These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

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

Vecitis, Chad David

2009-12-01

2

Aqueous chemical wash compositions  

SciTech Connect

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

Bannister, C.E.

1987-07-21

3

Explosivity Conditions of Aqueous Solutions  

Microsoft Academic Search

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

R. Thiéry; L. Mercury

2009-01-01

4

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

NASA Technical Reports Server (NTRS)

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

Weber, Arthur L.

2002-01-01

5

Plasmon-driven sequential chemical reactions in an aqueous environment  

PubMed Central

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

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

2014-01-01

6

Plasmon-driven sequential chemical reactions in an aqueous environment  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

7

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...

8

The importance of ternary complexes in defining basic conditions for the deposition of ZnS by aqueous chemical bath deposition  

Microsoft Academic Search

In the deposition of ZnS by chemical bath methods (CBD) at basic pH it is common to see improved deposition in the presence of a second ligand. These ternary systems (three components; two ligands one metal) are usually modelled by considering only the formation of binary species. This short paper outlines a strategy for considering the incorporation of ternary species

Paul O'Brien; David J. Otway; David Smyth-Boyle

2000-01-01

9

Chemical effect of swirling jet-induced cavitation: Degradation of rhodamine B in aqueous solution  

Microsoft Academic Search

The chemical effect of swirling jet-induced cavitation was investigated with the decomposing reaction of rhodamine B in aqueous solution. It was found that rhodamine B in aqueous solution can be degraded with swirling jet-induced cavitation and the degradation can be described by a pseudo-first-order kinetics. The effects of operating conditions such as pressure, temperature, initial concentration of rhodamine B, pH

Xikui Wang; Jingang Wang; Peiquan Guo; Weilin Guo; Guoliang Li

2008-01-01

10

Classes of Chemical Reactions Reactions in aqueous media  

E-print Network

Classes of Chemical Reactions Reactions in aqueous media · Precipitation reactions · Acid-Base+ , and Pb2+ #12;Classes of Chemical Reactions Acid-Base Reactions Acid - a substance that is a donor of H Acid-Base Reactions STRONG ACIDS WEAK ACIDS Hydrochloric acid, HCl Hydrofluoric acid, HF Hydrobromic

Zakarian, Armen

11

CHEMICAL SYNTHESES IN AQUEOUS MEDIA USING MICROWAVES  

EPA Science Inventory

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

12

Physical-chemical conditions of ore deposition  

NASA Astrophysics Data System (ADS)

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 S 2 and O 2 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.

Barton, Paul B.

13

Explosivity Conditions of Aqueous Solutions and L. Mercury2  

E-print Network

1 Explosivity Conditions of Aqueous Solutions R. Thiéry1 and L. Mercury2 Revised version February. Address: 1A, rue de la Férollerie, F-45071, Orléans Cedex, France. e-mail: lionel.mercury,version1-8Sep2009 #12;3 1 Introduction Water is the main natural explosive agent on the Earth. This fact

Paris-Sud XI, Université de

14

Application of chemically modified rice husk for the removal of heavy metals from aqueous solution.  

PubMed

The removal efficiency of lead, cadmium and zinc from aqueous solution on adsorption by using rice husk, a non-conventional material in its natural and chemically modified form has been presented in this paper. It has been observed that rate of adsorption is dependent on the nature of the adsorbent, adsorbent dose, particle size of the adsorbent, concentration, pH, contact time, temperature, etc. Under identical experimental condition chemically modified rice husk was found to possess greater adsorption capacity for all metals than untreated rice husk and chemically modified rice husk ash. Chemically modified rice husk could remove 99.8% Pb, 95% Cd and 97% Zn from aqueous solution at room temperature. PMID:21114100

Kayal, N; Sinhia, P K; Kundu, D

2010-01-01

15

Wetting under chemical equilibrium and nonequilibrium conditions  

Microsoft Academic Search

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

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

1974-01-01

16

FBX aqueous chemical dosimeter for measurement of dosimetric parameters.  

PubMed

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

Moussous, O; Medjadj, T; Benguerba, M

2011-02-01

17

Pavlovian conditioning and multiple chemical sensitivity.  

PubMed Central

Pavlovian conditioning processes may contribute to some symptoms of multiple chemical sensitivity (MCS). This review summarizes the potential relevance of the literature on conditional taste and olfactory aversions, conditional sensitization, and conditional immunomodulation to understanding MCS. A conditioning-based perspective on MCS suggests novel research and treatment strategies. PMID:9167990

Siegel, S; Kreutzer, R

1997-01-01

18

Estimating total aqueous and airborne chemical emissions from ozonated and chemically treated cooling towers  

SciTech Connect

Cooling tower operations result in aqueous and airborne emissions into the environment in the form of blowdown and drift, respectively. Increased regulatory and licensing requirements often obligate end users to quantify the nature and amount of any added chemicals in such emissions. This paper presents a methodology whereby cooling tower operators can perform such calculations for conventionally chemically treated cooling towers as well as ozonated cooling towers. Emissions from cooling towers depend on the operating characteristics of the tower (recirculation rate, drift rate), makeup and cooling water quality (makeup water mineral concentration, cooling water cycles of concentration), the amount of chemicals added to the cooling water, and/or the amount of ozone injected into the cooling water and the mass transfer efficiency of the ozone injection process.

Pryor, A. [Ozone Process Consultants, Inc., Sunnyvale, CA (United States)

1996-10-01

19

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...

20

Analyzing Aqueous Solution Imbibition into Shale and the Effects of Optimizing Critical Chemical Additives  

E-print Network

ANALYZING AQUEOUS SOLUTION IMBIBITON INTO SHALE AND THE EFFECTS OF OPTIMIZING CRITICAL CHEMICAL ADDITIVES An Undergraduate Research Scholars Thesis by MATTHEW WIESE, SAMMAZO PLAMIN and MAHA QURESHI Submitted to Honors and Undergraduate... 21 APPENDIX A 22 1 ABSTRACT Analyzing Aqueous Solution Imbibition into Shale and the Effects...

Wiese, Matthew Michael

2013-09-29

21

Modelling of Chlorophenol Treatment in Aqueous Solutions. 1. Ozonation and Ozonation Combined with UV Radiation under Acidic Conditions  

Microsoft Academic Search

Treatment of 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) in aqueous solutions with direct photolysis (254 nm), ozonation and ozonation with photolysis was studied. A model was developed to simulate chlorophenol treatment in a semibatch column using these processes under acidic conditions in which the chemical reactions are slow. Satisfactory results were obtained in simulating the chlorophenol and ozone concentrations,

Marjaana Hautaniemi; Juha Kallas; Rein Munter; Marina Trapido

1998-01-01

22

'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION 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-alkylation t...

23

Pulse radiolysis of tetrazolium violet in aqueous and aqueous-alcoholic solutions under oxidative and reductive conditions  

NASA Astrophysics Data System (ADS)

The radiolytic reduction of colourless tetrazolium salts to coloured formazans in liquid and solid state is suggested for dosimetry purposes. In order to clarify the reaction mechanism, a pulse radiolysis study was conducted in aqueous and aqueous-alcoholic solutions under oxidative and reductive conditions. Under reducing conditions, fast formation of the electron adduct tetrazolinyl radical was observed: coloured formazan final product formed during the decay of electron adduct. Both the decay of the tetrazolinyl radical and the formation of the formazan were found to be second order. The spectra of the formazan were similar in neutral and alkaline solutions, but with higher absorbance in the latter solutions due to the higher molar absorption coefficient. Under oxidative conditions formazan did not form; hydroxylated products through OH-adducts were observed in the pH range studied.

Kovács, A.; Wojnárovits, L.; Pálfi, T.; Emi-Reynolds, G.; Fletcher, J.

2008-09-01

24

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...

25

The Effect of Salt on Protein Chemical Potential Determined by Ternary Diffusion in Aqueous Solutions  

E-print Network

The Effect of Salt on Protein Chemical Potential Determined by Ternary Diffusion in Aqueous as a function of salt concentration, (b) compare the behavior of the protein chemical potential for the three salts, which we found to be consistent with the Hofmeister series, and (c) discuss our thermodynamic

Annunziata, Onofrio

26

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

27

A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase  

NASA Astrophysics Data System (ADS)

Photochemical reactions represent the main pathway for the removal of non-methane volatile organic compounds (VOCs) in the atmosphere. VOCs may react with hydroxyl radical (OH), the most important atmospheric oxidant, or they can be photolyzed by actinic radiation. In the presence of clouds and fog, VOCs may partition into the aqueous phase where they can undergo aqueous photolysis and/or reaction with dissolved OH. The significance of direct aqueous photolysis is largely uncertain due to the lack of published absorption cross sections and photolysis quantum yields. In light of this, we strive to identify atmospherically relevant VOCs where removal by aqueous photolysis may be a significant sink. The relative importance of different photochemical sinks is assessed by calculating the ratios of the removal rates inside air parcels containing cloud and fog droplets. This relative approach provides useful information in spite of the limited aqueous photolysis data. Results of this work should help guide researchers in identifying molecules that are the most likely to undergo aqueous OH oxidation and photolysis. For example, we find that out of the 27 atmospherically relevant species investigated, the removal of glyceraldehyde and pyruvic acid by aqueous photolysis is potentially an important sink. We also determine the relative magnitudes of these four chemical sinks for the set of relevant organic compounds.

Epstein, S. A.; Nizkorodov, S. A.

2012-09-01

28

A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase  

NASA Astrophysics Data System (ADS)

Photochemical reactions represent the main pathway for the removal of non-methane volatile organic compounds (VOCs) in the atmosphere. VOCs may react with hydroxyl radical (OH), the most important atmospheric oxidant, or they can be photolyzed by actinic radiation. In the presence of clouds and fog, VOCs may partition into the aqueous phase where they can undergo aqueous photolysis and/or reaction with dissolved OH. The significance of direct aqueous photolysis is largely uncertain due to the lack of published absorption cross sections and photolysis quantum yields. In light of this, we strive to identify atmospherically relevant VOCs where removal by aqueous photolysis may be a significant sink. The relative importance of different photochemical sinks is assessed by calculating the ratios of the removal rates inside air parcels containing cloud and fog droplets. This relative approach provides useful information in spite of the limited aqueous photolysis data. Results of this work should help guide researchers in identifying molecules that are the most likely to undergo aqueous OH oxidation and photolysis. We find that out of the 27 atmospherically relevant species investigated, the removal of glyceraldehyde and pyruvic acid by aqueous photolysis is potentially an important sink. We also determine the relative magnitudes of these four chemical sinks for the set of relevant organic compounds.

Epstein, S. A.; Nizkorodov, S. A.

2012-04-01

29

Aqueous organic chemistry in the atmosphere: sources and chemical processing of organic aerosols.  

PubMed

Over the past decade, it has become clear that aqueous chemical processes occurring in cloud droplets and wet atmospheric particles are an important source of organic atmospheric particulate matter. Reactions of water-soluble volatile (or semivolatile) organic gases (VOCs or SVOCs) in these aqueous media lead to the formation of highly oxidized organic particulate matter (secondary organic aerosol; SOA) and key tracer species, such as organosulfates. These processes are often driven by a combination of anthropogenic and biogenic emissions, and therefore their accurate representation in models is important for effective air quality management. Despite considerable progress, mechanistic understanding of some key aqueous processes is still lacking, and these pathways are incompletely represented in 3D atmospheric chemistry and air quality models. In this article, the concepts, historical context, and current state of the science of aqueous pathways of SOA formation are discussed. PMID:25609552

McNeill, V Faye

2015-02-01

30

Optical techniques for nanoscale probing and chemical detection in aqueous environments  

NASA Astrophysics Data System (ADS)

We present an investigation of charge-dependent physical properties of water-soluble synthetic polymers and polymer-based layered structures, using optical detection methods in a visible range. We apply in situ nanoscale optical techniques to study response of polymer systems to changes in pH, polymer concentration, and concentration and type of counterions. This work describes three optical techniques and custom built instrumental setups for nanoscale polymer characterization in aqueous environment. Phase-modulated ellipsometry was applied to determine the refraction coefficient and the thickness of a hydrogel-like polymer layer on a substrate. The present study describes the sensitivity of the phase modulated ellipsometry to errors of measurement and determines conditions for decoupling film thickness and refraction index. It is shown that, for a certain range of film thickness, both the thickness and the refractive index can be determined from a single measurement with high precision. This optimal range of the film thickness is calculated for organic thin films, and the analysis is tested on crosslinked poly(methacrylic acid) polymer films in air and in water. Fluorescent correlation spectroscopy was used to investigate diffusion of a synthetic polyelectrolyte in aqueous solutions. Translational diffusion of Alexa-labeled poly(methacrylic acid) chains was studied in very dilute, 10-4 mg/ml, solutions as a function of polymer charge density and counterion concentration. The results illustrate the utility of the technique for studying hydrodynamic sizes of polyelectrolyte coils in response to variation in solution pH or concentration of salt and polyelectrolytes. We apply surface-enhanced Raman scattering (SERS) for studying of enhancement capabilities of individual silver nanoparticles attached to glass and silicon substrates. Nanoparticles were electrostatically bound to a self-assembled polyallylamine hydrochloride (PAH) monolayer, which was deposited on substrates from aqueous solution. We have shown that the coverage density of Ag nanoparticles on the glass substrates correlates with the amount of adsorbed PAH. The SERS-active substrates were robust and stable in 0.5 M NaCl solutions, as well in extreme acidic and basic conditions. Rhodamine 6G dye (R6G) was chosen as a model molecule for SERS spectra acquisition. The glass substrates with immobilized non-aggregated Ag nanoparticles exhibited SERS enhancement and provided in situ detection sensitivity of R6G at 5 ppt level, with estimated surface coverage of 2 to 4 R6G molecules per silver particle. The results will improve the design of SERS-active photonic crystal fibers for highly sensitive chemical and biological detection.

Pristinski, Denis

31

Aqueous phase oligomerization of methyl vinyl ketone through photooxidation - Part 2: Development of the chemical mechanism and atmospheric implications  

NASA Astrophysics Data System (ADS)

We developed a chemical mechanism based on laboratory experiments that have shown efficient oligomerization from methyl vinyl ketone (MVK) in the bulk aqueous phase. Kinetic data are applied (if known) or fitted to the observed MVK decay and oligomer mass increase. The mechanism is then implemented into a multiphase box model that simulates (i) oligomer formation upon uptake of MVK from the gas phase, and (ii) SOA formation from isoprene, as a precursor of MVK and methacrolein (MACR) in the aqueous and gas phases. Model results show that under atmospheric conditions, the oligomer formation rate strongly depends on the availability of dissolved oxygen. If oxygen is consumed too quickly or its solubility is kinetically or thermodynamically limited, oligomerization is accelerated, in agreement with the laboratory studies. The comparison of predicted oligomer formation shows that for most model assumptions (e.g. depending on the assumed partitioning of MVK and MACR), SOA formation from isoprene in the gas phase exceeds aqueous SOA formation by a factor 3-4. However, at high aerosol liquid water content and potentially high partitioning of oligomer precursors into the aqueous phase, SOA formation in both phases might be equally efficient.

Ervens, B.; Renard, P.; Ravier, S.; Clément, J.-L.; Monod, A.

2014-08-01

32

Photoluminescence study of ZnO structures grown by aqueous chemical growth G. Kenanakis a,b,c  

E-print Network

Photoluminescence study of ZnO structures grown by aqueous chemical growth G. Kenanakis a,b,c , M online 28 April 2011 Keywords: ZnO structures Aqueous chemical growth Photoluminescence ZnO micro electron microscopy and Raman spectroscopy. Photoluminescence spectra recorded at 18 and 295 K for 325 nm

33

Chemical Absorption of Carbon Dioxide into Aqueous Colloidal Silica Solution with Diethanolamine  

Microsoft Academic Search

The chemical absorption rate (RA) of CO2 was measured into the aqueous nanometer sized colloidal silica solution of 0–31 wt% and diethanoleamine of 0–2 kmol\\/m in the flat?stirred vessel with the impeller size of 0.034 m and its agitation speed of 50 rev\\/min at 25°C and 0.101 MPa, and compared with the values estimated from the model based on the film theory accompanied by chemical

2006-01-01

34

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

EPA Science Inventory

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

35

The chemical modification of lignins with succinic anhydride in aqueous systems  

Microsoft Academic Search

Chemical modification of oil palm trunk fibre lignin, poplar lignin, maize stem lignin, and barley, wheat, and rye straw lignins was achieved by esterification with succinic anhydride in aqueous solutions. FT–IR spectroscopy clearly revealed the differences in the structure of the modified lignins as a result of this succinoylation. These changes were reflected by thermal analyses such as thermogravimetric analysis

B. Xiao; X. F. Sun; RunCang Sun

2001-01-01

36

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

37

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

EPA Science Inventory

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

38

Tannin (Polyphenol) Stability in Aqueous Solutions  

Technology Transfer Automated Retrieval System (TEKTRAN)

Understanding the chemical stability of tannins (polyphenolics) in soils is critical to understanding their biological activities and fate. We examined the stability of chemically defined tannins in aqueous solutions under conditions simulating natural and laboratory conditions. We evaluated tanni...

39

Iron oxide functionalized graphene nano-composite for dispersive solid phase extraction of chemical warfare agents from aqueous samples.  

PubMed

Present study deals with the preparation and evaluation of graphene based magnetic nano-composite for dispersive solid phase extraction of Chemical Weapons Convention (CWC) relevant chemicals from aqueous samples. Nano-composite, Fe3O4@SiO2-G was synthesized by covalently bonding silica coated Fe3O4 onto the graphene sheets. Nerve agents (NA), Sulfur mustard (SM) and their non-toxic environmental markers were the target analytes. Extraction parameters like amount of sorbent, extraction time and desorption conditions were optimized. Dispersion of 20 milligram of sorbent in 200mL of water sample for 20min. followed by methanol/chloroform extraction produced average to good recoveries (27-94%) of targeted analytes. Recoveries of real agents exhibited great dependency upon sample pH and ionic strength. Sarin produced maximum recovery under mild acidic conditions (56% at pH 5) while VX demanded alkaline media (83% at pH 9). Salts presence in the aqueous samples was found to be advantageous, raising the recoveries to as high as 94% for SM. Excellent limits of detection (LOD) for sulphur mustard and VX (0.11ngmL(-1) and 0.19ngmL(-1) respectively) proved the utility of the developed method for the off-site analysis of CWC relevant chemicals. PMID:25828545

Chinthakindi, Sridhar; Purohit, Ajay; Singh, Varoon; Tak, Vijay; Goud, D Raghavender; Dubey, D K; Pardasani, Deepak

2015-05-15

40

Aqueous alteration of VHTR fuels particles under simulated geological conditions  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

41

Exploring Atmospheric Aqueous Chemistry (and Secondary Organic Aerosol Formation) through OH Radical Oxidation Experiments, Droplet Evaporation and Chemical Modeling  

NASA Astrophysics Data System (ADS)

Gas phase photochemistry fragments and oxidizes organic emissions, making water-soluble organics ubiquitous in the atmosphere. My group and others have found that several water-soluble compounds react further in the aqueous phase forming low volatility products under atmospherically-relevant conditions (i.e., in clouds, fogs and wet aerosols). Thus, secondary organic aerosol can form as a result of gas followed by aqueous chemistry (aqSOA). We have used aqueous OH radical oxidation experiments coupled with product analysis and chemical modeling to validate and refine the aqueous chemistry of glyoxal, methylglyoxal, glycolaldehyde, and acetic acid. The resulting chemical model has provided insights into the differences between oxidation chemistry in clouds and in wet aerosols. Further, we conducted droplet evaporation experiments to characterize the volatility of the products. Most recently, we have conducted aqueous OH radical oxidation experiments with ambient mixtures of water-soluble gases to identify additional atmospherically-important precursors and products. Specifically, we scrubbed water-soluble gases from the ambient air in the Po Valley, Italy using four mist chambers in parallel, operating at 25-30 L min-1. Aqueous OH radical oxidation experiments and control experiments were conducted with these mixtures (total organic carbon ? 100 ?M-C). OH radicals (3.5E-2 ?M [OH] s-1) were generated by photolyzing H2O2. Precursors and products were characterized using electrospray ionization mass spectrometry (ESI-MS), ion chromatography (IC), IC-ESI-MS, and ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Chemical modeling suggests that organic acids (e.g., oxalate, pyruvate, glycolate) are major products of OH radical oxidation at cloud-relevant concentrations, whereas organic radical - radical reactions result in the formation of oligomers in wet aerosols. Products of cloud chemistry and droplet evaporation have effective vapor pressures that are orders of magnitude lower when ammonium hydroxide is present (pH 7) than without (at lower pH). In Po Valley experiments, nitrogen-containing organics were prominent precursors and intermediates. Pyruvate and oxalate were among the products. Importantly, formation of aqSOA helps to explain the high O/C ratios found in atmospheric aerosols. While uncertainties remain large, global modeling suggests that aqSOA is comparable in magnitude to SOA formed through gas phase chemistry and vapor pressure driven partitioning (gasSOA).

Turpin, B. J.; Kirkland, J. R.; Lim, Y. B.; Ortiz-Montalvo, D. L.; Sullivan, A.; Häkkinen, S.; Schwier, A. N.; Tan, Y.; McNeill, V. F.; Collett, J. L.; Skog, K.; Keutsch, F. N.; Sareen, N.; Carlton, A. G.; Decesari, S.; Facchini, C.

2013-12-01

42

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

PubMed Central

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

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

2014-01-01

43

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...

44

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...

45

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

NASA Technical Reports Server (NTRS)

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

Madsen, Brooks C.

1992-01-01

46

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

47

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation  

Microsoft Academic Search

Hydrolyzed products of Al(III) have affinity below pHzpc for oppositely charged mono and bi?nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA\\/cm current density. Cathodic adsorption of chromium boosted up

Animes K. Golder; Ajoy K. Chanda; Amar N. Samanta; Subhabrata Ray

2007-01-01

48

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

PubMed

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

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

2012-10-01

49

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. PMID:23723676

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

2012-01-01

50

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

51

Polymerization of amino acids under high-pressure conditions: Implication to chemical evolution on the early Earth  

Microsoft Academic Search

Prebiotic polymerization of amino acids is the most fundamental reaction to promote the chemical evolution for origin of life. Polymerization of amino acids is the dehydration reaction. This questions as to if submarine hydrothermal conditions, thus hydrated enironments, were appropreate for peptide formations. Our previous experiments implied that non-aqueous and high-pressure environments (more than 20 MPa) would be suitable for

T. Kakegawa; S. Ohara; T. Ishiguro; H. Abiko; H. Nakazawa

2008-01-01

52

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. PMID:20921372

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

2010-01-01

53

Predicting Chemical Fingerprints of Vadose Zone Soil Gas and Indoor Air from NonAqueous Phase Liquid Composition  

Microsoft Academic Search

Complex mixtures of volatile organic chemical (VOC) vapors can exist over subsurface accumulations of non-aqueous phase liquids (NAPLs) and contaminated soils. The ability to predict the relative soil gas chemical composition arising from such NAPLs is relevant to studies of the sources and fate of soil gas, and in assessing the possible intrusion of soil gas chemical constituents to indoor

Allen D. Uhler; Kevin J. McCarthy; Stephen D. Emsbo-Mattingly; Scott A. Stout; Gregory S. Douglas

2010-01-01

54

Size-resolved aqueous-phase atmospheric chemistry in a three-dimensional chemical transport model  

NASA Astrophysics Data System (ADS)

Three-dimensional chemical transport models typically include a bulk description of aqueous-phase atmospheric chemistry. Previously, this bulk description has been shown to be often inadequate in predicting sulfate production. The pH of the bulk mixture does not adequately describe the pH of the typically heterogeneous droplet population found in clouds and fogs. This often leads to an inability of bulk models to predict sulfate production when pH-dependent production pathways are important. A more accurate size-resolved aqueous-phase chemistry model, however, has long been considered infeasible for incorporation in a three-dimensional chemical transport model because of high computational costs. Here we investigate the feasibility of adding a computationally efficient size-resolved aqueous-phase chemistry module (Variable Size Resolution Model (VSRM)) to a three-dimensional model (the latest version of the Comprehensive Air Quality Model with extensions (PMCAMx)). The VSRM treats mass transfer between the gas phase and the different droplet populations and executes bulk or two-section size-resolved chemistry calculations in each step on the basis of the chemical environment of each computational cell. A fall air pollution episode in California's South Coast Air Basin is simulated, and model predictions are compared to observations. In an environment where clouds or fogs are present, the model without aqueous-phase chemistry severely underpredicts secondary sulfate formation. In cases where there is a high potential for sulfate production and widely varying composition across the droplet spectrum (over the ocean and near the coast), there is a significant increase in sulfate production over bulk predictions with the activation of a size-resolved aqueous-phase chemistry module. Unfortunately, measurements were only available at inland sites, where the difference between bulk and size-resolved sulfate predictions was small. The effects of other uncertainties on sulfate production are also examined. For limited computational costs (5% overhead), the VSRM can be included in a three-dimensional chemical transport model.

Fahey, K. M.; Pandis, S. N.

2003-11-01

55

Stability of Lysozyme in Aqueous Extremolyte Solutions during Heat Shock and Accelerated Thermal Conditions  

PubMed Central

The purpose of this study was to investigate the stability of lysozyme in aqueous solutions in the presence of various extremolytes (betaine, hydroxyectoine, trehalose, ectoine, and firoin) under different stress conditions. The stability of lysozyme was determined by Nile red Fluorescence Spectroscopy and a bioactivity assay. During heat shock (10 min at 70°C), betaine, trehalose, ectoin and firoin protected lysozyme against inactivation while hydroxyectoine, did not have a significant effect. During accelerated thermal conditions (4 weeks at 55°C), firoin also acted as a stabilizer. In contrast, betaine, hydroxyectoine, trehalose and ectoine destabilized lysozyme under this condition. These findings surprisingly indicate that some extremolytes can stabilize a protein under certain stress conditions but destabilize the same protein under other stress conditions. Therefore it is suggested that for the screening extremolytes to be used for protein stabilization, an appropriate storage conditions should also be taken into account. PMID:24465983

van Streun, Erwin L. P.; Frijlink, Henderik W.; Hinrichs, Wouter L. J.

2014-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

57

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

PubMed

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

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

2014-04-15

58

Chemical reduction kinetics of nitrate in aqueous solution by Mg\\/Cu bimetallic particles  

Microsoft Academic Search

Synthesized magnesium\\/copper (Mg\\/Cu) bimetallic particles have shown good potential for use in the reduction of nitrate from aqueous solutions. This study was conducted to investigate the main factors affecting the kinetics of nitrate reduction by Mg\\/Cu particles (<100 µm) in uncontrolled reaction conditions. The Mg\\/Cu bimetallic particles removed the majority of the various nitrate concentrations tested (50, 100, 150, 200

S. B. Mortazavi; B. Ramavandi; G. Moussavi

2011-01-01

59

Intrinsic formation of nanocrystalline neptunium dioxide under neutral aqueous conditions relevant to deep geological repositories.  

PubMed

The dilution of aqueous neptunium carbonate complexes induces the intrinsic formation of nanocrystalline neptunium dioxide (NpO2) particles, which are characterised by UV/Vis and X-ray absorption spectroscopies and transmission electron microscopy. This new route of nanocrystalline NpO2 formation could be a potential scenario for the environmental transport of radionuclides from the waste repository (i.e. under near-field alkaline conditions) to the geological environment (i.e. under far-field neutral conditions). PMID:25479067

Husar, Richard; Hübner, René; Hennig, Christoph; Martin, Philippe M; Chollet, Mélanie; Weiss, Stephan; Stumpf, Thorsten; Zänker, Harald; Ikeda-Ohno, Atsushi

2015-01-25

60

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

61

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

62

CO? carbonation under aqueous conditions using petroleum coke combustion fly ash.  

PubMed

Fly ash from petroleum coke combustion was evaluated for CO2 capture in aqueous medium. Moreover the carbonation efficiency based on different methodologies and the kinetic parameters of the process were determined. The results show that petroleum coke fly ash achieved a CO2 capture yield of 21% at the experimental conditions of 12 g L(-1), 363°K without stirring. The carbonation efficiency by petroleum coke fly ash based on reactive calcium species was within carbonation efficiencies reported by several authors. In addition, carbonation by petroleum coke fly ash follows a pseudo-second order kinetic model. PMID:25000300

González, A; Moreno, N; Navia, R

2014-12-01

63

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. PMID:22423272

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

2012-01-01

64

Comprehensive study of the chemical reactions resulting from the decomposition of chloroform in alkaline aqueous solution  

NASA Astrophysics Data System (ADS)

Chloroform (CHCl3) is a volatile liquid, which has a rather slow rate of decomposition in ground water. It is a known carcinogen and one of the most common contaminants found at toxic waste sites. The dominant degradation process for chloroform in both the atmosphere and the groundwater is the reaction with the hydroxyl radical or hydroxide ion. This process triggers a sequence of reactions which ultimately yield carbon monoxide, hydrogen chloride, and formic acid. The rate of chloroform degradation is considerably larger in solution than that in the gas phase and it increases dramatically with increasing pH. However, only one of the viable reactions had been studied previously at a high level of theory in solution. It is of great interest to gain a deeper understanding of the decomposition reaction mechanism. Quantum mechanical methods are well suited for studying the mechanism of organic reactions. However, a full quantum mechanical treatment of the entire fluid system is not computationally feasible. In this work, combined quantum mechanical and molecular mechanical (QM/MM) methods are used for studying chemical reactions in condensed phases. In these calculations, the solute molecules are treated quantum mechanically (QM), whereas the solvent molecules are approximated by empirical (MM) potential energy functions. The use of quantum mechanics and statistical sampling simulation is necessary to determine the reaction free energy profile. In the present study, the ab initio Hartree-Fock theory along with the 3-21G basis set was used in the quantum mechanical calculations to elucidate the reaction pathways of chloroform decomposition, with a focus on basic reaction conditions. Statistical mechanical Monte Carlo approach was then applied in molecular mechanical simulations, employing the empirical TIP3P model for water. We employed state-of-the-art electronic structure methods to determine the gas-phase inter-nuclear potential energy profile for all the relevant reactions. Each gas-phase potential energy profile obtained at a high level of theory was used as a post-correction of the corresponding reaction free energy profile in aqueous solution. A detailed picture of the actual mechanism driving the decomposition pathway of chloroform has emerged from these simulations.

Estevez Mews, Jorge

65

EVALUATION OF CHEMICAL AMENDMENTS FOR PH AND REDOX STABILIZTION IN AQUEOUS SUSPENSIONS OF THREE CALIFORNIA SOILS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Many chemically and biologically important trace element, heavy metal, and organic contaminant reactions in soils are constrained by pH and redox conditions and changes in these conditions can significantly affect reaction rates. Although closed-system, batch methods have been used for many years to...

66

Chemical and Isotopic Study of Lab-formed Carbonates Under Cryogenic and Hydrothermal Conditions  

NASA Technical Reports Server (NTRS)

Aqueous environments on early Mars were probably relatively short-lived and localized, as evidenced by the lack of abundant secondary minerals detected by the TES instrument. In order to better understand the aqueous history of early Mars we need to be able to interpret the evidence preserved in secondary minerals formed during these aqueous events. Carbonate minerals, in particular, are important secondary minerals for interpreting past aqueous environments as illustrated by the carbonates preserved in ALH84001. Carbonates formed in short-lived, dynamic aqueous events often preserve kinetic rather than equilibrium chemical and isotopic processes, and predicting the behavior of such systems is facilitated by empirical data.

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

2004-01-01

67

Characterizing photochemical transformation of aqueous nC60 under environmentally relevant conditions.  

PubMed

Engineered nanomaterials may undergo transformation upon interactions with various environmental factors. In this study, photochemical transformation of aqueous nC60 was investigated under UVA irradiation. nC60 underwent photochemical transformation in the presence of dissolved O2, resulting in surface oxygenation and hydroxylation as demonstrated by XPS and ATR-FTIR analyses. The reaction followed a pseudo-first order rate law with the apparent reaction rate constant of 2.2 x 10(-2) h(-1). However, the core of the nanoparticles remained intact over 21 days of irradiation. Although no mineralization or dissolution of nC60 was observed, experiments using fullerol as a reference fullerene derivative suggested likely dissolution and partial mineralization of nC60 under long-term UVA exposure. Aquatic humic acid reduced nC60 transformation kinetics presumably due to scavenging of reactive oxygen species. Results from this study imply that photochemical transformation is an important factor controlling nC60 physical and chemical properties as well as its fate and transport in the natural aqueous environment. In addition, changes in nC60 surface chemistry drastically reduced C60 extraction efficiency by toluene, suggesting that the existing analytical method for C60 may not be applicable to environmental samples. PMID:20337472

Hwang, Yu Sik; Li, Qilin

2010-04-15

68

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

SciTech Connect

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

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

1999-05-01

69

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

70

Chemical characterization of the main products formed through aqueous-phase photonitration of guaiacol  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

71

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

PubMed

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

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

2011-09-01

72

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

PubMed

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

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

2014-01-01

73

Electrical conductivity of single CdS nanowire synthesized by aqueous chemical growth  

SciTech Connect

In this Letter, we report on the temperature-dependent conductivity and current-voltage curve of a single CdS nanowire, which was synthesized by a simple aqueous chemical growth method. A pair of platinum microleads was fabricated on the single CdS nanowire by focused ion-beam deposition. The room-temperature conductivity and the band gap of the single CdS wire are 0.82 {omega}{sup -1} cm{sup -1} and 0.055 eV, respectively. When the applied electric field is larger than 1090 V cm{sup -1}, the CdS nanowire shows a nonlinear I-V curve at room temperature.

Long Yunze; Chen Zhaojia; Wang Wenlong; Bai Fenglian; Jin Aizi; Gu Changzhi [Laboratory of Extreme Conditions Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080 (China); Laboratory of Organic Solids, Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080 (China); Laboratory of Microfabrication, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080 (China)

2005-04-11

74

Validity conditions for moment closure approximations in stochastic chemical kinetics.  

PubMed

Approximations based on moment-closure (MA) are commonly used to obtain estimates of the mean molecule numbers and of the variance of fluctuations in the number of molecules of chemical systems. The advantage of this approach is that it can be far less computationally expensive than exact stochastic simulations of the chemical master equation. Here, we numerically study the conditions under which the MA equations yield results reflecting the true stochastic dynamics of the system. We show that for bistable and oscillatory chemical systems with deterministic initial conditions, the solution of the MA equations can be interpreted as a valid approximation to the true moments of the chemical master equation, only when the steady-state mean molecule numbers obtained from the chemical master equation fall within a certain finite range. The same validity criterion for monostable systems implies that the steady-state mean molecule numbers obtained from the chemical master equation must be above a certain threshold. For mean molecule numbers outside of this range of validity, the MA equations lead to either qualitatively wrong oscillatory dynamics or to unphysical predictions such as negative variances in the molecule numbers or multiple steady-state moments of the stationary distribution as the initial conditions are varied. Our results clarify the range of validity of the MA approach and show that pitfalls in the interpretation of the results can only be overcome through the systematic comparison of the solutions of the MA equations of a certain order with those of higher orders. PMID:25173001

Schnoerr, David; Sanguinetti, Guido; Grima, Ramon

2014-08-28

75

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

76

Resistance to chemical disinfection under conditions of microgravity  

NASA Astrophysics Data System (ADS)

In unit gravity, bacteria and disinfecting resin beads co-sediment to the septum in a fluid processing apparatus (FPA) resulting in effective chemical disinfection. In microgravity bacteria in suspension have access to a larger volume of the FPA because of a lack of sedimentation. Further, when disinfecting resin beads are added to the FPA they also remain in suspension reducing their effective concentration. Typically, therefore, disinfection experiments in microgravity return larger numbers of viable bacteria than ground-based controls. Preliminary experiments aboard the MIR Space Station with Pseudomonas aeruginosa additionally suggest that the longer bacteria are retained in microgravity the more resistant they become to chemical disinfection. This phenomenon is probably due to additional time to develop resistant biofilms on the interior of the FPA. To partially solve these problems we have developed additional disinfecting materials to use in conjunction with polyiodide containing resin beads. One of these materials carbon beads coated with 3-trimethoxy silylpropyl dimethyloctadecyl ammonium chloride (Dow-Corning 5700®), acts synergistically with polyiodide resin disinfectants. Carbon beads so treated are still able to remove aqueous iodine from the water stream while providing an additional level of chemical disinfection. This additional capability prevents contamination of the carbon beads with heterotrophic bacteria and insures that bacteria surviving iodine disinfection are efficiently devitalized.

Marchin, George L.

1998-01-01

77

Aqueous based Povidone-iodine related chemical burn under the tourniquet (a case report) and literature review.  

PubMed

Chemical burn under pneumatic tourniquet is an iatrogenic preventable injury and is rarely reported in the literature. The important mechanisms are maceration, irritation, and prolonged use of the tourniquet and pressure. This rare adverse complication occurred in a 35-year old man who underwent anterior cruciate ligament reconstruction of left knee. 5% aqueous based Povidone-Iodine was used as topical antiseptic and partial thickness burn occurred underneath the area of tourniquet application. Previous reports shows that chemical burns are more common in alcohol based Povidone-iodine than aqueous based. Chemical burn develops when Povidone- iodine does not adequately dry, pools beneath a dependent body part during surgery, or is placed under an occlusive device. To reduce the complications like chemical burn, awareness of the risk and the possible pathogenesis as well as the preventive measures is important in surgical practice. PMID:24396233

Supradeeptha, Challa; Shandilya, Sudhir Mahadev; Naresh, Alavalapati; Satyaprasad, Jonnalagadda

2013-01-01

78

Aqueous based Povidone-iodine related chemical burn under the tourniquet (a case report) and literature review  

PubMed Central

Chemical burn under pneumatic tourniquet is an iatrogenic preventable injury and is rarely reported in the literature. The important mechanisms are maceration, irritation, and prolonged use of the tourniquet and pressure. This rare adverse complication occurred in a 35-year old man who underwent anterior cruciate ligament reconstruction of left knee. 5% aqueous based Povidone-Iodine was used as topical antiseptic and partial thickness burn occurred underneath the area of tourniquet application. Previous reports shows that chemical burns are more common in alcohol based Povidone-iodine than aqueous based. Chemical burn develops when Povidone- iodine does not adequately dry, pools beneath a dependent body part during surgery, or is placed under an occlusive device. To reduce the complications like chemical burn, awareness of the risk and the possible pathogenesis as well as the preventive measures is important in surgical practice. PMID:24396233

Supradeeptha, Challa; Shandilya, Sudhir Mahadev; Naresh, Alavalapati; Satyaprasad, Jonnalagadda

2013-01-01

79

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

EPA Science Inventory

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

80

Chemical Processing in High-Pressure Aqueous Environments. 7. Process Development for Catalytic Gasification of Wet Biomass  

E-print Network

Chemical Processing in High-Pressure Aqueous Environments. 7. Process Development for Catalytic (high-pressure, high-temperature liquid water) has received relatively limited study.5 Some recent catalyst, gasification of wet biomass can be accomplished with high levels of carbon conversion to gas

81

pH effect on the morphology of ZnO nanostructures grown with aqueous chemical growth  

E-print Network

pH effect on the morphology of ZnO nanostructures grown with aqueous chemical growth D. Vernardou a Available online 1 April 2007 Abstract ZnO nanostructures were grown for various pH values on Corning 7059 hexahydrate) and C6H12N4 (HMTA; hexamethylenetetramine). It was indicated that the increasing of the pH

82

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

83

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

EPA Science Inventory

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

84

Optimum conditions for composites fiber coating by chemical vapor infiltration  

Microsoft Academic Search

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

Stewart K. Griffiths; R. H. Nilson

1998-01-01

85

Chemical flowsheet conditions for preparing urania spheres by internal gelation  

Microsoft Academic Search

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

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

1979-01-01

86

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

87

Amphiphilic lauryl ester derivatives from aromatic amino acids: significance of chemical architecture in aqueous aggregation properties.  

PubMed

Lauryl esters of L-tyrosine (LET) and L-phenylalanine (LEP) were, in a previous interface adsorption study, found to adopt very different interfacial conformations. The present study is an investigation of their aqueous aggregation properties with the goal of elucidating the effects of the presence in LET and absence in LEP of the phenolic OH group on their aqueous aggregate structures and micellar conformations of the surfactant monomers. The measured properties included aggregation numbers from time-resolved fluorescence quenching (TRFQ), interface hydration index and microviscosity by electron spin resonance (ESR), chemical shifts of (1)H resonance lines by NMR, and Krafft temperatures and enthalpies of structural transitions by differential scanning calorimetry (DSC). The TRFQ, ESR, and NMR experiments were conducted at various temperatures from 23 to 70 degrees C for various surfactant concentrations from 0.050 to 0.200 M. Markedly different temperature dependences of aggregation number and (1)H NMR chemical shifts are exhibited by LET and LEP micelles. LET and LEP form ionic micelles. The aggregation number of LEP decreases as is characteristic of ionic micelles, but that of LET increases slightly with temperature. The changes with temperature in the NMR chemical shifts and width of the resonance lines are significantly greater for the various LEP protons than for those of LET. The differences in these properties and other fluorescence decay characteristics of fluorophores incorporated into the micelles could be attributed to the difference in the micellar conformations of LET and LEP which are postulated to be similar to that at oil-water interfaces. The phenolic group is hypothesized to be in the micelle-water interface as part of the headgroup in LET micelles, and its location does not change with temperature. On the other hand, in LEP micelles, the phenyl ring is folded into the core overlapping with the flexible hydrophobic chains. The resulting closer proximity between the phenyl ring and the flexible hydrocarbon chain causes interdependence of the phenyl ring and chain proton resonances, leading to the observed temperature dependence of the chemical shifts in LEP. The TRFQ and ESR data are combined together in a molecular space-filling model, referred to as the polar shell model, to derive the geometrical properties of the micelle. The DSC scans in the temperature range 10-55 degrees C showed the presence of distinctly different endotherms for LET and LEP. The Krafft temperatures, K(T), and the enthalpies were determined. The higher K(T) and broader peak of the DSC endotherm of LET as compared to LEP are attributed to the stabilization of fiberlike structures below the Krafft temperature due to its chirality and the hydrogen bonding capability of the phenolic OH and also to the ion-dipole interactions. Thus, all of the observed differences between LET and LEP could be attributed to the difference in their chemical architecture. PMID:19778004

Vijay, R; Singh, Jasmeet; Baskar, Geetha; Ranganathan, Radha

2009-10-22

88

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

PubMed

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

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

2014-06-30

89

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

USGS Publications Warehouse

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

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

2005-01-01

90

Chemical behavior of phthalates under abiotic conditions in landfills.  

PubMed

The phthalates comprise a family of phthalic acid esters that are used primarily as plasticizers in polymeric materials to impart flexibility during the manufacturing process and to the end product. It is estimated that the annual worldwide production of phthalate esters exceeds five million tons. Plasticizers are one of the most prominent classes of chemicals, but unfortunately, they possess endocrine-disrupting chemical properties. As endocrine-disrupting chemicals, plasticizers have produced adverse developmental and reproductive effects in mammalian animal models.Phthalates are easily transported into the environment during manufacture, disposal,and leaching from plastic materials, because they are not covalently bound to the plastics of which they are a component. Because of their fugitive nature and widespread use, the phthalates are commonly detected in air, water, sediment/soil, and biota, including human tissue. Large amounts of phthalic acid esters are often leached from the plastics that are dumped at municipal landfills.Phthalate esters undergo chemical changes when released into the environment.The primary processes by which they are transformed include hydrolysis, photolysis,and biodegradation. It is noteworthy that all of these degradation processes are greatly influenced by the local physical and chemical conditions. Hence, in the present review, we have sought to ascertain from the literature how the phthalate esters undergo transformation when they are released into lower landfill layers.Within the upper landfill layers, biodegradation prevails as the major degradation mechanism by which the phthalates are dissipated. Generally, biodegradation pathways for the phthalates consist of primary biodegradation from phthalate diesters to phthalate monoesters, then to phthalic acid, and ultimately biodegradation of phthalic acid to form C02 and/or CH4• We have noted that the phthalate esters are also degraded through abiotic means,which proceeds via both hydrolysis and photolysis. Photodegradation generally involves reactions of the phthalates in the atmosphere with hydroxyl radicals. The hydrolysis of phthalate diesters produces the corresponding monoesters, which are subsequently converted to phthalic acid. Phthalic acid has been observed to accumulate within landfill zones where phthalate contamination exists.Hydrolysis is usually not an important fate process for phthalate esters in the environment, including in upper landfill layers. However, the conditions prevalent at lower landfill layers are generally suitable for phthalate transformation via hydrolysis.The conditions in this zone include high temperatures and pressures, presence of chemical catalysts, as well as wide pH fluctuations. Such conditions foster hydrolysis that may be either acid- or base-catalyzed by metal ions, anions, or organic materials catalysts. In addition, research indicates that the propensity for ongoing hydrolysis increases as landfill depth increases.We can be emphatic in asserting that hydrolysis of phthalate esters in lower landfill layers is the dominant process for transforming these esters; in contrast,biodegradation is the predominant process in the upper landfill layers.We recommend that future research be performed to expand the understanding of what influence each reaction condition (high temperature, presence of chemical catalysts, etc.) has on the rate of chemical transformation of the phthalates in lower landfill zones. We also recommend that the combined effects of all conditions on the rate of chemical transformation at lower landfill layers be assessed for the phthalates.Such research could be achieved under simulated conditions. PMID:23232918

Huang, Jingyu; Nkrumah, Philip N; Li, Yi; Appiah-Sefah, Gloria

2013-01-01

91

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

92

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

2008-11-18

93

Electrostatic Deposition of Aerosol Particles Generated from an Aqueous Nanopowder Suspension on a Chemically Treated Substrate  

NASA Astrophysics Data System (ADS)

The state of electrostatically deposited aerosol particles from a suspension that contains TiO2 particles on the surface of a solid substrate using electrospray was demonstrated. The particles were initially electrosterically stable in 7.5 wt % aqueous solution with a mean particle size of 50 nm. During deposition, the particles were pumped with different flow rates between 0.6 and 1.2 mL/h through a stainless steel capillary tube of 0.1 mm inner diameter. The particles were emitted at the tip of the capillary tube as an electrified liquid cone before forming into a highly charged droplet. For comparison, two types of substrate surfaces with and without chemical treatment were prepared. Atomic force microscopy (AFM) scanning and contact angle measurements showed that surface treatment increased the substrate roughness and created a hydrophilic surface. Raman analysis also showed the existence of an oxide layer and a P-O network on the treated substrate. Field emission scanning electron microscopy FE-SEM image analysis showed that more TiO2 particles were deposited on the treated substrate than on the untreated substrate.

M. Nazli Naim,; Noor Fitrah Abu Bakar,; Motoyuki Iijima,; Hidehiro Kamiya,; I. Wuled Lenggoro,

2010-06-01

94

Hierarchically organized silica-titania monoliths prepared under purely aqueous conditions.  

PubMed

Hierarchically organized silica-titania monoliths were synthesized under purely aqueous conditions by applying a new ethylene glycol-modified single-source precursor, such as 3-[3-{tris(2-hydroxyethoxy)silyl}propyl]acetylacetone coordinated to a titanium center. The influence of the silicon- and titanium-containing single-source precursor, the novel glycolated organofunctional silane, and the addition of tetrakis(2-hydroxyethyl)orthosilicate on the formation of the final porous network was investigated by SEM, TEM, nitrogen sorption, and SAXS/WAXS. In situ SAXS measurements were performed to obtain insight into the development of the mesoporous network during sol-gel transition. IR-ATR, UV/Vis, XPS, and XAFS measurements showed that up to a Si/Ti ratio of 35:1, well-dispersed titanium centers in a macro-/mesoporous SiO2 network with a specific surface area of up to 582?m(2) ?g(-1) were obtained. An increase in Ti content resulted in a decrease in specific surface area and a loss of the cellular character of the macroporous network. With a 1:1 Si/Ti ratio, silica-titania powders with circa 100?m(2) ?g(-1) and anatase domains within the SiO2 matrix were obtained. PMID:25367386

Flaig, Sylvia; Akbarzadeh, Johanna; Dolcet, Paolo; Gross, Silvia; Peterlik, Herwig; Hüsing, Nicola

2014-12-22

95

Diverse Aqueous Conditions on Mars from New Orbital Detections of Carbonate and Sulfate  

NASA Astrophysics Data System (ADS)

Diverse aqueous environments on ancient Mars have been a key inference from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on NASA's Mars Reconnaissance Orbiter, which has identified many alteration minerals in a range of settings [e.g., 1-4]. Here we report two new minerals detected using CRISM. In the southern highlands northwest of the Hellas basin, a mid-sized crater exposes carbonate in its central uplift. Spectral absorptions at 1, 2.33, and 2.53 microns are most consistent with Fe-carbonate, distinct from the Mg-carbonates identified from orbit by [5]. Fe-carbonate is associated with Mg-phyllosilicate in fractured materials formerly buried kilometers beneath the surface, and--like the Mg/Fe-carbonate found by the Spirit rover [6]--suggests a reducing, neutral-to-alkaline alteration environment. One of the largest phyllosilicate exposures on Mars occurs in the Mawrth Vallis region [e.g., 7]. We identify bassanite (Ca-sulfate hemihydrate) in layers underlying the phyllosilicate-bearing beds [8], a stratigraphy distinct from that predicted by global models of martian aqueous history [9]. Bassanite could have formed via acid-sulfate alteration of Ca-carbonate, through dehydration of gypsum, or under hydrothermal conditions [10]. These detections expand the known mineralogic diversity of Mars and the range of environments to explore for past habitability. [1] Mustard, J. F. et al. (2008) Nature 454, 305-309. [2] Murchie, S. L. et al. (2009) J. Geophys. Res. 114, E00D06. [3] Ehlmann, B. L. et al. (2009) J. Geophys. Res. 114, E00D08. [4] Wray, J. J. et al. (2009) Geology 37, 1043-1046. [5] Ehlmann, B. L. et al. (2008) Science 322, 1828-1832. [6] Morris, R. V. et al. Science, in press, doi:10.1126/science.1189667. [7] Poulet, F. et al. (2005) Nature 438, 623-627. [8] Wray, J. J. et al. Icarus, in press, doi:10.1016/j.icarus.2010.06.001. [9] Bibring, J.-P. et al. (2006) Science 312, 400-404. [10] Vaniman, D. T. et al. (2009) LPSC 40, 1654.

Wray, James J.; Squyres, S. W.

2010-10-01

96

Fate of hydraulic fracturing chemicals under down-hole conditions  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

97

Chemically induced compaction bands: Triggering conditions and band thickness  

NASA Astrophysics Data System (ADS)

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

Stefanou, Ioannis; Sulem, Jean

2014-02-01

98

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

PubMed

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

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

2014-08-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

100

Induced Sporicidal Activity of Chlorhexidine against Clostridium difficile Spores under Altered Physical and Chemical Conditions  

PubMed Central

Background Chlorhexidine is a broad-spectrum antimicrobial commonly used to disinfect the skin of patients to reduce the risk of healthcare-associated infections. Because chlorhexidine is not sporicidal, it is not anticipated that it would have an impact on skin contamination with Clostridium difficile, the most important cause of healthcare-associated diarrhea. However, although chlorhexidine is not sporicidal as it is used in healthcare settings, it has been reported to kill spores of Bacillus species under altered physical and chemical conditions that disrupt the spore’s protective barriers (e.g., heat, ultrasonication, alcohol, or elevated pH). Here, we tested the hypothesis that similarly altered physical and chemical conditions result in enhanced sporicidal activity of chlorhexidine against C. difficile spores. Principal Findings C. difficile spores became susceptible to heat killing at 80°C within 15 minutes in the presence of chlorhexidine, as opposed to spores suspended in water which remained viable. The extent to which the spores were reduced was directly proportional to the concentration of chlorhexidine in solution, with no viable spores recovered after 15 minutes of incubation in 0.04%–0.0004% w/v chlorhexidine solutions at 80°C. Reduction of spores exposed to 4% w/v chlorhexidine solutions at moderate temperatures (37°C and 55°C) was enhanced by the presence of 70% ethanol. However, complete elimination of spores was not achieved until 3 hours of incubation at 55°C. Elevating the pH to ?9.5 significantly enhanced the killing of spores in either aqueous or alcoholic chlorhexidine solutions. Conclusions Physical and chemical conditions that alter the protective barriers of C. difficile spores convey sporicidal activity to chlorhexidine. Further studies are necessary to identify additional agents that may allow chlorhexidine to reach its target within the spore. PMID:25861057

Nerandzic, Michelle M.; Donskey, Curtis J.

2015-01-01

101

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

102

Effect of hydrophobic modification on rheological and swelling features during chemical gelation of aqueous polysaccharides.  

PubMed

Rheological characteristics during chemical gelation with the cross-linker ethylene glycol diglycidyl ether (EGDE) of semidilute aqueous solutions of hydroxyethylcellulose (HEC) and of two hydrophobically modified analogues (HM-1-HEC and HM-2-HEC) are reported. In addition, rheological features of gelling samples (dextran and its hydrophobically modified analogue (HM-dextran)) of a different structure have been examined. Some swelling experiments on these gels in the postgel region are also reported. The gelation time of the hydroxyethylcellulose systems decreased with increasing cross-linker concentration, and incorporation of hydrophobic units of HEC resulted in a slower gelation. The time of gelation for the dextran system was only slightly affected by the incorporation of hydrophobic groups (HM-dextran). At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional to omegan') and loss modulus (G'' proportional to omegan'') was observed for all gelling systems with n' = n'' = n. The attachment of hydrophobic moieties on the dextran chains had virtually no impact on the value of n (n = 0.77), and the percolation model describes the incipient dextran gels. By increasing the number of hydrophobic groups of the HEC polymer, the value of n for the corresponding incipient gel drops significantly, and the value of the gel strength parameter increases strongly. Incorporation of hydrophobic units in the HEC chains promotes the formation of stronger incipient gels because of the contribution from the hydrophobic association effect. The frequency dependence of the complex viscosity reveals that all the investigated gels become more solidlike in the postgel domain. Far into the postgel region, the hydrophobicity of HEC plays a minor role for the strength of the gel network, whereas the values of the complex viscosity are significantly higher for HM-dextran than for the corresponding dextran gel. The swelling experiments on HEC, HM-1-HEC, and HM-2-HEC systems disclose that the degree of swelling of the postgels in water is quite different, depending on the relative distance from the gel point at which the cross-linker reaction is quenched. At a given distance from the gel point, the swelling of the HEC gel is less pronounced than for the corresponding hydrophobically modified samples. At this stage, the swelling of the HM-dextran gel is stronger than for the dextran gel. PMID:17291098

Silioc, Christelle; Maleki, Atoosa; Zhu, Kaizheng; Kjøniksen, Anna-Lena; Nyström, Bo

2007-02-01

103

Adsorption of anionic dyes from aqueous solutions using chemically modified straw.  

PubMed

The effective disposal of redundant straw is a significant work for environmental protection and full utilization of resource. In this work, the wheat straw has been modified by etherification to prepare a kind of quaternary ammonium straw adsorbents. The adsorption behaviors of the modified straw for methyl orange (MO) and acid green 25(AG25) were studied in both batch and column systems. The adsorption capacity of the straw for both dyes improved evidently after modification. The maximal MO and AG25 uptakes were more than 300 and 950 mg g(-1), respectively. Furthermore, the adsorption equilibrium, kinetics and column studies all indicated that the adsorption behavior was a monolayer chemical adsorption with an ion-exchange process. In addition, after adsorption of anionic dyes, the used adsorbents were successfully applied to adsorb a cationic dye directly at suitable conditions in the secondary adsorption. This was due to the altered surface structures of the used adsorbents. PMID:22609712

Zhang, Wenxuan; Li, Haijiang; Kan, Xiaowei; Dong, Lei; Yan, Han; Jiang, Ziwen; Yang, Hu; Li, Aimin; Cheng, Rongshi

2012-08-01

104

Mass spectrometric elucidation of triacylglycerol content of Brevoortia tyrannus (menhaden) oil using non-aqueous reversed-phase liquid chromatography under ultra high pressure conditions.  

PubMed

A non-aqueous reversed phase high performance liquid chromatography method was developed, and optimized for triacylglycerol analysis in a Brevoortia tyrannus (menhaden) oil sample. Four columns were serially coupled to tackle such a task, for a total length of 60 cm of shell-packed stationary phase, and operated under ultra high pressure conditions. As detection, positive-ion atmospheric pressure chemical ionization mass spectrometry was used to attain identification of the analyzed sample components. A number of 137 triacylglycerols containing up to 19 fatty acids, with 14-22 carbon atom alkyl chain length and 0-6 double bonds, were positively identified in the complex lipidic sample. This is the first work that reports an extensive characterization of the triacylglycerol fraction of menhaden oil. PMID:22503927

Dugo, Paola; Beccaria, Marco; Fawzy, Nermeen; Donato, Paola; Cacciola, Francesco; Mondello, Luigi

2012-10-12

105

Epoxidized natural rubber toughened aqueous resole type liquefied EFB resin: Physical and chemical characterization  

NASA Astrophysics Data System (ADS)

A preliminary study on the reaction between aqueous resole type resinified liquefied palm oil empty fruit bunches fibres (RLEFB) with epoxidized natural rubber (ENR). Liquefaction of empty fruit bunches (EFB) is carried out at different ratio of phenol to EFB (P:EFB). Resole type phenolic resin is prepared using sodium hydroxide (NaOH) as the catalyst with the ratio of liquefied EFB (LEFB) to formaldehyde (LEFB:F) of 1:1.8. 50% epoxidation of epoxidized natural rubber (ENR-50) is used to react with resole resin by mixing with ENR with aqueous resole resin. The cured resin is characterized with FT-IR and SEM. Aqueous system have been found to be unsuitable medium in the reaction between resin and ENR. This system produced a highly porous product when RLEFB/ENR resin is cured.

Amran, Umar Adli; Zakaria, Sarani; Chia, Chin Hua

2013-11-01

106

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

USGS Publications Warehouse

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

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

1991-01-01

107

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

DOEpatents

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

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

1994-01-01

108

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

DOEpatents

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

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

1994-11-22

109

Trimming of aqueous chemically grown ZnO nanorods into ZnO nanotubes and their comparative optical properties  

NASA Astrophysics Data System (ADS)

Highly oriented ZnO nanotubes were fabricated on a silicon substrate by aqueous chemical growth at low temperature (<100 °C) by trimming of ZnO nanorods. The yield of nanotubes in the sample was 100%. Photoluminescence spectroscopy of the nanotubes reveals an enhanced and broadened ultraviolet (UV) emission peak, compared with the initial nanorods. This effect is attributed to whispering gallery mode resonance. In addition, a redshift of the UV emission peak is also observed. Enhancement in the deep defect band emission in the nanotubes compared to nanorods was also manifested as a result of the increased surface area.

Israr, M. Q.; Sadaf, J. R.; Yang, L. L.; Nur, O.; Willander, M.; Palisaitis, J.; Persson, P. O. A.?.

2009-08-01

110

Kinetics of growth and chemical composition of Fusarium moniliforme cultivated on carob aqueous extract for microbial protein production  

Microsoft Academic Search

The kinetics of growth and the chemical composition ofFusarium moniliforme cultivated on aqueous carob pod extract were investigated. The extract was adjusted to provide 0.5, 1.0, 2.0 and 4.0% carob sugars supplemented with inorganic salts at the ratio: carob sugar: NH4H2PO4: MgSO4.7H2O=1:0.6:0.012. The extract contained 16 mg tannic acid (Folin-Dennis) per g of carob sugar.

B. J. Macris; R. Kokke

1977-01-01

111

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...

112

Screening of carob bean yeasts. Chemical composition of Schizosaccharomyces versatilis grown on aqueous carob extract  

Microsoft Academic Search

Summary An improved extraction procedure for soluble sugars and tannins from carob bean is described. The yeast flora of the carob is rich, withSaccharomyces predominant; an isolate ofSchizosaccharomyces versatilis cultured in the aqueous extract utilizes tannins as well as sugars to give a high biomass and protein yield of good quality.

S. G. Marakis; A. D. Karagouni

1985-01-01

113

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

2013-03-21

114

Control of Convective Dissolution by Chemical Reactions: General Classification and Application to CO2 Dissolution in Reactive Aqueous Solutions  

NASA Astrophysics Data System (ADS)

In partially miscible two-layer systems within a gravity field, buoyancy-driven convective motions can appear when one phase dissolves with a finite solubility into the other one. We investigate the influence of chemical reactions on such convective dissolution by a linear stability analysis of a reaction-diffusion-convection model. We show theoretically that a chemical reaction can either enhance or decrease the onset time of the convection, depending on the type of density profile building up in time in the reactive solution. We classify the stabilizing and destabilizing scenarios in a parameter space spanned by the solutal Rayleigh numbers. As an example, we experimentally demonstrate the possibility to enhance the convective dissolution of gaseous CO2 in aqueous solutions by a classical acid-base reaction.

Loodts, V.; Thomas, C.; Rongy, L.; De Wit, A.

2014-09-01

115

Control of convective dissolution by chemical reactions: general classification and application to CO(2) dissolution in reactive aqueous solutions.  

PubMed

In partially miscible two-layer systems within a gravity field, buoyancy-driven convective motions can appear when one phase dissolves with a finite solubility into the other one. We investigate the influence of chemical reactions on such convective dissolution by a linear stability analysis of a reaction-diffusion-convection model. We show theoretically that a chemical reaction can either enhance or decrease the onset time of the convection, depending on the type of density profile building up in time in the reactive solution. We classify the stabilizing and destabilizing scenarios in a parameter space spanned by the solutal Rayleigh numbers. As an example, we experimentally demonstrate the possibility to enhance the convective dissolution of gaseous CO_{2} in aqueous solutions by a classical acid-base reaction. PMID:25259984

Loodts, V; Thomas, C; Rongy, L; De Wit, A

2014-09-12

116

SONOCHEMICAL DECHLORINATION OF HAZARDOUS WASTES IN AQUEOUS SYSTEMS. (R825513C004)  

EPA Science Inventory

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 chemic...

117

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

118

Transformations of biomass-derived platform molecules: from high added-value chemicals to fuels via aqueous-phase processing.  

PubMed

Global warming issues and the medium-term depletion of fossil fuel reserves are stimulating researchers around the world to find alternative sources of energy and organic carbon. Biomass is considered by experts the only sustainable source of energy and organic carbon for our industrial society, and it has the potential to displace petroleum in the production of chemicals and liquid transportation fuels. However, the transition from a petroleum-based economy to one based on biomass requires new strategies since the petrochemical technologies, well-developed over the last century, are not valid to process the biomass-derived compounds. Unlike petroleum feedstocks, biomass derived platform molecules possess a high oxygen content that gives them low volatility, high solubility in water, high reactivity and low thermal stability, properties that favour the processing of these resources by catalytic aqueous-phase technologies at moderate temperatures. This tutorial review is aimed at providing a general overview of processes, technologies and challenges that lie ahead for a range of different aqueous-phase transformations of some of the key biomass-derived platform molecules into liquid fuels for the transportation sector and related high added value chemicals. PMID:21713268

Serrano-Ruiz, Juan Carlos; Luque, Rafael; Sepúlveda-Escribano, Antonio

2011-11-01

119

Improved removal of malachite green from aqueous solution using chemically modified cellulose by anhydride.  

PubMed

Cellulose modified with maleic (M) and phthalic (P) anhydride, to be named CMA and CPA, were tested as feasible adsorbents for the removal of malachite green from aqueous solution. At the same time, the uptake ability of natural cellulose was also studied for comparison. The structure of material was characterized by FT-IR and XRD. The effects of solution pH, initial dye concentration, contact time and temperature were investigated in detail by batch adsorption experiments. The kinetic and isotherm studies suggested that the adsorption followed the pseudo-second-order model and Langmuir isotherm. The maximum adsorption capacity on CMA and CPA were 370mgg(-1) and 111mgg(-1), respectively. Furthermore, the thermodynamics studies indicated the spontaneous nature of adsorption of malachite green on adsorbents. All the studied results showed that the modified cellulose could be used as effective adsorption material for the removal of malachite green from aqueous solutions. PMID:25542168

Zhou, Yanmei; Min, Yinghao; Qiao, Han; Huang, Qi; Wang, Enze; Ma, Tongsen

2015-03-01

120

Chemical passivation of InSb (100) substrates in aqueous solutions of sodium sulfide  

SciTech Connect

The elemental composition and electronic structure of both native-oxide-covered InSb (100) substrates and substrates treated in aqueous solutions of sodium sulfide are analyzed by X-ray photoelectron spectroscopy. It is found that, as a result of treatment in a 1 M aqueous solution of Na{sub 2}S and subsequent annealing in vacuum at 150 Degree-Sign C, the surface layer consisting of complex antimony and indium oxides of nonstoichiometric composition is removed completely with the formation of a continuous layer of chemisorbed sulfur atoms coherently bound to indium atoms. According to atomic-force microscopy data, no etching of the host substrate material occurs during sulfide passivation. A shift (by 0.37 eV) of the In-Sb bulk photoemission towards higher binding energies is found, which indicates that the surface Fermi level shifts deeper into the conduction band.

Lvova, T. V., E-mail: tatyana.lvova.12@mail.ru; Dunaevskii, M. S.; Lebedev, M. V. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Shakhmin, A. L. [St. Petersburg State Polytechnical University (Russian Federation); Sedova, I. V.; Ivanov, S. V. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

2013-05-15

121

Effect of molecular weight on radiation chemical degradation yield of chain scission of ?-irradiated chitosan in solid state and in aqueous solution  

NASA Astrophysics Data System (ADS)

Chitosan A1, A2 and A3 with molecular weight of 471, 207 and 100 kDa respectively, produced from squid pen chitin was degraded by gamma rays in the solid state and in aqueous solution with various doses in air at ambient temperature. Effect of molecular weight on radiation chemical degradation yield of chain scission and degradation rate constants of ?-irradiated chitosan in solid state and in aqueous solution was investigated. The radiation chemical degradation yield G(s) and degradation rate values were calculated. The molecular weight changes were monitored by capillary viscometry method and the chemical structure changes were followed by UV analysis. The results showed that, the degradation of chitosan was faster in solution, than in solid state. The values of G(s) in solid state and in aqueous solution were respectively 1.1×10-8 mol/J and 0.074×10-7 mol/J for A1, 4.42×10-8 mol/J and 0.28×10-7 mol/J for A2 and 6.08×10-8 mol/J and 0.38×10-7 mol/J for A3. Degradation rate constants values ranged from 0.41×10-5 to 2.1×10-5 kGy-1 in solid state, whereas in solution they ranged from 13×10-5 to 68×10-5 kGy-1. The chitosan A3 was more sensitive to radiolysis than A1 and A2. The chain scission yield, G(s) and degradation rate constants seems to be greatly influenced by the initial molecular weight of the chitosan. Structural changes in irradiated chitosan are revealed by the apparition of absorption peaks at 261 and 295 nm, which could be attributed to the formation of carbonyl groups. In both conditions the peak intensity was higher in chitosan A3 than in A1 and A2, the oxidative products decreased with increasing molecular weight of chitosan.

Tahtat, Djamel; Mahlous, Mohamed; Benamer, Samah; Nacer Khodja, Assia; Larbi Youcef, Souad

2012-06-01

122

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 ...

123

Chemical characterization of the aqueous algistatic fraction of barley straw ( Hordeum vulgare ) inhibiting Microcystis aeruginosa  

Microsoft Academic Search

The algistatic properties of aqueous barley straw (Hordeum vulgare) extracts have been observed in laboratory studies and in situ. This reported algistatic property has been used by farmers\\u000a and horticulturists to control algal blooms in various systems and has become standard practice in some areas. However, both\\u000a inhibition and stimulation of algal growth in freshwater and marine species have been

Timothy J. Waybright; Daniel E. Terlizzi; M. Drew Ferrier

2009-01-01

124

Effect of Hydrolysis Conditions on the Direct Formation of Nanoparticles of Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions  

Microsoft Academic Search

The effect of the cation concentration, hydrolysis temperature, and composition in the CeO2–ZrO2 system on the direct precipitation of ceria–zirconia solid solutions and the structure of the precipitates from acidic aqueous solutions of (NH4)2Ce(NO3)6 and ZrOCl2 by hydrolysis under hydrothermal conditions were investigated. Nanometer-sized (8–10 nm) ceria–zirconia solid solution particles in a composition range of 0 to 60 mol% ZrO2

Masanori Hirano; Kaname Hirai

2003-01-01

125

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

NASA Technical Reports Server (NTRS)

Carbonaceous chondrites are primitive meteorites that are valuable because they preserve evidence of processes that occurred in the solar nebula and on asteroidal parent bodies. Among the carbonaceous chondrite groups, the CR group appears to contain a particularly pristine record of early solar system processes. Distinguishing characteristics of CR2 chondrites include a high abundance of chondrules (50-60 vol.%) and Fe, Ni metal (5-8 vol. %). These meteorites preserve evidence for varying degrees of aqueous alteration, manifested by progressive replacement of chondrule mesostasis by phyllosilicates. Recent studies have suggested that even in weakly altered chondrites, mass transfer occurred between chondrules and fine-grained matrices, implying that aqueous alteration must have followed lithification of the final meteorite parent body. Although petrographic characteristics of alteration in CR chondrites have been documented, mechanisms of alteration are still only poorly understood. For example, the relative rates and scales of elemental mobility as well as the sources and sinks for key elements are currently not constrained. An improved knowledge of these issues will contribute to an increased understanding of aqueous alteration reactions on meteorite parent bodies. This study expands on research conducted on Type IIA chondrules and chondrule fragments from two CR2 chondrites, EET 87770 and EET 92105. These chondrites have been weakly altered; chondrule mesostases show incipient alteration primarily where they are in direct contact with fine-grained matrices.

Burger, Paul V.; Brearley, Adrian J.

2005-01-01

126

The Chemical and Ionization Conditions in Weak Mg II Absorbers  

E-print Network

We present an analysis of the chemical and ionization conditions in a sample of 100 weak Mg II absorbers identified in the VLT/UVES archive of quasar spectra. Using a host of low ionization lines associated with each absorber in this sample, and on the basis of ionization models, we infer that the metallicity in a significant fraction of weak Mg II clouds is constrained to values of solar or higher, if they are sub-Lyman limit systems. Based on the observed constraints, we present a physical picture in which weak Mg II absorbers are predominantly tracing two different astrophysical processes/structures. A significant population of weak Mg II clouds, those in which N(Fe II) is much less than N(Mg II), identified at both low (z ~ 1) and high (z ~ 2) redshift, are potentially tracing gas in the extended halos of galaxies, analogous to the Galactic high velocity clouds. These absorbers might correspond to alpha-enhanced interstellar gas expelled from star-forming galaxies, in correlated supernova events. On the other hand, N(FeII) approximately equal to N(Mg II) clouds, which are prevalent only at lower redshifts (z < 1.5), must be tracing Type Ia enriched gas in small, high metallicity pockets in dwarf galaxies, tidal debris, or other intergalactic structures.

Anand Narayanan; Jane C. Charlton; Toru Misawa; Rebecca E. Green; Tae-Sun Kim

2008-08-19

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

2009-09-01

129

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

130

Molecular engineering of a cobalt-based electrocatalytic nanomaterial for H? evolution under fully aqueous conditions.  

PubMed

The viability of a hydrogen economy depends on the design of efficient catalytic systems based on earth-abundant elements. Innovative breakthroughs for hydrogen evolution based on molecular tetraimine cobalt compounds have appeared in the past decade. Here we show that such a diimine-dioxime cobalt catalyst can be grafted to the surface of a carbon nanotube electrode. The resulting electrocatalytic cathode material mediates H(2) generation (55,000 turnovers in seven hours) from fully aqueous solutions at low-to-medium overpotentials. This material is remarkably stable, which allows extensive cycling with preservation of the grafted molecular complex, as shown by electrochemical studies, X-ray photoelectron spectroscopy and scanning electron microscopy. This clearly indicates that grafting provides an increased stability to these cobalt catalysts, and suggests the possible application of these materials in the development of technological devices. PMID:23247177

Andreiadis, Eugen S; Jacques, Pierre-André; Tran, Phong D; Leyris, Adeline; Chavarot-Kerlidou, Murielle; Jousselme, Bruno; Matheron, Muriel; Pécaut, Jacques; Palacin, Serge; Fontecave, Marc; Artero, Vincent

2013-01-01

131

The aqueous root extract of Aristolochia ringens (Vahl.) Aristolochiaceae inhibits chemically-induced inflammation in rodents.  

PubMed

The potential of the aqueous root extract of Aristolochia ringens (AR) (10-100 mg/kg p.o) to inhibit inflammation induced by phlogistics was evaluated using the carrageenan and egg albumin induced rat paw oedema, formaldehyde induced arthritic inflammation and xylene induced mouse ear oedema models. AR (10-50 mg/kg) dose-dependently decreased rat paw oedema in the carrageenan and egg albumin induced inflammation, producing comparable inhibition of 57.1% and 65.6% to the 57.9% and 63.9% of indomethacin and diclofenac (10 mg/kg p.o) respectively at 50 mg/kg. AR (10-50 mg/kg) also dose dependently inhibited formaldehyde-induced arthritic paw oedema over the 10 day observation period, with a greater inhibition of 50% at 50 mg/kg than the 40.8% inhibition by diclofenac (10 mg/kg i.p). AR (50 mg/kg) also produced greater inhibition of 84.78% than the 65.21% by dexamethasone (1 mg/kg) in xylene-induced ear oedema. Results show that the aqueous root extract of Aristolochia ringens possesses antiinflammatory activity. PMID:25362593

Ruth, Aigbe Flora; Olaide, Adeyemi Olufunmilayo; Oluwatoyin, Sofidiya Margaret

2014-11-01

132

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...

133

Chemical analysis and aqueous solution properties of Charged Amphiphilic Block Copolymers PBA-b-PAA synthesized by MADIX  

E-print Network

We have linked the structural and dynamic properties in aqueous solution of amphiphilic charged diblock copolymers poly(butyl acrylate)-b-poly(acrylic acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the physico-chemical characteristics of the samples. Despite product imperfections, the samples self-assemble in melt and aqueous solutions as predicted by monodisperse microphase separation theory. However, the PBA core are abnormally large; the swelling of PBA cores is not due to AA (the Flory parameter chiPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA homopolymers (content determined by Liquid Chromatography at the Point of Exclusion and Adsorption Transition LC-PEAT). Beside the dominant population of micelles detected by scattering experiments, capillary electrophoresis CE analysis permitted detection of two other populations, one of h-PAA, and the other of free PBA-b-PAA chains, that have very short PBA blocks and never self-assemble. Despite the presence of these free unimers, the self-assembly in solution was found out of equilibrium: the aggregation state is history dependant and no unimer exchange between micelles occurs over months (time-evolution SANS). The high PBA/water interfacial tension, measured at 20 mN/m, prohibits unimer exchange between micelles. PBA-b-PAA solution systems are neither at thermal equilibrium nor completely frozen systems: internal fractionation of individual aggregates can occur.

M. Jacquin; P. Muller; R. Talingting-Pabalan; H. Cottet; J. -F. Berret; T. Futterer; O. Theodoly

2007-08-27

134

Dissolution of barite for the analysis of strontium isotopes and other chemical and isotopic variations using aqueous sodium carbonate  

USGS Publications Warehouse

A simple procedure for preparing barite samples for chemical and isotopic analysis is described. Sulfate ion, in barite, in the presence of high concentrations of aqueous sodium carbonate, is replaced by carbonate. This replacement forms insoluble carbonates with the cations commonly in barite: Ba, Sr, Ca and Pb. Sulfate is released into the solution by the carbonate replacement and is separated by filtration. The aqueous sulfate can then be reprecipitated for analysis of the sulfur and oxygen isotopes. The cations in the carbonate phase can be dissolved by acidifying the solid residue. Sr can be separated from the solution for Sr isotope analysis by ion-exchange chromatography. The sodium carbonate used contains amounts of Sr which will affect almost all barite 87Sr 86Sr ratios by less than 0.00001 at 1.95?? of the mean. The procedure is preferred over other techniques used for preparing barite samples for the determination of 87Sr 86Sr ratios because it is simple, rapid and enables simultaneous determination of many compositional parameters on the same material. ?? 1985.

Breit, G.N.; Simmons, E.C.; Goldhaber, M.B.

1985-01-01

135

Nanofiltration and sensing of picomolar chemical residues in aqueous solution using an optical porous resonator in a microelectrofluidic channel.  

PubMed

For the first time the use of a porous microresonator placed in a microelectrofluidic system for integrated functions of nanofiltration and sensing of small biomolecules and chemical analytes in extremely dilute solution was proposed and investigated. As an example, aminoglycosides in drug residues in food and livestock products were considered as the trace chemical analyte. The filtration process of the charged analyte in aqueous solution driven by an applied electrical field and the accompanying optical whispering-gallery modes in the resonator are modeled. The dynamic process of adsorption and desorption of the analyte onto the porous matrix is studied. Deposition of the analyte inside the porous structure will alter the material refractive index of the resonator, and thus induce an optical resonance frequency shift. By measuring the optical frequency shift, the analyte concentration as well as the absorption/desorption process can be analyzed. Through an intensive numerical study, a correlation between the frequency shift and the analyte concentration and the applied electrical voltage gradient was obtained. This reveals a linear relationship between the resonance frequency shift and the analyte concentration. The applied electrical voltage substantially enhances the filtration capability and the magnitude of the optical frequency shift, pushing the porous resonator-based sensor to function at the extremely dilute picomolar concentration level for small bio/chemical molecules down to the sub-nanometer scale. Moreover, use of the second-order whispering-gallery mode is found to provide better sensitivity compared with the first-order mode. PMID:22248873

Huang, Lei; Guo, Zhixiong

2012-02-17

136

CH 4/NH 3/H 2O 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 CH 4 + NH 3 + H 2O 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

137

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

Microsoft Academic Search

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

B. Vestergård

1994-01-01

138

Passivation of Zn3P2 substrates by aqueous chemical etching and air Gregory M. Kimball, Jeffrey P. Bosco, Astrid M. Mller, Syed F. Tajdar, Bruce S. Brunschwig et al.  

E-print Network

Passivation of Zn3P2 substrates by aqueous chemical etching and air oxidation Gregory M. Kimball, Jeffrey P. Bosco, Astrid M. Müller, Syed F. Tajdar, Bruce S. Brunschwig et al. Citation: J. Appl. Phys://jap.aip.org/about/rights_and_permissions #12;Passivation of Zn3P2 substrates by aqueous chemical etching and air oxidation Gregory M. Kimball

Kimball, Gregory

139

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

SciTech Connect

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

FRYE JM; KUNKEL JM

2009-03-05

140

Quantum chemical analysis of the energy of proton transfer from phenol and chlorophenols to H2O in the gas phase and in aqueous solution  

Microsoft Academic Search

Proton transfer energies of phenol and 14 chlorophenols with H2O as a base are analyzed in the gas phase and in solution using quantum chemical methods at the semiempirical and ab initio level of computation. The effect of aqueous solution was accounted for by applying the density functional theory (DFT) implementation of the conductor-like screening model (COSMO) as well as

Gerrit Schüürmann

1998-01-01

141

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

EPA Science Inventory

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

142

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

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

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

PubMed Central

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. Infrared spectra of experimental forsterite show absorption bands at 3525 and 3572 cm?1 that are characteristic for hydroxyl point defects associated with trace Ti substitutions, and strongly suggest that the TiO2 content of the system can influence the chlorine and OH incorporation via the stabilization of Ti-clinohumite-like point defects. The water contents for coexisting forsterite and enstatite in some runs were determined using unpolarized IR spectra and calculated water partition coefficients DH2Ofo/en are between 0.01 and 0.5. PMID:25843971

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

2013-01-01

145

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

USGS Publications Warehouse

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 25??C to 660??C and pressures up to 800 MPa. These pressure-temperature (P-T) conditions are more than sufficient for carrying out experimental measurements that can provide data valuable in the interpretation of fluid inclusions in minerals found in ore-forming hydrothermal systems as well as other important lithospheric processes involving water. (C) 2000 Elsevier Science B.V. All rights reserved.

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

2000-01-01

146

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

EPA Science Inventory

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

147

"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...

148

Molecular dynamics simulations of a chemical reaction; conditions for local equilibrium in a temperature gradient  

E-print Network

Molecular dynamics simulations of a chemical reaction; conditions for local equilibrium as in local chemical equilibrium (DrG = 0) in the supercritical fluid, for temperature gradients up to 1012 K in the hot region. 1. Introduction A chemical reaction that occurs far from global equilibrium, has a rate

Kjelstrup, Signe

149

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. PMID:23841065

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

2013-01-01

150

Chemical Enrichment and Physical Conditions in IZw18*  

NASA Technical Reports Server (NTRS)

Low-metallicity star-forming dwarf galaxies are prime targets to understand the chemical enrichment of the interstellar medium. The H I region contains the bulk of the mass in blue compact dwarfs, and it provides important constraints on the dispersal and mixing of heavy elements released by successive star-formation episodes. The metallicity of the H I region is also a critical parameter to investigate the future star-formation history, as metals provide most of the gas cooling that will facilitate and sustain star formation. Aims. Our primary objective is to study the enrichment of the H I region and the interplay between star-formation history and metallicity evolution. Our secondary obje ctive is to constrain the spatial- and time-scales over which the HI and H II regions are enriched, and the mass range of stars responsible for the heavy element production. Finally, we aim to examine the gas heating and cooling mechanisms in the H I region. Methods. We observed the most metal-poor star-forming galaxy in the Local Universe, I Zw 18, with the Cosmic Origin Spectrograph onboard Hubble. The abundances in the neutral gas are derived from far-ultraviolet absorption-lines (H I, CIII, CIIi*, N I, OI,...) and are compared to the abundances in the H II region. Models are constructed to calculate the ionization structure and the thermal processes. We investigate the gas cooling in the HIi region through physical diagnostics drawn from the fine-structure level of C+. Results. We find that H I region abundances are lower by a factor of approx 2 as compared to the H II region. There is no differential depletion on dust between the H I and H II region. Using sulfur as a metallicity tracer, we calculate a metallicity of 1/46 Z(solar) (vs. 1/31 Z(solar) in the H II region). From the study of the C/O, [O/Fe], and N/O abundance ratios, we propose that C, N, O, and Fe are mainly produced in massive stars. We argue that the H I envelope may contain pockets of pristine gas with a metallicity essentially null. Finally, we derive the physical conditions in the H I region by investigating the C II* absorption line. The cooling rate derived from C II* is consistent with collisions with H(sup 0) atoms in the diffuse neutral gas. We calculate the star-formation rate from the CII* cooling rate assuming that photoelectric effect on dust is the dominant gas heating mechanism. Our determination is in good agreement with the values in the literature if we assume a low dust-to-gas ratio (approx 2000 times lower than the Milky Way value).

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

2013-01-01

151

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

152

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

153

The chemical stability of formulations of some hydrolyzable insecticides in aqueous mixtures with hydrolysis catalysts  

Microsoft Academic Search

The active ingredients in commercial formulations of malathion, oxamyl, carbaryl, diazinon, and chlorpyrifos diluted to “spray tank”; concentrations with buffered distilled or natural water of pH 4–9 were stable for at least 24 hr. Formulations of trichlorfon were not stable at pH 7 or above but disappearance rates were slower than for the pure chemical in homogeneous solution. Cupric ion

Ralph A. Chapman; Carol Harris

1984-01-01

154

Behaviour of Sb(V) in the presence of dissolved sulfide under controlled anoxic aqueous conditions  

E-print Network

: D. Rickard Keywords: Antimony Dissolved sulfide Metastibnite HG-AFS Antimony (Sb) exists in natural concentrations and conditions. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Until recently, antimony(V) is usually the predominant oxidation state of antimony in oxic waters likely present as Sb(OH)6 - at p

Belzile, Nelson

155

Behaviour of Sb(V) in the presence of dissolved sulfide under controlled anoxic aqueous conditions  

E-print Network

: Antimony Dissolved sulfide Metastibnite HG-AFS Antimony (Sb) exists in natural waters in two oxidation. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Until recently, antimony (Sb) had largely been oxidation state of antimony in oxic waters likely present as Sb(OH)6 - at pH conditions of natural systems

Belzile, Nelson

156

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...

157

Resistance to chemical disinfection under conditions of microgravity  

Microsoft Academic Search

In unit gravity, bacteria and disinfecting resin beads co-sediment to the septum in a fluid processing apparatus (FPA) resulting in effective chemical disinfection. In microgravity bacteria in suspension have access to a larger volume of the FPA because of a lack of sedimentation. Further, when disinfecting resin beads are added to the FPA they also remain in suspension reducing their

George L. Marchin

1998-01-01

158

CHEMICAL SPECIATION OF INORGANIC COMPOUNDS UNDER HYDROTHERMAL CONDITIONS  

EPA Science Inventory

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

159

EFFECT OF TEMPERATURE ON PAD CONDITIONING PROCESS DURING CHEMICAL-MECHANICAL PLANARIZATION  

Microsoft Academic Search

Pad conditioning process is one of the crucial process steps during chemical-mechanical planarization (CMP). Pad needs to be conditioned at regular time intervals to regenerate a rough surface in order to maintain consistent and optimum polishing process. Inconsistent pad conditioning directly affects the repeatability of the process outcome. Thus, it is essential to study the factors influencing the conditioning process.

S. Raghu Mudhivarthi; Norm Gitis; Suresh Kuiry; Michael Vinogradov; Ashok Kumar

160

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

161

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

162

Behaviour of Sb(V) in the presence of dissolved sulfide under controlled anoxic aqueous conditions  

Microsoft Academic Search

Antimony (Sb) exists in natural waters in two oxidation states, Sb(V) and Sb(III), with the reduced form generally leading to more toxic behaviour. Factors leading to the appearance of Sb(III) are therefore important from toxicity, bioavailability and ultimately water quality standpoints, particularly under reducing conditions found in eutrophic lakes and sediment porewaters. In this study, kinetics of the reduction of

Russell Polack; Yu-Wei Chen; Nelson Belzile

2009-01-01

163

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

USGS Publications Warehouse

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

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

1996-01-01

164

Inhibitory Effect of Berberis vulgaris Aqueous Extract on Acquisition and Reinstatement Effects of Morphine in Conditioned Place Preferences (CPP) in Mice  

PubMed Central

Background: It has been elucidated that Berberis vulgaris (barberry) can alleviate morphine withdrawal syndrome. Also it has been reported that aqueous extract of barberry possibly have inhibitory effect on NMDA receptors. Objectives: In this study, we decided to evaluate the effects of aqueous extract of B. vulgaris fruit on morphine tendency in mice using conditioned place preference (CPP) method. Materials and Methods: In experiment 1 (acquisition phase), mice underwent morphine-induced conditioned place preference (CPP) training with injections of morphine (40 mg/kg). In experiment 2 (extinction and reinstatement phases), mice underwent the same CPP training as in experiment 1 and subsequent extinction training on day 16th a reinstatement by CPP was done by injection of reminding 10 mg/kg morphine. Results: The administration of morphine (40 mg/kg for four days) produced place preference. In the first method, the aqueous extract of barberry (200 mg/kg) prevented morphine tendency to white cell in CPP method. In the second method, after inter-peritoneal injection of aqueous extracts of barberry at 100 and 200 mg/kg, the animals tendency toward the white cells of CPP chamber on the sixteenth day (after a reminder injection of morphine 10 mg/kg) was significantly reduced. Conclusions: These results show that aqueous extract of barberry can reduce the acquisition and reinstatement of morphine-induced conditioned place preference. PMID:25237645

Imenshahidi, Mohsen; Qaredashi, Reza; Hashemzaei, Mahmoud; Hosseinzadeh, Hossein

2014-01-01

165

Chemical Processing in High-Pressure Aqueous Environments. 8. Improved Catalysts for Hydrothermal Gasification.  

SciTech Connect

Improved catalyst formulations have been developed and tested for hydrothermal gasification of wet organics. A high-pressure (about 20 MPa) and high-temperature (about 350?C) liquid water processing environment was used to treat organic chemical model compounds. The organic feedstocks were converted primarily to methane and carbon dioxide in the presence of a heterogeneous catalyst. Test results with different catalyst formulations showed that catalyst composition could be tailored for the hydrothermal environment to effectively process wet wastes and wastewater and to recover useful fuel gas.

Elliott, Douglas C.; Hart, Todd R.; Neuenschwander, Gary G.

2006-04-26

166

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

167

Chemical reactions in viscous liquids under space conditions  

Microsoft Academic Search

A long-term human flight needs a large-size space ships with artificial self-regulating ecological life-support system. The best way for creation of large-size space ship is a synthesis of light construction on Earth orbit, that does not need a high energy transportation carriers from Earth surface. The construction can be created by the way of chemical polymerisation reaction under space environment.

A. Kondyurin; B. Lauke; E. Richter

2004-01-01

168

Transparent ZnO Films Deposited by Aqueous Solution Process Under Various pH Conditions  

NASA Astrophysics Data System (ADS)

ZnO films were deposited using a spin-spray method with the source solution containing zinc nitrate and an oxidizing solution containing trisodium citrate onto glass substrates under various pH conditions. A ZnO film with a columnar structure was obtained at pH higher than 7.0, while no ZnO film was formed at a mixed solution pH of 6.7. The transparent and conductive ZnO film obtained from a mixed solution with pH 10.7 exhibited the lowest resistivity of 9.9 × 10-3 ? cm with a high transmittance above 90%.

Hong, Jeong Soo; Wagata, Hajime; Ohashi, Naoki; Katsumata, Ken-ichi; Okada, Kiyoshi; Matsushita, Nobuhiro

2015-02-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2009-08-01

170

Mars aqueous chemistry experiment  

NASA Technical Reports Server (NTRS)

The Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. Progress for the first year MACE PIDDP is reported in two major areas of effort: (1) fluids handling concepts, definition, and breadboard fabrication and (2) aqueous chemistry ion sensing technology and test facility integration. A fluids handling breadboard was designed, fabricated, and tested at Mars ambient pressure. The breadboard allows fluid manipulation scenarios to be tested under the reduced pressure conditions expected in the Martian atmosphere in order to validate valve operations, orchestrate analysis sequences, investigate sealing integrity, and to demonstrate efficacy of the fluid handling concept. Additional fluid manipulation concepts have also been developed based on updated MESUR spacecraft definition. The Mars Aqueous Chemistry Experiment Ion Selective Electrode (ISE) facility was designed as a test bed to develop a multifunction interface for measurements of chemical ion concentrations in aqueous solution. The interface allows acquisition of real time data concerning the kinetics and heats of salt dissolution, and transient response to calibration and solubility events. An array of ion selective electrodes has been interfaced and preliminary calibration studies performed.

Clark, Benton C.; Mason, Larry W.

1993-01-01

171

Chemical processing in high-pressure aqueous environments. 2. Development of catalysts for gasification  

SciTech Connect

A liquid water processing environment was used at 20 MPa and 350 C to convert organic compounds to methane and carbon dioxide in the presence of catalysts. This paper describes the evaluation of various types of base and noble metal catalysts and numerous support compositions for the process. The feedstock used in these tests was a mixture of p-cresol and water. Nickel, ruthenium, and rhodium were identified as active metals for the reaction. Other metals from groups VIII, VIB, IB, and IIB were inactive or readily oxidized and lost activity. Stable supports in the processing environment included [alpha]-alumina and zirconia. Silica and titania did not react chemically, but the tablet forms lost their physical integrity. Alumina forms, other than [alpha]-alumina, reacted with water to form boehmite ([gamma]-AlOOH) with significant loss of surface area and physical strength.

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

1993-08-01

172

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

173

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

SciTech Connect

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

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

1985-10-01

174

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

175

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

176

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

177

A new method of reconstituting the P-T conditions of fluid circulation in an accretionary prism (Shimanto, Japan) from microthermometry of methane-bearing aqueous inclusions  

NASA Astrophysics Data System (ADS)

In paleo-accretionary prisms and the shallow metamorphic domains of orogens, circulating fluids trapped in inclusions are commonly composed of a mixture of salt water and methane, producing two types of fluid inclusions: methane-bearing aqueous and methane-rich gaseous fluid inclusions. In such geological settings, where multiple stages of deformation, veining and fluid influx are prevalent, textural relationships between aqueous and gaseous inclusions are often ambiguous, preventing the microthermometric determination of fluid trapping pressure and temperature conditions. To assess the P-T conditions of deep circulating fluids from the Hyuga unit of the Shimanto paleo-accretionary prism on Kyushu, Japan, we have developed a new computational code, applicable to the H2O-CH4-NaCl system, which allows the characterization of CH4-bearing aqueous inclusions using only the temperatures of their phase transitions estimated by microthermometry: Tmi, the melting temperature of ice; Thyd, the melting temperature of gas hydrate and Th,aq, homogenization temperature. This thermodynamic modeling calculates the bulk density and composition of aqueous inclusions, as well as their P-T isochoric paths in a P-T diagram with an estimated precision of approximatively 10%. We use this computational tool to reconstruct the entrapment P-T conditions of aqueous inclusions in the Hyuga unit, and we show that these aqueous inclusions cannot be cogenetic with methane gaseous inclusions present in the same rocks. As a result, we propose that pulses of a high-pressure, methane-rich fluid transiently percolated through a rock wetted by a lower-pressure aqueous fluid. By coupling microthermometric results with petrological data, we infer that the exhumation of the Hyuga unit from the peak metamorphic conditions was nearly isothermal and ended up under a very hot geothermal gradient. In subduction or collision zones, modeling aqueous fluid inclusions in the ternary H2O-CH4-NaCl system and not simply in the binary H2O-NaCl is necessary, as the addition of even a small amount of methane to the water raises significantly the isochores to higher pressures. Our new code provides therefore the possibility to estimate precisely the pressure conditions of fluids circulating at depth.

Raimbourg, Hugues; Thiéry, Régis; Vacelet, Maxime; Ramboz, Claire; Cluzel, Nicolas; Le Trong, Emmanuel; Yamaguchi, Asuka; Kimura, Gaku

2014-01-01

178

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

179

Chemically exfoliated MoS? nanosheets as an efficient catalyst for reduction reactions in the aqueous phase.  

PubMed

Chemically exfoliated MoS2 (ce-MoS2) nanosheets that incorporate a large fraction of metallic 1T phase have been recently shown to possess a high electrocatalytic activity in the hydrogen evolution reaction, but the potential of this two-dimensional material as a catalyst has otherwise remained mostly uncharted. Here, we demonstrate that ce-MoS2 nanosheets are efficient catalysts for a number of model reduction reactions (namely, those of 4-nitrophenol, 4-nitroaniline, methyl orange, and [Fe(CN)6](3-)) carried out in aqueous medium using NaBH4 as a reductant. The performance of the nanosheets in these reactions is found to be comparable to that of many noble metal-based catalysts. The possible reaction pathways involving ce-MoS2 as a catalyst are also discussed and investigated. Overall, the present results expand the scope of this two-dimensional material as a competitive, inexpensive, and earth-abundant catalyst. PMID:25405770

Guardia, Laura; Paredes, Juan I; Munuera, José M; Villar-Rodil, Silvia; Ayán-Varela, Miguel; Martínez-Alonso, Amelia; Tascón, Juan M D

2014-12-10

180

Uniting Cheminformatics and Chemical Theory To Predict the Intrinsic Aqueous Solubility of Crystalline Druglike Molecules  

PubMed Central

We present four models of solution free-energy prediction for druglike molecules utilizing cheminformatics descriptors and theoretically calculated thermodynamic values. We make predictions of solution free energy using physics-based theory alone and using machine learning/quantitative structure–property relationship (QSPR) models. We also develop machine learning models where the theoretical energies and cheminformatics descriptors are used as combined input. These models are used to predict solvation free energy. While direct theoretical calculation does not give accurate results in this approach, machine learning is able to give predictions with a root mean squared error (RMSE) of ?1.1 log S units in a 10-fold cross-validation for our Drug-Like-Solubility-100 (DLS-100) dataset of 100 druglike molecules. We find that a model built using energy terms from our theoretical methodology as descriptors is marginally less predictive than one built on Chemistry Development Kit (CDK) descriptors. Combining both sets of descriptors allows a further but very modest improvement in the predictions. However, in some cases, this is a statistically significant enhancement. These results suggest that there is little complementarity between the chemical information provided by these two sets of descriptors, despite their different sources and methods of calculation. Our machine learning models are also able to predict the well-known Solubility Challenge dataset with an RMSE value of 0.9–1.0 log S units. PMID:24564264

2014-01-01

181

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

182

Differing chemical weathering conditions in meltwater catchments of western Greenland  

NASA Astrophysics Data System (ADS)

Chemical weathering in the proglacial environment is limited by moisture availability rather than by temperature and proceeds at rates comparable to more temperate catchments of similar specific discharge. Moisture originates from two sources during the ablation season in proglacial environments: snow melt from non-glacierized catchments and directly from glacial melt. The magnitudes of these water sources create differences in stream size and ecology, which may result in different styles and rates of weathering due to differences in water rock interaction time and acid sources. We test this hypothesis through observations of specific conductance (SpC) and stable isotopes of water collected from streams in the Paakitsoq region of western Greenland in July 2011. In the Paakitsoq region, snow and glacier melt waters flow through distinct drainage basins with different types and amounts of vegetation. Basins that only receive water from snow melt have small clear streams that flow through vegetated marshlands. In contrast, basins where the greatest water flux is derived from glacial melt host larger turbid streams that drain across frontal moraines and continue along largely unvegetated flow paths. Snow and glacier end members can be separated by stable isotopic compositions (snow: ?D: -107.3 %; ?18O: -14.8 % and glacier: ?D: -229.8 %; ?18O: -29.7 %). Water isotopes from the two types of streams fall between the snow and glacier end member compositions, reflecting addition of snow melt to the turbid streams and isotopic fractionation of the snow as it melts. Isotopic compositions of water in the turbid streams lie along the global meteoric water line (GMWL), but isotopic compositions from the clear streams lie to the left of the GMWL and reflect preferential weathering in the more highly vegetated watersheds. The greatest amount of chemical weathering occurs in flat, marshy areas in the clear stream catchments, presumably as a result of decreased pH caused by plant metabolism and/or microbial reactions, lower specific discharge, and longer residence times. Higher chemical weathering rates in the clear streams are supported by field measurements of SpC that increase downstream from the snow source. SpC of turbid streams are lower than clear streams but increase downstream as they discharge to a single braided, turbid channel that flows ~20 km to the ocean. Future work on these samples will include analyses of major and trace elements, inorganic and organic carbon species, and Sr and Nd isotopes of water and compositions of rock, suspended and bedload sediments. These measurements will aid in understanding which phases contribute the most weathering products to the water and how these products interact with the local ecosystem, as well as quantify the delivery of weathering products to the ocean. Our results reflect the control of ecology on weathering in high latitude areas. This linkage of weathering to ecology suggests that weathering rates and magnitudes will vary with time through the ablation season depending on melt rate, residence time of water in the stream channels and ecosystems, and magnitude of primary productivity.

Deuerling, K. M.; Martin, J. B.; Gulley, J.

2011-12-01

183

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

Microsoft Academic Search

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

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

1998-01-01

184

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

185

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

PubMed

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

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

2013-11-01

186

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...

187

Polymerization of amino acids under high-pressure conditions: Implication to chemical evolution on the early Earth  

NASA Astrophysics Data System (ADS)

Prebiotic polymerization of amino acids is the most fundamental reaction to promote the chemical evolution for origin of life. Polymerization of amino acids is the dehydration reaction. This questions as to if submarine hydrothermal conditions, thus hydrated enironments, were appropreate for peptide formations. Our previous experiments implied that non-aqueous and high-pressure environments (more than 20 MPa) would be suitable for polymerization of amino acids (Ohara et al., 2006). This leads to the hypothesis that the first peptides may have formed in the Hadean oceanic crustal environments, where dehydration proceeded with availability of appropriate temperatures and pressures. In the present study, experiments simulating the crustal conditions were performed with various pressures (1-175 MPa) and temperatures (100- 200 C degree) using autoclaves. Purified powders (100 mg) of alanine, glycine, valine and aspartic acid were used in the experiments without mixing water in order to examine the solid-solid reactions. The products were analyzed using HPLC and LC-MS. Results indicate that: (1) longer time is required to form peptide compared to those of previous aqueous experiments; (2) pressure has a role to limit the production of melanoidine and cyclic amino acids, which are inhibitors for elongation of peptides; (3) glycine was polymerized up to 11-mer, which was not formed in any previous experiments without catalyses; (4) valine was polymerized up to 3-mer; and (5) aspartic acid was polymerized to 4-mer, accompanied with production of other amino acids. It is noteworthy that high-pressure environments favor all examined polymerization reactions. Such situations would have happened inside of deep oceanic crusts of the early Earth.

Kakegawa, T.; Ohara, S.; Ishiguro, T.; Abiko, H.; Nakazawa, H.

2008-12-01

188

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...

189

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

190

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

Microsoft Academic Search

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

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

2000-01-01

191

Parametrization for chemical freeze-out conditions from net-charge fluctuations measured at RHIC  

E-print Network

We discuss details of our thermal model applied to extract chemical freeze-out conditions from fluctuations in the net-electric charge and net-proton number measured at RHIC. A parametrization for these conditions as a function of the beam energy is given.

Bluhm, M; Alberico, W; Bellwied, R; Sarti, V Mantovani; Nahrgang, M; Ratti, C

2014-01-01

192

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

Microsoft Academic Search

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

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

2001-01-01

193

Secondary organic aerosol formation from aqueous chemistry of glyoxal, methylglyoxal, and glycolaldehyde in atmospheric waters: Chemical insights and kinetic model studies  

NASA Astrophysics Data System (ADS)

Aqueous chemistry in clouds, fog and aerosol water is now considered an important source of secondary organic aerosol (SOA). Modeling studies confirm that the underlying chemistry is kinetically favorable. Laboratory studies have begun to validate and refine the aqueous chemical mechanisms. Field observations, such as the atmospheric abundance of oxalate, ubiquitous presence of high molecular weight or humic-like substances (HULIS), high ambient O/C ratios, and correlations between SOA and aerosol liquid water content provide atmospheric evidence for SOA formation through aqueous chemistry. In the aqueous phase, small and volatile (C2-C3) but water soluble organic compounds undergo radical (photooxidation) and non-radical (acid/base catalysis) reactions, or reactions with inorganic constituents (sulfate, nitrate or ammonia) to form low volatility products including organic acids, organic-inorganic complexes and oligomers. These products are expected to remain at least in part in the particle phase after water evaporation, forming SOA. While not traditionally considered to be SOA precursors, atmospherically abundant and water soluble organic compounds like glyoxal (C2), methylglyoxal (C3) and glycolaldehyde (C2) have great potential to form SOA via aqueous chemistry. This paper presents a unified reaction mechanism and full kinetic model for the aqueous-phase reaction of glyoxal, methylglyoxal, glycolaldehyde, pyruvic acid and acetic acid with OH radical and validates this mechanism, in part, with laboratory experiments. At cloud relevant concentrations (~1E-6 M), the major product is oxalic acid and formation is well predicted by the previous cloud model (Lim et al., 2005). As concentrations increase radical-radical reactions become increasingly important and yield higher molecular weight products. The full kinetic model suggests that SOA formed in aerosol water (where organic concentrations are > 1 M) is comprised of high molecular weight multifunctional compounds. Atmospheric aqueous chemistry can potentially explain the atmospheric formation of oxalate, oligomers and HULIS. The insights gained from the full kinetic model can be used to aid the development of simplified modules for incorporation of this SOA formation process into chemical transport models.

Lim, Y. B.; Tan, Y.; Altieri, K. E.; Perri, M. J.; Carlton, A. G.; Seitzinger, S.; Turpin, B. J.

2010-12-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

195

Serpentinization, iron oxidation, and aqueous conditions in an ophiolite: Implications for hydrogen production and habitability on Mars  

NASA Astrophysics Data System (ADS)

Molecular hydrogen produced through iron oxidation during formation of serpentine and magnetite can sustain terrestrial subsurface ecosystems. The Fe3+ in serpentine partitions into octahedral and tetrahedral sites differently as serpentinization proceeds, and tetrahedral Fe3+ is present toward the end of serpentinization. We map Fe oxidation states in a serpentinite to determine the degree to which serpentinization progressed and where hydrogen production has been maximized to assess habitability at an abandoned chrysotile mine in Norbestos, Quebec, in association with the Canadian Space Agency's Mars Methane Analogue Mission. We also analyzed stable isotopes of carbon and oxygen in carbonates to constrain the conditions of water-rock interaction during serpentinization. Iron oxidation and coordination was determined through field imaging of rock walls with a visible hyperspectral imager (420-720 nm), and samples collected from imaged rocks and elsewhere in the mine were imaged in the laboratory (420-1100 nm). Sample chemistry, mineralogy, and oxidation state were determined with laboratory measurements of visible through mid-infrared reflectance spectra, major element chemistry, mineralogy, and Mössbauer spectroscopy. Mapping with hyperspectral imaging of outcrops and hand samples shows that tetrahedral Fe3+ is common in serpentinites at this site, and results are confirmed through other measurements. Major element chemistry and mineralogy are consistent with serpentine plus minor carbonate. Carbonate samples show an exceptional range in ?13C (-13.14 to + 16.12 ‰ VPDB) and ?18O (-15.48 to - 3.20 ‰ VPDB) that vary with location in the mine. Carbonates south of a shear zone (?13C more positive) likely formed during periods of serpentinization in a carbon-limited reservoir closed to carbon addition but open to methane escape. Carbonates in a shear zone (?13C more negative) probably formed later at low temperatures through CO2-metasomatism or atmospheric weathering, and isotopic trends are consistent with kinetic fractionation. The extensive presence of tetrahedral Fe3+ in serpentine shows the system liberally produced H2 while the isotope systematics have implications for preservation of indicators of the aqueous conditions that formed serpentinites on Mars and their habitability.

Greenberger, Rebecca N.; Mustard, John F.; Cloutis, Edward A.; Pratt, Lisa M.; Sauer, Peter E.; Mann, Paul; Turner, Kathryn; Dyar, M. Darby; Bish, David L.

2015-04-01

196

OH-radical formation by ultrasound in aqueous solution – Part II: Terephthalate and Fricke dosimetry and the influence of various conditions on the sonolytic yield  

Microsoft Academic Search

Terephthalate and Fricke dosimetry have been carried out to determine the sonolytic energy yields of the OH free radical and of its recombination product H2O2 in aqueous solutions under various operating conditions (nature of operating gas, power, frequency, temperature). For example, in the sonolysis of Ar-saturated terephthalate solutions at room temperature, a frequency of 321kHz, and a power of 170Wkg?1,

Gertraud Mark; Armin Tauber; Rüdiger Laupert; Heinz-Peter Schuchmann; Dorothea Schulz; Andreas Mues; Clemens von Sonntag

1998-01-01

197

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

198

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

2006-02-01

199

Diurnal and seasonal variation in physico-chemical conditions within intertidal rock pools  

NASA Astrophysics Data System (ADS)

A study of the diurnal and seasonal variation in the physico-chemical conditions within intertidal rock pools on the West coast of Scotland was undertaken to provide data on the environmental conditions experienced by animals inhabiting these pools. The temperature, pH, partial pressure of oxygen ( PO2) and salinity were measured every hour for 24 h and the total alkalinity, partial pressure of carbon dioxide ( PCO2) and carbon dioxide content ( CCO2) calculated. This sampling regime was carried out once a month for 12 months to determine the extent of seasonal variation in conditions within temperate pools. Large diurnal variations were recorded in nearly all the physico-chemical parameters measured. The greatest variation was recorded in the temperature and PO2 of the water but significant changes in pH and PCO2 were also recorded. Total alkalinity varied little during any 24 h period but carbonate alkalinity, which was always lower than total alkalinity, showed slightly greater variation. There was also considerable variation in the magnitude of these diurnal changes between pools at different heights on the shore. Diurnal variation in the physico-chemical conditions within the pools were observed throughout the year although the magnitude of these changes varied seasonally. Detailed studies on individual pools demonstrated that appreciable local variation existed in the physico-chemical conditions within each pool.

Morris, S.; Taylor, A. C.

1983-09-01

200

Chemistry of the system: Al2O3(c)minus HCL aqueous. [chemical reactions resulting from propellant combustion of rocket propellants  

NASA Technical Reports Server (NTRS)

In order to study exhaust gas chemistry for the space shuttle, the vapor pressure of 2 to 1 weight mixtures of 3-M hydrochloric acid and Al2O3 was studied over a l80 minute reaction period at 31 C. The Al2O3 sample was one of high surface area furnished by NASA Langley Research Center. A brief review is given for aqueous aluminum chemistry, and the chemical reactions of combustion products (exhaust gases) of aluminum propellant binders for the space shuttle are listed.

Tyree, S. Y., Jr.

1975-01-01

201

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

202

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

203

Noble metals as permanent chemical modifiers for the determination of mercury in environmental reference materials using solid sampling graphite furnace atomic absorption spectrometry and calibration against aqueous standards  

NASA Astrophysics Data System (ADS)

Iridium, palladium, rhodium and ruthenium, thermally deposited on the platform, were investigated as permanent modifiers for the determination of mercury in ash, sludge, marine and river sediment reference materials, ground to a particle size of 50 ?m, using solid sampling graphite furnace atomic absorption spectrometry. A total mass of 250 ?g of each modifier was applied using 25 injections of 20 ?l of modifier solution (500 mg l -1), and executing a temperature program for modifier conditioning after each injection. The performance of palladium was found to be most consistent, taking the characteristic mass as the major criterion, resulting in an excellent correlation between the measured integrated absorbance values and the certified mercury contents. Mercury was found to be lost in part from aqueous solutions during the drying stage in the presence of all the investigated permanent modifiers, as well as in the presence of the palladium and magnesium nitrates modifier added in solution. A loss-free determination of mercury in aqueous solutions could be reached only after the addition of potassium permanganate, which finally made possible the use of aqueous standards for the direct analysis of solid samples. A characteristic mass of 55-60 pg Hg was obtained for the solid samples, using Pd as a permanent modifier, and also in aqueous solutions after the addition of permanganate. The results obtained for mercury in ash, sludge and sediment reference materials, using direct solid sapling and calibration against aqueous standards, as well as the detection limit of 0.2 mg kg -1 were satisfactory for a routine procedure.

da Silva, Alessandra Furtado; Welz, Bernhard; Curtius, Adilson J.

2002-12-01

204

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

205

Estimation of octanol/water partition coefficient and aqueous solubility of environmental chemicals using molecular fingerprints and machine learning methods  

EPA Science Inventory

Octanol/water partition coefficient (logP) and aqueous solubility (logS) are two important parameters in pharmacology and toxicology studies, and experimental measurements are usually time-consuming and expensive. In the present research, novel methods are presented for the estim...

206

Effects of biomass types and carbonization conditions on the chemical characteristics of hydrochar  

Technology Transfer Automated Retrieval System (TEKTRAN)

Effects of biomass types (sugar beet pulp vs. bark mulch) and hydrothermal carbonization (HTC) processing conditions (temperature, residence time, and the phase of reaction medium) on the chemical characteristics of hydrochars were examined by elemental analysis, advanced solid-state nuclear magneti...

207

Chemical regeneration of human tooth enamel under near-physiological conditions.  

PubMed

Regenerating the microstructure of human tooth enamel under near-physiological conditions (pH 6.0, 37 degrees C, 1 atm) using a simple chemical approach demonstrates a potential application to repair enamel damage in dental clinics. PMID:19787132

Yin, Yujing; Yun, Song; Fang, Jieshi; Chen, Haifeng

2009-10-21

208

ACCURACY OF PESTICIDE REFERENCE STANDARD SOLUTIONS. PART II. CHEMICAL STABILITY UNDER FOUR STORAGE CONDITIONS  

EPA Science Inventory

A study was undertaken to assess the long-term chemical stability of dilute standard pesticide solutions of 4 compound classes. The solutions were studied under 4 storage conditions: freezer at -15C; refrigerator at 3C; ambient temperature in the dark; and ambient temperature on ...

209

Adolescent Chemical Dependency as a Handicapping Condition: An Analysis of State Regulations.  

ERIC Educational Resources Information Center

Studied chemical dependency in secondary school age students as legally handicapping condition, considering implications and rulings from relevant federal legislation, Education for All Handicapped Children Act of 1975 and Section 504 of Rehabilitation Act of 1973. Examined responses from 36 state offices of special education concerning state…

Williams, Ronald W.

1990-01-01

210

CHEMICAL ANALYSIS OF LOUISIANA POLLEN AND COLONY CONDITIONS DURING A YEAR  

E-print Network

CHEMICAL ANALYSIS OF LOUISIANA POLLEN AND COLONY CONDITIONS DURING A YEAR Norbert M. KAUFFELD U in pollen collected by honey bees, Apis mellifera L., in Louisiana throughout a year. Proline, lysine centimeters of brood, volume of pollen collected, square centimeters of stored pollen, and amino acids present

Paris-Sud XI, Université de

211

UV – INDUCED SYNTHESIS OF AMINO ACIDS FROM AQUEOUS STERILIZED SOLUTION OF AMMONIUM FORMATE AND AMMONIA UNDER HETROGENEOUS CONDITIONS  

PubMed Central

Irradiation of sterilized aqueous solution of ammonium formate and ammonia with UV light in the presence and or absence of certain inorganic sensitizers for 25 hrs. gave six ninhydrin positive products in appreciable amounts. Out of the six products observed fiver were characterized as lysine, serine, glutemic acid, n-amino butyric acid and leucine. The sensitizing effect of additives on ammonium formate was observed in the order; uranium oxide > ammonium formate > ferric oxide > arsenic oxide. PMID:22556511

Bisht, G.; Bisht, L. S.

1990-01-01

212

Effects of precursor chemistry and thermal treatment conditions on obtaining phase pure bismuth ferrite from aqueous gel precursors  

Microsoft Academic Search

Phase pure BiFeO3 powders are synthesized by an entirely aqueous solution–gel route, starting from water soluble Fe(III) nitrate or citrate, and Bi(III) citrate as precursors. In order to obtain stable solutions, which transform to homogeneous gels upon drying, the pH is adjusted to 7 and a citric acid content equimolar to the metal ions is selected.The presence of nitrate strongly

A. Hardy; S. Gielis; H. Van den Rul; J. D’Haen; M. K. Van Bael; J. Mullens

2009-01-01

213

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...

214

Constraining the physical-chemical conditions of Pleistocene cavernous weathering in Late Paleozoic granites  

NASA Astrophysics Data System (ADS)

Cavernous weathering such as tafoni, alveoles and honeycomb structures have been recorded from a great variety of bedrocks and landforms. In the present study cavernous weathering from late Variscan granites was discussed as to its physical-chemical regime of formation. U/Pb dating yielded a maximum age of 1.52 ± 0.03 Ma. Supergene U mineralization is accompanied by kaolinite, nontronite and Fe(III) phosphates. Based upon Eh-pH diagrams calculated for U-Fe-P mineralization the physical-chemical conditions may be described as oxidizing with pH values fluctuating around neutral at near-ambient temperatures of 25 °C. Alteration occurs in two stages: dissolution of rock-forming minerals and neoformation of hydrosilicates under mildly acidic conditions, followed by phosphate precipitation under near-neutral conditions.

Dill, Harald G.; Weber, Berthold; Gerdes, Axel

2010-09-01

215

Chemical composition and photochemical formation of hydroxyl radicals in aqueous extracts of aerosol particles collected in Okinawa, Japan  

NASA Astrophysics Data System (ADS)

We investigated the chemical composition and photochemical formation of hydroxyl (OH) radicals in the water-soluble fractions (WSF) of aerosol particles collected in Okinawa, Japan. Bulk aerosol samples were collected for 2-7 days at a time by a high-volume air sampler over a 3-month period. Major ions present in the WSF solutions were SO 42-, Na +, and Cl -. Sulfate ion concentrations were much higher when Yellow Sand events occurred. The mass-based Cl -/Na + ratio found in the WSF solutions averaged 49.7%, much lower than the ratio in seawater, indicating that chlorine was lost from the aerosol particles. A negative correlation ( R=-0.67) was found between the Cl -/Na + ratio and the concentration of non-sea-salt-SO 42-. We confirmed the photochemical formation of OH radicals in the study samples using illumination experiments at 313 nm. The apparent quantum yields of OH radical photoformation, based on the total absorbance at 313 nm, ranged from ND to 0.0017, with a mean±1 SD of 0.0010±0.0005. Hydroxyl radical photoformation rates from nitrate and nitrite photolyses, estimated based on nitrate and nitrite ion concentrations and our illumination conditions, averaged 32±24% and <10%, respectively, of the total formation rates. Hydroxyl radical photoformation rates were strongly correlated with total dissolved iron concentrations ( R=0.88). A correlation also existed between OH radical photoformation rates and dissolved organic carbon concentrations ( R=0.69).

Arakaki, Takemitsu; Kuroki, Yukiko; Okada, Kouichirou; Nakama, Yoshihide; Ikota, Hirotsugu; Kinjo, Mika; Higuchi, Tomihiko; Uehara, Masaya; Tanahara, Akira

216

Removal of arsenic from aqueous environments by native and chemically modified biomass of Aspergillus niger and Neosartorya fischeri  

Microsoft Academic Search

Arsenic removal from aqueous solutions by biomass of two fungal strains, Aspergillus niger and Neosartorya fischeri, was assessed. The biosorption capacity of fungal biomass was studied within the As(V) concentration range of approximately 0.2 to 5.0 mg L at two different pH values (pH 5 and 7). With increasing initial arsenic concentration, the biosorption capacity of both fungal strains increased

Pavol Littera; Martin Urík; Jaroslav Ševc; Marek Kolen?ík; Katarína Gardošová; Marianna Molnárová

2011-01-01

217

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

NASA Astrophysics Data System (ADS)

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

Rampe, Elizabeth Barger

2011-12-01

218

Improving glutathione extraction from crude yeast extracts by optimizing aqueous two-phase system composition and operation conditions  

Microsoft Academic Search

PEG-Dextran and PEG-salt aqueous two-phase systems (ATPS) have been applied to separate glutathione (GSH) from crude yeast\\u000a extracts. Single-factor experiments were carried out to determine the important factors influencing the partition coefficient\\u000a and extraction yield. The effect of PEG molecular weight, phase-forming components, PEG and Dextran concentration, pH value,\\u000a and temperature on the GSH partitioning behavior in ATPS was investigated.

Xiangting Wu; Linmei Tang; Yinming Du; Zhinan Xu

2010-01-01

219

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

USGS Publications Warehouse

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

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

2003-01-01

220

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 1×10 -3 mol dm -3 methyl ethyl ketone (MEK) has been studied at a dose rate of 0.12 Gy s -1, 25°C and an initial pH of 10. Experiments were conducted in air-, Ar- or N 2O-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 rad 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 CO 2, 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

221

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

NASA Astrophysics Data System (ADS)

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 phase OH-initiated oxidation rate constants of several oxygenated organic compounds relevant to the atmosphere or chosen as test compounds (ethanol, t-butanol, 1-butanol, iso-propanol, 1-propanol, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, phenol, ethyl ter-butyl ether (ETBE), n-propyl acetate, acetone, methyl ethyl ketone (MEK), methyl iso-butyl ketone (MIBK), ethyl formate). Experiments took place in an aqueous phase photoreactor. The rate constants were determinated using the relative kinetic method. Different OH-radical sources were tested, as well as different reference compounds in order to detect any artifact. The results have shown validation of the experimental protocol on test compounds. The overall results allowed to propose a structure reactivity method in order to predict OH-oxidation rate constant of new compounds. Finally, tropospheric life times of the studied compounds were compared inside and outside a cloud.

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

2003-04-01

222

Effects of biomass types and carbonization conditions on the chemical characteristics of hydrochars.  

PubMed

Effects of biomass types (bark mulch versus sugar beet pulp) and carbonization processing conditions (temperature, residence time, and phase of reaction medium) on the chemical characteristics of hydrochars were examined by elemental analysis, solid-state ¹³C NMR, and chemical and biochemical oxygen demand measurements. Bark hydrochars were more aromatic than sugar beet hydrochars produced under the same processing conditions. The presence of lignin in bark led to a much lower biochemical oxygen demand (BOD) of bark than sugar beet and increasing trends of BOD after carbonization. Compared with those prepared at 200 °C, 250 °C hydrochars were more aromatic and depleted of carbohydrates. Longer residence time (20 versus 3 h) at 250 °C resulted in the enrichment of nonprotonated aromatic carbons. Both bark and sugar beet pulp underwent deeper carbonization during water hydrothermal carbonization than during steam hydrothermal carbonization (200 °C, 3 h) in terms of more abundant aromatic C but less carbohydrate C in water hydrochars. PMID:24004410

Cao, Xiaoyan; Ro, Kyoung S; Libra, Judy A; Kammann, Claudia I; Lima, Isabel; Berge, Nicole; Li, Liang; Li, Yuan; Chen, Na; Yang, John; Deng, Baolin; Mao, Jingdong

2013-10-01

223

Effect of cooling condition on chemical vapor deposition synthesis of graphene on copper catalyst.  

PubMed

Here, we show that chemical vapor deposition growth of graphene on copper foil is strongly affected by the cooling conditions. Variation of cooling conditions such as cooling rate and hydrocarbon concentration in the cooling step has yielded graphene islands with different sizes, density of nuclei, and growth rates. The nucleation site density on Cu substrate is greatly reduced when the fast cooling condition was applied, while continuing methane flow during the cooling step also influences the nucleation and growth rate. Raman spectra indicate that the graphene synthesized under fast cooling condition and methane flow on cool-down exhibit superior quality of graphene. Further studies suggest that careful control of the cooling rate and CH4 gas flow on the cooling step yield a high quality of graphene. PMID:25386721

Choi, Dong Soo; Kim, Keun Soo; Kim, Hyeongkeun; Kim, Yena; Kim, TaeYoung; Rhy, Se-hyun; Yang, Cheol-Min; Yoon, Dae Ho; Yang, Woo Seok

2014-11-26

224

Sludge conditioning characteristics of copper chemical mechanical polishing wastewaters treated by electrocoagulation.  

PubMed

Treatment of copper chemical mechanical polishing (Cu-CMP) wastewaters by batch electrocoagulation was found effective in simultaneously removing the very fine metal oxide particles, copper ion and organic pollutants in the previous investigations. In the present work, the continuous electrocoagulation tests were performed to explore their treatment efficiencies and to identify the optimum operating conditions. Inherently, this electrocoagulation process, in either batch or continuous operating mode, generates a significant amount of sludge that needs to be properly disposed. In this study, the freeze/thaw conditioning of sludge obtained from this process was investigated in an aim to greatly reducing the sludge volume. Experimental tests were conducted to identify proper freeze/thaw operating conditions. Several fundamental aspects, such as the moisture bonding energy estimated using DSC test data, were examined to elucidate the conditioning results. PMID:16765514

Lai, Chen-Lee; Lin, Kuen-Song

2006-08-21

225

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

226

117 I. A. Aksay, 6.E. Hoge, andd. A. Pask Wetting under Chemical Equilibrium and Nonequilibrium Conditions  

E-print Network

117 I. A. Aksay, 6.E. Hoge, andd. A. Pask Wetting under Chemical Equilibrium and Nonequilibrium equilibrium and nonequilibri- um conditions, based on the model of Gibbs, is discussed. Under chemical of mechanical equilibrium, the sysitem was assumed to be at chemical equilibrium, E 17 I no mass transport

Aksay, Ilhan A.

227

Inactivation of SARS Coronavirus by Means of PovidoneIodine, Physical Conditions and Chemical Reagents  

Microsoft Academic Search

The efficacy of several povidone-iodine (PVP-I) products, a number of other chemical agents and various physical conditions were evaluated for their ability to inactivate the severe acute respiratory syndrome coronavirus (SARS-CoV). Treatment of SARS-CoV with PVP-I products for 2 min reduced the virus infectivity from 1.17 × 106 TCID50\\/ml to below the detectable level. The efficacy of 70% ethanol was

Hiroaki Kariwa; Nobuhiro Fujii; Ikuo Takashima

2006-01-01

228

Relative toxicity of pyrolysis gases from materials - Effects of chemical composition and test conditions  

NASA Technical Reports Server (NTRS)

Relative toxicity test data on 270 materials are presented, based on test procedures developed at the University of San Francisco. The effects of chemical composition, using data on 13 types of synthetic polymers and eight types of fabrics, are discussed. Selected materials were evaluated using nine test conditions with the USF method, and using methods developed at the FAA Civil Aeromedical Institute, Douglas Aircraft Company and San Jose State University.

Hilado, C. J.; Cumming, H. J.

1978-01-01

229

Optimization of Synthesis Condition for Carbon Nanotubes by Catalytic Chemical Vapor Deposition (CCVD)  

Microsoft Academic Search

Carbon Nanotubes (CNT) were synthesized by Chemical Vapor Deposition on Fe-Mo-MgO catalyst, by using ethanol (C2H5OH) as a carbon source and argon (Ar) as a carrier gas. The Reaction conditions are important factors that influence the yield and quality of carbon nanotubes. The effects of temperature, synthesis time and flow rate of carrier gas were investigated to increase the yield

Setareh Monshi Toussi; A. Fakhru'l-Razi; Luqman Chuah A; A. R. Suraya

2011-01-01

230

Differentiation of Human Embryonic Stem Cells to Regional Specific Neural Precursors in Chemically Defined Medium Conditions  

Microsoft Academic Search

BackgroundHuman embryonic stem cells (hESC) provide a unique model to study early events in human development. The hESC-derived cells can potentially be used to replace or restore different tissues including neuronal that have been damaged by disease or injury.Methodology and Principal FindingsThe cells of two different hESC lines were converted to neural rosettes using adherent and chemically defined conditions. The

Slaven Erceg; Sergio Laínez; Mohammad Ronaghi; Petra Stojkovic; Maria Amparo Pérez-Aragó; Victoria Moreno-Manzano; Rubén Moreno-Palanques; Rosa Planells-Cases; Miodrag Stojkovic; Joseph Najbauer

2008-01-01

231

APPLICATION OF THE TRADESCANTIA MICRONUCLEUS ASSAY FOR THE GENETIC EVALUATION OF CHEMICAL MIXTURES IN SOIL AND AQUEOUS MEDIA  

EPA Science Inventory

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. he chemical mixtures were either (I) mixed into soil, and chemical exposure to the target cells w...

232

Aqueous-phase photooxidation of levoglucosan - a mechanistic study using aerosol time-of-flight chemical ionization mass spectrometry (Aerosol ToF-CIMS)  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

234

Molecular engineering of a cobalt-based electrocatalytic nanomaterial for H2 evolution under fully aqueous conditions  

NASA Astrophysics Data System (ADS)

The viability of a hydrogen economy depends on the design of efficient catalytic systems based on earth-abundant elements. Innovative breakthroughs for hydrogen evolution based on molecular tetraimine cobalt compounds have appeared in the past decade. Here we show that such a diimine-dioxime cobalt catalyst can be grafted to the surface of a carbon nanotube electrode. The resulting electrocatalytic cathode material mediates H2 generation (55,000 turnovers in seven hours) from fully aqueous solutions at low-to-medium overpotentials. This material is remarkably stable, which allows extensive cycling with preservation of the grafted molecular complex, as shown by electrochemical studies, X-ray photoelectron spectroscopy and scanning electron microscopy. This clearly indicates that grafting provides an increased stability to these cobalt catalysts, and suggests the possible application of these materials in the development of technological devices.

Andreiadis, Eugen S.; Jacques, Pierre-André; Tran, Phong D.; Leyris, Adeline; Chavarot-Kerlidou, Murielle; Jousselme, Bruno; Matheron, Muriel; Pécaut, Jacques; Palacin, Serge; Fontecave, Marc; Artero, Vincent

2013-01-01

235

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  

USGS Publications Warehouse

Synchrotron X-ray spectroscopy experiments were made on the Gd(III) aqua and chloro complexes in low pH aqueous solutions at temperatures ranging from 25 to 500????C and at pressures up to 480??MPa using a hydrothermal diamond anvil cell. Analysis of fluorescence Gd L3-edge X-ray absorption fine structure (XAFS) spectra measured from a 0.006m Gd/0.16m HNO3 aqueous solution at temperatures up to 500????C and at pressures up to 260??MPa shows that the Gd-O distance of the Gd3+ aqua ion decreases steadily at a rate of ??? 0.007??A??/100????C whereas the number of coordinated H2O molecules decreases from 9.0 ?? 0.5 to 7.0 ?? 0.4. The loss of water molecules in the Gd3+ aqua ion inner hydration shell over this temperature range (a 22% reduction) is smaller than exhibited by the Yb3+ 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 Gd3+ aqua ion relative to other REEs. Gd L3-edge XAFS measurements of 0.006m and 0.1m GdCl3 aqueous solutions at temperatures up to 500????C and pressures up to 480??MPa reveal that the onset of significant Gd3+-Cl- association occurs around 300????C. Partially-hydrated stepwise inner-sphere complexes most likely of the type Gd(H2O)??-nCln+3-n occur in the chloride solutions at higher temperatures, where ?? ??? 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 Yb3+ 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 H2O ligands of Gd(H2O)??-nCln+3-n complexes decreases steadily from 8.9 ?? 0.4 to 5.8 ?? 0.7 in the 0.006m GdCl3 aqueous solution and from 9.0 ?? 0.5 to 5.3 ?? 1.0 in the 0.1m GdCl3 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-OH2 bond of the partially-hydrated Gd(III) chloro complexes exhibits slightly smaller rates of length contraction (??? 0.005??A??/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. ?? 2006 Elsevier B.V. All rights reserved.

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

2007-01-01

236

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

2011-01-01

237

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

SciTech Connect

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

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

1999-03-01

238

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

239

Chemical and structural properties of Jordanian zeolitic tuffs and their admixtures with urea and thiourea: Potential scavengers for phenolics in aqueous medium  

SciTech Connect

Native Jordanian zeolitic tuffs, rich in phillipsite, were treated with urea and thiourea. The chemical and structural properties of the tuffs and their urea and thiourea admixtures were studied using SEM, XRF, XRD, and FTIR techniques, and their adsorption capacities were estimated by the methylene blue method. The urea and thiourea treatment has not affected the mineral constitution of the tuffs. The results revealed that urea and thiourea were linked by hydrogen bonding through the NH{sub 2} moiety to the zeolite substrate, with urea showing the strongest effect. Experiments were carried out to investigate the possible use of the prepared materials for the removal of phenol and chlorinated phenols from aqueous solutions. Although thiourea caused a reduction in the relative surface area, both urea and thiourea admixtures were more effective than the free zeolitic tuff in the removal of phenol and chlorinated phenols from water, with urea admixture displaying the largest removal capacity.

Yousef, R.I.; Tutunji, M.F.; Derwish, G.A.W. [Univ. of Jordan, Amman (Jordan). Dept. of Chemistry] [Univ. of Jordan, Amman (Jordan). Dept. of Chemistry; Musleh, S.M. [Natural Resources Authority, Amman (Jordan)] [Natural Resources Authority, Amman (Jordan)

1999-08-15

240

Construction and evaluation of an experimental station and reaction apparatus for the chemical reactions of aqueous solution systems with soft x rays from a synchrotron radiation light source  

SciTech Connect

An efficient experimental system for the chemical reactions of various aqueous solutions using soft x rays from synchrotron radiation has been designed, constructed, and evaluated. This system was installed at an end station on a beamline (BL-11) at the Synchrotron Radiation Center of Ritsumeikan University. To protect the storage ring and the beamline from accidental vacuum breaks and contamination caused by unexpected solution leakage in the reaction apparatus, the system has two main protection sections: a differential vacuum pumping section equipped with orifice gaskets of very small aperture and an emergency interlocking system section equipped with a fast closing shutter, etc., in addition to a safety mechanism in the reaction apparatus section. The outline of the system and preliminary experimental data obtained in the evaluation of the system are described.

Shimizu, Yuichi; Koike, Masato; Sano, Kazuo [Kansai Photon Science Institute, Quantum Beam Science Directorate, Japan Atomic, Energy Agency, 8-1 Umemidai, Kizu, Kyoto 619-0215 (Japan); Shimadzu Emit Co. Ltd., 1 Tamachi Nishigosyo Murasakino, Kita Kyoto 603-8165 (Japan)

2006-09-15

241

CHEMICAL REACTION MECHANISM AND MODELIZATION OF DETERIORATION PHENOMENON OF HARDENED CEMENT DAMAGED BY CHEMICAL EROSION DUE TO MIXED ACID AQUEOUS SOLUTION  

NASA Astrophysics Data System (ADS)

This study measured the mass decrease rate of the hardened cement specimens which deteriorated by sulfuric acid, hydrochloric acid, nitric acid and mixed acid which mixed these acids (i.e. sulfuric acid, hydrochloric acid, nitric acid) for the purpose of clarify the these chemical reaction mechanism. As a result, it was clarified that mass decrease rate of hardened cement is greatly dependent on concentration of sulfuric acid when mixed acids containing sulfuric acid and other acid (i.e. hydrochloric acid or nitric acid) act on hardened cement. In this study, it was apprehended that the cause of this chemical reaction mechanism is influence of molar fraction of sulfuric acid and it was indicated that this chemical reaction mechanism could be explained by Gibbs free energy and chemical kinetics. Moreover, in this study, it was proposed that prediction model of mass decrease rate based on these theories.

Miyamoto, Shintaro; Minagawa, Hiroshi; Hisada, Makoto

242

Aqueous phase processing of secondary organic aerosol from isoprene photooxidation  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

243

Validity conditions for stochastic chemical kinetics in diffusion-limited systems  

PubMed Central

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

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

2014-01-01

244

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

245

Growth kinetics and long-term stability of CdS nanoparticles in aqueous solution under ambient conditions  

Microsoft Academic Search

The ubiquity of naturally occurring nanoparticles in the aquatic environment is now widely accepted, but a better understanding\\u000a of the conditions that promote their formation and persistence is needed. Using cadmium sulfide (CdS) as a model metal sulfide\\u000a species, thiolate-capped CdS nanoparticles were prepared in the laboratory to evaluate how aquatic conditions influence metal\\u000a sulfide nanoparticle growth and stability. This

Katherine M. MullaughGeorge; George W. Luther

2011-01-01

246

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

PubMed Central

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

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

2014-01-01

247

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

248

Infrared spectra and chemical abundance of methyl propionate in icy astrochemical conditions  

NASA Astrophysics Data System (ADS)

We carried out an experiment in order to obtain the infrared (IR) spectra of methyl propionate (CH3CH2COOCH3) in astrochemical conditions and present the IR spectra for future identification of this molecule in the interstellar medium (ISM). The experimental IR spectrum is compared with the theoretical spectrum, and an attempt was made to assign the observed peak positions to their corresponding molecular vibrations in condensed phase. Moreover, our calculations suggest that methyl propionate must be synthesized efficiently within the complex chemical network of the ISM and therefore be present in cold dust grains, awaiting identification.

Sivaraman, B.; Radhika, N.; Das, A.; Gopakumar, G.; Majumdar, L.; Chakrabarti, S. K.; Subramanian, K. P.; Raja Sekhar, B. N.; Hada, M.

2015-04-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2000-06-01

250

The secondary formation of inorganic aerosols in the droplet mode through heterogeneous aqueous reactions under haze conditions  

NASA Astrophysics Data System (ADS)

Secondary inorganic aerosols play important roles in visibility reduction and in regional haze pollution. To investigate the characteristics of size distributions of secondary sulfates and nitrates as well as their formation mechanisms under hazes, size-resolved aerosols were collected using a Micro-Orifice Uniform Deposit Impactor (MOUDI) at an urban site in Jinan, China, in all four seasons (December 2007-October 2008). In haze episodes, the secondary sulfates and nitrates primarily formed in fine particles, with elevated concentration peaks in the droplet mode (0.56-1.8 ?m). The fine sulfates and nitrates were completely neutralized by ammonia and existed in the forms of (NH4)2SO4 and NH4NO3, respectively. The secondary formation of sulfates, nitrates and ammonium (SNA) was found to be related to heterogeneous aqueous reactions and was largely dependent on the ambient humidity. With rising relative humidity, the droplet-mode SNA concentration, the ratio of droplet-mode SNA to the total SNA, the fraction of SNA in droplet-mode particles and the mass median aerodynamic diameter of SNA presented an exponential, logarithmic or linear increase. Two heavily polluted multi-day haze episodes in winter and summer were analyzed in detail. The secondary sulfates were linked to heterogeneous uptake of SO2 followed by the subsequent catalytic oxidation by oxygen together with iron and manganese in winter. The fine nitrate formation was strongly associated with the thermodynamic equilibrium among NH4NO3, gaseous HNO3 and NH3, and showed different temperature-dependences in winter and summer.

Wang, Xinfeng; Wang, Wenxing; Yang, Lingxiao; Gao, Xiaomei; Nie, Wei; Yu, Yangchun; Xu, Pengju; Zhou, Yang; Wang, Zhe

2012-12-01

251

Chemical speciation of neptunium(VI) under strongly alkaline conditions. Structure, composition, and oxo ligand exchange.  

PubMed

Hexavalent neptunium can be solubilized in 0.5-3.5 M aqueous MOH (M = Li(+), Na(+), NMe4(+) = TMA(+)) solutions. Single crystals were obtained from cooling of a dilute solution of Co(NH3)6Cl3 and NpO2(2+) in 3.5 M [N(Me)4]OH to 5 °C. A single-crystal X-ray diffraction study revealed the molecular formula of [Co(NH3)6]2[NpO2(OH)4]3·H2O, isostructural with the uranium analogue. The asymmetric unit contains three distinct NpO2(OH)4(2-) ions, each with pseudooctahedral coordination geometry with trans-oxo ligands. The average Np?O and Np-OH distances were determined to be 1.80(1) and 2.24(1) Å, respectively. EXAFS data and fits at the Np L(III)-edge on solid [Co(NH3)6]2[NpO2(OH)4]3·H2O and aqueous solutions of NpO2(2+) in 2.5 and 3.5 M (TMA)OH revealed bond lengths nearly identical with those determined by X-ray diffraction but with an increase in the number of equatorial ligands with increasing (TMA)OH concentration. Raman spectra of single crystals of [Co(NH3)6]2[NpO2(OH)4]3·H2O reveal a ?1(O?Np?O) symmetric stretch at 741 cm(-1). Raman spectra of NpO2(2+) recorded in a 0.6-2.2 M LiOH solution reveal a single ?1 frequency of 769 cm(-1). Facile exchange of the neptunyl oxo ligands with the water solvent was also observed with Raman spectroscopy performed with (16)O- and (18)O-enriched water solvent. The combination of EXAFS and Raman data suggests that NpO2(OH)4(2-) is the dominant solution species under the conditions of study and that a small amount of a second species, NpO2(OH)5(3-), may also be present at higher alkalinity. Crystal data for [Co(NH3)6]2[NpO2(OH)4]3·H2O: monoclinic, space group C2/c, a = 17.344(4) Å, b = 12.177(3) Å, c = 15.273 Å, ? = 120.17(2)°, Z = 4, R1 = 0.0359, wR2 = 0.0729. PMID:23485079

Clark, David L; Conradson, Steven D; Donohoe, Robert J; Gordon, Pamela L; Keogh, D Webster; Palmer, Phillip D; Scott, Brian L; Tait, C Drew

2013-04-01

252

Conversion of Japanese red pine wood (Pinus densiflora) into valuable chemicals under subcritical water conditions.  

PubMed

A comparative study on the decomposition of Japanese red pine wood under subcritical water conditions in the presence and absence of phosphate buffer was investigated in a batch-type reaction vessel. Since cellulose makes up more than 40-45% of the components found in most wood species, a series of experiments were also carried out using pure cellulose as a model for woody biomass. Several parameters such as temperature and residence time, as well as pH effects, were investigated in detail. The best temperature for decomposition and hydrolysis of pure cellulose was found around 270 degrees C. The effects of the initial pH of the solution which ranged from 1.5 to 6.5 were studied. It was found that the pH has a considerable effect on the hydrolysis and decomposition of the cellulose. Several products in the aqueous phase were identified and quantified. The conditions obtained from the subcritical water treatment of pure cellulose were applied for the Japanese red pine wood chips. As a result, even in the absence of acid catalyst, a large amount of wood sample was hydrolyzed in water; however, by using phosphate buffer at pH 2, there was an increase in the hydrolysis and dissolution of the wood chips. In addition to the water-soluble phase, acetone-soluble and water-acetone-insoluble phases were also isolated after subcritical water treatment (which can be attributed mainly to the degraded lignin, tar, and unreacted wood chips, respectively). The initial wood:acid ratio in the case of reactions catalyzed by phosphate buffer was also investigated. The results showed that this weight ratio can be as high as 3:1 without changing the catalytic activity. The size of the wood chips as one of the most important experimental parameters was also investigated. PMID:19892325

Asghari, Feridoun Salak; Yoshida, Hiroyuki

2010-01-11

253

Optimizing chemical conditioning for odour removal of undigested sewage sludge in drying processes.  

PubMed

Emission of odours during the thermal drying in sludge handling processes is one of the main sources of odour problems in wastewater treatment plants. The objective of this work was to assess the use of the response surface methodology as a technique to optimize the chemical conditioning process of undigested sewage sludges, in order to improve the dewaterability, and to reduce the odour emissions during the thermal drying of the sludge. Synergistic effects between inorganic conditioners (iron chloride and calcium oxide) were observed in terms of sulphur emissions and odour reduction. The developed quadratic models indicated that optimizing the conditioners dosage is possible to increase a 70% the dewaterability, reducing a 50% and 54% the emission of odour and volatile sulphur compounds respectively. The optimization of the conditioning process was validated experimentally. PMID:25438118

Vega, Esther; Monclús, Hèctor; Gonzalez-Olmos, Rafael; Martin, Maria J

2015-03-01

254

Conditions for calibration of an isothermal titration calorimeter using chemical reactions.  

PubMed

The reaction of protonation of 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) is a suitable one for the calibration of isothermal titration calorimeter (ITC), providing that experimental conditions are appropriately chosen. The conditions and methods for handling experimental data from a nanowatt-ITC are discussed. Also, the binding of Ba(2+) to 18-Crown-6 is successfully used to check the accuracy and precision of the chemical calibration performed with TRIS. This latter reaction has the additional advantage that the data can also be used for a check on the determination of the value of a binding constant. The anomaly of the first injection in ITC is analyzed and, by combining calorimetric and spectroscopic measurements, it is shown that it mainly results from a backlash effect of the syringe plunger rather than from a diffusion effect. PMID:23196751

Sgarlata, Carmelo; Zito, Valeria; Arena, Giuseppe

2013-01-01

255

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

SciTech Connect

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

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

2012-07-26

256

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

USGS Publications Warehouse

We have performed INAA, petrographie, and noble gas analyses on seventeen chondrules from the Semarkona meteorite (LL3.0) primarily to study the relationship of the I-Xe system to other measured properties. We observe a range of ???10 Ma in apparent I-Xe ages. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. The initial 129I/127I ratio (R0) is apparently related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R0'S (later apparent I-Xe ages) than porphyritic and olivine-rich chondrules. In addition, chondrules with sulfides on or near the surface have lower R0S than other chondrules. The 129Xe/132Xe ratio in the trapped Xe component anticorrelates with R0, consistent with evolution of a chronometer in a closed system or in multiple similar systems. On the basis of these correlations, we conclude that the variations in R0 represent variations in ages, and that later event(s), possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules. ?? 1991.

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

1991-01-01

257

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

258

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

259

Chemical enrichment and separation of uranyl ions in aqueous media using novel polyurethane foam chemically grafted with different basic dyestuff sorbents.  

PubMed

The new type of the grafted polyurethane foam sorbents were prepared by coupling polyether polyol, toluene diisocyanate and basic dyestuff (Methylene blue, Rhodamine B and Brilliant green). The Me.B-PUF, Rh.B-PUF and Br.G-PUF were characterized using UV/vis, IR and TGA. The adsorption properties and chromatographic behaviour of these new adsorbents for preconcentration and separation of uranium(VI) ions at low concentrations from aqueous thiocyanate media were investigated by a batch process. The maximum sorption of U(VI) was in the pH ranges 1-4. The kinetics of sorption of the U(VI) by the Grafted-PUF were found to be fast with half life of sorption (t(1/2)) in 2.43min. The average sorption capacity of different sorbents 0.124meqg(-1) for uranyl ions, enrichment factors approximately 40 and the recovery 98-100% were achieved (R.S.D. approximately 0.73%). The basic dyestuff Grafted-PUF could be used many times without decreasing their capacities significantly. The value of the Gibbs free energy (DeltaG) for the sorbents is -7.3kJmol(-1), which reflects the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Grafted-PUF was also discussed. PMID:19071294

El-Shahat, M F; Moawed, E A; Farag, A B

2007-01-15

260

Physico-chemical characterization of steel slag. Study of its behavior under simulated environmental conditions.  

PubMed

The chemical and mineralogical composition of steel slag produced in two ArcelorMittal steel plants located in the North of Spain, as well as the study of the influence of simulated environmental conditions on the properties of the slag stored in disposal areas, was carried out by elemental chemical analysis, XRF, X-ray diffraction, thermal analysis, and scanning electron microscopy with EDS analyzer. Spectroscopic characterization of the slag was also performed by using FTIR spectroscopy. Due to the potential uses of the slag as low cost adsorbent for water treatment and pollutants removal, its detailed textural characterization was carried out by nitrogen adsorption-desorption at 77 K and mercury intrusion porosimetry. The results show that the slag is a crystalline heterogeneous material whose main components are iron oxides, calcium (magnesium) compounds (hydroxide, oxide, silicates, and carbonate), elemental iron, and quartz. The slags are porous materials with specific surface area of 11 m(2)g(-1), containing both mesopores and macropores. Slag exposure to simulated environmental conditions lead to the formation of carbonate phases. Carbonation reduces the leaching of alkaline earth elements as well as the release of the harmful trace elements Cr (VI) and V. Steel slags with high contents of portlandite and calcium silicates are potential raw materials for CO(2) long-term storage. PMID:20568743

Navarro, Carla; Díaz, Mario; Villa-García, María A

2010-07-15

261

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

262

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...

263

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

EPA Science Inventory

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

264

Amide cis-trans isomerization in aqueous solutions of methyl N-formyl-D-glucosaminides and methyl N-acetyl-D-glucosaminides: chemical equilibria and exchange kinetics.  

PubMed

Amide cis-trans isomerization (CTI) in methyl 2-deoxy-2-acylamido-d-glucopyranosides was investigated by (1)H and (13)C NMR spectroscopy. Singly (13)C-labeled methyl 2-deoxy-2-formamido-d-glucopyranoside (MeGlcNFm) anomers provided standard (1)H and (13)C chemical shifts and (1)H-(1)H and (13)C-(13)C spin-coupling constants for cis and trans amides that are detected readily in aqueous solution. Equipped with this information, doubly (13)C-labeled methyl 2-deoxy-2-acetamido-d-glucopyranoside (MeGlcNAc) anomers were investigated, leading to the detection and quantification of cis and trans amides in this biologically important aminosugar. In comparison to MeGlcNFm anomers, the percentage of cis amide in aqueous solutions of MeGlcNAc anomers is small ( approximately 23% for MeGlcNFm versus approximately 1.8% for MeGlcNAc at 42 degrees C) but nevertheless observable with assistance from (13)C-labeling. Temperature studies gave thermodynamic parameters DeltaG degrees , DeltaH degrees , and DeltaS degrees for cis-trans interconversion in MeGlcNFm and MeGlcNAc anomers. Cis/trans equilibria depended on anomeric configuration, with solutions of alpha-anomers containing less cis amide than those of beta-anomers. Confirmation of the presence of cis amide in MeGlcNAc solutions derived from quantitative (13)C saturation transfer measurements of CTI rate constants as a function of solution temperature, yielding activation parameters E(act), DeltaG degrees (), DeltaH degrees (), and DeltaS degrees () for saccharide CTI. Rate constants for the conversion of trans to cis amide in MeGlcNFm and MeGlcNAc anomers ranged from 0.02 to 3.59 s(-1) over 31-85 degrees C, compared to 0.24-80 s(-1) for the conversion of cis to trans amide over the same temperature range. Energies of activation ranged from 16-19 and 19-20 kcal/mol for the cis --> trans and trans --> cis processes, respectively. Complementary DFT calculations on MeGlcNFm and MeGlcNAc model structures were conducted to evaluate the effects of an acyl side chain and anomeric structure, as well as C2-N2 bond rotation, on CTI energetics. These studies show that aqueous solutions of GlcNAc-containing structures contain measurable amounts of both cis and trans amides, which may influence their biological properties. PMID:20225805

Hu, Xiaosong; Zhang, Wenhui; Carmichael, Ian; Serianni, Anthony S

2010-04-01

265

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA  

SciTech Connect

The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate ions H{sub 3}PO{sub 4}{sup 0}(aq), H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), or PO{sub 4}{sup 3-}(aq). Many divalent, trivalent, and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation requires comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier; with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H{sub 2}PO{sub 4}{sup -}(aq) and HPO{sub 4}{sup 2-}(aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ {center_dot} mol{sup -1} per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), and PO{sub 4}{sup 3-}(aq) ions at 298.15 K and p{sup o} = 1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S{sub m}{sup o}(H{sub 2}PO{sub 4}{sup -}, aq, 298.15 K) = 90.6 {+-} 1.5 J {center_dot} K{sup -1} mol{sup -1} was obtained.

Rard, J A; Wolery, T J

2007-01-30

266

Statistical and Experimental Analysis of Correlated Time-Varying Process Variables for Conditions Diagnosis in Chemical–Mechanical Planarization  

Microsoft Academic Search

During chemical-mechanical planarization (CMP) of semiconductor wafers, chemical and mechanical process variables are strongly correlated and jointly affect polishing performance. The correlation among these process variables could potentially be utilized to characterize process conditions for the purpose of diagnosis. However, process variables measured during CMP, such as the temperature distribution and coefficient of friction between wafer and pad, vary with

Xi Zhang; Hui Wang; Qiang Huang; Ashok Kumar; Jingmei Zhai

2009-01-01

267

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

NASA Astrophysics Data System (ADS)

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

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

268

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

NASA Technical Reports Server (NTRS)

The roles of thermal copolymers of amino acids (TCAA) were studied for the prebiotic degradation of RNA. A weak catalytic ability of TCAA consisted of Glu, L-Ala, L-Val, L-Glu, L-Asp, and optionally L-His was detected for the cleavage of the ribose phosphodiester bond of a tetranucleotide (5'-dCrCdGdG) in aqueous solution at 80 degees C. The rate constants of the disappearance of 5'-dCrCdGdG were determined in aqueous solutions using different pH buffer and TCAA. The degradation rates were enhanced 1.3-3.0 times in the presence of TCAA at pH 7.5 and 8.0 at 80 degrees C, while the hydrolysis of oligoguanylate (oligo(G)) was accelerated about 1.6 times at pH 8.0. A weak inhibitory activity for the cleavage of oligo(G) was detected in the presence of 0.055 M TCAA-Std. On the other hand, our recent study on the influences of TCAA for the template-directed reaction of oligo(G) on a polycytidylic acid template showed that TCAA has an acceleration activity for the degradation of the activated nucleotide monomer and an acceleration activity for the formation of G5' ppG capped oligo(G). This series of studies suggest that efficient and selective catalytic or inhibitory activities for either the degradation or formation of RNA under hydrothermal conditions could have hardly emerged from the simple thermal condensation products of amino acids. A scenario is going to be deduced on the chemical evolution of enzymatic activities and RNA molecules concerning hydrothermal earth conditions. c2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

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

2005-01-01

269

Study of CdS epitaxial films chemically deposited from aqueous solutions on InP single crystals  

SciTech Connect

Epitaxial growth of cadmium sulfide on InP single crystals is achieved by chemical bath deposition (CBD) in ammonia solutions at near room temperature. A better understanding of the correlations between the deposition parameters (temperature, bath composition) and the epitaxial quality is obtained by using electron diffraction and transmission techniques, x-ray diffraction, in combination with Raman spectroscopy. They are supplemented by electrochemical impedance and photocurrent experiments which give information on energetic structures between InP and CBD-CdS. Direct relations between the substrate properties and the growth habits of the CdS film (hexagonal vs. cubic, epitaxial vs. polycrystalline) are found.

Froment, M.; Bernard, M.C.; Cortes, R. [Univ. Pierre et Marie Curie, Paris (France). Physique des Liquides et Electrochimie; Mokili, B.; Lincot, D. [Ecole Nationale Superieure de Chimie de Paris (France). Lab. d`Electrochimie et de Chimie Analytique

1995-08-01

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

Sonochemical dechlorination of hazardous wastes in aqueous systems  

SciTech Connect

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

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

1995-12-31

272

Chitosan use in chemical conditioning for dewatering municipal-activated sludge.  

PubMed

This work aims to evaluate the potential use of chitosan as an eco-friendly flocculant in chemical conditioning of municipal-activated sludge. Chitosan effectiveness was compared with synthetic cationic polyelectrolyte Sedipur CF802 (Sed CF802) and ferric chloride (FeCl3). In this context, raw sludge samples from Beni-Messous wastewater treatment plant (WWTP) were tested. The classic jar test method was used to condition sludge samples. Capillary suction time (CST), specific resistance to filtration (SRF), cakes dry solid content and filtrate turbidity were analyzed to determine filterability, dewatering capacity of conditioned sludge and the optimum dose of each conditioner. Data exhibit that chitosan, FeCl3 and Sed CF802 improve sludge dewatering. Optimum dosages of chitosan, Sed CF802 and FeCl3 allowing CST values of 6, 5 and 9 s, were found, respectively, between 2-3, 1.5-3 and 6 kg/t ds. Both polymers have shown faster water removal with more permeable sludge. SRF values were 0.634 × 10(12), 0.932 × 10(12) and 2 × 10(12) m/kg for Sed CF802, chitosan and FeCl3 respectively. A reduction of 94.68 and 87.85% of the filtrate turbidity was obtained with optimal dosage of chitosan and Sed CF802, respectively. In contrast, 54.18% of turbidity abatement has been obtained using optimal dosage of FeCl3. PMID:25812088

Zemmouri, H; Mameri, N; Lounici, H

2015-01-01

273

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

E-print Network

9 to 15.5. Finally, according to these new measurements of the solubility of platinum systems: Pt-K-HC8H4O4-H2O (pH 4.02), Pt-Na-HCO3-Cl-H2O (pH 6.40), Pt-Na-K- H2PO4-HPO4-H2O (pH 6.90), Pt-Na-HCO3-H2O (pH 8.30), Pt-Na-OH-H2O (pH 8.54), and Pt- Na-HCO3-H2O (pH 9.91). The redox conditions

Boyer, Edmond

274

Review and analysis of high temperature chemical reactions and the effect of non-equilibrium conditions  

NASA Technical Reports Server (NTRS)

Chemical reactions at high temperatures have been considered extensively because of their importance to the heating effects on re-entry of space vehicles. Data on these reactions however, are not abundant and even when found there are discrepancies in data collected by various investigators. In particular, data for recombination reactions are calculated from the dissociation reactions or vice versa through the equilibrium constant. This involves the use of the principle of detailed balancing. This principle is discussed in reference to conditions where it is valid as well as to those where it is not valid. Related topics that merit further study or for which applicable information was available are briefly mentioned in an appendix to this report.

Johnson, R. E.

1986-01-01

275

Toxicity studies on Reactive Blue-2 leached from affinity material exposed to extreme chemical conditions.  

PubMed

Toxicity effects related to leached ligands from affinity sorbents that can contaminate biological preparations were investigated in the particular case of immobilized Reactive Blue-2. Initially, identification of the real chemical structure of leached dye has been done by HPLC after incubation in extreme conditions. Toxicity investigations in vitro involving several well known tests showed no toxic effects within the studied range of dye concentration. Cell cultures behaved normally when the adhesion phase was successful; polyploidy induction in human cells by the native dye and its derivatives identified as possible leached material was very similar to standard cultures. Genotoxicity studies did not evidence any toxic effect in E. Coli cultures of dyes themselves or of the same dyes after metabolic activation. PMID:7765494

Bertrand, O; Boschetti, E; Cochet, S; Girot, P; Hebert, E; Monsigny, M; Roche, A C; Santambien, P; Sdiqui, N

1994-10-01

276

Fluid Pressure, Thermal and Chemical Effects in Conditioning Permeability and Triggered Seismicity in Enhanced Geothermal Systems  

NASA Astrophysics Data System (ADS)

The evolution of permeability, heat or diffusive transfer area and triggered seismicity are intimately linked in forced-circulation systems such as EGS, CCS and unconventional hydrocarbon reservoirs where conditions are pushed far-from-equilibrium. We explore this evolution subject to coupled THMC processes in a prototypical EGS reservoir. We accommodate the influence of early-time changes in effective stress, mid-time changes in thermal stresses and ultimately incorporate long-term changes due to chemical effects. We develop a micromechanical model to represent the failure process and apply this model to represent energy release from individual critically oriented fractures. The changing stress state is calculated from the pore pressure, thermal drawdown and chemical effects for a coupled THMC model with dual porosity. This model is applied to a doublet geometry to explore the spatial and temporal migration for permeability evolution, access to reactive surface area and the triggering of seismicity as stimulation then production proceeds. Seismic activity is initially concentrated around the near-wellbore injection region. It is earliest for closely spaced fractures in reservoir rocks where the thermal drawdown of stress is largest at early times and results in numerous low-magnitude events. These observations are used to define the evolution of spatial changes within the reservoir and their migration with production, dependent on the mobilization of relic fractures.

Elsworth, D.; Izadi, G.; Zheng, B.; Taron, J.

2011-12-01

277

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

SciTech Connect

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

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

1985-01-22

278

Effective dispersion in a chemically heterogeneous medium under temporally fluctuating flow conditions  

NASA Astrophysics Data System (ADS)

We investigate effective solute transport in a chemically heterogeneous medium subject to temporal fluctuations of the flow conditions. Focusing on spatial variations in the equilibrium adsorption properties, the corresponding fluctuating retardation factor is modeled as a stationary random space function. The temporal variability of the flow is represented by a stationary temporal random process. Solute spreading is quantified by effective dispersion coefficients, which are derived from the ensemble average of the second centered moments of the normalized solute distribution in a single disorder realization. Using first-order expansions in the variances of the respective random fields, we derive explicit compact expressions for the time behavior of the disorder induced contributions to the effective dispersion coefficients. Focusing on the contributions due to chemical heterogeneity and temporal fluctuations, we find enhanced transverse spreading characterized by a transverse effective dispersion coefficient that, in contrast to transport in steady flow fields, evolves to a disorder-induced macroscopic value (i.e., independent of local dispersion). At the same time, the asymptotic longitudinal dispersion coefficient can decrease. Under certain conditions the contribution to the longitudinal effective dispersion coefficient shows superdiffusive behavior, similar to that observed for transport in s stratified porous medium, before it decreases to its asymptotic value. The presented compact and easy to use expressions for the longitudinal and transverse effective dispersion coefficients can be used for the quantification of effective spreading and mixing in the context of the groundwater remediation based on hydraulic manipulation and for the effective modeling of reactive transport in heterogeneous media in general.

Zavala-Sanchez, Vanessa; Dentz, Marco; Sanchez-Vila, Xavier

2007-05-01

279

Permafrost conditions in peatlands regulate magnitude, timing, and chemical composition of catchment dissolved organic carbon export.  

PubMed

Permafrost thaw in peatlands has the potential to alter catchment export of dissolved organic carbon (DOC) and thus influence downstream aquatic C cycling. Subarctic peatlands are often mosaics of different peatland types, where permafrost conditions regulate the hydrological setting of each type. We show that hydrological setting is key to observed differences in magnitude, timing, and chemical composition of DOC export between permafrost and nonpermafrost peatland types, and that these differences influence the export of DOC of larger catchments even when peatlands are minor catchment components. In many aspects, DOC export from a studied peatland permafrost plateau was similar to that of a forested upland catchment. Similarities included low annual export (2-3 g C m(-2) ) dominated by the snow melt period (~70%), and how substantial DOC export following storms required wet antecedent conditions. Conversely, nonpermafrost fens had higher DOC export (7 g C m(-2) ), resulting from sustained hydrological connectivity during summer. Chemical composition of catchment DOC export arose from the mixing of highly aromatic DOC from organic soils from permafrost plateau soil water and upland forest surface horizons with nonaromatic DOC from mineral soil groundwater, but was further modulated by fens. Increasing aromaticity from fen inflow to outlet was substantial and depended on both water residence time and water temperature. The role of fens as catchment biogeochemical hotspots was further emphasized by their capacity for sulfate retention. As a result of fen characteristics, a 4% fen cover in a mixed catchment was responsible for 34% higher DOC export, 50% higher DOC concentrations and ~10% higher DOC aromaticity at the catchment outlet during summer compared to a nonpeatland upland catchment. Expansion of fens due to thaw thus has potential to influence landscape C cycling by increasing fen capacity to act as biogeochemical hotspots, amplifying aquatic C cycling, and increasing catchment DOC export. PMID:24753046

Olefeldt, David; Roulet, Nigel T

2014-10-01

280

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...

281

A novel pad conditioning disk design of tungsten chemical mechanical polishing process for deep sub-micron device yield improvement  

Microsoft Academic Search

Chemical Mechanical Polishing (CMP) is widely used for global planarization in IC device structure. A pad conditioner is often used to remove polishing debris, and hence preventing the pad surface from glazing. The proper conditioning can assure the pad surface like new so it can hold slurry evenly for effective polishing. Diamond disks are commonly used for conditioning the CMP

T. C. Wang; T. E. Hsieh; Y. L. Wang; C. W. Liu; K. Y. Lo; J. K. Wang; W. Lee

2001-01-01

282

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

PubMed

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

Ishida, Naoyuki

2014-05-01

283

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

284

Sustainable 'Greener' Methods for Chemical Transformations and Applications of Nano-Catalysts  

EPA Science Inventory

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

285

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...

286

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

EPA Science Inventory

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

287

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

EPA Science Inventory

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

288

Kinetics of chemical degradation of isoxaflutole: influence of the nature of aqueous buffers (alkanoic acid/sodium salt vs phosphate).  

PubMed

A kinetic study of the chemical degradation of isoxaflutole (5-cyclopropyl-1,2-oxazol-4-yl alpha alpha alpha-trifluoro-2-mesyl-p-tolyl ketone) into its diketonitrile derivative (DKN), which is its active herbicide principle, in organic buffers at different pH values was carried out using a HPLC/UV detection method. The values of the pseudo-first-order rate constants Kobs for the reaction were calculated and compared with those previously obtained in inorganic buffers. In both cases, Kobs was found to be dependent on pH and temperature, but at pH 5.2 the degradation of isoxaflutole in CH3COOH/CH3COONa buffers was considerably faster than in KH2PO4/Na2HPO4 buffers, indicating that the compound was sensitive to the nature of the reagents used to prepare buffered solutions. The influence of phosphate and acetate concentrations and the influence of the R-substituent in RCOOH/RCOONa buffers were investigated. For the HA/A- buffers studied, the values of Kobs were linearly dependent on HA and A- concentrations, which meant that the degradation of isoxaflutole was subject to general catalysis. The values of Kobs were also found to be dependent on the number and the position of the CH3 groups of the R-substituent. The known degradation product of DKN (a benzoic acid derivative) was not detected throughout this study. PMID:11455816

Beltran, E; Fenet, H; Cooper, J F; Coste, C M

2001-04-01

289

Differentiation of Human Embryonic Stem Cells to Regional Specific Neural Precursors in Chemically Defined Medium Conditions  

PubMed Central

Background Human embryonic stem cells (hESC) provide a unique model to study early events in human development. The hESC-derived cells can potentially be used to replace or restore different tissues including neuronal that have been damaged by disease or injury. Methodology and Principal Findings The cells of two different hESC lines were converted to neural rosettes using adherent and chemically defined conditions. The progenitor cells were exposed to retinoic acid (RA) or to human recombinant basic fibroblast growth factor (bFGF) in the late phase of the rosette formation. Exposing the progenitor cells to RA suppressed differentiation to rostral forebrain dopamine neural lineage and promoted that of spinal neural tissue including motor neurons. The functional characteristics of these differentiated neuronal precursors under both, rostral (bFGF) and caudalizing (RA) signals were confirmed by patch clamp analysis. Conclusions/Significance These findings suggest that our differentiation protocol has the capacity to generate region-specific and electrophysiologically active neurons under in vitro conditions without embryoid body formation, co-culture with stromal cells and without presence of cells of mesodermal or endodermal lineages. PMID:18461168

Erceg, Slaven; Laínez, Sergio; Ronaghi, Mohammad; Stojkovic, Petra; Pérez-Aragó, Maria Amparo; Moreno-Manzano, Victoria; Moreno-Palanques, Rubén; Planells-Cases, Rosa; Stojkovic, Miodrag

2008-01-01

290

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

2013-01-01

291

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

PubMed

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

Ren, Yanlin; Fan, Guangyin; Wang, Chenyu

2014-06-15

292

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

EPA Science Inventory

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

293

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

294

Inactivation of SARS coronavirus by means of povidone-iodine, physical conditions and chemical reagents.  

PubMed

The efficacy of several povidone-iodine (PVP-I) products, a number of other chemical agents and various physical conditions were evaluated for their ability to inactivate the severe acute respiratory syndrome coronavirus (SARS-CoV). Treatment of SARS-CoV with PVP-I products for 2 min reduced the virus infectivity from 1.17 x 10(6) TCID(50)/ml to below the detectable level. The efficacy of 70% ethanol was equivalent to that of PVP-I products. Fixation of SARS-CoV-infected Vero E6 cells with a fixative including formalin, glutaraldehyde, methanol and acetone for 5 min or longer eliminated all infectivity. Heating the virus at 56 degrees C for 60 min or longer reduced the infectivity of the virus from 2.6 x 10(7) to undetectable levels. Irradiation with ultraviolet light at 134 microW/cm(2) for 15 min reduced the infectivity from 3.8 x 10(7) to 180 TCID(50)/ml; however, prolonged irradiation (60 min) failed to eliminate the remaining virus, leaving 18.8 TCID(50)/ml. PMID:16490989

Kariwa, Hiroaki; Fujii, Nobuhiro; Takashima, Ikuo

2006-01-01

295

Inactivation of SARS coronavirus by means of povidone-iodine, physical conditions, and chemical reagents.  

PubMed

The efficacy of several povidone-iodine (PVP-I) products, a number of other chemical agents, and various physical conditions were evaluated for their ability to inactivate the severe acute respiratory syndrome coronavirus (SARS-CoV). Treatment of SARS-CoV with PVP-I products for 2 min reduced the virus infectivity from 1.17 x 10(6) TCID50/ml to below the detectable level. The efficacy of 70% ethanol was equivalent to that of PVP-I products. Fixation of SARS-CoV-infected Vero E6 cells with a fixative including formalin, glutaraldehyde, methanol, and acetone for 5 min or longer eliminated all infectivity. Heating the virus at 56 degrees C for 5 min dramatically reduced the infectivity of the virus from 2.6 x 10(7) to 40 TCID50/ml, whereas heating the virus for 60 min or longer eliminated all infectivity. Irradiation with ultraviolet light at 134 microW/cm2 for 15 min reduced the infectivity from 3.8 x 10(7) to 180 TCID50/ml; however, prolonged irradiation (60 min) failed to eliminate the remaining virus, leaving 18.8 TCID50/ml. We believe that these findings will be useful for the implementation of infection control measures against SARS, and for the establishment of effective guidelines for the prevention of SARS outbreaks. PMID:15631008

Kariwa, Hiroaki; Fujii, Nobuhiro; Takashima, Ikuo

2004-11-01

296

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

PubMed

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

Lissalde, Sophie; Mazzella, Nicolas; Mazellier, Patrick

2014-08-01

297

Particle emissions from a marine engine: chemical composition and aromatic emission profiles under various operating conditions.  

PubMed

The chemical composition of particulate matter (PM) emissions from a medium-speed four-stroke marine engine, operated on both heavy fuel oil (HFO) and distillate fuel (DF), was studied under various operating conditions. PM emission factors for organic matter, elemental carbon (soot), inorganic species and a variety of organic compounds were determined. In addition, the molecular composition of aromatic organic matter was analyzed using a novel coupling of a thermal-optical carbon analyzer with a resonance-enhanced multiphoton ionization (REMPI) mass spectrometer. The polycyclic aromatic hydrocarbons (PAHs) were predominantly present in an alkylated form, and the composition of the aromatic organic matter in emissions clearly resembled that of fuel. The emissions of species known to be hazardous to health (PAH, Oxy-PAH, N-PAH, transition metals) were significantly higher from HFO than from DF operation, at all engine loads. In contrast, DF usage generated higher elemental carbon emissions than HFO at typical load points (50% and 75%) for marine operation. Thus, according to this study, the sulfur emission regulations that force the usage of low-sulfur distillate fuels will also substantially decrease the emissions of currently unregulated hazardous species. However, the emissions of soot may even increase if the fuel injection system is optimized for HFO operation. PMID:25202837

Sippula, O; Stengel, B; Sklorz, M; Streibel, T; Rabe, R; Orasche, J; Lintelmann, J; Michalke, B; Abbaszade, G; Radischat, C; Gröger, T; Schnelle-Kreis, J; Harndorf, H; Zimmermann, R

2014-10-01

298

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

2010-01-01

299

Conditionals  

E-print Network

This article introduces the classic accounts of the meaning of conditionals (material implication, strict implication, variably strict conditional) and discusses the difference between indicative and subjunctive/counterfactual ...

von Fintel, Kai

2011-01-01

300

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

301

Chemical Peels  

MedlinePLUS

... How to Choose the Best Skin Care Products Chemical Peels Uses for Chemical Peels Learn more about specific conditions where chemical ... damaged skin Sagging skin Wrinkles What is a chemical peel? A chemical peel is a technique used ...

302

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...

303

Transport and Fate of Bacteria in Porous Media: Coupled Effects of Chemical Conditions and Pore Space Geometry  

Technology Transfer Automated Retrieval System (TEKTRAN)

Experimental and theoretical studies were undertaken to explore the coupling 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 i...

304

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

305

Effects of different extrusion conditions on the chemical and toxicological fate of fumonisin B1 in maize: a review  

Technology Transfer Automated Retrieval System (TEKTRAN)

A series of experiments to investigate the chemical and toxicological fate of fumonisin B1 (FB1) under different extrusion conditions using both single- and twin-screw extruders is described. Maize grits were contaminated with FB1 at different concentrations by fermentation with Fusarium verticilli...

306

Mathematical Model of Carbon Dioxide Absorption into Mixed Aqueous Solutions  

Microsoft Academic Search

In this paper, a mathematical model of CO2 chemical absorption system using MDEA (MethylDiEthanolAmine) and PZ (Piperazine) aqueous solutions is investigated. Precisely, the complex reactive absorption behavior is modeled by an NLP mathematical model. The resulting mathematical model is implemented in GAMS and CONOPT is used as NLP solver. The proposed model will allow to optimize the operating conditions to

Patricia Mores; Nicolas Scenna; Sergio Mussati

2009-01-01

307

In vivo hepatoprotective activity of the aqueous extract of Artemisia absinthium L. against chemically and immunologically induced liver injuries in mice  

Microsoft Academic Search

Aim of the studyThis study aimed to evaluate in vivo hepatoprotective activity of the aqueous extract of Artemisia absinthium L. (AEAA), which has been used for the treatment of liver disorders in Traditional Uighur Medicine.

Nurmuhammat Amat; Halmurat Upur; Biljana Blažekovi?

2010-01-01

308

Metabolic profiling of Lolium perenne shows functional integration of metabolic responses to diverse subtoxic conditions of chemical stress.  

PubMed

Plant communities are confronted with a great variety of environmental chemical stresses. Characterization of chemical stress in higher plants has often been focused on single or closely related stressors under acute exposure, or restricted to a selective number of molecular targets. In order to understand plant functioning under chemical stress conditions close to environmental pollution conditions, the C3 grass Lolium perenne was subjected to a panel of different chemical stressors (pesticide, pesticide degradation compound, polycyclic aromatic hydrocarbon, and heavy metal) under conditions of seed-level or root-level subtoxic exposure. Physiological and metabolic profiling analysis on roots and shoots revealed that all of these subtoxic chemical stresses resulted in discrete physiological perturbations and complex metabolic shifts. These metabolic shifts involved stressor-specific effects, indicating multilevel mechanisms of action, such as the effects of glyphosate and its degradation product aminomethylphosphonic acid on quinate levels. They also involved major generic effects that linked all of the subtoxic chemical stresses with major modifications of nitrogen metabolism, especially affecting asparagine, and of photorespiration, especially affecting alanine and glycerate. Stress-related physiological effects and metabolic adjustments were shown to be integrated through a complex network of metabolic correlations converging on Asn, Leu, Ser, and glucose-6-phosphate, which could potentially be modulated by differential dynamics and interconversion of soluble sugars (sucrose, trehalose, fructose, and glucose). Underlying metabolic, regulatory, and signalling mechanisms linking these subtoxic chemical stresses with a generic impact on nitrogen metabolism and photorespiration are discussed in relation to carbohydrate and low-energy sensing. PMID:25618145

Serra, Anne-Antonella; Couée, Ivan; Renault, David; Gouesbet, Gwenola; Sulmon, Cécile

2015-04-01

309

Disruption of biofilms from sewage pipes under physical and chemical conditioning  

Microsoft Academic Search

Biofilms grown inside two sewage collecting pipes located in industrial and residential areas are studied. Bacterial biomass inside three layers of biofilms was evaluated. Biofilm cohesion under different mixing rate and ionic strength was also investigated. Effects of physical and chemical parameters in the biofilms were evaluated by monitoring turbidity, chemical and biochemical oxygen demands. Extracted organic matter from biofilms

Charbel Mahfoud; Antoine El Samrani; Rita Mouawad; Walid Hleihel; Rim El Khatib; Bruno S. Lartiges; Naïm Ouaïni

2009-01-01

310

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

311

Further studies of NO sub x control in aqueous scrubbers using ferrouster dot EDTA  

Microsoft Academic Search

Argonne National Laboratory has been conducting research on combined nitrogen oxides (NOâ) and sulfur dioxide (SOâ) control systems. The research program has recently been focused on studies of aqueous scrubber systems enhanced with chemical additives to promote NOâ removal. Tests have been conducted in a laboratory-scale scrubber system using experimental conditions selected to simulate the scrubbing of flue gas from

M. H. Mendelsohn; C. D. Livengood; J. B. L. Harkness

1991-01-01

312

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

313

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...

314

Journal of Chemical Ecology, Vol. 25, No. 12, 1999 CONDITIONED ALARM BEHAVIOR IN FATHEAD  

E-print Network

(Pimephales promelas) RESULTING FROM ASSOCIATION OF CHEMICAL ALARM PHEROMONE WITH A NONBIOLOGICAL VISUAL--Fathead minnows (Pimephales promelas) adopt antipredator (alarm) behavior when they detect alarm pheromone, Pimephales promelas, alarm pheromone, Schreckstoff, learned recognition of predation risk, red light. #12

Wisenden, Brian D.

315

Effect of chemical mechanical planarization processing conditions on polyurethane pad properties  

E-print Network

Chemical Mechanical Planarization (CMP) is a vital process used in the semiconductor industry to isolate and connect individual transistors on a chip. However, many of the fundamental mechanisms of the process are yet to ...

Ng, Grace Siu-Yee, 1980-

2003-01-01

316

CHEMICAL CHARACTERISATION OF BHUIAVALI (Phyllanthus niruri)  

PubMed Central

The present article describes the chemical characteristics such as pH of aqueous extract, fluorescence, aqueous and alcoholic extractives, lignans and TLC profile of aqueous extract of Bhuiavli (Phyllanthus niruri). PMID:22556737

Phadnis, A.D.

1995-01-01

317

Chemical conversion of cisplatin and carboplatin with histidine in a model protein crystallized under sodium iodide conditions  

PubMed Central

Cisplatin and carboplatin are platinum anticancer agents that are used to treat a variety of cancers. Previous X-ray crystallographic studies of carboplatin binding to histidine in hen egg-white lysozyme (HEWL) showed a partial chemical conversion of carboplatin to cisplatin owing to the high sodium chloride concentration used in the crystallization conditions. Also, the co-crystallization of HEWL with carboplatin in sodium bromide conditions resulted in the partial conversion of carboplatin to the transbromoplatin form, with a portion of the cyclobutanedicarboxylate (CBDC) moiety still present. The results of the co-crystallization of HEWL with cisplatin or carboplatin in sodium iodide conditions are now reported in order to determine whether the cisplatin and carboplatin converted to the iodo form, and whether this took place in a similar way to the partial conversion of carboplatin to cisplatin in NaCl conditions or to transbromoplatin in NaBr conditions as seen previously. It is reported here that a partial chemical transformation has taken place to a transplatin form for both ligands. The NaI-grown crystals belonged to the monoclinic space group P21 with two molecules in the asymmetric unit. The chemically transformed cisplatin and carboplatin bind to both His15 residues, i.e. in each asymmetric unit. The binding is only at the N? atom of His15. A third platinum species is also seen in both conditions bound in a crevice between symmetry-related molecules. Here, the platinum is bound to three I atoms identified based on their anomalous difference electron densities and their refined occupancies, with the fourth bound atom being a Cl atom (in the cisplatin case) or a portion of the CBDC moiety (in the carboplatin case). PMID:25195879

Tanley, Simon W. M.; Helliwell, John R.

2014-01-01

318

Conditions for tunnel formation in LPCVD (low pressure chemical vapor deposition) tungsten films on single crystal silicon  

SciTech Connect

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, concentration, and infusion method, dry and wet etch pretreatment, deposition temperature, reaction sequence, deposition time and phase of the tungsten film have all been studied. Three deposition techniques (two selective and one non-selective) have been identified which avoid tunnel formation for the wafer conditions considered in this investigation, thus providing an operational regime in which tunnel formation is not an issue. 14 refs., 10 figs., 1 tab.

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

1987-01-01

319

Atmospheric Pressure Dielectric Barrier Discharges Under Unipolar and Bipolar HV Excitation in View of Chemical Reactivity in Afterglow Conditions  

Microsoft Academic Search

This paper deals with atmospheric pressure DBDs driven under unipolar and bipolar pulsed excitation, in a context of chemical reactivity in flowing afterglow conditions. The resulting discharges in air and nitrogen are examined via electrical and optical diagnostics. Then, their yield in the production of active species (ozone for the air afterglow-atomic Nitrogen and N2(A) metastables for the N2 afterglow)

Emanuel Panousis; Nofel Merbahi; Franck Clement; Andre Ricard; Mohammed Yousfi; Leberis Papageorghiou; Jean-Francis Loiseau; Olivier Eichwald; Bernard Held; Nicolas Spyrou

2009-01-01

320

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

321

The effect of chemicals released by Gammarus lacustris on the depth distribution of Arctodiaptomus salinus in laboratory conditions  

Microsoft Academic Search

The effect of treatment water containing chemicals released by Gammarus lacustris or crushed\\/injured Arctodiaptomus salinus induced changes in vertical distribution of Arctodiaptomus in laboratory conditions. With food concentration in the medium corresponding to the maximum of algae concentration in Shira lake, A. salinus in an experimental vessel was situated higher than in the control. Average population depth of A. salinus decreased as

Yegor S. Zadereev; Michael V. Gubanov

2002-01-01

322

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

323

Dependence of electro-optical properties on the deposition conditions of chemical bath deposited CdS thin films  

SciTech Connect

Lately, there has been a sharp increase in the publication of papers on chemical bath deposition of CdS thin films and related materials due to successful results obtained using this method to fabricate CdS thin-film buffer layers for CuInSe{sub 2}- and CdTe-based polycrystalline thin-film solar cells. Generally, these papers focus on previously proposed methods of studying film characteristics without a systematic study of the influence of deposition conditions on film characteristics. In this paper the authors present an exhaustive study of the chemical bath-deposited CdS thin films electro-optical properties dependence on deposition variables. The authors propose not only a set of conditions for obtaining CdS thin films by this method but additionally, suitable deposition process conditions for certain application requirements, such as buffer layers for thin-film solar cells. The observed electro-optical characteristics dependence on the deposition variables corroborates the chemical mechanism that they proposed previously for this process.

Dona, J.M.; Herrero, J. [CIEMAT, Madrid (Spain). Inst. de Energias Renovables

1997-11-01

324

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

PubMed

Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural environment, including transport and dilution effects. To achieve this goal, Fisheries and Oceans Canada and the US Environmental Protection Agency (EPA) designed and constructed a wave tank system to study chemical dispersant effectiveness under controlled mixing energy conditions (regular non-breaking, spilling breaking, and plunging breaking waves). Quantification of oil dispersant effectiveness was based on observed changes in dispersed oil concentrations and oil-droplet size distribution. The study results quantitatively demonstrated that total dispersed oil concentration and breakup kinetics of oil droplets in the water column were strongly dependent on the presence of chemical dispersants and the influence of breaking waves. These data on the effectiveness of dispersants as a function of sea state will have significant implications in the drafting of future operational guidelines for dispersant use at sea. PMID:18325540

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

2008-05-01

325

THE JOURNAL OF CHEMICAL PHYSICS 134, 154503 (2011) pH-dependent x-ray absorption spectra of aqueous boron oxides  

E-print Network

- ommendation is the excess water required for hydration of hydrolysis reaction products--borate [B(OH)4-ray absorption fine structure (NEXAFS) spectra at the boron K-edge were measured for aqueous boric acid, borate reveal that water is arranged nearly isotrop- ically around boric acid and sodium borate

Cohen, Ronald C.

2011-01-01

326

All-aqueous multiphase microfluidics  

PubMed Central

Immiscible aqueous phases, formed by dissolving incompatible solutes in water, have been used in green chemical synthesis, molecular extraction and mimicking of cellular cytoplasm. Recently, a microfluidic approach has been introduced to generate all-aqueous emulsions and jets based on these immiscible aqueous phases; due to their biocompatibility, these all-aqueous structures have shown great promises as templates for fabricating biomaterials. The physico-chemical nature of interfaces between two immiscible aqueous phases leads to unique interfacial properties, such as an ultra-low interfacial tension. Strategies to manipulate components and direct their assembly at these interfaces needs to be explored. In this paper, we review progress on the topic over the past few years, with a focus on the fabrication and stabilization of all-aqueous structures in a multiphase microfluidic platform. We also discuss future efforts needed from the perspectives of fluidic physics, materials engineering, and biology for fulfilling potential applications ranging from materials fabrication to biomedical engineering. PMID:24454609

Song, Yang; Sauret, Alban; Cheung Shum, Ho

2013-01-01

327

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

EPA Science Inventory

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

328

Low-thrust chemical propulsion system propellant expulsion and thermal conditioning study. Executive summary  

NASA Technical Reports Server (NTRS)

Preferred techniques for providing abort pressurization and engine feed system net positive suction pressure (NPSP) for low thrust chemical propulsion systems (LTPS) were determined. A representative LTPS vehicle configuration is presented. Analysis tasks include: propellant heating analysis; pressurant requirements for abort propellant dump; and comparative analysis of pressurization techniques and thermal subcoolers.

Merino, F.; Wakabayashi, I.; Pleasant, R. L.; Hill, M.

1982-01-01

329

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

2013-01-01

330

Boundary conditions for the paleoenvironment: Chemical and Physical Processes in dense interstellar clouds  

NASA Technical Reports Server (NTRS)

The present research includes searches for important new interstellar constituents; observations relevant to differentiating between different models for the chemical processes that are important in the interstellar environment; and coordinated studies of the chemistry, physics, and dynamics of molecular clouds which are the sites or possible future sites of star formation. Recent research has included the detection and study of four new interstellar molecules; searches which have placed upper limits on the abundance of several other potential constituents of interstellar clouds; quantitative studies of comparative molecular abundances in different types of interstellar clouds; investigation of reaction pathways for astrochemistry from a comparison of theory and the observed abundance of related species such as isomers and isotopic variants; studies of possible tracers of energenic events related to star formation, including silicon and sulfur containing molecules; and mapping of physical, chemical, and dynamical properties over extended regions of nearby cold molecular clouds.

Irvine, W. M.; Schloerb, F. P.; Ziurys, L. M.

1986-01-01

331

Toxicity of Selected Chemicals to the Fairy Shrimp, Streptocephalus seali, under Laboratory and Field Conditions  

Microsoft Academic Search

Laboratory toxicity tests were conducted with six chemicals to determine their effect on fairy shrimp (Streptocephalus seali). Formalin (15 and 25 mg\\/1) and Diquat (0.25 to 2.0 mg\\/1) were not toxic to fairy shrimp. Paraquat (0.25 to 2.0 mg\\/1) and benzene hexachloride (0.10 and 0.25 mg\\/1) were moderately toxic. Dylox (0.10 and 0.25 mg\\/1) was highly toxic; mortality exceeded 82%

Jerry L. Moss

1978-01-01

332

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

333

Zooplankton diversity and physico-chemical conditions in three perennial ponds of Virudhunagar district, Tamilnadu.  

PubMed

Plankton diversity and physico-chemical parameters are an important criterion for evaluating the suitability of water for irrigation and drinking purposes. In this study we tried to assess the zooplankton species richness, diversity and evenness and to predict the state of three perennial ponds according to physico-chemical parameters. A total of 47 taxa were recorded: 24 rotifers, 9 copepods, 8 cladocerans, 4 ostracods and 2 protozoans. More number of zooplankton species were recorded in Chinnapperkovil pond (47 species) followed by Nallanchettipatti (39 species) and Kadabamkulam pond (24 species). Among the rotifers, Branchionus sp. is abundant. Diaphanosoma sp. predominant among the cladocerans. Among copepods, numerical superiority was found in the case of Mesocyclopes sp. Cypris sp. repeated abundance among ostracoda. Present study revealed that zooplankton species richness (R1 and R2) was comparatively higher (R1: 4.39; R2: 2.13) in Chinnapperkovil pond. The species diversity was higher in the Chinnapperkovil pond (H': 2.53; N1: 15.05; N2: 15.75) as compared to other ponds. The water samples were analyzed for temperature, pH, electrical conductivity alkalinity salinity, phosphate, hardness, dissolved oxygen and biological oxygen demand. Higher value of physico-chemical parameters and zooplankton diversity were recorded in Chinnapperkovil pond as compared to other ponds. The zooplankton population shows positive significant correlation with physico-chemical parameters like, temperature, alkalinity phosphate, hardness and biological oxygen demand, whereas negatively correlated with rainfall and salinity. The study revealed that the presence of certain species like, Monostyla sp., Keratella sp., Lapadella sp., Leydigia sp., Moinodaphnia sp., Diaptomus sp., Diaphanosoma sp., Mesocyclopes sp., Cypris sp. and Brachionus sp. is considered to be biological indicator for eutrophication. PMID:21046994

Rajagopal, T; Thangamani, A; Sevarkodiyone, S P; Sekar, M; Archunan, G

2010-05-01

334

Factors influencing the dressing rate of chemical mechanical polishing pad conditioning  

Microsoft Academic Search

The primary consumables in the chemical mechanical polishing (CMP) process are the polishing pad and the slurry. Among those\\u000a consumables, the polishing pad significantly influences the stability of the process and the cost of consumables (CoC). Furthermore,\\u000a the small holes on the pad surface will be filled by the reactant from the CMP process, and the surface of the pad

Pei-Lum Tso; Shuo-Young Ho

2007-01-01

335

A Study on the Aqueous Formation of Secondary Organic Aerosols  

NASA Astrophysics Data System (ADS)

The effect aerosols have on radiative forcing in the atmosphere is recognized as one of the largest uncertainties in the radiation budget. About 80% of organic aerosol mass in the atmosphere is estimated to be created though secondary processes. Recently, the aqueous formation of secondary organic aerosols (SOA) has become recognized as important when considering the source, transformation and radiative impacts of SOA. This work focuses on implementing a mechanism for aqueous SOA formation that can be used in atmospheric chemistry and models of all scales, from box to global. A box model containing a simplified chemical mechanism for the aqueous production of precursors of aqueous SOA (Myriokefalitakis et al. (2011) is coupled to gas-phase chemistry which uses the carbon bond mechanism (CBM) IV is presented. The model implements aqueous chemistry of soluble gases, both in-cloud and aerosol water, including organic compounds such as glyoxal and methylglyoxal, which have been shown as potentially significant sources for dissolved secondary organic aerosols. This mechanism implements aqueous phase mass transfer and molecular dissociation. The model's performance is evaluated against previous box model studies from the literature. A comparison is conducted between the detailed GAMMA model (McNeill et al., 2012), which is constrained with chamber experiments and the one developed here. The model output under different atmospheric conditions is explored and differences and sensitivities are assessed. The objective of this work is to create a robust framework for simulating aqueous phase formation of SOA and maximizing the computational efficiency of the model, while maintaining accuracy, in order to later use the exact mechanism in global climate simulations.

Sinclair, K.; Tsigaridis, K.

2013-12-01

336

The IUPAC aqueous and non-aqueous experimental pKa data repositories of organic acids and bases.  

PubMed

Accurate and well-curated experimental pKa data of organic acids and bases in both aqueous and non-aqueous media are invaluable in many areas of chemical research, including pharmaceutical, agrochemical, specialty chemical and property prediction research. In pharmaceutical research, pKa data are relevant in ligand design, protein binding, absorption, distribution, metabolism, elimination as well as solubility and dissolution rate. The pKa data compilations of the International Union of Pure and Applied Chemistry, originally in book form, have been carefully converted into computer-readable form, with value being added in the process, in the form of ionisation assignments and tautomer enumeration. These compilations offer a broad range of chemistry in both aqueous and non-aqueous media and the experimental conditions and original reference for all pKa determinations are supplied. The statistics for these compilations are presented and the utility of the computer-readable form of these compilations is examined in comparison to other pKa compilations. Finally, information is provided about how to access these databases. PMID:24952470

Slater, Anthony Michael

2014-10-01

337

Rapid screening procedures for the hydrolysis products of chemical warfare agents using positive and negative ion liquid chromatography–mass spectrometry with atmospheric pressure chemical ionisation  

Microsoft Academic Search

Qualitative screening procedures have been developed for the rapid detection and identification of the hydrolysis products of chemical warfare agents in aqueous samples and extracts, using liquid chromatography–mass spectrometry with positive and negative atmospheric pressure chemical ionisation (APCI). Previously reported screening procedures, which used positive APCI or electrospray ionisation (ESI), were modified by using LC conditions that allowed acquisition of

Robert W Read; Robin M Black

1999-01-01

338

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.-Ming; Burruss, R.C.; Yang, M.Z.

2006-01-01

339

Constant-trace anomaly as a universal condition for the chemical freeze-out  

NASA Astrophysics Data System (ADS)

Finding out the universal conditions describing the freeze-out parameters has been the subject of various phenomenological studies. In the present work, we introduce a new condition based on constant-trace anomaly (or interaction measure) calculated in the hadron resonance gas (HRG) model. Various extensions to the ideal HRG which are conjectured to take into consideration different types of interactions have been analyzed. When comparing HRG thermodynamics to that of lattice quantum chromodynamics, we conclude that the hard-core radii are practically irrelevant, especially when HRG includes all resonances with masses less than 2 GeV. It is found that the constant-trace anomaly (or interaction measure) agrees well with most previous conditions.

Tawfik, A.

2013-09-01

340

Effect of pedoclimatic conditions on the chemical composition of the Sigoise olive cultivar.  

PubMed

The present work focused on the quality and the chemical composition of monovarietal virgin olive oil from the Sigoise variety grown in two different locations in Tunisia, viz., a sub-humid zone (Béjaoua, Tunis) and an arid zone (Boughrara, Sfax). In addition to the quality characteristics (acidity, peroxide value, and the spectrophotometric indices K232 and K270) and the chemical composition (content of fatty acids, antioxidants, and volatile compounds) of the oil, the fruit characteristics of the olives were studied. Except for the content of the majority of the fatty acids, there were significant differences observed in the oil composition of olives that were cultivated in different locations. The content of total phenols and lipoxygenase (LOX) oxidation products was higher for olives grown at the higher altitude, whereas that of alpha-tocopherol, carotenes, and chlorophylls was higher for olives from the Boughrara region (lower altitude). Moreover, olives produced at the higher altitude showed a higher ripeness index and oil content than those cultivated at the lower altitude. PMID:20397230

Dabbou, Samia; Sifi, Samira; Rjiba, Imed; Esposto, Sonia; Taticchi, Agnese; Servili, Maurizio; Montedoro, Gian Francesco; Hammami, Mohamed

2010-04-01

341

Determination of formal kinetic constants of thermal decomposition of aqueous hydrogen peroxide solution in a mixture of magnetic powder, based on experimental thermogram, obtained in adiabatic conditions  

NASA Astrophysics Data System (ADS)

Process of thermal decomposition of hydrogen peroxide aqueous solution with the addition of magnetic powder in the form of toner for printers and lanthanum manganite were considered. Obtained resulting from an experiment in the Dewar container conducted thermogram analyzed using mass balance equations and heat. Formal kinetic parameters determined, and conclude that the magnetic powder in the mixture does not have catalytic properties. The described technique is recommended as a rapid analysis of the kinetics of the various reactions to substances having predefined thermal and thermodynamic properties.

Zaripov, Jamshed; Borisov, Boris; Bondarchuk, Sergey

2014-08-01

342

Development and Analysis of a High-Pressure Micro Jet Pad Conditioning System for Interlayer Dielectric Chemical Mechanical Planarization  

NASA Astrophysics Data System (ADS)

Conventional diamond disc pad conditioning methods employed in chemical mechanical planarization (CMP) have presented several problems for integrated circuit (IC) manufacturers. These include diamond wear, which reduces pad life, and diamond fracture, which causes the semiconductor devices to be scratched by loose diamond fragments. In order to attempt to overcome these problems, a high-pressure micro jet (HPMJ) conditioning system, in which pressurized ultra pure water (UPW) ranging from 3-30 MPa is sprayed on the pad surface, is proposed and developed. This study first analyzes the extent of the kinetic energy of water droplets ejecting from the HPMJ system and its utility in conditioning the pad surface. Subsequently, CMP is used to polish interlayer dielectric (ILD) films using both conventional diamond discs as well as HPMJ conditioning methods. Results, reported in the form of coefficient of friction (COF), removal rate, pad surface roughness and pad surface quality, highlight both the advantages as well as disadvantages of the HPMJ method compared to conventional conditioning schemes.

Seike, Yoshiyuki; DeNardis, Darren; Sugiyama, Masano; Miyachi, Keiji; Doi, Toshiro; Philipossian, Ara

2005-03-01

343

Monitoring and physical-chemical modeling of conditions of natural surface and underground waters forming in the Kola North.  

PubMed

Processes of surface and underground water forming in the Khibiny massif have been studied using a physical-chemical model of the "water-rock-atmosphere-organic substance" system. The obtained model solutions are indicative of the fact that formation of surface and underground water of the Khibiny massif takes place on the whole in the framework of the considered system without attracting a hypothetical outside source of pollutants. The results are of practical and methodological importance for assessment of prediction of the man-induced impact on water systems in conditions of Subarctic. PMID:22416860

Mazukhina, Svetlana I; Masloboev, Vladimir A; Chudnenko, Konstantin V; Bychinsky, Valeriy A; Svetlov, Anton V; Muraviev, Sergey V

2012-01-01

344

A comparison of conditional random fields and structured support vector machines for chemical entity recognition in biomedical literature  

PubMed Central

Background Chemical compounds and drugs (together called chemical entities) embedded in scientific articles are crucial for many information extraction tasks in the biomedical domain. However, only a very limited number of chemical entity recognition systems are publically available, probably due to the lack of large manually annotated corpora. To accelerate the development of chemical entity recognition systems, the Spanish National Cancer Research Center (CNIO) and The University of Navarra organized a challenge on Chemical and Drug Named Entity Recognition (CHEMDNER). The CHEMDNER challenge contains two individual subtasks: 1) Chemical Entity Mention recognition (CEM); and 2) Chemical Document Indexing (CDI). Our study proposes machine learning-based systems for the CEM task. Methods The 2013 CHEMDNER challenge organizers provided a manually annotated 10,000 UTF8-encoded PubMed abstracts according to a predefined annotation guideline: a training set of 3,500 abstracts, a development set of 3,500 abstracts and a test set of 3,000 abstracts. We developed machine learning-based systems, based on conditional random fields (CRF) and structured support vector machines (SSVM) respectively, for the CEM task for this data set. The effects of three types of word representation (WR) features, generated by Brown clustering, random indexing and skip-gram, on both two machine learning-based systems were also investigated. The performance of our system was evaluated on the test set using scripts provided by the CHEMDNER challenge organizers. Primary evaluation measures were micro Precision, Recall, and F-measure. Results Our best system was among the top ranked systems with an official micro F-measure of 85.05%. Fixing a bug caused by inconsistent features marginally improved the performance (micro F-measure of 85.20%) of the system. Conclusions The SSVM-based CEM systems outperformed the CRF-based CEM systems when using the same features. Each type of the WR feature was beneficial to the CEM task. Both the CRF-based and SSVM-based systems using the all three types of WR features showed better performance than the systems using only one type of the WR feature.

2015-01-01

345

Properties of chemical bath deposited CdS films at different annealing conditions  

SciTech Connect

The preparation of cubic CdS thin films with low resistivity by Chemical Bath Deposition (CBD) technique and subsequent annealings in S{sub 2} and H{sub 2}+ In is reported. Low temperature photoluminescence, x-rays and transmission spectra support the assumption that sulfur annealings contribute to fill the vacancies in the as-deposited films leading to an enlargement of the CdS cubic cell. This fact is revealed by increase in interplanar distances, evanescence of the PL red broad band and decrease in band gap energies. Cubic phase remains after H{sub 2}+ In annealing at higher temperatures. A resistivity as low as 11 {Omega}-cm was obtained at an optimum annealing temperature of 350{degree}C. {copyright} {ital 1996 American Institute of Physics.}

de Melo, O.; Hernandez, L.; Zelaya-Angel, O.; Lozada-Morales, R. [Physics Department, CINVESTAV-IPN, Aptdo. 14-740, 07000 (Mexico) D.F.; Vasco, E.; Puron, E. [Physics Faculty, University of Havana, 10400 La Habana (Cuba)

1996-07-01

346

Conditional glycosylation in eukaryotic cells using a biocompatible chemical inducer of dimerization.  

PubMed

Chemical inducers of dimerization (CIDs) are cell-permeable small molecules capable of dimerizing two protein targets. The most widely used CID, the natural product rapamycin and its relatives, is immunosuppressive due to interactions with endogenous targets and thus has limited utility in vivo. Here we report a new biocompatible CID, Tmp-SLF, which dimerizes E. coli DHFR and FKBP and has no endogenous mammalian targets that would lead to unwanted in vivo side effects. We employed Tmp-SLF to modulate gene expression in a yeast three-hybrid assay. Finally, we engineered the Golgi-resident glycosyltransferase FucT7 for tunable control by Tmp-SLF in mammalian cells. PMID:18788807

Czlapinski, Jennifer L; Schelle, Michael W; Miller, Lawrence W; Laughlin, Scott T; Kohler, Jennifer J; Cornish, Virginia W; Bertozzi, Carolyn R

2008-10-01

347

Conditional Glycosylation in Eukaryotic Cells Using a Biocompatible Chemical Inducer of Dimerization  

PubMed Central

Chemical inducers of dimerization (CIDs) are cell-permeable small molecules capable of dimerizing two protein targets. The most widely used CID, the natural product rapamycin and its relatives, is immunosuppressive due to interactions with endogenous targets and thus has limited utility in vivo. Here we report a new biocompatible CID, Tmp-SLF, which dimerizes E. coli DHFR and FKBP and has no endogenous mammalian targets that would lead to unwanted in vivo side effects. We employed Tmp-SLF to modulate gene expression in a yeast three-hybrid assay. Finally, we engineered the Golgi-resident glycosyltransferase FucT7 for tunable control by Tmp-SLF in mammalian cells. PMID:18788807

2008-01-01

348

Influence of Aqueous-Salt Conditions on the Structure and Dynamics of the Monomeric and Novel Dimeric forms of the Alzheimer s ABeta21-30 protein fragment  

NASA Astrophysics Data System (ADS)

The behavior of the Alzheimer's related peptide Abeta is the subject of much study. In typical computational studies the environment local to the peptide is assumed to be pure water; however, in vivo the peptide is found in the extracellular space near the plasma membrane which is rich in ionic species. In this thesis, the hypothesis that the presence of group I/IIA salts will result in increased sampling of disordered structures as well as modify the dynamics of meta-stable structural motifs in the small folding nucleus of the Abeta peptide (Abeta21-30) is examined under a variety of ionic environments and was shown that of the tested salts, CaCl2 (and MgCl2, to a much lesser degree) did increase the propensity for disordered states; while, the group IA salts, KCl and NaCl, had little effect on the secondary structure of the peptide. Further, study of three familial mutations of this peptide region is also performed under aqueous salt-environments to elucidate further mechanistic details of how aqueous salts modify the region's behavior. Finally, as experimental results have highlighted that aggregation rates of the full-length peptide are modified by the presence of CaCl2, this work examines novel dimers states of Abeta21-30 and their stabilities when exposed to CaCl2.

Smith, Micholas Dean

349

Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical  

NASA Astrophysics Data System (ADS)

Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (\\centerdot OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than \\centerdot OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

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

2014-08-01

350

Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical  

NASA Astrophysics Data System (ADS)

Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.

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

2014-12-01

351

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

352

Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical  

SciTech Connect

Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (•OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), desorption electrospray ionization mass spectrometry (DESIMS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O/C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than •OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O/C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

Yu, Lu; Smith, Jeremy; Laskin, Alexander; Anastasio, Cort N.; Laskin, Julia; Zhang, Qi

2014-12-23

353

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

NASA Astrophysics Data System (ADS)

Two instrumental setups for in situ soft X-ray absorption spectroscopy in liquid systems are demonstrated in this work. One for investigating chemical reactions in solutions and a new one for the solid component of a liquid / (as in both / absorber) solid interface. We used these setups for investigating two production processes for chalcopyrite solar cells under ambient conditions, probing the L-edge of Zn and Cu. The first one is a flow cell with a silicon nitride membrane to study the chemical bath deposition process for Cd-free buffer layers. Examining the electronic structure of involved Zn complexes allows to determine the exact reaction mechanism taking place during this process. The second setup is a rotating disk for investigating the bath/absorber interface upon the etching process of superficial binary copper compounds of the absorber as a function of time. The time resolution of the chemical reaction demonstrated in this study ranges from the second to minute time scale.

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

2010-02-01

354

Mars aqueous chemistry experiment  

NASA Technical Reports Server (NTRS)

Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. The second year of the MACE project has shown significant progress in two major areas. MACE Instrument concept definition is a baseline design that has been generated for the complete MACE instrument, including definition of analysis modes, mass estimates and thermal model. The design includes multiple reagent reservoirs, 10 discrete analysis cells, sample manipulation capability, and thermal control. The MACE Measurement subsystems development progress is reported regarding measurement capabilities for aqueous ion sensing, evolved gas sensing, solution conductivity measurement, reagent addition (titration) capabilities, and optical sensing of suspended particles.

Clark, Benton C.; Mason, Larry W.

1994-01-01

355

Effects of oxidizing agent and hydrodynamic condition on copper dissolution in chemical mechanical polishing electrolytes  

Microsoft Academic Search

The effects of H2O2 and Fe(NO3)3 on the electrochemical behavior, dissolution rate and surface characteristics of Cu in static and under rotating conditions were investigated. Rotating cylinder electrodes were used for potentiodynamic polarization curves measurements in 0.0078M citric acid (CA) base electrolytes with various concentration of H2O2 (0–12vol.%) and Fe(NO3)3 (0–0.2M). The rotating speed was varied in the range of

Jui-Chin Chen; Shiou-Ru Lin; Wen-Ta Tsai

2004-01-01

356

Investigations of chemical fraction of Co and Ni in industrial fly ash and mobility of metals in environmental conditions.  

PubMed

The quantitative evaluation of chemical fraction of Co and Ni in the industrial fly ash by methods of five step sequential extraction was carried out in order to characterize metal mobility in environmental conditions. The research involved (i) water-soluble (pH=7), (ii) acid-soluble (pH=5), (iii) oxide, (iv) sulfide and (v) residue metal fractions. It was discovered, that the total extraction of the studied metals from fly ash to solutions take place in the following quantities Co - 35.5 and Ni - 153.0mgkg(-1). The investigations of chemical fractions proved that the subject metals occur mainly in fly ash as: oxide (Co - 7.0, Ni - 28.5mgkg(-1)) and residue (Co - 11.5, Ni - 42.5mgkg(-1)) as well as sulfide (Co - 8.5, Ni - 46.5mgkg(-1)). Low concentrations of metals for water-soluble fraction (Co - 0.7, Ni - 1.2mgkg(-1)) and acid-soluble fraction (Co - 4.5, Ni - 23.5mgkg(-1)) were observed. The fractions of Co and Ni leachable from the ash in environmental conditions contain: 24.0% (Co) and 23.3% (Ni) of metal total amount in the industrial fly ash. The obtained mobility parameter of Co and Ni can be applied to estimate the concentration increase of mobile and hardly mobile forms of these metals in soil polluted with the ash. PMID:17150241

Soco, Eleonora; Kalembkiewicz, Jan

2007-02-01

357

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

358

Effect of seepage conditions on chemical attenuation of arsenic by soils across an abandoned mine site.  

PubMed

The effect of seepage velocity on the As leaching/adsorption by soils collected from abandoned mine sites was evaluated under batch equilibrium and different seepage settings. The breakthrough curves (BTCs) of As leaching from the mine soil column initially displayed the peak export and gradually leveled off over the leaching experiment. A similar As peak was observed after a flow interruption period. Adsorption by downgradient soils was clearly nonlinear, as Freundlich N was <1. In the BTCs of the layered columns, where downgradient soils were overloaded above the mine soil, the extended lag period of As appearance and lower steady-state As concentration observed for slow seepage velocity supported the idea of kinetically limited As attenuation driven by soil adsorption. The perturbation of As concentration was insignificant when the intra-column As concentration gradient was higher. The As concentration drop and time to recovery were greater for less adsorptive soil and fast seepage velocity. Desorption of As from soils retrieved from both batch adsorption and column experiment demonstrate hysteric behavior. The results of this work demonstrated that the risk of As leaching from an abandoned mine site can be greatly attenuated by intermediate downgradient soils via chemical adsorption, which tends to be kinetically limited and energetically hysteric (i.e., non-identical energy pathway). PMID:22300557

Hyun, Seunghun; Kim, Juhee; Kim, Dae-Young; Moon, Deok Hyun

2012-05-01

359

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

PubMed Central

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 that supports efficient self-renewal of hESCs grown on a Matrigel-coated surface over multiple passages. Expanded hESCs under such conditions maintain expression of multiple hESC-specific markers, retain the characteristic hESC morphology, possess a normal karyotype in vitro, as well as develop teratomas in vivo. Additionally, several growth factors were found to selectively induce monolayer differentiation of hESC cultures toward neural, definitive endoderm/pancreatic and early cardiac muscle cells, respectively, in our CDM conditions. Therefore, this CDM condition provides a basic platform for further characterization of hESC self-renewal and directed differentiation, as well as the development of novel therapies. PMID:16632596

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

2006-01-01

360

Low-thrust chemical propulsion system propellant expulsion and thermal conditioning study  

NASA Technical Reports Server (NTRS)

Thermal conditioning systems for satisfying engine net positive suction pressure (NPSP) requirements, and propellant expulsion systems for achieving propellant dump during a return-to-launch site (RTLS) abort were studied for LH2/LO2 and LCH4/LO2 upper stage propellant combinations. A state-of-the-art thermal conditioning system employing helium injection beneath the liquid surface shows the lowest weight penalty for LO2 and LCH4. A technology system incorporating a thermal subcooler (heat exchanger) for engine NPSP results in the lowest weight penalty for the LH2 tank. A preliminary design of two state-of-the-art and two new technology systems indicates a weight penalty difference too small to warrant development of a LH2 thermal subcooler. Analysis results showed that the LH2/LO2 propellant expulsion system is optimized for maximum dump line diameters, whereas the LCH4/LO2 system is optimized for minimum dump line diameter (LCH4) and maximum dump line diameter (LO2). The primary uncertainty is the accurate determination of two-phase flow rates through the dump system; experimentation is not recommended because this uncertainty is not considered significant.

Merino, F.; Wakabayashi, I.; Pleasant, R. L.; Hill, M.

1982-01-01

361

Collisions of small ice particles under microgravity conditions. II. Does the chemical composition of the ice change the collisional properties?  

NASA Astrophysics Data System (ADS)

Context. Understanding the collisional properties of ice is important for understanding both the early stages of planet formation and the evolution of planetary ring systems. Simple chemicals such as methanol and formic acid are known to be present in cold protostellar regions alongside the dominant water ice; they are also likely to be incorporated into planets which form in protoplanetary disks, and planetary ring systems. However, the effect of the chemical composition of the ice on its collisional properties has not yet been studied. Aims: Collisions of 1.5 cm ice spheres composed of pure crystalline water ice, water with 5% methanol, and water with 5% formic acid were investigated to determine the effect of the ice composition on the collisional outcomes. Methods: The collisions were conducted in a dedicated experimental instrument, operated under microgravity conditions, at relative particle impact velocities between 0.01 and 0.19 ms-1, temperatures between 131 and 160 K and a pressure of around 10-5 mbar. Results: A range of coefficients of restitution were found, with no correlation between this and the chemical composition, relative impact velocity, or temperature. Conclusions: We conclude that the chemical composition of the ice (at the level of 95% water ice and 5% methanol or formic acid) does not affect the collisional properties at these temperatures and pressures due to the inability of surface wetting to take place. At a level of 5% methanol or formic acid, the structure is likely to be dominated by crystalline water ice, leading to no change in collisional properties. The surface roughness of the particles is the dominant factor in explaining the range of coefficients of restitution.

Hill, C. R.; Heißelmann, D.; Blum, J.; Fraser, H. J.

2015-03-01

362

Effects of Atmospheric Conditions and the Land/Atmospheric Interface on Transport of Chemical Vapors from Subsurface Sources  

NASA Astrophysics Data System (ADS)

Understanding the movement of chemical vapors and gas through variably saturated soil subjected to atmospheric thermal and mass flux boundary conditions at the land/atmospheric interface is important to many applications, including landmine detection, methane leakage during natural gas production from shale and CO2 leakage from deep geologic storage. New, advanced technologies exist to sense chemical signatures and gas leakage at the land/atmosphere interface, but interpretation of sensor signals remains a challenge. Chemical vapors are subject to numerous interactions while migrating through the soil environment, masking source conditions. The process governing movement of gases through porous media is often assumed to be Fickian diffusion through the air phase with minimal quantification of other processes, such as convective gas flow and temporal or spatial variation in soil moisture. Vapor migration is affected by atmospheric conditions (e.g. humidity, temperature, wind velocity), soil thermal and hydraulic properties and contaminant properties, all of which are physically and thermodynamically coupled. The complex coupling of two drastically different flow regimes in the subsurface and atmosphere is commonly ignored in modeling efforts, or simplifying assumptions are made to treat the systems as de-coupled. Experimental data under controlled laboratory settings are lacking to refine the theory for proper coupling and complex treatment of vapor migration through porous media in conversation with atmospheric flow and climate variations. Improving fundamental understanding and accurate quantification of these processes is not feasible in field settings due to lack of controlled initial and boundary conditions and inability to fully characterize the subsurface at all relevant scales. The goal of this work is to understand the influence of changes in atmospheric conditions to transport of vapors through variably saturated soil. We have developed a tank apparatus with a network of soil and atmospheric sensors and a head space for air flow to simulate the atmospheric boundary layer. Experiments were performed under varying temperature values at the soil surface bounded by the atmospheric boundary layer. The model of Smits et al. [2011], accounting for non-equilibrium phase change and coupled heat, water vapor and liquid water flux through soil, was amended to include organic vapor in the gas phase and migration mechanisms often overlooked in models (thermal and Knudsen diffusion, density driven advection). Experimental results show increased vapor mass flux across the soil/atmospheric interface due to heat applied from the atmosphere and coupling of heat and mass transfer in the shallow subsurface for both steady and diurnal temperature patterns. Comparison of model results to experimental data shows dynamic interactions between transport in porous media and boundary conditions. Results demonstrate the value of considering interactions of the atmosphere and subsurface to better understand chemical gas transport through unsaturated soils and the land/atmospheric interface.

Rice, A. K.; Smits, K. M.; Cihan, A.; Howington, S. E.; Illangasekare, T. H.

2013-12-01

363

Chemical Profiling of Jatropha Tissues under Different Torrefaction Conditions: Application to Biomass Waste Recovery  

PubMed Central

Gradual depletion of the world petroleum reserves and the impact of environmental pollution highlight the importance of developing alternative energy resources such as plant biomass. To address these issues, intensive research has focused on the plant Jatropha curcas, which serves as a rich source of biodiesel because of its high seed oil content. However, producing biodiesel from Jatropha generates large amounts of biomass waste that are difficult to use. Therefore, the objective of our research was to analyze the effects of different conditions of torrefaction on Jatropha biomass. Six different types of Jatropha tissues (seed coat, kernel, stem, xylem, bark, and leaf) were torrefied at four different temperature conditions (200°C, 250°C, 300°C, and 350°C), and changes in the metabolite composition of the torrefied products were determined by Fourier transform-infrared spectroscopy and nuclear magnetic resonance analyses. Cellulose was gradually converted to oligosaccharides in the temperature range of 200°C–300°C and completely degraded at 350°C. Hemicellulose residues showed different degradation patterns depending on the tissue, whereas glucuronoxylan efficiently decomposed between 300°C and 350°C. Heat-induced depolymerization of starch to maltodextrin started between 200°C and 250°C, and oligomer sugar structure degradation occurred at higher temperatures. Lignin degraded at each temperature, e.g., syringyl (S) degraded at lower temperatures than guaiacyl (G). Finally, the toxic compound phorbol ester degraded gradually starting at 235°C and efficiently just below 300°C. These results suggest that torrefaction is a feasible treatment for further processing of residual biomass to biorefinery stock or fertilizer. PMID:25191879

Watanabe, Taiji; Shino, Amiu; Akashi, Kinya; Kikuchi, Jun

2014-01-01

364

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...

365

Physical and chemical conditions in methanol maser selected hot cores and UCHII regions  

NASA Astrophysics Data System (ADS)

We present the results of a targeted 3-mm spectral line survey towards the eighty-three 6.67GHz methanol maser selected star-forming clumps observed by Purcell. In addition to the previously reported measurements of HCO+(1-0), H13CO+(1-0) and CH3CN(5-4) and (6-5), we used the Mopra antenna to detect emission lines of N2H+(1-0), HCN(1-0) and HNC(1-0) towards 82/83 clumps (99 per cent), and CH3OH(2-1) towards 78/83 clumps (94 per cent). The molecular line data have been used to derive virial and local thermodynamic equilibrium masses, rotational temperatures and chemical abundances in the clumps, and these properties have been compared between subsamples associated with different indicators of evolution. The greatest differences are found between clumps associated with 8.6GHz radio emission, indicating the presence of an Ultra-Compact HII (UCHII) region, and `isolated' masers (without associated radio emission), and between clumps exhibiting CH3CN emission and those without. In particular, thermal CH3OH is found to be brighter and more abundant in UCHII regions and in sources with detected CH3CN, and may constitute a crude molecular clock in single dish observations. Clumps associated with 8.6GHz radio emission tend to be more massive and more luminous than clumps without radio emission. This is likely because the most massive clumps evolve so rapidly that a Hyper-Compact HII or UCHII region is the first visible tracer of star formation. The gas mass to submm/infrared luminosity relation for the combined sample was found to be L ~ M0.68, considerably shallower than expected for massive main-sequence stars. This implies that the mass of the clumps is comparable to, or greater than, the mass of the stellar content. We also find that the mass of the hot core is correlated with the mass of the clump in which it is embedded.

Purcell, C. R.; Longmore, S. N.; Burton, M. G.; Walsh, A. J.; Minier, V.; Cunningham, M. R.; Balasubramanyam, R.

2009-03-01

366

Effects of oxidizing agent and hydrodynamic condition on copper dissolution in chemical mechanical polishing electrolytes  

NASA Astrophysics Data System (ADS)

The effects of H 2O 2 and Fe(NO 3) 3 on the electrochemical behavior, dissolution rate and surface characteristics of Cu in static and under rotating conditions were investigated. Rotating cylinder electrodes were used for potentiodynamic polarization curves measurements in 0.0078 M citric acid (CA) base electrolytes with various concentration of H 2O 2 (0-12 vol.%) and Fe(NO 3) 3 (0-0.2 M). The rotating speed was varied in the range of 0-3000 rpm. The dissolution rates of Cu were determined using Tafel extrapolation, inductively coupled plasma-mass spectrometry (ICP) solution analysis, and weight loss measurements, depending on the electrolytes involved. The surfaces of specimens after immersion in the electrolytes for a certain period of time were characterized with Auger electron spectroscopy (AES), X-ray photo-electron spectroscopy (XPS), and atomic force microscopy (AFM). The experimental results showed that H 2O 2 with sufficient concentration could promote passivation of Cu in the CA base electrolyte, which was confirmed by AES and XPS. The addition of Fe(NO 3) 3 into the CA base electrolyte did not cause the formation of passive film and its presence enhanced the dissolution rate of Cu. In both H 2O 2 and Fe(NO 3) 3 containing electrolyte, the dissolution rates increased with increasing electrode rotating speed.

Chen, Jui-Chin; Lin, Shiou-Ru; Tsai, Wen-Ta

2004-06-01

367

Impact of operating conditions on the removal of endocrine disrupting chemicals by membrane photocatalytic reactor.  

PubMed

This study focuses on the performance of a submerged membrane photocatalytic reactor for the removal of 17beta-oestradiol (E2) in the presence of humic acid (HA). In addition to the impact of operating parameters, such as membrane pore size, ultraviolet (UV) intensity and hydraulic retention time (HRT), the influence of long-term operation was also assessed by advanced characterization of the fouling layer formed on the membrane. The tighter (0.04 microm) hollow fibre polyvinylydene fluoride (PVDF) membrane was found to exhibit not only higher HA removal than the (0.2 microm) module (85% and 75%, respectively), but also greater transmembrane pressure (TMP) values and higher irreversible fouling. Long-term operation conditions have been simulated by conducting an ageing catalyst process and demonstrated a decrease in performance obtained with time. The artificially aged TiO2 resulted in higher TMP values and lower HA removals (about 10-20% decrease) compared with the non-aged catalyst. For E2 removal in the presence of HA, the passive adsorption of the oestrogen onto the organic matter was found to be significant (40% of the E2 adsorbed after I h), demonstrating the importance of the nature of the water matrix for this type of treatment process. An increase in the UV light intensity was observed to favour the E2 elimination, leading to more than 90% removal when using 64 W combined with PVDF membrane and an HRT of 3 h. PMID:24956801

López Fernández, Raquel; Coleman, Heather M; Le-Clech, Pierre

2014-08-01

368

Conditioned Place Avoidance of Zebrafish (Danio rerio) to Three Chemicals Used for Euthanasia and Anaesthesia  

PubMed Central

Zebrafish are becoming one of the most used vertebrates in developmental and biomedical research. Fish are commonly killed at the end of an experiment with an overdose of tricaine methanesulfonate (TMS, also known as MS-222), but to date little research has assessed if exposure to this or other agents qualifies as euthanasia (i.e. a “good death”). Alternative agents include metomidate hydrochloride and clove oil. We use a conditioned place avoidance paradigm to compare aversion to TMS, clove oil, and metomidate hydrochloride. Zebrafish (n?=?51) were exposed to the different anaesthetics in the initially preferred side of a light/dark box. After exposure to TMS zebrafish spent less time in their previously preferred side; aversion was less pronounced following exposure to metomidate hydrochloride and clove oil. Nine of 17 fish exposed to TMS chose not to re-enter the previously preferred side, versus 2 of 18 and 3 of 16 refusals for metomidate hydrochloride and clove oil, respectively. We conclude that metomidate hydrochloride and clove oil are less aversive than TMS and that these agents be used as humane alternatives to TMS for killing zebrafish. PMID:24505365

Wong, Devina; von Keyserlingk, Marina A. G.; Richards, Jeffrey G.; Weary, Daniel M.

2014-01-01

369

Multiscale Influences on Physical and Chemical Stream Conditions Across Blue Ridge Landscapes  

NASA Astrophysics Data System (ADS)

Streams integrate biogeochemical processes operating at broad to local spatial scales and long term to short term time scales. Humans have extensively altered those processes in North America, with serious consequences for aquatic ecosystems. We collected data on Upper Tennessee River tributaries in North Carolina to: (1) compare landuse and landscape geomorphology with respect to their ability to explain variation in water quality, sedimentation measures, and large woody debris; (2) determine if landscape change over time contributed significantly to explaining present stream conditions; and (3) assess the importance of spatial scale in examining landuse influences on streams. Stream variables were related to both landuse and landscape geomorphology. Forest cover accounted for the most variation in nearly all models, supporting predictions of nutrient enrichment, thermal pollution, and sedimentation caused by landscape disturbance. Legacy effects from past catchment disturbance were apparent in sedimentation measures. Nitrogen and phosphorus concentrations, as well as stream temperature, were lower where riparian buffers had reforested. Models of stream physicochemistry fit better when predictors were catchment wide rather than more localized (i.e., within 2 km of a site). Cumulative impacts to streams due to changes in landuse must be managed from a watershed perspective with quantitative models that integrate across scales.

Scott, Mark C.; Helfman, Gene S.; McTammany, Matthew E.; Benfield, E. Fred; Bolstad, Paul V.

2002-10-01

370

Effects of spray-drying conditions on the chemical, physical, and sensory properties of cheese powder.  

PubMed

Dairy powders are produced to increase the shelf life of fresh dairy products and for use as flavoring agents. In this study, 24 cheese powders produced under 7 different conditions were used to investigate the effects of spray-drying parameters (e.g., inlet air temperature, atomization pressure, and outlet air temperature) on the quality of white cheese powder. Composition, color, physical properties, reconstitution, and sensory characteristics of white cheese powders were determined. The results revealed that the white cheese powders produced in this study had low moisture content ratios and water activity values. High outlet air temperatures caused browning and enhanced Maillard reactions. Additionally, high outlet air temperatures increased wettability and dispersibility and decreased the solubility of white cheese powders. Free fat content was positively correlated with inlet air temperature and negatively correlated with outlet air temperature and atomization pressure. Sensory analyses revealed that white cheese powder samples had acceptable sensory characteristics with the exception of the sample produced at an outlet air temperature of 100°C, which had high scores for scorched flavor and color and low scores for cheese flavor. PMID:25771045

Koca, Nurcan; Erbay, Zafer; Kaymak-Ertekin, Figen

2015-05-01

371

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

2008-05-01

372

Diketopiperazine-mediated peptide formation in aqueous solution  

NASA Astrophysics Data System (ADS)

Though diketopiperazines (DKP) are formed in most experiments concerning the prebiotic peptide formation, the molecules have not been paid attention in the studies of chemical evolution. We have found that triglycine, tetraglycine or pentaglycine are formed in aqueous solution of glycine anhydride (DKP) and glycine, diglycine or triglycine, respectively. A reaction of alanine with DKP resulted in the formation of glycylglycylalanine under the same conditions. These results indicate that the formation of the peptide bonds proceeds through the nucleophilic attack of an amino group of the amino acids or the oligoglycines on the DKP accompanied by the ring-opening. The formation of glycine anhydride, di-, tri- and tetraglycine was also observed in a mixed aqueous solution of urea and glycine in an open system to allow the evaporation of ammonia. A probable pathway is proposed for prebiotic peptide formation through diketopiperazine on the primitive Earth.

Nagayama, M.; Takaoka, O.; Inomata, K.; Yamagata, Y.

1990-05-01

373

Hematite Spherules in Basaltic Tephra Altered Under Aqueous, Acid-Sulfate Conditions on Mauna Kea Volcano, Hawaii: Possible Clues for the Occurrence of Hematite-Rich Spherules in the Burns Formation at Meridiani Planum, Mars  

NASA Technical Reports Server (NTRS)

Iron-rich spherules (>90% Fe2O3 from electron microprobe analyses) approx.10-100 microns in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe/Al ratio than the rim. Oxide totals less than 100% (93-99%) suggest structural H2O and/or /OH. The transmission Moessbauer spectrum of a spherule-rich separate is dominated by a hematite (alpha-Fe2O3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al(3+) for Fe(3+) substitution and structural H2O and/or /OH. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.

Morris, R. V.; Ming, D. W.; Graff, T. G.; Arvidson, R. E.; Bell, J. F., III; Squyres, S. W.; Mertzman, S. A.; Gruener, J. E.; Golden, D. C.; Robinson, G. A.

2005-01-01

374

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

SciTech Connect

Highlights: •We report a novel mechanism of radiation protection of DNA by chemical activity of ascorbic acid. •The “chemical repair” of DNA damage was revealed using biochemical assay and chemical kinetics analysis. •We found that ascorbic acid significantly repairs precursors of nucleobase lesions and abasic sites. •However, ascorbic acid seldom repairs precursors of DNA-strand breaks. -- Abstract: We quantified the damage yields produced in plasmid DNA by ?-irradiation in the presence of low concentrations (10–100 ?M) of ascorbic acid, which is a major antioxidant in living systems, to clarify whether it chemically repairs radiation damage in DNA. The yield of DNA single strand breaks induced by irradiation was analyzed with agarose gel electrophoresis as conformational changes in closed circular plasmids. Base lesions and abasic sites were also observed as additional conformational changes by treating irradiated samples with glycosylase proteins. By comparing the suppression efficiencies to the induction of each DNA lesion, in addition to scavenging of the OH radicals derived from water radiolysis, it was found that ascorbic acid promotes the chemical repair of precursors of AP-sites and base lesions more effectively than those of single strand breaks. We estimated the efficiency of the chemical repair of each lesion using a kinetic model. Approximately 50–60% of base lesions and AP-sites were repaired by 10 ?M ascorbic acid, although strand breaks were largely unrepaired by ascorbic acid at low concentrations. The methods in this study will provide a route to understanding the mechanistic aspects of antioxidant activity in living systems.

Hata, Kuniki [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Urushibara, Ayumi; Yamashita, Shinichi; Shikazono, Naoya; Yokoya, Akinari [Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan)] [Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Katsumura, Yosuke, E-mail: katsu@n.t.u-tokyo.ac.jp [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1188 (Japan)

2013-05-03

375

Tin selenide synthesized by a chemical route: the effect of the annealing conditions in the obtained phase  

NASA Astrophysics Data System (ADS)

The effects of different annealing conditions over the tin selenide obtained from a chemical route are presented in this work. The tin selenide was annealed at 300 and 600 °C under hydrogen, nitrogen and argon atmospheres. The materials were characterized by X-ray diffraction and 119Sn Mössbauer spectroscopy. In the 'as synthetized' material a considerably amount of tin oxide (57%) was detected by Mössbauer spectroscopy. After thermal annealing the amount of these oxides varied according to the temperature and atmosphere used. At 600 °C/hydrogen the smallest amount of tin oxide was obtained (20%). These oxides were formed during the synthetic procedure through the hydrolysis of tin chloride used as reagent.

Bernardes-Silva, Ana Cláudia; Mesquita, A. F.; de Moura Neto, E.; Porto, A. O.; de Lima, G. M.; Ardisson, J. D.; Lameiras, F. S.

2005-09-01

376

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

2013-07-01

377

The dissolution of benzene, toluene, m-xylene and naphthalene from a residually trapped non-aqueous phase liquid under mass transfer limited conditions  

NASA Astrophysics Data System (ADS)

The results of dissolution experiments for benzene, toluene, m-xylene and naphthalene (BTXN) from a relatively insoluble oil phase (tridecane), residually trapped in a non-sorbing porous medium, are described. This mixture was chosen to simulate dissolution of soluble aromatic compounds from a petroleum hydrocarbon mixture, e.g., crude oil, for which a large fraction of the mixture is relatively insoluble. The experiments were carried out at a small source length to interstitial velocity ratio, L/ v, so that dissolution would be mass transfer limited (MTL). When fitted to data for toluene, a multiregion mass transfer model was found to predict the experimental data satisfactorily for the other components without adjustment of the mass transfer rate parameters. These results indicate that the dissolution process can be generalized for various hydrophobic organic compounds present in a multicomponent non-aqueous phase liquid (NAPL) when mass transfer limitations are present. This also suggests that dissolution data obtained for one compound can be useful for predicting the dissolution histories for other compounds from petroleum hydrocarbon mixtures.

Garg, Sanjay; Rixey, William G.

1999-03-01

378

Effect of the water content on the retention and enantioselectivity of albendazole and fenbendazole sulfoxides using amylose-based chiral stationary phases in organic-aqueous conditions.  

PubMed

Four commercially available immobilized amylose-derived CSPs (Chiralpak IA-3, Chiralpak ID-3, Chiralpak IE-3 and Chiralpak IF-3) were used in the HPLC analysis of the chiral sulfoxides albendazole (ABZ-SO) and fenbendazole (FBZ-SO) and their in vivo sulfide precursor (ABZ and FBZ) and sulfone metabolite (ABZ-SO2 and FBZ-SO2) under organic-aqueous mode. U-shape retention maps, established by varying the water content in the acetonitrile- and ethanol-water mobile phases, were indicative of two retention mechanisms operating on the same CSP. The dual retention behavior of polysaccharide-based CSPs was exploited to design greener enantioselective and chemoselective separations in a short time frame. The enantiomers of ABZ-SO and FBZ-SO were baseline resolved with water-rich mobile phases (with the main component usually being 50-65% water in acetonitrile) on the IF-3 CSP and ethanol-water 100:5 mixture on the IA-3 and IE-3 CSPs. A simultaneous separation of ABZ (or FBZ), enantiomers of the corresponding sulfoxide and sulfone was achieved on the IA-3 using ethanol-water 100:60 (acetonitrile-water 100:100 for FBZ) as a mobile phase. PMID:24411094

Materazzo, Sabrina; Carradori, Simone; Ferretti, Rosella; Gallinella, Bruno; Secci, Daniela; Cirilli, Roberto

2014-01-31

379

Collisions of small ice particles under microgravity conditions (II): Does the chemical composition of the ice change the collisional properties?  

E-print Network

Context: Understanding the collisional properties of ice is important for understanding both the early stages of planet formation and the evolution of planetary ring systems. Simple chemicals such as methanol and formic acid are known to be present in cold protostellar regions alongside the dominant water ice; they are also likely to be incorporated into planets which form in protoplanetary disks, and planetary ring systems. However, the effect of the chemical composition of the ice on its collisional properties has not yet been studied. Aims: Collisions of 1.5 cm ice spheres composed of pure crystalline water ice, water with 5% methanol, and water with 5% formic acid were investigated to determine the effect of the ice composition on the collisional outcomes. Methods: The collisions were conducted in a dedicated experimental instrument, operated under microgravity conditions, at relative particle impact velocities between 0.01 and 0.19 m s^-1, temperatures between 131 and 160 K and a pressure of around 10^-5...

Hill, C R; Blum, J; Fraser, H J

2015-01-01

380

Identification of morphological and chemical markers of dry- and wet-season conditions in female Anopheles gambiae mosquitoes  

PubMed Central

Background Increased understanding of the dry-season survival mechanisms of Anopheles gambiae in semi-arid regions could benefit vector control efforts by identifying weak links in the transmission cycle of malaria. In this study, we examined the effect of photoperiod and relative humidity on morphologic and chemical traits known to control water loss in mosquitoes. Methods Anopheles gambiae body size (indexed by wing length), mesothoracic spiracle size, and cuticular hydrocarbon composition (both standardized by body size) were examined in mosquitoes raised from eggs exposed to short photoperiod and low relative humidity, simulating the dry season, or long photoperiod and high relative humidity, simulating the wet-season. Results Mosquitoes exposed to short photoperiod exhibited larger body size and larger mesothoracic spiracle length than mosquitoes exposed to long photoperiod. Mosquitoes exposed to short photoperiod and low relative humidity exhibited greater total cuticular hydrocarbon amount than mosquitoes exposed to long photoperiod and high relative humidity. In addition, total cuticular hydrocarbon amount increased with age and was higher in mated females. Mean n-alkane retention time (a measure of cuticular hydrocarbon chain length) was lower in mosquitoes exposed to short photoperiod and low relative humidity, and increased with age. Individual cuticular hydrocarbon peaks were examined, and several cuticular hydrocarbons were identified as potential biomarkers of dry- and wet-season conditions, age, and insemination status. Conclusions Results from this study indicate that morphological and chemical changes underlie aestivation of Anopheles gambiae and may serve as biomarkers of aestivation. PMID:24970701

2014-01-01

381

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

382

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. PMID:23667556

Gong, Liang; Chen, Yong; Hu, Zhen; Hu, Meiying

2013-01-01

383

Laboratory insights into the chemical and kinetic evolution of several organic molecules under simulated Mars surface UV radiation conditions  

NASA Astrophysics Data System (ADS)

The search for organic carbon at the surface of Mars, as clues of past habitability or remnants of life, is a major science goal of Mars' exploration. Understanding the chemical evolution of organic molecules under current martian environmental conditions is essential to support the analyses performed in situ. What molecule can be preserved? What is the timescale of organic evolution at the surface? This paper presents the results of laboratory investigations dedicated to monitor the evolution of organic molecules when submitted to simulated Mars surface ultraviolet radiation (190-400 nm), mean temperature (218 ± 2 K) and pressure (6 ± 1 mbar) conditions. Experiments are done with the MOMIE simulation setup (for Mars Organic Molecules Irradiation and Evolution) allowing both a qualitative and quantitative characterization of the evolution the tested molecules undergo (Poch, O. et al. [2013]. Planet. Space Sci. 85, 188-197). The chemical structures of the solid products and the kinetic parameters of the photoreaction (photolysis rate, half-life and quantum efficiency of photodecomposition) are determined for glycine, urea, adenine and chrysene. Mellitic trianhydride is also studied in order to complete a previous study done with mellitic acid (Stalport, F., Coll, P., Szopa, C., Raulin, F. [2009]. Astrobiology 9, 543-549), by studying the evolution of mellitic trianhydride. The results show that solid layers of the studied molecules have half-lives of 10-103 h at the surface of Mars, when exposed directly to martian UV radiation. However, organic layers having aromatic moieties and reactive chemical groups, as adenine and mellitic acid, lead to the formation of photoresistant solid residues, probably of macromolecular nature, which could exhibit a longer photostability. Such solid organic layers are found in micrometeorites or could have been formed endogenously on Mars. Finally, the quantum efficiencies of photodecomposition at wavelengths from 200 to 250 nm, determined for each of the studied molecules, range from 10-2 to 10-6 molecule photon-1 and apply for isolated molecules exposed at the surface of Mars. These kinetic parameters provide essential inputs for numerical modeling of the evolution of Mars' current reservoir of organic molecules. Organic molecules adsorbed on martian minerals may have different kinetic parameters and lead to different endproducts. The present study paves the way for the interpretation of more complex simulation experiments where organics will be mixed with martian mineral analogs.

Poch, O.; Kaci, S.; Stalport, F.; Szopa, C.; Coll, P.

2014-11-01

384

Bioenhanced dissolution of dense non-aqueous phase of trichloroethylene as affected by iron reducing conditions: model systems and environmental samples.  

PubMed

The anaerobic biotransformation of trichloroethylene (TCE) can be affected by competing electron acceptors such as Fe (III). This study assessed the role of Fe (III) reduction on the bioenhanced dissolution of TCE dense non-aqueous phase liquid (DNAPL). Columns were set up as 1-D diffusion cells consisting of a lower DNAPL layer, a layer with an aquifer substratum and an upper water layer that is regularly refreshed. The substrata used were either inert sand or sand coated with 2-line ferrihydrite (HFO) or two environmental Fe (III) containing samples. The columns were inoculated with KB-1 and were repeatedly fed with formate. In none of the diffusion cells, vinyl chloride or ethene was detected while dissolved and extractable Fe (II) increased strongly during 60 d of incubation. The cis-DCE concentration peaked at 4.0 cm from the DNAPL (inert sand) while it was at 3.4 cm (sand+HFO), 1.7 cm and 2.5 cm (environmental samples). The TCE concentration gradients near the DNAPL indicate that the DNAPL dissolution rate was larger than that in an abiotic cell by factors 1.3 (inert sand), 1.0 (sand+HFO) and 2.2 (both environmental samples). This results show that high bioavailable Fe (III) in HFO reduces the TCE degradation by competitive Fe (III) reduction, yielding lower bioenhanced dissolution. However, Fe (III) reduction in environmental samples was not reducing TCE degradation and the dissolution factor was even larger than that of inert sand. It is speculated that physical factors, e.g. micro-niches in the environmental samples protect microorganisms from toxic concentrations of TCE. PMID:25460750

Paul, Laiby; Smolders, Erik

2015-01-01

385

Aqueous cleaning design presentation  

NASA Technical Reports Server (NTRS)

The phase-out of CFC's and other ozone depleting chemicals has prompted industries to re-evaluate their present methods of cleaning. It has become necessary to find effective substitutes for their processes as well as to meet the new cleaning challenges of improved levels of cleanliness and to satisfy concerns about environmental impact of any alternative selected. One of the most popular alternatives being selected is aqueous cleaning. This method offers an alternative for removal of flux, grease/oil, buffing compound, particulates and other soils while minimizing environmental impact. What I will show are methods that can be employed in an aqueous cleaning system that will make it environmentally friendly, relatively simple to maintain and capable of yielding an even higher quality of cleanliness than previously obtained. I will also explore several drying techniques available for these systems and other alternatives along with recent improvements made in this technology. When considering any type of cleaning system, a number of variables should be determined before selecting the basic configuration. Some of these variables are: (1) Soil or contaminants being removed from your parts; (2) The level of cleanliness required; (3) The environmental considerations of your area; (4) Maintenance requirements; and (5) Operating costs.

Maltby, Peter F.

1995-01-01

386

Corrosion problems with aqueous coolants, final report  

SciTech Connect

The results of a one year program to characterize corrosion of solar collector alloys in aqueous heat-transfer media are summarized. The program involved a literature review and a laboratory investigation of corrosion in uninhibited solutions. It consisted of three separate tasks, as follows: review of the state-of-the-art of solar collector corrosion processes; study of corrosion in multimetallic systems; and determination of interaction between different waters and chemical antifreeze additives. Task 1 involved a comprehensive review of published literature concerning corrosion under solar collector operating conditions. The reivew also incorporated data from related technologies, specifically, from research performed on automotive cooling systems, cooling towers, and heat exchangers. Task 2 consisted of determining the corrosion behavior of candidate alloys of construction for solar collectors in different types of aqueous coolants containing various concentrations of corrosive ionic species. Task 3 involved measuring the degradation rates of glycol-based heat-transfer media, and also evaluating the effects of degradation on the corrosion behavior of metallic collector materials.

Diegle, R B; Beavers, J A; Clifford, J E

1980-04-11

387

Chemical equilibria model of strontium-90 adsorption and transport in soil in response to dynamic alkaline conditions.  

PubMed

Strontium-90 is a major hazardous contaminant of radioactive wastewater and its processing sludges at many Department of Energy (DOE) facilities. In the past, such contaminated wastewater and sludge have been disposed in soil seepage pits, lagoons, or cribs often under highly perturbed alkaline conditions (pH > 12) where 90Sr solubility is low and its adsorption to surrounding soil is high. As natural weathering returns these soils to near-neutral or slightly acidic conditions, the adsorbed and precipitated calcium and magnesium phases, in which 90Sr is carried, change significantly in both nature and amounts. No comprehensive computational method has been formulated previously to quantitatively simulate the dynamics of 90Sr in the soil-groundwater environment under such dynamic and wide-ranging conditions. A computational code, the Hydrologic Utility Model for Demonstrating Integrated Nuclear Geochemical Environmental Responses (HUMDINGER), was composed to describe the changing equilibria of 90Sr in soil based on its causative chemical reactions including soil buffering, pH-dependent cation-exchange capacity, cation selectivity, and the precipitation/dissolution of calcium carbonate, calcium hydroxide, and magnesium hydroxide in response to leaching groundwater characteristics including pH, acid-neutralizing capacity, dissolved cations, and inorganic carbonate species. The code includes a simulation of one-dimensional transport of 90Sr through a soil column as a series of soil mixing cells where the equilibrium soluble output from one cell is applied to the next cell. Unamended soil leaching and highly alkaline soil treatments, including potassium hydroxide, sodium silicate, and sodium aluminate, were simulated and compared with experimental findings using large (10 kg) soil columns that were leached with 90Sr-contaminated groundwater after treatment. HUMDINGER's simulations were in good agreement with dynamic experimental observations of soil exchange capacity, exchangeable cations, total 90Sr, and pH values of layers within the soil columns and of column effluents. PMID:11347611

Spalding, B P; Spalding, I R

2001-01-15

388

NaNO2-mediated transformation of aliphatic secondary nitroalkanes into ketones or oximes under neutral, aqueous conditions: how the nitro derivative catalyzes its own transformation.  

PubMed

The nitrosation of secondary nitro derivatives into ketones or oximes depending on the nitro substituents has been reinvestigated. The reaction efficiently takes place under neutral conditions, thus allowing acid-sensitive substrates to be converted in very good yields. The generation of nitrosating species under such mild conditions is unprecedented. Mechanistic investigations strongly suggest that they result from the nucleophilic attack of the nitrite anion on the aci-nitro(nate) form of the secondary nitroalkane. The latter acts in turn as an autocatalyst for its own transformation by means of the nitrosating species generated in situ from it. PMID:15609931

Gissot, Arnaud; N'Gouela, Silvere; Matt, Christophe; Wagner, Alain; Mioskowski, Charles

2004-12-24

389

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. PMID:16469105

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

2006-01-01

390

Noninvasive in-vivo near-infrared vibrational spectroscopic study of lipid and aqueous phases of skin and near-surface tissues  

Microsoft Academic Search

We report the use of near infrared vibrational spectroscopy to noninvasively probe the in-vivo lipid and aqueous phases of skin and near surface tissues under conditions of thermal and chemical modulation. We demonstrate thermally induced order- disorder transitions in lipids that can be directly compared to well known behavior of in-vitro samples of phospholipid bilayers and bulk fatty acids. We

Joseph Chaiken; William F. Finney; Karen P. Peterson; Charles M. Peterson; Paul E. Knudson; Ruth S. Weinstock; Paul Lein

2000-01-01

391

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

392

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

393

Chemical composition and anticancer activity of essential oils of Mediterranean sage (Salvia officinalis L.) grown in different environmental conditions.  

PubMed

Salvia officinalis L. can be found worldwide and its leaves are commonly used as ingredient in food industry. Sage essential oil is applied in the treatment of a range of diseases and has been shown to possess different biological activities. The objectives of our research were to study the effects of environment on crop, chemical composition and anticancer activity on S. officinalis essential oil. Sage was cultivated at eighteen experimental sites in south-central Italy (Molise) in different growing environments. The essential oils (S1-S18), extracted by hydrodistillation, were analyzed by GC and CG/MS. Results show that the main components were ?-thujone, camphor, borneol, ?-muurolene and sclareol for all the samples, but the percentages of these compounds varied depending on environmental factors such as altitude, water availability and pedo-climatic conditions. The growth-inhibitory and proapoptotic effects of the eighteen sage essential oils were evaluated in three human melanoma cell lines, A375, M14, and A2058. PMID:23291326

Russo, Alessandra; Formisano, Carmen; Rigano, Daniela; Senatore, Felice; Delfine, Sebastiano; Cardile, Venera; Rosselli, Sergio; Bruno, Maurizio

2013-05-01

394

Efficient generation of lens progenitor cells and lentoid bodies from human embryonic stem cells in chemically defined conditions  

PubMed Central

The eye lens is an encapsulated avascular organ whose function is to focus light on the retina. Lens comprises a single progenitor cell lineage in multiple states of differentiation. Disruption of lens function leading to protein aggregation and opacity results in age-onset cataract. Cataract is a complex disease involving genetic and environmental factors. Here, we report the development of a new 3-stage system that differentiates human embryonic stem cells (hESCs) into large quantities of lens progenitor-like cells and differentiated 3-dimensional lentoid bodies. Inhibition of BMP signaling by noggin triggered differentiation of hESCs toward neuroectoderm. Subsequent reactivation of BMP and activation of FGF signaling stimulated formation of lens progenitor cells marked by the expression of PAX6 and ?-crystallins. The formation of lentoid bodies was most efficient in the presence of FGF2 and Wnt-3a, yielding ?1000 lentoid bodies/30-mm well. Lentoid bodies expressed and accumulated lens-specific markers including ?A-, ?B-, ?-, and ?-crystallins, filensin, CP49, and MIP/aquaporin 0. Collectively, these studies identify a novel procedure to generate lens cells from hESCs that can be applied for studies of lens differentiation and cataractogenesis using induced pluripotent stem (iPS) cells derived from various cataract patients.—Yang, C., Yang, Y., Brennan, L., Bouhassira, E. E., Kantorow, M., and Cvekl, A. Efficient generation of lens progenitor cells and lentoid bodies from human embryonic stem cells in chemically defined conditions. PMID:20410439

Yang, Chunbo; Yang, Ying; Brennan, Lisa; Bouhassira, Eric E.; Kantorow, Marc; Cvekl, Ales

2010-01-01

395

Silylation reaction of dextran: effect of experimental conditions on silylation yield, regioselectivity, and chemical stability of silylated dextrans.  

PubMed

The controlled synthesis of biodegradable copolymers of dextran grafted with aliphatic polyesters first requires the preparation of polysaccharide derivatives soluble in organic solvents. Silylation of dextran can thus lead to such organosoluble derivatives and allows the polymerization of cyclic esters initiated from the nonsilylated OH functions. Silylation of dextran was studied in DMSO by different reactants such as 1,1,1,3,3,3-hexamethyldisilazane (HMDS) in the presence of various catalysts and N,O-bis(trimethylsilyl)acetamide (BSA). According to the silylating agent and the used experimental conditions, it was possible to obtain highly or totally silylated dextrans. In parallel, an investigation of the chemical stability of the dextran chain during silylation was performed. Thus, it was found that, when used at 50 degrees C, HMDS with or without catalysts gives a relatively high silylation yield and does not alter the dextran chain length, whereas at 80 degrees C, dextran degradation was observed. BSA is a very good silylating agent, which allows reaching 100% silylation even at 50 degrees C but provokes the degradation of the polysaccharide chains. The work was completed by a study of the reactivity order of the glucosidic OH functions toward silylation reaction. This order was found to be (OH(2) > OH(4) > OH(3)) as already reported for other reactions. 2D-NMR of highly silylated dextrans demonstrated that they are constituted of both quantitatively silylated glucose units and two types of disilylated ones. PMID:12959617

Nouvel, Cécile; Dubois, Philippe; Dellacherie, Edith; Six, Jean-Luc

2003-01-01

396

An aqueous-organic two-phase bioprocess for efficient production of the natural aroma chemicals 2-phenylethanol and 2-phenylethylacetate with yeast.  

PubMed

The natural aroma chemicals 2-phenylethanol (2-PE) and 2-phenylethylacetate (2-PEAc) are of high industrial relevance and can be produced from L-phenylalanine in a yeast-based process with growth-associated product formation. Due to product inhibition, in situ product removal is mandatory to obtain economically interesting concentrations. A fed-batch approach using polypropylene glycol 1200 as in situ extractant and the precursor in a saturated concentration led to the highest 2-PE productivity reported for a bioprocess so far. With Kluyveromyces marxianus CBS 600, 26.5 g/l 2-PE and 6.1 g/l 2-PEAc in the organic phase were obtained, corresponding to space-time yields of 0.33 and 0.08 g/l h, respectively. PMID:16397768

Etschmann, M M W; Schrader, J

2006-07-01

397

Large-scale green chemical synthesis of adjacent quaternary chiral centers by continuous flow photodecarbonylation of aqueous suspensions of nanocrystalline ketones.  

PubMed

To demonstrate the ease of scale-up and synthetic potential of some organic solid state reactions, we report the synthesis, crystallization, and solid state photochemistry of acyclic, homochiral, hexasubstituted (+)-(2R,4S)-2-carbomethoxy-4-cyano-2,4-diphenyl-3-pentanone 1. We demonstrate that solid state photodecarbonylation of (+)-(2R,4S)-1 affords (+)-(2R,3R)-2-carbomethoxy-3-cyano-2,3-diphenyl-butane 2 with two adjacent stereogenic, all-carbon substituted quaternary centers, in quantitative chemical yield and 100% diastereoselectivity and enantiomeric excess. The efficient multigram photodecarbonylation of (+)-(2R,4S)-1 as a nanocrystalline suspension in water using a continuous flow photoreactor shows that the large-scale synthesis of synthetically challenging compounds using photochemical synthesis in the solid state can be executed in a remarkably simple manner. PMID:25578232

Hernández-Linares, María Guadalupe; Guerrero-Luna, Gabriel; Pérez-Estrada, Salvador; Ellison, Martha; Ortin, Maria-Mar; Garcia-Garibay, Miguel A

2015-02-01

398

Reaction mechanism for the aqueous-phase mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions.  

PubMed

Mineral carbonation is known as one of the safest ways to sequester CO2. Nevertheless, the slow kinetics and low carbonation rates constitute a major barrier for any possible industrial application. To date, no studies have focused on reacting serpentinite with a relatively low partial pressure of CO2 (pCO2) close to flue gas conditions. In this work, finely ground and heat-treated serpentinite [Mg3Si2O5(OH)4] extracted from mining residues was reacted with a 18.2 vol % CO2 gas stream at moderate global pressures to investigate the effect on CO2 solubility and Mg leaching. Serpentinite dissolution rates were also measured to define the rate-limiting step. Successive batches of gas were contacted with the same serpentinite to identify surface-limiting factors using scanning electron microscopy (SEM) analysis. Investigation of the serpentinite carbonation reaction mechanisms under conditions close to a direct flue gas treatment showed that increased dissolution rates could be achieved relative to prior work, with an average Mg dissolution rate of 3.55 × 10(-11) mol cm(-2) s(-1). This study provides another perspective of the feasibility of applying a mineral carbonation process to reduce industrial greenhouse gas (GHG) emissions from large emission sources. PMID:24669999

Pasquier, Louis-César; Mercier, Guy; Blais, Jean-François; Cecchi, Emmanuelle; Kentish, Sandra

2014-05-01

399

Inverse hydrochemical models of aqueous extracts tests  

SciTech Connect

Aqueous extract test is a laboratory technique commonly used to measure the amount of soluble salts of a soil sample after adding a known mass of distilled water. Measured aqueous extract data have to be re-interpreted in order to infer porewater chemical composition of the sample because porewater chemistry changes significantly due to dilution and chemical reactions which take place during extraction. Here we present an inverse hydrochemical model to estimate porewater chemical composition from measured water content, aqueous extract, and mineralogical data. The model accounts for acid-base, redox, aqueous complexation, mineral dissolution/precipitation, gas dissolution/ex-solution, cation exchange and surface complexation reactions, of which are assumed to take place at local equilibrium. It has been solved with INVERSE-CORE{sup 2D} and been tested with bentonite samples taken from FEBEX (Full-scale Engineered Barrier EXperiment) in situ test. The inverse model reproduces most of the measured aqueous data except bicarbonate and provides an effective, flexible and comprehensive method to estimate porewater chemical composition of clays. Main uncertainties are related to kinetic calcite dissolution and variations in CO2(g) pressure.

Zheng, L.; Samper, J.; Montenegro, L.

2008-10-10

400

Flow of Aqueous Humor  

MedlinePLUS

... Involved Research Grants Special Events Flow of Aqueous Humor © 2000 BrightFocus Foundation Unauthorized reprints not allowed. Most , ... remains normal when some of the fluid (aqueous humor) produced by the eye's ciliary body flows out ...

401

Mukaiyama Aldol Reactions in Aqueous Media  

PubMed Central

Mukaiyama aldol reactions in aqueous media have been surveyed. While the original Mukaiyama aldol reactions entailed stoichiometric use of Lewis acids in organic solvents under strictly anhydrous conditions, Mukaiyama aldol reactions in aqueous media are not only suitable for green sustainable chemistry but are found to produce singular phenomena. These findings led to the discovery of a series of water-compatible Lewis acids such as lanthanide triflates in 1991. Our understanding on these beneficial effects in the presence of water will be deepened through the brilliant examples collected in this review. 1 Introduction 2 Rate Enhancement by Water in the Mukaiyama Aldol Reaction 3 Lewis Acid Catalysis in Aqueous or Organic Solvents 3.1 Water-Compatible Lewis Acids 4 Lewis-Base Catalysis in Aqueous or Organic Solvents 5 The Mukaiyama Aldol Reactions in 100% Water 6 Asymmetric Catalysts in Aqueous Media and Water 7 Conclusions and Perspective PMID:24971045

Kitanosono, Taku; Kobayashi, Sh?

2013-01-01

402

The Effect of Chemical Composition and Heat Treatment Conditions on Stacking Fault Energy for Fe-Cr-Ni Austenitic Stainless Steel  

NASA Astrophysics Data System (ADS)

In order to establish more reliable formulae for calculating stacking fault energies (SFE) from the chemical compositions of austenitic stainless steels, SFE values were measured for 54 laboratory-melted heats and 2 commercial heats. The results were checked against those of a first-principle, atomistic calculation approach. More than ~20,000 data points for the width and angle of the Burgers vectors were determined from dark-field images of isolated extended dislocations in 56 heats of austenitic stainless steel using weak electron beams with g-3g diffraction conditions. Based on these numerous observations and on fundamental thermodynamic analyses, it is concluded that the SFE values for austenitic stainless steels are changed not only by chemical composition but also by heat treatment. In this paper, new formulae for calculating SFE values from the chemical compositions in three different heat treatment conditions have been proposed for austenitic stainless steels within given limited chemical composition ranges. In these formulae, the SFE values are calculated from the nickel, chromium, molybdenum, silicon, manganese, nitrogen, and carbon contents for the each heat treatment condition. The three heat treatment conditions studied were water cooling after solution heat treating (SHTWC), furnace cooling after solution heat treating, and aging after SHTWC.

Yonezawa, Toshio; Suzuki, Ken; Ooki, Suguru; Hashimoto, Atsushi

2013-12-01

403

PLD deposition of tungsten carbide contact for diamond photodiodes. Influence of process conditions on electronic and chemical aspects  

NASA Astrophysics Data System (ADS)

Tungsten carbide, WC, contacts behave as very reliable Schottky contacts for opto-electronic diamond devices. Diamond is characterized by superior properties in high-power, high frequency and high-temperature applications, provided that thermally stable electrode contacts will be realized. Ohmic contacts can be easily achieved by using carbide-forming metals, while is difficult to get stable Schottky contacts at elevated temperatures, due to the interface reaction and/or inter-diffusion between metals and diamond. Novel type of contacts, made of tungsten carbide, WC, seem to be the best solution, for their excellent thermal stability, high melting point, oxidation and radiation resistance and good electrical conductivity. Our research was aimed at using pulsed laser deposition for WC thin film deposition, optimizing experimental parameters, to obtain a final device characterized by excellent electronic properties, as a detector for radiation in deep UV or as X-ray dosimeter. We deposited our films by laser ablation from a target of pure WC, using different reaction conditions (i.e., substrate heating, vacuum or reactive atmosphere (CH4/Ar), RF plasma activated), to optimize both the stoichiometry of the film and its structure. Trying to obtain a material with the best electronic response, we used also two sources of laser radiation for target ablation, i.e., nano-second pulsed excimer laser ArF, and ultra-short fs Ti:Sapphire laser. The structure and chemical aspects have been evaluated by Raman and X-ray photoelectron spectroscopy (XPS), while the dosimeter photodiode response has been tested by the I-V measurements, under soft X-ray irradiation.

Cappelli, E.; Bellucci, A.; Orlando, S.; Trucchi, D. M.; Mezzi, A.; Valentini, V.

2013-08-01

404

Cr(VI) removal from aqueous solution with bamboo charcoal chemically modified by iron and cobalt with the assistance of microwave.  

PubMed

Bamboo charcoal (BC) was used as starting material to prepare Co-Fe binary oxideloaded adsorbent (Co-Fe-MBC) through its impregnation in Co(NO3)2, FeCl3 and HNO3 solutions simultaneously, followed by microwave heating. The low-cost composite was characterized and used as an adsorbent for Cr(VI) removal from water. The results showed that a cobalt and iron binary oxide (CoFe2O4) was uniformly formed on the BC through redox reactions. The composite exhibited higher surface area (331 m2/g) than that of BC or BC loaded with Fe alone (Fe-MBC). The adsorption of Cr(VI) strongly depended on solution pH, temperature and ionic strength. The adsorption isotherms followed the Langmuir isotherm model well, and the maximum adsorption capacities for Cr(VI) at 288 K and pH 5.0 were 35.7 and 51.7 mg/g for Fe-MBC and Co-Fe-MBC, respectively. The adsorption processes were well fitted by the pseudo second-order kinetic model. Thermodynamic parameters showed that the adsorption of Cr(VI) onto both adsorbents was feasible, spontaneous, and exothermic under the studied conditions. The spent Co-Fe-MBC could be readily regenerated for reuse. PMID:24520714

Wang, Wei; Wang, Xuejiang; Wang, Xin; Yang, Lianzhen; Wu, Zhen; Xia, Siqing; Zhao, Jianfu

2013-09-01

405

Explicit modeling of volatile organic compounds partitioning in the atmospheric aqueous phase  

NASA Astrophysics Data System (ADS)

The gas phase oxidation of organic species is a multigenerational process involving a large number of secondary compounds. Most secondary organic species are water-soluble multifunctional oxygenated molecules. The fully explicit chemical mechanism GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) is used to describe the oxidation of organics in the gas phase and their mass transfer to the aqueous phase. The oxidation of three hydrocarbons of atmospheric interest (isoprene, octane and ?-pinene) is investigated for various NOx conditions. The simulated oxidative trajectories are examined in a new two dimensional space defined by the mean oxidation state and the solubility. The amount of dissolved organic matter was found to be very low (<2%) under a water content typical of deliquescent aerosols. For cloud water content, 50% (isoprene oxidation) to 70% (octane oxidation) of the carbon atoms are found in the aqueous phase after the removal of the parent hydrocarbons for low NOx conditions. For high NOx conditions, this ratio is only 5% in the isoprene oxidation case, but remains large for ?-pinene and octane oxidation cases (40% and 60%, respectively). Although the model does not yet include chemical reactions in the aqueous phase, much of this dissolved organic matter should be processed in cloud drops and modify both oxidation rates and the speciation of organic species.

Mouchel-Vallon, C.; Bräuer, P.; Camredon, M.; Valorso, R.; Madronich, S.; Herrmann, H.; Aumont, B.

2012-09-01

406

Explicit modeling of volatile organic compounds partitioning in the atmospheric aqueous phase  

NASA Astrophysics Data System (ADS)

The gas phase oxidation of organic species is a multigenerational process involving a large number of secondary compounds. Most secondary organic species are water-soluble multifunctional oxygenated molecules. The fully explicit chemical mechanism GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) is used to describe the oxidation of organics in the gas phase and their mass transfer to the aqueous phase. The oxidation of three hydrocarbons of atmospheric interest (isoprene, octane and ?-pinene) is investigated for various NOx conditions. The simulated oxidative trajectories are examined in a new two dimensional space defined by the mean oxidation state and the solubility. The amount of dissolved organic matter was found to be very low (yield less than 2% on carbon atom basis) under a water content typical of deliquescent aerosols. For cloud water content, 50% (isoprene oxidation) to 70% (octane oxidation) of the carbon atoms are found in the aqueous phase after the removal of the parent hydrocarbons for low NOx conditions. For high NOx conditions, this ratio is only 5% in the isoprene oxidation case, but remains large for ?-pinene and octane oxidation cases (40% and 60%, respectively). Although the model does not yet include chemical reactions in the aqueous phase, much of this dissolved organic matter should be processed in cloud drops and modify both oxidation rates and the speciation of organic species.

Mouchel-Vallon, C.; Bräuer, P.; Camredon, M.; Valorso, R.; Madronich, S.; Herrmann, H.; Aumont, B.

2013-01-01

407

Urban Air Pollution from Ethanol (E85) in the Presence of Aqueous Aerosols and Fog  

NASA Astrophysics Data System (ADS)

This is a study to examine the effect of ethanol (E85) versus gasoline on urban air pollution in the presence of aqueous aerosols and fog. In previous work, we analyzed the temperature-dependence of ethanol and gasoline exhaust chemistry and its impact on urban air pollution considering only gas-phase chemistry. We used the near-explicit Master Chemical Mechanism (MCM, version 3.1, LEEDS University) with the SMVGEAR II chemical ordinary differential solver to provide the speed necessary to simulate explicit chemistry. The MCM has over 13,500 organic reactions and 4,600 species. SMVGEAR II is a sparse-matrix Gear solver that reduces the computation time significantly while maintaining any specified accuracy. We found that the average ozone concentrations through the range of temperatures tested could be higher with E85 than with gasoline by up to 8 parts per billion volume (ppbv) at room temperature but much higher at cold temperatures and low sunlight (winter conditions) for a region with a high nitrogen oxide (NOx) to non-methane organic gases (NMOG) ratio. We also found that the solution to chemistry in a 3-D urban airshed model was practical. We now extend our study to include aqueous chemistry in the presence of aerosols and fog. We combine the Chemical Aqueous Phase Radical Mechanism, CAPRAM 3.0 with the MCM 3.1 and gas-particle transfer in box model calculations. CAPRAM treats aqueous phase chemistry among 390 species and 829 reactions (including 51 gas-to-aqueous phase reactions). We investigate the impact aqueous reactions have on unburned ethanol and acetaldehyde mixing ratios in the atmosphere in particular because acetaldehyde is an ozone precursor and carcinogen, and aqueous oxidation has potential to speed the conversion of unburned ethanol to acetaldehyde. Acetaldehyde also forms acetic acid in aqueous solution. Acetic acid vapor is an eye, nose, and lung irritant, so both species contribute negatively to human health. We look at the impact of aerosol and fog liquid water content and temperature on the degradation of emitted aromatic and other species as well, from both gasoline and E85.

Ginnebaugh, D. L.; Jacobson, M. Z.

2010-12-01

408

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

409

Chemical pumping of rhodium by a supported liquid membrane containing Aliquat 336 as carrier  

Microsoft Academic Search

The mass transfer of Rh(III) from aqueous feed chloride solutions containing SCN? through a solid-supported liquid membrane (SSLM) consisting of Aliquat 336 dissolved in dodecane has been studied. The influence of hydrodynamic conditions as well as the chemical composition of the system on the permeation rate was investigated. Among the reagents tested as carriers, quaternary amines have been shown to

C. Fontàs; E. Anticó; V. Salvadó; M. Valiente; M. Hidalgo

1997-01-01

410

Low temperature aqueous desulfurization of coal  

DOEpatents

This invention describes a chemical process for desulfurizing coal, especially adaptable to the treatment of coal-water slurries, at temperatures as low as ambient, comprising treating the coal with aqueous titanous chloride whereby hydrogen sulfide is liberated and the desulfurized coal is separated with the conversion of titanous chloride to titanium oxides.

Slegeir, W.A.; Healy, F.E.; Sapienza, R.S.

1985-04-18

411

Low temperature aqueous desulfurization of coal  

DOEpatents

This invention describes a chemical process for desulfurizing coal, especially adaptable to the treatment of coal-water slurries, at temperatures as low as ambient, comprising treating the coal with aqueous titanous chloride whereby hydrogen sulfide is liberated and the desulfurized coal is separated with the conversion of titanous chloride to titanium oxides.

Slegeir, William A. (Hampton Bays, NY); Healy, Francis E. (Massapequa, NY); Sapienza, Richard S. (Shoreham, NY)

1985-01-01

412

Aqueous Ozonation of Pesticides: A Review  

Microsoft Academic Search

The ozonation reactions of pesticides in aqueous solution have been reviewed. Degree of reaction and reaction product identity are included. Compounds are classified into five groups: chlorinated hydrocarbons, organophosphorus compounds, phenoxyalkyl acid derivatives, organonitrogen compounds, and phenolic compounds. Experimental conditions for each study are summarized. Much work has been carried out under conditions atypical of those encountered at drinking water

G. Reynolds; N. Graham; R. Perry; R. G. Rice

1989-01-01

413

Influence of Chemical Composition on Rupture Properties at 1200 Degrees F. of Forged Chromium-Cobalt-Nickel-Iron Base Alloys in Solution-Treated and Aged Condition  

NASA Technical Reports Server (NTRS)

The influence of systematic variations of chemical composition on rupture properties at 1200 degrees F. was determined for 62 modifications of a basic alloy containing 20 percent chromium, 20 percent nickel, 20 percent cobalt, 3 percent molybdenum, 2 percent tungsten, 1 percent columbium, 0.15 percent carbon, 1.7 percent manganese, 0.5 percent silicon, 0.12 percent nitrogen and the balance iron. These modifications included individual variations of each of 10 elements present and simultaneous variations of molybdenum, tungsten, and columbium. Laboratory induction furnace heats were hot-forged to round bar stock, solution-treated at 2200 degrees F., and aged at 1400 degrees F. The melting and fabrication conditions were carefully controlled in order to minimize all variable effects on properties except chemical composition. Information is presented which indicates that melting and hot-working conditions play an important role in high-temperature properties of alloys of the type investigated.

Reynolds, E E; Freeman, J W; White, A E

1951-01-01

414

Impact of Ambient Temperatures and Driving Conditions on the Chemical Composition of Particulate Matter Emissions from Non-Smoking Gasoline-Powered Motor Vehicles  

Microsoft Academic Search

The detailed chemical composition of particulate matter emissions from four non-smoking gasoline powered motor vehicles were measured using three different driving conditions: a cold-cold start Unified Driving Cycle (UDC), a hot UDC, and a steady state cruise driving cycle. The cold-cold start UDC tests were performed with a cold-cold start temperature of 0°C, which is significantly lower than the 24°C

J. J. Schauer; C. G. Christensen; D. B. Kittelson; J. P. Johnson; W. F. Watts

2008-01-01

415

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

2009-05-01

416

Chemical Models for Aqueous Biodynamical Processes  

E-print Network

. There are ionic liquids such as molten salts, metallic liquids which are composed of ions and mobile electrons, asso ciated liquids like water in which molecules are held together by means of hydrogen bonds, and finally molecular liquids in which cohesion... Isotopic Fractionation Factor 5 An Example 6 REFERENCES FOR CHAPTER I 13 CHAPTER II. THE MECHANISM OF WATER VISCOUS FLOW 16 The Liquid State 1 The Structure of Liquids 16 The Structure of Liquid Water 18 The Viscous Flow Process 9 Statement...

Mata-Segreda, Julio F.

1975-05-01

417

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

418

Morphological and chemical stability of silicon nanostructures and their molecular overlayers under physiological conditions: towards long-term implantable nanoelectronic biosensors  

PubMed Central

Background The detection of biological and chemical species is of key importance to numerous areas of medical and life sciences. Therefore, a great interest exists in developing new, rapid, miniature, biocompatible and highly sensitive sensors, capable to operate under physiological conditions and displaying long-term stabilities (e.g. in-body implantable sensors). Silicon nanostructures, nanowires and nanotubes, have been extensively explored as building blocks for the creation of improved electrical biosensing devices, by virtue of their remarkably high surface-to-volume ratios, and have shown exceptional sensitivity for the real time label-free detection of molecular species adsorbed on their surfaces, down to the sensitivity of single molecules. Yet, till this date, almost no rigorous studies have been performed on the temporal morphological stability of these nanostructures, and their resulting electrical devices, under physiological conditions (e.g. serum, blood), as well as on the chemical stability of the molecular recognition over-layers covering these structures. Results Here, we present systematic time-resolved results on the morphological stability of bare Si nanowire building blocks, as well on the chemical stability of siloxane-based molecular over-layers, under physiological conditions. Furthermore, in order to overcome the observed short-term morpho-chemical instabilities, we present on the chemical passivation of the Si nanostructures by thin metal oxide nanoshells, in the range of 3–10 nm. The thickness of the metal oxide layer influences on the resulting electrical sensitivity of the fabricated FETs (field effect transistors), with an optimum thickness of 3–4 nm. Conclusions The core-shell structures display remarkable long-term morphological stability, preventing both, the chemical hydrolytic dissolution of the silicon under-structure and the concomitant loss of the siloxane-based chemical over-layers, for periods of at least several months. Electrical devices constructed from these nanostructures display excellent electrical characteristics and detection sensitivities, with exceptionally high morphological and functional stabilities. These results pave the road for the creation of long-term implantable biosensing devices in general, and nanodevices in particular. PMID:24606762

2014-01-01

419

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...

420

OVIPOSITION OF THE SOUTHERN GREEN STINK BUG, NEZARA VIRIDULA (L.) ON ARTIFICIAL SUBSTRATES CONDITIONED BY CHEMICAL EXTRACTS FROM SOYBEAN PLANTS  

Technology Transfer Automated Retrieval System (TEKTRAN)

A laboratory bioassay was developed for testing oviposition preference of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae) toward <