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1

Chemical Behavior of Iodine in Aqueous Solutions Up to 150C. I. An Experimental Study of Nonredox Conditions.  

National Technical Information Service (NTIS)

The chemical behavior of iodine, I2, in (pH = 6 to 10) aqueous solutions containing 2500 ppm boron as H3BO3 (0.231 M) was studied at temperatures up to 150C. Absorption spectrophotometry was used to identify and monitor the iodine species present. Three o...

K. D. Pannell L. M. Toth O. L. Kirkland

1984-01-01

2

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

3

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

PubMed

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. PMID:12458737

Weber, Arthur L

2002-08-01

4

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...

5

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

6

Chemical Reactions in Non-Aqueous Media and Molten Salts.  

National Technical Information Service (NTIS)

The symposium on Chemical Reactions in Non-aqueous Media and Molten Salts was held at the Osmania University in Hyderabad, India. Forty papers were presented of which four papers were on non-aqueous chemistry in nuclear technology, nine papers on molten s...

M. V. Ramaniah D. D. Sood V. Venugopal

1978-01-01

7

Physical-chemical conditions of ore deposition  

USGS Publications Warehouse

Ore deposits form under a wide range of physical and chemical conditions, but those precipitating from hot, aqueous fluids-i.e. the hydrothermal deposits-form generally below 700??C and at pressures of only 1 or 2 kbar or less. Natural aqueous fluids in rocks may extract metal and sulfur from a variety of rock types or may acquire them as a residual heritage from a crystallizing silicate magma. Ore-forming hydrothermal fluids never appear as hot springs (except in deep, submarine situations) because they boil, mix with surface waters, and cool, thereby losing their ore-bearing ability before reaching the surface. Mineral systems function as chemical buffers and indicators just as buffers and indicators function in a chemical laboratory. By reading the record written in the buffer/indicator assemblages of minerals one can reconstruct many aspects of the former chemical environment. By studying the record of changing conditions one may deduce information regarding the processes functioning to create the succession of chemical environments and the ore deposits they represent. The example of the OH vein at Creede, Colorado, shows a pH buffered by the K-feldspar + muscovite + quartz assemblage and the covariation of S2 and O2 buffered by the assemblage chlorite + pyrite + quartz. Boiling of the ore fluid led to its oxidation to hematite-bearing assemblages and simultaneously produced an intensely altered, sericitic capping over the vein in response to the condensation of vapors bearing acidic components. The solubility of metals as calculated from experimental and theoretical studies of mineral solubility appears too low by at least one or two powers of ten to explain the mineralization at Creede. In contrast to Creede where the mineral stabilities all point to a relatively consistent chemistry, the Mississippi Valley type deposits present a puzzle of conflicting chemical clues that are impossible to reconcile with any single equilibrium situation. Thus we must seriously consider metastable equilibria; those most likely involve redox disequilibrium among the sulfur species in solution and perhaps also involve organic compounds. ?? 1981.

Barton, Jr. , P. B.

1981-01-01

8

Molecular simulation of aqueous electrolytes: Water chemical potential results and Gibbs-Duhem equation consistency tests  

NASA Astrophysics Data System (ADS)

This paper deals with molecular simulation of the chemical potentials in aqueous electrolyte solutions for the water solvent and its relationship to chemical potential simulation results for the electrolyte solute. We use the Gibbs-Duhem equation linking the concentration dependence of these quantities to test the thermodynamic consistency of separate calculations of each quantity. We consider aqueous NaCl solutions at ambient conditions, using the standard SPC/E force field for water and the Joung-Cheatham force field for the electrolyte. We calculate the water chemical potential using the osmotic ensemble Monte Carlo algorithm by varying the number of water molecules at a constant amount of solute. We demonstrate numerical consistency of these results in terms of the Gibbs-Duhem equation in conjunction with our previous calculations of the electrolyte chemical potential. We present the chemical potential vs molality curves for both solvent and solute in the form of appropriately chosen analytical equations fitted to the simulation data. As a byproduct, in the context of the force fields considered, we also obtain values for the Henry convention standard molar chemical potential for aqueous NaCl using molality as the concentration variable and for the chemical potential of pure SPC/E water. These values are in reasonable agreement with the experimental values.

Mou?ka, Filip; Nezbeda, Ivo; Smith, William R.

2013-09-01

9

Establishing and maintaining specific pathogen free (SPF) conditions in aqueous solutions using ozone  

NASA Astrophysics Data System (ADS)

The paper discusses the use of ozone in space applications for the elimination of pathogens, and the enhancement of the oxidation potential of ozone using hydrogen peroxide and ultraviolet radiation. These combinations will be possible to set up in space conditions. The sterilizing effect versus free radical generation is an important equilibrium to establish when specific pathogen free conditions are wanted in aqueous solutions containing organic matter. In situ sterilization of plant roots in hydroponic systems, as well as the oxidation of root exudates, will be discussed. The paper will contain examples of the chemical interaction of ozone with some of the other compounds found in hydroponic systems.

Vestergård, B.

1994-11-01

10

Catalytic conjugate additions of carbonyl anions under neutral aqueous conditions.  

PubMed

The conjugate addition of carbonyl anions catalyzed by thiazolium salts that is fully operative under neutral aqueous conditions has been accomplished. The combination of alpha-keto carboxylates and thiazolium-derived zwitterions produces reactive carbonyl anions in a buffered protic environment that readily undergo conjugate additions to substituted alpha,beta-unsaturated 2-acyl imidazoles. The scope of the reaction has been examined and found to accommodate various alpha-keto carboxylates and beta-aryl substituted unsaturated 2-acyl imidazoles. The optimal precatalyst for this process is the commercially available thiazolium salt 5, a simple analogue of thiamin diphosphate. In this process, no benzoin products from carbonyl anion dimerization are observed. The corresponding 1,4-dicarbonyl compounds can be efficiently converted into esters and amides by way of activation of the N-methylimidazole ring via alkylation. PMID:16231921

Myers, Michael C; Bharadwaj, Ashwin R; Milgram, Benjamin C; Scheidt, Karl A

2005-10-26

11

DERMAL ABSORPTION OF CHEMICALS: EFFECT OF APPLICATION OF CHEMICAL AS A SOLID, AQUEOUS PASTE, SUSPENSION OR IN VOLATILE VEHICLE  

EPA Science Inventory

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

12

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

2011-02-20

13

Pharmaceutical modulation of diffusion potentials at aqueous-aqueous boundaries under laminar flow conditions.  

PubMed

In this work, the modulation of the diffusion potential formed at the microfluidic aqueous-aqueous boundary by a pharmaceutical substance is presented. Co-flowing aqueous streams in a microchannel were used to form the stable boundary between the streams. Measurement of the open circuit potential between two silver/silver chloride electrodes enabled the diffusion potential at the boundary to be determined, which is concentration dependent. Experimental results for protonated propranolol as well as tetrapropylammonium are presented. This concept may be useful as a strategy for the detection of drug substances. PMID:21437916

Collins, Courtney J; Strutwolf, Jörg; Arrigan, Damien W M

2011-03-16

14

Uranyl Ion Uptake from Aqueous Solutions by Chemically Cross-linked Polyelectrolyte CAMA Hydrogels  

Microsoft Academic Search

Uranyl ion adsorption from aqueous solutions has been investigated by chemically cross-linked polyelectrolyte acrylamide\\/maleic acid (CAMA) hydrogels. CAMA hydrogels with various compositions were prepared from ternary mixtures of acrylamide (A), maleic acid (MA), and water by free radical polymerization in aqueous solution using multifunctional cross-linkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4-butanediol dimethacrylate (BDMA). Uranyl ion adsorption from aqueous

Ömer Bar?? Üzüm; Semiha Kundakci; Erdener Karada?

2007-01-01

15

Localized Chemical Redistribution During Aqueous Alteration in CR2 Carbonaceous Chondrites EET 87770 and EET 92105  

Microsoft Academic Search

Elemental exchange and chemical redistribution between chondrules and matrices is examined in CR2 carbonaceous chondrites EET 87770 and EET 92105. Results are used to place constraints on aqueous alteration reactions on meteorite parent bodies.

P. V. Burger; A. J. Brearley

2005-01-01

16

Title III section 313 release reporting guidance: Estimating chemical releases from formulation of aqueous solutions  

SciTech Connect

Formulators of aqueous solutions may be required to report annually any releases to the environment of certain chemicals regulated under Section 313, Title III, of the Superfund Amendments and Reauthorization Act (SARA) of 1986. The document has been developed to assist formulators of aqueous solutions, emulsions, and slurries in the completion of Part III (Chemical Specific Information) of the Toxic Chemical Release Inventory Reporting Form. Included herein is general information on toxic chemicals used and process wastes generated, along with several examples to demonstrate the types of data needed and various methodologies available for estimating releases.

Not Available

1988-03-01

17

Chemically designed inorganic polymer filters for aqueous mercury separation  

Microsoft Academic Search

The disposal of mercury [Hg] in dental waste water is recognized as a serious pollution control problem. Although technologies exist for effectively removing aqueous Hg ions from dental emissions, they are not commonly used because they are expensive, they can leach Hg back into the environment, they usually require the implementation of multiple separation techniques, and they have no potential

Jennifer A. Pierce; Kevin J. Thorne

1997-01-01

18

SORPTION AND TRANSPORT OF HYDROPHOBIC ORGANIC CHEMICALS IN AQUEOUS AND MIXED SOLVENT SYSTEMS: MODEL DEVELOPMENT AND PRELIMINARY EVALUATION  

EPA Science Inventory

A theoretical approach, based upon the assumption of predominance of solvophobic interactions, was formulated to quantitatively describe the sorption and transport of hydrophobic organic chemicals (HOC) from aqueous and aqueous-organic-solvent mixtures. In the theoretical approac...

19

Oxidation of cyanide in aqueous solution by chemical and photochemical process  

Microsoft Academic Search

Cyanide waste is found predominantly in industrial effluents generated from metallurgical operations. The toxicity of cyanide creates serious environmental problems. In this paper, oxidation of cyanide in aqueous solution was investigated using chemical and photochemical process. Chemical oxidation was studied at room temperature using H2O2 as oxidant and Cu2+ as catalyst. Photochemical oxidation was studied in an annular type batch

M. Sarla; M. Pandit; D. K. Tyagi; J. C. Kapoor

2004-01-01

20

Conditions of aqueous alteration of 9 CM chondrites estimated from mineralogy and compositional variations of matrix  

NASA Astrophysics Data System (ADS)

CM chondrites have undergone prevailed aqueous alteration in the parent asteroids and the alteration changed mineralogical and isotope signatures of water-bearing C-type asteroids.[1,2] In the previous studies, classification schemes of CM chondrites by the alteration degree were proposed by )[3,4] In the present study, we have performed a mineralogical study of 9 CM chondrites found in Antarctica in order to estimatie the nature and extents of aqueous alteration reactions. At first, small pieces (200 microns in size) of matrix were picked up and analyzed by synchroton radiation X-ray diffraction to identify minerals and relative abundances. The results of the X-ray diffraction analysis and SEM observations indicate that serpentine is present in the matrix of all samples as a major phase, suggesting that all samples have undergone aqueous alteration and have not been heated to temperature enough to dehydrate serpentine. Two out of 9 samples (LEW85311 and LAP03178 hereafter GroupA) contain Fe-Ni metal grains in both chondrule and matrix and anhydrous silicates (olivine and pyroxene) in matrix. Five of 9 samples (GRA06172, MET01072, LEW87022, LAP02269 and GRO95566 hereafter GroupB) contain fine-grained PCPs and anhydrous silicates but no metallic phases in matrix. In addition their chondrules are altered only in glassy parts and in limited parts of anhydrous silicates. The rest two of 9 samples (LAP031166 and MAC88100 hereafter GroupC) don't contain Fe-Ni metal and PCPs and contain little anhydrous silicates in matrix. In addition chondrules are almost completely altered. Since metallic phases are more susceptible to aqueous alteration than anhydrous silicates, the results suggest that the alteration degree is in the order of GroupA< GrouB< GroupC. The EPMA analysis indicates that most data of matrix composition fall within the triangle area defined by [1]: the area is enclosed by the composition of PCPs and two serpentines (the serpentin compositions are defined by those from Murry and Nogoya meteorites) in a Mg-Fe-Si ternary diagram. Nine samples have different compositional trends and PCP/(PCP+serpentine) ratios, suggesting that these 9 samples have suffered various extents of aqueous alteration. The matrix compositions reflect the conditions of aqueous alteration, because of its fine-grained nature. Therefore, it is expected that, for instance, GroupA samples show compositional trends similar within the Group, but different from other Groups. However, GroupA sample (LAP03178) has the same trend as GroupB sample (GRO95566), and GroupB sample (MET01072) has the same trend as GroupC sample (MAC88100).This suggests that aqueous alteration process is very complex: the starting matrix compositions are variable, and the resultant matrix compositions are also different. This indicates that matrix chemical composition alone is not enough to define the alteration degree. [1]McSween (1986), GCA 51, 2469-2477 [2]Clayton and Mayeda (1984) Earth and Planetary Science Letters 67, 151-161 [3]Zolensky et.al (1997) GCA 61, 5099-5115 [4]Rubin et al. (2007) GCA 71, 2361-2382

Yoshioka, K.; Nakamura, T.; Fujimaki, H.

2011-12-01

21

Chemical degradation of cyanides by Fenton's reagent in aqueous and soil-containing systems  

Microsoft Academic Search

A study was conducted on the effects of pH of the medium, composition of Fenton's reagent, and the effect of soil's preequilibration with the chemical, on the degradation of [sup 14]C-labeled free and complex cyanide in aqueous and soil-containing systems. The application of Fenton's reagent resulted in degradation of 80% and 67% of potassium cyanide in aqueous systems at pH

Boris N. Aronstein; Raheem A. Lawal; Andrea Maka

1994-01-01

22

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...

23

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

2010-06-23

24

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...

25

Mechanism of Tertiary Oil Recovery by Aqueous Chemical Flooding  

Microsoft Academic Search

The tertiary recovery of oil by chemical flooding is a complex process involving both micro and macroemulsions. Relying on fundamental considerations of theory, operation and economics it is suggested that in situ emulsification of the immobile residual oil (and mobile secondary oil) in the petroleum reservoir and its transport as such to the producing well is feasible and has many

Krishna Kamath; Anthony Zammerilli; Joseph Comberiati; Billy Taylor; Franklin Slagle

1982-01-01

26

Chemical mechanical modification of nanodiamond in an aqueous system  

Microsoft Academic Search

The effect of chemical-mechanical modification (CMM) on the ? potential and size distribution of nanodiamonds was studied.\\u000a Results show a significant change in the functional groups on its surface after CMM treatment by the anionic surface modifier\\u000a DN-10. The amount of hydroxyl groups decreases, and two peaks connected with the stretching vibration of carboxylate appear\\u000a instead of those of carbonyl.

Y. W. Zhu; X. Q. Shen; B. C. Wang; X. Y. Xu; Z. J. Feng

2004-01-01

27

A Review on Chemical Effects in Aqueous Solution induced by Plasma with Glow Discharge  

NASA Astrophysics Data System (ADS)

Chemical effects in different aqueous solutions induced by plasma with glow discharge electrolysis (GDE) and contact glow discharge electrolysis (CGDE) are described in this paper. The experimental and discharge characteristics are also reviewed. These are followed by a discussion of their mechanisms of both anodic and cathodic CGDE..

Gao, Jin-zhang; Wang, Xiao-yan; Hu, Zhong-ai; Hou, Jing-guo; Lu, Quan-fang

2001-06-01

28

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

29

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

30

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...

31

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

32

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

33

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

34

Chemical degradation of cyanides by Fenton's reagent in aqueous and soil-containing systems  

SciTech Connect

A study was conducted on the effects of pH of the medium, composition of Fenton's reagent, and the effect of soil's preequilibration with the chemical, on the degradation of [sup 14]C-labeled free and complex cyanide in aqueous and soil-containing systems. The application of Fenton's reagent resulted in degradation of 80% and 67% of potassium cyanide in aqueous systems at pH 7.2 and 10.0, respectively. No appreciable amount of K[sub 4][Fe(CN)[sub 6

Aronstein, B.N. (Inst. of Gas Technology, Des Plaines, IL (United States)); Lawal, R.A. (System Sensor, St. Charles, IL (United States)); Maka, A. (Metropolitan Water Reclamation District of Greater Chicago, Cicero, IL (United States))

1994-11-01

35

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

36

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

37

Pre-formulation and chemical stability studies of penethamate, a benzylpenicillin ester prodrug, in aqueous vehicles.  

PubMed

Penethamate (PNT) is a diethylaminoethyl ester prodrug of benzylpenicillin used to treat bovine mastitis via the intramuscular route. Because of its instability, PNT products must be reconstituted before administration and the reconstituted injection has a short shelf life (7 days at 2-8°C). The purpose of this paper was to investigate whether the stability of PNT can be improved in order to achieve a chemically stable ready-to-use aqueous-based PNT formulation or at least to extend the shelf life of the reconstituted suspension. A chemical stability study of PNT in aqueous-based solutions as a function of pH, buffer strength, solvent mixtures and temperature, supported by studies of its solubility in mixed solvents, allowed predictions of the shelf life of PNT solution and suspension formulations. PNT degraded in aqueous solutions by several pathways over the pH range 2.0-9.3 with a V-shaped pH-rate profile and a minimum pH of around 4.5. The stability of PNT solutions in mixed solvents was greater than in aqueous solutions. For example, in propylene glycol:citrate buffer (60:40, v/v, pH 4.5), the half-life of PNT was 4.3 days compared with 1.8 days in aqueous buffer. However, solubility of PNT in the mixed solvent was higher than that in aqueous solution and this had an adverse effect on the stability of suspensions. By judicious choosing of pH and mixed solvent, it is possible to achieve a storage life of a PNT suspension of 5.5 months at 5°C, not sufficient for a ready-to-use product but a dramatic improvement in the storage life of the reconstituted product. PMID:21696334

Jain, Rohit; Wu, Zimei; Bork, Olaf; Tucker, Ian G

2011-06-23

38

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

39

Highly Efficient Dye Removal from Aqueous Solutions Using Simple Chemical Modification of Wood Sawdust  

Microsoft Academic Search

This study examined the efficiency of oxidized wood meal for removal of methylene blue (MB) as a typical basic dye from aqueous waste streams. The adsorption process was performed using sawdust treated with KMnO4, K2Cr2O7, and H2O2 oxidants. Among the tested chemical oxidants, KMnO4 was found to be more effective for modification of sawdust for dye uptake. Based on the

Reza Ansari; Mahnaz Saghanejhad Tehrani; Ali Mohammad-Khah

2012-01-01

40

Removal of methylene blue from aqueous solutions by adsorption onto chemically activated halloysite nanotubes  

Microsoft Academic Search

This study examines the adsorption behavior of methylene blue (MB) from aqueous solutions onto chemically activated halloysite\\u000a nanotubes. Adsorption of MB depends greatly on the adsorbent dose, pH, initial concentration, temperature and contact time.\\u000a The Langmuir and Freundlich models were applied to describe the equilibrium isotherms and the Langmuir model agrees very well\\u000a with experimental data. The maximum adsorption capacities

Peng Luo; Bing Zhang; Yafei Zhao; Jinhua Wang; Haoqin Zhang; Jindun Liu

2011-01-01

41

Adsorption behavior of reactive dye in aqueous solution on chemical cross-linked chitosan beads  

Microsoft Academic Search

A batch system was applied to study the adsorption of reactive dye (reactive red 189) from aqueous solutions by cross-linked chitosan beads. The ionic cross-linking reagent sodium tripolyphosphate was used to obtain more rigid chitosan beads. To stabilize chitosan in acid solutions, chemical cross-linking reagent epichlorohydrin (ECH), glutaraldehyde and ethylene glycol diglycidyl ether was used and ECH shows a higher

M. S Chiou; H. Y Li

2003-01-01

42

Chemical and Physical Characteristics of Pulsed Electrical Discharge Within Gas Bubbles in Aqueous Solutions  

Microsoft Academic Search

The chemical and physical characteristics of pulsed electrical discharge within gas bubbles immersed in an aqueous solution\\u000a were investigated using a reactor with long protrusion length high voltage needle electrodes. Argon gas was introduced at\\u000a the base of the needle electrode causing gas bubbles to flow upwards in contact with the needle. The effects of needle protrusion\\u000a length were evaluated

Kai-Yuan Shih; Bruce R. Locke

2010-01-01

43

Removal of Acid Dyes from Aqueous Solutions using Chemically Activated Carbon  

Microsoft Academic Search

Textile dyes (Acid Yellow 17 and Acid Orange 7) were removed from its aqueous solution in batch and continuous packed bed adsorption systems by using thermally activated Euphorbia macroclada carbon with respect to contact time, initial dye concentration, and temperature. The activated carbon was prepared using a cheap plant-based material called Euphorbia macroclada, which was chemically modified with K2CO3. Lagergren-first-order

Özgül Gerçel; H. Ferdi Gerçel

2009-01-01

44

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

45

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

46

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

47

KEMOD: A mixed chemical kinetic and equilibrium model of aqueous and solid phase geochemical reactions  

SciTech Connect

This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength.

Yeh, G.T.; Iskra, G.A. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil Engineering; Szecsody, J.E.; Zachara, J.M.; Streile, G.P. [Pacific Northwest Lab., Richland, WA (United States)

1995-01-01

48

Adsorption behavior of aqueous europium on kaolinite under various disposal conditions  

Microsoft Academic Search

This work investigated the adsorption behavior of europium on kaolinite under various disposal conditions. Batch-wise adsorption\\u000a and precipitation experiments and equilibrium model calculations were performed over a pH range of 4–10 and CO2 concentration range of 0%, 0.03%, and 10%. Experimental precipitation behaviors are in agreement with the results of equilibrium\\u000a model calculations using the geochemical code MINTEQA2. Aqueous species

Mun Ja Kang; Pil Soo Hahn

2004-01-01

49

An efficient and recyclable water-soluble cyclopalladated complex for aqueous Suzuki reactions under aerial conditions  

Microsoft Academic Search

Several water-soluble cyclopalladated complexes with five- or six-membered rings have been prepared as air-stable solids from Schiff base ligands bearing an N-phenyl sulfonate groups. Cyclopalladated complexes with six-membered rings show high catalytic efficiency for the Suzuki reactions of aryl bromides with phenylboronic acid in aqueous solvents under mild conditions. Palladium complex 1 can be used for five reaction cycles in

Jin Zhou; Xiaoyan Li; Hongjian Sun

2010-01-01

50

Zero-Valent Iron Removal Rates of Aqueous Cr(VI) Measured Under Flow Conditions  

Microsoft Academic Search

The rates of Cr(VI) removal from the aqueous phase by zero-valent iron, Fe(0), was measured under flow conditions. The intent\\u000a of this work was to generate removal rate coefficients that would be applicable to the Reactive Well Technology, a groundwater\\u000a remediation technology that replaces the sand in a filter pack of a conventional well with a reactive material, such as

Daniel I. Kaplan; Tyler J. Gilmore

2004-01-01

51

Removal Rates of Aqueous Cr(VI) by Zero-Valent Iron Measured Under Flow Conditions  

Microsoft Academic Search

Studies were undertaken to measure the rate of Cr(VI) removal from the aqueous phase by zero-valent iron, Fe(0), under flow conditions. The intent of this work was to generate removal rate coefficients that would be applicable to the Reactive Well Technology, a groundwater remediation technology that replaces the sand in a filter pack of a conventional well with a reactive

2002-01-01

52

Aspects of glycosidic bond formation in aqueous solution: chemical bonding and the role of water.  

PubMed

A model of the specific acid-catalyzed glycosidic bond formation in liquid water at ambient conditions is studied based on constrained Car-Parrinello ab initio molecular dynamics. Specifically the reaction of alpha-D-glucopyranose and methanol is found to proceed by a D(N)A(N) mechanism. The D(N) step consists of a concerted protonation of the O(1) hydroxyl leaving group; this process results in the breaking of the C(1)-O(1) bond, and oxocarbenium ion formation involving C(1)=O(5). The second step, A(N), is the formation of the C(1)-O(m) glycosidic bond, deprotonation of the methanol hydroxyl group O(m)H(m), and re-formation of the C(1)-O(5) single bond. A focus of this study is the analysis of the electronic structure during this condensed phase reaction relying on both Boys/Wannier localized orbitals and the electron localization function ELF. This analysis allows the clear elucidation of the chemical bonding features of the intermediate bracketed by the D(N) and A(N) steps, which is a non-solvent equilibrated oxocarbenium cation. Most interestingly, it is found that the oxygen in the pyranose ring becomes "desolvated" upon double bond/oxocarbenium formation, whereas it is engaged in the hydrogen-bonded water network before and after this period. This demonstrates that hydrogen bonding and thus the aqueous solvent play an active role in this reaction implying that microsolvation studies in the gas phase, both theoretical and experimental, might lead to qualitatively different reaction mechanisms compared to solution. PMID:15729673

Stubbs, John M; Marx, Dominik

2005-04-22

53

Chemical recognition phase of the fluorescence chemical sensor for copper (II) ions in aqueous solution  

NASA Astrophysics Data System (ADS)

We review the principles of optical sensor based on the use of the sol-gel technique, in particular their fabrication. We also report on potential applications of the recognition phases prepared by encapsulation of fluorescent chemosensors which have been designed by means of a supramolecular approach: two anthryl groups linked to diaminodiethero group. Occurrence of the metal ion-receptor interaction is signaled through the enhancement of anthryl fluorescence. The enhancement takes place when the receptor is able to promote a photoinduced electron transfer mechanism. Cu(II) ions can be distinguished form other transition metal ions in aqueous solution by the recognition phase.

Klonkowski, Andrzej M.; Kledzik, K.; Ostaszewski, R.

2001-08-01

54

Lignin solubilization and aqueous phase reforming for the production of aromatic chemicals and hydrogen.  

PubMed

The solubilization and aqueous phase reforming of lignin, including kraft, soda, and alcell lignin along with sugarcane bagasse, at low temperatures (T?498?K) and pressures (P?29?bar) is reported for the first time for the production of aromatic chemicals and hydrogen. Analysis of lignin model compounds and the distribution of products obtained during the lignin aqueous phase reforming revealed that lignin was depolymerized through disruption of the abundant ?-O-4 linkages and, to a lesser extent, the 5-5' carbon-carbon linkages to form monomeric aromatic compounds. The alkyl chains contained on these monomeric compounds were readily reformed to produce hydrogen and simple aromatic platform chemicals, particularly guaiacol and syringol, with the distribution of each depending on the lignin source. The methoxy groups present on the aromatic rings were subject to hydrolysis to form methanol, which was also readily reformed to produce hydrogen and carbon dioxide. The composition of the isolated yields of monomeric aromatic compounds and overall lignin conversion based on these isolated yields varied from 10-15% depending on the lignin sample, with the balance consisting of gaseous products and residual solid material. Furthermore, we introduce the use of a high-pressure autoclave with optical windows and an autoclave with ATR-IR sentinel for on-line in?situ spectroscopic monitoring of biomass conversion processes, which provides direct insight into, for example, the solubilization process and aqueous phase reforming reaction of lignin. PMID:21246746

Zakzeski, Joseph; Weckhuysen, Bert M

2011-01-18

55

Chemical relaxation and equilibrium studies of association in aqueous solutions of bolaform detergents. Part 3  

SciTech Connect

Micelle formation in aqueous solutions of docasane-1,22-bis(trimethylammonium bromide) (C22ME6) has been investigated by means of conductivity, EMF (concentration cell and bromide ion and detergent ion specific electrodes), density, light scattering, fluorescence, and chemical relaxation (p-jump, t-jump, shock tube, ultrasonic absorption). The CMC, micelle ionization degree, micelle ionization degree, micelle aggregation number, and volume change upon micellization were calculated. The slope of the plot log CMC vs. number m of carbon atoms in the alkyl chain of bolaforms of the CMME6 type as well as several other results reveal that these bolaforms behave like detergents with 2 charged groups on the first carbon of the alkyl chain. The conclusion is that the bolaform alkyl chain may be somewhat folded both in aqueous solution and in the micellized state. 25 references.

Zana, R.; Yiv, S.; Kale, K.M.

1980-10-01

56

?-Chymotrypsin stability in aqueous-acetonitrile mixtures: is the native enzyme thermodynamically or kinetically stable under low water conditions?  

Microsoft Academic Search

Like many proteins, ?-chymotrypsin is denatured in 50% volume aqueous-acetonitrile mixtures. However, it also shows high catalytic activity in 70% or more acetonitrile. Good activity in two different aqueous organic composition ranges has been described for several other enzymes. The stability of the native protein under low water conditions is generally believed to be a kinetic phenomenon, though there are

Johann Partridge; Barry D Moore; Peter J Halling

1999-01-01

57

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

58

Adsorption of Pb(II) From Aqueous Solutions by Chemically Modified Zeolite Supported Carbon Nanotubes: Equilibrium, Kinetic and Thermodynamic Studies  

Microsoft Academic Search

Zeolite supported carbon nanotubes (ZCNTs) were synthesized by the catalytic chemical vapor deposition (CCVD) method. The physical and chemical properties such as surface area, pore diameter, surface functional groups and total acidic and basic sites of the ZCNTs were studied. They were employed as adsorbent to study the adsorption characteristics of Pb(II) in aqueous solution. The adsorption of Pb(II), increase

D. K. Venkata Ramana; D. Harikishore Kumar Reddy; B. Naresh Kumar; K. Seshaiah; G. Purna Chandra Rao; Chungsying Lu

2012-01-01

59

The chemistry of iomeprol and physico-chemical properties of its aqueous solutions and pharmaceutical formulations.  

PubMed

The synthesis and the chemical characterization of iomeprol, a new triiodinated nonionic radiographic contrast agent, are reported. The physico-chemical properties both of aqueous solutions of the pure compound and of its pharmaceutical formulations are presented and these last data are compared with those of other contrast media. The pharmaceutical development of the product is described. Iomeprol is obtained via a synthesis which is particularly friendly to the environment. The compound shows an unusually high solubility which allows the formulation of contrast media with the lowest osmolalities and viscosities as compared with corresponding contrast media of the same category. In view of these favourable characteristics and of the remarkably high stability of its solutions, iomeprol for injection is formulated also at 400 mgI/ml, the highest concentration so far available on the market for non-ionic contrast media. PMID:8020510

Gallotti, A; Uggeri, F; Favilla, A; Cabrini, M; de Haën, C

1994-05-01

60

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

2012-12-04

61

A general and facile one-pot process of isothiocyanates from amines under aqueous conditions  

PubMed Central

Summary A general and facile one-pot protocol for the preparation of a broad range of alkyl and aryl isothiocyanates has been developed from their corresponding primary amines under aqueous conditions. This synthetic process involves an in situ generation of a dithiocarbamate salt from the amine substrate by reacting with CS2 followed by elimination to form the isothiocyanate product with cyanuric acid as the desulfurylation reagent. The choice of solvent is of decisive importance for the successful formation of the dithiocarbamate salt particularly for highly electron-deficient substrates. This novel and economical method is suitable for scale-up activities.

Sun, Nan; Li, Bin; Shao, Jianping; Hu, Baoxiang; Shen, Zhenlu

2012-01-01

62

Synthesis of a Rotaxane Cu(I) Triazolide under Aqueous Conditions.  

PubMed

We describe the serendipitous isolation of a stable, neutral, monomeric mechanically interlocked Cu(I) triazolide under aqueous conditions. This "trapped" intermediate of the CuAAC catalytic cycle is sterically protected from reprotonation by the rotaxane architecture, which renders the Cu(I)-C bond stable toward moisture and air-even carboxylic acids protonate the Cu(I)-C bond only slowly. The isolation of this remarkably stable Cu(I) organometallic points toward potential applications of mechanical bonding in the study of reactive intermediates. PMID:23971866

Winn, Joby; Pinczewska, Aleksandra; Goldup, Stephen M

2013-08-28

63

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

64

Aqueous synthesis of CdTe/CdS/ZnS quantum dots and their optical and chemical properties.  

PubMed

In this paper, we described a strategy for synthesis of thiol-coated CdTe/CdS/ZnS (core-shell-shell) quantum dots (QDs) via aqueous synthesis approach. The synthesis conditions were systematically optimized, which included the size of CdTe core, the refluxing time and the number of monolayers and the ligands, and then the chemical and optical properties of the as-prepared products were investigated. We found that the mercaptopropionic acid (MPA)-coated CdTe/CdS/ZnS QDs presented highly photoluminescent quantum yields (PL QYs), good photostability and chemical stability, good salt tolerance and pH tolerance and favorable biocompatibility. The characterization of high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD) and fluorescence correlation spectroscopy (FCS) showed that the CdTe/CdS/ZnS QDs had good monodispersity and crystal structure. The fluorescence life time spectra demonstrated that CdTe/CdS/ZnS QDs had a longer lifetime in contrast to fluorescent dyes and CdTe QDs. Furthermore, the MPA-stabilized CdTe/CdS/ZnS QDs were applied for the imaging of cells. Compared with current synthesis methods, our synthesis approach was reproducible and simple, and the reaction conditions were mild. More importantly, our method was cost-effective, and was very suitable for large-scale synthesis of CdTe/CdS/ZnS QDs for future applications. PMID:20878652

Li, Zhong; Dong, Chaoqing; Tang, Lichuan; Zhu, Xin; Chen, Hongjin; Ren, Jicun

2010-09-27

65

Quantum chemical prediction of redox reactivity and degradation pathways for aqueous phase contaminants: an example with HMPA.  

PubMed

Models used to predict the fate of aqueous phase contaminants are often limited by their inability to address the widely varying redox conditions in natural and engineered systems. Here, we present a novel approach based on quantum chemical calculations that identifies the thermodynamic conditions necessary for redox-promoted degradation and predicts potential degradation pathways. Hexamethylphosphoramide (HMPA), a widely used solvent and potential groundwater contaminant, is used as a test case. Its oxidation is estimated to require at least iron-reducing conditions at low to neutral pH and nitrate-reducing conditions at high pH. Furthermore, the transformation of HMPA by permanganate is predicted to proceed through sequential N-demethylation. Experimental validation based on LC/TOF-MS analysis confirms the predicted pathways of HMPA oxidation by permanganate to phosphoramide via the formation of less methylated as well as singly and multiply oxygenated reaction intermediates. Pathways predicted to be thermodynamically or kinetically unfavorable are similarly absent in the experimental studies. Our newly developed methodology will enable scientists and engineers to estimate the favorability of contaminant degradation at a specific field site, suitable approaches to enhance degradation, and the persistence of a contaminant and its reaction intermediates. PMID:20608732

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

2010-08-01

66

Relative Contributions of Aqueous and Dietary Uptake of Hydrophobic Chemicals to the Body Burden in Juvenile Rainbow Trout  

Microsoft Academic Search

This study assessed the relative contributions of aqueous versus dietary uptake of three hydrophobic chemicals, 1,2,4-trichlorobenzene (1,2,4-TCB), 1,2,3,4,5-pentachloroben- zene (PeCB), and 2,29,4,49,6,69-hexachlorobiphenyl (HCBP). Juvenile rainbow trout (Oncorhynchus mykiss) were exposed separately to chemically spiked water and food for 4 days and 12 days, respectively. Chemical concentrations were measured in the food, water, and tissues, and this allowed calculation of uptake

P. Qiao; F. A. P. C. Gobas; A. P. Farrell

2000-01-01

67

Detailed investigation of the radical-induced destruction of chemical warfare agent simulants in aqueous solution.  

PubMed

The persistence of delivered chemical warfare agents (CWAs) in a variety of environmental matrices is of serious concern to both the military and civilian populations. Ultimately understanding all of the degradation pathways of the various CWAs in different environmental matrices is essential for determining whether native processes would offer sufficient decontamination of a particular material or if active chemical decontamination is required. Whereas much work on base-promoted chemical degradation has been reported, additional remediation strategies such as the use of advanced oxidation or reduction process free radical treatments may also be a viable option. We have examined here the primary kinetics and reaction mechanisms for an extensive library of chemical warfare agent simulants with the oxidizing hydroxyl radical and reducing hydrated electrons in water. From these values, it is seen that the reductive destruction occurs primarily through a single mechanism, consisting of hydrated electron capture at the phosphorus group with subsequent elimination, whereas hydroxyl radical oxidation shows two separate reaction mechanisms, dependent on the aqueous pK(a) of the leaving group. PMID:20469938

Abbott, Amberashley; Sierakowski, Tim; Kiddle, James J; Clark, Kristin K; Mezyk, Stephen P

2010-06-10

68

Sorted and aligned single-walled carbon nanotube networks for transistor-based aqueous chemical sensors.  

PubMed

Detecting trace amounts of analytes in aqueous systems is important for health diagnostics, environmental monitoring, and national security applications. Single-walled carbon nanotubes (SWNTs) are ideal components for both the sensor material and active signal transduction layer because of their excellent electronic properties and high aspect ratio consisting of entirely surface atoms. Submonolayer arrays, or networks of SWNTs (SWNTnts) are advantageous, and we show that topology characteristics of the SWNT network, such as alignment, degree of bundling, and chirality enrichment strongly affect the sensor performance. To enable this, thin-film transistor (TFT) sensors with SWNTnts were deposited using a one-step, low-cost, solution- based method on a polymer dielectric, allowing us to achieve stable low-voltage operation under aqueous conditions. These SWNT-TFTs were used to detect trace concentrations, down to 2 ppb, of dimethyl methylphosphonate (DMMP) and trinitrotoluene (TNT) in aqueous solutions. Along with reliable cycling underwater, the TFT sensors fabricated with aligned, sorted nanotube networks (enriched with semiconductor SWNTs) showed a higher sensitivity to analytes than those fabricated with random, unsorted networks with predominantly metallic charge transport. PMID:19856982

Roberts, Mark E; LeMieux, Melburne C; Bao, Zhenan

2009-10-27

69

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

1999-05-01

70

Prediction of aqueous solubility, vapor pressure and critical micelle concentration for aquatic partitioning of perfluorinated chemicals.  

PubMed

The majority of perfluorinated chemicals (PFCs) are of increasing risk to biota and environment due to their physicochemical stability, wide transport in the environment and difficulty in biodegradation. It is necessary to identify and prioritize these harmful PFCs and to characterize their physicochemical properties that govern the solubility, distribution and fate of these chemicals in an aquatic ecosystem. Therefore, available experimental data (10-35 compounds) of three important properties: aqueous solubility (AqS), vapor pressure (VP) and critical micelle concentration (CMC) on per- and polyfluorinated compounds were collected for quantitative structure-property relationship (QSPR) modeling. Simple and robust models based on theoretical molecular descriptors were developed and externally validated for predictivity. Model predictions on selected PFCs were compared with available experimental data and other published in silico predictions. The structural applicability domains (AD) of the models were verified on a bigger data set of 221 compounds. The predicted properties of the chemicals that are within the AD, are reliable, and they help to reduce the wide data gap that exists. Moreover, the predictions of AqS, VP, and CMC of most common PFCs were evaluated to understand the aquatic partitioning and to derive a relation with the available experimental data of bioconcentration factor (BCF). PMID:20958003

Bhhatarai, Barun; Gramatica, Paola

2010-10-19

71

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

72

Structure of a Novel Enzyme That Catalyzes Acyl Transfer to Alcohols in Aqueous Conditions  

SciTech Connect

The unusual architecture of the enzyme (MsAcT) isolated from Mycobacterium smegmatis forms the mechanistic basis for favoring alcoholysis over hydrolysis in water. Unlike hydrolases that perform alcoholysis only under anhydrous conditions, MsAcT demonstrates alcoholysis in substantially aqueous media and, in the presence of hydrogen peroxide, has a perhydrolysis:hydrolysis ratio 50-fold greater than that of the best lipase tested. The crystal structures of the apoenzyme and an inhibitor-bound form have been determined to 1.5 {angstrom} resolution. MsAcT is an octamer in the asymmetric unit and forms a tightly associated aggregate in solution. Relative to other structurally similar monomers, MsAcT contains several insertions that contribute to the oligomerization and greatly restrict the shape of the active site, thereby limiting its accessibility. These properties create an environment by which MsAcT can catalyze transesterification reactions in an aqueous medium and suggests how a serine hydrolase can be engineered to be an efficient acyltransferase.

Mathews, I.; Soltis, M.; Saldajeno, M.; Ganshaw, G.; Sala, R.; Weyler, W.; Cervin, M.A.; Whited, G.; Bott, R.

2009-06-03

73

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

74

Z-Scan Studies of the Nonlinear Optical Properties of Gold Aqueous Colloid Prepared by the Chemical Reaction Method  

Microsoft Academic Search

Nonlinear optical properties of gold aqueous colloid obtained with chemical reaction method are investigated using Z-scan technique with 38 ps pulses. Experimental results indicate that the colloid exhibits large nonlinear refraction and nonlinear absorption under the excitation of ps 532 nm pulses, while it presents large two photon absorption under ps 1064 nm pulses excitation. Meanwhile, the fluorescence emission spectrum

Ting-Jian Jia; Hong Cheng; Ting-Chao He; Yu-Ting Cui; Cui-Mei Liu

2011-01-01

75

Chemical transfection of cells in picoliter aqueous droplets in fluorocarbon oil.  

PubMed

The manipulation of cells inside water-in-oil droplets is essential for high-throughput screening of cell-based assays using droplet microfluidics. Cell transfection inside droplets is a critical step involved in functional genomics studies that examine in situ functions of genes using the droplet platform. Conventional water-in-hydrocarbon oil droplets are not compatible with chemical transfection due to its damage to cell viability and extraction of organic transfection reagents from the aqueous phase. In this work, we studied chemical transfection of cells encapsulated in picoliter droplets in fluorocarbon oil. The use of fluorocarbon oil permitted high cell viability and little loss of the transfection reagent into the oil phase. We varied the incubation time inside droplets, the DNA concentration, and the droplet size. After optimization, we were able to achieve similar transfection efficiency in droplets to that in the bulk solution. Interestingly, the transfection efficiency increased with smaller droplets, suggesting effects from either the microscale confinement or the surface-to-volume ratio. PMID:21967571

Chen, Fangyuan; Zhan, Yihong; Geng, Tao; Lian, Hongzhen; Xu, Peisheng; Lu, Chang

2011-10-17

76

Chemical Etching Using KOH Aqueous Solution for Corona-Charge Micropatterning of Soda-Lime Glass  

NASA Astrophysics Data System (ADS)

The selectivity of chemical etching for a soda-lime glass substrate to which a micropatterned electric field is applied by corona-charging treatment was investigated. A grating pattern with a period of 4 ?m was transferred in a soda-lime glass substrate via corona-charging treatment with a mask template. A diffraction efficiency of 0.02% was detected from the refractive index grating in a template-removed glass substrate. A surface relief grating with a period of 4 ?m was fabricated on the glass substrate by selective etching using KOH aqueous solution. The etching rate of the corona-charge-treated domain of the glass substrate was 1.6 times higher than that of normal glass. An enhancement of the etching rate of the glass substrate by the corona-charging treatment occurred up to a depth of approximately 200 nm from the surface. After the surface structural change from the refractive index grating, diffraction efficiency increased to 1.64%, which was 80 times higher than that before chemical etching.

Sakai, Daisuke; Harada, Kenji; Barada, Daisuke; Fukuda, Takashi

2013-03-01

77

Permanent physico-chemical properties of extremely diluted aqueous solutions of homeopathic medicines.  

PubMed

The purpose of this study was to obtain information about the influence of successive dilutions and succussions on the water structure. 'Extremely diluted solutions' (EDS) are solutions obtained through the iteration of two processes: dilution in stages of 1:100 and succussion, typically used in homeopathic medicine. The iteration is repeated until extreme dilutions are reached, so that the chemical composition of the solution is identical to that of the solvent. Nine different preparations, were studied from the 3cH to 30cH (Hahnemannian Centesimal Dilution). Four of those were without the active principle (potentized water). Two different active principles were used: Arsenicum sulphuratum rubrum (ASR), As4S4, 2,4-dichlorophenoxyacetic acid (2,4D). The solvents were: a solution of sodium bicarbonate and of silicic acid at 5 x 10(-5) M (mol/l) each, and solutions of sodium bicarbonate 5 x 10(-5), 7.5 x 10(-5) and 10 x 10(-5) M (mol/l) in double-distilled water. The containers were Pyrex glass to avoid the release of alkaline oxide and silica from the walls. Conductivity measurements of the solutions were carried out as a function of the age of the potencies. We found increases of electrical conductivity compared to untreated solvent. Successive dilution and succussion can permanently alter the physico-chemical properties of the aqueous solvent. But we also detected changes in physio-chemical parameters with time. This has not previously been reported. The modification of the solvent could provide an important support to the validity of homeopathic medicine, that employs 'medicines without molecules'. The nature of the phenomena here described remains still unexplained, nevertheless some significant experimental results were obtained. PMID:15287434

Elia, V; Baiano, S; Duro, I; Napoli, E; Niccoli, M; Nonatelli, L

2004-07-01

78

Alcohol-induced conditioned taste aversions in chemically labyrinthectomized rats.  

PubMed

Male rats were chemically labyrinthectomized (n = 22) by intratympanic injections of sodium arsanilate, and control rats (n = 15) received intratympanic injections of isotonic saline. All rats were tested for labyrinthine integrity and then adjusted to a 23 h.d-1 water deprivation schedule. Both labyrinthectomized and control rats were exposed to a conditioned taste aversion (CTA) procedure or a control procedure. The CTA technique involved pairing a novel saccharin taste with subsequent intraperitoneal injection of ethanol (1.5 g.kg-1; 15% solution). The control CTA procedure paired a novel saccharin taste with injections of isotonic saline. Following two conditioning trials and 3 d of water only, saccharin preference ratios were obtained in two-bottle choice tests (saccharin vs. water) over 4 consecutive days. Control rats conditioned with ethanol exhibited a strong CTA (p < 0.01) relative to control rats injected with saline. Labyrinthectomized rats drinking saccharin followed by ethanol injections showed a strong CTA (p < 0.01) if conditioning occurred 29-30 d post-labyrinthectomy. However, CTA's were not apparent in labyrinthectomized rats conditioned with ethanol 19 d post-labyrinthectomy. Thus, ethanol-induced CTA formation varied across the post-labyrinthectomy time period. PMID:7818451

Ossenkopp, K P; Rabi, Y J; Eckel, L A

1994-09-01

79

Characterizing stability of ``click'' modified glass surfaces to common microfabrication conditions and aqueous electrolyte solutions  

NASA Astrophysics Data System (ADS)

Microfluidic and nanofluidic systems are dominated by fluid-wall interactions due to enormous surface-area-to-volume ratios in these devices. Therefore, strategies to control wall properties in a reliable and repeatable manner can be important for device operation. Chemical modification of surfaces provides one such method. However, the stability of the surface adhered layers under fabrication and likely device operating conditions have not been evaluated in depth. This paper presents the stability analysis of three surface layers used in the `click' chemistry methodology for surface modification. The three surface layers have bromo, amine, and methyl termination on glass surfaces. All three surface groups are exposed to various wet and dry conditions including acid, base, solvent, electrolyte buffer solutions, oxidative plasmas, UV light, and thermal processing conditions. Contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscopy were used to quantify the stability of the adhered surface layers. The data show that the brominated surface was stable to most test conditions, while both the amine and methyl surface layers were stable to a narrower set of test conditions.Microfluidic and nanofluidic systems are dominated by fluid-wall interactions due to enormous surface-area-to-volume ratios in these devices. Therefore, strategies to control wall properties in a reliable and repeatable manner can be important for device operation. Chemical modification of surfaces provides one such method. However, the stability of the surface adhered layers under fabrication and likely device operating conditions have not been evaluated in depth. This paper presents the stability analysis of three surface layers used in the `click' chemistry methodology for surface modification. The three surface layers have bromo, amine, and methyl termination on glass surfaces. All three surface groups are exposed to various wet and dry conditions including acid, base, solvent, electrolyte buffer solutions, oxidative plasmas, UV light, and thermal processing conditions. Contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscopy were used to quantify the stability of the adhered surface layers. The data show that the brominated surface was stable to most test conditions, while both the amine and methyl surface layers were stable to a narrower set of test conditions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c1nr10261c

Prakash, Shaurya; Karacor, Mehmet B.

2011-08-01

80

Relative Contributions of Aqueous and Dietary Uptake of Hydrophobic Chemicals to the Body Burden in Juvenile Rainbow Trout  

Microsoft Academic Search

This study assessed the relative contributions of aqueous versus dietary uptake of three hydrophobic chemicals, 1,2,4-trichlorobenzene\\u000a (1,2,4-TCB), 1,2,3,4,5-pentachlorobenzene (PeCB), and 2,2?,4,4?,6,6?-hexachlorobiphenyl (HCBP). Juvenile rainbow trout (Oncorhynchus mykiss) were exposed separately to chemically spiked water and food for 4 days and 12 days, respectively. Chemical concentrations\\u000a were measured in the food, water, and tissues, and this allowed calculation of uptake rate

P. Qiao; F. A. P. C. Gobas; A. P. Farrell

2000-01-01

81

Ciprofloxacin adsorption from aqueous solution onto chemically prepared carbon from date palm leaflets.  

PubMed

A chemically prepared carbon was synthesized from date palm leaflets via sulphuric acid carbonization at 160 degrees C. Adsorption of ciprofloxacin (CIP) from aqueous solution was investigated in terms of time, pH, concentration, temperature and adsorbent status (wet and dry). The equilibrium time was found to be 48 hr. The adsorption rate was enhanced by raising the temperature for both adsorbents, with adsorption data fitting a pseudo second-order model well. The activation energy, Ea, was found to be 17 kJ/mol, indicating a diffusion-controlled, physical adsorption process. The maximum adsorption was found at initial pH 6. The wet adsorbent showed faster removal with higher uptake than the dry adsorbent, with increased performance as temperature increased (25-45 degrees C). The equilibrium data were found to fit the Langmuir model better than the Freundlich model. The thermodynamic parameters showed that the adsorption process is spontaneous and endothermic. The adsorption mechanism is mainly related to cation exchange and hydrogen bonding. PMID:23520864

El-Shafey, El-Said Ibrahim; Al-Lawati, Haider; Al-Sumri, Asmaa Soliman

2012-01-01

82

A lithography-free pathway for chemical microstructuring of macromolecules from aqueous solution based on wrinkling.  

PubMed

We report on a novel lithography-free method for obtaining chemical submicron patterns of macromolecules on flat substrates. The approach is an advancement of the well-known microcontact printing scheme: While for classical microcontact printing lithographically produced masters are needed, we show that controlled wrinkling can serve as an alternative pathway to producing such masters. These can even show submicron periodicities. We expect upscaling to larger areas to be considerably simpler than that for existing techniques, as wrinkling results in a macroscopic deformation process that is not limited in terms of substrate size. Using this approach, we demonstrate successful printing of aqueous solutions of polyelectrolytes and proteins. We study the effectiveness of the stamping process and its limits in terms of periodicities and heights of the stamps' topographical features. We find that critical wavelengths are well below 355 nm and critical amplitudes are below 40 nm and clarify the failure mechanism in this regime. This will permit further optimization of the approach in the future. PMID:18950207

Pretzl, Melanie; Schweikart, Alexandra; Hanske, Christoph; Chiche, Arnaud; Zettl, Ute; Horn, Anne; Böker, Alexander; Fery, Andreas

2008-10-25

83

The antioxidant activity of aqueous spinach extract: chemical identification of active fractions.  

PubMed

In previous studies we have elucidated the presence of powerful, natural antioxidants (NAO) in water extracts of spinach leaves and demonstrated their biological activity in both in vitro and in vivo systems. In the present study, the chemical identity of several of these antioxidant components is presented. Spinach leaves were extracted with water and the 20,000 g supernatant which contained the antioxidant activity was extracted with a water:acetone (1:9) solution. The 20,000 g supernatant obtained was further purified on reverse phase HPLC using C-8 semi-preparative column. Elution with 0.1% TFA resulted in five hydrophilic peaks. Elution with acetonitrile in TFA resulted in seven additional hydrophobic peaks. All the peaks were detected at 250 nm. All the fractions obtained showed antioxidant activity when tested using three different assays. Based on 1H and 13C NMR spectroscopy four of the hydrophobic fractions were identified as glucuronic acid derivatives of flavonoids and three additional fractions as trans and cis isomers of p-coumaric acid and others as meso-tartarate derivatives of p-coumaric acid. The present study demonstrates for the first time the presence of both flavonoids and p-coumaric acid derivatives as antioxidant components of the aqueous extract of spinach leaves. PMID:11524124

Bergman, M; Varshavsky, L; Gottlieb, H E; Grossman, S

2001-09-01

84

The radiolysis of aqueous acetonitrile - Compounds of interest to chemical evolution studies  

SciTech Connect

Oxygen free aqueous solutions of CH3CN (0.1 M, pH 6) were exposed to gamma rays from a Co-60 source, the mixtures of nonvolatile radiolytic products was fractionated and the fractions were analysed. Succinic, maleic, fumaric, malonic and pyruvic acids were identified. Glycol aldehyde, glucose and probably ribose were observed in the hydrolysate of fractionated material. It has been suggested that an oligomer is formed which has a fragment with the polyhydroxy structure and on hydrolysis releases the carbohydrates. Radiolytic products which release amino acids on hydrolysis were found in several fractions. The amino acid contents of the hydrolysates were up to about 2.8% of the fraction mass. The presence of several protein and nonprotein amino acids suggests that their origin should be in a peptidic structure, which is probably a fragment of an oligomer radiolytically produced. A direct analysis of the irradiated solution shows the presence of acetaldehyde, propionaldehyde, glyoxal and of biacetyl. Experimental findings are discussed and a free-radical mechanism is proposed to account for the chemical changes observed.

Draganic, I.G. (Institut za Nuclearne Nauke, Belgrade, Yugoslavia); Jovanovic, S. (Beograd, Univerzitet, Belgrade, Yugoslavia)

1980-07-01

85

Concentration of ginseng extracts aqueous solution by vacuum membrane distillation 2. Theory analysis of critical operating conditions and experimental confirmation  

Microsoft Academic Search

Membrane fouling mechanism in the vacuum membrane distillation (VMD) was studied both theoretically and experimentally by using ginseng crude extract aqueous solution as a model concentrate system. The concept of critical fouling operating conditions in VMD within which fouling is difficult to occur was introduced for the first time. By analyzing the forces acting on solute particles (microaggregates of biomacromolecules

Zhi-Ping Zhao; Chun-Yan Zhu; Dian-Zhong Liu; Wen-Fang Liu

2011-01-01

86

Peptide synthesis in aqueous environments: the role of extreme conditions and pyrite mineral surfaces on formation and hydrolysis of peptides.  

PubMed

A comprehensive study of free energy landscapes and mechanisms of COS-mediated polymerization of glycine via N-carboxy anhydrides (NCAs, "Leuchs anhydrides") and peptide hydrolysis at the water-pyrite interface at extreme thermodynamic conditions is presented. Particular emphasis is set on the catalytic effects of the mineral surface including the putative role of the ubiquitous sulfur vacancy defects. It is found that the mere presence of a surface is able to change the free energetics of the elementary reaction steps. This effect can be understood in terms of a reduction of entropic contributions to the reactant state by immobilizing the reactants and/or screening them from bulk water in a purely geometric ("steric") sense. Additionally, the pyrite directly participates chemically in some of the reaction steps, thus changing the reaction mechanism qualitatively compared to the situation in bulk water. First, the adsorption of reactants on the surface can preform a product-like structure due to immobilizing and scaffolding them appropriately. Second, pyrite can act as a proton acceptor, thus replacing water in this role. Third, sulfur vacancies are found to increase the reactivity of the surface. The finding that the presence of pyrite speeds up the rate-determining step in the formation of peptides with respect to the situation in bulk solvent while stabilizing the produced peptide against hydrolysis is of particular interest to the hypothesis of prebiotic peptide formation at hydrothermal aqueous conditions. Apart from these implications, the generality of the studied organic reactions are of immediate relevance to many fields such as (bio)geochemistry, biomineralization, and environmental chemistry. PMID:21561111

Schreiner, Eduard; Nair, Nisanth N; Wittekindt, Carsten; Marx, Dominik

2011-05-11

87

Polyelectrolyte multilayer membranes for desalination of aqueous salt solutions and seawater under reverse osmosis conditions  

NASA Astrophysics Data System (ADS)

Ultrathin, multilayered membranes of polyvinylamine (PVA) and polyvinylsulfate (PVS) were electrostatically adsorbed on a porous polymer (polyacrylonitrile/polyethylene terephthalate) support. Their use for desalination of aqueous salt solutions, diluted and non-diluted artificial seawater was investigated under reverse osmosis conditions. Using 60 layer pairs of PVA/PVS as separating membrane, it was possible to completely reject MgCl 2 and MgSO 4 from feed solutions of 1 and 10 mM concentration independently from the operative pressure applied. The rejection of NaCl and Na 2SO 4 increased from 84 and 96% at 5 bar to 93.5 and 98.5% at 40 bar, respectively. From diluted seawater (1:10; 1:100; 1:1000), 99 ± 1% of Mg 2+, 97.0 ± 1% of Ca 2+, and 92.5 ± 1% of Na + were rejected at 40 bar, and from non-diluted seawater, 98 ± 1% of Mg 2+, 96.4 ± 1% of Ca 2+, and 74.5 ± 0.8% of Na + were rejected at 40 bar. The permeation flux J increased linearly with the pressure applied. For a membrane of 60 PVA/PVS layer pairs, a flux value of 4 ± 0.2 L m -2 h -1 was found at 40 bar. The influence of the number of deposited layer pairs on R and J was also investigated.

Toutianoush, Ali; Jin, Wanqin; Deligöz, Hüseyin; Tieke, Bernd

2005-06-01

88

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

89

Investigation of aqueous-phase photooxidation of glyoxal and methylglyoxal by aerosol chemical ionization mass spectrometry: observation of hydroxyhydroperoxide formation.  

PubMed

Aqueous-phase processing of glyoxal (GLY) and methylglyoxal (MG) produces highly oxygenated, less volatile organic acids that can contribute to SOA formation and aging. In this study, aerosol chemical ionization mass spectrometry (aerosol CIMS) is employed to monitor aqueous-phase photooxidation of GLY and MG. Using iodide (I(-)) as the reagent ion, aerosol CIMS can simultaneously detect important species involved in the reactions: organic acids, peroxides, and aldehydes, so that the reconstructed total organic carbon (TOC) concentrations from aerosol CIMS data agree well with offline TOC analysis. This study also reports the first direct detection of hydroxyhydroperoxide (HHP) formation from the reaction of H(2)O(2) with GLY or MG. The formation of HHPs is observed to be reversible and an estimate of their equilibrium constants is made to be between 40 and 200 M(-1). Results of this study suggest that HHPs can form additional formic acid and acetic acid via photooxidation and regenerate GLY or MG during photooxidation, compensating their loss. HHP formation needs to be further studied for inclusion in aqueous-phase chemical models given that it may affect the aqueous partitioning of carbonyls in the atmosphere. PMID:22296207

Zhao, R; Lee, A K Y; Abbatt, J P D

2012-03-02

90

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

91

Removal of Cu and Ag from aqueous solution on a chemically-carbonized sorbent from date palm leaflets  

Microsoft Academic Search

A chemically-carbonized sorbent was prepared from date palm leaflets by sulphuric acid treatment at 170°C. Carbonization took place via the dehydration effect of the hot sulphuric acid producing a carbon with reduction property. Sorption of Cu and Ag from aqueous solution was investigated in terms of pH, contact time, metal concentration and temperature. A peculiar behaviour was found for the

El-Said Ibrahim El-Shafey; Salma Muhammed Zahran Al-Kindy

2012-01-01

92

Removal of Pb(II) from aqueous solutions using activated carbon from Sea-buckthorn stones by chemical activation  

Microsoft Academic Search

Two series of activated carbon have been prepared by chemical activation of Sea-buckthorn stones with phosphoric acid and zinc chloride for the removal of Pb(II) ions from aqueous solutions. To characterize the adsorptive characteristics of produced active carbon, surface area was calculated using the standard Brunauer–Emmet–Teller method. The microstructures of the resultant activated carbon were observed by scanning electron micrographs.

Sayed Zia Mohammadi; Mohammad Ali Karimi; Daryoush Afzali; Fatemeh Mansouri

2010-01-01

93

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

94

Effectiveness of chemical dispersants under breaking wave conditions  

SciTech Connect

A study is described in which the effectiveness of Corexit 9527 on Alaskan North Slope crude oil was assessed by conducting laboratory and wave basin tests. Three laboratory dispersant test systems were used: the MNS, Labofina and EXDET procedures. It was concluded that for the present purposes the EXDET system was most suitable, and it was used for subsequent tests. The dependence of effectiveness on dispersant to oil ratio, extent of weathering, temperature, water salinity, energy level and the presence of emulsified water (mousse) were determined. The results were used to guide a subsequent program of tests at the Esso Resources Canada Ltd. Wave Basin in Calgary in which the effectiveness was determined under breaking wave conditions. From the results a correlating equation was developed to express effectiveness as a function of dispersant to oil ratio and delay time between dispersant application and the onset of breaking waves. Significant quantities of oil were dispersed under breaking wave conditions, even at what are conventionally regarded as low dispersant to oil ratios. The implications of the results for assessing the actual and potential extent of chemical dispersion following the Exxon Valdez spill in March 1989 are discussed. Assuming that the dispersion efficiencies from the wave basin could have been achieved at the incident, it is believed that because of the onset of the storm with breaking wave conditions some 60 hours after the grounding, approximately 38% of the spilled oil could have been dispersed had available dispersants been applied to the spilled oil in the days following the grounding.

Mackay, D. [Univ. of Toronto, Ontario (Canada). Chemical Engineering Dept.

1995-06-01

95

Experimental reduction of aqueous sulphate by hydrogen under hydrothermal conditions: Implication for the nuclear waste storage  

NASA Astrophysics Data System (ADS)

Sulphate reduction by hydrogen, likely to occur in deep geological nuclear waste storage sites, was studied experimentally in a two-phase system (water + gas) at 250-300 °C and under 4-16 bars H 2 partial pressure in hydrothermal-vessels. The calculated activation energy is 131 kJ/mol and the half-life of aqueous sulphate in the presence of hydrogen and elemental sulphur ranges from 210,000 to 2.7 × 10 9 years at respective temperatures of 90 °C, the thermal peak in the site and 25 °C, the ambient temperature far from the site. The features and rate of the sulphate reduction by H 2 are close to those established for TSR in oil fields. The experiments also show that the rate of sulphate reduction is not significantly affected in the H 2 pressure range of 4-16 bars and in the pH range of 2-5, whereas a strong increase is measured at pH below 2. We suggest that the condition for the reaction to occur is the speciation of sulphate dominated by non symmetric species ( HSO4- at low pH), and we propose a three steps reaction, one for each intermediate-valence sulphur species, the first one requiring H 2S as electron donor rather than H 2. We distinguish two possible reaction pathways for the first step, depending on pH: reduction of sulphate into sulphur dioxide below pH 2 or into thiosulphate or sulphite + elemental sulphur in the pH range 2-5.

Truche, Laurent; Berger, Gilles; Destrigneville, Christine; Pages, Alain; Guillaume, Damien; Giffaut, Eric; Jacquot, Emmanuel

2009-08-01

96

Direct extraction of oil from sunflower seeds by twin-screw extruder according to an aqueous extraction process: Feasibility study and influence of operating conditions  

Microsoft Academic Search

The objective of this study was to evaluate the feasibility of an aqueous process to extract sunflower seed oil using a co-rotating twin-screw extruder. Aqueous extraction was carried out using whole seeds and the influence of the operating conditions on oil yield was examined. Operating conditions included screw profile, screw rotation speed, and input flow rates of sunflower seeds and

Ph. Evon; V. Vandenbossche; P. Y. Pontalier; L. Rigal

2007-01-01

97

FINAL REPORT. CHEMICAL SPECIATION OF INORGANIC COMPOUNDS UNDER HYDROTHERMAL CONDITIONS  

EPA Science Inventory

We have conducted measurements at 400 degrees C of the oxidation of Cr (III) to Cr (VI) by NO3-/NO2-. These spectra are to the best of our knowledge the first reported in situ spectroscopic observation of homogeneous aqueous redox chemistry at temperatures beyond the critical...

98

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 ...

99

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

100

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

101

Aqueous Chemical Modeling of Sedimentation on Early Mars with Application to Surface-Atmosphere Evolution.  

National Technical Information Service (NTIS)

This project was to investigate models for aqueous sedimentation on early Mars from fluid evaporation. Results focused on three specific areas: (1) First, a fluid evaporation model incorporating iron minerals was developed to compute the evaporation of a ...

D. C. Catling

2004-01-01

102

Chemical composition and thermodynamical properties of high-pressure aqueous fluids in subduction zones from experiments in the diamond-anvil cell  

NASA Astrophysics Data System (ADS)

Saline-rich aqueous fluids play an important role in metamorphic reactions and chemical transport in a wide range of geological environments at conditions ranging from those at the Earth's surface to those of the upper mantle. In subduction zones, high-pressure aqueous fluids are released into the mantle when the altered oceanic crust is subducted, leading to the important geochemical phenomena of mantle wedge metasomatism and arc magmatism. Recognizing the role of deep fluid in these processes a number of significant but unanswered questions arise as to their chemical composition, the extent of mass transfer, and the mechanism of elemental transport from the slab to the mantle wedge. Answers to these questions depend on quantitative thermodynamic modeling of fluid-mineral interactions, that is greatly limited by the lack of thermodynamic data of aqueous fluids at high pressure and temperature conditions. We have begun to address this problem by conducting a project of in-situ characterization of fluid-mineral interactions at high pressure and temperature (high P-T). These studies are based upon the use of the diamond-anvil cell in conjunction with Synchrotron X-ray and vibrational spectroscopic techniques. The focus of this contribution will be on recent advances on quantitative elemental analysis of high pressure fluids and on the determination of the thermodynamic properties of high saline aqueous fluids. We will present the application of Synchrotron X-ray Fluorescence spectroscopy (SXRF) to conduct in situ dissolution/precipitation kinetics studies and mineral solubility measurements with detection limits as low as 40 ppm in the diamond- anvil cell. Recent results on the solubility of carbonate minerals in water and NaCl fluids will be presented to illustrate the potentials of the new technique for in situ observations of mineral-fluids interactions at extreme conditions. Efforts on the evaluation of the thermodynamic properties of high pressure fluids will be illustrated by the determination of the equations of state from sound velocity measurements in the diamond-anvil cell by Brillouin scattering spectroscopy. Preliminary results on NaCl-H2O fluid will be discussed.

Sanchez-Valle, C.; Daniel, I.; Martinez, I.; Simionovici, A. S.; Bass, J.; Reynard, B.

2006-12-01

103

Mercury Bioaccumulation and Trophic Transfer in the Cache Creek Watershed, California, in Relation to Diverse Aqueous Mercury Exposure Conditions  

Microsoft Academic Search

Abstract Water and biota were sampled,throughout the Cache Creek watershed during a 20 month period between,January 2000 and August 2001. A range of mercury,(Hg) exposure conditions were investigated in relation to several mining and natural Hg point sources in the watershed. The study was conducted,to provide foundational,information,and baseline monitoring,data for future point source,remediation,efforts and TMDL regulation. Seasonal aqueous,sampling,was conducted in

Darell G. Slotton; Shaun M. Ayers; Thomas H. Suchanek; Ronald D. Weyand; Anne M. Liston

2003-01-01

104

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...

105

Chemical Speciation of Inorganic Compounds under Hydrothermal Conditions  

SciTech Connect

Measurements of oxidation. These spectra are to the best of our knowledge the first reported in situ spectroscopic observation of homogeneous aqueous redox chemistry at temperatures beyond the critical temperature of waste. We also observed a time-dependence for the growth of the Cr(VI) XANES peak and have therefore obtained both kinetic information as well as structural information on the reactants and products at the reaction temperature. We feel that these new techniques, when employed on actual waste components will elucidate the underlying chemistry.

Edward A Stern; John Fulton

2002-02-21

106

HCL solubility and liquid diffusion in aqueous sulfuric acid under stratospheric conditions  

NASA Astrophysics Data System (ADS)

The solubility of HCl in cold H2SO4/H2O solutions is central to an assessment of the role of stratospheric aerosol in polar ozone destruction. The interpretation of laboratory measurements of HCl uptake by aqueous H2SO4 requires a knowledge of (1) HCl solubility and (2) the HCl liquid phase diffusion coefficient. Neither quantity is easily determined because of the high H2SO4 concentration and low temperature of the solutions, making experimental data difficult to evaluate and to apply to the real stratospheric situation. To avoid these difficulties, we have used a new thermodynamic model for an improved estimate of HCl solubility, and a viscosity-based cubic cell model to obtain the diffusion coefficient. The calculated HCl solubility in aqueous H2SO4 below 200 K is up to three orders of magnitude greater than previously thought. This might promote chlorine activation particularly during volcanically perturbed periods with an enhanced stratospheric aerosol loading.

Luo, B. P.; Clegg, S. L.; Peter, Th.; Müller, R.; Crutzen, P. J.

1994-01-01

107

Complexes of earth-abundant metals for catalytic electrochemical hydrogen generation under aqueous conditions.  

PubMed

Growing global energy demands and climate change motivate the development of new renewable energy technologies. In this context, water splitting using sustainable energy sources has emerged as an attractive process for carbon-neutral fuel cycles. A key scientific challenge to achieving this overall goal is the invention of new catalysts for the reductive and oxidative conversions of water to hydrogen and oxygen, respectively. This review article will highlight progress in molecular electrochemical approaches for catalytic reduction of protons to hydrogen, focusing on complexes of earth-abundant metals that can function in pure aqueous or mixed aqueous-organic media. The use of water as a reaction medium has dual benefits of maintaining high substrate concentration as well as minimizing the environmental impact from organic additives and by-products. PMID:23034627

Thoi, V Sara; Sun, Yujie; Long, Jeffrey R; Chang, Christopher J

2012-10-04

108

Interfacial properties of methane\\/aqueous VC713 solution under hydrate formation conditions  

Microsoft Academic Search

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

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

2009-01-01

109

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...

110

Nature of the Chemical Bond of Aqueous Fe(2+) 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

2013-10-03

111

Plant Cell Walls: Basics of Structure, Chemistry, Accessibility and the Influence on Conversion - Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals  

SciTech Connect

This book is focused on the pretreatment of biomass, a necessary step for efficient conversion of the plant cell wall materials to fuels and other products. Pretreatment is required because it is difficult to access, separate, and release the monomeric sugars comprising the biopolymers within the biomass that can be further upgraded to products through chemical processes such as aqueous phase reforming or biological routes such as fermentation of the sugars to ethanol This resistance to degradation or difficulty to release the monomers (mostly sugars) is commonly referred to as recalcitrance. There are many methods to overcome plant recalcitrance, but the underlying cause of the recalcitrance lies in the complex combination of chemical and structural features of the plant cell walls.

Davison, Brian H [ORNL; Davis, Dr. Mark F. [National Renewable Energy Laboratory (NREL); Parks, Jerry M [ORNL; Donohoe, Bryan [National Renewable Energy Laboratory (NREL)

2013-01-01

112

Quantum-Chemical Calculations of Carbon-Isotope Fractionation in CO2(g), Aqueous Carbonate Species, and Carbonate Minerals  

SciTech Connect

Quantum chemical calculations on large supermolecular carbonate-water and carbonate mineral clusters are used to predict equilibrium constants for 13,12C-isotope-exchange reactions between CO2(g), aqueous carbonate species, and the common carbonate minerals. For the aqueous species, we evaluate the influence of the size and conformational variability of the solvation shell, the exchange-correlation functional, and the basis set. The choice of exchange-correlation functional (PBE vs B3LYP), the basis set (6-31G* vs aug-cc-pVDZ), and solvation shell size (first shell only vs first shell and a partial second shell) each produce changes of ~5-10 per mil in the reduced partition function ratio. Conformational variability gives rise to a standard error of ~0.5 per mil using ~10 solute-solvent conformations. The best results are obtained with the B3LYP/ aug-cc-pVDZ combination, but because the improvements in the basis set and exchange correlation functional drive the reduced partition function ratios in opposite directions, reasonably good results are also obtained with the PBE/6-31G* combination. To construct molecular clusters representative of mineral environments, a new method is introduced on the basis of conservation of Pauling bond strength. Using these clusters as models for minerals, calculations of mineral-gas and mineral-aqueous carbon-isotope fractionation factors, are in good agreement with experimental measurements. Carbon-isotope fractionation factors for gas, aqueous, and mineral phases are thus integrated into a single theoretical/computational framework.

Rustad, James R.; Nelmes, Sierra L.; Jackson, Virgil E.; Dixon, David A.

2008-01-24

113

Heat transfer and critical heat fluxes in the boiling of aqueous solutions of polyethylene oxide at reduced pressures under natural-convection conditions  

Microsoft Academic Search

Experimental data are presented on heat transfer and critical heat fluxes in the boiling of aqueous solutions of polyethylene oxide of different concentrations under conditions of natural convection at atmospheric and reduced temperatures.

B. P. Avksentyuk; Z. S. Mesarkishvili

1984-01-01

114

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

115

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

116

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

117

EFFICIENT CHEMICAL TRANSFORMATIONS USING ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

The diverse nature of chemical entities requires various green' strategic pathways in our quest towards attaining sustainability. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable...

118

LITERATURE VALUES FOR SELECTED CHEMICAL PHYSICAL PROPERTIES OF AQUEOUS BORIC ACID SOLUTIONS  

Microsoft Academic Search

Data are given for properties of aqueous solutions of boric acid: ; solubility for orthoboric acid (HâBOâ), specific gravity, pH, ionic-; dissociation constants, colligative properties (vapor-pressure lowering, boiling-; point elevation, freezing-point depression), solute volatility, thermal ; conductivity, electric conductivity, corrosion effects, and mistion and dilution). ; An attempt was made to secure complete literature coverage through mid-1957. ; (P.C.H.);

D. E. Byrnes; W. E. Foster

1961-01-01

119

Chemically selective membrane optode for Cr(VI) determination in aqueous samples  

Microsoft Academic Search

A methodology for simultaneous preconcentration and determination of Cr(VI) from aqueous samples was developed using a membrane optode formed by physical inclusion of a Cr(VI) selective chromophore 1,5-diphenylcarbazide (DPC) into a plasticized cellulose triacetate matrix. The inclusion of an anion exchanger (Aliquat-336) was found to be effective for immobilization of both DPC and Cr(VI)–DPC complex in the optode matrix itself.

Y. M. Scindia; A. K. Pandey; A. V. R. Reddy; S. B. Manohar

2004-01-01

120

Chemical oxidation of chlorinated non-aqueous phase liquid by hydrogen peroxide in natural sand systems  

Microsoft Academic Search

This study explored the Fenton-like oxidation of trichloroethylene (TCE) existing as dense non-aqueous phase liquid (DNAPL) in natural silica sand (iron=0.04g\\/kg) and the sand from an aquifer (iron=2.01g\\/kg). Glass bead containing no iron mineral was used as the control. Batch oxidation experiments were conducted to assess interactions between oxidant and TCE DNAPL. Column experiments were performed to evaluate dynamics of

Carol Kuei-Jyum Yeh; Hung-Ming Wu; Ting-Chien Chen

2003-01-01

121

In silico prediction of aqueous solubility: a multimodel protocol based on chemical similarity.  

PubMed

Aqueous solubility is one of the most important ADMET properties to assess and to optimize during the drug discovery process. At present, accurate prediction of solubility remains very challenging and there is an important need of independent benchmarking of the existing in silico models such as to suggest solutions for their improvement. In this study, we developed a new protocol for improved solubility prediction by combining several existing models available in commercial or free software packages. We first performed an evaluation of ten in silico models for aqueous solubility prediction on several data sets in order to assess the reliability of the methods, and we proposed a new diverse data set of 150 molecules as relevant test set, SolDiv150. We developed a random forest protocol to evaluate the performance of different fingerprints for aqueous solubility prediction based on molecular structure similarity. Our protocol, called a "multimodel protocol", allows selecting the most accurate model for a compound of interest among the employed models or software packages, achieving r(2) of 0.84 when applied to SolDiv150. We also found that all models assessed here performed better on druglike molecules than on real drugs, thus additional improvement is needed in this direction. Overall, our approach enlarges the applicability domain as demonstrated by the more accurate results for solubility prediction obtained using our protocol in comparison to using individual models. PMID:23072744

Chevillard, Florent; Lagorce, David; Reynès, Christelle; Villoutreix, Bruno O; Vayer, Philippe; Miteva, Maria A

2012-10-25

122

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

123

The decay of chemical weapons agents under environmental conditions  

SciTech Connect

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-m{sup 2} plots on three successive days; i.e., Tuesday through Thursday. The depositions were to be made so as to give an areal concentration of 10 g/m{sup 2}. Four felt pads of approximately 25 cm{sup 2} each were placed at the corners of each of the test plots. These were subsequently extracted and analyzed by CBDE to determine the actual agent concentration. Samples for LLNL (two different types of soil, disks of silicone rubber gasket material, and short cylinders of concrete were to be contaminated and analyzed. Results are described.

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

1993-04-09

124

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

125

Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction  

ERIC Educational Resources Information Center

|Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,…

Tellinghuisen, Joel

2006-01-01

126

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

127

Diffusion behavior of lysozyme in aqueous ammonium sulfate solutions under varying solution conditions as determined by dynamic light scattering  

SciTech Connect

As proteins gain significance in commercial applications such as pharmaceuticals, detergents, organic waste management and cosmetics, efficient and economical recovery of these valuable biomolecules is of increasing importance. the salting-out process has found widespread application in the area of protein separations. To date, salt-induced precipitation of proteins from complex aqueous solutions remains largely an empirical process; no comprehensive model exists to predict salting-out phase equilibria in protein solutions. Rational predictive models for salt-induced precipitation will therefore be of great value in protein purification, both on the preparative and the analytical scale. Any attempt to model theoretically salt-induced protein precipitation must include the known physics of protein interactions in aqueous solution. With this in mind, it is crucial to acknowledge that protein precipitation is fundamentally an aggregation process. In order to incorporate aggregation effects into ongoing efforts to model salting out of proteins, it is necessary to quantify the degree of aggregation as a function of solution conditions. Therefore, dynamic light scattering measurements were performed with a well-studied protein, hen-egg-white lysozyme, under several solution conditions.

Fornefeld, U.M.; Kuehner, D.E.; Blanch, H.W.; Prausnitz, J.M. (Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering Lawrence Berkeley Lab., CA (United States). Chemical Sciences Div.)

1994-12-01

128

Effect of aqueous environment in chemical reactivity of monolignols. A New Fukui Function Study.  

PubMed

The free radical reactivity of monolignols can be explained in terms of the Fukui function and the local hard and soft acids and bases (HSAB) principle to determine the potential linkages among them for reactions involving free radicals. Our results in gas-phase and aqueous environment elucidate the most probable free radical resonance structures in monolignols. Their reactivity toward nucleophilic or electrophilic species was described applying the Fukui function after a second analysis of the selected resonance structures. Methodology herein described could differentiate the inherent nature of one radical from another. PMID:19647459

Martínez, Carmen; Sedano, Miriam; Mendoza, Jorge; Herrera, Rafael; Rutiaga, Jose G; Lopez, Pablo

2009-08-03

129

The solubility of ozone and kinetics of its chemical reactions in aqueous solutions of sodium chloride  

Microsoft Academic Search

The solubility of ozone and the kinetics of its decomposition and interaction with chloride ions in a 1 M aqueous solution\\u000a of NaCl at 20°C and pH 8.4–10.8 were studied. The ratio between the concentration of O3 in solution and the gas phase was found to be 0.16 at pH 8.4–9.8. The concentration of dissolved ozone decreased sharply\\u000a as pH

A. V. Levanov; I. V. Kuskov; E. E. Antipenko; V. V. Lunin

2008-01-01

130

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

131

"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...

132

Cerium: A chemical tracer of paleo-oceanic redox conditions  

Microsoft Academic Search

The Ce anomalies found in marine carbonates provide a sensitive indicator for the study of paleo-oceanic redox conditions. The dependency of C{sub Ce} and a{sub CePOâ°} to the P{sub Oâ}, pH and P{sub COâ} of seawater can be used for deciphering some aspects of the paleo-ocean chemistry. The pH, which is related to P{sub COâ}, and P{sub Oâ} are major

T. G. Liu; M. R. U. Miah; R. A. Schmitt

1988-01-01

133

Photochemical processing of aldrin and dieldrin in frozen aqueous solutions under arctic field conditions.  

PubMed

Organochlorine (OC) contaminants are transported to the Polar Regions, where they have the potential to bioaccumulate, presenting a threat to the health of wildlife and indigenous communities. They deposit onto snowpack during winter, and accumulate until spring, when they experience prolonged solar irradiation until snowmelt occurs. Photochemical degradation rates for aldrin and dieldrin, in frozen aqueous solution made from MilliQ water, 500 ?M hydrogen peroxide solution or locally-collected melted snow were measured in a field campaign near Barrow, AK, during spring-summer 2008. Significant photoprocessing of both pesticides occurs; the reactions depend on temperature, depth within the snowpack and whether the predominant phase is ice or liquid water. The effect of species present in natural snowpack is comparable to 500 ?M hydrogen peroxide, pointing to the potential significance of snowpack-mediated reactions. Aldrin samples frozen at near 0 °C were more reactive than comparable liquid samples, implying that the microenvironments experienced on frozen ice surfaces are an important consideration. PMID:21396757

Rowland, Glenn A; Bausch, Alexandra R; Grannas, Amanda M

2011-03-10

134

Experimental chlorine partitioning between forsterite, enstatite and aqueous fluid at upper mantle conditions  

NASA Astrophysics Data System (ADS)

Cl partition coefficients between forsterite, enstatite and coexisting Cl-bearing aqueous fluids were determined in a series of high pressure and temperature piston cylinder experiments at 2 GPa between 900 and 1300 °C in the system MgO-SiO2-H2O-NaCl-BaO-C±CaCl2±TiO2±Al2O3±F. Diamond aggregates were added to the experimental capsule set-up in order to separate the fluid from the solid residue and enable in situ analysis of the quenched solute by LA-ICP-MS. The chlorine content of forsterite and enstatite was measured by electron microprobe, and the nature of hydrous defects was investigated by infrared spectroscopy. Partition coefficients show similar incompatibility for Cl in forsterite and enstatite, with DClfo/fl = 0.0012 ± 0.0006, DClen/fl = 0.0018 ± 0.0008 and DClfo/en = 1.43 ± 0.71. The values determined for mineral/fluid partitioning are very similar to previously determined values for mineral/melt. Applying the new mineral/fluid partition coefficients to fluids in subduction zones, a contribution between 0.15% and 20% of the total chlorine from the nominally anhydrous minerals is estimated.

Fabbrizio, Alessandro; Stalder, Roland; Hametner, Kathrin; Günther, Detlef

2013-11-01

135

Electroless chemical etching of silicon in aqueous NH4F/AgNO3/HNO3 solution  

NASA Astrophysics Data System (ADS)

One-step metal-assisted electroless chemical etching of silicon substrate was investigated. The etching was performed in aqueous NH4F/AgNO3/HNO3 solution at room temperature. The effect of several etching parameters on the morphology of etched layer was studied namely: silicon type, doping level and crystallographic orientation. It is shown that the morphology depends strongly on etching parameters. The reflectivity of the nanostructured layers was examined by reflectance spectroscopy and was found to depend on silicon resistivity. Indeed, the lowest average value of reflectance (a few percent) in the range 250-800 nm was obtained for 5-10 ? cm p-Si(1 0 0), 0.001-0.003 ? cm n++-Si(1 0 0) and 5-10 ? cm n-Si(1 0 0). Finally, the dissolution mechanism of silicon by Ag-assisted electroless etching is discussed.

Megouda, Nacéra; Hadjersi, Toufik; Szunerits, Sabine; Boukherroub, Rabah

2013-11-01

136

ZnO-organic hybrid white light emitting diodes grown on flexible plastic using low temperature aqueous chemical method  

NASA Astrophysics Data System (ADS)

We demonstrate white light luminescence from ZnO-organic hybrid light emitting diodes grown at 90 °C on flexible plastic substrate by aqueous chemical growth. The configuration used for the ZnO-organic hybrid white light emitting diodes (WLEDs) consists of a layer of poly (9, 9-dioctylfluorene) (PFO) on poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) coated plastic with top ZnO nanorods. Structural, electrical, and optical properties of these WLEDs were measured and analyzed. Room temperature electroluminescence spectrum reveals a broad emission band covering the range from 420 to 750 nm. In order to distinguish the white light components and contribution of the PFO layer we used a Gaussian function to simulate the experimental data. Color coordinates measurement of the WLED reveals that the emitted light has a white impression. The color rendering index and correlated color temperature of the WLED were calculated to be 68 and 5800 K, respectively.

Bano, N.; Zaman, S.; Zainelabdin, A.; Hussain, S.; Hussain, I.; Nur, O.; Willander, M.

2010-08-01

137

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

138

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

139

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

140

CH4/NH3/H2O spark tholin: Chemical analysis and interaction with Jovian aqueous clouds  

NASA Astrophysics Data System (ADS)

The organic solid (tholin) produced by spark discharge in a CH4 + NH3 + H2O atmosphere is investigated, along with the separable components of its water-soluble fraction. The chemistry of this material serves as a provisional model for the interaction of Jovian organic heteropolymers with the deep aqueous clouds of Jupiter. Intact (unhydrolyzed) tholin is resolved into four chemically distinct fractions by high-pressure liquid chromatography (HPLC). Gel filtration chromatography reveals abundant components at molecular weights ?600-700 and 200-300 Da. Gas chromatography/mass spectrometry of derivatized hydrolysis products of unfractionated tholin shows about 10% by mass protein and nonprotein amino acids, chiefly glycine, alanine, aspartic acid, ?-alanine, and ?-aminobutyric acid, and 12% by mass other organic acids and hydroxy acids. The stereospecificity of alanine is investigated and shown to be racemic. The four principal HPLC fractions yield distinctly different proportions of amino acids. Chemical tests show that small peptides or organic molecules containing multiple amino acid precursors are a possibility in the intact tholins, but substantial quantities of large peptides are not indicated. Candidate 700-Da molecules have a central unsaturated, hydrocarbon- and nitrile-rich core, linked by acid-labile (ester or amide) bonds to amino acid and carboxylic acid side groups. The core is probably not HCN ``polymer.'' The concentration of amino acids from tholin hydrolysis in the lower aqueous clouds of Jupiter, about 0.1 ?M, is enough to maintain small populations of terrestrial microorganisms even if the amino acids must serve as the sole carbon source.

McDonald, Gene D.; Khare, Bishun N.; Reid Thompson, W.; Sagan, Carl

1991-12-01

141

Chemical water/rock interaction under reservoir condition  

SciTech Connect

A simple model is proposed for water/rock interaction in rock fractures through which geothermal water flows. Water/rock interaction experiments were carried out at high temperature and pressure (200-350 C, 18 MPa) in order to obtain basic solubility and reaction rate data. Based on the experimental data, changes of idealized fracture apertures with time are calculated numerically. The results of the calculations show that the precipitation from water can lead to plugging of the fractures under certain conditions. Finally, the results are compared with the experimental data.

Watanabe, K.; Tanifuji, K.; Takahashi, H.; Wang, Y.; Yamasaki, N.; Nakatsuka, K.

1995-01-26

142

Adsorption of phenol and dye from aqueous solution using chemically modified date pits activated carbons  

Microsoft Academic Search

The adsorption of phenol and methylene blue (MB) on modified activated carbons has been investigated. The activated carbon was prepared from date pits by physical activation (CO2 as activating agent). Oxidation in the liquid phase with nitric acid and thermal treatment under flowing nitrogen were carried out in order to produce samples with different surface chemical properties but with no

Meriem Belhachemi; Zohra Belala; Driss Lahcene; Fatima Addoun

2009-01-01

143

Permanent physico-chemical properties of extremely diluted aqueous solutions of homeopathic medicines  

Microsoft Academic Search

The purpose of this study was to obtain information about the influence of successive dilutions and succussions on the water structure. ‘Extremely diluted solutions’ (EDS) are solutions obtained through the iteration of two processes: dilution in stages of 1:100 and succussion, typically used in homeopathic medicine. The iteration is repeated until extreme dilutions are reached, so that the chemical composition

V. Elia; S. Baiano; I. Duro; E. Napoli; M. Niccoli; L. Nonatelli

2004-01-01

144

The antioxidant activity of aqueous spinach extract: chemical identification of active fractions  

Microsoft Academic Search

In previous studies we have elucidated the presence of powerful, natural antioxidants (NAO) in water extracts of spinach leaves and demonstrated their biological activity in both in vitro and in vivo systems. In the present study, the chemical identity of several of these antioxidant components is presented. Spinach leaves were extracted with water and the 20,000 g supernatant which contained

Margalit Bergman; Lucy Varshavsky; Hugo E. Gottlieb; Shlomo Grossman

2001-01-01

145

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

146

Prediction of gas hydrate formation conditions in aqueous solutions containing electrolytes and (electrolytes + methanol)  

SciTech Connect

The prediction of gas hydrate formation conditions in solutions containing single electrolyte and mixed electrolytes and solutions containing both electrolytes and methanol has been performed using the modified Zuo-Gommesen-Guo hydrate model proposed by the authors. The results show that agreement between experimental and calculated values is satisfactory.

Liao, J.; Mei, D.H.; Yang, J.T.; Guo, T.M. [Univ. of Petroleum, Beijing (China). High-Pressure Fluid Phase Behavior and Property Research Lab.

1999-04-01

147

Effects of Carrier Gas Conditions on Concentration of Alcohol Aqueous Solution by Ultrasonic Atomization  

Microsoft Academic Search

The effects of carrier gas conditions on the concentration of ethanol by ultrasonic atomization are examined. With increasing height from vessel bottom to gas inlet and outlet, the ethanol content in the accompanied liquid increases and the flow rate of alcohol decreases. The ethanol content in the accompanied liquid becomes lower as the gas velocity becomes higher. The attachment of

Keiji Yasuda; Naofumi Tanaka; Lei Rong; Masaaki Nakamura; Li Li; Akiyoshi Oda; Yasuhito Kawase

2003-01-01

148

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

149

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

1997-03-05

150

[Physico-chemical properties of aqueous solutions, prepared in a membrane electrolyzer].  

PubMed

The physicochemical properties of aqueous solutions resulting from membrane electrolysis were studied. It was shown that the catholyte contains hydrogen peroxide at a concentration of 10(-7), which is formed during the reduction of soluble oxygen. It was found that the relaxation of the catholyte redox potential is caused by the transition of the reducing agent to the gaseous phase. The relaxation characteristics of the redox potentials of the catholyte and molecular hydrogen solution were compared. The similarity of the relaxation characteristics of the catholyte and the hydrogen solution as well as the fact that the catholyte, despite its low redox potential, does not reduce either potassium ferricyanide or 5-5'-dithiobis(2-nitrobenzoic acid) support the suggestion that the redox potential of the catholyte is due to molecular hydrogen. However, based on this suggestion, it is impossible to explain the increase in the relaxation time of the catholyte with increasing ionic strength and the fact that, as the redox potential of the catholyte decreases, the concentration of other gases dissolved in the catholyte remains unchanged. Thus, the question regarding the nature of the reducing agent remains open. PMID:15029717

Petrushanko, I Iu; Lobyshev, V I

151

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

152

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

153

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

154

Application of gas chromatography coupled to chemical ionisation mass spectrometry following headspace solid-phase microextraction for the determination of free volatile fatty acids in aqueous samples  

Microsoft Academic Search

Gas chromatography coupled to positive and negative ion chemical ionisation mass spectrometry was evaluated for the determination of free volatile fatty acids (VFAs) from aqueous samples by headspace solid-phase microextraction. Negative ion chemical ionisation in the selected ion monitoring mode using ammonia as reagent gas provided acceptable sensitivity and the highest selectivity for the determination of C2–C7 fatty acids using

M Ábalos; J. M Bayona

2000-01-01

155

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

156

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

157

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

158

Effects of Carrier Gas Conditions on Concentration of Alcohol Aqueous Solution by Ultrasonic Atomization  

NASA Astrophysics Data System (ADS)

The effects of carrier gas conditions on the concentration of ethanol by ultrasonic atomization are examined. With increasing height from vessel bottom to gas inlet and outlet, the ethanol content in the accompanied liquid increases and the flow rate of alcohol decreases. The ethanol content in the accompanied liquid becomes lower as the gas velocity becomes higher. The attachment of a demister is effective for the increase of the content in the accompanied liquid.

Yasuda, Keiji; Tanaka, Naofumi; Rong, Lei; Nakamura, Masaaki; Li, Li; Oda, Akiyoshi; Kawase, Yasuhito

2003-05-01

159

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...

160

Ion-pair solid-phase extraction and gas chromatography–mass spectrometric determination of acidic hydrolysis products of chemical warfare agents from aqueous samples  

Microsoft Academic Search

The chemical warfare agents (CWA) degrade rapidly in aqueous samples and convert to acidic degradation products. Extraction and identification of the degradation products from complex matrices using simple sample preparation and sensitive detection and identification is the most important step in the off-site analysis of samples. In this present study, we report a simple sample preparation step based on ion-pair

U. V. R. Vijaya Saradhi; S. Prabhakar; T. Jagadeshwar Reddy; M. Vairamani

2006-01-01

161

Removal of Cu2+ and Ag+ from aqueous solution on a chemically-carbonized sorbent from date palm leaflets.  

PubMed

A chemically-carbonized sorbent was prepared from date palm leaflets by sulphuric acid treatment at 170 degrees C. Carbonization took place via the dehydration effect of the hot sulphuric acid producing a carbon with reduction property. Sorption of Cu2+ and Ag+ from aqueous solution was investigated in terms of pH, contact time, metal concentration and temperature. A peculiar behaviour was found for the sorption of the two metals on the produced carbon. Sorption of Cu2+ was fast, reaching equilibrium within -2 h, whilst Ag+ sorption was slow and required -60 h to reach equilibrium. Activation energy (E(a)) for Cu2+ sorption was -16.1 kJ/mol indicating a diffusion-controlled ion exchange process; however, E(a) for Ag+ sorption was -44.3 kJ/mol indicating a chemically controlled process. Equilibrium sorption data were tested for the Langmuir and Freundlich equations. Sorption capacity appears to be much higher for Ag+ than for Cu2+ with increased uptake, for both metals, when increasing the temperature (25-45 degrees C). Ag+ was reduced to elemental silver on the sorbent surface and this was confirmed using scanning electron microscopy and x-ray powder diffraction; however, no reduction processes were involved in Cu2+ sorption. This paper discusses the sorption mechanism. PMID:23530353

El-Shafey, El-Said Ibrahim; Al-Kindy, Salma Muhammed Zahran

162

Hyphenation of sequential- and flow injection analysis with FTIR-spectroscopy for chemical analysis in aqueous solutions  

NASA Astrophysics Data System (ADS)

A survey of the principles of sequential (SIA)-and flow injection analysis (FIA) systems with FTIR spectroscopic detection is presented to introduce these hyphenations as powerful techniques for performing chemical analysis in aqueous solution. The strength of FIA/SIA-FTIR systems lies in the possibility to perform highly reproducible and automated sample manipulations such as sample clean-up and/or chemical reactions prior to spectrum acquisition. It is shown that the hyphenation of FIA/SIA systems with an FTIR spectrometer enhances the problem solving capabilities of the FTIR spectrometer as also parameters which can not be measured directly (e.g. enzyme activities) can be determined. On the other hand application of FTIR spectroscopic detection in FIA or SIA is also of advantage as it allows to shorten conventional analysis procedures (e.g. sucrose or phosphate analysis) or to establish and apply a multivariate calibration model for simultaneous determinations (e.g. glucose, fructose and sucrose analysis). In addition to these examples two recent instrumental developments in miniaturized FIA/SIA-FTIR systems, a ?-Flow through cell based on IR fiber optics and a micromachined SI-enzyme reactor are presented in this paper.

Lendl, B.; Schindler, R.; Kellner, R.

1998-06-01

163

Effects of Chemical Inhibition of N-WASP, a Critical Regulator of Actin Polymerization on Aqueous Humor Outflow through the Conventional Pathway  

PubMed Central

The integrity of actin cytoskeletal organization in aqueous humor outflow pathway is thought to play a critical role in modulation of aqueous humor outflow through the trabecular meshwork. Our understanding of the regulation of actin cytoskeletal dynamics in outflow pathway, however, is very limited. To explore the potential importance of Neural Wiskott-Aldrich syndrome protein (N-WASP), a critical regulator of actin polymerization/nucleation in aqueous humor outflow pathway, the effects of Wiskostatin, a selective pharmacological inhibitor of N-WASP, on aqueous humor outflow facility were evaluated using enucleated porcine eyes and a constant pressure perfusion system. Further, drug induced effects on actin cytoskeletal organization, cell adhesions, myosin II phosphorylation, matrix metalloproteinase (MMP) activity, and cytoskeletal protein profile in porcine trabecular meshwork (TM) cells were determined by immunofluorescence, zymography, and mass spectrometry. Aqueous humor outflow facility was increased significantly and progressively in the Wiskostatin perfused porcine eyes. The Wiskostatin perfused eyes appear to exhibit increased giant vacuoles in the inner wall of aqueous plexi and deformation of aqueous plexi. The Wiskostatin treated TM cells demonstrated extensive vacuoles in their cytosol, and both actin stress fibers and focal adhesions were decreased in a reversible manner. The drug treated TM cells also revealed decreased myosin II and actin in the cytoskeletal enriched triton insoluble fraction but did not affect myosin II phosphorylation or MMP-2 activity. These data demonstrate that the chemical inhibition of N-WASP increases aqueous humor outflow facility in association with decreased actomyosin interaction and cell adhesive interactions revealing the importance of N-WASP in homeostasis of aqueous humor outflow.

Inoue, Toshihiro; Pattabiraman, Padmanabhan P.; Epstein, David L.; Rao, P. Vasantha

2010-01-01

164

Neptunium carbonato complexes in aqueous solution: an electrochemical, spectroscopic, and quantum chemical study.  

PubMed

The electrochemical behavior and complex structure of Np carbonato complexes, which are of major concern for the geological disposal of radioactive wastes, have been investigated in aqueous Na(2)CO(3) and Na(2)CO(3)/NaOH solutions at different oxidation states by using cyclic voltammetry, X-ray absorption spectroscopy, and density functional theory calculations. The end-member complexes of penta- and hexavalent Np in 1.5 M Na(2)CO(3) with pH = 11.7 have been determined as a transdioxo neptunyl tricarbonato complex, [NpO(2)(CO(3))(3)](n-) (n = 5 for Np(V), and 4 for Np(VI)). Hence, the electrochemical reaction of the Np(V/VI) redox couple merely results in the shortening/lengthening of bond distances mainly because of the change of the cationic charge of Np, without any structural rearrangement. This explains the observed reversible-like feature on their cyclic voltammograms. In contrast, the electrochemical oxidation of Np(V) in a highly basic carbonate solution of 2.0 M Na(2)CO(3)/1.0 M NaOH (pH > 13) yielded a stable heptavalent Np complex of [Np(VII)O(4)(OH)(2)](3-), indicating that the oxidation reaction from Np(V) to Np(VII) in the carbonate solution involves a drastic structural rearrangement from the transdioxo configuration to a square-planar-tetraoxo configuration, as well as exchanging the coordinating anions from carbonate ions (CO(3)(2-)) to hydroxide ions (OH(-)). PMID:19908821

Ikeda-Ohno, Atsushi; Tsushima, Satoru; Takao, Koichiro; Rossberg, André; Funke, Harald; Scheinost, Andreas C; Bernhard, Gert; Yaita, Tsuyoshi; Hennig, Christoph

2009-12-21

165

Chemical and electrochemical considerations on the removal process of hexavalent chromium from aqueous media  

Microsoft Academic Search

Two methods were used to remove Cr(VI) from industrial wastewater. Although both are based in the same general reaction: 3Fe(II)(aq) + Cr(VI)(aq) ?; 3Fe(III)(aq) + Cr(III)(aq) the way in which the required amount of Fe(II) is added to the wastewater is different for each method. In the chemical method, Fe(II)(aq) is supplied by dissolving FeSO4 · 7(H2O)(s) into the wastewater,

C. Barrera-Díaz; M. Palomar-Pardavé; M. Romero-Romo; S. Martínez

2003-01-01

166

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

167

Chemical processing in high-pressure aqueous environments; 3: Batch reactor process development experiments for organics destruction  

SciTech Connect

A high-pressure (20 MPa) and high-temperature (350 C) liquid water processing environment was used to treat various wastewaters and model compounds. Organics were converted to methane and carbon dioxide in the presence of catalysts. Functional types included hydrocarbons, both aliphatic and aromatic; phenolics and other oxygenates; chlorinated hydrocarbon solvents; and sodium salts of organic acids. Tests with aqueous nickel ion showed negligible catalytic activity. Noncatalytic hydrolysis of sodium cyanide, carbon tetrachloride, and chloroform was also demonstrated. Ammonium destruction was proven by reaction with nitrate at these processing conditions. Several examples of test results with actual industrial waste streams showed that this process can be effectively used with catalysts to clean wastewater and recover waste organics as useful fuel gas.

Elliot, D.C.; Sealock, L.J. Jr.; Baker, E.G. (Pacific Northwest Lab., Richland, WA (United States))

1994-03-01

168

Influence of extreme thermodynamic conditions and pyrite surfaces on peptide synthesis in aqueous media.  

PubMed

Free energy landscapes and reaction mechanisms underlying the synthesis of diglycine in water were studied computationally. It was found that amino acid activation by carbonyl sulfide, leading to the formation of a cyclic alpha-amino acid N-carboxyanhydride (NCA, or Leuchs anhydride), preferentially follows an indirect pathway that involves an isocyanate intermediate. Extreme temperature and pressure conditions accelerate peptidization greatly compared to the ambient bulk water environment and are shown to favor, in general, concerted versus stepwise mechanisms. Finally, a pyrite surface, FeS2 (001), is found to lower reaction barriers further by decreasing fluctuations and by assisting the preformation of the cyclic five-membered NCA ring due to scaffolding. PMID:18254630

Schreiner, Eduard; Nair, Nisanth N; Marx, Dominik

2008-02-07

169

Removal of sparingly soluble organic chemicals from aqueous solutions with surfactant-coated ferrihydrite  

SciTech Connect

A surfactant, sodium dodecyl sulfate (SDS), was adsorbed onto ferrihydrite at low pH and desorbed at high pH. Adsorption isotherms of SDS on ferrihydrite yielded an S-shaped curve typical for surfactant adsorption on mineral surfaces. This behavior is due to the surfactant forming aggregate structures on the solid surface. SDS adsorption and desorption experiments revealed that both processes were fast, with equilibrium being reached within 1 h. Toluene, p-xylene, and trichloroethylene sorption experiments demonstrated that the SDS-coated ferrihydrite was able to remove these sparingly soluble organic chemicals (SSOCs) from solution. The amount of SSOC sorbed was directly related to the amount of SDS coating the ferrihydrite. The SSOC with the lowest solubility (p-xylene) had higher removals than the high-solubility SSOC (TCE).

Holsen, T.M.; Taylor, E.R.; Yong-Chan Seo; Anderson, P.R. (Illinois Inst. of Tech., Chicago (United States))

1991-09-01

170

Flow and morphological conditions associated with the directional solidification of aqueous ammonium chloride  

SciTech Connect

Using 27% aq. NH[sub 4]Cl solutions as transparent analog, shadowgraphy and dye injection were used to observe flow and morphology in unidirectional solidification (UDS) from below. Dendritic crystals that form at the cold surface reject lighter, solute-deficient fluid, and instability is shown by finger-type double-diffusive convection. As the mushy two-phase region grows, perturbations at the liquidus interface cause localized remelting and downward development of channels. Solsutal plumes emanate from the channels, and in time, double-diffusive convection layers also form in the melt. When the solution is chilled at the sides as well as at the bottom, conditions are influenced by detachment and settling of crystals from the sidewall and by plumes from slanted channels. When a slow, oscillatory rocking motion is imposed on UDS, the freckle-type segregates in the final cast is suppressed. Within the melt, plumes and double-diffusive convection are eliminated. Inertially induced convection mixes the melt and produces a dense slurry. Although channels are eliminated from the bottom mushy region, overall heat transfer and macrosegregation in the cavity are unaffected by the slow rocking. Numerical simulations qualitatively predict trends in the field variables and provide insights on interdendritic flows and macrosegregation (freckle-, A-type segregates), although its quantitative predictions are hampered by simplifying assumptions.

Magirl, C.S.; Incropera, F.P.

1993-01-01

171

Flow and morphological conditions associated with the directional solidification of aqueous ammonium chloride. Annual performance report  

SciTech Connect

Using 27% aq. NH{sub 4}Cl solutions as transparent analog, shadowgraphy and dye injection were used to observe flow and morphology in unidirectional solidification (UDS) from below. Dendritic crystals that form at the cold surface reject lighter, solute-deficient fluid, and instability is shown by finger-type double-diffusive convection. As the mushy two-phase region grows, perturbations at the liquidus interface cause localized remelting and downward development of channels. Solsutal plumes emanate from the channels, and in time, double-diffusive convection layers also form in the melt. When the solution is chilled at the sides as well as at the bottom, conditions are influenced by detachment and settling of crystals from the sidewall and by plumes from slanted channels. When a slow, oscillatory rocking motion is imposed on UDS, the freckle-type segregates in the final cast is suppressed. Within the melt, plumes and double-diffusive convection are eliminated. Inertially induced convection mixes the melt and produces a dense slurry. Although channels are eliminated from the bottom mushy region, overall heat transfer and macrosegregation in the cavity are unaffected by the slow rocking. Numerical simulations qualitatively predict trends in the field variables and provide insights on interdendritic flows and macrosegregation (freckle-, A-type segregates), although its quantitative predictions are hampered by simplifying assumptions.

Magirl, C.S.; Incropera, F.P.

1993-01-01

172

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

2013-05-14

173

The influence of pH and temperature on the aqueous geochemistry of neodymium in near surface conditions.  

PubMed

Geochemical calculations were employed for the solubility and speciation of neodymium in a model soil solution as a function of pH. The calculations were based on the recently determined stability constants for Nd and solubility product for the Nd end-member of mineral monazite (NdPO(4)). Simulations were carried out at near neutral pH (pH 6.0 to pH 7.5) and 25 degrees C at the atmospheric CO(2) partial pressure. Additional calculations were also performed to assess Nd mobility at the extreme temperature conditions (300 degrees C) at neutral pH. Our results suggest that relatively dilute (Ionic Strength, I = 0.1), low-temperature waters may transport very small quantities of rare earth elements and actinides to the surficial environment at near neutral pH conditions. Evidently, higher temperature or extreme fluid composition may have a greater potential for mobilization of these elements. The results are pertinent to researchers interested in engineering applications for the precipitation of Nd and surrogate actinides from aqueous nuclear wastes. PMID:18463986

Cetiner, Ziya S

2008-05-08

174

Phytoplankton spring bloom in the Tagus coastal waters: hydrological and chemical conditions  

Microsoft Academic Search

Spatial variability of phytoplankton as well as hydrological and chemical conditions in the Tagus coastal waters were studied during the spring of 1994. The highly patchy distribution of phytoplankton and the community structure were related to the specific abiotic conditions prevailing in the area. Two main water masses were distinguished: a tidally mixed one alongshore Lisbon-cape Espichel and a stratified

L. Cabeçadas; M. J. Brogueira; G. Cabeçadas

1999-01-01

175

Radiation chemical experiments relevant to studies of cometary nuclei: remarks on working conditions.  

PubMed

We survey some obstacles that a chemist encounters in defining conditions for radiation chemical experiments relevant to cometary nuclei. The choice of working conditions is examined in the light to present knowledge about comets and the facilities available for routine work in radiation chemistry. PMID:11537764

Draganic, I G; Draganic, Z D

1984-01-01

176

Regimes of chemical reaction waves initiated by nonuniform initial conditions for detailed chemical reaction models  

NASA Astrophysics Data System (ADS)

Regimes of chemical reaction wave propagation initiated by initial temperature nonuniformity in gaseous mixtures, whose chemistry is governed by chain-branching kinetics, are studied using a multispecies transport model and a detailed chemical model. Possible regimes of reaction wave propagation are identified for stoichiometric hydrogen-oxygen and hydrogen-air mixtures in a wide range of initial pressures and temperature levels, depending on the initial non-uniformity steepness. The limits of the regimes of reaction wave propagation depend upon the values of the spontaneous wave speed and the characteristic velocities of the problem. It is shown that one-step kinetics cannot reproduce either quantitative neither qualitative features of the ignition process in real gaseous mixtures because the difference between the induction time and the time when the exothermic reaction begins significantly affects the ignition, evolution, and coupling of the spontaneous reaction wave and the pressure wave, especially at lower temperatures. We show that all the regimes initiated by the temperature gradient occur for much shallower temperature gradients than predicted by a one-step model. The difference is very large for lower initial pressures and for slowly reacting mixtures. In this way the paper provides an answer to questions, important in practice, about the ignition energy, its distribution, and the scale of the initial nonuniformity required for ignition in one or another regime of combustion wave propagation.

Liberman, M. A.; Kiverin, A. D.; Ivanov, M. F.

2012-05-01

177

Chemical properties of positive singly charged astatine ion in aqueous solution  

Microsoft Academic Search

The mobility of oxidized astatine in solutions H(Na)ClO4 (=0.4 M) – 1·10–4M K2Cr2O7 has been measured at 25°C in the interval 0.63pH1.68. Under these conditions astatine migrates to the cathode only. The speed of the migration depends upon the concentration of hydrogen ions in solution: pH 1.68 Uc = 1.17 · 10-4 cm2 V-1 s-1 pH 0.63 Uc = 2.67

M. Milanov; V. Doberenz; V. A. Khalkin; A. Marinov

1984-01-01

178

An integrated approach to optimize the conditioning chemicals for enhanced sludge conditioning in a pilot-scale sludge dewatering process.  

PubMed

An integrated approach incorporating response surface methodology (RSM), grey relational analysis, and fuzzy logic analysis was developed to quantitatively evaluate the conditioning chemicals in sludge dewatering process. The polyacrylamide (PAM), ferric chloride (FeCl(3)) and calcium-based mineral powders were combined to be used as the sludge conditioners in a pilot-scale sludge dewatering process. The performance of conditioners at varied dosages was comprehensively evaluated by taking into consideration the sludge dewatering efficiency and chemical cost of conditioner. In the evaluation procedure, RSM was employed to design the experiment and to optimize the dosage of each conditioner. The grey-fuzzy logic was established to quantify the conditioning performance on the basis of grey relational coefficient generation, membership function construction, and fuzzy rule description. Based on the evaluation results, the optimal chemical composition for conditioning was determined as PAM at 4.62 g/kg DS, FeCl(3) at 55.4 g/kg DS, and mineral powders at 30.0 g/kg DS. PMID:22858481

Zhai, Lin-Feng; Sun, Min; Song, Wei; Wang, Gan

2012-07-05

179

Effect of O3 and Aqueous Ammonia on Crystallization of MgO Thin Film Grown by Mist Chemical Vapor Deposition  

NASA Astrophysics Data System (ADS)

Mist chemical vapor deposition (CVD) has been applied to fabricate MgO thin films under atmospheric pressure. In this work, to fabricate highly crystalline MgO thin films at low temperature, the effects of ozone gas (O3), aqueous ammonia (NH3), and a combination of O3 and NH3 on the crystallization temperature were studied by comparing samples grown under a standard condition of inactive gas such as argon (Ar). It was clarified that the crystallization temperature was decreased from 450 to 400 °C by the assistance of O3 and the crystallinity was improved by the addition of NH3. The growth of higher crystallinity MgO thin films at temperatures above 400 °C was possible by the combination of O3 and NH3, which caused stronger enhancement of the crystallization temperature and crystallinity. The causes of these effects were analyzed thermodynamically, and it was clarified that the results were due to the activated oxygen sources and the stability level of precursor materials in the solution.

Kawaharamura, Toshiyuki; Mori, Kazuharu; Orita, Hiroyuki; Shirahata, Takahiro; Fujita, Shizuo; Hirao, Takashi

2013-03-01

180

A phantom study on bladder and rectum dose measurements in brachytherapy of cervix cancer using FBX aqueous chemical dosimeter.  

PubMed

The ferrous sulphate-benzoic acid-xylenol orange (FBX) chemical dosimeter, due to its aqueous form can measure average volume doses and hence may overcome the limitations of point dosimetry. The present study was undertaken to validate the use of FBX dosimeter for rectum and bladder dose measurement during intracavitary brachytherapy (ICBT) and transperineal interstitial brachytherapy (TIB). We filled cylindrical polypropylene tubes (PT) and Foley balloons (FB) with FBX solution and used them as substitutes for rectum and bladder dose measurements respectively. A water phantom was fabricated with provision to place the Fletcher-type ICBT and MUPIT template applicators, and FBX filled PT and FB within the phantom. The phantom was then CT scanned for treatment planning and subsequent irradiation. Our results show that the average difference between DVH derived dose value and FBX measured dose is 3.5% (PT) and 13.7% (FB) for ICBT, and 9% (PT) and 9.9% (FB) for TIB. We believe that the FBX system should be able to provide accuracy and precision sufficient for routine quality assurance purposes. The advantage of the FBX system is its water equivalent composition, average volume dose measuring capability, and energy and temperature independent response as compared to TLD or semiconductor dosimeters. However, detailed studies will be needed with regards to its safety before actual in-vivo dose measurements are possible with the FBX dosimeter. PMID:22687710

Bansal, Anil K; Semwal, Manoj K; Arora, Deepak; Sharma, D N; Julka, P K; Rath, G K

2012-06-09

181

Passivation of Zn{sub 3}P{sub 2} substrates by aqueous chemical etching and air oxidation  

SciTech Connect

Surface recombination velocities measured by time-resolved photoluminescence and compositions of Zn{sub 3}P{sub 2} surfaces measured by x-ray photoelectron spectroscopy (XPS) have been correlated for a series of wet chemical etches of Zn{sub 3}P{sub 2} substrates. Zn{sub 3}P{sub 2} substrates that were etched with Br{sub 2} in methanol exhibited surface recombination velocity values of 2.8 Multiplication-Sign 10{sup 4} cm s{sup -1}, whereas substrates that were further treated by aqueous HF-H{sub 2}O{sub 2} exhibited surface recombination velocity values of 1.0 Multiplication-Sign 10{sup 4} cm s{sup -1}. Zn{sub 3}P{sub 2} substrates that were etched with Br{sub 2} in methanol and exposed to air for 1 week exhibited surface recombination velocity values of 1.8 Multiplication-Sign 10{sup 3} cm s{sup -1}, as well as improved ideality in metal/insulator/semiconductor devices.

Kimball, Gregory M.; Bosco, Jeffrey P.; Mueller, Astrid M.; Tajdar, Syed F.; Brunschwig, Bruce S.; Atwater, Harry A.; Lewis, Nathan S. [Noyes Laboratory, Watson Laboratory, and Beckman Institute, California Institute of Technology, Pasadena, California 91125 (United States)

2012-11-15

182

Particulate erosion–corrosion of Al in aqueous conditions: some perspectives on pH effects on the erosion–corrosion map  

Microsoft Academic Search

In the nomenclature to describe erosion–corrosion behaviour in aqueous conditions, there has been considerable confusion in relation to the terminology used to describe the various interactions. One such description has been to separate the effects into two main divisions, the effects (”synergistic”) of corrosion on the erosion rate (i.e. the change in mechanical response of the material due to corrosion)

M. M. Stack; N. Pungwiwat

2002-01-01

183

Influence of Variable Environmental Conditions on Presence and Concentration of Energetic Chemicals Near Soil Surface in the Vadoze Zone  

NASA Astrophysics Data System (ADS)

Many explosive-related compounds (ERCs) are found near the soil-atmospheric surface in sites containing buried explosive devices, such as landmines and unexploded ordnance, detonation-residual, and munitions residues from explosive manufacturing facilities. Accurate assessment of the fate and transport processes is essential for predicting their movement to the surface, groundwater, or any other important environmental compartment. The transport processes controlling the direction and magnitude of the movement, and chemical and physical processes controlling the fate of the chemicals vary with environmental conditions. This research addresses the effect of variable rainfall, evaporation, temperature, and solar radiation on fate and transport of 2,4,6-Trinitrotoluene (TNT), 2,4-Dinitrotoluene (DNT), and other related chemicals in partially saturated soil. Experiments have been conducted in a laboratory-scale 3D SoilBed placed inside an environmental chamber equipped with rainfall and solar radiation simulators, and temperature control settings. The SoilBed was packed with a sandy soil. Experiments have been conducted by burying a TNT/DNT source, simulating a landmine, and applying different rainfall and light radiation cycles while monitoring DNT, TNT, and other related ERCs solute concentrations temporally and spatially within the SoilBed. Experiments include different source characteristics, rainfall intensities, temperatures, and radiation cycles to evaluate their effect on the detection and movement of ERC in soils in both aqueous and vapor phases. Temporal and spatial data has been analyzed comparatively and quantitatively. Comparative analysis was developed using surfer®- and voxler®-generated images and 3D visualization models applying spatial interpolation and masking methods. Single and multi-variable statistical analysis has been employed to determine the most important factors affecting the fate, transport and detection of ERC near soil-atmospheric surfaces. Results show that rainfall, radiation, and temperature variations influence the presence, transport, and concentrations of TNT and DNT near the soil surface. Higher concentrations are observed near the end of rainfall events, both in the aqueous and gaseous phases. Higher rainfall intensity results in higher presence and concentrations. Lower TNT and DNT concentrations than their solubility limit indicate rate-limited mass transfer, dissolution limitations, and dilution processes. Radiation events and higher atmospheric temperatures result in greater presence and concentrations of DNT and TNT, indicating influence of these factors on fate and transport processes. TNT degradation by-products measured mostly in the upper segments of the SoilBed, suggest degradation processes resulting from radiation-induced conditions near the soil-atmospheric surface. Although the ERC source consists of equal mass of TNT and DNT, greater detection density and concentrations are observed for DNT. A generalized linear mixed statistical model has been applied to quantify the effect of environmental conditions on ERC detection and concentrations. The statistical analysis indicates that rainfall events and related water contents are the most influential factors affecting the presence and concentrations of ERCs in the aqueous and gaseous phase. Solar radiation, and related heat flux, is the second most influential parameter. Although atmospheric temperature influence the presence and concentration of ERCs in soils, it is the least influential parameter.

Anaya, A. A.; Padilla, I. Y.

2008-12-01

184

Effect of chemical conditioning on the triboelectrification of coal and mineral particles  

Microsoft Academic Search

Chemical conditioning was used to modify the triboelectrification of coal and mineral particles. The chemicals tested included starch, lignin, kerosene, ethanol, acetic acid, salicylic acid, sodium oleate, Sodium Hexametaphosphate (SH), sodium silicate, Sodium Dodecylbenzenesulfonate (SDBS), Sodium Bicarbonate (SB) and ammonia. A high-speed, dry mixing method was employed. The charge-to-mass ratio of the coal and mineral samples, both untreated and treated,

Haifeng WANG; Qingru CHEN; Xinxi ZHANG; Zhihai TAN; Shuai WANG; Nianxin ZHOU

2010-01-01

185

Chemical and physical reservoir parameters at initial conditions in Berlingeothermal field, El Salvador: a first assessment  

Microsoft Academic Search

A study has been madeto obtain the main chemical and physical reservoir conditions of the Berlin field (El Salvador)before the commencement of large-scale exploitation of the geothermal resource The upflowzone and the main flow path within the geothermal system have been determined from the arealdistribution of chemical parameters such as Cl concentrations ratios such as Na\\/KK\\/Mg,K\\/Ca,and temperatures computed from silica

Franco Damore; Jose Tenorio Mejia

1999-01-01

186

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

PubMed

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. PMID:15573498

Weber, Arthur L

2004-10-01

187

The selective peptide reactivity of chemical respiratory allergens under competitive and non-competitive conditions.  

PubMed

It is well established that certain chemicals cause respiratory allergy. In common with contact allergens, chemicals that induce sensitization of the respiratory tract must form stable associations with host proteins to elicit an immune response. Measurement of the reactivity of chemical allergens to single nucleophilic peptides is increasingly well-described, and standardized assays have been developed for use in hazard assessment. This study employed standard and modified peptide reactivity assays to investigate the selectivity of chemical respiratory allergens for individual amino acids under competitive and non-competitive conditions. The reactivity of 20 known chemical respiratory sensitizers (including diisocyanates, anhydrides, and reactive dyes) were evaluated for reactivity towards individual peptides containing cysteine, lysine, histidine, arginine, or tyrosine. Respiratory allergens exhibited the common ability to deplete both lysine and cysteine peptides; however, reactivity for histidine, arginine, and tyrosine varied between chemicals, indicating differences in relative binding affinity toward each nucleophile. To evaluate amino acid selectivity for cysteine and lysine under competitive conditions a modified assay was used in which reaction mixtures contained different relative concentrations of the target peptides. Under these reaction conditions, the binding preferences of reference respiratory and contact allergens (dinitrochlorobenzene, dinitrofluorobenzene) were evaluated. Discrete patterns of reactivity were observed showing various levels of competitive selectivity between the two allergen classes. PMID:23050863

Lalko, Jon F; Kimber, Ian; Dearman, Rebecca J; Api, Anne Marie; Gerberick, G Frank

2012-10-10

188

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

189

CHEMICAL TRANSFORMATIONS IN ACID RAIN. VOLUME 2. INVESTIGATION OF KINETICS AND MECHANISM OF AQUEOUS-PHASE PEROXIDE FORMATION  

EPA Science Inventory

The aqueous-phase reactions of O3 with a number of species have been studied in an effort to identify pathways leading to the production of hydrogen peroxide in solution. The aqueous-phase systems studied included the decomposition of O3 in pure water and the interaction of O3 wi...

190

Liquid-phase chemical hydrogen storage: catalytic hydrogen generation under ambient conditions.  

PubMed

There is a demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. Lithium and sodium borohydride, ammonia borane, hydrazine, and formic acid have been extensively investigated as promising hydrogen storage materials based on their relatively high hydrogen content. Significant advances, such as hydrogen generation temperatures and reaction kinetics, have been made in the catalytic hydrolysis of aqueous lithium and sodium borohydride and ammonia borane as well as in the catalytic decomposition of hydrous hydrazine and formic acid. In this Minireview we briefly survey the research progresses in catalytic hydrogen generation from these liquid-phase chemical hydrogen storage materials. PMID:20379965

Jiang, Hai-Long; Singh, Sanjay Kumar; Yan, Jun-Min; Zhang, Xin-Bo; Xu, Qiang

2010-05-25

191

Development and validation of a non-aqueous reversed-phase high-performance liquid chromatographic method for the determination of four chemical UV filters in suncare formulations  

Microsoft Academic Search

A non-aqueous reversed-phase high performance liquid chromatographic method (RP–HPLC) with UV detection at 313nm was developed and validated for simultaneous determination of methylene bis-benzotriazolyl tetramethylphenol (Tinosorb M) along with three other chemical UV filters, octocrylene (Eusolex OCR), octyl methoxycinnamate (Eusolex 2292) and octyl salicylate (Eusolex OS) in suncare products. An isocratic elution was performed on a Hypersil BDS RP-C18 column

C. G Smyrniotakis; Helen A Archontaki

2004-01-01

192

Soft magnetic Co–Fe–B–P and Co–Fe–V–B–P amorphous alloy nano-particles prepared by aqueous chemical reduction  

Microsoft Academic Search

Nano-sized amorphous alloy particles with excellent soft magnetic properties have been prepared in Co–Fe–B–P and Co–Fe–V–B–P alloy systems by using a chemical alloying process. In this process, Co, Fe and V ions were reduced by KBH4 and NaH2PO2 in an aqueous solution. The precipitated metal atoms (or atomic clusters) as well as the B and P atoms, which from KBH4

Ming Wen; Manfu Zhong; Kejia E; Jieda Wu; Lujiang Li; Haiquan Qi; Shixun Cao; Tao Zhang

2006-01-01

193

Preparation and characterization of activated carbon from Amygdalus Scoparia shell by chemical activation and its application for removal of lead from aqueous solutions  

Microsoft Academic Search

Two series of activated carbon have been prepared by chemical activation of Amygdalus Scoparia shell with phosphoric acid or zinc chloride for the removal of Pb(II) ions from aqueous solutions. Several methods were employed\\u000a to characterize the active carbon produced. The surface area was calculated using the standard Brunauer-Emmet-Teller method.\\u000a The microstructures of the resultant activated carbon were observed by

Sayed Z. Mohammadi; Mohammad A. Karimi; Daryoush Afzali; Fatemeh Mansouri

2010-01-01

194

The use of chemically modified and unmodified cassava waste for the removal of Cd, Cu and Zn ions from aqueous solution  

Microsoft Academic Search

The use of different chemically modified cassava waste biomass for the enhancement of the adsorption of three metal ions Cd, Cu and Zn from aqueous solution is reported in this paper. Treating with different concentrations of thioglycollic acid modified the cassava waste biomass.The sorption rates of the three metals were 0.2303 min?1 (Cd2+), 0.0051 min?1 (Cu2+), 0.0040 min?1 (Zn2+) and

A. A. Abia; M. Horsfall; O. Didi

2003-01-01

195

Chemical geothermometry and geobarometry in hydrothermal aqueous solutions: A theoretical investigation based on a mineral-solution equilibrium model  

SciTech Connect

The theoretical compositions of an aqueous solution in equilibrium with a mineral assemblage made up of low-albite, K-feldspar, either a Ca-Al-silicate or calcite, clinochlore, muscovite, quartz, anhydrite, and fluorite, under varying T-P{sub CO{sub 2}}-m{sub Cl} conditions of geothermal interest, indicate that (1) the total SO{sub 4} content as well as the Na/K,K{sup 2}/Mg, and SO{sub 4}/F{sup 2} ratios are potential geothermometers; (2) the total HCO{sub 3} content as well as the K{sup 2}/Ca,Ca/Mg, HCO{sub 3}/F, and (HCO{sub 3}){sup 2}/SO{sub 4} ratios are potential P{sub CO{sub 2}} indicators; (3) the Na, K, Ca, and Mg total contents as well as the Na{sup 2}/Mg and Na{sup 2}/Ca ratios are mainly controlled by the total ionic salinity and are therefore hardly suitable as geoindicators. A preliminary test of the equations involving total HCO{sub 3} content as well a K{sup 2}/Ca and HCO{sub 3}/F ratios as P{sub CO{sub 2}} indicators have provided satisfactory results.

Chiodini, G. (Univ. di Perugia (Italy)); Cioni, R. (Ist. di Geocronologia, Pisa (Italy)); Guidi, M.; Marini, L. (Geotermica Italiana srl, Pisa (Italy))

1991-10-01

196

Characterization of chemically modified corncobs and its application in the removal of metal ions from aqueous solution.  

PubMed

The objective of this work was to convert corncobs to activated carbon by low temperature chemical treatment for removing copper from wastewater. The parameters for developing a new adsorbent i.e. sorption capacity, selectivity, regenerability, suspension test, and kinetics were investigated. All studies were performed in batch experiments. Removal of copper from aqueous solutions varied with the amount of adsorbent, metal ion concentration, agitation time, solution pH and the species of copper present. It was found that the effect of temperature was very small. The Langmuir model was found to best fit the equilibrium isotherm data. Kinetics of copper removal at two different temperatures obeyed Lagergren pseudo-first-order equation. Effect of water hardness, other cations (Pb(2+) and Zn(2+)) on copper removal was also studied. Experiments with anionic and cationic complexes of copper showed that anionic copper species are not removed at all by the prepared material. To observe the nature of surface and pore structure scanning electron microscope (SEM) images of modified corncobs were used. To study the interaction forces between the adsorbent and the metal ion functional group analysis with infrared spectroscopy and proximate analysis were carried out. In addition, recovery of the metals ion and regeneration of spent adsorbent was possible by acidified hydrogen peroxide. Since the uptake capacity of the prepared adsorbent is 26mg Cu/g for copper, it can be a potential adsorbent for removing and recovering other heavy metal ions from contaminated wastewaters. The sorption capacity of the treated corncobs for copper was better than the reported capacity of other activated carbons prepared from agricultural sources. PMID:16911857

Nasiruddin Khan, M; Farooq Wahab, M

2006-07-03

197

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

198

Structure of Regenerated Cellulose Films from Cellulose\\/Aqueous NaOH Solution as a Function of Coagulation Conditions  

Microsoft Academic Search

The structure of regenerated cellulose films from cellulose\\/aqueous sodium hydroxide solution, prepared by coagulation of aqueous sulfuric acid, was investigated by X-ray diffraction and viscoelastic measurements. The X-ray crystallinity Xc and apparent crystal size decreased monotonically with increasing sulfuric acid concentration Csa and an abrupt decrease was seen at Csa?60 wt %. In the viscoelastic measurements, four kinds of dynamic

Guang Yang; Hitomi Miyamoto; Chihiro Yamane; Kunihiko Okajima

2007-01-01

199

Aqueous solution-chemical derived NiAl2O3 solar selective absorbing coatings. 2. Wetting agents and spreading of aqueous solutions on aluminum substrate  

NASA Astrophysics Data System (ADS)

Wettability of aluminum substrate by the aqueous solutions containing ethoxylated alcohol nonionic surfactants C12En- or Triton X-series was studied using dynamic contact angle measurements. The efficiency of wetting was found to strongly depend on the length of polyoxyethylene (POE) chain of C12En- or Triton X surfactants. For C12E4 that has a very short POE chain, it hardly made the aqueous solution spreading over aluminum. The others with a long POE chain were indeed very efficient in promoting the solution spreading. Moreover, all the spreading process could be completed within 10 s. The single-layer NiAl2O3 coatings were fabricated from the precursor solutions containing C12En- or Triton X surfactants and the reflectance spectra were measured by a UV/vis spectrophotometer equipped with an integrating sphere. The results indicated that the precursor solution with a long POE chain surfactant as wetting agent favored to fabricate a uniform film on the aluminum substrate and therefore to get a high solar absorptance.

Li, Zhenxiang; Zhao, Jianxi

2013-03-01

200

Preliminary investigation of the supply of chemical species to an aqueous solution using a hydrogen-oxygen flame.  

PubMed

A new method of supplying radical species to aqueous solutions using a hydrogen-oxygen flame is investigated. When a hydrogen-oxygen flame is directed on the surface of an aqueous solution, hydroxyl radicals (*OH) produced in the flame are extracted into the aqueous phase. The presence of *OH in the aqueous solution was confirmed by electron paramagnetic resonance with spin trapping using 5,5-dimethyl-1-pyrroline-N-oxide. The extraction of *OH into the aqueous solution was monitored using a quantitative analysis of hydrogen peroxide (H2O2). The effects of the hydrogen and oxygen gas flow rates, hydrogen/oxygen ratio, and atmosphere on H2O2 formation were studied. When the hydrogen-oxygen flame blew on a phosphate buffer solution (pH 6.7) under an Ar atmosphere, the concentration of H2O2 increased with the blowing time of the flame and the flow rate of hydrogen gas. Under air, nitrate and nitrite ions were formed in the aqueous phase in addition to H2O2, and the H2O2 concentration was lower than that under argon. The application of this new method to an aqueous solution of Cu(II)-ethylenediaminetetraacetic acid (EDTA) caused a remarkable decrease in the concentration of Cu(II)-EDTA and total organic carbon. PMID:16124325

Uchida, Miho; Sogabe, Takahiro; Ikoma, Tadaaki; Okuwakit, Akitsugu

2005-08-01

201

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 (DF) 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 DF 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, DF, floc size. PMID:23886852

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

2013-07-05

202

Chemical Modifications in Therapeutic Protein Aggregates Generated under Different Stress Conditions  

PubMed Central

In this study, we characterized the chemical modifications in the monoclonal antibody (IgG2) aggregates generated under various conditions, including mechanical, chemical, and thermal stress treatment, to provide insight into the mechanism of protein aggregation and the types of aggregate produced by the different stresses. In a separate study, additional biophysical characterization was performed to arrange these aggregates into a classification system (Joubert, M. K., Luo, Q., Nashed-Samuel, Y., Wypych, J., and Narhi, L. O. (2011) J. Biol. Chem. 286, 25118–25133). Here, we report that different aggregates possessed different types and levels of chemical modification. For chemically treated samples, metal-catalyzed oxidation using copper showed site-specific oxidation of Met246, His304, and His427 in the Fc portion of the antibody, which might be attributed to a putative copper-binding site. For the hydrogen peroxide-treated sample, in contrast, four solvent-exposed Met residues in the Fc portion were completely oxidized. Met and/or Trp oxidation was observed in the mechanically stressed samples, which is in agreement with the proposed model of protein interaction at the air-liquid interface. Heat treatment resulted in significant deamidation but almost no oxidation, which is consistent with thermally induced aggregates being generated by a different pathway, primarily by perturbing conformational stability. These results demonstrate that chemical modifications are present in protein aggregates; furthermore, the type, locations, and severity of the modifications depend on the specific conditions that generated the aggregates.

Luo, Quanzhou; Joubert, Marisa K.; Stevenson, Riki; Ketchem, Randal R.; Narhi, Linda O.; Wypych, Jette

2011-01-01

203

Establishing physico-chemical reference conditions in Mediterranean streams according to the European Water Framework Directive.  

PubMed

Type-specific physico-chemical reference conditions are required for the assessment of ecological status in the Water Framework Directive context, similarly to the biological and hydro-morphological elements. This directive emphasises that natural variability of quality elements in high status (reference condition) needs to be quantified. Mediterranean streams often present a marked seasonal pattern in hydrological, biological and geochemical processes which could affect physico-chemical reference conditions. This study establishes general physico-chemical reference conditions (oxygenation, nutrient, salinity and acidification conditions) for different Mediterranean stream types. 116 potential reference sites located in 23 Mediterranean catchments in Spain were sampled in spring, summer and autumn in 2003. All sites were subjected to a screening method for the selection of reference sites in Mediterranean streams (Mediterranean Reference Criteria) and classified using a pre-established stream typology that establishes five different stream types (temporary streams, evaporite-calcareous at medium altitude, siliceous headwaters, calcareous headwaters and large watercourses). Reference conditions (reference value and reference threshold equivalents to high-good class boundary) were calculated using two different methods according to the availability of reference sites: the reference site 75th percentile approach of all reference sites and the 25th percentile of the population approach. The majority of the studied potential reference sites (76 out of 116) were selected as reference sites. Regarding type-specific reference conditions, only siliceous headwaters could be considered different from the rest of stream types because lower conductivity and pH. All reference stream types presented seasonal differences as regards some parameters, except for temporary streams due to the high natural variation of this stream type. For those parameters which presented seasonal differences in a specific stream type, the least restrictive values were proposed as reference conditions. PMID:22386888

Sánchez-Montoya, María del Mar; Arce, Maria Isabel; Vidal-Abarca, María Rosario; Suárez, María Luisa; Prat, Narcís; Gómez, Rosa

2012-02-06

204

QUANTITATIVE ANALYSIS OF AQUEOUS SPECIES USING RAMAN SPECTROMETRY AND EQUILIBRIUM MODEL CALCULATIONS  

EPA Science Inventory

An analytical approach of quantifying various chemical species, using Raman spectrometry in conjunction with equilibrium modeling, has been tested on aqueous solutions containing Nd, Cu, and dipicolinic acid. Equilibrium modeling was used to select optimum conditions in simple so...

205

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

206

Modeling the kinetics of microbial degradation of deicing chemicals in porous media under flow conditions.  

PubMed

A quantitative knowledge of the fate of deicing chemicals in the subsurface can be provided by joint analysis of lab experiments with numerical simulation models. In the present study, published experimental data of microbial degradation of the deicing chemical propylene glycol (PG) under flow conditions in soil columns were simulated inversely to receive the parameters of degradation. We evaluated different scenarios of an advection-dispersion model including different terms for degradation, such as zero order, first order and inclusion of a growing and decaying biomass for their ability to explain the data. The general break-through behavior of propylene glycol in soil columns can be simulated well using a coupled model of solute transport and degradation with growth and decay of biomass. The susceptibility of the model to non-unique solutions was investigated using systematical forward and inverse simulations. We found that the model tends to equifinal solutions under certain conditions. PMID:22609860

Wehrer, Markus; Jaesche, Philipp; Totsche, Kai Uwe

2012-05-17

207

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

208

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

209

Kinematical Modeling of Pad Profile Variation during Conditioning in Chemical Mechanical Polishing  

NASA Astrophysics Data System (ADS)

Conditioning is the process of removing the glazing area from a polishing pad surface and restoring the quality of the surface to maintain a stable polishing performance. However, the conditioning process can induce a non-uniform profile variation of the pad, which can result in nonuniform material removal rates across the wafer. In this paper, a kinematical model based on Preston’s equation is proposed to examine the pad profile variation (PPV) induced by swing arm conditioning with a diamond disk. The proposed model was simulated with various swing arm velocity profiles (SAVPs), and the results were compared with experimental results. The results showed the relationship between kinematical parameters and the PPV. The PPV was proportional to sliding distance based on the kinematical model, and then the sliding distance distribution across the pad was dependent on the SAVP. This study has proven the effectiveness of the kinematical model on the PPV during conditioning in chemical mechanical polishing (CMP).

Lee, Sangjik; Jeong, Sukhoon; Park, Kihyun; Kim, Hyoungjae; Jeong, Haedo

2009-12-01

210

Nitrosation of nigerian medicinal plant preparations under ‘chemical’ and ‘simulated’ gastric conditions  

Microsoft Academic Search

Preparations of some tropical plants of medicinal importance, collected from the savannah vegetational belt of Nigeria, were nitrosated and analysed for volatile N-nitrosamines formed under chemical and simulated gastric conditions. N-Nitrosamines were determined on a Thermal Energy Analyser following gas chromatographic separation. Mean concentrations of N-nitrosodimethylamine (NDMA) in the range of 7 to 58 ppb and N-nitrosodiethylamine (NDEA) in the

S. E. Atawodi; A. G. Lamorde; B. Spiegelhalder; R. Preussmann

1995-01-01

211

Defining ecological and chemical reference conditions and restoration targets for nine European lakes  

Microsoft Academic Search

This paper aims to determine the ecological and chemical reference conditions (~1800–1850 AD) and degree of floristic change\\u000a at nine enriched lakes, covering a range of types across Europe, using fossil diatom assemblages in dated sediment cores and\\u000a application of total phosphorus (TP) transfer functions. Additionally the study assesses the potential of analogue matching\\u000a as a technique for identifying reference

Helen BennionGavin; Gavin L. Simpson; N. John Anderson; Gina Clarke; Xuhui Dong; Anders Hobæk; Piero Guilizzoni; Aldo Marchetto; Carl D. Sayer; Hansjörg Thies; Monica Tolotti

2011-01-01

212

Natural gas autoignition under diesel conditions. Experiments and chemical kinetic modeling  

Microsoft Academic Search

The effects of ambient gas thermodynamic state and fuel composition on the autoignition of natural gas under direct-injection diesel conditions were studied experimentally in a constant-volume combustion vessel and computationally using a detailed chemical kinetic model. Natural gas compositions representative of variations observed across the U.S. were considered. These results extend previous observations to more realistic natural gas compositions and

J. D. Naber; D. L. Siebers; C. K. Westbrook; J. A. Caton; S. S. Di Julio

1994-01-01

213

Analysis of initial reactions of MALDI based on chemical properties of matrixes and excitation condition.  

PubMed

This investigation concerns the initial chemical reactions that affect the ionization of matrixes in matrix-assisted laser desorption/ionization (MALDI). The study focuses on the relaxations of photon energy that occur on a comparable time scale to that of ionization, in which the available laser energy is shared and the ionization condition is changed. The relaxations include fluorescence, fragmentation, and nonradiative relaxation from the excited state to the ground state. With high absorption cross section and long excited-state lifetime, photoionization of matrix plays an important role if sufficient laser energy is used. Under other conditions, thermal ionization of the molecule in the ground state is predicted to be one of the important reactions. Evidence of change in the branching ratio of initial reactions with the matrix and the excitation wavelength was obtained with ?-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, and 2,4,6-trihydroxyacetophenone. These matrixes are studied by obtaining their mixed crystal absorption spectra, fluorescence properties, laser-induced infrared emission, and product ions. The exact ionization pathway depends on the chemical properties of matrixes and the excitation conditions. This concept may explain the diversity of experimental results observed in MALDI experiments, which provides an insight into the ensemble of chemical reactions that govern the generation of ions. PMID:22799495

Lai, Yin-Hung; Wang, Chia-Chen; Chen, Chiu Wen; Liu, Bo-Hong; Lin, Sheng Hsien; Lee, Yuan Tseh; Wang, Yi-Sheng

2012-08-01

214

A stronger necessary condition for the multistationarity of chemical reaction networks.  

PubMed

Biochemical reaction networks grow bigger and bigger, fed by the high-throughput data provided by biologists and bred in open repositories of models allowing merging and evolution. Nevertheless, since the available data is still very far from permitting the identification of the increasing number of kinetic parameters of such models, the necessity of structural analyses for describing the dynamics of chemical networks appears stronger every day.Using the structural information, notably from the stoichiometric matrix, of a biochemical reaction system, we state a more strict version of the famous Thomas' necessary condition for multistationarity. In particular, the obvious cases where Thomas' condition was trivially satisfied, mutual inhibition due to a multimolecular reaction and mutual activation due to a reversible reaction, can now easily be ruled out.This more strict condition shall not be seen as some version of Thomas' circuit functionality for the continuous case but rather as related and complementary to the whole domain of the structural analysis of (bio)chemical reaction systems, as pioneered by the chemical reaction network theory. PMID:24048547

Soliman, Sylvain

2013-09-19

215

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

PubMed

The use of negative ion monitoring mode with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass spectrometer [IM(tof)MS] to detect chemical warfare agent (CWA) degradation products from aqueous phase samples has been determined. Aqueous phase sampling used a traditional electrospray ionization (ESI) source for sample introduction and ionization. Certified reference materials (CRM) of CWA degradation products for the detection of Schedule 1, 2, or 3 toxic chemicals or their precursors as defined by the chemical warfare convention (CWC) treaty verification were used in this study. A mixture of six G-series nerve related CWA degradation products (EMPA, IMPA, EHEP, IHEP, CHMPA, and PMPA) and their related collision induced dissociation (CID) fragment ions (MPA and EPA) were found in each case to be clearly resolved and detected using the IM(tof)MS instrument in negative ion monitoring mode. Corresponding ions, masses, drift times, K(o) values, and signal intensities for each of the CWA degradation products are reported. PMID:16413205

Steiner, Wes E; Harden, Charles S; Hong, Feng; Klopsch, Steve J; Hill, Herbert H; McHugh, Vincent M

2006-01-18

216

Chemical residence time and hydrological conditions influence treatment of fipronil in vegetated aquatic mesocosms.  

PubMed

Fipronil, a phenyl-pyrazole insecticide, is often used in rice (Oryza sativa L.) production agriculture, with elevated runoff concentrations and loads having potential toxicological effects on downstream aquatic environments. This study evaluated two species of aquatic plants-broadleaf cattail (Typha latifolia L.) and powdery alligator-flag (Thalia dealbata Fraser ex Roscoe)-placed in series against a nonvegetated mesocosm in reducing concentrations and loads of fipronil, and associated metabolites. Vegetation type and hydrological condition (inundated vs. dry) were treatment effects used for comparison. The vegetated mesocosms significantly reduced higher loads and concentrations of fipronil, fipronil sulfone, and sulfide in both inundated and dry hydrological conditions over nonvegetated nesocosms. Under inundation conditions, vegetated mesocosms reduced >50% of influent fipronil concentrations and betweeen 60 and 70% of fipronil loads, which was significantly higher than the dry conditions (10-32% concentration and load). These results show that agricultural management strategies usingephemeral aquatic zones, such as drainage ditches, can be optimized to couple chemical applications with vegetation presence and hydrology to facilitate the reduction in chemical waste loads entering downstream aquatic ecosystems. Such reduction is critical for use with fipronil, where negative impacts have been demonstrated with several nontarget species. PMID:21520763

Kröger, Robert; Moore, Matthew T

217

Hydrothermal diamond anvil cell for XAFS studies of first-row transition elements in aqueous solution up to supercritical conditions  

Microsoft Academic Search

A hydrothermal diamond anvil cell (HDAC) has been modified by drilling holes with a laser to within 150 ?m of the anvil face to minimize the loss of X-rays due to absorption and scatter by diamond. This modification enables acquisition of K-edge X-ray absorption fine structure (XAFS) spectra from first-row transition metal ions in aqueous solutions at temperatures ranging from

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

2000-01-01

218

Application of the 'Tradescantia micronucleus' Assay for the Genetic Evaluation of Chemical Mixtures in Soil and Aqueous Media.  

National Technical Information Service (NTIS)

Genotoxic evaluation of nine binary and one tertiary mixtures of arsenic trioxide, dieldrin, and lead tetraacetate were performed using the Tradescantia micronucleus (Trad-MN) assay. The chemical mixtures were either (1) mixed into soil, and chemical expo...

B. S. Gill S. S. Sandhu

1992-01-01

219

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

220

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...

221

Development of the FMT chemical transport simulator: Advective transport sensitivity to aqueous density and mineral volume fraction coupled to phase compositions  

SciTech Connect

The Fracture-Matrix Transport (FMT) code couples saturated porous media advection and diffusion with mechanistic chemical models for speciation and interphase reactions. FMT is being developed to support actinide solubility and retardation studies for the Waste Isolation Pilot Plant (WIPP), USDOE facility for demonstrating safe disposal of transuranic waste. Hydrologic studies of water-bearing units above the WIPP indicate double-porosity transport behavior in some locations, with groundwater concentrations ranging which potable to highly concentrated. Previously, FMT simulated such systems in two-dimensions on the continuum from advection- to diffusion-dominated, with a user-specified velocity field that allows double-porosity transport. However, aqueous density was assumed constant, and reactive minerals were assumed to occupy negligible volume. Both of these assumptions can be considered poor for evaporite systems, where large changes in porosity and aqueous density can result from high mineral solubilities. Therefore, further development of FMT has relaxed these restrictions, allowing aqueous density to vary with phase composition, and allowing void volume to change as minerals dissolve and precipitate. This paper describes the additional mathematical complexity required to simulate such systems. The sensitivity of advection-dominated transport to these variables is explored through an extended example.

Novak, C.F.

1993-12-31

222

Chemical erosion of different carbon composites under ITER-relevant plasma conditions  

NASA Astrophysics Data System (ADS)

We have studied the chemical erosion of different carbon composites in Pilot-PSI at ITER-relevant hydrogen plasma fluxes (~1024 m-2 s-1) and low electron temperatures (Te~1 eV). Optical emission spectroscopy on the CH A-X band was used to characterize the chemical sputtering. Fine grain graphite (R 6650, SGL Carbon Group), ITER-reference carbon fiber composite material (SNECMA NB31 and NB41; Dunlop 3D), nano- and micro-crystalline diamond coatings on molybdenum and SiC (Silit® SKD Reaction-Bonded, Saint-Gobain Ceramics) were compared. The chemical sputtering was similar for the different composites under comparable plasma conditions, except for SiC, which produced a ten times lower rate. The CH emission was constant at electron temperatures Te>1 eV and ion fluxes ranging between 1023 and 1024 m- 2 s-1, but decreased at lower temperatures. This decrease is possibly due to changes in the excitation of CH and not due to a change in the chemical erosion rate.

Westerhout, J.; Borodin, D.; Al, R. S.; Brezinsek, S.; 't Hoen, M. H. J.; Kirschner, A.; Lisgo, S.; van der Meiden, H. J.; Philipps, V.; van de Pol, M. J.; Shumack, A. E.; De Temmerman, G.; Vijvers, W. A. J.; Wright, G. M.; Lopes Cardozo, N. J.; Rapp, J.; van Rooij, G. J.

2009-12-01

223

High-sensitivity chemical derivatization NMR analysis for condition monitoring of aged elastomers.  

SciTech Connect

An aged polybutadiene-based elastomer was reacted with trifluoroacetic anhydride (TFAA) and subsequently analyzed via 19F NMR spectroscopy. Derivatization between the TFAA and hydroxyl functionalities produced during thermo-oxidative aging was achieved, resulting in the formation of trifluoroester groups on the polymer. Primary and secondary alcohols were confirmed to be the main oxidation products of this material, and the total percent oxidation correlated with data obtained from oxidation rate measurements. The chemical derivatization appears to be highly sensitive and can be used to establish the presence and identity of oxidation products in aged polymeric materials. This methodology represents a novel condition monitoring approach for the detection of chemical changes that are otherwise difficult to analyze.

Assink, Roger Alan; Celina, Mathias Christopher; Skutnik, Julie Michelle

2004-06-01

224

Using chemical tracers in hillslope soils to estimate the importance of chemical denudation under conditions of downslope sediment transport  

NASA Astrophysics Data System (ADS)

We present a model of hillslope soils that couples the evolution of topography, soil thickness, and the concentration of constituent soil phases, defined as unique components of the soil with collective mass equal to the total soil mass. The model includes both sediment transport and chemical denudation. A simplified two-phase model is developed; the two phases are a chemically immobile phase, which has far lower solubility than the bulk soil and is not removed through chemical weathering (for example, zircon grains), and a chemically mobile phase that may be removed from the system through chemical weathering. Chemical denudation rates in hillslope soils can be measured using the concentration of immobile elements, but the enrichment of these immobile elements is influenced by spatial variations in chemical denudation rates and spatial variations in the chemical composition of a soil's parent material. These considerations cloud the use of elemental depletion factors and cosmogenic nuclide-based total denudation rates used to identify the relationship between physical erosion and chemical weathering if these techniques do not account for downslope sediment transport. On hillslopes where chemical denudation rates vary in space, estimates of chemical denudation using techniques that do not account for downslope sediment transport and spatial variations in chemical denudation rates may be adequate where the chemical denudation rate is a significant fraction of the total denudation rate but are inadequate in regions where chemical weathering rates are small compared to the total denudation rate. We also examine relationships between transient mechanical and chemical denudation rates. Soil particle residence times may affect chemical weathering rates, and the relationship between total landscape-lowering rates and soil particle residence times can thus be quantified.

Mudd, Simon Marius; Furbish, David Jon

2006-06-01

225

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

2012-06-09

226

Optimization of solar photocatalytic degradation conditions of Reactive Yellow 14 azo dye in aqueous TiO 2  

Microsoft Academic Search

The photocatalytic decolourisation and degradation of an azo dye Reactive Yellow 14 (RY14) in aqueous solution with TiO2-P25 (Degussa) as photocatalyst in slurry form have been investigated using solar light. The study on the effect of various photocatalysts on the decolourisation and degradation reveals the following order of reactivity: ZnO>TiO2-P25>TiO2 (anatase). CdS, Fe2O3 and SnO2 have negligible activity on RY14

M. Muruganandham; N. Shobana; M. Swaminathan

2006-01-01

227

An investigation on changes in chemical properties of pure ethylene-propylene-diene rubber in aqueous acidic environments  

Microsoft Academic Search

The influence of two aqueous acidic environments on two types of pure ethylene-propylene-diene (EPDM) rubber (i.e., elastomer) thin films is studied. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results revealed the formation of several oxygenated species on the surface after exposure. Raman spectroscopy along with ATR-FTIR results confirmed the vulnerability of the olefinic double bonds (CC) of 5-ethylidene-2-norbornene (ENB)

Susanta Mitra; Afshin Ghanbari-Siahkali; Peter Kingshott; Søren Hvilsted; Kristoffer Almdal

2006-01-01

228

Chemical and spectroscopic investigation of porewater and aqueous extracts of corresponding peat samples throughout a bog core (Jura Mountains, Switzerland)  

Microsoft Academic Search

Background, aim, and scope  Fluorescence and UV-visible spectroscopies are simple but useful methods to characterize organic matter in the aqueous phase\\u000a according to its aromatic nature and humification degree. Although there are several studies about porewater and water-extractable\\u000a organic matter (WEOM) from peat, at present, no comparative investigations are available in the literature. Thus, the aim\\u000a of the present study was

Claudio Zaccone; Valeria D’Orazio; William Shotyk; Teodoro M. Miano

2009-01-01

229

Meteorological conditions during the summer 1986 Chemical Instrumentation Testing and Evaluation (CITE) 2 flight series  

SciTech Connect

An overview of meteorological conditions during the NASA Global Tropospheric Experiment/Chemical Instrumentation Testing and Evaluation (GTE/CITE 2) summer 1986 flight series is presented. Computer-generated isentropic trajectories are used to trace the history of air masses encountered along each aircraft flight path. The synoptic-scale wind fields are depicted based upon Montgomery stream function analysis. Time series of aircraft-measured temperature, dew point, ozone, and altitude are shown to depict air mass variability. Observed differences between maritime tropical and maritime polar air masses are discussed.

Shipham, M.C.; Cahoon, D.R. (NASA Langley Research Center, Hampton, VA (USA)); Bachmeier, A.S. (PRC Kentron, Hampton, VA (USA))

1990-06-20

230

Impact of Pad Conditioning on Thickness Profile Control in Chemical Mechanical Planarization  

NASA Astrophysics Data System (ADS)

Chemical mechanical planarization (CMP) has been proven to be the best method to achieve within-wafer and within-die uniformity for multilevel metallization. Decreasing device dimensions and increasing wafer sizes continuously demand better planarization, which necessitates better understanding of all the variables of the CMP process. A recently highlighted critical factor, pad conditioning, affects the pad surface profile and consequently the wafer profile; in addition, it reduces defects by refreshing the pad surface during polishing. This work demonstrates the changes in the postpolish wafer profile as a function of pad wear. It also introduces a wafer material removal rate profile model based on the locally relevant Preston equation by estimating the pad thickness profile as a function of polishing time. The result is a dynamic predictor of how the wafer removal rate profile shifts as the pad ages. The model helps fine-tune the pad conditioner operating characteristics without the requirement for costly and lengthy experiments. The accuracy of the model is demonstrated by experiments as well as data from a real production line. Both experimental data and simulations indicate that the smaller conditioning disk size and extended conditioning sweep range help improve the post-CMP wafer planarization. However, the defectivity tends to increase when the conditioning disk sweeps out of the pad radius; hence, the pad conditioning needs to be designed by considering the specific requirements of the CMP process conducted. The presented model predicts the process outcomes without requiring detailed experimentation.

Kincal, S.; Basim, G. B.

2013-01-01

231

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

NASA Astrophysics Data System (ADS)

The steady-state ?-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 from MEK decomposition were analysed as a function of time (or total absorbed dose). The main initial step for the radiolytic decomposition of MEK is the H abstraction from MEK by OH, produced by ?-radiolysis of water, to form MEK radical. In the absence of O, the main decay path of the MEK radical appears to be dimerization to form 3,4-dimethyl-2,5-hexanedione. In the presence of oxygen, the MEK radical reacts primarily with O to form the MEK peroxyl radical. This radical ultimately results in a series of progressively smaller oxidation products. The formation of organic acids, and eventually CO2, reduces the pH of the solution. This paper presents the experimental data and proposes the MEK decay kinetics and mechanism.

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

2000-01-01

232

Growth Condition of CeO2 Thin Films Grown on Glass Substrate from Aqueous Solution and Their Optical Property  

NASA Astrophysics Data System (ADS)

Cerium dioxide (CeO2) thin film is an attractive material with multiple applications. In this study CeO2 precursor thin films were deposited onto glass substrates at a room temperature from an aqueous solution by applying constant electrical field and their optical properties were investigated. The precursor was an aqueous solution of Ce(NO3)3-6H2O, Y(NO3)3-6H2O, and NH3(aq). The thin film was deposited on the glass substrate of the minus electrode side. By applying the electrical field of 2.6-3.6 V, the Y-Ce(OH)3 thin film was effectively deposited on glass substrates for 20-60 min at room temperature. The as-deposited film was amorphous, and a crystalline phase of Y-CeO2 with a transparent and smooth surface can be obtained after annealing at 823 K for 5 h in air. Spectral transmission curves of visible to ultraviolet light region through Y-CeO2 films were measured and about 10 to 30 % absorption peaks were observed around 310 to 330 nm.

Saiki, A.; Kawai, C.; Hashizume, T.; Terayama, K.

2011-10-01

233

Preparation of TiO2, Ag-doped TiO2 nanoparticle and TiO2–SBA15 nanocomposites using simple aqueous solution-based chemical method and study of their photocatalytical activity  

Microsoft Academic Search

Nanocrystalline TiO2, Ag-doped TiO2 and TiO2–SBA-15 nanocomposites have been synthesised using a simple aqueous solution-based chemical method. Nanocrystalline TiO2 was synthesised by calcining the precursor prepared by using ethylenediamine tetraacetic acid and TiCl3 in aqueous medium. Formation of crystalline phase (anatase, rutile or mixed phase) and crystallite size were found to be dependent on calcination temperature. To enhance the photocatalytic

Bhanudas Naik; Chinthan Hemapa Manoratne; Akash Chandrashekhar; Abhishek Iyer; Vadakkethonippurathu Sivankutty Prasad; Narendra Nath Ghosh

2012-01-01

234

Chemical and isotopic kinetics of sulfate reduction by organic matter under hydrothermal conditions  

SciTech Connect

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 bisulfate and about one-half-order in initial dextrose concentration, and shows a very strong dependence on pH. The kinetics of sulfate reduction by fructose at 250C are virtually the same. The lack of sulfate reduction by formaldehyde, methanol, ethanol and acetic acid at 250 C indicates that the reducing power of dextrose and fructose cannot be attributed to carbonyl, carboxyl or hydroxyl functional groups. The form of the rate law for sulfate reduction by dextrose and the presence of an induction period rather suggest that the initial reduction of sulfate occurs with free radicals derived from the thermal decomposition of the hexoses or their alteration products. The inferred sulfate-reduction reaction mechanism suggest that aqueous sulfate may be reduced to sulfide in geologic environments such as deep sedimentary basins. The observed acid-catalysis of the reaction in the laboratory may be supplanted by clay-mineral catalysis in geologic environments. Sulfur isotopes are fractionated during the reduction of sulfate by dextrose under hydrothermal conditions. Computer simulations of the isotopic evolution of the experiments suggest that sulfate-sulfide isotopic exchange largely controls the isotopic composition of sulfate and sulfide. The extent of isotopic fractionation due solely to sulfate reduction thus cannot be determined from the experiments

Kaiser, C.J.

1988-01-01

235

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

2013-03-06

236

Behavioral response of Corophium volutator relative to experimental conditions, physical and chemical disturbances.  

PubMed

The preference/avoidance behavioral response of a widely used amphipod in toxicity tests, Corophium volutator, was investigated in relation to the presence of anthropogenic physical or chemical materials in sediments. Exposure conditions, including the density of amphipods, the depth of sediments, amount of overlying water, and exposure time, were examined for their influence on amphipods' preference for field sediments and avoidance of coarse sand. It was shown that these variables did not affect the response; thus, conditions similar to published standard toxicity tests were chosen. A gradient of sediments spiked with potential habitat disturbances that can be found on a beach or in contaminated sediments, such as those in harbors, were tested. These substances included sand, seaweed, burned wood, coal, crankcase oil, and diesel oil. To enhance the interpretation of results and decrease the variability observed when tests were conducted at different times over the summer, exposures were performed over a gradient of spike material in reference sediments. We conclude that physical obstacles added to reference sediments lead to less correlation with the behavioral response than observed with chemical interferences. Amphipods' behavior ranked harbor sediments similarly to previous studies concerning the health of intertidal mussels collected in proximity to the sediments sites. For five sites, preference of reference sediments was observed until the level of polycyclic aromatic hydrocarbons in diluted harbor sediments reached the Canadian Council of Ministers of the Environment sediment quality guidelines. PMID:16445086

Hellou, Jocelyne; Cheeseman, Kerri; Jouvenelle, Marie-Laure; Robertson, Sarah

2005-12-01

237

Role of roasting conditions in the profile of volatile flavor chemicals formed from coffee beans.  

PubMed

The volatile chemicals in dichloromethane extracts from green coffee beans, roasted at 230 degrees C for 12 min (light), at 240 degrees C for 14 min (medium), at 250 degrees C for 17 min (city), or at 250 degrees C for 21 min (French), were analyzed by gas chromatography and gas chromatography-mass spectrometry. Among the 52 volatile compounds identified, the major compounds were 5-hydroxymethylfurfural, furfuryl alcohol, and 6-methyl-3,5-dihydroxy-4H-pyran-4-one in light-roasted beans; furfuryl alcohol, 5-hydroxymethylfurfural, and gamma-butyrolactone in medium-roasted beans; furfuryl alcohol, gamma-butyrolactone, and 2-acetylpyrrole in city-raosted beans; and gamma-butyrolactone, furfuryl alcohol, and catechol in French-roasted beans. Furfural derivatives and furanones were yielded in relatively high concentrations under mild roasting conditions and then reduced at higher roasting intensities. More pyridines and pyrroles were formed by high roasting intensities than by mild roasting intensities. Chlorogenic acid degradation products, phenols, and a lactone were produced more by high roasting intensities than by low roasting intensities. The results of the present study suggest that controlling the roasting conditions according to the formation of particular chemicals can prepare a roasted coffee with preferable flavor. PMID:19579294

Moon, Joon-Kwan; Shibamoto, Takayuki

2009-07-01

238

Characterizing summertime chemical boundary conditions for airmasses entering the US West Coast  

NASA Astrophysics Data System (ADS)

The objective of this study is to analyze the pollution inflow into California during summertime and how it impacts surface air quality through combined analysis of a suite of observations and global and regional models. The focus is on the transpacific pollution transport investigated by the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission in June 2008. Additional observations include satellite retrievals of carbon monoxide and ozone by the EOS Aura Tropospheric Emissions Spectrometer (TES), aircraft measurements from the MOZAIC program and ozonesondes. We compare chemical boundary conditions (BC) from the MOZART-4 global model, which are commonly used in regional simulations, with measured concentrations to quantify both the accuracy of the model results and the variability in pollution inflow. Both observations and model reflect a large variability in pollution inflow on temporal and spatial scales, but the global model captures only about half of the observed free tropospheric variability. Model tracer contributions show a large contribution from Asian emissions in the inflow. Recirculation of local US pollution can impact chemical BC, emphasizing the importance of consistency between the global model simulations used for BC and the regional model in terms of emissions, chemistry and transport. Aircraft measurements in the free troposphere over California show similar concentration range, variability and source contributions as free tropospheric air masses over ocean, but caution has to be taken that local pollution aloft is not misinterpreted as inflow. A flight route specifically designed to sample boundary conditions during ARCTAS-CARB showed a prevalence of plumes transported from Asia and thus may not be fully representative for average inflow conditions. Sensitivity simulations with a regional model with altered BCs show that the temporal variability in the pollution inflow does impact modeled surface concentrations in California. We suggest that time and space varying chemical boundary conditions from global models provide useful input to regional models, but likely still lead to an underestimate of peak surface concentrations and the variability associated with long-range pollution transport.

Pfister, G. G.; Parrish, D.; Worden, H.; Emmons, L. K.; Edwards, D. P.; Wiedinmyer, C.; Diskin, G. S.; Huey, G.; Oltmans, S. J.; Thouret, V.; Weinheimer, A.; Wisthaler, A.

2010-11-01

239

Characterizing summertime chemical boundary conditions for airmasses entering the US West Coast  

NASA Astrophysics Data System (ADS)

The objective of this study is to analyze the pollution inflow into California during summertime and how it impacts surface air quality through combined analysis of a suite of observations and global and regional models. The focus is on the transpacific pollution transport investigated by the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission in June 2008. Additional observations include satellite retrievals of carbon monoxide and ozone by the EOS Aura Tropospheric Emissions Spectrometer (TES), aircraft measurements from the MOZAIC program and ozonesondes. We compare chemical boundary conditions (BC) from the MOZART-4 global model, which are commonly used in regional simulations, with measured concentrations to quantify both the accuracy of the model results and the variability in pollution inflow. Both observations and model reflect a large variability in pollution inflow on temporal and spatial scales, but the global model captures only about half of the observed free tropospheric variability. Model tracer contributions show a large contribution from Asian emissions in the inflow. Recirculation of local US pollution can impact chemical BC, emphasizing the importance of consistency between the global model simulations used for BC and the regional model in terms of emissions, chemistry and transport. Aircraft measurements in the free troposphere over California show similar concentration ranges, variability and source contributions as free tropospheric air masses over ocean, but caution has to be taken that local pollution aloft is not misinterpreted as inflow. A flight route specifically designed to sample boundary conditions during ARCTAS-CARB showed a prevalence of plumes transported from Asia and thus may not be fully representative for average inflow conditions. Sensitivity simulations with a regional model with altered BCs show that the temporal variability in the pollution inflow does impact modeled surface concentrations in California. We suggest that time and space varying chemical boundary conditions from global models provide useful input to regional models, but likely still lead to an underestimate of peak surface concentrations and the variability associated with long-range pollution transport.

Pfister, G. G.; Parrish, D. D.; Worden, H.; Emmons, L. K.; Edwards, D. P.; Wiedinmyer, C.; Diskin, G. S.; Huey, G.; Oltmans, S. J.; Thouret, V.; Weinheimer, A.; Wisthaler, A.

2011-02-01

240

What Hydra can teach us about chemical ecology -how a simple, soft organism survives in a hostile aqueous environment.  

PubMed

Hydra and its fellow cnidarians - sea anemones, corals and jellyfish - are simple, mostly sessile animals that depend on bioactive chemicals for survival. In this review, we briefly describe what is known about the chemical armament of Hydra, and detail future research directions where Hydra can help illuminate major questions in chemical ecology, pharmacology, developmental biology and evolution. Focusing on two groups of putative toxins from Hydra - phospholipase A2s and proteins containing ShK and zinc metalloprotease domains, we ask: how do different venom components act together during prey paralysis? How is a venom arsenal created and how does it evolve? How is the chemical arsenal delivered to its target? To what extent does a chemical and biotic coupling exist between an organism and its environment? We propose a model whereby in Hydra and other cnidarians, bioactive compounds are secreted both as localized point sources (nematocyte discharges) and across extensive body surfaces, likely combining to create complex "chemical landscapes". We speculate that these cnidarian-derived chemical landscapes may affect the surrounding community on scales from microns to, in the case of coral reefs, hundreds of kilometers. PMID:22689366

Rachamim, Tamar; Sher, Daniel

2012-01-01

241

DETERMINATION OF PHTHALATES IN WATER AND SOIL BY TANDEM MASS SPECTROMETRY UNDER CHEMICAL IONIZATION CONDITIONS WITH ISOBUTANE AS REAGENT GAS  

EPA Science Inventory

Phthalate determination is important because phthalates often are major impurities in samples and can have significant health effects. Tandem mass spectrometry under chemical ionization mass spectrometry conditions with isobutane as the reagent gas was used to determine 11 phthal...

242

Conditions for Tunnel Formation in LPCVD (Low Pressure Chemical Vapor Deposition) Tungsten Films on Single Crystal Silicon.  

National Technical Information Service (NTIS)

The occurrence of microscopic filamentary voids (''tunnels'' or ''worm holes'') in silicon beneath chemically vapor deposited tungsten films has been investigated over a wide range of wafer and deposition conditions. The effect of dopant type, concentrati...

M. E. Tracy R. S. Blewer T. J. Headley

1987-01-01

243

Process for the conversion of and aqueous biomass hydrolyzate into fuels or chemicals by the selective removal of fermentation inhibitors  

DOEpatents

A process of making a fuel or chemical from a biomass hydrolyzate is provided which comprises the steps of providing a biomass hydrolyzate, adjusting the pH of the hydrolyzate, contacting a metal oxide having an affinity for guaiacyl or syringyl functional groups, or both and the hydrolyzate for a time sufficient to form an adsorption complex; removing the complex wherein a sugar fraction is provided, and converting the sugar fraction to fuels or chemicals using a microorganism.

Hames, Bonnie R. (Westminster, CO); Sluiter, Amie D. (Arvada, CO); Hayward, Tammy K. (Broomfield, CO); Nagle, Nicholas J. (Broomfield, CO)

2004-05-18

244

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

Microsoft Academic Search

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

J. M. Salman; B. H. Hameed

2010-01-01

245

[Examination of the optimum condition that determines contamination for three-dimensions chemical shift imaging].  

PubMed

Magnetic resonance spectroscopy (MRS) is a useful tool for obtaining metabolic information non-invasively. However, low reducibility of MRS data, measuring biases caused by the operator, effects of relaxation time, and environmental contamination may sometimes become problematic. In this study, we examined contamination in echo time (TE) and the availability of outer volume suppression (OVS) by using the excitation and localization methods. In addition, we investigated the optimized condition for three-dimensions (3D)-chemical shift imaging (CSI) in gliomas. Contamination was dependent on resolution in the excitation and localization methods and on CSI resolution, but it was not dependent on TE. The additional installation of OVS and saturation pulse (SAT) corresponding to the target sites were extremely useful. There was concern about the influence of chemical shift, crosstalk, contamination, and no radio frequency (RF) uniformity in the marginal volume of interest (VOI). Metabolite distribution was deteriorated along the Z-axis but not in the X-Y plane. It, however, was improved by using a small voxel size in the Z-axis. PMID:22277818

Kikuchi, Chie; Inoue, Mitsuhiro

2012-01-01

246

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

2012-02-19

247

Phenanthrene removal from aqueous solutions using well-characterized, raw, chemically treated, and charred malt spent rootlets, a food industry by-product.  

PubMed

Malt spent rootlets (MSR) are biomaterials produced in big quantities by beer industry as by-products. A sustainable solution is required for their management. In the present study, MSR are examined as sorbents of a hydrophobic organic compound, phenanthrene, from aqueous solutions. Raw MSR sorb phenanthrene but their sorptive properties are not competitive with the respective properties of commercial sorbents (e.g., activated carbons). Organic petrography is used as a tool to characterize MSR after treatment in order to produce an effective sorbent for phenanthrene. Chemical and thermal (at low temperature under nitrogen atmosphere) treatments of MSR did not result in highly effective sorbents. Based on organic petrography characterization, the pores of the treated materials were filled with humic colloids. When pyrolysis at 800 °C was used to treat MSR, a sorbent with new and empty pores was produced. Phenanthrene sorption capacity was 2 orders of magnitude higher for the pyrolized MSR than for raw MSR. PMID:23764506

Valili, Styliani; Siavalas, George; Karapanagioti, Hrissi K; Manariotis, Ioannis D; Christanis, Kimon

2013-06-10

248

Kinetics of sulfur isotope exchange between aqueous sulfide and thiosulfate involving intra- and intermolecular reactions at hydrothermal conditions  

Microsoft Academic Search

Sulfur isotope exchange between sulfide (H2S) and thiosulfate (HSSO3H) can be described by the general rate law for a two-compound system (X and AB) with three exchangeable atoms (X, A, and B) proposed by [X. Chu, H. Ohmoto, Kinetics of isotope exchange reactions involving intra- and intermolecular reactions: I. Rate law for a system with two chemical compounds and three

Xuelei Chu; Hiroshi Ohmoto; David R. Cole

2004-01-01

249

Chemical Characterization of Extrasolar Super-Earths - Interiors, Atmospheres, and Formation Conditions  

NASA Astrophysics Data System (ADS)

Recent observations are allowing unprecedented measurements of masses and radii of low-mass transiting extrasolar planets, particularly super-Earths which are defined as planets with masses between 1 and 10 Earth masses. The observed masses, radii, and temperatures of super-Earths provide constraints on their interior structures, geophysical conditions, as well as their atmospheric compositions. Some of the most recently detected super-Earths span a wide gamut of possible compositions, from super-Mercuries and lava planets to water worlds with thick volatile envelopes. In this work, we report joint constraints on the interior and atmospheric compositions of several super-Earths and discuss their possible formation scenarios using new and comprehensive hybrid models of their interiors, non-gray atmospheres, and formation conditions. Our model constraints are based on the masses and visible radii, as well as the latest infrared measurements of transmission and emission spectrophotometry where available, in addition to revised estimates of the stellar parameters. We will present a comparative analysis of several transiting super-Earths currently known and will discuss in detail two super-Earths (GJ 1214b and 55 Cancri e) which have atmospheric data available and which represent two distinct end members in the thermo-chemical phase space of super-Earth conditions. We will also discuss the implications of our results for the diversity of geochemical and geophysical conditions on super-Earths. We will conclude with comments on new observational, theoretical, and experimental efforts that are critical to detailed characterization of super-Earths.

Madhusudhan, Nikku; Lee, K.; Uts, I.; Mousis, O.

2013-01-01

250

Selective olfactory choices of the honeybee among sunflower aromas: A study by combined olfactory conditioning and chemical analysis  

Microsoft Academic Search

A bioassay based on an olfactory conditioning method simulating the foraging situation in laboratory conditions was coupled with chemical analysis of volatile sunflower blends. Behavioural data obtained from for-agers'responses to volatile fraction point out that honeybees need to use only a limited fraction acting as a “simplified aromatic pattern” of the plant, among hundreds of compounds constituting the whole aroma.

M. H. Pham-Delegue; C. Masson; P. Etievant; M. Azar

1986-01-01

251

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

252

Soil structure, colloids, and chemical transport as affected by short-term reducing conditions: a laboratory study  

Technology Transfer Automated Retrieval System (TEKTRAN)

Upland soils in the Midwestern US often undergo reducing conditions when soils are temporally flooded during the spring and remain water saturated for days or weeks. Short-term reducing conditions change the chemistry of the soil and may affect soil structure and solution chemical transport. The eff...

253

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

SciTech Connect

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), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant data sets. We found that the predominant general surface orientation is (100), 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%.

Hui Tian; Michael Kelley; Charles Reece

2005-11-14

254

Meteorological conditions and anomalies during the Intercontinental Chemical Transport Experiment-North America  

NASA Astrophysics Data System (ADS)

Meteorological conditions are described during the Intercontinental Chemical Transport Experiment-North America (INTEX-NA) that was conducted over the United States during July and August 2004. Relatively zonal flow dominated the contiguous United States during the first 2 weeks of the mission, while a series of large amplitude troughs traversed the eastern half of the country during the final 4 weeks. These troughs were accompanied by cold fronts reaching the Gulf of Mexico, an uncommon occurrence during August. Frontal passages over the northeast were somewhat above average, but the short time interval between passages precluded the formation of stagnant high-pressure centers containing abundant pollution. Atmospheric chemistry during INTEX-NA was heavily influenced by record-breaking fires over Alaska and western Canada. Persistent high pressure over Alaska provided ideal conditions for the wildfires and for transporting their burning by-products southeastward toward the INTEX domain where they were sampled frequently by INTEX aircraft. Forward trajectories and satellite imagery showed that the plumes later were carried to parts of Europe, Africa, and even the Arctic. Deep convection and lightning were important factors during INTEX-NA. Cloud-to-ground (CG) lightning data show that horizontal patterns and numbers of lightning flashes during INTEX-NA are similar to those of 2003 and 2005. Statistics derived from 10 day backward trajectories indicate that the DC-8 often sampled lightning influenced air.

Fuelberg, Henry E.; Porter, Michael J.; Kiley, Christopher M.; Halland, Jeremy J.; Morse, Danielle

2007-06-01

255

Is vanadate reduced by thiols under biological conditions? Changing the redox potential of V(V)/V(IV) by complexation in aqueous solution.  

PubMed

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, electron paramagnetic resonance (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 based on coordination induced chemical shifts 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. On the basis of 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, antiamoebic agents, and interactions with vanadium binding proteins. PMID:20359175

Crans, Debbie C; Zhang, Boyan; Gaidamauskas, Ernestas; Keramidas, Anastasios D; Willsky, Gail R; Roberts, Chris R

2010-05-01

256

Properties of aqueous solutions of lithium and calcium chlorides: formulations for use in air conditioning equipment design  

Microsoft Academic Search

The dehydration of air, for air conditioning purposes, either for human comfort or for industrial processes, is done most of the times by making it contact a surface at a temperature below its dew point. In this process not only is it necessary to cool that surface continuously, but also the air is cooled beyond the temperature necessary to the

Manuel R. Conde

2004-01-01

257

[Studies on chemical protectors against radiation. XXXIV. Survival effects of aqueous extracts of various Chinese traditional medicines on radiation injury].  

PubMed

In order to develop a nontoxic radioprotector, 60 kinds of Chinese traditional medicines were chosen, and their aqueous extracts tested for their survival effects against the lethal effect of X-irradiation in mice. Radiation factors used were as follows: soft X-rays, 2100R (5.418 x 10(-1) Ckg-1), 70 kVp, 10 mA, 10 mm acrylic filter, 70R (1.806 x 10(-2) Ckg-1)/min. Among 60 medicines tested by intraperitoneal injection immediately before the irradiation, 15 are shown to have the significant survival effect. These 15 effective medicines were also tested by intraperitoneal injection after the irradiation, and the survival effect was recognized in Keisi-syakuyaku-chimo-to, Keigai-rengyo-to, Simotu-to, Syakuyaku-kanzo-to and Hange-syasin-to. On the other hand, the survival effects of 25 medicines including the above-mentioned 15 medicines were investigated by the oral administration at various times before or after the irradiation. As the result of these studies, only Keigai-rengyo-to and Bukuryo-in are shown to have the significant survival effect when administered 2 h before the irradiation. PMID:1941537

Wang, C M; Ohta, S; Shinoda, M

1991-06-01

258

Application of pervaporation and vapor permeation processes to separate aqueous ethanol solution through chemically modified Nylon 4 membranes  

SciTech Connect

The pervaporation performance of a Nylon 4 membrane, chemically grafted by N,N-dimethylaminoethyl methacrylate (DMAEM), DMAEM-g-N4, was studied by measurement of the permeation ratio and the pervaporation separation index. It was found that the water permselectivity and permeation rate for the chemically modified Nylon 4 membrane were higher than those of the unmodified Nylon 4 membrane. Optimum pervaporation results, a separation factor of 28.3, and a permeation rate of 439 g/m{sup 2}{center_dot}h, were obtained when the degree of grafting was 12.7%. It was also found that all the permeation ratios at low temperature were less than unity. In addition, compared with pervaporation, vapor permeation effectively increases the permselectivity of water.

Wang, Y.H.; Teng, M.Y.; Lee, K.R. [Nanya Junior Coll. of Technology, Chung Li (Taiwan, Province of China). Dept. of Chemical Engineering; Wang, D.M.; Lai, J.Y. [Chung Yuan Univ., Chung Li (Taiwan, Province of China). Dept. of Chemical Engineering

1998-08-01

259

Optimization of nickel adsorption from aqueous solution by using activated carbon prepared from waste apricot by chemical activation  

Microsoft Academic Search

Waste apricot supplied by Malatya apricot plant (Turkey) was activated by using chemical activation method and K2CO3 was chosen for this purpose. Activation temperature was varied over the temperature range of 400–900°C and N2 atmosphere was used with 10°C\\/min heat rate. The maximum surface area (1214m2\\/g) and micropore volume (0.355cm3\\/g) were obtained at 900°C, but activated carbon was predominantly microporous

S. Erdogan; Y. Önal; C. Akmil-Basar; S. Bilmez-Erdemoglu; Ç. Sarici-Özdemir; E. Köseoglu; G. Içduygu

2005-01-01

260

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

261

Multianalyte determination of 24 cytostatics and metabolites by liquid chromatography-electrospray-tandem mass spectrometry and study of their stability and optimum storage conditions in aqueous solution.  

PubMed

A multianalyte liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS/MS) method for determination of 19 cytostatics and 5 metabolites, from 6 different therapeutic families, has been developed, and the structures of the main characteristic fragment ions have been proposed. Instrumental limits of detection and quantification are in the range 0.1-10.3 and 1.0-34.3ngmL(-1), respectively. Moreover, the stability of the compounds in aqueous solution was investigated in order to establish the best conditions for preparation and storage of both calibration standards and water samples. Dimethylsulphoxide (DMSO) was selected as solvent for preparation of the stock solutions. At room temperature (25°C), 11 of the 24 target compounds were shown to be unstable in water (percentage of organic solvent 4%), with concentration losses greater than 20% in less than 24h. At 4°C (typical storage temperature for water samples) all compounds, except MTIC and chlorambucil, were stable for 24h, but the number of stable compounds decreased to 10 after 9 days. Freezing of the aqueous solutions improved considerably the stability of various compounds: after 3 months of storage at -20°C, 10 compounds, namely, 5-fluorouracil, carboplatin, gemcitabine, temozolomide, vincristine, vinorelbine, ifosfamide, cyclophosphamide, etoposide, and capecitabine, remained stable (in contrast to only carboplatin and capecitabine at 4°C). The addition of acid improved the stability of methotrexate and its metabolite hydroxy-methotrexate but not that of the rest of compounds. The addition of organic solvent (50% methanol or DMSO) prevented the degradation at 4°C of the otherwise unstable compounds oxaliplatin, methotrexate, erlotinib, doxorubicin, tamoxifen, and paclitaxel. To the authors' knowledge, five of the analytes investigated have never been searched for in the aquatic environment (imatinib, 6?-hydroxypaclitaxel, endoxifen, (Z)4-hydroxytamoxifen, and temozolomide), and for many of them the stability data provided, and even the analytical LC-MS/MS conditions, are the first ever published. PMID:24148406

Negreira, Noelia; Mastroianni, Nicola; López de Alda, Miren; Barceló, Damià

2013-05-24

262

Degradation of Sucrose, Glucose and Fructose in Concentrated Aqueous Solutions Under Constant pH Conditions at Elevated Temperature  

Microsoft Academic Search

The degradation of sucrose can decrease sucrose yield, reduce the efficiency of sugar factory and refinery processes, and effect end product quality. Characterization of sucrose degradation under modeled industrial processing conditions will underpin further technological improvements. Effects of constant reaction pH on sucrose degradation were investigated using simulated industrial model systems (100 °C; 65 °Brix [% dissolved solids]; N2; 0.05-3

G. Eggleston; J. R. Vercellotti

2000-01-01

263

Arsenic mobility in soils contaminated with metallurgical wastes as a function of variable chemical conditions  

Microsoft Academic Search

Arsenic is a pervasive contaminant of natural aqueous systems, such as groundwater and soils, its sources being both natural and anthropogenic. The present investigation was performed on soils contaminated with residues from ore processing activities and revealed the presence of arsenate [As(V)] species with a very low mobility, through natural attenuation processes. The stability of this attenuation was investigated by

D. G. Garcia Payne; M. Villalobos; A. Ceniceros; J. L. Lopez; M. Gutierrez

2008-01-01

264

Chemical and Physical Reactions of Wellbore Cement under CO2 Storage Conditions: Effects of Cement Additives  

NASA Astrophysics Data System (ADS)

Sequestration of CO2 into geologic formations requires long-term storage and low leakage rates to be effective. Active and abandoned wells in candidate storage formations must be evaluated as potential leakage points. Wellbore integrity is an important part of an overall integrated assessment program being developed at NETL to assess potential risks at CO2 storage sites. Such a program is needed for ongoing policy and regulatory decisions for geologic carbon sequestration. The permeability and integrity of the cement in the well is a primary factor affecting its ability to prevent leakage. Cement must be able to maintain low permeability over lengthy exposure to reservoir conditions in a CO2 injection and storage scenario. Although it is known that cement may be altered by exposure to CO2, the results of ongoing research indicate that cement curing conditions, fluid properties, and cement additives play a significant role in the rate of alteration and reaction. The objective of this study is to improve understanding of the factors affecting wellbore cement integrity for large-scale geologic carbon sequestration projects. Due to the high frequency use of additives (pozzolan) in wellbore cement, it is also essential to understand the reaction of these cement-pozzolan systems upon exposure to CO2 under sequestration conditions (15.5 MPa and 50°C). Laboratory experiments were performed to determine the physical and chemical changes, as well as the rate of alteration of commonly used pozzolan-cement systems under simulated sequestration reservoir conditions, including both supercritical CO2 and CO2-saturated brine. The rate of alteration of the cement-pozzolan systems is considerably faster than with neat cement. However, the alteration of physical properties is much less significant with the pozzolanic blends. Permeability of a carbonated pozzolanic cement paste remains sufficiently small to block significant vertical migration of CO2 in a wellbore. All of the experiments run to date suggest that the cement-pozzolans used will be an effective seal for CO2, as long as the well was properly installed and is initially undamaged.

Kutchko, B. G.; Strazisar, B. R.; Huerta, N.; Lowry, G. V.; Dzombak, D. A.; Thaulow, N.

2008-12-01

265

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

266

Influence of Aerosol Chemical Composition on Heterogeneous Ice Formation under Mid-Upper Troposphere Conditions  

NASA Astrophysics Data System (ADS)

Aerosols are involved in cooling/warming the atmosphere directly via interaction with incoming solar radiation (aerosol direct effect), or via their ability to act as cloud condensation or ice nuclei (IN) and thus play a role in cloud formation (indirect effect). In particular, the physical properties of aerosols such as size and solubility and chemical composition can influence their behavior and fate in the atmosphere. Ice nucleation taking place via IN is termed as heterogeneous ice nucleation and can take place with via deposition (ice forming on IN directly from the vapor phase), condensation/immersion (freezing via formation of the liquid phase on IN) or condensation (IN colliding with supercooled liquid drops). This presentation shows how the chemical composition and surface area of various tropospherically relevant aerosols influence conditions of temperature (T) and relative humidity (RH) required for heterogeneous ice formation conditions in the mid-upper troposphere regime (253 - 220K)? Motivation for this comes first from, the importance of being able to predict ice formation accurately so as to understand the hydrological cycle since the ice is the primary initiator of precipitation forming clouds. Second, the tropospheric budget of water vapour, an especially active greenhouse gas is strongly influenced by ice nucleation and growth. Third, ice surfaces in the atmosphere act as heterogeneous surfaces for chemical reactions of trace gases (e.g., SO2, O3, NOx and therefore being able to accurately estimate ice formation rates and quantify ice surface concentrations will allow a more accurate calculation of trace gas budgets in the troposphere. Ice nucleation measurements were conducted using a self-developed continuous flow diffusion chamber and static chamber. A number of tropospherically relevant particulates with naturally-varying and laboratory-modified surface chemistry/structure were investigated for their ice formation efficiency based on highest T and lowest RH required for ice formation. The particles investigated were classified into three categories, mineral dust aerosols, hygroscopic and non-hygroscopic particles which included organic and inorganic salts and/or coatings. In addition results ice formation results from ozone aged mineral particles will be presented. It is observed that changing functional groups on the surface of the particles can inhibit ice formation in the deposition mode. The ice forming efficiency of mineral aerosols was observed to be the highest, requiring RH with respect to ice as low as 105% at 233 K. Hydrophobic particles were comparatively weaker at forming ice and required RH close to or above water saturation for ice formation via deposition/condensation mode freezing. The high ice nucleation activity of mineral aerosols suggest that they could play an important role in ice forming and therefore precipitation processes in the troposphere and may have in impact on global and regional climate.

Kanji, Z. A.; Niemand, M.; Saathoff, H.; Möhler, O.; Chou, C.; Abbatt, J.; Stetzer, O.

2011-12-01

267

Transcriptome analysis of the phytobacterium Xylella fastidiosa growing under xylem-based chemical conditions.  

PubMed

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. PMID:20625415

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

2010-06-13

268

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

2011-10-20

269

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

270

Initial results from dissolution rate testing of N-Reactor spent fuel over a range of potential geologic repository aqueous conditions  

SciTech Connect

Hanford N-Reactor spent nuclear fuel (HSNF) may ultimately be placed in a geologic repository for permanent disposal. To determine whether the engineered barrier system that will be designed for emplacement of light-water-reactor (LWR) spent fuel will also suffice for HSNF, aqueous dissolution rate measurements were conducted on the HSNF. The purpose of these tests was to determine whether HSNF dissolves faster or slower than LWR spent fuel under some limited repository-relevant water chemistry conditions. The tests were conducted using a flowthrough method that allows the dissolution rate of the uranium matrix to be measured without interference by secondary precipitation reactions that would confuse interpretation of the results. Similar tests had been conducted earlier with LWR spent fuel, thereby allowing direct comparisons. Two distinct corrosion modes were observed during the course of these 12 tests. The first, Stage 1, involved no visible corrosion of the test specimen and produced no undissolved corrosion products. The second, Stage 2, resulted in both visible corrosion of the test specimen and left behind undissolved corrosion products. During Stage 1, the rate of dissolution could be readily determined because the dissolved uranium and associated fission products remained in solution where they could be quantitatively analyzed. The measured rates were much faster than has been observed for LWR spent fuel under all conditions tested to date when normalized to the exposed test specimen surface areas. Application of these results to repository conditions, however, requires some comparison of the physical conditions of the different fuels. The surface area of LWR fuel that could potentially be exposed to repository groundwater is estimated to be approximately 100 times greater than HSNF. Therefore, when compared on the basis of mass, which is more relevant to repository conditions, the HSNF and LWR spent fuel dissolve at similar rates.

Gray, W.J.; Einziger, R.E.

1998-04-01

271

Échange chromatographique de deux constituants indépendants entre un fluide aqueux et une solution solide à trois pôles ; application à la substitution Ca Fe Mn des grenats de skarnChromatographic exchange of two independent chemical components between an aqueous fluid and a three-component solid solution; application to the evolution of skarn Ca Mn Fe garnet  

NASA Astrophysics Data System (ADS)

The theory of metasomatism, as exemplified by chromatographic exchange, was set out by Korzhinskii [11] in the scalar case where one single component is exchanged between a solid and an interstitial fluid. In the present work, we discuss the case of two independent components and apply it to the chemical exchange of Ca, Fe and Mn between a migrating aqueous solution and a three-component solid solution for skarn garnet. The mathematical model is of hyperbolic type; it is simulated numerically and allows visualising the evolution of the composition of the solid for several types of initial and boundary condition.

Sedqui, Abderrahim; Guy, Bernard

2001-02-01

272

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

273

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

274

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

275

Preparation and characterization of activated carbon from cotton stalk by microwave assisted chemical activation--application in methylene blue adsorption from aqueous solution.  

PubMed

The activated carbon prepared from cotton stalk with ZnCl(2) as activation was investigated under microwave radiation. Effects on the yield and adsorption capacities of activated carbon were evaluated then, such as, microwave power, microwave radiation time and the impregnation ratio of ZnCl(2). It indicated that the optimum conditions were as follows: microwave power of 560 W, microwave radiation time of 9 min and the impregnation ratio of ZnCl(2) was 1.6g/g. Iodine number, amount of methylene blue adsorption and the yield of activated carbon prepared under optimum conditions were 972.92 mg/g, 193.50mg/g and 37.92%, respectively. Laboratory prepared activated carbons were characterized by pH(ZPC), SEM, FT-IR, S(BET) and pore structural parameters. Then they were used as adsorbent for the removal of methylene blue from aqueous solutions under varying conditions of initial concentration, carbon dosage and pH. It indicated that Langmuir isotherm was fitter than Freundlich isotherm and Temkin isotherm. PMID:19178998

Deng, Hui; Yang, Le; Tao, Guanghui; Dai, Jiulei

2008-12-25

276

Ion hydration and structural properties of water in aqueous solutions at normal and supercooled conditions: a test of the structure making and breaking concept.  

PubMed

We study with the method of molecular dynamics simulation the structural properties of aqueous solutions of NaCl, KCl and KF salts at ambient conditions and upon supercooling at constant pressure. The calculations are performed at increasing concentration of the salt starting from c = 0.67 mol kg(-1) up to 3.96 mol kg(-1). We investigate the modifications of the hydration shells and the changes in the water structure induced by the presence of the ions. The oxygen-oxygen structure is strongly dependent on the ionic concentration while it is almost independent from the cation. The hydrogen bonding is preserved at all concentrations and temperatures. The main effect of increasing the ionic concentration is the tendency of the water structure to assume the high density liquid form predicted for pure water upon supercooling. An important consequence of our analysis is that the concept of an ion as a structure maker or a structure breaker must be revisited to take into account the other ionic species, the ionic concentration and more generally the thermodynamic conditions of the solutions. PMID:22009186

Gallo, P; Corradini, D; Rovere, M

2011-10-19

277

Thermo-chemical ablation of heat shields under Earth reentry conditions  

NASA Astrophysics Data System (ADS)

The process of ablation for earth atmospheric entry is modeled. The flowfield surrounding the ablator is modeled by an extended set of Navier-Stokes equations that include the effects of thermochemical nonequilibrium. This set of equations encompasses the conservation of mass for each chemical species, conservation of momentum, the conservation of vibrational energy, and the conservation of total energy. The heat conduction into the ablator material is modeled by using Fourier's Law of heat conduction and the heat equation. The flowfield and ablator are coupled by a thermochemical ablation model that includes a surface mass balance and a surface energy balance. The ablation model takes into account chemical reactions of the flowfield species with the surface material, surface material acting as a catalytic surface, and sublimation of the surface material. To solve the governing equations for the model, a computational fluid dynamics approach is used where the flowfield is solved using a modified Steger-Warming flux vector splitting scheme and the solid is solved using a centrally differenced scheme. A Gauss-Seidel line relaxation technique is implemented to speed numerical convergence. The flowfield model is verified by comparing to flowfield computations of other researchers and to experimental data. The ablator/heat shield model is validated by a direct comparison between an exact analytical solution and a numerical solution. The thermochemical ablation model is verified by comparing to the experimental results of the Passive Nosetip Technology (PANT) program. The model is used to calculate steady-state ablation data for sphere-cone reentry bodies. Two bodies with nose radii of 0.0127 m and 0.1270 m are tested at a velocity of 8 km/s. The ablator material is selected to be a commercial grade graphite. Due to the ablator selection, the flowfield is limited to 11 chemical species and two internal energy modes. A standard earth atmosphere is selected at altitudes ranging from 40 km to 80 km. The major results concern the thermochemical ablation model. Both oxidation and sublimation mechanisms are evident and are dependent on freestream conditions and the reentry body shape.

Keenan, James Anthony

1994-04-01

278

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  

SciTech Connect

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 L{sub 3}-edge X-ray absorption fine structure (XAFS) spectra measured from a 0.006m Gd/0.16m HNO{sub 3} aqueous solution at temperatures up to 500 C and at pressures up to 260 MPa shows that the Gd-O distance of the Gd{sup 3+} aqua ion decreases steadily at a rate of {approx} 0.007 {angstrom}/100 C whereas the number of coordinated H{sub 2}O molecules decreases from 9.0 {+-} 0.5 to 7.0 {+-} 0.4. The loss of water molecules in the Gd{sup 3+} aqua ion inner hydration shell over this temperature range (a 22% reduction) is smaller than exhibited by the Yb{sup 3+} aqua ion (42% reduction) indicating that the former is significantly more stable than the later. We conjecture that the anomalous enrichment of Gd reported from measurement of REE concentrations in ocean waters may be attributed to the enhanced stability of the Gd{sup 3+} aqua ion relative to other REEs. Gd L{sub 3}-edge XAFS measurements of 0.006m and 0.1m GdCl{sub 3} aqueous solutions at temperatures up to 500 C and pressures up to 480 MPa reveal that the onset of significant Gd{sup 3+}-Cl{sup -} association occurs around 300 C. Partially-hydrated stepwise inner-sphere complexes most likely of the type Gd(H{sub 2}O){sub {delta}-n}Cl{sub n}{sup +3-n} occur in the chloride solutions at higher temperatures, where {delta} {approx} 8 at 300 C decreasing slightly to an intermediate value between 7 and 8 upon approaching 500 C. This is the first direct evidence for the occurrence of partially-hydrated REE Gd (this study) and Yb [Mayanovic, R.A., Jayanetti, S., Anderson, A.J., Bassett, W.A., Chou, I-M., 2002a. The structure of Yb{sup 3+} aquo ion and chloro complexes in aqueous solutions at up to 500 C and 270 MPa. J. Phys. Chem. A 106, 6591-6599.] chloro complexes in hydrothermal solutions. The number of chlorides (n) of the partially-hydrated Gd(III) chloro complexes increases steadily with temperature from 0.4 {+-} 0.2 to 1.7 {+-} 0.3 in the 0.006m chloride solution and from 0.9 {+-} 0.7 to 1.8 {+-} 0.7 in the 0.1m GdCl3 aqueous solution in the 300-500 C range. Conversely, the number of H{sub 2}O ligands of Gd(H{sub 2}O){sub {delta}-n}Cl{sub n}{sup +3-n} complexes decreases steadily from 8.9 {+-} 0.4 to 5.8 {+-} 0.7 in the 0.006m GdCl{sub 3} aqueous solution and from 9.0 {+-} 0.5 to 5.3 {+-} 1.0 in the 0.1m GdCl{sub 3} aqueous solution at temperatures from 25 to 500 C. Analysis of our results shows that the chloride ions partially displace the inner-shell water molecules during Gd(III) complex formation under hydrothermal conditions. The Gd-OH{sub 2} bond of the partially-hydrated Gd(III) chloro complexes exhibits slightly smaller rates of length contraction ({approx} 0.005 {angstrom}/100 C) for both solutions. The structural aspects of chloride speciation of Gd(III) as measured from this study and of Yb(III) as measured from our previous experiments are consistent with the solubility of these and other REE in deep-sea hydrothermal fluids.

Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I-Ming (SMSU); (Cornell); (SFX); (USGS)

2008-09-25

279

Self-conditioning of encapsulated abrasive pad in chemical mechanical polishing  

Microsoft Academic Search

Chemical mechanical polishing (CMP) is the process of planarization which was achieved by both chemical reaction and mechanical force. The polishing consists of moving wafer to be polished against the polyurethane pad, carrying slurry between wafer and polyurethane pad. There have been, however, some problems including dishing, erosion, high cost of consumables, environmental problems and scratches due to diamonds dropped

Hoyoun Kim; Hyoungjae Kim; Haedo Jeong; Heondeok Seo; Sangick Lee

2003-01-01

280

Chemical and toxicological evaluation of an emerging pollutant (enrofloxacin) by catalytic wet air oxidation and ozonation in aqueous solution.  

PubMed

This study evaluates the degradation efficiency of enrofloxacin (ENR) by catalytic wet air oxidation (CWAO) and ozonation. Results obtained by CWAO experiments show that 99.5% degradation, 37.0% chemical oxidation demand (COD) removal and 51.0% total organic carbon (TOC) conversion were obtained when 100 mol% FeCl(3) and 25 mol% NaNO(2) at 150 °C under 0.5 MPa oxygen pressure after 120 min are used. The degradation products are identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS), gas chromatography-mass spectrometry (GC-MS) and ion chromatography (IC). The oxidation end products, F(-), NO(3)(-) and NH(4)(+) were determined by IC. The BOD(5)/COD ratio as a measure of the biodegradability of the parent compound increased from 0.01 to 0.12 after 120 min of reaction time, indicating an improved biodegradability of the parent compound. The inhibition of bioluminescence of the marine bacteria V. fischeri decreased from 43% to 12% demonstrating a loss in toxicity of ENR during CWAO. Ozonation of 0.2 mM ENR was carried out with an ozone concentration of 7.3 g m(-3) at pH 7. ENR decomposition with a degradation rate of 87% was obtained corresponding to the reaction time. Moderate changes in COD (18%) and TOC (17%) removal has been observed. The bioluminescence inhibition increased from 8% to 50%, due to the generation of toxic degradation products during ozonation. In comparison to the widely use of well developed method of ozonation CWAO exhibits better performance in terms of COD, TOC removals and generates less toxic products. PMID:22858256

Li, Yan; Zhang, Feifang; Liang, Xinmiao; Yediler, Ayfer

2012-08-01

281

In situ investigation of wet chemical processes for chalcopyrite solar cells by Ledge XAS under ambient conditions  

Microsoft Academic Search

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,

Stefanie M. Greil; Iver Lauermann; Ahmed Ennaoui; Timo Kropp; Kathrin M. Lange; Matthieu Weber; Emad F. Aziz

2010-01-01

282

Agglomerated Large Particles under Various Slurry Preparation Conditions and Their Influence on Shallow Trench Isolation Chemical Mechanical Polishing  

Microsoft Academic Search

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

Dae-Hyeong Kim; Hyun-Goo Kang; Sang-Kyun Kim; Ungyu Paik; Jea-Gun Park

2005-01-01

283

Biological effects of plant residues with contrasting chemical compositions on plant and soil under humid tropical conditions  

Microsoft Academic Search

A study on plant residues with contrasting chemical compositions was conducted under laboratory, growth chamber and humid tropical field conditions to understand the function of the soil fauna in the breakdown of plant residues, the cycling of nutrients, in particular nitrogen, and the performance of maize as a test crop. Leaves from ten agroforestry and fallow plant species with a

G. Tian

1992-01-01

284

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

285

Evaluating the impact of chemical boundary conditions on near surface ozone in regional climate–air quality simulations over Europe  

NASA Astrophysics Data System (ADS)

A modeling system based on the air quality model CAMx driven off-line by the regional climate model RegCM3 is used for assessing the impact of chemical lateral boundary conditions (LBCs) on near surface ozone over Europe for the period 1996–2000. The RegCM3 and CAMx simulations were performed on a 50 km × 50 km grid over Europe with RegCM3 driven by the NCEP meteorological reanalysis fields and CAMx with chemical LBCs from ECHAM5/MOZART global model. The recent past period (1996–2000) was simulated in three experiments. The first simulation was forced using time and space invariant LBCs, the second was based on ECHAM5/MOZART chemical LBCs fixed for the year 1996 and the third was based on ECHAM5/MOZART chemical LBCs with interannual variability. Anthropogenic and biogenic emissions were kept identical for the three sensitivity runs.

Akritidis, D.; Zanis, P.; Katragkou, E.; Schultz, M. G.; Tegoulias, I.; Poupkou, A.; Markakis, K.; Pytharoulis, I.; Karacostas, Th.

2013-12-01

286

Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by cellulose and mercerized cellulose chemically modified with succinic anhydride.  

PubMed

This work describes the preparation of new chelating material from mercerized cellulose. The first part treats the chemical modification of non-mercerized cellulose (cell 1) and mercerized cellulose (cell 2) with succinic anhydride. Mass percent gains (mpg) and degree of succinylation (DS) of cell 3 (from cell 1) and cell 4 (from cell 2) were calculated. Cell 4 in relation to cell 3 exhibited an increase in mpg and in the concentration of carboxylic functions of 68.9% and 2.8 mmol/g, respectively. Cells 5 and 6 were obtained by treatment of cells 3 and 4 with bicarbonate solution to release the carboxylate functions and characterized by FTIR. The second part compares the adsorption capacity of cells 5 and 6 for Cu2+, Cd2+, and Pb2+ ions in an aqueous single metal solution. Adsorption isotherms were developed using Langmuir model. Cell 6 in relation to cell 5 exhibited an increase in Qmax for Cu2+ (30.4 mg/g), Cd2+ (86.0 mg/g) and Pb2+ (205.9 mg/g). PMID:17706418

Gurgel, Leandro Vinícius Alves; Júnior, Osvaldo Karnitz; Gil, Rossimiriam Pereira de Freitas; Gil, Laurent Frédéric

2007-08-13

287

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

288

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

289

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)

1995-12-31

290

Maximizing productivity of CHO cell-based fed-batch culture using chemically defined media conditions and typical manufacturing equipment.  

PubMed

A highly productive chemically defined fed-batch process was developed to maximize titer and volumetric productivity for Chinese hamster ovary cell-based recombinant protein manufacturing. Two cell lines producing a recombinant antibody (cell line A) and an Fc-fusion protein (cell line B) were used for development. Both processes achieved product titers of 10 g/L on day 18 under chemically defined conditions. For cell line B, the use of plant derived hydrolysates combined with the optimized chemically defined medium increased the titer to 13 g/L. Volumetric productivities were increased from a base line of about 200 mg/L/d to about 500 mg/L/d under chemically defined conditions and as high as 700 mg/L/d with cell line B using plant derived hydrolysates. Peak cell densities reached greater than 20E6 vc/mL, and cell viabilities were maintained above 80% on day 18 without the use of antiapoptotic genes or temperature shift. A rapid compound screening method was developed to effectively test positive factors within 72 h. Peak volumetric oxygen uptake rates (OUR) more than tripled from the baseline condition. Oxygen demand continued to increase after maximum cell density was reached with a maximal OUR of 3.7 mmol/L/h. The new process format was scaled up and verified at 100 L pilot scale using reactor equipment of similar configuration as used at manufacturing scale. PMID:20945494

Huang, Yao-Ming; Hu, WeiWei; Rustandi, Eddie; Chang, Kevin; Yusuf-Makagiansar, Helena; Ryll, Thomas

291

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...

292

Methane hydrate phase equilibrium in the presence of salt (NaCl, KCl, or CaCl 2) + ethylene glycol or salt (NaCl, KCl, or CaCl 2) + methanol aqueous solution: Experimental determination of dissociation condition  

Microsoft Academic Search

In this communication, we report dissociation conditions of methane hydrates in the presence of salt (NaCl, KCl, or CaCl2)+ethylene glycol or salt (NaCl, KCl, or CaCl2)+methanol aqueous solutions at different temperatures. The equilibrium data were generated using an isochoric pressure-search method. These data are compared with some selected experimental data from the literature on dissociation conditions of methane hydrates in

Amir H. Mohammadi; Dominique Richon

2009-01-01

293

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

294

Laboratory conditions and safety in a chemical warfare agent analysis and research laboratory.  

PubMed

Toxic chemicals have been used as weapons of war and also as means of terrorist attacks on civilian populations. Research focusing on chemical warfare agents (CWAs) may be associated with an increased risk of exposure to and contamination by these agents. This article summarizes some of the regulations concerning designation and safety in a CWA analysis and research laboratory and medical countermeasures in case of an accidental exposure. The design of such a laboratory, coupled with a set of safety guidelines, provides for the safe conduct of research and studies involving CWAs. Thus, a discussion of decontamination and protection means against CWAs is also presented. PMID:12188231

Kenar, Levent; Karayilano?lu, Turan; Kose, Songul

2002-08-01

295

EPR Detection of HNO2- in the Radiolysis of Aqueous Nitrite and Quantum Chemical Calculation of Its Stability and Hyperfine Parameters  

SciTech Connect

Experimental and theoretical evidence is presented to support a prior suggestion [Lymar et al. J. Phys. Chem. A 2002, 106, 7245] that radiolytically generated hydrogen atoms attack at the nitrogen, rather than the oxygen, of nitrite ions in aqueous solution. Time-resolved electron spin resonance detection was used to unambiguously identify the HNO2 ?- radicals formed. At pH 9 the radicals live about 10 ?s, and have quite broad (0.6 G) lines. The observed hyperfine splitting at nitrogen was aN 19.6 G, with each of the three nitrogen lines further split by the small hydrogen coupling, aH 4.5 G. The g factor for the radical is 2.0053. Although this is the first observation of this radical in fluid solution, the ESR parameters are consistent with previous observations in the solid phase. The identity of the radical was also confirmed by quantum chemical calculation of the ESR parameters, including the g factor. It was necessary to take into account vibrational modulation of the computed hyperfine parameters when comparing theory to experiment because of the large-amplitude motion of the hydrogen atom in the pyramidal radical. The yield of HNO2 ?- radicals was estimated at 70% of the available H atoms by a kinetic method. Computed thermodynamic parameters confirm that, in the gas phase, both HNO2 ?- and HONO?- are stable relative to the asymptotes H + NO2- and OH- + NO, with HNO2 ?- 40 kJ mol-1 above HONO?- but protected from rearrangement by a large barrier. In solution, calculations indicate that while HNO2 ?- is still bound with respect to dissociation into H + NO2-, it is now only 3.2 kJ mol-1 above HONO?- which, in turn, lies about 73 kJ mol-1 above OH- + NO, and dissociation is driven by the strong solvation of the hydroxide ion.

Hug, Gordon L.; Camaioni, Donald M.; Carmichael, Ian

2004-08-05

296

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

297

Chemical safety of conventionally and organically produced foodstuffs: a tentative comparison under Belgian conditions  

Microsoft Academic Search

This paper goes through the chemical risks able to affect the organic and the conventional agro-food products. For each type of contaminant a tentative assessment has been made in considering not only the levels of exposure but also the toxicological data when available. When comparing both production systems with regards to food safety, it appears that, for the well-known toxicants

Luc Pussemier; Yvan Larondelle; Carlos Van Peteghem

298

Chemical modification of L-asparaginase from Escherichia coli with a modified polyethyleneglycol under substrate protection conditions.  

PubMed

L-Asparaginase was chemically modified with 2,4-bis(O-methoxypolyethyleneglycol)-6-chloro-S-triazine (mPEG2) in the presence of L-asparagine. Optimal modification was performed under the condition that the molar ratio of mPEG2/-NH2 is 10. The modified enzyme retained 33% of initial enzymatic activity with complete abolishment of immunogenicity. In vitro half-life increment from 4.6 h to 33 h has been obtained. PMID:15195977

Zhang, Jian-Feng; Shi, Ling-Yang; Wei, Dong-Zhi

2004-05-01

299

Conditions required for citrate utilization during growth of Lactobacillus casei ATCC334 in chemically defined medium and Cheddar Cheese extract  

Microsoft Academic Search

Conditions required for citrate utilization by Lactobacillus casei ATCC334 were identified. Citrate was utilized by this microorganism in modified Chemically Defined Media (mCDM) as an energy source, solely in the presence of limiting concentrations of galactose. The presence of glucose inhibited citrate utilization by this microorganism even when added in limiting concentrations. Utilization of citrate occurred at pH 6.0 ± 0.2 and

Ilenys Díaz-Muñiz; James L. Steele

2006-01-01

300

Influence of sample surface condition on chemical analysis using laser ablation inductively coupled plasma atomic emission spectroscopy  

Microsoft Academic Search

The influence of sample surface condition on chemical analysis was investigated when using laser ablation sampling with inductively coupled plasma atomic emission spectroscopy (ICP-AES). The ablated mass quantity and composition were found to be significantly different from original vs. pre-ablated surfaces. The ablated mass quantity from original surfaces was much greater than that from pre-ablated surfaces, and the ablation rate

Xianglei Mao; Richard E. Russo; Wing-Tat Chan

1997-01-01

301

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

Microsoft Academic Search

The purpose of this study is to investigate the effects of the cooperative learning approach based on conceptual change conditions\\u000a over traditional instruction on 10th grade students' conceptual understanding and achievement of computational problems related\\u000a to chemical equilibrium concepts. The subjects of this study consisted of 87 tenth grade students from two intact classes\\u000a of a Chemistry Course instructed by

Ibrahim Bilgin; Ömer Geban

2006-01-01

302

Chemical reactions involved in the deep fat frying of foods. I. A laboratory apparatus for frying under simulated restaurant conditions  

Microsoft Academic Search

A laboratory apparatus has been designed which can be used to quantitatively collect the volatile decomposition products produced\\u000a during deep fat frying under simulated restaurant conditions. In order to study the chemical reactions of frying fat without\\u000a any inter-reaction with the food fried, moist cotton balls were fried in corn oil.\\u000a \\u000a The oil used for frying was shown to differ

R. G. Krishnamurthy; Tsukasa Kawada; S. S. Chang

1965-01-01

303

Transport and fate of bacteria in porous media: Coupled effects of chemical conditions and pore space geometry  

Microsoft Academic Search

(1) Experimental and theoretical studies were undertaken to explore the coupled effects of chemical conditions and pore space geometry on bacteria transport in porous media. The retention of Escherichia coli D21g was investigated in a series of batch and column experiments with solutions of different ionic strength (IS) and ultrapure quartz sand. Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations and results from batch experiments

Saeed Torkzaban; Shiva S. Tazehkand; Sharon L. Walker; Scott A. Bradford

2008-01-01

304

Effects of Calcination and Milling Process Conditions for Ceria Slurry on Shallow-Trench-Isolation Chemical-Mechanical Polishing Performance  

Microsoft Academic Search

To improve the performance of shallow trench isolation chemical-mechanical polishing (STI-CMP) in terms of the removal selectivity of oxide and nitride films and the formation of surface defects, we investigated the effects of the calcination and milling process conditions during ceria slurry synthesis. We have focused on the effects of particle size distribution, the large-particle size, and the dispersion stability

Jun-Seok Kim; Hyun-Goo Kang; Manabu Kanemoto; Ungyu Paik; Jea-Gun Park

2007-01-01

305

Long-term self-renewal and directed differentiation of human embryonic stem cells in chemically defined conditions  

Microsoft Academic Search

Chemically defined medium (CDM) conditions for controlling human embryonic stem cell (hESC) fate will not only facilitate the practical application of hESCs in research and therapy but also provide an excellent system for studying the molecular mechanisms underlying self-renewal and differentiation, without the multiple unknown and variable factors associated with feeder cells and serum. Here we report a simple CDM

Shuyuan Yao; Shuibing Chen; Julie Clark; Ergeng Hao; Gillian M. Beattie; Alberto Hayek; Sheng Ding

2006-01-01

306

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

307

Electrochemical studies of Copper, Tantalum and Tantalum Nitride surfaces in aqueous solutions for applications in chemical-mechanical and electrochemical-mechanical planarization  

NASA Astrophysics Data System (ADS)

This report will investigate fundamental properties of materials involved in integrated circuit (IC) manufacturing. Individual materials (one at a time) are studied in different electrochemical environmental solutions to better understand the kinetics associated with the polishing process. Each system tries to simulate a real CMP environment in order to compare our findings with what is currently used in industry. To accomplish this, a variety of techniques are used. The voltage pulse modulation technique is useful for electrochemical processing of metal and alloy surfaces by utilizing faradaic reactions like electrodeposition and electrodissolution. A theoretical framework is presented in chapter 4 to facilitate quantitative analysis of experimental data (current transients) obtained in this approach. A typical application of this analysis is demonstrated for an experimental system involving electrochemical removal of copper surface layers, a relatively new process for abrasive-free electrochemical mechanical planarization of copper lines used in the fabrication of integrated circuits. Voltage pulse modulated electrodissolution of Cu in the absence of mechanical polishing is activated in an acidic solution of oxalic acid and hydrogen peroxide. The current generated by each applied voltage step shows a sharp spike, followed by a double-exponential decay, and eventually attains the rectangular shape of the potential pulses. For the second system in chapter 5, open-circuit potential measurements, cyclic voltammetry and Fourier transform impedance spectroscopy have been used to study pH dependent surface reactions of Cu and Ta rotating disc electrodes (RDEs) in aqueous solutions of succinic acid (SA, a complexing agent), hydrogen peroxide (an oxidizer), and ammonium dodecyl sulfate (ADS, a corrosion inhibitor for Cu). The surface chemistries of these systems are relevant for the development of a single-slurry approach to chemical mechanical planarization (CMP) of Cu lines and Ta barriers in the fabrication of semiconductor devices. It is shown that in non-alkaline solutions of H2O2, the SA-promoted surface complexes of Cu and Ta can potentially support chemically enhanced material removal in low-pressure CMP of surface topographies overlying fragile low-k dielectrics. ADS can suppress Cu dissolution without significantly affecting the surface chemistry of Ta. Chapter 6 discusses anodic corrosion of Ta, which is examined as a possible route to voltage induced removal of Ta for potential applications in electrochemical mechanical planarization (ECMP) of diffusion barriers. This strategy involves electro-oxidation of Ta in the presence of NO3- anions to form mechanically weak surface oxide films, followed by removal of the oxide layers by moderate mechanical abrasion. This NO3 - system is compared with a reference solution of Br -. In both electrolytes, the voltammetric currents of anodic oxidation exhibit oscillatory behaviors in the initial cycles of slow (5 mV s-1) voltage scans. The frequencies of these current oscillations are show signature attributes of localized pitting or general surface corrosion caused by Br- or NO3 -, respectively. Scanning electron microscopy, cyclic voltammetry, polarization resistance measurements, and time resolved Fourier transform impedance spectroscopy provide additional details about these corrosion mechanism. Apart from their relevance in the context of ECMP, the results also address certain fundamental aspects of pitting and general corrosions. The general protocols necessary to combine and analyze the results of D.C. and A.C. electrochemical measurements involving such valve metal corrosion systems are discussed in detail. In chapter 7 potassium salts of certain oxyanions (nitrate, sulfate and phosphate in particular) are shown to serve as effective surface-modifying agents in chemically enhanced, low-pressure chemical mechanical planarization (CMP) of Ta and TaN barrier layers for interconnect structures. The surface reactions that form the basis of this CMP strategy are investigated he

Sulyma, Christopher Michael

308

Kinematical Modeling of Pad Profile Variation during Conditioning in Chemical Mechanical Polishing  

Microsoft Academic Search

Conditioning is the process of removing the glazing area from a polishing pad surface and restoring the quality of the surface to maintain a stable polishing performance. However, the conditioning process can induce a non-uniform profile variation of the pad, which can result in nonuniform material removal rates across the wafer. In this paper, a kinematical model based on Preston's

Sangjik Lee; Sukhoon Jeong; Hyoungjae Kim; Haedo Jeong

2009-01-01

309

Forest condition and chemical characteristics of atmospheric depositions: research and monitoring network in Lombardy  

Microsoft Academic Search

Since 1987, the Regional Forestry Board of Lombardy and the Water Research Institute of the National Research Council have been carrying out surveys of forest conditions and the response of the ecosystem to environmental factors. The study approach is based on a large number of permanent plots for extensive monitoring (Level 1). At this level, crown condition is assessed annually,

Raffaella BALESTRINI; Antonio TAGLIAFERRI; Gianni TARTARI; Flaminio DI GIROLAMO

310

Boundary conditions for flows with chemical reactions occurring on a surface  

Microsoft Academic Search

With the use of a solution of a model Boltzmann equation for a binary mixture in the Knudsen layer, we obtain the boundary conditions for the equations of gas dynamics when the reactionliAi?ljAj (li molecules of Ai change intolj molecules of Aj, and vice versa) is occurring on a surface. The boundary condition that we obtain differs from those that

M. N. Kogan; N. K. Makashev

1972-01-01

311

conditions  

Microsoft Academic Search

Real-time scheduling is both based on a broad theoretical background and available through a multitude of tools and infrastructures. The central input parameters to this discipline are the demand for execution time and the real- time conditions given as deadlines or periods. The former has attracted a lot of research efforts, mainly in the scope of worst case execution time

Dieter Z

312

[Extraction of alpha-cypermethrin from aqueous methanol solutions].  

PubMed

Alpha cypermethrin was extracted from aqueous methanol solutions using hydrophobic organic solvents. The efficiency of extraction was shown to depend on the chemical nature of the solvent, the water to methanol ratio, and saturation of the aqueous methanol layer with an electrolyte. Optimal extraction of alpha-cypermethrin was achieved using toluene as the solvent under desalinization conditions. The extraction factor for the removal of the sought amount of alpha-cypermethrin from the water-methanol solution (4:1) using various solvents was calculated. PMID:20734789

Shormanov, V K; Chigareva, E N; Belousova, O V

313

Electronic structure of DNA polynucleotides under the chemical-doping condition investigated by PES and NEXAFS  

NASA Astrophysics Data System (ADS)

During the last several years, the carrier transport through DNA between nm- spaced electrodes has been discussed without the understanding of their intrinsic electronic structures. As a result, its 'scattered' results in the controversial magnitude of conductivity, from a good conductor to an insulator, which is also assumed to be dependent on the chemical species surrounding DNA (H^+, counterion, etc.)@[ref.]. In this talk, we show electronic structures of the occupied- and unoccupied-states near the Fermi level. Systems exhibited here are well-defined sequence of DNA polynucleotides, Poly(dG)-poly(dC) and Poly(dA)-poly(dT), with- and without- chemical-doping (carrier-doping), in order to evaluate such an effect into DNA and also to propose the carrier conduction mechanism through DNA. [ref.] M. Taniguchi et al., submitted to JACS.

Furukawa, Masashi; Kato, H. S.; Taniguchi, M.; Hatsui, T.; Kosugi, N.; Komeda, T.; Kawai, Maki; Kawai, T.

2003-03-01

314

The effect of reaction condition on composition and properties of ultrafine amorphous powders in (Fe, Co, Ni)-b systems prepared by chemical reduction  

Microsoft Academic Search

Amorphous ultrafine powders in (Fe, Co, Ni)-B binary systems were prepared in different reduction conditions of metal ions\\u000a in an aqueous solution by use of KBH4, with the aim of clarifying the effect of reaction conditions on the composition, thermal stability, and magnetic properties\\u000a of the resultant amorphous powders. As the mol ratio of KBH4 to metal ions decreases, the

Junji Saida; Akihisa Inoue; Tsuyoshi Masumoto

1991-01-01

315

Delamination analysis of Cu\\/low-k technology subjected to chemical-mechanical polishing process conditions  

Microsoft Academic Search

The mechanical response at the interface between the silicon, low-k and copper layer of the wafer is simulated herein under the loading of the chemical-mechanical polishing (CMP). To identify the possible generation\\/propagation of the initial crack, the warpage induced by the thin-film fabrication process are considered, and applying pressure, status of slurry and the copper thickness are treated as the

CA Yuan; W. D. Van Driel; R. B. R. Van Silfhout; O. Van Der Sluis; R. A. B. Engelen; L. J. Ernst; F. Van Keulen; G. Q. Zhang

2006-01-01

316

Effect of chemical structure on the biodegradation of polyurethanes under composting conditions  

Microsoft Academic Search

Polyester–polyurethanes having different chemical structure were synthesized and their biodegradabilities were investigated. Average molecular weight of the synthesized polyurethanes ranged from 79106 to 161715(Mw) by gel permeation chromatography. Degradation experiments were conducted by: hydrolytic degradation in NaOH solution; enzymatic degradation by lipase; and composting. Hydrolytic and enzymatic degradation decreased with the increase of the diol carbon chains in polyol, and

Young Duk Kim; Sung Chul Kim

1998-01-01

317

Fluidized bed chemical vapor deposition of pyrolytic carbon – I. Effect of deposition conditions on microstructure  

Microsoft Academic Search

The effect of deposition temperature and precursor concentration on the microstructure of pyrolytic carbon (PyC) has been studied by using SEM, TEM, Raman spectroscopy, X-ray diffraction and porosimetry. PyC was produced by fluidized bed chemical vapor deposition (FBCVD) at deposition temperatures from 1250 to 1450°C and with acetylene and acetylene\\/propylene mixtures at different concentrations. Changes in the density, anisotropy, and

E. López-Honorato; P. J. Meadows; P. Xiao

2009-01-01

318

Physico­chemical Properties of Secondary Organic Aerosol (soa) Particles Generated Under Laboratory Photooxidation Conditions  

Microsoft Academic Search

The goal of this experiment is to investigate the chemical reactivity of secondary or- ganic aerosol particles (SOA) in the presence of NOx. of special interest is the ques- tion whether or not SOA enables the reduction of NO2 to HONO, an important photochemical OH precursor. We report the controlled production of SOA particles using 5ppm of toluene (C7H8) or

B. Demirdjian; M. J. Rossi

2002-01-01

319

Growth process conditions of vertically aligned carbon nanotubes using plasma enhanced chemical vapor deposition  

Microsoft Academic Search

The growth of vertically aligned carbon nanotubes using a direct current plasma enhanced chemical vapor deposition system is reported. The growth properties are studied as a function of the Ni catalyst layer thickness, bias voltage, deposition temperature, C2H2:NH3 ratio, and pressure. It was found that the diameter, growth rate, and areal density of the nanotubes are controlled by the initial

M. Chhowalla; K. B. K. Teo; C. Ducati; N. L. Rupesinghe; G. A. J. Amaratunga; A. C. Ferrari; D. Roy; J. Robertson; W. I. Milne

2001-01-01

320

Conditions  

Microsoft Academic Search

A shallow, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)- contaminated aquifer at Naval Submarine Base Bangor has been characterized as predominantly manganese-reducing, anoxic with local pockets of oxic conditions. The potential contribution of microbial RDX degradation to localized decreases observed in aquifer RDX concentrations was assessed in sediment microcosms amended with (U- 14 C) RDX. Greater than 85% mineralization of 14 C-RDX to 14 CO2

Paul M. Bradley; Richard S. Dinicola

321

Rheological Behavior of Pusher 500 under a Variety of Chemical and Thermal Conditions: Topical Report.  

National Technical Information Service (NTIS)

This project is designed to provide information to understand and model the rheological behavior of polymers under a variety of simulated reservoir conditions and to gain the knowledge of the fidelity with which external measurements characterize mobility...

H. W. Gao P. B. Lorenz S. Brock

1987-01-01

322

Chemical aspects of deposition\\/corrosion from coal-water fuels under gas turbine conditions  

Microsoft Academic Search

This patent describes a staged, subscale turbine combustor based on a promising rich-quench-lean combustion approach to reduce NOâ emissions used to evaluate deposition, erosion, and corrosion (DEC) from coal-water fuels (CWF). This combustor was operated with three CWF at conditions of a recuperated turbine. Specimens were exposed in two test sections at temperature conditions of the first stator vanes and

R. A. Wenglarz; R. G. Jr. Fox

1990-01-01

323

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

324

[Hygienic assessment of labor conditions in chemical industry sites during reconstruction].  

PubMed

In periods of reconstruction of chemical enterprises, hazardous compounds concentrations may exceed MAC, they are also characterized by contamination of the skin with toxic substances, welding aerosols discharge into the working zone, and microclimate distabilization. The workers' health states display functional shifts with concomitant decrease of labour productivity, increase heart rates, a higher 11-oxycorticosteroids contents in saliva and peroxidase activity. Morbidity with temporary disability also increases. A range of health improving measures is needed to be performed at the stages of preventive sanitary control. PMID:2376335

Mikha?luts, A P; Pershin, A N

1990-01-01

325

Chemical and microbiological changes in fluid milk as affected by packaging conditions  

Microsoft Academic Search

Changes in chemical and microbiological quality parameters of whole pasteurized milk stored under fluorescent light at 4°C in pouches made of (a) low density polyethylene (LDPE, clear and TiO2 pigmented, 60?m in thickness), (b) coextruded (LDPE\\/polyamide\\/LDPE, clear and TiO2 pigmented, 60?m in thickness) and (c) coextruded (LDPE+2% TiO2\\/LDPE+2% TiO2\\/LDPE+4% carbon black pigment\\/LDPE+2% TiO2\\/LDPE+2% TiO2), 60 and 110?m in thickness were

Evangelia Vassila; Anastasia Badeka; Efthymia Kondyli; Ioannis Savvaidis; Michael G Kontominas

2002-01-01

326

Sustainable Applications of Nano-Catalysts and Alternative Methods in the Greener Synthesis and Transformations of Chemical  

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...

327

Chemical Interaction of CdTe and CdZnTe with Aqueous Solutions of H2O2-HI-Tartaric Acid  

NASA Astrophysics Data System (ADS)

An iodine-based etching system, H2O2-HI-tartaric acid, was tested on CdTe samples with (110), (100), (111)A, and (111)B orientations. The etching rate of CdTe was shown to depend on the sample orientation, ratio of etchant composition components, temperature, and rotation speed of the disc. A study of the chemical composition and structure of the (211)B Cd1- x Zn x Te surfaces etched under different conditions was carried out. X-ray photoelectron spectroscopy (XPS) measurements showed that a nearly stoichiometric surface was achieved after heating of the etched surface in vacuum. Reflection high-energy electron diffraction (RHEED) measurements revealed a very good single-crystalline surface layer in samples etched with HI-based solutions as compared with bromine-methanol treatment.

Moravec, P.; Ivanits'ka, V. G.; Franc, J.; Tomashik, Z. F.; Tomashik, V. M.; Mašek, K.; Feychuk, P. I.; Shcherbak, L. P.; Höschl, P.; Grill, R.; Walter, J.

2009-08-01

328

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

DOEpatents

It is an object of the claimed invention to combine chemical treatment with microfiltration process to treat groundwater, leachate from contaminated soil washing, surface and run-off waters contaminated with toxic metals, radionuclides and trace amounts of organics from variety of sources. The process can also be used to treat effluents from industrial processes such as discharges associated with smelting, mining and refining operations. Influent contaminants amenable to treatment are from a few mg/L to hundreds of mg/L. By selecting appropriate precipitation, ion exchange and adsorption agents and conditions, efficiencies greater than 99.9 percent can be achieved for removal of contaminants. The filtered water for discharge can be targeted with either an order of magnitude greater or lower than contaminant levels for drinking water.

Vijayan, S.; Wong, Chi Fun; Buckley, L.P.

1992-12-31

329

Metal-free activation of H 2 O 2 by synergic effect of ionic liquid and microwave: chemoselective oxidation of benzylic alcohols to carbonyls and unexpected formation of anthraquinone in aqueous condition  

Microsoft Academic Search

H2O2 mediated oxidation of alcohols in ionic liquid is revisited, wherein, ionic liquids under the influence of microwave irradiation\\u000a have been found to facilitate activation of H2O2 without any metal catalyst in aqueous condition. The method utilizes a neutral ionic liquid [hmim]Br both as catalyst and\\u000a solvent for efficient and chemoselective oxidation of benzyl alcohol derivatives on aromatic (?, ?)

Rakesh Kumar; Nandini Sharma; Naina Sharma; Abhishek Sharma; Arun K. Sinha

330

Aqueous-phase chemical processes in deliquescent sea-salt aerosols: A mechanism that couples the atmospheric cycles of S and sea salt  

SciTech Connect

The aqueous-phase chemistry of deliquescent sea-salt aerosols in the remote marine boundary layer is investigated with a steady state box model. The model simulates the scavenging of soluble and reactive gaseous species by the sea-salt aerosols, the chemical reactions of these species and sea-salt ions in the deliquescent solution, and changes in the aerosol composition that occur as a result of these processes. The calculations indicate that deliquescent sea-salt aerosols are strongly buffered with a pH that remains close to 8 until the amount of acid added to the aerosol solution exceeds the alkalinity of sea salt. The oxidation of chloride by O[sub 3] and by free radicals is found to proceed at extremely slow rates, and thus these reactions cannot explain the high-chloride deficits recently observed over the North Atlantic Ocean. On the other hand, the oxidation of dissolved S[sub IV] by O[sub 3] in sea-salt aerosols is found to proceed at rates approaching 0.1 eq L[sup [minus]1] hr[sup [minus]1] and appears to be sufficiently rapid to qualitatively explain the observations of nss-SO[sub 4][sup +] in sea-salt aerosols over the North Atlantic Ocean. The calculations suggest the existence of a removal mechanism for atmospheric S that is largely controlled by the alkalinity of seawater and the flux of this alkalinity into the atmosphere in sea salt. It is estimated that this process will and ultimately remove about (1-4) [times] 10[sup 11]moles of SO[sub 2] from the atmosphere annually. Comparison of this loss rate with other elements of the atmospheric S cycle suggests that sea salt may remove a significant amount of S from the marine atmosphere and thereby depress the SO[sub 2] concentration in the marine boundary layer and limit the number of cloud condensation nuclei generated from the oxidation of SO[sub 2]. 59 refs., 11 figs., 7 tabs.

Chameides, W.L.; Stelson, A.W. (Georgia Inst. of Technology, Atlanta (United States))

1992-12-20

331

RESEARCHES CONCERNING THE CHEMICAL PRESERVATION OF WOOD USED IN CONDITIONS OF HAZARD CLASS 4  

Microsoft Academic Search

Depending on the forest exploitation, utilization and not in the last, on the climate conditions, the wood is subjected to biodeterioration. The wood infection with biological agents, can start from the forest, at living trees, extending it on the sawn timber stored, processed and even on the wood in service. Taking into account the whole variety of biotic and abiotic

OCTAVIA ZELENIUC

332

Nitrate and ammonium nutrition in ryegrass: Changes in growth and chemical composition under hydroponic conditions  

Microsoft Academic Search

Nitrogen (N) is one of the most critical elements affecting grass seed yield. In soil and cropping conditions of Western Oregon, ammonium?N may play an important role in the growth and development of ryegrass grown for seed. Our objectives were to determine the physiological and biochemical effects of ammonium and nitrate nutrition on ryegrass vegetative growth and subsequent expression of

Stephen M. Griffith; Donald J. Streeter

1994-01-01

333

Connection between body condition score, chemical characteristics of body and reproductive traits of rabbit does  

Microsoft Academic Search

Body condition scoring (BCS) is widely used to evaluate the nutritional status of livestock (cows, ewes, sows). In intensive systems, rabbit does are generally inseminated 11 days post partum and, due to a hormonal antagonism and an energy deficit caused by concurrent lactation and pregnancy, they show low fertility. The aim of this investigation was to assess an in vivo method

R. Cardinali; A. Dal Bosco; A. Bonanno; A. Di Grigoli; P. G. Rebollar; P. L. Lorenzo; C. Castellini

2008-01-01

334

Simulating the conditions for the formation of graphene and graphene nanowalls by semiempirical quantum chemical methods  

NASA Astrophysics Data System (ADS)

A "substrate-surface graphene island" is simulated by semiempirical quantum chemical methods for different substrates. It is established that such systems with various island sizes correspond to graphene growth on corresponding substrates when CVD is used. Carbon atoms can be incorporated into the island from either the side of the substrate or the side of the CVD reactor exposed to it. It is shown for a wide range of island sizes that the best configuration with respect to the substrate is the structure of a carbon nanowall oriented perpendicular to the substrate. It is emphasized that a transition to this configuration is possible in reality only if CVD is plasma-stimulated when there is a strong near-electrode field near the surface, and the preliminary scission of the carbon carrier material occurs simultaneously in the CVD reactor volume.

Alekseev, N. I.; Luchinin, V. V.; Charykov, N. A.

2013-10-01

335

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

336

Depth profiling nano-analysis of chemical environments using resonant Raman spectroscopy at grazing incidence conditions.  

PubMed

Both X-ray total reflection and X-ray Raman scattering techniques were combined to discriminate chemical environments in depth-profiling studies using an energy dispersive system. This allowed, for the first time, to resolve oxidation state on surface nanolayers with a low-resolution system. Samples of pure Cu and Fe oxidized in tap water and salty water, respectively, were studied in the Brazilian synchrotron facility using monochromatic radiation and an EDS setup. The measurements were carried out in total reflection geometry with incident energy lower and close to the K absorption edge of both elements. The results allowed observing the presence of very thin oxide layers, usually not observable with conventional geometries of irradiation. They also permit the identification of the compound present in a particular depth of the sample with nanometric, or even subnanometric, resolution using a low-resolution system. PMID:23782456

Leani, Juan José; Sánchez, Héctor J; Pérez, Roberto D; Pérez, Carlos

2013-07-12

337

Effect of chemical composition and sintering conditions on the mechanical properties of sintered duplex stainless steels  

Microsoft Academic Search

Duplex stainless steels were obtained through powder metallurgy technology from austenitic AISI 316L and ferritic AISI 430L powders mixed in different amounts to obtain ratios of austenite\\/ferrite of 25\\/75, 50\\/50 and 75\\/25. Prepared powder mixes were compacted at 650 or 750MPa and sintered in N2–H2 atmosphere (95%-5%) at several sintering conditions and with three sintering cooling rates (furnace, gas and

F. Martín; C. García; Y. Blanco

2011-01-01

338

Fluidized bed chemical vapor deposition of pyrolytic carbon – II. Effect of deposition conditions on anisotropy  

Microsoft Academic Search

Pyrolytic carbon coatings were deposited on top of alumina particles at deposition temperatures from 1250°C to 1450°C and with acetylene and acetylene\\/propylene mixtures at concentrations between 25% and 70%, v\\/v. The anisotropy of pyrolytic carbon coatings was quantified using electron diffraction and Raman peak intensities, and related to the deposition conditions and microstructure. In correlation with the TEM images, it

P. J. Meadows; E. López-Honorato; P. Xiao

2009-01-01

339

Emission characteristics of nitrogen- and sulfur-containing odorous compounds during different sewage sludge chemical conditioning processes.  

PubMed

Chemical conditioners are often used to enhance sewage sludge dewaterability through altering sludge properties and flocs structure, both affect odorous compounds emissions not only during sludge conditioning but also in subsequent sludge disposal. This study was to investigate emission characteristics of ammonia (NH(3)), sulfur dioxide (SO(2)), hydrogen sulfide (H(2)S) and carbonyl sulfide (COS) generated from sewage sludge conditioned by three representative conditioners, i.e., organic polymers, iron salts and skeleton builders, F-S (Fenton's reagent and skeleton builders) composite conditioner. The results demonstrate that polyacrylamide (PAM) has an insignificant effect on emission characteristics of nitrogen- and sulfur-containing odorous compounds, because the properties, sulfur and nitrogen speciations are similar in PAM-conditioned sludge and raw sludge (RS). Significant increases of SO(2) and H(2)S emissions in the H(2)SO(4) conditioning process were observed due to the accelerated decomposition of sulfur-containing amino acids in acidic environment. Fenton peroxidation facilitates the formation of COS. CaO can reduce sulfur-containing gases emission via generation of calcium sulfate. However, under strong alkaline conditions, free ammonia or protonated amine in sludge can be easily converted to volatile ammonia, resulting in a significant release of NH(3). PMID:22902143

Liu, Huan; Luo, Guang-Qian; Hu, Hong-Yun; Zhang, Qiang; Yang, Jia-Kuan; Yao, Hong

2012-08-07

340

Multiphase equilibria in aqueous systems containing hydrocarbons and natural gases  

Microsoft Academic Search

For processing fossil fuels toward thermal and chemical products, economic design requires quantitative information on phase-equilibrium properties for hydrocarbon-water systems. Two hydrocarbon water phase-equilibrium problems are studied in this thesis. The first study presents experimental measurements for liquid-liquid mutual solubilities and vapor pressures of aqueous mixtures containing aromatic hydrocarbons at high temperatures under conditions of three-phase (vapor-liquid-liquid) equilibrium. An apparatus

1985-01-01

341

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

342

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

PubMed Central

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 biomass ranging from 235 to 1029 g DW m?2 dry weight. Underneath mat-forming assemblages, the mean concentration of dissolved oxygen was reduced by 26% and irradiance by 96% compared with conditions above the mat, while concentrations of dissolved organic carbon and soluble reactive phosphorous increased by 26% and 267%, respectively. The difference was significant but less pronounced under canopy-forming assemblages. Dissolved oxygen declined and dissolved inorganic carbon and alkalinity increased with increasing algal biomass underneath mat-forming but not under canopy-forming assemblages. The responses of corals to conditions similar to those found underneath algal assemblages were investigated in an aquarium experiment. Coral nubbins of the species Acropora millepora showed reduced photosynthetic yields and increased RNA/DNA ratios when exposed to conditions simulating those underneath assemblages (pre-incubating seawater with macroalgae, and shading). The magnitude of these stress responses increased with increasing proportion of pre-incubated algal water. Our study shows that mat-forming and, to a lesser extent, canopy-forming macroalgal assemblages alter the physical and chemical microenvironment sufficiently to directly and detrimentally affect the metabolism of corals, potentially impeding reef recovery from algal to coral-dominated states after disturbance. Macroalgal dominance on coral reefs therefore simultaneously represents a consequence and cause of coral reef degradation.

Hauri, Claudine; Fabricius, Katharina E.; Schaffelke, Britta; Humphrey, Craig

2010-01-01

343

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

344

Physical properties, chemical composition, and cloud forming potential of particulate emissions from a marine diesel engine at various load conditions.  

PubMed

Particulate matter (PM) emissions from one serial 4-stroke medium-speed marine diesel engine were measured for load conditions from 10% to 110% in test rig studies using heavy fuel oil (HFO). Testing the engine across its entire load range permitted the scaling of exhaust PM properties with load. Emission factors for particle number, particle mass, and chemical compounds were determined. The potential of particles to form cloud droplets (cloud condensation nuclei, CCN) was calculated from chemical composition and particle size. Number emission factors are (3.43 +/- 1.26) x 10(16) (kg fuel)(-1) at 85-110% load and (1.06 +/- 0.10) x 10(16) (kg fuel)(-1) at 10% load. CCN emission factors of 1-6 x 10(14) (kg fuel)(-1) are at the lower bound of data reported in the literature. From combined thermal and optical methods, black carbon (BC) emission factors of 40-60 mg/(kg fuel) were determined for 85-100% load and 370 mg/(kg fuel) for 10% load. The engine load dependence of the conversion efficiency for fuel sulfur into sulfate of (1.08 +/- 0.15)% at engine idle to (3.85 +/- 0.41)% at cruise may serve as input to global emission calculations for various load conditions. PMID:20402501

Petzold, A; Weingartner, E; Hasselbach, J; Lauer, P; Kurok, C; Fleischer, F

2010-05-15

345

Chemical composition and electronic structure of the oxide films formed on 316L stainless steel and nickel based alloys in high temperature aqueous environments  

Microsoft Academic Search

Auger analysis, capacitance measurements and photoelectrochemical measurements have been used in order to study the oxide films formed on 316L stainless steel, Alloy 690 and Alloy 600 in high temperature aqueous environments at pH 8 and 10. The analytical study reveals the duplex character of the films formed on 316L stainless steel and Alloy 690. For these materials it is

M. F. Montemor; M. G. S. Ferreira; N. E. Hakiki; M. Da Cunha Belo

2000-01-01

346

Detection of Iodine Species in Dilute Aqueous Solutions and the Modification of the Physical and Chemical Properties of Iodide Salts with Macrocyclic Multidentate Ligands.  

National Technical Information Service (NTIS)

Quantitative methods for the detection and determination of the following iodine species in dilute aqueous solution have been explored: I(-1), I2, (I3(-1), HOI, HIO3 and HIO4. Qualitative procedures for the detection of I2 and I3 (starch indicator method,...

C. L. Liotta R. C. McFarland M. B. Bruce

1982-01-01

347

Surface Chemical and Micellar Properties of Binary and Ternary Surfactant Mixtures (Cetyl Pyridinium Chloride, Tween40, and Brij56) in an Aqueous Medium  

Microsoft Academic Search

Mixed micelles formed by cetyl pyridinium chloride (CPC), Tween-40, and Brij-56 mixed in different proportions in an aqueous medium have been physicochemically studied in detail using tensiometric, conductometric, and fluorimetric techniques. The critical micellar concentration (CMC), free energies of micellization and interfacial adsorption, counterion binding, micellar aggregation number, and micellar polarity have been determined. To understand the CMC, composition, mutual

Soumen Ghosh

2001-01-01

348

Characteristics and antioxidative activity of the acetone-soluble and -insoluble fractions of a defatted rice bran extract obtained by using an aqueous organic solvent under subcritical conditions.  

PubMed

The defatted rice bran extracts obtained by being treated with various subcritical aqueous fluids at 230 °C for 5 min were further subjected to an acetone-solubilization treatment. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity depended on the total phenolic content of a sample, the acetone-soluble fraction of the extract obtained with 40% (v/v) aqueous acetone showing the highest activity. Based on the UV spectrometric and HPLC analyses, the substances with higher absorbance around 280 nm and higher hydrophobicity were found solubilizing out from the extracts into the acetone during fractionation. A gel permeation chromatographic analysis suggested that the extracts comprised monomeric or oligomeric substances. The antioxidative activity was evaluated by a DPPH radical scavenging activity analysis, rancidity test, and autoxidation analysis, revealing that it would be most likely to exert a radical scavenging effect more effectively during the initial stage of lipid oxidation than during the propagation stage. PMID:23470769

Chiou, Tai-Ying; Kobayashi, Takashi; Adachi, Shuji

2013-03-07

349

Europium redox equilibria in aqueous solution  

Microsoft Academic Search

Thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous Eu2+ and Eu3+ over a wide range of temperatures and pressures. At low temperatures, near earth surface conditions, the aqueous geochemistry of europium should be dominated by the trivalent state, except possibly in the most reducing, alkaline pore waters of anoxic marine

Dimitri A. Sverjensky

1984-01-01

350

Partitioning of trace elements between olivine and aqueous fluids at high PT conditions: implications for the effect of fluid composition on trace-element transport  

Microsoft Academic Search

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

James M. Brenan; E. Bruce Watson

1991-01-01

351

Study of chemically induced pressure generation of hydrogels under isochoric conditions using a microfabricated device  

NASA Astrophysics Data System (ADS)

A method is proposed to study the behavior of stimulus-sensitive hydrogels under isochoric conditions. Freedom of swell movement of such a hydrogel was restricted in all directions by enclosing the hydrogel between a micropressure sensor and a porous cover. Water and external stimuli can be applied to the hydrogel through the pores of the cover to provoke swelling, which results in pressure generation measured by the pressure sensor. The method was put to the proof by examining the response of a pH-sensitive hydrogel to changes in pH, ionic strength, and buffer concentrations of the surrounding solution. Both equilibrium and dynamic pressure generation were observed. The results show that higher pressures are obtained by incorporating more ionizable groups into the hydrogel network or by lowering the ionic strength of the external solution. Furthermore it was proven that pressures reach equilibrium faster when less titratable groups are incorporated or at the presence of higher buffer concentrations in the surrounding solution. By using microfabrication techniques the dimensions of the hydrogel could be kept small with the advantage that responses are fast. A DMAEMA-co-HEMA hydrogel with 2.5% protonable groups and a thickness of 15 ?m generated a ?pressure of 0.67×105 Pa in 12 min when a pH step from 9 to 6 was applied. The presented method is a simple and fast manner to characterize the static and dynamic stimulus-dependent behavior of hydrogels.

Herber, S.; Eijkel, J.; Olthuis, W.; Bergveld, P.; van den Berg, A.

2004-08-01

352

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...

353

21 CFR 522.144 - Arsenamide sodium aqueous injection.  

Code of Federal Regulations, 2013 CFR

... 2013-04-01 false Arsenamide sodium aqueous injection. 522.144 Section...ANIMAL DRUGS § 522.144 Arsenamide sodium aqueous injection. (a) Chemical name...Carbamoylphenyl) arsylene]dithio diacetic acid, sodium salt. (b) Specifications....

2013-04-01

354

Deposition and reentrainment of Brownian particles in porous media under unfavorable chemical conditions: some concepts and applications.  

PubMed

The deposition and reentrainment of particles in porous media have been examined theoretically and experimentally. A Brownian Dynamics/Monte Carlo (MC/BD) model has been developed that simulates the movement of Brownian particles near a collector under "unfavorable" chemical conditions and allows deposition in primary and secondary minima. A simple Maxwell approach has been used to estimate particle attachment efficiency by assuming deposition in the secondary minimum and calculating the probability of reentrainment. The MC/BD simulations and the Maxwell calculations support an alternative view of the deposition and reentrainment of Brownian particles under unfavorable chemical conditions. These calculations indicate that deposition into and subsequent release from secondary minima can explain reported discrepancies between classic model predictions that assume irreversible deposition in a primary well and experimentally determined deposition efficiencies that are orders of magnitude larger than Interaction Force Boundary Layer (IFBL) predictions. The commonly used IFBL model, for example, is based on the notion of transport over an energy barrier into the primary well and does not address contributions of secondary minimum deposition. A simple Maxwell model based on deposition into and reentrainment from secondary minima is much more accurate in predicting deposition rates for column experiments at low ionic strengths. It also greatly reduces the substantial particle size effects inherent in IFBL models, wherein particle attachment rates are predicted to decrease significantly with increasing particle size. This view is consistent with recent work by others addressing the composition and structure of the first few nanometers at solid-water interfaces including research on modeling water at solid-liquid interfaces, surface speciation, interfacial force measurements, and the rheological properties of concentrated suspensions. It follows that deposition under these conditions will depend on the depth of the secondary minimum and that some transition between secondary and primary depositions should occur when the height of the energy barrier is on the order of several kT. When deposition in secondary minima predominates, observed deposition should increase with increasing ionic strength, particle size, and Hamaker constant. Since an equilibrium can develop between bound and bulk particles, the collision efficiency [alpha] can no longer be considered a constant for a given physical and chemical system. Rather, in many cases it can decrease over time until it eventually reaches zero as equilibrium is established. PMID:14740738

Hahn, Melinda W; O'Meliae, Charles R

2004-01-01

355

Measurement of chemical composition andpH profiles near the liquid-vapor interface of aqueous solutions using a unique confocal microscope system  

Microsoft Academic Search

The pH in aqueous solutions is important in a number of atmospheric processes, particularly reactions involving water and acid aerosols. Accurate knowledge of the pH is therefore necessary to understand such processes. Bulk pH is easily measured using pH electrodes or pH paper, and the pH at the water-air interface at equilibrium has recently been measured using surface specific techniques.

Christopher Brant Wilson

2007-01-01

356

Mastery of cultural conditions and physico-chemical properties improves the production and the catalytic efficiency of bglG.  

PubMed

Stachybotrys microspora is a filamentous fungus secreting multiple ?-glucosidases. Two of them were characterized. The third one, named bglG, was also characterized and used for various investigations. The current work undertakes the plausible role played by some cultural conditions and physico-chemical properties to improve bglG time course synthesis and also its catalytic efficiency. Indeed, bglG time course synthesis is slightly affected by light, but it is clearly affected by aeration and presence of baffle. On the same case, optimization of substrate and enzyme concentration contributes to the improvement of the catalytic efficiency of bglG. This biocatalyst tolerates a high ionic strength during its activity assay; ?-mercaptoethanol increases the enzymatic rate. BglG has the capacity to hydrolyse efficiently oleuropéin, with a recovery of 88%. PMID:23700144

Saibi, Walid; Gargouri, Ali

2013-05-23

357

Effects of Calcination and Milling Process Conditions for Ceria Slurry on Shallow-Trench-Isolation Chemical-Mechanical Polishing Performance  

NASA Astrophysics Data System (ADS)

To improve the performance of shallow trench isolation chemical-mechanical polishing (STI-CMP) in terms of the removal selectivity of oxide and nitride films and the formation of surface defects, we investigated the effects of the calcination and milling process conditions during ceria slurry synthesis. We have focused on the effects of particle size distribution, the large-particle size, and the dispersion stability in a ceria slurry. We determined the optimum bead size for milling and appropriate calcination temperatures in order to obtain a reasonable particle distribution, with lower numbers of fine primary particles and large, agglomerated particles, in ceria slurry. This was achieved by reducing the quantity of aggregated particles during milling and two-step calcination process generating higher-density particles. These results can be qualitatively explained by abrasive collisions occurring between the milling beads and the decarbonation of cerium carbonate through diffusion during the manufacturing process used for the ceria slurry.

Kim, Jun-Seok; Kang, Hyun-Goo; Kanemoto, Manabu; Paik, Ungyu; Park, Jea-Gun

2007-12-01

358

Transport and chemical conversion of air pollutants under convective conditions - Results of the COPS-TRACKS campaign  

NASA Astrophysics Data System (ADS)

Embedded in the COPS project, the TRACKS campaign (Transport and Chemical Conversion in Convective Systems) was carried out in summer 2007 in order to study the transport of atmospheric trace gases and aerosols under convective conditions. One focus of this experiment was to investigate the dilution of air pollutants in the surroundings of a metropolitan area in complex terrain due to dynamical and chemical processes. Therefore, trace gas distributions in the lee of the city of Karlsruhe had been detected by coordinated measurements of different airborne platforms, including several aircraft and a zeppelin. We study a summer day with convective boundary layer, characterized not by extreme but standard weather conditions with typical atmospheric pollution. The relevance of urban sources of atmospheric pollutants located in Karlsruhe is considered in relation to meteorological and transport conditions in the Upper Rhine Valley. The observed ozone concentrations inside the TRACKS area are moderate during this day and reach maximum values around 60 ppb. However, the measurements reveal specific horizontal structures in several trace gas distributions lee-side of Karlsruhe. At a distance of 40 km away from the city, the ozone concentration increases by about 10 ppb, although NO2 does not show a clear horizontal gradient. The correlation of O3 and CO provides an indicator for the origin of air masses. Near to Karlsruhe, the O3/CO correlation is not significant. However, in the remote lee area a significant positive correlation with a coefficient of determination R2 = 0.71 was found which refers to additional insertion of air pollutants by longer distance transport or vertical transport processes. A model simulation with COSMO-ART shows low NO2 concentrations in the lee of Karlsruhe which vary around 5 ppb and indicate that Karlsruhe does not develop a distinctive city plume by the combination of local emissions and atmospheric conditions at this day. In the afternoon around 15 UTC, the modeled O3/CO correlation is positive in different parts easterly of the Upper Rhine Valley (R2 ? 0.58). In the lee of Karlsruhe, horizontal transport of air masses which are originated in north-eastern parts of France and Southwestern Germany predominate the impact of local gas emission sources. This can be seen in the whole vertical extension of the boundary layer.

Wilms-Grabe, W.; Corsmeier, U.; Vogel, H.; Kottmeier, Ch.

2012-04-01

359

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  

USGS Publications Warehouse

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. ?? 2006 Society for Applied Spectroscopy.

Lu, W. J.; Chou, I. M.; Burruss, R. C.; Yang, M. Z.

2006-01-01

360

Distribution of fish, benthic invertebrate, and algal communities in relation to physical and chemical conditions, Yakima River basin, Washington, 1990  

USGS Publications Warehouse

Biological investigations were conducted in the Yakima River Basin, Washington, in conjunction with a pilot study for the U.S. Geological Survey's National Water-Quality Assessment Program. Ecological surveys were conducted at 25 sites in 1990 to (1) assess water-quality conditions based on fish, benthic invertebrate, and algal communities; (2) determine the hydrologic, habitat, and chemical factors that affect the distributions of these organisms; and (3) relate physical and chemical conditions to water quality. Results of these investigations showed that land uses and other associated human activities influenced the biological characteristics of streams and rivers and overall water-quality conditions. Fish communities of headwater streams in the Cascades and Eastern Cascades ecoregions of the Yakima River Basin were primarily composed of salmonids and sculpins, with cyprinids dominating in the rest of the basin. The most common of the 33 fish taxa collected were speckled dace, rainbow trout, and Paiute sculpin. The highest number of taxa (193) was found among the inverte- brates. Insects, particularly sensitive forms such as mayflies, stoneflies, and caddisflies (EPT--Ephemeroptera, Plecoptera, and Trichoptera fauna), formed the majority of the invertebrate communities of the Cascades and Eastern Cascades ecoregions. Diatoms dominated algal communities throughout the basin; 134 algal taxa were found on submerged rocks, but other stream microhabitats were not sampled as part of the study. Sensitive red algae and diatoms were predominant in the Cascades and Eastern Cascades ecoregions, whereas the abundance of eutrophic diatoms and green algae was large in the Columbia Basin ecoregion of the Yakima River Basin. Ordination of physical, chemical, and biological site characteristics indicated that elevation was the dominant factor accounting for the distribution of biota in the Yakima River Basin; agricultural intensity and stream size were of secondary importance. Ordination identified three site groups and three community types. Site groups consisted of (1) small streams of the Cascades and Eastern Cascades ecoregions, (2) small streams of the Columbia Basin ecoregions, and (3) large rivers of the Cascades and Columbia Basin ecoregions. The small streams of the Columbia Basin could be further subdivided into two groups--one where agricultural intensity was low and one where agricultural intensity was moderate to high. Dividing the basin into these three groups removed much of the influence of elevation and facilitated the analysis of land-use effects. Community types identified by ordination were (1) high elevation, cold-water communities associated with low agricultural intensity; (2) lower elevation, warm-water communities associated with low agricultural intensity, and (3) lower elevation, warm-water communities associated with moderate to high agricultural intensity. Multimetric community condition indices indicated that sites in the Cascades and Eastern Cascades site group were largely unimpaired. In contrast, all but two sites in the Columbia Basin site group were impaired, some severely. Agriculture (nutrients and pesticides) was the primary factor responsible for this impairment, and all impaired sites were characterized by multiple indicators of impairment. Three sites (Granger Drain, Moxee Drain, and Spring Creek) had high levels of impairment. Sites in the large-river site group were moderately to severely impaired downstream from the city of Yakima. High levels of impairment at large-river sites corresponded with high levels of pesticides in fish tissues and the occurrence of external anomalies. The response exhibited by invertebrates and algae to a gradient of agricultural intensity suggested a threshold response for sites in the Columbia Basin site group. Community condition declined precipitously at agricultural intensities above 50 (non-pesticide agricultural intensity index) and showed little respon

Cuffney, T. F.; Meador, M. R.; Porter, S. D.; Gurtz, M. E.

1997-01-01

361

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

362

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

NASA Astrophysics Data System (ADS)

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 MEK has been developed. The model consists of about 130 radiolytic decomposition reactions in addition to about 25 water radiolysis reactions. The model reproduces the observed dose profiles of MEK and its subsequent decomposition products (3-hydroxy-2-butanone, acetaldehyde, acetic acid and formaldehyde) very well. The worst case was formaldehyde, a tertiary molecular product from MEK decomposition, which was still reproduced to within 50%. The model also reproduces the observed dose profile of pH reasonably well. The key reactions controlling the behaviour (or dose profiles) of MEK and its decomposition products and the sensitivity of their behaviour to the rates of these reactions are discussed.

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

2000-03-01

363

Changes in fluid geochemistry and physico-chemical conditions of geothermal systems caused by magmatic input: The recent abrupt outgassing off the island of Panarea (Aeolian Islands, Italy)  

Microsoft Academic Search

Hydrothermal systems and related vents can exhibit dramatic changes in their physico-chemical conditions over time as a response to varying activity in the feeding magmatic systems. Massive steam condensation and gas scrubbing processes of thermal fluids during their ascent and cooling cause further compositional changes that mask information regarding the conditions evolving at depth in the hydrothermal system. Here we

A. Caracausi; M. Ditta; F. Italiano; M. Longo; P. M. Nuccio; A. Paonita; A. Rizzo

2005-01-01

364

Viscous fingering in a horizontal flow through a porous medium induced by chemical reactions under isothermal and adiabatic conditions  

NASA Astrophysics Data System (ADS)

In this work we analyze the viscous fingering instability induced by an autocatalytic chemical reaction in a liquid flowing horizontally through a porous medium. We have analyzed the behavior of the system for isothermal as well as adiabatic conditions. The kinetics of the reaction is chosen so that the rate depends on the concentration of only a single species. Since the reaction is autocatalytic the system admits a traveling wave solution. For endothermic reactions the concentration wave and temperature wave are mirror images, whereas for an exothermic reaction they are similar or parallel. The viscosity of the fluid is assumed to depend strongly on the concentration of the product and temperature of the medium. The dependence of viscosity on concentration (decrease with concentration) can destabilize the traveling wave resulting in the formation of viscous fingers. We have performed a linear stability analysis to determine the stability of the base traveling wave solution. The stability predictions have been confirmed by nonlinear simulations of the governing equations based on a finite difference scheme. We observe that including the temperature dependency of viscosity stabilizes the flow for an endothermic reaction, i.e., regions which exhibited viscous fingering now demonstrate stable displacement. For exothermic systems, however, the system exhibits less stable behavior under adiabatic conditions, i.e., it is destabilized by both concentration and temperature dependencies of viscosity.

Swernath, Subramanian; Pushpavanam, S.

2007-11-01

365

Synthetic surface for expansion of human mesenchymal stem cells in xeno-free, chemically defined culture conditions.  

PubMed

Human mesenchymal stem cells (HMSCS) possess three properties of great interest for the development of cell therapies and tissue engineering: multilineage differentiation, immunomodulation, and production of trophic factors. Efficient ex vivo expansion of hMSCs is a challenging requirement for large scale production of clinical grade cells. Low-cost, robust, scalable culture methods using chemically defined materials need to be developed to address this need. This study describes the use of a xeno-free synthetic peptide acrylate surface, the Corning® Synthemax® Surface, for culture of hMSCs in serum-free, defined medium. Cell performance on the Corning Synthemax Surface was compared to cells cultured on biological extracellular matrix (ECM) coatings in xeno-free defined medium and in traditional conditions on tissue culture treated (TCT) plastic in fetal bovine serum (FBS) supplemented medium. Our results show successful maintenance of hMSCs on Corning Synthemax Surface for eight passages, with cell expansion rate comparable to cells cultured on ECM and significantly higher than for cells in TCT/FBS condition. Importantly, on the Corning Synthemax Surface, cells maintained elongated, spindle-like morphology, typical hMSC marker profile and in vitro multilineage differentiation potential. We believe the Corning Synthemax Surface, in combination with defined media, provides a complete synthetic, xeno-free, cell culture system for scalable production of hMSCs. PMID:23940553

Dolley-Sonneville, Paula J; Romeo, Lori E; Melkoumian, Zara K

2013-08-05

366

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

367

Chemical Soil Physics Phenomena for Chemical Sensing of Buried UXO  

SciTech Connect

Technology development efforts are under way to apply chemical sensors to discriminate inert ordnance and clutter from live munitions that remain a threat to reutilization of military ranges. However, the chemical signature is affected by multiple environmental phenomena that can enhance or reduce its presence and transport behavior, and can affect the distribution of the chemical signature in the environment. For example, the chemical can be present in the vapor, aqueous, and solid phases. The distribution of the chemical among these phases, including the spatial distribution, is key in designing appropriate detectors, e.g., gas, aqueous or solid phase sampling instruments. A fundamental understanding of the environmental conditions that affect the chemical signature is needed to describe the favorable and unfavorable conditions of a chemical detector based survey to minimize the consequences of a false negative. UXO source emission measurements are being made to estimate the chemical flux from a limited set of ordnance items. Phase partitioning analysis has been completed to show what the expected concentrations of chemical analytes would be fi-om total concentrations measured in the soil. The soil moisture content in the dry region has been shown to be critical in the attenuation of soil gas concentrations by increased sorption to soil particles. Numerical simulation tools have been adapted to include surface boundary conditions such as solar radiation, surface boundary layer (which is a function of wind speed), precipitation and evaporation, and plant cover/root density to allow transport modeling and evaluate long term processes. Results of this work will provide performance targets for sensor developers and support operational decisions regarding field deployments.

Phelan, James, M.; Webb, Stephen W.

1999-06-14

368

Chemical and physical studies of type 3 chondrites. IX. Thermoluminescence and hydrothermal annealing experiments and their relationship to metamorphism and aqueous alteration in type < 3. 3 ordinary chondrites  

SciTech Connect

Samples of four type 3 chondrites have been annealed at 400-850/sup 0/C and 0.77-1 kbar for 10-500 h in the presence of various amounts of water (0-10 wt.%) and sodium disilicate (0-2 molal) and their thermoluminescence properties measured. After annealing for > 20 h at temperatures > 600/sup 0/C, the TL sensitivity of the samples increased by factors of up to 40. After annealing at < 600/sup 0/C for 10-500 h, or relatively short periods at high temperatures (e.g., less than or equal to 20 h at 850/sup 0/C), the TL sensitivity of the samples decreased by up to 2 orders of magnitude (depending on the original value). The TL peak temperatures observed in the present experiments are consistent with a low form of feldspar (the TL phosphor) being produced at < 800/sup 0/C and a high form being produced at > 800/sup 0/C. When both high and low forms were present originally, the low-form was destroyed preferentially. The authors suggest that these data are consistent with the TL-metamorphism trends observed in type > 3.2 chondrites, being due to the formation of feldspar by the devitrification of chondrule glass during metamorphism. For types < 3.2, the TL data are equally consistent with these types experiencing lower levels of metamorphism than the higher types, or with type 3.0 being produced from higher types by aqueous alteration. The presence of water with non-terrestrial D/H ratios, and petrographic evidence for aqueous alteration in Semarkona, lead to favoring the aqueous alteration hypothesis.

Guimon, R.K.; Lofgren, G.E.; Sears, D.W.G.

1988-01-01

369

Rheological behavior of Pusher 500 under a variety of chemical and thermal conditions: Topical report. [Partially hydrolyzed polyacrylamide  

SciTech Connect

This project is designed to provide information to understand and model the rheological behavior of polymers under a variety of simulated reservoir conditions and to gain the knowledge of the fidelity with which external measurements characterize mobility behavior under changing conditions. The understanding and modeling of the rheological behavior will lead to more effective use of polymers as mobility control agents in enhanced oil recovery processes. This report describes the progress made on the study of the rheological behavior of a partially hydrolyzed polyacrylamide, Dow Pusher 500, under a variety of thermal and chemical conditions. The rheological properties being considered include shear viscosity, screen factor, and flow resistance in cores. To account for the rate effect, screen factors (constant head) were measured with a modified screen factor viscometer. Viscosity and screen factor data were correlated with flow rate, polymer concentration, and salt concentration. The empirical correlations developed were then used to study the effects of alkali and temperature on these parameters. Flow resistance studies in a Berea core show that apparent viscosities in the low flow rate regime are lower than bulk solution viscosities and that viscoelasticity effects occur at a friction factor-Reynolds number product less than 1. Comparison of the rheological behavior in the Berea sandstone core with that measured outside the core shows that the effects of polymer and salt concentrations on the reduced apparent viscosity measured inside the core are similar to those on the reduced viscosity measured with a shear viscometer at low flow rates. The effects of these variables on the viscoelastic increment to the apparent viscosity are similar to that on the screen factor at high flow rates. These correlations can be used to predict the flow resistance of hydrolyzed polyacrylamides in Berea sandstone cores. 38 refs., 19 figs., 6 tabs.

Gao, H.W.; Lorenz, P.B.; Brock, S.

1987-02-01

370

Experimental constraints on storage conditions in the chemically zoned phonolitic magma chamber of the Laacher See volcano  

NASA Astrophysics Data System (ADS)

Phase relations of three samples of the Laacher See Tephra (LST) have been determined experimentally as a function of temperature (760 to 880°C), pressure (200, 300 and 400MPa), water content of the melt and oxygen fugacity (ƒO2). The crystallization experiments were carried out at ƒO2=NNO buffer and at NNO=+ 2.3logunits. The melt water contents varied between 6 and more than 8wt% H2O, corresponding to water-undersaturated and water saturated conditions respectively. The synthetic products are compared to the natural phases to constrain pre-eruptive conditions in the Laacher See magma chamber. The major phases occurring in the LST have been reproduced. The stability of hauyne is favoured at high ƒO2 ( NNO+2.3). The CaO contents in melt and plagioclase synthesized under water-saturated conditions are significantly higher than in the natural phases, implying that most of the differentiation of the phonolites took place under water-undersaturated conditions. However, this does not exclude the presence of a S-, Cl- and CO2-rich fluid phase in the upper parts of the magma chamber. The phase relationships and the TiO2 contents of melts show that the temperature was lower than 760°C in the upper part of the magma column (probably down to 720°C in the most differentiated levels) and that temperatures above 840-860°C prevailed in the lower part. The variation of the XMg of ferromagnesian minerals observed in both natural and experimental phases reflects the strong variations in ƒO2 in the lower magma chamber just prior to eruption (probably variation of about 2logunits). The most probable explanation for these ƒO2 variations is the injection of an oxidized alkali-rich magma, containing Mg-rich phenocrysts, at the base of a chemically zoned and more reduced magma column prior to eruption. Although the amount of injected magma may not have been very important, it was sufficient to change the ƒO2 conditions locally, explaining the heterogeneous XMg of ferromagnesian minerals and the formation of hauyne at the base of the chamber.

Berndt, Jasper; Holtz, François; Koepke, Jürgen

2001-01-01

371

Volatilisation of crop protection chemicals from crop and soil surfaces under controlled conditions—prediction of volatile losses from physico-chemical properties  

Microsoft Academic Search

Volatilisation of crop protection chemicals from soil and crop surfaces is one of a number of processes that may contribute to their dissipation in the environment. Therefore, information on the potential of a chemical to volatilise from these surfaces is required by international and national registration authorities. This paper reports the results of more than 190 experiments, which were carried

J. A. Guth; F. J. Reischmann; R. Allen; D. Arnold; J. Hassink; C. R. Leake; M. W. Skidmore; G. L. Reeves

2004-01-01

372

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

373

Lithium intercalation from aqueous solutions  

SciTech Connect

Lithium can be intercalated into a wide variety of materials using nonaqueous electrochemical cells. The use of aqueous methods is less common because of the reactivity of many lithium intercalation compounds with water. Here the authors show that lithium can be intercalated into host compounds from aqueous LiOH solution, provided the chemical potential of the intercalated lithium is sufficiently lower than the chemical potential of lithium in lithium metal. Using LiMn[sub 2]O[sub 4] as the host, the authors formed Li[sub 2]Mn[sub 2]O[sub 4] by intercalating Li from LiOH solution in an aqueous cell. This method may prove to be an economical way of preparing lithium transition metal oxides with high lithium contents for lithium-ion cell cathodes.

Li, W.; Dahn, J.R. (Simon Fraser Univ., Burnaby, British Columbia (Canada). Dept. of Physics); McKinnon, W.R. (National Research Council of Canada, Ottawa, Ontario (Canada). Inst. of Microstructural Sciences)

1994-09-01

374

Simulation of size-segregated aerosol chemical composition over northern Italy in clear sky and wind calm conditions  

NASA Astrophysics Data System (ADS)

The present article compares the outputs of the 3-D regional chemistry-transport model (CTM) CHIMERE against observations of the size-resolved aerosol chemical composition over northern Italy in clear sky and wind calm conditions. Two 4-day intensive field campaigns were carried out in July 2007 and February 2008 at three sites (urban, rural and mountain backgrounds) in the framework of the AEROCLOUDS project. Predicted levels are in reasonable agreement with observations for the urban and rural sites. Bias ranges from - 30%, for the rural site in winter, to + 38%, for the urban site during summer. In addition, the model is able to capture both the daily evolution of the bulk aerosol mass as well as its spatial gradients. Aerosol size distribution and chemical composition remain difficult to predict. The largest discrepancies were found for secondary organic aerosol (SOA) during summer and nitrates during the cold season. Compared with observations, modelled size distribution is shifted towards fine mode in winter, and towards coarse mode in summer. More accurate predictions can be achieved for both seasons by tuning the gas to particle absorption process. By reducing the SOA absorption rate by 25% at the urban sampling site in summer, the correlation between observed and simulated SOA size distributions increases from - 0.30 to + 0.70, and the bias is reduced from 200% to 0%. In winter, increasing the intra-sectional flux of particles from smaller to larger ones by a factor of 5, the Pearson correlation coefficient calculated over the nitrate size distribution goes up to + 0.85, compared to + 0.50 from CTRL, also resulting in a better agreement with the size distribution of PM10. As expected, the nitrate bulk mass concentration does not vary with respect to the base-case, and therefore nitrate overestimation remains present in the model.

Landi, T. C.; Curci, G.; Carbone, C.; Menut, L.; Bessagnet, B.; Giulianelli, L.; Paglione, M.; Facchini, M. C.

2013-05-01

375

Toward calculations of the 129Xe chemical shift in Xe@C60 at experimental conditions: relativity, correlation, and dynamics.  

PubMed

We calculate the 129Xe chemical shift in endohedral Xe@C60 with systematic inclusion of the contributing physical effects to model the real experimental conditions. These are relativistic effects, electron correlation, the temperature-dependent dynamics, and solvent effects. The ultimate task is to obtain the right result for the right reason and to develop a physically justified methodological model for calculations and simulations of endohedral Xe fullerenes and other confined Xe systems. We use the smaller Xe...C6H6 model to calibrate density functional theory approaches against accurate correlated wave function methods. Relativistic effects as well as the coupling of relativity and electron correlation are evaluated using the leading-order Breit-Pauli perturbation theory. The dynamic effects are treated in two ways. In the first approximation, quantum dynamics of the Xe atom in a rigid cage takes advantage of the centrosymmetric potential for Xe within the thermally accessible distance range from the center of the cage. This reduces the problem of obtaining the solution of a diatomic rovibrational problem. In the second approach, first-principles classical molecular dynamics on the density functional potential energy hypersurface is used to produce the dynamical trajectory for the whole system, including the dynamic cage. Snapshots from the trajectory are used for calculations of the dynamic contribution to the absorption 129Xe chemical shift. The calculated nonrelativistic Xe shift is found to be highly sensitive to the optimized molecular structure and to the choice of the exchange-correlation functional. Relativistic and dynamic effects are significant and represent each about 10% of the nonrelativistic static shift at the minimum structure. While the role of the Xe dynamics inside of the rigid cage is negligible, the cage dynamics turns out to be responsible for most of the dynamical correction to the 129Xe shift. Solvent effects evaluated with a polarized continuum model are found to be very small. PMID:18303877

Straka, Michal; Lantto, Perttu; Vaara, Juha

2008-02-28

376

Chemical immobilization of adult female Weddell seals with tiletamine and zolazepam: effects of age, condition and stage of lactation  

PubMed Central

Background Chemical immobilization of Weddell seals (Leptonychotes weddellii) has previously been, for the most part, problematic and this has been mainly attributed to the type of immobilizing agent used. In addition to individual sensitivity, physiological status may play an important role. We investigated the use of the intravenous administration of a 1:1 mixture of tiletamine and zolazepam (Telazol®) to immobilize adult females at different points during a physiologically demanding 5–6 week lactation period. We also compared performance between IV and IM injection of the same mixture. Results The tiletamine:zolazepam mixture administered intravenously was an effective method for immobilization with no fatalities or pronounced apnoeas in 106 procedures; however, there was a 25 % (one animal in four) mortality rate with intramuscular administration. Induction time was slightly longer for females at the end of lactation (54.9 ± 2.3 seconds) than at post-parturition (48.2 ± 2.9 seconds). In addition, the number of previous captures had a positive effect on induction time. There was no evidence for effects due to age, condition (total body lipid), stage of lactation or number of captures on recovery time. Conclusion We suggest that intravenous administration of tiletamine and zolazepam is an effective and safe immobilizing agent for female Weddell seals. Although individual traits could not explain variation in recovery time, we suggest careful monitoring of recovery times during longitudinal studies (> 2 captures). We show that physiological pressures do not substantially affect response to chemical immobilization with this mixture; however, consideration must be taken for differences that may exist for immobilization of adult males and juveniles. Nevertheless, we recommend a mass-specific dose of 0.50 – 0.65 mg/kg for future procedures with adult female Weddell seals and a starting dose of 0.50 mg/kg for other age classes and other phocid seals.

Wheatley, Kathryn E; Bradshaw, Corey JA; Harcourt, Robert G; Davis, Lloyd S; Hindell, Mark A

2006-01-01

377

First aqueous chemistry with Seaborgium (element 106).  

National Technical Information Service (NTIS)

Chemical separations of element 106 (Seaborgium, Sg) were performed in aqueous solutions. The isotopes (sup 265)Sg and (sup 266)Sg, produced in the (sup 248)Cm + (sup 22)Ne reaction, were continuously transported to the automated liquid chromatography sys...

M. Schaedel

1997-01-01

378

Predator-induced alarm responses in the common periwinkle, Littorina littorea: dependence on season, light conditions, and chemical labelling of predators  

Microsoft Academic Search

Chemically mediated alarm reactions of the common periwinkle, Littorina littorea (L.), were studied in laboratory experiments during two consecutive summers, and one intermediate autumn season. Responses\\u000a to chemical stimuli were detected as crawl-out responses, i.e. movements of snails out of the water. Snails were exposed to\\u000a extracts of injured conspecifics, extracts of the mussel Modiolus modiolus (L.), and water conditioned

H. P. Jacobsen; O. B. Stabell

1999-01-01

379

Standard partial molar volumes of some aqueous alkanolamines and alkoxyamines at temperatures up to 325 degrees C: functional group additivity in polar organic solutes under hydrothermal conditions.  

PubMed

Apparent molar volumes of dilute aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), N,N-dimethylethanolamine (DMEA), ethylethanolamine (EAE), 2-diethylethanolamine (2-DEEA), and 3-methoxypropylamine (3-MPA) and their salts were measured at temperatures from 150 to 325 degrees C and pressures as high as 15 MPa. The results were corrected for the ionization and used to obtain the standard partial molar volumes, Vo2. A three-parameter equation of state was used to describe the temperature and pressure dependence of the standard partial molar volumes. The fitting parameters were successfully divided into functional group contributions at all temperatures to obtain the standard partial molar volume contributions. Including literature results for alcohols, carboxylic acids, and hydroxycarboxylic acids yielded the standard partial molar volume contributions of the functional groups >CH-, >CH2, -CH3, -OH, -COOH, -O-, -->N, >NH, -NH2, -COO-Na+, -NH3+Cl-, >NH2+Cl-, and -->NH+Cl- over the range (150 degrees C aqueous organic solutes composed of these groups at temperatures up to approximately 310 degrees C and pressures of 10-20 MPa to within a precision of +/-5 cm3 x mol(-1). The model could not be extended to higher temperatures because of uncertainties caused by thermal decomposition. At temperatures above approximately 250 degrees C, the order of the group contributions to Vo2 changes from that observed at 25 degrees C, to become increasingly consistent with the polarity of each functional group. The effect of the dipole moment of each molecule on the contribution to Vo2 from long-range solvent polarization was calculated from the multipole expansion of the Born equation using dipole moments estimated from restricted Hartree-Fock calculations with Gaussian 03 (Gaussian, Inc., Wallingford, CT) and the Onsager reaction-field approximation for solvent effects. Below 325 degrees C, the dipole contribution was found to be less than 2 cm3 x mol(-1) for all the solute molecules studied. At higher temperatures and pressures near steam saturation, the effect is much larger and may explain anomalies in functional group additivity observed in small, very polar solutes. PMID:18412415

Bulemela, E; Tremaine, Peter R

2008-04-16

380

Synthesis Under 'Greener' Conditions: Role of Sustainable Nano-Catalysts  

EPA Science Inventory

The presentation summarizes our recent activity in chemical synthesis 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 varie...

381

Preparation of Micropore-Containing Adsorbents from Kenaf Fibers and Their Use in Mercury Removal from Aqueous Solution  

Microsoft Academic Search

Here, a number of activated carbon fibers (ACFs) prepared from kenaf natural fibers (KNFs) by chemical activation with KOH under different operation conditions have been used as adsorbents for the removal of mercury from aqueous solutions. Samples were characterized by N2 adsorption at 77 K, mercury porosimetry, scanning electronic microscopy (SEM), and FT-IR spectroscopy. The adsorption of mercury at 25°C

A. Macías-García; E. M. Cuerda-Correa; M. Olivares-Marín; M. Alexandre-Franco; V. Gómez-Serrano

2012-01-01

382

Zn(II)-cyclam based chromogenic sensors for recognition of ATP in aqueous solution under physiological conditions and their application as viable staining agents for microorganism.  

PubMed

Two chromogenic complexes, L.Zn (where L is (E)-4-((4-(1,4,8,11-tetraazacyclotetradecan-1-ylsulfonyl)phenyl)diazenyl)-N,N-dimethylaniline) and its [2]pseudorotaxane form (?-CD.L.Zn), were found to bind preferentially to adenosine triphosphate (ATP), among all other common anions and biologically important phosphate (AMP, ADP, pyrophosphate, and phosphate) ions in aqueous HEPES buffer medium of pH 7.2. Studies with live cell cultures of prokaryotic microbes revealed that binding of these two reagents to intercellular ATP, produced in situ, could be used in delineating the gram-positive and the gram-negative bacteria. More importantly, these dyes were found to be nontoxic to living microbes (eukaryotes and prokaryotes) and could be used for studying the cell growth dynamics. Binding to these two viable staining agents to intercellular ATP was also confirmed by spectroscopic studies on cell growth in the presence of different respiratory inhibitors that influence the intercellular ATP generation. PMID:21449545

Mahato, Prasenjit; Ghosh, Amrita; Mishra, Sanjiv K; Shrivastav, Anupama; Mishra, Sandhya; Das, Amitava

2011-03-30

383

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 Astrophysics Data System (ADS)

Iron-rich spherules (> 90% Fe 2O 3 from electron microprobe analyses) ˜10-100 ?m 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 H 2O and/or OH - 1 . The transmission Mössbauer spectrum of a spherule-rich separate is dominated by a hematite (?-Fe 2O 3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al 3+ for Fe 3+ substitution and structural H 2O and/or OH - 1 . 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.; Squyres, S. W.; Mertzman, S. A.; Gruener, J. E.; Golden, D. C.; Le, L.; Robinson, G. A.

2005-11-01

384

Degradation of the biocide 4-chloro-3,5-dimethylphenol in aqueous medium with ozone in combination with ultraviolet irradiation: operating conditions influence and mechanism.  

PubMed

Biocides usually persist during municipal sewage treatment and are subsequently distributed into aquatic environments. To explore the capability of advanced oxidation processes for the rapid removal of biocides, we examined the total organic carbon (TOC) reduction of 4-chloro-3,5-dimethylphenol (PCMX) with a combination of UV/O(3). Moreover, the related important parameters, including the mass transfer coefficient and light utilization efficiency, in PCMX degradation were determined. The UV/O(3) experimental results showed a pronounced synergistic effect, leading to the nearly complete elimination of TOC within 75 min. Thus, the effect of operating variables was investigated as a function of pH, ozone dosage, bulk temperature and the initial concentration of PCMX. The efficiency of PCMX mineralization increased with an increase in ozone dose up to 3.1 gh(-1), and a decrease in the initial concentration from 250 to 100mg L(-1). The optimal pH value was 4.0, and the preferred bulk temperature was 20 degrees C on the basis of the influence of temperature on reaction rate and ozone solubility. The major aromatic intermediates identified by gas chromatography/mass spectrometry were 2,6-dimethylbenzene-1,4-diol, 2,6-dimethylbenzo-1,4-quinone, 2,6-bis(hydroxymethyl)benzo-1,4-quinone, and 2,6-dimethylbenzo-1,4-aldehyde. Quantitative determination of related carboxylic acid and inorganic anions was done by ion chromatography. On the basis of the identified reaction products, a possible degradation pathway for the UV/O(3) oxidation of PCMX in aqueous media is proposed. PMID:19818989

Song, Shuang; Liu, Zhiwu; He, Zhiqiao; Li, Yu; Chen, Jianmeng; Li, Chaolin

2009-10-09

385

Aqueous Solutions and their Interfaces  

SciTech Connect

Preface of the special issue of the Journal of Physical Chemistry in conjunction with the international workshop "Aqueous Solutions and their Interfaces". The topics include the structure of liquid water, the analysis of X-ray and neutron scattering experimental data, the vibrational spectroscopy of liquid water, the structure and spectroscopy of aqueous interfaces and the development of theoretical approaches to model the structure and spectra of liquid water and interfaces. This work was supported by the US Department of Energy's Office of Basic Energy Sciences, Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for DOE.

Xantheas, Sotiris S.; Voth, Gregory A.

2009-04-02

386

Aqueous chemical growth of free standing vertical ZnO nanoprisms, nanorods and nanodiskettes with improved texture co-efficient and tunable size uniformity  

Microsoft Academic Search

Tuning the morphology, size and aspect ratio of free standing ZnO nanostructured arrays by a simple hydrothermal method is\\u000a reported. Pre-coated ZnO seed layers of two different thicknesses (?350 nm or 550 nm) were used as substrates to grow ZnO\\u000a nanostructures for the study. Various parameters such as chemical ambience, pH of the solution, strength of the Zn2+ atoms and thickness

S. D. Gopal Ram; G. Ravi; A. Athimoolam; T. Mahalingam; M. Anbu Kulandainathan

387

Chemical repair of base lesions, AP-sites, and strand breaks on plasmid DNA in dilute aqueous solution by ascorbic acid.  

PubMed

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. PMID:23567970

Hata, Kuniki; Urushibara, Ayumi; Yamashita, Shinichi; Shikazono, Naoya; Yokoya, Akinari; Katsumura, Yosuke

2013-04-06

388

A 13C CP\\/MAS NMR evaluation of the structural changes in wheat straw subjected to different chemical and biological pulping conditions  

Microsoft Academic Search

Wheat straw pulps prepared by chemical (soda) and biological (enzymatic or fungal) treatments were analyzed by 13C CP\\/MAS NMR spectrometry under quantitative acquisition conditions. The most significant changes reflected in the spectra as a result of soda cooking correspond to: (i) decrease of methoxyl content of the residual lignin (56, 153, 147 and 135 ppm), and (ii) deacetylation of hemicellulose

M. E. Guadalix; G. Almendros; A. T. Martínez; F. J. González-Vila; U. Lankes

1997-01-01

389

Effects of contrasting land use on physico?chemical conditions and benthic assemblages of streams in a Canterbury (South Island, New Zealand) river system  

Microsoft Academic Search

Physico?chemical conditions and benthic invertebrate assemblages in streams draining catchments dominated by different land use activities were investigated near Hanmer Springs, South Island. Four streams in pastoral, scrubland, exotic pine plantation forest (primarily Pinus spp.), and native beech forest (Nothofagus spp.) catchments were sampled in four seasons. Alkalinity, pH, and calcium concentrations were highest among scrubland streams, whereas iron and

Jon S. Harding; Michael J. Winterbourn

1995-01-01

390

Aqueous humour lactic dehydrogenase isoenzymes in retinoblastoma  

Microsoft Academic Search

LDH activity was determined in aqueous humour samples from 11 eyes (of 10 children), four of which contained retinoblastoma. Simultaneous serum LDH levels were also determined in eight of the children. There was no correlation between serum and aqueous humour LDH activity. Total aqueous humour LDH activity ranged from 0 to 99 i.u\\/l. in the seven eyes with non-neoplastic conditions.

J. Kabak; P. E. Romano

1975-01-01

391

Coordination Modes of Multidentate Ligands in fac-[Re(CO)3(polyaminocarboxylate)] Analogues of 99mTc Radiopharmaceuticals. Dependence on Aqueous Solution Reaction Conditions  

PubMed Central

We study Re analogues of 99mTc renal agents to interpret previous results at the 99mTc tracer level. The relative propensities of amine donors vs. carboxylate oxygen donors of four L = polyaminocarboxylate ligands to coordinate in fac-[ReI(CO)3L]n complexes were assessed by examining the reaction of fac-[ReI(CO)3(H2O)3]+ under conditions differing in acidity and temperature. All four L [N,N-bis-(2-aminoethyl)glycine (DTGH), N,N-ethylenediaminediacetic acid, diethylenetriamine-N-malonic acid, and diethylenetriamine-N-acetic acid] can coordinate as tridentate ligands while creating a dangling chain terminated in a carboxyl group. Dangling carboxyl groups facilitate renal clearance in fac-[99mTcI(CO)3L]n agents. Under neutral conditions, the four ligands each gave two fac-[ReI(CO)3L]n products with HPLC traces correlating well with known traces of the fac-[99mTcI(CO)3L]n mixtures. Such mixtures are common in renal agents because the needed dangling carboxyl group can compete for a coordination site. However, the HPLC separations needed to assess the biodistribution of a single tracer are impractical in a clinical setting. One goal in investigating this Re chemistry is to identify conditions for avoiding this problem of mixtures in preparations of fac-[99mTcI(CO)3L]n renal tracers. After separation and isolation of the fac-[ReI(CO)3L]n products, NMR analysis of all products and single crystal X-ray crystallographic analysis of both DTGH products as well as one product each from the other L allowed us to establish coordination mode unambiguously. The product favored in acidic conditions has a dangling amine chain and more bound oxygen. The product favored in basic conditions has a dangling carboxyl chain and more bound nitrogen. At the elevated temperatures used for simulating tracer preparation, equilibration was facile (ca. one hour or less), allowing selective formation of one product by utilizing acidic or basic conditions. The results of this fundamental study offer protocols and guidance useful for the design and preparation of fac-[99mTcI(CO)3L]n agents consisting of a single tracer.

Lipowska, Malgorzata; He, Haiyang; Xu, Xiaolong; Taylor, Andrew T.; Marzilli, Patricia A.; Marzilli, Luigi G.

2010-01-01

392

Effect of aqueous LiBr solutions on the corrosion resistance and galvanic corrosion of an austenitic stainless steel in its welded and non-welded condition  

Microsoft Academic Search

The corrosion resistance and galvanic behaviour of a highly alloyed austenitic stainless steel (UNS N08031) and a nickel–base alloy (UNS N06059) in its welded (GTAW) and non-welded condition were analysed in LiBr solutions by means of electrochemical measurements. Samples microstructure was studied by SEM and EDX analysis. The alloys considered showed passive behaviour and they were able to repassivate after

E. Blasco-Tamarit; A. Igual-Muñoz; J. García Antón; D. García-García

2006-01-01

393

Synthesis of Polyoxovanadates from Aqueous Solutions  

NASA Astrophysics Data System (ADS)

Polyoxovanadates have been synthesized from aqueous solutions of VV in the presence of inorganic Na+ and organic [N(CH3)4]+ cations. Decavanadate crystals are precipitated at room temperature around pH 7, whereas layered compounds Na[V3O8].H2O and N(CH3)4[V4O10] are formed at the same pH under hydrothermal conditions. In situ 51V NMR experiments show that upon heating solute decavanadate species are progressively transformed into cyclic metavanadates [V4O12]4-. A chemical mechanism is suggested for the formation of these layered vanadium oxides. It involves the ring-opening polymerization of cyclic metavanadates arising from co-ordination expansion favored by protonation or vanadium reduction. .

Bouhedja, L.; Steunou, N.; Maquet, J.; Livage, J.

2001-12-01

394

Snap-Frozen Brain Tissue Sections Stored With Desiccant at Ambient Laboratory Conditions Without Chemical Fixation are Resistant to Degradation for a Minimum of 6 Months  

PubMed Central

Cryosectioned tissues from snap-frozen samples offer the advantage of preserving proteins at the cellular and subcellular levels and maintaining overall cell integrity in the tissue of interest without the use of chemical fixatives. To prevent specific or nonspecific degradation of proteins by autolytic and/or proteolytic processes, it is common practice to immediately store frozen tissue sections obtained from a cryostat under cryogenic conditions, for example ?80°C. Our laboratory recently challenged this widely held belief by extracting proteins from brain tissue samples that were archived for 1 day, 1 week, 1 month, and 6 months at various storage conditions (frozen, ambient, or desiccated) without the use of chemical fixatives. Our results from immunofluorescent stains, immunoperoxidase stains, silver stains, and Western blot analyses demonstrated that snap-frozen, heat-dried tissue sections stored and desiccated at ambient laboratory conditions are comparable to frozen samples stored up to 6 months.

Sadler, Theodore R.; Khodavirdi, Ani C.; Hinton, David R.; Holschneider, Daniel P.

2009-01-01

395

The chemical conditions on the parent body of the murchison meteorite: Some conclusions based on amino, hydroxy and dicarboxylic acids  

NASA Astrophysics Data System (ADS)

Amino and hydroxy acids have been identified in the Murchison meteorite. Their presence is consistent with a synthetic pathway involving aldehydes, hydrogen cyanide and ammonia in an aqueous environment (Strecker-cyanohydrin synthesis). From the various equilibrium and rate constants involved in this synthesis, four independent estimates of the ammonium ion concentrations on the parent body at the time of compound synthesis are obtained; all values are about 2 × 10-3 M. Succinic acid and ?-alanine have also been detected in the Murchison meteorite. Their presence is consistent with a synthesis from acrylonitrile, hydrogen cyanide and ammonia. Using the equilibrium and rate constants for this synthetic pathway, and the succinic acid/?-alanine ratio measured in the Murchison meteorite, an estimate of the hydrogen cyanide concentration of 10-3 to 10-2 M is obtained. Since hydrogen cyanide hydrolyzes relatively rapidly in an aqueous environment (t1/2 < 104 yrs) this high concentration implies a period of synthesis of organic compounds as short as 104 years on the Murchison meteorite parent body.

Peltzer, E. T.; Bada, J. L.; Schlesinger, G.; Miller, S. L.

396

Chemical composition and physical quality characteristics of Ghanaian cocoa beans as affected by pulp pre-conditioning and fermentation  

Microsoft Academic Search

Investigations were conducted to evaluate the effects of pod storage (as a means of pulp preconditioning) and fermentation\\u000a on the chemical composition and physical characteristics of Ghanaian cocoa beans. A 4?×?2 full factorial design with factors\\u000a as pod storage (0, 7, 14, 21 days) and cocoa treatment (fermented and unfermented) were conducted. Samples were analyzed for\\u000a their chemical composition (moisture, crude

Emmanuel Ohene Afoakwa; Jennifer Quao; Jemmy Takrama; Agnes Simpson Budu; Firibu Kwesi Saalia

397

Response to Chemical Alarm Cues under Weakly Acidic Conditions: A Graded Loss of Antipredator Behaviour in Juvenile Rainbow Trout  

Microsoft Academic Search

A wide variety of aquatic organisms, including juvenile salmonids, assess local predation risks using chemosensory cues. Such\\u000a chemical cues are typically released from injured conspecifics and their detection may lead to species-typical antipredator\\u000a behaviour, increasing the probability of prey to survive during predator encounters. Studies have demonstrated however, that\\u000a under weak acidification (pH ~6.0), the response towards these chemical alarm

Antoine O. H. C. Leduc; Fabien C. Lamaze; Lindsay McGraw; Grant E. Brown

2008-01-01

398

Formation of titanium oxide nanotubes using chemical treatments and their characteristic properties  

Microsoft Academic Search

Needle-shaped titanium oxide crystals with a diameter of 8 nm were obtained when titania nanopowders were treated chemically with NaOH aqueous solution and subsequently with HCl aqueous solution under various conditions (e.g., at 110 °C for 20 h). Transmission electron microscopy showed that the needle-shaped products have a tube structure with an inner diameter of approximately 5 nm and an

Tomoko Kasuga

2006-01-01

399

Recovery of acetic acid from dilute aqueous solutions using catalytic dehydrative esterification with ethanol.  

PubMed

We have developed a direct esterification of aqueous acetic acid with ethanol (molar ratio=1:1) catalyzed by polystyrene-supported or homogeneous sulfonic acids toward the recovery of acetic acid from wastewater in chemical plants. The equilibrium yield was significantly increased by the addition of toluene, which had a high ability to extract ethyl acetate from the aqueous phase. It was shown that low-loading and alkylated polystyrene-supported sulfonic acid efficiently accelerated the reaction. These results suggest that the construction of hydrophobic reaction environments in water was critical in improving the chemical yield. Addition of inorganic salts was also effective for the reaction under not only biphasic conditions (toluene-water) but also toluene-free conditions, because the mutual solubility of ethyl acetate and water was suppressed by the salting-out effect. Among the tested salts, CaCl(2) was found to be the most suitable for this reaction system. PMID:23290939

Yagyu, Daisuke; Ohishi, Tetsuo; Igarashi, Takeshi; Okumura, Yoshikuni; Nakajo, Tetsuo; Mori, Yuichiro; Kobayashi, Sh?

2013-01-03

400

Removal of Indigo Carmine and Pb(II) Ion from Aqueous Solution by Polyaniline  

Microsoft Academic Search

In this work, we report the synthesis of polyaniline emaraldine salt (PAni-ES) by a chemical oxidative polymerization method. The obtained PAni-ES samples prepared under different conditions were used for the removal of indigo carmine anionic dye and Pb(II) ion from aqueous solutions. The results also showed that the pseudo–second-order kinetic model fitted better than the data obtained from pseudo–first-order model

Murat Ya?ar; Hüseyin Deligöz; Gamze Güçlü

2011-01-01

401

Pectin Extraction from Lemon By-Product with Acidified Date Juice: Effect of Extraction Conditions on Chemical Composition of Pectins  

Microsoft Academic Search

Mixtures of date and lemon pectins were extracted from lemon by-product with acidified date juice under different conditions\\u000a of temperature, pH and time. Individual pectins from date and lemon, respectively, were also extracted using the same experimental\\u000a conditions, then analysed and compared to pectin mixtures. It was found that the use of extreme conditions resulted in higher\\u000a galacturonic acid content,

Manel Masmoudi; Souhail Besbes; Fatma Abbes; Christelle Robert; Michel Paquot; Christophe Blecker; Hamadi Attia

402

Dynamics of the Local E-Region Neutral Winds at Midlatitudes Observed With a Sequence of Chemical Tracer Releases During Sporadic E Conditions  

NASA Astrophysics Data System (ADS)

On the night of June 30, 2003, four rockets were launched from Wallops Island, VA. The first three rockets each carried a chemical tracer experiment, and were launched with a separation of approximately two and a half and one hours, respectively. Each chemical tracer release provided upleg and downleg horizontal neutral wind profiles. This paper focuses on the shears in the wind profiles and the changes in the neutral winds over time. We also discuss the correspondence of the variations in the wind profiles to the ionosphere conditions obtained from the on-site ionosonde which showed persistent sporadic E layers throughout the observation period. Further, we compare the horizontal neutral wind measurements to previous wind observations above Wallops Island under similar conditions.

Bishop, R. L.; Larsen, M. F.; Earle, G. D.; Bullett, T.

2003-12-01

403

Effects of biological and chemical treatments on Botrytis stem canker and fruit yield of tomato under greenhouse conditions  

Microsoft Academic Search

Experiments were conducted to identify, by in vitro dual culture tests, potential biological control agents producing antibiotics and to evaluate selected biological and chemical agents for control of stem canker caused by Botrytis cinerea on tomato plants (Lycopersicon esculentum) grown in yellow cedar sawdust in a research greenhouse. Four strains of Bacillus subtilis and one each of Enterobacter agglomerans and

R. Utkhede; C. Bogdanoff; J. McNevin

2001-01-01

404

PHYSICAL, CHEMICAL AND BIOLOGICAL CONDITIONS OF THE SAGAVANIRKTOK RIVER AND NEARBY CONTROL STREAMS, SHAVIOVIK AND CANNING RIVERS  

EPA Science Inventory

Biological, physical and chemical data were collected from 28 stations on the Sagavanirktok River and five of its tributaries, the Canning River, Shaviovik River, two tundra lakes and Galbraith Lake. These stations are located on the North Slope of Alaska and in the area impacted...

405

Synthesis, chemical and enzymatic hydrolysis, and aqueous solubility of amino acid ester prodrugs of 3-carboranyl thymidine analogs for boron neutron capture therapy of brain tumors.  

PubMed

Various water-soluble L-valine-, L-glutamate-, and glycine ester prodrugs of two 3-Carboranyl Thymidine Analogs (3-CTAs), designated N5 and N5-2OH, were synthesized for Boron Neutron Capture Therapy (BNCT) of brain tumors since the water solubilities of the parental compounds proved to be insufficient in preclinical studies. The amino acid ester prodrugs were prepared and stored as hydrochloride salts. The water solubilities of these amino acid ester prodrugs, evaluated in phosphate buffered saline (PBS) at pH 5, pH 6 and pH 7.4, improved 48-6600 times compared with parental N5 and N5-2OH. The stability of the amino acid ester prodrugs was evaluated in PBS at pH 7.4, Bovine serum, and Bovine cerebrospinal fluid (CSF). The rate of the hydrolysis in all three incubation media depended primarily on the amino acid promoiety and, to a lesser extend, on the site of esterification at the deoxyribose portion of the 3-CTAs. In general, 3'-amino acid ester prodrugs were less sensitive to chemical and enzymatic hydrolysis than 5'-amino acid ester prodrugs and the stabilities of the latter decreased in the following order: 5'-valine > 5'-glutamate > 5'-glycine. The rate of the hydrolysis of the 5'-amino acid ester prodrugs in Bovine CSF was overall higher than in PBS and somewhat lower than in Bovine serum. Overall, 5'-glutamate ester prodrug of N5 and the 5'-glycine ester prodrugs of N5 and N5-2OH appeared to be the most promising candidates for preclinical BNCT studies. PMID:22889558

Hasabelnaby, Sherifa; Goudah, Ayman; Agarwal, Hitesh K; abd Alla, Mosaad S M; Tjarks, Werner

2012-07-27

406

Evaluating crude oil chemical dispersion efficacy in a flow-through wave tank under regular non-breaking wave and breaking wave conditions.  

PubMed

Testing dispersant effectiveness under conditions similar to that of the open environment is required for improvements in operational procedures and the formulation of regulatory guidelines. To this end, a novel wave tank facility was fabricated to study the dispersion of crude oil under regular non-breaking and irregular breaking wave conditions. This wave tank facility was designed for operation in a flow-through mode to simulate both wave- and current-driven hydrodynamic conditions. We report here an evaluation of the effectiveness of chemical dispersants (Corexit EC9500A and SPC 1000) on two crude oils (Medium South American [MESA] and Alaska North Slope [ANS]) under two different wave conditions (regular non-breaking and plunging breaking waves) in this wave tank. The dispersant effectiveness was assessed by measuring the water column oil concentration and dispersed oil droplet size distribution. In the absence of dispersants, nearly 8-19% of the test crude oils were dispersed and diluted under regular wave and breaking wave conditions. In the presence of dispersants, about 21-36% of the crude oils were dispersed and diluted under regular waves, and 42-62% under breaking waves. Consistently, physical dispersion under regular waves produced large oil droplets (volumetric mean diameter or VMD > or = 300 microm), whereas chemical dispersion under breaking waves created small droplets (VMD < or = 50 microm). The data can provide useful information for developing better operational guidelines for dispersant use and improved predictive models on dispersant effectiveness in the field. PMID:19157465

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

2009-01-20

407

MICROWAVE-ASSISTED CYCLOCONDENSATION OF HYDRAZINE DERIVATIVES WITH ALKYL DIHALIDES OR DITOSYLATES IN AQUEOUS MEDIA: SYNTHESES OF PYRAZOLE, PYRAZOLIDINE AND PHTHALAZINE DERIVATIVES  

EPA Science Inventory

Direct synthesis of 4,5-dihydro-pyrazole, pyrazolidine, and 1,2-dihydro-phthalazine derivatives via double alkylation of hydrazines by alkyl dihalides or ditosylates were accomplished in aqueous media under microwave irradiation conditions; the environmentally friendlier chemical...

408

Aqueous solutions of cesium salts and cesium hydroxide in hydrosilicate nanotubes of the Mg 3 Si 2 O 5 (OH) 4 composition  

Microsoft Academic Search

This paper reports on the results of studies on the filling of nanotubes of the Mg3Si2O5(OH)4 composition with aqueous solutions of hydroxide, chloride, and nitrate of cesium under different temperature-time conditions.\\u000a It has been established that the nanotubes differently interact with solutions of different chemical nature.

T. P. Maslennikova; E. N. Korytkova

2010-01-01

409

The identification and measurement of components in gasoline, kerosene, and no. 2 fuel oil that partition into the aqueous phase after mixing  

Microsoft Academic Search

Some of the most common spills in waterways involve petroleum products, which are complex mixtures of varying compositions, depending on source and refining procedures. The tendency for components of potential toxicological significance to distribute to the aqueous phase under spill conditions needs to be determined. This paper is devoted to the chemical analysis of the water-soluble fractions (WSF) of gasoline,

W. Emile Coleman; Jean W. Munch; Robert P. Streicher; H. Paul Ringhand; Frederick C. Kopfler

1984-01-01

410

Rheological behavior of Pusher 500 under a variety of chemical and thermal conditions: Topical report. [Partially hydrolyzed polyacrylamide  

Microsoft Academic Search

This project is designed to provide information to understand and model the rheological behavior of polymers under a variety of simulated reservoir conditions and to gain the knowledge of the fidelity with which external measurements characterize mobility behavior under changing conditions. The understanding and modeling of the rheological behavior will lead to more effective use of polymers as mobility control

H. W. Gao; P. B. Lorenz; S. Brock

1987-01-01

411

Aqueous phase processing of secondary organic aerosols  

NASA Astrophysics Data System (ADS)

The aging of secondary organic aerosol (SOA) by photooxidation in the aqueous phase was experimentally investigated. To simulate multiphase processes, the following experiments were sequentially performed in a smog chamber and in an aqueous phase photoreactor: (1) Gas-phase photooxidation of three different volatile organic compounds (VOC): isoprene, ?-pinene, and 1,3,5-trimethylbenzene (TMB) in the presence of NOx, leading to the formation of SOA which was subjected to on-line physical and chemical analysis; (2) particle-to-liquid transfer of water soluble species of SOA using filter sampling and aqueous extraction; (3) aqueous-phase photooxidation of the obtained water extracts; and (4) nebulization of the solutions for a repetition of the on-line characterization. SOA concentrations in the chamber measured with a scanning mobility particle sizer (SMPS) were higher than 200 ?g m-3, as the experiments were conducted under high initial concentrations of volatile organic compounds (VOC) and NOx. The aging of SOA through aqueous phase processing was investigated by measuring the physical and chemical properties of the particles online before and after processing using a high resolution time-of-flight aerosol mass spectrometer (AMS) and a hygroscopicity tandem differential mobility analyzer (H-TDMA). It was shown that, after aqueous phase processing, the particles were significantly more hygroscopic, and contained more fragmentation ions at m/z = 44 and less ions at m/z = 43, thus showing a significant impact on SOA aging for the three different precursors. Additionally, the particles were analyzed with a thermal desorption atmospheric pressure ionization aerosol mass spectrometer (TD-API-AMS). Comparing the smog chamber SOA composition and non processed nebulized aqueous extracts with this technique revealed that sampling, extraction and/or nebulization did not significantly impact the chemical composition of SOA formed from isoprene and ?-pinene, whereas it affected that formed from TMB. For the two first precursors, the aqueous phase chemical composition of SOA was further investigated using offline measurements, i.e. ion chromatography coupled to a mass spectrometer (IC-MS) and an atmospheric pressure chemical ionization mass spectrometer (APCI-MS) equipped with high pressure liquid chromatography (HPLC-MS). These analyses showed that aqueous phase processing enhanced the formation of some compounds already present in the SOA, thus confirming the aging effect of aqueous phase processes. For isoprene experiments, additional new compounds, likely oligomers, were formed through aqueous phase photooxidation, and their possible origins are discussed.

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

2011-07-01

412

Kinetics and equilibrium studies on biosorption of cadmium, lead, and nickel ions from aqueous solutions by intact and chemically modified brown algae.  

PubMed

The present study deals with the evaluation of biosorptive removal of Cd (II), Ni (II) and Pb (II) ions by both intact and pre-treated brown marine algae: Cystoseira indica, Sargassum glaucescens, Nizimuddinia zanardini and Padina australis treated with formaldehyde (FA), glutaraldehyde (GA), polyethylene imine (PEI), calcium chloride (CaCl(2)) and hydrochloric acid (HCl). Batch shaking adsorption experiments were performed in order to examine the effects of pH, contact time, biomass concentration, biomass treatment and initial metal concentration on the removal process. The optimum sorption conditions for each heavy metal are presented. One-way ANOVA and one sample t-tests were performed on experimental data to evaluate the statistical significance of biosorption capacities after five cycles of sorption and desorption. The equilibrium experimental data were tested using the most common isotherms. The results are best fitted by the Freundlich model among two-parameter models and the Toth, Khan and Radke-Prausnitz models among three-parameter isotherm models for Cd (II), Ni (II) and Pb (II), respectively. The kinetic data were fitted by models including pseudo-first-order and pseudo-second-order. From the results obtained, the pseudo-second-order kinetic model best describes the biosorption of cadmium, nickel and lead ions. PMID:20971556

Montazer-Rahmati, Mohammad Mehdi; Rabbani, Parisa; Abdolali, Atefeh; Keshtkar, Ali Reza

2010-09-22

413

Chemical fixation of carbon dioxide to cyclic carbonates under extremely mild conditions with highly active bifunctional catalysts  

Microsoft Academic Search

Chemical fixation of carbon dioxide to cyclic carbonates proceeds effectively under extremely mild temperature and pressure by using a bifunctional nucleophile–electrophile catalyst system of tetradentate Schiff-base aluminum complexes ((Salen)AlX) in conjunction with a quaternary ammonium salt (n-Bu4NY) in the absence of any organic solvent. Electrophilicity of central Al3+ ion and the steric factor of substituent groups on the aromatic rings

Xiao-Bing Lu; Ying-Ju Zhang; Bin Liang; Xiao Li; Hui Wang

2004-01-01

414

Oxidation pathways for formic acid under low temperature hydrothermal conditions: Implications for the chemical and isotopic evolution of organics on Mars  

NASA Astrophysics Data System (ADS)

In order to evaluate the oxidation effect of dissolved hydrogen peroxide and the catalytic role of iron oxides on the kinetics of formic acid decarboxylation, a series of flow-through hydrothermal experiments was conducted at temperatures ranging from 80 to 150 °C and pressures of 172-241 bar. ? 13C composition of residual HCOOH (aq) was also monitored to examine kinetic isotope effects associated with oxidation processes. Our results reveal that decomposition of H 2O 2(aq) in presence of magnetite follows pseudo first order kinetics, highly enhanced relative to the homogeneous H 2O 2(aq)-HCOOOH (aq)-H 2O system, which possibly reflect synthesis of hydroxyl radicals ( rad OH) through Fenton processes. The kinetic rate constants of HCOOH (aq) decarboxylation to CO 2(aq) are also elevated relative to those previously measured in H 2O 2(aq) free experiments. However, reaction kinetics are slightly slower in the case of H 2O 2(aq) aqueous solutions coexisting with magnetite than in the absence of mineral phases. This behavior is attributed to the possible formation of Fe-bearing hydroxyl formate aqueous species that could serve as stable transition states leading to a decrease in the activation entropy of formic acid decomposition. ? 13C values of residual formic acid in the homogeneous H 2O 2(aq)-HCOOH (aq)-H 2O system are consistent with previous studies. However, magnetite-bearing experiments produce a negative shift in ? 13C of residual formic acid, perhaps specific to rad OH-imposed oxidation of organic compounds. This would indicate that isotopic fractionations by this oxidation pathway are opposite to kinetic fractionation effects expected in biologically driven oxidation processes. This could have important implications for putative H 2O 2(aq)-bearing Martian subsurface environments and the evolution of organics at low-temperature hydrothermal conditions.

Foustoukos, Dionysis I.; Stern, Jennifer C.

2012-01-01

415

Chemical conditions favoring photosynthesis-induced CaCO 3 precipitation and implications for microbial carbonate formation in the ancient ocean  

NASA Astrophysics Data System (ADS)

Chemical conditions favoring photosynthesis-induced CaCO 3 precipitation (PCP) was examined to provide basic knowledge for understanding ancient ocean chemistry that enabled microbial carbonate formation. First, numerical simulations were conducted to examine the property of photosynthetic increase in CaCO 3 saturation state (??), an indicator for PCP introduced by previous studies. These simulations revealed that ?? attained a high value at high Ca 2+ concentration, low ionic strength, and optimum pH and dissolved inorganic carbon (DIC) where a low-DIC effect and CO 2/CO 32- buffering were insignificant. Second, microelectrode measurements were conducted using cyanobacteria-dominated stromatolite to examine the property of actual PCP. Although Ca 2+ concentration and ionic strength similarly affected actual PCP, the influences of pH and DIC were quite different from what was expected from simulations: significant PCP occurred even at high DIC (up to ˜300 mmol L -1) where the ?? increase was suppressed by CO 2/CO 32- buffering. Instead, actual PCP reflected the photosynthetically achieved saturation state (? aft), which is the sum of ?? and initial saturation state (? bef). Thus, the chemical conditions favoring PCP is an optimum pH-DIC condition where ?? achieves a high value and/or a high pH-DIC condition where ? bef achieves a high value, in addition to a sufficiently high Ca 2+ concentration and low ionic strength. The microelectrode measurements also revealed that the photosynthetic pH increase did not always reflect the occurrence and significance of PCP.

Shiraishi, Fumito

2012-01-01

416

The behavior of cellulose molecules in aqueous environments  

Microsoft Academic Search

Molecular motions of cellulose chains in aqueous environments were investigated by comparison with those in non-aqueous environments using molecular simulation techniques. The cellulose chains under non-aqueous conditions approached each other closely and then made tight aggregates that were formed by direct hydrogen bonding. Those in aqueous environments, such as in a bio-system, were separated from each other by water molecules

Fumio Tanaka; Noriko Fukui

2004-01-01

417

40 CFR 796.1050 - Absorption in aqueous solution: Ultraviolet/visible spectra.  

Code of Federal Regulations, 2010 CFR

...2009-07-01 2009-07-01 false Absorption in aqueous solution: Ultraviolet...Chemical Properties § 796.1050 Absorption in aqueous solution: Ultraviolet...methods which are applied to measure the absorption spectra. (b) Method...

2009-07-01

418

40 CFR 796.1050 - Absorption in aqueous solution: Ultraviolet/visible spectra.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 true Absorption in aqueous solution: Ultraviolet...Chemical Properties § 796.1050 Absorption in aqueous solution: Ultraviolet...methods which are applied to measure the absorption spectra. (b) Method...

2010-07-01

419

Is an assessment factor of 10 appropriate to account for the variation in chemical toxicity to freshwater ectotherms under different thermal conditions?  

PubMed

Ecotoxicity tests are often conducted following standard methods, and thus carried out at a fixed water temperature under controlled laboratory conditions. Yet, toxicity of a chemical contaminant may vary in a temperature-dependent manner, depending on the physiology of the test organism and physicochemical properties of the chemical. Although an assessment factor of 10 (AF10) is commonly adopted to account for variability in toxicity data related to temperature in the development of water quality guidelines and/or ecological risk assessment, no one has ever rigorously assessed the appropriateness of AF10 to account for potential variation in temperature-dependent chemical toxicity to aquatic organisms. This study, therefore, aims to address this issue through a meta-analysis by comparing median lethal concentration data for nine chemicals (cadmium, copper, nickel, lead, silver, zinc, arsenic, selenium and DDT) on a range of freshwater ectothermic animal species at different temperatures, and to assess whether AF10 is under- or over-protective for tropical and temperate freshwater ecosystems. Our results reveal varying extents of interaction between temperature and different chemicals on organisms and the complexity of these interactions. Applying AF10 sufficiently protects 90 % of the animal species tested over a range of temperatures for cadmium, copper, nickel, silver, zinc and DDT in the tropics, but it is insufficient to adequately encompass a larger temperature variation for most studied chemicals in temperate regions. It is therefore important to set specific AFs for different climatic zones in order to achieve the desired level of ecosystem protection. PMID:23640388

Lau, Edward Tak Chuen; Yung, Mana Man Na; Karraker, Nancy E; Leung, Kenneth Mei Yee

2013-05-01

420

Lithium Ion Aqueous Cells.  

National Technical Information Service (NTIS)

Lithium ion aqueous cells were investigated using lithium intercalating compounds as anodes and cathodes. The aqueous electrolyte consisted of 4 to 5 molar solutions of either lithium perchlorate or lithium nitrate which contained lithium hydroxide in mil...

E. J. Plichta W. K. Behl

1995-01-01

421

Ametryn degradation by aqueous chlorine: kinetics and reaction influences.  

PubMed

The chemical oxidation of the herbicide ametryn was investigated by aqueous chlorination between pH 4 and 10 at a temperature of 25 degrees C. Ametryn was found to react very rapidly with aqueous chlorine. The reaction kinetics can be well described by a second-order kinetic model. The apparent second-order rate constants are greater than 5 x 10(2)M(-1)s(-1) under acidic and neutral conditions. The reaction proceeds much more slowly under alkaline conditions. The predominant reactions were found to be the reactions of HOCl with neutral ametryn and the charged ametryn, with rate constants equal to 7.22 x 10(2) and 1.58 x 10(3)M(-1)s(-1), respectively. The ametryn degradation rate increases with addition of bromide and decreases with addition of ammonia during the chlorination process. Based on elementary chemical reactions, a kinetic model of ametryn degradation by chlorination in the presence of bromide or ammonia ion was also developed. By employing this model, we estimate that the rate constants for the reactions of HOBr with neutral ametryn and charged ametryn were 9.07 x 10(3) and 3.54 x 10(6)M(-1)s(-1), respectively. These values are 10- to 10(3)-fold higher than those of HOCl, suggesting that the presence of bromine species during chlorination could significantly accelerate ametryn degradation. PMID:19423216

Xu, Bin; Gao, Nai-yun; Cheng, Hefa; Hu, Chen-yan; Xia, Sheng-ji; Sun, Xiao-feng; Wang, Xuejiao; Yang, Shaogui

2009-04-07

422

Phytoplankton and physical-chemical conditions in selected rivers and the coastal zone of Lake Michigan, 1972  

SciTech Connect

A very large data set was obtained on the nearshore environment of Lake Michigan during 1972. The data set is probably unique in that samples were collected and analyzed for a number of physical-chemical parameters and for phytoplankton standing crop and species composition. Phytoplankton identified during the study totaled 431 taxa of which 306 were diatoms, which serves to illustrate the magnitude of available data. Results are presented for eleven different transects sampled in April and for three of these transects which were sampled in September. In addition, transects for the St. Joseph, Kalamazoo, and Grand Rivers were sampled four or five times and each of these rivers were sampled from seven to eleven times in July. Data collected with depth presented in this report include water temperature. Secchi disc transparency, pH, specific conductance, dissolved reactive silica, nitrate nitrogen, and total phosphorus as physical-chemical variables. On transects samples with depth were obtained at stations 0, .2, .8, 1.6, 3.2, 6.4, 13, 26, and 52 km from shore, although the stations from 13 to 52 km were not sampled on every transect. Data related to phytoplankton include species composition and abundance, species diversity, chlorophyll a, and rates of carbon fixation. All these data were obtained only at 2 meters.

Schelske, C.L.; Feldt, L.E.; Simmons, M.S.

1980-01-01

423

Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction  

SciTech Connect

The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. ? Elucidate the controls on the rate and extent of contaminant reactivity. (2) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

Scott C. Brooks; Wenming Dong; Sue Carroll; Jim Fredrickson; Ken Kemner; Shelly Kelly

2006-06-01

424

Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction  

SciTech Connect

The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

Scott C. Brooks; Wenming Dong; Sue Carroll; James K. Fredrickson; Kenneth M. Kemner; Shelly D. Kelly

2006-06-01

425

1H NMR investigation of self-association of vanillin in aqueous solution  

NASA Astrophysics Data System (ADS)

A self-association of vanillin have been studied by 1H NMR spectroscopy using the analysis of proton chemical shifts changes in aqueous solution as a function of concentration. The experimental results have been analysed using indefinite non-cooperative and cooperative models of molecular self-association, enabling the determination of equilibrium constants, parameters of cooperativity and the limiting values of vanillin proton chemical shifts in the complex. It was found that the dimer formation creates energetically favourable conditions for subsequent molecular association.

Bogdan, Mircea; Floare, Calin G.; Pîrnau, Adrian

2009-08-01

426

The role of conditioning film formation and surface chemical changes on Xylella fastidiosa adhesion and biofilm evolution.  

PubMed

Biofilms are complex microbial communities with important biological functions including enhanced resistance against external factors like antimicrobial agents. The formation of a biofilm is known to be strongly dependent on substrate properties including hydrophobicity/hydrophilicity, structure, and roughness. The adsorption of (macro)molecules on the substrate, also known as conditioning film, changes the physicochemical properties of the surface and affects the bacterial adhesion. In this study, we investigate the physicochemical changes caused by Periwinkle wilt (PW) culture medium conditioning film formation on different surfaces (glass and silicon) and their effect on X. fastidiosa biofilm formation. Contact angle measurements have shown that the film formation decreases the surface hydrophilicity degree of both glass and silicon after few hours. Atomic force microscopy (AFM) images show the glass surface roughness is drastically reduced with conditioning film formation. First-layer