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1

The Formation Of Glycerol Monodecanoate By A Dehydration Condensation Reaction: Increasing The Chemical Complexity Of Amphiphiles On The Early Earth  

Microsoft Academic Search

Dehydration\\/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into primitive cellular organisms. As a model of such reactions and to demonstrate this principle, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate (GMD). This amphiphile enhances robustness of self-assembled membranous structures of

Charles L. Apel; David W. Deamer

2005-01-01

2

The formation of glycerol monodecanoate by a dehydration condensation reaction: increasing the chemical complexity of amphiphiles on the early Earth.  

PubMed

Dehydration/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into primitive cellular organisms. As a model of such reactions and to demonstrate this principle, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate (GMD). This amphiphile enhances robustness of self-assembled membranous structures of carboxylic acids to the potentially disruptive effects of pH, divalent cation binding and osmotic stress. Experimental variables included temperature, water activity and hydrolysis of the resulting ester product, providing insights into the environmental conditions that would favor the formation and stability of this more evolved amphiphile. At temperatures exceeding 50 degrees C, the ester product formed even in the presence of bulk water, suggesting that the reaction occurs at the liquid interface of the two reactants and that the products segregate in the two immiscible layers, thereby reducing hydrolytic back reactions. This implies that esterification reactions were likely to be common in the prebiotic environment as reactants underwent cycles of wetting and drying on rare early landmasses at elevated temperatures. PMID:16228646

Apel, Charles L; Deamer, David W

2005-08-01

3

The formation of glycerol monodecanoate by a dehydration\\/condensation reaction: increasing the chemical complexity of amphiphiles on the early earth  

Microsoft Academic Search

Dehydration\\/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into protocellular structures. As a model of such reactions, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate. This amphiphile enhances robustness of self-assembled membranous structures of carboxylic acids to the potentially disruptive effects

C. L. Apel; D. W. Deamer

2004-01-01

4

An overview of dehydration, aldol-condensation and hydrogenation processes for production of liquid alkanes from biomass-derived carbohydrates  

Microsoft Academic Search

We present results for the conversion of carbohydrate feedstocks to liquid alkanes by the combination of dehydration, aldol-condensation\\/hydrogenation, and dehydration\\/hydrogenation processing. With respect to the first dehydration step, we demonstrate that HMF can be produced in good selectivity from abundantly available polysaccharides (such as inulin, sucrose) containing fructose monomer units using a biphasic batch reactor system. The reaction system can

Juben N. Chheda; James A. Dumesic

2007-01-01

5

The possible role of solid surface area in condensation reactions during chemical evolution: reevaluation.  

PubMed

Published data on adsorption and condensation of amino acids, purine and pyrimidine bases, sugars, nucleosides, and nucleotides are analyzed in connection with Bernal's hypothesis that clays and other minerals may have provided the most likely surface for adsorption and condensation of these molecules in prebiotic times. Using surface concentration and reaction rate as the main criteria for the feasibility of condensation reactions, four types of prebiotic environments were analyzed: (1) an ocean-sediment system, (2) a dehydrated lagoon bed produced by evaporation, (3) the surface of a frozen sediment, and (4) a fluctuating system where hydration (rainstorms, tidal variations, flooding) and dehysration (evaporation) take place in a cyclic manner. With the possible exception of nucleotides, low adsorption of organomonomers on sediment surfaces of a prebiotic ocean (pH 8) is expected, and significant condensation is considered unlikely. In dehydrated and frozen systems, high surface concentrations are probable and condensation is more likely. In fluctuating environments, condensation rates will be enhanced and the size distribution of the oligomers formed during dehydration may be influenced by a "redistribution mechanism" in which adsorbed oligomers and monomers are desorbed and redistributed on the solid surface during the next hydration-dehydration cycle. PMID:13225

Lahav, N; Chang, S

1976-12-30

6

Absence of expected side-reactions in the dehydration reaction of fructose to HMF in water over niobic acid catalyst  

Microsoft Academic Search

The catalytic dehydration of fructose (FRU) to 5-hydroxymethylfurfural (HMF) usually runs with the formation of several side products. Among these, levulinic acid (LA) is often reported as the product of a consecutive reaction of HMF re-hydration. In this work, side reactions of the dehydration of FRU performed in very green conditions (water as solvent and niobic acid as solid catalyst)

Paolo Carniti; Antonella Gervasini; Matteo Marzo

2011-01-01

7

Acetone condensation reaction on acid catalysts  

SciTech Connect

The condensation reaction of acetone on alumina and acid zeolites has been followed by FTIR. Under identical conditions, the reaction rate is faster on alumina, and the condensation goes beyond the formation of mesityl oxide. Zeolites without nonframework aluminum are poor catalysts. On HZSM-5 the reaction is about two orders of magnitude slower than on USY at 105 C. From these data, it appears that Lewis sites, even if they bound acetone less energetically than Broensted sites, are responsible for the activation of the molecule. On alumina, the reaction would take place between gas phase acetone and acetone adsorbed on Lewis sites. On zeolites with nonframework aluminum and, thus, with Lewis sites, the reaction would involve acetone molecules adsorbed on Broensted and Lewis sites, the activation occurring on the Lewis site.

Panov, A.G.; Fripiat, J.J. [Univ. of Wisconsin, Milwaukee, WI (United States)

1998-08-15

8

Dehydration of cyclohexanol as a test reaction for zeolite acidity  

Microsoft Academic Search

Dehydration of cyclohexanol was investigated using a fixed-bed continuous flow reactor with acidic mordenite-type, clinoptilolite-type, and faujasite-type (Y) zeolites as catalysts. The surface acidity of the catalysts employed was studied by IR using pyridine or 2,6-di-tert. butylpyridine as probe molecules. A correlation between the acidity and the rates of dehydration was clearly shown.

H. G. Karge; H. Kosters; Y. Wada

1984-01-01

9

Cellulose dehydration and depolymerization reactions during pyrolysis in the presence of phosphoric acid  

Microsoft Academic Search

The low-temperature pyrolysis process and dehydration reactions of cellulose impregnated with phosphoric acid (1–10 wt.%) have been studied. Based on the yield of pyrolytic water and alterations of glucopyranose units of cellulose, it has been confirmed that dehydrated cyclic structures are formed in the solid phase during cellulose pyrolysis in the temperature interval 200–250°C. Phosphoric acid also catalyzes the subsequent

G Dobele; G Rossinskaja; G Telysheva; D Meier; O Faix

1999-01-01

10

Effect of dehydration reactions on the temperature of faults during coseismic slip  

NASA Astrophysics Data System (ADS)

Recent experimental and theoretical studies have emphasized the possible importance of mineral reactions during coseismic slip. Here we present a series of High Velocity Friction experiments on gypsum solid blocks, performed at Hiroshima University. The temperature close to the sliding surface and the relative humidity around the sample was measured during slip tests at 1.3 m.s-1. The temperature on the sliding surface is remarkably stable during the dehydration reaction of gypsum. Microstructural investigations show that dehydration occurs at the very beginning of the test. Such reactions might be recorded within the wall rock by the presence of anhydrite crystal growth in the hottest parts of the sample. From a theoretical point of view at the fault scale, it is possible to include mineral dehydrations within the framework of Thermal Pressurization. Dehydrations are modeled as a source term for pore pressure because of the total volume change, and a sink term for temperature because they are endothermic. The solution is found numerically, taking into account fluid and heat transport and using an Arrhenius law to calculate the rate constant with temperature. The main effect of dehydration reactions is an increase of pore pressure and a stabilization of the temperature during slip, as illustrated by the HVE on gypsum.

Brantut, Nicolas; Han, Raehee; Alexandre, Schubnel; Toshihiko, Shimamoto; Jérôme, Corvisier

2010-05-01

11

Thermodynamic forward modeling of progressive dehydration reactions during subduction of oceanic crust under greenschist facies conditions  

NASA Astrophysics Data System (ADS)

We developed a new approach to the study of dehydration reactions using thermodynamic forward modeling based on the differential thermodynamic approach (the Gibbs' method) and the use of mass balance equations. We applied the modeling to mafic systems under conditions of the greenschist facies in order to investigate continuous, progressive dehydration reactions during subduction of oceanic crust. By specifying the changes in P-T, the model enables us to predict changes in modal mineralogy and composition as well as the incremental amount of water produced. Calculations for rocks of MORB (mid-ocean ridge basalt) bulk composition subducting along several typical P-T paths show that dehydration proceeds rapidly near the boundary between the greenschist and (epidote-) amphibolite facies, where chlorite is reacted out. The calculated depths for peak rates of dehydration correlate well with peaks in clusters of seismic activity and the depth ranges of low-frequency tremors and high-Poisson's ratio in the subduction zones of SW Japan and Cape Mendocino. This finding indicates a strong causal linkage between seismic phenomena and dehydration reactions in subducting oceanic crust.

Kuwatani, Tatsu; Okamoto, Atsushi; Toriumi, Mitsuhiro

2011-07-01

12

Effect of temperature on sucrose penetration and browning reactions in longan aril during osmotic dehydration  

Microsoft Academic Search

Sucrose penetration and browning reactions in longan aril during osmotic dehydration at various temperatures were examined by measurement of total soluble solid and colour parameter (b*) of longan aril. Mathematical modelling and Arrhenius equation were used to express the changes during the process and the effect of temperature respectively. Parabola models (Y = a0 + a1X + a2X 2 )

Wiwat Wangcharoen

13

Niobic acid and niobium phosphate as highly acidic viable catalysts in aqueous medium: Fructose dehydration reaction  

Microsoft Academic Search

The catalytic properties of niobic acid (Nb2O5·nH2O) and niobium phosphate (NbOPO4) surfaces were studied in the reaction of fructose dehydration carried out in water. The reaction was performed in a continuous reactor at different temperatures 90–110°C and pressures (from 2 to 6bar). Superior activity and selectivity to 5-hydroxymethyl-2-furaldehyde (HMF) of niobium phosphate compared to niobic acid was observed. The initial

Paolo Carniti; Antonella Gervasini; Serena Biella; Aline Auroux

2006-01-01

14

One-pot synthesis of olefins from aromatic ketones via tandem consecutive hydrogenation–dehydration reactions  

Microsoft Academic Search

In this work, the synthesis of aromatic olefins from the corresponding ketones via tandem consecutive hydrogenation–dehydration reactions was studied. The conversion of acetophenone (AP) to styrene (STY) was used as model reaction. Initially, the liquid-phase hydrogenation of AP to 1-phenylethanol (PHE), using cyclohexane as solvent, was investigated at 363K and 10bar over Ni, Co, Cu, Pd and Pt supported on

Nicolás M. Bertero; Carlos R. Apesteguía; Alberto J. Marchi

2011-01-01

15

Will water act as a photocatalyst for cluster phase chemical reactions? Vibrational overtone-induced dehydration reaction of methanediol  

NASA Astrophysics Data System (ADS)

The possibility of water catalysis in the vibrational overtone-induced dehydration reaction of methanediol is investigated using ab initio dynamical simulations of small methanediol-water clusters. Quantum chemistry calculations employing clusters with one or two water molecules reveal that the barrier to dehydration is lowered by over 20 kcal/mol because of hydrogen-bonding at the transition state. Nevertheless, the simulations of the reaction dynamics following OH-stretch excitation show little catalytic effect of water and, in some cases, even show an anticatalytic effect. The quantum yield for the dehydration reaction exhibits a delayed threshold effect where reaction does not occur until the photon energy is far above the barrier energy. Unlike thermally induced reactions, it is argued that competition between reaction and the irreversible dissipation of photon energy may be expected to raise the dynamical threshold for the reaction above the transition state energy. It is concluded that quantum chemistry calculations showing barrier lowering are not sufficient to infer water catalysis in photochemical reactions, which instead require dynamical modeling.

Kramer, Zeb C.; Takahashi, Kaito; Vaida, Veronica; Skodje, Rex T.

2012-04-01

16

Will water act as a photocatalyst for cluster phase chemical reactions? Vibrational overtone-induced dehydration reaction of methanediol  

SciTech Connect

The possibility of water catalysis in the vibrational overtone-induced dehydration reaction of methanediol is investigated using ab initio dynamical simulations of small methanediol-water clusters. Quantum chemistry calculations employing clusters with one or two water molecules reveal that the barrier to dehydration is lowered by over 20 kcal/mol because of hydrogen-bonding at the transition state. Nevertheless, the simulations of the reaction dynamics following OH-stretch excitation show little catalytic effect of water and, in some cases, even show an anticatalytic effect. The quantum yield for the dehydration reaction exhibits a delayed threshold effect where reaction does not occur until the photon energy is far above the barrier energy. Unlike thermally induced reactions, it is argued that competition between reaction and the irreversible dissipation of photon energy may be expected to raise the dynamical threshold for the reaction above the transition state energy. It is concluded that quantum chemistry calculations showing barrier lowering are not sufficient to infer water catalysis in photochemical reactions, which instead require dynamical modeling.

Kramer, Zeb C.; Takahashi, Kaito; Skodje, Rex T. [Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215 (United States); Vaida, Veronica [Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215 (United States); CIRES, University of Colorado, Boulder, Colorado 80309 (United States)

2012-04-28

17

Negative resists for i-line lithography utilizing acid-catalyzed intramolecular dehydration reaction  

NASA Astrophysics Data System (ADS)

Chemical amplification negative resist system composed of a novolak resin, a carbinol and an acid generator is investigated for i-line phase-shift lithography. The reaction in this resist is based on an acid-catalyzed intramolecular dehydration reaction. The dehydration products act as aqueous-base dissolution inhibitors, and carbinol compounds in unexposed areas work as dissolution promoters. The resist composed of a novolak resin, 1,4-bis((alpha) -hydroxyisopropyl) benzene (DIOL-1) and 2- naphthoylmethyltetramethylenesulfonium triflate (PAG-2) gives the best lithographic performance in terms of sensitivity and resolution. Line-and-space patterns of 0.275 micrometers are obtained using an i-line stepper (NA:0.45) in conjunction with a phase shifting mask.

Ueno, Takumi; Uchino, Shou-ichi; Hattori, K. T.; Onozuka, T.; Shirai, Sei-ichiro; Moriuchi, Noboru; Hashimoto, Michiaki; Koibuchi, S.

1994-05-01

18

Intrinsic reaction rate and the effects of operating conditions in dimethyl ether synthesis from methanol dehydration  

Microsoft Academic Search

The kinetic behavior of a commercial ?-Al2O3 catalyst for the methanol to dimethyl ether (DME) dehydration reaction has been investigated using a differential fixed bed\\u000a reactor at the pressure range 1–16 barg within a temperature range of 260–380 °C. The experimental runs were performed in\\u000a a wide range of feed to water ratios. The experiments were designed by general full

Gholamreza Moradi; Fereydoon Yaripour; Hossein Abbasian; Mostefa Rahmanzadeh

2010-01-01

19

Metamorphic dehydration reactions control the location of intermediate-depth seismicity  

NASA Astrophysics Data System (ADS)

The cause of intermediate-depth seismicity in subduction zones is not well understood. The viability of proposed mechanisms, that include dehydration embrittlement, shear instablities, and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature, and composition. A number of high resolution seismic studies have improved the location of earthquakes within the slab in Japan, Alaska and Cascadia. Intriguingly, the warm subduction zones of Nankai and Cascadia show that intermediate depth seismicity is located below the oceanic crust. In contrast, the colder subduction zones Alaska, Tohoku and Hokkaido have the upper plane of seismicity confined to the subducting crust, with a systematic deepening of the seismic belt with respect to the top of the slab with depth. We use high resolution thermal-petrological models to determine the metamorphic facies in the downgoing slab and to identify the main phase changes that cause dehydration. In Alaska and Northern Japan, the seismicity occurs at, or at shallower depths than, the blueschist-out boundary. In Nankai and Cascadia the seismicity disappears above the antigorite-out boundary. Seismicity in the lower plane of the double seismic zone in Northern Japan also occurs at pressures and temperatures below the antigorite-out boundary. These observations strongly suggest that intermediate-depth seismicity is limited by the first major dehydration reaction in the crust and mantle and that fluids liberated by this phase change are primarily responsible for causing the earthquakes.

van Keken, Peter E.; Kita, Saeko; Nakajima, Junichi; Abers, Geoff; Hacker, Brad

2013-04-01

20

Semicatalytic hydrogenation and dehydrational condensation in the mechanism of the iso synthesis  

Microsoft Academic Search

Summary 1.In the synthesis of hydrocarbons from carbon monoxide and hydrogen over nonhydrogenating oxide catalysts (Al2O3, ThO2), which is called the iso synthesis, the hydrogenation processes are in the nature of semicatalytic reactions: carbon monoxide molecules are activated at be catalyst surface and are attached to the surface during the reaction, but the hydrogen molecules are thermally activated and react

Yao T. Eidus

1953-01-01

21

Dehydration reactions and intermediate depth earthquakes: Is gypsum the right analog material for an experimental investigation?  

NASA Astrophysics Data System (ADS)

In addition to melting or runaway creep along shear zones, plastic instabilities and solid-solid phase transitions, the mechanical effect of dehydration reactions has been suggested as a process responsible for the occurrence of intermediate depth earthquakes: If the porosity and permeability of the source region are low and the overall molar volume change of the reaction is positive the effective pressure acting on the rock is significantly reduced. Rocks initially deforming in their ductile field could then embrittle and fail. Experimental investigations have previously been performed on both dehydrating gypsum as an analog material and natural rock samples like serpentinite (antigorite). Dehydration in nature occurs syntectonically and the occurrence of earthquakes always requires at least a partial release of stored elastic energy associated with a drop in stress. Therefore only those deformation experiments are significant that are performed in parallel with the progressing reaction. In addition, at constant strain rate, the measured stress-strain curve must show a significant and rapid stress drop which is symptomatic for brittle failure. If this feature is not observed for a specific analog material, it is not suitable for the investigation of the above process in the context of earthquakes. For this reaction induced embrittlement to be expected the hydrous material should show brittle failure at low confining pressures. Nominally dry cylindrical samples of finegrained natural gypsum were strained up to 15% in a gas-medium apparatus at 0.1 to 50 MPa confining pressure, 20 to 110^oC and a strain rate of 1.5 \\cdot 10-6 to 1.5 \\cdot 10-5 1/s. The samples showed nearly ideally ductile behavior suggesting cataclastic flow. The flow stress was independent of strain rate, decreased with decreasing confining pressure and increasing temperature and had a maximum of 80 MPa. Only at room temperature and ambient pressure did the samples show slow strain weakening indicating ductile stress relaxation. The maximum flow stress in this case was only 30 MPa. This raises the question if for the case of gypsum a reaction induced reduction in effective pressure can initiate embrittlement. Results on clarifying deformation experiments under reaction conditions will be presented in addition to the results summarized above.

Milsch, H.; Scholz, C.

2003-04-01

22

Exponential enhancement of nuclear reactions in a condensed matter environment  

Microsoft Academic Search

A mechanism that uses the environment to increase the probability of the nuclear reaction when a beam of accelerated nuclei collides with a target nucleus implanted in condensed matter is suggested. The effect considered is exponentially large for low collision energies. For t+p collision the mechanism becomes effective when the energy of the projectile tritium is below 1 KeV per

M. Yu. Kuchiev; B. L. Altshuler; V. V. Flambaum

2004-01-01

23

ABOUT DEUTERIUM NUCLEAR REACTION RATE IN CONDENSED MATTER  

Microsoft Academic Search

The Coulomb barrier penetrability of two approaching nuclei is computed in the frame of the W.K.B approximation. A simple model for describing the screening effect of the Coulomb nuclear barrier by the high electron concentration in condensed matter is presented. The nuclear reaction rate of the hydrogen isotope nuclei, trapped in a metallic lattice is assessed, both for the unscreened

Dan Chicea

24

The reaction mechanism for dehydration process catalyzed by type I dehydroquinate dehydratase from Gram-negative Salmonella enterica  

NASA Astrophysics Data System (ADS)

The fundamental reaction mechanism for the dehydration process catalyzed by type I dehydroquinate dehydratase from Gram-negative Salmonella enterica has been studied by density functional theory calculations. The results indicate that the dehydration process undergoes a two-step cis-elimination mechanism, which is different from the previously proposed one. The catalytic roles of both the highly conserved residue His143 and the Schiff base formed between the substrate and Lys170 have also been elucidated. The structural and mechanistic insight presented here may direct the design of type I dehydroquinate dehydratase enzyme inhibitors as non-toxic antimicrobials, anti-fungals, and herbicides.

Yao, Yuan; Li, Ze-Sheng

2012-01-01

25

Porous magnesium carboxylate framework: synthesis, X-ray crystal structure, gas adsorption property and heterogeneous catalytic aldol condensation reaction.  

PubMed

A new three-dimensional alkaline-earth metal-organic framework (MOF) compound, [Mg(Pdc)(H(2)O)](n) (1) (H(2)Pdc = pyridine-2,5-dicarboxylic acid), has been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 features a 3D porous framework afforded by the Mg(2)-diad centers through formation of interconnected chair like structural motifs. A nitrogen adsorption study confirms the microporosity of compound 1 with a BET surface area of 211 ± 12 m(2) g(-1). Upon dehydration, the BET surface area of 1 is enhanced to a value of 463 ± 36 m(2) g(-1) due to removal of coordinated water molecule. After rehydration, the compound reverts to its original form as evidenced by powder X-ray diffraction and IR spectroscopic analysis and N(2) sorption measurement. Compound 1 retains its pore structure with a variable BET surface area in several cycles of dehydration and rehydration processes indicating robustness of the framework in [Mg(Pdc)(H(2)O)](n) (1). Compound 1 catalyzes the aldol condensation reactions of various aromatic aldehydes with acetone and cyclohexanone in heterogeneous conditions. Notably, the catalytic activity of the compound is enhanced upon dehydration. The catalyst can be recycled and reused several times without significant loss of activity. PMID:22584602

Saha, Debraj; Sen, Rupam; Maity, Tanmoy; Koner, Subratanath

2012-05-14

26

Structure-sensitivity and ensemble effects in reactions of strongly adsorbed intermediates. Catalytic dehydrogenation and dehydration of formic acid on nickel  

Microsoft Academic Search

Formic acid (HCOOH) dehydrogenates and dehydrates catalytically on Ni surfaces by unimolecular decomposition of strongly adsorbed formate intermediates. The rate of these reactions and the identity and decomposition selectivity of surface formate are not affected by Ni dispersion or by changes in Ni ensemble size resulting from Cu alloying or from coadsorption of Co and oxygen. Dehydrogenation and dehydration occur

Enrique Iglesia; Michel Boudart

1991-01-01

27

Catalytic reactions accompanied by capillary condensation. 1. Formulation of the problems  

Microsoft Academic Search

Capillary condensation was found to accompany gasphase catalytic reactions, in particular motor fuel hydrotreatment. Reaction conditions appear to differ significantly in large pores (filled with gas) and small ones (filled with liquid). Regarding capillary condensation we explain the “strange” dependences observed in this study or described in the literature. We have simulated jet fuel dearomatization taking into account capillary condensation

N. M. Ostrovskii; N. M. Bukhavtsova; V. K. Duplyakin

1994-01-01

28

Mechanistic insights into the rhenium-catalyzed alcohol-to-olefin dehydration reaction.  

PubMed

Rhenium-based complexes are powerful catalysts for the dehydration of various alcohols to the corresponding olefins. Here, we report on both experimental and theoretical (DFT) studies into the mechanism of the rhenium-catalyzed dehydration of alcohols to olefins in general, and the methyltrioxorhenium-catalyzed dehydration of 1-phenylethanol to styrene in particular. The experimental and theoretical studies are in good agreement, both showing the involvement of several proton transfers, and of a carbenium ion intermediate in the catalytic cycle. PMID:23946099

Korstanje, Ties J; Jastrzebski, Johann T B H; Klein Gebbink, Robertus J M

2013-08-14

29

Catalytic consequences of hydroxyl group location on the rate and mechanism of parallel dehydration reactions of ethanol over acidic zeolites  

Microsoft Academic Search

The effects of zeolite topology on the dehydration of oxygen-containing molecules were probed in steady-state and isotopic chemical reactions of ethanol over proton-form zeolite materials (FER, MFI and MOR) at low temperatures (368–409K). The measured rate of diethyl ether (DEE) synthesis was largely independent of ethanol partial pressure on all proton-form zeolites (FER, MFI, and MOR), indicating that DEE formation

Hsu Chiang; Aditya Bhan

2010-01-01

30

A DFT based equilibrium study on the hydrolysis and the dehydration reactions of MgCl2 hydrates  

NASA Astrophysics Data System (ADS)

Magnesium chloride hydrates are characterized as promising energy storage materials in the built-environment. During the dehydration of these materials, there are chances for the release of harmful HCl gas, which can potentially damage the material as well as the equipment. Hydrolysis reactions in magnesium chloride hydrates are subject of study for industrial applications. However, the information about the possibility of hydrolysis reaction, and its preference over dehydration in energy storage systems is still ambiguous at the operating conditions in a seasonal heat storage system. A density functional theory level study is performed to determine molecular structures, charges, and harmonic frequencies in order to identify the formation of HCl at the operating temperatures in an energy storage system. The preference of hydrolysis over dehydration is quantified by applying thermodynamic equilibrium principles by calculating Gibbs free energies of the hydrated magnesium chloride molecules. The molecular structures of the hydrates (n = 0, 1, 2, 4, and 6) of MgCl2 are investigated to understand the stability and symmetry of these molecules. The structures are found to be noncomplex with almost no meta-stable isomers, which may be related to the faster kinetics observed in the hydration of chlorides compared to sulfates. Also, the frequency spectra of these molecules are calculated, which in turn are used to calculate the changes in Gibbs free energy of dehydration and hydrolysis reactions. From these calculations, it is found that the probability for hydrolysis to occur is larger for lower hydrates. Hydrolysis occurring from the hexa-, tetra-, and di-hydrate is only possible when the temperature is increased too fast to a very high value. In the case of the mono-hydrate, hydrolysis may become favorable at high water vapor pressure and at low HCl pressure.

Smeets, B.; Iype, E.; Nedea, S. V.; Zondag, H. A.; Rindt, C. C. M.

2013-09-01

31

A DFT based equilibrium study on the hydrolysis and the dehydration reactions of MgCl2 hydrates.  

PubMed

Magnesium chloride hydrates are characterized as promising energy storage materials in the built-environment. During the dehydration of these materials, there are chances for the release of harmful HCl gas, which can potentially damage the material as well as the equipment. Hydrolysis reactions in magnesium chloride hydrates are subject of study for industrial applications. However, the information about the possibility of hydrolysis reaction, and its preference over dehydration in energy storage systems is still ambiguous at the operating conditions in a seasonal heat storage system. A density functional theory level study is performed to determine molecular structures, charges, and harmonic frequencies in order to identify the formation of HCl at the operating temperatures in an energy storage system. The preference of hydrolysis over dehydration is quantified by applying thermodynamic equilibrium principles by calculating Gibbs free energies of the hydrated magnesium chloride molecules. The molecular structures of the hydrates (n = 0, 1, 2, 4, and 6) of MgCl2 are investigated to understand the stability and symmetry of these molecules. The structures are found to be noncomplex with almost no meta-stable isomers, which may be related to the faster kinetics observed in the hydration of chlorides compared to sulfates. Also, the frequency spectra of these molecules are calculated, which in turn are used to calculate the changes in Gibbs free energy of dehydration and hydrolysis reactions. From these calculations, it is found that the probability for hydrolysis to occur is larger for lower hydrates. Hydrolysis occurring from the hexa-, tetra-, and di-hydrate is only possible when the temperature is increased too fast to a very high value. In the case of the mono-hydrate, hydrolysis may become favorable at high water vapor pressure and at low HCl pressure. PMID:24089772

Smeets, B; Iype, E; Nedea, S V; Zondag, H A; Rindt, C C M

2013-09-28

32

Thermodynamics and kinetics of the dehydration reaction of FePO4·2H2O  

NASA Astrophysics Data System (ADS)

The thermal decomposition kinetics of FePO4·2H2O in dynamical air atmosphere was studied by mean TG-DTG-DTA. The stage and product of the thermal decomposition were determined. A number of kinetic models and calculation procedures were used to determine the kinetic triplet and thermodynamic parameters characterizing the dehydration process. The obtained activation energy and most kinetic model indicate the single kinetic mechanism and three-dimension diffusion as “Ginstling-Brounstein equation (D4 model)”, respectively. The thermodynamic functions (?H*, ?G* and ?S*) of the dehydration reaction are calculated by the activated complex theory and indicate that the process is non-spontaneous without connecting with the introduction of heat. The kinetic and thermodynamic results were satisfactory which present good correlation with a linear correlation coefficient close to unit a low standard deviation.

Boonchom, Banjong; Puttawong, Spote

2010-05-01

33

Condensation  

NSDL National Science Digital Library

In this activity, learners explore the process of condensation. After seeing water vapor condense, learners will help design a test to see if cooling water vapor has an effect on the rate of condensation.

Kessler, James H.; Galvan, Patricia M.

2007-01-01

34

A new BPO 4 catalyst in organic reactions. Dehydration of cycloalkanols  

Microsoft Academic Search

The synthesis of some new and economical BPO4 catalysts is described. The chemical and textural properties and the thermogravimetric analysis (TGA) of these catalysts is given. The dehydration of cyclohexanol, cycloheptanol and cyclooctanol catalyzed by these new BPO4 catalysts is studied using the microcatalytic pulse technique.

J. M. Marinas; J. V. Sinisterra

1985-01-01

35

Variational principles for describing chemical reactions: Condensed reactivity indices  

NASA Astrophysics Data System (ADS)

Two recent papers [P. W. Ayers and R. G. Parr, J. Am. Chem. Soc. 122, 2010 (2000); 123, 2007 (2001)] have shown how variational principles for the energy may be used to derive and elucidate the significance of the chemical reactivity indices of density-functional theory. Here, similar ideas are applied, yielding a systematic, mathematically rigorous, and physically sound approach to condensed reactivity indices. First, we use the variational principle for the energy to derive an expression for the condensed Fukui function index in terms of the condensed hardness kernel. Next, we address an important open problem pertaining to condensed reactivity indices: when (if ever) is the condensed Fukui function for an atom in a molecule negative? In particular, our analysis confirms the observation, hitherto based only on computational evidence, that the Hirshfeld partitioning is optimal for obtaining non-negative Fukui functions. We also hypothesize that the strong diagonal dominance of the condensed hardness kernel is sufficient for the non-negativity of the Fukui function. Errors in the partitioning of molecules into atoms and inadequate treatment of correlation are pinpointed as the most likely causes of negative condensed Fukui functions. We conclude by noting that the condensed Fukui functions are, in some respects, more appropriate indicators of a molecular site's reactivity than the Fukui function itself.

Ayers, Paul W.; Morrison, Robert C.; Roy, Ram K.

2002-05-01

36

Mining chemical reactions using neighborhood behavior and condensed graphs of reactions approaches.  

PubMed

This work addresses the problem of similarity search and classification of chemical reactions using Neighborhood Behavior (NB) and Condensed Graphs of Reaction (CGR) approaches. The CGR formalism represents chemical reactions as a classical molecular graph with dynamic bonds, enabling descriptor calculations on this graph. Different types of the ISIDA fragment descriptors generated for CGRs in combination with two metrics--Tanimoto and Euclidean--were considered as chemical spaces, to serve for reaction dissimilarity scoring. The NB method has been used to select an optimal combination of descriptors which distinguish different types of chemical reactions in a database containing 8544 reactions of 9 classes. Relevance of NB analysis has been validated in generic (multiclass) similarity search and in clustering with Self-Organizing Maps (SOM). NB-compliant sets of descriptors were shown to display enhanced mapping propensities, allowing the construction of better Self-Organizing Maps and similarity searches (NB and classical similarity search criteria--AUC ROC--correlate at a level of 0.7). The analysis of the SOM clusters proved chemically meaningful CGR substructures representing specific reaction signatures. PMID:22894688

de Luca, Aurélie; Horvath, Dragos; Marcou, Gilles; Solov'ev, Vitaly; Varnek, Alexandre

2012-09-04

37

Knoevenagel condensation reaction between benzaldehyde and ethyl acetoacetate in microreactor and membrane microreactor  

Microsoft Academic Search

The Knoevenagel condensation reaction between benzaldehyde and ethyl acetoacetate was performed in microreactor using Cs-exchanged NaX catalyst and NaA membrane. The laminar flow and slow diffusion of the bulky product molecules in the microchannel resulted in the further reactions of the main Knoevenagel condensation product, 2-acetyl-3-phenylacrylic acid ethyl ester that led to byproduct formation and poorer reaction selectivity. Replacing the

W. N. Lau; K. L. Yeung; R. Martin-Aranda

2008-01-01

38

Onion dehydration  

SciTech Connect

This article describes the onion dehydration process as generally practiced in the United States. The actual processing steps from harvest to final product, and geothermal applications for power production and energy requirements in the dehydration industry are discussed. A design of a dehydrator converted to geothermal energy usage is included.

Lund, J.W.; Lienau, P.J.

1994-07-01

39

The possible role of solid surface area in condensation reactions during chemical evolution: Reevaluation  

Microsoft Academic Search

Summary Published data on adsorption and condensation of amino acids, purine and pyrimidine bases, sugars, nucleosides, and nucleotides are analyzed in connection with Bernal's hypothesis that clays and other minerals may have provided the most likely surface for adsorption and condensation of these molecules in prebiotic times. Using surface concentration and reaction rate as the main criteria for the feasibility

N. Lahav; S. Chang

1976-01-01

40

Heteroatom directed aromatic lithiation reactions for the synthesis of condensed heterocyclic compounds  

Microsoft Academic Search

Heteroatom directed aromatic lithiation reaction is now widely used for the synthesis of condensed heterocyclic compounds. New synthesis of condensed heterocyclic compounds are now known which can provide compounds not readily available by the usual acid catalysed methods. In this chapter these newer methods and their applications to several natural products are presented. Also presented, in some cases, are other

Nurani Sivaramakrishna Narasimhan; Raghao Shivaram Mali

41

Surfactant-assisted organic reactions in water. Effect of ultrasound on condensation reactions between active methylene compounds and arylaldehydes.  

PubMed

A series of quaternary ammonium salts has been tested as phase transfer agents to promote condensation reactions in an aqueous solution of sodium hydroxide in the absence of any organic solvent. Methyltrioctylammonium chloride (Aliquat 336) emerges as the most efficient catalyst. Sonication of the reaction media has a poor but positive kinetic effect. PMID:11105320

Vanden Eynde, J J; Mutonkole, K; Van Haverbeke, Y

2001-01-01

42

Hydrolysis/dehydration/aldol-condensation/hydrogenation of lignocellulosic biomass and biomass-derived carbohydrates in the presence of Pd/WO3-ZrO2 in a single reactor.  

PubMed

Hydrolysis/dehydration/aldol-condensation/hydrogenation of lignocellulosic-biomass (corncobs) and biomass-derived carbohydrates (tapioca flour) to produce water-soluble C5-C15 compounds was developed in a single reactor system. WO3-ZrO2 efficiently catalyzed the hydrolysis/dehydration of these feedstocks to 5-hydroxymethylfurfural and furfural, while the impregnation of WO3-ZrO2 with Pd allowed sequential aldolcondensation/hydrogenation of these furans to C5-C15 compounds. The highest C5-C15 yields of 14.8-20.3% were observed at a hydrolysis/dehydration temperature of 573 K for 5 min, an aldol-condensation temperature of 353 K for 30 h, and a hydrogenation temperature of 393 K for 6 h. The C5-C15 yield from tapioca flour was higher than that from corncobs (20.3% compared to 14.8%). Tapioca flour produced more C6/C9/C15, whereas corncobs generated more C5/C8/C13 compounds due to the presence of hemicellulose in the corncobs. These water-soluble organic compounds can be further converted to liquid alkanes with high cetane numbers for replacing diesel fuel in transportation applications. PMID:20934873

Dedsuksophon, W; Faungnawakij, K; Champreda, V; Laosiripojana, N

2010-09-22

43

Interaction of Yeasts with the Products Resulting from the Condensation Reaction between (+)Catechin and Acetaldehyde  

Microsoft Academic Search

The condensation reaction between (+)-catechin and acetaldehyde was studied in model solutions in the presence and absence yeasts in order to evaluate its contribution to color changes in fermented drinks such as white wine. On the basis of the results, the yeasts retain the oligomers produced in the reaction, their retention ability increasing for higher polymerization degrees. As a result,

Azahara Lopez-Toledano; Debora Villaño-Valencia; Manuel Mayen; Julieta Merida; Manuel Medina

2004-01-01

44

Behaviour of dehydrated baker’s yeast during reduction reactions in a biphasic medium  

Microsoft Academic Search

The behaviour of dry baker’s yeast ( Saccharomyces cerevisiae type II, Sigma) used as biocatalyst without preliminary growth for the synthesis of 2-heptanol from 2-heptanone in a biphasic system is presented. Cells undergo intracellular trehalose consumption with a stoichiometric ethanol production during the first 15 h of the process. This metabolism is then replaced by acetate accumulation. These reactions are disconnected

L. Cappaert; C. Larroche

2004-01-01

45

Structure-sensitivity and ensemble effects in reactions of strongly adsorbed intermediates. Catalytic dehydrogenation and dehydration of formic acid on nickel  

SciTech Connect

Formic acid (HCOOH) dehydrogenates and dehydrates catalytically on Ni surfaces by unimolecular decomposition of strongly adsorbed formate intermediates. The rate of these reactions and the identity and decomposition selectivity of surface formate are not affected by Ni dispersion or by changes in Ni ensemble size resulting from Cu alloying or from coadsorption of Co and oxygen. Dehydrogenation and dehydration occur via identical intermediates that require small Ni ensembles (1-2 surface atoms) and that decompose with similar activation energy, a surprising result because the required molecular rearrangements differ markedly in the two decomposition modes. The authors suggest that reaction trajectories bifurcate after the formation of the activated complex in the rate-determining formate-decomposition step, leading to two kinetically indistinguishable decomposition paths. The decomposition selectivity on metal catalysts is controlled by entropy differences between the two reaction paths and by the binding energy of adsorbed oxygen atoms on these metal surfaces.

Iglesia, E. (Exxon Research and Engineering Co., Annandale, NJ (United States)); Boudart, M. (Stanford Univ., CA (United States))

1991-09-05

46

Ion-molecule condensation reactions: a mechanism for organic synthesis in ionized reducing atmospheres.  

PubMed

The CH3+ ion, formed in ionized methane, undergoes consecutive eliminative condensation reactions with methane to form the carbonium ions C2H5+, i-C3H7+ and t-C4H9+. At T smaller than 500 degrees K, NCH4 greater than 10(16) cm-3 these ions react with NH3 in competitive condensation -- H+ transfer reactions, e.g. C2H5 + NH3 M leads to C2H5NH3+ leads to NH4+ + C2H4 At particle densities of NCH4 smaller than 10(16) cm-3 proton transfer is the only significant reaction channel. At NCH4 greater than 10(17) cm-3 condensation constitutes 5--20% of the overall reactions. The product of the condensation reaction further associates with CO2 to form C2H5NH3+ . CO2; the atomic composition of this cluster ion is identical with the protonated amino acid alanine. The carbonium ions i-C3H7+ and t-C4H9+ condense also with HCN to yield protonated isocyanides. HCNH% also appears to condense with HCN at T greater than 570 degrees K, and form cluster ions with HCN at lower temperatures. The rate constants of the condensation reactions vary with temperature and pressure in a complex manner. Under conditions similar to those on Titan at an altitude of 100 km (T = 100--150 degrees K, NCH4 approximately 10(18) cm-3), with a methane atmosphere containing 1% H2 and traces of NH3 and H2O, ion-molecule condensation reactions followed by H+ transfer are expected to lead to the atmospheric synthesis of C2H6, C3H8, CH3OH, C2H5OH and the terminal ions NH4+, CH3NH3+ and C2H5NH3+. At higher temperatures (250 degrees K smaller than T smaller than 400 degrees K), the synthesis of i-C4H10, i-C3H7OH and t-C4H9OH and of the ions i-C3H7NH3+ and t-C4H9NH3+ is also expected. Electron recombination of the terminal ions may yield amines, imines and nitriles. Cycles of protonation and dissociative recombination of the alkanes and alcohols produced in condensation reactions will also produce unsaturated hydrocarbons, ketones and aldehydes in the ionized atmosphere. PMID:752132

Meot-Ner, M

1978-12-01

47

Organic reactions catalyzed by methylrhenium trioxide: Dehydration, amination, and disproportionation of alcohols  

SciTech Connect

Methylrhenium trioxide (MTO) is the first transition metal complex in trace quantity to catalyze the direct formation of ethers from alcohols. The reactions are independent of the solvents used: benzene, toluene, dichloromethane, chloroform, acetone, and in the alcohols themselves. Aromatic alcohols gave better yields than aliphatic. Reactions between two different alcohols could also be used to prepare unsymmetric ethers, the best yields being obtained when one of the alcohols is aromatic alcohols proceeding in better yield. When primary (secondary) amines were used as the limiting reagent, direct amination of alcohols catalyzed by MTO gave good yields of the expected secondary (tertiary) amines at room temperature. Disproportionation of alcohols to alkanes and carbonyl compounds was also observed for aromatic alcohols in the presence of MTO. On the basis of the results of this investigation and a comparison with the interaction between MTO and water, a concerted process and a mechanism involving carbocation intermediates have been suggested. 5 tabs.

Zhu, Zuolin; Espenson, J.H. [Iowa State Univ., Ames, IA (United States)

1996-01-12

48

Stereochemistry of heterogeneous catalytic reactions. Dehydrogenation and dehydration of stereoisomeric cyclohexanediols on copper  

Microsoft Academic Search

Transformations of six isomeric cyclohexanediols on copper catalysts were studied. The transformation rate sequence is 1,4<1,2<1,3. 1,3-diols selectively yield cyclohexanone (and cyclohexanol). On Cu\\/Al, 1,2-and 1,4-diols give several products, mainly cyclohexanone and hydroxycyclohexanones. Cn Cu, these latter are formed with much higher selectivity. A correlation was found between the diol stereostructures and reaction directions.

Á. Molnár; M. Bartók

1976-01-01

49

Theory of reversible electron transfer reactions in a condensed phase.  

PubMed

We have derived an exact analytical expression for the average forward rate of a reversible electron transfer reaction, modeled through a reaction coordinate undergoing diffusive motion in arbitrary potential wells of the reactant and the product in presence of a localized sink of arbitrary location and strength. The dynamics of diffusive motion is described by employing two coupled generalized diffusion reaction (Smoluchowski) equations with coordinate dependent diffusivity and delta sink. The average forward electron transfer rate constant obtained here for the system, with equilibrium or nonequilibrium distributions as initial condition, is determined by the forward and backward rate constants calculated based on the transition state theory and the weighted average rate for the well dynamics. We also discuss various limiting cases for the rate of electron transfer reactions corresponding to the different experimental situations. As an illustrative example, we have considered back electron transfer (ET) reaction and shown that the present theory can explain the non-Marcus free energy gap dependence of the rate of ET reactions. More importantly, the approach presented here can easily be extended to systems describing the dynamics of diffusive motion in coupled multipotential surfaces associated with electron transfer reactions. PMID:20866692

Dhole, Kajal; Modak, Brindaban; Samanta, Alok; Ghosh, Swapan K

2010-07-20

50

Tandem Aldol Condensation - Platinacycle-Catalyzed Addition Reactions of Aldehydes, Methyl Ketones and Arylboronic Acids  

PubMed Central

Tandem aldol condensation of aldehydes with methyl ketones followed by anionic four-electron donor-based (Type I) platinacycle-catalyzed addition reactions of arylboronic acids to form ?-arylated ketones is described. Good to excellent yields of ?-arylated ketones were obtained for the tandem reactions of aromatic/aliphatic aldehydes, methyl ketones and arylboronic acids, and moderate yields were observed for the tandem reaction with ?, ?-unsaturated aldehydes as the aldehyde source.

Liao, Yuan-Xi; Hu, Qiao-Sheng

2013-01-01

51

Tandem Aldol Condensation - Platinacycle-Catalyzed Addition Reactions of Aldehydes, Methyl Ketones and Arylboronic Acids.  

PubMed

Tandem aldol condensation of aldehydes with methyl ketones followed by anionic four-electron donor-based (Type I) platinacycle-catalyzed addition reactions of arylboronic acids to form ?-arylated ketones is described. Good to excellent yields of ?-arylated ketones were obtained for the tandem reactions of aromatic/aliphatic aldehydes, methyl ketones and arylboronic acids, and moderate yields were observed for the tandem reaction with ?, ?-unsaturated aldehydes as the aldehyde source. PMID:23335856

Liao, Yuan-Xi; Hu, Qiao-Sheng

2012-09-01

52

Phenylboronic acid mediated triple condensation reactions of phloroglucinol and unsaturated carbonyl compounds.  

PubMed

[reaction: see text] A remarkable phenylboronic acid mediated triple condensation reaction of phloroglucinol (1,3,5-trihydroxybenzene) with a series of alpha,beta-unsaturated carbonyl compounds is reported. This experimentally simple reaction afforded novel C3-symmetric 2H-chromene derivatives. These derivatives represent structural analogues of the natural product xyloketal A, which has been reported to be a potent inhibitor of acetylcholine esterase. PMID:15673266

Pettigrew, Jeremy D; Cadieux, Jay A; So, Simon S S; Wilson, Peter D

2005-02-01

53

Bimolecular condensation of ethanol to 1-butanol catalyzed by alkali cation zeolites  

SciTech Connect

This study reports that ethanol is converted primarily into 1-butanol by a bimolecular condensation on alkali cation zeolites. For this base-catalyzed reaction, Rb-LiX exhibits the highest reaction activity and 1-butanol selectivity among zeolites employed. The reaction temperature and the contact time have a distinct influence on the condensation reactivity. It is also confirmed that the reaction does not proceed through aldol condensation. Thus, the authors propose a reaction mechanism in which one molecule of ethanol, whose C-H bond in the [beta]-position is activated by the basic zeolite, condenses with another molecule of ethanol by dehydration. 15 refs., 8 figs., 5 tabs.

Chun Yang; Zhongyue Meng (Nanjing Normal Univ., People's Republic (China))

1993-07-01

54

Optical pump-terahertz spectroscopy of condensed phase reaction dynamics  

Microsoft Academic Search

The general theoretical and experimental principles of optical pump-THz probe spectroscopy of chemical reactions in liquids is presented. Background on specific difficulties encountered in the experimental observation is reviewed. Chiefly, signal-to-noise ratios currently limit the quality of information that can be extracted from optical pump-THz prove data on chemical reactions. This issue is shown to be connected to the assumption

Bret N. Flanders; Norbert F. Scherer

1998-01-01

55

Electron transfer reactions in condensed phase: effect of reversibility.  

PubMed

We propose a generalized one-dimensional kinetic equation for multidimensional reversible electron transfer (ET) reaction with a nonequilibrium situation as the initial condition. The rate constant for the forward reversible ET reaction obtained here consists of the rate for the corresponding irreversible ET reaction, and an extra term due to reversibility of the ET process which includes the rates of diffusion dynamics in the reactant and product wells. In order to understand the effect of reversibility, we consider back ET reaction in a system consisting of an electron donor-acceptor pair in a solvent modeled through low frequency solvent collective coordinates (multidimensional) characterized by the orientational polarization and slowly relaxing one-dimensional vibrational mode. We propose here a new generalized polarization energy functional corresponding to the extension of the continuum version for the same, which has opened up the possibility of inclusion of molecular nature of the solvent into the solvent reorganization energy. We then derive an exact expression for the ET rate for this model system. The numerical results calculated by using the proposed one-dimensional approach are shown to be in good agreement with the available experimental results. Non-Marcus free energy gap dependence of the rates observed here for the reversible and irreversible ET reactions are very close to each other in the barrierless region, while for other situations, the rate for the former process is found to be less than the latter. The extra term, which makes the difference between the rate constants for irreversible and reversible ET reactions, is found to be contributed by the diffusion dynamics from both reactant and product wells but the dominating contribution is provided mainly by the product well. PMID:22463277

Dhole, Kajal; Jena, Naresh K; Samanta, Alok; Ghosh, Swapan K

2012-02-07

56

Cross-condensation reactions in an organically modified silica sol-gel  

SciTech Connect

High resolution {sup 29}Si NMR has been used to study the extent of cross condensation taking place in a hybrid organic/inorganic sol-gel system. Tetraethoxysilane (TEOS) and methltriethoxysilane (MTEOS) sol-gels were chosen for this purpose. The sols were prepared by acid catalyzed hydrolysis of TEOS and MTEOS with a H{sub 2}O/Si ratio of 0.3. {sup 29}Si NMR shows signals due to both self-condensation and cross-condensation between TEOS and MTEOS. Resonance assignments were made by comparing the positions and intensities of peaks in the spectra of single and multicomponent systems. It was found that, within experimental error, the self- and cross-condensation rates are equal and that extensive molecular level mixing takes place during the early stages of the reaction.

Prabakar, S.; Raman, N.K. [New Mexico Univ., Albuquerque, NM (United States); Assink, R.A. [Sandia National Labs., Albuquerque, NM (United States); Brinker, C.J. [New Mexico Univ., Albuquerque, NM (United States)]|[Sandia National Labs., Albuquerque, NM (United States)

1993-12-31

57

A biocompatible condensation reaction for controlled assembly of nanostructures in live cells  

PubMed Central

Through controlled synthesis and molecular assembly, biological systems are able to organize molecules into supramolecular structures that carry out sophisticated processes. Although chemists have reported a few examples of supramolecular assembly in water, the controlled covalent synthesis of large molecules and structures in vivo has remained challenging. Here we report a condensation reaction between 1,2-aminothiol and 2-cyanobenzothiazole that occurs in vitro and in living cells under the control of pH, disulfide reduction and enzymatic cleavage. In vitro, the size and shape of the condensation products, and nanostructures subsequently assembled, were different in each case and could thus be controlled by tuning the structure of the monomers. Direct imaging of the products obtained in the cells revealed their locations – near the Golgi bodies under enzymatic cleavage control – demonstrating the feasibility of a controlled and localized reaction in living cells. This intracellular condensation process enabled the imaging of the proteolytic activity of furin.

Liang, Gaolin; Ren, Hongjun; Rao, Jianghong

2011-01-01

58

2-Quinazolylguanidines in Heterocyclization Reactions. 2. Condensation with ?,?-Unsaturated Carbonyl Compounds  

Microsoft Academic Search

4,6,6-Trimethyl-1,4-dihydropyrimidines have been synthesized by condensation of 2-quinazolylguanidines with mesityl oxide. The analogous reaction with benzalacetone leads to unstable 4-methyl-6-phenyl-1,4-dihydropyrimidines, which are oxidized to the corresponding 4-methyl-6-phenylpyrimidines.

Kh. S. Shikhaliev; A. V. Falaleev; G. I. Ermolova; A. S. Solov'ev

2002-01-01

59

Probing the Rate-Determining Step of the Claisen-Schmidt Condensation by Competition Reactions  

ERIC Educational Resources Information Center

Competition experiments are a useful tool for preliminary study of the linear free energy relationship of organic reactions. This article describes a physical organic experiment for upper-level undergraduates to identify the rate-determining step of the Claisen-Schmidt condensation of benzaldehyde and acetophenone by studying the linear free…

Mak, Kendrew K. W.; Chan, Wing-Fat; Lung, Ka-Ying; Lam, Wai-Yee; Ng, Weng-Cheong; Lee, Siu-Fung

2007-01-01

60

Probing the Rate-Determining Step of the Claisen-Schmidt Condensation by Competition Reactions  

ERIC Educational Resources Information Center

|Competition experiments are a useful tool for preliminary study of the linear free energy relationship of organic reactions. This article describes a physical organic experiment for upper-level undergraduates to identify the rate-determining step of the Claisen-Schmidt condensation of benzaldehyde and acetophenone by studying the linear free…

Mak, Kendrew K. W.; Chan, Wing-Fat; Lung, Ka-Ying; Lam, Wai-Yee; Ng, Weng-Cheong; Lee, Siu-Fung

2007-01-01

61

An investigation of the role of water on retrograde/condensation reactions and enhanced liquefaction yields  

SciTech Connect

Changes in coal structure that occur during coal drying and steam pretreatments will be measured in order to determine what effect water has on retrograde/condensation reactions, and to determine how water enhances coal reactivity toward liquefaction. Coal drying experiments were begun using thermal, microwave, and chemical methods; NMR data were collected. A stirred microautoclave reactor system was acquired.

Miknis, F.P.

1992-10-01

62

Negative Resist for i-Line Lithography Utilizing Acid Catalyzed Silanol-Condensation Reaction  

NASA Astrophysics Data System (ADS)

Negative resist systems composed of a novolak resin, diphenylsilanediol (Ph2Si(OH)2) and an acid generator are investigated for i-line lithography. The reaction in this resist system is based on an acid-catalyzed condensation reaction; the acid produced in the exposed area induces a condensation reaction of Ph2Si(OH)2 during post-exposure baking. The condensation product, siloxane, acts as an aqueous-base dissolution inhibitor, while silanol compounds in unexposed areas work as dissolution accelerators. The resist composed of a novolak resin, Ph2Si(OH)2 and 2-naphthoylmethyl-tetramethylenesulfonium hexafluoroantimonate (NMTMS-SbF6) shows a sensitivity of about 200 mJ/cm2 at 365 nm. This sensitivity is lower than that at 248 nm when triphenylsulfonium triflate (Ph3S+OTf-) is used as an acid generator, which can be ascribed to the low quantum yield of acid generation from NMTMS-SbF6. Using this resist, 0.3 ?m space patterns with 1 ?m film thickness were obtained by combining an i-line stepper with a phase-shifting mask.

Hayashi, Nobuaki; Tadano, Keiko; Tanaka, Toshihiko; Shiraishi, Hiroshi; Ueno, Takumi; Iwayanagi, Takao

1990-11-01

63

Rate-promoting vibrations and coupled hydrogen-electron transfer reactions in the condensed phase: A model for enzymatic catalysis  

Microsoft Academic Search

A model is presented for coupled hydrogen-electron transfer reactions in condensed phase in the presence of a rate promoting vibration. Large kinetic isotope effects (KIEs) are found when the hydrogen is substituted with deuterium. While these KIEs are essentially temperature independent, reaction rates do exhibit temperature dependence. These findings agree with recent experimental data for various enzyme-catalyzed reactions, such as

Joshua S. Mincer; Steven D. Schwartz

2004-01-01

64

Rate-promoting vibrations and coupled hydrogen–electron transfer reactions in the condensed phase: A model for enzymatic catalysis  

Microsoft Academic Search

A model is presented for coupled hydrogen–electron transfer reactions in condensed phase in the presence of a rate promoting vibration. Large kinetic isotope effects (KIEs) are found when the hydrogen is substituted with deuterium. While these KIEs are essentially temperature independent, reaction rates do exhibit temperature dependence. These findings agree with recent experimental data for various enzyme-catalyzed reactions, such as

Joshua S. Mincer; Steven D. Schwartz

2004-01-01

65

Gas-Phase Condensation Reactions of SixOyHz- Oxyanions with H2O  

SciTech Connect

Water was reacted with gas-phase oxyanions having the general composition SixOyHz- that were formed and isolated in an ion trap-secondary ion mass spectrometer (IT-SIMS). The radical SiO2- reacted slowly with H2O to abstract HO, forming SiO3H-, at a rate of 8 × 10-13 cm3 molecule-1 s-1, corresponding to an efficiency of about 0.03% compared with the theoretical collision rate constant (average dipole orientation). The product ion SiO3H- underwent a consecutive condensation reaction with H2O to form SiO4H3- at a rate that was approximately 0.4-0.7% efficient. SiO4H3- did not undergo further reaction with water. The multiple reaction pathways by which radical SiO3- reacted with H2O were kinetically modeled using a stochastic approach. SiO3- reacted with water by three parallel reaction pathways: (1) abstraction of a radical H to form SiO3H-, which then reacted with a second H2O to form SiO4H3-; (2) abstraction of a radical OH to form SiO4H-, which further reacted by consecutive H abstractions to form SiO4H2- and then SiO4H3-; and (3) condensation with H2O to form SiO4H2-, which subsequently abstracted a radical H from a second H2O to form SiO4H3-. In all of these reactions, the rate constants were determined to be very slow, as determined by both direct measurement and stochastic modeling. For comparison, the even electron ion Si2O5H- was also investigated: it underwent condensation with H2O to form Si2O6H3-, with a rate constant corresponding to 50% efficiency. The reactions were also modeled using ab initio calculations at the UB3LYP/6-311+G(2d,p) level. Addition of H2O to SiO3-, SiO3H-, and Si2O5H- was calculated to be approximately 42, 45, and 55 kcal mol-1 exothermic, respectively, and encountered low activation barriers. Modeling of SiO2- and SiO3- reactions with H2O failed to produce radical abstraction reaction pathways observed in the IT-SIMS, possibly indicating that alternative reaction mechanisms are operative.

Groenewold, Gary Steven; Scott, Jill Rennee; Gianotto, Anita Kay; Hodges, Brittany DM; Kessinger, Glen Frank; Benson, Michael Timothy; Wright, J. B.

2001-09-01

66

Kinetics of acid-catalyzed aldol condensation reactions of aliphatic aldehydes  

NASA Astrophysics Data System (ADS)

Field observations of atmospheric aerosols have established that organic compounds compose a large fraction of the atmospheric aerosol mass. However, the physical/chemical pathway by which organic compounds are incorporated into atmospheric aerosols remains unclear. The potential role of acid-catalyzed reactions of organic compounds on acidic aerosols has been explored as a possible chemical pathway for the incorporation of organic material into aerosols. In the present study, ultraviolet-visible (UV-vis) spectroscopy was used to monitor the kinetics of formation of the products of the acid-catalyzed aldol condensation reaction of a range of aliphatic aldehydes (C 2-C 8). The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature. While the kinetic data are generally consistent with previous laboratory reports of aldehyde reactivity in various sulfuric acid media, the aldol condensation reactions involving aliphatic aldehydes do not appear fast enough to be responsible for significant transfer of organic material into atmospheric aerosols.

Casale, Mia T.; Richman, Aviva R.; Elrod, Matthew J.; Garland, Rebecca M.; Beaver, Melinda R.; Tolbert, Margaret A.

67

The base catalyzed hydrolysis and condensation reactions of dilute and concentrated TEOS (Tetraethylorthosilicate) solutions: Draft  

SciTech Connect

The synthesis of submicron silica particles by the hydrolysis and condensation of dilute and concentrated solutions of tetraethylorthosiliate (TEOS) has been studied in low-molecular weight alcohols (C/sub 1/--C/sub 4/). A base (ammonia) is used to catalyze the reaction. Raman spectroscopy, gas chromatography and the molybdate method are used to establish the hydrolysis and condensation kinetics. Dynamic and classical light-scattering techniques are employed to monitor particle growth and particle number concentration kinetics, and particle size distribution. The effects of solvent and TEOS concentration on the degree of monodispersity of the particles will be discussed. Furthermore, the chemical and particle growth data will be used to test the theories of homogeneous nucleation and coagulative nucleation, which have been proposed as the mechanisms that govern the growth of submicron monodisperse silica particle by TEOS hydrolysis. 13 refs., 4 figs., 1 tab.

Harris, M.T.; Byers, C.H.; Brunson, R.R.

1989-01-01

68

A solid-state NMR study of condensation/retrograde reactions during coal liquefaction  

SciTech Connect

The objective of this work is to perform an NMR study of the aromaticity in coal, coal derived products and/or model compounds generated by pyrolysis and thermal solubilization of coal in the presence of a hydrogen donor solvent. Cross Polarization with Magic-Angle Spinning (CP/MAS) will be used to measure the carbon aromaticity, and Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR techniques will be used to measure the hydrogen aromaticity. From these NMR measurements the aromatic hydrogen-to-carbon ratio will be obtained and used to study condensation/retrograde reactions during coal liquefaction. 2 refs., 1 fig.

Miknis, F.P.

1989-11-01

69

A novel convenient approach towards pyrrolo[1,2-b]pyridazines through a domino coupling-isomerization-condensation reaction.  

PubMed

A novel Pd/Cu catalyzed domino reaction for the synthesis of functionalized pyrrolo[1,2-b]pyridazines from readily accessible (hetero)aryl propargyl alcohols and 1-amino-2-bromopyrroles was developed. This cascade process involves a Sonogashira cross-coupling reaction, an isomerization and an intramolecular condensation. PMID:23487245

Wang, Meng; Tan, Cun; He, Qian; Xie, Yuyuan; Yang, Chunhao

2013-04-28

70

Study on the Condensation Reaction of preparing Vanillin from Guaiacol and Glyoxylic Acid by a novel Catalyst  

Microsoft Academic Search

As an intermediate for preparing vanillin derived from glyoxylic acid, 3-methoxy-4-hydroxymandelic acid (MHMA) was synthesized based on condensation of guaiacol with glyoxylic acid in the presence of a novel catalyst. The influence of the novel catalyst on the condensation reaction was investigated. The experimental results showed that the novel catalyst was suitable for the formation of 3-methoxy-4-hydroxymandelic acid from guaiacol

WEI Guo-feng; LIU Nai-qing

71

Photochemical reactions in dehydrated photosynthetic organisms, leaves, chloroplasts and photosystem II particles: reversible reduction of pheophytin and chlorophyll and oxidation of ?-carotene  

NASA Astrophysics Data System (ADS)

Photoreactions of dehydrated leaves, isolated broken chloroplasts and PSII membrane fragments of spinach ( Spinacia oleracea) were studied at different air humidities and compared with photoreactions of dry fronds of a fern, Polypodium vulgare, and a dry lichen, Parmelia sulcata, which in contrast to spinach are insensitive to photoinactivation in the dry state. Even in very dry air, P700 in the reaction center of photosystem I of dry leaves was oxidized, and the primary quinone acceptor Q A in the reaction center of photosystem II was photoreduced by low light. These reactions were only very slowly reversed in the dark and saturated under low light intensity. Light-minus-dark difference absorption spectra of the dry leaves, isolated chloroplasts and PSII membrane fragments measured at higher light intensities revealed absorbance changes of ?-carotene at 500 nm (light-dependent bleaching) and 980 nm (light-dependent band formation) and bleaching of chlorophyll at 436 and 680 nm with appearance of bands at 450 and 800 nm. Decrease of chlorophyll fluorescence upon strong illumination indicated photoaccumulation of a quencher. All these changes were kinetically related and readily reversible. They are interpreted to show light-induced oxidation of ?-carotene (Car) and reduction of chlorophyll-680 (Chl-680) in the reaction center of photosystem II of the dried leaves, chloroplasts and photosystem II particles. The fluorescence quencher was suggested to be Chl-680 - or Car + in close proximity to P680, the primary electron donor. Appreciable photoaccumulation of reduced pheophytin was only observed in dry leaves after Q A reduction had been lost during heat treatment of hydrated leaves prior to dehydration. The observations are interpreted to show light-dependent cyclic electron flow within the reaction center of photosystem II in which Chl-680 (or Pheo) is reduced by P680 * and Car is oxidized by P680 + with consequent recombination of Car + and Chl-680 - (or Pheo -). Cyclic electron flow is thought to be moderately photoprotective by reducing the concentration of the strong oxidant P680 +. Nevertheless, prolonged strong illumination caused considerable photodamage in the dry spinach leaves, much less damage in dry fern fronds and no damage in the dry lichen in which distinct photoreactions were not expressed at light intensities which were effective in dry leaves and fern fronds.

Shuvalov, Vladimir A.; Heber, Ulrich

2003-11-01

72

A kinetic study of the aldol condensation of acetone using an anion exchange resin catalyst  

Microsoft Academic Search

The rate of the reversible aldol condensation of acetone (Ac) to diacetone alcohol (DAA) catalysed by Amberlite IRA-900 anion exchange resin in the hydroxide form is measured in the liquid phase, without solvent, using batch and continuous reactors. The desired reaction product is DAA, but its dehydration leads to the formation of mesityl oxide (MO) as a byproduct. Although the

G. G. Podrebarac; F. T. T. Ng; G. L. Rempel

1997-01-01

73

Kinetics of Acid-Catalyzed Aldol Condensation Reactions of Aliphatic Aldehydes  

NASA Astrophysics Data System (ADS)

While it is well established that organic compounds compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, ultraviolet-visible (UV-Vis) spectroscopy was used to monitor the kinetics of formation of the products of the aldol condensation reaction of a range of aliphatic aldehydes (C2-C8) The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature.

Elrod, M. J.; Casale, M. T.; Richman, A. R.; Beaver, M. R.; Garland, R. M.; Tolbert, M. A.

2006-12-01

74

Progress toward chemcial accuracy in the computer simulation of condensed phase reactions  

SciTech Connect

A procedure is described for the generation of chemically accurate computer-simulation models to study chemical reactions in the condensed phase. The process involves (1) the use of a coupled semiempirical quantum and classical molecular mechanics method to represent solutes and solvent, respectively; (2) the optimization of semiempirical quantum mechanics (QM) parameters to produce a computationally efficient and chemically accurate QM model; (3) the calibration of a quantum/classical microsolvation model using ab initio quantum theory; and (4) the use of statistical mechanical principles and methods to simulate, on massively parallel computers, the thermodynamic properties of chemical reactions in aqueous solution. The utility of this process is demonstrated by the calculation of the enthalpy of reaction in vacuum and free energy change in aqueous solution for a proton transfer involving methanol, methoxide, imidazole, and imidazolium, which are functional groups involved with proton transfers in many biochemical systems. An optimized semiempirical QM model is produced, which results in the calculation of heats of formation of the above chemical species to within 1.0 kcal/mol of experimental values. The use of the calibrated QM and microsolvation QM/MM models for the simulation of a proton transfer in aqueous solution gives a calculated free energy that is within 1.0 kcal/mol (12.2 calculated vs. 12.8 experimental) of a value estimated from experimental pKa`s of the reacting species.

Bash, P.A.; Levine, D.; Hallstrom, P. [Argonne National Lab., IL (United States); Ho, L.L. [Yale Univ., New Haven, CT (United States). Dept. of Physics; Mackerell, A.D. Jr. [Univ. of Maryland, Baltimore, MD (United States). Dept. of Pharmaceutical Sciences

1996-03-01

75

An investigation of the role of water on retrograde/condensation reactions and enhanced liquefaction yields  

SciTech Connect

The overall objectives of this work are to conduct research that will provide the basis for an improved liquefaction process, and to facilitate our understanding of those processes that occur when coals are initially dissolved. Changes in coal structure that occur during coal drying and steam pretreatments will be measured in order to determine what effect water has on retrograde/condensation reactions, and to determine the mechanism by which water enhances coal reactivity toward liquefaction. Different methods for coal drying will be investigated to determine if drying can be accomplished without destroying coal reactivity toward liquefaction, thereby making coal drying a relatively economical and efficient method for coal pretreatment. Coal drying methods will include conventional thermal drying, microwave drying, and chemical drying at low temperature. State-of-the-art solid-state nuclear magnetic resonance (NMR) techniques using combined rotation and multiple pulse spectroscopy (CRAMPS) and cross polarization with magic-angle spinning (CP/MAS) will be employed: (1) to measures changes in coal structure brought about by the different methods of drying and by low temperature oxidation, and (2) to obtain direct measurements of changes in the aromatic hydrogen-to-carbon ratio of the solid/semi-solid material formed or remaining during pretreatment and the initial stages of liquefaction. The aromatic hydrogen-to-carbon ratios are difficult, if not impossible, to measure without the use of solid-state NMR, and as a result this ratio will be used to monitor the retrograde/condensation reactions that take place during coal liquefaction in the presence and absence of steam and various inert gases.

Miknis, F.P.

1992-07-01

76

Thermodynamic properties of aqueous NaCl solutions to 1073 K and 4.5 GPa, and implications for dehydration reactions in subducting slabs  

NASA Astrophysics Data System (ADS)

NaCl is the most common solute in aqueous fluids in many geological settings but the thermodynamic properties of binary NaCl-H2O solutions have remained understudied at pressures above 0.5 GPa. We report the first high-pressure (>0.5 GPa) density data for NaCl-H2O fluids derived from acoustic velocity measurements in 1m and 3m NaCl solutions in diamond anvil cells to 673 K and 4.5 GPa using Brillouin scattering spectroscopy. An empirical equation of state (EoS) for NaCl-H2O fluids has been generated fitting the new density data together with literature data for water, and used for extrapolation of thermodynamic data to 1073 K and 4.8m NaCl at 0.5-4.5 GPa, spanning the conditions for fluids expelled by subducted slabs. The EoS yields densities for binary NaCl-H2O solutions with uncertainty lower than 0.3-0.5% below 673 K and lower than 2-4% in the extrapolation region. The EoS may allow extrapolations beyond 1073 K although the resulting uncertainties are difficult to assess. Densities for NaCl-H2O fluids computed from the EoS at 0.5 GPa generally agree within 1% with published data below 673 K, although differences of up to 5% are observed at 1073 K. The experimentally-based EoS is more reliable in the calculation of pure water fugacities and phase equilibria involving fluid phases than previous formulations, particularly in the high pressure range. The presence of dissolved NaCl substantially decreases the activity of water, indicating large non-ideality in NaCl aqueous fluids at subduction zone conditions. This behavior has important implications for the localization of dehydration reactions in the slab, as the dehydration boundaries of hydrous phases shift toward shallower depths in the presence of dissolved NaCl in the fluid.

Mantegazzi, Davide; Sanchez-Valle, Carmen; Driesner, Thomas

2013-11-01

77

Dehydration reactions, mass transfer and rock deformation relationships during subduction of Alpine metabauxites: insights from LIBS compositional profiles between metamorphic veins  

NASA Astrophysics Data System (ADS)

In subduction zones, the significant amounts of aqueous fluid released in the course of the successive dehydration reactions occurring during prograde metamorphism are expected to strongly influence the rock rheology, as well as kinetics of metamorphic reactions and mass transfer efficiency. Mineralized veins, ubiquitous in metamorphic rocks, can be seen as preserved witnesses of fluid and mass redistribution that partly accommodate the rock deformation (lateral segregation). However, the driving forces and mechanisms of mass transfer towards fluid-filled open spaces remain somewhat unclear. The aim of this study is to investigate the vein-forming processes and the modalities of mass transfer during local fluid-rock interactions, and their links with fluid production and rock deformation, with new insights from Laser Induced Breakdown Spectroscopy (LIBS) profiles. This study focuses on karstic pockets (metre scale) of Triassic metabauxites embedded in thick carbonate units, that have been isolated from large-scale fluid flow during HP-LT Alpine metamorphism (W. Vanoise, French Alps). These rocks display several generations of metamorphic veins containing various Al-bearing minerals, which give particular insights into mass transfer processes. It is proposed that the internally-derived fluid (~13 vol% produced by successive dehydration reactions) has promoted the opening of fluid-filled open spaces (euhedral habits of vein minerals) and served as medium for diffusive mass transfer from rock to vein. Based on mineralogical and textural features, two vein types can be distinguished: (1) some veins are filled with newly formed products of either prograde (chloritoid) or retrograde (chlorite) metamorphic reactions; in this case, fluid-filled open spaces seem to offer energetically favourable nucleation/growth sites; (2) the second vein type is filled with cookeite (Li-Al-rich chlorite) or pyrophyllite, that were present in the host rock prior to the vein formation. In this closed chemical system, mass transfer from rock to vein was achieved through the fluid, in a dissolution-transport-precipitation process, possibly stress-assisted. To investigate the modalities of mass transfer towards this second vein type, LIBS profiles were performed in the rock matrix, taking Li concentration as a proxy for cookeite distribution. Cookeite is highly concentrated (40-70 vol%) in regularly spaced veins, and the LIBS profiles show that cookeite is evenly distributed in the rock matrix comprised between two veins. The absence of diffusion profiles suggests that the characteristic diffusion length for Li, Al and Si is greater than or equal to the distance separating two cookeite veins (3-6 cm). This is in agreement with characteristic diffusion lengths calculated from both grain boundary and pore fluid diffusion coefficients, for the estimated duration of the peak of metamorphism. Concerning mass transfer driving forces, phyllosilicates have very different morphologies in the rock matrix (fibers) compared to veins (euhedral crystals): fluid-mineral interfacial energy may be maximal in the small matrix pores, which can maintain higher cookeite solubility than in fluid-filled open spaces. Therefore, as soon as veins open, chemical potential gradients may develop and drive cookeite transfer from rock matrix to veins.

Verlaguet, Anne; Brunet, Fabrice; Goffé, Bruno; Menut, Denis; Findling, Nathaniel; Poinssot, Christophe

2013-04-01

78

A solid-state NMR study of condensation/retrograde reactions during coal liquefaction  

SciTech Connect

The objective of this work is to perform an NMR study of the aromaticity in coals, coal derived products and/or compounds generated by pyrolysis and thermal solubilization of coal in the presence of a hydrogen donor solvent. Cross Polarization with Magic-Angle Spinning (CP/MAS) will be used to measure the carbon aromaticity, and Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR techniques will be used to measure the hydrogen aromaticity. From these NMR measurements the aromatic hydrogen-to- carbon ratio will be obtained and used to study condensation/retrograde reactions during coal liquefaction. The study consists of four tasks: (1)develop NMR methods to determine aromatic carbon by CP/MAS and aromatic hydrogen by CRAMPS for low hydrogen containing organic solids such as coals, and coal residues; (2) characterize the feasibility of applying the NMR method for quantitative measures in coals; (3) analyze selected samples of coals and coal-derived products to demonstrate applicability of the NMR methods to study coal liquefaction, and (4) report the results to the Department of Energy. 4 refs., 5 figs., 2 tabs.

Miknis, F.P.

1990-01-01

79

A solid-state NMR study of condensation/retrograde reactions during coal liquefaction  

SciTech Connect

The objective of this work is to perform an NMR study of the aromaticity in coals, coal derived products and/or model compounds generated by pyrolysis and thermal solubilization of coal in the presence of a hydrogen donor solvent. Cross Polarization with Magic-Angle Spinning (CP/MAS) will be used to measure the carbon aromaticity, and Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR techniques will be used to measure the hydrogen aromaticity. From these NMR measurements the aromatic hydrogen-to- carbon ratio will be obtained and used to study condensation/retrograde reactions during coal liquefaction. The study consists of the following tasks: develop NMR methods to determine aromatic carbon by CP/MAS and aromatic hydrogen by CRAMPS for low hydrogen containing organic solids such as coals, and coal residues; characterize the feasibility of applying the NMR methods for quantitative measurements in coals; and analyze selected samples of coals and coal-derived products to demonstrate applicability of the NMR methods to study-coal liquefaction. 5 refs., 7 figs., 1 tab.

Miknis, F.P.

1989-01-01

80

Intramolecular condensation reactions of {alpha}, {omega}- bis(triethoxy-silyl)alkanes. Formation of cyclic disilsesquioxanes  

SciTech Connect

Under acidic sol-gel polymerization conditions, 1,3-bis(triethoxysilyl)-propane (1) and 1,4-bis(triethoxysilyl)butane (2) were shown to preferentially form cyclic disilsesquioxanes 3 and 4 rather than the expected 1,3-propylene- and 1,4-butylene-bridged polysilsesquioxane gels. Formation of 3 and 4 is driven by a combination of an intramolecular cyclization to six and seven membered rings, and a pronounced reduction in reactivity under acidic conditions as a function of increasing degree of condensation. The ease with which these relatively unreactive cyclic monomers and dimers are formed (under acidic conditions) helps to explain the difficulties in forming gels from 1 and 2. The stability of cyclic disilsesquioxanes was confirmed withe the synthesis of 3 and 4 in gram quantities; the cyclic disilsesquioxanes react slowly to give tricyclic dimers containing a thermodynamically stable eight membered siloxane ring. Continued reactions were shown to perserve the cyclic structure, opening up the possibility of utilizing cyclic disilsesquioxanes as sol-gel monomers. Preliminary polymerization studies with these new, carbohydrate-like monomers revealed the formation of network poly(cyclic disilsesquioxanes) under acidic conditions and polymerization with ring-opening under basic conditions.

Loy, D.A.; Carpenter, J.P.; Myers, S.A.; Assink, R.A.; Small, J.H. [Sandia National Labs., Albuquerque, NM (United States); Greaves, J.; Shea, K.J. [California Univ., Irvine, CA (United States). Dept. of Chemistry

1996-08-01

81

Dehydration kinetics of neotame monohydrate.  

PubMed

The dehydration of neotame monohydrate was monitored at various temperatures by differential scanning calorimetry (DSC), thermogravimetry (TGA), hot-stage microscopy (HSM), powder X-ray diffractometry (PXRD), and (13)C solid-state nuclear magnetic resonance (SSNMR) spectroscopy. This work emphasizes kinetic analysis of isothermal TGA data by fitting to various solid-state reaction models and by model-free kinetic treatment. The dehydration of neotame monohydrate follows the kinetics of a two-dimensional phase boundary reaction (R2) at 40-50 degrees C with an activation energy of 75 +/- 9 kJ/mol, agreeing well with 60-80 kJ/mol from model-free kinetics. At a low heating rate in DSC and TGA, neotame monohydrate undergoes dehydration to produce anhydrate Form E, which then converts to anhydrate Form A, followed by the melting of A. Neotame monohydrate under dry nitrogen purge at 50 mL/min undergoes partial isothermal dehydration at 50 degrees C to produce neotame anhydrate Form A. When neotame monohydrate is heated very slowly from 50 to 65-70 degrees C over 24 h, pure Form A is obtained. PMID:12115842

Dong, Zedong; Salsbury, Jonathon S; Zhou, Deliang; Munson, Eric J; Schroeder, Steve A; Prakash, Indra; Vyazovkin, Sergey; Wight, Charles A; Grant, David J W

2002-06-01

82

Oriented growth of garnet by topotactic reactions and epitaxy in high-pressure, mafic garnet granulite formed by dehydration melting of metastable hornblende-gabbronorite (Jijal Complex, Kohistan Complex, north Pakistan)  

Microsoft Academic Search

Garnet growth in high-pressure, mafic garnet granulites formed by dehydration melting of hornblende- gabbronorite protoliths in the Jijal complex (Kohistan palaeo-island arc complex, north Pakistan) was investigated through a microstructural EBSD-SEM and HRTEM study. Composite samples preserve a sharp transition in which the low-pressure precursor is replaced by garnet through a millimetre-sized reaction front. A magmatic foliation in the gabbronorite

J. A. PADRÓN-NAVARTA; C. J. GARRIDO; A. SÁNCHEZ-NAVAS; A. TOMMASI; V. LÓPEZ SÁNCHEZ-VIZCAÍNO; M. T. GÓMEZ-PUGNAIRE; S. S. HUSSAIN

2008-01-01

83

First-principles molecular dynamics simulations of condensed-phase V-type nerve agent reaction pathways and energy barriers.  

PubMed

Computational studies of condensed-phase chemical reactions are challenging in part because of complexities in understanding the effects of the solvent environment on the reacting chemical species. Such studies are further complicated due to the demanding computational resources required to implement high-level ab initio quantum chemical methods when considering the solvent explicitly. Here, we use first-principles molecular dynamics simulations to examine condensed-phase decontamination reactions of V-type nerve agents in an explicit aqueous solvent. Our results include a detailed study of hydrolysis, base-hydrolysis, and nucleophilic oxidation of both VX and R-VX, as well as their protonated counterparts (i.e., VXH(+) and R-VXH(+)). The decontamination mechanisms and chemical reaction energy barriers, as determined from our simulations, are found to be in good agreement with experiment. The results demonstrate the applicability of using such simulations to assist in understanding new decontamination technologies or other applications that require computational screening of condensed-phase chemical reaction mechanisms. PMID:22298156

Gee, Richard H; Kuo, I-Feng W; Chinn, Sarah C; Raber, Ellen

2012-02-01

84

Catalytic behaviors of lanthanum and neodymium oxides for dehydrogenation/dehydration of ethanol  

SciTech Connect

Ethanol dehydrogenation and dehydration reactions have been employed to investigate the nature and behavior of catalytically active sites on lanthanum and neodymium sesquioxides. In support of this objective, x-ray powder diffraction, surface area determinations, and thermogravimetric analyses have been performed to augment previously reported characterization results. Activated lanthanum and neodymium oxide catalysts have been prepared by thermal dehydration of the corresponding trihydroxides. The catalytic reaction data on these materials, when correlated with complemented with infrared spectroscopic measurements of adsorbed species reported in the literature, indicate that arrays of at least two dissimilar types of catalytically active sites are generated. One kind of site (designated Type I) is much less numerous than the other (Type II) but is more strongly basic and has a much higher initial activity for alcohol dehydration. The latter reaction probably occurs via an ethoxide intermediate at 300-400/sup 0/C. The parallel alcohol dehydrogenation pathway, on the other hand, occurs only on Type II sites which have only moderate dehydration activity. The resulting aldehyde product re-absorbs exclusively on the more strongly basic Type I sites, where it undergoes a series of secondary condensation/decarboxylation reactions and consequently leads to a decrease in the overall rate of alcohol dehydration. The contrasting behavioral features of the two kinds of sites may be due to differing surface environments with Type I sites being in structurally more defective and/or more energetic surface locations than are Type II sites. Increases in prior pretreatment temperature of the oxides cause thermally-induced transformations of Type I sites into Type II sites by a surface annealing or re-structuring process with corresponding modifications in the observed catalytic behaviors for the two alcohol decomposition pathways.

Koprowski, R.J.

1985-01-01

85

Experimental Test of Bose-Einstein Condensation Mechanism for Low Energy Nuclear Reaction in Nanoscale Atomic Clusters  

Microsoft Academic Search

We report preliminary results of experimental test of the Bose-Einstein condensation (BEC) mechanism for ultra low energy nuclear fusion in nano-scale atomic clusters at pressures up to a 20,000 psi and at both room temperature and liquid nitrogen temperatures. BEC of integer-spin nuclei was suggested as a possible mechanism for ultra low-energy nuclear reaction in 1998. Recently, theoretical studies of

Yeong E. Kim; David S. Koltick; Ryan Prenger; Jeff Myers; Rhoda Koltick

2005-01-01

86

Imidazolium-Based Phosphinite Ionic Liquid (IL-OPPh2) as Reusable Catalyst and Solvent for the Knoevenagel Condensation Reaction  

Microsoft Academic Search

A task-specific ionic liquid (IL, OPPh2) that bears a phosphinite weak Lewis base group in an imidazolium cation was found to efficiently catalyze the Knoevenagel condensation of arylaldehydes with malononitrile, dimethyl(diethyl)malonate, and ethyl cyanoacetate. This IL plays a dual role as both the reaction media and also catalyst, and it can be easily recovered and reused in several runs. Satisfactory

Hassan Valizadeh; Hamid Gholipour

2010-01-01

87

Quantum effects in ab-initio calculations of rate constants for chemical reactions occuring in the condensed phase  

Microsoft Academic Search

An overview of recent advances in the development of methods designed to calculate rate constants for chemical reactions obeying mass action kinetic equations in condensed phases is presented. A general framework addressing mixed quantum-classical systems is elaborated that enables quantum features such as tunneling effects, zero-point vibrations, dynamic quantum coherence, and non-adiabatic effects to be calculated. An efficient Monte Carlo

Jeremy Schofield

2006-01-01

88

Dissolution processes, hydrolysis and condensation reactions during geopolymer synthesis: Part II. High Si\\/Al ratio systems  

Microsoft Academic Search

The mechanisms of speciation of aluminate and silicate phases during dissolution and condensation stages of alumino-silicate\\u000a geopolymer reactions characterised by Si\\/Al ? 3, have been investigated and the results compared to predictions of the partial\\u000a charge model. Solid-state nuclear magnetic resonance (NMR) traces indicate that free [Al(OH)4]? species, present in lower silicate formulations such as Si\\/Al ? 1, do not occur in the present

K. Sagoe-Crentsil; L. Weng

2007-01-01

89

Synthesis of 1,5-benzodiazepine and its derivatives by condensation reaction using H-MCM-22 as catalyst.  

PubMed

A simple and versatile method for the synthesis of 1,5-benzodiazepines is via condensation of o-phenylenediamines (OPDA) and ketones in the presence of catalytic amount of H-MCM-22 using acetonitrile as solvent at room temperature. In all the cases, the reactions are highly selective and are completed within 1-3 h. The method is applicable to both cyclic and acyclic ketones without significant differences. The reaction proceeds efficiently under ambient conditions with good-to-excellent yields. PMID:22570531

Majid, Sheikh Abdul; Khanday, Waheed Ahmad; Tomar, Radha

2012-04-11

90

Synthesis of 1,5-Benzodiazepine and Its Derivatives by Condensation Reaction Using H-MCM-22 as Catalyst  

PubMed Central

A simple and versatile method for the synthesis of 1,5-benzodiazepines is via condensation of o-phenylenediamines (OPDA) and ketones in the presence of catalytic amount of H-MCM-22 using acetonitrile as solvent at room temperature. In all the cases, the reactions are highly selective and are completed within 1–3?h. The method is applicable to both cyclic and acyclic ketones without significant differences. The reaction proceeds efficiently under ambient conditions with good-to-excellent yields.

Majid, Sheikh Abdul; Khanday, Waheed Ahmad; Tomar, Radha

2012-01-01

91

Origin of saline, neutral-pH, reduced epithermal waters by reaction of acidic magmatic gas condensates with wall rock  

SciTech Connect

Fluid inclusions in quartz and sphalerite of epithermal veins containing galena, sphalerite and chalcopyrite with silver sulfides and electrum commonly have salinities of 2 to 10 weight percent NaCl equivalent. Examples include Bohemia, OR, Comstock, NV, and Creede, CO. Salinities in such base metal-rich systems are apparently greater than those in gold-adularia, base metal-poor systems such as Sleeper, NV, Republic, WA, and Hishikare, Kyushu. Saline epithermal fluids are commonly assumed to have been derived from saline magmatic brines, from local host formations, as has been suggested for Creede, or from evaporative concentration (boiling) of more dilute meteoric ground water. Another possibility, which may be the most common origin, is reaction of wall rocks with magmatic gas condensates rich in HCl and sulfuric acid. A mixture of one part Augustine Volcanic gas condensate in 10 parts cold ground water has a pH of 0.7 and the dominant cation is H[sup +] by a factor of 10[sup 4]. Calculated reaction of this condensate mixture with andesite at 300 C to a water/rock ratio (w/r) of 4.6 yields an NaCl-dominated fluid with a total salinity of 2.1 wt %. and pH 3.7. Further reaction, to w/r 0.14 yields a fluid salinity of 2.6 wt % and pH of 5.7; this fluid is in equilibrium with a propylitic alteration assemblage. Aqueous sulfide accumulates during the rock reaction as sulfate is reduced to sulfide when ferrous iron is oxidized to ferric iron. Sulfide concentration in the latter fluid is 32 ppm, far exceeding sulfate concentration. In the overall reaction, hydrogen ion is exchanged for base cations (including base metals) and sulfate is reduced to sulfide.

Reed, M.H. (Univ. of Oregon, Eugene, OR (United States). Dept. of Geological Sciences)

1993-04-01

92

Solving the Mathematics of a Kinetic and Regiochemical Problem: The Dehydration Reaction of a cis-trans Mixture of 2-Methylcycloalkanols  

NASA Astrophysics Data System (ADS)

A take-home exam is presented. It is based on an experiment that studied the dehydration of a cis-trans mixture of 2-methylcyclohexanols. The "givens" are the idealized kinetic and regiochemical data. The focus is strictly on the mathematics, not the experimental details.The goal is to calculate six specific rate constants using a little ingenuity and some fundamental mathematics, to show that the Saytzeff elimination rule is followed for the dehydration of each of the two reactant isomeric alcohols.

Cawley, John J.

1999-01-01

93

Mechanism of the intramolecular Claisen condensation reaction catalyzed by MenB, a crotonase superfamily member.  

PubMed

MenB, the 1,4-dihydroxy-2-naphthoyl-CoA synthase from the bacterial menaquinone biosynthesis pathway, catalyzes an intramolecular Claisen condensation (Dieckmann reaction) in which the electrophile is an unactivated carboxylic acid. Mechanistic studies on this crotonase family member have been hindered by partial active site disorder in existing MenB X-ray structures. In the current work the 2.0 Å structure of O-succinylbenzoyl-aminoCoA (OSB-NCoA) bound to the MenB from Escherichia coli provides important insight into the catalytic mechanism by revealing the position of all active site residues. This has been accomplished by the use of a stable analogue of the O-succinylbenzoyl-CoA (OSB-CoA) substrate in which the CoA thiol has been replaced by an amine. The resulting OSB-NCoA is stable, and the X-ray structure of this molecule bound to MenB reveals the structure of the enzyme-substrate complex poised for carbon-carbon bond formation. The structural data support a mechanism in which two conserved active site Tyr residues, Y97 and Y258, participate directly in the intramolecular transfer of the substrate ?-proton to the benzylic carboxylate of the substrate, leading to protonation of the electrophile and formation of the required carbanion. Y97 and Y258 are also ideally positioned to function as the second oxyanion hole required for stabilization of the tetrahedral intermediate formed during carbon-carbon bond formation. In contrast, D163, which is structurally homologous to the acid-base catalyst E144 in crotonase (enoyl-CoA hydratase), is not directly involved in carbanion formation and may instead play a structural role by stabilizing the loop that carries Y97. When similar studies were performed on the MenB from Mycobacterium tuberculosis, a twisted hexamer was unexpectedly observed, demonstrating the flexibility of the interfacial loops that are involved in the generation of the novel tertiary and quaternary structures found in the crotonase superfamily. This work reinforces the utility of using a stable substrate analogue as a mechanistic probe in which only one atom has been altered leading to a decrease in ?-proton acidity. PMID:21830810

Li, Huei-Jiun; Li, Xiaokai; Liu, Nina; Zhang, Huaning; Truglio, James J; Mishra, Shambhavi; Kisker, Caroline; Garcia-Diaz, Miguel; Tonge, Peter J

2011-10-11

94

Effect of the method of preparation and the presence of a carrier on the catalytic activity of chromic oxide in dehydrogenation and dehydration reactions  

Microsoft Academic Search

Summary 1.Activation energies were determined for the dehydrogenation of methylcyclohexane, isopropyl alcohol, and formic acid and the dehydration of isopropyl alcohol and formic acid over chromic oxide prepared in different ways. From these date the energies of the bonds formed by hydrogen, carbon, and oxygen with the chromic oxide surface were found.2.The effect of molecular structure and the method of

A. A. Tolstopyatova; K. A. Dulitskaya; A. A. Balandin

1956-01-01

95

Elastic-wave velocity in crustal and mantle rocks at high pressure and temperature: the role of the high-low quartz transition and of dehydration reactions  

NASA Astrophysics Data System (ADS)

The compressional- and shear-wave velocities, VP and VS, in typical crustal and mantle rocks were determined in a cubic anvil apparatus over a range of constant confining pressure up to 6 kbar and temperatures ranging from 20-750°C. Samples range between acidic and ultramafic with mean atomic weights between 20.4 and 23.0 and bulk densities of 2.66-3.50 g cm -3 at 6 kbar. Compressional-wave velocities are only roughly related to densities and do not generally follow lines of constant mean atomic weights. However, the rocks typical for the upper mantle, the continental and oceanic crust clearly separate into three distinct areas in the velocity versus density plot. In plutonic and metamorphic rocks velocities are strongly dependent on the mineral composition. Both VP and VS increase with increasing amphibole, garnet, pyroxene and olivine content. High feldspar content produces high Poisson's ratios as a consequence of relatively high compressional wave velocities compared to the respective shear wave velocities. Increasing quartz content results in a decrease of VP and an accompanying increase of VS, thereby significantly lowering Poisson's ratio. Elastic-wave propagation is affected to a large degree by flat cracks and pore spaces. High confining pressures act to reduce microcracks; heating causes an increase in porosity. However, microfracturing is increasingly suppressed by the simultaneous action of confining pressure. A pressure increase of at least 10 bar per 1°C is needed to prevent the opening of cracks. Velocities are highly affected by the ?-? quartz transition. Due to stress concentrations in polycrystalline material the quartz transition temperature is shifted to higher values than might be expected from single crystal measurements. Dehydration reactions in zeolite-bearing basalts cause the velocities to decrease as a consequence of lowering the effective pressure and of a reconstitution of pore geometry. Velocity anisotropies observed in some plutonic rocks, and most metamorphic rocks, at high confining pressures and high temperatures correlate well with preferred lattice orientation of the constituent major minerals. The effect of dimensional orientation and microcracks seems to be of minor importance for the directional dependence of wave velocities under conditions of high pressure.

Kern, H.

1982-07-01

96

Purification and Characterization of OleA from Xanthomonas campestris and Demonstration of a Non-decarboxylative Claisen Condensation Reaction*  

PubMed Central

OleA catalyzes the condensation of fatty acyl groups in the first step of bacterial long-chain olefin biosynthesis, but the mechanism of the condensation reaction is controversial. In this study, OleA from Xanthomonas campestris was expressed in Escherichia coli and purified to homogeneity. The purified protein was shown to be active with fatty acyl-CoA substrates that ranged from C8 to C16 in length. With limiting myristoyl-CoA (C14), 1 mol of the free coenzyme A was released/mol of myristoyl-CoA consumed. Using [14C]myristoyl-CoA, the other products were identified as myristic acid, 2-myristoylmyristic acid, and 14-heptacosanone. 2-Myristoylmyristic acid was indicated to be the physiologically relevant product of OleA in several ways. First, 2-myristoylmyristic acid was the major condensed product in short incubations, but over time, it decreased with the concomitant increase of 14-heptacosanone. Second, synthetic 2-myristoylmyristic acid showed similar decarboxylation kinetics in the absence of OleA. Third, 2-myristoylmyristic acid was shown to be reactive with purified OleC and OleD to generate the olefin 14-heptacosene, a product seen in previous in vivo studies. The decarboxylation product, 14-heptacosanone, did not react with OleC and OleD to produce any demonstrable product. Substantial hydrolysis of fatty acyl-CoA substrates to the corresponding fatty acids was observed, but it is currently unclear if this occurs in vivo. In total, these data are consistent with OleA catalyzing a non-decarboxylative Claisen condensation reaction in the first step of the olefin biosynthetic pathway previously found to be present in at least 70 different bacterial strains.

Frias, Janice A.; Richman, Jack E.; Erickson, Jasmine S.; Wackett, Lawrence P.

2011-01-01

97

An investigation of the role of water on retrograde/condensation reactions and enhanced liquefaction yields. Final report  

SciTech Connect

While great strides have been made in developing the technology of coal liquefaction processes in recent years, many unsolved problems still remain before a viable and economical process can be achieved. The technological problems that still exist can be solved through a more fundamental understanding of the chemistry associated with each stage of the coal liquefaction process, starting with any pretreatment steps that may be carried out on the coal itself. Western Research Institute, under the a contract from the US Department of Energy, has conducted a study of different methods of coal drying as pretreatment steps before liquefaction. The results of that study are the subject of this report. Coals that were dried or partially dried thermally and with microwaves had lower liquefaction conversions than coals containing equilibrium moisture contents. However, chemically dried coals had conversions equal to or greater than the premoisturized coals. The conversion behavior is consistent with changes in the physical structure and cross linking reactions because of drying. Thermal and microwave drying appear to cause a collapse in the pore structure, thus preventing donor solvents such as tetralin from contacting reactive sites inside the coals. Chemical dehydration does not appear to collapse the pore structure. From the study of the kinetics of the chemical dehydration of coals, it was possible to quantify the amount of water on the surface, the amount readily accessible in pores, and the amount more strongly bonded in the internal structure of the coals. The results indicate that high-rank coals have proportionally less surface and easily accessible water than the lower rank coals.

Miknis, F.P.; Netzel, D.A.; Wallace, J.C. Jr.; Butcher, C.H.; Mitzel, J.M.; Turner, T.F.

1995-02-01

98

Activation of Mg–Al Hydrotalcite Catalysts for Aldol Condensation Reactions  

Microsoft Academic Search

The condensation of benzaldehyde and acetone to aldol has been investigated in the liquid phase at 273 K on hydrotalcites transformed into basic solids by activation following different procedures. No activity was observed on the pure hydrotalcite (carbonated) or on the solid just decarbonated at 723 K. The activity went through a maximum after calcination at 723 K, followed by

Kottapalli Koteswara Rao; Monique Gravelle; Jaime Sanchez Valente; François Figueras

1998-01-01

99

Unusual synthesis of new glycine antagonists via sequential aldol condensation-lactonization-elimination reaction  

Microsoft Academic Search

Compounds 2 and 3 were designed in order to probe the North-East region of the strichnine-insensitive glycine binding site of the NMDA receptor. The two products were obtained readily by a tandem aldol condensation-lactonization-elimination step which affords the desired E isomer with complete regioselection.

Simone A. Giacobbe; Davide Baraldi; Romano Di Fabio

1998-01-01

100

The nature of catalytic sites on lanthanum and neodymium oxides for dehydration/dehydrogenation of ethanol  

SciTech Connect

The multi-pathway (dehydration/dehydrogenation) conversion of ethanol has been used to investigate the nature and behavior of catalytically active sites on lanthanum and neodymium sesquioxides. Catalytic reaction data, coupled with infrared spectroscopic characterizations of adsorbed species, indicate that at least two different types of catalytically active sites are generated on activated La{sub 2}O{sub 3} and Nd{sub 2}O{sub 3} surfaces that are prepared by thermal dehydration of the corresponding trihydroxides. One kind of site (designated Type I) is much less numerous than the other (Type II), but is more strongly basic and has a much higher initial activity for alcohol dehydration, via a probable ethoxide intermediate, at 300-400{degree}C. The parallel alcohol dehydrogenation pathway, on the other hand, occurs only on Type II sites, which also have moderate dehydration activity. The resulting aldehyde products readsorbs exclusively on the more strongly basic Type I sites, where it undergoes a series of secondary condensation reactions that cause a decrease in the overall rate of alcohol dehydration. The comparative behavioral features of the two kinds of sites may be due to differing surface environments, with Type I sites being in structurally more defective and/or more energetic surface locations than are Type II sites. Increases in pretreatment temperature of the oxides cause thermally induced transformations of Type I sites into Type II sites by a surface annealing or restructuring process, with corresponding modifications in the observed catalytic behavior for the two alcohol conversion pathways. 33 refs.

Rosynek, M.P.; Koprowski, R.J.; DelliSante, G.N. (Texas A and M Univ., College Station (USA))

1990-03-01

101

Structural requirements and reaction pathways in condensation reactions of alcohols on Mg{sub y}AlO{sub x} catalysts  

SciTech Connect

The effect of composition and of surface properties on alcohol-coupling reactions was studied on Mg{sub y}AlO{sub x} catalysts using C{sub 2}H{sub 5}OH or {sup 13}CH{sub 3}OH/1-{sup 12}C{sub 3}H{sub 7}OH mixtures as reactants. Samples with Mg/Al ratios of 0.5--9.0 were obtained by thermal decomposition of precipitated hydrotalcite precursors. The nature, density, and strength of surface basic sites were obtained by temperature-programmed desorption (TPD) of CO{sub 2} and by {sup 13}CO{sub 2}/{sup 12}CO isotopic switch methods, whereas the acid site densities were measured by TPD or NH{sub 3}. The catalyst ability for activating H-H bonds was investigated by performing H{sub 2}-D{sub 2} steady-state equilibration reactions. Isotopic tracer studies were carried out in order to probe chain growth pathways in the synthesis of isobutanol. The rates and product selectivity for C{sub 2}H{sub 5}OH or CH{sub 3}OH/C{sub 3}H{sub 7}OH reactions strongly depended on the chemical composition of Mg{sub y}AlO{sub x} samples. In turn, the chemical composition affected the acid-base properties of Mg{sub y}AlO{sub x} samples by modifying surface acid and base site densities and the distribution of strength for such sites. The rate of alcohol dehydration to ethers and olefins increased with increasing Al content. Al-rich Mg{sub y}AlO{sub x} samples contained a high density of Al{sup 3+}{minus}O{sup 2{minus}} site pairs and of moderate strength basic sites, the combination of which promoted the formation of ethylene or propylene from primary alcohols via E{sub 2} elimination pathways. The competitive dehydration to form ethers involved the adsorption of two alcohol molecules on neighboring active sites offering different acid-base properties.

Di Cosimo, J.I.; Apesteguia, C.R.; Gines, M.J.L.; Iglesia, E.

2000-03-10

102

Convenient synthetic route to a dehydrorotenoid via selective intramolecular aldol condensation of 1,2-diaryl diketone  

Microsoft Academic Search

Synthesis of dehydrorotenoid (1) was successfully achieved via an intramolecular aldol reaction of the corresponding 1,2-diaryl diketone intermediate. The 1,2-diaryl diketone was prepared using a ruthenium-catalyzed oxidation of the corresponding substituted diaryl acetylene. Treatment of this 1,2-diketone with l-proline induced a selective intramolecular aldol condensation reaction, forming the desired benzopyranone over the alternative benzofuran. Deprotection, cyclization, and dehydration gave the

Jumreang Tummatorn; Prapas Khorphueng; Amorn Petsom; Nongnuch Muangsin; Narongsak Chaichit; Sophon Roengsumran

2007-01-01

103

Electronic and Ionic Screening For Low-Energy Nuclear Reactions In Condensed Matter  

Microsoft Academic Search

Screening for nuclear reactions plays an important role in enhancing reaction cross sections at low energy region. In the present work, results so far obtained in experiments of the D+D reactions in metal environment is overviewed and the origin of the screening potential is discussed; i.e., electronic and ionic screening. For the ionic screening we have performed Li+p,d reactions in

J. Kasagi; H. Yonemura

2009-01-01

104

Synthesis of Dibenzoxepine Lactams via a Cu-Catalyzed One-Pot Etherification/Aldol Condensation Cascade Reaction: Application toward the Total Synthesis of Aristoyagonine.  

PubMed

A general synthesis of dibenzoxepine lactams has been developed using a one-pot Cu-catalyzed etherification/aldol condensation cascade reaction. The reaction of 4-hydroxyisoindolin-1-one with a wide range of 2-bromobenzaldehydes in the presence of a copper catalyst provided various aristoyagonine derivatives in good yields. PMID:24000941

Lim, Hye Sun; Choi, Young Lok; Heo, Jung-Nyoung

2013-09-03

105

Dehydration of Magnesium Chloride.  

National Technical Information Service (NTIS)

The patent application discloses a method for dehydrating magnesium chloride hydrates or brines by complexing with amine hydrochlorides. Magnesium chloride hydrate or brine is reacted to an amine hydrochloride to form a complex which is then heated to fir...

H. Dolezal

1975-01-01

106

Condensed phase combustion travelling waves with sequential exothermic or endothermic reactions  

Microsoft Academic Search

The one-dimensional propagation of a combustion wave through a premixed solid fuel for two-stage kinetics is studied. We re-examine the analysis of a single reaction travelling-wave and extend it to the case of two-stage reactions. We derive an expression for the travelling wave speed in the limit of large activation energy for both reactions. The analysis shows that when both

F Liu; D L S McElwain

2003-01-01

107

Condensed Tannins: Reactions of Model Compounds with Furfuryl Alcohol and Furfuraldehyde  

Microsoft Academic Search

Reaction products of phloroglucinol or catechin with furfuryl alcohol and furfuraldehyde were studied. In reactions of furfuryl alcohol with phloroglucinol, only 2-furyl-1?,3?,5?-trihydroxyphenyl) methane was obtained as product, and 53% of the phloroglucinol was recovered. Reactions of furfuryl alcohol with catechin gave 2-furyl-(8-catechinyl) methane and 2-furyl-(6-catechinyl) methane in 4.0% and 1.5% yields, respectively, while 62% of the catechin was unreacted. Polymeric

L. Yeap Foo; Richard W. Hemingway

1985-01-01

108

Experimental Deformation of Dehydrating Antigorite: Challenging Models of Dehydration Embrittlement  

NASA Astrophysics Data System (ADS)

To test the hypothesis that intermediate depth earthquakes in subduction zones are caused by the dehydration of hydrous phases, we conducted temperature-ramping experiments on antigorite serpentinite. Drilled cylinders and cold-pressed powders of antigorite were deformed to a high differential stress at 400 °C and 1.0 GPa, within the antigorite stability field, where we have shown that deformation localizes. Temperature was then increased at different rates, 1800 °C/hr and 180 °C/hr, to cross the reaction boundary while samples continued to deform at strain rates of 10-4 s-1, 10-5 s-1 and 10-6 s-1. Our results show that although the decrease in stress during temperature ramping is large, stress relaxes stably, even after dehydration. In addition, we find that stress relaxes over several minutes, which is not characteristic of an earthquake. We find that the slopes of the unloading curves are approximately the same for constant values of the ratio (ramp rate/strain rate) and that the unloading slope is greater for higher values of this ratio. In addition, we find that the unloading curves with the greatest slopes are similar to the apparatus compliance, suggesting that we are generating “slow earthquakes” in our experiments over the course 5 to 10s of minutes. Strain rate stepping experiments indicate that antigorite has velocity strengthening behavior at 700 °C and pressures of 1.0 and 1.5 GPa providing an explanation for why unstable slip does not occur. Our results thus suggest that antigorite dehydration does not result in “dehydration embrittlement” but that it may promote slow earthquakes and/or slow slip events. In contrast to antigorite, an experiment using a Balsam Gap dunite core demonstrates stick-slip behavior at 400 °C, 1.0 GPa and a strain rate of 1.5 x 10-5 s-1. Sample strength increased to a maximum at 5% strain when a fault developed. Subsequent deformation to 12% strain was accompanied by small stick slip events, accompanied by audible “tinking” noises. This result indicates that lab earthquakes can be generated in the Griggs rig and strengthens our assertion that antigorite dehydration does not directly produce seismicity. We have also studied the role of effective pressure on deformation behavior after dehydration. A sample composed of 75% cold-pressed antigorite powder and 25% coarse-grained olivine powder at the top was deformed at 700 °C, 1.5 GPa and a strain rate of 1.5 x 10-5 s-1. The sample with the reservoir was significantly stronger than samples deformed at the same conditions without the porous olivine reservoir even though all samples deformed by macroscopically ductile processes. We hypothesize that the highly porous and permeable olivine layer provided a reservoir for the water released by the dehydration reaction and suggests that the strength of antigorite depends on the effective normal stress.

Chernak, L. J.; Hirth, G.

2010-12-01

109

Reaction mechanism of recombinant 3-oxoacyl-(acyl-carrier-protein) synthase III from Cuphea wrightii embryo, a fatty acid synthase type II condensing enzyme.  

PubMed

A unique feature of fatty acid synthase (FAS) type II of higher plants and bacteria is 3-oxoacyl-[acyl-carrier-protein (ACP)] synthase III (KAS III), which catalyses the committing condensing reaction. Working with KAS IIIs from Cuphea seeds we obtained kinetic evidence that KAS III catalysis follows a Ping-Pong mechanism and that these enzymes have substrate-binding sites for acetyl-CoA and malonyl-ACP. It was the aim of the present study to identify these binding sites and to elucidate the catalytic mechanism of recombinant Cuphea wrightii KAS III, which we expressed in Escherichia coli. We engineered mutants, which allowed us to dissect the condensing reaction into three stages, i.e. formation of acyl-enzyme, decarboxylation of malonyl-ACP, and final Claisen condensation. Incubation of recombinant enzyme with [1-(14)C]acetyl-CoA-labelled Cys(111), and the replacement of this residue by Ala and Ser resulted in loss of overall condensing activity. The Cys(111)Ser mutant, however, still was able to bind acetyl-CoA and to catalyse subsequent binding and decarboxylation of malonyl-ACP to acetyl-ACP. We replaced His(261) with Ala and Arg and found that the former lost activity, whereas the latter retained overall condensing activity, which indicated a general-base action of His(261). Double mutants Cys(111)Ser/His(261)Ala and Cys(111)Ser/His(261)Arg were not able to catalyse overall condensation, but the double mutant containing Arg induced decarboxylation of [2-(14)C]malonyl-ACP, a reaction indicating the role of His(261) in general-acid catalysis. Finally, alanine scanning revealed the involvement of Arg(150) and Arg(306) in KAS III catalysis. The results offer for the first time a detailed mechanism for a condensing reaction catalysed by a FAS type II condensing enzyme. PMID:10600651

Abbadi, A; Brummel, M; Schütt, B S; Slabaugh, M B; Schuch, R; Spener, F

2000-01-01

110

Reaction mechanism of recombinant 3-oxoacyl-(acyl-carrier-protein) synthase III from Cuphea wrightii embryo, a fatty acid synthase type II condensing enzyme.  

PubMed Central

A unique feature of fatty acid synthase (FAS) type II of higher plants and bacteria is 3-oxoacyl-[acyl-carrier-protein (ACP)] synthase III (KAS III), which catalyses the committing condensing reaction. Working with KAS IIIs from Cuphea seeds we obtained kinetic evidence that KAS III catalysis follows a Ping-Pong mechanism and that these enzymes have substrate-binding sites for acetyl-CoA and malonyl-ACP. It was the aim of the present study to identify these binding sites and to elucidate the catalytic mechanism of recombinant Cuphea wrightii KAS III, which we expressed in Escherichia coli. We engineered mutants, which allowed us to dissect the condensing reaction into three stages, i.e. formation of acyl-enzyme, decarboxylation of malonyl-ACP, and final Claisen condensation. Incubation of recombinant enzyme with [1-(14)C]acetyl-CoA-labelled Cys(111), and the replacement of this residue by Ala and Ser resulted in loss of overall condensing activity. The Cys(111)Ser mutant, however, still was able to bind acetyl-CoA and to catalyse subsequent binding and decarboxylation of malonyl-ACP to acetyl-ACP. We replaced His(261) with Ala and Arg and found that the former lost activity, whereas the latter retained overall condensing activity, which indicated a general-base action of His(261). Double mutants Cys(111)Ser/His(261)Ala and Cys(111)Ser/His(261)Arg were not able to catalyse overall condensation, but the double mutant containing Arg induced decarboxylation of [2-(14)C]malonyl-ACP, a reaction indicating the role of His(261) in general-acid catalysis. Finally, alanine scanning revealed the involvement of Arg(150) and Arg(306) in KAS III catalysis. The results offer for the first time a detailed mechanism for a condensing reaction catalysed by a FAS type II condensing enzyme.

Abbadi, A; Brummel, M; Schutt, B S; Slabaugh, M B; Schuch, R; Spener, F

2000-01-01

111

The Aldol Addition and Condensation: The Effect of Conditions on Reaction Pathway  

ERIC Educational Resources Information Center

|The reaction of a ketone and an aldehyde in aqueous Na[subscript 2]CO[subscript 2] is described. This experiment is performed in the absence of strong bases or organic solvents and offers the opportunity for students to observe the critical role that reaction temperature and base strength have in determining the product of the base-mediated…

Crouch, R. David; Richardson, Amie; Howard, Jessica L.; Harker, Rebecca L.; Barker, Kathryn H.

2007-01-01

112

Linking the historical and chemical definitions of diabatic states for charge and excitation energy transfer reactions in condensed phase  

NASA Astrophysics Data System (ADS)

Marcus theory of electron transfer (ET) and Förster theory of excitation energy transfer (EET) rely on the Condon approximation and the theoretical availability of initial and final states of ET and EET reactions, often called diabatic states. Recently [Subotnik et al., J. Chem. Phys. 130, 234102 (2009)], diabatic states for practical calculations of ET and EET reactions were defined in terms of their interactions with the surrounding environment. However, from a purely theoretical standpoint, the definition of diabatic states must arise from the minimization of the dynamic couplings between the trial diabatic states. In this work, we show that if the Condon approximation is valid, then a minimization of the derived dynamic couplings leads to corresponding diabatic states for ET reactions taking place in solution by diagonalization of the dipole moment matrix, which is equivalent to a Boys localization algorithm; while for EET reactions in solution, diabatic states are found through the Edmiston-Ruedenberg localization algorithm. In the derivation, we find interesting expressions for the environmental contribution to the dynamic coupling of the adiabatic states in condensed-phase processes. In one of the cases considered, we find that such a contribution is trivially evaluable as a scalar product of the transition dipole moment with a quantity directly derivable from the geometry arrangement of the nuclei in the molecular environment. Possibly, this has applications in the evaluation of dynamic couplings for large scale simulations.

Pavanello, Michele; Neugebauer, Johannes

2011-10-01

113

Optical Pump-Terahertz Probe Spectroscopy of Condensed Phase Reaction Dynamics  

Microsoft Academic Search

The general theoretical and experimental principles of optical pump-THz probe spectroscopy of chemical reactions in liquids is presented. Background on specific difficulties encountered in the experimental observation is reviewed. Chiefly, signal-to-noise ratios currently limit the quality of information that can be extracted from optical pump-THz probe data on chemical reactions. This issue is shown to be connected to the assumption

Bret N. Flanders; Norbert F. Scherer

114

The Effect of Vibrational Energy on the Isomerization Reaction of Trans-Stilbene in the Condensed Phase  

NASA Astrophysics Data System (ADS)

We study the effect of vibrational energy on the isomerization reaction of trans-stilbene in deuterated chloroform. We first excite a ground-state C-H stretch overtone or a stretch-bend combination and allow vibrational relaxation to occur within the molecule before photoinitiating the excited-state isomerization with an ultraviolet photon. Once the stilbene molecule is on the excited state, we monitor the isomerization dynamics via broadband transient absorption spectroscopy. We measure an excited-state lifetime of 55 ± 9 ps when exciting through the C-H stretch overtone and a lifetime of 56 ± 7 ps for excitation through the stretch-bend combination. The trans-stilbene excited-state lifetime after single photon vertical excitation is 52 ± 6 ps with the total added energy being the same for all measurements. Unlike in gas phase studies, where vibrational motion can change the outcome of a chemical reaction, there is no observed difference in the reaction dynamics when exciting this condensed phase system with a single photon versus exciting through a ground-state vibrational mode. Interactions with the solvent cause fast vibrational relaxation on the excited state, though the insensitivity of the rate to vibrational energy may also be due to excess vibrational energy not being promptly partitioned into modes along the isomerization coordinate.

Briney, Kristin A.; Herman, Leslie V.; Boucher, Dave S.; Crim, F. Fleming

2010-06-01

115

Plastic and dehydration instabilities of antigorite serpentinite  

NASA Astrophysics Data System (ADS)

We conducted a constant displacement rate test of antigorite serpentinite by a triaxial solid medium deformation apparatus installed at Hiroshima University. Experimental conditions were P = ca. 1.0 GPa, T = 450 C to 800 C, which cover from stability to dehydration conditions of antigorite, and strain rate of digit of 10-5 /sec. Samples were cylindrical shape cored from serpentinite and their sizes were 7 mm x 7 mm and 5 mm x 5 mm in diameter by length. Faults were observed in recovered samples from all temperature conditions. Mechanical data of faulted samples showed stress drop of several 10 MPa during experiments. The followings summarize microstructural observations of the recovered samples, and propose generation processes of fault at stability and dehydration conditions. 1) Stability field (plastic instability): Antigorite grains develop a lattice preferred orientation (LPO) along a fault, which characterized by (001) cleavage face parallel to fault plane. This fact suggests the fault is generated by the following process. i) Antigorite grains on the plane applied by maximum shear stress are preferentially deformed by plastic manner, and then develop the LPO. ii) The arrangement of cleavage face gradually reduces the strength of this plane. iii) Eventually, embrittlement occurs at the critical point when the rock strength along this weak plane becomes smaller than shear stress. 2) Dehydration condition (dehydration instability): Fine grained dehydration phases less than 1 micrometer in size such as olivine and talc are detected as a thin vein along the fault. Moreover, talc and olivine, or antigorite ca. 1 - 5 micrometers in size with angular shape are observed within the fault as a fault gauge. These facts suggest the following generation process of fault. i) Dehydration reaction of antigorite begins on the plane applied by maximum shear stress and expands along this plane. ii) The dehydration gradually reduces the strength of this plane. iii) Eventually, embrittlement occurs at the critical point when the rock strength along this weak plane becomes smaller than shear stress.

Ando, J.; Katayama, I.; Ohfuji, H.; Terada, Y.

2008-12-01

116

Reaction engineering of co-condensing (methyl)ethoxysilane mixtures: Kinetic characterization and modeling  

SciTech Connect

Molecular homogeneity frequently plays a decisive role in the effective application of organically modified silicate copolymers. However, methods of directly characterizing copolymerization extent in siloxanes generated from mixed alkoxysilanes are not always available or convenient. The authors present an alternative tool for determining kinetic parameters for models of alkoxysilane hydrolytic copolycondensation. Rather than restricting attention to single step batch reactors, they use a semibatch reactor with varying time of injection of one component. They describe the fitting method and show that all necessary kinetic parameters can be determined from a series of ordinary {sup 29}Si NMR data in a straightforward case study: copolymerization of dimethyldiethoxy silane and trimethylethoxysilane. Under conditions providing no direct {sup 29}Si NMR signature of copolymerization, they find kinetic trends consistent with those previously reported. As further validation, the results of a new series of experiments (varying the ratio of mono-functional to difunctional monomer) are predicted by the semibatch copolymerization model and measured parameters. Based on these results, they are able to calculate the molecular homogeneity in the copolymer products investigated. Even for this relatively simple system, the optimal injection time is a complex function of residence time, but early injection of the faster-condensing monomer gives the best homogeneity at long residence times.

RANKIN,STEPHEN E.; MCCORMICK,ALON V.

2000-01-26

117

Method for dehydrating manganese dioxide  

SciTech Connect

A method is described for preparing a water-free lithium-manganese dioxide battery comprising: assembling the battery comprising lithium anode, a cathode comprising carbon and manganese dioxide, and a cell container; adding to the cell container a fluid containing a dehydrating agent which reacts with water bound to the manganese dioxide to form a reaction product that is extractable from the manganese dioxide; removing the fluid from the cell container; hermetically sealing and connecting the container to a vacuum source; establishing a vacuum within the compartment to pull off any remaining amount of the fluid and any volatile reaction product from the manganese dioxide; releasing the vacuum; and adding anhydrous electrolyte and hermetically sealing the cell.

Marincic, N.; Fuksa, R.

1987-05-05

118

Experimental evidence for condensation reactions between sugars and proteins in carbonate skeletons  

NASA Astrophysics Data System (ADS)

Melanoidins, condensation products formed from protein and polysaccharide precursors, were once thought to be an important geological sink for organic carbon. The active microbial recycling of the precursors, coupled with an inability to demonstrate the formation of covalent linkages between amino acids and sugars in melanoidins, has shaped a powerful argument against this view. Yet, melanoidins may still be an abundant source of macromolecules in fossil biominerals such as shells, in which the proteins and polysaccharides are well protected from microbial degradation. We have modelled diagenetic changes in a biomineral by heating at 90°C mixtures of protein, polysaccharides and finely ground calcite crystals in sealed glass vials. Changes to the protein bovine serum albumin (BSA, fraction V) were monitored by means of gel electrophoresis and immunology. In the presence of water, BSA was rapidly hydrolyzed and remained immunologically reactive for less than 9 h. Under anhydrous conditions the protein was immunologically reactive for the whole period of the experiment (1281 h), unless mono- or disaccharide sugars were also present. In the presence of these reactive sugars, browning, a discrete increase in molecular weight of the protein and a concomitant loss of antigenicity confirmed that the sugars were attaching covalently to the protein, forming melanoidins. The de novo formation of products cross-reactive with antibodies raised against organic matter isolated from the shells of a fossil mollusc ( Mercenaria mercenaria) indicated that at least in part the model simulated natural diagenesis. We roughly estimate that, at the global scale, 2.4 × 10 6 tonnes of calcified tissue matrix glycoproteins is processed annually through the melanoidin pathway. This amount would be equivalent to 7 per mil of the total flux of organic carbon into marine sediments.

Collins, M. J.; Westbroek, P.; Muyzer, G.; de Leeuw, J. W.

1992-04-01

119

Model path-integral dynamics for nonadiabatic reactions in the condensed phase  

NASA Astrophysics Data System (ADS)

We introduce mapping-variable ring polymer molecular dynamics (MV-RPMD), a direct, real-time dynamic technique for the atomistic simulation of nonadiabatic reactions. The dynamics are based on the recently derived exact path-integral Stock-Thoss (PI-ST)representation for the quantum Boltzmann operator that has been previously used to calculate equilibrium properties for N-level systems, and as a way to initialize semiclassical trajectories for the calculation of thermal correlation functions. Both these methods use the Stock-Thoss (ST) mapping protocol to map from a discrete electronic states basis to a continuous Cartesian variables basis, providing the even-handed treatment of electrons and nuclei required to accurately describe their dynamically coupled motions and to describe resonance energy transfer. Like the existing RPMD approach, this method can be used to generate statistically meaningful ensembles of reactive trajectories but, unlike RPMD, it is applicable to photochemical reactions and reactions where proper electronic state quantization is essential. We present the results of simulations using MV-RPMD to calculate correlation functions for a series of model N-level systems over a wide range of nonadiabatic coupling strengths.

Ananth, Nandini; Menzeleev, Artur; Miller, Thomas

2013-03-01

120

An investigation of the role of water on retrograde/condensation reactions and enhanced liquefaction yields. Quarterly progress report, July 1, 1992--September 30, 1992  

SciTech Connect

Changes in coal structure that occur during coal drying and steam pretreatments will be measured in order to determine what effect water has on retrograde/condensation reactions, and to determine how water enhances coal reactivity toward liquefaction. Coal drying experiments were begun using thermal, microwave, and chemical methods; NMR data were collected. A stirred microautoclave reactor system was acquired.

Miknis, F.P.

1992-10-01

121

Rehydration of Dehydrated Foods  

Microsoft Academic Search

Dehydrated products readily take up moisture when immersed in a liquid medium, leading to significant changes in their thermophysical properties. The rehydration kinetics, the structural properties (apparent density, true density, specific volume and internal porosity), the viscoelastic behavior (compression tests), and the flavor losses were investigated during rehydration of various fruits and vegetables. The effect of temperature on the above

M. K. Krokida; C. Philippopoulos

2005-01-01

122

Theory of Bose–Einstein condensation mechanism for deuteron-induced nuclear reactions in micro\\/nano-scale metal grains and particles  

Microsoft Academic Search

Recently, there have been many reports of experimental results which indicate occurrences of anomalous deuteron-induced nuclear\\u000a reactions in metals at low energies. A consistent conventional theoretical description is presented for anomalous low-energy\\u000a deuteron-induced nuclear reactions in metal. The theory is based on the Bose–Einstein condensate (BEC) state occupied by deuterons\\u000a trapped in a micro\\/nano-scale metal grain or particle. The theory

Yeong E. Kim

2009-01-01

123

Intramolecular condensation reactions of {alpha},{omega}-bis(triethoxysilyl)alkanes. Formation of cyclic disilsesquioxanes  

SciTech Connect

In this paper, we used mass spectrometry and {sup 29}Si NMR spectroscopy to discover that the length of the alkylene-bridging groups had a pronounced effect on the competition between cyclization and polymerization of {alpha},{omega}-bis(triethoxysilyl)alkanes and on the formation of polymeric gels. While the intramolecular reaction clearly slows gelation, the cyclic disilsesquioxanes are still tetrafunctional monomers theoretically capable of forming polymeric gels. If the ring structures, which bear a striking resemblence to carbohydrates, are preserved through the polymerization, the resulting poly(cyclic disilsesquioxane) gels may have structural similarities to branched or cross-linked carbohydrates, such as cellulose or chitosan. Under base-catalyzed sol-gel polymerization conditions, 3 and 4 (six- and seven-membered cyclic disilsesquioxanes, respectively) quickly reacted to give gels with significant ring opening as determined from the {sup 29}Si chemical shifts in solid-state (CP MAS) NMR spectra. However, gels prepared under acidic conditions reveal some or all of the cyclic disilsesquioxane functionality was preserved in the polymers. 13 refs., 1 fig.

Loy, D.A.; Carpenter, J.P.; Myers, S.A.; Assink, R.A. [Sandia National Lab., Albuquerque, NM (United States); Small, J.H.; Greaves, J.; Shea, K.J. [Univ. of California, Irvine, CA (United States)

1996-09-04

124

Catalytic solid substrate room temperature phosphorimetry for the determination of trace rhamnose based on its condensation reaction with calcein  

NASA Astrophysics Data System (ADS)

Calcein (R) could not only emit strong and stable room temperature phosphorescence (RTP) on filter paper using I - as perturber, but also could be oxidized by H 2O 2 to form a non-phosphorescence compound (R'), resulting in the quenching of RTP signal of R. Moreover, the ortho-hydrogen of phenolic hydroxyl in R took condensation reaction with rhamnose (Rha) to produce non-phosphorescence compound (R-Rha) causing the RTP signal of R to further quench, and R-Rha was oxidized by H 2O 2 to form R' and Rha, bringing about the sharp RTP signal quenching of R. Thus, a new solid substrate room temperature phosphorimetry (SSRTP) for the determination of trace Rha based on its strong catalytic effect on H 2O 2 oxidizing R has been established, with the detection limit (LD) of 7.8 zg spot -1 (corresponding concentration: 2.0 × 10 -17 g ml -1, sample volume: 0.40 ?l spot -1). This method has been applied to determine trace Rha in cigarettes and jujubes, with the results coinciding well with those determined by a high performance liquid chromatography (HPLC). The component of R-Rha also was analyzed by means of HPLC, mass spectrometer and nuclear magnetic resonance (NMR) measurements. The mechanism of catalytic SSRTP for the determination of trace Rha was discussed.

Liu, Jia-Ming; Lin, Li-Ping; Wang, Hong-Xin; Lin, Shao-Qin; Zhang, Li-Hong; Cai, Wen-Lian; Lin, Xuan; Pan, You-Zhu; Wang, Xin-Xing; Li, Zhi-Ming; Jiao, Li; Cui, Ma-Lin

2011-12-01

125

[Pathophysiology of dehydration].  

PubMed

The pathophysiology of dehydration is reviewed. The normal response to dehydration, i.e. decreased effective arterial blood volume or effective circulating volume is described. Due to water retention and drinking following stimulation of ADH secretion and thirst, osmoregulation is overruled by volume conservatory mechanisms, which lead to hyponatremia. Only patients with impaired mental function or those who are unable to drink will develop a progressive water deficit--with or without salt depletion--recognizable by hypernatremia. Decreased effective arterial blood volume and hypernatremia affect cerebral function in a way that perception of external stimuli as well as perception of pain will be impaired. Alert dehydrated patients are disturbed mainly by thirst and dryness of the mouth. Both symptoms are perceived more intensely by young than by elderly persons. Dryness of the mouth increase thirst on its own. Distress by thirst and oral dryness increases as a function of the level and the rapidity of developing hypernatremia. The simple act of filling the oral cavity with fluid and swallowing alleviates thirst in the absence of any change in plasma sodium concentration. Thirst quenching efficacy is increased by administering chilled hypotonic fluid with lemon or other fruit acid added (for stimulation of salivation). PMID:8362127

Brunner, F P

1993-07-20

126

Novel dehydration of carbohydrates to 5-hydroxymethylfurfural catalyzed by Ir and Au chlorides in ionic liquids  

Microsoft Academic Search

Catalytic dehydration of carbohydrates into 5-hydroxymethylfurfural (5-HMF) has been studied in the presence of ionic liquids, i.e., 1-butyl-3-methyl imidazolium chloride ([BMIM]Cl) and triethylamine sulphate ([Et3NH][HSO4]) using metal salts as catalysts. Novel metal chlorides IrCl3 and AuCl3·HCl as catalysts in ionic liquid showed remarkable activity and selectivity to 5-HMF for the reaction of fructose dehydration. The reaction conditions of fructose dehydration

Zuojun Wei; Yan Li; Dilantha Thushara; Yingxin Liu; Qilong Ren

2011-01-01

127

New poly(anhydride-ester)s and the development of new melt condensation polymerization method and solution polymerization method for their syntheses  

NASA Astrophysics Data System (ADS)

The thesis discusses the development of a series of degradable poly(anhydride-ester)s and synthesis methods thereof. Acyl chloride facilitated condensation polymerization and dehydrative coupling using (trimethylsilyl)ethoxyacetylene as the dehydrating agent are two of the novel aspects of this work. Availability of polyanhydrides of desirable properties for controlled drug delivery is limited by the traditional condensation polymerization method by which they are usually synthesized, because of the low reactivity and harsh reaction conditions of this method. Poly(anhydride-ester)s are expected to be surface eroding and enrich the pool of available polyanhydrides. In this work, a series of symmetrical and unsymmetrical diacids are synthesized as monomers for the preparation of poly(anhydride-ester)s of appropriate thermal and degradation properties. Two new methods have been developed for effective preparation of poly(anhydride-ester)s from these monomers at conditions that are milder than that of the traditional melt polycondensation method. Polymerization of the diacid monomers was carried out using the three methods: (1) traditional melt condensation polymerization of acetylated diacids, (2) melt condensation polymerization facilitated by acyl chloride, (3) solution condensation polymerization using (trimethylsilyl)acetylene as the dehydrating agent. The traditional condensation method failed to yield poly(anhydride-ester)s with appreciable results, due to the major side reactions as transacylation, transesterification and decarboxylation at all the attempted polymerization temperatures. The effects of these side reactions were greatly reduced in the system of acyl chloride facilitated condensation polymerization. The success of this method is due to the higher reactivity of carboxylic acid chlorides in exchange reactions, as well as the reduced transacylation reactivity of bulky acylated polymer chain ends in ring-forming transacylation reactions. Back-biting of the acylated polymer chain ends are believed to be the major cause of cyclization. (Trimethylsilyl)ethoxyacetylene was found to be an efficient dehydrating agent in dehydrative coupling of the monomers under mild conditions. High molecular weight products were obtained from certain monomers, whereas others show inclinations to forming cyclic anhydrides upon polymerization. Solvent hydrogen bonding is an important controlling factor for this method. Changing composition and structure of the repeating unit was shown to be an effective way to modify the monomer polymerization behaviors and properties of the polymers.

Qian, Haitao

128

Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water  

NASA Astrophysics Data System (ADS)

We present a novel kinetic multi-layer model for gas-particle interactions in aerosols and clouds (KM-GAP) that treats explicitly all steps of mass transport and chemical reaction of semi-volatile species partitioning between gas phase, particle surface and particle bulk. KM-GAP is based on the PRA model framework (Pöschl-Rudich-Ammann, 2007), and it includes gas phase diffusion, reversible adsorption, surface reactions, bulk diffusion and reaction, as well as condensation, evaporation and heat transfer. The size change of atmospheric particles and the temporal evolution and spatial profile of the concentration of individual chemical species can be modeled along with gas uptake and accommodation coefficients. Depending on the complexity of the investigated system and the computational constraints, unlimited numbers of semi-volatile species, chemical reactions, and physical processes can be treated, and the model shall help to bridge gaps in the understanding and quantification of multiphase chemistry and microphysics in atmospheric aerosols and clouds. In this study we demonstrate how KM-GAP can be used to analyze, interpret and design experimental investigations of changes in particle size and chemical composition in response to condensation, evaporation, and chemical reaction. For the condensational growth of water droplets, our kinetic model results provide a direct link between laboratory observations and molecular dynamic simulations, confirming that the accommodation coefficient of water at ~270 K is close to unity (Winkler et al., 2006). Literature data on the evaporation of dioctyl phthalate as a function of particle size and time can be reproduced, and the model results suggest that changes in the experimental conditions like aerosol particle concentration and chamber geometry may influence the evaporation kinetics and can be optimized for efficient probing of specific physical effects and parameters. With regard to oxidative aging of organic aerosol particles, we illustrate how the formation and evaporation of volatile reaction products like nonanal can cause a decrease in the size of oleic acid particles exposed to ozone.

Shiraiwa, M.; Pfrang, C.; Koop, T.; Pöschl, U.

2012-03-01

129

Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water  

NASA Astrophysics Data System (ADS)

We present a novel kinetic multi-layer model for gas-particle interactions in aerosols and clouds (KM-GAP) that treats explicitly all steps of mass transport and chemical reaction of semi-volatile species partitioning between gas phase, particle surface and particle bulk. KM-GAP is based on the PRA model framework (Pöschl-Rudich-Ammann, 2007), and it includes gas phase diffusion, reversible adsorption, surface reactions, bulk diffusion and reaction, as well as condensation, evaporation and heat transfer. The size change of atmospheric particles and the temporal evolution and spatial profile of the concentration of individual chemical species can be modeled along with gas uptake and accommodation coefficients. Depending on the complexity of the investigated system, unlimited numbers of semi-volatile species, chemical reactions, and physical processes can be treated, and the model shall help to bridge gaps in the understanding and quantification of multiphase chemistry and microphysics in atmospheric aerosols and clouds. In this study we demonstrate how KM-GAP can be used to analyze, interpret and design experimental investigations of changes in particle size and chemical composition in response to condensation, evaporation, and chemical reaction. For the condensational growth of water droplets, our kinetic model results provide a direct link between laboratory observations and molecular dynamic simulations, confirming that the accommodation coefficient of water at ~270 K is close to unity. Literature data on the evaporation of dioctyl phthalate as a function of particle size and time can be reproduced, and the model results suggest that changes in the experimental conditions like aerosol particle concentration and chamber geometry may influence the evaporation kinetics and can be optimized for efficient probing of specific physical effects and parameters. With regard to oxidative aging of organic aerosol particles, we illustrate how the formation and evaporation of volatile reaction products like nonanal can cause a decrease in the size of oleic acid particles exposed to ozone.

Shiraiwa, M.; Pfrang, C.; Koop, T.; Pöschl, U.

2011-12-01

130

Dehydration of fermentative 2,3-butanediol into methyl ethyl ketone  

SciTech Connect

A solid acid catalyst consisted of sulfonic groups covalently bound to an inorganic matrice was developed to dehydrate 2,3-butanediol into methyl ethyl ketone. Rate constant and apparent activation energy of the dehydration reaction were determined. The decay course of the catalyst was a two-stage curve. The catalyst was deactivated more rapidly in the first stage than in the second stage. The strategy of maintaining constant degree of dehydration was employed to lengthen the lifetime of catalyst. Treatment of the 2,3-butanediol containing fermentation broth with activated carbon greatly facilitated the subsequent dehydration reaction.

Tran, A.V.; Chambers, R.P.

1987-01-01

131

7 CFR 993.15 - Dehydrator.  

Code of Federal Regulations, 2013 CFR

...PRUNES PRODUCED IN CALIFORNIA Order Regulating Handling Definitions § 993.15 Dehydrator. Dehydrator means any person who produces prunes by drying or dehydrating plums by means of sun-drying or artificial...

2013-01-01

132

VACUUM OSMOTIC DEHYDRATION OF FRUITS  

Microsoft Academic Search

Vacuum osmotic dehydration leads a special behaviour of mass transfer in fruit-sugar soluion system.Vacuum treatments intensify the capillary flow function and increase water transfer ratio.but have no significant influence on sugar uptake.Fruits such as pineapples which have higher porosity are more suitable to be treated under vacuum during the osmotic dehydration.

Xian Quan Shi; Pedro Fito Maupoey

1993-01-01

133

Advances in dehydration of foods  

Microsoft Academic Search

Food dehydration is still one of the most relevant and challenging unit operations in food processing, although the art of food preservation through the partial removal of water content dates back several centuries. This article provides essential information on the fundamental, including psychrometry, and applied engineering aspects of food dehydration with up-to-date available commercial applications. The evolution of drying technology,

Humberto Vega-Mercado; M. Marcela Góngora-Nieto; Gustavo V. Barbosa-Cánovas

2001-01-01

134

Voluntary dehydration and cognitive performance in trained college athletes.  

PubMed

Cognitive and mood decrements resulting from mild dehydration and glucose consumption were studied. Men and women (total N = 54; M age = 19.8 yr., SD = 1.2) were recruited from college athletic teams. Euhydration or dehydration was achieved by athletes completing team practices with or without water replacement. Dehydration was associated with higher thirst and negative mood ratings as well as better Digit Span performance. Participants showed better Vigilance Attention with euhydration. Hydration status and athlete's sex interacted with performance on Choice Reaction Time and Vigilance Attention. In a second study, half of the athletes received glucose prior to cognitive testing. Results for negative mood and thirst ratings were similar, but for cognitive performance the results were mixed. Effects of glucose on cognition were independent of dehydration. PMID:19831106

D'anci, Kristen E; Vibhakar, Arjun; Kanter, Jordan H; Mahoney, Caroline R; Taylor, Holly A

2009-08-01

135

DNA condensation  

Microsoft Academic Search

Recent progress in our understanding of DNA condensation includes the observation of the collapse of single DNA molecules, greater insights into the intermolecular forces driving condensation, the recognition of helix-structure perturbation in condensed DNA, and the increasing recognition of the likely biological consequences of condensation. DNA condensed with cationic liposomes is an efficient agent for the transfection of eukaryotic cells,

Victor A Bloomfield

1996-01-01

136

Onion dehydration: a review.  

PubMed

Onion (Allium cepa), a very commonly used vegetable, ranks third in the world production of major vegetables. Apart from imparting a delicious taste and flavour due to its pungency in many culinary preparations, it serves several medicinal purposes also. Processing and preservation of onion by suitable means is a major thrust area since a long time. The various kinds of treatments followed for dehydration of onion such as convective air drying, solar drying, fluidized bed drying, vacuum microwave drying, infrared drying and osmotic drying are reviewed here. These techniques are mainly used for preservation and value addition of onion. Several researchers have tried for decades to model the drying kinetics and quality parameters, which are also compiled here briefly. PMID:23729847

Mitra, Jayeeta; Shrivastava, S L; Rao, P S

2011-04-27

137

Dehydration–hydrogenation of glycerol into 1,2-propanediol at ambient hydrogen pressure  

Microsoft Academic Search

The vapor-phase reaction of glycerol was performed over copper metal catalysts at ambient hydrogen pressure. Glycerol was converted into 1,2-propanediol (1,2-PDO) through the dehydration into hydroxyacetone, followed by the hydrogenation into 1,2-PDO. The yield of 1,2-PDO was limited up to 80% at a constant temperature of 190°C because of a trade-off problem between the dehydration and the hydrogenation. The dehydration

Masaki Akiyama; Satoshi Sato; Ryoji Takahashi; Kanichiro Inui; Masahiro Yokota

2009-01-01

138

An investigation of the role of water on retrograde/condensation reactions and enhanced liquefaction yields. Quarterly progress report, January 1, 1994--March 31, 1994  

SciTech Connect

The results of coal swelling measurements using 1,4-dioxane as the swelling reagent for premoisturized coals (raw) and coal dried thermally, chemically, and with microwave radiation are presented. An increase in the swelling ratio relative to raw coal indicates a decrease in the amount of cross-linking in the coal. Conversely, a decrease in the ratio indicates an increase in cross-linking. The extent of cross-linking (as measured by 1,4-dioxane) for Texas, Black Thunder, and Eagle Butte Coals are about the same. Illinois {number_sign}6 coal appears to have less cross-linking relative to the other three coals. These results are expected on the basis of coal rank. The increase in cross linking is most pronounced for coals dried thermally and with microwave radiation. A decrease in the swelling ratios for all four coals suggests that cross-linking had occurred possibly due to partial devolatilization process. However, low temperature, chemical dehydration of the coals causes only a small or no change in the internal structure for Texas and Illinois {number_sign}6 coals whereas a significant decrease in the cross-linking structure for the Black Thunder and Eagle Butte coals is observed. It is possible that the solvent (CH{sub 3}OH) and products resulting from the chemical dehydrating (acetone and methanol) occupy the surface sites that water had before the reaction and thus preventing cross-linking to occur. These reagents can also promote swelling of coals and may account for some of the decrease in the cross-linking of the coal structure observed for the chemically dried coals.

Miknis, F.P.; Netzel, D.A.

1994-04-01

139

Reactions of 3-isochromanone with aromatic aldehydes--microwave assisted condensations performed on solid basic inorganic supports.  

PubMed

An improved Knoevenagel condensation of 3-isochromanone and aromatic aldehydes can be achieved by microwave irradiation on solid supports in the presence of various catalysts. This synthetic method offers some major advantages, especially the possibility to change the ratio of E/Z isomers. PMID:16678272

Vass, András; Földesi, András; Lóránd, Tamás

2006-03-27

140

Synthesis, crystal structures and investigations on the dehydration reaction of the new coordination polymers poly[diaqua-(?2-squarato-O,O')-(?2-4,4'-bipyridine-N,N')Me(II)] hydrate (Me=Co, Ni, Fe)  

NASA Astrophysics Data System (ADS)

The three new isostructural coordination polymers poly[diaqua-(?2-squarato-O,O')-(?2-4,4'-bipyridine-N,N')Me(II)] hydrate (Me=Fe, Co, Ni) were prepared by hydrothermal reaction. All compounds are isostructural and crystallize in the monoclinic space group P21/c with 4 formula units in the unit cell (a=18.893 (1) Å, b=11.450 (1) Å, c=8.0985 (4) Å, ?=93.032 (5)°, V=1749.5 (2) Å3, [Fe(C4O4)(C10H8)(H2O)2].(H2O)3 a=18.937 (1) Å, b=11.342 (1) Å, c=8.0545 (5) Å, ?=91.83 (1)°, V=1725.3 (2) Å3, [Co(C4O4)(C10H8)(H2O)2].(H2O)3; a=18.271 (1) Å, b=11.340 (1) Å, c=7.8946 (4) Å, ?=90.69 (5)°, V=1633.1 (2) Å3, [Ni(C4O4)(C10H8)(H2O)2](H2O)1.7). In the crystal structures the metal atoms are coordinated by two squarate dianions, two 4,4'-bipyridine ligands and two water molecules. The metal atoms are connected via the squarate dianions and the 4,4'-bipyridine ligands into layers, which interpenetrate forming a three-dimensional coordination network. This arrangement yields channels in which additional water molecules are embedded. Thermoanalytic investigations show that upon heating the channel water is removed in the first step and that the water coordinated to the metal atoms is emitted in the second step. Both steps are fully reversible with the former reaction proceeding via a topotactic reaction. The hydration and dehydration of the compounds are accompanied with a continuous change of the color of the materials. The de- and reintercalation processes were investigated using single crystal structure analysis, X-ray powder diffraction, temperature-dependent X-ray powder diffraction, simultaneous differential thermoanalysis and thermogravimetry coupled to mass spectroscopy, differential scanning calorimetry and time-dependent UV-Vis spectroscopy. The results of the investigations are discussed and compared with those for the previously reported manganese compound.

Greve, Jan; Jeß, Inke; Näther, Christian

2003-11-01

141

Dehydration and hyponatremia during triathlons.  

PubMed

In ultraendurance triathlons, dehydration and electrolyte balance are important factors in race completion and level of performance. Dehydration is the most common reason for a triathlete in the Hawaii Ironman Triathlon to need medical assistance. Hyponatremia is the predominant electrolyte disturbance. We have previously described exercise-induced hyponatremia and documented its incidence as a function of race length and state of hydration. This syndrome, dehydration plus hyponatremia, is extremely rare in races lasting less than 4 h but becomes common in races lasting longer than 8 h. Recommendations are made to help ultraendurance athletes understand and maintain proper fluid and electrolyte balance. PMID:2691834

Hiller, W D

1989-10-01

142

Gas-particle interactions of tropospheric aerosols: Kinetic and thermodynamic perspectives of multiphase chemical reactions, amorphous organic substances, and the activation of cloud condensation nuclei  

NASA Astrophysics Data System (ADS)

Aerosols are of central importance in the Earth system, influencing the atmosphere, biosphere, climate, and public health. This article outlines recent advances and perspectives in the investigation and effects of gas-particle interactions in tropospheric aerosols, including physical, chemical and biological aspects. In particular, it addresses how multiphase processes and heterogeneous chemical reactions can be efficiently described by kinetic models, how amorphous organic substances can influence the kinetics of water uptake and phase transitions, and how the abundance and activation of cloud condensation nuclei (CCN) depend on thermodynamic and kinetic parameters.

Pöschl, Ulrich

2011-08-01

143

A solid-state NMR study of condensation/retrograde reactions during coal liquefaction: Quarterly progress report, January 1, 1989--March 31, 1989  

SciTech Connect

The objective of this work is to perform an NMR study of the aromaticity in coals, coal derived products and/or model compounds generated by pyrolysis and thermal solubilization of coal in the presence of a hydrogen donor solvent. Cross Polarization with Magic-Angle Spinning (CP/MAS) will be used to measure the carbon aromaticity, and Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR techniques will be used to measure the hydrogen aromaticity. From these NMR measurements the aromatic hydrogen-to-carbon ratio will be obtained and used to study condensation/retrograde reactions during coal liquefaction. 8 refs., 2 tabs.

Miknis, F.P.

1989-04-01

144

[Dehydration due to "mouth broken"].  

PubMed

Two children were admitted to a medical centre due to dehydration after an oral injury and the extraction of a tooth. One child complained of "mouth broken". Dehydration is the most common water-electrolyte imbalance in children. Babies and young children are prone to dehydration due to their relatively large body surface area, the high percentage extracellular fluid, and the limited ability of the kidneys to conserve water. After the removal ofa tooth, after an oral trauma or in case of oral discomfort, a child is at greater risk of dehydration by reduced fluid and food intake due to oral pain and/or discomfort and anxiety to drink. In those cases, extra attention needs to be devoted to the intake of fluids. PMID:23050378

Meijler, D P M; van Mossevelde, P W J; van Beek, R H T

2012-09-01

145

Conservation of yeasts by dehydration  

Microsoft Academic Search

The presented material concerns the theoretical basis for obtaining high-quality active dry biopreparations. It deals with the present understanding of anabiosis, contains data on yeast resistance against dehydration and the limits for preserving the viability of microorganisms in anabiosis. The process of water transport in yeast biomass during dehydration is discussed.\\u000a The changes and transformations in yeast cells occuring after

Martin Beker; Alexander Rapoport

146

Dehydration of synthetic and natural vivianite  

Microsoft Academic Search

Thermal analyses of synthetic and natural vivianite (Fe2+)3(PO4)2·8H2O) were determined using a high-resolution thermal analyser coupled to a mass spectrometer.Five dehydration weight loss steps were observed for the natural vivianite at 105, 138, 203, 272 and 437°C. The first weight loss step involves the reaction (Fe2+)3(PO4)2·8H2O?(Fe2+)3(PO4)2·3H2O+5H2O. The TGA\\/MS for the synthetic vivianite gave similar results to that of the natural

Ray L Frost; Matt L Weier; Wayde Martens; J. Theo Kloprogge; Zhe Ding

2003-01-01

147

Kinetic analysis of palladium(II) adsorption process on condensed-tannin gel based on redox reaction models  

Microsoft Academic Search

We have developed a novel recovery system of palladium (Pd) from wastes such as spent catalysts or scraps, using tannin gel particles synthesized from condensed-tannin molecules. The Pd(II) ionic species are reduced to metallic Pd(0) on the network of the tannin gel: a two-electron transfer from the tannin gel to Pd(II). The kinetic study of the electron transfer was performed

Yeon-Ho Kim; Takeshi Ogata; Yoshio Nakano

2007-01-01

148

DABCO?Catalyzed Efficient Synthesis of Naphthopyran Derivatives via One?Pot Three?Component Condensation Reaction at Room Temperature  

Microsoft Academic Search

Diazabicyclo[2.2.2]octane (DABCO) has been used as a mild and efficient catalyst for synthesis of 2?amino?3?cyano naphthopyran derivatives via a one?pot three?component reaction of aromatic aldehydes, naphthols, and malononitrile at room temperature. The short reaction times, easy workup, good to excellent yields, and mild reaction conditions make this domino Knoevenagel–Michael reaction both practical and attractive.

Saeed Balalaie; Sorour Ramezanpour; Morteza Bararjanian; Jürgen H. Gross

2008-01-01

149

Direct synthesis of dimethyl ether from carbon-monoxide-rich synthesis gas: Influence of dehydration catalysts and operating conditions  

Microsoft Academic Search

Various dehydration catalysts were studied in the synthesis of dimethyl ether (DME) directly from carbon-monoxide-rich synthesis gas under a series of different reaction conditions. The investigated catalyst systems consisted of combinations of a methanol catalyst (CuO\\/ZnO system) with catalysts for methanol dehydration based on ?-Al2O3 or zeolites and ?-Al2O3 was identified as the most favorable dehydration catalyst. Various reaction parameters

Miriam Stiefel; Ruaa Ahmad; Ulrich Arnold; Manfred Döring

2011-01-01

150

Condensed isoquinolines 24. Reaction of 6,11-dihydro-13H-isoquino[3,2- b ]quinazolin-13-one with carbonyl compounds  

Microsoft Academic Search

The reaction of 6,11-dihydro-13H-isoquino[3,2-b]quinazolin-13-one with carbonyl compounds occurs at the C(6) and\\/or N(5) atoms depending on the nature of the reagent and the conditions. Condensation with aldehydes gives 6-arylidene-6,11-dihydro-13H-isoquino[3,2-b]quinazolin-13-ones.\\u000a Acylation using acid anhydrides or acid chlorides gave 5-acyl-, 6-acyl-, and 5,6-diacyl-5,11-dihydro-13H-isoquino[3,2-b]quinazolin-13-ones\\u000a depending again on the reaction conditions. Acylation using chloroacetyl chloride is accompanied by an intramolecular alkylation\\u000a to give 7H,8H-2a,

L. M. Potikha; V. A. Kovtunenko

2007-01-01

151

Dehydrations of Ca(H 2 PO 4 ) 2 ·H 2 O and Mg(H 2 PO 4 ) 2 ·2H 2 O and their reactions with KCl, examined with simultaneous TG, DTG, DTA and EGA  

Microsoft Academic Search

The dehydrations of Ca(H2PO4)2·H2O and Mg(H2PO4)2 H2O were examined with a simultaneous TG, DTG, DTA and EGA method, partly under conventional, and partly under quasi-isothermal and quasi-isobaric conditions. It was found among others that the dehydrations of the examined compounds took place gradually between 100 and 500°, a series of intermediates being formed. The end-products were [Ca(PO3)2]3 and Mg(PO3)2. The

M. Pyldme; K. Tynsuaadu; F. Paulik; J. Paulik; M. Arnold

1979-01-01

152

Carbohydrate Dehydration Demonstrations.  

ERIC Educational Resources Information Center

|Discusses the impact of various factors on the "charring reaction" of a carbohydrate with concentrated sulfuric acid including the type of sugar, the degree of fineness of the sugar crystals, and the amount of water added. (JRH)|

Dolson, David A.; And Others

1995-01-01

153

Preparation of mordenite membranes for dehydration of water–UDMH  

Microsoft Academic Search

Mordenite membranes were prepared on the outer surface of ceramic tubular tubes via hydrothermal synthesis and evaluated for dehydration pervaporation of water unsymmetrical dimethylhydrazine UDMH mixtures. Highly water-selective mordenite membranes were prepared and the optimum reaction condition was found to be 24h crystallization time and 170°C crystallization temperature. Effect of gel composition on separation factor and water flux of the

Mansoor Kazemimoghadam; Toraj Mohammadi

2010-01-01

154

The solvent-free thermal dehydration of tetritols on zeolites  

Microsoft Academic Search

A new alditol dehydration method at high temperatures, in the presence of molecular sieves without solvent in an argon atmosphere, is described. Investigations on tetritols have been carried out. Products arising after the intramolecular and intermolecular elimination of water, with retention or inversion of the configuration of asymmetric carbon atoms, were observed. Complete analytical separation of reaction products was achieved

Maria Kurszewska; Eugenia Skorupa; Regina Kasprzykowska; Pawe? Sowi?ski; Andrzej Wi?niewski

2000-01-01

155

The solvent-free thermal dehydration of tetritols on zeolites.  

PubMed

A new alditol dehydration method at high temperatures, in the presence of molecular sieves without solvent in an argon atmosphere, is described. Investigations on tetritols have been carried out. Products arising after the intramolecular and intermolecular elimination of water, with retention or inversion of the configuration of asymmetric carbon atoms, were observed. Complete analytical separation of reaction products was achieved by means of GLC. The chemical structures of the compounds obtained were assigned using co-injection with standards, GLC-CIMS and GLC-EIMS analyses. Two intermolecular dehydration products of tetritols were isolated by HPLC and identified by 1H and 13C NMR spectroscopy. PMID:10890272

Kurszewska, M; Skorupa, E; Kasprzykowska, R; Sowi?ski, P; Wi?niewski, A

2000-06-30

156

Bifunctional building blocks in the Ugi-azide condensation reaction: a general strategy toward exploration of new molecular diversity.  

PubMed

1,5-Disubstituted tetrazoles are an important drug-like scaffold known for their ability to mimic the cis-amide bond conformation. The scaffold is readily accessible via substitution of the carboxylic acid component of the Ugi multi-component reaction (MCR) with TMSN3 in what is herein denoted the Ugi-azide reaction. This full paper presents a concise, novel, general strategy to access a plethora of new heterocylic scaffolds utilizing tethered aldo/keto-acids/esters in the Ugi-azide reaction followed by a ring closing event that generates novel highly complex bis-heterocyclic lactam-tetrazoles. PMID:23912086

Gunawan, Steven; Hulme, Christopher

2013-09-28

157

Concerted reactions and mechanism of glucose pyrolysis and implications for cellulose kinetics.  

PubMed

Concerted reactions are proposed to be keys to understanding thermal decomposition of glucose in the absence of ionic chemistry, including molecular catalysis by ROH molecules such as H(2)O, other glucose molecules, and most of the intermediates and products. Concerted transition states, elementary-reaction pathways, and rate coefficients are computed for pyrolysis of ?-D-glucose (?-D-glucopyranose), the monomer of cellulose, and for related molecules, giving an improved and elementary-reaction interpretation of the reaction network proposed by Sanders et al. (J. Anal. Appl. Pyrolysis, 2003, 66, 29-50). Reactions for ring-opening and formation, ring contraction, retro-aldol condensation, keto-enol tautomerization, and dehydration are included. The dehydration reactions are focused on bicyclic ring formations that lead to levoglucosan and 1,6-?-D-anhydrousglucofuranose. The bimolecular ROH-assisted reactions are found to have lower activation energy compared to the unimolecular reactions. The same dehydration reaction to levoglucosan should occur for cellulose going to cellosan (e.g., cellotriosan) plus a shortened cellulose chain, a hypothesis supported by the very similar activation energies computed when alternate groups were substituted at the C1 glycosidic oxygen. The principles of Sanders et al. that distinguish D-glucose, D-fructose, sucrose, and cellulose pyrolysis prove useful in providing qualitative insights into cellulose pyrolysis. PMID:23082925

Seshadri, Vikram; Westmoreland, Phillip R

2012-11-09

158

Dehydration of glycerol over niobia-supported silicotungstic acid catalysts.  

PubMed

Liquid-phase dehydration of glycerol to acrolein over nanosized niobia-supported silicotungstic acid catalysts was performed to investigate the effect of the silicotungstic acid loading on the catalytic performance of the catalysts. The catalysts were prepared by following an impregnation method with different HSiW loadings in the range of 10-50 wt%. The prepared catalysts were characterized by N2 physisorption, XRD, FT-IR, TPD of ammonia, and TGA. Dehydration of glycerol was conducted in an autoclave reactor under the conditions of controlled reaction temperatures under corresponding pressure. Increasing HSiW loading rapidly increased the acidity of HSiW/Nb205 catalyst and rate of glycerol conversion, but acrolein selectivity decreased due to enhanced deactivation of the catalyst by carbon deposit. Consequently, it was confirmed that catalytic activity for the dehydration of glycerol to acrolein was dependant on the acidity of catalyst and can be controlled by HSiW loading. PMID:23646735

Lee, Young Yi; Ok, Hye Jeong; Moon, Dong Ju; Kim, Jong Ho; Park, Nam Cook; Kim, Young Chul

2013-01-01

159

Enhancement of the promiscuous aldolase and dehydration activities of 4-oxalocrotonate tautomerase by protein engineering.  

PubMed

Double play: The enzyme 4-oxalocrotonate tautomerase (4-OT) catalyzes not only the initial cross-coupling of acetaldehyde and benzaldehyde to yield 3-hydroxy-3-phenylpropanal, but also the subsequent dehydration of this aldol compound to yield cinnamaldehyde as the final product. Mechanism-inspired engineering provided an active site mutant (F50A) with strongly enhanced aldol condensation activity. PMID:22615135

Zandvoort, Ellen; Geertsema, Edzard M; Quax, Wim J; Poelarends, Gerrit J

2012-05-21

160

The effect of condensed water on the poorly-soluble volatile organic compounds oxidation: kinetics and mechanism of an aqueous phase isoprene reaction with hydroxyl radical and ozone  

NASA Astrophysics Data System (ADS)

Increasing attention has been paid to the aqueous phase chemistry of organic compounds in the atmosphere. Noticeably, the aqueous phase reaction of the poorly-soluble volatile organic compounds (PSVOCs) has not been much concerned in the atmospheric chemical processes. A number of studies on the adsorption of poorly-soluble gases at air-liquid interface suggested a much higher interface concentration compared to the gas phase concentration. Considering the large global abundance of the poorly-soluble but highly reactive VOCs and the large collective surface of liquid droplets in the atmosphere, it may be important to study the chemical processes of VOCs on the surface of droplets. However, currently little information is available regarding the kinetics and mechanism of the aqueous phase chemical processes of PSVOCs. Here, we focused on the aqueous hydroxyl radical/ozone initiated oxidation of isoprene. For example, we determined the rate constant for the aqueous reaction of isoprene with hydroxyl radical as 1.2 {±}1010 M-1s-1 at 283 K, and observed that the ratio of the yields of MVK to MACR in the aqueous phase isoprene oxidation was approximately double that observed for the corresponding gas phase reaction. On the basis of a box model simulation, we hypothesized that this might be explained by a water-induced enhancement in the self-reaction of a hydroxy isoprene peroxyl radical (HOCH2C(CH3)(O2)CH=CH2) produced in the aqueous reaction. For the aqueous phase ozone oxidation, interestingly, two unknown peroxides were not observed under aqueous conditions, whereas they were detected in the gas phase reaction under dry and humid conditions; the combined yield of MAC and MVK, as well as the total yield of peroxides observed in the aqueous isoprene ozonolysis is much higher than that in the corresponding gas phase reaction under dry and humid conditions. We suggest that these high yields of carbonyls and peroxides are related to the condensed water's greater capability of stabilizing the energy rich Criegee radicals compared with the water vapor. Finally, we evaluated the relative importance of aqueous surface hydroxyl radical/ozone oxidation of isoprene. Our study suggests that air-liquid interface reaction may be an important pathway for atmospheric chemical evolution of isoprene, and the condensed water would considerably affect the kinetics and mechanisms of the reactions. However, further studies are needed for better understanding the relative importance of aqueous chemical processes of isoprene, as well as other PSVOCs, in particular, with an special emphasis on the key parameters, such as the oxidant concentration on the droplet surface, the residence time of PSVOCs on the surface of droplets, and the interface reaction rate constant of the PSVOCs.

Huang, D.; zhang, X.; Wang, H.; Chen, Z.; Zhao, Y.; Shen, X.

2011-12-01

161

Strain-promoted retro-Dieckmann-type condensation on [2.2.2]- and [2.2.1]bicyclic systems: a fragmentation reaction for the preparation of functionalized heterocycles and carbocycles.  

PubMed

The fragmentation reaction of differently functionalized [2.2.2]- and [2.2.1]bicyclic systems that leads to substituted five membered heterocycles and five/six membered carbocycles is broadly studied. This reaction is carried out through a retro-Dieckmann-type condensation on strained [2.2.1]bicyclic ?-ketosulfones and their counterparts ?-ketoesters under very mild catalytic acid or basic conditions and short reaction times. The same reaction is also achieved on [2.2.2]bicyclic ?-ketosulfones requiring harsher reaction conditions. PMID:24057443

Moreno-Clavijo, Elena; Moreno-Vargas, Antonio J; Carmona, Ana T; Robina, Inmaculada

2013-09-25

162

Kinetics and transport effects in the dehydration of crystalline potassium carbonate hydrate  

Microsoft Academic Search

The reaction kinetics and physical transport processes governing the thermal dehydration of solid KâCOâ.3\\/2HâO particles were investigated. Isothermal reaction rate data were gathered using a thermogravimetric balance in which narrowly-sized KâCOâ.3\\/2HâO crystals were dehydrated under a water vapor atmosphere at different pressures and temperatures. The magnitudes of the heat and mass transfer resistances external to and within the solid product

M. A. Stanish; D. D. Perlmutter

1983-01-01

163

An investigation of the role of water on retrograde/condensation reactions and enhanced liquefaction yields. Quarterly progress report, April 1, 1992--June 30, 1992  

SciTech Connect

The overall objectives of this work are to conduct research that will provide the basis for an improved liquefaction process, and to facilitate our understanding of those processes that occur when coals are initially dissolved. Changes in coal structure that occur during coal drying and steam pretreatments will be measured in order to determine what effect water has on retrograde/condensation reactions, and to determine the mechanism by which water enhances coal reactivity toward liquefaction. Different methods for coal drying will be investigated to determine if drying can be accomplished without destroying coal reactivity toward liquefaction, thereby making coal drying a relatively economical and efficient method for coal pretreatment. Coal drying methods will include conventional thermal drying, microwave drying, and chemical drying at low temperature. State-of-the-art solid-state nuclear magnetic resonance (NMR) techniques using combined rotation and multiple pulse spectroscopy (CRAMPS) and cross polarization with magic-angle spinning (CP/MAS) will be employed: (1) to measures changes in coal structure brought about by the different methods of drying and by low temperature oxidation, and (2) to obtain direct measurements of changes in the aromatic hydrogen-to-carbon ratio of the solid/semi-solid material formed or remaining during pretreatment and the initial stages of liquefaction. The aromatic hydrogen-to-carbon ratios are difficult, if not impossible, to measure without the use of solid-state NMR, and as a result this ratio will be used to monitor the retrograde/condensation reactions that take place during coal liquefaction in the presence and absence of steam and various inert gases.

Miknis, F.P.

1992-07-01

164

Dehydrated Soups for USAF Aircraft.  

National Technical Information Service (NTIS)

Laboratory tests were conducted on dehydrated soups for the development of soups for use aboard aircraft operating above 15,240 meters (50,000 feet). These tests involved storage studies on seven different commercially available soups after repacking in f...

H. Gorfien A. R. Rahman E. M. Powers D. E. Westcott

1974-01-01

165

Home Dehydrators For Food Preservation  

Microsoft Academic Search

A method for drying and storing foods for home use is described. A study of convection and forced-air dehydrators disclosed that the forced-air type has the ability to dry faster and is the more efficient dryer at little extra cost. Safe food storage is assured with the use of humidity indicating cards. These cards, which contain a variety of absorbed

J. F. Sullivan; H. Weber

1982-01-01

166

Treatment of diarrheal dehydration1  

Microsoft Academic Search

A regimen for the treatment of diarrheal dehydration is presented. It was devised for use in conditions found in developing countries. Application to large number of patients has been successful. One of its characteristics is the infusion at the start of treatment of a larger amount of fluid than generally recommended. The advantages of magnesium supplemen- tation and phosphate supplementation

G. Sperotto; F. R. Carrazza; E. Marcondes

167

99HRT Dehydration and Asthma.  

National Technical Information Service (NTIS)

At least part of the reason for airway narrowing with exercise is due to the exercise-related loss of fluid from the airways. We performed a series of studies to determine if whole body dehydration would affect this response in people known to have asthma...

F. Cerny P. Maxwell

2003-01-01

168

Deformation and Metamorphism Interactions Illustrated by Serpentinite Dehydration  

NASA Astrophysics Data System (ADS)

Whilst some previous experimental studies have examined the mechanical response of a rock after a metamorphic transformation, little attention has been given to how a rock behaves during the course of a reaction. Dehydration reactions are likely to have a major influence on the deformation of rocks and serpentinite dehydration is well suited to such investigation because the reaction occurs rapidly (a few hours to days depending on the amount of overstep) under moderate temperatures (500 - 600oC). The effect of weakening and embrittlement under undrained conditions is well known, although the competition between fluid pressure elevation and stress relaxation is not. Previous work has shown that, under drained conditions, so that build-up of pore pressure is prevented, the formation of ultrafine grained reaction products can promote extreme weakening and ductility. This effect has been found in other metamorphic reactions and inferred from studies of naturally deformed rocks. Serpentinite dehydration under drained conditions of zero effective pressure also produces a net reduction in solid phase volume, so that substantial new porosity is created. We have studied experimentally the enhancement of deformability in serpentinite that results from the formation of this new fluid-filled porosity, which renders the mechanical properties comparable to those of a porous soil. When differential stress is applied, shear-enhanced compaction causes transient weakening and overall ductility, but with strain hardening as the reaction runs to completion. The majority of the porosity is eliminated and the serpentinite is progressively replaced by olivine plus talc. Thus deformability enhancement during a metamorphic transformation cannot be described by a steady state flow law. In isothermal experiments each rock type is expected to be characterized by a particular range of effects that depend on the evolution of effective pressure. In the case of endothermic reactions such as dehydrations, the overall deformation rate in nature is controlled largely by the heat flux.

Brodie, K.; Llana-Funez, S.; Rutter, E.; Arkwright, C.

2006-12-01

169

DABCO-triggered mild cascade reaction of electron-deficient cyclopentadienone: facile and efficient synthesis of condensed carbocycles  

Microsoft Academic Search

2,5-Bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1) reacts with 4-phenylbut-3-yn-2-one (2b) in the presence of DABCO to give the bicyclic carbocycles (6b) and the tetracyclic carbocycle (7b) under extremely mild reaction conditions.

Koki Yamguchi; Masashi Eto; Kenta Higashi; Yasuyuki Yoshitake; Kazunobu Harano

2011-01-01

170

Kinetics of Osmotic Dehydration under Vacuum  

Microsoft Academic Search

Osmotic dehydration under vacuum was studied. The effect of vacuum application was explained on the basis of the diffusional osmotic transport parameter, the mass transfer coefficient and interfacial area. A mathematical model is proposed to explain the mechanism of water transport during osmotic dehydration based on a more fundamental parameter, the osmotic pressure. Osmotic pressure ratios were calculated for dehydration

N. K. Rastogi; K. S. M. S. Raghavarao

1996-01-01

171

Kinetics of dehydrogenation and dehydration of alcohols and dehydrogenation of hydrocarbons on WS 2 and MoS 2 catalysts  

Microsoft Academic Search

1.It was shown that on the sulfide catalysts WS2 and MoS2 dehydrogenation and dehydration of alcohols and dehydrogenation of hydrocarbons take place, accompanied by partial cracking. The activation energies of these reactions were determined.2.In respect to dehydrogenation of isopropyl alcohol MoS2 was much more active than WS2; in addition only dehydration took place on WS2, whereas dehydrogenation and dehydration occurred

A. A. Tolstopyatova; A. A. Balandin; V. Kh. Matyushenko; Yu. I. Petrov

1961-01-01

172

Distortions in the photocycle of bacteriorhodopsin at moderate dehydration  

SciTech Connect

The photoreaction of bacteriorhodopsin was studied in moderately dehydrated films (relative humidities between 100 and 65%). Time-resolved difference spectra from a gated optical multichannel analyzer, between 100 ns and 100 ms after photoexcitation, were decomposed into sums of difference spectra of the intermediates K, L, M, N, and O, and the kinetics obtained were fitted to various alternative schemes. The data confirm the model of a single reaction sequence with reversible reactions we proposed recently for purple membrane suspensions but including reversibility also for the reaction K in equilibrium with L in addition to L in equilibrium with M, M in equilibrium with N, and N in equilibrium with O. With increasing dehydration the kinetics were increasingly dominated by the reverse reactions. As before, fitting the data required the existence of two M species in series: L in equilibrium with M1 in equilibrium with M2 in equilibrium with N. The M1 in equilibrium with M2 reaction was greatly slowed at lower humidities. This step might be the switch for the unidirectional transfer of protons. With increasing dehydration recovery of BR occurred less and less via the N intermediate and increasingly via direct shunts from the two M species. As indicated earlier by electrical measurements with similarly dried bacteriorhodopsin films. The latter are pathways not necessarily associated with net proton translocation.

Varo, G.; Lanyi, J.K. (Univ. of California, Irvine (USA))

1991-02-01

173

Acid-catalyzed condensed-phase reactions of limonene and terpineol and their impacts on gas-to-particle partitioning in the formation of organic aerosols.  

PubMed

We investigated the condensed-phase reactions of biogenic VOCs with C double bond C bonds (limonene, C(10)H(16), and terpineol, C(10)H(18)O) catalyzed by sulfuric acid by both bulk solution (BS) experiments and gas-particle (GP) experiments using a flow cell reactor. Product analysis by gas chromatography-mass spectrometry (GC-MS) showed that cationic polymerization led to dimeric and trimeric product formation under conditions of relative humidity (RH) <20% (in the GP experiments) and a sulfuric acid concentration of 57.8 wt % (in the BS experiments), while hydration occurred under conditions of RH > 20% (in the GP experiments) and sulfuric acid concentrations of 46.3 wt % or lower (in the BS experiments). Apparent partitioning coefficients (K(p,rxn)) were estimated from the GP experiments by including the reaction products. Only under extremely low RH conditions (RH < 5%) did the values of K(p,rxn) ( approximately 5 x 10(-6) m(3)/microg for limonene and approximately 2 x 10(-5) m(3)/microg for terpineol) substantially exceed the physical partitioning coefficients (K(p) = 6.5 x 10(-8) m(3)/microg for limonene and =2.3 x 10(-6) m(3)/microg for terpineol) derived from the absorptive partitioning theory. At RH higher than 5%, the apparent partitioning coefficients (K(p,rxn)) of both limonene and terpineol were in the same order of magnitude as the K(p) values derived from the absorptive partitioning theory. Compared with other conditions including VOC concentration and degree of neutralization (by ammonium) of acidic particles, RH is a critical parameter that influences both the reaction mechanisms and the uptake ability (K(p,rxn) values) of these processes. The finding suggests that RH needs to be considered when taking the effects of acid-catalyzed reactions into account in estimating organic aerosol formation from C double bond C containing VOCs. PMID:20550185

Li, Yong Jie; Cheong, Gema Y L; Lau, Arthur P S; Chan, Chak K

2010-07-15

174

Dissolution processes, hydrolysis and condensation reactions during geopolymer synthesis: Part I—Low Si\\/Al ratio systems  

Microsoft Academic Search

Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have\\u000a been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial\\u000a charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra\\u000a disclose the existence of monomeric [Al(OH)4]? species after two hours of dissolution, consistent with

L. Weng; K. Sagoe-Crentsil

2007-01-01

175

Cyclopentyl methyl ether: a green co-solvent for the selective dehydration of lignocellulosic pentoses to furfural.  

PubMed

The effects of cyclopentyl methyl ether (CPME) addition during the aqueous xylose dehydration reaction to furfural are reported here. These investigations were conducted by using pure xylose and Cynara cardunculus (cardoon) lignocellulose as sugar source and H(2)SO(4) as catalyst. The research was also applied to aqueous solutions containing NaCl, since it has been previously demonstrated that NaCl incorporation to these reaction mixtures remarkably increases the furfural formation rate. It has been found that CPME incorporation inhibits the formation of undesired products (resins, condensation products and humins). Thus, cardoon lignocellulosic pentoses were selectively transformed into furfural (near 100%) at the following reaction conditions: 1 wt.% H(2)SO(4), 4 wt.% biomass referred to aqueous solution, 30 min reaction, 443 K, CPME/aqueous phase mass ratio equals to 2.33, and NaCl/aqueous solution mass ratio of 0.4. In contrast, no effect was observed for cellulosic glucose transformation into hydroxymethylfurfural and levulinic acid at identical reaction conditions. PMID:23128237

Campos Molina, M J; Mariscal, R; Ojeda, M; López Granados, M

2012-09-24

176

Use of hypodermoclysis to manage dehydration.  

PubMed

Older people, particularly those who are frail, are vulnerable to dehydration. Management of dehydration in older people can be more complex than in younger adults because of the physical effects of ageing. As the population ages, nurses will increasingly care for older patients in every setting. This article provides an overview of the physiological changes that affect the ability of older people to maintain a normal fluid balance. Risk factors for dehydration are reviewed and strategies for the prevention, detection and management of dehydration are discussed. The article focuses on subcutaneous fluid replacement for the management of dehydration in older adults. PMID:21736101

Scales, Katie

2011-06-01

177

CONDENSATION CAN  

DOEpatents

An apparatus is designed for condensing a vapor to a solid at relatively low back pressures. The apparatus comprises a closed condensing chamber, a vapor inlet tube extending to the central region of the chamber, a co-axial tubular shield surrounding the inlet tube, means for heating the inlet tube at a point outside the condensing chamber, and means for refrigeratirg the said chamber. (AEC)

Booth, E.T. Jr.; Pontius, R.B.; Jacobsohn, B.A.; Slade, C.B.

1962-03-01

178

Iron sulfide catalyzed redox/condensation cascade reaction between 2-amino/hydroxy nitrobenzenes and activated methyl groups: a straightforward atom economical approach to 2-hetaryl-benzimidazoles and -benzoxazoles.  

PubMed

Iron sulfide generated in situ from elemental sulfur and iron was found to be highly efficient in catalyzing a redox/condensation cascade reaction between 2-amino/hydroxy nitrobenzenes and activated methyl groups. This method represents a straightforward and highly atom economical approach to 2-hetaryl-benzimidazoles and -benzoxazoles. PMID:23249371

Nguyen, Thanh Binh; Ermolenko, Ludmila; Al-Mourabit, Ali

2012-12-26

179

One-pot three component condensation reaction in water: an efficient and improved procedure for the synthesis of furo[2,3- d]pyrimidine-2,4(1 H,3 H)-diones  

Microsoft Academic Search

The environment-friendly three component condensation reactions of N,N?-dimethylbarbituric acid, 4-nitrobenzaldehyde and alkyl or aryl isocyanides to afford the corresponding furo[2,3-d]pyrimidine-2,4(1H,3H)-diones, in water, in high yields after several minutes are reported.

Ahmad Shaabani; Mohammad Bagher Teimouri; Hamid Reza Bijanzadeh

2002-01-01

180

Facile and efficient synthesis of acridinediones from primary amino alcohols via three-component condensation reactions assisted by microwave irradiation  

Microsoft Academic Search

Microwave irradiation of three component reaction of dimedone, appropriate aromatic aldehydes and amino alcohols in a stoichiometrical ratio 2:1:1 for few minutes afforded the formation of a stable fused three membered ring of the corresponding 3,6,6-tetramethyl-2,3,4,5,6,7,8,9,10-decahydroacridine-1,8-dione derivatives in an excellent yield (80–91%). The structure of all products has been characterized by X-ray crystal structural analyses, 13C NMR, 1H NMR, IR

Antar A. Abdelhamid; S. K. Mohamed; A. M. Maharramov; A. N. Khalilov; M. A. Allahverdiev

181

The thiolase reaction mechanism: the importance of Asn316 and His348 for stabilizing the enolate intermediate of the Claisen condensation.  

PubMed

The biosynthetic thiolase catalyzes a Claisen condensation reaction between acetyl-CoA and the enzyme acetylated at Cys89. Two oxyanion holes facilitate this catalysis: oxyanion hole I stabilizes the enolate intermediate generated from acetyl-CoA, whereas oxyanion hole II stabilizes the tetrahedral intermediate of the acetylated enzyme. The latter intermediate is formed when the alpha-carbanion of acetyl-CoA enolate reacts with the carbonyl carbon of acetyl-Cys89, after which C-C bond formation is completed. Oxyanion hole II is made of two main chain peptide NH groups, whereas oxyanion hole I is formed by a water molecule (Wat82) and NE2(His348). Wat82 is anchored in the active site by an optimal set of hydrogen bonding interactions, including a hydrogen bond to ND2(Asn316). Here, the importance of Asn316 and His348 for catalysis has been studied; in particular, the properties of the N316D, N316A, N316H, H348A, and H348N variants have been determined. For the N316D variant, no activity could be detected. For each of the remaining variants, the k(cat)/K(m) value for the Claisen condensation catalysis is reduced by a factor of several hundred, whereas the thiolytic degradation catalysis is much less affected. The crystal structures of the variants show that the structural changes in the active site are minimal. Our studies confirm that oxyanion hole I is critically important for the condensation catalysis. Removing either one of the hydrogen bond donors causes the loss of at least 3.4 kcal/mol of transition state stabilization. It appears that in the thiolytic degradation direction, oxyanion hole I is not involved in stabilizing the transition state of its rate limiting step. However, His348 has a dual role in the catalytic cycle, contributing to oxyanion hole I and activating Cys89. The analysis of the hydrogen bonding interactions in the very polar catalytic cavity shows the importance of two conserved water molecules, Wat82 and Wat49, for the formation of oxyanion hole I and for influencing the reactivity of the catalytic base, Cys378, respectively. Cys89, Asn316, and His348 form the CNH-catalytic triad of the thiolase superfamily. Our findings are also discussed in the context of the importance of this triad for the catalytic mechanism of other enzymes of the thiolase superfamily. PMID:19842716

Meriläinen, Gitte; Poikela, Visa; Kursula, Petri; Wierenga, Rik K

2009-11-24

182

Can overshooting convection dehydrate the tropical tropopause layer?  

NASA Astrophysics Data System (ADS)

A numerical model is used to investigate the potential for irreversible dehydration near the tropical tropopause caused by overshooting deep convection. We show that convective updrafts overshooting the cold point tropopause can generate extremely cold, dry air within the updrafts. However, the updrafts contain sufficient mass in small (?20 ?m radius) ice crystals that do not sediment out of the short-lived overshoots, such that when the overshoots collapse and warm back to the ambient temperature, these small crystals sublimate and rehydrate the air, resulting in no irreversible dehydration. Despite maximizing crystal size (and fall speed) by assuming low aerosol concentrations and using large ice-ice collection efficiencies, we find no evidence to support the hypothesis that overshooting convection can dehydrate the tropical tropopause layer (TTL) when it is initially ice subsaturated. Only when the TTL is initially supersaturated with respect to ice do we find that deep convection can draw down the humidity, as vapor in excess of saturation condenses on the ice crystals. The overall impact of deep convection on the TTL water vapor budget depends on the climatology of TTL relative humidity in convective regions.

Jensen, E. J.; Ackerman, A. S.; Smith, J. A.

2007-06-01

183

OSMOTIC DEHYDRATION KINETICS OF BLUEBERRIES  

Microsoft Academic Search

The kinetics of moisture loss and solids gain during osmotic dehydration of blueberries under different conditions of temperature (37°C - 60°C), concentration of the sucrose solution (47°Brix - 70°Brix) and contact time between fruit and sucrose solution (0.5 h - 5.5 h) were studied, and modeled based on Fick's law of unsteady state diffusion. The study showed that all factors

F. Nsonzi; H. S. Ramaswamy

1998-01-01

184

Abiotic Condensation Synthesis of Glyceride Lipids and Wax Esters Under Simulated Hydrothermal Conditions  

NASA Astrophysics Data System (ADS)

Precursor compounds for abiotic proto cellular membranes are necessary for the origin of life. Amphipathic compounds such as fatty acids and acyl glycerols are important candidates for micelle/bilayer/vesicle formation. Two sets of experiments were conducted to study dehydration reactions of model lipid precursors in aqueous media to form acyl polyols and wax esters, and to evaluate the stability and reactions of the products at elevated temperatures. In the first set, mixtures of n-nonadecanoic acid and ethylene glycol in water, with and without oxalic acid, were heated at discrete temperatures from 150 ?C to 300 ?C for 72 h. The products were typically alkyl alkanoates, ethylene glycolyl alkanoates, ethylene glycolyl bis-alkanoates and alkanols. The condensation products had maximum yields between 150 ?C and 250 ?C, and were detectable and thus stable under hydrothermal conditions to temperatures < 300 ?C. In the second set of experiments, mixtures of n-heptanoic acid and glycerol were heated using the same experimental conditions, with and without oxalic acid, between 100 ?C and 250 ?C. The main condensation products were two isomers each of monoacylglycerols and diacylglycerols at all temperatures, as well as minor amounts of the fatty acid anhydride and methyl ester. The yield of glyceryl monoheptanoates generally increased with increasing temperature and glyceryl diheptanoates decreased noticeably with increasing temperature. The results indicate that condensation reactions and abiotic synthesis of organic lipid compounds under hydrothermal conditions occur easily, provided precursor concentrations are sufficiently high.

Rushdi, Ahmed I.; Simoneit, Bernd R. T.

2006-04-01

185

Temperature-programmed reaction of C sub 4 oxygenates on unpromoted and K-promoted ZnCr oxide in relation to the mechanism of the higher alcohol synthesis  

SciTech Connect

The reaction mechanisms operating in the chain growth to C{sub 3+}primary alcohols and in the formation of ketones, secondary alcohols, methyl esters, ethers, and hydrocarbons during higher alcohol synthesis (HAS) over high-temperature modified methanol catalysts have been investigated by the temperature-programmed surface reaction (TPSR) technique. Experiments with linear and branched C{sub 4} alcohols, aldehydes, and acids over an unpromoted ZnCr oxide sample have indicated a series of major catalyst functions, namely aldol-like condensation (also with oxygen retention reversal), decarboxylation and decarboxylative condensations, hydrogenation-dehydrogenation, dehydration and hydrolysis, along with isomerization and cracking. TPSR experiments with linear C{sub 4} molecules over K-promoted ZnCr oxide have demonstrated the effects of alkali addition on the catalyst functions. The results are supportive of a mechanism of chain growth to C{sub 3+} primary alcohols based on a sequence of aldolic condensations of aldehydes, which do not operate over 2-methyl species. Formation of ketones under TPSR conditions is explained by decarboxylative condensation reactions of aldehydic and carboxylate species, as well as by aldol-like condensation reactions with oxygen retention reversal. Secondary alcohols detected in the products of the synthesis are formed by hydrogenation of ketones. Methyl esters and ethers are produced in the synthesis by alcoholysis of carboxylate and alkoxide species, respectively. Decarboxylation of carboxylate species, along with dehydration, may also play a role in the formation hydrocarbons during HAS.

Lietti, L.; Forzatti, P.; Tronconi, E.; Pasquon, I. (Dipartimento di Chimica Industriale ed Ingegneria Chimica G. Natta del Politecnico, Milano (Italy))

1990-12-01

186

Dehydration of fructose to 5-hydroxymethylfurfural over H-mordenites  

Microsoft Academic Search

Dehydration of fructose to 5-hydroxymethylfurfural was performed in a batch mode in the presence of a series of dealuminated H-form mordenites as catalysts, at 165°C, and in a solvent mixture consisting of water and methyl isobutyl ketone (1:5 by volume).Under the operating conditions used, the reaction was not controlled by external or internal diffusional limitations. Fructose conversion and selectivity to

Claude Moreau; Robert Durand; Sylvie Razigade; Jean Duhamet; Pierre Faugeras; Patrick Rivalier; Pierre Ros; Gérard Avignon

1996-01-01

187

Orifluoroacetylation and dehydration of 20-hydroxyecdysone acetonides. Synthesis of stachisterone B  

Microsoft Academic Search

Orifluoroacetylation of the 25(OH)-group with subsequent dehydration of the 14(OH)-group takes place in the reaction of 20-hydroxyecdysone 20,22-acetonide and 2,3:20,22-diacetonide with trifluoroacetic anhydride in the presence of pyridine. Dehydration of the 14(OH)-group gives rise to stachisterone B derivatives, which are hydrolyzed to give the phytoecdysteroid stachisterone B.

V. N. Odinokov; I. V. Galyautdinov; D. V. Nedopekin; L. M. Khalilov

2003-01-01

188

Dehydration of fermentative 2,3-butanediol into methyl ethyl ketone  

Microsoft Academic Search

A solid acid catalyst consisted of sulfonic groups covalently bound to an inorganic matrice was developed to dehydrate 2,3-butanediol into methyl ethyl ketone. Rate constant and apparent activation energy of the dehydration reaction were determined. The decay course of the catalyst was a two-stage curve. The catalyst was deactivated more rapidly in the first stage than in the second stage.

Ai V. Tran; Robert P. Chambers

1987-01-01

189

An Efficient Method for Site-specific 18F-Labeling of Biomolecules Using the Rapid Condensation Reaction between 2-Cyanobenzothiazole and Cysteine  

PubMed Central

An efficient method based on a rapid condensation reaction between 2–cyanobenzothiazole (CBT) and cysteine has been developed for 18F–labeling of N–terminal cysteine–bearing peptides and proteins. An 18F–labeled dimeric cRGD ([18F]CBTRGD2) has been synthesized with an excellent radiochemical yield (92% based on radio–HPLC conversion, 80% decay–corrected and isolated yield) and radiochemical purity (>99%) under mild conditions using 18F–CBT, and shown good in vivo tumor targeting efficiency for PET imaging. The labeling strategy was also applied to the site–specific 18F–labeling of a protein, Renilla lucifierase (RLuc8) with a cysteine residue at its N–terminus. The protein labeling was achieved with 12% of decay–corrected radiochemical yield and more than 99% radiochemical purity. This strategy should provide a general approach for an efficient and site–specific 18F–labeling of various peptides and proteins for in vivo molecular imaging applications.

Jeon, Jongho; Shen, Bin; Xiong, Liqin; Miao, Zheng; Lee, Kyung Hyun; Rao, Jianghong; Chin, Frederick T.

2012-01-01

190

Polynuclear copper(ii) pyrazolate complexes: temperature-dependent protonolysis reactions, crystal structures and high catalytic activity toward the condensation of nitriles with 2-aminoalcohol.  

PubMed

Reaction of Cu(OAc)2·H2O and 1H-pyrazole-3,5-dicarboxylic acid dimethyl ester (Hdcmpz) in MeOH at room temperature afforded one tetranuclear Cu(ii)/pyrazolate complex [{Cu2(?-OAc)2}2(?-dcmpz)2(?-OAc)2] () in 89% yield. The similar reaction in refluxing MeOH produced a hexanuclear metallamacrocyclic Cu(ii)/pyrazolate complex [{Cu(?-dcmpz)}2(?-OMe)2]3 () in 85% yield. Treatment of the same components under solvothermal conditions resulted in the formation of another tetranuclear Cu(ii)/pyrazolate/carboxylate complex [{Cu(MeOH)}4(?-mcccpz)4] (, Hmcccpz = 5(3)-(methoxycarbonyl)-1H-pyrazole-3(5)-carboxylic acid) in 30% yield. The mcccpz(2-) ion in was in situ generated via the hydrolysis of one of two esters on dcmpz ligand. Complexes were characterized by elemental analysis, IR and single-crystal X-ray diffraction. An X-ray analysis revealed that contains two {Cu(?-OAc)}2 fragments that are interconnected by two ?-?(2),?(2)-dcmpz(-) ligands and two ?-?(1),?(1)-OAc(-) ions, forming a unique tetrameric structure. Complex is composed of three {Cu(?-dcmpz)}2 fragments linked by three pairs of ?-OMe(-) anions, forming a metallamacrocyclic crown structure. consists of four {Cu(MeOH)} fragments linked by two pairs of ?-?(1),?(2)-mcccpz(2-) ligands, forming a tetrameric [2 × 2] grid-like structure. Complexes displayed high catalytic activity toward the condensation of nitriles with 2-aminoalcohol under solvent-free conditions to produce various 2-oxazolines. PMID:24085112

Wang, Ling; Guo, Bin; Li, Hong-Xi; Li, Qi; Li, Hai-Yan; Lang, Jian-Ping

2013-10-22

191

Dehydration  

MedlinePLUS

... less and their bodies turn over water and electrolytes more quickly. The elderly and people with illnesses ... rate Shock Tests include: Blood chemistries (to check electrolytes , especially sodium, potassium, and bicarbonate levels) Blood urea ...

192

Dehydration  

MedlinePLUS

... replace lost fluids. Preteens and teens who participate in sports may be especially susceptible, both because of their ... Montain SJ. Hydration recommendations for sport 2008. Current Sports Medicine Reports. 2008;7:187. Manz F. Hydration in children. Journal of the American College of Nutrition. ...

193

Dehydration of plutonium trichloride hydrate  

DOEpatents

A process of preparing anhydrous actinide metal trichlorides of plutonium or neptunium by reacting an aqueous solution of an actinide metal trichloride selected from the group consisting of plutonium trichloride or neptunium trichloride with a reducing agent capable of converting the actinide metal from an oxidation state of +4 to +3 in a resultant solution, evaporating essentially all the solvent from the resultant solution to yield an actinide trichloride hydrate material, dehydrating the actinide trichloride hydrate material by heating the material in admixture with excess thionyl chloride, and recovering anhydrous actinide trichloride is provided.

Foropoulos, J. Jr.; Avens, L.R.; Trujillo, E.A.

1991-12-31

194

Understanding clinical dehydration and its treatment.  

PubMed

Dehydration in clinical practice, as opposed to a physiological definition, refers to the loss of body water, with or without salt, at a rate greater than the body can replace it. We argue that the clinical definition for dehydration, ie, loss of total body water, addresses the medical needs of the patient most effectively. There are 2 types of dehydration, namely water loss dehydration (hyperosmolar, due either to increased sodium or glucose) and salt and water loss dehydration (hyponatremia). The diagnosis requires an appraisal of the patient and laboratory testing, clinical assessment, and knowledge of the patient's history. Long-term care facilities are reluctant to have practitioners make a diagnosis, in part because dehydration is a sentinel event thought to reflect poor care. Facilities should have an interdisciplinary educational focus on the prevention of dehydration in view of the poor outcomes associated with its development. We also argue that dehydration is rarely due to neglect from formal or informal caregivers, but rather results from a combination of physiological and disease processes. With the availability of recombinant hyaluronidase, subcutaneous infusion of fluids (hypodermoclysis) provides a better opportunity to treat mild to moderate dehydration in the nursing home and at home. PMID:18519109

Thomas, David R; Cote, Todd R; Lawhorne, Larry; Levenson, Steven A; Rubenstein, Laurence Z; Smith, David A; Stefanacci, Richard G; Tangalos, Eric G; Morley, John E

2008-06-01

195

A dehydration mechanism for the stratosphere  

NASA Astrophysics Data System (ADS)

Although mean circulations are generally credited with dehydration of the earth's stratosphere, convective instability in the tropics converts mean circulations to small residuals of local convective circulations. The effects of large cumulonimbus which penetrate the stratosphere and form huge anvils in the lower stratosphere are discussed with respect to hydration and dehydration of the stratosphere. Radiative heating at anvil base combined with cooling at anvil top drives a dehydration engine considered essential to explain the dry stratosphere. Seasonal and longitudinal variations in dehydration potentials are examined with maximum potential attributed to Micronesian area during winter and early spring.

Danielsen, Edwin F.

196

Fast Kinetics of Dehydration of Hydrous minerals at Subduction Zone Conditions  

NASA Astrophysics Data System (ADS)

In a number of subduction zones, earthquakes are not located on a single upper Benioff plane, but on two dipping planes separated by 20-40 km, defining a double seismic zone (DSZ). The likelihood origin for those earthquakes is hydraulic embrittlement, due fluids released by dehydration reactions. Such a model relies on the coincidence between the loci of the dehydration reaction and hypocenters, on the rheology of the rocks, and on their dehydration rate, which needs to be fast enough to locally raise fluid pressure. From phase equilibrium experiments, antigorite, talc, chlorite and 10Å phase appear as likely candidate minerals, since their dehydration occur also at P-T conditions compatible with those of the DSZ earthquakes. However, little was known about the speed of those reactions. Hence, we have measured the kinetics of dehydration of antigorite, talc, and 10Å phase, under H2O unsaturated and saturated conditions, in order to decide whether their dehydration might trigger earthquakes in subduction zones. Measurements were done by real-time in situ X-ray diffraction at HP and HT in the Paris-Edinburgh press at the European Synchrotron Radiation Facility (ESRF, ID27), with time resolution shorter than 1min. Hydrous minerals were loaded in a cold-sealed double wall capsule of h-BN outside, and Ti inside closed by a thin Au foil at both ends. They were pressurized, and then subsequently heated in the Paris-Edinburgh press. P and T conditions were calculated from the unit-cell parameters of Au and NaCl, according to the cross- calibration method. While approaching the dehydration reactions, X-ray diffraction pattern were acquired and inspected for new diffraction lines to identify the onset of reaction. As dehydration began, P-T conditions were held constant, until transformation was significant, if not completed. The extent of transformation as a function of time was deduced from the relative intensity of the diffraction peaks of the reaction products vs the reactants. The transformation-time data were analysed in terms of the Avrami's theory. Grain size and shape were inferred from SEM observations, on the recovered samples. This allowed to calculate the rate of release of aqueous fluids by the dehydration of the various minerals as a function of depth, to compare dehydration and viscous deformation rates, and to discuss the possibility of fluid embrittlement.

Daniel, I.; Chollet, M.; Koga, K. T.; Petitgirard, S.; Morard, G.

2007-12-01

197

Condensation of dichlorodimethylsilane in silent discharges  

Microsoft Academic Search

1.Dichlorodimethylsilane has been condensed under the action of silent discharges, and the composition of the condensate has been investigated. The main reaction products were chloro sila-hydrocarbons in which silicon and carbon atoms alternate in the main chain, which were formed by the condensation of two or three (CH3)2SiCl2 molecules. The yield of condensation products was 68–70% on the amount of

D. N. Andreev; Akademii Nauk

1960-01-01

198

Dehydration of different ketoses and aldoses to 5-hydroxymethylfurfural.  

PubMed

5-Hydroxymethylfurfural (HMF) is considered an important building block for future bio-based chemicals. Here, we present an experimental study using different ketoses (fructose, sorbose, tagatose) and aldoses (glucose, mannose, galactose) under aqueous acidic conditions (65?g?L(-1) substrate, 100-160?°C, 33-300?mM H2 SO4 ) to gain insights into reaction pathways for hexose dehydration to HMF. Both reaction rates and HMF selectivities were significantly higher for ketoses than for aldoses, which is in line with literature. Screening and kinetic experiments showed that the reactivity of the different ketoses is a function of the hydroxyl group orientation at the C3 and C4 positions. These results, in combination with DFT calculations, point to a dehydration mechanism involving cyclic intermediates. For aldoses, no influence of the hydroxyl group orientation was observed, indicating a different rate-determining step. The combination of the knowledge from the literature and the findings in this work indicates that aldoses require an isomerization to ketose prior to dehydration to obtain high HMF yields. PMID:24039165

van Putten, Robert-Jan; Soetedjo, Jenny N M; Pidko, Evgeny A; van der Waal, Jan C; Hensen, Emiel J M; de Jong, Ed; Heeres, Hero J

2013-08-23

199

Evidence for alpha-cluster condensation in the 0{sub 2}{sup +} state at E{sub x} = 7.654 MeV in {sup 12}C via the (p,p') reaction at 300 MeV  

SciTech Connect

We measured the differential cross sections for the 0{sub 2}{sup +} state at E{sub x} = 7.654 MeV in {sup 12}C via the (p,p') reaction at an incident energy of 300 MeV, and in an angular range from 2.7 deg. to 40 deg. We analyzed the data with the distorted-wave Born-approximation (DWBA) employing transition densities obtained in a macroscopic collective model, a microscopic alpha-cluster model, and a microscopic alpha-cluster condensation model. It is concluded that the present results for the {sup 12}C(p,p') reaction at 300 MeV is quite consistent with the assumption that the 0{sub 2}{sup +} state at E{sub x} = 7.654 MeV has the wave function with the alpha-cluster condensation.

Okamoto, A.; Yamagata, T.; Akimune, H.; Hara, K. Y.; Kinoshita, M.; Utsunomiya, H.; Warashina, N. [Department of Physics, Konan University, Kobe 658-8501 (Japan); Fujiwara, M. [Research Center for Nuclear Physics, Osaka University, Osaka 567-0047 (Japan); Kansai Photon Science Institute, Japan Atomic Energy Agency, Kizu 619-0215 (Japan); Fushimi, K.; Hayami, R.; Nakayama, S. [Department of Physics, University of Tokushima, Tokushima 770-8502 (Japan); Greenfield, M. B. [Department of Physics, International Christian University, Tokyo 113-0033 (Japan); Hara, K.; Hashimoto, H.; Kawase, K.; Nakanishi, N.; Yosoi, M. [Research Center for Nuclear Physics, Osaka University, Osaka 567-0047 (Japan); Hirabayashi, H. [Information Initiative Center, Hokkaido University, Sapporo 060-0811 (Japan); Tanaka, M. [Department of Clinical Technology, Kobe Tokiwa University, Kobe 654-0838 (Japan)

2010-06-01

200

21 CFR 73.40 - Dehydrated beets (beet powder).  

Code of Federal Regulations, 2013 CFR

... (a) Identity. (1) The color additive dehydrated beets is a dark red powder prepared by dehydrating sound, mature, good quality, edible beets. (2) Color additive mixtures made with dehydrated beets may contain as diluents...

2013-04-01

201

MASS TRANSFER IN OSMOTIC DEHYDRATION OF CHAYOTE  

Microsoft Academic Search

In this research, the drying kinetics and equilibr ium conditions during osmotic dehydration of chayote (Sechium edule, Sw.) were studied using 20 and 40 % (w\\/v) sucrose solutions. A thermostatic ba th was built to allow the experimental evaluation of o smotic dehydration kinetics and equilibrium moistur e content determination. The experiments were carried out at three different temperatures (30

Maurício Cordeiro Mancini; Jônatas de Aguiar Ferreira; Stefan Padar; Cláudia Miriam Scheid

202

Dehydration mechanism of optical clearing in tissue  

Microsoft Academic Search

Previous studies identified various mechanisms of light scattering reduction in tissue induced by chemical agents. Our results suggest that dehydration is an important mechanism of optical clearing in collagenous and cellular tissue. Photographic and optical coherence tomography images indicate that air-immersed skin and tendon specimens become similarly transparent to glycerol-immersed specimens. Transmission electron microscopy images reveal that dehydration causes individual

Christopher G. Rylander; Oliver F. Stumpp; Thomas E. Milner; Nathaniel J. Kemp; John M. Mendenhall; Kenneth R. Diller; Ashley J. Welch

2006-01-01

203

Dehydration of cyclohexanol on aluminum-chromium and aluminum-molybdenum catalysts  

Microsoft Academic Search

The purpose of this work was to investigate the activity of chromium and molybdenum oxides deposited on ..gamma..-AlâOâ in the conversion reaction of cyclohexanol. The authors established that chromium oxide deposited on aluminum oxide has a high activity in the dehydration reaction of cyclohexanol. The yield of ketone reached 95 mole %. They showed that Al-Mo catalysts possess emphasized acidic

D. A. Sibarov; T. G. Dokuchaeva; S. U. Lezdin; A. V. Titova; E. V. Karpenko

1988-01-01

204

Dehydration of xylose into furfural over micro-mesoporous sulfonic acid catalysts  

Microsoft Academic Search

Surfactant-templated micro-mesoporous silicas possessing sulfonic acid groups (SAGs) have been prepared, characterized, and tested as catalysts in the dehydration of d-xylose to furfural. All of the materials possessed catalytic activity. In general, selectivity to furfural was lower for a poorly ordered microporous hybrid material, prepared via the co-condensation of (3-mercaptopropyl)trimethoxysilane with bis(trimethoxysilylethyl)benzene, than for mesoporous MCM-41 silica anchored with SAGs

Ana S. Dias; Martyn Pillinger; Anabela A. Valente

2005-01-01

205

Gas phase dehydration of C 6 alcohols promoted by Y zeolite and supported nafion catalysts  

Microsoft Academic Search

The gas phase dehydration of hexan-1-ol, hexan-2-ol and cyclohexanol (473K?T?573K) has been studied over NaY, HY and Ni\\/NaY zeolites and the action of each has been compared with a commercially available 13% w\\/w Nafion\\/SiO2 composite. The Ni exchanged zeolite and Nafion catalysts exhibited a high selectivity in terms of alkene formation. Condensation to generate the respective ether represented a secondary

Colin Park; Mark A Keane

2001-01-01

206

Bronsted Acid Catalyzed Dehydration of Neat Supercritical tert-Butanol in a Capillary Micro-Reactor  

SciTech Connect

Dehydration of supercritical t-butanol to yield 2-methyl-propene was observed to occur rapidly and in high yield at elevated pressures without addition of a catalyst. A capillary micro-reactor was used to carry out the reaction at pressures up to 3.1 kbar. The products were characterized in-situ using FTIR, GC-MS and NMR. The dehydration reaction is proposed to occur by a self-catalyzed Bronsted acid mechanism. An addition driving force for the reaction was the phase separation of the 2-methyl-propene product. Self-catalyzed dehydration of t-butanol is a limiting factor for operations in supercritical t-butanol, but it implies the t-butanol may be employed as a self-neutralizing catalyst under these conditions.

Henry, Matthew C.; Yonker, Clement R.

2006-02-01

207

Serpentine dehydration kinetics up to 1023 K and 4 GPa  

NASA Astrophysics Data System (ADS)

Serpentine minerals are ubiquitous within the oceanic lithosphere and are hypothesized to be a significant source of water, released during thermal dehydration, in subduction zones. Additionally, serpentinized oceanic mantle has been hypothesized to represent a fluid and incompatiable element reservoir that could be a major part of element cycling in subduction zones. Data detailing the kinetics of serpentine breakdown are difficult to obtain and require in situ analyses. Candela et al., 2007 ( Am. Min., In Press) and Frank et al., 2005 ( GSA Abs. Programs) illustrated that the breakdown of serpentine minerals (chrysotile and lizardite, respectively) is complex and results in the variable release of H2O. Further, it has been noted that the reaction products proceed in a step-wise fashion as a function of temperature and these ''steps'' are not the same for all serpentine minerals. In order to understand the release of volatile phases from serpentine minerals in subduction zones, we studied the thermal decomposition of lizardite over a range of temperature, 500- 750°C in 25° increments, at atmospheric pressure. High-pressure experiments ranged from 2-5 GPa and were conducted from 550-700°C. The thermal decomposition of lizardite was monitored by using a hydrothermal diamond anvil cell and synchrotron X-ray radiation. The experiments were conducted at the GSECARS 13-BM-D beam line (Advanced Photon Source at Argonne National Laboratory), using monochromatic X-ray radiation, with a wavelength of 0.3344 Å, and a MAR 345 online imaging system. The diffraction data were used to monitor the dehydration reactants and products as a function of temperature and time. The reaction products of serpentine dehydration are dominantly forsterite (at all temperatures and pressure of dehydration) with minor amounts of talc-like and anthophyllite-like phases. Enstatite could not be identified definitively. Further, forsterite nucleates before more silica-rich phases, at generally lower temperatures and persists throughout the duration of the experiments, and at lower temperatures than have been reported previously in the bulk of the literature. Increasing temperature, at any given pressure, increased the rate of reaction up to complete dehydration of serpentine in less than five minutes at 700-750°C. Our results constrain the products of serpentine thermal decomposition and the potential mechanism of H2O release within serpentine-rich subduction zones.

Frank, M. R.; Scott, H. P.; Maglio, S.; Aarestad, B.; Uesugi, J.; Prakapenka, V.

2007-12-01

208

Dropwise condensation  

PubMed Central

Dropwise condensation of water vapor from a naturally cooling, hot water reservoir onto a hydrophobic polymer film and a silanized glass slide was studied by direct observation and simulations. The observed drop growth kinetics suggest that smallest drops grow principally by the diffusion of water adsorbed on the substrate to the drop perimeter, while drops larger than 50 ?m in diameter grow principally by direct deposition from the vapor onto the drop surface. Drop coalescence plays a critical role in determining the drop size distribution, and stimulates the nucleation of new, small drops on the substrates. Simulations of drop growth incorporating these growth mechanisms provide a good description of the observed drop size distribution. Because of the large role played by coalescence, details of individual drop growth make little difference to the final drop size distribution. The rate of condensation per unit substrate area is especially high for the smallest drops, and may help account for the high heat transfer rates associated with dropwise condensation relative to filmwise condensation in heat exchange applications.

Leach, R. N.; Stevens, F.; Langford, S. C.; Dickinson, J. T.

2008-01-01

209

The chemical signatures of progressive dehydration stages in subducted serpentinites  

NASA Astrophysics Data System (ADS)

Fluids mediate chemical cycling in subduction zones. Nonetheless, the chemistry of serpentinite-dehydration fluids from down-going slabs and their chemical effects on ascent are only very poorly constrained. We report new data on discontinuous dehydration reactions, including the measurement of individual fluid inclusions in prograde minerals from natural occurrences, and one case study tracing the infiltration of serpentinite-derived fluid in mafic eclogite. Together, these studies demonstrate that serpentinite-derived fluids are commonly dilute, but that there may be selected trace element abundances (and ratios ?) that characterize such fluid provenance. Brucite dehydration represents the first relevant liberation of crystal-bound water from serpentinites formed on the ocean floor (ocean floor mantle hydration chemistry is addressed in Kodolanyi et al., this session). Discordant olivine-Ti-clinohumite-antigorite-clinopyroxene-magnetite veins in ca. 2.3 GPa antigorite serpentinites of the Erro Tobbio in the Ligurian Alps, Italy, formed from aqueous, dilute fluids containing Li, Sr, Ba, Rb, Pb as determined on texturally-early fluid inclusions in olivine. This prograde olivine preserves high Ni (1500 - 3000 µg/g) and is identified most readily by elevated Li (1-20 µg/g), B (1-20 µg/g) and Mn contents. Aqueous fluid inclusions in some clinopyroxene (Cpx) of the same veins host variably (sometimes highly) saline fluid inclusions, interpreted to represent the "spent" fluid after formation of hydrous vein minerals (chlorite, antigorite). Vein bulk-rock trace-element concentrations show enrichment in Ti, Ba, Nb, Li, HREE and Cu relative to the wall rocks, accompanied by depletion in Cr. This mostly reflects the mineral transformations (sources / sinks) occurring at this stage of serpentinite dehydration. Antigorite-breakdown is arguably the most prominent water release from down-going slabs. Olivine-orthopyroxene-chlorite rocks at Cerro del Almirez (Spain), recording this dehydration event, contain olivine-hosted polyphase inclusions interpreted to represent fluid inclusions trapped during antigorite breakdown. Preliminary compositional data show enrichments in B, Cs, Pb, Li, Sr, Rb, K, Ba (decreasing order) and depletions in Ca, Ti, La relative to primitive mantle, closely corresponding to the incompatible element pattern of typical island arc lavas. Transfer of such fluids to the melting source of island arc magmas may be critical to developing their distinctive trace element signatures. Omphacite-rich (± garnet, rutile, talc and zircon) veins cutting eclogite (Fe-Ti gabbro protolith, Monviso, W Italian Alps) record serpentinite-derived fluid pathways though the subducted slab at ca. 70 km depth. Although these veins largely formed by local eclogite-derived fluids, they also preserve discrete generations of vein minerals enriched in Mg, Cr, Ni, B, As and Sb, and zircon with elevated Epsilon(Hf) compared to host-rock eclogite zircon. These chemical and isotopic characteristics suggest external fluid input, from serpentinite dehydration. Moreover, distinctive oscillatory or irregular Cr zonations observed in omphacite, garnet and rutile from the veins are interpreted to record episodic fracturing and fluid infiltration over >10 m along transient brittle fractures at high pressures. Our current data suggest that dehydration fluid pervades the rock at the site of liberation, and that episodic fluid escape from the dehydration site may be effectively channelized. This supports growing evidence for highly focused reactive fluid flow through slabs. Robust constraints on the chemical composition and nature of dehydration fluids from serpentinites and how they evolve during ascent may greatly aid in recognizing such features from outcrop to thin-section scales, in turn providing us with more comprehensive sample material to advance our understanding on fluid-mediated cycling in subduction zones. Reference Kodolanyi et al., this session

Pettke, T.; Spandler, C.; Kodolanyi, J.; Scambelluri, M.

2009-04-01

210

A study of the acid-catalyzed hydrolysis of cellulose dissolved in ionic liquids and the factors influencing the dehydration of glucose and the formation of humins.  

PubMed

An investigation was carried out into the hydrolysis of cellulose dissolved in 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]) and 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) catalyzed by mineral acids. Glucose, cellobiose, and 5-hydroxymethylfurfural (5-HMF) were observed as the primary reaction products. The initial rate of glucose formation was determined to be of first order in the concentrations of dissolved glucan and protons and of zero order in the concentration of water. The absence of a dependence on water concentration suggests that cleavage of the ?-1,4-glycosidic linkages near chain ends is irreversible. The apparent activation energy for glucose formation is 96 kJ mol(-1). The absence of oligosaccharides longer than cellobiose suggests that cleavage of interior glycosidic bonds is reversible due to the slow diffusional separation of cleaved chains in the highly viscous glucan/ionic liquid solution. Progressive addition of water during the course of glucan hydrolysis inhibited the rate of glucose dehydration to 5-HMF and the formation of humins. The inhibition of glucose dehydration is attributed to stronger interaction of protons with water than the 2-OH atom of the pyranose ring of glucose, the critical step in the proposed mechanism for the formation of 5-HMF. The reduction in humin formation associated with water addition is ascribed to the lowered concentration of 5-HMF, since the formation of humins is suggested to proceed through the condensation polymerization of 5-HMF with glucose. PMID:21809450

Dee, Sean J; Bell, Alexis T

2011-08-02

211

Linked strategy for the production of fuels via formose reaction.  

PubMed

Formose reaction converts formaldehyde to carbohydrates. We found that formose reaction can be used linking the biomass gasification with the aqueous-phase processing (APP) to produce liquid transportation fuel in three steps. First, formaldehyde from syn-gas was converted to triose. This was followed by aldol condensation and dehydration to 4-hydroxymethylfurfural (4-HMF). Finally, 4-HMF was hydrogenated to produce 2,4-dimethylfuran (2,4-DMF) or C(9)-C(15) branched-chain alkanes as liquid transportation fuels. In the linked strategy, high energy-consuming pretreatment as well as expensive and polluting hydrolysis of biomass were omitted, but the high energy recovery of APP was inherited. In addition, the hexoketoses via formose reaction could be converted to HMFs directly without isomerization. A potential platform molecule 4-HMF was formed simultaneously in APP. PMID:23393625

Deng, Jin; Pan, Tao; Xu, Qing; Chen, Meng-Yuan; Zhang, Ying; Guo, Qing-Xiang; Fu, Yao

2013-02-07

212

Linked strategy for the production of fuels via formose reaction  

PubMed Central

Formose reaction converts formaldehyde to carbohydrates. We found that formose reaction can be used linking the biomass gasification with the aqueous-phase processing (APP) to produce liquid transportation fuel in three steps. First, formaldehyde from syn-gas was converted to triose. This was followed by aldol condensation and dehydration to 4-hydroxymethylfurfural (4-HMF). Finally, 4-HMF was hydrogenated to produce 2,4-dimethylfuran (2,4-DMF) or C9-C15 branched-chain alkanes as liquid transportation fuels. In the linked strategy, high energy-consuming pretreatment as well as expensive and polluting hydrolysis of biomass were omitted, but the high energy recovery of APP was inherited. In addition, the hexoketoses via formose reaction could be converted to HMFs directly without isomerization. A potential platform molecule 4-HMF was formed simultaneously in APP.

Deng, Jin; Pan, Tao; Xu, Qing; Chen, Meng-Yuan; Zhang, Ying; Guo, Qing-Xiang; Fu, Yao

2013-01-01

213

DEHYDRATION OF LOW WATER CONTENT ETHANOL  

EPA Science Inventory

Pervaporation has emerged as an economically viable alternative technology for the dehydration of organic solvents, removal of organic compounds from water and organic/organic separations. Development of a membrane system with suitable flux and selectivity characteristics plays a...

214

Advances in preconcentration and dehydration of foods  

Microsoft Academic Search

This symposium comprised four sessions; fundamentals; non-membrane concentration; membrane concentration; spray drying; and freeze-drying and other novel dehydration techniques. Twenty-seven papers were presented. (LK)

Spicer

1974-01-01

215

Process conditions effect on the quality of banana osmotically dehydrated  

Microsoft Academic Search

Banana is greatly perishable and does not resist freezing, hence dehydration is the preservation technique of choice. This paper deals with the effect of process conditions on both the dehydration kinetics and the final quality of banana osmotically dehydrated. Banana slices (5mm thick, 23mm diameter) were osmotically dehydrated for 4h, following a 32 full factorial design (temperature (30, 40, and

L. Atares; M. J. Sousa Gallagher; F. A. R. Oliveira

2011-01-01

216

Microcrystalline hexagonal tungsten bronze. 2. Dehydration dynamics.  

PubMed

Low-temperature (25-600 degrees C) thermal transformations have been studied for hydrothermally prepared, microcrystalline hexagonal tungsten bronze (HTB) phases A(x)WO(3+x/2).zH(2)O as a function of temperature, where A is an exchangeable cation (in this case Na(+) or Cs(+)) located in hexagonal structural tunnels. Thermal treatment of the as-prepared sodium- and cesium-exchanged phases in air were monitored using a conventional laboratory-based X-ray diffractometer, while thermal transformations in vacuum were studied using synchrotron X-ray and neutron diffraction. Concurrent thermogravimetric, diffuse reflectance infrared (DRIFT), and (23)Na and (133)Cs magic angle spinning (MAS) NMR spectroscopic studies have also been undertaken. For the cesium variant, cell volume contraction occurred from room temperature to about 350 degrees C, the regime in which water was "squeezed" out of tunnel sites. This was followed by a lattice expansion in the 350-600 degrees C temperature range. Over the entire temperature range, a net thermal contraction was observed, and this was the result of an anisotropic change in the cell dimensions which included a shortening of the A-O2 bond length. These changes explain why Cs(+) ions are locked into tunnel positions at temperatures as low as 400 degrees C, subsequently inducing a significant reduction in Cs(+) extractability under low pH (nitric acid) conditions. The changing Cs(+) speciation as detected by (133)Cs MAS NMR showed a condensation from multiple Cs sites, presumably associated with differing modes of Cs(+) hydration in the tunnels, to a single Cs(+) environment upon thermal transformation and water removal. While similar lattice contraction was observed for the as-prepared sodium variant, the smaller radius of Na(+) caused it to be relatively easily removed with acid in comparison to the Cs(+) variant. From (23)Na MAS NMR studies of the parent material, complex Na(+) speciation was observed with dehydrated and various hydrated Na(+) species being identified, and a subsequent dynamic interchange within this speciation was observed upon thermal treatment. PMID:19518109

Luca, Vittorio; Griffith, Christopher S; Hanna, John V

2009-07-01

217

Dehydration of cyclohexanol on aluminum-chromium and aluminum-molybdenum catalysts  

SciTech Connect

The purpose of this work was to investigate the activity of chromium and molybdenum oxides deposited on ..gamma..-Al/sub 2/O/sub 3/ in the conversion reaction of cyclohexanol. The authors established that chromium oxide deposited on aluminum oxide has a high activity in the dehydration reaction of cyclohexanol. The yield of ketone reached 95 mole %. They showed that Al-Mo catalysts possess emphasized acidic properties, and that the main reaction products with these catalysts are cyclohexene and cyclohexane.

Sibarov, D.A.; Dokuchaeva, T.G.; Lezdin, S.U.; Titova, A.V.; Karpenko, E.V.

1988-09-20

218

Solvent-Free, Cross-Aldol Condensation Reaction Using Silica-Supported, Phosphorus-Containing Reagents Leading to ?,??Bis(arylidene)cycloalkanones  

Microsoft Academic Search

This article describes an efficient, simple, and clean method for the synthesis of ?,??-bis(arylidene, furylidene and cinnamylidene)cycloalkanones under solvent-free conditions. The cross-aldol condensation of cycloalkanones with aldehydes in the presence of silica-supported phosphorus pentoxide (P2O5\\/SiO2) or silicaphosphinoxide (silphox, [POCl3-n(SiO2)n]) as heterogeneous reagents produces the title compounds in good to excellent yields.

Alireza Hasaninejad; Abdolkarim Zare; Laleh Balooty; Hadis Mehregan; Mohsen Shekouhy

2010-01-01

219

Enantioselective organocatalytic one-pot amination/aza-Michael/aldol condensation reaction sequence: synthesis of 3-pyrrolines with a quaternary stereocenter.  

PubMed

Primary amine-catalyzed direct conversion of ?,?-disubstituted aldehydes into 3-pyrrolines with a quaternary stereocenter is reported. The one-pot enantioselective sequence is based on a ?-amination, an aza-Michael addition of hydrazine, an aldol condensation dehydratation and proceeds with good yields and excellent levels of enantioselectivity. Synthetically attractive applications including the formation of aziridinopyrrolidine or epoxypyrrolidine derivatives with good yields and selectivities are also described. PMID:22927036

Desmarchelier, Alaric; Coeffard, Vincent; Moreau, Xavier; Greck, Christine

2012-08-27

220

Aseismic Serpentinite Dehydration at High Pressure and Temperature Evidenced by Simultaneous Acoustic Emissions Monitoring and Synchrotron X-Ray Diffraction  

NASA Astrophysics Data System (ADS)

We have successfully developed an experimental setup that allows collecting in situ X-ray powder diffraction and simultaneously recording full waveform acoustic emissions (AE) at high pressure and temperature (PT) in a DIA multi-anvil device. This setup is a powerful tool for investigating rock embrittlement at high PT due to phase transitions and/or mineral reactions since both reaction progress (and kinetics) and AE triggering can be simultaneously monitored. The dehydration of natural serpentinite samples (antigorite-rich) under deviatoric stress has been investigated by this method since antigorite dehydration is believed to trigger intermediate depth earthquakes through dehydration embrittlement. We performed, beforehand, a series of tests on the cold compression of reference materials with contrasted mechanical behaviors (quartz beads and kaolinite powder). Due to grain crushing, cold compression of quartz gave rise to numerous AE events (several hundreds), which were located within the sample. Cold compression and heating of kaolinite, a ductile material, yielded no AEs, demonstrating that the pressure assembly is noiseless. Unexpectedly, antigorite-rich serpentinite samples produced no detectable AEs in the course of their dehydration under the differential stress imposed by alumina waveguides. The only AEs that were recorded occurred during cold compression. Sample microstructures indicate that conjugate faults inherited from the cold compression stage are activated during or after dehydration of the sample. The "aseismic" slip along these faults could be attributed to the presence of talc (or a talc-like phase) or of fine-grained materials (dehydration reaction products) in the fault gouge. Furthermore, AE triggering can also be influenced by hydraulic diffusivity and the differential stress level on the sample, two parameters that are not controlled in conventional multi-anvil experiments. Our results highlight the fact that coupling between dehydration reactions and seismicity might not be as straightforward as previously thought. In fact, fast reaction kinetics or high reaction extent may inhibit the nucleation of mechanical instabilities through rapid stress relaxation of the solid matrix.

Gasc, J.; Schubnel, A. J.; Brunet, F.; Guillon, S.; Mueller, H. J.; Lathe, C.

2011-12-01

221

Structural characterization and dehydration kinetics of Kirka inderite mineral: Application of non-isothermal models  

SciTech Connect

Coats-Redfern, Arrhenius, Ozawa, Kissinger, and Doyle non-isothermal kinetic models were used to calculate the dynamic kinetic parameters for dehydration reaction of Mg-borate mineral, inderite (Kirka - Turkey) based on thermogravimetric analysis, derivative thermogravimetric analysis and differential thermal analysis. Dehydration experiments were carried out at different heating rates of 2, 5, 10, 15, and 20 deg. C/min in a pure nitrogen atmosphere. Structural and morphological properties have been characterized by X-Ray diffraction, Fourier transform-infrared spectroscopy, Scanning electron microscopy-energy dispersive spectroscopy, and Inductively coupled plasma-optical emission spectroscopy techniques.

Figen, Aysel Kantuerk, E-mail: akanturk@yildiz.edu.tr [Yildiz Technical University, Department of Chemical Engineering, Davutpasa Campus., N.127, Esenler, Istanbul (Turkey); Yilmaz, Muege Sari, E-mail: mugesari@yildiz.edu.tr [Yildiz Technical University, Department of Chemical Engineering, Davutpasa Campus., N.127, Esenler, Istanbul (Turkey); Piskin, Sabriye, E-mail: piskin@yildiz.edu.tr [Yildiz Technical University, Department of Chemical Engineering, Davutpasa Campus., N.127, Esenler, Istanbul (Turkey)

2010-06-15

222

Dehydration of 3-hydroxyacyl-CoA in brain very-long-chain fatty acid synthesis  

Microsoft Academic Search

Rat brain microsomes actively dehydrate 3-hydroxyacyl-CoAs. Using chemically synthesized [1-14C] (R,S) 3-hydroxyeicosanoyl-CoA, we investigated the biochemical characteristics of the dehydration and reduction steps of stearoyl-CoA elongation.The reaction products, separated and identified as trans2,3-enoyl-CoAs and, in the presence of NADPH, as saturated acyl-CoAs, were released from the enzyme as thioesters which were partly hydrolysed. A kinetic analysis of the two coupled

Anja Knoll; Jean-Jacques Bessoule; Françoise Sargueil; Claude Cassagne

1999-01-01

223

Study of kinetic laws of dehydration of dimethylvinylcarbinol of phosphoric acid catalyst  

SciTech Connect

The dehydration of dimethylvinylcarbinol (DMVC) to isoprene on phosphoric acid catalyst at 60-90/sup 0/C and in the concentrations range of 40-60 wt. % of the acid was studied by the microreactioning gas-chromatographic method. The overall consumption constants of DMVC with time were determined, as well as consumption constants of DMVC k/sub 1q/, taking into account the absorption of the reagent on the catalysts. It was shown that the dehydration reaction is irreversible, is first order with respect to DMVC, and the equation log k/sub 1q/ + H/sub 0/ = const, where H/sub 0/ is the acidity function holds.

Malinskii, V.S.; Vinnik, M.I.

1987-04-01

224

Understanding Condensation  

NSDL National Science Digital Library

Monica Hartman, Assistant Director for Science in St. Clair County, Michigan, conducted this research while she was the learning specialist in a small suburban district just outside a large Midwestern city. While teaching full time in this district she was also completing her doctoral program in education at the University of Michigan. In this chapter, she tells the story of a "science talk" about condensation among fifth graders. She acted as a source and facilitator of change as she and the fifth-grade teacher worked collaboratively to help students share responsibility for their own learning. She describes their continual assessment of student understanding that occurred as their students struggled to explain observations and as they, the teachers, carefully resisted the temptation to end the struggle by saying "that's right!"

Hartman, Monica

2007-12-01

225

Geothermal demonstration: Zunil food dehydration facility  

SciTech Connect

A food dehydration facility was constructed near the town of Zunil, Guatemala, to demonstrate the use of geothermal energy for industrial applications. The facility, with some modifications to the design, was found to work quite satisfactorily. Tests using five different products were completed during the time geothermal energy was used in the plant. During the time the plant was not able to use geothermal energy, a temporary diesel-fueled boiler provided the energy to test dehydration on seven other crops available in this area. The system demonstrates that geothermal heat can be used successfully for dehydrating food products. Many other industrial applications of geothermal energy could be considered for Zunil since a considerable amount of moderate-temperature heat will become available when the planned geothermal electrical facility is constructed there. 6 refs., 15 figs., 7 tabs.

Maldonado, O. (Consultecnia, Guatemala City (Guatemala)); Altseimer, J.; Thayer, G.R. (Los Alamos National Lab., NM (United States)); Cooper, L. (Energy Associates International, Albuquerque, NM (United States)); Caicedo, A. (Unidad de Desarrollo Geotermico, Guatemala City (Guatemala). Inst. Nacional de Electrificacion)

1991-08-01

226

Vapor-phase reaction of acetophenone with methanol or dimethyl carbonate on magnesium oxide and magnesium phosphates  

SciTech Connect

The vapor-phase reaction of acetophenone with methanol on magnesium oxide, various magnesium phosphates, and combinations of the two types of catalysts was studied. The process was found to involve the Meerwein-Ponndorf-Verley reaction, aldol condensations, dehydrations, and hydrogenations. The presence of basic sites is indispensable for the reaction to develop; however, acid sites also play an active role. The selectivity for each reaction product depends on the particular catalyst used. The total conversion is maximal with the catalysts containing the largest populations of acid and basic sites. Also, catalysts with large numbers of acid sites exhibit an increased selectivity towards the corresponding alkenes. The use of dimethyl carbonate instead of methanol alters the reaction selectivity to an extent dependent on the particular catalyst and operating conditions. However, this also results in markedly decreased total conversion in some instances.

Aramendia, M.A.; Borau, V.; Jimenez, C.; Marinas, J.M.; Romero, F.J. [Univ. of Cordoba (Spain). Dept. of Organic Chemistry

1999-04-01

227

Dehydration mechanism of optical clearing in tissue  

NASA Astrophysics Data System (ADS)

Previous studies identified various mechanisms of light scattering reduction in tissue induced by chemical agents. Our results suggest that dehydration is an important mechanism of optical clearing in collagenous and cellular tissue. Photographic and optical coherence tomography images indicate that air-immersed skin and tendon specimens become similarly transparent to glycerol-immersed specimens. Transmission electron microscopy images reveal that dehydration causes individual scattering particles such as collagen fibrils and organelles to become more densely packed, but does not significantly alter size. A heuristic particle-interaction model predicts that the scattering particle volume fraction increase can contribute substantially to optical clearing in collagenous and cellular tissue.

Rylander, Christopher G.; Stumpp, Oliver F.; Milner, Thomas E.; Kemp, Nathaniel J.; Mendenhall, John M.; Diller, Kenneth R.; Welch, Ashley J.

2006-07-01

228

Effect of enzyme dehydration on alcalase-catalyzed dipeptide synthesis in near-anhydrous organic media.  

PubMed

The effect of enzyme dehydration by molecular sieves on the coupling of phenylalanine amide and the carbamoylmethyl ester of N-protected phenylalanine in near-anhydrous tetrahydrofuran was investigated. This coupling was catalyzed by Alcalase covalently immobilized onto macroporous acrylic beads (Cov); these immobilized enzymes were hydrated prior to use. The dehydration kinetics of Cov by molecular sieve powder were determined by incubating Cov with different amounts of molecular sieve powder for different periods of time (0-80 h). Subsequently, the remaining coupling activity of Cov was measured. Dehydration-induced inactivation of Cov by molecular sieve powder was found to occur in three phases: (1) an initial, rapid, major dehydration-induced inactivation that takes place during the first activity measurement, (2) a phase of first-order inactivation, and (3) a plateau phase in activity. These dehydration kinetics were incorporated into a previously found reaction kinetics model. The resulting model was then used to fit progress curve data of the coupling in the presence of different amounts of molecular sieve powder. Upon establishment of parameter values, the model was used to predict independent data sets and found to work well. PMID:23554404

Vossenberg, Petra; Beeftink, Rik; Stuart, Martien Cohen; Tramper, Hans

2013-05-02

229

One-Pot, Multicomponent Condensation Reaction in Neutral Conditions: Synthesis, Characterization, and Biological Studies of Fused Thiazolo[2,3-b]quinazolinone Derivatives  

Microsoft Academic Search

A new series of 12-(2-chloro-6-quinoline-3-yl)-3,3,8-substituted-2,3,4,12-tetrahydro-benzo[4,5]thiazolo[2,3-b]quinazolin-1-ones 4 was synthesized in one pot by condensing various 2-chloro-3-formylquinolines 1, 2-amino-6-substituted-benzothiazoles 2, and 1,3-cyclohexanedione 3 in ethanol. All the compounds were characterized by IR, H NMR, C NMR spectra and elemental analysis. All the synthesized compounds were screened for their antibacterial activity against Grampositive bacterial species Bacillus cereus and Bacillus substilus, Gram-negative bacterial species

Nirav K. Shah; Manish P. Patel; Ranjan G. Patel

2009-01-01

230

TEMPLATE CONDENSATION REACTIONS 1 VIII. Cr(III), Ni(II) AND Cu(II) COMPLEXES RESULTING IN THE SYSTEM 5,5`-DIETHYLBARBITURIC ACID - ETHYLENEDIAMINE  

Microsoft Academic Search

A series of new complexes of Cr(III), Ni(II) and Cu(II) with with general formula (ML(NO3)2)(NO3)n?mH2O (where L is the Schiff base resulting in (3+2) condensation of 5,5`-diethylbarbituric acid (DEBA) with ethylenediamine (en), (1) M=Cr, n=1, m=2; (2) M=Ni, n=0, m=2; (3) M=Cu, n=0, m=3 have been synthesised and characterised. The free ligand has been isolated by treatment of Cu(II) complex

Elena Cristurean; Dana Marinescu; Rodica Olar; Mihaela Badea; Aurelia Meghea; N. Stanica; Lacramioara Sarbu

231

Kinetics of dehydrogenation and dehydration of isopropyl alcohol and dehydrogenation of tetralin on ytterbium oxide  

Microsoft Academic Search

1.The influence of the heat effect of the reaction is shown from kinetic measurements, and determinations are made of the apparent activation energies of the dehydrogenation and dehydration of isopropyl alcohol and the dehydrogenation of tetralin on Yb2O3 under isothermal conditions.2.Determinations are made of the relative adsorptive coefficients of the products of the above reactions under isothermal conditions, the values

A. A. Tolstopyatova; P'eng Pi-Hsiang; A. A. Balandin

1962-01-01

232

Dehydration kinetics of piroxicam monohydrate and relationship to lattice energy and structure  

Microsoft Academic Search

The dehydration kinetics of piroxicam monohydrate (PM) is analyzed by both model-free and model-fitting approaches. The conventional model-fitting approach assuming a fixed mechanism throughout the reaction is found to be too simplistic. The model-free approach allows for a change of mechanism and activation energy, Ea, during the course of a reaction and is therefore more realistic. The complexity of the

Agam R. Sheth; Deliang Zhou; Francis X. Muller; David J. W. Grant

2004-01-01

233

Rate of Nucleation in Condensed Systems  

Microsoft Academic Search

On the basis of the nucleation theory developed by Volmer, Becker, and co-workers, and the theory of absolute reaction rates, an expression is derived for the absolute rate of nucleation in condensed systems.

D. Turnbull; J. C. Fisher

1949-01-01

234

Nutritional Acceptability of a Dehydrated Diet.  

National Technical Information Service (NTIS)

Precooked, dehydrated and bite size compressed foods were arranged into a nutritionally balanced four-day cycle experimental menu with four meals per day. A control menu composed of frozen, fresh and heat processed foods was prepared to match the experime...

E. W. Speckmann K. J. Smith J. E. Vanderveen G. M. Homer D. W. Dunco

1965-01-01

235

FIVE YEAR NEURODEVELOPMENTAL OUTCOME OF NEONATAL DEHYDRATION  

PubMed Central

Objective To determine the long-term outcome of neonatal dehydration. Study design We identified 182 newborns rehospitalized with dehydration (weight loss ?12% of birth weight and/or serum sodium ?150 mEq/L) and 419 randomly selected controls from a cohort of 106,627 term and near-term infants ?2000 g born from 1995 through 1998 in Northern California Kaiser Permanente hospitals. Outcomes data were obtained from electronic records, interviews, questionnaire responses, and neurodevelopmental evaluations performed in a masked fashion. Results Follow-up data to the age of at least two years were available for 173/182 children with a history of dehydration (95%) and 372/419 controls (89%) and included formal evaluation at a mean (±SD) age of 5.1±0.12 years for 106 children (58%) and 168 children (40%) respectively. None of the cases developed shock, gangrene, or respiratory failure. Neither crude nor adjusted scores on cognitive tests differed significantly between groups. There was no significant difference between groups in the proportion of children with abnormal neurologic examinations or neurologic diagnoses. Frequencies of parental concerns and reported behavior problems also were not significantly different in the two groups. Conclusions Neonatal dehydration in this managed care setting was not associated with adverse neurodevelopmental outcomes in infants born at or near term.

Escobar, Gabriel J.; Liljestrand, Petra; Hudes, Esther S.; Ferriero, Donna M.; Wu, Yvonne W.; Jeremy, Rita J.; Newman, Thomas B.

2007-01-01

236

Dehydration and Burning Produced by the Tornado  

Microsoft Academic Search

The explanation generally offered for the observed dehydration, heating and burning effects associated with tornadoes is based on either of two mechanisms. The first involves a hot wind while the second involves corona discharges sometimes called St. Elmos fire, while the smell of `brimstrone' often appears to be overlooked. An alternate explanation which could deal with both phenomena is obtained

P. A. Silberg

1966-01-01

237

Compressed, Dehydrated and Flaked Meat Bar.  

National Technical Information Service (NTIS)

A method is disclosed for making a dehydrated, compressed food bar consisting essentially of meat or meat and vegetables, wherein the meat is subdivided by flaking and then formed into a solid mass which is cooked to inactivate enzymes. The meat mass is t...

J. M. Tuomy W. J. Fitzmaurice F. E. DiLeo V. A. Loveridge

1981-01-01

238

Bioethanol dehydration: State of the art  

Microsoft Academic Search

This article is a survey of the present-day methods of dehydration of ethanol resulting from fermentation processes. The existing\\u000a separation techniques for water-ethanol mixtures of various compositions are compared, and the conditions under which each\\u000a particular technique is preferable are formulated.

A. K. Frolkova; V. M. Raeva

2010-01-01

239

Dehydration and Survivability in Warm Shelters.  

National Technical Information Service (NTIS)

The physiological basis for dehydration symptoms is discussed in terms of the factors influencing moisture loss from skin and lungs by diffusion, sweat loss, and urinary output. Normal water and salt balance is shown to be achieved by ingestion of a surpl...

W. V. Blockley

1968-01-01

240

Decision Tree and Postpartum Management for Preventing Dehydration in the \\  

Microsoft Academic Search

Dehydration and poor weight gain in breastfed infants are common but potentially preventable problems. Serious consequences are severe hypernatremic dehydration, severe weight loss, and severe hyperbilirubinemia with possible irreversible damage to the baby's brain or other vital organs. The dangers of dehydration have been emphasized by recent media reports of severe cases. These reports have resulted in increased, but often

Jack Newman

1996-01-01

241

Dehydration and rehydration of a tuff vitrophyre  

SciTech Connect

The basal vitrophyre of the Topopah Spring Member of the Paintbrush Tuff at Yucca Mountain, Nevada, is a perlitic glass with 2.8 to 4.6% water. The dehydration of this vitrophyre was studied by thermogravimetric analysis (TGA) and by isothermal heating at 50{degrees}, 100{degrees}, 200{degrees}, and 400{degrees}C for 3.4 years followed by 1.1 years of rehydration at high controlled humidity ({approximately}79% relative humidity). No crystallization of the glass was observed in long-term dehydration or rehydration; the only observed chemical alteration was loss of up to 60% of original fluorine. TGA studies show a characteristic two-stage dehydration of the vitrophyre, with two-thirds to three-fourths weight loss occurring most rapidly at temperatures ranging from 278{degrees} to 346{degrees}C in 10{degrees}C/min heating experiments. The remaining water, about 1% in all of the vitrophyre samples studied regardless of total water content, is lost only on second-stage heating to temperatures above 650{degrees}C. Long-term isothermal heating at {le}400{degrees}C releases only the first-stage water. Loss of essentially all first-stage water occurred in less than 1 hour at 400{degrees}C; proportionately lower losses were obtained at 200{degrees} and 100{degrees}C. Small (0.2%) water loss occurred in the 50{degrees}C experiment. A time-temperature-dehydration diagram generated from the isothermal heating data shows a clustering of dehydration contours that are the equilibrium equivalent of the rapid first-stage water loss in dynamic TGA experiments. These dry-heating experiments provide an end-member characterization of glass transformations for comparison with water-saturated heating experiments in which glass alteration is prominent. 29 figs., 7 figs., 7 tabs.

Vaniman, D.; Bish, D., Chipera, S. [Los Alamos National Lab., NM (United States)

1993-12-10

242

Clusters: Elucidating the dynamics of ionization events and ensuing reactions in the condensed phase. Final technical report, March 1, 1991--February 28, 1994.  

National Technical Information Service (NTIS)

Chemical reactions that proceed following either a photophysical or ionizing event, are directly influenced by the mechanisms of energy transfer and dissipation away from the site of absorption. Neighboring solvent or solute molecules can affect this by c...

A. W. Castleman

1994-01-01

243

Polyaromatic hydrocarbons and the condensation of carbon in stellar winds  

NASA Astrophysics Data System (ADS)

The condensation of carbon in cool stellar winds is described by two processes: the formation and the growth of carbon particles. In contrast to the assumptions of conventional droplet theory of condensation, these particles were found to be PAH's. Their formation and growth is described in terms of chemical reactions. The derived temperature of effective condensation fits the observations. Structure and abundances of the molecules and particles at the end of the condensation process are discussed.

Keller, Rudolf

244

Steam condenser developments  

NASA Astrophysics Data System (ADS)

Factors determining condenser size and tube arrangement are reviewed, including steam side pressure drop; incondensible blanketing; effect of incondensibles on heat transfer; vent requirements; deaeration; condensate depression; cooling water velocity; tube material and diameter selection; fouling; and enhanced heat transfer tubes. Tube nest shapes and condenser concepts are described. Thermal design, and condenser acceptance testing are treated; field test results on "Church Window'' condensers are reported.

Lang, H. V.

245

Mutants of the Zinc Ligands of Lacticin 481 Synthetase Retain Dehydration Activity but Have Impaired Cyclization Activity†  

PubMed Central

Lantibiotics are ribosomally synthesized and post-translationally modified peptide antibiotics. The modifications involve dehydration of Ser and Thr residues to generate dehydroalanines and dehydrobutyrines, followed by intramolecular attack of cysteines onto the newly formed dehydro amino acids to produce cyclic thioethers. LctM performs both processes during the biosynthesis of lacticin 481. Mutation of the zinc ligands Cys781 and Cys836 to alanine did not affect the dehydration activity of LctM. On the other hand, these mutations compromised cyclization activity when investigated with full length or truncated peptide substrates. Mutation of His725, another residue that is fully conserved in lantibiotic cyclases, to Asn resulted in a protein that still catalyzed dehydration of the substrate peptide and also retained cyclization activity, but at a decreased level compared to wild type enzyme. Collectively, these results show that the C-terminal domain of LctM is responsible for cyclization, that the zinc ligands are critical for cyclization, and that dehydration takes place independently from the cyclization activity. Furthermore, these mutant proteins are excellent dehydratases and provide useful tools to investigate the dehydration activity as well as to generate dehydrated peptides for study of the cyclization reaction by wild type LctM.

Paul, Moushumi; Patton, Gregory C.; van der Donk, Wilfred A.

2008-01-01

246

Simulations of condensation and cloud condensation nuclei from biogenic SO{sub 2} in the remote marine boundary layer  

SciTech Connect

The authors present a model which simulates the formation of condensation nuclei, and cloud condensation nuclei in the remote marine boundary layer by reaction of biogenic sulfur dioxide to produce sulfuric acid - water condensates. Their model is not able to account for the observed formation results for cloud condensation nuclei in the boundary layer itself, using typical atmospheric conditions observed in the boundary layer. They offer several possible explanations for the discrepanacies

Raes, F.; Van Dingenen, R. [Environment Institute, Ispra (Italy)

1992-08-20

247

In situ infrared study of SBA-15 functionalized with carboxylic groups incorporated by a co-condensation route.  

PubMed

Two samples of SBA-15 mesoporous silica with a different content of carboxylic groups (-COOH) were prepared by a co-condensation route, using 4-(triethoxysilil)butyronitrile as the organosilane agent, then treating the samples with sulfuric acid, which removes the template and simultaneously hydrolyses the -CN to -COOH groups, as shown by IR spectroscopy. Both incorporation of organosilane agents and subsequent acid treatment do not affect the ordered SBA-15 structure. The proton-donor ability of carboxylic groups, as well their accessibility to reactants, has been studied in the IR by dosing ammonia, which forms reversibly COO- groups and NH4+ ions. The related equilibrium constants have been determined by elaboration of IR data. Outgassing the samples at progressively increasing temperatures destabilizes to an increasing extent the ammonium/carboxylate ion pair, because of the decrease in surface polarity brought about by dehydration: this decreases the related equilibrium constants. The amount of carboxylic groups undergoing reaction appears instead to be constant with dehydration, and to coincide with the whole population of COOH groups. Titration with alkali solutions yielded surface concentrations for the two samples of ca. 1.0 and 0.45 COOH/nm2. Proportionality between the surface concentrations and the intensities of the C=O IR band is observed: this suggests that COOH groups are noninteracting with each other and allows the computation of the related extinction molar coefficient. PMID:16853129

Fiorilli, Sonia; Onida, Barbara; Bonelli, Barbara; Garrone, Edoardo

2005-09-01

248

Gas–particle interactions of tropospheric aerosols: Kinetic and thermodynamic perspectives of multiphase chemical reactions, amorphous organic substances, and the activation of cloud condensation nuclei  

Microsoft Academic Search

Aerosols are of central importance in the Earth system, influencing the atmosphere, biosphere, climate, and public health. This article outlines recent advances and perspectives in the investigation and effects of gas–particle interactions in tropospheric aerosols, including physical, chemical and biological aspects. In particular, it addresses how multiphase processes and heterogeneous chemical reactions can be efficiently described by kinetic models, how

Ulrich Pöschl

2011-01-01

249

Fasting headache, weight loss, and dehydration.  

PubMed

Recently, we showed that fasting is a strong headache precipitator unrelated to coffee, tea, or smoking withdrawal or to oversleeping. In the current study, we evaluated the role of dehydration as a possible precipitator of fasting headache. The effects of a 25-hour fast of the Jewish Yom Kippur (Day of Atonement) were studied in women who participated in our previous Yom Kippur study. We asked the subjects to weigh themselves at the beginning and at the end of the Yom Kippur fast, assuming that the weight loss would largely reflect dehydration. In all but 1 of the 56 participants, the fast resulted in weight loss but only 28 (50%) reported headache. The average weight loss was 1.4 +/- 0.8 kg in those who developed headache and 1.2 +/- 0.5 kg in those who did not. This small difference was not statistically significant. We conclude that dehydration, as reflected by acute weight loss, is an unlikely cause of headache during a single day of fasting. The mechanism of fasting headache remains unclear. PMID:15613218

Mosek, A; Korczyn, A D

1999-03-01

250

Solar energy food dehydration system: Concept development  

SciTech Connect

The research activities to be carried out to form the body of this work were planned, first, to increase the general knowledge in the areas of solar energy application and, secondly, to provide sufficient data for the development of a new solar energy powered food dehydrating system. The research work does not aim merely at pursuing the study and development of a new component or a new type of material to be used in the solar industry. But the final and main part of this research is devoted to the development and design of a solar energy system uncharted before the purpose of dehydrating various agricultural products. This proposed solar powered system development is thereby a contribution of technological knowledge to the field of Applied Sciences. It is one of the viable and effective solutions to solving the world's food and energy shortage problem, especially in the less developed regions of the world. The body of this work, thus is divided into three major parts as follows: (1) The search for a thorough understanding of the origin and fundamental characteristics of solar energy. (2) Past and present applications of solar energy. (3) The development and design of a new solar energy powered system for the dehydration of food crops.

Pham, L.V.

1988-01-01

251

Crude oil dehydrator/desalter control system  

SciTech Connect

A system is described for controlling the content of an impurity in a crude oil stream consisting of: means for adding a demulsifier to a stream of produced wet crude oil, means for receiving the produced wet crude oil stream with demulsifier for separating produced water and gas from the crude oil to provide a separated crude oil stream, at least one mixing means receiving wash water and the separated crude oil stream for mixing the wash water with the separated crude oil stream in accordance with a control signal to provide a crude oil/wash water stream, means for sensing a pressure drop across the mixing means and providing a pressure drop signal representative thereof, and at least one dehydrator means for removing substantial amounts of water from the crude oil/wash water stream to provide a dehydrated crude oil stream, means for monitoring the content of the impurity in the dehydrated crude oil stream and providing an impurity content signal representative thereof, and control means for providing the control signal in accordance with the impurity content signal and the pressure drop signal so as to control the impurity content of the dry crude oil stream.

Richter, A.P. Jr.; Tuggle, R.; Clinard, R.H. Jr.; Campsey, R.L.; Lankford, F.L. Jr.

1986-04-08

252

NUTRITIONAL VALUE OF CONDENSED SOYBEAN SOLUBLES FOR BEEF CATTLE AND SHEEP 1 ,~z  

Microsoft Academic Search

SUMMARY One cattle experiment and two lamb experi- ments were conducted to study the nutritive value of condensed soy solubles (CSS). In the cattle trial CSS was substituted for cane molas- ses in a high urea beef cattle supplement, in the presence of either 14% dehydrated alfalfa meal or 14% ground corn cobs in the supplement. Performance (rate of gain

T. W. Perry; J. B. Outhouse; W. M. Beeson; M. T. Mohler; W. L. Le Grand

2010-01-01

253

Optimizing process vacuum condensers  

SciTech Connect

Vacuum condensers play a critical role in supporting vacuum processing operations. Although they may appear similar to atmospheric units, vacuum condensers have their own special designs, considerations and installation needs. By adding vacuum condensers, precondensers and intercondensers, system cost efficiency can be optimized. Vacuum-condensing systems permit reclamation of high-value product by use of a precondenser, or reduce operating costs with intercondensers. A precondenser placed between the vacuum vessel and ejector system will recover valuable process vapors and reduce vapor load to an ejector system--minimizing the system`s capital and operating costs. Similarly, an intercondenser positioned between ejector stages can condense motive steam and process vapors and reduce vapor load to downstream ejectors as well as lower capital and operating costs. The paper describes vacuum condenser systems, types of vacuum condensers, shellside condensing, tubeside condensing, noncondensable gases, precondenser pressure drop, system interdependency, equipment installation, and equipment layout.

Lines, J.R.; Tice, D.W. [Graham Mfg. Co., Batavia, NY (United States)

1997-09-01

254

Discovery-Oriented Approach To Organic Synthesis: Tandem Aldol Condensation-Michael Addition Reactions. Identifying Diastereotopic Hydrogens in an Achiral Molecule by NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

We have found a beautiful example of anisochrony of diastereotopic acyclic methylene hydrogens in a symmetric diketone, synthesized by techniques traditionally performed in an introductory organic laboratory course. Synthesis of the diketone is high-yielding and easy to carry out, and the products can be directly isolated with a good degree of purity with no need of further manipulation. The reaction can be accomplished in a single laboratory session.

Wachter-Jurcsak, Nanette; Reddin, Kendra

2001-09-01

255

Nonisothermal Kinetics Analysis of the Dehydration of Ziprasidone Hydrochloride Monohydrate by Thermogravimetry  

PubMed Central

In the current work the kinetics of dehydration of ziprasidone hydrochloride monohydrate was studied by nonisothermal thermogravimetry. Ziprasidone hydrochloride monohydrate was heated from 30 to 150° with a heating rate of 5° per min under nitrogen gas atmosphere and weight loss data were collected. Powder X-ray difraction was used to characterize the solid before and after dehydration. The well accepted Coats-Redfern model fitting approach was applied to the thermogravimetry data for the kinetic analysis. Thirteen solid state reaction models were studied; among them one-dimensional diffusion model was found to be the best fit model for this reaction with an excellent correlation 0.9994. The Arrhenius parameters, activation energy, and pre-exponential factor were determined, the values were found to be 28 k.cal/mol and 9.53×1013 sec?1, respectively.

Ravikiran, A.; Arthanareeswari, M.; Kamaraj, P.; Praveen, C.

2013-01-01

256

Catalytic dehydration of propylene glycol with salts in near-critical water  

Microsoft Academic Search

We carried out the dehydration of propylene glycol in near-critical water to study the reactivity of diol under high temperature and pressure. The end product, 2-methyl-2-pentenal (MP), was identified by GS-MS. The yield of MP was 1.8wt.% in pure water at 300°C for 120min. As the catalyst, zinc chloride (ZnCl2) and sodium carbonate (Na2CO3) were added in the reaction mixture

Ziyue Dai; Bunpei Hatano; Hideyuki Tagaya

2004-01-01

257

Dehydration of fructose into 5-hydroxymethylfurfural in the presence of ionic liquids  

Microsoft Academic Search

The acid-catalyzed dehydration of fructose was performed in a microbatch reactor at 80 °C using two commercially available ionic liquids, a hydrophilic one, 1-butyl 3-methyl imidazolium tetrafluoroborate (BMIM+BF4?), and a hydrophobic one, 1-butyl 3-methyl imidazolium hexafluorophosphate (BMIM+PF6?). When the reaction is carried out in 1-butyl 3-methyl imidazolium tetrafluoroborate as solvent and Amberlyst-15 as catalyst, a yield up to 50% in

Clément Lansalot-Matras; Claude Moreau

2003-01-01

258

Effect of compression on the properties of dehydrogenation and dehydration catalysts  

Microsoft Academic Search

Summary 1.A study has been made of the effect of compression at 20,000 aim on the properties of zinc oxide, titanium dioxide, thorium dioxide, and normal calcium phosphate in dehydrogenation and dehydration reactions characteristic for these catalysts.2.It has beer, shown that as a result of compression the apparent specific volume of these catalysts is reduced by the factors indicated:Zinc oxide3.3Titanium

L. F. Vereshchagin; L. Kh. Freidlin; I. U. Numanov; S. G. Kulikov

1954-01-01

259

Condensate Mixtures and Tunneling  

SciTech Connect

The experimental study of condensate mixtures is a particularly exciting application of the recently developed atomic-trap Bose-Einstein condensate (BEC) technology: such multiple condensates represent the first laboratory systems of distinguishable boson superfluid mixtures. In addition, as the authors point out in this paper, the possibility of inter-condensate tunneling greatly enhances the richness of the condensate mixture physics. Not only does tunneling give rise to the oscillating particle currents between condensates of different chemical potentials, such as those studied extensively in the condensed matter Josephson junction experiments, it also affects the near-equilibrium dynamics and stability of the condensate mixtures. In particular, the stabilizing influence of tunneling with respect to spatial separation (phase separation) could be of considerable practical importance to the atomic trap systems. Furthermore, the creation of mixtures of atomic and molecular condensates could introduce a novel type of tunneling process, involving the conversion of a pair of atomic condensate bosons into a single molecular condensate boson. The static description of condensate mixtures with such type of pair tunneling suggests the possibility of observing dilute condensates with the liquid-like property of a self-determined density.

Timmermans, E.

1998-09-14

260

Condensed Matter Physics  

Microsoft Academic Search

A modern, unified treatment of condensed matter physics This new work presents for the first time in decades a sweeping review of the whole field of condensed matter physics. It consolidates new and classic topics from disparate sources, teaching \\

Michael P. Marder

2000-01-01

261

Condensation of trichloromethylsilane in silent discharges  

Microsoft Academic Search

Summary 1.It was shown that, under the action of silent discharges, trichloromethylsilane undergoes condensation and gives a mixture of polyehloromethylsilanes in a yield of about 50%. The main reaction products are compounds formed by the condensation of two or three CH3SiCl3 molecules.2.We established the presence of the following compounds among the condensation products: 1,1,1,3,3-pentachloro-1,3-disilabutane, 1,1,1,4,4-pentachloro-1,4-disilapentane, and mixtures of isomers of

D. N. Andreev

1957-01-01

262

Unprecedented Construction of C?C Double Bonds via Ir-Catalyzed Dehydrogenative and Dehydrative Cross-Couplings.  

PubMed

Unprecedented constructions of C?C double bonds have been achieved by Ir-catalyzed intramolecular dehydrogenative and dehydrative cross-coupling of tertiary amines and ketones. The reactions are proposed to proceed via an Ir-mediated C-H activation mechanism. PMID:23621093

Nie, Shao-Zhen; Sun, Xiang; Wei, Wen-Tao; Zhang, Xue-Jing; Yan, Ming; Xiao, Jian-Liang

2013-04-26

263

The Acid Catalyzed Dehydration of an Isomeric 2-Methylcyclohexanol Mixture: A Kinetic and Regiochemical Study of the Evelyn Effect  

Microsoft Academic Search

This paper details an experiment which serves as an introduction to organic laboratory research. The reaction is the dehydration of a cis, trans mixture of 2-methylcyclohexanols. At intervals of times the reactant mixture is sampled for the cis and trans reactants. At those same intervals of times the receiver flasks of product cyclohexanes being collected are changed, such that sequential

John J. Cawley; Patrick E. Linder

1997-01-01

264

A multidisciplinary approach to the study of the plasma membrane of Zea mays pollen during controlled dehydration  

Microsoft Academic Search

A multidisciplinary approach (freeze-fracture, nuclear magnetic resonance, differential scanning calorimetry, isoelectric focusing and fluorochromatic reaction test) has been used to follow the behaviour of Zea mays pollen during dehydration - and to estimate its quality. At anthesis, the water content of maize pollen is 57–58% and the vegetative plasma membrane is continous and well structured with a very low density

C. Kerhoas; G. Gay; C. Dumas

1987-01-01

265

Dehydration of isobutanol to isobutene in a slurry reactor  

SciTech Connect

The April 1990 Alternative Fuels Proposal to the Department of Energy involved the development of new technology, based on the liquid phase process, for conversion of coal-derived synthesis gas to oxygenated hydrocarbon fuels, fuel additives, and fuel intermediates. The objective of this work was to develop a slurry reactor based process for the dehydration of isobutanol to isobutene. The isobutene can serve as a feedstock for the high octane oxygenated fuel additive methyl tertiary-butyl either (MTBE). Alumina catalysts were investigated because of their wide use as a dehydration catalyst. Four commercially available alumina catalysts (Catapal B, Versal B, Versal GH, and Al-3996R) were evaluated for both activity and selectivity to the branched olefin. All four catalysts demonstrated conversions greater than 80% at 290 C, while conversions of near 100% could be obtained at 330 C. The reaction favors low pressures and moderate to low space velocities. A yield of 0.90 mole isobutene per mole reacted isobutanol or better was obtained at conversions of 60--70% and higher. From 75 to 98% conversion, the four catalysts all provide isobutene yields ranging from 0.92 to 0.94 with the maximum occurring around 90% conversion. At low conversions, the concentration of diisobutyl ether becomes significant while the concentration of linear butenes is essentially a linear function of isobutanol conversion. Doping the catalyst with up to 0.8 wt % potassium showed a modest increase in isobutene selectivity; however, this increase was more than offset by a reduction in activity. Investigations using a mixed alcohols feed (consistent with isobutanol synthesis from syngas) demonstrated a small increase in the C4 iso-olefin selectivity over that observed for a pure isobutanol feed. 55 refs.

Latshaw, B.E.

1994-02-01

266

Condensation in Microchannels  

Microsoft Academic Search

Condensation in microchannels has applications in a wide variety of advanced microthermal devices. Presented here is a review of both experimental and theoretical analyses of condensation in these microchannels, with special attention given to the effects of channel diameter and surface conditions on the flow regimes of condensing flows occurring in these channels. This review suggests that surface tension, rather

Yongping Chen; Mingheng Shi; Ping Cheng; G. P. Peterson

2008-01-01

267

Efficient condensate removal  

Microsoft Academic Search

Achieving stable control of product temperatures on reboilers and other steam\\/product heat exchangers has long been a problem area where conventional steam control and condensate trapping methods were used. Application of a non-electric condensate pump and steam trap sidesteps the problem. Removal of condenser under all conditions, from full load to zero load, is readily achieved. Steam flow control then

Armer

1988-01-01

268

Dehydration effects on D96N bacteriorhodopsin films  

Microsoft Academic Search

Dehydration effects on gelatin films of the D96N mutant bacteriordopsin (BR) and wild-type BR were studied. Unlike the wild-type BR films, wherein dehydration to 12% humidity results in an approximate 200-fold increase in the lifetime of the M state. D96N BR films dehydrated to the same extent have been shown to exhibit only a 17- to 20-fold increase in the

Tatyana V Dyukova; Evgeny P Lukashev

1996-01-01

269

Optimization of Dehydration of Lactobacillus salivarius Using Radiant Energy Vacuum  

Microsoft Academic Search

Radiant energy under vacuum (REV) as a rapid dehydration method was employed to dehydrate Lactobacillus salivarius 417 along with different concentrations of skim milk powder as protective medium. Two optimization methods: response surface\\u000a methodology and random centroid analysis (RCO) were applied and compared to optimize the dehydration parameters for maximum\\u000a viability—microwave power, absolute pressure in the drying chamber, and protective

Shafique Ahmad; Parastoo Yaghmaee; Tim Durance

270

[Severe hypernatraemic dehydration in collodion baby].  

PubMed

Case report on severe hypernatraemic dehydration in a non-recognised collodion baby who also suffered from hydrops fetalis caused by supraventricular tachycardia. Excessive transcutaneous fluid loss caused s-Na+ reaching 182 mmol/l within 36 hours of birth. The infant was cautiously rehydrated during the following three days. No sign of neurologic impairment was observed. It is emphasized that early observation of the collodion baby must take place in a humidified incubator. Major weight changes in the newborn should always result in analysis of serum sodium. PMID:17425931

Magid, Tobias; Fenger-Grøn, Jesper; Nymann, Peter; Hansen, Bo Mølholm

2007-03-26

271

Intraslab earthquakes: dehydration of the Cascadia slab.  

PubMed

We simultaneously invert travel times of refracted and wide-angle reflected waves for three-dimensional compressional-wave velocity structure, earthquake locations, and reflector geometry in northwest Washington state. The reflector, interpreted to be the crust-mantle boundary (Moho) of the subducting Juan de Fuca plate, separates intraslab earthquakes into two groups, permitting a new understanding of the origins of intraslab earthquakes in Cascadia. Earthquakes up-dip of the Moho's 45-kilometer depth contour occur below the reflector, in the subducted oceanic mantle, consistent with serpentinite dehydration; earthquakes located down-dip occur primarily within the subducted crust, consistent with the basalt-to-eclogite transformation. PMID:14615535

Preston, Leiph A; Creager, Kenneth C; Crosson, Robert S; Brocher, Thomas M; Trehu, Anne M

2003-11-14

272

Modulation of Dehydration Tolerance in Soybean Seedlings (Dehydrin Mat1 Is Induced by Dehydration but Not by Abscisic Acid).  

PubMed Central

Germinated soybean (Glycine max L. cv Williams 82) seedlings subjected to rapid dehydration begin to lose the ability to recover when the relative water content of the plant decreases below 60%. The expanded cells of the hypocotyl appear more susceptible to dehydration-induced damage than do cells in the hypocotyl zone of cell growth. Pretreatment of seedlings prior to rapid dehydration with nonlethal water deficit or exogenous abscisic acid (ABA) shifts this viability threshold to progressively lower relative water contents, indicating the acquisition of increased dehydration tolerance. Increased tolerance is associated with osmotic adjustment in the hypocotyl zone of cell growth and with increases in soybean dehydrin Mat1 mRNA levels. The accumulation of Mat1 mRNA is dehydration dependent but insensitive to ABA. Induction of Mat1 mRNA accumulation by dehydration but not by ABA makes it an unusual member of the dehydrin family.

Whitsitt, M. S.; Collins, R. G.; Mullet, J. E.

1997-01-01

273

Afm Study on Condensation of DNA by Spermidine  

NASA Astrophysics Data System (ADS)

We studied on condensates of a circular and a linear plasmid pUC19 DNA with spermidine in view of reaction time. DNA-spermidine condensates were produced by mixture of 2?l of 5?g/ml DNA solution with 2?l of 0.5mM spermidine aqueous solution. Reaction time is the time elapsed until the mixture is dropped on mica substrate to be imaged with a tapping mode AFM. The reaction times are 30, 15 and 1min. The intermediate progress of DNA-spermidine condensation was found from AFM images dependent on the reaction time.

Katsumata, Shunji; Kigasawa, Harunori; Utsuno, Kuniharu

2001-04-01

274

RuCl 3 catalyses aldol condensations of aldehydes and ketones  

Microsoft Academic Search

Anhydrous RuCl3 catalyses the efficient cross aldol condensations of different ketones with various aromatic aldehydes in sealed tube under solvent free conditions without the occurrence of any self condensations. Regioselective self condensation reaction of some ketones and aldehydes are also described. The catalytic effect of Ru(III) is shown by performing similar reactions under thermal conditions without catalyst.

Nasser Iranpoor; Foad Kazemi

1998-01-01

275

Experimentally based water budgets for dehydrating slabs and consequences for arc magma generation  

NASA Astrophysics Data System (ADS)

Phase diagrams of hydrous mid-ocean ridge (MOR) basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones. A synthesis of our experimentally determined phase relations of chlorite, lawsonite, epidote-zoisite, amphibole, paragonite, chloritoid, talc, and phengite in basalts and of phase relations from the literature of serpentine, talc, chlorite, amphibole, and phase A in ultramafics permits calculation of H 2O contents in hydrous phase assemblages that occur in natural compositions. This yields the information necessary to calculate water budgets for descending slabs. Starting from low-grade blueschist conditions (10-20 km depth) with H 2O contents between 5 and 6 wt% for hydrated oceanic crust, complete dehydration is achieved between 70 and >300 km depth as a function of individual slab geotherms. Hydrous phases which decompose at depth below volcanic arcs are lawsonite, zoisite, chloritoid, and talc (± phengite) in mafic compositions and chlorite and serpentine in peridotite. Approximately 15-35% of the initially subducted H 2O are released below volcanic arcs. The contribution of amphibole dehydration to the water budget is small (5-20%) and occurs at relatively shallow depth (65-90 km). In any predicted thermal structure, dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab. Such a dehydration characteristic is incompatible with `single phase dehydration models' which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts. As a consequence of continuously progressing dehydration, water ascending from the slab will be generally available to depth of ca. 150-200 km. The fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge. We propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas. Thermal models show that such an isotherm (ca. 1300°C) locates below volcanic fronts, slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts.

Schmidt, Max W.; Poli, Stefano

1998-11-01

276

Methanol and 2-methyl-1-propanol (isobutanol) coupling to ethers and dehydration over Nafion H: Selectivity, kinetics, and mechanism  

SciTech Connect

The dehydration of a mixture of methanol and isobutanol has been studied over the sulfonic acid Nafion H catalyst. Dehydration products consisted of dimethyl ether (DME), di-isobutyl ether (DIBE), methyl-isobutyl ether (MIBE), butenes, octenes, and traces of methyl-tertiarybutyl ether (MTBE). At low temperatures and high alcohol pressures (P [ge] 150 kPa), the dehydration product slate was dominated by ether formation with selectivity within the ethers significantly in favor of the mixed ether, MIBE. The rates of ether and butene formation as a function of alcohol pressure could be described by Langmuir-Hinshelwood kinetics in which competitive adsorption of the two alcohols on the surface -SO[sub 3]H sites was the dominant feature. The kinetics of isobutanol dehydration to isobutene were consistent with a dual-site mechanism involving the cooperative action of a free surface -SO[sub 3]H site and an adjacent adsorbed alcohol molecule. Dehydration to ethers was consistent with the reaction of two adsorbed alcohols, also by a dual-site mechanism. As a consequence, dehydration to symmetric ethers showed saturation-type kinetics as a function of alcohol pressure, while the rate of isobutene formation went through a distinct maximum. Due to the competitive adsorption of methanol and isobutanol, the mixed ether MIBE was formed at a maximum rate with an optimum ratio of partial pressures of the two alcohols. The high selectivity to MIBE was explained by stronger adsorption of isobutanol on the catalyst surface as compared to methanol. The absence of MTBE and the predominance of products such as MIBE and 2,5-dimethylhexene suggests that dehydration to give free carbenium ions that subsequently rearrange to the more stable tertiary intermediate was not occurring. It was proposed that the alcohols react with the -SO[sub 3]H groups to give oxonium ions or esters. These intermediates couple to give the product ethers or octenes. 24 refs., 13 figs., 1 tab.

Nunan, J.G.; Klier, K.; Herman, R.G. (Lehigh Univ., Bethlehem, PA (United States))

1993-02-01

277

The relationship of intermediate- and deep-focus seismicity to the hydration and dehydration of subducting slabs  

NASA Astrophysics Data System (ADS)

Previous studies suggest that intermediate- and deep-focus earthquakes in subducting slabs may result from dehydration reactions. We investigate the importance of dehydration in facilitating intermediate- and deep-focus earthquakes by comparing the seismicity rate with the calculated slab dehydration flux (van Keken et al., 2011) as a function of depth in 56 subduction zones worldwide. For each region, the seismicity rate per km of trench length per year as a function of depth between 1990 and 2009 was determined from the Preliminary Determination of Epicenters (PDE) catalog. The number of earthquakes between 75 and 240 km depth was compared to the calculated slab dehydration flux in 25 km increments. Deeper than 240 km, dehydration rates were not calculated, so seismicity is instead compared to the calculated flux of water that remains mineralogically bound in the slab at that depth. No strong correlation between the dehydration flux and the seismicity rate was found at any depth. This suggests that some factor besides the presence of water, such as the stress state of the slab, controls intermediate-focus seismicity. For depths greater than 240 km, there is a correlation between the amount of mineralogically-bound H2O and the seismicity rate. In particular, although deep slabs with small amounts of bound water show a wide range of seismicity rates (and many have no seismicity whatsoever), all deep slabs with appreciable water transported below 240 km show significant seismicity. We conclude that the presence of water may be a necessary condition for deep seismicity in conjunction with other factors. We also note that slab temperature and dehydration are linked. Traditionally the limitations on deep earthquake occurrence have been linked to temperature, but this study suggests that similar arguments can be made linking deep earthquakes with the presence of water.

Barcheck, C. Grace; Wiens, Douglas A.; van Keken, Peter E.; Hacker, Bradley R.

2012-10-01

278

Dehydration softening of serpentine and its roles in the intermediate-depth earthquakes  

NASA Astrophysics Data System (ADS)

A popular hypothesis for the occurrence of double seismic zones in subducting slabs, located at the depth of about 50-200 km, is dehydration embrittlement of serpentinized mantle. Brittle failure of serpentinite has been attributed to excess pore fluid pressure caused by dehydration reaction (Raleigh and Paterson, 1965, JGR; Murrell and Ismail, 1976, Tectonophysics). However, in previous deformation experiments of serpentinites and other hydrous minerals using gas-medium apparatus, confining pressure was limited to 500 MPa, which corresponds to the depth of the middle crust (~15 km). It is questionable if the same mechanism could be effective in subducting slabs at higher pressures. We conducted constant strain-rate experiments of a serpentinite sample, which consists of almost pure antigorite, using solid-medium deformation apparatus. Cylindrical specimens of serpentinite with the diameter of 10 mm and the length of 15 mm were cut from the serpentinite sample and jacketed in Ag tubes. Deformation experiments were conducted at 500 oC and 700 oC under the confining pressure of 800 MPa. The temperature of the dehydration reaction is about 650 oC at this pressure. The strain rate ranges from 3.3x10-5 to 2x10-4 sec-1. At 500 oC, antigorite was very hard and not yielded even after differential stress exceeded 900 MPa. The samples deformed at 700 oC without pre-heating exhibited brittle failures and strain hardening. Dehydration reaction had not occurred in these samples. On the contrary, samples deformed at 700 oC after static heating exhibited steady creep behaviors. The yield strength of preheated samples were 200-280 MPa. The differential stress was slightly increased when the sample strain exceeds 5%. Velocity step tests indicated that the yield stress is insensitive to the strain rate. In the pre-heated samples, intergranular pores were developed. No cracks nor microfaults were observed after deformation experiments. The color of antigorite changed from dark green to pink, possibly due to highly oxidized atmosphere caused by free water release. Reaction products of olivine (forsterite) exhibited host-controlled weak lattice preferred orientation (LPO) but there was no evidence for intracrystalline slip. Mechanical behaviors and microstructural features both indicated that the dominant deformation mechanism of pre-heated samples was cataclastic flow of reaction products. Significant volume loss in these samples suggests compaction and escape of water during deformation experiments. Strain localization in the serpentinized parts of mantle due to dehydration softening and high fluid pressure caused by pore collapse would trigger earthquakes in surrounding peridotite mantle.

Shimizu, I.; Watanabe, Y.; Michibayashi, K.

2010-12-01

279

New experimental data on the antigorite dehydration in silica enriched serpentinite  

NASA Astrophysics Data System (ADS)

There is a growing body of evidences for complex interaction between highly reactive fluids and ultramafic lithologies. Silica metasomatism, for example, can occur at the basement of slow-spreading mid-ocean ridges and during prograde metamorphism of chaotically intermixing in mélange zones of ultramafic rocks, metasediments and metabasites in subduction settings. The resulting assemblage diagnostic of metaperidotites that experienced silica metasomatism are talc-schist and talc-bearing serpentinite. These lithologies may hence be common in subduction settings and will undergo different dehydration reactions. Antigorite and talc will react at lower temperature than the terminal antigorite dehydration. Although this reaction is not expected to be as important in the transfer of water to mantle depth as the breakdown of antigorite, it represents nevertheless a dehydration event in subduction zones that has not been considered so far. We anticipate that this reaction might be particularly important for the fore-arc mantle wedge. Piston cylinder experiments were performed to constrain the pressure and temperature conditions for two high-pressure antigorite dehydration reactions found in silica-enriched serpentinites from Cerro del Almirez (Nevado-Filábride Complex, Betic Cordillera, southern Spain) [1]. At 630-660°C and pressures greater than 1.6 GPa, antigorite first reacts with talc to form orthopyroxene ± chlorite + fluid. We show that orthopyroxene + antigorite is restricted to high-pressure metamorphism of silica-enriched serpentinite. This uncommon assemblage is helpful in constraining metamorphic conditions in cold subduction environments, where antigorite serpentinites have no diagnostic assemblages over a large range in PT space [2,3]. The second dehydration reaction leads to the breakdown of antigorite to olivine + orthopyroxene + chlorite + fluid. The maximum stability of antigorite is found at 680°C at 1.9 GPa, which also corresponds to the maximum pressure limit for tremolite coexisting with olivine + orthopyroxene [4]. [1] Trommsdorff, López Sánchez-Vizcaíno, Gómez-Pugnaire, and Müntener (1998), Contrib Mineral Petr 132 139-148. [2] Hermann, Müntener, and Scambelluri, (2000) Tectonophysics 327, 225-238. [3] Scambelluri, Müntener, Hermann, Piccardo, and Trommsdorff, Geology 23, 459-462. [4] Padrón-Navarta, Hermann, Garrido, López Sánchez-Vizcaíno, and Gómez-Pugnaire (2010), Contrib Mineral Petr 159, 25-42.

Padrón-Navarta, José Alberto; Hermann, Jörg; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Gómez-Pugnaire, María. Teresa

2010-05-01

280

Instabilities in strain-rate hardening, chemically-weakening rocks: revisiting the mechanism of "dehydration-embrittlement"  

NASA Astrophysics Data System (ADS)

Serpentinized rocks undergoing dehydration generally exhibit a significant weakening due to various mechanisms (e.g., Rutter et al., 2009). We study here on the effects of "intrinsic" weakening mechanisms, such as the production of fine grained dehydration products (as opposed to "extrinsic" effects such as the weakening induced by changes in pore fluid pressures) on the stability of (1) steady slip and (2) homogeneous shear. General assumptions of rate-hardening and chemically-weakening rheology are used to model the deformation of the reacting rock. In a spring-slider configuration, a linear perturbation analysis provides analytical expressions of the critical stiffness below which unstable slip occurs. In the framework of a frictional constitutive law, numerical tests are performed to study the effects of a non linear reaction kinetics on the evolution of the instability. Slip instabilities can be stopped at relatively small slip rates (only a few orders of magnitude higher than the forcing velocity) when the reactant is fully depleted. The stability analysis of homogeneous shear provides an independent estimate of the thickness of the shear localisation zone due to the reaction weakening, which can be as low as 0.1 m in the case of lizardite dehydration. The potential effect of thermo-chemical pore fluid pressurisation during dehydration is discussed, and shown to be negligible compared to the reaction-weakening effect. Even though much work is still needed to constrain the particular rheology of reacting rocks as well as the reaction kinetics, the assumptions under which the stability conditions are derived are very general. Hence we argue that the slip instabilities originating from the reaction-weakening process could be a plausible candidate for intermediate depth earthquakes in subduction zones, as an alternative to the "dehydration-embrittlement" mechanism based on the effects of pore fluid pressure.

Brantut, N.; Sulem, J.

2012-04-01

281

Treatment of dredged sludge by mechanical dehydration  

SciTech Connect

Sludge deposits in the water area damage the ecosystems and environments; their elimination has always been an urgent task for human communities. Generally, sludge deposits are dredged out of the bottom of the water area, transported to, and discharged at a large disposal area on land. Recently, however, it has become increasingly difficult to secure disposal areas and routes of speedy transportation for disposal of dredged sludge. Accordingly, there is an urgent need to reduce both the volume of dredged sludge and the size of the disposal area. This mechanical method is different from the conventional engineering dehydration by loading, consolidation, and drainage in that the dredged sludge is separated into sludge cakes and clean water that can be returned to the water area through mechanical centrifugal dehydration. Sludge deposits are distributed thin and wide on the bottom of the water area, and a pump dredge has been proved effective in many cases for dredging the upper layers of sludge deposits accurately and without creating turbidity in water. This mechanical sludge treatment technique can be most efficient when used in combination with a pump dredge. This method offers the following advantages: (a) It requires smaller space for treatment and disposal of dredged sludge than the conventional method. (b) Facilities and costs for transportation can be reduced. (c) Various systems can be adopted for transportation of sludge cakes. (d) This system is transportable and compact and can be constructed anywhere either on land or on water.

Maekawa, T.

1992-03-01

282

Cryoprotective dehydration is widespread in Arctic springtails.  

PubMed

Cryoprotective dehydration (CPD) is a cold tolerance strategy employed by small invertebrates that readily lose water by evaporation when subjected to sub-zero temperatures in the presence of ice. Until now, relatively few species have been investigated using methods by which CPD can be shown. In the present study we investigated the cold tolerance strategy of seven soil arthropod species from the high Arctic Spitzbergen, and compared water content and water loss, body fluid melting points (MP) and survival under cold and desiccating conditions. We tested the hypothesis that CPD is a commonly occurring cold hardiness strategy among soil arthropods. We found that four springtail species (Hypogastrura viatica, Folsomia quadrioculata, Oligaphorura groenlandica and Megaphorura arctica; Collembola) went through severe dehydration and MP equilibration with ambient temperature, and thus overwinter by employing CPD, whereas a beetle (Atheta graminicola) and one of the springtails (Isotoma anglicana) were typical freeze avoiding species over-wintering by supercooling. Desiccation tolerance of the red velvet mite (Neomolgus littoralis) was also investigated; very low water loss rates of this species indicated that it does not survive winter by use of CPD. All in all, the results of the present study confirm the hypothesis that CPD is an effective over-wintering strategy which is widespread within soil arthropods. PMID:21396373

Sørensen, Jesper Givskov; Holmstrup, Martin

2011-03-17

283

Dehydration Parameters and Standards for Laboratory Mice  

PubMed Central

Water deprivation and restriction are common features of many physiologic and behavioral studies; however, there are no data-driven humane standards regarding mice on water deprivation or restriction studies to guide IACUC, investigators, and veterinarians. Here we acutely deprived outbred CD1 mice of water for as long as 48 h or restricted them to a 75% or 50% water ration; physical and physiologic indicators of dehydration were measured. With acute water deprivation, the appearance and attitude of mice deteriorated after 24 h, and weight loss exceeded 15%. Plasma osmolality was increased, and plasma volume decreased with each time interval. Plasma corticosterone concentration increased with duration of deprivation. There were no differences in any dehydration measures between mice housed in conventional static cages or ventilated racks. Chronic water restriction induced no significant changes compared with ad libitum availability. We conclude that acute water deprivation of as long as 24 h produces robust physiologic changes; however, deprivation in excess of 24 h is not recommended in light of apparent animal distress. Although clearly thirsty, mice adapt to chronic water restriction of as much as 50% of the ad libitum daily ration that is imposed over an interval of as long as 8 d.

Bekkevold, Christine M; Robertson, Kimberly L; Reinhard, Mary K; Battles, August H; Rowland, Neil E

2013-01-01

284

Condensed phase preparation of 2,3-pentanedione  

DOEpatents

A condensed phase process for the preparation of purified 2,3-pentanedione from lactic acid and an alkali metal lactate is described. The process uses elevated temperatures between about 200 to 360 C for heating a reaction mixture of lactic acid and an alkali metal lactate to produce the 2,3-pentanedione in a reaction vessel. The 2,3-pentanedione produced is vaporized from the reaction vessel and condensed with water. 5 figs.

Miller, D.J.; Perry, S.M.; Fanson, P.T.; Jackson, J.E.

1998-11-03

285

Condensed phase preparation of 2,3-pentanedione  

DOEpatents

A condensed phase process for the preparation of purified 2,3-pentanedione from lactic acid and an alkali metal lactate is described. The process uses elevated temperatures between about 200.degree. to 360.degree. C. for heating a reaction mixture of lactic acid and an alkali metal lactate to produce the 2,3-pentanedione in a reaction vessel. The 2,3-pentanedione produced is vaporized from the reaction vessel and condensed with water.

Miller, Dennis J. (Okemos, MI); Perry, Scott M. (Beaumont, TX); Fanson, Paul T. (Stockbridge, MI); Jackson, James E. (Haslett, MI)

1998-01-01

286

Proceedings: Condenser technology conference  

SciTech Connect

Seam surface condenser and associated systems performance strongly affects availability and heat rate in nuclear and fossil power plants. Thirty-six papers presented at a 1990 conference discuss research results, industry experience, and case histories of condenser problems and solutions. This report contains papers on life extension, performance improvement, corrosion and failure analysis, fouling prevention, and recommendation for future R D. The information represents recent work on condenser problems and solutions to improve the procurement, operation, and maintenance functions of power plant personnel. Several key points follow: A nuclear and a fossil power plant report show that replacing titanium tube bundles improves condenser availability and performance. One paper reports 10 years of experience with enhanced heat transfer tubes in utility condensers. The newly developed enhanced condenser tubes could further improve condensing heat transfer. A new resistance summation method improves the accuracy of condenser performance prediction, especially for stainless steel and titanium tubed condensers. Several papers describe improved condenser fouling monitoring techniques, including a review of zebra mussel issues.

Tsou, J.L. (ed.)(Electric Power Research Inst., Palo Alto, CA (United States)); Mussalli, Y.G. (comp.)(Stone and Webster Engineering Corp., Boston, MA (United States))

1991-08-01

287

Effect of Dehydration on Cardiovascular Responses and Electrolytes Following Hypertonic Saline Dextran Treatment for Moderate Hemorrhage.  

National Technical Information Service (NTIS)

The efficacy of hypertonic saline/dextran (HSD) for treating hemorrhage in the presence of dehydration was evaluated in conscious swine. Following surgical preparation, animals were euhydrated or dehydrated for 24 hr or 48 hr. Dehydration resulted in a re...

A. Blackmon C. E. Wade E. Potanko F. J. Tillman J. A. Loveday

1989-01-01

288

40 CFR 63.765 - Glycol dehydration unit process vent standards.  

Code of Federal Regulations, 2010 CFR

...2009-07-01 false Glycol dehydration unit process vent standards...Facilities § 63.765 Glycol dehydration unit process vent standards...section applies to each glycol dehydration unit subject to this...

2009-07-01

289

40 CFR 63.765 - Glycol dehydration unit process vent standards.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 false Glycol dehydration unit process vent standards...Facilities § 63.765 Glycol dehydration unit process vent standards...section applies to each glycol dehydration unit subject to this...

2010-07-01

290

40 CFR 63.1275 - Glycol dehydration unit process vent standards.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 true Glycol dehydration unit process vent standards...Facilities § 63.1275 Glycol dehydration unit process vent standards...section applies to each glycol dehydration unit subject to this...

2010-07-01

291

40 CFR 63.1275 - Glycol dehydration unit process vent standards.  

Code of Federal Regulations, 2010 CFR

...2009-07-01 false Glycol dehydration unit process vent standards...Facilities § 63.1275 Glycol dehydration unit process vent standards...section applies to each glycol dehydration unit subject to this...

2009-07-01

292

Air-Drying Kinetics of Osmotically Dehydrated Fruits  

Microsoft Academic Search

The air drying kinetics of fresh and osmotically dehydrated fruits (apples) was determined. Two sugars, glucose and sucrose, were used as osmotic dehydration agents. Three levels of sugar concentration (15%, 30% and 45%) and several times of immersion into the sugar solution were used. Following the osmotic preconcentration, the fruit samples were dried at 55°C and the weight of material

V. T. Karathanos; A. E. Kostaropoulos; G. D. Saravacos

1995-01-01

293

Retention of quality characteristics of dehydrated green leaves during storage  

Microsoft Academic Search

Green leafy vegetables are the most underexploited class of vegetablesdespite high nutritional value. Reports on nutritional composition andstorage of some of the fresh leaves are available but the storage behaviorof dehydrated leaves apparently has not been studied. Therefore, in thepresent study, two green leafy vegetables, savoy beets (Beta vulgarisvar. bengalensis) and fenugreek (Trigonella foenumgraecum) were dehydrated in a low temperature

P. S. Negi; S. K. Roy

2001-01-01

294

Osmotic dehydration of Aloe vera ( Aloe barbadensis Miller)  

Microsoft Academic Search

Aloe vera possess immunomodulatory, anti-inflammatory, antibacteria effects and wound and burn healing properties, but it is a very unstable product due to its high water content. Osmotic dehydration can be used to obtain stable products from aloe. In this work the effect of osmotic dehydration (OD) on Aloe vera (Aloe barbadensis Miller) leaves was studied. Peeled and unpeeled Aloe vera

P. García-Segovia; C. Mognetti; A. Andrés-Bello; J. Martínez-Monzó

2010-01-01

295

A Method for Continuous Kinetic Evaluation of Osmotic Dehydration  

Microsoft Academic Search

A method to determine the kinetics of osmotic dehydration was developed. The method involves the measurement of weight loss in a single sample and its final moisture at the end of the process. The method was tested in the osmotic dehydration of apple disks of 4.6 cm diameter and 0.4 cm thickness. Temperature was set at 30 °C and a

Ebner Azuara; Cesar I. Beristain; Gustavo F. Gutiérrez

1998-01-01

296

Dehydration of alcohols on synthetic zeolite of structure Y  

Microsoft Academic Search

1.A study was made of the dehydration of the C2-C4 alcohols and cyclohexanol on zeolite CaY, with a SiO2\\/Al2O3 ratio equal to 3.4.2.The optimum temperatures at which the alcohols are completely dehydrated to the corresponding olefins were determined.

Kh. M. Minachev; V. I. Garanin; Ya. I. Isakov

1964-01-01

297

Solids Rheology for Dehydrated Food and Biological Materials  

Microsoft Academic Search

Mechanical properties of food products and biological materials are greatly affected by the drying process and are considered one of the most important quality attributes of dehydrated products. The aim of this work was to review theoretical principles and mathematical modeling, analyzing the measurement techniques and major experimental results that exist in the literature about rheological properties of dehydrated foods

V. R. N. Telis; J. Telis-Romero; A. L. Gabas

2005-01-01

298

Smackerels of Somethings: Dehydrating Food and How to Use It.  

ERIC Educational Resources Information Center

|Provides ideas about how to add variety, flavor, texture, and nutrition to outdoor meals by dehydrating food and using it on camping trips. The goal is to prepare nutritious and appealing meals without spending a lot of money on commercially dehydrated or freeze-dried foods. Includes instructions for rehydrating foods. (LP)|

Ditzler, Carmen

1994-01-01

299

OSMOTIC DEHYDRATION OF FOODS: MASS TRANSFER AND MODELING ASPECTS  

Microsoft Academic Search

Biological materials contain a variety of individual soluble components. When cellular biological materials are immersed in osmotic solution, multicomponent mass transfer occurs, which ultimately leads to the loss of water from the food, or osmotic dehydration. Mass transfer of food constituents during osmotic dehydration may cause changes in food quality in terms of nutritional value, texture, color, and taste. The

John Shi; Marc Le Maguer

2002-01-01

300

Precedence of head homoeothermia over trunk homoeothermia in dehydrated men  

Microsoft Academic Search

Summary  Three male humans were subjected repeatedly to 20 min exercise on a bicycle ergometer: twice when hydrated normally and twice when dehydrated. Tympanic (Tty) and oesophageal (Tes) temperatures were recorded and sweat rates on forehead and back were measured. Dehydration did not change the forehead sweat rate, but on the back it reduced significantly, resulting in an increase of Tes.

M. Caputa; M. Cabanac

1988-01-01

301

Air-dry primer coatings from dehydrated lesquerella oil  

Microsoft Academic Search

Lesquerella oil (LO), a domestic vegetable oil of hydroxy fatty acid content, was dehydrated (DLO) and the product used to synthesize oil modified polyesters. The polyesters were comparatively evaluated with analogous dehydrated castor oil (DCO) polyesters. Accordingly, polyesters were synthesized from DLO and DCO, and subsequently formulated into air-drying, anti-corrosive primers for evaluation. The DLO and DCO coatings gave comparable

Shelby F. Thames; Haibin Yu; Min D. Wang

1997-01-01

302

Avoiding failed reconstitution of ultradeformable liposomes upon dehydration.  

PubMed

Although freeze-drying is an ordinarily used technique to dehydrate conventional liposomes, we have found that ultradeformable liposomes (UDLs) suffered irreversible aggregation when rehydrated upon freeze-drying (99.4% water elimination), even in high sugar content (4/1 sucrose/lipid mass ratio). When dehydrated by speed vac and vacuum drying, two alternative techniques that rendered less pronounced dehydration (94.27 and 96.2% water elimination, respectively) and avoid ice formation, however, UDL could only be successfully rehydrated when vacuum dried in 4/1 sucrose/lipid mass ratios. Conventional liposomes, on the other hand, were successfully reconstituted upon dehydrated by the three methods in lower sugar content (2/1 sucrose/lipid mass ratio). These results indicated that the 27% mole sodium cholate within the UDL lipid matrix was responsible for a greater and differential mechanical sensitivity of the bilayers to the different dehydration stress, as compared to conventional liposomes. PMID:19429279

Montanari, J; Roncaglia, D I; Lado, L A; Morilla, M J; Romero, E L

2009-01-21

303

Qualitative and quantitative characterization of thein vitro dehydration process of hydrogel contact lenses  

Microsoft Academic Search

Purpose: To investigate the in vitro dehydration process of conventional hydrogel and silicone-hydrogel contact lens materials. Methods: Eight conventional hydrogel and five silicone-hydrogel contact lenses were dehydrated under controlled environmental conditions on an analytical balance. Data were taken at 1-min intervals and dehydration curves of cumulative dehydration (CD), valid dehydration (VD), and dehydration rate (DR) were obtained. Several quantitative descriptors

José M. González-Méijome; Antonio López-Alemany; José B. Almeida; Manuel A. Parafita; Miguel F. Refojo

2007-01-01

304

Dehydration of isopropanol and its comparison with dehydration of butanol isomers from thermodynamic and molecular aspects  

Microsoft Academic Search

By examining the dehydration of aqueous isopropanol (IPA) systems using two Sulzer commercially available polyvinyl alcohol (PVA)\\/polyacrylonitrile (PAN) membranes which were prepared from different cross-linking agents, we have (1) investigated the membrane performance from the standpoints of flux versus permeance and separation factor versus selectivity plots and (2) determined the effects of membrane properties such as degrees of cross-linking and

Xiangyi Qiao; Tai-Shung Chung; Wei Fen Guo; Takeshi Matsuura; May May Teoh

2005-01-01

305

Condensed Matter Physics  

NSDL National Science Digital Library

Founded in 1993 by the Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, the journal Condensed Matter Physics is a peer-reviewed, English-language journal covering such aspects of condensed matter as phase transition theory, statistical mechanics of spin and spin-electron systems, metals and alloys, liquids, solutions, electrolytes, surface phenomena, and plasma physics. Selected issues of Condensed Matter Physics from January 1994 to March 2000 are now available free, online in LaTeX format.

306

Thermal theory of heterogeneous ignition of gasifying condensed substances  

SciTech Connect

These authors consider the ignition of gasifying condensed substances with special attention to the development at the surface of heterogeneous exothermic chemical reactions. They proceed through a series of mathematical computations to establish an equation, written in the dimensional form in rectification coordinates, which makes it possible to analyze experimental data on the ignition of condensed substances.

Egorov, M.E.; Matveev, V.V.

1984-11-01

307

An aggregate urine analysis tool to detect acute dehydration.  

PubMed

Purpose: Urine sampling has previously been evaluated for detecting dehydration in young male athletes. The present study investigated whether urine analysis can serve as a measure of dehydration in men and women of a wide age span. Methods: Urine sampling and body weight measurement were undertaken before and after recreational physical exercise (median time: 90 min) in 57 volunteers age 17-69 years (mean age: 42). Urine analysis included urine color, osmolality, specific gravity, and creatinine. Results: The volunteers' body weight decreased 1.1% (mean) while they exercised. There were strong correlations between all 4 urinary markers of dehydration (r = .73-.84, p < .001). Researchers constructed a composite dehydration index graded from 1 to 6 based on these markers. This index changed from 2.70 before exercising to 3.55 after exercising, which corresponded to dehydration of 1.0% as given by a preliminary reference curve based on seven previous studies in athletes. Men were slightly dehydrated at baseline (mean: 1.9%) compared with women (mean: 0.7%; p < .001), though age had no influence on the results. A final reference curve that considered both the present results and the 7 previous studies was constructed in which exercise-induced weight loss (x) was predicted by the exponential equation x = 0.20 dehydration index1.86. Conclusion: Urine sampling can be used to estimate weight loss due to dehydration in adults up to age 70. A robust dehydration index based on four indicators reduces the influence of confounders. PMID:23994895

Hahn, Robert G; Waldréus, Nana

2013-08-01

308

Cloud condensation nuclei  

Microsoft Academic Search

The state of knowledge of the particles upon which liquid droplets condense to form atmospheric water clouds is presented. The realization of cloud condensation nuclei (CCN) as a distinct aerosol subset originated with the cloud microphysical measurements and theoretical insights of Patrick Squires 40 years ago. He helped originate and continue the development of CCN counters and made significant CCN

James G. Hudson

1993-01-01

309

Dehydration of aliphatic alcohols on phosphoric acid catalyst with the addition of calcium phosphate  

SciTech Connect

The kinetic regularities of dehydration of sec- and tert-butyl alcohols on a catalyst consisting of a mixture of calcium phosphate and H/sub 3/PO/sub 4/, deposited on molten quartz were studied by pulsed gas chromatography. At an equal water vapor pressure in the system, the activity of a catalyst consisting of a pure H/sub 3/PO/sub 4/ is higher than that of a catalyst with the addition of a salt. The experimentally observed dehydration rate constants and those determined with the retention volumes taken into account were measured. Activation energies, rate constants, and the heat of dissolution of tert-butyl alcohol on calcium phosphate catalyst were determined in the range of 80-110/sup 0/C. The dehydration of sec-butyl alcohol was studied at 140/sup 0/C. It was found that in a liquid phase, the reaction rate constant is not very dependent on the salt/acid ratio.

Obraztsov, P.A.; Batalin, O.E.; Malinskii, V.S.; Shubenok, L.F.; Vinnik, M.I.

1986-12-01

310

Support Effects on Bronsted acid site densities and alcohol dehydration turnover rates on tungsten oxide domains  

SciTech Connect

Initial activity and acid site density of several WAl, WSi (MCM41) and one WSn sample were determined. Trans/cis 2-butene selectivity is dependent on the support. Presumably, these differences are due to subtle differences in base strengths. 2-Butanol dehydration rates (per W-atom) reached maximum values at intermediate WOx surface densities on WAl, as reported for 2-butanol dehydration reactions on WZr. Titration results indicate that Bronsted acid sites are required for 2-butanol dehydration on WAl, WSi and WSn. UV-visible studies suggest that WAl is much more difficult to reduce than WZr. The detection of reduced centers on WAl, the number of which correlates to Bronsted acid site density and catalyst activity, as well as the temperature dependence of Bronsted acid site density indicate the in-situ formation of these active sites. We infer that this mechanism is common among all supported WOx samples described in this study. Turnover rates are a function of Bronsted acid site density only. High acid site densities lead to high turnover rates. Higher active site densities may cause stronger conjugate bases, as a higher electron density has to be stabilized, and thus weaker acidity, enabling a faster rate of product desorption. The maximum achievable active site density is dependent on the support. WZr reaches a higher active site density than WAl.

Macht, Josef; Baertsch, Chelsey D.; May-Lozano, Marcos; Soled, Stuart L.; Wang, Yong; Iglesia, Enrique

2005-03-01

311

Elastic wave velocity and acoustic emission monitoring during Gypsum dehydration under triaxial stress conditions  

NASA Astrophysics Data System (ADS)

Dehydration experiments were performed on natural Gypsum polycrystal samples coming from Volterra, Italy in order to study contemporaneously the evolution of P and S elastic wave velocities and acoustic emission (AE) triggering. During these experiments, temperature was slowly raised at 0.15 degrees C per minute under constant stress conditions. Two experiments were realized under quasi-hydrostatic stress (15 and 55 MPa respectively). The third experiment was realized under constant triaxial stress (?3=45MPa, ?1=75MPa). All three were drained (10MPa constant pore pressure). In each experiments, both P and S wave velocities reduced drastically (as much as approx. 50% in the low confining pressure case) at the onset of dehydration. Importantly, the Vp/Vs ratio also decreased. Shortly after the onset of decrease in P and S wave velocities, the dehydration reaction was also accompanied by bursts of AEs. Time serie locations of the AEs show that they initiated from the pore pressure port, ie from where the pore fluid could easily be drained, and then slowly migrated within the sample. In each experiments, the AE rate could be positively correlated to the reaction rate, inferred from pore volumetry. In such a way, the AE rate reached a peak when the reaction was the fastest. Focal mechanism analysis of the largest AEs showed they had a large volumetric component in compaction, confirming that AEs were indeed related to pore closure and/or collapse. In addition, the AE rate also increased with confinement, ie when a larger amount of compaction was observed. Interestingly, when under differential stress conditions, AE focal mechanisms were mainly in shear. Additional dehydration experiments performed within an environmental scanning electron microscope under low vacuum highlight that, in drained conditions at least, the reaction seems to take place in two phases. First, cracks are being opened along cleavage planes within a single gypsum crystal, which allows for the fluid to escape. Second, the solid volume shrinks and pore collapse can occur. Such a scenario is also consistent with our in-situ analysis under pressure. Finally, a differential effective medium theory approach is used to invert crack density and crack average aspect ratio from elastic wave velocity measurements. Coupling this to Biot-Gassman equation, we can correct for some of the dispersion effects (mainly squirt flow) between the ultrasonic (MHz) and the seismic frequency (Hz) ranges. When doing so, we observe, that, under low confining pressures and in drained conditions at least, the evolution of elastic wave velocities is dominated by the effect due to nucleation of low aspect ratio crack during dehydration. Our results thus seem to point out that, because dehydration reaction are accompanied with crack nucleation, the signature of these reactions in nature, should, in fact, possibly be that of a low Vp/Vs ratio, contrarily to what has been instinctively assumed until now.

Brantut, N.; David, E. C.; Héripré, E.; Schubnel, A. J.; Zimmerman, R. W.; Gueguen, Y.

2010-12-01

312

Tandem multicomponent\\/click reactions: synthesis of functionalized oxazoles and tetrazoles from acyl cyanides  

Microsoft Academic Search

The combination of multicomponent condensations with post-condensation dipolar cycloaddition reactions provides a useful route to densely functionalized oxazoles and tetrazoles in just two synthetic steps.

Isabelle F. Clémençon; Bruce Ganem

2007-01-01

313

Neuropsychological Performance, Postural Stability, and Symptoms After Dehydration  

PubMed Central

Context: Dehydration and concussion are common in athletic performance. Some experts have speculated that dehydration may negatively influence performance on tests commonly used for concussion assessment. Objective: To determine how the signs and symptoms, neuropsychological performance, and postural stability are affected by dehydration. Design: Repeated-measures design assessing subjects in the euhydrated and dehydrated conditions. Setting: Sports Medicine Research Laboratory. Patients or Other Participants: Twenty-four healthy, male recreational athletes participated in the study. Intervention(s): Subjects participated in 2 counterbalanced sessions (euhydrated and dehydrated) separated by at least 7 days. Subjects were dehydrated using fluid restriction and an exercise task. No direct intervention was provided for the euhydrated condition. Main Outcome Measure(s): We used the Standardized Assessment of Concussion to test mental status, the Automated Neuropsychological Assessment Metrics (ANAM) to evaluate neuropsychological performance, the NeuroCom Sensory Organization Test and Balance Error Scoring System to test postural stability, the Graded Symptom Checklist to assess symptom presence and severity in our participants, and urine specific gravity and body mass to determine hydration status. Results: No differences were noted for the Standardized Assessment of Concussion, total Balance Error Scoring System errors, composite Sensory Organization Test, and composite ANAM scores between conditions. Subjects in the dehydrated condition had significant deterioration in visual memory (t23 = 2.130, P < .001) and fatigue measures (t23 = ?7.880, P < .001) as assessed by ANAM. The dehydrated condition resulted in subjects reporting a significantly higher number (t23 = ?8.585, P < .001) and severity (t23 = ?7.673, P < .001) of symptoms than the euhydrated subjects on the Graded Symptom Checklist. Conclusions: Our results suggest that moderate dehydration (?2.5 ± 0.63%) significantly influenced the self-report of symptoms commonly associated with concussion. Dehydration resulted in a deterioration of visual memory and increases in the self-report of fatigue. Despite these findings, dehydration did not affect other neuropsychological and postural stability objective testing measures for concussion.

Patel, Akshay V; Mihalik, Jason P; Notebaert, Andrew J; Guskiewicz, Kevin M; Prentice, William E

2007-01-01

314

Afm Study on Condensation of DNA by Spermidine  

Microsoft Academic Search

We studied on condensates of a circular and a linear plasmid pUC19 DNA with spermidine in view of reaction time. DNA-spermidine condensates were produced by mixture of 2mul of 5mug\\/ml DNA solution with 2mul of 0.5mM spermidine aqueous solution. Reaction time is the time elapsed until the mixture is dropped on mica substrate to be imaged with a tapping mode

Shunji Katsumata; Harunori Kigasawa; Kuniharu Utsuno

2001-01-01

315

Electrolyte vapor condenser  

DOEpatents

A system is disclosed for removing electrolyte from a fuel cell gas stream. The gas stream containing electrolyte vapor is supercooled utilizing conventional heat exchangers and the thus supercooled gas stream is passed over high surface area passive condensers. The condensed electrolyte is then drained from the condenser and the remainder of the gas stream passed on. The system is particularly useful for electrolytes such as phosphoric acid and molten carbonate, but can be used for other electrolyte cells and simple vapor separation as well.

Sederquist, Richard A. (Newington, CT); Szydlowski, Donald F. (East Hartford, CT); Sawyer, Richard D. (Canton, CT)

1983-01-01

316

Retention of nutrients in green leafy vegetables on dehydration  

Microsoft Academic Search

The objective of the study was to investigate the influence of dehydration on nutrient composition of Amaranthus gangeticus, Chenopodium album, Centella asiatica, Amaranthus tricolor and Trigonella foenum graecum. The green leafy vegetables (GLV) were steam blanched for 5 min after pretreatment and dried in an oven at 60 °C for 10–12 h.\\u000a The fresh and dehydrated samples were analyzed for selected proximate constituents,

Sheetal Gupta; B. S. Gowri; A. Jyothi Lakshmi; Jamuna Prakash

317

The dehydration process of gypsum under high pressure  

NASA Astrophysics Data System (ADS)

The effects of pressure on the dehydration of gypsum materials were investigated up to 633 K and 25 GPa by using Raman spectroscopy and synchrotron X-ray diffraction with an externally heated diamond anvil cell. At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO4 hemihydrate, which completely dehydrates to ?-anhydrite at 488 K. All the sulphate modes decrease linearly between 293 and 427 K with temperature coefficients ranging from -0.119 to -0.021 cm-1 K-1, where an abrupt change in the ?3 mode and in the OH-stretching region indicates the beginning of dehydration. Increasing the temperature to 488 K, the OH-stretching modes completely disappear, marking the complete dehydration and formation of ?-anhydrite. Moreover, the sample changes from transparent to opaque to transparent again during the dehydration sequence gypsum-bassanite-?-anhydrite, which irreversibly transforms to ?-anhydrite form at 593 K. These data compared with the dehydration temperature at room pressure indicate that the dehydration temperature increases with pressure with a ? P/? T slope equal to 230 bar/K. Synchrotron X-ray diffraction experiments show similar values of temperature and pressure for the first appearance of bassanite. Evidence of phase transition from ?-anhydrite structure to the monazite type was observed at about 2 GPa under cold compression. On the other hand at the same pressure (2 GPa and 633 K), ?-anhydrite was found, indicating a positive Clausis-Clayperon slope of the transition. This transformation is completely reversible as showed by the Raman spectra on the sample recovered after phase transition.

Comodi, P.; Kurnosov, A.; Nazzareni, S.; Dubrovinsky, L.

2012-01-01

318

When to treat dehydration in a terminally ill patient?  

PubMed

The need to treat dehydration in terminally ill patients has become a very controversial topic. Numerous reports in the literature illustrate opposing view-points from both clinical and ethical perspectives. Arguments for the maintenance of hydration in terminally ill patients have tended to come from "the traditional medical model". Many health care professionals looking after terminally ill patients have reacted to the generalized use of intravenous fluids in dying patients and the perceived negative effects of this management. Our palliative care group has argued that the viewpoint that dehydration in dying patients is not a cause of symptom distress overlooks commonly reported problems, such as agitated delirium, that can be prevented or reversed by the management of dehydration. This review presents a summary of the traditional arguments, a different perspective on the controversy, biochemical parameters reported in terminally ill cancer patients, recent dehydration research, and the use of hypodermoclysis and rectal hydration. We conclude that the data reported to date are insufficient to allow a final conclusion on the benefit or harm of dehydration in terminally ill patients. Nevertheless, it is worth considering that while some dying patients may not suffer any ill effects from dehydration, there may be others who do manifest symptoms, such as confusion or opioid toxicity, that might be alleviated or prevented by parenteral hydration. PMID:9176966

Fainsinger, R L; Bruera, E

1997-05-01

319

Risk factors and outcomes associated with hospital admission for dehydration.  

PubMed

The hospital admission rate for dehydration is one of the Agency for Healthcare Research and Quality Prevention's Quality Indicators, which are considered screening tools for potential quality issues. Thus, admission for dehydration may reflect the quality of care provided in community settings. Using a case-control design, this study estimated the incidence, risk factors, and outcomes of dehydration in adults admitted to the hospital. The overall prevalence rate for three International Classification of Diseases codes for dehydration at admission was 0.55%. Cases and controls differed significantly on a number of clinical variables at admission, including weight, body mass index, pulse, blood pressure, use of bulk-forming laxatives, serum sodium and chloride, and presence of generalized weakness or hemiplegia, edema, diarrhea, vomiting, and having nothing by mouth before admission. Mortality rates at 30 and 180 days after discharge were not significantly different between the two groups. Dehydration in community-dwelling adults may delay rehabilitation or result in hospital admission. Prevention, monitoring, and management are critical to preventing dehydration-associated problems. PMID:19024237

Wakefield, Bonnie J; Mentes, Janet; Holman, John E; Culp, Kennith

320

Seawater drinking restores water balance in dehydrated harp seals.  

PubMed

The purpose of this study was to answer the question of whether dehydrated harp seals (Phoca groenlandica) are able to obtain a net gain of water from the intake of seawater. Following 24 h of fasting, three subadult female harp seals were dehydrated by intravenous administration of the osmotic diuretic, mannitol. After another 24 h of fasting, the seals were given 1,000 ml seawater via a stomach tube. Urine and blood were collected for measurement of osmolality and osmolytes, while total body water (TBW) was determined by injections of tritiated water. In all seals, the maximum urinary concentrations of Na(+) and Cl(-) were higher than in seawater, reaching 540 and 620 mM, respectively, compared to 444 and 535 mM in seawater. In another experiment, the seals were given ad lib access to seawater for 48 h after mannitol-induced hyper-osmotic dehydration. In animals without access to seawater, the mean blood osmolality increased from 331 to 363 mOsm kg(-1) during dehydration. In contrast, the blood osmolality, hematocrit and TBW returned to normal when the seals were permitted ad lib access to seawater after dehydration. In conclusion, this study shows that harp seals have the capacity to gain net water from mariposa (voluntarily drinking seawater) and are able to restore water balance after profound dehydration by drinking seawater. PMID:17375309

How, Ole-Jakob; Nordøy, Erling S

2007-03-21

321

May the best friend be an enemy if not recognized early: hypernatremic dehydration due to breastfeeding.  

PubMed

Hypernatremic dehydration is a serious condition in the newborn period. We present 5 infants with hypernatremic dehydration due to breastfeeding; one of them died because of brain edema during treatment.Hypernatremic dehydration in breast-fed newborns is secondary to insufficient lactation and all mothers should be encouraged about breastfeeding, taught the signs of successful breastfeeding, and the warning signs of dehydration. Here, we discuss hypernatremic dehydration in breastfeeding neonates, its causes and treatment. PMID:16027579

Yldzda?, Hacer Yapco?lu; Satar, Mehmet; Tutak, Ercan; Narl, Nejat; Büyükçelik, Mithat; Ozlü, Ferda

2005-07-01

322

Ghost condensate busting  

Microsoft Academic Search

Applying the Thomas–Fermi approximation to renormalizable field theories, we construct ghost condensation models that are free of the instabilities associated with violations of the null-energy condition.

Neven Bili?; Gary B. Tupper; Raoul D. Viollier

2008-01-01

323

Ghost condensate busting  

Microsoft Academic Search

Applying the Thomas-Fermi approximation to renormalizable field theories, we construct ghost condensation models that are free of the instabilities associated with violations of the null-energy condition.

Neven Bilic; Gary B. Tupper; Raoul D. Viollier

2008-01-01

324

Beware of condenser fouling  

SciTech Connect

Many chemical process plants generate steam for power production and process use. Recovering this steam as condensate, and returning it to the boiler, is an economical way to recycle heat. This is usually done in a watercooled, steam-surface condenser located at the exhaust of a turbine. Poor performance of such a condenser -- which is really a large heat exchanger -- can significantly decrease a plant`s heat-recycling efficiency. The most-common causes of condenser inefficiency are: microbiological growth on the water side, scale formation on the water side, tube pluggage by debris and air in-leakage on the steam side. These problems can cost a plant dearly. Well-planned treatment programs to combat these causes, however, pay for themselves many times over. The paper discusses these four types of fouling and solutions to their mitigation.

Buecker, B. [Burns and McDonnell Engineering, Kansas City, MO (United States)

1995-04-01

325

Forecasting Aircraft Condensation Trails.  

National Technical Information Service (NTIS)

Aircraft condensation trails (contrails) are caused by aircraft aerodynamics or engine exhaust in the proper atmospheric conditions. Engine-exhaust trails are the most common and are discussed in this report. Jet aircraft contrail-formation graphs facilit...

1981-01-01

326

Catalytic dehydration of bioethanol to ethylene over TiO 2\\/?-Al 2O 3 catalysts in microchannel reactors  

Microsoft Academic Search

Ethylene is essential material for the petrochemical industry. Ethylene production via catalytic dehydration of ethanol over TiO2\\/?-Al2O3 catalysts in multi-microchannel reactors is reported in this paper. The physicochemical properties of these catalysts are characterized by X-ray diffraction (XRD) and FT-IR spectrum. The effects of operation parameters, such as ethanol concentration, reaction temperature and liquid hourly space velocity, have been investigated

Guangwen Chen; Shulian Li; Fengjun Jiao; Quan Yuan

2007-01-01

327

Mechanisms of liquefaction and pyrolysis reactions of biomass  

Microsoft Academic Search

In the liquefaction process, the micellar-like broken down fragments produced by hydrolysis are degraded to smaller compounds by dehydration, dehydrogenation, deoxygenation and decarboxylation. These compounds once produced, rearrange through condensation, cyclization and polymerization, leading to new compounds. Thermal depolymerization and decomposition of biomass, cellulose, hemicelluloses and products were formed as well as a solid residue of charcoal. The mechanism of

A. Demirba?

2000-01-01

328

Enantioselective dehydration of butan-2-ol using zeolite Y modified with dithiane oxides  

SciTech Connect

Modification of zeolite H-Y by dithiane oxides (2-R-1,3-dithiane 1-oxide; R = H, CH{sub 3}, C{sub 6}H{sub 5}) is shown to enhance significantly its activity for the acid catalyzed gas phase dehydration of butan-2-ol. The rate enhancement is observed for catalysts that are prepared by adding the dithiane oxide to the zeolite synthesis gel or by adsorption of the dithiane oxide onto commercial samples of zeolite H-Y. The origin of the rate enhancement is considered to result from a specific interaction between the dithiane oxide modifier with both the extra-framework and framework aluminum in the zeolite. Modification of zeolite H-Y with (R)-1,3-dithiane 1-oxide enhances the conversion of (S)-butan-2-ol compared to (R)-butan-2-ol in the temperature range 110-150{degrees}C when the two enantiomers are reacted separately. Modification with (S)-2-phenyl-1,3-dithiane 1-oxide gives a catalyst for which (R)-butan-2-ol is the most reactive of the two enantiomers. Reaction of racemic butan-2-ol over these chirally modified H-Y zeolites demonstrates that this modification procedure makes the zeolite enantiomerically discriminating and one enantiomer preferentially reacts, although both are present in the micropores under the reaction conditions. This effect is considered to be due to enantioselective rate enhancement, since, although the rate of dehydration of both enantiomers is enhanced in the chiral environment, the dehydration rate of one enantiomer is accelerated relative to the other. It is suggested that the effect is due to preferential adsorption at the chiral active site. 34 refs., 7 figs., 6 tabs.

Feast, S.; Siddiqui, H.; Bethell, D. [Univ. of Liverpool (United Kingdom)] [and others

1997-04-15

329

Mild dehydration impairs cognitive performance and mood of men.  

PubMed

The present study assessed the effects of mild dehydration on cognitive performance and mood of young males. A total of twenty-six men (age 20·0 (sd 0·3) years) participated in three randomised, single-blind, repeated-measures trials: exercise-induced dehydration plus a diuretic (DD; 40 mg furosemide); exercise-induced dehydration plus placebo containing no diuretic (DN); exercise while maintaining euhydration plus placebo (EU; control condition). Each trial included three 40 min treadmill walks at 5·6 km/h, 5 % grade in a 27·7°C environment. A comprehensive computerised six-task cognitive test battery, the profile of mood states questionnaire and the symptom questionnaire (headache, concentration and task difficulty) were administered during each trial. Paired t tests compared the DD and DN trials resulting in >1 % body mass loss (mean 1·59 (sd 0·42) %) with the volunteer's EU trial (0·01 (sd 0·03) %). Dehydration degraded specific aspects of cognitive performance: errors increased on visual vigilance (P = 0·048) and visual working memory response latency slowed (P = 0·021). Fatigue and tension/anxiety increased due to dehydration at rest (P = 0·040 and 0·029) and fatigue during exercise (P = 0·026). Plasma osmolality increased due to dehydration (P < 0·001) but resting gastrointestinal temperature was not altered (P = 0·238). In conclusion, mild dehydration without hyperthermia in men induced adverse changes in vigilance and working memory, and increased tension/anxiety and fatigue. PMID:21736786

Ganio, Matthew S; Armstrong, Lawrence E; Casa, Douglas J; McDermott, Brendon P; Lee, Elaine C; Yamamoto, Linda M; Marzano, Stefania; Lopez, Rebecca M; Jimenez, Liliana; Le Bellego, Laurent; Chevillotte, Emmanuel; Lieberman, Harris R

2011-06-07

330

Enthalpies of formation and dehydration of uranium-containing compounds of the series M{sup I}AsUOâ·nHâO  

Microsoft Academic Search

The standard enthalpies of formation of uranium-containing compounds M¹AsUOâ at 298.15 K (M¹=Li, Na, K, Rb, and Cs) were calculated according to Hess` law from the standard enthalpies of the corresponding reactions. The standard enthalpies of dehydration of the compounds studied were calculated from the data obtained. 9 refs.

N. V. Karyakin; G. N. Chernorukov

1994-01-01

331

Dehydration of Methylcyclohexanol Isomers in the Undergraduate Organic Laboratory and Product Analysis by Gas Chromatography-Mass Spectroscopy (GC-MS)  

ERIC Educational Resources Information Center

|Dehydrations of "cis"- and "trans"-2-methylcyclohexanol mixtures were carried out with 60% sulfuric acid at 78-80 [degrees]C as a function of time and the products were identified by gas chromatography-mass spectroscopy (GC-MS) analysis. The compounds identified in the reaction mixtures include alkenes, 1-, 3-, and 4-methylcyclohexenes and…

Clennan, Malgorzata M.; Clennan, Edward L.

2011-01-01

332

Psychomotor and physiological responses to prolong walking in the heat in hydrated and dehydrated conditions among relaxation-trained army reserved personnel  

Microsoft Academic Search

The present study examined the effects of prolonged walking in the heat on choice reaction time, heart rate and rectal temperature among army reserved personnel. Using purposive sampling, 23 male reserved army personnel were recruited for this study and they were randomly assigned into hydrated and dehydrated groups. The experimental protocols consist of two experimental sessions (pre- and post-relaxation training).

Hairul Anuar Hashim; Zabidi Azhar Hussin; Chen Chee Keong; Asok Kumar Ghosh

2010-01-01

333

Dehydration in the tropical tropopause layer: A possible sink of inorganic bromine?  

NASA Astrophysics Data System (ADS)

Recent studies have shown the importance of bromine very short-lived substances (VSLS) for the stratospheric bromine budget and their potential impact on ozone depletion. In this study, bromine loading in the tropical upper troposphere/lower stratosphere (UTLS) due to VSLS is investigated with a 3D chemical transport model with a detailed chemistry scheme, including parametrizations of particle adsorption and scavenging as well as heterogeneous reactions on corresponding surfaces. On the source gas side, the long-lived halons and methyl bromide and the two most important bromine short-lived substances, bromoform and dibromomethane, are included. On the other hand, the partitioning of inorganic bromine product gases (Bry) is also explicitly calculated. Our results suggest that loss of soluble inorganic bromine in the tropical UTLS due to dehydration is negligible, in contrast to most earlier studies. The main reasons can be summarized as follows: The majority of bromine short-lived source gases is still intact at the UTLS and is therefore not susceptible to dehydration. Furthermore, the fraction of inorganic bromine which is actually adsorbed on ice particles is generally lower than 25%. Finally, the model shows that the small amount of adsorbed bromine that could be scavenged is released efficiently into gas phase by heterogeneous reactions.

Aschmann, J.; Sinnhuber, B.-M.

2012-04-01

334

Efficient condensate removal  

SciTech Connect

Achieving stable control of product temperatures on reboilers and other steam/product heat exchangers has long been a problem area where conventional steam control and condensate trapping methods were used. Application of a non-electric condensate pump and steam trap sidesteps the problem. Removal of condenser under all conditions, from full load to zero load, is readily achieved. Steam flow control then regulates heat flow to match load requirements, with stable product temperatures and fast response to control action. Avoidance of waterhammer and corrosion problems within the exchangers are added side benefits. Difficulties with conventional hookups begin when the surface area of the heater and the heat transfer coefficient means that the steam temperature within the heater must be lower than design levels. Part-load operation or even use of generous fouling factors at design stage both call for lowered steam temperatures and pressures. When steam pressures approach the back pressure on the traps, condensate flow slows down and can stop completely. Flooding of the heat exchange surface follows and heat transfer slows down. The temperature control then opens up the steam valve, as it responds to falling product temperature. With the increased steam pressure, the condensate clears through the trap. The exchanger is then filled with steam at a higher temperature and pressure than it needs, so the product temperature begins to climb again.

Armer, A.

1988-01-01

335

Condensed Genome Structure  

PubMed Central

Large, tailed dsDNA-containing bacteriophage genomes are packaged to a conserved and high density (~500 mg/ml), generally in ~2.5-nm, duplex-to-duplex, spaced, organized DNA shells within icosahedral capsids. Phages with these condensate properties, however, differ markedly in their inner capsid structures: (1) those with a naked condensed DNA, (2) those with many dispersed unstructured proteins embedded within the DNA, (3) those with a small number of localized proteins, and (4) those with a reduced or DNA-free internal protein structure of substantial volume. The DNA is translocated and condensed by a high-force ATPase motor into a procapsid already containing the proteins that are to be ejected together with the DNA into the infected host. The condensed genome structure of a single-phage type is unlikely to be precisely determined and can change without loss of function to fit an altered capsid size or internal structure. Although no such single-phage condensed genome structure is known exactly, it is known that a single general structure is unlikely to apply to all such phages.

Black, Lindsay W.

2013-01-01

336

Dehydration and the Dynamic Dimensional Changes within Dentin and Enamel  

PubMed Central

Objectives The objectives of this study were to quantify the dimensional changes in dentin and enamel during dehydration, and to determine if there are differences between the responses of these tissues from young and old patients. Methods Microscopic Digital Image Correlation (DIC) was used to evaluate deformation of dentin and enamel as a function of water loss resulting from free convection in air. Dimensional changes within both tissues were quantified for two patient age groups (i.e. young 18?age?30 and old 50?age) and in two orthogonal directions (i.e. parallel and perpendicular to the prevailing structural feature (dentin tubules or enamel prisms)). The deformation histories were used to estimate effective dehydration coefficients that can be used in quantifying the strains induced by dehydration. Results Both dentin and enamel underwent contraction with water loss, regardless of the patient age. There was no significant difference between responses of the two age groups or the two orthogonal directions. Over one hour of free convection, the average water loss in dentin was 6% and resulted in approximately 0.5 % shrinkage. In the same time period the average water loss in the enamel was approximately 1% and resulted in 0.03% shrinkage. The estimated effective dehydration coefficients were -810 µm/m/(% weight loss) and -50 µm/m/(% weight loss) for dentin and enamel, respectively. Significance The degree of deformation shrinkage resulting from dehydration is over a factor of magnitude larger in dentin than enamel.

Zhang, D.; Mao, S.; Lu, C.; Romberg, E.; Arola, D.

2009-01-01

337

Effect of elevated stress and temperature on smectite dehydration in subducting sediments - an experimental approach  

NASA Astrophysics Data System (ADS)

Smectite-rich subduction inputs have been in the focus of convergent margin researchers because of their mechanical weakness, their ability to store water in interlayer sites and to release it at greater depth. The release of bound water in smectite during the transition to illite is widely acknowledged to cause the omnipresent fluid freshening at convergent margins. Freshened fluids are often considered as tracer for lateral fluid flow because illitization occurs at greater depths with temperatures >60°C. Instead, laboratory experiments showed that smectite is able to dehydrate partially when an effective stress level of ~1.3 MPa is exceeded. This observation is still poorly constrained when regarding the hydrogeochemistry of subduction zones. To shed light on this process the set-up of a backpressured uniaxial consolidation apparatus (hydrothermal oedometer) was chosen, which provides a large spectrum of pressure (P) and temperature (T) conditions. Three hydrothermal consolidation tests were conducted at constant temperatures of 20°C, 60°C and 100°C up to stresses of 70 MPa. The specimen used was a smectite-rich silty claystone to emphasize dehydration reactions. It is mineralogically similar to smectite-rich end members from the Nankai Trough subduction zone (Japan), Barbados accretionary wedge and Costa Rica margin. The fluids expelled at different stress intervals during the compaction tests were analyzed for major and trace elements to evaluate potential fluid-rock interaction with increasing PT conditions in the shallow subduction zone. The results confirm that smectite dehydration starts at stresses as low as ~2 MPa. However, the interlayer collapse can be also related to the decreasing availability of water in the water-rock system. This assumption is favored by the good accordance with literature data of the experimentally determined relationship between smectite's basal spacing and the water-smectite mass ratio. In addition, the data from the room-temperature experiment was sufficient to formulate for the first time a relationship between the water-rock mass ratio (w/r) and the dehydrated smectite fraction in the sediment. This allows a holistic view of 3 different depth-temperature stages of smectite dehydration in the subduction zone. In shallow parts (approx. <250 mbsf) and in overpressured layers where the sediment is able to maintain w/r mass ratios greater than 0.44 g/g and the temperature is low no smectite dehydration occurs. At greater depth where w/r mass ratios are smaller 0.44 g/g dehydration generates low chlorinity fluids. The fluid freshening is associated with less K and Mg and increased concentrations of Na as well as volatile elements (B, Li, Si). This is caused by the change in cation selectivity towards weakly hydrated ions when the interlayer collapse from 18.5 Å to a 15.4 Å hydrate and the increasing temperature. The third stage is characterized by temperatures >60 °C and w/r mass ratios smaller 0.44 g/g. The previous processes are accentuated by higher temperatures and smaller w/r mass ratios but the pore fluid is overprinted by the smectite-illite transition.

Huepers, A.; Kopf, A.

2010-12-01

338

Structural Ordering of Disordered Ligand-Binding Loops of Biotin Protein Ligase into Active Conformations as a Consequence of Dehydration  

PubMed Central

Mycobacterium tuberculosis (Mtb), a dreaded pathogen, has a unique cell envelope composed of high fatty acid content that plays a crucial role in its pathogenesis. Acetyl Coenzyme A Carboxylase (ACC), an important enzyme that catalyzes the first reaction of fatty acid biosynthesis, is biotinylated by biotin acetyl-CoA carboxylase ligase (BirA). The ligand-binding loops in all known apo BirAs to date are disordered and attain an ordered structure only after undergoing a conformational change upon ligand-binding. Here, we report that dehydration of Mtb-BirA crystals traps both the apo and active conformations in its asymmetric unit, and for the first time provides structural evidence of such transformation. Recombinant Mtb-BirA was crystallized at room temperature, and diffraction data was collected at 295 K as well as at 120 K. Transfer of crystals to paraffin and paratone-N oil (cryoprotectants) prior to flash-freezing induced lattice shrinkage and enhancement in the resolution of the X-ray diffraction data. Intriguingly, the crystal lattice rearrangement due to shrinkage in the dehydrated Mtb-BirA crystals ensued structural order of otherwise flexible ligand-binding loops L4 and L8 in apo BirA. In addition, crystal dehydration resulted in a shift of ?3.5 Å in the flexible loop L6, a proline-rich loop unique to Mtb complex as well as around the L11 region. The shift in loop L11 in the C-terminal domain on dehydration emulates the action responsible for the complex formation with its protein ligand biotin carboxyl carrier protein (BCCP) domain of ACCA3. This is contrary to the involvement of loop L14 observed in Pyrococcus horikoshii BirA-BCCP complex. Another interesting feature that emerges from this dehydrated structure is that the two subunits A and B, though related by a noncrystallographic twofold symmetry, assemble into an asymmetric dimer representing the ligand-bound and ligand-free states of the protein, respectively. In-depth analyses of the sequence and the structure also provide answers to the reported lower affinities of Mtb-BirA toward ATP and biotin substrates. This dehydrated crystal structure not only provides key leads to the understanding of the structure/function relationships in the protein in the absence of any ligand-bound structure, but also demonstrates the merit of dehydration of crystals as an inimitable technique to have a glance at proteins in action.

Khare, Garima; Salunke, Dinakar M.; Surolia, Avadhesha; Tyagi, Anil K.

2010-01-01

339

Evaporation, Condensation, and Precipitation  

NSDL National Science Digital Library

After completion of this project students should have an understanding of evaporation, condensation, and precipitation in the water cycle. Use the websites provided to answer the questions. Record your answers on the spreadsheet provided. Do you understand how the water cycle works? Begin by watching this short video about the water cycle.water cycle video Use the website to define condensation, precipitation, and evaporation?water cycle List the different types of precipitation from the site.types of precipitation Follow the directions to the experiment on this website to get a better understanding of how evaporation takes ...

Brown, Miss

2009-10-21

340

Dehydration Process of Protein Crystals by Micro-Brillouin Scattering  

NASA Astrophysics Data System (ADS)

Polymorphism and dehydration process have been studied by the micro-Brillouin scattering technique in hen egg white lysozyme crystals without cross-linking. Two types of crystal with tetragonal and monoclinic systems have been successfully grown by the two-liquid interface method. The dehydration processes of tetragonal and monoclinic crystals have been investigated by the exposure of crystals to open air. Sound velocity increases markedly owing to the increase in intermolecular interaction between lysozyme molecules, while the attenuation of sound wave decreases markedly owing to the decrease in friction generated by mobile water. The time dependences of sound velocity in two crystals have been discussed on the basis of the Avrami-Erofe’ev model. It is found that a monoclinic crystal dehydrates much faster than a tetragonal one.

Hashimoto, Eiji; Aoki, Yuichiro; Seshimo, Yuichi; Sasanuma, Keita; Ike, Yuji; Kojima, Seiji

2008-05-01

341

Geothermal vegetable dehydration at Brady`s Hot Springs, Nevada  

SciTech Connect

This article describes the utilization of the Brady`s Springs geothermal resource for heat generation used in the food dehydration process. This geothermal system is located in the Forty-Mile Desert area of Nevada. Geothermal Food Processors, Inc. of Reno, Nevada started construction of the geothermal vegetable dehydration plant in 1978, and the plant started operations in 1979. The industrial process of vegetable dehydration at the plant is described. In July of 1992, the Brady`s Springs geothermal system began being used for power generation by the Brady`s Hot Springs geothermal power plant, operated by Oxbow Power Services, Inc. As a result, the water levels in the food processing plant wells have dropped below usable levels and the geothermal brine is now being supplied by the Oxbow power plant.

Lund, J.W.

1994-07-01

342

Dehydration decreases saliva antimicrobial proteins important for mucosal immunity.  

PubMed

The aim of the study was to investigate the effect of exercise-induced dehydration and subsequent overnight fluid restriction on saliva antimicrobial proteins important for host defence (secretory IgA (SIgA), ?-amylase, and lysozyme). On two randomized occasions, 13 participants exercised in the heat, either without fluid intake to evoke progressive body mass losses (BML) of 1%, 2%, and 3% with subsequent overnight fluid restriction until 0800 h in the following morning (DEH) or with fluids to offset losses (CON). Participants in the DEH trial rehydrated from 0800 h until 1100 h on day 2. BML, plasma osmolality (Posm), and urine specific gravity (USG) were assessed as hydration indices. Unstimulated saliva samples were assessed for flow rate (SFR), SIgA, ?-amylase, and lysozyme concentrations. Posm and USG increased during dehydration and remained elevated after overnight fluid restriction (BML = 3.5% ± 0.3%, Posm = 297 ± 6 mosmol·kg?¹, and USG = 1.026 ± 0.002; P < 0.001). Dehydration decreased SFR (67% at 3% BML, 70% at 0800 h; P < 0.01) and increased SIgA concentration, with no effect on SIgA secretion rate. SFR and SIgA responses remained unchanged in the CON trial. Dehydration did not affect ?-amylase or lysozyme concentration but decreased secretion rates of ?-amylase (44% at 3% BML, 78% at 0800 h; P < 0.01) and lysozyme (46% at 3% BML, 61% at 0800 h; P < 0.01), which were lower than in CON at these time points (P < 0.05). Rehydration returned all saliva variables to baseline. In conclusion, modest dehydration (~3% BML) decreased SFR, ?-amylase, and lysozyme secretion rates. Whether the observed magnitude of decrease in saliva AMPs during dehydration compromises host defence remains to be shown. PMID:22686429

Fortes, Matthew B; Diment, Bethany C; Di Felice, Umberto; Walsh, Neil P

2012-06-12

343

Efficient dehydration of fructose to 5-hydroxymethylfurfural catalyzed by a recyclable sulfonated organic heteropolyacid salt.  

PubMed

The dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) with room temperature ionic liquids (ILs) is a way of producing liquid fuels from renewable resources, but separation of products and IL is energy intensive. In this work, a heteropolyacid salt of an IL-forming cation functionalized with a propanesulfonate group, 1-(3-sulfonicacid)propyl-3-methyl imidazolium phosphotungstate ([MIMPS](3)PW(12)O(40)), was used as a catalyst-rather than as a solvent-in the conversion of fructose to 5-HMF. The maximum yield of 5-HMF was 99.1% at 120°C after 2h using sec-butanol as solvent, and the catalyst was separated from the reaction mixture by a simple process at the end of the reaction and reused six times without loss of activity. PMID:22201545

Qu, Yongshui; Huang, Chongpin; Zhang, Jie; Chen, Biaohua

2011-12-04

344

Simple Simulations of DNA Condensation  

SciTech Connect

Molecular dynamics simulations of a simple, bead-spring model of semiflexible polyelectrolytes such as DNA are performed. All charges are explicitly treated. Starting from extended, noncondensed conformations, condensed structures form in the simulations with tetravalent or trivalent counterions. No condensates form or are stable for divalent counterions. The mechanism by which condensates form is described. Briefly, condensation occurs because electrostatic interactions dominate entropy, and the favored Coulombic structure is a charge ordered state. Condensation is a generic phenomena and occurs for a variety of polyelectrolyte parameters. Toroids and rods are the condensate structures. Toroids form preferentially when the molecular stiffness is sufficiently strong.

STEVENS,MARK J.

2000-07-12

345

Polariton Condensation in Photonic Molecules  

NASA Astrophysics Data System (ADS)

We report on polariton condensation in photonic molecules formed by two coupled micropillars. We show that the condensation process is strongly affected by the interaction with the cloud of uncondensed excitons and thus strongly depends on the exact localization of these excitons within the molecule. Under symmetric excitation conditions, condensation is triggered on both binding and antibinding polariton states of the molecule. On the opposite, when the excitonic cloud is injected in one of the two pillars, condensation on a metastable state is observed and a total transfer of the condensate into one of the micropillars can be achieved. Our results highlight the crucial role played by relaxation kinetics in the condensation process.

Galbiati, Marta; Ferrier, Lydie; Solnyshkov, Dmitry D.; Tanese, Dimitrii; Wertz, Esther; Amo, Alberto; Abbarchi, Marco; Senellart, Pascale; Sagnes, Isabelle; Lemaître, Aristide; Galopin, Elisabeth; Malpuech, Guillaume; Bloch, Jacqueline

2012-03-01

346

Process and apparatus for dehydrating waste solids concentrates  

SciTech Connect

An apparatus and process are disclosed for dehydrating waste solids concentrates including secondary and digested sewage sludges and those concentrates prone to form emulsions upon the addition of oil are obtained and accomplished by mixing the sludge or other concentrate with fluidizing oil prior to dehydration by heat evaporation to maintain pumpability; recycling a portion of the substantially anhydrous waste solids and oil evaporator output slurry, and admixing it with the fluidizing oil and input sludge or concentrate to regulate the solids content and viscosity of the steady state feed mixture and thereby prevent fouling of the evaporator heat transfer surfaces and convert emulsions to suspensions.

Bonanno, A.J.; Greenfield, C.

1981-06-30

347

Process and apparatus for dehydrating waste solids concentrates  

SciTech Connect

An apparatus and process for dehydrating waste solids concentrates including secondary and digested sewage sludges and those concentrates prone to form emulsions upon the addition of oil are obtained and accomplished by mixing the sludge or other concentrate with fluidizing oil prior to dehydration by heat evaporation to maintain pumpability; recycling a portion of the substantially anhydrous waste solids and oil evaporator output slurry, and admixing it with the fluidizing oil and input sludge or concentrate to regulate the solids content and viscosity of the steady state feed mixture and thereby prevent fouling of the evaporator heat transfer surfaces and convert emulsions to suspensions.

Bonanno, A.J.; Greenfield, C.

1983-03-22

348

Interlayer Spaces Associated with Hydration and Dehydration in Synthetic Saponite  

NASA Astrophysics Data System (ADS)

Positron annihilation lifetime spectroscopy was conducted for a synthetic saponite to investigate hydration and dehydration behaviour occurring in nanoscale interlayer spaces. Long positron lifetime of ~ 24 ns was observed with the intensity of ~ 8 % when the sample is evacuated at ~ 10-5 Torr. The radius of open nanospace evaluated from the positron lifetime is ~ 10 Å, which corresponds to the interlayer spaces of saponite. The open nanospace increases up to 13 % after baking at 423 K for 8 h under the vacuum. The present results imply that positron annihilation spectroscopy is powerful tool to investigate hydration and dehydration behavior through the local structural changes in the interlayer spaces of clay minerals.

Sato, K.; Fujimoto, K.; Nakata, M.; Shikazono, N.

2010-11-01

349

EPR study on gamma-irradiated fruits dehydrated via osmosis  

NASA Astrophysics Data System (ADS)

The shape and time stability of the electron paramagnetic resonance (EPR) spectra of non- and ?-irradiated papaya, melon, cherry and fig samples dehydrated via osmosis are reported. It is shown that non-irradiated samples are generally EPR silent whereas ?-irradiated exhibit “sugar-like” EPR spectra. The recorded EPR spectra are monitored for a period of 7 months after irradiation (stored at low humidity and in the dark). The results suggest longer period of unambiguous identification of the radiation processing of osmose dehydrated fruits. Therefore, the Protocol EN 13708,2001 issued by CEN is fully applicable for the studied fruit samples.

Yordanov, N. D.; Aleksieva, K.

2007-06-01

350

A bulge-induced dehydration failure mode of nanocomposite hydrogel  

NASA Astrophysics Data System (ADS)

Since hydrogels are very soft and usually weak in swollen state, they pose unique challenges to traditional mechanical experiments. The mechanical property of nanocomposite poly(N-isopropylacrylamide) hydrogel was characterized by the bulge test in this investigation. A dehydration failure phenomenon of the hydrogel was found and the failure mechanism was presented. A criterion is proposed that when strain reaches the threshold, water molecules migrate out of the polymer networks and the dehydration failure occurs. The critical strain keeps constant for orifices with different diameters. This failure mode can be applied in the controllable release of drugs.

Tang, Jingda; Yu, Zejun; Sun, Youyi; Pei, Yongmao; Fang, Daining

2013-10-01

351

Detail of Bright Angel stone vault, containing condenser, Hoffman condensation ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Detail of Bright Angel stone vault, containing condenser, Hoffman condensation pump, Jennings vacuum heating pump, and misc. pipes and valves. - Grand Canyon Village Utilities, Grand Canyon National Park, Grand Canyon Village, Coconino County, AZ

352

Kinetic study of the thermal dehydration of copper(II) dipicolinates: Crystal and molecular structure of Cu(II) (Pyridine 2,6-Dicarboxylato) DI- and Trihydrated  

NASA Astrophysics Data System (ADS)

As a basis for the description of dehydration mechanisms, the molecular structures of two copper(II) dipicolinates, Cu(dipic).2H2O (triclinic) and Cu(dipic).3H2O, are presented and compared with those of other copper(II) dipicolinates. The kinetics of the isothermal dehydration of the monoclinic and triclinic polymorphs of Cu(dipic).2H2O were measured. The monoclinic variety dehydrates in a two-step process; a linear ?/t relationship is found for the first step and a two-dimensional diffusion-controlled reaction (D2) law ((1 - ?)ln(1 - ?) + a = kt) for the second. Triclinic Cu(dipic).2H2O dehydrates in a one-step process. The relation between ? and time is linear at lower temperatures but gradually changes to an Avrami-Erofe'ev (A2) model (- ln (1 - ?)1/n = kt) at higher temperatures. A qualitative model based on optical microscopic observations, structural determinations and thermogravimetric data is proposed. The general relationship between dehydration behavior and structure in this series of compounds is discussed.

Sileo, E. E.; Rigotti, G.; Rivero, B. E.; Blesa, M. A.

1997-07-01

353

Detonation Sensitivity and Failure Diameter in Homogeneous Condensed Materials  

Microsoft Academic Search

A model is proposed for steady detonation waves in homogeneous condensed materials. The model is one in which the pressure profile in the direction of the wave motion is square between shock front and Chapman-Jouguet surface. The reaction rate in the steady zone is allowed to vary with the steady detonation wave velocity according to the temperature in the reaction

Marjorie W. Evans

1962-01-01

354

Contribution to the study of the aldol condensation process  

Microsoft Academic Search

The reaction course of aldol condensation has been studied. Diacetone alcohol is produced from acetone, using a basic ion exchanger as a catalyst. Experiments are carried out in a laboratory set-up (batch process). The analysis of reactants and products is made by the method of refractometry and gas chromatography, respectively. The reaction is performed at 293, 303, 313 and 323

N. Sišul; N. Cikovi?; J. Jelen?i?; N. Wolf

1989-01-01

355

Influence of acid–base properties of catalysts in the gas-phase dehydration–dehydrogenation of cyclohexanol on amorphous AlPO 4 and several inorganic solids  

Microsoft Academic Search

A series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al\\/Fe=Al\\/Ca=1) mixed systems: FeAl(PO4)2 and Ca3Al3(PO4)5, were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. Gas-phase competitive dehydration\\/dehydrogenation reaction of cyclohexanol was carried out as a probe reaction and cyclohexene was usually the main

F. M Bautista; J. M Campelo; A Garc??a; D Luna; J. M Marinas; R. A Quirós; A. A Romero

2003-01-01

356

Condensed matter physics journals  

Microsoft Academic Search

On the basis of a citation\\/reference criterion, 20 core journals are selected in the field of condensed matter physics. Citation data and indicators from 1980Journal Citation Reports reveal their different characteristic features such as applied orientation, communication function and longevity. The manually obtained data for the core journals are written into a matrix in order to determine an appropriate ranking

R. Todorov

1983-01-01

357

Soft condensed matter physics  

Microsoft Academic Search

Soft condensed matter physics is the study of materials, such as fluids, liquid crystals, polymers, colloids and emulsions, that are “soft” to the touch. This article will review some properties, such as the dominance of entropy, that are unique to soft materials and some properties such as the interplay between broken-symmetry, dynamic mode structure and topological defects that are common

T. C. Lubensky

1997-01-01

358

Condensed Matter Physics  

Microsoft Academic Search

Condensed matter physics constitutes nowadays an enormous field of knowledge. To write a good textbook covering all main topics in that field in a suitable way and in a reasonable volume is very hard indeed. I believe Michael Marder has achieved this goal with great success. The text is arranged in six parts. Part I describes the atomic structure of

I Strzalkowski

2000-01-01

359

Condensate removal device  

SciTech Connect

A condensate removal device is disclosed which incorporates a strainer in unit with an orifice. The strainer is cylindrical with its longitudinal axis transverse to that of the vapor conduit in which it is mounted. The orifice is positioned inside the strainer proximate the end which is remoter from the vapor conduit.

Maddox, J.W.; Berger, D.D.

1984-10-23

360

MUNICIPAL LANDFILL GAS CONDENSATE  

EPA Science Inventory

New regulations relative to air emissions from municipal landfills may require the installation of gas collection systems at landfills. As landfill gas (LFG) is collected, water and other vapors in the gas condense in the system or are purposely removed in the normal treatment of...

361

Soft Condensed Matter  

Microsoft Academic Search

The author states in the preface of the book that the aim is '...to give a unified overview of the various aspects of the physics of soft condensed matter'. The book succeeds in fulfilling this aim in many respects.i) The style is fluent and concise and gives the necessary explanations to make its content understandable to people with some knowledge

Richard A L Jones

2002-01-01

362

Modular invariant gaugino condensation  

SciTech Connect

The construction of effective supergravity lagrangians for gaugino condensation is reviewed and recent results are presented that are consistent with modular invariance and yield a positive definite potential of the noscale type. Possible implications for phenomenology are briefly discussed. 29 refs.

Gaillard, M.K.

1991-05-09

363

Synthesis and Spectroscopic Analysis of a Cyclic Acetal: A Dehydration Performed in Aqueous Solution  

NASA Astrophysics Data System (ADS)

The treatment of aldehydes (and ketones) with diols in the presence of acid gives acetals (and ketals) in an equilibrium reaction. Treatment of pentaerythritol with benzaldehyde in aqueous acid gives the monoacetal, 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane. The reaction has a number of interesting features. The isolated product is the monobenzal not the dibenzal, and the reaction, a dehydration, is performed in water. The reaction proceeds to provide the acetal owing to the insolubility of the product in the aqueous reaction medium, thus removing the product from the equilibrium. This experiment is suitable for incorporation into the undergraduate organic laboratory as the synthesis of a product for characterization by melting point, solubility, and proton nuclear magnetic resonance. Only through recognition of the three-dimensional structure of the dioxane ring can students explain the appearance of the 1H NMR spectrum of the product. The hydroxymethyl groups of the product are inequivalent, as are the hydrogens of the methylenes in the ring. The experiment may also be presented as a group exercise to optimize the conditions of a reaction to maximize the yield of the desired product.

Collard, David M.; Jones, Adolphus G.; Kriegel, Robert M.

2001-01-01

364

Biomarker reproducibility in exhaled breath condensate collected with different condensers  

Microsoft Academic Search

Optimal collection and analysis of exhaled breath condensate (EBC) are prerequisites for standardisation and reproducibility of assessments. The present study aimed to assess reproducibility of EBC volume, hydrogen peroxide (H2O2), 8-isoprostane and cytokine measurements using different condensers, including a newly developed glass condenser. At four points in time, 30 healthy subjects performed sequential EBC collections randomly using the following four

P. P. Rosias; C. M. Robroeks; A. Kester; G. J. den Hartog; W. K. Wodzig; G. T. Rijkerse; L. J. Zimmermann; C. P. van Schayck; Q. Jobsis; E. Dompeling

2008-01-01

365

Alteration and Dehydration in the Parent Asteroid of Allende  

NASA Astrophysics Data System (ADS)

CV3 chondrites experienced various degrees of late-stage modification, including: fayalitic rims around forsteritic grains, secondary mineralization (e.g., nepheline, sodalite, magnetite) in CAIs and chondrules, and formation of phyllosilicates [1]. Our literature survey show that these secondary features probably have a related origin [2]. Although an asteroidal origin is generally accepted for most phyllosilicates [3] and proposed for magnetite [4], the other secondary features have been attributed to reactions of CV3 components with a hot (> 1500 K) and oxidized (H2O/H2 about 1) nebular gas [5]. The Allende meteorite is considered to be a primitive CV3, because phyllosilicates are absent in the matrix and metamorphic effects are not apparent [6]. However, all other secondary features are well-developed. Studies of dark inclusions (DIs) in CV3s [7] provide a key to understanding the secondary features in Allende. Mineralogical, chemical and isotopic data indicate that DIs and CV3s have related origins. Matrices of the DIs resemble the Allende matrix, but the chondrules show a wider range of alteration textures. In some DIs, the chondrules have only fayalitic rims like those in Allende, but in others there are chondrule-shaped regions of porous fayalitic olivine. In DIs of intermediate type, the chondrules consist of forsteritic cores, which have fayalitic rims, surrounded by porous fayalitic olivine. We conclude that the sequence observed among DIs reflects various degrees of replacement of chondrules by fayalitic olivine. The presence of veins of fayalitic olivine, nepheline and Ca-pyroxene throughout DIs [7] which experienced the most pervasive alteration argues for asteroidal processing of DIs. Like Kojima and Tomeoka [7], we infer that porous fayalitic olivine formed by metamorphic dehydration of phyllosilicates on an asteroid. We suggest that the Allende host and Allende-like DIs represent the initial stages of the alteration sequence from material similar to reduced CV3s. Nearly all of the matrix, the outer edges of the chondrules and the mesostases were aqueously altered to phyllosilicates. Magnetite and Ni-rich sulfides formed at this time. Subsequent heating of Allende resulted in equilibration of opaque assemblages at about 770 K and high fO2 and fS2 [4], dehydration of the phyllosilicates and formation of fayalitic rims and plate-like matrix olivine. Nepheline and sodalite, which occur in veins and/or intergrowths with fayalitic olivine in Allende DIs and matrix, and as alteration products in chondrules and CAIs along with grossular, wollastonite, hedenbergite, and andradite, probably formed simultaneously with fayalitic olivine. Inferred initial ^26Al/^27Al ratios in grossular and sodalite, show that CAI alteration occurred at least 2-4 Myr after CAI crystallization [8]. Variations in the initial ^129I/^127I for chondrules and CAIs in Allende suggest that the alteration lasted for about 10 Myr [9]. Oxidation during aqueous alteration and dehydration of the Allende components also provides a simple explanation for the absence of phyllosilicates in the Allende matrix, depletions in planetary noble gases [10], interstellar SiC, diamonds, and graphite [11]. We thank K. Tomeoka, T. Kojima and P. Buchanan for critical discussions. This work was supported by NASA grant NAGW-3281. References: [1] Krot A. N. and Scott E. R. D. (1995) LPS XXVI, 803-804. [2] Scott E. R. D. et al. (1995) LPS XXVII. [3] Keller L. P. et al. (1994) GCA, 58, 5589-5598. [4] Blum J. D. et al. (1989) GCA, 53, 543-556. [5] Palme H. et al. (1991) Meteoritics, 25, 383. [6] Weinbruch S. et al. (1994) GCA, 58, 1019-1030. [7] Kojima T. and Tomeoka K. (1994) Meteoritics, 29, 484. [8] Davis A. M. et al. (1994) LPS XXV, 315-316. [9] Swindle T. D. et al. (1988) GCA, 52, 2215-2227. [10] McSween H. Y. Jr. (1977) GCA, 41, 1777-1790. [11] Huss G. R. and Lewis R. S. (1995) GCA, 59, 115-160.

Krot, A. N.; Scott, E. R. D.; Zolensky, M. E.

1995-09-01

366

Computer program predicts condenser cleanliness  

SciTech Connect

Depending on unit size, condenser tube fouling can cost a utility hundreds of thousands of dollars per year in lost efficiency. Because the condenser is the largest heat exchanger in the condensate-feed-water circuit, condenser performance can significantly affect unit heat rates. This paper reports that good condenser monitoring procedures can improve efficiency and avoid tube corrosion and fouling. The primary cause of poor performance in cooling water condensers is tube fouling, a problem which can result from a variety of mechanisms. Two of the most common are mineral deposition on internal tube surfaces, and microbiological growth on the cooling water side of the condenser. In addition, air leakage through the condenser shell or auxiliary equipment can blanket the steam side of the tubes with undissolved gases. Although each of these contaminants has its own characteristics, all of them have the same effect: they reduce heat transfer.

Buecker, B.

1992-06-01

367

The Chemistry of Gypsum and its Dehydration Products. Translated Works. Volume I.  

National Technical Information Service (NTIS)

Selected papers from the Soviet and Polish literature on the chemistry of gypsum and its dehydration products was translated into English. The topics covered include the solution and solid state dehydration and rehydration of gypsum and the growth of gyps...

S. E. Edinger

1972-01-01

368

Evidence for Human Adaptive Response to Dehydration: Increase of Circulating Protein Mass,  

National Technical Information Service (NTIS)

Previously, it was believed that humans do not adapt to dehydration. Data are presented here showing that within 15 hours after dehydration is reached, humans increase circulating protein mass to facilitate the redistribution of body water from the inters...

M. N. Sawka C. B. Wenger

1987-01-01

369

Gas condensates as diesel fuel  

Microsoft Academic Search

The data of Table 1 show that the distillation curve of the gas condensate from the Yangi-Kazgan field matches that of A-72 gasoline; the Gazli condensate corresponds to light TS-I jet fuel; the Urtabulak, Gazli-Neft', and Urengoi condensates correspond to wide-cut jet fuel; the Kultak, Zevardy, l~barek, and Shurtan condensates correspond to wide-cut engine fuel. It will be noted that

A. A. Kukushkin; V. S. Azev; G. N. Gerasimova; V. M. Aprelenko; A. I. Kirsanov

1985-01-01

370

Nanostructure-induced DNA condensation  

NASA Astrophysics Data System (ADS)

The control of the DNA condensation process is essential for compaction of DNA in chromatin, as well as for biological applications such as nonviral gene therapy. This review endeavours to reflect the progress of investigations on DNA condensation effects of nanostructure-based condensing agents (such as nanoparticles, nanotubes, cationic polymer and peptide agents) observed by using atomic force microscopy (AFM) and other techniques. The environmental effects on structural characteristics of nanostructure-induced DNA condensates are also discussed.

Zhou, Ting; Llizo, Axel; Wang, Chen; Xu, Guiying; Yang, Yanlian

2013-08-01

371

Nanostructure-induced DNA condensation.  

PubMed

The control of the DNA condensation process is essential for compaction of DNA in chromatin, as well as for biological applications such as nonviral gene therapy. This review endeavours to reflect the progress of investigations on DNA condensation effects of nanostructure-based condensing agents (such as nanoparticles, nanotubes, cationic polymer and peptide agents) observed by using atomic force microscopy (AFM) and other techniques. The environmental effects on structural characteristics of nanostructure-induced DNA condensates are also discussed. PMID:23838744

Zhou, Ting; Llizo, Axel; Wang, Chen; Xu, Guiying; Yang, Yanlian

2013-09-21

372

On detonation diffraction in condensed-phase explosives  

Microsoft Academic Search

We consider cases that are designed to model condensed-phase explosives to study the diffraction of a detonation into an unconfined region of explosive. We use direct numerical simulations and study dynamic transients in self-similar coordinates. We consider an ideal equation of state and state-insensitive and state-sensitive reaction rate laws that mimic condensed explosives. We find through an analysis of shock

Bradley L. Wescott

2005-01-01

373

DEHYDRATION OF ALCOHOLS VIA PERVAPORATION USING A NOVEL HYDROHILIC MEMBRANE  

EPA Science Inventory

Pervaporation has emerged as an economically viable alternative technology for the dehydration of organic solvents, removal of organic compounds from water and organic/organic separations. Development of a suitable membrane system with high flux and high selectivity plays a criti...

374

DEHYDRATION OF ALCOHOLS VIA PREVAPORATION USING A NOVEL HYDROPHILIC MEMBRANE  

EPA Science Inventory

Pervaporation has emerged as an economically viable alternative technology for the dehydration of organic solvents, removal of organic compounds from water and organic/organic separations. Development of a suitable membrane system with high flux and high selectivity plays a criti...

375

Peptide translocators with engineered dehydration-prone hydrogen bonds  

NASA Astrophysics Data System (ADS)

The unfavorable crossing of cell membranes by water-soluble peptides poses a challenge to peptide-based drug delivery. Thus the authors engineered a conformational switch that modulates cellular translocation. The peptide design hinges on dehydration propensities of hydrogen bonds that form to mitigate polar-group internalization penalties and is experimentally corroborated through cell-internalization assays.

Maddipati, Sridhar; Fernández, Ariel

2007-02-01

376

Dehydration, dehydroxylation, and rehydroxylation of single-walled aluminosilicate nanotubes.  

PubMed

Single-walled metal oxide (aluminosilicate) nanotubes are excellent candidates for addressing the long-standing issue of functionalizing nanotube interiors, due to their high surface reactivity and controllable dimensions. However, functionalization of the nanotube interior is impeded by its high surface silanol density (9.1 -OH/nm(2)) and resulting hydrophilicity. Controlled dehydration of the nanotubes is critical for the success of functionalization efforts. We employ a range of solid-state characterization tools to elucidate dehydration and dehydroxylation phenomena in the nanotubes as a function of heat treatment up to 450 degrees C. Vibrational spectroscopy (Fourier transform infrared, FT-IR), thermogravimetric analysis-mass spectrometry (TGA-MS), nitrogen physisorption, solid-state NMR, and X-ray diffraction (XRD) reveal that a completely dehydrated condition is achieved at 250 degrees C under vacuum and that the maximum pore volume is achieved at 300 degrees C under vacuum due to partial dehydroxylation of the dehydrated nanotube. Beyond 300 degrees C, further dehydroxylation partially disorders the nanotube wall structure. However, a unique rehydroxylation mechanism can partially reverse these structural changes upon re-exposure to water vapor. Finally, detailed XRD simulations and experiments allow further insight into the nanotube packing, the dimensions, and the dependence of nanotube XRD patterns on the water content. PMID:20684571

Kang, Dun-Yen; Zang, Ji; Wright, Elizabeth R; McCanna, Arthur L; Jones, Christopher W; Nair, Sankar

2010-08-24

377

Science Study Aids 1: Dehydration for Food Preservation.  

ERIC Educational Resources Information Center

|This publication is the first of a series of seven supplementary investigative materials for use in secondary science classes providing up-to-date research-related investigations. This unit is structured for grades 9 through 12. It is concerned with the osmatic dehydration of fruits. The guide provides students with information about food…

Boeschen, John; And Others

378

Nutrient losses during drying and storage of dehydrated foods  

Microsoft Academic Search

The loss of nutrients during processing and storage of foods is an important quality aspect that must be considered by the processor. With respect to dehydration, problems exist in interpreting or predicting losses due to the time?temperature?moisture gradient existing during the process. During storage, moisture may also change. This review summarizes the kinetic data available on nutrient losses and shows

Theodore P. Labuza; Steven R. Tannenbaum

1972-01-01

379

Methylene blue adsorption from aqueous solution by dehydrated peanut hull  

Microsoft Academic Search

Dyes are colour organic compounds which can colorize the other substances. These substances usually presents in the effluent water of many industries, such as textiles, leather, paper, printing and cosmetics. To observe the potential feasibility of removing colour, peanut hull as an agricultural by-product was dehydrated with sulphuric acid (DPH) and used for adsorption of methylene blue (MB) from aqueous

Dursun Özer; Gülbeyi Dursun; Ahmet Özer

2007-01-01

380

The early history of the treatment for dehydration.  

PubMed

The difficulties of managing dehydration in infants, along with the special problems of infant feeding in the wake of the industrial revolution, led to the specialty of pediatrics. The scientific and clinical beginnings that preceded the specialty are reviewed; much that came later can be credited to pediatric scientists. PMID:9452711

Finberg, L

1998-01-01

381

POULTRY EXCRETA DEHYDRATION AND UTILIZATION: SYSTEM DEVELOPMENT AND DEMONSTRATION  

EPA Science Inventory

A manure handling and drying system involving caged layers with daily manure collection, air drying, and dehydration in a flash-type dryer has been studied. Objectives of the study were to: (1) Develop a complete manure handling system to maximize pollution control; (2) determine...

382

Catalytic dehydration of cyclohexanol on magnesium sulfate-protactinium-231  

Microsoft Academic Search

In contrast to the previously found effect of radiation from S35 and C45 on the catalytic activity of magnesium sulfate in the dehydration of cyclohexanol, the action ofa-particles from Pa231 does not alter its catalytic activity.

Vikt. I. Spitsyn; A. A. Balandin; N. P. Dobrosel'skaya; R. A. D'yachkova

1964-01-01

383

Dehydration Kinetics and Glass Transition of Poly(Acrylic Acid).  

National Technical Information Service (NTIS)

The kinetics of dehydration and decarboxylation as well as the glass transition temperature as a function of anhydride content were measured for poly(acrylic acid). It was found that the glass transition of PAA is of the order of 103C and increases with i...

A. Eisenberg T. Yokoyama E. Sambalido

1968-01-01

384

Dehydration Selectively Increases Dopamine Synthesis in Tuberohypophyseal Dopaminergic Neurons  

Microsoft Academic Search

The concentration of dopamine (DA) and the accumulation of DOPA following the administration of a decarboxylase inhibitor were determined in the rat striatum, median eminence and posterior pituitary, regions containing terminals of nigrostriatal, tuberoinfundibular and tuberohypophyseal DA nerves, respectively. Severe dehydration (2 days water deprivation followed by 3 days of 2% NaCI substituted for drinking water) incressed the concentration of

R. H. Alper; K. T. Demarest; K. E. Moore

1980-01-01

385

The Jewish patient and terminal dehydration: A hospice ethical dilemma  

Microsoft Academic Search

Culturally competent nursing care regarding the ethical dilemma of terminal dehydration (withholding or withdrawing food and fluid) for the Jewish hospice patient involves applying the ethical principles of justice, autonomy, beneficence, and nonmaleficence to nursing interventions by identifying outcomes that focus on the high value Jews place on life; avoiding stereotyping as to what it means to be Jewish; knowledge

Janet Bodell; Marie-Ange Weng

2000-01-01

386

Hypodermoclysis to treat dehydration: a review of the evidence.  

PubMed

Dehydration is a serious acute condition in older adults associated with significant morbidity and mortality. Hypodermoclysis (HDC; the infusion of fluids into the subcutaneous tissue) can provide an alternative to intravenous (i.v.) rehydration of older adults. This article reviews the relevant literature on the use of HDC to treat mild to moderate dehydration in older adults. A comprehensive search of the literature was conducted to identify research reports on the use of HDC to treat dehydration in older adults. Articles published in English during the previous 10 years were reviewed to reflect current standards of practice. One systematic review; two randomized, controlled trials; and six cohort studies were identified and appraised. Only one study was conducted in the United States; the remainder were conducted in Europe, Asia, and Canada. The evidence indicated that HDC is as effective as i.v. rehydration of older adults with mild to moderate dehydration. The literature cites advantages of HDC over i.v. hydration, including the same number of or fewer complications, cost savings, greater patient comfort, and less nursing time to start and maintain the infusion. It remains unclear from the literature why HDC is used infrequently in the United States. PMID:17971137

Remington, Ruth; Hultman, Todd

2007-10-29

387

Double seismic zone and dehydration embrittlement of the subducting slab  

Microsoft Academic Search

Dehydration embrittlement of metamorphosed oceanic crust and mantle in the subducting slab may be responsible for the occurrence of intermediate-depth earthquakes. We explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast Japan, southwest Japan, northeast Taiwan, northern Chile, Cape Mendocino, and eastern Aleutians. We calculate transient temperature structures of slabs based

Tadashi Yamasaki; Tetsuzo Seno

2003-01-01

388

When to treat dehydration in a terminally ill patient?  

Microsoft Academic Search

The need to treat dehydration in terminally ill patients has become a very controversial topic. Numerous reports in the literature\\u000a illustrate opposing viewpoints from both clinical and ethical perspectives. Arguments for the maintenance of hydration in\\u000a terminally ill patients have tended to come from \\

R. L. Fainsinger; Eduardo Bruera

1997-01-01

389

Potential of calorimetry to study osmotic dehydration of food materials  

Microsoft Academic Search

A new method, thermocalorimetry, was developed to study osmotic dehydration. The kinetic data from the method was comparable to more traditional methods in the determination of rate constants for water loss. Thermocalorimetry measurements indicated a 2–3 kinetic phases, a relatively rapid process followed by a relatively slow process. The first phase is possibly due to water removal from the cut

C. Tortoe; J. Orchard; A. Beezer; M. O’Neil

2007-01-01

390

Apparatus for the dehydration of waste and vegetable matter  

SciTech Connect

An apparatus is disclosed for dehydrating organic waste material in a rotary oven. The oven is within an insulated chamber and the oven is heated by a burner. The waste gases from the oven are recycled and burnt in the burner. The dried product is usable for soil enrichment and for feeding to animals.

Trouillard, C.

1980-03-04

391

Study of wound dressing structure and hydration/dehydration properties  

NASA Astrophysics Data System (ADS)

Hydrogels manufactured by radio-induced crosslinking and simultaneous sterilisation of hydrogels of PVP, PEG and agar, according to the Rosiak method, have many desirable properties for using as wound dressings. However, some properties need to be improved or better controlled. The membranes need to be strong enough to be freely used. Another important property to be controlled is the capacity of absorption of exudate and the kinetics of drying. Therefore, it was necessary to understand the role of main parameters (agar, PVP, PEG concentration and dose) in the structure of the net and in the hydration and dehydration properties. The structure of the membranes was studied by sol analysis and the hydrating/dehydrating properties were studied by isothermal thermogravimetric analysis. The gel content for all samples were always in agreement with expected values considering that only PVP undergoes crosslinking. The hydrating and dehydration results did not show variation with the tested parameters. It was concluded that the network was solely composed of crosslinked PVP plasticezed by the other compounds. The properties of hydration/dehydration is related rather to diffusion than to capillarity or osmose and to the chemical retention of water in the polymeric matrix.

Lugão, A. B.; Machado, L. D. B.; Miranda, L. F.; Alvarez, M. R.; Rosiak, J. M.

1998-06-01

392

Dehydrating Magnesium Chloride by Double-Salt Decomposition.  

National Technical Information Service (NTIS)

Federal Bureau of Mines studies show that some organic hydrochlorides can be used as dehydrating agents for producing anhydrous MgCl2 from hydrates and brines. Double salts are formed, and these salts dissociate without decomposition of the magnesium chlo...

J. T. May V. E. Edlund D. C. Seidel

1978-01-01

393

Reconstruction of orbital fractures with dehydrated human dura mater  

Microsoft Academic Search

Purpose: The best method for reconstructing the fractured orbital floor remains controversial. This article evaluates the usefulness of dehydrated human dura mater for orbital floor reconstruction after facial trauma. Patients and Methods: A retrospective analysis of 55 patients who had undergone surgical repair of orbital fractures was performed. The dura mater was used when the disruption was less than 2

Mario F. Muñoz Guerra; Jesús Sastre Pérez; Francisco J. Rodriguez-Campo; Luis Naval Gías

2000-01-01

394

Glacial isostatic adjustment constrains dehydration stiffening beneath Iceland  

NASA Astrophysics Data System (ADS)

During melting in the upper mantle the preferred partitioning of water into the melt will effectively dehydrate the solid residue. Linear extrapolation of laboratory experiments suggests that dehydration can produce a sharp viscosity contrast (increase) of a factor 500 across the dry solidus. In this study we show that the suggested magnitude of dehydration stiffening in a plume-ridge setting is incompatible with the present glacial isostatic adjustment (GIA) in Iceland. Using GPS observations of current GIA in Iceland, we find that the data are best fit by a viscosity contrast over the dry solidus in the range 0.5-3. A viscosity contrast higher than 10 requires a mantle viscosity below the dry solidus lower than 4-8×1018Pas, depending on the thickness of the dehydrated layer. A viscosity contrast of 100 or more demands a mantle viscosity of 1018Pas or less. However, we show here that a non-linear extrapolation of the laboratory data predicts a viscosity contrast as low as a factor 3-29, assuming conditions of constant strain rate to constant viscous dissipation rate. This is compatible with our GIA results and suggests that the plume-ridge interaction beneath Iceland is governed by a non-linear rheology and controlled by a combination of kinematic and dynamic boundary conditions rather than buoyant forces alone.

Schmidt, Peter; Lund, Björn; Árnadóttir, Thóra; Schmeling, Harro

2012-12-01

395

Age, dehydration and fatigue crack growth in dentin.  

PubMed

A preliminary study of the effects from age and dehydration on fatigue crack growth in human dentin was conducted. Compact tension (CT) fatigue specimens of coronal dentin were prepared from extracted molars and subjected to high cycle fatigue (10(5)dehydrated dentin (mean age=20+/-2 years) were examined. Fatigue crack growth rates were quantified according to the Paris Law in terms of the crack growth exponent (m) and coefficient (C). The average fatigue crack growth exponent for the young hydrated dentin (m=13.3+/-1.1) was significantly less than that for the hydrated old (m=21.6+/-5.2; p<0.003) and dehydrated young dentin (m=18.8+/-2.8; p<0.01). Fatigue cracks in the old dentin underwent initiation at a lower stress intensity range than in young dentin and propagated at as significantly faster rate (over 100x). Differences in the microscopic features of the fracture surfaces from the old and young dentin suggested that particular mechanisms contributing to energy dissipation and crack growth resistance in the young hydrated dentin were not present in the old dentin. Based on results of this study, the fatigue crack growth resistance of human dentin decreases with both age of the tissue and dehydration. PMID:16338002

Bajaj, Devendra; Sundaram, Naryana; Nazari, Ahmad; Arola, D

2005-12-09

396

Unexpected Preferential Dehydration of Artemisinin in Ionic Liquids  

NASA Astrophysics Data System (ADS)

Thermodynamic measurements (at 298 K) reveal that a crucial step in the extraction process of the key antimalarial drug artemisinin by ionic liquids (ILs), namely, precipitation through the addition of water, is driven by artemisinin dehydration due to the differences in the water's interaction with the bulk ILs, rather than with the artemisinin itself.

Sanders, Marc W.; Wright, Lawrence; Tate, Lauren; Fairless, Gayle; Crowhurst, Lorna; Bruce, Neil C.; Walker, Adam J.; Hembury, Guy A.; Shimizu, Seishi

2009-09-01

397

Process for the dehydration and liquefaction of water-containing coal  

SciTech Connect

In a process wherein a slurry of water-containing coal and a solvent is heated to 100/sup 0/-350/sup 0/ C and then subjected to vapor-liquid separation by which water vapor is separated from the slurry to obtain a dehydrated slurry, a slurry to be dehydrated is mixed with a part of the dehydrated slurry and then heated. The dehydrated slurry thus obtained is suitable for use as a starting material for the hydrogenolysis of coal.

Komiyama, T.; Kubo, I.; Mori, S.; Ohnishi, N.; Oi, S.; Takata, T.

1982-08-17

398

The effect of blanching and freezing on osmotic dehydration of pumpkin  

Microsoft Academic Search

The aim of this work was to analyze the influence of pretreatment (blanching, freezing) on osmotic dehydration of pumpkin. Pumpkin cubes (10×10×10mm) were dehydrated in sucrose, glucose and starch syrup solutions. The process took 180min. Peleg’s and exponential equations can be satisfactory applied to describe osmotic dehydration of raw and pretreated pumpkin. Osmotic dehydration of pumpkin in sugar solution at

Hanna Kowalska; Andrzej Lenart; Dominika Leszczyk

2008-01-01

399

Condensation Processes in Geothermal Systems  

Microsoft Academic Search

We model condensation processes in geothermal systems to understand how this process changes fluid chemistry. We assume two processes operate in geothermal systems: 1) condensation of a vapor phase derived by boiling an aqueous geothermal fluid into a cool near surface water and 2) condensation of a magmatic vapor by a deep circulating meteoric thermal fluid. It is assumed that

D. I. Norman; J. N. Moore

2005-01-01

400

Mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab.  

PubMed

Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressure-temperature conditions of fluids are few. This report describes CO2-bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaCl-equivalent magnesite crystals, CO2-bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830 °C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO2-bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H2O and affect the chemical evolution of the mantle wedge. PMID:23716664

Kawamoto, Tatsuhiko; Yoshikawa, Masako; Kumagai, Yoshitaka; Mirabueno, Ma Hannah T; Okuno, Mitsuru; Kobayashi, Tetsuo

2013-05-28

401

Effect of a modifying additive on the kinetics and mechanism of the dehydration of phosphoric gypsum  

Microsoft Academic Search

A study was carried out on the effect of a modifying additive on the kinetics of the dehydration of phosphoric gypsum. The\\u000a dehydration of gypsum materials occurs through a mechanism of continuous localization in the bulk of the crystal. The modification\\u000a of phosphoric gypsum leads to a considerable decrease in the activation energy of dehydration.

I. M. Astrelin; V. P. Serbin; A. S. Ptichnikov; A. B. Aleiner

2007-01-01

402

Treatment of mild to moderate dehydration in children with oral rehydration therapy  

Microsoft Academic Search

Purpose: To review current literature on the effectiveness of oral rehydration therapy (ORT) in the treatment of mild to moderate dehydration in children. Data sources: Recommendations from American Academy of Pediatrics (AAP), World Health Organization (WHO), selected research articles (2000-2006), and Internet sources. Conclusions: Dehydration is a common diagnosis in pediatric primary care. The literature indicates that dehydration is more

Kristene C. Diggins

2008-01-01

403

STUDIES ON ALKALINE-EARTH METAL POLYMETAPHOSPHATES PREPARED BY PRECIPITATION AND DEHYDRATION  

Microsoft Academic Search

Barium, strontium, calcium and magnesium polymetaphosphate hydrate powders were prepared by precipitation from aqueous solution and their dehydrations to amorphous anhydrous powders were studied in detail by a variety of physico-chemical methods. Anhydrous barium and strontium polymetaphosphates were formed through two dehydration processes whereas calcium and magnesium polymetaphosphates were formed through dehydration, hydrolysis (with depolymerisation) and repolymerisation processes, over the

A. Packter; W. O. S. Doherty

1983-01-01

404

Antidiuretic Hormone Release in the Monkey During Hypo- and Hyper-Osmotic Dehydration.  

National Technical Information Service (NTIS)

Release of antidiuretic hormone in two types of dehydration was studied in monkeys. It was found that dehydration with high plasma osmolarity led to a tremendous elevation of plasma ADH level, and dehydration with low plasma osmolarity also led to a signi...

T. K. Young R. A. Phillips

1967-01-01

405

Composition and Nutritive Value of Dehydrated Alfalfa for Lactating Dairy Cows  

Microsoft Academic Search

The composition of 85 samples of dehydrated alfalfa grown in the northern agricultural region of Saskatchewan was determined. Differences in composition of dehydrated alfalfa between processing plants were small, and although differ- ences of acid detergent fiber-nitrogen were significant, percent acid detergent fiber-nitrogen in the dry matter was not greater than .22%. Differences between cuttings were also minor. Dehydrated alfalfa

David A. Christensen; M. I. Cochran

1983-01-01

406

Hypernatraemic dehydration in patients in a large hospital for the mentally handicapped  

Microsoft Academic Search

OBJECTIVE--To determine the prevalence of hypernatraemic dehydration and to assess the hydration and nutritional state of patients in a large hospital for the mentally and physically handicapped; also to assess the efficacy of an intervention programme to reduce the prevalence of hypernatraemic dehydration in the hospital. DESIGN--Prospective study of patients admitted with hypernatraemic dehydration from a large hospital for mentally

N. J. Macdonald; K. N. McConnell; M. R. Stephen; M. G. Dunnigan

1989-01-01

407

Global Transcriptional Analysis of Dehydrated Salmonella enterica Serovar Typhimurium  

PubMed Central

Despite the scientific and industrial importance of desiccation tolerance in Salmonella, knowledge regarding its genetic basis is still scarce. In the present study, we performed a transcriptomic analysis of dehydrated and water-suspended Salmonella enterica serovar Typhimurium using microarrays. Dehydration induced expression of 90 genes and downregulated that of 7 genes. Ribosomal structural genes represented the most abundant functional group with a relatively higher transcription during dehydration. Other main induced functional groups included genes involved in amino acid metabolism, energy production, ion transport, transcription, and stress response. The highest induction was observed in the kdpFABC operon, encoding a potassium transport channel. Knockout mutations were generated in nine upregulated genes. Five mutants displayed lower tolerance to desiccation, implying the involvement of the corresponding genes in the adaptation of Salmonella to desiccation. These included genes encoding the isocitrate-lyase AceA, the lipid A biosynthesis palmitoleoyl-acyltransferase Ddg, the modular iron-sulfur cluster scaffolding protein NifU, the global regulator Fnr, and the alternative sigma factor RpoE. Notably, these proteins were previously implicated in the response of Salmonella to oxidative stress, heat shock, and cold shock. A strain with a mutation in the structural gene kdpA had a tolerance to dehydration comparable to that of the parent strain, implying that potassium transport through this system is dispensable for early adaptation to the dry environment. Nevertheless, this mutant was significantly impaired in long-term persistence during cold storage. Our findings indicate the involvement of a relatively small fraction of the Salmonella genome in transcriptional adjustment from water to dehydration, with a high prevalence of genes belonging to the protein biosynthesis machinery.

Gruzdev, Nadia; McClelland, Michael; Porwollik, Steffen; Ofaim, Shany; Pinto, Riky

2012-01-01

408

Global transcriptional analysis of dehydrated Salmonella enterica serovar Typhimurium.  

PubMed

Despite the scientific and industrial importance of desiccation tolerance in Salmonella, knowledge regarding its genetic basis is still scarce. In the present study, we performed a transcriptomic analysis of dehydrated and water-suspended Salmonella enterica serovar Typhimurium using microarrays. Dehydration induced expression of 90 genes and downregulated that of 7 genes. Ribosomal structural genes represented the most abundant functional group with a relatively higher transcription during dehydration. Other main induced functional groups included genes involved in amino acid metabolism, energy production, ion transport, transcription, and stress response. The highest induction was observed in the kdpFABC operon, encoding a potassium transport channel. Knockout mutations were generated in nine upregulated genes. Five mutants displayed lower tolerance to desiccation, implying the involvement of the corresponding genes in the adaptation of Salmonella to desiccation. These included genes encoding the isocitrate-lyase AceA, the lipid A biosynthesis palmitoleoyl-acyltransferase Ddg, the modular iron-sulfur cluster scaffolding protein NifU, the global regulator Fnr, and the alternative sigma factor RpoE. Notably, these proteins were previously implicated in the response of Salmonella to oxidative stress, heat shock, and cold shock. A strain with a mutation in the structural gene kdpA had a tolerance to dehydration comparable to that of the parent strain, implying that potassium transport through this system is dispensable for early adaptation to the dry environment. Nevertheless, this mutant was significantly impaired in long-term persistence during cold storage. Our findings indicate the involvement of a relatively small fraction of the Salmonella genome in transcriptional adjustment from water to dehydration, with a high prevalence of genes belonging to the protein biosynthesis machinery. PMID:22941081

Gruzdev, Nadia; McClelland, Michael; Porwollik, Steffen; Ofaim, Shany; Pinto, Riky; Saldinger-Sela, Shlomo

2012-08-31

409

Modeling of Rapid Direct Contact Condensation.  

National Technical Information Service (NTIS)

The focus of the study is on rapid direct-contact condensation phenomena, that is, direct contact condensation situations characterized by extremely high condensation rates and violent mixing at the liquid-vapor interface. Rapid condensation phenomena ari...

G. B. Wallis H. J. Richter J. A. Valenzuela P. H. Rothe

1985-01-01

410

Ice condensation on sulfuric acid tetrahydrate: Implications for polar stratospheric ice clouds  

NASA Astrophysics Data System (ADS)

The mechanism of ice nucleation to form Type 2 PSCs is important for controlling the ice particle size and hence the possible dehydration in the polar winter stratosphere. This paper probes heterogeneous ice nucleation on sulfuric acid tetrahydrate (SAT). Laboratory experiments were performed using a thin-film, high-vacuum apparatus in which the condensed phase is monitored via Fourier transform infrared spectroscopy and water pressure is monitored with the combination of an MKS baratron and an ionization gauge. Results show that SAT is an efficient ice nucleus with a critical ice saturation ratio of S*ice = 1.3 to 1.02 over the temperature range 169.8-194.5 K. This corresponds to a necessary supercooling of 0.1-1.3 K below the ice frost point. The laboratory data is used as input for a microphysical/photochemical model to probe the effect that this heterogeneous nucleation mechanism could have on Type 2 PSC formation and stratospheric dehydration. In the model simulations, even a very small number of SAT particles (e.g., 10-3 cm-3) result in ice nucleation on SAT as the dominant mechanism for Type 2 PSC formation. As a result, Type 2 PSC formation is more widespread, leading to larger-scale dehydration. The characteristics of the clouds are controlled by the assumed number of SAT particles present, demonstrating that a proper treatment of SAT is critical for correctly modeling Type 2 PSC formation and stratospheric dehydration.

Fortin, T. J.; Drdla, K.; Iraci, L. T.; Tolbert, M. A.

2003-07-01

411

Ice condensation on sulfuric acid tetrahydrate: implications for polar stratospheric ice clouds  

NASA Astrophysics Data System (ADS)

The mechanism of ice nucleation to form Type 2 PSCs is important for controlling the ice particle size and hence the possible dehydration in the polar winter stratosphere. This paper probes heterogeneous ice nucleation on sulfuric acid tetrahydrate (SAT). Laboratory experiments were performed using a thin-film, high-vacuum apparatus in which the condensed phase is monitored via Fourier transform infrared spectroscopy and water pressure is monitored with the combination of an MKS baratron and an ionization gauge. Results show that SAT is an efficient ice nucleus with a critical ice saturation ratio of Sice= 1.3 to 1.02 over the temperature range 169.8-194.5 K. This corresponds to a necessary supercooling of 0.1-1.3 K below the ice frost point. The laboratory data is used as input for a microphysical/photochemical model to probe the effect that this heterogeneous nucleation mechanism could have on Type 2 PSC formation and stratospheric dehydration. In the model simulations, even a very small number of SAT particles (e.g. 10-4 cm-3) result in ice nucleation on SAT as the dominant mechanism for Type 2 PSC formation. As a result, Type 2 PSC formation is more widespread, leading to larger-scale dehydration. The characteristics of the clouds are controlled by the assumed number of SAT particles present, demonstrating that a proper treatment of SAT is critical for correctly modeling Type 2 PSC formation and stratospheric dehydration.

Fortin, T. J.; Drdla, K.; Iraci, L. T.; Tolbert, M. A.

2003-02-01

412

Synthesis and crystal structure of Schiff bases obtained by condensation of 2-aminopyridines with acrylic aldehydes  

Microsoft Academic Search

We synthesized a series of novel imines by reactions of 2-amino-4-methylpyridine with (hetero)aromatic derivatives of acrolein in the presence of molecular sieves (as a dehydrating and acid-catalyzing agent). We determined the molecular and crystal structure of two 2-pyridylazomethines containing the CH=CH–CH=N group by X-ray diffraction analysis.

I. Iovel; L. Golomba; S. Belyakov; E. Lukevics

2000-01-01

413

Topology and Fermionic Condensate  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to investigate an influence of a space-time topology on the formation of fermionic condensate in the model with four-fermion interaction ()2. The value for the space-time with topology of R1 × R1 × S1 is found. Moreover a relation of the value of fermionic condensate to a periodic length is studied. In this connection the possibility of a relation of the topologic deposits to structure of hadrons is discussed.Translated AbstractTopologie und FermikondensatEs wird der Einfluß einer Raum-Zeittopologie auf die Bildung des Fermikondensats in einem Modell mit Vierfermionenwechselwirkung ()2 untersucht. Für eine Raum-Zeit mit der Topologie R1 × R2 × S1 werden die Parameter gegeben. Weiterhin wird die Relation der Größe des Fermikondensats zu einer periodischen Länge untersucht. In diesem Zusammenhang wird die Verbindung des topologischen Depots zur Struktur der Hadronen diskutiert.

Kulikov, I.; Pronin, P.

414

ADHM is tachyon condensation  

Microsoft Academic Search

We completely realize the ADHM construction of instantons in D-brane language of tachyon condensations. Every step of the construction is given a physical interpretation in string theory, in a boundary state formalism valid all order in alpha'. Accordingly, equivalence between Yang-Mills configurations on D4-branes and D0-branes inside the D4-branes is proven, which shows that small instanton configurations of the Yang-Mills

Koji Hashimoto; Seiji Terashima

2006-01-01

415

New technology in condensate polishing  

SciTech Connect

Sulfonic acid ion exchange resins. when carried into a boiler or steam generator, thermally decompose releasing large amounts of corrosive, sulfates. Replacement of the sulfonic acid resin with a carboxylic acid resin would eliminate this source of contamination. The sulfonic acid resin is a strong acid: the carboxylic acid resin is a weak acid. The carboxylic acid resin alone is not capable of splitting salts which limits its use to mixed resin beds or to its use in single or individual beds with feeds of high alkalinity or high pH values. Laboratory, pilot plant and full scale plant tests compared the two resins in precoat filters. When the resins in mixed beds were in the acid form, the weakly acid resin was almost as effective in removing sodium ion as the strongly acid resin. In the ammonium form. the weakly acid resin was generally more effective in removing sodium than the strongly acid resin. Condensate polishing reduced the sodium ion to a few parts per billion (ppB). Complete resin separation before regeneration is more important for the weakly acid resin than for the strongly acid resin. Another development found that the hydrazine reaction with oxygen could be catalyzed by powdered activated carbon combined with microfibers on a Powdex substrate. The carbon should be thoroughly washed to reduce its residual sodium content. In plant tests, the carbon reduced the oxygen concentration in condensate about 50% during startup. In preliminary tests believed to be typical, carbon lowered the oxygen concentration below 10 ppB in about 6 hours compared to 18 hours without the carbon. Oxygen is also reduced during normal operation.

Kunin, R.; Salem, E.; Libutti, B. (Graver Co., Union, NJ (United States). Water Div.)

1992-08-01

416

Synthesis of alcohols from carbon oxides and hydrogen. VIII. A temperature-programmed reaction study of n-butanal on a Zn-Cr-O catalyst  

SciTech Connect

The interaction of n-butanal with a Zn-Cr-O catalyst has been studied by temperature-programmed reaction. Using combined GC, GC-FTIR, and GC-MS techniques, a large number of desorption products have been identified, including 1-butanol, C/sub 8/ and C/sub 12/ aldehydes, C/sub 7/ and C/sub 8/ ketones, and C/sub 3/, C/sub 4/, and C/sub 7/ olefins, as well as CO/sub 2/, dienes, trienes, aromatics, and light hydrocarbons. The formation of most products is explained by assuming surface reactions of two classes of intermediate species originating from the adsorption of n-butanal and from the surface aldol-like condensation of two molecules of n-butanal. Results indicate that the Zn-Cr oxide catalyst is active in performing aldehyde condensation, hydrogenation, hydrolysis, dehydrogenation, decarboxylation, and dehydration, along with isomerization and cracking reactions. Different functionalities are associated with different temperature ranges. The detected chemical functionalities are discussed with respect to their relevance to the direct synthesis of methanol and higher alcohols from CO and H/sub 2/.

Lietti, L.; Botta, D.; Forzatti, P.; Mantica, E.; Tronconi, E.; Pasquon, I.

1988-06-01

417

Hydrothermal Dehydration of Aqueous Fructose Solutions in a Closed System  

SciTech Connect

The synthesis of materials with targeted size and shape has attracted much attention. Specifically, colloidal spheres with targeted and uniform sizes have opened the door for a variety of applications associated with drug delivery, and manipulation of light (photonic band-gap crystals). Surface modification is a key to realizing many of these applications owing to the inherent inert surface.The remarkable transformation of carbohydrate molecules including sugars to homogeneous carbon spheres is found to readily occur by a dehydration mechanism and subsequent sequestering in aqueous solutions that are heated at 160-180oC in a pressurized vessel. Under such conditions, these molecules actually dehydrate even though they are dissolved in water. Size-tunable metal and metal oxides with uniform shells have also been prepared by using carbon spheres as templates.

Yao, Chunhua; Shin, Yongsoon; Wang, Li Q.; Windisch, Charles F.; Samuels, William D.; Arey, Bruce W.; Wang, Chong M.; Risen Jr., William M.; Exarhos, Gregory J.

2007-10-25

418

Confinement Contains Condensates  

SciTech Connect

Dynamical chiral symmetry breaking and its connection to the generation of hadron masses has historically been viewed as a vacuum phenomenon. We argue that confinement makes such a position untenable. If quark-hadron duality is a reality in QCD, then condensates, those quantities that have commonly been viewed as constant empirical mass-scales that fill all spacetime, are instead wholly contained within hadrons; i.e., they are a property of hadrons themselves and expressed, e.g., in their Bethe-Salpeter or light-front wave functions. We explain that this paradigm is consistent with empirical evidence, and incidentally expose misconceptions in a recent Comment.

Brodsky, Stanley J.; Roberts, Craig D.; Shrock, Robert; Tandy, Peter C.

2012-03-12

419

Cosmological tachyon condensation  

SciTech Connect

We consider the prospects for dark matter/energy unification in k-essence type cosmologies. General mappings are established between the k-essence scalar field, the hydrodynamic and braneworld descriptions. We develop an extension of the general relativistic dust model that incorporates the effects of both pressure and the associated acoustic horizon. Applying this to a tachyon model, we show that this inhomogeneous 'variable Chaplygin gas' does evolve into a mixed system containing cold dark matter like gravitational condensate in significant quantities. Our methods can be applied to any dark energy model, as well as to mixtures of dark energy and traditional dark matter.

Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D. [Rudjer Boskovic Institute, 10002 Zagreb (Croatia); Centre of Theoretical Physics and Astrophysics, University of Cape Town, Rondebosch 7701 (South Africa)

2009-07-15

420

Confinement contains condensates  

NASA Astrophysics Data System (ADS)

Dynamical chiral symmetry breaking and its connection to the generation of hadron masses has historically been viewed as a vacuum phenomenon. We argue that confinement makes such a position untenable. If quark-hadron duality is a reality in QCD, then condensates, those quantities that have commonly been viewed as constant empirical mass scales that fill all space-time, are instead wholly contained within hadrons; i.e., they are a property of hadrons themselves and expressed, e.g., in their Bethe-Salpeter or light-front wave functions. We explain that this paradigm is consistent with empirical evidence and incidentally expose misconceptions in a recent Comment.

Brodsky, Stanley J.; Roberts, Craig D.; Shrock, Robert; Tandy, Peter C.

2012-06-01

421

Atomic structure and dehydration mechanism of amorphous silica: Insights from 29Si and 1H solid-state MAS NMR study of SiO2 nanoparticles  

NASA Astrophysics Data System (ADS)

Detailed knowledge of the atomic structure of hydrous species on surface of amorphous silica and the effect of temperature and particle size on their atomic configurations are essential to understand the nature of fluids-amorphous silicates interactions and the dehydration processes in the amorphous oxides. Here, we report the 29Si, 1H MAS, and 1H-29Si heteronuclear correlation (HetCor) NMR spectra of 7 nm and 14 nm amorphous silica nanoparticles—a model system for natural amorphous silica—where previously unknown details of changes in their atomic structures with varying dehydration temperature and particle size are revealed. Diverse hydroxyl groups with varying atomic configurations and molecular water apparently show distinct dehydration trends. The dehydration (i.e., removal of water) of amorphous silica nanoparticles mostly results in the increase of isolated silanol by removing water molecules from hydrogen-bonded silanols associated water molecules. With further increase in dehydration temperature, the intensity of isolated silanol peak decreases above ˜873 K, suggesting that the condensation of isolated silanol may occur mainly above ˜873 K. The entire dehydration (and dehydroxylation) process completes at ˜1473 K. Both the water (i.e., physisorbed water and hydrogen-bonded water) and hydrogen-bonded silanol species show a dramatic change in the slope of intensity variation at ˜873 K, indicating that most of silanols is hydrogen-bonded to water rather than to other silanols. The fraction of hydrogen-bonded proton species is also much smaller in 14 nm amorphous silica nanoparticles than in 7 nm amorphous silica nanoparticles mainly due to the presences of larger fractions of water and hydrogen-bonded silanol species. 29Si NMR results show that with increasing dehydration temperature, the fraction of Q4 species apparently increases at the expense of Q2 and Q3 species. The fractions of Q2 and Q3 structures in 7 nm amorphous silica nanoparticles are larger than those in 14 nm amorphous silica nanoparticles. Dehydration of 7 nm amorphous silica nanoparticles occurs at a lower temperature than that of 14 nm amorphous silica nanoparticles. 29Si MAS NMR results show that a possible simultaneous dehydroxylation can also occur with removal of the hydrogen bonded silanol in the 7 nm silica nanoparticles. The energy penalty of dehydroxylation estimated from 29Si MAS NMR spectra varies with Q species and is smaller in 7 nm than in 14 nm amorphous silica nanoparticles. These results demonstrate that the particle size of nanoparticles plays an important role in controlling the hydrogen contents, and thus overall hydrogen bond strength of hydroxyl groups and atomic structure of silanols can control dehydroxylation of amorphous silica nanoparticles. The structural information and mechanistic details obtained from the current study provide insights into the structure of hydrous species and dehydration mechanisms in crystalline and amorphous silicates in diverse geological settings, highlighting usually unknown effects of particle size on the dehydration processes.

Kim, Hyun Na; Lee, Sung Keun

2013-11-01

422

Dehydration in cryopreservation of moist plant tissues and seed maturation  

Microsoft Academic Search

The feasibility of long-term cryopreservation of plant objects depends on their moisture content. In orthodox seed, dehydration\\u000a takes place at the late stage of maturation and is accompanied by accumulation of protective sugars and proteins. Such seed\\u000a easily withstand cryopreservation. Moist objects such as meristems and recalcitrant seed must be desiccated in the presence\\u000a of sucrose before freezing. In both

E. P. Chetverikova

2008-01-01

423

The geometric isomers of conjugated octadecadienoates from dehydrated methyl ricinoleate  

Microsoft Academic Search

The dehydration of methyl ricinoleate by heatingin vacuo in the presence of KHSO4 resulted in the formation of the following conjugated octadecadienoates expressed as a percentage of the final product:cis, trans (trans, cis), 14.3;cis, cis, 11.2;trans, trans, 7.3. The isomers contained the double bonds predominantly in the 9,11 position but the possible presence of traces of 8,10\\u000a and other conjugated

D. R. Body; F. B. Shorland

1965-01-01

424

Influence of heat-stress induced dehydration on mental functions  

Microsoft Academic Search

The effect of primary dehydration of various levels (1, 2 and 3% body-weight deficits) on mental functions of different complexities were studied in eight heat-acclimatized subjects drawn from tropical regions of India. These subjects were also studied after a bout of exercise in heat under two conditions viz., Hot Dry (45°C DB, 30% rh), and Hot Humid (39DC DB, 60%

V. M. SHARMA; K. SRIDHARAN; G. PICHAN; M. R. PANWAR

1986-01-01

425

DEHYDRATION OF PRIMARY DODECYL ALCOHOL BY MAGNESIUM SULPHATE  

Microsoft Academic Search

MgSOâ containing normal suIfur and radioactive S³⁵ (l6.6 and ; 19.l mc\\/g) was used as a catalyst in the dehydration of n-dodecanol. The yield ; of unsaturated hydrocarbons was determined by bromine titration. The yield of ; unsaturated hydrocarbons is lower with the use of a radioactive catalyst MgS\\/sup ; 35\\/Oâas compared with the yield with a non-radioactive catalyst MgSOâ.

I. Spitsyn; I. E. Mikhailenko; G. N. Pirogova

1961-01-01

426

Colour and flavour changes during osmotic dehydration of fruits  

Microsoft Academic Search

Andes berry (Rubus glaucus Benth.) and tamarillo (Solanum betaceum Cav., dark-red strain) fruit were separately submitted to osmotic dehydration with three different osmotic agents: sucrose (70%), sucrose (70%)-glycerol (65%) 1:1, and ethanol. This process decreased the water activity in the fruits and promoted the transfer of main pigments (anthocyanins) and flavour constituents to the osmotic solutions. Tristimulus colorimetry was applied

Coralia Osorio; Martha Sofía Franco; Maria Paola Castaño; Maria Lourdes González-Miret; Francisco J. Heredia; Alicia Lucía Morales

2007-01-01

427

Effect of water activity on carotenoid degradation in dehydrated carrots  

Microsoft Academic Search

The effect of water activity on the stability of carotenoids in dehydrated carrots was studied.Freeze-dried carrots from blanched and unblanched batches were placed in air-tight glass jars containing saturated salt solutions with water activity ranging from 0.052 to 0.75, at 40°C. The equilibrium moisture, water activity, ?- and ?-carotene, and lutein contents were analysed at different storage times.The Guggenheim–Anderson–de Boer

Vera Lavelli; Bruno Zanoni; Anna Zaniboni

2007-01-01

428

Microwave-assisted air dehydration of apple and mushroom  

Microsoft Academic Search

Microwave-assisted hot-air dehydration of apple and mushroom was performed with low-power microwave energy. The purpose of the investigation was to compare hot-air drying and microwave-assisted hot-air drying. The air velocity, the microwave output power and the air temperature were the variables in the experiments. The microwave energy was supplied by either microwave applicators with transverse magnetic (TM) modes as dominant

Tomas Funebo; Thomas Ohlsson

1998-01-01

429

Salt depletion and dehydration in hypertensive preterm infants  

Microsoft Academic Search

.   Three preterm infants presented with both severe or moderate arterial hypertension and dehydration due to increased water\\u000a and sodium urinary excretion. In patient 1, water and sodium wasting were extremely severe and peaked at 575 ml\\/kg per day\\u000a and 73 mEq\\/kg per day, respectively. In all infants, urinary water and sodium excretion dramatically decreased when hypertension\\u000a resolved. The overall

J. B. Gouyon; S. Bernardini; D. S. Semama; M. Francoise

1997-01-01

430

30. BUILDING NO. 527, DEHYDRATING PRESSES, LOOKING SOUTH. ALUMINUM NARROWGUAGE ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

30. BUILDING NO. 527, DEHYDRATING PRESSES, LOOKING SOUTH. ALUMINUM NARROW-GUAGE GONDOLA CAR IN LEFT BACKGROUND BROUGHT MOISTENED GUN COTTON FROM REST HOUSE (BUILDING NO. 320-B) IN CANS. (ONE OF THESE CANS IS ON UNLOADING PLATFORM RUNNING BESIDE PRESSES). CONTENTS OF CANS WERE UNLOADED INTO PRESSES BY HAND. - Picatinny Arsenal, 500 Area, Powder Factory & Power House, State Route 15 near I-80, Dover, Morris County, NJ

431

Selective brain cooling in goats: effects of exercise and dehydration.  

PubMed

1. Measurements of brain and central blood temperature (Tbr and Tbl), metabolic rate (MR) and respiratory evaporative heat loss (REHL) were made in trained goats walking on a treadmill at 4.8 km h-1 at treadmill inclines of 0, 5, 10, 15 and 20% when they were fully hydrated and at 0% when they had been deprived of water for 72 h. 2. In hydrated goats, exercise MR increased progressively with increasing treadmill incline. Both Tbl and Tbr rose during exercise, but Tbl always rose more than Tbr, and selective brain cooling (SBC = Tbl - Tbr) increased linearly with Tbl. Significant linear relationships were also present between REHL and Tbl and between SBC and REHL. Neither the slope of the regression relating SBC to Tbl nor the threshold Tbl for onset of SBC was affected by exercise intensity. Manual occlusion of the angularis oculi veins decreased SBC in a walking goat, while occlusion of the facial veins increased SBC. 3. Dehydrated goats had higher levels of Tbl, Tbr and SBC during exercise, but the relationship between SBC and Tbl was the same in hydrated and dehydrated animals. In dehydrated animals, REHL at a given Tbl was lower and SBC was thus maintained at reduced rates of REHL. 4. It is concluded that SBC is a linear function of body core temperature in exercising goats and REHL appears to be a major factor underlying SBC in exercise. The maintenance of SBC in spite of reduced REHL in dehydrated animals could be a consequence of increased vascular resistance in the facial vein and increased flow of cool nasal venous blood into the cranial cavity. PMID:8120829

Baker, M A; Nijland, M J

1993-11-01

432

Hetero-azeotropic distillation: combining fungal dehydration and lipid extraction.  

PubMed

A low-cost single-stage laboratory process combining fungal dehydration and lipid extraction was compared with a traditional two-stage method employing freeze-drying and subsequent mechanical disruption in the presence of solvent. The ability of a number of organic solvents to form hetero-azeotropes with water was exploited. Chloroform, cyclohexane and hexane were assessed in their abilities to both dry and extract lipid from the oleaginous phycomycete Mortierella alpina (ATCC 32222). Drying rate and lipid extraction were maximised under conditions that prevented fungal agglomeration. The total processing time was limited by the rate of dehydration rather than by the rate of lipid extraction. In all cases azeotropic distillation facilitated a greater rate of dehydration than was possible with freeze-drying. A consequent reduction in overall processing time was observed. Uniquely, both the solvent used and the mode of mixing employed controlled the morphology of the aggregates formed during distillation. In combination with mild mixing chloroform discouraged agglomeration whereas cyclohexane and hexane promoted aggregation. Successful lipid extraction was dependent on the use of dry biomass rather than on the application of heat to effect distillation. Neither the application of heat nor the solvent employed had any significant effect on the lipid composition of the extracted oil. PMID:16232815

Tough, A J; Isabella, B L; Beattie, J E; Herbert, R A

2000-01-01

433

Cryopreservation of Vanda coerulea protocorms by encapsulation-dehydration.  

PubMed

Protocorms of Vanda coerulea were successfully cryopreserved by encapsulation-dehydration in combination with a loading solution. Protocorms were selected 70 days after sowing seeds harvested from 7-month-old fruits. After encapsulation in an alginate matrix composed of 2 percent Na-alginate, 2 M glycerol plus 0.4 M sucrose (loading solution), the protocorms were precultured in modified Vacin and Went (1949) (VW) liquid medium supplemented with 0.7 M sucrose on a shaker (110 rpm) at 25 +/- 3 degree C for 20 h. Encapsulated protocorms were then dehydrated in a sterile air-flow in a laminar air-flow cabinet at 25 +/- 3 degree C for 0-10 h and then directly plunged into liquid nitrogen for 1 d. After thawing at 40 degree C for 2 min, cryopreserved beads were cultured on modified VW agar medium for regrowth. The highest regrowth of 40 percent was observed with cryopreserved beads with 35 percent water content after 8 h dehydration. No morphological variation was detected between non-cryopreserved and cryopreserved plantlets, and ploidy level was unchanged as a result of cryopreservation. PMID:18754065

Jitsopakul, Nipawan; Thammasiri, Kanchit; Ishikawa, Keiko

434

Inhibition of chloroplastic respiration by osmotic dehydration. [Spinacia oleracea L  

SciTech Connect

The respiratory capacity of isolated spinach (Spinacia oleracea L.) chloroplasts, measured as the rate of {sup 14}CO{sub 2} evolved from the oxidative pentose phosphate cycle in darkened chloroplasts exogenously supplied with ({sup 14}C)glucose, was progressively diminished by escalating osmotic dehydration with betaine or sorbitol. Comparing the inhibitions of CO{sub 2} evolution generated by osmotic dehydration in chloroplasts given C-1 and C-6 labeled glucose, 54% and 84%, respectively, indicates that osmotic dehydration effects to a greater extent the recycling of the oxidative pentose phosphate intermediates, fructose-6P and glyceraldehyde-3P. Respiratory inhibition in the darkened chloroplast could be alleviated by addition of NH{sub 4}Cl (a stromal alkylating agent), iodoacetamide (an inhibitor of glyceraldehyde-3P dehydrogenase), or glycolate-2P (an inhibitor of phosphofructokinase). It is concluded that the site which primarily mediates respiratory inhibition in the darkened chloroplast occurs at the fructose 1,6-bisphosphatase/phosphofructokinase junction.

Willeford, K.O.; Ahluwalia, K.J.K.; Gibbs, M. (Brandeis Univ., Waltham, MA (USA))

1989-04-01

435

Dehydration Influences Mood and Cognition: A Plausible Hypothesis?  

PubMed Central

The hypothesis was considered that a low fluid intake disrupts cognition and mood. Most research has been carried out on young fit adults, who typically have exercised, often in heat. The results of these studies are inconsistent, preventing any conclusion. Even if the findings had been consistent, confounding variables such as fatigue and increased temperature make it unwise to extrapolate these findings. Thus in young adults there is little evidence that under normal living conditions dehydration disrupts cognition, although this may simply reflect a lack of relevant evidence. There remains the possibility that particular populations are at high risk of dehydration. It is known that renal function declines in many older individuals and thirst mechanisms become less effective. Although there are a few reports that more dehydrated older adults perform cognitive tasks less well, the body of information is limited and there have been little attempt to improve functioning by increasing hydration status. Although children are another potentially vulnerable group that have also been subject to little study, they are the group that has produced the only consistent findings in this area. Four intervention studies have found improved performance in children aged 7 to 9 years. In these studies children, eating and drinking as normal, have been tested on occasions when they have and not have consumed a drink. After a drink both memory and attention have been found to be improved.

Benton, David

2011-01-01

436

Thermal dehydration-induced thirst in lithium-treated rats.  

PubMed

Lithium is used as the primary treatment for bipolar disorder but has the common side effects of diuresis and thirst. In the present study, the effects of lithium on water balance responses of male Sprague-Dawley rats to thermal dehydration were examined. Rats ate either unadulterated food or food containing 2 g/kg lithium carbonate for 10 days. Then the control and lithium-treated rats were exposed to either 25 or 37.5 degrees C without food or water for 4 h. The rats were then allowed access to water for 3 h at 25 degrees C or were anesthetized and blood samples were taken. Lithium treatment caused an initial decrease in food intake, a decrease in body weight, and an increase in urine output. Heat exposure caused similar increases in evaporative water loss in control and lithium-treated rats. Heat exposure led to changes in blood indicators of body water status indicative of dehydration, whereas lithium had no effects on blood indicators of body water status. Water intake was increased by both heat exposure and by lithium treatment with the lithium-treated rats being more responsive to the thirst-inducing effects of thermal dehydration. Lithium treatment does not appear to impair water balance responses to heat exposure. PMID:12873625

Barney, Christopher C; Kurylo, Dorothy M; Grobe, Justin L

2003-05-01

437

Glucose and fructose decomposition in subcritical and supercritical water: Detailed reaction pathway, mechanisms, and kinetics  

SciTech Connect

The authors are developing a new catalyst-free process of cellulose decomposition in supercritical water. In their initial study on the cellulose decomposition in supercritical water, the main products of cellulose decomposition were found to be oligomers of glucose (cellobiose, cellotriose, etc.) and glucose at short residence times (400 C, 25 MPa, 0.05 s). The kinetics of glucose at these conditions can be useful in understanding the reaction pathways of cellulose. Experiments were performed on the products of glucose decomposition at short residence times to elucidate the reaction pathways and evaluate kinetics of glucose and fructose decomposition in sub- and supercritical water. The conditions were a temperature of 300--400 C and pressure of 25--40 MPa for extremely short residence times between 0.02 and 2 s. The products of glucose decomposition were fructose, a product of isomerization, 1,6-anhydroglucose, a product of dehydration, and erythrose and glyceraldehyde, products of C-C bond cleavage. Fructose underwent reactions similar to glucose except that it did not form 1,6-anhydroglucose and isomerization to glucose is negligible. The mechanism for the products formed from C-C bond cleavage could be explained by reverse aldol condensation and the double-bond rule of the respective enediols formed during the Lobry de Bruyn Alberda van Ekenstein transformation. The differential equations resulting from the proposed pathways were fit to experimental results to obtain the kinetic rate constants.

Kabyemela, B.M.; Adschiri, T.; Malaluan, R.M.; Arai, K. [Tohoku Univ., Sendai (Japan). Dept. of Chemical Engineering

1999-08-01

438

Flow Boiling and Condensation Experiment  

NASA Video Gallery

The Flow Boiling and Condensation Experiment is another investigation that examines the flow of a mixture of liquids and the vapors they produce when in contact with hot space system equipment. Cooling hot surfaces in these systems occur when cool liquids vaporize or boil when flowing past the hot surface. Scientists recognize the lack of understanding of the behavior of mixtures of liquids and their vapor flow in condensers and boilers in low gravity. This video shows condensation film in microgravity.

Kristine Rainey

2013-01-11

439

Pion condensation in holographic QCD  

SciTech Connect

We study pion condensation at zero temperature in a hard-wall holographic model of hadrons with isospin chemical potential. We find that the transition from the hadronic phase to the pion condensate phase is first order except in a certain limit of model parameters. Our analysis suggests that immediately across the phase boundary the condensate acts as a stiff medium approaching the Zel'dovich limit of equal energy density and pressure.

Albrecht, Dylan; Erlich, Joshua [Particle Theory Group, Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795 (United States)

2010-11-01

440

Non-condensible ejection system for closed cycle rankine apparatus  

SciTech Connect

This patent describes an apparatus for ejecting non-condensible gases from a closed Rankine cycle motion producing system including a boiler, an engine, a condenser and means for circulating a condensible working fluid in a closed path through the boiler, engine and condenser, the apparatus comprising: a valve having an inlet connected to the closed path, an outlet and a valve element controlling the flow of fluid between the inlet and the outlet; a fluid ejector including a power fluid inlet, an ejection fluid inlet and an outlet and being operative upon flowing a pressurized power fluid from the power fluid inlet to the outlet, to create a reduced pressure at the ejection fluid inlet, the ejection fluid inlet being connected to the valve outlet; a reaction chamber connected to the power fluid inlet and adapted to contain an exothermic chemical reaction which provides a pressured power fluid as a product; at least one reactant chamber for containing a reactant for the exothermic chemical reaction and connected to the reaction chamber; means for controlling the flow of the reactant from the reactant chamber to the reaction chamber.

Sutrina, T.A.

1987-04-21

441

An advance in condensable composites.  

PubMed

With the constant advance of technology and the public's increasing awareness of esthetically pleasing restorations, alternatives for amalgam and early composite materials have been brought to the forefront of dentistry. Condensable composites offer characteristics that distinguish them from their traditional hybrid counterparts: decreased wear, packability, and bulk curing with less polymerization shrinkage. Prodigy Condensable expands the first generation of condensables by altering its resin phase to make the material more packable. Through increased filler content and methacryoyloxyethlpolycaprolactonephosphate and rheological control additives, this second-generation condensable composite possesses strength and ease of use comparable to and even exceeding amalgam while demonstrating superior esthetics for all posterior restorations. PMID:12089755

Munoz-Viveros, C A

1999-01-01

442

Mechanism and temperature-dependent kinetics of the dehydration of tert-butyl alcohol in hot compressed liquid water  

SciTech Connect

In the presence of acid or base, or under neutral conditions, isobutylene is the only observed product of the reactions of tert-butyl alcohol in compressed liquid water at 225, 250, and 320 C. On the basis of a kinetic analysis of limited results at 250 C, an earlier paper concluded that tert-butyl alcohol dissociates as an Arrhenius acid at 250 C and thereby catalyzes its own dehydration to isobutylene. Kinetic analyses of the data sets contained in this paper do not corroborate the alleged ability of tert-butyl alcohol to protonate water. Instead, the authors find that hydronium ions formed by the ordinary dissociation of water are the primary catalytic agents for the dehydration reaction. In agreement with the earlier work, all three data sets are consistent with a heterolytic reaction mechanism involving protonated alcohol, carbocation, di-tert-butyl ether, and protonated ether as intermediates. The kinetics still suggest that tert-butyl alcohol weakly dissociated as a Bronsted acid at these conditions. Values of K{sub w} determined by the kinetic model enjoy good agreement with electrochemical values available in the literature. Values of the other parameters (rate constants) which compose the kinetic model are evaluated with less precision, and a novel method is proposed to estimate the uncertainty associated with each parameter.

Xu, X.; Antal, M.J. Jr. [Univ. of Hawaii, Honolulu, HI (United States); Anderson, D.G.M. [Harvard Univ., Cambridge, MA (United States). Aiken Computation Lab.

1997-01-01

443

Effects of dehydration on organ metabolism in the frog Pseudacris crucifer : hyperglycemic responses to dehydration mimic freezing-induced cryoprotectant production  

Microsoft Academic Search

The metabolic effects of evaporative water loss at 5 °C were assessed for both fall- and spring-collected spring peepersPsuedacris crucifer. Frogs readily endured the loss of 50% of total body water. During dehydration organ water content was defended with no change in water content in skeletal muscle, gut, and kidney of 50% dehydrated frogs and reduced water content in liver,

T. A. Churchill; K. B. Storey

1994-01-01

444

One-Pot Synthesis of 3-Triazolyl-2-iminochromenes via a Catalytic Three Component Cascade Reaction.  

PubMed

A variety of 3-triazolyl-2-iminochromenes were synthesized in a one-pot, catalytic, three component condensation. In this event, a Cu(I)-catalyzed cycloaddition between 2-azidoacetonitrile and an acetylene formed a triazole and activated the neighboring methylene group, inducing an aldol-cyclization-dehydration sequence in the presence of a salicylaldehyde. Further elaboration led to more complex polyheterocycles. PMID:23751086

Qian, Wenyuan; Amegadzie, Albert; Winternheimer, David; Allen, Jennifer

2013-06-10

445

Condensation Processes in Geothermal Systems  

NASA Astrophysics Data System (ADS)

We model condensation processes in geothermal systems to understand how this process changes fluid chemistry. We assume two processes operate in geothermal systems: 1) condensation of a vapor phase derived by boiling an aqueous geothermal fluid into a cool near surface water and 2) condensation of a magmatic vapor by a deep circulating meteoric thermal fluid. It is assumed that the condensation process has two stages. Initially the condensing fluid is under saturated in gaseous species. Condensation of the vapor phase continues until the pressure on the fluid equals the sum of the partial pressures of water and the dissolved gaseous species. At that time bubbles flux through the condensing fluid. In time the fluid and fluxing gas phase come to equilibrium. Calculation shows that during the second stage of the condensation process the liquid phase becomes enriched in more soluble gaseous species like CO2 and H2S, and depleted in less soluble species like CH4 and N2. Stage 2 condensation processes can therefore be monitored by ratios of more and less condensable species like CO2/N2. Condensation of vapor released by boiling geothermal fluids results in liquids with high concentrations of H2S and CO2 like is seen in geothermal system steam-heated waters. Condensation of a magmatic vapor into circulating meteoric water has been proposed, but not well demonstrated. We compare to our models the Cerro Prieto, Mexico gas analysis data set collected over twelve years time by USGS personnel. It was assumed for modeling that the Cerro Prieto geothermal fluids are circulating meteoritic fluids with N2/Ar ratios about 40 to which is added a magmatic vapor with N2/Ar ratio = 400. The Cerro Prieto analyses show a strong correlation between N2/Ar and CO2/N2 as predicted by calculation. Two dimensional image plots of well N2/Ar + CO2/N2 show a bull's-eye pattern on the geothermal field. Image plots of analyses collected over a year or less time show N2/Ar and CO2/N2 hot spots. Plotting data for individual wells show a hysteresis like loops on time vs. CO2/N2 diagrams. Our analysis demonstrates that condensation of magmatic vapor into convecting meteoric waters is a viable process. Condensation explains variations in Cerro Prieto geothermal system gas chemistry and is compatible with helium isotope data. Locally condensation appears to wax and wane over a time periods of about 10 years.

Norman, D. I.; Moore, J. N.

2005-12-01

446

Structural Aspects of the Dehydration and Dehydroxylation of gamma-Titanium Phosphate, gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O.  

PubMed

The thermal transformations of gamma-titanium phosphate, gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O, have been studied using thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, and temperature-resolved in-situ powder diffraction. The transformation sequence goes from gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O over a new partially dehydrated form gamma'-Ti(PO(4))(H(2)PO(4)).(2-x)H(2)O (x approximately 1) to the anhydrous form beta-Ti(PO(4))(H(2)PO(4)) and then through a two-step condensation process where layered titanium pyrophosphate, Ti(PO(4))(H(2)P(2)O(7))(0.5), is formed first and finally cubic titanium pyrophosphate TiP(2)O(7). The dehydration of gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O and the dehydroxylation/condensation process from beta-Ti(PO(4))(H(2)PO(4)) to layered titanium pyrophosphate,Ti(PO(4))(H(2)P(2)O(7))(0.5), was followed in-situ. A new partially dehydrated phase, gamma'-Ti(PO(4))(H(2)PO(4)).(2-x)H(2)O (x approximately 1), which forms at approximately 50 degrees C has been detected and characterized. The unit cell is monoclinic with the lattice parameters a = 23.670(1) Å, b = 6.264(1) Å, c = 5.036(1) Å, beta = 102.41(1) degrees, and Z = 4. Layered titanium pyrophosphate, Ti(PO(4))(H(2)P(2)O(7))(0.5), which forms at 375 degrees C has been characterized. The unit cell is monoclinic with lattice parameters a = 16.271(3) Å, b = 6.319(1) Å, c = 5.122(1) Å, beta = 90.59(2) degrees, and Z = 4. PMID:11670567

Krogh Andersen, Anne Marie; Norby, Poul

1998-08-24

447

Enthalpies of formation and dehydration of uranium-containing compounds of the series M{sup I}PUOâ ·nHâO  

Microsoft Academic Search

The standard enthalpies of reactions of uranium-containing compounds of the series M¹PUOâ (M¹=Li, Na, K, Rb, and Cs) and of their crystal hydrates M¹PUOâ·nHâO with aqueous HF were determined experimentally at 298.15 K. The standard enthalpies of formation and dehydration of the crystal hydrates studied were calculated from the data obtained. 4 refs.

N. V. Karyakin; G. N. Chernorukov

1994-01-01

448