived homogeneous ice freezing temperatures and upper limits of the homogeneous ice nucleation rate coefficients are compared with corresponding predictions of the water-activity-based ice nucleation theory [T. Koop, B. P. Luo, A. Tsias and T. Peter, Nature, 2000, 406, 611]. It is found that the water-activity-based ice nucleation theory can capture the experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients of the aqueous (NH4)2SO4 and aqueous levoglucosan particles. However, the level of agreement between experimentally derived and predicted values, in particular for homogeneous ice nucleation rate coefficients, crucially depends on the extrapolation method to obtain water activities at corresponding freezing temperatures. It is suggested that the combination of experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients can serve as a better validation of the water-activity-based ice nucleation theory than when compared to the observation of homogeneous ice freezing temperatures alone. The atmospheric implications with regard to the application of the water-activity-based ice nucleation theory and derivation of maximum ice particle production rates are briefly discussed. PMID:19727513

Knopf, Daniel Alexander; Lopez, Miguel David

2009-09-28

66

Wet Etching of HgCdTe in Aqueous Bromine Solutions: a Quantitative Chemical Approach  

NASA Astrophysics Data System (ADS)

The ability to pattern HgCdTe surfaces using a wet etching solution is an important challenge for processing of third-generation infrared detectors. The reduction of pixel size, the increase of pixel density, and two-color array technology require perfectly mastered etching to remove very thin layers and to control the state of the surface. To perform this process, a new quantitative chemical approach was developed to carry out very accurate wet etching in aqueous HBr/Br2 solutions. This approach was established to identify the key parameters that govern the etching process and to understand the etching mechanism.

Causier, A.; Gerard, I.; Bouttemy, M.; Etcheberry, A.; Pautet, C.; Baylet, J.; Mollard, L.

2011-08-01

67

Process for preparing chemically modified micas for removal of cesium salts from aqueous solution  

DOEpatents

A chemically modified mica composite formed by heating a trioctahedral mica in an aqueous solution of sodium chloride having a concentration of at least 1 mole/liter at a temperature greater than 180 degrees Centigrade for at least 20 hours, thereby replacing exchangeable ions in the mica with sodium. Formation is accomplished at temperatures and pressures which are easily accessed by industrial equipment. The reagent employed is inexpensive and non-hazardous, and generates a precipitate which is readily separated from the modified mica.

Yates, Stephen Frederic (1539 S. Kennicott Dr., Arlington Heights, IL 60005); DeFilippi, Irene (208 E. Edgewood La., Palatine, IL 60067); Gaita, Romulus (6646 Davis Rd., Morton Grove, IL 60053); Clearfield, Abraham (Department of Chemistry, Texas A& M University, College Station, TX 77843); Bortun, Lyudmila (Department of Chemistry, Texas A& M University, College Station, TX 77843); Bortun, Anatoly (Department of Chemistry, Texas A& M University, College Station, TX 77843)

2000-09-05

68

Chemistry of Sediments and Aqueous Fluids Produced by Chemical Weathering in Cold, Arid Systems  

NASA Astrophysics Data System (ADS)

Analyses of Antarctic Dry Valley sediment and water samples suggest that cold, arid, proglacial systems produce unique chemical and textural weathering products. High surface areas play a key role in the weathering process at these conditions.

Elwood Madden, M. E.; Keiser, L.; Marra, K.; Sorreghan, G. S.; Stumpf, A.; Hall, B.

2011-03-01

69

Enhanced dissolution of manganese oxide in ice compared to aqueous phase under illuminated and dark conditions.  

PubMed

Manganese is one of the common elements in the Earth's crust and an essential micronutrient for all living things. The reductive dissolution of particulate manganese oxide is a dominant process to enhance mobility and bioavailability of manganese for the use of living organisms. In this work, we investigated the reductive dissolution of manganese oxides trapped in ice (at -20 °C) under dark and light irradiation (visible: ? > 400 nm and UV: ? > 300 nm) in comparison with their counterparts in aqueous solution (at 25 °C). The reductive dissolution of synthetic MnO?, which took place slowly in aqueous solution, was significantly accelerated in ice phase both in the presence and absence of light: about 5 times more dissolution in ice phase than in liquid water after 6 h UV irradiation in the presence of formic acid. The enhanced dissolution in ice was observed under both UV and visible irradiation although the rate was much slower in the latter condition. The reductive dissolution rate of Mn(II)(aq) (under both irradiation and dark conditions) gradually increased with decreasing pH below 6 in both aqueous and ice phases, and the dissolution rates were consistently faster in ice under all tested conditions. The enhanced generation of Mn(II)(aq) in ice can be mainly explained in terms of freeze concentration of electron donors, protons, and MnO? in liquid-like ice grain boundaries. The outdoor solar experiment conducted in Arctic region (Ny-Ålesund, Svalbard, 78°55'N) also showed that the photoreductive dissolution of manganese oxide is enhanced in ice. The present results imply that the dissolution of natural minerals like manganese oxides can be enhanced in icy environments such as polar region, upper atmosphere, and frozen soil. PMID:23153016

Kim, Kitae; Yoon, Ho-Il; Choi, Wonyong

2012-12-18

70

Covalent attachment of mechanoresponsive luminescent micelles to glasses and polymers in aqueous conditions.  

PubMed

Covalent attachment of mechanoresponsive luminescent organic or organometallic compounds to other materials is a promising approach to develop a wide variety of mechanoresponsive luminescent materials. Here, we report covalently linkable mechanoresponsive micelles that change their photoluminescence from yellow to green in response to mechanical stimulation under aqueous conditions. These micelles are composed of a dumbbell-shaped amphiphilic pyrene derivative having amine groups at the peripheral positions of its dendrons. Using a well-established cross-linker, the micelles were covalently linked via their peripheral amine groups to the surface of glass beads, polylactic acid (PLA) beads, and living cells under aqueous conditions. Vortexing of glass beads bearing the micelles in a glass vial filled with water caused a photoluminescence color change from yellow to green. PLA beads bearing the micelles showed no change in photoluminescence color under the same conditions. We ascribe this result to the lower density and stiffness of the PLA beads, because the color of the PLA beads changed on vortexing in the presence of bare glass beads. HeLa cells and HL-60 cells bearing the micelles showed no obvious photoluminescence color change under vortexing. The structure, photophysical properties, and mechanism of photoluminescence color change of the micellar assemblies were examined. PMID:24571353

Sagara, Yoshimitsu; Komatsu, Toru; Ueno, Tasuku; Hanaoka, Kenjiro; Kato, Takashi; Nagano, Tetsuo

2014-03-19

71

Experimental study of brucite dissolution and precipitation in aqueous solutions: surface speciation and chemical affinity control  

NASA Astrophysics Data System (ADS)

Dissolution and precipitation rates of brucite (Mg(OH) 2) were measured at 25°C in a mixed-flow reactor as a function of pH (2.5 to 12), ionic strength (10 -4 to 3 M), saturation index (-12 < log ? < 0.4) and aqueous magnesium concentrations (10 -6 to 5·10 -4 M). Brucite surface charge and isoelectric point (pH IEP) were determined by surface titrations in a limited residence time reactor and electrophoretic measurements, respectively. The pH of zero charge and pH IEP were close to 11. A two-pK, one site surface speciation model which assumes a constant capacitance of the electric double layer (5 F/m 2) and lack of dependence on ionic strength predicts the dominance of >MgOH 2+ species at pH < 8 and their progressive replacement by >MgOH° and >MgO - as pH increases to 10-12. Rates are proportional to the square of >MgOH 2+ surface concentration at pH from 2.5 to 12. In accord with surface speciation predictions, dissolution rates do not depend on ionic strength at pH 6.5 to 11. Brucite dissolution and precipitation rates at close to equilibrium conditions obeyed TST-derived rate laws. At constant saturation indices, brucite precipitation rates were proportional to the square of >MgOH 2+ concentration. The following rate equation, consistent with transition state theory, describes brucite dissolution and precipitation kinetics over a wide range of solution composition and chemical affinity: R=k Mg+ · {>MgOH 2+} 2 · (1-? 2) where kMg+ is the dissolution rate constant, {> i} is surface species concentration (mol/m 2), and ? is the solution saturation index with respect to brucite. Measurements of nonsteady state brucite dissolution rates, in response to cycling the pH from 12 to 2 (pH-jump experiments), indicate the important role of surface hydroxylation — that leads to the formation of Mg oxo or -hydroxo complexes — in the formation of dissolution-active sites. Replacement of water molecules by these oxygen donor complexes in the Mg coordination sphere has a labilizing effect on the dynamics of the remaining water molecules and thus increases reaction rates.

Pokrovsky, Oleg S.; Schott, Jacques

2004-01-01

72

Optimization of growth conditions of ZnO nano thin films by chemical double dip technique  

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) nano thin films have been deposited by the chemical double-dip technique using aqueous ZnSO4 and NaOH solutions. The ZnO films were characterized in terms of surface morphology by x-ray diffraction, energy-dispersive x-ray analysis (EDX), the use of a scanning electron microscope (SEM) and atomic force microscope (AFM) for surface morphology. The films exhibited a smooth morphology. The chemical states of oxygen and zinc in the ZnO nano thin films were also investigated by x-ray photoelectron spectroscopy (XPS). In the present investigations, highly textured ZnO thin films with a preferential (002)-orientation were prepared on glass substrates. The deposition conditions were optimized to obtain device-quality films for practical applications.

Anandamoorthy Vijayan, Thirukonda; Chandramohan, Rathinam; Valanarasu, Santiyagu; Thirumalai, Jagannathan; Venkateswaran, Sivasuriyan; Mahalingam, Thaiyan; Ramachandran Srikumar, Subbiah

2008-07-01

73

Optimum conditions for composites fiber coating by chemical vapor infiltration  

Microsoft Academic Search

A combined analytical and numerical method is employed to optimize process conditions for composites fiber coating by chemical vapor infiltration. For a first-order deposition reaction, the optimum pressure yielding the maximum deposition rate at a preform center is obtained in closed form and is found to depend only on the activation energy of the deposition reaction, the characteristic pore size,

Stewart K. Griffiths; R. H. Nilson

1998-01-01

74

Chemical flowsheet conditions for preparing urania spheres by internal gelation  

Microsoft Academic Search

Small, ceramic urania spheres can be prepared for use as nuclear fuel by internal chemical gelation of uranyl nitrate solution droplets. Decomposition of hexamethylenetetramine (HMTA) dissolved in the uranyl nitrate solution releases ammonia to precipitate hydrated UOâ. Previously established flowsheet conditions have been improved and modified at ORNL and have been applied to prepare dense UOâ spheres with average diameters

P. A. Haas; J. M. Begovich; A. D. Ryon; J. S. Vavruska

1979-01-01

75

Promoted oxidation of phenol in aqueous solution using molecular oxygen at mild conditions  

SciTech Connect

Wet oxidation with molecular oxygen at mild conditions (temperature < 200 C, pressure {le} 2 MPa) is an economically attractive pretreatment step for non-biodegradable aqueous waste streams. In order to overcome the low reactivity of molecular oxygen towards organic molecules at these mild process conditions, an initiator was used in combination with ferrous ions in the acidic range. The promoted oxidation of phenol in aqueous solution was investigated in a 4 liters stirred autoclave. It was possible to degrade the phenol at temperatures as low as 100 C without observing an induction time. The remaining solution contained mainly acetic and formic acid and was well biodegradable. The oxidative behavior of the oxygen/phenol system could be explained using the well-known autoxidation mechanism for aliphatic molecules. 4-hydroperoxy-phenol is suggested as a key intermediate. Measured products are p-benzoquinone, hydroquinone, catechol, maleic, oxalic, pyruvic, formic, and acetic acid. Dimers could also be identified in sample extracts. A global pathway including all identified products is presented.

Vogel, F.; Harf, J.; Hug, A.; Rohr, P.R. von [Swiss Federal Inst. of Tech., Zuerich (Switzerland). Inst. of Process Engineering] [Swiss Federal Inst. of Tech., Zuerich (Switzerland). Inst. of Process Engineering

1999-05-01

76

Aqueous fluid composition in CI chondritic materials: Chemical equilibrium assessments in closed systems  

NASA Astrophysics Data System (ADS)

Solids of nearly solar composition have interacted with aqueous fluids on carbonaceous asteroids, icy moons, and trans-neptunian objects. These processes altered mineralogy of accreted materials together with compositions of aqueous and gaseous phases. We evaluated chemistry of aqueous solutions coexisted with CI-type chondritic solids through calculations of chemical equilibria in closed water-rock-gas systems at different compositions of initial fluids, water/rock mass ratios (0.1-1000), temperatures (<350 °C), and pressures (<2 kbars). The calculations show that fluid compositions are mainly affected by solubilities of solids, the speciation of chlorine in initial water-rock mixtures, and the occurrence of Na-bearing secondary minerals such as saponite. The major species in modeled alkaline solutions are Na+, Cl-, CO32-,HCO3-, K+, OH-, H2, and CO2. Aqueous species of Mg, Fe, Ca, Mn, Al, Ni, Cr, S, and P are not abundant in these fluids owing to low solubility of corresponding solids. Typical NaCl type alkaline fluids coexist with saponite-bearing mineralogy that usually present in aqueously altered chondrites. A common occurrence of these fluids is consistent with the composition of grains emitted from Enceladus. Na-rich fluids with abundant CO32-,HCO3-, and OH- anions coexist with secondary mineralogy depleted in Na. The Na2CO3 and NaHCO3 type fluids could form via accretion of cometary ices. NaOH type fluids form in reduced environments and may locally occur on parent bodies of CR carbonaceous chondrites. Supposed melting of accreted HCl-bearing ices leads to early acidic fluids enriched in Mg, Fe and other metals, consistent with signs of low-pH alteration in chondrites. Neutralization of these solutions leads to alkaline Na-rich fluids. Sulfate species have negligible concentrations in closed systems, which remain reduced, especially at elevated pressures created by forming H2 gas. Hydrogen, CO2, and H2O dominate in the gaseous phase, though the abundance of methane cannot be fairly estimated.

Zolotov, Mikhail Yu.

2012-08-01

77

Chemical Characterization of Secondary Organic Aerosol Formed from Atmospheric Aqueous-phase Reactions of Phenolic Compounds  

NASA Astrophysics Data System (ADS)

Phenolic compounds, which are released in significant amounts from biomass burning, may undergo fast aqueous-phase reactions to form secondary organic aerosol (SOA) in the atmosphere. Understanding the aqueous-phase reaction mechanisms of these compounds and the composition of their reaction products is thus important for constraining SOA sources and predicting organic aerosol properties in models. In this study, we investigate the aqueous-phase reactions of three phenols (phenol, guaiacol and syringol) with two oxidants - excited triplet states (3C*) of non-phenolic aromatic carbonyls and hydroxyl radical (OH). By employing four analytical methods including high-resolution aerosol mass spectrometry, total organic carbon analysis, ion chromatography, and liquid chromatography-mass spectrometry, we thoroughly characterize the chemical compositions of the low volatility reaction products of phenols and propose formation mechanisms based on this information. Our results indicate that phenolic SOA is highly oxygenated, with O/C ratios in the range of 0.83-1.03, and that the SOA of phenol is usually more oxidized than those of guaiacol and syringol. Among the three precursors, syringol generates the largest fraction of higher molecular weight (MW) products. For the same precursor, the SOA formed via reaction with 3C* is less oxidized than that formed via reaction with OH. In addition, oxidation by 3C* enhances the formation of higher MW species, including phenolic dimers, higher oligomers and hydroxylated products, compared to reactions initiated by OH, which appear to favor the formation of organic acids. However, our results indicate that the yields of small organic acids (e.g., formate, acetate, oxalate, and malate) are low for both reaction pathways, together accounting for less than 5% of total SOA mass.

Yu, L.; Smith, J.; Anastasio, C.; Zhang, Q.

2012-12-01

78

Removal of methylene blue from aqueous solutions by chemically modified bamboo.  

PubMed

Chemically modified bamboo (CMB) was utilized for removing methylene blue (MB) from aqueous media in the present study. The adsorbent was characterized by Fourier transform infrared (FTIR) spectra and elemental analysis, which confirms that carboxyl groups and diethylenetriamine were successfully introduced into the surface of bamboo. The effects of initial MB concentration (100-900mgL(-1)), contact time (15-315min), the pH of the solution (3-10), temperature (298-318K), adsorbent dosage (0.4-2.6gL(-1)) and salt concentration on the adsorption efficiency of CMB towards MB were investigated. It was found that the adsorption of MB in CMB fits Langmuir mode well, and the maximum adsorption capacity of CMB achieved 606mgg(-1) at 298K, which is much higher than those obtained from previously investigated bioadsorbents. The adsorption kinetics can be described by pseudo-second-order kinetic model, and the adsorption of MB on CMB was an exothermic process. The results of the present study suggest that CMB is an effective biosorbent for removal of organic pollutants from aqueous solutions. PMID:24997922

Guo, Jian-Zhong; Li, Bing; Liu, Li; Lv, Kangle

2014-09-01

79

Morphological and chemical features of nano and macroscale carbons affecting hydrogen peroxide decomposition in aqueous media.  

PubMed

Chemical and structural factors of carbon materials affect their activity in adsorption and surface reactions in aqueous media. Decomposition of hydrogen peroxide studied is a probe reaction for exploring parameters of carbons that might be involved, such as specific surface area, nitrogen and oxygen doping and conformational changes. To date, a detailed comparison of the behavior of carbon nanoscale (Carbon Nanotubes, CNT, Single Layer Graphene Oxide, SLGO) with macroscale (Activated carbons, AC) materials in this reaction has not been forthcoming. Herein, we demonstrate that on their first cycle, ACs in doped and undoped forms outperform all nanoscale carbons tested in the H(2)O(2) decomposition. Among the nanocarbons, nitrogen-doped CNT exhibited the highest activity in this reaction. However, subsequent recycling of each carbon, without chemical regeneration between uses, reveals SLGO exhibits greater reaction rate stability over an extended number of cycles (n>8) than other carbons including nitrogen-doped CNT and ACs. The effects of pH, temperature and concentration on the reaction were analyzed. Quantum-chemical modeling and reaction kinetics analysis reveal key processes likely involved in hydrogen peroxide decomposition and show evidence that the reaction rate is linked to active sites with N-and O-containing functionalities. PMID:21676406

Voitko, Kateryna V; Whitby, Raymond L D; Gun'ko, Vladimir M; Bakalinska, Olga M; Kartel, Mykola T; Laszlo, Krisztina; Cundy, Andrew B; Mikhalovsky, Sergey V

2011-09-01

80

Helical CdS nanowire ropes by simple aqueous chemical growth  

NASA Astrophysics Data System (ADS)

Long and flexible crystalline CdS nanowire ropes were synthesized in bulk quantities via a simple aqueous chemical growth route, which has previously been successful for the growth of short CdS nanorods. The as-grown CdS nanoropes exhibit a unique helically twisted structural feature, as confirmed by both microscopic observation and circular dichroism spectroscopic characterization. The nucleation and growth kinetics of these related CdS one-dimensional(1D) nanocrystals was investigated by monitoring the temporal evolution of the UV-visible spectrum. It was found that cadmium and sulfide monomers were first nucleated out as ``magic number'' CdS nanoclusters in the initial nucleation stage, and then grew to regular sized CdS 1D nanocrystals during the subsequent Ostwald ripening process.

Wang, Wenlong; Bai, Fenglian

2005-11-01

81

In situ Raman study and thermodynamic model of aqueous carbonate speciation in equilibrium with aragonite under subduction zone conditions  

NASA Astrophysics Data System (ADS)

Carbonate minerals may be recycled into the mantle at subduction zones. However, the evolution of carbonate minerals in equilibrium with aqueous fluids as well as the nature of the chemical species of dissolved carbon in the deep crust and mantle at high PT conditions are still unknown. In this study, we report an integrated experimental and theoretical study of the equilibration of CaCO3 minerals with pure water at subduction zone conditions over the pressure and temperature ranges 5–80 kbar and 300–400 °C. The fluid speciation was studied using in situ Raman spectroscopy. The relative amounts of dissolved carbonate and bicarbonate were estimated from the corrected areas of the Raman bands of the carbonate and bicarbonate ions and used to constrain a theoretical thermodynamic model of the fluid speciation and solubility of aragonite. At 300–400 °C, our results indicate that the proportion of dissolved C present as CO2 strongly decreases in fluids in equilibrium with aragonite at P > 10 kbar. CO2 is replaced by HCO3? and CaHCO3+ which predominate until P > 40 kbar, where CO32? and CaCO30 become the dominant C-species. At higher temperatures, the theoretical model indicates that CO2 again becomes a major species in fluids in equilibrium with aragonite depending on the pressure.

Facq, Sébastien; Daniel, Isabelle; Montagnac, Gilles; Cardon, Hervé; Sverjensky, Dimitri A.

2014-05-01

82

Kinetic studies of Cd (II) and Pb (II) ions biosorption from aqueous media using untreated and chemically treated biosorbents.  

PubMed

Untreated and chemically treated Albizia coriaria, Erythrina abyssinica and Musa spp. were studied in batch for uptake of Cd(2+) and Pb(2+) ions at pH 2.0-9.0 and agitation time of 30-390 min. Optimum biosorption conditions were pH 4 for Pb(2+) ions and pH 5 for Cd(2+) ions, contact time was 3.5 hours at 24 ± 1 °C for 10 mg/L biosorbent dosage and initial metal ions concentration of 20 mg/L. Chemical treatment had a 10-17% biosorption efficiency enhancement for Cd(2+) ions and a 1.6-2.3% reduction effect for Pb(2+) ions. The sorption capacities for Cd(2+) and Pb(2+) ions for treated biosorbents were 1.760-1.738 mg g(-1) compared to 1.415-1.539 mg g(-1) for untreated materials. The pseudo second-order model suitably fitted the Cd(2+) and Pb(2+) ions biosorption data with regression coefficients (R(2)) of 0.9784-0.9999. Fitting of the Ho model to the experimental data showed that the biosorption mechanism for both metal ions studied was mainly a chemisorption process. Therefore, treated A. coriaria, E. abyssinica and Musa spp. were potential biosorbents for remediation of Cd(2+) ions and the untreated materials suitable for removing Pb(2+) ions from contaminated aqueous media. PMID:24901616

Bakyayita, G K; Norrström, A C; Nalubega, M; Kulabako, R N

2014-01-01

83

Secondary organic aerosol (trans)formation through aqueous phase guaiacol photonitration: chemical characterization of the products  

NASA Astrophysics Data System (ADS)

One of the largest primary sources of organic aerosol in the atmosphere is biomass burning (BB) (Laskin et al. 2009); in Europe its contribution to annual mean of PM10 is between 3 and 14 % (Maenhaut et al. 2012). During the process of wood burning many different products are formed via thermal degradation of wood lignin. Hardwood burning produces mainly syringol (2,6-dimetoxyphenol) derivatives, while softwood burning exclusively guaiacol (2-methoxyphenol) and its derivatives. Taking into account physical properties of methoxyphenols only, their concentrations in atmospheric waters might be underestimated. So, their aqueous phase reactions can be an additional source of SOA, especially in regions under significant influence of wood combustion. An important class of compounds formed during physical and chemical aging of the primary BBA in the atmosphere is nitrocatechols, known as strong absorbers of UV and Vis light (Claeys et al. 2012). Very recently, methyl-nitrocatechols were proposed as suitable markers for highly oxidized secondary BBA (Iinuma et al. 2010, Kitanovski et al. 2012). In the present work, the formation of SOA through aqueous phase photooxidation and nitration of guaiacol was examined. The key objective was to chemically characterize the main low-volatility products and further to check their possible presence in the urban atmospheric aerosols. The aqueous phase reactions were performed in a thermostated reactor under simulated sunlight in the presence of H2O2 and nitrite. Guaiacol reaction products were first concentrated by solid-phase extraction (SPE) and then subjected to semi-preparative liquid chromatography.The main product compounds were fractionated and isolated as pure solids and their structure was further elucidated by using nuclear magnetic resonance spectroscopy (1H, 13C and 2D NMR) and direct infusion negative ion electro-spray ionization tandem mass spectrometry (( )ESI-MS/MS). The main photonitration products of guaiacol (4-nitroguaiacol, 6-nitroguaiacol and 4,6-dinitroguaiacol) were examined for their presence in winter aerosol samples by using an optimized HPLC-(?)ESI-MS/MS. 4-nitroguaiacol and 4,6-dinitroguaiacol were unambiguously identified in winter PM10 from Ljubljana, Slovenia, whereas the absence of 6-nitroguaiacol was further explained with the help of long-term reaction monitoring. To our knowledge, our study represents the first report on the identification of 4,6-dinitroguaiacol in ambient aerosols. Laskin, A. et al. (2009) Environ. Sci. Technol. 43, 3764-3771. Maenhaut, W. et al. (2012) Sci. Tot. Environ. 437, 226-236. Claeys, M. et al. (2012) Environ. Chem. 9, 273-284. Iinuma, Y. et al. (2010) Environ. Sci. Technol. 44, 8453-8459. Kitanovski, Z. et al. (2012)J. Chromatogr. A 1268, 35-43.

Grgi?, Irena; Kitanovski, Zoran; Krofli?, Ana; ?usak, Alen

2014-05-01

84

Aqueous Dissolution of Silver Iodide and Associated Iodine Release Under Reducing Conditions with Sulfide  

SciTech Connect

Aqueous dissolution tests of silver iodide (AgI) were performed in Na{sub 2}S solutions in order to evaluate, empirically, dissolution of AgI to release iodine under reducing conditions with sulfide. The results indicated that AgI dissolves to release iodine being controlled by mainly precipitation of Ag{sub 2}S. However, the dissolution of AgI can be depressed to proceed, and the thermodynamic equilibrium cannot be attained easily. Solid phase analysis for the reacted AgI suggested that a thin layer of solid silver forming at AgI surface may evolve to be protective against transportation of reactant species, which can lead to the depression in the dissolution of AgI. (authors)

Yaohiro Inagaki; Toshitaka Imamura; Kazuya Idemitsu; Tatsumi Arima [Kyushu University, Fukuoka, 819-0395 (Japan); Osamu Kato [Kobe Steel Inc., Kobe, 657-0845 (Japan); Hidekazu Asano; Tsutomu Nishimura [RWMC, Tokyo, 105-0001 (Japan)

2007-07-01

85

In-cloud processes of methacrolein under simulated conditions - Part 1: Aqueous phase photooxidation  

NASA Astrophysics Data System (ADS)

The photooxidation of methacrolein was studied in the aqueous phase under simulated cloud droplet conditions. The obtained rate constant of OH-oxidation of methacrolein at 6°C in unbuffered solutions was 5.8 (±0.9)×109 M-1 s-1. This kinetic study showed that the oxidation proceeds mainly by OH-addition on the C=C bond. This was confirmed by the mechanism established on the study of the reaction products (at 25°C in unbuffered solutions) where methylglyoxal, formaldehyde, hydroxyacetone and acetic acid/acetate were the main reaction products. An upper limit for the total carbon yield was estimated to range from 53 to 85%, indicating that some reaction products remain unidentified. A possible source of this mismatch is the formation of higher molecular weight compounds as primary reaction products which are presented in El Haddad et al. (2009) and Michaud et al. (2009).

Liu, Y.; El Haddad, I.; Scarfogliero, M.; Nieto-Gligorovski, L.; Temime-Roussel, B.; Quivet, E.; Marchand, N.; Picquet-Varrault, B.; Monod, A.

2009-03-01

86

Fate of hydraulic fracturing chemicals under down-hole conditions  

NASA Astrophysics Data System (ADS)

Hydraulic fracturing is a method to increase the yield of oil and natural gas extraction from unconventional rock formations. The process of hydrofracturing occurs via injecting water, sand, and chemicals into the production well and subjecting this mixture to high pressures to crack the rock shale, allowing increased amounts of gas and oil to seep out of the target formation. Typical constituents of the chemical mixtures are biocides, which are applied to inhibit growth of sulfate reducing bacteria in order to prevent pipe corrosion and production of hazardous gases. However, very little is known about the persistence, fate, and activity of biocides when subjected to the high temperatures and pressures of down-hole conditions. Thus, the objective of this talk is to present data from ongoing experiments focused on determining the fate of biocides commonly used for hydraulic fracturing under conditions simulating down-hole environments. Using stainless steel reactors, the high pressures and temperatures of down-hole conditions in the Marcellus shale are simulated, while concentration, speciation, and degradation of priority biocides are observed as a function of time, using primarily LC/MS techniques. The impact of water quality, shale, temperature, and pressure on the transformation kinetics and pathways of biocides will be discussed. Finally, field samples (both sediments and flowback brine) from the Marcellus shale are analyzed to verify that our lab simulations mirror real-life conditions and results.

Blotevogel, J.; Kahrilas, G.; Corrin, E. R.; Borch, T.

2013-12-01

87

Corrosion of aluminium in the aqueous chemical environment of a loss-of-coolant accident at a nuclear power plant  

Microsoft Academic Search

Aluminium corrosion is a significant concern in the aqueous chemical environment of the reactor containment building following a hypothetical loss-of-coolant accident (LOCA) at a nuclear power plant. Aluminium corrosion may lead to the formation of precipitates that can, in combination with insulation debris, block the recirculation sump screens. This study investigated aluminium corrosion experimentally at both bench and pilot scale

Dong Chen; Kerry J. Howe; Jack Dallman; Bruce C. Letellier

2008-01-01

88

Temporal Changes in Aqu/C60 Physical-Chemical, Deposition, and Transport Characteristics in Aqueous Systems  

EPA Science Inventory

Little is known about how temporal changes in the physical?chemical properties of C60 aggregates formed in aqueous systems (termed aqu/C60) can impact transport pathways contributing to ecological exposures. In this study three aqu/C60 suspensions of short-term (100 days), interm...

89

Chemically induced compaction bands: Triggering conditions and band thickness  

NASA Astrophysics Data System (ADS)

compaction band formation, various mechanisms can be involved at different scales. Mechanical and chemical degradation of the solid skeleton and grain damage are important factors that may trigger instabilities in the form of compaction bands. Here we explore the conditions of compaction band formation in quartz- and carbonate-based geomaterials by considering the effect of chemical dissolution and grain breakage. As the stresses/deformations evolve, the grains of the material break, leading to an increase of their specific surface. Consequently, their dissolution is accelerated and chemical softening is triggered. By accounting for (a) the mass diffusion of the system, (b) a macroscopic failure criterion with dissolution softening, and (c) the reaction kinetics at the microlevel, a model is proposed and the conditions for compaction instabilities are investigated. Distinguishing the microscale (grain level) from the macrolevel (representative elementary volume) and considering the heterogeneous microstructure of the representative elementary volume, it is possible to discuss the thickness and periodicity of compaction bands. Two case studies are investigated. The first one concerns a sandstone rock reservoir which is water flooded and the second one a carbonate rock in which CO2 is injected for storage. It is shown that compaction band instabilities are possible in both cases.

Stefanou, Ioannis; Sulem, Jean

2014-02-01

90

IMPROVED DECONTAMINATION: INTERFACIAL, TRANSPORT, AND CHEMICAL PROPERTIES OF AQUEOUS SURFACTANT CLEANERS  

EPA Science Inventory

This investigation is focused on decontamination using environmentally benign aqueous solutions, specifically the removal of organics and associated radionuclide and heavy metal contaminants by synthetic surfactants. Aqueous-based solutions promise several advantages for deconta...

91

QUANTITATIVE ANALYSIS OF 68 POLAR COMPOUNDS FROM TEN CHEMICAL CLASSES BY DIRECT AQUEOUS INJECTION GAS CHROMATOGRAPHY  

EPA Science Inventory

Porous polymer packings have been used successfully in many applications of direct aqueous injection gas chromatography. The authors have expanded the use of aqueous injection to the quantitative analysis of 68 alcohols, acetates, ketones, ethers, sulfides, aldehydes, diols, dion...

92

Investigations on foamability of surface-chemically pure aqueous solutions of functionalized alkylaldonamides.  

PubMed

The foamability of the aqueous solutions of functionalized, surface-chemically pure surfactants of the nonionic saccharide-type: N,N-di-n-alkylaldonamides, N-alkyl-N-(2-hydroxyethyl)aldonamides, and N-cycloalkylaldonamides, derivatives of D-glucono-1,5-lactone and/or D-glucoheptono-1,4-lactone, were investigated. The approach of Lunkenheimer and Ma?ysa for the characterization of the foamability and foam stability of these surfactant solutions was applied for these investigations. Using standard parameters related to the different physical stages of the foaming process, foam stability can be described in a simple and easy manner. In general, the investigated alkylaldonamides form foams of medium stability. However, for some homologues a transition from unstable to stable foam systems is observed with increasing concentration. Modifications of the molecular structure of the alkylaldonamides are distinctly reflected in their foam properties. This fact concerns not only changes of the hydrophobic moiety and its functionalization but also slight variations of the saccharide residue. Each homologous series reveals an exceptional foam behavior. In the case of the N,N-di-n-alkylaldonamides the increase of the n-alkyl chain length is accompanied by an increase of the foam stability. The aqueous solutions of the N-alkyl-N-(2-hydroxyethyl)aldonamides reveal most favorable foaming properties for homologues with average alkyl chain lengths. Moreover, it was found that the occurrence of a phase transition in the adsorption layers of the N-cyclooctylgluconamides previously observed by surface tension and surface potential measurements is also remarkably reflected in their foam stability. PMID:16154577

Pi?akowska-Pietras, Dorota; Lunkenheimer, Klaus; Piasecki, Andrzej

2006-02-15

93

Comparison of the flow properties of aqueous suspension corticosteroid nasal sprays under differing sampling conditions.  

PubMed

Many aqueous suspension corticosteroid nasal sprays become less viscous when shaken and sprayed, then return to a more viscous state after application. This time-dependent, reversible loss of viscosity under shear (e.g., shaking or spraying) can be quantified in the rheological property of thixotropy. The flow properties of 5 corticosteroid nasal sprays were measured over a range of shear rates. The formulations tested included Nasonex, Vancenase AQ, Nasacort AQ, Rhinocort Aqua, and Flonase. The yield stress values, as well as an estimate of thixotropy, were compared by using three different sampling techniques, including one that simulated patient use (shaking for 30 sec, spraying, and immediately transferring the sample to the rheometer). The rheological properties of all products indicated that when initially shaken and dispensed, they flowed more freely, followed by recovery of viscosity that would likely inhibit the suspensions from flowing out of the nasal cavity. Under all three tested conditions, Nasonex exhibited the highest yield stress, the largest apparent initial and final viscosities, and the highest apparent thixotropy. The study protocol that simulated patient-use conditions produced the following rank order of measured thixotropy: Nasonex > Flonase > Vancenase AQ > Rhinocort Aqua > Nasacort AQ. The thixotropy of Nasonex was 3.4 to 21.4 times greater and the final viscosity was 3.2 to 17.4 times greater than the values of the other tested products. PMID:14606664

Sharpe, S A; Sandweiss, V; Tuazon, J; Giordano, M; Witchey-Lakshmanan, L; Hart, J; Sequeira, J

2003-10-01

94

Oxidative degradation of organic pollutants in aqueous solution using zero valent copper under aerobic atmosphere condition.  

PubMed

Oxidative degradation of organic pollutants and its mechanism were investigated in aqueous solution using zero valent copper (ZVC) under aerobic atmosphere condition. Diethyl phthalate (DEP) was completely oxidized after 120min reaction by ZVC at initial pH 2.5 open to the air. DEP degradation followed the pseudo-first-order kinetics after the lag period, and the degradation rate of DEP increased gradually with the increase of ZVC dosage, and the decrease of initial pH from 5.8 to 2.0. ZVC required a shorter induction time and exhibited persistent oxidation capacity compared to that of zero valent iron and zero valent aluminium. The mechanism investigation showed that remarkable amount of Cu(+)/Cu(2+) and H2O2 were formed in ZVC acidic system, which was due to the corrosive dissolution of ZVC and the concurrent reduction of oxygen. The addition of tert-butanol completely inhibited the degradation of DEP and the addition of Fe(2+) greatly enhanced the degradation rate, which demonstrated that hydroxyl radical was mainly responsible for the degradation of DEP in ZVC acidic system under aerobic atmosphere condition, and the formation of hydroxyl radical was attributed to the Fenton-like reaction of in situ formed Cu(+) with H2O2. PMID:24857902

Wen, Gang; Wang, Sheng-Jun; Ma, Jun; Huang, Ting-Lin; Liu, Zheng-Qian; Zhao, Lei; Xu, Jin-Lan

2014-06-30

95

Chemical reactions in viscous liquids under space conditions  

NASA Astrophysics Data System (ADS)

A long-term human flight needs a large-size space ships with artificial self-regulating ecological life-support system. The best way for creation of large-size space ship is a synthesis of light construction on Earth orbit, that does not need a high energy transportation carriers from Earth surface. The construction can be created by the way of chemical polymerisation reaction under space environment. But the space conditions are very specific for chemical reactions. A high vacuum, high energy particles, X-rays, UV- and VUV-irradiations, atomic oxygen, microgravity have a significant influence on chemical reactions. Polymerisation reactions in liquid active mixture were studied in simulated space environment. The epoxy resins based on Bisphenol A and amine curing agents were investigated under vacuum, microwave plasma discharge and ion beam. An acceleration of polymerisation reaction with free radicals formation was observed. The polymerisation reaction can be carried out under space environment. The study was supported by Alexander von Humboldt Foundation (A. Kondyurin) and European Space Agency, ESTEC (contract 17083/03/NL/Sfe "Space Environmental Effects on the Polymerisation of Composite Structures").

Kondyurin, A.; Lauke, B.; Richter, E.

96

Effects of pressure on aqueous chemical equilibria at subzero temperatures with applications to Europa  

USGS Publications Warehouse

Pressure plays a critical role in controlling aqueous geochemical processes in deep oceans and deep ice. The putative ocean of Europa could have pressures of 1200 bars or higher on the seafloor, a pressure not dissimilar to the deepest ocean basin on Earth (the Mariana Trench at 1100 bars of pressure). At such high pressures, chemical thermodynamic relations need to explicitly consider pressure. A number of papers have addressed the role of pressure on equilibrium constants, activity coefficients, and the activity of water. None of these models deal, however, with processes at subzero temperatures, which may be important in cold environments on Earth and other planetary bodies. The objectives of this work were to (1) incorporate a pressure dependence into an existing geochemical model parameterized for subzero temperatures (FREZCHEM), (2) validate the model, and (3) simulate pressure-dependent processes on Europa. As part of objective 1, we examined two models for quantifying the volumetric properties of liquid water at subzero temperatures: one model is based on the measured properties of supercooled water, and the other model is based on the properties of liquid water in equilibrium with ice. The relative effect of pressure on solution properties falls in the order: equilibrium constants(K) > activity coefficients (??) > activity of water (aw). The errors (%) in our model associated with these properties, however, fall in the order: ?? > K > aw. The transposition between K and ?? is due to a more accurate model for estimating K than for estimating ??. Only activity coefficients are likely to be significantly in error. However, even in this case, the errors are likely to be only in the range of 2 to 5% up to 1000 bars of pressure. Evidence based on the pressure/temperature melting of ice and salt solution densities argue in favor of the equilibrium water model, which depends on extrapolations, for characterizing the properties of liquid water in electrolyte solutions at subzero temperatures, rather than the supercooled water model. Model-derived estimates of mixed salt solution densities and chemical equilibria as a function of pressure are in reasonably good agreement with experimental measurements. To demonstrate the usefulness of this low-temperature, high-pressure model, we examined two hypothetical cases for Europa. Case 1 dealt with the ice cover of Europa, where we asked the question: How far above the putative ocean in the ice layer could we expect to find thermodynamically stable brine pockets that could serve as habitats for life? For a hypothetical nonconvecting 20 km icy shell, this potential life zone only extends 2.8 km into the icy shell before the eutectic is reached. For the case of a nonconvecting icy shell, the cold surface of Europa precludes stable aqueous phases (habitats for life) anywhere near the surface. Case 2 compared chemical equilibria at 1 bar (based on previous work) with a more realistic 1460 bars of pressure at the base of a 100 km Europan ocean. A pressure of 1460 bars, compared to 1 bar, caused a 12 K decrease in the temperature at which ice first formed and a 11 K increase in the temperature at which MgSO4. 12H2O first formed. Remarkably, there was only a 1.2 K decrease in the eutectic temperatures between 1 and 1460 bars of pressure. Chemical systems and their response to pressure depend, ultimately, on the volumetric properties of individual constituents, which makes every system response highly individualistic. Copyright ?? 2005 Elsevier Ltd.

Marion, G. M.; Kargel, J. S.; Catling, D. C.; Jakubowski, S. D.

2005-01-01

97

Evaluation of an evanescent fiber optic chemical sensor for monitoring aqueous volatile organic compounds  

SciTech Connect

Linear chemometric algorithms were used to model the quantitative response of an evanescent fiber optic chemical sensor in aqueous mixtures with concentrations between 20 and 300 ppm. Four data sets were examined with two different experimental arrangements. Two data sets contained trichloroethene, 1,1,2 trichloroethane, and toluene. Partial Least Squares, PLS, and Principal Component Regression, PCR, algorithms performed comparably on these calibration sets with cross-validated root mean squared errors of prediction (RMSEP) for trichloroethene, 1,1,1 trichloroethane, and toluene of approximately 26, 29 and 22 ppm, respectively. The third data set contained trichloroethene, 1,1,2 trichloroethane, toluene, and chloroform and the fourth contained these four analytes as well as tetrachloroethene. Again, both chemometric algorithms performed comparably on a given data set with RMSEP for trichloroethene, 1,1,2 trichloroethane, toluene, and chloroform of approximately 6, 6, 9, and 16 ppm from the first set, and 7, 11, 13, and 31 ppm from the second set with tetrachloroethene RMSEP of 31 ppm. The decrease in the quantitative performance of the sensor for modeling toluene and chloroform upon addition of tetrachloroethene to the sample solutions is due to increased cladding absorption features in the spectral response matrix. These features overlap with the analyte absorption features of toluene and chloroform. These results suggest one of the limitations with this type of sensing format.

Blair, D.S.

1997-04-01

98

Quantum chemical studies of the hydration of Sr2+ in vacuum and aqueous solution.  

PubMed

The geometric structures of gas-phase Sr(2+) hydrates are calculated quantum chemically by using hybrid (B3LYP) and meta-GGA (TPSS) density functional theory, and a range of thermodynamic data (including sequential bond enthalpies, entropies and free energies for the reactions Sr(2+)(H(2)O)(n-1)+H(2)O?Sr(2+)(H(2)O)(n)) are shown to be in excellent agreement with experiment. When the number of coordinating water molecules exceeds six, such that water begins to occupy the second solvation shell, it is found that detailed analysis based on both geometrical and conformational entropy is required in order to confidently identify the experimentally observed structures. The significant increase in coordination number observed experimentally between the gas- and aqueous-phase species is successfully reproduced, as is the first solvation shell geometry. Inaccurate second shell geometries imply that larger model systems may be required to achieve agreement with experiment. Candidate species for on-going computational studies of the interaction of hydrated Sr(2+) with brucite surfaces have been identified. PMID:21433126

Kerridge, Andrew; Kaltsoyannis, Nikolas

2011-04-26

99

[Long-term preservation of DNA in aqueous solutions in the presence of the chemical analogues of microbial autoregulators].  

PubMed

The fact of long-term preservation of the physicochemical properties of DNA molecules in aqueous solutions in complexes with methylresorcinol, hexylresorcinol, and tyrosol, the chemical analogues of microbial autoregulators (d1 factors) from the group of alkylhydroxybenzenes (AOB), was established. Compared to the control variants of storage of aqueous DNA solutions, the AOB influence consisted in the sum of correlating effects: the prevention of DNA degradation (according to spectrophotometric parameters) and the preservation of its viscous characteristics and electrophoretic mobility. The initial DNA properties were preserved to the greatest degree in the presence of hexylresorcinol, the compound with the longest alkyl radical. Possible mechanisms of the protective action of alkylhydroxybenzenes in relation to DNA are discussed, namely, the prevention of its hydrolysis due to isolation from the aqueous environment and maintaining DNA stability in the dormant forms of microorganisms. PMID:17091589

Davydova, O K; Deriabin, D G; El'-Registan, G I

2006-01-01

100

Dynamic nuclear polarization of 13C in aqueous solutions under ambient conditions.  

PubMed

The direct enhancement of the (13)C NMR signal of small molecules in solution through Overhauser-mediated dynamic nuclear polarization (DNP) has the potential to enable studies of systems where enhanced signal is needed but the current dissolution DNP approach is not suitable, for instance if the sample does not tolerate a freeze-thaw process or if continuous flow or rapid re-polarization of the molecules is desired. We present systematic studies of the (13)C DNP enhancement of (13)C-labeled small molecules in aqueous solution under ambient conditions, where we observe both dipolar and scalar-mediated enhancement. We show the role of the three-spin effects from enhanced protons on (13)C DNP through DNP experiments with and without broadband (1)H decoupling and by comparing DNP results with H(2)O and D(2)O. We conclude that the efficiency of (13)C Overhauser DNP in small molecules strongly depends on the distance of closest approach between the electron and (13)C nucleus, the presence of a scalar contribution to the coupling factor, and the magnitude of the three-spin effect due to adjacent polarized protons. The enhancement appears to depend less on the translational dynamics of the (13)C-labeled small molecules and radicals. PMID:19783462

Lingwood, Mark D; Han, Songi

2009-12-01

101

Dynamic nuclear polarization of 13C in aqueous solutions under ambient conditions  

NASA Astrophysics Data System (ADS)

The direct enhancement of the 13C NMR signal of small molecules in solution through Overhauser-mediated dynamic nuclear polarization (DNP) has the potential to enable studies of systems where enhanced signal is needed but the current dissolution DNP approach is not suitable, for instance if the sample does not tolerate a freeze-thaw process or if continuous flow or rapid re-polarization of the molecules is desired. We present systematic studies of the 13C DNP enhancement of 13C-labeled small molecules in aqueous solution under ambient conditions, where we observe both dipolar and scalar-mediated enhancement. We show the role of the three-spin effects from enhanced protons on 13C DNP through DNP experiments with and without broadband 1H decoupling and by comparing DNP results with H 2O and D 2O. We conclude that the efficiency of 13C Overhauser DNP in small molecules strongly depends on the distance of closest approach between the electron and 13C nucleus, the presence of a scalar contribution to the coupling factor, and the magnitude of the three-spin effect due to adjacent polarized protons. The enhancement appears to depend less on the translational dynamics of the 13C-labeled small molecules and radicals.

Lingwood, Mark D.; Han, Songi

2009-12-01

102

Optimum conditions for composites fiber coating by chemical vapor infiltration  

SciTech Connect

A combined analytical and numerical method is employed to optimize process conditions for composites fiber coating by chemical vapor infiltration (CVI). For a first-order deposition reaction, the optimum pressure yielding the maximum deposition rate at a preform center is obtained in closed form and is found to depend only on the activation energy of the deposition reaction, the characteristic pore size, and properties of the reactant and product gases. It does not depend on the preform specific surface area, effective diffusivity or preform thickness, nor on the gas-phase yield of the deposition reaction. Further, this optimum pressure is unaltered by the additional constraint of a prescribed deposition uniformity. Optimum temperatures are obtained using an analytical expression for the optimum value along with numerical solutions to the governing transport equations. These solutions account for both diffusive and advective transport, as well as both ordinary and Knudsen diffusion. Sample calculations are presented for coating preform fibers with boron nitride.

Griffiths, S.K.; Nilson, R.H.

1997-04-01

103

Optimum conditions for composites fiber coating by chemical vapor infiltration  

SciTech Connect

A combined analytical and numerical method is employed to optimize process conditions for composites fiber coating by chemical vapor infiltration. For a first-order deposition reaction, the optimum pressure yielding the maximum deposition rate at a preform center is obtained in closed form and is found to depend only on the activation energy of the deposition reaction, the characteristic pore size, and properties of the reactant and product gases. It does not depend on the preform specific surface area, effective diffusivity or preform thickness, nor on the gas-phase yield of the deposition reaction. Further, this optimum pressure is unaltered by the additional constraint of a prescribed deposition uniformity. Optimum temperatures are obtained using an analytical expression for the optimum value along with numerical solutions to the governing transport equations. These solutions account for both diffusive and advective transport, as well as both ordinary and Knudsen diffusion. Sample calculations are presented for coating preform fibers with boron nitride.

Griffiths, S.K.; Nilson, R.H. [Sandia National Labs., Livermore, CA (United States)

1998-04-01

104

Biological and chemical phosphorus solubilization from pyrolytical biochar in aqueous solution.  

PubMed

Biochar, a massive byproduct of biomass pyrolysis during biofuel generation, is a potential P source for the mitigation of P depletion. However, the chemical and biological effect of the release of P from biochar is still unclear. In this study, two types of Lysinibacillus strains (Lysinibacillussphaericus D-8 and Lysinibacillus fusiformis A-5) were separated from a sediment and their P-solubilizing characteristics to biochar was first reported. Compared with the bacterial mixture W-1 obtained from a bioreactor, the introduction of A-5 and D-8 significantly improved P solubilization. The release of P from biochar by A-5 and D-8 reached 54% and 47%, respectively, which is comparable to that under rigorous chemical conditions. SEM images and XPS spectra demonstrated that the physicochemical properties of the biochar surface have changed in the process which may be caused by the activities of the microbes. PMID:25065807

He, Hui; Qian, Ting-Ting; Liu, Wu-Jun; Jiang, Hong; Yu, Han-Qing

2014-10-01

105

Improved Decontamination: Interfacial Transport, and Chemical Properties of Aqueous Surfactant Cleaners  

SciTech Connect

The aqueous cleaning parameter of interest in this series of studies was the pH of the aqueous cleaning solution. A sessile droplet of industrial quench oil was analyzed to determine the effect of varied solution pH its removal from a stainless steel surface.

Robert M. Counce

2003-05-30

106

Sorption for removing Lauths Violets in aqueous solutions by chemically crosslinked poly(AAm-co-SA) hydrogels  

Microsoft Academic Search

Summary Superswelling poly(acrylamide-co-sodium acrylate) hydrogels were prepared by free radical polymerization in aqueous solution of acrylamide (AAm) with sodium acrylate (SA) as comonomer and a multifunctional crosslinker such as trimethylolpropane triacrylate (TMPTA). In the sorption studies, binding of a cationic dye such as Lauths Violet (Thionin, LV) onto chemically crosslinked poly(AAm-co-SA) hydrogels has been investigated. Sorption of LV onto poly(AAm-co-SA)

Erdener Karada?; Ömer Bar?? Üzüm

2005-01-01

107

Uptake of Basic Blue 17 from aqueous solutions by using chemically crosslinked polyelectrolyte AAm\\/AASS hydrogels  

Microsoft Academic Search

In this study, the removal of a cationic thiazin dye such as Basic Blue 17 (Toluidin Blue, BB 17) by chemically crosslinked\\u000a acrylamide (AAm)\\/acrylic acid sodium salt (AASS) hydrogels was investigated. Super water retainer AAm\\/AASS hydrogels with\\u000a various compositions were prepared from ternary mixtures of AAm, AASS and water by free radical polymerization in aqueous\\u000a solution using multifunctional crosslinkers such

Ömer Bar?? Üzüm; Erdener Karada?

2006-01-01

108

Control of dual stimuli-responsive vesicle formation in aqueous solutions of single-tailed ferrocenyl surfactant by varying pH and redox conditions.  

PubMed

This paper reports a method to control the formation and disruption of vesicles from a novel single-tailed surfactant (11-ferrocenylundecylammonium bromide, 11-FAB), which contains two stimuli-responsive groups corresponding to pH variation and redox reaction conditions, by external stimuli. Although 11-FAB is a single-tailed surfactant, pure 11-FAB spontaneously forms vesicles in water. Microscopic observations of 2.5 mM aqueous solutions of pure 11-FAB (pH = 5.2) show that a number of 11-FAB vesicles are giant, with diameters of 10-30 ?m. The disruption of vesicles is observed in aqueous 11-FAB solutions under basic conditions. The vesicles are then reformed under acidic conditions. Reduced 11-FAB also forms large vesicles in electrolyte solutions. These vesicles are disrupted by electrochemical oxidation and reformed by subsequent chemical reduction. This reversible disruption and reformation of vesicles is attributed to the drastic change in the molecular structure of 11-FAB. To our knowledge, this is the first report of control over the formation and disruption of vesicles using two stimuli responses. PMID:24492378

Hata, Shinichi; Takahashi, Hiro; Takahashi, Yutaka; Kondo, Yukishige

2014-02-26

109

Modeling aqueous ozone/UV process using oxalic acid as probe chemical.  

PubMed

A kinetic model that describes the removal of organic pollutants by an ozone/UV process is described. Oxalic acid, which reacts with a very low rate constant with ozone and relatively high rate constant with hydroxyl radical (OH*), was used as the probe chemical to model the process. The model was verified by experimental data on concentrations of oxalic acid and hydrogen peroxide (H202) under various experimental conditions, i.e., ozone gas dosage, UV light intensity, and varying oxalic acid concentrations. PMID:16295862

Garoma, Temesgen; Gurol, Mirat D

2005-10-15

110

Optimization for the removal of orthophosphate from aqueous solution by chemical precipitation using ferrous chloride.  

PubMed

The precipitation reaction between the orthophosphate and Fe2+ ions was studied to describe the optimum condition for the removal of orthophosphate from the aqueous solution. The effects of pH, Fe:P molar ratio, and alkalinity were evaluated for the initial orthophosphate concentrations in the range from 1.55 to 31.00 mg/L - PO4(3-) -P. The optimum pH was found to be 8.0 in all orthophosphate concentration ranges. When the stoichiometric moles of Fe2+ were added, the removal efficiencies were significantly less than the theoretical values. It is likely that the precipitation of Fe(OH)2(s) is partially formed. For the initial orthophosphate concentration of 3.10 mg/L PO4(3-) -P or greater, the removal efficiencies with the Fe:P molar ratio of 3.0:1.0 approached to the theoretical values, yielding greater than 98.5%. If the molar ratio of Fe:P was great enough, the precipitation reaction was completed within 1 h. As the alkalinity increases, the experimental removal efficiencies were significantly greater than the theoretical values. This is because the formation of vivianite is favoured over FeCO3(s). Finally, it was demonstrated that the orthophosphate (1.40-6.80 mg/L PO4(3-) -P) in the secondary effluents from wastewater treatment plants was effectively removed by dosing sufficient amount of Fe2+ ions. PMID:24956757

An, Ju-Suk; Back, Ye-Ji; Kim, Ki-Chul; Cha, Ran; Jeong, Tae-Young; Chung, Hyung-Keun

2014-08-01

111

Chemical evolution: The mechanism of the formation of adenine under prebiotic conditions  

PubMed Central

Fundamental building blocks of life have been detected extraterrestrially, even in interstellar space, and are known to form nonenzymatically. Thus, the HCN pentamer, adenine (a base present in DNA and RNA), was first isolated in abiogenic experiments from an aqueous solution of ammonia and HCN in 1960. Although many variations of the reaction conditions giving adenine have been reported since then, the mechanistic details remain unexplored. Our predictions are based on extensive computations of sequences of reaction steps along several possible mechanistic routes. H2O- or NH3-catalyzed pathways are more favorable than uncatalyzed neutral or anionic alternatives, and they may well have been the major source of adenine on primitive earth. Our report provides a more detailed understanding of some of the chemical processes involved in chemical evolution, and a partial answer to the fundamental question of molecular biogenesis. Our investigation should trigger similar explorations of the detailed mechanisms of the abiotic formation of the remaining nucleic acid bases and other biologically relevant molecules.

Roy, Debjani; Najafian, Katayoun; von Rague Schleyer, Paul

2007-01-01

112

Mutagenic effect by phenylalanine during gamma-irradiation of plasmid DNA in aqueous solution under oxic conditions.  

PubMed

Irradiation of DNA in aqueous solution or in cells with gamma-rays results in different mutational spectra, indicating that in both situations different patterns of DNA damages are induced. One of the causes for these different types of damages might be the formation of secondary, organic radicals, if cells are irradiated. Some organic compounds, including the amino acid phenylalanine, are well known to produce radicals during irradiation. Under oxic conditions these secondary radicals react with oxygen, thus forming peroxyl radicals which can be very harmful to DNA, and which may, therefore, induce DNA damage leading to mutations. This study examines the influence of the presence of phenylalanine during gamma-irradiation of DNA in aqueous solution under oxic conditions. The results indicate that the formation of phenylalanine radicals influences the types of induced mutations in the gamma-radiation-induced mutation spectrum. The most prominent difference is the increase in G:C to T:A transversions and the decrease in G:C to A:T transitions in the presence of phenylalanine. Further, it appears that the gamma-radiation-induced mutation spectrum after irradiation of DNA in aqueous solution is more comparable to the intracellular gamma-radiation-induced mutation spectrum in E. coli cells, if phenylalanine is present during irradiation. Therefore, these results suggest that the presence of phenylalanine during irradiation of DNA in aqueous solution gives a better impression of gamma-radiation-induced mutations in bacterial systems than water only. PMID:11035161

Reitsma-Wijker, C A; Slotman, B J; Lafleur, M V

2000-11-01

113

Kinetics of Organic Transformations Under Mild Aqueous Conditions: Implications for the Origin of Life and Its Metabolism  

NASA Technical Reports Server (NTRS)

The rates of thermal transformation of organic molecules containing carbon, hydrogen, and oxygen were systematically examined in order to identify the kinetic constraints that governed origin-of-life organic chemistry under mild aqueous conditions. Arrhenius plots of the kinetic data were used to estimate the reaction half-life at 50 C, and to reveal the effect of functional groups on reactivity. This survey showed that hydrocarbons and organic substances containing a single oxygenated group were kinetically the most stable (i. e. acetate decarboxylation half-life was l0(exp 18) years at 50 C); whereas, organic substances containing two oxygenated groups in which one group was a beta-positioned carbonyl group were the most reactive (i. e. acetoacetate decarboxylation half-life was l0(exp-2) years at 50 C). Of all functional groups the beta-positioned carbonyl group (aldehyde or ketone) was the strongest activating group, giving rates of reaction that were up to 10(exp 24)-times faster than rates of similar molecules lacking the beta-carbonyl group. From this knowledge of organic reactivity and the inherent constraints of autocatalytic processes, we concluded that an origins-of-life process based on autocatalytic transformation of C,H,O-substrates was constrained to using the most reactive organic molecules that contain alpha- or beta-carbonyl groups, since small autocatalytic domains of plausible catalytic power that used less reactive substrates could not carry out chemical transformations fast enough to prevent catastrophic efflux (escape) of reaction intermediates. Knowledge of the kinetics of organic transformations is useful, not only in constraining the chemistry of the earliest autocatalytic process related to the origin of life, but also in establishing the relative reactivity of organic molecules on the early Earth and other planets that may or may not be related to the origin of life.

Weber, Arthur L.

2003-01-01

114

Experimental study of the influence of chemical reactions on convective dissolution of CO2 in aqueous solutions.  

NASA Astrophysics Data System (ADS)

Within the global context of climate change, carbon dioxide (CO2) sequestration into deep saline aquifers is one of the technologies being considered in order to tackle the accumulation of anthropogenic CO2 in the atmosphere. Upon injection of CO2 into these porous geological formations, the less dense CO2 rises above the aqueous phase, spreads laterally under the upper impermeable cap rock and starts to dissolve into the underlying brine. This leads to a buoyantly unstable stratification of denser CO2-enriched brine on top of less dense brine, which can give rise to density-driven convective fingering in the fluid. This hydrodynamic instability is a favorable process for CO2 sequestration as it accelerates the mixing of CO2 into the aqueous phase and therefore enhances the safety of the storage in the saline aquifer (by reducing the risks of leaks of CO2 to the atmosphere). The influence of chemical reactions and of the physico-chemical characteristics of the geological reservoir on the development of this instability is, however, still not completely understood. In this context, we study experimentally in a laboratory-scale reactor the influence of chemical reactions on convective fingering occurring during dissolution of CO2 in reactive aqueous solutions. Experiments are performed in Hele-Shaw cells (constructed of two vertical transparent plates separated by a thin gap) in which gaseous CO2 at atmospheric pressure flows above aqueous solutions containing chemical reactants. Dynamics occurring within the transparent fluids are visualized by Schlieren techniques, which track dynamical changes in refractive index related to density gradients in the solutions. We show that in some cases the convection can be enhanced by chemical reactions as they accelerate the development of the fingers, shorten their onset time and increase the number of fingers. In particular, we show that the presence of a color indicator (for instance bromocresol green) in the aqueous solution can affect the fingering dynamics. Color indicators should therefore be used with caution in this kind of study.

Thomas, Carelle; Lemaigre, Lorena; Haudin, Florence; Zalts, Anita; D'Onofrio, Alejandro; De Wit, Anne

2014-05-01

115

Equilibrium hydrate formation conditions for hydrogen sulfide, carbon dioxide, and ethane in aqueous solutions of ethylene glycol and sodium chloride  

SciTech Connect

Natural gas components such as hydrogen sulfide, carbon dioxide, and ethane form gas hydrates of structure I under suitable temperature and pressure conditions. Information on such conditions is vital to the oil and gas industry in order to design and operate processing equipment and pipelines so that hydrate formation is avoided. Incipient equilibrium hydrate formation conditions for hydrogen sulfide, carbon dioxide, and ethane in aqueous solutions of ethylene glycol and sodium chloride were experimentally obtained in the temperature range 264--290 K and the pressure range 0.23--3.18 MPa. A variable-volume sapphire cell was used for the measurements.

Majumdar, A.; Mahmoodaghdam, E.; Bishnoi, P.R.

2000-02-01

116

CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

117

The Influence of Conditions on Synthesis Hydroxyapatite By Chemical Precipitation Method  

NASA Astrophysics Data System (ADS)

Particles of Hydroxyapatite (HAp) were synthesized by means of chemical precipitation method, under atmosphere pressure. The starting solution with the Ca/P ratio of 1.67 was prepared by mixing 0.167 mol·dm-3 Ca(NO3)2·4H2O, 0.100 mol·dm-3 (NH4)2HPO4, 0.500 mol·dm-3 (NH2)2CO and 0.10 mol·dm-3 HNO3 aqueous solutions. The hydroxyapatite were prepared by heating the solution at 80 °C for 24 hour and then at 90°C for 72 hour. Then followed, the dry powers were heat treatment at 660°C temperatures for 8 hour. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA. The results showed that obtained HAp powers were greatly influenced by synthetic conditions. HAp powders with various morphologies, such as sphere, rod, layered, dumbbell, fibre, scaly, were obtained by controlling the synthetic conditions.

Zhu, Jianping; Kong, Deshuang; Zhang, Yin; Yao, Nengjian; Tao, Yaqiu; Qiu, Tai

2011-10-01

118

Weathering and Dissolution Rates Among Pb Shot Pellets of Differing Elemental Compositions Exposed to Various Aqueous and Soil Conditions  

Microsoft Academic Search

The present study was performed to investigate the weathering and dissolution rates of Pb shot pellets differing in elemental\\u000a composition (Pb, Sb, and As) exposed under various aqueous and soil conditions using five commercial shot pellet preparations.\\u000a Upon immersion in distilled water, the dissolution rates of shot pellets, calculated from the difference in weight before\\u000a versus after immersion, decreased with

Takejiro Takamatsu; Tomoyoshi Murata; Masami K. Koshikawa; Mirai Watanabe

2010-01-01

119

An Aqueous Extract of the Dry Mycelium of Penicillium chrysogenum Induces Resistance in Several Crops under Controlled and Field Conditions  

Microsoft Academic Search

We have examined the effect of Pen, an aqueous extract of the dry mycelium of Penicillium chrysogenum, on plant–pathogen interactions. Pen controlled a broad range of pathogens on several crop plants under greenhouse and field\\u000a conditions. Pen protected grapevine from downy and powdery mildew (caused by Plasmopara viticola and Uncinula necator), tomato from early blight (caused by Phytophthora infestans), onion

Barbara Thuerig; Andres Binder; Thomas Boller; Urs Guyer; Sonia Jiménez; Christina Rentsch; Lucius Tamm

2006-01-01

120

Influence of processing and curing conditions on beads coated with an aqueous dispersion of cellulose acetate phthalate  

Microsoft Academic Search

The influence of fluidized-bed processing conditions, as well as curing parameters with and without humidity, on drug release from beads coated with cellulose acetate phthalate (CAP) aqueous dispersion was investigated. Theophylline beads prepared by extrusion–spheronization were coated with diethyl phthalate (DEP)-plasticized CAP dispersion (Aquacoat® CPD) using a Strea-1 fluidized-bed coater. The parameters investigated were plasticizer level, outlet temperature, spray rate

Robert O. Williams III; Jiping Liu

2000-01-01

121

One-step growth of structured ZnO thin films by chemical bath deposition in aqueous ammonia solution  

NASA Astrophysics Data System (ADS)

Structured ZnO films have been fabricated on soda-lime glass slides at a low temperature (80-85 °C) by a chemical bath deposition method in one step without seed layers. Mixed aqueous solutions of zinc sulfate, ammonia and thiourea were used at alkaline conditions. The influence of the ammonia concentration in the initial solution on the property of the deposited film was investigated systematically. The morphology, structural and optical properties of the deposited films were examined and characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy x-ray diffraction (EDX), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectroscopy. Structural analyses with XRD, EDX and SEM revealed that the formed films exhibit a wurtzite hexagonal phase. The deposited film was more preferentially oriented in the (0 0 2) direction with an increase in the ammonia concentration from 0.75 to 2 mol l-1. The optical-phonon E2 mode at 437 cm-1 in the Raman spectrum, together with the XRD and EDX analyses, showed that flower-like and columnar crystalline ZnO films were formed in two ammonia concentration ranges, 0.75-1.4 mol l-1 and 1.6-2.0 mol l-1, respectively. Furthermore, PL spectra showed strong and high intensity peaks of UV emission with suppressed green emission for these deposited ZnO films. ZnS films were formed with a high ammonia concentration of 3.0 M. The formation mechanisms of ZnO, Zn(OH)2 and ZnS phases were discussed.

Huang, S M; Bian, Z Q; Chu, J B; Wang, Z A; Zhang, D W; Li, X D; Zhu, H B; Sun, Z

2009-03-01

122

Interfacial properties of methane/aqueous VC-713 solution under hydrate formation conditions.  

PubMed

The interfacial tensions between methane and aqueous solutions of different contents of VC-713 (a terpolymer of N-vinylpyrrolidone, N-vinylcaprolactam, and dimethylamino-ethyl-methacrylate) were measured at different temperatures and pressures in the hydrate formation region. The surface adsorption free energies of methane were calculated accordingly in order to investigate the effect of this kinetic inhibitor on the nucleation of hydrate. The results show that the presence of VC-713 lowers the interfacial tension, increasing the concentration of methane on the surface of the aqueous phase, and thus promotes nucleation of hydrate at the gas/liquid interface. Additionally, the measured interfacial tension data suggest that VC-713 tends not to form micelles in water. Subsequently, the lateral growth rate of hydrate film on the surface of a methane bubble suspended in the aqueous phase was measured at different pressures to investigate the effect of VC-713 on the growth of hydrate. The results show that the lateral growth rate of hydrate film from aqueous VC-713 solution is much lower than that from pure water, demonstrating that VC-713 significantly inhibits the hydrate growth. The mechanism of the inhibition is also discussed. PMID:19447402

Peng, Bao-Zi; Sun, Chang-Yu; Liu, Peng; Liu, Yan-Tao; Chen, Jun; Chen, Guang-Jin

2009-08-15

123

Physico-chemical factors influencing autologous conditioned serum purification.  

PubMed

Autologous conditioned serum (ACS) is a recent biotherapy based on certain cytokines anti-inflammatory properties mainly used for the reduction of osteoarthritis (OA) symptoms. Here we investigated different physico-chemical factors influencing ACS purification and cytokine production. Human venous blood was incubated in the presence of different diameter beads (respectively 2.5, 3, 3.5, and 4?mm) or glass beads with different types of coating (polished or coated with CrSO4). Sera were recovered, and the concentrations of pro-inflammatory and anti-inflammatory relevant cytokines were measured using Luminex(®) technology. Fresh whole blood incubated for 24?h highly increased production of interleukin (IL)-6 and IL-8 cytokines. At the same time, the concentrations of IL-1?, IL-1 receptor agonist (IL-1Ra), IL-10, and tumor necrosis factor (TNF)-? were slightly induced. The highest cytokine concentrations were obtained with the exposure of whole blood to 3-mm glass beads and 3.5-mm polished beads. The minimum IL-1?/IL-1Ra ratio obtained was 3.2±1.3 after 24-h incubation without any beads. ACS has been shown to alleviate clinical symptoms of OA in clinical studies. This descriptive study demonstrated that different pro- and anti-inflammatory cytokines are present in ACS since no selective anti-inflammatory cytokines were produced based on the different protocols. Furthermore, we showed that CrSO4-treated glass beads are not necessary and that the absence of beads combined with a 24-h incubation could also lead to an enriched serum. PMID:24570844

Magalon, Jeremy; Bausset, Olivier; Veran, Julie; Giraudo, Laurent; Serratrice, Nicolas; Magalon, Guy; Dignat-George, Françoise; Sabatier, Florence

2014-02-01

124

CHEMICAL AND BIOLOGICAL TREATMENT OF THERMALLY CONDITIONED SLUDGE RECYCLE LIQUORS  

EPA Science Inventory

The objective of this research project was to demonstrate and evaluate the feasibility of treating undiluted heat treatment liquor prior to its rerouting back to the head of the sewage treatment plant. Chemical and biological treatment processes were studied. Chemical treatment w...

125

Parameterizing the equilibrium distribution of chemicals between the dissolved, solid particulate matter, and colloidal matter compartments in aqueous systems  

USGS Publications Warehouse

The manner in which a chemical material partitions among the dissolved (D), participate (P), and colloidal (C) phases affects both its chemical and physical behavior in the aquatic environment. The fractions of the chemical that are present in each of these three phases will be determined by the values of two simple parameters, KpSp/??w and KcSc/??w. The variables Kp and Kc are the particle/water and colloid/water partition constants (mL/g), respectively, Sp and Sc are the volume concentrations of particulate and colloidal material (mg/L), respectively, and ??w is the fractional volume of the system that is aqueous. This parameterization allows a rapid overview of how partitioning (1) changes as a function of chemical partitioning properties and water type, (2) affects apparent partition constants (i.e., Kpapp values) computed between the particulate phase and the remainder of the system, and (3) causes Kpapp values to become independent of chemical properties at high values of KcSc/??w. ?? 1991 American Chemical Society.

Pankow, J. F.; McKenzie, S. W.

1991-01-01

126

Investigation of optimal conditions for zinc electrowinning from aqueous sulfuric acid electrolytes  

Microsoft Academic Search

Results are reported of an experimental investigation of the effects of aqueous zinc(II) and sulfuric acid concentrations\\u000a on current efficiencies and deposit morphologies of metallic zinc, aimed at designing a process for zinc recovery from solid\\u000a industrial wastes by leaching and electrodeposition. Voltammetry and chronopotentiometry of additive-free solutions of zinc(II)\\u000a sulfate and sulfuric acid were used to determine the zinc(II)

P. Guillaume; N. Leclerc; C. Boulanger; J. M. Lecuire; François Lapicque

2007-01-01

127

Anomalously strong effect of the ion sign on the thermochemistry of hydrogen bonded aqueous clusters of identical chemical composition.  

PubMed

The sign preference of hydrogen bonded aqueous ionic clusters X+/-(H(2)O)(i) (n =1-5, X = F; Cl; Br) has been investigated using the Density Functional Theory and ab initio MP2 method. The present study indicates the anomalously large difference in formation free energies between cations and anions of identical chemical composition. The effect of vibrational anharmonicity on stepwise Gibbs free energy changes has been investigated, and possible uncertainties associated with the harmonic treatment of vibrational spectra have been discussed. PMID:19333418

Nadykto, Alexey B; Yu, Fangqun; Natsheh, Anas Al

2009-02-01

128

Chemical and Kinetic Properties of HO sub 2 /O sub 2- in Aqueous Solutions.  

National Technical Information Service (NTIS)

The two most important properties of the HO sub 2 /O sub 2- radical pair (perhydroxyl radical/superoxide radical) in aqueous solutions are that they are in a pH-dependent equilibrium with each other, and that they disproportionate by a second-order proces...

B. H. J. Bielski

1984-01-01

129

CHEMICAL TRANSFORMATION MODULES FOR EULERIAN ACID DEPOSITION MODELS. VOLUME 2. THE AQUEOUS-PHASE CHEMISTRY  

EPA Science Inventory

This study focuses on the review and evaluation of mechanistic and kinetic data for aqueous-phase reactions that lead to the production of acidic substances in the environment. The intent of this research is to provide a framework that can be used to develop a state-of-the-art aq...

130

Chemical Flowsheet Conditions for Preparing Urania Spheres by Internal Gelation.  

National Technical Information Service (NTIS)

Small, ceramic urania spheres can be prepared for use as nuclear fuel by internal chemical gelation of uranyl nitrate solution droplets. Decomposition of hexamethylenetetramine (HMTA) dissolved in the uranyl nitrate solution releases ammonia to precipitat...

P. A. Haas J. M. Begovich A. D. Ryon J. S. Vavruska

1979-01-01

131

Chemical and Biological Treatment of Thermally Conditioned Sludge Recycle Liquors.  

National Technical Information Service (NTIS)

The objective of this research project was to demonstrate and evaluate the feasibility of treating undiluted heat treatment liquor prior to its rerouting back to the head of the sewage treatment plant. Chemical and biological treatment processes were stud...

M. B. Heyda J. D. Edwards R. F. Noland

1980-01-01

132

The decay of chemical weapons agents under environmental conditions  

Microsoft Academic Search

The rate and mechanism of decay of chemical agents in the environment was studied via live agent field trials at the chemical and Biological Defence Establishment, Porton Down, UK. The plan was to deposit the agents GD (Soman), VX, and H (sulfur mustard) on separate l-m² plots on three successive days; i.e., Tuesday through Thursday. The depositions were to be

R. R. McGuire; J. S. Haas; R. J. Eagle

1993-01-01

133

Waste treatment process for removal of contaminants from aqueous, mixed-waste solutions using sequential chemical treatment and crossflow microfiltration, followed by dewatering  

DOEpatents

In processes of this invention aqueous waste solutions containing a variety of mixed waste contaminants are treated to remove the contaminants by a sequential addition of chemicals and adsorption/ion exchange powdered materials to remove the contaminants including lead, cadmium, uranium, cesium-137, strontium-85/90, trichloroethylene and benzene, and impurities including iron and calcium. Staged conditioning of the waste solution produces a polydisperse system of size enlarged complexes of the contaminants in three distinct configurations: water-soluble metal complexes, insoluble metal precipitation complexes, and contaminant-bearing particles of ion exchange and adsorbent materials. The volume of the waste is reduced by separation of the polydisperse system by cross-flow microfiltration, followed by low-temperature evaporation and/or filter pressing. The water produced as filtrate is discharged if it meets a specified target water quality, or else the filtrate is recycled until the target is achieved. 1 fig.

Vijayan, S.; Wong, C.F.; Buckley, L.P.

1994-11-22

134

Waste treatment process for removal of contaminants from aqueous, mixed-waste solutions using sequential chemical treatment and crossflow microfiltration, followed by dewatering  

DOEpatents

In processes of this invention aqueous waste solutions containing a variety of mixed waste contaminants are treated to remove the contaminants by a sequential addition of chemicals and adsorption/ion exchange powdered materials to remove the contaminants including lead, cadmium, uranium, cesium-137, strontium-85/90, trichloroethylene and benzene, and impurities including iron and calcium. Staged conditioning of the waste solution produces a polydisperse system of size enlarged complexes of the contaminants in three distinct configurations: water-soluble metal complexes, insoluble metal precipitation complexes, and contaminant-bearing particles of ion exchange and adsorbent materials. The volume of the waste is reduced by separation of the polydisperse system by cross-flow microfiltration, followed by low-temperature evaporation and/or filter pressing. The water produced as filtrate is discharged if it meets a specified target water quality, or else the filtrate is recycled until the target is achieved.

Vijayan, Sivaraman (Deep River, CA); Wong, Chi F. (Pembroke, CA); Buckley, Leo P. (Deep River, CA)

1994-01-01

135

Nature of the chemical bond of aqueous Fe2+ probed by soft X-ray spectroscopies and ab initio calculations.  

PubMed

Aqueous iron(II) chloride is studied by soft X-ray absorption, emission, and resonant inelastic Raman scattering techniques on the Fe L-edge and O K-edge using the liquid-jet technique. Soft X-ray spectroscopies allow in situ and atom-specific probing of the electronic structure of the aqueous complex and thus open the door for the investigation of chemical bonding and molecular orbital mixing. In this work, we combine theoretical ab initio restricted active space self-consistent field and local atomic multiplet calculations with experimental soft X-ray spectroscopic methods for a description of the local electronic structure of the aqueous ferrous ion complex. We demonstrate that the atomic iron valence final states dominate the resonant inelastic X-ray scattering spectra of the complex over the ligand-to-metal charge transfer transitions, which indicates a weak interaction of Fe(2+) ion with surrounding water molecules. Moreover, the oxygen K-edge also shows only minor changes due to the presence of Fe(2+) implying a small influence on the hydrogen-bond network of water. PMID:24063525

Atak, Kaan; Bokarev, Sergey I; Gotz, Malte; Golnak, Ronny; Lange, Kathrin M; Engel, Nicholas; Dantz, Marcus; Suljoti, Edlira; Kühn, Oliver; Aziz, Emad F

2013-10-17

136

Chemical oxidation of p-hydroxyphenylpyruvic acid in aqueous solution by capillary electrophoresis with an electrochemiluminescence detection system.  

PubMed

A system of capillary electrophoresis with electrochemiluminescence detection (CE-ECL) together with UV spectroscopic and electrochemical methods were used to study the chemical oxidation of p-hydroxyphenylpyruvic acid (pHPP) by dissolved oxygen in aqueous solution. The pHPP was observed to be readily oxidized by dissolved oxygen in alkaline solution and yielded a compound that strongly enhanced the electrochemiluminescence of Ru(bpy)23+. This compound was separated and detected by a new CE-ECL system and revealed to be oxalate by being compared with an authentic sample of oxalate. The chemical oxidation mechanism of pHPP by dissolved oxygen was discussed in this paper. PMID:16465714

Chen, Guonan; Chi, Yuwu; Wu, Xiaoping; Duan, Jianping; Li, Nianbin

2003-12-01

137

The effect of precipitation conditions and aging upon characteristics of particles precipitated from aqueous solutions  

SciTech Connect

Precipitation of a dissolved species from aqueous solutions is one of the techniques used to grow particles with certain size or composition characteristics. Various factors affecting the particle properties for sparingly soluble substances are briefly discussed here, including homogeneous versus heterogeneous nucleation, the effect of relative supersaturation on the number of nuclei and their relative size, particle growth by way of Ostwald Ripening, the Ostwald Step Rule and nucleation of metastable phases, diffusion-controlled versus surface reaction-controlled growth, incorporation of dopants into the precipitate, and dendritic growth. 13 refs.

Rard, J.A.

1989-10-01

138

Photoenhanced toxicity of aqueous phase and chemically dispersed weathered Alaska North Slope crude oil to Pacific herring eggs and larvae.  

PubMed

The photoenhanced toxicity of weathered Alaska North Slope crude oil (ANS) was investigated in the eggs and larvae of Pacific herring (Clupea pallasi) with and without the chemical dispersant Corexit 9527. Oil alone was acutely toxic to larvae at aqueous concentrations below 50 microg/L total polycyclic aromatic hydrocarbons (tPAH), and median lethal (LC50s) and effective concentrations (EC50s) decreased with time after initial oil exposure. Brief exposure to sunlight (approximately 2.5 h/d for 2 d) significantly increased toxicity 1.5- to 48-fold over control lighting. Photoenhanced toxicity only occurred when oil was present in larval tissue and increased with increasing tPAH concentration in tissue. Ultraviolet radiation A (UVA) treatments were less potent than natural sunlight, and UVA + sunlight caused greater toxicity than sunlight alone. The toxicity of chemically dispersed oil was similar to oil alone in control and UVA treatments, but oil + dispersant was significantly more toxic in the sunlight treatments. The chemical dispersant appeared to accelerate PAH dissolution into the aqueous phase, resulting in more rapid toxicity. In oil + dispersant exposures, the 96-h no-observed-effect concentrations in the UVA + sunlight treatment were 0.2 microg/L tPAH and 0.01 microg/g tPAH. Exposure of herring eggs to oil caused yolk sac edema, but eggs were not exposed to sun and UVA treatment did not cause phototoxicity. These results are consistent with the hypothesis that weathered ANS is phototoxic and that UV can be a significant and causative factor in the mortality of early life stages of herring exposed to oil and chemically dispersed oil. PMID:12627655

Barron, Mace G; Carls, Mark G; Short, Jeffrey W; Rice, Stanley D

2003-03-01

139

Crack size effects on the chemical driving force for aqueous corrosion fatigue  

Microsoft Academic Search

Small crack size accelerates corrosion fatigue propagation through high strength 4130 steel in aqueous 3 pct NaCl. The size\\u000a effect is attributed to crack geometry dependent mass transport and electrochemical reaction processes which govern embrittlement.\\u000a For vacuum or moist air, growth rates are defined by stress intensity range independent of crack size (0.1 to 40 mm) and applied\\u000a maximum stress

R. P. Gangloff

1985-01-01

140

Adsorption of chromium(VI) from aqueous solutions by chemically treated water hyacinth Eichhornia crassipes  

Microsoft Academic Search

The adsorption potential of water hyacinth Eichhornia crassipes for the removal of Cr(VI) from aqueous solutions has been stidied. The influence of various parameters including contact time, temperature, solution pH, initial adsorbate and adsorbent concentrations and effect of competing anions were studied. Results obtained indicate that the treated weed Eichhornia crassipes has remarkable adsorption capacity for Cr(VI) at pH below

Sujana M Gude; S N Das

141

Morphology and Optical Properties of Zinc Oxide Films Grown on Metal Coated Glass Substrates by Aqueous Chemical Growth  

NASA Astrophysics Data System (ADS)

Zinc oxide films were deposited on three different metal coated substrates (gold, nickel and platinum) by aqueous chemical growth method. This paper discusses the effect of metal coated substrates on the morphology and optical properties of grown ZnO films. X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and UV-visible spectroscopy (UV-vis) were employed to characterize the samples. All the as-deposited ZnO films exhibit crystalline hexagonal wurzite structure. The crystallite size of the ZnO films were in the range of 29 to 32 nm. FESEM micrographs revealed hexagonal rod, oval-like and flower-like ZnO structures formed on all metal coated substrates. The Pt coated film contains higher density hexagonal rod as compared to others metal coated substrate. Most probably the Pt lattice parameter is the nearest to ZnO compared to nickel and gold. The optical band gap energy, Eg of ZnO films were estimated to be 3.30 eV which is near to bulk Eg, 3.37 eV. This indicates that the ZnO grown by aqueous chemical growth is able to produce similar quality properties to other conventional method either films or bulk size.

Bakar, M. A.; Hamid, M. A. A.; Jalar, A.; Shamsudin, R.

2013-04-01

142

Structure sensitive chemical reactivity by palladium concave nanocubes and nanoflowers synthesised by a seed mediated procedure in aqueous medium  

NASA Astrophysics Data System (ADS)

Palladium nanocubes and their transformation to concave nanocubes and nanoflowers are realised by a seed mediated procedure in aqueous medium and at room temperature using cationic surfactants. The concave nanocubes and nanoflowers were found to be enclosed by high index facets. The under co-ordinated atoms present on the high index facets make these nanostructures chemically more active towards Suzuki coupling and Heck coupling reactions compared to the conventional nanocubes and spherical nanoparticles of similar size.Palladium nanocubes and their transformation to concave nanocubes and nanoflowers are realised by a seed mediated procedure in aqueous medium and at room temperature using cationic surfactants. The concave nanocubes and nanoflowers were found to be enclosed by high index facets. The under co-ordinated atoms present on the high index facets make these nanostructures chemically more active towards Suzuki coupling and Heck coupling reactions compared to the conventional nanocubes and spherical nanoparticles of similar size. Electronic supplementary information (ESI) available: Additional HRTEM images, UV-Vis spectra and details of TOF calculation. See DOI: 10.1039/c4nr01283f

Sreedhala, S.; Sudheeshkumar, V.; Vinod, C. P.

2014-06-01

143

Chemical enrichment and physical conditions in I Zw 18  

NASA Astrophysics Data System (ADS)

Context. Low-metallicity star-forming dwarf galaxies are prime targets to understand the chemical enrichment of the interstellar medium. The H i region contains the bulk of the mass in blue compact dwarfs, and it provides important constraints on the dispersal and mixing of heavy elements released by successive star-formation episodes. The metallicity of the H i region is also a critical parameter to investigate the future star-formation history, as metals provide most of the gas cooling that will facilitate and sustain star formation. Aims: Our primary objective is to study the enrichment of the H i region and the interplay between star-formation history and metallicity evolution. Our secondary objective is to constrain the spatial- and time-scales over which the H i and H ii regions are enriched, and the mass range of stars responsible for the heavy element production. Finally, we aim to examine the gas heating and cooling mechanisms in the H i region. Methods: We observed the most metal-poor star-forming galaxy in the Local Universe, I Zw 18, with the Cosmic Origin Spectrograph onboard Hubble. The abundances in the neutral gas are derived from far-ultraviolet absorption-lines (H i, C ii, C ii*, N i, O i, ...) and are compared to the abundances in the H ii region. Models are constructed to calculate the ionization structure and the thermal processes. We investigate the gas cooling in the H i region through physical diagnostics drawn from the fine-structure level of C+. Results: We find that H i region abundances are lower by a factor of ~2 as compared to the H ii region. There is no differential depletion on dust between the H i and H ii region. Using sulfur as a metallicity tracer, we calculate a metallicity of 1/46 Z? (vs. 1/31 Z? in the H ii region). From the study of the C/O, [O/Fe], and N/O abundance ratios, we propose that C, N, O, and Fe are mainly produced in massive stars. We argue that the H i envelope may contain pockets of pristine gas with a metallicity essentially null. Finally, we derive the physical conditions in the H i region by investigating the C ii* absorption line. The cooling rate derived from C ii* is consistent with collisions with H0 atoms in the diffuse neutral gas. We calculate the star-formation rate from the C ii* cooling rate assuming that photoelectric effect on dust is the dominant gas heating mechanism. Our determination is in good agreement with the values in the literature if we assume a low dust-to-gas ratio (~2000 times lower than the Milky Way value). Appendix A is available in electronic form at http://www.aanda.org

Lebouteiller, V.; Heap, S.; Hubeny, I.; Kunth, D.

2013-05-01

144

ROS initiated oxidation of dopamine under oxidative stress conditions in aqueous and lipidic environments.  

PubMed

Dopamine is known to be an efficient antioxidant and to protect neurocytes from oxidative stress by scavenging free radicals. In this work, we have carried out a systematic quantum chemistry and computational kinetics study on the reactivity of dopamine toward hydroxyl (•OH) and hydroperoxyl (•OOH) free radicals in aqueous and lipidic simulated biological environments, within the density functional theory framework. Rate constants and branching ratios for the different paths contributing to the overall reaction, at 298 K, are reported. For the reactivity of dopamine toward hydroxyl radicals, in water at physiological pH, the main mechanism of the reaction is proposed to be the sequential electron proton transfer (SEPT), whereas in the lipidic environment, hydrogen atom transfer (HAT) and radical adduct formation (RAF) pathways contribute almost equally to the total reaction rate. In both environments, dopamine reacts with hydroxyl radicals at a rate that is diffusion-controlled. Reaction with the hydroperoxyl radical is much slower and occurs only by abstraction of any of the phenolic hydrogens. The overall rate coefficients are predicted to be 2.23 × 10(5) and 8.16 × 10(5) M(-1) s(-1), in aqueous and lipidic environment, respectively, which makes dopamine a very good •OOH, and presumably •OOR, radical scavenger. PMID:21919526

Iuga, Cristina; Alvarez-Idaboy, J Raul; Vivier-Bunge, Annik

2011-10-27

145

Oxidative weathering chemical migration under variably saturated conditions and supergene copper enrichment  

SciTech Connect

Transport of oxygen gas from the land surface through an unsaturated zone has a strong influence on oxidative weathering processes. Oxidation of sulfide minerals such as pyrite (FeS{sub 2}), one of the most common naturally occurring minerals, is the primary source of acid drainage from mines and waste rock piles. Here we present a detailed numerical model of supergene copper enrichment that involves the oxidative weathering of pyrite (FeS{sub 2}) and chalcopyrite (CuFeS{sub 2}), and acidification that causes mobilization of metals in the unsaturated zone, with subsequent formation of enriched ore deposits of chalcocite (CuS) and covellite (Cu{sub 2}S) in the reducing conditions below the water table. We examine and identify some significant conceptual and computational issues regarding the oxidative weathering processes through the modeling tool. The dissolution of gaseous oxygen induced by the oxidation reduces oxygen partial pressure, as well as the total pressure of the gas phase. As a result, the gas flow is modified, then the liquid phase flow. Results indicate that this reaction effect on the fluid flow may not be important under ambient conditions, and gas diffusion can be a more important mechanism for oxygen supply than gas or liquid advection. Acidification, mobilization of metals, and alteration of primary minerals mostly take place in unsaturated zone (oxidizing), while precipitation of secondary minerals mainly occurs in saturated zone (reducing). The water table may be considered as an interface between oxidizing and reducing zones. Moving water table due to change of infiltration results in moving oxidizing zone and redistributing aqueous chemical constitutes and secondary mineral deposits. The oxidative weathering processes are difficult to model numerically, because concentrations of redox sensitive chemical species such as O{sub 2}(aq), SO{sub 4}{sup 2-} and HS{sup -} may change over tens of orders of magnitude between oxidizing and reducing conditions. In order to simulate substantial reaction progress over geologic time, one can benefit from the quasi-stationary state (QSS) approximation. A significant saving of computing time using QSS is demonstrated through the example. In addition, changes in porosity and permeability due to mineral dissolution and precipitation are also addressed in some degree. Even though oxidative weathering is sensitive to many factors, this work demonstrates that our model provides a comprehensive suite of process modeling capabilities, which could serve as a prototype for oxidative weathering processes with broad significance for geoscientific, engineering, and environmental applications.

Xu, Tianfu; Pruess, K.; Brimhall, G.

1999-04-01

146

Abiotic Formation of Hydrocarbons Under Hydrothermal Conditions: Constraints from Chemical and Isotope Data  

SciTech Connect

To understand reaction pathways and isotope systematics during mineral-catalyzed abiotic synthesis of hydrocarbons under hydrothermal conditions, experiments involving magnetite and CO{sub 2} and H{sub 2}-bearing aqueous fluids were conducted at 400 C and 500 bars. A robust technique for sample storage and transfer from experimental apparatus to stable isotope mass spectrometer provides a methodology for integration of both carbon and hydrogen isotope characterization of reactants and products generated during abiogenic synthesis experiments. Experiments were performed with and without pretreatment of magnetite to remove background carbon associated with the mineral catalyst. Prior to experiments, the abundance and carbon isotope composition of all carbon-bearing components were determined. Time-series samples of the fluid from all experiments indicated significant concentrations of dissolved CO and C{sub 1}-C{sub 3} hydrocarbons and relatively large changes in dissolved CO{sub 2} and H{sub 2} concentrations, consistent with formation of additional hydrocarbon components beyond C{sub 3}. The existence of relatively high dissolved alkanes in the experiment involving non-pretreated magnetite in particular, suggests a complex catalytic process, likely involving reinforcing effects of mineral-derived carbon with newly synthesized hydrocarbons at the magnetite surface. Similar reactions may be important mechanisms for carbon reduction in chemically complex natural hydrothermal systems. In spite of evidence supporting abiotic hydrocarbon formation in all experiments, an 'isotopic reversal' trend was not observed for {sup 13}C values of dissolved alkanes with increasing carbon number. This may relate to the specific mechanism of carbon reduction and hydrocarbon chain growth under hydrothermal conditions at elevated temperatures and pressures. Over time, significant {sup 13}C depletion in CH{sub 4} suggests either depolymerization reactions occurring in addition to synthesis, or reactions between the C{sub 1}-C{sub 3} hydrocarbons and carbon species absorbed on mineral surfaces and in solution.

Fu, Q. [University of Minnesota; Lollar, Barbara Sherwood [University of Toronto; Horita, Juske [ORNL; Lacrampe-Couloume, Georges [University of Toronto; Seyfried, W. E. [University of Minnesota

2007-01-01

147

CHEMICAL SPECIATION OF INORGANIC COMPOUNDS UNDER HYDROTHERMAL CONDITIONS  

EPA Science Inventory

This research will utilize the high-intensity x-rays available at the Advance Photon Source (APS) to study the inorganic chemistry occurring during the hydrothermal oxidation of tank waste and the chemistry associated with tank waste vitrification. Although the chemical conversio...

148

Necessary and sufficient conditions for complex balancing in chemical kinetics  

Microsoft Academic Search

In a recent publication (Horn & Jackson [1]) it was shown that complex balancing together with mass action type rate laws ensures certain stability properties of a kinetic system, thereby precluding sustained oscillations, bistability and other types of irregular dynamics. In this paper a necessary condition for complex balancing in general kinetics and necessary and sufficient conditions for complex balancing

F. Horn

1972-01-01

149

Detection of aqueous phase chemical warfare agent degradation products by negative mode ion mobility time-of-flight mass spectrometry [IM(tof)MS  

Microsoft Academic Search

The use of negative ion monitoring mode with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass\\u000a spectrometer [IM(tof)MS] to detect chemical warfare agent (CWA) degradation products from aqueous phase samples has been determined.\\u000a Aqueous phase sampling used a traditional electrospray ionization (ESI) source for sample introduction and ionization. Certified\\u000a reference materials (CRM) of CWA degradation products for the detection

Wes E. Steiner; Charles S. Harden; Feng Hong; Steve J. Klopsch; Vincent M. McHugh

2006-01-01

150

Measurements of aerosol chemical composition in boreal forest summer conditions  

NASA Astrophysics Data System (ADS)

Boreal forests are an important biome, covering vast areas of the northern hemisphere and affecting the global climate change via various feedbacks [1]. Despite having relatively few anthropogenic primary aerosol sources, they always contain a non-negligible aerosol population [2]. This study describes aerosol chemical composition measurements using Aerodyne Aerosol Mass Spectrometer (C-ToF AMS, [3]), carried out at a boreal forest area in Hyytiälä, Southern Finland. The site, Helsinki University SMEAR II measurement station [4], is situated at a homogeneous Scots pine (Pinus sylvestris) forest stand. In addition to the station's permanent aerosol, gas phase and meteorological instruments, during the HUMPPA (Hyytiälä United Measurements of Photochemistry and Particles in Air) campaign in July 2010, a very comprehensive set of atmospheric chemistry measurement instrumentation was provided by the Max Planck Institute for chemistry, Johannes Gutenberg-University, University of California and the Finnish Meteorological institute. In this study aerosol chemical composition measurements from the campaign are presented. The dominant aerosol chemical species during the campaign were the organics, although periods with elevated amounts of particulate sulfates were also seen. The overall AMS measured particle mass concentrations varied from near zero to 27 ?g/m observed during a forest fire smoke episode. The AMS measured aerosol mass loadings were found to agree well with DMPS derived mass concentrations (r2=0.998). The AMS data was also compared with three other aerosol instruments. The Marga instrument [5] was used to provide a quantitative semi-online measurement of inorganic chemical compounds in particle phase. Fourier Transform Infrared Spectroscopy (FTIR) analysis was performed on daily filter samples, enabling the identification and quantification of organic aerosol subspecies. Finally an Atmospheric Pressure Chemical Ionization Ion Trap Mass Spectrometer (APCI-IT-MS, [6]) was measuring gas and particle phase aerosol composition, offering additional information on molecular compositions. Overall, the availability of a variety of aerosol chemical characterization instruments provided a good opportunity for a comparison of the results obtained by these four very different measurement approaches. Overall the results were found to agree. The inorganic particulate masses measured with the AMS and Marga were found to correlate especially well for sulphates (r2=0.92) and ammonia compounds (r2=0.82). The organic mass seen by the AMS was correlated with the FTIR filter analysis (r2=0.87) and the APCI-IT-MS (r2=0.88).

?ijälä, M.; Junninen, H.; Ehn, M.; Petäjä, T.; Vogel, A.; Hoffmann, T.; Corrigan, A.; Russell, L.; Makkonen, U.; Virkkula, A.; Mäntykenttä, J.; Kulmala, M.; Worsnop, D.

2012-04-01

151

Chemical processing in high-pressure aqueous environments. 1. Historical perspective and continuing developments  

Microsoft Academic Search

Use of high-temperature pressurized liquid water has been investigated as a reaction medium for conducting chemical reactions and conversion. Results of these studies have demonstrated that high-temperature pressurized liquid water, especially in the presence of suitable catalysts, has unique chemical and physical properties. An overview of fundamental investigations and processing considerations in this environment is presented including details regarding the

L. John Sealock; Douglas C. Elliott; Eddie G. Baker; R. Scott Butner

1993-01-01

152

Composition and freezing of aqueous H2SO4/HNO3 solutions under polar stratospheric conditions  

NASA Technical Reports Server (NTRS)

The results of laboratory investigations of the freezing behavior of aqueous acid solutions indicate that in the stratosphere H2SO/H2O aerosol droplets would not freeze at temperatures above the ice frost point in the absence of HNO3; however, in the presence of typical levels of HNO3 liquid sulfuric acid aerosols take up significant amounts of HNO3 and H2O vapors and freeze much more readily. This is a consequence of the very rapid change in composition of the liquid droplets as the temperature drops to within two to three degrees of the equilibrium temperature at which HNO3 and H2O vapors would co-condense to form a liquid solution. In the high latitude stratosphere this HNO3/H2O 'dew point' is typically around 192-194 K at 100 mbar.

Beyer, K. D.; Seago, S. W.; Chang, H. Y.; Molina, M. J.

1994-01-01

153

Oxidation of 1,4-dichloro-2-butene by aqueous sodium hypochlorite under phase transfer conditions  

SciTech Connect

In the industrial process for the production of chloroprene from butadiene, the problem of reducing the organic impurities in the waste water to 2000 mg/liter has not yet been solved. A method has been patented for the oxidation of organic compounds by sodium hypochlorite at high temperatures and high pressure but this method is limited by the oxidation of soluble organic compounds. The oxidation of 1,4-dichloro-2-butene by aqueous sodium hypochlorite was studied. A sharp increase in the reaction rate was found in the presence of phase transfer catalysts and surfactants. The involvement of oxygen as a cooxiant and the effect of surfactants on the absorption of atmospheric oxygen by the reaction system were demonstrated.

Grigoryan, G.S.; Karoyan, I.L.; Malkhasyan, A.Ts.; Martirosyan, G.T.; Artamkina, G.A.; Beletskaya, I.P.

1987-11-10

154

Modeling of UO{sub 2} aqueous dissolution over a wide range of conditions  

SciTech Connect

Previously it was not possible to predict reliably the rate at which spent fuel would react with groundwater because of conflicting data in the literature. The dissolution of the UO{sub 2} spent fuel matrix is a necessary step for aqueous release of radioactive fission products. Statistical experimental design was used to plan a set of UO{sub 2} dissolution experiments to examine systematically the effects of temperature (25--75C), dissolved oxygen (0.002--0.2 atm overpressure), pH (8--10) and carbonate (2-200{times}10{sup {minus}4} molar) concentrations on UO{sub 2} dissolution. The average uranium dissolution rate was 4.3 mg/m{sub 2}/day. The regression fit of the data indicate an Arrhenius type activation energy of 8750 cal/mol and a half-power dependence on dissolved oxygen in the simulated groundwater.

Steward, S.A.; Weed, H.C.

1993-11-01

155

Comparison of the chemical composition and pharmacological effects of the aqueous and ethanolic extracts from a Tibetan "Snow Lotus" (Saussurea laniceps) herb.  

PubMed

To understand the impacts of different processing methods on the composition and effects of the herb Saussurea laniceps (SL), the present study report the first comparison of the chemical constituents of aqueous and ethanolic SL extracts using chromatographic analysis, and to compare their pharmacological effects in a mouse anti-inflammatory, anti-nociceptive model and an in vitro anti-oxidant test. Chemical comparison demonstrated that the types of chemicals in the two extracts were identical, but the contents of the main constituents in the aqueous extract were lower than those of the ethanolic extract. A transesterification of dicaffeoylquinic acids took place in the aqueous extract during boiling. As for pharmacological effects, oral administration of aqueous and ethanolic SL extracts significantly inhibited croton oil-induced mice ear edema, and significantly inhibited acetic acid-induced mice writhings, respectively. In the DPPH anti-oxidant activity test, the IC50 values were calculated as 409.6 mg/L and 523.4 mg/L for the ethanolic and aqueous extracts, respectively. The inhibitory effects of the ethanolic extract were more potent than those of the aqueous extract in all pharmacological tests, although there was no significant difference. This study suggests that the two preparations should be distinguished when used. PMID:22692242

Yi, Tao; Lo, Hongwing; Zhao, Zhongzhen; Yu, Zhiling; Yang, Zhijun; Chen, Hubiao

2012-01-01

156

A purge and trap integrated microGC platform for chemical identification in aqueous samples.  

PubMed

The majority of current micro-scale gas chromatography (?GC) systems focus on air sampling to detect volatile organic compounds (VOCs). However, purging the VOCs from a water sample using microsystems is an unchartered territory. Various organic compounds used in everyday life find their way to water bodies. Some of these water organic compounds (WOCs) persist or degrade slowly, threatening not just human existence but also aquatic life. This article reports the first micro-purge extractor (?PE) chip and its integration with a micro-scale gas chromatography (?GC) system for the extraction and analysis of water organic compounds (WOCs) from aqueous samples. The 2 cm × 3 cm ?PE chip contains two inlet and outlet ports and an etched cavity sealed with a Pyrex cover. The aqueous sample is introduced from the top inlet port while a pure inert gas is supplied from the side inlet to purge WOCs from the ?PE chip. The outlets are assigned for draining water from the chip and for directing purged WOCs to the micro-thermal preconcentrator (?TPC). The trapped compounds are desorbed from the ?TPC by resistive heating using the on-chip heater and temperature sensor, are separated by a 2 m long, 80 ?m wide, and 250 ?m deep polydimethylsiloxane (OV-1) coated ?GC separation column, and are identified using a micro-thermal conductivity detector (?TCD) monolithically integrated with the column. Our experiments indicate that the combined system is capable of providing rapid chromatographic separation (<1.5 min) for quaternary WOCs namely toluene, tetrachloroethylene (PCE), chlorobenzene and ethylbenzene with a minimum detection concentration of 500 parts-per-billion (ppb) in aqueous samples. The proposed method is a promising development towards the future realization of a miniaturized system for sensitive, on-site and real-time field analysis of organic contaminants in water. PMID:24837988

Akbar, Muhammad; Narayanan, Shree; Restaino, Michael; Agah, Masoud

2014-06-01

157

Chemical Waste Management for the Conditionally Exempt Small Quantity Generator  

NASA Astrophysics Data System (ADS)

Management of hazardous chemical wastes generated as a part of the curriculum poses a significant task for the individual responsible for maintaining compliance with all rules and regulations from the Environmental Protection Agency and the Department of Transportation while maintaining the principles of OSHA's Lab Standard and the Hazard Communication Standard. For schools that generate relatively small quantities of waste, an individual can effectively manage the waste program without becoming overly burdened by the EPA regulations required for those generating large quantities of waste, if given the necessary support from the institution.

Zimmer, Steven W.

1999-06-01

158

Chemical characterization of the main secondary organic aerosol (SOA) products formed through aqueous-phase photonitration of guaiacol  

NASA Astrophysics Data System (ADS)

Guaiacol (2-methoxyphenol) and its derivatives can be emitted into the atmosphere by thermal degradation (i.e. burning) of wood lignins. Due to its volatility, guaiacol is predominantly distributed in the atmospheric gaseous phase. Recent studies have shown the importance of aqueous-phase reactions in addition to the dominant gas-phase and heterogeneous reactions of guaiacol, in the formation of secondary organic aerosol (SOA) in the atmosphere. The main objectives of the present study were to chemically characterize the low-volatility SOA products of the aqueous-phase photonitration of guaiacol and examine their possible presence in urban atmospheric aerosols. The aqueous-phase reactions were carried out under simulated sunlight and in the presence of H2O2 and nitrite. The formed guaiacol reaction products were concentrated by using solid-phase extraction (SPE) and then purified by means of semi-preparative high-performance liquid chromatography (HPLC). The fractionated individual compounds were isolated as pure solids and further analyzed with liquid-state 1H, 13C and 2D nuclear magnetic resonance (NMR) spectroscopy and direct infusion negative ion electrospray ionization tandem mass spectrometry ((-)ESI-MS/MS). The NMR and product ion (MS2) spectra were used for unambiguous product structure elucidation. The main products of guaiacol photonitration are 4-nitroguaiacol (4NG), 6-nitroguaiacol (6NG), and 4,6-dinitroguaiacol (4,6DNG). Using the isolated compounds as standards, 4NG and 4,6DNG were unambiguously identified in winter PM10 aerosols from the city of Ljubljana (Slovenia) by means of HPLC/(-)ESI-MS/MS. Owing to the strong absorption of UV and visible light, 4,6DNG could be an important constituent of atmospheric "brown" carbon, especially in regions affected by biomass burning.

Kitanovski, Z.; ?usak, A.; Grgi?, I.; Claeys, M.

2014-04-01

159

'GREENER' CHEMICAL SYNTHESES USING MICROWAVES UNDER SOLVENT-FREE CONDITIONS OR AQUEOUS MEDIA  

EPA Science Inventory

A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of recyclable mineral supports such as alumina, silica, clay, or 'doped' surfaces is presented which is applicable to a wide range of cleavage, condensation, cycl...

160

"GREENER" CHEMICAL SYNTHESES USING AN ALTERNATE REACTION CONDITIONS OR AQUEOUS MEDIA  

EPA Science Inventory

A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of recyclable mineral supports such as alumina, silica, clay, or 'doped' surfaces is presented which is applicable to a wide range of cleavage, condensation, cycl...

161

Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid.  

PubMed

The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under chromatographic conditions more aqueous than those described so far in the literature. Frontal analysis (FA) was performed on columns packed with these polymers, using an optimized mobile phase composed of methanol/phosphate buffer (50/50, v/v), to extract adsorption isotherm data and retrieve binding parameters from the best isotherm model. Surprisingly, the template had comparable and strong affinity for both MIP (K = 3.8x10(4) M(-1)) and NIPA (K = 1.9x10(4) M(-1)), although there was a marked difference in the saturation capacities of selective and non-selective sites, as one would expect for an imprinted polymer. NIPB acts as a true control polymer in the sense that it has relatively low affinity for the template (K = 8.0x10(2) M(-1)). This work provides the first frontal chromatographic characterization of such a polymer in a water-rich environment over a wide concentration range. The significance of this work stems from the fact that the chromatographic approach used is generic and can be applied readily to other analytes, but also because there is an increasing demand for well-characterised imprinted materials that function effectively in aqueous media and are thus well-suited for analytical science applications involving, for example, biofluids and environmental water samples. PMID:17456420

Legido-Quigley, C; Oxelbark, J; De Lorenzi, E; Zurutuza-Elorza, A; Cormack, P A G

2007-05-15

162

Computer Simulation of Ion Cluster Speciation in Concentrated Aqueous Solutions at Ambient Conditions  

PubMed Central

Dynamic simulations are used to investigate ion cluster formation in unsaturated aqueous NaCl at 25 °C. Statistical, structural, and dynamic properties are reported. An effort is made to identify general behaviors that are expected to hold beyond the limitations of the force field. Above ~1 M, clusters with more than ten ions begin to form after ~10–20 ns of simulation time, but no evidence of irreversible ion aggregation is observed. Cluster survival times are estimated, showing that the kinetics becomes increasingly complex as salt is added, leading to multiple decay rates. Cluster dipole moment distributions show characteristic peaks that reflect the cluster preferred conformations in solution. These are modulated by electrostatic and liquid-structure forces, and are described in detail for clusters of up to five ions. For a given size and charge, the cluster morphology is independent of salt concentration. Below ~2 M, clusters affect the structure of water in their first hydration shells, so dipole moments parallel to the cluster macrodipoles are induced. These effects show a weak dependence with concentration below ~2 M, but vanish in the 2–3 M range. A possible connection with the structural transition recently suggested by NMR data in concentrated electrolytes is discussed. The effects of electrostatics on cluster speciation and morphology are discussed based on results from a set of simulations carried out with the ionic charges removed.

Hassan, Sergio A.

2008-01-01

163

Oligo-Glycine Synthesis in an Aqueous Solution of Glycine Under Oxidative Conditions  

NASA Astrophysics Data System (ADS)

Di-and tri-glycine were synthesized in 1M aqueous solution of glycine by bubbling for 90 hr with oxygen discharged in the path from an oxygen cylinder. The peptides were also produced by an incubation at 37°C of 2M glycine solution prepared with 75% hydrogen peroxide, and the yields were traced for 200 days. The final yields were about 0.25% and 0.01% for di-and tri-glycine, respectively. The solution at 166 days of incubation was applied to a Sephadex G 10 column, and the fractions around the top of the chromatogram were found to increase the intensity of ninhydrin color about 4˜5 times after hydrolysis, indicating an existence of oligo-glycine. The solutions of 1M glycine and 0.5M diglycine prepared with 30% hydrogen peroxide were incubated at 37°C for 38 days, and di-and tetra-glycine were detected in the yields of 0.12% and 0.33%, respectively.

Yamagata, Yukio; Yamashita, Atsunori; Inomata, Katsuhiko

1980-03-01

164

Chemical effects induced by gamma-irradiation in solid and in aqueous methanol solutions of 4-iodophenol  

NASA Astrophysics Data System (ADS)

The present work is a study on radiolyses of 4-iodophenol in aqueous methanol solutions. The radiolysis products are separated and identified using spectrophotometric and chromatographic techniques. The radiolytic products (I-2, I- and IO3-) formed in aerated solutions at room temperature were identified and the yields are investigated as a function of absorbed gamma-ray dose. The formation of I-2 is mainly dependent on the acidity of solution and produced via the pathway of secondary free radical reactions. Aromatic products of lower and higher molecular weight than the corresponding investigated compound were analysed and separated by HPLC. The results have been discussed in view of mechanisms based on free radicals and ion-molecule interactions. The chemical effects induced by gamma-irradiation in solid 4-iodophenol have also been investigated and the degradation products were identified in solid state by NMR, GC/MS experiments and HPLC after dissolution in aqueous methanol. The results were evaluated and compared with radiolysis data.

Mahfouz, R. M.; Siddiqui, M. R. H.; Al-Wassil, A. I.; Al-Resayes, S. I.; Al-Otaibi, A. M.

2005-05-01

165

Conditions Affecting Germination of Clostridium botulinum 62A Spores in a Chemically Defined Medium1  

PubMed Central

Spores of Clostridium botulinum type 62A were germinated in a chemically defined medium (8 mm l-cysteine, 11.9 mm sodium bicarbonate, 4.4 mm sodium thioglycolate; buffered with 100 mm TES, pH 7.0). The rate and extent of germination were increased when an aqueous spore suspension was heated sublethally (80 C, 60 min) before addition to the germination medium. Neither sublethal nor lethal doses of gamma radiation had any marked effect on subsequent germination. Maximum germination (>90% in 2 hr) in the defined medium occurred in the pH range of 6.5 to 7.5, at 30 to 37 C, with an l-cysteine level of 8 mm. Increasing l-cysteine to 32 mm increased the rate (over that with 8 mm l-cysteine) but not the extent of germination. The rate and extent of germination increased with NaHCO3 addition to 8.3 mm, but increasing levels to 11.9 mm had no further effect. For maximum germination, 2.2 mm sodium thioglycolate was required and higher levels (to 8.8 mm) had no further enhancing or inhibitory effect. Under optimal conditions for germination, 97% of the spores had become heat sensitive; 98% had become sensitive to radiation; 88 and 91% had become phase dark and stainable, respectively, and the spore suspension had lost 46% of its initial optical density by 2 hr. Loss of heat resistance preceded loss of radiation resistance, acquisition of stainability, and phase darkening by about 12 min.

Rowley, Durwood B.; Feeherry, Florence

1970-01-01

166

Experimental investigation and modeling of uranium (VI) transport under variable chemical conditions  

USGS Publications Warehouse

The transport of adsorbing and complexing metal ions in porous media was investigated with a series of batch and column experiments and with reactive solute transport modeling. Pulses of solutions containing U(VI) were pumped through columns filled with quartz grains, and the breakthrough of U(VI) was studied as a function of variable solution composition (pH, total U(VI) concentration, total fluoride concentration, and pH-buffering capacity). Decreasing p H and the formation of nonadsorbing aqueous complexes with fluoride increased U(VI) mobility. A transport simulation with surface complexation model (SCM) parameters estimated from batch experiments was able to predict U(VI) retardation in the column experiments within 30%. SCM parameters were also estimated directly from transport data, using the results of three column experiments collected at different pH and U(VI) pulse concentrations. SCM formulations of varying complexity (multiple surface types and reaction stoichiometries) were tested to examine the trade-off between model simplicity and goodness of fit to breakthrough. A two-site model (weak- and strong-binding sites) with three surface complexation reactions fit these transport data well. With this reaction set the model was able to predict (1) the effects of fluoride complexation on U(VI) retardation at two different pH values and (2) the effects of temporal variability of pH on U(VI) transport caused by low p H buffering. The results illustrate the utility of the SCM approach in modeling the transport of adsorbing inorganic solutes under variable chemical conditions.

Kohler, M.; Curtis, G. P.; Kent, D. B.; Davis, J. A.

1996-01-01

167

Simulation of gas absorption with chemical reaction: The selective removal of hydrogen sulfide by aqueous methyldiethanolamine in packed columns  

SciTech Connect

The design of separation devices, particularly for solvent-based selective removal of H{sub 2}S from CO{sub 2}, requires an accurate mathematical model. Unfortunately, this requirement for high accuracy is often in conflict with the need for efficient computation. The addition of more and more complicated analyses, such as a move from Henry's law to a method incorporating gas and liquid activities for computing vapor liquid equilibria, may give a more accurate solution, but only at the cost of decreased computational efficiency. The efforts in this work have been directed toward two goals. The first was to develop an accurate mathematical model for the aqueous methyldiethanolamine (MDEA) system. The steady-state packed column model developed in this work has been tested with data from Schubert (1988) to verify its accuracy. The second goal was to modify the model to improve its computational efficiency. Areas such as vapor-liquid equilibrium calculations, flow hydrodynamics, and thermal effects were examined to determine what simplifications could be made, and how these simplifications affected both the accuracy and the efficiency of the model. The result of this effort is a mathematical model for multicomponent chemical absorption in a continuous contactor that balances computation efficiency with rigorous physical and chemical treatment. This model is useful not only for the analysis of the MDEA-H{sub 2}S-CO{sub 2} system, but the same framework also could be applied to other chemical absorption systems.

Lindner, J.R.

1988-01-01

168

Biosorption of Cr(VI) from aqueous solution by chemically modified potato starch: equilibrium and kinetic studies.  

PubMed

The biosorption capacity of chemically modified potato starch (CPS) for Cr(VI) from aqueous solution was investigated. The materials derived from carbohydrates are biodegradable and are generally regarded as safe and environmentally acceptable. The hydroxyl, carboxyl and carbonyl groups are responsible for the biosorption process. In the present study, the influence of various important parameters such as pH, time, biosorbent dose and initial Cr(VI) concentration on the biosorption capacity were investigated. The isotherms such as Langmuir, Freundlich and Tempkin were studied. The Freundlich and the Redlich-Peterson isotherms had been well fitted the biosorption of Cr(VI) with chemically modified potato starch. The kinetics of Cr(VI) removal using chemically modified potato starch was well explained by second-order kinetic model. The thermodynamic parameters were also evaluated from the biosorption measurements. Among the various desorbing agents tested, 98.2 percent chromium recovery was achieved with 0.1molL(-1) NaOH. PMID:23499185

Pillai, Saumya S; Mullassery, Manohar D; Fernandez, Noeline B; Girija, N; Geetha, P; Koshy, Mathew

2013-06-01

169

Multilayered coated infra-red surface plasmon resonance fibre sensors for aqueous chemical sensing  

NASA Astrophysics Data System (ADS)

A series of surface plasmonic fibre devices were fabricated by depositing multiple thin coatings on a lapped section of a standard single mode telecoms fibre forming a D-shaped section and then inscribing a grating-type structure using UV light. The coatings consisted of base coatings of semi-conductor (germanium) and dielectric (silicon dioxide) materials, followed by different metals. These fibre devices showed high spectral refractive index sensitivity with high coupling efficiency in excess of 40 dB for indices in the aqueous regime and below, with estimated index sensitivities of ? ?/? n = 90-800 nm from 1 to 1.15 index range and ? ?/? n = 1200-4000 nm for refractive indices from 1.33 to 1.39.

Allsop, T.; Neal, R.; Mou, C.; Brown, P.; Rehman, S.; Kalli, K.; Webb, D. J.; Mapps, D.; Bennion, I.

2009-10-01

170

Physical and chemical effects of direct aqueous advanced oxidation processing on green sand foundry mold materials  

NASA Astrophysics Data System (ADS)

Iron foundries using the common green sand molding process have increasingly been incorporating aqueous advanced oxidation (AO) systems to reduce the consumption of sand system bentonite clay and coal raw materials by and to decrease their volatile organic compound (VOC) emissions. These AO systems typically use a combination of sonication, ozone aeration, and hydrogen peroxide to treat and recycle slurries of sand system baghouse dust, which is rich in clay and coal. While the overall effects of AO on raw material consumption and organic emissions are known, the mechanisms behind these effects are not well understood. This research examined the effects of bench-scale direct aqueous AO processing on green sand mold materials at the micro level. Bench-scale AO processing, including acoustic sonication, ozone/oxygen aeration, and hydrogen peroxide dramatically decreased the particle sizes of both western bentonite and foundry sand system baghouse dust. Bench-scale AO processing was shown to effectively separate the clay material from the larger silica and coal particles and to extensively break up the larger clay agglomerates. The acoustic sonication component of AO processing was the key contributor to enhanced clay recovery. Acoustic sonication alone was slightly more effective than combined component AO in reducing the particle sizes of the baghouse dust and in the recovery of clay yields in the supernatant during sedimentation experiments. Sedimentation separation results correlated well with the increase in small particle concentrations due to AO processing. Clay suspension viscosity decreased with AO processing due to enhanced dispersion of the particles. X-ray diffraction of freeze-dried baghouse dust indicated that AO processing does not rehydrate calcined montmorillonite and does not increase the level of interlayer water hydration in the dry clays. Zeta potential measurements indicated that AO processing also does not produce any large changes in the surface charge of the small clay particles upon AO treatment.

Clobes, Jason Kenneth

171

Effects of aqueous-phase acidity and salinity on isotonic swelling of W\\/O\\/W emulsion liquid membranes under agitation conditions  

Microsoft Academic Search

The effects of aqueous-phase acidity and salinity on the isotonic swelling behavior of water-in-oil-in-water (W\\/O\\/W) emulsion liquid membranes (ELMs) under agitation conditions was studied. A non-ionic surfactant (EMSORB 2500) was used to stabilize the membranes. The acidity of the aqueous phase was controlled by sulfuric acid and the salinity was controlled by sodium sulfate. The swelling of the ELMs was

Jun Yan; Rajinder Pal

2004-01-01

172

The Chemical Impact of Physical Conditions in the Interstellar Medium  

NASA Astrophysics Data System (ADS)

We examine the role cosmic rays, X-rays and ultra-violet (UV) photons play in the chemical evolution of the interstellar medium, and how astrophysical processes like massive star formation can change the fluxes of these energetic particles. We connect star formation rates to interstellar chemistry. We first explore the basic effects of cosmic-ray and X-ray ionization and UV photodissociation on the chemistry. For cosmic-ray and X-ray ionization, increasing the ionization rates enriches the chemistry, up to a value of 10(-14) s-1, whereupon molecules and ions are quickly destroyed due to the high electron fraction. Isolated from other effects, the UV field tends to dissociate species much more efficiently than ionizing them, and generally reduces molecular abundances, especially those of complex molecules. The combination of a high ionization rate and a high UV field can enhance the production of some molecular species, such as small hydrocarbons. We investigate the role of cosmic rays and UV photons in the Horsehead Nebula, and determine the impact a column-dependent cosmic ray ionization rate makes on photodissociation region (PDR) chemistry. The column-dependence of cosmic rays is solved using a three-dimensional two-fluid magnetohydrodynamics model, treating the cosmic rays as a fluid governed by the relativistic Boltzmann Transport Equation, and treating the interstellar medium as a second fluid, governed by the standard non-relativistic magnetohydrodynamics equations. We then utilize a modified version of the Morata-Herbst time-dependent PDR model, incorporating our function for cosmic ray ionization. Our results help solve a chemical mystery concerning high abundances of small hydrocarbons at the edge of the nebula. We discuss predictions the model makes for species currently unobserved in the Horsehead Nebula. Finally, we examine the role of star formation on interstellar astrochemistry in the Orion KL region. We develop a new astrochemical gas-grain PDR model with a time-dependent UV radiation field and X-ray and cosmic ray flux, scaled to the star formation rate and radiative contributions of different spectral-type stars. The results provide an explanation for OH+, H2O+ and water observations, and H3O+ non-detection in the region, as well as make unique predictions for HCO+ and other molecules. These results allow us to constrain the age of the Orion KL region. We predict an age for Orion KL of one hundred thousand to one million years after OB star formation.

Rimmer, Paul B.

2012-03-01

173

The Chemical Impact of Physical Conditions in the Interstellar Medium  

NASA Astrophysics Data System (ADS)

We examine the role cosmic rays, X-rays and ultra-violet (UV) photons play in the chemical evolution of the interstellar medium, and how astrophysical processes like massive star formation can change the fluxes of these energetic particles. We connect star formation rates to interstellar chemistry. We first explore the basic effects of cosmic-ray and X-ray ionization and UV photodissociation on the chemistry. For cosmic-ray and X-ray ionization, increasing the ionization rates enriches the chemistry, up to a value of 10 -14 s-1, whereupon molecules and ions are quickly destroyed due to the high electron fraction. Isolated from other effects, the UV field tends to dissociate species much more efficiently than ionizing them, and generally reduces molecular abundances, especially those of complex molecules. The combination of a high ionization rate and a high UV field can enhance the production of some molecular species, such as small hydrocarbons. We investigate the role of cosmic rays and UV photons in the Horsehead Nebula, and determine the impact a column-dependent cosmic ray ionization rate makes on photodissociation region (PDR) chemistry. The column-dependence of cosmic rays is solved using a three-dimensional two-fluid magnetohydrodynamics model, treating the cosmic rays as a fluid governed by the relativistic Boltzmann Transport Equation, and treating the interstellar medium as a second fluid, governed by the standard non-relativistic magnetohydrodynamics equations. We then utilize a modified version of the Morata-Herbst time-dependent PDR model, incorporating our function for cosmic ray ionization. Our results help solve a chemical mystery concerning high abundances of small hydrocarbons at the edge of the nebula. We discuss predictions the model makes for species currently unobserved in the Horsehead Nebula. Finally, we examine the role of star formation on interstellar astrochemistry in the Orion KL region. We develop a new astrochemical gas-grain PDR model with a time-dependent UV radiation field and X-ray and cosmic ray flux, scaled to the star formation rate and radiative contributions of different spectral-type stars. The results provide an explanation for OH+, H2O + and water observations, and H3O+ non-detection in the region, as well as make unique predictions for HCO+ and other molecules. These results allow us to constrain the age of the Orion KL region. We predict an age for Orion KL of one hundred thousand to one million years after OB star formation.

Rimmer, Paul Brandon

2012-09-01

174

Chemically and biologically modified activated carbon sorbents for the removal of lead ions from aqueous media  

Microsoft Academic Search

A method is described for hybridization of the adsorption and biosorption characteristics of chemically treated commercial activated carbon and baker's yeast, respectively, for the formation of environmental friendly multifunctional sorbents. Activated carbon was loaded with baker's yeast after acid-base treatment. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) Spectroscopy were used to characterize these sorbents. Moreover, the sorption capabilities

Mohamed E. Mahmoud; Tarek M. Abdel-Fattah; Maher M. Osman; Somia B. Ahmed

2012-01-01

175

Chemical Composition of Meridiani Sediments: Traces of Aqueous Past on Martian Surface  

NASA Astrophysics Data System (ADS)

Measurements of outcrop samples by the Alpha Particle X-Ray Spectrometer (APXS), onboard the NASA Mars Exploration Rover Opportunity at Meridiani, showed strong sulfur peaks in the x-ray spectra. Sulfur concentrations increased from natural (as is) rock surfaces over brushed to abraded rocks that turned out to be sulfur-loaded sediments. Along the 11-kilometer traverse of the rover many abraded surfaces could be measured by the APXS because the softness of the outcrops permitted grinding by the Rock Abrasion Tool (RAT) until today. All outcrop samples exhibited high sulfur concentrations of more than 6 weight percent; some samples exceeded 10 wt-% making S a major element and indicating a special history of these sediments. Element concentrations of all abraded rocks along the traverse were studied as function of sulfur content. A linear relationship with a negative slope was found for the silicon-sulfur pair. A similar relation holds for Al, Na, K, P, Ti, and Cr versus S. Iron shows a weak correlation with S (only a slight negative slope). Constant concentrations are exhibited by Mn and Ni. Calcium, Mg, and Zn, reveal a slight increase with increasing S contents (positive slope). During the first half of the traverse Mg and S are strongly correlated, later almost none. The formation of the sediments can be described by a two-component mixing model, where sulfur is mainly present in one component. The composition of the other component, the siliciclastic material, was extrapolated from above sample compositions to low S contents. The derived siliciclastic composition differs from encountered basaltic material, such as 'Bounce Rock' at Meridiani or the Adirondack Class rocks at Gusev crater, but, is similar to rocks discovered near Home Plate (Gusev). Best compositional matches are found for 'Masada Clod', 'Raquelme3', and others, which are significantly altered from an original basaltic composition. Apparently this composition type is wider spread on the Martian surface. The other mixing component contains various sulfates. Assuming large volcanic exhalations of sulfur, any original aqueous solution became very acidic. 'Normal' rocks were rapidly leached and gradually dissolved to form new compounds and large quantities of sulfates in an aqueous system. To bring the two components together, either wind and/or water did the transport. The small scatter of the concentration data points (mostly around a straight line) suggests that there was a concentration gradient in bodies of standing water on a kilometer-wide scale at least for a short period of time. The concentrations of many elements (Si, Al, Na, K, P, Ti, and Cr) are diluted by increasing sulfur contents. Hence, these elements were mainly part of the siliciclastic component. On the other hand, elements whose concentrations increase with increasing S (e.g. Ca, Mg, and Zn) were part of sulfates and of mafic minerals (in the siliciclastic component). Iron showing some dilution by sulfur was determined by Mössbauer spectroscopy to be present also as ferric sulfate. The above observations reveal that several elements formed sulfates in these sediments: Mg, Ca, Fe, and Zn. An aqueous system existed during the period of sediment formation and left unique traces in the sedimentary composition.

Brueckner, J.; Gellert, R.; D'Uston, C.; Treguier, E.; Squyres, S. W.

2007-12-01

176

Abiotic formation of hydrocarbons under hydrothermal conditions: Constraints from chemical and isotope data  

Microsoft Academic Search

To understand reaction pathways and isotope systematics during mineral-catalyzed abiotic synthesis of hydrocarbons under hydrothermal conditions, experiments involving magnetite and CO2 and H2-bearing aqueous fluids were conducted at 400°C and 500 bars. A robust technique for sample storage and transfer from experimental apparatus to stable isotope mass spectrometer provides a methodology for integration of both carbon and hydrogen isotope characterization

Qi Fu; Barbara Sherwood Lollar; Juske Horita; Georges Lacrampe-Couloume; William E. Seyfried

2007-01-01

177

N-Alkylations of chitosan promoted with sodium hydrogen carbonate under aqueous conditions.  

PubMed

Chitosan was reacted with four alkyl halides, monobromoacetic acid, benzyl bromide, 2-bromoethanol, and monochloroacetic acid, in the presence of NaHCO(3) in water. Chemical structures, degrees of substitution, and degrees of polymerization of reaction products were studied by FT-IR, NMR, SEC-MALLS, and elementary analyses. All alkyl groups were introduced selectively into the C2-amine groups of chitosan, and the yields of the N-alkyl chitosans were >90% by this method. N-Carboxymethyl chitosan (N-CMCh) and N-benzyl chitosan (N-BnCh) with high degrees of substitution (DS) up to 200% and 164% of the C2-amine groups, respectively, were obtained; N,N-dicarboxymethyl and N,N-dibenzyl chitosans were obtained in high yields. Degrees of polymerization (DP) of N-CMCh decreased during the reaction. The greater the amount of monobromoacetic acid added, the lower the DP of N-CMCh. PMID:22197793

Kurita, Y; Isogai, A

2012-04-01

178

Biosorption of zinc from aqueous solution using chemically treated rice husk.  

PubMed

In this study, adsorption of zinc onto the adsorbent (untreated rice husk and NaOH-treated rice husk) was examined. During the removal process, batch technique was used, and the effects of pH and contact time were investigated. Langmuir isotherm was applied in order to determine the efficiency of NaOH-treated rice husk used as an adsorbent. The zinc adsorption was fast, and equilibrium was attained within 30?min. The maximum removal ratios of zinc for untreated rice husk and NaOH-treated rice husk after 1.5?h were 52.3% and 95.2%, respectively, with initial zinc concentration of 25?mg/L and optimum pH of 4.0. Data obtained from batch adsorption experiments fitted well with the Langmuir isotherm model. Maximum adsorption capacity of zinc onto untreated rice husk and NaOH-treated rice husk was 12.41?mg/g, and 20.08?mg/g respectively, at adsorbent dosage of 1?g/L at 25°C. The nature of functional groups (i.e., amino, carboxyl, and hydroxyl) and metal ion interactions was examined by the FT-IR technique. It was concluded that the NaOH-treated rice husk had stronger adsorption capacity for Zn(2+) compared with the untreated rice husk. The NaOH-treated rice husk is an inexpensive and environmentally friendly adsorbent for Zn(2+) removal from aqueous solutions. PMID:23841065

Zhang, Ying; Zheng, Ru; Zhao, Jiaying; Zhang, Yingchao; Wong, Po-Keung; Ma, Fang

2013-01-01

179

Biosorption of Zinc from Aqueous Solution Using Chemically Treated Rice Husk  

PubMed Central

In this study, adsorption of zinc onto the adsorbent (untreated rice husk and NaOH-treated rice husk) was examined. During the removal process, batch technique was used, and the effects of pH and contact time were investigated. Langmuir isotherm was applied in order to determine the efficiency of NaOH-treated rice husk used as an adsorbent. The zinc adsorption was fast, and equilibrium was attained within 30?min. The maximum removal ratios of zinc for untreated rice husk and NaOH-treated rice husk after 1.5?h were 52.3% and 95.2%, respectively, with initial zinc concentration of 25?mg/L and optimum pH of 4.0. Data obtained from batch adsorption experiments fitted well with the Langmuir isotherm model. Maximum adsorption capacity of zinc onto untreated rice husk and NaOH-treated rice husk was 12.41?mg/g, and 20.08?mg/g respectively, at adsorbent dosage of 1?g/L at 25°C. The nature of functional groups (i.e., amino, carboxyl, and hydroxyl) and metal ion interactions was examined by the FT-IR technique. It was concluded that the NaOH-treated rice husk had stronger adsorption capacity for Zn2+ compared with the untreated rice husk. The NaOH-treated rice husk is an inexpensive and environmentally friendly adsorbent for Zn2+ removal from aqueous solutions.

Zheng, Ru; Zhao, Jiaying; Zhang, Yingchao; Wong, Po-keung; Ma, Fang

2013-01-01

180

Ferrate(VI): a green chemical for the oxidation of cyanide in aqueous/waste solutions.  

PubMed

The higher oxidation state of iron, i.e. Fe(VI), was employed for the oxidation of the important toxic ion cyanide in aqueous/waste waters. Cyanide was oxidized to cyanate, which is 1,000 times less toxic than cyanide, and can often be accepted for its ultimate disposal. It was noted that Fe(VI) is a very powerful oxidizing agent, and can oxidize most of the cyanide within a few minutes, ca 5 minutes, of contact. The extent of the reduction of Fe(VI) was obtained using the UV-Visible measurements. Further, the UV-Visible data was used to explain the reaction kinetics involved in the redox reaction between ferrate(VI) and cyanide. The pseudo-first-order rate constant was calculated by maintaining the cyanide concentration in excess, with the overall second order rate constant values obtained for initial Fe(VI) concentrations of 1.0 and 0.1 mmol/L. The oxidation of cyanide was again confirmed using a cyanide probe. Fe(VI) was further employed for its possible application in the treatment of industrial wastewaters containing cyanide, along with some heavy metals, such as those obtained from electroplating industries. PMID:17474007

Tiwari, Diwakar; Kim, Hyoung-Uk; Choi, Bong-Jong; Lee, Seung-Mok; Kwon, Oh-Heung; Choi, Kyu-Man; Yang, Jae-Kyu

2007-05-01

181

Aqueous chemical growth of alpha-Fe2O3-alpha-Cr203 nanocompositethin films  

SciTech Connect

We are reporting here on the inexpensive fabrication and optical properties of an iron(III) oxide chromium(III) oxide nanocomposite thin film of corundum crystal structure. Its novel and unique-designed architecture consists of uniformed, well-defined and oriented nanorods of Hematite (alpha-Fe2O3) of 50 nm in diameter and 500nm in length and homogeneously distributed nonaggregated monodisperse spherical nanoparticles of Eskolaite (alpha-Cr2O3) of 250 nm in diameter. This alpha-Fe2O3 alpha-Cr2O3 nanocomposite thin film is obtained by growing, directly onto transparent polycrystalline conducting substrate, an oriented layer of hematite nanorods and growing subsequently, the eskolaite layer. The synthesis is carried out by a template-free, low-temperature, multilayer thin film coating process using aqueous solution of metal salts as precursors. Almost 100 percent of the light is absorbed by the composite film between 300 and 525 nm and 40 percent at 800 nm which yields great expectations as photoanode materials for photovoltaic cells and photocatalytic devices.

Vayssieres, Lionel; Guo, Jinghua; Nordgren, Joseph

2001-06-30

182

Radiation Chemical and MR Studies of Aqueous Agarose Gels Containing Ferrous Ions.  

NASA Astrophysics Data System (ADS)

Aqueous agarose gels containing ferrous ions, in 0.05 N sulfuric acid have been studied after irradiation with 6-18 MeV electrons or ^{137} Cs gamma-rays. Such gels can sustain a radiolytic chain reaction, producing Fe ^{3+} with G(Fe^ {3+})-values up to 100 having been observed. The Fe^{3+} production is independent of dose rate between 0.434 and 3.74 Gy min ^{-1}. Dissolved oxygen is needed to maintain the chain reaction, and initial ferric yields are increased if the gel is oxygen saturated or if the ferrous concentration is decreased below 1 mM. The oxidation of ferrous to ferric alters the magnetic moment of the ion and its electron spin relaxation time, which in turn affects its ability to promote proton spin relaxation rates. Longitudinal proton magnetic relaxation rates are increased in proportion to ferric production, permitting visualization of dose levels in these gels by magnetic resonance imaging (MRI) techniques. Non-uniform dose distribution images of electron irradiated ferrous/agarose (FA) systems have been obtained using MRI. Images of radiation doses surrounding capillary tubes filled with radioactive material embedded in FA systems have also been obtained. In this work, another new method of using the ferrous/agarose gel system doped with xylenol orange to visualize the radiation dose distribution directly by eye has been developed. The color change developed depends both quantitatively and qualitatively on the concentrations of solutes in the gel.

Leghrouz, Amin Ahmad

183

Ultrasonic relaxation and fast chemical kinetics of some carbohydrate aqueous solutions  

SciTech Connect

Molecular relaxation properties of the monosaccharides (a) D-glucose, (b) methyl {beta}-D-glucopyranoside, (c) methyl {alpha}-D-mannopyranoside, (d) D-xylose, (e) D-arabinose, (f) methyl {beta}-D-xylopyranoside, (g) methyl {beta}-D-arabinopyranoside, (h) methyl {alpha}-L-(6-deoxy)mannopyranoside, and (i) 1,6-anhydro-{beta}-D-glucopyranoside, all in aqueous solution, have been studied using broad band ultrasonic spectrometry in the frequency range 0.2-2000 MHz. Ultrasonic excess absorption with relaxation characteristics near 80 MHz was found for glucose and the methyl glucosides of D-glucose and D-mannose, but no relaxation process was detected for the other monosaccharides in the same frequency range. From structural aspects it is deduced that the most likely process causing the observed relaxation is the rotation of the exocyclic -CH{sub 2}OH group, placing rotational isomerization on the nanosecond time scale. Relaxation parameters for D-glucose and methyl {beta}-D-glucopyranoside solutions were further investigated as a function of concentration and temperature, in order to confirm the assignment of the relaxation process, and to determine some of its thermodynamic and kinetic parameters. 19 refs., 7 figs., 1 tab.

Behrends, R. [Max-Planck-Institut fuer Biophysikalische Chemie, Goettingen-Nikolausberg (Germany)] [Max-Planck-Institut fuer Biophysikalische Chemie, Goettingen-Nikolausberg (Germany); [Georg-August-Universitaet, Goettingen (Germany); Cowman, M.K.; Majewski, J.; Petrucci, S. [Polytechnic Univ., Farmingdale, NY (United States)] [Polytechnic Univ., Farmingdale, NY (United States); Eggers, F.; Richmann, K.H. [Max-Planck-Institut fuer Biophysikalische Chemie, Goettingen-Nikolausberg (Germany)] [Max-Planck-Institut fuer Biophysikalische Chemie, Goettingen-Nikolausberg (Germany); Eyring, E.M. [Univ. of Utah., Salt Lake City, (United States)] [Univ. of Utah., Salt Lake City, (United States); Riech, M.; Kaatze, U. [Georg-August-Universitaet, Goettingen (Germany)] [Georg-August-Universitaet, Goettingen (Germany)

1997-03-05

184

Crack size effects on the chemical driving force for aqueous corrosion fatigue  

NASA Astrophysics Data System (ADS)

Small crack size accelerates corrosion fatigue propagation through high strength 4130 steel in aqueous 3 pct NaCl. The size effect is attributed to crack geometry dependent mass transport and electrochemical reaction processes which govern embrittlement. For vacuum or moist air, growth rates are defined by stress intensity range independent of crack size (0.1 to 40 mm) and applied maximum stress (0.10 to 0.95 ?ys). In contrast small (0.1 to 2 mm) surface elliptical and edge cracks in saltwater grow up to 500 times faster than long (15 to 40 mm) cracks at constant ?K. Small cracks grow along prior austenite grain boundaries, while long cracks propagate by a brittle transgranular mode associated with tempered martensite. The small crack acceleration is maximum at low ?K levels and decreases with increasing crack length at constant stress, or with increasing stress at constant small crack size. Reductions in corrosion fatigue growth rate correlate with increased brittle transgranular cracking. Crack mouth opening, proportional to the crack solution volume to surface area ratio, determines the environmental enhancement of growth rate and the proportions of inter- and transgranular cracking. Small cracks grow at rapid rates because of enhanced hydrogen production, traceable to increased hydrolytic acidification and reduced oxygen inhibition within the occluded cell.

Gangloff, R. P.

1985-05-01

185

SH-SAW Sensor Platform for Chemical Detection in Aqueous Solutions  

SciTech Connect

Chemically sensitive polymers coated on delay lines utilizing shear horizontal surface acoustic wave (SH-SAW) sensors are investigated for the detection of organic analytes in liquid environments. The SH-SAW sensor platform was designed and fabricated on 36{degree} rotated Y-cut LiTaO{sub 3}. By depositing a SiO{sub 2} dielectric layer over the entire device prior to applying the polymer film, partial electrical passivation of the interdigital transducers (IDT) is obtained while increasing the mass sensitivity of the device. Changes in the mechanical properties of the chemically sensitive polymer materials were clearly detectable through a frequency shift at least one order of magnitude larger than that of a coated-quartz crystal resonator (QCR) in a similar experiment.

Casalnuovo, Steve; Cernosek, Richard; Josse, Fabien; Ricco, Antonio; Zhou, Rongnong

1999-07-20

186

Determination of the optimum conditions for boric acid extraction with carbon dioxide gas in aqueous media from colemanite containing arsenic  

SciTech Connect

The Taguchi method was used to determine optimum conditions for the boric acid extraction from colemanite ore containing As in aqueous media saturated by CO{sub 2} gas. After the parameters were determined to be efficient on the extraction efficiency, the experimental series with two steps were carried out. The chosen experimental parameters for the first series of experiments and their ranges were as follows: (1) reaction temperature, 25--70 C; (2) solid-to-liquid ratio (by weight), 0.091 to 0.333; (3) gas flow rate (in mL/min), 66.70--711; (4) mean particle size, {minus}100 to {minus}10 mesh; (5) stirring speed, 200--600 rpm; (6) reaction time, 10--90 min. The optimum conditions were found to be as follows: reaction temperature, 70 C; solid-to-liquid ratio, 0.091; gas flow rate, 711 (in mL/min); particle size, {minus}100 mesh; stirring speed, 500 rpm; reaction time, 90 min. Under these optimum conditions, the boric acid extraction efficiency from the colemanite containing As was approximately 54%. Chosen experimental parameters for the second series of experiments and their ranges were as follows: (1) reaction temperature, 60--80 C; (2) solid-to-liquid ratio (by weight), 0.1000 to 0.167; (3) gas pressure (in atm), 1.5; 2.7; (4) reaction time, 45--120 min. The optimum conditions were found to be as follows: reaction temperature, 70 C; solid-to-liquid ratio, 0.1; gas pressure, 2.7 atm; reaction time, 120 min. Under these optimum conditions the boric acid extraction efficiency from the colemanite ore was approximately 75%. Under these optimum conditions, the boric acid extraction efficiency from calcined colemanite ore was approximately 99.55%.

Ata, O.N.; Colak, S.; Copur, M.; Celik, C.

2000-02-01

187

Solubility of AmOHCO{sub 3} in aqueous solution under atmospheric conditions  

SciTech Connect

Modeling calculations on the solubility of americium have indicated that basic americium carbonate, and not americium trihydroxide, is the solubility-controlling solid in the pH range from 6 to 10 under the influence of atmospheric CO{sub 2}. The solubility of crystalline {sup 243}AmOHCO{sup 3} has been investigated in batch experiments in near-neutral and basic solutions as a function of dissolution time in 0.1 M NaClO{sup 4} at room temperature under oxic conditions. After the solutions reached steady-state conditions, the influence of dissolved solids on the americium concentration in the supernatant solution was studied by utilizing several experimental methods to separate the solution phase from the solid. The solids were characterized by X-ray powder diffraction analysis.

Nitsche, H.

1987-12-01

188

Solubility of AmOHCO sub 3 in aqueous solution under atmospheric conditions  

SciTech Connect

Modeling calculations on the solubility of americium have indicated that basic americium carbonate, and not americium trihydroxide, is the solubility-controlling solid in the pH range from 6 to 10 under the influence of atmospheric CO{sub 2}. The solubility of crystalline {sup 243}AmOHCO{sup 3} has been investigated in batch experiments in near-neutral and basic solutions as a function of dissolution time in 0.1 M NaClO{sup 4} at room temperature under oxic conditions. After the solutions reached steady-state conditions, the influence of dissolved solids on the americium concentration in the supernatant solution was studied by utilizing several experimental methods to separate the solution phase from the solid. The solids were characterized by X-ray powder diffraction analysis.

Nitsche, H.

1987-12-01

189

Destruction of VX by aqueous-phase oxidation using peroxydisulfate (direct chemical oxidation)  

SciTech Connect

Chemical warfare agents may be completely destroyed (converted to H{sub 2}O, CO{sub 2}, salts) by oxidation at 90--100 C using acidified ammonium peroxydisulfate, with recycle of NH{sub 4}SO{sub 4} byproduct. The process requires no toxic or expended catalysts and produces no secondary wastes other than the precipitated inorganic content of the agents. To determine oxidative capability of peroxydisulfate at low reductant contents, we measured rate data for oxidation of 20 diverse compounds with diverse functional groups; 4 of these have bonds similar to those found in VX, HD, and GB. On an equivalence basis, integral first-order rate constants for 100 C oxidation are 0.012{plus_minus}0.005 min{sup {minus}1} for di-isopropyl-methyl-phosphonate, methyl phosphonic acid, triethylamine, and 2,2{prime}-thiodiethanol at low initial concentrations of 50 ppM(as carbon) and pH 1.5. To provide scale-up equations for a bulk chemical agent destruction process, we measured time-dependent oxidation of bulk model chemicals at high concentrations (0.5 N) and developed and tested a quantitative model. A practical process for bulk VX destruction would begin with chemical detoxification by existing techniques (eg, hydrolysis or mild oxidation using oxone), followed by mineralization of the largely detoxified products by peroxydisulfate. Secondary wastes would be avoided by use of commercial electrolysis equipment to regenerate the oxidant. Reagent requirements, mass balance and scaleup parameters are given for VX destruction, using peroxydisulfate alone, or supplemented with hydrogen peroxide. For the use of 2.5 N peroxydisulfate as the oxidant, a 1 m{sup 3} digester will process about 200 kg (as C) per day. The process may be extended to total destruction of HD and hydrolysis products of G agents.

Cooper, J.F.; Krueger, R.; Farmer, J.C.

1995-10-11

190

SH-SAW Sensor Platform for Chemical Detection in Aqueous Solutions  

Microsoft Academic Search

Chemically sensitive polymers coated on delay lines utilizing shear horizontal surface acoustic wave (SH-SAW) sensors are investigated for the detection of organic analytes in liquid environments. The SH-SAW sensor platform was designed and fabricated on 36° rotated Y-cut LiTaOâ. By depositing a SiOâ dielectric layer over the entire device prior to applying the polymer film, partial electrical passivation of the

Steve Casalnuovo; Richard Cernosek; Fabien Josse; Antonio Ricco; Rongnong Zhou

1999-01-01

191

Alkyl and alkoxyl monolayers directly attached to silicon: chemical durability in aqueous solutions.  

PubMed

For practical application of self-assembled monolayers (SAMs), knowledge of their chemical durability in acidic or basic solutions is important. In the present work, a series of SAMs directly immobilized on a silicon (111) surface through Si-C or Si-O-C covalent bonds without a native oxide layer were prepared by thermally activated chemical reactions of a hydrogen-terminated Si(111) substrate with linear molecules, i.e., 1-hexadecene, 1-hexadecanol, 1-dodecanol, and n-dodecanal, to investigate the durability of the SAMs to HF and Na2CO3 solutions. While grazing incidence X-ray reflectivity measurements showed that all the as-prepared SAMs had almost the same film density and molecular coverage, keeping the original step and terrace structure of Si(111) as is observed by atomic force microscopy, they gave different degradation behaviors, i.e., pitting and concomitant surface roughening in both solutions. 1-hexadecene SAM was stable against immersion in both solutions, while the other SAMs were damaged within 60 min, most likely due to the difference in chemical bonding modes at the SAM/Si interface, i.e., Si-C and Si-O-C. PMID:19334747

Sano, Hikaru; Maeda, Hajime; Ichii, Takashi; Murase, Kuniaki; Noda, Kei; Matsushige, Kazumi; Sugimura, Hiroyuki

2009-05-19

192

DEFINITIVE SOX CONTROL PROCESS EVALUATIONS: AQUEOUS CARBONATE AND WELLMAN-LORD (ACID, ALLIED CHEMICAL, AND RESOX) FGD (FLUE GAS DESULFURIZATION) TECHNOLOGIES  

EPA Science Inventory

The report gives results of economic evaluations of two processes: the Rockwell International aqueous carbonate process (ACP) and the Wellman-Lord process, the latter applied to a sulfuric acid plant, the Foster Wheeler Resox process, and the Allied Chemical coal reduction proces...

193

APPLICATION OF STIR BAR SORPTIVE EXTRACTION TO ANALYSIS OF VOLATILE AND SEMIVOLATILE ORGANIC CHEMICALS OF POTENTIAL CONCERN IN SOLIDS AND AQUEOUS SAMPLES FROM THE HANFORD SITE  

SciTech Connect

Stir bar sorptive extraction was applied to aqueous and solid samples for the extraction and analysis of organic compounds from the Hanford chemicals of potential concern list, as identified in the vapor data quality objectives. The 222-S Laboratory analyzed these compounds from vapor samples on thermal desorption tubes as part of the Hanford Site industrial hygiene vapor sampling effort.

FRYE JM; KUNKEL JM

2009-03-05

194

Definitive SOx control process evaluations: aqueous carbonate and WellmanLord (acid, allied chemical, and resox) FGD (flue gas desulfurization) technologies. Final report Apr 78Apr 81  

Microsoft Academic Search

The report gives results of economic evaluations of two processes: the Rockwell International aqueous carbonate process (ACP) and the Wellman-Lord process, the latter applied to a sulfuric acid plant, the Foster Wheeler Resox process, and the Allied Chemical coal reduction process, all for sulfur production. The ACP uses a spray dryer flue gas desulfurization (FGD) system and molten salt reduction

J. R. Byrd; K. D. Anderson; S. V. Tomlinson; R. L. Torstrick

1981-01-01

195

Copper(II) removal from aqueous solutions by adsorption on non-treated and chemically modified cactus fibres.  

PubMed

The adsorption efficiency of a biomass by-product (cactus fibres) regarding the removal of copper(II) from aqueous solutions has been investigated before and after its chemical treatment. The chemical treatment of the biomass by-product included phosphorylation and MnO2-coating. The separation/removal efficiency has been studied as a function of pH, Cu(II) concentration, ionic strength, temperature and contact time. Evaluation of the experimental data shows that the MnO2-coated product presents the highest adsorption capacity, followed by the non-treated and phosphorylated material. Regarding the effect of ionic strength/salinity on the adsorption, in contrast to the removal efficiency of the phosphorylated product, which is significantly affected, the MnO2-coated and non-treated material don't show any effect, indicating the formation of inner-sphere surface complexes. The adsorption reaction is in all cases endothermic and relatively fast, particularly the adsorption on the MnO2-coated product. The results of the present study indicate that for the removal of bivalent metal-ions from contaminated waters the MnO2-coated material is expected to be the most effective adsorbent and an alternative to MnO2 resins for the treatment of environmentally relevant waters. PMID:24334902

Prodromou, M; Pashalidis, I

2013-01-01

196

Saffron Aqueous Extract Inhibits the Chemically-induced Gastric Cancer Progression in the Wistar Albino Rat  

PubMed Central

Objective(s): Gastric cancer is the first and second leading cause of cancer related death in Iranian men and women, respectively. Gastric cancer management is based on the surgery, radiotherapy and chemotherapy. In the present study, for the first time, the beneficial effect of saffron (Crocus sativus L.) aqueous extract (SAE) on the 1-Methyl-3-nitro-1-nitrosoguanidine (MNNG)-induced gastric cancer in rat was investigated. Materials and Methods: MNNG was used to induce gastric cancer and then, different concentrations of SAE were administered to rats. After sacrificing, the stomach tissue was investigated by both pathologist and flow cytometry, and several biochemical parameters was determined in the plasma (or serum) and stomach of rats. Results: Pathologic data indicated the induction of cancer at different stages from hyperplasia to adenoma in rats; and the inhibition of cancer progression in the gastric tissue by SAE administration; so that, 20% of cancerous rats treated with higher doses of SAE was completely normal at the end of experiment and there was no rat with adenoma in the SAE treated groups. In addition, the results of the flow cytometry/ propidium iodide staining showed that the apoptosis/proliferation ratio was increased due to the SAE treatment of cancerous rats. Moreover, the significantly increased serum LDH and decreased plasma antioxidant activity due to cancer induction fell backwards after treatment of rats with SAE. But changes in the other parameters (Ca2+, tyrosine kinase activity and carcino-embryonic antigen) were not significant. Conclusion: SAE inhibits the progression of gastric cancer in rats, in a dose dependent manner.

Bathaie, S. Zahra; Miri, Hamidreza; Mohagheghi, Mohammad-Ali; Mokhtari- Dizaji, Manijeh; Shahbazfar, Amir-Ali; Hasanzadeh, Hadi

2013-01-01

197

Radiation-chemical and MR studies of aqueous agarose gels containing ferrous ions  

SciTech Connect

Aqueous agarose gels containing ferrous ions, in 0.05 N sulfuric acid have been studied after irradiation with 6-18 MeV electrons or {sup 137}Cs {gamma}-rays. Such gels can sustain a radiolytic chain reaction, producing Fe{sup 3+} with G (Fe{sup 3+})-values up to 100 having been observed. The Fe{sup 3+} production is independent of dose rate between 0.434 and 3.74 Gy min{sup {minus}1}. Dissolved oxygen is needed to maintain the chain reaction, and initial ferric yields are increased if the gel is oxygen saturated or if the ferrous concentration is decreased below 1 mM. The oxidation of ferrous to ferric alters the magnetic moment of the ion and its electron spin relaxation time, which in turn affects its ability to promote proton spin relaxation rates. Longitudinal proton magnetic relaxation rates are increased in proportion to ferric production, permitting visualization of dose levels in these gels by magnetic resonance imaging (MRI) techniques. Non-uniform dose distribution images of electron irradiated ferrous/agarose (FA) systems have been obtained using MRI. Images of radiation doses surrounding capillary tubes filled with radioactive material embedded in PA systems have also been obtained. In this work, another new method of using the ferrous/agarose gel system doped with xylenol orange to visualize the radiation dose distribution directly by eye has been developed. The color change developed depends both quantitatively and qualitatively on the concentrations of solutes in the gel.

Leghrous, A.A.

1989-01-01

198

Corrosion of Carbon Steel at High Temperature in Reducing Chemical Conditions.  

National Technical Information Service (NTIS)

Corrosion tests of carbon steel were carried out in a dynamic loop at high temperature and pressure under reducing chemical conditions. These experiments were performed in ammoniated water, with and without oxygen, at temperatures up to 250 C. Corrosion r...

P. A. Borroni E. Diacci R. Rizzi C. Ronchetti

1981-01-01

199

SIMULATION OF ECOLOGICALLY CONSCIOUS CHEMICAL PROCESSES: FUGITIVE EMISSIONS VERSUS OPERATING CONDITIONS: JOURNAL ARTICLE  

EPA Science Inventory

NRMRL-CIN-1531A Mata, T.M., Smith*, R.L., Young*, D., and Costa, C.A.V. "Simulation of Ecologically Conscious Chemical Processes: Fugitive Emissions versus Operating Conditions." Paper published in: CHEMPOR' 2001, 8th International Chemical Engineering Conference, Aveiro, Portu...

200

Inhibited Cr(VI) reduction by aqueous Fe(II) under hyperalkaline conditions.  

PubMed

This study investigated Cr(VI) reduction by dissolved Fe(II) in hyperalkaline pH conditions as found in fluid wastes associated with the U.S. nuclear weapons program. The results show that Cr(VI) reduction by Fe(II) at alkaline pH solutions proceeds very quickly. The amount of Cr(VI) removed from solution and the amount reduced increases with Fe(II):Cr(VI) ratio. However, the Cr(VI) reduction under alkaline pH condition is nonstoichiometric, probably due to Fe(II) precipitation and mixed iron(III)-chromium-(III) (oxy)hydroxides blocking Fe(II) surface sites, as well as removing Fe(II) from solution through O2 oxidation. After Cr(VI) was reduced to Cr(III), it precipitated out as mixed Fe(x)Cr1-xO3(solids) and various Fe(III) precipitates with an overall Cr:Fe ratio of 1:3; all Cr remaining in the solution phase was unreduced Cr(VI). EXAFS data showed that Cr-O and Cr-Cr distances in the precipitates equal to 1.98 and 3.01 A, respectively, consistent with the spinel-type structure as chromite. PMID:15575269

He, Y Thomas; Chen, Chia-Chen; Traina, Samuel J

2004-11-01

201

Immobilization of selenate by iron in aqueous solution under anoxic conditions and the influence of uranyl  

NASA Astrophysics Data System (ADS)

In proposed high level radioactive waste repositories a large part of the spent nuclear fuel (SNF) canisters are commonly composed of iron. Selenium is present in spent nuclear fuel as a long lived fission product. This study investigates the influence of iron on the uptake of dissolved selenium in the form of selenate and the effect of the presence of dissolved uranyl on the above interaction of selenate. The iron oxide, and selenium speciation on the surfaces was investigated by Raman spectroscopy. X-ray Absorption Spectroscopy was used to determine the oxidation state of the selenium and uranium on the surfaces. Under the simulated groundwater conditions (10 mM NaCl, 2 mM NaHCO 3, <0.1 ppm O 2) the immobilized selenate was found to be reduced to oxidation states close to zero or lower and uranyl was found to be largely reduced to U(IV). The near simultaneous reduction of uranyl was found to greatly enhance the rate of selenate reduction. These findings suggest that the presence of uranyl being reduced by an iron surface could substantially enhance the rate of reduction of selenate under anoxic conditions relevant for a repository.

Puranen, Anders; Jonsson, Mats; Dähn, Rainer; Cui, Daqing

2009-08-01

202

Chemical characteristics of O-carboxymethyl chitosans related to the preparation conditions  

Microsoft Academic Search

Carboxymethyl chitosan (CM-chitosan) was prepared by chemical reaction with monochloroacetic acid under various conditions, and the chemical structure was analyzed by IR and NMR. The water solubility of the CM-chitosans had close relationships to the modifying conditions and the degree of carboxymethylation. The CM-chitosans, prepared at temperatures of 0–10 °C were soluble in water. But the CM-chitosan prepared between 20

Xi-Guang Chen; Hyun-Jin Park

2003-01-01

203

Effect of the glass composition on the chemical durability of zinc-phosphate-based glasses in aqueous solutions  

NASA Astrophysics Data System (ADS)

The chemical durability of glasses with the composition 40P2O5-55ZnO-1Ga2O3-4Ag2O and 41P2O5-51ZnO-8Ga2O3 (mol%) was studied by measuring the rates of aqueous dissolution in neutral, acidic and alkaline aqueous solutions and discussed as a function of the glass composition. The change in the pH of the solutions as a function of the immersion time of the samples was used to study the dissolution mechanism. Using XRD and SEM/EDXA, we showed that the dissolution in deionized (DI) water and HCl consists of the leaching of the phosphate chains into the medium along with (i) the formation of a hydrated layer with the composition Zn2P2O7·3H2O and also of AgCl agglomerates when immersed in HCl and (ii) a leaching out of P, Ga and Ag when immersed for more than 180 min in DI water and for more than 60 min in HCl. The dissolution in NaOH-Na2CO3 consists of a net consumption of the OH- along with the formation of layers of Zn3(PO4)2·(H2O)4 and Zn(H2PO2)2·H2O with no apparent diffusion of P, Ga and Ag when immersed for as long as 240 min. Increasing the Ga2O3 concentration in zinc-phosphate glass at the expense of Ag2O lowers the dissolution rate when immersed in DI water, HCl and NaOH-Na2CO3 probably due to a reinforcement of the glass network.

Massera, J.; Bourhis, K.; Petit, L.; Couzi, M.; Hupa, L.; Hupa, M.; Videau, J. J.; Cardinal, T.

2013-01-01

204

Diffusion and polymerization of styrene in an aqueous solution of potassium persulfate under static conditions  

SciTech Connect

The potassium persulfate-initiated polymerization of styrene in a mechanically agitated mixture of water and monomer leads to the formation of a stable, monodisperse latex. In order to explain the mechanism of the stabilization of the latex particles in this system, the authors present a detailed investigation of the polymerization of styrene in a specially constructed electrochemical cell under static conditions. A schematic of the cell is shown. Results show that the capacity of the electrical double layer on the platinum electrode remains constant with time in a system containing only a solution of electrolyte, either K/sub 2/SO/sub 4/ or K/sub 2/S/sub 2/O/sub 8/.

Oganesyan, A.A.; Boyadzhyan, V.G.; Gritskova, I.A.; Gukasyan, A.V.; Matsoyan, S.G.; Pravednikov, A.N.

1985-10-01

205

Solubility of aqueous methane under metastable conditions: implications for gas hydrate nucleation.  

PubMed

To understand the prenucleation stage of methane hydrate formation, we measured methane solubility under metastable conditions using molecular dynamics simulations. Three factors that influence solubility are considered: temperature, pressure, and the strength of the modeled van der Waals attraction between methane and water. Moreover, the naturally formed water cages and methane clusters in the methane solutions are analyzed. We find that both lowering the temperature and increasing the pressure increase methane solubility, but lowering the temperature is more effective than increasing the pressure in promoting hydrate nucleation because the former induces more water cages to form while the latter makes them less prevalent. With an increase in methane solubility, the chance of forming large methane clusters increases, with the distribution of cluster sizes being exponential. The critical solubility, beyond which the metastable solutions spontaneously form hydrate, is estimated to be ~0.05 mole fraction in this work, corresponding to the concentration of 1.7 methane molecules/nm(3). This value agrees well with the cage adsorption hypothesis of hydrate nucleation. PMID:23639139

Guo, Guang-Jun; Rodger, P Mark

2013-05-30

206

Model Chemical Decontamination Studies of Phosphate Esters in Aqueous and Microemulsion Media  

Microsoft Academic Search

The hydrolysis of 4-nitrophenylphosphate (NPP) in the presence of several cobalt(III) amine model systems in oil-in-water microemulsion media was investigated. The reaction was monitored by measuring the absorbance of the nitrophenolate ion produced in the reaction aliquots with time under the experimental condition. The order of effectiveness of the microemulsion system toward the hydrolysis of NPP was found to be

Fikru Tafesse; Kennedy Eguzozie

2008-01-01

207

CO-conditioning and dewatering of chemical sludge and waste activated sludge  

Microsoft Academic Search

The conditioning and dewatering behaviors of chemical and waste activated sludges from a tannery were studied. Capillary suction time (CST), specific resistance to filtration (SRF), and bound water content were used to evaluate the sludge dewatering behaviors. Zeta potentials were also measured. Experiments were conducted on each sludge conditioned and dewatered separately, and on the sludge mixed at various ratios.

G. R Chang; J. C Liu; D. J Lee

2001-01-01

208

Transport of Chemical Vapors from Subsurface Sources to Atmosphere as Affected by Shallow Subsurface and Atmospheric Conditions  

NASA Astrophysics Data System (ADS)

Understanding the movement and modeling of chemical vapor through unsaturated soil in the shallow subsurface when subjected to natural atmospheric thermal and mass flux boundary conditions at the land surface is of importance to applications such as landmine detection and vapor intrusion into subsurface structures. New, advanced technologies exist to sense chemical signatures at the land/atmosphere interface, but interpretation of these sensor signals to make assessment of source conditions remains a challenge. Chemical signatures are subject to numerous interactions while migrating through the unsaturated soil environment, attenuating signal strength and masking contaminant source conditions. The dominant process governing movement of gases through porous media is often assumed to be Fickian diffusion through the air phase with minimal or no quantification of other processes contributing to vapor migration, such as thermal diffusion, convective gas flow due to the displacement of air, expansion/contraction of air due to temperature changes, temporal and spatial variations of soil moisture and fluctuations in atmospheric pressure. Soil water evaporation and interfacial mass transfer add to the complexity of the system. The goal of this work is to perform controlled experiments under transient conditions of soil moisture, temperature and wind at the land/atmosphere interface and use the resulting dataset to test existing theories on subsurface gas flow and iterate between numerical modeling efforts and experimental data. Ultimately, we aim to update conceptual models of shallow subsurface vapor transport to include conditionally significant transport processes and inform placement of mobile sensors and/or networks. We have developed a two-dimensional tank apparatus equipped with a network of sensors and a flow-through head space for simulation of the atmospheric interface. A detailed matrix of realistic atmospheric boundary conditions was applied in a series of experiments. Water saturation, capillary pressure, air and soil temperature, and relative humidity were continuously monitored. Aqueous TCE was injected into the tank below the water table and allowed to volatilize. TCE concentration exiting the tank head space was measured through interval sampling by direct injection into a gas chromatograph. To quantify the transient concentration of TCE vapor in the soil pore space a novel use of Solid Phase Micro-Extraction (SPME) was developed. Results from our numerical simulations were compared with the experimental data, which demonstrated the importance of considering the interaction of the atmosphere with the subsurface in conceptualization and numerical model development. Results also emphasize that soil saturation and transient sorption have a significant effect on vapor transport through the vadose zone. Follow-up tests and detailed analyses are still underway. Additional applications of this work include carbon sequestration leakage, methane contamination in the shallow subsurface and environmental impact of hydraulic fracturing.

Rice, A. K.; Smits, K. M.; Hosken, K.; Schulte, P.; Illangasekare, T. H.

2012-12-01

209

Evaluation of laboratory and industrial meat and bone meal combustion residue as cadmium immobilizing material for remediation of polluted aqueous solutions: "chemical and ecotoxicological studies".  

PubMed

Meat and Bone Meals (MBM) combustion residues (ashes) are calcium and phosphate-rich materials. The aim of this work is to evaluate ashes efficiency for remediation of cadmium-contaminated aqueous solutions, and to assess the bioavailability of cadmium on Xenopus laevis larvae. In this study both industrial (MBM-BA) and laboratory (MBM-LA) ashes are compared regarding their efficiency. Kinetic investigations reveal that cadmium ions are quickly immobilized, with a maximum cadmium uptake at 57 mg Cd(2+)/g of ashes for MBM-LA, two times higher than metal uptake quantity of MBM-BA, in our experimental conditions. Chemical and X-ray diffraction analysis (XRD) reveal that Cd(2+) is mainly immobilized as Ca(10-x)Cd(x)(PO(4))(6)(OH)(2) by both ashes, whereas otavite, Cd(CO(3)), is also involved for MBM-LA in cadmium uptake. Otavite formation could be explained by the presence of carbonates in MBM-LA, as observed by IR. Genotoxicity of cadmium solution on Xenopus larvae is observed at 0.02, 0.2 and 2mg Cd(2+)/L. However addition of only 0.1g/L MBM-LA inhibits these effects for the above concentration values whereas Cd(2+) bioaccumulation in larvae's liver is similar for both experiments, with and without ashes. PMID:19162394

Coutand, M; Deydier, E; Cyr, M; Mouchet, F; Gauthier, L; Guilet, R; Savaete, L Bernues; Cren, S; Clastres, P

2009-07-30

210

Degradation of endocrine disrupting chemicals in aqueous solution by interaction of photocatalytic oxidation and ferrate (VI) oxidation.  

PubMed

In this study, the degradation of bisphenol A in aqueous suspension by interaction of photocatalytic oxidation and ferrate(VI) oxidation was investigated under different conditions. The results indicate that the formation of Fe(V) and Fe(IV) is in the photocatalytic reduction of Fe(VI) by electron (ecb-) on the surface of TiO2. The oxidation efficiency of the photocatalytic oxidation in the presence of Fe(VI) was much greater than that without. In addition, the decomposition of Fe(VI) under different conditions was also investigated. The results indicate that the Fe(VI) reduction was accelerated by photocatalytic reaction and the adsorption capacity of Fe(VI) on TiO2 surface decreased as pH increased. The characteristics of solid potassium ferrate prepared were investigated by X-ray diffraction. It was found that the potassium ferrate solid has a tetrahedral structure with a space group of D2h (Pnma) and a = 7.705 A, b = 5.863 A, and c = 10.36 A. PMID:17305143

Li, C; Li, X Z

2007-01-01

211

Rare-earth metal oxide doped transparent mesoporous silica plates under non-aqueous condition as a potential UV sensor.  

PubMed

Transparent mesoporous silica plates doped with rare-earth metal oxide were prepared using solvent-evaporation method based on the self-organization between structure-directing agent and silicate in a non-aqueous solvent. A triblock copolymer, Pluronic (F127 or P123), was used as the structure-directing agent, while tetraethyl orthosilicate (TEOS) was used as a silica source. The pore diameter and the surface area of the mesoporous silica plate prepared with the optimized conditions were ca 40 A and 600 m2 g(-1), respectively, for both structure-directing agent. Rare-earth metal oxides (Eu, Tb, Tm oxide) in mesochannel were formed via one-step synthetic route based on the preparation method of a silica plate. Optical properties of rare-earth metal oxide-doped mesoporous silica plates were investigated by UV irradiation and photoluminescence (PL) spectroscopy. Under the exitation wavelength of 254 nm, the doped mesoporous silica plates emitted red, green and blue for Eu, Tb and Tm oxides, respectively. Rare-earth metal oxide-doped mesoporous silica plates showed enhanced PL intensity compared to that of the bulk rare-earth metal oxide. PMID:24245274

Lee, Sang-Joon; Park, Sung Soo; Lee, Sang Hyun; Hong, Sang-Hyun; Ha, Chang-Sik

2013-11-01

212

Kinetics of organic transformations under mild aqueous conditions: implications for the origin of life and its metabolism  

NASA Technical Reports Server (NTRS)

The rates of thermal transformation of organic molecules containing carbon, hydrogen, and oxygen were systematically examined in order to identify the kinetic constraints that governed origin-of-life organic chemistry under mild aqueous conditions. Arrhenius plots of the kinetic data were used to estimate the reaction of half-lifes at 50 degrees C. This survey showed that hydrocarbons and organic substances containing a single oxygenated group were kinetically the most stable; whereas organic substances containing two oxygenated groups in which one group was an alpha- or beta-positioned carbonyl group were the most reactive. Compounds with an alpha- or beta-positioned carbonyl group (aldehyde or ketone) had rates of reaction that were up to 10(24)-times faster than rates of similar molecules lacking the carbonyl group. This survey of organic reactivity, together with estimates of the molecular containment properties of lipid vesicles and liquid spherules, indicates that an origins process in a small domain that used C,H,O-intermediates had to be catalytic and use the most reactive organic molecules to prevent escape of its reaction intermediates.

Weber, Arthur L.

2004-01-01

213

Effects of physical conditioning on heat tolerance in chemical-defense gear. Master's thesis  

SciTech Connect

Today the threat of chemical warfare is real. The only effective defense is the use of chemical defense gear and gas masks. Since they render chemical-warfare gases and liquids impermeable to penetration, they also prohibit sweat evaporation in conditions of thermal stress and thus, contribute to heat illness development. Historically, it has been the hot, humid tropics where United Nation's peacekeeping forces have been called, thus the use of chemical-defense gear in these regions is a realistic possibility and heat illness could affect the outcome of any mission carried out there. The human body only operates within a narrow range of core temparatures, and heat illness is the result of a breakdown in homeostasis. Many factors influence heat tolerance, thus maintaining core temperature within a safe range. Adequate hydration, acclimitization to heat, low body weight, young age, low alcohol intake, and physical fitness all contribute to heat tolerance. This proposal attempts to look specifically at the effect of physical conditioning on heat tolerance in chemical-defense gear as a possible solution to the heat-stress problem noted in this gear. Trainee graduates attending technical training schools at Lackland AFB, Texas, will be tested for maximum oxygen uptake (VO/2max) and heat tolerance time (HTT) in chemical defense gear on bicycle ergometers at Brooks AFB, Texas. Half of these subjects will be physically conditioned for 12 weeks.

Nauss, M.M.

1986-06-01

214

Co-conditioning and dewatering of chemical sludge and waste activated sludge.  

PubMed

The conditioning and dewatering behaviors of chemical and waste activated sludges from a tannery were studied. Capillary suction time (CST), specific resistance to filtration (SRF), and bound water content were used to evaluate the sludge dewatering behaviors. Zeta potentials were also measured. Experiments were conducted on each sludge conditioned and dewatered separately, and on the sludge mixed at various ratios. Results indicate that the chemical sludge was relatively difficult to be dewatered, even in the presence of polyelectrolyte. When the waste activated sludge was mixed with the chemical sludge at ratios of 1:1 and 2:1, respectively, the dewaterability of chemical sludge improved remarkably while the relatively better dewaterability of the waste activated sludge deteriorated only to a limited extent. As the mixing ratios became 4:1 and 8:1, the dewaterability of the mixed sludge was equal to that of the waste activated sludge. The optimal polyelectrolyte dosage for the mixed sludge was equal to or less than that of the waste activated sludge. It is proposed that the chemical sludges act as skeleton builders that reduce the compressibility of the mixed sludge whose dewaterability is enhanced. Bound water contents of sludge decreased at low polyelectrolyte dosage and were not significantly affected as polyelectrolyte dosage increased. Advantages and disadvantages of co-conditioning and dewatering chemical sludge and waste activated sludge were discussed. PMID:11228978

Chang, G R; Liu, J C; Lee, D J

2001-03-01

215

Chemical flooding of oil reservoirs 8. Spontaneous oil expulsion from oil- and water-wet low permeable chalk material by imbibition of aqueous surfactant solutions  

Microsoft Academic Search

Spontaneous imbibition experiments in nearly oil-wet, low permeable chalk material saturated with oil are performed at ambient conditions with and without the cationic surfactant dodecyltrimethylammonium bromide present in the aqueous solution. Without surfactant present in the water, the rate of imbibition is, as expected, very small, and only ?13% of the oil was expelled from the core within 90 days.

T. Austad; B. Matre; J. Milter; A. Sævareid; L. Øyno

1998-01-01

216

Steady-state ?-radiolysis of aqueous methyl ethyl ketone (2-butanone) under postulated nuclear reactor accident conditions  

Microsoft Academic Search

The steady-state ?-radiolysis of aqueous solutions containing 1×10?3 mol dm?3 methyl ethyl ketone (MEK) has been studied at a dose rate of 0.12 Gy s?1, 25°C and an initial pH of 10. Experiments were conducted in air-, Ar- or N2O-purged aqueous solutions, or in Ar-purged solutions with added tert-butanol. MEK, its radiolytic products, and the change in pH resulting from

P. Driver; G. Glowa; J. C. Wren

2000-01-01

217

Chemical Compositional Indications of Aqueous Alteration for Whitewater Lake Boxworks, Veneers and Veins at Cape York, Mars  

NASA Astrophysics Data System (ADS)

An area of partially-veneered, flat-lying rocks which also includes boxwork and linear veins contains a variety of compositions which are each indicative of minor to major aqueous alteration processes in the Cape York rim of Endeavour Crater. As analyzed by APXS x-ray fluorescence spectroscopy, the sets of unique elemental compositions correspond variously to Al-Si rich clays in boxwork veins, with Fe- and Cl-enriched salt veneers (Esperance samples); swarms of Ca sulfate veins (Ortiz samples); and, as indicated by remote sensing, mafic smectite alteration products in veneers (Chelmsford covering Azilda samples). Multiple offset analyses by APXS reveal clear trends and associations of certain elements, allowing inferences of mineralogies. In contrast to the acidic environment deduced for the genesis of the multiple-sulfate Burns formation sediments and shallow ferric-rich sulfate deposits beneath soils, these alteration products formed at more near-neutral pH, often with major chemical segregations and requiring high water-rock ratios comparable to a wide range of eminently habitable terrestrial environments. Several of these compositions are also rated high with respect to their potential for preservation of organic materials and biomarkers. Within distances of just tens of meters inside this so-called Whitewater Lake unit, this broad diversity exemplifies the tantalizing opportunities as well as challenges for future sample return missions to the red planet, which in this case could also be expanded to include nearby samples of Burns Fm sandstones, hematite concretions, light-toned spherules (Kirkwood), large gypsum veins (Homestake), martian global soils and surface dust.

Clark, Benton; Gellert, R.; Squyres, S.; Arvidson, R.; Yen, A.; Rice, J.; Athena Science Team

2013-10-01

218

Solubility of platinum in aqueous solutions at 25°C and pHs 4 to 10 under oxidizing conditions  

NASA Astrophysics Data System (ADS)

Platinum has been found to be mobile under supergene conditions, including placers and weathering profiles. To elucidate the nature of Pt mobility in supergene environments, the dissolution of platinum metal was investigated under physicochemical conditions similar to those found in such environments. The solubility of platinum metal was measured at 25°C in several systems: Pt-K-HC 8H 4O 4-H 2O (pH 4.02), Pt-Na-HCO 3-Cl-H 2O (pH 6.40), Pt-Na-K-H 2PO 4-HPO 4-H 2O (pH 6.90), Pt-Na-HCO 3-H 2O (pH 8.30), Pt-Na-OH-H 2O (pH 8.54), and Pt-Na-HCO 3-H 2O (pH 9.91). The redox conditions of these experiments were relatively oxidizing, with measured Eh values ranging from +280 to +590 mV. The ionic strength of the aqueous solutions did not exceed 0.30 (molal scale). The interpretation of the solubility results, in terms of the following reaction and its equilibrium constant, Pt( s)+ nH2O ? Pt( OH) 2- nn+ nH++2 e- served to identify the importance of the hydroxylated complex PtOH + in the pH range (4 to 10) and to determine its stability constant at 25°C. Linear regression of the solubility data using the function log [ Pt]-2 pe= npH+ logKn yielded a value of 1.01 ± 0.07 for n, the average ligand number, and -31.76 ± 0.55 for the thermodynamic equilibrium constant of reaction. The resulting stability constant (? 1) of PtOH + (Pt 2+ + OH - ? PtOH +) is 24.91 ± 0.50, assuming the same value of the free energy of formation of Pt 2+, ?G fo(Pt 2+) as that given by Glushko et al. ( Thermodynamic Constants of Matter, Academy of Science, USSR, 1972). The range of values of ?G fo(Pt 2+) proposed to date is +185.63 to +258.74 kJ/mol. The value of Glushko et al. (1972) (+244.11 kJ/mol) appears to fit better with our measurements at pH 4 to 10 and with those of Wood (Wood S. A., "Experimental determination of the hydrolysis constants of Pt 2+ and Pd 2+ at 25°C from the solubility of Pt and Pd in aqueous hydroxide solutions," Geochim. Cosmochim. Acta55, 1759-1767, 1991) at pH 9 to 15.5. Finally, according to these new measurements of the solubility of platinum, the recommended values for Gibbs free energy (?G fo, in kiloJoule per mole) of the different aqueous species of Pt are +244.11 (Pt 2+), -55.96 (PtOH +), and -234.48 (Pt(OH) 2(aq)). The integration of data from the literature for chloride and sulfate complexes was used to calculate the speciation of platinum in seawater and in solutions with variable chlorinity (0.1, 1, and 3 mol/L NaCl) at 25°C. These calculations showed that in the absence of strong ligands (i.e., S 2O 32-, CN -), the transport of platinum in supergene environments primarily occurs in the form of PtOH + (90%) and Pt(OH) 2(aq) (9.7%). Chloride complexes (PtCl 42- and PtCl 3-) account for less than 1% of the dissolved platinum. This study clearly shows that the hydroxylated complexes (PtOH + and Pt(OH) 2(aq)) can play a very important role in controlling platinum transfer mechanisms in surface fluids (soils, placers, weathering profiles, etc.). Because the charged species PtOH + is largely predominant, the mobility and transfer of platinum can also be affected by adsorption-desorption mechanisms onto oxides and hydroxides.

Azaroual, Mohamed; Romand, Bruno; Freyssinet, Philippe; Disnar, Jean-Robert

2001-12-01

219

Chemical Kinetic Study of Toluene Oxidation Under Premixed and Nonpremixed Conditions  

SciTech Connect

A study was performed to elucidate the chemical-kinetic mechanism of combustion of toluene. A detailed chemical-kinetic mechanism for toluene was improved by adding a more accurate description of the phenyl + O{sub 2} reaction channels, toluene decomposition reactions and the benzyl + O reaction. Results of the chemical kinetic mechanism are compared with experimental data obtained from premixed and non-premixed systems. Under premixed conditions, predicted ignition delay times are compared with new experimental data obtained in shock tube. Also, calculated species concentration histories are compared to experimental flow reactor data from the literature. Under non-premixed conditions, critical conditions of extinction and autoignition were measured in strained laminar flows in the counterflow configuration. Numerical calculations are performed using the chemical-kinetic mechanism at conditions corresponding to those in the experiments. Critical conditions of extinction and autoignition are predicted and compared with the experimental data. Comparisons between the model predictions and experimental results of ignition delay times in shock tube, and extinction and autoignition in non-premixed systems show that the chemical-kinetic mechanism predicts that toluene/air is overall less reactive than observed in the experiments. For both premixed and non-premixed systems, sensitivity analysis was used to identify the reaction rate constants that control the overall rate of oxidation in each of the systems considered. Under shock tube conditions, the reactions that influence ignition delay time are H + O{sub 2} chain branching, the toluene decomposition reaction to give an H atom, and the toluene + H abstraction reaction. The reactions that influence autoignition in non-premixed systems involve the benzyl + HO{sub 2} reaction and the phenyl + O{sub 2} reaction.

Costa, I D; Bozzelli, J W; Seiser, R; Pitz, W J; Westbrook, C K; Chen, C -; Fournet, R; Seshadri, K; Battin-Leclerc, F; Billaud, F

2003-12-10

220

Surface studies of niobium chemically polished under conditions for superconducting radio frequency (SRF) cavity production  

Microsoft Academic Search

The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back

Hui Tian; Charles E. Reece; Michael J. Kelley; Shancai Wang; Lukasz Plucinski; Kevin E. Smith; Matthew M. Nowell

2006-01-01

221

Surface studies of niobium chemically polished under conditions for superconducting radiofrequency cavity production  

Microsoft Academic Search

The performance of niobium superconducting radiofrequency accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD),

Hui Tian; Michael Kelley; Charles Reece

2005-01-01

222

F-18 labeling protocol of peptides based on chemically orthogonal strain-promoted cycloaddition under physiologically friendly reaction conditions.  

PubMed

We introduce the high-throughput synthesis of various (18)F-labeled peptide tracers by a straightforward (18)F-labeling protocol based on a chemo-orthogonal strain-promoted alkyne azide cycloaddition (SPAAC) using aza-dibenzocyclootyne-substituted peptides as precursors with (18)F-azide synthon to develop peptide based positron emission tomography (PET) molecular imaging probes. The SPAAC reaction and subsequent chemo-orthogonal purification reaction with azide resin proceeded quickly and selectively under physiologically friendly reaction conditions (i.e., toxic chemical reagents-free, aqueous medium, room temperature, and pH ?7), and provided four (18)F-labeled tumor targetable bioactive peptides such as cyclic Arg-Gly-Asp (cRGD) peptide, bombesin (BBN), c-Met binding peptide (cMBP), and apoptosis targeting peptide (ApoPep) in high radiochemical yields as direct injectable solutions without any HPLC purification and/or formulation processes. In vitro binding assay and in vivo PET molecular imaging study using the (18)F-labeled cRGD peptide also demonstrated a successful application of our (18)F-labeling protocol. PMID:22770524

Sachin, Kalme; Jadhav, Vinod H; Kim, Eun-Mi; Kim, Hye Lan; Lee, Sang Bong; Jeong, Hwan-Jeong; Lim, Seok Tae; Sohn, Myung-Hee; Kim, Dong Wook

2012-08-15

223

Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants.  

PubMed

This study investigated the effects of chemical conditioning with three representative inorganic coagulants (FeCl3, polyaluminum chloride (PACl) and high performance PACl (HPAC) on sludge dewaterability. We monitored the particle size, kinetic viscosity (KV), fractal dimension (D(F)) and extracellular polymeric substances (EPS) located in different layers of sludge floc (soluble, loosely-bound (LB), tightly-bound (TB)) to understand the correlation of dewaterability and physicochemical properties of sludge under chemical conditioning. The conditioning process included the rapid aggregation of sludge particles induced by charge neutralization and bridging followed by floc densification caused by double electric layer compression. The floc size and D(F) were increased after chemical conditioning, indicating that larger and more compact floc formed. The floc conditioned with FeCl3 was smaller but denser than that of PACl and HPAC. Furthermore, sludge dewaterability correlated well with the change in concentration of soluble EPS, LB-EPS and TB-EPS, but not with KV, D(F), floc size. PMID:23886852

Niu, Meiqing; Zhang, Weijun; Wang, Dongsheng; Chen, Yu; Chen, Ronglai

2013-09-01

224

Evaluating Dense Non-Aqueous Phase Liquid Dissolution and Chemical Oxidation in a three-dimensional, bench-scale fracture network  

NASA Astrophysics Data System (ADS)

Dense non-aqueous phase liquid (DNAPL) present in fractured bedrock settings at residual saturation introduces remediation challenges that are dramatically different from porous media settings. Evaluating DNAPL distribution in a field-scale setting is generally impractical, yet DNAPL distribution plays a critical role in the DNAPL dissolution kinetics. This research uses a three-dimensional (3-D), bench-scale network comprised of low-porosity, fractured sandstone to evaluate the dissolution kinetics of tetrachloroethylene (PCE) DNAPL at residual saturation. DNAPL dissolution kinetics were evaluated during ambient groundwater conditions as well as during in situ chemical oxidation (ISCO) in the 3-D fractured sandstone experiment. DNAPL dissolution in the fracture network was evaluated and described using an effective parameter, the bulk mass transfer coefficient (KL). Results from dissolution experiments revealed a positive, statistically significant correlation between KL with DNAPL-water interfacial area and KL with DNAPL saturation. Results of ISCO experiments with potassium permanganate (KMnO4) determined that the formation of reaction products (manganese dioxides and carbon dioxide) likely altered the primary flow paths and decreased effectiveness of the ISCO application in the fracture network. The formation of reaction products was believed to cause flow bypassing and reduce the DNAPL-oxidant contact, which reduced mass transfer rates. The effectiveness of ISCO was improved (over dissolution alone) if the ISCO application was discontinued after an initial period of effective mass removal. The findings of this research indicate that DNAPL dissolution and oxidation effectiveness in a fracture network setting are not directly correlated to aperture size, which was unexpected, but appear to be primarily impacted by flow path variability and heterogeneous DNAPL distribution.

Christensen, K.; McCray, J. E.; Schaefer, C.

2011-12-01

225

Steady-state gamma-radiolysis of aqueous methyl ethyl ketone (2-butanone) under postulated nuclear reactor accident conditions  

Microsoft Academic Search

The steady-state gamma-radiolysis of aqueous solutions containing 1x10-3 mol dm-3 methyl ethyl ketone (MEK) has been studied at a dose rate of 0.12 Gy s-1, 25 degC and an initial pH of 10. Experiments were conducted in air-, Ar- or N2O-purged aqueous solutions, or in Ar-purged solutions with added tert-butanol. MEK, its radiolytic products, and the change in pH resulting

P. Driver; G. Glowa; J. C. Wren

2000-01-01

226

Kinetics of OH-initiated oxidation of some oxygenated organic compounds in the aqueous phase under tropospheric conditions  

Microsoft Academic Search

The interest for multiphase interactions of Volatile Organic Compounds (VOCs) in the troposphere has increased for a few years. Inside the clouds water droplets, soluble VOCs can be oxidized by free radicals thus modifying the droplet composition. This reactivity has an impact on the tropospheric oxidizing capacity as well as the aerosols' properties. In the present work, we measured aqueous

L. Poulain; S. Grubert; S. François; A. Monod; H. Wortham

2003-01-01

227

Chemical insights, explicit chemistry, and yields of secondary organic aerosol from OH radical oxidation of methylglyoxal and glyoxal in the aqueous phase  

NASA Astrophysics Data System (ADS)

Atmospherically abundant, volatile water-soluble organic compounds formed through gas-phase chemistry (e.g., glyoxal (C2), methylglyoxal (C3), and acetic acid) have great potential to form secondary organic aerosol (SOA) via aqueous chemistry in clouds, fogs, and wet aerosols. This paper (1) provides chemical insights into aqueous-phase OH-radical-initiated reactions leading to SOA formation from methylglyoxal and (2) uses this and a previously published glyoxal mechanism (Lim et al., 2010) to provide SOA yields for use in chemical transport models. Detailed reaction mechanisms including peroxy radical chemistry and a full kinetic model for aqueous photochemistry of acetic acid and methylglyoxal are developed and validated by comparing simulations with the experimental results from previous studies (Tan et al., 2010, 2012). This new methylglyoxal model is then combined with the previous glyoxal model (Lim et al., 2010), and is used to simulate the profiles of products and to estimate SOA yields. At cloud-relevant concentrations (~ 10-6 - ~ 10-3 M; Munger et al., 1995) of glyoxal and methylglyoxal, the major photooxidation products are oxalic acid and pyruvic acid, and simulated SOA yields (by mass) are ~ 120% for glyoxal and ~ 80% for methylglyoxal. During droplet evaporation oligomerization of unreacted methylglyoxal/glyoxal that did not undergo aqueous photooxidation could enhance yields. In wet aerosols, where total dissolved organics are present at much higher concentrations (~ 10 M), the major oxidation products are oligomers formed via organic radical-radical reactions, and simulated SOA yields (by mass) are ~ 90% for both glyoxal and methylglyoxal. Non-radical reactions (e.g., with ammonium) could enhance yields.

Lim, Y. B.; Tan, Y.; Turpin, B. J.

2013-09-01

228

Chemically transferable coarse-grained potentials from conditional reversible work calculations.  

PubMed

The representability and transferability of effective pair potentials used in multiscale simulations of soft matter systems is ill understood. In this paper, we study liquid state systems composed of n-alkanes, the coarse-grained (CG) potential of which may be assumed pairwise additive and has been obtained using the conditional reversible work (CRW) method. The CRW method is a free-energy-based coarse-graining procedure, which, by means of performing the coarse graining at pair level, rigorously provides a pair potential that describes the interaction free energy between two mapped atom groups (beads) embedded in their respective chemical environments. The pairwise nature of the interactions combined with their dependence on the chemically bonded environment makes CRW potentials ideally suited in studies of chemical transferability. We report CRW potentials for hexane using a mapping scheme that merges two heavy atoms in one CG bead. It is shown that the model is chemically and thermodynamically transferable to alkanes of different chain lengths in the liquid phase at temperatures between the melting and the boiling point under atmospheric (1 atm) pressure conditions. It is further shown that CRW-CG potentials may be readily obtained from a single simulation of the liquid state using the free energy perturbation method, thereby providing a fast and versatile molecular coarse graining method for aliphatic molecules. PMID:23083154

Brini, E; van der Vegt, N F A

2012-10-21

229

A general synthesis for PEDOT-coated nonconductive materials and PEDOT hollow particles by aqueous chemical polymerization.  

PubMed

A method for coating functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) on nonconductive substrates in aqueous solution allows the deposition of PEDOT thin layers on various substrates, including silica and polystyrene (PS) nanoparticles, siliceous mesocellular foam, and chitosan-alginate fibers. The surface property is tuned by controlling the monomer composition in the aqueous solutions. Using appropriate organic solvents to remove the PS cores of PEDOT-coated PS nanoparticles, hollow PEDOT particles with single holes and PEDOT capsules can be formed. PMID:18949792

Luo, Shyh-Chyang; Yu, Hsiao-hua; Wan, Andrew C A; Han, Yu; Ying, Jackie Y

2008-11-01

230

Effect of preparation conditions of oil palm fronds activated carbon on adsorption of bentazon from aqueous solutions.  

PubMed

Oil palm fronds (OPF) were used to prepare activated carbon (PFAC) using physiochemical activation method, which consisted of potassium hydroxide (KOH) treatment and carbon dioxide gasification. The effects of the preparation variables, which were activation temperature, activation time and chemical impregnation ratios (KOH: char by weight), on the carbon yield and bentazon removal were investigated. Based on the central composite design (CCD), two factor interaction (2FI) and quadratic models were, respectively, employed to correlate the PFAC preparation variables to the bentazon removal and carbon yield. From the analysis of variance (ANOVA), the most influential factor on each experimental design response was identified. The optimum conditions for preparing activated carbon from OPF were found as follows: activation temperature of 850 degrees C, activation time of 1h and KOH:char ratio of 3.75:1. The predicted and experimental results for removal of bentazon and yield of PFAC were 99.85%, 20.5 and 98.1%, 21.6%, respectively. PMID:19879687

Salman, J M; Hameed, B H

2010-03-15

231

Influence of tumour physico-chemical conditions on interleukin-2-stimulated lymphocyte proliferation  

Microsoft Academic Search

The proliferative response of murine lymphocytes to interleukin-2 (IL-2) was examined under physico-chemical conditions present in solid tumours, namely low oxygen and glucose concentrations and acidic pH. Lymphocytes were cultured for four days in 30 U ml-1 IL-2 to simulate serum IL-2 concentrations attainable with high-dose systemic IL-2 therapy. Lymphocyte proliferation was significantly (P < 0.05) reduced by low oxygen

DA Loeffler; PL Juneau; S Masserant

1992-01-01

232

Use of pervaporation to separate butanol from dilute aqueous solutions: Effects of operating conditions and concentration polarization  

Microsoft Academic Search

This study deals with the separation of n-butanol from aqueous solutions by pervaporation. The effects of feed concentration, temperature, and membrane thickness on the separation performance were investigated. Over the low feed butanol concentration range (0.03–0.4wt%) studied, the butanol flux was shown to increase proportionally with an increase in the feed butanol concentration, whereas the water flux was relatively constant.

Elsayed A. Fouad; Xianshe Feng

2008-01-01

233

Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid  

Microsoft Academic Search

The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under

C. Legido-Quigley; J. Oxelbark; E. De Lorenzi; A. Zurutuza-Elorza; P. A. G. Cormack

2007-01-01

234

DETERMINATION OF STABLE VALENCE STATES OF CHROMIUM IN AQUEOUS AND SOLID WASTE MATRICES - EXPERIMENTAL VERIFICATION OF CHEMICAL BEHAVIOR  

EPA Science Inventory

The objective of the research effort was to experimentally assess the chemical behavior of the stable species of chromium during the preparation, chemical manipulation, and spectrophotometric analyses of simulated and authentic environmental samples for hexavalent chromium. The d...

235

Potential Usage of Aqueous Alum for Decomposition of Chemical Warfare Agents. Part 2: Reactions with VX and QL.  

National Technical Information Service (NTIS)

The destruction of chemical warfare agents (CWA's), particularly 0- ethyl- S- 2-(diisopropylamino)ethyl methyiphosponothiolate (VX), has been the focus of many articles in the popular media and in professional news journals such as Chemical and Engineerin...

D. J. Williams V. L. Bevilacqua W. R. Creasy D. J. McGarvey J. S. Rice

2006-01-01

236

Chemical stability of reversed phase high performance liquid chromatography silica under sodium hydroxide regeneration conditions.  

PubMed

Chromatographic sorbents used within the purification of peptide or protein based active pharmaceutical ingredients (APIs) are commonly subjected to caustic regeneration procedures, so-called CIP treatments. While polymeric materials remain unaffected by this treatment, silica-based sorbents are at an intrinsic risk of dissolution under high pH conditions, such as, e.g. 0.1M NaOH. It is common misconception that silica-based materials simply cannot be subjected to alkaline conditions above pH 9. Moreover, most studies covering the chemical stability of HPLC sorbents above pH 9 have been limited to the chromatographic conditions used for the separations themselves. Such studies have used buffered mobile phases up to pH 11 or 12. Very little focus has been put on the stability of the stationary phases when subjected to shorter but harsher pH conditions required for regeneration purposes, such as 0.1M NaOH (pH 13). Knowledge about the amount of so-called leachables, degradation products originating from the stationary phase, is of growing importance for the registration of pharmaceuticals for human use and is addressed in this work. This study compares the chemical stability of different commercially available reversed phase silica materials (C18) that are used in industrial scale preparative HPLC. The silica materials were subjected to NaOH regeneration conditions and it is shown that some materials are able to withstand 0.1M NaOH conditions without significant harm. It is demonstrated that contaminants present in the effluent in the range of 10-50 microg/mL can lead to significant contamination of API product fraction. PMID:16999967

Pettersson, Sylvia Winkel; Collet, Eric; Andersson, Ulrika

2007-02-16

237

Ultra resolution chemical fingerprinting of dense non-aqueous phase liquids from manufactured gas plants by reversed phase comprehensive two-dimensional gas chromatography.  

PubMed

Ultra resolution chemical fingerprinting of dense non-aqueous phase liquids (DNAPLs) from former manufactured gas plants (FMGPs) was investigated using comprehensive two-dimensional gas chromatography coupled with time of flight mass spectrometry (GC×GC TOFMS). Reversed phase GC×GC (i.e. a polar primary column coupled to a non-polar secondary column) was found to significantly improve the separation of polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues. Sample extraction and cleanup was performed simultaneously using accelerated solvent extraction (ASE), with recovery rates between 76% and 97%, allowing fast, efficient extraction with minimal solvent consumption. Principal component analysis (PCA) of the GC×GC data was performed in an attempt to differentiate between twelve DNAPLs based on their chemical composition. Correlations were discovered between DNAPL composition and historic manufacturing processes used at different FMGP sites. Traditional chemical fingerprinting methods generally follow a tiered approach with sample analysis on several different instruments. We propose ultra resolution chemical fingerprinting as a fast, accurate and precise method of obtaining more chemical information than traditional tiered approaches while using only a single analytical technique. PMID:21652041

McGregor, Laura A; Gauchotte-Lindsay, Caroline; Daéid, Niamh Nic; Thomas, Russell; Daly, Paddy; Kalin, Robert M

2011-07-22

238

Relaxation of the structure of simple metal ion complexes in aqueous solutions at up to supercritical conditions  

USGS Publications Warehouse

Recently x-ray absorption fine structure (XAFS) studies of various ions in aqueous solutions showed a variation of cation-ligand bond lengths, often coupled with other structure changes, with increasing temperatures. Thus, the variations of the structure of several metal ion complexes with temperature based on observations from the X-ray absorption fine structure (XAFS) studies in the hope that it will stimulate the development of either first- principles theory or molecular dynamics simulations that might adequately describes these results are discussed.

Mayanovic, R. A.; Jayanetti, S.; Anderson, A. J.; Bassett, W. A.; Chou, I. -M.

2003-01-01

239

Chemical Changes during Anaerobic Decomposition of Hardwood, Softwood, and Old Newsprint under Mesophilic and Thermophilic Conditions.  

PubMed

The anaerobic decomposition of plant biomass is an important aspect of global organic carbon cycling. While the anaerobic metabolism of cellulose and hemicelluloses to methane and carbon dioxide are well-understood, evidence for the initial stages of lignin decomposition is fragmentary. The objective of this study was to look for evidence of chemical transformations of lignin in woody tissues [hardwood (HW), softwood (SW), and old newsprint (ONP)] after anaerobic decomposition using Klason and acid-soluble lignin, CuO oxidation, and 2D NMR. Tests were conducted under mesophilic and thermophilic conditions, and lignin associations with structural carbohydrates are retained. For HW and ONP, the carbon losses could be attributed to cellulose and hemicelluloses, while carbon loss in SW was attributable to an uncharacterized fraction (e.g., extractives etc.). The 2D NMR and chemical degradation methods revealed slight reductions in ?-O-4 linkages for HW and ONP, with no depolymerization of lignin in any substrate. PMID:24967726

De la Cruz, Florentino B; Yelle, Daniel J; Gracz, Hanna S; Barlaz, Morton A

2014-07-01

240

ToF–SIMS chemical mapping study of protein adsorption onto stainless steel surfaces immersed in saline aqueous solutions  

Microsoft Academic Search

It is now well established that protein adsorption constitutes the first step of the biofouling process. As seawater contains several salts (mainly, NaCl, MgCl2 and CaCl2) and their influence on the protein adsorption is not yet clear, the aim of this contribution was to bring new insight on their role. For this purpose, different aqueous solutions containing salts mixtures have

C. Poleunis; C. Rubio; C. Compère; P. Bertrand

2003-01-01

241

Purification characteristics of pothos for airborne chemicals in growing conditions and its evaluation  

NASA Astrophysics Data System (ADS)

Plants have a purification capability to various kinds of airborne chemicals. The capability largely depends on the growing conditions of the plant. In this study, the capabilities of the plants growing in the following three conditions were examined: (a) put the subjective plant in a bowl of tap water, (b) put the one in a pot of growing water for over 1 year and (c) in the pot-soil. The room temperature and light intensity were changed in the experiments. As a result, it became obvious that the capability to formaldehyde varied in some degree according to room temperature. The capability decreased linearly in 12-25 °C in the case of (a), it did not change largely in the case of (b) and it indicated maximum value at 21 °C in the case of (c). The temperature belonged to optimal growth range of the plant. The capability-order is as follows: (a)<(b)<(c). The capability increased as the light intensity increased in each growth-condition. The capabilities to acetone, toluene and xylene were also examined. It became obvious that the capability became lower as the molecular weight of the chemical became larger.

Sawada, Ayako; Oyabu, Takashi

242

Validity conditions for stochastic chemical kinetics in diffusion-limited systems.  

PubMed

The chemical master equation (CME) and the mathematically equivalent stochastic simulation algorithm (SSA) assume that the reactant molecules in a chemically reacting system are "dilute" and "well-mixed" throughout the containing volume. Here we clarify what those two conditions mean, and we show why their satisfaction is necessary in order for bimolecular reactions to physically occur in the manner assumed by the CME and the SSA. We prove that these conditions are closely connected, in that a system will stay well-mixed if and only if it is dilute. We explore the implications of these validity conditions for the reaction-diffusion (or spatially inhomogeneous) extensions of the CME and the SSA to systems whose containing volumes are not necessarily well-mixed, but can be partitioned into cubical subvolumes (voxels) that are. We show that the validity conditions, together with an additional condition that is needed to ensure the physical validity of the diffusion-induced jump probability rates of molecules between voxels, require the voxel edge length to have a strictly positive lower bound. We prove that if the voxel edge length is steadily decreased in a way that respects that lower bound, the average rate at which bimolecular reactions occur in the reaction-diffusion CME and SSA will remain constant, while the average rate of diffusive transfer reactions will increase as the inverse square of the voxel edge length. We conclude that even though the reaction-diffusion CME and SSA are inherently approximate, and cannot be made exact by shrinking the voxel size to zero, they should nevertheless be useful in many practical situations. PMID:24511926

Gillespie, Daniel T; Petzold, Linda R; Seitaridou, Effrosyni

2014-02-01

243

Treatment of hydrocarbon contamination under flow through conditions by using magnetite catalyzed chemical oxidation.  

PubMed

Soil pollution by hydrocarbons (aromatic and aliphatic hydrocarbons) is a major environmental issue. Various treatments have been used to remove them from contaminated soils. In our previous studies, the ability of magnetite has been successfully explored to catalyze chemical oxidation for hydrocarbon remediation in batch slurry system. In the present laboratory study, column experiments were performed to evaluate the efficiency of magnetite catalyzed Fenton-like (FL) and activated persulfate (AP) oxidation for hydrocarbon degradation. Flow-through column experiments are intended to provide a better representation of field conditions. Organic extracts isolated from three different soils (an oil-contaminated soil from petrochemical industrial site and two soils polluted by polycyclic aromatic hydrocarbon (PAH) originating from coking plant sites) were spiked on sand. After solvent evaporation, spiked sand was packed in column and was subjected to oxidation using magnetite as catalyst. Oxidant solution was injected at a flow rate of 0.1 mL min(-1) under water-saturated conditions. Organic analyses were performed by GC-mass spectrometry, GC-flame ionization detector, and micro-Fourier transform infrared spectroscopy. Significant abatement of both types of hydrocarbons (60-70 %) was achieved after chemical oxidation (FL and AP) of organic extracts. No significant by-products were formed during oxidation experiment, underscoring the complete degradation of hydrocarbons. No selective degradation was observed for FL with almost similar efficiency towards all hydrocarbons. However, AP showed less reactivity towards higher molecular weight PAHs and aromatic oxygenated compounds. Results of this study demonstrated that magnetite-catalyzed chemical oxidation can effectively degrade both aromatic and aliphatic hydrocarbons (enhanced available contaminants) under flow-through conditions. PMID:22684901

Usman, M; Faure, P; Lorgeoux, C; Ruby, C; Hanna, K

2013-01-01

244

The Effects of Chemical Weathering on Thermal-Infrared Spectral Data and Models: Implications for Aqueous Processes on the Martian Surface  

NASA Astrophysics Data System (ADS)

Chemical and mineralogical data from Mars shows that the surface has been chemically weathered on local to regional scales. Chemical trends and the types of chemical weathering products present on the surface and their abundances can elucidate information about past aqueous processes. Thermal-infrared (TIR) data and their respective models are essential for interpreting Martian mineralogy and geologic history. However, previous studies have shown that chemical weathering and the precipitation of fine-grained secondary silicates can adversely affect the accuracy of TIR spectral models. Furthermore, spectral libraries used to identify minerals on the Martian surface lack some important weathering products, including poorly-crystalline aluminosilicates like allophane, thus eliminating their identification in TIR spectral models. It is essential to accurately interpret TIR spectral data from chemically weathered surfaces to understand the evolution of aqueous processes on Mars. Laboratory experiments were performed to improve interpretations of TIR data from weathered surfaces. To test the accuracy of deriving chemistry of weathered rocks from TIR spectroscopy, chemistry was derived from TIR models of weathered basalts from Baynton, Australia and compared to actual weathering rind chemistry. To determine how specific secondary silicates affect the TIR spectroscopy of weathered basalts, mixtures of basaltic minerals and small amounts of secondary silicates were modeled. Poorly-crystalline aluminosilicates were synthesized and their TIR spectra were added to spectral libraries. Regional Thermal Emission Spectrometer (TES) data were modeled using libraries containing these poorly-crystalline aluminosilicates to test for their presence on the Mars. Chemistry derived from models of weathered Baynton basalts is not accurate, but broad chemical weathering trends can be interpreted from the data. TIR models of mineral mixtures show that small amounts of crystalline and amorphous silicate weathering products (2.5-5 wt.%) can be detected in TIR models and can adversely affect modeled plagioclase abundances. Poorly-crystalline aluminosilicates are identified in Northern Acidalia, Solis Planum, and Meridiani. Previous studies have suggested that acid sulfate weathering was the dominant surface alteration process for the past 3.5 billion years; however, the identification of allophane indicates that alteration at near-neutral pH occurred on regional scales and that acid sulfate weathering is not the only weathering process on Mars.

Rampe, Elizabeth Barger

245

Carbon nanofiber aerogels for emergent cleanup of oil spillage and chemical leakage under harsh conditions.  

PubMed

To address oil spillage and chemical leakage accidents, the development of efficient sorbent materials is of global importance for environment and water source protection. Here we report on a new type of carbon nanofiber (CNF) aerogels as efficient sorbents for oil uptake with high sorption capacity and excellent recyclability. Importantly, the oil uptake ability of the CNF aerogels can be maintained over a wide temperature range, from liquid nitrogen temperature up to ca. 400°C, making them suitable for oil cleanup under harsh conditions. The outstanding sorption performance of CNF aerogels is associated with their unique physical properties, such as low density, high porosity, excellent mechanical stability, high hydrophobicity and superoleophilicity. PMID:24518262

Wu, Zhen-Yu; Li, Chao; Liang, Hai-Wei; Zhang, Yu-Ning; Wang, Xin; Chen, Jia-Fu; Yu, Shu-Hong

2014-01-01

246

Bake condition effect on hybrid lithography process for negative-tone chemically amplified resists  

NASA Astrophysics Data System (ADS)

This paper presents the process optimization study of negative tone Chemically Amplified Resists (CAR) under E-Beam exposure. The importance of post apply bake temperature choice on resolution is underlined. The process study determines the process window in which optimal conditions of both post apply and post exposure bake steps are defined and present a method to define more precisely the thermal cross-linking onset. Finally lithographic performances of CARs are studied and we show that resolution can be pushed down to 40 nm.

Pain, Laurent; Sala, F.; Higgins, C.; Dal'zotto, B.; Tedesco, Serge V.

2000-06-01

247

Theoretical study of the influence of chemical reactions and physical parameters on the convective dissolution of CO2 in aqueous solutions  

NASA Astrophysics Data System (ADS)

Subsurface carbon sequestration has emerged as a promising solution to the problem of increasing atmospheric carbon dioxide (CO2) levels. How does the efficiency of such a sequestration process depend on the physical and chemical characteristics of the storage site? This question is emblematic of the need to better understand the dynamics of CO2 in subsurface formations, and in particular, the properties of the convective dissolution of CO2 in the salt water of aquifers. This dissolution is known to improve the safety of the sequestration by reducing the risks of leaks of CO2 to the atmosphere. Buoyancy-driven convection makes this dissolution faster by transporting dissolved CO2 further away from the interface. Indeed, upon injection, the less dense CO2 phase rises above the aqueous layer where it starts to dissolve. The dissolved CO2 increases the density of the aqueous solution, thereby creating a layer of denser CO2-rich solution above less dense solution. This unstable density gradient in the gravity field is at the origin of convection. In this framework, we theoretically investigate the effect of CO2 pressure, salt concentration, temperature, and chemical reactions on the dissolution-driven convection of CO2 in aqueous solutions. On the basis of a linear stability analysis, we assess the stability of the time-dependent density profiles developing when CO2 dissolves in an aqueous layer below it. We predict that increasing CO2 pressure destabilizes the system with regard to buoyancy-driven convection, because it increases the density gradient at the origin of the instability. By contrast, increasing salt concentration or temperature stabilizes the system via effects on CO2 solubility, solutal expansion coefficient, diffusion coefficient and on the viscosity and density of the solution. We also show that a reaction of CO2 with chemical species dissolved in the aqueous solution can either enhance or decrease the amplitude of the convective dissolution compared to the non reactive one. On the basis of a reaction-diffusion-convection model, we classify the various possible cases and show that the difference between the solutal expansion coefficients of the reactant and of the product governs the type of density profile building up in the aqueous solution and thus the stability of the system. By contrast to non reactive density profiles, reactive density profiles can feature a minimum that induces a delay of the buoyancy-driven convection. This work identifies the parameters that could influence the dissolution-driven convection in the aquifers, and thus impact the safety of the sequestration. In other words, this theoretical study shows that it is crucial to analyse the composition and reactivity of potential storage sites to choose those that will be most efficient for long-term CO2 sequestration.

Loodts, Vanessa; Rongy, Laurence; De Wit, Anne

2014-05-01

248

Effects of chemical modifications in the partition behavior of proteins in aqueous two-phase systems: a case study with RNase A.  

PubMed

Chemical modification of proteins is gaining importance due to the improvement in properties and the broader range of applications that these protein conjugates have. Once modified, several purification strategies need to be applied to isolate the conjugates of interest. Aqueous two-phase systems (ATPS) are an attractive alternative for the primary recovery of proteins and their conjugates. However, to better understand which biochemical parameters affect in greater degree the partition behavior of these modified proteins in ATPS, it becomes necessary to characterize the partition behavior of different species. In this work, ribonuclease A (RNase A) was selected as a model protein to address the partition behavior of chemically modified proteins in ATPS. Native, mono-PEGylated, Uniblue A, Dabsyl Chloride, and Direct Red 83 chemically modified RNase A's were partitioned in 16 different polyethylene glycol (PEG)-potassium phosphate ATPS. Results suggest that while the effects of system design parameters govern the partition of native RNase A, the behavior of the chemically modified species is more influenced by the physicochemical characteristics of the modifying molecules, that in most cases promote partition toward the top polymer-rich phase with recovery percentages as high as 86%. It has been found that both, the hydrophobicity and molecular weight of the modifying species play a preponderant role in conjugate partition behavior since as hydrophobicity increases partition is promoted towards the PEG-rich phase balancing the effect of the molecular weight of the modifying molecules that tends to shift partition towards the salt rich phase. PMID:23296881

González-Valdez, José; Rito-Palomares, Marco; Benavides, Jorge

2013-01-01

249

Laboratory studies of the aqueous-phase oxidation of polyols: submicron particles vs. bulk aqueous solution  

NASA Astrophysics Data System (ADS)

Oxidation in the atmospheric aqueous phase (cloud droplets and deliquesced particles) has received recent attention as a potential pathway for the formation of highly oxidized organic aerosol. Most laboratory studies of aqueous-phase oxidation, however, are carried out in bulk solutions rather than aqueous droplets. Here we describe experiments in which aqueous oxidation of polyols (water-soluble species with chemical formula CnH2n+2On) is carried out within submicron particles in an environmental chamber, allowing for significant gas-particle partitioning of reactants, intermediates, and products. Dark Fenton chemistry is used as a source of hydroxyl radicals, and oxidation is monitored using a high-resolution aerosol mass spectrometer (AMS). Aqueous oxidation is rapid, and results in the formation of particulate oxalate; this is accompanied by substantial loss of carbon to the gas phase, indicating the formation of volatile products. Results are compared to those from analogous oxidation reactions carried out in bulk solution. The bulk-phase chemistry is similar to that in the particles, but with substantially less carbon loss. This is likely due to differences in partitioning of early-generation products, which evaporate out of the aqueous phase under chamber conditions (in which liquid water content is low), but remain in solution for further aqueous processing in the bulk phase. This work suggests that the product distributions from oxidation in aqueous aerosol may be substantially different from those in bulk oxidation experiments. This highlights the need for aqueous oxidation studies to be carried out under atmospherically relevant partitioning conditions, with liquid water contents mimicking those of cloud droplets or aqueous aerosol.

Daumit, K. E.; Carrasquillo, A. J.; Hunter, J. F.; Kroll, J. H.

2014-05-01

250

Chemical transformations of lead compounds under humid conditions: implications for bioaccessibility.  

PubMed

This short communication documents chemical transformations caused by weathering of two Pb compounds that commonly occur in house dust. Chamber experiments were designed to simulate humid indoor environment conditions to determine whether Pb compounds undergo chemical transformations influencing bioaccessibility. Reference compounds of Pb metal (12 % bioaccessibility) and Pb sulfate (14 % bioaccessibility) were subjected to an oxygenated, humidified atmosphere in closed chambers for 4 months. X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) spectroscopy were used to characterize the main Pb species, and the change in Pb bioaccessibility was determined using a simulated gastric acid digestion. At the end of the weathering period a small amount of Pb carbonate (9 % of total Pb) appeared in the Pb sulfate sample. Weathering of the Pb metal sample resulted in the formation of two compounds, hydrocerussite (Pb hydroxyl carbonate) and Pb oxide, in significant amounts (each accounted for 26 % of total Pb). The formation of highly bioaccessible Pb carbonate (73 % bioaccessibility), hydrocerussite (76 % bioaccessibility), and Pb oxide (67 % bioaccessibility) during weathering resulted in a measurable increase in the overall Pb bioaccessibility of both samples, which was significant (p = .002) in the case of the Pb metal sample. This study demonstrates that Pb compounds commonly found in indoor dust can 'age' into more bioaccessible forms under humid indoor conditions. PMID:22740126

Maclean, Lachlan C W; Beauchemin, Suzanne; Rasmussen, Pat E

2013-02-01

251

An evaluation of the chemical, radiological, and ecological conditions of West Lake on the Hanford site  

SciTech Connect

West Lake and its immediate surrounding basin represent a unique habitat that is dominated by highly saline water and soil. The basin offers a valuable research site for studies of a rare and complex wetland area in the desert. This report is an evaluation of the chemical, radiological, and ecological conditions at West Lake and describes how ground water influences site properties. The scope of this evaluation consisted of a sampling program in 1989 and a review of data from the perspective of assessing the impact of Hanford Site operations on the physical, chemical, and ecological conditions of West Lake and its surrounding basin. The water level in West Lake fluctuates in relation to changes in the water table. The connection between West Lake and ground water is also supported by the presence of {sup 3}H and {sup 99}Tc in the ground water and in the lake. There are relatively high concentrations of uranium in West Lake; the highest concentrations are found in the northernmost isolated pool. Analyses of water, sediment, vegetation, and soil indicate possible shifts of isotropic ratios that indicate a reduction of {sup 235}U. Uranium-236 was not detected in West Lake water; its presence would indicate neutron-activated {sup 235}U from fuel reprocessing at Hanford. Trace metals are found at elevated concentrations in West Lake. Arsenic, chromium, copper, and zinc were found at levels in excess of US Environmental Protection Agency water quality criteria. Levels of radiological and chemical contamination in the West Lake basin are relatively low. Concentrations of fission isotopes exceed those that could be explained by atmospheric fallout, but fall short of action levels for active waste management areas. 31 refs., 8 figs., 18 tabs.

Poston, T.M.; Price, K.L.; Newcomer, D.R.

1991-03-01

252

Chemical processing in high-pressure aqueous environments. 6: Demonstration of catalytic gasification for chemical manufacturing wastewater cleanup in industrial plants  

SciTech Connect

Catalytic gasification of organics has been demonstrated at the engineering development scale as an option for chemical manufacturing wastewater cleanup. A high-pressure (about 20 MPa) and high-temperature (about 350 C) liquid water processing environment was used to treat wastewaters at two industrial sites. Organic byproducts from chemical manufacturing were converted primarily to methane and carbon dioxide in the presence of a fixed bed of nickel/ruthenium catalyst. Test results with chemical manufacturing wastewater streams showed that this process could be effectively used with the appropriate catalyst to clean up wastewater and recover waste organics as useful fuel gas. Preliminary process economics were determined.

Elliott, D.C.; Neuenschwander, G.G.; Phelps, M.R.; Hart, T.R.; Zacher, A.H.; Silva, L.J. [Pacific Northwest National Lab., Richland, WA (United States)] [Pacific Northwest National Lab., Richland, WA (United States)

1999-03-01

253

Aqueous-phase photooxidation of levoglucosan - a mechanistic study using Aerosol Time of Flight Chemical Ionization Mass Spectrometry (Aerosol-ToF-CIMS)  

NASA Astrophysics Data System (ADS)

Levoglucosan (LG) is a widely employed tracer for biomass burning (BB). Recent studies have shown that LG can react rapidly with hydroxyl (OH) radicals in the aqueous phase, despite many mass balance receptor models assuming it to be inert during atmospheric transport. In the current study, aqueous-phase photooxidation of LG by OH radicals was performed in the laboratory. The reaction kinetics and products were monitored by Aerosol Time of Flight Chemical Ionization Mass Spectrometry (Aerosol-ToF-CIMS). Approximately 50 reaction products were detected by the Aerosol-ToF-CIMS during the photooxidation experiments, representing one of the most detailed product studies yet performed. By following the evolution of mass defects of product peaks, unique trends of adding oxygen (+O) and removing hydrogen (-2H) were observed among the products detected, providing useful information to determine potential reaction mechanisms and sequences. As well, bond scission reactions take place, leading to reaction intermediates with lower carbon numbers. We introduce a data analysis framework where the average oxidation state (OSc) is plotted against a novel molecular property: double bond equivalence to carbon ratio (DBE / #C). The trajectory of LG photooxidation on this plot suggests formation of poly-carbonyl intermediates and their subsequent conversion to carboxylic acids as a general reaction trend. We also determined the rate constant of LG with OH radicals at room temperature to be 1.08 ± 0.16 × 109 M-1 s-1. By coupling an Aerosol Mass Spectrometer (AMS) to the system, we observed a rapid decay of the mass fraction of organic signals at mass-to-charge ratio 60 (f60), corresponding closely to the LG decay monitored by the Aerosol-ToF-CIMS. The trajectory of LG photooxidation on a f44-f60 correlation plot matched closely to literature field measurement data. This implies that aqueous-phase photooxidation might be partially contributing to aging of BB particles in the ambient atmosphere.

Zhao, R.; Mungall, E. L.; Lee, A. K. Y.; Aljawhary, D.; Abbatt, J. P. D.

2014-04-01

254

Assessment Of Chemical Dispersant Effectiveness In A Wave Tank Under Regular Non-Breaking And Breaking Wave Conditions  

EPA Science Inventory

Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditio...

255

Sensitive determination of bromine and iodine in aqueous and biological samples by electrothermal vaporization inductively coupled plasma mass spectrometry using tetramethylammonium hydroxide as a chemical modifier.  

PubMed

A procedure for the simultaneous determination of bromine and iodine by inductively coupled plasma (ICP) mass spectrometry was investigated. In order to prevent the decrease in the ionization efficiencies of bromine and iodine atoms caused by the introduction of water mist, electrothermal vaporization was used for sample introduction into the ICP mass spectrometer. To prevent loss of analytes during the drying process, a small amount of tetramethylammonium hydroxide solution was placed as a chemical modifier into the tungsten boat furnace. After evaporation of the solvent, the analytes instantly vaporized and were then introduced into the ICP ion source to detect the (79)Br(+), (81)Br(+), and (127)I(+) ions. By using this system, detection limits of 0.77 pg and 0.086 pg were achieved for bromine and iodine, respectively. These values correspond to 8.1 pg mL(-1) and 0.91 pg mL(-1) of the aqueous bromide and iodide ion concentrations, respectively, for a sampling volume of 95 microL. The relative standard deviations for eight replicate measurements were 2.2% and 2.8% for 20 pg of bromine and 2 pg of iodine, respectively. Approximately 25 batches were vaporizable per hour. The method was successfully applied to the analysis of various certified reference materials and practical situations as biological and aqueous samples. There is further potential for the simultaneous determination of fluorine and chlorine. PMID:18496883

Kataoka, Hiroko; Tanaka, Sachiko; Konishi, Chie; Okamoto, Yasuaki; Fujiwara, Terufumi; Ito, Kazuaki

2008-06-01

256

Quantum chemical investigation on indole: vibrational force field and theoretical determination of its aqueous pK(a) value.  

PubMed

Indole and its derivatives are molecules which play important roles in different fields, from biology to pharmacology. Here we report a thorough investigation on the anharmonic force fields of indole as well as the ab initio determinations of its gas phase basicity and aqueous pK(a) value. For the geometry optimizations, the calculations have been performed using both density functional (DFT) and second-order Møller-Plesset (MP2) levels of theory employing different basis sets. Anharmonic force fields have been obtained employing both the B3LYP and the B97-1 functionals and an hybrid approach: the best agreement to the experimental data has been determined employing the B3LYP functional combined with the recently developed N07D basis set (mean unsigned error, MUE, of 5.1 cm(-1) and a root-mean-square error, RMSE, of 7.2 cm(-1)). Gas phase basicity and proton affinity have been computed employing several computational schemes, namely the G3 and G4 Gaussian models, the complete basis set (CBS) extrapolation methods of Petersson and co-workers, several DFT calculations, and different hybrid extrapolation schemes based on combining single-point energy calculations performed at MP2 as well as at coupled cluster level of theory with single, double and perturbative triple excitations, CCSD(T). Regarding the aqueous pK(a) computations, two implicit solvation models (SMD and SM8) have been employed to determine the free energy of solvation and the corresponding pKa value. PMID:23899419

Pietropolli Charmet, Andrea; Quartarone, Giuseppe; Ronchin, Lucio; Tortato, Claudio; Vavasori, Andrea

2013-08-01

257

Transcriptome Analysis of the Phytobacterium Xylella fastidiosa Growing under Xylem-Based Chemical Conditions  

PubMed Central

Xylella fastidiosa is a xylem-limited bacterium responsible for important plant diseases, like citrus-variegated chlorosis (CVC) and grapevine Pierce's disease (PD). Interestingly, in vitro growth of X. fastidiosa in chemically defined media that resemble xylem fluid has been achieved, allowing studies of metabolic processes used by xylem-dwelling bacteria to thrive in such nutrient-poor conditions. Thus, we performed microarray hybridizations to compare transcriptomes of X. fastidiosa cells grown in 3G10-R, a medium that resembles grape sap, and in Periwinkle Wilt (PW), the complex medium traditionally used to cultivate X. fastidiosa. We identified 299 transcripts modulated in response to growth in these media. Some 3G10R-overexpressed genes have been shown to be upregulated in cells directly isolated from infected plants and may be involved in plant colonization, virulence and environmental competition. In contrast, cells cultivated in PW show a metabolic switch associated with increased aerobic respiration and enhanced bacterial growth rates.

Ciraulo, Maristela Boaceff; Santos, Daiene Souza; Rodrigues, Ana Claudia de Freitas Oliveira; de Oliveira, Marcus Vinicius; Rodrigues, Tiago; de Oliveira, Regina Costa; Nunes, Luiz R.

2010-01-01

258

Surfactant-enabled epitaxy through control of growth mode with chemical boundary conditions.  

PubMed

Property coupling at interfaces between active materials is a rich source of functionality, if defect densities are low, interfaces are smooth and the microstructure is featureless. Conventional synthesis techniques generally fail to achieve this when materials have highly dissimilar structure, symmetry and bond type-precisely when the potential for property engineering is most pronounced. Here we present a general synthesis methodology, involving systematic control of the chemical boundary conditions in situ, by which the crystal habit, and thus growth mode, can be actively engineered. In so doing, we establish the capability for layer-by-layer deposition in systems that otherwise default to island formation and grainy morphology. This technique is demonstrated via atomically smooth {111} calcium oxide films on (0001) gallium nitride. The operative surfactant-based mechanism is verified by temperature-dependent predictions from ab initio thermodynamic calculations. Calcium oxide films with smooth morphology exhibit a three order of magnitude enhancement of insulation resistance. PMID:21897372

Paisley, Elizabeth A; Losego, Mark D; Gaddy, Benjamin E; Tweedie, James S; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L; Maria, Jon-Paul

2011-01-01

259

Photocatalytic elimination of indoor air biological and chemical pollution in realistic conditions.  

PubMed

The photocatalytic elimination of microorganisms from indoor air in realistic conditions and the feasibility of simultaneous elimination of chemical contaminants have been studied at laboratory scale. Transparent polymeric monoliths have been coated with sol-gel TiO(2) films and used as photocatalyst to treat real indoor air in a laboratory-scale single-step annular photocatalytic reactor. The analytical techniques used to characterize the air quality and analyze the results of the photocatalytic tests were: colony counting, microscopy and PCR with subsequent sequencing for microbial quantification and identification; automated thermal desorption coupled to gas chromatography with mass spectrometry detection for chemical analysis. The first experiments performed proved that photocatalysis based on UVA-irradiated TiO(2) for the reduction of the concentration of bacteria in the air could compete with the conventional photolytic treatment with UVC radiation, more expensive and hazardous. Simultaneously to the disinfection, the concentration of volatile organic compounds was greatly reduced, which adds value to this technology for real applications. The fungal colony number was not apparently modified. PMID:22349060

Sánchez, Benigno; Sánchez-Muñoz, Marta; Muñoz-Vicente, María; Cobas, Guillermo; Portela, Raquel; Suárez, Silvia; González, Aldo E; Rodríguez, Nuria; Amils, Ricardo

2012-05-01

260

A Molecular Dynamics Study of Chemical Reactions of Solid Pentaerythritol Tetranitrate at Extreme Conditions  

SciTech Connect

We have carried out density functional based tight binding (DFTB) molecular dynamics (MD) simulation to study energetic reactions of solid Pentaerythritol Tetranitrate (PETN) at conditions approximating the Chapman-Jouguet (CJ) detonation state. We found that the initial decomposition of PETN molecular solid is characterized by uni-molecular dissociation of the NO{sub 2}groups. Interestingly, energy release from this powerful high explosive was found to proceed in several stages. The large portion of early stage energy release was found to be associated with the formation of H{sub 2}O molecules within a few picoseconds of reaction. It took nearly four times as long for majority of CO{sub 2} products to form, accompanied by a slow oscillatory conversion between CO and CO{sub 2}. The production of N{sub 2} starts after NO{sub 2} loses its oxygen atoms to hydrogen or carbon atoms to form H{sub 2}O or CO. We identified many intermediate species that emerge and contribute to reaction kinetics, and compared our simulation with a thermo-chemical equilibrium calculation. In addition, a detailed chemical kinetics of formation of H{sub 2}O, CO, and CO{sub 2} were developed. Rate constants of formations of H{sub 2}O, CO{sub 2} and N{sub 2} were reported.

Wu, C J; Manaa, M R; Fried, L E

2006-05-30

261

Efficient and selective chemical transformations under flow conditions: The combination of supported catalysts and supercritical fluids  

PubMed Central

Summary This paper reviews the current trends in the combined use of supported catalytic systems, either on solid supports or in liquid phases and supercritical fluids (scFs), to develop selective and enantioselective chemical transformations under continuous and semi-continuous flow conditions. The results presented have been selected to highlight how the combined use of those two elements can contribute to: (i) Significant improvements in productivity as a result of the enhanced diffusion of substrates and reagents through the interfaces favored by the scF phase; (ii) the long term stability of the catalytic systems, which also contributes to the improvement of the final productivity, as the use of an appropriate immobilization strategy facilitates catalyst isolation and reuse; (iii) the development of highly efficient selective or, when applicable, enantioselective chemical transformations. Although the examples reported in the literature and considered in this review are currently confined to a limited number of fields, a significant development in this area can be envisaged for the near future due to the clear advantages of these systems over the conventional ones.

Burguete, M Isabel; Garcia-Verdugo, Eduardo

2011-01-01

262

INITIAL CHEMICAL AND RESERVOIR CONDITIONS AT LOS AZUFRES WELLHEAD POWER PLANT STARTUP  

SciTech Connect

One of the major concerns of electric utilities in installing geothermal power plants is not only the longevity of the steam supply, but also the potential for changes in thermodynamic properties of the resource that might reduce the conversion efficiency of the design plant equipment. Production was initiated at Los Azufres geothermal field with wellhead generators not only to obtain electric energy at a relatively early date, but also to acquire needed information about the resource so that plans for large central power plants could be finalized. Commercial electric energy production started at Los Azufres during the summer of 1982 with five 5-MWe wellhead turbine-generator units. The wells associated with these units had undergone extensive testing and have since been essentially in constant production. The Los Azufres geothermal reservoir is a complex structural and thermodynamic system, intersected by at least 4 major parallel faults and producing geothermal fluids from almost all water to all steam. The five wellhead generators are associated with wells of about 30%, 60%, and 100% steam fraction. A study to compile existing data on the chemical and reservoir conditions during the first two years of operation has been completed. Data have been compiled on mean values of wellhead and separator pressures, steam and liquid flowrates, steam fraction, enthalpy, and pertinent chemical components. The compilation serves both as a database of conditions during the start-up period and as an initial point to observe changes with continued and increased production. Current plans are to add additional wellhead generators in about two years followed by central power plants when the data have been sufficiently evaluated for optimum plant design. During the next two years, the data acquired at the five 5-MWe wellhead generator units can be compared to this database to observe any significant changes in reservoir behavior at constant production.

Kruger, P.; Semprini, L.; Verma, S.; Barragan, R.; Molinar, R.; Aragon, A.; Ortiz, J.; Miranda, C.

1985-01-22

263

Universal RF-Powered Aqueous Extractor-on-a-Chip Instrument for Identification of Chemical Signatures of Life on Mars  

Microsoft Academic Search

The prospect of finding chemical signatures of present or past life on Mars is one of the important drivers behind Mars exploration program (MEP). One of the technical challenges facing MEP is the lack of compact and universal sample processing technology that enables the cataloging of organic molecules in Martian crustal materials. In the past year, we have been developing

X. Amashukeli; H. Manohara; G. Chattopadhyay; E. Urgiles; R. Lin; A. Peralta; A. Fisher

2009-01-01

264

Chemical evolution of RNA under hydrothermal conditions and the role of thermal copolymers of amino acids for the prebiotic degradation and formation of RNA  

NASA Astrophysics Data System (ADS)

The roles of thermal copolymers of amino acids (TCAA) were studied for the prebiotic degradation of RNA. A weak catalytic ability of TCAA consisted of Glu, L-Ala, L-Val, L-Glu, L-Asp, and optionally L-His was detected for the cleavage of the ribose phosphodiester bond of a tetranucleotide (5'-dCrCdGdG) in aqueous solution at 80 °C. The rate constants of the disappearance of 5'-dCrCdGdG were determined in aqueous solutions using different pH buffer and TCAA. The degradation rates were enhanced 1.3-3.0 times in the presence of TCAA at pH 7.5 and 8.0 at 80 °C, while the hydrolysis of oligoguanylate (oligo(G)) was accelerated about 1.6 times at pH 8.0. A weak inhibitory activity for the cleavage of oligo(G) was detected in the presence of 0.055 M TCAA-Std. On the other hand, our recent study on the influences of TCAA for the template-directed reaction of oligo(G) on a polycytidylic acid template showed that TCAA has an acceleration activity for the degradation of the activated nucleotide monomer and an acceleration activity for the formation of G 5' ppG capped oligo(G). This series of studies suggest that efficient and selective catalytic or inhibitory activities for either the degradation or formation of RNA under hydrothermal conditions could have hardly emerged from the simple thermal condensation products of amino acids. A scenario is going to be deduced on the chemical evolution of enzymatic activities and RNA molecules concerning hydrothermal earth conditions.

Kawamura, K.; Nagahama, M.; Kuranoue, K.

265

Temperature and density effects on structural features of a dilute aqueous lithium chloride solution at near- and supercritical conditions  

Microsoft Academic Search

The structural features of a 0.24molal LiCl(aq) solution at near- (T=573K, ?1=1.0g\\/cm3, ?2=0.65g\\/cm3) and supercritical (T=1073K, ?=0.65g\\/cm3) conditions were studied by the extended RISM integral equation method. It was found that on transition from ambient conditions into the supercritical state the tetrahedral network of water is destroyed, ions are thermally dehydrated and ion association to contact ion pairs is promoted.

Marina V. Fedotova

2011-01-01

266

Surface Studies of Niobium Chemically Polished Under Conditions for Superconducting Radio Frequency (SRF) Cavity Production  

SciTech Connect

The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant datasets. We found that the predominant general surface orientation is (1 0 0), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3-1.4 times that resulting from static solution. The standard deviation of the roughness measurements is {+-}30% and that of the surface composition is {+-}5%.

Tian,H.; Reece, C.; Kelley, M.; Wang, S.; Plucinski, L.; Smith, K.; Nowell, M.

2006-01-01

267

Surface studies of niobium chemically polished under conditions for superconducting radio frequency (SRF) cavity production  

NASA Astrophysics Data System (ADS)

The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant datasets. We found that the predominant general surface orientation is (1 0 0), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3-1.4 times that resulting from static solution. The standard deviation of the roughness measurements is ±30% and that of the surface composition is ±5%.

Tian, Hui; Reece, Charles E.; Kelley, Michael J.; Wang, Shancai; Plucinski, Lukasz; Smith, Kevin E.; Nowell, Matthew M.

2006-11-01

268

Molecules in interstellar clouds. [physical and chemical conditions of star formation and biological evolution  

NASA Technical Reports Server (NTRS)

The physical conditions and chemical compositions of the gas in interstellar clouds are reviewed in light of the importance of interstellar clouds for star formation and the origin of life. The Orion A region is discussed as an example of a giant molecular cloud where massive stars are being formed, and it is pointed out that conditions in the core of the cloud, with a kinetic temperature of about 75 K and a density of 100,000-1,000,000 molecules/cu cm, may support gas phase ion-molecule chemistry. The Taurus Molecular Clouds are then considered as examples of cold, dark, relatively dense interstellar clouds which may be the birthplaces of solar-type stars and which have been found to contain the heaviest interstellar molecules yet discovered. The molecular species identified in each of these regions are tabulated, including such building blocks of biological monomers as H2O, NH3, H2CO, CO, H2S, CH3CN and H2, and more complex species such as HCOOCH3 and CH3CH2CN.

Irvine, W. M.; Hjalmarson, A.; Rydbeck, O. E. H.

1981-01-01

269

Mutation spectrum in the lacI gene, induced by gamma-radiation in aqueous solution under oxic conditions.  

PubMed

Irradiation of DNA in a cellular environment leads to many types of DNA damage, resulting from various effects of gamma-radiation. One of these effects is the formation of water-derived radicals (e.g., .OH radicals), which are formed in the vicinity of DNA (indirect effect). To study the influence of the indirect effect on gamma-radiation-induced mutations, a newly constructed plasmid, containing the lacI gene as a target gene, was irradiated with 60Co gamma-radiation in aqueous solution, in the presence of oxygen. Under these circumstances, only .OH radicals will be responsible for the induced mutations. Sequence analysis of the gamma-radiation-induced mutations showed that 96% of all mutations were base pair substitutions, 87% of which occurred in the lacI gene, the others are formed in the lac operator part. All gamma-radiation-induced mutations in the lacI gene occurred exclusively on G:C base pairs, and no mutations at A:T base pairs could be detected. In the spontaneous mutation spectrum, 83% of all mutations were base pair substitutions, 35% of which occurred in the lacI gene and 48% in the lac operator part. Base pair substitutions on G:C base pairs were very similar in the gamma-radiation-induced and in the spontaneous mutation spectrum, implying a high contribution of .OH radicals to spontaneous mutagenesis. A:T to G:C transitions accounted for 10% of all spontaneous base pair substitutions in the lacI gene and are probably the result of effects, other than just .OH radicals. It can be concluded that .OH radicals are an important source for mutations at G:C base pairs. In this paper, the extracellular gamma-radiation-induced mutation spectrum is also compared to the previously obtained, intracellular gamma-radiation-induced mutation spectrum of the lacI gene. Comparison shows some differences, such as relative high amounts of mutations at A:T base pairs, G:C to T:A transversions and frameshift mutations in the intracellular gamma-radiation-induced mutation spectrum, as compared to the extracellular gamma-radiation-induced mutation spectrum. Since the extracellular gamma-radiation-induced mutation spectrum shows that .OH radicals are mainly responsible for base pair substitutions on G:C base pairs, mutations at A:T base pairs in the intracellular gamma-radiation-induced mutation spectrum are apparently the result of additional or other factors. PMID:9726014

Wijker, C A; Wientjes, N M; Lafleur, V M

1998-07-17

270

Effects of cultivation conditions on the uptake of arsenite and arsenic chemical species accumulated by Pteris vittata in hydroponics  

Microsoft Academic Search

The physiological responses of the arsenic-hyperaccumulator, Pteris vittata, such as arsenic uptake and chemical transformation in the fern, have been investigated. However, a few questions remain regarding arsenic treatment in hydroponics. Incubation conditions such as aeration, arsenic concentration, and incubation period might affect those responses of P. vittata in hydroponics. Arsenite uptake was low under anaerobic conditions, as previously reported.

Masayoshi Hatayama; Takahiko Sato; Kozo Shinoda; Chihiro Inoue

2011-01-01

271

Assessment of chemical dispersant effectiveness in a wave tank under regular non-breaking and breaking wave conditions  

Microsoft Academic Search

Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural environment, including transport and dilution effects. To achieve this goal, Fisheries and Oceans Canada and the US Environmental Protection Agency

Zhengkai Li; Kenneth Lee; Thomas King; Michel C. Boufadel; Albert D. Venosa

2008-01-01

272

Aqueous chemical growth of alpha-Fe2O3-alpha-Cr2O3 nanocomposite thin films.  

PubMed

We are reporting here on the inexpensive fabrication and optical properties of an iron(III) oxide-chromium(III) oxide nanocomposite thin film of corundum crystal structure. Its novel and unique-designed architecture consists of uniformed, well-defined and oriented nanorods of Hematite (alpha-Fe2O3) of 50 nm in diameter and 500 nm in length and homogeneously distributed nonaggregated monodisperse spherical nanoparticles of Eskolaite (alpha-Cr2O3) of 250 nm in diameter. This alpha-Fe2O3-alpha-Cr2O3 nanocomposite thin film is obtained by growing, directly onto transparent polycrystalline conducting substrate, an oriented layer of hematite nanorods and growing subsequently, the eskolaite layer. The synthesis is carried out by a template-free, low-temperature, multilayer thin film coating process using aqueous solution of metal salts as precursors. Almost 100% of the light is absorbed by the composite film between 300 and 525 nm and 40% at 800 nm which yields great expectations as photoanode materials for photovoltaic cells and photocatalytic devices. PMID:12914078

Vayssieres, L; Guo, J; Nordgren, J

2001-12-01

273

In situ dynamic analysis of solids or aqueous solutions undergoing chemical reactions by RBS or PIXE with external beams  

NASA Astrophysics Data System (ADS)

Non-conventional applications of IBA techniques are under development on an external micro-beam line dedicated to the study of materials relevant to cultural heritage. Special set-ups have been designed to investigate the kinetics of materials transformation by dynamic (real-time) analysis using either RBS or PIXE. The first technique is well fitted to the study of the thermal oxidation of solids in air, whereas the second one is suitable for measuring the rate of elemental release in the liquid phase during solid-solution interaction. Preliminary tests have been performed to demonstrate the usefulness of this approach. On one hand we have applied dynamic micro-RBS to study the oxidation kinetics at 360 °C of pure copper and a copper-gold alloy and on the other hand we have checked the ability of micro-PIXE to measure in real time the release of lead in solution during the aqueous dissolution of lead containing glass or glaze.

Bouquillon, A.; Dran, J.-C.; Lagarde, G.; Martinetto, P.; Mathis, F.; Moignard, B.; Salomon, J.; Walter, Ph.

2002-04-01

274

Chemical relevance of the copper(II)— L-carnosine system in aqueous solution: A thermodynamic and spectrophotometric study  

NASA Astrophysics Data System (ADS)

The copper(II)— L-carnosine (L -) system has been re-investigated in aqueous solution, at I = 0.1 mol dm -1, different temperatures (5? t?45°C) and with metal to ligand ratios ranging from 3:1 to 1:3. Both potentiometry and visible spectrophotometry were employed. From an overall consideration of all experiments, [CuLH] 2+, [CuL] +, [CuLH -1]°, [Cu 2L 2H -2]° and [Cu 2LH -1] 2+ were recognized as the species which provide the best interpretation of experimental data. The complex formation constants, determined at different temperatures, allowed us to obtain reliable values of ? H° and good estimates of ? C° p. From visible spectrophotometric measurements, carried out at different pH and metal to ligand ratios, it was possible to calculate the electronic spectrum of each complex formed in solution. A structure is also proposed for each species, on the basis of thermodynamic and spectral results.

Daniele, Pier G.; Prenesti, Enrico; Zelano, Vincenzo; Ostacoli, Giorgio

1993-08-01

275

Iodine-xenon, chemical, and petrographic studies of Semarkona chondrules - Evidence for the timing of aqueous alteration  

NASA Technical Reports Server (NTRS)

The relationship of the I-Xe system of the Semarkona meteorite to other measured properties is investigated via INAA, petrographic, and noble-gas analyses on 17 chondrules from the meteorite. A range of not less than 10 Ma in apparent I-Xe ages is observed. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. It is argued that the initial I-129/I-127 ratio (R0) is related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R0s than porphyritic and olivine-rich chondrules. Chondrules with sulfides on or near the surface have lower R0s than other chondrules. The He-129/Xe-132 ratio in the trapped Xe component anticorrelates with R0, consistent with the evolution of a chronometer in a closed system or in multiple systems. It is concluded that the variations in R0 represent variations in ages, and that later events, possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules.

Swindle, T. D.; Grossman, J. N.; Olinger, C. T.; Garrison, D. H.

1991-01-01

276

Chemical Processing in High-Pressure Aqueous Environments. 9. Process Development for Catalytic Gasification of Algae Feedstocks  

SciTech Connect

Through the use of a metal catalyst, gasification of wet algae slurries can be accomplished with high levels of carbon conversion to gas at relatively low temperature (350 C). In a pressurized-water environment (20 MPa), near-total conversion of the organic structure of the algae to gases has been achieved in the presence of a supported ruthenium metal catalyst. The process is essentially steam reforming, as there is no added oxidizer or reagent other than water. In addition, the gas produced is a medium-heating value gas due to the synthesis of high levels of methane, as dictated by thermodynamic equilibrium. As opposed to earlier work, biomass trace components were removed by processing steps so that they did not cause processing difficulties in the fixed catalyst bed tubular reactor system. As a result, the algae feedstocks, even those with high ash contents, were much more reliably processed. High conversions were obtained even with high slurry concentrations. Consistent catalyst operation in these short-term tests suggested good stability and minimal poisoning effects. High methane content in the product gas was noted with significant carbon dioxide captured in the aqueous byproduct in combination with alkali constituents and the ammonia byproduct derived from proteins in the algae. High conversion of algae to gas products was found with low levels of byproduct water contamination and low to moderate loss of carbon in the mineral separation step.

Elliott, Douglas C.; Hart, Todd R.; Neuenschwander, Gary G.; Rotness, Leslie J.; Olarte, Mariefel V.; Zacher, Alan H.

2012-07-26

277

Electric Current Activated Combustion Synthesis and Chemical Ovens Under Terrestrial and Reduced Gravity Conditions  

NASA Technical Reports Server (NTRS)

Combustion synthesis (CS) generally involves mixing reactants together (e.g., metal powders) and igniting the mixture. Typically, a reaction wave will pass through the sample. In field activated combustion synthesis (FACS), the addition of an electric field has a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product as well as capillary flow, mass-transport in porous media, and Marangoni flows, which are influenced by gravity. The objective is to understand the role of an electric field in CS reactions under conditions where gravity-related effects are suppressed or altered. The systems being studied are Ti+Al and Ti+3Al. Two different ignition orientations have been used to observe effects of gravity when one of the reactants becomes molten. This consequentially influences the position and concentration of the electric current, which in turn influences the entire process. Experiments have also been performed in microgravity conditions. This process has been named Microgravity Field Activated Combustion Synthesis (MFACS). Effects of gravity have been demonstrated, where the reaction wave temperature and velocity demonstrate considerable differences besides the changes of combustion mechanisms with the different high currents applied. Also the threshold for the formation of a stable reaction wave is increased under zero gravity conditions. Electric current was also utilized with a chemical oven technique, where inserts of aluminum with minute amounts of tungsten and tantalum were used to allow observation of effects of settling of the higher density solid particles in liquid aluminum at the present temperature profile and wave velocity of the reaction.

Unuvar, C.; Fredrick, D.; Anselmi-Tamburini, U.; Manerbino, A.; Guigne, J. Y.; Munir, Z. A.; Shaw, B. D.

2004-01-01

278

Some physico-chemical properties of Moringa oleifera seed oil extracted using solvent and aqueous enzymatic methods  

Microsoft Academic Search

The physico-chemical properties of oil from Moringa oleifera seed were determined following extraction either with petroleum ether or 2% Neutrase 0.8L (a neutral bacterial protease from Bacillus amyloiquefaciens, Novozyme Bagsvaerd Denmark). The enzyme was chosen following a preliminary study conducted on the enzymatic extraction of M. oleifera seed oil using four commercial enzymes that showed Neutrase to be the best

S. M. Abdulkarim; K. Long; O. M. Lai; S. K. S. Muhammad; H. M. Ghazali

2005-01-01

279

Interaction of chemical and physical processes during deformation at fluid-present conditions: a case study from an anorthosite-leucogabbro deformed at amphibolite facies conditions  

NASA Astrophysics Data System (ADS)

We present microstructural and chemical analyses of chemically zoned and recrystallized plagioclase grains in variably strained samples of a naturally deformed anorthosite-leucogabbro, southern West Greenland. The recorded microstructures formed in the presence of fluids at mid-crustal conditions (620-640 °C, 7.4-8.6 kbar). Recrystallized plagioclase grains (average grain size 342 ?m) with a random crystallographic orientation are volumetrically dominant in high-strain areas. They are characterized by asymmetric chemical zoning (An80 cores and An64 rims) that are directly associated with areas exhibiting high amphibole content and phase mixing. Analyses of zoning indicate anisotropic behaviour of bytownite plagioclase with a preferred replacement in the < {0 10} rangle direction and along the (001) plane. In areas of high finite strain, recrystallization of plagioclase dominantly occurred by bulging recrystallization and is intimately linked to the chemical zoning. The lack of CPO as well as the developed asymmetric zoning can be explained by the activity of grain boundary sliding accommodated by dissolution and precipitation creep (DPC). In low-strain domains, grain size is on average larger and the rim distribution is not related to the inferred stress axes indicating chemically induced grain replacement instead of stress-related DPC. We suggest that during deformation, in high-strain areas, pre-existing phase mixture and stress induced DPC-caused grain rotations that allowed a deformation-enhanced heterogeneous fluid influx. This resulted in local plagioclase replacement through interface-coupled dissolution and precipitation and chemically induced grain boundary migration, accompanied by bulging recrystallization, along with neocrystallization of other phases. This study illustrates a strong interaction and feedback between physical and chemical processes where the amount of stress and fluids dictates the dominant active process. The interaction is a cause of deformation and external fluid infiltration with a result of strain localization and chemical re-equilibration at amphibolite facies conditions.

Svahnberg, Henrik; Piazolo, Sandra

2013-03-01

280

Basalt and olivine dissolution under cold, salty, and acidic conditions: What can we learn about recent aqueous weathering on Mars?  

NASA Astrophysics Data System (ADS)

To test which variables may be important for weathering on Mars, the effects of temperature (22°C, 6°C, and -19°C), high ionic strength, and oxygen concentrations were investigated in batch dissolution experiments containing forsterite, fayalite, and basalt glass. CaCl2-NaCl-H2O brine can remain liquid to temperatures of -55°C and thus may be liquid in the cold, dry climate that currently characterizes Mars. To understand weathering under such conditions, dissolution rates were measured in experiments in distilled water with and without CaCl2 and NaCl. As observed by others, dissolution rates increased with temperature, and only fayalite dissolution was significantly affected by the presence or absence of oxygen. Enhanced fayalite dissolution under anoxic conditions suggests that Fe-rich olivine would dissolve more rapidly than Mg-rich olivine on Mars. Dissolution in the two most dilute experimental solutions (deionized water and CaCl2-NaCl-H2O solution of ionic strength = 0.7 m) were the same within uncertainty, but apparent dissolution rate constants in CaCl2-NaCl-H2O brines were significantly slower. Steady silica concentrations are decreased in the brines, consistent with other work, and precipitation rates of silica decrease with decreasing temperatures. These results suggest that enhanced silica precipitation could be an indicator of high ionic strength solutions on Mars. Consistent with these observations, weathering of basalt has been observed to sometimes be accompanied by precipitated layers of silica in cold, dry environments on Earth. If dissolution on Mars occurs or occurred under conditions similar to our experiments, cation leaching would be expected to be accompanied by silica precipitates on weathering surfaces.

Hausrath, E. M.; Brantley, S. L.

2010-12-01

281

Conditional Toxicity Value (CTV) Predictor for Generating Toxicity Values for Data Sparse Chemicals (Poster)  

EPA Science Inventory

Various stakeholders and expert groups, including the National Research Council in Science and Decisions, call for “default approaches to support risk estimation for chemicals lacking chemical-specific information.” This project aims to address this challenge through ...

282

Application of Zero-Valent Iron Nanoparticles for the Removal of Aqueous Zinc Ions under Various Experimental Conditions  

PubMed Central

Application of zero-valent iron nanoparticles (nZVI) for Zn2+ removal and its mechanism were discussed. It demonstrated that the uptake of Zn2+ by nZVI was efficient. With the solids concentration of 1 g/L nZVI, more than 85% of Zn2+ could be removed within 2 h. The pH value and dissolved oxygen (DO) were the important factors of Zn2+ removal by nZVI. The DO enhanced the removal efficiency of Zn2+. Under the oxygen-contained condition, oxygen corrosion gave the nZVI surface a shell of iron (oxy)hydroxide, which could show high adsorption affinity. The removal efficiency of Zn2+ increased with the increasing of the pH. Acidic condition reduced the removal efficiency of Zn2+ by nZVI because the existing H+ inhibited the formation of iron (oxy)hydroxide. Adsorption and co-precipitation were the most likely mechanism of Zn2+ removal by nZVI. The FeOOH-shell could enhance the adsorption efficiency of nZVI. The removal efficiency and selectivity of nZVI particles for Zn2+ were higher than Cd2+. Furthermore, a continuous flow reactor for engineering application of nZVI was designed and exhibited high removal efficiency for Zn2+.

Liang, Wen; Dai, Chaomeng; Zhou, Xuefei; Zhang, Yalei

2014-01-01

283

Universal RF-Powered Aqueous Extractor-on-a-Chip Instrument for Identification of Chemical Signatures of Life on Mars  

NASA Astrophysics Data System (ADS)

The prospect of finding chemical signatures of present or past life on Mars is one of the important drivers behind Mars exploration program (MEP). One of the technical challenges facing MEP is the lack of compact and universal sample processing technology that enables the cataloging of organic molecules in Martian crustal materials. In the past year, we have been developing a super-compact, lightweight and low power-consumption microfluidic extractor-on-a-chip (?EX) instrument that will address this challenge for in situ Mars exploration missions and Mars Sample Return sample analysis. The core operational principle of ?EX is based on a unique property of water - the ability to change its permittivity (i.e., dielectric constant) as a function of frequency to match the dielectric constants of organic solvents. In our instrument, the dielectric constant of water decreases when 180 GHz RF radiation interacts with translational modes in a solution by disrupting orientation of the water molecules’ individual molecular dipoles. Since “like dissolves like”, ?EX can then extract biomarkers from soil samples by simply applying 180 GHz radiation to water, without the use of any other chemicals. Consequently, target biomarkers that are characterized by very different properties (e.g., size, charge, volatility, polarity, etc.), and which are typically only soluble in organic solvents, can now be easily extractable from the solid matrices and soluble in water. Here we present our research results, which include characterization of ?EX operation and data on organics extracted from Mars-analog soil samples.

Amashukeli, X.; Manohara, H.; Chattopadhyay, G.; Urgiles, E.; Lin, R.; Peralta, A.; Fisher, A.

2009-12-01

284

Size-resolved aerosol chemical composition over the Italian Peninsula during typical summer and winter conditions  

NASA Astrophysics Data System (ADS)

In the frame of the MIUR-AEROCLOUDS project (Study of Direct and Indirect Aerosol Effects on Climate), night-time and daytime size-segregated aerosol samples were collected concurrently at five different sites (near-city, urban, rural, marine and mountain background sites). The paper reports on the daily evolution of the main aerosol chemical characteristics as a function of particle size in different environments over the Italian Peninsula, spanning from the Po Valley to the south Tyrrhenian coast. Two 4-day intensive observation periods (IOPs) were undertaken in July 2007 and February 2008, under meteorological conditions typical of the summer and winter climate for Italy. In the summer IOP, under stable atmospheric conditions, at the low-altitude continental sites the diurnal evolution of the planetary boundary layer (PBL), induces an atmospheric dilution effect driving the particulate matter (PM) concentrations, while, at the mountain site, it determines the upward motion of polluted air masses from the Po Valley PBL in daytime. The fine fraction was dominated by ammonium salts and carbonaceous matter (water-soluble organic matter, WSOM, and water-insoluble carbonaceous matter, WINCM). High concentrations of ammonium sulphate and WSOM due to enhanced photochemical activity constituted the background aerosol composition over the whole country, whereas, ammonium nitrate and WINCM were more associated to local emissions (e.g. urban site with concentrations peaking in the finest size range due to strong local traffic-related sources of ultrafine particles). During the winter IOP in the Po Valley, the shallow PBL depths and low wind velocity, especially at night, favoured the condensation of semi-volatile species (i.e. organic matter and ammonium nitrate), causing the high fine PM concentration observed at ground level.

Carbone, C.; Decesari, S.; Mircea, M.; Giulianelli, L.; Finessi, E.; Rinaldi, M.; Fuzzi, S.; Marinoni, A.; Duchi, R.; Perrino, C.; Sargolini, T.; Vardè, M.; Sprovieri, F.; Gobbi, G. P.; Angelini, F.; Facchini, M. C.

2010-12-01

285

Polar organic chemical integrative samplers for pesticides monitoring: Impacts of field exposure conditions.  

PubMed

This study focuses on how Polar Organic Chemical Integrative Samplers (POCIS) work in real environmental conditions. A selection of 23 polar pesticides and 8 metabolites were investigated by exposure of triplicates of integrative samplers in two rivers in France for successive 14-day periods. The pesticides and metabolites were trapped not only in Oasis HLB sorbent but also in the polyethersulfone (PES) membrane of the POCIS. The distribution of pesticides depended on the molecular structure. The use of the Performance Reference Compound (PRC) is also discussed here. The impact of some environmental parameters and exposure setup on the transfer of pesticides in POCIS sorbent was studied: river flow rate, biofouling on membranes, sampler holding design and position in the stream. Results show a significant impact of river flow velocity on PRC desorption, especially for values higher than 4cm·s(-1). Some fouling was observed on the PES membrane which could potentially have an impact on molecule accumulation in the POCIS. Finally, the positioning of the sampler in the river did not have significant effects on pesticide accumulation, when perpendicular exposures were used (sampler positioning in front of the water flow). The POCIS with PRC correction seems to be a suitable tool for estimating time-weighted average (TWA) concentrations, for all the molecules except for one of the nine pesticides analyzed in these two French rivers. PMID:24830931

Lissalde, Sophie; Mazzella, Nicolas; Mazellier, Patrick

2014-08-01

286

Theoretical modeling of chemical nonequilibrium stagnation point boundary layer heat transfer under rarefied conditions  

NASA Astrophysics Data System (ADS)

This paper theoretically studies the recombination-dominated nonequilibrium reacting flow inside the stagnation point boundary layer (SPBL) and the heat transfer characteristics under rarefied conditions. A general model is intuitively proposed to describe the energy transfer and conversion along the stagnation streamline towards a slightly blunted nose with non-catalytic wall surface. It is found that the atoms recombination effects inside the SPBL could be equivalent to a modification on the degree of dissociation in the external flow. As a result, a recombination nonequilibrium criterion Da r , that is a specific Damköhler number, is introduced to characterize the nonequilibrium degree of the reacting flow in the SPBL, and then, based on the general model and Da r , a bridging function indicating the nonequilibrium chemical effects on the SPBL heat transfer is established. By using the explicitly analytical bridging function, the flow and heat transfer mechanisms, including the real gas flow similarity law and the nonequilibrium flow regimes classification, are discussed. In addition, the direct simulation Monte Carlo (DSMC) method has also been employed to systematically validate the analytical results.

Wang, ZhiHui; Bao, Lin; Tong, BingGang

2013-05-01

287

Chemical looping combustion in a rotating bed reactor--finding optimal process conditions for prototype reactor.  

PubMed

A lab-scale rotating bed reactor for chemical looping combustion has been designed, constructed, and tested using a CuO/Al(2)O(3) oxygen carrier and methane as fuel. Process parameters such as bed rotating frequency, gas flows, and reactor temperature have been varied to find optimal performance of the prototype reactor. Around 90% CH(4) conversion and >90% CO(2) capture efficiency based on converted methane have been obtained. Stable operation has been accomplished over several hours, and also--stable operation can be regained after intentionally running into unstable conditions. Relatively high gas velocities are used to avoid fully reduced oxygen carrier in part of the bed. Potential CO(2) purity obtained is in the range 30 to 65%--mostly due to air slippage from the air sector--which seems to be the major drawback of the prototype reactor design. Considering the prototype nature of the first version of the rotating reactor setup, it is believed that significant improvements can be made to further avoid gas mixing in future modified and up-scaled reactor versions. PMID:21970700

Håkonsen, Silje Fosse; Blom, Richard

2011-11-15

288

Accounting for natural organic matter in aqueous chemical equilibrium models: a review of the theories and applications  

NASA Astrophysics Data System (ADS)

Soil organic matter consists of a highly complex and diversified blend of organic molecules, ranging from low molecular weight organic acids (LMWOAs), sugars, amines, alcohols, etc., to high apparent molecular weight fulvic and humic acids. The presence of a wide range of functional groups on these molecules makes them very reactive and influential in soil chemistry, in regards to acid-base chemistry, metal complexation, precipitation and dissolution of minerals and microbial reactions. Out of these functional groups, the carboxylic and phenolic ones are the most abundant and most influential in regards to metal complexation. Therefore, chemical equilibrium models have progressively dealt with organic matter in their calculations. This paper presents a review of six chemical equilibrium models, namely N ICA-Donnan, E Q3/6, G EOCHEM, M INTEQA2, P HREEQC and W HAM, in light of the account they make of natural organic matter (NOM) with the objective of helping potential users in choosing a modelling approach. The account has taken various faces, mainly by adding specific molecules within the existing model databases (E Q3/6, G EOCHEM, and P HREEQC) or by using either a discrete (W HAM) or a continuous (N ICA-Donnan and M INTEQA2) distribution of the deprotonated carboxylic and phenolic groups. The different ways in which soil organic matter has been integrated into these models are discussed in regards to the model-experiment comparisons that were found in the literature, concerning applications to either laboratory or natural systems. Much of the attention has been focused on the two most advanced models, W HAM and N ICA-Donnan, which are able to reasonably describe most of the experimental results. Nevertheless, a better knowledge of the humic substances metal-binding properties is needed to better constrain model inputs with site-specific parameter values. This represents the main axis of research that needs to be carried out to improve the models. In addition to humic substances, more non-humic compounds should also be introduced in model databases, notably the ones that readily interact with the soil microorganisms. Thermodynamic data are generally available for most of these compounds, such as low molecular-weight organic acids. However, the more complex non-humic substances, exhibiting a ratio of hydrophobic versus hydrophilic bonds lower than humic substances, need to be further characterised for a comprehensive implementation in chemical equilibrium models.

Dudal, Yves; Gérard, Frédéric

2004-08-01

289

Aqueous phase processing of secondary organic aerosol from isoprene photooxidation  

NASA Astrophysics Data System (ADS)

Transport of reactive air masses into humid and wet areas is highly frequent in the atmosphere, making the study of aqueous phase processing of secondary organic aerosol (SOA) very relevant. We have investigated the aqueous phase processing of SOA generated from gas-phase photooxidation of isoprene using a smog chamber. The SOA collected on filters was extracted by water and subsequently oxidized in the aqueous phase either by H2O2 under dark conditions or by OH radicals in the presence of light, using a photochemical reactor. Online and offline analytical techniques including SMPS, HR-AMS, H-TDMA, TD-API-AMS, were employed for physical and chemical characterization of the chamber SOA and nebulized filter extracts. After aqueous phase processing, the particles were significantly more hygroscopic, and HR-AMS data showed higher signal intensity at m/z 44 and a lower signal intensity at m/z 43, thus showing the impact of aqueous phase processing on SOA aging, in good agreement with a few previous studies. Additional offline measurement techniques (IC-MS, APCI-MS2 and HPLC-APCI-MS) permitted the identification and quantification of sixteen individual chemical compounds before and after aqueous phase processing. Among these compounds, small organic acids (including formic, glyoxylic, glycolic, butyric, oxalic and 2,3-dihydroxymethacrylic acid (i.e. 2-methylglyceric acid)) were detected, and their concentrations significantly increased after aqueous phase processing. In particular, the aqueous phase formation of 2-methylglyceric acid and trihydroxy-3-methylbutanal was correlated with the consumption of 2,3-dihydroxy-2-methyl-propanal, and 2-methylbutane-1,2,3,4-tetrol, respectively, and an aqueous phase mechanism was proposed accordingly. Overall, the aging effect observed here was rather small compared to previous studies, and this limited effect could possibly be explained by the lower liquid phase OH concentrations employed here, and/or the development of oligomers observed during aqueous phase processing.

Liu, Y.; Monod, A.; Tritscher, T.; Praplan, A. P.; DeCarlo, P. F.; Temime-Roussel, B.; Quivet, E.; Marchand, N.; Dommen, J.; Baltensperger, U.

2012-07-01

290

Interaction of carbon nanotubes and diamonds under hot-filament chemical vapor deposition conditions  

NASA Astrophysics Data System (ADS)

A composite of CNTs and diamond can be expected to have unique mechanical, electrical and thermal properties due to the synergetic combination of the excellent properties of these two allotropes of carbon. The composite may find applications in various fields that require a combination of good mechanical, thermal, electrical and optical properties such as, wear-resistant coatings, thermal management of integrated chips (ICs), and field emission devices. This research is devoted to the experimental studies of phase stability of diamond and CNTs under chemical vapor deposition conditions to investigate the possibility of combining these materials to produce a hybrid composite. Growth of the hybrid material is investigated by starting with a pre-existing film of CNTs and subsequently growing diamond on it. The diamond growth phase space is systematically scanned to determine optimal conditions where diamond nucleates on the CNT without destroying it. Various techniques including SEM, TEM, and Micro Raman spectroscopy are used to characterize the hybrid material. A selective window where the diamond directly nucleates on the CNT without destroying the underlying CNT network is identified. Based on the material characterization, a growth mechanism based on etching of CNT at the defective sites to produce sp3 dangling bonds onto which diamond nucleates is proposed. Though a hybrid material is synthesized, the nucleation density of diamond on the CNTs is low and highly non-homogenous. Improvements to the CNT dispersion in the hybrid material are investigated in order to produce a homogenous material with predictable CNT loading fractions and to probe the low nucleation density of diamond on the CNT. The effect of several dispersion techniques and solvents on CNT surface homogeneity is studied using SEM, and a novel, vacuum drying based approach using CNT/dichlorobenzene dispersions is suggested. SEM and Raman analysis of the early stage nucleation are used to develop a hypothesis of diamond nucleation enhancement by CNT under HFCVD conditions. It is found that the nucleation takes places by etching of the CNT to create a new carbonaceous surface, onto which diamond nucleates. This mechanism is different from the present understanding of the diamond nucleation enhancement by CNTs.

Shankar, Nagraj

291

Mass spectral analysis of N-oxides of Chemical Weapons Convention related aminoethanols under electrospray ionization conditions.  

PubMed

N,N'-Dialkylaminoethanols are the hydrolyzed products or precursors of chemical warfare agents such as V-agents and nitrogen mustards, and they are prone to undergo oxidation in environmental matrices or during decontamination processes. Consequently, screening of the oxidized products of aminoethanols in aqueous samples is an important task in the verification of chemical weapons convention-related chemicals. Here we report the successful characterization of the N-oxides of N,N'-dialkylaminoethanols, alkyl diethanolamines, and triethanolamine using positive ion electrospray ionization mass spectrometry. The collision-induced dissociation (CID) spectra of the [M+H](+) and [M+Na](+) ions show diagnostic product ions that enable the unambiguous identification of the studied N-oxides, including those of isomeric compounds. The proposed fragmentation pathways are supported by high-resolution mass spectrometry data and product/precursor ion spectra. The CID spectra of [M+H](+) ions included [MH-CH(4)O(2)](+) as the key product ion, in addition to a distinctive alkene loss that allowed us to recognize the alkyl group attached to the nitrogen. The [M+Na](+) ions show characteristic product ions due to the loss of groups (R) attached to nitrogen either as a radical (R) or as a molecule [R+H or (R-H)] after hydrogen migration. PMID:21259362

Sridhar, L; Karthikraj, R; Murty, M R V S; Raju, N Prasada; Vairamani, M; Prabhakar, S

2011-02-28

292

Experimental investigation and planetary implications of the stability of clathrate hydrates in aqueous solution at icy satellite conditions  

NASA Astrophysics Data System (ADS)

Clathrate hydrates consist of hydrogen-bonded water molecules forming cages in which gas molecules are trapped individually. They are among the favored volatile reservoirs in solar system bodies, and are expected to play an important role in many processes: accretion of volatiles in planetesimals, outgassing on Titan, Enceladus, and comets. Their insulating thermal properties and high mechanical strength also bear important implications for understanding the evolution of icy satellites like Europa. However, the conditions allowing for their formation and/or their dissociation and the release of volatiles to the atmosphere (Titan) or the plumes (Enceladus) are still poorly understood. This is mainly because of a lack of knowledge on the stability of mixed clathrate hydrates in presence of anti-freeze agents such as ammonia. We have developed a high-pressure cryogenic calorimeter to address this deficiency in the literature. This liquid nitrogen - cooled Setaram BT2.15 calorimeter is located at the JPL Ice Physics Laboratory. The temperature range achievable with this instrument is 77-473 K. This calorimeter uses Calvet elements (3D arrays of thermocouples) to measure the heat flow required to follow a predefined heating rate within a sample and a reference cell with a resolution of 0.1 ?W. A gas handling system has been designed and fabricated in house to reach pressures up to 100 bars, corresponding to several km depth in icy satellites. The thermodynamic properties of CO2 and CH4 clathrates with ammonia are under investigation, and the results will be used to constrain a statistical thermodynamic model of clathrates for applications to planetary environments. Preliminary results will be shown at the meeting. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Support from the Minnesota Space Grant Consortium, the NASA Outer Planets Research program, and government sponsorship are gratefully acknowledged.

Dunham, M.; Choukroun, M.; Barmatz, M.; Hodyss, R. P.; Smythe, W. D.

2012-12-01

293

Chemical Interactions between Nano-ZnO and Nano-TiO2 in a Natural Aqueous Medium.  

PubMed

The use of diverse engineered nanomaterials (ENMs) potentially leads to the release of multiple ENMs into the environment. However, previous efforts to understand the behavior and the risks associated with ENMs have focused on only one material at a time. In this study, the chemical interactions between two of the most highly used ENMs, nano-TiO2, and nano-ZnO, were examined in a natural water matrix. The fate of nano-ZnO in Lake Michigan water was investigated in the presence of nano-TiO2. Our experiments demonstrate that the combined effects of ZnO dissolution and Zn adsorption onto nano-TiO2 control the concentration of dissolved zinc. X-ray absorption spectroscopy was used to determine the speciation of Zn in the particulate fraction. The spectra show that Zn partitions between nano-ZnO and Zn(2+) adsorbed on nano-TiO2. A simple kinetic model is presented to explain the experimental data. It integrates the processes of nano-ZnO dissolution with Zn adsorption onto nano-TiO2 and successfully predicts dissolved Zn concentration in solution. Overall, our results suggest that the fate and toxicity potential of soluble ENMs, such as nano-ZnO, are likely to be influenced by the presence of other stable ENMs, such as nano-TiO2. PMID:24918623

Tong, Tiezheng; Fang, Kaiqi; Thomas, Sara A; Kelly, John J; Gray, Kimberly A; Gaillard, Jean-François

2014-07-15

294

Iron isotope fractionation among magnetite, pyrrhotite, chalcopyrite, rhyolite melt and aqueous fluid at magmatic-hydrothermal conditions  

NASA Astrophysics Data System (ADS)

Fractionation of non-traditional stable isotopes (NTSI) such as Fe in magmatic systems is a relatively understudied subject. The fractionation of Fe stable isotopes has been quantified in some natural igneous samples, but there is a paucity of experimental data that could provide further insight into the causative processes of the observed fractionation. Substantial experimental work has been performed at higher temperatures pertaining to the formation of chondrites and the Earth's core, but only a handful of studies have addressed crustal rocks. To fill this knowledge gap, we performed isothermal, isobaric experiments containing mineral (e.g., magnetite, Fe-sulfides) and fluid, or mineral, rhyolite melt, and fluid assemblages to quantify equilibrium fractionation factors (?). These data, to our knowledge, are the first data that quantify the effect of a fluid phase on iron isotope fractionation at conditions appropriate for evolving magmatic systems. Charges were run inside gold capsules held in a René-41 cold seal vessel, and heated to 400, 600, or 800°C at 150 MPa for mineral-fluid, and 800°C and 100 MPa for mineral-melt-fluid runs. Use of the René vessel fixed the fO2 at the NNO buffer, an oxidation state consistent with arc magmas. The isotopic compositions of the starting and quenched phases were obtained by using a Multi-Collector Plasma Mass Spectrometer (MC-ICP-MS). Equilibrium was assessed by performing time-series runs and the three-isotope method, used only once before in a similar Fe isotope study. Correlation between Fe isotope mass and oxidation state is also being explored. Magnetite-fluid results indicate enrichment of heavy Fe isotopes in the mineral relative to the fluid, consistent with measurements of felsic igneous rocks. Magnetite-melt-fluid relationships are also consistent with measurements of natural samples. In the latter assemblage, over the course of the run, the rhyolite melt becomes heavy relative to the fluid while magnetite takes on a heavier Fe isotope signature than the starting value. These data corroborate the hypothesis that fluid exsolution caused the isotopic patterns observed in highly-differentiated igneous rocks. Further, owing to the ubiquitous importance of melt degassing as a critical process for the formation of magmatic-hydrothermal ore deposits, these data may be potentially serve as an exploration tool. This work contributes to our overall understanding of igneous processes by elucidating the Fe isotope fingerprints observed in the field as well as develop the laboratory techniques needed to study NTSI fractionation in magmatic systems and build a reliable dataset for interpretation of natural systems.

Bilenker, L. D.; Simon, A.; Lundstrom, C.; Gajos, N.

2012-12-01

295

Development of methods for on-line measurements of chemical conditions in compacted bentonite  

NASA Astrophysics Data System (ADS)

This work describes the development of an on-line method for studying the chemical conditions in compacted water-saturated bentonite. The equipment includes a squeezing cell, measurement electrodes, a reference electrode, and a data-logging system. IrO x wire was used for the pH measurements and Au and Pt wires for the redox measurements. The electrodes were made in-house at VTT. The reference electrode was a commercial leak-free electrode. The measurement electrodes were installed in the bentonite, while the reference electrode was placed in water outside the clay. The contact between the reference electrode and the measurement electrodes was established via the solution in a tube. The work included first a test and calibration of the electrodes in various standard solutions. The performance of the electrodes was subsequently studied in compacted MX-80 in squeezing cell experiments. The squeezing cell initially contained MX-80 mixed with different solutions at a dry density of 0.8-0.9 Mg/m 3. The pore water was then slowly squeezed out from the clay until the final density of 1.5 Mg/m 3 was reached. The measurement electrodes were then placed in the clay and the potential measurements were started. At the end of the experiments the electrodes were removed from bentonite and recalibrated. The pH and Eh in the squeezed pore waters were determined for comparison. The results obtained so far have led to the conclusion that it is possible to perform pH measurements in compacted bentonite by using IrO x electrodes. The electrode can survive the swelling pressure inside compacted water-saturated clay without losing its ability to function as a pH electrode. It is also possible to perform Eh measurements in compacted clay by using Au and Pt electrodes.

Muurinen, A.; Carlsson, T.

296

Mechanisms involved in chemical vapor generation by aqueous tetrahydroborate(III) derivatization. Role of hexacyanoferrate(III) in plumbane generation  

NASA Astrophysics Data System (ADS)

The role played by K 3Fe(CN) 6 (0.08 or 1.5 g l - 1 ) in producing strong enhancement factors in the generation efficiency of plumbane in the reaction of NaBH 4 (10 or 40 g l - 1 ) with Pb(II) (50 ?g l - 1 ) in 0.1 M HCl solution, was investigated by using continuous flow chemical vapor generation coupled with atomic fluorescence spectrometry (CF-CVG-AFS). Different mixing sequences and reaction times of reagents were tested using different chemifold setups. Part of CF-CVG-AFS experiments were performed using the on-line, delayed addition of Pb(II) to a K 3Fe(CN) 6 + NaBH 4 reaction mixture. Kinetic calculations estimating the concentration of K 3Fe(CN) 6 remaining in the K 3Fe(CN) 6 + NaBH 4 reaction mixture before it merged with Pb(II) solution were also performed. Batch experiments measuring the amount of hydrogen evolved (pressure of H 2 vs time) and pH variation during K 3Fe(CN) 6 + NaBH 4 + HCl reaction were performed in order to have a correct estimation of the concentration of K 3Fe(CN) 6 remaining in the reaction system. The comparison of CF-CVG-AFS experiments with kinetic calculations indicates that strong enhancement factors of plumbane generation can be obtained without any interaction of K 3Fe(CN) 6 with Pb(II). The key role of K 3Fe(CN) 6 is recognized in its reaction with NaBH 4 to give "special" borane complex intermediates, which are highly effective in the generation of plumbane from Pb(II).

D'Ulivo, Alessandro; Onor, Massimo; Spiniello, Roberto; Pitzalis, Emanuela

2008-08-01

297

A method for simultaneous analysis of phytosterols and phytosterol esters in tobacco leaves using non aqueous reversed phase chromatography and atmospheric pressure chemical ionization mass spectrometry detector.  

PubMed

While numerous analytical methods for phytosterols have been reported, the similar polarity and large molecules of phytosterol esters have made the methods lengthy and complicated. For this reason, an analytical method that could completely separate phytosterol esters including the higher fatty acids such as palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid in addition to phytosterols without preliminary separation was developed. The separation was accomplished by non-aqueous reversed phase chromatography technique using only acetone and acetonitrile. An atmospheric pressure chemical ionization/mass spectrometry detector configured at selected ion monitoring mode was hyphenated with the separation system to detect phytosterols and phytosterol esters. Twenty-four types of these were consequently separated and then identified with their authentic components. The calibration curve was drawn in the range of about 5 to 25,000 ng/mL with a regression coefficient over 0.999. The limit of detection and limit of quantification, respectively, ranged from 0.9 to 3.0 ng/mL and from 3.0 to 11.0 ng/mL. Recovery rates ranged from 80 to 120%. The quantification results were subjected to statistical analysis and hierarchical clustering analysis, and were used to determine the differences in the amounts of phytosterols and phytosterol esters across tobacco leaves. The newly developed method succeeded in clarifying the whole composition of phytosterols and phytosterol esters in tobacco leaves and in explaining compositional differences across the variety of tobacco leaves. PMID:24690307

Ishida, Naoyuki

2014-05-01

298

Sodium Borohydride Reduction of Aqueous Silver-Iron-Nickel Solutions: a Chemical Route to Synthesis of Low Thermal Expansion-High Conductivity Ag-Invar Alloys  

NASA Astrophysics Data System (ADS)

Thermal management is a critical concern in the design and performance of electronics systems. If heat extraction and thermal expansion are not properly addressed, the thermal mismatch among dissimilar materials may give rise to high thermal stresses or interfacial shear strains, and ultimately to premature system failure. In this article, we present a chemical synthesis process that yields Ag-Invar (64Fe-36Ni) alloys with a range of attractive properties for thermal management applications. Sodium borohydride reduction of an aqueous Ag-Fe-Ni metal salt solution produces nanocrystalline powders, and conventional powder processing converts this powder to fine-grained alloys. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy, thermomechanical analysis, and electrical conductivity measurements; thermal conductivity is estimated using the Wiedemann-Franz law. Sintering of Ag-Fe-Ni powders leads to the formation of two-phase silver-Invar alloys with low coefficients of thermal expansion (CTEs) and relatively high electrical conductivities. A sample of 50Ag-50Invar exhibits a CTE of 8.76 ?m/(m· °C) and an estimated thermal conductivity of 236 W/(m·K). The Ag-Invar alloys offer thermodynamic stability and tailorable properties, and they may help address the need for improved packaging materials.

Sterling, E. A.; Stolk, J.; Hafford, L.; Gross, M.

2009-07-01

299

Chemical equilibrium model for interfacial activity of crude oil in aqueous alkaline solution: the effects of pH, alkali and salt  

SciTech Connect

A chemical equilibrium model for interfacial activity of crude in aqueous alkaline solution is proposed. The model predicts the observed effects of pH and concentrations of alkali and salt on the interfacial tension (IFT). The model proposed was shown to describe the observed effects of acid content, pH, and sodium ions on the interfacial activity of crude oil in water. Once the pH of the interface reaches the pKa of the acids, sometimes with the help of addition of some salt, the IFT experiences a sudden steep drop to the range of 10/sup -2/ dynes/cm. After that, further addition of sodium either in the form of NaOH or NaCl is going to increase the IFT due to a shift of equilibriumn to the formation of undissociated soap. This was confirmed by the difference in the observed effect of sodium on the IFT of the extracted soap molecules which are dissociated easily and those which are associated highly and precipitated easily. These soap molecules have dissociation constant values ranging from below 10/sup -2/ to above one. 13 references.

Chan, M.; Yen, T.F.

1980-11-01

300

Atomistic Simulations of Chemical Reactivity of TATB Under Thermal and Shock Conditions  

Microsoft Academic Search

The study of chemical transformations that occur at the reactive shock front of energetic materials provides important information for the development of predictive models at the grain-and continuum scales. A major shortcoming of current high explosives models is the lack of chemical kinetics data of the reacting explosive in the high pressure and temperature regimes. In the absence of experimental

M R Manaa; E J Reed; L E Fried

2009-01-01

301

Irradiation of MEK — II: A detailed kinetic model for the degradation of 2-butanone in aerated aqueous solutions under steady-state ?-radiolysis conditions  

Microsoft Academic Search

The radiolytic decomposition of aqueous phase 2-butanone (methyl ethyl ketone (MEK)) has been studied extensively to gain a detailed mechanistic understanding of the effects of organic impurities on the behaviour of iodine in containment following a nuclear reactor accident. Based on the experimental results reported previously, a detailed reaction kinetic model for the steady-state ?-radiolysis of aerated aqueous solutions containing

Glenn Glowa; Paul Driver; Jungsook Clara Wren

2000-01-01

302

Remarkably Facile Heck Reactions in Aqueous Two-Phase System Catalyzed by Reusable Pd\\/C Under Ligand-Free Condition  

Microsoft Academic Search

A fast and convenient Heck reaction was achieved catalyzed by Pd\\/C in aqueous two-phase system. The aqueous two-phase system has been shown to be a highly active solvent for Heck reactions of aryl halides even in the absence of organic ligands.

Yan-Qin Yuan; Sheng-Rong Guo

2011-01-01

303

Remarkably Facile Heck Reactions in Aqueous Two-Phase System Catalyzed by Reusable Pd\\/C Under Ligand-Free Conditions  

Microsoft Academic Search

A fast and convenient Heck reaction was achieved catalyzed by Pd\\/C in aqueous two-phase system. The aqueous two-phase system has been shown to be a highly active solvent for Heck reactions of aryl halides even in the absence of organic ligands.

Yan-Qin Yuan; Sheng-Rong Guo

2012-01-01

304

DES-code: A metacode to aid calculation of the chemical potential of aqueous solutions at elevated temperatures and pressures  

NASA Astrophysics Data System (ADS)

The DH-ASF (Debye-Hückel-asymmetric formalism) model is a recently developed activity-composition model that can be used to calculate the thermodynamic effects of mixing in strong electrolyte and mixed solvent supercritical solutions at high pressures ( >3kbar) and temperatures ( >400C). The model uses a mole fraction concentration scale, and calculations are based on a pre-defined independent set of end-members that define speciation within the solution. This differs from the conventional use of molal concentration scales with sets of end-members that define the composition of the solution, but not the speciation (apparent end-members). This work presents DES (dual end-member sets)-code, a code that takes a conventional molal scale description of solution composition and implements the DH-ASF model for that solution. The code converts between apparent and independent end-member sets, and calculates standard state chemical potentials, ideal activities and activity coefficients using the DH-ASF model for molal and mole fraction concentration scales. The code runs in MathematicaTM 4.1 onwards, but it is written in a general meta-code form so that it can be implemented on a variety of platforms. Inputs to the code can be made manually, read from an auxiliary file, or presented to the input modules as passed variables. The code is provided with thermodynamic data from the Holland and Powell data set, but can be used with any data specified by the user. Outputs are designed to be modified by the user. Calculations on the systems NaCl- H2O, NaCl- CaCl2- H2O and NaCl- CO2- H2O are used to demonstrate the utility of the DES-code. Calculations predict that ion association increases with increasing temperature and concentration of salt and CO2, and with decreasing pressure. This is consistent with experimental observation and the results of molecular simulations. The DES-code is suitable for use as it stands, or for modification and incorporation into existing or new Gibbs energy minimisation or equilibrium solving thermodynamic codes.

Evans, Katy; Powell, Roger

2007-06-01

305

Chemical and Physical Environmental Conditions Underneath Mat and Canopy-Forming Macroalgae, and Their Effects on Understorey Corals  

Microsoft Academic Search

Disturbed coral reefs are often dominated by dense mat- or canopy-forming assemblages of macroalgae. This study investigated how such dense macroalgal assemblages change the chemical and physical microenvironment for understorey corals, and how the altered environmental conditions affect the physiological performance of corals. Field measurements were conducted on macroalgal-dominated inshore reefs in the Great Barrier Reef in quadrats with macroalgal

Claudine Hauri; Katharina E. Fabricius; Britta Schaffelke; Craig Humphrey; Stuart Humphries

2010-01-01

306

The Effect of Cooperative Learning Approach Based on Conceptual Change Condition on Students' Understanding of Chemical Equilibrium Concepts  

ERIC Educational Resources Information Center

The purpose of this study is to investigate the effects of the cooperative learning approach based on conceptual change conditions over traditional instruction on 10th grade students' conceptual understanding and achievement of computational problems related to chemical equilibrium concepts. The subjects of this study consisted of 87 tenth grade…

Bilgin, Ibrahim; Geban, Omer

2006-01-01

307

Structural, Chemical, Physical, and Functional Alterations in Mammalian Nucleus Following Different Conditions of Freezing, Storage, and Thawing.  

National Technical Information Service (NTIS)

The best structural preservation of nuclei of frozen mammalian tissue appears to be attained with the most rapid possible cooling from O C to below approximately-100 C. Conditions of slow freezing, which are better in general for preservation of chemical ...

R. E. Stowell D. E. Young E. A. Arnold B. F. Trump

1964-01-01

308

Aqueous hydrodechlorination of 4-chlorophenol over an Rh/reduced graphene oxide synthesized by a facile one-pot solvothermal process under mild conditions.  

PubMed

Reduced graphene oxide (RGO) supported rhodium nanoparticles (Rh-NPs/RGO) was synthesized through one-pot polyol co-reduction of graphene oxide (GO) and rhodium chloride. The catalytic property of Rh-NPs/RGO was investigated for the aqueous phase hydrodechlorination (HDC) of 4-chlorophenol (4-CP). A complete conversion of 4-CP into high valued products of cyclohexanone (selectivity: 23.2%) and cyclohexanol (selectivity: 76.8%) was successfully achieved at 303K and balloon hydrogen pressure in a short reaction time of 50min when 1.5g/L of 4-CP was introduced. By comparing with Rh-NPs deposited on the other supports, Rh-NPs/RGO delivered the highest initial rate (111.4mmol/gRhmin) for 4-CP HDC reaction under the identical conditions. The substantial catalytic activity of Rh-NPs/RGO can be ascribed to the small and uniform particle size of Rh (average particle size was 1.7±0.14nm) on the surface of the RGO sheets and an electron-deficient state of Rh in the catalyst as a result of the strong interaction between the active sites and the surface function groups of RGO. PMID:24762698

Ren, Yanlin; Fan, Guangyin; Wang, Chenyu

2014-06-15

309

Radiation-induced degradation of carboxymethylated chitosan in aqueous solution  

Microsoft Academic Search

Aqueous solutions of carboxymethylated chitosan (CM-chitosan) were radiated with ?-ray in various conditions. The degradations of CM-chitosan were faster in the presence of nitrous oxide or hydrogen peroxide, but it was inhibited obviously after adding isopropanol because of the changes of the concentration of hydroxyl radicals in above different conditions. The radiation chemical yields of CM-chitosan degradation were found to

Ling Huang; Maolin Zhai; Jing Peng; Jiuqiang Li; Genshuan Wei

2007-01-01

310

Application of high resolution Chemical Ionization Mass Spectrometry (CI-ToFMS) to study SOA composition: focus on formation of oxygenated species via aqueous phase processing  

NASA Astrophysics Data System (ADS)

This paper demonstrates the capabilities of Chemical Ionization Mass Spectrometry (CIMS) to study secondary organic aerosol (SOA) composition with a high resolution (HR) time-of-flight mass analyzer (aerosol-CI-ToFMS). In particular, by studying aqueous oxidation of Water Soluble Organic Compounds (WSOC) extracted from ?-pinene ozonolysis SOA, we assess the capabilities of three common CIMS reagent ions: (a) protonated water clusters (H2O)nH+, (b) acetate CH3C(O)O- and (c) iodide water clusters I(H2O)n- to monitor SOA composition. As well, we report the relative sensitivity of these reagent ions to a wide range of common organic aerosol constituents. We find that (H2O)nH+ is more selective to the detection of less oxidized species, so that the range of O/C and OSC (carbon oxidation state) in the SOA spectra is considerably lower than those measured using CH3C(O)O- and I(H2O)n-. Specifically, (H2O)nH+ ionizes organic compounds with OSC ? 1.3, whereas CH3C(O)O- and I(H2O)n- both ionize highly oxygenated organics with OSC up to 4 with I(H2O)n- being more selective towards multi-functional organic compounds. In the bulk O/C and H/C space, i.e. in a Van Krevelen plot, there is a remarkable agreement in both absolute magnitude and oxidation trajectory between CI-ToFMS data and those from a high resolution aerosol mass spectrometer (HR-AMS). This indicates that the CI-ToFMS data captures much of the chemical change occurring in the particle and that gas phase species, which are not detected by the HR-AMS, do not dominate the overall ion signal. Finally, the data illustrate the capability of aerosol-CI-ToFMS to monitor specific chemical change, including the fragmentation and functionalization reactions that occur during organic oxidation, and the oxidative conversion of dimeric SOA species into monomers. Overall, aerosol-CI-ToFMS is a valuable, selective complement to some common SOA characterization methods, such as AMS and spectroscopic techniques. Both laboratory and ambient SOA samples can be analyzed using the techniques illustrated in the paper.

Aljawhary, D.; Lee, A. K. Y.; Abbatt, J. P. D.

2013-07-01

311

Sonochemical dechlorination of hazardous wastes in aqueous systems  

SciTech Connect

Physical processes resulting from ultrasonication of aqueous solutions and suspensions produce extreme conditions that can affect the chemistry of dissolved and suspended chemicals. The purpose of this work was to explore the use of sonochemistry in treating chlorinated chemicals in water. The compounds examined for susceptibility to aqueous sonochemical transformation were chlorpyrifos, 3,3{prime},4,4{prime}-tetrachloroazoxybenzene, 2-chlorobiphenyl, 2,4,8-trichlorodibenzofuran, lindane (hexachlorocyclohexane, {gamma}-isomer), hexachlorobenzene, aldrin, and a complex mixture of chlorinated olefins, paraffins, and aromatics from a Louisiana Superfund Site. It was fond that many chemicals were dechlorinated and/or otherwise transformed by sonochemical treatment under minimal conditions. Evidence for sonochemical transformation and dechlorination of the target chemicals and mixtures was obtained from controlled experiments measuring (1) increases in titratable chloride from sonochemical treatment, (2) decreases in pH, (3) changes in aqueous phase UV/visible absorption spectra, (4) changes in aqueous electrochemistry, and (5) generation of sonolysis products and/or decreases in target compounds vs appropriate control in internally standardized GC-MS analysis of extracts.

Catallo, W.J.; Junk, T. [Louisiana State Univ., Baton Rouge, LA (United States)] [Louisiana State Univ., Baton Rouge, LA (United States)

1995-12-31

312

Changes in chemical forms of lead in temperate and semiarid soils in sterile and unsterile conditions  

Microsoft Academic Search

Sequential extraction has been used as a suitable method for fractionation of chemical forms of trace elements and study of\\u000a their plant availability. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with\\u000a temperate and semiarid climates. The chemical forms of Pb in the Pb(NO3)2-treated (400 ?g Pb g?1) soils have been studied in solid

Ali Akbar Safari Sinegani; Hossein Mirahamdi Araki

2010-01-01

313

Sensitivity of chemical exergy for atmospheric gases and gaseous fuels to variations in ambient conditions  

Microsoft Academic Search

The variations of chemical exergy with ambient temperature from ?30°C to 45°C, pressure from 0.6 to 1.1bar and relative humidity (RH) from 10% to 100% were investigated for gaseous fuels and atmospheric gases on the basis of Szargut’s model. It was found that the variations are significant. At ambient pressure of 1atm and RH at 70%, the chemical exergy of

Ivar S. Ertesvåg

2007-01-01

314

Greener Syntheses and Chemical Transformations: Sustainable Alternative Methods and Applications of Nano-Catalysts  

EPA Science Inventory

The presentation summarizes our sustainable chemical synthesis activity involving benign alternatives, such as the use of supported reagents, and greener reaction medium in aqueous or solvent-free conditions.1 The synthesis of heterocyclic compounds, coupling reactions, and a var...

315

Greener Syntheses and Chemical Transformations: Sustainable Alternative Methods and Applications of Nano-Catalysts. (Florence, Italy)  

EPA Science Inventory

The presentation summarizes our sustainable chemical synthesis activity involving benign alternatives, such as the use of supported reagents, and greener reaction medium in aqueous or solvent-free conditions. The synthesis of heterocyclic compounds, coupling reactions, and a vari...

316

Greener Synthesis and Chemical transformations Using Sustainable Alternative Methods and Applications of Nano-Catalysts  

EPA Science Inventory

The presentation summarizes our sustainable chemical synthesis activity involving benign alternatives, namely greener reaction medium in aqueous or solventfree conditions and using alternative activation via microwave or photocatalytic activation. Eco-friendly synthesis of nanoma...

317

Greener Syntheses and Chemical Transformations Using SustainableAlternative Methods and Nano-Catalysts  

EPA Science Inventory

The presentation summarizes our sustainable chemical synthesis activity involving benign alternatives, namely greener reaction medium in aqueous or solventfree conditions and using alternative activation via microwave or photocatalytic activation. Eco-friendly synthesis of nanoma...

318

Clinical vocabulary as a boundary object in multidisciplinary care management of multiple chemical sensitivity, a complex and chronic condition  

PubMed Central

Background: Research has shown that accurate and timely communication between multidisciplinary clinicians involved in the care of complex and chronic health conditions is often challenging. The domain knowledge for these conditions is heterogeneous, with poorly categorized, unstructured, and inconsistent clinical vocabulary. The potential of boundary object as a technique to bridge communication gaps is explored in this study. Methods: A standardized and controlled clinical vocabulary was developed as a boundary object in the domain of a complex and chronic health condition, namely, multiple chemical sensitivity, to improve communication among multidisciplinary clinicians. A convenience sample of 100 patients with a diagnosis of multiple chemical sensitivity, nine multidisciplinary clinicians involved in the care of patients with multiple chemical sensitivity, and 36 clinicians in the community participated in the study. Results: Eighty-two percent of the multidisciplinary and inconsistent vocabulary was standardized using the Systematized Nomenclature of Medicine – Clinical Terms (SNOMED® CT as a reference terminology. Over 80% of the multidisciplinary clinicians agreed on the overall usefulness of having a controlled vocabulary as a boundary object. Over 65% of clinicians in the community agreed on the overall usefulness of the vocabulary. Conclusion: The results from this study are promising and will be further evaluated in the domain of another complex chronic condition, ie, chronic pain. The study was conducted as a preliminary analysis for developing a boundary object in a heterogeneous domain of knowledge.

Sampalli, Tara; Shepherd, Michael; Duffy, Jack

2011-01-01

319

Study of Chemical Surface Structure of Natural Sorbents Used for Removing of Pb2+ Ions from Model Aqueous Solutions (part Ii)  

NASA Astrophysics Data System (ADS)

This article presents the results of the chemical structure research of organic sorbent surface such as walnut shells, plums stones and sunflower hulls with using such methods as infrared spectrometry (FTIR) and elemental analysis. Based on the IR spectra identification of functional groups present on the surface of studied materials has been done as well as determination of their effect on the sorption mechanism of Pb2+ ions from aqueous model solutions W artykule przedstawiono wyniki bada? chemicznej struktury powierzchni sorbentów organicznych takich jak: ?upiny orzecha w?oskiego, pestki ?liwek oraz ?uski s?onecznika z wykorzystaniem metody spektrometrii w podczerwieni (FTIR) oraz analizy elementarnej. W oparciu o uzyskane widma IR dokonano identyfikacji grup funkcyjnych obecnych na powierzchni tych materia?ów i okre?lono ich wp?yw na mechanizm sorpcji jonów Pb2+ z modelowych roztworów wodnych. Analiza elementarna wykaza?a, ?e spo?ród badanych sorbentów, najwi?ksz? zawarto?? w?gla (49,91%) i wodoru (5,93%) maj? pestki ?liwek. Najwi?cej azotu (1,59%) zawieraj? ?uszczyny s?onecznika (tabela 1). Zawarto?? siarki we wszystkich badanych materia?ach jest znikoma, dlatego nie uda?o si? jej oznaczy? t? metod?. Obecno?? pozosta?ych pierwiastków mo?e ?wiadczy? o istnieniu zarówno alifatycznych jak i aromatycznych po??cze? organicznych. Potwierdzeniem tego s? równie? zarejestrowane widma IR (rysunki 1-3). W oparciu o uzyskane wyniki mo?na przypuszcza? tak?e, i? udzia? procesu wymiany jonowej w sorpcji o?owiu z roztworów wodnych jest znacz?cy. ?wiadcz? o tym m.in. intensywno?ci pasm na widmach IR dla próbek badanych materia?ów po ich kontakcie z roztworami jonów Pb2+ (rysunki 4-6).

Bo??cka, Agnieszka; Bo??cki, Piotr; Sanak-Rydlewska, Stanis?awa

2014-03-01

320

Integrating (31) P DOSY NMR Spectroscopy and Molecular Mechanics as a Powerful Tool for Unraveling the Chemical Structures of Polyoxomolybdate-Based Amphiphilic Nanohybrids in Aqueous Solution.  

PubMed

Novel organic-inorganic hybrids of various sizes were generated by reaction of 1,8-octanediphosphonic acid (ODP) and (NH4 )6 Mo7 O24 in aqueous solution. The formation of rodlike hybrids with variable numbers of covalently bound ODP and polyoxomolybdate (POM) units can be tuned as a function of increasing (NH4 )6 Mo7 O24 concentration at fixed ODP concentration. The chemical structure of the ODP/POM hybrids was characterized by (1) H, (31) P, and (95) Mo NMR spectroscopy. Heteronuclear (31) P DOSY (diffusion- ordered NMR spectroscopy) and molecular mechanics (MM) calculations were applied to determine the size and shape of the nanosized hybrids generated at various ODP/POM ratios. For this purpose, the structures of ODP/POM hybrids with variable numbers of ODP and POM units were optimized by MM and then approximated as cylinder-shaped objects by using a recently described mathematical algorithm. The thus-obtained cylinder length and diameter were further used to calculate the expected diffusion coefficients of the ODP/POM hybrids. Comparison of the calculated and experimentally determined diffusion coefficients led to the most probable ODP/POM hybrid length for each sample composition. The (31) P DOSY results show that the length of the hybrids increases with increasing POM concentration and reaches a maximum corresponding to an average of 8?ODP/7?POM units per chain at a sample composition of 20?mM ODP and 14?mM POM. With excess POM, above the latter concentration, the formation of shorter-chain hybrids terminated by Mo7 clusters at one or both ends was evidenced on further increasing the POM concentration. The results demonstrate that the combination of (31) P DOSY and MM, although virtually unexplored in POM chemistry, is a powerful innovative strategy for the detailed characterization of nanosized organic-inorganic POM-based hybrids in solution. PMID:24729454

Shestakova, Pavletta; Absillis, Gregory; Martin-Martinez, Francisco J; De Proft, Frank; Willem, Rudolph; Parac-Vogt, Tatjana N

2014-04-25

321

Reaction of aqueous 2-(N-methylamino)ethanol solutions with carbon dioxide. Chemical species and their conformation studied by vibrational spectroscopy and ab initio theories  

SciTech Connect

The recovery and removal of carbon dioxide from flue gases by using CO{sub 2}-amine-H{sub 2}O systems have been of fundamental interest and industrial importance in the problem of preventing global warming. The reaction systems of aqueous 2-(N-methylamino)ethanol (MAE) solutions with dissolved CO{sub 2} (CO{sub 2}-MAE-H{sub 2}O system) and of liquid MAE with dissolved CO{sub 2} (CO{sub 2}-MAE system) have been studied by vibrational spectroscopy and ab initio theories. The chemical species, molecular conformations, and intramolecular and intermolecular hydrogen bonding in these systems have been elucidated. The species produced in the CO{sub 2}-MAE-H{sub 2}O system are the carbamate anion (MAECO{sub 2}{sup {minus}}), the protonated cation (MAEH{sup +}), hydrogencarbonate ion (HCO{sub 3}{sup {minus}}), and carbonate ion (CO{sub 3}{sup 2{minus}}) while the species produced in the CO{sub 2}-MAE system are MAECO{sub 2}{sup {minus}} and MAEH{sup +}. In the CO{sub 2}-MAE-H{sub 2}O system, MAE (secondary amine) reacts with CO{sub 2} to form MAECO{sub 2}{sup {minus}} and MAEH{sup +}, and MAECO{sub 2}{sup {minus}} subsequently reacts with H{sub 2}O and CO{sub 2} to form MAEH{sup +} and HCO{sub 3}{sup {minus}}. This reaction mechanism is contrasted with the mechanism for 2-(N,N-dimethylamino)ethanol (DMAE, tertiary amine), which reacts with CO{sub 2} and H{sub 2}O to form directly DMAEH{sup +} and HCO{sub 3}{sup {minus}}.

Ohno, Keiichi; Inoue, Yutaka; Yoshida, Hiroshi; Matsuura, Hiroatsu [Hiroshima Univ., Kagamiyama, Higashi-Hiroshima (Japan). Dept. of Chemistry] [Hiroshima Univ., Kagamiyama, Higashi-Hiroshima (Japan). Dept. of Chemistry

1999-05-27

322

On the formation and structure of rare-earth element complexes in aqueous solutions under hydrothermal conditions with new data on gadolinium aqua and chloro complexes  

Microsoft Academic Search

Synchrotron X-ray spectroscopy experiments were made on the Gd(III) aqua and chloro complexes in low pH aqueous solutions at temperatures ranging from 25 to 500 °C and at pressures up to 480 MPa using a hydrothermal diamond anvil cell. Analysis of fluorescence Gd L3-edge X-ray absorption fine structure (XAFS) spectra measured from a 0.006m Gd\\/0.16m HNO3 aqueous solution at temperatures up to

Robert A. Mayanovic; Alan J. Anderson; William A. Bassett; I-Ming Chou

2007-01-01

323

Effect of leukemia inhibitory factor on bovine embryos produced in vitro under chemically defined conditions  

Microsoft Academic Search

The objective of these experiments was to assess putative embryotrophic effects of leukemia inhibitory factor (LIF) on bovine preimplantation development in chemically defined media. Recombinant human LIF was added to embryo culture media at a concentration of 100ng\\/ml. When added for culture of morulae LIF had no positive effect on the proportion of embryos reaching the blastocyst stage. However, LIF

S Sirisathien; H. J Hernandez-Fonseca; P Bosch; B. R Hollet; J. D Lott; B. G Brackett

2003-01-01

324

THE INSTABILITY OF ESTROGENIC CHEMICALS DURING LABORATORY STATIC EXPOSURE CONDITIONS WITH MALE FATHEAD MINNOWS  

EPA Science Inventory

Endocrine disrupting chemicals (EDCs) such as Para-nonylphenol (NP), estradiol (E2), estrone (E1), estriol (E3) and ethynylestradiol (EE2) are shown to be ubiquitous in surface waters, sediments and sludge. These EDCs are known to induce vitellogenin gene (Vg) expression in male...

325

Water Quality Investigations, Lake Michigan Basin. Physical and Chemical Quality Conditions.  

National Technical Information Service (NTIS)

The report presents the physical and chemical results of a comprehensive study of Lake Michigan waters conducted by the Great Lakes-Illinois River Basins Project from April 1962 to July 1964. The study was conducted through the collection of appropriate s...

1968-01-01

326

Numerical simulation of the middle atmosphere chemical composition and temperature under changing solar conditions  

NASA Technical Reports Server (NTRS)

There are given results of the numerical experiments on modelling the influence of solar activity on chemical composition and temperature of the middle atmosphere. The consideration is made for peculiarities of solar activity impact under different values of antropogenic pollution of the atmosphere with chlorofluorocarbons and other stuff.

Zadorozhny, A. M.; Dyominov, I. G.; Tuchkov, G. A.

1989-01-01

327

Low-thrust chemical propulsion system propellant expulsion and thermal conditioning study. Executive summary  

NASA Technical Reports Server (NTRS)

Preferred techniques for providing abort pressurization and engine feed system net positive suction pressure (NPSP) for low thrust chemical propulsion systems (LTPS) were determined. A representative LTPS vehicle configuration is presented. Analysis tasks include: propellant heating analysis; pressurant requirements for abort propellant dump; and comparative analysis of pressurization techniques and thermal subcoolers.

Merino, F.; Wakabayashi, I.; Pleasant, R. L.; Hill, M.

1982-01-01

328

Agglomerated Large Particles under Various Slurry Preparation Conditions and Their Influence on Shallow Trench Isolation Chemical Mechanical Polishing  

NASA Astrophysics Data System (ADS)

The effects of various slurry manufacturing conditions, such as suspension pH, abrasive contents, and the calcination temperature of abrasive ceramic particles on the formation of agglomerated large particles of ceria slurry were investigated. The agglomerated large particles in slurry have much influence on the micro-scratches on the wafer surface in shallow trench isolation chemical mechanical polishing (STI CMP). The formation of large agglomerated particles is affected by the conformation of the organic additives in the slurry as a function of the suspension pH and the specific surface area of the abrasive particle. Regarding the solid content, abrasive particles are more easily dispersed at lower solid loading, which prevents additional agglomeration even under acidic conditions. The influence of agglomerated large particles on STI CMP was investigated through a polishing experiment with plasma-enhanced tetra-ethyl-ortho-silicate (PETEOS) and a low-pressure chemical vapor deposition (LPCVD) nitride layer.

Kim, Dae-Hyeong; Kang, Hyun-Goo; Kim, Sang-Kyun; Paik, Ungyu; Park, Jea-Gun

2005-11-01

329

Diurnal fluctuations in the physico-chemical conditions of the Shatt al-Arab and the Ashar Canal  

Microsoft Academic Search

Diel fluctuations of temperature, dissolved oxygen, carbon dioxide, pH, total alkalinity and chlorosity in the Shatt al-Arab\\u000a River and the Ashar Canal at Basrah, Iraq were studied. The study covered three 24-hour periods in three different months.\\u000a Appreciable diurnal changes in the physico-chemical conditions and considerable heterogeneity were noted at the three stations\\u000a selected. The ranges of diurnal differences between

A L Sarker; S K Al-Nasiri; S A Hussein

1980-01-01

330

Localization of lectin-binding sites on the surface of Trypanosoma cruzi grown in chemically defined conditions  

Microsoft Academic Search

The transformation of Trypanosoma cruzi epimastigotes to mammal-infective metacyclic trypomastigotes (metacyclogenesis) can be performed in vitro under chemically\\u000a defined conditions (TAU 3AAG medium). During this process, changes in the nature of cell surface sugar composition and sugar\\u000a distribution was evaluated using FITC and gold-labeled lectins and observed by flow cytometry and transmission electron microscopy.\\u000a The pattern of labeling with the

Saulo C. Bourguignon; Wanderley de Souza; T. Souto-Padrón

1998-01-01

331

Assessment of chemical dispersant effectiveness in a wave tank under regular non-breaking and breaking wave conditions.  

PubMed

Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural environment, including transport and dilution effects. To achieve this goal, Fisheries and Oceans Canada and the US Environmental Protection Agency (EPA) designed and constructed a wave tank system to study chemical dispersant effectiveness under controlled mixing energy conditions (regular non-breaking, spilling breaking, and plunging breaking waves). Quantification of oil dispersant effectiveness was based on observed changes in dispersed oil concentrations and oil-droplet size distribution. The study results quantitatively demonstrated that total dispersed oil concentration and breakup kinetics of oil droplets in the water column were strongly dependent on the presence of chemical dispersants and the influence of breaking waves. These data on the effectiveness of dispersants as a function of sea state will have significant implications in the drafting of future operational guidelines for dispersant use at sea. PMID:18325540

Li, Zhengkai; Lee, Kenneth; King, Thomas; Boufadel, Michel C; Venosa, Albert D

2008-05-01

332

Sensitivity of the chemical exergy for atmospheric gases and gaseous fuels to variations in ambient conditions  

Microsoft Academic Search

Variation of the chemical exergy with ambient temperature from ?30 ºC to 45 ºC, pressure from 0.6 to 1.1 bar, and relative humidity (RH) from 10% to 100% was investigated for gaseous fuels and atmospheric gases on the basis of Szargut's model. It was found that the variation is significant. At ambient pressure at 1 atm and RH at 70%,

Ivar S. Ertesvåg

333

Effect of outdoor conditions on growth rate and chemical composition of Gelidium crinale in culture  

Microsoft Academic Search

A comprehensive study of the major environmental factors affecting growth and chemical composition of Gelidium crinale is presented here for the first time. The purpose of this study was to analyze the significance of the major growth factors\\u000a and to formulate them into regression models. For this purpose summer and winter experiments were conducted in small aerated\\u000a seawater tanks under

Areen Boulus; Ehud Spaneir; Michael Friedlander

2007-01-01

334

Ceramic repair: influence of chemical and mechanical surface conditioning on adhesion to zirconia.  

PubMed

Aims: To evaluate the influence of mechanical surface treatment and chemical primer application on the composite shear bond strength to zirconia. Methods: Eighty blocks of Lava Frame Zirconia were randomly assigned to the experimental groups, according to the several possible combinations between mechanical (untreated/aluminum oxide sandblast) and chemical treatment (no primer/Monobond Plus/Experimental Zirkon-Primer/Z-Prime Plus) (n=10). Adhesive system and composite resin were then applied, and samples were thermal cycled (5°C-55°C, 500 cycles). Shear bond strength tests and failure mode analysis were performed. SBS data were analyzed by two-way ANOVA, followed by Student-Newman-Keuls post-hoc tests, and failure mode by Kruskal-Wallis and Mann-Whitney tests (p<0.05). Results: Shear bond strength mean values ranged from 6.9 to 23.2 MPa. Surface treatment with aluminum oxide sandblasting allowed a statistically significant increase (p<0.05) in bond strength values. The group treated with Z-Prime Plus achieved (p<0.05) higher bond strength results than the other chemical treatments. Conclusions: The surface mechanical treatment almost doubled the bond strength values. Z-Primer Plus have enhanced bond strength values of composite to zirconia. PMID:24984615

Barragan, Goncalo; Chasqueira, Filipa; Arantes-Oliveira, Sofia; Portugal, Jaime

2014-06-01

335

Bacterial adhesion to solid substrata coated with conditioning films derived from chemical fractions of natural waters  

Microsoft Academic Search

Dissolved organic carbon from seawater and freshwater was separated into hydrophilic-base, hydrophilic-neutral, hydrophilic-acid as well as hydrophobic-base, hydrophobic-neutral, and hydrophobic-acid fractions which were used to form conditioning films on hydrophilic stainless steel and aluminium as well as on hydrophobic polypropylene and perspex. Water contact angles indicated that every conditioning film modified the wettability of clean substrata; the wettability of hydrophobic

Rene P. Schneider

1997-01-01

336

The effect of chemical composition and austenite conditioning on the transformation behavior of microalloyed steels  

SciTech Connect

In this investigation, by using continuous cooling torsion (CCT) testing, the transformation behavior of four microalloyed steels under two circumstances of austenite conditioning and non-conditioning was studied. A full scale hot-rolling schedule containing a 13-pass deformation was employed for the conditioning of the austenite. The CCT tests were then employed till temperature of {approx} 540 Degree-Sign C and the flow curves obtained from this process were analyzed. The initial and final microstructures of the steels were studied by optical and electron microscopes. Results show that alloying elements would decrease the transformation temperature. This effect intensifies with the gradual increase of Mo, Nb and Cu as alloying elements added to the microalloyed steels. As well, austenite conditioning increased the transformation start temperature due mainly to the promotion of polygonal ferrite formation that resulted from a pancaked austenite. The final microstructures also show that CCT alone would decrease the amount of bainite by inducing ferrite transformation in the two phase region. In addition, after the transformation begins, the deformation might result in the occurrence of dynamic recrystallization in the ferrite region. This could lead to two different ferrite grain sizes at the end of the CCT. Moreover, the Nb bearing steels show no sign of decreasing the strength level after the transformation begins in the non-conditioned situation and their microstructure is a mix of polygonal ferrite and bainite indicating an absence of probable dynamic recrystallization in this condition. In the conditioned cases, however, these steels show a rapid decrease of the strength level and their final microstructures insinuate that ferrite could have undergone a dynamic recrystallization due to deformation. Consequently, no bainite was seen in the austenite conditioned Nb bearing steels. The pancaking of austenite in the latest cases produced fully polygonal ferrite structures. - Highlights: Black-Right-Pointing-Pointer Adding alloying elements would decrease the transformation temperatures. Black-Right-Pointing-Pointer Austenite conditioning increases the transformation start temperature. Black-Right-Pointing-Pointer Deformation could induce the occurrence of dynamic recrystallization in ferrite region.

Mousavi Anijdan, S.H., E-mail: hashem.mousavi@mail.mcgill.ca [Department of Mining and Materials Engineering, McGill University, 3610 University Street, Montreal, Quebec, H3A 2B (Canada); Rezaeian, Ahmad [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Yue, Steve [Department of Mining and Materials Engineering, McGill University, 3610 University Street, Montreal, Quebec, H3A 2B (Canada)

2012-01-15

337

Impact of oxygen cut off and starvation conditions on biological activity and physico-chemical properties of activated sludge.  

PubMed

Physico-chemical and biological parameters were monitored both throughout different oxygen cut off and starvation (OCS) times (6 h-72 h) and after the restoration of normal operational conditions. Sludge apparent viscosity and soluble extracellular polymeric substances (EPS) characteristics were measured to determine the activated sludge (AS) properties. Oxygen transfer, biological activity with specific oxygen uptake rate (SOUR) measurements during endogenous/exogenous conditions (without any external substrate/with external substrate consumption) and chemical oxygen demand (COD) removal were measured to assess the AS performances. During the different stress times, AS deflocculated as a decrease of apparent viscosity was observed and microorganisms biodegraded the released EPS to survive. After aeration return, and under endogenous conditions, size exclusion chromatographic fingerprints of soluble EPS were modified and macromolecules probably of type humic-like substances appeared in significant quantities. These new macromolecules presumably acted as biosurfactants. Consequently, the liquid surface tension, as well as the oxygen transfer rate (OTR), decreased. Under exogenous conditions, high biological activity (SOUR = 11.8 +/- 2.1 mg(O2 x g(MLVSS)(-1) x h(-1)) compensated the decrease of oxygen transfer. Finally, AS biomass maintained a constant COD degradation rate (15.7 +/- 1.9 mg(O2) x g(MLVSS)(-1) x h(-1)) before and after the disturbances for all times tested. This work demonstrates that AS microorganisms can counteract concomitant oxygen and nutrients shortage when the duration of such a condition does not exceed 72 h. Dissociation of endogenous/exogenous conditions appears to offer an ideal laboratory model to study EPS and biomass activity effects on oxygen transfer. PMID:23837341

Villain, Maud; Clouzot, Ludiwine; Guibaud, Gilles; Marrot, Benoit

2013-01-01

338

Relationship between foliar chemical parameters measured in Melia Azedarach L. and environmental conditions in urban areas  

Microsoft Academic Search

A diagnostic study was done on Melia azedarach L. in relation to atmospheric pollutants in Córdoba city, Argentina. The study area receives regional pollutants, and it was categorized taking into account traffic level, industrial level, location of the sample point in relation to the corner, treeless condition, building type, topographic level and distance to the river. Water content and Specific

Mar??a L Pignata; Gustavo L Gudiño; Martha S Cañas; Liliana Orellana

1999-01-01

339

Chemical composition of the essential oils of Ziziphora growing under various ecological conditions  

Microsoft Academic Search

It has been established that, in spite of different ecological conditions of the growth of the endemic speciesZiziphora vychodceviana, Z. pedicellata, andZ. persica, they are characterized by identical biosyntheses of terpenoids and differ by the ratio of the main components of their essential\\u000a oils.

A. D. Dembitskii; E. Sh. Bergaliev; I. M. Kyazimov

1994-01-01

340

Low-Thrust Chemical Propulsion System Propellant Expulsion and Thermal Conditioning Study.  

National Technical Information Service (NTIS)

Thermal conditioning systems for satisfying engine net positive suction pressure (NPSP) requirements, and propellant expulsion systems for achieving propellant dump during a return-to-launch site (RTLS) abort were studied for LH2/LO2 and LCH4/LO2 upper st...

F. Merino I. Wakabayashi R. L. Pleasant M. Hill

1982-01-01

341

Chemically defined conditions for human iPS cell derivation and culture  

PubMed Central

We reexamine the individual components for human ES and iPS cell culture, and formulate a cell culture system in which all protein reagents for liquid media, attachment surfaces, and splitting are chemically defined. A major improvement is the lack of a serum albumin component, as variations in either animal or human sourced albumin batches have previously plagued human ES and iPS cell culture with inconsistencies. Using this new medium (E8) and vitronectin-coated surfaces, we demonstrate improved derivation efficiencies of vector-free human iPS cells with an episomal approach. This simplified E8 medium should facilitate both the research use and clinical applications of human ES and iPS cells and their derivatives, and should be applicable to other reprogramming methods.

Chen, Guokai; Gulbranson, Daniel R.; Hou, Zhonggang; Bolin, Jennifer M.; Ruotti, Victor; Probasco, Mitchell D.; Smuga-Otto, Kimberly; Howden, Sara E.; Diol, Nicole R.; Propson, Nicholas E.; Wagner, Ryan; Lee, Garrett O.; Antosiewicz-Bourget, Jessica; Teng, Joyce M. C.; Thomson, James A.

2011-01-01

342

Response of Anastrepha obliqua (Diptera: Tephritidae) to visual and chemical cues under seminatural conditions.  

PubMed

The West Indian fruit fly, Anastrepha obliqua (Macquart), is considered one of the most important pests of several fruit crops in Latin America. Studies on the sensorial ecology of A. obliqua may contribute to the improvement of a trapping system for monitoring this fruit fly species. In this study, we investigated the responses of both sexes of A. obliqua to different visual cues and to the combination of visual and chemical cues in field cages tests. Both sexes were more attracted to lime-green, orange, and yellow spheres than to red, black, or white spheres. Flies were more attracted to three-dimensional models than to flat models. A. obliqua was more attracted to 8-, 10-, and 12-cm-diameter spheres than to 4- and 6-cm-diameter spheres. Flies were more attracted to lime-green spheres baited with mombin fruit odor, Spondias mombin L., than to spheres offering either visual or cues alone. PMID:19610408

López-Guillén, Guillermo; Valle-Mora, Javier; Cazares, Celina Llanderal; Rojas, Julio C

2009-06-01

343

?-pinene photooxidation under controlled chemical conditions - Part 2: SOA yield and composition in low- and high-NOx environments  

NASA Astrophysics Data System (ADS)

The gas-phase oxidation of ?-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with ?-pinene have been found in field samples and some are used as tracers of ?-pinene oxidation. ?-pinene reacts readily with OH and O3 in the atmosphere followed by reactions with both HO2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low- and high-NOx OH oxidation of ?-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O3 concentrations to ensure that OH was the main oxidant and low ?-pinene concentrations such that the peroxy radical (RO2) reacted primarily with either HO2 under low-NOx conditions or NO under high-NOx conditions. SOA yield was suppressed under conditions of high-NOx. SOA yield under high-NOx conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NOx conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NOx products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of ?-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NOx conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.

Eddingsaas, N. C.; Loza, C. L.; Yee, L. D.; Chan, M.; Schilling, K. A.; Chhabra, P. S.; Seinfeld, J. H.; Wennberg, P. O.

2012-08-01

344

?-pinene photooxidation under controlled chemical conditions - Part 2: SOA yield and composition in low- and high-NOx environments  

NASA Astrophysics Data System (ADS)

The gas-phase oxidation of ?-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with ?-pinene have been found in field samples and some are used as tracers of ?-pinene oxidation. ?-pinene reacts readily with OH and O3 in the atmosphere followed by reactions with both HO2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low- and high-NOx OH oxidation of ?-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O3 concentrations to ensure that OH was the main oxidant and low ?-pinene concentrations such that the peroxy radical (RO2) reacted primarily with either HO2 under low-NOx conditions or NO under high-NOx conditions. SOA yield was suppressed under conditions of high-NO. SOA yield under high-NO conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NOx conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NOx products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of ?-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NOx conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.

Eddingsaas, N. C.; Loza, C. L.; Yee, L. D.; Chan, M.; Schilling, K. A.; Chhabra, P. S.; Seinfeld, J. H.; Wennberg, P. O.

2012-04-01

345

Chemical and isotopic kinetics of sulfate reduction by organic matter under hydrothermal conditions  

Microsoft Academic Search

This study investigated the feasibility of nonbacterial sulfate reduction by organic matter in geologic environments. Sulfate is reduced by dextrose under acidic conditions at temperatures of 230-270 C. Reaction products include sulfide and organic-sulfur compounds; sulfite, thiosulfate and elemental sulfur were not detected. The rate law for the initial one- or two-electron reduction of sulfate at 250C is first-order in

1988-01-01

346

Identification of chemically modified peptide from poly(D,L-lactide-co-glycolide) microspheres under in vitro release conditions  

Microsoft Academic Search

The purpose of this research was to study the chemical reactivity of a somatostatin analogue octreotide acetate, formulated\\u000a in microspheres with polymers of varying molecular weight and co-monomer ratio under in vitro testing conditions. Poly(D,L-lactide-co-glycolide)\\u000a (PLGA) and poly(D,L-lactide) (PLA) microspheres were prepared by a solvent extraction\\/evaporation method. The microspheres\\u000a were characterized for drug load, impurity content, and particle size. Further,

Santos B. Murty; Jack Goodman; B. C. Thanoo; Patrick P. DeLuca

2003-01-01

347

Development and Analysis of a High-Pressure Micro Jet Pad Conditioning System for Interlayer Dielectric Chemical Mechanical Planarization  

NASA Astrophysics Data System (ADS)

Conventional diamond disc pad conditioning methods employed in chemical mechanical planarization (CMP) have presented several problems for integrated circuit (IC) manufacturers. These include diamond wear, which reduces pad life, and diamond fracture, which causes the semiconductor devices to be scratched by loose diamond fragments. In order to attempt to overcome these problems, a high-pressure micro jet (HPMJ) conditioning system, in which pressurized ultra pure water (UPW) ranging from 3-30 MPa is sprayed on the pad surface, is proposed and developed. This study first analyzes the extent of the kinetic energy of water droplets ejecting from the HPMJ system and its utility in conditioning the pad surface. Subsequently, CMP is used to polish interlayer dielectric (ILD) films using both conventional diamond discs as well as HPMJ conditioning methods. Results, reported in the form of coefficient of friction (COF), removal rate, pad surface roughness and pad surface quality, highlight both the advantages as well as disadvantages of the HPMJ method compared to conventional conditioning schemes.

Seike, Yoshiyuki; DeNardis, Darren; Sugiyama, Masano; Miyachi, Keiji; Doi, Toshiro; Philipossian, Ara

2005-03-01

348

Physico-chemical conditions for plankton in Lake Timsah, a saline lake on the Suez Canal  

NASA Astrophysics Data System (ADS)

Lake Timsah receives high salinity water from the Suez Canal, mainly from the south, and freshwater from a Nile canal and other sources, producing a salinity stratification with surface salinities of 20-40‰ and over 40‰ in deeper water. Water temperature at a depth of 50-70 cm fell to below 20 °C in winter and rose to above 30 °C in summer; oxygen concentration at the same depth ranged between 6-10 mg l -1 and the pH was 8·1-8·3, and at mid-day this water was supersaturated with oxygen through 6-8 months of the year. The main chemical nutrients reached their highest levels in winter (December-February) and their lowest levels in summer (May-August), silicate varying between 1-7 ? M, phosphate between 0·1 and 0·8 ? M and nitrate between 4-10 ? M; nitrite varied in a more complex manner, usually between 0·25 and 0·4 ? M. The atomic ratio of N/P was generally well above the Redfield ratio level, except for a few months in midwinter. These nutrient concentrations are high in comparison with those of unpolluted seas of the region, but are typical of the more eutrophic coastal waters in most parts of the world.

El-Serehy, H. A. H.; Sleigh, M. A.

1992-02-01

349

Strength change and chemical reactivity of ceramic breeder materials near operation conditions  

NASA Astrophysics Data System (ADS)

Measurements of mechanical strength achieved on pellet samples of various ceramic breeder materials which had been irradiated in the COMPLIMENT experiment (1.8 dpa, 0.4-1.4% lithium burnup, 400-450°C and 650-700°C) indicated a general strength reduction. The Young's modulus decreased to 70-80%, and the compressive strength down to about 30% of the initial values. Concerning the fracture strength, increasing irradiation sensitivity was indicated in the order: LiAlO 2, Li 2ZrO 3 ? Li 2SiO 3, Li 4SiO 4. The largest irradiation effect seems to be due to coarse microstructure damage and could be advanced by the tritium production. The cladding attack observed in the sealed breeder rod samples was compared with the amount expected from tritium water production and, on the other hand, with that in annealing tests at 1 Pa H 2O. Such tests were found to be conservative. Major chemical attack of the steel cladding seemed to be connected with an unusual content of oxidizing impurities in the breeder material.

Dienst, W.; Zimmermann, H.

1994-09-01

350

NonAqueous Battery Systems  

Microsoft Academic Search

Lithium and sodium are light and highly electronegative elements which form the basis of anodes for high-energy-density battery systems. Their high chemical reactivity requires the use of ionic conductors based on non-aqueous solvents, polymers, solid electrolytes or fused salts. An associated range of cathode materials enables cells to be fabricated with open-circuit voltages from 1.5 to 4.0 V. Practical non-aqueous

Colin A. Vincent

1996-01-01

351

Low-thrust chemical propulsion system propellant expulsion and thermal conditioning study  

NASA Technical Reports Server (NTRS)

Thermal conditioning systems for satisfying engine net positive suction pressure (NPSP) requirements, and propellant expulsion systems for achieving propellant dump during a return-to-launch site (RTLS) abort were studied for LH2/LO2 and LCH4/LO2 upper stage propellant combinations. A state-of-the-art thermal conditioning system employing helium injection beneath the liquid surface shows the lowest weight penalty for LO2 and LCH4. A technology system incorporating a thermal subcooler (heat exchanger) for engine NPSP results in the lowest weight penalty for the LH2 tank. A preliminary design of two state-of-the-art and two new technology systems indicates a weight penalty difference too small to warrant development of a LH2 thermal subcooler. Analysis results showed that the LH2/LO2 propellant expulsion system is optimized for maximum dump line diameters, whereas the LCH4/LO2 system is optimized for minimum dump line diameter (LCH4) and maximum dump line diameter (LO2). The primary uncertainty is the accurate determination of two-phase flow rates through the dump system; experimentation is not recommended because this uncertainty is not considered significant.

Merino, F.; Wakabayashi, I.; Pleasant, R. L.; Hill, M.

1982-01-01

352

Comparison among air pollutants, meteorological conditions and some chemical parameters in the transplanted lichen Usnea amblyoclada.  

PubMed

The response of Usnea amblyoclada (Müll. Arg.) Zahlbr. to real concentrations of atmospheric pollutants measured by two automatic monitoring stations, was studied in Córdoba City, Argentina. The influence of different weather conditions on the biomonitor's response was also assessed. The concentration of chlorophyll a, chlorophyll b, hydroperoxy-conjugated dienes, and malondialdehyde were quantified in lichen thalli collected from a clean area and in transplanted thalli after 1 month of exposure in an urban area, from April to October, 1996. The dry weight/fresh weight, chlorophyll b/chlorophyll a and phaeophytin a/chlorophyll a ratios were also calculated. Data sets were evaluated by two-way analysis of variance and correlation analysis. It was observed that hydroperoxy-conjugated dienes, malondialdehyde, chlorophylls, and pigment degradation increase during winter-time, when higher levels of suspended particles, non-methane hydrocarbons, hydrogen sulfide and ozone were also measured. These findings would be connected mainly with meteorological conditions, as most pollutants did not exceed prescribed threshold levels. PMID:11202714

Carreras, H A; Pignata, M L

2001-01-01

353

Direct density measurements under mantle and core conditions and chemical characterization of high-PT samples (Invited)  

NASA Astrophysics Data System (ADS)

We simulate the physical conditions of Earth’s interior in multi-anvil apparatus and diamond-anvil cell (DAC) that can routinely generate pressure(P)-temperature(T) conditions corresponding to the top of the lower mantle and the outer core, respectively. The challenges have been to obtain precious measurements of physical properties of mantle and core material under well-controlled simultaneous high P-T conditions and to obtain chemical information of the recovered high P-T diamond-anvil cell samples. We have developed a range of complementary high-PT devices to optimize sample environment and P-T stability. They include large-volume multi-anvil apparatus, externally heated DAC, internal-heating DAC, laser-heating DAC, combination of internal- and laser-heating DAC, and combination of externally heated and laser-heating DAC. The externally heated and laser-heating DACs are complementary in P-T range and heating stability, whereas the combination of externally heated and laser-heating DAC shows great promises to achieve stable simultaneous high P-T conditions. We have take the internal resistance heating of metallic sample in the diamond-anvil cell into a new level, generating stable heating up to 2100 K at 70 GPa with iron foil. Higher, stable temperatures were achieved by combination of internal- and laser-heating, a promise technique for studying conductive samples at high pressure and temperature. The combination of improved high-PT technique and advancement in synchrotron X-ray diffraction has significantly expanded our capability to investigate the physical properties of the Earth’s mantle and core. We have determined the densities of (Al,Fe)-bearing mantle perovskite and (Mg,Fe)O solid solutions, with high precision, up to 135 GPa and 2700 K, covering the entire lower mantle P-T conditions. I will also show density measurements of iron alloys at simultaneous high P-T, using internal- and laser-heating DACs and combination of internal- and laser-heating. Stable temperature generation in the DAC is a key to obtaining reproducible, reliable chemical information of the laser-heated samples. Use of micro- and nano-analytical tools such as FIB and FE-SEM to recover and analyze recovered DAC samples will be demonstrated. The complete characterization of chemical and physical properties of the mantle and core materials at high pressure and temperature will further advance our understanding of the Earth’s interior.

Fei, Y.

2009-12-01

354

In situ investigation of wet chemical processes for chalcopyrite solar cells by L-edge XAS under ambient conditions  

NASA Astrophysics Data System (ADS)

Two instrumental setups for in situ soft X-ray absorption spectroscopy in liquid systems are demonstrated in this work. One for investigating chemical reactions in solutions and a new one for the solid component of a liquid / (as in both / absorber) solid interface. We used these setups for investigating two production processes for chalcopyrite solar cells under ambient conditions, probing the L-edge of Zn and Cu. The first one is a flow cell with a silicon nitride membrane to study the chemical bath deposition process for Cd-free buffer layers. Examining the electronic structure of involved Zn complexes allows to determine the exact reaction mechanism taking place during this process. The second setup is a rotating disk for investigating the bath/absorber interface upon the etching process of superficial binary copper compounds of the absorber as a function of time. The time resolution of the chemical reaction demonstrated in this study ranges from the second to minute time scale.

Greil, Stefanie M.; Lauermann, Iver; Ennaoui, Ahmed; Kropp, Timo; Lange, Kathrin M.; Weber, Matthieu; Aziz, Emad F.

2010-02-01

355

Design and characterization of chemically modified electrodes with iron(III) porphyrinic-based polymers: study of their reactivity toward nitrites and nitric oxide in aqueous solution  

Microsoft Academic Search

This study gives new examples of iron porphyrin film electrodes prepared either by electrochemical polymerization or by incorporation in pre-electropolymerized pyrrole derivatives. It shows also the different kinds of interactions between nitric oxide, nitrites and the supported iron porphyrins in acidic and neutral aqueous solutions. It gives clear indications, by cyclic voltammetry and UV-visible spectrophotometry of the formation of the

Fethi Bedioui; Stéphane Trevin; Valérie Albin; Maria Guadalupe; Gomez Villegas; Jacques Devynck

1997-01-01

356

A review of catalytic issues and process conditions for renewable hydrogen and alkanes by aqueous-phase reforming of oxygenated hydrocarbons over supported metal catalysts  

Microsoft Academic Search

We have recently developed a single-step, low-temperature process for the catalytic production of fuels, such as hydrogen and\\/or alkanes, from renewable biomass-derived oxygenated hydrocarbons. This paper reviews our work in the development of this aqueous-phase reforming (APR) process to produce hydrogen or alkanes in high yields. First, the thermodynamic and kinetic considerations that form the basis of the process are

R. R. Davda; J. W. Shabaker; G. W. Huber; R. D. Cortright; J. A. Dumesic

2005-01-01

357

Resistance of Acanthamoeba castellanii cysts to physical, chemical, and radiological conditions.  

PubMed

Resistance of Acanthamoeba castellanii cysts to disinfection agents, antimicrobial agents, heat, freeze-thawing, ultraviolet radiation (UV), gamma irradiation, and cellulase were evaluated in vitro. Following exposure to different agents, the cysts were removed and cultured for A. castellanii trophozoites for 3-14 days. Solutions containing 20% isopropyl alcohol or 10% formalin effectively killed A. castellanii cysts. Hydrogen peroxide (3%, AOSept Disinfectant) effectively killed A. castellanii cysts after 4 hr of exposure. Polyhexamethylene biguanide (0.02%), clotrimazole (0.1%), or propamidine isethionate (Brolene) were effective in killing A. castellanii cysts in vitro. Acanthamoeba castellanii cysts were resistant to both 250 K rads of gamma irradiation and 800 mJ/cm2 of UV irradiation. Excystment of trophozoites was accelerated after exposure to 10, 100, and, 1,000 units of cellulase. These results suggest that A. castellanii cysts benefit by enhanced survival because of their resistance to very harsh environmental conditions. PMID:12099437

Aksozek, A; McClellan, K; Howard, K; Niederkorn, J Y; Alizadeh, H

2002-06-01

358

CHEMICAL CHARACTERISATION OF BHUIAVALI (Phyllanthus niruri).  

PubMed

The present article describes the chemical characteristics such as pH of aqueous extract, fluorescence, aqueous and alcoholic extractives, lignans and TLC profile of aqueous extract of Bhuiavli (Phyllanthus niruri). PMID:22556737

Phadnis, A D

1995-10-01

359

Investigations of chemical fraction of Co and Ni in industrial fly ash and mobility of metals in environmental conditions.  

PubMed

The quantitative evaluation of chemical fraction of Co and Ni in the industrial fly ash by methods of five step sequential extraction was carried out in order to characterize metal mobility in environmental conditions. The research involved (i) water-soluble (pH=7), (ii) acid-soluble (pH=5), (iii) oxide, (iv) sulfide and (v) residue metal fractions. It was discovered, that the total extraction of the studied metals from fly ash to solutions take place in the following quantities Co - 35.5 and Ni - 153.0mgkg(-1). The investigations of chemical fractions proved that the subject metals occur mainly in fly ash as: oxide (Co - 7.0, Ni - 28.5mgkg(-1)) and residue (Co - 11.5, Ni - 42.5mgkg(-1)) as well as sulfide (Co - 8.5, Ni - 46.5mgkg(-1)). Low concentrations of metals for water-soluble fraction (Co - 0.7, Ni - 1.2mgkg(-1)) and acid-soluble fraction (Co - 4.5, Ni - 23.5mgkg(-1)) were observed. The fractions of Co and Ni leachable from the ash in environmental conditions contain: 24.0% (Co) and 23.3% (Ni) of metal total amount in the industrial fly ash. The obtained mobility parameter of Co and Ni can be applied to estimate the concentration increase of mobile and hardly mobile forms of these metals in soil polluted with the ash. PMID:17150241

Soco, Eleonora; Kalembkiewicz, Jan

2007-02-01

360

Impact of operating conditions on the removal of endocrine disrupting chemicals by membrane photocatalytic reactor.  

PubMed

This study focuses on the performance of a submerged membrane photocatalytic reactor for the removal of 17beta-oestradiol (E2) in the presence of humic acid (HA). In addition to the impact of operating parameters, such as membrane pore size, ultraviolet (UV) intensity and hydraulic retention time (HRT), the influence of long-term operation was also assessed by advanced characterization of the fouling layer formed on the membrane. The tighter (0.04 microm) hollow fibre polyvinylydene fluoride (PVDF) membrane was found to exhibit not only higher HA removal than the (0.2 microm) module (85% and 75%, respectively), but also greater transmembrane pressure (TMP) values and higher irreversible fouling. Long-term operation conditions have been simulated by conducting an ageing catalyst process and demonstrated a decrease in performance obtained with time. The artificially aged TiO2 resulted in higher TMP values and lower HA removals (about 10-20% decrease) compared with the non-aged catalyst. For E2 removal in the presence of HA, the passive adsorption of the oestrogen onto the organic matter was found to be significant (40% of the E2 adsorbed after I h), demonstrating the importance of the nature of the water matrix for this type of treatment process. An increase in the UV light intensity was observed to favour the E2 elimination, leading to more than 90% removal when using 64 W combined with PVDF membrane and an HRT of 3 h. PMID:24956801

López Fernández, Raquel; Coleman, Heather M; Le-Clech, Pierre

2014-08-01

361

Chemical and structural modifications of laser treated WTi surfaces at different ambient conditions  

NASA Astrophysics Data System (ADS)

In this work we have studied the influence of laser modification on the composition and structure of tungsten titanium (WTi) thin films, deposited on n-type (100) silicon wafers. After deposition, the samples were multi-pulse laser irradiated in a nitrogen, oxygen, and helium ambient. The composition of the WTi/Si sample was determined by Elastic Recoil Detection Analysis (ERDA). Surface morphology was monitored by Atomic Force Microscopy (AFM). In the experiment, typical laser output parameters were: wavelength 1064 nm, pulse duration 150 ps, and laser pulse energy 30 mJ. Surface concentrations of W and Ti, as well as the concentration of gas components nitrogen and oxygen were determinated before and after the action of laser radiation in different ambient conditions. The contents of W and Ti decreased after irradiation due to adsorbed gases from the surrounding atmosphere. After surface irradiation in the inert ambient (He), the concentrations of the components were not significantly changed. In other cases, oxygen was the dominant component at the surface, probably due to the high affinity of thin film components. Also, the morphological changes occurred at the surface of WTi, as an increase in the surface roughness and formation of the granular structures are a result of laser-induced surface oxidation and recrystallization.

Petrovi?, S.; Peruško, D.; Milovanovi?, D.; Siketi?, Z.; Jakši?, M.; Kova?, J.; Gakovi?, B.; Milosavljevi?, M.; Trtica, M.

2011-11-01

362

Detection of chemical signatures from TNT buried in sand at various ambient conditions: phase II  

NASA Astrophysics Data System (ADS)

New analytical methods have been developed and existing methods have been improved for the detection of explosives and their degradation products by increasing their sensitivity and selectivity. Some of the analytical methods available for detection of explosives and degradation products are gas chromatography, mass spectrometry, high performance liquid chromatography, and gas chromatography with mass spectrometry. This work presents the design and development of the experiments for the detection of the spectroscopic signature of TNT buried in sand and its degradation products. These experiments are conducted using a series of soil tanks with controlled environmental conditions such as: temperature, soil moisture content, relative humidity and radiation (UV and VIS). Gas chromatography and solid-liquid extraction with acetonitrile were used for the analysis of explosives. Sampling of tanks was performed in three points on the surface. The results show that TNT and 2,4-DNT are the main explosives that reach the surface of tanks. Temperature and water content play a most important role in the degradation and diffusion of TNT. Finally, the tanks were disassembled and sampling in deep with the objective to obtain a concentration profile. The results demonstrated that the highest concentration was located at 5 cm from surface.

Báez, Bibiana; Florián, Vivian; Hernández-Rivera, Samuel P.; Cabanzo, Andrea; Correa, Sandra; Irrazabal, Maik; Briano, Julio G.; Castro, Miguel E.

2006-06-01

363

Potentiation of high hydrostatic pressure inactivation of Mycobacterium by combination with physical and chemical conditions.  

PubMed

Mycobacterium abscessus is an important hospital-acquired pathogen involved in infections associated with medical, surgical, and biopharmaceutical materials. In this work, we investigated the pressure-induced inactivation of two strains [2544 and American Type Culture Collection (ATCC) 19977] of M. abscessus in combination with different temperatures and pH conditions. For strain 2544, exposure to 250 MPa for 90 min did not significantly inactivate the bacteria at 20 °C, whereas at -15 °C, there was complete inactivation. Exposure to 250 MPa at ?60 °C caused rapid inactivation, with no viable bacteria after 45 min. With 45 min of exposure, there were no viable bacteria at any temperature when a higher pressure (350 MPa) was used. Extremes of pH (4 or 9) also markedly enhanced the pressure-induced inactivation of bacteria at 250 MPa, with complete inactivation after 45 min. In comparison, exposure of this strain to the disinfecting agent glutaraldehyde (0.5 %) resulted in total inactivation within 5 min. Strain 19977 was more sensitive to high pressure but less sensitive to glutaraldehyde than strain 2544. These results indicate that high hydrostatic pressure in combination with other physical parameters may be useful in reducing the mycobacterial contamination of medical materials and pharmaceuticals that are sensitive to autoclaving. PMID:23836348

de Souza, Ancelmo Rabelo; da Costa Demonte, Ana Luísa Silva Sampaio Moreira; de Araujo Costa, Karina; Faria, Mariana Alcantara Cardoso; Durães-Carvalho, Ricardo; Lancellotti, Marcelo; Bonafe, Carlos Francisco Sampaio

2013-08-01

364

EMERGING TECHNOLOGY BULLETIN: REMOVAL OF PHENOL FROM AQUEOUS SOLUTIONS USING HIGH ENERGY ELECTRON BEAM IRRADIATION  

EPA Science Inventory

Irradiation of aqueous solutions with high-energy electrons results in the formation of the aqueous electron, hydrogen radical, H-, and the hydroxyl radical, OH-. These reactive transient species initiate chemical reactions capable of destroying organic compounds in aqueous solut...

365

Effects of Atmospheric Conditions and the Land/Atmospheric Interface on Transport of Chemical Vapors from Subsurface Sources  

NASA Astrophysics Data System (ADS)

Understanding the movement of chemical vapors and gas through variably saturated soil subjected to atmospheric thermal and mass flux boundary conditions at the land/atmospheric interface is important to many applications, including landmine detection, methane leakage during natural gas production from shale and CO2 leakage from deep geologic storage. New, advanced technologies exist to sense chemical signatures and gas leakage at the land/atmosphere interface, but interpretation of sensor signals remains a challenge. Chemical vapors are subject to numerous interactions while migrating through the soil environment, masking source conditions. The process governing movement of gases through porous media is often assumed to be Fickian diffusion through the air phase with minimal quantification of other processes, such as convective gas flow and temporal or spatial variation in soil moisture. Vapor migration is affected by atmospheric conditions (e.g. humidity, temperature, wind velocity), soil thermal and hydraulic properties and contaminant properties, all of which are physically and thermodynamically coupled. The complex coupling of two drastically different flow regimes in the subsurface and atmosphere is commonly ignored in modeling efforts, or simplifying assumptions are made to treat the systems as de-coupled. Experimental data under controlled laboratory settings are lacking to refine the theory for proper coupling and complex treatment of vapor migration through porous media in conversation with atmospheric flow and climate variations. Improving fundamental understanding and accurate quantification of these processes is not feasible in field settings due to lack of controlled initial and boundary conditions and inability to fully characterize the subsurface at all relevant scales. The goal of this work is to understand the influence of changes in atmospheric conditions to transport of vapors through variably saturated soil. We have developed a tank apparatus with a network of soil and atmospheric sensors and a head space for air flow to simulate the atmospheric boundary layer. Experiments were performed under varying temperature values at the soil surface bounded by the atmospheric boundary layer. The model of Smits et al. [2011], accounting for non-equilibrium phase change and coupled heat, water vapor and liquid water flux through soil, was amended to include organic vapor in the gas phase and migration mechanisms often overlooked in models (thermal and Knudsen diffusion, density driven advection). Experimental results show increased vapor mass flux across the soil/atmospheric interface due to heat applied from the atmosphere and coupling of heat and mass transfer in the shallow subsurface for both steady and diurnal temperature patterns. Comparison of model results to experimental data shows dynamic interactions between transport in porous media and boundary conditions. Results demonstrate the value of considering interactions of the atmosphere and subsurface to better understand chemical gas transport through unsaturated soils and the land/atmospheric interface.

Rice, A. K.; Smits, K. M.; Cihan, A.; Howington, S. E.; Illangasekare, T. H.

2013-12-01

366

Development of a reduced aqueous phase chemistry mechanism  

NASA Astrophysics Data System (ADS)

Recent model studies have implicated the necessity of more complex aqueous phase processes to be considered in future higher scale chemistry transport models (CTMs). Important chemical cloud effects are mainly not yet considered or less represented in currently available regional scale CTMs. To this end, a mechanism reduction of the detailed aqueous phase chemistry mechanism CAPRAM 3.0i (Chemical Aqueous Phase RAdical Mechanism, Herrmann et al. [2005]) with about 777 reactions have been performed to develop simplified mechanism with less than 250 processes. For the mechanism reduction manual methods including detailed process investigations and automatic techniques [see Mauersberger, 2005] were applied. Both investigations have been done in order to provide a less computationally intensive mechanism which is operational in higher scale CTMs and accurately represents the main chemical aqueous phase processes. The results of the manual reduction have been compared with the output of an automatic reduction. This comparison showed a quite good agreement. Based on the restrictions of both reduction methods, a final reduced mechanism was derived which describes the main characteristics of inorganic and organic aqueous phase processes occurring in tropospheric warm clouds. With less than 200 reactions, the reduced mechanism is nearly a factor of 4 smaller than the detailed CAPRAM 3.0i mechanism. Most of the chemical reduction potential has been realised in the organic chemistry with 393 unimportant reactions. Moreover, the number of aqueous phase species decreased from 380 in the full CAPRAM 3.0i mechanism to 130 in the final reduced version. Furthermore, 11 unimportant phase transfer processes and 36 insignificant chemical equilibriums have been identified according to their minor relevance for the preselected reduction key species. The calculated percentage deviations between the full and reduced mechanism are mostly below 5% for the most important target compounds. Additionally, numerical sensitivity tests have been performed focusing on the relevance of both the relative and absolute integration error tolerances for an accurate and efficient modelling. The sensitivity studies have shown that cloud formation and particularly evaporation periods are circa three times more computationally intensive than in cloud conditions. This indicates the requirement for sufficiently accurate tolerance levels particularly there. Comparisons of the required CPU times between the full and final reduced mechanism showed reductions of approximately 40%. Prospectively, the final reduced aqueous phase mechanism represents the basis for studying chemical cloud effects on regional scale with future CTMs and will be important for a better understanding of the multiphase aerosol cloud processing effects on regional scale as well as the interpretation of field data.

Tilgner, A.; Deguillaume, L.; Wolke, R.; Herrmann, H.

2009-04-01

367

Aqueous chemical growth of free standing vertical ZnO nanoprisms, nanorods and nanodiskettes with improved texture co-efficient and tunable size uniformity  

NASA Astrophysics Data System (ADS)

Tuning the morphology, size and aspect ratio of free standing ZnO nanostructured arrays by a simple hydrothermal method is reported. Pre-coated ZnO seed layers of two different thicknesses (?350 nm or 550 nm) were used as substrates to grow ZnO nanostructures for the study. Various parameters such as chemical ambience, pH of the solution, strength of the Zn2+ atoms and thickness of seed bed are varied to analyze their effects on the resultant ZnO nanostructures. Vertically oriented hexagonal nanorods, multi-angular nanorods, hexagonal diskette and popcorn-like nanostructures are obtained by altering the experimental parameters. All the produced nanostructures were analysed by X-ray powder diffraction analysis and found to be grown in the (002) orientation of wurtzite ZnO. The texture co-efficient of ZnO layer was improved by combining a thick seed layer with higher cationic strength. Surface morphological studies reveal various nanostructures such as nanorods, diskettes and popcorn-like structures based on various preparation conditions. The optical property of the closest packed nanorods array was recorded by UV-VIS spectrometry, and the band gap value simulated from the results reflect the near characteristic band gap of ZnO. The surface roughness profile taken from the Atomic Force Microscopy reveals a roughness of less than 320 nm.

Ram, S. D. Gopal; Ravi, G.; Athimoolam, A.; Mahalingam, T.; Kulandainathan, M. Anbu

2011-12-01

368

RADIATION CHEMICAL AND PHOTOPHYSICAL PROPERTIES OF C60(C4H8SO3Na)n IN AQUEOUS SOLUTION: A LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS STUDY  

Microsoft Academic Search

Optical absorption studies on aqueous solutions of C60(C4H8SO3Na)n (n = 4–6) revealed deviation from the Beer-Lambert law in the 250–350 nm region, which is assigned to the formation of solute aggregates at concentrations higher than 1 × 10 mol dm. Dynamic light scattering experiments showed aggregates with an average size of ?100 nm. The solute has a broad weak fluorescence

Hari Mohan; D. K. Palit; L. Y. Chiang; J. P. Mittal

2001-01-01

369

Partitioning of trace elements between olivine and aqueous fluids at high P-T conditions: implications for the effect of fluid composition on trace-element transport  

NASA Astrophysics Data System (ADS)

In order to investigate the effect of fluid composition on trace-element transport at high pressure and temperature, olivine/fluid partition coefficients ( D) were measured in experiments involving aqueous carbonate-, chlorine- and NaOH- bearing fluids at 1.0 GPa and 1000°C. Radiotracers of Ce, Gd, Yb, Ba, Sr, Cs, and Na were used to monitor trace-element levels. D values were calculated by mass balance using the trace-element contents of acid-washed olivines from run-products combined with whole-sample abundances. A single reversal experiment in which pre-doped olivine was annealed in tracer-free water yielded results consistent with forward experiments involving olivine + H 2O. This result suggests crystal/fluid equilibrium was approached over the 5-day durations used for all experiments. Partition coefficients were found to vary with fluid chemistry and, with the exception of the D's for Na, olivine/fluid values are markedly lower than those determined for olivine/H 2O. Interelement ratios in the fluid also vary with fluid chemistry as exemplified by enhanced partitioning of Ce relative to Gd into Na, K or Cs carbonate-bearing compositions. Consideration of the trace-element exchange equilibria between olivine and fluid suggests that variation in the activity coefficient for aqueous trace-element and charge-balancing cations is likely to account for the interfluid variation in D values. Na partitioning is interpreted to be coupled to the formation of Na sbnd Al complexes as has been suggested in previous studies. These data indicate that, although trace elements do not partition strongly into H 2O coexisting with olivine, the addition of dissolved salts dramatically changes this result. Such variation in D values for different fluid chemistries suggests that fluid composition, in addition to residual mineralogy, may affect both absolute trace-element abundances and interelement fractionation in high P-T aqueous fluids.

Brenan, James M.; Bruce Watson, E.

1991-12-01

370

Protective effect of conditioning agents on Afro-ethnic hair chemically treated with thioglycolate-based straightening emulsion.  

PubMed

Straightening is a chemical process by which excessively curly hair is straightened in an irreversible way. Generally, products are formulated as emulsions with high pH value (9.0-12.0), which, after applied on hair, cause considerable damage, making it dry and fragile. This research work evaluated the protective effect of lauryl PEG/PPG-18/18 methicone, cyclopentasiloxane (and) PEG-12 dimethicone cross-polymer, jojoba oil, and aqua (and) cystine bis-PG propyl silanetriol, as conditioning agents, on Afro-ethnic hair locks treated with thioglycolate-based straightening emulsions by protein loss, combability, and traction to rupture. Standard Afro-ethnic hair locks were prepared following a protocol for straightening emulsion application. Considering the assays performed, the addition of conditioning agents to the straightening emulsion with ammonium thioglycolate benefited the hair fiber, thus diminishing protein loss, protecting the hair thread, and improving resistance to breakage. Jojoba oil and lauryl PEG/PPG-18/18 methicone were the conditioning agents that presented the best results. Straightening emulsions with ammonium thioglycolate containing aqua (and) cystine bis-PG propyl silanetriol and cyclopentasiloxane (and) PEG-12 dimethicone cross-polymer were the ones that provided higher breakage resistance of the thread. PMID:18482015

Dias, Tania Cristina de Sá; Baby, André Rolim; Kaneko, Telma Mary; Velasco, Maria Valéria Robles

2008-06-01

371

Experimental studies of a single-effect absorption refrigerator using aqueous lithium-bromide: Effect of operating condition to system performance  

SciTech Connect

This paper describes an experimental investigation of a single-effect absorption using aqueous lithium-bromide as working fluid. A 2 kW cooling capacity experimental refrigerator was tested with various operating temperatures. It was found that the solution circulation ratio (SCR) has a strong effect on the system performance. The measured SCR was 2-5 times greater than the theoretical prediction. This was due to the low performance of the absorber. The use of solution heat exchanger could increase the COP by up to 60%. (author)

Aphornratana, Satha [Sirindhorn International Institute of Technology, Thammasat University, P.O. Box 22, Thammasat Rangsit Post Office, Patumthani 12121 (Thailand); Sriveerakul, Thanarath [Department of Mechanical Engineering, Ubon Ratchathani University, Ubon Ratchathani 34190 (Thailand)

2007-11-15

372

Aqueous humor catecholamines.  

PubMed

The catecholamines norepinephrine, (NE) epinephrine (E) and dopamine (DA) were detected for the first time in the aqueous humor of humans under general anesthesia and monkeys under ketamine. The catecholamine levels in aqueous humor of 9 humans were assayed. NE was 0.796 +/- 0.457 ng./ml., E ranged between 0 and 0.132 ng./ml. in 4 out of 9 subjects, and DA was found in 2 of the 9 eyes. (0. 123ng ./ml. and 0. 318ng ./ml..) Plasma levels were measured in 8 of the human subjects at the time of aqueous sampling -NE was 0.311 +/- 0.171, E ranged between 0 and 0.097 (4 out of 8 subjects) and DA was detected in one subject- 0.037 ng./ml.. Monkey aqueous levels were NE:2.843 +/- 0.668 and DA:0.462 +/- 0.177 ng./ml., with an intact iris. (N = 8 eyes.) NE was 0.497 +/- 0.049, and DA 0.426 +/- 0.218 ng./ml. after total iridectomy. (N = 4 eyes) E was not detected in the monkey under these conditions. Whilst NE may be produced in part by the iris, DA levels were not affected by iridectomy. This implies that DA may be produced by structures unrelated to sympathetic nerve endings of the iris in the anterior segment of the non-human primate eye, perhaps by diffusion from the ciliary body or retina. Ketamine is known to inhibit catecholamine uptake, which may explain the high levels measured in the monkey. Human aqueous catecholamine levels measured under anesthesia may be affected by a variety of the drugs used. It is postulated that dopaminergic neurones and associated receptors may be present in the anterior segment of the eye. This may explain the presence of aqueous humor dopamine and the effects of dopaminergic drugs on intraocular pressure. PMID:6734261

Cooper, R L; Constable, I J; Davidson, L

1984-06-01

373

Bacterial peptide methionine sulphoxide reductase: co-induction with glutathione S-transferase during chemical stress conditions.  

PubMed Central

Peptide methionine sulphoxide reductase (MsrA; EC 1.8.4.6) is a ubiquitous enzyme catalysing the reduction of methionine sulphoxide to methionine in proteins, while the glutathione S-transferases (GSTs) are a major family of detoxification enzymes. A gene homologous to MsrA was identified in a chromosomal fragment from the bacterium Ochrobactrum anthropi, and this gene is located just downstream of a GST gene identified previously (OaGST) [Favaloro, Tamburro, Angelucci, De Luca, Melino, Di Ilio and Rotilio (1998) Biochem. J. 335, 573-579]. This raises the question of whether the products of these two genes may be involved in a common cellular protection function. To test this hypothesis, the hypothetical MsrA protein has been overexpressed in Escherichia coli as a functional 51 kDa GST fusion protein. Following cleavage with thrombin and purification, the soluble 24 kDa protein showed MsrA activity with N-acetylmethionine sulphoxide as substrate, as well as with other sulphoxide compounds. Therefore polyclonal antibodies were raised against the recombinant protein, and the modulation of MsrA in this bacterium, grown in the presence of different stimulants simulating several stress conditions, was investigated. The level of expression of MsrA was detected both by measuring the mRNA level and by immunoblotting experiments, in addition to measuring its catalytic activity. MsrA is a constitutive enzyme which is also inducible by chemical stress involving phenolic compounds such as phenol and 4-chlorophenol. Recently we reported that the GST of this bacterium, like MsrA, is only modulated by toxic chemical compounds [Favaloro, Tamburro, Trofino, Bologna, Rotilio and Heipieper (2000) Biochem. J. 346, 553-559]; therefore this is the first indication of a co-induction of the MsrA and GST enzymes during chemical stress.

Tamburro, A; Allocati, N; Masulli, M; Rotilio, D; Di Ilio, C; Favaloro, B

2001-01-01

374

In situ study of mass transfer in aqueous solutions under high pressures via Raman spectroscopy: a new method for the determination of diffusion coefficients of methane in water near hydrate formation conditions.  

PubMed

A new method was developed for in situ study of the diffusive transfer of methane in aqueous solution under high pressures near hydrate formation conditions within an optical capillary cell. Time-dependent Raman spectra of the solution at several different spots along the one-dimensional diffusion path were collected and thus the varying composition profile of the solution was monitored. Diffusion coefficients were estimated by the least squares method based on the variations in methane concentration data in space and time in the cell. The measured diffusion coefficients of methane in water at the liquid (L)-vapor (V) stable region and L-V metastable region are close to previously reported values determined at lower pressure and similar temperature. This in situ monitoring method was demonstrated to be suitable for the study of mass transfer in aqueous solution under high pressure and at various temperature conditions and will be applied to the study of nucleation and dissolution kinetics of methane hydrate in a hydrate-water system where the interaction of methane and water would be more complicated than that presented here for the L-V metastable condition. PMID:16542563

Lu, W J; Chou, I M; Burruss, R C; Yang, M Z

2006-02-01

375

Chemical and morphological characterization of Chardonnay and Gewürztraminer grapes and changes during chamber-drying under controlled conditions.  

PubMed

In this work, the morphological and chemical properties of Chardonnay and Gewürztraminer aromatic grapes (northern Spain) have been studied with the aim to assess their response to chamber-drying under controlled conditions and compare it with that of Pedro Ximenez grapes (southern Spain). Morphological characteristics, such as weight, size and roundness, and other of the skin such as thickness, enabled discrimination of the two types of grapes varieties. Changes in browning index, colour, antioxidant activity, aroma compounds determined by GC-MS and flavan-3-ols and flavonols concentrations determined by HPLC-DAD were studied during drying. Based on the results, Chardonnay and Gewürztraminer grapes contained increased amounts of flavan-3-ol derivatives, which are the greatest contributors to polymerization and condensation reactions. Also, their smaller size resulted in faster drying and leads to sugary musts that were lighter-coloured, less brown and more aromatic than Pedro Ximenez grapes. PMID:24767035

Serratosa, Maria P; Marquez, Ana; Moyano, Lourdes; Zea, Luis; Merida, Julieta

2014-09-15

376

Studies on the phytoplankton populations and physico-chemical conditions of treated sewage discharged into Lake Manzala in Egypt.  

PubMed

Over a full year, the phytoplankton populations and physico-chemical conditions of treated sewage discharged into Lake Manzala in Egypt were investigated. Sixty-seven species of algae were identified, 18 Cyanophyta (Cyanobacteria), 19 Chlorophyta, 21 Bacillariophyta, 6 Euglenophyta, 2 Cryptophyta and one species Pyrrhophyta. Nitzschia (6 spp.), Scenedesmus (6 spp.), Navicula (4 spp.), Oscillatoria (4 spp.) and Euglena (4 spp.) were the most common genera. A remarkable seasonal variation in species composition and standing crop of the phytoplankton populations was noted during the study. The total phytoplankton standing crop appeared to be mainly dependent on the growth of certain species viz., Oscillatoria chalybea, O. princepes, O. tenuis, Microcystis aeruginosa, Anabaena constricta (Cyanophyta), Nitzschia obtusa, Bacillaria paradoxa, Cocconeis placentula, Cyclotella meneghiniana (Bacillariophyta), Pandorina morum, Volvox sp. (Chlorophyta) and Phacus curvicauda (Euglenophyta). The continuous presence of Anabaena constricta and Nitzschia palea was recorded in the treated sewage. The least represented algal divisions were Pyrrhophyta and Cryptophyta, both in terms of quality and quantity. The data indicate that the secondary effluents were unstable in their chemical features and grossly polluted. Therefore, the treatment systems must treat the discharged sewage to a tertiary level before discharging into Lake Manzala. PMID:9579343

el-Naggar, M E; Shaaban-Dessouki, S A; Abdel-Hamid, M I; Aly, E M

1998-04-01

377

Identification of morphological and chemical markers of dry- and wet-season conditions in female Anopheles gambiae mosquitoes  

PubMed Central

Background Increased understanding of the dry-season survival mechanisms of Anopheles gambiae in semi-arid regions could benefit vector control efforts by identifying weak links in the transmission cycle of malaria. In this study, we examined the effect of photoperiod and relative humidity on morphologic and chemical traits known to control water loss in mosquitoes. Methods Anopheles gambiae body size (indexed by wing length), mesothoracic spiracle size, and cuticular hydrocarbon composition (both standardized by body size) were examined in mosquitoes raised from eggs exposed to short photoperiod and low relative humidity, simulating the dry season, or long photoperiod and high relative humidity, simulating the wet-season. Results Mosquitoes exposed to short photoperiod exhibited larger body size and larger mesothoracic spiracle length than mosquitoes exposed to long photoperiod. Mosquitoes exposed to short photoperiod and low relative humidity exhibited greater total cuticular hydrocarbon amount than mosquitoes exposed to long photoperiod and high relative humidity. In addition, total cuticular hydrocarbon amount increased with age and was higher in mated females. Mean n-alkane retention time (a measure of cuticular hydrocarbon chain length) was lower in mosquitoes exposed to short photoperiod and low relative humidity, and increased with age. Individual cuticular hydrocarbon peaks were examined, and several cuticular hydrocarbons were identified as potential biomarkers of dry- and wet-season conditions, age, and insemination status. Conclusions Results from this study indicate that morphological and chemical changes underlie aestivation of Anopheles gambiae and may serve as biomarkers of aestivation.

2014-01-01

378

Effects of cultivation conditions on the uptake of arsenite and arsenic chemical species accumulated by Pteris vittata in hydroponics.  

PubMed

The physiological responses of the arsenic-hyperaccumulator, Pteris vittata, such as arsenic uptake and chemical transformation in the fern, have been investigated. However, a few questions remain regarding arsenic treatment in hydroponics. Incubation conditions such as aeration, arsenic concentration, and incubation period might affect those responses of P. vittata in hydroponics. Arsenite uptake was low under anaerobic conditions, as previously reported. However, in an arsenite uptake experiment, phosphorous (P) starvation-dependent uptake of arsenate was observed under aerobic conditions. Time course-dependent analysis of arsenite oxidation showed that arsenite was gradually oxidized to arsenate during incubation. Arsenite oxidation was not observed in any of the control conditions, such as exposure to a nutrient solution or to culture medium only, or with the use of dried root; arsenite oxidation was only observed when live root was used. This result suggests that sufficient aeration allows the rhizosphere system to oxidize arsenite and enables the fern to efficiently take up arsenite as arsenate. X-ray absorption near edge structure (XANES) analyses showed that long-duration exposure to arsenic using a hydroponic system led to the accumulation of arsenate as the dominant species in the root tips, but not in the whole roots, partly because up-regulation of arsenate uptake by P starvation of the fern was caused and retained by long-time incubation. Analysis of concentration-dependent arsenate uptake by P. vittata showed that the uptake switched from a high-affinity transport system to a low-affinity system at high arsenate concentrations, which partially explains the increased arsenate abundance in the whole root. PMID:21185228

Hatayama, Masayoshi; Sato, Takahiko; Shinoda, Kozo; Inoue, Chihiro

2011-03-01

379

Photolysis of oxyfluorfen in aqueous methanol.  

PubMed

Photolysis of oxyfluorfen, an herbicide of the nitrodiphenyl ether class, was studied in aqueous methanol under UV and sunlight. UV irradiation was carried out in a borosilicate glass photoreactor (containing 250 ppm oxyfluorfen in 50% aqueous methanol) equipped with a quartz filter and 125 watt mercury lamp (maximum output 254 nm) at 25 ± 1°C. Sunlight irradiation was conducted at 28 ± 1°C in borosilicate Erlenmeyer flasks containing 250 ppm oxyfluorfen in 50% aqueous methanol. The samples from both the irradiated conditions were withdrawn at a definite time interval and extracted to measure oxyfluorfen content by gas chromatography-flame ionization detector for rate study. The half-life values were 20 hours and 2.7 days under UV and sunlight exposure, respectively. Photolysis of oxyfluorfen yielded 13 photoproducts of which three were characterized by infrared spectrophotometer and (1)H NMR and (13)C NMR spectroscopy. The rest of the photoproducts were identified by gas chromatography-mass spectrometry (GC-MS) and thin layer chromatography (TLC). An ionization potential 70 eV was used for electron impact-mass spectrometry (EI-MS) and methane was used as reagent gas for chemical ionization-mass spectrometry (CI-MS). Two of the photoproducts were also synthesized for comparison. The main phototransformation pathways of oxyfluorfen involved nitro reduction, dechlorination, and hydrolysis as well as nucleophiles displacement reaction. PMID:23998303

Chakraborty, Subhasish K; Chakraborty, Savitri; Bhattacharyya, Anjan; Chowdhury, Ashim

2013-01-01

380

Testing Insecticidal Activity of Novel Chemically Synthesized siRNA against Plutella xylostella under Laboratory and Field Conditions  

PubMed Central

Background Over the last 60 years, synthetic chemical pesticides have served as a main tactic in the field of crop protection, but their availability is now declining as a result of the development of insect resistance. Therefore, alternative pest management agents are needed. However, the demonstration of RNAi gene silencing in insects and its successful usage in disrupting the expression of vital genes opened a door to the development of a variety of novel, environmentally sound approaches for insect pest management. Methodology/Principal Findings Six small interfering RNAs (siRNAs) were chemically synthesized and modified according to the cDNA sequence of P. xylostella acetylcholine esterase genes AChE1 and AChE2. All of them were formulated and used in insecticide activity screening against P. xylostella. Bioassay data suggested that Si-ace1_003 and Si-ace2_001 at a concentration of 3 µg cm?2 displayed the best insecticidal activity with 73.7% and 89.0%, mortality, respectively. Additional bioassays were used to obtain the acute lethal concentrations of LC50 and LC90 for Si-ace2_001, which were 53.66 µg/ml and 759.71 µg/ml, respectively. Quantitative Real-time PCR was used to confirm silencing and detected that the transcript levels of P. xylostella AChE2 (PxAChE2) were reduced by 5.7-fold compared to the control group. Consequently, AChE activity was also reduced by 1.7-fold. Finally, effects of the siRNAs on treated plants of Brassica oleracea and Brassica alboglabra were investigated with different siRNA doses. Our results showed that Si-ace2_001 had no negative effects on plant morphology, color and growth of vein under our experimental conditions. Conclusions The most important finding of this study is the discovery that chemically synthesized and modified siRNA corresponding to P. xylostella AChE genes cause significant mortality of the insect both under laboratory and field conditions, which provides a novel strategy to control P. xylostella and to develop bio-pesticides based on the RNA interference technology.

Gong, Liang; Chen, Yong; Hu, Zhen; Hu, Meiying

2013-01-01

381

The Effect of Variety and Growing Conditions on the Chemical Composition and Nutritive Value of Wheat for Broilers  

PubMed Central

The aim of this study was to examine the effect of variety and growing conditions of wheat on broiler performance and nutrient digestibility. One hundred and sixty-four wheat samples, collected from a wide range of different sources, locations, varieties and years, were analyzed for a range of chemical and physical parameters. Chemical and physical parameters measured included specific weight, thousand grain weight (TG), in vitro viscosity, gross energy, N, NDF, starch, total and soluble non-starch polysaccharides (NSP), lysine, threonine, amylose, hardness, rate of starch digestion and protein profiles. Ninety-four of the wheat samples were selected for inclusion in four bird trials. Birds were housed in individual wire metabolizm cages from 7 to 28 d and offered water and feed ad libitum. Dry matter intake (DMI), live weight gain (LWG) and gain:feed were determined weekly. A balance collection was carried out from 14 to 21 d for determination of apparent metabolizable energy (AME), ME:gain, DM retention, oil and NDF digestibility. At 28 d the birds were sacrificed, the contents of the jejunum removed for determination of in vivo viscosity and the contents of the ileum removed for determination of ileal DM, starch and protein digestibility. The wheat samples used in the study had wide-ranging chemical and physical parameters, leading to bird DMI, LWG, gain:feed, ME:GE, AME content and ileal starch and protein digestibility being significantly (p<0.05) affected by wheat sample. A high level of N fertilizer application to the English and NI wheat samples tended to benefit bird performance, with increases of up to 3.4, 7.2 and 3.8% in DMI, LWG and gain:feed, respectively. Fungicide application also appeared to have a positive effect on bird performance, with fungicide treated (+F) wheat increasing bird DMI, LWG and gain:feed by 6.6, 9.3 and 2.7%, over the non-fungicide treated (-F) wheats. An increase (p<0.1) of 9.3% in gain:feed was also observed at the low seed rate of 40 compared to 640 seeds/m2. It was concluded that the type of wheat sample and environmental growing conditions significantly affects bird performance when fed wheat-based diets.

Ball, M. E. E.; Owens, B.; McCracken, K. J.

2013-01-01

382

Applicability of DLVO Approach to Predict Trends in Iron Oxide Colloid Mobility Under Various Physical And Chemical Soil Conditions  

NASA Astrophysics Data System (ADS)

In soil and groundwater, highly mobile iron oxide colloids can act as "shuttles" for transport of adsorbed contaminants such as heavy metals and radionuclides. Artificial iron oxide colloids are injected into polluted porous media to accelerate bacterial degradation of pollutants in the context of bioremediation purposes. The mobility of iron oxide colloids is strongly affected by the hydraulic, physical and chemical conditions of the pore space, the solid particle surface properties, the fluid phase, and the colloids themselves. Most pioneering studies focused on iron oxide colloid transport and retention in simplified model systems. The aim of this study is to investigate iron oxide colloid mobility under more complex, soil-typical conditions that have as yet only been applied for model microspheres, i.e. functionalized latex colloids. Among these conditions is the pivotal impact of organic matter, either dissolved or adsorbed onto solid particles, modifying wettability properties. Of particular importance was to determine if effective chemical surface parameters derived from contact angle and zeta potential measurements can be used as a tool to predict general tendencies for iron oxide colloid mobility in porous media. In column breakthrough experiments, goethite colloids (particle size: 200-900 nm) were percolated through quartz sand (grain size: 100-300 µm) at pH 5. The impact of a multitude of conditions on colloid mobility was determined: dissolved organic matter (DOM) concentration, ionic strength, flow velocity, flow interruption, partial saturation, and drying with subsequent re-wetting. The solid matrix consisted of either clean sand, organic matter-coated sand, goethite-coated sand, or sand hydrophobized with dichlorodimethylsilane. Additionally, contact angles and zeta potentials of the materials applied in the column experiments were measured. By means of these surface parameters, traditional DLVO interaction energies based on zeta potential as well as extended DLVO energies including Lewis acid-base parameters based on contact angle measurements were estimated. The results elucidate that high mobility of goethite colloids was distinctly restricted to a narrow set of conditions: presence of DOM, sufficient flow velocity and constant flow, low ionic strength, full saturation as well as an uncoated and hydrophilic quartz sand matrix. Any deviation from these favorable transport conditions led from varying degrees of colloid retention up to complete immobilization. Results yielded by both traditional and extended DLVO interaction energy calculations demonstrated that increasing secondary minimum depth correlated well with higher colloid retention. Extended DLVO calculations revealed strong repulsive forces due to Lewis acid-base interactions at close distances that did not comply with experimental data. It is likely that Lewis acid-base interactions were limited due to surface roughness of the sand grains and colloids. It can be concluded that the impact of various soil and hydraulic conditions on goethite colloid mobility is in principle assessable with column flow experiments. Moreover, with restrictions for the interpretation of close-distance interactions, DLVO interaction energies are capable of predicting general trends of goethite colloid mobility.

Florian Carstens, Jannis; Bachmann, Jörg; Neuweiler, Insa

2014-05-01

383

Nutation frequency modulation on NMR signal of nuclear spins in chemical exchange with solvent water under the BEST conditions.  

PubMed

Solvent exchange properties of protein backbone amide protons provide valuable residue-specific information on protein solvent accessibility, structure stability and flexibility and hence are of significant interest in structural biology. NMR has served as a unique means for the characterization of chemical exchange including proton amide exchange with solvent water at residue-specific levels across a broad range of exchange rates. One of the methods used for the characterization of protein backbone amide exchange by NMR involves the use of progressive selective irradiation of the water resonance. Here, we report the experimental observation of the nutation frequency (strength of RF field used for the irradiation of water resonance) modulation on amide proton signals for those in exchange with the solvent water under the band-selective excitation short transient (BEST) conditions. Compared with conventional saturation transfer of water magnetization experiments, this nutation frequency modulation observed on signal of nuclear spins under the BEST conditions potentially offers a quick identification of protein backbone amides in rapid exchange with solvent water. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24459096

Yao, Shenggen; Keizer, David W

2014-04-01

384

Phosphorylation of adenosine in aqueous solution by electric discharges.  

PubMed

Dehydration reactions involving condensing reagents in aqueous solution have been studied as models of chemical evolution, and one such reagent has been found to be produced in the supposed primitive Earth conditions. We assumed that the dehydration condensation in aqueous solution could occur if the condensing reagents, which appear to be produced by electric discharges in the gas phase, could be carried to the aqueous solution through the recycling of water washing the wall of the vessel. We present here an experimental study of the dehydration condensation between phosphate and adenosine in aqueous solution using a new discharge apparatus (Fig. 1) which simulates prebiotic chemical evolution. The apparatus was designed so that water recycles in a vessel containing a solution at a relatively low temperature (approximately 30 degrees C), achieved by showering water at 18 degrees C from above the vessel. This is a simulation of the recycling system of water on the Earth, depending on a large difference in temperature between the ocean surface and the sky. PMID:228198

Yamagata, Y; Matsukawa, T; Mohri, T; Inomata, K

1979-11-15

385

Is Vanadate Reduced by Thiols under Biological Conditions?: Changing The Redox Potential of V(V)/V(IV) by Complexation in Aqueous solution  

PubMed Central

Although dogma states that vanadate is readily reduced by glutathione, cysteine and other thiols, there are several examples documenting that vanadium(V)-sulfur complexes can form and be observed. This conundrum has impacted life scientists for more than two decades. Investigation of this problem requires an understanding of both the complexes that form from vanadium(IV) and (V) and a representative thiol in aqueous solution. The reactions of vanadate and hydrated vanadyl cation with 2-mercaptoethanol have been investigated using multinuclear NMR, EPR and UV-vis spectroscopy. Vanadate forms a stable complex of 2:2 stoichiometry with 2-mercaptoethanol at neutral and alkaline pH. In contrast, vanadate can oxidize 2-mercaptoethanol; this process is favored at low pH and high solute concentrations. The complex that forms between aqueous vanadium(IV) and 2-mercaptoethanol has a 1:2 stoichiometry and can be observed at high pH and high 2-mercaptoethanol concentration. The solution structures have been deduced and speciation diagrams prepared. This work demonstrates that both vanadium(IV) and (V)-thiol complexes form and that redox chemistry also takes place. Whether reduction of vanadate takes place is governed by a combination of parameters: pH, solute- and vanadate-concentrations and the presence of other complexing ligands. Based on these results it is now possible to understand the distribution of vanadium in oxidation states (IV) and (V) in the presence of glutathione, cysteine and other thiols and begin to evaluate the forms of the vanadium compounds that exert a particular biological effect including the insulin-enhancing agents, anti-amoebic agents and interactions with vanadium binding proteins.

Crans, Debbie C.; Zhang, Boyan; Gaidamauskas, Ernestas; Keramidas, Anastasios D.; Willsky, Gail R.; Roberts, Chris R.

2010-01-01

386

Chemical equilibria model of strontium-90 adsorption and transport in soil in response to dynamic alkaline conditions.  

PubMed

Strontium-90 is a major hazardous contaminant of radioactive wastewater and its processing sludges at many Department of Energy (DOE) facilities. In the past, such contaminated wastewater and sludge have been disposed in soil seepage pits, lagoons, or cribs often under highly perturbed alkaline conditions (pH > 12) where 90Sr solubility is low and its adsorption to surrounding soil is high. As natural weathering returns these soils to near-neutral or slightly acidic conditions, the adsorbed and precipitated calcium and magnesium phases, in which 90Sr is carried, change significantly in both nature and amounts. No comprehensive computational method has been formulated previously to quantitatively simulate the dynamics of 90Sr in the soil-groundwater environment under such dynamic and wide-ranging conditions. A computational code, the Hydrologic Utility Model for Demonstrating Integrated Nuclear Geochemical Environmental Responses (HUMDINGER), was composed to describe the changing equilibria of 90Sr in soil based on its causative chemical reactions including soil buffering, pH-dependent cation-exchange capacity, cation selectivity, and the precipitation/dissolution of calcium carbonate, calcium hydroxide, and magnesium hydroxide in response to leaching groundwater characteristics including pH, acid-neutralizing capacity, dissolved cations, and inorganic carbonate species. The code includes a simulation of one-dimensional transport of 90Sr through a soil column as a series of soil mixing cells where the equilibrium soluble output from one cell is applied to the next cell. Unamended soil leaching and highly alkaline soil treatments, including potassium hydroxide, sodium silicate, and sodium aluminate, were simulated and compared with experimental findings using large (10 kg) soil columns that were leached with 90Sr-contaminated groundwater after treatment. HUMDINGER's simulations were in good agreement with dynamic experimental observations of soil exchange capacity, exchangeable cations, total 90Sr, and pH values of layers within the soil columns and of column effluents. PMID:11347611

Spalding, B P; Spalding, I R

2001-01-15

387

A Study on the Aqueous Formation of Secondary Organic Aerosols  

NASA Astrophysics Data System (ADS)

The effect aerosols have on radiative forcing in the atmosphere is recognized as one of the largest uncertainties in the radiation budget. About 80% of organic aerosol mass in the atmosphere is estimated to be created though secondary processes. Recently, the aqueous formation of secondary organic aerosols (SOA) has become recognized as important when considering the source, transformation and radiative impacts of SOA. This work focuses on implementing a mechanism for aqueous SOA formation that can be used in atmospheric chemistry and models of all scales, from box to global. A box model containing a simplified chemical mechanism for the aqueous production of precursors of aqueous SOA (Myriokefalitakis et al. (2011) is coupled to gas-phase chemistry which uses the carbon bond mechanism (CBM) IV is presented. The model implements aqueous chemistry of soluble gases, both in-cloud and aerosol water, including organic compounds such as glyoxal and methylglyoxal, which have been shown as potentially significant sources for dissolved secondary organic aerosols. This mechanism implements aqueous phase mass transfer and molecular dissociation. The model's performance is evaluated against previous box model studies from the literature. A comparison is conducted between the detailed GAMMA model (McNeill et al., 2012), which is constrained with chamber experiments and the one developed here. The model output under different atmospheric conditions is explored and differences and sensitivities are assessed. The objective of this work is to create a robust framework for simulating aqueous phase formation of SOA and maximizing the computational efficiency of the model, while maintaining accuracy, in order to later use the exact mechanism in global climate simulations.

Sinclair, K.; Tsigaridis, K.

2013-12-01

388

Comparison and characterization of chemical surfactants and bio-surfactants intercalated with layered double hydroxides (LDHs) for removing naphthalene from contaminated aqueous solutions  

Microsoft Academic Search

Chemical surfactants or bio-surfactants intercalated into layered double hydroxides (LDHs) are considered as potential organic pollutant sorbents. This study evaluates the effects of (1) using either calcined or uncalcined LDH, and various solid\\/solution ratios, (2) the concentrations of the chemical surfactant sodium dodecyl sulfate (SDS) or the bio-surfactant rhamnolipid (RL), and (3) reaction temperatures and times on the synthesis of

Ya-Hui Chuang; Cheng-Hua Liu; Yu-Min Tzou; Jo-Shu Chang; Po-Neng Chiang; Ming-Kuang Wang

2010-01-01

389

Chemical and physical transitions of periodate oxidized potato starch in water  

Microsoft Academic Search

Physical and chemical transitions of dialdehyde starch in aqueous suspensions have been determined as a function of temperature and pH. The pH conditions were restricted to neutral or lower, since alkaline degradation is commonly recognized. Physical alterations were determined by measuring viscosity transitions at room temperature and upon heating. Chemical degradation was surveyed by controlling the amount of aldehydes, the

S. Veelaert; D. de Wit; K. F. Gotlieb; R. Verhé

1997-01-01

390

MODEL OF CHEMICAL REACTION EQUILIBRIUM OF SULFURIC ACID SALTS OF TRIOCTYLAMINE  

Microsoft Academic Search

The chemical reaction of trioctylamine (TOA) and sulfuric acid in organic solvent\\/aqueous solution was carried out. TOA salt products of various kinds were obtained based on different conditions of operation and organic solvents. An equilibrium model, based on the chemical reaction of sulfuric acid and trioctylamine, is proposed. The equilibrium constants of various reactions of trioctylamine and sulfuric acid were

MAW-LING WANG; KWAN-HUA HU

1993-01-01

391

Competitive Intramolecular/Intermolecular Chelation Options Operative during Indium-Promoted Additions to Pyridyl Aldehydes and to Glyoxylic Acid under Aqueous Conditions.  

PubMed

The stereochemical course of the 1,2-addition of six allylindium reagents to 2- and 3-pyridinecarboxaldehyde and to glyoxylic acid has been investigated in order to assess the level and direction of diastereoselectivity in these coupling reactions. When 2-PyCHO is involved, the results strongly suggest that the ring nitrogen becomes chelated to the indium atom in the aqueous environment. One striking observation is the crossover in stereoselectivity seen relative to the use of 3-PyCHO. A second revealing fact is the significantly faster rate of reaction of 2-PyCHO, as long as steric effects are not allowed to interfere. The varying product distributions observed in the latter experiments are attributed to other control elements such as intramolecular chelation within the indium reagent and nonbonded steric restrictions resident in either or both reaction partners. In the absence of extramolecular chelating events (e.g., when 3-PyCHO is involved), adherence to Felkin-Anh transition-state alignments is presumably exercised. The previous working assumption that indium(III) is capable of chelation to flanking heteroatomic centers in water is supported by the present investigation. PMID:11674106

Paquette, Leo A.; Rothhaar, Roger R.

1999-01-01

392

Short-term variability of the phytoplankton community in coastal ecosystem in response to physical and chemical conditions' changes  

NASA Astrophysics Data System (ADS)

The short-term dynamics (time scale of a few days) of phytoplankton communities in coastal ecosystems, particularly those of toxic species, are often neglected. Such phenomena can be important, especially since these very species can endanger the sustainability of shellfish farming. In this study, we investigated the short-term changes in phytoplankton community structure (species succession) in two coastal zones in parallel with physical and chemical conditions. Mixing events with allochtonous waters could thus be distinguished from local processes associated with population growth when it was associated with a change in light or nutrient limitation. Mixing events and water advection influenced fluctuations in total phytoplankton biomass and concentration of dominant species, while local processes influenced delayed changes in community structure. The estuarine species Asterionellopsis glacialis increased in concentration when the water mass mixed with the nearest estuarine water masses. The biological response, measured as photosynthetic capacity, occurred after a time-lag of a few hours, while the changes in community structure occurred after a time-lag of a few days. Finally, the coastal water mass was constantly mixed with both the nearest estuarine and marine water masses, leading in turn to delayed changes in phytoplankton community structure. These changes in species composition and dominance were observed on a time scale of a few days, which means that some toxic species may be missed with a bi-weekly sampling strategy.

Pannard, Alexandrine; Claquin, Pascal; Klein, Cécile; Le Roy, Bertrand; Véron, Benoît

2008-11-01

393

Chemical repair of base lesions, AP-sites, and strand breaks on plasmid DNA in dilute aqueous solution by ascorbic acid  

SciTech Connect

Highlights: •We report a novel mechanism of radiation protection of DNA by chemical activity of ascorbic acid. •The “chemical repair” of DNA damage was revealed using biochemical assay and chemical kinetics analysis. •We found that ascorbic acid significantly repairs precursors of nucleobase lesions and abasic sites. •However, ascorbic acid seldom repairs precursors of DNA-strand breaks. -- Abstract: We quantified the damage yields produced in plasmid DNA by ?-irradiation in the presence of low concentrations (10–100 ?M) of ascorbic acid, which is a major antioxidant in living systems, to clarify whether it chemically repairs radiation damage in DNA. The yield of DNA single strand breaks induced by irradiation was analyzed with agarose gel electrophoresis as conformational changes in closed circular plasmids. Base lesions and abasic sites were also observed as additional conformational changes by treating irradiated samples with glycosylase proteins. By comparing the suppression efficiencies to the induction of each DNA lesion, in addition to scavenging of the OH radicals derived from water radiolysis, it was found that ascorbic acid promotes the chemical repair of precursors of AP-sites and base lesions more effectively than those of single strand breaks. We estimated the efficiency of the chemical repair of each lesion using a kinetic model. Approximately 50–60% of base lesions and AP-sites were repaired by 10 ?M ascorbic acid, although strand breaks were largely unrepaired by ascorbic acid at low concentrations. The methods in this study will provide a route to understanding the mechanistic aspects of antioxidant activity in living systems.

Hata, Kuniki [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Urushibara, Ayumi; Yamashita, Shinichi; Shikazono, Naoya; Yokoya, Akinari [Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan)] [Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Katsumura, Yosuke, E-mail: katsu@n.t.u-tokyo.ac.jp [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1188 (Japan)

2013-05-03

394

Detection of component segregation in granules manufactured by high shear granulation with over-granulation conditions using near-infrared chemical imaging.  

PubMed

The objective of this study was to evaluate the high shear granulation process using near-infrared (NIR) chemical imaging technique and to make the findings available for pharmaceutical development. We prepared granules and tablets made under appropriate- and over-granulation conditions with high shear granulation and observed these granules and tablets using NIR chemical imaging system. We found an interesting phenomenon: lactose agglomeration and segregation of ingredients occurred in experimental tablets when over-granulation conditions, including greater impeller rotation speeds and longer granulation times, were employed. Granules prepared using over-granulation conditions were larger and had progressed to the consolidation stage; segregation between ethenzamide and lactose occurred within larger granules. The segregation observed here is not detectable using conventional analytical technologies such as high pressure liquid chromatography (HPLC) because the content of the granules remained uniform despite the segregation. Therefore, granule visualization using NIR chemical imaging is an effective method for investigating and evaluating the granulation process. PMID:23247019

Koide, Tatsuo; Nagato, Takuya; Kanou, Yoshiyuki; Matsui, Kou; Natsuyama, Susumu; Kawanishi, Toru; Hiyama, Yukio

2013-01-30

395

Hematite Spherules in Basaltic Tephra Altered Under Aqueous, Acid-Sulfate Conditions on Mauna Kea Volcano, Hawaii: Possible Clues for the Occurrence of Hematite-Rich Spherules in the Burns Formation at Meridiani Planum, Mars  

NASA Technical Reports Server (NTRS)

Iron-rich spherules (>90% Fe2O3 from electron microprobe analyses) approx.10-100 microns in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe/Al ratio than the rim. Oxide totals less than 100% (93-99%) suggest structural H2O and/or /OH. The transmission Moessbauer spectrum of a spherule-rich separate is dominated by a hematite (alpha-Fe2O3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al(3+) for Fe(3+) substitution and structural H2O and/or /OH. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.

Morris, R. V.; Ming, D. W.; Graff, T. G.; Arvidson, R. E.; Bell, J. F., III; Squyres, S. W.; Mertzman, S. A.; Gruener, J. E.; Golden, D. C.; Robinson, G. A.

2005-01-01

396

Utilizing platforms for the observation of chemical transformations to surface-bound noble metal nanoparticles in environmentally relevant conditions  

NASA Astrophysics Data System (ADS)

Nanoparticles are increasingly incorporated into consumer products because of their unique, size-dependent properties. Although these properties are commercially appealing, data are lacking regarding the fate and reactivity of nanoparticles once incorporated into materials. This information gap prevents accurate assessment of hazards that these materials potentially present to consumers and the environment. To address this concern, new research is needed to investigate the reactivity and transformations of nanoparticles. This dissertation describes the use of an electron transparent characterization platform to observe nanoparticle transformations. Nanoparticles were tethered to the surface of an analysis platform, exposed to a variety of conditions, and evaluated for reactivity and response. The characterization of silver nanoparticles revealed the generation of new daughter nanoparticles on surfaces in ambient humid conditions. Our observations showed that the transport of material is highly dependent on relative humidity and that pH equilibria drives the deposition of new particles and degradation. We discovered, by applying these findings to macro-silver objects, that bulk silver generates new nanoparticles on surfaces. This illuminated the possibility of other, yet undiscovered, naturally occurring nanoparticles. In the second model system, 1.5 nm gold nanoparticles were tethered by a robust metal oxide bond from the terminal group of the stabilizing ligand. This strategy facilitated precise control over thiol ligand removal using a dilute ozone oxidation. Tracking particle oxidation over time allowed us to gain unprecedented control over core exposure, size maintenance, and surface tethering. This platform was also utilized as a proof-of-concept for direct observation of transformations in complex media. Ligand and core transformations were monitored in a variety of biologically relevant conditions using tethered nanoparticles. Morphological and chemical transformations were characterized and correlated to results from solution monitoring. The use of a platform based approach to evaluating the reactivity of nanoparticles in the environment holds promise for evaluations of nanoparticles and their transformation products. The demonstration of monitoring reactivity in systems equilibria, carefully controlled transformations, or complex media shows the versatility of this strategy. Only through the use of this analysis platform was the direct observation of nanoparticle transformations possible. This dissertation includes previously published, unpublished, and co-authored materials.

Glover, Richard David

397

Extraction of uranium and molybdenum from aqueous solutions: A survey of industrial materials for use in chemical barriers for uranium mill tailings remediation  

Microsoft Academic Search

Laboratory experiments were performed to simulate the interaction of contaminated pore fluids with a variety of industrial materials. The objective was to evaluate the materials for use in a chemical barrier under a repository containing uranium mill tailings. Pore water would pass through the barrier, but contaminants would remain fixed in the solid fraction. More than 99% of the dissolved

Stan J. Morrison; Robert R. Spangler

1992-01-01

398

Halogen production from aqueous tropospheric particles.  

PubMed

Box model studies have been performed to study the role of aqueous phase chemistry with regard to halogen activation for marine and urban clouds and the marine aerosol as well. Different chemical pathways leading to halogen activation in diluted cloud droplets and highly concentrated sea salt aerosol particles are investigated. The concentration of halides in cloud droplets is significantly smaller than in sea-salt particles, and hence different reaction sequences control the overall chemical conversions. In diluted droplets radical chemistry involving OH, NO(3), Cl/Cl(2)(-)/ClOH(-), and Br/Br(2)(-)/BrOH(-) gains in importance and pH independent pathways lead to the release of halogens from the particle phase whereas the chemistry in aerosol particles with high electrolyte concentrations is controlled by non-radical reactions at high ionic strengths and relatively low pH values. For the simulation of halogen activation in tropospheric clouds and aqueous aerosol particles in different environments a halogen module was developed including both gas and aqueous phase processes of halogen containing species. This module is coupled to a base mechanism consisting of RACM (Regional Atmospheric Chemistry Mechanism) and the Chemical Aqueous Phase Radical Mechanism CAPRAM 2.4 (MODAC-mechanism). Phase exchange is described by the resistance model by Chemistry of Multiphase Atmospheric Systems, NATO ASI Series, 1986. It can be shown that under cloud conditions the bromine atom is mainly produced by OH initiated reactions, i.e. its concentration maximum is reached at noon. In contrast, the concentration level of chlorine atoms is linked to NO(3) radical chemistry leading to a smaller amplitude between day and night time concentrations. The contribution of radical processes to halogen atom formation in the particle phase is evident, e.g. by halogen atoms which undergo direct phase transfer. Furthermore, the application of the multiphase model for initial concentrations for sea-salt aerosols shows that the particle phase can act as a main source of halogen containing molecules (Cl(2), BrCl, Br(2)) which are photolysed in the gas phase to yield halogen atoms (about 70% of all Cl sources and more than 99% for Br). PMID:12738274

Herrmann, H; Majdik, Z; Ervens, B; Weise, D

2003-07-01

399

Capillary electrophoresis with capacitively coupled contactless conductivity detection applied to the quantitation and to the determination of physical-chemical properties of peroxycarboxylates in aqueous medium.  

PubMed

CE with C?D (CE-C?D) was successfully applied to the investigation of performate, peracetate, and perpropionate in aqueous medium. Ionic mobilities, diffusion coefficients, and hydrodynamic radii were obtained for the first time for these species. CE-C?D was also used to estimate the pKa values of the peroxycarboxylic acids. Because the peroxycarboxylates (POCs) undergoes hydrolysis while migrating, a simple calibration curve cannot be used for quantitation. Thus, an indirect calibration approach was used. The new method was used to monitor the formation of peroxycarboxylic acids from hydrogen peroxide and the carboxylic acid as well as to the quantitation of peracetic acid in a commercial sample. The CE-C?D method compares favorably with the conventional titration method because of the possibility of speciation of the POC, the low sample consumption, and the low LOD (14, 8, and 24 ?mol/L for performate, peracetate, and perpropionate, respectively). Although POCs are structural isomers of monoalkyl carbonates, they have greater hydrodynamic radii, which suggests that the positions of the oxygen atoms in the molecules have a direct impact in the charge density and consequently on the hydration atmosphere. PMID:23595363

Vidal, Denis T R; do Lago, Claudimir L

2013-07-01

400

Polypyrrole (PPy) chemical synthesis with xylan in aqueous medium and production of highly conducting PPy\\/nanofibrillated cellulose films and coatings  

Microsoft Academic Search

Polypyrrole was chemically synthesised by using, for the first time, Birchwood xylan as additive, and ammonium peroxydisulfate\\u000a (APS) as oxidant. The impact of additive concentration, polymerisation time and reagents concentration on PPy conductivity\\u000a was studied. It was shown that, once fixed the pyrrole (Py)\\/APS and Py\\/xylan optimal ratios, the best conductivities (26 S\\/cm)\\u000a were obtained for short polymerisation times (30 min) and

Claudia Sasso; Nicolas Bruyant; Davide Beneventi; Jerôme Faure-Vincent; Elisa Zeno; Michel Petit-Conil; Didier Chaussy; Mohamed Naceur Belgacem